• A-weighting
    the most commonly used frequency weighting function for humans that accounts for the fact that human hearing is less sensitive to low frequencies; units dB(A) or dBA.
  • absorption
    the conversion of acoustic energy to heat energy
  • acceleration
    the rate of change of velocity with respect to magnitude or direction.
  • accelerometer
    a device that measures the vibration, or change in motion (acceleration) of a structure or organism. The force caused by vibration or a change in motion causes piezoelectric material within the device to be squeezed, which produces an electrical charge that is proportional to the force exerted upon it. Since the charge is proportional to the force, and mass remains constant, the charge is also proportional to the acceleration.
  • accuracy
    the degree of closeness of measurements of a quantity to its actual value.
  • acoustic environment
    the composite of all sounds in an environment. The perception of the acoustic environment for each animal will vary depending on its hearing abilities.
  • acoustic fish tag
    a transmitter implanted or attached to a fish to monitor fish movement
  • acoustic impedance
    the amount of sound pressure generated by a given vibration at a specific frequency.
  • acoustic index
    a statistic that summarizes several aspects of the distribution of acoustic energy and information.  Acoustic indices have been developed to estimate characteristics of the acoustic production of biological communities including richness and heterogeneity.
  • acoustic lens
    a delay-and-sum beamformer in which the delays and sums are accomplished by the refraction and concentration of acoustic rays induced by the curved surface of the lens.
  • acoustic masking

    when sounds (masking sounds or maskers) interfere with an animal’s ability to perceive, detect, or discriminate a different sound.

  • acoustic modem
    a wireless communication device used to transmit data and information through the ocean
  • acoustic propagation models
    conceptual and numerical models that compute how sound travels through the water, taking into account many variables such as water temperature, salinity, bottom topography, etc.
  • acoustic reflex (AR)
    the contraction of the middle-ear muscles in response to sound stimulation. The reflex decreases the transmission of vibrational energy to the cochlea.
  • acoustic release
    a device which holds onto the anchor of a buoyant instrument until it is commanded to release it
  • acoustic signature
    acoustic characteristics or attributes of a sound source that can be used for its identification.
  • acoustic telemetry
    to transmit acoustic signals automatically and at a distance, as between a ground station and an artificial satellite, space probe, or the like, especially in order to record information, operate guidance apparatus, etc
  • acoustic threshold
    the received level at which an effect from acoustic exposure may begin to occur.
  • acoustic tomography
    uses the travel time of sound in the ocean to measure the temperature of the ocean over large areas
  • acoustic trauma
    severe traumatic injury from sound
  • acoustical shadowing
    a condition that occurs when refraction or reflection prevents direct sound waves from reaching a region (called a shadow zone)
  • active acoustics
    sound is purposefully generated and received
  • acute
    severe condition with a sudden onset.
  • adaptation
    an alteration in the structure or function of an organism or any of its parts that results in the organism becoming better fitted to survive and multiply in its environment.
  • ADCP
    Acoustic Doppler Current Profiler; an instrument used to measure the current using acoustic sound and the knowledge of the Doppler effect
  • African penguin
    Spheniscus demersus
  • agonistic behavior
    aggressive or defensive social interaction (such as fighting, fleeing, or submitting) between individuals usually of the same species
  • airgun
    An airgun is designed to release compressed air, which forms bubbles. The formation of bubbles produces a loud sound that is used to explore the geologic structure of the ocean floor. Airguns primarily produce sound at low frequencies (between 10-500 Hz); however, high frequency noise is also created. A small airgun that releases 0.16 Liters of air can create source amplitudes up to 216 underwater dB at 1 meter. A large airgun that releases 32.8 Liters of air can have a source level of up to 232 underwater dB at 1 meter.
  • algorithm
    a step-by-step procedure for calculations/solving a problem.
  • alongshore flow
    A surface current that flows parallel to the shore.
  • Amazon river dolphin
    Inia geoffrensis
  • ambient noise
    background sound in the ocean. Examples of sound sources contributing to ambient noise include waves, wind, rain, shrimp, earthquakes, volcanoes, and distant sources, such as shipping and airguns.
  • American lobster
    Homarus americanus
  • American paddlefish
    Polyodon spathula
  • American shad
    Alosa sapidissima
  • amphibious
    living or able to live on land and in the water
  • amplitude
    the maximum distance that a vibrating particle moves from its equilibrium; how much the medium is disturbed
  • anadromous
    fish that are born in fresh water, migrate to the ocean to grow into adults, and return to fresh water to spawn.
  • anemometer
    a weather instrument that measures wind speed.
  • angle of incidence
    the angle that the incident wave makes with a line perpendicular or normal to the reflecting surface
  • angle of reflection
    the angle that the reflected wave makes with a line perpendicular or normal to the reflecting surface
  • animated frequency spectrum
    An animated frequency spectrum is a series of frequency spectra that show just the frequencies present at each moment in time. You can see what frequencies are associated with each part of a sound.
  • annelid

    worms or wormlike animals of the phylum Annelida, characterized by an elongated, cylindrical, segmented body with movable bristles (or setae); includes the earthworms, polychaete worms, and leeches.

  • Antarctic minke whale
    Balaenoptera bonaerensis
  • anthropogenic
    caused by humans
  • Aristotle's lantern
    claw-like mouth on a sea urchin that contains five calcium carbonate teeth that are used for feeding
  • array elements
    a single hydrophone in a receiving array or a single projector (sound source) in a projector array
  • arthropods
    invertebrates of the phylum Arthropoda that have jointed appendages and a chitinous, segmented exoskeleton. Arthropods include insects, spiders, crabs, and lobsters.
  • Atlantic croaker
    Micropogonias undulatus
  • Atlantic mackerel
    Scomber scombrus
  • Atlantic salmon
    Salmo salar
  • Atlantic spotted dolphin
    Stenella frontalis
  • Atlantic Undersea Test and Evaluation Center (AUTEC)
    a deep-water laboratory located in the Bahamas (in the Tongue of the Ocean (TOTO)) that is instrumented with a variety of acoustic beacons and sensors to provide testing, evaluation, and certification for U.S. Navy submarine captains and their crews, as well as the accuracy of their undersea weapons. A Marine Mammal Monitoring (M3R) system has been established at AUTEC to monitor vocalizing animals via the 91 range hydrophones.
  • atmospheric pressure
    the force per unit area exerted by the weight of the atmosphere; also known as barometric pressure.
  • attenuate
    reduce the force or effect of; the gradual loss of flux intensity through a medium.
  • attenuation
    the decrease in the intensity of a wave due to the loss of acoustic energy to heat energy
  • audiogram
    a graph expressing hearing loss (hearing sensitivity) as a function of frequency
  • audiometric curve
    a graph displaying the range of sounds that humans can hear.
  • auditory brainstem response (ABR)
    Whenever a sound wave is detected by the ear, it triggers a number of neuro-physiological responses along the auditory pathway. An auditory brainstem response test is an objective test that measures the electrical potential produced in response to sound stimuli by the synchronous discharge of the first through sixth order neurons in the auditory nerve and brainstem. Also sometimes known as brainstem auditory evoked potential (BAEP) or brainstem auditory evoked response (BAER).
  • auditory bulla
    a hollow, bony structure that encloses parts of the middle and inner ear.
  • auditory fatigue
    when the intensity level or duration of sound overwhelms the hair cells so they cannot respond to sounds appropriately
  • auditory meatus or ear canal
    an air-filled canal that leads from the ear flap to the ear drum. It helps direct sound waves to the ear drum.
  • auditory system
    the sensory system for hearing, consisting of the ear and the central nervous system.
  • auditory weighting function
    a mathematical equation that compensates for the fact that animals do not hear equally well at all frequencies.
  • austral
    southern hemisphere
  • Australian freshwater crayfish
    Cherax destructor
  • automatic gain control (AGC)
    a system that automatically controls the increase in the amplitude of an electrical signal. “Gain” controls how loud something is before it goes through any processing.
  • Automatic Identification System (AIS)
    an automated tracking system used to electronically identify and locate ships. AIS uses GPS-linked, very high frequency radio signals that allow for ship-to-ship and ship-to-shore information transfer. Information transmitted includes a ship's name, position, speed, heading, and other information. These details are transmitted multiple times each minute.
  • autonomous
    existing and/or functioning independently; with regards to ocean-going vehicles, one which travels at the surface or underwater without requiring input from an operator.
  • axial muscles
    folded muscle segments that, when contracted, produce a wavelike motion that moves the fish through the water
  • backscatter
    the deflection of sound in a scattering process through an angle greater than 90 degrees. Backscatter is the term commonly used to describe the return of sound from the seafloor to the receiver in an active sonar.
  • Baiji
    Lipotes vexillifer
  • baleen
    series of horny plates that hang from the gums of the upper jaw of some large whales (called Mysticetes). The baleen is made from the same materials as human hair and fingernails. It is used to filter small bits of food from the water.
  • baleen whales
    These large cetaceans are usually more than 9.1 m (30 ft) long and can be found throughout the ocean. Instead of teeth, mysticetes have a series of horny plates called baleen. The baleen is made from the same materials as human hair and fingernails. The baleen plates hang from the gums of the upper jaw and are used to filter small bits of food from the water. Baleen whales have symmetrical skulls and have two (or paired) blowholes.

    The mysticetes are divided into four families: rorquals (blue, humpback, minke, sei, fin, and Bryde's whales), right whales, pygmy right whales, and gray whales. Rorquals have throat pleats, or ventral grooves, that expand when the whales gulp large amounts of water during feeding. Baleen whales can migrate up to hundreds of miles to feed in cooler areas with lots of food. On the feeding grounds baleen whales filter out small organisms from the water either by skimming the surface or gulping large quantities of water to filter. Baleen whales are not known to echolocate but produce a variety of sounds used for communication. Echoes from baleen whale vocalizations may help in navigating under ice or detecting the ocean floor.
  • bandpass filter

    a signal processing technique that allows a range of frequencies to be heard, while blocking higher and lower frequencies.

  • bandwidth
    the frequency span of a signal, calculated as the difference between the highest frequency of a signal and the lowest frequency of a signal.
  • barometric pressure
    the force per unit area exerted by the weight of the atmosphere; also known as atmospheric pressure.
  • barotrauma
    The result of an inability to equalize pressures between the environment and an air-filled area of the body.  This can happen in air (such as ear discomfort and ear drum injury when planes descend or ascend) or in water (such as injuries to lung tissues or middle ears when scuba diving). Barotrauma typically occurs at much lower pressures than shock wave related blast injuries and can generally be prevented by processes (changing depth, altitude, releasing gases) that equilibrate pressures as needed.
  • Barth’s myochordotonal organs (Barth’s MCO)
    thin-walled sensory organ found in the exoskeleton on each leg of semi-terrestrial ocypodid crabs.
  • basilar membrane
    a membrane in the cochlea of the ear that vibrates in response to sound. As sound vibrations progress down the ear, a fluid wave that is created by the movement of the third ossicle, the stapes, moves the basilar membrane. The basilar membrane is the part of the cochlea that separates sounds according to their frequency.
  • basking shark
    Cetorhinus maximus
  • bathymetry
    charting of the sea floor using water depth measurements
  • bathythermograph
    an instrument that makes a record of the temperature at various depths in the ocean
  • beacon
    an acoustic signaling device that continually sends out a repetitive signal. Acoustic beacons, sometimes called pingers, are used to mark the locations of underwater objects.
  • beam pattern
    a graphical or other description of the response of a transducer used for sound transmission or reception as a function of the direction of the transmitted or incident sound waves.
  • beamforming
    a general signal processing technique used to control the directionality of the reception or transmission of a signal on an array of sensors. Using beamforming during sound transmission, the majority of signal energy is transmitted in a specified direction. During sound reception, beamforming allows sensors to predominantly receive energy from a specified direction
  • beamforming
    a signal processing technique for the directional transmission or directional reception of a signal.
  • bearded seal
    Erignathus barbatus
  • bearing
    measurement of direction; the angle, with respect to magnetic north, to where the target is located
  • bedrock
    the hard, solid rock beneath surface materials such as soil as well as sand and other sediments on the ocean floor.
  • bel
    a unit used in the comparison of power levels or of intensities of sounds corresponding to an intensity ratio of 10:1.
  • beluga whale
    Delphinapterus leucas
  • benthic
    living on the bottom of the sea (or a lake).
  • biodiversity
    a contraction of “biological diversity,” it generally refers to the amount of variability within species, among species, and among ecosystems.
  • biologically significant
    an action or activity that affects an animal's ability to grow, survive, or reproduce.
  • biomagnification
    the process by which a compound (such as a pollutant or pesticide) increases its concentration in the tissues of organisms as it travels up the food chain. (also known as bioamplification or biological magnification)
  • biomass
    measure of the amount of living material in an area, usually expressed in units of weight per unit volume
  • bistatic sonar
    when the sound source and receiver are located in different places
  • bivalve
    an aquatic mollusk that has a compressed body enclosed within a hinged shell, such as oysters, clams, mussels, and scallops.
  • black drum
    Pogonias cromis
  • black-legged kittiwake
     Rissa tridactyla
  • black rockfish
    Sebastes melanops
  • Blainville's beaked whale
    Mesoplodon densirostris
  • blast injury
    Injuries that occur as a result of an explosion (blast) which produces a shock wave with rapid shifts to extremely high pressures (compression) followed by lower than ambient pressures (rarefaction).  These sudden pressure extremes can produce direct physical injury to body tissues or indirect injuries from debris or transport of bodies into other objects.  Blast injuries can range from lethal to relatively minor injuries, depending upon the multiple factors such as distance from the blast, size of the explosive charge, and animal size.  In addition to shock wave related injuries, animals can also be harmed by the high sound pressure levels of the sound wave that accompanies a blast which may produce temporary or permanent hearing loss.
  • blue-fin tuna
    Thunnus thynnus
  • blue rockfish
    Sebastes mystinus
  • blue shark
    Prionace glauca
  • blue whale
    Balaenoptera musuculus
  • blue whiting
    Micromesistius poutassou
  • bottlenose dolphin
    Tursiops truncatus
  • bottom reverberation
    sound scattering that occurs at or near the sea bottom
  • bowhead whale
    Balaena mysticetus
  • bowriding
    a common activity of dolphins and other cetaceans in which marine mammals swim in front of a vessel, riding or surfing on the pressure wave created by the vessel
  • brisance
    the ability to shatter nearby objects because of the rapid release of energy and the rapid increase in pressure by explosives.
  • broadband
    a sound signal that includes acoustic energy across a wide range of frequencies.
  • Bryde’s whale
    Balaenoptera edeni edeni
  • bubble feeding
    a feeding process where whales trap a school of prey (fish or krill) by blowing a series of bubbles as the whales swim to the surface. The bubbles form a curtain that rises to the surface of the water and concentrates the prey in the center. The whales charge through with their mouths open to engulf the fish or krill.
  • bubble frequency
    the frequency equal to the reciprocal of the time interval between the shock wave and the first bubble pulse.
  • bubble pulses
    secondary shock waves of explosions in which the bubbles repeatedly grow larger and smaller.
  • buccal cavity
    the anterior portion of the oral cavity, also sometimes referred to as the vestibule or entry area of the oral cavity. It is the region bounded by teeth and gums, jaws, and cheeks.
  • buoyancy
    the upward force on a free floating or submerged object, independent of the object's weight; gives submerged objects the weightless appearance.
  • burst-pulse sounds
    a rapid series of broadband clicks similar to those used in echolocation, but with a much shorter interclick interval of 0.5-10ms. Given this very high pulse repetition rate, greater than 300 pulses/second, more clicks are produced per unit time with burst-pulsed sounds.
  • bycatch
    the harvest of fish (or any marine organism) other than the species for which the fishing gear was set
  • byssal threads
    string like substance that is secreted by mussels to allow the mussel to attach to hard substrates like rocks
  • C-weighting
    a frequency weighting function that was originally designed to predict the human ear’s sensitivity to tones at high noise levels; however, nearly all noise measurements for hearing conservation are measured with A-weighting; units dB(C) or dBC.
  • caldera
    depression formed at the summit of a volcano
  • California mantis shrimp
    Hemisquilla californiensis
  • California sea lion
    Zalophus californianus
  • callosities
    thick, white patches of hardened skin, called chitin, that are covered with tiny crustaceans, called whale lice." These patches are found on the heads
  • calve
    the sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, or ice shelf.
  • canine teeth
    sharp, fang-like teeth adapted for capturing and penetrating prey
  • Cape fur seal
    Arctocephalus pusillus
  • capillaries
    the smallest of the network of blood vessels throughout an organism
  • carapace
    A hard, protective, shell-like outer covering found in crustaceans (e.g. crabs and lobsters) as well as turtles.
  • carbon sink

    a carbon sink takes up more carbon from the atmosphere than it releases, resulting in a net decrease of carbon in the atmosphere

  • cardioid
    a heart-shaped curve generated by a point on a circle that rolls without slipping on another fixed circle of the same diameter.
  • Caribbean spiny lobster
    Panulirus argus
  • catadromous
    fish that are born in saltwater, migrate into freshwater as juveniles where they grow into adults, before migrating back into the ocean to spawn.
  • caudal peduncle
    The narrow part of the body to which the caudal fin (or tail) attaches to the body.
  • cavitation
    formation of gas-filled cavities in liquids in motion when the pressure is reduced to a critical value. Low pressure regions are often created by rotating ship propellers. As the propellers rotate, bubbles form in the water. A loud acoustic sound is created when these bubbles collapse.
  • center frequency
    when describing a sonar system, the frequency with the highest intensity, usually listed as the operating frequency of the sonar.
  • central nervous system
    the complex of nerve tissues that controls the activities of the body. In vertebrates it comprises the brain and spinal cord.
  • cephalopod
    squid, cuttlefish, octopods, and nautilus.
  • cetacean
    order of mammals that includes whales, dolphins and porpoises
  • Channel catfish
    Ictalurus punctatus
  • characteristic acoustic impedance
    the specific acoustic impedance of a plane wave propagating horizontally.
  • characteristic impedance
    a material property of a medium, defined as the density of the medium times the sound speed through the medium.
  • chelae

    hinged, pincer-like claws at the end of certain limbs of some crustaceans and arachnids (e.g. crabs, lobsters, and scorpions). Typically, chelae are curved and sharply pointed and are used for feeding, defense, and courtship. They can be referred to as claws, nippers, or pincers; legs bearing chelae are called chelipeds.

  • cheliped
    one of the pair of legs that bears the large chelae in decapod crustaceans. A male fiddler crab has an enlarged claw or cheliped.
  • Chinook salmon
    Oncorhynchus tshawytscha 
  • chirp
    a signal in which the frequency changes with time; the opposite type of signal is a pure-frequency tone where the frequency remains the same throughout the signal.
  • chordotonal organs
    for Crustaceans, they are located at the joint segments and they serve as mechanoreceptors (sensory organs).
  • chronic
    developing over an extended period of time and long-lasting. Chronic conditions are long term in nature, and usually have slow to develop symptoms that potentially worsen over time.
  • cichlids
    family (Cichlidae) of freshwater fishes found throughout tropical and subtropical waters of the Americas, Africa and parts of Asia
  • cilia
    hair cells of the neuromast
  • circumference
    the enclosing boundary (perimeter) of a curved geometric figure, especially a circle.
  • circumpolar
    located around or found in one of Earth's polar regions
  • Clay

    both a grain size (1µm - 3.9 µm) and a type of aluminum silicate mineral

  • cleaner shrimp
    Periclimenes longicarpus
  • click
    a short pulse of sound, often used to describe pulses produced by toothed whales for echolocation.
  • click train
    rapid sequence of clicks, produced by whales and dolphins, that are associated with echolocation. The clicks are emitted from the melon of the whale.
  • climatologist
    a scientist who studies climate
  • clupeids
    fish belonging to the herring family
  • coalesced
    fused or grown together
  • cochlea
    the spiral-shaped chamber within the inner ear that transforms sound waves into nerve impulses. The cochlea is a fluid-filled organ that houses many structures related to hearing, including the basilar membrane and the organ of Corti. It is considered the organ of hearing.
  • cod
    Gadus morhua
  • coelenterates

    a group of aquatic invertebrates that includes jellyfishes, corals, and sea anemones. They are distinguished by having a saclike body with a single opening ringed with tentacles.

  • common carp
    Cyprinus carpio carpio
  • Common cockle

    Cerastoderma edule

  • common dolphin
    Delphinus capensis (long-beaked common dolphin), Delphinus delphis (short-beaked common dolphin)
  • common octopus
    Octopus vulgaris
  • common prawn
    Palaemon serratus
  • communication space
    the area over which one individual can detect the signal of another.
  • complementary angle
    two angles are complementary when they add up to 90°.
  • Comprehensive Nuclear-Test-Ban Treaty
    The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions on Earth whether for military or for peaceful purposes. It was adopted by the United NAtions General Assembly in 1996. The treaty contains provisions for monitoring which include acoustic monitoring. The treaty is not yet in force because it has not been ratified by some nations.
  • conditioned response
    a response that becomes associated with a previously unrelated stimulus as a result of pairing the stimulus with another stimulus normally yielding the response.
  • conductivity-temperature-depth (CTD)
    oceanographic tool used to determine the essential physical properties of sea water: conductivity (salinity), temperature, and depth. Depth measurements are derived from measurement of hydrostatic pressure and salinity is measured from electrical conductivity. The CTD may be incorporated into an array of sampling bottles referred to as a carousel" or ""rosette"". The sampling bottles close at predefined depths
  • conspecific
    animals (or plants) belonging to the same species
  • contact calls
    sounds produced by closely associated conspecifics (individuals of the same species) as a means of keeping in touch. Contact calls are important for individual, mate, and kin recognition as well as group cohesion and movement coordination. A wide variety of social information can be encoded in the acoustic structure of contact calls.
  • continental shelf
    the gently sloping undersea region between a continent and the deep ocean.
  • corticosteroid
    a type of hormone produced by the adrenal glands. Corticosteroids levels may be elevated as a response to stress.
  • courtship
    behaviors in animals, that are used to initiate mating
  • critical angle
    the arrival angle at which a sound wave traveling from one medium to another medium will be refracted along the interface of the two media. If a wave traveling from one medium to another medium with a higher speed of sound hits the interface between the two media at an arrival angle less than the critical angle, only reflection will occur; at an arrival angle above the critical angle, some of the sound will be reflected and some will be refracted into the faster medium.
  • critical bandwidth

    the bandwidth of a masking sound at which the detection threshold of a tone at the center of the masking sound ceases to increase with increasing width of the masking bandwidth; an estimate of the bandwidth of the auditory filter at the center frequency.

  • critical habitat
    specific geographic area(s) that contains features essential for the conservation of a threatened or endangered species and that may require special management and protection.
  • critical ratio
    the ratio, in decibels, of the signal power to the noise power in a 1-Hz band (centered at the test frequency) required to reliably detect a signal at some predetermined level of correctness
  • critically endangered
    A category on the IUCN Red List of Threatened Species which indicates a taxon is considered to be facing an extremely high risk of extinction in the wild.
  • crustaceans
    a class of mainly aquatic, gill-breathing arthropods such as crabs, lobsters, shrimp, and barnacles. They usually have a hard exoskeleton and two pairs of antennae.
  • ctenophore

    gelatinous, aquatic invertebrate also known as a "comb jelly". They use rows of cilia ("combs") to swim. Most species have eight strips, called comb rows, that run the length of their bodies and bear comb-like bands of cilia, called "ctenes". When the cilia beat, those of each comb touch the comb below . The name "ctenophora" means "comb-bearing" in Greek.

  • cupula
    gel-like cover of cilia in the neuromast
  • Cuvier's beaked whale
    Ziphius cavirostris
  • Cuvier’s beaked whale
    Ziphius cavirostris
  • Cycle
    one complete vibration of a particle through a wave, e.g., from equilibrium to the crest through equilibrium to the trough and back to equilibrium.
  • cylindrical spreading
    energy spreading out from a sound source in the shape of a cylinder; no energy radiates above the top or below the bottom of the cylinder
  • dB peak
    a unit of relative pressure when the pressure of the sound wave is characterized as the peak pressure.
  • dB peak-peak
    a unit of relative pressure when the pressure of the sound wave is characterized as the peak-to-peak pressure.
  • decapod crustacean
    crustacean that has five pairs of walking legs, a segmented body, and chitinous exoskeleton. Examples include lobsters, crayfish, crabs, shrimps, and prawns.
  • decibel
    a relative unit used to describe sound intensities. Written as dB. See Advanced Topic: Introduction to Decibels.
  • decompression sickness
    known as the bends, a condition that occurs in deep-sea divers caused by the formation of nitrogen bubbles in the blood and tissues following a sudden decrease in the surrounding pressure. This occurs when ascending rapidly from a deep dive and is characterized by severe pains in the joints and chest, skin irritation, cramps, and paralysis.
  • delphinid
    cetaceans of the family Delphinidae, the most diverse of cetacean families. Includes oceanic whales and dolphins, such as, killer whales, pilot whales, common dolphins and bottlenose dolphins
  • demersal
    living and/or feeding on or near the bottom of seas or lakes.
  • density
    the distribution of a quantity (such as mass, electricity, or energy) per unit usually of space (such as length, area, or volume); the degree of compactness or concentration of a substance.
  • depredate
    the removal and/or damage of netted or hooked fish and bait from fishing gear.
  • derived
    formed or developed from something else; not original. NOTE: different areas of science have more specialized definitions for this term (e.g. in paleontology, derived characteristics means something has evolved to fit a particular pressure).
  • detection probability p(D)
    the probability of correctly deciding on the basis of a statistical test that a signal is present when it is in fact present.
  • detection threshold
    the signal-to-noise ratio (SNR) (in decibels) required to achieve a specified probability of detection p(D) for a given probability of false alarm p(FA) when deciding whether or not a signal is present at a receiver.
  • detonation
    to explode
  • diadromous
    migrating between saltwater and freshwater to complete a life cycle.
  • dialect

    vocalizations or calls of cetaceans that are stereotyped, distinctive, and discrete to a particular group or pod.

    Directional Frequency Analysis and Recording device; passive acoustic sonobuoy
  • diffuse

    the spreading out of molecules or atoms (or energy), generally away from from higher concentrations

  • digital data
    information that is represented in a coded form, as a series of zeros and ones
  • dinner bell "effect"
    when an underwater sound (or some other stimulant) acts like a dinner bell, alerting and attracting an animal to the presence of a food source.
  • directional
    producing or receiving sound only from certain angles or directions
  • displacement
    the linear distance in a given direction between a point and a reference position.
  • distribution
    the frequency of occurrence of a specific value in a set of measurements.
  • diurnal
    of or during the day.
  • doppler effect
    the raising or lowering of the frequency of a sound due to the motion of the source of the sound relative to the listener. The most common example is the rising frequency of a train whistle as the train approaches.
  • dorsal
    of or pertaining to the upper surface.
  • dorsal fin
    the main fin found on the back of fishes and some marine mammals. Some whales, such as the killer whale, have tall dorsal fins, while other whales (i.e. belugas and bowheads) have no dorsal fin.
  • downsweep
    a signal that decreases in frequency over time.
  • drumming
    to vibrate a muscle in, on, or near, the swim bladder that produces a loud, low-pitched grunt sound
  • ducts
    internal passage involved in the flow of fluids through an organism
  • Dugong
    Dugong dugon
  • duration
    the length of a sound in seconds.
  • echinoderm
    marine invertebrates with tube feet and five-part radially symmetrical bodies. The group includes sea urchins, sea stars, sea cucumbers, brittle stars, and crinoids.
  • echo-counting
    when individual (sonar) targets are spaced far enough apart that they can be distinguished from one another, the number of targets are counted (and the number of fish estimated).
  • echo-integration
    when more than one target (e.g. a fish school) is located in an acoustic beam at the same depth, and it is not possible to resolve them separately.  The total acoustic energy backscattered by the school or aggregation is integrated together, and this total is divided by the (previously determined) backscattering coefficient of a single animal, giving an estimate of the total number. Echo-integration assumes that the total acoustic energy scattered by a group of targets is the sum of the energy scattered by each individual target.    
  • echo ranging
    determining the distance to an object by measuring the time between transmitting a sound signal and hearing its echo.
  • echo signature
    a unique sonar return (reflection) that can be used to identify individual species of marine organisms, such as fish, or other submerged objects
  • echolocation
    a process for locating distant or hard-to-see objects using the reflection of sound waves. The distance of objects or depth of the seafloor can be determined by measuring the time it takes for reflected sound waves (echoes) to return to the sound source. Some whales and dolphins use echolocation to identify underwater objects and to help find food.
  • echosounder
    an instrument that uses sound echoes to determine the water depth. The instrument emits sound waves that travel to the bottom of the ocean and are reflected back. Depth is determined by timing how long it takes the sound pulse to leave the instrument, travel to the seafloor, and return to the receiver on the ship.
  • echosounding
    the technique of measuring the depth of a body of water by means of an echosounder, an electrical depth sounder that uses sound echoes. The instrument emits sound waves that travel to the bottom of the ocean and are reflected back. Depth is determined by timing how long it takes the sound pulse to leave the instrument, travel to the seafloor, and return to the receiver on the ship.
  • ecological risk assessment
    the process of calculating the probability of adverse ecological effects
  • ecology
    the scientific study of the relationship between organisms and their environment.
  • ecotype
    ecologically distinct groups or communities; in this case, groups exhibiting different dietary specializations and corresponding behavioral adaptions, such as hunting techniques and acoustic repertoires.
  • eddy
    energetic, swirling, unsteady flows that are found almost everywhere in the ocean
  • effective source level
    the source level of an array when considered as a single omnidirectional sound source
  • efferent
    moving or carrying outward or away from a central part. For example: efferent blood vessels carrying blood away from the heart or efferent nerves carrying signals away from the brain.
  • elasmobranch
    a group of cartilaginous fish that comprises the sharks, rays, and skates.
  • elasmobranchs
    a group of fishes, including sharks, rays and skates, that has a skeleton made of cartilage rather than bone; they also do not have a swim bladder.
  • electro-physiological response
    the electrical activity of neurons when stimulated (see auditory brainstem response (ABR)).
  • elephant seal
  • endangered
    any species that is in danger of extinction
  • endemic
    native to or prevalent in a particular area or region; not found in other places.
  • ensonified
    filled with sound.
  • entanglement
    whales, seals, sea lions, and other marine animals may come into contact with lost or active fishing gear, causing the gear to become twisted around their bodies and/or snagged on different body parts. When this occurs, the animal is considered entangled.
  • epicenter
    the point on the earth's surface (on land or underwater) vertically above the focus of an earthquake.
  • Epicenter
    the surface location of an earthquake.
  • equal energy hypothesis
    assumption that sounds of equal SELcum produce an equal risk for hearing loss (i.e., if the SELcum of two sources are similar, a sound from a lower level source with a longer exposure duration may have similar risks to a shorter duration exposure from a higher level source).
  • equal latency
    the assumption in hearing studies that sounds that are perceived to be equally loud result in equal response times, thereby allowing response time to be a proxy for perceived loudness.
  • equal loudness curve
    a graph of the perceived intensity (loudness) of sounds. The loudness of a sound is different for different frequencies.
  • equilibrium
    the rest position of the particles in a medium
  • essential fish habitat (EFH)
    those waters and substrate necessary for fish for spawning, feeding, or growth to maturity.
  • estuary
    a coastal body of water formed when freshwater from rivers and streams flows into the ocean, mixing with the seawater. Estuaries and the lands surrounding them are places of transition from land to sea, and from freshwater to saltwater. Although influenced by the tides, estuaries are protected from the full force of ocean waves, winds, and storms by the reefs, barrier islands, or fingers of land, mud, or sand that surround them.
  • European perch
    Perca fluviatilis
  • European sea bass
    Dicentrarchus labrax
  • European spiny lobster
    Palinurus elephas
  • exoskeleton
    a hard outer structure, such as the carapace of a lobster or crab, that provides protection or support for an organism (especially invertebrates).
  • expendable bathythermograph
    a probe which is dropped from a ship and measures the temperature as it falls through the water. Two very small wires transmit the temperature data to the ship where it is recorded for later analysis. The probe is designed to fall at a known rate, so that the depth of the probe can be inferred from the time since it was launched. By plotting temperature as a function of depth, the scientists can get a picture of the temperature profile of the water.
  • explosive sound source
    a device that uses explosive material to generate controlled acoustic energy.
  • extant
    still existing; not extinct.
  • extinction
    the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to reproduce and recover may have been lost before this point).
  • extirpation
    the movement of an entire population out of a region
  • extrapolate
    to estimate or expand unknown data based on known facts and/or observations.
  • extrapolation
    using evidence and inferences from a similar situation to project information about a related event or process. Extrapolation can also be used to apply or transfer experimental observations from a model to the real world.
  • false alarm
    incorrectly deciding on the basis of a statistical test that a signal is present when it is in fact absent. A false positive.
  • false alarm probability p(FA)
    the probability of incorrectly deciding on the basis of a statistical test that a signal is present when it is in fact absent.
  • false killer whale
    Pseudorca crassidens
  • false negative
    an error when one concludes that there is not a real difference between two means when, in fact, there is a difference; also called a Type II error.
  • false positive
    an error when one concludes that there is a real difference between two means when, in fact, there is not; also called a Type I error.
  • far field
    the sound field at a distance from a sound source array where the wave fronts created by the individual sound sources are in phase
  • fat emboli
    a fat globule in the bloodstream that is often caused by physical trauma such as fracture of long bones, soft tissue traum, or burns.
  • fathead minnow
    Pimephales promelas
  • fecund, prolific
    fruitful in offspring or vegetation
  • fertility
    the ability to produce offspring; fecundity. Fertility rate is the number of offspring born per mating pair, individual, or population.
  • filtering
    a signal processing technique that selects frequencies of interest during the analysis of signals.
  • fin whale
    Balaenoptera physalus
  • finfish
    teleost bony fishes, in other words, not sharks/skates/rays, and not shellfish.
  • finless porpoise
    Neophocaena phocaenoides
  • fishery
    the industry or occupation devoted to the catching, processing, or selling of fish, shellfish, or other aquatic animals.
  • fishes
    two or more fish species. For example, if you have three fish species in an aquarium (such as a clownfish, damselfish, and goby), you would say "three fishes." If you have three clownfish (all of the same species), you would say "three fish".
  • fluke
    the two lobes of a whale tail.
  • focal animal observations
    observations concentrated on individual animals that record everything they do
  • foraging
    to search for food
  • foraging behavior
    the way in which an animal searches for food; the process, or series of actions, that an animal goes through to find food
  • Franciscana dolphin
    Pontoporia blainvillei
  • frequency
    the rate of repetition of a regular event. The number of cycles of a wave per second. Expressed in units of Hertz (Hz)
  • Frequency selectivity

    the ability of an animal to discern the frequency of one sound in the presence of sounds of different frequencies.

  • frequency spectrum
    a graph of a sound that plots the intensity of each frequency in the sound. Plural is spectra.
  • frequency weighting
    a method for quantitatively compensating for the fact the animals do not hear equally well at all frequencies within their hearing range.
  • fright response
    responding out of fear
  • front
    a boundary between two water masses with differing properties such as temperature and salinity
  • fundamental frequency
    the lowest frequency in a complex wave.
  • ganglion cells
    nerve cells that have their cell bodies outside of the central nervous system (the brain and spinal cord). Auditory ganglion cells carry sound information from the inner hair cells to the auditory nerve.s
  • gas gland
    a modification of the inner lining of the bladder, which works with the rete mirabile to force gases into the bladder
  • goldfish
    Carassius auratus auratus
  • goliath grouper
    Epinephelus itajara
  • gray triggerfish
    Balistes capriscu
  • gray whale
    Eschrichitus robustus
  • grazing angle
    the angle formed by the incident ray or the reflected ray and the plane(surface).
  • Great cormorant
    Phalacrocroax carbo sinensis
  • great white shark
    Carcharodon carcharias
  • Green sea turtle
    Chelonia mydas
  • greenhouse gas
    a gas that traps heat in the atmosphere.
  • grey seal
    Halichoerus grypus
  • gross tonnage
    a measure of the cargo carrying capacity or the volume of a ship.
  • ground truth
    information, or the determination of facts, provided by direct observation.  Often performed to check the accuracy of data or other observations.
  • gudgeon
    Gobio gobio
  • habitat impediment
    a hindrance or obstruction that restricts migratory movements and/or prevents a species from accessing habitat necessary for spawning, foraging, and other activities.
  • habituate
    to become accustomed to something through repeated or prolonged exposure
  • haddock
    Melanogrammus aeglefinus
  • hair cells
    mechano-transducers that detect energy or pressure changes. They are complex structures that include a cell body on the surface of a membrane. At the base of the hair cell are one or more neural synapses. On the upper surface of the hair cell are hair-like projections called stereocilia, commonly in bundles. These stereocila bend in response to a range of stimuli based on the species, some from fluid motion, some in association with crystals or otoliths, some because of being embedded in a second membrane. When these stereocila bend, they trigger a release of chemicals that initiates the electrical signal (neural impulse) that is carried to and processed by the brain.
  • hake
    Merluccius merluccius
  • harbor porpoise
    Phocoena phocoena
  • harbor seal
    Phoca vitulina
  • harmonic distortion
    distortion of a pure tone associated with the presence of undesired harmonics at frequencies that are a multiple of the fundamental frequency of the signal.
  • harmonic frequency
    the part of a signal whose frequency is an integer multiple of the fundamental frequency. Harmonic frequencies are related to each other by simple whole number ratios, for example if the fundamental frequency is f, the harmonics have frequencies of 2f, 3f, 4f, etc.
  • hawaiian monk seal
    Monachus schauinslandi
  • Heard Island Feasibility Test (HIFT)
    an expedition to Heard Island in the southern Indian Ocean during which acoustic sources suspended below a ship transmitted acoustic signals to receivers around the globe. Heard Island was selected because signals transmitted from that location can reach both coasts of North America. HIFT showed that underwater acoustic signals could be received worldwide and serve as a method for measuring global ocean warming.
  • hearing generalist
    a fish species in which the swim bladder aids very little or not at all in hearing sensitivity
  • hearing groups
    groups of marine mammals defined by the generalized range of frequencies that species in the group can hear.
  • hearing range
    the range of frequencies the ear of an animal can detect.
  • hearing threshold
    the minimum intensity at which a sound of a specific frequency is reliably detected in absolute quiet conditions. The intensity level varies with frequency. Also called threshold of hearing.
  • heavy oil
    very thick oil that has little to no evaporation and/or dissolution properties and weathers very slowly. Heavy oil is depleted in hydrogen relative to light oil, and fewer refined products are derived from heavy oil. Cleanup of heavy oils is also very difficult.  Heavy crude oil is an example of a heavy oil.
  • hemorrhages
    flow of blood from a ruptured blood vessels; excessive bleeding
  • herbivore

    an organism that feeds mostly on plants.

  • hermaphroditic
    an animal or plant having both male and female reproductive organs
  • Hertz
    the unit of frequency; the number of cycles, or wavelengths, in a second (cycles/second)
  • hierarchy
    a system or organization in which people, animals, or groups are ranked one above the other according to status or authority.
  • High Arctic
    the northernmost part of the Arctic, including the circumpolar Arctic Ocean with its surface ice and its most northerly coastal margins and islands.
  • histogram
    a representation of a distribution by means of rectangles whose widths represent class intervals and whose areas are proportional to the corresponding frequencies of occurrence.
  • homologous
    similar in position, structure, and evolutionary origin but not necessarily in function.
  • hull
    the main body of a ship or vessel (most of which goes under the water), including the bottom, sides, and deck but not the masts, superstructure, rigging, engines, and other fittings.
  • humpback whale
    Megaptera novaeangliae
  • hydrate
    water ice with methane molecules trapped within the ice structure.
  • hydraulic hammer
    a large, industrial hammer that is operated by a fluid that is under pressure (hydraulics). A hydraulic hammer is a modern type of piling hammer used in place of diesel and air hammers for driving steel pipe, precast concrete, and timber piles.
  • hydroacoustic
    acoustics in water
  • hydrocarbon
    an organic compound containing only hydrogen and carbon; often occurring in crude oil, natural gas, and coal, as well as plant life.
  • hydrodynamic
    of, relating to, or operated by the force of liquid in motion
  • hydrofoil
    a vessel that is lifted partially above the water by wing-like structures mounted on struts below the hull of a boat.
  • hydrokinetic
    the conversion of kinetic energy produced by flowing water into electricity, or other forms of energy.
  • hydrophone
    an underwater microphone that will listen to, or pick up, acoustic signals. A hydrophone converts acoustic energy into electrical energy and is used in passive underwater systems to listen only.
  • hydrophone array
    several hydrophones attached to each other at known fixed distances so the location of sound sources can be calculated.
  • hydrostatic pressure
    The pressure at a point in a fluid at rest due to the weight of the fluid above it.
  • hydrothermal
    relating to hot water circulation in the ocean crust.
  • Hydrothermal
    relating to hot water circulation in the ocean crust.
  • hydrothermal vent
    a hot spring on the seafloor
  • hyperthermia
    a condition where the body produces or absorbs more heat than it can dissipate, causing one's body temperature to become elevated to a potentially dangerous level.
  • hypothermia
    a condition where the body loses heat faster than it can produce it, causing one's body temperature to become dangerously low.
  • hypothesis
    a tentative explanation proposed by a scientist for observations that cannot be explained by existing scientific theories. A careful statement of a tentative or provisional conclusion to be tested.
  • ice floe
    a sheet of floating sea ice.
  • ice keel
    the underwater portion of an ice ridge.
  • IES
    Inverted Echosounder; an instrument used to measure the temperature of the water column at a single point
  • immunological response
    a bodily defense reaction that recognizes an invading substance (such as a virus, fungus, or bacteria, or a transplanted organ) and produces antibodies specific to that invading substance.
  • impulsive sound
    a broadband signal generated by sound sources such as explosions and airguns in which the sound pressure is very large at the instant of the explosion and then decays rapidly away; the duration of the peak pressure pulse is usually only a few milliseconds.
  • incident wave
    the wave moving towards the reflector
  • Infauna

    marine animals that live in the seafloor such as clams or worms

  • infrasonic
    sound waves that have a frequency that is lower than what humans can hear (i.e. below about 20 hertz). Baleen whales, such as blue and fin whales, produce these low frequency sounds. The sounds may be used to communicate over long distances and to detect large-scale topography of the seafloor. On land, elephants also use these powerful infrasonic sounds to communicate over long distances.
  • inhomogeneities
    parts that are not the same as the larger whole or not uniform in composition
  • inner ear
    the innermost part of the ear that is surrounded by the skull bone. It contains the organs of balance and hearing. The inner ear contains the vestibular system that helps maintain our balance. It also contains the cochlea that transforms sound waves into nerve impulses that are carried to the brain.
  • intensity
    the average amount of sound power (sound energy per unit time) transmitted through a unit area in a specified direction. The unit of intensity is watts per square meter. For simplicity, the magnitude of the intensity is often referred to as the intensity, without specifying the direction in which the sound is traveling.
  • inter-click interval
    the time it takes an echolocation signal to be sent out and an echo to return, combined with the time the animal needs to receive and process that echo.
  • interface wave

    a type of wave that is only found at the interface between two dissimilar media such as at the boundary of the sea floor and the ocean

  • invertebrate
    an animal that lacks a backbone (marine examples include lobsters, shrimp, squid, clams, crabs, and sea stars).
  • ion
    an atom or a group of atoms that has an electric charge. Positive ions, or cations, are formed by the loss of electrons; negative ions, or anions, are formed by the gain of electrons.
  • kelp rockfish
    Sebastes atrovirens
  • kerplunks
    technique used by dolphins to drive fish away from protected areas such as sea grass beds. A dolphin will lift its tail and lower body out of the water and crash it down on the water surface. This causes a loud splash and creates a trail of bubbles under the water. The bubbles startle the fish hiding in the seagrass and flush them from their hiding places, making it easier for the dolphin to detect them.
  • keystone
    a species on which other species in an ecosystem largely depend, such that if it were removed, the ecosystem would drastically change
  • killer whale
    Orcinus orca
  • Kina
    Evechinus chloroticus
  • kinetic energy
    the energy possessed by a system or object as a result of its motion.
  • knots
    a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph.
  • krill
    small, shrimp-like invertebrates (also called euphausiids) that swarm in dense patches within the water column or at the sea surface. They have hard mouths and tail parts that reflect sound. Krill is an important food source for many marine organisms including whales and seals.
  • labyrinth
    a complex system of interconnecting bony or membranous cavities, particularly those concerned with hearing and balance
  • ladyfish
    Elops saurus
  • Lake sturgeon
    Acipenser fulvescens
  • lanugo
    the soft, downy hair that covers some newborn mammals; in Arctic seals, it is a white fur that is highly prized by seal hunters, most famously associated with the hunting of harp seal pups
  • Largemouth bass
    Micropterus salmoides
  • laryngeal sac
    an inflatable “pouch”, or often a pair of pouches, that are generally located ventral to the larynx in many mammals, particularly in primates (but not in humans), hooved mammals (e.g., reindeer, horses, antelopes), and cetaceans. The functions of laryngeal sacs are not completely understood. Like the vocal sacs of frogs, laryngeal sacs may amplify calls but in some species, they may assist extended, rapid vocalizations by acting as air reservoirs.
  • larynx
    the upper part of the trachea (air passage) that contains the vocal folds
  • lateral line
    sensory organ, found in fishes, that runs long the length of their body. The lateral line allows fish to sense movement.
  • latitude
    the angular distance of a place north or south of the earth's equator, or of a celestial object north or south of the celestial equator, usually expressed in degrees and minutes.
  • leopard seal
    Hydrurga leptonyx
  • leopard shark
    Triakis semifasciata
  • ligaments
    strong, flexible bands of tissue that hold two or more bones together at moveable joints. They help restrain the movement of bones at the joint.
  • light oil
    very fluid oil that has a strong odor, high concentrations of soluble, toxic compounds, and a high evaporation rate. Light oils consist largely of benzene and toluene.  Gasoline and diesel fuel are examples of light oils.
  • little skate
    Raja erinacea
  • localize
    determine the direction the sound is coming from.
    Low Frequency and Ranging sonobuoy; a type of passive acoustic sonobuoy
  • logarithmic
    of, relating to, or expressed in terms of logarithms. A logarithm is the power to which a base, such as 10, must be raised to produce a given number.
  • Lombard Effect
    the unconscious tendency of a person or animal to raise and/or lower their voice when going from a relatively quiet to a noisy environment and vice versa
  • Long-spined sea urchin
    Diadema setosum
  • longfin squid
    Loligo pealeii
  • longitudinal wave
    a disturbance in which the particles and the energy move in the same direction
  • loudness
    how loud a person perceives a sound to be. Not the same as the intensity of the sound. The perceived loudness varies with frequency.
  • lunge-feeding
    a method of feeding underwater in which the predator moves forward with its mouth open, engulfing the prey along with the water surrounding it.
  • Lusitanian toadfish
    Halobatrachus didactylus
  • magnetic resonance imaging (MRI)
    method of producing a three-dimensional image of object by recording the signals the object emits when placed in a magnetic field
  • manatee
    Large, herbivorous, aquatic mammal that inhabits warm coastal and inland waters of the southeastern U.S., West Indies, northern South America, and West Africa. Manatees have a robust, rounded body, small head, paddle-shaped flippers, and a flattened, rounded tail. The animals are members of the genus Trichechus.
  • mandible
    one of the jaw structures of animals. For example, in vertebrates, it is the lower jaw bone; in insects it is one of the anterior mouth parts.
  • marine fouling
    the accumulation of microorganisms, plants, algae, and/or animals on surfaces immersed in the ocean.  Buildup on marine vessels poses a significant problem.
  • masking
    reduced ability to detect, recognize, or understand sounds of interest because of interference by other sounds
  • masking sounds

    sounds that compete with sounds of interest for reception and processing in the ear of an animal. Also known as "maskers".

  • mass stranding
    a stranding event where 2 or more animals, excluding mother-calf pairs, unless a third animal strands, strand together in time and place.
  • matched-filter processing
    to detect and classify signals of sound sources within acoustic recordings by comparing against known signal (matched filtering).
  • matched filtering
    to detect and classify signals of sound sources within acoustic recordings by comparing against known signals (matched-filter processing).
  • mean
    the average of a set of measurements defined to be the sum of all of the measurements divided by the number of measurements.
  • mechanoreceptors
    sensory organs that cause response to displacement, pressure and vibrations
  • median
    the "middle" value in the list of numbers. To find the median, observations are arranged in order from smallest to largest value. If there is an odd number of observations, the median is the middle value. If there is an even number of observations, the median is the average of the two middle values.
  • medium
    substance or material that carries or transports the wave from its source to other locations. In the open ocean, the medium through which the wave travels is the ocean water.
  • melon
    lipid-filled sac in the forehead of whales that helps to focus sound
  • Melon-headed whale
    Peponocephala electra
  • mesopelagic boundary community
    small (less than 4 inches long) fishes, shrimps, and squids that live in the middle of the water column and near islands
  • metamorphosis
    the process of transformation from an immature form to an adult form.
  • methane flux
    rate of movement of methane from one reservoir to another, between seafloor sediments and the water column.
  • mid-ocean ridge
    underwater mountain chain where new ocean crust is created.
  • Mid-ocean ridge
    underwater mountain chain where new ocean crust is created.
  • middle ear
    the air-filled cavity that lies between the outer ear and the inner ear. The middle ear contains the ossicles which conduct sound vibration from the eardrum to the inner ear.
  • migration
    movement of a group of animals from one location to another
  • common minke whale
    Balaenoptera acutorostrata
  • miss
    Incorrectly deciding on the basis of a statistical test that a signal is absent when it is in fact present. A false negative.
  • mitigate
    to make (something) less severe or harmful.
  • mollusks

    invertebrates that possess a soft, unsegmented body and live in aquatic or damp habitats. Many have an external, calcareous shell (although some do not). Phylum Mollusca is the second-largest phylum of invertebrate animals after the arthropods (Arthropoda), and includes gastropods (e.g. snails and slugs), cephalopods (e.g. octopuses), and bivalves (e.g. clams).

  • molt
    to shed the outer covering, or shell, which is then replaced by a new shell that is produced by the organism
  • monostatic sonar
    when the sound source and receiver are located in the same place
  • mooring
    equipment (often consisting of anchors and chains) which holds an item (such as a boat or underwater instrument) stable and secure in one place
  • moratorium
    a temporary prohibition of an activity.
  • moratorium
    the suspension (postponement and/or delay) of a particular activity.
  • morphology
    the form and structure of an organism or any of its parts
  • mudflat fiddler crab
    Uca rapax
  • multi-channel seismics
    using multiple hydrophone arrays or streamers to record the reflected and refracted sounds from an air gun array
  • multibeam sonar
    a sonar system that emits sound waves in a fan shape toward the sea floor and can measure the ocean depth over a wide swath.
  • multiyear ice
    sea ice that has survived at least more than one melting season (i.e. one summer). Multiyear ice contains much less brine and more air pockets than first-year ice. Less brine means "stiffer" ice that is more difficult for icebreakers to navigate and clear.
  • Mysticetes
    these large cetaceans are usually more than 9.1 m (30 ft) long and can be found throughout the ocean. Instead of teeth, mysticetes have a series of horny plates called baleen. The baleen is made from the same materials as human hair and fingernails. The baleen plates hang from the gums of the upper jaw and are used to filter small bits of food from the water. Baleen whales have symmetrical skulls and have two (or paired) blowholes.
  • narial passages
    the air spaces that connect the throat region with the openings of the nose, known as the nares. It is also sometimes referred to as the nasal passages.
  • narrowband
    sounds made up of only a small range of frequencies
  • narwhal
    Monodon monoceros
  • natal
    grown, produced, or originating in a particular place or in the vicinity (of, relating to, or present at birth).
  • near field
    the sound field near a sound source array where complex constructive and destructive interference occurs among the wave fronts created by the individual sound sources
  • necropsies
    the examination and dissection of a body to determine the cause of death; autopsy
  • NeMO Net
    New Millennium Observatory Network; a project, which records and transmits daily temperature and pressure readings from Axial Volcano
  • Neural impulses
    an electrical and chemical signal sent along nerve fibers
  • neuromasts
    small, sensory receptors of arranged hair cells located along the lateral line, which respond to motion between the fish and the surrounding water
  • new england mussel
    Mytilus edilus
  • noise
    an unwanted sound or a sound that interferes with the perception of another signal, whether it be through recording or hearing.
  • non-vocal sounds
    sounds made without the use of vocal folds or other body parts whose primary function is moving air for sound production. These sounds are typically made by slapping a body part on the water or land surface, or by forcefully clapping body parts together. Non-vocal sounds may be used to communicate acoustically.
  • normal line
    a line that is perpendicular (makes a 90 degree angle) to a surface
  • North Atlantic right whale
    Eubalaena glacialis
  • North Pacific right whale
    Eubalaena japonica
  • Northern bottlenose whale
    Hyperoodon ampullatus
  • Northern elephant seal
    Mirounga angustirostris
  • Northern fur seal
    Callorhinus ursinus
  • Northern seahorse
    Hippocampus erectus
  • Northern shrimp
    Pandalus borealis
  • Atlantic herring
    Clupea harengus
  • null decision
    correctly deciding on the basis of a statistical test that a signal is absent when it is in fact absent.
  • null hypothesis
    the hypothesis that there is not a real difference between the means of two data sets.
  • ocean acidification
    a reduction in the pH of the ocean over an extended period of time, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere. When CO2 is absorbed by seawater, chemical reactions occur that reduce seawater pH, carbonate ion concentration, and saturation states of biologically important calcium carbonate minerals. These chemical reactions are termed "ocean acidification" or "OA" for short.
  • ocean front
    the interface between two water masses of different  physical  characteristics
  • ocean observatory
    a networked array of sensor systems that measure the physical, chemical, geological and biological variables in the ocean and seafloor as well as the overlying atmosphere.
  • oceanographic variable
    a characteristic of the ocean that changes
  • octave band sound
    sound over a range of frequencies where the frequency in Hertz of the upper end of the range is twice the frequency of the lower end.
  • octavo-lateralis system
    comprised of the lateral line and inner ear of fish; provides fish with balance, hearing, and the ability to feel vibrations from a distance
  • odontocete
    group of mammals that includes the toothed cetaceans. This includes some whales (such as sperm whales, orca or killer whales, and beaked whales) as well as all dolphins and porpoises.
  • offspring
    next generation or baby of a certain species
  • olfactory organ
    an organ for smelling
  • omnidirectional
    having no directional component; producing or receiving sounds from all directions
  • omnivore

    an organism that eats plants and animals.

  • omnivorous
    organisms that eat both animals and plants
  • opportunistic feeding
    a type of foraging in which an animal feeds on a wide variety of prey and is able to adapt to whatever food becomes available.
  • oral cavity
    the mouth, which forms the first chamber of the digestive system. It includes the space surrounded by the lips, teeth, hard and soft palates, cheeks, and tongue. The oral cavity ends at border of the pharynx, which is approximately the line just anterior to the tonsils.
  • organ of Corti
    the sensory part of the inner ear that converts sound signals into nerve impulses. Located on the basilar membrane, it contains sensory cells that transform vibrations into neural code for sound processing by the brain. It contains many important cells including the inner and outer hair cells.
  • oscar
    Astronotus ocellatus
  • oscillation
    a flow periodically changing direction.
  • ossicles
    three tiny bones - the incus (anvil), malleus (hammer), and stapes (stirrup) - that lie in the middle ear. The ossicles conduct sound across the middle ear to the inner ear by forming a bridge between the eardrum and the oval window.
  • otariids or eared seals
    fur seals and sea lions that have visible ear flaps. They have an elongated neck and long front flippers. Their hind flippers can be turned forward for walking on land.
  • otolith
    small bones in the inner ear which provide balance, and, in fish, aid in hearing
  • ototoxic
    causing damage to the ear or its nerve supply.
  • outer ear
    the outermost part of the ear that is external to the ear drum or tympanic membrane. It directs sound waves down the air-filled ear canal onto the eardrum.
  • oval squid
    Sepiotheutis lessoniana
  • oval window
    a membrane-covered opening between the middle ear and the inner ear. The oval window is connected to the third ear ossicle (stapes) and passes sound vibrations to the inner ear.
  • overpressure
    The pressure in the shock wave from an explosion that exceeds the existing atmospheric or hydrostatic pressure in the medium through which the shock wave is propagating.
  • oyster toadfish
    Opsanus tau
  • Pacific humpback dolphin
    also known as the Indo-Pacific humpback dolphin; Sousa chinensis
  • Pacific Missile Range Facility (PMRF)
    a U.S. Naval facility off the island of Kauai, Hawaii, that is the world's largest instrumented, multi-dimensional testing and training missile range. It is the only range in the world where submarines, surface ships, aircraft, and space vehicles can operate and be tracked simultaneously. There are over 1,100 square miles of instrumented underwater range and over 42,000 square miles of controlled airspace. Additional bottom-mounted hydrophones are being installed at PMRF in early 2011, and similar to AUTEC and SCORE, a Marine Mammal Monitoring (M3R) system is being installed to monitor vocalizing animals.
  • Pacific oyster

    Magallana gigas

  • Pacific white-sided dolphin
    Lagenorhynchus obliquidens
  • pack ice
    a large expanse of floating ice
  • pack ice
    a large area of floating ice pieces that have been driven together by wind, currents, etc. to form a nearly continuous mass of ice
  • pallid sturgeon
    Scaphirhynchus albus
  • pan bone
    thin bone in the back of the lower jaw that helps transmit sound to the middle ear
  • parallel
    being an equal distance apart everywhere, extending in the same direction, never meeting or intersecting
  • particle motion
    the change in position of a particle with respect to time; in acoustics, particle motion is vibratory motion in which the particles move back and forth around an equilibrium point.
  • passive acoustic monitoring (PAM)
    observation method where an acoustic device is deployed in the ocean to capture sounds from the surrounding environment (the instrument does not produce any sounds). The sounds received by the instrument are identified and classified. PAM has become an important tool in observing cetaceans, especially deep-diving species.
  • passive acoustics
    listening to sound sources; sound is only received.
  • passive margin
    the transition between oceanic and continental landmasses that is not a plate boundary and therefore experiences little to no volcanic or earthquake activity.
  • patchiness

    degree of irregular, or uneven, appearance or quality.

  • peak pressure
    the range in pressure between zero and the greatest pressure of the signal.
  • peak pressure/0-to-peak pressure
    the range in pressure between zero and the greatest pressure of the signal
  • peak-to-peak pressure
    the range in pressure between the most negative and the most positive pressure of the signal
  • pectoral fins
    the uppermost of the paired fins on a fish
  • pectoral flipper
    forelimbs of whales and dolphins that are used for stability and steering. These appendanges are generally flattened and paddle-like. Humpback whales have very large pectoral flippers, reaching 5 m (15 ft) in length.
  • pectoral free rays
    rays that are part of the fishes pectoral fins but are free from the actual fin skin. These rays aid in the movement of the fish.
  • pectoral girdle
    the bony or cartilaginous arch that supports the forelimbs of a vertebrate
  • peer-reviewed
    scientific papers that have been subjected to evaluation by highly qualified experts in the field, the reviewers are usually anonymous and check the papers for inconsistencies, invalid conclusions and editorial errors
  • peer review
    a process by which a scholarly work (such as a paper or a research proposal) is checked by a group of experts in the same field to make sure it meets the necessary standards before it is published or accepted
  • pelagic
    of, relating to, or living or occurring in the open ocean.
  • pelagic species
    organisms that swim or drift in the water; these organisms are distinct from those living on or in the bottom sediments.
  • perceive
    to recognize, discern, or understand.
  • Period
    the time duration between any point on a wave and the same point on the next wave, e.g., from one wave crest to the next wave crest; the time for a particle to make one complete cycle at a given point
  • permanent threshold shift (PTS)
    a permanent increase in the threshold of hearing (minimum intensity needed to hear a sound) at a specific frequency above a previously established reference level
  • perpendicular
    being at right angles
  • pH
    a figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acid, and higher values more alkaline (basic).
  • pharyngeal
    teeth located in the gill or throat region
  • phase
    the location of a point within a wave cycle of a repetitive waveform, measured as the fraction of a wave cycle and often expressed as an angle; one cycle is 360º or 2 π radians.
  • phocids or true seals
    seals, such as harbor seals, that have no visible ear flap. They have a streamlined body with short front flippers. Their hind flippers are directed backward and they are not used for walking on land.
  • phon
    a unit of loudness for pure tones that accounts for the perceived loudness of tones; the number of phon of a sound is the decibel of a sound at 1 kHz that is perceived to be just as loud.
  • photophores
    light producing organs that appear as bright spots on various marine animals, including fishes and cephalopods.
  • physiological stress
    a reaction to a change that requires a physical, mental or emotional adjustment or response.
  • piezoelectric effect
    the ability of some materials (notably crystals and certain ceramics) to generate electricity in response to applied mechanical stress
  • piezoelectric material
    a material that produces electrical charges when subjected to pressure changes
  • pilot whale
    Globicephala spp.
  • ping
    to query (another computer on a network, or in this case, an acoustic transponder) to determine the location of it.
  • pink snapper
    Pagrus auratus
  • pink snappers
    Pagrus auratus
  • pinna, auricle
    the ear flap or outer part of the ear that extends from the head. The pinna funnels sound down the outer ear canal to the eardrum.
  • pinniped
    group of mammals that includes seals, sea lions and walruses
  • pitch
    an up-or-down movement of the front (bow) of a vessel (ship, glider, etc.).
  • pitch
    a ship pitch motion is an up or down, front to back motion.
  • plainfin midshipman
    Porichthys notatus
  • plane wave
    a wave in which the wave fronts are a series of parallel planes.
  • planktivore

    an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton.

  • plankton
    relatively small organisms that drift or float passively in the water and are carried wherever currents and tides take them. Plankton are often microscopic and are an important food source for other aquatic organisms. There are two types of plankton- phytoplankton (plants and autotrophs) and zooplankton (animals).
  • plectrum
    part of the spiny lobster that is found underneath the files. It is a soft piece of tissue that is found at the base of the antennae. The plecta is what the lobster pulls over the files to produce sound
  • pneumatic
    containing or operated by air or gas under pressure.
  • pod
    a social group of whales that are clustered together. Some toothed whales, such as orcas travel in large, sometimes stable pods. They may group together to hunt their prey and/or migrate.
  • polar bear
    Ursus maritimus
  • pollack
    Pollachius pollachius
  • polyps
    small marine invertebrates that have hard, cup-like, limestone skeletons. Polyps live in large colonies where they take-in the calcium from the ocean and to build a hard shell around themselves. The skeletons grow one on top of one another and as a result a coral reef is able to grow.
  • population
    the entire collection of individuals or items from which samples are drawn.
  • porosity
    a measure of the pore space in a material, often expressed as a percentage of total volume
  • potential energy
    the energy possessed by an object as a result of its position relative to other objects, stresses within itself, its electric charge, or other factors.    
  • power
    the probability of rejecting the null hypothesis in a statistical test when it is false.
  • power
    the rate at which work is done; the amount of energy transmitted over a given amount of time.
  • power spectral density level

    the power present in a signal as a function of frequency, measured in units per Hz.

  • precision
    the degree to which repeated measurements under unchanged conditions show the same results; reproducibility; repeatability.
  • prehensile
    adapted for seizing, grasping, or holding, especially by wrapping around an object.
  • pressure
    the amount of force per unit area measured in units of Pascal (which is defined as 1 Newton acting on an area of 1 square meter).
  • pressure ridge
    a ridge produced on floating ice by buckling or crushing under lateral pressure of wind or waves (tide).
  • pressure wave

    a longitudinal wave in the seafloor or solid Earth (also called a compression wave)

  • profile
    the change of an oceanographic variable with water depth
  • projector
    an instrument that sends out sound waves; consists of a transmitter and a transducer
  • projector arrays
    a collection of individual projectors used together to generate a directional sound beam
  • propagation
    the movement of sound through a medium.
  • pulse
    a short duration broadband signal.
  • pulse train
    a repetitive series of short duration, broadband signals that are separated in time by a fixed and often constant interval
  • pure tone
    a sound that consists of one single frequency
  • queen parrotfish
    Scarus vetula
  • radionuclide
    a radioactive atom.
  • RAFOS floats
    floating instruments designed to move with a current and track the current's movements
  • rainbow trout
    Oncorhynchus mykiss
  • ramp-up
    gradually increasing the sound source level
  • rarefaction
    the instantaneous, local reduction in density of a gas or other medium resulting from passage of a sound wave.
  • Rayleigh wave

    A Rayleigh wave is a surface wave causing retrograde elliptical particle motion at the surface. Rayleigh waves are one type of seismic wave produced by earthquakes. Found at an interface between a solid and a vacuum or a low-density gas medium such as the Earth’s atmosphere.  Also called ground roll.

  • receiver
    something that listens for or receives sound; it may or may not record the sound
  • receiver-operating-characteristic (ROC) curve
    a curve that plots the cumulative distribution functions of the false-alarm probability and the detection probability on the x-axis and y-axis, respectively, to select the optimal detection threshold.
  • recess
    hole, corner or niche. For example, a rock recess, a place surrounded by rocks where a fish can hide
  • rectified diffusion
    when acoustic energy causes supersaturated gas to be pumped into an existing small bubble, making the bubble increase in size
  • red drum
    Sciaenops ocellatus
  • red grouper
    Epinephelus morio
  • red hind
    Epinephelus guttatus
  • reflected wave
    the wave moving away from the reflector
  • reflection
    the deflection of the path of a sound wave by an object or by the boundary between two media
  • reflector
    any boundary between two media that causes the reflection of a wave
  • refraction
    the bending of a sound wave towards a region of slower sound speed.
  • repertoire
    suite of behaviors that an animal may use in different contexts; in this case, the number of call types that have been distinguished based on categorization of vocal behavior.
  • resistance
    resistive force is a force whose direction is opposite to the velocity of the body, or of the sum of the other forces; may be referred to as "friction" or "drag".
  • resonance
    when sounds of specific frequencies cause air- or fluid-filled organs to vibrate with amplitudes that are large compared to the amplitude of incoming soundwaves
  • resonator
    something that fills with sound and acts as a natural amplifier
  • rete mirabile
    a tightly packed bundle of capillaries which works with the gas gland to force gases into the bladder
  • reverberation
  • reverberation
    the total sound reflected by multiple scatterers
  • ringed seal
    Phoca hispida
  • rip current
    a strong, narrow surface current that flows rapidly away from the shore, returning the water carried shoreward by waves.
  • rise time
    the time it takes for the leading edge of an [acoustic] pulse to rise from its minimum to its maximum value.
  • risk function
    calculation to predict the probability of a behavioral response based on several factors, including sound received levels
  • Risso's dolphin
    Grampus griseus
  • Risso's dolphin
    Grampus griseus
  • roll
    the rotation of a vessel about its longitudinal (front/back) axis.
  • roll
    a ship roll motion in a side-to-side tilting motion.
  • root-mean-square pressure
    the square root of the average of the square of the pressure of the sound signal over a given duration. Root-mean-square is often abbreviated rms
  • rorquals
    whales of the family Balaenopteridae which includes humpbacks, sei, minke, fin, blue and Bryde's whales. They have throat pleats or ventral grooves that expand when the whales gulp large amounts of water while feeding.
  • rostrum
    upper jaw of whales that is elongated and looks like a beak
  • sablefish
    Anoplopoma fimbria
  • saithe
    Pollachius virens
  • salinity
    the total amount of salt dissolved in seawater; the units most often used are parts per thousand (ppt) but practical salinity unit (psu) is now the accepted standard in oceanography. An average salinity value for seawater is 35 ppt (psu) or 35 parts of salt in 1000 parts of water.
  • salt domes
    a layer of salt in a domed structure that was formed beneath the Earth's surface by the movement of salt over long periods of time. Salt domes are often associated with oil and gas deposits.
  • sample
    a subset of the population.
  • sample size
    the number of individuals or items in a subset or sample of the population from which estimates of various statistical measures of the whole population are calculated.
  • sand fiddler crab
    Uca pugilator
  • sardines
    small, silvery, slender fish of the herring family that have one short dorsal fin and no scales on their heads
  • Sargassum or Gulfweed
    a type of brown algae (of the genus Sargassum) that have a branching thallus (body) with lateral outgrowths differentiated as leafy segments, air bladders, or spore-bearing structures
  • satellite altimetry
    satellite radar altimeters measure the ocean surface height (sea level) by measuring the time it takes a radar pulse to make a round-trip from the satellite to the sea surface and back. Features on the sea floor such as mountains add extra pull to Earth's gravity field, drawing more water around them and bulging the sea surface outward. The sea surface height can then be used to estimate ocean bathymetry. In 2014 satellite based bathymetry could resolve features of approximately 1.5 km (0.93 miles) or larger.
  • saturate

    when no more of something can be dissolved, or the degree or extent to which something is dissolved or absorbed compared with the maximum possible, usually expressed as a percentage

  • scattered/scattering
    the diffusion of the sonar signal in many directions through refraction, diffraction and reflection, primarily due to the material properties of the seafloor. Scattering is one of the causes of attenuation in sonar, resulting in signal weakening.
  • scatterer
    an object that reflects sound energy, can be a particle in seawater or the sea surface or the seafloor
  • scattering
    when the path of a sound wave is broken up by objects (volume scattering) or the sea floor or sea surface (boundary scattering)
  • Scholte wave

    a surface wave causing elliptical motion at the interface. Found at an interface between a solid and an elastic medium such as the seafloor and water. Also called ground roll.

  • school
    a large group of marine animals, for example fish, that swim together. The appearance of a large number of individuals may ward off potential predators.
  • Sciaenidae
    family of fishes that contains approximately 270 species distributed in the Atlantic, Pacific, and Indian Oceans. This family is commonly known as the drums, which are renowned for their sound producing ability.
  • scientific method
    the orderly process by which scientists ask questions about the natural world and test their observations
  • scuttle
    to sink (a vessel) deliberately.
  • sea otter
    Enhydra lutris
  • sea state
    condition of the surface of the ocean, measured on a scale 0-9, categorized by wave height.
  • Sediment

    solid particles of inorganic or organic material deposited in water on the bottom

  • sei whale
    Balaenoptera borealis
  • seismic
    relates to an earthquake, earth vibration or volcano
  • seismic reflection
    a technique for examining the layers of the seafloor that uses the sound energy that is reflected by different layers in the seafloor.
  • seismic refraction
    a technique for examining the layers of the seafloor that uses the sound energy that is refracted by different layers in the seafloor.
  • seismic wave
    a wave of energy caused by the sudden movement of rock, as in an earthquake, or by an explosion. Seismic waves travel trough the Earth and are recorded by a seismometer.
  • seismometer
    an instrument that records ground movement; used to detect and measure earthquakes
  • semi-terrestrial
    living mostly on land but requiring water and/or a moist environment (esp. as a breeding site). Most amphibians (e.g. frogs) and many crustaceans (e.g. crabs) are semi-terrestrial.
  • sensorineural hearing loss
    hearing loss due to damage to the nerves or inner ear structures
  • sensory hair cells
    bundles of hair like projections (cilia) located on the surface of the inner ear that become stimulated by movement of the otolith against them. Stimulation of the hair cells results in sending a signal to the brain which is interpreted as sound.
  • sequestration

    the process of depositing carbon from the atmosphere in a pool , or reservoir. In terms of carbon sequestration, it presumes a reservoir that is not easily transferable to the atmosphere or only transfers over a long time period.

  • setae
    a stiff hair, bristle, or bristle like part on an organism.
  • sexual dimorphism
    distinct difference in size or appearance between male and female sexes of an animal
  • shadow zone
    a region of low sound intensity that sound waves traveling away from a source in the ocean do not reach, usually because the sound waves are refracted away from that region
  • shear wave

    a transverse wave in the seafloor or solid Earth

  • shelf-edged habitats
    ocean habitat on the edge of the continental shelf
  • shoal
    a large school of fish
  • shock wave
    a fully developed compression wave of large amplitude, across which density, pressure, and particle velocity change drastically.
  • side scan sonar
    sonar is an acronym for sound navigation and ranging equipment. Sonar systems use sound waves to detect underwater objects by listening to the returning echoes. Side scan sonar uses the strength of the returning echo, not the travel time, to map the seafloor and identify objects on the seafloor.
  • signal
    sound that is used for a specific task, such as to convey information.
  • signal excess
    the amount (in decibels) by which the signal- to-noise ratio (SNR) exceeds the detection threshold (DT).
  • signal processing
    analyzing sounds from a receiver to detect and classify sound sources
  • signal processing
    the analysis of signals to obtain information.
  • signal-to-noise (SNR) ratio
    the ratio that compares the received level of a sound signal and the background noise level. For example, it is easy to hear conversations in a quiet room, where the signal-to-noise ratio is high, but it is difficult to hear conversations at a noisy party, where the signal-to-noise ratio is low.
  • signature sound
    a unique sound that is associated with a specific sound source
  • signature whistle
    tonal sounds produced by whales and dolphins that are unique to a particular individual and distinct from any other member of the group. Signature whistles provide a way to recognize individuals and help maintain group cohesion.
  • silver perch
    Bairdiella chrysoura
  • sirenians
    group of mammals that includes manatees and dugongs
  • smolt
    a young salmon (or trout) at the stage of development when it assumes the silvery color of the adult and is ready to migrate to the sea.
  • snapping shrimp
    Alpheus heterochaelis
  • SOFAR channel
    SOFAR stands for SOund Fixing And Ranging. The sound speed minimum at 800-1000 meters of water depth is called the deep sound channel or, more historically, the SOFAR channel.
  • sonar
    an acronym for SOund Navigation And Ranging equipment. Sonar systems use sound waves to detect underwater objects by listening to the returning echoes. The distance to the object or the seafloor can be calculated by measuring the time between when the signal is sent out and when the reflected sound, or echo, is received.
  • sonic muscle
    a muscle that is attached to the swim bladder. Rapid flexure of the sonic muscle against the swim bladder produces drum-like sounds commonly associated with courtship and spawning behavior.
  • sonic muscle - swim bladder
    a combined mechanism used by fishes to produce sound. The swim bladder is a gas filled organ primarily used for buoyancy control and is also important for hearing in some fishes. The sonic muscle is attached to the swim bladder. Rapid flexure of the sonic muscle against the swim bladder produces drum-like sounds commonly associated with courtship and spawning behavior.
  • soniferous
    sound producing
  • sonobuoy
    instrument that is dropped into the ocean (from either an aircraft or ship) to record underwater sounds. It includes a hydrophone and a radio transmitter to send sound signals back to the aircraft or ship. The U.S. Navy uses this instrument to listen for enemy submarines. Sonobuoys may also be used to record marine mammal calls and listen for earthquake activity.
  • sonogram
    graphic presentation of a sound. A sonogram plots the frequency vs. time and represents the different intensity of the frequencies with different colors. It is similar to a contour map or bathymetric map where the different colors represent different water depths. Also called a spectrogram
  • sonoluminescence
    the production of light as a result of the passing of sound waves through a liquid medium. The sound waves cause the formation of bubbles that emit bright flashes of light when they collapse.
  • sound channel
    an area of slow sound speed that causes sound waves to become focused at this water depth
  • sound channel axis
    depth of the minimum sound speed within the sound channel. Sound waves cycle above and below the axis as they move through the sound channel.
  • sound exposure level (SEL)
    the decibel level of the time integral (summation) of the squared pressure over the duration of a sound event; units of dB re 1 µPa2/s
  • sound field
    the level of sound at different distances and depths from the source
  • sound intensity level
    10 times the logarithm of the ratio of the intensity of a sound wave to a reference intensity; also known as intensity.
  • sound level
    10 times the logarithm of the ratio of the mean-square pressure of a sound to the square of a reference sound pressure. Sound pressure level will usually be shortened to sound level on the DOSITS website. Sound pressure level is given in relative units named decibels (dB). Sound pressures for transient signals are sometimes given as peak or peak-to-peak pressures, rather than mean-square pressure. To avoid ambiguity, the units for sound pressure level can be written dB rms for dB root-mean-square.
  • sound receptor
    something that receives sound; sound receiver
  • sound source
    something that creates sound
  • sound spreading loss
    the decrease in intensity that occurs when a sound wave expands as it moves away from a source
  • Sound Surveillance System (SOSUS)
    a network of hydrophones mounted on the seafloors of the North Atlantic and North Pacific oceans maintained by the US Navy
  • soundscape
    acoustic environment as perceived or experienced and/or understood by a listener. (ISO Technical Committee on Acoustics, Noise Subcommittee, ISO 12913-1:2014).
  • source array
    multiple sound sources combined to operate together for a specific purpose
  • source level
    the amount of sound radiated by a sound source. It is defined as the intensity of the radiated sound at a distance of 1 meter from the source, where intensity is the amount of sound power transmitted through a unit area in a specified direction. Source level is given as a relative intensity in units named decibels (dB). In underwater sound, decibels are referenced to a pressure of 1 microPascal (µPa). Therefore, source level is reported in units of dB re 1 µPa @ 1 m.
  • Southern California Offshore Range (SCORE)
    a state-of-the-art facility that provides training and testing services to the U.S. Navy’s Pacific Fleet. The underwater tracking range is located west of San Clemente Island, CA, and consists of 84 bottom-mounted hydrophones that provide a coverage area of approximately 660 square nautical miles. Similar to AUTEC, a Marine Mammal Monitoring (M3R) system has been established at SCORE to monitor vocalizing animals via the bottom-mounted range hydrophones.
  • southern right whale
    Eubalaena australis
  • Sparker
    a sound source that uses an electric spark to generate a broadband signal.
  • spatial resolution
    the minimum difference or distance between two measured or computed values or objects that can be distinguished. It defines the limit of accuracy for a technique.
  • spatulate
    having a narrow base and a broad body (spade-shaped).
  • spawning
    to produce, release, or deposit eggs for reproduction
  • specific acoustic impedance
    the ratio of acoustic pressure to the associated particle speed in a medium.
  • spectral

    the frequency composition of sound.

  • spectrogram
    a graphic presentation of a sound. A spectrogram plots the frequency vs. time and represents the different intensity of the frequencies with different colors. It is similar to a contour map or bathymetric map where the different colors represent different water depths. Also called a sonogram
  • spectrum
    a catalog of the amplitude of a signal as a function of frequency or pitch, with graphics showing low frequencies on the left of the x-axis and high frequencies on the right.
  • sperm whale
    Physeter macrocephalus
  • spermaceti organ
    an elongated connective tissue sac in the forehead of the sperm whale that contains a waxy fluid called spermaceti
  • spherical spreading
    energy spreading out from a sound source in the shape of a sphere; the power is radiated equally in all directions from the sound source
  • spinner dolphin
    Stenella longirostris
  • Spiny Lobster
    Palinurus elephas
  • sprat
    Sprattus sprattus
  • spreading loss
    a decrease in the intensity of a wave as it spreads out from a source
  • spy-hopping
    a common whale activity in which they lift their heads above the surface of the water and observe what is happening on the surface. Whales will often spin around in order to observe in all directions.
  • squid
    mollusks of the family Cephalopoda that are a favorite food of the sperm whale
  • standard deviation
    an estimate of the variability of a set of measurements about the mean value; it is calculated by computing the square root of the variance.
  • standard deviation of the mean
    an estimate of the variability of the mean value computed from a specific set of measurements; it is calculated by dividing the standard deviation of the measurements by the square root of the number of measurements; also often called the standard error of the mean.
  • startle response
    a largely involuntary, defensive response to a sudden and/or threatening stimuli, such as a flash of light, a sudden  movement, or loud noise.  In fishes, this behavior is often displayed as a sudden bending of the body, and is a characteristic escape response.    
  • static diffusion
    when particles move from a region of higher concentration to a region of lower concentration
  • statistically significant
    findings of an experiment or study that have a low probability of being due to chance alone
  • statistics
    mathematical analysis that is used to explain and compare numerical data. This analysis helps make broader generalizations about a population from a smaller number of specific observations.
  • statocyst
    a sac-like structure containing a mineralized mass (statolith) in association with numerous sensory cells.
  • steps
    a break or irregular change in frequency of a whistle.
  • stereo
    short for stereophonic: a sound-reproduction system that uses two or more separate channels to give a more natural distribution of sound.
  • stereocilia
    long, flexible hair-like structures that occur as a brush border on the surface of some membranes
  • stereociliary bundles
    groups of hair-like projections on the upper surface of a hair cell. When stereocila bend, they trigger a release of chemicals that initiates the electrical signal (neural impulse) that is carried to and processed by the brain.
  • stereotyped
    fixed or settled in form.
  • stewardship
    the conducting, supervising, or managing of something, especially, the careful and responsible management of something entrusted to one's care.
  • stranding
    an event where an aquatic animal, especially a marine mammal, lands on a beach or becomes stuck in shallow water, is dead or sometimes alive, and probably in distress.
  • stratification
    separation of water layers based on strong density differences
  • streaked gurnards
    Trigloporus lastoviza
  • streamers
    a long (2000-6000 m) string of hydrophones typically used with air-gun arrays
  • stress
    when an optimal steady state is threatened by internal and/or external forces, and is counteracted by a physiological or biological response (to maintain/establish equilibrium).
  • stress response
    the natural coping mechanism that allows the body to deal with stressful events. A group of physiological and behavioral processes enable an animal to adapt to changes in their environment.
  • stressor
    anything that causes the body to respond by releasing stress hormones.
  • stridulation
    to produce a sound by rubbing two body parts together. Some fish make a shrill creaking noise by rubbing together bodily structures, especially skeletal parts.
  • striped dolphin
    Stenella coeruleoalba
  • stripers
    Morone saxatilis
  • sub-arctic
    relating to the region immediately south of the Arctic Circle.
  • subduction zones
    places where two tectonic plates move toward each other, and one plate plunges beneath the other plate. Often ocean crust is subducting beneath continental crust
  • submarine
  • submarine canyon
    narrow, steep-sided valleys on the seafloor.
  • subsonic
    a frequency that is below the audible range
  • substrate
    the surface or medium on which an organism lives or grows, or the material on the bottom of the ocean.
  • substratum (substrate)
    the surface that an organism grows on or is attached to
  • supersaturated
    more highly concentrated than is normally possible under given conditions of temperature and pressure
  • surf zone
    The zone within which waves approaching the coastline start breaking; also called the breaker zone.
  • surface reverberation
    sound scattering that occurs on or at the sea surface
  • surface wave

    a sound wave (or seismic wave) that travels only at an interface boundary

  • Surveillance Towed Array Sensor System (SURTASS)
    a passive sonar system used to listen for noises produced by submarines. The system consists of a long string of underwater hydrophones that are towed behind a ship and pick up sounds in the ocean.
  • SUS (Signal, Underwater Sound)
    an explosive sound source used by the U.S. Navy that consists of 0.82-kg (1.8-lb) of TNT explosive material.
  • swath
    an area shaped like a broad strip.
  • Swift scallop

    Chlamys swifti

  • swim bladder
    a gas filled organ that is primarily used for buoyancy control but is also important for hearing in some fishes.
  • swim bladder (also called an air bladder)
    an expandable, gas-filled sac that helps fish maintain buoyancy in the water. This organ is also important for hearing in some species of fish.
  • symbiotic
    having an interdependent relationship that benefits both parties involved.
  • synapse
    a junction between a nerve cell and another nerve cell or a nerve fiber or a sensory receptor
  • t-test
    a statistic that compares the sample means with the standard deviations of the sample means to determine whether the two sample means are statistically different.
  • target strength
    the amount of sound reflected back toward a sonar by a target.
  • tectonic
    relating to the deformation of the earth's crust
  • tectorial membrane
    a membrane that covers the surface of the organ of Corti in the cochlea of the inner ear
  • telemetry
    measuring and transmitting data from a remote location
  • temperature
    a measure of the atomic and molecular vibration in a substance, in degrees. The response of a solid, liquid, or gas to the input or removal of heat energy.
  • temporary threshold shift (TTS)
    a temporary increase in the threshold of hearing (minimum intensity needed to hear a sound) at a specific frequency that returns to its pre-exposure level over time
  • terrestrial
    something that lives on land as opposed to in the water. Some animals, such as sea lions spend time both on land and in the water, they are considered to be both terrestrial and marine.
  • Terrigenous

    derived from land,  referring to weathered rock grains and minerals

  • territoriality/territorial
    behavior in which an organism, for example a fish, defends its home
  • Tertiary wave
    seismic energy that has been converted into acoustic energy in the ocean. Also known as a T-wave"."""
  • Tertiary wave
    seismic energy that has been converted into acoustic energy in the ocean. Also a T-wave.
  • test
    the outer skeleton of a sea urchin. It is made up of plates that encircle the sea urchin. Spines of the sea urchin grow from the test.
  • Thalassia
    a broad-bladed seagrass occurring in shallow tropical and subtropical estuaries and nearshore marine waters
  • theory
    a hypothesis or group of hypotheses that have been consistently validated through scientific observations or experiments. Geology's theory of plate tectonics is an example of a well-documented and widely accepted theory.
  • thermocline
    a layer of water in an ocean or certain lakes, that separates warmer surface water from colder deep water. Temperature rapidly changes with depth in this region of the water column.
  • thermometry
    the measurement of temperature
  • thick-billed murre
     Uria lomvia
  • threatened
    any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range (as defined in the U.S. Endangered Species Act).
  • threshold of hearing
    the minimum intensity at which a sound of a specific frequency is reliably detected in absolute quiet conditions. The intensity level varies with frequency. Also called hearing thresholds.
  • threshold of pain
    the intensity level where sound is physically painful. Usually at 115-130 dB.
  • threshold shift
    an increase (worsening) in the threshold of hearing for an ear at a specified frequency
  • tidewater glaciers

    valley glaciers that flow all the way down to the ocean.

  • tiger shark
    Galeocerdo cuvier
  • TNT
    trinitrotoluene; a chemical compound used as an explosive material.
  • toadfish
    opsanus tau
  • tonal

    a sound consisting of a single frequency.

  • tone pips
    acoustic stimuli that are presented as single frequency, pure tone(s).
  • tonotopic organization
    to be organized by frequency.
  • tonotopically organized

    frequency-dependent resonance, in which the basilar membrane vibrates more near the base with high frequencies, while lower frequencies cause the membrane to vibrate most towards the apex.

  • towfish
    an instrument, such as a side scan sonar, that is towed behind a ship
  • trachea
    a large membranous tube reinforced by rings of cartilage, extending from the larynx to the bronchial tubes and conveying air to and from the lungs; the windpipe.
  • transducer
    the part of the sonar system that functions like an antenna, sending out sonar signals (sound waves) and receiving return echoes. The transducer converts electrical energy into sound waves and vice versa.
  • transmission loss
    the decrease in acoustic intensity (due to spreading and/or attenuation) as an underwater sound wave propagates outwards from a source.
  • transmitter
    an instrument that sends out slectrical signals
  • transponder
    a device for receiving an acoustic signal and automatically transmitting a unique return signal in response. Transponders are often used to show the location of something.
  • transverse wave
    a disturbance in which the particles vibrate up-and-down and the energy moves left-and-right
  • triangulation
    method for determining the location of a target of interest. Three distances from three known points are measured, and from these distances, a unique point of intersection can determined (this calculation is usually performed by computers).  The point of intersection indicates the target's location.
  • trill
    a fluttering sound that alternates rapidly with another note
  • trophic level

    a particular step or position within a food chain, food web, or ecological pyramid where a group of organisms exist.

  • tropical cyclone

    a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. These intense circular storms originate over warm tropical oceans.

  • tsunami
    a tsunami is a series of ocean waves generated by sudden displacements in the sea floor, landslides, or volcanic activity. In the deep ocean, the tsunami wave may only be a few inches high at the sea surface. When a tsunami wave comes ashore it will increase in height and can become a fast moving wall of water several meters high.
  • tubercle
    a small rounded projection.
  • tuned airgun array
    multiple airguns of different, carefully selected volumes that are fired at the same time.
  • turbidity
    the measure of relative clarity of a liquid. It is an optical characteristic of water and is a measurement of the amount of light that is scattered by material in the water when a light is shined through the water sample. Turbidity makes water cloudy or opaque. The higher the intensity of scattered light, the higher the turbidity. Material that causes higher levels of turbidity include clay, silt, algae, plankton, and other microscopic organisms.
  • tympanic membrane or eardrum
    a membrane that separates the outer ear from the middle ear. The eardrum vibrates in response to sound waves and passes the vibrations on to the bones of the middle ear.
  • Type I Error
    an error when one concludes that there is a real difference between two means when, in fact, there is not; also called a false positive error.
  • Type II Error
    an error when one concludes that there is not a real difference between two means when, in fact, there is a difference; also called a false negative error.
  • ultrasonic
    sound waves that have a frequency that is higher than what humans can hear (i.e. greater than 20,000 Hz). Bats and dolphins use these high frequency sounds for communication and navigation.
  • ultrasound signal
    sound vibrations that have frequencies above the range of human hearing
  • underwater dB
    the relative unit used to specify the intensity of an underwater sound. The phrase underwater dB is used on DOSITS to indicate decibels computed using root-mean-square (rms) pressure unless otherwise indicated. Underwater dB are referenced to a pressure of 1 microPascal (µPa), which is abbreviated as dB re 1 µPa. To be able to compare relative intensities given in dB to one another, a standard reference intensity or reference pressure must always be used. Scientists have agreed to use 1 microPascal (µPa) as the reference pressure for underwater sound. In air, however, scientists have agreed to use a higher reference pressure of 20 microPascals. It is important to remember that sound intensity given in underwater dB is not the same as sound intensity given in air dB. See the Advanced Topics Introduction to Decibels and Introduction to Signal Levels for additional information.
  • underwater soundscape

    characterization of the ambient sound in terms of its spatial, temporal, and frequency attributes, and the types of sources contributing to the sound field (ISO Technical Committee on Acoustics, Underwater Acoustics Subcommittee, ISO 18405:2017). Underwater soundscape is sometimes used synonymously with acoustic environment (or ambient sound) to refer to the composite of all sounds in an environment.

  • upsweep
    a signal that increases in frequency over time.
  • utricle
    the larger of the two fluid-filled cavities forming part of the inner ear (the other being the sacculus).
  • vacuum
    a space from which all gas and other matter has been removed
  • vaquita
    Phocoena sinus
  • variance
    an estimate of the variability of a set of measurements about the mean value; it is calculated by subtracting the mean from each of the measurements, squaring the differences, adding all of the squared differences together, and dividing by one less than the total number of measurements; the square root of the variance is the standard deviation.
  • vector
    a quantity, such as a velocity or force, that has both magnitude and direction.
  • velocity
    the linear speed of an object in a specified direction.
  • ventral
    of, pertaining to, or situated at the back or upper side.
  • vertebrate
    having vertebrae or having a backbone or spinal column. Fish and humans are examples of vertebrates.
  • vertical migration
    a pattern of movement that some marine organisms undertake each day. Usually organisms move to shallow waters at night and return to deeper waters during the day.
  • vestibular system
    a fluid-filled maze of canals and chambers inside the inner ear that helps maintain orientation and balance.
  • viscosity
    a molecule's resistance to motion
  • vital rates
    factors that determine the abundance or density of a population, including birth rate, death rate, emigration, age structure, and sex ratios. These factors influence population dynamics and allow scientists and managers to track population demographics through time.
  • vocal cords
    small bands of tissue within the larynx that vibrate (when air passes over them) to produce the sound.
  • vocal fold ligament
    connective tissue that strengthens the vocal folds via stiffness and support
  • vocal learning
    the modification of an animal’s vocalization(s) based on acoustic signals in its environment, such as vocalizations by conspecifics.
  • vocalization
    sounds intentionally produced by animals that may be used for communication, navigation, and feeding. In humans, air is moved from the lungs and across the vocal folds (also known as vocal cords). The vibration of the vocal folds produce sounds that are formed into words and other vocal communication signals. We do not know how sound is produced by many species of marine mammals. The term vocalization is commonly used to refer to sounds that are produced by marine mammals; however, the use of the word vocalization does not imply that marine animals are using vocal folds to produce the sounds.
  • volume reverberation
    sound scattering caused by interactions with marine life, inanimate matter, and inhomogeneities in the water
  • vulnerable
    susceptible to being hurt or damaged.
  • wake
    the track of waves left by a ship or other solid object moving through the water.  It is caused by the flow of the fluid around the body.
  • walleye pollock
    Gadus chalcogrammus (also known as Alaska pollock)
  • walrus
    Odobenus rosmarus
  • wave
    disturbance caused by the movement of energy through a medium
  • wave front
    a surface consisting of all points on a wave at the same position in a wave cycle.
  • waveform
    a waveform presents the sound in a graph as positive and negative pressure on a relative scale (often from -1 to 1) through time. The relative pressure is related to the intensity of the sound.
  • waveguide
    a structure that guides waves by restricting the wave movement in one or more dimensions resulting in efficient transmission of the wave. For example, the SOFAR channel is a waveguide in the ocean.
  • wavelength
    the length of one cycle of a wave (one crest and one trough)
  • Weberian ossicles
    a series of bones which connect the swim bladder to the inner ear and carry vibrations between to the two, aiding in hearing.
  • weddell seal
    Leptonychotes weddelli
  • whistles
    narrow-band, tonal sounds produced by many toothed whales for communication purposes. Whistles are frequency-modulated, which means the pitch of the sound changes over time.
  • white-beaked dolphin
    Lagenorhynchus albirostris
  • white noise
    a heterogeneous mixture of sound waves extending over a wide frequency range (but equal intensities).
  • white-sided dolphin
    Lagenorhynchus spp.
  • Yangtze finless porpoise
    Neophocaena phocaenoides
  • yaw
    a ship yaw motion is rotation about a vertical axis through the ship or left to right turning of the ship.
  • Yellow perch
    Perca flavescens
  • yellowtail rockfish
    Sebastes flavidus
  • zooplankton
    microscopic animals, such as crustaceans and fish larvae, that drift in the water column.
  • exclusive economic zone
    a zone extending up to 200 nautical miles (370km) from a nation's territorial waters into the ocean where that nation has jurisdiction over natural resources such as fisheries and energy production. The Exclusive Economic Zone is defined in the United Nations Convention on the Law of the Sea. Also called the EEZ.
  • Precipitation
    any liquid or frozen water that forms in the atmosphere (clouds) and falls back to the Earth (e.g. rain, hail, sleet, and snow).