Tutorial: Echosounders

Echosounders are a type of sonar commonly used for a variety of tasks, including navigation, measuring bottom depth, and detecting schools of fish and plankton. Single beam echosounders emit a pulse of sound in a narrow cone (2°-12°).

Echosounders estimate bottom depth by measuring the time it takes for the acoustic signal to reach the bottom and the echo to return to the ship. Image Credit DOSITS.

Another type of echosounder, multibeam sonar, was developed to produce more detailed maps of the seafloor. These systems produce a fan-shaped beam (see figure) that spreads downward to the seafloor. The area of the ensonified seaflooris called the swathand is typically 1° by 120° wide.

 

Illustration of multibeam sonar from both a ship and a towed instrument to map the seafloor. Image credit: NOAA Ocean Explorer, Bermuda: Search for Deep Water Caves 2009.

Echosounders have variable source levels and can transmit a wide variety of frequencies. Source levels typically range from 185 dB re 1μPa at 1m to 230 dB re 1μPa at 1m. These systems use short duration pulses of 10 milliseconds or less. Deep water mapping systems typically use frequencies from 12 kHz to 20 kHz, while shallow water (less than 100 m depth) systems can use frequencies up to 455 kHz.

Potential Effects: Marine Mammals

There are both field and modeling studies on the potential effects of echosounders on marine mammals. Field studies have shown that beaked whales and short finned pilot whales may react to echosounder signals. During a 2013 cetacean assessment survey along the U.S. eastern seaboard, single beam echosounders, transmitting at 18, 38, 70, 120, and 200 kHz, were used to assess prey abundance, while a shipboard navigational echosounder was operated at 50 kHz. The echosounders were turned off every other day, including the navigational echosounder when it was deemed safe for the ship. Beaked whales were identified visually by observers and their echolocation clicks were detected by a towed hydrophone array (passive acoustics). When the echosounders were on, there was a significant decrease in the acoustic detection of beaked whales (3% of the acoustic detections while the echosounders were operating vs. 97% when they were off).  The data suggest the beaked whales altered their behavior when they detected the echosounders.

Data from digital acoustic recording tags (DTAGs) attached to pilot whales showed more changes of direction by the whales when exposed to a 38 kHz echosounder than when the echosounders were off. There were no detectable differences in foraging behavior whether the echosounder was on or off. While the reaction to the echosounder was considered to be subtle, it demonstrates that the animals can detect and may respond to the echosounder signal.

Modeling the potential audibility of 38 kHz echosounder signals found that a number of odontocete species could detect the sound as far as 3 to 5 km from the source. Harbor seals would also be likely to detect the sound up to 2 km from the source.  In contrast, humpback whales would likely not detect signals at this frequency

Echosounders can emit frequencies above or below their center frequencies[new glossary term], known as side lobes. For example, captive animal studies with grey seals exposed to 200 kHz echosounders showed changes of behavior, even though this center frequency is above their hearing range. Measurements confirmed that the echosounders were producing side lobes at frequencies and sound levels within the hearing range of grey seals.

Potential Effects: Fish

Most fishes do not hear in the frequencies used by echosounders. Some species in the herring family have been shown to respond to frequencies up to 200 kHz.  Research suggests American Shad change schooling behavior in the presence of a 120 kHz echosounder.

 

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Next Section: Pile Driving

 

Anthropogenic Sound Sources Tutorial Sections:

 

Commercial Vessel Traffic

Echosounders

Pile Driving

Seismic Airguns

Sonar
Wind Turbine

 

Additional Links on DOSITS

References

  • Cholewiak, D., DeAngelis, A. I., Palka, D., Corkeron, P. J., & Van Parijs, S. M. (2017). Beaked whales demonstrate a marked acoustic response to the use of shipboard echosounders. Royal Society Open Science, 4(12), 170940. https://doi.org/10.1098/rsos.170940
  • Deng, Z. D., Southall, B. L., Carlson, T. J., Xu, J., Martinez, J. J., Weiland, M. A., & Ingraham, J. M. (2014). 200 kHz Commercial Sonar Systems Generate Lower Frequency Side Lobes Audible to Some Marine Mammals. PLoS ONE, 9(4), e95315. https://doi.org/10.1371/journal.pone.0095315
  • Hastie, G. D., Donovan, C., Götz, T., & Janik, V. M. (2014). Behavioral responses by grey seals (Halichoerus grypus) to high frequency sonar. Marine Pollution Bulletin, 79(1–2), 205–210. https://doi.org/10.1016/j.marpolbul.2013.12.013
  • MacGillivray, A. O., Racca, R., & Li, Z. (2014). Marine mammal audibility of selected shallow-water survey sources. The Journal of the Acoustical Society of America, 135(1), EL35–EL40. https://doi.org/10.1121/1.4838296
  • Mayer, L. A. (2006). Frontiers in seafloor mapping and visualization. Marine Geophysical Researches, 27(1), 7–17. https://doi.org/10.1007/s11001-005-0267-x
  • Quick, N., Scott-Hayward, L., Sadykova, D., Nowacek, D., & Read, A. (2017). Effects of a scientific echo sounder on the behavior of short-finned pilot whales ( Globicephala macrorhynchus). Canadian Journal of Fisheries and Aquatic Sciences, 74(5), 716–726. https://doi.org/10.1139/cjfas-2016-0293
  • Velez, S. (2015). Effects of ultrasonic frequencies on schooling behavior of American shad (Alosa sapidissima). Journal of Aquaculture & Marine Biology, 2(2). https://doi.org/10.15406/jamb.2015.02.00019