Tutorial: Sound Level Exposure
What are the sound levels to which the animals are likely to be exposed?
The following figure shows the level of sound at different distances and depths as the sound travels away from the ATOC/NPAL source towards the island of Kauai. Sound travels in all directions away from the source, but only the slice related to the humpback whale example is shown. The ATOC/NPAL source is moored on the seafloor at a depth of approximately 800 meters (2600 feet), approximately 14.8 kilometers (8 nautical miles) north of Kauai. It has a source level of 195 underwater dB at 1 meter and operates at a frequency of 75 Hertz. In this picture, the source is in the upper left hand corner near the dark red. The gray area represents the sea floor. The colors in the picture show the sound level decreasing as it moves away from the sound source. You can also see that the level of sound varies with both water depth and distance from the source.
This figure shows sound traveling away from the ATOC source towards Kauai (due south). As the sound travels further away from the source, the level of sound decreases.
The third step is to combine the sound field created in the first step with the marine animal field created in the second step. One example of what a slice of this picture could look like is found below.
This is the same sound field shown in the picture above. As before, the sound source is at the upper left hand corner near the dark red. The gray area represents the sea floor. The two black diamonds are humpback whales that are predicted to be in the area while the source is transmitting. By combining the picture of the sound field with the probable locations of the marine animals, the amount of sound energy the animals might be exposed to can be estimated.
Tutorial Sections: Determine if a sound affects a marine animal