Determining the Distance of Sperm Whales in the Norther Gulf of Mexico from an Underwater Acoustic Recoding Device

Kendal Leftwich – kmleftwi@uno.edu

George Druant – George.Drouant@oit.edu

Julia Robe – jerobe@uno.edu

Juliette Ioup – jioup@uno.edu

University of New Orleans

2000 Lakeshore Drive

New Orleans, LA 70148

 

Determining the range to marine mammals in the Northern gulf of Mexico via bayesian acoustic signal processing

Presented Acoustic Localization IV afternoon, December 8, 2020

179th ASA Meeting, Acoustics Virtually Everywhere

 

The Littoral Acoustic Demonstration Center – Gulf Ecological Monitoring and Modeling (LADC-GEMM) has been collecting underwater acoustic data in the Northern Gulf of Mexico (GoM) since 2002 through 2017.  Figure 1 shows the collection sites and the location of the BP oil spill in April 2010.  The data are collected by a hydrophone, an underwater microphone, which records the acoustic signals or sounds of the region.

 

One of the goals of the research at the University of New Orleans (UNO) is to identify individual marine mammals by their acoustic signal.  Part of this identification includes being able to locate them.   In this paper we will briefly explain how we are attempting to locate sperm whales in the GoM.

 

First, we need to understand how the whale’s sounds travel through the water and what happens to them as they do.  Any sound that travels through a medium (air, water, or any material) will have its loudness decreased.  For example, it is much easier to hear a person talking to you when you are in the same room, but if they are talking to you through a wall their voice level is reduced because the signal travels through a medium (the wall) that reduces its loudness.  Therefore, as the whale signal travels through the GoM to our hydrophones the loudness of the signal is reduced.  The impact that this has on the whale’s signal is determined by the temperature, the depth of the recording device below the surface, the salinity, and the pH level of the water.  Using this information, we can determine how much the loudness of the whale’s signal will decrease per kilometer that the signal travels.  This can be seen in figure 2.

 

 

We will use the known signal loudness of the sound emitted by a sperm whale and the recorded loudness of the signal along with the impact of the GoM on the signal to determine how far away the sperm whale is from our hydrophone.   Unfortunately, due to technical limitations of the equipment we can only do this for a single hydrophone so we cannot currently locate the sperm whale’s exact position. We can only tell you where it is located at a certain distance around the hydrophone.  Figures 3 shows graphically the results of our calculations for two of the 276 sperm whale signals we used with our model to estimate how far away the whale is from our hydrophone.

 

 

 

 

 

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