Acquiring and Analyzing the Bioacoustic Communication of Marine Mammals Using NI LabVIEW and USB Data Acquisition

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"Integration with LabVIEW gives us more functionality for logging, monitoring, and analysis, and we can display and save results in the same application with the LabVIEW MathScript routine"

- Magnus Wahlberg, Fjord & Bælt

The Challenge:
Developing a reliable data acquisition system capable of collecting and analyzing the ultrasonic signals produced by wild killer whales and harbor porpoise in captivity.

The Solution:
Designing a friendly, multichannel system based on LabVIEW software and data acquisition (DAQ) hardware to perform live audio monitoring and movement tracking.

Author(s):
Magnus Wahlberg - Fjord & Bælt
Katja Petersen - Fjord and Baelt
Ida Eskesen - Fjord and Baelt

Several animal species, including killer whales, use biological sonar, also known as echolocation, for communication, identification, and navigation. The whale emits short ultrasonic “clicks” that travel long distances because of the acoustical properties of water. The echoes of the clicks are returned from various objects in the environment and provide the whale with information regarding its surroundings.

To learn more about how these whales use echolocation in their natural habitat, it is important to understand the properties of the clicks. For example, the echolocation clicks of a sperm whale have very high source levels and the potential to operate in long-range biosonar systems. On the other hand, low-amplitude sounds, such as those produced by small-toothed whales, work only with short-range biosonar systems.

Challenges in Acquiring and Analyzing Echolocation Clicks

To learn more about the ultrasonic emissions and how they are used in the wild, we need to collect the signals from wild killer whales for analysis. Because the killer whales that we want to monitor live in the North Sea in very cold, rough waters above the Arctic Circle, we need to use sophisticated software and hardware that can stand up to the harsh environmental elements and are easy to use in the field. We also faced the challenge of potential interference from other noise sources including boats and other animals.

Using LabVIEW and USB Data Acquisition

Historically, it has been challenging to find reliable equipment for use in these types of environments; however, we developed a system based on  LabVIEW software and NI data acquisition hardware that met all of our criteria. The recording gear consists of a linear hydrophone array, a multichannel preamplifier, and a bandpass filter connected to a digital recorder. We use high-speed digital recorders with signal processing software based on LabVIEW. Additionally, all the equipment is battery-powered to avoid noise interferences from other electrical units on board the ship.

The hardware includes a high-speed M Series multifunction DAQ module to provide the required resolution and channel count. We used the USB interface to manage large amounts of data, up to 30 to 50 GB each day, and had a dedicated software solution for logging, alarming, playback, and analysis.

Benefits of a System Based on the NI Platform

Our original system required us to manually insert the data and then note the data or print the graph after each new data point. However, with the new system based on LabVIEW, we can load wave files, prefilter, and automatically find and measure click locations using peak detection. The new system has 16 bits rather than 12.

Additionally, integration with LabVIEW gives us more functionality for logging, monitoring, and analysis, and we can display and save results in the same application with the LabVIEW MathScript routine. We can also process amplitude demodulation and envelope detection as well as make adjustments for filtering and squelch functions using LabVIEW.

We modified this software to monitor the birth and echolocation development of the first harbor porpoise calf ever to survive in captivity. We simultaneously recorded 10 signals sampling at 500 kHz each on one laptop for several hours every day, without any software or hardware problems. We were impressed with the system performance during this study, which resulted in hundreds of gigabytes of unique data on toothed-whale echolocation.

Author Information:
Magnus Wahlberg
Fjord & Bælt
Denmark
magnus@fjord-baelt.dk

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