How it Works

Equipped with advanced sensors and autonomous capabilities, our vehicle platforms provide a reliable and efficient means to track and monitor marine mammals, contributing to our understanding of their ecology and conservation.

The robots carry the digital acoustic monitoring instrument or DMON, a passive acoustic instrument that is capable of recording and processing audio in realtime. We have implemented a low-frequency detection and classification system (LFDCS; Baumgartner and Mussoline 2011) on the DMON to identify marine mammal calls from a variety of autonomous platforms, including gliders, profiling floats, and moorings (Baumgartner et al. 2013). The LFDCS produces pitch tracks of sounds, which describe changes in the frequency (pitch) of a call over time. Scientists typically examine spectrograms to identify marine mammal calls, such as the one below, and pitch tracks are derived from these spectrograms.

What is a Spectrogram?

Spectrograms are a method to visualize sound, and they describe how the frequency (pitch) of sounds change over time. They also describe the loudness or amplitude of a sound (in the spectrogram above, calls that are louder appear brighter). Very simply, the LFDCS seeks to "draw a line" through each call in the spectrogram. These lines, or pitch tracks, can be used to describe the call. The pitch tracks depicted below were generated from the spectrogram above (the colors indicate the loudness of the call; cooler colors are quieter, warmer colors are louder).

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Note that the calls shown in the spectrogram are easily recognizable by their corresponding pitch tracks. The LFDCS extracts simple statistics of each pitch track (e.g., duration, average frequency, rate of change of frequency with time) and uses quadratic discriminant function analysis to classify each call. Classification is based on a known set of calls contained in a call library that is defined prior to deployment of the DMON/LFDCS. Through communications with the robot, and ultimately with a shore-based computer via Iridium satellite transmission, the DMON/LFDCS remotely reports tallies of calls for each call type in its call library, as well as a subset of pitch tracks. Because of limitations in the amount of data that can be transmitted via satellite, the DMON/LFDCS relays a maximum of 8 KB of pitch track data every hour.