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Marine Species Monitoring

Autonomous Real-Time Passive Acoustic Monitoring of Baleen Whales for Mitigating Interactions with Naval Activities

Introduction & Objectives

The Navy regularly conducts studies of marine mammal distribution and occurrence in association with training exercises to better monitor potential interactions between marine mammals and naval activities. Methods used for these studies include visual surveys and acoustic monitoring via passive acoustic recorders; however, these methods have significant drawbacks. Visual surveys from ships and airplanes are expensive, and they cannot be conducted during nighttime or periods of high winds, rough seas, or poor visibility. Although passive acoustic recorders have large detection ranges and can be used to persistently detect vocalizing marine mammals regardless of weather conditions, recordings can be accessed only after recovery of the recording instrument. In addition, acoustic analysis by a trained person is time consuming and expensive.

Recent advances in low-power digital signal processors, detection algorithms, and satellite communications have made near real-time (within hours of sound detection) audio processing, sound detection, classification, and reporting from autonomous platforms feasible. This project will demonstrate a passive acoustic detection and classification hardware/software system that is capable of detecting the calls of four species of endangered baleen whales—fin (Balaenoptera physalus), humpback (Megaptera novaeangliae), sei (Balaenoptera borealis), and right (Eubalaena glacialis)—from three different autonomous platforms (Slocum gliders, wave gliders, moored buoys). In particular, the project seeks to: (1) demonstrate year-round, large-scale near real-time acoustic surveillance from these autonomous platforms; (2) validate near real-time acoustic detections using audio recorded in situ and airplane-, ship-, and land-based visual observations; and (3) develop best practices for integrating near real-time acoustic detections from autonomous platforms into persistent visual monitoring programs such as the current National Oceanic and Atmospheric Administration and Navy marine mammal aerial survey programs off the U.S. east coast.

Technical Approach

The enabling technology for this project is the digital acoustic monitoring (DMON) instrument/low-frequency detection and classification system (LFDCS), a combined hardware (DMON) and software (LFDCS) system capable of detecting and reporting a wide variety of low-frequency vocalizations in near real time. The DMON collects, conditions, processes, and records audio from up to three attached hydrophones. Because it is programmable, applications can be developed to detect, classify, and report sounds from the collected audio in near real time. The LFDCS is software that detects and describes sounds using pitch tracking, and it classifies those sounds using quadratic discriminant function analysis. The DMON/LFDCS is capable of reporting detection information on a wide variety of calls produced by several species from both mobile and stationary autonomous platforms.

The DMON/LFDCS is deployed on three autonomous platforms – a Slocum glider, a Liquid Robotics, Inc. Waveglider, and a moored buoy. Data are reported via Irridum satellite in real-time and recorded in archival form on the DMON. Real-time data are posted to and analyzed by researchers at WHOI and NOAA’s Northeast Fisheries Science Center. A subset of detections are ground truthed through visual observations from ship, air, and land-based surveys.

Progress & Results

Initial deployments of a wave glider and a Slocum glider equipped with DMON/LFDCS systems were deployed in the Great South Channel in 2015. A moored buoy was also deployed to the north of Mt Desert Rock in Maine. Subsequent deployments have involved refurbishing the buoy as needed, and a second successful Slocum glider deployment during the spring of 2016. The 2016 deployment also included a Slocum glider owned and piloted by the Naval Oceanographic Office as a demonstration of the viability of the technology operating on a Navy asset. During the 2016 deployment, visual observations were conducted from the NOAA research vessel Gordon Gunter, allowing for ground-truthing of the acoustic detections relayed by the gliders.  Data analyses for these deployments are currently in progress. The wave glider will be redeployed during 2016 and is planned to complete a circuit of the Gulf of Maine.

Slocum glider
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