Aerial and Acoustic Marine Mammal Detection and Localization on Navy Ranges

Abstract

Acoustic monitoring and aerial visual surveys of marine mammal activity were conducted simultaneously at the Navy's Pacific Missile Range Facility near Kauai, HI, during times of both high- and low-whale density from February 2002 to March 2003. Specifically, recordings from the range's 24 broadband hydrophones were made during 11 of 16 "in-season" and during six of ten "off-season" aerial surveys. Basic acoustic detections consisted primarily of humpback whale calls and sperm-whale clicks, and those two species were also reported in the visual surveys. The relative number of acoustic detections roughly corresponded with the visual survey results throughout the year. The same acoustic data were also provided to a passive-acoustic-localization algorithm based on acoustic propagation models which generated estimates of sperm-whale movement through the range. The acoustic localizations are in close proximity in space and time to the visual observations of sperm whales. Verification of the model-based localization algorithm's accuracy was demonstrated in a controlled-source experiment at the Navy's Atlantic Undersea Test and Evaluation Center (AUTEC) range in the Bahamas where the recordings of sperm-whale clicks were broadcast and successfully tracked. The localization accuracy of the model-based technique and traditional hyperbolic techniques is compared. These results raise the possibility of using existing Navy assets to detect and track marine mammals, particularly during times when visual sighting conditions are not favorable, in efforts to minimize their exposure to underwater sound.