Underwater sensing and surveying with autonomous vehicles

The increasing capabilities of autonomous underwater vehicles is leading to a variety of new possibilities for underwater sensing and surveying. Portland State University and the Centre for Maritime Research and Experimentation (CMRE) have been working for several years on developing capabilities for underwater sensing with autonomous vehicles- mainly gliders or hybrid glider/powered vehicles. These vehicles have long deployment durations (weeks to months) but move relatively slowly. Two applications have been the focus of the work, seabed characterization and marine mammal population density estimation. For seabed sensing, the ambient noise field (e.g., breaking wave sounds) is being used as the sound source but one of the challenges for this method has been the limitations on the size of the hydrophone receiver array that can be deployed from the vehicle. For the marine mammal population density studies a glider has been customized with two hydrophones on the wings and various species are localized in bearing using time difference of arrival methods. Previous density estimation methods used a single, fixed hydrophone. In this presentation, experiments, challenges, and results will be described from several studies using autonomous vehicles for seabed characterization and marine mammal population density estimation.