From acoustic scattering models of zooplankton to acoustic surveys of large regions

The bioacoustics research group at the Woods Hole Oceanographic Institution is actively conducting field surveys, laboratory acoustic scattering experiments, and theoretical modeling of acoustic scattering. While the focus of the research has been on zooplankton, we have also investigated the scattering by internal waves and suspended sediment. The field surveys are taking advantage of the newly developed towed instrument, BIOMAPER-II, that contains a suite of acoustical (43 kHz to 1 MHz), optical, and environmental sensors. The system has been used to map portions of Georges Bank near Cape Cod, MA, US. Our laboratory contains a wide range of acoustic transducers (24 kHz to 1.4 MHz, some of which are broadband) that are used to measure the acoustic backscattering as a function of acoustic frequency and animal orientation. The system has been used to measure the acoustic scattering properties of live tethered animals, either at sea on the deck of a ship with freshly caught animals or on land with live animals that have been maintained. The laboratory data have provided a basis for the development of physics-based acoustic scattering models of the zooplankton which have been used to interpret the field surveys. The models take into account the material properties of the animals, size, shape, and orientation, as well as acoustic frequency. Broadband echo classification methods have been developed based on the models and data. Finally, two new systems are under development: one is used to measure target strength of individuals in situ and the other is to be used to measure sound speed of the animals in situ