Office of Naval Research Graduate Traineeship Award in Ocean Acoustics for Ankita Deepak Jain

Abstract

OBJECTIVESA primary goal of this research is to model biological clutter in the continental shelf environments of the ocean. We aim to do this by modeling scattered returns from fish shoals in continental shelf environments using a full field matched filter approach as well as its single frequency approximation. This will help in characterizing clutter and will help distinguish scattered fields of moving targets from stationary background reverberation and submerged targets in sonar data.We aim to develop a unified theory and model for ocean reverberation dependent on seafloor parameters such as density, compressibility and coherence volume. We will use a full field matched filter approach and its time harmonic approximation to model reverberation from volume inhomogeneities. A Monte-Carlo approach based on the parabolic equation will be applied to model acoustic wave propagation in a fluctuating ocean waveguide. We aim at using the model to invert for these parameters and obtain accurate estimates by calibrating modeled returns with data collected during past Ocean Acoustic Waveguide Remote Sensing (OAWRS) experiments in 2003 and 2006 in the New Jersey continental shelf and the Gulf of Maine, respectively.Another goal of this research is to test the hypothesis that inexpensive underwater acoustic measurements can be used to determine the wind speed and classify the destructive power of a hurricane with greater accuracy than standard satellite remote sensing techniques and with at least the same accuracy as hurricane hunting aircraft. APPROACH During the past OAWRS experiments in 2003 and 2006, we demonstrated that fish schools are the dominant cause of clutter in typical continental shelf environments [4,5]. Based on the inverted parameters of fish such as neutral buoyancy depth, target strength and population density [6], scattered returns from fish distributions can be modeled and calibrated with measured returns. This model can then be extended to simulate wide-area images and movies, similar to those developed from collected data in the past [4,5], showing temporal and spatial evolution of vast oceanic fish shoals.We formulate a unified theory to model scattered returns from randomly distributed seafloor inhomogeneities in range-dependent ocean waveguides using the Rayleigh-Born approximation to