A Unified Approach to Passive and Active Ocean Acoustic Waveguide Remote Sensing

Abstract

Ocean acoustic waveguide remote sensing (OAWRS) is the basis for the primary undersea surveillance systems of the US Navy for both passive and active detection, localization, imaging and monitoring. Here OAWRS refers to all applications of acoustic remote sensing in an ocean waveguide. The primary objective of this work is to continue the data analysis and model development initiated in a series of major ocean acoustics experiments the PI has conducted, which has been summarized in an invited paper in IEEE Spectrum [1]. We applied fundamental physical and statistical principles inherent in waveguide propagation and scattering to advance the state of the art in undersea surveillance. The approach was to use the extensive data analysis, software and fundamental waveguide scattering, propagation, reverberation and statistical models developed by the PI, his collaborators, graduate students and subcontractors during the various experimental programs the PI has directed. WORK COMPLETED/RESULTS Bistatic, long-range measurements of acoustic scattered returns from vertically extended, air-filled cylindrical targets were made during three distinct field experiments [2-6] in fluctuating continental shelf environments. It is shown that Sonar Equation estimates of mean target-scattered intensity lead to large errors, differing by an order of magnitude from both the measurements and waveguide scattering theory. This is because the sonar equation approximation is not generally valid for targets with directional scatter functions in an ocean waveguide. The use of the Ingenito scattering model is also shown to lead to significant errors in estimating mean target-scattered intensity in the field experiments because they were conducted in range-dependent ocean environments with large variations in sound speed structure over the depth of the targets, scenarios that violate basic assumptions of the Ingenito model. A Greens' theorem based full-field model (VETWS) [7] that describes scattering from vertically extended cylindrical targets in range-dependent ocean waveguides by taking into account non-uniform sound speed structure over the target's depth extent is shown to accurately describe the statistics of the targets' scattered field in all three field experiments [8]. To account for the scintillation in the measured scattered intensity caused by fluctuations of the ocean waveguide [9,10], Monte-Carlo simulations of the scattered field are computed by implementing the full-field model in a rangedependent environment randomized by internal waves [9]. Returns from the man-made target are also 8. PERFORMING ORGANIZATION REPORT NUMBER