ADAPTIVE PROCESSING FOR SHALLOW WATER LFA OPERATIONS

The overall objective of the proposed research is to develop effective monostatic and bistatic adaptive processing techniques for shallow water Low Frequency Active (LFA) operationa. The focus of our proposed research is to achieve spatial reverberation cancellation for the complex shallow water environment using adaptive beamforming techniques. Our efforts will extend the favorable results we achieved for a deep-water, wideband active sonar adaptive beamformer to the shallow water environment. The previous work resulted in two promising adaptive algorithms: Cholesky Factorization - Minimum Variance Distortionless Response (CF - MVDR) and Constraint Preprocessor/Joint Process Least-Squares Lattice Adaptive Filter (CP/JPLSL). We will apply a beam-space adaptive filter to provide Coherent Spatial Discrimination (CSD). The adaptive filter operates on beam data whereby, in addition to the selected primary beam, one or more adjacent reference beams are selected on each side of the primary beam. The reference beams are constructed such that they receive the interference, but are essentially prevented from receiving signals coming in from the primary beam look direction. The adaptive filter uses the reference beams to provide a good estimate of the interference contaminant in the primary beam. It then subtracts the adaptive filter output from the primary beam output to obtain the desired "interference canceled" beam.