MATCHED MODE PROCESSING FOR SPARSE 3-DIMENSIONAL ARRAYS

Matched mode processing (MMP) has been demonstrated to localize underwater sound sources with vertical hydrophone arrays. Two new MMP algorithms for arbitrarily shaped three-dimensional arrays in a range-independent environment are presented. The first algorithm, exact matched mode processing (EMMP), is a generalization of vertical array MMP; its mode decomposition depends on source bearing. The second algorithm, approximate matched mode processing (AMMP), ignores bearing dependence during mode decomposition, reinserting it afterward. The AMMP azimuth beam pattern is similar to that of matched field processing (MFP) and conventional beamforming. The performance of the EMMP and AMMP algorithms is investigated and compared with MFP using simulated data. A slanted vertical array, a horizontal array, and a T-shaped array composed of horizontal and vertical segments were considered. It was found that the AMMP and MFP yield similar peak-to-sidelobe ratio (PSR) and peak-to-average-sidelobe ratio (PASR) in range and depth localization. In contrast, the EMMP yields higher PSR and PASR in range and depth localization for known source bearings. Its bearing search properties were not investigated; they may be less robust than AMMP, MFP and conventional beamforming.