BEAMFORMING FOR CHANGING HYDROPHONE GEOMETRY

CURRENT BEAMFORMERS OF INTEREST ASSUME A KNOWN AND FIXED HYDROPHONE GEOMETRY. THIS IS NOT ALWAYS THE CASE. AN IMPORTANT CASE OF INTERESTIS WHEN THE HYDROPHONE POSITIONS CHANGE WITH TIME. IN THIS CASE, THE PERFORMANCE OF BEAMFORMER DESIGNED FOR FIXED HYDROPHONE GEOMETRY WILL BE SIGNIFICANTLY DEGRADED. ON THE OTHER HAND, MODIFYING A BEAMFORMER TO RESPOND TO HYDROPHONE TIME TRAJECTORIES WILL REQUIRE CHANGES IN THE FUNDAMENTAL SHIPBOARD SIGNAL PROCESSING ARCHITECTURE, WHICH IS COSTLY AND INCONVENIENT. THIS PROPOSAL PRESENTS THE POSSIBILITY OF DEVELOPING A STAND-ALONE DEVICE WHICH WOULD SUPPLY INCREMENTAL DELAYS IN RESPONSE TO ARRAY GEOMETRY CHANGES SO THAT THE HYDROPHONE OUTPUTS WHICH GO TO THE CENTRAL BEAMFORMER WILL "APPEAR" TO BE COMING FROM UNDISTORTED GEOMETRY. THUS, THIS DEVICE WILL EFFECTIVELY UPGRADE EXISTING CONVENTIONAL BEAMFORMERS TO HANDLE CHANGING HYDROPHONES GEOMETRY WITHOUT HAVING TO CHANGE THE BEAMFORMER ARCHITECTURE. TWO APPROACHES ARE PROPOSED - THE FORMER FOR SITUATIONS WHERE TRAJECTORIES ARE KNOWN, AND THE LATTER FOR UNKNOWN HYDROPHONE POSITIONS WITH KNOWN NOMINAL (MEAN) POSITIONS.