Space-time processing for suppression of bottom reverberation

The major problem for sonars operating in shallow water is the detection of low Doppler targets in the presence of severe bottom reverberation. For a modern sonar with an azimuthally omni-directional transmitter; the Doppler of bottom reverberation is proportional to /spl nu/cos /spl theta/ where /spl nu/ is the speed of the sonar platform and /spl theta/ is measured from the bow or heading direction. For a towed array receiver, reverberation of various Doppler arriving on sidelobes limits the effectiveness of advanced waveforms. This smearing of sidelobe reverberation over a Doppler range of /spl plusmn//spl nu/ makes it difficult to detect targets with speeds less than that of the sonar platform. Standard adaptive beamforming algorithms are ineffective due to the conflict between desire for narrow frequency bins for good Doppler confinement and wide frequency bins for rapid convergence. We present space-time processing algorithms that overcome these difficulties and permit the detection of low Doppler targets from moving platforms.