Sonar waveforms for reverberation rejection, Part IV: Adaptive processing.

For littoral ASW, reverberation is a big problem and rejection of reverberation is of utmost importance. The influence of the transmitted signal on the signal to reverberation ratio has been presented in three preceding papers. In this paper, the influence of improved signal processing on the receiver side is investigated. It is known that low sidelobes of the beampattern reduce the received reverberation. Two different types of port-starboard (PS) beamforming are compared, viz. cardioid and adaptive PS beamforming. Also three types of waveforms are considered: FM pulses, CW pulses and a train of linear FM pulses (PTFM). Experimental results on signal to reverberation ratios are presented and compared to theory. It appears that adaptive PS beamforming leads to very low sidelobes, which improves the reverberation rejection with 10 dB or more.