MULTISTATIC SONAR STUDIES IN SHALLOW WATER ENVI- RONMENT IN THE GULF OF FINLAND

Abstract: Reverberation is the major limitation for active sonar performance in shallow wa-ter environment. Broadband waveforms with good resolution in range and Doppler do sup-press reverberation but their power is limited in shallow confined waters by time-spreading due to multipath propagation. The problem was tried to mitigate by using novel normaliza-tion and fusion techniques. Linear Kalman filter was used for tracking multiple simulated targets with variable target strength and velocity. The non-linearity problem related to target doppler information was solved by using separate linear filters for individual target doppler values. These values were then used for data association to update the tracks with the true positions and doppler values obtained from different sensors. The tracking was tested using measured and simulated signals. A three-dimensional model for active sonar was developed for the simulation. The model has a single transmitter and multiple receivers in arbitrary configuration and it accepts multiple underwater and surface targets. The active sonar pro-gram creates complex signals for each sensor hydrophone and it includes environmental pa-rameters for water layer, ambient noise, bottom sediment and reverberation. The properties of several broadband waveforms were simulated and verified in multistatic sonar experi-ments carried out in shallow water environment in the Gulf of Finland. An echo repeater was used in the sea trials to emulate underwater targets. The FM/up-down waveform was supe-rior in detecting static and slowly moving targets with good range accuracy. The Hamming windowed CW was better in detecting weak targets and it performed well even in the pres-ence of strong static targets