Research On Windband Doppler Sensitive Signal For Active Sonar

In this thesis, the signal waveforms of an active sonar in shallow waters are studied, in particular, the structure of wideband Doppler sensitive signals are emphasized. Several active sonar signal waveforms, their advantages and disadvantages as well as appropriate operation environment are analyzed and compared. The time-space reverberation spectra of the active towed array are modeled and the wideband Doppler sensitive signal—PTFM (pulse train frequency modulated) and its reverberation signal are analyzed. Then the detection method is presented in the paper.For an active sonar operating in shallow waters, reverberation is the main background interference, especially at low frequency. The transmission attenuation is small, but the reverberation is high. So it is very hard and important for us to find ways to suppress reverberation for active towed array sonars. Anyhow, selection of optimized signal forms is an important measure for reverberation suppression. We know that the Doppler resolution of narrowband CW pulses is good and the influence of reverberation on high speed and low speed moving targets is different. Because frequency widening can effectively disperse reverberation spectrum energy, the wideband FM pulse signal can increase the output SNR in reverberation environment.Based on the National Project for the tenth Five-Year Plan "Active Towed Line Array Sonar" signal processing researches, the characteristics of the PTFM spectrum are described, its detection performance in reverberation environment analyzed using the ambiguity function and the PTFM matched filtering method studied in the paper. Verification is performed at lake experiments and good results are obtained. A novel concept is proposed for detection of very weak signals of low Doppler targets in shallow water environment.