Research On Dual-transmitter And Multiple-receiver Synthetic Aperture Sonar Technology

Synthetic Aperture Sonar is the primary means of underwater imaging and detection. The system is similar to the SAR, which has a wide range of imaging and constant resolution, that other sonar systems can not match. However, due to the underwater acoustic complex environment, SAS has been plagued by low efficiency of working. This thesis studies MIMO technology of synthetic aperture sonar system designed to improve the efficiency of SAS imaging system, making it more performance can play out in practice.This thesis mainly focused on a new type of dual-transmitter and multiple-receiver Synthetic Aperture Sonar technology. Starting with system design, and then optimization of the original single-transmitter-line-array sonar system architecture, this thesis presents a dual-transmitter and multiple-receiver synthetic aperture sonar structure, and puts forward its basic sound-path relation and a signal processing flow.Because of the layout of orthogonality dual-transmitters, the new system compared with the old doubles the equivalent phase center. Double equivalent phase center allows the system to get double azimuth sampling times within a multi-pulse period under other conditions unchanged, thus the new design improve the efficiency of the SAS system.The key technology is the synthetic aperture MIMO orthogonal transmit waveform design to ensure that there is no mutual interference between the signals of each group.This thesis proposes four typical signals: the multi-frequency-bands chirp signals, upand down- chirp signals, frequency hopping signals and quadrature encoder signals.derivation and simulation analyze their orthogonality, and the power spectrum of each signal, and the matched filter. Using genetic algorithm improve the inter-related function and correlation joint of frequency hopping signals. And compare the advantages and disadvantages of various quadrature signals. Derived dual-transmitter Synthetic Aperture Sonar echo signal model.Imaging algorithm is the core of signal processing system. This thesis simulate imaging based on classic imaging algorithm with the signals which designed above,and evaluates the imaging quality of the new system. Motion compensation technology is an important means to improve the image quality. This section studys and improves the DPC algorithm under the new SAS system, and presents the simulation results.Finally, this thesis researches on a new method of underwater measuring relative speed and positioning based on the up- and down- chirp signals. This method only uses the information of one-time echo signals to position a underwater stationary target in the aperture. Pulse compression results of the up-chirp signal and down-chirp signal in the same Doppler shift have the opposite phase offset, thereby the phase offset is related with the relative speed, combined with information of the sound path obtained by pulse compression to position the target location.This technology will make more accurate positioning of the synthetic aperture sonar target.