Research On Synthetic Aperture Sonar Imaging Algorithm And Medium Instability Effects

The notable advantage of Synthetic Aperture Sonar (SAS) is getting high Azimuth resolution by applying the array with small size, and is independent of working frequency and detecting range. In the field of underwater acoustic research and sea bottom mapping, SAS has broad applied potentials, but it also has strict request to underwater acoustic environment and to the motion of sonar carrier.The SAS imaging bases on the coherence of sonar signal, aiming at the underwater medium having temporal and spatial instability, the coherence of high frequency SAS imaging in shallow sea is analyzed, and the measuring method of signal coherence is presented. At the same time, SAS imaging experiment is conducted in tank, and the experiment witch tests the effect of instable medium on SAS imaging is also done in Songhua Lake.The SAS imaging algorithms basing on time domain, frequency domain and wave-number domain are introduced and simulated in the thesis. The conclusion that instable medium limits the length of synthetic aperture and reduces the SAS imaging resolution is obtained by analyzing the coherence of high frequency SAS imaging in shallow sea. The simulation of coherence measurement precision is also made out, the result approves that, in a given SNR range, estimation of phase applying Notch filter and estimation of time delay applying three-point interpolation method are applicable. In the tank, point target and distributing target are imaged clearly in the area of reverberation, the analysis indicates that the SAS imaging has capability of anti-reverberation. In the experiment done in Songhua Lake, the emphases is put on the measurement of floatation of phase and time delay with the variation of time and space, the result validates that instable medium really has effects on SAS imaging.