Study On Synthetic Aperture Ladar Technology

As the key techniques in Synthetic Aperture Ladar (SAL), optical heterodyne detection and synthetic aperture processing are studied in this thesis. Firstly, because of the large detecting distance and complicated target, the phase of the backscattered wave varies randomly, this factor will influence the coherent detection. The optical heterodyne experiment by use of a diode pumped solid-state laser has been made. The importance of beam collimation in Optical heterodyne detection is discussed. And the output optical field distribution from the acousto-optic modulator is examined. The distribution of the diffracted light is non-uniform owing to the finite area of acoustic field, it leads to the poor performance of the receiver. To overcome the detecting difficulty, two methods—local oscillator beam expansion method and telescope based receiver have been presented. The properties of the two type of receiver have been analyzed.Secondly, strip-band SAL in orthogonal mode is investigated. The theoretical model of target echo signals is established. The characteristics of the signals are analyzed. To process the signals, a method of deramp compression and azimuth matched filter imaging algorithm from SAR is adopted. The model of target imaging is obtained. Based on the theory and imaging algorithm obtained, imaging performances of multi-point targets are simulated numerically by means of MATLAB software for SAL.