| Laser communication is a potential broadband means of satellite communications, and the performance of APT affects succeeds or fails of the satellite laser communications directly. In APT system, laser spot image localization method with high-precision, fast and strong anti-noise is one of the key technologies of satellite laser communications.According to experiment result that we have got and laser spot signal distribution got by satellite communication test between Japanese and European, we have constructed the laser spot objective's mathematic model: the target of 4 pixels×4 pixels in 128 pixels×128 pixels unsymmetry spot image. And according to this model, we have comparing different localization method and macropixels method is proposed: it divides the spot image into macropixels and the macropixels whose grey level is maximal is chose as target region and iteration formula is used to compute centroid in the target region.A term, valid pixel ratio, has been put forward and then is applied to analyze the effects of noise and asymmetry on the location for initial target region, and then got the most macropixels and restricting operation way to confirm the objective macropixels. For the unsymmetry target spot image, the most macropixels is 36 pixels and target macropixels is enlarged by 2 pixels. The value of r is 1 when SNR is 6dB. For precise target location, we have obtained macropixels method by improving Zeev Z's method. By improving weight function, ration function of Zeev Z's method and adjust the size of macropixels along with changing direction of iterative, the ability to restrict noise is enhanced obviously. For objective model, when SNR is -5 dB, centroid error using macropixels method is only 0.38 pixels.The experiments show that the localization error of about 2.5μrad was achieved and its processing speed was about 18-20 frames/s for the macropixels method in measuring systems, and can be used in APT systems absolutely. |
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