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Principle of High-resolution Airborne SAR Aerial triangulation supported by sparse GCPs  Fig.2 Independent models based airborne SAR triangulation vector model The structure of an independent model unit is based on the two adjacent flight paths. The designed flight course plan satisfies the demand of 60% overlap degree, and the overlap parts between two imaging paths must be divided into several segments, two segments of the same area comprising a independent model. The model coordinates of ground point P based on the three axes: X- azimuth direction, Y-range direction, Z-sky direction, with point O as the origin, and can be computed according for the formula (1) as follows:  Where, (X, Y, Z) are model coordinates of P; Si are space position of radar station on i flight trajectory, corresponding to the zero Doppler frequency and the position of ground object point P; Vi are corresponding flight velocity. Thus, all of the independent models connect into a block network by tie points between adjacent models, once we have computed out the model coordinates of ground point P, for example, in Model i, we can obtain the absolute ground coordinates through block adjustment. The transform mathematic relations see as formula (2):  Where,?i is the ground coordinate scale of Model i; Ri is the transform matrix from Model i to the ground coordinates; O'is the origin of ground coordinates. What should be pointed out is that, independent models based SAR triangulation demands only sparse GCPs around the mapping area, but the using of a lot of tie points maybe bring computation burden. 3.3 GPS/INS supported airborne SAR triangulation model without GCPs An adaptive method of airborne SAR triangulation is supported by GPS and INS inertial navigation data. GPS data provided with the space position coordinates of the radar station Si on flight trajectory, and INS data present the corresponding instant velocity Vi. So that, airborne SAR triangulation become simple and direct when provided with the flight trajectory control vector parameters. The vector model for it sees as Fig. 3.  Fig.3 GPS/INS supported airborne SAR triangulation vector model |