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Abstract

A method that provides precise target location measurement using a synthetic aperture radar (SAR) system jointly with a global positioning inertial navigation system (GPS/INS) located on a moving aircraft. The SAR system provides a precise measurement of the round trip elapsed radar wave propagation time from the aircraft location to a selected pixel in a ground map that includes a portion of the target. The velocity of radar wave propagation is measured at the same time that the range time lapse to the designated SAR map pixel is measured. When combined with position and velocity information derived from the GPS/INS inertial navigation system, the radar wave propagation time is used to calculate the position of the target pixel in GPS/INS coordinates, thereby improving measurement accuracy. The method comprises flying an aircraft containing GPS/INS and SAR systems along a predetermined flight path. The relative position and velocity of the aircraft along the flight path is accurately measured using the the global positioning system. A first SAR map is generated. A target pixel in the first SAR map that corresponds to the target is then designated. A minimum of two additional SAR maps are generated and the target pixel in each of the additional SAR maps is designated. The position of the target pixel relative to GPS/INS coordinates and the velocity of radar wave propagation to the target using aircraft position data derived from the global positioning system are then simultaneously measured. Finally, a more accurate position for the target pixel is calculated using the computed value for the radar wave propagation velocity.

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First Claim