Abstract: A synthetic aperture radar system includes a distortion correction device arranged for autofocussing of raw data by contrast maximization. Reference functions are selected on the basis of a range of trial accelerations. The acceleration producing the highest contrast is taken as the current radar platform across-track acceleration. This information is used to generate phase and range corrections for the data.

Abstract: In a synthetic aperture radar system, information concerning the radar reflectivity of a point on the ground is placed in an image at an azimuthal (cross-range) position which corresponds to the position of zero Doppler frequency shift of the received signal, under the assumption that the antenna has followed a straight line trajectory. In practice, the antenna trajectory will undergo small deviations about this straight line path which are not taken into account in the azimuth processing and which, consequently, cause incorrect azimuthal positioning in the image of the information concerning a point target on the ground.The invention uses the value of the slope of the frequency modulation of the received signal, calculated by means of an autofocus procedure, to determine the intercept of this frequency modulation at successive azimuth positions.