Focusing of COSMO/SkyMed spotlight data with discrete antenna steering

In the spotlight mode the imaging platform steers the antenna to increase the illumination interval of a target to the aim of achieving very high-resolution images at microwave frequencies. The steering is carried out by beam switching on bursts during the data acquisition interval. Due to the change of the beam orientation over bursts, phase shifts can occur from burst to burst. Phase shifts can be also due to the atmosphere in very long integration intervals. In this work we propose a procedure, based on the image contrast maximization technique, able to estimate and compensate such phase shifts. The effectiveness of the proposed solution is demonstrated by its application to real data acquired by the COSMO-SkyMed sensor.