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An experiment for high resolution airborne SAR imaging based on phase gradient autofocus

All coherent imaging techniques require extreme phase stability. Phase fluctuations can be induced by platform motion error or microwave propagation effect in turbulent atmosphere. Thus phase error correction can't be neglected for advanced precision airborne SAR imaging processing. This paper introduces an experiment of high-resolution airborne SAR imaging based on phase gradient autofocus. This method is developed to compensate the phase error in SAR signal while the aircraft platform motion compensation system is not provided. The whole algorithm can be divided into the following steps: SAR complex image creation; center cyclic shifting of the strongest point target; adding window for the point target; fast Fourier transform in the azimuth direction; estimation of phase error; phase error correction and inverse fast Fourier transform. Experiments show that the imaging algorithm based on phase gradient autofocus can effectively measure and compensate the phase error, thus obtain an obviously improved airborne SAR image in azimuth resolution, which is 2 meters in the experiment compared with 6 meters achieved by using conventional imaging method. The processing results proved the effectiveness of this algorithm for high-resolution airborne SAR imaging.