A SAR auto-focus technique based on azimuth scaling

This paper proposes a new approach for automatic estimation of the Doppler rate during the SAR image formation process. The new technique is based on the scaling property in the azimuth direction applied to chirp signals. The measurement of the scaling error between two processed images with low resolution is used to estimate the effective sensor velocity. The achieved results show superior performance when compared to traditional auto-focus techniques. For a standard ERS-1 image, the velocity estimation can be performed with an accuracy better than 0.5 m/s.