Determination of phase errors in spaceborne SAR

The phase of a radar signal can be disturbed in the active microwave instrument itself, by spurious motion errors of the platform or due to propagation through the atmosphere. These phase errors lead to geometric distortions and blurring of the SAR image. The phase errors caused by the atmosphere and some types of phase errors of the radar system can be evaluated using the reflectivity displacement method (RDM). The RDM analyses the frequency shift between two ground reflectivity functions of adjacent and strong overlapping azimuth spectra. This frequency shift is caused by the movement of the platform and corresponds to the Doppler difference between any individual scatterer´s contribution to the signal records of the adjacent spectra. The Doppler shift due to the constant forward velocity of the satellite can be separated from the frequency shift by a low pass filter. The remaining part is caused by atmospheric distortion and instrument errors