PRF ambiguity resolving for SAR

For high-precision SAR (synthetic aperture radar) processing, the determination of the absolute Doppler centroid is indispensable. The Doppler frequency estimated from azimuth spectra, however, suffers from the fact that the data are sampled with the PRF (pulse repetition frequency), resulting in ambiguity about the correct PRF band. Five methods for ambiguity resolution are discussed together with the known technique of look correlation. None of these methods has a requirement on the mission schedule. It is shown that the following effects can be used to measure the absolute Doppler frequency: the Doppler shift of range spectra, range migration, image geometric misregistration, and the use of multifrequency-radar data.