Improvement of the location model for iixels in spaceborne SAR imagery

For spaceborne synthetic aperture radar system, the location of ground-targets is necessary. In this paper R-D location model is used to obtain the accurate geographic position with no reference points. Because the uncertainty of Doppler parameters influences the precise of this method greatly, the improved estimation of Doppler parameters by fractional Fourier transform is present to increase the precision of R-D location method. It is proved reasonable and valid in practice by simulation.