TABLE OF CONTENTS The range Doppler algorithm presented in Chapter 6 was the first algorithm developed for civilian satellite SAR processing. It is still the most widely used algorithm because of its favorable tradeoff between maturity, simplicity, efficiency, and accuracy. However, under certain conditions, two disadvantages can become apparent. First, a high computing load is experienced when a long kernel is used to obtain high accuracy in the RCMC operation. Second, it is not easy to incorporate the azimuth frequency dependence of SRC, which can limit its accuracy in certain high squint and wide-aperture cases.
The chirp scaling algorithm (CSA) was developed specifically to eliminate the interpolator used for RCMC [1]. It is based on a scaling principle described by Papoulis [2], whereby a frequency modulation is applied to a chirp-encoded signal to achieve a shift or scaling of the signal. Using this "chirp scaling" principle, the required range-variant RCMC shift can be implemented, using phase multiplies instead of a time-domain interpolator. The algorithm has the additional benefit that SRC can be made azimuth frequency dependent. This benefit arises because the data are available in the two-dimensional frequency domain at a convenient stage in the processing.
The maximum shift or change of scale implemented by the frequency modulation cannot be too large, or the associated change in the signal's center frequency and bandwidth would become problematic. This restriction is neatly avoided by applying RCMC in two steps, whereby only the difference in RCM between signals at different ranges is corrected...
