TABLE OF CONTENTS An essential part of SAR processing is the estimation of the Doppler parameters of the received data the Doppler centroid frequency and the azimuth FM rate [1, 2]. The estimation of the Doppler centroid is covered in this chapter, while the estimation of the azimuth FM rate is described in Chapter 13.
Because the azimuth (i.e., Doppler) signal is observed in a sampled fashion, it is useful to consider the Doppler frequency as having two components. The sampling rate is the PRF, which limits the highest observable rate of the Doppler frequency. In the received signal, only frequencies between -0.5 PRF to +0.5 PRF can be observed. The component corresponding to these frequencies is referred to as the baseband or fractional PRF part of the Doppler frequencies.
Frequencies outside this range are not directly observable, but are important for SAR processing. For convenience, they are quantized to an integer multiple of the PRF, and are referred to as the Doppler ambiguity. For processing, the average or center Doppler frequency must be known, which is referred to as the Doppler centroid frequency, or simply the Doppler centroid.
More details of the Doppler centroid are given in Section 5.4, where it is shown that the centroid can be expressed as
| (12.1) |  |
where 
is the fractional PRF part, M amb is the...
