Along-Track Resolution Enhancement Forwide-Bandwidth, Low-Frequency SAR by Accounting for the Wavelength Change over the Bandwidth

Common methods for processing SAR data, such as the Range-Doppler Algorithm (RDA) and the Chirp Scaling Algorithm (CSA), make certain approximations about the SAR signal. As the transmit frequency drops, the bandwidth grows, and the beamwidth increases, the approximations miss important factors required to precisely process the data. This paper shows that the approximations correspond to keeping lower order terms of the expansion of the SAR transfer function. We demonstrate the limits for focusing low frequency SAR data with these approximations. Previous methods for correcting the approximation errors are shown and a new method for including an arbitrary number of terms in processing the data is discussed. The concepts presented are verified using simulated SAR data.