ABSTRACT
This chapter mainly deals with image formation or focusing. We present in a systems point of view, along with numerical simulation, the exploration of synthetic aperture radar (SAR) imaging properties that are profoundly associated with platform motion and trajectory, as presented in the previous chapter. Two major issues closely embracing image focusing are particularly addressed: estimation of Doppler centroid and estimation of Doppler rate [1-9]. Motion compensation that, in most cases, is necessary to refine the focusing quality will be treated in Chapter 6 in more detail. Commonly used focusing algorithms, the range-Doppler algorithm (RDA) and chirp scaling algorithm (CSA) are illustrated through numerical simulations. Of these algorithms, each bears its own advantages and shortcomings, with some suitable for large swaths and others better able to handle greater fluctuating sensor trajectories, such as an airborne system. Since the mentioned algorithms are well documented in the literature [10-17], it would be exhaustive and redundant to repeat descriptions of the algorithms here. Instead, for the purpose of this book, we will only focus on the RDA and CSA algorithms. For other algorithms, such as the ω − k method and focusing on the spotlight imaging mode, useful references are given in [10,11]. A modified RDA for the frequency-modulated continuous-wave (FMCW) system was presented in [18]. The technical issues addressed in RDA and CSA are equally and equivalently applied to the rest of the available methods.
