Imaging Issues in Inverse Synthetic Aperture Radar
While applying the inverse synthetic aperture radar (ISAR) imaging algorithms, there are some design parameters, such as reformatting the raw ISAR data and applying window functions, that should be carefully handled such that the resultant ISAR image quality can be improved. In this chapter, we will describe and discuss how to tweak these parameters to obtain a good quality ISAR image.
5.1 FOURIER-RELATED ISSUES
The concept of Fourier transform (FT) is very important in synthetic aperture radar (SAR)/ISAR imaging as has been demonstrated in many different places in this book. The classic way of forming the ISAR image is accomplished by transforming the scattered field data from the frequency-angle domain to the image domain by applying the FT operation.
In SAR/ISAR processing, the collected data sequence is usually digitized such that the digital signal processing algorithms are used to form the final image [1, 2]. The process of digitizing the signal has already been shown in Chapter 1, Section 1.6. After the data are converted to the digital form, the Fourier processing can be readily applied with the help of discrete Fourier transform (DFT) operations. Next, we will briefly explain the very basic but also very critical issues regarding getting a well-implemented and good quality ISAR image.
5.1.1 DFT Revisited
The sampling and digitizing processes of an analog signal are demonstrated in Figure 5.1. Let x(t) be the ...