Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms. Caner Ozdemir

Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms - Caner Ozdemir


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      Aliasing is a type of signal distortion due to undersampling the signal of interest. According to Nyquist–Shannon sampling theorem (Shannon 1949), the sampling frequency fs should be equal to or larger than twice the maximum frequency content; fmax of the signal to be able to perfectly reconstruct the original signal:

      (1.29)equation

      Since processing the analog radar signal requires sampling of the received data, the concept of aliasing should be taken into account when dealing with radar signals.

Graphs depicts the (a) Monostatic radar configuration, (b) scattered field versus frequency, (c) range profile of the target. Schematic illustration of simulated range profile of an airplane.

      The FT operations are also extensively used in synthetic aperture radar (SAR) imaging as well. Since the SAR data are usually huge and processing this amount of data is an extensive and time‐consuming task, the FTs are usually utilized to speed up signal processing procedures such as range and azimuth compression.

      Source: Caner Ozdemir.

Schematic illustration of the famous hook of Cape Cod, Massachusetts, USA.

      Source:www.jpl.nasa.gov/radar/sircxsar/capecod2.html.

      In radar applications, the data are collected within a finite bandwidth of frequencies. According to the sampling theory, if the radar signal is g(t) and its spectrum is G(f), the frequency components beyond a specific frequency B is zero, that is

      (1.31)equation

      then the time‐domain signal g(t) should be sampled at least twice the bandwidth in frequency as

      (1.32)equation

      where fs stands for the sampling frequency.

      When the radar imaging is concerned, the scattered electric field has the form as given in Eq. 1.30. The sampling theorem can be applied in the following manner:

      Suppose that target to be imaged lies in the range direction within the range width or range extend of Rmax


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