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12.9. A Three-Dimensional SAR Imaging Technique
This section presents a new three-dimensional (3-D) Synthetic Aperture
Radar (SAR) imaging technique.
1
It utilizes a linear array in transverse motion
to synthesize a two-dimensional (2-D) synthetic array. Elements of the linear
array are fired sequentially (one element at a time), while all elements receive
in parallel. A 2-D information sequence is computed from the equiphase two-
way signal returns. A signal model based on a third-order Taylor series expan-
sion about incremental relative time, azimuth, elevation, and target height is
used. Scatterers are detected as peaks in the amplitude spectrum of the infor-
mation sequence. Detection is performed in two stages. First, all scatterers
within a footprint are detected using an incomplete signal model where target
height is set to zero. Then, processing using the complete signal model is per-
formed only on range bins containing significant scatterer returns. The differ-
ence between the two images is used to measure target height. Computer
simulation shows that this technique is accurate and virtually impulse invari-
ant.
12.9.1. Background
Standard Synthetic Aperture Radar (SAR) imaging systems are generally
used to generate high resolution two-dimensional (2-D) images of ground ter-
rain. Range gating determines resolution along the first dimension. Pulse com-
pression techniques are usually used to achieve fine range resolution. Such
techniques require the use of wide band receiver and display devices in order
to resolve the time structure in the returned signals. The width of azimuth cells
provides resolution along the other dimension. Azimuth resolution is limited
by the duration of the observation interval.
This section presents a three-dimensional (3-D) SAR imaging technique
based on Discrete Fourier Transform (DFT) processing of equiphase data col-
lected in sequential mode (DFTSQM). It uses a linear array in transverse
motion to synthesize a 2-D synthetic array. A 2-D information sequence is
computed from the equiphase two-way signal returns. To this end, a new signal
model based on a third-order Taylor series expansion about incremental rela-
tive time, azimuth, elevation, and target height is introduced. Standard SAR
imaging can be achieved using an incomplete signal model where target height
is set to zero. Detection is performed in two stages. First, all scatterers within a
footprint are detected using an incomplete signal model, where target height is
set to zero. Then, processing using the complete signal model is performed
1. This section is extracted from: Mahafza, B. R. and Sajjadi, M., Three-Dimensional
SAR Imaging Using a Linear Array in Transverse Motion,
IEEE - AES Trans.
, Vol.
32, No. 1, January 1996, pp. 499-510.
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