IEEE - Aerospace and Electronic Systems - October 2021 - 8

A Ground-Based Interferometric Synthetic Aperture Radar Design
displacement or deformation value by calculating the
phase difference of the target area at different times.
Assume that the ground-based InSAR system antenna
acquired a complex image A1 after one complete scan
along a fixed linear guided path, and continue acquired
another complex image A2 after a period of time. The
deformation of the target object in the slant distance is
defined as DR. The complex numbers of the radar echo
signals S1 and S2 received during the two measurements
can be written as
S1 RðÞ ¼ u1 RðÞexp i; RðÞ
ðÞ
S2 Rþ DRðÞ¼ u2 Rþ DRðÞexp i; Rþ DRðÞ
(3)
ðÞ (4)
where u(R) is referred to the amplitude response of the
scan target. After the registration of the two images, the
complex interferograms of the corresponding pixels in the
complex image are multiplied to obtain the complex interferogram
via the following equation:
S1 RðÞS
2 Rþ DRðÞ¼ S1S
2
exp ið;1;2ðÞÞ:
(5)
The phase information of the interferogram is mainly
determined by the path difference of the signal DR, and it
can be written as
;¼
4p
DR:
(6)
In practical applications, the phase difference '
obtained is the main value in the interval of (-p,p) and the
actual phase difference needs to be obtained after unwrapping
the interference phase f
;¼ ' þ 2pN
(7)
where N¼ 0,1,2,.. .
After extracting the true phase difference, the actual
deformation magnitude in the slant range direction can be
calculated via the following equation:
DR ¼;
:
4p
GROUND-BASED SAR DEFORMATION ESTIMATION
PROCESS
It can be observed that compared to spaceborne or airborne
InSAR, ground-based InSAR has fewer data processing
main steps such as baseline estimation, removal of
flat ground effects, and redefinition of orbits [20]. The
flowchart of data processing for ground-based InSAR
monitoring system is shown in Figure 4.
8
(8)
MULTIPLESLCIMAGESREGISTRATION
Although the ground-based GBSARmonitoring system uses
a fixed linear guided path, there will still be slight difference
in the traveling orbits, viewing angles, or time deviations in
the actual use process, resulting in a certain degree ofdistortion
or misalignment of the obtained SAR complex image,
which makes the coherency between the SLC images is
reduced, which ultimately affects the measurement accuracy
of the monitoring system. Since the measurement accuracy
ofthe GBSARmonitoring system needs to reach millimeters
or even submillimeters, during the data processing, highprecision
registration of two ground-based InSAR complex
images must be carried out, i.e., to make sure the pixels at
the same position in the image correspond to the same echo
point. Usually, the original complex image needs to be interpolated
before image registration. There are many high-precision
image registration methods, such as gray-scale image
registration method, interference fringe-based registration
method, and interferogram spectrum-based registration
method. Although the computation load is large, the high
accuracy data can be obtained.
GENERATINGTHEINTERFEROGRAM
The two GBSAR SLC images after high-precision registration
are conjugated and multiplied to generate an interference
phase map (interferogram). The generated
interferogram at this process contains the deformation
information of the scanned target area.
IEEE A&E SYSTEMS MAGAZINE
OCTOBER 2021
Figure 4.
Flowchart of ground-based InSAR monitoring system data
processing.
IEEE - Aerospace and Electronic Systems - October 2021

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