IEEE Geoscience and Remote Sensing Magazine - March 2020 - 53

information on the temperature, pressure, and humidity
changes associated with elevation differences. This compensates for severe height-dependent atmospheric artifacts.
The distribution of the refractive-index N across the troposphere is modeled as a parametric model with both sloping and elevation:
Tz(t 1, t 2)atm = b 1 $ R n + b 2 $ h n $ R n, (26)

where h n and R n are the elevation and slant distance of the
nth PS point, respectively, and b 1 and b 2 are defined as

b1 =

4rfc
-6
c $ 10 $ TN R(t 1, t 2), (27)

b2 =

2rfc
-6
c $ 10 $ TN 1(t 1, t 2), (28)

where N R is the refractive index of the height of the radar
sensor. The external digital elevation model (DEM) is used
to solve the multiple linear regression (MLR) equation that
compensates for the atmospheric phase.
DEFORMATION INVERSION
After reducing the noise phase and compensating for the atmospheric phase, only the deformation phase component is included in the interferometry phase. At this time, the radar LOS
deformation of the observation region can be calculated by

TR = -

m
m
=, (29)
4r(z - z atm - z noise)
4rz def

where z def represents the deformation phase component
and TR is the LOS deformation.
The ideal position placement of the GB-DInSAR platform
should enable the LOS direction to be parallel with the deformation direction [81]. When the LOS direction is perpendicular to the deformation direction, the target deformation
information cannot be reflected. To fully obtain the deformation information of the observation area, some researchers
have focused on the 3D deformation monitoring technique.
TYPICAL GB-DInSAR SYSTEM
LINEAR SCANNING SYSTEM
A commercially available system, IBIS-L, is manufactured
by IDS. It can deliver areal displacements with high accuracy and precision (0.01-1 mm depending on the distance
and application). Its applications are various and range
from high-rate dynamic monitoring of man-made structures (such as dams, bridges, and towers) to long-period
monitoring of natural hazards (for instance, landslides,
avalanches, glaciers, and volcanoes) [11].
LiSA is based on a vector network analyzer with a 5-mlong rail structure mounted in a trailer. It mainly aims to
complement other monitoring techniques in typical civil
protection tasks as well as for cultural heritage protection
[14]. RiskSAR was developed by UPC. The whole radar,
weighing only 8.5 kg, is mounted on a linear motion unit
MARCH 2020

IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE

to make a synthetic aperture up to 5.5-m long [17]. Among
linear scanning systems, the FastGB-SAR system takes the
shortest amount of time (5 s) to acquire echo signals, while
other systems all take a few minutes [15].
A typical linear scanning system adopts the mechanical
movement of antennas along the rail track, which leads to
a low deformation rate of measurement. For detecting moving targets using a faster acquisition time, some researchers
introduced the multiple-input/multiple-output (MIMO)
technique into the system called MELISSA [84], which has
16 transmitter (Tx) and 16 receiver (Rx) elements with longer
synthetic apertures of 2.56 m and a much faster scanning
time of roughly 1 ms. Another MIMO GB-DInSAR system
was developed by the Beijing Institute of Technology (BIT)
with 16 Tx and 32 Rx elements in 16 GHz, which has been
used for actual open-pit iron mine monitoring [85].
NCUT developed a linear multiangle scanning system
to solve the problem of the limited monitoring range of
existing linear scanning methods. The radar is mounted
on a rotatable bracket so that the radar beam direction can
be controlled by software and high-squint imaging can be
performed during each scanning in the range of ! 60° in
the side-looking directions. Thus, the system field of view
can reach up to 120°, with multiple images of different
squint angles made into a panorama image. Each scanning
time is less than 1 min [86]-[91]. Even though the linear
multiangle scanning system can expand the field of view, it
does not reduce acquisition time. Meanwhile, because the
phase center of the antenna is offset at different angles, the
data at different angles cannot be directly used for interferometry. It is therefore not an optimal solution for panoramic scanning.
The aforementioned linear scanning systems are shown
in Figure 14. Table 1 lists the parameters of all the previously mentioned linear scanning GB-DInSAR systems.
ARC SCANNING SYSTEM
To better solve the problem of increasing the field of view,
the IDS GeoRadar company in Italy developed an IBISArcSAR system that has a monitoring angle of 360° and a
maximum monitoring distance of 5 km. It takes only 40 s to
monitor 360° at a monitoring distance of 5 km. Moreover, it
introduced the MIMO technique into the arc scanning system, which allows for the acquisition of four data streams
at different baselines. Using this method, with only one acquisition it is possible to derive and estimate the interferometric phase; it is also capable of obtaining the DEM of the
observed area [19].
The ArcSAR system developed by KNU has two different
imaging modes: spotlight and scanning. The latter obtains
a wider range of images but has a lower resolution than the
former. The system can even achieve a 360° full-angle observation centered on the system's position [18].
IECAS developed an Arc-FMCW-SAR system in X band
and has performed experiments on open-pit mine monitoring [20]. NCUT increased the arc scanning speed to 180°
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IEEE Geoscience and Remote Sensing Magazine - March 2020

Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - March 2020