IEEE Geoscience and Remote Sensing Magazine - March 2020 - 59

611
610

250

-5

200

-10

150

-15

100

-20

-25

-30

-50
-100
900
700
500
300
100

-35
-40
-45

-1

-2

-3

-4

-50

Height (m)

300

Power (dBm)

MIMO-SAR APPLICATION
Hu et al. used MIMO-SAR to
COMPARING THE
monitor an open-pit iron mine
CONSECUTIVE
located in Qian'an City, Hebei
INTERFEROGRAMS STEP BY
Province, China [85]. The MISTEP, IT IS POSSIBLE TO
MO-SAR system was indepenFOLLOW THE LANDSLIDE'S
dently developed by BIT. The
radar system utilizes 16 Tx anEVOLUTION IN DETAIL.
tennas to constitute one sparse
transmitting array and 32 Rx
antennas to constitute two
dense receiving arrays. An equivalent large aperture with
512 sampling intervals can be synthesized. To better make

Azimuth (m)
FIGURE 23. The radar power image of the target scene projected

on the DEM of the slope [2].

600
Displacement (mm)

accuracy every 4 h by the motorized theodolite and the
electronic distance meter of the topographic system.
A radar-powered image of the target scene projected
on the DEM is shown in Figure 23. An appreciation can
be gained for how the highest reflectivity (light colors)
comes from the bare or scarcely vegetated soil (for example, grass and low shrubs). The boundaries of those zones
with a high reflectivity closely correspond to the vegetation limit. The areas densely vegetated with trees or dense
shrubs have low reflectivity and are represented by dark
colors in the image.
As displayed in Figure 22, only two benchmarks, labeled 610 and 611, were positioned inside the sectors,
which moved during the radar measurements. The curves
displayed in Figure 24 refer to benchmark 610 and show
a nearly constant displacement rate of roughly 11.7 mm/h
over a total time interval of 48 h. The plot shows a very
close agreement between the two independent techniques
and a maximum discrepancy lower than 3 mm.
A close inspection of the interferogram sequence depicted in Figure 25 shows a complex displacement field,
with two evident sectors in motion located beneath
the landslide main scarp. Both sectors have an elongated
shape, and the eastern one close to the left landslide flank
progressively expands upward throughout the sequence.
This sequence allows for the area of maximum displacement to be identified within the western sector (near the
right landslide f lank), showing a peak rate of roughly
8.5 mm over 14 min and then of approximately 36 mm/h.
This displacement pattern is clearly related to the propagation and retrogression of the superficial earth flows caused
by rainfall, which occurred during the measurement campaign (that is, 10.6 mm of rain from 09:00 of 04/10/2000
to 09:00 of 05/10/2000, after 99.6 mm had fallen in the
preceding four days). Comparing the consecutive interferograms step by step, it is possible to follow the landslide's evolution in detail.

Radar (125 Observations)
Optical (13 Observations)

500
400
300
200
100
0

500

1,000 1,500 2,000
Elapsed Time (min)

2,500 3,000

Benchmark Number: 610
Start Time: 4 Oct. 2000 12:02 GMT+1
End Time: 6 Oct. 2000 12:02 GMT+1
Total Displacement: 561.9 mm
Average Displacement Rate = 11.7 mm/h
Maximum Error = ±3 mm
FIGURE 22. A photo of the target scene (the depletion zone of

the Tessina landslide) with the position of the optical benchmarks.
The two benchmarks labeled 610 and 611 are included in the zone
affected by displacements during the radar campaign [2].
MARCH 2020

IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE

FIGURE 24. The cumulated displacements measured by the
electronic distance meter at a benchmark of 610 compared with
radar displacements in the corresponding pixel (from the 12:02 h of
04/10/2000 and the 12:02 h of 06/10/2000, GMT + 1) [2].

IEEE Geoscience and Remote Sensing Magazine - March 2020

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