IEEE Geoscience and Remote Sensing Magazine - March 2020 - 77

PROS AND CONS OF THE DIFFERENT METHODS
Compared with the InSAR+model method, the multitrack/
multisensor method is prior-model independent. Therefore, the latter could potentially be used to retrieve 3D displacements in any mining area for different mineral sources
(e.g., coal mines and metallic mineral mines) and different
mining methods (e.g., open-pit mining and underground
mining as well as open-pit and underground mining combined), which the former methods cannot do.
However, the multitrack/multisensor method has some
inherent drawbacks. First, it theoretically requires synchronous SAR image pairs from at least three independent viewing geometries so that it can accurately estimate 3D mining
displacements from InSAR measurements [105] due to the
high nonlinear deformation rates of mining areas (especially coal mining areas). Unfortunately, such a requirement is
MARCH 2020

IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE

0.3
600

0.2

300
0

(m)

0.4

A

A′

0

300

600

0.1

900 1,200 1,500
(m)
(a)

0

1.2

1,200

0.8
900

0.4
0

600

(m)

where i 0 is the mining influence propagation angle (a prior
model parameter). Note that the inclined direction of coal
seam extraction is assumed along an east-north direction in
(9). Simulation and real data tests suggest that the extended
prior model could effectively improve the accuracy of 3D
mining displacement estimates, especially for extracting
inclined coal seams.
In addition to the previously mentioned prior models,
in recent years, researchers have attempted to solve 3D mining displacements by integrating InSAR measurements with
other deformation models. For instance, in 2019, Zheng
et al. [103] first retrieved the mining-induced displacement
component in the northern direction using the probability integral method [(PIM), a mining deformation model]
and then estimated the remaining two displacement components in vertical and eastern directions from multitrack
InSAR measurements. Furthermore, Tang et al. [104] interpreted the symmetry of mining subsidence as prior information to completely retrieve 3D mining displacements.

0.5

-0.4
300
0

-0.8
-1.2
0

300

600

900 1,200 1,500
(m)
(b)

1,200

2

900

1

600

anci

300
0

0

Adv

0

300

600

ng D

irect

ion

900 1,200 1,500
(m)
(c)

(m)

E = B E $ TW E + W cot i 0
, (9)
N = B N $ TW N

N

900
(m)

(

1,200

(m)

	

usually difficult to meet in most mining areas because of
the different repeat cycles and flight orbits of current spaceborne SAR sensors, although they can acquire SAR images
with different imaging angles to produce independent imaging geometries. Second, the near-polar orbit configuration causes significantly poor accuracy for movement estimates in the northern direction (thousands of times the
LOS deformation accuracy) [106]. Finally, an underlying
assumption behind this method is that the 3D displacement components in the different SAR acquisition periods

(m)

theoretical constraints to improve the robustness of 3D
mining displacement estimation. To reveal the spatiotemporal evolution of 3D mining displacements with InSAR, TS
methods have been proposed for multimagnitude (i.e., millimeters to meters) 3D mining displacement estimation
from single-geometry SAR data sets by integrating (8), and
using weighted least-squares [100] or robust estimation solvers
[101]. Figure 3 presents the TS 3D mining displacements in
the Datong coal mining area of China between 16 August
2007 and 16 May 2008, generated from ascending ALOS
PALSAR images with assistance from the prior model of (8).
Because the prior model of (8) generally cannot hold well
in the case of extracting inclined coal seams, errors have
arisen in the solved 3D displacement estimates. In 2019, Fan
et al. [102] extended this prior model to inclined coal seam
extraction by taking the influence of vertical subsidence on
horizontal movements into account in that case, i.e.,

-1
-2

FIGURE 2. Full 3D mining displacement estimates in the (a) vertical, (b) eastern, and (c) northern directions in the Daliuta coal
mining area of China between 21 November 2011 and 2 April 2013,
generated by integrating OT-derived LOS deformation observations
using the prior model of (8) [97].

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IEEE Geoscience and Remote Sensing Magazine - March 2020

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