=Paper=
{{Paper
|id=Vol-3006/61_short_paper
|storemode=property
|title=Calculation of vertical displacement of the earth surface in the "Vostochny" open pit using radar data
|pdfUrl=https://ceur-ws.org/Vol-3006/61_short_paper.pdf
|volume=Vol-3006
|authors=Leonid S. Mikov,Semyon E. Popov,Vadim P. Potapov
}}
==Calculation of vertical displacement of the earth surface in the "Vostochny" open pit using radar data==
https://ceur-ws.org/Vol-3006/61_short_paper.pdf
Calculation of vertical displacement of the earth
surface in the “Vostochny” open pit using radar data
Leonid S. Mikov1 , Semyon E. Popov1 and Vadim P. Potapov1
1
Federal Research Center for Information and Computational Technologies, Kemerovo, Russia
Abstract
The paper deals with the issues of assessment of the condition and changes in the land surface on
the territory of the Vostochny open pit (Kemerovo region). The application of the multi-pass series of
Sentinel-1 satellite radar data using the Small Baseline Subset (SBaS) method to determine the Earth
surface displacement dynamics using constructed vertical displacement maps is demonstrated.
Keywords
Radar data, Vostochny open pit, Small Baseline Subset, Sentinel-1, earth’s surface deformations.
1. Introduction
Currently Kuzbass is one of the largest mining regions in Russia. The high technogenic load
associated with the annual increase in the volume of coal mining leads to a redistribution
of the stress-strain state of significant volumes of rock mass with adverse consequences for
the environment [1]. Deformations of the earth’s surface in such regions, resulting from
uneven subsidence and horizontal displacements of rocks, reach large areas and are a source of
emergency situations, which, in turn, can harm not only the environment and the operating
mode of the enterprise, but also human lives.
At the Vostochny open-pit mine, active open-cut coal mining has been carried out for
10 years. For example, in 2010, 950 thousand tons of coal were mined, and in 2018 — already
4.3 million tons [2]. Such intensive mining has a direct impact on the relief, therefore, to prevent
emergencies, it is necessary to monitor the state of the earth’s surface.
2. Methods for processing satellite radar data
Today, satellite radar data are actively used to determine the deformations of the earth’s surface.
Their advantage lies in the relatively low price per square kilometer, as well as the independence
of shooting from weather conditions and time of day. To process such data, 3 main methods
have been developed:
— differential interferometry (DinSAR). Used to process two images;
— method of persistent scatterer (PS). It is used for point estimation of deformations based
on a multi-pass series of images;
SDM-2021: All-Russian conference, August 24–27, 2021, Novosibirsk, Russia
" mikov@ict.sbras.ru (L. S. Mikov); popov@ict.sbras.com (S. E. Popov); vadimptpv@gmail.com (V. P. Potapov)
© 2021 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR
Workshop
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http://ceur-ws.org
ISSN 1613-0073 CEUR Workshop Proceedings (CEUR-WS.org)
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Leonid S. Mikov et al. CEUR Workshop Proceedings 519–525
— small baseline subset (SBaS). Used for areal strain assessment based on a multi-pass series
of images.
The principle of radar interferometry is as follows. Each pixel of a satellite image contains
information about the real and imaginary parts of the wave reflected from a section of the
earth’s surface and received by the satellite. Thus, a satellite image has two components: real
and imaginary parts, which can be converted into amplitude (brightness) and phase components
of the image. Note that the typical size of the earth’s surface in one pixel of the image exceeds a
square meter, which makes it impossible to determine the millimeter offsets from the brightness
component of the image. For this purpose, the analysis of the phase components of the set of
images is used.
Based on the set of phase components of SAR images obtained by the satellite at different
points in time (with a periodicity, for example, one image per day), the change in the phase
component over time is calculated. The change in the phase component is associated with a
linear relationship with the path difference of the wave reflected from the surface and, thus,
it becomes possible to measure the vertical displacements of objects on the earth’s surface,
comparable to the satellite signal wavelength, which is of the order of several centimeters [3].
The main difference between the methods is the amount of initial data for processing. For
example, the differential interferometry method uses a pair of radar images taken with a
short time interval (from several days to a couple of weeks). As a result, we get a map of the
displacements of the earth’s surface, which occurred during the period between surveys. SBaS
requires at least three images and PS requires at least thirty. The last two methods make it
possible to assess the dynamics of changes in the earth’s surface over a long period of time
(from several months to several years). Let’s consider all these methods in more detail.
Differential interferometry is a classic pairwise method for calculating areal displacements. It
includes the following stages: formation of an interferogram, filtering and calculation of coher-
ence, phase sweep, correction and refinement of orbits, recalculation of phase into displacements.
At the output, we get a map of displacements of the earth’s surface.
PS (Persistent Scatterers) method — calculation of displacements of point targets, which are
permanent reflectors for a radar satellite. Allows you to measure detailed displacements on
infrastructure objects. It is used, as a rule, for areas with urban areas. Includes the same steps
as the SBaS method. At the output, we also get a map of the average rates of change in surface
displacements.
SBaS (Small Baseline subset) method — calculates accurate areal displacements using a
series of satellite images with small baselines. It includes the following stages: formation of an
interferogram with subsequent filtering and sweeping, correction of orbital errors, first inversion,
second inversion (atmospheric correction) and orthorectification, geocoding of processing
results. The output is a point vector file, which is a map of the average rates of change in the
displacements of the earth’s surface [3, 4].
3. Results and conclusions
In our work, we used the latter method, since it allows us to reveal the dynamics of areal
deformations of the earth’s surface over a long period of time.
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The territory of the Vostochny open-cut mine was chosen as the object of research. For
calculations, 32 radar images from the Sentinel-1B spacecraft were selected for the period from
09/10/2019 to 10/27/2020. with a shooting frequency of 12 days. This spacecraft performs
imaging in the C-band with a resolution of 5×20 m/pixel (in the Interferometric Wide Swath
mode) and with VV and VH wave polarizations.
Typically, the initial radar image covers a large area (several tens of thousands of square
kilometers), therefore, in order to reduce processing time, a separate area of interest with an
area of about 15 square kilometers was allocated to the territory of the Vostochny mine. To
reduce the volume of temporary and intermediate processing data, images with VV polarization
were used. In addition, it has been experimentally established that such polarization is better
suited for determining displacements than VH. All processing was carried out in the developed
software package within the framework of the RFBR project. The scheme for calculating the
displacements by the small baseline subset method is shown in Figure 1, and the description of
the procedures in Table 1. The SRTM digital elevation model was used for more accurate core
registration of radar images.
At the first stage, combinations of pairs of images (master image — auxiliary image) are
determined, which are used to form several differential interferograms.
It should be noted that those pairs of images that do not exceed the baseline threshold value
are suitable for processing (the default value is 100%). If the value is exceeded, then the pairs
are excluded from further processing.
Figure 1: Complete scheme for calculating displacements using the SBaS — preliminary processing
steps are highlighted with a dotted line.
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Table 1
Description of SBaS preprocessing procedures for radar data.
Number of images
Procedure name Contents of the procedure
Input Output
TOPS Split Extract subbands (burst) from a selected swath (swath) 1 1
of a survey in an image.
Apply-Orbit-File Updating orbit state vectors in image metadata. 1 1
Back-Geocoding Correlation of two images (master and slave) in the 2 1
same strip using orbital metadata and digital elevation
model (DEM).
Interferogram Calculation of the folded phase of an interferogram by 2 1
pointwise complex multiplication of two images cor-
rected for the reference phase using an interpolation
polynomial of the 2nd degree
TOPS Deburst Combining contiguous sub-bands in the direction of the 1 1
shooting range (range) and in the direction of the az-
imuth (azimuth).
Topographic Phase
The procedure performs “smoothing” of the interfero- 1 1
Removal
gram by removing the topographic phase. The procedure
simulates (forms in the RAM) an interferogram based on
a reference elevation matrix (DEM) and subtracts it pixel
by pixel from the original interferogram.
Goldstein Phase
Phase filtering to reduce phase residuals and improve 1 1
Filtering
unwrapped phase accuracy using Goldstein’s nonlinear
adaptive algorithm.
Phase Unwrapping 2D phase unwrapping — recovering the absolute phase 1 1
values from a 2D array of baseline phase values using
the least cost flow method.
Subset Selecting a sub-area of an image. 1 1
Terrain Correction The procedure is designed to correct geometric distor- 1 1
tions (location of each pixel) of the image using a digital
elevation model. These distortions are caused by the
“side effect of the geometry of the survey”, which appears
due to the installation of the radar perpendicular to the
direction of flight. These are the so-called topographic
distortions, which do not allow correctly displaying the
obtained images in geographic coordinate systems, for
example, on an electronic map.
Then, standard interferometric processing was performed with core registration, filtration,
and phase unfolding of the pairs of images selected at the first stage. For core registration of
images, incoherent accumulation parameters were used equal to 1 in azimuth and 5 in range.
To improve the accuracy, an SRTM v4 digital elevation model was used with a spatial resolution
of about 30 meters (1 arc second). The noise was filtered using the Goldstein filter. After that,
the procedure for correcting the phase incursion from the Earth’s ellipsoid [5] was performed,
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at which the topographic phase was removed from the obtained interferograms. The next step
is two stages of inversion. The first step is to determine the resulting height and displacement
rate. On the second, date offsets are obtained, which are filtered to remove atmospheric phase
components. Finally, the results are geocoded, filtered by velocity and altitude to remove areas
with high noise readings (areas with rich vegetation).
During the processing of the initial images by the SBaS method, a map of the average rates
of change in the vertical displacements of the earth’s surface was built (Figure 2). This map is a
vector file with 11861 points. Each point contains a set of attributes, such as geographic coordi-
nates, average displacement rate value, and so on. Points with negative vertical displacements
are highlighted in blue, which indicate subsidence of the earth’s surface, and in red, elevations
of the earth’s surface.
To connect the obtained results with real terrain, we used a digital terrain model (DTM) built
on the basis of UAV data, dated October 21, 2019 (Figure 3). Further, in the QGIS program, the
resulting map of average rates of change in displacements was superimposed on this DTM
(Figure 4). Figure 3 shows that most of the displacements are recorded on the dumps of the
Vostochny open-pit mine. The elevations of the earth’s surface are recorded in the northwestern
Figure 2: Map of average rates of change in vertical displacements. Google Maps background.
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Figure 3: Digital terrain model of the “Vostochny” Figure 4: Digital terrain model of the “Vostochny”
open pit. open pit with an overlaid map of average rates of
change in vertical displacements.
part of the stockpile, where the rock extracted during mining is stored. In the western part of
the stockpile, subsidence of the earth’s surface is recorded. Here, presumably, work is underway
to level the stockpile, this is indirectly indicated by the rise of the earth’s surface on the sides.
Drawdowns were also identified in the western part of the open pit on the border of the open
pit and the stockpile. The mean displacement rates for the observation period ranged from
−203 mm/year to +117 mm/year.
Thus, the use of radar data from the Sentinel-1 spacecraft is expedient for monitoring landslide
phenomena, especially in areas with intensive mining operations. The results obtained can
become the basis for the development of monitoring systems and measures to prevent landslides.
Acknowledgments
The reported study was funded by RFBR and Kemerovo region, project No. 20-47-420002.
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