The issue of monitoring surface motions in post-mining areas in Europe is important due to the fact that a significant number of post-mining areas lie in highly-urbanized and densely-populated regions. Examples can be found in: Belgium, the Czech Republic, France, Germany, the Netherlands, Spain, the United Kingdom, as well as the subject of this study, the Polish Walbrzych Hard Coal Basin. Studies of abandoned coal fields show that surface deformations in post-mining areas occur even several dozen years after the end of underground coal extraction, posing a threat to new development of these areas. In the case of the Walbrzych area, fragmentary, geodetic measurements indicate activity of the surface in the post-mining period (from 1995 onward). In this work, we aimed at determining the evolution of surface deformations in time during the first 15 years after the end of mining, i.e., the 1995–2010 period using ERS 1/2 and Envisat satellite radar data. Satellite radar data from European Space Agency missions are the only source of information on historical surface movements and provide spatial coverage of the entirety of the coal fields. In addition, we attempted to analyze the relationship of the ground deformations with hydrogeological changes and geological and mining data. Three distinct stages of ground movements were identified in the study. The ground motions (LOS (Line Of Sight)) determined with the PSInSAR (Persistent Scatterer Interferometry) method indicate uplift of the surface of up to +8 mm/a in the first period (until 2002). The extent and rate of this motion was congruent with the process of underground water table restoration in separate water basins associated with three neighboring coal fields. In the second period, after the stabilization of the underground water table, the surface remained active, as indicated by local subsidence (up to −5 mm/a) and uplift (up to +5 mm/a) zones. We hypothesize that this surface activity is the result of ground reaction disturbed by long-term shallow and deep mining. The third stage is characterized by gradual stabilization and decreasing deformations of the surface. The results accentuate the complexity of ground motion processes in post-mining areas, the advantages of the satellite radar technique for historical studies, and provide information for authorities responsible for new development of such areas, e.g., regarding potential flood zones caused by restoration of groundwater table in subsided areas.
Mining operations cause negative changes in the environment. Therefore, such areas require constant monitoring, which can benefit from remote sensing data. In this article, research was carried out on the environmental impact of underground hard coal mining in the Bogdanka mine, located in the southeastern Poland. For this purpose, spectral indexes, satellite radar interferometry, Geographic Information System (GIS) tools and machine learning algorithms were utilized. Based on optical, radar, geological, hydrological and meteorological data, a spatial model was developed to determine the statistical significance of the selected factors’ individual impact on the occurrence of wetlands. Obtained results show that Normalized Difference Vegetation Index (NDVI) change, terrain height, groundwater level and terrain displacement had a considerable influence on the occurrence of wetlands in the research area. Moreover, the machine learning model developed using the Random Forest algorithm allowed for an efficient determination of potential flooding zones based on a set of spatial variables, correctly detecting 76% area of wetlands. Finally, the GWR (Geographically Weighted Regression (GWR) modelling enabled identification of local anomalies of selected factors’ influence on the occurrence of wetlands, which in turn helped to understand the causes of wetland formation.
In this article, we present a possible approach to use satellite radar data for a complete description of the formation process of a subsidence trough resulting from an induced seismic event—a mining tremor. Our main goal was to verify whether SAR data allow for the calculation of the basic indicators for the trough (w—subsidence, T—trough slope, K—curvature, u—horizontal displacements, ε—horizontal deformations). We verified the extent to which the Mogi and Yang models can be fitted to match the actual displacements recorded after an induced seismic tremor. The calculations were performed for the Legnica-Glogow Copper Belt (LGCB) area in southwest Poland. Due to intensive mining operations and specific geological and tectonic conditions, the area shows a high level of induced seismic activity. Our detailed analysis focused on four powerful mining tremors: the first tremor occurred on 29 November 2016 (MW3.4), the second on 7 December 2017 (MW3.3), the next on 26 December 2017 (MW3.6) and the last tremor on 29 January 2019 (MW3.7). For each analyzed event, we determined the displacements based on the Differential Interferometric Synthetic Aperture Radar (DInSAR) method and Sentinel 1 synthetic aperture radar (SAR) data from two paths (22 and 73). Additionally, for the period from November 2014 to October 2020, we calculated the displacements using the Small Baseline Subset method (SBAS) time series method. In all cases, the tremor was followed by the development of long-lasting surface deformations. The obtained results allowed us to conclude that it is possible to calculate indicators that result from a specific induced mining event. Considering the full moment tensor and nature of the tremor source, we demonstrated that the Mogi and Yang models can be employed to describe the influence of an induced tremor on the surface in an area of mining activity. We also confirmed the global character of the influence of the reduced troposphere on SAR data calculations. Our conclusions indicate that accounting for the tropospheric correction does not distort horizontal and vertical displacement values in regions influenced by mining activity/tremors.
The article presents a proposal to make simultaneous allowance for both ionospheric and tropospheric corrections in differential synthetic aperture radar interferometry (DInSAR) measurements. Atmospheric delay in the interferometric phase may cause the detection of terrain-surface changes to be impossible or significantly distorted. This fact remains of special importance in the case of surface changes that show limited amplitude and spatial range. Two areas were chosen to verify the validity of the proposed solution. The first area includes terrains affected by underground copper-ore mining activity (Poland), which shows high induced seismic activity. Mining tremors recorded in this area cause the terrain surface to locally subside. The authors analyzed three tremors that were recorded in 2016, 2017, and 2019. Each of the tremors exceeded a magnitude of Mw 4.0. The second area is located in the coastal region of Chile, in the Cardenal Caro province. In this case, the authors focused on a series of three earthquakes recorded on 11 March 2010. The strongest of the earthquakes was of Mw 7.0 magnitude. In the first case, calculations were based on obtained data from the Sentinel 1 satellites, and in the second case from the ALOS-1 satellite. It is demonstrated that simultaneous allowance for both the tropospheric and ionospheric corrections significantly improves the final results. The authors were also able to use the analyzed cases to demonstrate that implementation of the corrections does not have negative influence on the range and magnitude of local ground-surface deformations. At the same time, such implementation minimizes local displacement fluctuations and reduces displacement values in areas affected by deformations. The examples used in the article served to show that tropospheric correction is mainly responsible for global corrections (i.e., within the whole analyzed spatial range), while ionospheric correction reduces local fluctuations.
Underground mining activity in the region of the Upper Silesian Coal Basin (USCB) results in ground displacements scattered on a large area. Both the locations and the velocities of the displacements depend on many factors, such as the current location of the mining front, the mining depth and system, as well as geological conditions. Although SAR interferometry techniques allow the monitoring of such ground displacements, in a regional scale (as is the case of the USCB) SAR images must be appropriately processed (from a number of frames and swaths), and this is the problem addressed in this article. The implementation of algorithms for analyzing time series allows observations of displacements in both time and space. The authors also analyze the influence of mining operations on the road infrastructure and mining waste heaps located in the area and investigate the potential for the monitoring of secondary influence (due to induced seismic tremors). As a result of these investigations, the article presents the quality of the InSAR-SBAS data and the potential for their employment in the measurements.
Dynamic climate changes are particularly apparent in polar regions. Glaciers are retreatng towards the land at a very fast pace. This study demonstrates the application of the feature tracking method in the analysis of ice flow velocity in the region of the Hornsund fiord, southern Spitsbergen, in the years 2018–2022. The calculations were based on the Geogrid and autoRIFT environments and on the Sentinel 1 images. The study also employed external data, such as a numerical terrain model and reference velocity values. The input data, e.g., the chip size and the search limit, were prepared accounting for the specific character of the investigated area. The velocities were calculated for nine biggest glaciers which terminated in the fiord. The accuracy of the results was identified by calculating the median absolute deviation (MAD) of the obtained displacement velocity values from the reference value for areas identified as stable. The study also attempted a causal analysis of the influence of weather factors on the dynamics of ice mass displacement. A systematic year-to-year decrease of the velocity was observed for the entire fiord. In the case of several glaciers, changes related to the ablation season (summer) are also clearly visible. The research results are promising and fill a research gap related to the absence of permanent monitoring and analysis of the dynamics of ice flow in polar regions. It is the first complex and precise study of glacier surface velocity changes, performed on the basis of satellite radar images for the entire Hornsund fiord.
<p>Human activity, in particular mining operations are the cause of terrain changes, manifesting on the terrain surface in form of subsidence troughs. Presence of subsidence troughs in inhabited areas may be the cause of significant damage to the structure of buildings, roads and other man-made objects. Both vertical and horizontal terrain displacements occuring inside the trough could be the reason for deterioration of mentioned objects. Hence the need to measure the impact of mining activity on the terrain surface. Current measurement techniques used to determine terrain displacements include GNSS, leveling and SAR interferometry. One of the limitations of interferometric measurements is that displacement values are in the satellites Line-of-Sight (LOS). The fact that the values are only quasi-vertical causes an ambiguity when it comes to determining whether the dominating component of displacement is vertical or horizontal. Projecting the one-dimentional LOS motion to the vertical direction using only the incidence angle can cause significant errors if the magnitude of horizontal motion is considerable. However, the specific 3-dimentional diplacement components can be derived using different acquisition geometries. In order to determine all 3 components (horizontal North-South, East-West and vertical Up-Down), 3&#160;different viewing geometries have to be used so that the equation can be solved. However, the North-South component can be neglected due to low sensitivity of Sentinel-1 SAR instrument to displacement in that direction. Following that, 2 different viewing geometries can be sufficient to derive the East-West and vertical components.</p><p>The aim of the study is to determine how mining activity affects the surface in terms of both horizontal and vertical displacements. Radar pairs from Sentinel-1 ascending and descending orbit were used to create interferograms, based on which LOS displacement fields were calculated. The North-South and East-West components of displacement were solved through the inversion of the linear equation system based on incidence angles, headings and LOS displacements of ascending and descending radar pairs.</p><p>The horizontal and vertical components were determined for differential interferograms obtained with the DInSAR method using Sentinel-1 imagery, as well as for time series displacement fields derived from the Small Baseline Subset (SBAS) approach over selected mining areas in Poland. The results have shown that data from ascending and descending orbits can be successfully merged in order to obtain both the horizontal (East-West) and vertical components of displacement over mining areas. Obtained values of displacements from both DInSAR and SBAS have confirmed that areas affected by mining activity are under the influence of changes in height, as well as shifts in horizontal direction. Thus it is important to take into consideration multiple acquisition geometries when it comes to studying deformations over mining areas.</p>
<p>Satellite radar interferometry, in particular time series techniques, allow to monitor the activity of the surface of vast areas, making them a complement and alternative to traditional geodetic methods, the use of which in such areas is often associated with significant restrictions. The above-mentioned areas definitely include open-cast mines, among others the analyzed Be&#322;chat&#243;w Brown Coal Mine (Poland).<br />During the studies, 216 satellite images acquired from the Sentinel-1A and Sentinel-1B satellites (path 175) for the period from October 17, 2014 to June 11, 2019 were used. Due to the fact that the research area was on two adjacent stages, it was necessary to combine data for the correct performance of the calculation process. The use of the SBInSAR imaging processing algorithm allowed to generate 839 interferograms carrying information about the difference in interferometric phases between pairs of images which satisfy the condition of the boundary size of the spatial and temporal base. As a consequence, it allowed to determine the displacements in the direction of the electromagnetic beam LOS (Line of Sight) that occurred in the mining area during this period.<br />Based on the carried out calculations, significant activity of the area around the open-pit mine was perceived. Dumping ground were analyzed - external Szczerc&#243;w Fields and internal Be&#322;chat&#243;w Fields, as well as excavations where mineral extraction is currently taking place. Continuous deformations (depressions and uplifts) associated with intensively conducted mining exploitation and complicated geological and mining conditions occurring in this area were observed (arrangement of rock layers, faults, the D&#281;bina salt debris separating the Be&#322;chat&#243;w Field from the Szczerc&#243;w Field).</p>
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