The Sentinel-1 satellite system continuously observes European countries at a relatively high revisit frequency of six days per orbital track. Given the Sentinel-1 configuration, most areas in Czechia are observed every 1–2 days by different tracks in a moderate resolution. This is attractive for various types of analyses by various research groups. The starting point for interferometric (InSAR) processing is an original data provided in a Single Look Complex (SLC) level. This work represents advantages of storing data augmented to a specifically corrected level of data, SLC-C. The presented database contains Czech nationwide Sentinel-1 data stored in burst units that have been pre-processed to the state of a consistent well-coregistered dataset of SLC-C. These are resampled SLC data with their phase values reduced by a topographic phase signature, ready for fast interferometric analyses (an interferogram is generated by a complex conjugate between two stored SLC-C files). The data can be used directly into multitemporal interferometry techniques, e.g., Persistent Scatterers (PS) or Small Baseline (SB) techniques applied here. A further development of the nationwide system utilising SLC-C data would lead into a dynamic state where every new pre-processed burst triggers a processing update to detect unexpected changes from InSAR time series and therefore provides a signal for early warning against a potential dangerous displacement, e.g., a landslide, instability of an engineering structure or a formation of a sinkhole. An update of the processing chain would also allow use of cross-polarised Sentinel-1 data, needed for polarimetric analyses. The current system is running at a national supercomputing centre IT4Innovations in interconnection to the Czech Copernicus Collaborative Ground Segment (CESNET), providing fast on-demand InSAR results over Czech territories. A full nationwide PS processing using data over Czechia was performed in 2017, discovering several areas of land deformation. Its downsampled version and basic findings are demonstrated within the article.
This case study presents the verification of two surface subsidence prediction models for longwall mining at depths greater than 400 m. The surface subsidence points were surveyed and compared for both models. The first model uses empirical calculations to predict the surface subsidence. This method is reliable for predicting surface subsidence at shallower depths. At present, however, coal mining has progressed to great depths. The second model is the 2-dimensional finite element method to predict surface subsidence. In contrast to the first method, this method is based on the regional parameters and uses the rock mass properties to evaluate surface subsidence for multiseams at any depth. Results show that the finite element method gives a better approximation of the measured surface subsidence than the Knothe method. The maximum surface subsidence, which was determined by the FEM method, was used to adjust the extraction coefficient in the Knothe's method. The predicted value differs from the measured value by 8 %. The slope of the predicted subsidence trough was within the range of 2-8 % from the surveyed subsidence. This case study proposes a procedure for using both models to successfully predict the surface subsidence.
Deep extraction of minerals is accompanied by deformations of the strata overlying extracted coal seams. Deformations of overlying layers run up to the surface where a subsidence trough gradually forms. The movement of individual surface points is curvilinear, spatial and, in relation to the time pattern, not uniform. In some cases, during the formation of a subsidence trough, temporary uplifts of the surface occur. This paper gives a particular area in which uplifts of the surface occurred when the rigid overlying strata was disturbed. The character of deformations of the overlying rocks is evaluated on the basis of a comparison of the results of the measurement of subsidence of the surface using geodetic methods with the development of mined-out areas and with their extracted thickness. For specifying the time of failure of the overlying strata, also information obtained from a system of continuous monitoring of seismic events is used. The spatial extent of the subsidence trough is identified by satellite radar interferometry (InSAR) techniques applied to TerraSAR-X images. The subsidence wave was possible to detect using a short temporal difference of 11 days between satellite radar images. This shows the potential of short-temporal high resolution InSAR for monitoring of progress of subsidence troughs. A good knowledge of extents and shape of subsidence trough formation in time allows to verify values of parameters used for prediction purposes. Application of the short temporal InSAR appears very effective for spatio-temporal studies of the current subsidence trough development and helps understanding the physical process as well as identifying deviations from the behaviour expected by models.
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