Multi-Sensor Monitoring of Mining Induced Subsidence Using Persistent Scatterer Interferometry
Salepci, Nesrin; Kuehl, A.; Thiel, C.; Schmullius, C.
Friedrich Schiller University of Jena, GERMANY

In this study Persistent Scatterer Interferometry (PSI) technique is employed to multi-sets of SAR scenes from different sensors in order to monitor temporal and spatial patterns of the subsidence due to mining in Sondershausen, Germany. The work is a part of ongoing INFLUINS project funded by the German Federal Ministry of Education and Research.

Mining salt in Sondershausen began in the early 1980s and was active till mid-1990s. During this period the subsidence rate due to mining activities has gradually increased reaching its maximum in the early 1990s almost to a rate of 250 mm/year. However, since 1996 the mine is backfilled with industrial backfill material leading to a gradual decrease in the subsidence rate in those parts of the city undermined, consequently, reducing the risk of hazardous rock burst. The SAR scenes cover the period of backfilling between 1995 and 2010. The displacement rates for the first ten years 1995-2005 are derived by ERS-1/2 scenes. The next period (2004-2010) is covered by ENVISAT-ASAR stack providing overall 15 years of monitoring of the subsidence. In addition to ENVISAT-ASAR, for the span of 3 years from 2007 to 2010 ALOS-PALSAR stack is additionally processed in order to exploit the different information provided by different sensors.

The main deformational area lies in the Sondershausen urban area, therefore sufficient number of Persistent Scatterers (PS) is found and PSI technique is successfully applied, such that good estimation of subsidence rates and clear spatial pattern of the displacement could be captured by the PS, found in the city of Sondershausen. The PSI processing is utilized separately to all the three sets of SAR data (ERS/ASAR/PALSAR). In Figure 1, displacement rates of each PS derived from ASAR stack are presented on an average amplitude image. The subsidence rates in the main deformational area reach up to 16 mm/year which is surrounded by stable points represented by dark blue color.

In the following steps the results from different sensors are combined first in temporal direction, ERS-ASAR providing continuous monitoring, then in spatial direction, ASAR-PALSAR. Owing to finer spatial resolution, on PALSAR scenes higher PS density is found, however, due to its shorter wavelength ASAR stack is more sensitive to the subsidence. In spatial combination, both of these advantages are exploited.

In the framework of this analysis the deformation rates obtained by PS processing is also compared to the geodetic surveying data covering the time span of observation period (1995-2010) for validation of the results, furthermore for analyzing the differences between the values of PS results and the surveying.

Figure 1: Vertical deformation rates of each persistent scatterer estimated by ENVISAT-ASAR stack. Assigned colors of the points represent the amount of sinking rate in mm/year, ranging from 0 indicating stable areas (dark blue points) to around -16 mm/year (red points)