Subsidence monitoring in the Ordos basin using integrated SAR differential and time-series interferometry techniques

Recent researches have illustrated with the image tracking method that Ordos, China is suffering from a significant drop in earth surface level. However, such method can lead to bias in terms of its accuracy. In this paper, land displacement in Ordos between 8 January 2007 and 19 January 2011 was mapped using L-band ALOS Phased Array type L-band Synthetic Aperture Radar (PALSAR) data. Twenty PALSAR images were utilized to generate both Differential Synthetic Aperture Radar Interferometry (DInSAR) and time-series InSAR (TS-InSAR) results. Several locations in the eastern Ordos experiencing rapid land subsidence were identified. The subsidence rates ranging from -30 mm year(-1) to 30 mm year(-1) were measured in line-of-sight direction. The comparison between TS-InSAR and DInSAR results, although showing good agreement in general, reveals some gaps in time-series map near Qu Jia Liang coalmine mainly due to sudden changes within the four-year period. DInSAR result was exploited to fill these gaps after removing the tropospheric stratification phase delay and the verification step was conducted over the relatively stable region identified by TS-InSAR analysis. At last, the refined DInSAR result was converted into time-series velocity map and superimposed to TS-InSAR outcome to generate a final product.