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The study aims at detection, mapping and monitoring of land subsidence in Jharia Coalfield, Jharkhand, India by spaceborne DInSAR, GPS and precision levelling techniques. Using multi-frequency C-and L-band DInSAR, both slowly and rapidly subsiding areas were identified and DInSAR-based subsidence maps were prepared. C-band DInSAR was found useful for detection of slowly subsiding areas whereas L-band DInSAR for rapidly subsiding and/or adverse land cover areas. Due to dynamic nature of mining and adverse land cover, temporal decorrelation poses a serious problem particularly in C-band DInSAR. Specially designed InSAR coherence guided adaptive filtering was found useful to highlight the deformation fringes. Collateral GPS and levelling observations were conducted in three test sites to validate DInSAR measurements and to determine the net displacement vectors. We observed an appreciable horizontal displacement component of land subsidence in all the test sites. For comparison of results, we calculated InSAR coherence weighted LOS displacement rates from the unwrapped differential interferograms of smaller spatial subsets and LOS projected ground-based displacement rates in three test sites. We found good agreement between DInSAR and ground-based measurements except for C-band observation in Dobari test site primarily due to large difference in observation periods and temporally inconsistent land subsidence. Collateral spaceborne and ground-based observations were also found useful for characterization of subsidence phenomena to determine net displacement vector and horizontal displacement component. In coal mining areas with spatially scattered and temporally irregular land subsidence phenomena, the adopted methodology can be used successfully for detection, mapping and monitoring of the subsiding areas vulnerable to future collapse. This will facilitate efficient planning and designing of surface infrastructures and other developmental structures in the mining areas and mitigation management of subsidence induced hazards.

ABSTRACT:Differential SAR-Interferometry (D-InSAR) is one of the potential source to measure land surface motion induced due to underground coal mining. However, this technique has many limitation such as atmospheric in homogeneities, spatial de-correlation, and temporal decorrelation. Persistent Scatterer Interferometry synthetic aperture radar (PS-InSAR) belongs to a family of time series InSAR technique, which utilizes the properties of some of the stable natural and anthropogenic targets which remain coherent over long time period. In this study PS-InSAR technique has been used to monitor land subsidence over selected location of Jharia Coal field which has been correlated with the ground levelling measurement. This time series deformation observed using PS InSAR helped us to understand the nature of the ground surface deformation due to underground mining activity

ABSTRACT:Differential Interferometric synthetic aperture RADAR (D-InSAR) has emerged as one of the influential tools for the measurement of Earth's topography deformation. The temporal variability of atmosphere plays a contaminative role in degrading the accuracy of Interferometric measurements as it causes the path delay in the propagating RADAR signal. The Ionosphere and Troposphere are the two atmospheric layers which are responsible for the path delay error in the Interferometric measurement. In this study ground based meteorological data integrated with spaceborne meteorological data was used to mitigate the path delay induced by the atmosphere on the Radarsat-2 data. In this study Jharia Coal Fields, Jharkhand, was selected where active mining has taken place since 1894. The DInSAR was generated from Radarsat-2 data. In Troposephric path delay calculation ground based data like water vapor, temperature and humidity acquired during the time of the pass as well as spaceborne meteorological data were used as input. The TEC from IRI-2007 model was used as input to calculate the ionospheric path delay. These Ionospheric as well as Tropospehric delay was subtracted from a Differential Interferrogram to obtain atmospheric artifacts free differential interferrogram. The corrected Diffrential Interferrogram was used to delineate subsidence areas. We observed that D-InSAR and levelling results shows good agreement with each other. The Diffrential Interferomteric pairs with low coherence causes phase unwrapping problem. Therefore, only those pairs with good coherence were considered for the study. The used technique provides an opportunity to understand the contribution of Ionospehric and Tropospehric path delay effects on the D-InSAR results.

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