Persistent Scatterer Interferometry (PSI) is a novel remote sensing technique for monitoring land deformation on large scale. It is economic and can be used for detection of land surface deformation in the past given that the sensor should have passed over the area. The millimetric precision of the technique makes it very useful. One of its application is monitoring of slow moving landslides. In this study we have focused upon monitoring of slow moving landslides in Tehri region of Uttarakhand state of India. This area is landslide prone. Its susceptibility to landslide has increased due to construction of artificial reservoir in the region. The variation in reservoir drawdown level can be cited as one of the reasons. In this study we have applied Persistent Scatterer Interferometry on the stack of 20 Single Look Complex (SLC) scenes of Envisat satellite of European Space Agency. We have performed time-series analysis for period starting from 12 May 2008 to 26 July 2010. The methodology consists of selection of master image, coregistration of other slave images to master image, calculation of amplitude stability index, generation of reflectivity map. After this 19 interferograms were generated. On basis of this selection of Persistent Scatterers (PS) is done. After that estimation and removal of Atmospheric Phase Screen (APS) was done. In the end calculation of time-series displacement of PSs is performed. From this analysis we are able to identify the spatial location of slow moving landslides. In this study we have identified PSs having nearly 40 mm/year of velocity. Detected areas showing land movement away from the line of sight of satellite, can be found on the rim of reservoir as well as areas 4 kilometres interior, away from the boundary of reservoir. These areas are located near roads and places where anthropogenic interference is there.

The coal fires that started over a century ago in Jharia Coal Fields constitute a significant threat to the coal reserves, infrastructure, and residents’ lives. The fires burn underground coal leaving the surface with no support, leading to land subsidence and roof collapse. This will have a multiplier effect as it creates cracks and crevices that pump in more oxygen to aggravate the coal fires further. Despite the various measures taken by authorities, coal fires and land subsidence still have an increasing presence. In this study, we investigated the two hazards and their impact on the coal mines and surrounding settlements. We observed the subsidence and coal fires in the study area with the help of Persistent Scatterer Interferometry analysis of Sentinel-1 images and Temperature anomaly mapping of Thermal Infrared Imagery from Landsat-8, respectively. The subsidence velocity results and the coal fire zones are analysed, and a significant spatial overlap of both hazards is noticed. A few key locations severely affected by both the hazards are identified and examined to understand the mutual effect of coal fires and land subsidence. The subsidence of up to 20 cm/yr is observed in the study area. The results show that nearly 80% of the subsiding area is also affected by coal fires. Kusunda, Bararee and Keshalpur collieries are critically affected by both the hazards and need immediate intervention. Subsidence and coal fires extending towards the residential zones in several collieries is a matter of concern. In conclusion, the study presents an efficient methodology for multi-hazard monitoring, and the findings assist the authorities in enforcing appropriate disaster management strategies.