InSAR coherence and phase information for mapping environmental indicators of opencast coal mining: a case study in Jharia Coalfield, Jharkhand, India

Mapping and monitoring the environmental indicators of opencast coal mining can help immensely for efficient planning and management of mining operations, assessment of environmental impacts on land use, and execution of reclamation measures. Previous workers have found that areas of opencast mining can be delineated efficiently from optical multispectral data. However, it is difficult to distinguish unreclaimed abandoned or closed opencast mines from the active opencast mines in optical multispectral images. Similarly, overburden dumps cannot be distinguished from flat-lying degraded lands and recently reclaimed quarries covered with overburden materials. Overburden materials have a spectral response similar to that of bare rock outcrops and therefore are difficult to separate. In addition, coal dumps have a spectral response similar to that of the opencast mining area, occupied by coal seams and coaliferous matter, and therefore are also difficult to separate. In this work, the differential temporal decorrelation criterion of the terrain elements in InSAR data pairs has been utilized to distinguish unreclaimed abandoned or closed opencast mines from active opencast mines. Coherence information of InSAR data pairs with diverse temporal baselines provides temporal decorrelation of the scattering elements in individual resolution cells or pixels of the terrain elements. Contrast in coherence values between abandoned or closed opencast mines and active opencast mines or other land use - land cover classes is more pronounced in the InSAR data pairs with shorter temporal baselines. Shorter temporal baseline InSAR data pairs also facilitate the generation of a high-quality DEM from InSAR phase information due to substantially less temporal decorrelation noise. An ERS SAR tandem data pair with a 1-day temporal baseline was found to be the best suited for delineating unreclaimed abandoned or closed opencast mines from the active opencast mines among all the data pairs. High overall coherence in the data pair also facilitates the generation of a good quality, spatially consistent DEM from which overburden and coal dumps could be successfully delineated from the surrounding areas due to their higher relative elevations.