LANDSAT-TM DATA FOR ESTIMATING GROUND TEMPERATURE AND DEPTH OF SUBSURFACE COAL FIRE IN THE JHARIA COALFIELD, INDIA

Coal fires are a ubiquitous problem in coal-mines, the world over. They burn our prime energy resource, lead to atmospheric pollution and render mining of coal hazardous. Processes leading to coal combustion and spread of subsurface fires are briefly examined in this paper and the role of remote sensing in surveillance of coal fires is presented. The present study aims at developing a quick method for estimating the temperature of the ground surface directly above subsurface coal fires. Utility of TM6 and TM7-band data for temperature estimation is briefly reviewed. It is argued that temperature calculations of surface anomalies related to subsurface fires can only be done on the basis of 8-14 mu m band data, due to the low temperatures involved. In the Jharia coalfield, it is noted that subsurface fires in various coal-mines are associated with surface thermal anomalies, as has also been confirmed by ground checks. The pattern of TM6 data distribution and ground truth is used to isolate thermal anomalies, and the TM6 digital numbers are converted into kinetic temperature values. It is observed that for the Landsat-TM scene (28 November 1990) the kinetic temperatures range from 16.0 degrees C to 31.6 degrees C in the Jharia coalfield, with a threshold value of 25.6 degrees C associated with the anomalies. Depth estimation of fire has been carried out using field structural geology data and pixel locations of thermal anomalies. It is inferred that the depth of subsurface coal fire ranges between 45-55 m, in most cases, which is in general agreement with the field data. Limitations of the method are indicated.