Surface fires in Jharia coalfield, India-their distribution and estimation of area and temperature from TM data
Surface fires occur at a number of places in the Jharia coalfield and are high-temperature phenomena of relatively local extent. The use of Landsat Thematic Mapper (TM) shortwave infrared (SWIR) bands in estimating temperatures of high-temperature objects is briefly reviewed. Study of data of TM7 and TM5 bands indicate the existence of surface fires in the Jharia coalfield at 59 pixels and this was supported by limited field checks. Pixel-integrated temperatures of surface fire areas are estimated to be in the range of 217 C to 410 C. However, as these fires often do not occupy the whole pixel area, the pixelintegrated temperatures are less than the actual fire temperatures. The relation between spectral radiance and temperature is nonlinear. Therefore, radiant temperature in TM5 and TM7 can be used to estimate the subpixel area and temperature of surface fires (provided there is no band saturation). In the Jharia coalfield, the subpixel area of some of the surface fires has been found to range between 0.2 of a pixel (180m2) to 0.003 of a pixel (27m2). The subpixel temperature corresponding to these instances has been found to range 342 C to 731 C. The limitations and operational aspects of these techniques are indicated.