REMOTE SENSING BASED COAL FIRE STUDIES IN JHARIA COALFIELD, INDIA

Abstract

Jharia Coalfield (JCF) is known for one of the densest congregations of surface-subsurface coal fires in the world. It has witnessed numerous severe accidents and continuous loss of valuable coal reserves due to uncontrolled coal fires. Coal fire affected areas are often inaccessible and here can be precisely investigated by remote sensing techniques. In the present study, suitable methods for mapping and monitoring of coal fires have been developed and surface-subsurface coal fires have been systematically analyzed. The attempts made here are mainly emphasized on developing a novel approach for thresholding and mapping of surface coal fires, and monitoring spatial dynamics of coal fires in JCF through time and space. Surface-subsurface coal fires are the typical characteristic of a coal mine area. Surface fires are common in coalfields where coal is exposed to sunlight for long durations of time. The heat energy emitted from these fires affects the signal recorded by sensors operating in the shortwave infrared regions of the electromagnetic spectrum. The Landsat TM/ETM+ band-7 is sensitive to solar reflected as well as emitted radiations from a target. The „maximum solar reflection threshold‟ method proposed in this study uses the highest spectral radiance that can be attributed to solar reflection as the conservative threshold to segregate the pixels with emitted component from those with reflected component of the EM energy. Investigations with Landsat TM/ETM+ data indicate a reflectance value of 0.23-0.25 as the most representative highest reflectance (threshold) in coal mining areas. The method apparently has the advantage as it is based on the reflectance characteristics of materials (sandstone-shale mixtures) typically found in coal mining areas and is applicable in wide range of geographical setting. To facilitate sustainable mining for industrial growth, temporal monitoring of coal fires has to be executed at regular interval. In the present approach, two ratio indices namely; „Normalized Difference Coal Index (NDCI)‟ and „Normalized Difference Coal-fire Index (NDCfI)‟ have been proposed to systematically map the coal seam fires using Advance Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The adopted methodology has been implemented in Jharia Coalfield. Statistical thresholding of indices precisely segregate the pixels attributed to surface coal fires (high intensity coal seam surface fire and low intensity smoldering surface fire) and shows that the surface coal fires closely follow the pattern of the excavated coal seams. Surface fires are distributed mainly in the eastern and south-eastern part of the study area with a cumulative coverage of 3.93 km2. Reliability of the obtained results has vi been validated by computing an error matrix with overall accuracy of 87.7%. The adopted methodology precisely localized the surface coal fire affected areas and closely represents the actual scenario of surface coal fires in JCF. Beside its conservative and robust nature, the method introduced here is rapidly practicable and allows quick retrieval of surface coal fires. Systematic investigation of actual scenario of coal fire is always been a critical issue for coal fire research community. ASTER provides data at high temporal and radiometric quantization level, and is unique in its ability to monitor the fluctuation in spatial extent of coal fire. Time series analysis of three consecutive sets of ASTER data evaluates the spatial dynamics and trend of coal fires propagation in Jharia. Results indicated that the magnitude of coal fires in JCF have been fluctuated with time from 2000 to 2009. The area located around the Shatabdi opencast, Barora, Sijua opencast, Godhar colliery, Kusunda, Bokapahari, Kujama and Lodna are under intense coal fire. From 2000 to 2004, spatial extent of coal fire has shown a minor decrease of 6.74% and then shows a substantial increase of 11.93% between 2004 and 2009. Coal fires are quite persistent in western part of the JCF from 2000 to 2004. However, between 2004 and 2009, considerable decrease of 1.157 km2 of fire has been noticed in west and east Barora, Block II Project and Govindpur collieries located in western most part of the JCF. It has been noticed that the west-central part of the JCF comprising Katras, Sijua, Western Jharia-II and Kusunda collieries are most affected. Since 2004, spatial extent of the fire exclusively in Kusunda colliery is increased by 1.122 km2. This remarkable increase in spatial extent fire is due to the appearance of new surface fire site located south of Kusunda and north of Alkusha in 2009. In south-eastern part of the JCF, fire is quite persistent from 2004 to 2009. However, minor increases in Kustor, Bastacolla and Lodna collieries have been noticed from 2004 to 2009. Surface fires in JCF are highly sporadic and exhibits minor fluctuation in spatial extent between 2000 and 2008. It has increased by 8.6% since 2000 to 2004 and then decreased by 14.66% from 2004 to 2008, respectively. The increase in fire extent in 2008 has been marked by appearance of two new surface fires sites noticed near Kantapahari, in Katras colliery and north of Alkusha quarry in Katras colliery. vii To evaluate the propagation of fire in JCF, coal fire maps of three consecutive years have been interpreted together with structural map on GIS platform. Systematic analysis of the obtained results reveals that the movement of fire is structurally controlled. Propagation of the fire has been well noticed in Kustor, Bastacolla and Lodna collieries. Fire appears to be moving toward Jharia. In 2009, it has been observed that the fire located east of Jharia, near Bokapahari (in Bastacolla colliery) is propagating towards NNW and fire located Jiyalgarh, Lodna is propagating northerly toward Jharia (in Lodna colliery). While fires located near Bokapahari and SE of Alkusha (in Kustor colliery) are propagating in south and SE direction heading toward Jharia. Both these fires have been observed to be moving along the strike of coal seam. Fire located SE of Alkusha (in Kustor colliery) may also under control of two NW-SE trending faults causing propagation of fire toward south and SE. Coal fires in JCF causes tons of coal loss by burning and actively contributed to the instability in the area from safety point of view. Problem of coal fire in Jharia has long back history and is still persisting. Local villages and inhabitants lying in the vicinity of Jharia township are on the verge of major devastation. Status of the fire is demanding some firm measures to control them. Systematic investigations of coal fires are essentially required to facilitate plan sustainable mining and safety measurements for industrial growth on long term basis in Jharia.