# A Novel Index for Detecting Bare Coal in Open-Pit Mining Areas Based on Landsat Imagery
## 2 Materials  
### Study Area  
Inner Mongolia is an autonomous region in northern China, renowned for its abundant coal reserves, making the coal industry a crucial economic pillar in the region. However, due to its location in an ecologically fragile zone, combined with unique geographical features and highly sensitive ecosystems, the region is particularly vulnerable to the impacts of open-pit coal mining. Therefore, monitoring open-pit coal mining in Inner Mongolia is essential not only for ensuring the efficient utilization of resources but also for safeguarding the region's ecological environment, maintaining social stability, and supporting sustainable economic growth. Additionally, as illustrated in Figure 1, Inner Mongolia spans a longitude of 28\({}^{\circ}\)52\({}^{\prime}\), with a straight-line distance of over 2400 km from east to west, resulting in diverse climatic conditions and coal types, which in turn affect the spectral reflectance of coal. To investigate the spectral characteristics of the different coal types in remote sensing images and to develop a more generalized bare coal index, this study selected the Chenqi, Shengli, and Dongsheng coalfields as research areas. Among these, both the Chenqi and Shengli coalfields produce lignite. However, due to significant differences in natural background conditions and the extent of human activities between these areas, the Chenqi Coalfield is also designated as a separate research area for comparative analysis. The details are as follows:  
1. Chenqi Coalfield is located on the western slope of the Greater Khingan Mountain Range and the north bank of the Hailar River. The center of the coalfield lies 25 km from Hailar City, within the jurisdiction of the Prairie Chenbarhu Banner in the HulunBair League of the Inner Mongolia Autonomous Region. Its geographical coordinates are 119\({}^{\circ}\)12\({}^{\prime}\)-120\({}^{\circ}\)15\({}^{\prime}\)E, 49\({}^{\circ}\)13\({}^{\prime}\)-49\({}^{\circ}\)39\({}^{\prime}\)N. Situated on the HulunBair Plateau, the coalfield is bordered by low hills to the north and northeast, with the terrain sloping from high in the northeast to low in the southwest, at an elevation of 602 to 724 m. The area features gentle undulating slopes. The coalfield has a mid-temperate semi-arid climate, with an average annual precipitation of 306.8 mm, evaporation of 1329 mm, and vegetation cover ranging from 50% to 70%. Lignite is the primary type of coal found here.
2. Shengli Coalfield is located in Shengli Sumu, northwest of Xilinhot City, within the XilinGol League of the Inner Mongolia Autonomous Region. Its geographical coordinates are 115\({}^{\circ}\)30\({}^{\prime}\)-116\({}^{\circ}\)26\({}^{\prime}\)E, 43\({}^{\circ}\)57\({}^{\prime}\)-44\({}^{\circ}\)14\({}^{\prime}\)N. Positioned in the eastern part of the Inner Mongolia Plateau and on the northern slope of the western extension of the Greater Khingan Mountain Rainge, the terrain consists of gently undulating foothill plains. Elevations range from 970 to 1326 m, with higher terrain in the west and lower in the east. The coalfield features a mid-temperate, semi-arid continental monsoon climate, with an average annual precipitation of 294.7 mm, evaporation of 1794.6 mm, and vegetation cover between 10% and 35%. Lignite is the dominant coal type in this area.
3. Dongsheng Coalfield is located in Ordos City and Ejin Horo Banner of the Inner Mongolia Autonomous Region, with geographic coordinates of 108\({}^{\circ}\)40\({}^{\prime}\)-110\({}^{\circ}\)50\({}^{\prime}\)E, 39\({}^{\circ}\)20\({}^{\prime}\)-40\({}^{\circ}\)15\({}^{\prime}\)N. Situated in the northeastern part of the Ordos Plateau, the terrain is hilly, with elevations ranging from 1120 to 1584 m, gradually decreasing from the central part towards the north and south. The coalfield has an arid to semi-arid continental plateau climate, with an average annual precipitation of 368.2 mm, evaporation of 2163.8 mm, and vegetation cover between 10% and 30%. Bituminous coal is the main type of coal found here.