Study on Directional Near-Infrared Reflectance Spectra of Typical Types of Coal
YANG En1, WANG Shi-bo2*
1. School of Intelligent Manufacturing, Jiangsu Vocational Institute of Architectural Technology, Xuzhou 221116, China
2. School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, China
Abstract：Hyperspectral remote sensing is an effective method for coal mining area detection, and it is of great significance for coal resource surveys and environmental monitoring in the mining area. At the same time, reflectance spectrum characteristics of remotely measured objects such as coal, gangue, vegetation and water body in all directions are the basis of hyperspectral remote sensing in the coal mine. In this paper, the directional reflectance spectra of typical types of coal were studied. Four typical types of coal in the three major coal types anthracite, bituminous and lignite were collected from different mining areas in China. According to the increasing rank, these coals included No.1 anthracite, meager coal, gas coal and No.2 lignite. Spectral reflectance curves of each type of coal in all directions in hemispheric space were measured in the near-infrared band (1 000~2 500 nm) using the spherical coordinate device for directional reflection measurement in the laboratory. By waveforms of spectral reflectance curves acquired, it was found that near-infrared reflectance spectrum curves of the same coal in different reflection directions show similar waveforms. However, there are some differences in overall reflectance and local waveforms, and the rule is that the absorption valleys become more obvious with increasing overall reflectance. With increasing reflection angle, reflectance spectrum curves of all these four types of coal rise on the whole in the forward direction (180° azimuth), but the change is relatively small in the backward direction (0° azimuth). In each directional reflectance spectrum curve in the hemispheric space of each coal, five characteristic wavelength points, including 1 400, 1 700, 1 900, 2 200 and 2 300 nm were selected. By polar nephograms of the spatial distribution of reflectance at the five wavelength points, it was found that all these four types of coal show bidirectional reflection and prominent hot spots in the forward direction and relatively weaker hot spots in the backward direction. The hot spots in the backward direction of No.1 anthracite appear relatively more obvious than those of meager coal, gas coal and No.2 lignite. With decreasing coal rank, meager coal, gas coal, and No.2 lignite show the rule of relatively enhanced hot spots in the backward direction. The correlation between reflectance and reflection angle of backward and forward direction at the five wavelength points of each type of coal were analyzed. It was found that the correlations between reflectance and reflection angle are approximately linear and Gaussian functions in forwarding and backward direction respectively. Moreover, with decreasing coal rank, the peak of the Gaussian fitting curve moves to a larger reflection angle. This study provides the basis for the selection of the optimal detection geometry and reference for precise detection of coal resources in hyperspectral remote sensing of mining areas.
Key words：Coal mining area; Hyperspectral remote sensing; Near infrared; Directional reflection; Characteristic wavelength point
杨 恩，王世博. 典型煤的近红外反射光谱特征的方向性研究[J]. 光谱学与光谱分析, 2022, 42(03): 847-858.
YANG En, WANG Shi-bo. Study on Directional Near-Infrared Reflectance Spectra of Typical Types of Coal. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(03): 847-858.
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