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Geology/Disaster 2
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Application of the Thermal Infrared Remote Sensing Technology in detection and investigation of underground coal fire
- Estimation of Detectable Depth
As we know generally, it is almost impossible to detect directly the depth and location of UBA by only the thermal information extracted from thermal images, but if we ignore the radiative background caused by normal ground thermal flow and the day-night change of solar radiative energy on the ground, it is possible to consider that the thermal radiative energy in GBA depends on the thermal energy conducted up to surface from UBA, and a close correspondent relationship exists between them. The depth study of remote sensing potential for detecting underground coal fire through the analysis of thermal structure and the determination of thermal anomaly in images, combined with know geological and exploration data, is definitely necessary and interested.
According to the existing exploitation in burning area, No2 coal seam, which is burning severally, has 160m depths mostly and average depth 86m. The "depth" here means the distance from coal seam roof to ground surface. Actually, these GBA correspondent to the o 2 burning seam all he thermal anomaly equal or exceed the setting of HI reference source (BB2) in air-borne thermal IR scanning images, indicating the depth value detectable by it could be deeper.
Preliminary study shows that the detectable depth is depend on many factors, such as thickness of coal seam, the burning time period, the basic features of roof rocks, etc. in this case, since burning coal seam is very thick , the roof rocks are mainly sandstone and there are many cracks, the detectable depth is much bigger than the value reported in abroad reference.
- GBA Delineation and Width Estimation Using Satellite Data
During the creations of TM (6.4.3) or (6,7,5) color compositions, a method of threshold compression segmentally was used to determine GBA boundary from the intensity anomaly in TM6 image where has been delineated as GBA by airborne thermal image interpretation. Experimental results show that the boundary anomaly area after intensity compressed to be half of the previous could be consider as the boundary of GBA.
The reason of selecting half compressed intensity to determine boundary of GBA is related to the high correlation of TM data, the effects of mixed-pixels and the way of TM6 data creation (interpolated from 120m to 30m resolution). The integrated effect is that the width of GBA in TM6 image has been increased notably comparing to the true width, that is, the integrated effect looks like positive.
Summary
A part from the preliminary study of some basic technical problems, this experimental investigation has got remarkable result sin standardized procedure establishment and in engineering application.
- The two temporal situations of underground coal fire in the test site before 1986 and within 1986-1988 have become clear, the new and old burning areas are delineated, the total loss of coal resources for severest fire in each burning area were predicted. All results have been used as one of basic data & information sets for the drafting of "The engineering design of underground coal fire prevention and cure project in Ruqige coalfield".
- Besides verifying TM6 data's capability of detecting burning area detected by airborne thermal scanning data, two new burning areas have been found newly in TM6 image of 1988.
- A se of apply able techniques & procedures for underground coal fire detail investigation by using mainly airborne thermal IR was established while the method of using satellite thermal data as the reconnaissance tool was studies also.
- The results have greatly promoted the carry outing of large-scale investigation for underground coal fire by using remote sensing technology in north part of China.
Acknowledgement
The authors wish to thank prof. Zeng Shaomign and Mr. Zhou Fuzhen very much for their valuable helps in conducting and paper drafting. Thanks also to the project participating colleagues from CRSG, Ruqige coalfield and the Professional Design Institute, Ministry of Railway.
References
- Wang Guoqin, song Dexiang: "Coal Geography Worldwide", Business Publishing House, 1987.
- Helan Coal Geology Exploration inc.: "Detail Exploration Report for Ruqige Coalfield", 1966.
- Robert N. Colwell et al: "Manual of Remote Sensing", Second Edition, American Society of Phorogrammetry, 1983.
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