Abstract
Over the last ten years remote sensing techniques in China coal industry have been developed rapidly. Through theoretical researches, the regularity of thermal radiation and differential of optical reflectance of coal seams have been found. The correlativity between ground observational data and space image data has been discovered. During method test, a Test Area for coal remote prehensive test conducted, the suitable fields and the optimal procedure for application of remote sensing technique in coal industry determined. The theories and methods established in the researches have been applied in the practical production in respect to coal field general investigation, prediction, coal reconnaissance, coal geological surveys, detecting fire, flood and pollution in coal mines, and have yielded remarkable economic, techniques results and social benefits. This paper describes mainly the theory, methods, and practical results for coal remote sensing.

Theoretical Researches

1. Contents of Research


The study of the physical characters of coal seams in the light and thermal fields is a basic job in the coal remote sensing. Through four successive years of spectral tests, and infrared observing temperature work, a lot of data were obtained. These data were elabozated systematically in order to probe reflective character of coal seam in light field, to look for the regularity of radiation of the coal seam in the thermal field, to develop applied theories and define the criteria for applications used for coal remote sensing.


2. Reflection Characteristics of Coal Seam in the Light Field.


The Measurements show that reflectivity of coal seam within 0.5-0.8mm is less than 10%; between 0.9-0.95mm is about 12% (peak value), within 0.95-1.1mm is decreasing. Compared with other rocks, the reflectivity of the coal seams is the lowest in 0.4-1.1mm band, it's reflectivity is 5-30% lower than that of other rocks.

The research proves that various photographic and scanning means of remote sensing in the light field are applicable to the recognition of coal seams and detection of coal measures.


3. Regularities of Radiation of Coal Seams in the Thermal Fields.



1. The light-heat conversion effect of the coal seam


When the coal absorbs the solar light, the states of vibration and rotation of molecules change. In the process of such changes, light energy is converted into heat energy^[2]. Coal is made of combustible substances. It has a porosity of about 8-20% and the general molecular formula is C₁₀₂H₇₈O₁₀N₂. There is a hydrogen-rich lateral chin in the structure model of the coal molecule. In the process of conversion of light energy to heat energy due to absorption of sunlight, thermal decomposition of the molecular structure of the coal and volatilization takes place, the components such as carbon; hydrogen and sulfur are oxidized successively. In the process of exition, the temperature increases gain, thus promoting redecomposition, revolatilization and reoxidation, forming light-heat-chemistry heat chain reaction and increasing the temperature of coal seams sharply. These are physic-chemical reaction characteristic of the coal seam after the sun illuminates the coal measures, and also the substantial properties of the thermal anomaly f the coal seams.


2. The characteristic of the thermal radiation of coal seams with different deep


The deep coal seam has a geothermal gradient 1-2°C^[3]greater than the normal geothermal gradient. For the shallow coal seam, strong oxidation generally results in large-scale spontaneous combustion, so it constitutes the strongest thermal radiation source of the coal field: The surface coal seam interacts with the electromagnetic wave emitted by the sun while oxidation proceeds and owing to the influence of the day-night and seasons, there appears a periodic regularity of the thermal radiation for the surface coal seam.

The above study shows the termal-infrared remote sensing is the optical method used for coal industry.