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J. Zhang, C. Künzer:
"Thermal surface characteristics of coal fires 1: Results of in-situ measurements";
Journal of Applied Geophysics, 63 (2007), 117 - 134.

Natural underground coal fires are fires in coal seams occurring subsurface. The fires are ignited through a process named
spontaneous combustion, which occurs based on a natural reaction but is usually triggered through human interaction. Coal mining
activities expose coal to the air. This leads to the exothermal oxidation of the carbon in the coal with the air's oxygen to CO2 and - under
certain circumstances - to spontaneous combustion.Coal fires occur inmany countries worldwide - however, currently the Chinese coal
mining industry faces the biggest problems with coal fires. Coal fires destroy the valuable resource coal and furthermore lead to many
environmental degradation phenomena such as the deterioration of surrounding vegetation, land subsidence and the emission of toxic
gasses (CO, N2O). They additionally contribute to the emission of green house relevant gasses such as CO2 and CH4 to the atmosphere.
In this paper we present thermal characteristics of coal fires as measured in-situ during a field campaign to the Wuda coal fire
area in south-central Inner Mongolia, China. Thermal characteristics include temperature anomaly measurements at the surface,
spatial surface temperature profiles of fire areas and unaffected background areas, diurnal temperature profiles, and temperature
measurements inside of coal fire induced cracks in the overlying bedrock. For all the measurements the effects of uneven solar
heating through influences of slope and aspect are considered.
Our findings showthat coal fires result in strong or subtle thermal surface anomalies. Especially the latter can easily be influenced by
heating of the surrounding background material through solar influences. Temperature variation of background rocks with different
albedo, slope, aspect or vegetation cover can substantially influence the detectability of thermal anomalies. In the worst case coal fire
related thermal anomalies can be completely masked by solar patterns during the daytime. Thus, night-time analysis is the most suitable
for thermal anomaly mapping of underground coal fires, although this is not always feasible. The heat of underground coal fires only
progresses very slowly through conduction in the rock material.Anomalies of coal fires completely covered by solid unfractured bedrock
are very weak and were only measured during the night. The thermal pattern of underground coal fires manifested on the surface during
the daytime is thus the pattern of cracks and vents, which occur due to the volume loss underground and which support radiation and
convective energy transport of hot gasses. Inside coal fire temperatures can hardly be measured and can only be recorded if the glowing
coal is exposed through a wider crack in the overlaying bedrock. Direct coal fire temperatures measured ranged between 233 °C and
854 °C. The results presented can substantially support the planning of thermal mapping campaigns, analyses of coal fire thermal
anomalies in remotely sensed data, and can provide initial and boundary conditions for coal fire related numerical modeling.
In a second paper named "Thermal Characteristics of Coal Fires 2: results of measurements on simulated coal fires" [Zhang J.,
Kuenzer C., Tetzlaff A., Oettl D., Zhukov B.,WagnerW., 2007. Thermal Characteristics of Coal Fires 2: Result of measurements on
simulated coal fires. Accepted for publication at Journal of Applied Geophysics. doi:10.1016/j.jappgeo.2007.08.003] we report about
thermal characteristics of simulated coal fires simulated under simplified conditions. The simulated set up allowed us to measure even
more parameters under undisturbed conditions - especially inside fire temperatures. Furthermore we could demonstrate the differences between open surface coal fires and covered underground coal fires. Thermal signals of coal fires in near range thermal
remotely sensed imagery from an observing tower and from an airplane are presented and discussed.

geophysical field studies, temperature measurements, coal fires, mining, China

http://dx.doi.org/10.1016/j.jappgeo.2007.08.002