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J. Zhang, C. Künzer, A. Tetzlaff, D. Oertel, B. Zhukov, W. Wagner:
"Thermal characteristics of coal fires 2: Results of measurements on simulated coal fires";
Journal of Applied Geophysics, 63 (2007), 135 - 147.

In this paper we present thermal characteristics of coal fires as measured during simulated fires under an experimental setting in
Germany in July 2002. It is thus a continuation of the previously published paper "Thermal surface characteristics of coal fire 1:
Results of in-situ measurement", in which we presented temperature measurements of real subsurface coal fires in China [Zhang, J.,
Kuenzer, C., accepted for publication. Thermal Surface Characteristics of Coal Fires 1: Results of in-situ measurements. Accepted
for publication at Journal of Applied Geophysics.]. The focus is on simulated coal fires, which are less complex in nature than fires
under natural conditions. In the present study we simulated all the influences usually occurring under natural conditions in a
controllable manner (uniform background material of known thermal properties, known ventilation pathways, homogeneous coal
substrate), creating two artificial outdoor coal fires under simplified settings. One surface coal fire and one subsurface coal fire
were observed over the course of 2 days. The set up of the fires allowed for measurements not always feasible under "real" in-situ
conditions: thus compared to the in-situ investigations presented in paper one we could retrieve numerous temperature
measurements inside of the fires. Single temperature measurements, diurnal profiles and airborne thermal surveying present the
typical temperature patterns of a small surface-and a subsurface fire under undisturbed conditions (easily accessible terrain, 24 hour
measurements period, homogeneous materials). We found that the outside air temperature does not influence the fire's surface
temperature (up to 900 °C), while fire centre temperatures of up to 1200 °C strongly correlate with surface temperatures of the fire.
The fires could heat their surrounding up to a distance of 4.5 m. However, thermal anomalies on the background surface only
persist as long as the fire is burning and disappear very fast if the heat source is removed. Furthermore, heat outside of the fires is
transported mainly by convection and not by radiation. In spatial thermal line scanner data the diurnal thermal patterns of the coal
fire are clearly represented. Our experiments during that data collection also visualize the thermal anomaly differences between
covered (underground) and uncovered (surface) coal fires. The latter could not be observed in-situ in a real coal fire area. Subsurface
coal fires express a much weaker signal than open surface fires and contrast only by few degrees against the background. In
airborne thermal imaging scanner data the fires are also well represented. Here we could show that the mid-infrared domain
(3.8 ìm) is more suitable to pick up very hot anomalies, compared to the common thermal (8.8 ìm) domain. Our results help to understand coal fires and their thermal patterns as well as the limitations occurring during their analysis. We believe that the results
presented here can practicably help for the planning of coal fire thermal mapping campaigns - including remote sensing methods
and the thermal data can be included into numerical coal fire modelling as initial or boundary conditions.

thermal analyses, temperatures, coal fires, simulated heat sources, diurnal measurements, China, remote sensing

http://dx.doi.org/10.1016/j.jappgeo.2007.08.003