Geology Reference
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anomalies caused by differential solar heating. TIR surveys conducted during the fall (e.g., during November) also
helped to reduce anomalies created by solar heating and/or by the transpiration of vegetation.
A recent development in the use of airborne TIR imaging for detecting coal fires is the development of forward
looking infrared (FLIR) imaging. This is a digital TIR system that looks forward from the platform rather than
vertically downward and from side-to-side as do the older scanners (Figure 13.1.1; Wikipedia, 2009). FLIR offers a
number of operational and logistical advantages, including the acquisition of oblique images of a coal fire, not
available with the older TIR scanners. Andrup-Henriksen et al. (2007) discuss the use of FLIR in studying coal
fires in the Jharia coalfield in India, although the scanner was not mounted in an aircraft. Another advantage of
FLIR is being able to mount the scanner in a helicopter, permitting much closer coordination with ground-based
units. Technical Innovation and Professional Services (2005) describes a survey of coal fires in North Dakota
where the scanner was mounted in a Cobra AH-1 helicopter. Detection of coal fires using a FLIR systems Star
SAFIRE III camera was good, but it was weather dependent. The primary problem was solar heating during sunny
days because this created numerous false anomalies. The number of anomalies can be reduced by conducting FLIR
surveys before sunrise (Ellyett and Fleming, 1974; Rathmore and Wright, 1993; Vice 2007). The anomalies may
also be reduced and corrected by conducting field surveys.
Color Infrared Imaging
C olor infrared (CIR) imaging involves the use of color photo film that been changed so that the spectral
sensitivities of the film can record energy in the 0.7
m range of the electromagnetic spectrum (Sabins,
1997). One advantage of CIR film is that it shows the health of vegetation, often before any stress in the vegetation
is visible to the person on the ground (i.e., the previsual stage). Thus, healthy vegetation in a broadleaf forest will
show as various shades of red to magenta color while stressed vegetation will exhibit shades of pink to blue in the
previsual stage (Sabins, 1997). Broadleaf forest vegetation can be stressed by drought, disease, insect infestation, or
other factors that will prevent the leaves from getting water (Sabins, 1997).
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0.9
μ
The ability to detect stress in vegetation before it is visible to the naked eye has led to attempts to use CIR for
detecting the location and extent of a coal fire. Shallenberger (1993) suggested that heat from a burning coal fire
would reduce the available capillary moisture in the soil (i.e., water held in the pore spaces between soil particles by
surface tension) and thus move the plant toward the wilting stage more quickly than nearby plants that are unaffected
by the coal fire. In addition, continuously heating deep-rooted plants like broadleaf trees, in the area around Centralia,
killed them. An area where this occurs produces a geobotanical anomaly, a change in the health of the plants and/or
barren ground where the plants were killed. This appears in CIR imagery in colors other than red.
Early Use
A lthough TIR imaging has been used to study coal fires since 1964, which was shortly after the technology was
declassified by the Defense Department, the literature seems to suggest an early rush of studies in the 1960s and
1970s followed by only limited use in the 1980s. However, starting in the 1990s the use of TIR increased again and
has gone beyond detecting coal fires to get additional information from the imagery. Much of the published work in
the past 10
15 years has been by researchers in Europe and/or China. This study makes an arbitrary division of the
TIR studies in the literature into an early group from 1964 to 1993 and a later group, which extends from 1990 to
the present. There is some overlap in time between the two groups.
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Slavecki (1964) published the results of the first study of coal fires using TIR imagery. A Reconofax IV, Mark 2,
instrument was used to look for fires in culm banks at the Huber Colliery near Wilkes-Barre and the Richmond
Colliery at Scranton. This study demonstrated that the TIR scanner could be used to detect fires in coal beds and in
refuse piles (or culm banks) and was the first to test the effectiveness of TIR for detecting coal fires after the
technology had been declassified by the Defense Department.
Fisher and Knuth (1968) briefly describe a TIR study of several coal fires by the Pennsylvania Department of
Mines and Mineral Industries. The authors noted that the TIR imagery detected the coal fires and suggested that the
extent of the fires could be determined. An HRB-Singer instrument was used for the study (Fisher and Knuth,
1968).
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