Geology Reference
In-Depth Information
Table 14.2.2
Regions of the electromagnetic spectrum and their significance in coal-mining and coal-fire studies.
Region of spectrum Wavelength range
Significance in coal-mining and coal-fire studies
Blue (B)
0.4
-
0.5
μ
m
Well suited for mapping atmospheric haze, smoke from fires, and
pollution in water. It is also helpful in differentiating soil and
water. Together with G, R, and NIR, it is used for differentiating,
e.g., deciduous from coniferous vegetation.
Green (G)
0.5
-
0.6
μ
m
Green vegetation shows a small reflection peak in this region.
Together with other spectral bands, it is used for vegetation
differentiation and general land cover and land use mapping.
Red (R)
0.6
-
0.7
μ
m
Green vegetation shows strong absorption in the red band. Together
with the NIR region, this band is ideally suited to map vegetation
density, health, stress, biomass, leaf area index, etc. Together with
B and SWIR, this region is also useful for alteration-mineral
mapping.
Near infrared (NIR)
0.7
-
1.3
μ
m
NIR is also known as the vegetation band. Vegetation reflects very
strongly in the NIR region. The edge between the R and NIR
region where the vegetation shows a sudden jump in reflection is
known as the
and is characteristic of vegetation type. In
the NIR region, vegetation also shows a constant high reflection.
This high flat reflection region, known as
“
red edge
”
is
indicative of vegetation health. In the NIR, water and coal show
strong absorption. NIR is therefore also used to delineate bodies of
coal and water and to categorize soil by its moisture content.
“
NIR plateau,
”
Shortwave infrared
(SWIR)
1.3
-
3.0
μ
m
In combination with the NIR and G bands, SWIR is used for
differentiating coal from water. SWIR is also used to map
variations in soil and vegetation moisture. In combination with the
R or NIR regions, it helps accentuate the signal from urban areas
and differentiation of soil types. Based on Planck
s law, high
temperature bodies such as surface fires that have temperatures
around 1000 K show peak emittance in the SWIR region. SWIR is
therefore used for detection and quantitative characterization of
surface coal fires.
'
Mid infrared (MIR)
3.0
-
8.0
μ
m
Recent research is focused on using the CO
2
absorption peak in this
region to characterize and quantify the locally anomalous CO
2
concentration near coal fires. The region, in principle, is also
suitable for moderately high-temperature mapping.
Thermal infrared
(TIR)
8.0
-
14
μ
m
TIR region is most important for mapping subtle surface temperature
increases associated with underground fires. It is extensively used
in underground coal-fire detection, mapping, monitoring and
depth estimation. Land surface temperature and emissivity
variations estimated from TIR images also provide information
about land cover that is complimentary to the information from
other spectral regions.
Microwave
55.7 cm
-
1m
Primarily used for mapping surface texture, soil moisture, surface
manifestation of faults, elevation estimations, and for mapping
and monitoring land subsidence due to coal mining and coal fires.
Note
: In the literature, there is little consensus on the nomenclature for different parts of the spectrum and on the specific wavelengths associated
with these parts. The nomenclature and range shown in this table is the one that is most commonly followed by the coal-fire remote sensing
community.
Source: Table by Anupma Prakash and Rudiger Gens, this work.
Table 14.2.2 summarizes the important wavelength regions of the electromagnetic spectrum in which remote
sensing data is acquired, and the significance of each of these regions to coal mining and coal-fire remote sensing.
