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GEOLOGIC REMOTE SENSING IN THE THERMAL INFRARED 
Anne B. Kahle, Andrew D. Morrison 
Jet Propulsion Laboratory 
4800 Oak Grove Drive, MS 183-501 
Pasadena, CA 91109 USA 
H. Tsu 
Earth Remote Sensing Data Analysis Center 
5th Floor, Forefront Tower, 3-12-1 Kachidoki, Chuo-ku Tokyo, 104, JAPAN 
Y. Yamaguchi 
JAPEX Geoscience Institute, Inc., NYK Tennoz Bldg. 17F, Higashishinagawa, Shinagawa-ku, Tokyo, 140, JAPAN 
Commission VII, Working Group 4 
KEY WORDS: 
ABSTRACT 
Remote Sensing; Geology; Multispectral Infrared Imagery 
Remote sensing of emitted radiance from the Earth's surface in the thermal infrared region (8 to 13 Jum) is useful for 
geologic studies including lithology and soil and mineral mapping. Since 1982, new airborne, field portable and 
spaceborne instruments have been demonstrating the advantages of multispectral measurements in this region for 
geologic applications. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), presently 
being built in Japan, is the newest of the spaceborne multispectral instruments. ASTER, which has fourteen channels in 
the visible out through the thermal infrared, will be flown aboard NASA's EOS AMI platform in 1998. Other 
multispectral instruments, including PRISM, IRSUTE and Sacagawea, are projected to be built and flown after ASTER. 
The advent of these sensors is expected to result in a demand for more high spatial-resolution multispectral thermal 
infrared data. 
INTRODUCTION 
The feasibility of using multispectral thermal infrared 
remote sensing for geologic applications has been recog- 
nized by a number of users, but advancement has been 
limited by lack of sensors. The use of the visible and near 
infrared (VNIR) and shortwave infrared (SWIR) spectral 
data made a tremendous leap forward with the advent of the 
Landsat satellite sensors (MSS, TM). We anticipate a 
similar phenomenon when orbital multispectral thermal 
infrared data becomes generally available with the launch 
of the Advanced Spaceborne Thermal Emission and 
Reflection Radiometer (ASTER) in 1998. The ASTER 
instrument will be the first spaceborne multispectral 
thermal infrared instrument with spatial and spectral reso- 
lution adequate for geologic applications. From thermal 
data one can derive both surface temperature and surface 
spectral emissivity. The primary application of the emis- 
sivity is for surface lithologic mapping. The temperature 
data can be used both for studies of thermal inertia of sur- 
face materials, and for studies of thermal processes related 
lo volcanism and hydrology. 
THEORETICAL BACKGROUND 
At terrestrial temperatures, the thermal infrared spectral 
radiance emitted by the surface is at a maximum around 10 
0 11 um, dropping off sharply to the shorter and longer 
Wavelengths. The best atmospheric window lies between 
about 8 and 13 um with another window between 3 and 5 
um Interpretation of data from the 3 to 5 jum region is 
complicated by overlap with reflected solar radiation 
Which, although dropping rapidly in intensity with increa- 
327 
sing wavelength, makes a large contribution during the 
day. Thus, the 8 to 13 jun region is the best thermal 
infrared spectral region to use and has received most atten- 
tion to date. This is also a spectral region containing 
diagnostic spectral information for many minerals, includ- 
ing the silicates which make up the great majority of con- 
tinental surface rocks. 
Spectral features of minerals in the thermal infrared region 
are the result of vibrational molecular motions. The loca- 
tion, strength and form of these features vary systemati- 
cally with composition and crystal structure. The most 
intense band in the spectra of all silicates (the reststrahlen 
effect) occurs between 8 and 12 um. Typically, this spec- 
tral feature shifts to shorter wavelengths as the bond 
strength within the lattice increases (Hunt, 1980; Lyon, 
1965). The carbonates, sulfates, phosphates, and hydrox- 
ides are other important mineral groups that have spectral 
features in the thermal infrared (Hunt and Salisbury, 1974, 
1975, 1976). 
The range of minerals found in soils is usually quite limi- 
ted, particularly with older, more developed soils, in 
which iron oxides, quartz and clays almost always domi- 
nate, except in arid climates where carbonates may be 
important. The relative amounts of these minerals should 
vary systematically, depending on climate and the compo- 
sition of the parent rock. Using remote sensing, these 
minerals can all be detected and identified, based on their 
spectral properties. Iron oxides produce absorption fea- 
tures in the VNIR, clays and carbonates in the SWIR, 
while quartz has characteristic features only in the thermal 
infrared (TIR). Thus, remote soil mapping, like geologic 
mapping, will be enhanced by combining VNIR, SWIR 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996