and TIR wavelength regions.
In addition to the spectral emissivity, accurate values of
ground surface temperature can also be determined by mul-
tispectral thermal IR measurements. If these surface
kinetic temperature and emissivity measurements are made
on a diurnal basis, then one can also calculate thermal
inertia of the surface materials, using appropriate models
(Kahle, 1977; Kieffer et al., 1977). Thermal inertia pro-
vides a measure of the effective particle size of dry mate-
rial and can be a useful tool for discrimination and map-
ping of bedrock versus surficial deposits. Day-night tem-
perature variation also provides an indication of moisture
at or near the surface, as the heat of evaporation moderates
diurnal temperature variation.
AIRBORNE AND FIELD PORTABLE
SENSORS
Since 1982, NASA's airborne Thermal Infrared
Multispectral Scanner (TIMS) has allowed demonstration
of the utility of this wavelength region for geologic appli-
cations (Kahle and Goetz, 1983). TIMS has six spectral
channels between 8.0 and 11.7 um, with a NEAT of
<0.2K in each channel, and an IFOV of 2.5 milliradians
which provides ground resolution from 5 to 50 m, depend-
ing upon aircraft altitude. Like the initial airborne sensors
that provided the stimulus for space platforms in the
VNIR, this instrument has demonstrated the utility of this
wavelength region for compositional mapping, has proven
that we can observe spectral features on natural surfaces,
and has helped to define the functional requirements for
thermal infrared remote sensing instruments. Other air-
borne instruments are now available including the
Multispectral Infrared and Visible Imaging Spectrometer
(MIVIS), the Airborne Hyperspectral Scanner (AHS) built
by Daedalus, the Geoscan Scanner from Australia, the
ATLAS Sensor developed and flown by Stennis Space
. Center, and the MODIS Airborne Simulator (MAS),
flown at NASA's Ames Research Center. In addition,
portable field spectrometers have become available includ-
ing the uFTIR from Designs and Prototypes (Hook and
Kahle, 1995), the MIDAC instrument from MIDAC that
has been used both in aircraft and on the ground to mea-
sure downwelling and upwelling radiance and THIRSPEC,
developed in Canada by Rivard, et al. to provide geologic
ground truth in support of airborne and satellite data.
These new instruments further demonstrate the interest in
the thermal region for geologic applications.
SPACEBORNE INSTRUMENTS
Over the last several years, instruments have been flown
in orbit to image the Earth's surface in a few thermal
infrared bands at a spectral resolution of about a kilometer
or more. These include such instruments as AVHRR and
ATSR. While these instruments have proved extremely
useful for measurement of sea surface temperature, their
utility over land is somewhat reduced because of the high
spatial variability of land surfaces and the nonuniform
spectral emissivity of the land surface materials, These
factors combine to make an accurate determination of lang
temperatures difficult. Landsat, while having a better
spatial resolution in the thermal infrared — 120 m — py
had only a single channel in this wavelength region so m
multispectral data could be obtained. However, in the
next few years we can anticipate new instruments which
will have several to many bands in this region with much
higher spatial resolution. These new instruments wi]
allow much more accurate determination of surface spec-
tral emissivity and surface temperature. One of the first of
this new generation of thermal infrared imaging instr.
ments will be ASTER. Other projected instrument;
include PRISM from ESA (Rast and Kealy, 1993)
IRSUTE from CNES (Durpaire et al., 1995), and
Sacagawea from NASA, but they will probably be à
couple of years or more later than ASTER.
ASTER (Yamaguchi, et al., 1994; Kahle et al., 199];
Fujisada, 1995) is a facility instrument selected for launch
in 1998 on the first NASA Earth Observing System
spacecraft, EOS-AM1 (Asrar and Dokken, 1993). The
ASTER instrument is being sponsored and built in Japan,
with funding provided by the Japanese Ministry of
International Trade and Industry (MITI). The Japan
Resources Observation Systems Organization (JAROS) is
responsible for the design and development of ASTER
which is subcontracted by JAROS to NEC, MELCO,
Fujitsu and Hitachi.
The objectives for the ASTER instrument are to obtain
high spatial resolution multispectral targeted data in the
visible and infrared wavelength regions. An international
team of scientists are developing the algorithms and soft
ware that will be used to process the data from the instru
ment into standard and special data products. The standard
data products will be produced at the Earth Resources
Observation System (EROS) Data Center (EDC) Land
Processes Distributed Active Archive Center (LPDAAC
at Sioux Falls, South Dakota. Special data products wil
be produced by the Science Team members at their home
institutions.
The ASTER standard data products that will be ready a
launch will include radiance at the sensor, brightness fem:
perature at the sensor, atmospherically-corrected surface-
leaving radiance, surface emissivity, surface kinetic tem
peratures, decorrelation stretch images and local Digital
Elevation Models (DEMs). In addition, other standard data
products may be developed postlaunch, and several special
data products will be produced by the ASTER investis
tors at their home institutions. These data products can
used by the general science community in studies of ge
logy, surface radiation balance, evaporation and evapottar
spiration, vegetation, soils, the hydrogeologic cycle
surface-atmosphere fluxes, surface change detection
glacial studies, volcanic processes, sea ice and clouds.
ASTER is comprised of three radiometers: (1) a thre?
channel visible-near infrared two-telescope radiomël
(VNIR) that is capable of providing stereo data for ll
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