IGCP Board; 10th session; Report of the ... - unesdoc - Unesco

interpretation for mineral and energy exploration,
plant siting, waste disposal and the development
of models for regional and continental
tectonics. New spaceborne methods and associated
technologies are being developed to produce
data from which geologic information about
large areas can be derived much more rapidly
than by conventional techniques". The authors
provide a generally balanced overview of progress
and yet stress the spectral mapping approach
to defining mineralized ground that they
have developed. As principal investigators of
SMIRR, they tested the Landsat-D Thematic
Mapper (TM) and the Shuttle Multispectral Infrared
Radiometer (SMIRR) first from aircraft
altitudes over Nevada and Utah mineral-rich
test sites.
1. Space Shuttle Flight: Two geological experiments
were included in the scientific payload
of the second flight of the Space Shuttle on 12-
14 November, 1981. The objectives of the
SMIRR experiment were: (1) Obtain 10-channel
radiometric data from orbit from a significant
sample of geologic units world-wide in the spectral
region 0.6 to 2.5 um with emphasis on the
region beyond 1.0 um; (2) Determine the value
of the spectral bands chosen in the separation of
lithologie units based on their reflectances;
(3) Determine the correlation between the radiances
measured from orbit and the reflectance
data obtained by a portable field spectrometer
system; (4) Assess the effect of variable atmospheric
absorption on the radiance values, particularly
in the 2.0 to 2.5 um region; (5) Determine
the spectral bands to be used in future multispectral
scanners designed specifically for geological
mapping uses; and (6) Test the value of
Shuttle as a platform for low-cost measurements
of parameters vital to the design of new instrumentation
for future flights.
Measurements were made with a single 20-cm
telescope containing a linear array of ten detectors
and associated filters aligned along the spacecraft
ground track. Data were obtained in
100 x 100 m segments in a continuous strip along
the subspacecraft track. A 16-mm framing camera
was used to identify the position of the
ground track. Alex Goetz, Jet Propulsion Laboratory,
Pasadena, California, is the principal
investigator on SMIRR, and Larry Rowan, US
Geological Survey, Reston, Virginia, is the coinvestigator.
The results of that mission are
being evaluated. Data were gathered mainly
over desert regions of Mexico, Spain, Italy,
Greece, Turkey, Morocco, Egypt, and Saudi
Arabia. Data are to be distributed to scientists
where cooperating investigations have been established
through this Project. Unfortunately,
weather masses over the United States and Australia
limited operations in these areas.
The other experiment was the Shuttle Imaging
Radar (SIR-A). The objective of the Shuttle
Imaging Radar-A experiment was to evaluate the
potential of spaceborne imaging radars in geolo­
42
gic mapping and to determine the advantages of
using radar imagery in conjunction with Landsat
imagery for Earth resources observation.
The SIR-A is a synthetic aperture imaging radar
which uses the coherent echo from the surface to
generate a high-resolution image. It uses its
own energy to illuminate the surface, and generates
an image from the backscatter echoes. It
provides an all-weather capability because the
relatively long waves (microwave) are not effectively
reflected or scattered by cloud water droplets.
The SIR-A sensor operates at L-band frequencies
of 23. 5-cm wavelength. The incidence angle
at the surface is 50° at the centre of swath and differs
by± 3° at the edges. The sensor is designed to
be sensitive to surface backscatter cross-sections
between -8 dB and -28 dB. The SIR-A data were
recorded optically on board the Shuttle and all but
6 feet of its film was used during the mission.
After the shuttle landing, the signal film was retrieved,
developed, and processed. Then it was
converted to an image using an optical correlator.
Charles Elachi, Jet Propulsion Laboratory, Pasadena,
California, is the SIR-A principal investigator.
Data were collected at numerous sites
located between 39° N latitude and 38° S latitude
in both experiments.
2. Preliminary Metallogenic Map of North America
and Landsat Mosaic: Under the chairmanship
of P.W. Guild (1981a, b, c) a team of six
geologists representing Canada, Greenland, Mexico,
and Central America published the first
"Preliminary Metallogenic Map of North America"
at a scale of 1: 5, 000, 000. It is accompanied by
a complex explanation which categorise 4, 215 ore
deposits by commodities according to size, geologic
environment, age, and minéralogie nature.
Two USGS Circulars (858-A and -B) provide (A)
numerical listing of deposits and (B) an alphabetical
listing of deposits. This remarkable map
was reproduced on an equal area - bipolar oblique
conic conformai projection by electronic colour
scanning of a hand-coloured original map. It will
serve as an excellent basis for formulating new
mineral exploration strategies and, we believe,
will be enhanced further when a new, ail-digitally
processed Landsat Image Mosaic and Lineament
Map of the North American Plate are completed.
Present plans, however, call for the mosaic to
be cast on a Transverse Mercator projection.
3. Geobotanical Anomalies related to Porphyry
Copper Mineralization: Birnie and Francica
(1981) described the results of using an airborne
multichannel spectrometer with a range from
450-1000 m m over the known Mesatchee Creek
porphyry copper prospect in central Washington.
The entire area is covered with Douglas Fir and
lesser amounts of western larch. Spectra from
within the pyrite halo were anomalously high at
565 nm and anomalously low at 465 nm. Individual
spectra with a 565 nm/465 nm reflected radiance
ratio value greater than 1.7 fall dominant -
ly within the pyrite halo. The zone of mineralization
was defined clearly by the cluster of anomalous
spectra.