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Pohn, H. A.

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https://ntrs.nasa.gov/search.jsp?R=19760021506 2020-03-22T14:28:52+00:00Z
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DISCRIMINATION OF GEOLOGIC MATERIALS
USING SKYLAB S-192 DATA
by Howard A. Pohn
Introduction
The Skylab Skylab S-192 multispectral scanner has proved
useful in the discrimination of several types of materials in
the southwestern Nevada desert. Although the extremes in DN
(density number) in any single channel are sr^ail, a comparison
within and among channels has shown that five different types
of materials can probably be distinguished.
Technique
An S-192 multispectral scanner tape (accession number
33-32882) for a portion of the U.S. Geological Survey Nevada
test area (fig. 1) was supplied to us by the Johnson Space
Center. This tape was reformatted using the U.S. Geological
Survey DEC-1070 to make J t
 
compatible with our Optronics
Photomation 1700 write/scan microdensitometer. The images
produced by the DEC-1070 were played back on film using the
Optronics system and software written by the Remote Sensing
Image Processing Group.
1.
(E7(,-10405) DISCRIMINATION F GEOLOGIC
	 N76-28594
MATERIALS USING SKYLAB S-19 -
 2ATA, PART 3
Final Report (Geological Survey) 6 p HC
$3.50	 CSCL 08G
	 Unclas
G3/43 00405
1
lThe images thus produced were compared with a geologic
map of the area (Stewart and Carlson, 1974) and two or three
test sites were selected for each of five different materials.
relocation of the test sites is seen on figure 2. The materials
included basalt, andesite, welded ash-flow tuff, playa, and
salt-marsh deposits. The DN values values of brightness in a
256-step gray scale) for each test site were extracted from
the tape, and means and standard deviations were determined
for each of the channels. The results are given in table 1.
Analysis
In most channels the basalts cannot be distinguished from
andesites; however, channels 1 and 17 (0.52-0.56 u m and 12.0-13.0
um, respectively show a reasonably unambiguous set of densities
that can be used to discriminate basalt from andesite. This
observation is borne out by examining the laboratory spectral
curves for the two materials in Hunt et al (1973, 1974). The
curves show a relatively high reflectivity for andesite at
0.5-0.6 um when compared with basalt; this reflectivity is
probably due to the higher percentage of ferric iron and the
concomitant reddish color observed on the surface of many andesites.
The ambiguity in the rest of the characteristic spectra of
andesites and basalts may be caused by the usually low albedo
of the andesites in this region (L. Rowan, oral communication,
1975). The higher DN for andesites in the daytime image at
2.
'	 ^	 v
1=.0-13.0 um is at present unexplained, but it may be due to the
lower percentage of mafic minerals (and lower density) in the
andesites. This lower percentage of mafic minerals would also
cause the andesites to have a lower thermal inertia and suggests
that they could be discriminated from basalts using thermal images.
Welded ash-flow tuffs are easily distinguishable from basalts
and andesites by the higher DN values of the tuffs at all wave-
lengths except for 1.09-1.19 um, where it is ambiguous.
A rather peculiar phenomenon occurs in the spectra of the
playas and salt marshes. The spectra for playas are relatively
higher than for salt marshes at all wavelengths from 0.46-1.03 um;
however, in the two channels from 1.09-1.75 um, this relationship
is reversed. At still longer wavelengths, the higher DN values
of the playas persist.
The cause of this phenomenon is not known, but the obser-
vations appear to be contrary to the expected result. The channel
from 1.55-1.75 um occurs at the edge of a water absorption band,
and it would be expected that a salt marsh (most probably a
deposit of evaporites and muds containing a large amount of water)
would have a lower DN value than a playa, which, in the Nevada
desert, is typically a deposit of silts and clays with very low
water content.
Qualifications.
The preceding statements must be qualified. First, the
3.
I	 ^	 ^
test areas have not been carefully examined in the field.
Thus, it is difficult to say with certainty that we are
detecting differences in playa and salt-marsh deposits,
because the compositions of salt marsh and playa were inferred.
Second, a sampling of two or three areas on a single Skylab
image is not felt to be sufficiently representative to make
a broad unequivocal statement as to its capability to discriminate
materials using spectral information. And third, the calibrated
Skylab S-192 radiance values need to be correlated with field
and laboratory spectra of the test areas to see if they are
comparable.
4.
t._t
References Cited
-Hunt, G.R., Salisbury, J.W., and Lenhoff,' C.J. 1973,
Visible and near-infrared spectra of minerals and
rocks -VIII. Intermediate igneous rocks: Modern
Geology, v.4, pp 237-244.
1974, Visible and near infrared spectra of minerals
and rocks: IX. Basic and ultrabasic igneous rocks;
Modern Geology, v.5, pp 15-22.
3Stewart, J. H.,and Carlson, J.E., 1974, Preliminary geologic
map of Nevada, U.S. Geological Survey Miscellaneous
field studies, MF-609.
i
5
Figure 1 Location map of the U.S. Geological Survey
Nevada test area
Figure 2. Negative print of S-192 channel 5 (.62-.67 um)
showing location of the test sites. B=basalt,
A-andesite, W=welded ash-flow tuff, P=plays,
S-salt marsh. Note: the incompatibility
between figures 1 and 2 is due to the fact that
the S-192 tape received by the U.S. Geological Survey
was not corrected for the circular scan mode used on
board the spacecraft. There is extreme distortion
in the southwest; for this reason, no scale is
provided.
Table 1	 Means and standard deviations ii,  DN for the test
sites.	 (0 is dark, 255 is bright).


Discrimination of geologic materials using Skylab S-192 data, part 3

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