UND TRUTH
1AMETERS
isurements
“HED CARDS
in the
rally
iere
1976),
.uding
'oblems,
jisary
--wheel-
. about
20 man-months (counting the scientists only) were spent in the
field for sampling, measuring sections, spectral reflectance
measurements and checking out the geological interpretations.
LANDSAT imagery was purchased from the US Geological Survey's
EROS Center in Sioux Falls in the form of positive film
transparencies at a scale of 1:1 ooo ooo and computer compa-
tible digital tapes. The visual interpretation was done on
1:500 ooo positive transparencies since earlier experiences
had convinced us that this was the optimum scale (LIST,
ROLAND & HELMCKE 1974; LIST & PÓHLMANN 1975; LIST, HELMCKE,
MEISSNER, PÓHLMANN & ROLAND 1978). Mostly spectral bands
7 and 4 were used; the latter especially for mapping the dune
fields the knowledge of which proved very advantageous in the
field for picking the best routes for travel. The interpreta-
tion was plotted with special ink on transparent film so no
details of the transparencies were lost.
From the LANDSAT 1:500 ooo transparencies a controlled mosaic
was assembled to fit the LAMBERT-GAUSS conical projection as
used in the topographic maps "World 1:500 ooo Series 1404",
from which some control points and information on names and
altitudes were taken. This mosaic formed the topographic base
on which the colored interpretation map was printed.
In the original LANDSAT imagery it was sometimes difficult to
discriminate between similar lithological units. So additional
image processing techniques had to be used to extract more in-
formation.
Of all LANDSAT scenes color composites were produced by
printing the spectral bands 4, 6 and 7 on yellow, cyan and
magenta Diazo films and superimposing them to color subtractive
composites. These proved very useful where small differences
in spectral reflectance of rocks had to be distingushed; for
instance, light colored limestone outcrops in many cases
showed up in the same grey tone as sand in band 7. On the
color composites, they could easily be separated by their
