150
1B 10 km
Figure 1A. Shuttle Radar Image over Esfideh, Horasan
province (East Iran).
Figure 1B. Shuttle hand-held photography over same
area. Notice the differences in length of the strike
ridges between a and b on the two images.
color image of the Linhof camera. The ridges can be
followed over 16 km running parallel to the flight
track of the shuttle before they disappear towards
the east under superficial fan material. This super
ficial cover forms a uniform tonal area on the space
photo intersected only by two not very well express
ed dry river valleys having a "V" shape (fig. 1B at
c and d).
The eastern branch is clearly discernible also on
the radar image (fig. 1A at a) as a lighter-toned
zone because of difference in surface roughness
between the dry riverbed, with relative coarse ma
terial, and the smooth surface of the more sandy fan
material. A vague gulley pattern typical for a
desert fan is present.
The western branch of the riverbed is only very
faintly visible on the radar (fig. 1A at c).
The Eocene to Oligocene strike ridges can be follow
ed on the radar image over a length of 28 km, which
is 12 km longer than the distance measured on the
photo image, although over the last 12 km the tonal
contrast on the radar between the two horizons and
the surrounding material is less distinct.
There remains the question if spatial resolution
of the Linhof camera may not be insufficient to
allow for further discrimination of these two hori
zons. It seems clear that the outcrops are not con
tinuing as strike ridges, but they may continue as
concentrations of loose rock material on the pedi
ment slope or sand sheet, although no tonal differ
entiation on the photo suggests this possibility and
a thin sand cover is more likely. The author has
neither succeeded in obtaining ground information
nor in obtaining aerial photographs over this area
to study the differences in more detail to come to
convincing conclusions.
SUDAN/EGYPT
In the area of the Red Sea hills (Sudan) and east
ern desert (Egypt), a comparison was made of SIR-B
radar data, Landsat and Large Format Camera (LFC)
images. The spatial resolution of the radar data
and the LFC photos is approximately of the same
order (Table 1). So they were the index components
in the comparison (fig. 2).
Table 1. Ground resolution of RS-data.
Shuttle Imaging Radar - azimuth resolution: 29.4 m
(4 look) SIR-B range resolution : 17.8 m
Landsat 3 MSS - 80 m
Large Format Camera (LFC) - 15-20 m
(film B/W 3412)
The Large Format Camera has the further advantage
that topographic height differences can be observed
by stereo viewing of overlapping photographs, in
creasing the confidence level of interpretation.
The radar data were acquired during the 17th
shuttle flight (SIR-B mission) data take 097.5 on
12 October 1984. The radar incidence angle was
52.1° towards the beam center. In contrast with
SIR-A where only optical processed data were avail
able, SIR-B allowed digital correlation.
GEOLOGY OF THE RED SEA HILLS
The oldest rocks occurring in the area are the
granitic gneisses and amphibolites of the Lower-
Middle Proterozoic Kashebib Group (Vail, 1979),
referred to by Gabert et al. (1960) as Kashebib
series. The rock sequence also occasionally con
tains some marbles. They are correlated with the
Mitig gneisses from the Egyptian eastern desert
(Said, 1971; Schurmann, 1974).
The sequence forms in general a high relief. A
coarse metamorphic trend direction is visible on
Landsat and LFC photographs. The tone of the out
cropping rocks on the B/W LFC photos is slightly
dark but less so than the ultrabasic and basic rock
types.
The Kashebib group is followed upwards by the
Nafirdeib group (Ruxton, 1956) consisting of meta
sediments and acid to basic metavolcanites. They
form a typical green schist assemblage with occa
sional ultramafic masses and serpentinites. Hashad
(1980) gives an age of 1200 Ma on the basis of
radiometric Rb/Sr measurements for similar rock
types in the eastern desert op Egypt.
The metasediments and metavolcanites are well re
cognizable on the remote sensing images as a result
of their metamorphic texture. Finely aligned meta
morphic strike ridges are typical for these rocks.
Relief is in general rather subdued and intricate
fold structures can be recognised. The ultramafic
rocks are very dark in tone on Landsat MSS and LFC
images.
The Proterozoic intrusive rocks consist of older
batholitic granites, granodiorites, thonalites and
pegmatites. These rocks are often mildly foliated.
They form intrusive contacts with the metasedimen
tary sequence. The ages of the older granitoids are
given by Hashad (op.cit.) as 1000-850 Ma for the
egyptian part. Most of the granodioritic batholiths
in Sudan are assigned a slightly younger age (700
Ma) . These granitoid bodies have a very subdued
relief due to intensive weathering (Dixon, 1982).
They are extensively covered by sand sheets and
crop out only on the edges of the batholiths.
These sandy areas appear dark in tone on the radar
in contrast to the light tones on the MSS and LFC
images.
