images from the AVHRR (Advanced Very High Resolution
Radiometer) sensor of the NOAA series of meteoroid
ogical satellites. On a much finer scale, Fig. 1
shows a TM band 4 quarter scene (90 x 90 kms) taken
from the Landsat 4 satellite. The intricate geological
structures trending east-west are the southern most
vestiges of the Atlas mountains. Note how easy it is
to identify complex folding (A) and faults (B). Whole
drainage networks can be studied and the ease by which
dry ephemeral channels(C) can be separated from rivers
with flowing water (D) demonstrates the ability of
such imagery to monitor geomorphological phenomena in
areas of difficult terrain.
b
Figure 2. TM4 of Chott El Guettar: a) 29-1-1983
b) 23-9-1985
The effectiveness of multi-date satellite imagery in
monitoring geomorphological activity is demonstrated
by Figure 2, two TM band 4 images (15 xl5 kms) of a
fine grained, saline depression known as a playa or
chott in southern Tunisia are shown. Figure 2a is a
winter image (29-1-83) while Fig. 2b is taken at the
end of the dry season (23-9-85). Marked differences in
the playa are clearly visible which are mainly assoc
iated with surface moisture. The summer image shows a
dry playa with water, and therefore wetter surface,
entering:the playa from the west. Most of this is
residue from the irrigation of oasis further up the
channel. The winter image shows a different situation
with a greater flow of water from the western channel,
but also inputs from numerous ephemeral channels, on
the east, which were previously dry resulting in the
flooding of the playa.
3 SATELLITE THEMATIC MAPPER
The Landsat series of Earth observation satellites has
been well documented (Colwell 1983, USGS 1979) and the
numerous applications to which data from their sensors
have been used. The marked difference between the
first and second generation Landsat satellites was the
development of the TM sensor (Table 1). The TM differs
from the earlier MSS system in many respects. The
major changes include an improvement in spacial reso-
b
Figure 3. A comparison of the spatial resolution of
MSS (a) and TM (b). Note the clarity by which gully
networks are visible on the TM image (both images
are near infra-red and 512 x 512 pixels).
