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).