Table 1. Potential geomorphic applications for single TM bands. 
TM 
BANDS 
WAVELENGTH 
(um) 
GEOMORPHIC APPLICATIONS 
1 
0.45-0.52 
(blue-green) 
Studies of sediment laden water, longshore drift, esturine plumes, suspended sediment in 
lakes and rivers. Indentification of sediment source areas. Bathymetry. Surface propert 
ies of snow and ice. Soil organic matter. 
2 
0.52-0.60 
(green) 
Biogeomorphic indicators-soil erosion. Pedological studies, soil toxicity and disturbed 
ground. Ratio 2/4-limonitic rock mapping and for redness on desert sands. 
3 
0.63-0.69 
(red) 
Vegetation cover mapping and identification of cropping practices for erosion studies. 
Ratio 3/4-geobotanical relationships. Lithological separation (iron rich rocks) and 
structural studies. 
4 
0.79-0.90 
(near IR) 
Water body delineation (lakes, rivers, wetlands and active ephemeral channels), spring 
line and drainage network morphometry, reconnaissance mapping and geobotanical studies. 
5 
1.55-1.75 
(mid IR) 
Lithological mapping, bedrock/drift separation. Soil moisture mapping. Ratio 4/5-separ 
ates hydrous and iron rich rocks, ratio 5/7-clay mineral differentiation. 
6 
10.4-12.5 
(thermal) 
Lithological mapping, geological reconnaissance studies, thermal mapping of sediments. 
Ground water studies, topographic mapping and extraction of sub-surface anomalies. Bath 
ymetry of lakes and discrimination of silicious rich rocks. 
7 
2.08-2.35 
(mid IR) 
Lithological discrimination, metamorphic rocks, hydrous minerals (OH-clay minerals) and 
carbonates (C03-calcites, etc.) separation. Hydrothermal alteration. 
lution (79 to 30m) (Figure 3), more spectral bands 
(4 to 7) and narrower bandwidths, which are better 
suited for Earth science applications. 
Table 1 summarises the potential geomorphological app 
lications for each TM band based on a specific spectr 
al response in that wavelength. Band 1 (blue-green) 
and the inclusion of the reflective middle infra-red 
bands (5 and 7) which are very use-ful for discrimin 
ating specific lithologies and clay minerals (especia 
lly hydroxyls). Also of interest is the thermal infra 
red (band 6) which senses both reflected and emitted 
energy. This wavelength is very useful in mapping 
silicious-rich rocks but suffers from having a very 
coarse resolution (NASA 1984). 
4 STUDY AREA AND DATA SOURCE 
To effectively assess the potential of TM imagery for 
landform investigations, a number of test areas were 
selected in southern-central and southern Tunisia 
because of their varied geomorphology. Climatically 
the field areas are semi-arid to arid with annual 
precipitation ranging from 50mm to 150mm and summer 
temperatures up to 40 C. The main example used in 
this paper is centred to the east of the oasis town 
of Gafsa around the chott of El Guettar. 
The area shown in figure 3b was thoroughly mapped 
in the field as part of a research project by the 
author and a geomorphological map of the area prod 
uced (Fig 4). Briefly, the area is composed of an 
east-west trending mountain range in the north, flank 
ed by course, classtic, unvegetated alluvial fans. 
These deposites grade into a fine grained, saline 
depression known as a chott or playa. The area to the 
west of the chott is subjected to aeolian deposition 
from the playa due to the prevailing easterly winds. 
To the south, a striking breached pericline which has 
been subjected to thrust faulting exhibits many geol 
ogical and geomorphological phenomena notably faults, 
escarpments and alluvial fans. Due to a slight change 
in lithology, the alluvial fans flanking this area of 
higher relief have a much finer texture. A number of 
river channels can be seen draining into the closed 
basin. To the south of the pericline, a dissected 
bahada grades down to a large ephemeral channel. 
Fuller descriptions of such landforms can be obtained 
in Doehring (1980) and Mabbut (1977). 
5 IMAGE PROCESSING 
Having studied some of the advantages of satellite 
remote sensing for geomorphological mapping, this sec 
tion is concerned with the digital processing of TM 
imagery and how it can lead to greater information 
extraction. It will be considered in two sections. 
Firstly, an indication is given of what image proces 
sing can be applied to single band imagery and the 
nature of the information content, then secondly, to 
multiple bands, 
Figure 3b gives an indication of the detail which 
can be obtained from single band images. However, 
even this image has had some image processing applied 
to it in the form of contrast stretching to improve 
its interpretability. Even more information can be 
extracted if a contrast stretch is applied to a spec 
ific area or landform so that only pixel values as 
defined within the area are subjected to a contrast 
stretch. Nearly all results using this technique 
have shown excellent results even if other detail is 
bleached out (Fig 5). 
Figure 5. Contrast stretching applied only to playa 
area. 
In order to assess specific TM bands for their geom 
orphological content, a number of landforms in the 
study area were selected and the ease by which they 
could be identified on single band imagery and selec 
ted false colour composites (FCC) was scored. Table 2 
lists the landforms and the scores- obtained for the 
relative bands.