oxydes et hydroxydes de fer montrent des similitudes d'allure par rapport aux échantillons - images, alors que la 
simulation des argiles (Kaolinite) est décevante car le TM5 et le TM7 ne caractérisent par les deux absorptions des 
argiles. Ceci peut être en partie expliqué par les conditions d ’affleurements du HOGGAR en général et aussi de prise 
de vue du système Landsat. 
1. THE STRATEGIC LEVEL 
1.1 Interpretation by Landsat Thematic 
Mapper satellite data at the 1/500 000 scale 
1.1.4 Methodology 
The steps followed for the geologic cartography are 
based on the photointerpretation of satellite images. The 
delimitation of the geologic contours of homogeneous 
units were made on the basis of the analysis of the three 
fundamental  photointerpretation criterias  (Scanvic, 
1978), which are in this case: 
a) analysis of the level of grey (specter which determine 
the hue or the color of the objects), 
b) analysis of the structures and textures (defining the 
mode of arrangement of the hues (homogeneity, 
granulometry, etc...), 
c) the forms of the picture (form of objects and their 
mode of outcrop). 
The interpretation is made in two stages ( Chorowicz, 
1984a). A first interpretation associating the facies 
picture to the three criteria of identification and a second 
stage, where the previous interpretation is confronted 
and completed as regard to the existing documentation: 
synthetic analysis by remote sensing. 
1.2 THE SPECTRAL INTERPRETATION 
1.2.1 The Polycyclique Central Hoggar 
1.2.1.1 The Interpretaion of sedimentary 
domain 
In the North West part of our zone, the cartography of 
the limits of outcrops between the sedimentary domain 
and cristalline rocks was achieved by the slant data of 
the infrared band TM6. 
The dissimilary spectral that represents these two 
domains, translating by a change of hue and texture (fine 
and same coarse), let us draw the limit between the 
precambrian basement and sedimentary cover perferctly 
of Cambro-Ordovician. This limit corresponds to the 
abnormal contact type discordance. 
The utilization of the infrared images shows correctly the 
difference between the outcrops of basement by 
advantageous heightening the structural aspects. 
In the West South part of the sedimentary basin , the 
spectral hue suggest a border which would correspond to 
the limit between the outcrops Carboniferous and those 
of Devonian. But then, the geology limit of silurian in 
contact with Devonian is less obvious. The band of 
thermal infrared let us more or less to enhance it and 
especially in the West part. In this part except for TM5 
band. the contact is obvious in the other bands of visible . 
The geologic contour between the Cambro-Ordovician 
and the other formations of cristalline rocks is cleaner. 
The latter is of structural orderowing to the intense 
fracturation. 
Except the mid infrared bands (TM7) and the thermal 
infrared of TM6, the channels 1.2,3, and 4 of visible 
specter also permits to indivuadualize certain linear 
structures perfectly sometimes not obvious or apparent in 
either bands 
1.2.1.2 The Interpretation of cristalline 
domain 
As for. the interpretation of cristalline domain, it 
presents also several outcrops of homogeneous units 
(Rapport Sonarem-Armines, 1977b). 
The character morpho-structural and radiometric that 
desengages the syn-orogenic granitc specifies it in clean 
manner. It is a structure intensely fractured with weak 
radiometric to very weak with regard to the neighboring 
sets in North West part. 
To analyze the forms and mode of outcops (structural 
anomaly) is often and sufficiently characteristics in order 
to be directly associated to a phenemenon particular to 
geology. So, in the East part of central Hoggar, a heap 
circumscribes, intrusive, to texture fairly fine and weak 
radiometric, we allow to delimit this whole flushing to 
the bosom of lower proterozoic. 
As for, the middle proterozoic (ALEKSOD series in the 
North West part), present two keys of identification. The 
first key is the presence particular (dykes) to the various 
forms and the second resides in the value in terms of 
radiometric temperature elevated in band of T.M6. Its 
geologic limit in the other channels of visible is not 
obvious. 
The whole of lower Proterozoic (gneiss and migmatites) 
present besides a calmness tectonic and tonality even 
more clear therefore the higher values; concerns few 
outcrops in the west part of central Hoggar. 
In the  opposit, these metamorphic sediment 
indifferenciated is poured out in the East part of 
polycyclic Hoggar and presents differently in terms of 
mode of outcrop. It presents the structures characteristics 
with compression axis East West and North West-South 
602 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 
  
  
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