Application of Remote Sensing in . Lithological Mapping and Reconstruction of the Stratigraphy of North - western Mekele Area, Ethiopia.
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Date
1995-05
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Addis Ababa Universty
Abstract
The area under study is located within the Mekele out
lier. It comprises Mesozoic sedimentary rocks unconformably
overlain by trap volcanics.
Landsat-TM images have been processed and geologically
analysed in combination with revision of the previous works
and present field survey for lithological mapping and
reconstruction of the stratigraphy of the study area.
In remote sensing the sensor and the obj ect to be
sensed are located remotely apart. The link is due to
electromagnatic (EM) waves. Thus in image processing and
interpretation the knowledge of how EM radiation is
generated, propagated, and modified when it interacts with
materials is the main key.
Materials produce a diagnostic spectral signature in
response to the EM interaction. Generally, spectral
signatures are related to the nature of the corresponding
rock, which help to identi fy a material through image
processing. Image processing includes statistical and
graphical evaluation, ratioing, contrast enhancement,
principal and canonical component analyses, combination of
selected bands, texture and vegetation index analyses,
classification, and visual interpretation of the images.
Structures and other lineaments, lithological
boundaries, and drainage patterns are traced directly from
the screen during image interpretation. Ten mappable units
are recognized both by digital image processing and visual
interpretation. These are from youngest to oldest: Dolorite,
Basalt, Amba Aradam Formation, Agula Shale, five separately
mappable Antalo Limestone units, and Adigrat Sandstone.
From sedimentary point of view, Adigrat Sandstone is
fluviatile in origin, while the Antalo Limestone and Agula
Shale are related with transgression and regression of the
sea during Jurassic time. Amba Aradam Formation, on the
contrary, lying unconformably on Agula Shale, is probably
due to the withdral of the sea caused by an uplift of
cratonic area related to the separation of America and
Africa plates during the Cretaceous time.
The final thematic images are geometrically rectified
using selected ground control points to refer them with
other maps. Digitally processed images expose fairly well
the main lithologic units with some limitation.
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Keywords
Lithological Mapping and Reconstruction