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59Journal of Geomatics

1. Introduction

The Eastern Desert of Egypt has undergone intense tectonic activities resulting into formation of structural landforms not only within the study area, but also in the surrounding areas along the Red Sea and the Gulf of Aqaba. The resulting landforms are much more conspicuous, particularly where the basement rocks dominantly characterize the ground surface. Structural landform as a term refers to landforms that have .originated primarily by geological structure and they gain considerable .attention nowadays as a cornerstone of the tectonic geomorphology. Application and integration of remote sensing and Geographic Information System (GIS) for studying these features involve firstly determination of structural lineaments. The early usage of structural lineament as a term was prior to the availability of aerial photographs. It was originally used by Hobbs (1904) for describing significant lines of landscape that reveal the hidden architecture of the basement rocks (Campbell, 1996). Seventy-two years later, O'Leary et al. (1976) defined lineament as “a mappable, simple or composite linear feature of a surface whose parts are aligned in a rectilinear or slightly curvilinear relationship. It differs from the pattern of adjacent features and presumably reflects some subsurface phenomenon”. Definition given by O'Leary et al. (1976) has been widely accepted and applied by Akhir and Abdullah (1997), Briere and Scanlon (2001), and Miyatake (2002).

However, Ramsay & Huber (1987) defined such features as narrow linear fracture zones of regional scale, which give rise to marked topographic features easily recognizable on air photographs and satellite images. Peters and Shea (1988) derived such linear features from aerial photos and satellite images as guides to probable geologic structure that are assumed to represent faults and other fractures. Lineaments are defined by Drury (1993) as long line-like character often subtle, linear arrangements of various topographic, tonal, geologic, geophysical and geochemical features. In that manner, Clark and Wilson (1994) defined lineaments as straight linear elements visible at the earth's surface and are the representations of geologic and/or geomorphologic phenomena. According to Campbell (1996), lineament as a name was given by geologists to lines or edges, which presume geologic origin and visible on remotely sensed images. Such features are also referred to as linears or lineations, which are applied to specific geologic or geomorphic features as topographic features, lithologic contacts and/or zone of fracture. Lillesand & Kiefer (2000) referred to lineaments as regional linear features that are caused by linear alignment of regional morphological features such as: streams, escarpments and mountain ranges and tonal features that are the surface expressions of fractures or fault zones. Arcasoy et al. (2004) used the term geological lineament to refer to the linear features detected on aerial photographs and satellite images, which presumably have a

Integration of remotely sensed data and GIS for lineaments extraction and analysis in the Eastern Desert of Egypt.

1 2B.M. Moawad and J. Grunert1Department of Geography, Faculty of Arts, Ain-Shams University, Cairo, Egypt.

2 Institute of Geography, Johannes Gutenberg Universität, Mainz, Germany.moawad@uni-mainz.de

(Received 29 June 2008; in final form 25 December, 2008)

ISG

© Indian Society of Geomatics

Vol 2 No.2 October 2008

Abstract: The Eastern Desert of Egypt has undergone intense tectonic activities resulting into formation of distinct landforms exhibiting linear structures. The major objectives of this study were to detect and to analyze structural lineaments in the coastal area extending from Safaga to El Quseir in the Central Eastern Desert of Egypt using integrated GIS, ETM+ and SRTM images.

stSince lineaments are only seen in a certain specific direction, the study of ETM + data is based primarily on the 1 derivative ndedge enhancement filter to manifest lineaments from the four directions (N-S, NE-SW, E-W, NW-SE) and the 2 derivative

edge (Laplacian) filter was used to enhance edges regardless of edge direction. Processed shaded and painted relief maps derived from SRTM data were used to improve the topography showing areas to be hilly or plain, steep or gentle. Shaded and painted relief maps depicted small linear features that could not be effectively seen using original image data. Lineaments were manually digitized based on visual image interpretation using linear tonal variations, linear features separation, geological units of different texture, ridges, and the main wadi channels. Extracted image data were integrated with ancillary geologic maps. The

0output lineament map contains a total of 7329 linear features of a total length 5212 km. Rose diagrams of 10 showed three conspicuous trends or peaks of lineaments i.e. N-S, NE-SW, NW-SE. They represent 9.59 %, 7.6%, 7.5% of the total frequency and 10.85%, 8.46%, 8.26% of the total length. Other directions were also noticeable but they are of a lesser significance. Spatial analysis shows that lineaments are more concentrated along the coastal plain where the mountain ranges are in the vicinity of the coastline. The isolines become less intense and divergent relative to each other in other parts because of the older granite. The epicentres are spatially dispersed and confined mostly to plutonic intrusions of the younger granite and Dokhan volcanics. No particular orientation could be given to distinguish specific rock units in the study area.

Keywords: Egypt, Red Sea, Lineaments, Edge detection, Laplacian filter, Shaded and painted relief maps.

Journal of GeomaticsJournal of Geomatics Vol 2 No.2 October 2008Vol 2 No.2 October 2008