The Utilization of Spatial Enhancement of Landsat Images in the Delineation of Structural Elements, Red Sea Hills, NE – Sudan

Introduction:
Sudan is a vast country occupying (about) 2.5 million km2. In the last three decades considerable efforts were made to properly map the main geological units in this country and to better understand their tectonic settings. Despite this, large areas remain inadequately mapped and little is known about their tectonic evolution let alone their potential natural resources. The enormous areal extent of the Red Sea Hills area together with its harsh environment made it almost inaccessible for the conventional field based type of surveys. Delineation of structural is time consuming and at very high cost. Therefore, remote sensing techniques qualify themselves as an alternative or at least a major tool in mapping and delineation of structural elements. This type of data provides a synoptic view and offers a wide range of spectral characteristics of the land covers mainly rocks and soils. Hence, offering a good tool for mapping large areas in a short time with relatively low cost data acquisition techniques and reasonable accuracy.

Spatial Enhancements:
In contrast to spectral image enhancements, spatial filters emphasize or de-emphasize image data of various spatial frequencies. The applications of filters make visible linear structures, joints and faults not otherwise discernible on the un-enhanced image (Alexander et al., 1973). Spatial filtering is a local operation wherein pixel values in an original image are modified in the basis of gray levels of neighboring pixels.
In this work different convolution filter were applied. A mid-low pass filter of 3x3 window has provided no improvements over the original images.
Both directional and non-directional high pass filters were performed. The selected directions were W, NW and NE based on the previous knowledge of the tectonic history of the area. Three directionally filtered images were then selected to facilitate the production of a color composite image. Wherein, most of the structural elements in the area are clear and esily descernible. Subtle enhancements on the structural lineaments in the area enabled the author to produce a structural map of the area under investigation.

Conclusion:
The importance of the spatial enhancement stems from the ability to enhance edges whereby linear features, drainage system and geological boundaries are emphasized.