Abstract
This study aims to assess and to evaluate band ratios, brovey and HSV (Hue-Saturation-Value) techniques for discrimination and mapping the basement rock units exposed at Wadi Bulghah area, Saudi Arabia using multispectral Landsat ETM+ and SPOT-5 panchromatic data. FieldSpec instrument is utilized to collect the spectral data of diorite, marble, gossan and volcanics, the main rock units exposed at the study area. Spectral profile of diorite exhibits very distinguished absorption features around 2.20 μm and 2.35 μm wavelength regions. These absorption features lead to lowering the band ratio values within the band-7 wavelength region. Diorite intrusions appear to have grey and dark grey image signatures on 7/3 and 7/2 band ratio images respectively. On the false color composite ratio image (7/3:R; 7/2:G and 5/2:B), diorite, marble, gossan and volcanics have very dark brown, dark blue, white and yellowish brown image signatures respectively. Image fusion between previously mentioned FCC ratio image and high spatial resolution (5 meters) SPOT-5 panchromatic image is carried out by using brovey and HSV transformation methods. Visual and statistical assessment methods prove that HSV fused image yields best image interpretability results rather than brovey image. It improves the spatial resolution of the original FCC ratios image with acceptable spectral preservation.
Highlights
The Neoproterozoic Arabian Shield is composed of five distinct terranes separated by four ophiolite-bearing suture zones: three ensimatic island arc terranes in the western part of the shield (Asir, Hijaz and Midyan) and Afif and Ar Rayn terranes of continental affinity further to the east [1,2,3]
It shows the four main different rock units exposed at the study area; diorite, marble, gossan and Hulayfah volcanics
Discontinuous marble bands forming nearly N-S to NNW trending ridges were exposed in the central part of the study area to the east of Figure 1. 3D perspective view of Landsat false color composite (FCC) image draped over Shuttle Radar Topography Mission (SRTM) digital elevation model shows the different rock units exposed at the study area
Summary
The Neoproterozoic Arabian Shield is composed of five distinct terranes separated by four ophiolite-bearing suture zones: three ensimatic island arc terranes in the western part of the shield (Asir, Hijaz and Midyan) and Afif and Ar Rayn terranes of continental affinity further to the east [1,2,3]. It shows the four main different rock units exposed at the study area; diorite, marble, gossan and Hulayfah volcanics. The oldest rock units exposed at the study area, are made up of the older Afna Formation and the younger Nuqrah Formation, intruded by syn- to late-tectonic diorite intrusions. Andesitic volcanic rocks and volcaniclastic derivatives commonly occur in the western and eastern part of the area and may represent rocks of Afna formation.
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