Jabal Arkanu and Gabal El Uweinat – Using NIR/SWIR Images to Visualize Different Rock Types

Making use of Sentinel-2A's NIR/SWIR bands to get a different view

Taking a look at some rocks

In this image you can see the Jabal Arkanu (top), a mountain in Libya, and the Gabal El Uweinat (bottom), a somewhat bigger mountain in Libya, Sudan, and Egypt (Google Maps). For both mountains you can find other names, based on different transliterations of the original Arabic names جبل أركنو and جبل العوينات.

They are both located on the Gilf Kebir plateau, a sandstone plateau rising from the Libyan Desert and one of the driest places on the planet.

While not immediately apparent in the natural color image, both mountains feature different kinds of rock. They are made up of sandstone, siltstone, and shale with granite intrusions in their western parts.

If you take a look at the first slider, you can see a natural color image, made up of data from bands 4, 3, and 2 of Sentinel-2A’s Multispectral Instrument (MSI) and a near-infrared/short wave infrared (NIR/SWIR) image, using data from bands 12, 11, and 8.

Move the slider and quite distinctive differences can be seen. The Jabal Arkanu shows a more or less circular granite intrusion (showing up slightly purplish in the NIR/SWIR image), flanked by a sandstone component (greenish in the NIR/SWIR image) in the north-east. The Gabal El Uweinat also has a circular granite intrusion, with sandstone and siltstone components surrounding much of the intrusion, pretty much looking like a big “hand of sandstone” holding a “granite ball“.

 

A little closer

This next slider just focuses on the Gabal El Uweinat. You can see the circular intrusion of a collapsed granite dome with a diameter of about 25 kilometers opening up to three valleys in the west. The small bright spot in the eastern part is a volcanic structure. While of course not visible, the mountain massif features a large number of prehistoric petroglyphs (rock art and drawings made by manipulating the rock surface) and fossils.

 

And even closer

This last slider is showing the transition from granite to sandstone up close. The images here have a scale of 10 meters/pixel. The NIR/SWIR image looks a bit blurry compared to the natural color version, the reason for that is rooted in the resolution of the different bands. While all bands in the natural color version have a 10 meters/pixel resolution, two of the bands in the NIR/SWIR image have a resolution of just 20 meters/pixel, making the resulting image slightly more blurry.

Download

You can download full-size versions with a scale of 10 meters/pixel here on Flickr. The 12-8-2 version is an additional version with a quite nice look, sandstone shows up in reddish hues in this version, granite in blue hues.

Natural color version
NIR/SWIR view (12-8-2)
NIR/SWIR view (12-11-8)

References and more information

Brügge, Norbert. “Structure and Geology of Jebel Uweinat in the three country triangle Egypt-Sudan-Libya.”, 2 Jan. 2016, www.b14643.de/Sahara/Geology_Jebel-Uweinat/index.htm. Accessed 8 Mar. 2017.
Earth Outreach. “Google Timelapse: Gabal El Uweinat, Libya Sudan Egpyt.” YouTube, Earth Outreach, 29 Nov. 2016, www.youtube.com/watch?v=CCpnb8XAHLs. Accessed 8 Mar. 2017.
Scott, Michon, et al. “Jebel Uweinat.” NASA Earth Observatory, NASA Earth Observatory, 9 Mar. 2013, earthobservatory.nasa.gov/IOTD/view.php?id=80599. Accessed 8 Mar. 2017.

Contains modified Copernicus Sentinel data [2017]

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