Using InSAR Coherence for Investigating the Interplay of Fluvial and Aeolian Features in Arid Lands: Implications for Groundwater Potential in Egypt

Abstract

Despite the fact that the Sahara is considered the most arid region on Earth, it has witnessed prolonged fluvial and aeolian depositional history, and might harbor substantial fresh groundwater resources. Its ancient fluvial surfaces are, however, often concealed by aeolian deposits, inhibiting the discovery and mapping of potential groundwater recharge areas. However, recent advances in synthetic aperture radar (SAR) imaging offer a novel approach for detecting partially hidden and dynamic landscape features. Interferometry SAR coherence change detection (CCD) is a fairly recent technique that allows the mapping of very slight surface changes between multidate SAR images. Thus, this work explores the use of the CCD method to investigate the fluvial and aeolian morphodynamics along two paleochannels in Egypt. The results show that during wetter climates, runoff caused the erosion of solid rocks and the rounding of sand-sized grains, which were subsequently deposited in depressions further downstream. As an alternating dry climate prevailed, the sand deposits were reshaped into migrating linear dunes. These highly dynamic features are depicted on the CCD image with very low coherence values close to 0 (high change), while the deposits within the associated ephemeral wadis show low to moderate coherence values ranging from 0.2 to 0.4 (high to moderate change), and the country rocks show a relative absence of change with high coherence values close to 1. These linear dunes crossed their parent's stream courses and dammed the runoff to form lakes during rainy seasons. Part of the dammed surface water would have infiltrated the ground to recharge the permeable wadi deposits. The alternation of fluvial and aeolian depositional environments produced unique hydromorphometrically trapped lakes that are very rare in arid regions, but of great interest because of their significance to groundwater recharge.

Multispectral and RADAR images integration for geologic, geomorphic, and structural investigation in southwestern Arabian Shield, Al Qunfudhah area, Saudi Arabia

“…The fused subset ALOS/PALSAR and OLI (Figure 10(c)) showed better results from the combined information. This is because the L-band of PALSAR data provides even deeper penetration and can characterize the hidden features' lines as well as their structural geometry [1,8,20]. The dark tones arise as a result of the backscattering of radar waves on the sand deposits.…”

“…Remote sensing plays a significant role in revealing the geomorphic, geologic, hydrologic, and structural use of land and mineral resources. Advanced analysis and interpretation of remote sensing data provides a unique opportunity to get remote access to the earth surface geology [1][2][3][4], marine surface [5,6], aeolian landforms [7,8] and atmospheric conditions [9][10][11][12]. The advent of remote sensing technology has heralded a new era in the field of applied geology, with the knowledge of new approaches towards characterizing the types of rocks and the tectonic features affecting the rocks [4,13,14].…”

Exploring Groundwater Resources and Recharge Potentialities at El‐Gallaba Plain, Western Desert, Egypt

“…The study area is within a hydrographic basin of around 360 km 2 , which can receive runoff during the rainy season from the western calcareous structural plateau and its bounding slopes, which flush the plain from the west (Gaber et al 2018). During past pluvial periods, the Nile water passed through Wadi El-Kubbanyia resulting in the formation of a large fan system with fluvial sediments (Thurmond et al 2004;Roden et al 2011;Gaber et al 2015).…”

Detecting Areas Vulnerable to Sand Encroachment Using Remote Sensing and GIS Techniques in Nouakchott, Mauritania

“…The CCD approach combines two SAR images of the same area taken at different times to detect changes on the surface [69,70]. In arid environments, changes in sand dunes are controlled by erosion/deposition processes and sediment transport, which also affects the backscatter retrieved by the sensor [30]. We downloaded four Sentinel 1 images in Single Look Complex format in Vertical-Vertical polarization acquired in Interferometric Wide mode.…”

“…In addition to the information provided by satellite platform optical sensors, radar remote sensing and interferometry have an enormous capacity to detect surface changes and desertification [22,30,31]. Synthetic Aperture Radar sensors (SAR) differ from optical sensors in the mechanism they use to detect electromagnetic energy [32].…”