Mapping Palaeohydrography in Deserts: Contribution from Space-Borne Imaging Radar

Abstract

Space-borne Synthetic Aperture Radar (SAR) has the capability to image subsurface features down to several meters in arid regions. A first demonstration of this capability was performed in the Egyptian desert during the early eighties, thanks to the first Shuttle Imaging Radar mission. Global coverage provided by recent SARs, such as the Japanese ALOS/PALSAR sensor, allowed the mapping of vast ancient hydrographic systems in Northern Africa. We present a summary of palaeohydrography results obtained using PALSAR data over large deserts such as the Sahara and the Gobi. An ancient river system was discovered in eastern Lybia, connecting in the past the Kufrah oasis to the Mediterranean Sea, and the terminal part of the Tamanrasett river was mapped in western Mauritania, ending with a large submarine canyon. In southern Mongolia, PALSAR images combined with topography analysis allowed the mapping of the ancient Ulaan Nuur lake. We finally show the potentials of future low frequency SAR sensors by comparing L-band (1.25 GHz) and P-band (435 MHz) airborne SAR acquisitions over a desert site in southern Tunisia.

The European Space Agency BIOMASS mission: Measuring forest above-ground biomass from space

“…This provided an unprecedented opportunity to study the palaeo-environment and palaeo-climate of terrestrial deserts (Paillou et al, 2010), and led to the discovery of two major palaeo-rivers in North Africa: the Kufrah river, a 900 km long palaeo-drainage system, which in the past connected southeastern Libya to the Gulf of Sirt (Paillou et al, 2009;Paillou et al, 2012), and the Tamanrasett River in Mauritania, which connected a vast ancient river system in the western Sahara to a large submarine channel system, the Cap Timiris Canyon (Skonieczny et al, 2015). Besides its value in studying the past climates of desert regions, the sub-surface imaging capability of L-band SAR also helps to build more complete and accurate geological maps in support of future water prospecting in arid and semi-arid regions (Paillou, 2017).…”

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

“…Starting in the 1980s, space shuttle missions have been used for exploring large-scale and difficult-to-access areas along the eastern Sahara [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Space-borne images of the earth provide different levels of information that can be interpreted into considerable information of geomorphological, geological, and hydrological features.…”

“…Space-borne images of the earth provide different levels of information that can be interpreted into considerable information of geomorphological, geological, and hydrological features. Radar sensors, such as the ones onboard of the space shuttle missions, have the ability to penetrate the dry sand sheet of the deserts and provide valuable information about the near-surface features, which is used as complementary information to that provided by visible and infrared sensors [14,[28][29][30]. The Great Sahara, including the Egyptian deserts, are considered by many researchers as a type locality, which exemplifies the driest Earth environment.…”

Mapping a Subsurface Water Channel with X-Band and C-Band Synthetic Aperture Radar at the Iron Age Archaeological Site of ‘Uqdat al-Bakrah (Safah), Oman

“…Early theoretical work proposed that longer wavelengths (L-band) were able to penetrate deeper than 5 m in dry sand [6,12,14] while later investigations supported more conservative penetration depths of 0.05-0.3 m for X-band, 0.1-0.5 m for C-band and 0.4-2.0 m for L-band in the silica blow sand and alluvium of Egypt's Western desert [15]. Because of their ability to penetrate further, longer wavelengths such as P-band (270-430 MHz frequency or 80-110 cm wavelength) and L-Band (1-2 GHz frequency or 15-30 cm wavelength) are often chosen for archaeological subsurface prospection in these environments [8,13,[16][17][18]. However, C-band (4-8 GHz frequency or 3.75-7.5 cm wavelength) [17,19] and X-band (8-12.5 GHz frequency or 2.5-3.75 cm wavelength) [20,21] have also been used.…”