Abstract
Imlili Sebkha is a stable and flat depression in southern Morocco that is more than 10 km long and almost 3 km wide. This region is mainly sandy, but its northern part holds permanent water pockets that contain fauna and flora despite their hypersaline water. Google Earth Engine (GEE) has revolutionized land monitoring analysis by allowing the use of satellite imagery and other datasets via cloud computing technology and server-side JavaScript programming. This work highlights the potential application of GEE in processing large amounts of satellite Earth Observation (EO) Big Data for the free, long-term, and wide spatio-temporal wet/dry permanent salt water cavities and moisture monitoring of Imlili Sebkha. Optical and radar images were used to understand the functions of Imlili Sebkha in discovering underground hydrological networks. The main objective of this work was to investigate and evaluate the complementarity of optical Landsat, Sentinel-2 data, and Sentinel-1 radar data in such a desert environment. Results show that radar images are not only well suited in studying desertic areas but also in mapping the water cavities in desert wetland zones. The sensitivity of these images to the variations in the slope of the topographic surface facilitated the geological and geomorphological analyses of desert zones and helped reveal the hydrological functions of Imlili Sebkha in discovering buried underground networks.
Highlights
Sebkhas are wet depressions in desert environments that are generally regarded as floodplains of significant environmental interest and have been closely linked to many environmental issues, such as climate change, water quality, wildlife habitat, and biodiversity
We used microwave-normalized difference polarization index (MNDPI) to monitor the changes in the surface moisture state, and we combined this index with another index extracted from the optical domain to obtain Sar/Optic Saltwater Cavity Index (SOSWCI), which mixed passive radiometry with active radiometry
Our study focused on the mapping and monitoring of the wet/dry conditions of a very vulnerable Saharan wetland ecosystem
Summary
Sebkhas are wet depressions in desert environments that are generally regarded as floodplains of significant environmental interest and have been closely linked to many environmental issues, such as climate change, water quality, wildlife habitat, and biodiversity. While the median part of this sebkha holds over tens (161) of pockets of permanent water with diameters ranging from 1 m to 10 m, these pockets have a depth of approximately 4.6 decimetres and a water salinity of 24 g/L to 350 g/L (Figure 1a). These water pockets host many animals and fish (Figure 1b) as reported during a scientific field trip in April 2017. Its high salinity has caused birds to flee, Imlili Sebkha has created a favorable habitat for a Cichlid fish species associated with Tilapia guineensis, a species previously unknown in Morocco and whose northern limit was previously limited to the Senegal River
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