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Abstract
Sand movement is one of the main environmental hazards in Northern Sudan that threaten livelihood and rural communities. This paper investigates for the first time the use of the Synthetic Aperture Radar (SAR) offset tracking technique for detecting sand movement in Northern Sudan, and distinguishes the impact of the movement influencing factors: wind speed/direction, vegetation and topography. High-resolution images from the Sentinel-1 satellite were used for the generation of displacement maps. Three different dune fields with different characteristics were investigated for a study period between 4 June and 14 October 2017 (133 days). Dune field 1 is vegetated and near a built-up area, dune field 2 is in an open environment with sand dunes overlaying rocky substrate, and dune field 3 is located near mountains. The cumulative east displacement over the study period was 1.8 m, −1.1 m and 4.8 m for the three dune fields, respectively, while the cumulative north displacement was 0.7 m, 2.9 m and 4.2 m. Large movement is detected in the non-vegetated dune fields, with an average dune velocity of 0.18 m/d, while the vegetated dune field had a velocity of 0.09 m/d, which emphasizes the fact that vegetation is an effective stabiliser of dune movement. The pixel offset results showed a positive correlation between the wind speed/direction and the dune movement. In addition to vegetation, topography also played a major role in diverting the direction of the blown sand mainly near the edges to the mountains and the vegetation barriers. This technique showed high competency in monitoring the movement of sand dunes, in addition to identifying areas exposed to large sand drifting as a risk mapping technique.
Highlights
Sand movement is one of the main environmental phenomena in Sudan that threaten livelihood and rural communities, where sand overwhelms built-up areas, agricultural fields, and irrigation canals [1,2,3]
We investigate the impact of the topography, vegetation cover and wind behaviour on dune movement by using Synthetic Aperture Radar (SAR) images with small temporal baselines (12 days) of the SAR images to reduce decorrelation effects
Epigraphic evidence found in the temple of Taharqo at the Kawa archaeological site in Northern Sudan records an inscription of Irike-Amanote, a Kushite King of Meroe, showing the clearing of sand from the processional way in the second half of the 5th century BC [1]
Summary
Sand movement is one of the main environmental phenomena in Sudan that threaten livelihood and rural communities, where sand overwhelms built-up areas, agricultural fields, and irrigation canals [1,2,3]. Due to the large area of desert in Sudan, traditional land surveying techniques (e.g., GNSS, levelling) are not effective for monitoring dune field motions because of the size of the areas to be investigated and the costs involved. These techniques can be used to measure the elevation changes of individual dunes by repeating surveys [7]. The use of SAR offset tracking technique was investigated for detecting the movement of sand dunes. We investigate the impact of the topography, vegetation cover and wind behaviour (speed and direction) on dune movement by using SAR images with small temporal baselines (12 days) of the SAR images to reduce decorrelation effects
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