Estimating the sand saltation thresholds from Sentinel-1 SAR data in the Gobi Desert, Mongolia

Abstract

Spatial information about the sand saltation threshold is essential to quantify sand transport and dust emission. Quantitatively estimating the threshold over a wide area is challenging, however, because its main influencing factors (surface roughness elements) are unknown. Here, we explored the use of Sentinel-1 Synthetic Aperture Radar (SAR) data to quantify surface roughness conditions and their temporal changes and map the threshold. Thresholds were obtained by in situ observations in dry spring periods during 2018–2020 at three year-round and eight temporary sites during natural sand and dust storms. We found a linear relationship (r = 0.91, p < 0.0001) between the SAR gamma naught VV intensity and the observed threshold where the site surface was stony or vegetated, indicating that SAR data can be used to quantify the spatial-temporal distribution of the threshold during dry periods. We then estimated thresholds from SAR data for spring 2017–2021 and found high thresholds on slopes and mountains, mainly due to stone and vegetation effects, whereas thresholds in the topographic depression varied because of changes in surface roughness conditions. Thresholds estimated from SAR data should greatly improve wide-area simulations of sand horizontal transport and dust emission fluxes by numerical dust models.