Ground-penetrating Radar for Monitoring the Distribution of Near-surface Soil Water Content in the Gurbantünggüt Desert

Desert soils in an arid rain-fed environment exhibit low and limited water contents, in which soil water availability plays a key role in root growth and function. In the Gurbantünggüt Desert, snowfall usually accounts for 30%–50% of the annual precipitation. The melting of this snow cover briefly induces relatively moist soil conditions in spring, thus creating favorable conditions for germination and growth of plants over a comparatively short period of time. This results in a distinct desert ecosystem dominated by fixed and semi-fixed sand dunes with vegetation coverage of 40%–50% and 15%–25%, respectively. In order to further the understanding of biological, physiological, and hydrological processes of this desert ecosystem, robust information about the spatial and temporal variation of soil water content is needed.

To determine the near-surface soil water content distribution of semi-vegetated dunes located at the rim of the Gurbantünggüt Desert, QIN Yanfang et al. carried out a series of ground-penetrating radar (GPR) measurements on sites characterized by semi-vegetated dunes both in April 2010 and 2011. They compared water contents calculated from the GPR direct ground wave signal to both point scale validation measurements by time-domain reflectometry (TDR) and gravimetric sampling.

The results show that GPR is an effective method to rapidly obtain a detailed image of the field scale soil water content distribution in the Gurbantünggüt Desert with an accuracy similar to TDR. Observed large scale soil water content variations are dominated by dune topography. During snow melting, melt water was found to trickle slowly from the dune ridges to interdune valleys, increasing the soil water content there while the dune ridges quickly started to dry down. In dune valleys, smaller scale near-surface soil water content changes were dominated by variations in the vegetation coverage, leading to snowmelt funnels at distinct locations. The snowmelt initially occurred around the stems and branches of plants, forming funnel-shaped melt water induced holes through the snow cover and leading to an increasing amount of melt water collected around these plant roots.

The comparison of data from 2010 to 2011 furthermore suggests a temporally stable distribution of near-surface soil water content. This has important ecological significance for controlling desertification and for restoring and reconstructing vegetation in the Gurbantünggüt Desert. The result was published in Environmental Earth Sciences in November 2013.