Determining soil moisture and sediment availability at White Sands Dune Field, NM from apparent thermal inertia data

Determinations of soil moisture and sediment availability in arid regions are important indicators of local climate variability and the potential for future dust storm events desertification. Data from the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer are used to derive the relationships amongst potential soil erosion, soil moisture and thermal inertia (TI) at the spatial scale of aeolian landforms. To accomplish this, a series of cloud-free, dayand night-time ASTER image pairs were assembled between May 2000 and March 2008 for the White Sands Dune Field. The broadband albedo and brightness temperature of the land surface were derived from these data and combined to extract land surface apparent thermal inertia (ATI) data. The ATI data were extended further to derive an approximation of actual TI in order to then estimate the wind threshold velocity ratio (WTR) The WTR is a ratio of the wind velocity thresholds at which soil erosion occurs for wet soil versus dry soil. The same data set was generated using the Moderate Resolution Imaging Spectroradiometer (MODIS) which has a higher temporal resolution but an order of magnitude lower spatial resolution in the thermal infrared (TIR). The spatial and temporal patterns of ASTERand MODIS-derived retrievals of soil moisture compared well after scaling the ASTER albedo to that of MODIS. The ASTER-derived soil moisture retrievals and the changes through time were compared to local weather station data and independently modeled soil moisture predictions. These data sets were useful in explaining variability and the hydrologic forcing of soil moisture at White Sands, which was interpreted to be driven primarily by precipitation. The presence of a perched groundwater table may also influence certain areas of the aeolian system. The sediment availability was determined to be consistently higher (WTR < 2.5) on dunes, active playa surfaces, and the margin of the alluvial fans adjacent to the active playas if compared to the average land surface (WTR > 3.0), including interdune areas. Sediment availability was highly variable on the playa surfaces and exhibits a trend through time similar to that of interdune areas. The sediment availability derived from ASTER can be primarily explained by the precipitation events and the number of dry days prior to the data acquisition. However other factors such as vegetation and the amount of surface crusting could also influence soil mobility, but were not measured in the field. This approach showed the highest modeled sediment availability values just days prior to the largest dust emission event at White Sands in decades. Such an approach could be extended to a global monitoring technique for arid land systems that are prone to dust storms and for other regional land surface studies in the Sahara.