Multispectral Surface Reflectance as an Indicator of Groundwater Depth for Salt Crust Systems: Insights From the Bonneville Salt Flats, Utah

Abstract The Bonneville Salt Flats (BSF) in northwestern Utah, USA, has experienced changes in area, thickness, and hydrology over the past century. This study investigates the relationship between multispectral Halite Index (HI) values, which are sensitive to halite moisture content, from Landsat and Sentinel‐2 imagery and groundwater depth (GWD) measured by nine piezometers, based on the principle that surface moisture in the halite crust is driven primarily by depth of groundwater and secondarily by atmospheric precipitation or humidity. Linear regressions reveal moderately strong correlations, and regression coefficients are used to calibrate HI values to GWD. Satellite‐calibrated GWD time series show temporal alignment with piezometer records, with a median absolute deviation less than 15 cm for seven of the nine piezometers. Spatial interpolations of regression coefficients are used to calibrate HI imagery to GWD imagery, highlighting the groundwater table's spatiotemporal variability and relation to climate. Groundwater depth is observed to be very sensitive to climatic conditions, as GWD across the crust scales with Palmer Drought Severity Index data. The methodology is tested for available piezometer data at the Badwater Basin, Salar de Uyuni, and Salar de Atacama to explore global applicability. The results from this study confirm the potential of multispectral remote sensing for monitoring GWD at the BSF and suggest the methodology could be transferable to similar salt crusts globally.