TOWARDS A WATER BUDGET FOR ANTARCTIC WATER TRACKS AND SEASONAL WETLANDS: REMOTE SOIL MOISTURE DETECTION USING DRONE-BORNE REFLECTANCE SPECTROSCOPY AND MICROWAVE RADIOMETRY

Water tracks are active layer groundwater flow conduits similar to ephemeral streams that route meltwater and solutes across hillslopes in permafrost environments. Water tracks in the McMurdo Dry Valleys (MDV) of Antarctica are zones of the highest concentrations of soil moisture, pore water solutes, soil organic matter, and chemical weathering products, suggesting that these seasonal wetlands may be focal points for soil development under hyperarid, hypothermal climate conditions. Here, we report drone-based remote sensing and ground-truth results from water track soils collected in 2022-2023 in the MDV that aim to address how much water is flowing through Antarctic water tracks, what remote sensing reveals about water track melt sources, and what impacts water track flow has on soil biogeochemical processes. Water tracks were measured using drone-borne remote sensing: a Headwall Extended VNIR imaging spectrometer (900 – 1700 nm spectral range) and a TerraRad Tech PoLRa 3.1 L-band radiometer. Soil moisture content was measured during UAV flights using co-located soil moisture probes, and was extrapolated beyond probe locations across the water track and adjacent dry soil using a linear fit between in situ measured soil water content (from ground-truth sampling and high-cadence soil moisture probes) and the depth of the shoulder of the 1.4 µm water absorption measured in the spectroscopic data. Water track surface soils span ~0-7% water content by mass, and increase in soil moisture content to saturation at the base of the ice table (40-60 cm). Soil moisture is found to vary spatially across the water track, increasing from near 0% in dry, off-track soils to a maximum near the center of the water track. This pattern is observed both in the ground-based sampling and in the remote sensing data. Soil moisture content and depth of thaw also vary down-track based on remote sensing and ground-truth measurements, providing the first snapshot of summertime water storage in these Antarctic groundwater features. This work expands on previous studies by presenting multiple wavelengths of remote sensing data, capable of beginning to close the water budget for the upper 5-10 cm of the active layer, and by integrating deeper soil sensor and ground-truth measurements to more fully explore the entire active layer.