How flat is flat? Investigating snow topography and the spatial variability of snow surface temperature on landfast sea ice using UAVs in McMurdo Sound, Antarctica

Abstract. How do snow distribution patterns influence the surface temperature of snow on sea ice? Despite its crucial role in the sea-ice energy balance, snow on Antarctic sea ice remains under-sampled and poorly understood. In our study, we combined Uncrewed Aerial Vehicle (UAV) and ground-based measurements to obtain high resolution (9 cm per pixel) maps of snow topography (Digital Elevation Model; DEM), surface temperature, and modeled irradiance over a 200 m × 200 m test site on relatively uniform landfast sea ice (2.4 ± 0.04 m thick) in McMurdo Sound, Ross Sea, Antarctica. A key technical advance presented here is a new algorithm to correct thermal camera drift from Non-Uniformity Correction (NUC) events in the DJI Matrice 30T, enabling consistent, accurate airborne temperature retrievals with applications beyond polar research. Based on MagnaProbe measurements, the average snow depth for the test site is 0.1 ± 0.04 m. Snow surface temperatures average −14.7 ± 0.4 °C, with local variations up to 12 °C. Small-scale topography strongly affects local irradiance (modeled 592 ± 45 vs. 593 ± 20 Wm−2 measured), revealing that flat-surface assumptions underestimate local variability of irradiance. Statistical analyses identify irradiance and visible sediment deposition as dominant predictors of surface temperatures, while snow depth plays only a minor role. These results highlight that assuming that snow-covered sea ice is a flat surface fails to represent the full irradiance range, potentially impacting non-linear energy balance processes. Our study provides new insights into drivers of snow surface temperatures over sea ice with potential implications for the sea-ice energy balance.