Observations of Coherence Changes in C-Band SAR Linked to Snow Thermodynamics and Wind Redistribution on First-Year Sea Ice

Abstract We present novel observations of C-band Synthetic Aperture Radar (SAR) coherence sensitivities and patterns for snow on first-year sea ice (FYI) consistent with snow thermodynamics and wind redistribution. Wintertime SAR coherence and backscatter change observations of landfast FYI in Dease Strait, Nunavut, Canada are made using 12-day repeat-pass Sentinel-1A SAR image pairs in four case studies. Observations in three cases are consistent with changes in basal snow brine volume influenced by eutectic thresholds, snow thickness, and air temperature, with one case further influenced by upper layer snow moisture. Observations in one case are consistent with snow redistribution, whereby coherence patterns align with wind direction, speed, and lee effects. Coherence losses are explained primarily through volumetric changes and heterogeneity in phase delay. These observations establish that temporal and/or spatial coherence variations should be expected for FYI whenever air temperatures change and/or snow redistributions occur.