Speaker
Description
Seasonal snow is a dynamic component of the cryosphere whose physical properties evolve continuously through accumulation, metamorphism, melt–refreeze events, and ablation. Active microwave observations can be sensitive to these changes, but the radar response depends strongly on frequency, incidence angles, polarization, and snow conditions. Multifrequency and high-temporal-resolution measurements are an interesting resource for characterizing the evolution of radar backscatter and interferometric observables throughout the snow season, and for assessing their potential for retrieving snow properties such as snow water equivalent (SWE). New and upcoming SAR missions, including NISAR, ROSE-L, and the proposed Hydroterra+, provide opportunities to exploit and combine frequency bands and increasingly frequent observations for monitoring seasonal snow.
As part of ESA's HydroSWE study, the WBSCAT ground-based radar has been deployed at a boreal site in Sodankylä, Finland, over four winter seasons. WBSCAT is a fully polarimetric wideband scatterometer operating between 1 and 40 GHz. Measurements were acquired at L-, C-, X-, Ku- and Ka-bands with 800 MHz bandwidth, over a range of incidence angles and were complemented by detailed snow, soil and meteorological observations. Measurements were acquired with as short as 3-hour temporal resolution, enabling the evolution of radar observables to be followed at substantially shorter intervals than typical satellite revisit times.
We investigate the temporal evolution of multifrequency radar backscatter, interferometric phase, coherence, and phase closure throughout the snow season. Their sensitivity to changes in snow and environmental conditions was assessed. The dense temporal sampling allows the radar response to accumulation, melt–refreeze events, and spring ablation to be investigated. The observations show extended periods of stable interferometric coherence during dry-snow conditions, interrupted by strong decorrelation associated with changes in the snowpack such as melt events. For dry snow conditions, changes in interferometric phase provide sensitivity to changes in SWE.