Remote Sensing of Snow on Sea Ice – What are we Missing?

Abstract:

Snow on sea ice and its seasonal changes are most important contributors to the year-round sea ice mass balance and are in many ways more characteristic of sea ice satellite signatures than sea ice properties themselves. Snow thickness, density, and stratigraphy are among the most important snow variables, affecting snow optical properties, thermal conductivity, and microwave signatures. All these are interconnected and vary on diurnal, seasonal, annual as well as spatial time scales. Our physical understanding and observational capabilities are still inadequate to sufficiently observe, understand, and predict snow and its impact on the ice, climate, and eco systems. Similarly, the collection of in-situ data to support development and validation of snow retrieval algorithms is hampered by challenges related to the inherent small- and large-scale variability of snow properties and to differing footprint sizes of all methods. Here we present results from efforts to collect in-situ data on Antarctic and Arctic sea ice to validate satellite microwave products and airborne snow thickness retrievals. Data were collected during cruises of the German icebreaker RV Polarstern and airborne ESA CryoSat Validation and NASA Icebridge campaigns. Results show that there is still a lack of understanding of satellite microwave products affected by variations in snow properties, and of the penetration and resolution of snow-penetrating snow thickness radars which can lead to wrong interpretations of data and results. However, there also remains uncertainty about “true” snow properties and processes within satellite or airborne footprints because even more extensive in-situ validation campaigns may not be able to sufficiently observe these, lacking advanced methodologies and a combination of spatial resolution and spatial coverage.