Estimation of snow water equivalent over first-year sea ice using AMSR-E and surface observations

Keywords: Snow water equivalent Arctic First-year sea ice Passive microwaves Surface based radiometer AMSR-E Ice roughness Climate change A SWE retrieval algorithm developed in-situ using passive microwave surface based radiometer data is applied to the Advanced Microwave Scanning Radiometer for Earth Observation System (AMSR-E). Snow water equivalent is predicted from two pixels located in Canadian Arctic Shelf Exchange Study (CASES) overwintering study area in Franklin Bay, N.W.T., Canada. Results show that the satellite SWE predictions are statistically valid with measured in-situ snow thickness data in both smooth and rough ice environments where predicted values range from 15 to 25 mm. Stronger correlation between measured and predicted data is found over smooth ice with R 2 value of 0.75 and 0.73 for both pixels respectively. Furthermore, a qualitative study of sea ice roughness using both passive and active microwave satellite data shows that the two pixels are rougher than the surrounding areas, but the SWE predictions do not seem to be affected significantly. Snow cover plays a primary role determining the thermodynamic state of the sea ice by controlling both radiative and mass transfers across the ocean-sea ice-atmosphere interface (e.g., Eiken, 2003). The surface energy balance (SEB) along with sea ice freeze-up and decay are strongly influenced by snow thickness and its thermophysical properties such as density, temperature, salinity and grain size (e.g., Langlois and Barber, 2007b). Given the recent dramatic ice depletion observed in the Arctic over the past three decades (Francis, Hunter, Key, Wang, 2005; Stroeve et al., 2005), global accurate snow measurements are required to assess the impact of the current and future changes in the Arctic environment. Passive microwave satellite remote sensing is known as the best tool for regional snow thickness studies Most of the satellite studies make use of a combination of 19 and 37 GHz channels to retrieve snow depth, whereas results from in-situ measurements using surface based radiometers (SBR) provide better predictions using single frequency/polarization algorithms One of the main challenges in global SWE retrieval studies over sea ice relates to spatial heterogeneity (e.g., Sturm et al., 2006). For instance, brightness temperatures from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) include emission contributions from different surface features (smooth ice, rough ice, open water) found in a pixel of 12.5× 12.5 km (e.g., Mäkynen and Hallikainen, 2005) that can potentially alter SWE predictions thus, the effect of ice roughness on existing …