Thickness of Snow on Arctic Sea Ice Derived from SMOS
Kaleschke, Lars; Tian-Kunze, Xiangshan; Maaß, Nina
University of Hamburg, GERMANY
The 1.4 GHz brightness temperature measured by the ESA's Soil Moisture and Ocean Salinity Mission (SMOS) over sea ice covered regions is mainly influenced by the sea ice thickness, snow thickness, ice salinity, ice temperature and ice concentration. Here we describe a simple semi-empiric retrieval approach that neglects the variability of ice salinity, temperature and ice concentration to derive sea ice and snow thickness. We use measurements of near nadir brightness temperature, henceforth simply called intensity, to derive the sea ice thickness for thin ice and the snow thickness over thick ice.
The intensity varies with sea ice thickness because of the relatively large penetration depth in cold sea ice. The intensity increases from about 100 K for zero thickness (open water) to about 240 K for ice of about half a meter thickness. The increase of brightness temperature is described by the Lambert-Beer law as a function of sea ice thickness. An additional dry snow layer further increases the brightness temperature by about 0.25 K per cm. The dependency between brightness temperature and snow depth is assumed to be linear because of the very small dielectric loss of dry snow at 1.4 GHz.
We compare the snow thickness as retrieved from SMOS with snow thickness measurements from NASA's Operation IceBridge campaign 2012. Both data sets agree within a root-mean-square error of 6 cm. The high degree of correlation (R=0.8) between the SMOS and the IceBridge data further justifies our assumptions.