Thickness of thin sea ice retrieved from SMOS and SMAP

Sea ice is an important quantity for the radiation budget of the Earth's climate system. In this paper we present a comparison of SMAP and SMOS measured brightness temperatures and translate a validated retrieval algorithm for the thickness of thin sea ice from SMOS to SMAP radiometer observations. For October to December all observations of SMAP in forward and backward direction are compared as daily averages and found with low RMSD of 2.25K and 2.42K in T
_B,v
and T
_B,h
, respectively. The mean of forward and backward observations from SMAP are mapped to SMOS equivalent brightness temperatures using a linear regression. SMAP was found to yield lower brightness temperatures compared to SMOS by about 5K in both polarizations while difference decreases with increasing brightness temperatures. An existing ice thickness retrieval for SMOS using averaged brightness temperatures in the incidence angles range of 40° to 50° is transferred to SMAP using another linear regression. Ice thicknesses retrieved from both sensors show good agreement with a correlation of r = 0.969 and RMSD of 3.31 cm for ice thicknesses from 1 cm to 50 cm.