Atmospheric Correction of Sea Ice Concentration Retrieval for 89 GHz AMSR-E Observations

Abstract

An improved sea ice concentration (SIC) retrieval algorithm named ASI2 that uses weather corrected polarization difference (PD) of brightness temperatures (TBs) at 89 GHz measured by AMSR-E/2 is developed. Effects of wind, total water vapor, liquid water path, and surface temperature on the TBs are evaluated through a radiative transfer model. TBs of open ocean yield higher sensitivity to the atmospheric water due to its low emissivity, whereas that of sea ice is more influenced by the surface conditions such as temperature and ice type. The weather effects are corrected by simulating changes in TBs caused by the atmospheric water absorption/emission and wind roughened ocean surface using numerical weather prediction reanalysis data fields as atmospheric profiles. ASI2 is validated on a collection of AMSR-E observations over open water and 100% SIC. The correction significantly reduces the standard deviation and bias of SIC over open water, yet yields little change over 100% SIC. Combined with an improved weather filter based on the corrected TBs at lower frequencies, ASI2 allows retrieval of low ice concentration and resolves a more exact ice concentration gradient across the ice edge compared to the original ASI algorithm.