Retrieving the Emissivities of Polar Sea Ice from AMSR-E Measurements Using the Combined Fresnel Equation

Abstract:

Recently, a sea ice temperature retrieval algorithm has been developed using the combined Fresnel equation which combines two Fresnel equations for polarized reflectivities into one. The retrieved temperatures from Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) 6.925 GHz brightness temperatures are highly correlated with U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) buoy-measured ice surface temperatures with a correlation coefficient of 0.989. In this study, we develop a new approach to calculate polarized emissivities of the polar sea ice at AMSR-E frequencies such as 10.65, 18.7, 23.8, and 36.5 GHz, based on the sea ice temperature data from the 6.9 GHz measurements by assuming that the emitting layer temperature is nearly independent throughout the 6 – 37 GHz frequency range. The results show that the emissivities are well coincident with theoretically-driven values. Furthermore, the ice surface roughness is estimated by assuming that departure of the retrieved polarized emissivities from specular emissivities is attributed to the surface roughness. The retrieved emissivities obtained from this research are compared with the theoretical values as well as with previously measured or retrieved emissivities.