Retrieving Ice Concentration From SMOS

The Soil Moisture and Ocean Salinity (SMOS) Ice project explored the potential of retrieving sea-ice information from the SMOS satellite, a polar-orbiting L-band radiometer successfully launched in November 2009. Toward this end, radiance measurements were collected over the Northern Baltic during the Pol-Ice campaign. We test a simple ice-concentration retrieval algorithm on these data and compare the results with ARTIST Sea Ice (ASI) maps derived from the Advanced Microwave Scanning Radiometer on the Earth Observing System. All operational ice-concentration algorithms are based on the same principle which, for the campaign data, reduces to a linear scaling of the radiances because, effectively, only one channel was available. Because of biases introduced by the different footprint sizes of the two radiometers (airborne and satellite), the linear flight path, and pilot selection of preferred surface type, Pol-Ice and ASI concentrations were compared using three different levels of averaging. In the first case, the individual measurements from the airborne radiometer were compared with interpolated ASI values; in the second, they were averaged over the pixels in the ASI maps; and in the third, they were averaged by binning the ASI values in 1% intervals. The correlations were 0.59, 0.67, and 0.76, respectively. Because of the unique operating principle of SMOS, each ground point will be viewed at multiple effective angles within a short time span. It is proposed to exploit this extra information by interpolating to a single effective viewing angle.