Low‐frequency passive‐microwave observations of sea ice in the Weddell Sea

Abstract

The microwave emission properties of first-year sea ice were investigated from the R/V Polarstern during the Antarctic Winter Weddell Gyre Project in 1989. Radiometer measurements were made at 611 MHz and 10 GHz and were accompanied by video and visual observations. Using the theory of radiometric emission from a layered medium, a method for deriving sea ice thickness from radiometer data is developed and tested. The model is based on an incoherent reflection process and predicts that the emissivity of saline ice increases monotonically with increasing ice thickness until saturation occurs. 22,569 22,570 MENASHI ET AL.' LoW-FREQUENCY PASSIVE-MICROWAVE OBSERVATIONS OF SEA ICE 0i Greenland, Nature, 345, 795-797, 1990. Wadhams, P., M. A. Lange, and S. F. Ackey, The thickness distribution across the Atlantic sector of the Antarctic Ocean in midwinter, J. Geophys. Res., A. W. Lohanick, Naval Oceanographic and Atmospheric Research Laboratory, Polar Oceanography Branch Office, Hanover, NH 03755.

SMOS-derived thin sea ice thickness: algorithm baseline, product specifications and initial verification

“…The basis of the SMOS ice thickness retrievals Algorithm I and II is the sea ice radiation model adapted from Menashi et al (1993). While for Algorithm I the radiation model is used to calculate the constant attenuation factor γ for a representative T ice and S ice in the Arctic, in Algorithm II the model is used to calculate TB at variable T ice and S ice .…”

“…Besides soil moisture and ocean salinity information, for which SMOS was originally designed, L-band radiometry on SMOS can also be used to obtain sea ice thickness, which is due to its large penetration depth in sea ice (Kaleschke et al, 2010(Kaleschke et al, , 2012. The measured L-band brightness temperature mainly depends on the ice concentration, the molecular temperatures of the sea and the ice, and their emissivities (Menashi et al, 1993;Kaleschke et al, 2010). Sea ice emissivity depends on the microphysical sea ice structure, but inhomogeneities, like brine pockets and air bubbles, are much smaller than the SMOS wavelength of 21 cm (Kaleschke et al, 2010(Kaleschke et al, , 2012.…”

“…where d ice is the ice thickness, T 1 and T 0 are two constant tie points, which were estimated from the observed SMOS brightness temperatures over open water and thick first year ice during the freezing period of 2010 in the Arctic, and γ is a constant attenuation factor, which was derived from a sea ice radiation model (Menashi et al, 1993) for a representative bulk ice temperature and salinity in the Arctic. The advantage of Algorithm I is the retrieval of ice thickness from the brightness temperature (TB) without any auxiliary data set.…”

“…Ice salinity can be estimated from the underlying sea surface salinity (SSS) with an empirical function (Ryvlin, 1974). With these two parameters, we can calculate brightness temperature with the sea ice radiation model (Menashi et al, 1993). However, both ice temperature and ice salinity are, in turn, functions of ice thickness.…”

“…In the radiation model of Menashi et al (1993), a plane ice layer is assumed. However, natural sea ice exhibits a statistical thickness distribution within the spatial resolution of SMOS, due to dynamic-thermodynamic growth and deformation processes (Bartels-Rausch et al, 2012).…”