Sea Ice Brightness Temperature as a Function of Ice Thickness, Part II: Computed curves for thermodynamically modelled ice profiles

TL;DR

This study models the relationship between sea ice thickness and microwave radiance at frequencies used by SMOS and AMSR, emphasizing the roles of surface 'skim' formation and scattering in radiance signatures.

Contribution

It introduces a thermodynamic growth model to predict salinity profiles and radiance, incorporating surface 'skim' effects and scattering across a range of microwave frequencies.

Findings

Surface 'skim' significantly affects radiance at low frequencies.

Scattering influences radiance primarily at higher frequencies.

The growth model produces realistic salinity profiles but overestimates bulk salinity.

Abstract

Ice thickness is an important variable for climate scientists and is still difficult to accurately determine from microwave radiometer measurements. There has been some success detecting the thickness of thin ice and with this in mind this study attempts to model the thickness-radiance relation of sea ice at frequencies employed by the Soil Moisture and Ocean Salinity (SMOS) radiometer and the Advanced Microwave Scanning Radiometer (AMSR): between 1.4 and 89 GHz. In the first part of the study, the salinity of the ice was determined by a pair of empirical relationships, while the temperature was determined by a thermodynamic model. Because the thermodynamic model can be used as a simple ice growth model, in this, second part, the salinities are determined by the growth model. Because the model uses two, constant-weather scenarios representing two extremes ("fall freeze-up" and "winter cold snap"), brine expulsion is modelled with a single correction-step founded on mass conservation. The growth model generates realistic salinity profiles, however it over-estimates the bulk salinity because gravity drainage is not accounted for. The results suggest that the formation of "skim" on the ice surface is important in determining the radiance signature of thin ice, especially at lower frequencies, while scattering is important mainly at higher frequencies but at all ice thicknesses.