Dg. Barber et al., THE ROLE OF SNOW ON MICROWAVE EMISSION AND SCATTERING OVER FIRST-YEARSEA-ICE, IEEE transactions on geoscience and remote sensing, 36(5), 1998, pp. 1750-1763
The primary objective of this paper is to investigate the geophysical
and thermodynamic effects of snow on sea ice in defining the electroma
gnetic (EM) interaction within the microwave portion of the spectrum.
We combine observational evidence of both the physical and thermodynam
ic characteristics of snow with direct measurements of scattering and
emission at a variety of frequencies. We explain our observational res
ults using various ''state-of-the-art'' forward scattering and emissio
n models. Results show that geophysical characteristics of snow effect
emission above about 37 GHz and above 5 GHz for active microwave scat
tering. We understand these effects to be driven by grain size and its
contribution to volume scattering in both passive and active interact
ions within the volume. With snow cover, the Brewster angle effect is
not significant and there is a gradual rise in emission from 10 to 37
GHz, We find emissivity to be dominated by direct emission from saline
ice through the snow layer. Hence, the influence of grain size is sma
ll but the trend is clearly a drop in total emission as the grain size
increases. We find that the role of the volume fraction of snow on em
ission and scattering is a complex relationship between the number den
sity of scatterers relative to the coherence of this scattering ensemb
le. At low volume fractions, we find that independent scattering domin
ates, resulting in an increase in albedo and the extinction coefficien
t of the snow with frequency. The thermodynamic effects of snow on mic
rowave scattering and emission are driven by the role that thermal dif
fusivity and conductivity play in the definition of brine volumes at t
he ice surface and within the snow volume, Prior to the presence of wa
ter in liquid phase within the snow volume, we find that the indirect
effects are dominated by an impedance matching process across the snow
-ice interface. We find that the complex permittivity at the snow-ice
interface is considerably higher than over the bare ice surface. Our r
esults showed that only a small change occurs between the cold and war
m cases at lower frequencies, but as expected, the change in emissivit
y is larger at higher frequencies. Once water in liquid phase appears
within the snow cover, we find that both emission and scattering are d
irectly affected by the high complex permittivity of this volume fract
ion within the snow layer.