Because much of Earth's surface is covered by frost, snow, and ice, th
e spectral emissivities of these materials are a significant input to
radiation balance calculations in global atmospheric circulation and c
limate change models, Until now,however, spectral emissivities of fros
t and snow have been calculated from the optical constants of ice. We
have measured directional hemispherical reflectance spectra of frost,
snow, and ice from which emissivites can be predicted using Kirchhoffs
law (e=1-R). These measured spectra show that contrary to conclusions
about the emissivity of snow drawn from previously calculated spectra
, snow emissivity departs significantly from blackbody behavior in the
8-14 mu m region of the spectrum; snow emissivity decreases with both
increasing particle size and increasing density due to packing or gra
in welding; while snow emissivity increases due to the presence of mel
twater.