Observations of snowpack properties to evaluate ground-based microwave remote sensing

Active microwave radar has been shown to have great potential for estimating snow water equivalent (SWE) globally from space. To help evaluate optimal active microwave sensor configurations to observe SWE, we evaluated ground-based Frequency Modulated Continuous Wave (FMCW) radar (12–18 GHz, cross-polarisation) using very high resolution in-situ observations of snowpack layering, dielectric permittivity and density over a 10 m snow trench on Toolik Lake, Alaska. Results showed that the thicknesses of layers within the 10 m trench were highly variable over short distances (<1 m), even where total snow depth changed very little. Layer boundaries observed using NIR photography identified all bands of high radar backscatter. Although additional observations of density and dielectric permittivity helped to explain the causes of backscatter, not all snowpack properties which cause backscatter were coincident with strong vertical changes in density or permittivity. Further observations of high surface roughness in layer boundaries explained some areas of weak backscatter, nonetheless it was shown that a suite of coincident observations, rather than a single technique in isolation, were required to adequately explain the variability of backscatter and the influence of snowpack properties upon it.