Snow Wetness Retrieved from L-Band Radiometry.

The present study demonstrates the successful use of the high sensitivity of L-band brightness temperatures to snow liquid water in the retrieval of snow liquid water from multi-angular L-band brightness temperatures. The emission model employed was developed from parts of the "microwave emission model of layered snowpacks" (MEMLS), coupled with components adopted from the "L-band microwave emission of the biosphere" (L-MEB) model. Two types of snow liquid water retrievals were performed based on L-band brightness temperatures measured over (i) areas with a metal reflector placed on the ground ("reflector area"-TB,R), and (ii) natural snow-covered ground ("natural area"-TB,N). The reliable representation of temporal variations of snow liquid water is demonstrated for both types of the aforementioned quasi-simultaneous retrievals. This is verified by the fact that both types of snow liquid water retrievals indicate a dry snowpack throughout the "cold winter period" with frozen ground and air temperatures well below freezing, and synchronously respond to snowpack moisture variations during the "early spring period". The robust and reliable performance of snow liquid water retrieved from TB,R, together with their level of detail, suggest the use of these retrievals as "references" to assess the meaningfulness of the snow liquid water retrievals based on TB,N. It is noteworthy that the latter retrievals are achieved in a two-step retrieval procedure using exclusively L-band brightness temperatures, without the need for in-situ measurements, such as ground permittivity εG and snow mass-density rS. The latter two are estimated in the first retrieval-step employing the well-established two-parameter (ρS, εG) retrieval scheme designed for dry snow conditions and explored in the companion paper that is included in this special issue in terms of its sensitivity with respect to disturbative melting effects. The two-step retrieval approach proposed and investigated here, opens up the possibility of using airborne or spaceborne L-band radiometry to estimate (ρS, εG) and additionally snow liquid water as a new passive L-band data product. [ABSTRACT FROM AUTHOR]