| Abstract: |
The high sensitivity of L-band brightness temperatures to volumetric snow liquid water content W_S is successfully used to retrieve W_S 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 W_S retrievals were performed based on L-band brightness temperatures measured over i) areas with a metal reflector placed on the ground (“reflector area”—T_(B,R)), and ii) natural snow-covered ground (“natural area”— T_(B,N)). The reliable representation of temporal variations of snow moisture is demonstrated for both types of the aforementioned quasi-simultaneous retrievals. This is verified by the fact that both types of W_S 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 W_S retrieved from T_(B,R), together with their level of detail, suggest the use of these retrievals as “references” to assess the meaningfulness of the W_S retrievals based on T_(B,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 ancillary data such as in-situ measured ground permittivity ε_G and snow mass-density ρ_S. The latter two are estimated in the first retrieval-step employing the well-established two-parameter (ε_G,ρ_S) retrieval scheme [1, 2]. The proposed and investigated two-step retrieval approach opens up the possibility of using airborne or spaceborne L-band radiometry to estimate (ε_G,ρ_S) and additionally snow wetness W_S as a new passive L-band data product.
References
[1] M. Schwank, C. Mätzler, A. Wiesmann, U. Wegmüller, J. Pulliainen, J. Lemmetyinen, K. Rautiainen, C. Derksen, P. Toose, and M. Drusch, "Snow Density and Ground Permittivity Retrieved from L-Band Radiometry: A Synthetic Analysis," IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 8, pp. 3833-3845, 2015.
[2] J. Lemmetyinen, M. Schwank, K. Rautiainen, A. Kontu, T. Parkkinen, C. Mätzler, A. Wiesmann, U. Wegmüller, C. Derksen, P. Toose, A. Roy, and J. Pulliainen, "Snow density and ground permittivity retrieved from L-band radiometry: Application to experimental data," Remote Sensing of Environment, vol. 180, pp. 377-391, 2016. |
