Snow Density and Ground Permittivity Retrieved from L-Band Radiometry: Melting Effects

Abstract

Ground permittivity and snow density retrievals are performed using the tower-based experimental L-band radiometry data from the winter 2016/2017 campaign at the Davos-Laret Remote Sensing Field Laboratory. The performance of multi-angle two-parameter retrieval algorithms to estimate snow density and ground permittivity $P^{RM}=(\rho_{S}^{RM},\varepsilon_{G}^{RM})$ is assessed using in-situ measured $\varepsilon_{G}$ and $\rho_{S}$ . Additionally, a synthetic retrieval sensitivity analysis is conducted which studies impacts of “melting effects” on retrievals $(\rho_{S}^{RM},\varepsilon_{G}^{RM})$ in the form of snow liquid water. Experimental and synthetic analyses show that snow liquid water noticeably disturbs the retrievals and result in increased correlation $R^{2}(\rho_{S}^{RM},\varepsilon_{G}^{RM})$ between them. The strength of this correlation is used as a quality-indicator flag to filter out highly correlated retrieval pairs. It is demonstrated that this filtering significantly improves the accuracy of both ground permittivity and snow density retrievals compared to corresponding reference in-situ data. Our analysis shows that retrievals $P^{{}^{\prime\prime}V^{\prime\prime}}=(\rho s^{{}^{\prime\prime}V^{\prime\prime}},\varepsilon_{G}^{{}^{\prime\prime}V^{\prime\prime}})$ using vertical polarization only (RM = “V”) are predominantly least prone to snow liquid water. The presented experimental results indicate that retrievals match in-situ observations best for the “snow-free period” and the “cold winter period” when snow liquid water is at minimum.