L-Band Radiometry of Alpine Seasonal Snow Cover: 4 Years at the Davos-Laret Remote Sensing Field Laboratory

Abstract

This study reports on four consecutive winter campaigns (2016 &#x2013; 2020) at the &#x201C;Davos-Laret Remote Sensing Field Laboratory&#x201D; in the Swiss Alps to gain insight into the L-band microwave emission of ground covered with seasonal snow. Close-range L-band Brightness temperatures <inline-formula><tex-math notation="LaTeX">$T_\mathrm{{B}}^{p,\phi }(\theta)$</tex-math></inline-formula> were measured over the site scanning different observation nadir angles <inline-formula><tex-math notation="LaTeX">$\theta$</tex-math></inline-formula> and azimuth angles <inline-formula><tex-math notation="LaTeX">$\phi$</tex-math></inline-formula> at Horizontal and Vertical polarizations <i>p</i> = {H,V}. State parameters of the snowpack (e.g., height, density, SWE) and the subnivean soil (permittivity, temperature) were measured quasi-simultaneously using in-situ sensors and sampling, as well as meteorological data. In each campaign <inline-formula><tex-math notation="LaTeX">$T_\mathrm{{B}}^{p,\phi }(\theta)$</tex-math></inline-formula> were measured over a &#x201C;natural area&#x201D; and a &#x201C;reflector area&#x201D; with a metal mesh reflector laid on the ground before snow accumulation. The radiometer measurements over &#x201C;reflector area&#x201D; allowed to retrieve the time-series of Snow liquid Water-Content <inline-formula><tex-math notation="LaTeX">$W_\mathrm{{S}}$</tex-math></inline-formula> and Snow liquid Water-Column <inline-formula><tex-math notation="LaTeX">$WC_\mathrm{{S}}$</tex-math></inline-formula> which are employed as &#x201C;derived measurements&#x201D; to support interpretation of <inline-formula><tex-math notation="LaTeX">$T_\mathrm{{B}}^{p,\phi }(\theta)$</tex-math></inline-formula> measured over &#x201C;natural areas&#x201D; during different Winter phases. The detailed approach for the estimation of <inline-formula><tex-math notation="LaTeX">$W_\mathrm{{S}}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$WC_\mathrm{{S}}$</tex-math></inline-formula> using L-band radiometer data is presented. The data and analyses in this paper address the following major points: i) Determination of the characteristic features of measured <inline-formula><tex-math notation="LaTeX">$T_\mathrm{{B}}^{p,\phi }(\theta)$</tex-math></inline-formula> during different periods in each of the four winter campaigns; ii) effects of dry- and wet snow precipitation on L-band radiometer data compared to corresponding simulations; iii) effect of removal and compression of the snowpack on <inline-formula><tex-math notation="LaTeX">$T_\mathrm{{B}}^{p,\phi }(\theta)$</tex-math></inline-formula>; and iv) effects of spatial heterogeneity on brightness temperatures. Finally, the study is concluded with recommendations relevant for future close-range remote sensing campaigns.