A PRELIMINARY INVESTIGATION INTO THE POTENTIAL OF HY-4A/MICAP DATA FOR SOIL MOISTURE RETRIEVAL
Marzo 25, 2026NUMERICAL 3D MAXWELL’S EQUATIONS PATHWAYS TO SNOW MICROPHYSICS: WET SNOW EFFECTIVE PERMITTIVITY FOR L-BAND RADIOMETRY
Marzo 25, 2026C. Mätzler1,2
1Institute of Applied Physics, University of Bern, 2Gamma Remote Sensing, Switzerland
Dry snow is a two-component medium of air and ice. If the snow temperature is close to the melting point of 0.0°C, a so-called “quasi-liquid layer” covers the surface of the ice particles. Its thickness increases with temperature from about -10°C to 0°C. However, different measurement methods (X-ray diffraction, proton channelling, optical ellipsometry, nuclear magnetic resonance) led to quite different results (Petrenko, 1994, 1999). Can microwave radiometry help? Microwave dielectric properties of water and ice are very different.
Therefore, the microwave-radiometric sensitivity to liquid water in snow is very high, corresponding to an equivalent integrated water-layer thickness of about 0.001 mm. This also means that the study of microwave emission of snow might reveal properties of a quasi-liquid layer. During our microwave investigations of snowpacks over more than 20 years in Switzerland and in Austria (from 1 to 94 GHz, especially with focus on 21 and 35 GHz), we often found occasions of dry snow approaching the melting point. Since the specific surface of fine-grained snow is large, the effect of a quasi-liquid layer should be especially evident for fresh snow near the surface. We often found suitable situations. However, we never found any influence of a quasi-liquid layer. Only after delivering sufficient heat by the sun to the snowpack to overcome the latent heat of melting – while the snow was constant at 0°C – we observed an increase of brightness temperature. Examples from Kaunertal in Austria (Mätzler et al. 1997) will be presented. All our results indicate that the quasi-liquid layer has dielectric properties of ice, or at least similar without noticeable absorption. Changes only occur with the appearance of free liquid water at the start of melting. On the other hand, the classical snowball test indicated stickiness of snow well before melting started.
References
Christian Mätzler, T. Strozzi, T. Weise, D. Floricioiu and H. Rott, “Microwave snowpack studies made in the Austrian Alps during the SIR-C/X-SAR experiment”, Internat. J. Remote Sensing, Vol. 18, pp. 2505-2530 (1997).
Victor F. Petrenko “The Surface of Ice”, US Army Corps of Engineers, CRREL Special Report 94-22 (1994).
Victor F. Petrenko “The Physics of Ice”, Clarendon Press (1999).
