MEMLS (Microwave Emission Model of Layered Snowpacks)

The Microwave Emission Model of Layered Snowpacks (MEMLS) was originally developed for microwave emissions of snowpacks in the frequency range 5–100 GHz.

microwave emissionssnowpacks
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contributed at 2020-01-08

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Affiliation:  
Institute of Applied Physics, University of Bern, Bern, Switzerland
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Application-focused categoriesNatural-perspectiveFrozen regions

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Quoted fromWiesmann, Andreas, and Christian Mätzler. "Microwave emission model of layered snowpacks." Remote Sensing of Environment 70, no. 3 (1999): 307-316. https://doi.org/10.1016/S0034-4257(99)00046-2 

      The observation of passive microwave signatures of different types of snowpacks (e.g., Mätzler, 1994) and the need to simulate their microwave emission for future applications was the motivation for the development of a microwave emission model of layered snowpacks (MEMLS). Since the penetration depth of microwaves and the scattering coefficient depend on frequency and snow properties, a reasonable model should account for realistic snow profiles of the sensitive parameters, such as correlation length, density, and temperature, and in case of wet snow also the liquid-water content. A successful model might then be used for the development of remote sensing tools for observing processes on and within the snowpack. An important internal process, being responsible for the release of large avalanches, is temperature-gradient metamorphism, often taking place near the bottom of the snowpack. This process is based on large water-vapor gradients; it leads to the formation of cohesionless depth hoar Armstrong 1977Armstrong 1985. Microwave emission of depth-hoar layers are very special due to the enhanced volume-scattering by the large crystals (Weise, 1996). On the other hand, snowpack stratification has important implications for physical processes, such as avalanche formation by weak layers Föhn et al. 1998Fierz 1998, reduced vertical diffusion of water vapor and heat transfer, and percolation of liquid water in case of wet snow (Arons and Colbeck, 1995, and references therein). Snow layers also mark meteorological events in the history of snowpacks, and thus they contain information about past weather conditions. Specific microwave signatures related to stratification are expressed, for instance, by polarization features of microwave emission, and sometimes by special spectral properties. Since the earliest radiometer observations, interest has been paid to layering of polar ice sheets Gurvich et al. 1973Zhang et al. 1989Rott et al. 1998Surdyk and Fily 1993Steffen and Abdalati 1999, and layer effects were also found in snow-covered sea ice (e.g., Mätzler et al., 1984). Microwave emission of layered media, such as firn, was computed in the past by several authors (e.g., Gurvich et al. 1973Djermakoye and Kong 1979West et al. 1996). Their models are applicable at frequencies below about 20 GHz, where volume scattering by the granular snow structure is not dominant.

      When both volume scattering by snow grains and by the stratification are relevant, the models become more complex. An example is the strong fluctuation theory (Stogryn, 1986). In the implementation by Surdyk (1992), this model was tested by the experimental snow data of Weise (1996) to be used also in the present work. The model validation clearly failed, probably because multiple scattering is ignored. Indeed, West et al. (1993) showed on the basis of the dense-medium radiative transfer theory applied to backscattering from snow that multiple scattering by snow grains is important.

      Driven by the need for a realistic snowpack emission model, we started with the development of MEMLS, including multiple scattering both by stratification and by the granular snow structure, and a tuned combination of coherent and incoherent superpositions of different scattering contributions. First, the detailed behavior of single layers was investigated experimentally by Weise (1996) and later by Wiesmann et al. (1998). The work lead to a physical model of the emissivity of homogeneous snow slabs in the frequency range from 10 GHz to 100 GHz and for correlation lengths from 0.05 mm to 0.3 mm. With the exception of the empirical determination of the scattering coefficient, the parameters are physically based. In MEMLS this information is applied to describe the behavior of individual layers. Here, the snowcover is considered as a stack of n horizontal, planar layers, characterized by thickness, correlation length, density, liquid-water content, and temperature. The sandwich model of Wiesmann et al. (1998) is extended to couple internal scattering and reflections at the interfaces of all layers. Internal volume scattering is accounted for by a six-flux model (streams in all space directions). Homogeneity in the horizontal directions reduces to the well-known two-stream model (up- and downwelling streams) where the two-stream absorption and scattering coefficients are functions of the six-flux parameters. The absorption coefficient depends on density, frequency, and temperature, and the scattering coefficient depends on the correlation length, density, and frequency (Wiesmann et al., 1998). The purpose of this article is to describe and illustrate the model and to pave the way for further improvements. Details on the realization are given by Wiesmann and Mätzler (1998).

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How to Cite

Andreas Wiesmann and Christian Mätzler (2020). MEMLS (Microwave Emission Model of Layered Snowpacks), Model Item, OpenGMS, https://geomodeling.njnu.edu.cn/modelItem/52391061-5e5f-43c7-8feb-acb5bb12bea8
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Initial contribute: 2020-01-08

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Affiliation:  
Institute of Applied Physics, University of Bern, Bern, Switzerland
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