The Microwave Snow Grain Size: A New Concept to Predict Satellite Observations Over Snow‐Covered Regions
International audience Snow is a random heterogeneous medium composed of ice, air and possibly water and impurities. All its physical properties depend not only on the properties of these constituent materials but also on their geometrical arrangement at the micrometer scale, the so called microstru...
Published in: | AGU Advances |
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Main Authors: | , , , , , , , , , |
Other Authors: | , , , , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2022
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Subjects: | |
Online Access: | https://hal.science/hal-04389380 https://hal.science/hal-04389380/document https://hal.science/hal-04389380/file/picard_2022_microwave_grain_size.pdf https://doi.org/10.1029/2021av000630 |
Summary: | International audience Snow is a random heterogeneous medium composed of ice, air and possibly water and impurities. All its physical properties depend not only on the properties of these constituent materials but also on their geometrical arrangement at the micrometer scale, the so called microstructure (Torquato, 2002). This applies in particular to the electromagnetic properties that control the propagation of waves in snow, such as the scattering and absorption coefficients. Scattering in snow is caused by the dielectric contrast between air and ice, and its amplitude highly depends on the length scales of the microstructure. The "snow grain size" is an intuitive property commonly estimated in the field (Fierz et al., 2009). However, it is loosely defined from a geometrical point of view because snow crystals often have very complex shapes, leading to imprecise and subjective measurements. Moreover this single metric is insufficient to fully describe all the length scales. Finding a rigorous mathematical representation Abstract Satellite observations of snow-covered regions in the microwave range have the potential to retrieve essential climate variables such as snow height. This requires a precise understanding of how microwave scattering is linked to snow microstructural properties (density, grain size, grain shape and arrangement). This link has so far relied on empirical adjustments of the theories, precluding the development of robust retrieval algorithms. Here we solve this problem by introducing a new microstructural parameter able to consistently predict scattering. This "microwave grain size" is demonstrated to be proportional to the measurable optical grain size and to a new factor describing the chord length dispersion in the microstructure, a geometrical property known as polydispersity. By assuming that the polydispersity depends on the snow grain type only, we retrieve its value for rounded and faceted grains by optimization of microwave satellite observations in 18 Antarctic sites, and for ... |
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