Abstract

The modular Snow Microwave Radiative Transfer (SMRT) model simulates microwave scattering behavior in snow via different selectable theories and snow microstructure representations, which is well suited to intercomparisons analyses. Here, five microstructure models were parameterized from X-ray tomography and thin-section images of snow samples and evaluated with SMRT. Three field experiments provided observations of scattering and absorption coefficients, brightness temperature, and/or backscatter with the increasing complexity of snowpack. These took place in Sodankylä, Finland, and Weissfluhjoch, Switzerland. Simulations of scattering and absorption coefficients agreed well with observations, with higher errors for snow with predominantly vertical structures. For simulation of brightness temperature, difficulty in retrieving stickiness with the Sticky Hard Sphere microstructure model resulted in relatively poor performance for two experiments, but good agreement for the third. Exponential microstructure gave generally good results, near to the best performing models for two field experiments. The Independent Sphere model gave intermediate results. New Teubner–Strey and Gaussian Random Field models demonstrated the advantages of SMRT over microwave models with restricted microstructural geometry. Relative model performance is assessed by the quality of the microstructure model fit to micro-computed tomography (CT) data and further improvements may be possible with different fitting techniques. Careful consideration of simulation stratigraphy is required in this new era of high-resolution microstructure measurement as layers thinner than the wavelength introduce artificial scattering boundaries not seen by the instrument.

Highlights

  • S microstructure knowledge is essential to determine the scattering properties of snow at microwave frequencies

  • Scaling has been applied to observations of traditional grain size [2] as used in the Helsinki University of Technology (HUT) model [3], [4], exponential correlation length [5] as used in the Microwave Emission Model of Layered Snowpacks (MEMLS) [6], [7], and sticky hard sphere (SHS) [8] as used by models based on Dense Media Radiative Transfer (DMRT) theory [9]

  • Low TB tends to be underestimated and high TB overestimated for Arctic Snow Microstructure Experiment (ASMEx)

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Summary

Introduction

S microstructure knowledge is essential to determine the scattering properties of snow at microwave frequencies. The Snow Microwave Radiative Transfer (SMRT) model has recently been developed in order to examine the impact of the representation of the microstructure, to provide consistent theoretical treatment for passive and active simulations, and as a basis for a community model open to future developments [1]. Many previous simulations of microwave emission and scattering in the snow using inputs from in situ measurements or snowpack evolution model simulations have a common feature: scaling of the microstructure parameters is applied in order to obtain reasonable comparison with observed radiometric data. Stickiness itself is a challenging parameter to quantify [14]

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