Comparison of snow emission models HUT and MEMLS

Measurements of physical parameters (Table 2) were used in both the single layer HUT snow emission model and MEMLS, to produce brightness temperature simulations of all 13 dry slabs, upon absorbing and reflecting bases. The simulations were compared to the observed brightness temperature, and the RMSE was calculated at both horizontal and vertical polarization, on both the absorbing and reflective bases (Figure 5).

Upon the absorbing base, HUT performs equal to or better than MEMLS at 18.7, 21.0, and 36.5 GHz, while performing equal to or worse than MEMLS on the reflecting plate at the same frequencies. At the higher frequencies (89.0 and 150.0 GHz), with the exception of the horizontal absorbing case, HUT is routinely less accurate than MEMLS. These large errors in HUT may be explained due to the extinction coefficient used only being valid between 18-60 GHz (Pulliainen et al., 1999). The scattering coefficients used in MEMLS are valid between 5-100 GHz (Wiesmann & Mätzler, 1998), thus explaining why the RMSE values are consistent across the four situations shown in Figure 5.

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Figure 4. a) SMP measurements, b) In situ density measurement, c) IceCube

instrument for SSA measurement, d) In situ temperature measurement

4. CONCLUSION

The brightness temperature of homogeneous snow slabs extracted from the natural snowpack during ASMEx has been simulated with both the HUT snow emission model, and MEMLS.

The HUT simulations had a lower RMSE value than MEMLS for the three lower frequencies measured; on top of the absorbing base. MEMLS simulations had lower errors associated with them for the reflective base cases. Errors at the two higher frequencies can begin to be explained by being outside the operational frequency range of the two models.

The errors in the lower three frequencies exist due to unaccounted internal scattering within the snow. These errors will be reduced in the future, via an improved understanding of internal scattering, and a revised extinction coefficient model. This revised extinction model will be calculated from microstructure information (from both modern and traditional methods) as well as radiometric data collected during ASMEx. The revised model for extinction will be implemented in the HUT snow emission model, and will aim to improve the current SWE estimations from model inversions with satellite observations.

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Figure 5. Brightness temperature RMSE at H and V polarizations for absorber material base (ABS) and reflective metal plate base (REF) for HUT model and MEMLS simulations.

AKNOWLEDGEMENT

We thank the staff of FMI Arctic Research Centre in Sodankylä for performing the ground-based radiometer measurements and in situ measurements. We also thank the staff of WSL Institute of Snow and Avalanche Research SLF from SMP instrument and becoming micro-CT analyses of snow samples. We thank especially Dr. Juha Lemmetyinen, Dr. Mel Sandells and Dr. Martin Schneebeli of planning and fulfillment the project.

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Measurement of snowmelt in a subarctic site using low