Evaluation of Wet Snow Dielectric Mixing Models for L-Band Radiometric Measurement of Liquid Water Content in Greenland Percolation Zone

Determining the effective permittivity of wet snow is essential for accurate estimation of liquid water (LWA) in snow and firn. Here, we compare ten commonly used microwave dielectric mixing models for estimating LWA in snow and firn using L-band radiometry. We specifically focus on the Greenland Percolation Zone, where the average volume fraction of liquid water is within about 6%. We used L-band brightness temperature (TB) observations from the NASA Soil Moisture Active Passive (SMAP) mission in an inversion-based framework to estimate LWA, applying different dielectric mixing formulations in forward simulation. We compared the permittivities of the mixing models over a range of conditions and their impact on the LWA retrieval. We also compared the LWA retrievals to the corresponding LWA from two state-of-the-art Surface Energy and Mass Balance (SEMB) models. Both SEMB models were forced with in situ measurements from automatic weather stations (AWS) of the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) and Greenland Climate Network (GC-Net) located in the percolation zone of the GrIS and initialized with relevant in situ profiles of density, snow and firn stratigraphy, and the sub-surface temperature measurements. The results showed that the mixing models produce substantially different real and imaginary parts of the dielectric constant. The choice of mixing models had a significant impact on the LWA retrieved from SMAP TB. The correspondence with the SEMB LWA varied by model and site. The analysis facilitates an appropriate choice of dielectric mixing model on the LWA retrieval algorithm.