Loew, A.

Mauser, W.

Muerth, M.

Schlenz, F.

MPG.PuRe

Geophysical Research AbstractsVol. 12, EGU2010-14320, 2010EGU General Assembly 2010© Author(s) 2010Coupled simulation of soil energy and water content to compare dielectricbehaviour with TDR measurements in frozen soilMarkus Muerth (1), Florian Schlenz (1), Alexander Loew (2), and Wolfram Mauser (1)(1) Department of Geography, University of Munich (LMU), Luisenstraße 37, 80333 Munich(m.muerth@iggf.geo.uni-muenchen.de), (2) Max-Planck-Institut of Meteorology, Bundesstraße 53, 20146 Hamburg, GermanyIn the field of soil moisture monitoring both, on-site time domain reflectometry (TDR) methods and microwaveremote sensing, measure the actual soil water content via the dielectric behavior of the soil-water-air mixture.Basically, the dielectric behavior is not only influenced by soil water content, but also by temperature, soil icecontent, soil texture and porosity. However, many TDR and microwave techniques relate soil water content directlyto soil dielectric behavior, because they lack the ability to determine the other relevant soil properties directly. Theadvantage of the combination of modeling and monitoring techniques for soil moisture monitoring is the abilityto understand and compare spatial and temporal patterns, especially if other land surface properties influence theretrieved soil moisture signal. In this case, the hydrological land surface model PROMET (Processes of Mass,Energy and Radiation Transfer) is combined with TDR probe measurements taken at multiple sites and multipledepths during the winter 2008/2009 in south-eastern Germany. The harsh conditions, especially during January andFebruary 2009 led to low measured liquid water contents in the upper 20 cm of the investigated soils, although thetotal water content remained nearly constant over time. Additionally, soil temperature and meteorological driverswere measured at nearby agrometeorological stations. Because PROMET has shown to simulate moisture contentof non-frozen soils well, compared to TDR probe and remote sensing data, we investigate its ability to simulatefrozen soil water content, when enhanced with an energy balance driven soil temperature module. Furthermore, asemi-empirical dielectric mixing model is implemented to directly compare the simulated soil dielectric behaviorwith the available TDR probe time series.It is shown that the explicit computation of the soil surface energy balance coupled with a physically based soiltemperature model is able to simulate the freeze-thaw cycles within the top soil layers and may significantlyenhance the prediction of the liquid soil water content compared to the available measurements. However, ourstudy also shows, that the calculated dielectric behavior derived from simulated temperature and moisture withthe dielectric mixing model does not compare well with the dielectricity values of the TDR time series. In fact,the range of potential dielectricity values of the two mixing models used for moisture calculation from TDR dataand for the computation of dielectric behavior from model outputs respectively strongly differs. This indicatesthat the dielectric properties measured with TDR probes may not be adequate to validate a land surface modelthat computes soil dielectric behavior from temperature and moisture, although such models could be useful forinter-comparison with or assimilation of remote sensing data to better predict spatially explicit soil moisture fields.

Coupled simulation of soil energy and water content to compare dielectric behaviour with TDR measurements in frozen soil

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