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Comparison of observed and simulated microwave land surface emissivities over bare soil

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In this paper we evaluate data obtained during the VALEM (Validation of Land Surface Emissivity Models) experiment, which took place in September 1998 near Ludwigslust in north-eastern Germany.

The emphasis of the eld campaign was to generate datasets to validate land surface emissivity models in the microwave spectral range. We describe the approach to derive land surface emissivities from the observed data and compare observed and simulated land surface emissivities in order to further validate the Free University of Berlin's newly developed microwave emissivity model. This model explicitly accounts for any given type of structured surfaces by splitting the surface into large-scale facets and a small-scale surface roughness. A model description can be found in previous work (PAAPE et al., 2000) so that in the current paper we only present a brief overview on the model structure and concentrate on its validation at frequency ranges between 24 and 157 GHz.

The range of variability of the observed surface emissivity is about 18% (0.80-0.98) for the different frequencies and test sites. Comparing simulated and observed nadir emissivities we find deviations between 0.9% and 2.5% dependent on frequency. The deviations are in the range of uncertainty introduced by the various input parameters into the emissivity model. Comparing model results with radiometer observations at different incidence angles, we nd that the model realistically resembles the variation of the surface emissivity with zenith angle at different frequencies.

In diesem Artikel zeigen wir Ergebnisse der Validierung des Modells der Freien Universität Berlin zur Beschreibung des Emissionsvermögens von Landoberächen im Mikrowellenbereich. Wir werten hierzu Daten aus, die während des VALEM-Experiments gemessen wurden. Dieses Experiment fand im September 1998 nahe Ludwigslust statt.

Das Bodenemissionsmodell erlaubt es, das Emissionsvermögen beliebig strukturierter Oberächen zu simulieren, indem frequenzabhängig zwischen großskaligen und kleinskaligen Rauhigkeiten unterschieden wird. Eine Modellbeschreibung wurde bereits zuvor in PAAPE et al. (2000) veröffentlicht, so dass das Hauptaugenmerk im vorliegenden Artikel auf die Validierung des Modells im Frequenzbereich zwischen 24 und 157 GHz gelegt wird.

Der Schwankungsbereich des gemessenen Emissionsvermögens beträgt circa 18% (0,80-0,98) abhängig von Frequenz und Testgebiet. Der Vergleich des simulierten und gemessenen Emissionsvermögens von brachen Böden zeigt Abweichungen im Bereich zwischen 0,9% bis maximal 2,5% in Abhängigkeit von der Messfrequenz. Die gefundenen Abweichungen sind im Bereich der Ungenauigkeit, die durch die zahlreichen Eingangsdaten für das Modell zu erwarten ist. Sowohl die Frequenzabhängigkeit als auch die Abhängigkeit des Emissionsvermögens vom Beobachterzenitwinkel werden vom Modell gut wiedergegeben.
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Document Type: Research Article

Publication date: 01 January 2002

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  • Meteorologische Zeitschrift (originally founded in 1866) is the joint periodical of the meteorological societies of Austria, Germany and Switzerland. It accepts high-quality peer-reviewed manuscripts on all aspects of observational, theoretical and computational research out of the entire field of meteorology, including climatology. Meteorologische Zeitschrift represents a natural forum for the meteorological community of Central Europe and worldwide.
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