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Derivation of near-surface soil moisture from ALOS PALSAR Fine mode (Dual polarization) data in agricultural areas

Christian Koyama(1), Wolfgang Korres(1), Peter Fiener(1) and Karl Schneider(1)

(1) University of Cologne, Albertus-Magnus-Platz, 50923 Cologne, Germany

Abstract

Fluxes of water and energy at the land surface-atmosphere interface are highly dependent on the surface soil water content that varies strongly over time and space. Despite the importance of soil moisture information for a large range of scientific applied tasks, information on the spatio-temporal development is lacking. This is in part due to the fact that model results often deviate significantly from measurements. On the other hand, field measurements are time consuming and cost intensive. They can not provide a spatially continuous coverage and are also subject to measurement errors. Numerous studies have shown the potential of microwave remote sensing to provide spatially distributed patterns of surface soil water contents. Applications such as irrigation planning, flood forecast, soil moisture pattern analysis or SVAT models studies require frequent repetition of soil moisture data and high resolution coverage. Within the Transregional Collaborative Research Centre 32 entitled “Patterns in Soil-Vegetation-Atmosphere Systems: Monitoring, Modelling and Data Assimilation” our group seeks to improve the understanding of spatio-temporal patterns of soil moisture in agricultural landscapes on different spatial scales and to analyse the effects of these patterns on water and carbon fluxes. The research is based on a combination of extensive field measurements, spaceborne microwave remote sensing (ERS-2, ENVISAT, ALOS) and land surface process modelling (PROMET-V). Field measurements are carried out in two test sites within the river Rur catchment, Western Germany. One test site (Rollesbroich, 32 ha) represents a typical grassland within the rolling topography of the Eifel, the other one (Selhausen, 41 ha) represents an intensively used agricultural area. Starting in May 2007 surface soil moisture (0-5 cm) is measured in a 50 m x 50 m grid on days with satellite passes over the test sites using TDR and FDR probes. In addition to the measuring campaigns soil moisture is continuously monitored in three depths (10, 30, 60 cm) at three locations. Meteorological and water flux measurements with an Energy-Flux-Station and an Eddy-Flux-Tower along with laser scanner measurements of surface roughness as well as biomass measurements complement our ground truth data. The paper discusses the measurement concept and first results of spatially distributed field measurements. Furthermore first results of retrieving soil moisture patterns from Daichi PALSAR data using a semi-empirical parameter inversion approach are presented.

 

 

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