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Abstract. The Soil Moisture and Ocean Salinity Mission (SMOS) acquires surface soil moisture data of global coverage every three days. Product validation for a range of climate and environmental conditions across continents is a crucial step. For this purpose, a soil moisture and soil temperature sensor network was established in the Skjern River Catchment, Denmark. The objectives of this article are to describe a method to implement a network suited for SMOS validation, and to present sample data collected by the network to verify the approach. The design phase included (1) selection of a single SMOS pixel (44 × 44 km), which is representative of the land surface conditions of the catchment and with minimal impact from open water (2) arrangement of three network clusters along the precipitation gradient, and (3) distribution of the stations according to respective fractions of classes representing the prevailing environmental conditions. Overall, measured moisture and temperature patterns could be related to the respective land cover and soil conditions. Texture-dependency of the 0-5 cm soil moisture measurements was demonstrated. Regional differences in 0-5 cm soil moisture, temperature and precipitation between the north-east and south-west were found to be small. A first comparison between the 0-5 cm network averages and the SMOS soil moisture (level 2) product is in range with worldwide validation results, showing comparable trends for SMOS retrieved soil moisture (R 2 of 0.49) as well as initial soil moisture and temperature from ECMWF used in the retrieval algorithm (R 2 of 0.67 and 0.97, respectively). While retrieved/initial SMOS soil moisture indicate significant under-/overestimation of the network data (biases of −0.092/0.057 m 3 m −3 ), the initial temperature is in good agreement (bias of −0.2 • C). Based on these findings, the network performs according to expectations and proves to be well-suited for its purpose. The discrepancies between network and SMOS soil moisture will be subject of subsequent studies.

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The Soil Moisture and Ocean Salinity Mission (SMOS) delivers global surface soil moisture fields at high temporal resolution which is of high relevance for water management and climate predictions. For data validation, an airborne campaign with the L-band radiometer EMIRAD-2 and concurrent ground sampling was carried out within one SMOS pixel in the Skjern River Catchment, Denmark. By means of this dataset the objective of this study is a step-wise comparison of brightness temperatures from point via air-to spaceborne (SMOS) scale. From soil moisture samples brightness temperatures were estimated through the L-band Microwave Emission of the Biosphere (L-MEB) model with land-cover specific model settings. A simple uncertainty assessment by means of a set of model runs with parameters varied within a most likely interval resulted in a considerable range of brightness temperatures. Under certain constellations the ground data was in good agreement with EMIRAD. Likewise was the latter in accordance with SMOS data. The comparison of more sophisticated upscaling by means of air-and spaceborne weighting functions and a simple mean showed no significant change. Small temporal variability in soil moisture conditions and RFI-prone SMOS data throughout the campaign limited the extent of the validation work. Further attempts over longer time frames are planned by means of soil moisture network data as well as studies on the impacts of organic layers under natural vegetation and higher open water fractions at surrounding grid nodes.

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Abstract-EMISAR is a high-resolution (2 2 2 2 2 m), fully polarimetric, dual-frequency (L-and C-band) synthetic aperture radar (SAR) system designed for remote-sensing applications. The SAR is operated at high altitudes on a Gulfstream G-3 jet aircraft. The system is very well calibrated and has low sidelobes and low cross-polar contamination. Digital technology has been utilized to realize a flexible and highly stable radar with variable resolution, swath width, and imaging geometry. Thermal control and several calibration loops have been built into the system to ensure system stability and absolute calibration. Accurately measured antenna gains and radiation patterns are included in the calibration. The processing system is developed to support data calibration, which is the key to most of the current applications. Recent interferometric enhancements are important for many scientific applications.

Abstract-The

Abstract-In this paper, the L-band Microwave Emission of the Biosphere (L-MEB) model used in the Soil Moisture and Ocean Salinity (SMOS) Level 2 Soil Moisture algorithm is calibrated using L-band (1.4 GHz) microwave measurements over a coniferous (Pine) and a deciduous (mixed/Beech) forest. This resulted in working values of the main canopy parameters optical depth (τ ), single scattering albedo (ω), and structural parameters tt(H) and tt(V), besides the soil roughness parameters H R and N R . Using these calibrated values in the forward model resulted in a root mean-square error in brightness temperatures from 2.8 to 3.8 K, depending on data set and polarization. Furthermore, the relationship between canopy optical depth and leaf area index is investigated for the deciduous site. Finally, a sensitivity study is conducted for the focus parameters, temperature, soil moisture, and precipitation. The results found in this paper will be integrated in the operational SMOS Level 2 Soil Moisture algorithm and used in future inversions of the L-MEB model, for soil moisture retrievals over heterogeneous, partly forested areas.Index Terms-Forest, L-band, microwave radiometry, soil moisture, Soil Moisture and Ocean Salinity (SMOS).