Verónica González

Fast Processing Tool for SMOS Data

A software package to fully process SMOS data from level 0 up to brightness temperature at antenna plane (level 1B) is described. The raw data downloaded from the payload are converted to correlations and voltages; then to calibrated visibility and antenna temperature; and finally to brightness temperature. Results at different levels are saved in separate files for further post-processing and a visualization tool is provided in order to check the data at various levels, as well as producing brightness temperature maps in the (xi, eta) domain. The software has been developed independently from the official SMOS-mission Level-1 processor but a detailed process of cross-checking of data at all levels is being carried out in order to consolidate the end product of both.

AMIRAS—An Airborne MIRAS Demonstrator

This paper describes AMIRAS, an airborne demonstrator of the Microwave Imaging Radiometer with Aperture Synthesis, which is the instrument onboard ESAs Soil Moisture and Ocean Salinity (SMOS) mission. The main electrical, mechanical, thermal, and control elements of the demonstrator are shown, together with its capabilities and performances as demonstrator of the spaceborne instrument. AMIRAS main tests inside an anechoic chamber, field ground experiments, and its first two maiden flights are reported, and some results of these tests are highlighted. AMIRAS will further be used in some calibration and validation campaigns of the SMOS mission.

Review of the CALIMAS Team Contributions to European Space Agency’s Soil Moisture and Ocean Salinity Mission Calibration and Validation

This work summarizes the activities carried out by the SMOS (Soil Moisture and Ocean Salinity) Barcelona Expert Center (SMOS-BEC) team in conjunction with the CIALE/Universidad de Salamanca team, within the framework of the European Space Agency (ESA) CALIMAS project in preparation for the SMOS mission and during its first year of operation. Under these activities several studies were performed, ranging from Level 1 (calibration and image reconstruction) to Level 4 (land pixel disaggregation techniques, by means of data fusion with higher resolution data from optical/infrared sensors). Validation of SMOS salinity products by means of surface drifters developed ad-hoc, and soil moisture products over the REMEDHUS site (Zamora, Spain) are also presented. Results of other preparatory activities carried out to improve the performance of eventual SMOS follow-on missions are presented, including GNSS-R to infer the sea state correction needed for improved ocean salinity retrievals and land surface parameters. Results from CALIMAS show a satisfactory performance of the MIRAS instrument, the accuracy and efficiency of the algorithms implemented in the ground data processors, and explore the limits of spatial resolution of soil moisture products using data fusion, as well as the feasibility of GNSS-R techniques for sea state determination and soil moisture monitoring.

SMOS' brightness temperatures validation: First results after the commisioning phase

Soil Moisture and Ocean Salinity (SMOS) mission is the second of European Space Agencys (ESA) Living Planet Programme Earth Explorer Opportunity Missions. SMOSs objective is to provide global and frequent Soil Moisture and Sea Surface Salinity maps. The single payload embarked on SMOS is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), it is a 2D interferometric radiometer operating at the protected L-band with a nominal frequency of 1413.5 MHz. Since SMOS is the first 2D interferometric radiometers put in orbit so far, the characterization of the interferometrically measured brightness temperatures is an attractive topic for the scientific community. This study is focused on the estimation of the systematic antenna-based pattern in the measured brightness temperatures. Two improvements to the currently used method (Ocean Target Transformation) are proposed: • The elimination of the use of any forward model in the estimation of the bias. • The homogenization of the geophysical parameters distribution within the SMOS Field of View. Ocean Target Transformation is introduced in section 2, the proposed model-free methodology is described in section 3, while the effect of homogenizing the geophysical parameters distribution inside the FOV is assessed in section 4. The main conclusions are presented in section 5.

Optimum Intercalibration Time in Synthetic Aperture Interferometric Radiometers: Application to SMOS

Interpolation strategies for calibration of the Soil Moisture and Ocean Salinity (SMOS) mission of the European Space Agency are tested and compared. Calibration strategy (how and how often) is critical in achieving the required performance of any instrument, but it is even more important in very complex instruments such as the new family of synthetic aperture interferometric radiometers and, in particular, in the Microwave Imaging Radiometer by Aperture Synthesis instrument aboard the SMOS mission. On one hand, frequent calibration reduces the available observation time. On the other hand, the calibration requirements for soil moisture applications are more relaxed than those for ocean salinity, so the intercalibration time requirements are very different. Since SMOS drifts are stationary, half-orbit information is available to perform different interpolation strategies. In this letter, these approaches are tested to estimate the calibration parameters between consecutive calibrations. The average root-mean-square phase error is then used to find the optimum interpolation strategy and intercalibration time. On the other side, in real-time instruments, the “future” calibration data are not available at the time of taking the measurements, and predictors are required to estimate the evolution of the calibration parameters from past data only. For these systems, the extended Kalman filter can be used. The intercalibration time in a real-time instrument is evaluated, and the requirements and performances are compared to offline instruments.

On-flight characterization of the SMOS payload during the commissioning phase

The SMOS in-orbit commissioning phase will start at launching and will last about 6 months. During this phase an extensive activity will start, particularly aimed at providing full confidence on the products that the mission will produce during its operational phase. As part of this activity, the payload MIRAS will be fully characterized using specific orbits dedicated to check all instrument modes. First, the procedures carried out during the on-ground characterization will be repeated so as to obtain a realistic temperature characterization and updated internal calibration. Additionally, a new concept of external calibration, consisting of periodic sky looks, will be tested providing the first-ever absolute instrument calibration parameters. Finally, the imaging capability of the instrument both in dual polarization and full polarimetric will be assessed using images of the Earth surface and the Galaxy. As a final result, the higher level overall performance parameters, such as stability, radiometric sensitivity, radiometric accuracy and absolute accuracy will be evaluated.

MIRAS ground characterization

On-ground characterization of the complete microwave imaging radiometer with aperture synthesis (MIRAS), successfully manufactured by EADS-CASA Espacio, is briefly described. The characterization includes (a) Basic functionality tests and internal calibration assessment carried out at the manufacturer premises, (b) Operation under extreme thermal conditions at the ESApsilas Large Space Simulator and (c) Image validation tests at the ESApsilas Maxwell anechoic chamber including also response to point sources. Description of the different tests carried out and detailed results of the instrument characterization including graphics of the different parameters retrieved and images of the empty chamber are provided.