Publications (6)3.51 Total impact
Article: SMOS Payload In-Orbit Performance[Show abstract] [Hide abstract]
ABSTRACT: SMOS is ESA's second Earth Explorer mission with the objective of producing global maps of Soil Moisture and Ocean Salinity over the Earth. It carries a single payload on-board, MIRAS, the first-ever spaceborne L-band Microwave Imaging Radiometer with Aperture Synthesis in two dimensions. The performance requirements of MIRAS are demanding in terms of spatial resolution, accuracy, stability and precision, all critical to fulfil its scientific objectives. SMOS was launched 2 November 2009. Following its launch, a six month commissioning phase started consisting of four phases. The first 2.5 weeks were devoted to the Launch and Early Operation Phase (LEOP) where the commissioning of PROTEUS, the service module, was carried out. After this phase came 4.5 weeks of Switch-On and Data Acquisition Phase (SODAP), where the satellite-ground links and the ground segment in charge of the mission control, commanding and data processing, were brought up into full operation. This subsequent period, which is the current phase in January 2010 and the subject of this presentation, consists of 6 weeks of Payload Commissioning, which will be followed by 13.5 weeks of a Pseudo-operational phase which will precede the operational one. Within the five Payload Commissioning weeks, several activities are dedicated to verify that the payload is in good working conditions and to characterise its performance. The first week is dedicated to test the thermal and electrical stability of the instrument and to acquire the Flat Target Response of the instrument. All physical temperatures of the instrument were expected and later verified to be within a range of 6°C peak to peak around a set point temperature of 22°C. During the electrical stability, internal calibration signals are injected and several instrument parameters are derived such as the gain, offset and equivalent noise temperature of all receivers of MIRAS. The calibration signals are first referenced to two standards, one being a matched load at a known physical temperature, the other being the cosmic microwave background radiation near the poles of our galaxy. The measurement of the latter target, the Flat Target Response, is the aim of the external calibration. The second week is dedicated to study the calibration of the phase of the local oscillator (LO). This is necessary because the 12 different LO circuits (one per arm segment plus three in the hub) follow slightly different thermally-driven phase histories. The third week is dedicated to an early test of the full-pol mode of the instrument, which up to this point has been operating largely in dual-pol. The last two weeks are devoted to consolidate the LO calibration and to perform several external calibrations to test different issues, such as possible electromagnetic contamination from the S and X-band transmitters, the star tracker or the solar array driving mechanism. This presentation will include some of the most relevant results from the 5 weeks of Payload Commissioning.
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ABSTRACT: The purpose of the Soil Moisture and Ocean Salinity (SMOS) mission is to measure soil moisture and sea surface salinity (SSS). The measurement of SSS using microwave radiometry requires a very sensitive instrument. In SMOS, the image is formed using the interferometric technique complemented by the average brightness temperature, or zero baseline, to set the absolute level of the image. Therefore, the measurement of the zero baseline is very critical for the success of the mission. In this paper, the radiometric resolution and stability of the radiometers dedicated to the measurement of zero baseline on SMOS are estimated. The results of a measurement campaign carried out in an anechoic electromagnetic compatibility chamber are used. The results show that the zero-baseline radiometers have the potential for relative accuracy better than 20 mK, depending on the integration scenario, satisfying the mission requirement for SSS retrieval.IEEE Transactions on Geoscience and Remote Sensing 04/2010; 48(3-48):1389 - 1397. DOI:10.1109/TGRS.2009.2031102 · 3.51 Impact Factor
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ABSTRACT: The sensitivity of a radiometer to the brightness temperature variations of the target is one of the critical parameters of any radiometric measurement. The sensitivity is limited by the noise in the measurement and the stability of the instrument. In this study measurements in an anechoic chamber are used to evaluate the sensitivity limit of radiometers, which are the noise injection radiometers of European Space Agency's SMOS (Soil Moisture Ocean Salinity) satellite. The sensitivity is especially important for the measurement of sea surface salinity (SSS), one of the retrieval objectives of SMOS. The methods used include comparisons of the measurements to the physical temperature estimation of the chamber, both in relative and absolute sense, and comparison of different radiometer channels with each other. The analysis demonstrates the reliability of the methods in consistency of both brightness temperature values and physical temperature measurements. Finally, the results show that the noise injection radiometers satisfy the measurement requirement for SSS retrieval.Geoscience and Remote Sensing Symposium,2009 IEEE International,IGARSS 2009; 08/2009
Article: SMOS Payload Pre-Launch Performance[Show abstract] [Hide abstract]
ABSTRACT: SMOS is ESA's second Earth Explorer mission with the objective of producing global maps of Soil Moisture and Ocean Salinity over the Earth. It will fly a single payload, MIRAS, the first-ever spaceborne L-band Microwave Imaging Radiometer with Aperture Synthesis in two dimensions. The performance requirements of MIRAS are demanding in terms of spatial resolution, accuracy, stability and precision, all critical to fulfil its scientific objectives. During the ground test campaigns both at payload and satellite levels the performance of the instrument was checked against the original system requirements. The verification of the requirements, written in terms of brightness temperatures (Level-1 data), included some image processing of the raw correlations (Level-0 data) acquired inside an empty anechoic chamber. All requirements are satisfied with some margin. This presentation will include a description of the Level-1 performances to be met by SMOS, the measurement configurations and methods with which they were verified, and the final results. The Level-1 instrument performance, given mostly at snapshot level for a 50 km spatial resolution, is then propagated to the equivalent accuracy in the Level-2 geophysical parameters, soil moisture and sea surface salinity, assuming one full overpass and simplified models.
Conference Paper: MIRAS-SMOS antenna relative phase calibration[Show abstract] [Hide abstract]
ABSTRACT: SMOS is the acronym of dasiaSoil Moisture and Ocean Salinitypsila and it refers to a European Space Agency (ESA) mission aimed at providing global maps of soil moisture over land and sea surface salinity over oceans. The mission has a single payload, the Microwave Imaging Radiometer with Aperture Synthesis (MIRAS), which is an L-band radiometer using an interferometric technique to synthesize high resolution beams. It is formed by 69 antennas evenly distributed on a Y-shaped mechanical structure. The instrument was manufactured by EADS-CASA Espacio (ES) and was delivered to ESA for testing in May 2007. The payload is now integrated with the platform and ready for launching in November 2008.Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE; 08/2008
Conference Paper: MIRAS imaging validation[Show abstract] [Hide abstract]
ABSTRACT: A reduced Y-shape interferometric radiometer has been used to simulate the performance of MIRAS, the single payload of the ESA SMOS mission. The hardware has been designed according to initial MIRAS specifications using first versions of antennas, L-band receivers, digital correlators and calibration subsystems. A complete set of experiments to assess basic operation, calibration methods and instrument performance has been successfully carried out and is described in this paper.Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International; 08/2003