The Soil Moisture and Ocean Salinity (SMOS) mission, launched in November 2009, is the European Space Agency's (ESA) second Earth Explorer Opportunity mission. The scientific objectives of the SMOS mission directly respond to the need for global observations of soil moisture and ocean salinity, two key variables used in predictive hydrological, oceanographic and atmospheric models. SMOS observations also provide information on vegetation, in particular plant available water and water content in a canopy, drought index and flood risks, surface ocean winds in storms, freeze/thaw state and sea ice and its effect on ocean-atmosphere heat fluxes and dynamics affecting large-scale processes of the Earth's climate system.Significant progress has been made over the course of the now 6-year life time of the SMOS mission in improving the ESA provided level 1 brightness temperature and level 2 soil moisture and sea surface salinity data products. The main emphasis of this paper is to review the status of the mission and provide an overview and performance assessment of SMOS data products, in particular with a view towards operational applications, and using SMOS products in data assimilation.Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.SMOS is in excellent technical condition with no limiting factors for operations beyond 2017. The instrument performance fulfils the requirements. The radio-frequency interference (RFI) contamination originates from man-made emitters on ground, operating in the protected L-band and adding signal to the natural radiation emitted by the Earth. RFI has been detected worldwide and has been significantly reduced in Europe and the Americas but remains a constraint in Asia and the Middle East. The mission's scientific objectives have been reached over land and are approaching the mission objectives over ocean.This review paper aims to provide an introduction and synthesis to the papers published in this RSE special issue on SMOS. Highlights► SMOS is in excellent technical conditions. ► No technical limits exist to operate the mission beyond 2017. ► New data products for operational users have been included in the SMOS portfolio. ► SMOS data are already used in data assimilation and operational forecasting systems. ► SMOS observed interannual changes have great potential for climate research.
The SMOS Satellite was launched on 2nd November 2009, being the second Earth Explorer Mission of the European Space Agency. The SMOS Payload is a single instrument, the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS), which is basically composed of 69 antennas distributed in a Y-shape configuration (3 deployable Arms with 3 individual Segments each plus a central body which is called Hub).To ensure the proper operation of the Payload, specific thermal requirements were set for the receivers of the 69 antennas in order to guarantee the validity of the scientific data. In particular, the target temperature of the receivers is 22°C with a maximum spatial gradient of 6°C among all of them and a maximum orbital excursion of 4°C. The SMOS Payload Thermal Control Subsystem (TCS) is based on a passive design supported by heaters. The TCS, as well as the rest of the Payload design, has a distributed architecture. The central computer of the Payload controls in closed loop remotely distributed units (12 in total) named Control and Monitoring Node (CMN) units. Each CMN unit acquires the telemetry of the temperature sensors (6 per heater line) for the heater control lines distributed in the Arms and in the Hub. The Thermal Control is enabled during all payload operational modes including measurement and calibration.We present in this paper some features of the TCS observed during more than four years in orbit: fulfillment of target temperature requirements, seasonal effects, anomalies seen in-flight and recovery from failure states. In particular, a failure due to an anomalous temperature reading in one of the CMN units that happened in flight and produced an abnormal heating in one of the Arm Segments is analyzed in detail. This failure may eventually lead to the in-operability of the Payload. However, it is shown that it is possible to implement an "Alternative Thermal Control" for one sector of the instrument. The Alternative Thermal Control produces only minimal changes for the thermal control of the Segment and it is acceptable for the quality of the scientific data.
The SMOS Payload is a single instrument, the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS), which was built by EADS-CASA Espacio. MIRAS consists in a passive microwave (L-Band) 2D-interferometer with a Y-shaped 3 arms synthetic aperture antenna. Since PLM switch-on in November 2009, several anomalies have taken place which in some cases put constraints on the availability of the instrument. We present here a brief description of the instrument and of the reported anomalies, and which measures have been taken to reduce their impact on the mission. We also present unavailability figures, showing that the operational measures that were taken have been successful to bring the unavailability time down to a minimum.
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