Secondary Payloads Science Assessment

Scientia Marina, 2012

Capability for sea surface salinity observation was an important gap in ocean remote sensing in the last few decades of the 20th century. New technological developments during the 1990s at the European Space Agency led to the proposal of SMOS (Soil Moisture and Ocean Salinity), an Earth explorer opportunity mission based on the use of a microwave interferometric radiometer, MIRAS (Microwave Imaging Radiometer with Aperture Synthesis). SMOS, the first satellite ever addressing the observation of ocean salinity from space, was successfully launched in November 2009. The determination of salinity from the MIRAS radiometric measurements at 1.4 GHz is a complex procedure that requires high performance from the instrument and accurate modelling of several physical processes that impact on the microwave emission of the ocean’s surface. This paper introduces SMOS in the ocean remote sensing context, and summarizes the MIRAS principles of operation and the SMOS salinity retrieval approach. It describes the Spanish SMOS high-level data processing centre (CP34) and the SMOS Barcelona Expert Centre on Radiometric Calibration and Ocean Salinity (SMOS-BEC), and presents a preliminary validation of global sea surface salinity maps operationally produced by CP34

2016

The first three of a series of new generation satellites operating at L-band microwave frequencies have been launch in the last decade. L-band is particularly sensitive to the presence of water content in the scene under observation, being considered the optimal bandwidth for measuring the Earth's global surface soil moisture (SM) over land and sea surface salinity (SSS) over oceans. Monitoring these two essential climate variables is needed to further improve our understanding of the Earth's water and energy cycles. Additionally, remote sensing at L-band has been proved useful for monitoring the stability in ice sheets and measuring sea ice thickness. The ESA's Soil Moisture and Ocean Salinity (SMOS, 2009-2017) is the first mission specifically launched to monitor SM and SSS. It carries on-board a novel synthetic aperture radiometer with multi-angular and full-polarization capabilities. NASA's Aquarius (2011-2015) was the second mission, devoted to SSS monitoring wi...

2013

Sensors

The "Cooperative Airborne Radiometer for Ocean and Land Studies" (CAROLS) L-Band radiometer was designed and built as a copy of the EMIRAD II

IEEE Transactions on Geoscience and Remote Sensing, 2000

We examine how the rough sea surface scattering 5 of L-band celestial sky radiation might affect the measurements 6 of the future European Space Agency Soil Moisture and Ocean 7 Salinity (SMOS) mission. For this purpose, we combined data 8 from several surveys to build a comprehensive all-sky L-band 9 celestial sky brightness temperature map for the SMOS mission 10 that includes the continuum radiation and the hydrogen line 11 emission rescaled for the SMOS bandwidth. We also constructed a 12 separate map of strong and very localized sources that may exhibit 13 L-band brightness temperatures exceeding 1000 K. Scattering by 14 the roughened ocean surface of radiation from even the strongest 15 localized sources is found to reduce the contributions from these 16 localized strong sources to negligible levels, and rough surface 17 scattering solutions may be obtained with a map much coarser 18 than the original continuum maps. In rough ocean surface condi-19 tions, the contribution of the scattered celestial noise to the recon-20 structed brightness temperatures is not significantly modified by 21 the synthetic antenna weighting function, which makes integration 22 over the synthetic beam unnecessary. The contamination of the 23 reconstructed brightness temperatures by celestial noise exhibits 24 a strong annual cycle with the largest contamination occurring 25 in the descending swaths in September and October, when the 26 specular projection of the field of view is aligned with the galactic 27 equator. Ocean surface roughness may alter the contamination by 28 over 0.1 K in 30% of the SMOS measurements. Given this poten-29 tially large impact of surface roughness, an operational method is 30 proposed to account for it in the SMOS level 2 sea surface salinity 31 algorithm. 32 Index Terms-Microwave radiometry, sea surface electromag-33 netic scattering.

… and Remote Sensing …, 2004

Soil Moisture and Ocean Salinity (SMOS) is an Earth Explorer Opportunity Mission from the European Space Agency with a launch date in 2007. Its goal is to produce global maps of soil moisture and ocean salinity variables for climatic studies using a new dual-polarization L-band (1400-1427 MHz) radiometer Microwave Imaging Radiometer by Aperture Synthesis (MIRAS). SMOS will have multiangular observation capability and can be optionally operated in full-polarimetric mode. At this frequency the sensitivity of the brightness temperature () to the sea surface salinity (SSS) is low: 0.5 K/psu for a sea surface temperature (SST) of 20 C, decreasing to 0.25 K/psu for a SST of 0 C. Since other variables than SSS influence the signal (sea surface temperature, surface roughness and foam), the accuracy of the SSS measurement will degrade unless these effects are properly accounted for. The main objective of the ESA-sponsored Wind and Salinity Experiment (WISE) field experiments has been the improvement of our understanding of the sea state effects on at different incidence angles and polarizations. This understanding will help to develop and improve sea surface emissivity models to be used in the SMOS SSS retrieval algorithms. This paper summarizes the main results of the WISE field experiments on sea surface emissivity at L-band and its application to a performance study of multiangular sea surface salinity retrieval algorithms. The processing of the data reveals a sensitivity of to wind speed extrapolated at nadir of 0.

IEEE Transactions on Geoscience and Remote Sensing, 2008

We examine how the rough sea surface scattering 5 of L-band celestial sky radiation might affect the measurements 6 of the future European Space Agency Soil Moisture and Ocean 7 Salinity (SMOS) mission. For this purpose, we combined data 8 from several surveys to build a comprehensive all-sky L-band 9 celestial sky brightness temperature map for the SMOS mission 10 that includes the continuum radiation and the hydrogen line 11 emission rescaled for the SMOS bandwidth. We also constructed a 12 separate map of strong and very localized sources that may exhibit 13 L-band brightness temperatures exceeding 1000 K. Scattering by 14 the roughened ocean surface of radiation from even the strongest 15 localized sources is found to reduce the contributions from these 16 localized strong sources to negligible levels, and rough surface 17 scattering solutions may be obtained with a map much coarser 18 than the original continuum maps. In rough ocean surface condi-19 tions, the contribution of the scattered celestial noise to the recon-20 structed brightness temperatures is not significantly modified by 21 the synthetic antenna weighting function, which makes integration 22 over the synthetic beam unnecessary. The contamination of the 23 reconstructed brightness temperatures by celestial noise exhibits 24 a strong annual cycle with the largest contamination occurring 25 in the descending swaths in September and October, when the 26 specular projection of the field of view is aligned with the galactic 27 equator. Ocean surface roughness may alter the contamination by 28 over 0.1 K in 30% of the SMOS measurements. Given this poten-29 tially large impact of surface roughness, an operational method is 30 proposed to account for it in the SMOS level 2 sea surface salinity 31 algorithm. 32 Index Terms-Microwave radiometry, sea surface electromag-33 netic scattering. 34 I. INTRODUCTION 35 C ELESTIAL sky L-band radiation scattered by the ocean 36 surface can contaminate spaceborne measurements of up-37 welling sea surface brightness temperature used to retrieve sea 38 surface salinity (SSS). The sensitivity of the linearly polarized 39 sea surface brightness temperature to salinity ranges from about 40 0.2 to 0.8 K/psu [1] (depending on ocean surface temperature, 41 incidence angle, and polarization). Since the open ocean surface 42

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2013

The Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) on-board the Soil Moisture and Ocean Salinity (SMOS) mission is providing useful data since November 2009, and proving the potential of 2D interferometry from space. With the end of its nominal operation phase in November 2012, the mission is expected to extend its lifetime for at least more than two additional years. Along with all the current improvements on data processing and exploitation, the SMOS trail might need to be continued with the aim of providing data to the users in the coming years. This paper presents a SMOS follow-on operational mission which is the result of integrating the actual lessons learnt from MIRAS with a novel hexagonal array geometry, proving robustness against radio-frequency interferences (RFI) and receiver failures. The performance and the instrument architecture enhancements are exposed, along with a practical deployment solution.

It is now well understood that soil moisture and sea surface s alinity are required to improve meteorological and climatic predictions. These two quantities are not yet available globally and with an adequate temporal sampling. So as to cover this data gap, it has been recognized that, provided it is possible to accommodate a suitable antenna on board a satellite, L Band radiometry was most probably the most promising way to fulfill this gap. It is within this framework that the European Space Agency (ESA)'s selected the second Earth Explorer Opportunity Mission, namely the Soil Moisture and Ocean Salinity (SMOS) mission. The SMOS mission a joint program lead by ESA with the CNES in France and the CDTI in Spain. SMOS carries a single payload, an L band 2D interferometric radiometer in the 1400-1427 MHz protected band. This wavelength penetrates well through the vegetation and the atmosphere is almost transparent. Consequently, the instrument probe s the Earth surface emissivity...

Proceedings of the IEEE, 2000

| Soil Moisture and Ocean Salinity, European Space Agency, is the first satellite mission addressing the challenge of measuring sea surface salinity from space. It uses an L-band microwave interferometric radiometer with aperture synthesis (MIRAS) that generates brightness temperature images, from which both geophysical variables are computed. The retrieval of salinity requires very demanding performances of the instrument in terms of calibration and stability. This paper highlights the importance of ocean salinity for the Earth's water cycle and climate; provides a detailed description of the MIRAS instrument, its principles of operation, calibration, and imagereconstruction techniques; and presents the algorithmic approach implemented for the retrieval of salinity from MIRAS observations, as well as the expected accuracy of the obtained results.