Remote Sensing of Sea Surface Salinity: Comparison of Satellite and In Situ Observations and Impact of Retrieval Parameters

Since 2009, three low frequency microwave sensors have been launched into space with the capability of global monitoring of sea surface salinity (SSS). The European Space Agency’s (ESA’s) Microwave Imaging Radiometer using Aperture Synthesis (MIRAS), onboard the Soil Moisture and Ocean Salinity mission (SMOS), and National Aeronautics and Space Administration’s (NASA’s) Aquarius and Soil Moisture Active Passive mission (SMAP) use L-band radiometry to measure SSS. There are notable differences in the instrumental approaches, as well as in the retrieval algorithms. We compare the salinity retrieved from these three spaceborne sensors to in situ observations from the Argo network of drifting floats, and we analyze some possible causes for the differences. We present comparisons of the long-term global spatial distribution, the temporal variability for a set of regions of interest and statistical distributions. We analyze some of the possible causes for the differences between the various satellite SSS products by reprocessing the retrievals from Aquarius brightness temperatures changing the model for the sea water dielectric constant and the ancillary product for the sea surface temperature. We quantify the impact of these changes on the differences in SSS between Aquarius and SMOS. We also identify the impact of the corrections for atmospheric effects recently modified in the Aquarius SSS retrievals. All three satellites exhibit SSS errors with a strong dependence on sea surface temperature, but this dependence varies significantly with the sensor. We show that these differences are first and foremost due to the dielectric constant model, then to atmospheric corrections and to a lesser extent to the ancillary product of the sea surface temperature.

[1]  David M. Le Vine,et al.  Status of Aquarius and Salinity Continuity , 2018, Remote. Sens..

[2]  J. Boutin,et al.  New SMOS Sea Surface Salinity with reduced systematic errors and improved variability , 2018, Remote Sensing of Environment.

[3]  David M. Le Vine,et al.  The Salinity Retrieval Algorithms for the NASA Aquarius Version 5 and SMAP Version 3 Releases , 2018, Remote. Sens..

[4]  E. Guilyardi,et al.  Northward Pathway Across the Tropical North Pacific Ocean Revealed by Surface Salinity: How do El Niño Anomalies Reach Hawaii? , 2018 .

[5]  Emmanuel P. Dinnat,et al.  L-Band Model Function of the Dielectric Constant of Seawater , 2017, IEEE Transactions on Geoscience and Remote Sensing.

[6]  J. Comiso,et al.  Satellite Observed Salinity Distributions at High Latitudes in the Northern Hemisphere: A Comparison of Four Products. , 2017, Journal of geophysical research. Oceans.

[7]  Jinzheng Peng,et al.  Soil Moisture Active/Passive L-Band Microwave Radiometer Postlaunch Calibration , 2017, IEEE Transactions on Geoscience and Remote Sensing.

[8]  Joaquim Ballabrera-Poy,et al.  Debiased non-Bayesian retrieval: A novel approach to SMOS Sea Surface Salinity , 2017 .

[9]  Emmanuel P. Dinnat,et al.  Improved Sea Ice Fraction Characterization for L-Band Observations by the Aquarius Radiometers , 2017, IEEE Transactions on Geoscience and Remote Sensing.

[10]  Tong Lee,et al.  Satellite and In Situ Salinity: Understanding Near-Surface Stratification and Subfootprint Variability , 2016 .

[11]  Thomas Meissner,et al.  Sensitivity of Ocean Surface Salinity Measurements From Spaceborne L-Band Radiometers to Ancillary Sea Surface Temperature , 2016, IEEE Transactions on Geoscience and Remote Sensing.

[12]  Jacqueline Boutin,et al.  Mitigation of systematic errors in SMOS sea surface salinity , 2016 .

[13]  R. Lang,et al.  Accurate measurements of the dielectric constant of seawater at L band , 2016 .

[14]  David M. Le Vine,et al.  Aquarius L-band Radiometers Calibration Using Cold Sky Observations , 2015, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[15]  Thomas Meissner,et al.  Atmospheric absorption model for dry air and water vapor at microwave frequencies below 100 GHz derived from spaceborne radiometer observations , 2015 .

[16]  Liang Hong,et al.  Aquarius L-Band Microwave Radiometer: 3 Years of Radiometric Performance and Systematic Effects , 2015, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[17]  David M. Le Vine,et al.  Status of Aquarius/SAC-D and Aquarius Salinity Retrievals , 2015, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[18]  J. Boutin,et al.  Inter-Comparison of Aquarius and SMOS Calibration and Impact on Sea Surface Salinity Products , 2014 .

[19]  Jacqueline Boutin,et al.  SMOS salinity in the subtropical North Atlantic salinity maximum: 1. Comparison with Aquarius and in situ salinity , 2014 .

[20]  Thomas Meissner,et al.  The emission and scattering of L‐band microwave radiation from rough ocean surfaces and wind speed measurements from the Aquarius sensor , 2014 .

[21]  Wenqing Tang,et al.  Aquarius geophysical model function and combined active passive algorithm for ocean surface salinity and wind retrieval , 2014 .

[22]  Adriano Camps,et al.  SMOS and Aquarius Radiometers: Inter-Comparison Over Selected Targets , 2014, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[23]  Matthias Drusch,et al.  Snow thickness retrieval over thick Arctic sea ice using SMOS satellite data , 2013 .

[24]  Matthias Drusch,et al.  SMOS-derived thin sea ice thickness: algorithm baseline, product specifications and initial verification , 2013 .

[25]  Vardis Tsontos,et al.  Aquarius and SMOS detect effects of an extreme Mississippi River flooding event in the Gulf of Mexico , 2013 .

[26]  Wenqing Tang,et al.  The rain effect on Aquarius' L-band sea surface brightness temperature and radar backscatter , 2013 .

[27]  Jacqueline Boutin,et al.  Biases Between Measured and Simulated SMOS Brightness Temperatures Over Ocean: Influence of Sun , 2013, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[28]  Manuel Martín-Neira,et al.  SMOS instrument performance and calibration after 6 years in orbit , 2013, 2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS).

[29]  Bertrand Chapron,et al.  Haline hurricane wake in the Amazon/Orinoco plume: AQUARIUS/SACD and SMOS observations , 2012 .

[30]  Naoto Ebuchi,et al.  Evaluation of sea surface salinity observed by Aquarius and SMOS , 2012, 2013 IEEE International Geoscience and Remote Sensing Symposium - IGARSS.

[31]  Jacqueline Boutin,et al.  First Assessment of SMOS Data Over Open Ocean: Part I—Pacific Ocean , 2012, IEEE Transactions on Geoscience and Remote Sensing.

[32]  Thomas Meissner,et al.  The Emissivity of the Ocean Surface Between 6 and 90 GHz Over a Large Range of Wind Speeds and Earth Incidence Angles , 2012, IEEE Transactions on Geoscience and Remote Sensing.

[33]  C. Donlon,et al.  The Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) system , 2012 .

[34]  Yann Kerr,et al.  SMOS: The Challenging Sea Surface Salinity Measurement From Space , 2010, Proceedings of the IEEE.

[35]  David M. Le Vine,et al.  Aquarius and Remote Sensing of Sea Surface Salinity from Space , 2010, Proceedings of the IEEE.

[36]  Yann Kerr,et al.  The SMOS Mission: New Tool for Monitoring Key Elements ofthe Global Water Cycle , 2010, Proceedings of the IEEE.

[37]  Eric P. Chassignet,et al.  US GODAE: Global Ocean Prediction with the Hybrid Coordinate Ocean Model (HYCOM) , 2004 .

[38]  Simon Yueh,et al.  The Aquarius/SAC-D mission: Designed to meet the salinity remote-sensing challenge , 2008 .

[39]  Jacqueline Boutin,et al.  Overview of the SMOS Sea Surface Salinity Prototype Processor , 2008, IEEE Transactions on Geoscience and Remote Sensing.

[40]  Thomas M. Smith,et al.  Daily High-Resolution-Blended Analyses for Sea Surface Temperature , 2007 .

[41]  Thomas Meissner,et al.  The complex dielectric constant of pure and sea water from microwave satellite observations , 2004, IEEE Transactions on Geoscience and Remote Sensing.

[42]  Jacqueline Boutin,et al.  Surface Salinity Retrieved from SMOS Measurements over the Global Ocean: Imprecisions Due to Sea Surface Roughness and Temperature Uncertainties , 2004 .

[43]  Philippe Waldteufel,et al.  Ionospheric effects for L-band 2-D interferometric radiometry , 2004, IEEE Transactions on Geoscience and Remote Sensing.

[44]  Jacqueline Boutin,et al.  Issues concerning the sea emissivity modeling at L band for retrieving surface salinity , 2003 .

[45]  A. Shibata.  A change of microwave radiation from the ocean surface induced by air‐sea temperature difference , 2003 .

[46]  R. Morrow,et al.  Surface temperature and salinity variations between Tasmania and Antarctica, 1993–1999 , 2002 .

[47]  Jacqueline Boutin,et al.  Influence of sea surface emissivity model parameters at L-band for the estimation of salinity , 2002 .

[48]  Simon Yueh,et al.  Error sources and feasibility for microwave remote sensing of ocean surface salinity , 2001, IEEE Trans. Geosci. Remote. Sens..

[49]  Philip W. Rosenkranz,et al.  Atmospheric 60-GHz oxygen spectrum : new laboratory measurements and line parameters , 1992 .

[50]  K. Moffett,et al.  Remote Sens , 2015 .

[51]  J. Carton,et al.  Year-to-year salinity changes in the Amazon plume: Contrasting 2011 and 2012 Aquarius/SACD and SMOS satellite data , 2014 .

[52]  C. Swift,et al.  An improved model for the dielectric constant of sea water at microwave frequencies , 1977, IEEE Journal of Oceanic Engineering.