Status of Aquarius and the Salinity Retrieval
[11-Apr-2016] Le Vine, D., Dinnat, E., Meissner, T., Wentz, F., and Lagerloef, G.
Presented at the 14th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment
Aquarius is a radiometer/scatterometer combination specifically designed for remote sensing of sea surface salinity. The instrument was lost on June 7, 2015 when a power failure on the satellite resulted in loss of control of the observatory. This paper will report the plans for the mission and data processing and the status of the validation of the SSS data against Argo measurements. Aquarius functioned well from the time it was turned on August 25, 2011 until the observatory was lost in June, 2015, providing almost 4 years of data on the global sea surface salinity field. This included a short look at the inter-annual variability. A plan for terminating the mission has recently been approved that includes a final reprocessing of the Aquarius data (version 5.0) to be completed late in 2016 or early 2017 followed by an official end of the mission in June, 2017. Just before the observatory failure in June, Aquarius released Version 4.0 of the salinity retrieval. This version included several changes to improve the retrieval. The most significant are an update of the corrections for land and ice in the radiometer FOV and inclusion of the SST bias into the geophysical model function for emissivity. In addition, an error estimate is now provided for the retrieval, the RFI algorithm has been tuned to have equal false alarms rates over ocean and land, and density has been added as a product in the level 2 file. Version 4.0 retrievals meet the requirement of 0.2 psu in most areas of the ocean, although high latitudes still present problems. Matchups with Argo will be presented to illustrate the overall performance of V4.0 and also the remaining dependence on latitude. Work is currently under way on a final version of the retrieval, V5.0, which will be produced before the mission is closed by June 2017. This will include several issues that have been the subject of research by the project including an instrument-dependent correction for gain and drift, update of the full-range calibration (i.e. land, ocean and sky), effect of rain, optimum choice of ancillary values of SST, improved model for land emission (consistency with SMAP), performance at high latitudes, and improvements in the RFI detection algorithm. After the mission ends, the Aquarius data and documentation will remain available to the public for other applications and future reprocessing. There is hope that SMAP will help continue the legacy of SSS measurements.