| Paper: | TU-P2.5 |
| Session: | Ocean Applications of Radiometry |
| Time: | Tuesday, March 27, 17:00 - 17:20 |
| Presentation: |
Oral
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| Topic: |
Snow, ice and oceans: |
| Title: |
Status of Aquarius Salinity |
| Authors: |
David Le Vine; NASA Goddard Space Flight Center | | |
| | Gary Lagerloef; Earth and Space Research | | |
| | Emmanuel Dinnat; Goddard Space Flight Center | | |
| | Thomas Meissner; Remote Sensing Systems | | |
| | Frank Wentz; Remote Sensing Systems | | |
| | Liang Hong; SAIC | | |
| | Tong Lee; NASA Jet Propulsion Laboratory | | |
| | Hsun-Ying Kao; Earth and Space Research | | |
| Abstract: |
Aquarius is an L-band active/passive (radar/radiometer) combination instrument designed to map ocean salinity. It was launched June 10, 2011 as part of the Aquarius/SAC-D observatory, a partnership between NASA, which provided Aquarius, and the Argentine space agency (CONAE) which provided the spacecraft bus, SAC-D. The observatory was lost on June 7, 2015 when a failure in the power distribution network resulted in loss of control of the spacecraft. Operations have ended and the science team will deliver the Project’s final version of the salinity retrieval (Version 5.0) in the Fall 2017.
Version 5.0 of the SSS product reflects the understanding developed by the Science Team over the lifetime of the mission. Version 5.0 will be available with documentation at the NASA PO.DAAC: https://podaac.jpl.nasa.gov/aquarius. On a global basis, Aquarius already meets its primary goal of mapping SSS with an accuracy of 0.2 psu. Version 5.0 has focused on improvements such as tuning calibration and reducing regional biases and trends such as the SST-dependent bias. Among the significant changes are:
• Return to the Liebe model for effect Oxygen in atmospheric absorption.
• Use of the Scripps Argo SSS as the reference salinity field (replacing HYCOM) for calibration
• Improvement in the correction for galactic background signal reflected from the ocean surface based on measurements from SMAP fore/aft looks.
• Improvements in the roughness correction including SST dependence and removal of the dependence of SWH.
• Filtering for rain in the calibration files
• Use of both V-pol and H-pol observations with equal weight in the retrieval.
On a global basis compared to in situ measurements (e.g. Argo floats and buoys), the bias in the Aquarius SSS for Version 5.0 is very small (e.g. less than 0.01 psu) and the standard deviation for Level 2 data is about 0.3 psu (on the basis of matchups with Argo data without additional temporal averaging). There is a latitudinal dependence (better performance at low latitudes and poorer at high latitudes). An attempt to remove the effect of errors associated with the in situ measurements (e.g. via a triple point analysis) suggests a true RMS error in the Aquarius SSS on the order of 0.17 psu. The global difference of Aquarius Level 3 SSS (monthly temporal average and 100 km spatial average) and smoothed Argo data has a standard deviation of about 0.18 psu.
The advantage of having a very stable instrument is that each improvement in the retrieval algorithm opens the door to additional possibilities. Among the things remaining to be done are:
• Determining the sources of the SST bias
• Refining the model for the dielectric constant of sea water (i.e. functional dependence on SST and SSS)
• Identifying and correcting a remaining small annual cycle (not due to changes in salinity).
• Merging Aquarius, SMOS and SMAP salinity maps into a single product.
• Improving the theory for the roughness correction for emission and reflection of signals.
• Improving the level of missed detection in the RFI algorithm.
The future: The Aquarius Project will no longer exist after December 31, 2017. But there are plans within NASA to continue the research on remote sensing of SSS. In particular, research is planned to retrieve salinity using data from SMAP over the ocean. This work began under Aquarius and has already produced images. The plan is that this work will continue with funds for the “Salinity Continuity Program” and that there will also be resources to continue to improve the Aquarius SSS product.
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