| Paper: | TU-P2.3 |
| Session: | Ocean Applications of Radiometry |
| Time: | Tuesday, March 27, 16:20 - 16:40 |
| Presentation: |
Oral
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| Topic: |
Snow, ice and oceans: |
| Title: |
Ocean Surface Salinity and Wind Speed from the SMAP L-Band Radiometer |
| Authors: |
Thomas Meissner; Remote Sensing Systems | | |
| | Frank Wentz; Remote Sensing Systems | | |
| | Lucrezia Ricciardulli; Remote Sensing Systems | | |
| | Carl Mears; Remote Sensing Systems | | |
| | Andrew Manaster; Remote Sensing Systems | | |
| Abstract: |
The Soil Moisture Active Passive Mission SMAP was launched in January 2015 and has been providing science data since April 2015. Though originally designed to measure soil moisture the SMAP radiometer has also excellent capabilities to measure ocean surface salinity and wind speed.
Our paper presents the major steps in instrument calibration, retrieval methodology and validation of these two ocean parameters. We also discuss advantages and disadvantages of the SMAP sensor for measuring ocean salinity and wind speed compared with other spaceborne L-band sensors such as SMOS and Aquarius.
Because SMAP has lost its radar, it is not possible to simultaneously retrieve salinity and wind speed without ancillary fields. Salinity and wind speed retrievals are performed in two separate algorithms. The SMAP salinity retrieval uses an external wind speed from WindSat or SSMIS to perform the surface roughness correction. The SMAP wind speed retrieval algorithm uses an external salinity field (HYCOM) to calculate the emissivity of the flat ocean surface.
The calibration accuracy of the standard SMAP brightness temperatures on which the soil moisture product is based on, is not sufficient for the ocean products. Additional efforts in the instrument calibration need to be made, which we discuss in our presentation. An important issue is the fact that the SMAP mesh antenna is emissive. It is necessary to perform an accurate correction in order to avoid spurious biases that correlate with the solar heating of the antenna.
The SMAP salinity retrievals have an accuracy close to the ones from Aquarius, which can be shown by comparing them with in-situ salinity measurements from ARGO floats. The resolution of SMAP is about 40 km, which is much higher than the Aquarius resolution of 100 – 150 km. It allows SMAP to measure accurately salinity closer to the shore and sea ice edge than Aquarius did. This aids in the study of river outflows and sea ice melt.
SMAP wind speeds become particularly valuable in tropical and extratropical cyclones, as the L-band radiometer keeps good sensitivity at high wind speeds and is very little affected by precipitation. Remote Sensing Systems is producing SMAP wind fields in near-real time. From that images and the crucial parameters that characterize size and intensity of tropical cyclones are extracted and provided in near real time to the Automated Tropical Cyclone Forecast (ATCF) of the US Navy, the National Hurricane Center and Joint Typhoon Warning Center.
In our presentation we will also discuss ongoing improvements in the SMAP salinity and wind speed retrieval algorithm. The upcoming data release will include all the updates to the geophysical model that have been implemented in the Aquarius Version 5 release, in particular the changes to the correction for the absorption by atmospheric oxygen. The ancillary wind field that is used in the ocean surface roughness correction will come from the Cross Calibrated Multiplatform (CCMP) wind field that is now being produced by Remote Sensing Systems in near-real time. We are also taking steps to improve the sidelobe correction for intrusion from land surfaces in the coastal areas.
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