Aquarius Scatterometer Winds
Abstract
Aquarius is a combined passive/active L-band microwave instrument developed to map the salinity field at the surface of the ocean from space. The data will support studies of the coupling between ocean circulation, the global water cycle, and climate. The primary science objective of this mission is to monitor the seasonal and interannual variation of the large scale features of the surface salinity field in the open ocean with a spatial resolution of 150 km and a retrieval accuracy of 0.2 psu globally on a monthly basis. The measurement principle is based on the response of the L-band (1.413 GHz) sea surface brightness temperatures to sea surface salinity. To achieve the required 0.2 psu accuracy, the impact of sea surface roughness (e.g. wind-generated ripples and waves), along with several additional factors impacting the observed brightness temperature, must be corrected to better than a few tenths of a degree Kelvin. To this end, Aquarius includes a scatterometer to help correct for this surface roughness effect. The Aquarius/SACD was launched successfully on June 10, 2011, and the instrument is expected to be turned on in August. The prelaunch tests of Aquarius showed that the instrument should be extremely stable at the week-to-month time scale with drift of less than 0.1 K for the radiometer and 0.1 dB for the scatterometer. The current baseline algorithm for Aquarius is to use the scatterometer data in conjunction with the NCEP wind direction to derive the ocean surface wind speed and then a radiometer roughness correction. The pre-launch simulations predict 1 m/s wind speed accuracy. This will be tested using the Aquarius data collected in the coming few months. To quantify the benefits of combining passive and active microwave sensors for ocean salinity remote sensing, the Passive/Active L-band Sensor (PALS) was used to acquire data over a wide range of ocean surface wind conditions during the High Ocean Wind (HOW) Campaign in 2009. The PALS brightness temperatures and the radar σ0 from the campaign show response to ocean surface wind speed as well as direction. The brightness temperature changes are about 0.2 to 0.3 K for every one m/s change in wind speed. In addition, there is significant wind direction dependence for high winds (>10 m/s), about 0.5 K peak to peak at 9 m/s wind speed and 1.5 K at 24 m/s wind speed. Using the PALS data, we have tested the ability to use the combined active and passive microwave to retrieve the wind speed and direction. The accuracy of retrievals is estimated to be about 1 m/s in wind speed and 15 degrees in direction. Using the Aquarius data, we will update the geophysical model functions for scatterometer and radiometer, which will then be applied for the retuning of wind retrieval algorithms. The retrieval analyses using PALS data and preliminary calibrated Aquarius data will be presented.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMOS32A..06Y
- Keywords:
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- 4200 OCEANOGRAPHY: GENERAL;
- 4594 OCEANOGRAPHY: PHYSICAL / Instruments and techniques