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QuikSCAT Global Ocean Surface Wind Velocity and Divergence, Science Quality
Program: NASA QuikSCAT Winds
Spacecraft: Quick Scatterometer (QuikSCAT)
Data Stream: L3 Science Quality from Remote Sensing Systems Inc., Santa Rosa, CA
Primary Geophysical Parameter: Ocean Surface Wind Velocity and Divergence
Nominal Accuracy: ± 2 m/s in speed and 20° in direction
Spatial grid: 0.25 degrees longitude by 0.25 degrees latitude, geographic
Spatial coverage: Global
Temporal Coverage: July, 1999 to Present
FGDC Metadata Data Quality Act Documentation
CoastWatch distributes wind velocity measurements derived from the Seawinds instrument aboard NASA's QuikSCAT satellite. The Seawinds instrument is a dual-beam microwave scatterometer designed to measure wind magnitude and direction over the global oceans. The QuikSCAT satellite offers daily coverage of 90% of the earth's oceans. The reference height for all wind velocity measurements is 10 meters above surface. CoastWatch further processes wind velocity data to wind divergence. This is a Science Quality dataset, which is made available on a delayed time frame to allow for improvements in the data processing.
Data originates from the SeaWinds sensor on NASA's QuikSCAT satellite. The SeaWinds sensor is a dual-beam, rotating microwave scatterometer. The SeaWinds scatterometer bounces radar signals off the ocean surface and measures the strength of the returning backscatter signal. Wind roughens the ocean surface, which affects the backscatter signal and enables measurement of wind velocity. As the satellite passes over a site, measurements of that site are taken at differing azimuth and incident angles. The combination of these measurements is processed to wind velocity (speed and direction) using NASA-developed wind retrieval algorithms (Freilich, 2000 and Lungu, 2001).
In this processing, the assumption is made that wind is the only force affecting surface roughness. Rainy areas must be masked because rain will also modify the ocean surface, leading to erroneous measurements. To ensure complete masking of rain-affected areas, the ultra-conservative Multidimensional Histogram (MUDH) rain-masking algorithm is applied to the wind data (Huddleston and Stiles, 2000).
CoastWatch retrieves wind velocity measurements from Remote Sensing Systems Inc. at 0.25 degree resolution. Wind velocity data is made available in zonal wind (E-W direction), meridional wind (N-S direction), wind modulus (magnitude of wind velocity), and vectored wind products. CoastWatch also processes wind velocity to wind divergence. All computations, including derivatives, are performed on the individual swath data, which are then mapped to an equal angle grid of 0.25 degrees latitude by 0.25 degrees longitude using a simple arithmetic mean to produce individual and composite images of various durations (e.g., 1, 3, 8, and 14-days, and monthly).
Despite our best efforts, incorrect data may often appear within near real time data sets. NOAA CoastWatch accepts no liability for use of these data products. It is recommended that these products NOT be used for navigation.
If this data is used for presentation or publication, please acknowledge the NOAA CoastWatch Program and the Remote Sensing Systems In.
References and suggested citations:
Freilich, M. 2000. SeaWinds: Algorithm Theoretical Basis Document. NASA ATBD-SWS-01.
Huddleston, J.N. and B.W. Stiles. 2000. Multidimensional Histogram (MUDH) Rain Flag Product Description, Version 2.1. Jet Propulsion Laboratory, Pasadena, CA.
Lungu, Ted, ed. 2001. QuikSCAT Science Data Product User's Manual, Version 2.2, JPL Document D-18053, Jet Propulsion Laboratory, Pasadena, CA.