Wind observations from automated weather stations on research vessels were used to validate winds determined from observations of the NASA Scatterometer (NSCAT). This validation was first performed on the 50 km resolution data from the NSCAT-1 algorithm (Bourassa et al., 1997). The examples shown herein are from 25 km and 50 km resolution products determined with the NSCAT-2 algorithm. NSCAT winds are shown to be tremendously accurate. The research vessel observations are clearly a practical source of the high quality observations required for such calibration/validation efforts.

One advantage of using observations from several research vessels is the sampling of a wide range of winds and sea states. Winds are sampled in many regions of the globe, insuring that the calibration of the remotely sensed winds is applicable to winds over any ocean. The results from each R/V were similar, indicating that there was no significant regional bias in the open ocean. The ship tracks and locations of collocations (ship and satellite observations) are shown for each of the three research vessels used in this study:

The ship data is quality controlled to insure the proper calculation of true winds, and to remove data that is likely to be in error due to flow distortion, erroneous data transmission, and other problems ( Smith et al. 1999). The satellite and ship observations were found to be sufficiently accurate so that times when the ship was accelerating (which, due to the averaging technique commonly used, leads to errors in ship-based winds) were found to have statistically significant increases in the differences between ship and satellite winds.

Both the wind speed and the wind direction are validated. There is little difference between the results for 25 km and 50 km resolution satellite winds.

The accuracy of NSCAT speeds and directions provided a remarkable increase in the accuracy and quantity of wind observations over earth's bodies of water. It has been shown that much of the uncertainty in wind speeds can be accounted for in better considerations of the surface currents (personal communication, Peter Cornillon, 1998).

Acknowledgments.

We thank Barrie Walden and Lane Abrams for providing observations from the R/V Knorr, Kieran Jacka and Gordon Keith for providing observations from the RSV Aurora Australis, and Shawn Smith, Dan Gilmore, and Jiraporn Whalley for quality-controlling the ship data. Funding for this project is from the NASA JPL NSCAT Project. COAPS receives its base funding from ONR's Secretary of Navy Grant to Dr. James J. O'Brien.

References

Bourassa, M. A., M. H. Freilich, D. M. Legler, W. T. Liu, and J. J. O'Brien, 1997: Wind observations from new satellite and research vessels agree. EOS Trans. of Amer. Geophys. Union, 597 & 602.

Smith, R. S, M. A. Bourassa, and R. J. Sharp, 1998: Establishing more truth in true winds. J. Atmos. Oceanic Technol., in press.