Marineland Aircraft Observations of L-Band Radar Backscatter Dependence upon Wind Direction
Radar observations of the ocean during the Marineland Experiment have been examined to establish whether L-band backscatter varies with surface wind direction. This complements recent aircraft and SEASAT observations which indicate that L-band backscatter from the ocean at angles of incidence near 20° varies as the square root of the wind speed. The Marineland data are particularly well suited for this since flights over instrumented surface sites were conducted in a number of directions for several different days.
The Marineland data show two distinct types of behavior. In all cases except one, the data suggest that there is little or no dependence of L-band backscatter upon wind direction. In the exceptional case where there was a moderate wind and unstable atmosphere, there was a strong directional dependence of L-band backscatter with wind. In particular, these data suggest a 40% change in backscatter between the weakest echoes (when the radar is looking cross-wind) and the strongest echoes (when the radar is looking up- or downwind).
Unusual synthetic aperture radar (SAR) images are also associated with the one case with the strong dependence upon wind direction. These SAR images show bright kilometer-sized splotches which are likely surface expressions of turbulent eddies imbedded in the unstable atmosphere. These splotches appear only when the radar is looking near the up- or downwind directions. These splotches do not appear in SAR images when the radar is looking cross-wind. Also, these splotches are most intense on the warmer Gulf Stream waters and disappear near shore where the fetch is small. The features in the SAR image correlated with cumulus clouds observed with simultaneous aircraft photography.
KeywordsWind Direction Synthetic Aperture Radar Synthetic Aperture Radar Image Gulf Stream Strip Chart
Unable to display preview. Download preview PDF.
- Jones, W. L., V. E. Delmore, and E. M. Bracalente (1981): The study of mesoscale ocean winds. Spaceborne Synthetic Aperture Radar for Oceanography (R. Beal, P. S. Deleonibus, I. Katz, eds.), Johns Hopkins Press, Baltimore, 87–97.Google Scholar
- Liu, W. T. (1978): The Molecular Effects of Air-Sea Exchanges. Ph.D. dissertation. University of Washington, Seattle.Google Scholar
- Roll, H. U. (1965): Physics of the Marine Atmosphere, Academic Press, New York.Google Scholar
- Thompson, T. W. (1976): JPL Radar Operations: Marineland-GASP Test Series, 25 November to 16 December 1975. JPL Internal Report, April 15.Google Scholar
- Weissman, D. E., and T. W. Thompson (1977): Detection and interpretation of ocean roughness variations across the Gulf Stream inferred from radar cross section observations. Oceans ‘77 Conference Record 1, 14B1–14B10.Google Scholar