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Napolitano, D.J., 1991

Synthetic aperture radar measurements of the ocean surface during the Gulf of Alaska experiment

Bibliographic Reference

Napolitano, D.J., 1991, Synthetic aperture radar measurements of the ocean surface during the Gulf of Alaska experiment: Palo Alto, California, Stanford University, Ph.D. dissertation, 486 p., illust., maps.


On June 26, 1978 the spacecraft SEASAT was launched for the purpose of monitoring the ocean surface using synthetic aperture radar (SAR). Ships, aircraft, and buoys provided an in situ data set in the Gulf of Alaska and therefore, the experiment was entitled the Gulf of Alaska Experiment (GOASEX). Eleven digitally processed SAR images from GOASEX are examined, with oceanographic parameters extracted for comparison with the in situ data. However, the complex relationship between the ocean surface and the SAR image intensity that involves electromagnetic scattering, hydrodynamics, etc., has led to many theories and controversy regarding the SAR imaging of ocean waves. These theories generally are divided into two classes, namely distributed surface theories and velocity bunching theories; the distinction attributed to the manner in which the time dependence of the ocean surface is incorporated. To help resolve this controversy, a theoretical comparison between three representative theories--namely those of Rotheram, Alpers, and Harger, is performed. The results show that while different in approach, upon appropriate formulation and correction of errors, the theories produce virtually identical results for the linear relationship between the ocean surface height and the SAR image intensity. The velocity bunching phenomenon, an imaging mechanism for waves traveling parallel to the SAR flight path, is a natural result of the distributed surface theories considered, with the discrepancies attributed mainly to focusing issues. The results of comparing oceanographic parameters extracted from the SAR images and buoys show very good agreement. Next, the theoretical linear modifications introduced by the SAR imaging process are removed from the SAR data. This slightly improves the agreement between SAR and buoy estimates. In analyzing the SAR spectra, artifacts that suggest windrows are observed. Windrows are the surface manifestation of circulatory flow in either the sub-surface ocean waters (Langmuir circulations), or atmosphere (atmospheric roll vortices), and aligned with the local wind. Employing currently understood theory, correlations are performed using the in situ data and SAR spectra. While not conclusive, the results do suggest the observation of atmospheric roll vortice effects and possibly, Langmuir circulation effects.

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