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Azimuth Modulation of the Radar Backscatter at Near-Normal Incidence Azimuth Modulation of the Radar Backscatter at Near-Normal Incidence

by Greenwood, Andrew D.

Abstract (Summary)

Radar observations of the ocean surface are becoming increasingly important. Common applications are wind retrieval and global weather forecasting and characterization. Because of the common use of ocean radar measurements, it is important to understand the sensitivity of the backscatter to both radar parameters and surface parameters.

At near-normal incidence angles, it has been assumed that the radar backscatter exhibits little or no azimuth dependence (Colton, 1989). However, recent data taken by the BYU YSCAT radar system suggests that this is not the case. At an incidence angle of 10°, the YSCAT radar data shows from a fraction of a decibel to up to 10 decibels of azimuth modulation, depending on the surface conditions. In this thesis, a physical optics approach is used with a two-dimensional surface model to derive the electromagnetic backscatter from the ocean surface. If the waves on the ocean surface are directed, azimuth modulation is predicted at near-normal incidence angles. The effects of surface and radar parameters on the azimuth modulation are studied, and the results are compared to data taken by the YSCAT radar system. It is shown that the theory correctly predicts of the shape of the curve when the normalized radar cross-section is plotted as a function of azimuth angle. The theory also predicts the correct trend of the modulation magnitude as function the surface roughness. However, the simplifications in the model limit its prediction of the frequency dependence of the modulation. Relaxing some of the assumptions of the model is likely to correct this problem.

Bibliographical Information:

Advisor:

School:Brigham Young University

School Location:USA - Utah

Source Type:Master's Thesis

Keywords:yscat scatterometry air sea interaction radar backscatter

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