The effects of the surface slopes joint probability density, the shadowing function, the skewness of sea waves and the curvature of the surface on the backscattering from the ocean surface are discussed and an improved two-scale model modified by these four aspects is used to calculate the backscattering coefficient of the dynamic ocean surface. In order to deal with the surface skewness driven by wind, a new complementary term derived from the small perturbation method is included in the improved model, in which the Fourier transform of the third-order cumulant function, surface bispectrum, is employed. On this basis, with the oceanic whitecap coverage taken into account, a composite model for predicting the ocean surface backscattering coefficient is constructed tentatively, which incorporates the volume scattering into the total one. Finally, with the vector radiative transfer (VRT) theory employed, numerical illustrations are carried out for the backscattering coefficients versus wind speed, incidence angle and azimuth angle, respectively. The predictions of the composite model are verified in Ku- and Ka-bands through the comparison of numerical results with many sets of measured data and the aircraft measurement experiment carried out in ZHOUSHAN sea area also supports this model.
2. Valenzuela, G. R., "Theories for the interaction of electromagnetic and oceanic waves — A review," Boundary-layer Meteorology, Vol. 13, 61-85, 1978.
3. Fung, A. K. and K. K. Lee, "A semi-empirical sea-spectrum model for scattering coefficient estimation," IEEE J. Ocean. Eng., Vol. 7, No. 4, 166-176, 1982.
4. Fung, A. K. and N. C. Kuo, "Backscattering from multi-scale and exponentially correlated surfaces," Journal of Electromagnetic Waves and Applications, Vol. 20, No. 1, 3-11, 2006.
5. Fung, A. K. and K. S. Chen, "Kirchhoff model for a skewed random surface," Journal of Electromagnetic Waves and Applications, Vol. 5, No. 1, 205-216, 1991.
6. Ulaby, F. T., R. K. Moore, and A. K. Fung, Microwave Remote Sensing-active and Passive, Vol. 2, Addision-Wesbey Pu. Co., 1982.
7. Tsang, L., J. A. Kong, and K. H. Ding, Scattering of Electromagnetic Waves, Vol. 1, Wiley-Interscience, New York, 2000.
8. Guissard, A., "Multispectra for ocean-like random rough surface scattering," Journal of Electromagnetic Waves and Applications, Vol. 10, 1413-1443, 1996.
9. McDaniel, S. T., "Microwave backscatter from non-Gaussian seas," IEEE Trans. Geosci. Remote Sens., Vol. 41, No. 1, 52-58, 2003.
10. Soriano, G. and C. A. Guerin, "A cutoff invariant two-scale model in electromagnetic scattering from sea surfaces," IEEE Trans. Geosci. Remote Sens., Vol. 5, No. 2, 199-203, 2008.
11. Wang, Y.-H., L.-X. Guo, and Z.-S.Wu, "Modified two-scale model for electromagnetic scattering from the non-Gaussian oceanic surface," Chinese Physics Letters, Vol. 22, No. 11, 2808-2811, 2005.
12. Droppleman, J. D., "Apparent microwave emissivity of sea foam," J. Geophys. Res., Vol. 75, No. 3, 696-698, 1970.
13. Rosenkranz, P. W. and D. H. Stealin, "The microwave emissivity of ocean foam and its effect on nadiral radiometric measurements," J. Geophys. Res., Vol. 77, No. 33, 6528-6538, 1972.
14. Chen, D., et al., "Microwave emission and scattering of foam based on Monte Carlo simulations of dense media," IEEE Trans. Geosci. Remote Sens., Vol. 41, No. 4, 782-790, 2003.
15. Huang, X.-Z. and Y.-Q. Jin, "Scattering and emission from two-scale randomly rough sea surface with foam scatterers," IEE Proc. Microw. Antennas Propag., Vol. 142, No. 2, 109-114, 1995.
16. Guo, L.-X. and Z.-S. Wu, "Application of the extended boundary condition method to electromagnetic scattering from rough dielectric fractal sea surface," Journal of Electromagnetic Waves and Applications, Vol. 18, No. 9, 1219-1234, 2004.
17. Guo, J. J., et al., "Applications of dense media radiative transfer theory for passive microwave remote sensing of foam covered ocean," IEEE Trans. Geosci. Remote Sens., Vol. 39, No. 5, 1019-1027, 2001.
18. Chen, K. S., A. K. Fung, J. C. Shi, and H. W. Lee, "Interpretation of backscattering mechanisms from non-gaussian correlated randomly rough surfaces," Journal of Electromagnetic Waves and Applications, Vol. 20, No. 1, 105-118, 2006.
19. Smirnov, A. V., I. M. Fuks, and K. A. Naugolnykh, "Crosswind ocean radar backscatter and two-scale scattering model at low grazing angles," Radio Science, Vol. 38, No. 2, 8037-8044, 2003.
20. Bourlier, C., G. Berginc, and J. Saillard, "One and two-dimensional shadowing functions for any height and slope stationary uncorrelated surface in the monostatic and bistatic configurations," IEEE Trans. Antennas Propag., Vol. 50, No. 3, 312-324, 2002.
21. Voronovich, A. G., "On the theory of electromagnetic waves scattering from the sea surface at low grazing angles," Radio Science, Vol. 31, No. 6, 1519-1530, 1996.
22. Chen, K. S. and A. K. Fung, "A Bragg scattering model for skewed sea surface," OCEANS’90. `Engineering in the Ocean Environment'. Conference Proceedings, 249-252, 1990.
23. Chen, K. S., A. K. Fung, and D. E. Weissman, "A backscattering model for ocean surface," IEEE Trans. Geosci. Remote Sens., Vol. 30, No. 4, 811-817, 1992.
24. Jin, Y.-Q., "Some results from the radiative wave equation for a slab of randomly, densely-distributed scatterers," J. Quant. Spectr. Radiat. Transfer, Vol. 39, No. 2, 83-98, 1988.
25. Schroeder, L. C., et al., "The relationship between wind vector and normalized radar cross section used to derive SEASAT-A satellite scatterometer winds," J. Geophys. Res., Vol. 87, No. C5, 3318-3336, 1982.
26. Zhou, P., et al., "Results of airborne measurement of sea surface backscattering and analysis," Systems Engineering and Electronics, Vol. 28, No. 3, 325-328, 2006.