Interpretation of Backscattered HF Radio Waves from the Sea

Abstract

Radar oceanographers have long relied upon a simple diffraction grating model of the sea surface to explain the predominant features in the backscattered Doppler frequency spectrum. It is argued in this paper, however, that the ruled diffraction grating model with scattering localized to wave crests is incorrect and that a sinusoidal grating of period one-half the radio wavelength, with scattering from the entire surface, is the simplest representation of the sea surface which is consistent with both rigorous theory and experimental observation.

Scattering of HF Radio Waves from the Sea: A Review of the Theory Based upon a Simplified Model

“…Physically, these features may readily be understood in terms of Bragg resonance due to scattering by ocean waves of wavelength ~Ao moving towards and away from the source/receiver respectively. An analogy is often made with the scattering of light from a ruled diffraction grating, but this model is incorrect, as pointed out by Naylor and Robson (1986), and the correct analogy is with a sinusoidal diffraction grating.…”

Frequency shift of the Bragg and Non-Bragg backscattering from periodic water wave

“…So, k 1 = −2 k 0 / N , and . If the wave height a 1 is very small comparing to the wave length L 1 , the backscatter model of the surface is close to a sinusoidal diffraction grating 5 12 17 18 , that means, c 1 ≫ c 2 , c 3 , in Eq. 2 .…”

“…E.D.R.Shearman 6 proposed that sea waves of length not only Bragg wave, but also of L = λ , 3 λ /2, 2 λ , 5 λ /2, , etc , which contains harmonics of Bragg wave, may take place Bragg resonant backscatter, and these harmonics correspond Doppler-shifted contributions should appear in the echo spectrum at . All of the above and other models 7 8 9 10 11 12 13 14 15 , were deduced from the scattering measurement data collected from actual sea surface based on Doppler effect, and has not been verified under man-made conditions.…”