facet normal (electromagnetic Interactions) and through the 

 amplitude and wavelength modulation of the Bragg scattering 

 waves as they propagate through the variable orbital cur- 

 rents and vertical accelerations of the carrier waves 

 (hydrodynamlc interactions). The model is meaningful only 

 if these modifications are large compared with the errors 

 incurred through the indeterminacy relations (i.e. the 

 Fraunhofer patterns) in restricting the area of the Bragg 

 scattering waves to a finite facet rather than an infinite 

 plane. The condition may be expressed as k c,>>\ [25] 



3 



where k is the vertical wavenumber component of the 

 incident radiation and C is the wave height. 



Theoretical investigations of the wave-facet model 

 have been restricted hitherto to the electromagnetic inter- 

 actions. Except for rather low grazing angles (less than 

 about 20°), these are not found to appreciably affect the 

 backscatter cross-sections. Moreover, the modifications 

 are proportional to the mean square wave slopes, which are 

 only weakly dependent on the main part of the wind-sea 

 spectrum. Stronger effects are found in the doppler 

 spectra, the wind-sea signatures here being determined by 

 the mean square orbital velocities and the mean products 

 of the orbital velocities and wave slopes [25], both of 

 which represent spectral moments weighted towards the 

 principal components of the wind-sea spectrum. In prin- 



25-39 



