found to be valid In each of these ranges of incident angle, 

 so that the following discussion of backscatter models will 

 naturally tend to emphasize the type of measurement associ- 

 ated with a given model. However, it is conceivable that a 

 more detailed investigation of the properties of the complete 

 doppler spectrum or scattering function would reveal valu- 

 able additional sea state signatures not discernible in the 

 usual measurements but nonetheless accessible by standard 

 linear signal processing techniques. 



7. THE SPECULAR REFLEXION AND BRAGG SCATTERING MODELS 



The simplest description of surface scattering Is the 

 specular reflexion of an ensemble of rays by a statistical 

 distribution of infinitesimal surface facets, as originally 

 applied by Cox and Munk [12] [13] to the analysis of sun 

 glitter from the sea surface. For microwaves, the model 

 is applicable for angles of incidence less than about 20° 

 from the vertical. At larger angles, specular reflexion 

 becomes negligible and the backscatter is dominated by 

 first-order Bragg interactions in accordance with the 

 resonance conditions (2). These define two backscattering 

 surface-wave components with wavelengths equal to half the 

 horizontal wavelength of the incident radiation, propagating 

 towards or away from the microwave source. 



Both models are found to be in good accord with obser- 



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