For large fetches, a should then attain an asymptotic 

 value independent of wind speed. If a variation of a 

 with wind speed Is nevertheless observed for large fetches, 

 this implies either that Phillips' power law is invalid 

 (the wind dependence corresponding in this case to an 

 inverse frequency dependence through the dimensional condi- 

 tion a = a(uf/g) , or that additional dimensional 

 factors (e.g. surface tension or contamination) are involved. 

 It follows generally that the wind dependence cannot be 

 investigated consistently without regard to the other para- 

 meters which determine the energy level of the wave spectrum 

 at high wavenumbers. 



The second, more direct course is to develop higher- 

 order Interaction models which predict backscatter signa- 

 tures dependent not only on the short scattering waves, but 

 also on the longer wind-wave components. Progress in this 

 direction may indeed be a prerequisite for the success of 

 the first approach, for even after the interrelationship 

 between the high-wavenumber energy, the wind-sea spectrum 

 and the wind speed has been clarified, knowledge of the 

 high wavenumber range of the spectrum alone will probably 

 prove insufficient to solve for the remaining two factors 

 determining the equilibrium without additional data on the 

 longer wind-sea components . 



25-37 



