components. As pointed out In §5, however, many details of 

 the spectral energy balance at very high wavenumbers still 

 need to be resolved. Several of the inconsistencies in the 

 reported wind dependences of microwave and acoustic cross- 

 sections or in the values of Phillips' constant are presum- 

 ably due to inadequate consideration of all factors influen- 

 cing the high-wavenumber equilibrium (cf.[l] [11] [29] [3^] 

 [39] [4^] [^6] [55]). 



It has not always been sufficiently appreciated in this 

 context that an observed wind dependence of backscatter 

 cross-sections or Phillips' constant necessarily implies a 

 dependence on further parameters by dimensional arguments 

 alone, independent of detailed dynamical considerations. If 

 the surface-wave spectrum is expressed in terms of a general- 

 ised Phillips' form E (£,6) = a (f , 9) 0^2'^) ""^f "= , 



2 



the non-dimensional form factor a can depend (besides on 

 the non-dimensional direction 6 ) only on non-dimensional 

 combinations of f and various external parameters such as the 

 wind speed u , the fetch x , and g . Thus 



if it is assumed that these are the only relevant external 

 variables and a is observed to be independent of f 

 (Phillips' power law), it can be a function only of the 

 non-dimensional combination xg/u^ (Kitaigorodskii ' s 

 similarity relation); the determination of wind dependence 

 is meaningful in this case only if the fetch is defined. 



25-36 



