standard linear scattering methods. To lowest order the 

 backscattered signals (for finite angles of Incidence) yield 

 information only on the cm-dm wavelength components of the 

 spectrum. The "wind-sea spectrum" itself (using the term 

 here to denote the wavelength region of the spectrum between 

 about 5 m and 500 m which contains most of the surface 

 wave energy) is accessible to measurement only indirectly 

 through higher order signal characteristics arising from 

 hydrodynamic and electromagnetic interactions between the 

 short scattering waves and longer waves. 



We are still far from a complete understanding of the 

 many processes contributing to this coupling. The JONSWAP 

 results indicate that most of the energy received by the 

 short waves is transferred across the spectrum from the 

 longer waves, rather than directly from the atmosphere. 

 Unfortunately, the measurements did not extend to the very 

 short waves in the cm-dm range responsible for microwave 

 scattering. Moreover, this range of the spectrum poses 

 theoretical difficulties in that the coupling of very short 

 waves to the wind-sea spectrum cannot be treated by the 

 resonant interaction theory applicable within the wind-sea 

 spectrum itself (cf. [24]). In particular, it appears that, 

 in contrast to resonant interactions, a consistent treatment 

 of short-long wave interactions must include dissipation and 

 the coupling with the wind. To achieve quantitative micro- 

 wave measurements of sea state, surface winds, or other sea- 



25-6 



