and Dasslve radiometry methods. To first order time 

 averaged microwave signals contain Information only on 

 the short-wave region of the surface-wave spectrum, and can 

 be related to the energy-containing long-wave part of the 

 spectrum (the "wind-sea spectrum") only if the dynamical 

 interrelationships between the two wavenumber ranges are 

 properly understood. Signal signatures directly dependent 

 on the wind-sea spectrum can be derived from higher-order 

 backscatter (or emissivity) models, but these also are 

 governed by the hydrodynamical coupling between short and 

 long waves. Delay-time measurements appear to be more 

 closely connected to significant sea-state characteristics. 

 If the illuminated area is large compared with the charac- 

 teristic wavelength of the surface (the usual case for 

 satellite altimeters), the mean shape of the backscattered 

 radar pulse can be related to the mean square wave height, 

 and further sea state parameters can probably be inferred 

 from a more detailed analysis of the pulse statistics. Inter- 

 actions between short and long waves are also important in 

 radar altimetery in producing higher-order modifications of 

 the pulse shape which could introduce systematic errors in 

 the measurement of mean sea level. Although JONSWAP demon- 

 strated the significance of wave-wave interactions for. the 

 overall energy balance of the wind-sea spectrum, many 



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