balance in §§5 and 7. They can be treated formally by the 

 WKBJ method appropriate to the two-scale approximation of 

 the wave-facet model (cf.[24]), but as pointed out above, 

 a basic difficulty of the theory is that a complete analysis 

 requires, among other processes, the inclusion of dissipa- 

 tive losses due to white capping and the regeneration of 

 short waves by wind, both of which are only poorly knovm . 

 As before, we conclude that significant progress in the 

 determination of sea state from cross-section data requires 

 detailed experiments to clarify the various processes 

 determining the short-wave energy balance. 



9 . RADAR ALTIMETRY 



The analysis of microwave backscatter signals with 

 respect to delay time yields wave information of a basic- 

 ally different nature from that obtained from time-averaged 

 cross-section or doppler data. Thus with the simplest form 

 of signal treatment, altimeters provide a measurement of 

 the mean square wave-height, a basic characteristic of the 

 wave field which was not accessible to direct measurement 

 by CW methods. 



On reflection from the sea surface, an initially step- 

 function pulse is transformed to a pulse with the famaliar 

 average shape shown in Fig. 9. If the sea surface is 

 almost calm (except for very small slope variations which 

 broaden the average reflection of a unidirectional ray into 



25-43 



