before the techniques can be usefully applied. Investiga- 

 tions are needed particularly in two areas: 



(1) A detailed theoretical analysis of the complete doppler 

 spectrum (or scattering function) and the non-Gaussian 

 properties of backscatter signals may be expected to reveal 

 additional useful sea-state signatures not contained in the 

 traditional cross-section, doppler and travel-time measure- 

 ments. This applies particularly to the backscatter 

 statistics for radar altimeters, which appear to be intim- 

 ately related to the wind-sea spectrum. 



(2) Higher-order models of the radar return from the sea 

 surface are strongly dependent on the interactions between 

 very short waves and the longer wind-sea components. A 

 second basic input for these models is the energy level of 

 the wave spectrum at high wavenumbers. Both questions 

 represent Interrelated aspects of the energy balance of 



the short-wave region of the spectrum, and can be understood 

 only through detailed measurements covering several decades 

 of surface wavelengths from a few cms to several hundred 

 meters. A broad-band wave experiment of this nature^ com- 

 bined with radar backscatter data — supplemented, if 

 possible, by microwave-temperature and acoustic backscatter 

 measurements as Independent tests of the theoretical models- 

 would be very helpful in clarifying some of the basic mech- 

 anisms involved in the interpretation of microwave back- 

 scatter from the sea surface. 



25-50 



