RADAR BACK-SCATTER FROM THE SEA SURFACE 



K. Hasselmann and M. Schleler 



Institut fuer Geophysik 

 University of Hamburg 



ABSTRACT 



Doppler spectra of electromagnetic backscatter from 

 the sea surface are interpreted in terms of general- 

 ized Bragg models. The observed broadening of the 

 spectra about the Bragg line is attributed to higher- 

 order nonlinear processes. At conventional radar 

 frequencies, good agreement with the measurements 

 is achieved by an extension of the wave-facet inter- 

 action model considered by Wright, Bass et al. and 

 other workers. The correlation of wave slope's and 

 orbital velocities in the joint probability distribution 

 of carrier-wave facets leads to significant differences 

 between the Doppler spectra for vertical, horizontal and 

 cross polarization. In the HF band, the Doppler 

 broadening is interpreted in terms of quadratic wave- 

 wave interactions. For the usual case that the electro- 

 magnetic wave lengths are small compared with the 

 principal wave lengths of the sea, the theoretical Doppler 

 spectrum consists of the lowest-order Bragg line and 

 superimposed images of the complete ocean wave fre- 

 quency spectrum folded on either side of the Bragg line. 

 Both wave -facet and wave -wave interaction models give 

 promise of extracting significant information on the 

 "state of the sea" from electromagnetic Doppler return 

 at wave lengths short compared with the dominant wave 

 lengths of the sea . 



* 



Presently at Woods Oceanographic Institution, 



361 



