Pierson, Tick, and Baer 



likely to rest on ad hoc hypotheses, the validity of which can be established only 

 by a series of careful measurements. This will require time; meanwhile, prac- 

 tical necessity dictates the use of semiempirical models, in which the theoreti- 

 cal developments can be accommodated in the best tradition of engineering. 

 Dr. Pierson and his colleagues have led the way in the development and testing 

 of such models and are to be congratulated on their success. 



DISCUSSION 



Klaus Hasselmann 



Institut fiir Schiffbau der Universitat Hamburg 



Hamburg, Germany 



and 



Institute for Geophysics and Planetary Physics, LaJolla Laboratories 



University of California, San Diego 



LaJolla, California 



I congratulate the authors on this paper, which I feel represents an appre- 

 ciable advance in the art of wave prediction. It may be recalled that at the time 

 of the last Ocean Wave Conference at Easton, in 1961, wave forecasting was in a 

 very unsatisfactory state. It was one of the principal conclusions at that meet- 

 ing that a reliable wave forecasting technique would need to be based on the nu- 

 merical integration of the radiative transfer equation, and I feel that the authors 

 have given very encouraging support to this view. It may be mentioned that sim- 

 ilar forecasting techniques have been developed by Gelci and collaborators (the 

 "DSA" method, cf. Gelci and Cazale, J. d. Math. Phys. de I'Atmosph. 2(No. 16): 

 15-41, 1962, Fons, Cah. Ocean. 18:16-33, 1966) and Barnett (Ph.D. thesis, 

 Scripps Inst, of Oceanography, 1966). The most urgent need now appears to be 

 for more detailed measurements of wave growth, as the source functions used 

 by different authors in the transfer equation still differ appreciably. As regards 

 the significance of the nonlinear energy transfer, it should be pointed out that 

 the recent measurements of Snodgrass et al. (1) have clearly demonstrated that 

 it is important and will need to be included in the source function. 



REPLY TO DISCUSSION 



WlUard J. Pierson, Jr., Leo J. Tick, and Ledolph Baer 



Since the preparation of our paper we have had the opportunity to study the 

 two possible sources, suggested by Dr. Miles, of the discrepancies we found. 



530 



