1.0 INTRODUCTION 



Why waves form when air flows over water is a question about nature which 

 has not yet been satisfactorily answered. This is no fault of the theoreticians, how- 

 ever, for several theories that could account for wave generation have been advanced. 

 The real problem is that, with the exception of Snyder and Cox (1966), it has not been 

 possible to observe adequately the manner(s) in which the wind actually adds energy to 

 the wave spectrum. With this in mind, the U. S. Naval Oceanographic Office has 

 initiated a series of field experiments designed to measure the rate of growth of the 

 energy spectrum under steady wind conditions. This paper will describe the method 

 and results of the first of these experiments. 



The basic idea was to observe steady state, fetch-limited wave spectra that had 

 been developed by a geophysically uniform wind field and that were representative of 

 a number of different fetch lengths. From these observations it was possible to «^ain 

 estimates of spectral growth. In practice, the experiment was timed to take place after 

 a strong low pressure system hod passed over the East Coast of the United States and 

 the offshore winds behind the frontal system hod established a stationary wave syst«n 

 in the area within about 100 nautical miles of the coast. An aircraft, equipped with 

 a high-resolution radar altimeter, was then sent aloft to d)tain continuous profiles of 

 the sea surface from the coast downwind to a desired distance. A similar run was made 

 upwind. The data were subsequently transformed Into spectra representative of various 

 distances from the coast „ These spectra eventually provided estimates of spectral 

 growth over the major frequency range of the spectrum. A key issue in the analysis 

 was that the wind field should have been constant during and for a given time before 

 the flight. This requirement Is treated at length In Section 4. 



2.0 GENERAL THEORY AND BACKGROUND 



The method employed in reducing the sea surface profiles, as seen from the 

 plane, to the final estimates of real spectral growth will be discussed in later sections 

 of this paper. For the moment attention is confined to a description of the general 

 theoretical approach to and appropriate background information on the overall experi- 

 ment. 



Hasselmann (1960) and Groves & Melcer (1961) independently proposed the 

 following general equation to describe the energy balance of the wave spectrum in 

 deep water: 



