energy content of the wave frequencies present and provides an estimate 

 of the height distribution of the waves as well as certain other statistical 

 quantities. However, hindcasting the wave spectrum is unsatisfactory for 

 two reasons: 1) Estimation of the wind field from sparse observations 

 spaced six hours apart is highly subjective; and 2) No specific energy 

 spectrum formulation has as yet been verified. 



There is still another method for description of the seaway. If the 

 waves at a fixed point can be measured for a sufficient length of time, 

 then this sample record can be converted into a wave (energy) spectrum 

 that will adequately characterize the state of the sea. 



There are many systems that will measure waves, but the requirement 

 that wave measurements complement simultaneous ship motion measurements 

 in all states of sea eliminates most of the known instruments. In 

 particular, it is required that the waves be observed at a fixed point 

 for a period of hours, while the ship conducts certain maneuvers which 

 may remove it several miles from the point of observation. This means 

 that the wave measurement system must be physically divorced from the 

 ship.* Furthermore, many tests will be made in heavy seas, so that it 

 will not be practical to seek out the instrument and recover it. As a 

 consequence of the conditions imposed by the particular problem stated 

 here, the wave measuring system must be able to: 



1. Telemeter information to the ship for at least 7 hours at 

 a distance of at least 8 nautical miles; 



2. Be launched from the deck of a ship in waves perhaps 25 

 feet high; and 



3. Be inexpensively constructed ($125.00 - $150.00) so as to 

 be expendable. 



*The wave measurement system may be integral with the ship if measure- 

 ments are made at zero forward speed. 



