from the wave-height buoy is received at the ship with a wide band 

 receiver which converts the frequency changes of the transmitter into a 

 varying d-c voltage. The varying d-c voltage is proportional to the 

 acceleration being sensed by the accelerometer . The received signal 

 contains high-frequency components which are caused by the very short 

 waves (which contribute little to the ship motions being studied) as 

 well as by mechanical noise of the transmitter unit. These signals are 

 of such a magnitude that if they were allowed to appear on the recording, 

 they would completely mask the desired signal. That is, the gain of the 

 recording system would have to be set so low that the desired signal 

 (associated with frequencies below 1/3 cps) would be too small to read 

 accurately. For this reason, the output of the reciever is applied to a 

 low-pass filter which removes the undesirable high frequencies but allows 

 the desired information to pass through unaltered, except for some phase 

 distortion which is not considered significant for the intended applica- 

 tion. The output of the filter is then recorded by whatever means are 

 available, i.e., tape recorder, direct writing recorder, etc. 



Calibration of the system is accomplished by establishing a zero 

 reference with the wave- height buoy level and then tilting the buoy 

 through 60- degrees. The tilt will produce a frequency change in the 

 transmitter which represents the 1/2-g change which the accelerometer 

 senses due to the 60 degree tilt. When the signal is recieved, the 

 receiver will produce a steady d-c voltage output proportional to the 

 transmitter change in frequency and therefore proportional to acceleration. 

 This d-c voltage and the zero obtained when the buoy is level are recorded. 

 The difference between the zero and the voltage produced due to the 60- 

 degree tilt is the calibration for 1/2-g, and all records from that partic- 

 ular wave- height buoy may be referred to this calibration. 



DETAILED DESCRIPTION OF COMPONENTS 



BUOY ASSEMBLY 



The buoy assembly of the SPLASHNIK is composed of a buoyancy unit 



4 



