

Fig. 2. Weather buoy instrument package. 



daytime and the other at night. If the station 

 is operated on demand it will respond on the fre- 

 quency used for interrogation. The two methods 

 of control are completely compatible . The main 

 instrument package is shown in. Fig. 2. 



MEASUREMENT OF SEA CONDITIONS 



The first additional oceanographic sensor to 

 he investigated is a sensor to obtain some 

 measure of the sea condition. One description 

 of the sea surface is that of an energy spectrum 

 which gives estimates of wave energy as a func- 

 tion of frequency. Energy spectra are usually 

 obtained by digital computer processing of a 

 time series of data of the surface elevations 

 taken over a time interval of the order of 20 

 minutes . The area under such a spectrum is a 

 measure of the total energy of all the waves . 



Since the weather buoy cannot be equipped with 

 a complex computer, nor is it practical to supply 

 the power required to transmit 20 minutes of wave- 

 height data to a shore station for analysis, the 

 possibility of obtaining the integrated value of 

 the mean square of the surface deviation over a 

 20-minute period using a pressure transducer 

 suspended below the buoy and working into an 



integrating device was explored. The fact that 

 this integrated value is a measure of the total 

 energy of the measured waves added to the desira- 

 bility of this arrangement . 



Further study indicated that a vertical array 

 of sensors could provide a certain amount of 

 wave period information and this will be discussed. 



Wave Measurements 



Trochoidal wave theory depicts ocean waves as 

 circular motions of water particles which decrease 

 exponentially with the depth expressed in wave 

 length. If one prefers to consider the ocean 

 surface as an infinitely broad distribution of 

 sinusoidal waves, the variations in pressure due 

 to the waves decrease with depth, the rate of 

 decrease being a function of the wave length. 

 For water depths of the order of a few wave 

 lengths either concept results in virtually the 

 same rate of decay of wave effects with depth. 



Because the wave effects diminish with depth 

 as a function of wave length and because wave 

 length is directly related to the square of the 

 wave period, there is available a means of 



108 



