140 



agreement between different combinations of gauges is not as good for 

 this set that represents a "ragged" sea state. This is most probably 

 because each of the two gauges, separated a finite distance, 

 independently measure more slightly different wave activity than in 

 the first data set shown. For such a confused sea state of 

 relatively short period waves, it was not possible to verify which 

 channel, dP2 or dP4, gave the more accurate estimate of wave 

 direction (if indeed there was any one principal direction) . 

 Accurate radar and visual observations are practically impossible 

 during such conditions. As expected, the omnidirectional energy 

 spectra generated from the DPG data for this confused sea state 

 agrees in form with that of the computer-simulated case of one wave 

 frequency with two directions as shown in Figures IV-10 and IV-11. 



7. Energy Spectra from Differential Pressure Gauges 



Figure VI-IA illustrates one record's wave energy spectra 

 generated from the absolute pressure gauge and the water surface 

 slope energy spectrum from each of the two perpendicular differential 

 pressure gauges dP2 and dP3. The record was taken during wave 

 activity from the northwest — the direction in which DPG arm 3 is 

 oriented towards. Accordingly, one observes that there is 

 considerably more energy contained in the slope spectrum from dP3 

 than from dP2. This is because there are relatively small slope (and 

 pressure) differences along the wave crests and troughs which are 



