response curves for pitch and roll of a typical 

 oceanographic ship. To the right of the appro- 

 priate natural frequency the ship response is 

 l80° out of phase with the slope of the waves and 

 to the left it is in phase. Maximum amplitude 

 of pitch response is expected to be less than 8 

 and roll response will not ordinarily be of much 

 greater magnitude because the ship is required to 

 be hove to and headed into the sea during wave 

 measurements. Since the major portion of the 

 pitch response is in phase with the wave slopes, 

 the incidence of the echo ranging beam will usu- 

 ally be near perpendicular and signal loss will 

 be minimized. For higher frequencies, corres- 

 ponding to pitching that is out of phase with the 

 wave slope, the pitch amplitudes and wave slopes 

 are smaller. 



To provide the necessary accuracy of roll sta- 

 bilization at the frequencies near the peak of 

 the spectrum, the servo bandwidth has been set 

 considerably higher than the frequency of peak 

 wave response. The accelerometer pitch cradle 

 servo bandwidth is several times that of the 

 roll servo. 



CONCLUSIONS 



The shipboard wave height sensor has been 

 designed for accurate wave measurement at sea. 

 It is believed that this design provides capa- 

 bilities far exceeding those of existing systems, 

 particularly with respect to measurement of 

 large waves in deep water. 



ACKNOWLEDGMENT 



Development and construction of the equipment 

 described herein was supported by the U. S. Navy 

 Oceanographic Office under contract number 



N62306-932. 



REFERENCES 



COX, C. and W. MUNK, Measurements of the sea 

 surface from photographs of the sun's 

 glitter, J. Optical Soc . Amer ., kk , 37-^0, 

 January 195^- • 



COX, C. and W. MUNK, Statistics of the sea 

 surface derived from sun glitter, J. Mar. 

 Res ., 13, 198-227, November 195^. ~~ 



105 



