SHIPBOARD ULTRASONIC WAVE HEIGHT SENSOR 



R. B. MARK 



Radio Corporation of America 



Burlington, Massachusetts 



ABSTRACT 



This paper describes a self-contained, elec- 

 tronic wave measuring and recording system 

 developed for the U. S. Navy Oceanographic Office. 

 In waves up to kO feet it measures relative dis- 

 placement of the sea surface from mean sea level 

 with an accuracy of better than 5$, while compen- 

 sating for all significant ship motions. Verti- 

 cal distance is measured by a box-mounted, 

 pulsed ultrasonic echo ranging unit . Ship motion 

 is measured by a doubly integrated, accelerometer- 

 vertical gyro system. The two signals are com- 

 bined with a fixed offset to produce true wave 

 height . 



GENERAL SYSTEM DESCRIPTION 



A new approach to wave measurement is embodied 

 in the shipboard wave height sensor developed by 



RCA for the Navy Oceanographic Office. This 

 instrument is capable of long-term, unattended 

 operation in the normal shipboard environment of 

 vibration, temperature change and poorly regu- 

 lated primary power supply. Data in the form of 

 displacement of the local sea surface from mean 

 sea level is recorded on a strip chart at a 

 sampling rate of 10 per second. Height resolu- 

 tion is 2 inches with maximum wave height of 

 !+0 feet or greater and accuracy of better than 

 5$. Long-term, stable integration of ship accel- 

 erations permits accurate recording of waves 

 having periods of 2 to 25 seconds . 



The mode of operation of the wave height sensor 

 is shown in the block diagram of Fig. 1. The 

 rugged, watertight, stabilized housing shown in 

 Fig. 2 is mounted at the ship's bow projecting 

 over the surface of the water. This housing con- 

 tains and protects the vertical gyro, acceler- 

 ometer and roll and pitch stabilization drives . 



BOW MOUNTED HOUSING 



INTERIOR ELECTRONICS 



VERTICAL 

 GYRO 



ACCELER- 

 OMETER 



T 



ROLL 



STABILIZATION 



DRIVE 



PITCH 

 CRADLE 

 DRIVE 



I 



TRANSDUCERS 



DOUBLE 

 NTEGRATOR 



SUMMING 

 AMPLIFIER 



TRUE 



WAVE 

 HEIGHT 



STRIP 



CHART 



RECORDER 



HEIGHT SENSOR 



MEASURING 



CIRCUITS 



AIR TEMPERATURE 

 COMPENSATION 



Fig. 1. Block diagram of wave height sensor. 



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