THE NAVY OCEAN SCIENCE PROGRAM 57 



Major instrumental improvements also are being made for 

 obtaining higher resolution measurements on the thicknesses 

 and structures of sediments and rocks beneath the bottom. These 

 are the seismic profilers employing an electrical "sparker" 

 and, more recently, the pneumatic "air-gun." The principal 

 achievement of these systems is to permit the investigator to 

 maintain continuity of observation of complex and rapidly 

 changing geological structure during long sea passages. The 

 new sound sources also reduce the requirement for using high 

 explosives. New towed hydrophone arrays are being developed 

 to permit these seismic reflection measurements to be made at 

 higher speeds, and buoys to act as receiving hydrophone arrays 

 are being used to permit single-ship seismic refraction and 

 reflection experiments. These instruments are also of importance 

 to the Navy because of its need to study the behavior of acoustic 

 energy in the ocean. 



Improvements are being made to gravity meters used aboard 

 surface ships. As a result of the Navy Ocean Science Program, 

 this type of meter has become sufficiently reliable to provide 

 many sorely needed gravity measurements at sea. Further 

 increases in reliability of the gravity measurements are being 

 anticipated at the present time, both because of increased meter 

 accuracy and because of newly improved ship navigation control. 



Another device has been under continuing development for 

 determination of the slope of the sea surface from a ship. This 

 determination involves measuring the astronomical position of 

 the ship with a theodelite on a very accurate gyrocompass. The 

 device now provides measurements of the vertical that are 

 accurate to within 10 to 15 seconds of arc. This astronomical 

 position, when compared with the ship's geographic position 

 obtained from navigation data, provides a measure of the de- 

 flection of the vertical, and thus departures of sea level from the 

 earth's ellipsoid. The instrumentation is being refined to provide 

 deflection measurements that are accurate to about two seconds 

 of arc. The application of this instrument is important to the 

 Navy's gravity program and holds promise for oiu" knowledge 

 of oceanic circulation based on density structure. 



