38 THE NAVY OCEANOGRAPHIC OPERATIONS PROGRAM 



The Oceanographic Office maintains a Magnetic Data Library 

 for the Department of Defense and makes this information 

 available to the scientific community in a variety of formats at a 

 nominal cost. Project MAGNET data are available in microfilms 

 of the original data collection tapes or in special publications giving 

 total magnetic intensity, magnetic declination (variation), mag- 

 netic dip, horizontal intensity, and vertical intensity values at 

 closely spaced intervals throughout the world. 



Techniques for improvement of the measurement, analysis, 

 and display of the earth's magnetic field are under development. 

 Models are being developed for upward extrapolation of the 

 magnetic field. The accuracy of the spherical harmonic surface 

 at sea level has been verified from the data incorporated in the 

 1965 World Variation Charts. Spatial coherence of short-period 

 variations in the magnetic field is being tested by simultaneous 

 records made at two or more stations. Finally, a geological 

 interpretation of the total magnetic field data collected along the 

 east coast of the United States is underway in cooperation with 

 the U. S. Geological Survey. 



GRAVITY SURVEYING 



For many years the Navy's gravity collecting capability con- 

 sisted of land meters used by geodetic parties supplemented by 

 gimbal-suspended spring-balance meters in submerged submarines. 

 Taking submarine gravity measurements around remote islands 

 and combining these with gravity measurements and astronomical 

 observations ashore was virtually the only method of tying these 

 islands geodetically to the rest of the world. Later, underwater 

 meters set on the bottom in the relatively shallow off-shore waters 

 filled the void between the submarine and land measurements, 

 allowing more precise positioning. These methods -are also used 

 extensively for delineating the geologic structure of the earth's 

 crust and the investigation of possible oil and mineral deposits. 

 Underwater meters placed on the bottom give measurements com- 

 parable to land meter accuracies; Navy geophysicists in cooperation 

 with the Army Map Service recently used them in a gravity survey 

 of Lake Superior. 



In the 1950's, as a greater knowledge of the earth's gravity 

 field became increasingly important for the refinement of inertial 



