76 THE NAVY OCEAN SCIENCE PROGRAM 



low-density material in the crust. Many island areas, particularly 

 the Hawaiian Island archipelago, contain large mass excesses. 

 In the Hawaiian area this mass may have resulted from the 

 outpourings of lava flows that occurred so rapidly that the crust 

 and mantle have not readjusted (by rock creep and flow) com- 

 pletely to this excess of material. 



GRAVITY AND GEODESY 



Means have been developed for measuring the earth's gravity 

 field in oceanic areas. Extensive gravity measurements have 

 been obtained from the Navy Ocean Science Program, the 

 oceanographic operations program, and in the operations of 

 other agencies. The measurements have provided valuable data 

 over many ocean areas, and particularly over selected regions. 

 Many times more data, and also more accurate data, are required, 

 however, before the Navy's needs in navigation can be satisfied. 



The sea gravity measurements that have been obtained have 

 had considerable impact on the development of a world geodetic 

 system, on the calculation of local deflections of the vertical 

 (deviations of the vertical to the earth's reference due to local 

 mass anomalies), and on providing the data required to improve 

 our knowledge on the shape of the earth's geoid (approximate 

 sea-level surface). These factors all have had application to im- 

 proving navigational control at sea. Attempts are now being 

 made to use the calculated gravity anomalies at sea to improve 

 the predicted orbital paths of satellites and, hence, to improve 

 the accuracy of the navigational satellite system developed by 

 the Navy. The gravity anomalies also have had wide application 

 to interpreting crustal and subcrustal structures in the ocean 

 areas. 



ARCTIC 



The Navy has successfully occupied the polar ice islands, 

 operated aircraft and navigated ships and submarines in arctic 

 waters, developing by these means both extensive and detailed 



