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WORZEL, AND HARRISON 



[chap. 9 



extensively used in the open ocean with a success that may be gauged from 

 Fig. 10, which shows a survey in the Pacific Ocean off Southern CaHfornia. 



E. Airborne Gravity Measurements 



Tlie method of reading the LaCoste-Romberg gravity meter, in which the 

 couple on the beam is computed from the full equation of motion (see 2-D), 

 allows gravity measurements to be taken extremely rapidly. Aircraft flying in 

 quiet air are much steadier than a surface ship of moderate size under normal 



Fig. 10. Gravity survey of continental borderland of Southern California. 



sea conditions, so that accurate gravity measurements are possible. The chief 

 difficulty with airborne measurements is that corrections for the speed of the 

 airplane are very large and must, therefore, be determined with great accuracy. 

 Even a slow airplane is moving very quickly compared with a surface ship and 

 therefore covers a considerable distance during an averaging time suitable for 

 use on ships. For instance, a plane travelling at 180 mph covers 36 miles in 

 the 12-min averaging time found convenient for shipboard measurements. 

 While this averaging time can be reduced considerably, it is clear that airborne 

 surveys cannot yield great detail. On the other hand, for geodetic and some 

 geophysical purposes, measurements averaged over, say, 10 miles would be 

 quite adequate. The measurements could be made at a height of, say, 20,000 ft, 

 which means that it would be possible to map gravity over practically the 



