navigation system), radio bearings, Loran, search radar, periscopic 

 sextant, driftmeter, and visual observations. Data are combined 

 to determine dead-reckoned positions for selected times. Periodic fixes 

 and lines-of-position are used to correct or modify the dead-reckoned 

 positions. The positions required for tabulation and computation along 

 with magnetometer data are interpolated along the track. The respon- 

 sibility for exe-eution of navigation and tracking lies with the aircraft 

 operating per-sonnel. Navigational errors, in mid-ocean and under 

 reasonably good flight conditions, should not exceed about five miles. 

 The accuracy of navigation is largely weather-dependent. 



An AN/AVN-1 astro-navigational set is being obtained to supplement 

 the navigational periscopic sextant. In addition this unit is being modified 

 to provide RB and thereby supplement or replace the portion of the VAM 

 system devoted to obtaining RB. RB from the AN/AVN-1 modified 

 system will be indicated on a visual mechanical counter and will be 

 recorded periodically along with other navigational data by a 35 mm. 

 data- re cording camera. 



It is recommended that, as a long range goal, the recording system 

 of the VAM system be modified to eliminate the manual operations. 

 Data ultimately should be recorded directly in a format suitable for 

 direct input to a computer. Reliability, simplicity, and accuracy must, 

 however, be retained or improved if possible. Provided that the 

 AN/AVN-1 astro- navigational set proves successful, data from it also 

 should be recorded for direct computer input. 



B. Gravity Instruments (A. L. McCahan) 



Gravity survey instruments for land surveys are currently accurate to 

 ±0.1 milligal. This accuracy is sufficient for all foreseeable geodetic pur- 

 poses. Ocean survey instruments are currently accurate to ± 3 milligals. 

 This accuracy is sufficient for present needs but should be improved to 

 ±1 milligal for future requirements. Sea gravimeters are currently 

 available for submarine and surface ship use. Inaccuracies in ocean 

 gravity readings obtained by submarines are due primarily to errors 

 in navigation, including effects of subsurface currents. Reports on sea 

 trials of gravimeters are included in Transactions of American Geophy- 

 sical Union, Vol. 39, No. 3, 1958, and in unpublished Navy reports. With 

 the advent of surface ship gravimeters, new methods for data processing 

 must be adapted to handle the large volume of data which will be obtained. 



Encl. (3) to Code 5401-BEO/bah memo of 23 Jul 1958 



B-12 



