3. KS-124 Photoelectric Sextant 



An AN/AVN-1 astro- navigational set has been modified by the 

 manufacturer to specifications provided by the Hydrographic Office 

 to measure precise, averaged, celestial relative bearings. This auto- 

 matic star-tracking device has been coupled with the VAM program 

 timers to provide synchronized data. KS-124 data are presented on 

 mechanical counters and recorded automatically by a synchronized data 

 camera. 



The KS-124 ultimately should replace the manually operated VAM 

 periscopic sextant, resulting in increased accuracy and permitting 

 the observer to assist in monitoring the magnetometer and naviga- 

 tional equipment. However, the necessary reliability and accuracy 

 have not yet been demonstrated for this instrument. 



4. Accuracy of airborne magnetic surveys 



Under good flight conditions, the VAM system is believed to 

 be sufficiently accurate for present and proposed future require- 

 ments of the world charting program. The accuracy of the survey 

 depends upon: (1) Magnetometer accuracy, (2) aircraft compensation 

 accuracy, (3) navigational accuracy, (4) presence of magnetic anom- 

 alies, and (5) size of magnetic temporal variations. 



a. Magnetometer accuracy 



To a large extent the measurements to define the direction 

 of the magnetic vector are weather dependent. Turbulence and acceler- 

 ation cause vertical reference errors which, in turn, can lead to 

 substantial errors in the computed results. Gross errors, however, 

 should be readily apparent in a sequence of closely spaced readings 

 along a track line. Cloud cover prevents measurement of the relative 

 bearing (RB), and thus of declination (D). 



b. Aircraft compensation accuracy 



Horizontal components of the permanent and induced fields 

 of the aircraft are compensated until the deviations in measured F with 

 respect to the aircraft^ MH, for cardinal headings, is about 5 gammas 

 or less. When this is done at a site where the inclination, I, is about 

 60°, the residual horizontal field of the aircraft should not exceed about 

 10 gammas. The vertical component of the air craft 1 s own field is some- 

 what more difficult to identify. The residual vertical field of the aircraft, 

 after compensation, is probably not more than 10 gammas for a limited 



XIV- 6 



