II. SURVEY OPERATIONS 



A. Conduct of Survey 



The PEIEVAIL departed New York on 17 July and arrived in 

 Washington, D. C., on 25 July after completing almost 2500 

 miles of survey track. As shown in Figure 1, average track 

 spacing was approximately 30 miles with the tracks trending north- 

 west and southeast. This particular survey track configuration was 

 established to best meet both magnetic and bathythermal survey 

 requirements. The average speed of advance over the survey track 

 was 12.5 knots. 



B. Control 



Survey control was by Loran-A with additional position deter- 

 minations by radar where possible. The position of the ship was 

 determined every fifteen minutes and then plotted on Mercator 

 Plotting Sheets (H.O. 3000 series). On the shoreward side of the 

 survey area, both Loran-A and radar were used. Here, the probable 

 position accuracy is estimated as being within + 1 mile. On the 

 seaward side of the survey area, radar fixes were not available, 

 and only Loran-A fixes were taken. Here, the probable position 

 accuracy is estimated as being within + 2 miles. 



C. Instrumentation 



A Varian nuclear resonance magnetometer, Model XN-4901, was 

 used to measure the earth's total magnetic field intensity. With 

 this instrument, the total field intensity can be measured to an 

 accuracy of about + 1 gamma (0.00001 oersted). Magnetometer equip- 



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