II. SURVEY OPERATIONS 



A. Conduct of Survey 



The main survey was conducted in a rectangular area cover- 

 ing 56,000 square miles. Survey lines were run in an east-west 

 direction at a spacing of five to seven miles, progressing from 

 south to north. (See Track Chart, Figure 2.) Eight develop- 

 ment surveys were conducted in locations where seamounts occur, 

 (See Index Chart, Figure 1.) The development-area survey lines, 

 in general, were from five to fifteen miles long and were run in 

 both north-south and east-west directions. The average ship's 

 speed when surveying was 12 knots. Bathymetric and magnetic 

 data were collected simultaneously along all survey lines. 



Throughout the survey area, the ship's position was fixed 

 by Loran-A, The fix interval was normally 30 minutes (10 minutes 

 on development surveys) , Fix accuracies ranged from +^ mile to 

 +2 miles. The most accurate fixes were in the south-central part 

 of the area and the least accurate in the southwesteim part. 



B. Instrumentation 



Magnetic total intensity measurements were made with a Varian 

 nuclear resonance magnetometer, model V-4931, modified for use 

 as a marine survey instrument. The sensor unit was towed approxi- 

 mately 500 feet astern of the ship to reduce the effect of the 

 ship's magnetic field. Because of equipment design, magnetic 

 data were recorded as "magnetometer counts", a unit of measurement 



2 



