II. SURVEY OPERATIONS 



A. Conduct of Survey 



This survey was conducted in an 18,000 - square-mile area 

 located northeast of the southern Bahama Islands (figure 1, Index 

 Chart) . Primary survey lines were run in a northeast-southwest 

 direction perpendicular to the trend of the southern Bahamas. Average 

 track spacing was 5 miles. Five cross-check lines were run to check 

 navigational control and to define more clearly certain bathymetric 

 features (figure 2, Track Chart). The ship's average speed while 

 surveying was 12.5 knots. Magnetic and bathymetric data were collected 

 simultaneously along all survey lines. 



In the survey area, the ship's position was fixed at 15 minute 

 time intervals using Loran-A. Fix accuracy, as determined by cross- 

 check lines, was within one mile. The most accurate fixes were in the 

 west-central part of the survey area, and the least accurate occurred 

 in the eastern part. Loran-A fixes at 30-minute time intervals were 

 used to plot the tracks to and from the survey area. 



B. Instrumentation 



Total magnetic intensity measurements were made with a Varian 

 nuclear resonance magnetometer, model V-4914. To diminish the effect 

 of the ship's magnetic field, the sensor unit was towed approximately 

 700 feet astern of the ship. Because of equipment design, magnetic 

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

 inversely related to the magnetic field intensity. These units were 

 recorded in analog form on a Sanborn Galvanometric Recorder. 



