III. DATA PROCESSING 



A. Preliminary Data Processing 



The magnetometer recorder traces were scaled at time intervals 

 of fifteen minutes and also wherever maximum and minimum magnetic 

 intensity values were recorded. These values were converted from 

 magnetometer counts to gammas and plotted on the smooth plot of the 

 survey track. The Precision Depth Recorder traces were scaled in 

 a similar manner. 



B. Magnetic Temporal Variations 



No attempt was made to remove temporal variations of the 

 earth's magnetic field from the data. Records of the Fredericksburg, 

 Virginia, Magnetic Observatory indicate that no severe disturb- 

 ances occurred during the time of the survey. Magnetograms and 

 calibration data are reproduced in the Appendix. 



The Fredericksburg observatory is approximately 150 miles 

 from the shoreward side of the survey area and about 500 miles 

 from the seaward side. Because of these distances, it is not pos- 

 sible to determine accurately the magnitude of the errors intro- 

 duced by the temporal variations. Nevertheless, the magnetograms 

 should indicate times when the data cannot be considered completely 

 reliable. Variations that occurred will introduce small errors 

 in the location of contour lines, particularly in the areas of 

 shallow magnetic relief. However, it is considered that they had 

 little effect on the magnitude and position of the most signifi- 

 cant anomalies. 



