B. Instrumentation 



Absolute total magnetic intensity measurements were made with a 

 model V-4914 Varian proton precession airborne magnetometer, adapted 

 for use as a marine survey instrument. The sensor unit was towed 

 approximately 500 feet astern of the ship to minimize the effect of 

 the ship's magnetic field. A toroidal-coil epoxy sensor, or "fish", 

 was used successfully during the first two weeks of the survey. Its 

 use then was abandoned when a loose electrical connection within the 

 casting caused noise and loss of signal. During the remainder of 

 the survey operations, a rebuilt Varian model XN-49-818 fish with 

 omnidirectional coils gave excellent results. In both cases the 

 hydrocarbon sample in the fish was ship'sdiesel oil. 



The V-4914 instrument measures the intensity of the magnetic 

 field by measuring the period of time required to count 1024 cycles 

 of the proton precession frequency. This time measurement was 

 accomplished by counting pulses of a 400 KC reference frequency 

 during the 1024 cycle gate period. The reference frequency count 

 was recorded in analog form on a Sanborn recorder. The sensitivity 

 of the measurements was about + 1 gamma. 



Bathymetric data were recorded on a Precision Depth Recorder 

 (MK XI) used in conjunction with an AN/UQN-lc Echo Sounding Set. 



