The development of small, simple, easily towed total magnetic field 

 sensors which are virtually insensitive to motion, temperature, pres- 

 sure, etc. has made possible the routine acquisition of magnetic data 

 from ships. 



The sensitivity of the nuclear precession magnetometer is generally 

 adequate for measurement of the total intensity value of the magnetic 

 field, but is not sufficient to allow use of the instrument as a high 

 resolution magnetic field gradiometer. A more recent development, 

 the rubidium vapor magnetometer, offers a higher order of sensitivity 

 (in the order of 0.01 gamma). This instrument appears to possess all 

 of the important advantages of the nuclear precession instrument 

 together with a sufficiently high accuracy to make it suitable for gradio- 

 meter use. 



3. Land measurements 



In order to facilitate repeat station observations and reduce the 

 time required to occupy a station, it would be useful to employ a 

 portable electrical magnetometer with which a set of readings could 

 be obtained in a matter of minutes. Such a device has been developed 

 by the Dominion Observatory of Canada. 



4„ Special purpose surveys 



Further development of instruments is required in order to 

 be able to define the magnetic environment of an area. In part, existing 

 instruments have been found to be unwieldy in operation. New gradio- 

 meter equipment is currently under development and should overcome 

 the deficiencies of the present instruments. A magnetic temporal 

 variation recorder must be developed to meet existing requirements. 

 Equipment for this purpose is not currently available. 



H. RECOMMENDATIONS 



1. Airborne geomagnetic surveys 



The short-term instrumentation program for airborne surveys 

 should be directed towards satisfying several present deficiencies 

 in such a way as to reduce manual operations, obtain maximum reli- 

 ability, and yet utilize available components wherever possible. In 

 this connection, it is recommended that the Hydrographic Office: 



a. Develop and construct a low-drift voltage standard for use 

 in the VAM total intensity circuit; also evaluate the silicon zener 



XIV- 9 



