SEISMIC METHODS 905 



On calm days, between 200 and 300 profiles may be obtained. Two or three 

 days may then be lost due to bad weather, or occasionally to breakdown of 

 equipment. The overall cost of water seismic operations may vary from 

 $20,000 to $75,000 per month, depending on the type of operation. Because 

 of high production the unit cost per profile is often comparable to or less 

 than that of land operations. 



During the interval from 1945 to 1950 a variety of war-surplus boats 

 has been used in ofifshore seismograph operations, including sub-chasers, 

 air-sea rescue boats, and mine sweepers. (See Figure 569.) Various types 

 of fishing boats are also widely used. The total number of boats per crew 

 may vary from 1 to 7, depending on the requirements of the operation. 

 Operating crews may comprise from 10 to 40 men. The crew usually stays 

 out for a period of ten days. Good management and coordination are 

 required for smooth and efficient operation and satisfied personnel. Numer- 

 ous supply problems, including food, provisions, water and fuel, require 

 constant attention. Close attention must also be paid to weather conditions 

 to insure safety of the men and equipment. 



RADIO SURVEYING TECHNIQUES 



During World War II a tremendous amount of research and develop- 

 mental effort went into radar and related electronic techniques. After the 

 war, military security measures were lifted, and many geophysicists 

 returned to their former jobs equipped with new skills acquired in govern- 

 ment-sponsored research and military service. Applications of these tech- 

 niques to problems in geophysics were soon recognized. 



Radar and associated radio navigation aids have been applied to geo- 

 physical field work for the purpose of quickly locating observation stations 

 in unmapped land areas and offshore operations. Much of the military 

 equipment was not directly suited to this work, but since some of this 

 equipment became available after the war to geophysical workers, it was 

 used as a stop-gap until more suitable apparatus could be designed and 

 constructed. At the present time many laboratories are in the process of 

 developing radio survey gear for geophysical applications. It is too early in 

 this program to forecast what form these new developments may finally 

 take. Probably no one type of equipment will meet adequately all of the 

 Varying needs of the different geophysical surveying operations. Radio 

 surveying techniques are described in the literaturef and only a general 

 outline of the basic operating principles and the general limitations of the 

 systems will be given. ij: 



Radio navigation systems can be divided into two basic classes, i.e., 

 pulsed systems and c.w. (continuous wave) systems. The pulsed systems 

 include Radar, Ratran, and Shoran. The c.w. systems include Lorac and 

 Raydist. Basically the pulsed systems have the advantage that they gen- 



t Radiation Laboratory Series, by M.I.T. Staff, McGraw-Hill, 1947. 



t Eugene A. Slusser, "Radio Location in Oil Prospecting," Electronics, August, 1949. 



