32 sHOR [chap. 2 



such as the continental shelves, trenches and seamounts, changes may take 

 place within the length of the profile that will make interpretation difficult or 

 ini])ossil)le. Des])ite the a]>parent disadvantages, the advantages are many. 

 The method requires only a single set of i)ersonnel and equi])ment for receiving, 

 and only one ship need carry explosives. Safe and legal handling and stowage 

 of large quantities of explosives at sea is not simple, and on many ships nearly 

 impossible. Similarly, the maintenance of receiving equipment in the marine 

 environment })resents many ])roblems. The two ships never cover the same 

 track, making for better bathymetric coverage in reconnaissance areas (of 



• ) 



FAN 



AREA SURVEYS 



Fig. 9. Station arrangements. 



which tile oceans have many). Programs requiring time on station can be 

 concentrated on the receiving ship while the shooting ship carries equipment 

 used underway such as a magnetometer and a gravimeter. Split profiling has 

 been done primarily by the SIO group. 



C. Reversed Profile 



Reversed j)r()filing requires either that two ships be used each of which is 

 capable of both shooting and receiving or that the ships interchange positions 

 at the end of each rtui, losing considerable time. Determination of dip and 

 elimination of errors due to structiu'al changes along the line of profiling is 

 improved, especially if second arrivals can be read from the records. If only 

 first arrivals can be used, as is too often the case, true reverse coverage of 



