SECT. 1] 



REFRACTION AND REFLECTION TECHNIQUES AND PROCEDURE 



31 



two hydrophones. The relative frequency response of the LGO transistor 

 amphfiers is shown in Fig. 8, as given by Luskin and Koelsch (1958). 



a- 

 § 



-Cl 



10 



!00 1000 



Frequency ~ c/s 



10,000 



Fig. 8. Response of LGO amplifiers relative to maximum for each channel. 



4. Plan of Operations 



The lines of shots described earlier can be combined in a number of ways to 

 make a seismic station. Combinations of linear profiles in common use are 

 shown in Fig. 9 and may be classified as : 



1. Single profiles 



2. Split profiles 



3. Reversed profiles 



4. Overlapping profiles 



5. Compound profiles 



6. Fan profiles 



7. Area surveys 



A. Single Profile 



The single profile is, as its name implies, a single line of shots extending 

 radially from the receiving ship. Variations in layer thickness along the line 

 of shooting cannot be detected in this method and will give false velocity and 

 depth determinations ; this method is, therefore, avoided if possible. 



B. Split Profile 



The split profile consists of two single profiles forming a straight line with 

 the receiving ship in the middle. If there are no large variations in dip within 

 the length of the profile, this method will give velocity, layer thickness, and an 

 indication of dip. It is most ajDplicable to work in areas of broad structure 

 such as the normal ocean basins and the great rises. In areas of comjDlexity, 



