levels and pulse characteristics; thus, there are a considerable number of 

 options available from which to choose a sound source to best meet the needs 

 of a specific field survey. For borrow source exploration, the principal 

 types of sound sources used are low to moderate energy, electrically driven 

 piezoelectric (pinger) , electromechanical (boomer) , and electric arc (sparker) 

 types with high resolution capability. Seismic reflection profilers using 

 these three sources are reviewed below in detail. 

 Vertical resolution and penetration 



80. The two most important capabilities of a seismic reflection system 

 are its vertical resolution and degree of penetration. Vertical resolution is 

 the ability to differentiate closely spaced reflectors. This ability is pri- 

 marily a function of the compressional wave velocity of the medium and the 

 frequency of the acoustic signal and can be approximated as follows: 



T - °: 5v (2) 



where 



T = thickness of a unit between two reflectors that can be resolved 



v = compressional wave velocity of the material 



f = dominant frequency of the acoustic pulse 

 From this expression, it can be seen that the higher the dominant frequency, 

 the finer the resolution. Unfortunately, raising the frequency of the acous- 

 tic pulses increases attenuation of the signal and consequently decreases the 

 effective penetration. For borrow source exploration, it is necessary to 

 obtain good resolution because of the importance of relatively thin layers in 

 calculating sediment volumes and overburden thickness. However, to achieve 

 good reflector continuity and obtain a coherent pattern of the subbottom 

 stratigraphy, it is necessary in many places to use equipment that has greater 

 penetration capability than the high resolution profilers in general use. To 

 obtain the needed resolution and penetration, it is a common practice to use 

 two seismic reflection systems simultaneously during the survey; one having 

 high resolution capabilities and the other being capable of greater penetra- 

 tion. Generally, the data from both systems can be displayed, one over the 

 other, on a single strip chart record. Since the major expense of geophysical 



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