108. Noise suppression has been a primary objective of attempts to 

 increase the quality of seismic reflection equipment. Available technology 

 includes several measures for noise suppression that have considerably 

 improved record quality. In addition, techniques for interpretation of rec- 

 ords have improved with growing experience, and much of the ordinary noise can 

 be recognized and dealt with by the analyst. Multiple traces, however, remain 

 a major problem, especially in the relatively shallow waters where borrow 

 source explorations are normally carried out. Here, closely spaced multiples 

 often conceal upper sub-bottom reflectors, or create a possibility of their 

 being interpreted as valid reflectors. 



109. Seismic reflection profilers are in many places limited in pene- 

 tration by materials in the bottom or sub-bottom deposits that cause severe 

 attenuation of the acoustic pulse, and consequent loss of data on underlying 

 materials. Coarse sand and gravel, glacial till, and highly organic sediments 

 often create such conditions. In some cases, increases of power and using 

 lower frequency acoustic pulses can achieve penetration but at a necessary 

 reduction in resolution that may greatly diminish record quality. 



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