to yield subbottom reflections. The pinger system is most commonly either 

 fixed over the side of the survey vessel or towed behind. The former method 

 is used most often on CERC's surveys because it lessens interference when other 

 equipment is being towed from the vessels. A convenient feature of the pinger 

 is that, unlike other seismic systems, the same transducer is used to both 

 transmit and receive the acoustical signals, thus minimizing problems associated 

 with equipment deployment and retrieval . 



b. Boomer Systems . The boomer seismic systems (Fig. 3) use an electro- 

 mechanical energy source having a variable power output from 100 to about 1500 

 joules depending on the particular system used. An advantage of boomer systems 

 is that they yield high resolution of geological detail (Fig. 4) with subbottom 

 penetration as great as 300 feet (91 meters) . Almost no bubble pulse appears on 

 the record to mask the data return in contrast to some sparker equipment; this 



is an advantage when interpreting the profiles. Since boomer profiles yield such 

 detailed data on sedimentary bedding and contracts, they are especially useful in 

 making correlations with cores and borings that may also be taken as part of a 

 survey. Boomer transducers are normally towed about 30 feet (10 meters) behind 

 and to the side of the survey vessel on a catamaran. The reflected signals are 

 received by a 10- to 12-element "eel" or hydrophone that is towed to the oppo- 

 site side. The seismic profile data are graphically displayed on a dry paper 

 recorder. 



c. Engineering Sparker . The engineering sparker system, sometimes called 

 a "minisparker," is an intermediate penetration, medium resolution device 

 that is particularly useful for surveys where the sea floor is firm or compact. 

 The sparker will yield geological data in areas where boomer or pinger systems 

 cannot penetrate the subbottom, but the resolution is generally not as high as 

 with the other systems. Also, the presence of a thicker bubble pulse on the 

 profiles makes geological interpretation more difficult. Like the boomer, the 

 sparker is normally towed about 30 feet behind the survey vessel, along with a 

 hydrophone array used to receive the reflected signals and transmit them to 



a graphic recorder. 



3. Operation of Equipment and Data Interpretation . 



The mobilization and the day-to-day operation of the various seismic pro- 

 filers are straightforward and do not vary much from the start of the survey 

 to its completion. However, the operation does require trained technicians; a 

 highly skilled electronic technician is necessary to take care of equipment 

 breakdowns and regular maintenance of the equipment during the survey phase. 



If the geophysical profiles are recorded on roll paper, as opposed to mag- 

 netic tape, at the end of each survey day the records should be removed from the 

 survey vessel and stored ashore in a secure area. At the end of the survey, the 

 collection of seismic profile records should be hand-carried to the office to 

 insure there is no loss, damage, or undue delay. The records are the final 

 product of an expensive and time-consuming survey — security in transit cannot 

 be overemphasized. 



One of the most difficult problems with analysis and interpretation of a 

 large number of seismic records is their printout length and width. The records 

 are normally 19 inches (48 centimeters) wide, and even with considerable vertical 

 to horizontal scale exaggeration, a typical survey with several hundred kilo- 

 meters of trackline coverage yields several rolls of long records. Because 



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