Apnendix R 



PRELIMINARY ENGINEERING COMMENTS ON COMMERCIAL 

 SUBBOTTOM PROFILING SYSTEMS 



The author has made a preliminary investigation of the capahilities 

 of current continuous reflection profiling systems from manufacturers' 

 specifications, users' comments, and at-sea experience with an emphasis 

 on their suitability for the marine engineering applications. No attempt 

 will be made to summarize each system's operating capabilities and speci- 

 fications; the reader is referred to the excellent studv by Schlank (1968). 

 Furthermore, the opinions expressed in this section are those of the author 

 alone and in no wav are to be interpreted as the expressed or implied 

 opinion of the Naval Civil Engineering Laboratory or the U. S. Navy. 



It appears that, to the best of the author's knowledge, no presently 

 available commercial subbottom system meets all the specifications drawn 

 in Appendix A. Perhaps the system best approximating the specifications 

 is the large-transducer Edo-Western 3.5 kHz Model 400. The transducer for 

 the Model 400 is difficult to tow; records mav be poor in shallow (<600 

 feet) water; resolution is less because several cycles of energy are 

 transmitted. Perhaps some of these deficiencies could be remedied. 



An alternative approach would be to use two commercial systems, a 

 high and a low resolution system, in lieu of one "do everything" system, 

 the combination of which should meet the majority of engineering needs. 



Since a sparker system is standard equipment aboard the USNS BARTLETT 

 (T-AG0R-13) and it is assumed that this vessel, or one with similar equip- 

 ment, will be used by the Navy in marine survey applications, this sparker 

 system provides a deep penetration, low resolution capability. 



In conjunction with the sparker system, and to provide a hi^h- 

 resolution capability, it is suggested that a small-transducer 3.5 kHz 

 subbottom system similar, but not limited, to the Edo-Western Model 415, 

 Ocean Research Equipment Model 1036, or equivalent, be used. The sparker 

 system would provide low-resolution about the geological setting while 

 the 3.5 kHz system would supply the high-resolution information on the 

 sediment structure. 



There are, nevertheless, limitations on the operating conditions of 

 the small-transducer 3.5 kHz systems. These high-resolution systems, for 

 example, generally give satisfactory performance in continental shelf 

 depths (<600 feet); certainly not meeting any requirements of 6,000 feet. 



To obtain satisfactory high-resolution performance in deep (~6,000 

 feet) water, a higher powered system such as the large-transducer Edo- 

 Western Model 400, the EO&G High Resolution Boomer™, or similar would 

 have to be used. 



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