Ch. 4— Technologies for Exploring the Exclusive Economic Zone * 133 



Figure 4-8.— Frequency Spectra of Various Acoustic Imaging Methods 



10 100 



Frequency 



SOURCE: B.W. Flemming, "A Historical Introduction to Underwater Acoustics, With Special Reference to Ectio Sounding, Sub-bottom Profiling, and Side Scan Sonar,' 

 In W.G.A. Russell-Cargill (ed.), Recent Developments in Sidescan Sonar Tecliniques (Capetown, South Africa: ABC Press, Ltd., 1982). 



range in frequency from about 5 hertz to 1 kilo- 

 hertz. The systems with sound frequencies in this 

 range are very useful to the oil and gas industry. 

 Most often these are expensive multi-channel sys- 

 tems. Since most mineral deposits of potential eco- 

 nomic interest are on or near the surface of the 

 seabed, deep penetration systems have limited use- 

 fulness for mineral exploration. Seismic systems 

 most often used for offshore mineral exploration 

 are those that operate at acoustic frequencies be- 

 tween 1 and 1 4 kilohertz (typically 3 . 5 kilohertz) . 

 These systems, known as sub-bottom profilers, pro- 

 vide continuous high-resolution seismic profile 

 recordings of the uppermost 30 meters of strata. ^^ 



^°P.K. Trabant, Applied High-Resolution Geophysicai Methods: 

 Offshore Geoengineering Hazards (Boston, MA: International Hu- 

 man Resources Development Corp., 1984), p. 81. 



TypiccJly, they are single-channel systems. They 

 can be operated at the same ship speeds as bathy- 

 metric and sonar systems. A few towed vehicles are 

 equipped with both side-looking sonar and sub- 

 bottom profiling capability using the same coaxial 

 tow cable. ^^ 



One drawback with single-channel systems is that 

 they suffer from various kinds of multi-path and 

 pulse reverberation problems, problems best han- 

 dled by multi-channel systems. A 100 or 500 hertz 

 multi-channel system is able to provide shallow 

 penetration data while avoiding the problems of 



"C.J. Ingram, "High-Resolution Side-Scan Sonar/Subbottom 

 Profiling to 6000M Water Depth," unpublished, presented at the Pa- 

 cific Congress on Marine Technology, sponsored by Marine Tech- 

 nology Society, Hawaii Section, Honolulu, HA, Mar. 24-28, 1986. 



