Ch. 4— Technologies for Exploring the Exclusive Economic Zone * 127 



Table 4-4.— Bathymetry Systems^ 



Frequency Beams 

 System kilohertz no. 



Sea Beam 12 



Super Sea Beam (proposed) 12 



Towed Sea Beam (proposed) 17 



BSVHydrochart II 36 



KRUPP Atlas Hydrosweep" 19.5 



Honeywell ELAC Supercharf^ 12 



50 



Minichart 50 



SIMRAD EM100 95 



HOLLMING Echos 15/625 12 



Echos XD 15 



45 



BENTECH Benlgraph'' 1 ,000 



740 

 500 



Swath Max System 



Beamwidth angle depth cost 



degrees degrees meters $10^ 



^Interferometric systems (e.g., SeaMARC II) are considered in table 4-2; however, ttiey could be considered in ttie bathymetric table as well, as they have the potential 

 of producing bathymetric data equivalent to that of multibeam systems. This system does not yet produce adequate bathymetric information, but improved versions 

 are under development. Another system, the Bathyscan 300, has recently become commercially available. This system has demonstrated acceptable accuracy. It oper- 

 ates at 300 kilohertz, covers swaths of 200 meters width in waters less than 70 meters deep, weighs about 550 pounds, and costs about $400,000. 



'^Krupp-Atlas' Hydrosweep is installed on the Meteor 11, but is not yet operational. 



^The characteristics of Honeywell's ELAC are quoted from proposals. Honeywell claims no system was built other than an experimental one. The company did supply 

 transducers to the Hollming Shipyard in Finland for three Soviet ships. Data from Hollming indicates that the systems that were built using these transducers were 

 virtual clones of the Sea Beam system. 



dBentech's Benigraph is oriented toward use in pipeline construction. The unit has very high resolution and a short range and can easily be scaled to lower frequencies 

 and used as a mapping system. Company management has stated that this approach is their intention. 



SOURCE: National Oceanic and Atmospheric Administration. 



Figure 4-5.— Sea Beam Beam Patterns 



TRANSMITTED 

 BEAM 



The Sea Beam swath width at the seafloor depends on water 

 depth. In 200 meters of water the swath width is about 150 

 meters; in 5,000 meters of water, the swath width is approxi- 

 mately 4,000 meters. 



SOURCE: R. Tyce, Sea Beam Users Group. 



Hence, an upgraded SASS is now being designed 

 that will be more reliable and will feature improved 

 beam-forming and signal-processing capabilities. 

 These should improve performance of the outer 

 beams in deep water. 



Improvements in Sea Beam, which has per- 

 formed very well but which is now considered to 

 be old technology, have also been proposed. One 

 proposed modification is to develop a capability to 

 quantify the strength of the signal returning from 

 the bottom. 2^ With such information, it would be 

 possible to predict certain bottom characteristics. 

 Nodule fields, for example, already have been 

 quantified using acoustic backscatter information. 

 Another proposed modification is to build a towed 

 Sea Beam system. Such a system could be moved 

 from ship to ship as required.^' 



All bathymetric systems have resolution and 

 range limits imposed by wave front spreading, ab- 

 sorption, and platform noise. However, by reduc- 

 ing Sea Beam's current beam width, its resolution 

 can be improved. There are limitations to using 

 the immense amounts of data that would be col- 

 lected by a higher resolution system. Only a small 

 fraction (2 percent) of existing Sea Beam data are 



^^C. deMoustier, "Inference of Managese Nodule Coverage From 

 Sea Beam Acoustic Backscattering Data," Geophysics 50, 1985, pp. 

 989-1001. 



^'D. Wfiite, Vice President, General Instruments, OTA Workshop 

 on Technologies for Surveying and Exploring the Exclusive Economic 

 Zone, Washington, DC, June 10, 1986. 



