130 • Marine Minerals: Exploring Our New Ocean Frontier 



Figure 4-7.— Comparing SeaMARC and Sea Beam Swath Widths 



SeaMARC II 

 contoured swath 



350% 

 of towflsti altitude 



Sea Beam 



contoured swath 



80% 



of water depth 



The SeaMARC II system can acquire both bathymetric data and sonar imagery and has a swath width more than four times 

 that of the Sea Beam system. The Sea Beam system, however, produces more accurate bathymetry. 



SOURCE: International Submarine Technology, Ltd., Redmond, WA. 



Stopped in 1982, due to limited funds. The Cana- 

 dian system, the Larsen 500, is now being used by 

 the Canadian Hydrographic Service. The Aus- 

 tralian laser depth sounding system, WRELADS, 

 has been used experimentally to map a swath 200 

 meters wide.^° Water must be clear (i.e., without 

 suspended sediments) for the airborne lasers to 

 work. Towed underwater lasers have not yet been 

 developed. 



Another method currently under development 

 for use in very shallow water is airborne electromag- 

 netic (AEM) bathymetry. This technique has re- 

 cently been tested at sea by the Naval Ocean Re- 



'"R.K. Bullard, "Land Into Sea Does Not Go," Remote Sensing 

 Applications In Marine Science and Technology, A. P. Cracknell (ed.) 

 (Hingham, MA: D. Reidel Publishing Co., 1983), p. 366. 



search and Development Activity (NORDA).^' 

 NORDA reports that with additional research and 

 development, the AEM method may be able to pro- 

 duce accurate bathymetric charts for areas as deep 

 as 100 meters. Passive multispectral scanners also 

 have been applied to measuring bathymetry. ^^ A 

 combination of laser, AEM, and multispectral tech- 

 niques may be useful to overcome the weather and 

 turbidity limits of lasers alone. Satellite altimeters 

 and synthetic aperture radar images of surface ex- 

 pressions can also indicate bathymetry, but much 



"I.J. Won and K. Smits, "Airborne Electromagnetic Bathyme- 

 try," Norda Report 94, U.S. Navy, Naval Ocean Research and De- 

 velopment Activity, April 1985. 



'^D.R. Lyzenga, "Passive Remote Sensing Techniques for Map- 

 ping Water Depth and Bottom Features," Applied Optics, vol. 17, 

 No. 3, February 1978, pp. 29-33. 



