662 



minute are normally classified by the Navy. However, this 

 particular example was taken from a data collection in a test 

 area used by the Navy for understanding the utility of high 

 resolution data. 



Figure 25. Sample Bathymetry Data at High 



AND Low RESOLirriONS 



The original multibeam bathymetric sonar data are archived at 

 NAVOCEANO and can be accessed in their original raw form. 

 Returning to these raw sonar data could provide researchers 

 with the highest level of detail available. These data were used 

 in the construction of the gridded database summaries. 

 Multibeam data from the Sonar Array Survey System (SASS) 

 became available starting in the mid-1960s. SeaBeam data 

 collection began in 1987. SIMRAD systems, including EM- 

 100 (1992) and now the EM- 121 A and SeaBeam 2000/2012 

 systems ( 1 995), are die latest bathymetric mapping equipment 

 in use today. 



b. AccessibiUty 



Accessibihty to some of the bathymetric databases is possible 

 at the unclassified level except for sensitive regions where the 

 location of detailed surveys may compromise location-specific 

 issues. Detailed gravity surveys that include bathymetry data 

 were generally conducted at locations that are not associated 

 with such systems and where gravity variability is high. There 

 are also high resolution databases that are classified in their 

 entirety. Distribution of the DBDBs to government users is 

 through the Defense Mapping Agency with assistance from the 

 Naval Oceanographic Office. A 5 arc minute resolution, global 

 grid DBDB is available to the public through the National 

 Geophysical Data Center. There is an effort underway to 

 produce an unclassified database with variable resolution 

 (DBDB-V) that would incorporate some 0.5 arc minute data. 



Multibeam bathymetric sonar data are mostly classified or 

 restiicted. Restiicted data are often the result of a cooperative 

 data collection with a foreign government or under a bilateral 

 agreement. The host government would have to give its 

 approval before these data dissemination restrictions could be 

 removed. While possible, tiiis could be very difficult in 

 practice. 



c. Scientific Utility 



The joint availability of magnetics and seafloor topography 



data would greatly improve plate tectonic reconstructions. 



This composite figure shows the topography of a small section of the 

 seafloor off the coast of California. The upper illustration is from 

 bathymetric data having a resolution of 0.1 arc minute lie.. 0.1 nautical 

 mile). The lower illustration is from halhymeinc data having a resolution, 

 an order of magnitude coarser, of 1.0 arc minute (i.e.. I nautical mile). In 

 areas where there is little relief {e.g.. the center of the area) the two 

 representations differ little In areas of significant relief the southwestern 

 comer for example, the high resolution data show a much greater degree 

 of irregularity. 



Detailed bathymetry data, accompanying marine magnetics 

 data, and geoid data from Geosat/ERS-1 would allow detailed 

 reconstructions of plate motions through time to include the 

 oldest Jurassic and Cretaceous lithosphere. 



As new oceanic litiiosphere is created at mid-ocean ridges and 

 spreads away from volcanic centers, the lithosphere cools. 



34 



