Canadian Range. The Navy maintains an acoustic range in the Straits 

 of Georgia, northeast of Nanaimo, British Columbia, Canada (Green, 1969; 

 Daniels, 1969). The range, established in 1965, contains six hydrophones 

 located in approximately 1 ,350 feet of water. Bathymetry in the area is 

 relatively flat, and sediments are predominantly siliceous oozes. 



Two configurations have been used for supporting the acoustic 

 instrumentation. The older hydrophones are attached to buoyant spheres 

 and anchored to the bottom. This configuration is flexible, and bottom cur- 

 rents of about 0.1 knot cause undesirable hydrophone movements. The newer 

 and more successful supporting structures consist of a 50-foot tripod apparatus 

 with each corner supported on a 3- by 3-foot concrete footing. The entire 

 apparatus weighs approximately 10,000 pounds in air. 



Since sediments in the area were extremely soft, a unique device was 

 designed to minimize attitude change due to differential footing settlement. 

 A universal joint was placed between the hydrophone and the tripod, and a 

 buoyant sphere was attached to the hydrophone. If the base settles differen- 

 tially into the sediment so that the tripod tilts, the buoyant sphere moves the 

 hydrophone back to a vertical position by rotating the system about the flexible 

 joint. The entire system remains flexible for approximately 2 weeks, after which 

 time the hydrophone's position is fixed rigidly relative to the tripod. 



The magnitude of settlement during the first 2 weeks was approximately 

 1 foot. This value varied according to the buoyant force supplied by the sphere 

 and the properties of the bottom sediments at the specific location. Although 

 some further tilting has been noted subsequent to clamping of the hydrophones, 

 operation of the range has been satisfactory. 



Daybob Bay Range. In 1958, the Navy established an acoustic range 

 west of Seattle, Washington, in Daybob Bay (Green, 1969; Daniels, 1969). 

 Fifteen hydrophones were placed in approximately 650 feet of water on a 

 silty sediment. Each hydrophone is attached to a 15-foot length of pipe atop 

 a 4- by 4-foot concrete anchor block. A buoyant sphere and two universal 

 joints maintain vertical position. No unusual performance problems have 

 been noted with the 1,000-pound negatively buoyant configuration. 



SCARF. The Santa Cruz Island Acoustic Range Facility (SCARF) is 

 a three-dimensional acoustic tracking range belonging to General Motors Cor- 

 poration's A. C. Electronics— Defense Research Laboratory (A.C. Electronics, 

 1968; Chalfant and Buck, 1968; Engstrom, 1969; Momsen, 1970). The hydro- 

 phone arrays were implanted in 1 965 at an average water depth of 4,200 feet 

 some 6 miles south of Santa Cruz Island (Figure 10). 



