. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 1] BEFRACTION AND REFLECTION TECHNIQUES AND PROCEDURE 25 In the SIO method, the receiving ship hes to or steams slowly into the wind, and three or four hydrophones on neutrally buoyant suspensions are laid out at distances of 300 to 2000 ft from the ship, as shown in Fig. 3a. Each hydro- phone has been previously balanced by use of an aluminum float and small lead weights so that it is very slightly buoyant at the surface and will be as nearly as possible neutral at operating depth. A 50-ft leader cable without built
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 1] BEFRACTION AND REFLECTION TECHNIQUES AND PROCEDURE 25 In the SIO method, the receiving ship hes to or steams slowly into the wind, and three or four hydrophones on neutrally buoyant suspensions are laid out at distances of 300 to 2000 ft from the ship, as shown in Fig. 3a. Each hydro- phone has been previously balanced by use of an aluminum float and small lead weights so that it is very slightly buoyant at the surface and will be as nearly as possible neutral at operating depth. A 50-ft leader cable without built-in buoyancy is supported to neutral buoyancy by small aluminum floats distributed along its length. In field use the cable hangs in loops between the small floats, creating a mechanical filter to eliminate disturbances propagated along the cable. The end of the leader is fastened to a heavy weight. From the DRIFTING 0-lOOFT/MIN (a) NEUTRALLY BOUYANT (b). SINKING SLOWLY 20FT/HIN Fig. 3. Hydrophone suspensions: (a) SIO method; (b) LGO-WHOI method. weight a neutrally buoyant cable leads up 200 ft to the water surface where it is fastened to a group of small i:)lastic floats and then back to a cable-puller or a winch on the ship. The hydrophone system is shown in Fig. 4. During reception of a seismic station other operations such as coring, heat- flow measurements, underwater photography, hydrographic casts, bathy- thermograph observations, and normal laboratory and ship work are continued so that in all cases the ship's auxiliary power is kept on. In windy conditions the main propulsion engines are on, and the ship heads into the wind with the screw turning over slowly to keep the hydrographic wire vertical and the hydrophone cables slack. If ship drift becomes too great and the hydrophone cables pull tight the mechanical filtering action is lost, the hydrojihones rise toward the surface, and wave and flow noise develop. In such cases, if steaming. Please note that these images a
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
