. The Earth beneath the sea : History . Fig. 4. Photograph of tiHJ hydrophone system. Is not adequate or if for some reason it is not possible to steam (as in the case where the dredge is down and currents are pulhng the hydrophones), cable is paid out from the winches into a heap on deck and paid out rapidly at shot â fime for the most distant shots only. A block diagram of the SIO shooting and receiving system is shown in Fig. 5. The hydrophones used are normally either Brush Electronics Model AX-58C or Research Manufacturing Co. Model R-100. The former uses Rochelle salt crystals immersed i
. The Earth beneath the sea : History . Fig. 4. Photograph of tiHJ hydrophone system. Is not adequate or if for some reason it is not possible to steam (as in the case where the dredge is down and currents are pulhng the hydrophones), cable is paid out from the winches into a heap on deck and paid out rapidly at shot â fime for the most distant shots only. A block diagram of the SIO shooting and receiving system is shown in Fig. 5. The hydrophones used are normally either Brush Electronics Model AX-58C or Research Manufacturing Co. Model R-100. The former uses Rochelle salt crystals immersed in castor oil, the latter barium titanate ceramic cylinders cast in plastic. Both types produce a signal of approximately 100 [xV per dyne/cm2 for signals between 2 c/s and 20 kc/s. The output is at high im- pedance and must be matched to the cable with a cathode follower pre- amplifier (current amplifier) at the hydrophone; the SIO, LGO and WHOI pre-amplifier circuits are shown in Fig. 6. Batteries to operate the pre-amplifier are located not in the hydrophone but at the weight (actually a brass box filled with batteries) 50 ft away; this eliminates the need to open the hydro- phone case or to re-balance at times of battery change. Hydrophones turn on when the battery case is right-side-up. The least signal from sea noise in calm weather in the low-frequency (2 to 20 c/s) range of interest for seismic refraction is of the order of 10 (xV hydroi)hone output; first stage noise must therefore be
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
