SECT. 1] 



REFRACTION AND REFLECTION TECHNIQUES AND PROCEDURE 



29 



outputs of two of the hydrophones on the first arrivals, and high- and low- 

 frequency outputs from one of the hydrophones on the water-borne arrivals. 

 Information from the monitor records is used by the recording operator to 

 check for instrument trouble or noise, and to decide on changes in charge size 

 to be called to the shooting ship. A running plot of rough readings from the 

 monitor records is maintained during the run for preliminary interpretation. 

 Whenever a roll of recording paper has been run through the oscillograph, it is 

 removed and developed to check on the quality of the photographic recording 

 on all channels and to jjermit the beginning of data reduction aboard ship. 



The recording system used at SIO is completely transistorized except for 

 the pre-amplifiers. 



lOO 



Frequency ~ c/s 



1000 



10.000 



Fig. 7. Response of SIO system from hydrophone output to oscillograph trace; dB 

 relative to maximum response of each channel. 



Auxiliary information that must be noted includes all of the information 

 listed for the shooting ship plus attenuator settings, depth at the receiving 

 ship and a running record of instrument connections and settings. At the 

 conclusion of each station, electrical calibrations are made on one more of the 

 hydrophones by inserting a series of calibration signals (from 2 c/s to 20 kc/s) 

 to the calibration resistor in the pre-amplifier and taking a brief record. This 

 gives the total response of the system excluding the hydrophone element ; an 

 example of the response of the system from hydrophone output to oscillograph 

 trace is given in Fig. 7. 



In the system of recording developed at Lamont and Woods Hole, most of 

 the differences in procedure stem from the practice of silencing the ship during 



