40 HILL [chap. 3 



(d) At present there is only one channel from each buoy. Multi-channel radio 

 transmission from each buoy could greatly improve the amount of information 

 received at the ship. 



These disadvantages are, however, to some extent outweighed by some ob- 

 vious advantages apart from that of being able to operate with a single ship: 



(a) Multiple receiving points can easily be obtained; this not only results in 

 economy in the use of explosives but also.for exam])le,in information concerning 

 the di]) of the strata being obtained without reversal of the line. 



(6) Ship-made noise is not picked up by the hydrophones. There are no 

 moving parts in the buoys and quieter operation should, therefore, be possible 

 than with hydrophones near ships. 



•6-25 miles- 



Rodio waves 



Sono- radio buoys 





Bosement rock 



Fig. 1. The sono-radio buoy system of seismic refraction .shooting. Explosions are fired 

 from the ship and the signals received by hydrophones below the buoy are trans- 

 mitted back to the ship for recording. 



The disadvantages of the limited radio range of the sono-radio buoys could 

 be overcome by increasing the radio power transmitted, but the increase 

 required, say, to double the range to 00 km would be of the order of twenty 

 times. This results in a cumbersome buoy. During early 1962, however, an 

 alternative system for long-range seismic refraction shooting has been developed 

 and successfully tried by the Department of Geodesy and Geophysics. A film 

 recorder and radio receiver are installed in the sono-radio buoy. This recorder 

 is switched on and off by the ship's radio transmitter and the shot instant 

 transmitted to the buoy. This greatly increases the range of operation since the 



