. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. 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 exam])le,in information concerning the di]) of the strata bei
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. 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 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. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work
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