642 HYDROGRAPHIC MANUAL PagE 596 



breakdown of the apparatus; he can keep batteries charged and the station at maximum 

 operating efficiency; and he can Hsten to the bomb signals as they are received and 

 measure the ampHtude of the sound. A knowledge of the relative strength of the bomb 

 signal, radioed to the survey ship by the technician, is valuable in plotting and in 

 determining the size of bombs to use. 



A shore station tended by a radio technician will generally require less servicing 

 from the survey ship than any other type of station, but in isolated localities the station 

 must be supplied from the ship, even to the extent of drinking water. 



Hydrophone sites for shore stations are generally difficult to select. Frequently 

 the position of the hydrophone must be moved several times before it is where sound 

 will be received from the desired directions. (See 2612a.) 



Depending on the locality, from 1 to 3 days may be required to establish a shore 

 station, and because a comparatively smooth sea is required to lay the cable, the 

 establishment of a station on the open coast may frequently be delayed several weeks 

 by bad weather or a heavy swell. 



642. Ship R.A.R. Stations 



The use of ship R.A.R. stations in extensive areas of comparatively shoal water 

 was a necessary expedient before the automatic sono-radio buoy was developed, because 

 the attenuation of the sound in such areas was so great that the sound would reach shore 

 stations from only comparatively short distances offshore. The shore station equip- 

 ment was installed on board ships and the ships were anchored where stations were 

 needed, but their maintenance was exceedingly costly. Ship stations had all the 

 important advantages of shore stations and in addition they were mobile. A station 

 ship could be moved to a new position without delaying, and generally without 

 interrupting, the operations of the survey ship. They are no longer used as R.A.R. 

 stations. (See 262.) 



643. Sono-Radio Buoy Stations 



The sono-radio buoy is a fully automatic subaqueous sound-receiving and radio- 

 transmitting unit that may be used in most localities as an R.A.R. station. Using 

 the Parkhurst anchor-detaching apparatus (see 2834 and 2851), it is probable that a 

 sono-radio buoy can be anchored in any depth of water; consequently accurately con- 

 trolled hydrographic surveys can be made in any oceanic area (see 25). However, 

 because it is unattended, a sono-radio buoy has a somewhat shorter effective range 

 than a shore station has. 



The sono-radio buoy was developed to eliminate two of the then most objectionable 

 features of R.A.R. — the use of expensive ship stations along the Atlantic Coast, and the 

 difficulty of laying cable through the surf in establishing shore stations on the Pacific 

 Coast and in Alaska. A number of buoys can be operated at the cost of operating 

 one shore station. 



Where strong currents prevail there is some difficulty in maintaining a buoy in a 

 nearly upright position. Occasionally the anchoring gear fails, resulting in the loss 

 of the sono-radio buoy, or at least the position. 



Several types of sono-radio buoys are used by the Coast and Geodetic Survey. 

 The different types have resulted from the efforts of individual experimenters to de- 

 velop a sono-radio buoy best suited to overcome the particular conditions found in 

 the waters being surveyed. The physical construction of sono-radio buoy structures 



