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CONTROL AND SIGNAL BUILDING 



2573 



(Fig. 39.) The selection of sites for stations will depend principally on the effective- 

 ness of R.A.R. in the particular locality. 



The offshore limit of the area to be surveyed is frequently beyond the limit of reli- 

 able acoustic distances and R.A.R. stations must be established farther offshore to 

 furnish reliable control. Shore stations may not be visible from these offshore posi- 

 tions to provide three-point fix locations of the R.A.R. stations, but they may be 

 located by acoustic distances by the method described in 2533. 



2573. Traverse for R.A.R. Control 



Where the hydrographic survey of an offshore shoal area is to be controlled by 

 R.A.R. methods, but the coast is so low that shore signals are visible for only a short 

 distance offshore, a buoy traverse may be used to extend the ccntrol to the offshore 

 area, and from buoy positions so determined, R.A.R. stations may be located farther 

 offshore by acoustic distances. This method is frequently used on the Atlantic and 

 Gulf Coasts where inshore areas have been previously surveyed and it is desirable to 

 extend control to offshore areas in a rapid and economic manner. 



Figure 40.— Sono-radio buoys located by traverse and acoustic distances. 



The lines of buoy stations between A, C, H, and J in figure 40 are located and 

 observed so that they may be computed and adjusted as a closed traverse between 

 fixed positions at A and J (see 944). The distance between adjacent buoys in the area 

 previously surveyed may be a maximum, but the buoys in the area to be surveyed 

 should be spaced to provide for three-point fixes if it is desired to control the area adja- 

 cent to the buoy lines by this method. Frequently, in an area of this character, the 

 buoys in the traverse may be spaced at a maximum distance throughout and the entire 

 area controlled by R.A.R. methods. 



Sono-radio buoys are located at intervals in the traverse line, as indicated by the 

 double concentric circle symbols, which are lettered from B to I in the figure. The 

 required distance between adjacent sono-radio buoys depends on the efficiency of 



