Page 119 ' CONTROL and signal building 2524 



at one of the stations between the buoy and the other station. To obtain the reverse 

 azimuth from the observed azimuth it is necessary to make a preliminary position 

 computation, or make an approximate computation of Aa (see 942). Using this angle 

 and the angle observed at the buoy the triangle may be concluded and the position 

 computation made in the usual manner. 



Figure 23.— Buoy location from one angle at the buoy and Figure 24.— Buoy location by sun azimuths 



an azimuth to a shore station. to shore stations. 



2524. Sun Azimuths From a Buoy to Two Shore Statiotis 



If two or more shore stations are visible from positions offshore fi'om the buoy 

 and for any reason it is impracticable to observe sextant angles, the buoy may be 

 located by observing sun azimuths from ship stations on range with the buoy and the 

 respective shore stations (fig. 24). 



The position of the buoy may be computed when it is determined by this method. 

 The three angles of the triangle may be derived from the observed sun azimuths between 

 the buoy and the two shore stations and the azimuth between the shore stations. 

 The triangle computation and the position computation are made in the standard 

 manner. In taking the differences between the azimuths to obtain the desired angles, 

 the azimuth in the correct direction must be used. When the reverse of one of the 

 observed azimuths is required the observed value must be corrected as explained in 

 2523. 



2525. Sun Azimuth and Distance 



The method of locating one buoy from another by a sun azimuth and distance 

 is the fundamental principle of the system of buoy traverses. There are several ways 

 of measuring distances at sea beyond the sight of shore objects; the most accurate is 

 with the taut-wire apparatus (see 446), and all long distances between buoys should 

 be measured with it when the apparatus is available. 



It is to be noted that the farther apart two intervisible buoys are the more accu- 

 rately the sun azimuth can be measured, and in a taut-wire sun-azimuth traverse based 

 on a number of intervisible buoys, errors of observation in the sun a.zimuths tend to 

 compensate. In contrast, any errors in distance measurements are likely to be 

 accumulative. 



Other methods of measuring the distance between two buoys are less accurate 

 and should be used with discretion. When one of two buoys is a sono-radio buoy, 

 the distance between them can be measured by subaqueous sound ranging, but this 

 method should be used only where the velocity of sound is accurately known (see 635). 



