Page 109 control and signal building 248 



If some of the cuts are taken from positions comparatively close inshore, considerable 

 care must be exercised to avoid mistaking shoulders of hills for the hilltops. At the 

 angle from which these are observed a shoulder projecting seaward frequently resembles 

 a hilltop. Hills and peaks located for use as control for the hydrography should be 

 located from the area in which they are to be used; or if greater accuracy of position 

 can be obtained closer inshore, each of the objects should be viewed from various 

 directions throughout the offshore as well as the inshore area to ensure that the top is 

 being viewed from both areas. 



Rounded indefinite hilltops should rarely be used as control in hydrographic sur- 

 veys, but in lieu of better objects they may be used with sufficient accuracy in the off- 

 shore area or when combined with two much nearer control stations (see 3336a). 



In addition to peaks and hilltops other natural objects not noticeable to the topog- 

 rapher along the beach frequently show up very distinctly from considerable distances 

 offshore. Among these are waterfalls, rock slides, scars on hillsides which have been 

 denuded of trees, and discolored spots on cliffs. In populated areas most artificial 

 objects useful as hydrographic stations, such as water tanks, stacks, and conspicuous 

 buildings, will have been located by the topographer. But occasionally there are 

 buildings, lone trees, or clumps of trees, etc., which do not appear distinctive from the 

 topographer's nearer viewpoint but which make excellent hydrographic stations for 

 offshore use. 



248. Records 



All observed data for locating hydrographic stations shall be recorded in a clear 

 and understandable manner with copious explanatory notes, because these data must 

 be used to plot the stations on the smooth sheet by personnel who probably were not 

 present during the field work. 



When a number of such stations is located during a hydrographic survey the data 

 shaU be recorded in a separate sounding volume or notebook apart from the hydrog- 

 raphy. When only a few such stations are located the data may be recorded in the 

 regular Sounding Record, as observed in connection with the hydrographic survey. 

 In case a separate sounding volume or notebook is used, it should be numbered 

 as one of the sounding volumes of the hydrographic survey and forwarded as part of tho 

 records of that survey (see 8321). 



When the data are interspersed through the Sounding Records, an index of the 

 stations shall be provided on page 2 of volume No. 1, with references to the volume 

 and page numbers on which are recorded all the data for the location of any given 

 station. Wlien the data are recorded in a separate volume or notebook the index 

 shall be in the front of this. 



The cuts should be recorded immediately after the three-point fix position at which 

 they are taken. Each new station to which cuts are taken should be referred to by 

 name in the records and at one place in the records each such station should be 

 described. If it is a natural object the description should be complete enough to ensure 

 its identification during the survey and at future dates. 



Recoverable stations shall be described on Form 524 (see 2351). 



25. CONTROL BUOYS 



A system of accurately located buoys on which three-point fixes can be observed, 

 or to which distances can be measured by radio acoustic methods, furnishes the most 

 economic means of extending accurate hydrographic surveys beyond the limit of 



