CHARTING THE OCEANS FOR SAFE NAVIGATION 69 



structed for individual geographic areas for precise hydrographic 

 or oceanographic surveying; ship or equipment positioning, 

 installation, or recovery; and related operations and planning. 

 The simplest type of sheet — the optical plotting chart — permits 

 determination or recovery of position by visual reference to estab- 

 lished shore stations, and the azimuth readings and azimuth lines 

 which are shown on the chart. Most precise positioning plotting 

 sheets, however, are produced for use with electronic navigational 

 systems. 



Electronic positioning plotting sheets, constructed at very 

 large scale, are used to record oceanographic and hydrographic 

 observations and to locate or recover underwater objects. 

 Navigational lattice overprints are included on these charts for 

 the particular electronic navigational systems being used, 

 including Loran A, Loran C, LORAC, DECCA, RAYDIST, 

 and LAMDA. Charts on which field observations have been 

 plotted become a primary source of new standard nautical chart 

 revision or construction data. 



Perhaps the best known special purpose charts provided by the 

 Oceanographic Office are the Pilot Charts. These present to the 

 mariner and scientist a summary of oceanographic, meteorol- 

 ogical, and navigational information needed to assist in 

 planning operations in the North Atlantic and North Pacific 

 Oceans. For other major ocean areas, the information is pub- 

 lished in atlas form. 



Pilot Charts, first published in 1847 as Maury's "Wind and 

 Current Charts", are the exchange medium for the wealth of 

 marine information collected through the years by the Navy and 

 the Weather Bureau. The Pilot Chart of the North Atlantic 

 Ocean was first published as such in 1883, that of the North 

 Pacific in 1894. Pilot Charts are published monthly; in addition 

 to the chart itself, each contains a timely article of professional 

 or technical interest on the reverse side. A different article 

 appears each month, and subjects covered include biological 

 oceanography, Arctic ice and its drift, subsurface navigational 

 hazards, shiphandling, the Gulf Stream, and numerous other topics 

 of marine interest. 



General development maps, for areas such as the McMurdo 

 Scientfic Station in Antarctica, have been photogram metrically 



