1056 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1957 



Table II — Methods of Presenting Sounding Data 



Source 



Coast and Geodetic 

 Survey, U. S. 

 Dept. of Com- 

 merce 



Hydrographic Of- 

 fice, U. S. Navy. . . 



Lamont Geological 

 Observatory 



British Admiralty 

 Hvdrographic 

 Dept.. 



International Hy- 

 drographic Bu- 

 reau 



Japanese Hydro- 

 graphic Office ... 



Depth Units 



Fathoms 

 Fathoms 

 Fathoms 



Fathoms 



Meters 

 Meters 



Sounding Velocity 



820 or 800 fm/sec 

 800 fm/sec 

 800 fm/sec 



820 fm/sec 



Note D 



1500 meters /sec 



Velocity Correction 



Note A 



No 



No — Note E 



Yes — Note C 



Yes 



? 



Slope Correction 



NoteB 



No 



No — Note E 



No 



Note D 

 ? 



1. All agencies use Mercator projection charts. 



2. All deep sea soundings on 4" = 1° longitude charts; various larger scales 

 used near shore. 



A. use & GS usually makes velocitj^ correction according to data taken at 

 time of sounding. 



B. use & GS makes slope and drift corrections where deemed necessary. 



C. Admiralty data velocity corrections are made according to D. J. Matthews.* 



D. International Hydrographic Bureau takes no data of its own, but publishes 

 data received from various surveyors. 



E. Although corrections are made in surveys of specific areas, soundings are 

 first compiled in uncorrected form. 



many miles. This produces an uneven spacing of numbers on the chart, 

 and in some areas the soundings have to be crowded together to show 

 all crests and valleys. In this method the sounding is written alongside a 

 dot which represents the location of the soimding. Another method is 

 to write the sounding without a dot but centered over the place where 

 the sounding was taken. This produces a more pleasing drawing but 

 all detail must be left out in complicated areas since the physical size of 

 the letters limits the number of soundings that can be so recorded on 

 the chart. 



2.3.2 Methods of Evaluation 



Evaluation of topographic data starts with a comparison of data | 

 from all the different sources, with all the soundings plotted to the 

 same scale on one set of charts. Soundings from different sources must 

 be reduced to a common base. 



When the soundings from all sources are compiled on the same sheet, 

 many ob\-ious discrepancies will be noted. A great number of these 



