OCEANOGRAPHIC INFORMATION FOR SUBMARINE CABLES 1055 



was fraught with error because there was no adequate sensing device 

 to indicate when the bottom was reached, and because the sounding 

 line might be swept far from a true vertical by the action of currents 

 between the surface and the bottom. These difficulties could cause 

 errors as great as 50 per cent. Echo sounding was thus a tremendous 

 improvement despite its own inherent inaccuracies. 



Ocean bottom soundings are available from a number of sources 

 including, in this country, government agencies such as the Navy's 

 Hydrographic Office and the U. S. Coast and Geodetic Survey, and 

 private oceanographic institutions. Abroad, national hydrographic 

 offices, such as the British Admiralty's Hydrographic Department, the 

 Japanese Hydrographic Office, and the International Hydrographic 

 Bureau, collect and publish soundings. 



Depending upon the organization which compiles the soundings, 

 various corrections are applied to the raw data, each organization 

 selecting both the corrections it wishes to apply and the method of 

 application. If all soundings for an area off the continental shelf of the 

 United States were compiled, there might be available soundings in 

 feet, corrected for velocity, supplied by the U. S. Coast and Geodetic 

 Survey; uncorrected soundings in fathoms supplied by the U. S. Navy 

 Hydrographic Office; similar soundings supplied by Lamont Geological 

 Observatory; corrected soundings in fathoms supplied by the British 

 Admiralty; and corrected soundings in meters supplied by the Inter- 

 national Hydrographic Bureau. In addition, there would be a quantity 

 of hemp, wire and discrete echo soundings on published charts. One 

 difficulty in using the soundings printed on the published charts arises 

 from the fact that hemp line, wire, and echo soundings of all types, 

 both corrected and uncorrected, are all plotted on the same chart usually 

 without designation as to method or corrections. 



Table II summarizes the methods of presenting sounding data used 

 by various agencies. 



Several methods of recording continuous depth records are used. 

 The most common, and least satisfactory, is to read the echo sounder 

 and plot the sounding at the appropriate point on the chart at discrete 

 intervals, say every 10 or 20 minutes. This achieves an orderliness in 

 printing but has the disadvantage that canyons, mountains, or other 

 features which cannot be adequately represented by such spacing are 

 ignored and obscured in the plotted soundings. Better results are ol)- 

 tained by use of the "texture method," where soundings are recorded 

 at each crest, valley, or chajige of slope, and soundings at uniform time 

 intervals are only used in ai-eas where a continuous slope extends for 



