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PREFACE ^h>v^'n^ 



The Hydrographic Manual has been prepared and is issued to provide a textbook 

 in which modern methods of hydrographic surveying and equipment are described. 

 In it are stated the general requirements of the United States Coast and Geodetic 

 Survey for the execution of hydrographic surveys. It is one of a series of manuals 

 covering the various survey operations of the Bureau. 



This Manual describes in detail for the first time instruments and methods used in 

 echo sounding and Radio Acoustic Ranging. Many of the methods and details con- 

 tained herein are based on the reports of officers and employees of the Bureau, too 

 numerous for individual mention, who by their zeal and ingenuity in devising or develop- 

 ing new methods and equipment have contributed largely to the progress of hydro- 

 graphic surveying during recent years. This is particularly true of the Radio Acoustic 

 Ranging method of locating the positions of soundings, wliich has been brought to 

 its present state of efficiency by this Bureau through the untiring efforts of personnel 

 interested in attaining greater accuracy and reliability. 



The subject matter in this Manual has been identified by a decimal numbering 

 system and all referencing is by these numbers. The reader should understand the 

 significance of these numbers. There are nine chapters, each of which is divided 

 into not more than nine sections. Each section is subdivided into not more than 

 nine subjects and each subject into not more than nine numbered headings. The 

 first digit of a number identifies the chapter, the second digit the section, the third 

 digit the subject, and the fourth the heading. For example 7326, Verification of the 

 Projection, is the sixth heading under the second subject in the third section of chapter 

 7, entitled "The Smooth Sheet." 



This edition of the Hydrographic Manual has been prepared under the direction 

 of Captain Gilbert T. Rude, Chief of the Division of Coastal Surveys. Much valuable 

 assistance and advice have been received from officers and personnel both in the field 

 and Office. Several officers contributed to the actual compilation of the text, but 

 special credit is due to Commander Henry B. Campbell who wrote section 91, Coast 

 Pilot, and to Lieutenant Commander John C. Mathisson and Mr. Thomas J, Hickley, 

 associate electrical engineer, who wi'ote most of chapter 5, Echo Sounding, and chapter 

 6, Radio Acoustic Ranging, and to Mr. Aaron L. Shalowitz, principal cartographic 

 engineer. Division of Charts, for his collaboration in writing chapter 7, The Smooth 

 Sheet, and for his assistance in reviewing and editing the entire manuscript. 



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