1. GKNEKAL REQUIREMENTS 



(Change 1) 5 



1-13 Field numbers. — For convenient 

 reference while ;i survey is in progress, each 

 hydropraphic sheet shall be assigned a field 

 number. A permanent field number shall not 

 be assigned to any sheet until hydrography 

 is started on the sheet; and the number shall 

 not thereafter be changed even though the 

 survey is completed by another vessel. Un- 

 used boat sheets constructed by or for one 

 survey unit and subsequently transferred to 

 another unit shall be assigned a field number 

 by the latter when the survey is started. The 

 final two digits of the field number represents 

 the calendar year in which the survey was 

 initiated and are not to be changed if the 

 survey extends into the following calendar 

 year. 



The field number shall be a hyphened com- 

 bination of lettei"s, which identify vessel or 

 party starting the sui'vey, and numbers that in- 

 dicate scale of survey, sequence of survey (re- 

 gardless of project number) in vessel's current 

 series at that scale, and year in which survey 

 was started. Examples follow. 



EX-2.5-1-58 = EXPLORER — scale 

 1 :2,500 — first sheet in the series at that 

 scale — survey begun in 1958. 



ECFP-1 0-1 1-59 = East Coast Field Party 

 —.scale 1 : 10,000— nth sheet— 1959. 



LJ-25-2-60— LESTER JONES = scale 

 1 :25,000— 2nd sheet— 1960. 



PI_200-4-60 = PIONEER— scale 1:200,- 

 000— 4th sheet— 1960. 



Completed surveys are normally referred 

 to by their registry numbers in correspond- 

 ence 



1-14 Regi.stry numbers. — At the end of 



each season, or at such times as circumstan- 

 ces dictate, the Chief of Party shall request 

 from the Washington Oflice the assignment 

 of registry numbers to completed hydro- 

 graphic surveys, or surveys which will be 

 completed during the season. Numbers 

 should not be requested for incomplete 

 surveys. 



1-15 Horizontal control. — The control 

 for all hydrographic surveys, except track 

 line and reconnaissance surveys, shall be 

 based on triangulation of third order accu- 

 racy or higher (see 4-1). All established 

 triangulation stations in a project area shall 

 be searched for and appropriate reports sub- 



mitted. If new triangulation is required, the 

 field work shall be accomplished in accord- 

 ance with instructions and specifications 

 containetl in Special Publication No. 247, 

 Manual of Geodetic Triangulation. Points se- 

 lected for the location of electronic shore sta- 

 tions shall be located by triangulation or 

 traverse of third order accuracy or higher. 



1-16 Photogrammetric surveys. — Nearly 

 all topographic surveys are now being made 

 photogrammetrically, and the hydrographic 

 party will be furnished photographs, manu- 

 scripts, and other data to support hydrogra- 

 phic operations. Except in Ala.ska and other 

 remote areas, the Photogrammetry Division 

 will accomplish all field work required to 

 produce advance manuscripts, and, in most 

 cases, will assign a photogrammetrist to 

 build and locate signals to provide visual 

 control for hydrography. 



Outside continental United States, hydro- 

 graphic parties shall establish and identify 

 control and accomplish the field inspection 

 required in advance of photogrammetric 

 compilation. On occasion the party may be 

 furnished preliminary manuscripts which are 

 based on office identified control. See Chap- 

 ter 4 for a discussion of manuscript classi- 

 fications and uses. 



A marked triangulation station can seldom 

 be identified on a photograph and substitute 

 points in the immediate vicinity are used. 

 (See Photogrammetry Instruction 22, Revi- 

 sion 1, dated 1 November 1959.) At least 

 two such points should be identified and per- 

 tinent information recorded on a Control 

 Station Identification (C.S.I.) card (Form 

 152). Identification must be precise, as mis- 

 identified control will warp the compilation 

 and will seriously affect the location of the 

 supplemental photo-hydro stations (see 4- 



11). 



Supplemental control for hydrography 

 shall be located by photogrammetric methods 

 wherever practicable (see 4-18). The sta- 

 tions shall be established in accordance with 

 Photogrammetry Instruction 45, Revision 1, 

 dated 15 March 1954. Discrepancies in the 

 location of photo-hydro stations should not 

 exceed 0.5 mm. at the scale of the manu- 

 script. 



The Photogrammetry Instructions referred 

 to in this section are part of a series which 

 cover field operations in photogrammetric 



