6. THE SMOOTH SHEET 



229 



may effect the accuracy of the hydrographic 

 survey. 



The first step in verifying a smooth sheet 

 is to ascertain that the projection, control, 

 and shoreline details have been checked in 

 the field, and that all processing in the sound- 

 ing records through the reduction of sound- 

 ings has been checked as shown by initials 

 in the processing stamp. The verifier then 

 checks the descriptive report, boat sheet, and 

 other pertinent reports for information af- 

 fecting verification of the survey. He then 

 proceeds with a methodical verification of 

 the smooth plotting beginning with the first 

 page of volume one of the sounding records 

 checking the accuracy and completeness of 

 the penciled hydrographic data. The sound- 

 ings and other hydrographic data are then 

 inked in chronological order. . 



Specific areas of discrepancy are some- 

 times revealed during verification of the final 

 data plotted on the smooth sheet. Because 

 of the complexity of factors affecting the 

 plotted data, the verifier may find it neces- 

 sary to review fathograms, bar checks or 

 other echo sounder calibration data, tidal 

 information, calibrations of electronic con- 

 trol systems, or sounding line adjustments 

 in order to resolve discrepancies and prop- 

 erly revise the hydrographic data. 



6-83 Cover sheet. — The verifier should 

 refer to 6-42 for a discussion of the need 

 to protect a smooth sheet. Sections of obso- 

 lete charts are satisfactory covers to protect 

 unused portions of the smooth sheet. The 

 cover sheets should not be shifted about 

 while weighted with a metal protractor, 

 sounding volumes, or other heavy objects. 



6-84 Verifier's preliminary inspection. — 



The verifier should make a preliminary in- 

 spection of the smooth sheet to identify areas 

 where errors may exist. These may be indi- 

 cated by crossing discrepancies, unnatural 

 bottom configuration as shown by the pen- 

 ciled depth curves, disagreement of depths at 

 junctions, conflicts of depths with shoreline, 

 or other inconsistencies which may neces- 

 sitate extensive replotting of positions or 

 soundings. The boat sheet is an independent 



plot of the survey and should be used as a 

 guide in the preliminary inspection and dur- 

 ing the detailed verification. The descriptive 

 report and the smooth plotter's report should 

 be consulted for information on discrepan- 

 cies which were not resolved. 



6-85 Replotting positions. — Since the to- 

 tal hydrography, including depth curves, 

 provides a partial check on individual sound- 

 ings, it is not necessary to verify the 

 plotting of each hydrographic position of 

 a consecutive series on line. Sufficient verifi- 

 cation shall be done to eliminate inaccura- 

 cies in plotted positions of important hy- 

 drographic information. 



All detached positions should be replotted 

 and the positions serving to locate the least 

 depth on important hydrographic features 

 should be replotted. All positions which ap- 

 pear to be erroneous and conflict with sup- 

 plementary information such as dead reckon- 

 ing should be replotted. Selected positions 

 in areas noted by the verifler in his pre- 

 liminary inspection should be replotted. 

 When the sounding lines extend into areas 

 of weak fixes, selected positions should be 

 replotted in order to evaluate the accuracy 

 of the plotting. Consistently excessive dif- 

 ferences in plotted positions may indicate 

 that the smooth plotter used an unadjusted 

 or uncompensated protractor. A further 

 check on the accuracy of plotted positions is 

 obtained by the spacing divider when sound- 

 ings are being inked and any position which 

 appears to be incorrectly plotted should be 

 replotted. 



Where the verifier has found that the 

 original plotting of positions has been ac- 

 curately done, the amount of checking should 

 be held to a minimum. 



6-86 Revised positions. — Hydrographic 

 positions of soundings shall not generally be 

 revised where the correct position is within 

 the limits of the sounding numeral. Differ- 

 ences between the two positions should sel- 

 dom exceed 1 mm. Positions locating critical 

 soundings and other important features shall 

 be accurately plotted and shall be revised in 

 verification where necessary. The original 



