utility of comparison. Questionable data, where no clear error could be 

 discerned, were noted and compared with the next survey as well. This pro- 

 vides a double check. Errors were also identified using the measured location 

 of the reference prism shot in during the stationing procedures. Use of these 

 measurements will be discussed in the next section. 

 Error correction 



34. Corrections made to the data consist of two primary types; deletion 

 of points, and addition or subtraction of biases. The biases were either 

 constant because of improper stationing of the instrument or gradual (distance 

 dependent) resulting from improper leveling of the instrument. Vertical 

 errors from mis-leveling become increasingly evident with increasing dis- 

 tance. Vertical corrections to the data were made employing the known eleva- 

 tion of the reference prism and by comparison with surveys of the same profile 

 immediately before and after the questionable data. 



35. Most often the constant vertical offsets were the result of either 

 improper stationing of the instrument (setting its elevation incorrectly), or, 

 rarely, improper entry of the elevation of the prism cluster on the CRAB. 

 Both of these errors could be traced to the data through the recorded setup 

 procedure. If there was no evidence of a mistake in stationing the Zeiss or 

 entry of the prism height, removal of the suspected bias was dependent on two 

 factors; the bias had to extend over the entire profile (past the normal 

 closure point), and there had to be no reason to expect evidence of profile 

 activity at depth. For instance, if the measured profile showed significant 

 erosion at a depth below the extreme profile closure depth during a period of 

 below-normal wave activity, errors were strongly suspected. However, the bias 

 was removed from the data only after a second survey of the profile further 

 indicated that an error had been made. 



36. Gradual biases, or rotations of the data, which result from calibra- 

 tion or leveling errors rather than stationing errors, can be more difficult 

 to discern in the data. These corrections were made only to the early level 

 and stadia board data. The shift in the data could be directly attributed to 

 a miscalibration of the automatic level, or to a leveling error during or 

 after setup of the instrument. The rotation needed to correct the data was 

 determined by recalibration of the level. 



37. Another category of data editing was the removal and/or correction 

 of obviously erroneous data points. These points were usually the result of 



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