Figure 19. Pipe profile control survey. 



profile data were recorded on a plastic writing board, and transferred to 

 the notebook immediately following the dive. The pipe profile data were 

 then transferred to a standardized data sheet for use in an IBM optical 

 mark page reader. 



3. Survey Precision . 



Each profile line was referenced to an existing known bench mark in 

 the area.. Pipe stations were located to the nearest foot along the pro- 

 file line, and the elevations of reference marks on the pipes were lo- 

 cated to the nearest one-tenth of a foot. Reference marks were initially 

 notches in the pipe. Later, the pipe tops were used for reference eleva- 

 tions. An instrument survey of all pipe stations was completed three 

 times during the study. Individual pipe stations were resurveyed using 

 hand level techniques whenever they were repaired or replaced. 



The profile surveys consisted of sand level measurements from the 

 pipe reference marks. These measurements were recorded to the nearest 

 inch, but before January 1972 were rounded to the nearest 0.5 foot (15.2 

 centimeters) for computer processing. After January 1972 the sand level 

 measurements were rounded to the nearest 2 inches. The rounding was felt 

 necessary in order to keep the data reporting form, which was designed 

 for use by untrained observers, as simple as possible. The pipe profile 

 method is discussed in Section IV. 



Profile documentation data, including bench-mark locations, profile 

 azimuths, and pipe-stationing and reference elevations are presented in 

 Appendix B. 



4. Data Reduction . 



Before being converted to standard punchcard format, the data sheets 

 were visually checked for proper coding of date and location and for 

 obvious errors. LEO data were tabulated by month and visually edited 



34 



