technique of sending a rodperson along the transect, stopping at regular 

 intervals and breaks in slope. 



Early Stadia Surveys 



15. From January to June 1981, the position and elevation of the CRAB 

 were determined using an automatic level, located on the beach, to read a 

 12.3-m-high stadia board attached to the CRAB. This system was slow and 

 sensitive to a wide range of errors. Primary sources of error included out- 

 of-level or poorly aligned instruments, stadia reading errors, fieldbook and 

 transcription errors, and instrument stationing errors. Estimated accuracy in 

 distance was from +0.3 to + 6 m. Vertical accuracy was estimated to vary from 

 +0.03 to +0.6 m. Single points or surveys may have been in greater error. 



16. Errors tended to increase with distance. This resulted from the 

 increased difficulty in reading the stadia board and the greater impact of 

 out-of-level errors. Because of these errors, data collected prior to June 

 1981 end approximately 600 m offshore. Points farther offshore were of ques- 

 tionable accuracy and have been dropped. 



17. Although of inferior quality to later surveys, the stadia survey 

 data have been retained in the data set because the configuration of the 

 profile lines (which is accurately represented) during this period is unusual 

 and not later repeated. 



Electronic Survey System 



18. In order to improve the speed and accuracy of the surveys, a Zeiss 

 Elta-2 electronic surveying instrument with automatic data recording was used 

 after June 1981 (Figure 5). This instrument incorporates in one compact unit 

 a first-order electronic theodolite, distance meter, microprocessor, recharge- 

 able power supply, and interchangeable solid state memory module. When opti- 

 cally aimed at a reflecting prism on the CRAB, the instrument uses a col- 

 limated infrared beam to measure the distance and the electronic theodolite to 

 measure both horizontal and vertical angles. The microprocessor then uses 

 these measurements plus the coordinates of the instrument to compute X, Y, and 

 Z Cartesian coordinates of the ground point under the CRAB (corrected for 



11 



