Gradual biases, or rotations of the data, which resulted from calibration or leveling errors 

 rather than stationing errors, were more difficult to discern in the data. If the shift in the data 

 could be directly attributed to a miscalibration of the internal level compensation, or to a 

 leveling error during or after setup of the instrument, then the rotation needed to correct the 

 data was determined by recalibration of the level. 



All changes made to the data, with the exception of the tilt adjustment of the CRAB, were 

 recorded in processing and data collection logbooks and were coded into the data file. 

 Meanings and formats of the codes are presented in Appendix B. 



Accuracy of the Survey Systems 



The stated range of distance measurement of the Zeiss is 2 km with a triple prism 

 assembly as used on the CRAB. The distance accuracy is +2 cm in the rapid measurement 

 mode. The angle accuracy of the Zeiss is ±0.6 sec, of which vertical accuracy is +1.5 cm 

 at 1,000 m. Actual accuracy in a repetitive survey program is less, due to the errors 

 described above. The accuracy of the Zeiss survey system is shown in Figure 8 (Birkemeier 

 and Mason 1984), which plots 10 repetitive surveys of a profile line collected over a 2-day 

 period under near ideal conditions. While there is movement of the nearshore bar during the 

 period shown, of greater interest is the stability of the offshore zone. Seaward of 220 m, the 

 average range in elevation was 5.0 cm. The standard deviation of the 10 elevations for a 

 given distance was usually less than 2.0 cm. 



The stated operating range of the Geodimeter is 5.5 km with a single circular prism array. 



Dacs 



llOO S >Tai. S3 



1200 8 JXTL. 82 



1300 a OTTIj 82 



14,00 8 OTTI. 82 



Distance (m) 



Figure 8. Results of 10 repetitive surveys of a single profile line using the CRAB/Zeiss 

 system 



Chapter 2 Profile Data 



13 



