Figure 5. Zeiss Elta-2 electronic surveying instrument 



earth curvature) . 



19. The stated operating range is 2 km with a triple prism assembly as 

 used on the CRAB. Working accuracy of +3 cm or better is possible in both 

 horizontal and vertical coordinates. Actual accuracy in a repetitive survey 

 program is less because of changing atmospheric conditions, different instru- 

 ment setups, and differences in the actual points surveyed. 



20. The high accuracy of the system is shown in Figure 6 (Birkemeier and 

 Mason 1984), which shows 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, the stability of the offshore zone 

 is of greater interest. Seaward of 220 m, the average range in elevation was 



5 cm. The standard deviation of the 10 elevations for a given distance was 

 usually less than 2 cm. 



21. Only about 10 sec are required to aim, shoot, and record each survey 

 point. Because the actual coordinates of each point are displayed, the CRAB 

 can easily be kept on line to within +1 . 5 m through radio communications 

 between the CRAB driver and the instrument operator. 



12 



