to 14 deg of tilt were recorded on steep portions of the beach. Tilt angle less than 3 deg was 

 ignored. The survey data were adjusted during processing to account for the tilt. 



The Geodimeter Auto-Tracking Survey System 



From May 1990 to December 1991, an auto-tracking survey system, the Geodimeter 140T, 

 was used to enhance the speed of the surveys (Figure 6). The Geodimeter HOT consists of 

 an electronic theodolite, distance meter, tracker, joystick, and cables. The system is designed 

 to track the position of a moving object with the aid of a servo unit, which permits automatic 

 motorized rotation of the instrument in the horizontal and vertical directions. The angle and 

 distance measuring unit is both mechanically and electronically connected to a top-mounted 

 tracker unit. The initial aiming of the instrument is controlled by a joystick. Once locked 

 onto the prism array mounted on the CRAB, the Geodimeter HOT continues to follow it. 

 Hence, the CRAB is able to run continuously. 



With the auto-tracking ability of the Geodimeter 140T, it took, on average, just 25 min to 

 survey one profile line. Position information was obtained every 2-3 m along the survey 

 transect. The average number of data points for a survey of a profile line was 236. 

 Therefore, the important advantages of the auto-tracking system were its ability to detect 

 small features that were not observed in the Zeiss surveys, as well as its higher survey speed. 



The data were collected by a PC 

 connected to the system, using the 

 RG7 program (for " Read 

 Geodimeter" ) developed by Mr. 

 Michael W. Leffler. After a 

 survey, the collected data were 

 processed using ISRP. 



Errors due to the tilt of the 

 CRAB were removed using an 

 iterative technique in the analysis. 

 The measured slope was used as a 

 first guess to adjust the data points 

 both horizontally and vertically. 

 A new slope was then determined 

 and a second pass, if required, was 

 made. On a 10-deg slope, the 

 CRAB tilt can result in a 4-20-cm 

 vertical adjustment to the data. 



Figure 6. 



The Geodimeter MOT auto-tracking 

 survey instrument 



Chapter 2 Profile Data 



