A2 
the electronic theodolite measures 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 prism 
(corrected for earth curvature). 
The ELTA-2s was primarily used for positioning the instrumented sled, the 
instrument pipes, and for beach surveying. It is classed as a first-order survey 
instrument with 0.6-sec horizontal and vertical angle reading accuracy. 
Unfortunately, it began malfunctioning during the latter half of the experiment 
with some impact on the positioning of the instrumented sled. The errors 
resulted from a problem in the horizontal rotation of the instrument and were 
easily identified as inconsistent changes in horizontal position. 
Geotronics Geodimeter 140-T 
The Geodimeter 140-T (Figure A1) 
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 140-T 
continues to follow it. 
Figure A1. Geodimeter 140-T 
With the auto-tracking ability of the Geodimeter 140-T, the CRAB was able 
to move continuously, obtaining position information every 2-3 m along the 
survey transect. Data were collected by a shore-based personal computer, and 
steering information was radioed to the driver. The Geodimeter was put into 
use at the FRF early in 1990 and the DELILAH surveys were the first real 
production surveys with the instrument. 
A combination of unfamiliarity with the instrument and several unique 
quirks resulted in problems processing and interpreting some of the Geodimeter 
survey data, particularly the 13-m deep data. The problems affect elevation 
measurement. There were three types of problems. 
One of the instrument errors of the Geodimeter results from the separation 
of the tracking unit and the angle measurement unit. For accurate vertical 
measurements, the two units must be parallel. Instead of attempting to fine 
adjust the parallelism, the angular error was computed based on targeting a 
Appendix A Surveying 
