Electronic Surveying: Accuracy of Tellurometer Over Short Distances

Experience has shown that the relative accuracy of microwave distance measuring instruments drops rapidly when measurements are made over short lines. This is caused by the presence of an instrument error and an instrument constant independent of the distance. Ground and side reflections affect the accuracy in that they are also independent of distance, but are highly dependent on the excess length between the direct and reflected ray paths. An excess length of 7.5 m causes the maximum distortion in the phase angle. A baseline 432 m long was used to test a Model MRA-1 Tellurometer. In connection with the instrument constant determination, correlation between the measuring error and the existing absolute humidity was found. Absolute humidity primarily affected the reverse fine readings. VHP-3 microwave absorbents were used for experimental purposes to reduce the ground and side reflections. Results were promising.