Abstract
The two instruments, Geomensor and ME5000 are capable of measuring distance with a very high resolving power of sub-mm. The Geomensor uses a white ray from a xenon lamp, whereas the ME5000, a red helium-neon laser. These were simultaneously used along the same baseline. On a 1.6 km baseline, the change of line length due to atmospheric change was about 8 mm during seven hours. It was reduced within 0.9 mm by a multi-wave correction. In another experiment on a 3.6 km baseline, the difference between corrected line lengths measured on two consecutive days was less than 1 mm.