Ni2
The Ni2 was the world's first automatic level . It was developed by Zeiss - Opton (Oberkochen) in the early 1950s and, due to its quality, robustness and accuracy , could be sold to geodesy companies and institutes for decades . Thousands of levels of this type are still in use today.
Method of "automatic weighing in"
In an automatic level, a pendulous structure is built into the beam path of the telescope , which sets the target line exactly in the horizontal even if the measuring instrument is not set up exactly horizontally. In the Ni2, a reflective glass prism takes over this function, which hangs on a patented, high-precision manufactured system of 4 fine wires. A small inclination of the device (which can go up to about 0.05 degrees) is compensated for in the optical beam path.
This patent has not only accelerated the leveling method - because the tedious "importing" of dragonflies for every sighting can now be omitted - it has also increased the accuracy in many projects . Because now one could limit oneself to merely “rough” leveling with the circular level and could concentrate one's attention on the actual aiming through the telescope. Only on heavily vibrating structures (eg. As bridges ) to resort to the traditional Dragonfly Levels because the compensator device in certain vibrations in continual tremors.
Instrument data and accuracy
The Ni2 (the name means level type 2 ) has a telescope with a 4 cm aperture and 30x magnification and weighs around 2.1 kg (without horizontal circle) or 2.4 kg (with horizontal circle). Its measurement accuracy was originally designed to be at least ± 1 ", which would correspond to a measurement error of 0.5 mm at 100 m, because the oscillating prism cannot compensate 100% of the remaining instrument inclination, but only about 99.5% In fact, the achievable measurement accuracy turned out to be an impressive ± 0.3 "- a value that z. B. a laboratory physicist would need a telescope 10 to 100 times heavier. With special measuring arrangements, evaluation methods and 1–2 repeated measurements, even ± 0.15 "can be achieved.
A tried and tested trick for this is the “ red pants method ”. Of the two men who alternately walk in front of and behind the measuring device with the leveling staff, one wears a striking color. If the observer now always adjusts the Ni2 in the direction in which he sees the "red pants", the tiny residual errors of 0.5% of the axis inclination are almost completely eliminated.
Ni2 astrolabe
Another precision method was implemented around 1960 in the Ni2 astrolabe , with which an experienced geodesist or astronomer can measure the exact direction of the perpendicular using stars . A 60 ° glass prism is placed in front of the level, which deflects the beam path from the horizontal at a precisely 30 ° zenith distance . In a special thread network , the times of about 20 precalculated star passages are stopped, the analysis of which in comparison with the coordinates of the measurement point finally results in the deviation from the perpendicular .
The originally designed accuracy of 0.6 to 1 "could be increased to about ± 0.4" after a few years with refined computer programs. Large-scale series of measurements by Adolf Rödde (IfAG Frankfurt) and Gottfried Gerstbach (TU Wien) brought a further increase to 0.2 "by mathematically modeling the effects of night temperature , star locations and personal timing and aiming errors For example, it was possible to improve previous geoid determinations by 2 to 3 times to ± 5 cm around 1980. In Austria , 700 measuring points on mountain peaks and in climatically favorable valleys were used for this purpose in 5–6 years with the Ni2 In the 20 years since then, the accuracy has been doubled again through mathematical collocation , with the Technical University of Hanover and Graz leading the way.This has led to a geoid that is almost cm-accurate in Germany, Austria and Switzerland and has broadened the applicability of GPS .
Not least, the light but accurate and flexible instrument measurements allows high precision to normal surveying - stands to make. Until the 1960s , separate measuring pillars had to be built for astrogeodesy in order to be able to control the inevitable small instrument errors during the nightly cooling . The size of the measuring teams could also be reduced from 4 to 2 people.
literature
- Carl Zeiß GmbH: Instructions for use of the Ni2 astrolabe. Oberkochen 1960.
- Karl Ramsayer : Geodetic Astronomy . JEK Volume IIa, Stuttgart 1969.
- Gottfried Gerstbach: Optimization of astrolabe observations . Geoscientific Mitt. Issue 7, TU Vienna 1978.