Precision leveling
The precision leveling is the most accurate form of terrestrial height measurement . It takes place in the type of technical leveling , but differs in several points:
- Automatic levels of the highest accuracy class are used as leveling instruments , with an accuracy of only a few tenths of a second .
- There are temperature-invariant Leveling with Invar used -division that regularly in the laboratory kompariert be (for dimensional accuracy checks).
- Newer automatic methods use digitally readable measuring rods.
- The standard is the use of two staffs, alternately for the rear and foresight of the instrument - see procedure "Rote Hose" .
- The sightings are because of the refraction limited to about 30 meters and kept exactly the same size in the back and foresight.
- The measured height differences must be reduced because of the path-dependent change in gravity (theoretical loop closure error ).
- The usual double leveling (the measuring distance there and back) is repeated on a second day so that the accuracy reaches the range of 0.5 mm / km.
European height network UELN -95 of precision leveling
Between vertical control points of the first order (in the rock or in very stable, old buildings) measured height differences are after their adjustment to a height network km associated with mesh sizes of about 30 to 50 that the basic surveying is one of a country. Often the nodes are identical to those of the respective gravity network . These basic networks have been connected to international networks since the middle of the 20th century, which today can cover entire continents with an accuracy of 5–10 cm (see picture).
See also
literature
- Karl Ledersteger : Astronomical and Physical Geodesy (Chapter XV, Level and Gravity , p. 787-845). Volume V of the series of reference books Jordan-Eggert-Kneissl, Handbuch der Vermessungskunde, Verlag JB Metzler, Stuttgart 1969
- Wolfgang Torge : Geodesy , 3rd edition. Verlag de Gruyter, Berlin 2001.