Instrumental equation
In astrometry and geodesy, the instrumental equation is the effect of small systematic errors in a measuring instrument or a measuring method, which remain almost constant in their overall effect on the determination of time , plumbness and location .
The name was created by analogy with the term " personal equation " when, around 1930, the observer began to reduce the effects of time and target errors through (partial) automation .
Just like the personal equation , the instrumental equation can only be determined by reference measurements at a precisely known reference point .
causes
The instrumental equation is mainly caused by the following effects:
- uneven thermal expansion of parts of the instrument, v. a. by cooling the air at night
- minor wobble of the vertical axis (systematic proportions about 1 ")
- irregular backlash during the fine movement of the telescope
- small zero point errors in micrometers (can be partially eliminated by measuring arrangement)
- Delays in the signal reception of the time signal transmitter (according to R.Sigl less than 0.01s)
- Irregularities in the registration micrometer
- residual target axis error after adjustment
- the hall refraction in observatory domes .
Sometimes meteorological effects such as zenith or side refraction are also included in the instrumental errors, provided that they have a systematic component (e.g. due to the slope of the terrain ). They arise from thermal layer inclinations in the lower troposphere . A pillar rotation caused by cooling also has a systematic effect .
See also
literature
- Karl Ramsayer : Geodetic Astronomy ( Handbook of Surveying Volume 2a). 10th, completely revised and restructured edition. JB Metzler-Verlag, Stuttgart 1970.
- Joachim Höpfner: Astronomical differences in length and latitude of the basic observatories Potsdam, Irkutsk and Simeiz . Astronom. News 304/5, p. 265-275, Berlin 1983.
supporting documents
- ↑ Gottfried Gerstbach : For the azimuth measurement with second theodolites . Austrian Magazine for surveying 64/2, p. 53-68, Vienna 1977
- ^ Rudolf Sigl : The influence of systematic .. observation errors on the Laplace equation , Bull.Géod. 44/1, doi: 10.1007 / BF02526434 .