Zenith camera

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Digital zenith camera from the University of Hanover for measuring deviation and direction of the perpendicular
Historic zenith camera made by Max Fechner in Potsdam (around 1900)

A zenith camera is a compact camera with which the stars in the vicinity of the zenith are photographed in order to determine the perpendicular direction .

Zenith cameras are important measuring instruments in modern astrogeodesy and, in addition to determining plumb bobbins and geoid (measuring geographical longitude , latitude and their changes), can also be used to measure time and star locations. There are two versions:

  • Photographic : camera with a focal length of 30 to 100 cm, highly sensitive photo plates , precise turntable for 90 ° or 180 ° rotations around a vertical axis.
  • Digital camera : focal length 10–50 cm and CCD sensor instead of the photo plate. The axis of rotation does not have to be manufactured so precisely because of the shorter design and exposure time , which enables the construction of easily transportable devices.

After the first exposure (approx. 5–10 seconds), it is rotated 180 ° and further exposure (s) are made. The measurement of the short star trails gives the axis of rotation with respect to the starry sky and thus the plumb direction if the axis is exactly vertical. Any slight inclination is determined with dragonflies or plumbing sensors .

The older, photographic design is hardly used today, because measuring the photo plates with a comparator takes about 1–2 hours. The measurement data consist of the image coordinates of all star trails (about 100 stars). The star coordinates are measured automatically with digital sensors and digital image processing methods.

With digital zenith cameras, the accuracy of the measured plumb line direction is between 0.05 "and 0.1", depending on the complexity, which enables local geoid and quasigeoid determinations with millimeter accuracy .

Zenith cameras were developed at the University of Hanover , the TU Vienna and the ETH Zurich and successfully automated using CCD. Over the next few years, they will help to achieve the centimeter geoid that has been strived for since 1995 in the countries of Central Europe .


  • Albert Schödlbauer : Geodetic Astronomy. ISBN 3-11-015148-0 , de Gruyter-Verlag, Berlin 2000.
  • Christian Hirt, Beat Bürki, Anna Somieski, Günter Seeber: Modern Determination of Vertical Deflections using Digital Zenith Cameras . Journal Surveying Engineering 136 (1), Feb 2010, 1-12. doi : 10.1061 / (ASCE) SU.1943-5428.0000009 , 2010 ( PDF-File )
  • Gottfried Gerstbach, Helmut Pichler: A small CCD zenith camera (ZC-G1) -developed for rapid geoid monitoring in difficult projects . Publ.Astron.Observatory Belgrade ( ISSN  0373-3742 ) No.75, p. 221-228, 2003 ( html file ).

See also

Individual evidence

  1. Digital zenith camera TZK2-D. In: Institute for Earth Measurement, Leibniz University Hannover. Retrieved March 14, 2019 .
  2. ^ Research area gravity field. In: Institute for Geodesy and Photogrammetry, Eidgenössische Technische Hochschule Zürich. Retrieved March 14, 2019 .