Helmert Tower
The Helmert Tower is an astronomical-geodetic observation tower on the Telegrafenberg in Potsdam and belongs to the GeoForschungsZentrum Potsdam . It is a listed building.
history
After Johann Jacob Baeyer's death , Friedrich Robert Helmert took over the management of the Geodetic Institute in 1886 . In 1892 Helmert gave the decisive impetus for the construction of the geodetic-astronomical observatory . In addition to other buildings, a tower for angle measurements (today's Helmert Tower) and observation houses for latitude and time measurements (meridian houses) were built.
The meridian houses had a special roof construction that could be opened for star observation. The roof structure ensured ventilation that was useful for temperature compensation. The foundations of the installed passage instruments were decoupled from the house foundations to avoid the transmission of vibrations.
In the immediate vicinity of the tower and the meridian houses, three small miren houses were built to protect the target marks.
To check the basic settings of the optical measuring devices, two more distant Miren houses were built, which are located on a north-south axis to the Helmert Tower in Königswald and on the Kleiner Ravensberg . These mires were used to adjust the meridian circle of the passage instruments. They were mostly realized as artificial stars , often as bearing mirrors that were sighted with a telescope.
1 Helmert Tower, Telegrafenberg Potsdam
2 Mirenhaus Süd, am Kleiner Ravensberg
3 Mirenhaus Nord, Königswald
At its third meeting on November 27 and 28, 1924 in Dresden , the Advisory Board for Surveying, at the request of its chairman Prof. Ernst Kohlschütter , the then director of the Prussian Geodetic Institute in Potsdam, decided on the observation tower of the Geodetic Institute after the one who died in 1917 rename former director Friedrich Robert Helmert .
Potsdam date
The trigonometric point Rauenberg was destroyed in 1910 by gravel mining. The fundamental point of the Prussian national triangulation was thus useless.
By decision of the Advisory Board for surveying should intermediate point 1st order of Triangulationskette Berlin Shubin (Helmertturm) as a new fundamental point to be introduced by the German Triangulationsnetzes.
The astronomical values for the new central point were determined by the Reichsamt für Landesaufnahme (based on the 'Rauenberg date') using an adjustment calculation of the Berlin – Schubin triangulation chain (measured 1908–1913 ):
Latitude B = 52 ° 22 ′ 53.9559 ″
Length L = 30 ° 44 ′ 1.1358 ″ - 17 ° 40 ′ = 13 ° 4 ′ 1.1358 ″
Azimuth A = 154 ° 47 ′ 32.41 ″
The Central European vertical deviation system was determined by the Geodetic Institute in order to improve the astronomical basis of the triangulation network. The vertical deviation components of the 'Rauenberg datum' were determined in a second approximation by means of an adjustment calculation:
- ξ R = + 2.40 ″
- λ R = + 3.31 "
The vertical deviation components of the new fundamental point Potsdam were calculated from this:
- ξ P = + 0.673 ″ + 1.0000 ξ R + 0.0026 λ R = + 3.082 ″
- λ P = - 0.675 ″ - 0.0097 ξ R + 0.9966 λ R = + 2.647 ″
The ellipsoidal coordinates of the Helmert Tower were calculated from the astronomical observations of the Helmert Tower and these calculated deviation components:
- B ell = B astr - 3.082 ″
- L ell = L astr - 2.647 ″
- A ell = A astr - 2.647 ″ sin B = A astr - 2.097 ″
These “most probable values” for the Helmert Tower, which were calculated from the vertical deviation components of the “Rauenberg date”, differ considerably from the stipulations of the Advisory Board for Surveying . These deviations are so small that the determination of a new fundamental point (Helmert Tower) was not changed due to the considerable practical disadvantages:
- Conversion of all trigonometric points
- Difference in length from Ferro to Greenwich would be a non-round number (previously 17 ° 40 ')
- The sheet borders of the measuring table sheets no longer correspond to full tens of minutes
Due to these considerable contradictions in the state registration , the newly determined values of the 'Potsdam date' could not be established for the official Prussian state triangulation. Thereupon the Advisory Board for Surveying decided at its second meeting on May 2 and 3, 1923 in Kassel to keep the 'Rauenberg date' and to formally define the observation tower of the Geodetic Institute as the central point (with the coordinates related to the 'Rauenberg date' ).
Accordingly, the Helmert Tower point never assumed the function of a central point as it was intended for it, neither in the Prussian triangulation network, nor in the Reich triangular network or in the German main triangular network (DHDN). The DHDN's date designation 'Potsdam-Datum (Zentralpunkt Rauenberg)' is misleading because - as in the earlier networks - the 'Rauenberg-Datum' was retained.
Significance for the national survey
In the course of the Europe-wide joint tasks, uniform geodetic bases for the whole of Europe became indispensable. The basis for the ED 50 was the recalculation of the Central European Network (ZEN) from 1945 to 1947 by the former Institute for Earth Measurement in Bamberg. For the ZEN, the triangulation of the Reich Triangle Network (REN) was balanced out together with other European measurements. The Helmert Tower was set as the starting point for the calculation. This rebalancing was known as the ED 50. The European date 1950 was the geodetic basis of the NATO map series until the 1990s .
Significance for astronomical geodesy
Measurements with the optical zenith telescope
After the first conference of the International Earth Survey in 1888, the International Broad Service started in 1889 . Within this service, the Helmert Tower on the Telegrafenberg in Potsdam was an observation station. The same stars were observed at different stations and the variations in the zenith distances were measured. Within this latitude service, the right-angled coordinates of the polar movement from 1890.0 to 1922.7 were calculated in an interval of 0.1 years. The optical zenith telescope developed by Julius Wanschaff from Berlin was used for the measurement . The optical parts came from Carl Zeiss from Jena and the dragonflies from Carl Reichel from Berlin. Due to a political instruction, the broad-based observations of the International Broad Service ended in May 1919.
Measurements with the Danjon astrolabe
The International Geophysical Year took place in 1957/1958 . On this occasion, the National Committee of the GDR made funds available to purchase a new observation device for the Helmert Tower. This was a semi-automatic astrolabe by André Danjon . He was director of the Paris Observatory from 1945 to 1963.
With the Danjon astrolabe, the latitude of a station was determined in one night to 10–40 milli-arcseconds (mas) and the results were used to record the polar movement. This instrument was used until the 1980s.
Photogrammetric satellite observations
From 1963 to 1974 photogrammetric satellite measurements were carried out. A portable camera for satellite observations was first used for this purpose. In 1966 an automatic camera for astrogeodesy (SBG 420) was installed.
The satellite distance measurements
The Satellite Laser Ranging (SLR) means that it is determined from the surface the distance to the satellite by laser measurements.
In 1974, in the first generation of Satellite Laser Ranging, a satellite tracking camera from Carl Zeiss from Jena was installed on the Helmert Tower in Potsdam . This laser measuring station had a ruby laser.
The second generation started in 1981. The new laser was a single-channel ruby laser that provided a significant increase in accuracy. He was employed in operational business from 1983.
The third generation started in 1986 and ended in 1990. A 1 m SLR telescope was created. This telescope was erected in a historic building near the Helmert Tower and was used between January 1993 and 2001.
Need for repair
The state of construction of the Helmert Tower has deteriorated increasingly since it was abandoned. Extensive work is necessary to preserve it and the outbuildings. Above all, further ingress of water and the progressive corrosion of the load-bearing parts must be prevented. The leaky emergency dome, which was installed after World War II, also has to be replaced. Since the building is not used for the tasks of the GeoForschungszentrum, no structural maintenance work can be financed from the GFZ budget according to the statutes. For this reason, the DVW - Society for Geodesy, Geoinformation and Land Management Berlin-Brandenburg eV, together with the German Foundation for Monument Protection , initiated a collection of donations in 2015 in order to ensure maintenance in the medium term, the whole ensemble is accessible to the public and the 15 meter high To make the tower on the Telegrafenberg accessible as a lookout point.
See also
literature
- Dr. E. Kohlschütter: The coordinates of the central point of the German triangulations , ZfV 1924
- Karl Levasseur: The Central European Triangle Network - Basics , publications of the Institute for Earth Measurement, 1949, p. 71, Bamberg: Meisenbach 1949
- G. Schliephake: Land surveying, textbook for surveying skilled workers 1963 , issue 7, p. 111, VEB Verlag für Bauwesen, Berlin
- Oskar Albrecht: The Advisory Board for Surveying in the German Empire 1921–1933 , Series E, Issue 21, 1984, 1st Conference Sections 4.1 and 5.1, History and Development of Geodesy, German Geodetic Commission. Munich
- R. Schmidt: The reference areas of the location point field and the height point field in the Federal Republic of Germany and their mutual relationships , German Geodetic Commission, Series B, 1986, issue No. 282
- Helmut Wolf: Date determination in the German national survey , ZfV 8/1987
- Wolfgang Augath and Klaus Kummer: The reference systems of basic measurement, ZfV 11/1987, p. 406
- Ernst Buschmann: Once on the Telegraphenberg in Potsdam , Brandenburg surveying 2/96
- Bernd Sorge: The Helmert Tower in Potsdam needs your help! , Surveying Brandenburg 2/2015
Individual evidence
- ↑ Rescue for the historic Helmert Tower on the website of the German Foundation for Monument Protection, accessed on December 21, 2018.
Coordinates: 52 ° 22 ′ 49 ″ N , 13 ° 3 ′ 55 ″ E