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--- information_for_astronomers:user_guide:antenna [2018/05/24 12:18]
akraus
+++ information_for_astronomers:user_guide:antenna [2024/06/14 14:30] (current)
akraus
@@ Line 1: / Line 1: @@
-=== Antenna ===
+==== Antenna ====
 The 100-m telescope has a Gregorian design with a 100-m primary mirror (a paraboloid) and a 6.5-m secondary mirror (an ellipsoid).
@@ Line 15: / Line 15: @@
 Latitude 50°31'29.4" North (50.52483°);
 </code>
-the Altitude (track level/elevation axis) is 367/417m (height over the reference ellipsoid). These positions are based on
+the Altitude (elevation axis = reference point) is 416.825 m (height over the reference ellipsoid). These positions are based on
-[[http://www.ccivs.bkg.bund.de/EN/Quarterly/VTRF-Results/VTRF-Stations/vtrf-stations_node.html|observations]] of the
+[[https://www.ccivs.bkg.bund.de/index.php?uri=quarterly/stationcoordinates/xyz|geodetic VLBI observations]] of the
-[[http://ivscc.bkg.bund.de|Internation VLBI Service for Geodesy & Astrometry (IVS)]]
+[[http://ivscc.bkg.bund.de|International VLBI Service for Geodesy & Astrometry (IVS)]]. The cartesian coordinates
+<code>
+x = 4033947.225142 m
+y = 486990.906449 m
+z = 4900431.141999 m (as of May 2019)
+</code>
+are have been used to determine the geographic coordinates above
 (Reference frame is the Earth ellipsoid defined by [[http://en.wikipedia.org/wiki/World_Geodetic_System|WGS84]]).
+Note, that these values correspond to the cross-section of the azimuth and elevation axis (i.e., the height of the
+elevation axis given above). That's the reference point ("geodetic point") of the antenna.\\
+The corresponding track level height is 366.8 m.
+For some purposes, the height with respect to the [[https://en.wikipedia.org/wiki/Geoid|Geoid]] (i.e. "above mean sea level") is relevant. There are different models for the Earth gravitational field (which defines the amsl level), e.g., [[https://en.wikipedia.org/wiki/EGM96|EGM96]] or [[http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008/egm08_wgs84.html|EGM2008]]. In Germany, also the [[https://de.wikipedia.org/wiki/Deutsches_Haupth%C3%B6hennetz|DHHN2012]] model is in use (sometimes also the older DHHN92). The latter is the basis for most topographic map material of the area. On the other hand, [[https://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Mission|SRTM]] data are with respect to the EGM96 Geoid.
+With these models, the following heights can be derived
+^Model^Correction w.r.t. WGS84 ellipsoid^Elevation axis height (amsl)^Track level height (amsl)^
+|EGM96    | -48.0586 | 368.6445 | 318.6445 |
+|EGM2008  | -47.5935 | 369.1096 | 319.1096 |
+|DHHN2012 | -47.698  | 369.0051 | 319.0051 |
+(Based on results with online calculators from [[http://gibs.bkg.bund.de/geoid/gscomp.php?p=g|BKG]] and [[https://geographiclib.sourceforge.io/cgi-bin/GeoidEval|geographiclib]])
 == Axis limits / Cable wrap ==
 The Effelsberg telescope has an altazimuth-mount, with the limits:\\
-.5° ≤ Azi ≤ 503° (0° is North, 90° East)\\
+.5° ≤ Azi ≤ 503° (i.e., 360° + 143° - there is an overleap in the East, 0° is North, 90° East)\\
 .1° ≤ Elv ≤ 89°\\
@@ Line 43: / Line 62: @@
 {{:information_for_astronomers:user_guide:10k.horizont.png|}}
+==== Focussing ====
+Focussing is possible in six axes (x, y, z - linear and rotational) - see the plot below for the definition of the coordinate system.
+Due to the homology of the telescope, the focal point is shifted when the telescope is being tilted, and the focus has to be adjusted accordingly.
+{{:information_for_astronomers:user_guide:100mrt_Focus.png?480|}}

Effelsberg 100m Teleskop

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