Abstract
Geodetic Very Long Baseline Interferometry (VLBI) uses radio telescopes as sensor networks to determine Earth orientation parameters and baseline vectors between the telescopes. The TWIN Telescope Wettzell 1 (TTW1), the first of the new 13.2 m diameter telescope pair at the Geodetic Observatory Wettzell, Germany, is currently in its commissioning phase. The technology behind this radio telescope including the receiving system and the tri-band feed horn is depicted. Since VLBI telescopes must operate at least in pairs, the existing 20 m diameter Radio Telescope Wettzell (RTW) is used together with TTW1 for practical tests. In addition, selected long baseline setups are investigated. Correlation results portraying the data quality achieved during first initial experiments are discussed. Finally, the local 123 m baseline between the old RTW telescope and the new TTW1 is analyzed and compared with an existing high-precision local survey. Our initial results are very satisfactory for X-band group delays featuring a 3D distance agreement between VLBI data analysis and local ties of 1 to 2 mm in the majority of the experiments. However, S-band data, which suffer much from local radio interference due to WiFi and mobile communications, are about 10 times less precise than X-band data and require further analysis, but evidence is provided that S-band data are well-usable over long baselines where local radio interference patterns decorrelate.
Highlights
Geodetic Very Long Baseline Interferometry (VLBI) telescopes observe radio sources at frequencies around 2 GHz (S-band) and 8 GHz (X-band)
The reference points of all instruments at the observatory are regularly measured via a precise local network survey, so reference data are available including the new TWIN Telescope Wettzell 1 (TTW1)
The reference point of all VLBI telescopes at the Observatory is defined as the intersection point of the azimuth and the elevation axes
Summary
Geodetic VLBI telescopes observe radio sources at frequencies around 2 GHz (S-band) and 8 GHz (X-band). Signals from these distant quasi-stellar objects (Quasars) are received and recorded by at least two telescopes simultaneously. These signals are transferred to a correlator facility and cross-correlated. The geometrical delay between the signal arrival time at the two telescopes, as derived from the correlation process, is a measure of the baseline length [1,2]. Geodetic VLBI has become an important space geodetic technique, because it is the only state-of-the-art technique to establish a precision link between the inertial and the Earth-fixed reference frame. It is the only technique to determine the difference between the Coordinated Universal Time UTC, an atomic timescale, and UT1, the principal form of the Universal Time, which is tied to the rotation of the
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