A modified approach for automated reference point determination of SLR and VLBI telescopes

Abstract

The International Terrestrial Reference Frame (ITRF) is derived by combining several space geodetic techniques. Basically, a meaningful combination of the geodesic space techniques is impossible without further geometrical information, i. e. local-ties. Local-tie vectors are defined between the geometrical reference points of space geodetic techniques at co-location stations. These local-ties are introduced during the inter-technique combination process, to overcome the weak physical connection between the space geodetic techniques. In particular, the determination of the reference point of radio telescopes or laser telescopes is a challenging task and requires indirect methods. Moreover, the Global Geodetic Observing System (GGOS) strives for an automated and continued reference point determination with sub-millimeter accuracy, because deviations in local-ties bias global results.This investigation presents a modified approach for automated reference point determination. The new approach extends the prior work of Lösler but evades the synchronization between the terrestrial instrument and the telescope. Thus, synchronization errors are omitted and the technical effort is reduced. A proof of concept was carried out at Geodetic Observatory Wettzell in 2018. Using a high-precision, mobile laser-tracker, the reference point of the Satellite Observing System Wettzell (SOS-W) was derived. An extended version of the in-house developed software package HEIMDALL was employed for a mostly automated data collection. To evaluate the estimated reference point, the derived results are compared with the results of two approved models.

ILRS Reference Point Determination Using Close Range Photogrammetry

“…Moreover, the axis offset is close to zero and is insignificant. This result confirms prior investigations using a mobile laser tracker [26]. The derived standard deviations of the reference point coordinate components are comparable to the standard deviations of marker positions at the telescope.…”

“…Thus, the coordinates of P i,k are indicated as an explicit function of the unknowns, and a Gauß-Markov model can be used to estimate the parameters. However, as shown by Lösler et al [26], the resulting normal equation matrix is rank-deficient, because the observed object coordinates are insensitive to define the orientation of the telescope frame. The rank deficiency becomes D = 1, if the trajectories of at least two markers p i are observed, and concerns the rotation around the elevation axis with angle ω k .…”

“…Here, y 0 i , z 0 i are the approximation values of p i , and dy i , dz i are the estimated corrections. A detailed derivation of the refer-ence point determination model and possible alternative datum conditions are discussed by Lösler et al [26,27].…”

“…Nine interoperable drift nests (DN) are also mounted at the dome wall. They magnetically support reference markers for photogrammetric systems and corner cube reflectors for multilateration coordinate measurement systems [47] and for polar measurement systems such as laser trackers [26]. This interoperability of measurement systems is essential to combine different measurement techniques in a consistent reference frame, e.g., the station survey network.…”

Uncertainty assessment of a prototype of multilateration coordinate measurement system

“…Indeed, their performances highly depend on the relative alignment between their components. Lastly, LVM can also be applied over radio telescopes used in geodetic and astrometric very-long-baseline interferometry (VLBI) for monitoring of their spatial position and for estimation of their geometrical reference point [5,6]. In this case, a positioning accuracy better than 1 mm is anticipated in the coming years.…”