Observing APOD with the AuScope VLBI Array

Abstract

The possibility to observe satellites with the geodetic Very Long Baseline Interferometry (VLBI) technique is vividly discussed in the geodetic community, particularly with regard to future co-location satellite missions. The Chinese APOD-A nano satellite can be considered as a first prototype—suitable for practical observation tests—combining the techniques Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS) and VLBI on a single platform in a Low Earth Orbit (LEO). Unfortunately, it has hardly been observed by VLBI, so major studies towards actual frame ties could not be performed. The main reason for the lack of observations was that VLBI observations of satellites are non-standard, and suitable observing strategies were not in place for this mission. This work now presents the first serious attempt to observe the satellite with a VLBI network over multiple passes. We introduce a series of experiments with the AuScope geodetic VLBI array which were carried out in November 2016, and describe all steps integrated in the established process chain: the experiment design and observation planning, the antenna tracking and control scheme, correlation and derivation of baseline-delays, and the data analysis yielding delay residuals on the level of 10 ns. The developed procedure chain can now serve as reference for future experiments, hopefully enabling the global VLBI network to be prepared for the next co-location satellite mission.

Position determination of the Chang’e 3 lander with geodetic VLBI

“…The only difference between the processing of quasar and lunar data in this case is the utilization of the passband option of Fourfit, allowing to restrict the cross-power spectra to windows of one MHz for each of the four DOR tones, without including the carrier frequency. A quite similar approach, related to DOR tones and Fourfit, has been successfully applied to observations of Earth-orbiting satellites with geodetic VLBI (Hellerschmied et al 2018). In Step III, quasar-only delays in S band and X band were analyzed with νSolve (Bolotin et al 2014) to resolve ambiguities and derive ionosphere delays.…”

“…When considering quasar observations, the geodetic VLBI analysis follows a well-established modeling approach (Petit and Luzum 2010). This, however, is not applicable to artificial radio sources on the Moon and the conventional VLBI delay model needs to be replaced with a model considered for targets at a finite distance (Duev et al 2012) and applied both to correlation and data analysis (Klopotek et al 2017a;Hellerschmied et al 2018).…”

“…Step IVb by a constrained estimation (with σ = ± 3 TEC units) of the VTEC biases (one per station per 24 h) along with the lander's position components. In the same step, one additional clock offset per station was estimated as a constant parameter in order to handle ambiguities, potential absolute timing issues (Hellerschmied et al 2018) as well as to correct for an unknown constant offset caused by instrumental delays at X band. The latter is usually absorbed by the clock model in the geodetic parameter estimation in the case of dual-frequency quasar data (Sekido et al 2003;Hobiger et al 2006).…”

Impact of network constraining on the terrestrial reference frame realization based on SLR observations to LAGEOS

“…Therefore, the relevance of Etalon-1/-2 data is thus marginal. The contribution of other geodetic satellites, such as Starlette, Stella, and Ajisai (Sośnica et al 2014;Sośnica 2014;Bloßfeld et al 2018), active low Earth-orbiting satellites (Arnold et al 2018;Guo et al 2018;Hellerschmied et al 2018;Strugarek et al 2019), as well as the constellation of Global Navigation Satellite Systems (GNSS) (Thaller et al 2011;Zajdel et al 2017;Sośnica et al 2018Sośnica et al , 2019 is still being investigated by many researchers. SLR integrates the three major pillars of the Global Geodetic Observing System (GGOS) (Plag and Pearlman 2009), i.e., the Earth gravity field, Earth rotation, and Earth geometry in one common adjustment (Bloßfeld et al 2015).…”

Estimation of SLR station coordinates by means of SLR measurements to kinematic orbit of LEO satellites

“…According to Rothacher (2000), the challenging subject involving multiple geodetic techniques' integration should be solved at the following three different levels: parameter estimation, observation model and station network. At the station network level, the IERS fundamental sites (colocated sites) can give the only effective solutions for the multi-technique integration (Ray 2000;Munghemezulu et al 2014;Glaser et al 2015;Hellerschmied et al 2018). The inter-technique link is the terrestrial ties obtained from ground geodetic measurements of reference points for different space geodetic instruments (Ray 2000).…”