Short-baseline interferometry local-tie experiments at the Onsala Space Observatory

We present results from observation, correlation and analysis of interferometric measurements between the three geodetic very long baseline interferometry (VLBI) stations at the Onsala Space Observatory. In total, 25 sessions were observed in 2019 and 2020, most of them 24 h long, all using X band only. These involved the legacy VLBI station ONSALA60 and the Onsala twin telescopes, ONSA13NE and ONSA13SW, two broadband stations for the next-generation geodetic VLBI global observing system (VGOS). We used two analysis packages: $$\nu $$ ν Solve to pre-process the data and solve ambiguities, and ASCOT to solve for station positions, including modelling gravitational deformation of the radio telescopes and other significant effects. We obtained weighted root mean square post-fit residuals for each session on the order of 10–15 ps using group-delays and 2–5 ps using phase-delays. The best performance was achieved on the (rather short) baseline between the VGOS stations. As the main result of this work, we determined the coordinates of the Onsala twin telescopes in VTRF2020b with sub-millimetre precision. This new set of coordinates should be used from now on for scheduling, correlation, as a priori for data analyses, and for comparison with classical local-tie techniques. Finally, we find that positions estimated from phase-delays are offset $$\sim +3$$ ∼ + 3 mm in the up-component with respect to group-delays. Additional modelling of (elevation dependent) effects may contribute to the future understanding of this offset.

Short-baseline interferometry at Onsala Space Observatory

<p>A growing number of geodetic VLBI stations participate in the VLBI Global Observing System (VGOS). Multiple sites operate both new VGOS telescopes and legacy S/X VLBI telescopes. At Onsala Space Observatory, Sweden, we operate two 13.2 m diameter VGOS radio telescopes, ONSA13NE (OE) and ONSA13SW (OW), as well as the 20~m legacy S/X telescope ONSALA60 (ON). Transitioning from the legacy system and providing continuity of the terrestrial and celestial reference frames necessitate establishing ties between S/X and VGOS telescopes. Since spring 2019, we have carried out more than 20 short-baseline (550 m) interferometric observations at X-band to establish local-tie vectors between ON, OE and OW. The obtained data were correlated at Onsala Space Observatory using DiFX, post-processed using HOPS and analysed with nuSolve and ASCOT. In this presentation we given an overview of the observations, analysis, and results of these local-tie experiments. We investigate the impact of modeling e.g. gravitational deformation, and the possibility of using phase-delays to improve the precision. Finally, we present a comparison with preliminary results from two other methods: global mixed-mode observations and classical local-tie measurements.</p>

Local tie survey of the SLR and GNSS stations at the Shimosato Hydrographic Observatory

<p>The Japan Coast Guard (JCG) operates Satellite Laser Ranging (SLR) and GNSS observation at the Shimosato Hydrographic Observatory (SHO) in Wakayama Prefecture, Japan. The SLR and GNSS observation results obtained at the SHO are submitted to the ILRS and the IGS, respectively, and have contributed to the development of the International Terrestrial Reference Frame (ITRF). The SHO, operating two types of global geodetic observation, is now one of the sites of the Global Geodetic Observing System (GGOS).</p><p>Observation sites such as the SHO that operate multiple geodetic techniques function as co-location sites, where the different geodetic techniques can be linked together by precisely determining the local tie between these techniques. In November 2020, the JCG and the Geospatial Information Authority of Japan (GSI) have performed a local tie survey at the SHO to determine the local tie between the SLR telescope and the GNSS station. In our survey, we mounted several targets on the SLR telescope, which we observed from four survey sites that were temporarily set in the SHO. During the survey, we rotated the telescope along the azimuth and the elevation axes at fixed intervals, observing the target positions for each rotation angle. The measured target positions form arcs, from which we can estimate the rotation axes of the telescope; the origin of the axes was determined as the center of the SLR telescope. For the calculation of the local tie, we used the software pyaxis, developed by Land Information New Zealand (LINZ).</p><p>In our presentation, we will show the methods of our survey and calculation described above, and the estimated local tie vector. As of January 2021, we are preparing to submit the co-location SINEX file to the IERS, to contribute to the construction of the upcoming ITRF2020.</p>

VLBI-GNSS co-location survey at the Ishioka Geodetic Observing Station in 2018 and 2020

<p>Geospatial Information Authority of Japan has a VLBI antenna (ISHIOKA) and an IGS station (ISHI) at the Ishioka Geodetic Observing Station. The Ishioka VLBI antenna has participated in the IVS sessions and IGS station ISHI has continuously provided the GNSS data.</p><p>We conducted co-location surveys in November 2018 and September 2020 to determine a local tie vector between the Ishioka VLBI antenna and the IGS station ISHI. In the surveys, we determined the position of ISHI w.r.t. four surrounding reference pillars by angle/distance measurements and leveling. To determine the position of the VLBI antenna reference point w.r.t. the pillars, we adopted the “inside method” (Munekane, 2019), where the position of the VLBI reference point is determined by observing mirror installed inside the AZ cabin from the fixed point inside the cabin; its position is determined by angle/distance measurements from the pillars. We plan to finish the calculation early this year and submit the results to IERS ITRS Center so as to contribute to the ITRF2020.</p><p>In this presentation, we will outline the inside method and compare the results in 2018 and 2020.</p>

Indian opposition parties may prioritise local tie-ups

Headline INDIA: Opposition parties may prioritise local tie-ups