Abstract
We investigated the suitability of the astronomical 15 GHz Very Long Baseline Array (VLBA) observing program MOJAVE-5 for estimation of geodetic parameters, such as station coordinates and Earth orientation parameters. We processed a concurrent dedicated VLBA geodesy program observed at 2.3 GHz and 8.6 GHz starting on September 2016 through July 2020 as reference dataset. We showed that the baseline length repeatability from MOJAVE-5 experiments is only a factor of 1.5 greater than from the dedicated geodetic dataset and still below 1 ppb. The wrms of the difference of estimated Earth orientation parameters with respect to the reference IERS C04 time series are a factor of 1.3 to 1.8 worse. We isolated three major differences between the datasets in terms of their possible impact on the geodetic results, i.e. the scheduling approach, treatment of the ionospheric delay, and selection of target radio sources. We showed that the major factor causing discrepancies in the estimated geodetic parameters is the different scheduling approach of the datasets. We conclude that systematic errors in MOJAVE-5 dataset are low enough for these data to be used as an excellent testbed for further investigations on the radio source structure effects in geodesy and astrometry.
Highlights
Group delay of an extended source observed with very long baseline interferometry (VLBI) differs from the group delay of a point source
We show three solutions computed with pSolve similar to those introduced by the baseline length repeatability, i.e., Earth orientation parameters (EOP) from MOJAVE-5 dataset, EOP from RV&CN sessions including all stations, and EOP from RV&CN sessions using the Very Long Baseline Array (VLBA) telescopes only
We show the sky coverage during the MOJAVE-5 session bl229bc observed on December 22, 2019, in the upper plots and the cn1924 session observed with the same network on December 09, 2019, in the lower plots
Summary
Group delay of an extended source observed with very long baseline interferometry (VLBI) differs from the group delay of a point source. A typical geodetic schedule splits the network into a number of ad hoc subarrays, so a subset of stations observes one source and a subset of other stations observes another source at the same time, and upon completion of integration another subset of stations observes the source This leads to a substantial reduction of the number of closures in phase and amplitude required for robust imaging. Group delay uncertainty at a given signal-to-noise ratio (SNR) was an order of magnitude worse than from geodetic schedules Such data were still useful for astrometry (Petrov 2011, 2013), they were too coarse for precise geodesy. In case the goal of astronomical observation requires wide spanned bandwidth, e.g., for VLBA (Very Long Baseline Array) Imaging and Polarimetry Survey at 5 GHz (Helmboldt et al 2007), processing astronomical data in a geodetic/astrometric mode was feasible and provided good results (Petrov and Taylor 2011). The program started in 1994 (Lister et al 1996) and is focused on observations of bright active galactic nuclei (AGNs) with discernible structure at 15 GHz
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