Seminars

Terrestrial Reference Frames (TRFs) underpin all modern navigational techniques, which depend on the accuracy and stability of these reference frames to derive consistent positions that can be related to each other at different epochs and locations. A critical determining factor in the accuracy and stability of combination TRFs is the accuracy of inter-technique local tie vectors, which relate the positions of the space geodetic techniques that are used together to realize the TRF.
With the help of a team at UT’s Applied Research Laboratories and NASA’s Goddard Space Flight Center, I have developed a novel strategy to determine these tie vectors directly between the geodetic reference points of Global Navigation Satellite Systems (GNSS) antennas and Very Long Baseline Interferometry (VLBI) radio telescopes through co-observation of radio frequency sources. These radio sources are either GNSS satellites or Active Galactic Nuclei (AGNs), which are black holes billions of light years away that channel large jets of charged particles that can outshine their host galaxies at radio frequencies.
By collecting differential range and phase measurements through observing a common source, we can directly estimate the difference in position of the instruments to realize a local tie vector. This work is enabled by the High- Rate Tracking Receiver (HRTR), a high-performance GNSS software-defined receiver that records baseband data similar to a VLBI receiving system. We have completed a series of experiments with the Very Long Baseline Array (VLBA) to realize the first local tie vectors between radio telescopes and colocated GNSS antennas using this technique.