Optimal Placement of VGOS Telescope in India: Simulation Insights for 24-Hour and 1-Hour VLBI Sessions

Geodetic applications depend on the precise transformation between terrestrial and celestial reference frames, which are tied by the Earth Orientation Parameters (EOP). Very Long Baseline Interferometry (VLBI) is the only space geodetic technique capable of observing the complete set of EOP, which includes polar motion, UT1-UTC, and celestial pole offsets. Over the past three to four years, India has been planning the establishment of a VLBI Global Observing System (VGOS) telescope. Thus, identifying the optimal location for these antennas is critical for enhancing the precision of EOP estimation. The International VLBI Service for Geodesy and Astrometry (IVS) conducts its VLBI observing program in two formats: 24-hr sessions and 1-hr sessions. While 24-hr sessions typically involve a global network of stations and measure the full set of EOP, the 1-hr sessions, called Intensive sessions, focus on determining UT1-UTC with a short latency and generally involve two to three stations.

This study uses VieSched++ software to simulate the optimal position of VGOS telescopes in the Indian subcontinent separately for both 24-hr and 1-hr sessions. For the 24-hr sessions, 14 potential VLBI stations, co-located with GPS stations, are selected and simulated in addition to three different reference networks. Additionally, the study assesses the significance of using station-specific tropospheric turbulence parameters and wind speed in finding the optimal position. For 1-hr sessions, simulations were conducted by varying the VGOS telescope’s location in India on a regular 5 × 5 degree grid. It investigates the change in the precision of different baseline solutions when a third station from India is added in both regular mode and tag-along mode. Furthermore, it also identifies a new baseline, which includes one Indian station and one other station, that could be part of future Intensive sessions. 

Our findings show that the southern and north-eastern regions of India are optimal for improving EOP precision from 24-hr and 1-hr VGOS observing sessions, respectively. The findings also highlight that while a station may be geometrically advantageous for 24-hr sessions, the location might not be favorable if the tropospheric turbulence value is too high.