Impact of atmospheric turbulence on VGOS telescope location in India

Very Long Baseline Interferometry (VLBI) is the only space geodetic technique capable of accurately determining the complete set of Earth Orientation Parameters (EOP), including polar motion, UT1−UTC, and celestial pole offsets. Atmospheric turbulence, quantified by the refractive index structure constant (Cn), is a significant source of error in geodetic VLBI, so it is essential to consider this factor when selecting optimal telescope locations. This study identifies 14 potential VLBI station locations across India, co-located with existing GPS stations and distributed homogeneously, to simulate their suitability for the VLBI Global Observing System (VGOS) telescope. Using zenith wet delay variances derived from GPS data over a 24-hour period, station-specific Cn values are calculated and incorporated into multiple scheduling simulations via VieSched++. These simulations evaluate the precision of EOP estimation in configurations that reflect current and future VGOS networks. The results indicate that the southern stations are optimal for polar motion and celestial pole offsets, while the eastern stations are most effective for UT1−UTC estimation. Comparisons with utilizing an average Cn value (1.80 × 10^−7 m^−1/3) highlight the critical impact of station-specific Cn values on determining optimal telescope locations, particularly for networks with fewer stations. Stations with a Cn value higher than 2.60 × 10^−7 m^−1/3 impacts the UT1−UTC precision, and the precision of CPO and PM estimation degrades when the Cn value exceeds 3.00 × 10^−7 m^−1/3. Moreover, the study reveals that, despite a station being geometrically well-positioned, a high Cn value can make it unfavourable. This research underscores the importance of integrating stationspecific atmospheric turbulence parameters in the planning of VGOS telescope networks to improve EOP precision.