Initial Findings on Epoch-Wise Realization of a Regional Reference Frame Using Indian CORS Sub-Network Observations

A high-precision Terrestrial Reference Frame (TRF) is essential for accurately monitoring geophysical activities. Currently, India lacks its own Regional Reference Frame (RRF) and relies on the global frame for local applications. With the recent installation of more than 1000 GNSS stations forming the so called CORS (Continuously Operating Reference Stations) network by the Survey of India (SoI), the need for a precise RRF for India has become evident.

The RRF can be realized using either a conventional secular Multi-Year Reference Frame (MRF) or a (geocentric) Epoch-based Reference Frame (ERF). An MRF is realized by aligning the regional network to a global frame such as the ITRF or IGS TRF. However, the accuracy of MRFs diminishes over time as coordinates are extrapolated beyond the observation period using linear velocities. Additionally, MRFs provide limited geophysical information and can’t be utilized with desired accuracy for quasi-instantaneous applications or after large earthquakes.

To address these limitations, this study aims to develop an ERF for the Indian CORS sub-network by adopting the methodology introduced by Kehm (2022) for creating a geocentric ERF in Latin America. The proposed ERF ensures that the frame's origin aligns with the Earth's instantaneous center of mass across all time scales within the observation period.

In this presentation, we will outline the approach to develop the Indian ERF, which involves combining weekly normal equations from global GNSS, SLR, and VLBI networks. Specifically, SLR determines the origin, SLR and VLBI jointly determine the scale, and a homogeneously distributed global GNSS network is used to realise the orientation of the frame. The results will be compared to those obtained using the conventional MRF realization approach. Furthermore, an independent validation strategy will be implemented to evaluate the accuracy of the developed ERF.