GNSS Processing in the CR-SIRGAS geodetic frame: influence of observation and reference epochs

Abstract

The satellite observations derived from the GNSS constellations are fully correlated with the moment in which the measurements are made, however, users can transfer them to different epochs as long as the necessary parameters are available. The quality of the GNSS measurements will in principle be affected by taking them to a different epoch than the original. In the case of the national geodetic frame of Costa Rica CR-SIRGAS, its current reference epoch is t₀ = 2019,24 [1] but the georeferencing of spatial information for cadastral purposes must be in the reference time tk = 2014,59 [2]. A fixed adjustment process was carried out at the epoch t_i = 2021.53 using as observations the baselines of each new point to a maximum of four CR-SIRGAS stations with their respective final weekly coordinates. This adjustment was then repeated using the same, but as reference coordinates the official reference epoch t₀, implying a marked decrease in the original weight of the observations by a factor of 1.5 to 9.5. In addition, it was possible to quantify the discrepancies in the coordinates, accuracies and observations adjusted directly at this time t₀. Finally, the official transformation parameters given by [1] were applied to take the set of coordinates from epoch t0 to epoch t_k.