Activities of the International GPS Service (IGS) Reference Frame Working Group

Abstract

Natural Resources Canada's (NRCan) Geodetic Survey Division (GSD), on behalf of the International GPS Service (IGS) and its Reference Frame Working Group, combines sets of station coordinates, velocities, Earth Rotation Parameters (ERP) and apparent geocenter positions to produce the IGS official station position/ERP solutions in the Software Independent Exchange (SINEX) format. The weekly combination includes solutions from the Analysis Centers (AC), while the Global Network Associate Analysis Centers (GNAAC) provide quality control. The weekly AC solutions include estimates of weekly station coordinates, apparent geocenter positions and daily ERPs. The ACs also provide separately, satellite orbit and clock estimates as part of their daily products, which are independently but consistently combined by the IGS AC Coordinator to produce the IGS orbit/clock products. All the AC products are required to be in a consistent reference frame. The combination of station coordinates originating from different ACs involves removing all available constraints and re-scaling the covariance information. The weekly combined station coordinates are accumulated in a cumulative solution containing estimated station coordinates and velocities at a reference epoch.