Signal-in-Space Monitoring Accuracy (SISMA) is regarded as a key indicator for the integrity monitoring of the BeiDou Navigation Satellite System (BDS-3). It is used to evaluate the quality of broadcast ephemeris in real time. However, the conventional SISMA estimation method in the BDS-3 ground operation and control system is severely constrained by the deployment of ground monitoring stations, which are mainly located within China. As a result, the monitoring arcs for BDS-3 in regions outside