Integrated Precise Orbit Determination of Multi- GNSS and Large LEO Constellations
remote sensing Article Integrated Precise Orbit Determination of Multi- GNSS and Large LEO Constellations Xingxing Li 1,*, Keke Zhang 1, Fujian Ma 1, Wei Zhang 1, Qian Zhang 1, Yujie Qin 1, Hongmin Zhang 1, Yansong Meng 2 and Lang Bian 2 1 School of Geodesy and Geomatics, Wuhan University, 129 Luoyu Road, Wuhan 430079, China; kkzhang@whu.edu.cn (K.Z.); fjmasgg@whu.edu.cn (F.M.); zw10147@whu.edu.cn (W.Z.); qianzhang23333@whu.edu.cn (Q.Z.); 2015301610178@whu.edu.cn (Y.Q.); hongminzhang@whu.edu.cn (H.Z.) 2 China Academy of Space Technology (Xi’an), Xi’an 710100, China; mengys@cast504.com (Y.M.); bianl35@cast504.com (L.B.) * Correspondence: xxli@sgg.whu.edu.cn Received: 30 August 2019; Accepted: 24 October 2019; Published: 27 October 2019 Abstract: Global navigation satellite system (GNSS) orbits are traditionally determined by observation data of ground stations, which usually need even global distribution to ensure adequate observation geometry strength. However, good tracking geometry cannot be achieved for all GNSS satellites due to many factors, such as limited ground stations and special stationary characteristics for the geostationary Earth orbit (GEO) satellites in the BeiDou constellation. Fortunately, the onboard observations from low earth orbiters (LEO) can be an important supplement to overcome the weakness in tracking geometry. In this contribution, we perform large LEO constellation-augmented multi-GNSS precise orbit determination (POD) based on simulated GNSS observations. Six LEO constellations with different satellites numbers, orbit types, and altitudes, as well as global and regional ground networks, are designed to assess the influence of different tracking configurations on the integrated POD.
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