1. School of Geomatics, Liaoning Technical University, 47 Zhonghua Road, Fuxin 123000, China
2. School of Electronic and Information Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191, China
3. GNSS Research Center, Wuhan University, 129 Luoyu Road, Wuhan 430079, China
4. German Research Centre for Geosciences (GFZ), 14473 Potsdam, Germany