Dr. Jim Ray of the National Geodetic Survey USA visited Institute of Geodesy and Geophysics CAS on invitation and gave an academic lecture titled ‘Surface Pressure Loading Effects Observed by GNSS’ in the morning of May 20. This seminar was conducted by Dr. Yuan Yunbin, the associate director of State Key Laboratory of Geodesy and Earth’s Dynamics.

Dr. Jim Ray firstly introduced the influence of mass variant of surface fluid to gravity, reference frame and surface displacement and the differences and relationships between them. Then he pointed out that whether to consider the influence of mass variant of surface fluid to GNSS measurement, one need to take the noise-signal ratio of GNSS signal into account. He made a special note that the signal aliasing is a key problem that affect GNSS precision and have not been solved yet. In addition he introduced some surface fluid models that frequently used, and presented the frequency spectrum feature of polar motion, mass variant of atmosphere and displacement of GPS stations, then he analyzed the noise feature and magnitude of mass variant of surface fluid and displacement of GPS stations. At last he made a summary of the outlook of GNSS. Dr. Jim Ray explained profound theories in simple language using vivid figures and data, the listeners benefit a lot from his lecture. At the end of the seminar Dr. Jim Ray had a heated discussion with the listeners.

Dr. Jim Ray is a scientist of National Geodetic Survey USA and a famous specialist in GNSS space survey, his main areas of expertise include: GPS orbit determination software, refining geophysical models, establish and maintain regional and global reference frame, GNSS EOP parameter estimation and refining and so on.