Verification and Validation of the GNSS Stations at the Prototype Core Site for NASA's Next Generation Space Geodesy Network

Two operational GNSS stations, GODN and GODS, were established within 100 m of each other at the prototype core site of NASA's next generation Space Geodesy Network. The planned network will co-locate each of the four space geodetic techniques, GNSS, SLR, VLBI, and DORIS, with the goal of meeting modern requirements for the International Terrestrial Reference Frame. This prototype site is located at NASA's Geophysical and Astronomical Observatory at the Goddard Space Flight Center. The two GNSS stations at the prototype site have been producing tracking data from the GPS, GLONASS, and Galileo constellations since January 17, 2012. We present results from the verification and validation of these two stations, focusing in particular on GPS-based positioning of these two sites to monitor their relative baseline vector. We compare baseline recovery from independent precise point positioning of each station to a network-based approach. We also show the impact on the baseline as well as station repeatability from various improvements to our processing approach, namely the application of empirical antenna calibrations, elevation-dependent weighting, and site-specific troposphere modeling. Together, these approaches have resulted in a factor of two improvement in the precision of the baseline length. The standard deviation of the baseline vector, when using independent precise positioning of each station, is 0.5, 0.4, 1.6, and 0.4 mm in the east, north, up, and length components. The difference between the GPS-based baseline length and that from an independent local tie survey is < 1 mm.