Geo++ GNPCV in Real-Time
Geo++ has developed a method for absolute calibration of GNSS antennas using a field procedure in a common research project together with the Institut für Erdmessung (ife), Universität Hannover. The method is based on tilting and rotating the antenna to determine absolute phase variations independent from any reference antenna and independent from multipath effects. The main purpose is the precise determination of phase center offsets and phase variations (PCV).
A robot is used for the operational use of the method to enable precise inclinations and rotations of the tested antenna around a virtual but fixed point in space. The guidance of the robot is conducted with the program GNROBOT, which is configured with additional modules of the Geo++® GNSMART software package to execute the calibration of GNSS antennas.
Basically a two station GNSS processing is set-up. In addition a special program GNRTANT for the automated guidance of the robot is used. The required data streams can be reduced to two RCVR_IN modules (raw data streams from the receiver of the antenna examine and a reference station nearby), pre-processing of the GNSS observations by GNRT, processing of the GNSS observations and estimation of phase variations with GNNET and the feedback guidance using the actual satellite constellation with GNRTANT. The program flow is depicted in the following figure.
Supporting but not essential tools can be used additionally for the calibration (GNMAIN, STAGRA, GNPROTO). In the above figure also the post-processing of the result-file is shown. The file contains the determined phase variations stored in a spherical harmonic expansion with complete variance-covariance matrix.