GNPCV

Geo++® GNPCV are program packages which allows an absolute antenna calibration from GNSS observations in the field.

Geo++® has developed  realtime and post-processing procedures for the absolute determination of antenna offsets, as well as elevation- and azimuth-dependent phase centre variations, from field measurements.

State-of-the-art is the absolute field calibration with a robot in real-time. The method rduces to the best extend or eliminates multipath effects acting on the accuracy and the calibration results.

The post-processing with GEONAP has been used during the development of the real-time calibration as a first implementation and for verification. Multipath effects can be reduced using siderial differences. Of disadvantage is, that the siderial differences assume comparable weather conditions and identical environment.

Antenna phase centre

An exact knowledge of the receiving properties of the installed antenna is necessary both for high precision GNSS measurements and where a mixture of different types or makes of antenna is being used. The phase centre of a GNSS receiving antenna is not a single exact point; rather does it vary in accordance with the direction of the received signal. The simplest description of these phase centre variations (PCV) is the antenna offset, which indicates the mean influence of the PCV. A complete model of the receiving characteristics of an antenna requires the addition of functions of elevation and azimuth.

Absolute antenna calibration

The absolute determination of antenna offsets, as well as elevation- and azimuth-dependent phase centre variations, from field measurements requires special processing approaches. The influence of multi-path effects as an important error source is eliminated to the greatest possible extent, and the calibration is completely independent of any reference antenna. By means of special measurement and analysis procedures the effective measurement noise is significantly improved.

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azimut- and elevation depending L1-PCV of an Ashtech Geodetic II GPS antenna

The modelling of the PCV is achieved by means of a spherical function and allows various approaches and solutions. From the resulting PCV an antenna offset and additional PCV parameters are generated, which allows the use of either a mean correction or the full calibration. From the spherical function, tables of PCV corrections are prepared, whose contents are compatible with the International GPS Service for Geodynamics (IGS).

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elevation depending L1-PCV of a Trimble Choke Ring GPS antenna

Geo++® GNPCV application areas

Antenna calibrations with GNPCV are necessary for many tasks. These may include:

  • all activities requiring high precision positioning,
  • reference stations (e.g. SAPOS, IGS),
  • geodynamics with GNSS,
  • deformation monitoring with GNSS,
  • applications with a mixture of types or makes of antennas,
  • and many others.

GeoService® GNPCV antenna calibration

The Geo++ associated company, GeoService®, offers the service of absolute antenna calibration with the necessary measurement devices as well as further levels of calibration and test procedures.

Geo++ GNPCVDB allows the access to phase variation type corrections of GNSS antennas calibrated by the Automated Absolute Field Calibration.

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