ON GNSS IN-SITU STATION CALIBRATION OF NEAR-FIELD MULTIPATH

SUMMARY AND DISCUSSION Near-field multipath has an significant impact on GNSS applications and is of importance for the separation of error components, performance of sophisticated modeling, reliability and accuracy of applications. Especially flat and horizontal reflectors are critical, which are often present on today's reference station setups.There are systematic errors through near-field multipath clearly present in positioning. Looking at the mainly affected component height, raises the general question how to determine GNSS height without any systematic error. Hence, the need for taking near-field multipath into account for GNSS processing becomes obvious.An in-situ station calibration approach has been developed, which is based on a combination of several strategies to separate the near-field multipath for a single station to the best. Calibrated, near-field free stations allow for an easy setup at a reference station site and operation over short distances to access the original GNSS observable. In addition the approach is scalable and uses redundancy to obtain e.g. the complete GNSS visibility of the reference station.From observations at the reference site GNSS phase and code corrections as well as weighting schemes of near-field multipath are derived. The application of the correction and weighting in a GPS processing gives very promising results. Further analysis and experiences of the in-situ station calibration are still necessary, for example environmental changes (e.g. weather condition).A general recommendation is also to perform more analysis and assessment of station dependent errors and avoiding near-field multipath already in the beginning while setting up new GNSS stations.The system will be further developed into a complete in-situ station calibration equipment and analysis software.