Site survey and co-location Sten Bergstrand July 2017 SAFETY AND TRANSPORT MEASUREMENT SCIENCE AND TECHNOLOGY

Introduction Local ties are geometric vectors measured between reference points of different stations, including the full covariance information in both temporal and spatial domain Definitions are important to convey information Following Paris workshop 2013 http://iersworkshop2013.ign.fr/ Resolution between services available at IERS URL: https://www.iers.org/SharedDocs/Publikationen/EN/IERS/WorkingGroups/SiteSu rvey/Bergstrand_etal_REFAG2014_TieResolution.pdf (not REFAG2014 proceedings…) Rotation of surveying results into ITRF via GNSS currently destroys any survey…

Every station has one geometric reference point Stations have DOMES numbers Reference points are geometrically determined points on the stations The definitions of these points are determined by the services The term ”reference point” needs to be used exclusively for this geometrically determined point

One geometric reference point Example of internet search result for ”gnss antenna reference point” – not recommended for clarity… Other relations, e.g. - PCO - PCV - pointing - internal geometries - time delays - systematic errors - deformation - etc… are part of the service obligation (with aid from surveyors, where applicable)

Every site should be represented by a physical marker. Invariant to station changes Permanent Preferably attached to bedrock

Exemplified by DORIS antenna Courtesy: Saunier et al.

VLBI Automatic schedule-generated terrestrial monitoring system developed, applied e.g. at CONT14 (Lösler et al.) GNSS antennas mounted on telescopes

How to incorporate local ties and uncertainties in next ITRF? Plans, gateways, commitments, timings? Recommendations are already available since many years. Surveying techniques should generally perform better than current discrepancies between analytic site solutions Quality or quantity? Focus on any separate technique? More surveys? If so: who and how?

General Ishikawa diagram? Reference point Ref. point to rec. unit Local network Geometry Deformation n points GNSS Temperature Geometry Accessibility Arcs Constraints Size Cables Rec.unit Definition Ground stability n measurements Elevation dependence Orientation of vertical Points Variation Frequency Observations Cut-offs Operator Play Repeatability Solar radiation Traceability Interval Temperature Pressure Temperature Length Longevity Stability Met.sensor height Monument Temporal evolution Instrument calibration

Thankyou – Please provide input! Sten Bergstrand sten.bergstrand@ri.se SAFETY AND TRANSPORT MEASUREMENT SCIENCE AND TECHNOLOGY