1. Footprint Observations at the Fundamental Station Wettzell Wolfgang Schlüter Thomas Klügel Christian Schade Bundesamt für Kartographie und Geodäsie Fundamentalstation Wettzell Germany

2. Why a Footprint Network? A footprint network consists of geodetic markers in the area of the geodetic observatory, spread away several km from the observatory (dependant on geological structure of the area itself) Continuous observations with highest accuracy allow the documentation of the local, geological stability of the observatory site, which is important for the knowledge of e. g. representing station motion the plate motion. Footprint network is needed in addition to a local survey network, which allows the determination of local ties e.g. between VLBI and GPS reference points

3. GPS Footprint Network Wettzell permanent installed GPS receivers: Ashtech Z12 Wettzell (WTZZ) Arber (ARBR) Hohenwarth (HOWA) Prackenbach (PRAC) Miltach (MILT) 19.0km 7.0 km 8.2 km 7.1 km

4. Local Survey Network Pillar 21 GPS-Array RTW

5. GPS Antenna Array GPS Array –WTZR Turbo Rogue ACT –WTZA Ashtech Z12T –WTZZ Javad (GPS/GLONASS) –WTZT Trimble 4000SSI –WTZJ Javad (Real Time) WEB Cam –Taking pictures (clouds, snow,sunshine)

6. Pillar 21 Survey Pillar with an integrated AGI 722 borehole tiltmeter, resolution <100nrad) GPS Receiver Ashtech Z12 for continuous observations

7. Pillar 21 - Stability

8. Analysis Strategy for Daily Solutions Bernese Software, Version 5.0 RINEX - Raw Data Orbit/EOP - Information Preprocessing L3 Ambiguity-Float Solution Ambiguity Resolution L3 Ambiguity-Fixed Solution Reciever Clock Cycle Slips Widelane/ Narrowlane NEQ Files: Combination Local Troposphere Model Baselines RMS- Dependent Strategy

9. Residuals in Height of GPS Array WTZA and WTZR with reference to Pillar 21 Snow WTZA WTZR 100d 10 mm Snow

10. Residuals in North of GPS Array WTZA and WTZR with reference to Pillar 21 WTZA WTZR 1mm

11. Residuals in East of GPS Array WTZA and WTZR with reference to Pillar 21 WTZA WTZR 1mm

12. Residuals in Height of the Footprint Points with respect to pillar 21 ARBR HOWA MILT PRAC Antenna change 10mm 100d

13. Residuals in North of the Footprint Points with respect to pillar 21 ARBR HOWA MILT PRAC 2mm 100d

14. Residuals in East of the Footprint Points with respect to pillar 21 ARBR HOWA MILTPRAC

15. Conclusion Monitoring of stability below 1mm repeatability Seasonal effects can be detected –No significant height changes! –Seasonal effect in the North components (1mm amplitude) –Significant seasonal effect in East components (up to 2mm amplitude) Influence of snow on the antenna in winter decrease the monitoring to few millimeter and creates systematic effects The area around the FSW is stable! Is the order of variations in positions transferable to the 20m RTW reference point?