How can we refer to the ITRF from arbitrary locations?

1. Accurate reference frame access at arbitrary points on EarthGPS Dancer projectHennoBoomkampDancer algorithms, JAVA programming, JXTA, P2P & internet, graphics & testing:Boomkamp, H.; Briant, V.; Clemencaux, M.; Cicconi, A.; Daniels, J; Gonzalez Diaz, M; Gebhardt, F.; de Groot, C.; Krikorian, R.; Miller, J.; Moreaux, J.; Müller, P.; le Petit, P.; Randolph, C.; Salomon, R.; Séjan, V.; Simmons, P.; Verstrynge., J.; Wilkins., S.&members of the IAG WG 1.1.1 2004 - 2010&members of the IGS LEO WG 2003 - 2010

2. How can we refer to the ITRF from arbitrary locations? IGS global products (orbits, sat clocks, ERP) 1 regional reference station Global products fixed, user solves local coordinates PPP 2 User solves 3D offset to near-by reference site DGPS 3 Geodetic GPS user

3. How accurate do IGS stations represent the ITRF? 1 Baseline sigma 2.80 mm Repeatability 2.84 mm Polyhedrons with ~ 80,000 baselines daily IGS SINEX files for week 1750 (~400 sites) Scalar “noise” of IGS polyhedrons with respect to IGb08 datum Baseline estimation sigma and repeatability (mm) day of GPS week 1750

4. How accurate can PPP transfer the IGS datum? 2 • PPP: fixed orbits & sat clocks • Weak geometry, DOP • Arguably the best PPP accuracy • shown by routine checks by ACC 10 mm Hor 20 mm Vert

5. How accurate can a user really do a PPP solution? 2 • PPP software is usually based on • minimizing observation residuals • Errors in models & standards move • into the output products rather than • in the observation residuals! • Many ways to do it wrong, • only one way to do it right IGS & IERS standards define ~ 60 models, ~ 130 configurable details ~ 10 time-dependent input files 10 examples of user PPP with errors (ANTEX, DCB, …)  residuals do not reflect the errors 19 mm RMS H 30 mm RMS V L3 residuals (mm)

6. How accurate can a user perform a DGPS solution? 3 • DGPS is insensitive to satellite errors • Orbit • Clock • Attitude • Antenna offset • etc. • Modeling errors almost impossible • Accuracy can get close to L3 noise • …degrades with baseline length observable regional reference station DGPS baselines ~3 mm RMS short baseline • DGPS is insensitive to common station errors • Troposphere, ionosphere • Earth rotation • Tidal uplifts, loading effects • etc. Geodetic GPS user 6

7. How accurate are the ITRF densification networks? 3 • Regional reference station: SAPOS • SAPOS is aligned to ETRF (EUREF) • EUREF is aligned to ITRF08 • Multiple analysis layers exist between • user and ITRF realization of the IGS www.sapos.de Note: ITRF collocated EUREF is of course accurate to 2-3 mm RMS EUREF product list 2011 • Densification network coordinates based on fixed global products (PPP) • DGPS accuracy at user level is not better than PPP accuracy 7

8. The only known cure to the PPP virus:include all ~25,000 permanent sites in IGS-style solutions “…but our computers can not handle more than 200 sites in a global network solution!” so, the workload must be distributed over many computers “…but only a quarter of the reference stations publish their observation data!” if the “many computers” are collocated with the data, the data remains private “…but in the end you would need one computer per receiver ?!” …excellent: 200 times more processing power per receiver • Welcome to the Dancer project • Pure P2P analysis on internet • One computer per receiver • Scalable network solution • Future smart receivers run an • embedded Dancer process

9. free The GPS Dancer software is ready for action Percentage completed • Three sites kept on-line, in repro mode • Occasional tests run 40+ stations • Next milestone: all 400 IGS sites on-line • Allows full operational validation • Offers backbone network to other users for all technical details GPSdancer.org

10. How to deploy Dancer for all 400 IGS sites? • Voluntary campaign has been “postponed indefinitely“… • Required computing capacity is not available in IGS • Cloud computingis ideal for Dancer • Unlimited capacity, reliable, low cost, easy access • No firewall issues, no user hardware needed • Some external funding is needed (…now!) • Internal network traffic at cloud computing provider is free 400 Dancer peers 10 IGS ACs 35 TB / month

11. Size of the geodetic GNSS data set Pasadena WS Berne WS Second decade First decade IGS  Third decade % of GNSS data in ITRF (30 second data samples) Smart Receivers Dancer-in-the-cloud GGOS 1 mm IGS dancer implementation

12. IGS and GPS Dancer need each other • Dancer can do what IGS has always dreamed about: • Unlimited network size • 30 sec data rates • hourly updates, and faster in the future (…near real-time) • Spare capacity for new GNSS satellites & frequencies … but: Dancer cannot do science • IGS is good at science, models, formats, etc. … but: high accuracy is irrelevant if it does not reach the users

13. Conclusions • Today’s datum definition is excellent • ITRF realization by IGS is accurate to 2.8 mm • … but only for 400 stations • Today’s datum transferis inadequate • At user level GPS is not better than 10 ... 20 mm • “P”PP is unreliable as a user technique • DGPS is limited by PPP-style densification layers • Dancer can make the ITRF denser • All permanent sites can be brought to 2.8 mm accuracy level of IGS • Problem already reduced to finding <50k for next 5 - 8 years • DGPS users can get ITRF coordinates < 5 mm accurate • PPP users can have reliable Dancer results at 10 - 20 mm • IGS (/IAG/GGOS) is out of touch with modern computational science