Accurate reference frame access at arbitrary points on Earth GPS Dancer project Henno Boomkamp Dancer 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 & members of the IGS LEO WG

How can we refer to the ITRF from arbitrary locations? 2 Geodetic GPS user IAG 2013 Postdam regional reference station Global products fixed, user solves local coordinates Global products fixed, user solves local coordinates PPP 2 User solves 3D offset to near-by reference site User solves 3D offset to near-by reference site DGPS 3 IGS global products (orbits, sat clocks, ERP) 1

day of GPS week 1750 How accurate do IGS stations represent the ITRF? 3IAG 2013 Postdam 1 daily IGS SINEX files for week 1750 (~400 sites) Polyhedrons with ~ 80,000 baselines Baseline sigma 2.80 mm Repeatability 2.84 mm Scalar “noise” of IGS polyhedrons with respect to IGb08 datum Baseline estimation sigma and repeatability (mm)

4IAG 2013 Postdam 2 How accurate can PPP transfer the IGS datum? 10 mm Hor 20 mm Vert PPP: fixed orbits & sat clocks Weak geometry, DOP Arguably the best PPP accuracy shown by routine checks by ACC

5IAG 2013 Postdam 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 2 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) How accurate can a user really do a PPP solution?

6IAG 2013 Postdam 3 How accurate can a user perform a DGPS solution? 6 Geodetic GPS user regional reference station DGPS is insensitive to common station errors Troposphere, ionosphere Earth rotation Tidal uplifts, loading effects etc. 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 DGPS baselines ~3 mm RMS short baseline observable

7IAG 2013 Postdam 3 How accurate are the ITRF densification networks? 7 EUREF product list 2011 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 Densification network coordinates based on fixed global products (PPP) DGPS accuracy at user level is not better than PPP accuracy Note: ITRF collocated EUREF is of course accurate to 2-3 mm RMS

The only known cure to the PPP virus: include all ~25,000 permanent sites in IGS-style solutions 8IAG 2013 Postdam “…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

The GPS Dancer software is ready for action 9IAG 2013 Postdam 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 free

Voluntary campaign has been “postponed indefinitely“… Required computing capacity is not available in IGS Cloud computing is 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 How to deploy Dancer for all 400 IGS sites? 10IAG 2013 Postdam 10 IGS ACs 400 Dancer peers 35 TB / month

Size of the geodetic GNSS data set IAG 2013 Postdam11 IGS % of GNSS data in ITRF (30 second data samples) Dancer-in-the-cloud Smart Receivers Berne WS Pasadena WS dancer implementation First decade Second decade Third decade IGS  GGOS 1 mm

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 IAG 2013 Postdam12

Conclusions 13IAG 2013 Postdam Today’s datum definition is excellent ITRF realization by IGS is accurate to 2.8 mm … but only for 400 stations Today’s datum transfer is inadequate At user level GPS is not better than 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 years DGPS users can get ITRF coordinates < 5 mm accurate PPP users can have reliable Dancer results at mm IGS (/IAG/GGOS) is out of touch with modern computational science