New satellite mission for improving the Terrestrial Reference Frame: means and impacts

Transcription

1 Fourth Swarm science meeting and geodetic missions workshop ESA, March 2017, Banff, Alberta, Canada New satellite mission for improving the Terrestrial Reference Frame: means and impacts Richard Biancale, CNES/GRGS, France 3PM2a: Future of geodesy from space

2 The International Terrestrial Reference Frame (ITRF): a 30-year history BTS84-87: yearly TRF precursors worked out in the framework of BIH (Boucher & Altamimi, 1985) from VLBI, SLR, LLR, and Doppler/TRANSIT data 1987: creation of IERS (International Earth rotation - and reference systems - service) ITRF88-89 : positions of ~100 sites. Velocities from AMO2 tectonic model (Minster & Jordan, 1978) ITRF : GPS introduced; position aligned on EOP/IERS, velocities estimated and aligned to NNR-NUVEL-1 (Argus & al., 1991) ITRF94: DORIS introduced; use of variance matrices of coordinate series ITRF (~500 sites) 1997: first international celestial reference frame (ICRF) ITRF2005: jointly determined time series of TRF and EOP ITRF2008: merging normal equations instead of time series 2009: ICRF2 ITRF2014: last realization of positions + velocities of ~1500 stations over ; 2 adjustment of periodical annual and semi-annual terms and post-seismic effects

3 TRF validity in the long term Lageos and Lageos2 SLR residuals with ITRF2008 and ITRF2014 over the period Source CNES/GRGS ITRF2008 residuals tend to increase regularly from that clearly depicts uncertainties in linear station velocities. 3

4 ITRF tests on 3 LAGEOS 7-day arcs from 1986 to 2016 Solve for orbit parameters, solar pressure factor, tangential bias ITRF2014: ~12 mm over 24 years ~0.5 mm/yr RMS of fit metre Number of measurements per week 4

5 ITRF comparisons on SLR stations Evolution of some ITRF realizations in terms of SLR station positions and velocities SLR station position comparisons with ITRF2014 in position (mm) in velocity (mm/yr) Number of SLR stations Comparisons of station positions are more consistent when using ITRF2014 velocities. The global standard deviation on coordinate discrepancies is between 1 and 2 cm. Velocity standard deviations improved by a factor of ~6 over 20 years ( ) up to ~.6 mm/yr (difference ITRF ITRF2008) 5

6 ITRF2014 co-locations 1499 stations located in 975 sites 91 co-location sites with 2 or more instruments which were or are currently operating Co-locations: 40 GNSS VLBI 33 GNSS SLR 46 GNSS DORIS Tie discrepancies means differences between terrestrial ties and space geodesy estimates Percentage of tie discrepancies < 5 mm > 5 mm GNSS VLBI: 42 % 58 % GNSS SLR: 29 % 71 % GNSS DORIS: 23 % 77 % Altamimi et al., Review of IDS contribution to ITRF2014, IDS workshop

7 An example: Yarragadee As example, discrepancies between GNSS/IGS and DORIS/IDS velocities at Yarragadee (West Australia) from 1995 to 2016 reach up to 0.5 mm/yr North GPS DORIS SLR (mm/yr) N: 58.0 E: 38.7 U: -0.6 East Up VLBI (mm/yr) N: 57.2 E: 40.1 U: years of data only Altamimi et al., Review of IDS contribution to ITRF2014, IDS workshop

8 The geodetic triad quasars Mission types Geometry Gravimetry Altimetry provide Reference system and orbit Geoid Topography and sea surface Reference system VLBI Tide gauge Altimeter ERS, T/P, Jason, Sentinel3 Sea surface Geoid Tracking systems Reference system GRACE, GOCE 8

9 TRF impact on sea level height as determined by altimetry due to TRF discrepancy Effect of the reference frame difference between ITRF2014 and ITRF2008 on: Jason-3 radial orbit difference Jason-2 regional sea level trend (cycle 1-22 / 2016) ( ) mm Radial orbit differences exhibit a degree 1 pattern with a 3 mm amplitude mm/yr Zonal bias and peak differences reach 0.2 mm/yr at high latitudes Lemoine et al., Status of POD for Altimeter Satellites at GSFC, OSTST

10 TRF impact on sea level height as determined by tide gauges and corrected by land vertical motion PSMSL > 40 yrs Wöppelmann et al.,

11 Tide gauge vertical motions Availability of results: The University of La Rochelle (ULR6) solution: Median: 0.36 mm/yr Santamaría-Gómez et al.,

12 ITRF2014 / GIA model comparison Geophysical processes affect TRF velocities: - plate tectonics - glacial isostatic adjustment - present ice melting (loading) RMS ITRF2014 GNSS vertical velocities: - merge past and present climatic signatures Vertical Difference velocities between of ITRF2014 ITRF2014 GNSS stations vertical velocities and ICE6G velocities mm/yr Vertical velocities induced by the post-glacial rebound (ICE6G ; Peltier et al., 2016) Quadratic means between modelled and observed vertical velocities for different ITRF solutions Métivier et al.,

13 Other effects to be considered in the TRF Localisation Pole Motion wrt the Earth surface (crust) Large-scale elastic radial deformation pattern over 10 years related to non-linear polar motion drift as correction to the IERS Conventions, King and Watson, 2014 Geocenter (center of mass) motion wrt the center of figure Sea level trend generated by uncertainty in the ITRF geocenter, Plag, GGOS

14 How to go further? Improvement will go through better modeling or measuring: GIA and loading effects Propagation delays Gravity field variations Non-gravitational accelerations Instrument bias determination Satellite eccentricity vectors Time synchronization need of better geophysical models need of an μ-accelerometer need of gathering all tracking instruments on a unique platform For reaching the GGOS/IAG requirements for 2020: 1 mm position precision 0.1 mm/yr velocity precision 14

15 mission objective On-board colocation of DORIS, GNSS, SLR, VLBI systems aiming at determining intersystem biases at 0.1 mm Precise clock (mphm) for synchronization on-board synchronization of GNSS-DORIS-VLBI-SLR data on-ground synchronization by T2L2 Highly eccentric orbit for long baseline visibility km altitude, 63.4 deg. inclination Additional payload for precision μstar accelerometer to measure surface accelerations to m/s2/ Hz (linear acc.) and the center of mass position to 0.1 mm (angular acc.) The whole for TRF objectives global accuracy of 1 mm and stability of 0.1 mm/yr improved by a factor 5 wrt current knowledge 15

16 science objectives Unification of reference frames and Earth rotation Geocenter and scale Long-wavelength gravity field Altimetry and sea level rise Determination of ice mass loss Geodynamics, geophysics, natural hazards Improvement in global positioning GNSS antenna phase center calibration Positioning of satellites and space probes Relativistic physics (gravitational redshift) High-thermospheric density (accelerometer) Radiative budget (accelerometer) Jason-2 sea level trend difference between ITRF2014 and ITRF