1 / 15

Do Annual Geopotential Variations Affect IGS Products ?

Test effect of GRACE RL05 annual model fits from CSR consider terms (2,0), (2,1), (2,2), & (3,1) Compare GPS results for two extreme weeks 1668 = 25 - 31 Dec 2011 1694 = 24 -30 Jun 2012 Impacts at levels up to several mm Other ACs should test & consider using in Repro2.

cain
Télécharger la présentation

Do Annual Geopotential Variations Affect IGS Products ?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Test effect of GRACE RL05 annual model fits from CSR • consider terms (2,0), (2,1), (2,2), & (3,1) • Compare GPS results for two extreme weeks • 1668 = 25 - 31 Dec 2011 • 1694 = 24 -30 Jun 2012 • Impacts atlevels up to several mm • OtherACsshould test & considerusing in Repro2 Do Annual Geopotential Variations Affect IGS Products ? J. Ray NOAA/NGS with major help from S. Bettadpur, J. Ries U. Texas/CSR T.-S. Bae Sejong U. X. Collilieux IGN/LAREG T. van Dam U. Luxembourg K. Choi, J. Griffiths NOAA/NGS IGS Workshop 2012, AC Splinter Meeting, Olsztyn, Poland, 26 July 2012

  2. Annual Geopotential Terms Considered wk 1668 wk 1694 • Pick two extreme weeks 6 months apart for testing: 1668 & 1694 • Difference NGS solutions WITH & WITHOUT adding annual terms

  3. Compare Test Orbits

  4. Compare Test Terrestrial Frames • Orbit & TRF frames both shift by about -1 mm in Z component • probably due to N/S network asymmetry • recall that current IGS Z bias wrt SLR origin is ~10 larger • global WRMS impact on stations positions at level of ~0.5 mm

  5. Distribution of dU Shifts Week 1668 (25-31 Dec 2011) TASH - (IGS-load)

  6. IGS Repro1 Residuals (TASH – Loads) • TASH heights are too low each December • annual geopotential effect might partially compensate ?

  7. Distribution of dU Shifts Week 1694 (24-30 Jun 2012) Sometimes regions of good correlation - (IGS-load)

  8. Distribution of dN Shifts Week 1668 (25-31 Dec 2011) - (IGS-load)

  9. Distribution of dN Shifts Week 1694 (24-30 Jun 2012) - (IGS-load)

  10. Distribution of dE Shifts Week 1668 (25-31 Dec 2011) - (IGS-load)

  11. Distribution of dE Shifts Week 1694 (24-30 Jun 2012) But also sometimes areas of poor correlation - (IGS-load)

  12. Compare Test ERPs

  13. Conclusions & Recommendations • Annual geopotential variations have small but non-negligible impacts for IGS products • DZ component of orbit & terrestrial frames shifted by ~1 mm • LOD is biased by few µs • subdaily orbit residuals differ up to ~4 mm WRMS • station positions shift by up to ~0.7 mm horizontal, ~3 mm vertical, probably seasonally • systematic geographic shifts may significantly alias inferred GPS load signatures • however, annual geopotential effect generally appears to be smaller than annual (GPS – load) residuals, esp for dN & dE • Recommend further testing by other ACs • need longer spans of results & further comparisons • Recommend possible adoption for Repro2 • if preliminary NGS results confirmed, IGS should consider adopting a conventional model for annual geopotential variations for Repro2 • must coordinate with GRACE, SLR, & IERS groups • Srinivas Bettadpur working on GRACE fit to degree 15

  14. Models Used from S. Bettadpur & J. Ries (1/2) Subject: Estimates of non-tidal degree-2 annual geopotential variability Author: Srinivas Bettadpur Date: June 27, 2012 Version: v 0.0 The total variability at the annual frequency is a sum of many processes. Not all of these are included in the estimates here. Total_Annual = 3rd Body Pert (relevant only for orbits) <<-- This is NOT included below + All tides (solid, ocean, solid+ocean pole tide) <<-- This is NOT included below + Atmosphere + non-tidal oceans (AOD1B contents) <<-- This is included below + Everything else left over (GSM contents) <<-- This is included below The estimates for "Everything else left over" depends on what was modeled for the parts labeled "NOT included below". This list is included below: 3rd Body Pert: DE405 for luni-solar positions Solid Tide: Eq. 6.xx from IERS2010, with anelastic earth klm Ocean Tide: Self-consistent equilibrium Solid Earth pole tide: IERS C04 pole series with an-elastic earth klm Ocean pole tide: IERS C04 pole series with self-consistent equilibrium model of Desai To calculate the contributions to the Clm/Slm, in the same normalization as in the Conventions: omega = 2*pi/365.2426 theta = omega*( t_mjd - 54101.0 ) dClm( t_mjd ) = CBAR_cos * cos(theta) + CBAR_sin * sin(theta) dSlm( t_mjd ) = SBAR_cos * cos(theta) + SBAR_sin * sin(theta)

  15. Models Used from S. Bettadpur & J. Ries (2/2) Table below gives the values of the annual amplitudes for all the degree-2 harmonics. The GRACE+GAC values are labeled as "ANNUAL". For the (2,0) harmonic, the SLR+GAC based estimates are also provided. name N M CBAR_cos CBAR_sin SBAR_cos SBAR_sin ========== ========== ========== ========== ========== ANNUAL 2 0 0.1103E-09 0.8033E-10 0.0000E+00 0.0000E+00 SLRGAC 2 0 9.9868E-10 1.1105E-10 0.0000E+00 0.0000E+00 ANNUAL 2 1 0.7377E-11 -.2024E-10 0.7651E-10 -.2273E-10 ANNUAL 2 2 -.1394E-10 -.7749E-11 0.5471E-10 -.4229E-10 ------------------------------------------------------------------------------------------------- Subject: Re: degree-2 annual coefficients Date: Wed, 27 Jun 2012 15:40:36 -0500 From: John C. Ries <ries@csr.utexas.edu> Hi Jim, I imagine that degree 2 is the 'tall pole' for GPS, but I'm curious about the effect of an odd-degree order 1 term. I think it will be too small for GPS, but it has shown to be important for lower satellites. A quick fit to RL05 gets, in the same convention as Srinivas: name N M CBAR_cos CBAR_sin SBAR_cos SBAR_sin ========== ========== ========== ========== ========== ANNUAL 3 1 0.22E-10 -0.08E-10 0.31E-10 0.39E-10 I have to suspect that the higher degrees are not very important. JR

More Related