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POD/Geoid Splinter Summary. OSTS Meeting, Hobart 2007. POD report Revised orbit error budget. Contributors to the orbit error budget have not changed since TOPEX/Poseidon static gravity tide models variable gravity solar radiation pressure station / data errors reference frame
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POD/Geoid Splinter Summary OSTS Meeting, Hobart 2007
POD reportRevised orbit error budget • Contributors to the orbit error budget have not changed since TOPEX/Poseidon • static gravity • tide models • variable gravity • solar radiation pressure • station / data errors • reference frame • geocenter motion • orbit determination noise • but they are now lower and better characterized
Static Gravity • Differences between newer GRACE models are small • order 1 harmonics contribute largest GCEs
Time-Varying Atmospheric Gravity • SLR residuals RMS globally reduced by ~1 mm when adding atmospheric gravity
AOD1B SHDP GDR-B Impact on GCEs Mean Radial Difference relative to JPL06b in mm(averaged over cycles 22 to 99 = Aug 02 to Sep 04) • Atmospheric gravity reduces geographically correlated differences with JPL06b reduced dynamics orbits
Grace-derived time-variable gravity to 20x20 (annual terms only) • Monthly solutions from KBRR data only • Fit mean, trend, & annual harmonic • 2 solutions: 1-yr & 3-yr data span Reference: ‘Monthly spherical harmonics gravity field solutions determined from GRACE inter-satellite data alone,’ Luthcke et al., Geophyscal Research Letters, 2006.
POD Results for JASON 12.7 mm 12.2 mm 11.9 mm 11.5 mm .3219 mm/s .3185 mm/s .3185 mm/s .3181 mm/s 54.7 mm 54.6 mm 54.6 mm 54.3 mm RMS values of one arc per month of the obervations residuals after orbit adjustment
Solar radiation pressure • There is evidence of small residual errors in both the scaled box-wing (GDR-B) and the UCL (JPL) model from L. Cerri
Solar Radiation Pressure SRP is largest surface force acting on T/P and Jason-1 (T/P area-to-mass ratio is half that of Jason-1) Z variation due to 3% scale error in SRP model It is easily shown that a bias in the SRP model interacts with estimated empirical 1/rev parameters to create periodic Z-shift correlated with beta-prime from J. Ries
Solar radiation pressure • GSFC’s attempt to rescale model at GSFC leads to mixed results from F. Lemoine
Solar radiation pressure Z-shift induced by rescaling of SRP model not sufficient to explain Z offset between DORIS/SLR and GPS orbits
Jason DORIS SAA correction: Comparison of SLR/DORIS & SLR/Crossover Orbits ~ 0.9 mm oscillator jump at cycle 91
Reference frame • ITRF2005 • results indicate that ITRF2005 corrects a drift in the centering of ITRF2000 • Z drifts between the various orbits are significantly reduced with ITRF2005 • transition from ITRF2000 to ITRF2005 will induce a shift in Z
TOPEX Radial Orbit Difference Trends (ITRF2005 – GDR (CSR95)) Geographically correlated error (GGM02C-JGM3) Annual signal amplitude (TVG annual – none)
Long-term Orbit Error and the Terrestrial Reference Frame (TRF) Jason (and TOPEX) radial orbit differences are driven by the difference in Z
TOPEX Radial Orbit Difference Trend ITRF2005 – GDR (CSR95) Consequent error in estimated regional and global MSL trends