Global VLBI Solution OPA 2007a 1. Purpose of solution: TRF/CRF and EOP series 2. Analysis center: OPA ( Paris Observatory ) 3. Short narrative description of solution: The solution estimates station position and velocity and source position parameters to define the TRF/CRF for computing EOP time series. The TRF is attached to ITRF 2000 by imposing no-net-rotation and no-net-translation conditions for the positions of a subset of stations and, similarly, no-net-rotation and no-net-translation conditions for the velocities of a subset of stations determined in prelimary solutions. The CRF is attached to the ICRF by a no-net-rotation condition using the 247 stable sources of Feissel-Vernier (2005). Positions and velocities of all stations were estimated as global parameters. Positions of most of the sources were estimated as global parameters. These sources were considered eligible for estimation as global parameters based on the following criteria: 1) the source had 40 or more good observations; 2) the source was observed during two or more sessions; and 3) the source had N.R.D. less than 1.3 in preliminary solutions. Positions for additional sources were estimated for each session independently (treated as arc parameters). 4. Estimated parameters: a. celestial frame: right ascension, declination (mostly global, some local) b. terrestrial frame: X, Y, Z, Xdot, Ydot, Zdot (global) c. Earth orientation: x, y, UT1-UTC, xdot, ydot, UT1dot, dpsi, deps (all local) d. zenith troposphere: continuous piece-wise linear; 20-min interval; rate constraint generally 50 ps/hr; NMF wet partial derivative (segmented) e. troposphere gradients: 8-hour East and North piece-wise continuous at all stations except a set of 110 stations; offset constraint 0.5 mm, rate constraint 2.0 mm/day (segmented) f. station clocks: quadratic + continuous piece-wise linear with 60-min interval; rate constraint generally 5.0E-14 (segmented) g. baseline clocks: set in initial analysis - usually used (local) h. other: global antenna axis offsets for 61 stations (global) 5. Celestial reference frame: a. a priori source positions: ICRF-Ext.2 b. source positions adjusted in solution: yes If yes, c. definition of orientation: no-net-rotation tie to the Feissel-Vernier (2005) 247 stable sources (see control file for list) d. source position estimation: mostly global and some local (see control file) 6. Terrestrial reference frame: a. a priori station positions: ITRF 2000 b. a priori station velocities: ITRF 2000 c. reference epoch for site positions: 1997.0 d. station positions/velocities adjusted in solution: yes If yes, e. definition of origin, orientation, and their time evolution: No-net- translation and no-net-rotation of position and velocity with respect to ITRF 2000 for 35 stations: ALGOPARK BR-VLBA DSS45 FD-VLBA FORTLEZA HARTRAO HATCREEK HAYSTACK \ HN-VLBA HOBART26 KASHIM34 KASHIMA KAUAI KOKEE KP-VLBA LA-VLBA \ MATERA MK-VLBA NL-VLBA NOTO NRAO20 NRAO85_3 NYALES20 ONSALA60 \ OV-VLBA OVRO_130 PIETOWN RICHMOND SANTIA12 SC-VLBA SESHAN25 TSUKUB32 \ VNDNBERG WESTFORD WETTZELL f. station parameter estimation: X, Y, Z, Xdot, Ydot, Zdot globally for all stations, some with constraints g. stations with constraints: a priori velocity of U, E, and N components were constrained to the ITRF 2000 velocities with reciprocal weights 0.1, 3.0, and 3.0 mm/yr respectively for stations having too short history of observations, in many cases only one occupation. h. stations with discontinuous positions and date of discontinuity: YAKATAGA 871201 * Earthquake SOURDOGH 871201 * Earthquake WHTHORSE 871201 * Earthquake FORTORDS 891001 * Seismic event PRESIDIO 891001 * Seismic event MOJAVE12 920627 * Earthquake DSS15 920627 * Earthquake MEDICINA 960601 * Rail reparing EFLSBERG 961001 * Rail reparing DSS65 970415 * Rail reparing MIURA 000601 * Seismic event TATEYAMA 000601 * Seismic event GGAO7108 030101 * Station relocation SINTOTU3 030915 * h/z i. stations with nonlinear velocities: GILCREEK, HRAS_085, PIETOWN j. relativity scale: G_oo = -(1 - (2W/c^2 + W^2/c^4) + 2L_g ) G_oa = -4W^a/c^3 G_ab = \delta_ab (1 + 2W/c^2 - 2L_g) ) k. permanent tide correction: yes 7. Earth orientation: a. a priori precession model: IERS 2003 b. a priori nutation model: MHB 2000 c. a priori short-period tidal variations in x, y, UT1 were taken into account in accordance with the model hf1102 d. EOP estimation: X, Y, UT1, Xdot, Ydot, UT1dot, deps, dpsi each day with a priori error of 45 mas for pole and 3 ms for UT1, 45 mas/day and 3 ms/day for pole rate and UT1 rate; The output deps and dpsi are relative to IAU 1976 precession and IAU 1980 nutation models. Time tag of EOP series is the middle epoch of the observing session. The model of high frequency variations in polar motion and UT1 hf1102 was added to the apriori EOP during data reduction. The reported values of polar motion and UT1 are the sum of the adjustments and the apriori EOP without contribution due to the high frequency variations. Thus, the final series of polar motion and UT1 do not contain contributions due to the high frequency variations. 8. A priori geophysical models: a. troposphere: NMF dry mapping function; Saastamoinen zenith delay calculated using logged pressure, temperature; a priori mean gradients from VLBI data or DAO weather model. b. solid Earth tide: IERS Conventions 1996, p.56-65, step 1 and step 2, anelasticity variant, including tides of the 3-rd order. c. pressure loading: pmvd97d 9. Data type: group delays 10. Data editing: 6 degree elevation cutoff 11. Data weighting: weights are defined as follows: 1/sqrt ( f**2 + a**2 ) where "f" is the formal uncertainty of the ionosphere free linear combination of group delays at X- and S-band obtained by fringe fitting on the base of achieved signal to noise ratio. Station-dependent parameter "a" was computed for each session by an iterative procedure such that the ratio of the sum of squares of the weighted residuals to the estimate of their mathematical expectation is about unity. 12. Standard errors reported: all errors are derived from least-squares estimation propagated from the data weights and the constraints applied to the troposphere, clock and EOP parameters. 13. Software: CALC 10.0, SOLVE revision date 2006.06.08.