Technical description of solution cgs2014a_snx Purpose of solution: Provide estimates of Earth orientation parameters, site positions, source positions, the covariance matrix of the estimates and decomposed normal equations for each VLBI session with duration of 18 hours or longer. Analysis center: CGS (Centro di Geodesia Spaziale, Matera, Italy). - ANALYSIS DESCRIPTION 1. Origin of input data: CALC/SOLVE databases from IVS Data Center, version 4 or more. 2. Authentic processing steps after data retrieval: Re-Calc to Calc version 11.0. 3. Origin of meteorological data: use database content. 4. Use numerical weather model: ECMWF for computing VMF1 [Boehm et al. 2006]. 5. Setting of mapping functions: VMF1 (software from GSFC). 6. Origin of cable cal data: use database content. 7. Application of cable cal flags: use database settings. 8. Selection/settings of geophysical models: replace database settings. 8.1 A priori Earth orientation: a. precession/nutation model: IAU2000A precession/nutation model modified using the IAU2006 precession model b. short-period tidal variations in X, Y and UT1 were taken into account in accordance with IERS Conventions 2010 implemented in Calc11.0. c. UT1 and polar motion: usno_finals.erp (http://gemini.gsfc.nasa.gov/solve_save/usno_finals.erp) d. Source positions: A priori coordinates from ICRF2. 8.2 A priori geophysical models: a. Solid Earth tide: IERS Conventions 2010, p.81-88 b. Ocean loading: TPX07.2 implemented in Calc11.0. c. Pole tide: IERS Conventions 2010. Mean pole coordinates used for computation of pole tide deformation were set to the IERS 2003 Conventions recommended values (Chapter 7, eqns 23a, 23b) implemented in Calc11.0.. d. Atmospheric loading: provided by the Goddard VLBI group which are available on the Web at http://gemini.gsfc.nasa.gov/aplo (Petrov & Boy, 2004) e. Antenna thermal deformation: IVS antenna thermal expansion model [Nothnagel 2009] http://vlbi.geod.uni-bonn.de/Analysis/Thermal/antenna-info.txt f. Axis offsets: Taken from: http://lupus.gsfc.nasa.gov/files_IVS-AC/gsfc_itrf2013.axo e. Site positions and velocities: vtrf2008 completed by D.MacMillan on 2008.10.22 files: http://gemini.gsfc.nasa.gov/500/oper/solve_save_files/vtrf2008a.sit http://gemini.gsfc.nasa.gov/500/oper/solve_save_files/vtrf2008a.vel 8.3 A priori atmospheric gradient a. a priori gradient valus from the GSFC Data Assimilation Office (DAO) updated with the current GSFC GMAO model: http://lupus.gsfc.nasa.gov/files_IVS-AC/gsfc_dao_gmao.mgr b. gradient model mapped to the elevation of the source using the Chen and Herring gradient mapping function. 9. Estimated Parameters: a. Station positions: X,Y,Z for all stations for each session. b. Source positions: right ascension and declination estimated for all sources for each session. c. Earth Orientation: X-pole, Y-pole, UT1, Xdot, Ydot, UT1dot, X-nutation and Y-nutation for each session. Constraints of 45 mas for X-pole, Y-pole and 3 sec for UT1. Constraints of 45 mas/day for Xdot, Ydot and 3 sec/day for UT1. Stronger constraints applied to network with weak geometry. d. Baseline Clocks: As set in initial analysis usually used. 9.1 Station clocks: second order polynomial plus a continuous piecewise linear function with 60 min interval and rate constraint of 5.0E-14. 9.2 Atmosphere: a. wet zenith tropospheric delays as 60 min piecewise continuous linear function, with rate constraints of 50 psec/hr b. Troposphere Gradient: 6 hours east and north piecewise continuous linear function at all stations; offset constraint 0.5 mm and rate constraint 2.0 mm/day 10. Outlier elimination: the database settings are generally used. 12. Generation of pre-reduced datum-free normal equations: using standard Solve routines. 13. Further details a. Data type: Group delays only. b. Data editing: 5 deg elevation cutoff. For each session data are not used if: - stations have less than 8 observations - sources have less than 2 observations - baseline have less than 3 observations c. Data weighting: reweight of the observations are done on a baseline basis [J.Gipson et al. 2008] d. Sources: loose NNR applied using the 295 ICRF2 defining sources with sigma 1.0E-10 rad. e. Stations: loose NNT/NNR on positions with sigma 1.0E-4 m applied to all stations except: GGAO7108 KASHIM34 TIGOCONC TSUKUB32 VERAMZSW WHTHORSE AZORES BREST CTVASBAY DEADMANL FTD_7900 HALEAKAL HOFN HOHNBERG KARLBURG MAMMOTHL MCD_7850 METSHOVI MILESMON MOJ_7288 NOBEY_6M NRAO85_1 OCOTILLO OVR_7853 PBLOSSOM PVERDES SANPAULA SEATTLE1 SEST SINTOTU3 TOULOUSE TROMSONO UCHINOUR VICTORIA WHTHORSE YELLOWKN f. Software: CALC 11; SOLVE ftp://gemini.gsfc.nasa.gov/pub_lacerta/SOLVE/SOLVE_mk5_20140221b.tar Note: About 20% of the sessions use a slightly different editing of the data and/or parameterization. References: Chen, G. and T.A. Herring, Effects of atmospheric azimuthal asymmetry on the analysis of space geodetic data, J. Geophys. Res., 102, B9, 20489-20502, 1997. IERS Technical Note 32 (2003), 'IERS Conventions 2003'. L. Petrov, J.-P. Boy (2004), 'Study of the atmospheric pressure loading signal in VLBI observations', Journal of Geophysical Research, 10.1029/2003JB002500, Vol. 109, No. B03405. Boehm J,Werl B, Schuh H (2006), 'Troposphere mapping functions for GPS and very long baseline interferometry from European Centre for Medium-Range Weather Forecasts operational analysis data'. J Geophys Res 111:B02406. doi:10.1029/2005JB003629 Gipson, John; MacMillan, Daniel; Petrov, Leonid (2008), 'Improved Estimation in VLBI through Better Modeling and Analysis', Proceedings of the Fifth IVS General Meeting, St. Petersburg. ISBN 978-5-02-025332-2, p. 158-159. Axel Nothnagel (2009), 'Conventions on thermal expansion modelling of radio telescopes for geodetic and astrometric VLBI'; Journal of Geodesy, Vol. 83(3), 787-792, DOI: 10.1007/s00190-008-0284-z IERS Technical Note 35 (2009), 'The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry'. IERS Technical Note 36 (2010), 'IERS Conventions 2010'. Z. Altamimi, X. Collilieux and L. Mtivier, 'Analysis and results of ITRF2008', IERS Technical Note No. 37 (2012)