Technical description of gsf2019a Intensive series UT1 Sinex solution 2019-Aug-12 1. Purpose of solution: Generation of Sinex files for the UT1 Intensive NEOS VLBI sessions. 2. Analysis center: GSF (NASA Goddard Space Flight Center). 3. Short narrative description of solution: Intensive solution gsf2019a is for the estimation of UT1 from the 1-hour NEOS and K4 Intensive sessions. Most sessions consist of ~12-30 observations on one baseline. The solution includes all usable Intensive sessions from 2005.05.13 through 2019.07.22. The primary single-baseline session networks have been: WESTFORD/WETTZELL, NRAO85-3/WETTZELL, NRAO20/WETTZELL, KOKEE/WETTZELL, and TSUKUB32/WETTZELL. Beginning in 2005, some sessions contain 3 stations, primarily NYALES20/TSUKUB32/WETTZELL and KOKEE/SVETLOE/WETTZELL and a handful contain 4 stations. Each session was processed independently. The initial solution used a total of 7451 sessions. 4. Differences with respect to previous (gsf2014a) solution: a. The site mod file comes from the gsf2019a solution. The velocity mod file is also from the gsf2019a solution. The gsf2019a solution was based on ITRF2014 [1]. b. The source position mod file is from the gsf2019a solution and is based on ICRF3 [2]. 5. Estimated parameters: a. UT1 angle. b. Atmosphere path delay offset at each station. c. Coefficients of the second order polynomial clock functions. 6. Celestial reference frame: a. A priori source positions: /500/oper/solve_save_files/2019a.src This catalog was created from the gsf2019a solution. The positions of the 303 ICRF3 defining sources were replaced by their ICRF3 [2] positions. b. Source positions adjusted in solution: No 7. Terrestrial reference frame: a. A priori station positions: /500/oper/solve_save_files/sitmod_pos_2019a. This catalog was created from the gsf2019a solution. The post-seismic model from ITRF2014 [1] is also applied to site positions. b. A priori station velocities: /500/oper/solve_save_files/sitmod_vel_2019a. This catalog was created in the gsf2019a solution and is based on ITRF2014 [1]. c. Reference epoch: 2014.0. d. Station positions/velocities adjusted in solution: No. e. Permanent tide correction: Yes. "Yes" means that both the permanent and the periodic tides have been modeled, so that the output station position is for after the removal of both the permanent and the periodic tidal effect. The model used includes tide displacements for zero frequency with Love numbers h2(freq=0) = 0.6078, l2(freq=0) = 0.0847 8. Earth orientation: a. A priori Precession-Nutation: IAU2006/2000A Precession/Nutation, IERS Conventions 2010 [3] implementation in Calc 11. b. A priori short-period tidal variations in X-pole, Y-pole, and UT1 due to tidal and libration effects were computed in Calc 11, IERS Conventions 2010 [3] implementation. c. EOP estimation: UT1 (without any constraints). d. A priori UT1 and polar motion: usno_finals.erp (ftp://cddis.gsfc.nasa.gov/pub/vlbi/gsfc/ancillary/solve_apriori/) obtained by adding a small linear shift and drift to the left columns of original usno finals file generated by USNO (ftp://maia.usno.navy.mil/ser7/finals.data) in such a manner that there is no shift or secular drift with respect to the gsf2019a.eops series over the period 2000.01.05 - 2019.06.20. 9. A priori geophysical models and other corrections: a. Troposphere: NMF total mapping function; Saastamoinen zenith delay calculated using logged pressure and temperature; a priori mean gradients from VLBI data or DAO weather model. [Note: We do not use the VMF model because the necessary data is usually not available at the time of processing of new Intensive sessions.] b. Solid Earth tide: IERS Conventions 2010 [3], chapter 7, steps 1 and 2, including tides of the 2-nd and 3-rd order. c. Ocean loading: The Hardisp model in Calc11 is applied. Coefficients computed using the TPXO7.2 model. These were obtained from the ocean loading web site at http://holt.oso.chalmers.se/loading/, which is provided by H.-G. Scherneck, Onsala Space Observatory. d. Pole tide: Mean pole coordinates used for computation of pole tide deformation were set to the IERS 2010 Conventions [3] recommended values (Chapter 7). e. Ocean pole tide loading: An ocean pole tide loading correction was applied, using the model of Desai 2002 [8]. These were computed by Calc 11, and are described in the IERS Conventions (2010), chapter 7, pages 116-118. This small correction should have an ~14 month period. f. Mean site gradients were computed from the GSFC Data Assimilation Office (DAO) model for met data from 1990-95. The atmospheric gradient delay is modeled as: tau = m_grad(el) * [GN*cos(az)+GE*sin(az)], where el and az are the elevation and azimuth of the observation and the gradient mapping function is m_grad. The gradient vector has East and North components GE and GN. Refer to references [4] and [5]. g. Antenna thermal deformation: Antenna heights were adjusted, based on the average daily temperatures, using the IVS antenna thermal deformation model of Nothnagel 2008 [6]. 10. Data type: Group delays only. 11. Data editing: Elevation cutoff 5 degrees. 12. Data weighting. Weights are defined as follows: 1/sqrt ( f**2 + a**2 ) where "f" is 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. Session-dependent parameter "a" was computed for each session by an iterative procedure such that the ratio of the sum of squares of weighted residuals to the estimate of their mathematical expectation is about unity. 13. Standard errors reported: All errors derived from least-squares estimation propagated from the data weights and the constraints applied to the troposphere, clock and EOP parameters. 14. Software: CALC 11, SOLVE revision date 2019.04.19. References: 1. Altamimi, Z., P. Rebischung, L. Mtivier, and X. Collilieux, "ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions, J. Geophys. Res. Solid Earth, vol. 121, Issue #8, pp. 6109-6131, 2016. doi:10.1002/2016JB013098. 2. Charlot, P., et al, 'The Third Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry'; Astronomy and Astrophysics, 2019, in preparation. Also see: https://iers.obspm.fr/icrs-pc/newwww/icrf/ 3. Petit, Gerard and Luzum, Brian, 'IERS Conventions (2010), IERS Technical Note 36, 2010. 4. MacMillan, D.S. and C. Ma, "Atmospheric Gradients from Very Long Baseline Interferometry Observations", Geophys. Res. Lett., 22, 1041-1044, 1995. 5. MacMillan, D.S. and C. Ma, "Atmospheric Gradients and the VLBI Terrestrial and Celestial Reference Frames", Geophys. Res. Lett., 24, 453-456, 1997. 6. Nothnagel, A., "Short Note: Conventions on Thermal Expansion Modelling of Radio Telescopes for Geodetic and Astrometric VLBI," Journal of Geodesy, DOI: 10.1007/s00190-008-0284-z, 2008.