Technical description of gsf2014a Intensive series UT1 solution 2014-May-14 1. Purpose of solution: Determination of UT1 from short, ~1.0 hour, NEOS Intensive VLBI sessions. 2. Analysis center: GSF (NASA Goddard Space Flight Center). 3. Short narrative description of solution: Intensive solution gsf2014a 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 1991.10.01 through 2014.05.12. 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 6275 sessions, of which several hundred were 3- or 4-station sessions for which the gsf2014a.eopi file contains 4 or more UT1 values - from the full network and from each separate baseline. Japan experienced a large earthquake off its coast on 11-March-2011. Many Japanese VLBI stations underwent large episodic motions from the earthquake, and have not yet returned to their pre-earthquake tectonic motions. The position used for TSUKUB32 after the earthquake is provided by a user program, which uses individual GPS and VLBI measurements. 4. Differences with respect to previous (gsf2012a) solution: a. The site and velocity mod files are from the gsf2014a solution and are based on ITRF2008 [1]. b. The source position mod file is from the gsf2014a_astro solution and is based on ICRF2 [2]. c. Calc 11 is now used. 5. Estimated parameters: a. UT1 angle. b. Atmosphere path delay offset at each station. c. Coefficients of the second order polynomial of clock functions. 6. Celestial reference frame: a. A priori source positions: /500/oper/solve_save_files/2014a_astro.src This catalog was created in the gsf2014a_astro solution and is based on ICRF2 [2]. The positions of the 295 ICRF2 defining sources were replaced by their ICRF2 positions. b. Source positions adjusted in solution: No 7. Terrestrial reference frame: a. A priori station positions: /500/oper/solve_save_files/gsf2014a.sit. This catalog was created in the gsf2014a solution and is based on ITRF2008 [1]. b. A priori station velocities: /500/oper/solve_save_files/gsf2014a.vel. This catalog was created in the gsf2014a solution. c. Reference epoch: 2013.0. 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.data http://gemini.gsfc.nasa.gov/solve_save/usno_finals.erp obtained by adding small linear shift and drift to the left columns of original finals.data 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 gsf2014a.eops series over the period 1997.01.01 - 2014.03.24. 9. A priori geophysical models: 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 did 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: 3D ocean loading displacements computed by SPOTL software. The model of displacements caused by ocean loading contains 18 constituents. The following ocean tide models were used: 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. 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]. f. 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: Manual, 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 2014.02.21. References: 1. Altimimi, Z., X. Collilieux, and L. Metivier, " ITRF2008: an improved solution of the international terrestrial reference frame", Journal of Geodesy, 2011, DOI 10.1007/s00190-011-0444-4. 2. IERS Technical Note 35, 'The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry'; A.L. Fey, D. Gordon, C.S. Jacobs, editors; 2009. http://www.iers.org/IERS/EN/Publications/TechnicalNotes/tn35.html 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.