Technical description of sinex solution gsf2016a
2016.09.26
1. Purpose of solution: TRF/CRF and EOP series.
2. Analysis center: GSF (NASA Goddard Space Flight Center).
3. Short narrative description of solution:
Solution gsf2016a_snx is the daily Sinex file version of quarterly update
solution gsf2016a. All regular X/S dual-band Mark-3/Mark-4/Mark-5/K3/K4/VLBA
VLBI observations from 1979.08.03 through 2016.08.22, with durations of 18
hours or longer (5938 sessions, 10,807,922 group delays) were used in the
2016a solution. The series will be updated with new sessions using the same
control file.
The positions of all stations were estimated as local parameters. Station
velocities are not estimated. A priori site positions and velocities are
from the ITRF2014 [1] catalog.
Source positions are estimated for each session and included in the sinex
files. The a priori source positions are from the gsf2016a_astro solution,
with the positions of the 295 ICRF2 [2] defining sources replaced with their
official ICRF2 positions. In the gsf2016a_astro solution, most of the source
positions were estimated globally using a no-net-rotation constraint on the
295 ICRF2 defining sources. However, the positions of the 39 most unstable
sources (the 'special handling' sources of ICRF2) were estimated in each
session individually. Also, all sources which did not have at least 3 good
observations in at least one session were excluded from the solution. Three
gravitational lenses (0218+357/0218+35A/0218+35B, 1830-21A/1830-21B/1830-211,
and 1422+231) were also excluded from the dataset.
Mean site gradients were applied. These were computed from the GSFC Data
Assimilation Office (DAO) model from met data from 1990-95. Residual East and
North gradients were then estimated at 6 hr intervals. Refer to references [3]
and [4] for more details.
4. Estimated parameters:
a. Source positions: Most a priori source positions are from the
gsf2016a_astro solution, with the positions of the 295 ICRF2 defining
sources replaced with their ICRF2 positions. Source positions are
estimated for each session and included in the Sinex files. Sources
with fewer than 3 good observations in the global solution version and
3 gravitational lenses were excluded from the single session Sinex
solutions.
b. Station positions: X,Y,Z station positions for each session.
c. Earth Orientation: X-pole, Y-pole, UT1-TAI, Xdot, Ydot, UT1dot,
X-nutation and Y-nutation for each session. The IAU2000/2006
Precession/Nutation model was applied.
d. Zenith Troposphere: Linear spline 20-min interval; rate constraint
with reciprocal weights generally 50 ps/hr; VMF wet partial
derivative (segmented).
e. Troposphere Gradient: 6-hour East and North linear splines at
all stations using offset and rate constraints with reciprocal
weights of 0.5 mm and 2.0 mm/day (segmented).
f. Station Clocks: Quadratic + linear spline with 1-hr interval
(segmented); rate constraint with reciprocal weights, generally
5.0E-14.
g. Baseline Clocks: As set in initial analysis usually used.
5. A priori Earth orientation:
a. A priori precession/nutation model: IAU2006/2000A Precession/Nutation,
IERS 2010 [5] implementation in Calc 11.
b. A priori short-period in X-pole, Y-pole and UT1 due to short period
tidal and libration effects were applied. These were computed by
Calc 11, as recommended in the IERS 2010 Conventions [5], chapter 5.
6. A priori geophysical models:
a. Troposphere: VMF1 total (dry+wet) mapping function; Saastamoinen
zenith delay calculated using logged pressure and temperature;
a priori mean gradients from DAO weather model.
b. Solid Earth tide: IERS Conventions 2010 [5], chapter 7, steps 1 and 2,
including tides of the 2-nd and 3-rd order.
c. Ocean loading: 3D ocean loading displacements computed using the
Hardisp model. Ocean loading 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 [5] recommended
values (Chapter 7, p. 114-116).
e. Ocean pole tide loading: An ocean pole tide loading correction was
applied, using the model of Desai 2002 [6]. 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 approximately
14 month period.
f. Antenna thermal deformation: Antenna heights were adjusted, based
on the average daily temperatures, using the IVS antenna thermal
deformation model of Nothnagel 2008 [7].
g. Axis offsets: Taken from 2016a.axof, from the 2016a quarterly.
7. Data type: Group delays only.
8. Data editing: 5 deg elevation cutoff.
9. Data weighting: Weights are defined as follows: 1/sqrt ( f**2 + a**2 ).
Quantity "f" is the formal uncertainty of the ionosphere free linear
combination of group delays at X- and S-band obtained by fringe fitting.
The station-dependent parameter "a" was computed for each session by an
iterative procedure such that the ratio of the sum of the squares of
the weighted residuals to the estimate of their mathematical expectation
is about 1.0.
10. Software: Calc 11, SOLVE revision date 2016.09.07.
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. 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. MacMillan, D.S. and C. Ma, "Atmospheric gradients from very long baseline
interferometry observations", Geophys. Res. Lett., 22, 1041-1044, 1995.
4. MacMillan, D.S. and C. Ma, "Atmospheric gradients and the VLBI terrestrial
and celestial reference frames", Geophys. Res. Lett., 24, 453-456, 1997.
5. Petit, Gerard and Luzum, Brian, 'IERS Conventions (2010), IERS Technical
Note 36, 2010.
6. Desai, S.D., "Observing the pole tide with satellite altimetry," J.
Geophysical Research, vol. 107 (C11), p.3186. doi:10.1029/2002JC001224.
7. 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.