Technical description of solution gsf2011a_snx
2011.10.17
1. Purpose of solution: Single session sinex files of station positions
and EOP.
2. Analysis center: GSF (NASA Goddard Space Flight Center).
3. Short narrative description of solution:
Solution gsf201la_snx is the daily Sinex file version of quarterly update solution
gsf2011a. All regular X/S dual-band Mark-3/Mark-4/Mark-5/K3/K4/VLBA VLBI
observations from 1979.08.03 through 2011.04.07, with durations of 18 hours
or longer (4943 sessions, 72286284812 group delays) were used in the 2011a solution.
The positions of all stations were estimated as local parameters. Station
velocities are not estimated. A priori site positions and velocities are
from the gsf2011a quarterly solution.
Source positions are estimated for each session and included in the sinex files.
The a priori source positions are from the file gsf2011a.src which was
generated during the gsf2011a quarterly solution. From this source list, the
positions of the 295 ICRF2 defining sources were replaced with their official
ICRF2 positions. In the gsf2011a 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 so called
'special handling' sources of ICRF2, see Appendix A) 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, and 3 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 [2] and [3] for more details.
The latest version (2011.04.26) of Solve was used which directly estimates the X and Y
nutation/precession components. The IAU2006 precession model was also applied.
4. Estimated parameters:
a. Source positions: Most a priori source positions are from the gsf2011a
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 IAU 2006 Precession
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, except a set of 98 weak sites (Appendix B) that do
not have an entry in the mean gradient file. Used 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: IAU2000A Precession-Nutation,
IERS 2003 [4] implementation, modified using the IAU2006
precession model.
b. A priori short-period tidal variations in X, Y and UT1 due to short
period tidal and nutation effects were applied. These were computed by
Calc 10, as recommended in the IERS 2003 Conventions [4], chapter 5,
p. 5.
6. A priori geophysical models:
a. Troposphere: VMF 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 2003 [4], 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
28 constituents. The following ocean tide models were used:
Harmonic Phase rad Frequency rad/sec Model Comment
k2-a 1.324501D+00 1.458530140651D-04 GOT00 admittance
k2 3.506941D+00 1.458423171028D-04 GOT00
s2 6.283185D+00 1.454441043329D-04 GOT00
s2-a 4.312500D-02 1.452450074576D-04 GOT00 admittance
m2 2.169437D+00 1.405189027044D-04 GOT00
m2-a 1.210284D+00 1.405082057420D-04 GOT00 admittance
n2 6.097067D+00 1.378796996516D-04 GOT00
k1-a 1.141827D+00 7.293185551375D-05 GOT00 admittance
k1 3.324267D+00 7.292115855138D-05 GOT00
k1-b 2.365113D+00 7.291046158901D-05 GOT00 admittance
p1 2.958919D+00 7.252294578148D-05 GOT00
p1-a 3.002044D+00 7.232384890619D-05 GOT00 admittance
o1 5.128356D+00 6.759774415297D-05 GOT00
o1-a 1.027610D+00 6.758704719061D-05 GOT00 admittance
q1 2.772800D+00 6.495854110023D-05 GOT00
q1-a 4.955240D+00 6.494784413786D-05 GOT00 admittance
mtm-a 4.652212D+00 7.973314413516D-06 NAO99.l admittance
mtm 5.514660D-01 7.962617451151D-06 NAO99.l
mf-a 2.296657D+00 5.334111360775D-06 NAO99.l admittance
mf 4.479096D+00 5.323414398410D-06 NAO99.l
msf 9.721550D-01 4.925201628510D-06 NAO99.l
mm 5.497148D+00 2.639203052741D-06 NAO99.l
msm 4.899785D+00 2.285998575769D-06 NAO99.l
ssa 3.653480D-01 3.982127698995D-07 NAO99.l
paw 5.012885D+00 1.991063797295D-07 equilibrium
sa 3.098467D+00 1.990968752920D-07 NAO99.l
pcw 2.003605D+00 1.671771314171D-07 equilibrium
18.6 4.100746D+00 1.069696236521D-08 equilibrium
d. Pole tide: Mean pole coordinates used for computation of pole tide
deformation were set to the IERS 2003 Conventions [4] recommended
values (Chapter 7, p. 15).
e. Antenna thermal deformation: Antenna heights were adjusted, based
on the average daily temperatures, using the IVS antenna thermal
deformation model of Nothnagel 2008 [5].
f. Axis offsets: Taken from IVS file antenna_info.txt and not adjusted.
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 10.00/10.01/10.02; SOLVE, revision date 2011.04.26.
11. References:
1. 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
2. MacMillan, D.S. and C. Ma, "Atmospheric Gradients from Very Long Baseline
Interferometry Observations", Geophys. Res. Lett., 22, 1041-1044, 1995.
3. MacMillan, D.S. and C. Ma, "Atmospheric Gradients and the VLBI Terrestrial
and Celestial Reference Frames", Geophys. Res. Lett., 24, 453-456, 1997.
4. McCarthy, D.D., Petit, G., IERS Technical Note 32, IERS Conventions
(2003), 2003.
5. 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.
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Appendix A. List of 39 special handling sources for which Right Ascensions
and Declinations were estimated as local parameters:
0014+813 0235+164 0637-752 0738+313 1308+326 1448+762 2145+067
1610-771 0208-512 0438-436 0451-282 0919-260 0607-157 2243-123 NGC1052
2128-123 3C279 0106+013 2134+00 1021-006 3C273B 0528+134 2121+053
0202+149 3C454.3 1611+343 OQ208 2201+315 2234+282 OK290 4C39.25
3C345 0711+356 3C84 1739+522 1044+719 0212+735 3C309.1 3C120
Appendix B. List of 98 sites where troposphere gradients were not estimated:
AUSTINTX AZORES BERMUDA BLKBUTTE BLOOMIND BREST CARNUSTY CARROLGA
CHLBOLTN CTVASBAY CTVASTJ DAITO DEADMANL ELY FLAGSTAF FORTORDS
FORT_ORD FTD_7900 GBT-VLBA GGAO7108 GIFU11 GIFU3 GORF7102 GRASSE
HALEAKAL HOFN HOHENFRG HOHNBERG JPL_MV1 KAINAN KANOZAN KARLBURG
KASHIM11 KIRSBERG KODIAK KOGANEI KOGANEI3 LEONRDOK MAMMOTHL MARCUS
MARPOINT MCD_7850 METSAHOV METSHOVI MIAMI20 MILESMON MIURA MIYAZAKI
MIZNAO10 MIZUSGSI MOJ_7288 MON_PEAK MV2ONSLA NOBEY_6M NOME NRAO85_1
OCOTILLO ONSALA85 OVR_7853 PBLOSSOM PENTICTN PINFLATS PLATTVIL PRESIDIO
PT_REYES PVERDES QUINCY ROBLED32 SAGARA SANPAULA SEATTLE1 SHANGHAI
SINTOTU SINTOTU3 SNDPOINT SOURDOGH SUWON TATEYAMA TITIJIMA TOMAKO11
TOULOUSE TROMSONO TRYSILNO TIDBIN64 TIGOWTZL TSUKUBA TSUKU3 USSURISK
USUDA64 VERNAL VICTORIA VLA VLA-N8 WHTHORSE YAKATAGA YEBES
YELLOWKN YUMA