Quarterly VLBI EOP Solution opa2008d
1. Purpose of solution: TRF/CRF and EOP series
2. Analysis center: OPA ( Paris Observatory )
3. Short narrative description of solution: The OPA quarterly solution estimates
all EOP and rates and station positions/velocities and radio source coordinates.
All station and source coordinates are estimated as global parameters except for
poorly observed sources and station with strong nonlinear motion which are
treated as arc parameters or modeled by splines. The NNR is applied to the
247 stable sources of Feissel-Vernier et al. (2006).
4. Estimated parameters:
a. celestial frame: right ascension, declination (mostly global, some local)
b. terrestrial frame: X, Y, Z, Xdot, Ydot, Zdot (global)
c. Earth orientation: x, y, UT1-UTC, xdot, ydot, UT1dot, dpsi, deps (all local)
d. zenith troposphere: continuous piece-wise linear; 20-min interval; rate
constraint generally 50 ps/hr; NMF wet partial derivative (segmented)
e. troposphere gradients: 8-hour East and North piece-wise continuous at all
stations except a set of 110 stations; offset constraint 0.5 mm, rate
constraint 2.0 mm/day (segmented)
f. station clocks: quadratic + continuous piece-wise linear with 60-min
interval; rate constraint generally 5.0E-14 (segmented)
g. baseline clocks: set in initial analysis - usually used (local)
h. other: global antenna axis offsets for 61 stations (global)
5. Celestial reference frame:
a. a priori source positions: ICRF-Ext.2
b. source positions adjusted in solution: yes
If yes,
c. definition of orientation: no-net-rotation tie to the Feissel-Vernier
(2006) 247 stable sources (see control file for list)
d. source position estimation: mostly global and some local (see control file)
6. Terrestrial reference frame:
a. a priori station positions: ITRF 2000
b. a priori station velocities: ITRF 2000
c. reference epoch for site positions: 1997.0
d. station positions/velocities adjusted in solution: yes
If yes,
e. definition of origin, orientation, and their time evolution: no-net-
translation and no-net-rotation of position and velocity with respect to
ITRF 2000 for 35 stations:
ALGOPARK BR-VLBA DSS45 FD-VLBA FORTLEZA HARTRAO HATCREEK HAYSTACK \
HN-VLBA HOBART26 KASHIM34 KASHIMA KAUAI KOKEE KP-VLBA LA-VLBA \
MATERA MK-VLBA NL-VLBA NOTO NRAO20 NRAO85_3 NYALES20 ONSALA60 \
OV-VLBA OVRO_130 PIETOWN RICHMOND SANTIA12 SC-VLBA SESHAN25 TSUKUB32 \
VNDNBERG WESTFORD WETTZELL
f. station parameter estimation: X, Y, Z, Xdot, Ydot, Zdot globally for all
stations, some with constraints
g. stations with constraints: a priori velocity of U, E, and N components
were constrained to the ITRF 2000 velocities with reciprocal weights 0.1,
3.0, and 3.0 mm/yr respectively for stations having too short history of
observations, in many cases only one occupation.
h. stations with discontinuous positions and date of discontinuity:
YAKATAGA 1987.12.01: Earthquake
SOURDOGH 1987.12.01: Earthquake
WHTHORSE 1987.12.01: Earthquake
FORTORDS 1989.10.01: Earthquake
PRESIDIO 1989.10.01: Earthquake
MOJAVE12 1992.06.27: Earthquake
DSS15 1992.06.27: Earthquake
MEDICINA 1996.06.01: Rail repair
EFLSBERG 1996.10.01: Rail repair
DSS65 1997.04.15: Rail repair
MIURA 2000.06.01: Earthquake
TATEYAMA 2000.06.01: Earthquake
GGAO7108 2003.01.01: Station relocation
SINTOTU3 2003.09.15: h/z
i. stations with nonlinear velocities: GILCREEK, HRAS_085
j. relativity scale:
G_oo = -(1 - (2W/c^2 + W^2/c^4) + 2L_g )
G_oa = -4W^a/c^3
G_ab = \delta_ab (1 + 2W/c^2 - 2L_g) )
k. permanent tide correction: yes
7. Earth orientation:
a. a priori precession model: IAU 2000A
b. a priori nutation model: IAU 2000A
c. a priori short-period tidal variations in x, y, UT1: hf1102
d. EOP estimation: X, Y, UT1, Xdot, Ydot, UT1dot, dX, dY each day with a
priori error of 45 mas for pole and 3 ms for UT1, 45 mas/day and 3 ms/day for
pole rate and UT1 rate.
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***** IMPORTANT CHANGE WRT PREVIOUS SOLUTIONS *****
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In this solution, the option NUTATION XY_OFFSET is turned on, so that
estimated nutation quantities are the celestial pole offsets dX, dY wrt
the IAU 2000 precession-nutation (consisting of the IAU 2000A nutation
and the IAU 1976 precession corrected by Herring et al. 2002) using the
non-rotating origin-based coordinate transformation between the TRF and the
CRF (Capitaine et al. 2003). The .eob file produced by a homemade getpar
program contains these offsets (and NOT the old-fashioned quantities dpsi
and deps referred to the older models).
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Time tag of EOP series is the middle epoch of the observing session. The
model of high frequency variations in polar motion and UT1 hf1102 was added
to the apriori EOP during data reduction. The reported values of polar motion
and UT1 are the sum of the adjustments and the apriori EOP without contribution
due to the high frequency variations. Thus, the final series of polar motion
and UT1 do not contain contributions due to the high frequency variations.
8. A priori geophysical models:
a. troposphere: NMF dry mapping function; Saastamoinen zenith delay calculated
using logged pressure, temperature; a priori mean gradients from VLBI data or
DAO weather model.
b. solid Earth tide: IERS Conventions 1996, p.56-65, step 1 and step 2,
anelasticity variant, including tides of the 3-rd order.
c. pressure loading: 3D ocean loading displacements computed by SPOTL
software are used. The model of displacements caused by ocean loading contains
28 constituents. 3D displacements computed by convolving global surface
pressure field on a 2.5x2.5 degrees grid with 6 hour temporal resolution
using the NCEP Reanalysis model (APLO service, Petrov & Boy 2004).
9. Data type: group delays
10. Data editing: 6 degree elevation cutoff
11. Data weighting: weights are defined as follows: 1/sqrt ( f**2 + a**2 )
where "f" is the 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. Station-dependent parameter "a" was computed
for each session by an iterative procedure such that the ratio of the sum of
squares of the weighted residuals to the estimate of their mathematical
expectation is about unity.
12. Standard errors reported: all errors are derived from least-squares
estimation propagated from the data weights and the constraints applied
to the troposphere, clock and EOP parameters.
13. Software: CALC 10.0, SOLVE revision date 2008.07.31.
14. Other information: solution is reported at http://ivsopar.obspm.fr/