Technical description of solution opa2008x
1. Purpose of the solution: daily SINEX files
2. Analysis center: OPA ( Paris Observatory )
3. Short narrative description of solution: The solution estimates position
of all stations, all EOP and rates and positions of some radio sources for
each session. NNR/NNT constraint is applied to station position.
4. Estimated parameters:
a. celestial frame: right ascension, declination of the sources that were
already estimated as locals in the opa2008x global solution (see list
in the batch solve control listed in the comment part of the SINEX file)
for each session independently.
b. terrestrial frame: X, Y, Z (local)
c. Earth orientation: x, y, UT1-UTC, xdot, ydot, UT1dot, dpsi, deps (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)
5. Celestial reference frame:
a. a priori source positions: opa2008x catalogue
b. source positions adjusted in solution: yes (some)
If yes,
c. definition of orientation: no-net-rotation with respect to the opa2008x
catalogue tied to the 212 ICRF defining sources.
d. source position estimation: when estimated, as local parameters
6. Terrestrial reference frame:
a. a priori station positions: opa2008x catalogue
b. a priori station velocities: opa2008x catalogue
c. reference epoch: 1997.0
d. station positions/velocities adjusted in solution: positions only
e. definition of origin, orientation, and their time evolution: no-net
-translation and no-net-rotation of position with respect to the
opa2008x catalogue. All stations except GILCREEK participate in equations
of constraints. Equations of constraints are equally weighted.
f. station parameter estimation: X, Y, Z, locally for all stations
g. stations with constraints: none
h. stations with discontinuous positions and date of discontinuity: none
i. stations with nonlinear velocities: none
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: IERS 2003
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, deps, dpsi 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; The output deps and dpsi are relative to IAU 1976
precession and IAU 1980 nutation models. 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 deg 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 2006.06.08.
14. Other information: solution is reported at http://ivsopar.obspm.fr/