Intensive solution maintained at OPAR opa2009i
1. Purpose of solution: UT1 series.
2. Analysis center: OPA (Paris Observatory).
3. Short narrative description of solution: The solution processes intensives
sessions after 2006.01.01 in order to produce UT1 consistent with VTRF 2008a,
ICRF-Ext.2 and C04 Earth orientation data.
4. Estimated parameters:
a. UT1.
b. zenith troposphere: offset.
c. station clocks: quadratic drift.
5. Celestial reference frame:
a. a priori source positions: ICRF-Ext.2.
b. source positions adjusted in solution: no.
6. Terrestrial reference frame:
a. a priori station positions: VTRF 2008a.
b. a priori station velocities: VTRF 2008a.
c. reference epoch for site positions: 2000.01.01.
d. station positions/velocities adjusted in solution: no.
7. Earth orientation:
a. a priori precession model: IAU 2000.
b. a priori nutation model: IAU 2000 + an adjustment through the nutation
offsets as computed in the IERS EOP 05 C 04 data set. The adjusted terms
are: a drift, circular 18.6-yr and 9.3-yr terms both prograde and retrograde,
and the time-variable amplitude and phase of the FCN mode.
The latter mode is taken of fixed period -430.21 days
and the adjustment is done over a 2-yr sliding window displaced by
one year.
c. a priori short-period tidal variations in x, y, UT1: IERS 2003.
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: 5 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 2008.12.05.
14. Other information: solution is reported at http://ivsopar.obspm.fr.