Intensive solution maintained at OPAR opa2011j

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. This solution is overpara-
meterized and produces rms as low as for 24-hr sessions, i.e., lower than
2011i by a factor of two. New parameters include segmented troposhere delay
and station positions.

4. Estimated parameters:
 
a. UT1.

b. zenith troposphere: offset every 10 mn.
 
c. station clocks: quadratic drift.

5. Celestial reference frame:
 
a. a priori source positions: ICRF2.
 
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. station positions adjusted in solution: yes, w/ NNR/NNT uniformly applied
to all stations.

7. Earth orientation:

a. a priori precession model: IAU 2000.
 
b. a priori nutation model: IAU 2000 + correction fitted to C04. The correction
includes a variable FCN model, a slope, and a number of tidal periodic terms.
 
c. a priori short-period tidal variations in x, y, UT1: IERS 2003.
 
8. A priori geophysical models:
 
a. troposphere: VMF1.
 
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: ocean loading displacements computed from FES 2004.
Atmospheric loading displacements obtained from the 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 2010.05.21.

14. Other information: solution is reported at http://ivsopar.obspm.fr.