Technical description of solution opa2009a
1. Purpose of the solution: daily SINEX files.
2. Analysis center: OPA (Paris Observatory).
3. Short narrative description of solution: The solution estimates positions
of all stations, all EOP and rates and positions of some radio sources for
each session.
****
Routine analysis of newly arrived diurnal sessions:
For routine analysis, we only consider R1/R4 experiments. Other diurnal
experiments are skipped, except if it is explicitely asked to process
them.
Version 4 or higher of databases are processed. We strictly use the
database files disseminated on the IVS data center (i.e., we never
edit the data and process higher versions made by ourselves).
The routine analysis aims at providing solutions aligned onto a
preliminary global solution. That global solution provides us with:
- the radio source coordinate catalogue,
- the station coordinate and velocity catalogue, and
- the list of sources that will be removed, fixed or estimated.
E.g., in opa2009a, 99 sources were not sufficiently observed and
were removed from the solution. Positions of 658 well-observed sources
were estimated globally in the prelimary solution, and therefore fixed
in the routine analysis. However, the remaining 461 sources (that were
estimated locally in the preliminary solution because of their poor
observational history) are still estimated in the routine analysis.
To be consistent with other AC's solutions, we apply a no-net rotation
on the coordinates of the 212 ICRF defining sources. (At the 2008
IVS GM in St Petersburg, Sarah mentionned a bias showing up in OPAR
nutation. The reason was that, at this time, we applied the NNR over
another set of sources.)
Station coordinates are estimated, with a loose NNR/NNT constraint of
about 1 km, uniformly applied. All EOP and PM/UT1 rates are estimated
too, together with gradients and clocks parameters.
The SINEX file is produced by Solve (release 2008.12.05) and directly
ftp'ed to the data center.
****
4. Estimated parameters:
a. celestial frame: right ascension, declination of the sources that were
already estimated as locals in the opa2009a 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;
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 (segmented).
f. station clocks: quadratic + continuous piece-wise linear with 60-min
interval (segmented).
g. baseline clocks: set in initial analysis - usually used (local).
5. Celestial reference frame:
a. a priori source positions: opa2009a catalogue.
b. source positions adjusted in solution: yes (some).
If yes,
c. definition of orientation: no-net-rotation with respect to the opa2009a
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: opa2009a catalogue.
b. a priori station velocities: opa2009a 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
opa2009a catalogue. All stations except GILCREEK, HRAS_085 and PIETOWN
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: IAU 2000.
b. a priori nutation model: IAU 2000.
c. a priori short-period tidal variations in x, y, UT1: IERS 2003 (Table 5.1
of the IERS Conventions 2003).
d. EOP estimation: X, Y, UT1, Xdot, Ydot, UT1dot, dX, dY each day.
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 dX and dY (and NOT dpsi and deps) wrt IAU 2006 consisting
of the IAU 2000 nutation supplemented by the P03 precession of
Capitaine et al. (2003). Time tag of EOP series is the middle epoch
of the observing session. The IERS 2003 model of high frequency variations
in polar motion and UT1 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).
d. thermal expansion modeling: model of Nothnagel (2008).
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.