Technical description of session EOP solution usn2010a.eopi
2010.01.29
1. Purpose of solution: Determination of UT1 from short, ~1.0 hour,
NEOS Intensive VLBI sessions.
2. Analysis center: USN (U.S. Naval Observatory).
3. Short narrative description of solution:
Solution gsfint24 is for the estimation of UT1 from the 1-hour NEOS and
K4 Intensive sessions. Most sessions consist of ~12-30 observations on
one baseline. The solution includes all usable Intensive sessions from
2000.JUL06 through 2010.JAN26. The primary single-baseline sessions have
been: WESTFORD/WETTZELL, NRAO85-3/WETTZELL, NRAO20/WETTZELL,
KOKEE/WETTZELL, and TSUKUB32/WETTZELL. Beginning in 2007, some sessions
periodically contain 3 stations, primarily NYALES20/TSUKUB32/WETTZELL and
KOKEE/SVETLOE/WETTZELL. Each session was processed independently. There
are a total of 3043 sessions.
3a. Differences with respect to previous (usn2008a) solution:
Axis offsets file was updated from measured_20050110.axo to 2007c.axo.
Mean Gradient file changed from gsfc_dao_9095.mgr to icrf2-gd2.mgr.
4. Estimated parameters:
-- UT1 angle.
-- Atmosphere path delay offset at each station.
-- Coefficients of the second order polynomials of clock function.
5. Celestial reference frame:
a. A priori source positions: usno_2010a_for_int.src.
This catalog was created in the usn2010a solution.
b. Source positions adjusted in solution: No
6 - Terrestrial reference frame:
a. A priori station positions: usno_2010a_for_int.sit.
This catalog was created in the usn2010a solution.
b. A priori station velocities: usno_2010a_for_int.vel.
This catalog was created in the usn2010a solution.
c. Reference epoch: 1997.0.
d. Station positions/velocities adjusted in solution: No.
j. Relativity scale: The terrestrial reference frame is defined using
the following metric tensor:
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) )
Specifically the old formula 29 in IERS Conventions 1992, page 127-136
was used, although it is known to have a deficiency.
THIS METRIC TENSOR DOES NOT CONFORM TO IAU 2000 RESOLUTIONS!
k. Permanent tide correction: Yes.
"Yes" means that both the permanent and the periodic tides have
been modeled, so that the output station position is for after the
removal of both the permanent and the periodic tidal effect.
The model used includes tide displacements for zero frequency with
Love numbers h2(freq=0) = 0.6078, l2(freq=0) = 0.0847
7. Earth orientation:
a. A priori Precession-Nutation: IAU2000A Precession-Nutation, IERS
Conventions 2003 [1] implementation, modified to use the IAU2006
Precession model.
b. A priori short-period tidal variations in X, Y, UT1 were computed
in Calc 10.0, IERS Conventions 2003 [1] implementation.
c. EOP estimation: UT1 (without any constraints).
d. A priori UT1 and polar motion: usno_finals.data
http://gemini.gsfc.nasa.gov/solve_save/usno_finals.erp obtained
by adding small linear shift and drift to the left columns of
original finals.data file generated by USNO,
ftp://maia.usno.navy.mil/ser7/finals.data in such a manner that there
is no shift or secular drift with respect to the usn2010a.eops series
over the period 1997.0 - present.
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 2003 [4], chapter 7, p. 9, steps
1 and 2, including tides of the 2-nd and 3-rd order.
c. Ocean loading: 3D ocean loading displacements computed by SPOTL
software. The model of displacements caused by ocean loading contains
18 constituents. The following ocean tide models were used:
Harmonic Frequency rad/sec Model
k2-a 1.324501D+00 1.458530140651D-04 GOT00 admittance
k2 3.506941D+00 1.458423171028D-04 GOT00
s2 6.283185D+00 1.454441043329D-04 GOT00
s2-a 4.312500D-02 1.452450074576D-04 GOT00 admittance
m2 2.169437D+00 1.405189027044D-04 GOT00
m2-a 1.210284D+00 1.405082057420D-04 GOT00 admittance
n2 6.097067D+00 1.378796996516D-04 GOT00
k1-a 1.141827D+00 7.293185551375D-05 GOT00 admittance
k1 3.324267D+00 7.292115855138D-05 GOT00
k1-b 2.365113D+00 7.291046158901D-05 GOT00 admittance
p1 2.958919D+00 7.252294578148D-05 GOT00
p1-a 3.002044D+00 7.232384890619D-05 GOT00 admittance
o1 5.128356D+00 6.759774415297D-05 GOT00
o1-a 1.027610D+00 6.758704719061D-05 GOT00 admittance
q1 2.772800D+00 6.495854110023D-05 GOT00
q1-a 4.955240D+00 6.494784413786D-05 GOT00 admittance
mtm-a 4.652212D+00 7.973314413516D-06 NAO99.l admittance
mtm 5.514660D-01 7.962617451151D-06 NAO99.l
mf-a 2.296657D+00 5.334111360775D-06 NAO99.l admittance
mf 4.479096D+00 5.323414398410D-06 NAO99.l
msf 9.721550D-01 4.925201628510D-06 NAO99.l
mm 5.497148D+00 2.639203052741D-06 NAO99.l
msm 4.899785D+00 2.285998575769D-06 NAO99.l
ssa 3.653480D-01 3.982127698995D-07 NAO99.l
paw 5.012885D+00 1.991063797295D-07 equilibrium
sa 3.098467D+00 1.990968752920D-07 NAO99.l
pcw 2.003605D+00 1.671771314171D-07 equilibrium
18.6 4.100746D+00 1.069696236521D-08 equilibrium
d. Pole tide: Mean pole coordinates used for computation of pole tide
deformation were set to the IERS 2003 Conventions [4] recommended
values (Chapter 7, p. 15).
e. Mean site gradients were computed from the GSFC Data Assimilation
Office (DAO) model for met data from 1990-95. The atmospheric gradient
delay is modeled as:
tau = m_grad(el) * [GN*cos(az)+GE*sin(az)],
where el and az are the elevation and azimuth of the observation and
the gradient mapping function is m_grad. The gradient vector has East
and North components GE and GN. Refer to [1], [2].
f. Antenna thermal deformation: Antenna heights were adjusted, based
on the average daily temperatures, using the IVS antennae thermal
deformation model of Nothnagel 2008 [5].
9. Data type: Group delays.
10. Data editing: Manual, elevation cutoff 6 degrees.
11. Data weighting. Weights are defined as follows: 1/sqrt ( f**2 + a**2 )
where "f" is 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. Session-dependent parameter "a" was
computed for each session by an iterative procedure such that the ratio
of the sum of squares of weighted residuals to the estimate of their
mathematical expectation is about unity.
12. Standard errors reported: All errors 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.
References:
1. McCarthy, D.D., Petit, G., IERS Technical Note 32, IERS Conventions
(2003), 2003.
2. MacMillan, D.S. and C. Ma, "Atmospheric Gradients from Very Long Baseline
Interferometry Observations", Geophys. Res. Lett., 22, 1041-1044, 1995.
3. MacMillan, D.S. and C. Ma, "Atmospheric Gradients and the VLBI Terrestrial
and Celestial Reference Frames", Geophys. Res. Lett., 24, 453-456, 1997.
4. Nothnagel, A., "Short Note: Conventions on Thermal Expansion Modelling of
Radio Telescopes for Geodetic and Astrometric VLBI," Journal of Geodesy,
DOI: 10.1007/s00190-008-0284-z, 2008.