Technical description of session EOP solution usn2017b.eopi
2017 September
1. Purpose of solution: Determination of UT1 from short, ~1.0 hour,
IVS Intensive VLBI sessions.
2. Analysis center: USN (U.S. Naval Observatory).
3. Short narrative description of solution:
Solution usn2017b is for the estimation of UT1 from the 1-hour IVS
Intensive sessions. Most sessions consist of ~12-30 observations on
one baseline.
4. Differences with respect to previous solution:
a. The site and velocity mod files are from the usn2017b solution
and are based on ITRF2014 [1].
b. The source position mod file is also from the usn2017b solution
and is based on ICRF2 [2].
5. Estimated parameters:
a. UT1 angle.
b. Atmosphere path delay offset at each station.
c. Coefficients of the second order polynomial of clock functions.
6. Celestial reference frame:
a. A priori source positions: usn2017b_for_int.src.
This catalog was created in the usn2017b solution and is based on
ICRF2 [2].
b. Source positions adjusted in solution: No
7 - Terrestrial reference frame:
a. A priori station positions: usn2017b_for_int.sit.
This catalog was created in the usn2017b solution and is based on
ITRF2014 [1].
b. A priori station velocities: usn2017b_for_int.vel.
This catalog was created in the usn2017b solution.
c. Reference epoch: 2014.0.
d. Station positions/velocities adjusted in solution: No.
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
8. Earth orientation:
a. A priori Precession-Nutation: IAU2006/2000A Precession/Nutation, IERS
Conventions 2010 [3] implementation in Calc 11.
b. A priori short-period tidal variations in X-pole, Y-pole, and UT1
due to tidal and libration effects were computed in Calc 11,
IERS Conventions 2010 [3] implementation.
c. EOP estimation: UT1 (without any constraints).
d. A priori UT1 and polar motion: last_usno_finals.erp
Earth orientation parameters series from finals USNO series. Original
data were taken from ftp://maia.usno.navy.mil/ser7/finals.all and
replaced with ftp://maia.usno.navy.mil/ser7/finals.daily and then
linear regerssion was subtracted from those series in order to
eliminate shift and drift with respect to series.
9. 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 2010 [3], chapter 7, 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.
d. Pole tide: Mean pole coordinates used for computation of pole tide
deformation were set to the IERS 2010 Conventions [3] recommended
values (Chapter 7).
e. Mean site gradients were computed from the GSFC Data Assimilation
Office (DAO) model for met data for ICRF2 [2] (icrf2-gd2.mgr). 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 [4], [5].
f. Antenna thermal deformation: Antenna heights were adjusted, based
on the average daily temperatures, using the IVS antenna thermal
deformation model of Nothnagel 2008 [6].
10. Data type: Group delays.
11. Data editing: Manual, elevation cutoff 5 degrees.
12. 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.
13. 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.
14. Software: CALC 11, SOLVE revision date 2014.02.21.
References:
1. ITRF2014a
2. IERS Technical Note 35, 'The Second Realization of the International
Celestial Reference Frame by Very Long Baseline Interferometry';
A.L. Fey, D. Gordon, C.S. Jacobs, editors; 2009.
http://www.iers.org/IERS/EN/Publications/TechnicalNotes/tn35.html
3. Petit, Gerard and Luzum, Brian, 'IERS Conventions (2010), IERS Technical
Note 36, 2010.
4. MacMillan, D.S. and C. Ma, "Atmospheric Gradients from Very Long Baseline
Interferometry Observations", Geophys. Res. Lett., 22, 1041-1044, 1995.
5. MacMillan, D.S. and C. Ma, "Atmospheric Gradients and the VLBI Terrestrial
and Celestial Reference Frames", Geophys. Res. Lett., 24, 453-456, 1997.
6. 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.