Technical description of solution usn2015a
2015 April
1. Purpose of solution: TRF/CRF for session EOP
2. Analysis center: USN ( United States Naval Observatory )
3. Short narrative description of solution:
Solution usn2015a estimates station position and velocity
parameters to define the TRF/CRF for computing EOP time
series. Source positions are also estimated. The TRF is attached
to ITRF2008 by imposing no-net-rotation and no-net-translation
conditions for the positions of a subset of stations and,
similarly, no-net-rotation and no-net-translation conditions for
the velocities of a subset of stations. The CRF is attached to
the ICRF by a no-net-rotation condition using the 295 ICRF2
defining sources [1].
Parameters are split into three groups:
a) global - parameters estimated over all sessions;
b) local - parameters estimated for each 24-hour session;
c) segmented - parameters estimated over 60 minute time spans.
Positions and velocities of 147 stations were estimated as global
parameters. Positions of 1723 sources were estimated as global
parameters. Positions for the 39 ICRF-2 special handling sources
were estimated for each session independently (treated as arc
parameters). Finally, 140 sources (APPENDIX B) were excluded from
the solution due to bad data or insufficient number of
observations (less than 3).
Mean site gradients were computed from a GSFC Data Assimilation
Office (DAO) model for met data for ICRF2 [1] (gsfc_dao_gmao.mgr).
Atmospheric gradient delay is modeled as
tau = m_grad(el,az) * [GN*cos(az)+GE*sin(az)],
where el and az are the elevation and azimuth of the the
observation and the gradient mapping function is m_grad. The
gradient vector has east and north components GE and GN. Refer to
[2], [3].
3a. Differences with respect to previous solution:
Added an additional 186 databases with 770,519 addtional observations.
CALC 11 was used.
3b. Handling of earthquakes:
TICOCONC was affected by a large nearby earthquake in Chile on Feb. 27,
2010, and experienced an episodic offset of more than 3 meters, mostly in
the westward direction. An episodic break cannot model the motion properly.
Therefore, we have continued to use a user partial program to estimate
offsets at TIGOCONC for each session after the earthquake.
A large earthquake also ocurred of the coast of Japan on March 11, 2011.
The motions of several Japanese stations have been non-linear since then,
and so the same user partial program was also used to estimate the
positions of TIGOCONC, TSUKUB32, KASHIM34, KASHIM11, VERAMZSW, SINTOTU3,
USUAD64, and KOGANEI for each session after the March 11, 2011 earthquake.
Several episodic breaks are solved for. These are listed in section 6h.
4. Estimated parameters:
a. celestial frame: right ascension, declination (global and
local)
b. terrestrial frame: X, Y, Z, Xdot, Ydot, Zdot (global)
c. Earth Orientation: X-pole, Y-pole, UT1-TAI, Xdot, Ydot, UT1dot,
X-nutation, Y-nutation (local parameters).
d. zenith troposphere: continuous piece-wise linear; 20 min
interval; rate constraint generally 50 ps/hr; NMF wet partial
derivative (segmented)
e. troposphere gradient: 6 hour east and north piece-wise
continuous at all stations except a set of 110 stations (APPENDIX
C); offset constraint 0.5 mm, rate constraint 2.0 mm/day
(segmented)
f. station clocks: quadratic + continuous piece-wise linear with 60
min interval; rate constraint generally 5.0E-14 (segmented)
g. baseline clocks: set in initial analysis - usually used (local)
h. other: global antenna axis offsets for 88 stations
(APPENDIX D) (global)
5. Celestial reference frame:
a. a priori source positions: ICRF2
b. source positions adjusted in solution: yes
If yes,
c. definition of orientation: no-net-rotation tie to the ICRF2
using only ICRF2 defining sources
d. source position estimation: 846 global and 852 local
6. Terrestrial reference frame:
a. a priori station positions: ITFRF008
b. a priori station velocities: ITRF2008
c. reference epoch for site positions: 2008.0
d. station positions/velocities adjusted in solution: yes
If yes,
e. definition of origin, orientation, and their time evolution:
no-net-translation and no-net-rotation of position with respect to
ITRF2008 for 33 stations:
ALGOPARK BR-VLBA DSS45 FD-VLBA FORTLEZA HARTRAO HATCREEK HAYSTACK \
HN-VLBA HOBART26 -ASHIM34 KASHIMA KAUAI KOKEE KP-VLBA LA-VLBA \
MATERA -K-VLBA NL-VLBA NOTO NRAO20 NRAO85_3 NYALES20 ONSALA60 \
OV-VLBA OVRO_130 PIETOWN RICHMOND SANTIA12 SC-VLBA SESHAN25 -SUKUB32 \
VNDNBERG WESTFORD WETTZELL SVETLOE
no-net-translation and no-net-rotation of velocity with respect to
ITRF2008 for the same 33 stations:
ALGOPARK BR-VLBA DSS45 FD-VLBA FORTLEZA HARTRAO HATCREEK HAYSTACK \
HN-VLBA HOBART26 -ASHIM34 KASHIMA KAUAI KOKEE KP-VLBA LA-VLBA \
MATERA -K-VLBA NL-VLBA NOTO NRAO20 NRAO85_3 NYALES20 ONSALA60 \
OV-VLBA OVRO_130 PIETOWN RICHMOND SANTIA12 SC-VLBA SESHAN25 -SUKUB32 \
VNDNBERG WESTFORD WETTZELL SVETLOE
f. station parameter estimation: X, Y, Z, Xdot, Ydot, Zdot
globally for all stations, some with constraints
g. stations with constraints:
A priori velocity of U, E, and N components for the stations
listed in APPENDIX E were constrained to the ITRF2008
velocities with reciprocal weights 0.1, 3.0, and 3.0 mm/yr
respectively because the stations have too short history of
observations, in many cases only one occupation.
The velocities of the stations listed in APPENDIX F
were constrained to be the same.
h. stations with discontinuous positions and date of discontinuity:
YAKATAGA 871201 * Earthquake
SOURDOGH 871201 * Earthquake
WHTHORSE 871201 * Earthquake
FORTORDS 891001 * Seismic event
PRESIDIO 891001 * Seismic event
MOJAVE12 920627 * Earthquake
DSS15 920627 * Earthquake
MEDICINA 960601 * Rail reparing
EFLSBERG 961001 * Rail reparing
DSS65 970415 * Rail reparing
MIURA 000901 * Dike intrusion, June-Aug. 2000
TATEYAMA 000901 * Dike intrusion, June-Aug. 2000
GGAO7108 030101 * Station relocation
SINTOTU3 030915 * h/z
** SVETLOE 060701 * Rail repair ??????
MK-VLBA 061015 * Earthquake
ZELENCHK 070701 * Rail repair ??????
AIRA 080614 * M7.2 Iwate Miyagi Nairiku earthquake
CHICHI10 080614 * M7.2 Iwate Miyagi Nairiku earthquake
KASHIM34 080614 * M7.2 Iwate Miyagi Nairiku earthquake
TSUKUB32 080614 * M7.2 Iwate Miyagi Nairiku earthquake
VERAMZSW 080614 * M7.2 Iwate Miyagi Nairiku earthquake
* TIGOCONC 100227 * Big Earthquake
* TSUKUB32 110311 * Big Earthquake in Japan
* KASHIM11 110311 * Big Earthquake in Japan
* KASHIM34 110311 * Big Earthquake in Japan
* VERAMZSW 110311 * Big Earthquake in Japan
VERAISGK 110311 * Big Earthquake in Japan
SINTOTU3 110311 * Big Earthquake in Japan
i. stations with nonlinear velocities:
HRAS_085, GILCREEK, PIETOWN
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) )
Specifically, the old formula 29 in IERS Conventions 1992, page 127-136.
k. permanent tide correction: yes
"Yes" means that both the permanent and the periodic tides have
been included in the model, 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 model: IAU2006/2000A Precession/Nutation,
IERS Conventions 2010 [6] as implementated in Calc 11.
b. A priori short-period tidal variations in X, Y, UT1 due to short
period tidal and nutation effects were applied. These were computed by
Calc 11, as recommended in the IERS 2010 Conventions [6], chapter 5,
p. 50-51.
c. EOP estimation: Two tables are given:
usn2015a.eoxy: X, Y, UT1, Xdot, Ydot, UT1dot, X-nutation, Y-nutation,
each session. Using a priori error of 45 mas for pole and 3 ms for UT1,
45 mas/day and 3 ms/day for pole rate and UT1 rate to allow estimation
for one-baseline sessions; X-nutation and Y-nutation are relative to
IAU2000A/2006 Nutation/Precession models. Time tag of the EOP series
is the middle epoch of the observing session.
usn2015a.eops: X, Y, UT1, Xdot, Ydot, UT1dot, Deps, Dpsi, each session.
Deps and Dpsi are relative to the IAU 1976 precession and IAU 1980
nutation models.
{Internally, Calc/Solve estimated offsets to the X and Y
precession/nutation quantities, relative to the IAU2000A/2006
nutation/precession models, using the IERS 2010 Conventions [6]
implementation. These were converted to classical Dpsi and Deps nutation
offsets relative to the IAU 2000A nutation model. These were then
converted to the IAU 1976/1980 precession/nutation (Wahr) model by
adding the following terms:
Deps: -25.24*Cent - 6.8192 (m-arc-sec), and
Dpsi: -299.65*Cent - 41.775 (m-arc-sec), where Cent is the epoch
in fractional centuries since 2000.0 (Julian date 2451545.0).
This conversion is not quite correct though. There are some long
term drifts that are not accounted for. See reference [7].}
High frequency variations in polar motion and UT1, as computed by
Calc 11, were added to the a priori EOP during the Solve/Globl
solution. 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 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 DAO weather model.
b. Solid Earth tide: IERS Conventions 2010 [6], 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 by Leonid Petrov. Harmonic model 2007b_oclo.hps
d. atmosphere loading: 3D displacements computed by convolving global
surface pressure field on 2.5x2.5 degrees grid with 6 hour temporal
resolution using the NCEP Reanalysis model by Leonid Petrov.
f. Antenna thermal deformation: Antenna heights were adjusted, based
on the average daily temperatures, using the IVS antenna thermal
deformation model of Nothnagel 2008 [7].
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 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. The station-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 estimated parameters.
13. Software: Calc 11, SOLVE revision date 2014.02.21.
14. Other information:
Mean pole coordinates used for computation of pole tide
deformation were set to 0.0, 0.0
References:
1. 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
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. Takashima, K., et al., "Status and Results of GSI Domestic
VLBI Network", Bulletin of the Geographical survey Institute,
Vol. 46, March 2000, p. 1-9.
5. Petrov, L. and J.-P. Boy, "Study of the atmospheric pressure loading
signal in VLBI observations", J. Geophys. Res., 10.1029/2003JB002500,
vol. 109, No. B03405, 2004.
6. Petit, Gerard and Luzum, Brian, 'IERS Conventions (2010), IERS Technical
Note 36, 2010.
7. 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.
APPENDIX A.
-----------
APPENDIX B.
-----------
*
* 6 gravitational lenses with equal components
* (really just two sources with three names each)
*
0218+357 0218+35A 0218+35B 1830-211 1830-21A 1830-21B \
*
* 3 sources with really bad data (not sure why?)
*
0753-425 0833-450 2224-308 \
*
* 123 sources with less than 3 (0,1,2) observations in crf2015a_00
*
0000-160 0008-300 UG00192 4C+00.02 OB338 0036-216 0040+517 0045-255 \
NGC0253 0106+130 0127+145 0131-450 0131-367 0201-440 M77 0250+178 \
0253-218 NGC1167 UXARI 0328-272 0333-276 0340+044 0428+205 0434+299 \
HD32918 0515-674 0512+249 0514+109 0521+793 0535+677 NGC2110 0611+139 \
MRK003 NGC2146 0629+104 0633-263 0731-465 0802-276 0809+483 0817+472 \
0830+115 0833+441 4C+32.26 0844+387 0855+143 0858-279 0902+343 0937-282 \
0941-080 M82 0951+699 NGC3079 1017+109 1020-103 1020+191 1026-179 \
1030-590 1039-474 1045+155 1046-026 1046+588 NGC3690 M106 1225-023 \
1224-854 1239-044 1243-412 1245-197 1305-241 1313+200 NGC5077 1320-407 \
1331+512 1421-490 1422+268 TON202 1438-390 1439+327 HD132742 1511+238 \
1528-274 1528-509 SIGCRB 1622+238 1623-243 3C343 3C343.1 NGC6240 \
1707-376 1709-342 1710-269 1713+218 1714-336 1722+401 1729-373 1741-312 \
SGR-A 1742-283 1744-299 1752-217 1801+010 1805-214 1813-241 1817+512 \
1827-360 1848+333 NAQL93 1920+154 1921+14B 1934+207 2027+383 NGC6946 \
2101-715 2134-470 2209+184 2212-299 2226-411 2227-210 2310-417 2314+038 \
2317-372 2318-195 2332-531 \
*
* 8 radio stars
*
HD32918 HD132742 SIGCRB HR1099 UXARI LSI61303 LANA SN1993J
*
APPENDIX C.
-----------
Stations for which troposphere gradients were not estimated:
None.
APPENDIX D.
-----------
Stations for which axis offsets were estimated as global parameters:
AXIS NO EXCEPT \
AIRA ALGOPARK BR-VLBA CHICHI10 DSS15 \
DSS45 DSS65 FD-VLBA FORTLEZA GBT-VLBA \
GGAO7108 GIFU11 GILCREEK GOLDVENU HARTRAO \
HATCREEK HAYSTACK HN-VLBA HRAS_085 KASHIM11 \
KASHIM34 KASHIMA KAUAI KOGANEI KOKEE \
KP-VLBA LA-VLBA MARPOINT MATERA MIAMI20 \
MIURA MIZNAO10 MK-VLBA MOJAVE12 NL-VLBA \
NOTO NRAO_140 NRAO20 NRAO85_1 NRAO85_3 \
OHIGGINS OV-VLBA OVRO_130 PIETOWN RICHMOND \
SANTIA12 SC-VLBA SESHAN25 SINTOTU3 SVETLOE \
TATEYAMA TIGOCONC TIGOWTZL TOMAKO11 TSUKUB32 \
URUMQI VNDNBERG WESTFORD YEBES YLOW7296 \
ZELENCHK BADARY CRIMEA DSS65A EFLSBERG \
HOBART26 MEDICINA NYALES20 ONSALA60 PARKES \
YEBES40M WETTZELL KWAJAL26 METSAHOV SEST \
SYOWA TIDBIN64 DSS13 MARCUS TSUKUBA \
VERAISGK VERAMZSW HOBART12 WARK12M YARRA12M \
KATH12M KUNMING UCHINOUR \
**NB**
HART15M
APPENDIX E.
-----------
Stations with constraints on velocity:
VELOCITIES XYZ NO UEN NO SIGMA 0.1 3.0 3.0 EXCEPT \
*
AUSTINTX AZORES BADARY BERMUDA BLOOMIND \
BREST CARNUSTY CARROLGA CHLBOLTN CTVASBAY \
CTVASTJ DAITO GRASSE HOFN HOHENFRG \
HOHNBERG KAINAN KANOZAN KARLBURG KIRSBERG \
LEONRDOK MCD_7850 METSHOVI MILESMON NOBEY_6M \
OCOTILLO SAGARA SEST SUWON TIDBIN64 \
TITIJIMA TOMAKO11 TOULOUSE USSURISK VERAIRIK \
VERAISGK VERAOGSW USUDA64 VICTORIA \
**NB**
* KUNMING UCHINOUR \
KASHIM11 TIANMA65 SEJONG RAEGYEB \
YARRA12M KATH12M WARK12M
APPENDIX F.
-----------
Velocities of these sets of stations were constrained to be the same:
VELOCITY_TIE \
DSS15 DSS13 GOLDMARS GOLDVENU \
AND DSS45 TIDBIN64 \
AND DSS65 DSS65A \
AND ROBLED32 MADRID64 \
AND FORTORDS FORT_ORD \
AND GIFU11 GIFU3 \
AND GGAO7108 GORF7102 \
AND HARTRAO HART15M \
AND HOBART26 HOBART12 \
AND KASHIM34 KASHIM11 KASHIMA \
AND KOGANEI KOGANEI3 \
AND METSAHOV METSHOVI \
AND MIZNAO10 VERAMZSW MIZUSGSI \
AND MOJAVE12 MOJ_7288 \
AND NRAO20 NRAO_140 NRAO85_1 NRAO85_3 GBT-VLBA \
AND MV2ONSLA ONSALA85 \
AND OVRO_130 OVR_7853 \
AND RICHMOND MIAMI20 \
AND SESHAN25 SHANGHAI \
AND SINTOTU SINTOTU3 \
AND TSUKU3 TSUKUBA TSUKUB32 \
AND WETTZELL TIGOWTZL \
AND YEBES YEBES40M \
AND YLOW7296 YELLOWKN