> \^[a 'Ojbjb11 &r[[>`8 4T,`q,},R"}}"&T*6Xhq5olq ``$
d``3.5.2 Rapid Service/Prediction Centre
Processing Techniques
The algorithm used by the IERS Rapid Service/Prediction Centre for the determination of the quick-look Earth orientation parameters (EOP) is based on a weighted cubic spline with adjustable smoothing fit to contributed observational data (McCarthy and Luzum, 1991a). Contributed data are corrected for possible systematic differences. Biases and rates are determined with respect to the 97 C04 system of the IERS Earth Orientation Centre (EOC). Statistical weighting used in the spline is proportional to the inverse square of the estimated accuracy of the individual techniques. Minimal smoothing is applied, consistent with the estimated accuracy of the observational data.
Weights in the algorithm may be either a priori values estimated by the standard deviation of the residual of the techniques or values based on the internal precision reported by contributors. Estimated accuracies of data contributed to the IERS Rapid Service/Prediction Centre are given in Table 1. These estimates are based on the residuals of between the series and the combined EOP solution for 2006.
Table 1: Estimated accuracies of the techniques in 2006. Units are milliseconds of arc for x, y, d(, d(, dX, and dY and milliseconds of time for UT1UTC and LOD.
Operationally, the weighted spline uses as input the epoch of observation, the observed value, and the weight of each individual data point. The software computes the spline coefficients for every data point which are then used to interpolate the Earth orientation parameter time series so that x, y, UT1UTC, d(, and d( values are computed at the epoch of zero hours UTC for each day. Since the celestial pole offset software is written in terms of d( and d(, the IAA VLBI dX and dY values are converted to d( and d( for the combination process. The LOD are computed by inputting the UT1UTC data into a cubic spline. The analytical expression for the first derivative of the cubic spline passing through the UT1UTC data is used to estimate the LOD at the epoch of the UT1UTC data.
The only data points that are excluded from the combination process are the points whose errors, as reported by the contributors, are greater than three times their average reported precision or those points that have a residual that is more than four times the associated a priori error estimate. Since all of the observations are reported with the effects of sub-daily variations removed, the input data are not corrected for these effects (see IERS Gazette No. 13, 30 January 1997).
Table 2: Mean and standard deviation of the differences between the Rapid Service/Prediction Centre solutions and IERS Bulletin B and C04 EOP solutions for 2006. Polar motion X and Y values are in milliseconds of arc and UT1UTC values are in units of milliseconds of time.
The uncertainties in the daily values listed in Bulletin A are derived from the quality of the spline fit in the neighborhood of the day in question. Table 2 shows the accuracies of Rapid Service/Prediction Centres combination solution for the running, the weekly, and the daily products compared to the Bulletin B and 97 C04 series maintained by the IERS EOC at the Paris Observatory. The running solution is the combination solution over the past 365-day period. The statistics for the running solution at years end show the agreement between the Bulletin A running combination solution and the Bulletin B/97 C04 series for the entire year. The comparison of the 52 weekly solutions to the Bulletin B/97 C04 series gives the statistics of the residuals computed over the new combination results for the 7-days prior to the solution epoch. The statistics for the daily solution are the differences for the day of the solution epoch. EOP accuracies for the Bulletin A rapid weekly solution for the new combination for the day of the solution run and daily solution at the time of solution epoch are similar and therefore, not included in the table.
Figure 1 shows the residuals between the daily Bulletin A rapid solution and two other series (i.e., Bulletin B and 97 C04) and presents the data used in Table 2 for the determination of the Bulletin A daily solution statistics. This year Bulletin A had only small reductions in the mean difference while he standard deviations were mostly comparable. Overall, the agreement between the Bulletin A solutions and the IERS EOC solutions is quite good.
Fig. 1: Differences between daily Bulletin A rapid solutions at each daily solution epoch for 2006 and the Earth orientation parameters available in Bulletin B and 97 C04 series produced in July 2007.
Prediction Techniques
Polar motion predictions are based on the extrapolation of an annual and semiannual ellipse and a Chandler circle fit to the previous 400 days of observed values of x and y (McCarthy and Luzum, 1991b; Johnson, 2002). The differences between the last observed pole position and rate and those of the curve are computed. These differences are then used to adjust the extrapolated curve by an amount that decreases with the length of the forecast. In February 1998, the near-term polar motion predictions (less than about 30 days) were improved significantly by modifying the transition process from the last observed polar motion result to the long-term predictions. Continuity in the first derivatives was enforced placing great weight on the observed polar motion rate reported by the IGS in their Rapid series. The improvement was most pronounced for the shortest prediction intervals.
The procedure for UT1UTC involves a simple technique of differencing (McCarthy and Luzum, 1991b). All known effects such as leap seconds, solid Earth zonal tides, and seasonal effects are first removed from the observed values of UT1UTC. Then, to determine a prediction of UT1UTC n days into the future, (UT1TAI)n, the smoothed time value from n days in the past, <(UT1RTAI)n> is subtracted from the most recent value, (UT1RTAI)0
(UT1TAI)n =2(UT1RTAI)0 <(UT1RTAI)n>.
The amount of smoothing used in this procedure depends on the length of the forecast. Short-term predictions with small values of n make use of less smoothing than long-term predictions. Once this value is obtained, it is possible to account for known effects in order to obtain the prediction of UT1UTC. This process is repeated for each days prediction.
The UT1UTC prediction out to a few days is strongly influenced by the observed daily Universal Time estimates derived at USNO from the motions of the GPS orbit planes reported by the IGS Rapid service. The IGS estimates for LOD are combined with the GPS-based UT estimates to constrain the UT1 rate of change for the most recent observation.
The UT1UTC prediction also makes use of a UT1-like data product derived from the operational NOAA AAM analysis and forecast data (UTAAM). In September 2006, the U.S. Navy NOGAPS AAM data were combined with the NOAA AAM data. AAM-based predictions are used to determine the UT1 predictions out to a prediction length of 5 days. For longer predictions, the LOD excitations are combined smoothly with the longer-term UT1 predictions described above.
Errors of the estimates are derived from analyses of the past differences between observations and the published predictions. Formulas published in Bulletin A can be used to extend the tabular data. The predictions of d( and d( are based on the IERS Conventions (McCarthy, 1996; McCarthy and Petit, 2004). Table 3 shows the standard deviation of the differences between the Bulletin A daily solution predictions and the 97 C04 solution for 2003. Initial estimates indicated that the UT1UTC prediction performance would be improved by 42% at 10 days into the future by the addition of UTAAM to the combination and prediction process (Johnson et al., 2005). However, comparisons of the UT1UTC prediction performance from 2003 to those estimated in 2001 (before UTAAM was introduced) indicated a better than 50% improvement in prediction error at both 10 day and 20 days into the future.
For 2006, the prediction errors were fairly comparable to those of 2005. Note that the statistics reported in Table 3 have been changed from standard deviation to root mean square to give a better indication of the overall accuracy of the predictions. The only unusual increase in error is for the 90-day UT1-UTC predictions that suffered from some unusually large prediction errors in the beginning of 2006. Excluding these predictions, the errors were more consistent with past prediction errors. The longer-term polar motion predictions also continued to have larger than historically computed errors. This is due to the presence of small sub-monthly retrograde loops in the polar motion. The operational prediction method does not solve for these loops although the least-squares plus autoregressive (LS+AR) polar motion prediction implemented in early 2007 may help in the future.
Table 3: Standard deviation of the differences between the EOP time series predictions produced by the daily Bulletin A rapid solutions and the C04 combination solutions for 2006.
The predictions of celestial pole offsets (both dX/dY and d(/d( representations) are produced through the use of the KSV1996 model. In addition, a bias between the model and the last 20 days worth of celestial pole offset observations is computed. This bias is tapered so that as the prediction length is extended, the bias becomes increasingly small. Since celestial pole offsets
are based solely on VLBI data, if no new VLBI 24-hour session observations are available, a new rapid combination/prediction of these angles is not determined. Therefore, the predictions of celestial pole offset start before the solution epoch and the length of the prediction into the future can and does vary in the daily solution files. The differences between the daily Bulletin A predictions and the 97 C04 for 2006 are given in Table 4.
Table 4: Standard deviation of the differences between the nutation prediction series produced by the daily Bulletin A rapid solutions and the 97 C04 solution for 2006.
Predictions of TTUT1 up to 2016 January 1, are given in Table 5. They are derived using a prediction algorithm similar to that employed in the Bulletin A predictions of UT1UTC. Up to twenty years of past observations of TTUT1 are used. Estimates of the expected one-sigma error for each of the predicted values are also given. These are based on analyses of the past performance of the model with respect to the observations.
Additional information on improvements to IERS Bulletin A and the significance for predictions of GPS orbits for real-time users is available (Luzum et al., 2001; Wooden et al., 2004).
Table 5: Predicted values of TTUT1, 20072016. Note that UT1-TAI can be obtained from this table using the expression UT1TAI = 32.184s (TTUT1).
Centre Activities in 2006
During 2006 a number of changes occurred that affected the performance of IERS Bulletin A. Electronic-VLBI (e-VLBI) became operational for certain aspects of the VLBI Intensive observations. Additional efforts included improving operational software, automating the process for updating data sets used in the combination, updating and monitoring currently used datasets, investigating potential new data sets, and investigating the improvement of polar motion prediction technique. Additional work on better establishing an alternate site to mirror data storage for the combination processing was carried out.
New global solutions were received from GSFC, and USNO VLBI analysis centers. These new solutions were examined and new rates and biases were computed.
Collaborative efforts with colleagues at Poland's Center for Space Research showed the potential for improving our polar motion predictions by 20%30% at 2 to 3 months into the future. Using updated software algorithms, efforts to utilize this new method into the operational software came to fruition with the incorporation of the algorithm in January 2007.
Availability of Rapid Service
The data available from the IERS Rapid Service/ Prediction Centre consist mainly of the data used in the IERS Bulletin A. These data include: x, y, UT1UTC, dX and dY from IAA VLBI; x, y, UT1UTC, d( and d( from GSFC VLBI; x, y, UT1 UTC, d( and d( from USNO VLBI; x, y, UT1 UTC, d( and d( from IVS combination VLBI; UT1 UTC from Saint Petersburg University 1-day Intensives; UT1 UTC from GSFC 1-day Intensives; UT1 UTC from USNO 1-day Intensives; x, y, UT1UTC from CSR LAGEOS 3-day SLR; x, y from Delft University of Technology 1-day SLR; x, y from Institute of Applied Astronomy 1-day SLR; x, y from the Russian Mission Control Centre 1-day SLR; x, y, LOD from the International GPS Service; UT from USNO GPS; UT from NRCanada (EMR) GPS; UT from NCEP AAM; UT from NAVY NOGAPS AAM; x, y, UT1UTC, d( and d( from the IERS Rapid Service/Prediction Centre; x, y, UT1 UTC, d( and d( from the IERS Earth Orientation Centre; and predictions of x, y, UT1 UTC from the IERS Rapid Service/Prediction Centre.
In addition to this published information, other data sets are available. These include: UT0UTC from University of Texas as Austin LLR, UT0UTC from JPL LLR; UT0UTC from CERGA LLR; UT0UTC from JPL VLBI; latitude and UT0UTC from Washington PZTs 1,3,7; latitude and UT0UTC from Richmond PZTs 2,6; x and y from CSR LAGEOS 5-day SLR; x and y from Delft 3- and 5-day SLR; and x, y, UT1UTC, d( and d( from IRIS VLBI.
The data described above are available from the Centre in a number of forms. You may request a weekly machine-readable version of the IERS Bulletin A containing the current ninety day s worth of predictions via electronic mail from
ser7@maia.usno.navy.mil or through http://maia.usno.navy.mil/.
Internet users can also direct an anonymous FTP to
ftp://maia.usno.navy.mil/ser7
where the IERS Bulletin A and more complete databases can be accessed including the daily Bulletin solutions.
Centre Staff
The Rapid Service/Prediction Centre staff consisted of the following members:
William Wooden director
Thomas Johnson program manager, research, and software maintenance
Brian Luzum program manager, research, and software maintenance
Merri Sue Carter assists in daily operations and
support
At the end of October, 2006, Tom Johnson left USNO. Brian Luzum is now the program manager for the EOP Combination and Prediction Program. In the first half of 2007, Nicholas Stamatakos and Gillian Brockett have joined the IERS Rapid Service and Prediction Center.
References
Johnson, T.J, 2002, Rapid Service/Prediction Centre, IERS Annual Report 2001, 4755.
Johnson, T.J, Luzum, B.J., and Ray, J.R., 2005, Improved near-term UT1R predictions using forecasts of atmospheric angular momentum, J. Geodynamics, 39(3), 209.
Luzum, B.J., Ray, J.R., Carter, M.S., and Josties, F.J., 2001, Recent Improvements to IERS Bulletin A Combination and Prediction, GPS Solutions, 4(3), 34.
McCarthy, D.D. and Luzum, B.J., 1991a, Combination of Precise Observations of the Orientation of the Earth, Bulletin Geodesique, 65, 22.
McCarthy, D.D. and Luzum, B.J., 1991b, Prediction of Earth Orientation, Bulletin Geodesique, 65, 18.
McCarthy, D.D. (ed.), 1996, IERS Conventions (1996), IERS Technical Note No. 21, Paris Observatory, France.
McCarthy, D.D. and G. Petit (eds.), 2004, IERS Conventions (2003), IERS Technical Note No. 32, Verlag des Bundesamts fr Kartographie und Geodsie, Frankfurt, Germany.
Wooden, W.H., Johnson, T.J., Carter, M.S., and Myers, A.E., 2004, Near Real-time IERS Products, Proc. Journes Systmes de Rfrence Spatio-Temporels, St. Petersburg, 2225 Sept 2003,160163.
Wooden, W.H., Johnson, T.J., Kammeyer, P.C., Carter, M.S., and Myers, A.E., 2005, Determination and Prediction of UT1 at the IERS Rapid Service/Prediction Center, Proc. Journees Systemes de Reference Spatio-Temporels, Paris, 2022 Sept 2004, 260264.
Brian Luzum, CONTACT _Con005AC60A1 Thomas Johnson, Merri Sue Carter, Nicholas Stamatakos, Gillian Brockett, William Wooden
&<>
&(*&(wjwhQ,J6CJOJQJ^JhhQ,J6CJOJQJ^Jh5hQ,J6CJOJQJ^J jehQ,JCJOJQJ^J jyhQ,JCJOJQJ^JhQ,JCJOJQJ^JhQ,JCJOJQJ^Jh5hQ,J6OJQJ^JhQ,JOJQJ^JhQ,JhQ,J5OJQJ^JhQ,JCJOJQJ^J'&'=>
XY^gdQ,J^
^ ^`
%O&O]#$Y#$)*+ , . 7 8 E F S U Y &&}n}n}n}dhQ,JOJQJ^JhQ,JH*OJQJ^JmHsHhQ,JOJQJ^JmHsHhQ,JH*OJQJ^JhQ,J5OJQJ^JhQ,J6CJOJQJ]^JhQ,JhQ,JCJOJQJ^Jh8hQ,JCJOJQJ^Jh?hQ,JOJQJ^Jh?hQ,JOJQJhQ,JOJQJ^JhhQ,JCJOJQJ^J#wx- . X Y !!##$$))----P02222c4
gdQ,J
&&&&&)----......222233555556<777485878889888F9R9ż駱鏂wwododohuhQ,JOJQJhQ,JOJQJh*[9hQ,JOJQJh*[9hQ,JOJQJ^Jh0ChQ,JOJQJ^JhQ,J5OJQJ^JhQ,J
hQ,JCJhQ,J6OJQJ^Jh8hQ,J^Jh8hQ,JOJQJ^J jehQ,JOJQJ^JhQ,JOJQJ^JhQ,JOJQJ^J jyhQ,JOJQJ^J'c4d4555555588888;:<:Z:[:AA4D6DFFDFEFxFyFFFgdQ,J
R9e9f999::;:<:[:::<<<<<<R<T<V<`<b<d<<<<<<<@>A>@@@@@@@@@@@@DDDDDDFɾ jehQ,JOJQJ^J jyhQ,JOJQJ^JhQ,JOJQJ^JhQ,JCJOJQJ^JhQ,JOJQJ^JhQ,J5OJQJ^JHhYFhQ,JOJQJh*hQ,JOJQJhQ,JOJQJhQ,J6OJQJ^JhuhQ,JOJQJ1FDFEFGGdGeG=H>HIIJITIIII0J>J@JBJJJJSKhKjKKKK
LL$LLLLIM~MMMMMMMJNLN۸۬xnxnxnxhQ,JCJOJQJh#DhQ,JCJOJQJhQ,JCJOJQJ]^JhQ,J5CJOJQJ^JhQ,J6CJOJQJ^JhQ,JCJOJQJ^JhQ,J6OJQJ^JhEhQ,JOJQJ^JhQ,J5OJQJ^JhQ,JOJQJ^JhQ,JCJOJQJ^Jh`%hQ,JOJQJ^JaJ+FGGGGdGeG}GGH4H=H>HIIJIUIVIILJJpKKALLMN^gdQ,J^
PLNNNNNNNNNNNNNNNNNNNNNNNNN'O˿jhQ,JUhQ,JhQ,JCJOJQJ^Jh#DhQ,JCJOJQJ^JhQ,JCJOJQJh#DhQ,JCJOJQJh#DhQ,J6CJOJQJNNN%O&O'O^gdQ,J$&P/R / =!"#$%8@8Normal_HmH sH tH J@J Heading 1$$@&^a$6CJ<@< Heading 2$@&>*CJ>@> Heading 3$@&
5>*CJN@N Heading 4$`@&^``
5>*CJ<@< Heading 5$@&5CJ>@> Heading 6$@&
56CJDA@DDefault Paragraph FontVi@VTable Normal :V44
la(k@(No ListTC@TBody Text Indent@^@`6CJ2B@2 Body TextCJLR@LBody Text Indent 2
^CJLS@"LBody Text Indent 3
^CJ0U@10 Hyperlink>*B*@YB@Document Map-D OJQJ4@R4Header
!4 @b4Footer
!@V@q@FollowedHyperlink>*B*6P@6Body Text 26HHBalloon TextCJOJQJ^JaJ<Z@<
Plain TextOJQJ^J>r!z z z z z6@-8>t&'=>xy/0
)*nop9:;QRij-."#####X%''''k)l)%*&*****=-@---C/D/b/c/K3L3445566K6L6j6k666667787P77788899(9)9~9::C;;<<|=w>x>y>>H000000ʀ00ʀ00ʀ00ʀ0ʀ0ʀ00ʀ00ʀ0x0ʀ0ʀ00ʀ0x00 00ʀ0ʀ0ʀ0x0ʀ0000x0ʀ0 0ʀ0 0ʀ00ʀ0 0ʀ00ʀ0ʀ00ʀ0(0ʀ000000ʀ0000(0ʀ000ʀ0ʀ0ʀ0000ʀ000000ʀ0000ʀ0000000000ʀ0ʀ0ʀ0ʀ0ʀ0ʀ0000000000ʀ0H000ʀ-C/>
@0z00X&R9FLN'O-02457c4FN'O.1368&O/>>>>^8@0(
B
S ?_Hlt60568155>@6>#8>000 032;2?4C4n4r4778888I:P:/;9;;;s<y<~<<<<<<<<"=*=+=3=7=@=A=Q=%>->.>6>D>T>>>>>cdQ
Y
/7""##X%[%&&&&''5555k6p6888'889>>::::::::::::::::::::A2@8888TRR$%(0(12345>P@P
P@PP @P&PP@P.P`@P<P|@P@P@PDP@UnknownUnknownUnknown20050531T17256016YFGTimes New Roman5Symbol3Arial5Tahoma? Courier New"1h)&cC&
a9z
s<4dwF
G2qH(?Xn,Sub-Bureau for Rapid Service and PredictionsLW2Brian Luzum
Oh+'0 ,8
Xdp
|'0Sub-Bureau for Rapid Service and PredictionsLW2NormalBrian Luzum38Microsoft Word 11.3.5@Z@ZD@7@pmi
a9
՜.+,D՜.+,\hp
'USNOzwF-Sub-Bureau for Rapid Service and PredictionsTitleL@'C_AdHocReviewCycleID_EmailSubject
_AuthorEmail_AuthorEmailDisplayName_PreviousAdHocReviewCycleID'nRIERS Annual Report 2005 wooden.william@usno.navy.milWooden, William H.
!"#$%&'()*+,-./0123456789;<=>?@ABCDEFGHIJLMNOPQRTUVWXYZ]Root Entry F_1Table: WordDocument&rSummaryInformation(KDocumentSummaryInformation8SCompObjX FMicrosoft Word DocumentNB6WWord.Document.8