1/16 35th igs governing board meeting december 13, 2009 – san francisco transition of the igs...

35th IGS Governing Board MeetingDecember 13, 2009 – San Francisco

1/16

TRANSITION OF THE IGSREFERENCE FRAME COORDINATION

FROM NRCAN TO IGN-

STATUS AND PROSPECTS


2/16

Tasks of the RF Coordinator

• Operational tasks:– Weekly combination of the AC SINEX

(Stations coordinates, ERP, apparent geocenter)– Accumulation of the weekly combined solutions

(Stations coordinates and velocities)– Detection of stations discontinuities

• Occasional tasks:– Provide official IGS submissions to the ITRF– Issue official IGS RF realizations– Provide satellite antenna offsets– Combine and accumulate AC reprocessed solutions

operational

automation to be done


3/16

Weekly combination: NRCAN strategy

• Preprocessing of AC solutions:– Unconstraining– Augmentation with explicit geocenter parameters– Alignment to IGS05– Detection and removal of outliers

• Iterative combinations:(weighted stacking of normal equations)– AC variance factors = (WRMS of the “AC vs. cumulative” comparison)²– No transformation parameters estimated– No detection of outliers– Until: convergence of the variance factors


4/16

Weekly combination: IGN strategy

• Preprocessing of AC solutions:– Unconstraining– Detection and removal of outliers

• Iterative combinations:– AC variance factors: degree of freedom estimator– “AC ↔ combined” transformation parameters estimated– Detection of outliers– Until: No outliers + 1 iteration

• Last combination:– Augmentation of the AC solutions with explicit geocenter parameters– Transformation parameters fixed– The combined solution is finally rescaled and aligned to IGS05.


5/16

AC variance factors

• NRCAN: : residuals of the “AC ↔ cumulative” comp. : number of common stations : normal matrix of AC solution

• IGN:

: redundancy factor : AC residuals from the combination : number of observations from this AC : design matrix for this AC : combined covariance matrix

stas

ssTs

s nvNv

32

s

ssTs

s fvNv

2

sTss

obsss NQAAtrnf

svstasn

sN

svobssnsAQ

Example: VF comparison for week 1558

AC NRCAN √VF

IGN √VF x2.941(*)

Ratio

COD 25.443 21.058 1.208

EMR 6.583 6.667 0.987

ESA 5.619 9.129 0.616

GFZ 16.509 11.614 1.422

JPL 10.733 17.408 0.617

MIT 2.616 1.997 1.310

NGS 39.219 49.294 0.796

SIO 2.388 2.282 1.046

(*) The IGN combined solution is finally rescaled. For week 1558, SF = (2.941) ²


6/16

Transformation parameters

• NRCAN:– No transformation parameters are estimated since all AC solutions

are aligned to IGS05.(⇒ They are supposed to be in the same frame.)

– But the set of reference stations is different for each AC…

• IGN:– Each AC solution is in its own frame.– Alignment to IGS05 is made at the level of the combined solution.


7/16

IGN vs. NRCAN: Stations coordinates

• Agreement at:– 0.3-0.4 mm in N, E– ~ 1 mm in Up

• Accidents:– Week 1505: YKRO– Week 1514: CONT– Week 1519: STR1– Week 1531: SAMP– Week 1552: BAKO– Week 1555: KATZ


8/16

IGN vs. NRCAN: Helmert parameters• All below 1 mm

• And there is an explanation!

• Sets of reference stations are not the same because of:

– Solution numbers– Outliers

• Green lines:TIGN / IGS05-NRCAN

- TNRCAN / IGS05-IGN


9/16

IGN vs. NRCAN: ERP

dXPO(µas)

dYPO(µas)

dXPOR(µas/d)

dYPOR(µas/d)

dLOD(µs)

Mean 2.9 0.9 9.1 15.8 -1.3

Abs.max 36.3 28.7 236.7 338.1 8.8

Std 9.0 9.9 55.5 79.8 2.6

• Differences are globallybelow the level of uncertainty

• XPOR, YPOR: SIO estimates are included in IGN solutions

• XPOR, YPOR, LOD: part of the differences can be explained by the different AC weightings


10/16

IGN vs. NRCAN: Geocenter

dXGC(mm)

dYGC(mm)

dZGC(mm)

Mean 0.7 -0.5 0.1

Abs.max 3.4 2.8 5.6

Std 1.2 1.0 2.6

• Differences sometimes higher than the level of uncertainty(1.5 mm, 1.3 mm, 3.0 mm)

• GFZ geocenter is included in the IGN solutions.

• Influence of AC weightings


11/16

Metadata

• NRCAN:– From igs.snx for IGS stations– From AC solutions for other stations

• IGN:– Sites logs are gathered from several sources.

(IGS, EPN, CORS, UNAVCO…)– Metadata are extracted from the sites logs.– Week 1558: Sites logs were available for 396 stations over 408.


12/16

Cumulative solution

• NRCAN strategy was reproduced:– Addition of a loosely constrained weekly solution

to a loosely constrained cumulative solution(No transformation parameters are estimated.)

– Rejection of stations without domes or with poor velocity estimates– Addition of internal constraints

• Start point is IGS09P45_all.snx.(cumulative solution for week 1557)


13/16

IGN09P46.snx vs. IGS09P46.snx

TX(mm)

TY(mm)

TZ(mm)

SCL(ppb)

RX(mas)

RY(mas)

RZ(mas)

0.2 0.0 -0.1 -0.02 0.001 -0.005 -0.002dTX / dt(mm/y)

dTY / dt(mm/y)

dTZ / dt(mm/y)

dSCL / dt(ppb/y)

dRX / dt(mas/y)

dRY / dt(mas/y)

dRZ / dt(mas/y)

-0.0 -0.1 0.0 0.00 -0.001 0.001 0.002

Helmert parameters:

WRMS :

Differences are all (far) below the uncertainties.

N(mm)

E(mm)

U(mm)

VN(mm/y)

VE(mm/y)

VU(mm/y)

0.10 0.12 0.14 0.04 0.06 0.04


14/16

Discontinuities

• Currently, there is no discontinuity catalogue compatible with the IGS cumulative solution.(ALL.snx was modified according to the repro1 results.)

• This catalogue was built from ALL.snx and older versions.

• A SOLUTION/DISCONTINUITY block will be included in each IGN cumulative solution.


15/16

Plans

• January 2010: Test of orbits/clocks combination using IGN products

• February 2010: IGN becomes the operational RF coordinator.

• Early 2010: – IGS08 (subset of ITRF2008?)– Backsolve repro1 to derive satellite offsets consistent with IGS08– IGN combination of repro1?

• Later: – Replacement of the operational cumulative solution by a solution based on

repro1 (NRCAN? or IGN?)– Website devoted to IGS RF


16/16

THANKS FOR YOUR ATTENTION


17/16

IGN vs. NRCAN: AC geocenters


18/16

IGN vs. NRCAN: AC geocenters STD


19/16

IGS05


20/16

Reference stations left on week 1558

1/16 35th igs governing board meeting december 13, 2009 – san francisco transition of the igs...

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