08 Schuh - Determination of UT1 by VLBI

BALGEOS II W k hBALGEOS II Workshopp

Skopje, Sept. 2009 S opje, Sep 009

Determination of UT1 by VLBIDetermination of UT1 by VLBIDetermination of UT1 by VLBIDetermination of UT1 by VLBIyy

H S h hH. SchuhH. SchuhJ. BöhmJ. Böhm S BöhmS. Böhm A NothnagelA. Nothnagel

O tliO tliOutlineOutlineOutlineOutlineIntroductionIntroduction

dUT1 - IVS analysisdUT1 IVS analysis

24h sessions, 1h Intensive sessions24h sessions, 1h Intensive sessions

I t f i t ti dUT1 f INTImpact of errors in nutation on dUT1 from INTImpact of errors in nutation on dUT1 from INT

I t f i i di t dUT1 f INTImpact of a priori gradients on dUT1 from INTp p g

Comparison of geodetic and atmosphericComparison of geodetic and atmospheric p g p

excitation with sub-diurnal periodsexcitation with sub diurnal periods

Tid l ff t dUT1 t t t d hTidal effects on dUT1: not treated hereTidal effects on dUT1: not treated here

S i 2 U i l Ti D t i ti f UT1 b VLBISession 2 – Universal Time Determination of UT1 by VLBI

G l t t t d id tiG l t t t d id tiGeneral statements and considerationsGeneral statements and considerations

VLBI is the only space geodetic technique whichVLBI is the only space geodetic technique which allows mid- and long-term determination of UT1allows mid- and long-term determination of UT1 (different to all satellite techniques)(different to all satellite techniques)

S iti it f VLBI b li / t k t UT1 iSensitivity of VLBI baseline / network to UT1 is yti l t E t W t t tproportional to East-West extentp p

VLBI accuracy of UT1 today:VLBI accuracy of UT1 today:

6 7 s from 24h- 6-7 s from 24h

10 15 s from 1h- 10-15 s from 1h

S i 2 U i l Ti I t d tiSession 2 – Universal Time Introduction

R l it i f UT1 (+ ll th EOP)R l it i f UT1 (+ ll th EOP)Regular monitoring of UT1 (+all other EOP) Regular monitoring of UT1 (+all other EOP) g g ( )g g ( )in 24h sessions (R1 R4)in 24h sessions (R1 R4)in 24h sessions (R1, R4)in 24h sessions (R1, R4)

examplesp

ffor

R1R1

andand

R4R4

networknetwork

configurationsconfigurations

24h i SETUP24h sessions SETUP

dUT1dUT1 IVSIVSdUT1dUT1 -- IVSIVSdUT1 dUT1 IVSIVS

Residuals of UT1-TAI results of IVS Analysis Centers w.r.t. IVS yCombined Solution WRMS = 2 4 s (Böckmann et al 2009)Combined Solution, WRMS = 2.4 s (Böckmann et al., 2009)

dUT1 CONSISTENCYdUT1 CONSISTENCY

VLBI I t i i (1h)VLBI I t i i (1h)VLBI Intensive sessions (1h)VLBI Intensive sessions (1h)VLBI Intensive sessions (1h) VLBI Intensive sessions (1h) i d t di d t dcarried out every daycarried out every dayy yy y

IVS Intensive Networks INT1INT1

K k P k- Mo-Fr ~18:30

Kokee Park

K k W tt llTsukuba - Kokee - WettzellTsukuba

INT2INT2Sa Su 7:30- Sa-Su ~7:30

- Tsukuba - Wettzell- Tsukuba - Wettzell

Ny Alesund INT3y INT3- Mo ~6:00Mo 6:00

Wettzell - Tsukuba - Wettzell -Wettzell

Ny AlesundNy Alesund

- Operational since– INT1 – INT2 – INT3

Operational since A t 2007INT1 INT2 INT3 August 2007

I t i S i SETUPIntensive Sessions SETUP

UltUlt id dUT1id dUT1 VLBI i (1h)VLBI i (1h)UltraUltra--rapid dUT1 erapid dUT1 e--VLBI sessions (1h)VLBI sessions (1h)UltraUltra rapid dUT1 erapid dUT1 e VLBI sessions (1h)VLBI sessions (1h)

e-INT: near real time dUT1e INT: near real time dUT1- Two almost parallel baselines: p

O l T k bOnsala - Tsukuba

Metsähovi KashimaMetsähovi - Kashima

- Real time data transfer quasi realReal time data transfer, quasi real ti l ti

4time correlation

)

4 IERS EOP C04 data - Correlation by software

sec) Prediction of dUT1 (Bulletin-A) April 19

e-VLBI measurement- Correlation by software

ms e-VLBI measurement

nd

(

Results from Kashima - Onsala

ren Results from Kashima - Onsala

ar

t

pilot experiment

ne

a pilot experiment

–li - Time delay of < 30min!!

T1 y

dU

T

April | May 2007

d

-10 April | May 200710

SETUPI t i S i SETUPIntensive Sessions

I t f i t ti dUT1I t f i t ti dUT1Impact of errors in nutation on dUT1Impact of errors in nutation on dUT1Impact of errors in nutation on dUT1 Impact of errors in nutation on dUT1 f I t i if I t i ifrom Intensive sessionsfrom Intensive sessionsfrom Intensive sessionsfrom Intensive sessions

Th dj t t d f I t i iThe adjustment procedure of Intensive sessions e adjust e t p ocedu e o te s e sess o si th t l ti d t ti llrequires that polar motion and nutation, as wellrequires that polar motion and nutation, as well

h i l d h l i l fas the terrestrial and the celestial referenceas the terrestrial and the celestial reference frame be introduced as known quantities.frame be introduced as known quantities.

Due to the derivation of UT1 from GreenwichDue to the derivation of UT1 from Greenwich mean sidereal time (GMST) a change ormean sidereal time (GMST) a change or ( ) ginsufficiency of the used nutation model directlyinsufficiency of the used nutation model directly y yinfl ences the definition of UT1influences the definition of UT1.

ΔGASTGMST 0cosεψ ⋅Δ−= GASTGMST 0cosεψΔGASTGMST

I t i S i IMPACT f i NUTATIONIntensive Sessions IMPACT of errors in NUTATION

Diff i dUT1 i d d b f d 1Diff i dUT1 i d d b f d 1Differences in dUT1 induced by an enforced 1 Differences in dUT1 induced by an enforced 1 masmaserror in the nutation in longitudeerror in the nutation in longitudeerror in the nutation in longitudeerror in the nutation in longitude

Solid lines from theoretical considerationsSolid lines from theoretical considerations (Nothnagel and Schnell, 2008)( g )


Diff i dUT1 i d d b f d 1Diff i dUT1 i d d b f d 1Differences in dUT1 induced by an enforced 1 Differences in dUT1 induced by an enforced 1 masmaserror in the nutation in obliquityerror in the nutation in obliquityerror in the nutation in obliquityerror in the nutation in obliquity

Solid lines from theoretical considerationsSolid lines from theoretical considerations (Nothnagel and Schnell, 2008)( g )


C l i i t f t tiC l i i t f t tiConclusion: impact of nutation errorsConclusion: impact of nutation errorsConclusion: impact of nutation errorsConclusion: impact of nutation errors

UT1 determinations from VLBI 1h IntensiveUT1 determinations from VLBI 1h Intensive sessions need better nutation models andsessions need better nutation models and observationsobservations.

Th IAU2000A t ti d l ithThe IAU2000A nutation model, with an accuracy , yf 0 2 ld till i d tof ~0.2mas would still induce an error component p

i th UT1 lt f b t 7 f d 3 fin the UT1 results of about 7 s for and 3 s forin the UT1 results of about 7 s for and 3 s for

In order to reduce the UT1 uncertainty to aboutIn order to reduce the UT1 uncertainty to about 1 s the introduced a priori nutation should be1 s the introduced a priori nutation should be accurate to ~0 03masaccurate to ~0.03mas

IMPACT f i NUTATIONI t i S i IMPACT of errors in NUTATIONIntensive Sessions

I t f i i t h di tI t f i i t h di tImpact of a priori troposphere gradientsImpact of a priori troposphere gradientsImpact of a priori troposphere gradients Impact of a priori troposphere gradients UT1 f INT iUT1 f INT ion UT1 from INT sessionson UT1 from INT sessionson UT1 from INT sessions on UT1 from INT sessions

Troposphere gradients describe the azimuthalTroposphere gradients describe the azimuthal asymmetry of troposphere delays around a stationasymmetry of troposphere delays around a station

Un modeled positive east gradients move stationsUn-modeled positive east gradients move stations towards west or decrease UT1 if the station is fixedtowards west or decrease UT1 if the station is fixed

EastWest

I t i S i IMPACT f i i GRADIENTSIntensive Sessions IMPACT of a priori GRADIENTS

A i i di t d UT1 f INT2A i i di t d UT1 f INT2A priori gradients and UT1 from INT2A priori gradients and UT1 from INT2A priori gradients and UT1 from INT2A priori gradients and UT1 from INT2

Analysis o f Intensive sessions: state-of-the-artAnalysis o f Intensive sessions: state of the art

one offset and one rate between the two clocks- one offset and one rate between the two clocks

one zenith wet delay offset per station- one zenith wet delay offset per station

one UT1 offset- one UT1 offset

i e 5 unknowns- i.e. 5 unknowns

ti ti f di t- no estimation of gradientsg

I t i S i IMPACT f i i GRADIENTSIntensive Sessions IMPACT of a priori GRADIENTS

R l f th bR l f th bRule of thumbRule of thumbRule of thumbRule of thumb

UT1 is changed by 15 s per 1mm sum of eastUT1 is changed by 15 s per 1mm sum of east gradients at the two stationsgradients at the two stations

I t k i th ll tIn network sessions the average over all east gdi t t d t bgradients tends to be zerog

IMPACT f i i GRADIENTSI t i S i IMPACT of a priori GRADIENTSIntensive Sessions

A i i di tA i i di tA priori gradientsA priori gradientsA priori gradientsA priori gradients

KARAT: Kashima Ray-tracing tools (Hobiger etKARAT: Kashima Ray tracing tools (Hobiger et al 2008)al., 2008)

from JMA (Japan Meteorological Agency)- from JMA (Japan Meteorological Agency)

grid size 10km- grid size 10km

LHG Li H i t l G di t (B h t lLHG: Linear Horizontal Gradients (Boehm et al., G ea o o ta G ad e ts ( oe et a ,2007)2007)2007)

- from ECMWF (European Centre for Medium-Rangefrom ECMWF (European Centre for Medium Range )Weather Forecasts))

- grid size 25kmgrid size 25km


E t di t t T k bE t di t t T k bEast gradients at TsukubaEast gradients at TsukubaEast gradients at TsukubaEast gradients at Tsukuba

KARATKARATLHGLHG


UT1 t t tUT1 t t t ff thth ttUT1 w r t stateUT1 w r t state--ofof--thethe--artartUT1 w.r.t. stateUT1 w.r.t. state ofof thethe artart

KARATKARATLHGLHG


P i dP i d f d i ti ff d i ti fPeriodogramPeriodogram for deviations fromfor deviations fromPeriodogramPeriodogram for deviations from for deviations from S CS CIERS 05 C04IERS 05 C04IERS 05 C04IERS 05 C04


C l i i i di tC l i i i di tConclusions: a priori gradientsConclusions: a priori gradientsConclusions: a priori gradientsConclusions: a priori gradients

No significant improvement when comparing withNo significant improvement when comparing with IERS 05 C04IERS 05 C04

R d ti f i l d l UT1Reduction of semi-annual and annual UT1 d i ti f IERS 05 C04 ith KARAT (b tdeviations from IERS 05 C04 with KARAT (but (i f h t i d d i ti )increase of short period deviations)p )


“Geodetic” excitation (observed UT1/LOD) vs“Geodetic” excitation (observed UT1/LOD) vsGeodetic excitation (observed UT1/LOD) vs. Geodetic excitation (observed UT1/LOD) vs. t h i it ti ( i l th d l d t )t h i it ti ( i l th d l d t )atmospheric excitation (numerical weather model data) atmospheric excitation (numerical weather model data) p ( )p ( )

atat subsub--diurnaldiurnal periodsperiodsat at subsub diurnaldiurnal periodsperiods

Hourly Earth rotation parameters andHourly Earth rotation parameters and atmospheric angular momentum functions foratmospheric angular momentum functions for CONT08 (Boehm et al 2009)CONT08 (Boehm et al., 2009)

CONT08CONT08Continuous VLBIContinuous VLBI

icampaignp g

14 days in August 200814 days in August 2008 (b f hi h b(because of higher sub-( gdiurnal variability)diurnal variability)

11 t ti11 stations

CONT08 1h ERP & AAMFCONT08 1h ERP & AAMF

At h i it tiAt h i it tiAtmospheric excitationAtmospheric excitationAtmospheric excitationAtmospheric excitation

Motion termsMotion terms

wind fields v- wind fields vρρ

M tMass terms

- surface pressuresurface pressure

- vertical density distribution pvertical density distribution pSS


AAMFAAMF i l ti l tAAMFAAMF -- axial componentaxial componentAAMF AAMF axial componentaxial component(f ECMWF 6h l i d t )(f ECMWF 6h l i d t )(from ECMWF 6h analysis data)(from ECMWF 6h analysis data)(from ECMWF 6h analysis data)(from ECMWF 6h analysis data)

Matter 1hMatter 1hMatter 6hMatter 6hMotion 1hMotion 1h

s Motion 6hs Motion 6h


C i ith b d LODC i ith b d LODComparison with observed LODComparison with observed LODComparison with observed LODComparison with observed LOD

GPS solutionGPS solution

Reprocessed CODE series Bernese Software- Reprocessed CODE series, Bernese Software

retrograde diurnal terms blocked- retrograde diurnal terms blocked

VLBI l tiVLBI solution

- Goddard Space Flight Center, Calc/SolveGoddard Space Flight Center, Calc/Solve

- retrograde diurnal terms removedretrograde diurnal terms removed


CONT08 h l LODCONT08 h l LODCONT08: hourly LODCONT08: hourly LODCONT08: hourly LODCONT08: hourly LOD

GPSGPSVLBIVLBI

ssin

d

e

tud

plit

mp

a


CONT08 h l LODCONT08 h l LODCONT08: hourly LODCONT08: hourly LODCONT08: hourly LODCONT08: hourly LOD

GPSGPSVLBIVLBI

s Masss MassM ti

in

Motionde

tu

dp

litm

pa


C l i 1h LOD & AAMF CONT08C l i 1h LOD & AAMF CONT08Conclusion: 1h LOD & AAMF, CONT08Conclusion: 1h LOD & AAMF, CONT08Conclusion: 1h LOD & AAMF, CONT08Conclusion: 1h LOD & AAMF, CONT08

Atmosphere can only explain a small fraction ofAtmosphere can only explain a small fraction of diurnal and sub-diurnal variabilitydiurnal and sub-diurnal variability


G l l iG l l iGeneral conclusionsGeneral conclusionsGeneral conclusionsGeneral conclusions

VLBI provides a unique capability to directlyVLBI provides a unique capability to directly access the rotation phase of the Earthaccess the rotation phase of the Earth.

A VLBI i th l t h i t di tlAs VLBI is the only technique to directly y q yd t i UT1 ith hi h i i it i thdetermine UT1 with high precision it is rather g pdiffi lt t j d th f th bt i ddifficult to judge the accuracy of the obtained j g y

ltresults.results.

S i 2 U i l Ti D t i ti f UT1 b VLBISession 2 – Universal Time Determination of UT1 by VLBI

THANKTHANKTHANK YOU!YOU!YOU!YOU!

harald schuh@tuwien ac [email protected]@

UT1UT1 TAITAI i hi h h lh l l il i ff CONT05CONT05UT1UT1‐‐TAITAI withwith hourlyhourly resolutionresolution fromfrom CONT05CONT05UT1UT1 TAI TAI withwith hourlyhourly resolutionresolution fromfrom CONT05CONT05

OOrange: standard analysis with outliers at session borders due to g ymissing observations Black: Modified analysis with stacking ofmissing observations. Black: Modified analysis with stacking of

l ti (A t t l 2007)normal equations (Artz et al., 2007)

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08 Schuh - Determination of UT1 by VLBI