Äîęóěĺíň âç˙ň čç ęýřŕ ďîčńęîâîé ěŕřčíű. Ŕäđĺń îđčăčíŕëüíîăî äîęóěĺíňŕ : http://www.gao.spb.ru/english/as/j2014/presentations/tercjak.pdf Äŕňŕ čçěĺíĺíč˙: Sun Sep 28 20:10:43 2014 Äŕňŕ číäĺęńčđîâŕíč˙: Sun Apr 10 01:12:16 2016 Ęîäčđîâęŕ: Ďîčńęîâűĺ ńëîâŕ: çŕęîí âčíŕ

Estimation of nutation rates from combination of ring laser and VLBI data
A.

M. Tercjak, J. BĆhm, A. Brzeziski, Gebauer, T. KlÝgel, U. Schreiber, M. Schindelegger
B.


Motivation
· Ring laser gyroscopes (RLG) are instruments which present a dynamical approach to the determination of Earth rotation parameters. They enable measuring Earth rotation on the surface of the Earth, as they are sensitive to variations in the instantaneous rotation vector. They are considered as a potential complement to space geodetic techniques in studying Earth rotation. · To date many experiments have been conducted in order to investigate possible advantages of combining ring laser observations and data from space techniques, especially from Very Long Baseline Interferometry (VLBI). The majority of those experiments concern polar motion and UT1 variations. In this work we examine the potential usage of ring laser observations for estimation of nutation rates.
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Investigation
· checking possibility of nutation rates estimation based on RLG observations simulation level · combination of simulated RLG data with real VLBI data · comparison of estimates based on real RLG data (Wettzell) with results of simulation

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Simulation level
Based on equation for relative Sagnac frequency:
= cot cos + sin + + +


and taking into accord relations between CIP and IRP:
1 0 - + - 0 1 = -0 - + + 0 = = 1.0027 1

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Simulation level
We constructed the design matrix A, assuming one value of the nutation offset rates dX and dY and the instrumental error per day as unknowns, the right-hand side vector is L = Sobs ­ Scomp + random noise, where:
polar motion (xp, yp) dUT1 C04 08 series + ocean tides nutation (dX, dY) The IAU 2000/2006 model + offsets from C04 08 series The IAU 2000/2006 model

S
S

obs

C04 08 series + ocean tides

comp

and the weigthing matrix: P = diag((2)-1), with = 10-11, the first day of observations ­ 15 Sep. 2011
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Simulation level

RMS of the residuals for 1 to 6 ring laser respectively (x10 -7 mas/s): dX 0.3944 0.3781 0.0495 0.0468 0.0603 0.0464
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Simulation level

RMS of the residuals for 1 to 6 ring laser respectively (x10 -7 mas/s): dY 0.6307 0.2179 0.1267 0.1235 0.1274 0.1227
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Investigation
· checking possibility of nutation rates estimation based on RLG observations simulation level · combination of simulated RLG data with real VLBI data · comparison of estimates based on real RLG data (Wettzell) with results of simulation

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Simulated RLG data + VLBI
·Cont11 session, processed with VieVS (Vienna VLBI Software) according to Nilsson et al. (2012) ·Combination on the normal equation level:
= 0


0


, =

=

; = 0 0
Nutation rates = nutation finite differences
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...
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Simulated RLG data + VLBI
·Computation for one, three and six RLG instruments · Starting with present-day accuracy level 10-8 followed by refinement: 10-9, 10-10, 10-11

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Simulated data + VLBI

(ac. lev. 10-8)

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Simulated data + VLBI

(ac. lev. 10-9)

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Simulated data + VLBI

(ac. lev. 10-10)

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Simulated data + VLBI

(ac. lev. 10-11)

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JOURNčES 2014


Simulated data + VLBI

(ac. lev. 10-9)

24-Sep-14

JOURNčES 2014


Investigation
· checking possibility of nutation rates estimation based on RLG observations simulation level · combination of simulated RLG data with real VLBI data · comparison of estimates based on real RLG data (Wettzell) with results of simulation

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Simulated and real RLG data
· Data from the Wettzell Observatory
· Time span 24 days (01 may to 25 may 2010)

· Present-day accuracy level 10-8

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Simulated and real RLG data

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Simulated and real RLG data

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Conclusions:
On a first, very positive note, the estimation of nutation rates from ring laser observations is possible, but... · there should be at least three RLG instruments · the accuracy level should be three orders higher than it is nowadays · even combination with VLBI observation requires at least 10-10 accuracy level and three instruments · our simulations appeared to be more optimistic than real data.
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Our goals for future:
· Combination with GNSS data · Investigation of a more sophisticated model of the relative Sagnac frequency

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Acknowledgements:
Local Organization Committee for free accommodation and waiving the registration fee, IAG for Young ScientistsTravel Award

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