Nutation terms adjustment to VLBI and implication for the Earth rotation resonance parameters

2019 ◽  
Vol 220 (2) ◽  
pp. 759-767 ◽  
Author(s):  
I Nurul Huda ◽  
S Lambert ◽  
C Bizouard ◽  
Y Ziegler
Keyword(s):  
Polar Motion ◽  
Inner Core ◽  
Resonance Parameters ◽  
Free Core Nutation ◽  
Long Baseline ◽  
The Earth ◽  
Significant Difference ◽  
Tidal Correction ◽  
Global Parameters

SUMMARY The nutation harmonic terms are commonly determined from celestial pole offset series produced from very long baseline interferometry (VLBI) time delay analysis. This approach is called an indirect approach. As VLBI observations are treated independently for every session, this approach has some deficiencies such as a lack of consistency in the geometry of the session. To tackle this problem, we propose to directly estimate nutation terms from the whole set of VLBI time delays, hereafter referred as a direct approach, in which the nutation amplitudes are taken as global parameters. This approach allows us to reduce the correlations and the formal errors and gives significant discrepancies for the amplitude of some nutation terms. This paper is also dedicated to the determination of the Earth resonance parameters, named polar motion, free core nutation, and free inner core nutation. No statistically significant difference has been found between the estimates of resonance parameters based upon ‘direct’ and ‘indirect’ nutation terms. The inclusion of a complete atmospheric-oceanic non-tidal correction to the nutation amplitudes significantly affected the estimates of the free core nutation and the free inner core nutation resonant frequencies. Finally, we analyzed the frequency sensitivity of polar motion resonance and found that this resonance is mostly determined by the prograde nutation terms of period smaller than 386 d.

Study of the Earth rheological properties from polar motion

2020 ◽  
Author(s):  
Christian Bizouard ◽  
Ibnu Nurul Huda ◽  
Sébastien Lambert
Keyword(s):  
Rheological Properties ◽  
Solid Earth ◽  
Polar Motion ◽  
Inner Core ◽  
Dynamical Behavior ◽  
Chandler Wobble ◽  
Love Number ◽  
Resonance Parameters ◽  
Global Circulation Models ◽  
The Earth

<pre>Since the beginning of the 20th century, the observation of the Earth rotation variations through astro-geodetic <br />techniques enables to investigate the global rheological properties of the Earth, in particular, the resonance <br />parameters of the free rotation modes reflect the solid Earth anelasticity, the ocean response to an external <br />forcing, and the properties of the fluid inner core, eventually of the solid inner core. Better constraints on <br />these resonance parameters can be obtained by confronting the observed terrestrial motion of the rotation pole <br />(the so-called polar motion) - including nutation as a retrograde diurnal polar motion - to the modeled excitation <br />producing it. The more precise the modeled excitation and the observed polar motion are, the better the<br />Earth rheological properties will be determined. For now, the best precision is reached in the<br />nutation band. So, the analysis has been first dedicated to a direct adjustment of the nutation components<br />from VLBI delays, then the adjustment of the resonance parameters in the transfer function between the observed <br />nutation terms and the corresponding rigid nutation terms that reflects the luni-solar forcing. The obtained <br />resonance parameters confirms in particular the shortening of the polar motion resonance period of about 40 - 50 day <br />in the retrograde diurnal band. Then, we show that the dynamical behavior of the oceans in the diurnal band is <br />mostly responsible for that. We also predicted a supplementary change of the resonance parameters in the vicinity<br />of the free core nutation resonance, as expected from the solid Earth response, and confirmed by the adjustment of <br />these parameters through the nutation terms. In addition to the nutation band, we revisit the estimation of the <br />polar motion resonance parameters in the seasonal band, dominated by the Chandler wobble, in light of the most <br />recent global circulation models of the hydro-atmospheric layers. Finally, we extend the investigation of polar motion resonance to the<br />prograde diurnal polar motion, where the excitations mostly result from the ocean tides. We obtain a resonance <br />period of about 393 days, and confirmed by our prediction based on the ocean tidal models. These results allow us to <br />impose constraints on the frequency dependence of the Love number k<sub>2</sub> and the Love number oceanic k<sub>o</sub>, characterizing <br />respectively the response of the solid Earth and the oceans to an external potential of degree 2. </pre>

scholarly journals VLBI studies of the nutations of the earth

1988 ◽  
Vol 129 ◽  
pp. 371-375
Author(s):  
T. A. Herring
Keyword(s):  
Truncation Error ◽  
Very Long Baseline Interferometry ◽  
Long Baseline ◽  
The Earth ◽  
Vlbi Data ◽  
One Year ◽  
Nutation Series ◽  
Theoretical Considerations ◽  
Active Investigation

The application of very–long–baseline interferometry (VLBI) to the study of the nutations of the earth has yielded unprecedented accuracy for the experimental determination of the coefficients of the nutation series. The analysis of six years of VLBI data has yielded corrections to the coefficients of the seven largest terms in the IAU 1980 nutation series with periods of one year or less, with accuracies approaching the truncation error of this nutation series (0.1 mas). The nutation series coefficients computed from the VLBI data, and those obtained from theoretical considerations (the IAU 1980 nutation series), are in excellent agreement. The largest corrections are to the coefficients of the retrograde annual nutation [2.0 ± 0.1 mas], the prograde semiannual nutation [(0.5 - ι 0.4) ±0.1 mas], and the prograde 13.7 day nutation [−0.4 ± 0.1 mas]. (The imaginary term for the semiannual nutation represents a term 90° out–of–phase with the arguments of the nutation series.) The geophysical implications of these results are currently under active investigation. We discuss the methods used to extract the nutation information from the VLBI data, the calculations of the uncertainties of the resultant corrections to the coefficients of the nutation series, and the current research into the nutations of the earth.

scholarly journals Stability of Determining the Earth Rotation Parameters (ERP) with VLBI

1988 ◽  
Vol 129 ◽  
pp. 417-420
Author(s):  
Shifang Luo ◽  
Dawei Zheng
Keyword(s):  
Earth Rotation ◽  
Polar Motion ◽  
Systematic Errors ◽  
Geometric Effect ◽  
The Earth ◽  
Geometric Uncertainty ◽  
Earth Rotation Parameters ◽  
Rotation Parameters ◽  
The Stability

By using the observations of IRIS network, the stability of determinang ERP with VLBI is studied. It is concluded that the uncertainties from initial values of ERP, the errors of other parameters are at the same level as the formal errors in determination of ERP. The geometric effect on determination of ERP is important and appears as systematic errors. Geometric uncertainty on polar motion is greater than that on UT1. and specially much worse for the continenal network. The stability of determining ERP with VLBI can be improved either by increasing new stations at reasonable location in a VLBI network or by increasing new networks.

scholarly journals Agreements and Disagreements between Theories of Rigid Earth Nutation

1997 ◽  
Vol 165 ◽  
pp. 319-324
Author(s):  
J. Souchay
Keyword(s):  
Very Long Baseline Interferometry ◽  
Laser Ranging ◽  
Lunar Laser Ranging ◽  
Theoretical Determination ◽  
Long Baseline ◽  
The Earth ◽  
Lunar Laser ◽  
Rigid Earth ◽  
Good Agreement

AbstractThe necessity to elaborate a theory of nutation and precession matching the accuracy of very modern techniques as Very Long Baseline Interferometry and Lunar Laser Ranging led recently to various works. We discuss here the good agreement between those related to the nutation when considering the Earth as a solid body. In comparison we show the uncertainty concerning the modelisation of the transfer function leading to theoretical determination of the nutation coefficients when including dominant geophysical characteristics.

scholarly journals Application of klauder wavelet for generation of synthetic seismic signals

2018 ◽  
Vol 7 (2.7) ◽  
pp. 903
Author(s):  
S Neelima ◽  
A Saritha ◽  
K S.Ramesh ◽  
S Koteswara rao
Keyword(s):  
Wavelet Transforms ◽  
Seismic Waves ◽  
Inner Core ◽  
Seismic Signal ◽  
Petroleum Exploration ◽  
Seismic Signals ◽  
Efficient Tool ◽  
The Earth ◽  
Complete Extraction

Analysis of reflected seismic waves gives the information about the earth and its inner core. This aids in monitoring earthquake, petroleum exploration, determination of the earth’s core structure, etc. Wavelet transforms is an efficient tool for analysis of seismic reflected signals. These transforms helps in complete extraction of the seismic signal buried in noise. In this paper an attempt is made to analyze a synthetic seismic signal by using Klauder wavelets.  The synthetic seismic signal is extracted by convoluting with the Klauder wavelet. Noise is completely removed as the wavelet spans a large spectrum of signals.  

scholarly journals Determination of UT1 and Polar Motion by the Deep Space Network Using Very Long Baseline Interferometry

1979 ◽  
Vol 82 ◽  
pp. 199-209 ◽  
Author(s):  
J. L. Fanselow ◽  
J. B. Thomas ◽  
E. J. Cohen ◽  
P. F. MacDoran ◽  
W. G. Melbourne ◽  
...  
Keyword(s):  
Polar Motion ◽  
Very Long Baseline Interferometry ◽  
Deep Space ◽  
Deep Space Network ◽  
Accuracy Requirement ◽  
Space Network ◽  
Long Baseline ◽  
Navigation Accuracy ◽  
Better Than

The Deep Space Network (DSN) [operated by JPL under contract to the National Aeronautics and Space Administration] is implementing a Very Long Baseline Interferometry (VLBI) capability at DSS 63 (Spain), DSS 14 (California, USA), and DSS 43 (Australia) to support the navigation requirements of planetary space missions. The early development work for this system has already demonstrated the capability of measuring UT1 with a formal accuracy as low as 0.6 msec with only 6 hours of data. Further, a radio astrometric catalog of approximately 45 sources whose positions are known to better than has been constructed. In addition to these measurements, this paper describes the characteristics and anticipated performance of the complete VLBI system being implemented within the DSN for operational use in mid-1979. In particular, one of the capabilities of this system will be the measurement of UT1 and polar motion at weekly intervals. Although the navigation accuracy requirement is only 50 cm for the Voyager mission, this system should be capable of delivering UT1 and polar motion determinations with decimeter accuracy if it is operated at maximum performance. An additional requirement of this operational system is that it have the capability of providing these results within 24 hours of the actual observations.

scholarly journals Consistent Relativistic VLBI Theory with Picosecond Accuracy

1991 ◽  
Vol 127 ◽  
pp. 351-358
Author(s):  
M. Soffel ◽  
J. Müller ◽  
X. Wu ◽  
C. Xu
Keyword(s):  
Reference Frames ◽  
Very Long Baseline Interferometry ◽  
Barycentric Coordinates ◽  
Measuring Process ◽  
Long Baseline ◽  
The Earth ◽  
Rotation Parameters ◽  
Residual Values ◽  
Geocentric Coordinates

The accuracy of Very Long Baseline Interferometry (VLBI), representing one of the most important space techniques of modern geodesy, especially for the determination of the Earth’s rotation parameters and baselines, is steadily increasing. Presently, delay residuals are of the order of 30 - 50 ps, corresponding to an uncertainty in length of about 1 centimeter e.g. in the determination of baselines or the position of the rotation pole. As has already been stressed by many authors, at this level of accuracy a relativistic formulation of the VLBI measuring process is indispensable (e.g. the gravitational time delay for rays getting close to the limb of the Sun amounts to 170 ns!). Starting with the work by Finkelstein et al. (1983) a series of papers has meanwhile been published on a relativistic VLBI theory (Soffelet al., 1986; Hellings, 1986; Zeller et al., 1986; Herring, 1989). However, possibly apart from Brumberg’s treatment in his new monograph (Brumberg, 1990) all of these theories have one fatal drawback: they are not based upon some consistent theory of reference frames, which relates the global, barycentric coordinates, in which the measuring process is primarily formulated and in which positions and velocities of the bodies of the solar system are computed, with the local, geocentric coordinates, comoving with the Earth, in which the geodetically meaningful baselines are defined. Furthermore, none of these theories (including Brumberg’s (1990) treatment) have the accuracy of one picosec which seems desirable with respect to the achieved residual values.

Determination of UT1 and Polar Motion by the Deep Space Network using very Long Baseline Interferometry

1979 ◽  
pp. 199-209 ◽  
Author(s):  
J. L. Fanselow ◽  
J. B. Thomas ◽  
E. J. Cohen ◽  
P. F. MacDoran ◽  
W. G. Melbourne ◽  
...  
Keyword(s):  
Polar Motion ◽  
Very Long Baseline Interferometry ◽  
Deep Space ◽  
Deep Space Network ◽  
Space Network ◽  
Long Baseline

scholarly journals Kimura's Z-Term and the Liquid Core Theory

1972 ◽  
Vol 48 ◽  
pp. 189-191
Author(s):  
Yasujiro Wako
Keyword(s):  
Polar Motion ◽  
Liquid Core ◽  
The Earth ◽  
Core Theory ◽  
Latitude Variation ◽  
Annual Term ◽  
Phase Angles ◽  
Theoretical Results

Kimura (1902) pointed out that there might be an unknown cause other than polar motion which would produce an apparent latitude variation, and introduced the Z-term as, Δϕ = Xcos λ + + Ysin λ + Z.The theoretical results by Jeffreys-Vicente (1957) and Molodensky (1961) have shown that the effect of a liquid core of the Earth may increase the coefficients of the semi-annual solar nutation term (2 ⊙) which is involved in the diurnal nutation (the so-called Oppolzer term) by 0″.02. It is reasonable to accept this correction which will appear in the Z-term with an argument of (2 ⊙ −α).From comparison of the observed amplitudes and the phase angles of the annual Z-terms derived from the ILS data, it is concluded that the argument of the principal annual term in Z is (2 ⊙ −α) and not ⊙. The following results were obtained for the annual Z-term for 1955-1966 from the analysis of data by two independent methods (Wako, 1970): 0″.0137 sin (2 ⊙ −α + 2°.2), 0″.0203 sin (2 ⊙ −α + 4°.3).Melchior (1970) proposed another effect of the Earth's liquid core for the annual nutation in obliquity, thus a term such as a sin (⊙ +α + A) would appear in the Z-term and it might cause a part of semi-annual Z-term. For the determination of these corrections, analysis of Kimura's Z-term is the most effective method.

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