Celestial reference frames at multiple radio wavelengths

2012 ◽  
Vol 10 (H16) ◽  
pp. 213-214
Author(s):  
C. S. Jacobs
Keyword(s):  
High Frequency ◽  
Reference Frames ◽  
High Accuracy ◽  
Extended Source ◽  
Current Limiting ◽  
Vlbi Data ◽  
Limiting Errors ◽  
Celestial Reference Frame ◽  
Core Shift ◽  
Systematic Noise

AbstractIn 1997 the IAU adopted the International Celestial Reference Frame (ICRF) built from S/X VLBI data. In response to IAU resolutions encouraging the extension of the ICRF to additional frequency bands, VLBI frames have been made at 24, 32, and 43 GHz. Meanwhile, the 8.4 GHz work has been greatly improved with the 2009 release of the ICRF-2. This paper discusses the motivations for extending the ICRF to these higher frequency radio bands. Results to date will be summarized including evidence that the high frequency frames are rapidly approaching the accuracy of the 8.4 GHz ICRF-2. We discuss current limiting errors and prospects for the future accuracy of radio reference frames. We note that comparison of multiple radio frames is characterizing the frequency dependent systematic noise floor from extended source morphology and core shift. Finally, given Gaia's potential for high accuracy optical astrometry, we have simulated the precision of a radio-optical frame tie to be ~10–15 μas (1-σ, per component).

scholarly journals An Improved Time Integration Method Based on Galerkin Weak Form with Controllable Numerical Dissipation

2021 ◽  
Vol 11 (4) ◽  
pp. 1932
Author(s):  
Weixuan Wang ◽  
Qinyan Xing ◽  
Qinghao Yang
Keyword(s):  
High Frequency ◽  
Integration Method ◽  
Time Integration ◽  
Low Frequency ◽  
Weak Form ◽  
High Accuracy ◽  
Numerical Dissipation ◽  
Frequency Range ◽  
Time Integration Method ◽  
Numerical Damping

Based on the newly proposed generalized Galerkin weak form (GGW) method, a two-step time integration method with controllable numerical dissipation is presented. In the first sub-step, the GGW method is used, and in the second sub-step, a new parameter is introduced by using the idea of a trapezoidal integral. According to the numerical analysis, it can be concluded that this method is unconditionally stable and its numerical damping is controllable with the change in introduced parameters. Compared with the GGW method, this two-step scheme avoids the fast numerical dissipation in a low-frequency range. To highlight the performance of the proposed method, some numerical problems are presented and illustrated which show that this method possesses superior accuracy, stability and efficiency compared with conventional trapezoidal rule, the Wilson method, and the Bathe method. High accuracy in a low-frequency range and controllable numerical dissipation in a high-frequency range are both the merits of the method.

An Efficient Galerkin BEM to Compute High Acoustic Eigenfrequencies

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Mario Durán ◽  
Jean-Claude Nédélec ◽  
Sebastián Ossandón
Keyword(s):  
Numerical Method ◽  
Integral Equations ◽  
High Frequency ◽  
High Accuracy ◽  
Integral Representations ◽  
Stability And Convergence ◽  
Symmetric Matrices ◽  
Frequency Interval ◽  
Numerical Treatment ◽  
The Stability

An efficient numerical method, using integral equations, is developed to calculate precisely the acoustic eigenfrequencies and their associated eigenvectors, located in a given high frequency interval. It is currently known that the real symmetric matrices are well adapted to numerical treatment. However, we show that this is not the case when using integral representations to determine with high accuracy the spectrum of elliptic, and other related operators. Functions are evaluated only in the boundary of the domain, so very fine discretizations may be chosen to obtain high eigenfrequencies. We discuss the stability and convergence of the proposed method. Finally we show some examples.

scholarly journals Variability and Performance of Short to Long-Range Single Baseline RTK GNSS Positioning in Indonesia

2019 ◽  
Vol 94 ◽  
pp. 01012 ◽  
Author(s):  
Irwan Gumilar ◽  
Brian Bramanto ◽  
Fuad F. Rahman ◽  
I Made D. A. Hermawan
Keyword(s):  
Long Range ◽  
High Frequency ◽  
Carrier Phase ◽  
Satellite System ◽  
High Accuracy ◽  
Gnss Positioning ◽  
And Performance ◽  
Gnss Network ◽  
Single Baseline ◽  
Global Navigation Satellite

As the modernized Global Navigation Satellite System (GNSS) method, Real Time Kinematic (RTK) ensures high accuracy of position (within several centimeters). This method uses Ultra High Frequency (UHF) radio to transmit the correction data, however, due to gain and power issues, Networked Transport of RTCM via Internet Protocol (RTCM) is used to transmit the correction data for a longer baseline. This Research aims to investigate the performance of short to long-range single baseline RTK GNSS (Up to 80 KM) by applying modified LAMBDA method to resolve the ambiguity in carrier phase. The RTK solution then compared with the differential GNSS network solution. The results indicate that the differences are within RTK accuracy up to 80 km are several centimeter for horizontal solution and three times higher for vertical solution.

scholarly journals The Hipparcos Extragalactic Link

1995 ◽  
Vol 166 ◽  
pp. 127-132 ◽  
Author(s):  
Jean Kovalevsky
Keyword(s):  
Reference Frames ◽  
Hubble Space Telescope ◽  
Visible Spectrum ◽  
Proper Motions ◽  
Time Intervals ◽  
Hipparcos Catalogue ◽  
Celestial Reference System ◽  
Celestial Reference Frame ◽  
Galactic Radio ◽  
Better Than

In conformity with the IAU resolutions on reference frames adopted in 1991, the Hipparcos catalogue will represent, in the visible spectrum, the celestial reference system defined by fixed positions of extra-galactic radio-sources. This will be realized by the strongest possible link between the IERS celestial reference frame with positions and/or proper motions of the largest possible number of Hipparcos stars determined also with respect to extragalactic objects. The data which will be used must be available before April 1995. It will include the following: positions and proper motions of radio stars observed by VLBI, VLA and MERLIN; photographic positions in fields including quasars; proper motions with respect to galaxies of the Lick, Yale, and Kiev programs, proper motions derived from pairs of photographic plates taken at large time intervals; and possibly data acquired by Hubble Space Telescope and from Earth's rotation data. The organization of the tasks within the working group is briefly described. The final accuracy of the link is expected to be of the order of, or better than, half a milliarcsecond.

scholarly journals Capabilities and performance of the upgraded Mark III correlator system

1988 ◽  
Vol 128 ◽  
pp. 429-437 ◽  
Author(s):  
Alan R. Whitney
Keyword(s):  
Reference Frames ◽  
Modular Design ◽  
Low Cost ◽  
Random Errors ◽  
Geodetic Vlbi ◽  
Vlbi Data ◽  
Artificial Earth ◽  
Continuum Radio ◽  
And Performance ◽  
Using Data

The Mark IIIA correlator system is currently operating at the U. S. Naval Observatory in Washington, D.C. in support of VLBI geodetic measurements being made by NASA, NGS, NRL, and USNO. This correlator system, developed at Haystack Observatory, is a second-generation version of the original Mark III correlator, and adds significant new capabilities such as double-speed operation, longer integration periods, and improved internal modelling.The Mark IIIA correlator can simultaneously process up to 10 baselines of data from 5 stations. Experiments including more than 5 stations may be processed with multiple passes through the correlator. The architecture of the correlator allows a future expansion to a maximum of 16 stations. Due to a simple modular design and the low cost of required computer-support equipment, expansion is straightforward and relatively economical.Although current geodetic VLBI observations are made using data from distant natural continuum radio sources, the Mark IIIA correlator was designed to also support processing of data collected from pulsars, artificial earth satellites, and from earth-orbiting antennas receiving signals from natural sources. These capabilities may be important in the future as efforts continue, for example, to tie satellite-related reference frames to current VLBI reference frames.The design approach of the Mark IIIA correlator will be discussed, including its performance with respect to systematic and random errors which may affect geodetic VLBI data.

scholarly journals Towards the Definition of a Unified Celestial Optical/Radio Reference Frame

1988 ◽  
Vol 129 ◽  
pp. 317-318
Author(s):  
K. J. Johnston ◽  
J. Russell ◽  
Ch. de Vegt ◽  
J. Hughes ◽  
D. Jauncey ◽  
...  
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Radio Observations ◽  
Minimum Density ◽  
Optical Reference ◽  
Definition Of ◽  
Celestial Reference Frame

An almost inertial celestial reference frame based upon extragalactic sources is in the process of being established. This reference frame is to be global with a minimum density of one source/100 square degrees. The source positions will be based upon radio observations and will allow optical reference frames to be related to this frame at the 0.03 arc second level.

Rotation Shaft Twist Angle Measurement Based on Moiré Fringe and Error Analysis

2011 ◽  
Vol 291-294 ◽  
pp. 2842-2845
Author(s):  
Hao Zhao
Keyword(s):  
High Frequency ◽  
Twist Angle ◽  
Torsion Test ◽  
High Accuracy ◽  
Angle Measurement ◽  
Conversion Error ◽  
Processing Error ◽  
Moire Fringe ◽  
Important Means ◽  
Moiré Fringe

Torsion test is an important means of determination engineering materials mechanical properties, a high accuracy twist angle measurement method is designed. The twist angle signal is acquired through grating and infrared photocell by Moiré fringe, then interpolation twist angle signal with high-frequency pulses, so as to convert it to pulses, the twist angle is received by processing pulses. This measurement system combined with FPGA and SCM, the function of FPGA are generating pulses、interpolating twist angle signal and counting the pulses, the result of count is processed by SCM. The twist angle accuracy is 0.002°.According to the experiment results, and the main errors of this system are received, they are signal processing error、electric conversion error and concentricity error. The errors sources are analysed, disposal methods for the errors sources are presented.

scholarly journals Stability of the Extragalactic Reference Frame Realized by VLBI

1991 ◽  
Vol 127 ◽  
pp. 135-144 ◽  
Author(s):  
C. Ma ◽  
D.B. Shaffer
Keyword(s):  
Reference Frame ◽  
Radio Sources ◽  
Dual Frequency ◽  
Real Motion ◽  
Rates Of Change ◽  
Upper Limits ◽  
Crustal Dynamics ◽  
Vlbi Data ◽  
Celestial Reference Frame ◽  
Right Ascension

AbstractThe 318 compact extragalactic radio sources with positions derived from dual frequency Mark III VLBI data acquired by the geodetic and astrometric programs of NASA, NOAA, NRL and USNO form a celestial reference frame with stability in orientation and relative position at the 1 mas level. This paper examines the reference frame realized using 461,000 observations from 1021 observing sessions between 1979 August and 1990 August in the NASA Crustal Dynamics Project VLBI data base. Catalogs of positions estimated from subsets of data (annual, seasonal, network) show differences in orientation typically less than 1 mas provided precession and nutation are adjusted using a reference day. For 17 sources with >5 year time span and >200 one-day position estimates, the rates of change of right ascension and declination are generally less than 5 mas/century, giving upper limits on real motion.

Sign in / Sign up

Export Citation Format

Share Document