A5006270380- Geophysics and Gravity Measurements
- GNSS positioning and interference
- Astronomical Observations and Instrumentation
- Radio Astronomy Observations and Technology
- Inertial Sensor and Navigation
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Ionosphere and magnetosphere dynamics
- Historical Astronomy and Related Studies
- Astro and Planetary Science
- Advanced Frequency and Time Standards
- History and Developments in Astronomy
- Planetary Science and Exploration
- Solar and Space Plasma Dynamics
- Pulsars and Gravitational Waves Research
- Adaptive optics and wavefront sensing
- Stellar, planetary, and galactic studies
- Calibration and Measurement Techniques
- Particle accelerators and beam dynamics
- Medical Imaging Techniques and Applications
- Antenna Design and Optimization
- Spacecraft and Cryogenic Technologies
- Particle Accelerators and Free-Electron Lasers
- Precipitation Measurement and Analysis
- Historical and Architectural Studies
Jet Propulsion Laboratory
2012-2024
California Institute of Technology
1993-2019
Space Applications Services (Belgium)
2016
National Radio Astronomy Observatory
2016
Altera (United States)
2015
Centre of Plasma Physics - Institute for Plasma Research
2014
Supélec
2014
United States Naval Observatory
2004-2005
Observatoire de Paris
2005
Goddard Space Flight Center
2005
A quasi-inertial reference frame is defined based on the radio positions of 212 extragalactic sources distributed over entire sky. The positional accuracy these better than about 1 mas in both coordinates. are upon a general solution for all applicable dual-frequency 2.3 and 8.4 GHz Mark III very long baseline interferometry data available through middle 1995, consisting 1.6 million pairs group delay phase rate observations. Positions details also given an additional 396 objects that either...
We present the second realization of International Celestial Reference Frame (ICRF2) at radio wavelengths using nearly 30 years Very Long Baseline Interferometry observations.ICRF2 contains precise positions 3414 compact astronomical objects and has a positional noise floor ∼40 μas directional stability frame axes ∼10 μas.A set 295 new "defining" sources was selected on basis lack extensive intrinsic source structure.The these defining their more uniform sky distribution eliminates two...
Interferometry at radio frequencies between Earth-based receivers separated by intercontinental distances has made significant contributions to astrometry and geophysics during the past three decades. Analyses of such very long baseline interferometric (VLBI) experiments now permit measurements relative positions points on Earth's surface angles celestial objects levels better than one cm nanoradian, respectively. The angular extragalactic sources inferred from this technique presently form...
We use very long baseline interferometry data obtained between mid-1995 and the end of 2002 May together with older to extend revise International Celestial Reference Frame (ICRF). Revised positions ICRF candidate "other" sources, based on inclusion additional data, are presented. Positions, in frame ICRF, for an 109 new sources also All but four located north δ = -30°. Positions defining remain unchanged. present a summary current astrometric geodetic observing programs discuss evolution...
A new realization of the International Celestial Reference Frame (ICRF) is presented based on work achieved by a working group Astronomical Union (IAU) mandated for this purpose. This follows initial ICRF completed in 1997 and its successor, ICRF2, adopted as replacement 2009. The frame, referred to ICRF3, nearly 40 years data acquired very long baseline interferometry at standard geodetic astrometric radio frequencies (8.4 2.3 GHz), supplemented with collected higher (24 GHz dual-frequency...
We present astrometric results for compact extragalactic objects observed with the Very Long Baseline Array at radio frequencies of 24 and 43 GHz. Data were obtained from ten hr observing sessions made over a five-year period. These observations motivated by need to extend International Celestial Reference Frame (ICRF) higher enable improved deep space navigation after 2016 improve state-of-the-art astrometry. Source coordinates 268 sources estimated GHz 131 The median formal uncertainties...
We have measured the sub-milli-arcsecond structure of 274 extragalactic sources at 24 and 43 GHz in order to assess their astrometric suitability for use a high frequency celestial reference frame (CRF). Ten sessions observations with Very Long Baseline Array been conducted over course $\sim$5 years, total 1339 images produced sources. There are several quantities that can be used characterize impact intrinsic source on including flux density, density variability, index, compactness,...
Aims. The IVS Working Group on Galactic Aberration (WG8) was established to investigate issues related incorporating the effect of aberration in analysis. circular motion solar system barycenter around center causes a change aberration, which case geodetic VLBI observing is over time scales several decades. One specific goals recommend model be applied by IAU ICRF3 working group generation as well other Studies made members have shown that three-dimensional acceleration vector can estimated...
Sagittarius A* (Sgr A*) is a strong, compact radio source believed to be powered by super-massive black hole at the galactic center. Extinction dust and gas in plane prevents observing it optically, but its position proper motion have previously been estimated using interferometry. We present new VLBI absolute astrometry measurements of precise frame third realization International Celestial Reference Frame, ICRF3. The observations used were made 52 epochs on VLBA K-band (24 GHz) between...
Ocean tidal effects on universal time and polar motion (UTPM) are investigated at four nearly diurnal ( K 1 , P O Q ) semidiurnal 2 S M N frequencies by analyzing very long baseline interferometry (VLBI) data extending from 1978 to 1992. We discuss limitations of comparisons between experiment theory for the retrograde components due their degeneracy with prograde nutation model. Estimating amplitudes contributions modeled VLBI observables these eight produces a statistically highly...
view Abstract Citations (49) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Astrometric Results of 1978-1985 Deep Space Network Radio Interferometry: The JPL 1987-1 Extragalactic Source Catalog Sovers, O. J. ; Edwards, C. D. Jacobs, S. Lanyi, G. E. Liewer, K. M. Treuhaft, R. N. An astrometric radio reference frame has been determined from inter- continental dual-frequency interferometric measurements. These measurements were carried out on a...
Abstract We present K -band (24 GHz) images of 731 compact extragalactic radio sources with submilliarcsecond resolution, based on interferometric observations made the Very Long Baseline Array 10 telescopes during 29 day long sessions spanning from 2015 to 2018 and recorded at 2048 Mbps. Many these are imaged resolution for first time frequencies above X band (8 GHz). From each images, we derive following source properties: peak brightness, core total flux density, ratio (compactness...
Two tropospheric calibration systems have been developed at the Jet Propulsion Laboratory (JPL) using different technologies to achieve levels of accuracy, timeliness, and range coverage for support interplanetary NASA flight operations. The first part this paper describes an automated GPS-based system that calibrates zenith delays. These calibrations cover all times can be mapped any line sight elevation mapping functions. Thus they serve spacecraft with no prior scheduling or special...
Planetary ephemerides have been developed and improved over centuries. They are a fundamental tool for understanding solar system dynamics, essential planetary small body mass determinations, occultation predictions, high-precision tests of general relativity, pulsar timing, interplanetary spacecraft navigation. This paper presents recent results from continuing program astrometric very long baseline interferometry (VLBI) observations the Cassini orbiting Saturn, using Very Long Baseline...
Accurate measurement of angular positions on the sky requires a well-defined system reference that is realized with accessible objects. The purpose this study to review international standard realization such system, International Celestial Reference Frame (ICRF). ICRF uses Very Long Baseline Interferometry (VLBI) technique as it has highest resolution any current astrometric for frames in order observe Active Galactic Nuclei (AGN) which are at great distances (typical redshift ∼1) there...
Accurate measurement of angular positions on the sky requires a well-defined system reference, something that in practice is realized by International Celestial Reference Frame (ICRF) with observations distant (typical redshift <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 1) Active Galactic Nuclei (AGN). At such great distances subset these objects exhibit as little 10...
The goal of this presentation is to report the latest progress in creation next generation VLBI-based International Celestial Reference Frame, ICRF3. Two main directions ICRF3 development are improvement S/X-band frame and extension ICRF higher frequencies. Another important task work preparation for comparison with new optical GCRF expected by end decade as a result Gaia mission.
Abstract We report results from multi-epoch radio astrometry of the Cassini spacecraft with Very Long Baseline Array (VLBA). These observations are part a program to determine series accurate positions for Saturn system barycenter in inertial International Celestial Reference Frame (ICRF) and use these position measurements improve our knowledge Saturn’s orbit planetary ephemeris. Our VLBA cover full duration orbital phase mission, insertion 2004 end mission 2017. This period covers more...
We present Hubble Space Telescope (HST) imagery and photometry of the active galaxy Markarian 421 its companion 14 arcsec to ENE. The HST images indicate that is a morphological spiral rather than elliptical as previous ground--based imaging has concluded. bright, compact nucleus, appearing unresolved in images. This suggestive Seyfert activity, or possibly highly luminous star cluster. also report results high dynamic range long-slit spectroscopy with slit placed extend across both galaxies...
The 50-meter Large Millimeter Telescope (LMT) operating on the Sierra Negra in Mexico is largest single- dish millimeter-wave telescope world. Although designed to work 3 mm and 1 bands, there significant potential for LMT observations at centimeter wavelengths. Here, we summarize scientific case operational arguments a K-band receiver system LMT, describe several of unique technical challenges that proposed installation would entail, mention some possible solutions these challenges.
Spacecraft carrying optical communication lasers can be treated as artificial stars, whose relative astrometry to Gaia reference stars provides spacecraft positions in the plane-of-sky for navigation. To comparable current Deep Space Network delta-Differential One-way Ranging measurements, thus sufficient navigation, nanoradian is required. Here we describe our error budget, techniques achieving level ground-base astrometry, and preliminary results from a 1 m telescope. We discuss also how...