A5020630790- GNSS positioning and interference
- Geophysics and Gravity Measurements
- Astronomical Observations and Instrumentation
- Radio Astronomy Observations and Technology
- Underwater Acoustics Research
- Astrophysics and Cosmic Phenomena
- Acoustic Wave Phenomena Research
- Underwater Vehicles and Communication Systems
- Ionosphere and magnetosphere dynamics
- African history and culture studies
- Astronomy and Astrophysical Research
- International Development and Aid
- Atmospheric Ozone and Climate
- Global Peace and Security Dynamics
- Arctic and Antarctic ice dynamics
- Historical Astronomy and Related Studies
- Atmospheric and Environmental Gas Dynamics
- Inertial Sensor and Navigation
- Adaptive optics and wavefront sensing
- Seismic Waves and Analysis
- earthquake and tectonic studies
- Galaxies: Formation, Evolution, Phenomena
- Speech and Audio Processing
- African studies and sociopolitical issues
- Stellar, planetary, and galactic studies
Bristol-Myers Squibb (United States)
2025
United States Naval Observatory
2005-2024
University of Oxford
2021
Bowling Green State University
2021
George Mason University
2021
Goddard Space Flight Center
2007-2020
University of Pennsylvania
2019
Centre for Social Justice
1999-2017
Australian National University
2016
Observatoire de Paris
2005
A catalog containing milliarcsecond--accurate positions of 1332 extragalactic radio sources distributed over the northern sky is presented - Very Long Baseline Array Calibrator Survey (VCS1). The have been derived from astrometric analysis dual-frequency 2.3 and 8.4 GHz VLBA snapshot observations; in a majority cases, images are also available. These suitable for use geodetic experiments, as phase-reference calibrators high-sensitivity astronomical imaging. VCS1 largest high-resolution...
We have analyzed 6 years of very long baseline interferometry (VLBI) data beginning in 1984 from a network sites Alaska, the Yukon, and conterminous United States. The analysis these 53 sets includes constrained, continuous, piecewise‐linear estimation site atmospheres clocks; application values correlations self‐consistent Earth orientation series derived other VLBI data; simultaneous positions velocities. From solution that 21,007 observations with fit 40 ps delay 64 fs/s rate, we...
This paper presents accurate absolute positions from a 24 GHz Very Long Baseline Array (VLBA) search for compact extragalactic sources in an area where the density of known calibrators with precise coordinates is low. The goals were to identify additional suitable use as phase galactic sources, determine their positions, and produce radio images. In order achieve these goals, we developed new software package, PIMA, determining group delays wide-band data much lower detection limit. With...
This paper presents an extension of the Very Long Baseline Array Calibrator Survey, called VCS2, containing 276 sources. survey fills in regions sky that were not completely covered by previous VCS1 calibrator survey. The VCS2 includes sources near Galactic plane, -30° < δ -45°, and VLA calibrators. positions have been derived from astrometric analysis group delays measured at 2.3 8.4 GHz using Goddard Space Flight Center CALC/SOLVE package. From VLBA snapshot observations, images...
This paper presents the third extension to Very Large Baseline Array (VLBA) Calibrator Survey, containing 360 new sources not previously observed with very long baseline interferometry (VLBI). The survey, based on three 24 hour VLBA observing sessions, fills areas sky above declination -45 degrees where calibrator density is less than one source within a 4 radius disk at any given direction. positions were derived from astrometric analysis of group delays determined 2.3 and 8.6 GHz frequency...
This paper presents the sixth part to Very Long Baseline Array (VLBA) Calibrator Survey. It contains positions and maps of 264 sources which 169 were not previously observed with very long baseline interferometry (VLBI). survey, based on two 24 hour VLBA observing sessions, was focused 1) improving 95 from previous surveys that either large a priori position errors or enough get reliable 2) remaining new flat-spectrum predicted correlated flux density in range 100-200 mJy surveys. Source...
This paper presents the fifth part of Very Long Baseline Array (VLBA) Calibrator Survey (VCS), containing 569 sources not observed previously with very long baseline interferometry in geodetic or absolute astrometry programs. campaign has two goals: (1) to observe additional that, together previous survey results, form a complete sample, and (2) find new strong suitable as phase calibrators. VCS extension was based on three 24 hr VLBA observing sessions 2005. It detected almost all...
This paper presents the fourth extension to VLBA Calibrator Survey, containing 258 new sources not previously observed with very long baseline interferometry (VLBI). survey, based on three 24 hr Very Long Baseline Array observing sessions, fills remaining areas sky above declination -40° where calibrator density is less than one source within a 4° radius disk in any given direction. The share of these was reduced from 4.6% 1.9%. Source positions were derived astrometric analysis group delays...
Abstract A prototype broadband geodetic very long baseline interferometry system has been implemented, and measurements of the length over approximately two years, between December 2014 January 2017, have made in process exercising system, developing operational procedures, assessing precision for new observing concept. In addition to a signal chain installing instrumentation on both 12‐m antenna at Goddard Geophysical Astrophysical Observatory 18‐m Westford Massachusetts Institute...
ABSTRACT Six very successful Very Long Baseline Array (VLBA) calibrator survey campaigns were run between 1994 and 2007 to build up a large list of compact radio sources with positions precise enough for use as long baseline interferometry (VLBI) phase reference calibrators. We report on the results second epoch VLBA Calibrator Survey campaign (VCS-II) in which 2400 VCS re-observed X S bands order improve upcoming third realization International Celestial Reference Frame (ICRF3) well their...
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...
Four years of very long baseline interferometry (VLBI) measurements involving fixed and mobile stations in the western United States are analyzed using weighted least squares. Baseline solution time series used to estimate rates change vector baselines between pairs VLBI stations. Horizontal motions determined for 18 sites with respect a site Mojave desert. Six west two just east San Andreas fault show northwestward motion closely parallel fault. Their range from 43 mm/yr significant at...
Do poverty definitions matter? the current state of research, Robert Pinker glossary - an alphabetically arranged explanation terms and concepts, with associated references, David Gordon, et al meaning 11 clusters definitions, Paul Spicker.
Total ozone measurements made by the SBUV and TOMS instruments on NIMBUS 7 spacecraft are compared with from 62 Dobson 18 M83 stations. On average, values 6.6% smaller than 9.1% M83; corresponding biases 8.3% 11.3%, respectively. Use of or as a transfer standard reveals an apparent bias between networks 3.0 2.5%respectively. Major portion space ground is attributed to uncertainties in absorption coefficients used processing measurements. Precision total retrieved either instrument shown be...
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...
Abstract Using very long baseline interferometry data for the sources that comprise third International Celestial Reference Frame (ICRF3), we examine quality of formal source-position uncertainties ICRF3 by determining excess astrometric variability (unexplained variance) each source as a function time. We also quantify multiple qualitatively distinct aspects seen in data, using variety metrics. Average position offsets, statistical dispersion measures, and coherent trends over time explored...
A global ozone data set covering the two years from November 1978 until October 1980, with an average of 1200 profiles per day, has been produced and archived solar backscattered ultraviolet (SBUV) instrument flown on NIMBUS 7 spacecraft. The SBUV are compared measurements chemical optical sensors launched balloons rockets obtained ground‐based Dobson spectrophotometers using Umkehr method. biases between results balloon generally less than 10%. These functions layer height latitude believed...
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...