A5071599126- GNSS positioning and interference
- Geophysics and Gravity Measurements
- Ionosphere and magnetosphere dynamics
- Astronomical Observations and Instrumentation
- Inertial Sensor and Navigation
- Radio Astronomy Observations and Technology
- Calibration and Measurement Techniques
- earthquake and tectonic studies
- Statistical and numerical algorithms
- Astronomy and Astrophysical Research
- Astrophysics and Cosmic Phenomena
- Methane Hydrates and Related Phenomena
- Ocean Waves and Remote Sensing
- Geophysics and Sensor Technology
- Earthquake Detection and Analysis
- Medical Imaging Techniques and Applications
- Geomagnetism and Paleomagnetism Studies
- Meteorological Phenomena and Simulations
- Advanced Frequency and Time Standards
- Spectroscopy and Laser Applications
- Solar and Space Plasma Dynamics
- Electromagnetic Scattering and Analysis
- Geochemistry and Geologic Mapping
- Seismology and Earthquake Studies
- Atmospheric Ozone and Climate
Goddard Space Flight Center
2011-2023
University of Maryland, College Park
1982-2008
Institute of Geodesy and Geophysics
2004
Flometrics (United States)
1992-1993
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...
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 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...
Azimuthal asymmetries in the atmospheric refractive index can lead to errors estimated vertical and horizontal station coordinates. Generally these gradients are not modeled standard very long baseline interferometry (VLBI) geodetic analysis. Daily average gradient effects be as large 50 mm of delay at a 7° elevation. To model gradients, constrained estimation parameters was added VLBI solution procedure. Here analysis two sets data is summarized: set all experiments from 1990–1993 series 12...
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...
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...
Gradients in the atmospheric refractive index can lead to errors estimated vertical and horizontal station coordinates. These produce systematic terrestrial celestial reference frames determined from our very long baseline interferometry (VLBI) measurements. Estimation of gradients for global VLBI data set changes frame length scale by −0.7 ppb produces position adjustments that vary approximately monotonically with latitude. Estimating reduces radio source declinations an amount peaks at...
We determined the improvement in baseline length precision and accuracy using new atmospheric delay mapping functions (Ifadis (Ifadis, 1986) MTT (Herring, 1992a)) by analyzing NASA Crustal Dynamics Project research development (R&D) experiments International Radio Interferometric Surveying (IRIS) A experiments. These reduce scatter about 20% below that CfA2.2 (Davis et al., 1985) dry Chao (Chao, 1974) wet functions. With newer functions, average station vertical inferred from observed...
We have analysed the Ny-Ålesund very long baseline interferometry (VLBI) data over period 1994 August to 2004 May, and we obtain secular displacement rates relative a NNR-NUVEL-1A reference frame of 0.2 ± 0.5 mm yr−1, −1.7 yr−1 4.8 1.1 for north, east vertical directions, respectively. The corresponding global positioning system (GPS) station same east, directions are 0.6 −2.3 6.4 1.5 at NYA1 -−0.1 −1.6 6.9 0.9 NALL, where these GPS were derived from ITRF2000 velocity solution Heflin. From...
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...
Atmospheric mass loading produces a primarily vertical displacement of the Earth's crust. This is correlated with surface pressure and large enough to be detected by very long baseline interferometry (VLBI) measurements. Using measured at VLBI stations, we have estimated atmospheric term for each station location directly from data acquired 1979 1992. Our estimates sensitivity change in range 0 −0.6 mm/mbar depending on station. These agree inverted barometer model calculations (Manabe et...
Abstract Tropospheric delay modeling error continues to be one of the largest sources in VLBI (very long baseline interferometry) analysis. For standard operational solutions, we use VMF1 elevation‐dependent mapping functions derived from European Centre for Medium‐Range Weather Forecasts data. These assume that tropospheric at a site is azimuthally symmetric. As this assumption not true, have instead determined ray trace along signal path through troposphere each quasar observation. We...
ABSTRACT The second realization of the International Celestial Reference Frame (ICRF2), which is current fundamental celestial reference frame adopted by Astronomical Union, based on Very Long Baseline Interferometry (VLBI) data at radio frequencies in X band and S band. European Space Agency’s Gaia mission, launched 2013 December 19, started routine scientific operations 2014 July. By scanning whole sky, it expected to observe ∼500,000 Quasi Stellar Objects optical domain an average 70...