Very long baseline interferometry

S-band stations with dual tracking capability have been used to gather double differential very long baseline interferometry data on Apollo 16 and Apollo 17. This was accomplished by simultaneously receiving both monochromatic radio signal emissions at each of two separated receiving stations, transmitting these data to a central processing facility, and calculating the differences between Doppler angular rates to determine the motion of the lunar roving vehicle

Principles of very-long-baseline interferometry

The basic principles of very-long-baseline interferometry as related to its use in the determination of vector baselines, polar motion, and earth rotation are presented. Aspects relevant to geodetic applications that involve observations of extragalactic radio sources are covered. The instrumentation used in these observations and the basic observables and their simplest interpretation are described. Complications of the interpretation due to the various geophysical 'signals' and nongeophysical 'noise' that affect the observables are considered

Photon Mass and Very Long Baseline Interferometry

A relation between the photon mass, its frequency, $\nu$, and the deflection parameter, $\gamma$, determined by experimentalists (which characterizes the contribution of space curvature to gravitational deflection) is found. This amazing result allows us to conclude that the knowledge of the parameters $\nu$ and $\gamma$ is all we need to set up gravitational bounds on the photon mass. By considering as inputs the most recent measurements of the solar gravitational deflection of radio waves obtained via the Very Long Baseline Interferometry, upper bounds on the photon mass are estimated.Comment: Accepted for publication in International Journal of Modern Physics

Very-long-baseline interferometry experiments

VLB observations have been made at many wavelengths from 2.8 to 270 cm. The highest resolution was obtained on the Greenbank-Crimea baseline, 2.9 x 10^8 wavelengths long at 2.8 cm on which two quasars showed interference fringes. The observations between Goldstone, California and Canberra, Australia (8.1 x 10^7 wavelengths at 13 cm) were the most sensitive, with a minimum detectable flux of 0.3 f.u. These gave fringes on 56 sources, and there are sufficient data to calibrate the interferometer and derive accurate positions, based on time delay and fringe rate. Typical accuracy is two seconds of arc. At 270 cm observations were made on the baselines Owens Valley-Greenbank-Arecibo. Three sources showed fringes. Preliminary values for the diameters are in rough agreement with values expected from the theory of interstellar scintillations

A very long baseline interferometry sky survey

A systematic very long baseline interferometry (VLBI) sky survey, undertaken to find a suitable set of compact celestial radio sources from which a more complete VLBI reference frame can be constructed, discussed. The survey was conducted by searching known celestial radio sources for compact components by means of VLBI observations. Baseline lengths were about 7 x 10 to the 7th power RF wavelengths (lambda = 13.1 cm), so the spatial wavelengths being sampled by the interferometer were generally on the order of a few milliarcseconds. Hence, the radio sources detected have a measurable portion of their total flux density contained in components that are no more than a few milliarcseconds in angular extent. Existing information of radio sources were used as clues to source size

Precision surveying using very long baseline interferometry

Radio interferometry measurements were used to measure the vector baselines between large microwave radio antennas. A 1.24 km baseline in Massachusetts between the 36 meter Haystack Observatory antenna and the 18 meter Westford antenna of Lincoln Laboratory was measured with 5 mm repeatability in 12 separate experiments. Preliminary results from measurements of the 3,928 km baseline between the Haystack antenna and the 40 meter antenna at the Owens Valley Radio Observatory in California are presented

Introduction to very-long-baseline interferometry

Long-baseline interferometry achieves high resolution by using two or more widely separated radio telescopes and recording video signals on magnetic tapes, which are later brought together and cross-correlated. This paper contains discussions of the coherence and timing requirements and of calibration procedures. Applications to measuring brightness distributions and to spectroscopy are reviewed briefly. Some pertinent phenomena connected with radio-wave scattering in irregular media are discussed

Astronomy using basic Mark 2 very long baseline interferometry

Two experiments were performed in April and September 1976 to determine precise positions of radio sources using conventional Mark 2 VLBI techniques. Four stations in the continental United States observed at a wavelength of 18 cm. The recording bandwidth was 2 MHz. The preliminary results using analyses of fringe rate and delay are discussed and the source positions compared with the results of other measurements

Lorentz symmetry and Very Long Baseline Interferometry

Lorentz symmetry violations can be described by an effective field theory framework that contains both General Relativity and the Standard Model of particle physics called the Standard-Model extension (SME). Recently, post-fit analysis of Gravity Probe B and binary pulsars lead to an upper limit at the $10^{-4}$ level on the time-time coefficient $\bar s^{TT}$ of the pure-gravity sector of the minimal SME. In this work, we derive the observable of Very Long Baseline Interferometry (VLBI) in SME and then we implement it into a real data analysis code of geodetic VLBI observations. Analyzing all available observations recorded since 1979, we compare estimates of $\bar s^{TT}$ and errors obtained with various analysis schemes, including global estimations over several time spans and with various Sun elongation cut-off angles, and with analysis of radio source coordinate time series. We obtain a constraint on $\bar s^{TT}=(-5\pm 8)\times 10^{-5}$, directly fitted to the observations and improving by a factor 5 previous post-fit analysis estimates.Comment: 5 pages, 3 figures, version accepted for publicatio

Very long baseline interferometry with the SKA

Adding VLBI capability to the SKA arrays will greatly broaden the science of the SKA, and is feasible within the current specifications. SKA-VLBI can be initially implemented by providing phased-array outputs for SKA1-MID and SKA1-SUR and using these extremely sensitive stations with other radio telescopes, and in SKA2 by realising a distributed configuration providing baselines up to thousands of km, merging it with existing VLBI networks. The motivation for and the possible realization of SKA-VLBI is described in this paper