M. B. Nechaeva

VLBI studies of the solar-wind plasma irregularities at 18 and 92 CM wavelengths in 1994–1996

We discuss the capabilities of VLBI studies of irregularities of the solar-wind plasma using multi-element radio interferometric facilities. We analyze the data obtained during international VLBI experiments at decimeter wavelengths (92 and 18 cm) in 1994–1996 and supposed that the irregularities have a “stream” structure. The “streams” are strongly elongated in the solar-wind direction (longitudinal size of about a few hundred thousand kilometers) and have the transverse size of about 0.5–2.0 thousand kilometers. The irregularities inside a single “stream” are almost isotropic. We discuss the restrictions imposed on operation of decimeter VLBI systems due to effects of the interplanetary medium.

INTERNATIONAL LOW-FREQUENCY VERY-LONG-BASELINE INTERFEROMETRY NETWORK PROJECT MILESTONES

The low-frequency very-long-baseline interferometry network (LFVN) project was started in 1996, having the purpose to arrange the international very-long-baseline interferometry (VLBI) cooperation with participation of former Soviet Union radio telescopes. Currently there are three directions of LFVN development: a Mk 2 subsystem at 92 cm wavelength for solar research, an international S2 ad hoc array at 18 cm for active Galactic nuclei and OH-maser survey, and VLBI radar at 6 cm for investigation of Solar System bodies. 14 VLBI experiments were carried out using various combinations of radio telescopes in Canada, China, England, India, Italy, Japan, Latvia, Poland, Russia, South Africa, Ukraine and USA. The five sessions were processed by the Jet Propulsion Laboratory (California Institute of Technology) Block II and Dominion Radio Astrophysics Laboratory Penticton correlators. The Russian Mk 2 correlator in Nizhny Novgorod is under development. The paper describes the main project milestones, results ob...

First Results of the VLBI Experiment on Radar Location of the Asteroid 2012 DA14

Abstract An international VLBI experiment on radio location of the asteroid 2012 DA14 was organized on 2013 February 15–16, during its flyby close to Earth. The purpose of observations was to investigate and specify orbital parameters of the asteroid, as well as to evaluate its rotation period and other characteristics. The irradiation of the asteroid was performed by the RT-70 transmitter at Evpatoria (Crimea, Ukraine), while the reflected signals were successfully accepted by the two 32 m radio telescopes at Medicina (Bologna, Italy) and Irbene (Ventspils, Latvia). Processing and interpretation of the data were performed both in the Radiophysical Research Institute at Nizhny Novgorod and in the Ventspils International Radio Astronomy Center. The first results of this experiment are presented and discussed.

Measurements of Interferometer Parameters at Reception of GLONASS and GPS Signals

Abstract The present paper deals with the calibration method of interferometers with antennas having a small effective area, on the quasinoise signals of GLONASS and GPS navigation satellites. Algorithms for calculation of antenna coordinates and instrumental delay from the analysis of correlation interferometer response to signals of satellites in the near field of the instrument were reviewed. The method was tested in VLBI experiments on interferometers with medium and large baselines that included radio telescopes of NIRFI and VIRAC. The values of the antenna coordinates and instrumental delay with an error within the limits of one discrete were obtained. The sources of measurement errors and ways to improve the accuracy of results were analysed.

Radio Interferometric Research of Ionosphere by Signals of Space Satellites

Abstract Since 2012, the Radiophysical Research Institute and the Lobachevsky State University at Nizhny Novgorod, Russia and the Ventspils International Radio Astronomy Centre at Irbene, Latvia are making radio interferometric experiments on study of ionosphere parameters in a quiet (natural) state of medium and research of artificial turbulence of the ionosphere, heated by the emission from the SURA facility. Remote diagnostics of the ionosphere is implemented using a method of radio sounding by signals of navigation satellites in combination with the Very Long Baseline Interferometry (VLBI) method. As a result of spectral and correlation analysis, interferometric responses of the two-element (RRI–UNN) and three-element (RRI–UNN–Irbene) interferometers were received by observations of 12 satellites of the navigation systems GLONASS and GPS. Here the first results are reported.

AN EXPERIMENT ON RADIO LOCATION OF OBJECTS IN THE NEAR-EARTH SPACE WITH VLBI IN 2012

Abstract An experiment on radar location of space debris objects using of the method of VLBI was carried out in April, 2012. The radar VLBI experiment consisted in irradiation of some space debris objects (4 rocket stages and 5 inactive satellites) with a signal of the transmitter with RT-70 in Evpatoria, Ukraine. Reflected signals were received by a complex of radio telescopes in the VLBI mode. The following VLBI stations took part in the observations: Ventspils (RT-32), Urumqi (RT-25), Medicina (RT-32) and Simeiz (RT-22). The experiment included measurements of the Doppler frequency shift and the delay for orbit refining, and measurements of the rotation period and sizes of objects by the amplitudes of output interferometer signals. The cross-correlation of VLBI-data is performed at a correlator NIRFI-4 of Radiophysical Research Institute (Nizhny Novgorod). Preliminary data processing resulted in the series of Doppler frequency shifts, which comprised the information on radial velocities of the objects. Some results of the experiment are presented.

VLBI-observations of Solar Wind Plasma by the method of radio raying; theory and experiments

We represent results of experiments on investigation of solar wind plasma by the method of radio sounding, when the signal from the radio source paths through the solar wind plasma and then it’s received at ground-based radiointerferometer. Heterogeneities of electron density of propagation media cause fluctuations of the received emission and distort the output signal of the instrument. The analysis of these disturbances allows to get information on physical characteristics of the propagation media. At using of VLBI the signals from the sources to separated antennas go through plasma by different paths. Relative fluctuations, arising at each trajectories, influent at the interferometer signal. The baseline projection onto the wavefront (100 km – 10000 km) determines the maximal heterogeneities’ scale, to which the interferometer is sensitive. Using interferometric complexes with various orientation of baseline projections allow to obtain information about spatial structure of solar wind plasma parameters. The observation of sources, located at different angular distances and position angles from the Sun let us to make certain conclusion about anisotropy of electron density of investigated medium. We carried out the analysis of international VLBI experiments on investigations of solar wind plasma, implemented in 1998, 1999, 2000. At the course of these experiments VLBI complex received the extragalactic source radio emission (wavelength 18 cm) passed through the turbulent plasma of solar wind. Radio sources were located at different angular distances from the Sun (4–37 degrees). These observations were realized with participation of radio telescopes, included at Low Frequency VLBI Network: Bear Lakes (RT-64, Russia), Puschino (RT-22, Russia), Hartebeesthock (RT-25, South Africa), Arecibo (RT-305, USA), Urumqi (RT-25, China), Noto (RT-25, Italy), Shanghai (RT-25, China), GMRT (RT-45, India). Preprocessing was carried out with using of S2 correlator at Penticton (Canada). We performed the post processing of experimental data. The results of spectral analysis of series realization were compared with theoretical conclusions, obtained before [1, 2].

Possibility of Fast Determination of Radio-Interferometer Parameters

We propose a method for fast determination and systematic monitoring of certain radio-interferometer parameters (the baseline projection and the mounting-site longitude). The method is based on reception of the emission from point radio sources at certain values of their hour angles with the subsequent processing of measurement results using a developed algorithm. We show that the method is applicable for determining the parameters of radio interferometers with both two- and one-channel receivers.