Using GPS-GLONASS-GALILEO data and IRI modeling for ionospheric calibration of radio telescopes and radio interferometers

摘要

VHF and HF radio signals are widely used to observe the Sun and pulsars. Nowadays, large low-frequency radio astronomical arrays (LOFAR, 30-240MHz; MIRA, 80-300MHz) are being constructed to record radiation of pulsars at the maximum distance. registration of the solar radio emission intensity at fixed frequencies and in the spectral VHF band is very important along with other methods of monitoring of coronal mass ejections. Interpreting radio astronomical data is known to be necessary to take into account possible distortions of these signals in the Earth ionosphere. However, in contrast to modern navigation systems (Global Position System (GPS), GLObal NAvigation Satellite System (GLONASS), GALILEO), in which a very accurate reconstruction of ionosphere parameters is a built-in function, in present-day radio astronomy a retrieve of ionosphere transfer characteristics has not been appropriately worked out. This collides with increasing requirements to accuracy of the analysis of a radio emission amplitude profile and to the angular and polarizing resolution of radio telescopes of new generation (LOFAR, SKA, etc.). We have developed a method and software to calculate the ionosphere rotation measure (RM) and dispersion measure (DM). We used the ionosphere model IRI-2001, magnetic field model IGRF-10, and the ionosphere total electron content values obtained from GPS measurements. The obtained values of DM and RM were recalculated into characteristics of the phase delay, Faraday amplitude modulation, and polarization changes. We calculated ones for different levels of geomagnetic activity as well as different angular positions of radio sources. Our main idea is to use a signal of navigation satellites (CPS, GLONASS, GALILEO) as a testing signal from a "reference" source located at minimal angle distance from a source studied. Our project allows development of methods and systems of ADAPTIVE RADIO ASTRONOMY, adaptive to the non-uniform and non-stationary ionosphere, by analogy with known systems of adaptive optics intended to adapt optical telescopes to varying conditions of the optically non-uniform and non-stationary troposphere. (C) 2008 Elsevier Ltd. All rights reserved.