RadioAstron Project. Calibration of the Space Radio Telescope in Flight — Automation of Data Processing

A. N. Ermakov, Yu. A. Kovalev

Transactions of IAA RAS, issue 54, 21–26 (2020)

DOI: 10.32876/ApplAstron.54.21-26

Keywords: RadioAstron, space telescope, main antenna parameters, SRT calibration, VLBI, telemetry, data processing automation

Abstract

Goals and objectives. Our present study is intended to automate the processing of calibration measurements in special observation sets by developing the new and updating the old software. We are attempting to develop the most complete automation of the data reduction and to use the results for the analysis of antenna parameters and calibration of Space Radio Telescope (SRT). Methods. The source data are binary files created by the standard telemetry system of the Spektr-R spacecraft with the RadioAstron Observatory on Board, based on the results of observations for astronomical calibrators in the mode of operation of the SRT as a single telescope. Automation is achieved by mass sequential processing of these files using the three key Programs. Program 1 converts input telemetry data into output text table, in which physical telemetry parameters are distributed in columns, and telemetry frames (time) are distributed in rows. Output data at wavelengths of 6.2, 18 and 92 cm (in the channels of the left and right circular polarizations) are made into a common table in form of a single output file. The data come to the input of Program 2, where using the standard regression and statistics methods (including the Singular Value Decomposition and the weighted averaging methods) the amplitudes in the voltage of the calibration source, the intrinsic noise of the SRT and four internal calibration noise signal sources per each polarization channel of the each wavelength band are obtained. These voltages for each polarization channel are written to text output lines in volts (one channel — one line). The strings are sent to the input of Program 3, where they are calibrated in a standard way and converted from the text strings with the measured voltages in volts to final text strings with units of spectral flux density (Jy) and with units of antenna temperatures (in K, through a known antenna gain). Conclusions. 1. In addition to the previous interactive processing tools, a new system CALIBR-SRT for automated reduction of radiometric data from interferometric receivers of the telescope has been developed. It was implemented in the current planned processing of observations under the RadioAstron project aimed at in-flight calibrating the SRT to the spectral flux density. 2. The system is designed to process the radiometric data obtained in special sets of measurements of primary calibration astronomical objects in 2011–2018 at the wavelengths of 6.2, 18 and 92 cm for channels of right and left circular polarizations. 3. The results obtained using the System were favourably compared to those of the previous Express processing tools in interactive mode. 4. Automation of mass measurements is achieved by the coordinated processing of a large amount of data using each of the three key programs. This approach can be also applied as a basis for data processing at the wavelength of 1.35 cm also. 5. Using the CALIBR-SRT system, the results of calibration have been obtained for SRT in flight in 2015–2018 at wavelenths of 6.2, 18 and 92 cm, relative to astronomical primary calibrators Cassiopeia-A and Crab Nebula in the spectral flux density scale [4] (it is presented to be published).

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