As a dedicated solar radioheliograph,the MingantU SpEctral RadioHeliograph(MUSER)has a maximum baseline of more than 3000 m and a frequency range of 400 MHz–15 GHz.According to the classical radio interferometry theo...As a dedicated solar radioheliograph,the MingantU SpEctral RadioHeliograph(MUSER)has a maximum baseline of more than 3000 m and a frequency range of 400 MHz–15 GHz.According to the classical radio interferometry theory,the non-coplanar baseline effect(i.e.,w-term effect)would be considered and calibrated for such a radio instrument.However,little previous literature made the qualitative or quantitative analyses on w-term effects of solar radioheliograph in-depth.This study proposes a complete quantitative analysis of w-term effects for the MUSER.After a brief introduction of the MUSER,we systematically investigate the baseline variations over a year and analyze the corresponding variations of w-term.We further studied the effects of the w-term in the imaging for the specified extended source,i.e.,the Sun.We discussed the possible effects of the w-term,such as image distortion and so on.The simulated results show that the w-term is an essential and unavoidable issue for solar radio imaging with high spatial resolution.展开更多
The Mingantu Spectral Radioheliograph(MUSER),a new generation of solar dedicated radio imagingspectroscopic telescope,has realized high-time,high-angular,and high-frequency resolution imaging of the Sun over an ultra-...The Mingantu Spectral Radioheliograph(MUSER),a new generation of solar dedicated radio imagingspectroscopic telescope,has realized high-time,high-angular,and high-frequency resolution imaging of the Sun over an ultra-broadband frequency range.Each pair of MUSER antennas measures the complex visibility in the aperture plane for each integration time and frequency channel.The corresponding radio image for each integration time and frequency channel is then obtained by inverse Fourier transformation of the visibility data.However,the phase of the complex visibility is severely corrupted by instrumental and propagation effects.Therefore,robust calibration procedures are vital in order to obtain high-fidelity radio images.While there are many calibration techniques available—e.g.,using redundant baselines,observing standard cosmic sources,or fitting the solar disk—to correct the visibility data for the above-mentioned phase errors,MUSER is configured with non-redundant baselines and the solar disk structure cannot always be exploited.Therefore it is desirable to develop alternative calibration methods in addition to these available techniques whenever appropriate for MUSER to obtain reliable radio images.In the case where a point-like calibration source contains an unknown position error,we have for the first time derived a mathematical model to describe the problem and proposed an optimization method to calibrate this unknown error by studying the offset of the positions of radio images over a certain period of the time interval.Simulation experiments and actual observational data analyses indicate that this method is valid and feasible.For MUSER’s practical data the calibrated position errors are within the spatial angular resolution of the instrument.This calibration method can also be used in other situations for radio aperture synthesis observations.展开更多
基金supported by the National SKA Program of China(2020SKA0110300)the Joint Research Fund in Astronomy(U1831204 and U1931141)+3 种基金the National Natural Science Foundation of China(NSFC)the Chinese Academy of Sciences(CAS)the Funds for International Cooperation and Exchange of the NSFC(11961141001)the NSFC(Grant No.11903009)。
文摘As a dedicated solar radioheliograph,the MingantU SpEctral RadioHeliograph(MUSER)has a maximum baseline of more than 3000 m and a frequency range of 400 MHz–15 GHz.According to the classical radio interferometry theory,the non-coplanar baseline effect(i.e.,w-term effect)would be considered and calibrated for such a radio instrument.However,little previous literature made the qualitative or quantitative analyses on w-term effects of solar radioheliograph in-depth.This study proposes a complete quantitative analysis of w-term effects for the MUSER.After a brief introduction of the MUSER,we systematically investigate the baseline variations over a year and analyze the corresponding variations of w-term.We further studied the effects of the w-term in the imaging for the specified extended source,i.e.,the Sun.We discussed the possible effects of the w-term,such as image distortion and so on.The simulated results show that the w-term is an essential and unavoidable issue for solar radio imaging with high spatial resolution.
基金supported by NSFC grants(11790301,11790305,11773043,U2031134,and 12003049)the National Key R&D Program of China(2021YFA1600500,2021YFA1600503,and 2018YFA0404602)+1 种基金supported by the National Major Scientific Research Facility Program of China with the Grant No.ZDYZ2009-3The MUSER calibration system is a part of the Chinese Meridian Project funded by China’s National Development and Reform Commission。
文摘The Mingantu Spectral Radioheliograph(MUSER),a new generation of solar dedicated radio imagingspectroscopic telescope,has realized high-time,high-angular,and high-frequency resolution imaging of the Sun over an ultra-broadband frequency range.Each pair of MUSER antennas measures the complex visibility in the aperture plane for each integration time and frequency channel.The corresponding radio image for each integration time and frequency channel is then obtained by inverse Fourier transformation of the visibility data.However,the phase of the complex visibility is severely corrupted by instrumental and propagation effects.Therefore,robust calibration procedures are vital in order to obtain high-fidelity radio images.While there are many calibration techniques available—e.g.,using redundant baselines,observing standard cosmic sources,or fitting the solar disk—to correct the visibility data for the above-mentioned phase errors,MUSER is configured with non-redundant baselines and the solar disk structure cannot always be exploited.Therefore it is desirable to develop alternative calibration methods in addition to these available techniques whenever appropriate for MUSER to obtain reliable radio images.In the case where a point-like calibration source contains an unknown position error,we have for the first time derived a mathematical model to describe the problem and proposed an optimization method to calibrate this unknown error by studying the offset of the positions of radio images over a certain period of the time interval.Simulation experiments and actual observational data analyses indicate that this method is valid and feasible.For MUSER’s practical data the calibrated position errors are within the spatial angular resolution of the instrument.This calibration method can also be used in other situations for radio aperture synthesis observations.
