Radio interferometric imaging samples visibility data in the spatial frequency domain and then reconstructs the image.Because of the limited number of antennas,the sampling is usually sparse and noisy.Compressed sensi...Radio interferometric imaging samples visibility data in the spatial frequency domain and then reconstructs the image.Because of the limited number of antennas,the sampling is usually sparse and noisy.Compressed sensingbased on convex optimization is an effective reconstruction method for sparse sampling conditions.The hyperparameter for the l_(1)regularization term is an important parameter that directly affects the quality of the reconstructed image.If its value is too high,the image structure will be missed.If its value is too low,the image will have a low signal-to-noise ratio.The selection of hyperparameters under different levels of image noise is studied in this paper,and solar radio images are used as examples to analyze the optimization results of compressed sensing algorithms under different noise conditions.The simulation results show that when the salt-and-pepper noise density is between 10%and 30%,the compressed sensing algorithm obtains good reconstruction results.Moreover,the optimal hyperparameter value has a linear relationship with the noise density,and the mean squared error of regression is approximately 8.10×10^(-8).展开更多
Here we briefly present some design approaches for a multifrequency 96-antenna radioheliograph. The configuration of the array antenna, transmission lines and digital receivers is the main focus of this work. The radi...Here we briefly present some design approaches for a multifrequency 96-antenna radioheliograph. The configuration of the array antenna, transmission lines and digital receivers is the main focus of this work. The radioheliograph is a T-shaped centrally condensed radiointerferometer operating in the frequency range 4–8 GHz.The justification for the choice of such a configuration is discussed. The signals from antennas are transmitted to a workroom by analog optical links. The dynamic range and phase errors of the microwave-over-optical signal are considered. The signals after downconverting are processed by digital receivers for delay tracking and fringe stopping. The required step of delay tracking and data rates are considered. Two 3-bit data streams（I and Q） are transmitted to a correlator with the transceivers embedded in Field Programmed Gate Array chips and with PCI Express cables.展开更多
The Square Kilometre Array(SKA)is the largest radio interferometer under construction in the world.Its immense amount of visibility data poses a considerable challenge to the subsequent processing by the science data ...The Square Kilometre Array(SKA)is the largest radio interferometer under construction in the world.Its immense amount of visibility data poses a considerable challenge to the subsequent processing by the science data processor(SDP).Baseline dependent averaging(BDA),which reduces the amount of visibility data based on the baseline distribution of the radio interferometer,has become a focus of SKA SDP development.This paper developed and implemented a full-featured BDA module based on Radio Astronomy Simulation,Calibration and Imaging Library(RASCIL).Simulated observations were then performed with RASCIL based on a full-scale SKA1-LOW configuration.The performance of the BDA was systematically investigated and evaluated based on the simulated data.The experimental results confirmed that the amount of visibility data is reduced by about 50%to 85%for different time intervals(Δt_(max)).In addition,differentΔt_(max)have a significant effect on the imaging quality.The smallerΔt_(max)is,the smaller the degradation of imaging quality.展开更多
文摘Radio interferometric imaging samples visibility data in the spatial frequency domain and then reconstructs the image.Because of the limited number of antennas,the sampling is usually sparse and noisy.Compressed sensingbased on convex optimization is an effective reconstruction method for sparse sampling conditions.The hyperparameter for the l_(1)regularization term is an important parameter that directly affects the quality of the reconstructed image.If its value is too high,the image structure will be missed.If its value is too low,the image will have a low signal-to-noise ratio.The selection of hyperparameters under different levels of image noise is studied in this paper,and solar radio images are used as examples to analyze the optimization results of compressed sensing algorithms under different noise conditions.The simulation results show that when the salt-and-pepper noise density is between 10%and 30%,the compressed sensing algorithm obtains good reconstruction results.Moreover,the optimal hyperparameter value has a linear relationship with the noise density,and the mean squared error of regression is approximately 8.10×10^(-8).
基金supported by the Russian Foundation of Basic Research (12-02-91161, 12-02-00173, 12-02-10006 and 13-02-90472)a Marie Curie International Research Staff Exchange Scheme Fellowship within the 7th European Community Framework Programmesupported in part by grants from the Ministry of Education and Science of the Russian Federation (State Contracts 16.518.11.7065 and 02.740.11.0576)
文摘Here we briefly present some design approaches for a multifrequency 96-antenna radioheliograph. The configuration of the array antenna, transmission lines and digital receivers is the main focus of this work. The radioheliograph is a T-shaped centrally condensed radiointerferometer operating in the frequency range 4–8 GHz.The justification for the choice of such a configuration is discussed. The signals from antennas are transmitted to a workroom by analog optical links. The dynamic range and phase errors of the microwave-over-optical signal are considered. The signals after downconverting are processed by digital receivers for delay tracking and fringe stopping. The required step of delay tracking and data rates are considered. Two 3-bit data streams（I and Q） are transmitted to a correlator with the transceivers embedded in Field Programmed Gate Array chips and with PCI Express cables.
基金supported by the National SKA Program of China(2020SKA0110300)the Joint Research Fund in Astronomy(U1831204,U1931141)under cooperative agreement between the National Natural Science Foundation of China(NSFC)and the Chinese Academy of Sciences(CAS)+3 种基金the Funds for International Cooperation and Exchange of the National Natural Science Foundation of China(11961141001)the National Science Foundation for Young Scholars(11903009)supported by the Astronomical Big Data Joint Research Centerco-founded by National Astronomical Observatories,Chinese Academy of Sciences and Alibaba Cloud。
文摘The Square Kilometre Array(SKA)is the largest radio interferometer under construction in the world.Its immense amount of visibility data poses a considerable challenge to the subsequent processing by the science data processor(SDP).Baseline dependent averaging(BDA),which reduces the amount of visibility data based on the baseline distribution of the radio interferometer,has become a focus of SKA SDP development.This paper developed and implemented a full-featured BDA module based on Radio Astronomy Simulation,Calibration and Imaging Library(RASCIL).Simulated observations were then performed with RASCIL based on a full-scale SKA1-LOW configuration.The performance of the BDA was systematically investigated and evaluated based on the simulated data.The experimental results confirmed that the amount of visibility data is reduced by about 50%to 85%for different time intervals(Δt_(max)).In addition,differentΔt_(max)have a significant effect on the imaging quality.The smallerΔt_(max)is,the smaller the degradation of imaging quality.
