HiFAST: An H i Data Calibration and Imaging Pipeline for FAST. III. Standing Wave Removal

Abstract The standing waves existing in radio telescope data are primarily due to reflections among the instruments, which significantly impact the spectral quality of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Eliminating these standing waves for FAST is challenging given the constant changes in their phases and amplitudes. Over a ten-second period, the phases shift by 18° while the amplitudes fluctuate by 6 mK. Thus, we developed the fast Fourier transform (FFT) filter method to eliminate these standing waves for every individual spectrum. The FFT filter can decrease the rms from 3.2 to 1.15 times the theoretical estimate. Compared to other methods such as sine fitting and running median, the FFT filter achieves a median rms of approximately 1.2 times the theoretical expectation and the smallest scatter at 12%. Additionally, the FFT filter method avoids the flux loss issue encountered with some other methods. The FFT is also efficient in detecting harmonic radio frequency interference (RFI). In the FAST data, we identified three distinct types of harmonic RFI, each with amplitudes exceeding 100 mK and intrinsic frequency periods of 8.1, 0.5, and 0.37 MHz, respectively. The FFT filter, proven as the most effective method, is integrated into the H i data calibration and imaging pipeline for FAST (HiFAST, https://hifast.readthedocs.io ).

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Publication Details

Journal
Research in Astronomy and Astrophysics
Published
2024-11-22
DOI
https://doi.org/10.1088/1674-4527/ad9653
Citations
4
Primary Topic
Advanced Computational Techniques and Applications
Type
article
Field-Weighted Citation Impact
1.39

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HiFAST: An H i Data Calibration and Imaging Pipeline for FAST. III. Standing Wave Removal

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HiFAST: An H i Data Calibration and Imaging Pipeline for FAST. III. Standing Wave Removal

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article en
4 citations

Abstract

Abstract The standing waves existing in radio telescope data are primarily due to reflections among the instruments, which significantly impact the spectral quality of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Eliminating these standing waves for FAST is challenging given the constant changes in their phases and amplitudes. Over a ten-second period, the phases shift by 18° while the amplitudes fluctuate by 6 mK. Thus, we developed the fast Fourier transform (FFT) filter method to eliminate these standing waves for every individual spectrum. The FFT filter can decrease the rms from 3.2 to 1.15 times the theoretical estimate. Compared to other methods such as sine fitting and running median, the FFT filter achieves a median rms of approximately 1.2 times the theoretical expectation and the smallest scatter at 12%. Additionally, the FFT filter method avoids the flux loss issue encountered with some other methods. The FFT is also efficient in detecting harmonic radio frequency interference (RFI). In the FAST data, we identified three distinct types of harmonic RFI, each with amplitudes exceeding 100 mK and intrinsic frequency periods of 8.1, 0.5, and 0.37 MHz, respectively. The FFT filter, proven as the most effective method, is integrated into the H i data calibration and imaging pipeline for FAST (HiFAST, https://hifast.readthedocs.io ).

Research in Astronomy and AstrophysicsVol. 25(1)
University of Science and Technology of China (CN), Guizhou University (CN), Chinese Academy of Sciences (CN), Beijing Normal University (CN), National Space Science Center (CN), National Astronomical Observatories (CN)
National Natural Science Foundation of China, Chinese Academy of Sciences, National Astronomical Observatories, Chinese Academy of Sciences
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Advanced Computational Techniques and Applications
1.39
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