Measuring the frequency Doppler shift of the radio waves reflected by the ionosphere is a classic technique for detecting the ionospheric disturbances.This paper describes a newly developed instrument in terms of the system architecture,the digital data flow and the methods for data post-processing.The instrument uses a universal software-defined radio platform as the frontend outputting wideband digital signals.The processing procedure,including the frequency selection,low-pass filter,and downsampling,is implemented in the software running on the host computer.This architecture offers the flexibility of freely changing the receiving frequency and optimizing the data flow,and reduces the system complexity and development cost.The methods of fast Fourier transform(FFT)and Hilbert transform to retrieve the frequency Doppler shift are examined.The two methods give similar results for monochromatic variations of the ionosphere,thought the FFT method has the ability to discriminate multiple Doppler frequencies;the Hilbert transform has the advantage of high time resolution.We further validate the instrument by comparing the data with an ionosonde,and calculate the velocity of a travelling ionospheric disturbance using three observation sites.The experiments validate the capability and reliability of the new instrument,which has replaced its predecessors of the Chinese Meridian Project,and will be deployed at 12 sites of the Phase Ⅱ network.
关键词
电离层扰动/电离层高频多普勒频移/软件无线电/子午工程
Key words
ionospheric disturbances/ionospheric high-frequency Doppler sounding/software-defined radio/Chinese Meridian Project
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