| 摘要(英) |
The distance between the Chunge-Li VHF radar station and Taiwan Taoyuan International Airport is about 12km. In the meanwhile, the Chunge-Li VHF radar station locates in the lane of the taking-off or landing airplane. When the missions of observing the atmosphere are performed by Chunge-Li VHF radar, the echo signal is always polluted by the echo power of the crossing-radar-beam airplane, so the quality of the atmospheric data would be influenced and low quality. However, in the paper, [洪萱芸, 2020], an algorithm was proposed firstly. The algorithm can filter out the signal of airplane by Hilbert-Huang Transform (HHT). The result of the algorithm is better than the result by using Wavelet Transform. The algorithm greatly improves the quality of the observation data. However, the condition is only for the vertical beam and the result of the algorithm isn’t applied to be calculated the 3-D wind field by Velocity-Azimuth Display (VAD) technology、raindrop size distribution …etc. Thus, this study attempts to find the adapting parameter in the algorithm to apply in the observation of the oblique beam. After the aircraft echo is filtered out, the result will try to calculate the 3-D wind field by Velocity-Azimuth Display (VAD) technology. Finally, the wind field would be compared with Central Weather Bureau wind profiler(449MHz) result, and the application would be further discussed.
Through the algorithm, the high frequency component of aircraft echo would be filtered out. However, if the aircraft echo contained the low-frequency component or the problem of mixing wave from doing Empirical Mode Decomposition (EMD), there would be anomalous strong signal at low-frequency of the spectrum. With these problems, the algorithm should be modified. The way is that, with the DC terms of the real part (In-Phase, I) and imaginary part (Quadrature, Q), the amplitude at the time of aircraft echo on the I and Q is replaced. The time of aircraft echo is still detected by the HHT. This algorithm is named “DC term replacement”. Finally, the root-mean-square error(RMSE) and correlation coefficient between the 3-D wind field by “filtering out by HHT” or “DC term replacing” and the wind field of the Central Weather Bureau (CWB) wind profiler can be calculated. In the meanwhile, two indexes between the wind field before filtered out and the wind field of CWB wind profiler can also be calculated. A comparison with two parameters of three different conditions would be made. Not only “filtering out” but also “DC term replacing” result can be more greatly improved than the result before filtered out. To the other condition, the comparison between “no aircraft”、“filtering out” and “DC term replacing” should be made. The results of “filtering out” and “DC term replacing” still need to be improved by comparing with the result of “no aircraft”. To the results of “filtering out” and “DC term replacing”, it is comparable each other. But, visually, the spectrum of “DC term replacement” is more reasonable. Eventually, DC term replacement would be recommended.
The distance between the Chunge-Li VHF radar station and Taiwan Taoyuan International Airport is about 12km. In the meanwhile, the Chunge-Li VHF radar station locates in the lane of the taking-off or landing airplane. When the missions of observing the atmosphere are performed by Chunge-Li VHF radar, the echo signal is always polluted by the echo power of the crossing-radar-beam airplane, so the quality of the atmospheric data would be influenced and low quality. However, in the paper, [洪萱芸, 2020], an algorithm was proposed firstly. The algorithm can filter out the signal of airplane by Hilbert-Huang Transform (HHT). The result of the algorithm is better than the result by using Wavelet Transform. The algorithm greatly improves the quality of the observation data. However, the condition is only for the vertical beam and the result of the algorithm isn’t applied to be calculated the 3-D wind field by Velocity-Azimuth Display (VAD) technology、raindrop size distribution …etc. Thus, this study attempts to find the adapting parameter in the algorithm to apply in the observation of the oblique beam. After the aircraft echo is filtered out, the result will try to calculate the 3-D wind field by Velocity-Azimuth Display (VAD) technology. Finally, the wind field would be compared with Central Weather Bureau wind profiler(449MHz) result, and the application would be further discussed.
Through the algorithm, the high frequency component of aircraft echo would be filtered out. However, if the aircraft echo contained the low-frequency component or the problem of mixing wave from doing Empirical Mode Decomposition (EMD), there would be anomalous strong signal at low-frequency of the spectrum. With these problems, the algorithm should be modified. The way is that, with the DC terms of the real part (In-Phase, I) and imaginary part (Quadrature, Q), the amplitude at the time of aircraft echo on the I and Q is replaced. The time of aircraft echo is still detected by the HHT. This algorithm is named “DC term replacement”. Finally, the root-mean-square error(RMSE) and correlation coefficient between the 3-D wind field by “filtering out by HHT” or “DC term replacing” and the wind field of the Central Weather Bureau (CWB) wind profiler can be calculated. In the meanwhile, two indexes between the wind field before filtered out and the wind field of CWB wind profiler can also be calculated. A comparison with two parameters of three different conditions would be made. Not only “filtering out” but also “DC term replacing” result can be more greatly improved than the result before filtered out. To the other condition, the comparison between “no aircraft”、“filtering out” and “DC term replacing” should be made. The results of “filtering out” and “DC term replacing” still need to be improved by comparing with the result of “no aircraft”. To the results of “filtering out” and “DC term replacing”, it is comparable each other. But, visually, the spectrum of “DC term replacement” is more reasonable. Eventually, DC term replacement would be recommended. |
| 參考文獻 |
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