| 摘要(英) |
The Chung-Li VHF radar group at National Central University has developed an ocean radar operating at VHF 52 MHz to exclusively observe the ocean wave and current. The 52 MHz sea radar was deployed on the seashore of Xinwu District in late October, 2015 and at Fangliao coast offshore in late June and early July, 2016, respectively, to collect the radar returns. During an experimental campaign collaborated with Taiwan Ocean Research Institute (TORI), we compared the VHF sea radar-measured radial velocities with those observed by Coastal Ocean Dynamics Applications Radar (CODAR) operated at 5.38 MHz. The comparisons of wind direction detected by a Lidar and retrieved by the VHF sea radar were also made in this study.
The Fast Fourier Transform (FFT) algorithm was utilized to derive the Doppler spectrum of the sea echoes. The incoherent integration was used to reduce the fluctuations of the random echo signals. In this study, we develop an new algorithm based on the method of moment and Root-Mean-Square-Error (RMSE) to determine the spectral peak location of the first-order sea echoes. We find that the sea echo intensities observed at Xinwu District were modulated by a salient and regular semidiurnal oscillation. After comparing with the in-situ measurements made with a local tidal gauge, it is believed that this semidiurnal oscillation in the echo power intensity is the result of lunar semidiurnal tide. We also analyzed the radial velocities of the sea echoes detected by the VHF radar and CODAR HF radar, which are associated with the ocean current in the echoing region. A comparison shows that noticeable difference in the radial velocities between VHF and HF radars is found. On the basis of the theory proposed by Fernandez et al. [1997], the surface wind directions extracted from the ratio of negative to positive first-order spectral peak values were compared with the measurement of the Lidar. The result indicates that the values of spreading parameter (s) at Fangliao station are in the range of 2-3 that is in good agreement with other results. |
| 參考文獻 |
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