| Summary: | 博士 === 國立中央大學 === 水文與海洋科學研究所 === 105 === The content of this thesis is divided into two parts. The first part is the development of S-band radar and the second part is the development of coherent-on-receive radar.
The first part: The high spatial resolutions of sea-clutter image sequences from X-band radar offer a means of deriving individual waves and wave field at low-cost. However, the performance of X-band radar is impaired under rainy conditions, which are usually accompanied by the severe weather at sea. In the present study, we examine the effectiveness of S-band radar for wave measurements under precipitation. The results of comprehensive comparative studies with sea-truth data show that S-band radar is capable of carrying out wave measurements in rainy conditions. Although the longer wavelength of the S-band leads to a coarser resolution of radar imagery, the S-band radar features at least the equivalent performance of the X-band system in non-rainy conditions, in terms of wave height measurement. The results suggest that the S-band and X-band could be complementary systems. In rainy conditions the S-band is more efficient but in the non-rainy periods the X-band gives more confident results. The relationship of significant wave height with radar signal-to-noise ratio (SNR), and the modulation transfer function (MTF) between radar spectrum and wave spectrum for the used X-band and S-band radars are established and discussed in this paper.
The second part: In present study, an X-band marine radar was installed at the northwestern coast of Taiwan. The IF signal from the super-heterodyne receiver of the marine radar was retrieved, amplified, band-pass filtered and digitized to be the raw dataset, from which the phase of transmitted and echo radar EM wave could be determined. Based on Doppler theory, the time rate change of the phases between succeeding pulses could be used for estimating the water particle velocity of wave orbital motion. Due to the fact that the magnetron in the marine radar produces random frequency jump, and leading to mis-estimate of the phase differences. We adopted the Ensemble Empirical Mode Decomposition method as a filter to exclude the effects of frequency jump.
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