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Akitsugu Nadai Hiroshi Kuroiwa Masafumi Mizutori Shinnchi Sakai 《Journal of Oceanography》1999,55(1):13-30
The Communications Research Laboratory (CRL) has been developing high-frequency ocean surface radars (HFOSRs). The CRL dual-site HFOSR system can clarify the distribution of surface currents with a nominal range of 50 km. This paper presents a theoretical and experimental analysis of the measurement error of the current vector obtained by the CRL HFOSR system, using a comparison of instantaneous current vectors acquired by the HFOSR system and current meters moored at a depth of 2 m, taking account of the vertical current shear. The theoretical analysis shows that the probability distribution of the measurement error of the current vector forms concentric ellipses at a spatial scale that depends on the RMS measurement error of radial current velocity and with an aspect ratio that depends only on the azimuthal difference of the radar beams. When the azimuthal difference is a right angle, the measurement error of the current vector is at a minimum. A comparison between instantaneous current vectors measured by the CRL HFOSR system and moored current meters shows that the distribution of the difference vector between the radar current and the meter current agrees well with the theoretical measurement error of the current vector and that the RMS of difference vector length is about 10 cm s–1 while the azimuthal difference between two radar beams is between 45 and 135 degrees. The accuracy of current measurement by the dual-site HFOSR system is therefore considered to be less than 10 cm s–1 in this range of azimuthal difference. The theoretical analysis will be applicable for a wider range of the azimuthal difference of the radar beams. 相似文献
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Uemoto Jyunpei Moriyama Toshifumi Nadai Akitsugu Kojima Shoichiro Umehara Toshihiko 《Natural Hazards》2019,95(3):485-503
Natural Hazards - The recognition of landslides and making their inventory map are considered to be urgent tasks not only for damage estimation but also for planning rescue and restoration... 相似文献
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With the purpose of detecting periodic oscillations or waves in a quiescent prominence, temporal variations of a Ca ii K line profile have been studied. The most conspicuous phenomenon found here is the fact that the edge of the prominence showed, over some 20000 km along the spectrograph-slit, periodic velocity fluctuations of nearly the same phase with periods of 210–240 s and with an amplitude of up to ± 2 kms –1. At other portions, several different periods of peaks (160–400 s) can also be seen in the power spectra, but less distinctly. As to the intensity and the line width, however, no periodic variations have been detected. 相似文献
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Hidetaka Takeoka Yoshio Tanaka Yuichi Ohno Yukiharu Hisaki Akitsugu Nadai Hiroshi Kuroiwa 《Journal of Oceanography》1995,51(6):699-711
Observations of sea surface currents by HF radar were carried out in the Bungo Channel in summer 1992. The current ellipses of M2 constituent obtained by the observational results agree quite well with those obtained by the ADCP observations, showing that the accuracy of the HF radar measurements is of the same level as ADCP. The results revealed the current structures and their change with the Kyucho in detail. The Kyucho is influenced by the complicated coastal geometry and does not propagate straightly into the Bungo Channel. It propagates further inward after charging the coastal bays with warm water. The current directions change largely, since the currents turn around the stagnant region in the bay filled with the warm water. The northward intrusion begins to be weakened in the southern part of the channel, while it still persists in the northern part. The northward current speeds of the observed Kyucho are about 50 cm/s and sometimes attain 60 to 70 cm/s. 相似文献
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