Applications Of High Frequency Ground Wave Radar To Coastal Ocean

Based on the mechanism that the vertically polarized electromagnetic wave of high frequency can diffract along a curved sea surface without significant energy diminishing,high frequency ground wave radar(HF radar) can monitor the information of the sea surface current,sea wave,wind and slow-moving objects. Compared with traditional marine instrumentations,it can measure longer distance, larger coverage area,much more factors and operating under all weather conditions. It has the advantages such as lower cost,higher spatial resolution and sampling frequency by comparision wiith marine satellite remote sensing.So,HF radar observations are important supplements to ocean research.This thesis is supported by the National 863 Plan Fujian Demonstration and the OSMAR2003 HF radar produced by Wuhan University.Significant diurnal variations of the samples observed by HF radar can be detected at the beginning of radar operation through June to July,2005,and that the coverage range reaches～125km at 50%sampling rate.The spatial pattern of tidal distribution and propagation characters for radial currents are generally consisted with previous investigation,which shows that the radar observational results are reasonable.And the stability of radar operational is also confimed.Using the measurements from buoy ADP and bottom_mounted ADCP,the observation error of the Fujian Demostration OSMAR2003 sea currents is testified. The distance root mean squre(RMS) of the current speed series is the defined validition standard.The RMSs of radial current speeds in Dongshan and Longhai site are 7.6-12.5cm/s and the error of the radial current bearing is less than 10 degree,and the vector current speeds and u,v components range between 8.6-13.0cm/s respectively.The RMS of the under-way ADCP's currents in Taiwan Bank and tidal current forecasted by the radar observations is 10.4cm/s.The errors of most of HF radar currents are mainly 10-20cm/s,which possibly caused by instrument errors and observation target differences.The OSMAR2003 has the same level of measurement precision with those by the same type of radars used other countries.The longterm observation has also testified the stability of the OSMAR2003 radars.With the current observations by HF radar,some applications researches in Taiwan Strait ocean dynamical process have been conducted,as presented follows. Using winter-time observations,we obtain the fine features of surface tidal current in the Dongshan-Longhai coast area.The tidal current characters are consitent with previous results.And the tidal ellipse rotating zero line of the M₂ constitunent is located near to the Futou bay,which is much norther than that reported in previous result.The distribution pattern of the S₂ and O₁ constitunets are similar to the M₂,and the tidal current amplitudes are one-third and one-tenth of that for M₂,respectively. Impacted by both the southwardly resonance and the northwardly tidal wave,a counter-clockwise rotational zero current point of the K₁ constitunent appears in the west of the Penghu Island.The annual variations of the sea surface current in the west Taiwan Strait are investigatied by using the observations in 2006.The variaition of the surface current indicates two patterns:from Novermber to next May,it is winter-time pattern,with the left months being the summer-time pattern.The pattern transformation is much slowly from the winter to the summer with～2-3 months;whereas,it is much quick from summer to winter,with only 1 month.These variabilities are mainly caused by the seasonal monsoon.With the ADCPs' profile observations,the relationship between the longshore wind and current details the northward background circulation exists all the year around from the surface to the bottom with averaged speed～10cm/s, and being 10～20cm/s in spring and summer and smaller than 5cm/s in winter.Forced by the seasonal monsoons,the surface current is obviously wind drift,and the currents under the Ekman layer are northward all the year.The original study of the sub-tidal fluctuations for the winter surface current in radar coverage area is explored,and the longshore component is the primary.The wind,sea current and sea level show similar variations with the significant periods of fluctuations being 8d,4.6d,3.2d and 2.3d.The 4.6d and 3.2d significant periods of current fluctuation are both affected by remote wind and local wind,with the former mainly effecting 4.6d and the latter affecting 3.2d.The sea level and current fluctuations of 2.3d significant period are not affected by the wind field metioned above.We also investigate the response of the near sea area to the typhoons' passages. Based on one case of the ocean inertial oscillations in the northern shelf of the South China Sea,we analyses the response of the Taiwan Strait to the No.0519 typhoon Longwang with the OSMAR2003 observations.And we find that,the effecting duration of typhoon is about～4-5 days and the current response is expeditious,the current direction changes with the wind direction and,current fields return to strong tidal force condition rapidly without any inertial oscillation occurring.By using the two year observations of the HF radar system in the Fujian Demonstration,we comprehensively summarize many aspects of HF radar in this thesis;also validate the measurement error of the OSMAR2003 radar,and exploit many application researches on the tidal currents,sea currents,sub-tidal fluctuations and response process to typhoon passage in the observation area.We procees many basic works for developments and applications of HF radar and oceanography researches in the Taiwan Strait.