A New X-band Radar Based On Time-shifted Linear Frequency Modulated Signal And Current Measurement Algorithm

Ocean current is one of the main parameters of ocean dynamics,and its real-time monitoring is of great significance for marine ecology,maritime transportation,coastal economy,global climate,marine development,and the military.Satellite remote sensing images are expensive,have low repetitive sampling times,and are susceptible to severe ocean weather.Although in situ current measurement has high observation accuracy,its spatial coverage is limited and the observation cost is high,thus making its use difficult in understanding the temporal and spatial changes in ocean currents.Shore-based radars can continuously measure a current field in coastal waters in real-time,thus compensating for these shortcomings.Compared with in situ current measurement and remote sensing measurement,X-band radar has the advantages of low maintenance cost,convenient use,and high spatial resolution,but its current measurement accuracy cannot be guaranteed.The HF radar considers the Doppler information on the ocean current's motion,but there is no image near the radar due to interference.As the distance from the radar increases,the echo gradually weakens and the imaging gradually blurs.In addition,when using linear frequency modulated(LFM)signals to measure speed,most of them measure the speed of a single scattering point target,and do not consider the problem of interference between the upward LFM signal and downward LFM signal.This thesis proposes a new X-band shore-based radar that uses time-shifted up-and-down LFM signals,which can meet the requirements of current speed measurement accuracy and imaging.This thesis also explains in detail the measurement principle using up-and-down LFM signals,and proposes a new speed measurement and imaging algorithm.We use simulation to generate the sea surface parameter field first,and then use the time-shifted up-and-down LFM X-band radar to measure the current speed.When the current speed is 56.35cm/s,the rootmean-square error of the speed measurement is 2.78cm/s,while the speed measurement error using the simultaneously transmitted up-and-down LFM signals is 6.95cm/s.It is proved that the X-band shore-based radar based on the time-shifted up-and-down LFM signals greatly improves the speed measurement accuracy.This thesis analyzes the speed based on the proposed speed measurement algorithm.We found,as the wind speed increases,the current speed measurement error gradually decreased.With the area of the measurement area increases,the speed measurement error also decreased.Then,we perform multiple Monte Carlo experiments under the assumption of ideal conditions,analyzed the speed measurement accuracy different current speeds,proving that our proposed speed measurement algorithm has higher accuracy.Based on the proposed imaging algorithm,this paper also gives the specific imaging process and the relevant results.The results show that imaging algorithm we proposed can be imaged and is relatively clear.Finally,although our work is a forward-looking work,there are still shortcomings.We summarize and look forward the future of the next research.