Research Of The Information Extraction Method Of The Surface Currents By Using S Band Doppler Radar

Surface current is an important phenomenon in the ocean,to understand and master the movement of surface current,will help to study the mechanism of generation,growth,propagation and recession of it,also has a great significance in aquaculture,transport and pollution discharge in nearshore area.There are a lot of surface current detection equipments,one of them is the microwave Doppler radar,it has many advantages,such as high space-time resolution,good capacity of resisting disturbance,all-weather work and small volume,which make it have good application prospect.This paper focuses on the ocean surface current information extraction method,based on the S band Doppler radar as the platform which researched and developed by the Radio Ocean Remote Sensing Laboratory of WuHan University,this will expand the detection function of S band Doppler radar.S band Doppler radar broadcast electromagnetic waves,and on the surface of the ocean,capillary waves produce Bragg scattering,and the small scale of capillary waves are modulated by the big scale of gravity waves,they carry the characteristics information of gravity waves.Based on the dispersion relations of frequency and wavenumber of gravity waves,we can extract the surface current information.At present,based on the microwave Doppler radar,the research of surface current extraction methods are dual frequency measurement technology and the method of time average velocity sequence.We use a single shore-based station S band Doppler radar to do the research of extracting surface current in this paper by using the dispersion relation of frequency and wavenumber of gravity waves.Through processing the two-dimensional sequence of radial velocity from radar measuring,we can extract the surface current information.At first,this paper introduces the information extraction method of the surface currents by using S band Doppler radar:to do two-dimensional Fourier transform with the two-dimensional sequence of radial velocity from radar measuring,we can get the frequency wavenumber spectrum,after the power spectrum is calculated,we propose a method that band-pass filter combined with adaptive threshold to select the discrete fitting points,based on the dispersion relation of frequency and wavenumber of gravity waves,and the principle of weighted least squares,we can get the dispersion curve fitting of gravity waves,so as to extract the radial velocity.We can extract six radial velocities from six radar antenna data,and compound vector current to get the speed and direction information.The next,we do the simulated analysis by using this algorithm.Based on simulation data,we verify the validity of the algorithm.By known ocean wave spectrum model,and taking the surface current factors into consideration,we can simulate two-dimensional radial velocity that joined the surface current information.Based on simulation data,we use the algorithm to extract the radial velocity by single antenna data and compound the vector current,the caculated error is very small compared with the theoretical results,and it shows that the algorithm is correct.In the end,we use the extraction algorithm that introduced on this paper to get the surface current information by the data from the S band Doppler radar measuring.Aiming at the singularities exist in the measured data,we analyze the time-spatial two dimensional Doppler spectrum parameters,and propose the method that to do the data preprocessing with removing the singularities from time-spatial space.Based on the measured data with single antenna,we can extract radial velocity,and compound the vector current with six radial velocities.Combining with the measured data of ZheLang island and ZhuJiaJian,we use multi-point data and all day data to analysis,the results show that the algorithm is feasible.