| The marine ecological environment has an important impact on global climate change,the health and development of human beings.Among them,phytoplankton chlorophyll-a,suspended matter,CDOM(Colored Dissolved Organic Matter)and seawater optical parameters are important indicators for monitoring marine ecological environment and studying optical properties of seawater.As an active optical remote sensing equipment,oceanic lidar has the advantages of high spatio-temporal resolution and all day detection.The information of optical parameters such as attenuation coefficient of subsurface seawater,and the concentration of water color elements such as chlorophyll-a,suspended matter and CDOM can be retrieved,which show great prospects in wide applications.The use of lidar for marine environmental monitoring and research is the research goal of this thesis.In this thesis,a miniaturized Dual-field-of-view oceanic lidar system(Dual-Field-of-View Oceanic Lidar,DFOL)is designed,and a data processing method of oceanic lidar is proposed.The continuous and effective observation data of lidar are used to study the concentration of chlorophyll-a,suspended matter and the attenuation coefficient of seawater in surface layer,which provides technical tools and research methods for the analysis and application of lidar data.In specific,the work and main achievements of the thesis are as follows:(1)Complete the design of DFOL.DFOL is mainly composed of a transmitting subsystem,a receiving subsystem,and a data acquisition and control subsystem.It employs a dual field of view receiving mode,which can control the receiving field of different echo signals,and solve the problem of excessive attenuation of beam intensity caused by frequent splitting of multiple channels and single receiving field of view,meanwhile,the influence of mie scattering signal on fluorescence and Raman scattering signal can be reduced.Furthermore,it can improve the system signal-to-noise ratio,and achieve effective acquisition of water fluorescence signals,Raman signals,and mie scattering signals.Based on this scheme,the selection of key components and the development of the system have been completed.(2)The data acquisition software and echo signal simulation software of oceanic lidar,as well as laser power measurement software and scanning control software are designed and developed.To realize the control of data acquisition card and synchronous acquisition of echo signal,it also realizes the analysis of the intensity and signal-to-noise ratio of oceanic lidar echo signal,as well as the measurement of laser emission energy and the control of scanning orientation of platform.The working parameters of the software and the actual working state of each equipment are tested simultaneously.(3)The processing method of experimental data is proposed,the geometric overlap factor of DFOL paraxial channel is analyzed,and the performance test and calibration experiment are carried out in the laboratory.And then,the measurement experiment of chlorophyll-a concentration was carried out,and the correlation coefficient(R~2)between the result and chlorophyll fluorimeter/nephelometer(ACLW-CAR)was 0.94.Furthermore,the chlorophyll-a concentration values measured at different laser emission energies,laser incidence angles,or under higher concentrations tend to be consistent with the results of ACLW-CAR.In addition,the calibration experiments were carried out on the concentration of suspended matter with different particle sizes.It was further compared with the results from the ACLW-CAR,where the corresponding coefficient of determination was above 0.91.Through the experimental analysis,different particle size would affect the calibration formula of suspended matter concentration.(4)The shore observation experiment was carried out.Firstly,the maximum detection distance of DFOL was evaluated,and the near shore surface chlorophyll-a,suspended matter concentration and attenuation coefficient were observed online.The calibration formulas for the inversion of chlorophyll-a and suspension matter concentration,as well as the correction formula of attenuation coefficient are determined respectively.The correlation coefficients between the detection results of chlorophyll-a and suspended matter concentration and the measurement results of ACLW-CAR are 0.74and 0.86 respectively.In addition,the correlation coefficient between the detection results of attenuation coefficient and the measurement results of hyperspectral attenuation meter(VIPER G2)is 0.69.The feasibility of the application of the independently developed oceanic lidar for detection of chlorophyll-a,suspended matter concentration and attenuation coefficient in the seawater surface was preliminarily verified.The research of this thesis has a distinct demand orientation,which provides technical tools and research methods for marine lidar to detect seawater surface chlorophyll-a,suspended matter concentration and attenuation coefficient,and has an important practical significance.Finally,an outlook was also presently. |
PDF Full Text Request