The Experiment System Of Ocean Lidar With Variable Field-of-view And Laser Induced Fluorescence Study By ICCD

As an active remote sensing technology for detecting the ocean, Ocean Lidar takesadvantage of larger detection dynamic ranges, higher temporal resolution, and highefficiency measurement. It can be used to measure both the backscattering energyfrom seawater and marine fluorescence in order to obtain a variety of oceanographicparameters. Therefore, the development of Ocean Lidar shows a good perspective forfast and effective oceanographic survey.In terms of the estimation of seawater optical parameters by ocean Lidar, the elasticbackscattering power of laser photons is a decaying exponential function of theattenuation lengths through the water. Generally, the Lidar attenuation coefficient(K lidar) from traditional equation cannot be used to estimate more than one parameterof the water optical properties due to the limitation of only once measurement with asingle field-of-view (FOV). Recent researches show that the Lidar attenuationcoefficient of this exponential decay is strongly dependent on the FOV of Lidar andon the optical properties of seawater. Thus, an approach for compensating thedeficiency in the information from traditional Lidar by using return signals obtainedwith a variable FOV receiver becomes a frontier topic in ocean Lidar applications.Developing the Lidar with multiple or variable FOV is becoming a trend in theapplication of oceanographic Lidar.On the other hand, in the apppliaction of marine fluorescence detection,time-resolved fluorescence technology can be used to analyze the characteristics offluorescent substances, and to estimate the distribution of fluorescent material inseawater. This is also a hot topic in the application of ocean Lidar.In this dissertation, a shipboard ocean Lidar with variable field-of-view is developed to study these two issues and used to detect multiple ocean opticalparameters. According to different probing mechanisms, this work is divided into twoparts.The first part is the development of an ocean Lidar with variable FOV and itsexperimental study. The specific content includes three aspects:(1) On the basis ofhistorical models of ocean Lidar to detect water optical properties parameters, Lidarreturn signals are simulated under different FOVs for analyzing the relationshipbetweenK lidarand the water optical parameters, namely the absorption coefficienta, the attenuation coefficient c and the diffuse attenuation coefficientK d. Basedon Walker-McLean model and Kopilevich model, a method for extracting multipleoptical parameters of water was proposed in the case of shipborne ocean Lidar.(2)According to the theoretical simulation results, an appropriateness of FOV should beset at the range from10.0mrad to174.5mrad with considering the impact ofbackground noise, and a shipboard ocean lidar system with variable FOV is designed.In the cases of different FOVs, the optical properties parameters of water bodies aremeasured in the laboratory and Qingdao coastal area. The experimental results showthat this Lidar can be used to measure optical property parameters of seawater.The second part is the experimental study of ocean fluorescence lidar based on theICCD, which is divided into the following aspects:(1) In order to effectively analyzethe fluorescence characteristics of seawater, with an excitation source at355nm,ICCD is used to measure fluorescent substances in seawater, i.e. the ChromophoricDissolved Organic Matter (CDOM) and chlorophyll for analyzing the fluorescencelifetimes. And in the application of oil spill detection, time-resolved fluorescencespectroscopies of oil samples are analyzed by using the principal component analysis(PCA) method, and a method for enlarging spectral differences of different delaytimes is used to improve the recognition rate of the oil spill types.(2) The nonlinearfluorescence changes of chlorophyll and oil with saturated excitation are studied forsupporting the measurement of ocean fluorescence Lidar. For oil fluorescence undersaturated excitation, the offset of spectral peak and the nonlinear changes of fluorescence intensity are studied for identifying oil samples which can not bedistinguished from each other by using ordinary fluorescence spectra.The innovations of the dissertation included three points:(1) a set of shipboardocean lidar system with variable FOV was designed on the basis of theoreticalderivation and simulation;(2) On the basis of historical models of ocean Lidar, amethod for extracting multiple optical parameters of water was proposed in the caseof shipborne ocean Lidar.(3) The nonlinear changes of oil fluorescence undersaturated excitation are analyzed and the three-dimensional oil fluorescence spectrabased on the excitation light energy are used to identify oil samples.