Retrieval Of Ocean Optical Parameters Based On Lidar Return

In recent years,the response of the oceans to global climate change has attracted the attention of all countries in the world.In the report of the 18 th National Congress of the Communist Party of China,it was pointed out that we should protect the marine environment,safeguard marine rights and interests,develop marine economy and build a powerful marine country.Ocean color remote sensing is one of the important ways to explore the ocean.It can realize the large-scale observation of ocean instantaneous information,and can also obtain long-term serial data for several years or even decades.It provides a huge database for the research of marine environmental protection,marine rights and interests maintenance and marine resources development.At present,the ocean data has entered the era of big data,but the main contribution is from the ocean surface data,the ocean vertical profile data is extremely scarce,so the breakthrough of a new generation of ocean exploration technology becomes extremely urgent.The ability of lidar to detect the vertical information of ocean makes it possible to become an important technical means to realize "three-dimensional telemetry".The lidar is independent of solar radiation and can work all day.It can not only obtain the precious ocean profile data,but also penetrate the subsurface layers of the ocean to reveal the ocean dynamic process.In this paper,the optical parameters of sea water and the subsurface layers detection in the South China Sea are studied by using lidar.The conclusions are as follows:(1)Based on the transmission performance of laser in the atmosphere,the air-sea interface and the ocean,the radiation transmission model of air-sea lidar is established by using Monte Carlo method.The influence of the optical characteristics of water body,multiple scattering,wind driven sea surface conditions,incidence angle of lidar and the stratified water body is analyzed.The relationship between the parameters of the lidar system and the optical parameters of the sea water is defined,which would provide a theoretical basis for lidar inversion algorithm.(2)Based on the Klett backward algorithm,a new inversion algorithm to retrieve ocean optical parameters from lidar return signal is proposed combing the bio-optical model.The reference value that the algorithm requried is determined by the slope method.The model attenuation coefficient of the water is calculated from the in-situ measured chlorophyll profile data.As the convergence value,it can determine the optimal backscatter extinction logarithmic ratio of the target water body and can improve the accuracy of the inversion method.In this paper,the lidar echo data of Wuzhizhou island in the South China Sea are retrieved by using this method,and are verified by the measured data.The results show that the algorithm can accurately retrieve the ocean attenuation coefficient.(3)In this paper,a new method of subsurface layers exploration is proposed,which is characterized by depth,thickness and intensity.Field experiments are carried out in the Sanya Bay of the South China Sea and the Qiandao Lake.The temporal and spatial distribution of subsurface characteristic factors is analyzed and verified by the measured chlorophyll profile data.In addition,the seasonal variation of the subsurface layers and the driving factors of the seasonal variation are analyzed.The results show that lidar has the potential to detect the subsurface layers of the ocean.