基于高光谱反演的南海浮游植物剖面分布特征及其与环境要素的关联

Research studies about the vertical variation of phytoplankton and its environmental driving mechanism are crucial for studying the marine ecosystem dynamics in South China Sea. Based on the optical characteristics of phytoplankton with varying biomass and community structures, optical inversion methods have been developed for monitoring phytoplankton distribution over different scales. Recently, new algorithms based on hyperspectral optical data have attracted much attention in the research studies of marine optics and remote sensing, which exhibited potential capability to exploit more spectral signatures of phytoplankton. Advances in hyperspectral optical measurement with high vertical resolution and the integration technique with multiple environmental sensors have provided us an important tool for investigating the vertical distribution of phytoplankton. .This project plans to perform multi-disciplinary comprehensive observation by integrating optical-hydrological-chemical sensors, and a large set of in situ profile data in the South China Sea will be collected during research cruises supported by the national natural science foundation. Phytoplankton profiles (including chlorophyll a concentration, diagnostic pigment composition and size classes) will be retrieved by interpreting the hyperspectral variability of optical properties with advanced data mining methods. Further studies about the vertical variations of phytoplankton in South China Sea and their connections with environmental variability (including nutrients, light, and thermocline) will be investigated by coupling the in situ measured multi-disciplinary data and remote sensing data. Our research results could provide important basis for studying the marine ecosystem dynamics in the South China Sea, which could also promote the development of marine hyperspectral optical observation in marine studies.

浮游植物剖面分布特征及环境影响机制是南海生态系统动力学研究的重要内容。浮游植物高光谱反演机理是近年来海洋光学和水色遥感研究的前沿热点问题。船载观测系统是目前获取高光谱水体光学特性的主要观测平台，进一步结合高分辨率光学剖面测量及多传感器集成同步观测优势，可为实现浮游植物剖面的综合观测研究提供重要手段。.本项目拟依托南海综合调查航次，集成海洋光学-水文学-化学等多学科传感器进行同步剖面观测；探索浮游植物剖面分布的高光谱反演机理，实现关键色素和粒级结构的定量反演及不同水层关键种群差异的分类识别；结合多学科参数剖面和多源卫星遥感，研究南海浮游植物剖面分布与环境要素（营养盐、光照、温跃层等）的关联。研究成果将推动海洋光学高光谱观测技术的发展，对于深入理解南海生态动力过程及响应机制具有重要科学意义。

浮游植物在海洋生物地球化学过程中扮演着关键角色，其剖面变化特征对于估算海洋初级生产力、揭示海洋动力过程的生态环境效应等具有重要的意义。.本项目从现场海洋生物光学调查数据出发,（1）探索了浮游植物色素结构的高光谱反演机理，建立了基于浮游植物吸收光谱、船载走航颗粒物吸收光谱以及剖面观测吸收光谱等反演典型色素浓度和种群结构的算法，展示了高光谱观测优势；同时指出针对部分种群信息，基于叶绿素a浓度的生物量算法也具有较好的反演效果，建议应用于遥感反演中可综合考虑多种算法的优势；（2）探讨了南海浮游植物剖面分布特征及其空间差异性，指出在沿岸水体叶绿素a浓度垂向分布存在多种类型；而外海水体剖面多呈现出典型的次表层极大值层（SCM）的特点；中尺度动力过程包括沿岸上升流、中尺度涡旋、黑潮水入侵等的调控作用明显；（3）研究了南海夏季外海层化水体中SCM的分布规律，采用指数幂分布函数进行了参数化模拟，与传统采用的高斯函数相比具有一定的优势；进一步综合同步观测的多学科数据，揭示了南海开阔水域SCM特征参数（包括厚度、深度和强度）与环境要素之间的关联，三个参数均表现出很大的空间变异性，如SCM深度在11到99 m之间变化，平均值为53 m; SCM的强度在0.12到4.47mg m-3之间变化。光衰减是影响其深度和强度变化的一个重要因素；动力过程对SCM参数变化的影响也很强，表现在SCM深度与温跃层深度（以1023Kg m-3等密度面深度为表征）之间的密切联系。以反气旋涡旋为例，水体通过下压等密度线同步加深营养盐跃层的深度，可能会加剧SCM层的营养盐限制，导致SCM深度加深，SCM强度减弱，叶绿素a在真光层内积分量下降。研究表明南海浮游植物剖面变化对环境动力过程响应明显，在估算南海海洋初级生产力的过程中不可忽略。.运用现场观测和卫星遥感数据，项目针对南海浮游植物碳含量的光学反演及时空分布差异也开展了初步探索。综合的研究成果为基于多平台生物光学观测阐明海洋动力过程影响下浮游植物分布及其生物地球化学过程提出重要参考。