渤海海冰漫射衰减系数的遥感估算

Sea ice is important in the marine system. It plays a key role in the global climate change. The sea ice will weaken the solar irradiance. Thereby, studying the energy budget in atmosphere-sea ice-sea water and biology community both in sea ice and water, should take care of the downwelling attenuation coefficient of sea ice(Kd). A theory will be studied to infer the Kd with the remote sensing data basing a radiative transfer model. This new method will be very useful for people to study the Kd in large region in the future. . The Bohai sea is an ideal place which is suitable for this study. A new method will be developed for observing the irradiance in the Bohai sea ice. It will study the reason which caused the changing of upwelling and downwelling irradiance in sea ice. The inherent optical properties of sea ice (absorbing (a) and scattering (b) coefficient, and the asymmetrical parameter (g)) would be inferred with a radiative transfer model. Then, a relationship between the inherent optical properties and Kd will be established. As a result, an remote sensing optical model is established after being validated and improved with the filed data. After separating the ice from sea water, inferring the ice thickness and reflective with the remote sensing data, this model can further to get the Kd in the Bohai sea.

海冰作为海洋系统的重要组成部分，在全球气候变化中起关键作用。海冰对太阳光辐射的衰减作用，是调控大气-海冰-海水界面能量收支的重要因子，同时也是决定冰下生态系统中光辐射分布特征的关键因素。基于光辐射传输模型，探索海冰光衰减系数的遥感反演机理，尝试以卫星作为新的观测手段，对于大区域空间上海冰光衰减分布特性的研究具有重要的意义。. 本项目以渤海海冰为研究对象，拟采用新的观测方案测量海冰上下界面及冰层内部太阳光谱辐射，深入研究上行及下行漫射衰减系数的变化特征及影响因素；建立耦合海冰及冰下海水层的光辐射传输模型，以海冰固有光学参量（包括吸收系数、散射系数和散射非对称性参数）和海冰厚度为中间参数，构建海冰反射率与漫射衰减系数之间的关系模型。基于现场观测数据改进现有模型，实现冰水分离、海冰厚度和反射率光谱的遥感提取，进一步实现对渤海海冰光衰减系数的遥感估算。

在北极海域，约有30%的光透射进入冰面以下，在冰层及其下层海水中进行分配。这部分的辐射能量对海洋上层的物理结构及生物生境具有重要作用。为了客观描述海冰内太阳辐射传输过程，引入了海冰漫射衰减系数（"K" _"d" (λ)）。海冰作为全球海洋系统的重要组成部分，建立其漫衰减系数与Albedo之间的关系，实现海冰"K" _"d" (λ)分布的遥感估算对研究冰区生态系统结构具有重要意义。但由于海冰"K" _"d" (λ)测量技术的局限及现场作业环境的恶劣，海冰光学性质的实测数据集很难获取，直接导致海冰遥感远远滞后于海洋水色遥感的发展。我们于2018年在渤海辽东湾进行了海冰光学特性的现场调查，获取了60组匹配的"K" _"d" 及Albedo数据集以及118组Albedo与颗粒物浓度数据集。然而获得的数据仍不足以支撑海冰"K" _"d" (λ)反演算法的开发，幸运的是，海水的辐射传输理论与海冰具有相似性。为了促进研究进程，先利用中国近海海水"K" _"d" (λ)数据集，开发了一个海水"K" _"d" (λ)的经验反演算法，并发现水色遥感中应用最为广泛的"K" _"d" (λ)半分析算法能够用于海冰"K" _"d" (λ)的反演，为海冰"K" _"d" (λ)的反演奠定了基础。另外，我们在渤海湾海冰光学性质与温度相关性的观测中发现，海冰的"K" _"d" (λ)对于温度变化的产生强烈正反馈。为了进一步确认这一现象，采用逐步优化的仪器，又分别在冰箱、温控实验室(TCL)、海冰环境研究设施(SERF)进行了3个独立实验。实验结果表明海冰漫射衰减系数与温度之间确实存在显著的负相关性，这对于预测气候变化下海冰的发展变迁具有重要意义，也为我们从温度变化的角度来判断海冰"K" _"d" (λ)的变化提供了理论基础。