基于浮标观测的东海赤潮高发区秋、冬季漫射衰减系数的反演

浮标测量的光学数据时间序列长、分辨率高, 能可靠地测量快速变化的漫射衰减系数(K_d)。东海赤潮高发区水体中的浮游植物生物量及悬浮泥沙含量存在较大的变化, 光学性质复杂。文章利用2013年9月至2014年1月的海洋光学浮标数据, 获得了该海域水体的表观光学特性, 基于K_d(490)与遥感反射比[R_rs(λ)]的相关关系建立了K_d(490)的经验算法, 并与已有7种反演算法进行了比较。结果表明, 该海域的K_d(λ)及R_rs(λ)具有显著的Ⅱ类水体光谱特征, 其中, K_d(490)的范围为0.01~4.31m^-1, 水体的浑浊程度变化大。K_d(490)与R_rs比值的相关性较好, 据此建立了以R_rs(650)/R_rs(510)、R_rs(555)/R_rs(510)作为自变量的K_d(490)双比值经验算法。将新建算法反演获得的K_d(490)与实测K_d(490)相比, 均方根误差、平均相对误差百分比和线性回归的决定系数分别为0.27m^-1、27.08%和0.77, 优于其他7种算法。算法精度的提高源于新建算法选择的R_rs能充分反映水体信息, 并适应水体组分的变化, 可为东海赤潮高发区K_d(490)的反演提供较好的选择, 并为海洋光学浮标在水体环境监测中的应用提供示例。

Retrieval of diffuse attenuation coefficient in high frequency red tide area of the East China Sea based on buoy observation

The optical data measured by a buoy, with long time series and high temporal resolution, can be reliably used for obtaining the rapidly changing diffuse attenuation coefficient (K_d). The biomass of phytoplankton and the concentration of suspended sediment vary widely in the high-incidence red tide area of the East China Sea, resulting in complex changes in optical properties. In this article, the spectrum data collected by a marine optical buoy from September 2013 to January 2014 were used to obtain the apparent optical characteristics of the sea area, then an empirical algorithm of K_d(490) was established based on the correlation between K_d(490) and remote sensing reflectance (R_rs(λ)), and compared with seven kinds of existing algorithms. The results indicated that K_d(λ) and R_rs(λ) present significant features of class Ⅱ water body spectrum, K_d(490) varies from 0.01 m^-1 to 4.31 m^-1, and the turbidity also varies greatly. According to the good correlation of K_d(490) and R_rs band ratio, a dual-band ratio empirical algorithm was established, taking R_rs(650) / R_rs(510) and R_rs(555) / R_rs(510) as independent variables. New algorithm is superior to the other seven algorithms, the root mean square error, absolute percentage difference and coefficient of correlation coefficient are 0.27 m ^-1, 27.08 % and 0.77, respectively, between the new algorithm inversion K_d(490) and the measured values. The improvement of the accuracy of the algorithm is due to the fact that the R_rs selected by the new algorithm can fully reflect water body information and adapt to the changes of water composition in this sea area. This study provides a better choice for the inversion of the high-incidence red tide area in the East China Sea, and an example for the application of marine optical buoy in water environment monitoring.