南海典型海区浮游植物吸收光谱特征及遥感反演产品的精度评估

The spectral characteristics of phytoplankton absorption coefficient and assessment of MODIS-Aqua products in typical sea areas of the South China Sea

基于遥感手段准确估算浮游植物吸收系数a_(ph)(l),可为长时间、大尺度范围识别浮游植物功能种群提供有力的数据和方法支撑。利用2003至2012年获取自南海、琼东、广东近岸和珠江口各典型海区的实测a_(ph)(l)数据,对比分析表层光谱特征,初步判断浮游植物种群结构差异;基于MODIS-Aqua二级遥感反射率产品,分别采用经验算法PL和半分析算法QAA对a_(ph)(l)遥感产品进行精度评估。结果表明,以南海、琼东为代表的清洁海域和以广东沿岸、珠江口为代表的浑浊海域表层a_(ph)(l)光谱差异明显;a_(ph)(l)在清洁海域量值较小但在颗粒物吸收中居于主导,而在浑浊海域并不占优;浮游植物单位吸收系数a_(ph)*(l)存在明显的空间差异,色素打包效应以及色素组成是造成差异的可能原因。经验算法PL较之于半分析算法QAA反演得到的a_(ph)(l)(l=412,443,490)遥感产品精度更高,平均相对误差APD小于22%;采用区域优化算法NOCI获得的Chl-a产品作为输入参数,算法PL所得的a_(ph)(l)遥感产品APD不超过14%。结果表明,基于水色遥感产品进行a_(ph)(l)遥感产品精度评估和探讨不同海区浮游植物功能种群具有较强应用前景。

Using remote sensing to accurately estimate phytoplankton absorption coefficient aph(λ)can provide basic data and useful method to distinguish different functions of phytoplankton species for long time and large spatial scale.In this paper,the characteristics of aph(λ)spectral are compared and analyzed in four typical areas of the South China Sea(SCS),east area of Qiongdong(QD),Guangdong Coastal area(GD),and the Pearl River Estuary(PE)by using field data collected during2003-2012.Then,the phytoplankton population structure differences are preliminarily identified.Furthermore,the performances of MODIS-Aqua aph(λ)products derived from the semi-analytical algorithm QAA and empirical algorithm PL by using MODIS-Aqua remote sensing reflectance Rrs(λ)products are compared in the SCS and QD waters based on the relaxed match-ups between MODIS-Aqua products and field data.The results show the differences of aph(λ)spectral features are obvious among the clear water represented by the SCS and QD and turbid waters represented by GD and PE.In the clear waters,the aph(λ)value is small but in a dominant position of particle absorption,while in the GD and PE areas,the aph(λ)value is relatively large but not in a dominant position.The aph(λ)coefficient have obvious spatial differences,and the possible causes are pigment packaging effect and the variation of pigment composition and concentration.MODIS-Aqua aph(λ)products derived from the empirical algorithm PL perform better than those from the semi-analytical algorithm QAA.The algorithm QAA-derived aph(λ)products underestimate the results compared to the field data,while the algorithm PL overestimate the results,with the average relative error(APD)less than 22%for both algorithms.There is a great improvement in the accuracy of the PL algorithm by using the Chl-a products derived from the optimized algorithm of OCI(named algorithm NOCI),with the APD less than 14%.In summary,there are strong application prospects to discuss different functions of ocean phytoplankton species by using remote sensing products.