基于水体固有光学特性的太湖浮游植物色素的定量反演

基于2005-05～2005-08对太湖全湖不同湖区92个样点吸收系数、光束衰减系数、后向散射系数等固有光学特性测定与计算,选择色素浓度反演的最佳波段组合,利用反射率比建立了太湖叶绿素a,叶绿素a与脱镁叶绿素的定量反演模型.结果表明,全湖4次采样叶绿素a、脱镁叶绿素的变化范围分别为3.9～149.8μg·L^-1、均值为(38.14±28.89)μg·L^-1;0～45.8μg·L^-1、均值为(8.49±7.24)μg·L^-1,存在很大空间差异,湖心区和草型湖区的东太湖、胥口湾、贡湖湾色素浓度一般要低于其他湖区.同样吸收系数和后向散射系数也存在很大的空间差异,a_t(440)的变化范围为0.86～23.25 m^-1、均值为(6.21±3.31)m^-1,b_t(550)的变化范围0.05～2.25m^-1、均值为(0.72±0.52)m^-1,东太湖、胥口湾、贡湖湾的值要低于其他湖区.400～650nm随波长增加总吸收系数大致呈下降趋势,680nm附近存在1个峰值,峰值的强弱与水体中色素浓度有关,而到720nm以后则逐渐增加,后向散射系数随波长增加则逐渐降低.反射率比R(706)/R(682)能较好地用于太湖色素浓度的反演,叶绿素a、叶绿素a与脱镁叶绿素之和幂函数反演的决定系数R²分别达0.823、0.864 5.模型能用于包括湖面反射率受湖底和沉水植物影响的全太湖.

Quantitative retrieval of phytoplankton pigment based on water inherent optical properties in Lake Taihu

Total 92 sampling waters were collected from different lake regions in Lake Taihu from May to August in 2005. Absorption coefficients of total particles and chromophoric dissolved organic matter (CDOM), beam attenuation coefficient, scattering coefficients, backscattering coefficients were measured and calculated. Spatial distributions of chlorophyll a, pheophytins concentrations, spectral features of total absorption coefficients and backscattering coefficients were also discussed. Chlorophyll a, pheophytins concentrations were in the range of 3.9 - 149.8 microg x L(-1) with a mean value of (38.14+/-28.89)microg x L(-1) ; 0 - 45.8 microg x(L-1) with a mean value of (8.49+/-7.24) microg x L(-1), respectively. A significant spatial difference was found for chlorophyll a, pheophytins concentrations with lower values in lake center, and typical macrophyte lake regions such as East Lake Taihu, Xukou Bay and Gonghu Bay. Similar significant spatial difference was found for total absorption coefficients and backscattering coefficients with lower values in typical macrophyte lake regions such as East Lake Taihu, Xukou Bay and Gonghu Bay. at(440) and bt(550) ranged from 0.86 to 23.25m(-1) with a mean value of (6.21+/-33.31)(m1)', from 0.05 to 2.25(m-)1 with a mean value of (0.72 +/-0.52)m(-1). Total absorption coefficients increased from 00 to 650nm with a peak near 680nm and increased from 720 to 750nm due to pure water absorption. Total backscattering coefficients generally decreased from 400 to 750nm An optimum band combination of reflectance R (706)/R (682) was selected to model chlorophyll a, pheophytins concentrations in Lake Taihu. Determination coefficients retrieving chlorophyll a concentrations, sum of chlorophyll a and pheophytins concentrations were 0.823, 0.864 5 based on reflectance ratio R (706) /R (682), respectively. Retrieval model of phytoplankton pigment can be used to all the lake including macrophyte lake regions with leaving-water reflectance affected by lake sediment and submerged plants.