Journal of Geo-information Science >
Phytoplankton Backscattering Coefficients Partitioning and Its Applications in Retrieving Chlorophyll-a Concentrations in Taihu Lake
Received date: 2014-03-17
Request revised date: 2014-04-18
Online published: 2014-11-01
Copyright
As key parameters in bio-optical model, the backscattering coefficients of phytoplankton plays an important role in modelling the reflectance spectra and retrieving chlorophyll-a (CHL-a) concentrations from eutrophic water. An exponential model is usually used to simulate the total backscattering coefficients by omitting the phytoplankton backscattering in inland water characterized by lower concentrations of CHL-a. However, the exponential model is not valid for inland water with high CHL-a concentrations, and high relative errors and residues may exist in retrieving the CHL-a concentrations in the algae blooming area, due to the errors made by omitting or introducing inaccurate backscattering coefficients of phytoplankton. Therefore, a precise determination of the phytoplankton backscattering coefficients is of great importance in retrieving chlorophyll-a concentrations. Based on the classical bio-optical model, we proposed a method to partition the phytoplankton backscattering coefficients. The variations of the backscattering coefficients of phytoplankton particles with wavelengths in 400~700 nm and the chlorophyll-a concentrations are illustrated and discussed in details. According to the results mentioned above, following conclusions are drawn: (a) it is appropriate to model the total backscattering coefficients by using exponential function in most Case 2 waters with lower concentrations of Chlorophyll-a, where the non-algal suspended sediments dominated the optical properties. However, it is not applicable in eutrophic waters with higher concentrations of chlorophyll-a, where the algal particles dominated the optical properties; (b) phytoplankton backscattering coefficients vary inversely to their absorption coefficients, and two backscattering peaks emerge in the wavelengths of 560nm and 700nm, which are significantly correlated with CHL-a concentrations; (c) compare to the exponential model, the accuracy of the bio-optical model using the partitioned phytoplankton backscattering coefficients has improved greatly: the correlation coefficient between the retrieved and the measured CHL-a is increased from 0.66 to 0.98, the average relative error decreases from 55% to 38% , and the RMSE decreases from 60.95 to 13.98 in estimating CHL-a concentrations.
Key words: phytoplankton; backscattering coefficients; partitioning; eutrophic water
YAN Fuli , LIU Shaofei , WANG Shixin , ZHOU Yi . Phytoplankton Backscattering Coefficients Partitioning and Its Applications in Retrieving Chlorophyll-a Concentrations in Taihu Lake[J]. Journal of Geo-information Science, 2014 , 16(6) : 989 -996 . DOI: 10.3724/SP.J.1047.2014.00989
Fig. 1 Sampling locations in Taihu Lake图1 太湖采样点分布图 |
Fig. 3 Backscattering coefficients of the total suspended particulates in Taihu Lake图3 太湖总悬浮颗粒的后向散射特性 |
Fig. 4 The relationship between the phytoplankton backscattering coefficients and the chlorophyll-a concentration图4 藻类颗粒物后向散射系数与叶绿素a浓度的关系 |
Fig. 5 The comparison between the phytoplankton scattering coefficients and its absorption coefficients图5 藻类颗粒物后向散射系数与吸收系数特征比较 |
Fig. 6 Comparison on the simulated reflectance spectrum of the water samples with different CHL-a concentrations.图6 不同叶绿素a浓度的模拟反射率光谱对比 |
Fig. 7 The retrieved CHL-a concentration and its relative errors by different simulating methods of the backscattering coefficients图7 不同后向散射系数模拟方法的叶绿素a反演结果与相对误差 |
Fig. 8 The retrieved CHL-a concentration and its relative errors by using the in-situ datasets obtained on October 27-28, 2003图8 2003年10月27-28日叶绿素a反演结果与相对误差. |
The authors have declared that no competing interests exist.
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