State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China.
Environ Monit Assess. 2010 Nov;170(1-4):231-44. doi: 10.1007/s10661-009-1228-7. Epub 2009 Nov 12.
Based on in situ water sampling and field spectral measurement from June to September 2004 in Lake Chagan, a comparison of several existing semi-empirical algorithms to determine chlorophyll-a (Chl-a) content was made by applying them to the field spectra and in situ chlorophyll measurements. Results indicated that the first derivative of reflectance was well correlated with Chl-a. The highest correlation between the first derivative and Chl-a was at 680 nm. The two-band model, NIR/red ratio of R710/670, was also an effective predictor of Chl-a concentration. Since the two-band ratios model is a special case of the three-band model developed recently, three-band model in Lake Chagan showed a higher resolution. The new algorithm named reverse continuum removal relies on the reflectance peak at 700 nm whose shape and position depend strongly upon chlorophyll concentration: The depth and area of the peak above a baseline showed a linear relationship to Chl-a concentration. All of the algorithms mentioned proved to be of value and can be used to predict Chl-a concentration. Best results were obtained by using the algorithms of the first derivative, which yielded R2 around 0.74 and RMSE around 6.39 μg/l. The two-band and three-band algorithms were further applied to MERIS when filed spectral were resampled with regard to their center wavelengths. Both algorithms showed an adequate precision, and the differences on the outcome were small with R2=0.70 and 0.71.
基于 2004 年 6 月至 9 月在查干湖进行的原位水样采集和野外光谱测量，应用几种现有的半经验算法对野外光谱和原位叶绿素测量值进行了对比分析，以确定叶绿素 a（Chl-a）含量。结果表明，反射率的一阶导数与 Chl-a 具有良好的相关性。在 680nm 处，一阶导数与 Chl-a 的相关性最高。NIR/red 比值模型（R710/670）也是预测 Chl-a 浓度的有效指标。由于双波段比模型是最近开发的三波段模型的特例，因此查干湖的三波段模型具有更高的分辨率。新的反连续体去除算法基于 700nm 处的反射率峰值，该峰值的形状和位置强烈依赖于叶绿素浓度：在基线以上的峰值的深度和面积与 Chl-a 浓度呈线性关系。所提到的所有算法都被证明是有价值的，可以用来预测 Chl-a 浓度。使用一阶导数算法得到了最好的结果，R2 约为 0.74，RMSE 约为 6.39μg/l。将野外光谱的中心波长重新采样后，将双波段和三波段算法进一步应用于 MERIS。这两种算法都具有足够的精度，结果的差异较小，R2 分别为 0.70 和 0.71。
