Environ Monit Assess (2010) 170:231–244 DOI 10.1007/s10661-009-1228-7 Comparison of different semi-empirical algorithms to estimate chlorophyll-a concentration in inland lake water Hongtao Duan · Ronghua Ma · Jingping Xu · Yuanzhi Zhang · Bai Zhang Received: 4 January 2009 / Accepted: 29 October 2009 / Published online: 12 November 2009 © Springer Science + Business Media B.V. 2009 Abstract 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 apply- ing them to the field spectra and in situ chloro- phyll 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- H. Duan (B ) · R. Ma State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China e-mail: htduan@niglas.ac.cn, htduan@gmail.com J. Xu State Key Laboratory of Remote Sensing Science, Jointly Sponsored by the Institute of Remote Sensing Applications of Chinese Academy of Sciences and Beijing Normal University, Beijing 100101, China Y. Zhang Institute of Space and Earth Information Science, The Chinese University of Hong Kong, Shatin, NT, Hong Kong B. Zhang Northeast Institute of Geography and Agricultural Ecology, Chinese Academy of Sciences, Changchun 130012, China band model, NIR/red ratio of R 710/670 , 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 con- tinuum 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 R 2 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 R 2 = 0.70 and 0.71. Keywords Field spectral · Lake Chagan · Continuum removal · Three-band model Introduction Lakes are valuable water resources and can be used for fishing, transport, agriculture, industry,