An Enhanced Three-Band Index for Estimating Chlorophyll-a in Turbid Case-II Waters: Case Studies of Lake Kasumigaura, Japan, and Lake Dianchi, China.
Wei Yang 1,2, Bunkei Matsushita 1*, Jin Chen2, Takehiko Fukushima1
1Graduate School of Life and Environmental Sciences, University of Tsukuba
1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8572, Japan
2 State key laboratory of earth surface processes and resource ecology, Beijing Normal University, Beijing, 100875, China
Abstract:
A three-band index was previously proposed and successfully utilized to estimate the chlorophyll-a concentration (Chl-a) in case-II waters. However, this index shows uncertainties in highly turbid situations. In this study, an enhanced three-band index is proposed to solve this problem. Since the new index employs bands that are identical to those of the original three-band index, it can be applied to Medium Resolution Imaging Spectrometer (MERIS) data. The performance of the index was evaluated using the data collected from two turbid Asian lakes: Lake Kasumigaura, Japan, and Lake Dianchi, China. The results showed that the Chl-a predicted by the enhanced three-band index was strongly correlated with the measured Chl-a (R-2 > 0.83), and the root-mean-square error (rmse) and the normalized root-mean-square error (NRMS) were both reduced for the two lakes (for Lake Kasumigaura, rmse from 13.97 to 8.68 mg . m(-3) and NRMS from 19.01% to 12.30%; for Lake Dianchi, rmse from 41.29 to 15.28 mg . m(-3) and NRMS from 35.83% to 21.34%). These findings imply that, if accurately atmospheric-corrected MERIS data are available, the enhanced three-band index could be used for mapping Chl-a even in highly turbid case-II waters.
Published in IEEE GEOSCIENCE AND REMOTE SENSING LETTERS, 7 (4): 655-659 OCT 2010 (SCI, Impact index 1.4).