Specific inherent optical properties of highly turbid productive water for retrieval of water quality after optical classification

• Published in: Environmental earth sciences 2015-03, Vol.73 (5), p.1961-1973
• Main Authors: Huang, Changchun, Chen, Xia, Li, Yunmei, Yang, Hao, Sun, Deyong, Li, Junsheng, Le, Chengfeng, Zhou, Liangcheng, Zhang, Mingli, Xu, Liangjiang
• Format: Article
• Language: English
• Subjects: Absorption; Biogeosciences; chlorophyll; Classification; Earth and Environmental Science; Earth Sciences; Environmental Science and Engineering; Geochemistry; Geology; Geophysics; Hydrology/Water Resources; Inland waters; Lakes; Optical properties; Original Article; Phytoplankton; Reflectance; Reflectivity; Remote sensing; Retrieval; Terrestrial Pollution; Water quality
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-014-3548-3

Assessments of specific inherent optical properties (SIOPs) and their variability in highly turbid and productive inland waters are essential for the accurate estimation of water quality. A new optical classification method including two classification criteria [i.e., normalized remote sensing reflectance slope (NS), and normalized remote sensing reflectance depth (ND)] was developed to divide remote sensing reflectance into four classes, i.e., class 1 (NS  0.009) is high turbid and high productive water. The relationships between phytoplankton absorption at 440 nm [aₚₕ(440)] and chlorophyll-a concentration [Ccₕₗₐ] as well as between particle backscattering coefficient at 440 nm [bbₚ(440)] and total suspended matter concentration (CTSM) after classification were obtained from a large number of in situ data in Lake Taihu. The measured specific phytoplankton absorption [Formula: see text] and particle backscattering coefficient [Formula: see text] show significant variations even within the same class. The mean values of [Formula: see text] at 440 nm [Formula: see text] for each class are 0.048 ± 0.013, 0.060 ± 0.012, 0.083 ± 0.021, and 0.056 ± 0.017 m²/mg, respectively. The mean values of [Formula: see text] at 440 nm [Formula: see text] for each class are 0.035 ± 0.01, 0.024 ± 0.004, 0.041 ± 0.009, and 0.038 ± 0.009 m²/g, respectively. The power functions of SIOPs and water constituents’ concentration indicate that [Formula: see text] and [Formula: see text] vary with Ccₕₗₐand CTSM. The validation results show that our proposed values for [Formula: see text] and [Formula: see text] cover a very wide range of water optical properties, which are characterized from clear water to highly turbid productive water. The validation results also suggest that the retrieval accuracy of Ccₕₗₐand CTSMbio-optical model was improved after classification. The root mean square error (RMSE) of Ccₕₗₐwas improved from 14.18 to 7.43 μg/L (mean value of all classes) and RMSE of CTSMwas improved from 32.98 to 26.10 mg/L (mean value of all classes). Thus, the temporal and spatial variation of [Formula: see text] and [Formula: see text] should be considered in the bio-optical retrieval model of water quality.