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Use of Reflectance Ratios as a Proxy for Coastal Water Constituent Monitoring in the Pearl River Estuary
Department of Computer Engineering, Suzhou Vocational University, Suzhou 215104, P.R. China
Public Laboratory of Environmental Science and Technology of Guangdong Province, Guangzhou Institute of Geography, Guangzhou 510070, P.R. China
The Water Supply Corporation of Panyu District, Guangzhou 511400, P.R. China
* Author to whom correspondence should be addressed.
Received: 11 December 2008; in revised form: 20 January 2009 / Accepted: 21 January 2009 / Published: 23 January 2009
Abstract: Spectra, salinity, total suspended solids (TSS, in mg/L) and colored dissolved organic matter (CDOM, ag(400) at 400 nm) sampled in stations in 44 different locations on December 18, 19 and 21, in 2006 were measured and analyzed. The studied field covered a large variety of optically different waters, the absorption coefficient of CDOM ([ag(400)] in m-1) varied between 0.488 and 1.41 m-1, and the TSS concentrations (mg/L) varied between 7.0 and 241.1 mg/L. In order to detect salinity of the Pearl River Estuary, we analyzed the spectral properties of TSS and CDOM, and the relationships between field water reflectance spectra and water constituents’ concentrations based on the synchronous in-situ and satellite hyper-spectral image analysis. A good correlation was discovered (the positive correlation by linear fit), between in-situ reflectance ratio R680/R527 and TSS concentrations (R2 = 0.65) for the salinity range of 1.74-22.12. However, the result also showed that the absorption coefficient of CDOM was not tightly correlated with reflectance. In addition, we also observed two significant relationships (R2 > 0.77), one between TSS concentrations and surface salinity and the other between the absorption coefficient of CDOM and surface salinity. Finally, we develop a novel method to understand surface salinity distribution of estuarine waters from the calibrated EO-1 Hyperion reflectance data in the Pearl River Estuary, i.e. channels with high salinity and shoals with low salinity. The EO-1 Hyperion derived surface salinity and TSSconcentrations were validated using in-situ data that were collected on December 21, 2006, synchronous with EO-1 Hyperion satellite imagery acquisition. The results showed that the semi-empirical relationships are capable of predicting salinity from EO-1 Hyperion imagery in the Pearl River Estuary (RMSE < 2‰).
Keywords: Pearl River Estuary; salinity; total suspended solid; colored dissolved organic matter; Hyperion imagery
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Fang, L.-G.; Chen, S.-S.; Li, D.; Li, H.-L. Use of Reflectance Ratios as a Proxy for Coastal Water Constituent Monitoring in the Pearl River Estuary. Sensors 2009, 9, 656-673.
Fang L-G, Chen S-S, Li D, Li H-L. Use of Reflectance Ratios as a Proxy for Coastal Water Constituent Monitoring in the Pearl River Estuary. Sensors. 2009; 9(1):656-673.
Fang, Li-Gang; Chen, Shui-Sen; Li, Dong; Li, Hong-Li. 2009. "Use of Reflectance Ratios as a Proxy for Coastal Water Constituent Monitoring in the Pearl River Estuary." Sensors 9, no. 1: 656-673.