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Assessment of the Water Quality Components in Turbid Estuarine Waters Based on Radiative Transfer Approximations
Citation:
Sokoletsky, L. G., R. S. LUNETTA, M. S. Wetz, AND H. W. Paerl. Assessment of the Water Quality Components in Turbid Estuarine Waters Based on Radiative Transfer Approximations. ISRAEL JOURNAL OF PLANT SCIENCES. Israel-LPPLtd. , Jerusalem, Israel, 60:209-229, (2013).
Impact/Purpose:
The retrieval of inherent optical properties (IOPs), including absorption (a) and backscattering (bb) coefficients, from reflectance is a useful conceptual tool for estimating water quality components (WQCs) in natural waters (Cauwer et al., 2004; Dall’Olmo and Gitelson, 2005; Gons, 1999; Peters et al., 2001; Ruddick et al., 2001; Smyth et al., 2006). These WQCs include chlorophyll a (Chl), volatile (organic) suspended solids (VSS), fixed (inorganic) suspended solids (FSS), total suspended solids (TSS), and chromophoric dissolved organic matter (CDOM) absorption (aCDOM). Decomposition from reflectance to IOPs spectra is important because reflectance data may be obtained using either in situ or remote-sensing (RS) data. IOPs can be directly related to Chl, suspended solids concentrations and aCDOM. Thus, reflectance spectra may finally be related with important WQCs and applied to solve various problems in hydrologic optics and hydrologic remote sensing.
Description:
Bio-geo-optical data collected in the Neuse River Estuary, North Carolina, USA were used to develop a semi-empirical optical algorithm for assessing inherent optical properties associated with water quality components (WQCs). Three wavelengths (560, 665 and 709 nm) were explored for algorithm development. WQCs included chlorophyll a (Chl), volatile suspended solids (VSS), fixed suspended solids (FSS), total suspended solids (TSS) and absorption of chromophoric dissolved organic matter (aCDOM). The relationships between the measured remote-sensing reflectance and the WQCs were derived based on the radiative transfer consideration. We simulated and analyzed impact of the CDOM absorption in the red and near infrared spectral domains, multiple scattering, and scattering phase function on accuracy of WQCs prediction. The algorithm was validated by comparing experimental Chl dynamics with predicted values and a numerical comparison between measured and modeled Chl values. The numerical comparison yielded the highest correlation between predicted and measured WQCs for Chl (R2 = 0.88) and the lowest for FSS (R2 = 0.00), while the best and worst mean-normalized root-mean-squares errors were obtained for aCDOM(412.5) and FSS (35% and 59%, respectively). WQCs retrieval accuracy was typically significantly better at values of aTSS, red > 0.5 m-1.