A semianalytical model developed to estimate the Secchi disk depth (ZSD) was used in eutrophic-to-hypereutrophic reservoirs (Ibitinga, Ibi, and Barra Bonita, BB) placed in the cascade system of the Tietê River, Brazil. The model was evaluated using the simulated remote sensing reflectance based on the Ocean and Land Color Instrument/Sentinel-3A and the Operational Land Imager/Landsat-8 from both reservoirs. Three quasianalytical algorithm (QAA) versions (QAAv5, QAAM14, and QAAW16) were evaluated to derive the absorption and backscattering coefficients, and then used for ZSD retrieval. For BB, where the chlorophyll-a concentration exceeded 200 mg m − 3, the model based on QAAv5 showed high uncertainties while the QAAW16, which was originally parameterized for BB showed better performance regarding the ZSD retrieval (mean absolute percentage errors—MAPE of 22%). However, QAAW16 did not perform satisfactorily for Ibi, which is dominated by colored dissolved organic matter (CDOM). For Ibi, QAAv5 provided the best result with MAPE of 34.60%, followed by QAAM14 with 34.65%. QAA-based ZSD models tend to perform poorly in waters with high concentration of chlorophyll-a possibly due to phytoplankton package effect, whereas the same models may require additional parameterization in waters dominated by CDOM. Landsat-8 data showed significant potential for ZSD retrieval in inland waters.
Several quasi-analytical algorithm (QAA) versions were developed to make it suitable for different inland water systems. QAABBHR and QAAOMW were reparameterized based on two reservoirs from the Tietê River cascading system (São Paulo State, Brazil), which present widely differing compositions. Considering the purpose of monitoring the entire cascade through a unique QAA version, we aimed to assess the suitability of these two QAA versions and, in addition, another two QAA native forms (versions 5 and 6), for retrieving inherent optical properties (IOPs) in Ibitinga hydroelectric reservoir (IHR), situated in the same cascading system. In addition to that, we addressed bio-optical characterization of IHR, using spectral and water quality data collected in a field campaign conducted in July 2016. Wide spatial variability of optically significant constituent (OSC) in IHR and colored dissolved organic matter predominance in its absorption budget was observed. None of the tested QAA versions were completely suitable in retrieving absorption coefficients for IHR in all wavelengths. However, results for wavelengths commonly used as proxy for OSC concentration retrieval were satisfactory in some of the models. Therefore, the results obtained in this study shows that QAAs versions can be used for specific purposes (e.g., chlorophyll-a mapping), by employing the best model for IOPs retrieval at a specific wavelength. This highlights the challenge of copying with high optical variability in cascading systems. In this sense, further research is necessary, for either achieving a QAA reparameterized version appropriate for aquatic systems with widely differing optical properties or another analytical scheme.