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This study utilizes satellite data to investigate water quality conditions in the San Francisco Estuary and its upstream delta, the Sacramento-San Joaquin River Delta. To do this, this study derives turbidity from the European Space Agency satellite Sentinel-2 acquired from September 2015 to June 2019 and conducts a rigorous validation with in situ measurements of turbidity from optical sensors at continuous monitoring stations. This validation includes 965 matchup comparisons between satellite and in situ sensor data across 22 stations, yielding R 2 = 0.63 and 0.75 for Nephelometric Turbidity Unit and Formazin Nephelometric Unit (FNU) stations, respectively. This study then applies remote sensing to evaluate patterns in turbidity during the Suisun Marsh Salinity Control Gates Action ("Gates action"), a pilot study designed to increase habitat access and quality for the endangered Delta Smelt. The basic strategy was to direct more freshwater into Suisun Marsh, creating more low salinity habitat that would then have higher (and more suitable) turbidity than upstream river channels. For all seven acquisitions considered from June 29 to September 27, 2018, turbidity conditions in Bays and Sloughs subregions were consistently higher (and more suitable) (26-47 FNU) than what was observed in the upstream River region (13-25 FNU). This overall pattern was observed when comparing images acquired during similar tidal stages and heights.

This study utilizes satellite data to investigate water quality conditions in the San Francisco Estuary and its upstream delta, the Sacramento--San Joaquin River Delta. To do this, this study derives turbidity from the European Space Agency satellite Sentinel-2 acquired from September 2015 to June 2019 and conducts a rigorous validation with in situ measurements of turbidity from optical sensors at continuous monitoring stations. This validation includes 965 matchup comparisons between satellite and in situ sensor data across 22 stations, yielding R² = 0.63 and 0.75 for Nephelometric Turbidity Unit and Formazin Nephelometric Unit (FNU) stations, respectively. This study then applies remote sensing to evaluate patterns in turbidity during the Suisun Marsh Salinity Control Gates Action ("Gates action"), a pilot study designed to increase habitat access and quality for the endangered Delta Smelt. The basic strategy was to direct more freshwater into Suisun Marsh, creating more low salinity habitat that would then have higher (and more suitable) turbidity than upstream river channels. For all seven acquisitions considered from June 29 to September 27, 2018, turbidity conditions in Bays and Sloughs subregions were consistently higher (and more suitable) (26-47 FNU) than what was observed in the upstream River region (13-25 FNU). This overall pattern was observed when comparing images acquired during similar tidal stages and heights. [ABSTRACT FROM AUTHOR]

Water quality degradation in inland water bodies during summer periods due to phytoplankton growth is a global problem. Lake Burley Griffin (LBG) in Canberra, Australia is an artificial, turbid, urban lake which is prone to water quality degradation in summer due to phytoplankton blooms. In Australia only limited (spatial, spectral and temporal) datasets are available that detail the full bio-optical condition of the water body during summer transformation processes. In this study, we conducted field campaigns in LBG to measure biogeochemical as well as inherent optical properties (IOP) during summer 2010 to understand the variability in the optical response. Optically active biogeochemical components such as total suspended solids (TSS), Chlorophyll- a (Chl- a ) and coloured dissolved organic matter (CDOM) varied over a wide range in response to changing environmental conditions during summer. The underwater optical environment was dominated by light scattering properties and the light absorption budget varied in response to changing CDOM and phytoplankton distributions. Specific inherent optical properties and spectral slopes of IOP observed here were different to other regional datasets, thus indicated the limitation in the extrapolation of optical models from other regions. Optical response as described by the scattering to absorption ratio and backscattering albedo showed that absorption due to CDOM and non-algal particulate matter (NAP) masked phytoplankton absorption features limiting the application of standard optical algorithms. A through description of bio-optical properties, relationships and their variability in response to changing summer biogeochemical conditions in a turbid optically complex lake is presented here. [ABSTRACT FROM AUTHOR]

Optical remote sensing in complex waters is challenging because the optically active constituents may vary independently and have a combined and interacting influence on the remote sensing signal. Additionally, the remote sensing signal is influenced by noise and spectral contamination by confounding factors, resulting in ill-posedness and ill-conditionedness in the inversion of the model. There is a need for inversion methods that are less sensitive to these changing or shifting spectral features. We propose WaveIN, a wavelet-enhanced inversion method, specifically designed for complex waters. It integrates wavelet-transformed high-spectral resolution reflectance spectra in a multiscale analysis tool. Wavelets are less sensitive to a bias in the spectra and can avoid the changing or shifting spectral features by selecting specific wavelet scales. This paper applied WaveIN to simulated reflectance spectra for the Scheldt River. We tested different scenarios, where we added specific noise or confounding factors, specifically uncorrelated noise, contamination due to spectral mixing, a different sun zenith angle, and specific inherent optical property (SIOP) variation. WaveIN improved the constituent estimation in case of the reference scenario, contamination due to spectral mixing, and a different sun zenith angle. WaveIN could reduce, but not overcome, the influence of variation in SIOPs. Furthermore, it is sensitive to wavelet edge effects. In addition, it still requires in situ data for the wavelet scale selection. Future research should therefore improve the wavelet scale selection. [ABSTRACT FROM PUBLISHER]

Recent and upcoming launches of new satellite sensors will provide the spatial, spectral and radiometric resolution to globally assess freshwater chromophoric dissolved organic matter (CDOM), and thus estimate dissolved organic carbon (DOC) concentration. However, estimating DOC from optical remote sensing requires a robust relationship between CDOM and DOC. This is particularly problematic for reservoirs because they have variable dissolved organic matter composition that complicates the CDOM–DOC relationship. We investigated six manmade reservoirs along a temperate to tropical gradient that represent a range of reservoir types and watershed conditions to determine whether a linear relation between CDOM and DOC could be established. We measured CDOM absorption and DOC concentration during the wet and dry seasons in the six reservoirs. We found the CDOM absorption coefficient and CDOM spectral slope were uncorrelated due to exogenous DOC inputs from multiple sources. Alone, the absorption coefficient of CDOM was a poor predictor of DOC concentration. Including both CDOM absorption coefficient and spectral slope in a multiple regression accounted for both composition and concentration, significantly improving the regression r 2 . By using both CDOM absorption coefficient and spectral slope, we identify a framework for a potential solution to overcome the influence of dissolved organic matter source and transformation history on the CDOM–DOC relationship. We conclude that local variability, seasonality and optical complexity should be considered in remote sensing based approaches for global freshwater DOC estimation. [ABSTRACT FROM AUTHOR]