Evaluation of Multi- and Hyper- Spectral Chl-A Algorithms in the RÍo De La Plata Turbid Waters During a Cyanobacteria Bloom

Abstract Remote sensing provides a global vision of the oceans; validation is, however, an essential previous step. IFREMER developed the empirical algorithm OC5 for highly turbid (or type 2) waters and it performed well for the northwestern European shelf. The aim of this study was to evaluate the performance of this algorithm for the Río de la Plata estuary, utilizing in situ observations of chlorophyll-a and suspended matter. Our results show a low point-to-point correlation between in situ and remote observations for both variables. In addition, the root mean square log error (RMSE) exceeded 35% for both variables, indicating a poor performance of the OC5 algorithm. This might be related to the empirical nature of the algorithm, to the amount and distribution of the data used for the analysis, to the species that compose the phytoplankton of the region, to the presence of other optically active substances in the water, and to errors in the atmospheric corrections and/or to the spatial variability of the analyzed variables. In conclusion, our results confirm the need to develop regional algorithms which take into account the particular physical and biological characteristics of the area under study.

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Atmospheric Correction of Satellite Optical Imagery over the Río de la Plata Highly Turbid Waters Using a SWIR-Based Principal Component Decomposition Technique

Remote Sensing ◽

10.3390/rs13061050 ◽

2021 ◽

Vol 13 (6) ◽

pp. 1050

Author(s):

Juan Ignacio Gossn ◽

Robert Frouin ◽

Ana Inés Dogliotti

Keyword(s):

Principal Components ◽

Near Infrared ◽

Atmospheric Correction ◽

Low Noise ◽

Optical Data ◽

Rio De La Plata ◽

Río De La Plata ◽

La Plata ◽

Turbid Waters ◽

The Impact

Estimating water reflectance accurately from satellite optical data requires implementing an accurate atmospheric correction (AC) scheme, a particularly challenging task over optically complex water bodies, where the signal that comes from the water prevents using the near-infrared (NIR) bands to separate the perturbing atmospheric signal. In the present work, we propose a new AC scheme specially designed for the Río de la Plata—a funnel-shaped estuary in the Argentine–Uruguayan border—highly scattering turbid waters. This new AC scheme uses far shortwave infrared (SWIR) bands but unlike previous algorithms relates the atmospheric signal in the SWIR to the signal in the near-infrared (NIR) and visible (VIS) bands based on the decomposition into principal components of the atmospheric signal. We describe the theoretical basis of the algorithm, analyze the spectral features of the simulated principal components, theoretically address the impact of noise on the results, and perform match-ups exercises using in situ measurements and Moderate Resolution Imaging Spectrometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) imagery over the region. Plausible water reflectance retrievals were obtained in the NIR and VIS bands from both simulations and match-ups using field data—with better performance (i.e., lowest errors and offsets, and slopes closest to 1) compared to existing AC schemes implemented in the NASA Data Analysis Software (SeaDAS). Moreover, retrievals over images in the VIS and NIR bands showed low noise, and the correlation was low between aerosol and water reflectance spatial fields.

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Detecting and Quantifying a Massive Invasion of Floating Aquatic Plants in the Río de la Plata Turbid Waters Using High Spatial Resolution Ocean Color Imagery

Remote Sensing ◽

10.3390/rs10071140 ◽

2018 ◽

Vol 10 (7) ◽

pp. 1140 ◽

Cited By ~ 13

Author(s):

Ana Dogliotti ◽

Juan Gossn ◽

Quinten Vanhellemont ◽

Kevin Ruddick

Keyword(s):

High Resolution ◽

Aquatic Plants ◽

Color Space ◽

Landsat 8 ◽

Rio De La Plata ◽

Río De La Plata ◽

La Plata ◽

Turbid Waters ◽

High Resolution Imagery ◽

Floating Vegetation

The massive development of floating plants in floodplain lakes and wetlands in the upper Middle Paraná river in the La Plata basin is environmentally and socioeconomically important. Every year aquatic plant detachments drift downstream arriving in small amounts to the Río de la Plata, but huge temporary invasions have been observed every 10 or 15 years associated to massive floods. From late December 2015, heavy rains driven by a strong El Niño increased river levels, provoking a large temporary invasion of aquatic plants from January to May 2016. This event caused significant disruption of human activities via clogging of drinking water intakes in the estuary, blocking of ports and marinas and introducing dangerous animals from faraway wetlands into the city. In this study, we developed a scheme to map floating vegetation in turbid waters using high-resolution imagery, like Sentinel-2/SMI (MultiSpectral Imager), Landsat-8/OLI (Operational Land Imager), and Aqua/MODIS (MODerate resolution Imager Spectroradiometer)-250 m. A combination of the Floating Algal Index (that make use of the strong signal in the NIR part of the spectrum), plus conditions set on the RED band (to avoid misclassifying highly turbid waters) and on the CIE La*b* color space coordinates (to confirm the visually “green” pixels as floating vegetation) were used. A time-series of multisensor high resolution imagery was analyzed to study the temporal variability, covered area and distribution of the unusual floating macroalgae invasion that started in January 2016 in the Río de la Plata estuary.

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