Spatiotemporal Variations in Biophysical Water Quality Parameters: An Integrated In Situ and Remote Sensing Analysis of an Urban Lake in Chile
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Author
Yépez, Santiago
Velásquez, Germán
Torres, Daniel
Saavedra-Passache, Rodrigo
Pincheira, Martin
Cid, Hayleen
Rodríguez-López, Lien
Contreras, Frédéric
Frappart, Frédéric
Pons, Xavier
Flores, Neftali
Bourrel, Luc
Publication date
2024-01-22ISSN
2072-4292
Abstract
This study aims to develop and implement a methodology for retrieving bio-optical
parameters in a lagoon located in the Biobío region, South-Central Chile, by analyzing time series
of Landsat-8 OLI satellite images. The bio-optical parameters, i.e., chlorophyll-a (Chl-a, in mg·m−3)
and turbidity (in NTU) were measured in situ during a satellite overpass to minimize the impact of
atmospheric distortions. To calibrate the satellite images, various atmospheric correction methods
(including ACOLITE, C2RCC, iCOR, and LaSRC) were evaluated during the image preprocessing
phase. Spectral signatures obtained from the scenes for each atmospheric correction method were
then compared with spectral signatures acquired in situ on the water surface. In short, the ACOLITE
model emerged as the best fit for the calibration process, reaching R2 values of 0.88 and 0.79 for Chl-a
and turbidity, respectively. This underlies the importance of using inversion models, when processing
water surfaces, to mitigate errors due to aerosols and the sun-glint effect. Subsequently, reflectance
data derived from the ACOLITE model were used to establish correlations between various spectral
indices and the in situ data. The empirical retrieval models (based on band combinations) yielding
superior performance, with higher R2 values, were subjected to a rigorous statistical validation and
optimization by applying a bootstrapping approach. From this process the green chlorophyll index
(GCI) was selected as the optimal choice for constructing the Chl-a retrieval model, reaching an R2 of
0.88, while the red + NIR spectral index achieved the highest R2 value (0.79) for turbidity analysis,
although in the last case, it was necessary to incorporate data from several seasons for an adequate
model training. Our analysis covered a broad spectrum of dates, seasons, and years, which allowed
us to search deeper into the evolution of the trophic state associated with the lake. We identified a
striking eight-year period (2014–2022) characterized by a decline in Chl-a concentration in the lake,
possibly attributable to governmental measures in the region for the protection and conservation of
the lake. Additionally, the OLI imagery showed a spatial pattern varying from higher Chl-a values
in the northern zone compared to the southern zone, probably due to the heat island effect of the
northern urban areas. The results of this study suggest a positive effect of recent local regulations
and serve as the basis for the creation of a modern monitoring system that enhances traditional
point-based methods, offering a holistic view of the ongoing processes within the lake.
Document Type
Article
Document version
Published version
Language
English
Subject (CDU)
628 - Public health engineering. Water. Sanitation. Illuminating engineering
Pages
25
Publisher
MDPI
Is part of
Remote Sensing
Citation
Yépez, Santiago, Germán Velásquez, Daniel J. Torres, Rodrigo Saavedra-Passache, Martin Pincheira, Hayleen Cid, Lien Rodríguez‐López, et al. 2024. “Spatiotemporal Variations in Biophysical Water Quality Parameters: An Integrated in Situ and Remote Sensing Analysis of an Urban Lake in Chile.” Remote Sensing 16 (2): 427. https://doi.org/10.3390/rs16020427.
Program
Ús Eficient de l'Aigua en Agricultura
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- ARTICLES CIENTÍFICS [2555]
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