Optical Characterization of Coastal Waters with Atmospheric Correction Errors: Insights from SGLI and AERONET-OC

Optical Characterization of Coastal Waters with Atmospheric Correction Errors: Insights from SGLI and AERONET-OC

This study identifies the characteristics of water regions with negative normalized water-leaving radiance (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><...

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Main Authors: Hiroto Higa, Masataka Muto, Salem Ibrahim Salem, Hiroshi Kobayashi, Joji Ishizaka, Kazunori Ogata, Mitsuhiro Toratani, Kuniaki Takahashi, Fabrice Maupin, Stephane Victori
Format: Article
Language:English
Published: MDPI AG 2024-09-01
Series:Remote Sensing
Subjects:
ocean color satellite
GCOM-C/SGLI
AERONET-OC
SeaPRISM
Tokyo Bay
Ariake Sea
Online Access:https://www.mdpi.com/2072-4292/16/19/3626
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Summary:This study identifies the characteristics of water regions with negative normalized water-leaving radiance (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula>) values in the satellite observations of the Second-generation Global Imager (SGLI) sensor aboard the Global Change Observation Mission–Climate (GCOM-C) satellite. SGLI Level-2 data, along with atmospheric and in-water optical properties measured by the sun photometers in the AErosol RObotic NETwork-Ocean Color (AERONET-OC) from 26 sites globally, are utilized in this study. The focus is particularly on Tokyo Bay and the Ariake Sea, semi-enclosed water regions in Japan where previous research has pointed out the occurrence of negative <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> values due to atmospheric correction with SGLI. The study examines the temporal changes in atmospheric and in-water optical properties in these two regions, and identifies the characteristics of regions prone to negative <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> values due to atmospheric correction by comparing the optical properties of these regions with those of 24 other AERONET-OC sites. The time series results of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> and the single-scattering albedo (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi mathvariant="sans-serif">ω</mi><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula>) obtained by the sun photometers at the two sites in Tokyo Bay and Ariake Sea, along with SGLI <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula>, indicate the occurrence of negative values in SGLI <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> in blue band regions, which are mainly attributed to the inflow of absorptive aerosols. However, these negative values are not entirely explained by <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi mathvariant="sans-serif">ω</mi><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> at 443 nm alone. Additionally, a comparison of in situ <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> measurements in Tokyo Bay and the Ariake Sea with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> values obtained from 24 other AERONET-OC sites, as well as the inherent optical properties (IOPs) estimated through the Quasi-Analytical Algorithm version 5 (QAA_v5), identified five sites—Gulf of Riga, Long Island Sound, Lake Vanern, the Tokyo Bay, and Ariake Sea—as regions where negative <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> values are more likely to occur. These regions also tend to have lower <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo><mo> </mo></mrow></semantics></math></inline-formula> values at shorter wavelengths. Furthermore, relatively high light absorption by phytoplankton and colored dissolved organic matter, plus non-algal particles, was confirmed in these regions. This occurs because atmospheric correction processing excessively subtracts aerosol light scattering due to the influence of aerosol absorption, increasing the probability of the occurrence of negative <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></semantics></math></inline-formula> values. Based on the analysis of atmospheric and in-water optical measurements derived from AERONET-OC in this study, it was found that negative <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>n</mi><msub><mrow><mi>L</mi></mrow><mrow><mi>w</mi></mrow></msub><mo>(</mo><mi>λ</mi><mo>)</mo><mo> </mo></mrow></semantics></math></inline-formula> values due to atmospheric correction are more likely to occur in water regions characterized by both the presence of absorptive aerosols in the atmosphere and high light absorption by in-water substances.
ISSN:2072-4292

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