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Water 2018, 10(5), 618; https://doi.org/10.3390/w10050618

Evaluation of Unified Algorithms for Remote Sensing of Chlorophyll-a and Turbidity in Lake Shinji and Lake Nakaumi of Japan and the Vaal Dam Reservoir of South Africa under Eutrophic and Ultra-Turbid Conditions

1
Graduate School of Engineering, Hiroshima University, Higashihiroshima 739-8527, Japan
2
Estuary Research Center, Shimane University, Matsue 690-8504, Japan
3
Faculty of Agriculture, Tottori University, Tottori 680-8550, Japan
4
Graduate School of Science and Engineering, Shimane University, Matsue 690-8504, Japan
5
Agricultural Research Council-Institute for Soil, Climate and Water, Pretoria 0001, South Africa
6
School of Geography, Archaeology, and Environmental Studies, University of the Witwatersrand, Johannesburg 2000, South Africa
*
Author to whom correspondence should be addressed.
Received: 19 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 9 May 2018
(This article belongs to the Section Water Quality and Ecosystems)
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Abstract

We evaluated unified algorithms for remote sensing of chlorophyll-a (Chla) and turbidity in eutrophic and ultra-turbid waters such as Japan’s Lake Shinji and Lake Nakaumi (SJNU) and the Vaal Dam Reservoir (VDR) in South Africa. To realize this objective, we used 38 remote sensing reflectance (Rrs), Chla and turbidity datasets collected in these waters between July 2016 and March 2017. As a result, we clarified the following items. As a unified Chla model, we obtained strong correlation (R2 = 0.7, RMSE = 2 mg m−3) using a two-band model (2-BM) and three-band model (3-BM), with Rrs(687)/Rrs(672) and [Rrs−1(687) − Rrs−1(672)] × Rrs(832). As a unified turbidity model, we obtained strong correlation (R2 = 0.7, RMSE = 260 NTU) using 2-BM and 3-BM, with Rrs(763)/Rrs(821) and Rrs(810) − [Rrs(730) + Rrs(770)]/2. When targeting the Sentinel-2 Multispectral Imager (MSI) frequency band, we focused on MSI Bands 4 and 5 (Rrs(740) and Rrs(775)) for the Chla algorithm. When optically separating SJNU and VDR data, it is effective to use the slopes of MSI Bands 3 and 4 (Rrs(560) and Rrs(665)) and the slopes of MSI Bands 7 and 9 (Rrs(775) and Rrs(865)). View Full-Text
Keywords: chlorophyll; turbidity; remote sensing; reflectance; lake; reservoir; Sentinel-2 chlorophyll; turbidity; remote sensing; reflectance; lake; reservoir; Sentinel-2
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Sakuno, Y.; Yajima, H.; Yoshioka, Y.; Sugahara, S.; Abd Elbasit, M.A.M.; Adam, E.; Chirima, J.G. Evaluation of Unified Algorithms for Remote Sensing of Chlorophyll-a and Turbidity in Lake Shinji and Lake Nakaumi of Japan and the Vaal Dam Reservoir of South Africa under Eutrophic and Ultra-Turbid Conditions. Water 2018, 10, 618.

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