Estimation of the relationship between humic substance concentration and Secchi depth using a calculated image

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  • フミン物質濃度と透明度の関係の計算画像による推計
  • フミン ブッシツ ノウド ト トウメイド ノ カンケイ ノ ケイサン ガゾウ ニ ヨル スイケイ

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<p>　Humic substances with soluble forms that are typically found in clear natural water were investigated to understand the effects that dissolved pollutants have on the Secchi depth (SD) in lakes and marshes. The relationship between humic substance concentration and color image SD (CISD) was obtained by comparing the calculated color images of the Secchi disk with the background. The calculation was based on first-order approximation of disk radiance and background light, with the incident angle of light on the water surface set to 40° and the known absorption characteristics of humic and fulvic acids used for each wavelength. A CISD of 126 m was obtained for 0 mgC L-1 humic acid, which decreased to 78 m at 0.0047 mgC L-1 before rapidly dropping to a local minimum of 60 m at 0.0048 mgC L-1. The CISD then increased to the local maximum of 68 m at 0.02 mgC L-1 before decreasing again to 0.3 m at 20 mgC L-1. The CISD of fulvic acid displayed the same tendencies as those observed for humic acid. The obtained CISD trend may be a result of changes in color causing changes in brightness. The function approximation was performed by region division where the CISD increased, and the root mean square of the relative error in the approximation function for concentration with respect to the increasing CISD was found to be less than 0.03 in all sections.</p>

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