A Study on the Blue Coloration of Ao-ike Pond, Aomori Prefecture, Japan: Formulation of a Physical Model in Terms of Radiance and Image Analyses

Ryuji Hanaishi,Kazuhisa A Chikita

doi:10.3390/app11199231

Abstract

The blue coloration model of a closed pond, Ao-ike Pond, Aomori Prefecture, Japan, was formulated in terms of radiance by applying a theory of observation devices proposed by Szirmay-Kalos (2008) and Hanaishi’s reverse ray tracing method. In this model, three potential contributions to the coloration were considered; irregular reflection at the Lambertian pond bottom, density fluctuation scattering by water, and Mie scattering by suspended solids. By utilizing model formulas for these mechanisms, some parameters were determined in order to duplicate the images of the pond surface without solar shading by tree leaves above the pond surface, in addition to the images with sunbeam trajectories by solar radiations passing through tree leaves, which are emitted from the water and visible on the surface. Simulating the pictures of the pond surface and the sun-beam-image analyses revealed that the blue colorations of Ao-ike Pond are mainly produced (1) by the density fluctuation scattering of water itself and the white Mie scattering by suspended solids and (2) by the red-light absorption by water in the optical paths before and after the two scatterings. Then, the density fluctuation scattering of water and the Mie scattering by suspended solids exhibited contributions of almost equal magnitude. The contribution of irregular reflections at the pond bottom was judged to be relatively small.

Highlights

The colorations of lakes and seas are important as a factor impressing landscapes and as an aspect of inspecting the chemistry of the water
Hanaishi et al [16,17] proposed a blue coloration mechanism of Ao-ike Pond in the Juni-ko Lakes group, Aomori Prefecture, Japan, where light absorption by water and density fluctuation scattering by water were considered under the approximation of the first-order scattering of light
The potent mechanisms that contributed to the coloration of Aoike Pond were concluded to be the density fluctuation scattering by water and the white Mie scattering by suspended solids, in this study

Summary

Introduction

The colorations of lakes and seas are important as a factor impressing landscapes and as an aspect of inspecting the chemistry of the water. Research in this field was performed in the 1970s, as represented by the pioneering textbook of Jerlov on ocean optics [1]. Morel et al [3] experimentally determined the spectral reflectance related to the color of sea water. They pointed out the importance of the light absorption by water and the density fluctuation scattering by water, which contributes to the reflectance in case of blue seawater

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