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- Title
Optical properties of the red tide in Isahaya Bay, southwestern Japan: Influence of chlorophyll a concentration.
- Authors
Hiroaki Sasaki; Akihiko Tanaka; Mitsunori Iwataki; Yasuharu Touke; Eko Siswanto; Chun Tan; Joji Ishizaka
- Abstract
Abstract Remote sensing reflectance [R rs(λ)] and absorption coefficients of red tides were measured in Isahaya Bay, southwestern Japan, to investigate differences in the optical properties of red tide and non-red tide waters. We defined colored areas of the sea surface, visualized from shipboard, as “red tides”. Peaks of the R rs(λ) spectra of non-red tide waters were at 565 nm, while those of red tides shifted to longer wavelengths (589 nm). The spectral shape of R rs(λ) was close to that of the reciprocal of the total absorption coefficient [1/a(λ)], implying that the R rs(λ) peak is determined by absorption. Absorption coefficients of phytoplankton [a ph(λ)], non-pigment particles and colored dissolved organic matter increased with increasing chlorophyll a concentration (Chl a), and those coefficients were correlated with Chl a for both red tide and non-red tide waters. Using these relationships between absorption coefficients and Chl a, variation in the spectrum of 1/a(λ) as a function of Chl a was calculated. The peak of 1/a(λ) shifted to longer wavelengths with increasing Chl a. Furthermore, the relative contribution of a ph(λ) to the total absorption in red tide water was significantly higher than in non-red tide water in the wavelength range 550–600 nm, including the peak. Our results show that the variation of a ph(λ) with Chl a dominates the behavior of the R rs(λ) peak, and utilization of R rs(λ) peaks at 589 and 565 nm may be useful to discriminate between red tide and non-red tide waters by remote sensing.
- Subjects
JAPAN; RED tide; OPTICAL properties; BAYS; TIDES; REMOTE sensing; CHLOROPHYLL; PHYTOPLANKTON; SPECTRUM analysis
- Publication
Journal of Oceanography, 2008, Vol 64, Issue 4, p511
- ISSN
0916-8370
- Publication type
Article
- DOI
10.1007/s10872-008-0043-z