A Novel Method Based on Backscattering for Discriminating Summer Blooms of the Raphidophyte (Chattonella spp.) and the Diatom (Skeletonema spp.) Using MODIS Images in Ariake Sea, Japan

Abstract

The raphidophyte Chattonella spp. and diatom Skeletonema spp. are the dominant harmful algal species of summer blooms in Ariake Sea, Japan. A new bio-optical algorithm based on backscattering features has been developed to differentiate harmful raphidophyte blooms from diatom blooms using MODIS imagery. Bloom waters were first discriminated from other water types based on the distinct spectral shape of the remote sensing reflectance R r s (λ) data derived from MODIS. Specifically, bloom waters were discriminated by the positive value of Spectral Shape, SS (645), which arises from the R r s (λ) shoulder at 645 nm in bloom waters. Next, the higher cellular-specific backscattering coefficient, estimated from MODIS data and quasi-analytical algorithm (QAA) of raphidophyte, Chattonella spp., was utilized to discriminate it from blooms of the diatom, Skeletonema spp. A new index b b p − i n d e x ( 555 ) was calculated based on a semi-analytical bio-optical model to discriminate the two algal groups. This index, combined with a supplemental Red Band Ratio (RBR) index, effectively differentiated the two bloom types. Validation of the method was undertaken using MODIS satellite data coincident with confirmed bloom observations from local field surveys, which showed that the newly developed method, based on backscattering features, could successfully discriminate the raphidophyte Chattonella spp. from the diatom Skeletonema spp. and thus provide reliable information on the spatial distribution of harmful blooms in Ariake Sea.

Detection and Tracking of Chattonella spp. and Skeletonema spp. Blooms Using Geostationary Ocean Color Imager (GOCI) in Ariake Sea, Japan

“…bloom, a backscattering indicator, , was proposed by Feng et al. (2020) based on bio‐optical models of seawater using MODIS data, to represent the backscattering properties at 555 nm (see their Equation 10, the satellite bands of MODIS and GOCI could be checked in Table 3). In this study, the index is adjusted to GOCI bands at 555 and 660 nm as follows: The is developed based on the bio‐optical models that the is the function from total absorption and backscattering (Gordon et al., 1988).…”

“…Since there is no GOCI match‐ups with similar Chl a between the two blooms, the graphs are derived from MODIS matched , for details, please check on Feng et al. (2020).…”

“…bloom waters in visible bands, and its Chl a content, 2–7 times higher than in Skeletonema spp. bloom waters (Feng et al., 2020). However, Chattonella spp.…”

“…The method proposed is an extension of the algorithms that we developed for MODIS‐Aqua in Feng et al. (2020). A algorithm is adjusted to GOCI bands to indicate the backscattering at 555 nm for bloom waters.…”

Sensitivity Analysis and Optimization of a Radiative Transfer Numerical Model for Turbid Lake Water

“…These spectra decrease exponentially with an increase in the wavelength (Figure 7a,c). Furthermore, the values of these spectra varied substantially with respect to the sampling points and periods due to the different compositions of the optical matter [81]. In particular, this study focused on variations in the backscattering coefficient in response to a change in the number of cyanobacteria cells, because the study area experiences frequent cyanobacteria bloom.…”