AWOC/KJWOC Online 2020 Presentation

Laster year I attended The \(\rm 8^{th} Asian/17^{th}\) Korea-Japan Workshop on Ocean Color and gave a presentation.

Spectral-spatial fusion between SGLI and MODIS in the Ariake Sea

\(\rm Zhenjia\ ZHOU^{1*}, Joji\ ISHIZAKA^{2}, Chi\ FENG^{3}\)

1 Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan

2 Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan

3 Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan

* e-mail: zhenjiazhou0127@gmail.com

Harmful algal bloom (HAB) is an environmental problem in both freshwater and marine systems. In Japan, HAB always appears in the western part, such as the Ariake Sea. Some toxic species, like raphidophytes, could reduce fishery production and thus cause economic loss. Therefore, it is essential to know the dynamic of the toxic and non-toxic HAB in Japan's coastal area.

The discrimination between different phytoplankton is based on the optical properties difference, such as remote sensing reflectance (Rrs), and derived backscattering and absorption in the visible light range. Nevertheless, there are two main restrictions from ocean color satellites in this field; spectral resolution and spatial resolution.

Currently, ocean color satellites could only carry a multi-spectral spectroradiometer, which could only get the optical properties in a few specific wavelengths. For example, the MODerate Resolution Imaging Spectroradiometer (MODIS) and the Second generation GLobal Imager (SGLI) measure only ten and six visible ocean bands, respectively. Such spectral resolution makes it hard to get unique optical properties of different phytoplankton.

Another restriction from the satellite is spatial resolution. MODIS takes 1 km spatial resolution data, and it may not be satisfactory to catch small HAB patches. Currently, SGLI is the highest spatial resolution (250 m) ocean color satellite in the Japanese coastal region.

This research aims to develop a method for the fusion between SGLI and MODIS in the Ariake Sea. The fusion product has high spatial (250 m)-spectral (14 wavelengths) resolution Rrs. First, we will adjust SGLI wavelength to MODIS wavelength to generate a reference image only from SGLI Rrs. Then the same wavelength MODIS Rrs will be used to calibrate the reference image through regression and interpolation. The spatial and optical properties will be investigated as a basis of the fusion process. Further evaluation will be done by in-situ data and the Aerosol Robotic Network-Ocean Color (AERONET-OC) established in the Ariake Sea. This is the first research that increases the spectral resolution of SGLI by image fusion. Moreover, this research could provide more spatial and spectral optical characteristic details of phytoplankton bloom than a single satellite.