Improving Coastal Decisions with Earth Observation for Algal Blooms

Challenge

Asian coasts face eutrophication and algal blooms that strain fisheries, tourism, and water safety, while agencies lack timely, consistent data.

Solution

Use satellite Earth observation, validate products, and align methods across platforms and countries to provide reliable indicators and decision tools.

Overview

Asia’s coastal waters face eutrophication and fast‑forming algal blooms, which put ecosystems, fisheries, and public health at risk. With support from the Asia‑Pacific Network for Global Change Research (APN), Eko Siswanto (Japan Agency for Marine‑Earth Science and Technology, Japan) is leading work that uses satellite Earth observation to track these pressures and provide consistent indicators for action.

Eutrophication is a build‑up of nutrients that feeds algae, and harmful algal blooms are episodes where algae reach damaging levels. The project reads ocean color from space and converts that signal into practical indicators such as chlorophyll‑a (algae) and total suspended matter (murkiness).

The researchers are using the Global Change Observation Mission – Climate (GCOM-C) satellite with the Second-generation Global Imager (SGLI), operated by the Japan Aerospace Exploration Agency (JAXA). SGLI provides ocean color measurements at 250 m resolution across 19 spectral bands, including a unique 380-nm band, and that data feeds standard water-quality products such as chlorophyll-a and total suspended matter.

One published article from the project groups Asian coastal waters into eight optical water types, which helps choose appropriate retrievals in turbid plumes and clearer offshore waters. Another article compares satellite color readings and water quality numbers from the two official JAXA platforms – G-Portal and JASMES – with measurements from coastal stations and research ships to see how closely the numbers match.”

Project publications report that processing choices affect results: agreement with in situ measurements varies by wavelength, G-Portal products perform better than JASMES at shorter wavelengths with lower errors and stronger correlations, JASMES yields about 12% more matchup points, and both platforms show improved agreement at longer wavelengths and capture stable interannual trends from roughly the 490-nm band onward.

Sensors, data, and methods

Satellites record how the sea surface reflects light. That color signal allows estimation of algae levels (chlorophyll‑a) and how murky the water is (total suspended matter). Because coastal waters differ, the project groups each area into optical water types and applies formulas that suit each type. The data come from G‑Portal and JASMES. The project compares the two and checks whether numbers stay steady over time, so indicators remain reliable for managers.

Regional collaboration and capacity

The work spans several Asian countries, where participating institutions are aligning methods for coastal monitoring and management. Because eutrophication and algal blooms cross borders, the network is building a shared evidence base that national and subnational agencies can use in planning and operations.

Ongoing activities

• Publishing and applying an optical water type algorithm tailored to Asian coastal waters to improve monitoring in optically complex settings.
• Comparing reflectance and water-quality products between JAXA’s G-Portal and JASMES platforms using comparisons with in situ measurements to evaluate retrieval accuracy across wavelengths and conditions.
• Developing an Earth observation-based monitoring approach that delivers regular indicators for eutrophication and algal blooms to support impact mitigation and adaptation across participating countries.

Project details

Acknowledgements

This project is supported by the Asia-Pacific Network for Global Change Research (APN) under its Collaborative Regional Research Programme (CRRP). Acknowledgements also go to the institutions named on the APN project page, including Burapha University, University of the Philippines, Bogor Agricultural University, Soka University, Kyoto University of Advanced Science, National Research and Innovation Agency, Sun Yat‑sen University, and Universiti Malaysia Terengganu.

Related information

• Project Permalink
• Salem, S.I., Toratani, M., Higa, H., Son, S., Siswanto, E., Ishizaka, J. (2025). Long-Term Evaluation of GCOM-C/SGLI Reflectance and Water Quality Products: Variability Among JAXA G-Portal and JASMES. Remote Sensing, 17 (p. 221). https://doi.org/10.3390/rs17020221
• Siswanto, E. (2025). Assessing optical water types in Asian coastal ocean waters from space using GCOM-C/SGLI observations. International Journal of Remote Sensing, 46(6), 2337–2357. https://doi.org/10.1080/01431161.2025.2450567
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