Discolored seawater detection using ASTER reflectance products: A case study of Satsuma-Iwojima, Japan

Discolored seawater caused by volcanic activity can be detected with satellite remote sensing at some submarine volcanoes and volcanoes near coastlines. We demonstrate that two kinds of discolored seawaters can be discriminated by their reflectance patterns using ASTER Reflectance Products at Satsuma-Iwojima, Japan. White to green seawater that is due to hydrous oxides formed when Al- and Fe-rich acidic waters mix with seawater shows high, medium and low reflectances at band 1 (central wavelength: 0.56 μm), band 2 (central wavelength: 0.66 μm), and band 3 (central wavelength: 0.81 μm), respectively. On the other hand, reddish-brown seawater that is due to the outflow of neutral-pH, iron-bicarbonate water shows high reflectance at band 2, medium reflectance at band 1 and low reflectance at band 3. The chemical composition of discolored seawater, which is one of the characteristics of volcanic activity, can be estimated from remote-sensing data. The ASTER Reflectance Product is a standard validated product generated by the ASTER Ground Data System using an atmospheric correction.