11:45 AM - 12:00 PM
[ACG45-11] Seasonal and interannual variability of seagrass distribution detected by Landsat TM, ETM+ and OLI images in western Nanao Bay
Keywords:seagrass, landsat, remote sensing, mapping, Nanao Bay
To study seasonal and interannual variability for seagrass, past Landsat archive images were analyzed to detect seagrass distribution. Since past field data of seagrass distribution were not sufficient, the K means unsupervised classification technique with the six classes was applied for mapping the seagrass distribution from past Landsat archive images. The classification result of the Landsat OLI image on June 1, 2015 was used as a reference to determine seagrass distributions as it had a good compliance with the ground truth data. Since two out of the six classes obtained from the unsupervised classification corresponded to a distribution pattern of (1) the dense seagrass and (2) the dense seagrass with Sargassum classes from the June 1, 2015, these two classes were merged into one class to represent seagrass distribution in Western Nanao Bay. A comparison of seasonal patterns of seagrass distribution estimated by the unsupervised classification of the Landsat archive data from November 22, 1991 to June 1, 1992 and from November 21, 2014 to June 1, 2015 showed consistent similar seasonal pattern; indicating seagrass recovery between late fall to early summer, which corresponds to seagrass seed germination periods. The Landsat archive data during the seagrass seed germination periods were also obtained to study interannual variability of seagrass distribution. The obtained results showed that there are fewer seagrass years (1994, 1996 and 1999) and more seagrass years (2000, 2004, 2007 and 2008) during the seagrass seed germination periods, indicating the survival rate of seagrass varied depending on the year.