Tidal flat reflectance model accommodating tidal conditions using Geostationary Ocean Color Imager (GOCI): Preliminary results

The objective of this study is to develop a tidal flat reflectance model according to tidal conditions. Tidal flat reflectance greatly varies with tidal conditions twice a day that causes changes in water contents along with exposure time, remnant water, etc. It is difficult to retrieve sediment grain size from optical reflectance alone without correcting the tidal condition effects. The Geostationary Ocean Color Imager (GOCI) is the first ocean color sensor mounted on the geostationary satellite, and provides images 8 times a day. A preliminary tidal flat reflectance model was obtained from 72 cloud free GOCI images in March, 2011. Two reflectance models were found to be minimally required for mud and mixed flats, while the differences between mixed and sand flats were insignificant. The models accommodate tidal conditions of flood or ebb tide. The results lead to a conclusion that the remnant surface water on the recently exposed tidal flats plays a significant role in influencing the optical reflectance. The surface reflectance increases gradually during the ebb tide, while the slope of decrease is steep during the flood tide.