DETERMINATION of SEA SURFACE MUCILAGE FORMATIONS USING MULTITEMPORAL SENTINEL-2 IMAGERY

Abstract

In recent years, there has been a markedly increase in temperatures of the Earth's surface including oceans and seas due to global warming. Mucilage, or sea saliva observed in the inland seas and bays is one of the destructive results of this phenomenon. Mucilage formations have been widely observed in May 2021 in the Marmara Sea, especially in the Izmit bay. The main purpose of this study is to determine mucilage formations observed in the Izmit bay using Sentinel-2A (S2A) imagery captured on May 19 and 24. For this purpose, three datasets were formed and utilized for classification of mucilage formations. While the first dataset is consisted of only the 10m spatial resolution bands of the S2A imagery, the second dataset is included 6 bands of the S2A imagery at 20m resolution. The third dataset includes 10 bands of the S2A imagery resampled at 10m spatial resolution. Random forest (RF) and XGBoost ensemble learning algorithms were utilized to classification of these three datasets created separately for the 19 and 24 May imagery. To assess the classification performances, overall accuracy and Kappa coefficient measures calculated from confusion matrix were utilized. Results showed that the highest overall classification accuracies were estimated as 98.9% and 98.5% with RF and XGBoost, respectively for 19 May 10-band S2A dataset. On the other hand, the lowest overall accuracies were obtained with the use of 4-bands at 10m spatial resolution for both 19 and 24 May S2A imagery with RF and XGBoost algorithms. This result confirms that the use of the 10m and 20m bands of S2A images together can have a positive effect on the classification accuracy. Whilst the mucilage covered area on Izmit bay was calculated as 15.3 km on May 19, it was calculated as 20.13 km on May 24. In other words, it was observed that mucilage formations increased by about 31% in the 5-day time period in the study area. This clearly indicating the harmful effect of the mucilage phenomenon on the Izmit bay. © 2022 Elsevier B.V., All rights reserved.