Long-Term Coastline Dynamics from Landsat 5 and Landsat 8 Multitemporal Images in Thanh Hóa Province, Vietnam

Abstract—In recent years, human activities have had a profound impact on the estuaries and coastal areas of Vietnam, resulting in the active erosion and accretion (enlargement) of the coastline. In this paper, Landsat images for the period of 1988–2022 are used to assess the coastline dynamics of Thanh Hóa Province (North Central Coast). NDWI, ANDWI, MNDWI, AWEInsh, AWEIsh, and BandWet, determined from Landsat images, are used to interpret the water surface. The Otsu threshold method is used to separate “water surface” from “land objects,” and the separation accuracy is then estimated based on the Kappa coefficient. The results showed that the ANDWI index has the highest accuracy in decoding the coastline of the study area; the Kappa coefficient reaches 0.95; and for other indices (NDWI, MNDWI, AWEInsh, AWEIsh, and BandWet), the Kappa coefficient is respectively equal to 0.91, 0.92, 0.93, 0.92, and 0.92. After decoding the water surface boundaries using ANDWI, the vectorization of boundaries and superimposition of vector images on each other are carried out to assess the coastline variability and the construction of a map of the coastline dynamics. It is found that, in the northern part of the coastal zone of Thanh Hóa Province, the active accretion of the coastline is observed. The average accretion rate was 150 m/year; the maximum rate was 457 m/year. On the contrary, on the southern coast of the Thanh Hóa Province, coastline erosion prevails with a maximum rate of 38 m/year and an average rate of about 10 m/year.