Monitoring coastline variations in the Pearl River Estuary from 1978 to 2018 by integrating Canny edge detection and Otsu methods using long time series Landsat dataset

The coastline of the Pearl River Estuary (PRE) experienced significant changes due to the increasing demand for land. Previous studies have focused on coastline changes of the mainland in China; thus changes of island coastlines have not been well investigated. In this study, the coastlines of the continent and islands of the Pearl River Estuary from 1978 to 2018 were extracted and analyzed by integrating Canny edge detection and Otsu methods based on Landsat data, and the coastline was classified into six types including biological, sandy, muddy, estuarine, rocky, and artificial via visual interpretation. The coastline length, coastline change rate and change area were calculated and analyzed for the 40 years period. The precision test showed that the coastline extraction methods presented in this paper meet the accuracy standard. The coastline length of the Pearl River Estuary was found to have increased rapidly from 789 km in 1978 to 979 km in 2018. During the past four decades, a large proportion of natural coastline converted into artificial one (66% in 2018), while 577 km(2) land increased in this area. The coastline of the western PRE demonstrates more rapid change rates than that of the eastern part, and more land reclamation has occurred in the western area. Between 1988 and 1997, the coastline length and area of reclamation experienced the most extensive changes. Both natural factors, including sediment transport, sea-level rise, wind, tide, as well as anthropogenic factors, such as land reclamation and dam construction, have impacted coastline variation of the Pearl River Estuary in the past four decades. In general, the western part of the study area showed more remarkable coastline change and experienced the enormous influence of land reclamation, dam construction and sediment transport, compared with the eastern part.