Time series analysis of the Caspian Sea shoreline in response to sea level fluctuation using remotely sensed data

Abstract

The Caspian Sea (CS), biggest inland water worldwide has experienced around 3 m oscillation in sea level during the 20th century. These rapid sea level fluctuations have had a great impact on the coastal habitat around this sea. Therefore, this study is aimed to investigate the long-term changes of the western part of the Caspian Sea shoreline and Anzali lagoon and their dynamic responses to the sea level fluctuation using time series analysis of remotely sensed data over the 40-years. To this end, the long-term Caspian Sea shoreline and the area and perimeter of the Anzali Lagoon were extracted from the time series of Landsat satellite imagery (1975 till 2016) by using an automatic procedure including the combination of the Tasseled-Cap and texture filter methods. Afterwards, shoreline erosion/accretion rates were evaluated by using the Net Shoreline Movement (NSM) and End Point Rate (EPR) techniques. Finally, the sea level changes of the CS, were extracted through the multiple altimetry satellite data and the relationship between the relative sea level fluctuation and CS shoreline and Anzali lagoon area were studied. Results of the changes of shoreline positions over the study period (1975–2016) indicate that the whole coastal study area is subjected to accretion and erosion of 20.37 and -19.22 (m/year) respectively. There is balance between the whole EPR in all transects and periods between 1975 and 2016. This shows that when erosion happens in a region, accretion will be happened in another region, and this behavior is symmetrical. When the sea level decreased, the EPR values showed the accretion/seaward and vice versa. So, the shoreline movement has a strong nonlinear response to the sea level fluctuation with a coefficient of determination of −0.66. Also results show the strong response of the Anzali lagoon to the sea level fluctuation with a coefficient of determination of 0.78 for a nonlinear relationship between the changes of area of Anzali Lagoon and the CS fluctuation. This lagoon experienced the greatest and lowest values of its area on 2003 and 1985, respectively, which are matched with the high and low stands of the Caspian Sea Level.