Mapping of morphological coastline changes based on aerial photographs and Discrete Fourier Transform, Hel Peninsula, Poland

The coast is a dynamic zone where constantly occurring hydrodynamic and morphodynamic processes affect the shape of the shore. The paper presents a method based on spatial and spectral analysis of changes in the coastline position based on data obtained from aerial photographs interpretation and Fourier analysis, on the example of the Hel Peninsula. The Hel Peninsula is one of the most interesting accumulation forms of the Polish Baltic coast, where dynamic changes of the seashore cause the occurrence of time-varying sections of accumulation-abrasion of the coastline. For the purpose of detecting the coastline changes, historical aerial photographs from the years 1947, 1957, 1963, 1991 were used. It was assumed that the over-40-year research period, which includes the obtained series of aerial photographs, would allow for a sufficient study of the long-term shoreline changes, which allow for distinguishing the length of characteristic coastline undulations. The quasi-wave signal of the shoreline changes obtained from the aerial photographs interpretation, after using Fourier analysis, enabled an effective and precise identification of the coastline undulation. The spatial analyses, showed that the Hel Peninsula is clearly divided into a part subjected to accumulation processes and an abraded one. Furthermore, the dynamics of coastline changes was determined, showing that the abrasive processes were intensifying. Moreover, spectral Fourier analysis allowed for the precise identification of coastline undulations with dominant lengths. The obtained results of spatial and spectral analysis indicate that abrasive-accumulation sections with a length of about 0.3–4.5 km dominate on the Hel Peninsula shoreline.