Coastal erosion trends were estimated (where possible) using available remote sensed information. Shorelines were detected using archived optical data such as aerial photographs and satellite imagery of high resolution collected in different times (Worldview and Pleiades satellites with 8 and 4 bands respectively). The study area was isolated from the optical data by focusing on the beach system, followed by pre-processing techniques that include conversion from digital to radiation values. 3 different radiometric calibration methods have been applied which are based on thresholding of the greyscale imagery that was derived after the initial process of each image: 1) Modified Redness Index – MRI, 2) WorldView Water Index – WVWI και 3) RGB Thresholding. The results of the aforementioned methods were compared with high precision topographic field data (recorded shoreline with an RTK-DGPS); it was found that the WVWI results had the best fit. A mask was created for each image with the use of a specialized index (Normalized Difference Water Index -NDWI) that is commonly used in areas that are covered by water in order to detect the water/land boundaries. 3 different shoreline limits have been extracted, the limit of waterline, the limit of the wave foaming and the upper limit of wave foaming. Finally, the SDAS tool in GIS was used and specific cross-shore beach sections have been selected in order to compare the shoreline movement at these points for the different dates of the optical data.
Recorded shoreline from satellite image. Example from a Worldview II image (19/11/2012) of Eresos beach (Lesvos)
