Assessment of the shoreline evolution using the CORONA declassified images. A case study in the north of Ilia prefecture, Peloponnese, Greece

A valuable archive of multiresolution imagery covering the period from 1960 to 1980 has been declassified by the United States of America (USA) government on February 22, 1995, and became available for sharing to the scientific community. This imagery is part of USA's top-secret program with the codename CORONA that ran since the Cold War. We tried to assess the accuracy of the declassified datasets and estimate if they can be used in synergy with classical aerial photos to estimate the future shoreline position. Furthermore, their contribution to estimating the shoreline's long-term changes using statistical tools such as the linear regression rate was examined. Two elongated coasts located in the Pinios and Andravida/Kyllini Municipalities located in the north of Ilias Prefecture, Peloponnese, Greece, were used as test sites. Two models were used that compared the actual and the forecasted. The results show that erosion prevails in the coastal area of the Pinios and Andravida/Kyllini municipalities with a mean EPR rate ranging from -0.16 to -0.43 m/y and from -0.18 to -0.31 m/y according to the actual and the forecasted models, respectively. Moreover, the respective maximum erosion rates are -1.15 and -1.57 m/y (actual model) and -2.04 and -1.89 m/y (forecasted model), whereas the maximum accretion rates are +0.76 and +1.02 m/y (actual model) and +1.68 and +2.00 m/y. The declination of the CORONA declassified imagery ranges from 2.63% to 6.62% in the Andravida/Kyllini territory and from 6.53% to 22.38% in the Pinios area. These results were cross-validated, using the R-squared rates, the root mean square error, and the mean annual error (MAE) statistical techniques. The MAE presented a better correlation as it provided equal rates (0.31 m/y) for both of the EPR datasets. (c) 2022 Society of Photo-Optical Instrumentation Engineers (SPIE)

Automated summary

This article presents a valuable archive of declassified multiresolution imagery from the USA government. It examines the accuracy of the datasets and their potential use in estimating future shoreline position and long-term changes. The study focuses on two coastal areas in Greece and demonstrates the efficacy of combining the declassified imagery with classical aerial photos to estimate erosion and accretion rates.