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25 years of satellite InSAR monitoring of ground instability andcoastal geohazards in the archaeological site of Capo Colonna, Italy

F. Cigna1, P. Confuorto2, A. Novellino3, D. Tapete1, D. Di Martire2, M. Ramondini4,

D. Calcaterra2, S. Plank5, F. Ietto6, A. Brigante7, A. Sowter3
1British Geological Survey, Natural Environment Research Council, Nicker Hill, Keyworth NG12 5GG, UK
2Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Largo San Marcellino 10, 80138 Napoli, Italy
3Geomatic Ventures Limited, Nottingham Geospatial Building, Nottingham, NG7 2TU, UK
4Dipartimento di Ingegneria Civile, Architettonica ed Ambientale, Università degli Studi di Napoli Federico II, Via Claudio 21, 80125, Napoli, Italy
5German Aerospace Center (DLR), German Remote Sensing Data Center (DFD), Oberpfaffenhofen, Münchener Straβe 20, 82234 Weβling, Germany
6Dipartimento di Biologia, Ecologia e Scienze della Terra, Universita` della Calabria, 87036 Arcavacata Di Rende (CS),Italy
7Brigante Engineering Srl, Italy
Proc. SPIE 10003, SAR Image Analysis, Modeling, and Techniques XVI, 100030Q, October 2016
For centuries the promontory of Capo Colonna in Calabria region, southern Italy, experienced land subsidence and coastline retreat to an extent that the archaeological ruins of the ancient Greek sanctuary are currently under threat of cliff failure, toppling and irreversible loss. Gas extraction in nearby wells is a further anthropogenic element to account for at the regional scale. Exploiting an unprecedented satellite Synthetic Aperture Radar (SAR) time series including ERS-1/2, ENVISAT, TerraSAR-X, COSMO-SkyMed and Sentinel-1A data stacks acquired between 1992 and 2016, this paper presents the first and most complete Interferometric SAR (InSAR) baseline assessment of land subsidence and coastal processes affecting Capo Colonna. We analyse the regional displacement trends, the correlation between vertical displacements with gas extraction volumes, the impact on stability of the archaeological heritage, and the coastal geohazard susceptibility. In the last 25 years, the land has subsided uninterruptedly, with highest annual line-of-sight deformation rates ranging between -15 and -20 mm/year in 2011-2014. The installation of 40 pairs of corner reflectors along the northern coastline and within the archaeological park resulted in an improved imaging capability and higher density of measurement points. This proved to be beneficial for the ground stability assessment of recent archaeological excavations, in an area where field surveying in November 2015 highlighted new events of cliff failure. The conceptual model developed suggests that combining InSAR results, geomorphological assessments and inventorying of wavestorms will contribute to unveil the complexity of coastal geohazards in Capo Colonna.
Key-words: InSAR, PSInSAR, SBAS, CPT, ground motion, coastal erosion, land subsidence, cultural heritage