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

Abstract

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.

From ERS 1/2 to Sentinel-1: Subsidence Monitoring in Italy in the Last Two Decades

“…Cigna et al (2014) stated that satellite data highlighted the "overall stability of the main monuments and archeological sites of the historic center and the absence of clear deformation patterns at local-scale." Tapete and Cigna (2012) and Cigna et al (2016) performed an interferometric analysis over the archeological site of Capo Colonna in Calabria Region, located on top of a promontory affected by both rockfalls, due to marine erosion, and land subsidence, related to gas extraction in nearby wells. Cigna et al (2016) exploited 40 artificial corner reflectors to increase the radar coherence of the area, obtaining a highest number of measurement points.…”

Sentinel-1 Big Data Processing with P-SBAS InSAR in the Geohazards Exploitation Platform: An Experiment on Coastal Land Subsidence and Landslides in Italy

“…This integrated system included satellite SAR surveys among the shallow monitoring techniques employed by ENI in their typical subsidence monitoring networks [44]. SAR was also used in research papers for high-resolution [45] and multi-temporal [46,47] assessment of land subsidence in the last 25 years.…”

“…Of these, the majority focused on InSAR datasets retrieved from one to two SAR sensor datasets. Whereas [46] provided not only the most recent assessment using COSMO-SkyMed ascending and descending (2011)(2012)(2013)(2014)(2015) and Sentinel-1A ascending (2014)(2015)(2016) data, but also a 25-year-long review of local land subsidence through the combination with other C-and X-band InSAR datasets from 1992 to 2010. Comparison of the Sentinel-1 P-SBAS outputs with past observations available in the literature allowed corroboration of the spatial patterns and the order of magnitude of the deformation rates affecting the study area.…”

“…Such corroboration is achieved through a significant improvement in terms of both InSAR processing and post-processing of coherent targets and their time series. In particular, most of the previous studies on Capo Colonna relied on LOS displacement values only [38,39,46] and, when the authors of those papers attempted the extraction of deformation components, they limited it to either the vertical [45,46] or east-west [28] deformation field. Therefore, the present study is the first that, at least for the last six years, is able to fully constrain the geometry of the land subsidence process at the promontory not only along the LOS, but also along both the vertical and east-west directions.…”

Locating and monitoring of landslides based on small baseline subset interferometric synthetic aperture radar

“…[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] To further improve region investigation and monitoring accuracy of landslides, InSAR has been combined with optical remote sensing, Global Navigation Satellite System, corner reflectors, and ground-based radar. [36][37][38][39][40][41][42][43][44][45] However, due to the influence of complex regional topography and land use, improving the locating and monitoring accuracy of time series (TS)-InSAR in detecting the development of regional landslides remains a problem that urgently needs to be solved. Plank et al 46 presented a geographical information system procedure to predict the areas of layover and shadowing due to the geometric distortion of radar image caused by rugged terrain.…”