Poorly known 2018 floods in Bosra UNESCO site and Sergiopolis in Syria unveiled from space using Sentinel-1/2 and COSMO-SkyMed

Abstract

The instability situation affecting the Middle East poses threats to preservation of cultural heritage. Mapping efforts based on satellite imagery currently concentrate more on recording human-induced damage than impacts of unforeseen natural events (e.g. floods). In 2018, the UNESCO World Heritage Site of Bosra and the landscape of Sergiopolis-Resafa in Syria were flooded after heavy rainfall. While the first incident was reported by heritage organisations (although information was limited to the main monument), the second event was completely unknown. Using optical and radar satellite images from the European Commission's Copernicus Sentinels fleet and the Italian Space Agency's COSMO-SkyMed constellation, we prove that these data are an enormous reservoir of information to assess comprehensively the duration, extent and severity of such natural events. In Bosra, several key assets were flooded besides the Roman Theatre, with waters taking from few days to several weeks to evacuate and dry out. In Sergiopolis, while the main ruins were sheltered by the fortification walls, the nearby floodplain was inundated. The floodwater-flow pattern resembled the simulations developed by archaeologists to prove the existence of an ancient system of embankments and dam. Our results suggest that many other events posing risk to heritage assets, otherwise unnoticed, may be unveiled if current satellite imagery archives, yet to analyse, are systematically screened.

Multi-Temporal Change Detection Analysis of Vertical Sprawl over Limassol City Centre and Amathus Archaeological Site in Cyprus during 2015–2020 Using the Sentinel-1 Sensor and the Google Earth Engine Platform

“…Indeed, the use of the Copernicus Sentinel-1 radar sensor [ 26 ] is still limited for heritage management applications, with exceptions in the application of interferometric synthetic-aperture radar (In-SAR) analysis [ 27 , 28 ]. This is well reported in [ 29 ] where the coarse spatial resolution of the radar data and the signal interference limits the potential use of the Sentinel-1 sensor.…”

Satellite-Based Methodology for Purposes of Rescue Archaeology of Cultural Heritage Threatened by Dam Construction

“…The archive of images produced by these satellites is available for free to everyone. Its application has already demonstrated considerable effectiveness in documenting different types of cultural heritage hazards such as flooding [67,68], looting [4,62] and urban sprawl [3,69]. For the scope of the present research, it is worth mentioning that recent research has proved how Sentinel-1 and Sentinel-2 data can be effectively used for detection of archaeological mounds [70,71].…”

Managing Flood Hazard in a Complex Cross-Border Region Using Sentinel-1 SAR and Sentinel-2 Optical Data: A Case Study from Prut River Basin (NE Romania)

“…At the same time, an SLC dataset provides the highest possible spatial resolution [56,57]. Level-1 Ground Range Detected (GRD) comprises of focused SAR data that has been detected, multi-looked and projected to ground range using an Earth ellipsoid model, such as WGS84, storing only amplitude (pixel intensity) without any remaining phase information [44]. The information recorded in both Level-1 product types lies in the measured echoes of the backscattered signal at the C-band wavelength [58].…”

“…The launch of European Space Agency (ESA) Copernicus Program and its particular SAR mission Sentinel-1 in April 2014 brought up new opportunities in terms of near real-time flood disaster monitoring, flood extent mapping and emergency management [37][38][39]. Given the new improved capabilities in terms of global coverage, free availability, 3-6 days revisit time and 10 m spatial resolution, Sentinel-1 SAR imagery proved its efficiency in numerous disaster-related studies that focused on similar topics [40][41][42][43][44]. Moreover, the practice of using Sentinel-1 SAR data in combination with cloud-free ESA Sentinel-2 optical imagery (when available) can lead to more acurate flood hazard and flood risk analysis products, such as spatio-temporal inundation maps [45].…”