|Paper title||COSMO-SkyMed for archaeological applications: achievements and new perspectives for site detection, regional mapping and multi-sensor condition assessment|
|Form of presentation||Poster|
In the current arena of satellite Synthetic Aperture Radar (SAR) missions, the COnstellation of small Satellites for Mediterranean basin Observation (COSMO-SkyMed) end-to-end Earth observation (EO) system of the Italian Space Agency (ASI), fully deployed and operational since 2011, represents the national excellence in space technology, not to forget its role as a Copernicus Contributing Mission. Four identical spacecrafts, each equipped with a multimode X-band SAR sensor, provide imagery at high spatial resolution (up to 1 m) and short revisit time (up to 1 day in tandem configuration), for different operational scenarios (e.g. regular acquisition of time series, on demand, emergency).
These characteristics, the consistency in interferometric acquisition parameters over long periods of time, alongside an easier accessibility owing to dedicated initiatives carried out by ASI to promote the exploitation by a wider spectrum of users , contributed to a significant increase in the use of COSMO-SkyMed data, also in the field of documentation, study, monitoring and preservation of cultural and archaeological heritage. While interferometric applications more rapidly attracted the interest in the geoscientific and heritage community for purposes of structural health monitoring, periodic monitoring and early warning, more efforts were required to disseminate the potentialities of COSMO-SkyMed for more traditional archaeological applications, e.g. site detection and mapping.
To this purpose, a portfolio of use-cases has been developed by ASI on sites across the Mediterranean and Middle East regions, to demonstrate the usefulness of COSMO-SkyMed data in four main domains, i.e.: archaeological prospection, topographic surveying, condition (damage) assessment, and environmental monitoring .
Among the main lessons learnt, it is worth highlighting that:
- COSMO-SkyMed Enhanced Spotlight data are most suited for local/site-scale investigations and fine archaeological mapping, while StripMap HIMAGE mode provides the best trade-off between high spatial resolution (less than 5 m) and areal coverage (40 km swath width);
- Regular, frequent, and consistent time series, being acquired according to a predefined acquisition plan (e.g. the Background Mission) provide an extraordinary resource for documentation of unexpected events, either of damage or related to conservation activities, that discontinuous observations definitely fail to capture, or lower spatial resolution global ones may not be able to depict with sufficient detail and scale of observation;
- Depending on the type and kinematic of the process(es) to investigate, and equally the land cover and physical properties of the targets to detect, coherence-based approaches may be more effective to delineate occurred changes, such as landscape disturbance.
These experiences not only showcase how COSMO-SkyMed can complement established archaeological research methods, but also allow the better envisioning of where the new functions (e.g. increased spatial resolution, more flexibility, enhanced polarimetric properties) now provided by COSMO-SkyMed Second Generation (CSG) can further innovate.
To expand the discussion, the present paper will also focus on two aspects (and associated applications) that have not been fully explored yet by the user community:
1. The exploitation of COSMO-SkyMed in combination with other sensors, according to the CEOS concept of “virtual constellation”, for site detection, multi-temporal monitoring and back-analysis of recent hazard events of potential concern for conservation;
2. The benefits that less used higher-level COSMO-SkyMed products, such as digital elevation models (DEMs), can bring to support specific tasks of interests for archaeologists, in integration with or as un upgrade of more established (mostly free) EO-derived DEM products.
The first topic will be demonstrated through the combination of COSMO-SkyMed images either from the Background Mission or bespoke acquisitions and Copernicus Sentinel-1 and Sentinel-2 time series, over three archaeological sites in Syria, to document otherwise unknown flooding events  and fires. The objective is to show how SAR and optical multispectral data from missions operating following different acquisition paradigms can be effectively exploited together, as if they were collected according to a coordinated observation scheme. Furthermore, the case studies highlight, on one side, the incredible wealth of information that is yet to be extracted from continuously growing image archives to document heritage and their conservation history; on the other, the role that thematic platforms, cloud computing resources and infrastructure can play to facilitate users to generate more advanced mapping products, regardless of their specialist expertise in SAR.
The second topic will be discussed in relation to two very recent experiences of regional-scale systematic mapping of archaeological mounds and detection of looting in Iraq. In the first case , the activity was carried out based on StripMap COSMO-SkyMed DEMs in comparison with the Shuttle Radar Topography Mission (SRTM) and Advanced Land Observing Satellite World 3D–30 m (ALOS World 3D) DEMs. The latter were purposely selected, given that they are the most common DEM sources used by archaeologists. In the second case, in comparison with Cartosat-1 Euro-Maps 3D Digital Surface Model made available by ESA through its Earthnet Third Party Missions (TPM) programme and the ad-hoc call for R&D applications. The demonstration highlights that, thanks to the 10 m posting and the consequent enhanced observation capability, COSMO-SkyMed DEM is advantageous to detect both well preserved and levelled or disturbed tells, standing out for more than 4 m from the surrounding landscape. Through the integration with other optical products and historical maps, the COSMO-SkyMed DEM not only provides the confirmation of the spatial location of sites known from the literature, but also allows for an accurate localization of sites that had not been previously mapped.
 BATTAGLIERE M.L., CIGNA F., MONTUORI A., TAPETE D., COLETTA A. (2021) Satellite X-band SAR data exploitation trends in the framework of ASI’s COSMO-SkyMed Open Call initiative, Procedia Computer Science, 181, 1041-1048, doi:10.1016/j.procs.2021.01.299
 TAPETE D. & CIGNA F. (2019) COSMO-SkyMed SAR for Detection and Monitoring of Archaeological and Cultural Heritage Sites. Remote Sensing, 11 (11), 1326, 25 pp. doi:10.3390/rs11111326
 TAPETE D. & CIGNA F. (2020) Poorly known 2018 floods in Bosra UNESCO site and Sergiopolis in Syria unveiled from space using Sentinel-1/2 and COSMO-SkyMed. Scientific Reports, 10, article number 12307, 16 pp. doi:10.1038/s41598-020-69181-x
 TAPETE D., TRAVIGLIA A., DELPOZZO E., CIGNA F. (2021) Regional-scale systematic mapping of archaeological mounds and detection of looting using COSMO-SkyMed high resolution DEM and satellite imagery. Remote Sensing, 13 (16), 3106, 29 pp. doi:10.3390/rs13163106