81 research outputs found
Geohazards affecting UNESCO WHL sites in the UK observed from geological data and satellite InSAR
Geohazards pose significant threats to cultural and natural heritage worldwide. In the UK, only 1 out of 29 UNESCO
World Heritage List (WHL) sites has been inscribed on the list of World Heritage in Danger, whilst it is widely accepted
that many more could be affected by geohazards. In this paper we set out the foundations of a methodological approach
to analyse geological, geohazard and remote sensing data available at the British Geological Survey to retrieve an
overview of geohazards affecting the UK WHL sites. The Castles and Town Walls (constructed in the time of King
Edward I) in Gwynedd in north Wales are used as test sites to showcase the methodology for geohazard assessment at
the scale of individual property also to account for situations of varied geology and local topography across multiproperty
WHL sites. How such baseline geohazard assessment can be combined with space-borne radar interferometry
(InSAR) data is showcased for the four UNESCO WHL sites located in Greater London. Our analysis feeds into the
innovative contribution that the JPI-CH project PROTHEGO âPROTection of European cultural HEritage from GeOhazardsâ
(www.prothego.eu) is making towards mapping geohazards in the 400+ WHL sites of Europe by exploiting
non-invasive remote sensing methods and surveying technologies
âLooting marksâ in space-borne SAR imagery: measuring rates of archaeological looting in Apamea (Syria) with TerraSAR-X Staring Spotlight
In archaeological remote sensing, space-borne Synthetic Aperture Radar (SAR) has not been used so far to monitor âlootingâ (i.e. illegal excavations in heritage sites) mainly because of the spatial resolution of SAR images, typically not comparable to the ground dimensions of looting features. This paper explores the potential of the new TerraSAR-X beam mode Staring Spotlight (ST) to investigate looting within a workflow of radar backscattering change detection. A bespoke time series of five single polarisation, ascending mode, ST scenes with an unprecedented azimuth resolution of 0.24 m was acquired over the archaeological site of Apamea in western Syria, from October 2014 to June 2015 with a regular sampling of one image every two months. Formerly included in the Tentative List of UNESCO, the site has been heavily looted from at least early 2012 to May 2014, as confirmed by Google Earth Very High Resolution (VHR) optical imagery. Building upon the theory of SAR imaging, we develop a novel conceptual model of âlooting marksâ, identify marks due to occurrence of new looting and discriminate them from alteration (e.g. filling) of pre-existing looting holes. âLooting marksâ appear as distinctive patterns of shadow and layover which are visible in the ground-range reprojected ST image and generated by the morphology of the holes. The recognition of looting marks within ratio maps of radar backscatter (Ï0) between consecutive ST scenes allows quantification of the magnitude, spatial distribution and rates of looting activities. In agreement with the estimates based on Google Earth imagery, the ST acquired in October 2014 shows that ~ 45% of the site was looted. In the following eight months new looting happened locally, with holes mainly dug along the margins of the already looted areas. Texture values of ~ 0.31 clearly distinguish these holes from the unaltered, bare ground nearby. Hot spots of change are identified based on the temporal variability of Ï0, and colour composites indicate where repeated looting and alteration of existing holes occurred. Most looting marks are observed north of the two main Roman decumani. Looting intensified almost steadily from December 2014, with over 1500 new marks in FebruaryâApril 2015. The estimated rates of looting increased from 214 looting marks/month in OctoberâDecember 2014 to over 780 marks/month in AprilâJune 2015, and numerically express the dynamic nature of the phenomenon to which Apamea is still exposed. The method of identifying looting marks in VHR radar images therefore proves a reliable opportunity for archaeologists and image analysts to measure remotely the scale of looting and monitor its temporal evolution
Understanding geohazards in the UNESCO WHL site of the Derwent Valley Mills (UK) using geological and remote sensing data
An analysis of the British Geological Surveyâs key hazard datasets (GeoSure, DiGMapGB, National Landslide Database,
Geological Indicators of Flooding and Susceptibility to Groundwater Flooding) has provided an enhanced understanding
of geohazards within the Core Area and Buffer Zone of the UNESCO Derwent Valley Mills World Heritage List (WHL)
site, UK. This knowledge contributes to the preservation of this industrial heritage site that is included as the UK
demonstration site of the Joint Programming Initiative on Cultural Heritage and Global Change (JPI-CH) Heritage Plus
project PROTHEGO: âPROTection of European cultural HEritage from GeO-hazardsâ which is mapping geohazards in
the 400+ WHL sites of Europe using satellite radar interferometry (InSAR) combined with geological information.
Acting as baseline geohazard characterisation to feed into PROTHEGOâs WP5-WP6, our analysis reveals that flooding
from fluvial water flow and emergence of groundwater at the ground surface (across over 50% and 40% of the Core
Area, respectively) are the main geohazards that require careful consideration, together with slope instability along the
steep sides of the Derwent river valley (e.g. 1.4 km2 landslide deposits found at Cromford within the Buffer Zone). The
UK Climate Projections 2009 (UKCP09) for the Derwent river catchment suggest drier summers (e.g. -15.1 to -19.4%
change in summer precipitation in 2050; -18.5 to -23.1% in 2080), wetter winters and increased annual temperatures (e.g.
+2.4 to +2.5 °C in 2050; +3.4 to +3.5 °C in 2080) under a medium greenhouse gas emission scenario. These could
exacerbate flooding and slope instability and extend the areas susceptible to geohazards, posing further challenges for
heritage management
Small Baseline Subset (SBAS) pixel density vs. geology and land use in semi-arid regions in Syria
36 ENVISAT ASAR images acquired in 2002 to 2010 along
descending passes with nominal revisiting time of 35 days
were processed over the whole region of Homs, western
Syria, by implementing the low-pass Small Baseline Subset
(SBAS) technique. More than 280,000 coherent pixels with
~100m ground resolution were obtained. We analysed pixel
spatial distribution in respect of local geology and land use,
to assess to what extent these factors can influence the
performance of an interferometric deformation analysis in a
semi-arid environment. Filtering out the amount of pixels
associated with the urban fabric of Homs and surrounding
villages, it is apparent that limestone and marl units are less
prone to generate coherent pixels if compared with the basalt
units in the north-western sector of the processed region.
The latter resulted in pixel density of ~50-60 pixels/km2,
which is comparable with that found over urban settlements
and man-made structures
Urban remote sensing in areas of conflict: TerraSAR-X and Sentinel-1 change detection in the Middle East
Timely availability of images of suitable spatial resolution, temporal frequency and coverage is currently one of the major technical constraints on the application of satellite SAR remote sensing for the conservation of heritage assets in urban environments that are impacted by human-induced transformation. TerraSAR-X and Sentinel-1A, in this regard, are two different models of SAR data provision: very high resolution on-demand imagery with end user-selected acquisition parameters, on one side, and freely accessible GIS-ready products with intended regular temporal coverage, on the other. What this means for change detection analyses in urban areas is demonstrated in this paper via the experiment over Homs, the third largest city of Syria with an history of settlement since 2300 BCE, where the impacts of the recent civil war combine with pre- and post-conflict urban transformation . The potential performance of Sentinel-1A StripMap scenes acquired in an emergency context is simulated via the matching StripMap beam mode offered by TerraSAR-X. Benefits and limitations of the different radar frequency band, spatial resolution and single/multi-channel polarization are discussed, as a proof-of-concept of regular monitoring currently achievable with space-borne SAR in historic urban settings. Urban transformation observed across Homs in 2009, 2014 and 2015 shows the impact of the Syrian conflict on the cityscape and proves that operator-driven interpretation is required to understand the complexity of multiple and overlapping urban changes
Trends and perspectives of space-borne SAR remote sensing for archaeological landscape and cultural heritage applications
This paper provides an overview of the opportunities that image analysts, archaeologists and conservation scientists currently have to use space-borne Synthetic Aperture Radar (SAR) imagery for prospection of cultural landscapes and investigation of environmental, land surface and anthropogenic processes that can alter the condition of heritage assets. The benefits of the recent developments in SAR satellite sensors towards higher resolution (up to less than 1 m) and shorter revisiting times (up to a few days) are discussed in relation to established techniques using the two key SAR parameters â amplitude and phase. Selected case studies from Middle East to South America illustrate how SAR can be effectively used to detect subtle archaeological features in modern landscapes, monitor historic sites and assess damage in areas of conflict. These examples form the basis to highlight the current trends in archaeological remote sensing based on space-borne SAR data in the era of the European Space Agency's Sentinel-1 constellation and on-demand high resolution space missions such as TerraSAR-X
Deformation analysis of a metropolis from C- to X-band PSI: proof-of-concept with Cosmo-Skymed over Rome, Italy
Stability of monuments and subsidence of residential
quarters in Rome (Italy) are depicted based on geospatial
analysis of more than 310,000 Persistent Scatterers (PS)
obtained from Stanford Method for Persistent Scatterers
(StaMPS) processing of 32 COSMO-SkyMed 3m-resolution
HH StripMap ascending mode scenes acquired between 21
March 2011 and 10 June 2013. COSMO-SkyMed PS
densities and associated displacement velocities are
compared with almost 20 years of historical C-band ERS-
1/2, ENVISAT and RADARSAT-1/2 imagery. Accounting
for differences in image processing algorithms and satellite
acquisition geometries, we assess the feasibility of ground
motion monitoring in big cities and metropolitan areas by
coupling newly acquired and legacy SAR in full time series.
Limitations and operational benefits of the transition from
medium resolution C-band to high resolution X-band PS
data are discussed, alongside the potential impact on the
management of expanding urban environments
Exploiting satellite SAR for archaeological prospection and heritage site protection
Optical and Synthetic Aperture Radar (SAR) remote sensing has a long history of use and reached a good level of maturity in archaeological and cultural heritage applications, yet further advances are viable through the exploitation of novel sensor data and imaging modes, big data and high-performance computing, advanced and automated analysis methods. This paper showcases the main research avenues in this field, with a focus on archaeological prospection and heritage site protection. Six demonstration use-cases with a wealth of heritage asset types (e.g. excavated and still buried archaeological features, standing monuments, natural reserves, burial mounds, paleo-channels) and respective scientific research objectives are presented: the Ostia-Portus area and the wider Province of Rome (Italy), the city of Wuhan and the Jiuzhaigou National Park (China), and the Siberian âValley of the Kingsâ (Russia). Input data encompass both archive and newly tasked medium to very high-resolution imagery acquired over the last decade from satellite (e.g. Copernicus Sentinels and ESA Third Party Missions) and aerial (e.g. Unmanned Aerial Vehicles, UAV) platforms, as well as field-based evidence and ground truth, auxiliary topographic data, Digital Elevation Models (DEM), and monitoring data from geodetic campaigns and networks. The novel results achieved for the use-cases contribute to the discussion on the advantages and limitations of optical and SAR-based archaeological and heritage applications aimed to detect buried and sub-surface archaeological assets across rural and semi-vegetated landscapes, identify threats to cultural heritage assets due to ground instability and urban development in large metropolises, and monitor post-disaster impacts in natural reserves
A user-oriented methodology for DInSAR time series analysis and interpretation: landslides and subsidence case studies
Recent advances in multi-temporal Differential Synthetic Aperture Radar (SAR) Interferometry (DInSAR) have greatly improved our capability to monitor geological processes. Ground motion studies using DInSAR require both the availability of good quality input data and rigorous approaches to exploit the retrieved Time Series (TS) at their full potential. In this work we present a methodology for DInSAR TS analysis, with particular focus on landslides and subsidence phenomena. The proposed methodology consists of three main steps: (1) pre-processing, i.e., assessment of a SAR Dataset Quality Index (SDQI) (2) post-processing, i.e., application of empirical/stochastic methods to improve the TS quality, and (3) trend analysis, i.e., comparative implementation of methodologies for automatic TS analysis. Tests were carried out on TS datasets retrieved from processing of SAR imagery acquired by different radar sensors (i.e., ERS-1/2 SAR, RADARSAT-1, ENVISAT ASAR, ALOS PALSAR, TerraSAR-X, COSMO-SkyMed) using advanced DInSAR techniques (i.e., SqueeSARâą, PSInSARâą, SPN and SBAS). The obtained values of SDQI are discussed against the technical parameters of each data stack (e.g., radar band, number of SAR scenes, temporal coverage, revisiting time), the retrieved coverage of the DInSAR results, and the constraints related to the characterization of the investigated geological processes. Empirical and stochastic approaches were used to demonstrate how the quality of the TS can be improved after the SAR processing, and examples are discussed to mitigate phase unwrapping errors, and remove regional trends, noise and anomalies. Performance assessment of recently developed methods of trend analysis (i.e., PS-Time, Deviation Index and velocity TS) was conducted on two selected study areas in Northern Italy affected by land subsidence and landslides. Results show that the automatic detection of motion trends enhances the interpretation of DInSAR data, since it provides an objective picture of the deformation behaviour recorded through TS and therefore contributes to the understanding of the on-going geological processes
- âŠ