Getting ready for the generation of a nationwide ground motion product for Great Britain using SAR dta stacks: feasibility, data volumes and perspectives

This paper discusses the feasibility of monitoring ground stability and motion across the entire British landmass using satellite InSAR techniques. The ERS-1/2 and ENVISAT archive data availability, topographic visibility and land cover constraints for multi-temporal InSAR techniques to succeed across Britain are analysed. Data volumes, hardware and software requirements for the generation of a nationwide InSAR product are discussed, with a view to both novel processing methods to extend InSAR across unfavourable land covers, and parallel and cloud computing systems to decrease InSAR processing time demands. The P-SBAS method implemented into ESA’s G-POD platform is tested for London and Newcastle using ERS-1/2 1992-2000 and ENVISAT 2002-2008 image stacks, revealing a decrease of the processing time demand from several days to only ~8 hours per image frame

On the use of the ISBAS Acronym in InSAR Aapplications. Comment on Vajedian, S.; Motagh, M.; Nilfouroushan, F. StaMPS Improvement for Deformation Analysis in Mountainous Regions: Implications for the Damavand Volcano and Mosha Fault in Alborz. Remote Sens. 2015, 7, 8323–8347

Vajedian et al. [1] present an improved method for the derivation of deformation parameters using satellite Interferometric Synthetic Aperture Radar (InSAR) data. The method is a modification of the Small Baseline Subset (SBAS) method as implemented in the StaMPS (Stanford Method for Persistent Scatterers) software. The modification includes many steps including the filtering of the differential interferograms, integration with GPS data and advanced phase unwrapping “to overcome a lot of short- and long-wavelength artifacts that are clearly visible in StaMPS results” (cf. [1], p. 8331). The authors refer to this new approach as the Improved SBAS, or ISBAS, method. [...

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 ‘PROTection of European cultural HEritage from GeOhazards’ (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

‘Looting marks’ 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 ‘looting’ (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 ‘looting marks’, identify marks due to occurrence of new looting and discriminate them from alteration (e.g. filling) of pre-existing looting holes. ‘Looting marks’ 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 (σ0) 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 σ0, 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 February–April 2015. The estimated rates of looting increased from 214 looting marks/month in October–December 2014 to over 780 marks/month in April–June 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

Nationwide monitoring of geohazards in Great Britain with InSAR: feasibility mapping based on ERS-1/2 and ENVISAT imagery

We model terrain visibility and topographic distortions to the ERS-1/2 SAR and ENVISAT ASAR IS2 satellite acquisition modes in Great Britain using the 5m NEXTMap DTM. Predictions of Persistent Scatterers (PS) densities identifiable over the landmass are drawn using the CORINE Land Cover 2006 dataset which is calibrated based on 6 PS datasets available for various areas of the UK. InSAR feasibility to monitor ground motions is discussed through the example of the Manchester area, with particular regard to landslide deposits in the Peak District

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

The application of the Intermittent SBAS (ISBAS) InSAR method to the South Wales Coalfield, UK

Satellite radar interferometry is a well-documented technique for the characterisation of ground motions over large spatial areas. However, the measurement density is often constrained by the land use, with best results obtained over urban and semi urban areas. We use an implementation of the Small Baseline Subset (SBAS) methodology, whereby areas exhibiting intermittent coherence are considered alongside those displaying full coherence, in the final result, to characterise the ground motion over the South Wales Coalfield, United Kingdom. 55 ERS-1/2 Synthetic Aperture Radar (SAR) C-band images for the period between 1992 and 1999 are processed using the ISBAS (Intermittent Small BAseline Subset) technique, which provides 3.4 times more targets, with associated measurements than a standard SBAS implementation. The dominant feature of the observed motions is a relatively large spatial area of uplift. Uplift rates are as much as 1 cm/yr. and are centred on the part of the coalfield which was most recently exploited. Geological interpretation reveals that this uplift is most likely a result of mine water rebound. Collieries in this part of the coalfield required a ground water to be pumped to enable safe coal extraction; following their closure pumping activity ceased allowing the water levels to return to equilibrium. The ISBAS technique offers significant improvements in measurement density ensuring an increase in detection of surface motions and enabling easier interpretation

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 Survey’s 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: ‘PROTection of European cultural HEritage from GeO-hazards’ 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 PROTHEGO’s 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