InSAR Monitoring of Landslides in Britain: BGS' Feasibility Map and First ISBAS Studies over the South Wales Coalfield
Cigna, Francesca¹; Bateson, Luke¹; Dashwood, Claire¹; Jordan, Colm¹; Sowter, Andrew^2
1British Geological Survey, UNITED KINGDOM; ²University of Nottingham, UNITED KINGDOM

The Earth and Planetary Observation and Monitoring, and the Shallow Geohazards and Risks Teams of the British Geological Survey (BGS) are carrying out innovative research to improve the understanding of landslide processes and routinely assessing new technologies for geohazard and ground motion mapping. Building upon the successful achievements of recent applications of SAR Interferometry (InSAR) to landslide hazards in Europe (e.g., Bally, 2012), and with the aim of enhancing further the research on radar EO for landslide management, the BGS has been carrying out a research project since the beginning of 2012 aimed at evaluating the potential of these techniques to better understand landslide processes over Great Britain, funded by internal NERC grants (Cigna et al., 2012).
InSAR feasibility was mapped over the entire landmass of Britain, based on the combined assessment and modelling of topographic and landuse effects. The latter were mapped by using medium to high resolution DEMs, landuse information from the EEA CORINE Land Cover map 2006, and six Persistent Scatterers (PS) datasets available over London, Stoke-on-Trent, Bristol/Bath, and the Northumberland-Durham region, which were made available to BGS through the projects ESA GMES Terrafirma and EU FP7 PanGeo.
The feasibility maps for the ERS-1/2 and ENVISAT ascending and descending modes showed that topography is not the major limitation over most of Britain, and areas of layover and shadow for each satellite mode do not exceed 1% of the entire landmass. Although the results from the landuse feasibility mapping confirm that landcover has stronger control on the potential of these technologies over Britain, the overall number of monitoring targets that might be identified over the entire landmass for each acquisition mode exceeds 12.8M with PS approaches. This number could increase by 1 order of magnitude using either input SAR data at higher resolutions (e.g. TerraSAR-X, COSMO-SkyMed) or improved processing approaches such as the newly developed ISBAS (Intermittent Small Baseline Subset), developed at the Nottingham Geospatial Institute of the University of Nottingham by Dr A. Sowter (Sowter et al., 2012, in press).
Based on the results of the feasibility mapping performed by BGS, we identified three categories of landsliding in Britain, over which we will carry out SAR-based ground motion studies with ERS-1/2 and ENVISAT data covering the past 20 years. The first test region coincides with the South Wales Coalfield, an area characterised by steep-sided, glaciated valleys incised into upland plateaux consisting of strong jointed sandstone caprock overlying weaker mudstones, shales and coal seams. In this region, the determination of the recent/present state of activity of these landslide features is of critical importance to establish if deep block movements are still contributing to landslide reactivation. ISBAS monitoring of this area between the years of 1992-2008 with ERS-1/2 SAR and ENVISAT ASAR ascending and descending data will support landslide research of this area, which is currently carried out by the landslide team at BGS using both traditional mapping techniques and new technologies, and help improve our understanding of ground motion and land processes affecting this area over the last two decades.
ERS-1/2 and ENVISAT data are made available by ESA through the Cat1 project id.13543: Enhancing landslide research and monitoring capability in Great Britain using C-band satellite SAR imagery and change detection, InSAR and Persistent Scatterers techniques.

References

Bally P. (2012), Scientific and Technical Memorandum of The International Forum on Satellite EO and Geohazards, 21-23 May 2012, Santorini Greece. doi:10.5270/esa-geo-hzrd-2012.
Cigna F., Bateson L., Jordan C., Dashwood C., 2012. Feasibility of InSAR technologies for nationwide monitoring of geohazards in Great Britain. RSPSoc 2012, 12-14 Sept 2012, London, UK.
Sowter et al., 2012. Land Motion Observed by DInSAR in the South Derbyshire and Leicestershire Coalfield. GRSG AGM 2012, 11-13 Dec. 2012, London, UK.
Sowter A., Bateson L., Strange P., Ambrose K., Syafiudin M., in press. DInSAR estimation of land motion using intermittent coherence with application to the South Derbyshire and Leicestershire coalfield. Geophysical Research Letters.