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| Titel |
Intermittent Small Baseline Subset (ISBAS) InSAR of rural and vegetated terrain: a new method to monitor land motion applied to peatlands in Wales, UK |
| VerfasserIn |
Francesca Cigna, Barry G. Rawlins, Colm J. Jordan, Andrew Sowter, Christopher D. Evans |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089636
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| Publikation (Nr.) |
 EGU/EGU2014-3844.pdf |
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| Zusammenfassung |
| It is renowned that the success of multi-interferometric Synthetic Aperture Radar (SAR)
methods such as Persistent Scatterer Interferometry (PSI) and Small BASeline Subset
(SBAS) is controlled by not only the availability of data, but also local topography and land
cover. Locations with sufficient temporal phase stability and coherence are typically limited
to either built-up, urban areas or areas of exposed bedrock. Whilst conventional PSI and
SBAS approaches have limited potential to monitor surface motions in areas where
few (or zero) scatterers or coherent targets exist, the newly developed Intermittent
SBAS (ISBAS) technique (Sowter et al. 2013) can fill the gap by providing a more
complete picture of ground movement in rural and vegetated regions. ISBAS is a
small baseline, multi-look, coherent target method, which considers the intermittent
coherence of rural areas and can work over a wide range of land cover classes including
agriculture and grassland. Building upon a nationwide study that the British Geological
Survey (BGS) undertook to assess the feasibility of InSAR techniques to monitor
the landmass of Great Britain (Cigna et al. 2013), we identified a rural region in
North Wales as an appropriate target area to evaluate the efficacy of ISBAS, where
conventional SBAS and PSI approaches are unlikely to succeed. According to the UK
Land Cover Map 2007 (LCM2007) from the Centre for Ecology & Hydrology
(CEH), this area is dominated by improved and acid grassland, heather, bog and
coniferous woodland, which are likely to result into extremely low PSI or SBAS point
densities and sparse coverage of monitoring results. We employed 53 ERS-1/2 C-band
(5.3GHz frequency) SAR data acquired in descending mode between 1993 and
2000, which were made available to BGS via the ESA Category 1 project id.13543.
In the framework of the Glastir Monitoring & Evaluation Programme (Emmett
et al. 2013), funded by the Welsh Government, we processed these using ISBAS
covering a 4,460 km2 region of interest. By using thresholds for perpendicular and
temporal baselines of 200 m and 4 years respectively, a total of 300 small baseline
interferograms were generated and good network redundancy was obtained. Average
temporal coherence of the processed scenes was rather low, with only ~4% of
the processed area showing values exceeding 0.25 (hence suitable for an SBAS
analysis), and most of the region revealed very low coherence, especially over areas of
peat, grass, forest and heather. Processing with ISBAS allowed us to consider the
intermittent behaviour of rural scatterers, dramatically improving the point density and
achieving areal coverage results of around 99%. This increased the total number of
monitored points by a factor of 25. The greatest improvement in terms of point
density was achieved for coniferous woodland, which showed ISBAS/SBAS ratios
exceeding 300, and densities increasing up to 150 points/km2 with ISBAS. Bog,
acid grassland and dwarf shrub heath showed densities increasing from 2-10 to
150-160 points/km2 when using ISBAS with respect to conventional SBAS. It is
worth noting that despite intermittence and the fact of relying only on a temporal
subset of interferograms, the vast majority of the ISBAS points showed velocity
standard deviations lower than 1.0-1.5 mm/yr, hence good quality of the estimated
ground motion rates was retained using ISBAS and intermittently coherent targets.
Geological interpretation, analysis and further discussion of the results in relation to
changes in surface elevation of blanket peat are presented by Rawlins et al. 2014 (cf.
BG2.3/SSS6.6).
REFERENCES
Cigna, F., Bateson, L., Jordan, C., & Dashwood, C. (2013). Nationwide monitoring of
geohazards in Great Britain with InSAR: feasibility mapping based on ERS-1/2 and
ENVISAT imagery. IEEE International Geoscience and Remote Sensing Symposium
(IGARSS), pp. 672:675.
Emmett B. E. & the GMEP team (2013). Glastir Monitoring & Evaluation Programme.
First Year Annual Report to Welsh Government (Contract reference: C147/2010/11). NERC
Centre for Ecology & Hydrology (CEH Project: NEC04780), pp. 393.
Rawlins, B. G., Cigna, F., Jordan, C., Sowter, A., & Evans, C. (2014). Monitoring
changes in surface elevation of blanket peat and other land cover types using a novel InSAR
processing technique. EGU 2014, Session BG2.3/SSS6.6.
Sowter, A., Bateson, L., Strange, P., Ambrose, K., & Syafiudin, M. (2013).
DInSAR estimation of land motion using intermittent coherence with application to the
South Derbyshire and Leicestershire coalfield. Remote Sensing Letters, 4, 979:987. |
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