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Summary of Proposal GEO2577

TitleUsing TSX INSAR to measurechanges of land surface elevationof cultivated fields for soil erosionestimation
Investigator Jordan, Colm - British Geological Survey, Earth and Planetary Observation and Monitoring
Team Member
Dr Rawlins, Barry - British Geological Survey, Soils Team
Dr Le Bissonnais, Yves - INRA, Erosion Team
Dr Cigna, Francesca - British Geological Survey, Earth & Planetary Observation & Monitoring
SummaryThe Soils team are currently (Feb 2014) undertaking a scientific reviewof earth observation techniques for soil threats on behalf of Defra; one of thesoil threats they wish to monitor in future is soil erosion using earthobservation and the newly developed ISBAS (Intermittent Small BAseline Subset;Sowter et al. 2013) technique offers great potential to achieve this. Thesuccess of InSAR methods is controlled by not only the availability of data,but also local topography and land cover, and locations with sufficienttemporal phase stability. Coherence is typically limited to either built-up,urban areas or areas of exposed bedrock (Cigna et al. 2013a). Whilstconventional InSAR approaches have limited potential to monitor surface elevationchanges in rural areas, by considering the intermittent coherence of non-urbanareas ISBAS can fill the gap and provide InSAR results in rural and vegetatedregions, as demonstrated by the BGS ISBAS research across a rural region inNorth Wales (Cigna et al., 2014; Rawlins et al., 2014). By exploiting this new imageprocessing technique, we aim to calculate and compare spatial and temporalchanges in land surface elevation for cultivated fields across a region ofsouthern France in the vicinity of Pau. Ourobjective is to determine whether this novel approach could be used to quantifythe magnitude and extent of soil erosion. This region of arable agriculture comprisessoils which are dominated by fine silt- and sand-sized material that are proneto erosive losses by water both through surface crusting, and through theformation of gullies due to saturated overland flow. We will use 100 metre pixel CORINE land covermaps to select cultivated fields, and a 50 metre Digital Elevation Model to undertaketerrain analysis which can be used as a proxy for erosion risk. We will determine the magnitude of elevationchange in non-eroding (low-slope) areas to determine a baseline for surfaceelevation change. We will also determine elevation changes in high risk(sloping areas) to assess whether these is evidence for soil erosion losses dueto water. Based on our analysis, themain deliverable will be an assessment of the “baseline” variations of changein land surface elevation over a period of 33 months for sloping andnon-sloping, un-vegetated cultivated fields, and the associated overall changein soil mass (loss/gain) across the landscape.These can be compared to published rates of soil erosion to determinethe potential for wider application of the technique. We have established that 40 scenesof TerraSAR-X data are available for our study region. These were acquiredbetween 31/05/2011 and 14/02/2014 in StripMap HH Single Polarization mode,using 33.6-36.6° incidence angles. The selected amount and modeof data products depends on both the availability of the archive imagery andthe acquisition geometries. The results will include: 1.Average motion velocitiesand time series retrieved via ISBAS processing of TerraSAR-X data for the cultivatedfields and other land cover types across the study region relative to a fixed referencepoint 2.Elevation changes fornon-sloping arable fields (<2º) to determine their magnitude for those areasunaffected by infiltration excess overland flow 3. Elevation changes forarable fields potentially affected by infiltration excess overland flow (basedon large sediment transport capacity index values) 4.Reports, peer reviewpapers, visualizations and public dissemination in the UK and internationally(European conferences).

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