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Summary of Proposal GEO0728

TitleMeasure of Mexico City subsidence by high resolution TerraSAR-X interferometry
Investigator Doin, Marie-Pierre - Ecole normale Supérieure, Laboratoire de Geologie, Département Géosciences
Team Member
Dr Doin, Marie-Pierre - Ecole normale Supérieure, CNRS, Geosciences Department
Dr Lopez-quiroz, Penelope - Centro de Investigación en Geografía y Geomática “Ing. Jorge L. Tamayo”, N/A
Dr Pinel, Virginie - Universite de Savoie, Laboratoire de Geophysique Interne et Tectonophysique
Dr Pinel-Puysségur, Béatrice - CEA/DAM/DASE/SLDG, DASE
Mr Quin, Guillaume - CEA/DAM/DASE/SLDG, DASE
SummaryWe propose to study by TerraSAR-X interferometry and image correlation techniques the very fast subsidence of Mexico Valley. Three areas will be studied: the historical center of Mexico city, the whole urban area including the precedent area and the Popocatepetl volcano. The first two areas cover the downtown with its large variety of buildings and infrastructures, and also a small volcano on which flanks extremely large displacement gradients exist. Images should be acquired during 2 years every 11 days due to high deformation rate. The first smaller area focuses on Mexico city historical center to measure differential subsidence between buildings and pavements, requiring high resolution Spotlight data. The larger second area, acquired in Stripmap mode, gives a global view of the city, including stable points. We regret not to be able to cover the whole subsiding area (70x70 km2, including stable mountain slopes) due to limitations in TerraSAR-X data policy. However, please note that a systematic data acquisition on Mexico City should prove useful for a later analysis of the archive. The third area focuses on the Popocatepetl volcano summit where vegetation is absent and possible deformation is expected. The dense series of SAR data will allow both a persistent scatterer analysis (STUN method), yielding heights and velocity on punctual man made objects, and a small baseline analysis that should offer a more continuous deformation and height field. In the latter case, DEM errors (partly related to building height) will be computed from the series of wrapped interferograms before spatial unwrapping. We will develop a specific unwrapping methodology adapted to the subsidence properties of Mexico City. Image correlation techniques will be tried on Mexico City (a maximum displacement of 0.8 m in 2 years might lead to recordable measurements in high resolution images). Furthermore, they will be used to see whether tree-top growth of Oyamel forests surrounding the Popocatepetl summit can be detected by TerraSAR-X data (as was the case with ERS-Envisat couples). Data requirements: First area (66+4images): -center: (N19°25’58”,W99°07’58”) -Spotlight images every 11 days during 2 years (66 images) -incidence angle: around 25°. -2 tandem couples for better DEM compensation (4 images). Second area (66+6 images): -center: (N19°24’40”, W99°08’04”), area: 30kmx50km -Stripmap images every 11 days during 2 years (66 acquisitions) -incidence angle of about 33° maximum (as deformation is mainly vertical) -ascending track. In order to avoid conflicts with the first area, they should not be acquired by the same orbit. -2 tandem couples at the beginning of the series and another one acquired 2 to 3 years later to see if deformation induced topography change could be measured (6 images). Third area (22+4 images): -center: (N19°01’43”, W98°37’22”), area: 30kmx50km -Stripmap mode (e.g. relative orbit 52, strip 004), every 33 days during 2 years (22 images) -2 tandem couples For all areas, the image acquisition conditions should allow for interferometric processing. Deliverables: Maps of mean subsidence/displacement over the 3 areas will be computed, as well as deceleration/acceleration maps. Subsidence maps comparison on the first two areas will highlight the contribution of Spotlight data and give a reference subsidence rate in the first area thanks to stable reference points in the second area. Comparison with prior results from Envisat time series or levelling data will help constrain the accuracy of subsidence maps. Deformation maps derived from Spotlight mode will be analysed to see if they are correlated with building foundation depth. The data will be funded by the "Laboratoire de Recherche Yves Rocard".

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