Ingénieur de recherche en géophysique, validation qualitative et quantitative de produits de déplacements du sol InSAR (H/F)

CNRS offer

Missions

Satellite radar interferometry (InSAR) is a space imaging technique that allows to follow in time and space all the deformations of the surface of the land with accuracies of the order of mm/year. Since the end of 2014, the Sentinel1 satellites, as part of the very ambitious European Copernicus "Observing the earth" program, have been acquiring radar images with a revisit of 6 to 12 days. The stacking of images acquired over the same area and with the same geometry (including up to 400 images) allows us to measure the speed of ground displacement with an accuracy of mm/year, as well as the temporal variability of this displacement. But such an advance implies a considerable growth in the volume of data processed by the processing chains. The EGMS (European Ground Motion Service) of Copernicus has commissioned a systematic processing over all of Europe, and the displacement products are made available online in open access. In addition, French scientists have developed a reference processing chain for the domain, NSBAS, based on principles very different from those used for EGMS processing. This processing chain is implemented on the CNES HPC in the framework of the FLATSIM project (ForM@Ter LArge-scale multi-Temporal Sentinel-1 Interferometric Measurement), a service for the massive and systematic production of INSAR time series over large regions. This service is offered in the framework of ForM@Ter, the Solid Earth cluster of the national research infrastructure Data Terra. ForM@Ter and the National Observation Service ISDeform have decided to process also the entire Sentinel-1 image archive over the national territory, using the FLATSIM service followed by an adapted reprocessing at the ISTerre laboratory. This processing is mainly intended for scientists, with a public algorithm, constant improvements and the publication of auxiliary products allowing an evaluation of the obtained displacement time series.
The mission of the research engineer is to validate the velocity maps and displacement time series obtained by the SNO ISDeform, and to compare them with EGMS products, based on external data (geological expert knowledge, leveling or GNSS measurements, etc.) on selected sites. The comparison of the ISDeform and EGMS solutions will be informed by the knowledge of the processing chains and their assumptions, limitations or complementarity. The validation with external data will be carried out with the support of collaboration within BRGM and IGN, part of the EGMS product validation consortium. Signals will be extracted and discussed on different types of targets (gas storage, mines or after mines, urban or coastal subsidence, landslides, slow slope instabilities, clay shrinkage-swelling, etc.).

Activities

The research engineer’s activities will be as follows:

• Extraction of line-of-sight velocities over several areas of interest (coastal subsidence, post-mine, open pit, urban subsidence, landslide, ...) for different ISDeform products (filtered/unfiltered) and qualitative comparison with EGMS velocity maps. The choice of these targets will be made in consultation with the SNO ISDeform partners and the IGN and BRGM.
• Extraction of quality factors and uncertainties on these same areas.
• Extraction of non-linear deformations, for example seasonal, and comparison on two sites, for example one with clay shrinkage and one with underground gas storage.
• Expert qualitative comparison using knowledge of the objects studied, in conjunction with BRGM and SNO ISDeform partners.
• Large scale comparison of the performance of ISDeform and EGMS velocity maps and their referencing in a system such as ITRF or EUREF, using GNSS data.
• Quantitative comparison of EGMS/ISDeform solutions at different scales and according to quality factors, informed by knowledge of the limitations of each treatment.
  
  

Skills

Expertise Required

• expertise in geophysics/geology and the origin of surface deformations
• basic geodesy (InSAR / GNSS)
• GIS background
• statistical and signal processing background
• ability to code in Python
• knowledge of Unix/Linux and HPC environment
• fluency in written and spoken English (C1 level)
• ability to work in a team

Expertise desired if possible:

• experience in radar interferometry processing
• Advanced statistics
  
  

Work context

The National Center for Scientific Research is a multidisciplinary public research organization under the supervision of the Ministry of Higher Education, Research and Innovation consisting of nearly 3.8 billion euros of budget, more than 33,000 agents including nearly 29,000 scientists, and more than 1100 research laboratories in France and abroad.
ISTerre is a Joint Research Unit of Grenoble Alpes University, CNRS, USMB, IRD and Gustave Eiffel University, located at 1381 rue de la Piscine 38400 Saint-Martin d’Hères and on the Bourget du Lac Scientific Campus.
It is part of the Observatoire des Sciences de l’Univers de Grenoble (OSUG) and of the PAGE research cluster of the Université Grenoble Alpes (UGA). It has a staff of about 300 people and an average annual budget of 7 M€.
It is organized around 9 research teams and services, the scientific objective being the physical and chemical study of the planet Earth, particularly by focusing on the coupling between observations of natural objects, experimentation and modeling of the associated complex processes.
ISTerre also provides solid Earth observation missions, hosts and maintains national fleets of geophysical instruments, and a data center.
The engineer will be provided with a conventional workstation for analysis of processing products. He will also have access to HPC computing resources (GRICAD mesocenter) with national or European projects.
Team description:
The engineer will be integrated in the "Seismic cycle and transient deformations" team, to which are attached researchers, PhD students, post-doctoral students and engineers with expertise in radar interferometry. The engineer will be integrated into the Geodata service (which federates the computer engineers of ISTerre) in connection with the OSUG. He will also be in contact with the researchers who will be able to help him in the geophysical validation of the deformation time series over France, in particular by providing complementary soil data. For this, short missions will take place within the framework of the collaboration with researchers from BRGM, IGN, and the various laboratories involved in the validation.