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Waves and Wave-Based Imaging in Virtual and Experimental Environments

Periodic Reporting for period 2 - WAVES (Waves and Wave-Based Imaging in Virtual and Experimental Environments)

Reporting period: 2017-01-01 to 2018-12-31

Demand for highly trained scientists with a deep understanding of wave propagation in complex media, and capable of exploiting this knowledge to develop imaging tools for seismology and acoustics, is very high in the Earth and environmental sciences. Wave-based imaging serves to map spatial and temporal variations in the structure of the Earth's interior, of the oceans and atmosphere; it is used to monitor faults and volcanoes and detect natural-resource reservoirs. It is relevant to other disciplines, medical imaging being one of its most widespread applications. Today’s Earth scientists are faced with a set of questions that require the application of wave-based imaging at unprecedented resolution. WAVES contributed to fostering scientific and technological advances in this context, stimulating knowledge exchange between seismologists and acousticians, and researchers in the public/private domains. Through WAVES, a new, unique international network of scientists has been created around a set of novel physical acoustics laboratories (managed by beneficiaries/partners of WAVES) with a strong record of experimental research on inter-disciplinary and seismology-related topics. WAVES has trained young scientists, working in academia and industry, in how to use this resource effectively, re-introducing the laboratory into the ideas-to-applications pipeline. Experiments helped us to develop new theory, addressing topics of current interest such as acoustic time-reversal, scattering-based imaging, source localisation in seismology and acoustics (including bioacoustics). A truly multidisciplinary network, WAVES has applied these new ideas in a number of contexts: medical elastography has been used as a tool to implement novel analogue models of seismic faults; wave sources were localized by a bio-inspired system making use of very few receivers, etc. Through WAVES, a critical mass of expertise has consolidated, contributing to defining the study of acoustic/elastic wave propagation and wave-based imaging/monitoring as an independent discipline, rich in applications of intellectual and societal relevance.
All WAVES ESRs have started their doctoral studies in the second half of 2015 and have now concluded their third year of research. Several of them have received their Ph.D.; those who haven't have received independent funding to continue their doctoral work for a few more months until graduation. As it is usually the case with Ph.D. theses, some weeks/months have initially been devoted by each ESR to complete the necessary background to their research project. By now, all students have also carried out tasks that involved original research. All ESRs have by now presented their work at international meetings—including, but not limited to the WAVES workshops. All ESRs have participated in non-WAVES international conferences. Almost all ESRs have published scientific papers as first authors on international peer-reviewed journals (the few who haven't are in the process of preparing their first manuscript for submission).

All the planned workshops, and several short courses have taken place as explained in detail in our report; besides strengthening their scientific background and helping them in pursuing their research projects, these activities successfully fostered the interaction of ESRs, who are now themselves connected in a network that will last in the coming years. As explained in our report and deliverable descriptions, WAVES research has contributed new theoretical formulations (e.g. on Marchenko imaging; the role of scattering in ambient-noise interferometry, etc.); new experimental data (experiments on bone conduction; on elastography in several different materials; on acoustic cloaking; metamaterials, etc.); and new interdisciplinary applications (new links between seismology and the medical sciences; seismology and physical acoustics; seismology and atmospheric infrasound acoustics, etc.).

Research advances associated with WAVES will partly be presented to the general public through an exhibition planned at FocusTerra in Zurich, Switzerland.
To a large extent, WAVES research has consisted of harnessing the current progress in our understanding of the physics of elastic and acoustic waves, to develop novel wave-based imaging techniques; these can be relevant e.g. to resources (oil industry), health and life sciences (medical imaging), environmental hazards (monitoring faults, volcanoes, landslide-prone areas; understanding seismic source processes), geophysics and deep-Earth processes. WAVES also goes beyond imaging: one ESR has contributed to understanding the auditory system of humans and other animals; much work has been devoted to the topic of auditory display of scientific data, etc.

All thesis projects in WAVES are at the cutting edge of current science, and go beyond the state of the art as explained in our original proposal and final report. Detailed and updated research plans for all our ESRs can be read online through the WAVES website: http://www.waves-itn.eu/en/research.html. In particular, some of the most sophisticated physical acoustics laboratories worldwide participated in WAVES, including LMA at Marseille (CNRS), ISTerre Grenoble (CNRS), Institut Langevin (ESPCI) and the geotechnology lab at TU Delft. Two new laboratories, RFPC at UEDIN and WaveLab at ETH, are growing and have been harnessed in the framework of WAVES. WaveLab provides the only experimental setup worldwide where perfect acoustic time reversal can in principle be achieved, via a dense array of transducers covering all the walls of a closed tank. The RFPC lab is a unique facility, allowing (through the work of WAVES ESRs) to predict real-future fracturing of materials under stress: this research is naturally relevant to the topic of earthquake forecast.

WAVES also forged new, unique interdisciplinary links: see for example the three research projects involving INSERM, UPMC and CNRS (Lyon, Paris, Grenoble), which are based on the collaboration between bio-medical researchers, seismologists, acousticians.
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