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24 février 2017

Atmospheric imaging and characterisation of sources of infrasounds in the coupled solid/atmosphere system : numerical modeling and instrumentation for terrestrial and planetary applications.

Catégorie : Doctorant

Supervisors :

  1. Raphael F. Garcia (HDR)
  2. Roland Martin (HDR)

Research teams :

  1. ISAE Recherche / DEOS / SSPA
  2. UPS/OMP/GET/ Equipe Géophysique

funding :

French DoD


Numerical simulations of the propagation of sound and gravity waves in planetary atmospheres do not currently give an exact description of the propagation of waves in 3D models from the surface to the limits of the thermosphere. The SSPA team of ISAE-SUPAERO, in collaboration with the geophysics' team of GET laboratory in Toulouse and the LMA in Marseille, is developing such a tool as part of a thesis that began in September 2014. The numerical tools developed in this framework (Brissaud et al., 2016, Brissaud et al., Submitted) make it possible to model the propagation of seismic, acoustic and gravity waves in solid/atmosphere coupled systems including surface topography and atmospheric models whose properties vary only as a function of altitude (wind profile, attenuation, changes in sound velocity and density). These tools have been validated, but they are currently limited to 2D applications in idealized atmospheres (isotherm for example).

Despite these limitations, the applications of the tool are already innumerable (explosions, influence of climatic variations on wave propagation, propagation of seismic waves in the atmosphere ...). We would like to dedicate a doctoral student to the implementation of a 3D tool in realistic models of planetary systems on a global scale (Earth, Venus, Mars).

For terrestrial applications, ISAE-SUPAERO's SSPA team is funded by the DGA both to develop balloon instrumentation for infrasound measurement, and has co-funded this thesis to develop tools for modeling of these measurements. For the planetary part, the SSPA team participates in two JPL Venus mission studies (NASA) to image the internal structure of Venus using atmospheric waves created by earthquakes (Garcia et al., 2005). The first project aims to develop a payload for the measurement of infrasounds on balloons, and thus joins the terrestrial instrumentation. The second one concerns the detection of these acoustic waves of seismic origin from the Venus orbit by imaging the variations of ariglow emissions of the upper atmosphere. In addition, proponents are also heavily involved in the NASA INSIGHT mission (also in collaboration with JPL / Caltech), which will go to Mars in 2018 and for which seismological and infrasound sensors will also constrain the internal structure of Mars (Garcia et al ., 2016).

PhD program

The objective of the thesis will be to explore the atmospheric signals (acoustic waves and gravity waves) created by the entry of bolides in the upper atmosphere, seismic vibrations of the ground, and atmospheric explosions (volcanoes, impacts of meteorites...) . This in order to define instrument specifications for future infrasound measurements on balloons in the atmospheres of Venus and Earth, but also to determine the characteristics of the sources and to image the propagation medium from the signals measured by the ballon experiments and the INSIGHT mission to Mars. Particular attention will be paid to the study of the effects of topography and winds on the propagation of waves.

First, the objective will be to extend the domain of simulations to regional and global scales in 3D and to integrate realistic atmospheric models in order to have a good representativeness of the coupled solid / ocean / Atmosphere of the planets considered. In addition, optimized absorbing boundary conditions will have to be developed in order to reduce the calculation costs.

Then, in order to determine the structure of the propagation medium (atmosphere, solid part of the planets), the student will have to set up and validate a modeling of the source of atmospheric waves, in particular for sources located in the atmosphere such as meteorite entries and sources from atmospheric dynamics (dust devils on Mars, polar vortex on Venus...). For this purpose, the combined use of acoustic and gravity waves (intrinsic to the simulation tool) will allow to remove the uncertainty on the source parameters.

The student will also develop data inversion tools to image the structure of the propagation medium. Depending on the type of source (earthquakes, explosion, atmospheric excitation, etc.) and its characterization level (spatio-temporal position, frequency content, etc.), but also depending on the type of sensor (ground or balloon pressure sensor, seismometer), various tools will be implemented to minimize the effect of uncertainties on the characteristics of the source in the imagery of the atmosphere.

Candidates profile

European (or swiss) nationality required.

Master of atmospheric sciences, geophysics, planetology, universe science, applied mathematics, preferentially with an engineer diploma. Scientific curiosity, interest for space exploration and numerical modeling, teamwork capabilities.

References of the team

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(c) GdR 720 ISIS - CNRS - 2011-2015.