Ludovic Bodet
Assistant professor in Geophysics
L.G.R.M.P.
Université du Maine - U.F.R. Sciences et Techniques
Bat. de Géologie, Avenue Olivier Messiaen
72085 Le Mans Cedex 09 - FRANCE
Phone : + 33 (0)2 43 83 32 35
E-mail : ludovic.bodet@univ-lemans.fr
http://www.univ-lemans.fr/~lbodet
Cable Surveys 2000-2002

Welcome to a short web page about my work...
I received my M.S. in Earth Sciences from `Geosciences Rennes´ (1999) and my Master degree in Geophysics from the `Institut de Physique du Globe de Paris´ in France (2000). I worked as an engineering geophysicist in Fugro France S.A. (marine seismic and resistivity surveys, Research & Development). I was a Ph.D. candidate at the `Laboratoire Central des Ponts et Chaussées´ in Nantes and the `Bureau de Recherches Géologiques et Minières´ in Orléans, France (2002-2005). I worked as a Research & Teaching Assistant at the Applied Geophysics Department (U.M.R. 7619 Sisyphe) in Pierre et Marie Curie-Paris6 University and am now `Maître de Conférences´ (assistant professor) in Le Mans (France) at `Maine University´ in the Earth sciences department (L.G.R.M.P.).
My current research interests include inverse problems in geophysics, numerical and physical modeling of wave propagation and more particularly surface-wave inversion applications and limitations in near-surface geophysics...

Here is a curriculum vitæ : [-->French version .pdf]...or jump directly to my main research `results´...


2006 - ... --- Assistant professor in Geophysics at Geosciences Lab./Le Mans
Teaching load : 192 hours (Licence 1 & 2, Master 1 & 2)
Topics : Earth sciences / (Geo)Physics / Wave propagation from NDT to Earth sciences / Natural Hazards... & some Structural Geology (field trips)
[Geophysical prospecting methods, seismology, geomagnetism, gravimetry, seismic signal processing, surface waves...]
---My "teaching" page---> in french + under construction...

2005 - 2006 --- Research & Teaching assistant at U.M.R. 7619 Sisyphe
Teaching load : 192 hours (Licence 3, Master 1 & 2, Engineers)
Topics : Earth sciences / (Geo)Physics
Field work : Geophysical --i.e. seismic, electric, electromagnetic, magnetic, gravimetric-- prospecting methods.
Teaching `practicals´ : Geophysical prospecting methods, seismology, geomagnetism, seismic signal processing... Geodynamics...
Université Pierre et Marie Curie - Paris 6

2002 - 2005 --- Ph.D. thesis - L.C.P.C./B.R.G.M.
Title: THEORETICAL AND EXPERIMENTAL LIMITATIONS OF RAYLEIGH-WAVE DISPERSION INTERPRETATION INFERRED FROM NUMERICAL AND PHYSICAL MODELLING
Keywords :
- Seismic wave propagation numerical & physical modeling;
- Seismic refraction & surface waves profiling techniques;
- Inverse problems & signal processing.
...defended in Nantes (France) -- 11/28/2005 -- available here .pdf [11 055 Ko]
Université de Nantes / Ecole Centrale de Nantes / Laboratoire Central des Ponts et Chaussées / Bureau de Recherches Géologiques et Minières

2000 - 2002 --- Engineering Geophysicist, FUGRO France S.A.
- Marine seismic refraction & resistivity (Research, Offshore);
- Seismic sources & resistivity streamers development;
- Refraction and resistivity offshore cable surveys (acquisition, data real-time processing, post-processing, geophysical/geotechnical correlations and interpretationand, reporting).
2000, February-July --- Interpretation and inversion of gravity gradiometric data (.pdf - in french) - I.P.G.P., Laboratoire de Gravimétrie et Géodynamique

1999, July-August --- Analogue modelling in geomorphology, Geosciences Rennes (-> publication) (.pdf here and...)
More info on dynamics of erosion at continental scale here.



Field Studies
2006, June --- Reflection seismic & ground-penetrating radar prospecting, Paris-6/WaterScan;
2004, December --- Surface-wave profiling study, B.R.G.M. ;
2003, November --- Geological & Geophysical Complementary Investigations, Pekin Man site at Zhoukoudian, E.D.F./L.C.P.C. - Refraction seismic and surface-wave prospection... ;
2001, December - 2002, January --- Cable route survey (Australia-Indonesia–Singapore) with RHOBAS marine resistivity system and GAMBAS marine seismic refraction system for FUJITSU & NAVA1 ;
2001, April-May --- Cable route survey (Japan; South-Corea) with RHOBAS marine resistivity system for ALCATEL SUBMARINE NETWORK & FLAG NORTH ASIAN LOOP.

Educational training (Field Work)
2000, May --- Cartography (Tectonic, Alps).
1999, May-June --- Feasibility study of geophysical prospecting methods on a levee using seismic and resistivity - Civil Engineering Department, I.U.T. de St. Nazaire.
1999, October --- Geophysical prospecting methods : seismic, electric, magnetic, gravimetric (Garchy Geophysical Research Center, CNRS, France).
1999, April --- North-armorican dyke swarm study using magnetic and gravimetric prospecting methods.
1999, March --- Geophysical prospecting methods: seismic, electric, E.M., magneto-telluric, magnetic, gravimetric (Biological Observation Center in the Brocéliande forest, Brittany, France).
1997, October --- Cartography : tectonic, stratigraphy, sedimentology (Montagne Noire, France).

Educational Qualifications
1997-1999 --- Master degree in Geophysics, Institut de Physique du Globe de Paris [DEA de Géophysique Interne].
1997-1999 --- M.S. in Earth Sciences Université de RENNES 1 [LICENCE et MAITRISE Sciences de la terre et de l`univers, Mention GEOPHYSIQUE].
1995-1997 --- DEUG Sciences de la matière, Université de POITIERS.

Computer skills : Unix/Linux/Windows/Macintosh;
- C, Fortran77, Java, Unix/Linux Shell script;
- Seismic Unix, Matlab, Gnuplot, Latex, Adobe Illustrator/Photoshop, Microstation.

Languages : English (Native French speaker), German (elementary knowledge), learning Arabic.

... « Basic Offshore Safety Course », Lorient (France) 2001.
... Driving Licence (Permis B).



Ph.D. Thesis
Bodet, L., 2006, Limites théoriques et expérimentales de l'interprétation de la dispersion des ondes de Rayleigh : apport de la modélisation numérique et physique. Mémoire de doctorat. Université et Ecole Centrale de Nantes, sous presse.(.pdf)

Master Thesis
Bodet L., 2000, Interprétation et inversion de données gradiométriques en gravimétrie. Mémoire de D.E.A., Institut de physique du globe de Paris.(.pdf)

ARTICLES

Bodet, L., Clorennec, D., A., Abraham, O., 2006, Near offsets effects on Rayleigh-wave dispersion measurements, in preparation for Near Surface Geophysics

Bodet, L., van Wijk, K. , Bitri, A., Abraham, O., Côte, Ph., Grandjean, G., and Leparoux, D., 2005, Surface-wave dispersion inversion limitations from laser-Doppler experiments, Journal of Environmental & Engineering Geophysics, vol. 10, issue 2, 151-162. (at P.A.L. which moves!..) (or here .pdf)

A. Crave, D. Lague, P. Davy, J. Kermarrec, D. Sokoutis, L. Bodet and R. Compagnon, 2000, Analogue Modelling of Relief Dynamics, Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy, Volume 25, Issues 6-7, Pages 549-553. (.pdf)

COMMUNICATIONS

Bodet, L., Surface-wave dispersion inversion limitations from numerical and laser-Doppler physical modeling, Geophysical lunch at the Department of Earth Sciences, Utrecht University, The Netherlands, Wednesday, June 1rst, 2005. Invited oral communication.

Bodet, L., Surface-wave dispersion inversion limitations from numerical and laser-Doppler physical modeling, Geophysics talks at the Department of Geotechnology, Delft T.U., Delft, The Netherlands, Monday, May 30th, 2005. Invited oral communication.

Bodet, L., van Wijk, K, Bitri, A., Abraham, O, Côte, Ph., Grandjean, G., and Leparoux, D., Surface wave dispersion inversion when the 1D assumption breaks down, European Geosciences Union, 1st General Assembly, Vienna, Austria, 24–29 April 2005. Session: SM4 Techniques of shallow seismic and georadar imaging. Poster.

Bodet, L., Sloping interfaces and surface waves profiling: numerical and laboratory experiments, Geophysics talks at the Department of Geotechnology, Delft TU, Delft, The Netherlands, Friday, September 3rd, 2004. Solicited oral communication.

Bodet, L., Apport des ondes de surface à la détermination des caractéristiques mécaniques des sols et des matériaux. Journée des Doctorants de l´école doctorale MTGC, 3 juin 2004, Université de Nantes. Oral communication.

Bodet, L., Abraham, O., Bitri, A., Leparoux, D., Côte, Ph., Effect of dipping layers on seismic surface waves profiling: a numerical study, European Geosciences Union, 1st General Assembly, Nice, France, 25–30 April 2004. Session GI1: Open session on Geophysical Instrumentation. Oral communication.

Bodet, L., Abraham, O., , Bitri, A., Leparoux, D., Côte, Ph. Effect of dipping layers on seismic surface waves profiling : a numerical study; in Proceedings, Symposium on the Application of Geophysics to Engineering and Environmental Problems, February 22-26, 2004, Colorado Springs, CO. Extended Abstract, oral communication. (.pdf)

Bodet, L., Apport des ondes de surface à la détermination des caractéristiques mécaniques des sols et des matériaux, Colloque de la Recherche de l´Intergroupe des Ecoles Centrales, AED 3 juillet 2003. Communication orale.


in preparation for Near Surface Geophysics
Near offsets effects on Rayleigh-wave dispersion measurements inferred from laser-Doppler physical modelling
Ludovic Bodet(1,3), Dominique Clorennec (5), Odile Abraham(1)

Abstract (meet me @ EGU-2007 .pdf)
Laboratory experiments using laser-Doppler vibrometry proved to be an efficient tool in physical modelling of wave propagation. It can provide useful realistic data, bridging the gap between numerical simulations and field studies. Both numerical and such physical experiments are used here to address issues in near offsets effects on Rayleigh-wave dispersion measurements. Surface-wave profiling techniques using active sources and linear arrays are often performed with short source-receivers distances compared to involved wavelengths. Dispersion measurements may then be corrupted by near field effects. Numerical modelling helped here to identify these effects as a systematic underestimation of measured phase velocity at low frequency. Laboratory experiments confirmed the results of our numerical findings and allowed to propose a lower cut-off frequency based on the seismic spread length : using active sources and purely linear arrays, the maximum measurable wavelength should not exceed 50 % of spread length.

Journal of Environmental & Engineering Geophysics, June 2005, Volume 10, Issue 2, pp. 151-162
Surface-wave inversion limitations from laser-Doppler physical modeling
Ludovic Bodet(1,3), Kasper van Wijk(2), Adnand Bitri(3), Odile Abraham(1), Philippe Côte(1), Gilles Grandjean(3) and Donatienne Leparoux(4)

Abstract (at P.A.L. which moves!..) (or here .pdf)
Surface-wave dispersion inversion is growing in popularity for geotechnical applications, due to its non invasive character, relative straightforward field procedures and interpretation, especially when the subsurface structure is locally assumed to be one-dimensional (1D). Here, laser-Doppler physical modeling of surface-wave propagation is used to address issues in surface-wave depth penetration, the presence of dipping layers, and the associated limitations and systematic errors propagated in conventional 1D surface-wave inversion. Flat-layered models show that, with an active source and linear spread, the maximum resolvable wavelength of the Rayleigh-wave fundamental mode is in the order of 40% of the spread length. Linearised inversions confirm the rule of thumb that depth penetration is 20-25% of the spread length, and that correct a-priori layer interface depths from refraction analysis allow more accurate results. However, even under optimal conditions, failing to account for a dominant higher mode at low frequency when a stiff shallow layer is present, causes an overestimate of deeper layer shear-wave velocity. Moreover, a dipping layer of only a few degrees can significantly bias the surface-wave inversion. If the incorrect a priori information from a single-shot refraction analysis is a-priori incorporated in the inverse problem, estimated interface depth depends on the shot position and deeper layer shear-wave velocity is underestimated. Even if correct a priori constraints are used, an underestimate of half-space shear-wave velocity of up to 25% remains.

in Proceedings, Symposium on the Application of Geophysics to Engineering and Environmental Problems, February 22-26, 2004, Colorado Springs, CO
Effect of dipping layers on seismic surface waves profiling : a numerical study
Ludovic Bodet(1,3), 0dile Abraham(1), Adnand Bitri(3), Donatienne Leparoux(4), Philippe Côte(1)

Abstract (.pdf)
Multichannel analysis of surface waves (MASW) can be implemented along linear sections to obtain profiles of subsurface layers shear waves velocities. However, one often overlooks the assumption of horizontally layered medium inherent to the inverse problem required during dispersion curves interpretation. Unfortunately, dipping layers or pronounced interfaces topography can invalidate this assumption. That is why we attempted to evaluate the reliability and the relevance of shear-wave velocity profiling using Rayleigh waves in such situations. Numerical simulations employing two-dimensional (2D) finite-element methods showed that the slope influence on dispersion curves cannot be summed up to a typical averaging of the media at the base of the receivers. In addition, the spread length is even a more limiting factor in the case of a sloping interface, and thus affect the obtained dispersion curves.

Unpublished… yet, but defended in Nantes, 11/28/2005 available here (.pdf)...
Ph.D. THESIS ABSTRACT
THEORETICAL AND EXPERIMENTAL LIMITATIONS OF RAYLEIGH-WAVE DISPERSION INTERPRETATION INFERRED FROM NUMERICAL AND PHYSICAL MODELLING
Supervisors: Ph. Côte(1), O. Abraham(1), A. Bitri(3), D. Leparoux(4) and G. Grandjean(3)
Key Words : Geophysics, inverse problems, physical and numerical modelling, seismic, signal processing, experimentation…

Abstract
The evaluation of soil shear modulus is of great concern in urban and suburban development. Shear-wave velocity can be estimated from surface-wave velocity measured using a simple mechanic source and receiver array. Surface-wave dispersion inversion is consequently growing in popularity for geotechnical applications due to its non-invasive character, relative straightforward field procedures and interpretation, especially when the subsurface structure is locally assumed to be one-dimensional. Unfortunately, dipping layers or pronounced interfaces topography can invalidate this assumption required during dispersion interpretation. Even if the 1D assumption is acceptable, experimental dispersion observations almost systematically underestimate surface-wave velocity at low frequency, and resolution is poor. The spread length is proposed as a factor of these low-frequency discrepancies.

Numerical simulations are used here to study these limitations and address issues in near offsets and spread length effects, surface-wave depth penetration, the presence of dipping layers and the associated limitations and systematic errors propagated into conventional 1D surface-wave inversion. But validation of theory and numerical code with an analysis of real data is generally necessary. However, most of the time the complexity of field studies do not allow us to isolate the parameters of interest. Physical modeling of surface waves using laser-Doppler vibrometry proved to provide useful data, bridging the gap between numerical simulations and field studies. The results of our findings outline -- and in some cases confirm existing -- rules of thumb in terms of resolution and limits on violations of the 1D assumption.

Homogeneous and flat-layered models show that, with an active source and linear spread, the maximum resolvable wavelength of the Rayleigh-wave fundamental mode is in the order of 40-50% of the spread length. Linearised inversions confirm the rule of thumb that depth penetration is 20-25% of the spread length, and that correct a priori layer interface depths from refraction analysis allow more accurate results. However, even under optimal conditions, failing to account for a dominant higher mode at low frequency when a stiff shallow layer is present, causes an overestimate of deeper layer shear-wave velocity. Moreover, a dipping layer of only a few degrees can significantly bias the surface-wave inversion. If the incorrect v information from a single-shot refraction analysis is a priori incorporated in the inverse problem, estimated interface depth depends on the shot position and deeper layer shear-wave velocity is underestimated. Even if correct a priori constraints are used, an underestimate of half-space shear-wave velocity of up to 25% remains.


1 Laboratoire Central des Ponts et Chaussées, Reconnaissance et Géophysique, Pt 86 route de Bouaye, BP 4129, 44341 BOUGUENAIS Cedex FRANCE odile.abraham@lcpc.fr , philippe.cote@lcpc.fr

2 Physical Acoustics Laboratory, Department of Geophysics, Colorado School of Mines, Golden, CO, USA kasper@cgiss.boisestate.edu now at Boise CGISS-->brand new P.A.L.

3 Bureau de Recherches Géologiques et Minières, Aménagement et risques naturels, 3 avenue Claude Guillemin, BP 6009, 45060 ORLEANS Cedex 2 FRANCE, a.bitri@brgm.fr, g.grandjean@brgm.fr

4 Institut de Physique du Globe de Paris, Géomatériaux, Boite 89 4 place Jussieu - 75252 Paris cedex 05 FRANCE, leparoux@ipgp.jussieu.fr

5 Laboratoire Ondes et Acoustique, E.S.P.C.I., 10 rue Vauquelin 75231 PARIS Cedex 05 France, dominique.clorennec@loa.espci.fr

Link(s)
Have at trip to Martinique!!! ---> SebaSite ;)...
Visit Dr. Julien Babault---> là ;)...
We're dOOmed!---> TBDLB ;)...

En vrac...
Please note this page is (still) under construction...
...d'j@ vu le coup des "trains d'ondes separateurs" :p


Baalbek, October 2003 ( © Bodet, L. , last update : 01/16/2006 - LGRMP/LEMANS ... this webpage birthday : 02/02/2006 -DGA/PARIS 6 ;)