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SUMMARY:Alternative formulations for full waveform inversion - Chauris\, H
  (Ecole des Mines de Paris)
DTSTART:20111214T093000Z
DTEND:20111214T100000Z
UID:TALK34959@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Classical full waveform inversion is a powerful tool to retrie
 ve the Earth properties (P- and S-velocities) from seismic measurements at
  the surface. It simply consists of minimizing the misfit between observed
  and computed data. However\, the associated objective function suffers fr
 om many local minima\, mainly due the oscillatory aspect of seismic data. 
 A local gradient approach does not usually converge to the global minimum.
 \n\nWe first review the classical full waveform inversion and its limitati
 ons. We then present two alternatives to avoid local minima in the determi
 nation of the background (large scale) velocity model. The first method is
  referred as the Normalized Integration Method (Liu et al.\, 2011).  The o
 bjective function measures the misfit between the integral of the envelope
  of the signal.  Because we only compare functions increasing with time\, 
 the objective function has a more convex shape.\n\nThe second method is a 
 differential version of the full waveform inversion. This method is closel
 y related the differential semblance optimization method (Symes\, 2008) us
 ed in seismic imaging to automatically determine the Earth properties from
  reflected data.\n\nWe illustrate the two methods on basic 2-D examples to
  discuss the advantages and limitations.\n
LOCATION:Seminar Room 1\, Newton Institute
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