A NUMERICAL INVESTIGATION OF THE VALIDITY OF THE BORN APPROXIMATION FOR DETERMINATION OF THE REFLECTION COEFFICIENTS OF UNDERDENSE PLASMA SLABS

1964 ◽  
Author(s):  
S. Zivanovic
Keyword(s):  
Numerical Investigation ◽  
Born Approximation ◽  
Reflection Coefficients ◽  
Underdense Plasma

Determination of background velocities by multiple migration fitting

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 476-490 ◽  
Author(s):  
Guy Chavent ◽  
Chester A. Jacewitz
Keyword(s):  
Numerical Investigation ◽  
Seismic Data ◽  
Synthetic Data ◽  
Similarity Index ◽  
Velocity Profiles ◽  
Additional Cost ◽  
Scalar Similarity ◽  
Local Gradient

We present an approach called multiple migration fitting (MMF) designed to automatically determine 2-D background velocities from prestack seismic data. In this approach, we maximize a scalar similarity index (SI) for a collection of migrated sections obtained by various illuminations of the same earth. Numerical investigation shows that this index is a rather smooth, nonoscillatory function of velocity that tends to be a maximum for good velocity profiles, and hence is amenable to maximization by local gradient techniques. This maximization will be practically feasible, as we prove that the exact gradient of SI can be computed at an additional cost of only twice that required for the computation of the collection of migrated sections, independently of the number of velocity unknowns. Application to synthetic data shows that MMF leads to enhanced background velocities and stacked migrated sections.

On: “Special Report of the Subcommittee on Polarity Standards” by Ben B. Thigpen, A. E. Dalby, and Ralph Landrum (GEOPHYSICS, August 1975, p. 694–699)

Geophysics ◽  
1976 ◽  
Vol 41 (2) ◽  
pp. 324-324
Author(s):  
W. T. Valenta
Keyword(s):  
Reflection Coefficient ◽  
Compressional Wave ◽  
Velocity Versus ◽  
Reflection Coefficients ◽  
Special Report ◽  
Sonic Logs ◽  
The Relationship

In their report, the authors recommend that the arrival of a compressional wave at a geophone or hydrophone shall ultimately produce a trough (downward or leftward kick) on a seismogram; but they don’t say why. On sonic logs and displays of velocity versus time, velocity increases are up; likewise for density increases on density logs; likewise for positive reflection coefficients on reflection coefficient logs computed from the previously mentioned logs. Should not seismograms, which ideally are bandlimited reflection coefficient logs, conform to the same convention? The committee succeeded in the objectives of establishing the relationship between impulse‐source systems and vibratory‐source systems and of establishing tests for the determination of the polarity of a given system. I feel strongly that the committee should recommend that a compressional arrival shall produce a peak on a seismogram.

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