March 11, 2014 Examples No comments
If you enjoyed Matt Hall‘s tutorial on smoothing surfaces and attributes in the last month’s issue of The Leading Edge, you can find it reproduced in Madagascar (with some extensions) under rsf/tutorials/smoothing.
If you like IPython notebooks, you can also reproduce this exercise using the provided notebook.
Madagascar users are encouraged to try improving this reproducible example.
March 11, 2014 Programs No comments
sflpad pads the input data by inserting zero traces and zero planes between traces and planes in the input. The following example from gee/lal/lace shows a classic example of interpolation beyond aliasing, which appears on the cover of Jon Claerbout’s book Processing Versus Inversion: 
March 7, 2014 Links No comments
XSEDE (Extreme Science and Engineering Discovery Environment) is hosting a workshop on reproducibility as a full-day event on Monday, July 14, 2014, during the XSEDE conference in Atlanta, Georgia. The workshop promises to address the issue of the reproducibility crisis in computational science addresses during the Data and Code Sharing Roundtable at Yale in 2009.
XSEDE is the world’s largest, most comprehensive distributed cyberinfrastructure for open scientific research, which integrates high-performance computers and other facilities around the US.
February 15, 2014 Documentation No comments
A new paper is added to the collection of reproducible documents:
Local skewness attribute as a seismic phase detector
We propose a novel seismic attribute, local skewness, as an indicator of localized phase of seismic signals. The proposed attribute appears to have a higher dynamical range and a better stability than the previously used local kurtosis. Synthetic and real data examples demonstrate the effectiveness of local skewness in detecting and correcting time-varying, locally-observed phase of seismic signals.
February 11, 2014 Celebration No comments
A Madagascar school will take place on April 11, 2014, in St. Petersburg, Russia, at a workshop during the EAGE convention. The workshop was proposed by Paul Sava.
See the workshop page for more information.
February 6, 2014 Programs No comments
sfdipfilter filters input data based on a range of dips (slopes).
The following example from rsf/su/rsfdipfilt (borrowed from one of Seismic Unix demos) shows a synthetic dataset with three events before and after dip filtering:
sfdipfilter operates in 2-D or 3-D Fourier transform domain, with the dimensionality specified by dim=. The dip range is specified either by angles (if angle=y) or by velocities (if angle=n). The four parameters (either ang1=, ang2=, ang3=, ang4= or v1=, v2=, v3=, v4=) specify the range. If pass=y, the range between v2 and v3 is passed, and the range below v1 or above v4 is rejected. If pass=n, the range between v2 and v3 is rejected, and the range below v1 or above v4 is passed. The transition between pass and reject regions is implemented with a sine tapering.
January 9, 2014 Programs No comments
sfinttest1 performs forward interpolation from a regular grid to irregular locations (in 1-D).
The following example from sep/forwd/chirp shows regularly sampled values of a variable-frequency signal and the error of its interpolation using linear and cubic-convolution interpolators.
The irregular coordinates for interpolation are supplied in a file specified by coord=. The type of the interpolator is specified by interp=. The currently implemented types are Lagrange (including linear and nearest-neighbor interpolation), cubic convolution, weighted sinc interpolation (with Kaiser, Lanczos, cosine, and Welsh windows), B-spline, and MOM (slightly improved B-spline). The size of the interpolation filter is given by nw=. The Kaiser-window interpolator requires an additional parameter, which is specified by kai=.
An alternative (using invertible cubic spline interpolation) is sfiwarp.
A 2-D version is sfinttest2. The following example from sep/forwd/chirp2 compares the error of Kaiser-windowed 8-point sinc interpolation and 8-point B-spline interpolator applied to interpolating a 2-D signal.
December 7, 2013 Documentation No comments
A new paper is added to the collection of reproducible documents:
Structural uncertainty of time-migrated seismic images
Structural information in seismic images is uncertain. The main cause of this uncertainty is uncertainty in velocity estimation. We adopt the technique of velocity continuation for estimating velocity uncertainties and corresponding structural uncertainties in time-migrated images. Data experiments indicate that structural uncertainties can be significant even when both structure and velocity variations are mild.
December 6, 2013 Documentation No comments
A new paper is added to the collection of reproducible documents:
A parallel sweeping preconditioner for heterogeneous 3D Helmholtz equations
A parallelization of a sweeping preconditioner for 3D Helmholtz equations without large cavities is introduced and benchmarked for several challenging velocity models. The setup and application costs of the sequential preconditioner are shown to be
and
, where
denotes the modestly frequency-dependent number of grid points per Perfectly Matched Layer. Several computational and memory improvements are introduced relative to using black-box sparse-direct solvers for the auxiliary problems, and competitive runtimes and iteration counts are reported for high-frequency problems distributed over thousands of cores. Two open-source packages are released along with this paper: Parallel Sweeping Preconditioner (PSP) and the underlying distributed multifrontal solver, Clique.
December 1, 2013 Programs No comments
sfcausint implements an operation of causal numerical integration. This is a simple operation, which mathematically amounts to recursion
$$yn = y{n-1} + x_n$$
or to inversion of a simple bidiagonal matrix. See Geophysical Image Estimation by Example for more explanation.
The only parameter in sfcausint is adj=, the flag for adjoint computation. The adjoint operation applies recursion backwards
$$x{n-1} = xn + y_{n-1}$$
The following example from gee/ajt/causint illustrates forward and ajoint causal integration with sfcausint:
