Celebration

Matching and merging seismic images

November 16, 2018 Celebration No comments

A new paper is added to the collection of reproducible documents: Matching and merging high-resolution and legacy seismic images

When multiple seismic surveys are acquired over the same area using different technologies that produce data with different frequency content, it may be beneficial to combine these data to produce a broader bandwidth volume. In this paper, we propose a workflow for matching and blending seismic images obtained from shallow high-resolution seismic surveys and conventional surveys conducted over the same area. The workflow consists of three distinct steps: (a) balancing the amplitudes and frequency content of the two images by non-stationary smoothing of the high-resolution image; (b) estimating and removing variable time shifts between the two images; and (c) blending the two images together by least-squares inversion. The proposed workflow is applied successfully to images from the Gulf of Mexico.

Fast time-to-depth conversion

November 16, 2018 Celebration No comments

A new paper is added to the collection of reproducible documents: Fast time-to-depth conversion and interval velocity estimation in the case of weak lateral variations

Time-domain processing has a long history in seismic imaging and has always been a powerful workhorse that is routinely utilized. It generally leads to an expeditious construction of the subsurface velocity model in time, which can later be expressed in the Cartesian depth coordinates via a subsequent time-to-depth conversion. The conventional practice of such conversion is done using Dix inversion, which is exact in the case of laterally homogeneous media. For other media with lateral heterogeneity, the time-to-depth conversion involves solving a more complex system of partial differential equations (PDEs). In this study, we propose an efficient alternative for time-to-depth conversion and interval velocity estimation based on the assumption of weak lateral velocity variations. By considering only first-order perturbative effects from lateral variations, the exact system of PDEs required to accomplish the exact conversion reduces to a simpler system that can be solved efficiently in a layer-stripping (downward-stepping) fashion. Numerical synthetic and field data examples show that the proposed method can achieve reasonable accuracy and is significantly more efficient than previously proposed method with a speedup by an order of magnitude.

Tutorial on 2-D Fourier Transform

October 17, 2018 Celebration No comments

As an exercise for the SEG Reproducibility Zoo, the example in rsf/tutorials/yilmaz1 reproduces examples from Oz Yilmaz’s famous book Seismic Data Analysis, the section on the 2-D Fourier transform.

Madagascar users are encouraged to try improving the results.

Tutorial on conjugate gradients

October 16, 2018 Celebration No comments

As an exercise for the SEG Reproducibility Zoo, the example in rsf/tutorials/cg reproduces the tutorial from Karl Schleicher on the method of conjugate gradients.

The tutorial was published in the April 2018 issue of The Leading Edge.

Madagascar users are encouraged to try improving the results.

madagascar-2.0

August 24, 2017 Celebration No comments

The major new release of Madagascar, stable version 2.0 was made during the Madagascar school in Shanghai and features 25 new reproducible papers and significant other enhancements including complete examples of seismic field data processing.

According to the SourceForge statistics, the previous 1.7 stable distribution has been downloaded nearly 12,000 times. The top country (with 28% of all downloads) was USA, followed by China, Brazil, Germany, and Columbia.

2017 Madagascar Schools

August 24, 2017 Celebration 1 comment

The 2017 Madagascar School on Reproducible Computational Geophysics took place in Shanghai, China, on July 10-11 and was hosted by Professor Jiubing Cheng at Tongji University.

The school attracted nearly 80 participants from 12 different universities and 5 other research organizations. The program included lectures given by 6 different instructors and hands-on exercises on different topics in the use of the Madagascar software framework, as well as presentations sharing experience of different research groupd. The school materials are available on the website.

Earlier this year, on April 21-22, another school took place at the University of Houston and was hosted by SEG Wavelets, the local SEG student chapter. The school materials are available on the website.

Elastic wave-vector decomposition

April 18, 2017 Celebration No comments

A new paper is added to the collection of reproducible documents: Elastic wave-vector decomposition in heterogeneous anisotropic media

The goal of wave-mode separation and wave-vector decomposition is to separate full elastic wavefield into three wavefields with each corresponding to a different wave mode. This allows elastic reverse-time migration to handle of each wave mode independently . Several of the previously proposed methods to accomplish this task require the knowledge of the polarization vectors of all three wave modes in a given anisotropic medium. We propose a wave-vector decomposition method where the wavefield is decomposed in the wavenumber domain via the analytical decomposition operator with improved computational efficiency using low-rank approximations. The method is applicable for general heterogeneous anisotropic media. To apply the proposed method in low-symmetry anisotropic media such as orthorhombic, monoclinic, and triclinic, we define the two S modes by sorting them based on their phase velocities (S1 and S2), which are defined everywhere except at the singularities. The singularities can be located using an analytical condition derived from the exact phase-velocity expressions for S waves. This condition defines a weight function, which can be applied to attenuate the planar artifacts caused by the local discontinuity of polarization vectors at the singularities. The amplitude information lost because of weighting can be recovered using the technique of local signal-noise orthogonalization. Numerical examples show that the proposed approach provides an effective decomposition method for all wave modes in heterogeneous, strongly anisotropic media.

Propagating decoupled elastic waves using low-rank approximation

November 21, 2016 Celebration No comments

A new paper is added to the collection of reproducible documents: Simulating propagation of decoupled elastic waves using low-rank approximate mixed-domain integral operators for anisotropic media

In elastic imaging, the extrapolated vector fields are decoupled into pure wave modes, such that the imaging condition produces interpretable images. Conventionally, mode decoupling in anisotropic media is costly as the operators involved are dependent on the velocity, and thus are not stationary. We develop an efficient pseudo-spectral approach to directly extrapolate the decoupled elastic waves using low-rank approximate mixed-domain integral operators on the basis of the elastic displacement wave equation. We apply k-space adjustment to the pseudo-spectral solution to allow for a relatively large extrapolation time-step. The low-rank approximation is, thus, applied to the spectral operators that simultaneously extrapolate and decompose the elastic wavefields. Synthetic examples on transversely isotropic and orthorhombic models show that, our approach has the potential to efficiently and accurately simulate the propagations of the decoupled quasi-P and quasi-S modes as well as the total wavefields, for elastic wave modeling, imaging and inversion.

Madagascar School in Zürich

October 31, 2016 Celebration No comments

Filippo Broggini reports:

The 2016 Madagascar School on Reproducible Computational Geophysics took place in Zürich, Switzerland, on June 6-7, 2016, and was hosted by the Exploration and Environmental Geophysics (EEG) group at ETH Zürich.

The school attracted more than 15 participants from 5 countries and 10 different universities. The program included lectures given by 5 different instructors and hands-on exercises on different topics in the use of the Madagascar software framework. The school materials are available on the website.

The genesis of Madagascar

November 12, 2015 Celebration No comments

The November 2015 issue of The Leading Edge contains an article about Madagascar: The Genesis of Madagascar by John Holden.

In July 2014, an unusual meeting took place at Rice University in Houston, Texas. Two dozen participants from numerous organizations gathered in a conference room for a workshop. Instead of the usual presentations and long talks one associates with scientific workshops, the participants immediately broke into small teams and gathered around laptop computers to write software code. Intense code-hacking sessions were interrupted only by necessary group discussions. This was the second “working workshop” of the Madagascar open-source software project.

One of the article’s features are user testimonials:

William W. Symes, Noah Harding Professor in Computational and Applied Mathematics and professor of earth science at Rice University, Houston, says, “I use Madagascar for everything! All of my computational research projects and those of my students take advantage of both the utility side of Madagascar (that is, its many useful commands for data manipulation and processing) and the reproducible research side. I have been convinced since learning the concept from J. F. Claerbout many years ago that reproducible research, in the sense epitomized by Madagascar, is not just an intellectually satisfactory mode (arguably the only such) for computational science research but a tremendous labor saver. Over the years, I have built a number of my own reproducible research (RR) frameworks but junked them all in favor of Madagascar several years ago. The utility suite is an incredible achievement, but the truly exceptional feature of Madagascar, in my opinion, is the suite of reproducible research tools. These are based on a full-featured language (Python) making them easily extensible, and they integrate TeX shell commands and (increasingly) HPC tools — this integration makes Madagascar the most powerful realization of the reproducible-research concept of which I am aware. It doesn’t solve all of the problems of RR — notably, the inability of software to keep itself maintained without human intervention — but it represents a quantum leap beyond other RR frameworks.”

Yang Liu, professor at the College of Geo-exploration Science and Technology, Jilin University, China, says, “I am using Madagascar software to implement new research ideas and provide reproducible examples for techniques in oil-gas exploration. For me the most attractive feature of the Madagascar open-source software is its reproducibility of computational modules, data-processing scripts, and research papers. Anyone could generate all examples and papers just by using several simple commands. The software package is also well maintained, and there is a group of developers who are continuously contributing their codes, which keeps the Madagascar software up to date. Many natural phenomena, including geologic events and geophysical data, are fundamentally nonstationary. So figuring out how to recover nonstationary signals from a noisy environment is a persistent problem in my field. We developed a 3D t-x-y adaptive prediction filter (APF) for random-noise attenuation in seismic exploration. The method is also able to deal with random noise in other fields, e.g., imaging processing. The core of the proposed method is based on existing source codes in the Madagascar environment. Therefore, we can implement the new theory in a short time. The computational modules and the corresponding paper are also reproducible in the updated Madagascar software package.”

Jeffrey Shragge, Woodside Professor of Computational Geoscience at the School of Earth and Environment/School of Physics, University of Western Australia, says, “My students and I use Madagascar for an integrated R & D environment on all aspects of my research. We develop and apply codes within the $RSFSRC/user/area and port these over to our R & D and local public (termed IVEC) HPC clusters. We are integrating Madagascar into our teaching through developing reproducible seismic labs. The package is unique because it integrates all of my R & D activities — code development, testing and verification, development of examples, easy extension to interface with HPC cluster systems, writing of manuscripts, etc. Most important, all of these activities can be undertaken in a reproducible environment. We have used codes written in the Madagascar package to address what type of microseismic signals we would expect from a large CO2 project being developed south of Perth. This required performing large-scale 3D elastic modeling on grids of the size 20003 using MPI+OpenMP codes developed using the Madagascar API. We have also used various Madagascar 2D/3D seismic-imaging codes for imaging geologic structures at this site to help prepare for pilot CO2 injection studies. We also use Madagascar for various near-surface geophysics investigations, including archaeological and forensic projects throughout Western Australia.”