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.


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.”

SEG Working Workshop 2015 – Land 3D Processing

September 23, 2015 Celebration No comments

A working workshop to create processing results for Land 3D seismic data held on August 19-22, 2015. Working Workshops as opposed to “talking workshops” are meetings where the participants collaborate in small groups to develop new software code or to conduct computational experiments addressing a particular problem.

This workshop invited participants to create processing results on the small, open data, 3D land project (Teapot Dome 3D). Participants were encouraged to use their own proprietary or open software. Our goal was a final presentation describing the programs, parameters, and data (input and output) in sufficient detail so the results can be reproduced after the workshop. Participants were encouraged to download the Teapot Dome 3D data before the workshop.

The photograph at the top of this post shows some of the 25 participants from 16 organizations who participated in the event. They were from diverse backgrounds including students, post docs, academic staff, faculty, early career professionals, and senior professionals.

A GitHub repository was established to share processing scripts. Final presentations were made in a Lightning talk (5 minute presentation) session on the final day. Presentations were saved and are publicly available.

The agenda for the event was: Wednesday – Optional informal Tutorials Install software and Teapot Dome data Thursday – Working started Introductions, team formation, team work Lunch and learn – SeaView Team work, team check in Friday – continue work sessions Team work, check in, workshop dinner Saturday – wrap up and presentations Create presentation, lunch, lightning talks

An overview of some of the presentations follows.

Bjorn Olofsson was invited to on Thursday to make a lunch and learn presentation on SEAVIEW the viewer from the OpenSeaSeis package. Seaview supports multiple seismic formats including SeaSeis, SEGY, SU, and Madagascar. Bjorn described issues related to visualization including how to handle aliasing. See Bjorn’s presentation and the full distribution of his demo.

Huang, Liau, Yu described the workshop effort to edit bad traces on the Teapot Dome survey. They used the Python API in IPython notebooks to access the data. They used the Mayavi Python library for 3D visualization. They observed three types of noise and developed a Python script to build a mask to edit one type of noise traces. The presentation is available.

Merzlikin and Cvetkovic presented results using diffraction imaging and oriented filtering on the teapot dome project. They estimated a 3D dip field and used it for 3D diffraction and structure oriented smoothing. The presentation is available.

Worthy-Blackwell and Staal worked on Velocity interpolation and NMO. They interpolated the commercial velocity field using scipy.interpolate.Rbf and applied it to a small subset of the data using sfbinint3 and sfnmo.

Yangkang Chen applied noise suppression to the post stack volume and evaluated results on output and difference volumes.

Bill Symes applied a basic processing sequence with Seismic Unix. He approximated the processing sequence in Excell’s processing report from the original processing. His sequence was tpow, decon, agc, nmo, and stack. No surface consistant decon or scaling is available in SU, so he used single trace processing. He showed incremental improvement at each stage on midpoint gathers and stacks. He also checked for residual moveout on CMP gathers and made updates to the velocity field. This was the most complete processing sequence produced at the workshop. His presentation is available.

In summary, the workshop was attended by a good mixture of academics and professionals with a broad range of experience. Turnout for the optional tutorial day was much larger then expected, about 20. Most attendees used Madagascar, but the most complete processing sequence was applied using Seismic Unix. Madagascar and Seismic Unix were both developed as a platform for university research and many basic processes are missing. Applying a full processing sequence to 3D land data with these systems is a challenging task. Unfortunately nobody used a commercial processing system to help guide improvements to these academic systems. SeaView shows promise as a viewer to help explore your data. Participants enjoyed the opportunity to learn, contribute and network.

Let’s do it again next year using the Stratton 3D Land seismic survey. Contact me at seismic.working.workshop@gmail.com to help organize the event.