A hexagonal finite difference mesh for 2D TTI RTM
Bibliographic record
Abstract
A common finite difference implementation of reverse time migration with tilted transverse isotropy (TTI) follows the formulation of Alkhalifah (2000), Fletcher et. al. (2008) and Zhou et. al. (2006). The finite difference implementation of these equations in Cartesian coordinates necessitates the computation of mixed partial derivatives of the acoustic pressure in the spatial domain. Different methods exist for the computation of these mixed derivatives including sequentially computing centered first derivatives in each direction, computing staggered first derivatives with interpolation or the pseudospectral method. The computation of centered first derivatives causes ringing in the output but using staggered derivatives requires interpolation of the staggered points back to the original grid. The pseudospectral method necessitates the computation of a 2D FFT in a 2D simulation. In this paper, we propose a hexagonal mesh for the finite difference implementation of 2D TTI RTM. The implementation eliminates the need for mixed partial derivatives and reduces grid dispersion in wave simulations.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".