Linearized inversion of surface seismic data for a model of the earth's subsurface requires estimating the sensitivity of the seismic response to perturbations in the earth's subsurface. This sensitivity, or Jacobian, matrix is usually quite expensive to estimate for all but the simplest model parameterizations. We exploit the numerical structure of the finite-element method, modern sparse matrix technology, and source-receiver reciprocity to develop an algorithm that explicitly calculates the Jacobian matrix at only the cost of a forward model solution. Furthermore, we show that we can achieve improved subsurface images using only one inversion iteration through proper scaling of the image by a diagonal approximation of the Hessian matrix, as predicted by the classical Gauss-Newton method. Our method is applicable to the full suite of wave scattering problems amenable to finiteelement forward modeling. We demonstrate our method through some simple 2-D synthetic examples.
We present a new, fast 3D traveltime calculation algorithm that employs existing frequency-domain waveequation downward-continuation software. By modifying such software to solve for a few complex (rather than real) frequencies, we are able to calculate not only the first arrival and the approximately most energetic traveltimes at each depth point but also their corresponding amplitudes. We compute traveltimes by either taking the logarithm of displacements obtained by the oneway wave equation at a frequency or calculating derivatives of displacements numerically. Amplitudes are estimated from absolute value of the displacement at a frequency. By using the one-way downgoing wave equation, we also circumvent generating traveltimes corresponding to near-surface upcoming head waves not often needed in migration. We compare the traveltimes computed by our algorithm with those obtained by picking the most energetic arrivals from finite-difference solutions of the one-way wave equation, and show that our traveltime calculation method yields traveltimes comparable to solutions of the one-way wave equation. We illustrate the accuracy of our traveltime algorithm by migrating the 2D IFP Marmousi and the 3D SEG/EAGE salt models.
The public reporting burden for this collection of information Is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Infonnation SPONSORING/MONITORING AGENCY NAME(S) AND AODRESS(ES) KOREA SCIENCE & ENGINEERING FOUNDATION BASIC RESEARCH PROGRAM REPORTING ORGANIZATION REPORT NUMBERNRL/JA/7430~04-4 SPONSOR/MONITOR'S ACRONYM{S) KOSEF SPONSORffl/IONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release.distribution is unlimited Approved for public release, distribution is unlimited SUPPLEMENTARY NOTESGEOSCIENCES JOURNAL, VOL. 8, NO 1, P.95 -103, MARCH 2004 ABSTRACTNonmal Incident acoustic techniques were used to determine values of sediment properties (acoustic impedance, sound speed, bulk density, porosity, shear strength, water content and mean grain size) and map those (acoustic impedance and grain size) In the northeastem Gulf of Mexico. The acoustic data were acquired using a 11 kHz normal incident echo sounder over approximately 2000 km of track line. A calibration factor for echo strength was determined by the comparison of acoustic data to measured impedance from five core samples (ground truth data). This echo strength calibration was used for the entire data set Values of sediment properties were calculated from sediment impedance using the regressions coriipiled from the historical core database. Comparison of ground troth and echo strength to data from 20 additional core locations shows close agreement. Discrepancies are probably due to navigation errors or weak retums in deeper water. In addition, sediment disturbance and frequency dispersion can be considered. Using acoustic derived sediment properties, four sediment provinces of the study area are defined as the following types: sandy/silty clay (impedance, 1.6-2.010" kg/m2 s), sand-silt-clay and/or clayey sand (impedance, 2.01-2.40106 kg/nrs), silt or fine sand (impedance, 2.41-2.90 106 kg/m2 s), medium/coarse sand (impedance, 2.91-4.0 106 kg/m2 s). The areal ' distributions of the four types coincide with the previous reports based on sediment sampling. Therefore, the acoustic technique can effectively be used to define and classify sediments and map sediment provinces. ABSTRACT: Normal incident acoustic techniques were used to determine values of sediment properties (acoustic impedance, sound speed, bulk density, porosity, shear strength, water content, and mean grain size) and map those (acoustic impedance and grain size) in the northeastern Gulf of Mexico. The acoustic data were acquired using a 11 kHz normal incident echo sounder over approximately 2000 km of track line. A calibration factor for echo strength was determined...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.