Prestack Migration Least Squares Migration Greens Theorem Intuitive
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Prestack Migration Least Squares Migration Green’s Theorem Intuitive
3 D Prestack Diffraction Stack Migration Motivation: ZO only good if no lateral vel change s g x
3 D Prestack Diffraction Stack Migration Trial image pt x = m(x) = s, g d(x’, sx+ xg ) s g x
Outline Prestack DS Migration Theory RTM vs Poststack vs Prestack MATLAB Code
Prestack Migration Question: Why Prestack when poststack migration seems good enough? Answer: Stacking to get stacked section assumes layered medium assumption. Solution: Migrate shot gathers so no layer assumption needed. This is prestack migration.
Diffraction Stack Migration: Prestack Down time T(s, g) = sx + Up time xg Where is scatterer? g s sx xg d(s, g, sx + xg ) s, g Narrow band case: direct wave correlated with data x
115. Diffraction Stack Modeling: Prestack T m d=Lm d ~ d(s, g) = 2 x ~ ) W( e i sx A(s, x) ~ m(x) e i xg A(g, x)
115. Diffraction Stack Migration: Prestack T ò m=Ld d ò 2 ~ m(x) = d . . ~* ) W( s, g m(x) = d(s, g, + sx xg s, g -i sx - i xg e ~ e d(s, g) A(s, x) ) A(g, x) Broadband case ~ W( )=1 A(s, x) A(x, g) Narrow band case: direct wave correlated with data
Outline Prestack DS Migration Theory RTM vs Poststack vs Prestack MATLAB Code
Prestack RTM vs One-way Wave Equation Migration
Prestack RTM vs One-way Wave Equation Migration
ZO Diffraction Stack Migration Trial image pt x m(x) = d (g, xg ) g x
ZO Diffraction Stack Migration Trial image pt x m(x) = d (g, xg ) g 2 D dot product of migration Operator and d(g, t) x Migration Image
ZO Reverse Time Migration Trial image pt x m(x) = d (g, xg ) g ~Scattered RTM x Super-resolution
ZO Reverse Time Migration Trial image pt x m(x) = d (g, xg ) g ~Scattered RTM x Super-resolution
Prestack RTM vs One-way Wave Equation Migration
Outline Prestack DS Migration Theory RTM vs Poststack vs Prestack MATLAB Code
Types of Traveltimes Shortest Traveltime or Shortest Raypath Maximum Energy Traveltimes Shortest path ray Maximum energy ray Shortest traveltime ray
Poststack vs Prestack Migration
Poststack vs Prestack Migration
RRTM vs KM Migration
RRTM vs KM Migration
Prestack RTM vs One-Way Mig.
Prestack RTM vs One-Way Mig.
Outline Prestack DS Migration Theory RTM vs Poststack vs Prestack DS MATLAB Code
MATLAB Prestack Migration
MATLAB Inefficient Prestack Migration for isx=1: nx % Loop over shot for igx=1: nx % Loop over receivers for ix=1: nx % Loop over model x for iz=1: nx % Loop over model z t=timer(ix, iz, isx)+timer(ix, iz, igx) sample=gather(isx, igx, t) % Shot gather has 2 time derivatives mig(ix, iz)=mig(ix, iz)+sample end end
MATLAB Prestack Migration
Prestack Migration 1. No assumption about velocity model 2. More sensitive to velocity model errors compared to poststack migration 2 6 3. More than 10 – 10 times slower than poststack migration 4. More sensitive to velocity model than time migration
Poststack vs Prestack Migration
Poststack vs Prestack Migration
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