ray tracing in matlab
DESCRIPTION
RAY TRACING IN MATLAB. Ruiqing He University of Utah Feb. 2003. Outline. Introduction Modeling Strategy and steps Reflection and multiple ray tracing Examples Conclusion. Introduction. Role of ray tracing in geophysics Practical requirements: accuracy, speed, ray path , - PowerPoint PPT PresentationTRANSCRIPT
RAY TRACING IN MATLABRAY TRACING IN MATLAB
Ruiqing He
University of Utah
Feb. 2003
OutlineOutline
• Introduction
• Modeling
• Strategy and steps
• Reflection and multiple ray tracing
• Examples
• Conclusion
IntroductionIntroduction
• Role of ray tracing in geophysics
• Practical requirements:
accuracy, speed, ray path,
reflection, multiples, 3D, amplitude.
• Matlab
Ray Tracing MethodsRay Tracing Methods
• Shortest path methods:
Fischer (1993), Moser (1991)
• Wave-equation-based:
Sava (2001)
This Ray TracerThis Ray Tracer
• Shortest path method:
Grid of velocity is finer than or
equal to the grid of ray path.
• Versatile: reflection & multiples
• Accurate
• Robust
ModelingModeling• Block model & grid model
StrategyStrategy• Fermat’s principle
• Huygen’s principle:
original source and secondary source
• Data structure: V(x,z), T(x,z), Ray(x,z,1:2)
• Flag(x,z): 0-unvisited; 1-visited; 2-decided
StepsSteps• Step 0: T(x0,z0)=0; Flag(x0,z0)=2;
Ray(x0,z0,1)=x0; Ray(x0,z0,2)=z0;
• Step 1: sub-ray tracing from the original source.
SearchSearch
• Step 2: all visited nodes record:
T(x,z) and Ray(x,z,1:2), Flag(x,z)=1.• Step 3: search nodes Flag(x,z)==1 & min(T(x,z)).• Step 4: decided node = next secondary source, as
original source, repeat from step 0, until all
interested nodes are decided.
SelectionSelection
Reflections and MultiplesReflections and Multiples
• Step 1: do one transmission ray tracing until all nodes on the reflector are decided.
• Step 2: keep these nodes and make them Flag=1, refresh all other nodes.
• Step 3: jump directly into step 3 in the transmission ray tracing loop.
So, 1 reflection ray tracing = 2 transmission ray tracing; 1 first order multiple ray tracing = 4 transmission ray tracing; 1 2nd order multiple ray tracing = 6 transmission ray tracing;
Reflections and MultiplesReflections and Multiples
Reflections and MultiplesReflections and Multiples
Frozen exploding reflector
ExamplesExamples• Linear gradient model
50 m 100 m
50 m
100 m
Travel time field Sec.
0.05
0.08
0
ComparisonComparison
T
Distance 95 m
0.09 s
0.07 s
75 m
Ray pathRay path
50 m100 m
100 m
50 m
Reflection ray tracingReflection ray tracing
50 m
50 m
100 m
100 m
Multiple ray tracingMultiple ray tracing
50 m
50 m
100 m
100 m
3D ray tracing3D ray tracing
Complex model ray tracingComplex model ray tracing
12000 ft
6000 ft
25000 ft 50000 ft
14000
6000
ft/sSalt Dome Model
Travel Time FieldTravel Time Field
12000 ft
6000 ft
25000 ft 50000 ft
Sec.5
3
0
Ray PathRay Path
6000 ft
12000 ft
25000 ft 50000 ft
SpeedSpeed
10,000 40,000 90,000
Grid size
CPU Time(Sec.)
2
10
16
CPU Time on a 2.2 GHZ AMD
ConclusionConclusion
• Flexibility: ray path, reflections & multiples
• Speed: depends on sub ray tracing length
• Accuracy and robustness
• Applications: tomography and migration
• Extendable: C or Fortran
• Available by email: [email protected]
ThanksThanks
• 2002 members of UTAM for financial support.