Method for reconstructing complex wave attributes from limited view measurements

• US 20050027769A1
• Filed: 03/01/2004
• Published: 02/03/2005
• Est. Priority Date: 07/28/2003
• Status: Active Grant

• Current Assignee: Alan Witten
• Original Assignee: Alan Witten
• Inventors: Witten, Alan
• Granted Patent: US 7,124,044 B2
• Time in Patent Office: Days
• US Class Current: 708/400
• CPC Class Codes: G01N 29/0672 by acoustic tomography medical tomography A61B8/13
• CPC Class Codes: G01N 29/07 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/11 by measuring attenuation of acoustic waves
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14
• CPC Class Codes: G01V 1/28 Processing seismic data, e.g. for interpretation or for event detection G01V1/48 takes precedence
• CPC Class Codes: G06F 17/141 Discrete Fourier transforms
• CPC Class Codes: G06F 17/17 Function evaluation by approximation methods, e.g. inter- or extrapolation, smoothing, least mean square method G06F17/18 takes precedence ; interpolation for numerical control G05B19/18

Abstract

A method is disclosed for reconstructing complex wave attributes from limited view measurements of a scattering object. The method involves the analytic continuation of the Fourier transform of the object function into the area in which there is an absence of K-space coverage by requiring objects to be an even function. (It is assumed that physical objects are even functions, and it is this assumption that allows analytic continuation.) When the object function is not centered at the origin, the measurements are shifted to the origin prior to determining the analytic continuation and returned to their original location following analytic continuation.

Claims

1. A method for reconstructing complex wave attributes described by an object function O from limited view measurements u of a measurement surface r with associated wavevector K, said method comprising the steps of:

processing said limited view measurements u to obtain Fourier transformed measurements ũ

;

determining a Fourier transformed object function Õ

of said object function O;

determining an analytic relationship between said Fourier transformed object function Õ and

said Fourier transformed measurements ũ

;

analytically extending said Fourier transform Õ

by specifying that Õ

(K)=Õ

(−

K), thereby obtaining an analytically extended Fourier transform of Õ

; and

,

reconstructing said complex wave attributes by inverting said analytically extended Fourier transform of Õ

.

2. The method of claim 1 wherein said complex wave attributes are wave speed and attenuation.

3. The method of claim 1 wherein said complex wave attributes are dielectric and electrical conductivity.

4. The method of claim 1 wherein said complex wave attributes are acoustic wave speed density and compressibility.

5. The method of claim 1 wherein said object function is one-dimensional.

6. The method of claim 1 wherein said object function is two-dimensional.

7. The method of claim 1 wherein said object function is three-dimensional.

8. The method of claim 1 wherein said measurement surface r comprises a ring.

9. The method of claim 1 wherein said measurement surface r comprises a sphere.

10. The method of claim 1 wherein said measurement surface r comprises a cylinder.

11. The method of claim 1 wherein said measurement surface r comprises a plurality of parallel lines.

12. The method of claim 1 wherein said measurement surface r comprises a plurality of perpendicular lines.

13. The method of claim 1 wherein said measurement surface r comprises a line and a curved surface.

14. The method of claim 1 wherein said limited view measurements are time domain measurements.

15. The method of claim 1 wherein said limited view measurements are frequency domain measurements.

16. A method for reconstructing complex wave attributes described by an object function O from limited view measurements u of an object with associated wavevector K, said method comprising the steps of:

processing said measurements u to obtain Fourier transformed measurements ũ

;

determining a midpoint of said object;

creating shifted Fourier transformed measurements ũ

_R by shifting said Fourier transformed measurements ũ

so that said midpoint is located at the origin;

determining an analytic relationship between said object function O and said shifted Fourier transformed measurements ũ

_R;

determining the Fourier transform Õ

of said object function O from said Fourier transformed measurements ũ

_R using said analytic relationship;

analytically extending said Fourier transform Õ

by specifying that Õ

(K)=Õ

(−

K), thereby obtaining an analytically extended Fourier transform of Õ

;

determining shifted complex wave attributes by inverting said analytically extended Fourier transform of Õ

; and

,

reconstructing said complex wave attributes by shifting said shifted complex wave attributes back to said midpoint.

17. The method of claim 16 wherein said step of determining a midpoint comprises the steps of:

determining the complex contrast of said object;

determining the magnitude of said complex contrast; and

,

choosing said midpoint to be the center location of said complex contrast.

18. The method of claim 16 wherein said step of determining a midpoint comprises the steps of:

determining the complex contrast of said object;

determining the magnitude of said complex contrast; and

,

choosing said midpoint to be the mid-depth of said complex contrast.

19. The method of claim 16 wherein said midpoint is a spatial component and said step of determining a midpoint comprises choosing said midpoint to be the depth achieved at the maximum measured travel time.

20. The method of claim 16 wherein said midpoint is a temporal component and said step of determining a midpoint comprises choosing said midpoint to be the maximum measured travel time.