Method of using a parabolic equation model for range-dependent seismo-acoustic problems

• US 9,945,971 B2
• Filed: 02/04/2016
• Issued: 04/17/2018
• Est. Priority Date: 02/10/2015
• Status: Active Grant

• Current Assignee: The Government Of The United States As Represented By The Secretary Of The Navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Collins, Michael D.
• Primary Examiner(s): Alsomiri, Isam A
• Assistant Examiner(s): Ndure, Amie M
• Application Number:
  US15/015,425
• Publication Number:
  US 20170045634A1
• Time in Patent Office: 803 Days
• CPC Class Codes: G01S 5/18 using ultrasonic, sonic, or infrasonic waves
• CPC Class Codes: G01V 1/187 Direction-sensitive hydrophones
• CPC Class Codes: G01V 1/282 Application of seismic models, synthetic seismograms
• CPC Class Codes: G01V 1/284 Application of the shear wave component and/or several components of the seismic signal
• CPC Class Codes: G01V 1/30 Analysis G01V1/50 takes precedence
• CPC Class Codes: G01V 1/38 specially adapted for water-covered areas G01V1/28 takes precedence
• CPC Class Codes: G01V 2210/123 Passive source, e.g. microseismics
• CPC Class Codes: G01V 2210/1232 Earthquakes
• CPC Class Codes: G01V 2210/614 Synthetically generated data
• CPC Class Codes: G01V 2210/65 Source localisation, e.g. faults, hypocenters or reservoirs
• CPC Class Codes: G01V 2210/673 Finite-element; Finite-difference

Abstract

A method of modeling an aquatic environment or locating an acoustic source in the aquatic environment. A range-dependent medium is approximated in terms of a series of range-independent regions and obtaining single-scattering solutions across the vertical interfaces between regions. One or more acoustic waves are propagated from a known acoustic source through the range-dependent medium to one or more known seismoacoustic receivers to model iteratively the various solid and liquid layers of the range-dependent medium. Alternatively, one or more acoustic waves are reverse-propagated from one or more known seismoacoustic receivers through the range-dependent medium to determine whether an acoustic source is present within a user-defined range.

Claims

1. A method of locating an acoustic source within a user-defined maximum range, the method comprising:

receiving an acoustic signal from the acoustic source through an aquatic environment using at least one seismoacoustic sensor, the acoustic signal comprising an acoustic pressure and an acoustic signal frequency, the acoustic signal comprising compressional waves and shear waves, the environment comprising a plurality of layers, the plurality of layers comprising at least one of solid layers and liquid layers, the solid layers propagating the compressional waves and the shear waves, the liquid layers propagating the compressional waves;

determining from the received acoustic signal a plurality of initial conditions, the plurality of initial conditions being based on the acoustic pressure and the acoustic signal frequency;

digitizing the aquatic environment into a plurality of range-independent regions and a plurality of vertical interfaces, each vertical interface of the plurality of vertical interfaces being located between adjacent range-independent regions of the plurality of range-independent regions;

determining an initial transmitted field for a range-independent region of the plurality of range-independent regions based on the plurality of initial conditions and determining a subsequent incident field;

determining a subsequent transmitted field for an adjacent vertical interlace of the plurality of vertical interfaces based on the subsequent incident field and determining a next incident field on an adjacent range-independent region of the plurality of range-independent regions;

determining the subsequent transmitted field for another range-independent region of the plurality of range-independent regions based on the next incident field and determining the subsequent incident field on another vertical interface of the at least one vertical interface;

repeating for the user-defined maximum range determining the subsequent transmitted field for another range-independent region of the plurality of range-independent regions based on the next incident field and determining the subsequent incident field on another vertical interface of the at least one vertical interface, thereby approximating a propagation of the received acoustic signal propagating from the acoustic source via the environment to the at least one seismoacoustic sensor;

determining an acoustic source location based on the approximation.

2. The method according to claim 1, wherein said determining the subsequent transmitted field for an adjacent vertical interface of the plurality of vertical interfaces based on the subsequent incident field and determining a next incident field on an adjacent range-independent region of the plurality of range-independent regions comprises using single scattering with a parabolic wave equation.

3. The method according to claim 2, wherein said determining the subsequent transmitted field for an adjacent vertical interlace of the plurality of vertical interfaces based on the subsequent incident field and determining a next incident field on an adjacent range-independent region of the plurality of range-independent regions comprises conserving horizontal displacement and tangential stress, and vertical displacement and normal stress.

4. The method according to claim 3, wherein said transmitted field comprises an average of the conserved horizontal displacement and the tangential stress, and the conserved vertical displacement and the normal stress.

5. The method according to claim 1, wherein the at least one seismoacoustic sensor comprises at least one of a one-dimensional vertical hydrophone array, a two-dimensional vertical hydrophone array, a three-dimensional vertical hydrophone array, a one-dimensional horizontal hydrophone array, a two-dimensional horizontal hydrophone array, a three-dimensional horizontal hydrophone array, a vertical water-body bottom-mounted hydrophone array, a horizontal water-body bottom-mounted hydrophone array, and a seismometer array.

6. The method according to claim 1, wherein the acoustic signal further comprises a solid layer motion, the plurality of initial conditions being further based on the solid layer motion.

7. The method according to claim 1, wherein the at least one seismoacoustic sensor is located one of on land, on a body of water, in the body of water, and under the body of water.

8. The method according to claim 1, wherein the acoustic source is located one of on land, in a body of water, and under the body of water.

9. A method of locating at least one object of interest in an aquatic environment within a user-defined maximum range, the method comprising:

receiving an actual acoustic signal from an acoustic source through the aquatic embroilment using at least one seismoacoustic sensor, the actual acoustic signal comprising an acoustic pressure, an acoustic signal frequency, and an acoustic source location, the actual acoustic signal comprising compressional waves and shear waves, the aquatic environment comprising a plurality of actual layers, the plurality of actual layers comprising at least one of solid actual layers and liquid actual layers, the solid actual layers propagating the compressional waves and the shear waves, the liquid actual layers propagating the compressional waves;

determining from the received actual acoustic signal a plurality of initial conditions, the plurality of initial conditions being based on the acoustic pressure, the acoustic signal frequency, and the acoustic source location;

digitizing an aquatic environment, model into a plurality of range-independent regions and a plurality of vertical interfaces, each vertical interface of the plurality of vertical interfaces being located between adjacent range-independent regions of the plurality of range-independent regions, the initial aquatic environment model comprising a plurality of model layers, the plurality of model layers comprising at least one of solid model layers and liquid, model layers, the plurality of model layers comprising a plurality of respective thickness geometries and a plurality of respective material densities;

determining an initial transmitted field for a range-independent region of the plurality of range-independent regions based on the plurality of initial conditions and determining a subsequent incident field;

determining a subsequent transmitted field for an adjacent vertical interface of the plurality of vertical interlaces based on the subsequent incident field and determining a next incident field on an adjacent range-independent region of the plurality of range-independent regions;

determining the subsequent transmitted field for another range-independent region of the plurality of range-independent regions based on the next incident field and determining the subsequent incident field on another vertical interface of the at least one vertical interface;

repeating for the user-defined maximum range determining the subsequent transmitted field for another range-independent region of the plurality of range-independent regions based on the next incident field and determining the subsequent incident field on another vertical interface of the at least one vertical interface, thereby approximating a propagation of the acoustic signal propagating from the acoustic source via the aquatic environment to the at least one seismoacoustic sensor;

determining a model acoustic signal based on the approximation;

determining whether the model acoustic signal is converging toward the received actual acoustic signal;

adjusting the aquatic environment model, if the model acoustic signal is not converging toward the actual acoustic signal, and repeating said determining an initial transmitted field step, said determining the subsequent transmitted field step for an adjacent vertical interlace, said determining the subsequent transmitted field for another range-independent region, said repeating step, said determining a model acoustic signal based on the approximation step, until the model acoustic signal converges toward the actual acoustic signal; and

using the aquatic environment model to locate at least one object of interest in the aquatic environment.

10. The method according to claim 9, wherein said determining the subsequent transmitted field for an adjacent vertical interface of the plurality of vertical interfaces based on the subsequent incident field and determining a next incident field on an adjacent range-independent region of the plurality of range-independent regions comprises using single scattering with a parabolic wave equation.

11. The method according to claim 10, wherein said determining the subsequent transmitted field for an adjacent vertical interface of the plurality of vertical interfaces based on the subsequent incident field and determining a next incident field on an adjacent range-independent region of the plurality of range-independent regions comprises conserving horizontal displacement and tangential stress, and vertical displacement and normal stress.

12. The method according to claim 11, wherein said transmitted field comprises an average of the conserved horizontal displacement and the tangential stress, and the conserved vertical displacement and the normal stress.

13. The method according to claim 9, wherein the at least one seismoacoustic sensor comprises at least one of a one-dimensional vertical hydrophone array, a two-dimensional vertical hydrophone array, a three-dimensional vertical hydrophone array, a one-dimensional horizontal hydrophone array, a two-dimensional horizontal hydrophone array, a three-dimensional horizontal hydrophone array, a vertical water-body bottom-mounted hydrophone array, a horizontal water-body bottom-mounted hydrophone array, and a seismometer array.

14. The method according to claim 9, wherein the acoustic signal further comprises a solid layer motion, the plurality of initial conditions being further based on the solid layer motion.

15. The method according to claim 9, wherein the at least one seismoacoustic sensor is located one of on land, in a body of water, and under the body of water.

16. The method according to claim 9, wherein the at least one object of interest comprises at least one extractable resource.

17. The method according to claim 16, wherein the at least one extractable resource comprises at least one of a mineral, natural gas, and oil.

18. The method according to claim 9, wherein the acoustic source is located one of on land, in a body of water, and under the body of water.