dynamical inverse scattering
play

Dynamical Inverse Scattering Roland Potthast Deutscher Wetterdienst - PowerPoint PPT Presentation

Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Dynamical Inverse Scattering Roland Potthast Deutscher Wetterdienst University of Reading (Uni G ottingen) Linz 24.11.2011 1/81 Introduction Orthogonality


  1. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Time-Domain to Frequency Domain ◮ We assume that we take a windowed Fast Fourier Transform of our available time-domain data. ◮ This leads to a large set of wave numbers for which data in the frequency domain is available. ◮ Usually we will have a ◮ low number of directions of incidence (sources) ◮ larger number of measurement points for the scattered or total wave. ◮ many wavenumbers u ∞ (ˆ x j , d ℓ , κ ξ ) , j = 1 , ..., N , ℓ = 1 , ..., M , ξ = 1 , ..., Q . (1) 8/81

  2. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Time-Domain to Frequency Domain ◮ We assume that we take a windowed Fast Fourier Transform of our available time-domain data. ◮ This leads to a large set of wave numbers for which data in the frequency domain is available. ◮ Usually we will have a ◮ low number of directions of incidence (sources) ◮ larger number of measurement points for the scattered or total wave. ◮ many wavenumbers u ∞ (ˆ x j , d ℓ , κ ξ ) , j = 1 , ..., N , ℓ = 1 , ..., M , ξ = 1 , ..., Q . (1) 8/81

  3. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Time-Domain to Frequency Domain ◮ We assume that we take a windowed Fast Fourier Transform of our available time-domain data. ◮ This leads to a large set of wave numbers for which data in the frequency domain is available. ◮ Usually we will have a ◮ low number of directions of incidence (sources) ◮ larger number of measurement points for the scattered or total wave. ◮ many wavenumbers u ∞ (ˆ x j , d ℓ , κ ξ ) , j = 1 , ..., N , ℓ = 1 , ..., M , ξ = 1 , ..., Q . (1) 8/81

  4. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Time-Domain to Frequency Domain ◮ We assume that we take a windowed Fast Fourier Transform of our available time-domain data. ◮ This leads to a large set of wave numbers for which data in the frequency domain is available. ◮ Usually we will have a ◮ low number of directions of incidence (sources) ◮ larger number of measurement points for the scattered or total wave. ◮ many wavenumbers u ∞ (ˆ x j , d ℓ , κ ξ ) , j = 1 , ..., N , ℓ = 1 , ..., M , ξ = 1 , ..., Q . (1) 8/81

  5. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Orthogonality Sampling Method A LGORITHM (O NE - WAVE OS, M ULTI - WAVE OS) For fixed wave number κ one-wave orthogonality sampling calculates � � � e i κ ˆ � x · y u ∞ (ˆ � µ ( y , κ ) = x ) ds (ˆ x ) (2) � � S y ∈ R m from the knowledge of the far field pattern u ∞ on on a grid G of points ˜ the unit sphere S . For fixed wave number κ multi-direction orthogonality sampling calculates � � � � e i κ ˆ � x · y u ∞ (ˆ � µ ( y , κ ) = x , θ ) ds (ˆ x ) � ds ( θ ) (3) � S S y ∈ R m from the knowledge of the far field pattern on a grid G of points ˜ u ∞ (ˆ x , θ ) for ˆ x , θ ∈ S . 9/81

  6. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Orthogonality Sampling Method A LGORITHM (O NE - WAVE OS, M ULTI - WAVE OS) For fixed wave number κ one-wave orthogonality sampling calculates � � � e i κ ˆ � x · y u ∞ (ˆ � µ ( y , κ ) = x ) ds (ˆ x ) (2) � � S y ∈ R m from the knowledge of the far field pattern u ∞ on on a grid G of points ˜ the unit sphere S . For fixed wave number κ multi-direction orthogonality sampling calculates � � � � e i κ ˆ � x · y u ∞ (ˆ � µ ( y , κ ) = x , θ ) ds (ˆ x ) � ds ( θ ) (3) � S S y ∈ R m from the knowledge of the far field pattern on a grid G of points ˜ u ∞ (ˆ x , θ ) for ˆ x , θ ∈ S . 9/81

  7. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Orthogonality Sampling Method A LGORITHM (O NE - WAVE OS, M ULTI - WAVE OS) For fixed wave number κ one-wave orthogonality sampling calculates � � � e i κ ˆ � x · y u ∞ (ˆ � µ ( y , κ ) = x ) ds (ˆ x ) (2) � � S y ∈ R m from the knowledge of the far field pattern u ∞ on on a grid G of points ˜ the unit sphere S . For fixed wave number κ multi-direction orthogonality sampling calculates � � � � e i κ ˆ � x · y u ∞ (ˆ � µ ( y , κ ) = x , θ ) ds (ˆ x ) � ds ( θ ) (3) � S S y ∈ R m from the knowledge of the far field pattern on a grid G of points ˜ u ∞ (ˆ x , θ ) for ˆ x , θ ∈ S . 9/81

  8. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Multi-frequency Orthogonality Sampling A LGORITHM (M ULTI -F REQUENCY ) The multi-frequency orthogonality sampling calculates � κ 1 � � � e i κ ˆ � x · y u ∞ (ˆ � µ ( y , θ ) = x , θ ) ds (ˆ x ) � d κ (4) � κ 0 S y ∈ R m from the knowledge of the far field pattern u ∞ on a grid G of points ˜ κ (ˆ x ) for ˆ x ∈ S and κ ∈ [ κ 0 , κ 1 ] . Here also multi-direction multi-frequency sampling is possible by adding the indicator functions for several directions of incidence. 10/81

  9. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation One Wave, one frequency: the simplest setting Graphics: Orthogonality sampling with κ = 1 or κ = 3 for fixed frequency, one direction of incidence 11/81

  10. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Multi-direction Ortho Sampling Graphics: Orthogonality sampling, many directions of incidence, fixed frequency 12/81

  11. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Multi-frequency Ortho Sampling Graphics: Orthogonality sampling, many directions of incidence, fixed frequency 13/81

  12. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Resolution Study: Large Scale Graphics: Multi-frequency Orthogonality sampling with κ between 0 . 1 and 1, i.e. with a frequency between λ = 6 and λ = 60, one direction of incidence 14/81

  13. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Resolution Study: Medium Scale Graphics: MDMF Orthogonality sampling with κ between 3 and 4, i.e. with a frequency between λ = 1 . 5 and λ = 2 15/81

  14. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Resolution Study: Medium Scale Graphics: MDMF Orthogonality sampling with κ between 6 and 15, i.e. with a frequency between λ = 0 . 4 and λ = 1 16/81

  15. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Resolution Study: Fine Scale Graphics: MDMF Orthogonality sampling with κ between 10 and 20, i.e. with a frequency between λ = 0 . 3 and λ = 0 . 6 17/81

  16. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Resolution Study: Very Fine Scale Graphics: MDMF Orthogonality sampling with κ between 20 and 40, i.e. with a frequency between λ = 0 . 15 and λ = 0 . 3 18/81

  17. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Resolution Study: Very Fine Scale Graphics: MDMF Orthogonality sampling with κ between 20 and 40, i.e. with a frequency between λ = 0 . 15 and λ = 0 . 3 19/81

  18. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Medium Reconstructions I Graphics: Orthogonality sampling for medium reconstruction, MD, fixed frequency κ = 9. 20/81

  19. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Medium Reconstructions II Graphics: Orthogonality sampling for medium reconstruction, MDMF . 21/81

  20. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Medium Reconstructions III Graphics: Orthogonality sampling for medium reconstruction, MDMF . 22/81

  21. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Medium Reconstructions IV Graphics: Orthogonality sampling for medium reconstruction, MDMF . 23/81

  22. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Neumann BC I Graphics: Orthogonality sampling for the Neumann BC, MF . 24/81

  23. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Neumann BC II Graphics: Orthogonality sampling for the Neumann BC, MDMF . 25/81

  24. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Neumann BC II Graphics: Orthogonality sampling for the Neumann BC, MDMF . 26/81

  25. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Orthogonality Sampling Convergence Dirichlet Case Theorem (Convergence or Ortho-Sampling, P 2007/08) The orthogonality sampling algorithm with the Dirichlet boundary condition for one-wave fixed frequency reconstructs the reduced scattered field, i.e. � j 0 ( κ | x − y | ) ∂ u ( y ) u s x ∈ R m . red ( x ) = ds ( y ) , (5) ∂ν ( y ) ∂ D Convergence analysis of the method can be based on the Funk-Hecke formula. 27/81

  26. Introduction Orthogonality Sampling Time-Domain Probe Method Data Assimilation Literature Potthast, R.: Acoustic Tomography by Orthogonality Sampling, Institute of Acoustics Spring Conference, Reading, UK 2008. Potthast, R: Orthogonality Sampling for Object Visualization, Inverse Problems 2010. Griesmaier, R: Multi-frequency orthogonality sampling for inverse obstacle scattering problems, Inverse Problems (2011) 28/81

  27. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Outline Introduction Orthogonality Sampling Time-Domain Probe Method Field & Shape Reconstruction Time-Domain Probe Data Assimilation 3dVar 4dVar Dynamic Inverse Scattering 29/81

  28. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Outline Introduction Orthogonality Sampling Time-Domain Probe Method Field & Shape Reconstruction Time-Domain Probe Data Assimilation 3dVar 4dVar Dynamic Inverse Scattering 30/81

  29. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Setup of Inverse Rough Surface Scattering ◮ Measurements on some surface Γ h , A ◮ Unknown surface Γ below measurement surface and above zero-surface. Dirichlet boundary condition. ◮ Measure total scattered field v from one time-harmonic incident field G ( · , z ) with source point z above or on Γ h , A . 31/81

  30. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Tasks of Inverse Rough Surface Scattering Tasks: 1. Reconstruct the total field u or scattered field u s . Since the incident field u i = G ( · , z ) is known, these tasks are equivalent. 2. Reconstruct the scattering surface Γ or any surface which generates the data for the given incident field u i = G ( · , z ) . Remark. If we do this for sufficiently many incident waves simultaneously, we have uniqueness of the reconstruction. 32/81

  31. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Tasks of Inverse Rough Surface Scattering Tasks: 1. Reconstruct the total field u or scattered field u s . Since the incident field u i = G ( · , z ) is known, these tasks are equivalent. 2. Reconstruct the scattering surface Γ or any surface which generates the data for the given incident field u i = G ( · , z ) . Remark. If we do this for sufficiently many incident waves simultaneously, we have uniqueness of the reconstruction. 32/81

  32. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Method of Kirsch-Kress or Potential Method I The idea of the Kirsch-Kress method is to calculate an approximation of the scattered field by a single-layer approach S ϕ defined on a subset of an auxiliary surface Γ t . It is carried out by minimization of the Tikhonov functional J α, B = � SP B ϕ − v � 2 + α � P B ϕ � 2 . (6) L 2 (Γ h , A ) � �� � � �� � = regularization = measured data The unknown scattering surface Γ by the minimization of the approximated total field � u � L 2 (Γ) = � G ( · , z ) + SP B ϕ � L 2 (Γ) (7) � �� � = field on surface over some suitable set U of admissible surfaces Γ . 33/81

  33. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Method of Kirsch-Kress or Potential Method I The idea of the Kirsch-Kress method is to calculate an approximation of the scattered field by a single-layer approach S ϕ defined on a subset of an auxiliary surface Γ t . It is carried out by minimization of the Tikhonov functional J α, B = � SP B ϕ − v � 2 + α � P B ϕ � 2 . (6) L 2 (Γ h , A ) � �� � � �� � = regularization = measured data The unknown scattering surface Γ by the minimization of the approximated total field � u � L 2 (Γ) = � G ( · , z ) + SP B ϕ � L 2 (Γ) (7) � �� � = field on surface over some suitable set U of admissible surfaces Γ . 33/81

  34. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Method of Kirsch-Kress or Potential Method I The idea of the Kirsch-Kress method is to calculate an approximation of the scattered field by a single-layer approach S ϕ defined on a subset of an auxiliary surface Γ t . It is carried out by minimization of the Tikhonov functional J α, B = � SP B ϕ − v � 2 + α � P B ϕ � 2 . (6) L 2 (Γ h , A ) � �� � � �� � = regularization = measured data The unknown scattering surface Γ by the minimization of the approximated total field � u � L 2 (Γ) = � G ( · , z ) + SP B ϕ � L 2 (Γ) (7) � �� � = field on surface over some suitable set U of admissible surfaces Γ . 33/81

  35. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Method of Kirsch-Kress or Potential Method II Burkard, C. and Potthast, R.: A multi-section approach for rough surface reconstruction via the Kirsch-Kress scheme, Inverse Problems Vol. 26, No. 4, 2010. Heinemeyer, E., Linder, M. and Potthast, R.: Convergence and numerics of a multi-section method for scattering by three-dimensional rough surfaces, SIAM J. Numer. Anal. 46, 1780 (2008), 1780-1798. Chandler-Wilde, S., Heinemeyer, E. and Potthast, R.: Acoustic Scattering by Mildly Rough Unbounded Surfaces in Three Dimensions. SIAM J. Appl. Math Vol. 66, Issue 3 (2006), 1001-1026. Chandler-Wilde, S.N., Heinemeyer, E. and Potthast, R. A well-posed integral equation formulation for three-dimensional rough surface scattering Proceedings of the Royal Society a-Mathematical Physical and Engineering Sciences, 462 (2006), 3683-3705 34/81

  36. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Numerical Examples I 35/81

  37. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Numerical Examples I 36/81

  38. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Numerical Examples II 37/81

  39. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Numerical Examples II 38/81

  40. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Numerical Examples III 39/81

  41. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Numerical Examples IV 40/81

  42. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Outline Introduction Orthogonality Sampling Time-Domain Probe Method Field & Shape Reconstruction Time-Domain Probe Data Assimilation 3dVar 4dVar Dynamic Inverse Scattering 41/81

  43. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Time-Domain Probe Method: the Idea ◮ Incident time-dependent pulse coming from some point z ∈ D . ◮ When the pulse reaches some point of the scattering surface, a scattered field starts to evolve. ◮ By reconstructing the time-dependent field we can probe the region and determine those points where a scattered field evolves right at the moment when the incident pulse first reaches a particular point. ◮ Use the potential method of Kirsch-Kress or the point-source method of the author to reconstruct U s ( x , t ) for x ∈ Ω , t ∈ R . 42/81

  44. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Idea 43/81

  45. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Idea 44/81

  46. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Idea 45/81

  47. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, References Chandler-Wilde, S. and Lines, C.: Inverse Scattering by Rough Surfaces in the Time Domain, Waves 2003 Chandler-Wilde, S. and Lines, C.: A Time Domain Point Source Method for Inverse Scattering by Rough Surfaces, Computing, Volume 75, Numbers 2-3, (2005), 157-180 Luke, D.R. and Potthast, R.: The point source method for inverse scattering in the time domain. Math. Meth. Appl. Sci. Volume 29, Issue 13 (2006) 1501-1521 Burkard, C. and Potthast, R.: A Time-Domain Probe Method for Three-dimensional Rough Surface Reconstructions, Inverse Problems and Imaging, Volume 3, No. 2 (2009) 46/81

  48. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Characteristics We need to study the range of influence of a time-dependent acoustic field ... 47/81

  49. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Characteristics We need to study the range of influence of a time-dependent acoustic field ... 47/81

  50. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Characteristics We need to study the range of influence of a time-dependent acoustic field ... 47/81

  51. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence I The basic idea behind a convergence proof: 48/81

  52. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence I The basic idea behind a convergence proof: 48/81

  53. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence II For a point x ∈ Ω we define the first hitting time with respect to the incident field U i by t ≥ 0 | U i ( x , t ) | > ρ, T ( x ) := inf (8) where we usually employ ρ = 0 or small ρ > 0 in dependence of the particular choice of the incident field. Lemma Let U i be an incident spherical pulse. For every point x ∈ Ω we have that U s ( x , t ) = 0 for all t < T ( x ) . (9) 49/81

  54. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence II For a point x ∈ Ω we define the first hitting time with respect to the incident field U i by t ≥ 0 | U i ( x , t ) | > ρ, T ( x ) := inf (8) where we usually employ ρ = 0 or small ρ > 0 in dependence of the particular choice of the incident field. Lemma Let U i be an incident spherical pulse. For every point x ∈ Ω we have that U s ( x , t ) = 0 for all t < T ( x ) . (9) 49/81

  55. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence II For a point x ∈ Ω we define the first hitting time with respect to the incident field U i by t ≥ 0 | U i ( x , t ) | > ρ, T ( x ) := inf (8) where we usually employ ρ = 0 or small ρ > 0 in dependence of the particular choice of the incident field. Lemma Let U i be an incident spherical pulse. For every point x ∈ Ω we have that U s ( x , t ) = 0 for all t < T ( x ) . (9) 49/81

  56. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence II For a point x ∈ Ω we define the first hitting time with respect to the incident field U i by t ≥ 0 | U i ( x , t ) | > ρ, T ( x ) := inf (8) where we usually employ ρ = 0 or small ρ > 0 in dependence of the particular choice of the incident field. Lemma Let U i be an incident spherical pulse. For every point x ∈ Ω we have that U s ( x , t ) = 0 for all t < T ( x ) . (9) 49/81

  57. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence III Since U s ( x , t ) = − U i ( x , t ) according to the Dirichlet boundary condition, we know that | U s ( x , t ) | > ρ ≥ 0 , T ( x ) < t < T ( x ) + ǫ, for x ∈ ∂ Ω , | U s ( x , t ) | = 0 , T ( x ) < t < T ( x ) + ǫ, for x �∈ ∂ Ω for ǫ > 0 sufficiently small. This can be used to detect the boundary ∂ Ω . Theorem (Convergence of Time-Domain Probe Method) The continous version of the Time-Domain Probe Method provides a complete reconstruction of the surface Γ above the rectangle Q. 50/81

  58. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence III Since U s ( x , t ) = − U i ( x , t ) according to the Dirichlet boundary condition, we know that | U s ( x , t ) | > ρ ≥ 0 , T ( x ) < t < T ( x ) + ǫ, for x ∈ ∂ Ω , | U s ( x , t ) | = 0 , T ( x ) < t < T ( x ) + ǫ, for x �∈ ∂ Ω for ǫ > 0 sufficiently small. This can be used to detect the boundary ∂ Ω . Theorem (Convergence of Time-Domain Probe Method) The continous version of the Time-Domain Probe Method provides a complete reconstruction of the surface Γ above the rectangle Q. 50/81

  59. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Convergence III Since U s ( x , t ) = − U i ( x , t ) according to the Dirichlet boundary condition, we know that | U s ( x , t ) | > ρ ≥ 0 , T ( x ) < t < T ( x ) + ǫ, for x ∈ ∂ Ω , | U s ( x , t ) | = 0 , T ( x ) < t < T ( x ) + ǫ, for x �∈ ∂ Ω for ǫ > 0 sufficiently small. This can be used to detect the boundary ∂ Ω . Theorem (Convergence of Time-Domain Probe Method) The continous version of the Time-Domain Probe Method provides a complete reconstruction of the surface Γ above the rectangle Q. 50/81

  60. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Reconstruction 1 51/81

  61. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Reconstruction 2 52/81

  62. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Reconstruction 3 53/81

  63. Introduction Orthogonality Sampling Field & Shape Reconstruction Time-Domain Probe Method Time-Domain Probe Data Assimilation Inverse Rough Surface Scattering Time-domain probe method, Reconstruction 4 54/81

  64. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Outline Introduction Orthogonality Sampling Time-Domain Probe Method Field & Shape Reconstruction Time-Domain Probe Data Assimilation 3dVar 4dVar Dynamic Inverse Scattering 55/81

  65. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Data Assimilation Task ◮ Dynamical system M : ϕ k �→ ϕ k + 1 , states at time t k , k = 1 , 2 , 3 , ... ◮ Measurement Operator H : ϕ k �→ f k with measurements f k at time t k ◮ Reconstruct ϕ k using the knowledge of M and of f k at t k ! Basic Notation: ◮ We call the reconstruction at time t k the analysis ϕ ( a ) . k ◮ The propagated state ϕ ( b ) k + 1 := M ( ϕ ( a ) is called background. k 56/81

  66. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Data Assimilation Task ◮ Dynamical system M : ϕ k �→ ϕ k + 1 , states at time t k , k = 1 , 2 , 3 , ... ◮ ◮ Measurement Operator H : ϕ k �→ f k with measurements f k at time t k ◮ Reconstruct ϕ k using the knowledge of M and of f k at t k ! Basic Notation: ◮ We call the reconstruction at time t k the analysis ϕ ( a ) . k ◮ The propagated state ϕ ( b ) k + 1 := M ( ϕ ( a ) is called background. k 56/81

  67. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Data Assimilation Task ◮ Dynamical system M : ϕ k �→ ϕ k + 1 , states at time t k , k = 1 , 2 , 3 , ... ◮ ◮ Measurement Operator H : ϕ k �→ f k with measurements f k at time t k ◮ Reconstruct ϕ k using the knowledge of M and of f k at t k ! Basic Notation: ◮ We call the reconstruction at time t k the analysis ϕ ( a ) . k ◮ The propagated state ϕ ( b ) k + 1 := M ( ϕ ( a ) is called background. k 56/81

  68. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Data Assimilation Task ◮ Dynamical system M : ϕ k �→ ϕ k + 1 , states at time t k , k = 1 , 2 , 3 , ... ◮ ◮ Measurement Operator H : ϕ k �→ f k with measurements f k at time t k ◮ Reconstruct ϕ k using the knowledge of M and of f k at t k ! Basic Notation: ◮ We call the reconstruction at time t k the analysis ϕ ( a ) . k ◮ The propagated state ϕ ( b ) k + 1 := M ( ϕ ( a ) is called background. k 56/81

  69. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Data Assimilation Task ◮ Dynamical system M : ϕ k �→ ϕ k + 1 , states at time t k , k = 1 , 2 , 3 , ... ◮ ◮ Measurement Operator H : ϕ k �→ f k with measurements f k at time t k ◮ Reconstruct ϕ k using the knowledge of M and of f k at t k ! Basic Notation: ◮ We call the reconstruction at time t k the analysis ϕ ( a ) . k ◮ The propagated state ϕ ( b ) k + 1 := M ( ϕ ( a ) is called background. k 56/81

  70. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Data Assimilation Task ◮ Dynamical system M : ϕ k �→ ϕ k + 1 , states at time t k , k = 1 , 2 , 3 , ... ◮ ◮ Measurement Operator H : ϕ k �→ f k with measurements f k at time t k ◮ Reconstruct ϕ k using the knowledge of M and of f k at t k ! Basic Notation: ◮ We call the reconstruction at time t k the analysis ϕ ( a ) . k ◮ The propagated state ϕ ( b ) k + 1 := M ( ϕ ( a ) is called background. k 56/81

  71. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Data Assimilation Task ◮ Dynamical system M : ϕ k �→ ϕ k + 1 , states at time t k , k = 1 , 2 , 3 , ... ◮ ◮ Measurement Operator H : ϕ k �→ f k with measurements f k at time t k ◮ Reconstruct ϕ k using the knowledge of M and of f k at t k ! Basic Notation: ◮ We call the reconstruction at time t k the analysis ϕ ( a ) . k ◮ The propagated state ϕ ( b ) k + 1 := M ( ϕ ( a ) is called background. k 56/81

  72. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Outline Introduction Orthogonality Sampling Time-Domain Probe Method Field & Shape Reconstruction Time-Domain Probe Data Assimilation 3dVar 4dVar Dynamic Inverse Scattering 57/81

  73. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Basic Approach Let H be the data operator mapping the state ϕ onto the measurements f . Then we need to find ϕ by solving the equation H ϕ = f (10) When we have some initial guess ϕ ( b ) , we transform the equation into H ( ϕ − ϕ ( b ) ) = f − H ϕ ( b ) (11) with the incremental form ϕ = ϕ ( b ) + H − 1 ( f − H ϕ ( b ) ) . (12) 58/81

  74. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Basic Approach Let H be the data operator mapping the state ϕ onto the measurements f . Then we need to find ϕ by solving the equation H ϕ = f (10) When we have some initial guess ϕ ( b ) , we transform the equation into H ( ϕ − ϕ ( b ) ) = f − H ϕ ( b ) (11) with the incremental form ϕ = ϕ ( b ) + H − 1 ( f − H ϕ ( b ) ) . (12) 58/81

  75. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Basic Approach Let H be the data operator mapping the state ϕ onto the measurements f . Then we need to find ϕ by solving the equation H ϕ = f (10) When we have some initial guess ϕ ( b ) , we transform the equation into H ( ϕ − ϕ ( b ) ) = f − H ϕ ( b ) (11) with the incremental form ϕ = ϕ ( b ) + H − 1 ( f − H ϕ ( b ) ) . (12) 58/81

  76. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Regularization 1 Consider an equation H ϕ = f (13) where H − 1 is unstable or unbounded. H ϕ = f H ∗ H ϕ = H ∗ f ⇒ ( α I + H ∗ H ) ϕ = H ∗ f . ⇒ (14) where ( α I + H ∗ H ) has a stable inverse! Tikhonov Regularization : Replace H − 1 by the stable version R α := ( α I + H ∗ H ) − 1 H ∗ (15) with regularization parameter α > 0. 59/81

  77. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Regularization 1 Consider an equation H ϕ = f (13) where H − 1 is unstable or unbounded. H ϕ = f H ∗ H ϕ = H ∗ f ⇒ ( α I + H ∗ H ) ϕ = H ∗ f . ⇒ (14) where ( α I + H ∗ H ) has a stable inverse! Tikhonov Regularization : Replace H − 1 by the stable version R α := ( α I + H ∗ H ) − 1 H ∗ (15) with regularization parameter α > 0. 59/81

  78. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Regularization 1 Consider an equation H ϕ = f (13) where H − 1 is unstable or unbounded. H ϕ = f H ∗ H ϕ = H ∗ f ⇒ ( α I + H ∗ H ) ϕ = H ∗ f . ⇒ (14) where ( α I + H ∗ H ) has a stable inverse! Tikhonov Regularization : Replace H − 1 by the stable version R α := ( α I + H ∗ H ) − 1 H ∗ (15) with regularization parameter α > 0. 59/81

  79. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Regularization 2: Least Squares Tikhonov regularization is equivalent to the minimization of � α � ϕ � 2 + � H ϕ − f � 2 � J ( ϕ ) := (16) The normal equations are obtained from first order optimality conditions ! ∇ ϕ J = 0 . (17) Differentiation leads to 0 = 2 αϕ + 2 H ∗ ( H ϕ − f ) 0 = ( α I + H ∗ H ) ϕ − H ∗ f , ⇒ (18) which is our well-known Tikhonov equation ( α I + H ∗ H ) ϕ = H ∗ f . 60/81

  80. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Regularization 2: Least Squares Tikhonov regularization is equivalent to the minimization of � α � ϕ � 2 + � H ϕ − f � 2 � J ( ϕ ) := (16) The normal equations are obtained from first order optimality conditions ! ∇ ϕ J = 0 . (17) Differentiation leads to 0 = 2 αϕ + 2 H ∗ ( H ϕ − f ) 0 = ( α I + H ∗ H ) ϕ − H ∗ f , ⇒ (18) which is our well-known Tikhonov equation ( α I + H ∗ H ) ϕ = H ∗ f . 60/81

  81. Introduction 3dVar Orthogonality Sampling 4dVar Time-Domain Probe Method Dynamic Inverse Scattering Data Assimilation Regularization 2: Least Squares Tikhonov regularization is equivalent to the minimization of � α � ϕ � 2 + � H ϕ − f � 2 � J ( ϕ ) := (16) The normal equations are obtained from first order optimality conditions ! ∇ ϕ J = 0 . (17) Differentiation leads to 0 = 2 αϕ + 2 H ∗ ( H ϕ − f ) 0 = ( α I + H ∗ H ) ϕ − H ∗ f , ⇒ (18) which is our well-known Tikhonov equation ( α I + H ∗ H ) ϕ = H ∗ f . 60/81

Download Presentation
Download Policy: The content available on the website is offered to you 'AS IS' for your personal information and use only. It cannot be commercialized, licensed, or distributed on other websites without prior consent from the author. To download a presentation, simply click this link. If you encounter any difficulties during the download process, it's possible that the publisher has removed the file from their server.

Recommend


More recommend