| 1. |
- Björkberg, Jonas, et al.
(författare)
-
Three-dimensional subterranean target identification by use of optimization techniques
- 1991
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The identification of a subterranean metallic ore from scattering experiments, conducted on the surface of the ground or in a bore hole, is a classic geophysical problem. In general this problem is not well-posed. However, a priori information about the shape of the target provides enough regularization to make the problem numerically stable. The problem is solved by minimizing the mean-square error between an eleven parameter model, based on the null field approach, and the data. The optimization is done with a Newton technique in which a singular value decomposition of the model Jacobian is employed. The algorithm is very stable to noise and makes good reconstructions from feasible starting guesses, for realistically noise contaminated data.
|
|
| 2. |
- Karlsson, Anders, et al.
(författare)
-
Wave splitting and imbedding equations for a spherically symmetric dispersive medium
- 1991
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The direct problem of time dependent electromagnetic scattering in the dispersive sphere is solved by a wave splitting technique. The electric field is expanded in a series involving vector spherical harmonics, leading to a system of wave equations for each term. These systems are reduced to scalar wave equations for each term, which are solved via reflection operators. Some preliminary numerical results are presented.
|
|
| 3. |
|
|
| 4. |
- Kristensson, Gerhard, et al.
(författare)
-
Scattering of transient electromagnetic waves in reciprocal bi-isotropic media
- 1991
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper propagation of transient electromagnetic waves in a reciprocal bi-isotropic medium is presented. The constitutive relations are convolution integrals with two susceptibility kernels that model the medium. The propagation problem is solved by the introduction of a wave-splitting technique. This wave-splitting is used to solve the propagation problem using either an imbedding approach or a Green function technique. In particular, the scattering problem of an electromagnetic wave that impinges normally on a slab of finite or infinite extent is solved. The slab is assumed to be inhomogeneous with respect to depth. The scattering problem consists of finding the reflected and the transmitted fields and the generic quantities are the reflection and the transmission kernels of the medium. Explicit expressions for the rotation and the attenuation of the wave front is presented for the inhomogeneous slab. In the special case of a homogeneous infinite slab it is proved that the reflection kernel satisfies a non-linear Volterra equation of the second kind, very suitable for numerical calculations. It is also proved that no cross polarization contribution appears for the homogeneous slab. Several numerical computations illustrate the analysis.
|
|
