A non-linear truncated SVD variance and resolution analysis of 2D magnetotelluric models
2006 (English)Conference paper (Other (popular science, discussion, etc.))
The resolution and variance properties of 2D models of electrical resistivity derived from magnetotelluric measurements are analysed with a truncated singular value decomposition (TSVD) scheme on a local subspace partly taking into account the non-linearity of the inverse problem.
The TSVD resolution and variance analysis is performed on a local subspace pertaining to one single cell of interest at a time. The trade-off between model variance and model resolution is used to determine a level of truncation by fixing a variance threshold.
Non-linear semi-axes describe the non-linear confidence surface in the directions of the model eigenvectors and replace the inverse singular values in the computation of model variances. The model variance of the cell considered is estimated from the sum of squares of the non-linear semi-axes up to the given variance threshold. This - in turn - gives the truncation level of the TSVD and the row of the model resolution matrix belonging to the considered cell can be computed from the model eigenvectors of the TSVD.
The validity of our non-linear model variance and resolution estimates is tested with a most-squares inversion which gives an independent and improved estimate of model variability.
A field example from the Skediga area (Sweden) shows that the electrical resistivity distribution of sand and gravel formations which are only laterally bounded by conductive clay lenses is relatively well resolved whereas there is little resolution for the transition between the sand and gravel layer and the basement under a clay cover.
Place, publisher, year, edition, pages
2006. S8-E4- p.
IdentifiersURN: urn:nbn:se:uu:diva-19479OAI: oai:DiVA.org:uu-19479DiVA: diva2:47251
18th International Workshop on Electromagnetic Induction in the Earth, El Vendrell - 2006, Spain