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![]() | Least-squares imaging and deconvolution using the hybrid norm conjugate-direction solver | ![]() |
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One disadvantage of this data-space inversion scheme is that it can not be computed in a target-oriented way, since theoretically even a local perturbation in the model space will affect the entire data space and vice versa. To overcome this difficulty, Valenciano (2006) transformed (1) to a model space inversion based on (2):
Valenciano (2008) and Tang (2008) showed that unlike L, matrix H is usually very sparse (i.e., most of the non-zero elements are centered around the diagonal); thus despite the huge size of H, it is feasible to store an approximation of H matrix by keeping only a few off-diagonal elements without losing much accuracy.
If we write
, and add a model
regularization term (since most likely H has a null space). Then the inversion formula is
in which we applied the hybrid norm to the regularization term.
Tang (2009) provided a way to efficiently compute the Hessian matrix using the phase-encoding technique, and this Hessian matrix is computed only once and stored for all iterations.
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![]() | Least-squares imaging and deconvolution using the hybrid norm conjugate-direction solver | ![]() |
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