The first uses IRLS to effectively change the norm of the problem to permit a ``spiky'' or ``sparse'' model residual, which leads to a ``blocky'' velocity model. The second uses an isotropic edge detector, the gradient magnitude, in a nonlinear scheme to compute a measure of the edges of the model. This edge measure is then used as a model residual weight.

Both methods give the expected results when applied in a 2-D real data set acquired in the Gulf of Mexico. Even though, the gradient magnitude method shows sharp objects with more geological appeal than the ``blocky'' method.

10/14/2003