Development of an inversion method for low velocity medium

The main problem with the inversion of a low velocity medium is the application of an appropriate ray tracing method after choosing a suitable model parameterization. block parameterization is not suitable,because it is not capable of representing the velocity model well. a large amount of blocks with a small grid size are needed to express the model well,but in that case,a ray coverage problem will be encountered. a knot-point parameterization model is better suited than a block model,because it can express the velocity model well,while the number of variables is much smaller. ray calculation using the pseudo-bending method is not appropriate for the velocity model because of an instability problem at high velocity gradients. the crucial problem of this method involves the initial ray-path that is optimized in order to obtain the true ray,but does not satisfy the fermat principle. these problems can be solved by applying the eikonal-solver method,because this can handle high-velocity gradients and does not need an initial ray path. using a suitable model parameterization and appropriate ray tracing method,the inversion can obtain good results that fit the desired output. applying a block model and the pseudo-bending method will not produce the desired output. © 2013 published by itb journal publisher.