What Does ‘Simultaneous’ Mean?
A simultaneous problem uses one or more sets of data to determine more than one parameter in a system.
When seismic data is used in an inverse problem, as with FWI and LSM, the parameters that control the forward modeling’s ability to recreate the acquired data are critical. The most important, or first-order parameter that needs resolving is the velocity model. Density is also important, particularly when reflection data is used. In PGS FWI the wave-equation reformulation uses vector-reflectivity as a proxy for density, so when using the full wavefield, reflectivity is also an important parameter.
Other terms have a much lower impact on modeling, so in PGS Ultima, the simultaneous parameters we invert for are velocity and reflectivity. One helps optimize the other; as the velocity model evolves, the reflectivity is improved, which in turn assists the model construction.