IMPLEMENTING MEASURED SOURCE SIGNATURES IN A COARSE-GRID, FINITE-DIFFERENCE MODELING SCHEME

In a marine seismic air-gun array, each gun location does not necessar ily coincide with a node in a finite-difference grid. Especially for c oarse-grid, finite-difference modeling, this problem must be handled w ith care since there might be up to three or four air guns between adj acent grid points. The real sources are represented by fictitious mono pole- and dipole source functions located at grid nodes. The effective sources are estimated from the extrapolated pressure field at a horiz ontal surface located below the sources. We find that an array consist ing of eight guns separated by a distance of 3 m and located at 7.5 m depth can be approximated by six monopole- and dipole source functions distributed on a finite-difference grid with 10 m spatial sampling, T he residual error energy norm between the actual wavefield and the cor responding finite-difference wavefield observed on a fictitious stream er placed at 95 m depth is less than 0.5 percent.