Data parallel implementation of 3-D PSPI
Claudio Bagaini, Ernesto Bonomi, E. Pieroni · 1995
This paper essentially addresses the extrapolation step which is by far the most intense computational one. The choice of the imaging condition impacts the amplitude handling but not seriously the computational effort. If the migration velocity field has no lateral velocity variations the wavefield extrapolation can be carried out in the wavenumber-frequency domain by simple phase shift (Gazdag, 1978). In the presence of lateral velocity variations the 3D explicit wavefield extrapolation can be approximated in the space-frequency domain by application of 2-D spatially varying operators for all frequencies of the band-limited signal (Holberg, (1988); Blacquiere, (1989); Thorbecke and Berkhout, (1994)) or by PSPI (Gazdag and Sguazzero, 1984). Space-frequencies methods, recently also implemented with the computational efficient McClellan's approach (Hale, 1991), rely on the locally homogeneous hypothesis, assuming that only imperceptible lateral velocity variation occurs inside the pyramid whose base is defined by the filter spatial extension and whose height is the depth extrapolation step. The Phase Shift operator, which is the basic component of the PSPI, is a FIR filter in the space-frequency domain whose length is equal to the extension of the acquisition domain and whose coefficients around the center grid point are largely dominant. This is in agreement with the physical intuition: wavefield values far from the center grid point have a weak influence on the extrapolated wavefield. The computational advantage of the Phase Shift is that the extrapolation step is performed by a single multiplication in the wavenumber domain. The most important factor which has limited in these years the large use of PSPI is the choice of reference velocities. We propose a strategy for ...