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As an alternative to downward continuation and interpolation of the source
and receiver at the same time, we can also finish the prestack slant stack migration
with

**dum1
**

Figure 2 Computational flow chart of prestack slant stack
migration with two-pass PSPI.

**fig1
**

Figure 3 The impulse response of prestack slant stack migration with PSPI;
p=.00021 s/m with *v*_{1}(*z*)=1500+0.5*z* m/s, and *v*_{2}(*z*)=2500+0.5*z* m/s.

**fig2
**

Figure 4 The superposition of the impulse response of *v*=2000 m/s and *v*_{1}(*z*)=1500
m/s at *y*=0 m and of *v*_{2}(*z*)=2500 m/s with *y*=2560 m by PSPI.

PSPI by splitting into two pass. Its implementation is illustrated in the steps shown
in Figure 2.
The *U*_{1S} and *U*_{2S} are the wavefields extrapolated by *v*_{1} and *v*_{2}
separately for the source. After the interpolation, we get *U*_{S}. Then wavefields are downward continued separately for the receiver by *v*_{1} and *v*_{2}.
By interpolating the wavefield between *U*_{1(S+G)} and *U*_{2(S+G)}, we
can complete
the whole wave extrapolation.

** Next:** DISCUSSION OF RESULTS
** Up:** IMPLEMENTATION FOR LATERAL VELOCITY
** Previous:** One-pass PSPI
Stanford Exploration Project

11/17/1997