As shown in Figure 2, the backward function is composed of three modules connected by FIFOs. Two of them labeled with R and S, similar to the forward streaming module, are designed to compute Receiver wavefield and reconstruct Source wavefield respectively. The module labeled with I (Imaging streaming module) realizes Equation (4), whic is used to compute the cross correlation between the two wavefields (Receiver and Source wavefields).
Figure 46 Figure 2. Backward streaming module