3.5 km with a 10 m grid interval (Figure 3.1)(a). The synthetic data are generated with a marine streamer geometry, where 400 shots are excited with a 20 m offset interval at the depth of 10 m. Each shot is recorded with a 2 km long cable with 201 receivers and 10 m interval. The minimum source-receiver offset is zero meters and the maximum offset is 2 km. A Ricker wavelet with 20 Hz peak frequency is used as the source wavelet. The record length is 8 sec in time and a 2-8 constant density finite difference code is used for the RTM.
The source wavelet and its frequency spectrum are plotted in Figure 3.2 and the frequency range is chosen to be 0-50 Hz. According to the Nyquist theorem, the frequency sampling rate should be 0.125 Hz. Therefore, there are 400 samples in the frequency domain (excluding the 0-Hz component), which means 400 shots can be accommodated in one supergather. In this example, all 400 shot gathers can be uniquely encoded in a supergather.