Using Ghost Reflections Rather than Removing Them

Abstract

In marine acquisition both a direct wavefield and a ghost wavefield are produced as well as recorded. Hence, the seismic data can be considered to be a natural blend of four wavefields related to the real sources, ghost sources, real detectors and ghost detectors respectively. We consider deghosting to be deblending ('echo-deblending'), leading to a non-causal, full-wavefield algorithm, characterized by utilizing the ghost. Therefore, echo-deblending is different from prediction-error solutions that aim at removing the ghost. Echo-deblending is independent of the subsurface complexity; only what happens at and near the surface is relevant. Depending on the sea state, the reflection coefficient is frequency dependent. Moreover, the water velocity varies due to variations in temperature, salinity and pressure. We propose to measure such parameters and/or estimate them from the data. The output of our method consists of four ghost-free records: one due to real sources at the actual location below the water level (+zs), one due to ghost source at the mirrored location above the water level (-zs), both being recorded by real detectors at (+zd) and by ghost detectors at (-zd). Optionally, these four records are transformed to one record at a common source-receiver datum (z0).