Wavefield separation makes is possible to remove the ghost reflection from the sea surface, so there are no receiver-depth influences on 4D noise or repeatability.
Hydrophone-only surveys require the streamer tow depth to be the same on both the baseline and the monitor surveys. Tow depth restrictions are not required for multisensor streamers like GeoStreamer, because collocated multisensor receivers enable wavefield separation of the up- and downgoing wavefields. The upgoing wavefield is broadband (ghost free) and benefits from the typically deeper tow quieter recording environment.
The level of 4D noise for a given combined source and receiver position error can therefore be reduced by limiting the exposure of the acquisition system to dynamic sea-state and environmental noise during survey acquisition, thereby improving 4D signal detectability. Variability in the emitted source wavefield is removed using calibrated shot-by-shot source signatures.
Many ocean bottom seismic datasets are also multisensor, so the deployment of nodes in monitor surveys may improve illumination in areas affected by obstructions, improve velocity model generation (long offsets + full azimuth), and be processed through broadband 4D workflows compatible with 4D GeoStreamer processing.
Shot gathers corresponding to the particle velocity sensors (left), the pressure sensors (middle), and the up-going pressure wavefield computed with wavefield separation (right). Note the complete removal of short-wavelength time static shifts and amplitude distortions associated with local receiver depth and / or sea-surface height variations (right).
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