3D Principles and Acquisition
Threedimensional seismic surveying makes use of very dense data collected in a way that the spatial resolution becomes similar along track as well as across track. This allows to image spatially complex geologic structures, but it requires much more time for acquisition and much more efforts for data processing and navigation.
While this is an established method for oil and gas exploration since 30 years, it is rarely used in academia. And the industrial technology is much more advanced, since many streamers (10 or more) of several (up to 12) km length are towed in parallel.
For high-resolution seismic work in academia, this has not been possible due to limited funds and limited performance of acquisition technology (cable bandwidth etc.) in general.
In the 2.5D approach, only a single streamer with a single source is used. The reach a high data densitly, a narrow spaing lines needs to be planned, for the MTU surveys it was 25 meters. The survey grids are organized in loops with minimal curve duration - typical spacing was 400 meters or less.
The most extensive surveys were carried out in the Bengal Fan (6 day, 6 hours with 137 profiles) and in the Gulf of Pozzuoli (10 days and 197 profiles).
True 3D surveys require several streamers in parallel and also more than one source, to create as many parallel alinged reflection points as possible. Reflection lines are in the middle between a source and the streamer, and with n streamers, n different profiles are generated. With 2 sources, the number is doubled, if the reflection lines are not overlapping, but offset from each other.