Abstract: A method and an apparatus for mass retrieval for an acoustic pulse generator are disclosed herein. In an impulse type seismic generating apparatus an air spring, mechanical spring, controlled pressurization of an air spring or other energy storage medium is employed to use potential energy to raise the impact mass to a resting position above an earth contacting baseplate as quickly as possible after the impact mass strikes the baseplate.

Abstract: A method and apparatus for deriving a three-dimensional seismic image from an irregular grid of two-dimensional seismic data is provided. The two-dimensional seismic data incldue a plurality of shot lines. For each of the shot lines, a two-dimensional migration is performed therealong (22) to create a plurality of migrated shot lines. For each of a plurality of three-dimensional image points, the following substeps are performed. A migrated trace (X) is selected from each of the migrated shot lines that is closest to the image point (I). A further migration (30) is performed on each selected migrated trace (28) with respect to the image point (I). A three-dimensional migrated image (30) comprising the image points is thereby obtained. The invention allows the use of historical, irregular two-dimensional grids of seismic data to be efficiently used for the three-dimensional imaging of subsurface features.

Abstract: A vertical gradient estimation technique is used to separate downgoing seismic ghost wavefields. The upgoing reflected seismic wavefield, allows the ghost wavefield to be attenuated to improve signal-to-noise ratio. The vertical gradient estimation technique is applicable to both marine seismic surveying using towed hydrophones, and to land seismic surveying using buried geophones. The technique allows the vertical signal gradient to be estimated from seismic signals measured at a single depth, and is based on a relationship between the measured seismic signals, and the source signature and the Green's function for the survey media. The technique involves determning (20) the source signature for the seismic source, and determining (21) the Green's function for the survey media. Seismic signals are then measured (22). These data are then processed to estimate (24) the vertical signal gradient as a function of source signature, Green's function and the measured seismic signals.