GB1375733A - - Google Patents

Abstract

1375733 Seismic signal processing UNITED GEOPHYSICAL CORP 9 Nov 1971 [9 Nov 1970] 52033/71 Heading H4D Digital representations of the earth's subsurface structure, which have been obtained by processing seismic traces and stored in a computer memory, are converted to a digital representation of a synthetic hologram which may be used to present a three-dimensional replica of the structure. In the embodiment described, traces are first obtained and processed generally as in Specification 1,359,719 (see Division H4) to accumulate a migrated digital "image" of subsurface points P in "subsurface" memory cells of the computer. Cells of a "hologram memory unit" are then assigned on a one-to-one basis with notional points N in a reference surface EL (plane or curved) in a known scale and geometrical relation with the subsurface. For each point P in the subsurface (associated with a respective cell of the subsurface memory) there is computed the amplitude distribution over surface EL for a wavefront from a hypothetical radiation source, at P, of wavelength # and of intensity corresponding to the accumulated trace amplitude in the subsurface memory cell associated with P, Each such distribution is in the form of a Fresnel pattern of rings. Measures of the amplitude values are stored in the appropriate cells of the hologram memory, where the measures for the various overlapping distributions add algebraically to form a digital synthetic hologram. This is converted by a plotter to an optical hologram transparency. The hologram image is reconstructed by directing laser light, of wavelength # through a lens system on to the trans parency, and viewed by placing a diffusing screen or volume of scattering material (e.g. smoke particles in air or particles dispersed in glass) in the image space. If # is in the ultraviolet range the scattering material may be fluorescent. To avoid ghost images or flare effects, broad-band (e.g. F.M.) seismic signals are used when obtaining the original seismic traces, the received seismic signals being correlated conventionally prior to the above digital processing.