Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Land-reflection type
Patent
1983-12-16
1989-01-17
Tarcza, Thomas H.
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Land-reflection type
367 42, G01V 136
Patent
active
047992018
ABSTRACT:
In seismic profiling systems utilizing sweeps of signals which change in repetition frequency during the transmission interval, interference results from a spurious correlation against an interfering sweep, usually produced by the first break reflection of a simultaneously transmitted sweep which is in the opposite sense for 3-D surveying or from another source. The first break interfering sweep repeats while correlating with time slipped replicas in surveying for deeper and deeper reflecting interfaces and appears as correlation sidelobe interference which has a significant contribution to the correlator output only when the interfering sweep and the replica are in a condition where their frequencies are identical or nearly so. This condition is known as stationary phase. The interference is reduced without adversely affecting the correlation integral of the sweep reflected from the reflection interface of interest by muting either input to the correlator for a short period of time surrounding the points of stationary phase between the interfering sweep from the first break and the replica or by selectively pre-whitening the received sweep signal prior to correlation. This action effectively removes the first break correlation noise without significantly reducing the correlation of the desired weak reflection with the replica and may also be used to remove harmonic ghost interference. 3-D surveys can therefore be conducted with sources of the upsweep and downsweep operating simultaneously, and surveys can be conducted even in the presence of interference from another source, as on an interfering surveying ship.
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Hydroacoustics Inc.
Lobo Ian J.
Lukacher Martin
Tarcza Thomas H.
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