GB1316479A - Seismic data records by frequency domain operation - Google Patents

Abstract

1316479 Processing seismic records MOBIL OIL CORP 23 Nov 1970 55550/70 Heading H4D Distortion, e.g. due to multiples, is removed from recorded seismic data by a frequencydomain filtering technique in which the filter functions are derived from the envelopes of the real and imaginary complex components of the seismic data in the frequency domain. In the Fig. 6 system an input seismic data trace S is Fourier-transformed at 31 into its frequency spectrum. The envelope of this spectrum is characteristic of the distortion and is used for deriving inverse filter functions for removing the distortion. To this end, the spectrum is separated into its real and imaginary components, the envelopes of these components are derived at 32, 33 (e.g. by convolution with operator functions), the modulus of the spectrum envelope is provided by squaring at 50, 51, adding at 52 and square-rooting at 53, the argument of the spectrum envelope is provided at 54, and the inverse filter functions are then derived at 40 from the modulus and argument. These filter functions are applied at 41 to the real and imaginary components, the resulting filtered data is band-limited at 42 to eliminate noise, and the band-limited signal is Fourier-transformed back to the time domain at 38 to provide a processed trace with the distortion removed. The above processing is applicable to seismograms obtained in marine or land surveying, and may be done by a digital computer (the input seismograms being recorded on magnetic tape). In a modification (Fig. 20, not shown) the modulus and argument of the Fourier spectrum signal produced at 31 are derived, the envelopes of the modulus and argument are obtained, the modulus is filtered with a function derived from the inverse of the modulus envelope, the argument is filtered by subtracting from it the argument envelope, the resulting filtered data is band-limited, and the band-limited data is then Fourier-transformed to the time-domain to provide the processed trace.