US 5,408,441 A · Method for seismic exploration in artic regions

Abstract

A method for obtaining seismic data in frigid regions without interference from flexural ice waves. In an exemplary embodiment, seismic data is produced by using an energy source to generate a seismic wave in a floating ice sheet. Seismic disturbances caused by the energy source are detected by one or more hydrophones and geophones, which produce hydrophone and geophone response signals, respectively. In a first embodiment, the hydrophone response signal is integrated. The integrated signal and/or the geophone response signal are scaled, and the two signals are then added. Alternatively, instead of integrating the hydrophone response signal, the geophone response signal may be differentiated prior to scaling and summing. A method is also disclosed for overcoming phase errors that might be introduced, for example, by the use of a transformer-coupled hydrophone. In another embodiment of the invention, a linear adaptive filter is applied to the hydrophone and geophone response signals to obtain an output signal having attenuated noise characteristics.

Claims58

Dependent claims

A method of obtaining seismic data in regions where ice covers water, comprising the steps of:

(a) using an energy source to generate a seismic wave in the ice;
(b) sensing seismic disturbances initiated by the energy source with a hydrophone and a geophone to produce a hydrophone signal and a geophone signal, respectively;
(c) integrating the hydrophone signal to produce an integrated hydrophone signal;
and
(d) providing a reduced noise signal by scaling and summing the integrated hydrophone signal and the geophone signal.

2 more elements

A method for obtaining seismic data without interference from flexural ice waves, comprising the steps of:

(a) using a vibrating energy source to generate a seismic wave in the ice;
(b) sensing seismic disturbances initiated by the vibrating energy source with a hydrophone and a geophone to produce an original hydrophone signal and an original geophone signal, respectively;
(c) establishing a window that includes the flexural ice wave, and modifying the original geophone signal by setting the original geophone signal to zero outside the window;
(d) performing a Fast Fourier Transform (FFT) operation on the modified geophone signal of step (d) to produce a geophone phase spectrum;
(e) modifying the original hydrophone trace by setting the original hydrophone trace to zero outside the window;
(f) performing an FFT operation on the modified hydrophone trace of step (e) to produce a first hydrophone phase spectrum;
(g) generating a first integrated hydrophone phase spectrum by subtracting 90.degree. from the first hydrophone phase spectrum;
(h) subtracting the first integrated hydrophone phase spectrum from the geophone phase spectrum to produce a spectral phase difference;
(i) smoothing the spectral phase difference and subtracting 180.degree. therefrom;
(j) performing an FFT operation on the original hydrophone signal to produce a hydrophone amplitude spectrum and a second hydrophone phase spectrum;
(k) integrating the hydrophone amplitude spectrum signal by dividing each spectral value of the hydrophone amplitude spectrum signal by 2.pi.f;
(1) generating a second integrated hydrophone phase spectrum by subtracting 90.degree. from the second hydrophone phase spectrum;
(m) generating a corrected hydrophone phase spectrum by subtracting the signal produced in step (i) from the second integrated hydrophone phase spectrum;
(n) performing an inverse FFT operation on the integrated hydrophone amplitude spectrum and the corrected hydrophone phase spectrum to create a time domain hydrophone signal;
and
(o) scaling and summing the original geophone signal and the time domain hydrophone signal.

13 more elements

A method for obtaining seismic data without interference from flexural ice waves, comprising the steps of:

(a) using a vibrating energy source to generate a seismic wave in the ice;
(b) sensing seismic disturbances initiated by the vibrating energy source with a hydrophone and a geophone to produce an original hydrophone signal and an original geophone signal, respectively;
(c) establishing a window that includes the flexural ice wave, and modifying the original hydrophone signal by setting the original hydrophone signal to zero outside the window;
(d) performing a Fast Fourier Transform (FFT) operation on the modified hydrophone signal of step (c) to produce a hydrophone phase spectrum;
(e) modifying the original geophone trace by setting the original geophone trace to zero outside the window;
(f) performing an FFT operation on the modified geophone trace of step (e) to produce a first geophone phase spectrum;
(g) generating a first differentiated geophone phase spectrum by adding 90.degree. to the first geophone phase spectrum;
(h) subtracting the first differentiated geophone phase spectrum from the hydrophone phase spectrum to produce a spectral phase difference;
(i) smoothing the spectral phase difference and subtracting 180.degree. therefrom;
(j) performing an FFT operation on the original geophone signal to produce a geophone amplitude spectrum and a second geophone phase spectrum;
(k) differentiating the geophone amplitude spectrum signal by multiplying each spectral value of the geophone amplitude spectrum signal by 2.pi.f;
(1) generating a second differentiated geophone phase spectrum by adding 90.degree. to the second geophone phase spectrum;
(m) generating a corrected geophone phase spectrum by subtracting the signal produced in step (i) from the second differentiated geophone phase spectrum;
(n) performing an inverse FFT operation on the differentiated geophone amplitude spectrum and the corrected geophone phase spectrum to create a time domain geophone signal;
and
(o) scaling and summing the original hydrophone signal and the time domain geophone signal.

13 more elements

Dependencies are inferred from the claim text.

Method for seismic exploration in artic regions

Life of this patent

Method for seismic exploration in artic regions

Life of this patent

Abstract

Claims58