TESTING A SENSOR TO PRODUCE A FILTER FOR NOISE ATTENUATION

• US 20090103394A1
• Filed: 07/08/2008
• Published: 04/23/2009
• Est. Priority Date: 10/19/2007
• Status: Active Grant

• Current Assignee: WesternGeco LLC
• Original Assignee: WesternGeco LLC
• Inventors: RONNOW, DANIEL
• Granted Patent: US 8,077,541 B2
• Time in Patent Office: Days
• US Class Current: 367/13
• CPC Class Codes: G01V 13/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00

Abstract

To test a seismic sensor, an output of the seismic sensor in response to a test signal applied by a signal generator is measured. According to a first function that corresponds to a reference response of the seismic sensor and according to a second function that corresponds to a signal containing noise in an environment of the seismic sensor, a filter is created to perform attenuation of the noise. The filter is applied to attenuate noise during testing of the seismic sensor.

Claims

1. A method of testing a seismic sensor, comprising:

measuring an output of the seismic sensor in response to a test signal applied by a signal generator;

according to a first function that corresponds to a reference response of the seismic sensor and according to a second function that corresponds to a signal containing noise in an environment of the seismic sensor, creating a filter to perform attenuation of the noise; and

applying the filter to attenuate the noise in the output of the seismic sensor during testing of the seismic sensor.

2. The method of claim 1, wherein creating the filter comprises creating a Wiener filter.

3. The method of claim 1, wherein creating the filter comprises creating a moving average filter.

4. The method of claim 1, wherein creating the filter comprises creating the filter that reduces noise while keeping a response of the seismic sensor unchanged.

5. The method of claim 1, wherein the test signal is a step input, and measuring the output of the seismic sensor comprises measuring a step response of the seismic sensor.

6. The method of claim 1, wherein the first function comprises a first autocorrelation function corresponding to the reference response, and wherein the second function comprises a second autocorrelation function corresponding to a noise signal representing the noise.

7. The method of claim 6, further comprising determining the second autocorrelation function to determine properties of the noise prior to applying the test signal to the seismic sensor.

8. The method of claim 7, further comprising:

after creating the filter, checking the noise in the environment of the seismic sensor and determining whether properties of the noise have changed by greater than one or more thresholds from properties of the noise prior to applying the test signal.

9. The method of claim 8, further comprising:

in response to determining that the noise parameters have changed by greater than one or more thresholds, repeating the filter creating task.

10. The method of claim 1, wherein the first function comprises a reference transfer function of the seismic sensor in an environment of reduced noise, and the second function comprises a second transfer function of the seismic sensor with noise present.

11. The method of claim 10, further comprising computing a difference transfer function that is based on a difference between the reference and second transfer functions,

wherein applying the filter to attenuate noise during testing of the seismic sensor comprises applying a moving average filter on the difference transfer function.

12. The method of claim 11, wherein applying the moving average filter on the difference transfer function comprises:

convolving the moving average filter with the difference transfer function to produce an output vector;

reversing an order of the output vector to produce a reversed output vector; and

convolving the moving average filter with the reversed output vector to produce a filtered output vector that represents the output of the seismic sensor in response to the test signal with noise attenuated.

13. The method of claim 11, wherein applying the filter to attenuate the noise during testing of the seismic sensor further comprises applying a moving average filter on a phase difference of the first and second transfer functions.

14. The method of claim 1, wherein applying the filter to attenuate the noise in the output comprises applying the filter on a difference between a magnitude of a step response representing the output and a magnitude representing the reference response, and applying the filter on a difference between a phase of the step response and a phase of the reference response.

15. The method of claim 1, further comprising obtaining at least one parameter based on the output with noise attenuated, the at least one parameter selected from among sensitivity, natural frequency, and damping of the seismic sensor.

16. An article comprising at least one computer-readable storage medium containing instructions that when executed cause a computer to:

measure properties of noise in an environment of a seismic sensor;

measure an output of the seismic sensor in response to a test signal applied by a signal generator;

according to the measured properties of the noise and properties of a reference response of the seismic sensor in an absence of noise, create a filter to perform attenuation of the noise; and

apply the filter to attenuate noise in the output of the seismic sensor during testing of the seismic sensor.

17. The article of claim 16, wherein measuring the properties of the noise comprises computing an autocorrelation function of the noise prior to applying the test signal to the seismic sensor.

18. The article of claim 17, wherein the properties of the reference response of the seismic sensor is based on a second autocorrelation function of the reference response.

19. The article of claim 16, wherein creating the filter comprises creating a Wiener filter.

20. The article of claim 16, wherein measuring the properties of the noise is performed prior to applying the test signal to the seismic sensor, and wherein the instructions when executed cause the computer to further:

measure properties of the noise in the environment of the seismic sensor after creating the filter;

compare the measured properties of the noise prior to applying the test signal to the measured properties after creating the filter;

determine whether the measured properties of the noise prior to applying the test signal differ by greater than one or more predetermined thresholds from the measured properties after creating the filter; and

in response to determining that the measured properties of the noise prior to applying the test signal to the seismic sensor differ by greater than the one or more predetermined thresholds from the measured properties of the noise after creating the filter, repeat creation of the filter.

21. A computer comprising:

a network interface to receive a measured output of a seismic sensor in response to a test signal applied by a signal generator; and

a processor to;

according to a first function that corresponds to a reference response of the seismic sensor and according to a second function that corresponds to a signal containing noise in an environment of the seismic sensor, create a filter to perform attenuation of the noise; and

apply the filter to attenuate noise in the output of the seismic sensor during testing of the seismic sensor.

22. The computer of claim 21, wherein the filter comprises a Wiener filter.

23. The computer of claim 21, wherein the filter comprises a moving average filter.