Removing noise from a seismic measurement

1. A method comprising:

spatially filtering a signal derived from a seismic acquisition, the filtering being associated with a filter having an order, wherein the filter has a pass band and a stop band and the order regulates a sharpness of a transition between the pass band and the stop band; and

varying the order of the filter with frequency.

2. The method of claim 1 , further comprising varying a transition bandwidth associated with the filtering based on the frequency being filtered.

3. The method of claim 1 , further comprising varying a stop band attenuation associated with the filtering based on the frequency being filtered.

4. The method of claim 1 , wherein the acts of spatially filtering the signal and varying the order of the filter comprise:

providing a time-space domain representation of the signal;

transforming the time-space domain representation into a frequency-space representation;

for each frequency, determining a filter order and determining a filter corresponding to the determined filter order; and

for each frequency using the determined filter to spatially filter the frequency-space representation of the signal.

5. The method of claim 3 , further comprising:

transforming the spatially filtered frequency space representation of the signal into a time domain representation of a spatially filtered signal.

6. The method of claim 1 , wherein the acts of spatially filtering the signal and varying the order of the filter comprise:

decomposing the signal in time to produce subbands, each subband being associated with at least different frequency ranges of the signal;

for each frequency range, determining a filter order and determining a filter corresponding to the determined filter order; and

for each frequency range, using the determined filter to spatially filter the signal.

7. The method of claim 1 , wherein the signal is associated with a given acquisition geometry and the acts of spatially filtering the signal and varying the order of the filter comprise:

providing a first signal indicative of measurements acquired in a seismic survey and being associated with a given acquisition geometry;

extrapolating the first signal to generate a second signal indicative of first measurements confined by the geometry and second measurements not confined by the geometry;

spatially filtering the second signal; and

after the spatial filtering of the second signal discarding a portion of the filtered second signal associated with the second measurements.

8. A method comprising:

decomposing a signal derived from a seismic acquisition into subbands, the subbands being associated with at least different frequency ranges;

reconstructing the signal from the subbands;

spatially filtering the subbands; and

for each subband, regulating a length of the filtering based on the frequency subband associated with the subband.

9. The method of claim 8 , wherein the act of decomposing is performed in successive stages, each stage decomposing an input subband to produce a first output subband used for the reconstruction and a second output subband used as the input subband for the next successive stage.

10. The method of claim 8 , wherein the act of reconstructing is performed in successive stages, each stage reconstructing an output subband based on a subband provided by the decomposing and an input subband provided as the output subband by another one of the stages.

11. A system comprising:

an interface to receive data indicative of a signal derived from a seismic acquisition; and

a processor to:

process the data to spatially filter the signal, the filtering being associated with a filter having an order; and

vary the order of the filter with frequency.

12. The system of claim 11 , wherein the processor is adapted to process the data to:

provide a time-space domain representation of the signal;

transform the time-space domain representation into a frequency-space representation;

for each frequency, determine a filter order and determine a filter corresponding to the determined filter order; and

for each frequency use the determined filter to spatially filter the frequency-space representation of the signal.

13. The system of claim 11 , wherein the processor is adapted to process the data to:

decompose the signal in time to produce subbands, each subband being associated with at least a different frequency range of the signal;

for each frequency range, determine a filter order and determine a filter corresponding to the determined filter order; and

for each frequency range, use the determined filter to spatially filter the signal.

14. A system comprising:

an interface to receive data indicative of a signal derived from a seismic acquisition; and

a processor to process the data to:

decompose the signal into subbands, the subbands being associated with at least different frequency ranges;

reconstruct the signal from the subbands;

spatially filter the subbands; and

for each subband, regulate a length of the filtering based on the frequency range associated with the subband.

15. The system of claim 14 , wherein the processor is further adapted to decompose the signal in successive stages, each stage decomposing an input subband to produce a first output subband used for the reconstruction and a second output subband used as the input subband for the next successive stage.

16. The system of claim 14 , wherein the processor is further adapted to process the data to perform the reconstruction in successive stages, each stage reconstructing an output subband based on a subband provided by the decomposition and an input subband provided as the output subband by another one of the stages.

17. The system of claim 14 , further comprising:

a spread of at least one streamer comprising seismic sensors to acquire data indicative of the signal derived from the seismic acquisition; and

a vessel to tow the spread.