Seismic source and method for intermodulation mitigation

1. A method for calculating intermodulation noise generated with one or more land seismic sources, the method comprising:

receiving seismic data generated by actuating the one or more land seismic source with a first sweep and a second sweep;

calculating with a computing device a first earth response (h 1 est) corresponding to the first sweep;

calculating with the computing device a second earth response (h 2 est) corresponding to the second sweep; and

calculating the intermodulation noise (IMD) based on the first and second earth responses (h 1 est, h 2 est);

removing from the seismic data the intermodulation noise (IMD); and

generating an image of a surveyed subsurface based on the seismic data, from which the intermodulation noise (IMD) has been removed, for identifying geophysical structures,

wherein the second sweep is a time reverse sweep of the first sweep.

2. The method of claim 1 , wherein the first and second sweeps are pseudo-random sweeps.

3. The method of claim 1 , wherein the step of calculating the intermodulation noise comprises:

calculating a combined earth response based on a sum of the first and second earth responses.

4. The method of claim 1 , wherein the step of calculating the first earth response comprises:

calculating the first earth response (H 1 est) in a frequency domain based on a first measured force (F 1 ) produced by the first sweep and a second measured force (F 2 ) produced by the second sweep.

5. The method of claim 4 , wherein the step of calculating the second earth response comprises:

calculating the second earth response (H 2 est) in a frequency domain based on the first measured force (F 1 ) produced by the first sweep and the second measured force (F 2 ) produced by the second sweep.

6. The method of claim 5 , further comprising:

calculating first and second intermodulation noise artifacts (noise 1 , noise 2 ) based on the first earth response (h 1 est) and the second earth response (h 2 est); and

calculating a filter D based on the first earth response (h 1 est) and the second earth response (h 2 est).

7. The method of claim 6 , further comprising:

calculating first and second reverse noise terms (rnoise 1 , rnoise 2 ) based on the first and second intermodulation noise artifacts (noise 1 , noise 2 ) and the filter D.

8. The method of claim 7 , further comprising:

removing from the received seismic data first and second reverse noise terms (rnoise 1 , rnoise 2 ) to obtain noise mitigated seismic data.

9. The method of claim 8 , further comprising:

generating the image of the surveyed subsurface based on the noise mitigated seismic data.

10. A computing device for calculating intermodulation noise generated with one or more land seismic sources, the computing device comprising:

an interface for receiving seismic data generated by actuating the one or more land seismic source with a first sweep and a second sweep; and

a processor connected to the interface and configured to,

calculate a first earth response (h 1 est) corresponding to the first sweep,

calculate a second earth response (h 2 est) corresponding to the second sweep,

calculate the intermodulation noise (IMD) based on the first and second earth responses (h 1 est, h 2 est),

remove from the seismic data the intermodulation noise (IMD); and

generate an image of a surveyed subsurface based on the seismic data, from which the intermodulation noise (IMD) has been removed, for identifying geophysical structures,

wherein the second sweep is a time reverse sweep of the first sweep.

11. The computing device of claim 10 , wherein the first and second sweeps are pseudo-random sweeps.

12. The computing device of claim 10 , wherein the processor is further configured to:

calculate a combined earth response based on a sum of the first and second earth responses.

13. The computing device of claim 10 , wherein the processor is further configured to:

calculate the first earth response (H 1 est) in a frequency domain based on a first measured force (F 1 ) produced by the first sweep and a second measured force (F 2 ) produced by the second sweep.

14. The computing device of claim 13 , wherein the processor is further configured to:

calculate the second earth response (H 2 est) in a frequency domain based on the first measured force (F 1 ) produced by the first sweep and the second measured force (F 2 ) produced by the second sweep.

15. The computing device of claim 14 , wherein the processor is further configured to:

calculate first and second intermodulation noise artifacts (noise 1 , noise 2 ) based on the first earth response (h 1 est) and the second earth response (h 2 est); and

calculate a filter D based on the first earth response (h 1 est) and the second earth response (h 2 est).

16. The computing device of claim 15 , wherein the processor is further configured to:

calculate first and second reverse noise terms (rnoise 1 , rnoise 2 ) based on the first and second intermodulation noise artifacts (noise 1 , noise 2 ) and the filter D.

17. The computing device of claim 16 , further comprising:

remove from the received seismic data first and second reverse noise terms (rnoise 1 , rnoise 2 ) to obtain noise mitigated seismic data.

18. The computing device of claim 17 , further comprising:

generate the image of the surveyed subsurface based on the noise mitigated seismic data.

19. A non-transitory computer readable medium including computer executable instructions, wherein the instructions, when executed by a computer, implement a method for calculating intermodulation noise generated with one or more land seismic sources, the method comprising:

receiving seismic data generated by actuating the one or more land seismic source with a first sweep and a second sweep;

calculating with a computing device a first earth response (h 1 est) corresponding to the first sweep;

calculating with the computing device a second earth response (h 2 est) corresponding to the second sweep;

calculating the intermodulation noise (IMD) based on the first and second earth responses (h 1 est, h 2 est),

removing from the seismic data the intermodulation noise (IMD); and

generating an image of a subsurface based on the seismic data, from which the intermodulation noise (IMD) has been removed, for identifying geophysical structures,

wherein the second sweep is a time reverse sweep of the first sweep.

20. The medium of claim 19 , wherein the first and second sweeps are pseudo-random sweeps.