Device and method for steering seismic vessel

1. A method for steering a vessel during a marine acquisition campaign, the method comprising:

obtaining a pre-plot track of a steered point, wherein the steered point is associated with an equipment spread towed by the vessel;

calculating an offset between a past position of the vessel and a current position of the steered point; and

steering the vessel along a vessel track, wherein the vessel track is calculated by shifting the pre-plot track of the steered point with at least a cross-line component of the offset,

wherein the current position of the steered point corresponds to a current time while the past position of the vessel corresponds to a time earlier than the current time.

2. The method of claim 1 , wherein the equipment spread is a seismic spread.

3. The method of claim 1 , wherein the steered point is located mid-point between two seismic source arrays.

4. The method of claim 3 , wherein the pre-plot track of the steered point is a mean course of two pre-plot tracks of the two seismic source arrays towed by the vessel.

5. The method of claim 3 , wherein the pre-plot track of the steered point is a filtered mean course of the two pre-plot tracks of the two source arrays.

6. The method of claim 1 , wherein the steered point is an abstract point logically linked to the equipment spread.

7. The method of claim 1 , wherein the vessel track is further shifted with an inline component of the offset relative to the pre-plot track of the steered point.

8. The method of claim 1 , wherein a new vessel track is recomputed when a variation of the offset is greater than a given threshold.

9. The method of claim 1 , further comprising:

determining a time interval Δt based at least on a speed of the vessel and an inline distance travelled by the steered point; and

determining the offset as a difference between the current position of the steered point at current time t and a past position of the vessel at a past time t−Δt.

10. The method of claim 2 , wherein the steered point is a virtual point corresponding to a given point in the seismic spread, the virtual point being the point where the given point would be if there had been no steering of a part of the seismic spread that includes the given point.

11. A method for steering a vessel during a marine seismic acquisition campaign, the method comprising:

determining a variation (δ) of a cross-line component (CO) of an offset between a past position of a vessel and a current position of a steered point (P) associated with a marine seismic spread towed by the vessel during the campaign; and

steering the vessel by offsetting a current track of the vessel with the variation (δ) when the variation (δ) is larger than a given threshold,

wherein the current position of the steered point corresponds to a current time while the past position of the vessel corresponds to a time earlier than the current time.

12. The method of claim 11 , wherein the steered point (P) is one of a center of the source array, a midpoint between source arrays, a center of a front end of streamers and a midpoint between the source arrays and a center of the front end of the streamers.

13. The method of claim 11 , further comprising:

calculating an inline offset (IO) between a path over ground of the steered point (P) and a path over ground of the vessel.

14. The method of claim 13 , further comprising:

determining the offset to be a vector having a first component the cross-line offset and the second component the inline offset.

15. The method of claim 11 , wherein the vessel advances along an inline direction and the cross-line offset is calculated along a cross-line direction, which is substantially perpendicular on the inline direction and within a plane substantially parallel to the water surface.

16. The method of claim 11 , further comprising:

generating in a control device commands for steering the vessel along the vessel track that is offset by the variation (δ) relative to the current track.

17. The method of claim 11 , further comprising:

determining an inline offset (IO) along the inline direction, between the past position of the vessel and the current position of the steered point (P); and

offsetting the current path of the vessel with the inline offset (IO) prior to determining the cross-line offset (CO) between the vessel and the steered point (P) during the campaign.

18. The method of claim 11 , further comprising:

receiving a pre-plot track of the steered point (P), where the pre-plot track includes a change in direction; and

further offsetting the current track of the vessel based on the change in direction.

19. The method of claim 11 , further comprising:

receiving a pre-plot track associated with the steered point (P);

storing in a control device a cable model that describes an interaction between the vessel and the marine spread associated with the steered point;

receiving environmental conditions; and

computing a new track of the vessel based on the offset, the pre-plot track of the steered point, the cable model and the environmental conditions.

20. A navigation system configured to steer a vessel and associated seismic equipment, the system comprising:

a global positioning system configured to generate a first position for the vessel and a second position for the associated seismic equipment; and

a navigation module that obtains a pre-plot track of a steered point, wherein the steered point is associated with the associated seismic equipment towed by the vessel, calculates an offset between a past position of the vessel and a current position of the steered point, and steers the vessel along a vessel track, wherein the vessel track is calculated by shifting the pre-plot track of the steered point with at least a cross-line component of the offset,

wherein the current position of the steered point corresponds to a current time while the past position of the vessel corresponds to a time earlier than the current time.