Spatial averaging method for coherent distributed acoustic sensing

1. A spatial averaging method for a coherent distributed acoustic sensing (DAS) system comprising:

generating by an interrogator, interrogating light and sending it into a length of optical sensing fiber;

detecting by a coherent detector, backscattered light that results from the interrogating light sent into the optical sensing fiber;

generating and outputting by a coherent detector, signals indicative of detected backscattered light; and

analyzing by a signal processor, the outputted signals indicative of detected backscattered light and determining strain signals associated with locations along the length of the optical sensing fiber that are indicative of a vibration and acoustic environment of the optical sensing fiber at the locations;

SAID METHOD CHARACTERIZED IN THAT:

differential beating and polarization combining of outputted signals for two locations along the length of the optical sensing fiber is used to determine a phase change in-between every location along the length of the optical sensing fiber; and

a moving average is applied to the differential beaten, polarization combined, outputted signals from multiple locations in the spatial domain.

2. The method of claim 1 FURTHER CHARACTERIZED IN THAT:

signals from individual locations are grouped into averaging groups and signals in one of the groups are aligned to a same direction;

locations with a group are first aligned to an elected location; and

locations spanning multiple groups employ a second alignment operation.

3. The method of claim 1 FURTHER CHARACTERIZED IN THAT:

the spatial domain moving average is applied following polarization combining and diversity combining including frequency or wavelength diversity.

4. The method of claim 2 FURTHER CHARACTERIZED IN THAT: an elected location is one having a maximum short-term averaged power within its group.

5. The method of claim 4 FURTHER CHARACTERIZED IN THAT: each location has a phase rotation for a phase alignment inside its group.

6. The method of claim 5 FURTHER CHARACTERIZED IN THAT: a rotated signal of the elected location is used as a reference.

7. The method of claim 6 FURTHER CHARACTERIZED IN THAT: a group internal alignment procedure in which each location with a group is used to determine a phase difference between its input signal with the reference and phase rotation is updated by an averaged difference.

8. The method of claim 7 FURTHER CHARACTERIZED IN THAT: an inter-group alignment procedure in which every group maintains a group difference with its neighbor group such that group G+1 maintains the difference with group G or group G maintains the difference with group G+1 and the group difference is used to align averaging locations spanning the group and its neighbor groups.

9. The method of claim 2 wherein the groups exhibit a fixed size equal to spatial averaging taps.