SECURITY MONITORING OF AN ASSET USING DISTRIBUTED ACOUSTIC SENSING WITH SELECTED GAUGE LENGTHS

Abstract

An asset such as a data transmission system, a perimeter security system, an oil well or a pipe line is monitored for events which are potentially damaging or threatening to the asset by installing an optical fiber continuously through the asset. The asset has many different zones of different physical condition, environment and/or of different risk factors which are expected therefore to generate different responses to events. The fiber is monitored using a distributed acoustic sensing (DAS) interrogator by effecting an analysis to determine the presence of an event in one or more of the zones The analysis includes applying different gauge length parameters to received data signals from the different zones at the same time.

Claims

1. A method for monitoring security of an asset for events which are potentially damaging or threatening to the asset, the method comprising: installing an optical fiber continuously through the asset to be monitored; the asset having at least two different zones of different physical condition, environment and/or of different risk factors where the optical fiber passes through said different zones to define different portions of the optical fiber each associated with a respective one of the zones; using a distributed acoustic sensing (DAS) interrogator to send signals into and receive data signals from the continuous optical fiber; effecting an analysis of the received data signals to determine the presence of an event in one or more of the zones; the analysis including gauge length parameters applied to the received data signals; and applying different gauge length parameters to received data signals from the different zones at the same time.

2. The method according to claim 1 wherein the received data signals from the different zones are analyzed with separate, optimized gauge length parameters.

3. The method according to any preceding claim wherein the selection and assignment of the gauge length parameters are determined by an operator.

4. The method according to any preceding claim wherein the selection and assignment of the gauge length parameters are determined automatically by the DAS interrogator.

5. The method according to any preceding claim wherein at least one portion is analyzed multiple times with different gauge length parameters.

6. The method according to claim 5 wherein the multiple analyses are concurrent

7. The method according to claim 5 wherein the multiple analyses are in a selected or random order

8. The method according to any preceding claim wherein the selection and assignment of the gauge length parameters are determined and adjusted dynamically in response to environmental or ambient conditions applied to the optical fiber in the different zones.

9. The method according to any preceding claim wherein the selection and assignment of the gauge length parameters are provided from a library of presets.

10. The method according to any preceding claim wherein the analysis includes an algorithm applied to the received data signals and wherein the selection and assignment of the gauge length parameters is carried out using data determined by the algorithm.

11. The method according to any preceding claim wherein the gauge length is adjusted to enhance sensitivity and to optimize signal-to-noise ratio.

12. The method according to any preceding claim wherein the asset has different zones, where different arrangements of installation of the optical fiber in relation to the asset is expected to generate different responses to events, and the zones are selected in response to the different arrangements of installation.

13. The method according to any preceding claim wherein the asset passes through different environments, which are expected to generate different responses to events, and the zones are selected in response to the different environments.

14. The method according to any preceding claim wherein the asset has different zones of different risk factor, which are expected to generate different responses to events, and the zones are selected in response to the different risk factors.

15. The method according to any preceding claim wherein the asset is monitored by a perimeter monitoring system having different zones using different installations of the optical fiber in the zones where the fiber is installed to different components of the asset in the different zones.

16. The method according to claim 15 wherein the different installations include different enclosure or fence types and/or installation in the ground.

17. The method according to claim 16 wherein the fiber is passed along a fence in a first zone and then buried in the ground in a second zone where the first zone is analyzed with a longer gauge length and the buried portion is analyzed with a shorter gauge length as it is a quiet environment.

18. The method according to claim 15, 16 or 17 wherein the shorter gauge length provides finer resolution allows post processing that is useful in buried perimeter applications such as analysis of the bidirectional propagation of the signal as a tool to differentiate footsteps and road noise, or to analyze the footsteps to determine parameters about the origin such as walking gate length.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIGS. 1, 2 and 3 show different locations of the portions of a continuous optical fiber connected to a DAS interrogator

[0048] FIG. 4 is a flow chart of a process to select different gauge lengths for different portions of an optical fiber using a DAS interrogator, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

[0049] In FIG. 1 is shown an optical fiber 10 which is installed in a perimeter monitoring system where the perimeter includes in a first zone 10A a fence 11 mounted above the ground 12 as shown. In a second zone 10B there is an open space and the same continuous fiber is installed below ground in the second zone. A DAS interrogator 13 of known type is connected at the end of the fiber and is used to send signals into and receive data signals from the continuous optical fiber. The interrogator then effects an analysis of the received data signals to determine the presence of an event in one or more of the zones. As described above the analysis includes applying gauge length parameters to the received data signals and applying different gauge length parameters to received data signals from the different zones at the same time.

[0050] In FIG. 2 the fiber passes through two fence panels forming a first zone and then is returned underground along the same fence to provide a second zone for secondary monitoring.

[0051] In FIG. 3 the fiber passes through two zones of different fence types.

[0052] One embodiment of the method herein is shown in the flow chart of FIG. 4 which includes the following steps:

[0053] Deploy an optical fiber on different portions of an asset monitoring system

[0054] Deploy an optical fiber on different portions of an asset monitoring system

[0055] Receive the DAS signals associated with intensity events on the fiber

[0056] Analyze the signals to generate data relating to the event in different portions

[0057] Apply different gauge length to different portions to determine additional data by one or more of the following: [0058] Select gauge length automatically from the data [0059] Operator input of gauge length [0060] Library of preset gauge lengths

[0061] Repeat analysis for selected portion using different gauge lengths