A temperature and strain separation method for long-distance optical fiber submarine cable monitoring

Abstract

The present invention provides a method for separating temperature and strain in long-distance optical fiber submarine cable monitoring. The method divides the submarine cable into a landing section, a flat section, and a booster station section. Based on the common variation of temperature and strain measured by BOTDA, the landing section and the booster station section additionally use a DTS device based on the ROTDR principle to measure the submarine cable temperature, thereby achieving physical separation of temperature and strain. In the flat section, the submarine cable temperature measured by the DTS device based on the ROTDR principle at the entry into the flat section is first used as the temperature baseline. Then, the point-type Brillouin frequency shift change is used as the temperature change caused by poor submarine cable insulation, and the segment-type Brillouin frequency shift change is used as the strain change caused by external force, thereby achieving the separation of temperature and strain judgment. The present invention realizes the separation of temperature and stress in the application of submarine cable monitoring systems, provides the corresponding submarine cable copper core temperature and stress change values caused by external force, and improves the online monitoring performance of submarine cables.

Description

Technical Field

[0001] The present invention is directed to a distributed optical fiber submarine cable monitoring system, and in particular relates to a temperature and strain separation method for submarine cable monitoring in a long-distance optical fiber manner. Background Art

[0002] Submarine cables are laid on the seabed, where they operate in a harsh operating environment. Influenced by the fishing industry, the oil industry, and seabed geology, these cables are susceptible to strain-related mechanical failures. Furthermore, aging of submarine cable insulation can trigger partial discharges, potentially causing temperature increases at the fault location. Currently, submarine cables often use composite optical fibers as sensing elements to monitor temperature, disturbances, and strain. Distributed fiber-optic sensing technologies such as Brillouin optical time-domain reflectometry (BOTDR) and Brillouin optical time-domain analysis (BOTDA), based on stimulated Brillouin scattering, can simultaneously measure temperature and strain changes in submarine cables and have therefore attracted widespread attention. However, because the frequency shift of Brillouin scattered light is linearly related to both strain and temperature, the cross-sensitivity between temperature and strain makes it difficult to simultaneously demodulate temperature and strain information from submarine cables, limiting their sensing applications. Consequently, the separation of temperature and strain has attracted considerable attention.

[0003] Currently, common methods for temperature-strain separation include the following: First, adding a relaxed optical fiber as a reference fiber to independently measure temperature, and then combining the temperature and strain information measured with the tight-buffered fiber to achieve temperature-strain separation; second, combining the Brillouin frequency shift and Brillouin light intensity to simultaneously demodulate temperature and strain; third, using the different temperature-strain coefficients of multiple Brillouin peaks present in specially designed optical fibers to simultaneously demodulate temperature and strain; and fourth, combining Brillouin scattering with Raman scattering, leveraging the strain-insensitive nature of Raman scattering to measure temperature and achieve temperature-strain separation. However, methods one and three require specially laid optical cables, limiting their practical engineering applications; and methods one and four are limited by signal-to-noise ratio issues and are not suitable for long-distance scenarios.

[0004] Therefore, there is an urgent need for a temperature-strain separation strategy suitable for long-distance submarine cables to effectively achieve simultaneous measurement of temperature and strain and improve the online monitoring performance of submarine cables. Summary of the Invention

[0005] As previously mentioned, the purpose of the present invention is to provide a method for separating temperature and strain in long-distance submarine cable monitoring, which can effectively separate temperature and strain and improve the online monitoring performance of submarine cables. To this end, the present invention adopts the following technical solutions:

[0006] A method for separating temperature and strain in submarine cable monitoring using long-distance optical fiber is characterized in that the laid submarine cable is divided into different cable segments, and different methods are used to separate temperature and strain in different cable segments. For the landing segment and booster station segment, since both are relatively short, temperature measurement is performed using a DTS device based on ROTDR in addition to BOTDA to measure the common variation of temperature and strain. This is used to monitor the submarine cable temperature in these two areas. The combination of BOTDA and ROTDR can achieve physical separation of temperature and strain.

[0007] For flat sections, even with ROTDR-based DTS equipment installed on both sides of the flat section, it is difficult to directly measure the temperature of the entire cable section due to the long distance. For flat sections, the temperature caused by poor insulation typically manifests as a point-wise change, while the strain caused by external forces manifests as a segment-wise change. Therefore, a separation strategy combining point-wise and segment-wise changes is adopted to detect temperature in the flat section of long-distance submarine cables. In the flat section, the cable temperature measured by the ROTDR-based DTS equipment at the point of entry is first used as the temperature baseline. Then, the point-wise Brillouin frequency shift change is used as the temperature change caused by poor cable insulation, and the segment-wise Brillouin frequency shift change is used as the strain change caused by external forces, thus separating the determination of temperature and strain.

[0008] Furthermore, for flat sections, the cable temperature measured by the ROTDR-based DTS device after entering the flat section is used as the temperature baseline for the flat section. Significant Brillouin frequency shift changes within a certain length range are considered temperature changes, preferably set to three times the spatial resolution. Significant Brillouin frequency shift changes greater than this length range are considered strain changes (possibly caused by natural settlement during installation). Significant Brillouin frequency shift changes refer to significant changes in Brillouin frequency shift, which can be defined based on the temperature or strain accuracy of the current equipment, preferably set to three times the temperature or strain accuracy.

[0009] The present invention analyzes the temperature and stress of submarine cables by region. After cable installation, the present invention divides the cable into three main areas: the landing section, the flat section, and the booster station. The starting points of these three areas are defined based on the water depth at the cable installation site. The landing section starts at the onshore control center; the flat section starts at the point where the cable extends to the average water depth; and the booster station section starts at a certain distance before the J-tube, preferably 50m to 1km.

[0010] The technical solution of the present invention is described in further detail below:

[0011] In shallow or dry water at the landing section, the cable temperature is primarily affected by three factors: weather changes, temperature rise caused by powering the cable, and temperature changes caused by cable defects. The first factor affects the entire cable along the landing section and varies gradually with water depth, consistent with weather trends. Long-term observations reveal the impact of weather and hydrological changes on temperature. The second factor exhibits a zero temperature rise when power is off, but produces a uniform temperature rise across the entire landing section (except for defective spots) when power is on. The third factor, primarily due to poor cable insulation (causing localized discharge heating) or high localized resistance (causing localized power consumption heating), manifests as point-type heating. Even considering conduction along the conductor, this heating effect is minimal over several meters. The landing section is unlikely to be accessible by ships, so anchor damage is unlikely. The cable is buried in mud and sand, making it less susceptible to extreme weather. Therefore, stress is assumed to remain largely constant after settlement stabilizes. Stress changes during construction and other factors are also predictable and can be disregarded. In addition, since the landing section is relatively close to the centralized control center, generally less than 3 km, it is considered to combine it with ROTDR technology to achieve temperature and strain separation.

[0012] The flat section is deep and less affected by the external temperature. The temperature of the submarine cable is mainly affected by the temperature rise caused by the power supply to the submarine cable, poor insulation of the submarine cable (causing local discharge heating), or high local resistance (causing local power consumption heating). The first item is manifested as a temperature rise of 0 when the power is off, and the same temperature rise is generated across the entire flat section when the power is on (except for the bad points). The second item is manifested as point heating, which, even considering conduction along the conductor, will not affect more than a few meters. Therefore, when the photovoltaic composite cable is not powered, the temperature of the flat section is theoretically almost constant. The flat section is deep and the distance is long, with many ships passing through it on the sea, which increases the risk of anchor damage. If anchor damage occurs, there are two possible scenarios: first, the anchor strikes the cable directly, causing no noticeable cable displacement. This presents as point damage (limited impact range), inducing strain (short-term strain or long-term plastic deformation) in the cable, but also inevitably causing vibration. Second, the anchor is attached to the cable, causing drag and significant cable displacement. Due to the cable's strength, the entire cable within a certain range is affected by the drag. This strain (short-term strain or long-term plastic deformation) can affect cables over a distance of more than 10 meters and is accompanied by long-term disturbances. Furthermore, the flat section is far from the control center and booster station, so a combination of point and segment-based variations is considered to achieve temperature-strain separation.

[0013] The temperature change in the booster station section is caused by the temperature rise caused by the power supply of the submarine cable, the poor insulation of the submarine cable (causing local discharge heating) or the large local resistance (causing local power consumption heating). The first item is manifested as a temperature rise of 0 when there is no power, and the same temperature rise is generated in the entire booster station section when power is supplied (except for the bad points). The second item is manifested as point heating. The temperature at the beginning of this section is theoretically close to the temperature of the flat section, and the temperature at the end is close to the temperature of the landing section. Due to the J-tube suspension, the booster station section is greatly affected by waves and ocean currents, and the disturbance is greater than that of the landing section and the flat section, and the possibility of short-term strain or long-term plastic deformation is greater. In addition, since the booster station section can deploy equipment, it is considered to combine it with ROTDR technology to achieve temperature and strain separation.

[0014] Finally, by analyzing and combining the corresponding separation strategies, the temperature stress of different laying sections of the submarine cable is separated, providing temperature and stress monitoring data for equipment maintenance personnel, and improving the online monitoring performance of the submarine cable.

[0015] According to a second aspect of the present invention, the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of the above-mentioned method for separating the temperature and strain of submarine cable monitoring are implemented.

[0016] According to a third aspect of the present invention, the present invention provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned method for separating temperature and strain of submarine cable monitoring when executing the program.

[0017] In summary, the present invention proposes a method for separating temperature and strain for a submarine cable monitoring system. Based on an analysis of the causes and impacts of submarine cable temperature stress, the present invention selects a combined judgment separation strategy to separate the temperature stresses of different submarine cable installation sections. This separation of temperature and stress can be achieved in submarine cable monitoring system applications, providing corresponding stress change values caused by the cable's copper core temperature and external forces, thereby improving the performance of online submarine cable monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the segmentation method for laying submarine cables;

[0019] Figure 2 A schematic diagram of a system for simultaneously measuring temperature and strain in a long-distance optical fiber submarine cable according to a preferred embodiment of the present invention;

[0020] Figure 3 Schematic diagram of the temperature and strain separation strategy of the present invention. DETAILED DESCRIPTION

[0021] The present invention's method for separating temperature and strain monitoring in long-distance optical fiber submarine cables primarily segments the laid submarine cable according to temperature and stress conditions, and then achieves temperature and strain separation by combining physical separation and judgment-based separation strategies. Preferred embodiments of the present invention are described below with reference to the accompanying drawings.

[0022] Figure 1 This is a schematic diagram of the segmented method for laying submarine cables. The landing section is the area from the onshore centralized control center to the point where the water depth is less than the average depth after entering the sea. The flat section is the area from the average water depth to 50m to 1km before the J-tube in front of the booster station. The booster station section is the area from 50m to 1km before the J-tube in front of the booster station to the booster station joint.

[0023] Figure 2 This diagram shows a system for simultaneously measuring temperature and strain over long-distance fiber-optic submarine cables, according to a preferred embodiment of the present invention. A BOTDA device and a ROTDR device are deployed at the onshore centralized control center, connected via a coupler and connected to one end of the sensing fiber. The ROTDR device is deployed at the booster station and connected to the other end of the sensing fiber.

[0024] Figure 3 This is a schematic diagram of the temperature and strain separation strategy of the present invention. For the landing section and booster station section, since both are relatively short, a DTS device based on ROTDR technology is added to monitor the submarine cable temperature within these two areas, in addition to the BOTDA measurement of the common changes in temperature and strain. Combining the BOTDA and ROTDR measurement results achieves physical separation of temperature and strain.

[0025] For the flat section, due to the long distance, even if DTS equipment based on the ROTDR principle is added on both sides of the flat section, it is difficult to directly measure the temperature of the entire submarine cable section. Since the external temperature of the flat section remains basically unchanged, only the internal temperature change and stress change need to be considered. The temperature caused by poor insulation of the submarine cable usually manifests as a point change, and the strain change caused by external force manifests as a segment change. Therefore, the judgment separation can be achieved through the point and segment changes of the Brillouin frequency shift. First, the temperature of the submarine cable that has entered the flat section measured by the ROTDR-based DTS equipment is used as the temperature baseline of the flat section submarine cable, and then the obvious Brillouin frequency shift change with a length less than 3 times the spatial resolution is set as a temperature change, and the obvious Brillouin frequency shift change greater than this length is regarded as a strain change (which may be caused by natural settlement during laying). The judgment separation can be performed by a computer.

[0026] Through the description of the above embodiments, it will be clear to those skilled in the art that the facilities of the present invention can be implemented by means of software plus the necessary general hardware platform. The embodiments of the present invention can be implemented using existing processors, or by a dedicated processor used for this or other purposes for an appropriate system, or by a hard-wired system. The embodiments of the present invention also include non-transitory computer-readable storage media, which include machine-readable media for carrying or having machine-executable instructions or data structures stored thereon; such machine-readable media can be any available medium that can be accessed by a general-purpose or special-purpose computer or other machine with a processor. For example, such machine-readable media can include RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store the required program code in the form of machine-executable instructions or data structures and can be accessed by a general-purpose or special-purpose computer or other machine with a processor. When information is transmitted or provided to a machine via a network or other communication connection (hard-wired, wireless, or a combination of hard-wired or wireless), the connection is also considered a machine-readable medium.

[0027] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A method for separating temperature and strain in long-distance optical fiber submarine cable monitoring, characterized in that The laid submarine cable is divided into a landing section, a flat section, and a booster station section. Based on the BOTDA measurement of the common changes in temperature and strain, the landing section and the booster station section are additionally equipped with a DTS device based on the ROTDR principle to measure the submarine cable temperature, completing the physical separation of temperature and strain. In the flat section, the temperature of the submarine cable entering the flat section measured by the DTS device based on the ROTDR principle is first used as the temperature baseline, and then the point-type Brillouin frequency shift change is used as the temperature change caused by poor insulation of the submarine cable, and the segment-type Brillouin frequency shift change is used as the strain change caused by external force, completing the judgment separation of temperature and strain.

2. The method for separating temperature and strain of long-distance optical fiber submarine cable monitoring according to claim 1, characterized in that: The landing section is the area from the onshore centralized control center to the area where the water depth is less than the average water depth after entering the sea; the area from the average water depth after entering the sea to 50m~1km in front of the J-type pipe in front of the booster station is the flat section; the area from 50m~1km in front of the J-type pipe in front of the booster station to the booster station joint is the booster station section.

3. The separation method according to claim 1, characterized in that Brillouin frequency shift changes with a set length less than 3 times the spatial resolution are considered point-type changes; Brillouin frequency shift changes with a set length greater than this are considered segment-type changes.

4. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for separating temperature and strain of submarine cable monitoring as claimed in any one of claims 1 to 3 are implemented.

5. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method for separating temperature and strain of submarine cable monitoring according to any one of claims 1 to 3 are implemented.

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