Method and device for monitoring a submarine cable
Device for monitoring a submarine cable ( 1 ) comprising at least one optical fiber ( 2 ) which is arranged in or on the submarine cable ( 1 ), at least one laser light source ( 3 ), the light of which can be coupled into the optical fiber ( 2 ), wherein portions of the light back-scattered in the optical fiber ( 2 ) can be coupled out from the optical fiber ( 2 ), detection and evaluation means ( 5 ) capable of detecting the back-scattered light and determining from the detected light spatially resolved the temperature of the optical fiber ( 2 ), detection means ( 6 ) for the electric current flowing in the submarine cable ( 1 ), evaluation means ( 7 ) capable of storing the time profile of the detected temperature and the time profile of the detected electric, wherein the evaluation means ( 7 ) are capable of calculating from the time profiles of the temperature and the electric current spatially resolved the thermal resistance of the soil surrounding the submarine cable ( 1 ) and inferring from the spatially resolved determined thermal resistance of the soil the cover height of the submarine cable ( 1 ).
1. A method for monitoring a submarine cable ( 1 ) using a fiber optic system for distributed temperature measurement including: (i) at least one optical fiber ( 2 ) for a spatially resolved temperature measurement, wherein the optical fiber is arranged in or on the submarine cable ( 1 ); (ii) at least one laser light source ( 3 ) producing light which is coupled into the optical fiber ( 2 ), wherein portions of the light generated by the laser light source ( 3 ) and back-scattered in the optical fiber ( 2 ) is coupled out from the optical fiber ( 2 ); (iii) detector and evaluation apparatus ( 5 ) that detects the back-scattered light and determines from the detected back-scattered light the spatially-resolved temperature measurement of the optical fiber ( 2 ); (iv) detector ( 6 ) for detecting electric current flowing in the submarine cable ( 1 ); and (v) evaluation device ( 7 ) for storing time profile of the determined spatially-resolved temperature and the time profile of the detected electric current, wherein the evaluation device ( 7 ) calculates from the time profiles of the determined spatially-resolved temperature and the detected electric current spatially-resolved thermal resistance of soil surrounding the submarine cable ( 1 ) and infers a covered height of the submarine cable ( 1 ) from the spatially-resolved thermal resistance of the soil; wherein the covered height of the submarine cable is a height of soil material arranged on top of the submarine cable, comprising the steps of:
determining using the evaluation device ( 7 ) the time profile of the spatially-resolved temperature measurement of the submarine cable ( 1 ),
determining using the evaluation device ( 7 ) the time profile of the detected electric current flowing through the submarine cable ( 1 ),
calculating using the evaluation device ( 7 ) a spatially-resolved thermal resistance of the soil surrounding the submarine cable ( 1 ) from the determined time profiles of the spatially-resolved temperature measurement and the detected electric current,
inferring using the evaluation device ( 7 ) the covered height of the submarine cable ( 1 ) from the calculated spatially resolved thermal resistance of the soil.
2. The method according to claim 1 , further comprising the step of:
determining the time profile of the spatially-resolved temperature measurement and/or the detected electric current over a period of at least one hour.
3. The method according to claim 1 , wherein the electric current changes during a time period, during which the time profile of the spatially-resolved temperature measurement and/or the detected electric current is determined.
4. The method according to claim 1 , wherein the spatially-resolved thermal resistance of the soil is calculated for a plurality of locations along the submarine cable ( 1 ).
5. The method according to claim 4 , wherein the spatially-resolved thermal resistance of the soil is calculated simultaneously for the plurality of locations along the submarine cable ( 1 ).
6. The method according to claim 1 , wherein the spatially-resolved thermal resistance of the soil is continuously calculated.
7. The method according to claim 1 , comprising the step of:
utilizing an algorithm for the evaluation of the detected time profiles of the spatially-resolved temperature measurement and the detected electric current, which adapts as variable parameters the spatially-resolved thermal resistance of the soil and temperature of the environment of the submarine cable ( 1 ) to the measured time profiles of the spatially-resolved temperature measurement and the detected electric current.
8. The method according to claim 1 , wherein the fiber optic system for distributed temperature measurement is based on Raman- or Brillouin-scattering.
9. A fiber optic system for distributed temperature measurement for monitoring a submarine cable ( 1 ), the system comprising:
at least one optical fiber ( 2 ) for a spatially resolved temperature measurement, wherein the optical fiber is arranged in or on the submarine cable ( 1 ),
at least one laser light source ( 3 ), the light of which is coupled into the optical fiber ( 2 ), wherein portions of the light generated by the laser light source ( 3 ) and back-scattered in the optical fiber ( 2 ) is coupled out from the optical fiber ( 2 ),
detector and evaluation apparatus ( 5 ) that detect the back-scattered light and determine from the detected back-scattered light the spatially resolved temperature measurement of the optical fiber ( 2 ),
detector ( 6 ) for detecting electric current flowing in the submarine cable ( 1 ),
evaluation device ( 7 ) for storing time profile of the determined spatially-resolved temperature measurement and the time profile of the detected electric current, wherein the evaluation device ( 7 ) calculates from the time profiles of the spatially-resolved temperature measurement and the detected electric current spatially resolved thermal resistance of soil surrounding the submarine cable ( 1 ) and infers a covered height of the submarine cable ( 1 ) from the determined spatially resolved thermal resistance of the soil; wherein the covered height of the submarine cable is a height of soil material arranged on top of the submarine cable.
10. The system according to claim 9 , wherein the system is suitable to execute the method according to claim 1 .
11. The method according to claim 1 , wherein the submarine cable is transporting energy.
12. The system for monitoring the submarine cable ( 1 ) according to claim 9 , wherein the submarine cable is transporting energy.
13. The method according to claim 2 , wherein the time profile of the spatially-resolved temperature measurement and/or the detected electric current is determined over a period of at least one day.
14. The method according to claim 2 , wherein the time profile of the spatially-resolved temperature measurement and/or the detected electric current is determined over a period of several days.
15. The method according to claim 2 , wherein the time profile of the spatially-resolved temperature measurement and/or the detected electric current is determined over a period of one week.
16. The method according to claim 4 , wherein the spatially-resolved thermal resistance of the soil is calculated for more than half of a length of the submarine cable ( 1 ) installed under water.
17. The method according to claim 4 , wherein the spatially-resolved thermal resistance of the soil is calculated for an entire length of the submarine cable ( 1 ) installed under water.