Optical fibre sensors for hydro-geological applications

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1 Optical fibre sensors for hydro-geological applications L. Schenato National Research Council, Research Institute for Hydro-Geological Protection - Padova Unit - Italy

2 2 Spoiler alert! Giving away the ending Optical Fibre Sensors enable revolutionary measurements which likely lead to transformative science

3 What is an optical fibre? Source: GIT2013: VIII Convegno Nazionale del Gruppo GIT, Chiavenna (IT) giugno

4 4 What is an optical fibre sensor? An optical fibre sensor is a SENSOR that uses optical fibre either as the sensing element THE FIBRE IS NOT USED FOR RELAYING THE SIGNAL TO THE ACTUAL SENSOR, THE FIBRE IS THE SENSOR Mechanism: polarization, intensity, phase, wavelength of the light Measurements: temperature, elongation, pressure, refractive index

element THE FIBRE IS NOT USED FOR RELAYING THE SIGNAL TO THE ACTUAL SENSOR, THE FIBRE

5 5 Motivation Scaling issue: measurements from cm to km to understand processes Data distribution issue: actual systems provide non dense measurements Cost-Effectiveness issue: expensive devices unlikely to factor in hydrology and geology

systems provide non dense measurements Cost-Effectiveness

6 6 Why Optical Fibres? Spans critical range from 0,05 to 5000 m Can execute distributed measurements in long distances and in wide range Can monitor total strain and temperatures of large areas Not need to provide electricity to fiber optic sensors Can be used in areas not immediately served by electricity cables Integrate sensing and communication function Is not effected by electromagnetic noise and lightning Can be used in mountains area Long service life and light weight Environmentally-friendly and maintenance free Inexpensive ( /m) High sensitivity

and temperatures of large areas Not need to provide electricity to fiber optic sensors Can be used in areas not immediately served by

7 7 Example: temperature sensing Resolution [m] Range Mechanism 0.5 m C 30 km C Raman or Brillouin Scattering/ Fiber Bragg Gratings Applications: volcanism; heat flux in geothermal reservoirs; aquifer and basin-scale ground-water flow, submarine ground-water discharge in coastal environments, ground-water/surface-water interaction in riverine, lacustrine, and wetland environments

heat flux in geothermal reservoirs; aquifer and basin-scale ground-water flow, submarine

8 8 Example: temperature sensing

9 Example: strain & displacement sensing Resolution [m] Range [km] Mechanism 0.5 m µε 100 Rayleigh or Brillouin Scattering/Fiber Bragg Gratings Applications: landslides, rockfalls, cracks, debris flow (replacement for inclinometer, strain gauges, extensometers, ) Source: Source: GIT2013: VIII Convegno Nazionale del Gruppo GIT, Chiavenna (IT) giugno

cracks, debris flow (replacement for inclinometer, strain gauges, extensometers, ) Source: http://spie.

10 Example: seismic monitoring Source: GIT2013: VIII Convegno Nazionale del Gruppo GIT, Chiavenna (IT) giugno

11 12 Example: seismic monitoring

12 Example: Vibration/AE monitoring GIT2013: VIII Convegno Nazionale del Gruppo GIT, Chiavenna (IT) giugno

13 14 Example: Vibration/AE monitoring Developed in collaboration of Vrjie University, Amsterdam

14 15 Example: Vibration/AE monitoring Tests by inducing cracks in trachyte rock blocks by filling some holes drilled into the blocks with highly expansive mortar.

15 Example: Vibration/AE monitoring * Figure: Typical signals (top row) and corresponding PSDs (bottom row) recorded by the three sensors (FCS, fiber coil sensor; FTC, ferrule-top cantilever; PZT, piezo-electric transducer). *PZT: VS30-SIC-46dB from Vallen Systeme GmbH, 46 db of electrical amplification. GIT2013: VIII Convegno Nazionale del Gruppo GIT, Chiavenna (IT) giugno

16 17 Other examples Source: X Source: Source:

http://www.aquadiva.unijena.de/spec/spec.

17 18 An economical perspective Fiber Optic Sensor Global Consumption Market Forecast (Value Basis, $Billion) Source: ElectroniCast

18 19 conclusions Optical Fibre Sensors enable revolutionary measurements which likely lead to transformative science Greatest scientific opportunities arise from optical fibre sensors

to transformative science Greatest scientific

19 20 Acknowledgements THANK YOU FOR YOUR ATTENTION MANY THANKS TO THE ORGANIZERS Fondazione Cassa di Risparmio di Padova e Rovigo under the project SMILAND

20 21 Sensing via light scattering Intensity of backscattered light time Incident Light Backscattered Light CHANGE WILL OCCUR TO POWER AND/OR FREQUENCY

21 22 Fiber Bragg Gratings:

22 23 Techniques Type Feature Applications Rayleigh scattering of light Brillouin scattering of light Raman scattering of light Generated from the scattering depending on the size within the medium. Has the same frequency components as incident light. Generated by interacting with acoustic modes within the medium. The shift frequency is dependent on strain and temperature. Generated by interacting with molecular vibrations within the medium. Mainly the strength of anti- Stokes light is dependent on temperature Common OTDR Loss distribution BOTDR Strain distribution & temperature distribution ROTDR temperature distribution

23 Rayleigh Scattering for Sensing Sensing approach: Continuous sensing in arbitrary sections (bending losses sensing); Sensing accuracy: ~40 db (dynamic range); Sensing time: from few seconds up to about 5 min (only static); Sensing distance: up to 40 km; Sensing of: Rayleigh scattering GIT2013: VIII Convegno Nazionale del Gruppo GIT, Chiavenna (IT) giugno

24 Brillouin Scattering for Sensing Sensing approach: Continuous sensing in arbitrary sections (distributed strain sensing); Sensing accuracy: ±50-100x10-6 (strain); Sensing time: about 10 min (it possibly detects slow change); Sensing distance: up to 80 km; Sensing of: Brillouin scattering GIT2013: VIII Convegno Nazionale del Gruppo GIT, Chiavenna (IT) giugno

25 26 Raman Scattering for Sensing Sensing approach: Continuous sensing in arbitrary sections (distributed temperature sensing); Sensing accuracy: ±0.5 to 1 (range: [-200,+300 ]; Sensing time: about 1 to 5 min; Sensing distance: up to 40 km; Sensing of: Raman scattering

26 Fiber Bragg Gratings for Sensing Sensing approach: Multipoint sensing with one fiber (up to 5-6 points with no multiplexing); Sensing accuracy: ±10-6 and smaller (strain); Sensing time: from 1 ms to few seconds (it can detect dynamic change); Sensing distance: up to 30 km; Sensing of: Bragg wavelength GIT2013: VIII Convegno Nazionale del Gruppo GIT, Chiavenna (IT) giugno

Christine E. Hatch University of Nevada, Reno

Christine E. Hatch University of Nevada, Reno Roadmap What is DTS? How Does it Work? What Can DTS Measure? Applications What is Distributed Temperature Sensing (DTS)? Temperature measurement using only