Distributed Temperature Sensing using Fiber Optics

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Distributed Temperature Sensing using Fiber Optics
Scott W. Tyler University of Nevada, Reno Dept.
of Geologic Sciences and Engineering tylers_at_unr.ed
u http//wolfweb.unr.edu/homepage/tylers/index.htm
l/
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What is Distributed Temperature Sensing (DTS)

• The measurement of temperature (and possibly
  strain) using only the properties of a fiber
  optic cable.
• The fiber optic cable serves as the thermometer,
  with a laser serving as the illumination source.
• Measurements of temperature every 1-2 meters for
  as long as 30 km can be resolved, every 1-60
  minutes, with temperature resolution of
  0.01-0.5oC

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How Does it Work?

• Rayleigh, Raman and Brillouin scattering all
  occur as light is passed through a fiber optic
  cable, although all are small signals. Well
  focus only on Raman in this talk.
• Raman scattering is produced by inelastic
  collisions of photons with atoms or molecules
  along the fiber optic cable. If a photon loses
  energy to the wall, the scattered wavelength is
  longer (Stokes Signal) if a scattered photon
  gains energy from the wall, its energy is larger
  and therefore its wavelength is shorter
  (anti-Stokes Signal)

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From Agilent, Inc.

• The Raman wavelengths are predictable and
  symmetric.
• The anti-Stokes (energy gaining) is strongly
  temperature dependant, but the Stokes is
  relatively independent of the temperature of the
  colliding molecule.
• The temperature of the scatterer is calculated
  from the ratio of the anti-Stokes/Stokes
  Intensity.

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According to Agilent Technologies.
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Advantages of DTS

• The cable serves as the measuring device
• Fiber optic cable is relatively inexpensive
  (0.50-10/meter) and robust (more on that
  later!).
• Cables typically have small thermal inertia.
• Once installed, continuous measurements do NOT
  disturb the fluid column (wells) or soils.
• Very high resolution and long cables can provide
  high density coverage of a landscape, lake, or
  groundwater reservoir.

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Instrument Response and Costs

• Tool costs range from 30-60K
• Cable 1-10K
• Several manufacturers interested in environmental
  applications
• 30K instrument, 5 min. integration, 2 meter
  spatial

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Previous Applications

• DTS systems have been used to monitor geothermal
  wells since 1993
• The bottom water temperature distribution (5 km)
  of Lake Geneva was measured in 1998.
• Applications to measure seepage through dams and
  strain rate since 2002.

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Sakaguchi and Matsushima (2000) showed reasonable
ability to detect fractures in geothermal wells
during Injection, and showed ability to measure
fluid level as shift over to steam.
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Why DTS Now?

• Several key hydrology researchers have explored
  new areas for DTS, and the costs are coming
  down.
• John Selker (Oregon State University)
  Groundwater inflows to streams, mine shaft
  circulation, high resolution lake and snow
  profiling.
• Fred Day-Lewis and John Lane (USGS)
  stream/groundwater interaction tidal influences
  on groundwaters in estuaries.

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Selected Environmental Application Examples

• Measuring temporal changes in snow/ground
  interface temperatures and ground freezing.
• Circulation in boreholes, fracture mapping,
  continuous borehole flowmeters
• Groundwater inflows to streams (see Selker et al,
  WRR and Day-Lewis et al., EOS)
• Ephemeral stream flows
• Lake mixing and invasive species migration
• Fish habitat and habitat restoration

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Circulation in Mine Shafts(Selker, Stekjal,
Zeman, Tyler and Lockington)

• Circulation in flooded Czech mines
• Thermal and salinity stratification
• Double diffusive steps clearly present
• DTS produced a very high resolution data without
  disturbance to the fluid column

Steps in both T and S occur over lt1 m
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Groundwater/Surface Water ExchangeCourtesy of
Fred Day-Lewis (USGS)

• Beginning in Spring 2006, the USGS Office of
  Ground Water, Branch of Geophysics initiated a
  demonstration/evaluation project for
  DTS technology, with PI Fred Day-Lewis.
• Study sites included (1) Waquoit Bay National
  Estuarine Research Reserve, MA (2) bedrock wells
  on the University of Connecticut campus (3) Fish
  Creek , WY (4) the Shenandoah River, VA (5)
  Allequash Creek , WI and (6) the San Pedro
  River, AZ
•  

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Courtesy of Fred Day-Lewis USGS (Provisional)
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Results
Courtesy of Fred Day-Lewis USGS (Provisional)
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Issues and the Future

• Instrument costs are likely to continue to come
  down.
• Power requirements are moderate to low.
• Cables are well suited for boreholes.
• Surface placement can put the cable at risk from
  breakage and rodents. More challenges in re-use.
• Cables can be repaired AND cable manufacturers
  are working with Agilent, Lios and Sensornet for
  improved cables for environmental.
• The future looks bright!!

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Recent Hydrology-Related Publications

• Selker, J. S., L. Thévenaz, H. Huwald, A. Mallet,
  W. Luxemburg, N. van de Giesen, M. Stejskal, J.
  Zeman, M. Westhoff, M. B. Parlange (2006),
  Distributed fiber-optic temperature sensing for
  hydrologic systems, Water Resour. Res., 42,
  W12202, doi10.1029/2006WR005326.
• Selker, J.S., N. van de Geisen, M. Poolman, W.
  Luxemburg and M. Parlange, In Press, Fiber Optics
  Open Window on Stream Dynamics, Geophysical
  Research Letters.
• AGU NS24A   MCS220   Tuesday  1600h
• NS24A-02 INVITED   Monitoring Submarine
  Ground-Water Discharge Using a Distributed
  Temperature Sensor, Waquoit Bay, Massachusetts
  Day-Lewis et al.

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Extra Slides follow that may be of use to John
and Fred
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Added Challenges

• Snow pack temperature experiment currently in
  place at Mammoth, CA.
• High winds relocated the cable several times
  before the snow fell.

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• Agilent Unit LIOS Unit

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Sensornet DTS Halo Unit, Preliminary