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Distributed Temperature Sensing: A Transformative Technology in Water Resources

Distributed Temperature Sensing: A Transformative Technology in Water Resources. Scott W. Tyler University of Nevada, Reno Dept. of Geologic Sciences and Engineering styler@unr.edu http://wolfweb.unr.edu/homepage/tylers/index.html/. What is Distributed Temperature Sensing (DTS).

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Distributed Temperature Sensing: A Transformative Technology in Water Resources

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  1. Distributed Temperature Sensing: A Transformative Technology in Water Resources Scott W. Tyler University of Nevada, Reno Dept. of Geologic Sciences and Engineering styler@unr.edu http://wolfweb.unr.edu/homepage/tylers/index.html/

  2. What is Distributed Temperature Sensing (DTS) • The measurement of temperature (and) 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. • Spatial location of temperature is resolved identically to Time Domain Reflectometry

  3. Optical Fiber – Basic Construction Total Internal Reflection Lower Refractive Index Higher Refractive Index Θa Core Cladding Θa = Acceptance Angle

  4. Raman Scattering for Temperature • Thermal energy drives oscillations within the lattice of the doped amorphous glass making up the fiber. • When excited by photons (from the laser illumination), the interactions between the photons and the electrons of the solid occurs, and results in light being scattered (re-emitted) and shifted to higher and lower frequencies • The scattered light is shifted in frequency equivalent to the resonant frequency of the oscillating lattice ( a constant for any particular molecular structure) • Higher intensity of thermal oscillation produces higher intensities of the scattered light.

  5. Distributed Temperature Sensing Tyler, et al., J Glaciology, 2008 Rayleigh Scattering Stokes Anti-Stokes shifts with temperature Brillouin Raman (Stokes) Raman (Anti-Stokes) inamplitude Brillouin infrequency Amplitude/ Intensity Frequency

  6. Currently used in fire monitoring, oil pipeline monitoring, high tension electrical transmission cables, down hole monitoring of oil production, dam seepage. • Detector serves as both OTDR (for distance) and intensity (for Stokes and anti-Stokes) Figure courtesy of AP Sensing.

  7. Advantages of DTS • The cable serves as the measuring device • Fiber optic cable is relatively inexpensive ($0.50-$10/meter) and robust and 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. • Installations can be temporary or permanent.

  8. Example Applications • Snow dynamics (Dozier, McNamara, Burak, Selker) • Measuring mixing in the thermocline of Lake Tahoe (Selker, Schladow Torgersen and Hausner • Towards developing integrated soil moisture at large spatial scales (Selker, Miller, Hatch) • Cave air circulation (Wilson, Barber and Jorgensen) • Stream/Groundwater Exchanges (Conklin, Bales, Hopmans)

  9. Challenges of Snow Installations • Cold Temperatures; Freeze/Thaw common • Rodents/Burrowing animals • Lack of access throughout winter • Significant strains possible due to creep, consolidation, metamorphosis and avalanche • Small thermal gradients need to be resolved • Solar heating on fiber, particularly in late stages of melt when snow is dominated by ice may affect observed temperatures

  10. Mammoth Mountain Ski Area (Sierra Nevada)

  11. Stokes/Anti Stokes Cable loss Typical DTS Signals

  12. Bare Ground vs. Buried Cable Note Scale Difference Below Snow Diurnal variations clearly define bare and snow covered areas From Tyler et al., 2008

  13. Lake Tahoe, CA Test Site

  14. Cable Deployment • Cables were deployed from the UC Davis research vessel John LeConte • Cable was lowered to the bottom of the lake, then pulled up 20 m • Total depth was approximately 411 m.

  15. Weather Conditions: June 6 • The previous day was very cold and windy • Strong westerly's

  16. WeatherConditions: June 7 • Warm, calm day • Smooth water

  17. Complete Vertical Profile: Single Ended

  18. Note the wavy pattern of the warm water interface! Causing mixing of nutrients to the bottom waters Detailed View of the Thermocline at ~40 meters From Tyler et al., 2008

  19. Measurement of Soil Moisture during Irrigated Agriculture • We can measure soil moisture only in the very uppermost portions of the soil with radar, but few methods are available to measure spatially distributed soil moisture IN the root zone! • Here, we use a passive approach, relying upon solar heating and time lag at 15 cm, τ, to estimate the soil thermal diffusivity every 1 meter along the cable. • τ (x, y, t) = f(thermal diffusivity, depth, x, y) • τ (t) = f(thermal diffusivity) ~ f(θ) • Active methods, in which a heater cable provides the input have also been developed at OSU and LBL and are analogous to heat dissipation sensors.

  20. Installing fiber optic cable • 1000m of armored cable installed at 15cm depth • Dragged and seeded

  21. Temperature vs. Time ∆t DRY SOIL KT ~ 30 cm2/hr  = 7% 30 25 20 15 10 35 30 25 20 15 Soil Temperature (ºC) Air Temperature (ºC) soil temperature air temperature 7/26 7/27 7/28 Time

  22. Soil Moisture & Thermal Diffusivity 25 20 15 10 5 100 80 60 40 20 irrigation event irrigation event drying Soil Moisture (%) - symbols Thermal Diffusivity (cm2/hr) - lines drying DRY SOIL 7/26 7/27 7/28 7/29

  23. Measuring Air Flow in Carlsbad Caverns Nat. Park • Air circulation in CCNP an important aspect of cave biology and cave management • Air circulation and thermal convection is believed to control many cave feature formation processes. • Air circulation may be an analog to fluid convection during cave formation. Hot, saline fluids believed to be dominant cave forming mechanism.

  24. Cave Air Temperatures Cave Entrance Wet Area

  25. STRATIFIED UPPER ROOM WELL MIXED LOWER ROOM VERTICAL THERMAL PROFILES IN A TALL (>30 m ) ROOM

  26. Stream/Meadow MonitoringSequoia National Park

  27. Stream Temperature Profile Meadow Deep Pools and Stream Ice Bath

  28. Conclusions and Vision • DTS can provide fundamental insights into exchange processes and thermal stratification (Tahoe gravity waves, cave circulation, diurnal variations in stream “dead-zone” volumes). • Data “granularity” allows us to probe small scale processes, while at the same time measuring across broad spatial scales (snow monitoring, soil moisture measurement) • CUAHSI/NSF-sponsored workshops in 2007 and 2008 have trained ~70 professionals and students, and also shaped our views on technology transfer. Another planned for July 2009 in Denmark. • Other applications on-going • Borehole logging and fracture flow, ASR • Monitoring prescribed fire soil temperatures • Lake/atmosphere exchange and evaporation from lakes • Vertical snow temperature monitoring • Stream/fish habitat recovery, both for cold water species (salmon) and thermophiles (Devils Hole pupfish) • Monitoring solar inputs to aquatic systems.

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