Fiber Optic Temperature
Sensing in the Walker Basin:
From Seedbeds to Seepage
Scott W. Tyler
University of Nevada, Reno
Dept. of Geologic Sciences and Engineering
tylers@unr.edu
http://wolfweb.unr.edu/homepage/tylers/index.html/
What is Fiber Optic Temperature
Sensing
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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
yards for as long as 20 miles can be
resolved, every 10 seconds to 60 minutes,
with temperature resolution of 0.02-1.0 oF.
How Does it Work?
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99.999% of the light energy goes down the
fiber optic cable without loss
However, Rayleigh, Raman and Brillouin
scattering all occur as light is passed
through a fiber optic cable.
The scattered returned light’s energy
(returned at different frequencies) is related
to the temperature of the glass fiber optic.
How do we know from where it
came?
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The scattered light returns to the detector at the
speed of light. So by counting the number of
nanoseconds between our laser pulse and the
returned signal, the distance is simply:
X = ½ c * time since the laser was fired
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For every 10 nanoseconds, the light pulse “flies”
about 1 meter.
Cable lengths up to 30 km
Resolution of Temperature every 1-2 meters!
Temperature accuracy up to 0.01 oC
Inexpensive fiber costs ($0.20-$1/yard)
Fiber is completely reusable and repairable in
the field.
Advantages
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Fiber optic methods offer unparallel ability
to continuously monitor temperatures
Cost of fiber optic cable is very low
($0.20-$1/yard)
Cable is easily deployed, removable and
completely repairable.
Why Study Temperature on the
Walker System?
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Many hydrologic, geologic and environmental
processes are governed by temperature.
In the Walker Basin, we can use temperature to
indicated areas where subsurface irrigation
return flows are entering the river.
We can also use it to measure seedbed
temperatures during transition to different
irrigation strategies.
Additional Project Support
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Project A: Measuring stratification and mixing in
Walker Lake to understand fish habitat
development.
Project A: Monitoring Walker River temperatures
to assess habitat and restoration.
Project B/C: Development of improved irrigation
scheduling by monitoring soil moisture status.
Project E: Assessing impacts of increased flows
on downstream temperatures and salinity.
Two Example Applications
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Measuring mixing in the thermocline
of Lake Tahoe (Selker, Schladow
Torgersen and Hausner)
Distributed soil temperature
monitoring at UNR’s Alternative
Agriculture Sites (Project F).
Deep Lake Tahoe
Measurements
June 7, 2007
Lake Tahoe, CA Test Site
Cable Deployment
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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.
Weather Conditions: June 6
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The previous day was very cold and windy
Strong westerly's
Weather Conditions: June 7
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Warm, calm day
Smooth water
Complete Vertical Profile: Single
Ended
Note the wavy pattern of the warm water
interface! Causing mixing of nutrients to
the bottom waters
Walker River Water Applications
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Understanding groundwater/river exchanges are crucial
to developing hydrologic models of the basin
Areas of localized saline groundwater inflows into the
Walker River will have cool waters during the summer
months.
Fiber optic cables will be deployed for 2-4 days along
selected reaches to map inflows.
Chemical sampling of inflows will be done using hand
drilled wells
Strategies for reducing saline inflows can then be
developed at the local scale.
Linear Parallel Seepage Monitoring
Walker Lake Studies
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The dynamics of the mixing of Walker Lake are
important for understanding habitat and refuges.
In coordination with project team members and
the USGS, periodic measurements of the vertical
temperature profile in the lake will be
performed.
Additional fibers will be installed in areas of
anticipated submarine groundwater inflows into
the lake for input into groundwater models being
developed.
Seedbed Temperatures
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Fiber optic cables can be used to measure, at large
scales, the shallow soil temperatures.
Alternative agriculture studies and reduced water
application can allow much higher soil temperatures to
develop, which may limit germination and plant growth.
Almost 2 miles of fiber have been installed 15 cm
beneath the soil at the 5C and Wildlife Refuge Test Sites
Temperature will be monitored to determine:
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Maximum daily soil temperatures during summer
Infiltration rates (measured by cooling of the soil)
Soil Moisture by time to maximum temperature
5C Ranch Data
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Base case temperatures measured in mid
February, prior to germination.
Soils are moderately coarse and
background soil moisture is uniform
Watch for part of the cable that is in the
air (cold at night, warm in the day)
Summary
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Fiber optic temperatures are supporting many of
UNR’s Walker Basin Project.
Low cost and detail of information in both the
lake, river and soil offer unique opportunities to
monitor both current conditions and the impacts
of future decisions on the Walker basin.
The system has benefits beyond the current
applications, specifically to improving water use
efficiency of irrigation.
Nevada is one of the leaders in this technology.