Wisconsin's Role in Great Lakes Restoration - American Water ...

Using Heated Distributed Temperature Sensing to Monitor Soil Water
**Arlen M. Striegl, Department of Civil and Environmental Engineering, University of
Wisconsin – Madison, Madison, WI striegl@wisc.edu
Steven P. Loheide II, Department of Civil and Environmental Engineering, University of
Wisconsin – Madison, Madison, WI loheide@cae.wisc.edu
Department of Civil and Environmental Engineering, University of Wisconsin – Madison,
Madison, WI
Vadose zone hydrology varies both spatially and temporally and is a primary factor governing
vegetation composition and patterning. Understanding site soil water dynamics is critical for
hydrologic model development, parameterization, and calibration. Soil water heterogeneity
and transience is difficult to capture using traditional measurement techniques.
When embedded in soil, commercially available single needle heat dissipation sensors have
been used to measure soil water by introducing a heat pulse into the soil and monitoring the
induced temperature response. Wet soils exhibit a more muted temperature response
because of their superior ability to conduct heat away from the needle as compared to dry
soils. Distributed temperature sensing (DTS) systems, which are also commercially available,
are capable of measuring temperatures at two meter intervals along fiber optic cables up to
30km long. By combining DTS with heat dissipation sensor methodology, we propose that soil
water can be monitored over large distributed scales previously unattainable. Numerical
simulations guided the design and fabrication of a custom bundle of fiber optics, resistance
heating conductors, and protective coatings. This custom cable was buried at a depth of
20cm to monitor the soil water dynamics of a floodplain transect near the Upper East Branch
Pecatonica River south of Barneveld, Wisconsin. The temperature response of the cable was
empirically related to co-located standard soil water measurements. Accurate and reliable
spatially distributed, temporally continuous measurements of soil water are now being
obtained using this technology.
** Graduate student presentation
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