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The double-ratio method (DRM): a robust three-probe sap flow technology that can accurately measure high, low and reverse flows
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  • Zijuan Deng,
  • Heather Vice,
  • Matthew Gilbert,
  • Mark Adams,
  • Thomas Buckley
Zijuan Deng
Flinders University of South Australia
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Heather Vice
University of California Davis
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Matthew Gilbert
UC Davis
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Mark Adams
Swinburne University of Technology
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Thomas Buckley
University of California Davis
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Abstract

Sap velocity measurements are useful in fields ranging from plant water relations to hydrology at a range of scales. Heat-pulse based techniques are among the most common methods to measure sap velocity, but most lack the ability to measure velocities across a wide range, including very high, very low and negative velocities (reverse flow). We propose a new method, the double-ratio method (DRM), which is robust across an unprecedented range of sap velocities and can provide real-time estimates of the thermal diffusivity of wood. The DRM employs one temperature sensor proximal and two distal to the heat pulse probe and facilitates several theoretical, heat-based approaches to quantifying sap velocity. We tested the DRM using whole-tree lysimetry in Eucalyptus cypellocarpa and found strong agreement across a wide range of velocities.