The effects of probe misalignment on sap flux density measurements and in situ probe spacing correction methods

- Probe misalignment causes inaccurate probe spacing calculation.
- Errors in probe spacing cause large errors in the measured sap flux density (J).
- The in situ spacing correction method can effectively reduce the errors in J.

The accurate measurement of sap flow is important for estimating transpiration. This paper is focused on the errors in sap flux density (J) caused by probe misalignment and on how to reduce these errors. We found that probe misalignment caused errors in the heat pulse velocity (Vh). Furthermore, probe misalignment had a large influence on thermal diffusivity (κ) and the determination of zero flow points. Assuming uniform axial thermal diffusivity and zero sap flow conditions, we developed a new in situ probe spacing correction method based on three temperature sensor measurements inside the same temperature probe, which can be used for correcting both linear and nonlinear misalignments. Laboratory experimental results verified that our method could significantly reduce the errors in determinations of J by using the Compensation Heat Pulse velocity (CHP) method, the Heat Ratio (HR) method and the T-max method.

Error in water flux density before and after in situ correction of probe spacing.171