[Insert Fig. 9 here]
4.3 Misalignment correction
Misalignment of probes is a major source of uncertainty for heat-pulse
techniques. It affects all methods and can bias inferred sap velocity
either positively or negatively. Burgess et al. (2001) suggested three
options to correct for misalignment in the HRM: forcing the calculated
sap velocity to equal zero under conditions when the true sap velocity
is known to be zero (e.g., after an extended period at 100% RH), by
correcting either the upstream (x 1) or downstream
(x 2) probe locations, or by averaging both of the
resulting corrected values, assuming misalignment for either probe is
equally likely (∆x 1=∆x 2,
where ∆xi is the misalignment correction for
Probe # i ). While all three methods result in matched calculated
and measured sap velocities under ”zero-flow” conditions, they do not
yield consistent day-time sap velocities (Fig. 10 ).