3
0
11.2 Base-line
A
symmetry Multipliers
Base-line asymmetry multipliers are typically left set to 1, as this typically does
not affect the reading.
11.3 Base-line Asymmetry O
ffsets
Base-line asymmetry offsets will need to be adjusted. Whether the offset is a
positive or negative adjustment will depend upon the convergence or divergence
of each needle relative to the heater. The magnitude of the adjustment can only be
assessed after an initial few days of measurements have been analysed. Therefore,
this
correction
parameter
must
be
entered
after
the
firs
t
few
days
of
data
have
been collected.
11.4
Thermal Diffusivity
Describes the manner in which heat moves through the woody matrix that is the
water conducting, sap wood of the tree. This can be left as a default value 0.0025
cm
-2
s
-1
taken
from
Marshall
1952
or
specifi
c
values
can
be
calculated
based
on
the fresh weight, fresh volume and dry weight calculations from a sample of the
sapwood of the tree being measured.
Note:
If entering the correction factors directly to the SFM1 for real-time data
processing, Thermal Diffusivity should be sampled and determined prior to
installation. The process can take up to a week due to the drying time of sapwood.
11.5 Wounding Coefficient
Describes the impact, cavitation of the vessels (caused by drilling) and heating
of the tissues by the heater resulting in tylosses around the heater needle, have
on the movement and transfer of heat to the measurement needles. These
coefficients have been modelled (Burgess 2001) and are available from
appendix A. These coefficients are automatically applied to the HRM Algorithm
in Sap Flow Tool software when a measured wound size is selected.
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