Campbell PC208 Instruction Manual download pdf (Page 8)

probes, and by the disruption of xylem tissue associated with their placement. These

perturbations produce a systematic underestimation in the measured heat-pulse velocity

(Cohen et al., 1981; Green and Clothier, 1988). Consequently, the heat-pulse velocity

must be corrected for the probe-induced effects of wounding. This correction can be done

empirically (e.g. Cohen et al., 1981), or it can be based on sound physical principals,

using an equation of the form:

(2)

where

[m s

-1

] is the corrected heat-pulse velocity and

is the raw heat-pulse velocity

given by Eq. (1). The correction coefficients

, and

have been derived by Swanson

and Whitfield (1981) from numerical solutions of Marshall’s (1958) equations, for

various wound sizes. The full range of correction factors are listed in Table 1. These

correction factors can also be seen in the ANALYSIS program, HPV-2000.FOR, which is

described later. The use of Eq. (2) puts the heat-pulse method on a sound theoretical

basis, and uses physical principals rather than an empirical calibration to obtain the best

estimate of the heat-pulse velocity.

Wound

width (mm)

0.0

0.000

1.000

0.000

1.6

0.393

1.356

0.036

2.0

0.807

1.203

0.058

2.4

1.184

1.072

0.087

2.8

1.524

0.964

0.124

3.2

1.826

0.879

0.169

3.6

2.090

0.818

0.221

Table 1. Wound corrections for Eq. (2)(From Swanson and Whitfield, 1981)

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 53 54

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