Measurement the phase yields value for and
778 36 Thermography to Measure Water Relations of Plant Leaves
Figure 36.5: Parameter images for constant heating: a time constant τ; b tem-
perature difference ∆T.
| div = | ||
|---|---|---|
data from the same species.
Periodic flux method. A varying energy flux density jact(t) is applied
| ∂f (t) | (36.30) | ||
|---|---|---|---|
| ∂t | ◦ |
|
that is, a time derivative of a function in the time domain becomes a
|
|||||
|---|---|---|---|---|---|
ˆz(ω) |
(36.32) | ||||
| and | ���� |
|
(36.33) | ||
| 36.4 Measurements | 779 | ||
|---|---|---|---|
|
|||
| 2π | |||
| 0 | |||
|
|||
| 2π | |||
| 0 | |||
| Figure 36.6: | Parameter images depicting the phase Eq. (36.33) for different | ||
In principle, a measurement of the phase ϕ(ω) yields a value for τ and, therefore, using Eq. (36.28), a value for (C/A)leaf.
The varying energy flux had the form of a rectangular function (the radiator was periodically switched on and off). As the Fourier spectrum of a rectangular function consists of all the odd harmonics, this can be considered as an application of several frequencies at once (with decreasing amplitude).
