APPARATUS AND METHOD FOR MEASURING THE TRANSPIRATION OF PLANTS

Abstract

The present disclosure relates to an apparatus and a method for ascertaining a transpiration rate of an object, in particular of a plant leaf or a plant needle. The method comprises the steps of ascertaining a first temperature difference between the temperatures on the surface of the object and on the surface of a reference body as well as a second temperature difference between the temperatures on the surface of the object or on the surface of the reference body and a respective measurement point (M1, M2) spaced apart therefrom, so as to finally calculate therefrom the transpiration rate of the object.

Claims

1. An apparatus for ascertaining a transpiration rate of an object, in particular of a plant leaf or a plant needle, the apparatus comprising: a reference body, an arrangement for determining a first temperature difference between the temperatures on a surface of the object and a surface of the reference body, an arrangement for determining a second temperature difference between the temperatures on the surface of the object and at a first measurement point spaced apart from the surface of the object, or between the temperatures on the surface of the reference body and at a second measurement point spaced apart from the surface of the reference body, as well as a data recorder for recording or calculating the first and second temperature differences.

2. The apparatus according to claim 1, characterized in that the apparatus comprises temperature sensors for measuring the temperatures.

3. The apparatus according to one of the preceding claims, characterized in that the apparatus comprises a thermopile for measuring the first or the second temperature difference.

4. The apparatus according to claim 3, characterized in that a compensating body is thermally connected to the thermopile.

5. A method for ascertaining a transpiration rate of an object, the method comprising the following steps: determining a first temperature difference between the temperatures on a surface of the object and on a surface of a reference body, determining a second temperature difference between the temperatures on the surface of the object and at a first measurement point spaced apart from the surface of the object, or between the temperatures on the surface of the reference body and at a second measurement point spaced apart from the surface of the reference body, ascertaining the transpiration rate of the object, taking into account the first and the second temperature difference.

6. The method according to claim 5, characterized in that the transpiration rate of the object is ascertained taking into account a calibration.

7. The method according to claim 5, characterized in that the calibration is carried out on the basis of a gravimetric measurement of the transpiration or of the transpiration rate.

8. The method according to claim 5, characterized in that the first measurement point is spaced apart from the surface of the object by a maximum distance of 10 cm, or that the second measurement point is spaced apart from the surface of the reference body by a maximum distance of 10 cm.

9. The method according to claim 5, characterized in that the object is a plant leaf or a plant needle.

10. The method according to claim 5, characterized in that the object and the reference body differ from each other with respect to a dimension, with respect to an absorption coefficient at a specific wavelength or in a specific wavelength range, with respect to a thermal capacity and/or with respect to a coefficient of thermal conductivity by a maximum of 20% in each case.

11. The method according to claim 10, characterized in that the object and the reference body differ from each other by a maximum of 10%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the following, advantageous embodiments of the present disclosure will be explained in more detail on the basis of a drawing. The individual figures show

[0028] FIG. 1 a schematic representation of a first embodiment;

[0029] FIG. 2 a schematic representation of a second embodiment;

[0030] FIG. 3 a schematic representation of a third embodiment; and

[0031] FIG. 4 a schematic representation of a fourth embodiment;

DETAILED DESCRIPTION

[0032] Like components are provided with like reference numerals throughout the figures.

[0033] FIG. 1 shows a first apparatus 100 for ascertaining a transpiration rate of an object 1, which is a plant leaf 1 that may e.g. lie on or be attached to a carrier T.

[0034] A reference body 2, which is similar to the leaf 1 as regards geometry as well as light and heat characteristics, but which does not transpire, is placed at a distance of a few millimeters to a maximum of approx. 50 cm from the leaf 1. In the context of the present disclosure, the phrase similar to the leaf as regards geometry as well as light and heat characteristics means that the object 1 and the reference body 2 differ from each other with respect to a dimension, with respect to an absorption coefficient at a specific wavelength or in a specific wavelength range, with respect to a thermal capacity of their material and/or with respect to a coefficient of thermal conductivity of their material or their surface by a maximum of 20% in each case, preferably by a maximum of 10%. For example, a dimension D2 of the reference body 2 may deviate by up to 20% from a corresponding dimension D1 of the object 1. The deviation may, for example, be considered taking as a basis the respective object 1, 2 in the case of which the size in question has the larger value. The aim is that the reference body 2 and the object 1 are as similar as possible with regard to one or more characteristics. This, however, does not apply to transpiration. Ideally, the reference body 2 is not transpiring at all, i.e. it does not contain any water, by way of example. In the embodiment according to FIG. 1, the reference body 2 is placed on a carrier of its own, which, however, is optional or which may also be the same carrier T for the object 1.

[0035] The temperatures at the leaf 1 (Tl), at the reference (Tr), as well as the temperature close to the leaf (Tla) or close to the reference (Tra) are now measured preferably in parallel. The Delta-T(ref-leaf) results from the difference between the temperatures Tl and Tr. The temperature difference between Tl and Tla as well as Tr and Tra shows the intensity with which the air at the boundary layer is removed by the wind. Hence, it is an indicator of the wind velocity at the boundary surface/ambient air of the leaf 1 and of the reference 2, respectively. The transpiration rate of the leaf 1 can be calculated with the following equation:

W=f(Delta-T(ref-leaf),(TrTra)) or

W=f(Delta-T(ref-leaf),(TlTla))

[0036] The parameters of these equations can be ascertained gravimetrically prior to the actual measurement, e.g. in the form of a calibration. When the setup is placed on a very precise scale and the transpiration and the four temperatures are thus measured gravimetrically (i.e. via the weight loss over a certain period of time) in parallel, the parameters can be determined deterministically or statistically, by way of example.

[0037] A concrete example of such an equation could be as follows:

W=a+b*(TrTl)+c*(TlTla)+d*(TrTra)

[0038] Parameters for the calibration function, ascertained via gravimetric comparative measurement on spruce, under variable ambient conditions (radiation, air temperature, humidity)

[0039] Coefficient of determination of the calibration function Rsq: 94.4%

a=+0.000274455
b=+0.452055039
c=0.005186585
d=0.000632594

[0040] The apparatus 100 in FIG. 1 comprises a first arrangement 101 for determining a first temperature difference between the temperatures on the surface 1a of the object 1 and on the surface 2a of the reference body 2. This first arrangement 101 comprises a first temperature sensor 9, which contacts the carrier T or even better directly the surface 1a of the object 1 and measures the temperature Tl of the latter, and a second temperature sensor 7, which directly measures the temperature on the surface 2a of the reference body 2. Furthermore, the apparatus 100 comprises a second arrangement 102 for determining a second temperature difference. For this purpose, two different variants are shown in FIG. 1. In one variant, the second arrangement 102 comprises the first temperature sensor 9 for measuring the temperature on the surface 1a of the object 1 and a further temperature sensor 8 at a first measurement point M1. The first measurement point M1 is here spaced apart from the first temperature sensor 9, the distance being, however, preferably not larger than 10 cm. In the case of this arrangement 102, the second temperature difference ascertained is the difference between the temperatures measured by the two temperature sensors 8, 9.

[0041] In a second variant, the arrangement 102 comprises the temperature sensor 7 for measuring the temperature on the surface 2a of the reference body 2 as well as a further temperature sensor 6, which measures the temperature at a second measuring point M2. This second measuring point M2 is spaced apart from the temperature sensor 7 and the surface 2a of the reference body 2, the distance being, however, preferably not larger than 10 cm.

[0042] The temperature difference between leaf 1 and reference 2 Delta-T(ref-leaf) is measured in FIG. 1 with temperature sensors 7 (Tr) and 9 (Tl). The temperature close to the leaf (Tla) and the temperature close to the reference (Tra) are measured with two further temperature sensors 6, 8. The data are transmitted to the data recorder 4 via a cable 3. The temperature recorder 4 may be a computer.

[0043] FIG. 2 shows a further possible embodiment. Instead of using temperature sensors for an absolute measurement, a thermopile 11 with windings 12 is here used for a direct measurement of the temperature difference. The thermopile 11 records several measurement points and thus takes into account the thermal inhomogeneity of the leaf 1. The temperature difference between the reference body 2 and the air close to the reference (TrTra) is measured with two thermistors used as temperature sensors 6 and 7.

[0044] It is obvious that the temperature sensors 7 and 6 may also be placed on the side of the leaf 1. Due to the different thermal characteristics, the calibration curve will then be different.

[0045] Analogously to the sensor for a leaf, a similar sensor may be produced for plant species with needle leaves 1 as an object. FIG. 3 shows one of the possible variants for needle leaves. Here, the measurement points of the thermopile 11 with windings 12 are arranged on the reference body 2, which has thermal characteristics similar to those of the needles 1. The other side of the thermopile 11 is inserted into the needle tuft 1, it measures the temperature in the interior of the needle tuft 1 at several points. The absolute temperature at the reference (Tr) and in the air close to the reference (Tra) is measured by temperature sensors 6 and 7.

[0046] For leaves 1 and needles 1 having an inhomogeneous thermal characteristic, the thermopiles 11 in FIGS. 2 and 3 can only with difficulty precisely measure the correct leaf temperature. In this case, a compensating body 10 is attached to one side of the leaf, as can be seen in FIG. 4. The compensating body 10 has the best possible thermal conductivity and reflects the average temperature of the leaf 1 or the needle 1, and transmits this to the thermopile 11.