Portable apparatus for measuring at least one flow of sap in a plant

Abstract

The invention relates to a portable apparatus (100) for measuring at least one flow of sap in a plant, the plant having an outer casing, the apparatus (100) comprising: - a microwave emitter (10) for emitting a microwave electromagnetic flux towards a first portion of the outer casing of the plant so as to heat an inner portion of the plant; - a thermal sensor (20) arranged to capture thermal radiation from the plant over time; - a processing unit (30) configured to determine, from the thermal radiation captured by the thermal sensor, a movement of the heat front over time in the plant and to estimate, on the basis of the movement of the heat front, the flow of sap.

Description

PORTABLE DEVICE FOR MEASURING AT LEAST ONE FLOW OF SAP IN A PLANT TECHNICAL FIELD OF THE INVENTION [1]The present invention generally relates to an apparatus for measuring at least one sap flow in a plant, for example in a herbaceous plant or in a woody plant. [2] It relates more particularly to a portable device for measuring at least one sap flow in a plant, and, optionally, a water content in this plant. STATE OF THE ART [3] Devices are known for measuring sap flow using a beam emitted by a laser diode emitting a light flux onto a part of the external envelope of the plant to cause external heating of this plant, this heating then propagating under the combined action of diffusion and transport of the sap. [4]These devices are functional but pose various problems, in particular damage to the plant. Indeed, the light flux penetrates with difficulty into the plant in question and consequently, it is necessary to remove part of the external envelope of this plant to allow diffusion of the light flux into the internal part of the plant. [5] Furthermore, due to the low penetration of the light flux into the plant in question, these devices are limited to plants of small diameters and consequently they are not very suitable for measuring plants of different diameters. [6] It also turns out that these devices are bulky due to the use of the laser diode. Therefore, these devices are not portable and seem poorly suited to on-site measurement. PRESENTATION OF THE INVENTION [7]In order to overcome the aforementioned drawbacks of the state of the art, the present invention proposes a portable device for measuring at least one sap flow in a plant, said plant having an external envelope, said device comprising: - a microwave transmitter for emitting a microwave electromagnetic flux towards a first part of the external envelope of said plant so as to heat an internal portion of said plant; - a thermal sensor arranged to capture thermal radiation from said plant over time; - a processing unit configured to determine, from the thermal radiation captured by the thermal sensor, a displacement of the heat front over time in said plant and to estimate, on the basis of the displacement of the heat front, the flow of sap. [8] Thus, the use of a microwave transmitter makes it possible to generate an electromagnetic flux which penetrates very well into the plant in question and which is very little attenuated by this plant. As a result, the measurement of the movement of the heat front does not damage the plant in question, which makes it possible to obtain an estimate of the sap flow from non-invasive measurements facilitating on-site measurements. [9] Furthermore, thanks to the combination of the thermal sensor and the microwave transmitter, the sap flow can be determined on plants of different sizes, which facilitates on-site measurement.

[0010] It also turns out that the use of the microwave transmitter makes it possible to limit the size of the measuring device. The resulting measuring device is therefore portable and very suitable for on-site measurement.

[0011] Other advantageous and non-limiting characteristics of the apparatus according to the invention, taken individually or in all technically possible combinations, are as follows.

[0012] In one embodiment, the thermal sensor is oriented opposite a second part of the outer envelope of the plant crossed by the electromagnetic flux. For example, such an arrangement can be used when the section of the plant studied is less than or equal to 2 cm.

[0013] In one embodiment, the thermal sensor is oriented towards the first part of the outer envelope of the plant. For example, such an arrangement can be used when the section of the plant studied is greater than 2 cm.

[0014] In one embodiment, the apparatus comprises an electromagnetic flux sensor arranged to capture the electromagnetic flux reflected or transmitted by the plant, said processing unit being configured to determine, from the reflected or transmitted electromagnetic flux, a water content of said plant.

[0015] In one embodiment, the processing unit uses, for determining the water content of the plant, a table linking a self-reflection or transmission coefficient of said plant to a water content, said table being a function of the nature of the plant.

[0016] In this embodiment, the microwave transmitter may comprise an antenna operating, on the one hand, in transmission to transmit the microwave electromagnetic flux and, on the other hand, in reception to capture the electromagnetic flux reflected by said plant and thus form said electromagnetic flux sensor.

[0017] In one embodiment, the apparatus comprises a focusing device arranged to focus said electromagnetic flux on the first part of the outer envelope of the plant.

[0018] In one embodiment, the microwave transmitter comprises a bi-quad antenna.

[0019] In one embodiment, the antenna of the electromagnetic flux sensor is separate from the antenna of the microwave transmitter.

[0020] In this embodiment, the antenna of the electromagnetic flux sensor is a bi-quad antenna. In this case, the antenna of the electromagnetic flux sensor may have an arrangement similar to that of the antenna of the microwave transmitter.

[0021] In one embodiment, the electromagnetic flux is emitted at a frequency between 1 GHz and 200 GHz, preferably between 1 GHz and 25 GHz, preferably between 1 GHz and 4 GHz. Using low frequencies allows the use of a less expensive microwave transmitter.

[0022] In one embodiment, the electromagnetic flux emitted by the microwave transmitter is a pulsed electromagnetic flux.

[0023] In one embodiment, the thermal sensor is included in a thermal camera arranged to acquire a video stream of the thermal radiation, said displacement of the heat front being determined from this video stream.

[0024] In one embodiment, the apparatus comprises a control circuit arranged to activate and deactivate the microwave transmitter and the thermal sensor, said activation of the microwave transmitter and the thermal sensor being performed asynchronously.

[0025] In this embodiment, during a period of time, the microwave transmitter and the thermal sensor may be activated.

[0026] In one embodiment, the apparatus includes an orientation adjustment device arranged to orient and maintain the microwave emitter relative to the thermal sensor, for example facing the thermal sensor or side by side with the thermal sensor.

[0027] In one embodiment, the apparatus comprises a position adjustment device arranged to adjust the position of the microwave emitter relative to the plant and to adjust the position of the thermal sensor relative to the plant.

[0028] In one embodiment, the apparatus comprises a portable support on which at least the microwave transmitter and the thermal sensor are mounted.

[0029] In one embodiment, the apparatus comprises: - a portable housing associated with the portable support and accommodating at least part of the microwave transmitter and at least part of the thermal sensor, the processing unit, - a device for holding the support on the ground or on said plant.

[0030] In one embodiment, the apparatus comprises a reference support arranged to define a distance between the microwave emitter and the external envelope of said plant.

[0031] In one embodiment, the apparatus comprises a servo device configured to capture an electromagnetic flux reflected by said plant and modify the electromagnetic flux emitted by the microwave transmitter as a function of the reflected electromagnetic flux.

[0032] The invention also relates to a method for measuring at least one sap flow in a plant, said plant having an outer envelope, said method comprising the following steps: - emission by a microwave transmitter of a microwave electromagnetic flux towards a first part of the external envelope of said plant so as to heat an internal portion of said plant; - capture by a thermal sensor of thermal radiation from said plant over time; - determination, by a processing unit, of a displacement of the heat front over time in said plant from the thermal radiation captured by the thermal sensor and estimation, on the basis of the displacement of the heat front, of the sap flow.

[0033] In one embodiment, said method also comprises a step of capturing, by an electromagnetic flux sensor, the electromagnetic flux reflected or transmitted by the plant and a step of determining, by the processing unit, a water content from the reflected or transmitted electromagnetic flux.

[0034] In one embodiment, said method comprises a step of focusing, by a focusing device, the electromagnetic flux on the first part of the external envelope of the plant.

[0035] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. DETAILED DESCRIPTION OF THE INVENTION

[0036] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0037] On the attached drawings:

[0038] Figure 1 is a schematic representation of a first embodiment of a portable measuring device according to the present disclosure and used on site;

[0039] Figure 2 is a schematic representation in top view of the apparatus according to the first embodiment;

[0040] Figure 3 is a schematic representation of a microwave transmitter seen from the front used in the apparatus according to the first embodiment;

[0041] Figure 4 is a schematic representation of a video stream of thermal radiation acquired by a thermal sensor included in the apparatus according to the first embodiment;

[0042] Figure 5 is a schematic representation of the steps of a first treatment of the video stream illustrated in figure 4 by a processing unit included in the apparatus according to the first embodiment and illustrating in a first curve A, axial profiles extracted from the video stream illustrated in figure 4, and in a second curve B, a temporal variation of the position of a reference point over time determined from the video stream illustrated in figure 4;

[0043] Figure 6 illustrates a temporal variation of the position of the reference point over time determined from the video stream illustrated in Figure 4 using a second processing of the video stream illustrated in Figure 4;

[0044] Figure 7 is a schematic representation in profile view of the apparatus according to the first embodiment;

[0045] Figure 8 is a schematic top view representation of a second embodiment of a measuring apparatus according to the present disclosure;

[0046] Figure 9 is a schematic representation in top view of an example of an arrangement of a second sub-housing included in the apparatus according to the second embodiment;

[0047] Figure 10 is a schematic top view representation of a third embodiment of a measuring apparatus according to the present disclosure;

[0048] Figure 11 is a schematic representation in profile view of a face of a housing or sub-housing included in an apparatus according to the first mode or second mode or third embodiment according to the present disclosure,

[0049] Figure 12 is a schematic representation of a method according to the present disclosure.

[0050] A first embodiment of an apparatus 100 (or device) for measuring at least one sap flow in a plant will now be described using figures 1 to 7 and figure 11.

[0051] In this disclosure, the term plant includes woody and herbaceous plants.

[0052] The term sap flow corresponds to a speed of the sap in a part of the plant studied. It can also designate the sap flow rate and be expressed in g / h. In the present disclosure, the sap flow corresponds to the speed of the sap in the part of the plant studied. The part of the plant studied here corresponds at least to the part of the plant receiving an electromagnetic flux emitted by the device 100.

[0053] The apparatus 100 may be portable (handheld device). In the present disclosure, portable means a device that is transportable. Therefore, this device is mobile.

[0054] As illustrated in Figure 1, this device is transportable in that it is movable by a user and can be taken on site, i.e., into the outdoor environment.

[0055] By on-site, we mean that the device can measure sap flow on the plant directly present in the environment, i.e. directly on the plant in question. Therefore, it is not necessary to take a sample of this plant (which would damage the plant in question) and carry out this measurement in the laboratory. However, it is understood that this device can also be used in the laboratory on plant samples.

[0056] In a non-limiting manner, in this example, the plant corresponds to a part of the plant studied, for example here a part of a branch of a tree 1. This part of the plant comprises an external envelope 2, corresponding here to a part of the bark of the tree, delimiting an internal part 3 of the plant 1. In the following, to facilitate reading, the expression plant is used to refer to the part of the plant studied.

[0057] Of course, the present invention works on all types of plants, for example on trees and shrubs, cereals, vines, flowers, etc.

[0058] The apparatus 100 illustrated in Figure 1 and Figure 2 comprises a microwave transmitter 10. The microwave transmitter 10 is arranged to emit an electromagnetic flux F onto the external envelope 2 of the plant and to heat, by means of this electromagnetic flux F, an internal portion 331 of the plant 1.

[0059] As illustrated in figure 2, this electromagnetic flux F is oriented towards a first part 224 of the external envelope 2 of the plant 1 in order to irradiate this first part 224 of the external envelope 2 of the plant 1. This electromagnetic flux F will then penetrate into the plant 1 and internally heat the internal portion 331 of the plant 1.

[0060] It is then understood that this emitter 10 is used as an external heating means arranged to heat the internal portion 331 of the plant 1.

[0061] In this embodiment, the internal portion 331 is located near a second part 226 of the external envelope 2 of the plant 1 crossed by the electromagnetic flux F. Of course, as will be explained with the aid of FIG. 9, the heated internal portion 331 can be located near the first part 224 of the external envelope 2 of the plant 1.

[0062] By the term “in the vicinity of” is meant close to. In other words, it is understood that the heated internal portion 331 of the plant 1 by the electromagnetic flux is spaced from the second part 226 of the external envelope 2 by a distance d2 which is less than a distance d1 separating the first part 224 of the external envelope 2 from the heated internal portion 331. In practice, this distance d1 can be considered by determining, for example, the position of a temperature maximum 5 in the internal portion 331 of the plant 1, the distance d1 and d2 being able to correspond to the distances defined with respect to a normal vector (noted n) passing through a point 7 of the first part 224 of the outer envelope 2 and passing through the maximum temperature 5.

[0063] It is also understood that the second part 226 of the external envelope 2 is a part which is crossed by the electromagnetic flux F propagating in the plant 1. In other words, the electromagnetic flux F leaves the plant (here from the part studied of the plant) by the second part 226 of the external envelope 2.

[0064] In this example, the microwave transmitter 10 comprises an antenna 11 operating in transmission emitting the microwave electromagnetic flux. This antenna is for example powered by a microwave generator included in the microwave transmitter 10. In this example, the antenna 11 is a bi-quad antenna comprising two loops made from a metal wire, for example copper or aluminum (here copper), and having a diameter of approximately 1.0 mm (in this example). Of course, other types of antenna can be used, for example dipole, loop, spiral, cup-shaped antennas (known as "cup antenna"), etc.

[0065] Typically, the bi-quad antenna 11 may correspond to the bi-quad antenna described in Arguelles, AZ, 2017, “Super high frequency reflective biquad antenna”, 10.1109 / APUSNCURSINRSM.2017.8073145.

[0066] As illustrated in Figure 3, the two loops of the antenna 11 are identical and have a geometric shape, here a square comprising sides L1 of 30 mm. Of course, the antenna 11 is not limited to this dimension and these two loops can be of different shapes, for example, they can be circular, triangular, etc.

[0067] Generally speaking, the L2 size of both loops is about 90.0 mm.

[0068] The two loops are in the same plane P positioned facing the part of the plant 1 studied, in particular here facing the first part 224 of the external envelope 2. This plane P is considered here as being a plane positioned on the surface of the antenna 11.

[0069] In one embodiment, the electromagnetic flux F microwave emitted by the antenna 11 propagates in a free field (i.e. propagation in free space), that is to say that the electromagnetic flux F microwave does not encounter any other element of the apparatus 100 before reaching the external envelope 2 of the plant 1.

[0070] In this case, the microwave transmitter 10 or here the antenna 11 is positioned at a distance d3 from the external envelope 2 (here from the first part 224) of the plant of between 1.0 mm and 10.0 mm. Thus the antenna 11 is positioned in the near field of the external envelope 2. In practice, this distance may depend on the plant, for example on the section of the plant. For example, for a plant with a studied section of between 1.0 cm and 5.0 cm, the distance d3 may be from 1 mm to 10 mm.

[0071] The microwave transmitter 10 is arranged to emit the electromagnetic flux F microwave at a frequency between 1 GHz and 200 GHz, preferably between 1 GHz and 4 GHz to limit the costs of the antenna 11. In practice, this frequency range is selected with respect to the absorption spectrum of water which includes several absorption windows centered on 2.45 GHz, 22 GHz, 183 GHz. Here, typically, the electromagnetic flux F microwave is emitted at a frequency of 2.45 GHz in order to obtain a good compromise between the penetration of electromagnetic waves into the plant and the cost of such a microwave transmitter 10.

[0072] Preferably, this microwave electromagnetic flux F is a pulsed electromagnetic flux F in which each pulse is emitted for a duration of between 5 seconds and 30 seconds (for example here 10 seconds) and at a rate of between 3.34 mHz and 1.67 mHz. Using a pulsed beam makes it possible to reduce the average power consumed by the microwave transmitter 10, thus limiting the power consumed by the device 100. The repetition of the pulse allowing heating makes it possible to monitor the sap flow. Of course, in a variant, the microwave electromagnetic flux is a continuous flow. Using a continuous flow is also functional but can pose problems, for example energy consumption.

[0073] The emitted electromagnetic flux F has, at the output of the microwave transmitter 10, a power greater than or equal to 1.0 W, and preferably less than 10.0 W to limit heating.

[0074] In this example, the microwave transmitter 10 also comprises a reflector 12, in the form of a metal plate positioned behind the antenna 11 on which the antenna 11 is fixed. This reflector 12 has a size adapted to the antenna 11 (i.e. greater than the antenna 11) which is here sized 160 mm x 100 mm. The metal plate is preferably made of aluminum because this material couples well with the material of the antenna 11, here made of copper (or aluminum). The combination of the reflector 12 and the bi-quad antenna 11 makes it possible to obtain a microwave transmitter 10 with a higher gain, thus improving the heating performance of electromagnetic flux in the heated internal portion 331 of the plant.

[0075] The antenna 11 is preferably connected to the reflector 12 by a metal core 13 oriented perpendicular to the reflector 12 and to the plane P of the antenna 11, being fixed at the intersection of the two loops of the antenna 11. This core makes it possible to adjust a distance between the reflector 12 and the plane of the antenna 11. Typically, this distance is (A being the operating wavelength of the antenna, deduced from the working frequency (f) and the speed (c) of light in a vacuum by the formula A = Optionally, the antenna 11 can be attached to the reflector 12 at its lower and upper ends using fastening means, such as spacers. As will be explained above, the reflector 12 is positioned on a movable support.

[0076] The apparatus 100 also comprises a thermal sensor 20 arranged to capture a thermal radiation of the plant over time. Typically here, the thermal sensor 20 captures the thermal radiation emitted by the heated internal portion 331 of the plant. It also captures the thermal radiation of the first part 224 of the external envelope and the second part 226 of the external envelope.

[0077] In this embodiment, the thermal sensor 20 is an infrared thermal sensor. Typically, this thermal sensor 20 can be included in an infrared camera. As will be explained below with the aid of FIG. 4, this thermal camera 21 is arranged to acquire a video stream of the thermal radiation over time.

[0078] Of course, in a variant, the thermal sensor 20 may comprise a matrix of pixels arranged to capture the thermal flux of the plant 1 or may comprise at least one thermocouple, for example positioned against the second part of the external envelope of the plant crossed by the electromagnetic flux F. Using a matrix of pixels makes it possible to obtain an inexpensive device 100.

[0079] In this example, the thermal sensor 20 used is included in a conventional thermal camera 21, for example the SmartlR640 infrared thermal camera. This thermal camera 21 comprises, for example, a pixel matrix of size 640x480 square pixels of 200 pm and has a maximum frame rate of 30 Hz and a thermal resolution of 50 mK.

[0080] In this embodiment, the thermal sensor, via the thermal camera 21, is arranged to convert the captured thermal radiation into a thermal signal (proportional to the captured thermal radiation) comprising the thermal fields and coded on 14 bits (i.e. 16384 digital level (DL)). This thermal signal corresponds here to a video stream. Typically here, for the study of the video stream, a variation of 1 Kelvin (K) corresponds to a variation of 588 DL.

[0081] As illustrated in Figure 2, the thermal sensor 20 is oriented facing the second part 226 of the external envelope 2 of the plant in order to capture the thermal radiation emitted by the surface of the plant 1. It is thus understood that the plant 1 is positioned between the microwave emitter 10 and the thermal sensor 20.

[0082] The thermal sensor 20 used preferably has a maximum size of 50.0 mm x 50.0 mm and a weight of less than 200.0 g in order to facilitate the arrangement of the thermal sensor 20 in the apparatus 100, which limits the size of the apparatus 100 and facilitates its mobility.

[0083] Furthermore, in this example, the thermal sensor 20 is very compact thanks to the use of a conventional thermal camera, which limits the size of the device 100. Using a thermal camera 21 also makes it possible to obtain precise and easily exploitable results as will be explained below.

[0084] In a non-limiting manner, the thermal sensor 20 may be included in a thermal detector comprising the thermal camera 21 described above as well as other sensors.

[0085] As will be described below, the thermal sensor 20 is arranged to capture all of the thermal radiation emitted by the plant, in particular here at least the thermal radiation emitted by the heated internal portion 331. Consequently, its technical characteristics and its position relative to the plant are adapted according to the thermal radiation emitted which is a function of the power of the electromagnetic flux F emitted by the microwave transmitter 10 and implicitly of the type of plant and the section of the part of the plant studied.

[0086] In the present disclosure, the term section corresponds to the dimension of the cutting plane of the plant, this cutting plane being defined as the transverse plane passing through a point of the first part 224 of the external envelope (for example point 7) and oriented along the normal vector n passing through this point. In a simplified manner, the section can be assimilated to the “diameter” of the part of the plant studied.

[0087] In this example, the thermal sensor 20 is positioned at a distance d4 from the outer envelope of the plant 1 (here from the second part 226 of the outer envelope 2) of between 300.0 mm and 600.0 mm so that the heated internal portion 331 is included in the field of the thermal sensor 20 (here from the thermal camera 21). This distance d4 is for example determined by taking a normal to an outer surface of the thermal camera 21 and intersecting the second part 226 of the outer envelope of the plant 1 at a point 8.

[0088] The apparatus 100 also comprises a processing unit 30. By processing unit is meant any calculation unit or processor or computer or any other electronic element making it possible to implement a succession of commands and / or calculations. This processing unit 30 typically comprises a processor, a memory and different input and output interfaces.

[0089] By means of its input and output interfaces, the processing unit 30 is programmed to receive any data measured by the sensors of the device 100.

[0090] Thanks to its memory, the processing unit 30 stores a computer application, consisting of computer programs comprising instructions whose execution by the processor allows the determination of the sap flow (and optionally the water content as will be explained below).

[0091] The processing unit 30 illustrated in Figure 2 is at least connected to the thermal sensor 20 described above. By connected, it is meant that the processing unit 30 is arranged to communicate with another element, for example, by being configured to transmit and / or receive data from this element (here for example by wire).

[0092] Here, in this case, the processing unit 30 is arranged for the data of the thermal radiation acquired by the thermal sensor 20 (here in particular receiving the video stream acquired by the thermal camera) and to process this data in order to determine from the thermal radiation a displacement of the heat front in the plant studied. Here by heat front, we mean the thermal wave. Thus, the displacement of the thermal wave is studied.

[0093] In practice, the data on the acquired thermal radiation (corresponding here to the video stream) are recorded in the memory of the processing unit 30 and the data analyzed from these acquired data are also recorded in the memory of the processing unit 30.

[0094] In this example, the thermal camera 21 is configured to capture thermal radiation at a frequency of 5 Hz for a time period, here being greater than 1 minute and less than 10 minutes. Typically here, the thermal camera 21 can record a video stream for 4 minutes.

[0095] Optionally, the apparatus 100 also comprises a control circuit 40 arranged to activate and deactivate the microwave transmitter 10 and the thermal sensor 20 (here the thermal camera 21). In practice, the control circuit 40 comprises a control unit 41 arranged to control the various elements of the apparatus 100, here in particular the transmitter 10, the thermal sensor 20 (or thermal camera 21), and the processing unit 30.

[0096] By control unit 41 is meant any calculation unit or processor or computer or any other electronic element making it possible to implement a succession of commands and / or calculations. This control unit 41 typically comprises a processor, a memory and different input and output interfaces. Typically, the control unit 41 may comprise a microcontroller.

[0097] Thanks to its input and output interfaces, the control unit 41 is programmed to receive any data measured by the sensors of the device 100 and / or any data analyzed by the processing unit 30. In a non-limiting manner, the device 100 comprises a screen 43 connected to the control unit (see description below of figure 11). The control unit is also programmed to control the screen 43 and more generally any human-machine interface making it possible to communicate information to a user using the device 100. This screen may or may not be touch-sensitive.

[0098] In practice, the processing unit 30 and the control unit 41 may be two separate calculation modules or a single calculation module, or be the same element performing the functions of the processing unit 30 and the control unit 41.

[0099] In this embodiment, the activation of the microwave transmitter 10 and the thermal sensor 20 is carried out asynchronously, for example by a synchronization device 43 included in the control circuit 40 which activates asynchronously asynchronously the thermal sensor 20 (or the thermal camera 21) and the microwave transmitter 10.

[0100] Typically, in this embodiment, the control circuit 40 is configured to firstly activate the thermal sensor 20 to measure a reference thermal radiation of the plant, i.e. when the latter is not heated by the microwave transmitter 10. In a second time, the control circuit 40 is configured to activate the microwave transmitter 10, the microwave transmitter 10, the activation of the thermal sensor 20 (here the thermal camera 21) being retained. As a result, in this time period, the thermal sensor 20 as well as the microwave transmitter 10 are activated. In a third time, the control circuit 40 is configured to deactivate the microwave transmitter 10 while retaining the activation of the thermal sensor 20.

[0101] By activating we mean turning on the element in question. In other words, when activated, the function associated with this element (for example, emitting a wave or acquiring a signal) is active. Conversely, by deactivating we mean putting this element on standby, turning it off, or deactivating its function.

[0102] Thus, for example, the control circuit 40 activates the thermal sensor 20 for a first time period of at least 5 seconds (here 10 seconds) to measure a reference thermal radiation of the plant, corresponding here to the initial thermal radiation of the plant before being heated by the electromagnetic flux F microwave.

[0103] After this first period, while maintaining the activation of the thermal sensor 20, this control circuit, via the synchronization device, activates the microwave transmitter 10 to heat the part of the plant studied for a second time period, preferably greater than or equal to 3 seconds and less than or equal to 20 seconds. Preferably, this second time period is between 5 seconds and 15 seconds, preferably between 5 seconds and 10 seconds to avoid saturating the thermal sensor 20. Here, in this example, this second period is 10 seconds, which makes it possible to heat the internal portion 331 of the plant sufficiently to record the thermal radiation while avoiding saturation of the thermal sensor 20.Finally, the control circuit 40 deactivates the microwave transmitter 10, for example by switching it off or by modifying its position so that the emitted electromagnetic flux F does not reach the plant, while keeping the thermal sensor 20 active for a third time period depending on the type of plant, in particular on known parameters of the plant affecting the sap flow, such as the plant species, the age of the plant, the section of the part of the plant studied, the state of the plant (diseased or not), etc. Typically, this third time period is greater than 50.0 seconds, preferably greater than 60.0 seconds in order to acquire the propagation of the radiation. thermal of the internal portion 331 which has been heated by the electromagnetic flux F. For a sap flow estimated as "fast", this third time period can be less than 400 seconds, preferably less than 300.0 seconds in order to obtain a faster measurement while limiting the energy consumption of the device. Here typically, the third period is 220 seconds. For a "long" sap flow, this period is suitable for the plant.

[0104] Two examples of treatment carried out by the treatment unit 30 to return to the sap flow will now be described using figures 4 to 6.

[0105] In the present disclosure, the processing unit 30 is configured to determine the sap flow based on a variation in the position of a temperature maximum in the heated internal portion 331 over time. The variation in the position of the temperature maximum in the heated internal portion 331 over time makes it possible to estimate a speed of the heat front of the heated region.

[0106] In the present disclosure, the velocity of the heat front may be estimated using an estimation algorithm or by performing an analytical study of the thermal radiation sensed by the thermal sensor 20.

[0107] In the case of the analytical study, the processing unit 30 is configured to sequence the recorded thermal radiation into several signals as a function of time, corresponding here to sequencing the video stream into several images Imgk, each image being associated with an acquisition time (evaluated here in seconds), noted Tk, with k an index corresponding to the number of the signal considered (here of the image) which is a function of the acquisition time of this signal.

[0108] For example, Figure 4 illustrates an example of seven images included in the video stream acquired by the thermal camera 21 during the third time period. The images are each spaced apart in time by a period Pa of 20 seconds.

[0109] For each of the images, the processing unit 30 is configured to determine a reference point, also called thermal maximum, and denoted Hk in Figure 4, with k the index corresponding to the number of the signal considered (here image number) which is a function of the acquisition time. Here, the point Hk (maximum of the temperature profile) initially included in the heated internal portion 331 moves, transported by the flow of sap.

[0110] To determine this reference point, the processing unit 30 can search for this maximum temperature point typically using the max function which determines the pixel exhibiting the maximum intensity in each image, and record its position.

[0111] The processing unit is configured to extract, in each image, an axial profile of the thermal signal comprising this maximum intensity, here in particular by selecting in the first image Imgi, the line Uk of pixels comprising the reference point Hk (said selected line also being called axial profile). As the images are of similar sizes, we extract, in the other images of the video stream, the axial profiles having the same spatial coordinates as the axial profile selected in the first image. Thus, the row Uk of pixels selected in each image Imgk is similar. The row of pixels selected in the image with index k = 1 (Imgi) corresponds to the row of pixels selected in the image with higher index k+1 (Img2).

[0112] All of these axial profiles are stored in the memory of the processing unit and can be viewed on curve A of figure 5 which illustrates the axial profiles of the thermal wave including the reference point Hk of each extracted axial profile.

[0113] The processing unit 30 is then configured to compile these axial profiles into a single image as a function of the acquisition time. Thus, this image has as its abscissa the acquisition time associated with each axial profile and as its ordinate the position of the pixels of the line Uk of pixels comprising the reference point.

[0114] Thus, these axial profiles are compiled in the same image to represent a spatio-temporal variation of the thermal radiation measured from these axial profiles (curve B of figure 5).

[0115] It is therefore possible from this last representation to deduce a displacement of the heat front over time from the reference point by extracting from the data of curve B, the coordinates of the reference point Hk at each time. For this purpose, the processing unit 30 is configured to determine a displacement of the heat front by extracting the coordinates of the reference point Hk from each axial profile, or by taking the coordinates of the point having the maximum temperature in each extracted axial profile. These coordinates are extracted and recorded in the memory of the processing unit 30. This variation is generally linear, so by carrying out a linear regression on the extracted data, the processing unit 30 is configured to determine the speed of displacement of the heat front in the plant from the direction coefficient of the linear line.

[0116] In a preferred embodiment, to increase the accuracy of the measurement, the maximum temperature (reference point) can be estimated in each signal (here each image of Figure 4), for example by using a local approximation of the least mean squares on the signals. Thus the processing unit is configured to estimate from the acquired heat flux a position of a maximum temperature point, for example here by using a quadratic local approximation whose coefficients are determined by the least squares method.

[0117] In practice, this approximation is defined by the following formula

[0118] [Math. 1] DL(i, li) — Ok 2 + + ^k

[0119] With i the position of the pixel concerned and ak, bk and Ck corresponding to the coefficients of the equation Math. 1 of the corresponding image k determined by solving the second degree polynomial equation described above.

[0120] The reference point Hj for the corresponding image k is given by the following formula:

[0121] [Math. 2]

[0122] By associating each estimated reference point H max k in each image with the image acquisition time, we can determine a temporal variation of the position of the reference point over time, as illustrated in curve C1 of Figure 6 and its approximation C2 by a linear regression (curve C2 of Figure 6).

[0123] Similarly, by performing a linear regression on the extracted data, the processing unit 30 determines the speed of movement of the heat front in the plant from the direction coefficient of the linear line, this speed being determined from the reference point corresponding here to the position of the maximum temperature of the heat front.

[0124] The processing unit 30 is then configured to determine the sap flow from the speed of movement of the determined heat front, noted in the sequence Vh P .

[0125] In practice, the processing unit 30 uses Marshall's law defined by the following formula:

[0126] [Math. 3]

[0127] with p corresponding to the volumetric mass density, C the thermal capacity of the plant studied, p s corresponding to the density of the sap of the plant concerned, C s corresponding to the thermal capacity of the sap of the plant concerned, u corresponding to the sap flow. Typically, these parameters (p s , C s, C, p) can be determined, for each species, using a table giving these parameters as a function of the type of plant (extracted from literature data) or using a database accessible to the device 100 via a communication module 42 (described below). Typically, this table can be recorded in the memory of the processing unit 30 and can be updated using the communication module 42.

[0128] Optionally, for the thermal capacity of the plant studied C, the latter can also be determined from the following formula:

[0129] [Math. 4] C = Cw + me Cs

[0130] with Cw corresponding to the thermal capacity of the water determined by a table, me the water content of the plant concerned (determined by another device external to the device 100 or by an additional measurement carried out by the device 100 and Cs the capacity of the sap of the plant concerned).

[0131] The parameter a of the equation Math. 3 can be estimated from the following ratio:

[0132] [Math. 5] ™ Aves a = ~ n sw

[0133] with Aves corresponding to a section of the xylem vessels in which the sap flow is transported and A sw corresponding to the section of the part of the plant considered in the plant concerned.

[0134] In the case of a tree, this section A sw corresponds to the diameter (or section) of the sapwood of the plant and can be determined by the following formula:

[0135] [Math. 6]

[0136] with d sw corresponding to the section of the anatomical region (trunk, branch or root) without the outer envelope 2 (i.e. without the bark) of the plant concerned and wp corresponding to the section of the plant concerned. These parameters (d sw , d wp) are also recorded in a table stored in the memory of the processing unit 30 which can be updated via the communication module 42 or recorded in a database accessible to the device via the communication module 42. Alternatively, they can also be deduced by a histological study on the plant concerned or on a control plant assuming that there is little intra-species variability.

[0137] Thus, the processing unit determines the sap flow u of the plant from formula Math. 3 using a table as described above, formula Math. 4 and, optionally, formula Math. 5 as described above.

[0138] It is understood that the selected transverse profile is assimilated to the region of vessels that has been heated. This profile is chosen by identifying the maximum temperature. Therefore, the determined sap flow u corresponds to the sap flow of the group of vessels of the plant that has been heated and in which the maximum temperature has been previously determined. However, to facilitate the determination of the sap flow, it is considered that all the vessels in the part of the plant studied have the same section (or diameter) and that the sap flow propagates uniformly in this plant.

[0139] Optionally, the apparatus 100 illustrated in figure 2 comprises a focusing device 50, positioned between the microwave emitter 10 and the plant, and comprising at least one focusing lens 51 for focusing the microwave electromagnetic flux F on the outer envelope of the plant. In practice here, the focusing lens is configured to focus the microwave electromagnetic flux F at the focal point of the lens. Thus, it is understood that the first part 224 of the outer envelope is positioned in the focal plane of the focusing device 50.

[0140] Using a focusing device 50 makes it possible to increase the distance d3 separating the microwave transmitter 10 from the external envelope 2 of the plant. Thus, depending on the focusing lens used, the microwave transmitter 10 (here the antenna 11) can be positioned at a distance d3 greater than 10 mm.

[0141] Typically, the focusing lens may be a lens made of a selected dielectric material, e.g., polycarbonate, as described in Abd Rahman, Amirah and Kamardin, Kamilia and Yamada, Yoshihide and Takahashi, Masaharu, "Design Method of a Focusing Dielectric Lens Antenna and Temperature Increment Measurement at the Focusing Spot," http: / / dx.doi.org / 10.2139 / ssrn.4377519 .

[0142] These optical characteristics are adapted to the size of the device 100. Typically, the focusing device or here the focusing lens 51 can be, for example, positioned at a distance d5 from the external envelope 2 greater than 10 cm, preferably 30 cm, and less than 100 cm. For example, here, the distance d3 can be 50 cm and the distance d5 can be 30 cm.

[0143] Optionally, the apparatus 100 illustrated in FIG. 1 also comprises an electromagnetic flux sensor 60. In this case, the apparatus 100 is also configured to measure a water content in this plant.

[0144] In this embodiment, this electromagnetic flux sensor 60 is arranged to capture an electromagnetic flux reflected by said plant via an antenna operating here in reception.

[0145] The antenna of the electromagnetic flux sensor 60 corresponds here to the antenna 11 of the microwave transmitter 10. As a result, the antenna 11 forms (or more generally the microwave sensor 10 forms), in this embodiment, the electromagnetic flux sensor 60. It is thus understood that the antenna 11 of the apparatus 100 is therefore arranged, on the one hand, to operate in transmission to emit the microwave electromagnetic flux F and, on the other hand, to operate in reception to capture the microwave electromagnetic flux reflected by the first part 224 of the external envelope 2 of the plant.

[0146] As illustrated in Figure 2, the electromagnetic flux sensor 60, in particular the antenna 11, is also connected to the processing unit 30 to receive and analyze the electromagnetic flux reflected by the plant.

[0147] In this embodiment, the processing unit 30 is also arranged to determine from the reflected electromagnetic flux a water content of said plant.

[0148] Here, the processing unit 30 is arranged to determine a self-reflection coefficient then, from this self-reflection coefficient, determine the water content.

[0149] In practice, the processing unit 30 determines, from the reflected electromagnetic flux, a received power, noted Pr, by formulas known to those skilled in the art and then determines a reflection coefficient of the reflected microwave electromagnetic wave by calculating a ratio between the received power Pr and the power emitted Pe by the antenna 11.

[0150] The processing unit 30 then uses a table that links the self-reflection coefficient to the water content for determining the water content of the plant. In practice, this table is at least a function of the nature of the plant. It may also depend on the section of the plant (Le. type of herbaceous plant or type of woody plant) on which the emitted electrometric flux F is reflected.

[0151] It is thus understood that the memory of the processing unit 30 can comprise several pre-recorded tables for the different types of plants, that is to say for different classes of herbaceous plants and different classes of woody plants, each linking at least the self-reflection coefficient to a water content. It is also understood that these classes can be divided into subclasses in order to take into consideration the section of the plant on which the emitted electromagnetic flux F is applied.

[0152] These pre-recorded tables can be updated and / or completed via a communication module 42 included in the control unit 40 of the device 100. This communication module 42 is configured to transmit and receive data external to the device 100. For example, this communication module can comprise a transmitter and a receiver. In practice, the communication module 42 uses a wireless communication network, for example based on WIFI technology, and / or 2G / 3G / 4G / 5G technology and / or Bluetooth technology. Thus, this communication module can be connected to the internet and can thus be connected to databases external to the device 100 or to an external server.

[0153] The measurement of the water content does not require heating of the internal portion 331 of the plant 1 (because it relies on the measurement of a self-reflection coefficient). Therefore, the electromagnetic flux emitted by the microwave transmitter 10 and used for measuring the water content may be low, for example it may be greater than or equal to 0 dBm (i.e. 1 mW on a 50 Ohm load) and preferably less than or equal to 10 dBm, or may be similar to that emitted during the second time period (described above) and used to measure the sap flow.

[0154] Thus, in this embodiment, the measurement of the water content can be carried out independently of the measurement of the sap flow. Thus, it is possible to carry out the measurement of the water content before or simultaneously or after the measurement of the sap flow. In the case of a simultaneous measurement, the activation of the microwave transmitter 10 and the sensor thermal 20 is similar to that described above.

[0155] In a non-limiting manner, the apparatus 100 also comprises an orientation adjustment device 71 arranged to orient and maintain the microwave emitter 10 relative to the thermal sensor 20, here in particular facing the thermal sensor 20. It also comprises an orientation adjustment device 72 to orient the electromagnetic flux sensor 60 relative to the first part 224 of the external envelope 2 of the plant 1. Typically, these orientation adjustment devices may be manual or motorized. For this purpose, each orientation adjustment device may comprise adjustment rings and / or at least one electric motor to adjust the orientation of the different elements of the apparatus 100, here in particular at least the emitter 10 and the thermal sensor 20.

[0156] The apparatus 100 may also comprise a position adjustment device 71 arranged to adjust the position of the microwave emitter 10 relative to the plant (along at least one spatial direction, here at least in translation along the z axis of the orthonormal reference frame represented at 7), and optionally a position adjustment device 72 arranged to adjust the position of the thermal sensor 20 relative to the plant (along at least one spatial direction, here at least in translation along the z axis), and optionally a position adjustment device 71 (or 74) arranged to adjust the position of the electromagnetic flux sensor 60 (or 110) relative to the first part 224 of the outer envelope 2 of the plant 1 (along at least one spatial direction). Typically each position adjustment device may be manual or motorized.For this purpose, each position adjustment device may comprise adjustment rings and / or at least one electric motor arranged to adjust the position of the elements of the device 100, i.e. here at least the thermal sensor 20 and the microwave transmitter 10.

[0157] Advantageously, each position adjustment device and orientation adjustment device of the same element are connected to each other or form a single element (called position and / or orientation adjustment device) in order to adjust more precisely the position and / or orientation of the element in question of the apparatus 100. In practice, each position and / or orientation adjustment device is controlled by the control unit 41 in order to obtain the desired position and orientation.

[0158] It is thus understood that each position and / or orientation adjustment device may comprise a mobile support on which an element of the apparatus 100 may be mounted. These different mobile supports may each comprise a motor (or may be controlled by a single motor) or an adjustment ring for adjusting the position of the mobile support in question by translation along the z axis and / or by translation along the transverse axes x, y and for adjusting the orientation of the mobile support in question by rotation around the x, y and / or z axes.

[0159] Thus, it is possible to adjust and / or adapt the distance d3 between the microwave emitter 10 and the first part 224 of the outer envelope 2 of the plant 1 (or here the distance d5 between the focusing device 50 and the first part 224 of the outer envelope 2 of the plant), the distance d4 between the second part 226 of the outer envelope 2 of the plant and the thermal sensor 20. These distances can be adjusted before the emission of the electromagnetic flux F microwave or adjusted during the emission of the electromagnetic flux F microwave. Similarly, a distance (d3 or d6) between the electromagnetic flux sensor 60 (or 110 in FIG. 8) and the outer envelope 2 of the plant can also be adjusted.

[0160] In a non-limiting manner, the apparatus 100 comprises a support 90 on which at least the microwave transmitter 10 and the thermal sensor 20 are mounted. This support 90 may be a portable support 90. By portable, it is meant that the support 90 can be moved by a user, for example if this support is not included in a housing.

[0161] Here, in particular, the portable support 90 is fixed and can correspond to a tray on which the processing unit 30, the control circuit 40, the microwave transmitter 10, the thermal sensor 20, the orientation adjustment device, the position adjustment device and the electromagnetic flux sensor 60 are mounted.

[0162] It is thus understood that the mobile supports described above controlled in orientation and / or in position by the control unit 41 are positioned on the support 90 to move at least the microwave transmitter 10, the thermal sensor 20 and, optionally, the electromagnetic flux sensor 60 relative to the plant 1.

[0163] As illustrated in Figure 7, the support 90 may comprise a rail 91 on which are mounted a mobile support 71 of the microwave transmitter 10 (carrying the reflector 12), a mobile support 72 of the thermal sensor 20 (carrying here the thermal camera 21), and optionally a mobile support 73 of the focusing device 50. As explained above, these mobile supports may move in translation and / or may also each comprise means for adjusting the orientation (for example by adjusting three rotations) of the element that they carry while being controlled by the control unit 41. It is understood that this rail 91 may protrude from the portable support 90 or may be formed in the thickness of the support 90. Of course, in a variant not illustrated, this rail 91 may be broken down into two rails, each rail being included in a housing of the apparatus 100 which will be described below.

[0164] As illustrated in Figure 1, the device 100 may comprise a portable housing 101 in which the various elements of the device 100 are mounted. Typically here, this portable housing 101 has an internal volume arranged to accommodate the various elements of the device 100, i.e. here at least part of the microwave transmitter 10, the thermal sensor 20, the processing unit 30, the electromagnetic flux sensor 60 and all another element of the apparatus 100 described above.

[0165] As in this embodiment, the plant 1 is positioned between the microwave transmitter 10 and the thermal sensor 20, it is understood that this housing 101 can be broken down into several sub-housings 101 (figure 7), each of the sub-housings having an internal volume, the portable support 90 being part of each sub-housing.

[0166] Here typically, the apparatus 100 may comprise: - a first sub-housing 101a comprising at least the microwave transmitter 10, the movable support 71 of the microwave transmitter 10, a part of the intermediate element (corresponding to a part of the rail 91) and optionally the electromagnetic flux sensor 60, the movable support of the electromagnetic flux sensor (if distinct from the microwave transmitter 10), the focusing device 50 and the movable support 73 of the focusing device 50, - a second sub-housing 101b comprising at least the processing unit 30, optionally the control circuit 40, the thermal sensor 20 and the mobile support 72 of the thermal sensor 20, another part of the intermediate element (here of the rail 91).

[0167] Such a case therefore makes it possible to protect and concatenate the different elements of the device 100 while providing suitable protection for these elements. In practice, this case is waterproof and resistant to shocks below 10 shore A. This case 101 is also waterproof. It can be made of plastic.

[0168] The apparatus 100 may also comprise a holding device 104, corresponding here to a device for holding the support on the ground. Typically, this holding device may comprise a foot, similar to a portable tripod or casters.

[0169] The apparatus 100 also includes an internal power source (not shown) arranged to power the various electronic and motorized elements of the apparatus 100. This internal power source may be batteries or a rechargeable battery.

[0170] Alternatively, each electronic or motorized element may include its own power source.

[0171] In this case, the processing unit 30, the microwave transmitter, the thermal sensor and optionally the other elements of the devices 100 such as the electromagnetic flux sensor, the control circuit, and the position and / or orientation adjustment devices can be powered by their own energy sources.

[0172] As illustrated in Figure 11, the housing 101 may comprise a screen 43 connected to the control circuit 40 positioned on one of the faces of the housing 101. This screen 43 serves as a human-machine interface and is therefore suitable for receiving input data. For example, a user can select the measurement to be carried out. The input data may include the type of measurement to be carried out (measurement of flow and sap and / or water content), the use or not of the focusing device (if present in the device 100), an adjustment or not of the distances of the different elements (if this is not automatic), a selection of the method of calculating the sap flow, etc. This screen is also adapted to display output data. For example, it can display the results of the measurements (here of the water content and / or the measurement of the sap flow). This screen 43 can be tactile (illustrated case) or not. In this case, the box 101 can include control buttons for entering the input data.

[0173] Optionally, the device 100 also comprises a reference support configured to define a (fixed) distance d7, d5 between the microwave transmitter (or the antenna) and the external envelope 2 of the plant. Such a support makes it possible to define a fixed, reproducible and controlled distance which improves the reliability and producibility of the measurements, for example when the device is to be moved.

[0174] In one embodiment, this reference support may be an element or an object positioned between the microwave transmitter 10 and the external envelope 2 of the plant. Typically, this object may be of any shape, for example parallelepiped-shaped, such as a rectangle or a square, or be circular-shaped. In this case, this reference support may extend in a main direction oriented parallel to the length L2 illustrated in FIG. 3 so as to cover the antenna 11.

[0175] In order to ensure the heating of the internal portion, this reference support is transparent to the microwave electromagnetic flux emitted by the microwave transmitter 10. By transparent, it is meant here that the reference support is configured to allow the microwave electromagnetic flux to pass through (i.e. it does not block or modify the propagation of the microwave electromagnetic flux).

[0176] For this purpose, the material of the marker support is selected to be transparent to the microwave electromagnetic flux. For example, the marker support can be made from at least one of the following materials: a plastic material such as Polyethylene (PE), Polytetrafluoroethylene (PTFE), Polypropylene (PP); a ceramic material such as Alumina (AI2O3), quartz; a glass such as Borosilicate glass, fused quartz glass; a composite material such as fiberglass, polystyrene foam.

[0177] Alternatively, this reference support may correspond to an element of the device for adjusting the position of the microwave transmitter relative to the plant, for example a pin, arranged to block the distance between the microwave transmitter 10 (or the antenna) and the external envelope of the plant. Typically, in this case, the housing 101 may be fixed to the plant by fixing collars and when the position of the transmitter is chosen, the latter is fixed by this reference support.

[0178] We therefore understand that here, we position the device according to the plant (here the diameter of the plant) by adjusting the distance d7 or d5 defining the distance between the microwave transmitter or the antenna and the external envelope 2 then this distance d7, d5 is fixed via the reference support (the pawn) described above.

[0179] Optionally, the apparatus 100 also comprises a control device (or control circuit) configured to capture an electromagnetic flux reflected by said plant and modify the electromagnetic flux emitted (for example its power, its intensity) by the microwave transmitter as a function of the reflected electromagnetic flux. Indeed, here, it is understood that if the control device records a variation in the power of the electromagnetic flux, it adapts the emitted electromagnetic flux to obtain a power of the reflected electromagnetic flux.

[0180] Such a device makes it possible to correct a power setpoint to deposit the same energy on the plant (and therefore have the same amplitude of the "thermal" signal). In practice, this control device may comprise an electromagnetic flux sensor arranged to capture the electromagnetic flux reflected by the external envelope 2. Typically, this sensor may be the antenna 11. In this case, it is understood that the antenna 11 may operate in reception to carry out this measurement. Alternatively, this sensor may be an additional sensor (not illustrated) of the device 100 (or 200), for example a microwave antenna operating in reception. In addition, this control device may also comprise a directional coupler, such as that described on the page ;-their-i i-and- in order to achieve power control. In practice, this control device is included in the processing unit 30 described above.

[0181] A second embodiment of an apparatus 200 according to the present disclosure will now be described with the aid of FIG. 8. Only the differences with the apparatus 100 described above will be described.

[0182] The apparatus 200 illustrated in Figure 8 comprises the microwave transmitter 10 comprising an antenna 11 as described above, (optionally) a focusing device 50 similar to that of the device 100, a thermal sensor 20 similar to that of the device 100, a processing unit 30 similar to that of the device 100, a control circuit 40 as described above, a position and / or orientation adjustment device similar to those of the device 100 (being broken down into different movable supports as described in the apparatus 100), a support 90 as described above.

[0183] This apparatus 200 also comprises an electromagnetic flux sensor 110. Unlike the apparatus 100 described above, it can be seen that in this embodiment, the electromagnetic flux sensor 110 is oriented facing the second part 226 of the external envelope 2 crossed by the electromagnetic flux F. In other words, this means that the electromagnetic flux sensor 110 is positioned on the side by which the electromagnetic flux F is transmitted through the plant (side by which the electromagnetic flux leaves the plant).

[0184] Thus, in this embodiment, the electromagnetic flux sensor 110 is arranged to capture an electromagnetic flux transmitted by the plant 2 via an antenna 111 included in the electromagnetic flux sensor 110 and operating in reception.

[0185] In this embodiment, the antenna 111 is therefore a second antenna of the device 200 and is therefore distinct from the antenna 11 of the microwave transmitter 10. This antenna 110 forms the electromagnetic flux sensor 110.

[0186] Thus, in this variant, the device 100 comprises two antennas, an antenna 11 of the microwave transmitter 10 which operates in transmission and the antenna 111 of the electromagnetic flux sensor 110 which operates in reception.

[0187] This antenna 110 is connected to the processing unit 30, which in this embodiment is configured to receive and analyze the transmitted electromagnetic flux, corresponding here to the outgoing electromagnetic flux at the second part 226 of the external envelope 2 of the plant. Thus, in this embodiment, the processing unit 30 determines a water content of the plant from the electromagnetic flux transmitted by the plant.

[0188] In a similar manner to the first embodiment, the processing unit 30 is arranged to determine a transmission coefficient from the transmitted electromagnetic flux Pr captured by the antenna 111 and the power emitted Pe by the antenna 11 by making the ratio of these quantities, and, from this transmission coefficient, determine the water content.

[0189] Similar to the previous embodiment, the water content is determined using a table relating this transmission coefficient to the water content. As before, this table depends on the nature of the plant and may also depend on the section of the plant receiving the microwave electromagnetic flux emitted by the antenna 11.

[0190] Typically here, for the measurement of the water content, the plant is positioned between the microwave transmitter 10 and the electromagnetic flux sensor 110.

[0191] It is thus understood that in this embodiment, the measurement of the sap flow and the water content are carried out alternately since in this example the thermal sensor 20 and the electromagnetic flow sensor 110 must be positioned towards the second part 226 of the external envelope 2 of the plant crossed by the electromagnetic flow F. To this end, it is understood that the position and / or orientation adjustment device is configured to adapt the position of the thermal sensor and the electromagnetic flow sensor for each measurement, for example by moving the electromagnetic flow sensor out of the field of the thermal sensor when measuring the sap flow and vice versa by moving the electromagnetic flow sensor out of the field of the electromagnetic flow sensor. the thermal sensor.

[0192] The electromagnetic flow sensor can be positioned between the plant and the thermal sensor. Therefore, when measuring the sap flow, the electromagnetic flow sensor can be moved in the spatial directions x, y to move this sensor out of the field of the thermal sensor and conversely reposition the electromagnetic flow sensor facing the second part 226 of the outer envelope of the plant when measuring the water content. Therefore, during this water content measurement, the thermal sensor can simply be deactivated or put on standby. In this case, it is understood that the support 90 can comprise at least one other rail oriented perpendicularly (here in the spatial direction y) to the rail 91 oriented in the spatial direction z. These two rails can be connected.Alternatively, as illustrated in FIG. 9, the support 90 of the housing 101 b may comprise a curved rail 92 making it possible to move the mobile support 72 of the thermal sensor 20 and the mobile support 74 of the magnetic flux sensor 110. The support 90 may also comprise a mobile plate 93 controlled by the control circuit 40 to move this rail in translation along the spatial direction z. Such an arrangement makes it possible to limit the size of the device 200.

[0193] A third embodiment of an apparatus 300 according to the present disclosure will now be described with reference to FIG. 10. The apparatus 300 comprises all the elements of the apparatus 100, so only the differences with the apparatus 100 described above will be described.

[0194] Unlike the first embodiment, the thermal sensor 20 is positioned on the same side as the microwave emitter 10. Therefore, in this embodiment, the thermal sensor 20 is oriented opposite the first part 224 of the external envelope 2 of the plant irradiated by the microwave electromagnetic flux F. Typically, the thermal sensor 20 and the microwave emitter 10 can be positioned on a curved rail (as described in FIG. 8). In the case of using a focusing device 50, the latter can be positioned on another rail positioned between the plant and the rail carrying the microwave emitter and the thermal sensor. These two rails can also be positioned on a movable plate adjusting a position of the elements in the housing 101a along the spatial direction z (as described in FIG. 8).

[0195] However, the function of the apparatus 300 is similar to that described in Figure 2.

[0196] In this embodiment, the holding device 104 may be similar to that described above or be a device for holding the apparatus to the plant, for example using holding rings or holding clips;

[0197] Such an arrangement can in particular be used when the plant subject to measurement has a sufficient section, for example a section greater than 2.0 cm. Indeed, in this case, the internal portion 331 is closer to the first part 224 of the envelope external 2 than the second part 226 of the external envelope 2.

[0198] Variants

[0199] The present invention is in no way limited to the embodiments described and shown, but those skilled in the art will be able to provide any variation in accordance with the invention. Typically, it is understood that the apparatus 300 illustrated in FIG. 10 can use, instead of the electromagnetic flow sensor 60 of the apparatus 100, the electromagnetic flow sensor 110 of the apparatus 200. Such an arrangement allows, as in the case of the apparatus 100, simultaneous measurement of the sap flow and the water content.

[0200] As illustrated in Figure 12, the invention also relates to a method 400 for measuring at least one sap flow in a plant. Typically, this method 400 is implemented by any of the devices described above.

[0201] The method 400 comprises a step of emission E1 by the microwave transmitter 10 of an electromagnetic flux F microwave in the direction of the first part of the external envelope of said plant so as to heat an internal portion of said plant.

[0202] The method 400 also comprises a step E2 of capturing by the thermal sensor 20 the thermal radiation of said plant over time as described, for example, in the device 100.

[0203] The method 400 also comprises a step E3 of determining, by the processing unit 30, the displacement of the heat front over time in said plant from the thermal radiation captured by the thermal sensor 20 and a step E4 of estimating, on the basis of the displacement of the heat front, the sap flow.

[0204] When the device also comprises an electromagnetic flux sensor, the method 100 may also comprise a step E5 of capturing the electromagnetic flux reflected or transmitted by the plant and a step E6 of determining, by the processing unit 30, a water content from the reflected or transmitted electromagnetic flux. As specified above, this capturing step E5 may be carried out by the antenna 11 or by another antenna 111 operating only in reception.

Claims

CLAIMS 1. Portable apparatus (100, 200, 300) for measuring at least one sap flow in a plant (1), said plant having an external envelope (2), said apparatus (100, 200, 300) comprising: - a microwave transmitter (10) for emitting a microwave electromagnetic flux towards a first part (224) of the external envelope (2) of said plant (1) so as to heat an internal portion (331) of said plant (1); - a thermal sensor (20) arranged to capture thermal radiation from said plant (1) over time; - a processing unit (30) configured to determine, from the thermal radiation captured by the thermal sensor (20), a displacement of the heat front over time in said plant (1) and to estimate, on the basis of the displacement of the heat front, the flow of sap.

2. Apparatus (100, 200, 300) according to claim 1 comprising an electromagnetic flux sensor (60, 110) arranged to capture the electromagnetic flux reflected or transmitted by the plant, said processing unit (30) being configured to determine, from the reflected or transmitted electromagnetic flux, a water content of said plant.

3. Apparatus (100, 200, 300) according to claim 2, in which the processing unit (30) uses, for determining the water content of the plant, a table linking a self-reflection or transmission coefficient of said plant to a water content, said table being a function of the nature of the plant.

4. Apparatus (100, 300) according to any one of claims 2 and 3, wherein the microwave transmitter comprises an antenna operating, on the one hand, in transmission to transmit the microwave electromagnetic flux and, on the other hand, in reception to capture the electromagnetic flux reflected by said plant and thus form said electromagnetic flux sensor.

5. Apparatus (100, 200, 300) according to any one of claims 1 to 4 comprising a focusing device (50) arranged to focus said electromagnetic flux on the first part of the external envelope of the plant.

6. Apparatus (100, 200, 300) according to any one of claims 1 to 5, wherein the microwave transmitter comprises a bi-quad antenna (11).

7. Apparatus (100, 200, 300) according to any one of claims 1 to 6, wherein the electromagnetic flux is emitted at a frequency between 1 GHz and 200 GHz.

8. Apparatus (100, 200, 300) according to any one of claims 1 to 7, wherein the electromagnetic flux emitted by the microwave transmitter (10) is a pulsed electromagnetic flux.

9. Apparatus (100, 200, 300) according to any one of claims 1 to 8, wherein the thermal sensor (20) is included in a thermal camera (21) arranged to acquire a video stream of the thermal radiation, said displacement of the heat front being determined from this video stream.

10. Apparatus (100, 200, 300) according to any one of claims 1 to 9 comprising a control circuit (40) arranged to activate and deactivate the microwave transmitter (10) and the thermal sensor (20), said activation of the microwave transmitter (10) and the thermal sensor (20) being carried out asynchronously.

11. Apparatus according to claim 9, wherein, during a time period, the microwave transmitter (10) and the thermal sensor (20) are activated.

12. Apparatus (100, 200, 300) according to any one of claims 1 to 11 comprising a reference support arranged to define a distance between the microwave emitter (10) and the external envelope (2) of said plant (1).

13. Apparatus (100, 200, 300) according to any one of claims 1 to 12 comprising an orientation adjustment device (71) arranged to orient and maintain the microwave transmitter (10) relative to the thermal sensor (20).

14. Apparatus (100, 200, 300) according to any one of claims 1 to 13 comprising a position adjustment device (71) arranged to adjust the position of the microwave emitter (10) relative to the plant and to adjust the position of the thermal sensor (20) relative to the plant.

15. Apparatus according to any one of claims 1 to 14 comprising a portable support (90) on which are mounted at least the microwave transmitter (10) and the thermal sensor (20), and optionally further comprising: - a portable housing (101) associated with the portable support (90) and accommodating at least part of the microwave transmitter (10) and at least part of the thermal sensor (20), the processing unit (30), - a device (104) for holding the support (90) on the ground or on said plant.

Images