Plant sensor device and active optical measurement method for plants

Abstract

The present invention aims to provide a plant sensor device that can quantify the growth rate of plants by suppressing the influence of ambient light and determining parameters related to the leaf mass of plants in a simple and low-cost configuration, and that can calculate the leaf area index with higher accuracy. [Solution] The present invention relates to a plant sensor device comprising: a group of two or more light sources that intermittently emit light rays toward a plant; a radiation sensor positioned on the opposite side of the plant from the group of light sources and on the optical axis of the light rays, which receives the transmitted light of the light rays that have passed through the plant and outputs an output value converted by photoelectricity; and a recording unit that records the output value from the radiation sensor, wherein the recording unit classifies the output value from the radiation sensor into (1) an irradiated output value during the light ray irradiation period and (2) a non-irradiated output value during the light ray extinction period.

Description

[Technical Field]

[0001] The present invention relates to a plant sensor device and an active optical measurement method for plants. [Background technology]

[0002] In recent years, with the advancement of data-related technologies, there has been a growing need to quantify the degree of plant growth. Known indicators of plant growth include the Leaf Area Index (LAI) and the fAPAR (fAPAR). For example, the Leaf Area Index is an index value that shows the sum of the area of ​​one side of all leaves of the vegetation above a unit horizontal area. For example, 1m 2 The total surface area of ​​leaves above ground is 2m 2 If so, LAI=2, meaning that when the leaves are laid out on the ground without any gaps, two leaves will overlap. The leaf area index for typical forest vegetation is around 3 to 7. The leaf area index is an important parameter for evaluating vegetation function and is widely used in agriculture, forest science, ecology, and global environmental science as an important indicator of photosynthetically active radiation absorption, photosynthetic capacity, transpiration rate, and the carbon absorption capacity of vegetation.

[0003] Patent Document 1 describes an optical vegetation index sensor comprising: a first radiation sensor that, upon receiving transmitted radiation transmitted through a leaf or foliage, corrects the spectral characteristics of the radiation in the visible radiation region of 400 nm to 700 nm using a correction filter to measure it in terms of photon flux density, and outputs a PAR output indicating either photosynthetically effective radiance or photosynthetic photon flux density by photoelectric conversion of the corrected radiation at the light receiving unit; a second radiation sensor that extracts radiation only in the infrared radiation region of 700 nm to 1000 nm from the received radiation using a bandpass filter, and outputs an NIR output indicating either radiance or photon flux density in units common to the PAR output by photoelectric conversion of this radiation at the light receiving unit; and a calculation unit that integrates the PAR output and the NIR output over time, calculates a ratio by dividing the integrated value of the NIR output by the integrated value of the PAR output, and calculates a leaf area index corresponding to the ratio. Furthermore, the optical vegetation index sensor described in Patent Document 1 utilizes the known correlation between the spectral intensity ratio Y (=800 / 675) of red radiation (wavelength 675 nm) and near-infrared radiation (wavelength 800 nm) that has passed through the vegetation, and the leaf area index X, with logY = 0.3813 + 0.0989X, and can be described as a "transmission NIR / PAR method".

[0004] Furthermore, Patent Document 1 describes other methods for determining the leaf area index, such as the "fisheye lens method," which uses a circular fisheye lens and an electronic image sensor to capture images of predetermined regions for near-infrared radiation and red radiation, and estimates the relative solar radiation by calculating the ratio of their brightness values; and the "plant canopy analyzer" (LAI-2000, etc.) developed by LI-COR in the United States, which optically divides the entire sky into five ring-shaped sections and measures the intensity distribution of blue radiation across the entire sky.

[0005] On the other hand, methods for optically determining growth conditions other than the leaf area index are known, and these can be divided into methods using transmitted light (similar to Patent Document 1), methods using scattered light (Patent Document 2), and methods using reflected light (Patent Document 3). Patent Document 2 describes a plant community transmitted light sensor unit used to determine the growth state of plants, comprising a visible light sensor for detecting visible light and a near-infrared light sensor for detecting near-infrared light, the plant community transmitted light sensor unit comprising a transparent pipe and a pair of black cover plates that close both ends of the pipe, wherein the visible light sensor and the near-infrared light sensor are mounted on the lower surface of the upper cover plate at the inner center of the pipe with their light-receiving surfaces facing downward when the pipe is standing upright in the vertical direction.

[0006] Patent Document 3 describes a plant sensor device comprising: a first light-emitting unit that emits a first measurement light of a first wavelength to irradiate a target for measuring the growth status; a second light-emitting unit that emits a second measurement light of a second wavelength to irradiate a target for measuring the growth status; a light-receiving unit that receives the reflected light of each measurement light from the target for measuring the growth status and outputs a light-receiving signal; a control unit that controls the emission of light from the first light-emitting unit and the second light-emitting unit at different timings; an optical path merging means that merges a first emission optical path of the first measurement light from the first light-emitting unit and a second emission optical path of the second measurement light from the second light-emitting unit; and a common emission optical path that connects the optical path merging means and an emission unit that emits the first measurement light and the second measurement light toward the target for measuring the growth status, wherein the emission unit has an optical member that has refractive power in only one direction when viewed in a plane perpendicular to the emission optical axis, and the optical member is held so as to be rotatable around the emission optical axis.

[0007] The present inventors have developed a method for classifying and recording output values ​​during the irradiation and extinction periods of near-infrared light from a radiation sensor, as an apparatus that achieves further cost reduction and high precision (Patent Document 4). Patent Document 4 discloses a light source that intermittently irradiates plants with near-infrared light (NIR), and a method for calculating a leaf area index from output values ​​obtained by receiving transmitted near-infrared light that has passed through the plant and converting it into photoelectric light, with the light source positioned on the opposite side of the plant from the light source. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2011-133451 [Patent Document 2] Patent No. 5410323 [Patent Document 3] Patent No. 5718153 [Patent Document 4] Japanese Patent Publication No. 2023-172610 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, the optical vegetation index sensor described in Patent Document 1 requires a total of two expensive radiation sensors equipped with filters, thus necessitating further cost reduction. The accuracy of the transmitted NIR / PAR method depends on the spectral stability of incident sunlight (solar radiation), but the NIR / PAR of incident solar radiation can fluctuate by more than 10% depending on sky conditions. Furthermore, with light sources other than sunlight, the NIR / PAR of the incident light fluctuates significantly, and is affected by the surrounding environment inside greenhouses, making it particularly difficult to use in artificial light environments. Regarding the other methods described in Patent Document 1, the fisheye lens method had the problem of not being able to use images from sunny days. LI-COR's plant canopy analyzer had the problem of not being usable in environments with large fluctuations in solar radiation or artificial light environments, as it required simultaneous measurements in both the in-forest and out-of-forest environments during cloudy days. The device described in Patent Document 2 also includes a total of two expensive sensors: a visible light sensor and a near-infrared light sensor. Furthermore, it requires black cover plates on the top and bottom to detect scattered light, and a second cover plate is needed for a horizontal configuration, resulting in a complex device configuration. In addition, Patent Document 2 describes canceling data from cloudy or rainy days to eliminate the effects of fluctuations in solar radiation, which presents a problem as the device is affected by ambient light. Therefore, further cost reduction and increased accuracy were required. Devices that detect reflected light using an irradiation sensor (light-receiving unit), such as those described in Patent Document 3, detect two types of measurement light with different wavelengths using a light-receiving unit formed by 2 to 6 photodiodes, in order to remove the effects of ambient light through calculation. Furthermore, in order to detect the reflected light from the two types of measurement light, the device configuration was complex, requiring an optical element (lens) with a refractive index that is held so as to be rotatable around the optical axis in the light source (emitting unit). Therefore, further cost reduction was required. The plant sensor disclosed in Patent Document 4 is capable of calculating the degree of plant growth with a simple and low-cost configuration by suppressing the influence of ambient light, and obtaining parameters related to the amount of leaves of plants. However, because it uses a single light source, there was a problem in that the calculated leaf area index had a large variation. Therefore, there was a need for the development of a plant sensor device that could calculate the leaf area index with higher accuracy.

[0010] The problem that this invention aims to solve is to provide a plant sensor device that can quantify the degree of plant growth by suppressing the influence of ambient light and determine parameters related to the amount of leaves of plants in a simple and low-cost configuration, and that can calculate the leaf area index with higher accuracy. [Means for solving the problem]

[0011] Examples of specific embodiments of the present invention are shown below.

[0012] [1] A group of light sources comprising two or more light sources that intermittently emit rays of light toward plants, A radiation sensor is positioned on the opposite side of the light source from the plant and on the optical axis of the light ray, receiving the transmitted light from the light ray that has passed through the plant and outputting a photoelectric value converted into an output value. It has a recording unit that records the output value from the radiation sensor, A plant sensor device in which the recording unit classifies the output values ​​from the radiation sensor into (1) irradiation output values ​​during the light irradiation period and (2) non-irradiation output values ​​during the light extinction period. [2] The plant sensor device according to [1], wherein the light ray is near-infrared light (NIR). [3] The plant sensor device described in [2], wherein the light source group consists only of near-infrared light sources. [4] The plant sensor device according to [3], wherein the near-infrared light source emits narrowband near-infrared light with a peak wavelength of 750 to 1100 nm and a full width at half maximum of 50 nm or less. [5] The light beam is emitted towards the radiation sensor, The plant sensor device according to any one of [1] to [4], wherein a plurality of optical axes irradiated from the light source group have different incident angles with respect to the radiation sensor. [6] The plant sensor device according to any one of [1] to [5], wherein the average distance between the light sources constituting the light source group is 20 mm or more. [7] The plant sensor device according to any one of [1] to [6], further comprising an arithmetic unit that calculates a difference A calculated from (irradiation output value) - (non-irradiation output value), and further converts the difference A into a leaf area index. [8] The plant sensor device according to [7], further comprising a growth control means for controlling at least one of fertilizer, moisture, temperature, and humidity so as to suppress the growth of the plant leaves when the leaf area index exceeds a predetermined range, or to promote the growth of the plant leaves when the leaf area index is below the predetermined range. [9] The plant sensor device according to any one of [1] to [8], wherein the output value in the intermediate period of 25 to 75% with respect to 100% from the start point to the end point of each of the irradiation period and the extinction period is used as the irradiation output value and the non-irradiation output value.

[10] The plant sensor device according to any one of [1] to [9], wherein the irradiation period and the extinction period are each 0.1 milliseconds to 1 minute.

[11] The plant sensor device according to any one of [1] to

[10] , wherein the plant is a leaf group or a plant community.

[12] The plant sensor device according to any one of [1] to

[11] , further comprising a radiation sensor fixing part for fixing the radiation sensor, a light source fixing part for fixing the light source, and a connecting member for connecting the radiation sensor fixing part and the light source fixing part.

[13] An active optical measurement method for plants using the plant sensor device according to any one of [1] to

[12] .

[14] The active optical measurement method for plants according to

[13] , which is used for ground truth of remote sensing from the air or space, plant growth measurement in a plant growth facility, vegetation measurement in a forest, or leaf amount measurement of a plant community or a leaf group. [Effects of the Invention]

[0013] According to the present invention, a plant sensor device is available that can quantify the growth rate of plants by suppressing the influence of ambient light and obtaining parameters related to the leaf mass of plants in a simple and low-cost configuration, and that can calculate the leaf area index with higher accuracy. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic diagram illustrating an example of the plant sensor device of the present invention. [Figure 2] Figure 2 is a schematic diagram illustrating another example of the plant sensor device of the present invention. [Figure 3] Figure 3 is a schematic diagram illustrating another example of the plant sensor device of the present invention. [Figure 4] Figure 4 is a graph showing the relationship between time from the measurement disclosure and the photon flux density (output value) in Example 1. [Figure 5] Figure 5 is a graph showing the relationship between leaf area index and 850nm transmittance in indoor and outdoor measurements. [Figure 6] Figure 6 is a schematic diagram illustrating the arrangement of light sources that make up the light source group used in the test example. [Figure 7] Figure 7 is a schematic diagram illustrating the arrangement of light sources that make up the light source group used in the test example. [Figure 8] Figure 8 is a schematic diagram illustrating the structure of the foliage group model (plant individual model) used in the test example. [Modes for carrying out the invention]

[0015] The present invention will be described in detail below. The following descriptions of constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits.

[0016] [Plant Sensor Device] This embodiment relates to a plant sensor device comprising a group of light sources having two or more light sources that intermittently emit light rays toward a plant, a radiation sensor positioned on the opposite side of the plant from the group of light sources and on the optical axis of the light rays, which receives the transmitted light rays that have passed through the plant and outputs an output value converted into photoelectric value, and a recording unit that records the output value from the radiation sensor. In the plant sensor device of this embodiment, the recording unit classifies the output value from the radiation sensor into (1) the irradiation output value during the light ray irradiation period and (2) the non-irradiation output value during the light ray extinction period.

[0017] Because the plant sensor device of this embodiment has the above configuration, it can quantify the growth rate of plants by suppressing the influence of ambient light and can determine parameters related to the leaf mass of plants with a simple and low-cost configuration. By using the plant sensor device of this embodiment, measurements can be performed while minimizing the influence of day and night, indoors and outdoors, and the surrounding environment, and calibration is also easy. Furthermore, since the plant sensor device of this embodiment can perform non-destructive testing, it is superior to conventional destructive testing methods such as the mowing method (a method of plucking all the leaves on a plant and calculating the leaf area index from the total value) in that it can measure plants in their vegetation state.

[0018] In this embodiment, the light source group comprises two or more light sources, and one radiation sensor is provided on the optical axis of the light rays emitted from these light sources. This makes it possible to obtain an output value that averages the spatial structure of the leaf group, thereby suppressing variability in the calculated leaf area index and enabling the calculation of the leaf area index with higher accuracy. Furthermore, by arranging multiple light sources, it is possible to sample the spatial arrangement structure of the heterogeneous plant leaves being measured and then calculate the leaf area index. In addition, in this embodiment, since the light source group comprises two or more light sources, spatial sampling can be performed efficiently, and the time required for measurement can be reduced.

[0019] In this specification, the term "leaf mass" of a plant includes not only growth conditions such as LAI, vegetative density, and above-ground biomass, but also physiological functions such as chlorophyll content, photosynthetic activity, aging, and stress response of the leaves.

[0020] <Overview of the plant sensor device> The general outline of the plant sensor device of this embodiment will be described with reference to the drawings. However, this embodiment is not to be interpreted as being limited by the drawings. Figure 1 is a schematic diagram showing a cross-section of an example of a plant sensor device according to this embodiment. The plant sensor device 100 shown in Figure 1 includes a light source group 11 that intermittently irradiates a plant 1 (a canopy, specifically a group of leaves) with near-infrared light 12, a radiation sensor 21 positioned on the opposite side of the plant 1 from the light source group 11 and on the optical axis of the light ray, which receives the transmitted light 13 of the near-infrared light that has passed through the plant 1 and outputs an output value converted by photoelectric conversion, and a recording unit 31 that records the output value from the radiation sensor 21. The light source group 11 comprises two or more light sources 10, and a light ray is emitted from each light source 10 toward one radiation sensor 21. Thus, in this embodiment, one radiation sensor 21 is positioned on the optical axis of the light ray emitted from the light source group 11 comprising multiple light sources 10, thereby enabling the calculation of parameters related to the amount of leaves of a plant with greater accuracy in a simple and low-cost configuration.

[0021] In the plant sensor device 100 shown in Figure 1, the recording unit 31 classifies the output values ​​from the radiation sensor 21 into (1) irradiation output values ​​during the light irradiation period and (2) non-irradiation output values ​​during the light extinction period. The recording unit 31 may also record the irradiation period and extinction period of near-infrared light from the light source group 11. The plant sensor device 100 shown in Figure 1 includes, in addition to the recording unit 31, an optional calculation unit 32 and control unit 33 inside the computer 30. The calculation unit 32 and control unit 33 may be part of the CPU 34. Furthermore, the computer 30 may be connected to an optional display unit 35, which can display arbitrary calculation results and other information. The computer 30 may also be connected to an external output unit 36, which can output data to another PC or printer. The computer 30 may also be equipped with input means (not shown). The input means may be used to store arbitrary programs in the recording unit 31 (such as memory). For example, a program for calculating the growth rate of plants in the calculation unit, or a program for controlling the growth means in the control unit, may be pre-stored in the recording unit 31. Furthermore, programs on external memory, networks, or the cloud may be operated by the computer 30 via the input means or output unit 36 ​​and controlled by the control unit. The plant apparatus shown in Figure 1 includes a growth means 51, which may be optionally provided. The growth means 51 can control at least one of fertilizer, water, temperature, and humidity to suppress the growth of the leaves of plant 1 when the leaf area index exceeds a predetermined range, or to promote the growth of the leaves of plant 1 when the leaf area index falls below a predetermined range.

[0022] The plant sensor device 100 of this embodiment may include a light source fixing unit 41 for fixing the light source group 11, as shown in Figure 2. In Figure 2, the light source fixing unit 41 fixes the light source group 11 above the measurement unit of the plant 1. In addition, it is preferable that the radiation sensor 21 in the plant sensor device 100 includes a bandpass filter 23, and the radiation sensor 21 may be fixed by a radiation sensor fixing unit 42. In Figure 2, the radiation sensor fixing unit 42 fixes the radiation sensor 21 below the measurement unit of the plant 1 with its light-receiving surface 22 facing the measurement unit. Furthermore, the plant sensor device 100 may include a connecting member 43 that connects the radiation sensor fixing unit 42 and the light source fixing unit 41, and the distance L from the light source group 11 to the light-receiving surface 22 of the radiation sensor 21 can be arbitrarily adjusted by the connecting member 43 exhibiting an extension and retraction function. The distance L from the light source group 11 to the light-receiving surface 22 of the radiation sensor 21 can be appropriately adjusted according to the size and shape of the plant 1. The distance L may be, for example, 1 cm or more, 5 cm or more, or 10 cm or more. Furthermore, there is no particular upper limit to the distance L, but for example, it may be 50 m or less, or 10 m or less.

[0023] The plant sensor device 100 may include a connecting member 43 that connects the light source group 11 and the radiation sensor 21. As shown in Figure 2, the connecting member 43 may connect a light source fixing part 41 that fixes the light source group 11 and a radiation sensor fixing part 42 that fixes the radiation sensor 21, or it may directly connect the light source group 11 and the radiation sensor 21. Furthermore, a gripping part 44 may be provided when the plant sensor device 100 is operated while being held. In this case, the plant sensor device 100 can also be used as a handheld plant sensor device that can be held by a person.

[0024] Furthermore, the plant sensor device 100 may include a display unit 35 that displays the LAI value and other information externally. The display unit 35 may be connected, for example, to the light source group 11 or the light source fixing unit 41. Note that in the plant sensor device 100 shown in Figure 2, the recording unit and CPU (including the calculation unit and control unit) shown in Figure 1 are omitted.

[0025] In the plant sensor device 100 of this embodiment, as shown in Figure 3, the relative positions of the light source group 11 and the radiation sensor 21 may be inverted vertically (the light source group 11 is positioned below). The plant sensor device 100 shown in Figure 3 is suitable for use as a large-scale device, for example, when broad-leaved trees are used as the measurement target for plant 1, and a portion of the leaf cluster of the broad-leaved tree is used as the measurement area. Note that even in the plant sensor device shown in Figure 3, the recording unit and CPU (including the calculation unit and control unit) are omitted.

[0026] In this embodiment, the plant sensor device 100 may be configured such that the light source group 11 and the radiation sensor 21 are not connected. For example, when measuring large plants such as trees or forests, the light source group 11 and the radiation sensor 21 are not connected, and a wide area can be measured by placing each component in a predetermined location. In such cases, the light source group 11 may be connected to another support, or it may be connected to a flying object such as a drone or a robot, and measurements may be performed from above or in space.

[0027] <Plant> There are no particular restrictions on the plants to be measured in this embodiment. Examples of plants include trees, grasses, mosses, ferns, and algae. Among these, it is preferable to measure leaf groups or plant communities, more preferable to measure plants that have chlorophyll, and even more preferable to measure trees and grasses that have flat leaves. Examples of trees include deciduous and evergreen conifers and broad-leaved trees. In this embodiment, it is preferable to measure conifers or broad-leaved trees with a low ratio of branches to leaves. Examples of plants include wild grasses, crops (including those grown for their fruits such as strawberries and watermelons), and horticultural plants (including those grown for their flowers). It is particularly preferable to measure vegetables grown in open fields, vegetables and horticultural plants grown in greenhouses, and vegetables and horticultural plants grown under artificial light in vegetable factories, etc.

[0028] The plant may be measured as a single specimen or as multiple specimens. Furthermore, when measuring multiple specimens, the plant species may be only one or multiple species. When measuring a single specimen, it is preferable to measure the foliage. When measuring multiple specimens, it is preferable to measure the foliage or plant community. In this embodiment, only a portion of the plant may be used as the measurement area. In particular, when measuring large plants such as trees or forests, or when measuring multiple specimens of small plants, it is preferable to measure only a portion of the plant.

[0029] Plants may be measured as they are in their vegetation state, or a portion of the plant may be taken as the measurement target. In this embodiment, it is preferable to measure plants as they are in their vegetation state. The plant sensor device of this embodiment is superior in that it can measure plants as they are in their vegetation state, unlike conventional destructive testing methods such as the mowing method (a method in which all leaves on a plant are removed and the leaf area index is calculated from the total number of leaves). When used as an optical sensor in the food industry, commercially available leafy vegetables may be used as the measurement target.

[0030] <Light source group> The plant sensor device of this embodiment includes a light source group comprising two or more light sources that intermittently emit light rays toward plants. The wavelength of the light rays emitted from the light source group is not particularly limited and may be near-infrared light (NIR), visible light, or the like. In particular, the light rays emitted from the light source group are preferably near-infrared light (NIR). The light source group may include a near-infrared light source and a light source with a wavelength other than near-infrared, but from the viewpoint of cost reduction, it is preferable that the light source group be composed only of near-infrared light sources. In this case, the light source group will be composed of multiple near-infrared light sources.

[0031] When the light emitted from a group of light sources is near-infrared (NIR) light, it is preferable that the near-infrared light source emits narrow-band near-infrared light with a peak wavelength of 750 nm to 1100 nm and a full width at half maximum of 50 nm or less. Such near-infrared light is preferable from the viewpoint of easily suppressing the influence of ambient light in the surrounding environment. Furthermore, in order to suppress the influence on plant photoreceptors and the influence due to differences in leaf water content, it is even more preferable to irradiate with near-infrared light with a peak wavelength of 800 to 900 nm. There are no particular restrictions on the type of such near-infrared light source, but examples include LEDs and lasers, with LEDs being preferred. A specific preferred near-infrared light source is an LED with a peak wavelength of about 850 nm. For example, LEDs commercially available for security camera use may be repurposed as the near-infrared light source for a plant sensor device. Near-infrared light with a peak wavelength of 750 nm to 1100 nm is preferable because it has little influence from absorption by plant-containing pigments (such as chlorophyll and carotene). Furthermore, near-infrared light above 800 nm is preferable because it is less affected by absorption by plant photoreceptors (phytochrome). Chlorophyll has two absorption bands, mainly absorbing blue light (400 nm to 500 nm) and red light (600 nm to 700 nm). There are also two types of phytochrome: Pr, which has an absorption wavelength center at 660 nm, and Pfr, which has an absorption wavelength center at 730 nm. Both types convert light and affect plant growth. Near-infrared light with a peak wavelength of 750 nm to 1100 nm is also preferable from the standpoint that it is less affected by ambient light noise from artificial light sources.

[0032] Light rays are emitted toward the radiation sensor. In this case, it is sufficient that the optical axis of the light rays is directed toward the radiation sensor, and it is preferable that the aforementioned plants are located on at least one of the multiple optical axes. In this embodiment, it is preferable that the radiation sensor is capable of receiving transmitted light and light rays from multiple directions, and it is preferable that the multiple optical axes irradiated from the light source group have different angles of incidence relative to the radiation sensor. If the light source group is equipped with three or more light sources, it is sufficient that the angles of incidence of the optical axes of the light rays emitted from two of the three or more light sources are different, and it is also possible that there are light sources that emit light rays with the same angle of incidence. By having multiple optical axes irradiated from the light source group have different angles of incidence relative to the radiation sensor, it is possible to obtain an output value that averages the spatial structure of the foliage, thereby suppressing variability in the output values ​​of parameters related to the amount of leaves of plants, such as LAI, and enabling calculation with higher accuracy.

[0033] The angle of incidence of the optical axis to the radiation sensor is the angle with respect to a line perpendicular to the horizontal plane passing through the center point of the radiation sensor, where the horizontal plane is the interface. The maximum value of the angle of incidence is preferably 60° or less, and more preferably 45° or less. The difference between the minimum value and the maximum value of the angle of incidence is preferably 1° or more, more preferably 2° or more, and even more preferably 3° or more. The difference between the minimum value and the maximum value of the angle of incidence is preferably 60° or less, and more preferably 50° or less.

[0034] The two or more light sources constituting the light source group may be arranged in a straight line (on the x-axis) or on a plane (on the xy-plane). It is preferable that the distance between the center point of the radiation sensor and each light source is approximately constant.

[0035] The average distance between two or more light sources constituting a light source group can be appropriately adjusted according to the size and shape of the plant being measured, but for example, it is preferably 20 mm or more, more preferably 25 mm or more, even more preferably 30 mm or more, even more preferably 40 mm or more, even more preferably 50 mm or more, even more preferably 60 mm or more, and particularly preferably 70 mm or more. Furthermore, the average distance between light sources is preferably 2000 mm or less. If the number of light sources constituting a light source group is three or more, the distances between the light sources do not all have to be the same, but they may be approximately the same. The average distance between light sources can be determined by measuring the distance between each light source and calculating the average value. By keeping the average distance between light sources within the above range, it is possible to suppress variations in parameters related to the leaf mass of plants, such as LAI, and calculate with higher accuracy.

[0036] The number of light sources constituting a light source group may be two or more, preferably three or more, more preferably four or more, and even more preferably five or more. Furthermore, there is no particular upper limit to the number of light sources constituting a light source group, but it is preferably 300 or less, more preferably 250 or less, and even more preferably 200 or less. By setting the number of light sources to be above the lower limit, it becomes easier to average the spatial structure of the foliage group, suppressing variability in parameters related to plant leaf mass, such as LAI, and enabling more accurate calculation. Additionally, by setting the number of light sources to be below the upper limit, the plant sensor device can be made lighter, increasing the flexibility of the measurement method.

[0037] In this embodiment, it is preferable to simultaneously emit light from the light source group and simultaneously extinguish the light source when extinguishing it. By simultaneously emitting and extinguishing the light source, an averaged output value of the plant's spatial structure can be obtained in one step, and at the same time, variability in plant leaf mass parameters such as LAI can be suppressed, making it easier to calculate with higher accuracy. On the other hand, when emitting light from the light source group, each light source may be emitted sequentially with a time difference and then extinguished sequentially. In this case, although the number of measurements increases in order to obtain the output value for each individual light source, it becomes possible to obtain more accurate leaf group spatial distribution information by utilizing the variance information of the obtained measurement values.

[0038] <Radiation sensor> The plant sensor device of this embodiment has a radiation sensor that is positioned on the opposite side of the plant from the light source group and on the optical axis of the light ray, and receives the transmitted light of the light ray that has passed through the plant and outputs an output value converted by photoelectricity. In this embodiment, it is preferable that the plant sensor device has only one radiation sensor. By positioning only one radiation sensor for multiple light sources in this way, it becomes possible to determine parameters related to the leaf volume of the plant in a simple and low-cost configuration.

[0039] The shape of the radiation sensor is not particularly limited, as long as it can receive transmitted light that has passed through plants and light rays that have not passed through plants. For example, it may be cylindrical, hemispherical, or rod-shaped, allowing transmitted light and light rays to be received from all directions. In this embodiment, since transmitted light is used rather than reflected light that is produced when light rays are reflected when irradiated onto plants, it is possible to reflect the properties of a specific part of the vegetation, including the average effects of light scattering and reflection within the vegetation. Furthermore, by increasing the area of ​​the light source group and radiation sensor, the measurement range can be expanded to reflect the properties of the entire vegetation.

[0040] The radiation sensor is preferably connected to a recording unit or a computer housing the recording unit via an output cable or wireless connection. The output value is the photon flux density (μmol·m³). -2 s -1Or irradiance (W·m -2 ) etc. can be output, but finally the transmittance (ratio) is taken, so the units used are not restricted. Here, the irradiance corresponds to the value obtained by converting the amount of photons per unit area (photon flux density) into energy (irradiance). Therefore, the output voltage (mV) indicating the change in the amount of charge photoelectrically converted by the radiation sensor is the photon flux density (μmol·m -2 s -1 ) or irradiance (W·m -2 ), and it can be output after being converted into either unit. By multiplying the photoelectrically converted voltage (mV) by a conversion coefficient (gain adjustment), it can be easily converted into either the unit of irradiance or the photon flux density. When one unit is adopted as the standard, the output can be easily changed from one to the other by changing the setting. Irradiance (W·m -2 ) = photon flux density (μmol·m -2 s -1 ) × Avogadro's number (mol -1 ) × Planck's constant (Js) × speed of light (m / s -1 ) / wavelength (m).

[0041] As the radiation sensor, a commercially available Si photodiode or solar radiation sensor can be used. The Si photodiode is a quantum type photodetector and usually has high linear sensitivity in the range of 400 nm to 900 nm. By making the light receiving surface (light receiving part) of the radiation sensor a photodiode in this way, miniaturization and cost reduction of the radiation sensor become possible.

[0042] The distance from the light source to the light receiving surface of the radiation sensor can be appropriately adjusted according to the size and shape of the plant. When the measurement object is grass, for example, it can be 1 cm or more, and preferably 10 to 100 cm. On the other hand, when targeting trees or forests, the distance can be more than 100 cm, and the upper limit value is not particularly restricted, but for example, it can be 50 m, and preferably it is 10 m (1000 cm) or less.

[0043] (Band-pass filter) A radiation sensor may be equipped with a bandpass filter to receive only light rays in the target wavelength band. For example, it may be equipped with a bandpass filter that filters out light with a wavelength band of less than 750 nm. This allows the radiation sensor to receive only near-infrared light with a wavelength band of 750 nm or more. By providing a bandpass filter that can filter out wavelengths shorter than the target near-infrared light band, the ambient light noise immunity of the radiation sensor can be improved. For example, when using an LED with a peak wavelength of 850 nm as the light source, it is more preferable for the bandpass filter to filter out light with a wavelength band of less than 800 nm, and particularly preferable for it to filter out light with a wavelength band of less than 800 nm and light with a wavelength band of 1100 nm or more.

[0044] Furthermore, in addition to the bandpass filter and light-receiving surface (light-receiving part), the radiation sensor may also be equipped with a circuit board for adjusting the gain of the photoelectrically converted voltage (detection signal) and outputting it, or known configurations such as a light diffuser may be adopted.

[0045] <Light source fixing part, radiation sensor fixing part, connecting member> The plant sensor device of this embodiment may include a light source fixing unit for fixing a group of light sources. Furthermore, the plant sensor device of this embodiment may also include a radiation sensor fixing unit for fixing a radiation sensor.

[0046] In one preferred embodiment of this design, the light source fixing unit is preferably positioned above the plant measurement unit. In this case, the radiation sensor fixing unit is preferably positioned below the plant measurement unit with the radiation sensor facing the measurement unit. On the other hand, when designing a large plant sensor device, a power supply, reflector, and optical system are required, and the light source is expected to be larger than the radiation sensor. Therefore, from the viewpoint of physical stability of the device, it is preferable to invert the design so that the light source fixing unit is positioned below the plant measurement unit, and the radiation sensor fixing unit is positioned above the plant measurement unit with the radiation sensor facing the measurement unit. In this case, since the radiation sensor faces downwards, the influence of ambient light from above can also be suppressed.

[0047] The plant sensor device of this embodiment can suppress the influence of ambient light, allowing for vertical use with the light source and radiation sensor positioned vertically relative to the plant, as well as horizontal and diagonal use with the light source and radiation sensor positioned horizontally or diagonally relative to the plant. The ability to use it horizontally or diagonally is particularly advantageous when it is a handheld device.

[0048] Furthermore, if the plant sensor device of this embodiment includes a radiation sensor fixing part and a light source fixing part, it is preferable to include a connecting member that connects the radiation sensor fixing part and the light source fixing part. It is preferable that the connecting member is extendable and retractable. It is also preferable that the distance from the light source to the light-receiving surface of the radiation sensor can be fixed at a desired distance.

[0049] In this embodiment, the connecting member may be provided with a gripping portion. There are no particular restrictions on the gripping portion; it may be a fixed handle or a strap.

[0050] <Records Department> The plant sensor device of this embodiment has a recording unit that records the output value from the radiation sensor. The recording unit is used as a so-called data logger.

[0051] The output from the radiation sensor is first input to the recording unit for recording, and then input to the calculation unit. However, the recording unit may be integrated into a component common to the control unit and calculation unit, and may be, for example, a CPU or a control panel.

[0052] In this embodiment, the recording unit classifies the output values ​​from the radiation sensor into (1) the irradiation output value during the near-infrared light irradiation period and (2) the non-irradiation output value during the near-infrared light extinction period. By classifying and recording the values ​​into irradiation output values ​​and non-irradiation output values ​​in this way, the calculation unit can use these to calculate parameters related to the leaf volume of the plant. In addition, in this embodiment, the recording unit may also record the irradiation period and extinction period of near-infrared light from the light source.

[0053] The recording unit can classify and record the output values ​​for the irradiation period and extinction period based on the time (timing) measured using a timing device such as a clock or timer (not shown in each drawing). Alternatively, if the control unit controls the irradiation period and extinction period, the recording unit can classify and record the output values ​​for the irradiation period and extinction period based on a time synchronized with the control unit.

[0054] In this embodiment, the control unit may control the near-infrared light in two stages: a first emission intensity and a second emission intensity, and use the difference to calculate parameters related to the leaf mass of the plant. In this case, the recording unit can further improve immunity to ambient light noise when the calculation unit uses these values ​​to calculate parameters related to the leaf mass of the plant by classifying and recording the first irradiation output value, the second irradiation output value, and the non-irradiation output value.

[0055] In this embodiment, it is preferable to store software, applications, or programs for calculating parameters related to the growth rate of each type of plant, or conversion formulas or conversion tables, in the recording unit.

[0056] <Arithmetic section> The plant sensor device of this embodiment preferably includes a calculation unit that calculates a difference A calculated from (irradiation output value) - (non-irradiation output value) and further converts the difference A into a leaf area index. Alternatively, if the control unit controls near-infrared light in two stages, a first emission intensity and a second emission intensity, the calculation unit may calculate a difference B calculated from (first irradiation output value) - (second irradiation output value) and convert it into a leaf area index. This can be used to improve immunity to ambient light noise when calculating parameters related to the leaf mass of plants.

[0057] The irradiated output value is the output value during the near-infrared light irradiation period (NIR), which is represented by a peak in the graph of the relationship between time since measurement disclosure and photon flux density (output value), as shown in Figure 4. The non-irradiated output value is the output value during the irradiation period (Non), which is represented by a peak in Figure 4. Difference A corresponds to the portion indicated as A in Figure 4. The non-irradiated output value is the output value measured based on ambient light such as sunlight. In this embodiment, the plant sensor device determines the leaf area index using the difference A calculated from (irradiated output value) - (non-irradiated output value), i.e., the fluctuation in output value due to light source irradiation, thus substantially eliminating the influence of ambient light in the surrounding environment.

[0058] In this embodiment, it is preferable that the leaf area index is a linear function of a logarithmic function whose argument is the difference A or a function of the difference A. The calculation unit can calculate the leaf area index from the difference A using the leaf area index conversion means. One example of the leaf area index conversion means is a program that calculates LAI from the difference A based on the fact that the natural logarithm Ln(A) of the difference A calculated from (irradiation output value) - (non-irradiation output value) is proportional to the leaf area index LAI. As shown in Figure 5, the relationship between the leaf area index LAI and the 850nm transmittance (difference A) is expressed by an exponential function. According to the indoor results in Figure 5, the 850nm transmittance (difference A) = 90.645e -0.564×LAI Therefore, taking the natural logarithm of both sides, we can calculate it using the relationship (1) Ln(A) = Ln(90.645) - 0.564 × LAI. In other words, the leaf area index LAI is expressed as a linear function of a logarithmic function with the difference A as the argument. If we store relationship (1) in the recording unit and perform the calculation, we can calculate the leaf area index from the difference A. Note that from Figure 5, R in relationship (1) 2 The result is 0.9915, indicating a very strong correlation between LAI and the difference A calculated from (NIR output value) - (non-irradiated output value). Therefore, the calculation results using this program can be used as an accurate leaf area index.

[0059] In this embodiment, a calibration curve or conversion table may be created in advance, and the leaf area index may be calculated from the difference A. Calibration curves for each type of vegetation can be stored in the recording unit, and the leaf area index corresponding to the calibration curve can be output based on this calibration curve and the difference A calculated from the measured (irradiation output value) - (non-irradiation output value). Alternatively, the leaf area index may be calculated from the difference A as a higher-order function of degree two or higher.

[0060] In the calculation unit, it is preferable to use the output values ​​during the intermediate period of 25-75% of the irradiation period and quenching period, with the entire period from the start to the end point of each period being 100%, as the irradiation output value and the non-irradiation output value, respectively. To explain using the graph in Figure 4 as an example, it is preferable to use the output values ​​during the intermediate period of 25-75% (ini; between 27.5 and 32.5 seconds from the start of measurement), with the period from the start of the irradiation period (ini; approximately 25 seconds from the start of measurement) to the end point (ter; approximately 30 seconds from the start of measurement) being 100% (corresponding to approximately 5 seconds), as the irradiation output value. The average value of the output values ​​per unit time during the intermediate period may be used as the irradiation output value, or the integrated value (or average value thereof) of the output values ​​during the intermediate period may be used as the irradiation output value. The start of the irradiation period refers to the point where the peak of the output value begins to rise at a certain peak in the graph of the relationship between time from the start of measurement and the photon flux density (output value), as shown in Figure 4. The end point of the irradiation period refers to the point where the output value reaches its minimum value after the peak has gradually decreased.

[0061] <Department Head> The plant sensor device of this embodiment preferably further comprises a control unit. The control unit preferably controls the light source so that the irradiation period and quenching period are considered as one cycle and the cycle is repeated. The irradiation period and quenching period of the light source are preferably 0.1 milliseconds to 1 minute, more preferably 1 millisecond to 10 seconds, and particularly preferably 10 milliseconds to 1 second.

[0062] The control unit may lengthen only one of the light source irradiation period or the quenching period, but it is preferable to control them at equal intervals. For example, it is preferable for the control unit to control the light source irradiation period and the quenching period to be at approximately equal intervals of ±30%, more preferably at approximately equal intervals of ±20%, and particularly preferably at approximately equal intervals of ±10%. For example, if the light source irradiation period is 5 seconds, the quenching period is preferably 3.5 to 6.5 seconds, more preferably 4 to 6 seconds, and particularly preferably 4.5 to 5.5 seconds.

[0063] In this embodiment, the control unit may control the near-infrared light in two stages: a first emission intensity and a second emission intensity. For example, the control unit may control the light source to irradiate with the first emission intensity, and then control the light source to irradiate with infrared light at a second emission intensity that is 1 / n times (n is a positive number) the first emission intensity. Irradiating the light source with two stages of emission intensity during measurement improves immunity to ambient light noise. For example, if the first emission intensity is 100%, then n=2, i.e., the second emission intensity can be 1 / n=0.5 times, or 50%. 1 / n is preferably 0.1 to 0.9, more preferably 0.3 to 0.7, and particularly preferably 0.4 to 0.6.

[0064] <Growing means> The plant sensor device of this embodiment may include growth means that control at least one of fertilizer, water, temperature, and humidity to suppress the growth of plant leaves when the leaf area index exceeds a predetermined range, or to promote the growth of plant leaves when the leaf area index falls below a predetermined range. Such growth means are preferably controlled by a control unit.

[0065] There are no particular restrictions on the cultivation methods; methods used in well-known vegetable factories and smart agriculture fields can be employed.

[0066] [Active optical measurement methods for plants] This embodiment may also relate to an active optical measurement method for plants using the plant sensor device described above. Unlike passive optical measurement methods for plants, this optical measurement method actively irradiates plants with near-infrared light, shortening the measurement period. As a result, it has the advantage of suppressing the influence of ambient light.

[0067] The active optical measurement method for plants according to this embodiment is preferably used for ground truth remote sensing from above or from space, measurement of plant growth in plant cultivation facilities, measurement of forest vegetation, and measurement of leaf mass in plant communities or foliage groups. In other words, these are also preferred applications of the plant sensor device of the present invention.

[0068] Other preferred embodiments of the active optical measurement method for plants in this embodiment are the same as preferred embodiments of the plant sensor device described above. [Examples]

[0069] The present invention will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples.

[0070] [Test Example 1: Evaluation of the Coefficient of Variation 1] A demonstration experiment of the plant sensor device configured as shown in Figure 1 was conducted using the following procedure, and the leaf area index (LAI) was measured using a foliage model. A single-light source was used as a comparative example, and the coefficient of variation of the leaf area index (LAI) was calculated.

[0071] As the light sources constituting the light source group, a single near-infrared LED light source with a peak wavelength of 850 nm and a full width at half maximum of 50 nm or less was used. The light source group was positioned above (vertically upward) the foliage group. The arrangement of the light sources constituting the light source group is as shown in Figures 6(a) to (d). (a) Three light sources (line light sources) with a distance of approximately 106 mm between them. (b) Three light sources (line light sources) with a distance of approximately 56 mm between them. (c) Five light sources (line light sources) with a distance of approximately 56 mm between them. (d) Single light source (comparative example)

[0072] A Si photodiode (a commercially available solar radiation sensor) was used as the radiation sensor. The radiation sensor was placed on the lower side (vertically downward) of the foliage (plant), opposite the light source. The memory of a PC equipped with a general-purpose CPU was used as the recording unit, and the output value obtained by photoelectric conversion from light received by the radiation sensor was recorded. The PC's CPU has an arithmetic unit and a control unit. The arithmetic unit can use a leaf area index conversion means (program) stored in memory to calculate the difference A calculated from (irradiated output value) - (non-irradiated output value), and further convert the difference A into a leaf area index.

[0073] Measurements were performed using leaf group panels corresponding to LAI=0.5, LAI=1, and LAI=1.5. Each leaf group panel consisted of Japanese evergreen oak leaves fixed to achieve a predetermined LAI. The control unit controlled the light source so that one cycle consisted of a period of 0.5 seconds of illumination followed by 0.5 seconds of extinction of the NIR light, starting 0.5 seconds after the start of measurement and then extinguishing the NIR light 0.5 seconds later. Measurements were taken for 3.0 seconds in one cycle. Under each of conditions (a) to (d), the horizontal position of the light source and radiation sensor relative to the foliage panel was randomly moved 10 times, and measurements were taken.

[0074] In measurements using each light source group, the transmitted near-infrared light that has passed through the foliage is received by a radiation sensor, and the radiance (W·m) is recorded as the output value after photoelectric conversion. -2 The output values ​​were recorded in the recording unit. During the irradiation period and the quenching period, the output values ​​during the intermediate period (mid) from 25% to 75% were used as the irradiation output value and the non-irradiation output value, respectively, with the period from the start point (ini) to the end point (ter) of each period being 100%. Furthermore, using a leaf area index conversion means (program) stored in memory, the difference A calculated from (irradiation output value) - (non-irradiation output value) was calculated, and then the difference A was converted into a leaf area index. The leaf area index conversion means (program) calculated Ln(A), the natural logarithm of the difference A calculated from (irradiation output value) - (non-irradiation output value), based on the fact that it is proportional to the leaf area index LAI, calculated from the difference A.

[0075] Next, the coefficient of variation was calculated for light source groups (a) to (d) using the following method. First, the same leaf panel was measured 10 times with different light source groups (a) to (d), and the mean and standard deviation were calculated. Then, the degree of variation (coefficient of variation) of the measured values ​​for each light source was quantified by dividing the standard deviation by the mean.

[0076] [Table 1]

[0077] As shown in Table 1, by using multiple light sources to constitute the light source group, the coefficient of variation of the calculated leaf area index (LAI) could be reduced. Furthermore, increasing the distance between light sources, as in (a) 3 light sources, effectively reduced the coefficient of variation when the LAI increased. In addition, increasing the number of light sources, as in (c) 5 light sources, enabled more stable measurements.

[0078] [Test Example 2: Evaluation of the Coefficient of Variation 2] The arrangement of light sources constituting the light source group was changed as shown in Figure 7(a) or (b), and the leaf area index LAI was calculated and the coefficient of variation was determined in the same manner as in Example 1, except that the following plant individual model was used as the leaf group model. (a) Five light sources (line light sources) with a distance of approximately 56 mm between them. (b) 21 light sources (circular surface arrangement light sources) with a distance of approximately 53 mm between light sources on the outer circumference and approximately 39 mm between light sources on the inner circumference.

[0079] As the foliage group model, we used the foliage group model shown in Figures 8(a) to 8(d) (plant individual model created by combining leaves of Quercus glauca). The coefficient of variation for each condition is shown below.

[0080] [Table 2]

[0081] As shown in Table 2, similar effects were obtained whether a linear light source or a circular surface light source was used. However, under conditions where the leaves were arranged three-dimensionally, such as condition C, the circular surface arrangement tended to suppress variations depending on the measurement position. [Explanation of Symbols]

[0082] 1 plant 2 Measuring part 10 light source 11 Light source group 12 Infrared light 13 Transmitted light 21 Radiation Sensor 22 Photosensitive surface 23 Bandpass filter 30 Computers 31 Records Section 32 Arithmetic section 33 Control Unit 34 CPU 35 Display section 36 Output section 41 Light source fixing part 42 Radiation sensor fixing part 43 Connecting member 44 Gripping part 51. Methods of growth 100 Plant Sensor Devices L: Distance from the light source to the light-receiving surface of the radiation sensor. A difference calculated from (irradiation output value) - (non-irradiation output value) NIR irradiation output value Non-irradiation output value ini starting point mid-term ter (terminus)

Claims

1. A group of light sources comprising two or more light sources that intermittently emit light rays toward plants, A radiation sensor is positioned on the opposite side of the light source group from the plant and on the optical axis of the light ray, and receives the transmitted light of the light ray that has passed through the plant and outputs a photoelectrically converted output value. It has a recording unit that records the output value from the radiation sensor, A plant sensor device in which the recording unit classifies the output values ​​from the radiation sensor into (1) irradiation output values ​​during the irradiation period of the light ray, and (2) non-irradiation output values ​​during the extinction period of the light ray.

2. The plant sensor device according to claim 1, wherein the light ray is near-infrared light (NIR).

3. The plant sensor device according to claim 2, wherein the light source group consists only of near-infrared light sources.

4. The plant sensor device according to claim 3, wherein the near-infrared light source emits narrowband near-infrared light with a peak wavelength of 750 to 1100 nm and a full width at half maximum of 50 nm or less.

5. The aforementioned light ray is emitted toward the radiation sensor, The plant sensor device according to claim 1, wherein multiple optical axes irradiated from the light source group have different incident angles with respect to the radiation sensor.

6. The plant sensor device according to claim 1, wherein the average distance between the light sources constituting the light source group is 20 mm or more.

7. The plant sensor device according to claim 1, further comprising a calculation unit that calculates a difference A calculated from (irradiation output value) - (non-irradiation output value) and converts the difference A into a leaf area index.

8. The plant sensor device according to claim 7, comprising growth means for controlling at least one of fertilizer, water, temperature, and humidity so as to suppress the growth of the plant's leaves when the leaf area index exceeds a predetermined range, or to promote the growth of the plant's leaves when the leaf area index falls below a predetermined range.

9. The plant sensor device according to claim 1, wherein the output values ​​during the intermediate period of 25 to 75% of the irradiation period and the quenching period, with the period from the start to the end of each being 100%, are used as the irradiation output value and the non-irradiation output value, respectively.

10. The plant sensor device according to claim 1, wherein the irradiation period and the quenching period are each 0.1 milliseconds to 1 minute.

11. The plant sensor device according to claim 1, wherein the plant is a foliage group or a plant community.

12. The plant sensor device according to claim 1, further comprising a radiation sensor fixing part for fixing the radiation sensor, a light source fixing part for fixing the light source, and a connecting member for connecting the radiation sensor fixing part and the light source fixing part.

13. An active optical measurement method for plants using a plant sensor device described in any one of claims 1 to 12.

14. An active optical measurement method for plants according to claim 13, for use in ground truth remote sensing from above or from space, measurement of plant growth in plant growing facilities, measurement of forest vegetation, and measurement of leaf mass of plant communities or foliage groups.

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