Plant sensor device and active plant optical measurement method

Abstract

To provide a plant sensor device that suppresses the influence of external light in the surrounding environment and allows parameters related to plant leaf volume to be determined with a simple and low-cost configuration, in order to quantify the degree of plant growth.SOLUTION: The present invention relates to a plant sensor device 100 comprising: a light source 11 that intermittently irradiates a plant with near-infrared light (NIR); a radiation sensor 21 disposed on the opposite side to the plant from the light source 11, which receives the transmitted light of near-infrared light transmitted through the plant and outputs a photoelectrically converted output value; and a recording unit 31 that records the output value from the radiation sensor 21. The recording unit 31 records the irradiation period and extinction period of the near-infrared light in the light source 11, and the recording unit 31 classifies the output values from the radiation sensor into (1) NIR output values during the near-infrared light irradiation period, and (2) non-irradiation output values during the near-infrared light extinction period. An optical measurement method of active plant is also provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, with the development of data-related technology, there has been a demand for quantifying the growth rate of plants. Indices that indicate the growth rate of plants include the Leaf Area Index (LAI) and the Absorbed Photosynthetic Radiation Rate (fAPAR). For example, the Leaf Area Index is an index value that indicates the total area of ​​one side of all the leaves of the vegetation above a unit horizontal area. For example, for 1m 2 The total area of ​​leaves above ground is 2m 2 then the LAI = 2, which means that when the leaves are lined up on the ground with no gaps between them, two will overlap. The leaf area index of normal 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, earth environmental science, etc. as an important indicator of the absorption of photosynthetically active radiation, photosynthetic capacity, transpiration rate, and the carbon absorption capacity of vegetation.

[0003] As a method for calculating the leaf area index, Patent Document 1 describes an optical vegetation index sensor that includes: a first radiation sensor that receives transmitted radiation that has passed through a leaf or group of leaves, corrects the spectral characteristics of radiation in the visible radiation region of 400 nm to 700 nm using a correction filter to measure it as photon flux density, and then photoelectrically converts the corrected radiation in a light-receiving unit to output a PAR output that indicates either photosynthetically active irradiance or photosynthetic photon flux density; a second radiation sensor that uses a bandpass filter to extract only radiation in the infrared radiation region of 700 nm to 1000 nm from the received radiation, and photoelectrically converts this radiation in a light-receiving unit to output an IR output that indicates either irradiance or photon flux density in units common to the PAR output; and a calculation unit that integrates the PAR output and IR output over time, divides the integrated value of the IR output by the integrated value of the PAR output to calculate a ratio, and calculates the leaf area index corresponding to the ratio. The optical vegetation index sensor in Patent Document 1 utilizes the known correlation of logY=0.3813+0.0989X between the spectral intensity ratio Y (=800 / 675) of red radiation (wavelength 675 nm) and near-infrared radiation (wavelength 800 nm) that have passed through vegetation and the leaf area index X. This can be said to be a "transmission NIR / PAR method."

[0004] Patent Document 1 also describes other methods for determining the leaf area index, such as the "fisheye lens method," which uses a full fisheye lens and an electronic image sensor to capture images of a specified area for near-infrared radiation and red radiation, and then determines the brightness value ratio to estimate the relative amount of solar radiation; and the "Plant Canopy Analyzer" (LAI-2000, etc.) developed by LI-COR, a U.S. company, which optically divides the entire sky into five rings and measures the intensity distribution of blue radiation across the entire sky.

[0005] On the other hand, there are known methods for optically determining not only the leaf area index but also other growth conditions, which can be divided into a method using transmitted light similar to Patent Document 1, a method using scattered light (Patent Document 2), and a method using reflected light (Patent Document 3). Patent Document 2 describes a plant community transmission light sensor unit that is equipped with a visible light sensor that detects visible light and a near-infrared light sensor that detects near-infrared light and is used to determine the growth state of plants, the plant community transmission light sensor unit including a transparent pipe and a pair of black cover plates that close both ends of the pipe, and with the pipe standing upright in a vertical direction, the visible light sensor and near-infrared light sensor are attached to the center of the inside of the pipe on the underside of the upper cover plate, with their light-receiving surfaces facing downwards.

[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 illuminate a growth condition measurement object; a second light-emitting unit that emits a second measurement light of a second wavelength to illuminate the growth condition measurement object; a light-receiving unit that receives the reflected light of each measurement light by the growth condition measurement object and outputs a light-receiving signal; a control unit that controls the emission from the first light-emitting unit and the emission from the second light-emitting unit at different timings; an optical path combining means that combines 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 combining means and the emission unit that emits the first measurement light and the second measurement light toward the growth condition measurement object, wherein the emission unit has an optical element that has refractive power in only one direction when viewed in a plane perpendicular to the emission optical axis, and the optical element is held rotatable around the emission optical axis. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-133451 [Patent Document 2] Japanese Patent Publication No. 2020-198804 [Patent Document 3] Patent No. 5718153 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the optical vegetation index sensor described in Patent Document 1 requires two expensive radiation sensors with filters, so further cost reductions are needed. The accuracy of the transmitted NIR / PAR method depends on the spectral stability of the incident sunlight (solar radiation), but the NIR / PAR of incident solar radiation can fluctuate by 10% or more depending on the sky conditions. Furthermore, with light sources other than sunlight, the NIR / PAR of incident light fluctuates significantly, and is affected by the surrounding environment inside a greenhouse, making it difficult to use, especially in artificial light environments. The other methods described in Patent Document 1 have the problem that the fisheye lens method cannot be used to capture images on sunny days. LI-COR's Plant Canopy Analyzer requires simultaneous measurements both inside and outside the forest on cloudy days, so it cannot be used in environments with large fluctuations in solar radiation or in artificial light environments. The device described in Patent Document 2 also includes two expensive sensors: a visible light sensor and a near-infrared light sensor. Furthermore, the device requires black cover plates on the top and bottom to detect scattered light, and a second cover plate is also required if the device is installed horizontally, resulting in a complex device configuration. Patent Document 2 also describes canceling data from cloudy and rainy days to eliminate the effects of fluctuations in solar radiation, which creates the problem of being affected by external light from the surrounding environment. Therefore, further cost reduction and higher accuracy are needed. In a device such as that described in Patent Document 3 that detects reflected light using an irradiation sensor (light receiving unit), two types of measurement light with different wavelengths are detected by a light receiving unit formed of two to six photodiodes in order to eliminate the influence of ambient light through calculation. Furthermore, in order to detect reflected light from the two types of measurement light, the light source (emitting unit) requires an optical element (lens) with a refractive index that is rotatable around the optical axis, making the device configuration complex. Therefore, further cost reductions have been desired.

[0009] The problem that the present invention aims to solve is to provide a plant sensor device that can quantify the degree of plant growth by suppressing the influence of external light from the surrounding environment and determining parameters related to the amount of leaves in a plant with a simple, low-cost configuration. [Means for solving the problem]

[0010] The present invention solves the above problem by (1) actively and intermittently irradiating near-infrared light from a light source and classifying and recording output values ​​from a radiation sensor during irradiation periods and extinction periods of near-infrared light, or (2) actively irradiating near-infrared light from a light source at two or more levels of intensity and classifying and recording output values ​​from a radiation sensor during irradiation periods of near-infrared light at a first emission intensity and a second emission intensity. The configuration of the present invention, which is a specific means for solving the above problem, and preferred configurations of the present invention are described below.

[0011] [1] A light source that intermittently irradiates plants with near-infrared light (NIR); a radiation sensor disposed on the opposite side of the plant from the light source, which receives near-infrared light transmitted through the plant and outputs an output value obtained by photoelectric conversion; a recording unit that records an output value from the radiation sensor; the recording unit records the irradiation period and extinction period of the near-infrared light from the light source; A plant sensor device in which the recording unit classifies the output value from the radiation sensor into (1) an NIR output value during the irradiation period of near-infrared light, and (2) a non-irradiation output value during the extinction period of near-infrared light. [2] The plant sensor device according to [1], further comprising a calculation unit that calculates a difference A calculated from (NIR output value) - (non-irradiated output value) and converts the difference A into a leaf area index. [3] The plant sensor device according to [2], wherein the leaf area index is a linear function of a logarithmic function with the difference A or a function thereof as the antilogarithm. [4] A plant sensor device according to [2] or [3], which is provided with a growth means for controlling at least one of fertilizer, moisture, temperature, and humidity so as 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 the predetermined range. [5] The plant sensor device according to any one of [1] to [4], wherein the plant is a foliage group or a plant community. [6] The plant sensor device according to any one of [1] to [5], wherein the light source is provided solely with a near-infrared light source. [7] The plant sensor device according to [6], wherein the near-infrared light source emits narrow-band near-infrared light having a peak wavelength of 750 nm to 1100 nm and a half-width of 50 nm or less. [8] A plant sensor device according to any one of [1] to [7], wherein the radiation sensor is provided with a bandpass filter that filters out light in a wavelength band of less than 750 nm, and extracts radiation of only near-infrared light in a wavelength band of 750 nm or more. [9] A radiation sensor fixing portion for fixing the radiation sensor, The plant sensor device according to any one of [1] to [8], wherein the radiation sensor fixing part fixes the radiation sensor below the measurement part of the plant with the light receiving surface facing the measurement part.

[10] A light source fixing unit for fixing a light source, The plant sensor device according to any one of [1] to [9], wherein the light source fixing unit fixes the light source above the measurement unit for the plant.

[11] A radiation sensor fixing portion for fixing the radiation sensor, a light source fixing portion for fixing the light source, and a connecting member for connecting the radiation sensor fixing portion and the light source fixing portion, The plant sensor device according to any one of [1] to

[10] , wherein the distance from the light source to the light receiving surface of the radiation sensor is 1 to 1000 cm.

[12] The plant sensor device according to

[11] , wherein the connecting member is provided with a gripping portion.

[13] A radiation sensor fixing part for fixing the radiation sensor and a light source fixing part for fixing the light source, The light source fixing unit fixes the light source below the plant measurement unit, The plant sensor device according to any one of [1] to

[12] , wherein the radiation sensor fixing part fixes the radiation sensor above the measurement part of the plant with the light receiving surface facing the measurement part.

[14] A plant sensor device described in any of [1] to

[13] , in which the output values ​​during the intermediate period of the illumination period and the extinction period, which are 25 to 75% of the illumination period and the extinction period, respectively, are used as the NIR output value and the non-illumination output value, with the periods from the beginning to the end being 100%.

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

[14] , wherein the illumination period and the extinction period are both between 1 millisecond and 1 minute.

[16] further comprising a control unit; The plant sensor device according to any one of [1] to

[15] , wherein the control unit controls the illumination period and extinction period of the light source to be approximately equal intervals within ±30% of each other.

[17] A light source that irradiates plants with near-infrared light (NIR); a radiation sensor disposed on the opposite side of the plant from the light source, which receives near-infrared light transmitted through the plant and outputs an output value obtained by photoelectric conversion; a recording unit that records an output value from the radiation sensor; a control unit; the control unit controls the light source to emit infrared light at a first emission intensity and a second emission intensity that is 1 / n times (n is a positive number) of the first emission intensity; A plant sensor device in which a recording unit classifies (1) NIR output values ​​during the irradiation period of near-infrared light among output values ​​from the radiation sensor into (1-1) first NIR output values ​​during the irradiation period of near-infrared light with a first emission intensity, and (1-2) second NIR output values ​​during the irradiation period of near-infrared light with a second emission intensity.

[18] The plant sensor device according to

[17] , comprising a calculation unit that converts the difference B calculated from (first NIR output value) - (second NIR output value) into a leaf area index.

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

[18] .

[20] The active optical plant measurement method described in

[19] is used for ground truthing of remote sensing from the air or space, measuring plant growth in plant growth facilities, measuring forest vegetation, and measuring leaf mass in plant communities or foliage. [Effects of the Invention]

[0012] According to the present invention, a plant sensor device can be provided that can quantify the growth level of a plant by suppressing the influence of external light in the surrounding environment and determining parameters related to the amount of leaves in a plant with a simple, low-cost configuration. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 is a schematic diagram showing a cross section of an example of the plant sensor device of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a cross section of another example of the plant sensor device of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing a cross section of another example of the plant sensor device of the present invention. [Figure 4] Figure 4 shows the spectrum of solar radiation and an LED light source (peak wavelength 850 nm). [Figure 5] FIG. 5 is a graph showing the relationship between the time from the start of measurement and the photon flux density (output value) in Example 1. [Figure 6] 6(A) is a photograph of a leaf of a plant that was the measurement target and the radiation sensor used in Example 2. FIG. 6(B) is a photograph of the configuration of the plant sensor device of Example 2. [Figure 7] Figure 7 is a graph showing the relationship between leaf area index and 850 nm transmittance in indoor and outdoor measurements. [Figure 8] FIG. 8 is a graph showing the relationship between the time from the start of measurement and the photon flux density (output value) in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. The following description of the constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0015] [Plant sensor device] A first aspect of the plant sensor device of the present invention includes a light source that intermittently irradiates a plant with near-infrared light (NIR); a radiation sensor disposed on the opposite side of the plant from the light source, which receives near-infrared light transmitted through the plant and outputs an output value obtained by photoelectric conversion; a recording unit that records an output value from the radiation sensor; the recording unit records the irradiation period and extinction period of the near-infrared light from the light source; The recording unit classifies the output values ​​from the radiation sensor into (1) NIR output values ​​during the irradiation period of near-infrared light, and (2) non-irradiation output values ​​during the extinction period of near-infrared light. A second aspect of the plant sensor device of the present invention includes a light source that irradiates a plant with near-infrared light (NIR); a radiation sensor disposed on the opposite side of the plant from the light source, which receives near-infrared light transmitted through the plant and outputs an output value obtained by photoelectric conversion; a recording unit that records an output value from the radiation sensor; a control unit; the control unit controls the light source to emit infrared light at a first emission intensity and a second emission intensity that is 1 / n times (n is a positive number) of the first emission intensity; The recording unit classifies (1) the NIR output value during the irradiation period of near-infrared light among the output values ​​from the radiation sensor into (1-1) a first NIR output value during the irradiation period of near-infrared light with a first emission intensity, and (1-2) a second NIR output value during the irradiation period of near-infrared light with a second emission intensity. With these configurations, the influence of external light in the surrounding environment can be suppressed in order to quantify the growth rate of a plant, and parameters related to the amount of leaves of the plant can be obtained with a simple and low-cost configuration. In this specification, the "leaf mass" of a plant includes not only growth levels such as LAI, luxuriance, and aboveground biomass, but also physiological functions such as leaf chlorophyll content, photosynthetic activity, senescence, and stress response. Preferred embodiments of the present invention will be described below. Preferred embodiments of the first aspect of the plant sensor device of the present invention will be mainly described below, but preferred embodiments of the first aspect of the plant sensor device of the present invention are also preferred embodiments of the second aspect of the present invention. Furthermore, preferred embodiments of the second aspect of the plant sensor device of the present invention are also preferred embodiments of the first aspect of the present invention.

[0016] <Outline of the plant sensor device> First, an outline of the plant sensor device of the present invention will be described with reference to the drawings, although the present invention should not be construed as being limited by the drawings. Fig. 1 is a schematic diagram showing a cross section of an example of a plant sensor device of the present invention. The plant sensor device 100 shown in Fig. 1 includes a light source 11 that intermittently irradiates near-infrared light 12 onto a plant 1 (a community, specifically, a group of leaves), a radiation sensor 21 that is disposed on the opposite side of the plant 1 from the light source 11 and receives near-infrared light 13 that has passed through the plant 1 and outputs an output value obtained by photoelectric conversion, and a recording unit 31 that records the output value from the radiation sensor 21. In the plant sensor device shown in Figure 1, the recording unit 31 records the irradiation period and extinction period of near-infrared light from the light source 11, and the recording unit 31 classifies the output value from the radiation sensor into (1) NIR output value during the irradiation period of near-infrared light and (2) non-irradiation output value during the extinction period of near-infrared light. 1 includes a recording unit 31 inside a computer 30, as well as an arithmetic unit 32 and a control unit 33, which may be optionally provided. The arithmetic unit 32 and the control unit 33 may be part of a CPU 34. A display unit 35, which may be optionally provided, is connected to the computer 30, and can display any calculation results, etc. The computer 30 may also be connected to an external output unit 36, and can output data to another PC, a printer, etc. The computer 30 may include an input means (not shown). Any program may be stored in the recording unit 31 (memory, etc.) from the input means. For example, a program for calculating the growth level of a plant by the calculation unit, or a program for controlling the growth means by the control unit may be stored in advance in the recording unit 31. Also, a program stored in an external memory, on a network, or on the cloud may be run by the computer 30 via the input means or output unit 36 ​​and controlled by the control unit. The plant device shown in Fig. 1 includes an optional growing means 51. The growing means 51 can control at least one of fertilizer, water, temperature, and humidity so as to suppress leaf growth of the plant 1 when the leaf area index of the plant 1 exceeds a predetermined range, or to promote leaf growth of the plant when the leaf area index is below the predetermined range.

[0017] Fig. 2 is a schematic diagram showing a cross section of another example of the plant sensor device of the present invention. In Fig. 2, a group of strawberry leaves is used as the plant 1. The plant sensor device shown in Fig. 2 includes a light source fixing unit 41 that fixes the light source 11. The light source fixing unit 41 fixes the light source 11 above the measurement unit of the plant 1. In the plant sensor device shown in Fig. 2, the radiation sensor 21 includes a bandpass filter 23 and is fixed to a radiation sensor fixing part 42. The radiation sensor fixing part 42 fixes the radiation sensor 21 below the measurement part of the plant 1 with the light receiving surface 22 facing the measurement part. The plant sensor device shown in Fig. 2 includes a connecting member 43 that connects the radiation sensor fixing part 42 and the light source fixing part 41, and the distance L from the light source 11 to the light receiving surface 22 of the radiation sensor 21 can be adjusted as desired. Alternatively, the distance L from the light source 11 to the light receiving surface 22 of the radiation sensor 21 may be fixed, and can be set to approximately 50 cm, for example, when strawberry leaves are the target. The plant sensor device shown in FIG. 2 is provided with a grip part 44 on a connecting member 43, and is used as a handheld plant sensor device that can be held by a person. The plant sensor device shown in FIG. 2 is provided with a display unit 35 as an integrally connected structure, and can display the LAI value externally. In the plant sensor device shown in FIG. 2, the recording unit and CPU (including the calculation unit and control unit) are omitted.

[0018] Fig. 3 is a schematic diagram showing a cross section of another example of the plant sensor device of the present invention. Fig. 3 shows an example of a large-scale device in which a broad-leaved tree is used as the measurement target plant 1 and a partial area of ​​the leaves of the broad-leaved tree is used as the measurement unit 2. The plant sensor device shown in FIG. 3 has a structure in which the positional relationship between the light source 11 and the radiation sensor 21 is upside down (light source 11 is at the bottom) compared to the plant sensor device shown in FIG. In the plant sensor device shown in FIG. 3, the recording unit and CPU (including the calculation unit and control unit) are omitted. Preferred embodiments of the plant sensor device of the present invention will be described in detail below.

[0019] <Plant> There are no particular limitations on the plants that can be measured in the present invention. The target may be trees, grasses, mosses, ferns, or algae. Among these, it is preferable to target plants having chlorophyll, and it is more preferable to target trees and grasses having flat leaves. The trees include deciduous or evergreen coniferous or broad-leaved trees, and the present invention is preferably directed to coniferous or broad-leaved trees with a low ratio of branches to leaves. Examples of grasses include wild plants, crops (including those whose fruits are edible, such as strawberries and watermelons), and horticultural plants (including those whose flowers are grown for ornamental purposes). In particular, it is preferable to target 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.

[0020] The target plant may be only one plant or multiple plant species. When multiple plant species are targeted, the plant species may be only one type or multiple types. When only one plant species is targeted, it is preferable to target the foliage. When multiple plant species are targeted, it is preferable to target the foliage or plant community. Only a part of the plant may be used as the measurement area, particularly when targeting large plants such as trees, forests, etc., or when targeting small plants with multiple strains, it is preferable to use only a part of the plant as the measurement area.

[0021] The plant may be the measurement target as it is, or a portion of the plant may be taken and used as the measurement target. In the present invention, it is preferable to use the plant as it is. That is, a preferred embodiment of the plant sensor device of the present invention allows for non-destructive testing, which is preferable to destructive testing such as the conventionally known pruning method (a method in which all leaves on a plant are plucked and the leaf area index is calculated from the total value). When used as an optical sensor in the food industry, commercially available leafy vegetables may also be used as the measurement target.

[0022] <Light source> The first aspect of the plant sensor device of the present invention includes a light source that intermittently irradiates a plant with near-infrared light, while the second aspect of the plant sensor device of the present invention only needs to include a light source that irradiates a plant with near-infrared light, and does not necessarily need to irradiate the plant intermittently. The light source may include at least one near-infrared light source. Multiple near-infrared light sources may be used, or a near-infrared light source and a light source of a wavelength other than near-infrared may be included. However, from the viewpoint of cost reduction, it is preferable that the light source include only a near-infrared light source.

[0023] It is preferable that the near-infrared light source irradiates near-infrared light with a peak wavelength of 750 nm to 1100 nm, as this makes it easier to suppress the effects of external light in the surrounding environment, and it is more preferable to irradiate near-infrared light with a peak wavelength of 800 to 900 nm in order to suppress the effects on plant photoreceptors and the effects of differences in leaf water content. Note that the light should not contain wavelength components shorter than 750 nm. The type of near-infrared light source is not particularly limited, but examples include LEDs and lasers, with LEDs being preferred. A specific example of a preferred near-infrared light source is an LED with a peak wavelength of approximately 850 nm. For example, a commercially available LED for security cameras can be used as the near-infrared light source for a plant sensor device. Figure 4 shows the spectra of sunlight and an LED light source (peak wavelength 850 nm). As shown in Figure 4, the spectrum of near-infrared light emitted from an LED light source with a peak wavelength of 850 nm (LED light source in Figure 4) corresponds to the wavelength band where the sunlight spectrum (sunlight in Figure 4) steadily and slightly decreases. Therefore, LEDs with a peak wavelength of approximately 850 nm are less affected by external light noise from sunlight. Furthermore, the spectrum obtained by adding sunlight and this LED light source (sunlight + LED in Figure 4) closely reflects the spectrum of this LED light source. Therefore, by subtracting the output value of sunlight alone (which serves as the baseline) from the output value of sunlight + LED from the radiation sensor, the difference A calculated from (NIR output value) - (non-irradiated output value) can be calculated with high accuracy and stability. On the other hand, near-infrared light with a peak wavelength of 750 nm to 1100 nm is preferable because it is less affected by absorption by plant pigments (such as chlorophyll and carotenoides). Furthermore, near-infrared light of 800 nm or more is even more preferable because it is less affected by absorption by plant photoreceptors (phytochromes). Chlorophyll has two absorption bands, primarily absorbing blue light (400 nm to 500 nm) and red light (600 nm to 700 nm). Phytochromes exist in two forms: Pr, which has an absorption wavelength center at 660 nm, and Pfr, which has an absorption wavelength center at 730 nm. Both types undergo photoconversion and affect plant growth. Further, near-infrared light with a peak wavelength of 750 nm to 1100 nm is also preferable from the viewpoint that it is less affected by external light noise from artificial light sources.

[0024] <Radiation sensor> The plant sensor device of the present invention has a radiation sensor that is placed on the opposite side of the plant from the light source, receives near-infrared light that has passed through the plant, and outputs an output value that has been photoelectrically converted. The shape of the radiation sensor is not limited as long as it can receive transmitted light that has passed through the plant. For example, it may be cylindrical, hemispherical, or rod-shaped so that transmitted light can be received from all directions. Since the present invention uses transmitted light rather than reflected light, it is possible to reflect the properties of a specific part of vegetation, including the average effects of light scattering, reflection, etc. within the vegetation. Furthermore, by increasing the area of ​​the light source and radiation sensor, the measurement range can be expanded to reflect the properties of the entire vegetation. The radiation sensor is preferably connected to a recording unit or a computer storing the recording unit via an optional output cable or wirelessly. The output value is expressed as photon flux density (μmol m -2 s -1 ) or irradiance (W m -2 ), but since the transmittance (ratio) is ultimately used, there are no restrictions on the units used. Here, irradiance corresponds to the amount of photons per unit area (photon flux density) converted into energy (irradiance). Therefore, the output voltage (mV) that indicates the change in the amount of charge photoelectrically exchanged in the radiation sensor is expressed as a photon flux density (μmol m -2 s-1 ) or irradiance (W m -2 ) and output can be converted into either unit. By multiplying the photoelectrically converted voltage (mV) by a conversion factor (gain adjustment), it can be easily converted into either unit of irradiance or photon flux density. If one unit is used as the standard, output can be easily changed from one to the other by changing the settings. -2 ) = photon flux density (μmol m -2 s -1 ) × Avogadro's number (mol -1 ) × Planck's constant (Js) × speed of light (ms -1 ) / wavelength (m). As a radiation sensor, commercially available Si photodiodes or solar radiation sensors can be used. Si photodiodes are quantum-type photodetectors, and typically have high linear sensitivity in the range of 400 nm to 900 nm. By using a photodiode as the light-receiving surface (light-receiving part) of the radiation sensor, it is possible to make the radiation sensor smaller and less expensive.

[0025] The distance from the light source to the light receiving surface of the radiation sensor can be, for example, 1 cm or more, preferably 10 to 100 cm, when targeting grass. On the other hand, when targeting trees or forests, the distance can be more than 100 cm, and although there is no particular upper limit, it can be, for example, 50 m, preferably 10 m (1000 cm) or less.

[0026] (bandpass filter) The radiation sensor preferably includes a bandpass filter that filters out light with a wavelength band of less than 750 nm. Furthermore, the radiation sensor preferably extracts radiation only from near-infrared light with a wavelength band of 750 nm or greater. By using a radiation sensor that can filter out wavelengths shorter than the target near-infrared light band, resistance to external light noise can be improved. When an LED with a peak wavelength of 850 nm is used as the light source, the bandpass filter more preferably filters out light with a wavelength band of less than 800 nm, and particularly preferably filters out light with a wavelength of less than 800 nm and light with a wavelength of 1100 nm or greater. In addition to the bandpass filter and the light receiving surface (light receiving section), the radiation sensor may also employ known components such as a substrate for adjusting the gain of the photoelectrically converted voltage (detection signal) and outputting it, and a light diffusion plate.

[0027] <Light source fixing part, radiation sensor fixing part, connecting member> The plant sensor device of the present invention preferably includes a light source fixing part that fixes the light source. The plant sensor device of the present invention preferably includes a radiation sensor fixing portion for fixing the radiation sensor.

[0028] In one preferred embodiment of the present invention, the light source fixing unit preferably fixes the light source above the plant measurement unit. In this case, the radiation sensor fixing unit preferably fixes the radiation sensor below the plant measurement unit with its light-receiving surface facing the measurement unit. On the other hand, in a large plant sensor device, a power source, a reflector, and an optical system are required, and it is expected that the light source will be larger than the radiation sensor. Therefore, from the viewpoint of physical stability of the device, it is preferable to turn the device upside down, so that the light source fixing unit fixes the light source below the plant measurement unit, and the radiation sensor fixing unit fixes the radiation sensor above the plant measurement unit with its light-receiving surface facing the measurement unit. Since the plant sensor device of the present invention can suppress the effects of external light, it can be used vertically by arranging the light source and radiation sensor above and below the plant, or horizontally or diagonally by arranging the light source and radiation sensor horizontally or diagonally relative to the plant. In particular, when it is a handheld type, the ability to use it horizontally or diagonally is an advantage.

[0029] Furthermore, when the plant sensor device of the present invention includes a radiation sensor fixing portion and a light source fixing portion, it is preferable to include a connecting member that connects the radiation sensor fixing portion and the light source fixing portion. The connecting member is preferably flexible and can fix the distance from the light source to the light receiving surface of the radiation sensor at a desired distance. In the present invention, it is preferable that the connecting member is provided with a grip portion. There are no particular restrictions on the grip portion, and it may be a fixed handle or a strap.

[0030] <Recording Department> The plant sensor device of the present invention has a recording unit that records the output value from the radiation sensor. The recording unit is used as a so-called data logger. The output from the radiation sensor is first input to the recording unit and recorded, and then input to the calculation unit. However, the recording unit may be integrated into a member common to the control unit and calculation unit, and may be, for example, a CPU or a control panel.

[0031] In a first aspect of the present invention, the recording unit records the irradiation period and extinction period of near-infrared light from the light source. The recording unit also classifies the output values ​​from the radiation sensor into (1) NIR output values ​​during the irradiation period of near-infrared light, and (2) non-irradiation output values ​​during the extinction period of near-infrared light. By classifying and recording the NIR output values ​​and non-irradiation output values ​​in this way, the calculation unit can use these to calculate parameters related to the leaf mass of the plant. In a second aspect of the present invention, among the output values ​​from the radiation sensor, (1) the NIR output value during the irradiation period of near-infrared light is classified into (1-1) a first NIR output value during the irradiation period of near-infrared light with a first emission intensity, and (1-2) a second NIR output value during the irradiation period of near-infrared light with a second emission intensity. By classifying and recording the first NIR output value and the second NIR output value in this way, a calculation unit can use these to calculate parameters related to the leaf amount of the plant. The recording unit can classify and record the output values ​​during the irradiation period and extinction period based on the time (timing) measured using timing means such as a clock or timer (not shown in the drawings). Alternatively, when the control unit controls the irradiation period and extinction period, the recording unit can classify and record the output values ​​during the irradiation period and extinction period based on the time synchronized with the control unit.

[0032] In the first aspect of the present invention, when the control unit (described later) controls the near-infrared light to two levels, a first emission intensity and a second emission intensity, as in the second aspect, it is more preferable that the recording unit classifies, among the output values ​​from the radiation sensor, (1) the NIR output value during the irradiation period of near-infrared light into (1-1) the first NIR output value during the irradiation period of near-infrared light at the first emission intensity, and (1-2) the second NIR output value during the irradiation period of near-infrared light at the second emission intensity. By classifying and recording the first NIR output value, the second NIR output value, and the non-irradiation output value in this manner, it is possible to further improve resistance to external light noise when the calculation unit uses these to calculate parameters related to the leaf mass of the plant.

[0033] In the present invention, it is preferable that the recording unit stores software, applications, programs, conversion formulas, conversion tables, etc. for calculating parameters relating to the growth rate of each type of plant.

[0034] <Arithmetic section> The plant sensor device of the present invention preferably includes a calculation unit that calculates a difference A calculated from (NIR output value) - (non-irradiation output value) and further converts the difference A into a leaf area index. The NIR output value is the output value (NIR) during the near-infrared light irradiation period at a peak in the graph of the relationship between time from the start of measurement and photon flux density (output value) as shown in Figure 5. The non-irradiated output value is the output value (Non) during the irradiation period at a peak in Figure 5. The difference A corresponds to the part marked A in Figure 5.

[0035] In the present invention, it is preferable that the leaf area index is a linear function of a logarithmic function with the difference A or a function thereof as the antilogarithm. The calculation unit can calculate the leaf area index from the difference A using a leaf area index conversion means. A program, which is an example of a leaf area index conversion means, calculates the LAI from the difference A based on the fact that the natural logarithm Ln(A) of the difference A calculated from (NIR output value) - (non-irradiated output value) is proportional to the leaf area index LAI. As shown in Figure 7, the relationship between the leaf area index LAI and the 850 nm transmittance (difference A) is expressed by an exponential function. According to the indoor results in Figure 7, the 850 nm transmittance (difference A) = 90.645e -0.564×LAI By taking the natural logarithm of both sides, the formula (1) can be used to calculate Ln(A) = Ln(90.645) - 0.564 × LAI. In other words, the leaf area index LAI is expressed as a linear function of the logarithm function with the difference A as the antilogarithm. By storing the relational expression (1) in the recording unit and performing the calculation, the leaf area index can be calculated from the difference A. Furthermore, from Figure 7, the R 2 = 0.9915, which shows that there is an extremely 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. Alternatively, a calibration curve or conversion table may be prepared in advance, and the leaf area index may be calculated from the difference A. A calibration curve for each vegetation type may be saved in the recording unit, and the leaf area index corresponding to the calibration curve may be output based on the difference A calculated from the calibration curve and the measured (NIR output value) - (non-irradiated output value).

[0036] In both the first and second aspects of the present invention, when the control unit (described later) controls the near-infrared light to two levels, the first emission intensity and the second emission intensity, it is preferable that the calculation unit calculates the difference B, calculated from (first NIR output value) - (second NIR output value), and converts it into a leaf area index. When using this to calculate parameters related to the leaf mass of a plant, the following mechanism can further improve resistance to external light noise. When recording NIR output values ​​at two levels, 100% and 50%, the 50% output value can be used as the baseline for calculations. In other words, the calculation unit calculates the difference B between (100% NIR output value) and (50% NIR output value) and converts it into a leaf area index, eliminating the influence of fluctuations in NIR transmission due to external light that may occur when using a non-irradiated output value as the baseline. The influence of fluctuations in NIR transmission due to external light can also be reduced by using the results of repeated measurements over a short period of time while repeatedly turning the near-infrared light from the light source on and off as the NIR output value.

[0037] In the calculation unit, it is preferable to use the output value in the intermediate period (25 to 75%) of the irradiation period and the extinction period as the NIR output value and the non-irradiation output value, with the period from the beginning to the end of each period being 100%. Using the graph in Figure 5 as an example, it is preferable to use the output value in the intermediate period (27.5 to 32.5 seconds from the start of measurement) of the irradiation period (ini; approximately 25 seconds from the start of measurement) to the end (ter; approximately 30 seconds from the start of measurement) of the irradiation period as 100% (corresponding to approximately 5 seconds) as the NIR output value. The average value of the output value per hour in the intermediate period may be used as the NIR output value, or the integrated value (or the average value) of the output value in the intermediate period may be used as the NIR output value. The beginning of the irradiation period refers to the part where the peak output value begins to rise in the graph of the relationship between the time from the start of measurement and the photon flux density (output value) as shown in Figure 5. The end of the irradiation period refers to the part where the peak output value gradually decreases and reaches its minimum value.

[0038] <Control unit> The plant sensor device of the present invention preferably further includes a control unit. The control unit preferably controls the light source to repeat a cycle consisting of an illumination period and an extinction period. The control unit may lengthen only one of the light source irradiation period and extinction period, but preferably controls them to be equally spaced. For example, the control unit preferably controls the light source irradiation period and extinction period to be approximately equally spaced within ±30% of each other, more preferably to be approximately equally spaced within ±20% of each other, and particularly preferably to be approximately equally spaced within ±10% of each other. For example, if the light source irradiation period is 5 seconds, the extinction period is preferably 3.5 to 6.5 seconds, more preferably 4 to 6 seconds, and particularly preferably 4.5 to 5.5 seconds.

[0039] The control unit preferably sets the illumination period and extinction period of the light source to 1 millisecond to 1 minute, more preferably 10 milliseconds to 10 seconds, and particularly preferably 0.1 seconds to 5 seconds.

[0040] In a first aspect of the present invention, the control unit preferably controls the light source to emit infrared light at a first emission intensity and a second emission intensity that is 1 / n times the first emission intensity (n is a positive number). In a second aspect of the present invention, the control unit controls the light source to emit infrared light at the first emission intensity and a second emission intensity that is 1 / n times the first emission intensity (n is a positive number). During measurement, irradiating the light source at two levels of emission intensity improves resistance to external light noise. For example, when the first emission intensity is 100%, n=2, i.e., the second emission intensity can be 50%, which is 1 / n=0.5. 1 / n is preferably 0.1 to 0.9, more preferably 0.3 to 0.7, and particularly preferably 0.4 to 0.6.

[0041] <Growing means> The plant sensor device of the present invention preferably includes a growth means for controlling at least one of fertilizer, water, temperature, and humidity so as 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 the predetermined range. The growing means is preferably controlled by a control unit. The growing means is not particularly limited, and can be any means used in known vegetable factories, smart agriculture fields, etc. It is preferable that the artificial light source of the wavelength band used in the growing means does not include near-infrared light.

[0042] [Optical measurement method for active plants] The active optical plant measurement method of the present invention is a method using the plant sensor device of the present invention. Unlike passive optical plant measurement methods, the plant sensor device of the present invention actively irradiates near-infrared light onto the plant, which has the advantage of being able to shorten the measurement period and suppress the influence of external light from the surrounding environment.

[0043] The active optical plant measurement method of the present invention is preferably used for ground truthing of remote sensing from the air or space, measuring plant growth in a plant growth facility, measuring forest vegetation, and measuring leaf mass in a plant community or foliage. These are, in other words, preferred applications of the plant sensor device of the present invention.

[0044] Other preferred aspects of the active plant optical measurement method of the present invention are the same as the preferred aspects of the plant sensor device of the present invention. [Example]

[0045] The present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0046] [Example 1: Plant sensor device of the first embodiment] The plant sensor device of Example 1 was examined. A demonstration experiment of the plant sensor device of Example 1 having the configuration shown in FIG. 1 was carried out in the following manner, and it was demonstrated that the leaf area index LAI can be measured outdoors.

[0047] The light source used was a single near-infrared LED light source with a peak wavelength of 850 nm and a half-width of 50 nm or less. The light source was placed above the leaves (vertically upward). A Si photodiode (commercially available solar radiation sensor) was used as the radiation sensor. The radiation sensor was placed on the lower side (vertically downward) of the leaves (plants), opposite the light source. The memory of a PC equipped with a general-purpose CPU was used as the recording unit, and the output values ​​photoelectrically converted from light received by the radiation sensor were recorded. The CPU of the PC is equipped with a calculation unit and a control unit. The calculation unit uses a leaf area index conversion means (program) stored in the memory to calculate the difference A calculated from (NIR output value) - (non-irradiated output value), and can further convert the difference A into a leaf area index.

[0048] The control unit controlled the light source to repeat one cycle, starting NIR irradiation 5 seconds after the start of measurement and turning the NIR off 5 seconds later, thereby intermittently irradiating the leaves with near-infrared light. In Example 1, the first cycle had no leaves (reference), the second cycle had a 5-second quenching period and a 5-second NIR irradiation period for the first set of leaves, and the third cycle had a 5-second quenching period and a 5-second NIR irradiation period for the second set of leaves. After the third cycle, an additional 5-second quenching period was added. The near-infrared light transmitted through the foliage is received by a radiation sensor, and the photoelectrically converted output value is converted into irradiance (W m -2 The output values ​​from the initiation (ini) to the end (ter) of the illumination period and extinction period were taken as 100%, and the output values ​​from 25 to 75% of the mid-period were used as the NIR output value and the non-illumination output value. Furthermore, using a leaf area index conversion means (program) stored in memory, the difference A calculated from (NIR output value) - (unirradiated output value) was calculated, and the difference A was then converted into a leaf area index. The results obtained are shown in Figure 5. Figure 5 is a graph showing the relationship between the time from the start of measurement and the photon flux density (output value) in Example 1. The leaf area index conversion means (program) calculates the leaf area index (LAI) from the difference A, based on the fact that the natural logarithm Ln(A) of the difference A calculated from (NIR output value) - (unirradiated output value) is proportional to the leaf area index (LAI). From Figure 5, it was found that the leaf area index of the first leaf group was LAI = 1, and that of the second leaf group was LAI = 2. It was also found that the leaf area index can be calculated even if the measurement time is short, on the order of several tens of seconds. Furthermore, the non-irradiated output value is an output value measured based on external light such as sunlight. The plant sensor device of Example 1 calculates the LAI using the difference A calculated from (NIR output value) - (non-irradiated output value), i.e., the fluctuation in the output value due to irradiation with the NIR light source, and therefore can substantially eliminate the influence of external light in the surrounding environment. Therefore, it was found that the plant sensor device of the present invention can quantify the degree of plant growth by suppressing the influence of external light from the surrounding environment and determining parameters related to the amount of plant leaves with a simple, low-cost configuration (only one irradiation sensor).

[0049] [Example 2: Plant sensor device of the first embodiment] A demonstration experiment of the plant sensor device of Example 2 was carried out in the following manner, and the measurement results obtained indoors and outdoors were compared. Fig. 6(A) is a photograph of the leaves of the plant that was the measurement target and the radiation sensor used in Example 2. Fig. 6(B) is a photograph of the configuration of the plant sensor device of Example 2. The plant sensor device of Example 2 used the same light source and radiation sensor as in Example 1. Indoors where sunlight does not enter, the number of leaves to be measured was increased, and the leaves were irradiated with near-infrared light from a light source in the same manner as in Example 1, to determine the leaf area index. Meanwhile, under outdoor sunlight, the number of leaves to be measured was increased while irradiating the leaves with near-infrared light from a light source in the same manner as in Example 1, and the leaf area index was determined. The 850nm transmittance values ​​for the indoor and outdoor measurements where the leaf area index was 1, 2, 3, or 4 were calculated and plotted on a graph. An exponential function was then used to create an approximate curve. The approximate curve obtained was calculated as follows: x is the leaf area index, y is the 850nm transmittance (corresponding to the difference A), and y is the 850nm transmittance (corresponding to the difference A). For indoor measurements, y = 90.645e -0.564x The correlation coefficient R 2 =0.9915. In the outdoors, y=90.557e -0.517x The correlation coefficient R 2 =0.983. The results are shown in Figure 7. Figure 7 is a graph showing the relationship between leaf area index and 850 nm transmittance in indoor and outdoor measurements. As can be seen from Figure 7, the results obtained were almost the same for indoor and outdoor measurements, and there was almost no effect from indoor lighting or sunlight. This shows that the plant sensor device of the present invention can be used in artificial light environments and environments with fluctuating solar radiation. In other words, it was found that the plant sensor device of the present invention can quantify the degree of plant growth by suppressing the influence of external light from the surrounding environment, and can obtain highly accurate parameters related to the amount of leaves in a plant with a simple, low-cost configuration.

[0050] [Example 3: Plant sensor device of the second embodiment] A demonstration experiment of the plant sensor device of Example 3 was carried out in the following manner, demonstrating that the leaf area index LAI can be measured outdoors when the light source is controlled to irradiate infrared light at a first emission intensity and a second emission intensity that is half the first emission intensity. In Example 3, measurements were carried out using the same plant sensor device as in Example 1, except that a calculation unit was used that was capable of calculating difference B from (first NIR output value) - (second NIR output value) using leaf area index conversion means (program) stored in memory as a calculation unit, and further converting difference B into a leaf area index, and the control unit was controlled as follows. The control unit started irradiating NIR at the first emission intensity (100%) 5 seconds after the start of measurement, then irradiated NIR at the second emission intensity (50% of the first emission intensity) 3 seconds later, and then turned off the NIR for 4 seconds 3 seconds later, forming one cycle.The control unit controlled the light source to repeat this cycle, intermittently irradiating the leaves with near-infrared light.

[0051] In Example 3, the first cycle had no leaves (reference). The second cycle had a 3-second NIR irradiation period at the first emission intensity, a 3-second NIR irradiation period at the second emission intensity, and a 4-second quenching period for the first leaves. The third cycle had a 3-second NIR irradiation period at the first emission intensity, a 3-second NIR irradiation period at the second emission intensity, and a 4-second quenching period for the first leaves. The leaf area index conversion means (program) calculates the leaf area index (LAI) from the difference B, based on the fact that the natural logarithm Ln(B) of the difference B calculated from (first NIR output value) - (second NIR output value) is proportional to the leaf area index (LAI). From Figure 8, it was found that the leaf area index of the first leaf group was LAI = 1, and that of the second leaf group was LAI = 2. It was also found that the leaf area index can be calculated even if the measurement time is short, on the order of several tens of seconds. Furthermore, the plant sensor device of Example 3 calculates the leaf area index using the difference B calculated from (first NIR output value) - (second NIR output value), i.e., the fluctuation in the output value due to irradiation with the NIR light source, thereby substantially eliminating the influence of external light in the surrounding environment. Therefore, it was found that the plant sensor device of the second aspect of the present invention can also suppress the influence of external light from the surrounding environment in order to quantify the degree of plant growth, and can obtain parameters related to the amount of plant leaves with a simple, low-cost configuration (only one irradiation sensor). [Explanation of symbols]

[0052] 1 plant 2 Measuring part 11 Light source 12 Infrared light 13 Transmitted light 21 Radiation Sensor 22 Photosensitive surface 23 Bandpass Filter 30 Computer 31 Recording Section 32 Arithmetic section 33 Control Unit 34 CPU 35 Display section 36 Output section 41 Light source fixing section 42 Radiation sensor fixing part 43 Connecting member 44 Gripping part 51 Growth Methods 100 Plant sensor device L is the distance from the light source to the receiving surface of the radiation sensor A is the difference calculated from (NIR output value) - (non-irradiated output value) NIR NIR output value Non-irradiation output value ini Beginning mid interim period Terminus

Claims

1. a light source that intermittently irradiates near-infrared light (NIR) onto plants; a radiation sensor disposed on the opposite side of the plant from the light source, the radiation sensor receiving the near-infrared light transmitted through the plant and outputting a photoelectrically converted output value; a recording unit that records an output value from the radiation sensor, the recording unit records the irradiation period and extinction period of the near-infrared light from the light source, A plant sensor device in which the recording unit classifies the output values ​​from the radiation sensor into (1) NIR output values ​​during the irradiation period of the near-infrared light, and (2) non-irradiation output values ​​during the extinction period of the near-infrared light.

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

3. 3. The plant sensor device according to claim 2, wherein the leaf area index is a linear function of a logarithmic function with the difference A or a function thereof as the antilogarithm.

4. 4. The plant sensor device according to claim 3, further comprising a growth means for controlling at least one of fertilizer, water, temperature, and humidity so as to suppress leaf growth of the plant when the leaf area index exceeds a predetermined range, or to promote leaf growth of the plant when the leaf area index falls below the predetermined range.

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

6. The plant sensor device of claim 1 , wherein the light source comprises a near-infrared light source alone.

7. 7. The plant sensor device according to claim 6, wherein the near-infrared light source emits near-infrared light in a narrow band having a peak wavelength of 750 nm to 1100 nm and a half-width of 50 nm or less.

8. 2. The plant sensor device according to claim 1, wherein the radiation sensor comprises a bandpass filter that filters out light in a wavelength band less than 750 nm, and extracts radiation only in a near-infrared wavelength band of 750 nm or more.

9. a radiation sensor fixing portion for fixing the radiation sensor; The plant sensor device according to claim 1 , wherein the radiation sensor fixing portion fixes the radiation sensor below the measurement portion of the plant with the light receiving surface facing the measurement portion.

10. a light source fixing portion that fixes the light source, The plant sensor device according to claim 1 , wherein the light source fixing unit fixes the light source above the measurement unit for the plant.

11. a radiation sensor fixing portion that fixes the radiation sensor, a light source fixing portion that fixes the light source, and a connecting member that connects the radiation sensor fixing portion and the light source fixing portion, 2. The plant sensor device according to claim 1, wherein the distance from the light source to the light receiving surface of the radiation sensor is 1 to 1000 cm.

12. The plant sensor device according to claim 11 , wherein the connecting member is provided with a gripping portion.

13. a radiation sensor fixing portion that fixes the radiation sensor, and a light source fixing portion that fixes the light source, the light source fixing unit fixes the light source below the plant measurement unit, The plant sensor device according to claim 1 , wherein the radiation sensor fixing portion fixes the radiation sensor above the measurement portion of the plant with the light receiving surface facing the measurement portion.

14. The plant sensor device of claim 1, wherein the output values ​​in the intermediate period of 25 to 75% of the illumination period and the extinction period, with the beginning to end of each period being 100%, are used as the NIR output value and the non-illumination output value.

15. The plant sensor device according to claim 1 , wherein the illumination period and the extinction period are both from 1 millisecond to 1 minute.

16. Further, a control unit is provided, The plant sensor device according to claim 1 , wherein the control unit controls the illumination period and the extinction period of the light source to be approximately equal intervals within ±30% of each other.

17. a light source that irradiates near-infrared light (NIR) onto plants; a radiation sensor disposed on the opposite side of the plant from the light source, the radiation sensor receiving the near-infrared light transmitted through the plant and outputting a photoelectrically converted output value; a recording unit that records an output value from the radiation sensor; a control unit; the control unit controls the light source to irradiate infrared light at a first emission intensity and a second emission intensity that is 1 / n times (n is a positive number) of the first emission intensity; A plant sensor device in which the recording unit classifies (1) the NIR output value during the irradiation period of the near-infrared light among the output values ​​from the radiation sensor into (1-1) a first NIR output value during the irradiation period of the near-infrared light at the first emission intensity, and (1-2) a second NIR output value during the irradiation period of the near-infrared light at the second emission intensity.

18. The plant sensor device according to claim 17, further comprising a calculation unit that calculates a difference B calculated from (first NIR output value) - (second NIR output value) and converts it into a leaf area index.

19. A method for active optical measurement of plants using the plant sensor device according to any one of claims 1 to 18.

20. The active optical measurement method for plants according to claim 19 is used for ground truthing of remote sensing from the air or space, measuring plant growth in plant growth facilities, measuring forest vegetation, and measuring leaf mass in plant communities or foliage.

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