JP5410323B2 - Optical vegetation index sensor - Google Patents

Description

  The present invention relates to an optical vegetation index sensor that optically and non-destructively measures the amount of plant leaves per unit surface area of vegetation (leaf area index) or photosynthetic effective radiation absorption rate.

The leaf area index (LAI) is an index value indicating the sum of areas on one side of all leaves of the vegetation on the upper vegetation per unit horizontal area. For example, if the total area of the leaves existing on the ground of 1 m ² is 2 m ² , LAI = 2, which means that when the leaves are arranged on the ground with no gap, two sheets overlap. Normal leaf vegetation leaf area index is about 3-7. The photosynthetic effective radiation absorption rate (fAPAR) is an index value indicating the ratio before and after absorption of photosynthetic active radiation (PAR) absorbed by the photosynthetic organ of vegetation. For example, in PAR is 2000μmol / m ² / s on canopy, PAR of forest floor at the same time is as long as 50μmol / m ² / s, fAPAR becomes 0.975.

  Leaf area index is an important parameter for evaluating vegetation function, and is an important indicator of absorption of photosynthetic effective radiation, photosynthesis and transpiration, and vegetation's carbon absorption capacity. Widely used in global environmental sciences. However, the development of the optical leaf area index sensor has been delayed, and no photosynthetic effective radiation absorptivity sensor that can measure the photosynthetic effective radiation absorptance due to vegetation without comparison with the outside has been developed so far.

  By the way, the leaf area index can be directly measured by logging. The mowing method or sampling method obtains this by cutting all leaves existing on the unit ground surface area and obtaining the total area. This method is accurate in principle, but cuts the vegetation, resulting in complete destruction of the vegetation to be measured. The burden of human labor is heavy, and it is difficult to actually implement it.

  On the other hand, a method using optical properties for measuring the leaf area index has also been proposed. Conventionally, solar radiation incident on vegetation has been known to attenuate gradually. However, red radiation (R: wavelength range of 650 to 700 nm) is attenuated while passing through the leaf group, but near-infrared radiation (FR: wavelength range of 700 to 800 nm) on the short wavelength side is not so attenuated even when passing through this. Considering the cause of such spectral absorption characteristics, when radiation in the wavelength region of 400 nm to 700 nm called photosynthesis effective radiation (PAR) effective for photosynthesis passes through the leaf group, the leaf functions almost as a black body. The main reason is that radiation is absorbed by the area. Therefore, a method for estimating the leaf area index using the spectral absorption characteristics of the leaves can be considered.

  For example, using a fisheye lens and an electronic image sensor under vegetation, for each of near-infrared radiation and red radiation, the exposure time is changed to a plurality of types and an image of a predetermined area in the vegetation is photographed. For each subdivided area, obtain a brightness value for each of near infrared radiation and red radiation, find a brightness value ratio between the near infrared radiation and red radiation for each subdivision area, and use the brightness value ratio to calculate relative solar radiation. A technique for estimating the amount and obtaining the leaf area index has been proposed (see Patent Document 1). The leaf area index is estimated by performing image processing on the captured image. The leaf area index is estimated by obtaining the spatial distribution of the ratio of the radiance of the narrow-band vegetation transmission radiation.

  In addition, it has been conventionally disclosed that the spectral intensity ratio (= 800/675) of red radiation (wavelength 675 nm) and near-infrared radiation (wavelength 800 nm) that has passed through vegetation increases as the amount of leaves increases ( Non-patent document 1). The leaf area index is determined by measuring the spectral intensity ratio of the narrow band.

This non-patent document 1 reports that there is a correlation between the leaf area index X and the spectral intensity ratio Y (= 800/675), and a relationship of log Y = 0.3813 + 0.0989X. . Further, it is predicted that there is a relationship of log Y = 0.3813 + 0.0002908x between chlorophyll xmg / m ² and the spectral intensity ratio Y. As described above, the radiation effective for photosynthesis is PAR (radiation in the wavelength region from 400 nm to 700 nm), and the amount of chlorophyll is almost proportional to the total amount of leaves, so the spectral intensity ratio Y (= 800/675) has increased. Sometimes radiation is absorbed by the leaves as they pass through the foliage, suggesting that photosynthesis is active.

  Furthermore, as an example of an optical leaf area index sensor that has been put into practical use, there is a plant canopy analyzer that measures light by optically dividing the whole sky into five rings by the US company LI-COR. This technique does not use near-infrared radiation, but determines the leaf area index by measuring the spatial distribution of narrow-band transmitted radiation using a sensor of blue radiation (320 to 490 nm).

  In addition, a method of measuring the PAR plane distribution in the forest and estimating the LAI from the fluctuation amount of the measured value has been put into practical use (see Non-Patent Document 2). In this technique, measurement is performed while moving the PAR sensor on a clear day, and the leaf area index is obtained by estimating the density of leaves from the PAR intensity distribution.

  Next, remote sensing using reflected radiation instead of transmitted radiation as described above has been proposed. The reflected radiation of solar radiation from the forest is measured with an artificial satellite, and the leaf area index is estimated using the following vegetation index (Normalized Differential Vegetation Index, NDVI). Here, when NIR is a near-infrared wavelength band reflectance and RED is a visible red wavelength band reflectance, NDVI = (NIR−RED) / (NIR + RED). In the case of LANDSAT-TM data, the wavelength of 4 bands (NIR) is 760 nm to 900 nm, and the wavelength of 3 bands (RED) is 630 nm to 690 nm. Therefore, NDVI can be said to be an index of the leaf area index based on the reflectance of the narrow band reflected radiation.

JP 2007-171033 A

Carl F. Jordan, “Derivation of Leaf-Area Index from quality of light on the forest floor” Ecology, 1969, vol. 50, No. 4, 663-666 Jing M. Chen and Josef Cihlar, “Plant canopy gap-size analysis theory for improving optical measurements of leaf area index”, Applied Optics, 1995, vol. 34, No. 27,6211-6222

  As described above, the vegetation is cut and destroyed by the cutting method or the sampling method in order to obtain the leaf area index. In addition, the burden of human labor is large, and in fact this method is difficult to measure.

  Then, using the fisheye lens and the electronic image pickup device, the technique of Patent Document 1 in which images of predetermined areas are taken for each of near-infrared radiation and red radiation, and the relative solar radiation amount is estimated by obtaining the luminance value ratio thereof. It is affected by the weather at the time of image capture (images in fine weather cannot be used), and it is necessary to capture the image with consideration for exposure, and then image processing is necessary. Continuous measurement is difficult because it is an expensive device and requires image processing.

  In addition, in the report of Non-Patent Document 1 that the ratio of the radiation intensity of red radiation and near-infrared radiation that has passed through vegetation having a certain leaf area index is almost constant, 675 nm and 800 nm are obtained from plant physiological knowledge in the laboratory. Are selected and the leaf area index is calculated. Moreover, in order to suppress the height of the sun and the scattering of radiation by the leaves, it is necessary to measure the radiation from directly above with a sensor having a narrow angle directivity, and measurement in cloudy weather is not recommended. Therefore, the leaf area index sensor using the technique of Non-Patent Document 1 is a narrow band sensor and has a narrow angle directivity, so that it is avoided that the radiation amount (radiation intensity) to the sensor is insufficient and the sensitivity is low. I can't. When field measurements were actually performed, the measured values varied greatly and were not practical.

  Further, as reported in Patent Document 1, using (narrowband) transmitted radiation, (near infrared radiation (spatial) integrated value) / (red radiation (spatial) integrated value) is calculated. Even if the relative solar radiation ratio is calculated, if the weight of the radiation amount in the part where the leaves are not thick becomes relatively high and the weight of the radiation amount in the part where the leaves are thick becomes low, the estimation accuracy decreases. is expected. It has already been reported in Patent Document 1 that the estimation of the leaf area index by this method has failed.

  Narrow-band sensors with narrow angles of red and near-infrared radiation are easily affected by red edge shifts at 700 nm and subtle differences in the spectral characteristics of leaves, with low output and stable measurements outdoors. It was difficult.

  In addition, narrowband optical leaf area index sensors that have already been put into practical use must be measured simultaneously in the forest and outside the forest, or moved in the forest and measured, and are resistant to the weather during measurement. It was affected. In addition, a complicated optical system is required, and a complicated analysis is required for the measured value. In addition, since human operation is required for the measurement, unattended measurement over a long period of time cannot be performed.

  In addition, remote sensing by satellite also requires high directivity to receive reflected radiation at high resolution, but reflected radiation decreases exponentially with respect to the leaf area index, so the leaf area index increases. At the same time, it was inevitable that the decrease in reflected radiation intensity could not be detected. In particular, when the LAI is 2 or more, the estimation accuracy is remarkably lowered, and the weather at the time of photographing is greatly affected. Various correction methods have been proposed, but no definitive correction method has been proposed.

  In this way, all of the conventional optical leaf area index sensors are narrowband sensors that can automatically and continuously measure over a long period of time, eliminating the need for simultaneous measurements inside and outside the vegetation. There is no optical leaf area index sensor that can perform stable measurement without receiving light, has a large output, and can perform broadband measurements, and it is difficult to obtain a leaf area index that is close to the actual measurement value using an optical method. It was. Moreover, a photosynthetic effective radiation absorptivity sensor that optically obtains photosynthetic effective radiation absorptance only by measuring in vegetation has not been developed. Thus, there is an expectation for an optical vegetation index sensor that can measure the leaf area index or the photosynthetic effective radiation absorption rate.

  Therefore, the present invention does not require simultaneous measurement inside and outside the vegetation, can automatically and stably perform radiation measurement over a long period of time, is inexpensive, small, lightweight, broadband with high output, and a leaf area index. Another object of the present invention is to provide an optical vegetation index sensor capable of measuring a photosynthetic effective radiation absorption rate.

  When the optical vegetation index sensor of the present invention receives transmitted radiation transmitted through a leaf or a group of leaves, the optical vegetation index sensor corrects spectral characteristics for measuring the photon flux density with a correction filter for radiation in the visible radiation region of 400 nm to 700 nm. And a first radiation sensor that outputs as a PAR output indicating either the photosynthetic effective radiance or the photosynthetic photon flux density by photoelectrically converting the corrected radiation at the light receiving unit, and a bandpass filter for the received radiation. Extracting radiation only in the infrared radiation region of 700 nm to 1000 nm, and photoelectrically converting this radiation at the light receiving unit, can output IR output indicating either unit radiance or photon flux density in common with PAR output. The radiation sensor, the PAR output and the IR output are integrated with time, and the integrated value of the IR output is divided by the integrated value of the PAR output. Calculated, and characterized mainly in that an arithmetic unit for determining the leaf area index that corresponds to the ratio.

  The optical vegetation index sensor according to the present invention corrects spectral characteristics for measuring the photon flux density with a correction filter for radiation in the visible radiation region of 400 nm to 700 nm when receiving transmitted radiation transmitted through a leaf or a group of leaves. A first radiant sensor that outputs as a PAR output indicating either the photosynthetic effective radiance or the photosynthetic photon flux density by photoelectrically converting the corrected radiation at the light receiving unit, and a bandpass filter for the received radiation By taking out the radiation only in the infrared radiation region of 700 nm to 1000 nm by means of this, and photoelectrically converting this radiation at the light receiving part, it is possible to output IR output indicating either unit radiance or photon flux density in common with the PAR output. Two radiation sensors, PAR output and IR output are integrated over time, and the integrated value of IR output is divided by the integrated value of PAR output Calculating the ratio, it is mainly characterized by having an arithmetic unit for obtaining the photosynthetically active radiation absorption ratio corresponding to the ratio.

  According to the optical vegetation index sensor of the present invention, it is possible to perform continuous and stable radiation measurement in a forest, and it is inexpensive, compact, lightweight, has a large output, and has broadband output without simultaneous measurement inside and outside the vegetation. An optical vegetation index sensor capable of measuring area index or photosynthetic effective radiation absorption rate can be provided.

1 is an overall configuration diagram of an optical vegetation index sensor in Embodiment 1 of the present invention. Structure diagram of PAR sensor of optical vegetation index sensor in Embodiment 1 of the present invention Structure diagram of IR sensor of optical vegetation index sensor in Embodiment 1 of the present invention Explanatory diagram of spectral characteristics showing absorption band of photosynthesis Illustration of photosynthetic photon flux density Explanatory diagram of spectral reflection and transmission characteristics of deigo leaves Illustration of the spectral characteristics of reflection and absorption of leaves on the front and back sides Explanatory diagram showing the correlation between the logarithm ln (IR / PAR) of the wide-area irradiance ratio (IR / PAR) and the leaf area index LAI Explanatory drawing which shows the correlation of the logarithm ln {(IR / PAR) -0.6} of the linear function of the wide-area irradiance ratio (IR / PAR) and the leaf area index LAI Explanatory diagram showing seasonal changes in leaf area index LAI of deciduous broad-leaved forest Overall configuration diagram of an optical vegetation index sensor in Embodiment 2 of the present invention Explanatory drawing which shows correlation of wide area irradiance ratio (IR / PAR) and photosynthetic effective radiation absorptivity (fAPAR)

  According to the first aspect of the present invention, when the transmitted radiation transmitted through the leaf or the leaf group is received, the spectral characteristic correction for measuring the photon flux density by the correction filter for the radiation in the visible radiation region of 400 nm to 700 nm is performed. A first radiant sensor that outputs as a PAR output indicating either the photosynthetic effective radiance or the photosynthetic photon flux density by photoelectrically converting the corrected radiation at the light receiving unit, and a bandpass filter for the received radiation By taking out the radiation only in the infrared radiation region of 700 nm to 1000 nm by means of this, and photoelectrically converting this radiation at the light receiving part, it is possible to output IR output indicating either unit radiance or photon flux density in common with the PAR output. Two radiation sensors, PAR output and IR output are integrated over time, and the ratio is calculated by dividing the integrated value of IR output by the integrated value of PAR output. And is optically vegetation index sensor, characterized in that an arithmetic unit for determining the leaf area index that corresponds to the ratio. With this configuration, the ratio of the integrated value of the IR output and the integrated value of the PAR output to the transmitted light transmitted through the leaf, for example, the ratio obtained by dividing the integrated value of the infrared radiance by the integrated value of the photosynthetic radiance, Since the area index can be obtained, it is possible to perform continuous and stable radiation measurement in the forest, without the simultaneous measurement inside and outside the vegetation, cheap, small, lightweight, high output, broadband and leaf area index An optical vegetation index sensor capable of measurement can be provided.

  According to a second aspect of the present invention, in the first aspect, a light diffusing plate capable of cosine correction of radiation is provided on the light receiving surfaces of the first radiation sensor and the second radiation sensor, and an incident angle of incident radiation. The optical vegetation index sensor is characterized in that the characteristic is set to a wide angle. With this configuration, the entire canopy is averaged, it is not greatly affected by the height of the sun or light scattering, etc., it can receive a large amount of light stably at a wide angle, and a high sensitivity, high output sensor can be realized, It is possible to provide an optical vegetation index sensor that is less affected by noise and can measure a leaf area index by broadband.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the arithmetic unit integrates the PAR output and the IR output, and the integrated value of the integrated IR output is integrated with the integrated PAR output. An optical vegetation index sensor comprising: a ratio calculation unit that calculates a ratio by dividing by a value; and a leaf area index conversion unit that calculates a leaf area index corresponding to the ratio based on the ratio. With this configuration, the integration means based on the ratio of the integrated value of the IR output to the integrated value of the PAR output with respect to the transmitted light transmitted through the leaf, for example, the ratio obtained by dividing the integrated value of the infrared radiation by the integrated value of the photosynthetic radiation And an accurate leaf area index can be obtained by simple calculation by the ratio calculating means and the leaf area index converting means.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the leaf area index is a linear function of a logarithmic function having a ratio or a true number of the function. It is an optical vegetation index sensor. With this configuration, an accurate leaf area index can be obtained simply by performing a simple calculation based on the ratio of the integrated value of the IR output and the integrated value of the PAR output to the transmitted light transmitted through the leaves. Provides an optical vegetation index sensor that can perform stable and stable radiation measurements, and is inexpensive, compact, lightweight, has high output, and can measure the leaf area index broadband, without simultaneous measurement inside and outside the vegetation can do.

  According to a fifth aspect of the present invention, when transmitted radiation transmitted through a leaf or a group of leaves is received, the spectral characteristic is corrected for measuring the photon flux density with a correction filter for radiation in the visible radiation region of 400 nm to 700 nm. A first radiant sensor that outputs as a PAR output indicating either the photosynthetic effective radiance or the photosynthetic photon flux density by photoelectrically converting the corrected radiation at the light receiving unit, and a bandpass filter for the received radiation By taking out the radiation only in the infrared radiation region of 700 nm to 1000 nm by means of this, and photoelectrically converting this radiation at the light receiving part, it is possible to output IR output indicating either unit radiance or photon flux density in common with the PAR output. Two radiation sensors, PAR output and IR output are integrated over time, and the ratio is calculated by dividing the integrated value of IR output by the integrated value of PAR output. It is optically vegetation index sensor, characterized by having an arithmetic unit for converting the photosynthetically active radiation absorption ratio corresponding to the ratio by. With this configuration, photosynthesis is based on the ratio of the integrated value of IR output and the integrated value of PAR output to the transmitted light transmitted through the leaves, for example, the ratio of the integrated value of infrared radiance divided by the integrated value of photosynthetic radiance. Since it can be converted into an effective radiation absorption rate, stable radiation measurement can be performed continuously in the forest, and it is inexpensive, compact, lightweight, high output, and broadband photosynthesis without simultaneous measurement inside and outside the vegetation. An optical vegetation index sensor capable of measuring an effective radiation absorption rate can be provided.

  Hereinafter, the optical vegetation index sensor according to the first embodiment of the present invention will be described. As shown in FIGS. 1, 2 and 3, an optical leaf area index sensor 1 which is an optical vegetation index sensor of Example 1 is a photosynthetic effective radiation area radiation sensor 2 (first radiation sensor in the present invention, hereinafter referred to as “first radiation sensor”). PAR sensor 2), infrared radiation sensor 3 (second radiation sensor in the present invention, hereinafter referred to as IR sensor 3), output cables 41 and 42 connected to PAR sensor 2 and IR sensor 3, respectively, and PAR sensor 2 , For each output (PAR output, IR output) from the IR sensor 3, a calculation unit 5 that calculates a ratio of both output values and converts it into a leaf area. The shape of the PAR sensor 2 and the IR sensor 3 is not limited to a cylindrical shape even if light is received from all directions, and is, for example, a long rod shape or a plurality of sensors so that average radiation in a forest can be measured. Also good. The calculation unit 5 may be configured as software in the computer 7 as shown by the wavy line in FIG. 1, or may be a device that performs analog calculation with other electrical calculation circuits.

First, as the first radiation sensor, the PAR sensor 2 that outputs the PAR output indicating the photosynthetic photon flux density (μmol / m ² / s) or the photosynthetic radiance (W / m ² ), as shown in FIG. This is a sensor provided with a housing 18 that accommodates a substrate 29 to which the section 11 is attached. A light diffusing plate 20 is provided on the top surface of the housing 18. Here, the photosynthesis radiance corresponds to a value obtained by converting the amount of photons per unit area (photosynthesis photon flux density) that can be used for photosynthesis into energy (radiance (W / m ² )) as described later. To do. Therefore, the output voltage (mV) indicating the change in the amount of charge photoelectrically exchanged in the light receiving unit 11 is converted into both units of radiance (W / m ² ) and photon flux density (μmol / m ² / s). Can be output. Here, it is preferable to employ, for example, a Si photodiode, which is a quantum photodetector, for the light receiving unit 11. Thus, by using the light receiving unit 11 as a photodiode, the PAR sensor 2 can be reduced in size and reduced in price. In the space between the light diffusing plate 20 and the light receiving unit 11, a UV / IR cut filter 13 and a blue extended filter 15 are disposed in order from the top. The output voltage (detection signal) photoelectrically converted by the light receiving unit 11 is output to the embedded connector 31 and output to the output cable 41 via the cable connector 32. The UV / IR cut filter 13 and the blue extended filter 15 correspond to the correction filter of the present invention.

  The casing 18 is cylindrical and has a recess on the top surface, and the light diffusing plate 20 protrudes and is installed with the top surface side open at the center of the recess. More preferably, R is given to the edge portion or the shape is made a dome shape. With the light diffusing plate 20 having such a structure, substantially sufficient incident angle characteristics (cosine correction) can be obtained. Further, an optical path for guiding the light emitted from the light diffusion plate 20 to the light receiving unit 11 is provided in the housing 18. The light diffusing plate 20 is configured to take light from all over the light receiving unit 11 widely at a wide angle. A UV / IR cut filter 13 and a blue extended filter 15 are disposed in the optical path for guiding the light emitted from the diffuser plate 20, and the wavelength region is limited to a specific range and the sensitivity is adjusted by the action of these filters. Although details will be described later, correction of spectral characteristics for measurement by the photon flux density is performed.

  Therefore, all the light from the outside through the vegetation enters from above the light diffusion plate 20, is cosine corrected, is diffused and averaged inside, and is emitted from the bottom surface into the housing 18. With these configurations, almost all light from the outside can be captured. Incident light from below is blocked by the housing 18. In the light receiving unit 11, a light receiving surface is placed on the upper surface side which is the light diffusion plate 20 side on the substrate 29. In the order from the top of the optical path, the members are arranged in the order of the light diffusing plate 20, the UV / IR cut filter 13, the blue expansion filter 15, and the light receiving unit 11.

  Note that the structure of the housing 18 is such that the UV / IR cut filter 13, the blue extended filter 15, the substrate 29, and the like can be securely fixed and arranged. It is sufficient if it can be converted, and the structure is not particularly limited. Further, the structure of the board 29, the embedded connector 31 and the cable connector 32 is not limited to a specific structure as long as the board 29 can adjust and output the gain of the detection signal.

  Next, as a second radiation sensor, an IR sensor 3 that measures the irradiance in an IR (Infrared) region and outputs an IR output is a housing that houses a substrate 30 to which a light receiving unit 12 made of a photodiode is attached. A body 19 is provided, and a light diffusing plate 21 is provided on the top surface of the housing 19. Since the Si photodiode is a quantum type photodetector and has a high linearity sensitivity in the range of 400 nm to 1000 nm, it is preferable to use an Si photodiode as the PAR sensor 2 for the light receiving unit 12. is there. By using a photodiode, the IR sensor 3 can be reduced in size and reduced in price. An IR pass filter 14 (a band pass filter in the present invention) is disposed in the space between the light diffusing plate 21 and the light receiving unit 12. The voltage (detection signal) photoelectrically converted by the light receiving unit 12 is output to the embedded connector 33 and output to the output cable 42 via the cable connector 34.

  The casing 19 is cylindrical and has a recess on the top surface, and a light diffusing plate 21 protrudes and is installed with the top surface side open at the center of the recess. Further, an optical path for guiding the light emitted from the light diffusion plate 21 to the light receiving unit 12 is provided in the housing 19. The light diffusing plate 21 has a configuration for diffusing and averaging light in order to take light from the whole sky into the light receiving unit 12 at a wide angle. An IR path filter 14 is disposed at the center of the casing 19 as an optical path of the emitted light, and the light receiving unit 12 is disposed below the IR path filter 14.

  The housing 19 is sufficient if the IR pass filter 14 can be securely fixed and arranged on the optical path of the received light, and the light can be photoelectrically converted by the light receiving unit 12 after adjusting the light to a predetermined characteristic. is there. Further, the embedded connector 33 and the cable connector 34 may have any structure that can output a detection signal.

  In the IR sensor 3, all the light that has passed through the vegetation is incident from above the light diffusion plate 21, diffused inside, and emitted from the bottom surface into the housing 19. The voltage (detection signal) photoelectrically converted by the light receiving unit 12 is output to the embedded connector 33 after gain adjustment, and is output to the output cable 42 via the cable connector 34. This IR pass filter 14 limits the wavelength region and adjusts the sensitivity.

  The main parts of the PAR sensor 2 and the IR sensor 3 can use parts common to the two radiation sensors. The PAR sensor 2 and the IR sensor 3 are partially different in structure such as a filter for adjusting the characteristics of light, but the configuration of the remaining main parts such as the main bodies of the casings 18 and 19 and the cable connectors 32 and 34 are common. It is possible to make specifications, and it is possible to share parts and share optical characteristics.

Next, a configuration for calculating a leaf area index based on outputs (PAR output and IR output) from two radiation sensors will be described. Each output from the PAR sensor 2 and the IR sensor 3 is input to the calculation unit 5. The voltage (mV) photoelectrically exchanged at the light receiving unit 11 can be converted into any unit of irradiance (W / m ² ) and photon flux density (μmol / m ² / s) depending on the setting. In the effective irradiance (W / m ² ), the latter becomes the photosynthetic photon flux density (μmol / m ² / s). By multiplying the photoelectrically exchanged voltage (mV) by a conversion factor (gain adjustment), it can be easily converted into any unit of radiance and photon flux density. When one unit is adopted as a reference, the output can be easily changed from one to the other by changing the setting. Note that the calculation unit 5 can also perform conversion. For the voltage (mV) photoelectrically exchanged in the light receiving unit 12, the irradiance in the infrared radiation region of 700 nm to 1000 nm (hereinafter referred to as infrared radiance (W / m ² )) and its photon flux density (hereinafter referred to as infrared photon flux). It can be converted into either unit of density (μmol / m ² / s). What is important for the present invention is that the unit of the radiance and photon flux density for PAR output and IR output is either radiance (W / m ² ) or photon flux density (μmol / m ² / s). Output or calculate in a common unit.

  The calculation unit 5 integrates the two output values, which are analog quantities, together with the sunshine hours counted using a timekeeping means (not shown) such as a clock, a timer, and the ratio, that is, the integrated value of IR output / integrated PAR output. An analog arithmetic circuit for calculating a value is provided. Alternatively, the calculation unit may be a software configuration that performs digital calculation in the computer 7 after A / D conversion. Here, the integrated value of the IR output corresponds to the total amount of change in the electric charge photoelectrically exchanged by the IR sensor 3, and the integrated value of the PAR output corresponds to the total amount of the change in electric charge photoelectrically exchanged by the PAR sensor 2. (Integrated value of IR output / Integrated value of PAR output) corresponds to the ratio of the total number of photons received in the visible radiation region of 400 nm to 700 nm and the infrared radiation region of 700 nm to 1000 nm. This ratio is substantially equal to either the ratio (integrated value of infrared radiance / integrated value of photosynthetic effective radiation) or (integrated value of infrared photon flux density / integrated value of photosynthetic photon flux density). It turns out that it is the same ratio. The same calculation result can be obtained with either unit of denominator and numerator quantity. As shown in FIG. 1, the two output values are integrated by the integrating means 53 provided in the calculating unit 5, and the ratio calculating means 51 outputs the ratio of the two integrated values. The software ratio calculating means 51 and the integrating means 53 are function implementing means for reading a program for calculating the ratio into the computer 7 and executing this processing.

  The calculation result is passed to the leaf area index conversion means 52 of FIG. 1 provided in the calculation unit 5, and the leaf area index conversion means 52 obtains the leaf area index corresponding to the ratio as the calculation result. In the calculation, in the case of the above-described software computing unit 5, a correlation function (conversion formula 61) between the ratio and the leaf area index is registered in advance in the memory 6, and the leaf area index conversion means 52 uses the conversion formula 61. The leaf area index is output by calculation from the ratio (integrated value of IR output / integrated value of PAR output). Alternatively, instead of directly calculating the ratio by the ratio calculation means 51 and outputting the leaf area index, the calculation unit 5 is provided with, for example, an irradiance estimation means (not shown), and the IR output and the PAR output in which the units are arranged in advance are provided. A calibration curve for each vegetation to be related, for example, a calibration curve for photosynthetic effective radiation (PAR output) and infrared radiation (IR output) is stored in the memory 6, and this calibration curve and the measured PAR output, for example, actually measured Based on the photosynthesis effective radiance, the IR output related by the calibration curve, for example, infrared radiance is obtained by the radiance estimating means, and these are integrated by the integrating means 53, and the ratio calculating means 51, leaf area index converting means The operation unit 5 can calculate the ratio (integrated value of IR output / integrated value of PAR output) by the action of 52 and output the leaf area index corresponding to this.

  Alternatively, unlike the calculation method, a conversion table 62 that associates a ratio with a leaf area index can be stored in the memory 6, and the leaf area index can be output with reference to the conversion table 62. In the case of an arithmetic circuit, the leaf area index is directly calculated from the ratio by analog calculation. A display device may be connected to the computer 7 so that the continuously measured ratios can be displayed as a list on the time axis. For example, as shown in FIG. 10 to be described later, a change in the seasonal change of the leaf area index can be seen.

The above description has focused on each structure of the optical leaf area index sensor 1, but sensitivity adjustment performed by the PAR sensor 2 and the IR sensor 3 will be described in detail. First, the PAR sensor 2 will be described. Hereinafter, the case where the PAR output is the photosynthetic effective radiation (W / m ² ) and the IR output is the infrared radiation (W / m ² ) will be described.

  The sensitivity adjustment of the PAR sensor 2 is performed to accurately represent the photon number within the photosynthetic effective wavelength. The light receiving unit 11 of the PAR sensor 2 is configured by a photodiode having sensitivity characteristics in a wavelength region of 400 nm to 700 nm that is a visible light region. Therefore, the UV / IR cut filter 13 blocks light in the ultraviolet (UV) region having a wavelength shorter than 400 nm and light in the infrared (IR) region having a wavelength longer than 700 nm.

  Subsequently, the blue expansion filter 15 corrects the spectral characteristics of the light whose wavelength in the ultraviolet region and the infrared region are cut so as to expand the vicinity of the blue color, and the light thus corrected is received by the light receiving unit 11. Receive light. Therefore, the spectral characteristic obtained by multiplying the transmission characteristic of the UV / IR cut filter 13 by the transmission characteristic of the blue extended filter 15 is corrected, and the light receiving unit 11 receives light with the characteristic multiplied by the sensitivity characteristic. Further, in the first embodiment, the output spectral characteristic is corrected so as to become a flat characteristic, which is photoelectrically exchanged and output from the cable 41 as an output indicating the photosynthetic effective radiation from the substrate 30.

  Here, the necessity of cutting the wavelength region in the ultraviolet region and the infrared region and correcting the spectral characteristics in the vicinity of blue will be described.

Plants use light radiant energy for photosynthesis. The energy of one photon is larger as the light has a shorter wavelength, and the energy decreases as the wavelength goes longer. That is, the amount of energy of the photon changes in inverse proportion to its wavelength. If the Planck's constant (6.63 × 10 ⁻³⁴ Js) is h, the speed of light is c (3 × 10 ⁸ m / s), and the wavelength is λ, the photon energy e is expressed as e = hc / λ.

  Moreover, the chlorophyll contained in the leaves has two absorption bands as shown in FIG. 4, and mainly absorbs red light (400 nm to 500 nm) and blue light (600 nm to 700 nm). However, since the wavelengths λ are different in these two regions, the energy possessed by one photon is different as described above. In plant photosynthesis, when chlorophyll absorbs light, it reacts in units of photons, so the number of photons absorbed is important. Irradiation with light that is not absorbed by chlorophyll does not contribute to photosynthesis, which is equivalent to no irradiation. Therefore, how much light can be used for photosynthesis varies depending on the wavelength.

Therefore, if the photon is measured as a unit of radiation, in other words, if the photon flux density (PFD) is used as the unit of light, the photosynthetic efficiency is evaluated without depending on the wavelength. Can do. Plants differ slightly from plant to plant in terms of leaf size, thickness, morphology, etc., but photosynthetic photon flux density (PPFD) absorbed by the leaves from plant to plant using radiation of 400 nm to 700 nm; (μmol / m ² / s) is measured, the degree of photosynthesis reaction can be determined. The photosynthetic activity is, on average, proportional to the amount of chlorophyll, and the amount of chlorophyll is proportional to the leaf area. Therefore, the amount of leaves is known for each plant from the absorption amount of the photosynthetic photon flux density. FIG. 5 shows the spectral characteristics of the photosynthetic photon flux density, and the photosynthetic effective radiation agrees well with the spectral distribution of the unit PFD.

  As described above, since the photosynthesis effective radiation is light of 400 nm to 700 nm, the UV / IR cut filter 13 cuts light in an unnecessary wavelength region that hinders measurement of the photosynthesis effective photon flux density. Further, the blue extended filter 15 corrects the characteristics so as to increase the sensitivity in the wavelength region near blue. This makes it possible to measure in units of photon flux density, that is, to measure radiance by the number of photons. This light is received by the photodiode according to the sensitivity characteristic of the photodiode, and is output as photosynthesis effective radiation after photoelectric exchange. It is known that the photosynthetic photon flux density is in good agreement with the photosynthetic effective radiation (PAR) of an average land plant.

  FIG. 6 shows spectral reflection characteristics and spectral transmission characteristics of the leaves of Deigo. In FIG. 6, the thick line is the reflectance on the back side of the deigo leaf (the back side with respect to sunlight), and the thin line is the reflectance on the front side of the deigo leaf. Moreover, a dashed-dotted line shows the transmittance.

  According to FIG. 6, it can be seen that the properties of light reflection and transmission change greatly with 700 nm as a boundary. The reflectance of the photon is 700 nm or less, and is relatively larger from the upper position of the leaf than from the lower position. On the other hand, in the wavelength region longer than 700 nm, the reflectance of about 3 to 6 times can be measured at both the upper and lower positions of the leaf.

  In terms of transmittance, light is not transmitted below 700 nm, but light is transmitted very well in the infrared region above 700 nm. That is, the proportion of infrared photons that cannot be used for photosynthesis in vegetation is increasing. Although FIG. 6 shows an example of measuring the leaves of a deigo, there is almost no difference between leaves or between species even when the spectral reflection characteristics of many plants such as pine oysters, bamboo, and a millipede are measured.

  By measuring the photosynthetic photon flux density in this way, it is possible to know by the PAR sensor 2 how much photosynthesis was performed while the transmitted light passed through the leaves and how much the light was attenuated.

  In contrast, sensitivity adjustment performed by the IR sensor 3 will be described. The sensitivity adjustment of the IR sensor 3 represents the infrared light quantum flux density in the infrared region of the transmitted light or the infrared radiation intensity corresponding to the light energy per unit area. In the IR sensor 3, the received light passes through only the infrared light of 700 to 1000 nm by the IR pass filter 14, and is received and photoelectrically converted by the photodiode of the light receiving unit 12 having a predetermined sensitivity characteristic. In other words, the gain adjustment is performed so that the transmission characteristic of the IR pass filter 14 is multiplied by the sensitivity characteristic of the light receiving unit 121 to further output infrared radiation.

  According to FIG. 6, in the infrared region of 700 nm or more, leaves or leaf groups transmit photons very stably and satisfactorily. That is, the proportion of infrared photons that could not be used for photosynthesis within the vegetation increases. Therefore, it is understood that the transmitted light radiation measurement may be performed using light having a wavelength region larger than at least 700 nm.

  What is most important when performing photosynthesis photon flux density and infrared radiation measurement is that the PAR sensor 2 must measure photon flux density (amount of photon) in the wavelength region of 400 nm to 700 nm. In addition, it is necessary to measure the photon flux density or radiant flux density (radiance) in the infrared light region larger than 700 nm with the IR sensor 3. In addition, both measurements need to have units aligned to either radiance or photon flux density. If either of the PAR sensor 2 and the IR sensor 3 is measured across a wavelength region including 700 nm, the photon flux density and the radiant flux density (radiance) in the infrared region are inaccurate values.

  In addition, when performing radiation measurement in the infrared region, it is not preferable to perform radiation measurement in an unlimited wide wavelength region. This is because the spectrum of the wavelength region longer than the predetermined wavelength fluctuates due to the influence of moisture on the leaves and the like. FIG. 7 shows the reflection and absorption spectrum characteristics of the front and back leaves of the pine moth. In the wavelength region exceeding 1000 nm, light is absorbed by the moisture of the leaves, the transmittance decreases, and unstable values are obtained. Show. In this way, when the radiation measurement of transmitted light is performed, a stable wavelength region of 1000 nm or less, that is, about 700 nm to 1000 nm, which is less affected by moisture content, is appropriate. The spectral characteristics from 700 nm to 1000 nm tend to be almost constant. These are not limited to edulis but also in other plants.

Here, the relationship between units will be described in detail. The unit of the photon flux density is μmol / m ² / s as described above. On the other hand, the unit of radiant flux density (radiance) is W / m ² .

This photon flux density can be converted to radiance. For this reason, the fact that the energy e of one photon is e = hc / λ is used. When the energy of one photon and the Avogadro number are added to the photon flux density, the irradiance (W / m ² ) is obtained. That is, irradiance (W / m ² ) = photon flux density (μmol / m ² / s) × Avocado number (1 / mol) × Planck constant (Js) × light velocity (m / s) / wavelength (m) is there.

From this relationship, the PAR sensor 2 can output a photosynthetic effective radiance (W / m ² ) corresponding to the photosynthetic photon flux density, and the IR sensor 3 can output an infrared radiance (W / m ² ) of 700 nm to 1000 nm. Can be output. Both are absolute quantities. And based on the relationship between the two, it is possible to evaluate how much leaves are growing at a given point in the vegetation according to the type of plant (woody, herbaceous, deciduous, evergreen). become.

  In addition, the present inventor has obtained the following knowledge regarding the photosynthetic effective radiance of transmitted light passing through leaves or vegetation and infrared radiance in a wavelength region of 700 nm to 1000 nm, or photosynthetic photon flux density and infrared photon flux density. It was. That is, the ratio of each integrated value integrated over the sunshine time of the PAR output (photosynthesis effective radiance or photosynthesis photon flux density) of the PAR sensor 2 and the IR output (infrared radiance or infrared photon flux density) of the IR sensor 3 is calculated. Then, this uses the daily integrated value (or the average value during the day by averaging), and the temporal and spatial variation factors of the radiation intensity ratio in the forest floor are averaged, and there is almost no dependence on the weather. It is a fact that it becomes almost constant for each vegetation.

  The following reasons can be considered for this. The photosynthesis effective photon flux density was measured as the radiant flux density (photosynthesis effective radiance) peculiar to the leaf or leaf group used for photosynthesis, and the measured range from 700 nm to 1000 nm is also a predetermined region of the leaf or leaf group. This is because the ratio of the radiant flux (infrared irradiance) becomes a value that is unique to the vegetation canopy (canopy) and is almost constant when a leaf or leaf group is determined. This is because the proportion of IR increases by the amount of absorption of PAR by the chlorophyll present in the region, and how much the vegetative canopy absorbs photosynthetic effective radiation (PAR) is uniquely determined. Both are absolute quantities, and the ratio does not depend much on the height of the sun, but depends only on the reflection / absorption rate of photons by the canopy. Although this ratio varies slightly depending on the type of plant, leaf morphology, leaf overlap, and weather (cloud volume), it is sufficiently small as a noise component against the IR / PAR ratio change due to leaves.

  FIGS. 8 and 9 show IR output integrated values indicating the infrared radiance or infrared photon flux density in the wavelength region of 700 nm to 1000 nm (this is expressed as IR) / photosynthesis effective in the wavelength region of 400 nm to 700 nm. Natural logarithm where e is the base and this wide irradiance ratio (IR / PAR) or its function is a true number when the integrated value of the PAR output indicating the radiance or photosynthetic photon flux density (this is expressed as PAR) That is, the logarithm ln (IR / PAR) of the wide-area irradiance ratio correlates with the leaf area index LAI. FIG. 8 shows the correlation between the leaf area index LAI and the logarithm ln (IR / PAR) of the wide-area irradiance ratio in a deciduous broad-leaved forest, and FIG. 9 shows the logarithm ln {(IR / PAR) -0. 6} is an explanatory diagram showing the correlation between the leaf area index LAI.

As shown in FIG. 8, the relationship between the leaf area index LAI and the logarithm ln (IR / PAR) of the wide-area irradiance ratio (IR / PAR) is almost a straight line. According to FIG. 8, it can be calculated by the relational expression (1) of LAI = 2.9285 · ln (IR / PAR) +1.0942. In other words, the leaf area index LAI is expressed as a linear function of a logarithmic function with the wide area irradiance ratio (IR / PAR) as a true number. The constants “2.9285” and “1.0942” have slightly different values for each vegetation. The relational expression (1) may be registered in the conversion formula 61 of the memory 6 in FIG. The correlation coefficient R when the correlation coefficient was R of the LAI and ln (IR / PAR) is 0.975, contribution ^{R 2} is a 0.9541, between LAI and ln (IR / PAR) is It can be seen that there is a very strong correlation. Therefore, the calculation result can be used as accurate information as it is. This can be used as LAI information when capturing seasonal changes in leaf quantity.

By the way, in the case of the whole sky (when there is no cover above the light diffusing plate), the leaf area index LAI is LAI = 0 and IR / PAR shows a value of about 0.8. LAI = 1.9635 · ln {(IR / PAR) −0.6} +2.8279 can also be substituted as shown in LAI = 1.9635 · ln {(IR / PAR) −0.6}. That is, LAI is expressed as a linear function of a logarithmic function having a linear function of the wide-area irradiance ratio (IR / PAR) as a true number. The relational expression (2) is registered in the conversion formula 61 of the memory 6 in FIG. The constants “1.9635” and “2.8279” have different values depending on the vegetation. When the LAI takes a small value by using this relationship, the rate at which the LAI becomes negative due to variations in (IR / PAR) can be reduced, and the arithmetic processing becomes easy. Moreover if the correlation coefficient R according to the equation (2) 0.985, contribution ^{R 2} is next to 0.9703, still shows the linearity than the relationship (1), a strong correlation appears.

  In addition, the relationship between LAI and (IR / PAR) in the relational expressions (1) and (2) described above is a correlation as an example obtained by a certain vegetation. Although it is likely that a similar tendency appears in other vegetation, LAI and (IR / PAR) are not always described by this function (1) (2). That is, there is a possibility that LAI can be described using (IR / PAR) as, for example, a first or higher power function of the above-described logarithmic function, or simply as a power function of (IR / PAR). The relationship between LAI and (IR / PAR) is not limited to (1) and (2).

  Using the relational expressions (1) and (2) between the logarithm ln (IR / PAR) of the wide-area irradiance ratio (IR / PAR) and the leaf area index LAI described above, the logarithm ln (IR / PAR) is converted into the leaf area index. It can be seen that it is very easy and accurate. Thereby, the calculation result can be used as accurate information of the leaf area index LAI, and the estimation accuracy of the leaf area index LAI can be greatly improved. This wide range of irradiance ratio (IR / PAR) corresponds to the ratio of the present invention. FIG. 10 shows the seasonal change in LAI of the deciduous broad-leaved forest by this relational expression (1) or (2). According to FIG. 10, it can be seen that leaves expand from spring to summer due to the change of seasons, and LAI increases to about 6.5, but autumn leaves and leaves fall, and LAI is close to zero.

  By the way, the optical leaf area index sensor 1 according to the first embodiment can perform calculations by other methods in addition to the calculation using the wide-area irradiance ratio (IR / PAR). As already described above, a calibration curve for each vegetation that associates the IR output and the PAR output in which the units are aligned in advance is stored in the memory 6, and the calculation unit 5 is provided with, for example, an irradiance estimation means (not shown). Line and PAR output, for example, IR output related to calibration curve based on photosynthesis effective radiance, for example, infrared radiance is obtained, integrated value of PAR output and IR output is calculated from these, and IR is further calculated based on these A leaf area index corresponding to a wide-area irradiance ratio obtained by dividing the integrated value of the output by the integrated value of the PAR output may be obtained.

  In addition, by using the optical leaf area index sensor 1 to measure the transmitted light in the vegetation and outside the vegetation in the same manner as in the past, the radiation absorption / transmission amount by wavelength region of the vegetation can be obtained. Moreover, the amount of leaves and the amount of trunk branches can also be estimated by comparing both measured values measured simultaneously. For this purpose, the arithmetic unit 5 can be provided with these arithmetic circuits. That is, when measured in the forest and outside the forest, if there is no leaf, (forest PAR / forest PAR) / (forest IR / forest IR) ≈1. On the other hand, if leaves are present, (forest PAR / forest PAR) / (forest IR / forest IR) <1 depending on the amount. The parameter α = (inside forest PAR / outside forest PAR) / (inside forest IR / outside forest IR) is calculated according to the values of the forest PAR, the forest PAR, the forest IR, and the forest IR measured by the optical leaf area index sensor 1. The LAI that is a function of α can be obtained by calculation. It should be noted that here, any of the forest PAR, the forest PAR, the forest IR, and the forest IR indicates the integrated value.

  In addition, the parameter β = (inside forest PAR / outside forest PAR) included in this α indicates the shade ratio of the entire vegetation by (branches / stems + leaves). The amount can be estimated. In addition to the ratio calculation means 51, calculation means for performing calculation based on the parameters α and β may be provided, and the LAI and the shadow ratio may be estimated by the calculation means. Furthermore, when calculating LAI as a function of α, a calibration curve that associates α with the leaf area index is stored in the memory in advance, and the calibration curve is calculated from the forest-to-forest ratio of the PAR and PAR outputs. Leaf area index can be obtained.

  As described above, according to the first embodiment of the present invention, a combination of a photosynthetic effective radiation range radiation sensor from 400 nm to 700 nm and an infrared range radiation sensor from 700 nm to 1000 nm is combined to quantitatively measure the vegetation canopy above the ground. The leaf area index, which is qualitative information, can be measured.

  In addition, broadband measurements using Si photodiodes are performed, and the amount of radiation is measured in two parts from 400 nm to 1000 nm, so that not only the ratio of the amount of radiation but also the absolute value of the amount of radiation can be obtained. Radiation absorption / transmission of vegetation by wavelength range can be obtained by performing simultaneous measurements inside and outside the new forest. Since it is an absolute amount, the amount of leaves and the amount of trunk branches can be estimated by comparing the measured values inside and outside the forest.

  When creating a calibration curve according to the species that make up the vegetation using a pair of photosynthetic effective radiation sensor and infrared radiation sensor in advance, it is not necessary to use an infrared radiation sensor in the field by using the calibration curve. Alternatively, the leaf area index can be determined without installing an infrared radiation sensor on site. The calibration curve data is stored in advance in a memory and referenced.

  The optical vegetation index sensor of the present invention does not set the incident angle characteristic to a narrow angle, but sets the incident angle characteristic to a wide angle, so that the output is large and the sensitivity is high. In addition, since transmitted light is used instead of reflected light, it reflects the properties of the entire vegetation including average effects such as light scattering and reflection within the vegetation.

  Furthermore, since it corresponds well to the wavelength range of NADI (TM3 band 630nm to 690nm, TM4 band 760nm to 900nm) calculated using satellite observation data, it is used as a ground truth sensor for satellite remote sensing. be able to.

  Hereinafter, the optical vegetation index sensor according to the second embodiment of the present invention will be described. The optical vegetation index sensor of Example 2 is a photosynthetic effective radiation absorption rate sensor. FIG. 11 shows the overall configuration of the optical vegetation index sensor in Example 2 of the present invention, and FIG. 12 shows the relationship between the wide-range irradiance ratio (IR / PAR) and the photosynthetic effective radiation absorption rate (fAPAR) of vegetation. Since the photosynthetic effective radiation absorption rate sensor 201 of the second embodiment performs calculations using the LAI obtained in the first embodiment, its configuration overlaps with the configuration of the optical leaf area index sensor 1 of the first embodiment. Accordingly, in the second embodiment, reference is also made to FIGS. 2 to 10, and the same reference numerals denote the same components in the configuration of the first embodiment and the configuration of the second embodiment. Omitted.

The photosynthetic effective radiation absorption rate (fAPAR) is an index value indicating the ratio of before and after absorption of photosynthetic effective radiation (PAR) absorbed by the photosynthetic organ of vegetation. For example, PAR in forest floor at the same time PAR on canopy in 2000μmol ^{/ m} 2 ^/ s is if 50μmol ^{/ m} 2 ^/ s, fAPAR becomes 0.975.

  As can be seen from Example 1, the optical vegetation index sensor of the present invention is a sensor that utilizes the property that the proportion of IR increases by the amount of absorption of PAR by chlorophyll. Therefore, if the vegetation canopy is determined, the amount of chlorophyll is determined, and it can be estimated how much optically synthesized effective radiation (PAR) is absorbed by each vegetation canopy. In some cases, fAPAR becomes a more important index, such as a global measurement index that absorbs carbon dioxide, which is also the cause of global warming. For these reasons, a photosynthetic effective radiation absorption rate sensor 201 that can optically measure photosynthetic effective radiation absorption rate (fAPAR) is desired.

  As shown in FIG. 11, the photosynthetic effective radiation absorption rate sensor 201 includes a PAR sensor 2, an IR sensor 3, a calculation unit 5, and a memory 6 similar to those in FIGS. 1 to 3. These detailed structures are basically the same as those of the first embodiment except for a predetermined configuration described below. The description is left to Example 1. As shown in FIG. 11, the arithmetic unit 5 includes an fAPAR calculating unit 54 for calculating the photosynthetic effective radiation absorption rate in addition to the configurations of the ratio calculating unit 51 for calculating the LAI, the leaf area index converting unit 52, and the integrating unit 53. Is provided. In the memory 6, an fAPAR conversion formula 63 for calculating the fAPAR based on the LAI is registered.

FIG. 12 shows the correlation between LAI parameters (IR / PAR) and photosynthetic effective radiation absorption rate (fAPAR). Both logarithmic graphs show a linear relationship. The correlation coefficient R between (1-fAPAR) and (IR / PAR) is 0.98, the contribution ratio R2 is 0.96, and there is a very strong correlation between fAPAR and ln (IR / PAR). I understand. For example, when k _{1 to} k ₃ are constants and the function forms of both are shown, the fAPAR conversion formula 63 (see FIG. 11) can be expressed in a form such as fAPAR = k ₁ · ln [k ₂ · LAI] + k ₃ . LAI can be an index for obtaining fAPAR. References related to this include Monsi M, Saeki T, “Uber den Lichtfaktor in den Pflanzengesellschaften und seine Bedeutung fur die Stoffproduktion”, Japanese Journal of Botany, 1953, vol.14, 22-52.

  Since fAPAR is obtained by subtracting the ratio of the PAR amount measured at the top of the vegetation and the PAR amount measured on the forest floor from 1, the PAR sensor 2 is used to directly measure these two PAR amounts. This can be calculated. However, this direct measurement requires simultaneous measurement inside and outside the vegetation, making continuous and stable radiation measurement more difficult. In this regard, the photosynthetic effective radiation absorption rate sensor 201 of Example 2 eliminates this difficulty.

  Since there is a relationship of fAPAR = 1− (PAR amount on the forest floor) / (PAR amount on the top of the vegetation), using this relationship, a calibration curve of fAPAR and PAR can be obtained for a certain vegetation. For example, by measuring the PAR within the vegetation, it is possible to easily estimate the upper part of the vegetation, that is, the PAR outside the vegetation. Therefore, in FIG. 11, a calibration curve for each vegetation that associates the IR output and the PAR output, which are aligned in advance, is stored in the memory 6, and an irradiance estimation means (not shown) is provided in the calculation unit 5. And PAR output (for example, photosynthetic effective irradiance), the IR output (for example, infrared radiance) related by the calibration curve is obtained, and from these, the integrated value of PAR output and IR output is calculated, and based on this The fAPAR corresponding to the wide-area irradiance ratio obtained by dividing the integrated value of the IR output by the integrated value of the PAR output is obtained. Thereby, a photosynthetic effective radiation absorption rate sensor using a calibration curve is obtained. Further, based on the fAPAR of this sensor, the PAR outside the forest can be estimated by conversion. And if the PAR outside the forest can be estimated, it is possible to estimate the irradiance of external solar radiation while measuring the inside of the forest. That is, the function of a pyranometer can be provided.

  As described above, according to the second embodiment, it is possible to perform continuous and stable radiation measurement in the forest, and without using simultaneous measurement inside and outside the vegetation. It is possible to provide a photosynthetic effective radiation absorption rate sensor capable of measuring the rate.

  The photosynthetic effective radiation absorption rate sensor of Example 2 has a large output and high sensitivity because the angle-of-incidence characteristic is set to a wide angle. In addition, since transmitted light is used instead of reflected light, the properties of the entire vegetation including average influences such as light scattering and reflection in the vegetation can be reflected.

  The present invention can be applied to an optical vegetation index sensor using a wide range of irradiance ratio (IR / PAR) such as an optical leaf area index sensor or a photosynthetic effective radiation absorption rate sensor.

1 Optical leaf area index sensor 2 Photosynthesis effective radiation area radiation sensor (PAR sensor)
3 Infrared radiation sensor (IR sensor)
DESCRIPTION OF SYMBOLS 5 Computation part 6 Memory 7 Computer 11, 12 Light-receiving part 13 UV / IR cut filter 15 Blue expansion filter 18, 19 Case 20, 21 Light diffusing plate 29, 30 Substrate 31, 33 Embedded connector 32, 34 Cable connector 41, 42 Output cable 51 Ratio calculating means 52 Leaf area index converting means 53 Accumulating means 54 fAPAR calculating means 61 Conversion formula 62 Conversion table 63 fAPAR conversion formula

Claims (5)

When the transmitted radiation transmitted through the leaf or the leaf group is received, the spectral characteristic for measuring the photon flux density is corrected by the correction filter for the radiation in the visible radiation region of 400 nm to 700 nm, and the corrected radiation is received by the light receiving unit. A first radiation sensor that outputs as a PAR output indicating either photosynthetic effective radiance or photosynthetic photon flux density by photoelectric conversion;
With respect to the received radiation, the radiation of only the infrared radiation region of 700 nm to 1000 nm is taken out by a band pass filter, and this radiation is photoelectrically converted by the light receiving unit, whereby the unit radiance or photon flux density in common with the PAR output is obtained. A second radiation sensor capable of outputting an IR output indicating either of them;
An arithmetic unit that integrates the PAR output and the IR output with time, calculates the ratio by dividing the integrated value of the IR output by the integrated value of the PAR output, and obtains a leaf area index corresponding to the ratio. An optical vegetation index sensor. 2. The optical system according to claim 1, wherein a light diffusing plate capable of cosine correction of radiation is provided on light receiving surfaces of the first radiation sensor and the second radiation sensor, and an incident angle characteristic of incident radiation is set to a wide angle. Vegetation index sensor. The calculation unit integrates the PAR output and the IR output, a ratio calculation unit that calculates the ratio by dividing the integrated value of the IR output by the integrated value of the PAR output, and the ratio 3. An optical vegetation index sensor according to claim 1, further comprising a leaf area index conversion means for obtaining a corresponding leaf area index based thereon. The optical vegetation index sensor according to any one of claims 1 to 3, wherein the leaf area index is a linear function of a logarithmic function in which the ratio or a function thereof is a true number. When the transmitted radiation transmitted through the leaf or the leaf group is received, the spectral characteristic for measuring the photon flux density is corrected by the correction filter for the radiation in the visible radiation region of 400 nm to 700 nm, and the corrected radiation is received by the light receiving unit. A first radiation sensor that outputs as a PAR output indicating either photosynthetic effective radiance or photosynthetic photon flux density by photoelectric conversion;
With respect to the received radiation, the radiation of only the infrared radiation region of 700 nm to 1000 nm is taken out by a band pass filter, and this radiation is photoelectrically converted by the light receiving unit, whereby the unit radiance or photon flux density in common with the PAR output is obtained. A second radiation sensor capable of outputting an IR output indicating either of them;
An arithmetic unit that integrates the PAR output and the IR output with time, and divides the integrated value of the IR output by the integrated value of the PAR output to calculate a ratio, thereby converting to a photosynthetic effective radiation absorption rate corresponding to the ratio An optical vegetation index sensor comprising:

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