JP2007171033A - Indirect measuring method and system of leaf area index - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine a leaf area index highly accurately, even if each solar radiation in a forest and out of the forest is not measured simultaneously, or even if measurement itself of the solar radiation out of the forest is omitted. <P>SOLUTION: When measuring indirectly the leaf area index, an image of a prescribed area is photographed by changing an exposure time in a plurality of kinds, relative to each of near-infrared light and red light by using a wide angle lens and an electronic imaging element, and an image whose brightness value is the nearest to the median of a gradation from insufficient exposure to excessive exposure is selected from among images having a plurality of kinds of exposure times, relative to each of the near-infrared light and the red light in each subdivided domain acquired by subdividing the prescribed area. A brightness value when the selected image is normalized into a prescribed exposure time is determined, and a brightness value ratio between the near-infrared light and the red light in each subdivided domain is determined from each brightness value of the near-infrared light and the red light determined in each subdivided domain, and a relative solar radiation is estimated by using the brightness value ratio, and the leaf area index is determined from the relative solar radiation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and system for indirectly measuring a leaf area index, which is a typical index value of forest biomass.

The leaf area index (LAI) is the total value of the area of one side of all the leaves of the above-ground part per unit horizontal area. For example, if LAI = 2, the leaf area index is 10 m ² . If the total area of one side is 20 m ² and leaves are arranged on the horizontal ground without any gaps, it can be interpreted as two overlapping.

  The above-mentioned leaf area index, which is a representative index value of forest biomass, is a main parameter of forest heat balance model, evapotranspiration model, photosynthesis model, etc., and is a main parameter of vegetation expression of global model of global warming research It is also adopted. It is also used as an explanatory item for test sites in various research related to forests.

  This leaf area index can be measured directly by whole tree cutting or standard tree cutting, but whole tree cutting has decreased in recent years due to the resistance to logging and the importance of seasonal changes and processes. Logging was difficult in forests with diverse species composition.

  On the other hand, it is known that the leaf area index is a function of the relative solar radiation amount (see Non-Patent Document 1), and indirect measurement of the leaf area index using this has been put into practical use and has become widespread (for example, non-patent document 1). Patent Document 2).

Also, a leaf area index is obtained with high accuracy by measuring the relative illuminance of each region divided by the zenith angle and azimuth angle using a fisheye lens (see Non-Patent Document 3).
Monsi & Saeki, 1953, Jpn. J. Bot. 14, 22-52. JM Welles and JM Norman 1991, Instrument for indirect measurement of canopy architecture, Agronomy Journal, 83.818-825. JM Norman & GS Campbell, Canopy structure, p.301-325, in RW Pearcy, J. Ehleringer, HA Mooney and PW Rundel (Eds.) Plant Physiological Ecology, 1989, Chapman & Hall, London, pp. 457.

  By the way, in order to obtain relative solar radiation, it is necessary to simultaneously measure solar radiation in the forest and outside the forest, but in forests with large tree height and spatial spread, simultaneous solar radiation measurement inside and outside the forest. In many cases, it is not easy to measure, so in practice, it is often measured with a time difference, which is a major error factor.

  In other words, the amount of solar radiation outside the forest may fluctuate by several orders due to changes in time and weather. For example, if there are two orders of difference, the leaf area index will differ by more than ± 4, which cannot be ignored. Thus, the reliability of the measured value of the leaf area index was greatly impaired.

  Therefore, in order to improve this situation, conventionally, when the solar radiation passes through the forest canopy, the intensity of attenuation differs between the near infrared light and the red light, and the solar radiation in the forest is near infrared light / red compared to the solar radiation outside the forest. Focusing on the fact that the light intensity ratio increases, it has also been proposed to calculate the leaf area index by estimating the relative solar radiation using this ratio, but this method eventually failed and was abandoned (Refer nonpatent literature 3).

  The reason for the failure is that the amount of light was not conventionally measured from the image, but the measurement was eventually calculated as (integrated value of near infrared light) / (integrated value of red light). For this reason, it is considered that the information weight of the part with a small number of leaf groups (that is, the part with high luminance) is increased, and the information weight of the part with a large number of leaf groups (that is, a part with low luminance) is reduced.

  An object of the present invention is to advantageously solve the above-described conventional problems, and the indirect measurement method of the leaf area index according to the present invention provides a wide-angle lens and an electronic method for indirectly measuring the leaf area index. For each of the near-infrared light and the red light using the imaging device, the exposure time is changed into a plurality of types, an image of a predetermined area is photographed, and for each subdivided area obtained by subdividing the predetermined area, near-infrared light and For each of the red light, the image having the brightness value closest to the median of the gradation between the underexposure and the overexposure is selected from the images of the plurality of types of exposure times, and the selected image is exposed to a predetermined amount. The luminance value when normalized to time is obtained, and the luminance value ratio between the near infrared light and the red light for each subdivision region is calculated from the luminance value of the near infrared light and the red light obtained for each subdivision region. Obtaining the relative solar radiation amount using the luminance value ratio, It is characterized in determining the leaf area index from pairs solar radiation.

  In addition, the indirect measurement system for leaf area index according to the present invention uses a wide-angle lens and an electronic imaging device to change the exposure time for each of the near-infrared light and the red light into a plurality of types and display an image of a predetermined region. For each subdivision area obtained by subdividing the predetermined area with the photographing means for photographing, the brightness value is between underexposure and overexposure in the images of the plurality of types of exposure time for each of near infrared light and red light. An image selection / brightness value calculation means for obtaining a luminance value when the image closest to the median value of the gradation is selected and the selected image is normalized to a predetermined exposure time, and a proximity value obtained for each subdivision area Luminance value ratio calculation means for obtaining a luminance value ratio between near infrared light and red light for each subdivision area from the luminance values of infrared light and red light, and estimation of relative solar radiation using the luminance value ratio Relative solar radiation amount estimating means, and from the relative solar radiation amount And leaf area index calculating means for calculating the area index is made comprises a.

  According to the indirect measurement method, for each subdivision area, an image whose luminance value is closest to the median value of gradation between underexposure and overexposure is selected, and the selected image is captured with a predetermined exposure time. In this case, the brightness value of the image is obtained, so that the brightness value of each subdivision area can be expressed with extremely high gradation levels and with high accuracy for each subdivision area obtained by subdividing the whole sky as a predetermined area. Since the luminance value of the accuracy is obtained, the difference in weight between the information of the part having a small number of leaf groups (that is, the part having high luminance) and the information of the part having a large number of leaf groups (that is, a part having low luminance) can be eliminated. The relative insolation amount is estimated by obtaining the luminance value ratio between near infrared light and red light using high-precision luminance values, and the leaf area index is obtained therefrom, so that the insolation amount in and outside the forest can be simultaneously calculated. Even without measuring, even outside the forest Even eliminating the measurement itself of injection amount, it is possible to determine the leaf area index with high accuracy.

  In the indirect measurement method of the leaf area index according to the present invention, the subdivision area may correspond to one or a plurality of pixels of the electronic imaging device, and in this way, each subdivision area The luminance value can be easily obtained.

  Furthermore, in the indirect measurement method of the leaf area index of the present invention, the predetermined area is divided into three large areas by the zenith angle from the zenith to the predetermined zenith angle, and the average of the luminance value ratio for each large area The value is obtained, the ratio of the gap as the relative solar radiation amount is estimated from the average value of the luminance value ratio for each large area, and the leaf area index may be obtained from the ratio of the gap. According to Non-Patent Document 2, the light intensity ratio between near-infrared light and red light for each region obtained by dividing the zenith to a predetermined zenith angle into three by the zenith angle, and a later-described LAI-2000 which is a commercially available LAI measuring instrument. Since it has been found that there is a monovalent relationship with the gap ratio measured in step 3, according to Non-Patent Document 2, each large region obtained by dividing the zenith to the predetermined zenith angle into three by the zenith angle. The average value of the luminance value ratio of the LAI measuring instrument The average value of the luminance value ratios is converted into a gap ratio using a monovalent relationship with the ratio of the gap, and the LAI value can be obtained by calculating according to Non-Patent Document 2 from the gap ratio. .

  On the other hand, according to the above indirect measurement system, the photographing means uses the wide-angle lens and the electronic image pickup device to change the exposure time for each of the near-infrared light and the red light into a plurality of types and display an image of a predetermined region. Shooting and image selection / brightness value calculation means underexposure of luminance values in the images of the plurality of types of exposure time for each of the near infrared light and red light for each subdivided area obtained by subdividing the predetermined area And selecting the image closest to the median of the gradation between the overexposure and the overexposure, obtaining the luminance value when the selected image is normalized to a predetermined exposure time, and the luminance value ratio calculation means The brightness value ratio between the near infrared light and the red light for each subdivision area is obtained from the brightness values of the near infrared light and the red light obtained every time, and the leaf area index calculating means calculates the brightness value ratio. Relative solar radiation amount estimation means for estimating relative solar radiation amount using Since the leaf area index is obtained from the relative solar radiation, the above indirect measurement method can be implemented, and the luminance value of each sub-region can be expressed with very high gradation levels, and the whole sky as a predetermined region can be expressed. Since the high-precision luminance value is obtained for each subdivided region, etc., the difference in weight between the information on the part with a small leaf group (that is, the part with high luminance) and the information on the part with a large leaf group (that is, a part with low luminance) Since the relative solar radiation amount is estimated from the luminance value ratio between near infrared light and red light using the high-precision luminance value, and the leaf area index is obtained therefrom, the forest The leaf area index can be obtained with high accuracy without simultaneously measuring the solar radiation amount inside and outside the forest, or even without measuring the solar radiation amount outside the forest itself.

  In the leaf area index indirect measurement system according to the present invention, the subdivision area may correspond to one or a plurality of pixels of the electronic imaging device. In this way, each subdivision area The luminance value can be easily obtained.

  Furthermore, in the leaf area index indirect measurement system of the present invention, the luminance value ratio calculating means divides the predetermined area from the zenith to the predetermined zenith angle into three large areas by the zenith angle, and the large area The average value of the luminance value ratio is calculated every time, and the relative solar radiation amount estimating means estimates the gap ratio as the relative solar radiation amount from the average value of the luminance value ratio of each large region, and calculates the leaf area index The means may obtain a leaf area index from the ratio of the gap, and according to the non-patent document 2, according to the non-patent document 2, the distance from the zenith to the predetermined zenith angle is divided into three by the zenith angle. It is known that there is a monovalent relationship between the ratio of the amount of light between infrared light and red light and the ratio of the gap measured with the LAI-2000 described later, which is a commercially available LAI measuring instrument. Follow Fig. 2 from the zenith to the specified zenith angle. The average value of the luminance value ratio is converted into the gap ratio using a monovalent relationship between the average value of the luminance value ratio for each large area divided into three by the corner and the gap ratio of a commercially available LAI measuring instrument. Then, the LAI value can be obtained by calculation according to Non-Patent Document 2 from the gap ratio.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing the configuration of an embodiment of an indirect measurement system for leaf area index according to the present invention, which is used in the implementation of an embodiment of the indirect measurement method for leaf area index of the present invention. FIG. 3 is a flowchart showing the procedure of the indirect measurement method of the leaf area index of the above embodiment, and FIGS. 3A and 3B show the average value and gap of IR / red light for each pixel obtained by the method of the above embodiment. FIG. 6 is a relational diagram showing the relationship between the ratio of the IR and the conventional IR cumulative value / red light cumulative value and the gap ratio.

  The indirect measurement system of the above embodiment shown in FIG. 1 includes a digital camera 2 fixed on a tripod 1, a fisheye lens 3 as a wide-angle lens attached to the digital camera 2, and an optical filter attached to the fisheye lens 3. 4, a personal computer (personal computer) 5 that sends a control command to the digital camera 2 and captures and records the captured image data from the digital camera 2, and a battery 6 that supplies power to the personal computer 5.

  Here, the digital camera 2 needs to be sensitive to both visible light and near-infrared light. As such a digital camera 2, for example, an IEEE1394 camera manufactured by Sony Corporation can be used. As the fish-eye lens 3, for example, a 1/2 inch single focal point and an angle of view of 104.0 × 77.0 manufactured by Tamron Co., Ltd. can be used. Further, as the optical filter 4, when photographing red light, for example, a near infrared absorption filter manufactured by Sigma Kogyo Co., Ltd. and a sharp cut filter manufactured by the same company can be used in two layers. When photographing near infrared light, an infrared transmission filter manufactured by the same company can be used. Can be used. As an interface between the digital camera 2 and the personal computer 5, for example, an IEEE1394 PC-Card manufactured by Ratoku System Co., Ltd. can be used.

  When performing indirect measurement of the leaf area index using the indirect measurement system of this embodiment, first, as shown in FIG. 2, photographing is performed in steps S1 to S3. That is, in step S1, the tripod 1 is placed under the canopy to be measured, and the digital camera 2 is fixed by using a level so that the visual axis of the digital camera 2 is directed vertically upward. The aperture of the digital camera 2 is adjusted appropriately so that the image changes from underexposure to overexposure when the shutter speed is sequentially changed from 1 / 100,000 seconds to 0.4 seconds, for example, in the subsequent steps S2 and S3. Keep it.

  Next, in step S2, an optical filter 4 that transmits only near-infrared light, such as the above-described infrared transmission filter, is mounted in front of the fisheye lens 3, and the shutter speed (exposure time) is set to, for example, 1 by a control command from the personal computer 5. / 100,000 seconds, 1 / 50,000 seconds, 1/20000 seconds, 0.000117 seconds, 0.000284 seconds, 0.000535 seconds, 0.001037 seconds, 0.00205 seconds, 0.00413 seconds, 0.00831 seconds, 0.016669 seconds, 0.033305 seconds, 0.066995 seconds, 0.133333 seconds, 0.2 seconds, The digital camera 2 takes 16 images of the whole sky while sequentially changing to 16 types of 0.4 seconds, and all the image data is transferred to the personal computer 5 and stored. In this shooting, the shutter speed (exposure time) change, shooting command, transfer of image data from the digital camera 2 to the personal computer 5, etc. are all processed automatically by the program installed on the personal computer 5 in advance. Is done.

  Next, in step S3, an optical filter 4 that transmits only red light, such as a double layer of the near-infrared absorption filter and the sharp cut filter, is attached to the front of the fisheye lens 3, and the control from the personal computer 5 is performed as in step S2. Shutter speed (exposure time) by command, for example, 1 / 100,000 seconds, 1 / 50,000 seconds, 1/20000 seconds, 0.000117 seconds, 0.000284 seconds, 0.000535 seconds, 0.001037 seconds, 0.00205 seconds, 0.00413 seconds, 0.00831 seconds, 0.016669 seconds, 0.033305 Sixteen sky images are taken with the digital camera 2 while sequentially changing to 16 types of seconds, 0.066995 seconds, 0.133333 seconds, 0.2 seconds, and 0.4 seconds, and all these image data are transferred to the personal computer 5 and stored. Even during this shooting, the shutter speed (exposure time) change, shooting command, transfer of image data from the digital camera 2 to the personal computer 5, etc. are all automatically performed by a program installed on the personal computer 5 in advance. It is processed.

  Therefore, the digital camera 2, the fisheye lens 3, the optical filter 4, and the personal computer 5 that executes the steps S2 and S3 correspond to photographing means. The number of images photographed as described above is, for example, 1024 × 768. Each pixel has a luminance value of, for example, 256 gradations for the three bands of blue, green, and red. Both near-infrared light and red light are captured as luminance values of the red band.

  Next, calculations are performed in steps S4 to S8. This calculation is also processed automatically by a program installed in advance on the personal computer 5.

  That is, in step S4, for example, from the 16 near-infrared light images captured in step S2, the luminance of the pixel for each pixel as a subdivision area for all pixels (for example, 1024 × 768 pixels) of the image. Select the image whose value is closest to the median value of the gradation (for example, 128 for 256 gradations), use the exposure time of the selected image, and normalize the image by 1/100 seconds, for example. calculate. With this process, the brightness value of the near-infrared light image can express a gradation value of about 7 orders.

  Next, in step S5, as in step S4, for example, from the 16 red light images captured in step S3, for each pixel as a subdivision area for all pixels (for example, 1024 × 768 pixels) of the image, Select the image whose pixel brightness value is closest to the median value of the gradation (for example, 128 for 256 gradations), use the exposure time of the selected image, and normalize the image by 1/100 seconds, for example Calculate the luminance value. With this processing, the luminance value of the red light image can also represent a gradation value of about 7 orders. Therefore, the personal computer 5 that executes the steps S4 and S5 corresponds to image selection / luminance value calculation means.

  Next, in step S6, the normalized luminance value of the near infrared light and the normalized luminance value of the red light for each pixel of all the pixels of the near infrared light image and the red light image (for example, 1024 × 768 pixels). The three major regions (regions) divided by the zenith angle (Zenith angle: 0 degrees above the vertical) 1: 0 to 14 degrees, area 2: 16 to 30 degrees, area 3: 31 to 45 degrees), the average value of the luminance value ratio for each large area is calculated. Therefore, the personal computer 5 that executes the step S6 corresponds to a luminance value ratio calculating means.

  By the way, according to Non-Patent Document 2, as described above, the light quantity ratio between near infrared light and red light for each region obtained by dividing the zenith to the predetermined zenith angle into three by the zenith angle, and a commercially available LAI measuring instrument. Since it has been found that there is a monovalent relationship between the gap ratio measured by a LAI-LOR measuring instrument LAI-2000 manufactured by a LI-COR company, the average value of the above luminance value ratio and a commercially available LAI measuring instrument For example, a monovalent relationship with the gap ratio measured by the above LAI-2000 is obtained in advance, and using this relationship, the average value of the luminance value ratio for each region is calculated as the gap ratio in the next step S7. In the subsequent step S8, the LAI value is calculated from the gap ratio in accordance with Non-Patent Document 2. Therefore, the personal computer 5 that executes the step S7 corresponds to a relative solar radiation amount estimating means, and the personal computer 5 that executes the step S8 corresponds to a leaf area index calculating means.

  That is, when comparing the near-infrared light image and the red light image obtained by the inventor of the present invention with the normalized luminance value as described above and the image representing the luminance value ratio of each pixel in terms of luminance, In both the red light image and the near infrared light image, the region with few leaves is bright and the trunk is dark, but in the image taking the ratio of the luminance values of both, the region with few leaves and the trunk are near infrared. The light normalized luminance value / red light normalized luminance value ratio is low (blackish in the image), whereas the area with many leaves has a high near infrared light normalized luminance value / red light normalized luminance value ratio (image It was bright). This is presumed to be because, in the region where the near-infrared light normalized luminance value / red light normalized luminance value ratio is high, the ratio of hindrance to the transmission of solar radiation is large.

  FIG. 3A shows each large area of the above three large areas of the near infrared light normalized luminance value / red light normalized luminance value ratio for each of 1024 × 768 pixels obtained by the method of the above embodiment. It is a figure which shows the relationship between the average value (horizontal axis) and the ratio (vertical axis) of the gap of a commercially available LAI measuring device (LAI-2000). For example, as shown by the straight line in the figure, near infrared light / red A monovalent relationship can be found between the average value of the light intensity ratio for each large area and the gap ratio measured with the LAI-2000, which is a commercially available LAI measuring device. Therefore, using this relationship, the gap ratio can be obtained as in steps S7 and S8, and the value of LAI can be calculated from the gap ratio as follows in accordance with Non-Patent Document 2. .

That is, it is known that the LAI value of a region (hereinafter referred to as a ring) divided by the zenith angle is obtained by the following equation (1) from the gap ratio of the ring (Non-patent Document 2).
“LAI value of a ring” = (− 1 / k) × ln (“ratio of gap of the ring”) × cos (“typical zenith angle value of the ring”) (1)
Here, the gap ratio is measured as relative illuminance. k is called an extinction coefficient in the field of ecology, and is an index corresponding to the inclination angle of leaves, and 0.5 is often adopted.

  According to Non-Patent Document 2, the ring breaks were set to ring 1: 0.0 to 12.3 degrees, ring 2: 16.7 to 28.6 degrees, ring 3: 32.4 to 43.4 degrees, and the zenith angle representative value of the ring was 7 degrees. , 23 degrees and 38 degrees. According to Non-Patent Document 2, when the LAI values of these three rings are averaged, a weight of 0.034: 0.104: 0.160 may be applied. That is, the average LAI value can be obtained with the extinction coefficient k being 0.5 and the weight values being 0.114, 0.349, and 0.537.

  In contrast, FIG. 3B shows the relationship between the ratio of the near-infrared light average value / red light average value (horizontal axis) and the gap ratio (vertical axis) that are not processed for each pixel. However, in this figure, their relationship is ambiguous as shown. The horizontal axis in this figure is considered to correspond to research by predecessors who do not use cameras.

  Therefore, according to the indirect measurement method and the indirect measurement system of the leaf area index of this embodiment, even if the solar radiation amount in the forest and the outside of the forest are not measured simultaneously, the solar radiation amount outside the forest is measured. Even without it, the leaf area index can be obtained with high accuracy. In addition, according to the method of this embodiment, it is possible to sufficiently sufficiently measure the leaves of coniferous trees and the leaves of variegated broad-leaved trees, which were conventionally difficult to measure.

  Although the present invention has been described based on the illustrated examples, the present invention is not limited to the above-described examples, and can be appropriately changed within the scope of the claims. For example, in the method and system of the above-described embodiments, Although the normalized luminance value is obtained with the subdivision area as one pixel, it may be a plurality of pixels instead.

  In addition, for example, by arranging a chamber portion that sandwiches the leaf vertically above the digital camera of the indirect measurement system of the above embodiment so that the leaf enters a predetermined area to be photographed, the shape and size of the leaf It can be used for standardization of measurement, and by placing an artificial light source above the chamber, indirect measurement of leaf red light transmission characteristics / near infrared light transmission characteristics (SPAD values) and consequently chlorophyll concentration in the leaves It can be used for comparison of photosynthetic characteristics according to tree species and age, etc. In this case, the object can be measured sufficiently satisfactorily as a coniferous leaf or a variegated broadleaf leaf, which has conventionally been difficult to measure.

  Furthermore, by placing an artificial light source in parallel with the digital camera, not above the chamber, but can be used for ground truth (ground verification measurement) in plant surveys by remote sensing. It can be measured satisfactorily as a coniferous leaf or a variegated broadleaf leaf, which has been difficult to measure in the past.

  In the indirect measurement system used indoors as described above, the personal computer (personal computer) may be driven by a commercial power supply instead of battery. The computer that controls the digital camera and stores the image data may be separate from the computer that performs the calculation process.

  Thus, according to the indirect measurement method and indirect measurement system of the leaf area index of the present invention, it is possible to eliminate the measurement of the solar radiation amount outside the forest itself, even if the solar radiation amount within the forest and the outside of the forest are not simultaneously measured. Also, the leaf area index can be obtained with high accuracy.

It is explanatory drawing which shows the structure of one Example of the indirect measurement system of the leaf area index of this invention used for implementation of one Example of the indirect measurement method of the leaf area index of this invention. It is a flowchart which shows the procedure of the indirect measurement method of the leaf area index | exponent of the said Example. (A) and (b) are the relationship between the average value of IR / red light and the ratio of gap for each pixel determined by the method of the above embodiment, and the average value and gap of conventional IR accumulated value / red light accumulated value. It is a related figure which shows the relationship with the ratio of each.

Explanation of symbols

1 Tripod 2 Digital Camera 3 Fisheye Lens 4 Optical Filter 5 Personal Computer (PC)
6 battery

Claims (6)

When measuring the leaf area index indirectly,
Using a wide-angle lens and an electronic image sensor, for each of near-infrared light and red light, the exposure time is changed into a plurality of types, and an image of a predetermined area is taken.
For each subdivision area obtained by subdividing the predetermined area, for each of near-infrared light and red light, the median value of the gradation between the underexposure and the overexposure in the images of the plurality of types of exposure times. Select the image closest to, find the brightness value when the selected image is normalized to the predetermined exposure time,
From the luminance value of near infrared light and red light obtained for each subdivision area, obtain the luminance value ratio of near infrared light and red light for each subdivision area,
The relative solar radiation amount is estimated using the luminance value ratio,
A leaf area index indirect measurement method, wherein a leaf area index is obtained from the relative solar radiation amount.   The indirect measurement method of a leaf area index according to claim 1, wherein the subdivided region corresponds to one or a plurality of pixels of the electronic image sensor. Dividing the predetermined area from the zenith to the predetermined zenith angle into three large areas by the zenith angle, and determining the average value of the luminance value ratio for each large area,
Estimating the ratio of the gap as the relative solar radiation amount from the average value of the luminance value ratio for each large area,
3. The leaf area index indirect measurement method according to claim 1, wherein a leaf area index is obtained from a ratio of the gap. An imaging means for taking an image of a predetermined area by changing the exposure time to a plurality of types for each of near-infrared light and red light using a wide-angle lens and an electronic imaging device;
For each subdivision area obtained by subdividing the predetermined area, for each of near-infrared light and red light, the median value of the gradation between the underexposure and the overexposure in the images of the plurality of types of exposure times. An image selection / brightness value calculating means for obtaining a luminance value when the selected image is normalized to a predetermined exposure time;
Luminance value ratio calculation means for obtaining a luminance value ratio between near infrared light and red light for each subdivision region from the luminance values of near infrared light and red light obtained for each subdivision region;
A relative solar radiation amount estimating means for estimating a relative solar radiation amount using the luminance value ratio;
A leaf area index calculating means for obtaining a leaf area index from the relative solar radiation amount;
An indirect measurement system for leaf area index.   The leaf area index indirect measurement system according to claim 4, wherein the subdivided region corresponds to one or a plurality of pixels of the electronic image sensor. The luminance value ratio calculation means divides the predetermined area from the zenith to the predetermined zenith angle into three large areas by the zenith angle, and obtains an average value of the luminance value ratio for each large area,
The relative solar radiation amount estimating means estimates a gap ratio as the relative solar radiation amount from an average value of a luminance value ratio for each large area,
6. The leaf area index indirect measurement system according to claim 4, wherein the leaf area index calculating means obtains a leaf area index from the gap ratio.

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