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Method for evaluating tree production capacity, image capture device for evaluating tree production capacity, and program for evaluating tree production capacity 新技術説明会

外国特許コード F110005163
掲載日 2011年8月25日
出願国 アメリカ合衆国
出願番号 09731406
公報番号 20090281733
公報番号 8352208
出願日 平成18年12月15日(2006.12.15)
公報発行日 平成21年11月12日(2009.11.12)
公報発行日 平成25年1月8日(2013.1.8)
国際出願番号 JP2006325084
国際公開番号 WO2007069736
国際出願日 平成18年12月15日(2006.12.15)
国際公開日 平成19年6月21日(2007.6.21)
優先権データ
  • 特願2005-361386 (2005.12.15) JP
  • 特願2006-272055 (2006.10.3) JP
  • 2006JP325084 (2006.12.15) WO
発明の名称 (英語) Method for evaluating tree production capacity, image capture device for evaluating tree production capacity, and program for evaluating tree production capacity 新技術説明会
発明の概要(英語) Evaluation of tree production capacity by a non-destructive method using a tree crown structure measurement device or using an image capture device with a fisheye lens mounted, for isolated trees or for trees existing at intervals, is enabled without requiring a large amount of time.
A semi-spheroid of revolution model is established as a representation of the outer shape of a tree, an optical tree structure measurement device is placed at a position apart from the main trunk by a prescribed distance, the intensity of light passing through tree leaves and the intensity of light not passing through tree leaves are measured, the optical path length of light incident on the tree is calculated using the semi-spheroid model and the total tree leaf area is determined from the measured light intensities and optical path length.
The total tree leaf area is also determined by placing an image capture device with a fisheye lens mounted in place of an optical tree structure measurement device and performing data processing of image data acquired by image capturing.
従来技術、競合技術の概要(英語) BACKGROUND OF THE INVENTION
In the past, various methods have been studied for non-destructive estimation of the leaf areas of tree, which is one index of tree production capacity; one of these is a method in which the total tree leaf area is estimated by measuring light transmitted by tree leaves using an optical tree structure measurement device.
Here, an optical tree structure measurement device is placed in positions below isolated trees or below a plurality of trees existing at intervals, light transmitted by tree leaves is measured, and the data obtained is used to estimate the total leaf area of tree to evaluate tree production capacity.
The following references disclose using a Plant Canopy Analyzer (PCA, a product name) as an optical tree structure measurement device to estimate the leaf area of trees.
Non-patent Reference 1
Takayuki Nakano, "Application of Plant Canopy Analyzer for Mature Tea (Camellia sinensis L.) Bush" (Japanese Journal of Crop Science, 69(3): 419-423 (2000))
Non-patent Reference 2
J. S. Broadhead et al, "Comparison of method for leaf area in tree rows", Agricultural and Forest Meteorology, 115:151-161 (2003))
In Non-patent Reference 1, a Plant Canopy Analyzer is applied to diagnosis of the leaf area of rows of tea bushes which constitute an isolated plant canopy.
During measurements, the PCA is directed toward the bush center portion, a view cap with an aperture of 90 deg. was mounted in order to regulate the field in the azimuthal direction (horizontal direction), and a field-regulating filter is mounted in order to regulate the field in the zenith angle direction from 0 deg. to 60 deg.. In this method, estimating leaf area, calculations are performed assuming a uniform population and in the case of tea bushes the quantity of branches is large compared with leaf groups, so the leaf area index is over-evaluated, thus making use in leaf area estimation difficult.
In Non-patent Reference 2, a Plant Canopy Analyzer was applied to estimation of the leaf area density (ratio of the area of leaves per unit volume) for rows of trees (Croton megalocarpus, Melia volkensil) in a savanna in Kenya, and assuming the cross-section of tree rows to be elliptical and using the estimated optical path lengths, the leaf area density was calculated based on a method of calculation for isolated trees.
Using this method, the correlation between calculation results and actually measured leaf area densities is low, and consequently the zenith angle distribution of inclination angles for individual leaves is newly measured, and the correlation between calculation results obtained from a model based on this and measured values is heightened.
However, because a new model is added, considerable time and effort are required to measure the inclination angles of individual leaves, and so this cannot be said to be a practical method.
A PCA (Plant Canopy Analyzer: U.S. LI-COR model LAI-2000) is a representative optical tree structure measurement device currently in use.
As shown in FIG. 1, this device comprises a lens system including a fisheye lens which captures light within an incident angle range of 148 deg. at the tip end, a reflecting mirror, a filter and a detector.
In the detector, photosensitive elements of silicon are disposed in a concentric circular array, so as to detect light with five different zenith angles.
Data obtained in measurements by the detector is processed and control of data transfer to a computer is executed.
The PCA is generally used for measurements of plant canopies, which have a radial-direction spreading of three or more times the height z of the population and which have a uniform leaf area distribution and a uniform height according to the azimuthal directions with a cross-sectional shape such as that shown in FIG. 2.
In this case, the optical path length S(theta ) at the zenith angle theta , at which the transmissivity of a population is measured on the earth's surface, is estimated using the following equation.
S(theta )=z/cos theta
However, in the case of an isolated plant canopy (a single isolated tree or similar) for which the assumption of the above equation is not adapted, in general there are a need for measurement of transmitted light with the sensor at the base of the trunk and oriented toward the outside of the plant canopy and also a need for measurement of optical path length at zenith angle theta at the measurement point.
Because the shape of an isolated plant canopy and the leaf area are not uniform but variable depending on the azimuthal direction, it is necessary to make measurements in approximately four azimuthal directions, and consequently length measurements must be performed in a total of 20 cases (five optical path lengths * four compass directions).
Further, because the sensor is directed outward of the plant canopy, the middle upper portion of the population is not subjected to measurements.
Also, because what is obtained in this method is the leaf area density (the leaf area per unit volume of tree), measurements for the volume of the plant canopy must be performed as another step in order to calculate the total leaf area.
The inventor measured transmitted light for tree of 33 citrus trees using a PCA and, assuming a plant population with a substantially uniform leaf area distribution and height with azimuthal direction as described above, estimated tree leaf areas.
As a result, the relation between the leaf area index (the ratio of the leaf area per unit area) as measured by a PCA and the tree crown leaf area index (the ratio of the leaf area to the area of the tree crown projected onto the ground) is shown in FIG. 3, where the correlation is low (r=0.418) with considerable dispersion regardless of the magnitude of the leaf area density.
Conceivable reasons for this low correlation between the leaf area index measured by PCA and the tree crown leaf area index include the fact that the citrus trees measured are not a tree canopy having uniform height, for which a PCA is originally intended.
A conventional method of tree crown leaf area estimation using an optical tree crown structure measurement device cannot be applied to trees having only old leaves (leaves which have lasted through winter) with low leave area densities, and measurement is often difficult, and there has also been such a problem that the ratio of new leaves (newly developed leaves which have not lasted through winter) to old leaves cannot be evaluated.
Further, when estimating the tree crown leaf area of trees which are isolated or which exist at intervals and do not constitute a tree group with uniform height, much time is required for estimation, and inevitably there is only low correlation between the leaf area index obtained as a result of measurement and the tree crown leaf area index.
Hence it has been sought to execute estimation without requiring much time, to heighten the correlation between the leaf area index obtained as a result of measurement and the tree crown leaf area index and to reduce required expenses.

特許請求の範囲(英語) [claim1]
1. An image capture device for evaluating tree production capacity, comprising: a fisheye lens; an image capture element disposed at the image-forming position of the fisheye lens; an image capture operation control portion; a processing circuit which performs data processing of image data acquired by the image capture element; and an output portion which outputs processed results of the processing circuit, characterized in that, while measuring light transmitted by a tree for the tree existing in isolation or for each of a plurality of trees existing at an interval, said processing circuit is so arranged as to perform: processing image data acquired by image capturing with the image capture device placed at a position close to the ground and apart from the main trunk by a prescribed distance so that an incident optical axis is directed upward in a vertical direction with respect to a horizontal plane to determine sky factors over a plurality of angular ranges from the image data of image portions of a plurality of angular ranges containing each of the plurality of zenith angles for measurement respectively,
determining an optical path length from an incident point on a surface of the semi-spheroid by the semi-spheroid model to the image capture device and a tree crown volume,
determining an amount of attenuation of light corresponding to an angular range containing each of the zenith angles from the sky factors and the optical path length corresponding the plurality of zenith angles, and
determining a leaf area density from said determined amount of attenuation of light and determining a total tree leaf area from the determined leaf area density and the tree crown volume.
[claim2]
2. The image capture device for evaluating tree production capacity according to claim 1, characterized in that the processing circuit is so arranged as to perform data processing to determine the sky factor T(theta i) for incident light at the plurality of zenith angles (theta i) by using the following equation (5),
(Equation image 17 not included in text)
and to determine the leaf area density (LAD) by using the following equation (2)
(Equation image 18 not included in text)
[claim3]
3. The image capture device for evaluating tree production capacity according to claim 1 or claim 2, characterized in that the semi-spheroid model is an upward-convex semi-ellipsoid of revolution model in which the main trunk of one tree is taken as an axis and a tree height and an average tree crown radius are taken as two radii.
  • 発明者/出願人(英語)
  • YAMAMOTO HARUHIKO
  • IWAYA KIYOSHI
  • TSUCHIYA YASUSHI
  • YAMAGUCHIUNIVERSITY
国際特許分類(IPC)
米国特許分類/主・副
  • 702/127
  • 356/629
  • 702/156
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