JP2012103155A - Apparatus, method and program for estimating laser density distribution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To assess an impact of a laser density arriving at a ground surface according to density of trees and an inclination of ground surface in an airborne laser measurement of a forest region and geography.SOLUTION: A distance between trees is estimated based on a standard density according to attribute (a tree type and a tree age) of trees, indicated in a yield table for forest (S64). An arrival rate of the laser to the ground surface is simulated to find an arrival rate function according to a distance from a tree according to an attribute. A laser arrival rate in a cell per tree in a vegetation area of each attribute is found from the distance between trees and the arrival rate function (S66). The attribute of a compartment or the like is acquired from a schematic drawing of forest, and an arrival laser density in the compartment or the like is defined based on the laser arrival rate in the cell of the corresponding attribute (S68). An inclination classification drawing 50 is made based on altitude data 48 (S72), and the inclination correction is performed on the arrival laser density (S70).

Description

  The present invention relates to a laser density distribution estimation apparatus, a laser density distribution estimation method, and a program for estimating the density distribution of a laser that reaches the ground surface in an aerial laser measurement of a forest.

  Aviation laser measurement can obtain the three-dimensional shape of the ground surface and features without the need for on-site surveys, and is very useful for topographic measurements in disaster areas, environmental conservation areas, and mountains. In addition, aerial laser measurement is different from measurement by aerial photography, and has a feature that enables measurement of ground surface elevation under a tree crown in a forest area. In this respect, the aviation laser measurement is advantageous for accurately acquiring the shape of the microtopography.

  The resolution and accuracy of topographic shape measurement by aerial laser measurement depends on the density of measurement points (laser reflection points) obtained on the ground surface. Specifically, the number of laser irradiations, the scan angle, the flight speed of the aircraft, and the altitude of the ground Depends on topographic conditions. When carrying out aviation laser measurement, a measurement plan is made so as to obtain a desired measurement density in consideration of these factors.

JP 2006-3332 A

  In forest areas, laser pulses that are swept to the ground from aircraft, etc. reach the ground surface in the area between trees, and part of the crown also passes through the gaps between the branches and leaves and reaches the ground surface below it. obtain. On the other hand, when the density of trees increases, the distance between the trees decreases, and the ratio of laser pulses blocked by the crown increases. In steep slopes, even if the horizontal distance between trees is the same as that on flat ground, if the distance along the ground surface increases and the effective density of measurement points decreases, or if the trees are dense, The crown can easily overlap due to the height difference between them, and the ratio of laser pulses passing through the crown can be reduced.

  The conventional measurement plan for forest areas including such elements has a problem that it depends on past experience and is not necessarily an appropriate plan. Therefore, for example, it was necessary to perform aviation laser measurement again or survey on the ground for a region where a sufficient measurement density was not obtained.

  The present invention has been made in order to solve the above-mentioned problems, and enables the density distribution in the forest of the laser pulses reaching the ground surface to be suitably estimated by the aerial laser measurement, thereby measuring the topography in the forest area. The purpose is to contribute to the formulation of an appropriate measurement plan.

  The laser density distribution estimation apparatus according to the present invention is an apparatus for estimating the distribution of the laser density reaching the ground surface in the aerial laser measurement in the forest, and for each tree having different attributes including tree species or tree age. An arrival rate function storage means for storing an arrival rate function representing the laser arrival rate to the surface as a function of the distance from the tree, and a tree spacing based on the standard density previously acquired for each attribute regarding the number of standing trees in the forest Inter-tree distance estimation means for estimating a distance, and allocation area laser arrival rate calculation for determining an allocation area laser arrival rate in an allocation area for each tree based on the inter-tree distance and the arrival rate function for each attribute And acquiring the attribute in the attention area based on the forest information acquired in advance including the distribution of the attribute in the forest and the distribution based on the allocation area laser arrival rate corresponding to the attribute. Having a reach laser density calculating means for determining the arrival laser density in the region of interest.

  The laser density distribution estimation apparatus according to another aspect of the present invention further includes an inclination calculating unit that calculates an inclination for each region of interest in a forest based on altitude data obtained on the ground surface in advance. The laser density calculating means performs correction according to the inclination when calculating the reached laser density.

  The laser density distribution estimation apparatus of the present invention can use a device obtained by simulating aviation laser measurement on a single tree using the three-dimensional tree model for each attribute as the arrival rate function. .

  The laser density distribution estimation method according to the present invention is a method for estimating the distribution of the laser density reaching the ground surface in an aerial laser measurement in a forest, and is acquired in advance by attributes including tree species or tree age regarding the number of standing trees in the forest. Based on the standard density, the inter-tree distance estimation step for estimating the inter-tree distance, the inter-tree distance for each attribute, and the laser arrival rate to the ground surface for each tree having the different attribute from the tree An allocation area laser arrival rate calculating step for obtaining an allocation area laser arrival rate within an allocation area to each tree based on an arrival rate function expressed as a function of the distance, and an altitude of the ground surface acquired in advance An inclination calculation step for calculating an inclination for each region of interest in the forest based on the data, and based on forest information acquired in advance including the distribution of the attribute in the forest, Get the serial attribute has a reach laser density calculation step of determining the arrival laser density in the region of interest from said inclined and the assigned area laser arrival rate corresponding to the attribute.

  A program according to the present invention is a program for causing a computer to perform a process of estimating a distribution of a laser density reaching a ground surface in an aerial laser measurement in a forest, the computer relating to the number of standing trees in the forest. Based on a standard density acquired in advance for each attribute including tree species or tree age, an inter-tree distance estimating means for estimating an inter-tree distance, to the ground surface for each tree having the above-mentioned attribute and the inter-tree distance and the attribute different Allocation area laser arrival rate calculating means for obtaining an allocation area laser arrival rate in an allocation area to each tree based on an arrival rate function that represents the laser arrival rate of the tree as a function of the distance from the tree, acquired in advance Inclination calculating means for calculating the inclination for each region of interest in the forest based on the altitude data of the ground surface, and the attribute distribution in the forest is acquired in advance. Based on forest information, the attribute in the attention area is acquired, and the reaching laser density calculating means for determining the reaching laser density in the attention area from the allocation area laser arrival rate and the slope corresponding to the attribute, To function as.

  According to the present invention, it is possible to suitably estimate the density distribution in the forest of laser pulses that reach the ground surface by aerial laser measurement, and it is easy to develop an appropriate measurement plan for topographic measurement in a forest area. It becomes.

It is a block diagram which shows the schematic structure of the laser density distribution estimation apparatus which concerns on embodiment of this invention. It is a general | schematic flowchart of the process by the laser density distribution estimation apparatus which concerns on embodiment of this invention. It is a schematic diagram of an example of the simulation result using a tree model. It is a graph which shows an example of the laser arrival rate according to the distance from a tree center.

  Hereinafter, a laser density distribution estimation apparatus 2 according to an embodiment of the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings. This device estimates the distribution of the laser density reaching the ground surface in the forest in aerial laser measurement.

  FIG. 1 is a block diagram showing a schematic configuration of the laser density distribution estimation apparatus 2. The system includes an arithmetic processing device 4, a storage device 6, an input device 8, and an output device 10. As the arithmetic processing device 4, it is possible to make dedicated hardware for performing various arithmetic processing of this system, but in this embodiment, the arithmetic processing device 4 uses a computer and a program executed on the computer. Built.

  A CPU (Central Processing Unit) of the computer constitutes an arithmetic processing unit 4, which will be described later, laser simulation means 20, intertree distance estimation means 22, in-cell laser arrival rate calculation means 24, inclination calculation means 26, and arrival laser density calculation. It functions as means 28 and measurement plan formulation support means 30.

  The storage device 6 is composed of a hard disk or the like built in the computer. The storage device 6 functions the arithmetic processing unit 4 as a laser simulation unit 20, an inter-tree distance estimation unit 22, an in-cell laser arrival rate calculation unit 24, an inclination calculation unit 26, an arrival laser density calculation unit 28, and a measurement plan formulation support unit 30. Programs and other programs are stored.

  The storage device 6 stores various data necessary for the processing of the system. For example, the storage device 6 stores the simulation results of the aviation laser measurement for a single tree performed using the three-dimensional tree model in the laser simulation means 20 of the present apparatus 2 or another apparatus.

  The simulation is performed for each tree attribute including tree species and tree age. Basically, information on the two-dimensional distribution of laser reflection points in the horizontal plane and whether the reflection point is the arrival point on the ground surface is required. . The simulation result stored in the storage device 6 may be information represented by the positions of reflection points distributed two-dimensionally, but is expressed in a format convenient for use in the laser density distribution estimation device 2 Is preferable. For example, the two-dimensional distribution is aggregated according to the distance from the tree, and an arrival rate function that associates the arrival rate that is the ratio of the arrival point to the ground surface with respect to the laser reflection point with the distance from the tree is obtained. It can be stored in the storage device 6.

  In an example of the reachability function, a plurality of donut-shaped regions that are separated by concentric circles with different radii centered on a tree are set in a horizontal plane. Then, the arrival rate in each donut-shaped region is defined as the value of the arrival rate function. In another example, the arrival rate in a circle centered on a tree is associated with the radius of the circle as the value of the arrival rate function. The storage device 6 of the present apparatus 2 stores, as a simulation result, a function in which the arrival rate in the circle is associated with the radius of the circle centered on the tree as the arrival rate function 40.

  In addition to this, the data stored in the storage device 6 includes in-cell laser arrival rate information 42, tree standard density information 44, forest information 46, altitude data 48, slope division map 50, and reaching laser density information 52.

  The tree standard density information 44 is information representing the standard density of the number of standing trees by tree type or tree age in the forest. The standard density is acquired in advance as a standard number of standing trees per unit area by measurement or the like. In Japan, there are few virgin forests, and most of them are natural forests and artificial forests. For natural forests and planted forests where thinning and other manpower are added, survey data is compiled. The survey data is totaled by tree type, and includes, for example, the number of trees per hectare (ha) for each age group. The tree standard density information 44 in the present apparatus 2 is configured using such survey data.

  The in-cell laser arrival rate information 42 is information including an arrival rate in the cell, where an area (allocation area) allocated to each tree is defined as a cell at the standard density represented by the tree standard density information 44. .

  The forest information 46 includes information on the spatial distribution of tree species and tree ages in the forest to be measured for which aviation laser measurement is to be performed. This information can be expected to be obtained through surveys for forest management of natural and planted forests. For example, in Japan, there are forest information such as forest plan maps and vegetation maps prepared by the country and prefectures, and the forest information 46 used in the apparatus 2 is also configured using such previously acquired information. it can.

  The altitude data 48 is numerical data representing a rough terrain. For example, in Japan, data such as a numerical map 50 m mesh (elevation) and a numerical map 250 m mesh (elevation) provided by the Geographical Survey Institute can be used. Although existing more detailed data can be used as the altitude data 48, the altitude data 48 is used by the laser density distribution estimation apparatus 2 to correct the inclination for each partial area (attention area) of the forest to be measured. Corresponding to the fact that the partial area is relatively wide, the altitude data 48 only needs to have the same horizontal resolution.

  The inclination division diagram 50 includes the inclination angle of each place in the forest as information.

  The reaching laser density information 52 includes the reaching laser density estimated by the laser density distribution estimation device 2 at various locations in the measurement target forest. In the laser density distribution estimation device 2, the reached laser density output from the reached laser density calculation unit 28 is held in the storage device 6 as the reached laser density information 52 for use in the measurement plan formulation support unit 30.

  The input device 8 is a keyboard, a mouse, or the like, and is used for a user to operate the system.

  The output device 10 is a display, a printer, or the like, and is used for, for example, displaying the reaching laser density calculated by the reaching laser density calculating unit 28 on the map and displaying it to the user by screen display, printing, or the like.

  FIG. 2 is a schematic flowchart of processing by the laser density distribution estimation apparatus 2. Each means of the arithmetic processing unit 4 will be described with reference to FIG.

  The laser simulation means 20 simulates aerial laser measurement of a single tree using a three-dimensional tree model for each tree attribute, and obtains a laser arrival distribution on the ground surface (S60). In the present apparatus 2, the laser simulation means 20 further generates the arrival rate function 40 based on the laser arrival distribution (S62).

  The tree model is generated using existing plant growth model software. A three-dimensional polygon model is generated as a tree model. Tree attributes can include seasons that affect leaf thickening as well as tree species and age. A tree model is generated for each attribute. Tree models can be generated in advance for various attributes and stored in the storage device 6, or only necessary ones can be generated each time depending on the vegetation of the measurement target forest and the measurement time. Good. By the way, tree types are broadly divided into conifers such as cedar, evergreen broadleaf trees such as camphor trees, and deciduous broadleaf trees such as cypress trees.

  The simulation calculates where a straight line representing a laser pulse swept from above at different angles intersects the tree model or the ground surface. FIG. 3 is a schematic diagram of an example of a simulation result, and is a diagram in which a laser reflection point is projected onto a horizontal plane. This figure shows concentric circles with the radius of the tree centered on the tree position (tree trunk), and the reflection point on the tree is indicated by “x” and the arrival point to the ground is indicated by “○”. ing. From FIG. 3, the laser arrival distribution of the simulation result qualitatively has a tendency that the laser is difficult to reach the ground surface at the center of the canopy, and the probability of passing through the branches and leaves to reach the ground surface becomes higher near the end of the crown. It is understood. This tendency is quantitatively grasped for each attribute of the tree by calculating the arrival rate by counting the number of arrival points to the ground surface for each distance from the tree in the simulation result. FIG. 4 is a graph showing an example of the laser arrival rate according to the distance from the center of the tree, and shows a simulation result for a hinoki tree of 25 years old. In FIG. 4, the horizontal axis represents the distance from the center, and the vertical axis represents the laser arrival rate.

  The laser arrival rate shown in FIG. 4 corresponds to the ratio of the arrival point to the ground surface with respect to the total number of reflection points in a donut-shaped region having a radius on the horizontal axis. On the other hand, the value of the arrival rate function 40 generated in the process S62 represents the ratio of the arrival point to the ground surface with respect to the total number of reflection points in the entire inside of the circle whose radius is the distance from the tree.

The distance between trees estimation means 22 estimates the distance between trees based on the tree standard density information 44 stored in the storage device 6 (S64). Specifically, the inter-tree distance estimation means 22 acquires the number of standing trees per ha for each attribute from the tree standard density information 44 and, for example, based on the following formula, the average between the centers (trunks) of adjacent trees The average distance is calculated in meters as the distance between trees d.
d = (10000 / n) ^1/2 (1)

  The in-cell laser arrival rate calculating means 24 calculates the in-cell laser arrival rate Rc of each tree based on the inter-tree distance d and the arrival rate function 40 for each attribute (S66). For example, the cell is set in a circular area centered on a tree and having a distance d between trees as a diameter. In this case, the intra-cell laser arrival rate is given by the value of the arrival rate function 40 when the distance is d / 2. The obtained in-cell laser arrival rate Rc is stored in the storage device 6 as in-cell laser arrival rate information 42.

  The reaching laser density calculation means 28 sets each place in the forest as an attention area, and acquires the attribute of the tree in the attention area from the forest information 46 of the storage device 6. Then, the in-cell laser arrival rate Rc corresponding to the attribute is acquired from the in-cell laser arrival rate information 42 held in the storage device 6. For example, the region of interest can be set in units of forest groups, forest subgroups, branch numbers, etc., used for describing forest plan maps.

  If the forest is relatively flat, the in-cell laser arrival rate Rc can be used as an index representing the arrival laser density D in the region of interest. In other words, using the in-cell laser arrival rate Rc, the relative size of the arrival laser density D in each region in the forest can be compared, and an estimated distribution map of the arrival laser density D in the forest is created. (S68).

  On the other hand, as the slope of the region increases, as described above, the effect of decreasing the effective laser density increases, so it is desirable to correct it. Therefore, the reaching laser density calculation means 28 of the present apparatus 2 acquires information on the inclination angle of the region of interest from the inclination division diagram 50 and performs inclination correction (S70).

  The inclination division diagram 50 used for the inclination correction is generated by the inclination calculating means 26 (S72). The inclination calculation means 26 sets each part of the forest as an attention area from the altitude data 48 stored in the storage device 6, calculates the inclination of the ground surface in each attention area, and creates an inclination division diagram 50. As described above, the gradient division diagram 50 is used for the inclination correction for each region of interest in the reaching laser density calculation unit 28 as described above. Therefore, the region of interest for which the inclination calculation unit 26 calculates the inclination is the region of interest in the reaching laser density calculation unit 28. It is preferable to determine so as to correspond to the region. Therefore, similarly to the arrival laser density calculation means 28, the inclination calculation means 26 can set the attention area in units such as forest groups.

The inclination angle Θ is defined by, for example, an angle formed by a plane representing the ground surface in a region of interest and a horizontal plane. If the ratio S of the area S of the ground surface having the inclination angle Θ to the area S0 projected on the horizontal plane is κ,
κ≡S / S0 = 1 / cosΘ (2)
It is. Further, the reached laser density D corrected for tilt is
D≡Rc / κ = Rc · cosΘ (3)
Given in. In the tilt section diagram 50, the tilt angle Θ may be recorded as tilt information as it is, or cos Θ or κ may be recorded instead of Θ.

  The reaching laser density calculating means 28 acquires the tilt information from the tilt section diagram 50 recorded in the storage device 6, calculates the tilt-corrected reaching laser density D based on the equation (3), and displays the distribution map. Create (S70). The created distribution map of the reaching laser density is recorded as reaching laser density information 52 in the storage device 6.

  The laser density distribution estimation device 2 is used to support the planning of terrain measurement using an aviation laser. Basically, in topographic measurement, it is preferable that sampling points from which positions are acquired are uniformly distributed at a density corresponding to a desired measurement resolution and accuracy. Here, the reaching laser density information 52 indicates the ratio of the laser that reaches the ground surface at each point when the laser is uniformly swept over the forest to be measured, and the density due to vegetation and topography may occur. . In formulating a measurement plan, for example, taking into account that the laser arrival point to the ground surface is necessary and sufficient at various locations in the forest and is obtained with a uniform density, and that the shooting course is shortened, Create a diagram. At that time, referring to the arrival laser density information 52, for example, in an area where the arrival rate of the laser to the ground surface is low, 1) increase the side wrap rate of the shooting course, and 2) multiple times with the course setting crossing the same point. 3) Take measures such as increasing the laser sweep density as a rotary wing aircraft that can fly at a relatively low speed instead of a high-speed airplane as the platform of the measuring instrument. In addition, when there is a region where deciduous broad-leaved trees are distributed, the arrival laser density information 52 is generated in which the measurement period is the deciduous period in which the laser can easily reach the ground surface, and the above-described measures that can increase the cost are not taken. A measurement plan can also be considered.

  The measurement plan formulation support means 30 performs a process S74 for assisting the user in formulating the measurement plan. For example, the measurement plan development support means 30 displays a map of the forest to be measured on the display that is the output device 10. When the user inputs measurement plan conditions such as a shooting course, flight altitude, flight speed, side lap rate, scan angle, number of scans, and pulse rate from the input device 8, the measurement plan formulation support means 30 Based on the information on the relative intensity of the reaching laser density represented by the reaching laser density information 52, the actual reaching laser density to the ground area corresponding to the imaging course is calculated. When the same region is imaged a plurality of times by side wrap or the like, the measurement plan formulation support means 30 adds the actual reached laser density obtained for each image to obtain the reached laser density of the region. The arrival laser density at each location of the measurement target forest calculated in this way can be displayed, for example, on a map of the measurement target forest on the display as a numerical value, hue, shading, etc. It can be judged whether it is appropriate.

  In this embodiment, the laser arrival distribution to the ground surface is obtained by computer simulation using a tree model, but this laser arrival distribution may be obtained by actual measurement.

  2 laser density distribution estimation device, 4 arithmetic processing device, 6 storage device, 8 input device, 10 output device, 20 laser simulation means, 22 tree distance estimation means, 24 intra-cell laser arrival rate calculation means, 26 tilt calculation means, 28 Achieving laser density calculation means, 30 Measurement plan formulation support means, 40 Reachability function, 42 In-cell laser reachability information, 44 Tree standard density information, 46 Forest information, 48 Elevation data, 50 Inclination division map, 52 Achieving laser density information.

Claims (5)

A laser density distribution estimation device that estimates the distribution of the laser density reaching the ground surface in an aerial laser measurement in a forest,
Reachability function storage means for storing a reachability function that represents a laser reachability to the ground surface as a function of the distance from the tree for each tree having different attributes including tree species or tree age,
An inter-tree distance estimation means for estimating an inter-tree distance based on a standard density acquired in advance for each of the attributes regarding the number of standing trees in the forest;
Based on the distance between trees and the arrival rate function for each attribute, an allocation region laser arrival rate calculating means for determining an allocation region laser arrival rate in an allocation region to each tree,
Based on the forest information acquired in advance including the distribution of the attribute in the forest, the attribute in the attention area is acquired, and the arrival in the attention area is based on the allocation area laser arrival rate corresponding to the attribute. A reaching laser density calculating means for determining a laser density;
A laser density distribution estimation apparatus comprising: In the laser density distribution estimation apparatus according to claim 1,
Based on the altitude data of the ground surface acquired in advance, it has an inclination calculating means for calculating an inclination for each region of interest in the forest,
The reaching laser density calculating means performs correction according to the inclination in calculating the reaching laser density;
An apparatus for estimating a laser density distribution. In the laser density distribution estimation apparatus according to claim 1 or 2,
2. The laser density distribution estimation apparatus according to claim 1, wherein the reachability function is obtained by simulating aviation laser measurement of a single tree using a three-dimensional tree model for each attribute. A laser density distribution estimation method for estimating a distribution of laser density reaching a ground surface in an aerial laser measurement in a forest,
An inter-tree distance estimation step for estimating an inter-tree distance based on a standard density acquired in advance for each attribute including tree species or tree age with respect to the number of standing trees in the forest;
Based on the distance between the trees for each attribute and the arrival rate function that represents the laser arrival rate to the ground surface for each tree having different attributes as a function of the distance from the tree, an allocation area to each tree An allocation area laser arrival rate calculating step for obtaining an allocation area laser arrival ratio in
An inclination calculation step for calculating an inclination for each region of interest in the forest based on altitude data of the ground surface acquired in advance;
Based on the forest information acquired in advance including the distribution of the attribute in the forest, the attribute in the attention area is acquired, and the attention area is obtained from the allocation area laser arrival rate and the slope corresponding to the attribute. A reaching laser density calculating step for determining the reaching laser density at
A laser density distribution estimation method characterized by comprising: A program for causing a computer to perform processing for estimating the distribution of the laser density reaching the ground surface in an aerial laser measurement in a forest,
An inter-tree distance estimation means for estimating an inter-tree distance based on a standard density acquired in advance for each attribute including the tree species or tree age with respect to the number of standing trees in the forest,
Based on the distance between the trees for each attribute and the arrival rate function that represents the laser arrival rate to the ground surface for each tree having different attributes as a function of the distance from the tree, an allocation area to each tree Allocation region laser arrival rate calculating means for determining the allocation region laser arrival rate in
An inclination calculation means for calculating an inclination for each region of interest in the forest based on altitude data of the ground surface acquired in advance, and
Based on the forest information acquired in advance including the distribution of the attribute in the forest, the attribute in the attention area is acquired, and the attention area is obtained from the allocation area laser arrival rate and the slope corresponding to the attribute. Reaching laser density calculating means for determining the reaching laser density at
A program characterized by functioning as

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