CN101319897A - Method for measuring area and shape of forest gap - Google Patents

Abstract

The invention relates to a method used for measuring the area and the shape of a forest gap in the field of forestry and ecology which includes the steps of: using a digital camera with a fish-eye lens to vertically upwards shoot a semi-spherical image at a certain position in the forest gap; measuring the parameters of the forest gap; processing the semi-spherical image and recording the coordinate of the highest point of the edge wood of the forest gap in the image; calculating the area and the shape of the forest gap according to the projection principle of the fish-eye lens as well as each coordinate point and the parameters of the forest gap. The invention firstly provides a method for measuring the shape of the forest gap and fills in the blank in the researching field. The method can be adopted to fast measure the area and the shape of the forest gap, thus avoiding the effect of anthropic factors in the existing method and improving the estimation precision of the area of the forest gap; the method is easily operated and the measuring result is not affected by the measuring position.

Description

A kind of method of measuring forest gap area and shape

Technical field

The present invention relates in forestry and the field of ecology about the measuring method of woods window feature specifically a kind of method of measuring forest gap area and shape.

Background technology

The woods window (or translations " woods crack ", gap) referring to will occupying and the space of upgrading of forming by new individuality by the above storey trees death of a strain, this notion is followed the research of forest cycle and is produced.It is that recurrent important small scale is disturbed in the forest community that the woods window disturbs, it is not only the driving key element of the natural forest succession of community, also the structure of forest, dynamically and bio-diversity play an important role in keeping, become one of current forest ecology research most active fields.The measurement of woods window feature is the basis of woods window research, mainly comprises forest gap area, shape, age etc.Wherein forest gap area is a woods window most important characteristic, be often used as the indirect index of the interior luminous environment of reflection woods window and other resource availability, also be the foundation of calculating forest cycle speed (forest recycle rate), the former accuracy directly influences the latter's estimation result.Therefore, measuring forest gap area rapidly and accurately is the focus that ecologists pay close attention to.The method of measuring forest gap area at present is more, here introduce 4 kinds: (1) elliptic method (Ellipse Method), the woods window is approximated to ellipse, measures major axis on major axis of woods window and the perpendicular direction and be used as oval long and short axle respectively and estimate forest gap area; (2) (Siogon Methods SMs), is approximated to equiangular polygon with the woods window to the equiangular polygon method, and measurement along a plurality of distances of dividing equally compass heading to the woods window edge, is calculated forest gap area from woods window center point then; According to the number of compass heading can be divided into isogonism 8 limit shape methods (Equiangular Octagon Method, EOM) and isogonism 16 limit shape methods (Equiangular Sixteen-gon Method, ESM); (3) isogonism elliptic sector method (Equiangular Elliptic Sectors, EESs), regarding an elliptic sector as along a plurality of compass heading adjacent areas between the two to the distance at woods window crown canopy edge of dividing equally, with these elliptic sector area sums estimation forest gap areas from the woods window center.Elliptic method is the simplest, use more, but low precision, especially when the woods window shape was complicated, its error was bigger.Isogonism 16 limit shape methods are developed by isogonism 8 limit shape methods, and the woods window is refined into more parts, and therefore, degree of accuracy is better than the former, but more consuming time, uses extensive far away from isogonism 8 limit shape methods.Isogonism elliptic sector method is to propose on the basis of equiangular polygon method, and computational accuracy is more accurate.But the common shortcoming of above each method is influenced greatly by human factor, and wasting time and energy in various degree.

The woods window shape also is a key character of woods window.The woods window shape plays an important role to the distribution and the validity of resource in the woods window.In general, the woods window shape is complicated more, the edge effect of woods window (edgeeffect) is remarkable more, resources such as light, temperature, soil moisture and soil nutrient will form a variable gradient from woods window center point to the woods window edge, thereby influence the Distribution Pattern of plant, and can improve and keep the floristics diversity of forest.A kind of method of measuring the woods window shape is not also proposed at present.Therefore, research has great importance for the woods window to find method quick, objective, that accurately measure woods window size and shape.

Summary of the invention

Be subjected to human factor to influence problem big and that waste time and energy at the measurement that has forest gap area in the prior art, the object of the present invention is to provide a kind of can objective, accurate and easy-operating measurement forest gap area and the method for shape.

For achieving the above object, the technical solution used in the present invention is:

A kind of method of measuring forest gap area and shape of the present invention has following steps: the hemisphere face image is taken vertically upward with the fish-eye digital camera of assembling in a certain position in the woods window, measures woods window parameter; Above-mentioned hemisphere face image is handled the coordinate of record photograph middle forest window edge wood peak; Area and shape according to fish-eye projection theory and each coordinate points calculating woods window.

The photographing request of described hemisphere face image is: certain a bit will be equipped with fish-eye digital camera positioned vertical on tripod in the woods window; Camera aperture transfers to minimum, and focal length transfers to the infinite distance; Select before full cloudy day, the sunrise or the post sunset shooting; It directly over the hemisphere face image compass direct north; Described woods window parameter comprises woods window edge wood average height, the gradient and aspect; By image processing software the hemisphere face image is handled, obtained all woods window edge wood peak coordinates, try to achieve the distance of each coordinate points to image center point;

Described calculating forest gap area may further comprise the steps: the woods window is approximated to polygon, calculates forest gap area (A) by following formula:

$A=0.5\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{D}_{\mathrm{\γ}(i+1)}\·D_{\mathrm{\γ}\left(i\right)}\·\sin (\mathrm{\γ}(i+1)-\mathrm{\γ}\left(i\right))$

Wherein, n is the quantity of woods window edge wood, and last point (i=n+1) also is starting point (i=1), and γ is the position angle of edge wood, D _γBe the vertical range of the wooden peak in the edge in γ orientation to the fish eye lens optical axis;

Described calculating woods window shape is specially:

Adopt girth/area ratio P/A or shape index (SI) to calculate the woods window shape, wherein $\mathrm{SI}=P/2\sqrt{\mathrm{\πA}};$ P is a woods window girth in the formula, and A is a forest gap area;

Described woods window girth (P) calculates by following formula:

$P=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\sqrt{{(D_{\mathrm{\γ}(i+1)}-D_{\mathrm{\γ}\left(i\right)}\·\cos (\mathrm{\γ}(i+1)-\mathrm{\γ}\left(i\right)))}^2+{(D_{\mathrm{\γ}\left(i\right)}\·\sin (\mathrm{\γ}(i+1)-\mathrm{\γ}\left(i\right)))}^2}$

Wherein, n is the quantity of woods window edge wood, and last point (i=n+1) also is starting point (i=1), and γ is the position angle of edge wood, D _{γ (i)}Be the vertical range of the wooden peak of the woods window edge in γ orientation to the fish eye lens optical axis;

Described woods window edge wood peak is to the vertical range (D of fish eye lens optical axis _γ) computing method as follows:

$D_{\mathrm{\&gamma;}}=\frac{H-\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="A20071001158000133.png"\; state="\{\{state\}\}">h</figure-callout>}}{\frac{1}{\tan \left(z\right)}+\tan \left(\mathrm{\&alpha;}\right)\&CenterDot;\cos (\mathrm{\&gamma;}-\mathrm{\&beta;})}$

In the formula, H is a woods window edge wood average height, and α is the gradient, and β is an aspect, and h is the height of camera lens apart from ground, and z is the zenith angle of edge wood peak to the fish eye lens vertical optical axis.

Described zenith angle (z) obtains by the following method:

Calculate the position angle (γ) of each coordinate points and, ask the zenith angle (z) of the wooden peak in edge according to woods window edge wood peak coordinate figure of subpoint in photograph to the fish eye lens vertical optical axis according to fish-eye polar coordinates projection theory formula to the distance (r) of photo center point:

z/90＝r/R

In the formula, the radius distance of subpoint in hemisphere face image when R is z=90.

The present invention has following beneficial effect and advantage:

1. propose to measure the method for woods window shape first, filled up the blank of this research field.

2. can measure forest gap area and shape fast, objectively.

3. has higher measuring accuracy.

4. measurement result is not subjected to the influence of measuring position.

Description of drawings

Fig. 1 is the imaging schematic diagram of hemisphere face image of the present invention;

Fig. 2 calculates the vertical height synoptic diagram of arbitrary orientation angle woods window edge wood above measurement point for the present invention;

Fig. 3 A is a hemisphere face image method data processing synoptic diagram of the present invention;

Fig. 3 B is the partial enlarged drawing of Fig. 3 A;

Fig. 4 is the graph of a relation of forest gap area and 2 shape indexs.

Embodiment

(1) experiment place

Sample plot click take from certain forest ecology experiment centre (41 ° of 51.102 ' N, 124 ° 54.543 ' E), height above sea level 252～1116m, weather belong to the continental monsoon climate in warm temperate zone, winter very long cold, summer is burning hot and rainy.3.9～5.4 ℃ of average temperatures of the whole year, 36.5 ℃ of the extreme highest temperatures, minimum subzero 37.6 ℃.Greater than 2497.5～2943.0 ℃ of 10 ℃ year active accumulated temperatures, frostless season 120～139d, annual 2433h at sunshine, annual precipitation 700～850mm, rainfall concentrates on for 6～August.Vegetation is under the jurisdiction of the Changbai Mountain fauna, based on Natural Secondary Forests, constructive species has Fraxinus rhynchophylla (Fraxinus rhynchophylla), Mongolian oak (Quercus mongolica), look wood maple (Acer mono), juglans mandshurica (Juglansmandshurica) etc., and part larix olgensis (Larix olgensis) artificial forest and Korean pine (Pinuskoraiensis) artificial forest are arranged, also have the remaining neutral red pine forest of small size.

(2) field survey

Selecting 12 artificial forest windows that vary in size and 18 wildwood windows is the respondent, select the full cloudy day, 5 random points and each wildwood window center point are settled tripod in each artificial forest window, and positioned vertical is furnished with fish-eye digital camera, and fish eye lens is than the high h in ground; Camera aperture transfers to minimum, and focus transfers to the infinite distance, takes 1 hemisphere face image vertically upward, selects 5 strain woods window edges wood to measure average height H simultaneously in each woods window at random, and measures gradient α and aspect β.In addition, settle forestry compass at each woods window center point, measure along 16 compass headings (0,22.5,45 ..., 337.5 degree) to the domatic distance that is parallel to of crown canopy edge-perpendicular subpoint.

(3) calculating of forest gap area

(1) hemisphere face image method principle

The hemisphere face image method is based on 2 hypothesis: I. woods window edge wood is high identical; II. the residing terrain slope unanimity of woods window, promptly α is a steady state value.The imaging mode of hemisphere face image is the polar coordinates projection patterns, and promptly edge wood crown canopy marginal point becomes linear dependence (formula (1)) to photo center point apart from r to the zenith angle z of fish eye lens vertical optical axis and subpoint:

As shown in Figure 1, E is an eyeball, and D is the vertical range of E to camera lens optical axis, r is the radius distance of E in the hemisphere face image, R is the radius distance of horizontal eyeball in the hemisphere face image, and z is the zenith angle of edge wood peak to the fish eye lens vertical optical axis, then has:

z/90＝r/R (1)

According to geometric relationship, can obtain formula (2):

D _γ＝H _γ·tan(z) (2)

In the formula, D _γBe the vertical range of γ position angle crown canopy marginal point to the fish eye lens optical axis, H _γBe the height of γ position angle crown canopy marginal point above fish eye lens.

As shown in Figure 2, O is measurement point (being the camera lens position), and ∠ OCB=α (being the gradient), AE are that woods window edge wood is high, and EE ' is the height (H of woods window edge wood above the O point _γ); Following relational expression is set up: AE//OB ⊥ Δ ABC, OE ' ⊥ AE, AC ⊥ Δ OBC, ∠ ABC=γ-β (wherein γ is the position angle, and β is the aspect angle), AB=D _γAccording to above relational expression, can try to achieve: AE '=OB=BCtan (α), BC=D _γCos (γ-β), AE '=tan (α) D _γCos (γ-β); According to the average height H that measures, gradient α and aspect β, can try to achieve the height H of γ orientation crown canopy marginal point above fish eye lens _γ(formula (3)):

H _γ＝H-AE′-h

H _γ＝H-tan(α)·D _γ·cos(γ-β)-h (3)

In the formula, h is the height of camera lens apart from ground.

In formula (3) substitution formula (2), can obtain formula (4):

$D_{\mathrm{\&gamma;}}=\frac{H-\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="A20071001158000133.png"\; state="\{\{state\}\}">h</figure-callout>}}{\frac{1}{\tan \left(z\right)}+\tan \left(\mathrm{\&alpha;}\right)\&CenterDot;\cos (\mathrm{\&gamma;}-\mathrm{\&beta;})}---\left(4\right)$

(2) equiangular polygon method (according to example):

Being parallel to domatic distance transform is horizontal range, and note is done: l ₁, l ₂..., l ₁₆, l ₁Compass heading be 0 degree, the position angle of other l increases successively with 22.5 degree, to l ₁₆Compass heading is 337.5 degree.The computing formula of equiangular polygon method is specially:

$A=0.5\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{l}_{i+1}\&CenterDot;l_i+\sin (2\mathrm{\&pi;}/n)---\left(8\right)$

When i=n, l _I+1Equal l ₁N equals 16 or at 8 o'clock, A be respectively isogonism 16 limit shape methods (equiangular sixteen-sided polygon method, ESM) or isogonism 8 limit shapes (equiangularoctagon method, EOM) forest gap area that calculates of method.In the present embodiment, measured the distance of 16 compass headings altogether, therefore, isogonism 8 limit shape methods have two kinds of situations of asking forest gap area, and they are respectively (l based on 2 groups of different pieces of informations ₁, l ₃..., l ₁₅) and (l ₂, l ₄..., l ₁₆).

(3) calculating of data processing and forest gap area and shape

Shown in Fig. 3 A, 3B, in image processing software (present embodiment adopts Adobe Illustrator), the hemisphere face image is amplified to 1600%.The coordinate (" * " is the peak of woods window edge wood among the figure) of the every strain woods window edge wood of record crown canopy peak if this woods window has n strain edge wood, then writes down n group coordinate figure altogether in the hemisphere face image; Calculate the position angle γ and the r thereof of each edge wood crown canopy peak according to coordinate figure, ask z, ask D according to formula (4) according to formula 1 _γ, then the woods window is approximated to n limit shape and asks forest gap area A and girth P (formula 5 and 6).

$A=0.5\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{D}_{\mathrm{\&gamma;}(i+1)}\&CenterDot;D_{\mathrm{\&gamma;}\left(i\right)}\&CenterDot;\sin (\mathrm{\&gamma;}(i+1)-\mathrm{\&gamma;}\left(i\right))---\left(5\right)$

$P=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}\sqrt{{(D_{\mathrm{\&gamma;}(i+1)}-D_{\mathrm{\&gamma;}\left(i\right)}\&CenterDot;\cos (\mathrm{\&gamma;}(i+1)-\mathrm{\&gamma;}\left(i\right)))}^2+{(D_{\mathrm{\&gamma;}\left(i\right)}\&CenterDot;\sin (\mathrm{\&gamma;}(i+1)-\mathrm{\&gamma;}\left(i\right)))}^2}---\left(6\right)$

In the formula, n is the quantity of woods window edge wood, and last point (i=n+1) also is starting point (i=1), adopts girth/area ratio (P/A) and shape index (SI:Shape index) to calculate woods window shape (formula 7) simultaneously:

$\mathrm{SI}=P/2\sqrt{\mathrm{\&pi;A}}---\left(7\right)$

(4) result and analysis

The area A of calculating the hemisphere face image method respectively is (in table 1 and the table 2 with A _HPMExpression), the area A of isogonism 16 limit shape methods _ESM, two isogonism 8 limit shape methods area A _{EOM_1}, A _{EOM_2}By expert data statistical analysis software Statistical Product and Service Solutions (SPSS, v13.0), calculate the correlativity between each method, with the difference between more above-mentioned each method of paired t-test (paired t-test), the influence of whether being taken with variance analysis (ANOVA) check hemisphere face image method.The calculated in various ways forest gap area the results are shown in table 1, paired t-test the results are shown in Table 2.

The statistical value of table 1. forest gap area

The pairing t-tests result of table 2. forest gap area

Annotate: when p＞0.05, show as no significant difference between two data; When p＜0.05, show as significant difference between two data; When p＜0.01, show as utmost point significant difference between two data.

Have high correlativity between hemisphere face image method, isogonism 16 limit shape methods, the isogonism 8 limit shape methods two two, wherein, minimum coefficient R ²=0.993 (n=30, p＜0.001), this shows between 3 kinds of methods and has high correlationship.

Paired t-test (table 2) shows, the forest gap area A that the hemisphere face image method records _HPMArea A with isogonism 16 limit shape methods _ESM, isogonism 8 limit shape methods area A _{EOM_1}There is not significant difference, but A _HPMMore approach A _ESMA _HPMCompare A _ESMLittle by 1.43%, compare A _{EOM_1}And A _{EOM_2}Difference big 2.95% and 15.89%.This explanation hemisphere face image method has precision preferably.

Variance analysis (ANOVA) shows that the hemisphere face image method forest gap area that diverse location records in the woods window does not have difference, and (d.f.=4, p=0.906), promptly the hemisphere face image method is not subjected to the influence of camera site.

2 the shape index P/A and the SI of 30 the woods windows of surveying are respectively 0.65 ± 0.55 (0.15～1.23) and 1.32 ± 0.35 (1.06～2.02).As shown in Figure 4, SI and P/A calculate gained by the hemisphere face image method, and solid line and dotted line are represented the value as woods window shape SI and P/A when circular respectively, and " * " and "+" is respectively the measured value of SI and P/A.When the woods window shape was circle, SI was steady state value (equaling 1), and P/A reduces along with the increase of forest gap area.The Pearson index of correlation shows, the correlativity of forest gap area and P/A (R=-0.759, p＜0.001) is than (R=-0.402, correlativity p=0.031) is big, shows that P/A is subjected to area effect bigger, and SI is subjected to area effect less with SI.This explanation SI be one than the better shape index of P/A.

Comprehensive above the analysis, we obtain following result: the hemisphere face image method is the method for a kind of objective, accurate and easy-operating measurement forest gap area and shape, and there is not remarkable influence in hemisphere face filming image position to measurement result; The hemisphere face image of the woods window by time series, this method can be monitored the variation of woods window size and shape well, therefore, this method for woods window feature chronically, comparative study is significant.

The forest gap area that calculated in various ways obtains is referring to table 3, and the forest gap area that the hemisphere face image method records at 5 diverse locations of artificial forest window is referring to table 4.

Forest gap area (the m that table 3. calculated in various ways obtains ²)

Table 4. hemisphere face image method records the forest gap area (m of 5 diverse locations of artificial forest window ²)

Claims (9)

1. method of measuring forest gap area and shape is characterized in that having following steps: the hemisphere face image is taken vertically upward with the fish-eye digital camera of assembling in a certain position in the woods window; Measure woods window parameter; Above-mentioned hemisphere face image is handled the coordinate of record photograph middle forest window edge wood peak; Area and shape according to fish-eye projection theory and each coordinate points and woods window calculation of parameter woods window.

2. according to the method for described measurement forest gap area of claim 1 and shape, it is characterized in that the photographing request of described hemisphere face image is: certain a bit will be equipped with fish-eye digital camera positioned vertical on tripod in the woods window; Camera aperture transfers to minimum, and focal length transfers to the infinite distance; Select before full cloudy day, the sunrise or the post sunset shooting; It directly over the hemisphere face image compass direct north.

3. according to the method for described measurement forest gap area of claim 1 and shape, it is characterized in that: described woods window parameter comprises woods window edge wood average height, the gradient and aspect.

4. according to the method for described measurement forest gap area of claim 1 and shape, it is characterized in that: by image processing software the hemisphere face image is handled, obtained all woods window edge wood peak coordinates, try to achieve the distance of each coordinate points to image center point.

5. according to the area of the described measurement of claim 1 woods window and the method for shape, it is characterized in that described calculating forest gap area may further comprise the steps: the woods window is approximated to polygon, calculates forest gap area (A) by following formula:

$A=0.5\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{D}_{\mathrm{\&gamma;}(i+1)}\&CenterDot;D_{\mathrm{\&gamma;}\left(i\right)}\&CenterDot;\sin (\mathrm{\&gamma;}(i+1)-\mathrm{\&gamma;}\left(i\right))$

Wherein, n is the quantity of woods window edge wood, and last point (i=n+1) also is starting point (i=1), and γ is the position angle of edge wood, D _γBe the vertical range of the wooden peak in the edge in γ orientation to the fish eye lens optical axis.

6. according to the area of the described measurement of claim 1 woods window and the method for shape, it is characterized in that described calculating woods window shape is specially:

Adopt girth/area ratio P/A or shape index (SI) to calculate the woods window shape, wherein $\mathrm{SI}=P/2\sqrt{\mathrm{\&pi;A}};$ P is a woods window girth in the formula, and A is a forest gap area.

7. according to the area of the described measurement of claim 1 woods window and the method for shape, it is characterized in that described woods window girth (P) calculates by following formula:

$P=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}\sqrt{{(D_{\mathrm{\&gamma;}(i+1)}-D_{\mathrm{\&gamma;}\left(i\right)}\&CenterDot;\cos (\mathrm{\&gamma;}(i+1)-\mathrm{\&gamma;}\left(i\right)))}^2+{(D_{\mathrm{\&gamma;}\left(i\right)}\&CenterDot;\sin (\mathrm{\&gamma;}(i+1)-\mathrm{\&gamma;}\left(i\right)))}^2}$

Wherein, n is the quantity of woods window edge wood, and last point (i=n+1) also is starting point (i=1), and γ is the position angle of edge wood, D _{γ (i)}Be the vertical range of the wooden peak of the woods window edge in γ orientation to the fish eye lens optical axis.

8. according to claim 5 or the area of 7 described measurement woods windows and the method for shape, it is characterized in that the vertical range (D of woods window edge wood peak to the fish eye lens optical axis _γ) computing method as follows:

$D_{\mathrm{\&gamma;}}=\frac{H-h}{\frac{1}{\tan \left(z\right)}+\tan \left(\mathrm{\&alpha;}\right)\&CenterDot;\cos (\mathrm{\&gamma;}-\mathrm{\&beta;})}$

In the formula, H is a woods window edge wood average height, and α is the gradient, and β is an aspect, and h is the height of camera lens apart from ground, and z is the zenith angle of edge wood peak to the fish eye lens vertical optical axis.

9. according to the area of the described measurement of claim 8 woods window and the method for shape, it is characterized in that described zenith angle (z) obtains by the following method:

Calculate the position angle (γ) of each coordinate points and, ask the zenith angle (z) of the wooden peak in edge according to woods window edge wood peak coordinate figure of subpoint in photograph to the fish eye lens vertical optical axis according to fish-eye polar coordinates projection theory formula to the distance (r) of photo center point:

z/90＝r?/R

In the formula, the radius distance of subpoint in hemisphere face image when R is z=90.

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