CN101916438A - Method for obtaining leaf area index and average leaf inclination of rice canopy by using hemisphere photographic process - Google Patents

Abstract

The invention discloses a method for obtaining the leaf area index and the average leaf inclination of rice canopy by using a hemisphere photographic process. The method comprises the following steps of: collecting a hemisphere image of rice canopy from bottom to top inside the rice canopy by using a digital hemisphere shooting system based on a fisheye lens; after performing gray conversion and binaryzation on the hemisphere image, obtaining the canopy porosity under the zenith angle at a viewing angle of 57 degrees, and calculating the rice canopies LAI and ALIA under the condition of the single zenith angle at the viewing angle of 57 degrees based on the Beer-Lambert law and a poisson model as well as the two characteristics of the blade projection function of the rice canopy; simulating the leaf inclination distribution of the rice canopy by an elliptic function and optimizing the rice canopies LAI and ALIA calculated by using the single-angle method so as to rapidly acquire the rice canopies LAI and ALIA. The rice canopies LAI and ALIA can be obtained in real time without picking up rice blade outdoors for destructive artificial measurement, and basic parameters for monitoring the rice growth in real time and remotely estimating the yield of rice are provided.

Description

The hemisphere Photographic technique obtains all methods at leaf inclination angle of rice canopy leaf area index peace

Technical field

The present invention relates to a kind of hemisphere Photographic technique and obtain all methods at leaf inclination angle of rice canopy leaf area index peace.

Background technology

Paddy rice is one of topmost cereal crops of China.Rice canopy is that interactional main place takes place for paddy rice and external environment, and many biophysics processes of paddy rice comprise processes such as photosynthetic, breathing, transpiration and precipitation intercepting and capturing, all occur in canopy.The canopy structure parameter is a reflection paddy growth situation, estimates the important indicator of rice yield.In many canopy structure parameters, what of plant blade area on the unit face of land are leaf area index (LAI) reflected; And (average leafinclination angle ALIA) has then expressed the space distribution of blade in the canopy at average leaf inclination angle.These two parameters have determined the ability that paddy rice utilizes and manages light, moisture etc. with other canopy structure parameters.

Traditional method of obtaining rice canopy LAI and ALIA mainly is " directly measuring method ", Li Yunmei (Li Yunmei. vegetation radiation transfer theory and application [M]. Nanjing: publishing house of Nanjing Normal University, 2005.) by surveying the leaf area and the blade tilt of rice canopy, calculate rice canopy leaf area index, extinction coefficient, and simulated the averaging projection's function of rice canopy and the distribution at leaf inclination angle.Warren Wikon (Warren Wilson, J., and Reeve, J, L., 1959.Analysis of the spatial distribution of foliage by two-dimensional point quadrats.New Phytol. 58:92-101.) then adopts " the throwing skill of handling needles " to measure canopy structure parameters such as plant leaf area index and leaf inclination angle.Xu Zhengjin (Xu Zhengjin, Dong Ke. assay method in the time of rice leaf base angle, the first transaction of a day's business angle and degree of hanging down loosely. Agricultural University Of Shenyang's journal, 1991,22 (2): 185-187.) then use " method of loci " to measure crop leaf length also by calculating canopy structure parameters such as obtaining LAI and leaf inclination angle.

The practical experience that the above " directly measures method ", " the throwing skill of handling needles ", " method of loci " depend on survey crew to a great extent be subject to the subjective factor influence, and speed is slow, working strength is big.Therefore, for can be objective, obtain crop canopies LAI and ALIA apace, researchers have studied new method.

Liu Guoan [Liu Guoan. a kind of projectional technique of crop leaf area index and leaf tilt profiles function. the Chinese agriculture meteorology, 1994,15 (6): 11-15.], use with the similarly simple least square method of multiple regression analysis and calculate the leaf area index and the leaf tilt profiles function of corn and rape colony indirectly according to mensuration to spot densities in the canopy and total solar radiation amount.Wumen is new, and (Wumen is new, Zhu Qijiang, Wang Jin ground, a yu-kin, Su Lihong, Zhou Xiaodong, Tang Shihao. the visual research of calculating of summer corn structural parameters and field corn canopy. Acta Agronomica Sinica, 2002,28 (6): 721-726.) on the basis of geometric figure method, parametric method and the direct method of measurement, the related data of utilizing measured data to obtain in conjunction with Digital Image Processing has been set up the regression model of image LAI with actual measurement LAI, and has obtained the LAI of summer corn in batches according to 5 these successes.Barrie (Julie Barrie, J.N.Greatorex-Davies, R.J.Parsell and R.H.Marrs.1990.A semi-automated method for analysing hemispherical photographs for the assessment of woodland shade.Biological Conservation.54 (4): 327-334), Becke (P.Becker, D.W.Erhart and A.P.Smith.1989.Analysis of forest light environments part I.Computerized estimation of solar radiation from hemispherical canopy photographs.Agricultural and Forest Meteorology.44 (3-4): 217-232), Chen (J.M.Chen, T.A.Black and R.S.Adams.1991.Evaluation of hemispherical photography for determining plant area index and geometry of a forest stand.Agricultural and Forest Meteorology.56 (1-2): 129-143), Baret (F.Baret, B.Andrieu and M.D.Steven.1993.Gap frequency and canopy architecture of sugar beet and wheat crops.Agricultural and Forest Meteorology.65 (3-4): 261-279)) in research separately, the digital hemisphere image that fish eye lens is obtained, handle by specific software, obtain crop canopies structural parameters such as forest arbor and wheat and beet.

And obtaining aspect the long-pending average leaf of the exponential sum inclination angle of rice leaf open source literature report not also both at home and abroad based on the hemisphere Photographic technique.

Summary of the invention

For the method that overcomes existing artificial field survey rice canopy LAI and ALIA wastes time and energy, is difficult to the quick in real time defective of accurately obtaining the result, the object of the present invention is to provide a kind of hemisphere Photographic technique to obtain all methods at leaf inclination angle of rice canopy leaf area index peace.

The step of the technical solution used in the present invention is as follows:

1) photographic images:, lie in a horizontal plane in rice canopy inside photographing rice canopy original color hemisphere image with the digital camera lens of hemisphere camera lens up, leave in the computer with the form of JPG image file;

2) coloured image gradation conversion: the original color hemisphere image that digital camera is photographed is converted to gray scale hemisphere image by image processing software, leaves in the computer;

3) gray level image binaryzation: with 2) the gray scale hemisphere image transitions in the step leaves in the computer for only containing the two-value hemisphere image of " deceiving ", " in vain " two kinds of picture dots;

4) calculate the canopy factor of porosity:, leave in the computer based on two-value hemisphere image calculation rice canopy factor of porosity;

5) leaf area index under 57 ° of single angle zenith angles of calculating and average leaf inclination angle:, calculate leaf area index and average leaf inclination angle under 57 ° of single angle zenith angles according to the relation of rice canopy leaf area index and canopy factor of porosity and two characteristics of leaf inclination angle projection function G function;

6) optimization at 57 ° of single angle leaf area index and average leaf inclination angle: with the leaf tilt profiles of elliptic function simulation rice canopy, substitute 5) the simple average leaf inclination angle that obtains in the step, carry out the iteration optimization at single angle leaf area index and average leaf inclination angle, obtain all leaf inclination angles of best rice canopy leaf area index peace;

7) whole calculating adopts Visual C#2005 programming to realize.

The beneficial effect that the present invention has is:

Utilization is obtained rice canopy numeral hemisphere image based on fish-eye hemisphere Photographic technique, need not open-airly pluck rice leaf and carry out destructive manual measurement leaf area, and measurement leaf inclination angle, can obtain rice canopy structural parameters LAI and ALIA real-time, for real-time monitoring paddy rice growing way, carry out the paddy rice Remote Sensing Yield Estimation underlying parameter is provided.

Description of drawings

Accompanying drawing is the changing trend diagram of rice canopy factor of porosity with the visual angle.

Embodiment

In selected field piece, distribute and set up 8 1m * 1m to take the sub-district, 36 strain paddy rice are arranged in average every sub-district by " S " type.Selecting early rice, late rice and the single harvest rice is reference object.The season of growth of paddy rice takes weekly once in season in each, per season paddy rice take 5-7 time.

1) take rice canopy hemisphere image:

The fish eye lens camera is placed in the central point of each sub-district, the maintenance level, camera lens is to photographs; Shooting time selects cloudy day or fine day but the sun carries out when being blocked by cloud layer; Horizontally rotate camera, every one of 45 ° of shooting, each sub-district obtains 8 rice canopy hemisphere images altogether; Handle the basic data of the mean value of the factor of porosity that these 8 images obtain as inverting canopy structure parameter.

2) coloured image gradation conversion:

Conversion formula adopts:

Gray(x，y)＝B(x，y) (1)

In the formula:

Gray (x, y)---point on the gray level image (x, the gray-scale value of y) locating,

B (x, y)---original color image mid point (x, the blue component value of y) locating;

3) image binaryzation:

$\mathrm{BW}(x,y)=\left\{\begin{array}{cc}0& \mathrm{Gray}(x,y)<T\\ 255& \mathrm{Gray}(x,y)\&GreaterEqual;T\end{array}\right.---\left(2\right)$

In the formula:

BW (x, y)---point on the bianry image (x, the pixel value of y) locating,

Gray (x, y)---point on the gray level image (x, gray-scale value y),

T---selected threshold value,

BW (x, y)=0---black, expression (x, y) the some place is a rice leaf,

BW (x, y)=255---white, (x y) locates to be sky in expression;

Threshold value is determined method:

Take rice canopy from bottom to top, can obtain typical bimodal pattern image: the pixel in the rice canopy produces a peak in the histogram, and background produces another peak in the histogram, the boundary vicinity of object and background has two gray levels between the peak value, its number of pixels is less relatively, thereby has produced two peak-to-peak paddy.Select paddy can obtain rational segmentation result as gray threshold.Gray-scale value is incorporated into greater than the picture dot of this threshold value is the sky picture dot, and gray-scale value then is considered to rice leaf less than this threshold value.

4) calculate the canopy factor of porosity:

With rice canopy hemisphere image center is the center of circle, every 10 ° be 9 concentric rings with image division, the corresponding zenith angle of each ring.From the inside to surface, each ring with 5 °, 15 °, 25 ° ..., 9 zenith angles such as 75 °, 85 ° represent its visual angle.By formula (3) calculate the ratio that each quantity of encircling interior sky pixel accounts for total pixel in the ring, promptly are somebody's turn to do the canopy factor of porosity that encircles under the corresponding visual angle:

$T\left(\mathrm{\&theta;}\right)=\frac{P_0\left(\mathrm{\&theta;}\right)}{P_0\left(\mathrm{\&theta;}\right)+P_1\left(\mathrm{\&theta;}\right)}---\left(3\right)$

In the formula:

T (θ)---the factor of porosity of view angle theta lower canopy,

P ₀(θ)---sky pixel quantity,

P ₁(θ)---the quantity of blade pixel.

Accompanying drawing is the variation tendency of paddy rice hemisphere image mesoporosity degree with the visual angle.

5) calculate single angle LAI and ALIA:

1. according to the Beer-Lambert law, the relation of rice canopy leaf area index and canopy factor of porosity is as follows:

$\mathrm{LAI}=\frac{-\ln T\left(\mathrm{\&theta;}\right)\&CenterDot;\cos \mathrm{\&theta;}}{G(\mathrm{\&theta;},\mathrm{\&alpha;})}---\left(4\right)$

In the formula:

LAI---rice canopy leaf area index,

T (θ)---zenith angle θ is the canopy factor of porosity at visual angle,

G (θ, α)---the leaf inclination angle is the projection of rice canopy blade on zenith angle θ direction of α.

2. the G function has had two characteristics:

A. when the visual angle zenith angle was 57 ° of left and right sides, (θ α)=0.5, and concerned little with the leaf inclination angle G;

B. in ° scope of 25 °＜θ＜65, (θ α) can regard linear function about θ as, its slope of tool to G

Relevant with the leaf inclination angle.

3. according to the characteristics A of G function, based on the canopy factor of porosity T under 57 ° of single angle zenith angles of hemisphere image calculation ₅₇, again by the LAI under 57 ° of single angle zenith angles of (5) formula calculating:

LAI＝-ln?T(57°)*cos(57°)/0.5 (5)

In the formula:

LAI---rice canopy leaf area index,

T (57 °)---the zenith angle θ that obtains from the hemisphere image is the canopy factor of porosity at 57 ° of visual angles,

2. calculate single angle A LIA according to the following steps:

From factor of porosity T (25 °)～T (65 °) of hemisphere image extraction corresponding to 25 °～65 ° of visual angles; Use formula (5) to calculate LAI; With the formula of substitution as a result (4) formula in above two steps, obtain corresponding G (θ) data G (25 °)～G (75 °); G (θ) data that obtain are carried out fitting a straight line, obtain its slope S; The calculating of S substitution (6) formula is promptly obtained

Be ALIA:

$\stackrel{\&OverBar;}{\mathrm{\&alpha;}}=56.63+2.52\&times;{10}^{3}S-141.47\&times;{10}^{-3}{S}^2-15.59\&times;{10}^{-6}{S}^3$

$+4.18\&times;{10}^{-9}{S}^4+442.83\&times;{10}^{-9}{S}^5---\left(6\right)$

In the formula:

$\stackrel{\&OverBar;}{\mathrm{\&alpha;}}-\mathrm{ALIA},$

S---according to the characteristics B of G function, in ° scope of 25 °＜θ＜65, (θ α) can be regarded as linear function about θ to averaging projection's function G, and S is the slope of this linear function.

6) optimization of single angle LAI and ALIA:

For LAI and the ALIA that is more optimized, the leaf tilt profiles with elliptic function simulation rice canopy substitutes 5) in a simple ALIA, at this moment:

$\left\{\begin{array}{c}G\left(\mathrm{\&theta;}\right)=\frac{{(x^2+{\tan }^2\mathrm{\&theta;})}^{1/2}\cos \mathrm{\&theta;}}{x+\left({\sin }^{-1}\mathrm{\&epsiv;}\right)/\mathrm{\&epsiv;}}\\ \mathrm{\&epsiv;}={(1-x^2)}^{1/2}\end{array}\right.---\left(7\right)$

$x=-3+{\left(\frac{\stackrel{\&OverBar;}{\mathrm{\&alpha;}}}{9.65}\right)}^{-0.6061}---\left(8\right)$

In the formula:

X---the ratio of the oval transverse axis and the longitudinal axis.

Carry out the iteration optimization of single angle LAI and ALIA as follows:

I. with 5) in single angle A LIA of obtaining

Substitution formula (8) obtains x;

Ii. with x substitution formula (7);

Iii. with formula (7) substitution formula (5), and make θ=57.5 ° in the formula (5), obtain G (57.5 °);

Iv. replace the G (57.5 °)=0.5 in the formula (5) to calculate new LAI value the G (57.5 °) that newly obtains among the iii;

V. utilize the canopy factor of porosity T (25 °) corresponding to the 25 °～65 ° of visual angles～T (65 °) that newly obtains the LAI value and obtain from image, substitution formula (4) obtains corresponding G (θ) data G (25 °)～G (75 °);

Vi. obtain straight slope S by linear fit to G and θ;

Vii. with S substitution formula (6), obtain one new

Viii. repeating step i-vii, up to LAI with

Value no longer change.

7) whole calculating adopts Visual C#2005 programming to realize.

Claims (1)

1. a hemisphere Photographic technique obtains all methods at leaf inclination angle of rice canopy leaf area index peace, it is characterized in that the step of this method is as follows:

1) photographic images:, lie in a horizontal plane in rice canopy inside photographing rice canopy original color hemisphere image with the digital camera lens of hemisphere camera lens up, leave in the computer with the form of JPG image file;

2) coloured image gradation conversion: the original color hemisphere image that digital camera is photographed is converted to gray scale hemisphere image by image processing software, leaves in the computer;

3) gray level image binaryzation: with 2) the gray scale hemisphere image transitions in the step leaves in the computer for only containing the two-value hemisphere image of " deceiving ", " in vain " two kinds of picture dots;

4) calculate the canopy factor of porosity:, leave in the computer based on two-value hemisphere image calculation rice canopy factor of porosity;

5) leaf area index under 57 ° of single angle zenith angles of calculating and average leaf inclination angle:, calculate leaf area index and average leaf inclination angle under 57 ° of single angle zenith angles according to the relation of rice canopy leaf area index and canopy factor of porosity and two characteristics of leaf inclination angle projection function G function;

6) optimization at 57 ° of single angle leaf area index and average leaf inclination angle: with the leaf tilt profiles of elliptic function simulation rice canopy, substitute 5) the simple average leaf inclination angle that obtains in the step, carry out the iteration optimization at single angle leaf area index and average leaf inclination angle, obtain all leaf inclination angles of best rice canopy leaf area index peace;

7) whole calculating adopts Visual C#2005 programming to realize.

Images