CN105678236A - Land vegetation canopy polarization reflection modeling method - Google Patents

Abstract

The invention relates to a land vegetation canopy polarization reflection modeling method. The method comprises the following steps: sampling in the scattering direction of skylight in the episphere space, and constructing a polarization degree distribution mode; according to the distribution mode of skylight polarization degree, calculating a Fresnel reflection coefficient for incident polarized light; based on a geometrical optical principle, respectively calculating the polarization reflectivity of single blade and the underlying surface soil; performing equally-spaced layering on the canopy, calculating the polarization reflectivity of the blade layer by layer, wherein the soil is taken as one layer; utilizing an adding method to calculate the polarization reflectivity of the whole canopy; and analyzing the distribution features of the vegetation canopy polarization reflectivity. The land vegetation canopy polarization reflection modeling method can realize accurate description of the polarization reflectivity features of the land vegetation canopy under the situation with different types of plants, different positions of the sun and different observation positions, and is an effectively technical method for analyzing the polarization direction reflection features and influence factors for the plants, and can provide an effective technical scheme for polarization information decoupling of an earth atmosphere system.

Description

A kind of land vehicles canopy reflection of polarization modeling method

(1) technical field

The present invention relates to a kind of land vehicles canopy reflection of polarization modeling method, belong to optics remote sensing fields, in vegetation reflection of polarization specificity analysis and ground vapour polarization information decoupling zero research, there is important theory significance and using value.

(2) background technology

Polarization detection is with a wide range of applications, and exploratory application has been carried out in current atmospheric polarization remote sensing, and the research of vegetation polarization is less. Vegetation polarization information is as the important component part of earth's surface, land polarization information, surface parameters inversion can not only be directly used in, and be the key realizing ground vapour polarization information decoupling zero, but, current existing vegetation model of polarization too simplifies, can not fully describing vegetation polarization characteristic, especially have ignored incident sky polarisation of light characteristic, this constrains the development of vegetation polarization remote sensing application to a great extent.

First the present invention sets up the sky polarization degree distribution pattern in episphere space, set up the polarized reflectance model of vegetation individual blade, the polarized reflectance model of underlying soil, the polarized reflectance model of Vegetation canopy more respectively, it is achieved the reflection of polarization modeling method of air vegetation soil coupled system. The directional reflectance ratio of canopy is decomposed into single scattering and repeatedly scattering sum, repeatedly scattering does not possess polarization characteristic, therefore the polarized reflectance that single scattering produces only is calculated, single scattering comprises canopy single scattering and soil single scattering, Vegetation canopy is vertically equally divided into horizontal direction equal by modeling process, some layers of vertical direction change, soil surface regards separately one layer as, adopts cumulative method to calculate the polarized reflectance of whole canopy; Land vehicles reflection of polarization modeling, calculates vegetation reflection of polarization characteristic for correct in remote sensing of the earth, it is achieved the classification of land vehicles, parametric inversion and ground vapour polarization information decoupling zero have important scientific meaning and using value.

(3) summary of the invention

The present invention relates to a kind of land vehicles canopy reflection of polarization modeling method, technical solution is: sampled in sky scattering of light direction in episphere space, builds sky polarisation of light degree distribution pattern; According to the distribution pattern of sky polarization degree, the Fresnel reflection coefficient of calculating section polarized light incidence; Based on geometric optical theory, substitute into polarization Fresnel reflection coefficient, build the polarized reflectance model of individual blade and underlying soil respectively; To spacing layerings such as Vegetation canopy carry out, calculating the polarized reflectance of blade by layer, soil regards separately one layer as, adopts the polarized reflectance of the tired whole canopy of additional calculation; Analyze the distribution characteristic of Vegetation canopy polarized reflectance.

1 one kinds of land vehicles canopy reflection of polarization modeling methods, it is characterised in that comprise following step:

(1) in episphere space, is sampled in sky scattering of light direction, build sky polarisation of light degree distribution pattern;

(2) according to the distribution pattern of sky polarization degree, the Fresnel reflection coefficient of calculating section polarized light incidence;

(3) based on geometric optical theory, substitute into polarization Fresnel reflection coefficient, build the polarized reflectance model of individual blade and underlying soil respectively;

(4) to spacing layerings such as canopy carry out, calculating the polarized reflectance of blade by layer, soil regards separately one layer as, adopts the polarized reflectance of the tired whole canopy of additional calculation;

(5) the distribution characteristic of Vegetation canopy polarized reflectance is analyzed.

" in episphere space, being sampled in sky scattering of light direction, build sky polarisation of light degree distribution pattern " described in 2 steps (1), specific implementation process is as follows:

1. sun incident direction is inputtedIn episphere space to the solid angles such as sky scattering of light direction carries out sampling, obtain the scattering direction of sample point atmospheric moleculeCalculate scattering angle γ

Wherein θ_sFor sun zenith angle,For azimuths of the sun, θ is scattering zenith angle,For scattering position angle;

2. semiempirical Rayleigh scattering model is adopted to calculate sky polarization degree δ

$\mathrm{\δ}={\mathrm{\δ}}_{max}\frac{{\sin }^2\mathrm{\γ}}{1+{\cos }^2\mathrm{\γ}}$

Wherein δ_maxFor maximum degree of polarization during specific sun zenith angle, method of calculation are

${\mathrm{\δ}}_{max}=0.56+\frac{0.07}{30}{\mathrm{\θ}}_s$

" according to the distribution pattern of sky polarization degree, the Fresnel reflection coefficient of calculating section polarized light incidence " described in 3 steps (2), specific implementation process is as follows:

1. according to the solar direction of inputAnd observed rayCalculate incident angle α

Wherein θ_vFor view zenith angle,For observed azimuth;

2. polarization Fresnel reflection coefficient F is calculated

F (α, n)=κ_sr_s ²-κ_pr_p ²

Wherein r_sFor reflected light is perpendicular to the component of the plane of incidence, r_pFor reflected light is parallel to the component of the plane of incidence, method of calculation are

$\left\{\begin{array}{c}{r}_s=\frac{cos\mathrm{\α}-\sqrt{n^2-{\sin }^2\mathrm{\α}}}{cos\mathrm{\α}+\sqrt{n^2-{\sin }^2\mathrm{\α}}}\\ r_p=\frac{n^{2}cos\mathrm{\α}-\sqrt{n^2-{\sin }^2\mathrm{\α}}}{n^{2}cos\mathrm{\α}+\sqrt{n^2-{\sin }^2\mathrm{\α}}}\end{array}\right.$

Wherein α is input angle, and n is the specific refractory power ratio of measured target and air;

κ_sAnd κ_pIt is respectively vertical component and parallel component accounts for the ratio of total energy and κ_s+κ_p=1.

" based on geometric optical theory, substituting into polarization Fresnel reflection coefficient, build the polarized reflectance model of individual blade and underlying soil respectively " described in 4 steps (3), specific implementation process is as follows:

1. blade surface is regarded as micro-bin of a lot of accurate minute surface, calculates the zenith angle θ of micro-bin normal direction_h

${\mathrm{\θ}}_h={\cos }^{-1}\left(\frac{{\mathrm{cos\θ}}_s+{\mathrm{cos\θ}}_v}{2\cos \mathrm{\α}}\right)$

There is mutually blocking between geometry impact and bin in blade specular reflection, calculates decay factor K

Wherein

$\left\{\begin{array}{c}{E}_1=\frac{2{\mathrm{cos\θ}}_h{\mathrm{cos\θ}}_v}{\cos \mathrm{\α}}\\ E_2=\frac{2{\mathrm{cos\θ}}_h{\mathrm{cos\θ}}_s}{\cos \mathrm{\α}}\end{array}\right.$

2. assume micro-bin normal direction Gaussian distributed of blade surface, calculate the polarized reflectance ρ of individual blade_leafp

Wherein n_lFor the specific refractory power ratio of vegetation blade and air, σ is blade surface Rough factor;

3. the polarized reflectance ρ of underlying soil is calculated_soilp

${\mathrm{\ρ}}_{soilp}=A\exp (-tan\mathrm{\α})\frac{F(\mathrm{\α},n_s)}{4({\mathrm{cos\θ}}_s+{\mathrm{cos\θ}}_v)}$

Wherein n_sFor the specific refractory power ratio of soil and air, A is the free parameter relevant with soil surface roughness.

" to spacing layerings such as canopy carry out, calculating the polarized reflectance of blade by layer, soil regards separately one layer as, adopts the polarized reflectance of the tired whole canopy of additional calculation " described in 5 steps (4), specific implementation process is as follows:

1. height z in optional position between given ground and canopy top, calculate this position two to porosity function Q

Wherein H is canopy height, p_s(z)·p_vZ () is that canopy camber z place can be illuminated by the sun, the joint probability that simultaneously can measure by the outer view of freedom of canopy, G (Ω_s) and G (Ω_v) it being respectively the projection of unit surface blade in sun incident direction and observed ray, S (z) is the unit leaf area index at height z place;

2. Vegetation canopy is vertically equally divided into N layer, and the optical characteristics of every layer of medium is considered as horizontal direction equal,

Vertical direction changes, and soil surface regards separately one layer as, calculates the height z of i-th vegetation unit's layer

$z=H-\frac{H}{N}i$

Wherein N is the number of plies, then the single scattering contribution of whole canopy is by i-th vegetation layer

WhereinFor Leaf angle inclination distribution probability density function, Q (z) be i-th vegetation layer place two to porosity function;

The single scattering contribution of whole canopy is by pedosphere

Wherein Q (H) is for two bottom canopy is to porosity function;

3. calculate the polarized reflectance of N-1 vegetation layer and underlying pedosphere respectively, adopt the polarized reflectance of the tired whole canopy of additional calculation.

" analyzing the distribution characteristic of Vegetation canopy polarized reflectance " described in 6 steps (5), specific implementation process is as follows: the solid angles such as observed ray carries out sampled, earth's surface type according to setting, input blade, soil and canopy optics and structural property parameter, calculate the Vegetation canopy polarized reflectance of each sampling point, analyze the distribution characteristic of polarized reflectance in episphere space.

The present invention's advantage compared with prior art is:

(1) academia lacks the technological method of the effective description land vehicles reflection of polarization characteristic considering incident light polarization characteristic at present, the present invention adopts tired additional calculation blade and underlying soil to the contribution of whole canopy polarized reflectance, there is significant novelty, enriched the research of vegetation polarization optics remote sensing fields.

(2) contemplated by the invention the factors such as the spatial structure characteristic of sky light polarization that atmospheric molecule scattering process causes, the Rough factor of soil and occlusion effect, vegetation, make model simulation results more close to truth, the Vegetation canopy that can be applicable under differ ent vegetation coverage or the polarization characteristic simulation of soil, have good application suitability.

(4) accompanying drawing explanation

Fig. 1 is the general technical schema of the present invention.

(5) embodiment

A kind of land vehicles canopy reflection of polarization modeling method that the present invention relates to illustrate better, utilizes the modeling method of the present invention to carry out Vegetation canopy reflection of polarization characteristic and analyzes. A kind of land vehicles canopy reflection of polarization modeling method of the present invention, it is achieved as shown in Figure 1, concrete implementation step is as follows for flow process:

Being sampled in sky scattering of light direction by step (1) in episphere space, builds sky polarisation of light degree distribution pattern:

1. the moment at high noon sun zenith angle θ is inputted_sAnd azimuths of the sunIn episphere space to the solid angles such as sky scattering of light direction carries out sampling, obtain scattering zenith angle θ and the scattering position angle of 1500 sample pointCalculate scattering angle γ

2. semiempirical Rayleigh scattering model is adopted to calculate sky polarization degree δ

$\mathrm{\δ}={\mathrm{\δ}}_{max}\frac{{\sin }^2\mathrm{\γ}}{1+{\cos }^2\mathrm{\γ}}$

Wherein δ_maxFor maximum degree of polarization during specific sun zenith angle, when sun zenith angle is 30 °, δ_maxValue 63%, the distribution pattern of step (2) foundation sky polarization degree, the Fresnel reflection coefficient of calculating section polarized light incidence:

1. view zenith angle θ is inputted_vAnd observed azimuthCalculate incident angle α

2. polarization Fresnel reflection coefficient F is calculated

F (α, n)=κ_sr_s ²-κ_pr_p ²

Wherein r_sFor reflected light is perpendicular to the component of the plane of incidence, r_pFor reflected light is parallel to the component of the plane of incidence, method of calculation are

$\left\{\begin{array}{c}{r}_s=\frac{\cos \mathrm{\α}-\sqrt{n^2-{\sin }^2\mathrm{\α}}}{\cos \mathrm{\α}+\sqrt{n^2-{\sin }^2\mathrm{\α}}}\\ r_p=\frac{n^2\cos \mathrm{\α}-\sqrt{n^2-{\sin }^2\mathrm{\α}}}{n^2\cos \mathrm{\α}+\sqrt{n^2-{\sin }^2\mathrm{\α}}}\end{array}\right.$

Wherein α is input angle, and n is the specific refractory power ratio of measured target and air;

κ_sAnd κ_pIt is respectively vertical component and parallel component accounts for the ratio of total energy, incident for natural light, κ_s=κ_p=0.5.

Step (3), based on geometric optical theory, substitutes into polarization Fresnel reflection coefficient, builds the polarized reflectance model of individual blade and underlying soil respectively:

1. blade surface is regarded as micro-bin of a lot of accurate minute surface, calculates the zenith angle θ of micro-bin normal direction_h

${\mathrm{\θ}}_h={\cos }^{-1}\left(\frac{{\mathrm{cos\θ}}_s+{\mathrm{cos\θ}}_v}{2\cos \mathrm{\α}}\right)$

There is mutually blocking between geometry impact and bin in blade specular reflection, calculates decay factor K

Wherein

$\left\{\begin{array}{c}{E}_1=\frac{2{\mathrm{cos\θ}}_h{\mathrm{cos\θ}}_v}{\cos \mathrm{\α}}\\ E_2=\frac{2{\mathrm{cos\θ}}_h{\mathrm{cos\θ}}_s}{\cos \mathrm{\α}}\end{array}\right.$

2. assume micro-bin normal direction Gaussian distributed of blade surface, calculate the polarized reflectance ρ of individual blade_leafp

Wherein n_lFor the specific refractory power ratio of vegetation blade and air, σ is blade surface Rough factor;

3. the polarized reflectance ρ of underlying soil is calculated_soilp

${\mathrm{\ρ}}_{soilp}=A\exp (-tan\mathrm{\α})\frac{F(\mathrm{\α},n_s)}{4({\mathrm{cos\θ}}_s+{\mathrm{cos\θ}}_v)}$

Wherein n_sFor the specific refractory power ratio of soil and air, A is the free parameter relevant with soil surface roughness.

Step (4), to spacing layerings such as canopy carry out, calculates the polarized reflectance of blade by layer, and soil regards separately one layer as, adopts the polarized reflectance of the tired whole canopy of additional calculation:

1. height z in optional position between given ground and canopy top, calculate this position two to porosity function Q

Wherein H is canopy height, p_s(z)·p_vZ () is that canopy camber z place can be illuminated by the sun, the joint probability that simultaneously can measure by the outer view of freedom of canopy, G (Ω_s) and G (Ω_v) it being respectively the projection of unit surface blade in sun incident direction and observed ray, S (z) is the unit leaf area index at height z place;

2. Vegetation canopy is vertically equally divided into N layer, and the optical characteristics of every layer of medium is considered as horizontal direction equal, and vertical direction changes, and soil surface regards separately one layer as, calculates the height z of i-th vegetation unit's layer

$z=H-\frac{H}{N}i$

Wherein N is the number of plies, then the single scattering contribution of whole canopy is by i-th vegetation layer

WhereinFor Leaf angle inclination distribution probability density function, Q (z) be i-th vegetation layer place two to porosity function;

The single scattering contribution of whole canopy is by pedosphere

Wherein Q (H) is for two bottom canopy is to porosity function;

3. calculate the polarized reflectance of N-1 vegetation layer and underlying pedosphere respectively, adopt the polarized reflectance of the tired whole canopy of additional calculation.

Step (5) analyzes the distribution characteristic of Vegetation canopy polarized reflectance: the solid angles such as observed ray carries out sampled, earth's surface type according to setting, input blade, soil and canopy optics and structural property parameter, calculate canopy polarized reflectance when each sample point sunlight and the incidence of sky light respectively, carry out weighted sum, finally analyze the distribution characteristic of polarized reflectance in episphere space.

Claims (6)

1. a land vehicles canopy reflection of polarization modeling method, it is characterised in that comprise following step:

(1) in episphere space, is sampled in sky scattering of light direction, build sky polarisation of light degree distribution pattern;

(2) according to the distribution pattern of sky polarization degree, the Fresnel reflection coefficient of calculating section polarized light incidence;

(3) based on geometric optical theory, substitute into polarization Fresnel reflection coefficient, set up the polarized reflectance model of individual blade and underlying soil respectively;

(4) Vegetation canopy the spacing vertical layered such as carrying out, calculate the polarized reflectance of blade by layer, soil regards separately one layer as, adopts the polarized reflectance of the tired whole canopy of additional calculation;

(5) the distribution characteristic of Vegetation canopy polarized reflectance is analyzed.

2. require described a kind of land vehicles canopy reflection of polarization modeling method according to right 1, it is characterized in that: " being sampled in sky scattering of light direction in episphere space; build sky polarisation of light degree distribution pattern " described in step (1), specific implementation process is as follows:

1. sun incident direction is inputtedIn episphere space to the solid angles such as sky scattering of light direction carries out sampling, obtain the scattering direction of sample point atmospheric moleculeCalculate scattering angle γ

Wherein θ_sFor sun zenith angle,For azimuths of the sun, θ is scattering zenith angle,For scattering position angle;

2. semiempirical Rayleigh scattering model is adopted to calculate sky polarization degree δ

Wherein δ_maxFor maximum degree of polarization during specific sun zenith angle, method of calculation are as follows:

。

3. a kind of land vehicles canopy reflection of polarization modeling method according to claim 1, it is characterized in that: " according to the distribution pattern of sky polarization degree; the Fresnel reflection coefficient of calculating section polarized light incidence " described in step (2), specific implementation process is as follows:

1. according to the solar direction of inputAnd observed rayCalculating incident angle α is as follows

Wherein θ_vFor view zenith angle,For observed azimuth;

2. polarization Fresnel reflection coefficient F is calculated

F (α, n)=κ_sr_s ²-κ_pr_p ²

Wherein r_sFor reflected light is perpendicular to the component of the plane of incidence, r_pFor reflected light is parallel to the component of the plane of incidence, method of calculation are

Wherein α is input angle, and n is the specific refractory power ratio of measured target and air;

κ_sAnd κ_pIt is respectively vertical component and parallel component accounts for the ratio of total energy and κ_s+κ_p=1.

4. a kind of land vehicles canopy reflection of polarization modeling method according to claim 1, it is characterized in that: " based on the geometric optical theory; substitute into polarization Fresnel reflection coefficient; set up the polarized reflectance model of individual blade and underlying soil respectively " described in step (3), specific implementation process is as follows:

1. blade surface is regarded as micro-bin of a lot of accurate minute surface, calculates the zenith angle θ of micro-bin normal direction_h

There is mutually blocking between geometry impact and bin in blade specular reflection, calculates decay factor K

Wherein

2. assume micro-bin normal direction Gaussian distributed of blade surface, calculate the polarized reflectance ρ of individual blade_leafp

Wherein n_lFor the specific refractory power ratio of vegetation blade and air, σ is blade surface Rough factor;

3. the polarized reflectance ρ of underlying soil is calculated_soilp

Wherein n_sFor the specific refractory power ratio of soil and air, A is the free parameter relevant with soil surface roughness.

5. a kind of land vehicles canopy reflection of polarization modeling method according to claim 1, it is characterized in that: " Vegetation canopy the spacing vertical layered such as the carrying out; calculate the polarized reflectance of blade by layer; soil regards separately a layer as; adopt the polarized reflectance of the tired whole canopy of additional calculation " described in step (4), specific implementation process is as follows:

1. height z in optional position between given ground and canopy top, calculate this position two to porosity function Q

Wherein H is canopy height, p_s(z)·p_vZ () is that canopy camber z place can be illuminated by the sun, the joint probability that simultaneously can measure by the outer view of freedom of canopy, G (Ω_s) and G (Ω_v) it being respectively the projection of unit surface blade in sun incident direction and observed ray, S (z) is the unit leaf area index at height z place;

2. Vegetation canopy is vertically equally divided into N layer, and the optical characteristics of every layer of medium is considered as horizontal direction equal, and vertical direction changes, and soil surface regards separately one layer as, calculates the height z of i-th vegetation unit's layer

Wherein N is the number of plies, then the single scattering contribution of whole canopy is by i-th vegetation layer

WhereinFor Leaf angle inclination distribution probability density function, Q (z) be i-th vegetation layer place two to porosity function;

The single scattering contribution of whole canopy is by pedosphere

Wherein Q (H) is for two bottom canopy is to porosity function;

3. calculate the polarized reflectance of N-1 vegetation layer and underlying pedosphere respectively, adopt the polarized reflectance of the tired whole canopy of additional calculation.

6. a kind of land vehicles canopy reflection of polarization modeling method according to claim 1, it is characterized in that: " the analyzing the distribution characteristic of Vegetation canopy polarized reflectance " described in step (5), specific implementation process is as follows: the solid angles such as observed ray carries out sampled, earth's surface type according to setting, input blade, soil and canopy optics and structural property parameter, calculate the Vegetation canopy polarized reflectance of each sampling point, analyze the distribution characteristic of polarized reflectance in episphere space.