CN104063621A - Polarization hyperspectral scene simulating method based on BRDF model and considering wall effect - Google Patents

Abstract

The invention relates to a polarization hyperspectral scene simulating method based on a BRDF model and considering wall effect and belongs to the field of the remote sensing or physical and optical image processing technique. The polarization hyperspectral scene simulating method solves the problems that few typical types of surface features are considered in the existing simulating scene, a big different exists between the considered types and the practical types, specular reflection is involved only when the effect between incident light and the wall is considered, directional scattering and uniform diffuse reflection are neglected, therefore, simulating results are inaccurate, and effect is poor; analysis forms of a BRDF are few, and computation is inconvenient. The polarization hyperspectral scene simulating method is characterized by comprising the steps of establishing the BRDF model of the analysis forms; solving emergent radiance of secondary scattering of the wall according to the BRDF model of the analysis forms; simulating a polarization hyperspectral scene. The polarization hyperspectral scene simulating method based on the BRDF model and considering wall effect is applied to the field of the remote sensing and physical and optical image processing technique.

Description

A kind of high spectrum scene simulation of polarization method of the consideration wall impact based on BRDF model

Technical field

The present invention relates to the high spectrum scene simulation of a kind of polarization method, relate in particular to a kind of high spectrum scene simulation of polarization method of the consideration wall impact based on BRDF model, belong to remote sensing or physical optics technical field of image processing.

Background technology

High light spectrum image-forming model can be regarded the coupling body of ground scene model and atmosphere model of place as, more comprehensive polarization remote sensing can realize the high spectrum scene simulation of polarization.Determinacy canopy model is that the geometric relationship by determining canopy in simulating scenes is calculated ground surface reflectance.Utilize FCR model (Kuusk A.A Fast, Invertible Canopy Reflectance Model[J] .RemoteSens.Environ, 1995, 51 (3): 342-350.) can ask for the spectral reflectivity of canopy, again in conjunction with mixed pixel model (LiX, Strahler A H.Geometric-optical Bidirectional Reflectance Modeling of the Discrete CrownVegetation Canopy:Effect of Crown Shape and Mutual Shadowing[J] .IEEE Trans.1992, 30 (2): 276-292.) can obtain the spectral reflectivity of canopy unit picture element, realize high spectrum ground scene model emulation.What Verhoef proposed is four stream earth's surface-atmospheric radiation transmission (Verhoef W non-homogeneous, Non Lambert reflector face based on earth's surface, Bach H.Simulation of hyperspectral and directional radiance images using coupled biophysical andatmospheric radiative transfer models[J] .Remote Sens.Environ, 2003,87 (1): 22-41.) precision is higher, and uses till today always.In conjunction with modtran simulation software, can obtain the radiance of the journey radiance of sensor reception, contiguous pixel radiance, the direct reflected sunlight of target and skylight, realize high spectrum atmosphere scene model emulation.Can realize the emulation of high-spectrum remote-sensing simple scenario by high-spectrum remote-sensing imaging system that is virtually reality like reality.

The high spectrum emulation of polarization is to add polarization information on high spectrum From Math, changes spectral reflectivity originally into polarized reflectance and just can obtain the polarized radiation brightness that sensor receives.Due to the existence of wall in simulating scenes, the energy that incides atural object infinitesimal not only comprises the skylight of scattering in the sunshine of direct incident and atmosphere, also comprises the solar radiation energy of wall reflection, and this is also to draw polarising reason.?

$L_o^{\mathrm{pol}}=L_{\mathrm{ref}-\mathrm{sky}}^{\mathrm{pol}}+L_{\mathrm{ref}-\mathrm{sun}}^{\mathrm{pol}}+L_{\mathrm{ref}-\mathrm{wall}}^{\mathrm{pol}}---(1-1)$

In formula represent total polarized radiation brightness that sensor receives, with represent to incide respectively the skylight of atural object infinitesimal, the polarized radiation brightness that sunshine and wall rescattering cause.

Because existing scene simulation has only been analyzed simple mirror-reflection effect in the time considering that wall rescattering affects, (Chen Dong comes, for the emulation mode of woodland complex scene high-spectrum remote sensing data, patent: 200910071357.8), there is larger error with real scene, therefore need to consider that bidirectional reflectance distribution function comprehensively analyzes the mirror-reflection of sunshine and between the walls, directional scattering and uniform diffuse reflection effect.

Bidirectional reflectance characteristic is a basic optical characteristic, accurately described due to the difference of target physical, chemical characteristic and texture structure form by the phenomenon of to all the winds scattering of incident electromagnetic wave.Conventionally the light that sensor receives is divided into area scattering and volume scattering two parts, the bidirectional reflectance distribution function (BRDF) of target develops for the area scattering and the volume scattering difference that quantize different incident and radiation direction just, can describe the space scattering distribution character of target comprehensively.Conventionally BRDF numerical value is measured or modeling method acquisition by experiment.Seldom there is general analytical form; The high spectrum scene simulation of existing polarization has been ignored directional scattering and uniform diffuse reflection effect in the time that analysis wall affects, and in emulation, exists and treats improved place.The high spectral investigation of polarization is started late, and development is at present ripe not enough, thereby shortage corresponding data is restricting the development of the high spectrum of polarization.

Summary of the invention

The object of the invention is to propose a kind of high spectrum scene simulation of polarization method of the consideration wall impact based on BRDF model, only consider most typical less class to solve for the setting of atural object in existing simulating scenes, differ larger with actual, the used time of doing of considering incident light and wall has only related to mirror-reflection, directional scattering and uniform diffuse reflection are ignored, make simulation result out of true, poor effect; BRDF analytical form is less, is not easy to the problem of calculating.

The present invention for solving the problems of the technologies described above adopted technical scheme is:

The high spectrum scene simulation of the polarization method of a kind of consideration wall based on BRDF model impact of the present invention, comprises the following steps: step 1, set up the BRDF model of analytical form, be specially:

Suppose that light propagation unit vector is wherein represent respectively the unit vector of light along incident direction and exit direction propagation; Polarization vector of unit length is wherein represent respectively polarization components vertical and the parallel plane of incidence, bidirectional reflectance distribution function (BRDF) is defined as:

Light is along exit direction the radiation flux of unit area, unit solid angle with along incident direction the ratio of the radiation flux of unit area, uses ρ _bdrepresent:

In formula represent the brightness of outgoing spoke, I _i, dw _irepresent respectively the brightness of incident spoke and incident solid angle, θ _i, θ _r, represent respectively zenith angle and the relative bearing of incident light and emergent light;

The BRDF model representation of analytical form is:

ρ _bd＝ρ _bd,sp+ρ _bd,dd+ρ _bd,ud(2-2)

ρ _{bd, sp}, ρ _{bd, dd}and ρ _{bd, ud}represent respectively the bidirectional reflectance that mirror-reflection, directional scattering and uniform diffuse reflection cause;

Step 2, BRDF model based on step 1 are asked for the outgoing spoke brightness of wall rescattering, comprise the steps:

Step 2 one, ask for the direct incident power of the sun that a face infinitesimal ds on wall receives;

The derivation of the irradiance that step 2 two, pointolite (m, n) produce target infinitesimal (x, y);

The derivation of the spoke brightness that step 2 three, whole wall produce target infinitesimal (x, y);

Step 3, the high spectrum scene simulation of polarization.

The invention has the beneficial effects as follows:

One, the present invention utilizes the BRDF model of analytical form, is more convenient for calculating.

Two, the BRDF model of analytical form is applied in wall rescattering analysis, mirror-reflection, directional scattering and the uniform diffuse reflection effect of incident sunshine and between the walls are accurately considered, make simulating scenes and reality more approaching, for follow-up more complicated scene imaging and modeling provide theoretical foundation.

Three, in the used time of doing of considering incident light and wall, the present invention has considered mirror-reflection, directional scattering and uniform diffuse reflection, makes simulation result more accurate, better effects if.

Brief description of the drawings

Fig. 1, based on physioptial BRDF model, sets up rectangular coordinate system xyz taking o as initial point, light propagation unit vector is wherein represent respectively the unit vector of light along incident direction and exit direction propagation; Polarization vector of unit length is wherein represent respectively polarization components vertical and the parallel plane of incidence.Dw _irepresent incident solid angle, θ _i, θ _r, represent respectively zenith angle and the relative bearing of incident light and emergent light.

Fig. 2 (a) mirror-reflection and wavelength relationship, Fig. 2 (b) directional scattering and wavelength relationship.In experiment, be taken into and penetrate zenith angle θ _i=60 °, reflection zenith angle θ _rchange to 90 ° from 0 °, incident and reflection position angle are respectively material surface Effective Roughness σ ₀=0.18 μ m, auto-correlation length τ=1.77 μ m, refractive index n=1.5.Wavelength X does not change to 7 μ m not etc. from 0.5 μ m.

The relation of Fig. 3 (a) mirror-reflection and Effective Roughness, the relation of Fig. 3 (b) directional scattering and Effective Roughness.In experiment, be taken into and penetrate zenith angle θ _i=60 °, reflection zenith angle θ _rchange to 90 ° from 0 °, incident and reflection position angle are respectively material surface auto-correlation length τ=1.77 μ m, refractive index n=1.5, wavelength X=2 μ m.Material surface Effective Roughness σ ₀do not change to 0.68 μ m not etc. from 0.18 μ m.

The imaging scene graph that Fig. 4 canopy and wall form, left and right sides square area is that (area is 150 × 150m to canopy ²), middle rectangular region part is that (floorage is 150 × 30m to artificial wall ², high 20m).

Fig. 5 pointolite is on target infinitesimal impact figure, the radiation intensity that J is pointolite, d _afor the area of target infinitesimal (x, y), L is that pointolite is to the distance of target infinitesimal, and θ is d _athe angle of normal n and incident light, d _Ωpointolite is to d _athe solid angle of being opened.

Fig. 6 wall rescattering geometric representation is set up the coordinate system x ' y ' z ' taking o ' as initial point, θ on wall _i, θ _r, represent that respectively the zenith angle of incident light and emergent light in BRDF model and position angle are (in figure ); Set up the coordinate system xy taking o as initial point in level ground, the horizontal ordinate of wall correspondence on surface level is from x ₀change to x ₁, ordinate is from y ₀change to y ₁; On wall, set up with o simultaneously ₁for the coordinate system mn of initial point, pointolite (m, n) is R to the distance of target infinitesimal (x, y).

The affect figure of Fig. 7 wall on left side scene.

The high spectrum scene simulation of the polarization of Fig. 8 based on BRDF model figure.

Embodiment

Embodiment one: the high spectrum scene simulation of the polarization method of a kind of consideration wall impact based on BRDF model described in present embodiment, comprises the following steps:

Step 1, set up the BRDF model of analytical form, be specially:

Suppose that light propagation unit vector is wherein represent respectively the unit vector of light along incident direction and exit direction propagation; Polarization vector of unit length is wherein represent respectively polarization components vertical and the parallel plane of incidence, bidirectional reflectance distribution function (BRDF) is defined as:

Light is along exit direction the radiation flux of unit area, unit solid angle with along incident direction the ratio of the radiation flux of unit area, uses ρ _bdrepresent:

In formula represent the brightness of outgoing spoke, I _i, dw _irepresent respectively the brightness of incident spoke and incident solid angle, θ _i, θ _r, represent respectively zenith angle and the relative bearing of incident light and emergent light;

The BRDF model representation of analytical form is:

ρ _bd＝ρ _bd,sp+ρ _bd,dd+ρ _bd,ud(2-2)

ρ _{bd, sp}, ρ _{bd, dd}and ρ _{bd, ud}represent respectively the bidirectional reflectance that mirror-reflection, directional scattering and uniform diffuse reflection cause;

Step 2, BRDF model based on step 1 are asked for the outgoing spoke brightness of wall rescattering, comprise the steps:

Step 2 one, ask for the direct incident power of the sun that a face infinitesimal ds on wall receives;

The derivation of the irradiance that step 2 two, pointolite (m, n) produce target infinitesimal (x, y);

The derivation of the spoke brightness that step 2 three, whole wall produce target infinitesimal (x, y);

Step 3, the high spectrum scene simulation of polarization.

Understand present embodiment in conjunction with Fig. 1.

Embodiment two: present embodiment is different from embodiment one: the detailed process of step 2 one is:

Suppose that the sun is positioned at the dead ahead of wall, to incide the light of wall be directional light to the sun; The gross energy of sunshine incident is E _s, solar zenith angle is θ _s, the direct incident power of the sun that a face infinitesimal ds on wall receives is:

P _i＝E _sτ _sssinθ _sds (3-1)

τ in formula _ssobtain by four stream earth's surface-atmospheric radiation transmission, represent that sunshine shines directly into the ratio of target by atmosphere;

For even wall, utilize the incident power P being irradiated in unit area _iwith emergent power dP _r, BRDF formula is rewritten as:

${\mathrm{\ρ}}_{\mathrm{bd}-\mathrm{wall}}=\frac{{\mathrm{dP}}_r}{P_i\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i}---(3-2)$

The emergent power in unit area is:

dP _r＝ρ _bd-wallP _icosθ _idw _i(3-3)

ρ in formula _bd-wallthe wall bidirectional reflectance calculating based on BRDF model, dw _ifor incident solid angle.Other step is identical with embodiment one.

Embodiment three: present embodiment is different from embodiment one or two: the detailed process of step 2 two is:

Emergent power in unit area is converted into outgoing intensity is: ρ _bd-wallp _icos θ _idw _i/ π; If ds is enough little for face infinitesimal, regard pointolite as; The irradiance that pointolite produces target infinitesimal (x, y) is derived as follows:

The radiation intensity of postulated point light source is J, and the area of target infinitesimal (x, y) is d _a, and pointolite is L to the distance of target infinitesimal, d _athe angle of normal and incident light is θ; Pointolite is to d _athe solid angle of being opened is d _a/ L ²; By defining of radiation intensity and irradiance the irradiance that receives of target infinitesimal is:

H＝Jcosθ/L ²(3-4)

Suppose that the point that sunshine incides on wall is o ', set up coordinate system x ' y ' z ' taking o ' as initial point, θ _i, θ _r, represent that respectively the zenith angle of incident light and emergent light in BRDF model and relative bearing are (in figure ); Set up the rectangular coordinate system xy taking o as true origin in level ground, the horizontal ordinate of wall on surface level is from x simultaneously ₀change to x ₁, ordinate is from y ₀change to y ₁, at wall and level ground x ₀, y ₀intersection point o ₁in place, set up with o ₁for the rectangular coordinate system mn of initial point, the pointolite (m, n) on wall to the distance of the target infinitesimal (x, y) in canopy is $R=\sqrt{{(x-x_0)}^2+{(n+y_0-y)}^2+m^2},$

Outgoing position angle in BRDF model cosine is outgoing zenith angle θ _rcosine is cos θ _r=| x-x ₀| R, by formula (3-4) must pointolite (m, n) to the irradiance of target infinitesimal (x, y) generation be:

$d_H=\frac{{\mathrm{\ρ}}_{\mathrm{bd}-\mathrm{wall}}{E}_s{\mathrm{\τ}}_{\mathrm{ss}}\sin {\mathrm{\θ}}_s\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i|x-x_0|d_s}{\mathrm{\π}{[{(x-x_0)}^2+{(n+y_0-y)}^2+m^2]}^{\frac{3}{2}}}---(3-5).$ Explain present embodiment in conjunction with Fig. 6.Other step is identical with embodiment one or two.

Embodiment four: present embodiment is different from one of embodiment one to three: the detailed process of step 2 three is:

The spoke brightness that pointolite (m, n) produces target infinitesimal (x, y) is:

$d_I=\frac{{\mathrm{\ρ}}_{\mathrm{bd}-\mathrm{wall}}{E}_s{\mathrm{\τ}}_{\mathrm{ss}}{\mathrm{\τ}}_{\mathrm{oo}}\sin {\mathrm{\θ}}_s\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i|x-x_0|d_s}{{\mathrm{\π}}^2{[{(x-x_0)}^2+{(n+y_0-y)}^2+m^2]}^{\frac{3}{2}}}(f_C{\mathrm{\ρ}}_C^{\′}+f_G{\mathrm{\ρ}}_{\mathrm{soil}}^{\′})---(3-6)$

τ in formula _ooobtain by four stream earth's surface-atmospheric radiation transmission, represent that the energy being produced by target reflection arrives the ratio of sensor, f _c, f _grespectively illumination vegetation face, the illumination soil face in mixed pixel model; ρ ' _c, ρ ' _soilrespectively to utilize the canopy based on wall rescattering and the scattered power of soil in the meadow that FCR model obtains;

Face infinitesimal d on wall _s=dmdn, the outgoing spoke brightness that the whole wall that sensor receives produces the target infinitesimal (x, y) in canopy is:

$I_{(x,y)}=\underset{m}{\∫}\underset{n}{\∫}\frac{{\mathrm{\ρ}}_{\mathrm{bd}-\mathrm{wall}}{E}_s{\mathrm{\τ}}_{\mathrm{ss}}{\mathrm{\τ}}_{\mathrm{oo}}\sin {\mathrm{\θ}}_s\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i|x-x_0|}{{\mathrm{\π}}^2{[{(x-x_0)}^2+{(n+y_0-y)}^2+m^2]}^{\frac{3}{2}}}(f_C{\mathrm{\ρ}}_C^{\′}+f_G{\mathrm{\ρ}}_{\mathrm{soil}}^{\′})\mathrm{dndm}---(3-7).$ Other step is identical with one of embodiment one to three.

Embodiment five: present embodiment is different from one of embodiment one to four: the calculating of the outgoing spoke brightness that the whole wall that the sensor described in step 2 three receives produces the target infinitesimal (x, y) in canopy utilizes Monte Carlo method to realize integral and calculating.Other step is identical with one of embodiment one to four.

Embodiment six: present embodiment is different from one of embodiment one to five: the detailed process of step 3 is: by adjusting the input parameter in modtran software, as solar zenith angle θ _s, the gross energy that obtains sunshine incident is E _s,, meanwhile, obtain τ in conjunction with four stream earth's surface-propagation in atmosphere models _ss, τ _oo; Obtain the polarized reflectance R of canopy part in conjunction with FCR model and mixed pixel model, by acquired results substitution obtain the polarization spoke brightness I of canopy, convolution (3-7) is realized the high spectrum scene simulation of polarization of considering wall rescattering.Other step is identical with one of embodiment one to five.

Experimental verification of the present invention is as follows:

Mirror-reflection is a part for minute surface cone reflection, and directional scattering is not to be desirable diffuse reflection and diffraction scattering in a direction of causing by surface, and evenly diffuse scattering is desirable lambertian based on surface.For the incident light of any polarized state, the concrete analytic expression of three class scatterings can be expressed as:

${\mathrm{\ρ}}_{\mathrm{bd},\mathrm{sp}}=\frac{{\mathrm{\ρ}}_s}{\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i}\mathrm{\Δ}---(2-3)$

${\mathrm{\ρ}}_{\mathrm{bd},\mathrm{dd}}=\frac{{\left|F\right|}^2}{\mathrm{\π}}\·\frac{G\·S\·D}{\cos {\mathrm{\θ}}_i\cos {\mathrm{\θ}}_r}---(2-4)$

ρ _bd,ud＝a(λ) (2-5)

Wherein the calculating of mirror-reflection and directional scattering is the emphasis that the present invention studies, and uniform diffuse reflection is often in conjunction with experimental result gained.

The ρ that mirror-reflection causes _{bd, sp}

Mirror-reflection analytic expression is provided by formula (2-5), wherein ρ _spresentation surface specular reflectivity, Δ is a δ function, minute surface cone reflection Δ=1, other situation Δ=0.

ρ _s＝|F| ²e ^-gS (2-6)

In formula, F represents Fresnel polarized reflectance (relevant with the refractive index n of surfacing), and g is surperficial Effective Roughness σ ₀function, S is shade function.

${\left|F\right|}^2=\frac{1}{2}({F_s}^2-{F_P}^2)---(2-7)$

F in formula _s ²and F _p ²represent respectively the reflectivity of s polarization and p polarised direction.

g＝[(2πσ/λ)(cosθ _i+cosθ _r)] ²(2-8)

$\mathrm{\σ}={\mathrm{\σ}}_0{[1+{\left(\frac{z_0}{{\mathrm{\σ}}_0}\right)}^2]}^{-\frac{1}{2}}---(2-9)$

$\sqrt{\frac{\mathrm{\π}}{2}}{z}_0=\frac{{\mathrm{\σ}}_0}{4}(K_i+K_r)\exp (-\frac{{z_0}^2}{2{{\mathrm{\σ}}_0}^2})---(2-10)$

Z in formula ₀the intermediate variable in order to calculate introducing, σ ₀presentation surface Effective Roughness.

$K_i=\tan {\mathrm{\θ}}_i\·\mathrm{erfc}\left(\frac{\mathrm{\τ}}{2{\mathrm{\σ}}_0}\cot {\mathrm{\θ}}_i\right)---(2-11)$

$K_r=\tan {\mathrm{\θ}}_r\·\mathrm{erfc}\left(\frac{\mathrm{\τ}}{2{\mathrm{\σ}}_0}\cot {\mathrm{\θ}}_r\right)---(2-12)$

τ presentation surface auto-correlation length in formula.

S＝S _i(θ _i)S _r(θ _r) (2-13)

For smooth surface, along with the increase of wavelength X and projection surface's roughness ratio, for example, as λ >> σ cos θ _itime, g → 0 is S → 1 simultaneously, and specular components no longer increases.While, directional scattering component reduced, thereby in the scattering of top layer, mirror-reflection is occupied an leading position along with g's reduces.Conventionally can be rewritten as for smooth surface mirror-reflection expression formula | F| ²/ cos θ _idw _i.

The ρ that directional scattering causes _{bd, dd}

When lambda1-wavelength less or both are suitable than projection surface roughness, for example, as λ～σ cos θ _itime, top layer scattering will be considered the impact of diffraction and interference effect.Now whole episphere is all mirror field.We claim this directed diffusion that is reflected into, i.e. scattering occurs in whole hemisphere, but has orientation, feature heterogeneous simultaneously.

Directional scattering has been described the Direction Distribution Characteristics of top layer scattering, and its analytic expression is provided by formula (2-6), and wherein G is a geometric parameter, and D represents the distribution function of directional scattering.

$G={\left(\frac{\stackrel{\→}{v}\·\stackrel{\→}{v}}{v_z}\right)}^2\·\frac{1}{{|\stackrel{\→}{k_r}\×\stackrel{\→}{k_i}|}^4}\·[{(\stackrel{\→}{s_r}\·\stackrel{\→}{k_i})}^2+{(\stackrel{\→}{p_r}\·\stackrel{\→}{k_i})}^2]\·[{(\stackrel{\→}{s_r}\·\stackrel{\→}{k_i})}^2+{(\stackrel{\→}{p_r}\·\stackrel{\→}{k_i})}^2]---(2-17)$

$\begin{array}{c}\stackrel{\→}{v}=\stackrel{\→}{k_r}-\stackrel{\→}{k_i}\\ \stackrel{\→}{s_i}=\frac{\stackrel{\→}{k_i}\×\stackrel{\→}{n}}{|\stackrel{\→}{k_i}\×\stackrel{\→}{n}|},\stackrel{\→}{s_r}=\frac{\stackrel{\→}{k_r}\×\stackrel{\→}{n}}{|\stackrel{\→}{k_r}\×\stackrel{\→}{n}|}\end{array}---(2-18)$

${\stackrel{\→}{p}}_i={\stackrel{\→}{s}}_i\×{\stackrel{\→}{k}}_i,{\stackrel{\→}{p}}_r={\stackrel{\→}{s}}_r\×{\stackrel{\→}{k}}_r---(2-19)$

$D=\frac{{\mathrm{\π}}^2{\mathrm{\τ}}^2}{4{\mathrm{\λ}}^2}\·\underset{m=1}{\overset{\∞}{\mathrm{\Σ}}}\frac{g^m{e}^{-g}}{m!\·m}\·\exp (-{v_{\mathrm{xy}}}^2{\mathrm{\τ}}^2/4m)---(2-20)$

${v_{\mathrm{xy}}}^2=\sqrt{{v_x}^2+{v_y}^2}---(2-12)$

Can find out that from expression formula directional scattering is relevant with the statistics of surfacing, for example Effective Roughness σ ₀with auto-correlation length τ.For smooth surface, along with σ/λ → 0 or g → 0, ρ _{bd, dd}be kept to gradually 0.For rough surface, along with the increase of σ/λ or g, in the scattering of top layer, directional scattering becomes leading factor gradually.For more smooth surface, directional scattering is obtained maximum value in mirror-reflection direction; For more coarse surface, directional scattering is obtained maximum value in non-mirror reflection direction; For very coarse surface, in the time that incident angle is glancing angle, directional scattering is obtained maximum value.

The ρ that evenly scattering causes _{bd, ud}

Superficial reflex relatively, the uniform diffuse reflection analysis that earth's surface Multiple Scattering or underground reflection cause is got up more difficult.For the very little metal material of surface slope or opaque material, uniform diffuse reflection effect is not obvious; And for surface slope compared with for large or the permeable nonmetallic materials of light, for example paint, pottery, plastics etc., uniform diffuse reflection effect highly significant.

For even incident light, a (λ) and directed hemispherical reflectance ρ _dhequate, and ρ _dheasily utilize integrating sphere reflectometry to obtain, thereby can estimate by experiment a (λ).

Related experiment and analysis

Comprehensive mirror-reflection, directional scattering and evenly known this BRDF model of scattering have three class input parameters: (1) geometric parameter and illumination parameter: the zenith angle of the sun and sensor and relative bearing, i.e. θ _i, θ _r, (2) statistical parameter of surfacing: Effective Roughness σ ₀with auto-correlation length τ; (3) optical parametric: the refractive index n of surfacing and wavelength X.The Different Effects of lower surface analysis input parameter to mirror-reflection and directional scattering.

Mirror-reflection, directional scattering and wavelength relationship

(1) input parameter: θ _i=60 °, σ ₀=0.18, τ=1.77, n=1.5

(2) experimental result: as can be seen from Figure 2 for smooth surface along with wavelength X increases, g is constantly reducing, as λ >> σ cos θ _itime, g → 0 is shade function S → 1, specular components ρ simultaneously _{bd, sp}be tending towards a definite value, no longer increase along with the increase of λ, and directional scattering component ρ _{bd, dd}constantly reduce and be tending towards gradually 0.Comparison diagram (a) (b) in known now top layer scattering mirror-reflection occupy an leading position.

Mirror-reflection, directional scattering and Effective Roughness relation

(1) input parameter: θ _i=60 °, λ=2, τ=1.77, n=1.5

(2) experimental result: as can be seen from Figure 3 along with surperficial Effective Roughness σ ₀increase specular components ρ _{bd, sp}with directional scattering component ρ _{bd, dd}all constantly reduce, but directional scattering absolute value is much larger than mirror-reflection absolute value, thereby in the scattering of top layer, directional scattering becomes leading factor gradually.

Simulating scenes arranges

The simple scenario of emulation of the present invention is as shown in Figure 4: left and right sides square area is covered by canopy that (area is 150 × 150m ²), middle rectangular region part is wall (floorage 150 × 30m ², high 20m).When emulation, establishing plant spacing in the canopy of two side areas is 0.003, and leaf area index is 1.2, and the average height of getting canopy is 80cm, and leaf inclination angle is 60o.

Fig. 7 and Fig. 8 are the high spectrum scene simulation of the polarization based on BRDF model figure, and wherein Fig. 7 is the impact of wall on left side scene, can find out that the local influence nearer apart from wall is larger, on the contrary, relatively less apart from the local influence that wall is far away; Fig. 8 is the scene simulation that vegetation, soil and wall form, and can find out that left side scene has small ascendant trend near wall place, and this causes just because of the rescattering effect of wall.

Claims (6)

1. the high spectrum scene simulation of a polarization method for the impact of the consideration wall based on BRDF model, is characterized in that said method comprising the steps of:

Step 1, set up the BRDF model of analytical form, be specially:

Suppose that light propagation unit vector is wherein represent respectively the unit vector of light along incident direction and exit direction propagation; Polarization vector of unit length is wherein represent respectively polarization components vertical and the parallel plane of incidence, bidirectional reflectance distribution function is defined as:

Light is along exit direction the radiation flux of unit area, unit solid angle with along incident direction the ratio of the radiation flux of unit area, uses ρ _bdrepresent:

In formula represent the brightness of outgoing spoke, I _i, dw _irepresent respectively the brightness of incident spoke and incident solid angle, θ _i, θ _r, represent respectively zenith angle and the relative bearing of incident light and emergent light;

The BRDF model representation of analytical form is:

ρ _bd＝ρ _bd,sp+ρ _bd,dd+ρ _bd,ud(2-2)

ρ _{bd, sp}, ρ _{bd, dd}and ρ _{bd, ud}represent respectively the bidirectional reflectance that mirror-reflection, directional scattering and uniform diffuse reflection cause;

Step 2, BRDF model based on step 1 are asked for the outgoing spoke brightness of wall rescattering, comprise the steps:

Step 2 one, ask for the direct incident power of the sun that a face infinitesimal ds on wall receives;

The derivation of the irradiance that step 2 two, pointolite (m, n) produce target infinitesimal (x, y);

The derivation of the spoke brightness that step 2 three, whole wall produce target infinitesimal (x, y);

Step 3, the high spectrum scene simulation of polarization.

2. the high spectrum scene simulation of the polarization method of a kind of consideration wall impact based on BRDF model as claimed in claim 1, is characterized in that the detailed process of step 2 one is:

Suppose that the sun is positioned at the dead ahead of wall, to incide the light of wall be directional light to the sun; The gross energy of sunshine incident is E _s, solar zenith angle is θ _s, the direct incident power of the sun that a face infinitesimal ds on wall receives is:

P _i＝E _sτ _sssinθ _sds (3-1)

τ in formula _ssobtain by four stream earth's surface-atmospheric radiation transmission, represent that sunshine shines directly into the ratio of target by atmosphere;

For even wall, utilize the incident power P being irradiated in unit area _iwith emergent power dP _r, BRDF formula is rewritten as:

${\mathrm{\ρ}}_{\mathrm{bd}-\mathrm{wall}}=\frac{{\mathrm{dP}}_r}{P_i\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i}---(3-2)$

The emergent power in unit area is:

dP _r＝ρ _bd-wallP _icosθ _idw _i(3-3)

ρ in formula _bd-wallthe wall bidirectional reflectance calculating based on BRDF model, dw _ifor incident solid angle.

3. the high spectrum scene simulation of the polarization method of a kind of consideration wall impact based on BRDF model as claimed in claim 2, is characterized in that the detailed process of step 2 two is:

Emergent power in unit area is converted into outgoing intensity is: ρ _bd-wallp _icos θ _idw _i/ π; If ds is enough little for face infinitesimal, regard pointolite as; The irradiance that pointolite produces target infinitesimal (x, y) is derived as follows:

The radiation intensity of postulated point light source is JJ, and the area of target infinitesimal (x, y) is d _a, and pointolite is L to the distance of target infinitesimal, d _athe angle of normal and incident light is θ; Pointolite is to d _athe solid angle of being opened is d _a/ L ²; By defining of radiation intensity and irradiance the irradiance that receives of target infinitesimal is:

H＝Jcosθ/L ²(3-4)

Suppose that the point that sunshine incides on wall is o ', set up coordinate system x ' y ' z ' taking o ' as initial point, θ _i, θ _r, represent respectively zenith angle and the relative bearing of incident light and emergent light in BRDF model; Set up the rectangular coordinate system xy taking o as true origin in level ground, the horizontal ordinate of wall on surface level is from x simultaneously ₀change to x ₁, ordinate is from y ₀change to y ₁, at wall and level ground x ₀, y ₀intersection point o ₁in place, set up with o ₁for the rectangular coordinate system mn of initial point,

Pointolite (m, n) on wall to the distance of the target infinitesimal (x, y) in canopy is

Outgoing position angle in BRDF model cosine is outgoing zenith angle θ _rcosine is cos θ _r=| x-x ₀|/R, by formula (3-4) must pointolite (m, n) to the irradiance of target infinitesimal (x, y) generation be:

$d_H=\frac{{\mathrm{\ρ}}_{\mathrm{bd}-\mathrm{wall}}{E}_s{\mathrm{\τ}}_{\mathrm{ss}}\sin {\mathrm{\θ}}_s\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i|x-x_0|d_s}{\mathrm{\π}{[{(x-x_0)}^2+{(n+y_0-y)}^2+m^2]}^{\frac{3}{2}}}---(3-5).$

4. the high spectrum scene simulation of the polarization method of a kind of consideration wall impact based on BRDF model as claimed in claim 3, is characterized in that the detailed process of step 2 three is:

The spoke brightness that pointolite (m, n) produces target infinitesimal (x, y) is:

$d_I=\frac{{\mathrm{\ρ}}_{\mathrm{bd}-\mathrm{wall}}{E}_s{\mathrm{\τ}}_{\mathrm{ss}}{\mathrm{\τ}}_{\mathrm{oo}}\sin {\mathrm{\θ}}_s\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i|x-x_0|d_s}{{\mathrm{\π}}^2{[{(x-x_0)}^2+{(n+y_0-y)}^2+m^2]}^{\frac{3}{2}}}(f_C{\mathrm{\ρ}}_C^{\′}+f_G{\mathrm{\ρ}}_{\mathrm{soil}}^{\′})---(3-6)$

τ in formula _ooobtain by four stream earth's surface-atmospheric radiation transmission, represent that the energy being produced by target reflection arrives the ratio of sensor, f _c, f _grespectively illumination vegetation face, the illumination soil face in mixed pixel model; ρ ' _c, ρ ' _soilbe respectively to utilize the canopy based on wall rescattering and the scattered power of soil in the meadow that FCR model obtains, spoke brill is W/ (m ²sr);

Face infinitesimal d on wall _s=dmdn, the outgoing spoke brightness that the whole wall that sensor receives produces the target infinitesimal (x, y) in canopy is:

$I_{(x,y)}=\underset{m}{\∫}\underset{n}{\∫}\frac{{\mathrm{\ρ}}_{\mathrm{bd}-\mathrm{wall}}{E}_s{\mathrm{\τ}}_{\mathrm{ss}}{\mathrm{\τ}}_{\mathrm{oo}}\sin {\mathrm{\θ}}_s\cos {\mathrm{\θ}}_i{\mathrm{dw}}_i|x-x_0|}{{\mathrm{\π}}^2{[{(x-x_0)}^2+{(n+y_0-y)}^2+m^2]}^{\frac{3}{2}}}(f_C{\mathrm{\ρ}}_C^{\′}+f_G{\mathrm{\ρ}}_{\mathrm{soil}}^{\′})\mathrm{dndm}---(3-7).$

5. the high spectrum scene simulation of the polarization method of a kind of consideration wall impact based on BRDF model as claimed in claim 4, the calculating that it is characterized in that the outgoing spoke brightness that whole wall that the sensor described in step 2 three receives produces the target infinitesimal (x, y) in canopy utilizes Monte Carlo method to realize integral and calculating.

6. the high spectrum scene simulation of the polarization method of a kind of consideration wall impact based on BRDF model as claimed in claim 5, is characterized in that the detailed process of step 3 is: by adjusting the input parameter in modtran software, as solar zenith angle θ _s, the gross energy that obtains sunshine incident is E _s,, meanwhile, obtain τ in conjunction with four stream earth's surface-propagation in atmosphere models _ss, τ _oo; Obtain the polarized reflectance R of canopy part in conjunction with FCR model and mixed pixel model, by acquired results substitution obtain the polarization spoke brightness I of canopy, convolution (3-7) is realized the high spectrum scene simulation of polarization of considering wall rescattering.