CN116305835A - Modeling method for visible light bidirectional scattering distribution function of fold cladding material - Google Patents
Modeling method for visible light bidirectional scattering distribution function of fold cladding material Download PDFInfo
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Abstract
The invention provides a modeling method of a visible light bidirectional scattering distribution function of a fold coating material, which comprises the steps of obtaining BRDF data of the coating material which is not subjected to fold treatment; solving the length reduction ratio of the satellite surface coating material in the X, Y direction under the flattening condition relative to the wrinkling condition; establishing a distribution statistical analysis function of the area occupation ratio coefficient of the fold fragments; deflecting the BRDF which is not wrinkled according to the inclination angle to obtain a fragment reflectivity value aiming at a substrate coordinate system; discretizing the inclination angle and substituting the discretized inclination angle into an analysis function to obtain the area occupation ratio coefficient of the fold fragments; the reflectivity of any oriented fragment is multiplied by the corresponding area ratio coefficient to obtain the reflectivity contribution of the fragment, and then the reflectivity contribution of all the folded fragments is obtained through accumulation. The method utilizes a BRDF model under a flattening condition, calculates BRDF characteristics after wrinkling according to a cladding condition, and provides data support for target optical scattering characteristic simulation.
Description
Technical Field
The invention belongs to the technical field of modeling simulation, and particularly relates to a modeling method for a visible light bidirectional scattering distribution function of a fold cladding material.
Background
The targets such as modern communication satellites, investigation satellites and deep space detectors are coated with a layer of protective material so as to protect the safety of the equipment in deep space. The protective material is a composite multilayer material, the outermost layer is a metal-like high-reflectivity material, and the protective material has extremely high brightness under the irradiation of the sun and is an important influencing factor for determining the visibility of a target.
The bidirectional scattering distribution function (BRDF) characteristics of the cladding material when flat are very stable and are easy to measure, but the cladding material can be subjected to a plurality of folds for being closely attached to the satellite surface when in use, and the folds are random, so that BRDF parameters obtained under the flat condition cannot accurately describe the surface reflection characteristics of the target.
The BRDF test on the surface of the fold adopts the mode of actual materials to measure, the materials are manually rubbed firstly in operation, then the materials are placed on a measuring table to measure the BRDF characteristics in the current state and are used as the BRDF on the surface of the fold, the simple approximation method can be used within a certain precision requirement range, but is not beneficial to high-precision data simulation calculation, the degree of the fold is different under different use conditions, the same set of BRDF data cannot adapt to all application conditions, and huge economic cost and time cost can be brought by repeated measurement.
When finite element analysis and calculation are carried out, the inclination of each fold cannot be accurately described due to the accuracy of geometric model construction, meanwhile, each inclined plane cannot be responded when a surface source is split, and a specific reflectance value cannot be adopted when the surface source is calculated, so that a fold coating material visible light bidirectional scattering distribution modeling method is required to be invented, and BRDF parameter values are provided for the folded random surface.
Disclosure of Invention
In view of the above, the invention provides a satellite surface fold coating material BRDF characteristic modeling method, by adopting the method, a modeling person can calculate the BRDF characteristic of the folded material according to the coating condition of the material by using a BRDF model measured under a leveling condition, and data support is provided for target optical scattering characteristic simulation.
The invention utilizes accurate BRDF measured values under the flattening condition, and constructs the BRDF model of the pleated material by using the pleat fragment statistical model and the coating material. The specific technical scheme is as follows:
step 1, setting the satellite surface to which the coating material is attached as a base plane, wherein the coating material can be understood as a complex plane consisting of countless small patches attached on the base plane. Constructing a coordinate system by using incident light and a substrate plane, wherein the normal line of the substrate is a Z axis, the direction of the incident light in the substrate plane is an X axis, and determining a Y axis according to a right-hand rule; the normal direction of each fragment is (u, v), u is the tangent value of the included angle between the normal angle of the folded fragment and the YZ plane, and v is the tangent value of the included angle between the normal angle of the fragment and the XZ plane;
step 2, measuring BRDF of the flat cladding material to obtain standard BRDF data of the material or obtaining BRDF data of the material before the material is subjected to wrinkle treatment through other ways, wherein the format of the BRDF data is R (a, alpha, beta), a is an included angle between the incident direction of light and a Z axis, alpha is an included angle between the measuring direction and the YZ plane in the step 1, and beta is an included angle between the measuring direction and the XZ plane in the step 1;
step 3, analyzing the use condition of the cladding material to obtain the area before and the front view area after the folding of the cladding material, solving the length reduction ratio A of the satellite surface cladding material in the X direction and the length reduction ratio B in the Y direction under the flattening condition relative to the folding condition, and taking A as an example, and recording the original length L of the satellite surface folding cladding material in the X direction under the flattening condition o The length of the folded satellite surface fold coating material in the X direction is L n Then there is
In general, the reduction ratio of the satellite coating material is within the range of [1,1.5 ]]The calculation method of B is the same as A, and is different in that the original length and the length after folding are in the Y directionLength of the upper part.
Step 4, statistical analysis function f (u, v) of material fold fragment distribution, wherein u is tangent value of fold fragment normal angle and YZ face included angle, v is tangent value of fragment normal angle and XZ face included angle, and the statistical analysis function f (u, v) meets two-dimensional normal distribution
Wherein sigma 1 ，σ 2 U and v are distributed with probability standard deviation in X and Y directions;
and 5, deflecting the non-pleated material BRDF according to the inclination angle of the fragments to obtain the reflectivity r (a, alpha, beta, u, v) of the pleated fragments, wherein the specific calculation formula is as follows:
r(a，α，β，u，v)＝R(a，α-2actan(u)，β-actan(v))；
step 6, discretizing the probability distribution function obtained in the step 4 to obtain u= + -3 sigma 1 And v= ±3σ 2 As boundaries, discretizing values of u and v into M and N parts in X and Y directions respectively according to u= (M-0.5X M) 6σ 1 /M，v＝(n-0.5*N)6σ 1 N, (M, N) is the number of the angle interval in the XY direction, and the values are integers of 1 to M and 1 to N respectively. Traversing the m and n values, taking the values into the normal-Ethernet distribution formula mentioned in the step 4, and calculating to obtain u and v within +/-3 sigma 1 And + -3σ 2 The area ratio coefficient F (m, n) of all fold fragments in the range;
In the step 2, the reflectivity of most coating materials is isotropic, the value range of the angle a of incident light is 0-90 degrees, the value range of alpha is-90 degrees, and the value range of beta is-90 degrees;
in step 3, the reduction ratios a and B of the length of the material in the two directions after folding are independent from each other, and can be obtained by measuring the measurement values in the two directions X and Y of the material before folding and dividing the measurement values in the two directions X and Y of the material after folding;
in step 4, σ 1 ，σ 2 Is related to the values of A and B in step 3, and the solving equation is:
advantageous effects
1) The invention provides a method for accurately estimating BRDF coefficients under the condition of target wrinkles under the condition of known BRDF coefficients;
2) The system can provide data support for target modeling simulation and light scattering analysis;
3) According to the invention, the BRDF parameters of the material after the target wrinkles can be accurately estimated without repeatedly measuring different states of the material;
4) Limiting the value range of u and v is beneficial to simplifying calculation;
5) BRDF model R of wrinkled material Fold The (a, alpha, beta) can be supported and converted into other models, is convenient to use, and does not influence scattering results.
6) The method has the advantages of short calculation time and high model accuracy.
Drawings
FIG. 1 is a schematic cross-sectional view of the material fold result
FIG. 2 schematic view of incident angle and observation angle
FIG. 3 schematic view of the angular definition of a pleated fragment
FIG. 4 is a flow chart of the method of the present invention
Detailed Description
The invention provides a modeling method of visible light bidirectional scattering distribution function of a fold cladding material, wherein the length of a flattened material shown in figure 1 is reduced after being folded on the section shown in the figure, the length reduction ratio L/L before and after folding is measured, and the length reduction ratio in all directions can be defaulted to be the same under the assumption of random kneading;
as shown in fig. 2, 101 is the incident light direction, 102 is the detection direction, because the material is isotropic, the rotation of the material along the normal direction does not affect the overall scattering property of the material, the incident direction and the normal direction of the substrate plane are set to form an XZ plane, the YZ plane is determined according to the right-hand spiral rule, a is the incident angle direction, α is the included angle between the measurement direction and the XZ plane, β is the included angle between the measurement direction and the YZ plane, and the BRDF model R (a, α, β) of the material based on a, α, β can be found by measurement or table lookup;
as shown in FIG. 3, 203 is the normal direction of the folded fragments, 201 is the angle between the normal direction and the XZ plane, 202 is the angle between the normal direction and the YZ plane, and the tangent values of the two angles 201 and 202 are calculated to obtain u and v, and two-dimensional normal distribution is established
Equation f (u, v) describes only the proportion of area coverage of the pleated chips at different angles of inclination, and does not reflect the specific location of the chips, consistent with the randomness of the surface after the material has been pleated. Wherein sigma 1 ，σ 2 U and v are distributed with probability standard deviation in X and Y directions; according to the length shortening ratio L/L and formula
Determining sigma 1 ，σ 2 The specific values of the areas of the fold fragments under different dip angles can be solved; a and B are common cases, and in this example it is assumed that a and B are equal.
For the convenience of calculation, limiting the value range of the u, v, setting u= +/-3 sigma 1 And v= ±3σ 2 Discretizing the inclination angle for the boundary, discretizing M and N parts in the X and Y directions respectively to obtain a calculation formula for discretizing and calculating areas of fold fragments with different orientations, wherein each part is respectively calculated according to u= (M-0.5X M) 6sigma 1 /M，v＝(n-0.5*N)6σ 1 N, carrying out calculation on the two-dimensional forward distribution formula obtained in the last step to obtain u and v within +/-3 sigma 1 And + -3σ 2 The area ratio coefficient of all the fold fragments in the range, and establishing a normal distribution function F (m, n) based on the sequence numbers m, n;
deflection of the non-wrinkled material BRDF according to the inclination of the pieces gives a reflectivity value of approximately R (a, α, β, m, n) =r (a, α -2actan ((m-0.5×m) 6σ) for the wrinkled pieces of the substrate coordinate system 1 /M)，β-actan((n-0.5*N)6σ 1 N), the fold fragment reflectivity of the sheet under all angles is traversed using the formula
BRDF model R of the wrinkled material can be calculated Fold (a, alpha, beta) the model can be supported and converted into other models for convenient use, and the scattering result is not affected.
Claims (10)
1. A modeling method for visible light bidirectional scattering distribution function of a fold coating material is characterized by comprising the following steps of: comprises the steps of,
1) Obtaining BRDF data for the non-pleated clad material;
2) Respectively solving the length reduction ratio A and the length reduction ratio B of the satellite surface coating material in the X, Y direction under the flattening condition relative to the wrinkling condition;
3) Establishing a distribution statistical analysis function f (u, v) of the area occupation ratio coefficient of the material fold fragments, wherein u is the tangent value of the normal angle of the fold fragments and the included angle of the YZ plane, and v is the tangent value of the normal angle of the fold fragments and the included angle of the XZ plane;
4) Deflecting the BRDF which is not wrinkled according to the inclination angle u, v to obtain a fragment reflectivity value aiming at a substrate coordinate system;
5) Discretizing u and v and substituting the discretized u and v into an analysis function F (u and v) to obtain an area ratio coefficient F (m and n) of all the fold fragments;
6) Multiplying the reflectivity of any oriented fragment by the corresponding area ratio coefficient to obtain the reflectivity contribution I of the fragment m，n And then adding up to obtain the reflection contribution rate of all the fold fragments, namely the reflection rate model of the whole coating material.
2. The modeling method for visible light bidirectional scattering distribution function of a pleated cover material according to claim 1, wherein the modeling method comprises the following steps: obtaining BRDF data of the material before the material is subjected to the wrinkling treatment further comprises the steps of:
step 1, setting the satellite surface to which a coating material is attached as a basal plane, wherein the coating material is a complex plane formed by countless small patches attached on the basal plane; constructing a coordinate system by using incident light and a substrate plane, wherein the normal line of the substrate is a Z axis, the direction of the incident light in the substrate plane is an X axis, and determining a Y axis according to a right-hand rule; the normal direction of each fragment is (u, v), u is the tangent value of the included angle between the normal angle of the folded fragment and the YZ plane, and v is the tangent value of the included angle between the normal angle of the fragment and the XZ plane;
and 2, measuring BRDF of the flat coating material to obtain standard BRDF data of the material or obtaining BRDF data of the material before the material is subjected to wrinkle treatment through other ways, wherein the format of the BRDF data is R (a, alpha, beta), a is an included angle between the incident direction of light and a Z axis, alpha is an included angle between the observation direction and the XZ plane in the step 1, and beta is an included angle between the observation direction and the YZ plane in the step 1.
3. The modeling method for visible light bidirectional scattering distribution function of a pleated cover material according to claim 1, wherein the modeling method comprises the following steps:
the calculation method of the length reduction ratio A in the X direction is that the original length of the satellite surface fold cladding material in the X direction under the leveling condition is recorded as L o The length of the folded satellite surface fold coating material in the X direction is L n Then there is
4. A method for modeling a visible light bidirectional scattering distribution function of a pleated cover according to claim 1 or 3, wherein:
the calculation method of B is the same as that of A, except that the original length and the length after folding are the lengths in the Y direction.
5. The modeling method for visible light bidirectional scattering distribution function of a pleated cover material according to claim 1, wherein the modeling method comprises the following steps:
the statistical analysis function f (u, v) of the distribution of the material fold fragments meets the two-dimensional normal distribution, and is specifically as follows:
wherein sigma 1 ，σ 2 Is the standard deviation of the probability of u and v being distributed in both directions X, Y.
6. The modeling method for visible light bidirectional scattering distribution function of a pleated cover material according to claim 5, wherein the modeling method comprises the following steps:
σ 1 ，σ 2 in relation to the values of A and B, the solution equation is:
7. the modeling method for visible light bidirectional scattering distribution function of a pleated cover material according to claim 1, wherein the modeling method comprises the following steps:
the specific calculation formula of the reflectance values r (a, α, β, u, v) of the pleated chips is as follows:
r(a，α，β，u，v)＝R(a，α-2actan(u)，β-actan(v))。
8. the modeling method for visible light bidirectional scattering distribution function of a pleated cover material according to claim 1, wherein the modeling method comprises the following steps:
the area occupation ratio F (m, n) of the fold fragments is obtained by the following steps: in u = ±3σ 1 And v= ±3σ 2 As boundaries, discretizing values of u and v into M and N parts in X and Y directions respectively according to u= (M-0.5X M) 6σ 1 /M，v＝(n-0.5*N)6σ 1 N, (M, N) is the sequence number of the angle interval in the XY direction, and the values are integers of 1-M and 1-N respectively; traversing the m and n values, introducing a distribution statistical analysis function f (u, v), and calculating to obtain u and v within + -3 sigma 1 And + -3σ 2 The area ratio F (m, n) of all pleat fragments in the range.
9. The modeling method for visible light bidirectional scattering distribution function of a pleated cover material according to claim 2, wherein the modeling method comprises the following steps:
the angle a of the incident light is in the range of 0-90 degrees, the angle alpha is in the range of-90 degrees, and the angle beta is in the range of-90 degrees.
10. The modeling method for visible light bidirectional scattering distribution function of a pleated cover material according to claim 1, wherein the modeling method comprises the following steps:
the obtained reflectivity model R Fold (a, alpha, beta) and converting the values into other BRDF parameter models which are convenient to use under the condition of unchanged values.
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