Calibration technology for multi-angle scattering light field rapid measurement system

Abstract

The invention discloses a calibration technology for a multi-angle scattering light field rapid measurement system, belongs to the technical field of light field measurement, and aims to solve the problems that long measurement time still has obvious defects, and a measurement mode based on a mechanical transmission structure cannot cope with sample scattering light distribution change in a variable environment due to the measurement time length. The method comprises the steps of angle mapping function establishment, noise elimination, light field meter calibration and calibration, conclusion analysis and the like, the measurement optical system of the hemispherical rapid light field meter is optimally designed, and the angle mapping function of the hemispherical rapid light field meter is established. An internal noise elimination algorithm of the hemispherical rapid light field measuring meter is provided, a calibration process of the hemispherical rapid light field measuring meter is constructed, and the accuracy and traceability of a measurement result of the hemispherical rapid light field measuring meter are ensured.

Description

Technical Field

[0001] The present invention relates to the field of light field measurement technology, and in particular to a multi-angle scattered light field rapid measurement system calibration technology. Background Art

[0002] The radiation characteristics of target and ambient light reflect the physical phenomena resulting from the interaction of light waves with the target and the environment. They reveal the inherent nature of the target and the environment, namely, the hemispherical spatial scattering characteristics of the target and ambient light. Scattered light distribution characteristics are widely used in numerous scientific research fields, including aerial remote sensing, imaging technology, materials analysis, environmental monitoring, and computer graphics. Among these applications, the measurement of light scattering field distribution in variable environments has long been a research hotspot. These include the impact of ambient light source variations on scattering characteristics, the study of the distribution characteristics of target surface scattered light at different temperatures, and the measurement of scattered light from dynamic objects.

[0003] With the development of scattered light distribution measurement based on mechanical transmission structures, long measurement time remains its obvious drawback. For the measurement of scattered light distribution of a sample in hemispherical space, even with a fast rotating worktable or a robot-based mechanical design, assuming measurements are taken at 5° intervals at the zenith angle and azimuth angle, the measurement time for the scattered light distribution on the surface of a sample is about 10 hours. If the measurement is performed at a step size of 1°, it will take about 10 days. The long measurement time makes the measurement method based on mechanical transmission structure unable to cope with the changes in the scattered light distribution of the sample in a changing environment.

[0004] To solve the above problems, a multi-angle scattered light field rapid measurement system calibration technology is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a multi-angle scattered light field rapid measurement system calibration technology, which uses this device to work, thereby solving the problem that the long measurement time is still its obvious defect in the above background, and the problem that the measurement time causes the measurement method based on the mechanical transmission structure to be unable to cope with the changes in the scattered light distribution of the sample in a changing environment.

[0006] To achieve the above object, the present invention provides the following technical solution: a multi-angle scattered light field rapid measurement system calibration technology, comprising the following steps:

[0007] S1: angle mapping function;

[0008] S2: noise cancellation;

[0009] S3: Calibration and calibration of light field measurement instrument;

[0010] S4: Conclusion analysis.

[0011] Furthermore, the angle mapping function described in S1 includes the following steps:

[0012] S11: measurement optical system;

[0013] S12: Angle mapping relationship.

[0014] Furthermore, the noise elimination in S2 includes the following steps:

[0015] S21: Noise cancellation principle;

[0016] S22: Noise removal algorithm.

[0017] Furthermore, the noise elimination algorithm described in S22 includes the following steps:

[0018] S221: Luminous flux distribution matrix establishment;

[0019] S222: Luminous flux calculation equation is established;

[0020] S223: Scattering flux solution.

[0021] Furthermore, the calibration and calibration of the light field measuring instrument described in S3 includes the following steps:

[0022] S31: Light field meter calibration;

[0023] S32: Calibration of light field meter.

[0024] Furthermore, the measurement optical system described in S11 is specifically as follows:

[0025] The optical system was optimized and improved to achieve measurement of the system zenith angle range of 0°-80° and the azimuth angle range of 0°-360°. The X and Y field of view directions of the optical system represent the azimuth and zenith angle directions of the measurement system. The field of view is established with an increment of 1° in the X and Y field of view directions centered at (0°, 0°) in the central field of view and (0°, 79°) at the edge field of view. The final optical system spot footprint diagram shows that the measurement angle resolution can reach 1°.

[0026] Furthermore, the angle mapping relationship described in S12 is specifically as follows:

[0027] The scattered light field acquisition imaging optical system is set up off-axis. In order to establish the correspondence between the scattered light distribution angle and the illumination received by the detector surface, ray tracing and numerical derivation are performed on the imaging acquisition optical system, and an angle mapping function calculation model is established based on the light field acquisition optical system.

[0028] The model coordinate system is established in the Zemax Opticstudio global coordinate system according to the optical system. The O(0,0,0) point is the center of the hemispherical dome and also the origin of the coordinate system. The O′(0,75,0) point is the center of the optical axis of the optical system. ec =75mm is the off-axis distance of the optical system, R is the radius of the hemispherical dome, G is any point on the inner wall of the dome that carries the light field information, l i is the distance from this point to the center of the aspheric reflector, ω x 、ω y is the field of view of the optical system, θ s 、 is the zenith angle and azimuth angle of the scattered light at point G. First, the corresponding relationship between the field of view angle of the optical system and the scattered light angle is established. The formula is as follows:

[0029]

[0030] We can get:

[0031]

[0032] It is known that the projection coordinates of point G on the XOY plane are (x, y) = (l i sinω y cosω x , -l i sinω y sinω x +l ec ), we can get:

[0033]

[0034] Based on the object-image mapping relationship of the optical system transfer matrix, the relationship between the object point coordinates (x, y) and the image point coordinates (x′, y′) is as follows:

[0035]

[0036] in

[0037] The mapping relationship between the optical system field angle and the scattered light angle is obtained as follows: The conversion relationship between the field of view angle of the optical system and the object point coordinates is (x, y) = u(ω x ,ω y ), and the mapping relationship between object points and image points is (x′, y′) T =A·(x,y) T .

[0038] Furthermore, the noise elimination principle described in S21 is specifically as follows:

[0039] Due to the low reflectivity diffuse reflection coating of the dome inner wall material, it is assumed that its diffuse reflection characteristics are close to Lambertian reflection, and the LR illumination calculation model is established;

[0040] Taking point S as the Lambertian reflection point, the main reflection direction of the Lambertian reflection has an intensity of I0, and the angle with the main reflection direction of the Lambertian reflection is The intensity of reflected light is recorded as We can get:

[0041]

[0042] The angle with the main direction of Lambertian reflection is Illuminance E at the illuminance test point P at a distance d from the main reflection point S P It can be expressed as:

[0043]

[0044] Establish a calculation model for the dome's "integral effect" background noise;

[0045] Assume that point O is the center of the spherical dome, points N1, N2, and N3 are points on a certain arc of the hemispherical dome, and the reflectivity of the inner wall of the dome is ξ. According to the Lambertian surface orientation-hemispherical reflection characteristics, the reflection angle of any point on the inner wall of the low-reflectivity hemispherical dome is η. i The reflected light intensity I η It can be expressed as:

[0046]

[0047] The light flux scattered by the sample at the center of the hemisphere received by point N1 is recorded as φ1, and the light intensity I1 reflected twice by point N1 to point N3 is:

[0048]

[0049] The illuminance reflected from point N1 to point N3 can be expressed as:

[0050]

[0051] Where R1 = 2Rcosη1, the illumination reflected from point N1 to point N3 can be summarized as:

[0052]

[0053] Similarly, the illuminance E2 reflected from point N2 to point N3 can be calculated as:

[0054]

[0055] make is a constant, then the secondary illumination superposition generated by all points on the inner wall of the dome at point N3 can be expressed as:

[0056]

[0057] It can be obtained that the illumination at point N3 after secondary reflection has nothing to do with its position. When the dome scattering rate and dome size are determined, it is only related to the total scattered light flux of the sample measured at the center of the dome in the hemispherical space. The formula is as follows:

[0058] E Total ∝φ Total .

[0059] Furthermore, the luminous flux distribution matrix described in S221 is established, and the specific contents are as follows:

[0060] When the light source parameters are selected, the illumination E incident on the sample surface i Assuming that the total scattered light flux of the sample in the hemispherical space is Φ S , then the radiance can be expressed as:

[0061]

[0062] According to the noise calculation formula and E Total ∝φ Total It can be seen that the quadratic superimposed illuminance at each point on the inner wall of the hemispherical dome is linearly related to the total scattered light flux of the measured sample distributed in the hemispherical space, and the formula is as follows:

[0063]

[0064] According to the illuminance calculation formula Φ=E·ΔS, the background noise luminous flux at the inner wall of the dome is It is also linearly related to the total scattered light flux, and the formula is as follows:

[0065]

[0066] According to the coordinate system of the CCD surface in the angle mapping function, the CCD surface luminous flux distribution matrix M is established ij , the matrix is composed of the light flux received by the i-row and j-column coordinate points on the CCD surface, let We can get:

[0067]

[0068] Dome inner wall light field luminous flux distribution matrix S ij And the noise flux distribution matrix N ij Can be expressed as and

[0069] The luminous flux calculation equation described in S222 is established, and the specific contents are as follows:

[0070] The light flux at each point on the inner wall of the dome is scattered by the inner wall of the dome, collected by the optical system, and finally reaches the CCD surface. The transfer coefficient of the light flux at each point in this process is ε ij , the light flux of the light field and the noise flux after passing through the optical system and reaching each coordinate point on the CCD surface are respectively:

[0071]

[0072] The luminous flux of each coordinate point in the detector surface luminous flux distribution matrix is the superposition of the scattered light field flux and the noise flux passing through the corresponding point on the inner wall of the dome. The formula is as follows:

[0073] M ij =ε ij [S ij +N ij ];

[0074] The total scattered light flux on the sample surface is:

[0075]

[0076] Then the noise flux at each point on the inner wall of the dome is:

[0077]

[0078] The luminous flux at each point on the detector surface can be expressed as:

[0079]

[0080] According to M ij =ε ij [S ij +N ij ]、 and The equations are as follows:

[0081]

[0082] Let χ ij is the energy calibration normalization factor, C2 is the normalization constant coefficient, and the above equations can be sorted out as follows:

[0083]

[0084] The scattering flux solution described in S223 is as follows:

[0085] Solve the total scattered light flux Φ according to the formula finally obtained in S222 S, the formula is as follows:

[0086]

[0087] The solution to the scattered light distribution at each point position can be expressed as:

[0088]

[0089] Furthermore, the light field measurement meter calibration described in S31 and the light field measurement meter calibration described in S32 are specifically as follows:

[0090] The calibration of the hemispherical light field meter uses the standard Lambertian surface as the calibration target, and uses the angle mapping function in S1 and the noise elimination algorithm in S22 to calibrate and calibrate the measurement system.

[0091] Compared with the prior art, the present invention has the following beneficial effects:

[0092] The present invention optimizes the measurement system and realizes the measurement of scattered light field distribution with an angular resolution of 1° without any moving parts. It also establishes an angle mapping function model suitable for the measurement system and proposes a noise elimination algorithm.

[0093] Based on the light scattering distribution characteristics of the Lambertian surface, this paper verifies the accuracy of the angle mapping function and noise elimination algorithm, and calibrates and demarcates the hemispherical light field and measurement results. After calibration, the maximum measurement error is 5.08% at the zenith angle of 73° and the azimuth angle of 200°. Within the full field of view measurement range of the system, the average error at the zenith angle of 75.5° is the largest, which is -0.397%. The research content of the paper provides theoretical support for the development and implementation of hemispherical fast light field measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Figure 1 It is the overall flow chart of the present invention;

[0095] Figure 2 is a flow chart of the angle mapping function of the present invention;

[0096] Figure 3 A flowchart of noise elimination according to the present invention;

[0097] Figure 4 A step diagram of the noise elimination algorithm of the present invention;

[0098] Figure 5 This is a flow chart of the calibration and demarcation of the light field measuring instrument of the present invention;

[0099] Figure 6 is the light scattering distribution diagram of the present invention;

[0100] Figure 7The measurement principle and structure diagram of the present invention;

[0101] Figure 8 A diagram of an improved optical system for light field acquisition and analysis of angular resolution according to the present invention;

[0102] Figure 9 The angle mapping function calculation model diagram of the present invention;

[0103] Figure 10 is the angle mapping function of the present invention;

[0104] Figure 11 is the LR illumination calculation model of the present invention;

[0105] Figure 12 A calculation model diagram of background noise of the present invention;

[0106] Figure 13 This is a flow chart of the measurement system calibration and demarcation process of the present invention;

[0107] Figure 14 This is the error diagram after system calibration of the present invention. DETAILED DESCRIPTION

[0108] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0109] In order to solve the technical problem that the long measurement time is still its obvious defect and the measurement time causes the measurement method based on the mechanical transmission structure to be unable to cope with the changes in the scattered light distribution of the sample in a changing environment, such as Figures 1-14 As shown, the following preferred technical solutions are provided:

[0110] 1. Measurement principle of hemispherical fast light field meter:

[0111] The essence of the scattered light field is the distribution characteristics of the physical properties of light in the spatial dimension. BRDF, as a research carrier of the scattered light field, can effectively describe the light scattering distribution on the surface of an object. The distribution of scattered light on the surface of an object in the hemispherical space is as follows: Figure 6 (a) As shown; According to the definition of BRDF, it is a function related to the incident zenith angle, incident azimuth angle, observation zenith angle, observation azimuth angle and wavelength. The spatial coordinate relationship is as follows: Figure 6 (b) is shown, where is the incident azimuth, is the incident zenith angle, is the exit azimuth, and is the exit zenith angle. The BRDF function expression is:

[0112]

[0113] Where λ is the incident wavelength, dL s is the scattered radiance, dE i is the incident irradiance.

[0114] According to the definition of BRDF, when measuring the target object, it is required to cover the scattered light distribution characteristics within a specific spatial angle range centered on the sample. The rapid measurement based on optical imaging technology is to collect the reflected radiance of the hemispherical space using a hemispherical or aspherical surface, and then feed it back to the subsequent imaging system. The principle and structure of the rapid measurement of the multi-angle scattered light field based on imaging technology are as follows: Figure 7 As shown, after the light source irradiates the sample, the scattered light from the sample is further collected by the inner wall of the hemispherical dome and fed back to the catadioptric imaging system, and finally captured by the detector for imaging.

[0115] Since it is more reasonable to use non-differential quantities in the experiment, the relevant quantities can be calculated using photometric quantities. λ The light source is calculated according to the zenith angle and azimuth angle θ i The irradiance incident on the sample surface is:

[0116]

[0117] Where r s is the incident light beam diameter.

[0118] The total scattered light flux from the light source irradiating the sample surface to the hemispherical space is Φ S , then the radiance is:

[0119]

[0120] After passing through the optical system, the detector (Charged-coupled Device) finally receives the radiance from the hemispherical spatial distribution: We can get:

[0121]

[0122] Where ξ is the dome scattering coefficient, and g(op) is the transfer function expression of the imaging optical system, which depends on factors such as the field of view and aperture of the system. The irradiance received on the CCD detector surface is considered to be equivalent to the radiance, and we can get:

[0123]

[0124] Finally, the measurement expression of BRDF can be obtained as:

[0125]

[0126] From the above calculations, it can be seen that the scattering distribution characteristics of the sample surface can be inverted according to the relative illumination distribution finally received by the detector of the light field measurement system.

[0127] 2. The angle mapping function in S1, the specific process is as follows:

[0128] 1. Measurement optical system in S11:

[0129] Previously, a method for synchronous measurement of multi-angle scattered light measurement was proposed. Based on the established mathematical model for scattered light field measurement, an off-axis catadioptric aspheric optical system was designed with an angular resolution of 3°, which can realize synchronous and rapid measurement of multi-angle scattered light field distribution on the surfaces of isotropic and anisotropic objects. In order to further improve the resolution of the test system, the optical system was optimized and improved, and the measurement of the system zenith angle of 0°-80° and the azimuth angle of 0°-360° was realized. The X and Y field of view directions of the optical system represent the azimuth and zenith angle directions of the measurement system. The field of view is established in the X and Y field directions with an interval of 1° as the increment in the central field of view with (0°, 0°) as the center and the edge field of view with (0°, 79°) as the center. It can be seen from the final optical system spot footprint diagram that the measurement angle resolution can reach 1°. The optical system and angular resolution spot footprint diagram after improvement are shown as follows Figure 8 shown.

[0130] 2. Angle mapping relationship in S12:

[0131] The scattered light field acquisition imaging optical system is set up off-axis. In order to establish the correspondence between the scattered light distribution angle and the illumination received by the detector surface, ray tracing and numerical deduction are performed on the imaging acquisition optical system, and an angle mapping function calculation model is established based on the light field acquisition optical system. Figure 9 As shown;

[0132] The model coordinate system is established in the Zemax Opticstudio global coordinate system according to the optical system. The O(0,0,0) point is the center of the hemispherical dome and also the origin of the coordinate system. The O′(0,75,0) point is the center of the optical axis of the optical system. ec =75mm is the off-axis distance of the optical system, R is the radius of the hemispherical dome, G is any point on the inner wall of the dome that carries the light field information, l i is the distance from this point to the center of the aspheric reflector, ω x 、ω y is the field of view of the optical system, θ s 、 is the zenith angle and azimuth angle of the scattered light at point G. First, the corresponding relationship between the field of view angle of the optical system and the scattered light angle is established. The formula is as follows:

[0133]

[0134] We can get:

[0135]

[0136] It is known that the projection coordinates of point G on the XOY plane are (x, y) = (l i sinω y cosω x , -l i sinω y sinω x +l ec ), we can get:

[0137]

[0138] Based on the object-image mapping relationship of the optical system transfer matrix, the relationship between the object point coordinates (x, y) and the image point coordinates (x′, y′) is as follows:

[0139]

[0140] in is the generalized transformation matrix of all optical elements in the optical system that the corresponding object point passes through;

[0141] The mapping relationship between the optical system field angle and the scattered light angle is obtained as follows: The conversion relationship between the field of view angle of the optical system and the object point coordinates is (x, y) = u(ω x ,ω y ), and the mapping relationship between object points and image points is (x′, y′) T =A·(x,y) T , the graphical result of the angle mapping function is as follows Figure 10 shown.

[0142] 3. Noise elimination in S2, the specific contents are as follows:

[0143] 1. Noise cancellation principle in S21:

[0144] Due to the low reflectivity diffuse reflection characteristic coating of the dome inner wall material, it is assumed that its diffuse reflection characteristic is close to Lambertian reflection, and the LR illumination calculation model is established as follows Figure 11 As shown;

[0145] Figure 11 Point S is the Lambertian reflection point. The main reflection direction of the Lambertian reflection has an intensity of I0, and the angle with the main reflection direction of the Lambertian reflection is The intensity of reflected light is recorded as We can get:

[0146]

[0147] The angle with the main direction of Lambertian reflection is Illuminance E at the illuminance test point P at a distance d from the main reflection point S P It can be expressed as:

[0148]

[0149] Where Φ P is the incident luminous flux at point P, AP is the irradiated area at point P, and Ω is the solid angle.

[0150] Establish a calculation model for the dome's "integral effect" background noise. Figure 12 As shown;

[0151] Figure 12 Point O is the center of the spherical dome, points N1, N2, and N3 are points on a certain arc of the hemispherical dome, and the reflectivity of the inner wall of the dome is ξ. According to the Lambertian surface orientation-hemispherical reflection characteristics, the reflection angle of any point on the inner wall of the low-reflectivity hemispherical dome is η. i The reflected light intensity I η It can be expressed as:

[0152]

[0153] Where φ is the incident luminous flux at that point.

[0154] The light flux scattered by the sample at the center of the hemisphere received by point N1 is recorded as φ1, and the light intensity I1 reflected twice by point N1 to point N3 is:

[0155]

[0156] The illuminance reflected from point N1 to point N3 can be expressed as:

[0157]

[0158] Where R1 = 2Rcosη1, the illumination reflected from point N1 to point N3 can be summarized as:

[0159]

[0160] Similarly, the illuminance E2 reflected from point N2 to point N3 can be calculated as:

[0161]

[0162] make is a constant, then the secondary illumination superposition generated by all points on the inner wall of the dome at point N3 can be expressed as:

[0163]

[0164] That is, the illumination at point N3 after secondary reflection has nothing to do with its position. When the dome scattering rate and dome size are determined, it is only related to the total scattered light flux of the sample measured at the center of the dome in the hemispherical space. The formula is as follows:

[0165] E Total ∝φ Total ;

[0166] According to the above calculations and analysis, the background noise generated by the secondary reflection received at a certain point on the inner wall of the hemispherical dome can be uniformly eliminated by the total luminous flux in a certain direction of the test sample - the hemispherical space.

[0167] 2. The noise elimination algorithm in S22 is as follows:

[0168] a: Luminous flux distribution matrix in S221 is established:

[0169] According to the scattered light field measurement principle, when the light source parameters are selected, the illumination E incident on the sample surface is i Assuming that the total scattered light flux of the sample in the hemispherical space is Φ S , then the radiance can be expressed as:

[0170]

[0171] At this time, each point on the inner wall of the dome carries the luminous flux φ containing the light field distribution information. S and the luminous flux φ containing background noise information N When the light field acquisition optical system collects the light field information of each point on the inner wall of the hemispherical dome, it also collects the background noise information in a superimposed manner. Finally, the data obtained by the detector contains both light field information and noise information.

[0172] According to the noise calculation formula and E Total ∝φ Total It can be seen that the quadratic superimposed illuminance at each point on the inner wall of the hemispherical dome is linearly related to the total scattered light flux of the measured sample distributed in the hemispherical space, and the formula is as follows:

[0173]

[0174] According to the illuminance calculation formula Φ=E·ΔS, the background noise luminous flux at the inner wall of the dome is It is also linearly related to the total scattered light flux, and the formula is as follows:

[0175]

[0176] In the formula, C1=C·ΔS, ΔS is the irradiated area of the point.

[0177] According to the coordinate system of the CCD surface in the angle mapping function, the CCD surface luminous flux distribution matrix M is established ij , the matrix is composed of the light flux received by the i-row and j-column coordinate points on the CCD surface, let We can get:

[0178]

[0179] Dome inner wall light field luminous flux distribution matrix S ij And the noise flux distribution matrix N ij Can be expressed as and

[0180] b: The luminous flux calculation equation in S222 is established:

[0181] The light flux at each point on the inner wall of the dome is scattered by the inner wall of the dome, collected by the optical system, and finally reaches the CCD surface. The transfer coefficient of the light flux at each point in this process is ε ij , the light flux of the light field and the noise flux after passing through the optical system and reaching each coordinate point on the CCD surface are respectively:

[0182]

[0183] The luminous flux of each coordinate point in the detector surface luminous flux distribution matrix is the superposition of the scattered light field flux and the noise flux passing through the corresponding point on the inner wall of the dome. The formula is as follows:

[0184] M ij =ε ij [S ij +N ij ];

[0185] The total scattered light flux on the sample surface is:

[0186]

[0187] Then the noise flux at each point on the inner wall of the dome is:

[0188]

[0189] The luminous flux at each point on the detector surface can be expressed as:

[0190]

[0191] According to M ij =ε ij [S ij+N ij ]、 and The equations are as follows:

[0192]

[0193] Let χ ij is the energy calibration normalization factor, C2 is the normalization constant coefficient, and the above equations can be sorted out as follows:

[0194]

[0195] c: Scattering flux solution in S223:

[0196] Solve the total scattered light flux Φ according to the formula finally obtained in S222 S , the formula is as follows:

[0197]

[0198] Where i, j, C1, and C2 are all constants. If the light flux and transfer coefficient on the detector surface are known, the total scattered flux can be solved.

[0199] The solution to the scattered light distribution at each point position can be expressed as:

[0200]

[0201] The background noise flux is eliminated through the above calculation, and the total scattered light flux and the scattered light flux distribution are extracted from the final measurement results.

[0202] 4. Calibration and calibration of the light field meter in S3:

[0203] The light field meter calibration in S31 is as follows:

[0204] The calibration of the hemispherical light field meter uses the standard Lambertian surface as the calibration target. The angle mapping function in S1 and the noise elimination algorithm in S22 are used to calibrate and calibrate the measurement system. The calibration process is as follows: Figure 13 shown.

[0205] in Figure 13 (a) is the calibration process of the measurement system; Figure 13 (b) is the rectangular coordinate system of the detector in the angle mapping function; Figure 13 (c) The energy distribution of the scattering surface with Lambertian distribution obtained by Lighttools software through light screening during the simulation process does not contain noise after passing through the measurement system; Figure 13(d) irradiating a scattering surface with a Lambertian distribution with a light source in the spectral range of 380 nm to 780 nm at an incident angle of 30° to obtain an energy distribution that characterizes its scattering distribution characteristics; Figure 13 (e) Using a hemispherical light field meter, a sample with Lambertian distribution characteristics is measured with Figure 13 (d) Energy distribution obtained by measuring under the same incident light source conditions, where the energy distribution information includes the required scattered light field distribution information as well as noise information; Figure 13 (f) is the light field distribution information extracted after calibration of the measurement results, which can characterize the scattering distribution characteristics of the sample with an ideal Lambertian distribution.

[0206] according to Figure 13 (a) The measurement system is calibrated and the required scattered light field distribution information is extracted, which includes the following steps:

[0207] a. Establish the corresponding relationship between the spatial angle polar coordinate system and the rectangular coordinate system according to the angle mapping function of the measurement system ( Figure 13 (b));

[0208] b. Using Lighttools software to obtain the energy distribution matrix of the Lambertian surface without noise after passing through the measurement system by light screening during the simulation process and establish the corresponding relationship between energy distribution and spatial angle. By comparing it with the known ideal energy distribution matrix of the Lambertian surface ( Figure 13 (d) The ratio of the corresponding angle energy values determines the transfer coefficient matrix of the measurement system, which is composed of the energy transfer coefficient ε of the measurement system ij composition;

[0209] c. Using a hemispherical light field meter to measure the energy distribution of a sample with Lambertian distribution characteristics including noise ( Figure 13 (e)) The measurement data is processed according to a noise elimination algorithm, and light field distribution information that can characterize its scattering distribution characteristics is extracted (13(f)).

[0210] The light field meter calibration in S32 is as follows:

[0211] The measurement error distribution of the calibrated hemispherical light field meter is as follows: Figure 14 As shown, Figure 14 (a) is the spatial distribution cloud map of the calibration error of the measuring instrument. The azimuth angle area where the maximum error of the system is located is extracted to draw the error curve. Figure 14 As shown in (b), the maximum error positions are at the zenith angle of 73° and the azimuth angle of 200°, and at the zenith angle of 75° and the azimuth angle of 82°, with error values of 5.08% and -4.923% respectively. The average error within the full field of view measurement range of the system is the largest at 75.5°, with an error value of -0.397%.

[0212] 5. Analysis of the conclusions in S4:

[0213] During the further development of the hemispherical light field rapid measurement instrument, the measurement system was optimized, achieving 1° angular resolution measurement of scattered light field distribution without any moving parts. To further improve measurement performance, a calibration method for the system was developed, an angle mapping function model suitable for the measurement system was established, a noise elimination algorithm was proposed, and the noise elimination process was detailed. Based on the light scattering distribution characteristics of the Lambertian surface, the accuracy of the angle mapping function and noise elimination algorithm was verified. The hemispherical light field and measurement results were calibrated and calibrated. After calibration, the maximum measurement error was 5.08% at the zenith angle of 73° and the azimuth angle of 200°. Within the full field of view of the system, the average error was the largest at the zenith angle of 75.5°, at -0.397%.

[0214] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0215] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A multi-angle scattered light field rapid measurement system calibration technology, characterized in that: The steps include: S1: angle mapping function; S2: noise cancellation; S3: Calibration and calibration of light field measurement instrument; S4: Conclusion analysis.

2. The multi-angle scattered light field rapid measurement system calibration technology according to claim 1, characterized in that: The angle mapping function described in S1 includes the following steps: S11: measurement optical system; S12: Angle mapping relationship.

3. The multi-angle scattered light field rapid measurement system calibration technique according to claim 2, wherein the noise elimination in S2 comprises the following steps: S21: Noise cancellation principle; S22: Noise removal algorithm.

4. The multi-angle scattered light field rapid measurement system calibration technology according to claim 3, characterized in that: The noise elimination algorithm described in S22 includes the following steps: S221: Luminous flux distribution matrix establishment; S222: Luminous flux calculation equation is established; S223: Scattering flux solution.

5. The multi-angle scattered light field rapid measurement system calibration technology according to claim 4, characterized in that: The calibration and calibration of the light field meter described in S3 includes the following steps: S31: Light field meter calibration; S32: Calibration of light field meter.

6. The multi-angle scattered light field rapid measurement system calibration technology according to claim 5, characterized in that: The measurement optical system described in S11 is as follows: The optical system was optimized and improved to achieve measurement of the system zenith angle range of 0°-80° and the azimuth angle range of 0°-360°. The X and Y field of view directions of the optical system represent the azimuth and zenith angle directions of the measurement system. The field of view is established with an increment of 1° in the X and Y field of view directions centered at (0°, 0°) in the central field of view and (0°, 79°) at the edge field of view. The final optical system spot footprint diagram shows that the measurement angle resolution can reach 1°.

7. The multi-angle scattered light field rapid measurement system calibration technology according to claim 6, characterized in that: The angle mapping relationship described in S12 is as follows: The scattered light field acquisition imaging optical system is set up off-axis. In order to establish the correspondence between the scattered light distribution angle and the illumination received by the detector surface, ray tracing and numerical derivation are performed on the imaging acquisition optical system, and an angle mapping function calculation model is established based on the light field acquisition optical system. The model coordinate system is established in the Zemax Opticstudio global coordinate system according to the optical system. The O(0,0,0) point is the center of the hemispherical dome and also the origin of the coordinate system. The O′(0,75,0) point is the center of the optical axis of the optical system. ec =75mm is the off-axis distance of the optical system, R is the radius of the hemispherical dome, G is any point on the inner wall of the dome that carries the light field information, l i is the distance from this point to the center of the aspheric reflector, ω x 、ω y is the field of view of the optical system, θ s 、 is the zenith angle and azimuth angle of the scattered light at point G. First, the corresponding relationship between the field of view angle of the optical system and the scattered light angle is established. The formula is as follows: We can get: It is known that the projection coordinates of point G on the XOY plane are (x, y) = (l i sinω y cosω x , -l i sinω y sinω x +l ec ), we can get: Based on the object-image mapping relationship of the optical system transfer matrix, the relationship between the object point coordinates (x, y) and the image point coordinates (x′, y′) is as follows: in The mapping relationship between the optical system field angle and the scattered light angle is obtained as follows: The conversion relationship between the field of view angle of the optical system and the object point coordinates is (x, y) = u(ω x ,ω y ), and the mapping relationship between object points and image points is (x′, y′) T =A·(x,y) T .

8. The multi-angle scattered light field rapid measurement system calibration technology according to claim 7, characterized in that: The noise cancellation principle described in S21 is as follows: Due to the low reflectivity diffuse reflection coating of the dome inner wall material, it is assumed that its diffuse reflection characteristics are close to Lambertian reflection, and the LR illumination calculation model is established; Taking point S as the Lambertian reflection point, the main reflection direction of the Lambertian reflection has an intensity of I0, and the angle with the main reflection direction of the Lambertian reflection is The intensity of reflected light is recorded as We can get: The angle with the main direction of Lambertian reflection is Illuminance E at the illuminance test point P at a distance d from the main reflection point S P It can be expressed as: Establish a calculation model for the dome's "integral effect" background noise; Assume that point O is the center of the spherical dome, points N1, N2, and N3 are points on a certain arc of the hemispherical dome, and the reflectivity of the inner wall of the dome is ξ. According to the Lambertian surface orientation-hemispherical reflection characteristics, the reflection angle of any point on the inner wall of the low-reflectivity hemispherical dome is η. i The reflected light intensity I η It can be expressed as: The light flux scattered by the sample at the center of the hemisphere received by point N1 is recorded as φ1, and the light intensity I1 reflected twice by point N1 to point N3 is: The illuminance reflected from point N1 to point N3 can be expressed as: Where R1 = 2Rcosη1, the illumination reflected from point N1 to point N3 can be summarized as: Similarly, the illuminance E2 reflected from point N2 to point N3 can be calculated as: make is a constant, then the secondary illumination superposition generated by all points on the inner wall of the dome at point N3 can be expressed as: It can be obtained that the illumination at point N3 after secondary reflection has nothing to do with its position. When the dome scattering rate and dome size are determined, it is only related to the total scattered light flux of the sample measured at the center of the dome in the hemispherical space. The formula is as follows: AND Total ∝φ Total 。 9. The multi-angle scattered light field rapid measurement system calibration technology according to claim 8, characterized in that: The luminous flux distribution matrix described in S221 is established, and the specific contents are as follows: When the light source parameters are selected, the illumination E incident on the sample surface i Assuming that the total scattered light flux of the sample in the hemispherical space is Φ S , then the radiance can be expressed as: According to the noise calculation formula and E Total ∝φ Total It can be seen that the quadratic superimposed illuminance at each point on the inner wall of the hemispherical dome is linearly related to the total scattered light flux of the measured sample distributed in the hemispherical space, and the formula is as follows: According to the illuminance calculation formula Φ=E·ΔS, the background noise luminous flux at the inner wall of the dome is It is also linearly related to the total scattered light flux, and the formula is as follows: According to the coordinate system of the CCD surface in the angle mapping function, the CCD surface luminous flux distribution matrix M is established ij , the matrix is composed of the luminous flux received by the i-row and j-column coordinate points on the CCD surface, let We can get: Dome inner wall light field luminous flux distribution matrix S ij And the noise flux distribution matrix N ij Can be expressed as and The luminous flux calculation equation described in S222 is established, and the specific contents are as follows: The light flux at each point on the inner wall of the dome is scattered by the inner wall of the dome, collected by the optical system, and finally reaches the CCD surface. The transfer coefficient of the light flux at each point in this process is ε ij , the light flux of the light field and the noise flux after passing through the optical system and reaching each coordinate point on the CCD surface are respectively: The luminous flux of each coordinate point in the detector surface luminous flux distribution matrix is the superposition of the scattered light field flux and the noise flux passing through the corresponding point on the inner wall of the dome. The formula is as follows: M ij =e ij [S ij +N ij ]; The total scattered light flux on the sample surface is: Then the noise flux at each point on the inner wall of the dome is: The luminous flux at each point on the detector surface can be expressed as: According to M ij =ε ij [S ij +N ij ]、 and The equations are as follows: Let χ ij is the energy calibration normalization factor, C2 is the normalization constant coefficient, and the above equations can be sorted out as follows: The scattering flux solution described in S223 is as follows: Solve the total scattered light flux Φ according to the formula finally obtained in S222 S , the formula is as follows: The solution to the scattered light distribution at each point position can be expressed as:

10. The multi-angle scattered light field rapid measurement system calibration technology according to claim 9, characterized in that: The light field meter calibration described in S31 and the light field meter calibration described in S32 are as follows: The calibration of the hemispherical light field meter uses the standard Lambertian surface as the calibration target, and uses the angle mapping function in S1 and the noise elimination algorithm in S22 to calibrate and calibrate the measurement system.

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