Bidirectional reflection distribution function multispectral measurement method and system based on blackbody radiation source

Abstract

The invention provides a bidirectional reflectance distribution function (BRDF) multispectral measurement method and system based on a blackbody radiation source, belongs to the technical field of bidirectional reflectance distribution function measurement, and is used for reflectance spectrum distribution measurement of materials at different wavebands and detection angles. An existing BRDF measurement method is generally limited by a light source, and BRDF distribution measurement under different wave bands is difficult to achieve. The mode that the blackbody radiation source and the optical filter are combined is adopted, the needed wave band can be selected autonomously, the two concave mirrors are used for light path adjustment and convergence to obtain the high signal-to-noise ratio, and meanwhile the high spatial resolution is obtained by carrying independent motion systems of the six-axis mechanical arm and the annular guide rail. During specific measurement, the blackbody radiation source is heated to a set temperature, light paths are adjusted through the two concave mirrors to converge light beams, and different optical filters are utilized to select corresponding wave bands for measurement. According to the method and the system, complete measurement of the BRDF is realized, and the method and the system have a wide application prospect in the aspect of material optical parameter measurement.

Description

Technical Field

[0001] The present invention proposes a method and system for multi-spectral measurement of bidirectional reflectance distribution function (BRDF) based on a blackbody radiation source, which belongs to the technical field of bidirectional reflectance distribution function measurement. The method and system combine a blackbody radiation source with a filter, breaking the limitation of the light source in measuring BRDF in different bands, and realizing multi-spectral measurement of BRDF. Background Art

[0002] Bidirectional Reflectance Distribution Function (BRDF) is a basic physical quantity that represents the spatial reflection characteristics of a material surface. It describes the distribution of reflected light from an incident light from a specified direction reflected from the material surface to all directions in space. It is defined as the ratio of the reflected brightness of a target in a certain direction to the illuminance in the incident direction.

[0003] The light source of the traditional BRDF measurement system is a single wavelength, and the detection results are difficult to meet the BRDF distribution of the required bands under different working conditions. If multiple sets of light sources and tunable lasers are prepared, the cost is high and the operation is complicated. The present invention combines a blackbody radiation source with a filter to solve the limitation of the light source when measuring BRDF in different bands, modulates and converges the incident light to obtain a high signal-to-noise ratio, and the six-axis mechanical arm and the circular guide rail cooperate to obtain high spatial resolution. By replacing different filters, a complete measurement of multi-spectral BRDF is achieved. Summary of the invention

[0004] In view of the problem that traditional BRDF measurement methods are generally limited by the wavelength of the light source, the present invention proposes a bidirectional reflectance distribution function (BRDF) multispectral measurement method and system based on a blackbody radiation source. This method adopts a combination of a blackbody radiation source and a filter to solve the limitation of the light source when measuring BRDF in different bands. At the same time, the incident light is modulated and focused to obtain a high signal-to-noise ratio, and the coordinated movement of the six-axis robotic arm and the circular guide rail obtains high spatial resolution.

[0005] The system consists of a blackbody radiation source, an aperture, a chopper, a concave mirror 1, a concave mirror 2, a sample to be tested, a filter, a photodetector, a six-axis robotic arm, a circular guide, a data acquisition card and a host computer. Except for the host computer, the above experimental devices are all placed on the same optical platform, and all experimental measurements are completed in an optical darkroom; the blackbody radiation source emits incident light with a wide spectrum, the aperture adjusts the intensity of the light beam, the chopper modulates the incident light into a fixed frequency and removes noise through filtering, the concave mirrors 1 and 2 adjust the light path to converge the light beam, and the modulated and converged light beam is irradiated on the surface of the sample to be tested, the sample to be tested is mounted on the six-axis robotic arm, and the reflection The incident light is detected by filters and photodetectors, which are installed on the circular guide rail. The detection signals of different illumination and detection angles are obtained through the rotation of the six-axis robot and the circular guide rail. The reflected signal of the detection surface is collected through the data acquisition card and uploaded to the host computer. The incident signal is calculated by measuring the hemispherical emissivity of the standard sample and uploaded to the host computer. The demodulation and filtering processing are performed in the host computer to obtain the reflected signal with a high signal-to-noise ratio. The BRDF distribution is obtained through numerical calculation and visualization technology. The black body radiation source is matched with different filters to realize multi-spectral BRDF measurement. The specific measurement steps are as follows:

[0006] Step 1: A BRDF multi-spectral measurement method and system based on a blackbody radiation source according to claim 1, characterized in that a blackbody radiation source is used in combination with a filter to measure the material reflection signal, and a high-precision measurement of the reflection intensity of the detection surface in different bands and detection angles is achieved through a six-axis robotic arm and a circular guide rail; first, the blackbody radiation source is heated to a set temperature to emit incident light with a wide spectrum, and the incident signal U is calculated by measuring the hemispherical emissivity of the standard sample. i (λ), where λ is the wavelength of the light source. The incident light is adjusted by the aperture to adjust the area and intensity of the light, and then modulated by the chopper to a fixed frequency. The light path is adjusted by two concave mirrors to converge the light beam to obtain a high signal-to-noise ratio. The relationship between the object distance, image distance and focus is determined by the concave mirror imaging principle:

[0007] 1 / d1+1 / d2=1 / f (6)

[0008] In the formula, d1 is the object distance, d2 is the image distance, f is the focal length of the concave mirror, and the modulated and converged incident light is irradiated on the surface of the sample to be tested. The incident direction is in, and θ i are the incident azimuth and zenith angle in the hemispherical space respectively. The distance between the detector and the laser irradiation point on the sample under test is D, and it is located at The reflection direction of and θ rThey are the reflection azimuth and zenith angle of the hemispherical space respectively. The reflected light passes through the filter to select the band, is detected by the photoelectric detector, and is collected in real time through the data acquisition card and uploaded to the host computer. The reflected signal is demodulated and filtered in the host computer to obtain The BRDF of the sample surface is the wavelength λ, the incident zenith angle θ i , incident azimuth Reflection zenith angle θ r and the reflected emission azimuth Since the detector has a certain aperture size, the measurement form of BRDF can be expressed as

[0009]

[0010] Where U r and U i are the reflected signal and the incident signal respectively, Ω r is the solid angle of the detection aperture.

[0011] Ω r =A / D 2 (8)

[0012] Where A is the surface area of ​​the detector and D is the distance from the center of the sample to the detector.

[0013] Step 2: A BRDF multi-spectral measurement method and system based on a blackbody radiation source according to claim 1, characterized in that the six-axis robotic arm and the circular guide rail are equipped with independent motion systems to obtain high resolution in hemispherical space. In the measurement system, the sample to be tested is installed on the six-axis robotic arm, and the filter and the photodetector are installed on the circular guide rail. First, the six-axis robotic arm and the circular guide rail are in the initial position, and the incident light is irradiated on the center of the sample to be tested. Through the coordinated movement of the six-axis robotic arm and the circular guide rail, the incident light is ensured to be φ on the sample to be tested. i ,θ i The irradiation point remains unchanged, the robot arm drives the sample to rotate around the incident light direction to the position of γ = (0, Δγ, 2Δγ, ..., π) and remains stationary, and the circular guide rail drives the detector from the reflection zenith angle θ r = -90° position and move continuously to θ r = 90°, the calculation formula of the rotation angle δ is as follows:

[0014] δ=-arctan(cotθ i / cosγ) (9)

[0015] If the detection range is the BRDF of the hemispherical space, the angle range of the detector rotation is:

[0016] [δ min ,δ max]=[-arctan(cotθ i / cosγ),π-arctan(cotθ i / cosγ)] (10)

[0017] Finally, the upper computer performs numerical calculation and visualization of formula (7) to obtain the hemispherical BRDF distribution of the surface of the measured sample. After completing this measurement, different filters are replaced and measured again to obtain the BRDF distribution in different bands, thus realizing the complete measurement of multi-spectral BRDF. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The invention is a typical structural diagram of a bidirectional reflectance distribution function multi-spectral measurement method and system based on a blackbody radiation source, and is composed of the following parts: a blackbody radiation source (1), an aperture (2), a chopper (3), a concave mirror 1 (4), a concave mirror 2 (5), a sample to be measured (6), a filter (7), a photodetector (8), a data acquisition card (9), a host computer (10), a circular guide rail (11), and a six-axis robotic arm (12).

[0019] Figure 2 It is a flow chart of the bidirectional reflectance distribution function measurement based on a blackbody radiation source.

[0020] Figure 3 It is a light path design diagram.

[0021] Figure 4 It is the BRDF distribution diagram measured in different bands. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with examples.

[0023] The structure of the present invention is as follows Figure 1As shown, a black body radiation source (1) emits incident light with a wide spectrum, an aperture (2) adjusts the intensity of the light beam, a chopper (3) modulates the incident light into a fixed frequency and removes noise through filtering, a concave mirror 1 (4) and a concave mirror 2 (5) adjust the light path to converge the light beam, and the modulated and converged light beam is irradiated on the surface of a sample to be tested (6), the sample to be tested is mounted on a six-axis robot arm (12), and the reflected light is detected by a filter (7) and a photodetector (8), the filter and the photodetector are mounted on a circular guide rail (11), and the six-axis robot is controlled by a host computer (10). The mechanical arm and the circular guide rail rotate to obtain detection signals of different illumination and detection angles, and the detection surface reflection signal is collected through the data acquisition card (9) and uploaded to the host computer; the incident signal is calculated by measuring the hemispherical emissivity of the standard sample and uploaded to the host computer; demodulation and filtering are performed in the host computer to obtain a reflection signal with a high signal-to-noise ratio, and the BRDF distribution is obtained through numerical calculation and visualization technology. The black body radiation source is matched with different filters to realize multi-spectral BRDF measurement. The specific process flow chart of the bidirectional reflection distribution function measurement based on the black body radiation source is as follows: Figure 2 As shown, the following steps are included:

[0024] Step 1: This example takes the high-temperature alloy MA956 sample as an example. The diameter of the sample to be tested is 50mm, the temperature of the blackbody radiation source is set to 1050℃, and the adjustable aperture is used to adjust the area and intensity of the incident light. The incident light is modulated into a fixed frequency of 200Hz by a chopper, and a filter is used to remove noise. The diameter of the concave spherical reflector used is Ф=75mm, and the focal length is f=500mm. The object distance and image distance are determined to converge the incident light to the surface of the sample to be tested. The reflected light is detected by the filter and the photodetector. The filter uses 3~5μm, 5~9μm and 8~14μm bandpass filters, which are installed in the filter wheel in sequence. The photodetector uses a HgCdTe detector with a response wavelength of 2~24μm. The optical path design diagram is as follows Figure 3 By measuring the hemispherical emissivity of the standard sample, the incident signal value is obtained by integral calculation.

[0025] Step 2: The host computer controls the six-axis robot and the circular guide rail to rotate to the initial position, and the incident light is irradiated on the center of the sample to be tested, with an incident azimuth angle of φ i is 0°, the incident zenith angle θ i The six-axis robot and the circular guide rail move in coordination to ensure that the incident light is φ i ,θ i The irradiation point remains unchanged, the robot arm drives the sample to rotate around the incident light direction with an angle γ in the range of [0,π], with an interval of 10°, and the circular guide rail drives the detector from the reflection zenith angle θ r = -90° position and move continuously to θ r= 90°, and the data is collected in real time by the data acquisition card and uploaded to the host computer. The reflected signal value is obtained by demodulation and filtering in the host computer. Then the BRDF distribution diagram is obtained by numerical calculation and visualization technology through the host computer. By replacing different filters with the filter wheel and repeating the experimental steps, the BRDF distribution in different bands is obtained. The BRDF distribution diagram is shown in the figure. Figure 4 As shown, the complete measurement of multi-spectral BRDF is achieved.

[0026] The above description of the present invention and its embodiments is not limited thereto, and the accompanying drawings are only one embodiment of the present invention. Without departing from the purpose of the present invention, any structure or embodiment similar to the technical solution designed without creativity shall fall within the protection scope of the present invention.

Claims

1. A bidirectional reflectance distribution function (BRDF) multi-spectral measurement method and system based on a blackbody radiation source, the system comprises a blackbody radiation source, an aperture, a chopper, a concave mirror 1, a concave mirror 2, a sample to be tested, a filter, a photodetector, a six-axis robot, a circular guide rail, a data acquisition card and a host computer. Except for the host computer, the above experimental devices are all placed on the same optical platform, and all experimental measurements are completed in an optical darkroom; a blackbody radiation source emits incident light with a wide spectrum, the aperture adjusts the intensity of the light beam, the chopper modulates the incident light into a fixed frequency and removes noise through filtering, the concave mirrors 1 and 2 adjust the optical path to converge the light beam, and the modulated and converged light beam is irradiated on the surface of the sample to be tested The sample to be tested is installed on a six-axis robotic arm, and the reflected light is detected by filters and photodetectors. The filters and photodetectors are installed on a circular guide rail. The detection signals of different illumination and detection angles are obtained through the rotation of the six-axis robotic arm and the circular guide rail. The reflected signal of the detection surface is collected through a data acquisition card and uploaded to the host computer. The incident signal is calculated by measuring the hemispherical emissivity of the standard sample and uploaded to the host computer. Demodulation and filtering are performed in the host computer to obtain a reflected signal with a high signal-to-noise ratio. The BRDF distribution is obtained through numerical calculation and visualization technology, and multi-spectral BRDF measurement is realized by using a blackbody radiation source with different filters.

2. A BRDF multi-spectral measurement method and system based on a blackbody radiation source according to claim 1, characterized in that: The blackbody radiation source is used in combination with the filter to measure the material reflection signal, and the six-axis robot and the circular guide rail are used to achieve high-precision measurement of the reflection intensity of the detection surface in different bands and detection angles. First, the blackbody radiation source is heated to the set temperature to emit incident light with a wide spectrum, and the incident signal U is calculated by measuring the hemispherical emissivity of the standard sample. i (λ), where λ is the wavelength of the light source. The incident light is adjusted by the aperture to adjust the area and intensity of the incident light. The chopper modulates the fixed frequency and the concave mirror converges the light beam. The modulated and converged incident light is irradiated on the surface of the sample under test. The incident direction is in, and θ i are the incident azimuth and zenith angle in the hemispherical space respectively. The distance between the detector and the laser irradiation point on the sample under test is D, and it is located at The reflection direction of and θ r They are the reflection azimuth and zenith angle in the hemispherical space respectively. The reflected light passes through the filter to select the band, is detected by the photodetector, and is collected in real time by the data acquisition card and uploaded to the host computer. The host computer performs demodulation and filtering to obtain (1) the reflection signal The BRDF of the sample surface is the wavelength λ, the incident zenith angle θ i , incident azimuth Reflection zenith angle θ r and the reflected emission azimuth Since the detector has a certain aperture size, the measurement form of BRDF can be expressed as Where U r and U i are the reflected signal and the incident signal respectively, Ω r is the solid angle of the detection aperture. Oh r =A / D 2 (2) Where A is the surface area of ​​the detector and D is the distance from the center of the sample to the detector. In the measurement system, the sample to be tested is installed on a six-axis robotic arm, and the filter and photodetector are installed on a circular guide rail. First, the six-axis robotic arm and the circular guide rail are in the initial position, and the incident light is irradiated on the center of the sample to be tested. Through the coordinated movement of the six-axis robotic arm and the circular guide rail, the incident light is ensured to be on the center of the sample to be tested. The irradiation point remains unchanged, the robot arm drives the sample to rotate around the incident light direction to the position of γ = (0, Δγ, 2Δγ, ..., π) and remains stationary, and the circular guide rail drives the detector from the reflection zenith angle θ r = -90° position and move continuously to θ r = 90°, the calculation formula of the rotation angle δ is as follows: δ=-arctan(cotθ i / cosγ) (3) If the detection range is the BRDF of the hemispherical space, the angle range of the detector rotation is: [δ min ,δ max ]=[-arctan(cotθ i / cosγ),π-arctan(cotθ i / cosγ)] (4) The upper computer performs numerical calculation and visualization of formula (1) to obtain the hemispherical BRDF distribution of the surface of the measured sample. After replacing the filter, measure again to obtain the BRDF distribution in different bands.

3. A BRDF multi-spectral measurement method and system based on a blackbody radiation source according to claim 1, characterized in that: Use two concave mirrors to adjust the optical path, converge the light beam to obtain a high signal-to-noise ratio, and determine the relationship between the object distance, image distance and focus through the concave mirror imaging principle: 1 / d1+1 / d2=1 / f (5) In the formula, d1 is the object distance, d2 is the image distance, and f is the focal length of the concave mirror.

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