Radiometer-based method and apparatus for measuring emissivity and transmissivity of a wave-transparent material

Abstract

The application discloses a radiometer-based emissivity and transmissivity measurement method and device of wave-transparent material, and belongs to the field of passive microwave / millimeter wave remote sensing and detection technology. The method comprises the following steps: preparing a blackbody material and a target material with the same physical temperature; constructing a uniform radiation environment, measuring the blackbody by using a radiometer to obtain a voltage measurement value V Abb ; placing a metal plate and the target material on the same position of the blackbody surface in sequence to measure corresponding radiation voltages V Ametal and V Atarget ; performing difference analysis on V Atarget , V Ametal and V Abb to obtain the sum of the emissivity and the transmissivity of the target material; irradiating the target material by using two kinds of radiation sources in sequence to measure radiation voltages V1 and V2; measuring the two kinds of radiation sources alone to obtain radiation voltages V3 and V4; and performing difference analysis on V1, V2, V3 and V4 to obtain the transmissivity of the target material. The application can eliminate the measurement error caused by the space solid angle occupied by the target, and realizes accurate measurement of the emissivity and the transmissivity of the wave-transparent material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of passive microwave / millimeter wave remote sensing and detection, and more particularly relates to a radiometer-based method and device for measuring the emissivity and transmissivity of a wave-transparent material. BACKGROUND

[0002] In nature, all physical materials with a temperature higher than absolute zero radiate energy in the form of electromagnetic waves, with a frequency range covering almost the entire band. Millimeter wave radiation detection technology has the advantages of all-weather, quasi-all-weather operation, concealment, and good penetration, and has important applications in remote sensing, target detection, and human safety inspection.

[0003] Millimeter wave emissivity is a key parameter for characterizing the millimeter wave radiation capability of a material object, and is also a key to interpreting millimeter wave radiation images. Generally, emissivity is related to the material and structural size of an object, and is a function of frequency, observation angle, and observation polarization. Accurate measurement of emissivity is a basic prerequisite for evaluating radiation characteristics, verifying radiation calculation models, and classifying and identifying based on radiation images. High-precision millimeter wave emissivity measurement methods are the basis for supporting accurate millimeter wave emissivity measurement.

[0004] The existing emissivity measurement methods such as brightness temperature method and voltage method are all proposed for non-wave-transparent material targets. Non-wave-transparent materials do not need to consider the transmission of background radiation when performing radiation measurement, while there is little research on emissivity measurement methods for wave-transparent materials in the field of millimeter wave remote sensing and detection. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a radiometer-based method and device for measuring the emissivity and transmissivity of a wave-transparent material, aiming to fill the gap in the field of millimeter wave remote sensing and detection for emissivity measurement methods for wave-transparent materials.

[0006] To achieve the above-mentioned purpose, the present application provides a radiometer-based method for measuring the emissivity and transmissivity of a wave-transparent material, and the measurement principle can be briefly described as follows:

[0007] When a radiometer is used to observe a scene at a very close distance, i.e. without considering path attenuation, the radiation intensity at the aperture of the radiometer antenna should be composed of three parts: the radiation of the scene itself, the reflection of the environmental radiation on the target surface, and the transmission of the background radiation. Based on the Rayleigh-King approximation and the Kirchhoff law, for a wave-transparent material, its brightness temperature T A is expressed as:

[0008] T A = eT PH + ρT G + γT B = eTPH + (1 - e - γ) T G + γ T B (1)

[0009] where T PH , T G , T B are the physical temperature of the target sample, the ambient radiation brightness temperature and the background radiation brightness temperature, respectively, and e, p and γ are the surface emissivity, the specular reflectivity and the transmissivity of the material, respectively.

[0010] In the physical temperature measurement of the target, the thermometer is usually used to measure the physical temperature of the target surface, and the measurement result is equivalent to the radiation measurement of the black body with the same physical temperature. If the background radiation brightness temperature T B is "calibrated" with the black body with the same physical temperature as its background, formula (1) can be expressed as:

[0011] T A = e T PH + (1 - e - γ) T G + γ T PH (2)

[0012] It can be obtained that:

[0013]

[0014] Based on the above formulas, the target material with "black body" as the background and the "black body" placed in the same position as the target material are measured by the radiometer, and the metal plate is measured alone, and T Atarget , T Abb and T Ametal are obtained, respectively:

[0015]

[0016]

[0017]

[0018] where T APtarget , T APbb , T APenvi are the apparent temperatures of the target material, the black body and the metal plate, respectively. T N (θ, φ) is the radiation brightness temperature of the non-target region covered by the beam, is the normalized directional diagram of the radiometer antenna, and Ω1 is the solid angle occupied by the target region in the antenna radiation directional diagram.

[0019] Then:

[0020]

[0021] Second step, the transmittance of the target, using the way of double radiation source, with the first radiation source irradiation of the object to be measured, and placed behind the object to be measured radiation meter, the antenna beam of the radiation meter aligns the center of the target, the radiation source, the center of the target and the antenna main beam center keep in the same straight line, T1 is measured, then the second radiation source is replaced by the first radiation source and measured again to get T2, then the first radiation source and the second radiation source are directly measured to get T3 and T4, the brightness temperature expression is respectively:

[0022] T1 = γT radio1 + eT pH + (1-e-γ)T G (8)

[0023] T2 = γT radio2 + eT pH + (1-e-γ)T G (9)

[0024] T3 = T radio1 (10)

[0025] T4 = T radio2 (11)

[0026] In the formula, T radio1 , T radio2 The brightness temperature of the first radiation source and the second radiation source respectively. Assuming that the environment does not change during the measurement, so the transmittance γ of the target material is expressed as:

[0027]

[0028] Substitute equation (7) to get the emissivity of the target material.

[0029] According to the calibration principle that the brightness temperature of radiation measurement is linearly related to the output voltage value of the radiometer, and the mathematical relationship based on the above method, the emissivity and transmittance method of the wave-transparent material based on the radiometer proposed by the application comprises the following steps:

[0030] (1) the target material and the same size of black body material are placed in the same temperature environment, so that the physical temperature of the target material and the black body material is the same;

[0031] (2) build a uniform radiation environment, the environmental radiation brightness temperature is not the same as the physical temperature of the black body material and the target material;

[0032] (3) fix the black body material, measure the fixed black body material with the radiometer, and get the voltage measurement value V Abb ;

[0033] (4) Put the metal plate and the target material on the same position of the surface of the blackbody material in turn, and measure the corresponding radiation voltage V under the same polarization mode and the same observation angle Ametal and V Atarget ;

[0034] (5) Perform difference analysis on V Atarget , V Ametal , and V Abb to obtain the sum of the emissivity and the transmissivity of the target material.

[0035] (6) Remove the blackbody material, fix the target material, adjust the adjustable intensity radiation source, and irradiate the fixed target material with the first radiation source and the second radiation source in turn. By adjusting the height of the radiation source to the ground, the radiation source, the target center, and the antenna main beam center are kept on the same straight line, and the radiation voltage of the target material is measured as V1 and V2 respectively.

[0036] (7) Remove the target material, and measure the first radiation source and the second radiation source separately to obtain the radiation voltage as V3 and V4 respectively.

[0037] (8) Perform difference analysis on V1, V2, V3, and V4 to obtain the transmissivity of the target material.

[0038] Further, the specific implementation of step (5) is that V Atarget is subtracted from V Ametal to obtain a first difference, V Atarget is subtracted from V Abb to obtain a second difference, and then the first difference is divided by the second difference to obtain the sum of the emissivity and the transmissivity of the target material.

[0039] Further, the specific implementation of step (8) is that the difference obtained by subtracting V3 from V4 is divided by the difference obtained by subtracting V1 from V2, which is the transmissivity of the target material. Then, the emissivity of the target material is obtained by subtracting the transmissivity from the result of the difference analysis in step (5).

[0040] Further, the specific implementation of step (4) is that the target material and the metal plate are placed on the surface of the blackbody material and are attached to the blackbody material.

[0041] Further, the radiation source of step (6) is adjustable in intensity. When the two intensity radiation sources irradiate the target material, their distances to the target material are equal. By adjusting the height of the radiation source to the observation level, the radiation source, the target center, and the antenna main beam center are kept on the same straight line.

[0042] Further, the present application has the beneficial effect that, by using the same physical temperature and the same size black body as the background, the background radiation does not need to be "calibrated" by a noise source, so that the measurement steps are simple and time-saving.

[0043] Further, all steps should be completed in a short time, which is in the order of minutes, so that the environment is basically unchanged during each measurement.

[0044] Another aspect of the present application provides a radiometer-based emissivity and transmissivity measurement device for wave-transparent materials, comprising a turntable, an adjustable intensity radiation source, a clamp, and a radiometer.

[0045] The adjustable intensity radiation source is fixed by the clamp, and the radiation source can adjust the radiation intensity, which is used to switch the radiation intensity for irradiating the black body material / metal plate / target material, and the main beam after transmission propagates to the radiometer fixed on the turntable, and the radiometer is used for radiation measurement of the black body material / metal plate / target material, and the emissivity and transmissivity of the target material are obtained based on the radiation voltage measured by the radiometer.

[0046] Further, the black body material is fixed, and the fixed black body material is measured by the radiometer to obtain the radiation voltage V Abb ; the metal plate and the target material are placed in the same position on the surface of the black body material in turn, and the radiometer is used for measurement under the same polarization mode and the same observation angle to obtain the radiation voltages V Ametal and V Atarget ; difference analysis is performed on V Atarget , V Ametal , and V Abb to obtain the sum of the emissivity and transmissivity of the target material.

[0047] By the above technical scheme conceived by the present application, compared with the prior art, the following beneficial effects can be achieved:

[0048] 1、The radiometer-based emissivity and transmissivity method and device for wave-transparent materials provided by the present application realize the elimination of the influence of environmental radiation, background radiation, and radiation outside the target area by using multiple auxiliary measurements, so as to realize the measurement of the emissivity and transmissivity of wave-transparent materials.

[0049] 2. The radiometer-based method for measuring the emissivity and transmittance of transparent materials provided by this invention can effectively eliminate errors introduced by beam sidelobes and overflow main lobes through difference analysis, which greatly improves the measurement accuracy of the emissivity and transmittance of transparent materials.

[0050] 3. This invention proposes a method and device for measuring the emissivity and transmittance of transparent materials based on a radiometer by "calibrating" the background radiation of the transparent materials, thus filling the gap in the measurement methods for the emissivity and transmittance of transparent materials in the field of millimeter-wave remote sensing and detection. Attached Figure Description

[0051] Figure 1 A flowchart illustrating the method for emissivity and transmittance of transparent materials based on a radiometer provided by this invention.

[0052] Figure 2 A schematic diagram of radiation measurement for the radiometer-based method for measuring the emissivity and transmittance of transparent materials provided by this invention;

[0053] Figure 3 A schematic diagram of the structure of the radiometer-based device for measuring the emissivity and transmittance of transparent materials provided by the present invention. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0055] like Figure 1 As shown, the method for emissivity and transmittance of transparent materials based on radiometers proposed in this invention specifically includes the following steps:

[0056] (1) Place the target material and a blackbody of the same size in the same temperature environment so that the physical temperatures of the target material and the blackbody material are the same;

[0057] (2) Construct a uniform radiation environment where the ambient radiation brightness temperature is different from the physical temperature of the blackbody material and the target material;

[0058] (3) Fix the blackbody material and use a radiometer to measure the fixed blackbody material to obtain the voltage measurement value V. Abb ;

[0059] (4) Place metal plates and target materials of the same size at the same positions on the surface of the blackbody, and measure the corresponding radiation voltages V. Ametal and V Atarget ;

[0060] (5) using V Atarget , V Ametal , V Abb to perform difference analysis to obtain the sum of the emissivity and transmissivity of the target material. Specifically, V

[0061] V Atarget is subtracted from V Ametal to obtain a first difference, V Atarget is subtracted from V Abb to obtain a second difference, and the first difference is divided by the second difference to obtain the sum of the emissivity and transmissivity of the target material, which is expressed by the formula:

[0062]

[0063] (6) Then, the transmissivity of the target material is measured. Specifically,

[0064] The blackbody material is removed, the target material is fixed, the adjustable intensity radiation source is adjusted, the first radiation source and the second radiation source with different intensities are used to irradiate the fixed target material in turn, the height of the radiation source to the ground is adjusted so that the radiation source, the target center and the antenna main beam center are kept on the same straight line, and the radiation voltages of the target material are measured as V1 and V2; the target material is removed, and the first radiation source and the second radiation source are measured separately to obtain the radiation voltages V3 and V4; difference analysis is performed using V1, V2, V3 and V4 to obtain the transmissivity of the target material. It is expressed by the formula:

[0065]

[0066] In combination with formula (13), the expression of the emissivity is:

[0067]

[0068] More specifically, in step (6), the distance between the two intensity radiation sources and the target material is equal; by adjusting the height of the radiation source to the observation level, the radiation source, the target center and the antenna main beam center are kept on the same straight line; during the four measurement processes, the distance between the radiometer and the noise source is unchanged. Figure 2 The radiation measurement schematic diagram of the method for measuring the emissivity and transmissivity of the wave-transparent material based on the radiometer provided by the present application is shown in the figure.

[0069] More specifically, the blackbody in steps (1) to (4) adopts a 500mm×500mm foam wave-absorbing material.

[0070] The present application also provides a device for measuring the emissivity and transmissivity of the wave-transparent material based on the radiometer, as shown in the figure, which comprises a turntable, an adjustable intensity radiation source, a clamp and a radiometer. Figure 3 ​

[0071] The adjustable intensity radiation source is fixed by a clamp. The radiation source can adjust the radiation intensity to switch the radiation intensity for irradiating the blackbody material / metal plate / target material. The transmitted main beam propagates to a radiometer fixed on a turntable. The radiometer is used to measure the radiation of the blackbody material / metal plate / target material. The emissivity and transmittance of the target material are obtained based on the radiation voltage measured by the radiometer.

[0072] Furthermore, the blackbody material is fixed, and the fixed blackbody material is measured using a radiometer to obtain the radiation voltage V. Abb The metal plate and the target material were placed sequentially at the same position on the surface of the blackbody material, and the radiation voltage V was obtained by measuring it with a radiometer under the same polarization and observation angle. Ametal and V Atarget ; Using V Atarget V Ametal V Abb Difference analysis was performed to obtain the sum of the emissivity and transmittance of the target material. The blackbody material was removed, and the target material was fixed. The adjustable intensity radiation source was adjusted, and the fixed target material was irradiated successively with the first and second radiation sources. By adjusting the height of the radiation source from the ground, the center of the radiation source, the target, and the center of the antenna main beam were kept on the same straight line, and the radiation voltages of the target material were measured as V1 and V2, respectively. The target material was removed, and the first and second radiation sources were measured separately, and the radiation voltages were obtained as V3 and V4, respectively. Difference analysis was performed using V1, V2, V3, and V4 to obtain the transmittance of the target material.

[0073] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for measuring the emissivity and transmissivity of a wave-transparent material based on a radiometer, characterized in that, The method comprises the following steps: (1) placing the target material and the blackbody material of the same size in the same temperature environment, so that the physical temperature of the target material and the blackbody material is the same; (2) constructing a uniform radiation environment, wherein the radiation brightness temperature of the environment is different from the physical temperature of the blackbody material and the target material; (3) The blackbody material is fixed, and a radiometer is used to measure the fixed blackbody material to obtain a voltage measurement value V Abb ; (4) The same size metal plate and target material are placed in the same position on the surface of the black body material in turn, and the corresponding radiation voltage is measured under the same polarization mode and the same observation angle V Ametal and V Atarget ; (5) using V Atarget , V Ametal , V Abb performing difference analysis to obtain the sum of the emissivity and the transmissivity of the target material; (6) remove the blackbody material, fix the target material, adjust the radiation source, irradiate the fixed target material with the first radiation source and the second radiation source in turn, adjust the height of the radiation source to the ground, so that the radiation source, the target center and the antenna main beam center are kept on the same straight line, and the radiation voltages of the target material are measured as V 1 and V 2 respectively; (7) The target material is removed, and the first and second radiation sources are measured separately, and the radiation voltages are obtained as V 3 and V 4, respectively. (8) Use V 1, V 2, V 3 and V 4 to perform difference analysis to obtain the transmittance of the target material.

2. The measurement method according to claim 1, characterized in that, The specific implementation mode of the step (5) is: Subtracting V Atarget Subtracting V Ametal Obtaining a first difference, V Atarget Subtracting V Abb Obtaining a second difference, and dividing the first difference by the second difference to obtain the sum of the emissivity and the transmissivity of the target material.

3. The measurement method according to claim 1, characterized in that, The specific implementation mode of the step (8) is: Use V 4Subtract V 3Divide the resulting difference by V 2Subtract V 1The resulting difference is the transmittance of the target material. Subtract the transmittance from the result of the difference analysis in step (5) to obtain the emissivity of the target material.

4. The measurement method according to claim 1, characterized by, The specific implementation mode of the step (4) is that the target material and the metal plate are placed on the surface of the blackbody material and are attached to the blackbody material.

5. The measurement method according to claim 1, characterized by, The radiation intensity of the radiation source of the step (6) is different; when the target material is irradiated by the radiation sources of two intensities, the distance of the target material to the radiation sources is equal; by adjusting the height of the radiation source to the observation level, the radiation source, the target center and the antenna main beam center are kept on the same straight line.

6. The measurement method according to claim 1, characterized by, The measurement time is in minutes, so that the environment is basically unchanged during each measurement.

7. The method of claim 1, wherein, During the measurement, the angle between the antenna main beam of the radiometer and the connecting line of the target center is always unchanged.

8. A device for measuring emissivity and transmissivity of a wave-transparent material based on a radiometer, characterized in that, The device comprises a turntable, a radiation source, a clamp and a radiometer; The radiation source is fixed by the clamp and is used for switching the radiation intensity for irradiating the blackbody material / metal plate / target material; the main beam after transmission is transmitted to the radiometer fixed on the turntable; the radiometer is used for measuring the radiation of the blackbody material / metal plate / target material; the emissivity and the transmissivity of the target material are obtained based on the radiation voltage measured by the radiometer; Fixing the blackbody material, measuring the fixed blackbody material by the radiometer to obtain a radiation voltage V Abb ; placing the metal plate and the target material in the same position on the surface of the blackbody material in turn, measuring by the radiometer under the same polarization mode and the same observation angle to obtain a radiation voltage V Ametal and V Atarget ; using V Atarget , V Ametal , V Abb performing difference analysis to obtain the sum of the emissivity and the transmissivity of the target material; The target material is also fixed, the radiation source is adjusted, the fixed target material is irradiated by the first radiation source and the second radiation source in turn, the height of the radiation source to the ground is adjusted, the radiation source, the target center and the antenna main beam center are kept on the same straight line, the radiation voltages of the target material are measured as V 1 and V 2 respectively; the target material is removed, the first radiation source and the second radiation source are measured separately, the radiation voltages are obtained as V 3 and V 4 respectively; difference analysis is carried out by using V 1, V 2, V 3 and V 4, and the transmittance of the target material is obtained.

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