A method for calculating the surface radiance of infrared extended source

Abstract

The present invention relates to a method for calculating the radiant illumination of an infrared extended source surface. By dividing the infrared extended source surface into grid surface sources, the radiation calculation between the infrared extended sources is converted into the radiation calculation between the grid surface sources. By looping through the grid surface sources, the radiant illumination cache of the grid surface sources is accumulated and calculated. By calculating the multi-level radiant illumination cache, the radiant illumination distribution of the infrared extended source surface is obtained. The method performs radiation transmission calculation from the scale of the grid surface source, takes into account the multiple reflections between the surface sources, and the calculation is closer to the real physical situation, and a more accurate radiant illumination distribution of the extended source surface can be obtained. The radiation transfer between the infrared extended source surfaces is discretized into the radiation transfer between the grid surface sources. Compared with the Monte Carlo method, the random noise caused by random sampling is avoided, and a stable and convergent result can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared emissivity testing and analysis, and in particular relates to a method for calculating the surface radiant illumination of an infrared extended source. Background Art

[0002] Infrared emissivity is one of the important parameters in infrared physics and technology. The infrared emissivity measurement methods are mainly divided into two categories: direct method and indirect method. The direct method measures according to the definition of emissivity, and the indirect method measures through the relationship between emissivity and reflectivity. The irradiation reflection method is a kind of indirect method. This method is: using an infrared radiation source, radiating twice to the target and the reference body respectively. The energy of the two radiations is different. The infrared thermal imager is used to receive the radiation brightness reflected by the target surface and the reference surface. The infrared emissivity of the target is calculated based on the difference between the radiation brightness of the target surface and the radiation brightness reflected by the reference surface.

[0003] The irradiance reflection method can realize non-contact measurement, and has the advantages of large measurement area and simple operation, but the measurement requires knowing the irradiance distribution on the surface of the target and the reference body. When the distance between the radiation source and the target and the reference body is far, the irradiance on the target surface is approximately uniform, and the irradiance distribution on the surface of the target and the reference body can be obtained through theoretical calculation. However, according to the principle of radiation transmission, the radiation intensity decays rapidly with the increase of the transmission distance. In order to increase the radiation energy to obtain a higher signal-to-noise ratio and better measurement effect, it is necessary to reduce the distance between the radiation source and the target. In this case, the irradiance distribution on the target surface cannot be simply considered to be uniform, and the reflection of radiation between the surfaces will also change the irradiance distribution. Therefore, it is necessary to correct these influencing factors in order to more accurately measure the emissivity.

[0004] The widely used numerical calculation method for irradiance is the Monte Carlo method, which can simulate the actual propagation process of light, so it can take into account the influence of radiation reflection between surfaces. However, the Monte Carlo method is based on random simulation and needs to obtain results through a large number of random sampling statistics. Therefore, the calculation results inevitably contain random noise, which limits the application of the Monte Carlo method in emissivity measurement correction. Therefore, it is urgent to develop a new general infrared extended source calculation method to solve this problem. Summary of the invention

[0005] In order to improve the accuracy of measuring the infrared emissivity of a target by using the irradiance reflection method, the present invention proposes a method for calculating the surface radiance of an infrared extended source.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A method for calculating the surface radiance of an infrared extended source comprises the following steps:

[0008] Step 1: Get the grid surface source set involved in the calculation

[0009] Taking the infrared extended source surface as the research object, all infrared extended source surfaces participating in the calculation are divided into structural grids, each structural grid corresponds to a grid surface source, and there are n grid surface sources in total, where n is a natural number greater than 2. The grid surface sources are numbered from 1 to n, and the numbered grid surface sources are marked as the nth grid surface source, referred to as grid surface source n. In addition, the number n must ensure that any two non-coplanar grid surface sources obtained by the division meet the small surface source condition, that is, the distance between any two non-coplanar grid surface sources must be greater than or equal to 10 times the maximum linear dimension of the two surface sources, and the set from the first grid surface source to the nth grid surface source is the set of grid surface sources participating in the calculation.

[0010] At this point, the set of grid surface sources involved in the calculation is obtained.

[0011] Step 2: Calculate the level l irradiance cache of any computational grid surface source

[0012] The i-th grid surface source is selected as the calculation grid surface source, i is a positive integer less than or equal to n; the other grid surface sources except the i-th calculation grid surface source are the j-th traversed grid surface source, j is a positive integer less than or equal to n, and j≠i. The numbers of the calculation grid surface source and the traversed grid surface source are the same as the numbers of the grid surface source.

[0013] Then the l-th level radiance cache of the i-th calculation grid surface source selected by the j-th traversed grid surface source is calculated. l is a natural number.

[0014] The irradiance cache of the selected i-th calculation grid surface source is the sum of the l-th level irradiance caches emitted by all traversed grid surface sources to the selected i-th calculation grid surface source. At this time, l is a natural number, which is expressed by the following formula:

[0015]

[0016] In formula (3), Calculates the level l irradiance cache for the i-th grid surface source.

[0017] Step 3: Get the set of level l irradiance caches of all grid surface sources

[0018] After the infrared extended source surface is divided, n grid surface sources are formed. Step 2 obtains the l-th level radiance cache of the ith calculation grid surface source. The l-th level radiance cache of each grid surface source is taken as an element of the set to form the l-th level radiance cache set of all grid surface sources, which is expressed as:

[0019]

[0020] In formula (4), E (l) A collection of level l irradiance caches for all mesh surface sources.

[0021] The set of level l irradiance caches E for all mesh surface sources (l) The maximum value in It is expressed as follows:

[0022]

[0023] As the value of l increases, it decreases gradually, that is, when When the convergence threshold is reached for the first time, the l value reaches its maximum value, which is called l max .

[0024] At this point, the l-th level radiance cache set of all grid surface sources is obtained.

[0025] Step 4: Obtain the radiant illumination distribution on the surface of the infrared extended source

[0026] For all grid surface sources obtained in step 3, from level 1 to level 1 max The radiance distribution of the infrared extended source surface is obtained by summing the level radiance cache set, as shown in the following formula:

[0027]

[0028] In formula (7), E is the radiant illumination distribution on the surface of the infrared extended source, and the symbol Represents the corresponding addition of set elements, E (1) 、E (2) , The first, second, and lth levels of all grid surface sources are max Level irradiance cache.

[0029] At this point, the radiant illumination distribution on the surface of the infrared extended source is obtained.

[0030] The above infrared extended source surface radiance calculation method, the jth traversed grid surface source is the lth level radiance cache of the i-th calculation grid surface source selected The calculation process is:

[0031] When l = 1, the calculation formula for the radiance cache is:

[0032]

[0033] In formula (1), L is the first-level radiance cache emitted by the jth traversed grid surface source to the i-th selected calculation grid surface source. j is the radiance of the jth traversed grid surface source, ΔA j is the area of ​​the jth traversed grid surface source, d i,j is the distance between the jth traversed grid surface source and the i-th selected calculation grid surface source, θ j and θ i They are the angles between the center line of the j-th traversed mesh surface source and the i-th selected calculation mesh surface source and their respective normal directions.

[0034] When l>1, the calculation formula of the radiance cache is:

[0035]

[0036] In formula (2), The l-th level radiance cache of the j-th traversed grid surface source for the i-th selected calculation grid surface source at the l-th level, f j is the bidirectional reflectance distribution function of the jth traversed grid surface source, is the l-1th level radiance cache of the jth traversed grid surface source, ΔA j is the area of ​​the jth traversed grid surface source, d i,j is the distance between the jth traversed grid surface source and the i-th selected calculation grid surface source, θ j and θ i They are the angles between the center line of the j-th traversed mesh surface source and the i-th selected calculation mesh surface source and their respective normal directions.

[0037] The above infrared extended source surface irradiance calculation method, the first level irradiance cache set E of all grid surface sources (l) The maximum value in As the value of l increases, it decreases gradually, that is:

[0038]

[0039] when When the convergence threshold is reached for the first time, that is, when equation (6) is satisfied for the first time, the l value reaches its maximum value, and the l value at this time is called l max .

[0040]

[0041] In formula (6), E threshold =10 -15 .

[0042] The beneficial effects of the present invention are:

[0043] A method for calculating the surface radiance of an infrared extended source performs radiation transmission calculations at the scale of a grid surface source, taking into account multiple reflections between surface sources. The calculation is closer to the actual physical situation and can obtain a more accurate distribution of the surface radiance of the extended source.

[0044] A method for calculating the radiant illumination of an infrared extended source surface discretizes the radiation transfer between infrared extended source surfaces into radiation transfer between grid surface sources. Compared with the Monte Carlo method, it avoids the random noise caused by random sampling and can obtain stable and convergent results.

[0045] A method for calculating the surface radiance of an infrared extended source can effectively calculate the radiance distribution of a target surface regardless of the distance of the radiation source, thereby realizing the correction of radiance non-uniformity in emissivity measurement. DETAILED DESCRIPTION

[0046] Example

[0047] A method for calculating the radiance of an infrared extended source surface is provided. The method divides the infrared extended source surface into grid surface sources, converts the radiation calculation between the infrared extended sources into the radiation calculation between the grid surface sources, loops through the grid surface sources, accumulates and calculates the radiance cache of the grid surface sources, and calculates the multi-level radiance cache to obtain the radiance distribution of the infrared extended source surface. The method specifically includes the following steps:

[0048] Step 1: Get the grid surface source set involved in the calculation

[0049] Taking the infrared extended source surface as the research object, all infrared extended source surfaces participating in the calculation are divided into structural grids, each structural grid corresponds to a grid surface source, and there are n grid surface sources in total, where n is a natural number greater than 2. The grid surface sources are numbered from 1 to n, and the numbered grid surface sources are marked as the nth grid surface source, referred to as grid surface source n. In addition, the number n must ensure that any two non-coplanar grid surface sources obtained by the division meet the small surface source condition, that is, the distance between any two non-coplanar grid surface sources must be greater than or equal to 10 times the maximum linear dimension of the two surface sources, and the set from the first grid surface source to the nth grid surface source is the set of grid surface sources participating in the calculation.

[0050] At this point, the set of grid surface sources involved in the calculation is obtained.

[0051] Step 2: Calculate the level l irradiance cache of any computational grid surface source

[0052] The i-th grid surface source is selected as the calculation grid surface source, i is a positive integer less than or equal to n; the other grid surface sources except the i-th calculation grid surface source are the j-th traversed grid surface source, j is a positive integer less than or equal to n, and j≠i. The numbers of the calculation grid surface source and the traversed grid surface source are the same as the numbers of the grid surface source.

[0053] Then, the l-th level radiance cache calculation of the i-th calculation grid surface source selected by the j-th traversed grid surface source is performed, where l is a natural number.

[0054] When the jth traversed grid surface source performs the first-level irradiance cache calculation on the i-th selected calculation grid surface source, that is, when l = 1, the calculation formula of the irradiance cache is:

[0055]

[0056] In formula (1), L is the first-level radiance cache emitted by the jth traversed grid surface source to the i-th selected calculation grid surface source. j is the radiance of the jth traversed grid surface source, ΔA j is the area of ​​the jth traversed grid surface source, d i,j is the distance between the jth traversed grid surface source and the i-th selected calculation grid surface source, θ j and θ i They are the angles between the center line of the j-th traversed mesh surface source and the i-th selected calculation mesh surface source and their respective normal directions.

[0057] When the jth traversed grid surface source performs the lth level irradiance cache calculation on the i-th selected calculation grid surface source, that is, when l>1, the calculation formula of the irradiance cache is:

[0058]

[0059] In formula (2), The l-th level radiance cache of the j-th traversed grid surface source for the i-th selected calculation grid surface source at the l-th level, f j is the bidirectional reflectance distribution function of the jth traversed grid surface source, is the l-1th level radiance cache of the jth traversed grid surface source, ΔA j is the area of ​​the jth traversed grid surface source, d i,j is the distance between the jth traversed grid surface source and the i-th selected calculation grid surface source, θ j and θ iThey are the angles between the center line of the j-th traversed mesh surface source and the i-th selected calculation mesh surface source and their respective normal directions.

[0060] The irradiance cache of the selected i-th calculation grid surface source is the sum of the l-th level irradiance caches emitted by all traversed grid surface sources to the selected i-th calculation grid surface source. At this time, l is a natural number, which is expressed by the following formula:

[0061]

[0062] In formula (3), Calculates the level l irradiance cache for the i-th grid surface source.

[0063] Step 3: Get the set of level l irradiance caches of all grid surface sources

[0064] After the infrared extended source surface is divided, n grid surface sources are formed. Step 2 obtains the l-th level radiance cache of the ith calculation grid surface source. The l-th level radiance cache of each grid surface source is taken as an element of the set to form the l-th level radiance cache set of all grid surface sources, which is expressed as:

[0065]

[0066] In formula (4), E (l) A collection of level l irradiance caches for all mesh surface sources.

[0067] The set of level l irradiance caches E for all mesh surface sources (l) The maximum value in It is expressed as follows:

[0068]

[0069] As the value of l increases, it decreases gradually, that is, when When the convergence threshold is reached for the first time, that is, when equation (6) is satisfied for the first time, the l value reaches its maximum value, and the l value at this time is called l max .

[0070]

[0071] In formula (6), E threshold is the convergence threshold.

[0072] E threshold It is set according to the calculation accuracy requirement. The smaller the value, the higher the accuracy. threshold =10 -15 .

[0073] At this point, the l-th level radiance cache set of all grid surface sources is obtained.

[0074] Step 4: Obtain the radiant illumination distribution on the surface of the infrared extended source

[0075] For all grid surface sources obtained in step 3, from level 1 to level 1 max The radiance distribution of the infrared extended source surface is obtained by summing the level radiance cache set, as shown in the following formula:

[0076]

[0077] In formula (7), E is the radiant illumination distribution on the surface of the infrared extended source, and the symbol Represents the corresponding addition of set elements, E (1) 、E (2) , The first, second, and lth levels of all grid surface sources are max Level irradiance cache.

[0078] At this point, the radiant illumination distribution on the surface of the infrared extended source is obtained.

Claims

1. A method for calculating the surface radiance of an infrared extended source, characterized in that: The steps include: Step 1: Get the grid surface source set involved in the calculation: Taking the infrared extended source surface as the research object, all infrared extended source surfaces participating in the calculation are divided into structural grids, each structural grid corresponds to a grid surface source, and there are n grid surface sources in total, where n is a natural number greater than 2. The grid surface sources are numbered from 1 to n, and the numbered grid surface sources are marked as the nth grid surface source, referred to as grid surface source n; in addition, the number n must ensure that any two non-coplanar grid surface sources obtained by the division meet the small surface source condition, that is, the distance between any two non-coplanar grid surface sources must be greater than or equal to 10 times the maximum linear dimension of the two surface sources, and the set from the first grid surface source to the nth grid surface source is the set of grid surface sources participating in the calculation; At this point, the set of grid surface sources involved in the calculation is obtained; Step 2: Calculate the level l radiance cache of any computational grid surface source: Select the i-th grid surface source as the calculation grid surface source, where i is a positive integer less than or equal to n; The other grid surface sources except the i-th calculation grid surface source are the j-th traversed grid surface source, where j is a positive integer less than or equal to n, and j≠i; The numbers of the calculated grid surface sources and the traversed grid surface sources are the same as the numbers of the grid surface sources; Then the l-th level radiance cache of the i-th calculation grid surface source selected by the j-th traversed grid surface source is calculated. l is a natural number; The irradiance cache of the selected i-th calculation grid surface source is the sum of the l-th level irradiance caches emitted by all traversed grid surface sources to the selected i-th calculation grid surface source. At this time, l is a natural number, which is expressed by the following formula: In formula (3), The l-th level irradiance cache for the i-th calculated grid surface source; Step 3, obtain the set of level l irradiance caches of all grid surface sources: After the infrared extended source surface is divided, n grid surface sources are formed. Step 2 obtains the l-th level radiance cache of the ith calculation grid surface source. The l-th level radiance cache of each grid surface source is taken as an element of the set to form the l-th level radiance cache set of all grid surface sources, which is expressed as: In formula (4), E (l) The l-th level irradiance cache collection for all grid surface sources; The set of level l irradiance caches E for all mesh surface sources (l) The maximum value in It is expressed as follows: As the value of l increases, it decreases gradually, that is, when When the convergence threshold is reached for the first time, the l value reaches its maximum value, which is called l max ; At this point, the l-th level radiance cache set of all grid surface sources is obtained; Step 4, obtain the radiant illumination distribution on the surface of the infrared extended source: For all grid surface sources obtained in step 3, from level 1 to level 1 max The radiance distribution of the infrared extended source surface is obtained by summing the level radiance cache set, as shown in the following formula: In formula (7), E is the radiant illumination distribution on the surface of the infrared extended source, and the symbol Represents the corresponding addition of set elements, E (1) 、E (2) , The first, second, and lth levels of all grid surface sources are max Level irradiance cache; At this point, the radiant illumination distribution on the surface of the infrared extended source is obtained.

2. The method for calculating the surface radiance of an infrared extended source according to claim 1, characterized in that: The jth traversed grid surface source is used to cache the level l radiance of the i-th calculation grid surface source selected The calculation process is: When l = 1, the calculation formula for the radiance cache is: In formula (1), L is the first-level radiance cache emitted by the jth traversed grid surface source to the i-th selected calculation grid surface source. j is the radiance of the jth traversed grid surface source, ΔA j is the area of ​​the jth traversed grid surface source, d i,j is the distance between the jth traversed grid surface source and the i-th selected calculation grid surface source, θ j and θ i are the angles between the center line of the jth traversed grid surface source and the i-th selected calculation grid surface source and their respective normal directions; When l>1, the calculation formula of the radiance cache is: In formula (2), The l-th level radiance cache of the j-th traversed grid surface source for the i-th selected calculation grid surface source at the l-th level, f j is the bidirectional reflectance distribution function of the jth traversed grid surface source, is the l-1th level radiance cache of the jth traversed grid surface source, ΔA j is the area of ​​the jth traversed grid surface source, d i,j is the distance between the jth traversed grid surface source and the i-th selected calculation grid surface source, θ j and θ i They are the angles between the center line of the j-th traversed mesh surface source and the i-th selected calculation mesh surface source and their respective normal directions.

3. The method for calculating the surface radiance of an infrared extended source according to claim 1, characterized in that: The first level irradiance cache set E of all grid surface sources (l) The maximum value in As the value of l increases, it decreases gradually, that is: when When the convergence threshold is reached for the first time, that is, when equation (6) is satisfied for the first time, the l value reaches its maximum value, and the l value at this time is called l max ; In formula (6), E threshold =10 -15 .

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