Operating distance calculation method of infrared polarization imaging system

Abstract

The invention relates to an operating distance calculation method of an infrared polarization imaging system, which comprises the following steps of: taking system performance parameters and atmospheric radiation characteristics of the infrared polarization imaging system as input parameters, and calculating the operating distance of the infrared polarization imaging system on the basis of noise equivalent temperature difference; combining the noise equivalent polarization degree difference and the minimum resolution polarization degree difference of the target and the scene to construct an operating distance calculation model of the infrared polarization imaging system; the detection advantage of the infrared polarization imaging system and the polarization radiation characteristic difference between the target and the background are comprehensively considered to calculate the operating distance of the infrared polarization imaging system under the specified target detection probability, and the method has the advantages of being high in system matching degree, good in scene adaptability, high in calculation precision and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of infrared polarization imaging, and in particular to a method for calculating a working distance of an infrared polarization imaging system. Background Art

[0002] Compared with traditional infrared thermal imaging technology, polarization imaging can realize multi-dimensional information perception of scene targets, and has the advantages of highlighting targets and suppressing backgrounds. It has shown great application potential in target search and aiming in complex environments such as radiation flooding and tree shade. As a key indicator for system performance evaluation and application capability assessment, the range has become the focus of extensive attention of current researchers. The range is not only related to the performance parameters of the detector, but also to many factors such as atmospheric transmission, target and background radiation characteristics, and environmental conditions. At present, the research on the range of traditional infrared imaging systems has been relatively complete, and the range estimation model under the influence of different factors has been given (for example: the patent publication number is: CN114199388A, the patent name is: a performance evaluation method for the range of infrared imaging systems; the patent publication number is: CN116127252A, the patent name is: an infrared range calculation method and system based on dichotomy). However, although the infrared polarization imaging system is based on the acquisition of radiation intensity, due to the differences in working modes and analytical methods (the solution of Stokes vector, polarization degree, etc.), the range estimation model of the traditional infrared imaging system is difficult to apply directly. In addition, although the infrared polarization imaging system has significant advantages in highlighting the target and suppressing the background in some scenes, due to the limitation of the principle of radiation energy attenuation, its effective range in practical application is still unclear, which is specifically manifested in the following two aspects: 1) Compared with the traditional infrared thermal imaging system, will the effective range of the infrared polarization imaging system increase or decrease when detecting long-distance targets? 2) For what types of scene targets can the effective range of the infrared polarization imaging system be improved for long-distance detection? Therefore, in order to better evaluate the target detection performance of the infrared polarization imaging system in actual long-distance applications, modeling and estimating the effective range of the infrared polarization imaging system is of great practical significance for system design, detection applications, and optoelectronic confrontation.

[0003] In order to evaluate the performance index of the effective range of infrared polarization imaging system in long-distance detection applications and clarify its applicable conditions and advantages, many researchers have carried out relevant research based on the effective range estimation model of traditional infrared imaging system. For example, Zhao Dapeng et al. (Infrared and Laser Engineering, 2013, 42 (5): 1146) analyzed the effective range gain of infrared polarization imaging system by establishing noise equivalent temperature difference model, minimum resolvable temperature difference model and effective range model. Although this method analyzes the change of minimum resolvable temperature difference of infrared polarization imaging system based on infrared imaging system, it lacks in-depth analysis of the polarization detection capability of the system and is difficult to reflect the influence of polarization characteristics difference between target object and background environment on effective range in real scene. With the continuous deepening of research, Jin Weiqi's team of Beijing Institute of Technology (Infrared and Laser Engineering, 2017, 46 (10): 1004003) established the effective range model of infrared polarization imaging system based on the minimum resolvable temperature difference (MRTD) method of infrared imaging system effective range estimation, and used this model to analyze the effective range of infrared polarization imaging system under the influence of background clutter. This method takes into account the influence of interference factors on the effective range of the infrared polarization imaging system, which is of great significance for solving the effective range estimation in complex backgrounds and the practical application of the system. However, this method only takes the single-channel polarization imaging system as the analysis basis, and has not yet considered the influence of the polarization characteristics of the target and the background polarization characteristics on the effective range. The calculation accuracy of the effective range of the infrared polarization imaging system is not high, and it is difficult to meet the use requirements of actual scenes. Although the existing research work has carried out performance analysis on the effective range of the infrared polarization imaging system by establishing a model, how to comprehensively consider the system performance parameters, the polarization feature analysis mechanism, and the influence of the polarization characteristics of the scene target on the effective range to achieve effective effective range estimation in long-distance target detection applications is a technical problem that needs to be solved in this field. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to break through the shackles of the traditional range estimation method based only on the temperature difference transfer model, consider the influence of the polarization characteristics of the target and the background on the range estimation, and improve the accuracy of the range calculation of the infrared polarization imaging system in the application of long-distance target detection.

[0005] The present invention provides a method for calculating the effective distance of an infrared polarization imaging system, wherein the infrared polarization imaging system is used to image a scene including a target and a background, and the method comprises: Step 1, obtaining the parameter information of the scene and the basic parameters of the infrared polarization imaging system; Step 2, presetting the detection probability and observation level of the infrared polarization imaging system, and calculating the initial working distance of the infrared polarization imaging system; Step 3, obtaining the environmental information of the scene and calculating the atmospheric transmittance of infrared radiation at the initial action distance; Step 4, based on the scene parameter information and infrared radiation atmospheric transmittance, respectively calculate the temperature value and polarization value of the target after atmospheric attenuation, as well as the temperature value and polarization value of the background; Step 5, based on the noise equivalent temperature difference, combining the noise equivalent polarization degree difference and the minimum resolution polarization degree difference of the target and the scene to construct a range calculation model for the infrared polarization imaging system; Step 6, preset the detection probability and observation level of the action distance calculation model to obtain a revised action distance calculation model; Step 7, inputting the target temperature value and polarization degree value obtained in step 4, as well as the background temperature value and polarization degree into the corrected action distance calculation model, and outputting the action distance of the infrared polarization imaging system; Step 8, determine whether the difference between the effective distance output in step 7 and the initial effective distance is less than a preset threshold value, if so, output the effective distance; if not, the initial effective distance decreases according to the preset decreasing threshold value, and return to step 3.

[0006] Compared with the prior art, the present application has the following advantages: on the basis of the noise equivalent temperature difference, the system performance parameters of the infrared polarization imaging system, the atmospheric radiation characteristics, the noise equivalent polarization degree difference and the minimum resolution polarization degree difference of the target and the scene are combined to construct a range calculation model for the infrared polarization imaging system, which has the advantages of strong matching, good scene adaptability and high calculation accuracy; the range calculation model constructed by the present application comprehensively considers the difference in polarization radiation characteristics between the target and the background, and realizes the accurate calculation of the range of the infrared polarization imaging system under the specified target detection probability.

[0007] In a possible implementation manner, the parameter information of the scene in step 1 includes the temperature of the target , Background temperature , target polarization , background polarization , target polarization angle , background polarization angle And the projection height of the target within the detection range and projection width The basic parameters of the infrared polarization imaging system include the focal length of the optical lens , pixel size of infrared detector .

[0008] In a possible implementation manner, the step 2 specifically includes: Step 201, based on the projection height of the target within the detection range and projection width Calculating critical dimensions , the calculation formula is: ; Step 202, calculating the instantaneous viewing angle field based on the basic parameters of the infrared polarization imaging system , the calculation formula is: ; Step 203: preset the detection probability and observation level of the range calculation model and calculate the number of pixels required for target imaging. , the calculation formula is: ; In the formula, represents the number of target equivalent band logarithms at the corresponding observation level under Johnson criterion; Probability of detection Number of equivalent bands to the target The relationship is: ; In the formula, represents the coefficient at the corresponding observation level, It represents the logarithm of target equivalent bands at the corresponding observation level when the detection probability is 50%; Step 204, initial range The calculation formula is: .

[0009] In a possible implementation, the environmental information of the scene in step 3 includes: atmospheric environment temperature, relative humidity, meteorological visibility, wavelength range, detection altitude and detection direction; based on the environmental information, MODTRAN is used to generate an atmospheric transmittance file to obtain the atmospheric transmittance of infrared radiation at the current initial action distance. .

[0010] In a possible implementation manner, step 4 specifically includes: Step 401, calculate the target Apparent spectral radiant emittance in polarization direction , the calculation formula is: ; In the formula, Indicates the target Spectral polarization emissivity in polarization direction, ; Expressed as Planck black body at temperature as well as Spectral radiant emittance in polarization direction, The calculation formula is: ; In the formula, Indicates the lower limit of the infrared detector integration band, Indicates the upper limit of the infrared detector integration band, represents the first radiation constant, represents the second radiation constant; Computational background Apparent spectral radiant emittance in polarization direction , the calculation formula is: ; In the formula, Indicates the background Spectral polarization emissivity in polarization direction; Planck black body at temperature as well as Spectral radiant emittance in polarization direction; Step 402, calculate the target after atmospheric attenuation Apparent spectral radiant emittance in polarization direction , the calculation formula is: ; In the formula, represents the atmospheric path radiation along the observation path; represents the ambient temperature of the scene along the observation path; After calculating the background attenuation through the atmosphere, Apparent spectral radiant emittance in polarization direction , the calculation formula is: ; Step 403, calculate the polarization degree of the target after atmospheric attenuation ; ; Calculate the polarization degree of the background after atmospheric attenuation; ; Step 404: correct the polarization degree of the target after atmospheric attenuation based on the transmittance deviation corresponding to the transmission axis of the polarization optical element. ; Correct the polarization of the background after atmospheric attenuation ; In the formula, represents the extinction ratio of the polarization optical element, , Indicates the transmittance corresponding to the maximum transmission axis of the polarization optical element, Indicates the transmittance corresponding to the minimum transmission axis of the polarization optical element.

[0011] In a possible implementation, the expression for constructing a range calculation model of an infrared polarization imaging system in step 5 by combining the noise equivalent polarization degree difference and the minimum resolution polarization degree difference of the target and the scene is: ; In the formula, ; Indicates the projection height of the target within the detection range; The frequency is The minimum resolvable polarization difference is calculated as: ; In the formula, represents the lateral instantaneous field of view of the infrared detector, It represents the longitudinal instantaneous field of view of the infrared detector; The threshold indicates the signal-to-noise ratio; represents the integration time of the human eye, represents the noise equivalent bandwidth, Indicates the frame rate, Indicates the dwell time, The spatial frequency is The transfer function of the infrared polarization imaging system is represents the noise equivalent polarization degree difference of the infrared polarization imaging system; where the transfer function The function expression is: ; In the formula, Represent the modulation transfer function of a polarization optical element: , represents the cutoff frequency of the optical lens, Indicates the clear aperture of the optical lens; Indicates the polarization direction; Represents the modulation transfer function of the optical lens: , represents the cutoff frequency of the optical lens, Indicates the clear aperture of the optical lens; Express the modulation transfer function of the infrared detector: , represents the instantaneous field of view of the infrared polarization imaging system, ; represents the horizontal instantaneous field of view of the infrared polarization imaging system, It represents the vertical instantaneous field of view of the infrared polarization imaging system; Represents the modulation transfer function of the information processing circuit: ; Express the modulation transfer function of the display: , represents the spatial characteristic frequency, , Represents the instantaneous field of view angle of the infrared polarization imaging system; The function expression is: ; In the formula, Differentiation symbols; represents the degree of polarization; It represents the spectral power of infrared radiation irradiated on the infrared detector; represents the blackbody temperature, It represents the spectral radiation emittance of a black body with temperature T; , represents the polarization degree of the incident target infrared radiation, , Indicates the F number of the optical lens. Represents the photosensitive area of ​​the infrared detector; Express the equivalent noise temperature difference: ; In the formula, Indicates the spectral sensitivity of the infrared detector; Indicates the F number of the optical lens. It represents the spectral radiation emittance of a black body with temperature T; Represents the RMS noise output voltage.

[0012] In a possible implementation manner, the detection probability and observation level of the preset action distance calculation model in step 6 are corrected to the action distance calculation model: ; In the formula, Represents the difference in polarization between the target and the background After atmospheric attenuation, the frequency of the infrared polarization imaging system at the spatial frequency is equal to The minimum resolvable polarization difference under The limiting spatial frequency is ; in: ; ; In the formula, Represents the corrected equivalent band logarithm patterned aspect ratio; ; Indicates the actual aspect ratio of the target; the corrected equivalent strip logarithm Based on the calculation formula get, represents the detection probability; represents the minimum resolvable polarization difference corrected proportionally, The threshold indicating the signal-to-noise ratio when the detection probability is 50%; The detection probability The threshold value shows the signal-to-noise ratio. Based on the correlation between image clarity and image signal-to-noise ratio, the calculation formula for the modified threshold value to show the signal-to-noise ratio is: .

[0013] In a possible implementation manner, in step 8, the expression for determining whether the difference between the action distance output in step 7 and the initial action distance is less than or equal to a preset threshold is: ; If it is less than or equal to the preset threshold, the effective distance is output is the working distance of the infrared polarization imaging system, and the iteration cycle ends; if it is greater than the preset threshold, then , is the preset decreasing threshold; and returns to step 3, Indicates the action distance, represents the initial action distance, Indicates the preset threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of polarization imaging detection of infrared targets according to a specific embodiment of the present invention; Figure 2 It is a curve showing the relationship between the detection probability and the logarithm of the target equivalent strip at different observation levels in a specific embodiment of the present invention; Figure 3 The atmospheric transmittance curves corresponding to different working bands in the specific embodiment of the present invention; Figure 4 is a curve showing the change of atmospheric path radiation with path distance in a specific embodiment of the present invention; Figure 5 is a curve diagram showing the relationship between MRPD and spatial frequency in a specific embodiment of the present invention; Figure 6 It is a curve diagram showing the relationship between MTF and spatial frequency in a specific embodiment of the present invention; Figure 7 is the x-direction and y-direction in the specific embodiment of the present invention. Graph of its relationship with spatial frequency. DETAILED DESCRIPTION

[0015] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0016] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0017] In the embodiments of the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0018] The present application is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] See also Figure 1 to Figure 7 As shown, the embodiment of the present application discloses a method for calculating the working distance of an infrared polarization imaging system, and an infrared polarization imaging system is used to image a scene including a target and a background. The infrared polarization imaging system of this specific embodiment includes an optical lens for receiving infrared radiation in a target band, a polarization optical element for obtaining polarization information collected by the optical lens, an infrared detector for responding to infrared radiation in the target band and converting it into an analog signal, a signal processor for converting the analog signal into a digital signal for transmission, and a host computer for receiving the digital signal and performing image processing and display; This specific implementation example Figure 1 The infrared polarization imaging system detection schematic diagram shown includes: 1) The infrared radiation polarization characteristics of the target and the background are converged on the focal plane of the infrared detector after being attenuated by atmospheric transmission and modulated by polarization optical elements. They are then converted, amplified and processed by the signal processor, and then displayed as a visual image by the host computer. Finally, the human eye observes the image and makes a judgment to determine whether the target exists and the target type. 2) Considering the technical advantages of polarization imaging, combined with hardware systems and back-end algorithms, the detection of infrared target polarization imaging systems can achieve the purpose of suppressing natural backgrounds such as trees and highlighting artificial targets; 3) When the infrared polarization imaging system is used for target detection, that is, extended source target detection, the angular size of the target needs to be greater than or equal to the instantaneous field of view of the system. In this case, the image information and effective range perceived by the infrared polarization imaging system depend on the size, shape, radiation characteristics and polarization characteristics of the target itself, and are also affected by many factors such as the difference in radiation polarization characteristics between the target and the background, atmospheric conditions, system performance, and the required observation level.

[0020] Among them, the infrared polarization imaging system parameters, target parameters, background parameters, atmospheric environment parameters and observation parameters are shown in Table 1: Table 1 Target infrared polarization imaging detection setting parameters

[0021] This specific embodiment provides a method for calculating the working distance of an infrared polarization imaging system, including: Step 1, obtaining parameter information of the scene and basic parameters of the infrared polarization imaging system; The scene parameter information includes the temperature of the target , Background temperature , target polarization , background polarization , target polarization angle , background polarization angle And the projection height of the target within the detection range and projection width ; The basic parameters of the infrared polarization imaging system include the focal length of the optical lens , pixel size of infrared detector .

[0022] Step 2: preset the detection probability and observation level of the infrared polarization imaging system, and calculate the initial working distance of the infrared polarization imaging system; this embodiment calculates the initial working distance of the infrared polarization imaging system under ideal conditions, specifically including: Step 201, based on the projection height of the target within the detection range and projection width Calculating critical dimensions , the calculation formula is: ; The critical size of the target in this embodiment .

[0023] Step 202, calculating the instantaneous viewing angle field based on the basic parameters of the infrared polarization imaging system , the calculation formula is: ; The instantaneous viewing angle of the infrared polarization imaging system in this specific embodiment .

[0024] Step 203: Preset the detection probability of the range calculation model and observation level, calculate the number of pixels required for target imaging , the calculation formula is: ; In the formula, represents the number of target equivalent band logarithms at the corresponding observation level under Johnson criterion; The detection probability of this specific embodiment The Johnson criterion is used. The Johnson criterion determines the recognition ability of the infrared thermal imager imaging system to the target by the resolution of the equivalent strip logarithm (number of spatial cycles) of the target within the minimum target angle without considering the nature of the target and image defects. Refer to Table 2. Under the probability of 50%, the Johnson criterion requires 1) the equivalent strip logarithm to be at least 1 for discovery, and the target can be found; 2) the equivalent strip logarithm to be at least 4 for recognition, and the target can be distinguished to which type of object it belongs, such as a car; 3) the equivalent strip logarithm to be recognized requires at least 6.4, and the observer can describe the specific model and category of the target.

[0025] Table 2 Equivalent band logarithms corresponding to different observation levels under 50% observation probability ; Probability of detection Number of equivalent bands to the target The relationship is: ; In the formula, Represents the coefficient under the corresponding observation level. When the observation level is the detection level, ; When the observation level is the recognition level, ; When the observation level is the recognition level, ; It indicates the number of equivalent bands of the target at the corresponding observation level when the detection probability is 50%; when the observation level is the detection level, ; When the observation level is the recognition level, ; When the observation level is the recognition level, ; like Figure 2 As shown in the figure, the relationship curve between the detection probability and the logarithm of the target equivalent strip under different observation levels shows that when the detection probability is the same, the higher the observation level, the more target equivalent strip logarithms are required; when the observation level is the same, the greater the detection probability, the more target equivalent strip logarithms are required; this means that the more equivalent strip logarithms the target has, the clearer the observed target is, which is conducive to target identification.

[0026] Step 204, the ideal conditions include the first condition that is satisfied at the same time: the temperature difference between the target and the scene exceeds the threshold; the second condition: atmospheric radiation attenuation is not considered; the third condition: the noise equivalent temperature difference of the infrared detector is less than or equal to the preset threshold; the fourth condition: the performance improvement effect of the image enhancement algorithm is ignored; the fifth condition: the performance loss caused by the upper computer display is ignored; the initial working distance of the infrared imaging polarization system The calculation formula is: ; In this specific embodiment, the initial action distance corresponding to the target .

[0027] Step 3, obtaining the environmental information of the scene and calculating the atmospheric transmittance of infrared radiation at the initial action distance; The environmental information of this specific embodiment includes: atmospheric environment temperature , water vapor content in the air (relative humidity) , meteorological sight distance 23km, wavelength range 8~12μm, detection height 0.5km and detection direction is horizontal path; based on environmental information, MODTRAN ( Moderate Spectral Atmospheric Transmittance Algorithm and Computer Model ) Generate the atmospheric transmittance file tape6, such as Figure 3 The atmospheric transmittance curves corresponding to different working bands are shown. The atmospheric transmittance of infrared radiation at the current working distance can be obtained by averaging. According to the Lambert-Beer law, the calculation formula for atmospheric transmittance on different paths is: ; In the formula, represents the atmospheric extinction coefficient, .

[0028] Step 4, based on the scene parameter information and infrared radiation atmospheric transmittance, respectively calculate the temperature value and polarization degree of the target and background after atmospheric attenuation; Due to the absorption and scattering of atmospheric molecules, the temperature values ​​of the target and background and the polarization characteristics of infrared radiation will attenuate during the transmission process, thus affecting the imaging quality and effective distance of the system.

[0029] The step 4 specifically includes: Step 401, calculate the target Apparent spectral radiant emittance in polarization direction , the calculation formula is: ; In the formula, Indicates the target Spectral polarization emissivity in polarization direction, ; Expressed as Planck black body at temperature as well as Spectral radiant emittance in polarization direction, The calculation formula is: ; In the formula, Indicates the lower limit of the infrared detector integration band, Indicates the upper limit of the infrared detector integration band, represents the first radiation constant, , represents the second radiation constant, ; In this specific embodiment, the apparent spectral radiation emittance of the target in the polarization directions of 0°, 45°, 90° and 135° can be calculated by Matlab software: , , , ; Computational background Apparent spectral radiant emittance in polarization direction , the calculation formula is: ; In the formula, Indicates the background Spectral polarization emissivity in polarization direction; Planck black body at temperature as well as Spectral radiant emittance in polarization direction; , , , .

[0030] Step 402, affected by the scattering of atmospheric molecules and aerosol particles (Rayleigh scattering, Mie scattering, etc.), the absorption of water vapor and the atmospheric radiation itself, the polarization degree of the target and the background is attenuated during the transmission process. Assuming that the depolarization effect of the scattering of atmospheric molecules and suspended particles in the air is ignored, and the polarization characteristics of the atmospheric radiation itself are not considered, only the superposition effect of the atmospheric path radiation (i.e., path radiation) between the imaging detector and the target is considered. Specifically, according to the preset atmospheric environment parameters, the spectral radiation emittance of the atmospheric radiation at different detection distances is calculated using MODTRAN software. The results are as follows: Figure 4 As shown, it can be seen that the atmospheric radiation brightness is small, and with the increase of path distance, it shows a trend of increasing first and then stabilizing; Calculate the target after atmospheric attenuation Apparent spectral radiant emittance in polarization direction , the calculation formula is: ; In the formula, represents the atmospheric path radiation along the observation path; represents the ambient temperature of the scene along the observation path; After atmospheric attenuation, the apparent spectral radiant emittance of the target in the polarization directions of 0°, 45°, 90° and 135° are: , , , ; After calculating the background attenuation through the atmosphere, Apparent spectral radiant emittance in polarization direction , the calculation formula is: ; After atmospheric attenuation, the apparent spectral radiant emittance of the background at 0°, 45°, 90° and 135° polarization directions are: , , , .

[0031] Step 403, calculate the polarization degree of the target after atmospheric attenuation ; ; This specific embodiment ; Calculate the polarization degree of the background after atmospheric attenuation; ; This specific embodiment .

[0032] Step 404: correct the polarization degree of the target after atmospheric attenuation based on the transmittance deviation corresponding to the transmission axis of the polarization optical element. ; Correct the polarization of the background after atmospheric attenuation ; In the formula, , represents the extinction ratio of the polarization optical element, Indicates the transmittance corresponding to the maximum transmission axis of the polarization optical element, Indicates the transmittance corresponding to the minimum transmission axis of the polarization optical element.

[0033] According to the preset parameters of the infrared polarization imaging system, the extinction ratio of the polarization optical element ; Therefore, when the polarization degrees of the target and background are attenuated by the atmosphere and modulated by the polarization optical element, the polarization degrees obtained by the imaging detector are: and .

[0034] Step 5. Due to the influence of radiation energy attenuation caused by polarization optical elements, the traditional infrared imaging system range calculation model is difficult to apply directly. The existing infrared polarization imaging system model only performs single-channel polarization range analysis based on the apparent temperature difference between the target and the background, and cannot comprehensively consider the polarization feature information analysis process and imaging detection performance. Therefore, the present invention is based on the traditional model, and on the basis of the noise equivalent temperature difference, combines the noise equivalent degree of linear polarization difference (NEPD) and the minimum resolvable degree of linear polarization difference (MRPD) of the target and the scene to construct a range calculation model for the infrared polarization imaging system. The range calculation model of the infrared polarization imaging system includes: 1) the polarization difference between the target and the background After atmospheric attenuation, the frequency of the infrared polarization imaging system must be greater than or equal to the spatial frequency of the system. The minimum resolvable polarization difference under ; 2) The angle of the target to the system It needs to be greater than or equal to the minimum resolvable angle required by the corresponding observation level; therefore, the expression of the working distance calculation model of the infrared polarization imaging system is: ; In the formula, ; Indicates the projection height of the target within the detection range; Indicates the frequency When the polarization difference between the target and the background gradually increases from zero until the observer confirms that he can distinguish (with a probability of 50%) a target pattern of four stripes, the polarization difference between the target and the background is called the minimum resolvable polarization difference (MRPD) in the space. This indicator is based on the subjective vision of the observer and measures the polarization sensitivity of the infrared polarization imaging system at different spatial frequencies. The smaller the MRPD value, the better the target polarization imaging detectability of the system. This specific embodiment simulates and calculates the MRPD of the infrared polarization imaging system according to the preset system parameters and observation parameters. When the detection probability is 50%, the threshold signal-to-noise ratio perceived by the human visual system is , the minimum resolvable polarization difference (MRPD) corresponding to different spatial frequencies is as follows Figure 5 As shown; the calculation formula of the minimum resolvable polarization difference (MRPD) is: ; In the formula, represents the lateral instantaneous field of view of the infrared detector, It represents the longitudinal instantaneous field of view of the infrared detector; The threshold indicates the signal-to-noise ratio; represents the integration time of the human eye, represents the noise equivalent bandwidth, Indicates the frame rate, Indicates the dwell time, The spatial frequency is The transfer function of the infrared polarization imaging system is It represents the noise equivalent polarization degree difference of infrared polarization imaging system; Specifically, the transfer function The function expression is: ; In the formula, Represent the modulation transfer function of a polarization optical element: , represents the cutoff frequency of the optical lens, , Indicates the clear aperture of the optical lens; Indicates the polarization direction; Represents the modulation transfer function of the optical lens: , represents the cutoff frequency of the optical lens, Indicates the clear aperture of the optical lens; Express the modulation transfer function of the infrared detector: , represents the instantaneous field of view of the infrared polarization imaging system, ; represents the horizontal instantaneous field of view of the infrared polarization imaging system, It represents the vertical instantaneous field angle of the infrared polarization imaging system; Represent the modulation transfer function of the signal processor: ; Represents the modulation transfer function of the host computer: , represents the spatial characteristic frequency, , Represents the instantaneous field of view angle of the infrared polarization imaging system; This specific embodiment simulates and calculates the MTF of the infrared polarization imaging system according to preset system parameters. Figure 6 The modulation transfer function (MTF) corresponding to different spatial frequencies.

[0035] Specifically, The function expression of is: ; In the formula, Differentiation symbols; represents the degree of polarization; It represents the spectral power of infrared radiation irradiated on the infrared detector; represents the blackbody temperature (, It represents the spectral radiation emittance of a black body with temperature T; , represents the polarization degree of the incident target infrared radiation, , Indicates the F number of the optical lens. Represents the photosensitive area of ​​the infrared detector; according to the literature ( SPIE. 1993, 4: 245-298 ) It can be seen that the expression of the equivalent noise temperature difference (NETD) of the traditional infrared imaging system is: ; In the formula, Indicates the spectral sensitivity of the infrared detector; Indicates the F number of the optical lens. It represents the spectral radiation emittance of a black body with temperature T; Represents the RMS noise output voltage.

[0036] In this specific embodiment, it is assumed that the NETD of the detector in the infrared polarization imaging system is 50mK (=0.05K), and it is calculated that the noise equivalent polarization degree difference NEPD of the infrared polarization imaging system is about 0.219%.

[0037] Step 6: Preset the detection probability of the range calculation model =50% and observation level, and the revised action distance calculation model is obtained; Among them, the corrected action distance calculation model is: ; In the formula, Represents the difference in polarization between the target and the background After atmospheric attenuation, the frequency of the infrared polarization imaging system at the spatial frequency is equal to The minimum resolvable polarization difference under The limiting spatial frequency is ; in: ; ; In the formula, Represents the corrected equivalent band logarithm patterned aspect ratio; ; Indicates the actual aspect ratio of the target; the corrected equivalent strip logarithm Based on the calculation formula get , represents the detection probability; represents the minimum resolvable polarization difference corrected proportionally, The threshold indicating the signal-to-noise ratio when the detection probability is 50%; The detection probability The threshold value shows the signal-to-noise ratio. Based on the correlation between image clarity and image signal-to-noise ratio, the calculation formula for the modified threshold value to show the signal-to-noise ratio is: According to the preset system parameters and observation parameters, the infrared polarization imaging system Through simulation calculation, when the detection probability is 50%, the threshold signal-to-noise ratio perceived by the human visual system is , different spatial frequencies The corresponding corrected minimum resolvable polarization difference (MRPD) is as follows Figure 7 As shown; The working distance of the infrared polarization imaging system of this specific embodiment R =(3.5 / 4)×(2×0.25)×1000=437.5m.

[0038] Step 7, input the temperature values ​​and polarization degrees of the target and background obtained in step 4 into the corrected action distance calculation model to output the action distance of the infrared polarization imaging system.

[0039] Step 8: The expression for judging whether the difference between the action distance outputted in step 7 and the initial action distance is less than or equal to the preset threshold is: ; This specific embodiment , if it is less than or equal to the preset threshold, then the action distance is output is the working distance of the infrared polarization imaging system, and the iteration cycle ends; if it is greater than the preset threshold, then , is the preset decreasing threshold; and returns to step 3, Indicates the action distance, represents the initial action distance, Indicates the preset threshold.

[0040] This specific embodiment finally obtains the effective distance of the infrared polarization imaging system to the target R ≈1110.2m.

[0041] In the description of the embodiments of the present application, it should be noted that in the description of the present application, terms such as "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is only for the convenience of description, and does not indicate or imply that the device or component must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present application.

[0042] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0043] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for calculating the effective distance of an infrared polarization imaging system, wherein the infrared polarization imaging system is used to image a scene including a target and a background, wherein: The method for calculating the working distance of the infrared polarization imaging system comprises: Step 1, obtaining parameter information of the scene and basic parameters of the infrared polarization imaging system; Step 2, presetting the detection probability and observation level of the infrared polarization imaging system and calculating the initial action distance; Step 3, obtaining the environmental information of the scene and calculating the atmospheric transmittance of infrared radiation at the initial action distance; Step 4, based on the scene parameter information and infrared radiation atmospheric transmittance, respectively calculate the temperature value and polarization value of the target after atmospheric attenuation, as well as the temperature value and polarization value of the background; Step 5, based on the noise equivalent temperature difference, combining the noise equivalent polarization degree difference and the minimum resolution polarization degree difference of the target and the scene to construct a range calculation model for the infrared polarization imaging system; Step 6, preset the detection probability and observation level of the action distance calculation model to obtain a revised action distance calculation model; Step 7, inputting the target temperature value and polarization degree value obtained in step 4, as well as the background temperature value and polarization degree into the corrected action distance calculation model, and outputting the action distance of the infrared polarization imaging system; Step 8, determine whether the difference between the effective distance output in step 7 and the initial effective distance is less than a preset threshold value, if so, output the effective distance; if not, the initial effective distance decreases according to the preset decreasing threshold value, and return to step 3.

2. The method for calculating the effective distance of the infrared polarization imaging system according to claim 1, characterized in that: The parameter information of the scene in step 1 includes the temperature of the target , Background temperature , target polarization , background polarization , target polarization angle , background polarization angle And the projection height of the target within the detection range and projection width The basic parameters of the infrared polarization imaging system include the focal length of the optical lens , pixel size of infrared detector .

3. The method for calculating the effective distance of the infrared polarization imaging system according to claim 2, characterized in that: The step 2 specifically includes: Step 201, based on the projection height of the target within the detection range and projection width Calculating critical dimensions , the calculation formula is: ； Step 202, calculating the instantaneous viewing angle field based on the basic parameters of the infrared polarization imaging system , the calculation formula is: ； Step 203: preset the detection probability and observation level of the range calculation model and calculate the number of pixels required for target imaging. , the calculation formula is: ； In the formula, represents the number of target equivalent band logarithms at the corresponding observation level under Johnson criterion; Probability of detection Number of equivalent bands to the target The relationship is: ； In the formula, represents the coefficient at the corresponding observation level, It represents the logarithm of target equivalent bands at the corresponding observation level when the detection probability is 50%; Step 204, initial range The calculation formula is: 。 4. The method for calculating the effective distance of the infrared polarization imaging system according to claim 3, characterized in that: The environmental information of the scene in step 3 includes: atmospheric environment temperature, relative humidity, meteorological visibility, wavelength range, detection altitude and detection direction; based on the environmental information, MODTRAN is used to generate an atmospheric transmittance file to obtain the atmospheric transmittance of infrared radiation at the current initial action distance. .

5. The method for calculating the effective distance of the infrared polarization imaging system according to claim 4, characterized in that: The step 4 specifically includes: Step 401, calculate the target Apparent spectral radiant emittance in polarization direction , the calculation formula is: ； In the formula, Indicates the target Spectral polarization emissivity in polarization direction, ; Expressed as Planck black body at temperature as well as Spectral radiant emittance in polarization direction, The calculation formula is: ； In the formula, Indicates the lower limit of the infrared detector integration band, Indicates the upper limit of the infrared detector integration band, represents the first radiation constant, represents the second radiation constant; Computational background Apparent spectral radiant emittance in polarization direction , the calculation formula is: ； In the formula, Indicates the background Spectral polarization emissivity in polarization direction; Planck black body at temperature as well as Spectral radiant emittance in polarization direction; Step 402, calculate the target after atmospheric attenuation Apparent spectral radiant emittance in polarization direction , the calculation formula is: ； In the formula, represents the atmospheric path radiation along the observation path; represents the ambient temperature of the scene along the observation path; After calculating the background attenuation through the atmosphere, Apparent spectral radiant emittance in polarization direction , the calculation formula is: ； Step 403, calculate the polarization degree of the target after atmospheric attenuation ; ； Calculate the polarization degree of the background after atmospheric attenuation; ； Step 404: correct the polarization degree of the target after atmospheric attenuation based on the transmittance deviation corresponding to the transmission axis of the polarization optical element. ; Correct the polarization of the background after atmospheric attenuation ; In the formula, represents the extinction ratio of the polarization optical element, , Indicates the transmittance corresponding to the maximum transmission axis of the polarization optical element, Indicates the transmittance corresponding to the minimum transmission axis of the polarization optical element.

6. The method for calculating the effective distance of the infrared polarization imaging system according to claim 5, characterized in that: The expression of the range calculation model of the infrared polarization imaging system constructed by combining the noise equivalent polarization degree difference and the minimum resolution polarization degree difference of the target and the scene in step 5 is: ； In the formula, ; Indicates the projection height of the target within the detection range; Indicates the frequency The minimum resolvable polarization difference is calculated as: ； In the formula, represents the lateral instantaneous field of view of the infrared detector, It represents the vertical instantaneous field of view of the infrared detector; The threshold indicates the signal-to-noise ratio; represents the integration time of the human eye, represents the noise equivalent bandwidth, Indicates the frame rate, Indicates the dwell time, The spatial frequency is The transfer function of the infrared polarization imaging system is represents the noise equivalent polarization degree difference of the infrared polarization imaging system; where the transfer function The function expression is: ； In the formula, Represent the modulation transfer function of a polarization optical element: ； In the formula, represents the cutoff frequency of the optical lens, , Indicates the clear aperture of the optical lens; Indicates the polarization direction; Represents the modulation transfer function of the optical lens: , represents the cutoff frequency of the optical lens, Indicates the clear aperture of the optical lens; Express the modulation transfer function of the infrared detector: , represents the instantaneous field of view of the infrared polarization imaging system, ; represents the horizontal instantaneous field of view of the infrared polarization imaging system, It represents the vertical instantaneous field of view of the infrared polarization imaging system; Represents the modulation transfer function of the information processing circuit: ； Express the modulation transfer function of the display: , represents the spatial characteristic frequency, , Represents the instantaneous field of view angle of the infrared polarization imaging system; The function expression of is: ； In the formula, represents the differential symbol; represents the degree of polarization; It represents the spectral power of infrared radiation irradiated on the infrared detector; represents the blackbody temperature, It represents the spectral radiation emittance of a black body with temperature T; , represents the polarization degree of the incident target infrared radiation, , Indicates the F number of the optical lens. Represents the photosensitive area of ​​the infrared detector; Express the equivalent noise temperature difference: ； In the formula, Indicates the spectral sensitivity of the infrared detector; Indicates the F number of the optical lens. It represents the spectral radiation emittance of a black body with temperature T; Represents the RMS noise output voltage.

7. The method for calculating the effective distance of the infrared polarization imaging system according to claim 6, characterized in that: The detection probability and observation level of the action distance calculation model are preset in step 6, and the corrected action distance calculation model is obtained as follows: ； In the formula, Represents the difference in polarization between the target and the background After atmospheric attenuation, the frequency of the infrared polarization imaging system at the spatial frequency is equal to The minimum resolvable polarization difference under The limiting spatial frequency is ; in: ； ； In the formula, Represents the corrected equivalent band logarithm patterned aspect ratio; ; Indicates the actual aspect ratio of the target; Corrected equivalent band logarithm Based on the calculation formula get, represents the detection probability; represents the minimum resolvable polarization difference corrected proportionally, The threshold indicating the signal-to-noise ratio when the detection probability is 50%; The detection probability The threshold value shows the signal-to-noise ratio. Based on the correlation between image clarity and image signal-to-noise ratio, the calculation formula for the modified threshold value to show the signal-to-noise ratio is: .

8. The method for calculating the effective distance of the infrared polarization imaging system according to claim 7, characterized in that: In step 8, the expression for judging whether the difference between the action distance output in step 7 and the initial action distance is less than or equal to the preset threshold is: ; If it is less than or equal to the preset threshold, the effective distance is output. is the working distance of the infrared polarization imaging system, and the iteration cycle ends; if it is greater than the preset threshold, then , is the preset decreasing threshold; and returns to step 3, Indicates the action distance, represents the initial action distance, Indicates the preset threshold.

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