A method for calculating the effective distance of an infrared polarization imaging system

Abstract

The present invention relates to a method for calculating the effective range of an infrared polarization imaging system. The method takes system performance parameters and atmospheric radiation characteristics of the infrared polarization imaging system as input parameters, and constructs an effective range calculation model for the infrared polarization imaging system based on the noise equivalent temperature difference, in combination with the noise equivalent polarization degree difference and the minimum resolution polarization degree difference between a target and a scene. The method comprehensively considers the detection advantages of the infrared polarization imaging system and the difference in polarization radiation characteristics between the target and the background to calculate the effective range of the infrared polarization imaging system under a specified target detection probability. The method has the advantages of strong system matching, good scene adaptability, high calculation accuracy, 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 the effective range of an infrared polarization imaging system. Background Art

[0002] Compared to traditional infrared thermal imaging technology, polarimetric imaging can achieve multi-dimensional information perception of scene objects, offering advantages such as highlighting targets and suppressing backgrounds. This technology demonstrates significant application potential in target search and targeting in complex environments such as radiation flooding and tree shade. As a key metric for evaluating system performance and applicability, range has become a focus of widespread research. Range is not only dependent on detector performance parameters, but also on numerous other factors, including atmospheric transmission, target and background radiation characteristics, and environmental conditions. Currently, research on the range of traditional infrared imaging systems is relatively comprehensive, with models for estimating range under the influence of various factors proposed (for example, Patent Publication No. CN114199388A, entitled "A Performance Evaluation Method for Range of Infrared Imaging Systems"; Patent Publication No. CN116127252A, entitled "Infrared Range Calculation Method and System Based on Bisection Method"). However, although infrared polarimetric imaging systems rely on radiation intensity, differences in operating modes and analytical methods (such as the Stokes vector and degree of polarization) make these range estimation models difficult to directly apply. Furthermore, while infrared polarization imaging systems offer significant advantages in highlighting targets and suppressing backgrounds in certain scenarios, their effective range in practical applications remains unclear due to limitations imposed by the principle of radiation energy attenuation. This is particularly evident in two key areas: 1) Compared to traditional infrared thermal imaging systems, does the effective range of infrared polarization imaging systems increase or decrease when detecting long-range targets? 2) For what types of scenarios can the effective range of infrared polarization imaging systems be improved? Therefore, to better evaluate the target detection performance of infrared polarization imaging systems in practical long-range applications, modeling and estimating their effective range is of great practical significance for system design, detection applications, and optoelectronic countermeasures.

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

[0005] The present invention provides a method for calculating the effective range 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:

[0006] Step 1: Obtain scene parameter information and basic parameters of the infrared polarization imaging system;

[0007] Step 2: Preset the detection probability and observation level of the infrared polarization imaging system and calculate the initial working range of the infrared polarization imaging system;

[0008] Step 3: Obtain the environmental information of the scene and calculate the infrared radiation atmospheric transmittance at the initial working distance;

[0009] Step 4, based on the scene parameter information and the infrared radiation atmospheric transmittance, respectively calculate the temperature value and polarization degree of the target after atmospheric attenuation, as well as the temperature value and polarization degree of the background;

[0010] Step 5: Based on the noise equivalent temperature difference, 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;

[0011] Step 6: Preset the detection probability and observation level of the range calculation model to obtain a revised range calculation model;

[0012] 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 value, into the revised range calculation model, and outputting the range of the infrared polarization imaging system;

[0013] 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. If so, output the effective distance; if not, decrease the initial effective distance according to the preset decreasing threshold, and return to step 3.

[0014] Compared with the existing technology, the present application has the following advantages: on the basis of the noise equivalent temperature difference, the system performance parameters and atmospheric radiation characteristics of the infrared polarization imaging system are combined with the noise equivalent polarization degree difference and the minimum resolution polarization degree difference of the target and the scene to construct an effective range calculation model of the infrared polarization imaging system, which has the advantages of strong matching, good scene adaptability and high calculation accuracy; the effective range calculation model constructed by the present application comprehensively considers the differences in polarization radiation characteristics between the target and the background, and realizes the accurate calculation of the effective range of the infrared polarization imaging system under the specified target detection probability.

[0015] In a possible implementation, the parameter information of the scene in step 1 includes the temperature of the target. , background temperature , target polarization degree , background polarization , target polarization angle , background polarization angle And the projected 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 .

[0016] In a possible implementation, step 2 specifically includes:

[0017] Step 201: Based on the projected height of the target within the detection range and projection width Calculating critical dimensions , the calculation formula is:

[0018] ;

[0019] Step 202: Calculate the instantaneous viewing angle based on the basic parameters of the infrared polarization imaging system. , the calculation formula is:

[0020] ;

[0021] Step 203: Preset the detection probability and observation level of the range calculation model to calculate the number of pixels required for target imaging. , the calculation formula is:

[0022] ;

[0023] Where, represents the number of target equivalent bands at the corresponding observation level under Johnson's criterion;

[0024] Probability of detection Number of equivalent bands to the target The relationship is:

[0025] ;

[0026] Where, represents the coefficient at the corresponding observation level, It represents the number of equivalent target bands at the corresponding observation level when the detection probability is 50%;

[0027] Step 204, initial range The calculation formula is:

[0028] .

[0029] In a possible implementation, the environmental information of the scene in step 3 includes: atmospheric 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 working distance. .

[0030] In a possible implementation, step 4 specifically includes:

[0031] Step 401, calculate the target Apparent spectral radiant emittance in polarization direction , the calculation formula is:

[0032] ;

[0033] Where, Indicates the target is Spectral polarization emissivity in polarization direction, ; Expressed as a Planck blackbody at temperature as well as Spectral radiant emittance in polarization direction, The calculation formula is:

[0034] ;

[0035] Where, 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;

[0036] Computational background in Apparent spectral radiant emittance in polarization direction , the calculation formula is:

[0037] ;

[0038] Where, Indicates the background Spectral polarization emissivity in polarization direction; Planck blackbody at temperature as well as Spectral radiant emittance in polarization direction;

[0039] Step 402, calculate the target after atmospheric attenuation Apparent spectral radiant emittance in polarization direction , the calculation formula is:

[0040] ;

[0041] Where, represents the atmospheric radiation along the observation path; Represents the ambient temperature of the scene along the observation path;

[0042] After calculating the background attenuation through the atmosphere Apparent spectral radiant emittance in polarization direction , the calculation formula is:

[0043] ;

[0044] Step 403: Calculate the polarization degree of the target after atmospheric attenuation ;

[0045] ;

[0046] Calculate the polarization degree of the background after atmospheric attenuation;

[0047] ;

[0048] Step 404: Based on the transmittance deviation of the polarization optical element corresponding to the transmission axis, the polarization degree of the target after atmospheric attenuation is corrected. ;

[0049] Correct the polarization of the background after atmospheric attenuation ;

[0050] Where, 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.

[0051] In one possible implementation, the expression for constructing the range calculation model of the 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:

[0052] ;

[0053] Where, ; Indicates the projected height of the target within the detection range; The frequency is The minimum resolvable polarization difference is calculated as:

[0054] ;

[0055] Where, represents the lateral instantaneous field of view of the infrared detector, It represents the longitudinal instantaneous field of view of the infrared detector; Indicates the threshold value showing 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, represents the noise equivalent polarization degree difference of the infrared polarization imaging system; where the transfer function The function expression is:

[0056] ;

[0057] Where, Express the modulation transfer function of a polarization optical element:

[0058] , represents the cutoff frequency of the optical lens, Indicates the clear aperture of the optical lens; Indicates the polarization direction;

[0059] Express the modulation transfer function of the optical lens: , represents the cutoff frequency of the optical lens, Indicates the clear aperture of the optical lens;

[0060] Express the modulation transfer function of the infrared detector:

[0061] , 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;

[0062] Represents the modulation transfer function of the information processing circuit:

[0063] ;

[0064] Express the modulation transfer function of the display:

[0065] , represents the spatial characteristic frequency, , represents the instantaneous field of view of the infrared polarization imaging system;

[0066] The function expression is:

[0067] ;

[0068] Where, differential symbols; represents the degree of polarization; Indicates the infrared radiation spectrum power 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, Indicates the photosensitivity area of the infrared detector; Express the equivalent noise temperature difference:

[0069] ;

[0070] Where, 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.

[0071] In a possible implementation, the range calculation model after the detection probability and observation level of the preset range calculation model in step 6 are corrected is:

[0072] ;

[0073] Where, Indicates the difference in polarization between the target and the background After atmospheric attenuation, the time it reaches the infrared polarization imaging system is equal to the spatial frequency of the infrared polarization imaging system. Minimum resolvable polarization difference under The limit spatial frequency is ;

[0074] in:

[0075] ;

[0076] ;

[0077] Where, 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 value indicating the signal-to-noise ratio when the detection probability is 50% is shown; Represents the detection probability The threshold value displays 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 displaying the signal-to-noise ratio is:

[0078] .

[0079] In a possible implementation, the expression for determining in step 8 whether the difference between the operating distance output in step 7 and the initial operating 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 iterative cycle ends; if it is greater than the preset threshold, then , is the preset decrement threshold; and returns to step 3, Indicates the action distance, represents the initial action distance, Indicates the preset threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 This is a schematic diagram of polarization imaging detection of infrared targets according to a specific embodiment of the present invention;

[0081] Figure 2 : is a curve showing the relationship between detection probability and target equivalent strip logarithm at different observation levels in a specific embodiment of the present invention;

[0082] Figure 3 The atmospheric transmittance curves corresponding to different working bands in the specific embodiment of the present invention;

[0083] Figure 4 The curve showing the change of atmospheric path radiation with path distance in a specific embodiment of the present invention;

[0084] Figure 5 is a graph showing the relationship between MRPD and spatial frequency in a specific embodiment of the present invention;

[0085] Figure 6 A graph showing the relationship between MTF and spatial frequency in a specific embodiment of the present invention;

[0086] Figure 7 In the specific embodiment of the present invention, the x direction and the y direction Graph of its relationship with spatial frequency. DETAILED DESCRIPTION

[0087] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of the present application and are not intended to limit the scope of protection of the embodiments of the present application. Those skilled in the art may adjust them as needed to suit specific application scenarios.

[0088] In the description of the embodiments of this application, it should be noted that, unless otherwise specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on the specific circumstances.

[0089] In the embodiments of the present application, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "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," and "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.

[0090] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0091] See also Figures 1 to 7 As shown, the embodiment of the present application discloses a method for calculating the effective range of an infrared polarization imaging system, which uses an infrared polarization imaging system to image a scene containing 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.

[0092] This specific implementation example Figure 1 The infrared polarization imaging system detection schematic diagram shown includes:

[0093] 1) The polarization characteristics of the infrared radiation from the target and background are attenuated by atmospheric transmission and modulated by polarization optical elements, converging onto the focal plane of the infrared detector. The signals 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 what type of target it is.

[0094] 2) Taking into account 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 background such as trees and highlighting artificial targets;

[0095] 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 perceived by the infrared polarization imaging system and the effective range 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.

[0096] Among them, the infrared polarization imaging system parameters, target parameters, background parameters, atmospheric environment parameters and observation parameters are shown in Table 1:

[0097] Table 1 Target infrared polarization imaging detection setting parameters

[0098]

[0099] This specific embodiment provides a method for calculating the effective range of an infrared polarization imaging system, including:

[0100] Step 1: Obtain scene parameter information and basic parameters of the infrared polarization imaging system;

[0101] The scene parameter information includes the temperature of the target , background temperature , target polarization degree , background polarization , target polarization angle , background polarization angle And the projected height of the target within the detection range and projection width ;

[0102] The basic parameters of the infrared polarization imaging system include the focal length of the optical lens , pixel size of infrared detector .

[0103] Step 2: Preset the detection probability and observation level of the infrared polarization imaging system and calculate the initial working range of the infrared polarization imaging system. This embodiment calculates the initial working range of the infrared polarization imaging system under ideal conditions, specifically including:

[0104] Step 201: Based on the projected height of the target within the detection range and projection width Calculating critical dimensions , the calculation formula is:

[0105] ;

[0106] The critical size of the target in this embodiment .

[0107] Step 202: Calculate the instantaneous viewing angle based on the basic parameters of the infrared polarization imaging system. , the calculation formula is:

[0108] ;

[0109] The instantaneous viewing angle of the infrared polarization imaging system in this specific embodiment .

[0110] 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:

[0111] ;

[0112] Where, represents the number of target equivalent bands at the corresponding observation level under Johnson's criterion;

[0113] The detection probability of this specific embodiment The Johnson Criterion is used to determine the infrared thermal imager's ability to identify a target, regardless of the target's nature or image defects. The Johnson Criterion measures the resolution of the target's equivalent stripe pairs (number of spatial periods) within the target's minimum angular span, regardless of the target's nature or image defects. As shown in Table 2, under the Johnson Criterion, with a 50% probability, 1) detection requires an equivalent stripe pair of at least 1, indicating the presence of the target; 2) recognition requires an equivalent stripe pair of at least 4, indicating the classification of the target, such as a car; and 3) identification requires an equivalent stripe pair of at least 6.4, indicating the observer can describe the target's specific model and category.

[0114] Table 2 Equivalent band logarithms corresponding to different observation levels under 50% observation probability

[0115] ;

[0116] Probability of detection Number of equivalent bands to the target The relationship is:

[0117] ;

[0118] Where, Represents the coefficient under the corresponding observation level. When the observation level is detection level, ; When the observation level is the identification level, ; When the observation level is the recognition level, ; It indicates the number of target equivalent bands at the corresponding observation level when the detection probability is 50%; when the observation level is detection level, ; When the observation level is the identification level, ; When the observation level is the recognition level, ;

[0119] like Figure 2 As shown in the figure, the relationship curve between detection probability and target equivalent strip logarithm under different observation levels shows that when the detection probability is the same, the higher the observation level, the more target equivalent strip logarithm is required; when the observation level is the same, the greater the detection probability, the more target equivalent strip logarithm is required; this means that the more equivalent strip logarithm of the target, the clearer the observed target is, which is conducive to target identification.

[0120] Step 204, the ideal conditions include the following: the first condition that the target and the scene have a temperature difference exceeding the threshold; the second condition that atmospheric radiation attenuation is not considered; the third condition that the noise equivalent temperature difference of the infrared detector is less than or equal to the preset threshold; the fourth condition that the performance improvement effect of the image enhancement algorithm is ignored; the fifth condition that the performance loss caused by the host computer display is ignored; the initial working distance of the infrared imaging polarization system The calculation formula is: ;

[0121] In this specific embodiment, the initial action distance corresponding to the target .

[0122] Step 3: Obtain the environmental information of the scene and calculate the infrared radiation atmospheric transmittance at the initial working distance;

[0123] The environmental information of this specific embodiment includes: atmospheric 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 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 the curves. According to the Lambert-Beer law, the calculation formula for atmospheric transmittance on different paths is:

[0124] ;

[0125] Where, represents the atmospheric extinction coefficient, .

[0126] Step 4: Calculate the temperature and polarization degree of the target and background after atmospheric attenuation based on the scene parameter information and infrared radiation atmospheric transmittance;

[0127] 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 be attenuated during the transmission process, thereby affecting the imaging quality and effective range of the system.

[0128] The step 4 specifically includes:

[0129] Step 401, calculate the target Apparent spectral radiant emittance in polarization direction , the calculation formula is:

[0130] ;

[0131] Where, Indicates the target is Spectral polarization emissivity in polarization direction, ; Expressed as a Planck blackbody at temperature as well as Spectral radiant emittance in polarization direction, The calculation formula is:

[0132] ;

[0133] Where, 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, ;

[0134] In this specific embodiment, the apparent spectral radiation emittance of the target at 0°, 45°, 90° and 135° polarization directions can be calculated using Matlab software and are: 、 、 、 ;

[0135] Computational background in Apparent spectral radiant emittance in polarization direction , the calculation formula is:

[0136] ;

[0137] Where, Indicates the background Spectral polarization emissivity in polarization direction; Planck blackbody at temperature as well as Spectral radiant emittance in polarization direction;

[0138] 、 、 、 .

[0139] In step 402, the polarization of the target and background is attenuated during the transmission process due to the scattering of atmospheric molecules and aerosol particles (Rayleigh scattering, Mie scattering, etc.), absorption of water vapor, and the atmosphere's own radiation. Assuming that the depolarization effect of scattering by atmospheric molecules and suspended particles in the air is ignored, and the inherent polarization characteristics of atmospheric radiation 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, based on the preset atmospheric environment parameters, the spectral radiation emittance of atmospheric radiation at different detection distances is calculated using MODTRAN software. The results are as follows: Figure 4 As shown in the figure, 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.

[0140] Calculate the target after atmospheric attenuation Apparent spectral radiant emittance in polarization direction , the calculation formula is:

[0141] ;

[0142] Where, represents the atmospheric radiation along the observation path; Represents the ambient temperature of the scene along the observation path;

[0143] After atmospheric attenuation, the apparent spectral radiant emittance of the target at 0°, 45°, 90° and 135° polarization directions are: 、 、 、 ;

[0144] After calculating the background attenuation through the atmosphere Apparent spectral radiant emittance in polarization direction , the calculation formula is:

[0145] ;

[0146] After atmospheric attenuation, the apparent spectral radiant emittance of the background at 0°, 45°, 90° and 135° polarization directions are: 、 、 、 .

[0147] Step 403: Calculate the polarization degree of the target after atmospheric attenuation ;

[0148] ;

[0149] This specific embodiment ;

[0150] Calculate the polarization degree of the background after atmospheric attenuation;

[0151] ;

[0152] This specific embodiment .

[0153] Step 404: Based on the transmittance deviation of the polarization optical element corresponding to the transmission axis, the polarization degree of the target after atmospheric attenuation is corrected. ;

[0154] Correct the polarization of the background after atmospheric attenuation ;

[0155] Where, , 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.

[0156] According to the preset parameters of the infrared polarization imaging system, the extinction ratio of the polarization optical element Therefore, after 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 .

[0157] 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. 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:

[0158] ;

[0159] Where, ; Indicates the projected height of the target within the detection range; Indicates the frequency The minimum resolvable polarization difference (MRPD) is the minimum resolvable polarization difference (MRPD). 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 4 stripes, the polarization difference between the target and the background is called the minimum resolvable polarization difference (MRPD) in that space. This indicator is based on the observer's subjective vision 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 based on 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:

[0160] ;

[0161] Where, represents the lateral instantaneous field of view of the infrared detector, It represents the longitudinal instantaneous field of view of the infrared detector; Indicates the threshold value showing 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, It represents the noise equivalent polarization degree difference of infrared polarization imaging system;

[0162] Specifically, the transfer function The function expression is:

[0163] ;

[0164] Where, Express the modulation transfer function of a polarization optical element:

[0165] , represents the cutoff frequency of the optical lens, , Indicates the clear aperture of the optical lens; Indicates the polarization direction;

[0166] Express the modulation transfer function of the optical lens:

[0167] , represents the cutoff frequency of the optical lens, Indicates the clear aperture of the optical lens;

[0168] Express the modulation transfer function of the infrared detector:

[0169] , 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, represents the vertical instantaneous field of view of the infrared polarization imaging system;

[0170] Represent the modulation transfer function of the signal processor:

[0171] ;

[0172] Represents the modulation transfer function of the host computer:

[0173] , represents the spatial characteristic frequency, , represents the instantaneous field of view of the infrared polarization imaging system;

[0174] This specific embodiment simulates and calculates the MTF of the infrared polarization imaging system based on preset system parameters. Figure 6 The modulation transfer function (MTF) corresponding to different spatial frequencies.

[0175] Specifically, The function expression is:

[0176] ;

[0177] Where, differential symbols; represents the degree of polarization; Indicates the infrared radiation spectrum power 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 ), the expression of the equivalent noise temperature difference (NETD) of the traditional infrared imaging system is:

[0178] ;

[0179] Where, 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.

[0180] In this specific embodiment, it is assumed that the NETD of the detector in the infrared polarization imaging system is 50 mK (= 0.05 K), and calculation shows that the noise equivalent polarization difference NEPD of the infrared polarization imaging system is approximately 0.219%.

[0181] Step 6: Preset the detection probability of the range calculation model =50% and observation level, and the revised action distance calculation model is obtained;

[0182] Among them, the corrected action distance calculation model is:

[0183] ;

[0184] Where, Indicates the difference in polarization between the target and the background After atmospheric attenuation, the time it reaches the infrared polarization imaging system is equal to the spatial frequency of the infrared polarization imaging system. Minimum resolvable polarization difference under The limit spatial frequency is ;

[0185] in:

[0186] ;

[0187] ;

[0188] Where, 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 value indicating the signal-to-noise ratio when the detection probability is 50% is shown; Represents the detection probability The threshold value displays 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 displaying 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 of the human visual system is , different spatial frequencies The corresponding corrected minimum resolvable polarization difference (MRPD) is as follows: Figure 7 As shown;

[0189] The working range of the infrared polarization imaging system of this specific embodiment R =(3.5 / 4)×(2×0.25)×1000=437.5m.

[0190] Step 7: Input the target and background temperature values and polarization degrees obtained in step 4 into the corrected range calculation model to output the range of the infrared polarization imaging system.

[0191] Step 8: Determine whether the difference between the effective distance output in step 7 and the initial effective distance is less than or equal to a preset threshold. The expression is: ; This specific embodiment 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 iterative cycle ends; if it is greater than the preset threshold, then , is the preset decrement threshold; and returns to step 3, Indicates the action distance, represents the initial action distance, Indicates the preset threshold.

[0192] This specific embodiment finally obtains the effective distance of the infrared polarization imaging system to the target R ≈1110.2m.

[0193] 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 accompanying 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.

[0194] 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" 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 can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0195] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for calculating the effective range of an infrared polarization imaging system, wherein the infrared polarization imaging system is used to image a scene containing a target and a background, characterized in that: The method for calculating the effective distance of the infrared polarization imaging system includes: Step 1: Obtain scene parameter information and basic parameters of the infrared polarization imaging system; Step 2: Preset the detection probability and observation level of the infrared polarization imaging system and calculate the initial range; specifically, Step 201: Calculate the critical dimension w based on the projected height H and projected width W of the target within the detection range. The calculation formula is: Step 202: Calculate the instantaneous field of view (IFoV) based on the basic parameters of the infrared polarization imaging system. The calculation formula is: Where a represents the pixel size of the infrared detector, and f represents the focal length of the optical lens; Step 203: Preset the detection probability and observation level of the range calculation model and calculate the number of pixels PPM required for target imaging. The calculation formula is: Where N e represents the number of target equivalent bands at the corresponding observation level under Johnson's criterion; Detection probability p and target equivalent strip logarithm N e The relationship is: Where, δ represents the coefficient at the corresponding observation level, and N0 represents the number of equivalent target bands at the corresponding observation level when the detection probability is 50%. In step 204, the calculation formula of the initial operating distance R0 is: Step 3: Obtain the environmental information of the scene and calculate the infrared radiation atmospheric transmittance at the initial working distance; Step 4, based on the scene parameter information and the infrared radiation atmospheric transmittance, respectively calculate the temperature value and polarization degree of the target after atmospheric attenuation, as well as the temperature value and polarization degree of the background; Step 5: Based on the noise equivalent temperature difference, 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; Step 6: Preset the detection probability and observation level of the range calculation model to obtain a revised range 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 value, into the revised range calculation model, and outputting the range 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. If so, output the effective distance; if not, decrease the initial effective distance according to the preset decreasing threshold, and return to step 3.

2. The method for calculating the effective range 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 T of the target t , background temperature T b , target polarization degree D t , background polarization degree D b , target polarization angle α t , background polarization angle α b And the projection height H and projection width W of the target within the detection range; the basic parameters of the infrared polarization imaging system include the focal length f of the optical lens and the pixel size a of the infrared detector.

3. The method for calculating the effective range of the infrared polarization imaging system according to claim 1, characterized in that: The environmental information of the scene in step 3 includes: atmospheric 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 τ of infrared radiation at the current initial working distance. R .

4. The method for calculating the effective range of the infrared polarization imaging system according to claim 3, characterized in that: The step 4 specifically includes: Step 401: Calculate the apparent spectral radiant emittance of the target in the θ polarization direction The calculation formula is: Where, ε t (λ,θ) represents the spectral polarization emissivity of the target in the θ polarization direction, θ = [0°, 45°, 90°, 135°]; M b (λ; T t ) represents the Planck black body at temperature T t and the spectral radiant emittance in the θ polarization direction, M b (λ; T t ) is calculated as: Wherein, λ1 represents the lower limit of the infrared detector integration band, λ2 represents the upper limit of the infrared detector integration band, c1 represents the first radiation constant, and c2 represents the second radiation constant; Calculate the apparent spectral radiance emittance of the background in the θ polarization direction The calculation formula is: Where, ε b (λ;θ) represents the spectral polarization emissivity of the background in the θ polarization direction; M b (λ; T b ) Planck black body at temperature T b and the spectral radiant emittance in the θ polarization direction; Step 402: Calculate the apparent spectral radiance of the target in the θ polarization direction after atmospheric attenuation. The calculation formula is: Where, represents the atmospheric radiation along the observation path; T atm Represents the ambient temperature of the scene along the observation path; Calculate the apparent spectral radiance emittance in the θ polarization direction after the background is attenuated by the atmosphere The calculation formula is: Step 403: Calculate the degree of polarization DoLP of the target after atmospheric attenuation t ; Calculate the polarization degree of the background after atmospheric attenuation; Step 404: Based on the transmittance deviation corresponding to the transmission axis of the polarization optical element, correct the polarization degree of the target after atmospheric attenuation. Correct the polarization of the background after atmospheric attenuation Where, e represents the extinction ratio of the polarization optical element, e = τ max / τ min , τ max Indicates the transmittance corresponding to the maximum transmission axis of the polarization optical element, τ min Indicates the transmittance corresponding to the minimum transmission axis of the polarization optical element.

5. The method for calculating the effective range of the infrared polarization imaging system according to claim 4, characterized in that: In step 5, the expression for constructing the range calculation model of the infrared polarization imaging system by combining the noise equivalent polarization difference and the minimum resolution polarization difference between the target and the scene is: Where, ΔDoLP(R)=DoLP t ′-DoLP b ′; H represents the projected height of the target within the detection range, and MRPD(f) represents the minimum resolvable polarization difference at frequency f. The calculation formula is: Where α represents the lateral instantaneous field of view of the infrared detector, β represents the longitudinal instantaneous field of view of the infrared detector; SNR TH Indicates the threshold value showing the signal-to-noise ratio; t e represents the integration time of the human eye, Δf represents the noise equivalent bandwidth, and f p represents the frame rate, τ d Indicates dwell time, MTF pp (f) represents the transfer function of the infrared polarization imaging system with a spatial frequency of f, and NEPD represents the noise equivalent polarization difference of the infrared polarization imaging system; where the transfer function MTF pp The function expression of (f) is: MTF pp (f)=MTF p (f)·MTF o (f)·MTF d (f)·MTF e (f)·MTF s (favorite) Where, MTF p (f) represents the modulation transfer function of the polarization optical element: Where f0 represents the cutoff frequency of the optical lens, f0 = D0 / λ, D0 represents the clear aperture of the optical lens; θ represents the polarization direction; MTF o (f) represents the modulation transfer function of the optical lens: f0 represents the cutoff frequency of the optical lens, f0=D0 / λ, D0 represents the clear aperture of the optical lens; MTF d (f) represents the modulation transfer function of the infrared detector: W represents the instantaneous field of view of the infrared polarization imaging system, W = α·β; α represents the horizontal instantaneous field angle of the infrared polarization imaging system, β represents the vertical instantaneous field angle of the infrared polarization imaging system; MTF e (f) represents the modulation transfer function of the information processing circuit: MTF e (f)=[1+(2·W 1 / 2 ·f) 2 ] -1 / 2 MTF s (f) represents the modulation transfer function of the display: MTF s (f) = exp[-2π 2 (0.25) 2 ·(f / f s ) 2 ], fs represents the spatial characteristic frequency, f s =1 / α, where α represents the instantaneous field of view of the infrared polarization imaging system; The functional expression of NEPD is: Where, represents the differential sign; P represents the degree of polarization; W(λ,α) represents the infrared radiation spectrum power irradiated on the infrared detector; T represents the blackbody temperature, M e (λ; T) represents the spectral radiation emittance of a blackbody with a temperature of T; D e (λ; T t ) represents the polarization degree of the incident target infrared radiation, F represents the F number of the optical lens, A d Represents the photosensitivity area of the infrared detector; NETD represents the equivalent noise temperature difference: Where R v Indicates the spectral sensitivity of the infrared detector; F represents the F number of the optical lens, M e (λ; T) represents the blackbody spectral radiation emittance with temperature T; V n Represents the RMS noise output voltage.

6. The method for calculating the effective range of the infrared polarization imaging system according to claim 5, characterized in that: The detection probability and observation level of the range calculation model are preset in step 6, and the corrected range calculation model is obtained as follows: Where f' represents the limit spatial frequency of the minimum resolvable polarization difference MRPD of the infrared polarization imaging system at the spatial frequency f when the polarization difference ΔDoLP(R) between the target and the background reaches the infrared polarization imaging system after atmospheric attenuation, that is, ΔDoLP(R) = MRPD p (f′); in: ΔDoLP(R)=DoLP t -DoLP b Where m represents the corrected equivalent band logarithm N e patterned aspect ratio; α0 represents the actual aspect ratio of the target; the corrected equivalent strip logarithm N e Based on the calculation formula We get, p represents the detection probability; MRPD p (f′) represents the minimum resolvable polarization difference corrected proportionally, SNR TH The threshold value indicates the signal-to-noise ratio when the detection probability is 50%. SNR indicates the threshold value indicates the signal-to-noise ratio when the detection probability is p. Based on the correlation between image clarity and image signal-to-noise ratio, the calculation formula for the modified threshold value is:

7. The method for calculating the effective range of the infrared polarization imaging system according to claim 6, characterized in that: 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: |R-R0|≤ε; If it is less than or equal to the preset threshold, the output working distance R is the working distance of the infrared polarization imaging system, and the iterative cycle ends; If it is greater than the preset threshold, is the preset decreasing threshold; and returns to step 3, R represents the action distance, R0 represents the initial action distance, and ε represents the preset threshold.

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