Infrared defocus plane polarization correction method based on polarizer reflection polarization characteristics

Abstract

The application discloses an infrared focal plane polarization correction method based on the reflection polarization characteristics of a polarizer and belongs to the technical field of polarization imaging and test measurement. The method of the application is as follows: a correction coefficient is added to adjust additional radiation to obtain a radiation transmission correction model of an infrared polarization imaging system with a front polarizer; a nonlinear method is used to fit the relationship between image gray scale and incident radiation to realize response correction of the infrared polarization imaging system with the front polarizer; the infrared polarization imaging system with the front polarizer is used to calibrate a temperature-controllable adjustable infrared polarization radiation source; a radiation transmission model of an infrared focal plane polarization imaging system is constructed; and the temperature-controllable adjustable infrared polarization radiation source is used to perform response correction and polarization correction on the infrared focal plane polarization imaging system. Compared with placing a high-extinction-ratio polarizer in front of a black body, the application can avoid over-correction of the parameters of a micro-polarizer array and improve the correction accuracy of the infrared focal plane polarization imaging system.

Description

TECHNICAL FIELD

[0001] The application relates to an infrared focal plane polarization correction method, in particular to an infrared focal plane polarization correction method based on the reflection polarization characteristics of a polarizer, and belongs to the technical field of polarization imaging and test metrology. BACKGROUND

[0002] Polarization is one of the main physical characteristics of electromagnetic waves. The introduction of polarization information in conventional imaging technology can effectively broaden the dimension of acquired information. Therefore, the polarization imaging technology has broad application prospects in the fields of military security, biomedicine, material science, environmental monitoring, etc., and can provide important technical support for target detection and identification, disease diagnosis and drug research, material characterization and defect detection, etc.

[0003] The focal plane polarization imaging system couples polarizers with different polarization directions on the surface of a detector, can simultaneously acquire the polarization state of a scene, and has no moving parts, a compact structure and is firm and reliable, thus becoming a research hotspot of the polarization imaging technology in recent years. However, the focal plane polarization imaging system has instantaneous field of view errors, which leads to reduced system resolution. In addition, the depolarization characteristics of the optical system, the non-ideality of the micro-polarizer array and the difference in the response of the detector pixels lead to serious non-uniformity problems of the focal plane polarization imaging system.

[0004] In the visible and near-infrared waveband, the spontaneous radiation and the reflection radiation of the polarizer can be ignored. However, in the mid-wave and long-wave infrared waveband, the spontaneous radiation and the reflection radiation of the polarizer cannot be ignored, and the spontaneous radiation can be considered as non-polarized radiation, but the reflection radiation is polarized radiation. When the polarizer is placed in front of a black body, even if the polarizer is an ideal polarizer, the polarization degree of the outgoing radiation is not ideal 1. When the black body temperature is lower than the ambient temperature, the polarization degree of the outgoing radiation is more affected by the ambient temperature.

[0005] In summary, for the infrared focal plane polarization imaging system, it is necessary to consider the polarization characteristics of the reflection radiation of the polarizer. How to accurately calibrate the micro-polarizer array parameters of the infrared focal plane polarization imaging system is a key problem to be solved. SUMMARY

[0006] The current infrared polarization imaging model regards the outgoing radiation of the high-extinction-ratio polarizer placed in front of the blackbody as complete polarized radiation or only considers that the transmission radiation of the polarizer is related to the polarization angle, and does not consider the polarization characteristics of the reflection radiation of the polarizer, so that the calibrated polarization imaging system parameters are overcorrected, and the purpose of the infrared split focal plane polarization correction method based on the reflection polarization characteristics of the polarizer is to: add a correction coefficient to adjust the additional radiation in the radiation transmission model of the front polarizer infrared polarization imaging system, so as to obtain the radiation transmission model of the front polarizer infrared polarization imaging system after the additional radiation is corrected; the relationship between the image gray value and the incident radiation is fitted by using a nonlinear method, so as to realize the response correction of the front polarizer infrared polarization imaging system; the radiation transmission model of the front polarizer infrared polarization imaging system after the additional radiation is corrected is used to calibrate the temperature-controlled adjustable infrared polarization radiation source, so as to improve the calibration accuracy of the temperature-controlled adjustable infrared polarization radiation source; the infrared split focal plane polarization imaging system is analyzed, and the radiation transmission model of the infrared split focal plane polarization imaging system is constructed; and the response correction and polarization correction of the infrared split focal plane polarization imaging system are realized by using the temperature-controlled adjustable infrared polarization radiation source and the radiation transmission model of the infrared split focal plane polarization imaging system.

[0007] The purpose of the present application is achieved by the following technical solutions.

[0008] The infrared split focal plane polarization correction method based on the reflection polarization characteristics of the polarizer disclosed by the present application adjusts the additional radiation by adding a correction coefficient to obtain a radiation transmission correction model of the front polarizer infrared polarization imaging system. The relationship between the image gray value and the incident radiation is fitted by using a nonlinear method, so as to realize the response correction of the front polarizer infrared polarization imaging system. The front polarizer infrared polarization imaging system is used to calibrate the temperature-controlled adjustable infrared polarization radiation source. The radiation transmission model of the infrared split focal plane polarization imaging system is constructed. The temperature-controlled adjustable infrared polarization radiation source is used to realize the response correction and polarization correction of the infrared split focal plane polarization imaging system. Compared with placing a high-extinction-ratio polarizer in front of the blackbody and regarding the outgoing radiation thereof as known input, the present application can avoid the overcorrection of the micro-polarizer array parameters and improve the correction accuracy of the infrared split focal plane polarization imaging system.

[0009] The infrared split focal plane polarization correction method based on the reflection polarization characteristics of the polarizer disclosed by the present application comprises the following steps:

[0010] Step 1, the pre-polarizer infrared polarization imaging system includes an optical system, a polarizer and a detector. The radiation reaching the polarizer includes incident radiation, spontaneous radiation of the optical system and spontaneous radiation of the polarizer reflected by the optical system. The radiation reaching the detector includes the radiation of the incident radiation passing through the polarizer, the spontaneous radiation of the polarizer and the spontaneous radiation of the detector reflected by the polarizer. Among them, the polarizer reflected radiation is a biased radiation, the main direction of which is perpendicular to the main direction of the transmitted radiation, resulting in a decrease in the degree of polarization of the radiation incident on the detector. At the same time, the spontaneous radiation of the optical system and the spontaneous radiation of the polarizer also cause the degree of polarization of the radiation incident on the detector to decrease.

[0011] The radiation transmission model of the pre-polarizer infrared polarization imaging system is constructed as shown in formula (1):

[0012]

[0013] Among them, the Stokes vector of the incident radiation without considering the circular polarization component is I np is the unbiased radiation intensity, τ os is the transmittance of the optical system, τ1 and τ2 are the main and secondary direction transmittances of the polarizer, and R is the additional radiation of the pre-polarizer infrared polarization imaging system.

[0014] The additional radiation introduced by the polarizer and the non-polarizer of the pre-polarizer infrared polarization imaging system is different. When the polarizer of the pre-polarizer infrared polarization imaging system is removed

[0015]

[0016] Among them, is the additional radiation without a polarizer, ε os and ε d are the spontaneous radiation rates of the optical system and the detector, and are the radiations of the optical system and the detector, ρ os is the reflection radiation rate of the optical system.

[0017] When the polarizing angle of the pre-polarizer infrared polarization imaging system is θ

[0018]

[0019] Among them, is the additional radiation with a polarizer, ε a is the spontaneous radiation rate of the polarizer, is the radiation of the polarizer.

[0020] The additional radiation is adjusted by adding a correction coefficient in the pre-polarizer infrared polarization imaging system radiation transmission model as shown in formula (1) to obtain the pre-polarizer infrared polarization imaging system radiation transmission model after the additional radiation is corrected as shown in formula (4):

[0021]

[0022] The correction coefficient is The ratio of the additional radiation without an analyzer to the additional radiation with an analyzer.

[0023] The pre-polarizer infrared polarization imaging system radiation transmission model after the additional radiation is corrected as shown in formula (4) improves the characterization accuracy of the pre-polarizer infrared polarization imaging system radiation transmission model on the pre-polarizer infrared polarization imaging system.

[0024] Step 2, using the pre-polarizer infrared polarization imaging system of step 1 to collect gray scale images of different incident radiation, using a nonlinear method to fit the relationship between image gray scale and incident radiation, realizing the conversion of image gray scale and incident radiation, that is, realizing the response correction of the pre-polarizer infrared polarization imaging system.

[0025] Step 2.1, remove the optical system of the pre-polarizer infrared polarization imaging system described in step 1 to avoid the influence of the optical system on the calibration. The pre-polarizer infrared polarization imaging system is closely attached to the blackbody radiation source to reduce the influence of stray radiation. The pre-polarizer infrared polarization imaging system is switched to the intensity channel to collect gray scale images of different incident radiation. The collected gray scale images corresponding to the same incident radiation are averaged to reduce the influence of time noise.

[0026]

[0027] DN(x,y,T) is the gray scale of the image at (x,y) corresponding to the blackbody temperature T, DN(x,y,T,i) is the gray scale of the image at (x,y) corresponding to the blackbody temperature T, and N is the number of images collected when the blackbody temperature is T.

[0028] Step 2.2, using a nonlinear method to fit the relationship between image gray scale and incident radiation, realizing the conversion of image gray scale and incident radiation, that is, realizing the response correction of the pre-polarizer infrared polarization imaging system.

[0029] According to the blackbody radiation formula, the incident radiation of the pre-polarizer infrared polarization imaging system corresponding to the waveband is calculated. According to formula (6), the incident radiation and the image gray scale are nonlinearly fitted to obtain the gain, bias and nonlinear coefficient of the pre-polarizer infrared polarization imaging system.

[0030] DN(x,y,T)=a(x,y)I(T)γ(x,y) + b(x, y) (6)

[0031] where I(T) is the incident radiation corresponding to the blackbody temperature T, a(x, y) is the gain at the image (x, y), b(x, y) is the offset at the image (x, y), and γ(x, y) is the nonlinear coefficient at the image (x, y).

[0032] The conversion of the image gray scale and the incident radiation is realized according to the formula (6), that is, the response correction of the pre-polarizer infrared polarization imaging system is realized.

[0033] Step 3, using the pre-polarizer infrared polarization imaging system in step 1 to collect the different detection angle images and intensity images of the pre-polarizer infrared polarization imaging system corresponding to different blackbody temperatures and different polarizer temperatures of the temperature-controllable adjustable infrared polarization radiation source. The radiation transfer model of the pre-polarizer infrared polarization imaging system after the additional radiation correction is used to calibrate the temperature-controllable adjustable infrared polarization radiation source, so as to improve the calibration accuracy of the temperature-controllable adjustable infrared polarization radiation source.

[0034] Step 3.1, using the pre-polarizer infrared polarization imaging system in step 1 to collect the different detection angle images and intensity images of the pre-polarizer infrared polarization imaging system corresponding to different blackbody temperatures and different polarizer temperatures of the temperature-controllable adjustable infrared polarization radiation source.

[0035] The polarizer is placed in the variable-temperature transmission bracket, and the blackbody radiation source and the variable-temperature transmission bracket form the temperature-controllable adjustable infrared polarization radiation source. The pre-polarizer infrared polarization imaging system is placed in front of the temperature-controllable adjustable infrared polarization radiation source, and the optical system is adjusted to clearly image. The blackbody temperature and the polarizer temperature are fixed, the polarizer is rotated, and multiple different detection angle images and intensity images are collected. The blackbody temperature and the polarizer temperature are changed, and the above process of collecting multiple different detection angle images and intensity images is repeated. The same blackbody temperature, the same polarizer temperature, the same detection angle image or the intensity image are averaged to reduce the influence of time noise.

[0036]

[0037] where DN(x, y, T, t, θ) is the gray scale of the image (x, y) corresponding to the blackbody temperature T, the polarizer temperature t, and the detection angle θ, DN(x, y, T, t, θ, i) is the gray scale of the image (x, y) corresponding to the blackbody temperature T, the polarizer temperature t, and the detection angle θ of the i-th image, and N is the number of images collected at the blackbody temperature T, the polarizer temperature t, and the detection angle θ.

[0038] Step 3.2, calibrate the temperature-controllable adjustable infrared polarized radiation source by using the additional radiation corrected pre-polarizer infrared polarized imaging system radiation transfer model obtained in step 1, and improve the calibration accuracy of the temperature-controllable adjustable infrared polarized radiation source.

[0039] The Stokes vector of the radiation reaching the detector is calculated by using the polarized image and the intensity channel image under the same blackbody temperature and the same polarizer temperature. According to the additional radiation corrected pre-polarizer infrared polarized imaging system radiation transfer model in step 1, the Stokes vector of the incident radiation of the pre-polarizer infrared polarized imaging system, i.e. the Stokes vector of the outgoing radiation of the temperature-controllable adjustable infrared polarized radiation source, is solved.

[0040] Step 4, the infrared split focal plane polarized imaging system includes an optical system, a micro-polarizer array and a focal plane array. The radiation reaching the micro-polarizer array includes the radiation of the incident radiation passing through the optical system, the spontaneous radiation of the optical system and the spontaneous radiation of the micro-polarizer array reflected by the optical system. The radiation reaching the focal plane array includes the radiation of the incident radiation passing through the micro-polarizer array, the spontaneous radiation of the micro-polarizer array and the spontaneous radiation of the focal plane array reflected by the micro-polarizer array. The infrared split focal plane polarized imaging system is analyzed, and an infrared split focal plane polarized imaging system radiation transfer model is constructed.

[0041] The constructed infrared split focal plane polarized imaging system radiation transfer model is shown in formula (8):

[0042]

[0043] Wherein, the Stokes vector of the incident radiation without considering the circular polarization component is I θ is the radiation reaching the focal plane array when the micro-polarizer array is at an angle of θ, τ os is the transmittance of the optical system, τ1 and τ2 are the main and secondary direction transmittances of the micro-polarizer array corresponding to the pixels, ε os , ε m and ε d are the spontaneous radiation rates of the optical system, the micro-polarizer array and the detector, respectively, and are the radiations of the optical system, the micro-polarizer array and the focal plane array, respectively, ρ os is the reflection radiation rate of the optical system.

[0044] In order to accurately obtain the parameters τ1, τ2 and θ of the micro-polarizer array, the Stokes vector of the incident radiation needs to be known. Due to the reflection polarization characteristics of the polarizer, the transmission and reflection of the radiation placed in front of the actual black body change with the polarization angle. Therefore, the micro-polarizer array parameters of the infrared focal plane polarization imaging system can be accurately obtained by using the temperature-controlled adjustable infrared polarized radiation source described in step 3.

[0045] Step 5, using the infrared focal plane polarization imaging system described in step 4 to collect gray scale images of different incident radiations, using a nonlinear method to fit the relationship between image gray scale and incident radiation, realizing the conversion of image gray scale and incident radiation, that is, realizing the response correction of the infrared focal plane polarization imaging system. Place the infrared focal plane polarization imaging system described in step 4 in front of the temperature-controlled adjustable infrared polarized radiation source described in step 3, and collect images of different black body temperatures, different polarizer temperatures and different polarization angles. According to the radiation transfer model of the infrared focal plane polarization imaging system constructed in step 4, the relationship between different incident radiations and image gray scale is fitted by using a nonlinear method, so as to obtain accurate micro-polarizer array parameters. According to the obtained micro-polarizer array parameters, the actual analysis matrix is constructed, and the infrared focal plane polarization imaging system described in step 4 is polarization corrected combined with the ideal analysis matrix. The exit radiation of the calibrated temperature-controlled adjustable infrared polarized radiation source is used as the known input, instead of the exit radiation of the high extinction ratio polarizer placed in front of the black body, which avoids the over-correction of the micro-polarizer array parameters of the infrared focal plane polarization imaging system and improves the correction accuracy of the infrared focal plane polarization imaging system.

[0046] Step 5.1, remove the optical system of the infrared focal plane polarization imaging system described in step 4 to avoid the influence of the optical system on the calibration. The infrared focal plane polarization imaging system is closely attached to the black body radiation source to reduce the influence of stray radiation. The gray scale images of different incident radiations are collected by using the infrared focal plane polarization imaging system, the collected gray scale images corresponding to the same incident radiation are averaged to reduce the influence of time noise. A nonlinear method is used to fit the relationship between image gray scale and incident radiation, realizing the conversion of image gray scale and incident radiation, that is, realizing the response correction of the infrared focal plane polarization imaging system.

[0047]

[0048] Wherein, τ1(x, y) is the main direction transmittance of the micro-polarizer array (x, y), τ2(x, y) is the secondary direction transmittance of the micro-polarizer array (x, y), and is the composite gain of the focal plane array and the micro-polarizer array.

[0049] Step 5.2, place the infrared split focal plane polarimetric imaging system described in step 4 in front of the temperature-controlled adjustable infrared polarized radiation source described in step 3, collect images at different blackbody temperatures, different polarizer temperatures, and different polarizing angles, and average each group of images to reduce the influence of time noise. According to the radiation transfer model of the infrared split focal plane polarimetric imaging system constructed in step 4, the relationship between different incident radiation and image gray scale is fitted by using a nonlinear method, so as to obtain accurate micro-polarizer array parameters. According to the obtained micro-polarizer array parameters, the actual analysis matrix is constructed, and the infrared split focal plane polarimetric imaging system is corrected in combination with the ideal analysis matrix. The exit radiation of the temperature-controlled adjustable infrared polarized radiation source is used as the known input, instead of the exit radiation of the high-extinction-ratio polarizer placed in front of the blackbody, to avoid over-correction of the micro-polarizer array parameters of the infrared split focal plane polarimetric imaging system and improve the correction accuracy of the infrared split focal plane polarimetric imaging system.

[0050] The actual analysis matrix and the ideal analysis matrix are shown in formulas (10) and (11), and the radiation after polarization correction is shown in formula (12):

[0051]

[0052]

[0053] wherein, and The main direction transmittance and the secondary direction transmittance corresponding to the detection angle of the micro-polarizer array are represented by and respectively.

[0054]

[0055] wherein, is the Stokes vector of the radiation after polarization correction, is the Stokes vector of the radiation before polarization correction.

[0056] Beneficial effects:

[0057] 1. The infrared split focal plane polarization correction method based on the reflective polarization characteristics of the polarizer disclosed in the application uses a temperature-controlled adjustable infrared polarized radiation source as the known input, which can accurately calibrate the micro-polarizer array parameters of the infrared split focal plane polarimetric imaging system, reduce the measurement and calculation errors of the micro-polarizer array parameters, avoid over-correction of the micro-polarizer array parameters, and improve the accuracy of the infrared split focal plane polarimetric imaging system in solving the polarization information of the external scene.

[0058] 2. The infrared split focal plane polarimetric correction method based on the reflective polarimetric characteristics of a polarizer, which considers the influence of the reflective radiation polarimetric characteristics of the polarizer, constructs a radiation transmission model of an infrared split focal plane polarimetric imaging system, and accurately reflects the radiation transmission process of the infrared split focal plane polarimetric imaging system.

[0059] 3. The infrared split focal plane polarimetric correction method based on the reflective polarimetric characteristics of a polarizer, which considers the additional radiation of the pre-polarizer infrared polarimetric imaging system when there is a polarimeter or no polarimeter, modifies the radiation transmission model of the pre-polarizer infrared polarimetric imaging system, and improves the characterization accuracy of the pre-polarizer infrared polarimetric imaging system by the radiation transmission model of the pre-polarizer infrared polarimetric imaging system.

[0060] 4. The infrared split focal plane polarimetric correction method based on the reflective polarimetric characteristics of a polarizer, which places a polarizer in a variable-temperature transmission support, and forms a temperature-controllable adjustable infrared polarimetric radiation source by combining a blackbody radiation source and the variable-temperature transmission support. By adjusting the temperature of the blackbody radiation source and the temperature of the polarizer, the polarization degree of the outgoing radiation of the temperature-controllable adjustable infrared polarimetric radiation source can be changed. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 It is a flow chart of the infrared split focal plane polarimetric correction method based on the reflective polarimetric characteristics of a polarizer.

[0062] Figure 2 It is an imaging principle diagram of a pre-polarizer infrared polarimetric imaging system.

[0063] Figure 3 It is a schematic diagram of a temperature-controllable adjustable infrared polarimetric radiation source.

[0064] Figure 4 It is an imaging principle diagram of an infrared split focal plane polarimetric imaging system.

[0065] Figure 5 It is the outgoing radiation polarization degree of the temperature-controllable adjustable polarimetric radiation source calibrated by the pre-polarizer infrared polarimetric imaging system.

[0066] Figure 6 It is the infrared split focal plane polarimetric correction result based on the reflective polarimetric characteristics of a polarizer, Figure 6 (a) is the change relationship between the gray scale and the polarization angle before correction, Figure 6 (b) is the change relationship between the irradiance and the polarization angle after response correction, Figure 6 (c) is the change relationship between the irradiance and the polarization angle after response correction and polarimetric correction.

[0067] Wherein: 1-Pre-polarizer infrared polarization imaging system optical system, 2-Pre-polarizer infrared polarization imaging system analyzer, 3-Pre-polarizer infrared polarization imaging system detector, 4-Surface temperature difference blackbody radiation source, 5-Temperature change transmission support, 6-High extinction ratio polarizer, 7-High transmittance window, 8-Focal plane polarization imaging system optical system, 9-Focal plane polarization imaging system micro-polarizer array, 10-Focal plane polarization imaging system focal plane array. DETAILED DESCRIPTION

[0068] In order to better illustrate the purpose and advantages of the present application, the content of the application is further illustrated below in combination with the drawings and examples.

[0069] Example 1:

[0070] As Figure 1 shown, the infrared focal plane polarization correction method based on the reflective polarization characteristics of the polarizer disclosed in this embodiment. First, the additional radiation is added to the pre-polarizer infrared polarization imaging system radiation transmission model to obtain the pre-polarizer infrared polarization imaging system radiation transmission model after the additional radiation is corrected. Secondly, the relationship between the image gray scale and the incident radiation is fitted by using the nonlinear method, and the response correction of the pre-polarizer infrared polarization imaging system is realized. Then, the temperature-controlled adjustable infrared polarization radiation source is calibrated by using the pre-polarizer infrared polarization imaging system radiation transmission model after the additional radiation is corrected, and the calibration accuracy of the temperature-controlled adjustable infrared polarization radiation source is improved. Next, the infrared focal plane polarization imaging system is analyzed, and the infrared focal plane polarization imaging system radiation transmission model is constructed. Finally, the response correction and polarization correction of the infrared focal plane polarization imaging system are realized by using the temperature-controlled adjustable infrared polarization radiation source and the infrared focal plane polarization imaging system radiation transmission model. The exit radiation of the calibrated temperature-controlled adjustable infrared polarization radiation source is used as the known input, instead of the exit radiation of the blackbody placed in front of the high extinction ratio polarizer, to avoid the over-correction of the micro-polarizer array parameters of the infrared focal plane polarization imaging system, and to improve the correction accuracy of the infrared focal plane polarization imaging system.

[0071] The infrared focal plane polarization correction method based on the reflective polarization characteristics of the polarizer of this embodiment includes the following specific implementation steps:

[0072] Step 1, as Figure 2The imaging principle diagram of the front polarizer infrared polarization imaging system disclosed in the embodiment is shown. The front polarizer infrared polarization imaging system comprises an optical system 1, a polarizer 2 and a detector 3. The radiation reaching the polarizer 2 comprises incident radiation, spontaneous radiation of the optical system 1 and spontaneous radiation of the polarizer 2 reflected by the optical system 1. The radiation reaching the detector 3 comprises radiation of the incident radiation passing through the polarizer 2, spontaneous radiation of the polarizer 2 and spontaneous radiation of the detector 3 reflected by the polarizer 2. The reflected radiation of the polarizer is a polarized radiation, the main direction of which is perpendicular to the main direction of the transmitted radiation, resulting in a decrease in the degree of polarization of the radiation incident on the detector. At the same time, the spontaneous radiation of the optical system and the spontaneous radiation of the polarizer also result in a decrease in the degree of polarization of the radiation incident on the detector.

[0073] When the front polarizer infrared polarization imaging system is a refrigeration type, the temperature of the detector plane array is extremely low, the influence of the spontaneous radiation of the detector can be ignored, and the additional radiation received by the detector is the spontaneous radiation of the optical system, the reflected radiation of the optical system and the spontaneous radiation of the polarizer. When the front polarizer infrared polarization imaging system is a non-refrigeration type, the spontaneous radiation of the detector cannot be ignored, and the temperature of the focal plane array changes with the working time, so it is necessary to try to ensure the stability of the core temperature when performing radiation correction of the non-refrigeration polarization thermal imager. According to formula (4), the relationship between the incident radiation Stokes vector and the radiation received by the detector can be obtained by using the JADE MWIR refrigeration thermal imager of the French Cedip company.

[0074]

[0075] wherein I0, I 60 , I 120 are the polarized radiation intensities at 0°, 60° and 120° respectively, I np is the unpolarized radiation intensity, θ0, θ 60 and θ 120 are the angles between the 0°, 60° and 120° of the polarizer and the reference direction respectively, R p is the additional radiation with the polarizer, and the correction coefficient k is the ratio of the additional radiation without the polarizer to that with the polarizer.

[0076] Step 2, remove the optical system of the pre-polarizer infrared polarization imaging system in step 1 to avoid the influence of the optical system on the calibration. The pre-polarizer infrared polarization imaging system is closely attached to the blackbody radiation source to reduce the influence of stray radiation. The pre-polarizer infrared polarization imaging system is switched to the intensity channel, the temperature range of the blackbody radiation source is set to 283.15K-373.15K, and the temperature changes every 5K, 300 gray images corresponding to different blackbody temperatures are collected, each group of 300 gray images is averaged to reduce the influence of time noise. According to formula (6), the relationship between image gray value and incident radiation is fitted by least squares method to obtain the gain, bias and nonlinearity coefficient of the pre-polarizer infrared polarization imaging system, and the response correction of the pre-polarizer infrared polarization imaging system is realized.

[0077] Step 3, as shown in Figure 3 , a temperature-controlled adjustable infrared polarized radiation source is disclosed in the embodiment. 4 is a high-precision surface temperature difference blackbody source of CDS 100-04 model of American EOI company, 5 is a variable temperature transmission support of P / NGS21525 model of British Specac company, 6 is an IR holographic grating polarizer #62771 of Edmund company, and 7 is a high-transmittance CaF2window. The radiation reaching the left CaF2window includes the spontaneous radiation of the blackbody, the spontaneous radiation of the CaF2window reflected by the blackbody, the spontaneous radiation of the external object and the spontaneous radiation of the polarizer transmitted through the CaF2window. The radiation reaching the polarizer includes the radiation of the incident radiation through the CaF2window, the spontaneous radiation of the CaF2window and the spontaneous radiation of the polarizer reflected by the CaF2window. The radiation reaching the right CaF2window includes the radiation of the incident radiation through the polarizer, the spontaneous radiation of the polarizer, the spontaneous radiation of the CaF2window reflected by the polarizer and the spontaneous radiation of the external object. The outgoing radiation of the temperature-controlled adjustable polarized radiation source includes the radiation of the incident radiation through the CaF2window, the spontaneous radiation of the CaF2window and the spontaneous radiation of the external object reflected by the CaF2window.

[0078] The pre-polarizer infrared polarization imaging system in step 1 is used to collect the pre-polarizer infrared polarization imaging system different detection angle images and intensity images corresponding to different blackbody temperatures and different polarizer temperatures of the temperature-controlled adjustable infrared polarization radiation source. Among them, the blackbody radiation source temperature range is 15-80℃, and the temperature changes every 5℃, the polarizer temperature range is-20-70℃, and the temperature changes every 5℃, the detection angle is 0°, 60° and 120°. According to formula (13), when the pre-polarizer infrared polarization imaging system detector receives radiation I0, I 60 , I 120 and I np , the transmittance of the optical system τ os, the primary direction transmittance τ1, the secondary direction transmittance τ2 and the correction coefficient k of the polarizer, the incident radiation Stokes vector of the pre-polarizer infrared polarization imaging system can be obtained, that is, the exit radiation Stokes vector of the temperature-controllable adjustable infrared polarization radiation source, and thus the exit radiation polarization degree of the temperature-controllable adjustable infrared polarization radiation source can be calculated, as shown in Figure 5

[0079] Step 4, as shown in Figure 4 , an imaging principle diagram of an infrared split focal plane polarization imaging system disclosed in the embodiment. The infrared split focal plane polarization imaging system includes an optical system 8, a micro-polarizer array 9 and a focal plane array 10. The radiation reaching the micro-polarizer array 9 includes the radiation of the incident radiation passing through the optical system 8, the spontaneous radiation of the optical system 8 and the spontaneous radiation of the micro-polarizer array 9 reflected by the optical system 8. The radiation reaching the focal plane array 10 includes the radiation of the incident radiation passing through the micro-polarizer array 9, the spontaneous radiation of the micro-polarizer array 9 and the spontaneous radiation of the focal plane array 10 reflected by the micro-polarizer array 9.

[0080] Step 5, remove the optical system of the infrared split focal plane polarization imaging system in step 4 to avoid the influence of the optical system on the calibration. Place the infrared split focal plane polarization imaging system close to the blackbody radiation source to reduce the influence of stray radiation. Use the infrared split focal plane polarization imaging system to collect gray scale images corresponding to different blackbody temperatures. The temperature of the blackbody radiation source changes in the range of 283.15-373.15 K, and changes every 5 K. Average the collected gray scale images corresponding to the same incident radiation to reduce the influence of time noise. According to formula (9), use the least square method to fit the relationship between the image gray scale and the incident radiation to obtain the cumulative gain, the bias and the nonlinearity coefficient of the infrared split focal plane polarization imaging system, and realize the response correction of the infrared split focal plane polarization imaging system, as shown in Figure 6 (b).

[0081] Place the infrared split focal plane polarization imaging system in step 4 in front of the temperature-controllable adjustable infrared polarization radiation source in step 3 to collect images of different blackbody temperatures, different polarizer temperatures and different polarizing angles. The temperature of the blackbody radiation source ranges from 15 to 80℃, and changes every 5℃. The temperature of the polarizer ranges from -20 to 60℃, and changes every 20℃. The polarizing angle ranges from 0 to 175°, and changes every 5°. According to formula (8), use the least square method to obtain the micro-polarizer array parameters corresponding to different blackbody radiation source temperatures and different polarizer temperatures.

[0082] For the infrared split focal plane polarization imaging system with four polarization directions of 0°, 45°, 90° and 135°, according to formulas (10) and (11), the ideal analysis matrix is

[0083] ​

[0084] The actual analysis matrix is

[0085]

[0086] wherein, and θ i (i = 0, 45, 90, 135) respectively represent the main direction transmittance, the secondary direction transmittance and the actual detection angle of the micro-polarizer array when the detection angle is 0°, 45°, 90° and 135°.

[0087] According to formula (12), the polarized radiation after correction can be calculated, and the polarization correction of the infrared split focal plane polarization imaging system is realized, as shown in (c). Figure 6 (c). Instead of taking the exit radiation of the high-extinction-ratio polarizer placed in front of the black body as the known input, the exit radiation of the temperature-controlled adjustable infrared polarized radiation source is taken as the known input, so as to avoid the over-correction of the micro-polarizer array parameters of the infrared split focal plane polarization imaging system and improve the correction accuracy of the infrared split focal plane polarization imaging system.

[0088] The above specific description further details the purpose, technical scheme and beneficial effects of the application. It should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. An infrared defocussing plane polarization correction method based on the reflection polarization characteristics of a polarizer, characterized by: It comprises the following steps, Step 1, the pre-polarizer infrared polarization imaging system comprises an optical system, a polarizer and a detector; the radiation reaching the polarizer comprises incident radiation, spontaneous radiation of the optical system and spontaneous radiation of the polarizer reflected by the optical system; The radiation reaching the detector comprises the radiation of the incident radiation passing through the polarizer, the spontaneous radiation of the polarizer and the spontaneous radiation of the detector reflected by the polarizer; wherein the polarizer reflected radiation is a biased radiation, the main direction of which is perpendicular to the main direction of the transmitted radiation, resulting in a decrease in the degree of polarization of the radiation incident on the detector; at the same time, the spontaneous radiation of the optical system and the spontaneous radiation of the polarizer also cause the degree of polarization of the radiation incident on the detector to decrease; The additional radiation introduced by the pre-polarizer infrared polarization imaging system with a polarizer and without a polarizer is different, and the additional radiation is adjusted by adding a correction coefficient to obtain an additional radiation corrected pre-polarizer infrared polarization imaging system radiation transfer model; Step 2, using the pre-polarizer infrared polarization imaging system of step 1 to collect gray scale images of different incident radiation, using a nonlinear method to fit the relationship between image gray scale and incident radiation, realizing the conversion of image gray scale and incident radiation, that is, realizing the response correction of the pre-polarizer infrared polarization imaging system; Step 3, using the pre-polarizer infrared polarization imaging system of step 1 to collect different polarizer angle images and intensity images of the pre-polarizer infrared polarization imaging system corresponding to different blackbody temperatures and different polarizer temperatures of the temperature-controlled adjustable infrared polarization radiation source; using the additional radiation corrected pre-polarizer infrared polarization imaging system radiation transfer model obtained in step 1, calibrating the temperature-controlled adjustable infrared polarization radiation source, and improving the calibration accuracy of the temperature-controlled adjustable infrared polarization radiation source; Step 4, the infrared split focal plane polarization imaging system comprises an optical system, a micro-polarizer array and a focal plane array; The radiation reaching the micro-polarizer array comprises the radiation of the incident radiation passing through the optical system, the spontaneous radiation of the optical system and the spontaneous radiation of the micro-polarizer array reflected by the optical system; The radiation reaching the focal plane array comprises the radiation of the incident radiation passing through the micro-polarizer array, the spontaneous radiation of the micro-polarizer array and the spontaneous radiation of the focal plane array reflected by the micro-polarizer array; analyzing the infrared split focal plane polarization imaging system and constructing an infrared split focal plane polarization imaging system radiation transfer model; Step 5, using the infrared defocus plane polarimetric imaging system described in step 4 to collect gray scale images of different incident radiations, using a nonlinear method to fit the relationship between image gray scale and incident radiation, realizing the conversion of image gray scale and incident radiation, that is, realizing the response correction of the infrared defocus plane polarimetric imaging system; placing the infrared defocus plane polarimetric imaging system described in step 4 in front of the temperature-controlled adjustable infrared polarized radiation source described in step 3, collecting images of different blackbody temperatures, different polarizer temperatures, and different polarizing angles; according to the radiation transfer model of the infrared defocus plane polarimetric imaging system constructed in step 4, using a nonlinear method to fit the relationship between different incident radiations and image gray scale, thereby obtaining accurate micro-polarizer array parameters; according to the obtained micro-polarizer array parameters, constructing an actual analysis matrix, and combining the ideal analysis matrix to correct the polarization of the infrared defocus plane polarimetric imaging system described in step 4; using the outgoing radiation of the calibrated temperature-controlled adjustable infrared polarized radiation source as the known input, instead of using the outgoing radiation of the high-extinction-ratio polarizer placed in front of the blackbody as the known input, to avoid over-correction of the micro-polarizer array parameters of the infrared defocus plane polarimetric imaging system, and to improve the correction accuracy of the infrared defocus plane polarimetric imaging system.

2. The method of infrared defocussing plane polarization correction based on the reflective polarizing characteristics of a polarizing sheet according to claim 1, characterized by: In step 1, The radiation transfer model of the pre-polarizer infrared polarimetric imaging system is shown in formula (1): Wherein, the Stokes vector of the incident radiation without considering the circular polarization component is The polarized radiation intensity corresponding to the detection angles θ0, θ1, θ2 respectively, I np The unbiased radiation intensity, τ os The transmittance of the optical system, τ1 and τ2 are the main and secondary direction transmittances of the polarizer, and R is the additional radiation of the front polarizer infrared polarization imaging system. The additional radiation introduced by the polarizer and the analyzer of the pre-polarizer infrared polarimetric imaging system is different; when the polarizer of the pre-polarizer infrared polarimetric imaging system is removed wherein is the additional radiation without a polarizer, ε os and ε d are the spontaneous emission rates of the optical system and the detector, respectively, and are the emissions of the optical system and the detector, respectively, ρ os is the reflection emission rate of the optical system; When the polarizing angle of the pre-polarizer infrared polarimetric imaging system is θ wherein, ε is the additional radiation with a polarizer, a is the spontaneous emission rate of the polarizer, is the radiation of the polarizer; By adding a correction coefficient to adjust the additional radiation in the radiation transfer model of the pre-polarizer infrared polarimetric imaging system as shown in formula (1), the radiation transfer model of the pre-polarizer infrared polarimetric imaging system after correction of the additional radiation is shown in formula (4): wherein the correction factor is the ratio of the additional radiation with and without an analyser. Through the radiation transfer model of the pre-polarizer infrared polarimetric imaging system after correction of the additional radiation as shown in formula (4), the characterization accuracy of the radiation transfer model of the pre-polarizer infrared polarimetric imaging system is improved.

3. The method of claim 2, wherein the infrared defocussing plane polarization correction is based on a polarizing sheet reflection polarization characteristic. The implementation method of step 2 is Step 2.1, remove the optical system of the pre-polarizer infrared polarimetric imaging system described in step 1 to avoid the influence of the optical system on calibration; place the pre-polarizer infrared polarimetric imaging system close to the blackbody radiation source to reduce the influence of stray radiation; switch the pre-polarizer infrared polarimetric imaging system to the intensity channel to collect gray scale images of different incident radiations; average the collected gray scale images corresponding to the same incident radiation to reduce the influence of temporal noise; Wherein, DN(x,y,T) is the gray scale of the image at (x,y) corresponding to the blackbody temperature T, DN(x,y,T,i) is the gray scale of the image at (x,y) of the i-th image when the blackbody temperature is T, and N is the number of images collected when the blackbody temperature is T; Step 2.2, using a nonlinear method to fit the relationship between image gray scale and incident radiation, realizing the conversion of image gray scale and incident radiation, that is, realizing the response correction of the pre-polarizer infrared polarimetric imaging system; According to the blackbody radiation formula, the incident radiation corresponding to the wave band of the pre-polarizer infrared polarization imaging system in step 1 is calculated; the incident radiation and the image gray scale are nonlinearly fitted according to formula (6), and the gain, bias and nonlinear coefficient of the pre-polarizer infrared polarization imaging system are obtained; DN(x,y,T)=a(x,y)I(T)γ(x,y)+b(x,y)(6) Wherein, I(T) is the corresponding incident radiation at blackbody temperature T, a(x,y) is the gain at image (x,y), b(x,y) is the bias at image (x,y), and γ(x,y) is the nonlinear coefficient at image (x,y). According to formula (6), the conversion of image gray scale and incident radiation is realized, that is, the response correction of the pre-polarizer infrared polarization imaging system is realized.

4. The method of claim 3, wherein the infrared defocussing plane polarization correction is based on a polarizing sheet reflection polarization characteristic. The implementation method of step 3 is, Step 3.1, using the pre-polarizer infrared polarization imaging system in step 1 to collect the pre-polarizer infrared polarization imaging system different detection angle images and intensity images corresponding to different blackbody temperatures and different polarizer temperatures of the temperature-controllable adjustable infrared polarization radiation source; The polarizer is placed in the variable temperature transmission bracket, and the blackbody radiation source and the variable temperature transmission bracket form a temperature-controllable adjustable infrared polarization radiation source; the pre-polarizer infrared polarization imaging system is placed in front of the temperature-controllable adjustable infrared polarization radiation source, and the optical system is adjusted to make it clear imaging; fix the blackbody temperature and the polarizer temperature, rotate the polarizer, collect multiple different detection angle images and intensity images; change the blackbody temperature and the polarizer temperature, repeat the above process of collecting multiple different detection angle images and intensity images; average the collected images of the same blackbody temperature, the same polarizer temperature and the same detection angle, to reduce the influence of time noise; Wherein, DN(x,y,T,t,θ) is the gray scale of image (x,y) corresponding to blackbody temperature T, polarizer temperature t and detection angle θ, DN(x,y,T,t,θ,i) is the gray scale of image (x,y) corresponding to blackbody temperature T, polarizer temperature t and detection angle θ of the i-th image, and N is the number of images collected at blackbody temperature T, polarizer temperature t and detection angle θ; Step 3.2, using the pre-polarizer infrared polarization imaging system radiation transfer model corrected by additional radiation obtained in step 1 to calibrate the temperature-controllable adjustable infrared polarization radiation source, and improve the calibration accuracy of the temperature-controllable adjustable infrared polarization radiation source; The Stokes vector of the radiation reaching the detector is calculated using the polarization image and the intensity channel image under the same blackbody temperature and the same polarizer temperature; according to the pre-polarizer infrared polarization imaging system radiation transfer model corrected by additional radiation in step 1, the Stokes vector of the incident radiation of the pre-polarizer infrared polarization imaging system is solved, that is, the Stokes vector of the outgoing radiation of the temperature-controllable adjustable infrared polarization radiation source.

5. The infrared defocussing plane polarization correction method based on the reflective polarizing characteristics of a polarizing sheet according to claim 4, characterized by: In step 4, The constructed infrared split focal plane polarization imaging system radiation transfer model is shown in formula (8): where S is the Stokes vector of the incident radiation, excluding the circularly polarized component I θ is the radiation reaching the focal plane array for a micro-polarizer array with a retardation angle θ, τ os is the transmittance of the optical system, τ1 and τ2 are the primary and secondary direction transmittances of the micro-polarizer array for the corresponding pixel, ε os , ε m , and ε d are the self-emission rates of the optical system, the micro-polarizer array, and the detector, respectively, and are the emissions of the optical system, the micro-polarizer array, and the focal plane array, respectively, ρ os is the reflection emission rate of the optical system; In order to accurately obtain the parameters τ1, τ2 and θ of the micro-polarizer array, the Stokes vector of the incident radiation needs to be known; due to the reflection polarization characteristics of the polarizer, the transmission radiation and the reflection radiation of the high-extinction-ratio polarizer placed in front of the actual black body change with the change of the polarizing angle; therefore, the temperature-controllable adjustable infrared polarized radiation source described in step 3 can be used to accurately obtain the micro-polarizer array parameters of the infrared focal plane polarization imaging system.

6. The infrared defocussing plane polarization correction method based on the reflective polarizing characteristics of a polarizer according to claim 5, characterized by: Step 5 realizes the method as, Step 5.1, remove the optical system of the infrared focal plane polarization imaging system described in step 4 to avoid the influence of the optical system on the calibration; place the infrared focal plane polarization imaging system close to the black body radiation source to reduce the influence of stray radiation; use the infrared focal plane polarization imaging system to collect gray-scale images of different incident radiations, average the collected gray-scale images corresponding to the same incident radiation to reduce the influence of time noise; use a nonlinear method to fit the relationship between image gray scale and incident radiation to realize the conversion of image gray scale and incident radiation, that is, realize the response correction of the infrared focal plane polarization imaging system; Wherein, τ1(x, y) is the main direction transmittance of the micro-polarizer array at (x, y), τ2(x, y) is the secondary direction transmittance of the micro-polarizer array at (x, y), and let be the composite gain of the focal plane array and the micro-polarizer array; Step 5.2, place the infrared focal plane polarization imaging system described in step 4 in front of the temperature-controllable adjustable infrared polarized radiation source described in step 3, collect images of different black body temperatures, different polarizer temperatures and different polarizing angles, and average each group of images to reduce the influence of time noise; according to the radiation transfer model of the infrared focal plane polarization imaging system constructed in step 4, use a nonlinear method to fit the relationship between different incident radiations and image gray scale to obtain accurate micro-polarizer array parameters; according to the obtained micro-polarizer array parameters, construct an actual analysis matrix, and combine the ideal analysis matrix to perform polarization correction on the infrared focal plane polarization imaging system; use the exit radiation of the temperature-controllable adjustable infrared polarized radiation source as the known input instead of using the exit radiation of the high-extinction-ratio polarizer placed in front of the black body as the known input to avoid over-correction of the micro-polarizer array parameters of the infrared focal plane polarization imaging system and improve the correction accuracy of the infrared focal plane polarization imaging system; The actual analysis matrix and the ideal analysis matrix are shown in formulas (10) and (11), and the radiation after polarization correction is shown in formula (12): wherein, and respectively represent the principal and secondary direction transmittances corresponding to the detection angles θ0, θ1, θ2and θ3in the array of micro-polarizing plates. wherein is the Stokes vector of the polarisation corrected radiation, is the Stokes vector of the pre-polarisation corrected radiation.

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