Small target infrared diffusion imaging method and device based on point source black body

Abstract

The invention discloses a small target infrared dispersion imaging method and device based on a point source black body, and the method comprises the steps: firstly constructing a small target dispersion imaging model based on a small target infrared imaging dispersion principle, and obtaining a theoretical dispersion area changing with the distance; calibrating the constructed small target dispersion imaging model according to the dynamic test performance to obtain a small target dispersion calibration area; and comparing the dispersion calibration area of the small target with the actual dispersion area of the actually measured small target, and verifying whether the derived dispersion calibration area accords with the imaging dispersion size of the small target. According to the method and the device, the problem that a target imaging principle in the prior art is not suitable for small target imaging blurring is solved, the accuracy of the small target imaging size can be effectively improved, and a test basis is provided for target identification in a future infrared imaging system.

Description

Technical Field

[0001] The invention relates to the technical field of optical imaging, and in particular to a small target infrared diffusion imaging method and device based on a point source black body. Background Art

[0002] Based on the precise requirements of infrared imaging systems to detect targets, target infrared imaging has gradually become a key task in the development of weapon systems. For infrared imaging targets in complex scenes, the diffusion phenomenon in the image makes the weak targets in the scene appear blurred. In order to accurately measure the actual size of weak targets in the image, it is necessary to conduct in-depth research on the imaging principle of infrared targets in the image and the detector effect. When using infrared detectors to detect small targets, the thermal radiation information of small targets forms grayscale information on the detector imaging interface. These grayscale features are the diffraction-limited light intensity distribution formed on the image plane after the target passes through the optical system. When the target is imaged under ideal conditions, the light intensity before and after the image plane is symmetrically distributed and changes according to the conversion of the field of view. In actual optical imaging, this symmetry is destroyed due to factors such as distortion, coma and aberration.

[0003] In the study of infrared radiation characteristic measurement of small point source targets, it is necessary to determine the real diffusion size of the target based on the transmission characteristics of its optical system. To this end, factors such as the imaging mechanism of optical diffusion, detector effect, and main performance parameters of target imaging need to be taken into account. The target imaging mechanism is experimentally verified using a black body, and a new target diffusion imaging model is constructed based on the characteristic effect of the detector itself to achieve accurate measurement of the diffusion phenomenon, providing a test basis for target recognition in future infrared imaging systems. Summary of the invention

[0004] The purpose of the present invention is to provide a small target infrared diffuse imaging method and device based on a point source blackbody. The method and device overcome the problem that the target imaging principle in the prior art is not suitable for the fuzzy imaging of small targets, can effectively improve the accurate measurement of the imaging size of small targets, and provide a test basis for the identification of targets in future infrared imaging systems.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A small target infrared diffusion imaging method based on a point source blackbody, the method comprising:

[0007] Step 1: Based on the diffusion principle of small target infrared imaging, a small target diffusion imaging model is constructed to obtain the theoretical diffusion area that varies with distance;

[0008] Step 2: According to the small target diffusion imaging model constructed by dynamic test performance calibration, a small target diffusion calibration area is obtained;

[0009] The dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference and minimum resolvable temperature difference;

[0010] Step 3: Compare the small target diffusion calibration area with the actual measured small target real diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

[0011] A small target infrared diffusion imaging device based on a point source black body, the device comprising:

[0012] A model building unit is used to build a small target diffusion imaging model based on the small target infrared imaging diffusion principle to obtain a theoretical diffusion area that varies with distance;

[0013] A model calibration unit, used to calibrate the constructed small target diffusion imaging model according to the dynamic test performance to obtain the small target diffusion calibration area; wherein the dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference and minimum resolvable temperature difference;

[0014] The verification unit is used to compare the small target diffusion calibration area with the actual measured small target real diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

[0015] An electronic device comprises a memory and a processor, wherein a computer program is stored in the memory, and the processor is configured to run the computer program to execute the above method.

[0016] A computer storage medium, characterized in that the computer storage medium stores a plurality of instructions, wherein the instructions are suitable for being loaded by a processor and executing the above method.

[0017] It can be seen from the technical solution provided by the present invention that the above method and device overcome the problem that the target imaging principle in the prior art is not suitable for the fuzzy imaging of small targets, can effectively improve the accurate measurement of the imaging size of small targets, and provide a test basis for the identification of targets in future infrared imaging systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0019] Figure 1 A schematic diagram of a small target infrared diffusion imaging method based on a point source blackbody provided in an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of the mapping relationship from the infrared imaging of a target to the detector according to an embodiment of the present invention;

[0021] Figure 3 It is a schematic diagram of the relationship between the total imaging modulation transfer function and the optical spatial frequency and the cut-off frequency according to an embodiment of the present invention;

[0022] Figure 4 A schematic diagram showing a comparison between the theoretical area of ​​diffusion imaging and the actual area varying with temperature and distance according to an embodiment of the present invention;

[0023] Figure 5 Schematic diagram of the comparison result between the actual imaging area of ​​the small target and the model calibration area according to the embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The following will further describe the embodiments of the present invention in detail in conjunction with the accompanying drawings. The contents not described in detail in the embodiments of the present invention belong to the prior art known to professionals in the field. In the embodiments of the present invention, if specific conditions are not specified, they are carried out according to the conditions of normal conditions in the field or the manufacturer's recommendations. If the manufacturer is not specified in the reagents or instruments in the embodiments of the present invention, they are all conventional products that can be purchased commercially.

[0026] like Figure 1 The figure is a schematic flow chart of a small target infrared diffusion imaging method based on a point source blackbody provided by an embodiment of the present invention, the method comprising:

[0027] Step 1: Based on the diffusion principle of small target infrared imaging, a small target diffusion imaging model is constructed to obtain the theoretical diffusion area that varies with distance;

[0028] In this step, the image of the target after passing through the infrared detection system conforms to the principle of optical refraction. The factors affecting the target imaging size are the target's real size and diffuse size, such as Figure 2 FIG. 1 is a schematic diagram showing the mapping relationship between the infrared imaging of the target and the detector according to an embodiment of the present invention, referring to FIG. Figure 2 , if d is the real size of the target, L is the distance between the target and the infrared detector, F is the focal length, and r is the radius of the diffusion circle, then the theoretical area s obtained on the imaging surface of the infrared detector is:

[0029]

[0030] Since the target will be diffused on the imaging surface, the diffused area obtained is different from the actual theoretical area. The target diffused size formed on the imaging surface is calculated according to the effective field of view of the detection:

[0031]

[0032] a is the effective field of view angle, expressed in radians or degrees, and α=nD / F, where D is the pixel size, n is the number of pixels after the target is imaged, and F is the focal length;

[0033] Substituting a into formula (2) yields:

[0034]

[0035] Then the actual imaging target diffusion size is:

[0036] nD=arctan(d / 2L)·F(4)

[0037] Therefore, the theoretical diffusion area formula without considering the detector effect is as follows:

[0038]

[0039] S L is the theoretical diffusion area obtained as the distance L changes.

[0040] Step 2: According to the small target diffusion imaging model constructed by dynamic test performance calibration, a small target diffusion calibration area is obtained;

[0041] In this step, the small target radiates to the focal plane array through the imaging detector, and then is converted into an electrical signal, and the grayscale radiation field of the small target is reproduced on the imaging software. During the entire link process, the intrinsic characteristics of the small target, path transmission, imaging front end, signal processing, and arrival at the imaging interface will affect the imaging characteristics of the small target. Dynamic test performance includes noise equivalent temperature difference (NETD), modulation transfer function (MTF), minimum detectable temperature difference (MDTD) and minimum resolvable temperature difference (MRTD). Specifically:

[0042] The noise equivalent temperature difference (NETD) is the equivalent temperature difference caused by the temperature difference between the target and the background after imaging being the same as the root mean square value of the detector noise. It reflects the sensitivity of the detection system and is defined as:

[0043]

[0044] Where V is the root mean square of the detector output voltage; F# is the optical F number of the detector; A dis the imaging area at the front end of the detector; λ is the wavelength; T is the temperature value within the wavelength range; τ is the atmospheric transmittance; M is the radiation emittance; R is the optical system response rate;

[0045] The modulation transfer function MTF includes the diffraction transfer function and the aberration transfer function. The diffraction transfer function depends on the aperture and wavelength and is expressed as:

[0046]

[0047] is the diffraction transfer function; f x is the frequency in the x direction of the imaging system space; f y is the frequency in the y direction of the imaging system space; f c is the cut-off frequency;

[0048] The energy distribution caused by aberration is a circularly symmetric Gaussian distribution, and the aberration transfer function is:

[0049] MTF(f)=exp(-2(π) 2 σ 2 f 2 )(8)

[0050] MTF(f) is the aberration transfer function; σ is the standard deviation; f is the optical spatial frequency;

[0051] The total modulation transfer function MTF is the product of the diffraction transfer function and the aberration transfer function, expressed as:

[0052]

[0053] In specific implementations, the total transfer function of the imaging system is generally between 0 and 1, such as Figure 3 It is a schematic diagram showing the relationship between the total imaging modulation transfer function and the optical spatial frequency and the cut-off frequency according to an embodiment of the present invention.

[0054] The minimum resolvable temperature difference MRTD is the minimum temperature difference between the target and the background after imaging at a fixed spatial frequency. It is used to evaluate the spatial resolution and temperature resolution of the system and is expressed as:

[0055]

[0056] In the formula, SNR TH The threshold signal-to-noise ratio for identifying 4 target features; σ tvh is the spatiotemporal random noise; k z (f) is the correction factor; MTF is the modulation transfer function; E t E is the time integral function of the human eye; h (f) and E v (f) is the spatial integration function for the human eye;

[0057] The minimum detectable temperature difference MDTD indicates the temperature difference between the target and the background at the position where the target of a specific size can be identified on the imaging interface, which is expressed as:

[0058]

[0059] Where, MTF is the modulation transfer function, MRTD(f) is the minimum resolvable temperature difference; is the relative average value of target imaging, expressed as:

[0060]

[0061] Where W T is the horizontal size of the target; H T is the vertical size of the target; a is the horizontal instantaneous field of view; β is the vertical instantaneous field of view.

[0062] The following specific experiments verify the difference between the theoretical area of ​​diffuse imaging and the actual area that varies with temperature and distance:

[0063] The experiment selected a point source cavity black body with a temperature range of 30℃~1250℃, a point source diameter of 0.25 inches, and a point source temperature resolution of 0.1℃. The uniformity of the point source black body is greater than 95%, and the emissivity is 0.999. The imaging detector uses IRCAMEquus 327km, with a medium wave wavelength range of 3.7um~5um, a resolution of 640*512, a focal length of 50mm, a pixel size of 15um, and an F# of F / 2.

[0064] In the experiment, the temperature of the point source blackbody was raised to 100°C, and the heat source was emitted from a 0.25-inch aperture. The point source target on the blackbody was then acquired using a detector. As the distance between the detector and the blackbody target gradually increased, the change in the imaging size of the point source target with distance could be obtained in the software interface.

[0065] Therefore, the focal length is selected at 25mm, the integration time is 20us, and the temperature is set at 100℃, 200℃, 300℃, 400℃, 500℃, and 600℃.

[0066] From the imaging diagrams of point source small targets on the detector at different distances, it can be seen that the size of the small target is getting smaller as the distance from the detector increases, and the pixels occupied in the image are gradually decreasing. By removing the background information of each image using MATLAB, the pixel values ​​occupied by the small target imaging are obtained, as shown in Table 1:

[0067] Table 1 Imaging area of ​​small targets at different temperatures and distances (mm) 2 )

[0068]

[0069] According to the theoretical model of small target diffuse imaging derived in step 1, the actual area of ​​the small target with a black body point source temperature varying with distance from 100℃ to 600℃ is compared, as shown in Figure 4 FIG. 1 is a schematic diagram showing a comparison between the theoretical area of ​​diffuse imaging and the actual area varying with temperature and distance according to an embodiment of the present invention. By comparing the variation curves of the two, it can be seen that the theoretical area curve of diffuse imaging of a small target and the actual area curve show a certain similarity. Figure 4 The actual area of ​​100℃-600℃ is larger than the theoretical area and is regularly distributed. Considering the dynamic imaging mechanism, the acquisition of the theoretical area does not take into account the modulation transfer function, noise equivalent temperature difference, minimum detectable temperature difference and other factors of the imaging detector, resulting in the theoretical area being smaller than the actual area. Therefore, it is necessary to calibrate the constructed small target diffuse imaging model based on the dynamic test performance. The specific process is as follows:

[0070] According to the theoretical diffusion area formula (5) of small target imaging obtained in step 1, by studying the dynamic imaging mechanism of the imaging system, the small target imaging area is obtained after preliminary correction:

[0071] S=(1+NETD)·S L +MDTD(13)

[0072] Right now:

[0073] S is the calibration area value obtained according to the distance change after the small target is imaged; NETD is the noise equivalent temperature difference; S L is the theoretical diffusion area obtained with the change of distance L; MTF is the modulation transfer function; MRTD(f) is the minimum resolvable temperature difference; is the relative average value of target imaging;

[0074] At the same time, the relationship between the small target imaging area and temperature can be seen:

[0075]

[0076] …

[0077]

[0078] The calibrated imaging diffusion area obtained with temperature change is:

[0079]

[0080] Where S1 is the calibrated diffuse area imaged at a temperature of 100°C; n is the value obtained by dividing the measured small target temperature by 100; T n is the small target temperature; Sn The calibration area obtained for different temperatures of the small target;

[0081] Then the small target dispersion calibration area S derived with the change of temperature and distance is:

[0082]

[0083] Step 3: Compare the small target diffusion calibration area with the actual measured small target real diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

[0084] For example, in order to verify that the calibrated small target diffusion calibration area is consistent with the actual measured area, the selected parameters are substituted into the calibration area model. The imaging detector used has a spatial resolution (MRTD) of 0.6 mrad, a noise equivalent temperature difference (NETD) of 25 mk, and a FOV of 21.7°×17.5°. By adding each parameter to the formula (18) of the small target diffusion calibration area S, we get:

[0085]

[0086] At the same time, the field of view formed by the small black body point source target in the detector is 7.24°×7.24°. Substituting it into equation (12), we get I=0.138.

[0087] Substituting the detector parameters into equations (7), (8) and (9), we obtain MTF = 0.5.

[0088] Therefore, the small target diffusion calibration area S is:

[0089]

[0090] The area obtained based on the above formula and parameter calibration is compared with the actual area, and the comparison results obtained by MATLAB processing are as follows: Figure 5 FIG. 1 is a schematic diagram showing the comparison between the actual imaging area of ​​a small target and the model calibration area according to an embodiment of the present invention. Figure 5 The small target diffusion calibration area that changes with temperature and distance is basically consistent with the actual imaging area. Even if there is a slight difference, it objectively verifies that the derived diffusion calibration area meets the requirements, providing authenticity for subsequent verification of simulation data.

[0091] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in the field.

[0092] Based on the method described in the embodiment of the present invention, the embodiment of the present invention further provides a small target infrared diffusion imaging device based on a point source black body, the device comprising:

[0093] A model building unit is used to build a small target diffusion imaging model based on the small target infrared imaging diffusion principle to obtain a theoretical diffusion area that varies with distance;

[0094] A model calibration unit, used to calibrate the constructed small target diffusion imaging model according to the dynamic test performance to obtain the small target diffusion calibration area; wherein the dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference and minimum resolvable temperature difference;

[0095] The verification unit is used to compare the small target diffusion calibration area with the actual measured small target real diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

[0096] The specific implementation process of each unit in the above device is described in the above method embodiment.

[0097] An embodiment of the present invention further provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor is configured to run the computer program to execute the steps in the above method embodiment.

[0098] The embodiment of the present invention further provides a computer storage medium, characterized in that the computer storage medium stores a plurality of instructions, and the instructions are suitable for being loaded by a processor and executing the steps in the above method embodiment. The above-mentioned storage medium can be a read-only memory, a disk or an optical disk, etc.

[0099] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A small target infrared diffusion imaging method based on point source blackbody, characterized in that: The method comprises: Step 1: Based on the diffusion principle of small target infrared imaging, a small target diffusion imaging model is constructed to obtain the theoretical diffusion area that varies with distance; Step 2: According to the small target diffusion imaging model constructed by dynamic test performance calibration, a small target diffusion calibration area is obtained; The dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference and minimum resolvable temperature difference; Step 3: Compare the small target diffusion calibration area with the actual measured small target real diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

2. According to the small target infrared diffusion imaging method based on point source blackbody of claim 1, it is characterized in that: In step 1, the image of the target after passing through the infrared detection system conforms to the principle of optical refraction. The factors affecting the target imaging size are the target's real size and diffusion size. If d is the target's real size, L is the distance between the target and the infrared detector, F is the focal length, and r is the radius of the diffusion circle, then the theoretical area s obtained on the infrared detector imaging surface is: Since the target will be diffused on the imaging surface, the diffused area obtained is different from the actual theoretical area. The target diffused size formed on the imaging surface is calculated according to the effective field of view of the detection: a is the effective field of view angle, expressed in radians or degrees, and α=nD / F, where D is the pixel size, n is the number of pixels after the target is imaged, and F is the focal length; Substituting a into formula (2) yields: Then the actual imaging target diffusion size is: nD=arctan(d / 2L)·F (4) Therefore, the theoretical diffusion area formula without considering the detector effect is as follows: S L is the theoretical diffusion area obtained as the distance L changes.

3. The small target infrared diffusion imaging method based on point source blackbody according to claim 1 is characterized in that: In step 2, The noise equivalent temperature difference (NETD) is the equivalent temperature difference caused by the temperature difference between the target and the background after imaging being the same as the root mean square value of the detector noise. It reflects the sensitivity of the detection system and is defined as: Where V is the root mean square of the detector output voltage; F# is the optical F number of the detector; A d is the imaging area at the front end of the detector; λ is the wavelength; T is the temperature value within the wavelength range; τ is the atmospheric transmittance; M is the radiation emittance; R is the optical system response rate; The modulation transfer function MTF includes the diffraction transfer function and the aberration transfer function. The diffraction transfer function depends on the aperture and wavelength and is expressed as: is the diffraction transfer function; f x is the frequency in the x direction of the imaging system space; f y is the frequency in the y direction of the imaging system space; f c is the cut-off frequency; The energy distribution caused by aberration is a circularly symmetric Gaussian distribution, and the aberration transfer function is: MTF(f)=exp(-2(π) 2 s 2 f 2 (8) MTF(f) is the aberration transfer function; σ is the standard deviation; f is the optical spatial frequency; The total modulation transfer function MTF is the product of the diffraction transfer function and the aberration transfer function, expressed as: The minimum resolvable temperature difference MRTD is the minimum temperature difference between the target and the background after imaging at a fixed spatial frequency. It is used to evaluate the spatial resolution and temperature resolution of the system and is expressed as: In the formula, SNR TH The threshold signal-to-noise ratio for identifying 4 target features; σ tvh is the spatiotemporal random noise; k z (f) is the correction factor; MTF is the modulation transfer function; E t E is the time integral function of the human eye; h (f) and E v (f) is the spatial integration function for the human eye; The minimum detectable temperature difference MDTD indicates the temperature difference between the target and the background at the position where the target of a specific size can be identified on the imaging interface, which is expressed as: Where, MTF is the modulation transfer function; MRTD(f) is the minimum resolvable temperature difference; is the relative average value of target imaging, expressed as: Where W T is the horizontal size of the target; H T is the vertical size of the target; a is the horizontal instantaneous field of view; β is the vertical instantaneous field of view.

4. The small target infrared diffusion imaging method based on point source blackbody according to claim 2 is characterized in that: The process of step 2 is specifically as follows: According to the theoretical diffusion area formula (5) of small target imaging obtained in step 1, by studying the dynamic imaging mechanism of the imaging system, the small target imaging area is obtained after preliminary correction: S=(1+NETD)·S L +MDTD(13) Right now: S is the calibration area value obtained according to the distance change after the small target is imaged; NETD is the noise equivalent temperature difference; S L is the theoretical diffusion area obtained by varying the distance L; MTF is the modulation transfer function; MRTD(f) is the minimum resolvable temperature difference; is the relative average value of target imaging; At the same time, the relationship between the small target imaging area and temperature can be seen: …… The calibrated imaging diffusion area obtained with temperature change is: Where S1 is the calibrated diffuse area imaged at a temperature of 100°C; n is the value obtained by dividing the measured small target temperature by 100; T n is the small target temperature; S n The calibration area obtained for different temperatures of the small target; Then the small target dispersion calibration area S derived with the change of temperature and distance is:

5. A small target infrared diffusion imaging device based on a point source black body, characterized in that: The device comprises: A model building unit is used to build a small target diffusion imaging model based on the small target infrared imaging diffusion principle to obtain a theoretical diffusion area that varies with distance; A model calibration unit, used to calibrate the constructed small target diffusion imaging model according to the dynamic test performance to obtain the small target diffusion calibration area; wherein the dynamic test performance includes noise equivalent temperature difference, modulation transfer function, minimum detectable temperature difference and minimum resolvable temperature difference; The verification unit is used to compare the small target diffusion calibration area with the actual measured small target real diffusion area to verify whether the derived diffusion calibration area is consistent with the small target imaging diffusion size.

6. An electronic device comprising a memory and a processor, characterized in that: A computer program is stored in the memory, and the processor is configured to run the computer program to perform the method according to any one of claims 1 to 4.

7. A computer storage medium, characterized in that: The computer storage medium stores a plurality of instructions, and the instructions are suitable for being loaded by a processor and executing the method according to any one of claims 1 to 4.

Images