Optical calibration method and system suitable for infrared characteristics of small target in air

Abstract

The invention provides an optical calibration method and system suitable for infrared characteristics of a small target in the air, and the method comprises the steps: calibrating the pixel response of a detector under different integral time conditions through a standard black body, converting the pixel response into the radiance of an incident detector image screen, and obtaining a standard detector gray curve; on the other hand, after the dynamic small target image in the air is collected and the influence of background noise is removed, the radiation characteristics of the small target image at different distances are calculated through the gray scale response curve of the detector, and high measurement precision and engineering value are achieved; according to the method, the dynamic infrared radiation characteristic of a typical target can be rapidly calibrated in engineering.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to an optical calibration method and system suitable for infrared characteristics of small targets in the air. BACKGROUND

[0002] The traditional target range infrared characteristic measurement system calibration method includes direct surface source method, indirect surface source method and point source method, which is more about calibrating the response of each pixel of the infrared detector by the standard black body, and lacks the part of how to use the calibrated detector to measure the infrared characteristics of the far-field target. This part of the process is usually through the built-in parameter setting of the detector, measuring the surface temperature of the target, combining the target material emissivity and other parameters, and converting it into radiation intensity through the Stefan-Boltzmann law to output the result. This calibration method has considerable advantages when it comes to close-range and large-area targets, but for small targets in the air or pixel-level / sub-pixel-level targets, the result often deviates greatly from the actual situation, and correction coefficients and other means are needed to calibrate the result.

[0003] Patent application document CN111751006A discloses a data calibration method, target radiation characteristic analysis method and device, relating to the technical field of target radiation characteristic analysis. The method includes: acquiring the working condition when collecting the target infrared image, and taking it as the first working condition; querying the pre-calibrated gray data table according to the first working condition; when there is no gray data under the first working condition in the gray data table, performing linear interpolation processing on the gray data in the gray data table to obtain the gray data under the first working condition; and performing curve fitting on the gray data under the first working condition and the pre-calibrated black body brightness data corresponding to different black body temperatures to determine the conversion relationship between the black body brightness and the image gray under the first working condition according to the curve fitting result. However, this patent cannot completely solve the existing technical problems, and cannot meet the needs of the present application. SUMMARY

[0004] In view of the defects in the prior art, the purpose of the present application is to provide an optical calibration method and system suitable for infrared characteristics of small targets in the air.

[0005] The optical calibration method suitable for infrared characteristics of small targets in the air provided by the present application comprises: Step 1: use a standard surface source black body, make the black body light aperture cover the entrance pupil of the detector, set different temperature levels, and obtain the initial gray response curve of each pixel of the infrared detector under the condition of rated integration time; Step 2: The detector is de-blinded and segmented for non-uniform correction, two-point non-uniform correction method is applied in different temperature intervals, gain factor and offset factor of individual pixels are calculated to make the corrected pixel output response curve converge; Step 3: The original image data of the detector under the temperature condition of the standard black body is collected, the target gray value and the background gray value of the detector response are obtained, and the radiance of the black body at the temperature is obtained, the target gray value is subtracted from the background gray value to obtain a set of gray and radiance data; Step 4: Adjust the temperature of the standard black body, fit the corresponding relationship between the target-background gray difference and the radiance difference under the condition of integration time, as the basis for target characteristic calibration; Step 5: Repeat steps 3 and 4 until the response curve of the infrared detector under different integration time conditions is calibrated; Step 6: Collect the gray image of the target during flight based on the ground fixed observation point, and select according to the preset requirements, and count the target and background gray curve; Step 7: According to the distance corresponding to the selected image time, the altitude of the observed target, and the altitude of the position where the detector is located, the atmospheric transmittance under the current waveband condition is calculated; Step 8: According to the calibrated detector response curve and the collected target gray value and background gray value, the target radiance received by the detector surface is obtained; Step 9: Based on the collected data and the detector calibration curve, the radiance of the target or black body reaching the detector surface under the two measurement environment conditions is equal, and the infrared radiation characteristics of the collected target under the current waveband condition are calculated; Step 10: For the response waveband of the detector, the calibration result is converted into the standard waveband statistical result under the corresponding temperature condition.

[0006] Preferably, the segmented non-uniform correction includes: under two different radiation conditions, the gray response of the pixel is and The gain factor and the offset factor have the following relationship:

[0007] Substituting and solving, we get:

[0008] wherein, and are the corrected gray response values.

[0009] Preferably, the radiance of the blackbody is calculated based on Planck's blackbody radiation law, and the formula for calculating the radiant exitance M is:

[0010] Where h is Planck's constant; c is the speed of light in a vacuum; k is Boltzmann's constant; and T is the blackbody temperature. λ represents the response band range of the detection device; λ is the wavelength of the electromagnetic wave. The relationship between radiance L and radiant exitance M is as follows:

[0011] in, The target radiance of a standard blackbody under temperature T; the radiance L is used to correspond to the grayscale value to form calibration data; When fitting the correspondence between the grayscale difference and the radiance difference between the target and the background, the blackbody temperature T is adjusted to obtain the blackbody temperature value T0 when the grayscale difference between the target and the background is 0. The detector noise floor is approximately equal to the radiance L0 of the standard blackbody under this temperature condition, where L0 is calculated by Planck's blackbody radiation law. T0 and L0 are used to compensate for background noise.

[0012] Preferably, the influence of the detector's noise floor is set as follows: Background radiance Then we have:

[0013]

[0014] in, The grayscale value of the target collected by the detector under temperature T. The background grayscale value collected by the detector under temperature T. Within the ideal operating range of the infrared detector, its grayscale response is approximately linear at the same time. Subtracting the two equations above, we get:

[0015] Substituting the target-background radiance and the target-background grayscale difference into the target-background radiance and detector grayscale response fitting curves, the calibration function expression of which is:

[0016] in, Let be the slope of the detector's grayscale response curve. This is the noise term.

[0017] Preferably, when calibrating the grayscale response curve of the infrared detector, a standard blackbody is placed in front of the infrared detector at a distance R1. The area of ​​the blackbody corresponding to the spatial angle of a single pixel is S0, and the detector operates within a unit solid angle. Within the space, the receiving area is The actual target irradiance received during the calibration process was obtained as follows:

[0018] For infrared point source targets, at a distance The target irradiance received by the detector at the location The expression is:

[0019] Combining the above formulas and setting them equal, we get:

[0020] Where J is the target radiation intensity. The distance is relative. denoted as Atmospheric transmittance at this distance.

[0021] An optical calibration system for the infrared characteristics of small airborne targets, provided by the present invention, includes: Module M1: Using a standard surface source blackbody, the blackbody aperture covers the entrance pupil of the detector. Different temperature settings are set to obtain the initial grayscale response curve of each pixel of the infrared detector under the rated integration time condition. Module M2: Performs blind pixel removal and segmented non-uniform correction on the detector. It applies a two-point non-uniform correction method in different temperature ranges to calculate the gain factor and offset factor of a single pixel, so that the output response curve of the corrected pixel converges. Module M3: Collects the detector's raw image data of a standard blackbody under temperature conditions, obtains the detector's response target gray value, background gray value, and the blackbody's radiance at that temperature, and subtracts the target gray value from the background gray value to obtain a set of gray value and radiance data; Module M4: Adjusts the standard blackbody temperature and fits the correspondence between the grayscale difference and radiance difference between the target and the background under the integral time condition, as the basis for target characteristic calibration; Module M5: Repeatedly call modules M3 and M4 until the response curves of the infrared detector under different integration time conditions are calibrated; Module M6: Based on a fixed ground observation point, it acquires grayscale images of the target during flight, selects them according to preset requirements, and statistically analyzes the grayscale curves of the target and the background. Module M7: Calculates the atmospheric transmittance under the current band conditions based on the distance corresponding to the selected image time, the altitude of the observed target, and the altitude of the detector's location. Module M8: Based on the calibrated detector response curve and the collected target grayscale values ​​and background grayscale values, obtain the target irradiance received on the detector surface; Module M9: Based on the collected data and detector calibration curve, it makes the irradiance of the target or blackbody reaching the detector surface equal under the two measurement environmental conditions, and calculates the infrared radiation characteristics of the target under the current band conditions. Module M10: Converts the calibration results into standard band statistical results under the corresponding temperature conditions for the detector's response band.

[0022] Preferably, the segmented non-uniformity correction includes: under two different radiation conditions, the gray-level responses of the pixels are respectively and Its gain factor and offset factor It has the following relationship:

[0023] Substituting the values ​​and solving, we get:

[0024] in, and This is the grayscale response value obtained after correction. It differs from the ordinary two-point correction algorithm in that the grayscale response of a typical detector is not linear over the entire domain. It requires multiple two-point correction fittings in different temperature ranges, each corresponding to a different curvature response. The final result is a piecewise response, not a straight line in the usual sense.

[0025] Preferably, the radiance of the blackbody is calculated based on Planck's blackbody radiation law, and the formula for calculating the radiant exitance M is:

[0026] Where h is Planck's constant; c is the speed of light in a vacuum; k is Boltzmann's constant; and T is the blackbody temperature. λ represents the response band range of the detection device; λ is the wavelength of the electromagnetic wave. The relationship between radiance L and radiant exitance M is as follows:

[0027] in, The target radiance of a standard blackbody under temperature T; the radiance L is used to correspond to the grayscale value to form calibration data; When fitting the correspondence between the grayscale difference and the radiance difference between the target and the background, the blackbody temperature T is adjusted to obtain the blackbody temperature value T0 when the grayscale difference between the target and the background is 0. The detector noise floor is approximately equal to the radiance L0 of the standard blackbody under this temperature condition, where L0 is calculated by Planck's blackbody radiation law. T0 and L0 are used to compensate for background noise.

[0028] Preferably, the influence of the detector's noise floor is set as follows: Background radiance Then we have:

[0029]

[0030] in, The grayscale value of the target collected by the detector under temperature T. The background grayscale value collected by the detector under temperature T. Within the ideal operating range of the infrared detector, its grayscale response is approximately linear at the same time. Subtracting the two equations above, we get:

[0031] Substituting the target-background radiance and the target-background grayscale difference into the target-background radiance and detector grayscale response fitting curves, the calibration function expression of which is:

[0032] in, Let be the slope of the detector's grayscale response curve. This is the noise term.

[0033] Preferably, when calibrating the grayscale response curve of the infrared detector, a standard blackbody is placed in front of the infrared detector at a distance R1. The area of ​​the blackbody corresponding to the spatial angle of a single pixel is S0, and the detector operates within a unit solid angle. Within the space, the receiving area is The actual target irradiance received during the calibration process was obtained as follows:

[0034] For infrared point source targets, at a distance The target irradiance received by the detector at the location The expression is:

[0035] Combining the above formulas and setting them equal, we get:

[0036] Where J is the target radiation intensity. The distance is relative. denoted as Atmospheric transmittance at this distance.

[0037] Compared with the prior art, the present invention has the following beneficial effects: This invention provides an optical calibration method applicable to the infrared characteristics of small aerial targets. It employs a pre-segmented non-uniform correction technique to improve the uniformity of the detector pixel array. Unlike traditional temperature test calibration methods, it uses the irradiance data received on the detector surface as a benchmark, evaluates background noise based on the detector grayscale response curve fitting results, and compensates for the target irradiance data, further reducing error terms in the calibration process and effectively improving the accuracy of the calibration results. Based on the calibration process of a single detector, a complete method from detector debugging to image data acquisition and processing is extracted, which has significant engineering application value. Attached Figure Description

[0038] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating the implementation process of this invention. Figure 2 These are the grayscale response curves of each pixel in the infrared detector; Figure 3 In the diagram, (a) to (g) are the original images acquired by the detector under different temperature conditions of the blackbody; Figure 4 It is the curve fitting the grayscale difference between the target and the background to the blackbody temperature; Figure 5 It is the target-background radiance and detector grayscale response fitting curve; Figure 6a and Figure 6b The results show the atmospheric transmittance calculations under relative distances of 40km and 120km, respectively. Figure 7 It is a set of infrared target images acquired in the field; Figure 8 It is the curve showing the change in target radiation intensity under fixed band conditions, obtained through calculation. Detailed Implementation

[0039] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0040] Example 1 This invention provides a calibration method for the infrared characteristics of small aerial targets, comprising the following steps: Step 1: Using a standard surface source blackbody, the blackbody aperture covers the entrance pupil of the detector. Different temperature settings are set to obtain the initial grayscale response curve of each pixel under the rated integration time of the infrared detector. Step 2 involves applying blind pixel removal and piecewise non-uniform correction to the detector. Two-point non-uniform correction is applied in different temperature ranges to calculate the gain factor and offset factor of individual pixels, enabling the corrected pixel output response curve to converge quickly and better approximate the responsivity of the actual infrared focal plane pixel. Step 3: Acquire raw image data of the detector under standard blackbody temperature T to obtain the target grayscale value of the detector response. Background grayscale value Meanwhile, the radiance of the blackbody at this temperature Background radiance Subtracting the two from the above, we get a set of grayscale and radiance data; Step 4: Adjust the standard blackbody temperature T, fit the correspondence between the grayscale difference and radiance difference between the target and the background under the integration time condition, and use it as the basis for target characteristic calibration;

[0041] Step 5: Following the process of steps 3 to 4, calibrate the response curves of the infrared detector under different integration time conditions. Step 6: When the weather is clear, take the fixed ground observation point as the reference and collect grayscale images of the target during its flight. Select the parts of the image where the target is unobstructed, the sun angle is not less than 15°, and there are no obvious interferences such as cloud cover in the sky, and count the grayscale curves of the target and the background. Step 7: Calculate the atmospheric transmittance under the current band conditions based on the distance corresponding to the selected image time, the altitude of the observed target, and the altitude of the detector location. Step 8: Based on the calibrated detector response curve and the collected target and background grayscale values, obtain the target irradiance received on the detector surface. ; Step 9: Combining the data collected above with the detector calibration curve, ensure that the irradiance of the target or blackbody reaching the detector surface is equal under the two measurement environmental conditions, and calculate the equivalent infrared radiation characteristics of the target under the current band conditions. Step 10: Based on this, for the response band of the detector, convert the calibration results into standard band statistical results under the corresponding temperature conditions.

[0042] During the process of detector calibration and target image acquisition, it is necessary to select an appropriate integration time range based on the theoretical range of the radiation intensity of the target to be measured, so as to ensure that the observed grayscale image response is within the ideal linear working range of the infrared detector. When correcting the response of each pixel of the detector, the higher the uniformity of the selected standard blackbody, the more accurate the grayscale data output by each pixel of the detector. When calibrating the detector grayscale response curve in steps 3 to 5, a telephoto lens needs to be placed in front of the detector, and a blackbody needs to be placed at the focal point of the lens. A pinhole aperture is also installed so that the light source emitted by the blackbody is converted into parallel light incident on the detector's optical system, which is consistent with the state when acquiring target images in the field. By fitting the function relationship between the target and background grayscale difference in acquired infrared images under different temperature conditions, the blackbody temperature T0 when the target-background grayscale difference is 0 can be obtained. This can be approximated as the detector noise floor being approximately equal to the radiance of a standard blackbody under this temperature condition. ; When acquiring target images, it is necessary to ensure that the weather is clear and cloudless, and the atmospheric visibility is not less than 10km. This is beneficial to the accuracy of calculating atmospheric transmittance.

[0043] Example 2 This invention provides an optical calibration method applicable to the infrared characteristics of small aerial targets. It fully elucidates the execution method of four steps: detector calibration, grayscale curve calibration, image acquisition, and statistical results. The following section provides a detailed explanation using the calibration calculation process of a specific optical detection device: (1) Please refer to Figure 1 The flowchart below shows the implementation process of this invention. The detector calibration part is related to the detector performance and integration time and other optical parameters. It is recommended that the actual state of the detector be calibrated and adjusted before each test in order to obtain the best calibration effect. (2) Please refer to Figure 2 The graph shows the grayscale response curves of each pixel in the infrared detector. The horizontal axis represents the blackbody temperature used for calibration, and the vertical axis represents the grayscale response of the detector. The blue line represents the uncalibrated grayscale response curve of each pixel, and the green line represents the calibrated response curve of all pixels. A multi-segment two-point calibration method is used, the principle of which is as follows: Suppose that under two different radiation conditions, the grayscale response of the pixel is respectively and The corrected grayscale response values ​​are as follows: and Its gain factor and offset factor It has the following relationship:

[0044] Substituting the values ​​and solving, we get:

[0045] (3) Please refer to Figure 3 , Figure 4 and Figure 5 The specific calibration method for the infrared detector is as follows: Assuming the response band of the detection device is According to Planck's law of blackbody radiation, the radiative exitance in this wavelength range The physical quantity being characterized is the radiant power of the target source into the hemispherical space per unit area (unit: W / cm²). 2 )for:

[0046] Planck's constant h is 6.626e-34, and its unit is J. s; c is the speed of light in a vacuum, taken as 3e8, in m / s; Boltzmann constant k = 1.3806e-23, in J / K; temperature T is in K.

[0047] Since a blackbody is a Lambert radiation source, its radiance... The radiation energy emitted by a radiating surface within a unit solid angle per unit projected area is expressed in W / m². 2 / sr. Assume its radiation direction deviates from the normal at an angle of... The radiance distribution in all directions within its space follows a distribution law:

[0048] For a point-source blackbody, its radiance It can be considered as the radiation intensity of the target along the normal in all directions, and its calculation relationship with the radiant exitance M is as follows:

[0049]

[0050] Please see Figure 3 In the table, (a) to (g) represent the original image acquisition results of the detector under the blackbody temperature T, which are 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, and 90℃, respectively. The average grayscale value of the target in the detector response is statistically analyzed. average gray value of the background and the radiance of the blackbody target The results are as follows: Table 1 Detector Calibration Parameters

[0051] Please see Figure 4 The graph represents the fitting curve between the target-background grayscale difference and the blackbody temperature. By analyzing the change in the grayscale difference between the target and the background in the infrared image acquired by the detector, the blackbody temperature T0 when the grayscale difference is close to 0 can be obtained. This can be approximated as the background radiance being approximately equal to the blackbody radiance under this temperature condition. Here, the background equivalent temperature is taken as 20℃.

[0052] Assuming the detector noise floor has the following effect: Background radiance We can obtain:

[0053]

[0054] Within the ideal operating range of the infrared detector, its grayscale response is approximately linear at the same time. Subtracting the two equations above, we get:

[0055] Please see Figure 5 Substituting the calculated target and background radiance values, along with the collected target-background grayscale difference, we obtain the target-background radiance and detector grayscale response fitting curves. We can see that they exhibit a roughly linear relationship; therefore, the calibration function expression is:

[0056] The calibration results in the example are as follows:

[0057] (4) Please refer to Figure 6a and Figure 6b The figures show the atmospheric transmittance calculation results under relative distances of 40km and 120km, respectively. The horizontal axis represents Wavelength in microns, and the vertical axis represents Transmission distance. The calculations were performed using MODTRAN 3.7 software, with the following conditions: observation point altitude 5km, target altitude 30km, summer season, dry desert climate, wind speed 8m / s, and atmospheric visibility 23km.

[0058] The statistics were compiled in 5km increments, and the results are as follows: Table 2 Atmospheric transmittance parameters under different distance conditions

[0059] (5) Please refer to Figure 7 A set of infrared target images acquired in the field and target-background grayscale values ​​were obtained; (6) Please refer to Figure 8 The specific calculation process for the target radiation intensity is as follows: Assuming that when calibrating the grayscale response curve of the infrared detector, a standard blackbody is placed in front of the infrared detector at a distance R1, and the area of ​​the blackbody corresponding to the spatial angle of a single pixel is S0, the detector's response per unit solid angle... Within the space, with a receiving area of ​​dS, the actual target irradiance received during the calibration process is:

[0060] For infrared point source targets, at a distance The target irradiance received by the detector at the location We can obtain:

[0061] Where J is the target radiation intensity, in units of , The distance is relative. Let be the atmospheric transmittance at this distance. Combining the above formula and setting them equal, we can obtain:

[0062] Through the above calculation process, we can obtain the curve of the target radiation intensity variation under the conditions of the detector acquisition band over a period of time. There are three possibilities for the fluctuation here: first, it is caused by the change between the target's attitude and the observation angle during flight; second, due to the possibility of cloud cover (or invisible factors such as aerosols and turbulence) along the path under long-distance observation conditions; and third, when the target is too far away, its actual spatial angle is less than one detector pixel unit. Due to atmospheric diffusion and other reasons, its energy may be distributed in multiple pixels, resulting in a certain deviation in the peak gray level of the target acquired by the detector.

[0063] Here are three processing methods; you can choose the one that suits your needs: a) The statistical average of this set of data can be used to characterize the general target characteristics of the target in a specific scenario; b) After discarding overly discrete erroneous sampling data, the lowest value of the remaining valid data is used to characterize the lowest value of its infrared target characteristics in a specific scenario, which is mainly used for engineering analysis and evaluation. c) After discarding overly discrete erroneous sampling data, the remaining valid data distribution range is used to represent the dynamic range of the target's infrared radiation characteristics in a specific scenario, which can be used for risk analysis or other operating conditions.

[0064] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0065] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. An optical calibration method for infrared signature of small targets in the air, characterized in that, The method comprises the following steps: Step 1: using a standard surface source black body, the black body light aperture covers the entrance pupil of the detector, sets different temperature positions, and obtains the initial gray response curve of each pixel of the infrared detector under the condition of the rated integration time; Step 2: the detector is subjected to blind pixel processing and segmented non-uniform correction, a two-point non-uniform correction method is applied in different temperature intervals, the gain factor and the offset factor of a single pixel are calculated, and the output response curve of the corrected pixel is converged; Step 3: the original image data of the detector under the temperature condition of the standard black body is collected, the target gray value, the background gray value and the radiance of the black body at the temperature are obtained, the target gray value is subtracted from the background gray value, and a set of gray and radiance data is obtained; Step 4: adjusting the temperature of the standard black body, fitting the corresponding relationship between the gray difference value and the radiance difference value of the target-background under the condition of the integration time, as the basis for target characteristic calibration; Step 5: repeating steps 3 and 4 until the response curve of the infrared detector under different integration time conditions is calibrated; Step 6: taking a fixed observation point on the ground as a reference, collecting the gray images of the target in the flight process, and selecting according to the preset requirements, and counting the target and background gray curves; Step 7: according to the distance corresponding to the selected image moment, the altitude of the observed target and the altitude of the position of the detector, the atmospheric transmittance under the current waveband condition is calculated; Step 8: according to the calibrated detector response curve and the collected target gray value and background gray value, the target radiation illuminance received by the detector surface is obtained; Step 9: based on the collected data and the detector calibration curve, the radiation illuminance of the target or the black body reaching the detector surface under the two measurement environment conditions is equal, and the infrared radiation characteristics of the collected target under the current waveband condition is calculated; Step 10: for the response waveband of the detector, the calibration result is converted into the standard waveband statistical result under the corresponding temperature condition.

2. The optical calibration method for infrared signature of small aerial targets according to claim 1, characterized in that, The piecewise non-uniform correction includes: under two different radiation conditions, the gray response of the pixel is respectively and The gain factor and the offset factor have the following relationship: By substituting and solving, we have: wherein and is the corrected gray scale response value.

3. The optical calibration method for infrared signature of small aerial targets according to claim 1, characterized in that, The radiance L of the black body is calculated based on the Planck black body radiation law, and the calculation formula of the radiation exitance M is: where h is Planck's constant; c is the speed of light in a vacuum; k is the Boltzmann constant; and T is the blackbody temperature; to probe the range of the response band of the device; and λ is the wavelength of the electromagnetic wave. The relationship between the radiance L and the radiation exitance M is: wherein, Ltarget is the target radiance of a standard black body at temperature T; the radiance L is used to correspond to a gray value to form calibration data; When fitting the corresponding relationship between the gray difference value and the radiance difference value of the target-background, the black body temperature T0 when the gray difference value of the target-background is 0 is obtained by adjusting the black body temperature T, and it is approximately considered that the detector noise floor is equal to the radiance L0 of the standard black body under the temperature condition, wherein L0 is calculated by the Planck black body radiation law, and T0 and L0 are used to compensate the background noise.

4. The optical calibration method for infrared signature of small aerial targets according to claim 3, characterized in that, Let the detector noise influence be , the background radiance , then we have: wherein, is the target gray value acquired by the detector under the temperature T condition; is the background gray value acquired by the detector under the temperature T condition; In the ideal working area of the infrared detector, for the same moment, the gray response is approximately linear response, the above two formulas are subtracted, and the following formula is obtained: By substituting the target-background radiance and the gray difference value of the target-background, the target-background radiance and the detector gray response fitting curve are obtained, and the calibration function expression is: wherein is the slope of the detector's gray scale response curve, is the noise term.

5. The optical calibration method for infrared signature of small aerial targets according to claim 4, characterized in that, In the process of calibrating the gray response curve of the infrared detector, a standard blackbody is placed in front of the infrared detector at a distance R1, the blackbody area corresponding to the spatial angular of a single pixel is S0, and the receiving area of the detector in the unit solid angle is . The actual received target radiation intensity of the detector in the calibration process is obtained as follows: For an infrared point source target, the target radiance received at the detector at a distance of 1 km is The expression is: Combining the above formula, let them be equal, and the following formula is obtained: where J is the target radiation intensity, is the relative distance, is the atmospheric transmittance under this distance condition.

6. An optical calibration system suitable for use in calibrating infrared signatures of small aerial targets, comprising: The method comprises the following steps: Module M1: using a standard surface source black body, the black body light aperture covers the entrance pupil of the detector, sets different temperature positions, and obtains the initial gray response curve of each pixel of the infrared detector under the condition of the rated integration time; Module M2: The detector is de-blinded and segmented for non-uniform correction, two-point non-uniform correction method is applied in different temperature intervals, gain factor and offset factor of a single pixel are calculated to make the corrected pixel output response curve converge; Module M3: The original image data of the detector under the temperature condition of the standard black body is collected, the target gray value and the background gray value of the detector response are obtained, and the radiance of the black body under the temperature is obtained, the target gray value is subtracted from the background gray value to obtain a set of gray and radiance data; Module M4: The temperature of the standard black body is adjusted, and the corresponding relationship between the target-background gray difference and the radiance difference under the integration time condition is fitted as the basis for target characteristic calibration; Module M5: Modules M3 and M4 are repeatedly called until the response curve of the infrared detector under different integration time conditions is calibrated; Module M6: The gray image of the target during flight is collected based on the ground fixed observation point as the reference, and the target and background gray curves are counted according to the preset requirements; Module M7: According to the distance corresponding to the selected image time, the altitude of the observed target, and the altitude of the position of the detector, the atmospheric transmittance under the current waveband condition is calculated; Module M8: According to the calibrated detector response curve and the collected target gray value and background gray value, the target radiance received by the detector surface is obtained; Module M9: Based on the collected data and the detector calibration curve, the radiance of the target or black body reaching the detector surface under two measurement environment conditions is equal, and the infrared radiation characteristics of the collected target under the current waveband condition are calculated equivalently; Module M10: The calibration result is converted into the standard waveband statistical result under the corresponding temperature condition for the response waveband of the detector.

7. The optical calibration system for infrared signature of small aerial targets according to claim 6, characterized in that, The piecewise non-uniformity correction includes: under two different radiation conditions, the gray response of the pixel is respectively and The gain factor and the offset factor have the following relationship: By substituting and solving, we get: wherein and is the corrected gray scale response value.

8. The optical calibration system for infrared signature of small aerial targets according to claim 6, characterized in that, The radiance of the black body is calculated based on the Planck black body radiation law, and the calculation formula of the radiation exitance M is: where h is Planck's constant; c is the speed of light in vacuum; k is the Boltzmann constant; and T is the blackbody temperature; to probe the range of the response band of the device; and λ is the wavelength of the electromagnetic wave. The relationship between the radiance L and the radiation exitance M is: wherein, Ltarget is the target radiance of a standard black body at temperature T; the radiance L is used to correspond to a gray value to form calibration data; When fitting the corresponding relationship between the target-background gray difference and the radiance difference, the black body temperature T0 when the target-background gray difference is 0 is obtained by adjusting the black body temperature T, and it is approximately considered that the detector noise is equal to the radiance L0 of the standard black body under the temperature condition, wherein L0 is calculated by the Planck black body radiation law, and T0 and L0 are used to compensate the background noise.

9. The optical calibration system for infrared signature of small aerial targets according to claim 8, characterized in that, Let the detector noise influence be , the background radiance , then we have: wherein, is the target gray value acquired by the detector under the temperature T condition; is the background gray value acquired by the detector under the temperature T condition; In the ideal working area of the infrared detector, for the same time, the gray response is approximately linear response, the above two formulas are subtracted to obtain: By substituting the target-background radiance and the target-background gray difference, the target-background radiance and the detector gray response fitting curve are obtained, and the calibration function expression is: wherein is the slope of the detector's gray scale response curve, is the noise term.

10. The optical calibration system for infrared signature of small aerial targets according to claim 9, characterized in that, In the process of calibrating the gray response curve of the infrared detector, a standard blackbody is placed in front of the infrared detector at a distance R1, the blackbody area corresponding to the spatial angular of a single pixel is S0, and the receiving area of the detector in the unit solid angle is . The actual received target radiation intensity of the detector in the calibration process is obtained as follows: For an infrared point source target, the target radiance received at the detector at a distance of 1000 meters is The expression is: According to the above formula, let them be equal to obtain: where J is the target radiation intensity, is the relative distance, is the atmospheric transmittance under this distance condition.

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