A method for evaluating the impact of complex inhomogeneous shock layer flow on target detection

Abstract

The present invention relates to a method for evaluating the influence of a complex non-uniform shock layer flow field on target detection. First, based on the close correlation between the infrared radiation transmission characteristics and factors such as temperature, pressure, and gas composition, the complex non-uniform shock layer is divided into a number of approximately constant temperature shock layers with infinitesimal thicknesses. Secondly, the infrared radiation spatial transmission line is fitted based on the discrete data of the "approximately constant temperature shock layer" and the continuous data related to the approximate constant temperature shock layer is solved. Then, the radiation attenuation coefficient of the approximate constant temperature shock layer is calculated and a discrete model of infrared radiation transmission of the complex non-uniform shock layer is constructed to approximately solve the shock layer transmittance and spontaneous radiation brightness. Finally, the attenuation of the shock layer on the target infrared radiation and the proportion of the shock layer's own radiation brightness are quantified to evaluate the degree of influence of the complex non-uniform shock layer flow field on target detection. The present invention comprehensively analyzes the complex and non-uniform dynamic change characteristics of the shock layer, and evaluates the degree of influence of the shock layer on target detection by calculating the ideal radiation transmission characteristics of the shock layer, providing theoretical support for correcting infrared detection images and improving target detection accuracy.

Description

Technical Field

[0001] The present invention relates to the field of infrared radiation transmission processing, and in particular to a method for evaluating the influence of a complex non-uniform shock layer flow field on target detection. Background Art

[0002] The photosensitive unit of an infrared detector is capable of sensing infrared radiation and quantifying it into an electrical signal. The signal strength is proportional to the detector's accumulated radiant brightness per unit time. By precisely measuring and analyzing the detector's output signal, the infrared radiation characteristics of the target and background can be captured. This difference in infrared characteristics between the target and background enables target detection and identification.

[0003] However, when an aircraft operates at high speeds, its shell interacts violently with the surrounding gas molecules, causing the gas to become highly compressed and its temperature and pressure to rise dramatically, forming a shock layer that differs significantly from the external environment. For high-speed aircraft that rely on infrared detection technology, the presence of a shock layer poses a significant challenge to their normal operation. Firstly, the high-temperature shock layer releases high-intensity infrared radiation noise, reducing the difference in infrared characteristics between the target and the background, lowering the signal-to-noise ratio. When the noise exceeds a certain threshold, the photosensitive elements saturate, obscuring target information and rendering the detection system ineffective. Secondly, molecules such as carbon dioxide, water, and nitrogen dioxide contained in the shock layer absorb target radiation, reducing target information. Furthermore, the pressure, temperature, and composition of the shock layer exhibit complex and non-uniform dynamic characteristics. At different temperatures and pressures, different molecules exhibit significant differences in their absorption characteristics for infrared radiation in different wavelengths, further complicating infrared target detection. Furthermore, some gas molecules absorb target radiation, generating intense excitation radiation, which introduces additional noise interference. This interference is particularly pronounced at high aircraft speeds. Therefore, accurately analyzing the infrared radiation characteristics of the complex inhomogeneous shock layer and evaluating the impact of the shock layer on target detection are of great significance for eliminating external noise interference, correcting infrared detection imaging, and improving target detection and identification accuracy.

[0004] Current methods for assessing the impact of shock layers on target detection are primarily based on computational models of shock layer infrared radiation transmission. Most of these models are simplified physical models based on idealized assumptions, such as uniform flow fields, single media, and radiation transmission calculations in a single wavelength band. These simplified models fail to reflect the complex and non-uniform characteristics of real flow fields and, therefore, are ineffective in assessing the impact of shock layers on target detection. While complex models such as line-by-line calculations, wide- and narrow-band calculations, and deep learning methods meet accuracy requirements, they consume significant computational resources and are extremely inefficient. Some methods are even inapplicable to practical applications.

[0005] In summary, there is currently a lack of a method for assessing the impact of complex, heterogeneous shock layers on target detection that balances accuracy and efficiency. Such a method should comprehensively consider the complex and heterogeneous dynamic characteristics of the shock layer flow field, enabling rapid and accurate assessment of its impact on target detection. This method would provide guidance for eliminating noise interference and highlighting target information, laying the foundation for correcting infrared detection images and improving target detection accuracy. Summary of the Invention

[0006] In response to the above technical deficiencies, the present invention provides a method for evaluating the impact of complex non-uniform shock layer flow fields on target detection. Based on the assumptions that the radiation source radiates instantaneously, the amount of transmitted radiation does not change with time, and the components in the shock layer are in equilibrium, the method divides the complex non-uniform shock layer into approximately constant-temperature shock layers according to the close relationship between infrared radiation transmission characteristics and factors such as temperature, pressure, and gas composition. The method fits the continuous data of the infrared radiation spatial transmission line based on the discrete data of the approximately constant-temperature shock layer. Then, the attenuation coefficient of each approximately constant-temperature shock layer is solved based on the continuous data, and a discrete model of infrared radiation transmission of the complex non-uniform shock layer is constructed to solve the shock layer transmittance and spontaneous radiation brightness. Finally, the shock layer's radiation attenuation ratio to the target and the proportion of the shock layer's radiation components are quantified, and the impact of the shock layer on target detection and feasible correction methods are evaluated.

[0007] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0008] A method for evaluating the impact of a complex non-uniform shock layer flow field on target detection includes the following steps:

[0009] 1) Based on the correlation between infrared radiation transmission characteristic parameters and temperature, the temperature interval is divided, and the complex non-uniform shock layer is divided into several approximately constant temperature shock layers with infinitesimal thickness;

[0010] 2) Construct a spatial transmission line according to the target radiation transmission direction, and fit the corresponding position value of the spatial transmission line according to the result of the approximate isothermal shock layer division;

[0011] 3) Based on the fitted spatial transmission line, calculate the attenuation coefficient of each approximately constant temperature shock layer;

[0012] 4) Construct a differential model of the infrared radiation transmission characteristics of the complex inhomogeneous shock layer and discretize it, substituting the spatial transmission line and attenuation coefficient to approximately solve the shock layer transmittance and spontaneous radiation brightness;

[0013] 5) The shock layer transmittance is used to quantify the target radiation attenuation ratio, and the detection system parameters are combined to quantify the proportion of shock layer radiation components, thereby evaluating the impact of the shock layer on target detection and possible correction solutions.

[0014] The step 1) comprises the following steps:

[0015] 1.1) Set the number of interval divisions n or the temperature division interval ΔT;

[0016] 1.2) Obtain the maximum temperature T in the shock layer data max and the minimum temperature T mtn , in T max and T min In the range of , a temperature interval set is established according to n or ΔT;

[0017] 1.3) Traverse all data points in the shock layer and divide them into corresponding interval sets according to the temperature value. Each set is regarded as an approximately constant temperature shock layer.

[0018] The step 2) comprises the following steps:

[0019] 2.1) Select the origin of space and establish the equation of the space line based on the parallel radiation transmission direction vector;

[0020] 2.2) Set the radius threshold R pex , using the transmission line as the axis to establish a radius R pex Space cylinder;

[0021] 2.3) Traverse each approximately isothermal shock layer and retain only the data points within the cylindrical surface;

[0022] 2.4) Establishing mesh surface association based on the retained data points;

[0023] 2.5) Obtain the intersection points of the spatial line and each approximately isothermal shock layer grid surface, and set the mean value of the grid surface constituent points as the intersection value;

[0024] 2.6) Map the spatial straight line to two-dimensional space and use the intersection value as the discrete data of the radiation transmission direction;

[0025] 2.7) Set the radiation transmission distance to divide the infinitesimal element ds, perform bilinear interpolation on the discrete data, and obtain the continuous data of the transmission line.

[0026] The attenuation coefficient is specifically:

[0027]

[0028] Among them, S i represents the integrated intensity of a single molecule spectrum line, F(η-η i ) represents the spectral line shape function, η is the selected wave number, η i ,η d ,η u are the wavenumber, lower limit and upper limit of spectral line broadening, respectively. irepresents the number of molecular components i, E represents the molecular component set, n represents the refractive index, N represents the total number of molecules, k η Represents the attenuation coefficient of the transmission medium at wavelength η.

[0029] The differential form of the differential model of the infrared radiation transmission characteristics of the complex inhomogeneous shock layer is:

[0030]

[0031] Where s represents the medium transmission distance, L λ (s) represents the wavelength λ, the radiant brightness at the medium transmission distance s, k λ (s) represents the wavelength λ, the attenuation coefficient of the transmission medium at the transmission distance s, B λ (s) represents the wavelength λ and the brightness of the shock layer spontaneous radiation at the medium transmission distance s. δ(s) represents the activation function, which is 1 when the medium transmission distance s meets the conditions for the generation of excitation radiation, and 0 otherwise. h represents Planck's constant, and c represents the speed of light.

[0032] Solving the differential model, we obtain:

[0033]

[0034] in, It represents the corrected attenuation coefficient at wavelength λ and medium transmission distance s, and L0 represents the initial radiation brightness of the target.

[0035] Discretize the differential model, specifically:

[0036]

[0037] Wherein, s′ represents the activation position in the medium transmission interval (0, s). When there is no excitation radiation, s′=s, n′ represents the infinitesimal division index of the activation position transmission distance. When there is no excitation radiation, n′=n, and Δ is the constant scaling term when excitation radiation exists.

[0038] The approximate solution for the shock layer transmittance and spontaneous radiation brightness is specifically:

[0039]

[0040]

[0041] Among them, Tr λ (s n ) represents the medium transmission distance s n Transmittance at point; Ra λ (s n ) represents the medium transmission distance s n The spontaneous radiation brightness.

[0042] The step 5) is specifically as follows:

[0043] Assume that the infrared detector responsivity function is H cam , the radiation component of the photosensitive window itself is Lw λ , the transmittance of the photosensitive window is Tw λ , sky background radiation Lb λ , the target radiation is approximated as parallel radiation, and the sky background radiation is approximated as Lambertian radiation;

[0044] When the aircraft is stationary and there is no shock layer, the radiation received by the detector includes target radiation, sky background radiation, and detection window radiation. The infrared detector imaging formula is:

[0045]

[0046] Among them, gray x,y It represents the linear response grayscale value of the transmitted radiation passing through the photosensitive target surface (x, y) unit; A represents the unit area of ​​the photosensitive target surface (x, y); Lt λ represents the target radiation brightness; λ max Indicates the upper limit of the infrared detection system's receiving wavelength, λ min Indicates the lower limit of the infrared detection system's receiving wavelength. At this time, the image contrast ρ between the target and the background is approximately:

[0047]

[0048] When the aircraft is running at high speed and there is a shock layer, the radiation received by the detector includes target radiation, sky background radiation, shock layer radiation, and detection window radiation. The infrared detector imaging formula is:

[0049]

[0050] Among them, Tr λ Indicates the transmittance of the shock layer at wavelength λ, Ra λ represents the spontaneous radiation brightness of the shock layer at wavelength λ. At this time, the image contrast between the target and the background is:

[0051]

[0052] Affected by the transmittance of the shock layer, the target radiation ratio decreases and the contrast decreases; at the same time, the shock layer radiation component Tw λ ·Ra λ The introduction of further reduces the target radiation ratio, resulting in a further decrease in contrast. Therefore, its impact is approximately:

[0053]

[0054] According to the degree of contrast influence, the detection image can be preliminarily corrected, and the result is:

[0055]

[0056] Among them, Gray x,y It represents the grayscale value correction result of the radiation response of the (x,y) unit on the photosensitive target surface.

[0057] The present invention has the following beneficial effects and advantages:

[0058] 1. The present invention can comprehensively consider the complex and non-uniform dynamic change characteristics of the shock layer and the transmission, absorption and scattering processes during radiation propagation, and quantify the interference of the shock layer's own radiation on target detection.

[0059] 2. The present invention successfully constructs an evaluation method for the impact of complex non-uniform shock layer flow fields on target detection, realizes simplified approximate calculations of the transmittance and spontaneous radiation brightness of complex shock layers, and provides a theoretical and technical solution for subsequent infrared detection imaging corrections. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is the overall flow chart of the present invention;

[0061] Figure 2 This is a schematic diagram of straight line data fitting of the present invention;

[0062] Figure 3 Schematic diagram of the shock layer infrared radiation transmission model of the present invention;

[0063] Figure 4 This is a schematic diagram of the division of the shock layer according to an embodiment of the present invention;

[0064] Figure 5 This is a diagram showing the transmittance calculation results of an embodiment of the present invention;

[0065] Figure 6 This is a graph showing the spontaneous radiation brightness results of an embodiment of the present invention. DETAILED DESCRIPTION

[0066] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0067] like Figure 1 The figure below is a flow chart of the method for evaluating the impact of the complex non-uniform shock layer flow field on target detection. The specific steps are as follows:

[0068] Step 1: Based on the correlation between the infrared radiation transmission characteristic parameters and temperature, the temperature interval is divided and the complex non-uniform shock wave layer is divided into several approximately constant temperature shock wave layers with infinitesimal thickness.

[0069] Step 2: Construct a spatial transmission line according to the target radiation transmission direction, and fit the corresponding position value of the spatial transmission line according to the approximate isothermal shock layer division result.

[0070] Step 3: Calculate the attenuation coefficient of each approximately isothermal shock layer by comprehensively considering environmental factors such as temperature, pressure, gas composition, and processes such as radiation transmission, absorption, and scattering.

[0071] Step 4: Construct a differential model of the infrared radiation transmission characteristics of the complex inhomogeneous shock layer and discretize it to approximately solve the shock layer transmittance and spontaneous radiation brightness.

[0072] Step 5: Use the shock layer transmittance to quantify the target radiation attenuation ratio, and combine it with the detection system's own parameters to quantify the proportion of the shock layer radiation component, and then evaluate the impact of the shock layer on target detection and feasible correction solutions.

[0073] The data for the evaluation method of the impact of a complex non-uniform shock layer flow field on target detection is based on the results of ANSYS\FLUENT smooth simulation of an aircraft model, including physical properties such as flow field temperature, pressure, component composition, charge ratio, and airflow rate.

[0074] The temperature characteristics of the complex non-uniform shock layer are correlated with the distance from the aircraft wall. The closer the non-uniform shock layer is to the aircraft wall, the higher the temperature. Since temperature is the determining factor in calculating the shock layer absorption coefficient, the original data set is divided into intervals based on temperature, including the following steps:

[0075] Step 1: Set the number of interval divisions (resolution) n or the temperature division interval ΔT;

[0076] Step 2: Obtain the maximum temperature T of the shock layer data max , minimum temperature T min , establish a set of temperature intervals;

[0077] Step 3: Traverse all data points in the shock layer and divide them into corresponding interval sets according to temperature values;

[0078] Step 4: Output each temperature range set.

[0079] The schematic diagram of establishing the spatial straight line equation and data fitting is as follows Figure 2 The specific steps are as follows:

[0080] Step 1: Select the origin of space and establish the equation of the line based on the parallel radiation transmission direction vector;

[0081] Step 2: Enter the radius threshold R pex , using the transmission line as the axis to establish a radius R pex Space cylinder;

[0082] Step 3: Traverse each temperature interval set and retain only the data points within the cylindrical surface;

[0083] Step 4: Establish grid surface association based on the retained data points in each temperature range;

[0084] Step 5: Find the intersection of the spatial line and the grid surface of each temperature interval, and set the mean value of the grid surface points as the intersection value;

[0085] Step 6: Map the spatial straight line to the two-dimensional space. The intersection value obtained in step 5 is the discrete data of the radiation transmission direction.

[0086] Step 7: Set the radiation transmission distance to divide the infinitesimal element ds, perform bilinear interpolation processing, and obtain continuous data of the transmission line.

[0087] The attenuation coefficient of the “approximately constant temperature shock layer” is calculated as follows:

[0088]

[0089] Among them, S i represents the integrated intensity of a single molecule spectrum line; F(η-η i ) represents the spectral line shape function; η is the selected wave number; η i ,η d ,η u N is the wave number, lower limit and upper limit of spectral line broadening respectively; i represents the number of molecular components i; E represents the set of molecular components; n represents the refractive index; N represents the total number of molecules; k η Represents the attenuation coefficient of the transmission medium at wavelength η.

[0090] The spectral line radiation integral intensity will change with temperature. To solve the spectral line integral intensity at a specific temperature, it is necessary to correct it according to the reference value. The correction model is:

[0091]

[0092] Where T0 is the initial reference temperature 296K; S η (t0) is the integrated intensity of the molecular line radiation at the initial reference temperature, in cm -1 / (mol·cm -2 ); E″ is the energy of the low-level transition of the spectral line, in cm -1 ;K B =1.380658×10 - 23 J / K, Boltzmann constant; h = 6.626069 × 10 -34 J·s is Planck's constant; c = 2.997925×108 m / s, the speed of light; Q V (T) is the vibration partition function. Ignoring the simplicity of harmonicity, the approximate solution is obtained based on the degeneracy and vibration frequency, with an error of less than 5%. R (T) is the rotational partition function, which is calculated based on the rotational constant, molecular moment of inertia, etc., assuming that the molecule is rigid.

[0093] The spectral line shape function is divided into three types according to the spectral line broadening mechanism: Lorentz linear shape, Doppler linear shape, and mixed linear shape.

[0094] The Lorentz line function is:

[0095]

[0096] Where η represents the central wave number; η i represents an arbitrary wave number position; γ L is the Lorentz half-width, which is proportional to the pressure P and the temperature Inversely proportional.

[0097] The Lorentz half-width solution is:

[0098]

[0099] Where T ref The reference temperature is 296K, p ref is the reference pressure 1 atm; γ air is the air half-width; γ self n is the medium self-increment half width; air is the temperature dependence coefficient.

[0100] The Doppler spectrum function is:

[0101]

[0102] Where η represents the central wave number; η i represents an arbitrary wave number position; γ D is the Doppler half-width, and Directly proportional.

[0103] The Doppler half-width solution is:

[0104]

[0105] Among them, N A is Avogadro's constant, m is the molecular molar mass, K B is the Boltzmann constant.

[0106] The mixed spectral line function is obtained by convolution of the Lorentz spectral line function and the Doppler spectral line function:

[0107]

[0108] In most cases, the mixed spectral line function is subject to computational complexity and is replaced by a regional approximation formula.

[0109] The spectral line shape function is selected based on the shock layer temperature and pressure. When the shock layer pressure is low, the Doppler broadening effect is significant, so the Doppler spectral line function is selected. When the shock layer is at high temperature or high pressure, the collision broadening effect is significant, so the Lorentz spectral line function is selected.

[0110] The infrared radiation transmission characteristic model of the non-uniform shock layer is as follows: Figure 3 As shown, its differential equation form is:

[0111]

[0112] Where s represents the medium transmission distance; L λ Indicates the radiation brightness at wavelength λ and medium transmission distance s; k λ It represents the attenuation coefficient of the transmission medium at the wavelength λ and the transmission distance s, and is represented by k η Transformation acquisition; B λ represents the spontaneous radiation brightness of the shock layer at wavelength λ and medium transmission distance s; δ(s) is the activation function, which is 1 when the medium transmission distance s meets the conditions for the generation of excitation radiation, and 0 otherwise.

[0113] The differential model of infrared radiation transmission characteristics of the non-uniform shock layer is solved to obtain:

[0114]

[0115] in, represents the corrected attenuation coefficient at wavelength λ and medium transmission distance s. In this model, It expresses the transmittance of the shock layer, and the second half expresses the cumulative radiation brightness of the shock layer itself.

[0116] The infrared radiation transmission characteristic model of the non-uniform shock layer is discretized to obtain:

[0117]

[0118] Wherein, s′ represents the activation position in the medium transmission interval (0, s). When there is no excitation radiation, s′=s; n′ represents the infinitesimal division index of the activation position transmission distance. When there is no excitation radiation, n′=n; Δ is the constant scaling term when excitation radiation exists.

[0119] According to the discrete approximation results, the shock layer transmittance and spontaneous radiation brightness models are constructed, and the following are obtained:

[0120]

[0121]

[0122] Among them, Tr λ (s n ) represents the medium transmission distance s n Transmittance at point; Ra λ (s n ) represents the medium transmission distance s n The spontaneous radiation brightness.

[0123] Assume that the infrared detector responsivity function is known to be H cam , the radiation component of the photosensitive window itself is Lw λ , the transmittance of the photosensitive window is Tw λ , sky background radiation Lb λ , the target radiation is approximated as parallel radiation, and the sky background radiation is approximated as Lambertian radiation.

[0124] When the aircraft is stationary and there is no shock layer, the radiation received by the detector includes target radiation, sky background radiation, and detection window radiation. The infrared detector imaging formula is:

[0125]

[0126] Among them, gray x,y It represents the linear response grayscale value of the transmitted radiation passing through the photosensitive target surface (x, y) unit; A represents the unit area of ​​the photosensitive target surface (x, y); Lt λ represents the target radiation brightness; λ max Indicates the upper limit of the infrared detection system's receiving wavelength, λ min Indicates the lower limit of the infrared detection system's receiving wavelength. At this time, the image contrast ρ between the target and the background is approximately:

[0127]

[0128] When the aircraft is running at high speed and there is a shock layer, the radiation received by the detector includes target radiation, sky background radiation, shock layer radiation, and detection window radiation. The infrared detector imaging formula is:

[0129]

[0130] Among them, Tr λ Indicates the transmittance of the shock layer at wavelength λ, Ra λ represents the brightness of the shock layer's spontaneous radiation at wavelength λ. The image contrast between the target and the background is:

[0131]

[0132] Affected by the transmittance of the shock layer, the target radiation ratio decreases and the contrast decreases; at the same time, the shock layer radiation component Tw λ ·Ra λ The introduction of further reduces the target radiation ratio, resulting in a further decrease in contrast. Therefore, its impact is approximately:

[0133]

[0134] According to the degree of contrast influence, the detection image can be preliminarily corrected, and the result is:

[0135]

[0136] Among them, Gray x,y It represents the grayscale value correction result of the radiation response of the (x,y) unit on the photosensitive target surface.

[0137] Example 1

[0138] like Figure 4 FIG. 1 is a schematic diagram showing the division results of a high-speed aircraft shock layer using step 1 of the method for calculating infrared radiation transmission characteristics of a complex non-uniform shock layer.

[0139] According to step 2 of the method for calculating the infrared radiation transmission characteristics of the complex non-uniform shock layer, the discrete data of the transmission line at a certain position on the upper surface of the aircraft is obtained and interpolated. The discrete data is shown in the following table.

[0140] Table 1

[0141]

[0142] According to the calculation method of infrared radiation transmission characteristics of complex non-uniform shock wave layer, step three is used to calculate and solve the spectrum line integral intensity, spectrum line shape and attenuation coefficient at each position of the spatial transmission line after interpolation processing in step two.

[0143] According to the calculation method of the infrared radiation transmission characteristics of the complex non-uniform shock layer in step 4, the attenuation coefficient is substituted into the calculation model, and the Planck function is used as the shock layer spontaneous radiation brightness function to calculate the shock layer transmittance and spontaneous radiation brightness. The results are as follows: Figure 5 、 Figure 6 As shown. The average transmittance is 0.99993 and the integrated radiance is 10 -5 W / (m 2 If the detection window and detector parameters are known, the impact of the shock layer on target detection and the preliminary correction results can be obtained by substituting them into the infrared detection imaging formula.

Claims

1. A method for evaluating the impact of complex non-uniform shock layer flow fields on target detection, characterized in that: The following steps are involved: 1) Based on the correlation between infrared radiation transmission characteristic parameters and temperature, the temperature interval is divided, and the complex non-uniform shock layer is divided into several approximately constant temperature shock layers with infinitesimal thickness; 2) Construct a spatial transmission line according to the target radiation transmission direction, and fit the corresponding position value of the spatial transmission line according to the result of the approximate isothermal shock layer division; 3) Based on the fitted spatial transmission line, calculate the attenuation coefficient of each approximately constant temperature shock layer; 4) Construct a differential model of the infrared radiation transmission characteristics of the complex inhomogeneous shock layer and discretize it, substituting the spatial transmission line and attenuation coefficient to approximately solve the shock layer transmittance and spontaneous radiation brightness; 5) The shock layer transmittance is used to quantify the target radiation attenuation ratio, and the detection system parameters are combined to quantify the proportion of shock layer radiation components, thereby evaluating the impact of the shock layer on target detection and possible correction solutions.

2. The method for evaluating the impact of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: The step 1) comprises the following steps: 1.1) Set the number of interval divisions n or the temperature division interval ΔT; 1.2) Obtain the maximum temperature T in the shock layer data max and the minimum temperature T min , in T max and T min In the range of , a temperature interval set is established according to n or ΔT; 1.3) Traverse all data points in the shock layer and divide them into corresponding interval sets according to the temperature value. Each set is regarded as an approximately constant temperature shock layer.

3. The method for evaluating the impact of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: The step 2) comprises the following steps: 2.1) Select the origin of space and establish the equation of the space line based on the parallel radiation transmission direction vector; 2.2) Set the radius threshold R pex , using the transmission line as the axis to establish a radius R pex Space cylinder; 2.3) Traverse each approximately isothermal shock layer and retain only the data points within the cylindrical surface; 2.4) Establishing mesh surface association based on the retained data points; 2.5) Obtain the intersection points of the spatial line and each approximately isothermal shock layer grid surface, and set the mean value of the grid surface constituent points as the intersection value; 2.6) Map the spatial straight line to two-dimensional space and use the intersection value as the discrete data of the radiation transmission direction; 2.7) Set the radiation transmission distance to divide the infinitesimal element ds, perform bilinear interpolation on the discrete data, and obtain the continuous data of the transmission line.

4. The method for evaluating the impact of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: The attenuation coefficient is specifically: Among them, S i represents the integrated intensity of a single molecule spectrum line, F(η-η i ) represents the spectral line shape function, η is the selected wave number, η i ,η d ,η u are the wavenumber, lower limit and upper limit of spectral line broadening, respectively. i represents the number of molecular components i, E represents the molecular component set, n represents the refractive index, N represents the total number of molecules, k η Represents the attenuation coefficient of the transmission medium at wavelength η.

5. The method for evaluating the impact of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: The differential form of the differential model of the infrared radiation transmission characteristics of the complex inhomogeneous shock layer is: Where s represents the medium transmission distance, L λ (s) represents the wavelength λ, the radiant brightness at the medium transmission distance s, k λ (s) represents the wavelength λ, the attenuation coefficient of the transmission medium at the transmission distance s, B λ (s) represents the wavelength λ and the brightness of the shock layer spontaneous radiation at the medium transmission distance s. δ(s) represents the activation function, which is 1 when the medium transmission distance s meets the conditions for the generation of excitation radiation, and 0 otherwise. h represents Planck's constant, and c represents the speed of light. Solving the differential model, we obtain: in, It represents the corrected attenuation coefficient at wavelength λ and medium transmission distance s, and L0 represents the initial radiation brightness of the target.

6. The method for evaluating the impact of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: Discretize the differential model, specifically: Wherein, s′ represents the activation position in the medium transmission interval (0, s). When there is no excitation radiation, s′=s, n′ represents the infinitesimal division index of the activation position transmission distance. When there is no excitation radiation, n′=n, and Δ is the constant scaling term when excitation radiation exists.

7. The method for evaluating the impact of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: The approximate solution for the shock layer transmittance and spontaneous radiation brightness is specifically: Among them, Tr λ (s n ) represents the medium transmission distance s n Transmittance at point; Ra λ (s n ) represents the medium transmission distance s n The spontaneous radiation brightness.

8. The method for evaluating the impact of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: The step 5) is specifically as follows: Assume that the infrared detector responsivity function is H cam , the radiation component of the photosensitive window itself is Lw λ , the transmittance of the photosensitive window is Tw λ , sky background radiation Lb λ , the target radiation is approximated as parallel radiation, and the sky background radiation is approximated as Lambertian radiation; When the aircraft is stationary and there is no shock layer, the radiation received by the detector includes target radiation, sky background radiation, and detection window radiation. The infrared detector imaging formula is: Among them, gray x,y It represents the linear response grayscale value of the transmitted radiation passing through the photosensitive target surface (x, y) unit; A represents the unit area of ​​the photosensitive target surface (x, y); Lt λ represents the target radiation brightness; λ max Indicates the upper limit of the infrared detection system's receiving wavelength, λ min Indicates the lower limit of the infrared detection system's receiving wavelength. At this time, the image contrast ρ between the target and the background is approximately: When the aircraft is running at high speed and there is a shock layer, the radiation received by the detector includes target radiation, sky background radiation, shock layer radiation, and detection window radiation. The infrared detector imaging formula is: Among them, Tr λ Indicates the transmittance of the shock layer at wavelength λ, Ra λ represents the spontaneous radiation brightness of the shock layer at wavelength λ. At this time, the image contrast between the target and the background is: Affected by the transmittance of the shock layer, the target radiation ratio decreases and the contrast decreases; at the same time, the shock layer radiation component Tw λ ·Ra λ The introduction of further reduces the target radiation ratio, resulting in a further decrease in contrast; therefore, its impact is approximately: According to the degree of contrast influence, the detection image can be preliminarily corrected, and the result is: Among them, Gray x,y It represents the grayscale value correction result of the radiation response of the (x,y) unit on the photosensitive target surface.

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