Method for evaluating influence of complex non-uniform shock wave layer flow field on target detection

Abstract

The invention relates to a method for evaluating the influence of a complex non-uniform shock wave layer flow field on target detection. The method comprises the following steps of: firstly, dividing a complex non-uniform shock wave layer into approximate constant-temperature shock wave layers with a plurality of thickness infinitesimal elements according to close correlation between infrared radiation transmission characteristics and factors such as temperature, pressure intensity and gas components; secondly, fitting an infrared radiation space transmission straight line according to discrete data of the approximate constant-temperature shock wave layer and solving related continuous data of the approximate constant-temperature shock wave layer; then, calculating an approximate constant-temperature shock wave layer radiation attenuation coefficient, constructing a complex non-uniform shock wave layer infrared radiation transmission discrete model, and approximately solving the transmittance and spontaneous radiation brightness of the shock wave layer; and finally, quantifying the attenuation of the shock wave layer on the target infrared radiation and the ratio of the radiation brightness of the shock wave layer so as to evaluate the influence degree of the complex non-uniform shock wave layer flow field on target detection. According to the method, the complex and non-uniform dynamic change characteristics of the shock wave layer are comprehensively analyzed, the influence degree of the shock wave layer on target detection is evaluated by calculating the ideal radiation transmission characteristics of the shock wave layer, and theoretical support is provided for correcting an infrared detection image and improving the target detection precision.

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 the infrared detector has the ability to sense infrared radiation and quantify it into electrical signals. The signal strength is proportional to the accumulated radiation brightness of the detector per unit time. By precisely measuring and analyzing the electrical signals output by the detector, the infrared radiation characteristics of the detection target and the background can be captured. According to the difference in infrared characteristics between the target and the background, target detection and identification can be achieved.

[0003] However, when the aircraft is running at high speed, its shell interacts violently with the surrounding gas molecules, causing the gas to be highly compressed, and the gas temperature and pressure rise sharply, forming a shock layer that is significantly different from the external environment. For high-speed aircraft that rely on infrared detection technology, the existence of the shock layer poses a severe challenge to its normal operation. On the one hand, the high-temperature shock layer will release high-intensity infrared radiation noise, which will reduce the difference in infrared characteristics between the target and the background and reduce the signal-to-noise ratio; when the noise exceeds a certain threshold, the photosensitive unit will fall into a saturated state and then submerge the target information, causing the detection system to fail. On the other hand, molecules such as carbon dioxide, water, and nitrogen dioxide contained in the shock layer will absorb target radiation, resulting in a reduction in target information. At the same time, the properties of the shock layer such as pressure, temperature, and component composition show complex and non-uniform dynamic change characteristics. Under different temperatures and pressures, different molecules have significant differences in the absorption characteristics of infrared radiation in different bands, which further aggravates the difficulty of infrared target detection. In addition, some gas molecules will produce violent excitation radiation after absorbing target radiation, introducing additional noise interference, especially when the aircraft is running at high speed, this interference is particularly significant. Therefore, accurately analyzing the infrared radiation characteristics of the complex non-uniform 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] The current methods for evaluating the impact of shock layers on target detection are mainly based on shock layer infrared radiation transmission calculation models, and most of these models are simplified physical models based on ideal assumptions, such as uniform flow field, single medium, and single-band radiation transmission calculations. Simplified models cannot reflect the characteristics of real complex and non-uniform flow fields, and thus cannot effectively evaluate the impact of shock layers on target detection. Complex models such as line-by-line calculation methods, wide and narrow band calculation methods, and deep learning methods meet accuracy requirements, but require a large amount of computing resources and are extremely inefficient. Some methods cannot even be applied to practical problems.

[0005] In summary, there is currently a lack of an evaluation method that takes into account both accuracy and efficiency and quantifies the degree of influence of complex non-uniform shock layers on target detection. This method should comprehensively consider the complex and non-uniform dynamic change characteristics of the shock layer flow field, and be able to quickly and accurately evaluate the influence of complex non-uniform shock layers on target detection, provide guidance for eliminating noise interference and highlighting target information, and lay the foundation for correcting infrared detection images and improving target detection accuracy. Summary of the invention

[0006] In view of the above technical deficiencies, the present invention provides a method for evaluating the impact of complex non-uniform shock layer flow field on target detection. This method is based on the assumption 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. According to the close relationship between the infrared radiation transmission characteristics and factors such as temperature, pressure, and gas composition, the complex non-uniform shock layer is divided into approximately constant temperature shock layers; the infrared radiation space transmission linear continuous data is fitted 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 complex non-uniform shock layer infrared radiation transmission discrete model is constructed to solve the shock layer transmittance and spontaneous radiation brightness; finally, the shock layer is quantified to quantify the attenuation ratio of target radiation and the proportion of shock layer radiation components, 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 effect of a complex non-uniform shock layer flow field on target detection comprises the following steps:

[0009] 1) According to the correlation between 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;

[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 approximate isothermal shock layer division result;

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

[0012] 4) Construct a differential model of infrared radiation transmission characteristics of a complex non-uniform 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's own parameters are combined to quantify the proportion of the shock layer radiation component, thereby evaluating the impact of the shock layer on target detection and feasible 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 highest 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 of 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 according to the parallel radiation transmission direction vector;

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

[0021] 2.3) Traverse each approximately isothermal shock layer and only retain the data points located 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 straight 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 the 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 transmission line continuous data.

[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 selected wave number, 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 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 spontaneous radiation brightness of the shock layer at wavelength λ and 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, otherwise it is 0, 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] The differential model is discretized as follows:

[0036]

[0037] Among them, s′ represents the activation position of 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 a 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 Ra λ (s n ) represents the medium transmission distance s n The spontaneous radiation brightness.

[0042] The step 5) is specifically:

[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 represents the linear response grayscale value of the transmitted radiation passing through the photosensitive target surface (x, y) unit; A represents the photosensitive target surface (x, y) unit area; Lt λ Indicates the target radiation brightness; λ max Indicates the upper limit of the infrared detection system receiving wavelength, λ min Indicates the lower limit of the infrared detection system 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 wave layer, the radiation received by the detector includes target radiation, sky background radiation, shock wave layer radiation, and detection window radiation. The infrared detector imaging formula is:

[0049]

[0050] Among them, Tr λ Represents the shock layer transmittance 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 reduction in contrast. Therefore, its impact is approximately:

[0053]

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

[0055]

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

[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 and imaging corrections. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0062] Figure 3 It is a schematic diagram of the shock layer infrared radiation transmission model of the present invention;

[0063] Figure 4 It is a schematic diagram of the division of the shock layer in 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 spontaneous radiation brightness result diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0066] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0067] like Figure 1 As shown in FIG. 1 , a flow chart of the evaluation method of the influence of the complex non-uniform shock layer flow field on target detection is shown. The specific steps are as follows:

[0068] Step 1: According to 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: Considering the environmental factors such as the temperature, pressure, gas composition, and radiation transmission, absorption, and scattering of the “quasi-isothermal shock layer”, calculate the attenuation coefficient of each quasi-isothermal shock layer.

[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 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 of the evaluation method for the influence of complex non-uniform shock layer flow field on target detection is based on the results of smooth simulation of the aircraft model imported into ANSYS\FLUENT, including physical properties such as flow field temperature, pressure, component composition, charge ratio, airflow rate, etc.

[0074] The temperature characteristics of the complex non-uniform shock layer are correlated with the distance from the aircraft wall. The closer to the aircraft wall, the higher the temperature of the non-uniform shock layer. Since the temperature is the determining factor for calculating the shock layer absorption coefficient, the original data set is divided into intervals according to the 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 fitting the data is as follows: Figure 2 As shown, 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 , with the transmission line as the axis, establish a radius of 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 mesh surface association based on the retained data points in each temperature interval;

[0084] Step 5: Find the intersection of the spatial straight line and the grid surface of each temperature interval, and set the mean value of the grid surface constituent 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 microelement 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 spectral 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 selected 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 integrated intensity will change with temperature, and the spectral line integrated intensity at a specific temperature needs to be corrected 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 spectral 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, is the Boltzmann constant; h = 6.626069 × 10 -34 J·s, Planck constant; c = 2.997925×108 m / s, the speed of light; Q V (T) is the vibration partition function, ignoring the simplicity of harmonicity, and approximating the solution 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 rotation constant, molecular moment of inertia, etc., assuming that the molecule is a rigid molecule.

[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 1atm; γ air is the half-width of air; self n is the self-incremental half width of the medium; 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 according to the temperature and pressure of the shock layer. When the shock layer pressure is low, the Doppler broadening effect is obvious, and the Doppler spectral line function is selected; when the shock layer is in a high temperature or high pressure state, the collision broadening effect is obvious, and 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 k represents the attenuation coefficient of the transmission medium at the wavelength λ and the medium transmission distance s. η Transformation acquisition; B λ It 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, otherwise it is 0.

[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] Among them, s′ represents the activation position of 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 a 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 results are obtained:

[0120]

[0121]

[0122] Among them, Tr λ (s n ) represents the medium transmission distance s n Transmittance at 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 represents the linear response grayscale value of the transmitted radiation passing through the photosensitive target surface (x, y) unit; A represents the photosensitive target surface (x, y) unit area; Lt λ Indicates the target radiation brightness; λ max Indicates the upper limit of the infrared detection system receiving wavelength, λ min Indicates the lower limit of the infrared detection system 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 wave layer, the radiation received by the detector includes target radiation, sky background radiation, shock wave layer radiation, and detection window radiation. The infrared detector imaging formula is:

[0129]

[0130] Among them, Tr λ Represents the shock layer transmittance 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:

[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 reduction in contrast. Therefore, its impact is approximately:

[0133]

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

[0135]

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

[0137] Example 1

[0138] like Figure 4 As shown, it is a schematic diagram of the division result 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 calculates and solves the spectral line integral intensity, spectral line shape and attenuation coefficient at each position of the spatial transmission line after interpolation processing in step two.

[0143] According to step 4 of the calculation method for infrared radiation transmission characteristics of complex non-uniform shock layer, 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 The average transmittance is 0.99993 and the integrated radiant brightness is 10 -5 W / (m 2 ·um). If the detection window and detector related 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 effect of complex non-uniform shock layer flow field on target detection, characterized in that: The following steps are involved: 1) According to the correlation between 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; 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; 3) Based on the fitted spatial transmission line, calculate the attenuation coefficient of each approximately isothermal shock layer; 4) Construct a differential model of infrared radiation transmission characteristics of a complex non-uniform 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's own parameters are combined to quantify the proportion of the shock layer radiation component, thereby evaluating the impact of the shock layer on target detection and feasible correction solutions.

2. The method for evaluating the effect 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 highest 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 of 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 effect 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 according to the parallel radiation transmission direction vector; 2.2) Set the radius threshold R pex , with the transmission line as the axis, establish a radius of R pex Space cylinder; 2.3) Traverse each approximately isothermal shock layer and only retain the data points located 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 straight 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 the 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 transmission line continuous data.

4. The method for evaluating the effect 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 selected wave number, 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 effect 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 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 spontaneous radiation brightness of the shock layer at wavelength λ and 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, otherwise it is 0, 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 effect of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: The differential model is discretized as follows: Among them, s′ represents the activation position of 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 a constant scaling term when excitation radiation exists.

7. The method for evaluating the effect 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 Ra λ (s n ) represents the medium transmission distance s n The spontaneous radiation brightness.

8. The method for evaluating the effect of complex non-uniform shock layer flow field on target detection according to claim 1, characterized in that: The step 5) is specifically: 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 represents the linear response grayscale value of the transmitted radiation passing through the photosensitive target surface (x, y) unit; A represents the photosensitive target surface (x, y) unit area; Lt λ Indicates the target radiation brightness; λ max Indicates the upper limit of the infrared detection system receiving wavelength, λ min Indicates the lower limit of the infrared detection system 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 wave layer, the radiation received by the detector includes target radiation, sky background radiation, shock wave layer radiation, and detection window radiation. The infrared detector imaging formula is: Among them, Tr λ Represents the shock layer transmittance 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 reduction in contrast. Therefore, its impact is approximately: According to the contrast influence, the detected image can be preliminarily corrected, and the result is: Among them, Gray x,y It represents the gray value correction result of the radiation response of the photosensitive target surface (x, y) unit.

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