Aircraft target infrared detection simulation imaging method

Abstract

The application discloses a kind of aircraft target infrared detection simulation imaging method, comprising the following steps: S1, establish unmanned aerial vehicle three-dimensional geometric model, and the outer surface of unmanned aerial vehicle is divided into several micro-element surface;S2, the solar radiation irradiance and sky radiation irradiance received by each micro-element surface are calculated;S3, based on solar radiation irradiance and sky radiation irradiance, the temperature of each micro-element surface is calculated using heat flow balance equation;S4, micro-element surface radiation irradiance is projected to detector pixel, realizes unmanned aerial vehicle target infrared radiation imaging.The outer surface of unmanned aerial vehicle is divided into multiple micro-element surface in the application, considering the comprehensive influence factors such as solar radiation, sky radiation, based on heat flow balance equation to solve the temperature of each micro-element surface, improve the accuracy of unmanned aerial vehicle surface temperature calculation, and then improve the precision of infrared radiation irradiance image.

Description

Technical Field

[0001] This invention relates to the field of infrared imaging simulation, and in particular to a method for simulating infrared detection of aircraft targets. Background Technology

[0002] In recent years, low-altitude small quadrotor unmanned aerial vehicles (UAVs) have seen rapid development and are being applied in surveying and remote sensing, ecological environment monitoring, and urban security. Quadrotor UAVs are powered by lithium batteries, which drive the rotors to rotate rapidly and provide lift. Due to their low flight speed and lack of significant aerodynamic heating, the battery is the primary source of radiant heat, resulting in relatively weak overall infrared radiation intensity, which poses a challenge for infrared detection. Therefore, it is necessary to establish accurate and rapid infrared imaging simulation methods for UAV targets, acquire a large amount of simulated infrared image sample data, and support target detection, tracking, and recognition based on deep learning methods.

[0003] Currently, infrared imaging simulation methods focus on aircraft. Aircraft exhaust plumes, nozzles, and other parts have strong heat sources, and temperature field simulations can be performed based on CFD methods. However, quadrotor UAVs have weak infrared radiation. For infrared characteristics and infrared image simulations of small targets, they are often approximated as point source targets, ignoring their heat source distribution and imaging geometry. The acquisition of infrared images mainly relies on infrared detection equipment such as thermal imagers. There is relatively little research on infrared imaging methods for quadrotor UAVs. Summary of the Invention

[0004] This invention proposes a simulation imaging method for infrared detection of aircraft targets, which can accurately and quickly acquire infrared images of aircraft targets under different flight conditions, providing a data source for aircraft target detection, tracking, and identification.

[0005] To achieve the above objectives, this invention proposes a simulation imaging method for infrared detection of aircraft targets, comprising the following steps:

[0006] S1. Establish a three-dimensional geometric model of the UAV and divide the outer surface of the UAV into several micro-element surfaces;

[0007] S2. Calculate the solar irradiance and sky irradiance received on the outer surface of the UAV;

[0008] S3. Based on solar irradiance and sky irradiance, the temperature of each micro-element surface is calculated using the heat flow balance equation;

[0009] S4. Project the irradiance of the micro-element surface onto the detector pixel to achieve infrared radiation imaging of the UAV target.

[0010] Furthermore, the solar radiation illuminance received by the micro-element surface of the UAV The calculation formula is:

[0011]

[0012]

[0013]

[0014] In the formula, Direct solar radiation illuminance; σ is the solar diffuse irradiance; σ is the angle between the micro-element surface of the UAV's outer surface and the horizontal plane of the ground; ω is the solar incidence angle; ψ is the solar altitude angle. Direct solar radiation illuminance; I0 is the solar diffuse irradiance; I0 is the solar constant, with a value of 1353 W / m2. 2 τ represents regional transparency;

[0015] The formula for calculating the sky irradiance received by the micro-element surface of the UAV is:

[0016]

[0017] In the formula, cc represents cloud cover; c is a coefficient related to clouds, with c taking 0.04 for cirrus clouds and 0.22 for cumulonimbus clouds. This represents atmospheric longwave radiation when the sky is cloudless.

[0018]

[0019] In the formula, ε is the surface emissivity; a = 0.61, b = 0.05 are empirical constants; e a ′ represents the near-surface water vapor pressure, T a It is a function of near-surface air temperature and relative humidity.

[0020] Furthermore, the method for calculating the temperature of each micro-element surface includes the following steps: calculating the temperature distribution of the micro-element surface of the UAV based on the heat flow balance equation; for each micro-element surface, ignoring heat conduction between micro-element surfaces, its heat flow balance equation is:

[0021]

[0022] In the formula, This indicates heat transfer between the outer surface micro-element and the atmosphere via convection. This represents the heat absorbed by the outer surface micro-element from the outside. This refers to the heat emitted by micro-elements on the outer surface of the fuselage towards the outside world;

[0023] The heat transfer flux between the micro-element surface of the UAV and the atmospheric convection is as follows:

[0024]

[0025] In the formula, h fs (t) is the convective heat transfer coefficient; T is the atmospheric temperature; T(0,t) is the surface temperature of the outer surface of the fuselage.

[0026] The heat emitted by the micro-element on the outer surface of the drone towards the outside is:

[0027]

[0028] In the formula, ε fs (λ) represents the emissivity of the micro-elemental surface of the fuselage; T(0,t) represents the temperature of the micro-elemental surface of the fuselage; L B (T(0,t)) represents Planck's blackbody radiation; λ min ~λ max For infrared detection band, λ min =8μm;λ max =12μm;

[0029] The heat absorbed by the micro-element surface of the drone from the outside is:

[0030]

[0031] In the formula, α fs (λ) is the spectral absorption coefficient of the micro-element surface of the fuselage outer surface; θ represents sky irradiance. in The angle between the sky radiation and the direction of the normal to the micro-elemental surface of the fuselage; Solar radiation illuminance; The angle between the direction of the normal to the micro-element surface of the fuselage and the direction of solar incidence;

[0032] Temperature of the micro-element surface located on the outer surface of the drone battery box Temperature of micro-element surfaces located in the non-battery box area of ​​the drone's surface Q represents the heat generated by the drone battery during operation;

[0033] Based on the above formula, the temperature T of each micro-element surface on the outer surface of the UAV can be calculated. W .

[0034] Furthermore, step S4 specifically includes the following steps:

[0035] S4.1 Number the micro-element surfaces of the UAV fuselage, where numbers 1 to M are the micro-element surfaces on the outer surface of the battery box, and M+1 to N are the micro-element surfaces in the non-battery box area.

[0036] S4.2 Select the micro-element surface numbered K=1, and initialize the irradiance H of each pixel of the detector. ij H ijThe value is 0, where i and j represent the pixel in the i-th row and j-th column of the detector, respectively;

[0037] S4.3 Perform projection analysis on the detector for the Kth micro-element surface;

[0038] S4.4 Determine whether the micro-element is visible to the detector. If it is visible, proceed to step S4.5; otherwise, execute K = K + 1 and return to step S4.3.

[0039] S4.5 Calculate the irradiance H projected onto the detector pixel from the infinitesimal surface. K ;

[0040] S4.6 Determine if K is equal to N. If not, execute K = K + 1 and return to step S4.3; if yes, execute step S4.7.

[0041] S4.7. Generate an infrared radiation map of the UAV target.

[0042] Furthermore, the irradiance H projected onto the detector pixel by the micro-element surface K The calculation method includes the following steps:

[0043] S4.5.1. Based on the temperature T of the micro-elemental surface of the UAV, using Planck's blackbody radiation law, combined with the emissivity of the micro-elemental surface and the detection direction, the intrinsic radiation of the micro-elemental surface is obtained:

[0044]

[0045] Where h is Planck's constant; c is the speed of light in a vacuum; k is Boltzmann's constant; λ is the wavelength; and ε(λ) is the infrared spectral emissivity of the surface material.

[0046] S4.5.2 Calculate the irradiance from the Kth micro-element surface to the detector pixel:

[0047]

[0048] Among them, A S τ represents the detectable area of ​​the micro-element; L represents the detection distance; and τ represents the atmospheric transmittance along the detection path.

[0049] S4.5.3. Accumulate the irradiance on the detected pixels:

[0050] H i.j =H i,j +H K .

[0051] Furthermore, the three-dimensional geometric model of the UAV includes, but is not limited to, rotors, support frames, and battery boxes.

[0052] This invention has the following advantages:

[0053] This invention divides the outer surface of a drone into multiple micro-surfaces. Taking into account the combined effects of solar radiation, sky radiation, and other factors, the temperature of each micro-surface is solved based on the heat flow balance equation, thereby improving the accuracy of drone surface temperature calculation and thus improving the accuracy of infrared radiation irradiance images. Attached Figure Description

[0054] Figure 1 This is a flowchart illustrating a simulation imaging method for infrared detection of aircraft targets.

[0055] Figure 2 This is a schematic diagram illustrating the process of projecting the irradiance of a micro-element surface onto a detector pixel. Detailed Implementation

[0056] The following will be combined with the embodiments of the present invention. Figures 1-2 The technical solutions, structural features, objectives and effects achieved in the embodiments of the present invention will be described in detail.

[0057] It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions. They are only used to facilitate and clarify the purpose of illustrating the embodiments of the present invention, and are not intended to limit the implementation conditions of the present invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationship, or adjustments to the size should still fall within the scope of the technical content disclosed in the present invention, provided that they do not affect the effects and objectives that the present invention can produce.

[0058] like Figure 1 As shown, this invention proposes a simulation imaging method for infrared detection of aircraft targets, comprising the following steps:

[0059] S1. Establish a three-dimensional geometric model of the UAV and divide the outer surface of the UAV into several micro-element surfaces.

[0060] Specifically, information such as the dimensions, structure, and materials of the quadcopter drone is obtained, and reverse modeling of the quadcopter drone is performed to obtain its three-dimensional geometric model. The three-dimensional geometric model of the quadcopter drone includes: rotor, support frame, battery box, etc., and the outer surface of the drone is divided into several micro-element surfaces by meshing.

[0061] S2. Calculate the solar irradiance and sky irradiance received on the surface of the UAV.

[0062] Specifically, the solar radiation received by the surface of a quadcopter drone is generally divided into two parts: direct sunlight and diffused sunlight. The formula for calculating solar radiation illuminance is:

[0063]

[0064]

[0065]

[0066] In the formula, Direct solar radiation illuminance; σ is the solar diffuse irradiance; σ is the angle between the micro-element surface of the UAV's outer surface and the horizontal plane of the ground; ω is the solar incidence angle; ψ is the solar altitude angle. Direct solar radiation illuminance; I0 is the solar diffuse irradiance; I0 is the solar constant, with a value of 1353 W / m2. 2 τ represents regional transparency.

[0067] As sunlight travels through the atmosphere to the Earth's surface, approximately 10% is absorbed by water vapor and carbon dioxide in the atmosphere. Simultaneously, the atmosphere absorbs reflected radiation from the ground, acquiring a certain temperature and thus producing medium- and long-wave radiation. The intensity of this radiation is generally determined by meteorological conditions such as cloud cover and atmospheric temperature. On a cloudless day, the atmospheric long-wave radiation is:

[0068]

[0069] In the formula, ε is the surface emissivity; a = 0.61, b = 0.05 are empirical constants; e a ′ represents near-surface water vapor pressure, in kPa, T a It is a function of near-surface air temperature and relative humidity.

[0070]

[0071] When there is cloud cover, the influence of long-wave infrared radiation from clouds should be considered. In this case, the above results need to be corrected to obtain the sky irradiance:

[0072]

[0073] In the formula, cc represents cloud cover; c is a coefficient related to clouds, with c taking 0.04 for cirrus clouds and c taking 0.22 for cumulonimbus clouds.

[0074] S3. Based on solar irradiance and sky irradiance, the temperature of each micro-element is calculated using the heat flow balance equation.

[0075] When solar and atmospheric radiation strike the surface of a drone, the radiant energy undergoes reflection and absorption. The surface temperature of the drone is determined using a heat balance equation, which is closely related to the properties of the surface material. These surface material characteristics include emissivity, absorptivity, specific heat capacity, thermal conductivity, and density. Based on different material types of the fuselage surface, the characteristic parameters of the micro-elemental surface materials are determined.

[0076] Assuming each micro-element surface of the fuselage is a basic thermal unit, a differential equation based on the conservation of heat flow is used to solve for the temperature distribution on the micro-element surface of the UAV. For each micro-element surface, neglecting heat conduction between micro-element surfaces, its heat flow balance equation is:

[0077]

[0078] in, This indicates heat transfer between the outer surface micro-element and the atmosphere via convection. This represents the heat absorbed by the outer surface micro-element from the outside. This refers to the heat emitted by the micro-element on the outer surface of the fuselage towards the outside.

[0079] Since drone batteries generate heat during operation, converting electrical energy into internal energy, the resulting heat acts as the heat source Q for the drone battery. Therefore, for the micro-elemental surface of the drone battery box... For the micro-elemental surface of the drone's surface in the area outside the battery box

[0080] The heat transfer flux between the micro-element surface of the UAV and the atmospheric convection is as follows:

[0081]

[0082] In the formula, h fs (t) is the convective heat transfer coefficient; T is the atmospheric temperature; T(0,t) is the surface temperature of the outer surface of the fuselage.

[0083] The heat emitted by the micro-element on the outer surface of the drone towards the outside is:

[0084]

[0085] In the formula, ε fs (λ) represents the emissivity of the micro-elemental surface of the fuselage; T(0,t) represents the temperature of the micro-elemental surface of the fuselage; L B (T(0,t)) represents Planck's blackbody radiation; λ min ~λ max For infrared detection band, λ min =8μm;λ max =12μm;

[0086] The heat absorbed by the micro-element surface of the drone from the outside is:

[0087]

[0088] In the formula, α fs (λ) is the spectral absorption coefficient of the micro-element surface of the fuselage outer surface; θ represents sky irradiance. in The angle between the sky radiation and the direction of the normal to the micro-elemental surface of the fuselage; Solar irradiance; θ surf The angle between the direction of the normal to the micro-element surface of the fuselage and the direction of solar incidence;

[0089] Based on the heat flow balance equation of the micro-element surface, the temperature T of each micro-element surface on the outer surface of the UAV is solved in sections. W .

[0090] S4. Project the irradiance of the micro-element surface onto the detector pixel to achieve infrared radiation imaging of the UAV target.

[0091] Specifically, each micro-element surface and detector pixel is numbered, and the process of projecting the irradiance of the micro-element surface onto the detector pixel is as follows:

[0092] S4.1 Number the micro-surfaces of the drone fuselage; In this embodiment, the drone fuselage is divided into N micro-surfaces, where 1 to M are the micro-surfaces on the outer surface of the battery box, and M+1 to N are the micro-surfaces in the non-battery box area.

[0093] S4.2 Select the micro-element surface number as K=1, and initialize the irradiance Hij of each pixel of the detector to 0, where i and j represent the pixel in the i-th row and j-th column of the detector, respectively;

[0094] S4.3 Perform detector projection analysis on the Kth micro-element surface;

[0095] S4.4 Determine whether the micro-element is visible to the detector. If it is visible, proceed to step S4.5; otherwise, execute K = K + 1 and return to step S4.3.

[0096] S4.5 Calculate the irradiance H projected onto the detector pixel from the infinitesimal surface. K ;

[0097] Specifically, the irradiance H projected onto the detector pixel from the micro-element surface. K The calculation method includes the following steps:

[0098] S4.5.1. Based on the temperature T of the micro-elemental surface of the UAV, using Planck's blackbody radiation law, combined with the emissivity of the micro-elemental surface and the detection direction, the intrinsic radiation of the micro-elemental surface is obtained:

[0099]

[0100] Where h is Planck's constant; c is the speed of light in a vacuum; k is Boltzmann's constant; λ is the wavelength; and ε(λ) is the infrared spectral emissivity of the surface material.

[0101] S4.5.2 Calculate the irradiance from the Kth micro-element surface to the detector pixel:

[0102]

[0103] Among them, A S τ represents the detectable area of ​​the micro-element; L represents the detection distance; and τ represents the atmospheric transmittance along the detection path.

[0104] S4.5.3. Accumulate the irradiance on the detected pixels:

[0105] H i.j =H i,j +H K

[0106] S4.6 Determine if K is equal to N. If not, execute K = K + 1 and return to step S4.3; if yes, execute step S4.7.

[0107] S4.7. Generate an infrared radiation map of the UAV target.

[0108] This invention considers the comprehensive influencing factors such as solar radiation, background radiation, and atmospheric convection, and establishes a heat flow balance-based equation for solving the surface temperature of UAVs in different regions, which can more accurately solve the temperature of different areas on the UAV surface. The surface temperature solution method of this invention, based on heat flow balance, starts from the basic principle of radiation transfer, obtains the intrinsic radiation of the fuselage surface, and directly reaches the detector through atmospheric transmission to form the irradiance image of the detector pixel, thus realizing a rapid infrared imaging method for UAV targets.

[0109] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for simulating infrared detection and imaging of aircraft targets, characterized in that, Includes the following steps: S1. Establish a three-dimensional geometric model of the UAV and divide the outer surface of the UAV into several micro-element surfaces; S2. Calculate the solar radiation illuminance and sky radiation illuminance received by each micro-element surface; The solar radiation illuminance received by the micro-element surface The calculation formula is: In the formula, Direct solar radiation illuminance; Solar diffuse irradiance; The angle between the micro-element surface of the UAV's outer surface and the horizontal plane of the ground; The angle of incidence of the sun; The solar altitude angle; Direct solar radiation illuminance; Solar diffuse irradiance; The solar constant is 1353 W / m. 2 ; For regional transparency; The formula for calculating the sky irradiance received by the micro-element surface is as follows: In the formula, Covered by clouds; For cloud-related coefficients, cirrus clouds Take 0.04, for cumulonimbus clouds Take 0.22, This represents atmospheric longwave radiation when the sky is cloudless. In the formula, Emissivity of the Earth's surface; , These are empirical constants; This is the near-surface water vapor pressure. It is a function of near-surface air temperature and relative humidity; S3. Based on solar irradiance and sky irradiance, the temperature of each micro-element surface is calculated using the heat flow balance equation; The method for calculating the temperature of each micro-element surface includes the following steps: calculating the temperature distribution of the micro-element surface of the UAV based on the heat flow balance equation; for each micro-element surface, ignoring heat conduction between micro-element surfaces, its heat flow balance equation is: In the formula, This indicates heat transfer between the outer surface micro-element and the atmosphere via convection. This represents the heat absorbed by the outer surface micro-element from the outside. This refers to the heat emitted by micro-elements on the outer surface of the fuselage towards the outside world; The heat transfer flux between the micro-element surface of the UAV and the atmospheric convection is as follows: In the formula, The convective heat transfer coefficient; Atmospheric temperature; The temperature of the micro-element surface on the outer surface of the fuselage; The heat emitted by the micro-element on the outer surface of the drone towards the outside is: In the formula, The emissivity of the micro-element surface of the fuselage; The temperature of the outer surface micro-element; This is Planck blackbody radiation; For infrared detection band, ; The heat absorbed by the micro-element surface of the drone from the outside is: In the formula, The spectral absorption coefficient of the micro-element surface on the outer surface of the fuselage; Sky irradiance; The angle between the sky radiation and the direction of the normal to the micro-elemental surface of the fuselage; Solar radiation illuminance; The angle between the direction of the normal to the micro-element surface of the fuselage and the direction of solar incidence; Temperature of the micro-element surface located on the outer surface of the drone battery box Temperature of the micro-element surface located in the non-battery box area of ​​the drone's surface ; Q This refers to the heat generated by the drone battery during operation. Based on the above formula, the temperature of each micro-element surface on the outer surface of the UAV can be calculated. ; S4. Project the irradiance of the micro-element surface onto the detector pixel to achieve infrared radiation imaging of the UAV target.

2. The infrared detection simulation imaging method for aircraft targets as described in claim 1, characterized in that, Step S4 specifically includes the following steps: S4.1 Number the micro-element surfaces of the UAV fuselage, where numbers 1 to M are the micro-element surfaces on the outer surface of the battery box, and M+1 to N are the micro-element surfaces in the non-battery box area. S4.2 Select the micro-element surface number as K=1, and initialize the irradiance of each pixel of the detector. =0, where and They represent the detector's first... Line number Columns; S4.3 Perform detector projection analysis on the Kth micro-element surface; S4.4 Determine whether the micro-element is visible to the detector. If it is visible, proceed to step S4.5; otherwise, execute K=K+1 and return to step S4.

3. S4.5 Calculate the irradiance projected onto the detector pixel from the infinitesimal surface. ; S4.6 Determine if K is equal to N. If not, execute K=K+1 and return to step S4.3; if yes, execute step S4.

7. S4.

7. Generate an infrared radiation map of the UAV target.

3. The infrared detection simulation imaging method for aircraft targets as described in claim 2, characterized in that, The irradiance projected onto the detector pixel by the micro-element surface The calculation method includes the following steps: S4.5.

1. Based on the temperature T of the micro-elemental surface of the UAV, using Planck's blackbody radiation law, combined with the emissivity of the micro-elemental surface and the detection direction, the intrinsic radiation of the micro-elemental surface is obtained: in, It is Planck's constant; The speed of light in a vacuum; Boltzmann's constant; Wavelength; The infrared spectral emissivity of the surface material; S4.5.2 Calculate the irradiance from the Kth micro-element surface to the detector pixel: in, The detectable area of ​​a micro-element surface; For detection distance; To detect atmospheric transmittance along the path; S4.5.

3. Accumulate the irradiance on the detected pixels: 。 4. The infrared detection simulation imaging method for aircraft targets as described in claim 1, characterized in that, The three-dimensional geometric model of the drone includes rotors, support frame, and battery box.

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