Simulation method and system for target millimeter wave radiation image under radome

Abstract

The invention belongs to the related technical field of electromagnetic simulation, and discloses a simulation method and system for a target millimeter wave radiation image under an antenna housing, and the simulation method comprises the steps: constructing a lookup table which comprises scattering data packets of the selected antenna housing at different incident angles; simulating a virtual ray according to the reverse direction of the received ray by taking the radiometer as a tracking starting point; calculating an intersection point of the virtual ray and the antenna housing, calculating an incident angle of the virtual ray at the intersection point according to the intersection point, and calculating a virtual ray reflected by the virtual ray after the virtual ray enters the intersection point and a virtual ray transmitted by the virtual ray based on the lookup table; continuously tracking the rays until the rays reach a preset upper limit of scattering times, and ending tracking; and obtaining reflection coefficients and transmission coefficients of different virtual rays based on the lookup table, and calculating brightness temperatures of all the virtual rays to obtain a millimeter wave radiation simulation image of the target. Through the method, the simulation precision and the simulation efficiency can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field related to electromagnetic simulation, and more specifically, relates to a simulation method and system for a millimeter-wave radiation image of a target under a radome. Background Art

[0002] As an important component of the aircraft, the radome can protect the internal antenna from the harsh external environment and ensure that the imaging system can work in all weather conditions. In order to take into account the aerodynamic characteristics and electrical performance of the radome, the radome shape usually adopts a rotating body structure such as von Karman shape, tangent arch shape, cone shape, ellipsoid shape, etc. The radome material usually adopts quartz ceramics, advanced composite materials and other materials with good electromagnetic properties, heat resistance, mechanical properties and corrosion resistance. Due to the non-ideal characteristics of the actual radome, such as the radome's own radiation and multiple reflections in the closed cover, it will cause errors to the millimeter wave radiation imaging system, resulting in distortion of the radiation image, decreased target contrast and other adverse effects.

[0003] The traditional millimeter-wave radiation image simulation method is to divide the target model into triangular facets, and then simulate the transmission of the scene radiation signal through ray tracing, and finally obtain the millimeter-wave radiation simulation image. For the radome placed at the front end of the radiometer, detailed facet division is required to obtain higher simulation accuracy, which causes the facet data to occupy more resources, increases the amount of calculation for the intersection of rays and facets, and seriously affects the simulation efficiency. At the same time, the ray tracing method assumes that the radiation characteristics of the smooth plane are consistent with the radiation characteristics of the infinite plane, and cannot consider the scattering characteristics of the radome, which will introduce errors when calculating multiple reflections and transmissions in the radome.

[0004] In summary, the traditional millimeter-wave radiation image simulation method has the problem of not being able to consider the scattering characteristics of the radome and having low simulation efficiency. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a simulation method and system for the millimeter-wave radiation image of a target under a radome, which aims to take into account the scattering characteristics of the radome, improve the simulation accuracy and improve the simulation efficiency.

[0006] To achieve the above object, the present invention provides a method for simulating a millimeter-wave radiation image of a target under a radome, which comprises:

[0007] Constructing a lookup table: the lookup table includes scattering data packets of the selected radome at different incident angles, each incident angle corresponds to a scattering data packet, each scattering data packet includes all {zenith angle, azimuth angle} combinations consisting of preset zenith angles and preset azimuth angles and reflection coefficients and transmission coefficients corresponding to each combination, the preset zenith angles are preset interval center zenith angles obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles are preset interval center azimuth angles obtained by dividing the azimuth angle range into preset azimuth angle intervals, the divided preset zenith angle intervals satisfy the integral consistency of the scattering coefficient gradient within each zenith angle interval, and the divided preset azimuth angle intervals satisfy the integral consistency of the scattering coefficient gradient within each azimuth angle interval;

[0008] Emitting rays: Using the radiometer as the starting point for tracing, simulate virtual rays in the opposite direction of the received rays;

[0009] Ray tracing: Calculate the intersection of the virtual ray and the radome, calculate the incident angle of the virtual ray at the intersection according to the intersection, obtain the {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate the virtual ray reflected and transmitted after the virtual ray is incident on the intersection, calculate the intersection of the virtual ray transmitted outside the radome and the target and determine the virtual ray reflected by the target; continue tracing the ray until the ray reaches the preset upper limit of the number of scattering times and then terminate the tracing;

[0010] Calculating brightness temperature: obtaining reflection coefficients and transmission coefficients of different virtual rays based on the lookup table, calculating the brightness temperatures of all virtual rays, and obtaining a millimeter-wave radiation simulation image of the target.

[0011] Optionally, when constructing the lookup table, the scattering coefficient gradient is calculated in a discrete manner, specifically including:

[0012] Collect a series of zenith angles and a series of azimuth angles, traverse the zenith angles and azimuth angles, calculate the scattering coefficients of the incident ray at the current incident angle corresponding to different {zenith angles, azimuth angles}, and form a series of discrete scattering coefficients;

[0013] The scattering coefficient gradient in each zenith angle interval and the scattering coefficient gradient in each azimuth angle interval are calculated based on the discrete scattering coefficient.

[0014] Optionally, when building the lookup table:

[0015] Dividing the zenith angle range into preset zenith angle intervals, including: dividing the zenith angle range into 5 to 10 zenith angle intervals;

[0016] Dividing the azimuth range into preset azimuth intervals includes: dividing the azimuth range into 5 to 10 azimuth intervals.

[0017] Optionally, when tracing a ray, the process of calculating the intersection point of the virtual ray with the radome includes:

[0018] Step S31: setting a cylindrical virtual bounding box to just surround the radome, and the cross-sectional radius of the bounding box is E;

[0019] Step S32: Calculate the intersection point P1 between the virtual ray and the bounding box, and the starting point of the virtual ray is recorded as P0;

[0020] Step S33: Calculate the distance d from the midpoint P2 of the line segment P0P1 to the axis, and calculate the radius D of the radome whose cross section passes through the midpoint P2, wherein the axis is the rotational symmetry axis of the radome;

[0021] Step S34: Compare d and E:

[0022] If d>E, it means that the current virtual ray has no intersection with the antenna cover, and the calculation ends;

[0023] If d≤E, it means that the current virtual ray intersects with the radome, and d and D are compared continuously: if d<D, the current midpoint P2 is used as the new starting point P0; otherwise, the current midpoint P2 is used as the new intersection point P1;

[0024] Step S35: Determine whether the length of the updated line segment P0P1 satisfies the accuracy δ. If P0P1>δ, return to step S33: If P0P1≤δ, use the current P1 as the intersection point of the virtual ray and the antenna cover.

[0025] Optionally, the precision δ is not more than 10 -4 mm.

[0026] Optionally, when tracing rays, the intersection of the virtual rays transmitted outside the antenna cover and the target is calculated using the face element intersection method. Before performing the face element intersection method, a three-dimensional geometric model of the target and scene is first established and triangular face element division is performed. The face element division does not involve the antenna cover.

[0027] Optionally, when computing brightness temperature:

[0028] If the virtual ray intersects the radome, the brightness temperature of the virtual ray incident on the radome includes the sum of the brightness temperatures of all virtual rays obtained after the radiation of the radome itself, the current incident virtual ray is reflected once by the radome, and the transmission;

[0029] If the virtual ray intersects the target, the brightness temperature of the virtual ray incident on the target includes the sum of the target's own radiation and the brightness temperature of the virtual ray obtained after the current incident virtual ray is reflected once by the target;

[0030] If the virtual ray has no intersection, the brightness temperature of the virtual ray is the brightness temperature of the atmospheric radiation in its direction.

[0031] The present invention also provides a simulation system for the millimeter wave radiation image of a target under a radome, which comprises:

[0032] A lookup table construction unit, used to construct a lookup table, the lookup table comprising scattering data packets of the selected radome at different incident angles, each incident angle corresponding to a scattering data packet, each of the scattering data packets comprising all {zenith angle, azimuth angle} combinations consisting of preset zenith angles and preset azimuth angles and a reflection coefficient and a transmission coefficient corresponding to each combination, the preset zenith angles being the central zenith angles of preset intervals obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles being the central azimuth angles of preset intervals obtained by dividing the azimuth angle range into preset azimuth angle intervals, the divided preset zenith angle intervals satisfying the integral consistency of the scattering coefficient gradient within each zenith angle interval, and the divided preset azimuth angle intervals satisfying the integral consistency of the scattering coefficient gradient within each azimuth angle interval;

[0033] A ray emitting unit, used to simulate virtual rays in the opposite direction of the received rays by taking the radiometer as the tracing starting point;

[0034] A ray tracing unit is used to calculate the intersection of the virtual ray and the antenna cover, calculate the incident angle of the virtual ray at the intersection according to the intersection, obtain the {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate the virtual ray reflected and transmitted after the virtual ray is incident on the intersection, calculate the intersection of the virtual ray transmitted outside the antenna cover and the target and determine the virtual ray reflected by the target; continue to trace the ray until the ray reaches a preset upper limit of the number of scattering times and then terminate the tracing;

[0035] The brightness temperature calculation unit is used to obtain the reflection coefficient and the transmission coefficient of different virtual rays based on the lookup table, calculate the brightness temperature of all virtual rays, and obtain the millimeter wave radiation simulation image of the target.

[0036] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of any of the above methods when executed by a processor.

[0037] The present invention also provides a computer program product, comprising a computer program or instructions, wherein when the computer program or instructions are executed by a processor, the steps of any of the above methods are implemented.

[0038] In general, compared with the prior art, the above technical solutions conceived by the present invention mainly have the following beneficial effects:

[0039] 1. The simulation method of the millimeter-wave radiation image of the target under the radome provided by the present invention first constructs a lookup table to determine the scattering data of the radome at different incident angles in advance, and then directly determines the rays reflected and transmitted by the radome at the current incident angle based on the lookup table when performing ray tracing, so as to realize ray tracing, and there is no need to divide the radome into facets for ray tracing, thereby speeding up the simulation efficiency; moreover, in the constructed lookup table, in the scattering data packet corresponding to the incident angle, a group of {zenith angle, azimuth angle} corresponds to a group of scattered rays, and the scattering data packet contains multiple groups of scattered rays. In the present invention, the zenith angle and azimuth angle in the scattering data packet are both the angles at the center of the interval obtained by interval division, and the interval division follows the integral consistency of the gradient of the scattering coefficient of each interval. Therefore, a method of dividing denser intervals near the angle where the scattering coefficient changes quickly (large gradient) and dividing sparser intervals near the angle where the scattering coefficient changes slowly (small gradient) can adaptively divide non-uniform rays to be closer to the actual scattering performance of the radome, thereby improving the calculation accuracy and reducing the calculation time at the same time.

[0040] 2. Optionally, the computational efficiency can be further improved by calculating the scattering coefficient gradient in a discrete manner.

[0041] 3. Optionally, by finding the intersection in a continuously approximate manner, the intersection point between the ray and the antenna cover can be quickly found, further improving the simulation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a flowchart of the steps of a method for simulating a millimeter-wave radiation image of a target under a radome in one embodiment of the present invention;

[0043] Figure 2 is a lookup table constructed according to an embodiment of the present invention;

[0044] Figure 3 is a schematic diagram of adaptively dividing non-uniform rays in a scattering coefficient distribution in one embodiment of the present invention;

[0045] Figure 4 is a schematic diagram of reverse tracing of rays in one embodiment of the present invention;

[0046] FIG5(a) is a schematic diagram showing that the center of a line segment is located inside the radome when a ray and a radome intersect rapidly in one embodiment of the present invention;

[0047] FIG5( b ) is a schematic diagram showing that the center of the line segment is located outside the radome when the ray and the radome are intersected quickly in one embodiment of the present invention;

[0048] FIG6( a ) is a millimeter wave radiation simulation image of the target itself in one embodiment of the present invention;

[0049] FIG6( b ) is a simulated image of the millimeter-wave radiation of a target under the radome in one embodiment of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0051] Example 1

[0052] The present invention provides a method for simulating the millimeter wave radiation image of a target under a radome, such as Figure 1 The figure shows a flow chart of the steps of a method for simulating a millimeter-wave radiation image of a target under a radome in one embodiment of the present invention, and each step thereof is introduced below.

[0053] Step S1, constructing a lookup table: the lookup table includes scattering data packets of the selected antenna cover at different incident angles, each incident angle corresponds to a scattering data packet, each scattering data packet contains all {zenith angle, azimuth angle} combinations consisting of preset zenith angles and preset azimuth angles and the reflection coefficient and transmission coefficient corresponding to each combination, the preset zenith angles are the central zenith angles of preset intervals obtained after dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles are the central azimuth angles of preset intervals obtained after dividing the azimuth angle range into preset azimuth angle intervals, the divided preset zenith angle intervals satisfy the integral consistency of the scattering coefficient gradient within each zenith angle interval, and the divided preset azimuth angle intervals satisfy the integral consistency of the scattering coefficient gradient within each azimuth angle interval.

[0054] like Figure 2 The figure shows a lookup table constructed by an embodiment of the present invention. Specifically, multiple incident angles can be traversed. The incident angle is the angle between the incident direction and the vector of the radome at the incident point, ranging from 0° to 90°. In this embodiment, the incident angles are traversed in steps of 0.1°. A scattering data packet corresponding to each incident angle is constructed. The scattering data packet reflects the scattering that may occur when the incident angle is incident on the surface of the radome. The scattering includes two situations: reflection and transmission.

[0055] When constructing a scattering data packet, the present invention can divide the zenith angle into preset zenith angle intervals, and divide the azimuth angle into preset azimuth angle intervals. For example, the zenith angle is divided into M zenith angle intervals, and the azimuth angle is also divided into N azimuth angle intervals. The zenith angle at the center of each interval and the azimuth angle at the center of each interval are calculated, thereby obtaining M zenith angles and N azimuth angles. The M zenith angles and N azimuth angles can be combined to obtain M*N {zenith angle, azimuth angle} combinations, and the reflection coefficient and the transmission coefficient under each {zenith angle, azimuth angle} combination can be calculated.

[0056] When performing interval division, the present invention proposes a division principle: the preset zenith angle intervals divided satisfy the integral consistency of the scattering coefficient gradient in each zenith angle interval, and the preset azimuth angle intervals divided satisfy the integral consistency of the scattering coefficient gradient in each azimuth angle interval.

[0057] Specifically, the gradients of the scattering coefficient in the θ and φ directions are calculated respectively. A large gradient indicates a rapid change, whereas a small gradient indicates a slow change. The length of each partition interval depends on the number of intervals to ensure that the integral of the scattering coefficient gradient in each partition interval is consistent.

[0058] For example, divide M intervals in the θ direction, with the center of the interval being θ i , then the interval [θ i -Δθ,θ i +Δθ] satisfies:

[0059]

[0060] Where |gradσ(θ,φ)| represents the gradient of the scattering coefficient in the zenith angle direction.

[0061] For example, divide N intervals in the φ direction, with the center of the interval being φ i , then the interval [φ i -Δφ,φ i +Δφ] satisfies:

[0062]

[0063] Where |gradσ(θ,φ)| represents the gradient of the scattering coefficient in the azimuthal direction.

[0064] Specifically, when calculating the scattering coefficient gradient, the scattering coefficient gradient can be calculated by derivatizing the function of the scattering coefficient. However, the amount of derivation calculation is large and sometimes it is difficult to implement the derivation calculation. Therefore, this embodiment adopts a discrete method to calculate the scattering coefficient gradient, which specifically includes:

[0065] The first step is to collect a series of zenith angles and a series of azimuth angles, traverse the zenith angles and azimuth angles, calculate the scattering coefficients of the incident rays at the current incident angle corresponding to different {zenith angles, azimuth angles}, and form a series of discrete scattering coefficients.

[0066] Among them, the calculation formula of the scattering coefficient can be expressed as:

[0067]

[0068] In the formula, is the scattering coefficient, θ and φ are the zenith angle and azimuth respectively, the subscripts i and s represent the incident and scattering respectively, R is the distance between the field point and the source point, A0 is the effective irradiation area, and the subscripts q and p both represent the polarization mode. represents the scattered electric field with polarization mode p, represents the incident electric field with polarization mode q.

[0069] Among them, when calculating the electric field, the tangential scattering field and tangential transmission field of the radome can be decomposed and calculated according to the incident wave. The surface current and surface magnetic current on the inner and outer surfaces of the radome are expressed as in is the normal vector of the radome. Then the field distribution inside and outside the radome is expressed as:

[0070]

[0071] Where μ is the magnetic permeability of the radome, k is the wave number, ω is the angular frequency, R is the distance between the field point and the source point, Ω' represents the surface of the radome, and the parameters G1, G2, and G3 are G1 = (k 2 R 2 -jkR-1)e -jkR / 4πR 3 , G2=(-k 2 R 2 +3jkR+3)e - jkR 4πR 3 , G3=(1+jkR)e -jkR 4πR 2 .

[0072] The second step is to calculate the scattering coefficient gradient in each zenith angle interval and the scattering coefficient gradient in each azimuth angle interval based on the discrete scattering coefficient.

[0073] According to the above division principle, adaptive non-uniform ray division can be performed according to the distribution of the radome scattering coefficient, such as Figure 3 FIG. 1 is a schematic diagram of adaptively dividing non-uniform rays with respect to scattering coefficient distribution in one embodiment of the present invention. It can be seen from the figure that the distribution of scattering coefficients in different intervals is different.

[0074] After determining the division intervals, we can get M zenith angles and N azimuth angles, which can be combined to get M*N {zenith angle, azimuth angle} combinations, and the reflection coefficient and transmission coefficient under each {zenith angle, azimuth angle} combination can be calculated. Specifically, the scattering coefficient can be integrated in each interval to get the corresponding reflection coefficient Γ and transmission coefficient Y, expressed as:

[0075]

[0076] In this way, it is possible to establish a lookup table of the center of the non-uniform ray partitioning interval and the corresponding reflection coefficient and transmission coefficient using the incident angle as the index.

[0077] In a specific embodiment, M can be 5 to 10, and N can also be 5 to 10. Within this range, the simulation accuracy is high and the simulation efficiency is fast.

[0078] Step S2, emitting rays: using the radiometer as the tracing starting point to simulate virtual rays in the opposite direction of the received rays.

[0079] Step S3, tracing rays: calculating the intersection of the virtual ray and the antenna cover, calculating the incident angle of the virtual ray at the intersection according to the intersection, obtaining the {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculating the virtual ray reflected and transmitted after the virtual ray is incident on the intersection, calculating the intersection of the virtual ray transmitted outside the antenna cover and the target and determining the virtual ray reflected by the target; continuing to trace the ray until the ray reaches a preset upper limit of the number of scattering times and then terminating the tracing.

[0080] Specifically, step S2 and step S3 are for reverse tracing the ray received by the radiometer, and the starting point of the tracing is the radiometer. That is, when reverse tracing is performed, the direction of the virtual ray is the opposite direction of the actual ray.

[0081] like Figure 4 The figure shows the schematic diagram of the reverse tracing of rays, where the arrow direction is the tracing direction. Figure 4 For example, assume that the virtual ray R 0 Launch from the radiometer observation point, intersect with the radome, and launch a transmission ray and a reflected ray Then the first transmitted ray intersects the target and emits a second reflected ray The primary reflected ray intersects the radome and emits a secondary transmitted ray and secondary reflected rays By analogy, the rays inside the antenna cover will generally be reflected multiple times, so an upper limit on the number of scattering times can be set, and the tracking will end when the upper limit is reached.

[0082] In the present invention, when performing the above-mentioned ray tracing, it is necessary to continuously query the lookup table constructed in step S1, search for all corresponding {zenith angle, azimuth angle} combinations based on the current incident angle, determine the scattering vector after the current virtual ray is incident on the antenna cover, and then trace the scattered virtual ray in the same way, and so on, to achieve the tracing of all rays.

[0083] It can be understood that when performing ray tracing, it is necessary to calculate the intersection points of the ray with the radome and the target to determine the specific scattering position.

[0084] In a specific embodiment, referring to FIG. 5( a ) and FIG. 5( b ), the intersection point between the virtual ray and the radome may be calculated as follows.

[0085] Step S31: a cylindrical virtual bounding box is set to just surround the radome, and the radius of the cross section of the bounding box is E.

[0086] Step S32: Calculate the intersection point P1 of the virtual ray and the bounding box, and the starting point of the virtual ray is recorded as P0.

[0087] Specifically, the current ray vector is The intersection point P1 can be expressed as t0 is a constant;

[0088] Step S33: Calculate the distance d from the midpoint P2 of the line segment P0P1 to the axis, and calculate the radius D of the radome whose cross section passes through the midpoint P2, where the axis is the rotational symmetry axis of the radome.

[0089] Specifically, the midpoint P2 can be expressed as P2 = t0v / 2 + P0. Substituting the x coordinate of P2 into the radome curve equation F(x, y, z) yields the radome radius D at that position.

[0090] Step S34: Compare d and E:

[0091] If d>E, it means that the current virtual ray has no intersection with the antenna cover, and the calculation ends;

[0092] If d≤E, it means that the current virtual ray intersects with the radome, and continue to compare d and D: If d<D, it means that P2 is inside the radome, and the current midpoint P2 is used as the new starting point P0; otherwise,

[0093] This indicates that P2 is outside the radome, and the current midpoint P2 is used as the new intersection point P1.

[0094] Step S35: Determine whether the length of the updated line segment P0P1 satisfies the accuracy δ. If P0P1>δ, return to step S33: If P0P1≤δ, use the current P1 as the intersection point of the virtual ray and the antenna cover.

[0095] Specifically, the value of precision δ does not exceed 10 -4 mm.

[0096] By using the above method to find the intersection, the intersection point of the ray and the antenna cover can be quickly obtained.

[0097] After the intersection is determined, the {zenith angle, azimuth angle} scattered at the intersection is determined based on the lookup table, and the virtual reflected ray direction and transmitted ray direction are determined. Specifically, a local coordinate system is established with the intersection as the origin and the plane where the radome normal vector and the incident vector are located as the xOz plane. With the intersection as the starting point, the reflected ray and transmitted ray vectors are calculated according to the zenith angle and azimuth angle at the center of the interval, and non-uniform reflected rays and transmitted rays are emitted. The above steps are repeated to achieve ray tracing.

[0098] For the transmitted rays of the radome, the traditional facet intersection method can be used to calculate the intersection point between the virtual rays transmitted outside the radome and the target. Before performing the facet intersection method, a three-dimensional geometric model of the target and scene is first established and triangular facet division is performed. The facet division does not involve the radome.

[0099] Through the above steps, ray tracing can be realized and all traced rays can be output.

[0100] Step S4, calculating brightness temperature: obtaining reflection coefficients and transmission coefficients of different virtual rays based on a lookup table, calculating the brightness temperatures of all virtual rays, and obtaining a millimeter-wave radiation simulation image of the target.

[0101] Specifically, the calculation method of ray brightness temperature is given for three conditions: the ray intersects with the radome, intersects with the target, and has no intersection:

[0102] (1) When the ray intersects the radome, the brightness temperature of the virtual ray incident on the radome includes the sum of the brightness temperatures of all virtual rays radiated by the radome itself, reflected once by the radome, and transmitted through the radome;

[0103] The specific calculation method of the ray brightness temperature is:

[0104] Step 1: Obtain the reflection coefficient Γ and transmission coefficient Y corresponding to each divided interval under the current incident angle by looking up the table, then the radome emissivity e is expressed as:

[0105] e=1-∑Γ-∑Y

[0106] Step 2: According to the emissivity e, reflection coefficient Γ and transmission coefficient Y, the ray brightness temperature is expressed as the sum of the radome's own radiation, multiple reflections and transmission brightness temperatures, that is:

[0107]

[0108] According to the interval center obtained by looking up the table, the reflection ray and the transmission ray vector are calculated, and the reflection ray and the transmission ray are emitted. Where i is the number of tracing times, T i is the physical temperature of the radome, TB i+1 TB i+2 They represent the brightness temperature of the reflected ray and the transmitted ray of the next tracing respectively;

[0109] (2) When the ray intersects the target, the brightness temperature of the virtual ray incident on the target includes the sum of the target's own radiation and the brightness temperature of the virtual ray obtained after the current incident virtual ray is reflected once by the target;

[0110] The specific calculation method of the ray brightness temperature is:

[0111] The emissivity e and reflectivity r are calculated based on the dielectric constant of the target. The ray brightness temperature is expressed as the sum of the target's own radiation and the reflected ambient brightness temperature, that is:

[0112] TB i =eT i +rTB i+1

[0113] The reflection ray vector is calculated based on the target normal vector, and the reflection ray is emitted. i is the physical temperature of the target element, TB i+1 is the brightness temperature of the reflected ray for the next trace;

[0114] (3) When the ray has no intersection, the brightness temperature of the ray is the atmospheric radiation brightness temperature in that direction, expressed as:

[0115] TB i =T atm

[0116] Where T atm Indicates the brightness temperature of atmospheric radiation in the direction of the ray. Ends the current ray tracing.

[0117] For example, Figure 4 The brightness temperatures for all rays shown are calculated as follows:

[0118]

[0119] Wherein, the superscript indicates the number of tracing times, the subscript indicates the ray number with the same number of tracing times, e, Γ, Y are the emissivity, reflection coefficient and transmission coefficient of the radome at the intersection of the current ray, e, r are the emissivity and reflectivity of the target at the intersection of the current ray, T atm is the atmospheric radiation brightness temperature in the current ray direction.

[0120] Figure 6 (a) and Figure 6 (b) are respectively the millimeter wave radiation simulation image of the target and the millimeter wave radiation simulation image of the target under the radome provided by the present invention. Among them, the target is a metal ship with a sea background, the observation distance is 1 km, the observation angle is -60°, the material of the radome is quartz ceramic, and the structure is an ellipsoidal structure. When the radome is placed directly in front of the observation point, the maximum contrast of the target changes from 100.1K to 74.8K, and the radiation characteristics change. By comparison, it can be seen that the millimeter wave radiation simulation image of the target under the radome provided by the present invention is very close to the millimeter wave radiation simulation image of the target itself, which shows that the simulation accuracy of the method proposed by the present invention is high. The present invention can process radomes of any temperature, shape, size and structure according to actual applications, and quickly calculate the millimeter wave radiation brightness temperature of different targets under different observation conditions to obtain the millimeter wave radiation simulation image of the target under the radome, which provides a basis for analyzing the influence of the radome on the radiation characteristics of the target.

[0121] Example 2

[0122] The present invention also relates to a simulation system for a millimeter wave radiation image of a target under a radome, comprising:

[0123] A lookup table construction unit, used to construct a lookup table, the lookup table including scattering data packets of the selected radome at different incident angles, each incident angle corresponding to a scattering data packet, each scattering data packet including all {zenith angle, azimuth angle} combinations consisting of preset zenith angles and preset azimuth angles and reflection coefficients and transmission coefficients corresponding to each combination, the preset zenith angles are the preset interval center zenith angles obtained after dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles are the preset interval center azimuth angles obtained after dividing the azimuth angle range into preset azimuth angle intervals, the divided preset zenith angle intervals satisfy the integral consistency of the scattering coefficient gradient within each zenith angle interval, and the divided preset azimuth angle intervals satisfy the integral consistency of the scattering coefficient gradient within each azimuth angle interval;

[0124] A ray emitting unit, used to simulate virtual rays in the opposite direction of the received rays by taking the radiometer as the tracing starting point;

[0125] A ray tracing unit is used to calculate the intersection of the virtual ray and the antenna cover, calculate the incident angle of the virtual ray at the intersection according to the intersection, obtain the {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate the virtual ray reflected and transmitted after the virtual ray is incident on the intersection, calculate the intersection of the virtual ray transmitted outside the antenna cover and the target and determine the virtual ray reflected by the target; continue to trace the ray until the ray reaches a preset upper limit of the number of scattering times and then terminate the tracing;

[0126] The brightness temperature calculation unit is used to obtain the reflection coefficient and transmission coefficient of different virtual rays based on the lookup table, calculate the brightness temperature of all virtual rays, and obtain the millimeter wave radiation simulation image of the target.

[0127] Specifically, the system can be installed on computing devices such as desktop computers, notebooks, PDAs, and cloud servers.

[0128] Example 3

[0129] The present invention also relates to a computer-readable storage medium having a computer program stored thereon, and the computer program implements the steps of the above method when executed by a processor.

[0130] Specifically, the memory may include a high-speed random access memory, and may also include a non-volatile memory, such as a hard disk, an internal memory, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0131] Example 4

[0132] The embodiment of the present invention provides a computer program product or a computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, so that the computer device performs the steps of the method of the above embodiment of the present invention.

[0133] The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. It should be noted that "in one embodiment", "for example", "for example", etc. of the present invention are intended to illustrate the present invention, rather than to limit the present invention.

[0134] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for simulating the millimeter wave radiation image of a target under a radome, characterized in that: include: Constructing a lookup table: the lookup table includes scattering data packets of the selected radome at different incident angles, each incident angle corresponds to a scattering data packet, each scattering data packet includes all {zenith angle, azimuth angle} combinations consisting of preset zenith angles and preset azimuth angles and reflection coefficients and transmission coefficients corresponding to each combination, the preset zenith angles are preset interval center zenith angles obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles are preset interval center azimuth angles obtained by dividing the azimuth angle range into preset azimuth angle intervals, the divided preset zenith angle intervals satisfy the integral consistency of the scattering coefficient gradient within each zenith angle interval, and the divided preset azimuth angle intervals satisfy the integral consistency of the scattering coefficient gradient within each azimuth angle interval; Emitting rays: Using the radiometer as the starting point for tracing, simulate virtual rays in the opposite direction of the received rays; Ray tracing: Calculate the intersection of the virtual ray and the radome, calculate the incident angle of the virtual ray at the intersection according to the intersection, obtain the {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate the virtual ray reflected and transmitted after the virtual ray is incident on the intersection, calculate the intersection of the virtual ray transmitted outside the radome and the target and determine the virtual ray reflected by the target; continue tracing the ray until the ray reaches the preset upper limit of the number of scattering times and then terminate the tracing; Calculating brightness temperature: obtaining reflection coefficients and transmission coefficients of different virtual rays based on the lookup table, calculating the brightness temperatures of all virtual rays, and obtaining a millimeter-wave radiation simulation image of the target.

2. The method for simulating the millimeter wave radiation image of a target under a radome as claimed in claim 1, characterized in that: When constructing the lookup table, the scattering coefficient gradient is calculated in a discrete manner, including: Collect a series of zenith angles and a series of azimuth angles, traverse the zenith angles and azimuth angles, calculate the scattering coefficients of the incident ray at the current incident angle corresponding to different {zenith angles, azimuth angles}, and form a series of discrete scattering coefficients; The scattering coefficient gradient in each zenith angle interval and the scattering coefficient gradient in each azimuth angle interval are calculated based on the discrete scattering coefficient.

3. The method for simulating the millimeter wave radiation image of a target under a radome according to claim 1 or 2, characterized in that: When building the lookup table: Dividing the zenith angle range into preset zenith angle intervals, including: dividing the zenith angle range into 5 to 10 zenith angle intervals; Dividing the azimuth range into preset azimuth intervals includes: dividing the azimuth range into 5 to 10 azimuth intervals.

4. The method for simulating the millimeter wave radiation image of a target under a radome as claimed in claim 1, characterized in that: When tracing a ray, the process of calculating the intersection of the virtual ray and the radome includes: Step S31: setting a cylindrical virtual bounding box to just surround the radome, and the cross-sectional radius of the bounding box is E; Step S32: Calculate the intersection point P1 between the virtual ray and the bounding box, and the starting point of the virtual ray is recorded as P0; Step S33: Calculate the distance d from the midpoint P2 of the line segment P0P1 to the axis, and calculate the radius D of the radome whose cross section passes through the midpoint P2, wherein the axis is the rotational symmetry axis of the radome; Step S34: Compare d and E: If d>E, it means that the current virtual ray has no intersection with the antenna cover, and the calculation ends; If d≤E, it means that the current virtual ray intersects with the radome, and d and D are compared continuously: if d<D, the current midpoint P2 is used as the new starting point P0; otherwise, the current midpoint P2 is used as the new intersection point P1; Step S35: Determine whether the length of the updated line segment P0P1 satisfies the accuracy δ. If P0P1>δ, return to step S33: If P0P1≤δ, use the current P1 as the intersection point of the virtual ray and the antenna cover.

5. The method for simulating the millimeter wave radiation image of a target under a radome as claimed in claim 4, characterized in that: The value of precision δ does not exceed 10 -4 mm.

6. The method for simulating the millimeter wave radiation image of a target under a radome as claimed in claim 1, characterized in that: When tracing rays, the surface element intersection method is used to calculate the intersection point between the virtual ray transmitted outside the antenna cover and the target. Before performing the surface element intersection method, a three-dimensional geometric model of the target and the scene is first established and triangular surface element division is performed. The surface element division does not involve the antenna cover.

7. The method for simulating the millimeter wave radiation image of a target under a radome as claimed in claim 1, characterized in that: When calculating brightness temperature: If the virtual ray intersects the radome, the brightness temperature of the virtual ray incident on the radome includes the sum of the brightness temperatures of all virtual rays obtained after the radiation of the radome itself, the current incident virtual ray is reflected once by the radome, and the transmission; If the virtual ray intersects the target, the brightness temperature of the virtual ray incident on the target includes the sum of the target's own radiation and the brightness temperature of the virtual ray obtained after the current incident virtual ray is reflected once by the target; If the virtual ray has no intersection, the brightness temperature of the virtual ray is the brightness temperature of the atmospheric radiation in its direction.

8. A simulation system for the millimeter wave radiation image of a target under a radome, characterized in that: include: A lookup table construction unit, used to construct a lookup table, the lookup table comprising scattering data packets of the selected radome at different incident angles, each incident angle corresponding to a scattering data packet, each of the scattering data packets comprising all {zenith angle, azimuth angle} combinations consisting of preset zenith angles and preset azimuth angles and a reflection coefficient and a transmission coefficient corresponding to each combination, the preset zenith angles being the central zenith angles of preset intervals obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles being the central azimuth angles of preset intervals obtained by dividing the azimuth angle range into preset azimuth angle intervals, the divided preset zenith angle intervals satisfying the integral consistency of the scattering coefficient gradient within each zenith angle interval, and the divided preset azimuth angle intervals satisfying the integral consistency of the scattering coefficient gradient within each azimuth angle interval; A ray emitting unit, used to simulate virtual rays in the opposite direction of the received rays by taking the radiometer as the tracing starting point; A ray tracing unit is used to calculate the intersection of the virtual ray and the antenna cover, calculate the incident angle of the virtual ray at the intersection according to the intersection, obtain the {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate the virtual ray reflected and transmitted after the virtual ray is incident on the intersection, calculate the intersection of the virtual ray transmitted outside the antenna cover and the target and determine the virtual ray reflected by the target; continue to trace the ray until the ray reaches a preset upper limit of the number of scattering times and then terminate the tracing; The brightness temperature calculation unit is used to obtain the reflection coefficient and the transmission coefficient of different virtual rays based on the lookup table, calculate the brightness temperature of all virtual rays, and obtain the millimeter wave radiation simulation image of the target.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer program product comprising a computer program or instructions, characterized in that When the computer program or instruction is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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