A method and system for simulating millimeter-wave radiation images of targets under a radome

Abstract

The present invention belongs to the technical field related to electromagnetic simulation and discloses a method and system for simulating the millimeter-wave radiation image of a target under a radome. The simulation method includes: constructing a lookup table, the lookup table including scattered data packets of a selected radome at different incident angles; simulating virtual rays in the opposite direction of the received rays using a radiometer as the tracking starting point; calculating the intersection of the virtual rays and the radome, calculating the incident angle of the virtual rays at the intersection based on the intersection, and calculating the virtual rays reflected and transmitted after the virtual rays are incident on the intersection based on the lookup table; continuously tracing the rays until the ray reaches a preset upper limit of the number of scattering times and then terminating the tracing; obtaining the reflection coefficient and transmission coefficient of different virtual rays based on the lookup table, calculating the brightness temperature of all virtual rays, and obtaining a simulated millimeter-wave radiation image of the target. The above method can improve simulation accuracy and efficiency.

Description

Technical Field

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

[0002] As a crucial component of an aircraft, the radome protects the internal antenna from the harsh external environment and ensures the imaging system can operate in all weather conditions. To balance aerodynamic and electrical performance, the radome's shape typically adopts a rotating body structure, such as a von Karman shape, a tangent arch, a cone, or an ellipsoid. Radome materials typically include quartz ceramics, advanced composite materials, and other materials with excellent electromagnetic, heat, mechanical, and corrosion resistance. Due to the non-ideal characteristics of actual radomes, such as their own radiation and multiple reflections within the enclosure, these can introduce errors into millimeter-wave radiation imaging systems, leading to distortion of the radiation image and decreased target contrast, among other adverse effects.

[0003] Traditional millimeter-wave radiation image simulation methods divide the target model into triangular facets and then use ray tracing to simulate the transmission of the scene's radiation signal, ultimately producing a simulated millimeter-wave radiation image. For the radome placed at the front end of the radiometer, detailed facet division is required to achieve higher simulation accuracy. This results in a large resource consumption of facet data, increases the computational complexity of ray-facet intersections, and severely impacts simulation efficiency. Furthermore, ray tracing assumes that the radiation characteristics of a smooth surface are consistent with those of an infinitely large plane, failing to account for the scattering characteristics of the radome. This introduces errors when calculating multiple reflections and transmissions within 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 response to 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 the 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 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 the reflection coefficient and transmission coefficient corresponding to each combination, the preset zenith angles being the center zenith angles of the preset intervals obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles being the center azimuth angles of the 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;

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

[0009] Ray tracing: Calculate the intersection point of the virtual ray and the radome, calculate the incident angle of the virtual ray at the intersection point based on the intersection point, obtain the {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate the virtual rays reflected and transmitted after the virtual ray is incident on the intersection point, calculate the intersection point of the virtual ray transmitted outside the radome with 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, 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 angle range into preset azimuth angle intervals includes: dividing the azimuth angle range into 5 to 10 azimuth angle 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 exactly surround the radome, with a cross-sectional radius of the bounding box being E;

[0019] 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;

[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, where 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 radome, and the calculation ends;

[0023] If d≤E, it means that the current virtual ray intersects with the radome, and we continue to compare d and D: 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 meets 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 point of the virtual ray transmitted outside the antenna cover and the target is calculated using the facet intersection method. 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 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 and the current incident virtual ray is reflected and transmitted by the radome once;

[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 by the target once;

[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, configured to construct a lookup table, the lookup table comprising scattering data packets of a selected radome at different incident angles, each incident angle corresponding to a scattering data packet, each scattering data packet 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 center zenith angles of preset intervals obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles being the center 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 for simulating virtual rays in the opposite direction of the received rays with the radiometer as the tracing starting point;

[0034] a ray tracing unit configured to calculate an intersection point of a virtual ray with the radome, calculate an incident angle of the virtual ray at the intersection point based on the intersection point, obtain {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate virtual rays reflected and transmitted by the virtual ray after the virtual ray is incident on the intersection point, calculate an intersection point of the virtual ray transmitted outside the radome with the target, and determine the virtual ray reflected by the target; and continuously trace the ray until the ray reaches a preset upper limit of scattering times, after which tracing is terminated;

[0035] 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.

[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, which implement the steps of any of the above methods when executed by a processor.

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

[0039] 1. The present invention provides a method for simulating the millimeter-wave radiation image of a target under a radome. First, a lookup table is constructed to predetermine the scattering data of the radome at different incident angles. Then, during ray tracing, the ray reflected and transmitted by the radome at the current incident angle is directly determined based on the lookup table, thereby achieving ray tracing. This eliminates the need to partition the radome into bins for ray tracing, thereby improving simulation efficiency. Furthermore, in the constructed lookup table, a set of {zenith angle, azimuth angle} in a scattering data packet corresponding to an incident angle corresponds to a set of scattered rays, and the scattering data packet contains multiple sets 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 partitioning, and the interval partitioning follows the integral of the scattering coefficient gradient of each interval. Therefore, the method divides the scattering coefficient into denser intervals near angles where the scattering coefficient changes rapidly (large gradient) and sparser intervals near angles where the scattering coefficient changes slowly (small gradient). This method, through adaptive partitioning of non-uniform rays, more closely matches the actual scattering performance of the radome, thereby improving calculation accuracy and reducing calculation 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 point of the ray and the radome in a continuously approximate manner, the intersection point 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 using 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 a situation in which the center of a line segment is located inside the radome when a ray and the radome are rapidly intersected in accordance with an embodiment of the present invention;

[0047] FIG5( b ) is a schematic diagram showing a situation in which the center of a line segment is located outside the radome when a ray and a radome are rapidly intersected in accordance with an embodiment of the present invention;

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

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

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining 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 may 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. Figure 1 FIG2 is a flowchart of a method for simulating a millimeter-wave radiation image of a target under a radome in an embodiment of the present invention, and each step 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 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 in each zenith angle interval, and the divided preset azimuth angle intervals satisfy the integral consistency of the scattering coefficient gradient in each azimuth angle interval.

[0054] like Figure 2 The following figure shows a lookup table constructed according to one embodiment of the present invention. Specifically, it can traverse multiple incident angles. The incident angle is the angle between the incident direction and the vector of the radome at the point of incidence, 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 light hits the radome surface at that incident angle. Scattering includes both reflection and transmission.

[0055] When constructing a scattering data packet, the present invention can divide the zenith angle into preset zenith angle intervals, and 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 transmission coefficient under each {zenith angle, azimuth angle} combination can be calculated.

[0056] When performing interval division, the present invention proposes the following division principle: the preset zenith angle intervals divided satisfy the integral consistency of the scattering coefficient gradient within each zenith angle interval, and the preset azimuth angle intervals divided satisfy the integral consistency of the scattering coefficient gradient within 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 interval center 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, and the center of the interval is 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 differentiating the function of the scattering coefficient. However, the amount of derivation is large and sometimes difficult to implement. 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 ray at the current incident angle corresponding to different {zenith angles, azimuth angles}, and form a series of discrete scattering coefficients.

[0066] The calculation formula of the scattering coefficient can be expressed as:

[0067]

[0068] Where, is the scattering coefficient, θ and φ are the zenith angle and azimuth angle respectively, the subscripts i and s represent the incident and scattered 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 scattered field and tangential transmitted 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] In the second step, 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.

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

[0074] After determining the partition intervals, we can obtain M zenith angles and N azimuth angles. These M zenith angles and N azimuth angles can be combined to obtain 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 obtain the corresponding reflection coefficient Γ and transmission coefficient Y, which can be expressed as:

[0075]

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

[0077] In a specific embodiment, M can be set to 5-10, and N can also be set to 5-10. 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, simulating virtual rays in the opposite direction of the received rays.

[0079] Step S3, tracing rays: Calculate the intersection of the virtual ray and the antenna cover, calculate the incident angle of the virtual ray at the intersection based on 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 tracing the ray until the ray reaches the preset upper limit of the scattering times and then end the tracing.

[0080] Specifically, steps S2 and S3 are for reverse tracing the ray received by the radiometer, with the starting point of the tracing being the radiometer. That is, when performing reverse tracing, 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 Emitted from the radiometer observation point, intersected with the radome, and emitted 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. Therefore, 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 is understandable 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 of the virtual ray and the radome may be calculated as follows.

[0085] Step S31: setting a cylindrical virtual bounding box to exactly surround the radome, with the bounding box cross-sectional radius being 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 location.

[0090] Step S34: Compare d and E:

[0091] If d>E, it means that the current virtual ray has no intersection with the radome, 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 meets 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 determining the intersection point, the {zenith angle, azimuth angle} scattered at that intersection is determined using a lookup table, and the virtual reflected and transmitted ray directions are determined. Specifically, a local coordinate system is established with the intersection point as the origin and the plane containing the radome normal vector and the incident vector as the xOz plane. Starting from the intersection point, the reflected and transmitted ray vectors are calculated based on the zenith angle and azimuth angle at the center of the interval. Non-uniform reflected and transmitted rays are emitted, and the above steps are repeated to achieve ray tracing.

[0098] For the transmitted rays of the radome, the traditional surface element intersection method can be used to calculate the intersection point of the virtual rays transmitted outside the radome and the target. Before performing the surface element intersection method, a three-dimensional geometric model of the target and scene is first established and triangular surface element division is performed. The surface element 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 the reflection coefficient and transmission coefficient of different virtual rays based on the lookup table, calculating the brightness temperature of all virtual rays, and obtaining the 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 obtained after the radiation of the radome itself and the current incident virtual ray is reflected and transmitted by the radome once;

[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. The radome emissivity e is expressed as:

[0105] e=1-∑Γ-∑Y

[0106] Step 2: Based on 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 temperature, that is:

[0107]

[0108] Calculate the reflection ray and transmission ray vectors based on the interval center obtained from the table, and emit the reflection ray and transmission ray. 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 temperatures of the reflected and transmitted rays 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 by the target once;

[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] Calculate the reflection ray vector according to the target normal vector and emit the reflection ray. i is the physical temperature of the target element, TB i+1 is the brightness temperature of the reflected ray in the next trace;

[0114] (3) When there is no intersection of the ray, 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 the atmosphere in the direction of the ray. Ends the current ray trace.

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

[0118]

[0119] Where, the superscript represents the number of tracing times, the subscript represents the ray number with the same number of tracing times, e, Γ, and Y are the emissivity, reflection coefficient, and transmission coefficient of the radome at the intersection of the current ray, respectively; e and r are the emissivity and reflectivity of the target at the intersection of the current ray, respectively. 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, quickly calculate the millimeter wave radiation brightness temperature of different targets under different observation conditions, and obtain the millimeter wave radiation simulation image of the target under the radome, providing 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, configured 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 scattering data packet 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 center zenith angles of preset intervals obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles being the center 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;

[0124] A ray emitting unit, used for simulating virtual rays in the opposite direction of the received rays with the radiometer as the tracing starting point;

[0125] A ray tracing unit is configured to calculate the intersection of the virtual ray and the radome, calculate the incident angle of the virtual ray at the intersection based on the intersection, obtain the {zenith angle, azimuth angle} corresponding to the incident angle based on a 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; and continuously trace the ray until the ray reaches a preset upper limit of the number of scattering times, at which point the ray ends 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, which implements the steps of the above method when the computer program is 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, a memory, a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (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 device.

[0131] Example 4

[0132] An embodiment of the present invention provides a computer program product or 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 executes the computer instructions, causing the computer device to perform the steps of the method of the above embodiment of the present invention.

[0133] The technical features of the above-described embodiments may be combined in any manner. To simplify the description, not all possible combinations of the technical features in the above-described 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 the phrases "in one embodiment," "for example," "and another example," etc., of the present invention are intended to illustrate the present invention and are not intended to limit the present invention.

[0134] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection 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 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 the reflection coefficient and transmission coefficient corresponding to each combination, the preset zenith angles being the center zenith angles of the preset intervals obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles being the center azimuth angles of the 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; Emitting rays: Using the radiometer as the starting point to trace, simulate virtual rays in the opposite direction of the received rays; Ray tracing: Calculate the intersection point of the virtual ray and the radome, calculate the incident angle of the virtual ray at the intersection point based on the intersection point, obtain the {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate the virtual rays reflected and transmitted after the virtual ray is incident on the intersection point, calculate the intersection point of the virtual ray transmitted outside the radome with 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, 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 according to claim 1, wherein: When constructing the lookup table, the scattering coefficient gradient is calculated in a discrete manner, specifically 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, wherein: 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 angle range into preset azimuth angle intervals includes: dividing the azimuth angle range into 5 to 10 azimuth angle intervals.

4. The method for simulating the millimeter-wave radiation image of a target under a radome according to claim 1, wherein: 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 exactly surround the radome, with a cross-sectional radius of the bounding box being E; 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; 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; Step S34: Compare d and E: If d>E, it means that the current virtual ray has no intersection with the radome, and the calculation ends; If d≤E, it means that the current virtual ray intersects with the radome, and we continue to compare d and D: 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 meets 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 according to claim 4, wherein: 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 according to claim 1, wherein: When tracing rays, the intersection point between the virtual ray transmitted outside the radome and the target is calculated using the facet intersection method. 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.

7. The method for simulating the millimeter-wave radiation image of a target under a radome according to claim 1, wherein: 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 and the current incident virtual ray is reflected and transmitted by the radome once; 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 by the target once; 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 millimeter wave radiation images of targets under a radome, characterized in that: include: a lookup table construction unit, configured to construct a lookup table, the lookup table comprising scattering data packets of a selected radome at different incident angles, each incident angle corresponding to a scattering data packet, each scattering data packet 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 center zenith angles of preset intervals obtained by dividing the zenith angle range into preset zenith angle intervals, the preset azimuth angles being the center 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 for simulating virtual rays in the opposite direction of the received rays with the radiometer as the tracing starting point; a ray tracing unit configured to calculate an intersection point of a virtual ray with the radome, calculate an incident angle of the virtual ray at the intersection point based on the intersection point, obtain {zenith angle, azimuth angle} corresponding to the incident angle based on the lookup table, calculate virtual rays reflected and transmitted by the virtual ray after the virtual ray is incident on the intersection point, calculate an intersection point of the virtual ray transmitted outside the radome with the target, and determine the virtual ray reflected by the target; and continuously trace the ray until the ray reaches a preset upper limit of scattering times, after which tracing is terminated; 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.

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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