阅读说明：本技术 基于lcim算法的三维模型微波光子回波成像方法 (Three-dimensional model microwave photon echo imaging method based on LCIM algorithm ) 是由 邢孟道 吴之鑫 高悦欣 于 2021-08-18 设计创作，主要内容包括：本发明提供的一种基于LCIM算法的三维模型微波光子回波成像方法,通过述目标几何形状的低精度模型再进行细剖分,获取高精度模型；基于高精度模型的坐标系,构建观测目标的多角度转台模型的坐标系,根据坐标系之间的基变换关系,确定高精度模型在自身坐标系下的多个雷达波入射方向。将发射信号按照入射方向照射在目标三角面元上,计算不再转射的目标三角面元的散射回波信号再进行矢量累计,获得整个目标的回波信号,再对目标全极化的二维ISAR图像进行成像。本发明可实现跨频段、大转角条件下目标的全极化散射回波计算,提高仿真目标散射回波二维图像质量,使其能够表征目标电磁散射特性的同时能准确反映目标几何结构。(The invention provides a three-dimensional model microwave photon echo imaging method based on LCIM algorithm, which comprises the steps of subdividing a low-precision model of a target geometric shape to obtain a high-precision model; and constructing a coordinate system of the multi-angle rotary table model of the observation target based on the coordinate system of the high-precision model, and determining a plurality of radar wave incidence directions of the high-precision model under the coordinate system of the high-precision model according to the basis transformation relation between the coordinate systems. The method comprises the steps of irradiating a transmitting signal on a target triangular surface element according to an incident direction, calculating a scattering echo signal of the target triangular surface element which is not reflected any more, carrying out vector accumulation to obtain an echo signal of the whole target, and imaging a fully polarized two-dimensional ISAR image of the target. The invention can realize the calculation of the total polarization scattering echo of the target under the conditions of cross-frequency band and large rotation angle, improve the quality of the two-dimensional image of the scattering echo of the simulated target, and ensure that the geometric structure of the target can be accurately reflected while representing the electromagnetic scattering characteristic of the target.)

1. A three-dimensional model microwave photon echo imaging method based on LCIM algorithm is characterized by comprising the following steps:

step 1: constructing a low-precision model describing the geometric shape of the target according to the acquired three-dimensional data of the target;

the low-precision model comprises a plurality of faces, and each face is formed by splicing a plurality of triangular surface elements;

step 2: finely dividing the low-precision model to enable the size of a triangular surface element in the finely divided low-precision model to be in positive correlation with the theoretical distance resolution of the microwave photon radar system parameters, and obtaining a high-precision model;

and step 3: constructing a coordinate system of a multi-angle rotary table model of the observation target based on the coordinate system of the high-precision model;

each surface in the high-precision model is composed of a plurality of target triangular surface elements;

and 4, step 4: determining a plurality of radar wave incidence directions of the high-precision model under the coordinate system of the high-precision model based on the basis transformation relation between the coordinate system of the multi-angle rotary table model and the coordinate system of the high-precision model;

and 5: for each radar wave incidence direction, determining a transmission signal in the incidence direction;

step 6: the emission signals are irradiated on a target triangular surface element in the high-precision model according to the incident direction, whether the target triangular surface element has multiple transshipment and shielding is judged, if yes, the target triangular surface element which does not transship is determined, and if not, the target triangular surface element is the target triangular surface element which does not transship;

and 7: calculating a scattering echo signal of the target triangular surface element which is not subjected to the reflection again according to the emergent electric field intensity and the direction of the target triangular surface element which is not subjected to the reflection again;

and 8: accumulating vectors of scattering echo signals of the target triangular surface element which is not reflected any more to obtain echo signals of the whole target;

and step 9: and imaging the fully polarized two-dimensional ISAR image of the target based on the echo signal of the whole target.

2. The three-dimensional model microwave photon echo imaging method of claim 1, wherein the low-precision model is represented as:

vertex＝[P₁ P₂ … P_m]^T

wherein n is the number of triangular surface elements in the model, m is the number of vertexes in the model, face_iThe ith triangular bin is shown as being,is the unit normal vector of the ith triangular bin,respectively, the coordinates of the ith triangular surface element vertex are numbered, vertex ═ P₁ P₂ … P_m]^TThree-dimensional coordinates of all vertices in the model.

3. The three-dimensional model microwave photon echo imaging method according to claim 1, wherein the step 2 comprises:

step 21: calculating theoretical distance resolution of microwave photon radar system parameters;

step 22: determining the point cloud interval for dividing each triangular surface element according to the theoretical calculation value of the distance resolution;

wherein the point cloud intervals comprise point cloud intervals of each edge on a triangular surface element;

step 23: dividing point cloud intervals of two edges except the longest edge in a grid line mode, determining points at the intersection of the two grid lines in each surface element, points at the intersection of each grid line and the edge and points divided by the point cloud intervals of the longest edge as point clouds, and obtaining a point cloud set of each triangular surface element;

step 24: converting the point cloud set of each triangular surface element into a triangular surface grid by using a Delaunay algorithm, and obtaining a target triangular surface element after fine dissection and a normal vector of the target triangular surface element;

step 25: correcting the normal vector of the target triangular surface element to ensure that the normal vector of the target triangular surface element is the same as the normal vector of the triangular surface element of the low-precision model;

step 26: and determining the model formed by each target triangular surface element as a high-precision model.

4. The three-dimensional model microwave photon echo imaging method according to claim 3, wherein the step 23 comprises:

step a: determining the side lengths of three edges in each triangular surface element of each low-precision model;

step b: for each triangular surface element, taking a common vertex of two edges except the longest edge as a first starting point, sequentially determining second starting points of grid lines along direction vectors of the two edges, and taking the second starting points as points of intersection of each grid line and the edges;

step c: drawing a line from a second starting point in the direction of the other side except the longest side of each side except the longest side to obtain a plurality of grid lines intersected with each side;

step d: and determining points at the intersection of the two grid lines in each surface element, the intersection of each grid line and the edge and the points of the longest edge divided at the point cloud intervals as point clouds to obtain a point cloud set of each triangular surface element.

5. The three-dimensional model microwave photon echo imaging method according to claim 1, wherein the step 3 comprises:

step 31: determining an initial observation angle of an observation target;

the initial observation angle comprises a pitch angle and an azimuth angle for observing a target;

step 32: determining an incident direction vector according to the pitch angle and the azimuth angle;

step 33: determining the opposite direction of the incident direction vector as an X' axis for constructing a multi-angle rotary table model coordinate system;

step 34: in an XOY plane under a coordinate system of the high-precision model, determining an emergent direction of an azimuth angle rotated by 90 degrees anticlockwise as a Y' axis for constructing a multi-angle rotary table model coordinate system;

step 35: and determining a Z' axis for constructing a multi-angle rotary table model coordinate system by using a right-hand spiral rule to obtain the coordinate system for constructing the multi-angle rotary table model.

6. The three-dimensional model microwave photon echo imaging method according to claim 5, wherein the step 4 comprises:

step 41: determining a base transformation relation between a coordinate system of the high-precision model and a coordinate system of a model for constructing the multi-angle rotary table;

step 42: determining an imaging corner in a multi-angle rotary table model coordinate system;

step 43: and determining a plurality of radar wave incidence directions of the high-precision model under the self coordinate system according to the basis transformation relation and the imaging rotation angle.

7. The three-dimensional model microwave photon echo imaging method according to claim 5, wherein the incident direction vector is expressed as:

[-cosφ -sinφ 0]

the multi-angle rotary table model coordinate system is expressed as:

the basis transform relationship is represented as:

the radar wave incidence direction is expressed as:

the transmit signal is represented as:

wherein theta'Respectively an initial pitch angle and an initial azimuth angle of an observed object in a coordinate system of the high-precision model, X, Y, Z respectively represents a direction axis of the coordinate system of the high-precision model, phi represents an imaging rotation angle in the coordinate system of the turntable model,is a horizontally polarized component of the radar wave,is a vertically polarized component of the radar wave,is the incident wave vector, k_n＝2πf_nThe/c is the free space wave number corresponding to different frequencies,is a position vector for a point in space,a unit vector representing the incident direction of the incident surface element.

8. The three-dimensional model microwave photon echo imaging method according to claim 1, wherein the step 6 comprises:

step 61: the emission signals are irradiated on a target triangular surface element in the high-precision model according to the incident direction, whether a rotating surface element intersected with the target triangular surface element exists in the emergent direction or not is judged, and if the rotating surface element exists, the target triangular surface element has multiple rotating surfaces;

step 62: aiming at a target triangular surface element with multiple transreflection, judging whether a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction, if so, determining a non-shielding area of the target triangular surface element according to the projection of the shielding surface element on the target triangular surface element, and if not, determining the target triangular surface element which is not transreflected according to the transreflection principle;

and step 63: when the non-shielded area is triangular, determining a target triangular surface element which is not subjected to transreflection according to a transreflection principle by taking the non-shielded area as an initial surface element;

step 64: and when the non-blocked area is a polygon, dividing the non-blocked area into a plurality of triangular surface elements, and determining a target triangular surface element which is not subjected to transreflection according to a transreflection principle by taking the triangular surface element as an initial surface element.

9. The three-dimensional model microwave photon echo imaging method according to claim 1, wherein the step 7 comprises:

step 71: randomly generating a normal adjustment factor for each target surface element;

step 72: calculating a scattering echo signal of the target triangular surface element which is not subjected to the re-reflection by using a remote integral formula and introducing a normal adjustment factor of the target triangular surface element according to the emergent electric field intensity and the direction of the target triangular surface element which is not subjected to the re-reflection;

the remote integral formula is expressed as:

wherein r is_sIs the local vector of the emergent surface, veck is the receiving direction of the radar echo, i.e. the vector in the direction opposite to the incident direction of the radar wave, the phase integration part is calculated by Gordon integration, A_θAndrespectively representing a parallel polarization component and a perpendicular polarization component of the far-field echo; b is_θAndk is calculated according to the electric and magnetic field intensity and the normal direction of an emergent surface element₀The number of free-space waves is represented,a coordinate vector representing a point on the target triangular bin,indicating the unit vector of the emission direction, dx_sdy_sIs to r_sE, H represent the electric and magnetic fields, respectively, across the model bin; p and T are unit vectors of a parallel polarization direction and a vertical polarization direction respectively;the normal vector of the outgoing target triangular surface element is shown,and delta n is a normal adjustment factor for the normal vector of the surface element after the surface element normal phase adjustment factor is introduced.

10. The three-dimensional model microwave photon echo imaging method according to claim 7, wherein the determining whether a transreflective surface element intersecting the target triangular surface element exists in the emission direction includes:

determining a first coordinate transformation matrix under the coordinate system of the high-precision model according to the radar emergent direction vector;

taking a plane coordinate system where each target triangular surface element is located as a ray local coordinate system;

determining a first transformation relation between a coordinate system of a high-precision model and the ray local coordinate system based on the first coordinate transformation matrix;

establishing a first variable expression of the target triangular surface element according to the point-surface relation in the ray local coordinate system and the first transformation relation;

solving the first variable expression to obtain a transverse axis variable and a longitudinal axis variable under a ray local coordinate system;

when the sum of the horizontal axis variable, the vertical axis variable, the horizontal axis variable and the vertical axis variable is not more than 1 and less than 0, determining that a transreflection surface element intersected with the target triangular surface element exists in the emergent direction;

the step of judging whether a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction aiming at the target triangular surface element with multiple times of reflection comprises the following steps:

determining a second coordinate transformation matrix under the coordinate system of the high-precision model according to the radar incident direction vector;

determining a second transformation relation between the coordinate system of the high-precision model and the ray local coordinate system based on the second coordinate transformation matrix;

establishing a second variable expression of the target triangular surface element according to the point-surface relation in the ray local coordinate system and the second transformation relation;

solving the second variable expression to obtain a transverse axis variable and a longitudinal axis variable under the ray local coordinate system;

and when the sum of the horizontal axis variable, the vertical axis variable, the horizontal axis variable and the vertical axis variable is not more than 1 and less than 0, determining that a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction.

Technical Field

The invention belongs to the technical field of radar ISAR imaging, and particularly relates to a three-dimensional model microwave photon echo imaging method based on an LCIM algorithm.

Background

The microwave photon radar has the capacity of receiving, transmitting and processing a cross-spectral-band large-bandwidth signal, but the acquisition cost of actually-measured echo data is high, the conditions are limited, and meanwhile, the movement track of a target is unpredictable, so that the echo data at an ideal observation angle is difficult to obtain. According to the set parameters of the microwave photon radar system, the computer is used for obtaining the full polarization ISAR echo of the target at any observation angle in an imitation mode, then the echo data is processed to obtain ISAR images of the target at any observation angle and frequency band, and technical support is provided for researches such as target electromagnetic characteristic estimation based on the echo data, target identification, three-dimensional reconstruction based on an image sequence and the like.

Common echo simulation methods include those based on physics optics, bouncing ray algorithms, scattering point models, and electromagnetic scattering models. Based on target echo data obtained by a physical optics or bouncing ray algorithm, a two-dimensional ISAR image after imaging processing is difficult to accurately reflect target surface structure information. The scattering point model method is simple and convenient and is fast to realize, but is limited to the conditions of small bandwidth and small corner of the traditional radar, and for the microwave photon radar which emits signals with large bandwidth and across frequency bands, the scattering point model cannot accurately describe the electromagnetic scattering characteristics of the target. The electromagnetic scattering model simulates radar signals to irradiate a target based on far field conditions, and far field echo data are obtained through computer simulation. For a spatial ISAR target, the target size is large, a target geometric model is usually constructed by adopting large surface elements, and due to the shielding judgment error between the surface elements, an electromagnetic calculation result has error, so that wrong scattering points are introduced during imaging.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a three-dimensional model microwave photon echo imaging method based on an LCIM algorithm. The technical problem to be solved by the invention is realized by the following technical scheme:

the invention provides a three-dimensional model microwave photon echo imaging method based on LCIM algorithm, which comprises the following steps:

step 1: constructing a low-precision model describing the geometric shape of the target according to the acquired three-dimensional data of the target;

the low-precision model comprises a plurality of faces, and each face is formed by splicing a plurality of triangular surface elements;

step 2: finely dividing the low-precision model to enable the size of a triangular surface element in the finely divided low-precision model to be in positive correlation with the theoretical distance resolution of the microwave photon radar system parameters, and obtaining a high-precision model;

and step 3: constructing a coordinate system of a multi-angle rotary table model of the observation target based on a coordinate system of the high-precision model;

each surface in the high-precision model is composed of a plurality of target triangular surface elements;

and 4, step 4: determining a plurality of radar wave incidence directions of the high-precision model under the coordinate system of the high-precision model based on the basis transformation relation between the coordinate system of the multi-angle rotary table model and the coordinate system of the high-precision model;

and 5: for each radar wave incidence direction, determining a transmission signal in the incidence direction;

step 6: irradiating the emission signal on a target triangular surface element in the high-precision model according to the incident direction, judging whether the target triangular surface element has multiple transreflection and shielding, if so, determining the target triangular surface element which does not have the transreflection, and if not, determining the target triangular surface element which does not have the transreflection;

and 7: calculating a scattering echo signal of the target triangular surface element which is not subjected to the reflection again according to the emergent electric field intensity and the direction of the target triangular surface element which is not subjected to the reflection again;

and 8: accumulating vectors of scattering echo signals of the target triangular surface element which is not reflected any more to obtain echo signals of the whole target;

and step 9: and imaging the fully polarized two-dimensional ISAR image of the target based on the echo signal of the whole target.

Optionally, the low-precision model is represented as:

vertex＝[P₁ P₂ … P_m]^T

wherein n is the number of triangular surface elements in the model, m is the number of vertexes in the model, face_iThe ith triangular bin is shown as being,is the unit normal vector of the ith triangular bin,respectively, the coordinates of the ith triangular surface element vertex are numbered, vertex ═ P₁ P₂ … P_m]^TThree-dimensional coordinates of all vertices in the model.

Optionally, step 2 includes:

step 21: calculating theoretical distance resolution of microwave photon radar system parameters;

step 22: determining the point cloud interval for dividing each triangular surface element according to the theoretical calculation value of the distance resolution;

the point cloud intervals comprise point cloud intervals of each edge on the triangular surface element;

step 23: dividing the point cloud intervals of the two edges except the longest edge in a grid line mode, determining the point at the intersection of the two grid lines in each surface element, the point at the intersection of each grid line and the edge and the point divided by the longest edge point cloud interval as point clouds, and obtaining a point cloud set of each triangular surface element;

step 24: converting the point cloud set of each triangular surface element into a triangular surface grid by using a Delaunay algorithm, and obtaining a target triangular surface element after fine dissection and a normal vector of the target triangular surface element;

step 25: correcting the normal vector of the target triangular surface element to ensure that the normal vector of the target triangular surface element is the same as the normal vector of the triangular surface element of the low-precision model;

step 26: and determining the model formed by each target triangular surface element as a high-precision model.

4. The three-dimensional model microwave photon echo imaging method of claim 3, wherein step 23 comprises:

step a: determining the side lengths of three edges in each triangular surface element of each low-precision model;

step b: for each triangular surface element, taking a common vertex of two edges except the longest edge as a first starting point, sequentially determining second starting points of grid lines along direction vectors of the two edges, and taking the second starting points as points of intersection of each grid line and the edges;

step c: drawing a line from a second starting point in the direction of the other side except the longest side of each side except the longest side to obtain a plurality of grid lines intersected with each side;

step d: and determining points at the intersection of the two grid lines in each surface element, the intersection of each grid line and the edge and the points on the longest edge divided at the point cloud intervals as point clouds to obtain a point cloud set of each triangular surface element.

Optionally, step 3 includes:

step 31: determining an initial observation angle of an observation target;

the initial observation angle comprises a pitch angle and an azimuth angle for observing a target;

step 32: determining an incident direction vector according to the pitch angle and the azimuth angle;

step 33: determining the opposite direction of the incident direction vector as an X' axis for constructing a multi-angle rotary table model coordinate system;

step 34: in an XOY plane under a coordinate system of the high-precision model, determining an emergent direction of an azimuth angle rotated by 90 degrees anticlockwise as a Y' axis for constructing a multi-angle rotary table model coordinate system;

step 35: and determining a Z' axis for constructing a multi-angle rotary table model coordinate system by using a right-hand spiral rule to obtain the coordinate system for constructing the multi-angle rotary table model.

Optionally, step 4 includes:

step 41: determining a base transformation relation between a coordinate system of the high-precision model and a coordinate system of a model for constructing the multi-angle rotary table;

step 42: determining an imaging corner in a multi-angle rotary table model coordinate system;

step 43: and determining a plurality of radar wave incidence directions of the high-precision model under the self coordinate system according to the basis transformation relation and the imaging rotation angle.

Wherein the incident direction vector is represented as:

[-cosφ -sinφ 0]

the multi-angle turntable model coordinate system is expressed as:

the basis transform relationship is represented as:

the radar wave incidence direction is expressed as:

the transmit signal is represented as:

wherein theta'Respectively an initial pitch angle and an initial azimuth angle of an observed object in a coordinate system of the high-precision model, X, Y, Z respectively represents a direction axis of the coordinate system of the high-precision model, phi represents an imaging rotation angle in the coordinate system of the turntable model,is a horizontally polarized component of the radar wave,is a vertically polarized component of the radar wave,is the incident wave vector, k_n＝2πf_nThe/c is the number of free space waves corresponding to different frequencies,is a position vector for a point in space,a unit vector representing the incident direction of the incident surface element,

optionally, step 6 includes:

step 61: irradiating the emission signal on a target triangular surface element in the high-precision model according to the incident direction, judging whether a transreflection surface element intersected with the target triangular surface element exists in the emergent direction, and if so, performing multiple transreflection on the target triangular surface element;

step 62: aiming at a target triangular surface element with multiple transreflection, judging whether a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction, if so, determining a non-shielding area of the target triangular surface element according to the projection of the shielding surface element on the target triangular surface element, and if not, determining the target triangular surface element which is not transreflected according to the transreflection principle;

and step 63: when the non-shielded area is triangular, determining a target triangular surface element which is not subjected to transillumination according to the transillumination principle by taking the non-shielded area as an initial surface element;

step 64: and when the non-blocked area is a polygon, dividing the non-blocked area into a plurality of triangular surface elements, and determining the target triangular surface elements which are not transmitted any more according to the transmission principle by taking the triangular surface elements as the starting surface elements.

Optionally, step 7 includes:

step 71: randomly generating a normal adjustment factor for each target surface element;

step 72: calculating a scattering echo signal of the target triangular surface element which is not re-reflected by using a remote integral formula and introducing a normal adjustment factor of the remote integral formula according to the emergent electric field intensity and the direction of the target triangular surface element which is not re-reflected;

the remote integral formula is expressed as:

wherein r is_sIs the local vector of the emergent surface, veck is the receiving direction of the radar echo, i.e. the vector in the direction opposite to the incident direction of the radar wave, the phase integration part is calculated by Gordon integration, A_θAndparallel polarization component and perpendicular polarization component respectively representing far-field echo; b is_θAndk is calculated according to the electric field strength, the magnetic field strength and the normal direction of an emergent surface element₀The number of free-space waves is represented,a coordinate vector representing a point on the target triangular bin,indicating the unit vector of the emission direction, dx_sdy_sIs to r_sE, H represent the electric and magnetic fields, respectively, across the model bin; p and T are unit vectors of a parallel polarization direction and a vertical polarization direction respectively;the normal vector of the outgoing target triangular surface element is shown,and delta n is a normal adjustment factor for the surface element normal vector after the surface element normal adjustment factor is introduced.

Optionally, the determining whether a transreflective surface element intersecting with the target triangular surface element exists in the emission direction includes:

determining a first coordinate transformation matrix under a coordinate system of a high-precision model according to the radar emergent direction vector;

taking a plane coordinate system where each target triangular surface element is located as a ray local coordinate system;

determining a first transformation relation between a coordinate system of the high-precision model and a ray local coordinate system based on the first coordinate transformation matrix;

establishing a first variable expression of a target triangular surface element according to the point-surface relation and the first transformation relation in the ray local coordinate system;

solving the first variable expression to obtain a transverse axis variable and a longitudinal axis variable under a ray local coordinate system;

when the sum of the horizontal axis variable, the vertical axis variable, the horizontal axis variable and the vertical axis variable is not more than 1 and less than 0, determining that a transreflection surface element intersected with the target triangular surface element exists in the emergent direction;

for a target triangular surface element with multiple reflection, judging whether a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction comprises the following steps:

determining a second coordinate transformation matrix under the coordinate system of the high-precision model according to the radar incident direction vector;

determining a second transformation relation between the coordinate system of the high-precision model and the ray local coordinate system based on the second coordinate transformation matrix;

establishing a second variable expression of the target triangular surface element according to the point-surface relation and the second transformation relation in the ray local coordinate system;

solving the second variable expression to obtain a transverse axis variable and a longitudinal axis variable under the ray local coordinate system;

and when the sum of the horizontal axis variable, the vertical axis variable, the horizontal axis variable and the vertical axis variable is not more than 1 and less than 0, determining that a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction.

The invention provides a three-dimensional model microwave photon echo imaging method based on LCIM algorithm, which comprises the steps of subdividing a low-precision model of a target geometric shape to obtain a high-precision model; and constructing a coordinate system of the multi-angle rotary table model of the observation target based on the coordinate system of the high-precision model, and determining a plurality of radar wave incident directions of the high-precision model under the coordinate system of the high-precision model according to the basis transformation relation between the coordinate systems. The method comprises the steps of irradiating a transmitting signal on a target triangular surface element according to an incident direction, calculating a scattering echo signal of the target triangular surface element which is not reflected any more, carrying out vector accumulation to obtain an echo signal of the whole target, and imaging a fully polarized two-dimensional ISAR image of the target. The invention can realize the calculation of the total polarization scattering echo of the target under the conditions of cross-frequency band and large rotation angle, improve the quality of the two-dimensional image of the scattering echo of the simulated target, and ensure that the geometric structure of the target can be accurately reflected while representing the electromagnetic scattering characteristic of the target.

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Drawings

Fig. 1 is a schematic flowchart of a three-dimensional model microwave photon echo imaging method based on an LCIM algorithm according to an embodiment of the present invention;

FIG. 2 is a diagram of a multi-precision model provided by an embodiment of the invention;

FIG. 3 is a schematic diagram of an imaging plane of different incidence direction expressions provided by an embodiment of the invention;

FIG. 4 is a schematic diagram of generating an initial bin according to an embodiment of the present invention;

FIG. 5 is a schematic view of a dihedral angle model provided by an embodiment of the present invention;

FIG. 6 is a diagram of the results of dihedral models under different calculation methods provided by embodiments of the present invention;

FIG. 7 is a graph of simulated imaging results of various methods provided by embodiments of the present invention;

fig. 8 is a diagram of simulation imaging results of different polarization modes provided by an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.

As shown in fig. 1, the three-dimensional model microwave photon echo imaging method based on the LCIM algorithm provided by the present invention includes:

step 1: constructing a low-precision model describing the geometric shape of the target according to the acquired three-dimensional data of the target; the low-precision model comprises a plurality of faces, and each face is formed by splicing a plurality of triangular surface elements; the low-precision model is represented as:

vertex＝[P₁ P₂ ··· P_m]^T

wherein n is the number of triangular surface elements in the model, m is the number of vertexes in the model, face_iThe ith triangular bin is shown as being,is the unit normal vector of the ith triangular bin,respectively, the coordinates of the ith triangular surface element vertex are numbered, vertex ═ P₁ P₂ ··· P_m]^TThree-dimensional coordinates of all vertices in the model.

Referring to fig. 2, fig. 2 is a schematic diagram of a multi-precision target model of a satellite model according to an embodiment of the present invention, and a left-side subgraph in fig. 2 is a schematic diagram of a low-precision model, where the model is composed of 84 triangular surfaces. The satellite body is of a cubic structure with the side length of 0.8 m. The connecting structure is a cuboid structure with the length of 0.2m, the width of 0.1m and the height of 0.2m, and the solar cell panel is a cuboid structure with the length of 0.9m, the width of 0.1m and the height of 0.8 m.

Step 2: finely dividing the low-precision model to enable the size of a triangular surface element in the finely divided low-precision model to be in positive correlation with the theoretical distance resolution of the microwave photon radar system parameters, and obtaining a high-precision model;

and step 3: constructing a coordinate system of a multi-angle rotary table model of the observation target based on a coordinate system of the high-precision model;

each surface in the high-precision model is composed of a plurality of target triangular surface elements;

and 4, step 4: determining a plurality of radar wave incidence directions of the high-precision model under the coordinate system of the high-precision model based on the basis transformation relation between the coordinate system of the multi-angle rotary table model and the coordinate system of the high-precision model;

and 5: for each radar wave incidence direction, determining a transmission signal in the incidence direction;

step 6: irradiating the emission signal on a target triangular surface element in the high-precision model according to the incident direction, judging whether the target triangular surface element has multiple transreflection and shielding, if so, determining the target triangular surface element which does not have the transreflection, and if not, determining the target triangular surface element which does not have the transreflection;

and 7: calculating a scattering echo signal of the target triangular surface element which is not subjected to the reflection again according to the emergent electric field intensity and the direction of the target triangular surface element which is not subjected to the reflection again;

and 8: accumulating vectors of scattering echo signals of the target triangular surface element which is not reflected any more to obtain echo signals of the whole target;

and step 9: and imaging the fully polarized two-dimensional ISAR image of the target based on the echo signal of the whole target.

The invention provides a three-dimensional model microwave photon echo imaging method based on LCIM algorithm, which comprises the steps of subdividing a low-precision model of a target geometric shape to obtain a high-precision model; and constructing a coordinate system of the multi-angle rotary table model of the observation target based on the coordinate system of the high-precision model, and determining a plurality of radar wave incident directions of the high-precision model under the coordinate system of the high-precision model according to the basis transformation relation between the coordinate systems. The method comprises the steps of irradiating a transmitting signal on a target triangular surface element according to an incident direction, calculating a scattering echo signal of the target triangular surface element which is not reflected any more, carrying out vector accumulation to obtain an echo signal of the whole target, and imaging a fully polarized two-dimensional ISAR image of the target. The invention can realize the calculation of the total polarization scattering echo of the target under the conditions of cross-frequency band and large rotation angle, improve the quality of the two-dimensional image of the scattering echo of the simulated target, and ensure that the geometric structure of the target can be accurately reflected while representing the electromagnetic scattering characteristic of the target.

As an optional embodiment of the present invention, step 2 includes:

step 21: calculating theoretical distance resolution of microwave photon radar system parameters;

the step can adopt a formulaAnd calculating theoretical distance resolution. Rho_rRepresenting radar image distance resolution, c representing the speed of light in vacuum, and B representing the theoretical bandwidth of the microwave photon radar system.

Step 22: determining the point cloud interval for dividing each triangular surface element according to the theoretical calculation value of the distance resolution;

the point cloud intervals comprise point cloud intervals of each edge on the triangular surface element; the point cloud interval on the jth edge of the ith triangular surface element is Meaning that the rounding is done up for a,representing the point cloud spacing on the jth edge on the ith triangular bin.Is the length of the jth edge on the ith triangular facet. N is the bin size coefficient, usually between 0.5 and 2, p_rA theoretical calculation value representing the distance resolution.

Step 23: dividing the point cloud intervals of the two edges except the longest edge in a grid line mode, determining the point at the intersection of the two grid lines in each surface element, the point at the intersection of each grid line and the edge and the point divided by the longest edge point cloud interval as point clouds, and obtaining a point cloud set of each triangular surface element;

step 24: converting the point cloud set of each triangular surface element into a triangular surface grid by using a Delaunay algorithm, and obtaining a target triangular surface element after fine dissection and a normal vector of the target triangular surface element;

step 25: correcting the normal vector of the target triangular surface element to ensure that the normal vector of the target triangular surface element is the same as the normal vector of the triangular surface element of the low-precision model;

step 26: and determining the model formed by each target triangular surface element as a high-precision model.

It can be understood that each bin in the low-precision model is spaced according to the respective edge d_i ^jAnd determining the point cloud subjected to subdivision processing on the triangular surface element, and converting the point cloud into a triangular surface grid by utilizing a Delaunay algorithm. And (3) constraining the triangular surface mesh by using normal vector information of the surface element of the low-precision target model, and correcting the direction of the external normal vector of the triangular surface mesh, namely the external normal vector of the triangular surface mesh is consistent with the external normal vector of the surface element in the low-precision model, so as to finally obtain the high-precision model.

As an alternative embodiment of the present invention, step 23 includes:

step a: determining the side lengths of three edges in each triangular surface element of each low-precision model;

step b: for each triangular surface element, taking a common vertex of two edges except the longest edge as a first starting point, sequentially determining second starting points of grid lines along direction vectors of the two edges, and taking the second starting points as points of intersection of each grid line and the edges;

step c: drawing a line from a second starting point in the direction of the other side except the longest side of each side except the longest side to obtain a plurality of grid lines intersected with each side;

step d: and determining points at the intersection of the two grid lines in each surface element, the intersection of each grid line and the edge and the points on the longest edge divided at the point cloud intervals as point clouds to obtain a point cloud set of each triangular surface element.

In the process of obtaining the point cloud set, for the ith triangular surface element ABC, the lengths of three edges and corresponding intervals are respectively calculatedSuppose thatCorresponding to the side AB of the triangular face ABC,corresponding to the side AC of the triangular face ABC,the side BC corresponding to the triangular surface ABC, BC being the longest side of the triangular surface ABC. Selecting a common vertex A of the two shorter sides AC and BC, determining point clouds in the sides AB and AC and the triangular surface ABC by taking the point A as a starting point and the points AB and AC as direction vectors:

wherein, the variables m and n need to satisfy the condition that m + n is less than 1, and the point cloud which does not satisfy the condition is discarded.

Taking a point B on the triangular surface ABC as a starting point,determining the point cloud on the edge BC for the direction vector:

and converting the point cloud into a triangular surface grid by utilizing a Delaunay algorithm after the point cloud on the ith triangular surface element ABC is obtained. Using the ith triangular surface element external normal vectorAnd correcting the normal vector direction of the triangular surface grid for constraint. The correction aim is to ensure that the normal vector of the target triangular surface element is the same as the normal vector of the triangular surface element of the low-precision model; in order to load the subdivided triangular surface mesh vertexes and surface element information into a high-precision model and update the coordinate numbers of the triangular surface element vertexes and the three-dimensional coordinates of the vertexes, each triangular surface element can be subjected toTo perform the above process until all bins are traversed.

Referring to fig. 2, the right sub-diagram in fig. 2 is a schematic diagram of the high-precision target model obtained by performing subdivision according to the bandwidth 6GHz and N being 1 in the above steps, where a certain bin in the model is subdivided according to the bandwidth 6GHz and N being 0.5.

As an optional embodiment of the present invention, step 3 includes:

step 31: determining an initial observation angle of an observation target;

the initial observation angle comprises a pitch angle and an azimuth angle for observing a target;

step 32: determining an incident direction vector according to the pitch angle and the azimuth angle;

step 33: determining the opposite direction of the incident direction vector as an X' axis for constructing a multi-angle rotary table model coordinate system;

step 34: in an XOY plane under a coordinate system of the high-precision model, determining an emergent direction of an azimuth angle rotated by 90 degrees anticlockwise as a Y' axis for constructing a multi-angle rotary table model coordinate system;

step 35: and determining a Z' axis for constructing a multi-angle rotary table model coordinate system by using a right-hand spiral rule to obtain the coordinate system for constructing the multi-angle rotary table model.

Wherein, the conventional incident direction vector is expressed as:

substituting the initial observation angle into the formula, and determining a multi-angle rotary table model coordinate system according to the right-hand spiral rule as follows:

selecting an imaging rotation angle phi, and obtaining a radar wave incident direction vector in the multi-angle rotary table model as follows:

[-cosφ -sinφ 0]

referring to fig. 3, fig. 3 is a schematic diagram of imaging planes with different incidence direction expressions according to an embodiment of the present invention. When the traditional direction vector expression is used as the incident direction vector of radar waves, the radar is bent relative to the imaging surface of a target, which is not beneficial to rapid imaging processing. As shown in a subgraph a in fig. 3, the pitch angle is 60 degrees, the azimuth angle change is 0-90 degrees, namely the imaging center angle is 60 degrees, the azimuth angle is 45 degrees, and the imaging surface constructed by the traditional direction vector is curved. In fig. 3, a sub-graph b is an imaging plane constructed by taking an imaging center angle as a pitch angle of 60 °, an azimuth angle of 45 °, an imaging rotation angle of ± 45 °, and a radar wave incident direction of a high-precision model coordinate system. As can be seen from comparison of fig. 3, an imaging plane constructed by the improved radar wave incident direction vector expression provided by the embodiment is not curved, and a turntable model at any observation angle can be constructed.

As an optional embodiment of the present invention, step 4 includes:

step 41: determining a base transformation relation between a coordinate system of the high-precision model and a coordinate system of a model for constructing the multi-angle rotary table;

step 42: determining an imaging corner in a multi-angle rotary table model coordinate system;

step 43: and determining a plurality of radar wave incidence directions of the high-precision model under the self coordinate system according to the basis transformation relation and the imaging rotation angle.

The basis transform relationship is represented as:

the radar wave incidence direction is expressed as:

as an alternative embodiment of the present invention, step 7 includes:

step 71: randomly generating a normal adjustment factor for each target surface element;

step 72: calculating a scattering echo signal of the target triangular surface element which is not re-reflected by using a remote integral formula and introducing a normal adjustment factor of the remote integral formula according to the emergent electric field intensity and the direction of the target triangular surface element which is not re-reflected;

the remote integral formula is expressed as:

wherein r is_sIs the local vector of the emergent surface, veck is the receiving direction of the radar echo, i.e. the vector in the direction opposite to the incident direction of the radar wave, the phase integration part is calculated by Gordon integration, A_θAndparallel polarization component and perpendicular polarization respectively representing far-field echoA component; b is_θAndk is calculated according to the electric field strength, the magnetic field strength and the normal direction of an emergent surface element₀The number of free-space waves is represented,a coordinate vector representing a point on the target triangular bin,unit vector representing emission direction, r_sIs a two-dimensional vector, dx, of the local coordinate system (third coordinate system) of the upper surface element of the emergent surface element of the model_sdy_sIs to r_sE, H represent the electric and magnetic fields, respectively, across the model bin; p and T are unit vectors of a parallel polarization direction and a vertical polarization direction respectively;the normal vector of the outgoing target triangular surface element is shown,a unit vector representing the incident direction of the incident surface element, thetaRespectively an initial pitch angle and an azimuth angle of an observation target in a first coordinate system, and phi is an imaging rotation angle in a second coordinate system (a turntable model coordinate system);in order to introduce the normal vector of the surface element after the surface element normal phase adjustment factor, Δ n is a normal adjustment factor, and in order to ensure that the normal adjustment factor does not influence the RCS characteristic of the target, optionally, the value is usually controlled at 10^-3～10^-2Magnitude.

It will be appreciated that when the target triangular bin has only one reflection, i.e. only one reflection, the field change on the path is:

in the formula (I), the compound is shown in the specification,is the electric field strength at the start of the ray path,the electric field strength representing the end point of the ray path,for the phase change caused by the ray path, (L)₁+L₂) To be the length of the ray path,representing the electric field strength before reflection of the radar wave occurs,the electric field strength after reflection occurs. Gamma-shaped^⊥Is the vertical polarization reflection coefficient, gamma, of radar waves^||Is the reflection coefficient of parallel polarization of radar wave, and the unit vector of the vertical polarization direction of radar wave isIncident radar wave parallel polarization unit vector isThe unit vector of the parallel polarization of the outgoing radar wave is

The transmit signal is represented as:

wherein, theta' represents a pitch angle,indicating the azimuth, X, Y, Z indicating the orientation axes of the coordinate system of the high-precision model, respectively, phi indicating the imaging rotation angle,is a horizontally polarized component of the radar wave,is a vertically polarized component of the radar wave,is the incident wave vector, k_n＝2πf_nThe/c is the free space wave number corresponding to different frequencies,is a position vector for a point in space.

As an alternative embodiment of the present invention, step 6 includes:

step 61: irradiating the emission signal on a target triangular surface element in the high-precision model according to the incident direction, judging whether a transreflection surface element intersected with the target triangular surface element exists in the emergent direction, and if so, performing multiple transreflection on the target triangular surface element;

step 62: aiming at a target triangular surface element with multiple transreflection, judging whether a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction, if so, determining a non-shielding area of the target triangular surface element according to the projection of the shielding surface element on the target triangular surface element, and if not, determining the target triangular surface element which is not transreflected according to the transreflection principle;

and step 63: when the non-shielded area is triangular, determining a target triangular surface element which is not subjected to transillumination according to the transillumination principle by taking the non-shielded area as an initial surface element;

step 64: and when the non-blocked area is a polygon, dividing the non-blocked area into a plurality of triangular surface elements, and determining the target triangular surface elements which are not transmitted any more according to the transmission principle by taking the triangular surface elements as the starting surface elements.

As an optional embodiment of the present invention, the determining whether or not a rotational surface element intersecting the target triangular surface element exists in the emission direction includes:

step a: determining a first coordinate transformation matrix under a coordinate system of a high-precision model according to the radar emergent direction vector;

step b: taking a plane coordinate system where each target triangular surface element is located as a ray local coordinate system;

step c: determining a first transformation relation between a coordinate system of the high-precision model and a ray local coordinate system based on the first coordinate transformation matrix;

step d: establishing a first variable expression of a target triangular surface element according to the point-surface relation and the first transformation relation in the ray local coordinate system;

step e: solving the first variable expression to obtain a transverse axis variable and a longitudinal axis variable under a ray local coordinate system;

step f: and when the sum of the horizontal axis variable, the vertical axis variable, the horizontal axis variable and the vertical axis variable is not more than 1 and less than 0, determining that a transreflection surface element intersected with the target triangular surface element exists in the emergent direction.

Wherein the target triangular bin expression gram is expressed as:

A+(B-A)u+(C-A)v,(0≤u≤1,0≤v≤1,u+v≤1)

according to the radar exit direction vectorObtaining a coordinate transformation matrix F, wherein the transformation relation between the coordinate system of the high-precision model and the ray local coordinate system of the surface element is as follows:

the equation can be established according to the point-line-surface relation in the ray local coordinate system:

F′·(O-A)＝u×[F′·(B-A)]+v×[F′·(C-A)]

wherein F' ═ F₁ F₂]^TAnd solving the binary equation set to obtain variables u and v of the ray local coordinate system, judging the intersection and intersection positions according to the requirements of u and v in the expression of the target triangular surface element, and determining the shielding related information by using a Z-Buffer principle.

For a target triangular surface element with multiple reflection, judging whether a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction comprises the following steps:

step a: determining a second coordinate transformation matrix under the coordinate system of the high-precision model according to the radar incident direction vector;

step b: determining a second transformation relation between the coordinate system of the high-precision model and the ray local coordinate system based on the second coordinate transformation matrix;

step c: establishing a second variable expression of the target triangular surface element according to the point-surface relation and the second transformation relation in the ray local coordinate system;

step d: solving the second variable expression to obtain a transverse axis variable and a longitudinal axis variable under the ray local coordinate system;

step e: and when the sum of the horizontal axis variable, the vertical axis variable, the horizontal axis variable and the vertical axis variable is not more than 1 and less than 0, determining that a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction.

The invention judges the shielding and the formula for judging the multiple reflection are the same, and the difference is that whether the multiple reflection exists in the emergent direction or not is judged, and the shielding is judged in the incident direction. The formula-based determination process is not described in detail.

Referring to fig. 4, the result is the initial surface result generated by different methods when the low-precision model shown in the left-side diagram of fig. 2 is irradiated in the incident direction of the radar wave. Wherein, case 1 is a virtual initial surface constructed in the model coordinate system space by the conventional method, and case 2 is an initial illuminable surface generated on the target model surface by the method provided by the embodiment. See table 1 for the bin numbers for the two initial bin results in fig. 4. As can be seen from the results, the method used in the present embodiment generates the exit surface based on the model surface, and the number of initial surface elements is less than that of the conventional method. Moreover, the conventional method generates an extra-area element, and the extra-area element vertex in the subsequent steps irradiates on the model vertex or edge, so that the updating process of the element is more complicated.

TABLE 1 initial binning

In summary, the bounce ray algorithm based on the LCIM algorithm and the method for calculating the scattering echo of the normal direction adjustment factor in the embodiment are provided. According to the method, a target low-precision model is obtained firstly, the model is subdivided by utilizing a Delaunay algorithm, a rotary table model is established based on the target model and an initial observation angle, and a unit vector of the incident direction of radar waves is determined. Meanwhile, in order to enable the two-dimensional image of the simulation data to accurately reflect the target geometric structure, a surface element method phase factor is introduced, and a bounce ray calculation method based on an LCIM algorithm is provided to enable the simulation data to accurately represent the electromagnetic scattering characteristics of the target.

As an optional embodiment of the present invention, for a target triangular surface element with multiple transshipment, determining whether an occlusion surface element overlapping the projection of the target triangular surface element exists in the incident direction includes:

determining a second coordinate transformation matrix under the coordinate system of the high-precision model according to the radar incident direction vector;

determining a second transformation relation between the coordinate system of the high-precision model and the ray local coordinate system based on the second coordinate transformation matrix;

establishing a second variable expression of the target triangular surface element according to the point-surface relation and the second transformation relation in the ray local coordinate system;

solving the second variable expression to obtain a transverse axis variable and a longitudinal axis variable under the ray local coordinate system;

and when the sum of the horizontal axis variable, the vertical axis variable, the horizontal axis variable and the vertical axis variable is not more than 1 and less than 0, determining that a shielding surface element overlapped with the projection of the target triangular surface element exists in the incident direction.

As an alternative embodiment of the present invention, step 7 includes:

step 71: randomly generating a normal adjustment factor for each target surface element;

step 72: calculating a scattering echo signal of the target triangular surface element which is not re-reflected by using a remote integral formula and introducing a normal adjustment factor of the remote integral formula according to the emergent electric field intensity and the direction of the target triangular surface element which is not re-reflected;

the remote integral formula is expressed as:

wherein r is_sIs the local vector of the emergent surface, veck is the receiving direction of the radar echo, i.e. the vector in the direction opposite to the incident direction of the radar wave, the phase integration part is calculated by Gordon integration, A_θAndparallel polarization component and perpendicular polarization component respectively representing far-field echo; b is_θAndk is calculated according to the electric field strength, the magnetic field strength and the normal direction of an emergent surface element₀The number of free-space waves is represented,a coordinate vector representing a point on the target triangular bin,unit vector representing emission direction, r_sIs a two-dimensional vector, dx, of the local coordinate system (third coordinate system) of the upper surface element of the emergent surface element of the model_sdy_sIs to r_sE, H represent the electric and magnetic fields, respectively, across the model bin; p and T are unit vectors of a parallel polarization direction and a vertical polarization direction respectively;the normal vector of the outgoing target triangular surface element is shown,a unit vector representing the incident direction of the incident surface element, thetaRespectively an initial pitch angle and an azimuth angle of an observed target in a first coordinate system (a high-precision model coordinate system), and phi is an imaging rotation angle in a second coordinate system (a rotary table model coordinate system);in order to introduce the normal vector of the surface element after the surface element normal phase adjustment factor, Δ n is a normal adjustment factor, and in order to ensure that the normal adjustment factor does not influence the RCS characteristic of the target, optionally, the value is usually controlled at 10^-3～10^-2Magnitude.

Next, the effect of the present invention was verified by a simulation experiment.

Experiment one

Please refer to fig. 5. FIG. 5 is a schematic diagram of a dihedral angle model provided by an embodiment of the present invention. The electromagnetic scattering calculation result of the model is calculated by using the algorithm provided by the embodiment, the physical optical algorithm in the commercial software FEKO and the SBR algorithm in the commercial software CST. The model size is shown in the figure, the length of the X-axis and Y-axis directions is 133mm, the height of the Z-axis direction is 138mm, the calculation frequency is 10GHz, the polarization mode is VV polarization, the pitch angle is 90 degrees, and the azimuth scanning angle is [0 degrees and 90 degrees ].

And (3) analyzing an experimental result:

please refer to fig. 6. As shown in fig. 6, sub-diagram a is: the method provided by the embodiment of the invention comprises a primary scattering calculation result, a physical optical algorithm calculation result in commercial software FEKO, an SBR algorithm calculation result in commercial software CST, a secondary scattering calculation result when no normal adjustment factor is added in the method provided by the embodiment of the invention, and a secondary scattering calculation result when a normal adjustment factor is added in the method provided by the embodiment of the invention. Fig. 6, panel b, is the error between the result of the second-order scattering calculation of the proposed method and the result of the calculation when the proposed method has no normal adjustment factor. The results in the figure show that the calculation result of the method provided by the embodiment is consistent with the commercial software result, and meanwhile, the introduction of the normal adjustment factor has little influence on the calculation result of the target electromagnetic scattering, and the calculation error is 10^-4Order of magnitude, and thus the feasibility of the method proposed in this example can be verifiedAnd (4) sex.

Experiment two

Referring to the high-precision model in the right diagram of fig. 2, the far-field scattering echo data of the model is simulated by the method of the present embodiment. The scanning frequency is 7-13 GHz, the bandwidth is 6GHz, and the sampling interval is 15 MHz; the change of the radar line of sight of the right sub-diagram in fig. 2 represents a turntable model constructed with a pitch angle of 30 degrees, an azimuth angle of 45 degrees, an imaging scanning angle of [ -17 degrees, and an imaging scanning angle of 17 degrees, and a sampling interval of 0.085 degrees, and the theoretical two-dimensional resolution under the condition is 2.5cm × 2.5 cm.

And (3) analyzing an experimental result:

referring to fig. 7, the horizontal and vertical coordinates have been converted to actual dimensions in m according to the imaging resolution. As shown in fig. 7, a sub-graph a is a simulation imaging result of point data in a panel of a model selected by a traditional point scattering model, and the image quality is poor; sub-graph b in fig. 7 shows the result of data simulation imaging of the method of the present embodiment, which has good image quality and can reflect the structure of the target model; fig. 7, sub-graph c is a data simulation imaging result when no normal adjustment factor is added in the method of the present embodiment, and the image quality is poor. Comparing the neutron maps a and b in fig. 7, it can be found that the scattering point model result is greatly different from the electromagnetic scattering model result: the brightness of I and II in the sub-graph a depends on the density of selected scattering points, and the imaging result of the electromagnetic calculation of the sub-graph b is more consistent with the brightness difference of the target ISAR image in the actual situation; the point III is a point scattering model which does not consider the shielding of the target part structure in the incident direction of the radar wave. As can be seen from the sub-graph c in fig. 7, when the normal adjustment factor is not added, the target echo is focused into a point after being imaged, and it is difficult to determine the target shape, while the image quality in the sub-graph b in fig. 7 is better, the target shape has a definite outline, and the target surface structure information can be better embodied.

The effect of the echo simulation imaging in different polarization modes can be verified through the following results.

Experiment three

Please refer to fig. 8. Fig. 8 is a diagram of simulation imaging results of different polarization modes provided by an embodiment of the present invention. Subgraphs a, c and e in fig. 8 are the data simulation imaging results of the polarization conditions of VV, HV and VH respectively. Subgraphs a, c and e in fig. 8 are the data simulation imaging results of VV, HV and VH polarization conditions, respectively, when the method proposed by the embodiment of the present invention is not added with normal adjustment factors. As can be seen in conjunction with the results of fig. 7, the introduction of the adjustment factor enables the imaging result to reflect the target surface information. The concrete expression is as follows: in the cross-polarization imaging result, the imaging results of the multiple scattering partial structure of the target can be seen in c and e in fig. 8, but the structural characteristics are not obvious after the echo imaging without the adjustment factor, and only two end points of the scattering structure can be seen, such as d and f in fig. 8.

In summary, the echo imaging processing images of different polarization modes obtained by the target complete polarization scattering echo calculation method provided by the embodiment of the invention have good effects, can accurately represent the electromagnetic scattering characteristics of the target, and can well reflect information such as the surface and the geometric structure of the target.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions may be made without departing from the spirit of the invention, which should be construed as belonging to the scope of the invention.