CN113671476A - Novel passive millimeter wave imaging method - Google Patents
Novel passive millimeter wave imaging method Download PDFInfo
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- CN113671476A CN113671476A CN202110850487.2A CN202110850487A CN113671476A CN 113671476 A CN113671476 A CN 113671476A CN 202110850487 A CN202110850487 A CN 202110850487A CN 113671476 A CN113671476 A CN 113671476A
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- 238000003384 imaging method Methods 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 abstract description 36
- 238000004088 simulation Methods 0.000 abstract description 18
- 230000005855 radiation Effects 0.000 abstract description 13
- 230000000007 visual effect Effects 0.000 abstract description 3
- 230000000694 effects Effects 0.000 abstract description 2
- 230000007547 defect Effects 0.000 abstract 1
- 238000010586 diagram Methods 0.000 description 15
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
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- 238000012360 testing method Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
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Abstract
The invention discloses a novel passive millimeter wave imaging method. The traditional ray emission method for passive millimeter wave radiation simulation generally adopts an equivalent angle emission method, which is more in accordance with the visual effect of a human body in the aspect of imaging effect, so that the defect of processing is that the size and the relative position of an image have large distortion, and the actual size and the position information of an object cannot be distinguished, thereby greatly influencing the accuracy of passive millimeter wave radiation simulation imaging. The invention is as follows: firstly, carrying out square grid division on a detected area. And secondly, emitting rays by taking the interior of the grid or the intersection point as a target and carrying out brightness temperature inversion. And thirdly, establishing a brightness-temperature distribution map in the detected area. Each pixel point of the brightness temperature distribution graph corresponds to the brightness temperature of one ray. The invention can more accurately detect the position and size information of the object, thereby greatly increasing the accuracy of passive millimeter wave imaging simulation. In addition, the invention can reduce the generation of overflow rays.
Description
Technical Field
The invention belongs to the technical field of computer aided analysis and design and software design, and particularly relates to a novel passive millimeter wave imaging method.
Background
The passive millimeter wave imaging simulation is an important link in the field of passive millimeter wave imaging, and can help to know the radiation characteristic of a target, explain the radiation phenomenon, search the radiation rule and judge the quality of an actual measurement result. The above advantages have led to increased importance in recent years for millimeter wave imaging simulations. So far, most of the work is focused on imaging according with the human body visual angle, but the imaging for accurately representing the position information of the target to be measured is just mentioned, and the traditional ray emission method is to emit rays by using the pitch angle, but the method can only present the image according with the human body visual angle. Therefore, a new ray emission method is needed to accurately distinguish the position information of the object, so as to expand the applicable range of passive millimeter wave radiation simulation and improve the resolving power thereof.
Disclosure of Invention
The invention aims to provide a novel passive millimeter wave imaging method.
The method comprises the following specific steps:
step one, carrying out square grid division on a detected area.
And step two, using a radiometer to emit rays inside each grid or at grid intersection points of the detected area.
And step three, performing brightness temperature inversion on each ray emitted by the radiometer to obtain a corresponding brightness temperature.
And step four, obtaining a brightness temperature distribution map in the detected region according to the brightness temperatures corresponding to all the rays. Each pixel point of the brightness temperature distribution graph corresponds to the brightness temperature of one ray.
Preferably, the direction vector of each emission of the radiometer is determined according to the connecting line of the radiometer and the detected point.
Preferably, each ray emitted by the radiometer is directed at a grid intersection.
Preferably, each ray emitted by the radiometer is directed toward the grid center point.
Preferably, before the radiometer emits the radiation, the area to be detected is subdivided, and the subdivided cells are tetrahedrons.
Preferably, the size of the single square grid is 300mm × 300mm to 500mm × 500 mm.
The invention has the beneficial effects that:
the method comprises the steps of carrying out square grid division on a region to be detected, and taking each grid intersection point as a ray emission target; because the distance between each grid intersection point is consistent, and each grid intersection point forms a pixel point on the image, the imaging result of the invention on the horizontal plane can not be distorted; compared with the imaging method of adjusting the pitch angle and the azimuth angle with equal values in the prior art, the method can detect the position and size information of the object more accurately, so that the accuracy of passive millimeter wave imaging simulation is greatly improved. In addition, the invention can reduce the generation of overflow rays.
Drawings
FIG. 1 is a diagram of a physical model of a scene under test according to the present invention;
FIG. 2 is a schematic diagram of a measured scene after being subdivided by a subdivision technique according to the present invention;
FIG. 3 is a schematic diagram of a single ray tracing of an air-to-ground scene model;
FIG. 4 is a schematic diagram of a single ray inversion of an air-to-ground scene model;
FIG. 5 is a simulated image of bright-warm imaging obtained by conventional ray emission method;
FIG. 6 is a simulation diagram of bright temperature imaging obtained by the present invention;
FIGS. 7(a) -7(e) are modeling diagrams of five experimental groups imaged by a conventional ray-emission method, respectively;
FIGS. 8(a) -8(e) are respectively modeling diagrams of five experimental groups imaged by the present invention;
FIGS. 9(a) -9(e) are imaging diagrams of five experimental groups obtained by a conventional ray emission method, respectively;
FIGS. 10(a) -10(e) are the images obtained by the present invention for five experimental groups, respectively;
FIG. 11 is a comparison graph of the ratio of edges of tetrahedral features to the diagonal of the bottom surface of a cube in a conventional ray-casting method, an image obtained by the present invention, and an actual modeling;
fig. 12 is a schematic view of a radiation emission range of a conventional radiation emission method.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
A novel passive millimeter wave imaging method comprises the following specific steps:
the method comprises the following steps of firstly, carrying out square grid division on the horizontal plane of a detected area, and enabling each grid intersection point on the horizontal plane of the detected area to correspond to one detection point of a radiometer. The dimensions of the individual square grids are 400mm x 400 mm.
Step two, a ray tracing part.
Respectively emitting rays to each grid intersection point of the detected area by using a radiometer; the direction vector of each emission of the radiometer is determined according to the connecting line of the intersection point of the radiometer and the detected grid. The ray emitted by the radiometer each time is tracked, and the specific final process belongs to the prior art and is not described herein. The process of ray tracing is shown in figure 3.
And step three, a bright temperature inversion part.
And after the ray tracing part is finished, inverting the brightness temperature to the emission source point from the terminal of each ray to obtain the corresponding brightness temperature.
And step four, after the brightness temperature represented by all the rays is calculated, obtaining a brightness temperature distribution map in the detected region. The process of bright temperature inversion is shown in fig. 4. Because different objects and bottom surfaces have different brightness and temperature distribution conditions, the actual position information of the objects can be distinguished.
Because each pixel point on the obtained brightness and temperature distribution diagram corresponds to one grid intersection point in the detected region, the size of the outline of the intersection line of the target and the horizontal plane on the obtained brightness and temperature distribution diagram is completely the same as that in the real scene, and no distortion exists; therefore, the real target size parameter can be obtained by multiplying the size parameter of the target on the brightness temperature distribution diagram by the scale. Similarly, the invention can obtain the accurate distance between a plurality of targets in the detected area.
The technical effects of the invention are further explained below with reference to a specific scenario; the specific scene is shown in fig. 1, and two observed objects are arranged at intervals in the scene. The two observed objects are respectively cubic and tetrahedral. One bottom edge of the tetrahedron is taken as a characteristic edge; according to the modeling data, the coordinates of two end points of the characteristic edge are (11,5,0) and (7,9,0), respectively, and the coordinates of two end points of one diagonal line of the bottom surface of the cube are (-3,3,0) and (-5,5,0), respectively. The characteristic edge length of the tetrahedron is twice as long as the diagonal length of the bottom surface of the cube through calculation.
After a specific scene is modeled, the model is subdivided by utilizing the existing subdivision software, and a tetrahedron is selected by a subdivision unit. The split model diagram is shown in fig. 2. And then, performing ray tracing and brightness temperature inversion on the specific scene. Storing the emission point with the coordinates of (17.68,17.68,25) in a start _ point (3) array; wherein, the x, y and z coordinates of the emission point are respectively stored in the start _ point (1), the start _ point (2) and the start _ point (3).
Tracking the nth ray, wherein the nth ray corresponds to the nth grid intersection point of the horizontal plane of the specific scene; the coordinates of the grid intersection point node (n) are (node X (n), node y (n) and node z (n)), the direction vector of the nth ray is calculated, the X coordinate of the corresponding grid intersection point node (n) is differed with the X coordinate of the emitting point, and the X-axis projection distance v is obtainedx(n) -start _ point (1), and obtaining the Y-axis projection distance v by subtracting the Y-coordinate of the corresponding grid intersection node (n) from the Y-coordinate of the emission pointy(n) start _ point (2), and obtaining the Z-axis projection distance v by subtracting the Z-coordinate of the corresponding grid intersection node (n) from the Z-coordinate of the emission pointzNodez (n) -start _ point (3). Calculating the distance between the n-th grid intersection point and the emitting point
The direction vector of the nth ray is (v)x/v，vy/v，vzV); FIG. 3 shows scattering models of several rough surfaces. FIG. 4 is a tracking model; when the ray meets the rough surface, a part of energy continues to track along the ray in the reflection direction, and another part of energy continues to track outwards from the surrounding rays until the number of tracking layers is reached or the ray passes out of the field of view. And after ray tracing, performing bright temperature imaging on the simulated scene to obtain a bright temperature imaging simulation diagram.
Respectively carrying out bright temperature imaging simulation on the specific scene by using a traditional ray emission method and the method provided by the invention; fig. 5 is a bright temperature imaging simulation diagram of a simulation scene obtained by a conventional ray emission method, and fig. 6 is a bright temperature imaging simulation diagram of a simulation scene obtained by a novel ray emission method. Comparing the two images, the brightness and temperature simulation image obtained by the invention can obtain the actual position information and the bottom surface size information of the object, but the image obtained by the prior art has obvious distortion on the horizontal plane and cannot obtain the size information such as the side length, the interval and the like of a cube and a tetrahedron.
In order to illustrate the superiority of the method in the reduction of the bottom surface size, the size of an observed object in a simulated scene is changed, the brightness temperature imaging simulation is carried out by the traditional ray emission method and the method, and the change of the actual information of the object in the imaging of the two ray emission methods is recorded and compared. The method comprises the following specific steps:
adjusting the size of the tetrahedron five times, wherein after the adjustment five times, the ratios of the characteristic edges of the tetrahedron to the diagonal lines of the bottom surface of the cube are respectively 1:2, 2:2, 3:2, 4:2 and 5:2, and the ratios are respectively recorded as experiment groups 1-5; each experimental group respectively uses the traditional ray emission method and the invention to carry out bright temperature simulation imaging; the models of the experimental groups 1 to 5 were measured according to the conventional ray emission method as shown in fig. 7(a) to 7(e), and the images thereof were shown in fig. 9(a) to 9 (e). The models of experimental groups 1-5 were measured according to the method provided by the present invention as shown in fig. 8(a) -8(e), and the images shown in fig. 10(a) -10(e) were obtained.
Measuring the characteristic edges of the tetrahedron in the imaging of FIGS. 9(a) -9(e) and FIGS. 10(a) -10(e) and the cube bottom surface diagonals, respectively; and calculating the ratio of the characteristic edge of the tetrahedron in each image to the diagonal of the bottom surface of the cube, and comparing the ratio with the ratio in the actual modeling. FIG. 11 is a graph comparing the ratio of the bottom edge of a tetrahedron to the diagonal of the bottom surface of a cube to the ratio in actual modeling in an imaging simulation generated by two emission methods, respectively. As can be seen from FIG. 11, the ratio of the present invention is substantially consistent with the actual value; the ratio measured by the prior art has larger error.
The traditional ray emission method can generate overflow rays, and the ray emission method provided by the invention can effectively solve the problem. The modeling of the two ray emission methods is compared. The radiation emission range corresponding to the conventional radiation emission method is shown in fig. 12. As can be seen from FIG. 12, the vertex coordinates are (17.68,17.68,25), and the coordinates of the four bottom end points are (-30.9119, -4.98,0), (-4.98, -30.9119,0), (7.1122,12.751,0), (12.751,7.1122, 0). The traditional method of ray emission is to determine the emitting direction of the ray according to the pitch angle theta and the azimuth angle phi. When the pitch angle theta is 26 degrees and the azimuth angle phi is 0 degrees, the intersection point coordinate of the ray emitting direction and the plane of the bottom surface is (-18.564, -18.564,0) and is positioned at the outer side of the bottom surface. In order to allow the emitted radiation to cover the bottom surface, the actual radiation emission range is bounded by a circular arc as shown in fig. 12.
Claims (6)
1. A novel passive millimeter wave imaging method is characterized in that: step one, carrying out square grid division on a detected area;
secondly, emitting rays inside each grid or at grid intersection points of the detected area by using a radiometer;
thirdly, performing brightness temperature inversion on each ray emitted by the radiometer to obtain corresponding brightness temperature;
step four, obtaining a brightness temperature distribution map in the detected region according to the brightness temperatures corresponding to all rays; each pixel point of the brightness temperature distribution graph corresponds to the brightness temperature of one ray.
2. A novel passive millimeter wave imaging method according to claim 1, characterized in that: the direction vector of each emission of the radiometer is determined according to the connecting line of the radiometer and the detected point.
3. A novel passive millimeter wave imaging method according to claim 1, characterized in that: each ray from the radiometer is directed at a grid intersection.
4. A novel passive millimeter wave imaging method according to claim 1, characterized in that: each ray from the radiometer is directed at the grid center point.
5. A novel passive millimeter wave imaging method according to claim 1, characterized in that: before the radiometer emits rays, subdivision processing is carried out on the detected area, and the subdivided cells are tetrahedrons.
6. A novel passive millimeter wave imaging method according to claim 1, characterized in that: the size of the single square grid is 300mm multiplied by 300mm to 500mm multiplied by 500 mm.
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