Radar imaging device, radar imaging method and program

Abstract

This radar imaging device, upon acquiring a radar signal by controlling an antenna that receives a reflected wave of an electromagnetic wave emitted to a target space P, generates, on the basis of the radar signal, a two-dimensional image showing the state of a prescribed height region S that is located at a prescribed height in the target space P and extends in two-dimensional directions. Next, the radar imaging device detects a target object region T that includes a prescribed target object from within the two-dimensional image. Additionally, this radar imaging device (10) generates, on the basis of the radar signal, a three-dimensional image that shows the state of a portion (image-forming space U) which is a partial space in the target space P and through which the target region T passes when the target region T is moved in the height direction of the target space P.

Description

Radar imaging device, radar imaging method, and recording medium

[0001] The present invention relates to a radar imaging device, a radar imaging method, and a recording medium.

[0002] There is a technology that irradiates electromagnetic waves such as millimeter waves, generates an image based on the signal of the reflected wave, and performs various inspections such as baggage inspection based on the image. Related technologies are disclosed in Patent Document 1 and Non-Patent Documents 1 and 2.

[0003] Patent Document 1 and Non-Patent Document 1 disclose a technique for generating a radar image based on a radar signal obtained by measurement using electromagnetic waves such as millimeter waves.

[0004] Non-Patent Document 2 discloses a technology in which the position of an object is identified by generating a low-resolution image that covers a wide range based on signals obtained from a small number of antennas concentrated in a relatively small area, and then a high-resolution image is generated limited to the area around the identified object based on signals obtained from a large number of antennas spread over a wide area.

[0005] International Publication No. 2020 / 261525

[0006] SS Ahmed, A. Schiessl, F. Gumbmann, M. Tiebout, S. Methfessel and L. Schmidt, "Advanced Microwave Imaging," in IEEE Microwave Magazine, vol. 13, no. 6, pp. 26-43, Sept.-Oct. 2012, doi: 10.1109 / MMM.2012.2205772.F. Adib et al., "Capturing the Human Figure Through a Wall," ACM Transactions on Graphics, Vol. 34, No. 6, Article 219, 2015.

[0007] When various inspections such as baggage inspections are conducted, if the object is required to be oriented in a predetermined state, this is inconvenient and reduces work efficiency. If various inspections such as baggage inspections could be conducted without imposing restrictions on the state of the object, for example, while the object is moving through a predetermined space, the above inconveniences would be resolved.

[0008] However, even if the target object is tilted, there are measurement positions where it is easy to capture reflected waves from the target object while it is moving. To include such measurement positions, the width of the target space P to be imaged must be made sufficiently wider than the radar aperture, as shown in FIG. 13. As a result, generating a 3D image showing the state of the entire target space P requires an enormous amount of computer calculation, which can lead to problems with the computer's processing load and processing time. Patent Document 1 and Non-Patent Document 1 do not disclose this problem or a means for solving it.

[0009] The technology disclosed in Non-Patent Document 2 can narrow the area in which a high-resolution image is generated, thereby alleviating the above problem. However, with the technology disclosed in Non-Patent Document 2, the radar aperture becomes narrow when a low-resolution image is generated, as shown in Figure 14. As a result, the area in which an object can be detected also becomes narrow. Figure 14 shows that, as a result of the narrowed radar aperture, an object Q (an object Q located at the edge of the target space P) that could be detected when the radar aperture was wide, as shown in Figure 13, can no longer be detected.

[0010] In view of the above-mentioned problems, one example of the object of the present invention is to provide a radar imaging device, a radar imaging method, and a program that solve the problem of reducing the processing load on a computer while suppressing the oversight of detection of an object in a technology that enables detection of an object present in a target space regardless of the orientation of the object.

[0011] According to one aspect of the present invention, there is provided a radar imaging device comprising: a radar signal acquisition means for acquiring a radar signal by controlling an antenna that receives reflected waves of electromagnetic waves irradiated into a target space; a first image generation means for generating, based on the radar signal, a two-dimensional image that shows the state of a predetermined height region located at a predetermined height in the target space and extending in two dimensions; an object region detection means for detecting an object region including a predetermined object from within the two-dimensional image; and a second image generation means for generating, based on the radar signal, a three-dimensional image that shows the state of a portion of the target space through which the object region passes when the object region is moved in the height direction of the target space.

[0012] According to one aspect of the present invention, a radar imaging method is provided in which a computer acquires a radar signal by controlling an antenna that receives reflected waves of electromagnetic waves irradiated into a target space, generates a two-dimensional image based on the radar signal, showing the state of a predetermined height area located at a predetermined height in the target space and extending in two dimensions, detects an object area including a predetermined object from the two-dimensional image, and generates a three-dimensional image based on the radar signal, showing the state of a portion of the target space through which the object area passes when the object area is moved in the height direction of the target space.

[0013] According to one aspect of the present invention, a program is provided that causes a computer to function as: radar signal acquisition means for acquiring radar signals by controlling an antenna that receives reflected waves of electromagnetic waves irradiated into a target space; first image generation means for generating, based on the radar signal, a two-dimensional image that shows the state of a predetermined height region located at a predetermined height in the target space and extending in two dimensions; object region detection means for detecting an object region including a predetermined object from within the two-dimensional image; and second image generation means for generating, based on the radar signal, a three-dimensional image that shows the state of a portion of the target space through which the object region passes when the object region is moved in the height direction of the target space.

[0014] According to one aspect of the present invention, a radar imaging device, a radar imaging method, and a program are realized that solve the problem of reducing the processing load on a computer while suppressing missed detection of objects in a technology that enables detection of objects present in a target space regardless of the orientation of the objects.

[0015] The above-mentioned objects, as well as other objects, features, and advantages, will become more apparent from the following description of the preferred embodiments and the accompanying drawings.

[0016] FIG. 1 is a diagram showing an example of a functional block diagram of a radar imaging device. FIG. 2 is a diagram for explaining an example of processing by the radar imaging device. FIG. 3 is a diagram showing an example of the hardware configuration of the radar imaging device. FIG. 4 is a diagram showing an example of a target space. FIG. 5 is a diagram showing another example of the target space. FIG. 6 is a diagram showing another example of the target space. FIG. 7 is a flowchart showing an example of the processing flow of the radar imaging device. FIG. 8 is a diagram showing another example of a functional block diagram of a radar imaging device. FIG. 9 is a diagram for explaining another example of processing by the radar imaging device. FIG. 10 is a diagram for explaining processing for projecting a three-dimensional image to generate a two-dimensional projected image. FIG. 11 is another diagram for explaining processing for projecting a three-dimensional image to generate a two-dimensional projected image. FIG. 12 is a diagram for explaining the problem of the present invention. FIG. 13 is another diagram for explaining the problem of the present invention.

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, like components are designated by like reference numerals, and the description thereof will be omitted as appropriate.

[0018] 1 is a functional block diagram showing an overview of a radar imaging device 10 according to a first embodiment. The radar imaging device 10 includes a radar signal acquisition unit 11, a first image generation unit 12, an object region detection unit 13, and a second image generation unit 14.

[0019] The radar signal acquisition unit 11 acquires radar signals by controlling an antenna that receives reflected waves of electromagnetic waves irradiated into the target space. The first image generation unit 12 generates a two-dimensional image based on the radar signals acquired by the radar signal acquisition unit 11, showing the state of a predetermined height region located at a predetermined height in the target space and extending in two dimensions. The object region detection unit 13 detects an object region including a predetermined object from the two-dimensional image generated by the first image generation unit 12. The second image generation unit 14 generates a three-dimensional image based on the radar signals acquired by the radar signal acquisition unit 11, showing the state of a portion (space) of the target space that the object region passes through when the object region is moved in the height direction of the target space.

[0020] The radar imaging device 10 having such a configuration solves the problem of reducing the processing load on the computer while suppressing missed detection of objects in a technology that enables detection of objects present in a target space regardless of the orientation of the objects.

[0021] Second Embodiment Overview The radar imaging device 10 of the second embodiment is a more specific version of the radar imaging device 10 of the first embodiment. An overview of the radar imaging device 10 of this embodiment will be described with reference to FIG. 2 .

[0022] The radar imaging device 10 acquires a radar signal by controlling an antenna (not shown) that receives reflected waves of electromagnetic waves irradiated into the target space P. Next, based on the radar signal, the radar imaging device 10 generates a two-dimensional image showing the state of a predetermined height region S located at a predetermined height in the target space P and extending in two dimensions. For example, if the target Q is a person, the two-dimensional image showing the state of the predetermined height region S shows a cross section of a predetermined part of the person's body. Next, the radar imaging device 10 detects an object region T including the predetermined target Q from the two-dimensional image showing the state of the predetermined height region S.

[0023] Next, based on the radar signal, the radar imaging device 10 generates a three-dimensional image showing the state of a portion (imaged space U) of the target space P that is a portion of the target space P and through which the target area T passes when the target area T is moved in the height direction of the target space P. As described above, the target area T is an area that includes the target Q. Therefore, the imaged space U described above is a space that includes the target Q.

[0024] In this way, the radar imaging device 10 identifies the position of the object Q based on a two-dimensional image showing the state of the predetermined height region S, and then generates a three-dimensional image showing the state of the imaged space U, which is a portion of the object space P and includes the object Q. The images generated by the imaging device 10 are a two-dimensional image showing the state of the predetermined height region S and a three-dimensional image showing the state of the imaged space U, which is a portion of the object space P. Such a radar imaging device 10 can reduce the amount of calculation required by a computer compared to generating a three-dimensional image showing the state of the entire object space P.

[0025] Furthermore, the radar imaging device 10 is positioned at a predetermined height in the target space P, generates a two-dimensional image showing the state of a predetermined height region S extending in two dimensions, and identifies the position of the target Q based on the two-dimensional image. Such a radar imaging device 10 can reduce the amount of computation required by a computer without reducing the number of antennas used, as in the technology disclosed in Non-Patent Document 2. Since there is no need to reduce the number of antennas, it is possible to prevent the target Q from being overlooked in detection.

[0026] Furthermore, the radar imaging device 10 has the above-described characteristic configuration that reduces the amount of calculation required by the computer, so that even if the width of the target space P is made sufficiently wider than the radar aperture, the processing load on the computer and the processing time are not significant. With such a radar imaging device 10, the width of the target space P can be made sufficiently wider than the radar aperture, so that the target Q present in the target space P can be detected regardless of the orientation of the target Q.

[0027] "Hardware Configuration" Next, an example of the hardware configuration of the radar imaging device 10 will be described. Each functional unit of the radar imaging device 10 is realized by any combination of hardware and software, centered around a CPU (Central Processing Unit) of any computer, memory, programs loaded into the memory, a storage unit such as a hard disk that stores the programs (this can store programs that are pre-loaded when the device is shipped, as well as programs downloaded from a recording medium such as a CD (Compact Disc) or a server on the Internet), and a network connection interface. Those skilled in the art will understand that there are many variations in the implementation method and device.

[0028] FIG. 3 is a block diagram illustrating an example of the hardware configuration of the radar imaging device 10. As shown in FIG. 3, the radar imaging device 10 has a processor 1A, a memory 2A, an input / output interface 3A, a peripheral circuit 4A, and a bus 5A. The peripheral circuit 4A includes various modules. The radar imaging device 10 does not necessarily have to have the peripheral circuit 4A. Note that the radar imaging device 10 may be composed of multiple devices that are physically and / or logically separated. In this case, each of the multiple devices can have the above hardware configuration.

[0029] The bus 5A is a data transmission path for the processor 1A, memory 2A, peripheral circuit 4A, and input / output interface 3A to mutually transmit and receive data. The processor 1A is, for example, a processing unit such as a CPU or a GPU (Graphics Processing Unit). The memory 2A is, for example, a memory such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The input / output interface 3A includes an interface for acquiring information from an input device, an external device, an external server, an external sensor, a camera, a radar, etc., and an interface for outputting information to an output device, an external device, an external server, a radar, etc. Examples of input devices include a keyboard, a mouse, a microphone, physical buttons, a touch panel, etc. Examples of output devices include a display, a speaker, a printer, a mailer, etc. The processor 1A can issue commands to each module and perform calculations based on the results of those calculations.

[0030] "Functional Configuration" Next, the functional configuration of the radar imaging device 10 according to the second embodiment will be described in detail. Fig. 1 shows an example of a functional block diagram of the radar imaging device 10. As shown in the figure, the radar imaging device 10 includes a radar signal acquisition unit 11, a first image generation unit 12, an object region detection unit 13, and a second image generation unit 14.

[0031] The radar signal acquisition unit 11 acquires radar signals by controlling an antenna that receives reflected waves of electromagnetic waves irradiated into the target space P. The radar signal acquisition unit 11 controls a transmitting antenna that irradiates electromagnetic waves such as millimeter waves and a receiving antenna that receives reflected waves of the electromagnetic waves irradiated from the transmitting antenna. The radar signal acquisition unit 11 controls, for example, the irradiation of electromagnetic waves from the transmitting antenna, specifically the irradiation timing, etc.

[0032] The electromagnetic waves emitted by the transmitting antenna can be, for example, continuous waves (CW), frequency modulated continuous waves (FMCW), stepped frequency continuous waves (SFCW), etc. The receiving antenna measures the complex amplitude of the received waves (a complex number representing the amplitude and phase shift from the transmitted wave) for each frequency, and the measurement results are used as radar signals. The radar signal can be expressed as S(n, m, f), where n is the transmitting antenna number, m is the receiving antenna number, and f is the frequency.

[0033] The antenna configuration is not particularly limited, and any configuration may be adopted. For example, an antenna panel R in which a plurality of transmitting antennas and a plurality of receiving antennas are arranged may be adopted.

[0034] The multiple antennas are installed in positions and orientations that irradiate electromagnetic waves into the target space P and receive the waves reflected by an object Q located within the target space P.

[0035] The target space P is a space where predetermined inspections such as baggage inspections are carried out. The above-mentioned antenna irradiates electromagnetic waves onto the target space P containing the target Q and receives the reflected waves. Various inspections are then carried out based on the radar signals of the reflected waves. The target space P is provided, for example, in a passageway through which the target Q passes. Then, while the target Q is moving within the target space P, electromagnetic waves are irradiated and the reflected waves are received. In this way, in one example of this embodiment, a walk-through type inspection is realized.

[0036] As shown in Figure 4, the shape of the target space P is, for example, a rectangular prism, but it may also be other prisms such as a circular cylinder or a triangular prism. The target space P is uniform in the height direction. That is, the cross section at any height has the same shape and size. In this embodiment, a coordinate system is set for such a prism-shaped target space P, with the x-axis in the direction of movement of the target object Q, the y-axis in a direction perpendicular to the x-axis and parallel to the bottom surface of the prism, and the z-axis in the height direction of the prism (the same as the height direction of the target space P).

[0037] The xy plane is parallel to the moving direction of the object Q. The xy plane may be a horizontal plane as shown in FIG. 4, or may not be a horizontal plane. For example, as shown in FIGS. 5 and 6, if the target space P is set as an escalator, stairs, an inclined passage, or the like, the moving direction of the object Q is not horizontal, but is inclined from the horizontal. Although the moving direction is upward in FIGS. 5 and 6, the moving direction may be downward.

[0038] The target space P may be divided into elements such as voxels so that image calculations can be performed, and representative coordinates may be defined for each element. The set of representative coordinates can be expressed as the following formula (1).

[0039]

[0040] For example, N ｘ ×N ｙ ×N ｚ When dividing the cell into voxels, P in Eq. (1) ＸＹ and P Ｚ can be expressed as the following formula (2): Note that although an example of dividing into voxels has been described here, it may also be expressed in another coordinate system such as polar coordinates.

[0041]

[0042] 1 , the first image generator 12 generates a two-dimensional image showing the state of a predetermined height region S located at a predetermined height in the target space P and extending in two-dimensional directions, based on the radar signal acquired by the radar signal acquirer 11. The two-dimensional directions are the x-axis direction and y-axis direction described above.

[0043] In this embodiment, the predetermined height is a predetermined fixed value, and is determined based on the size of the object Q and the posture of the object Q when moving through the target space P. For example, if the object Q is a person and the object Q is assumed to move through the target space P in a standing state (for example, walking), the predetermined height may be a height assumed to be near the waist or abdomen of a standing person.

[0044] The first image generation unit 12 may generate "one two-dimensional image that shows the state of one predetermined height region S that is located at one predetermined height in the target space P and spreads in a two-dimensional direction." Alternatively, the first image generation unit 12 may generate "plurality of two-dimensional images that show the state of each of multiple predetermined height regions S that are located at each of multiple predetermined heights in the target space P and spread in a two-dimensional direction."

[0045] An example of generating multiple two-dimensional images is to generate a two-dimensional image of the waist or abdomen of a standing person (e.g., a predetermined height of about 1.0 m) and a two-dimensional image of the legs of a standing person (e.g., a predetermined height of about 0.5 m).

[0046] When generating a two-dimensional image of the vicinity of a person's waist or abdomen, the movement of the waist or abdomen is relatively small, so it is possible to stably identify the position of the object Q based on the two-dimensional image. Furthermore, when generating a two-dimensional image of the vicinity of a person's legs, it is possible not only to detect (identify the position of) the person's legs, but also to detect luggage placed on the ground, such as a carry-on bag.

[0047] The generation of a two-dimensional image based on a radar signal can be realized by utilizing any of the techniques disclosed in Patent Document 1 and Non-Patent Document 1.

[0048] For example, a radar image I(x, y, z) is generated from a radar signal S(n, m, f) based on the following equation (3).

[0049]

[0050] As described above, S(n, m, f) is a radar signal expressed using the number n of the transmitting antenna, the number m of the receiving antenna, and the frequency f as arguments. ｎ，ｍ (x, y, z) is the sum of the distance from the nth transmitting antenna to the coordinate (x, y, z) and the distance from the coordinate (x, y, z) to the mth receiving antenna, and c is the speed of light.

[0051] The object region detection unit 13 detects an object region T including a predetermined object Q from the two-dimensional image generated by the first image generation unit 12. The object region T is a region of a predetermined shape and a predetermined size that encompasses the object Q. The predetermined shape is, for example, a rectangle, but can also be another shape such as a circle. The predetermined shape and the predetermined size are determined in advance. The object region T is a partial region of the predetermined height region S.

[0052] The object region detection unit 13 may execute, for example, any one of the following processing examples 1 to 3.

[0053] As a prerequisite for processing examples 1 to 3, the object region detection unit 13 processes the two-dimensional image generated by the first image generation unit 12 and detects the object region T. The two-dimensional image generated by the first image generation unit 12 can be expressed as I(x, y). When the first image generation unit 12 generates a plurality of two-dimensional images corresponding to a plurality of predetermined heights in the object space P, the object region detection unit 13 projects the plurality of two-dimensional images using an arbitrary method to generate a single two-dimensional image I(x, y), and then performs the following processing. Examples of projection methods include methods of calculating statistical values ​​(maximum value, minimum value, average value, median, mode, sum, etc.) of data at the same coordinates (coordinates where x and y coincide) of a plurality of two-dimensional images, statistical values ​​of the absolute values ​​of the data, statistical values ​​of the squares of the data, etc.

[0054] (Processing Example 1) First, the object region detection unit 13 identifies the coordinates (x, y) where I(x, y) satisfies a predetermined condition (e.g., maximum, or greater than a predetermined value), i.e., the coordinates (x, y) where the strength of the reflected wave satisfies a predetermined condition (e.g., maximum, or greater than a predetermined value). Then, the object region detection unit 13 detects a predetermined region including the identified coordinates (x, y), for example, a region of a predetermined shape and a predetermined size centered on the identified coordinates (x, y), as the object region T.

[0055] The object region detection unit 13 may identify a plurality of coordinates (x, y) where the strength of the reflected wave satisfies a predetermined condition (e.g., maximum, or equal to or greater than a predetermined value).The object region detection unit 13 may then detect a plurality of object regions T that include each of the identified plurality of coordinates.

[0056] The entire area of ​​the target space P is divided into equally spaced voxels, and the target area T is L in the xy plane. ｘ ×L ｙ When the target area T is a rectangular area of ​​cells, it is as follows: Lx is the length of the target area T in the x-axis direction (number of cells), and Ly is the length of the target area T in the y-axis direction.

[0057] First, the coordinate (x) where I(x, y) is maximum Ｍ , y Ｍ ) is the coordinate number corresponding to (i Ｍ , j Ｍ ) That is, x Ｍ = x ０ +i Ｍ Δx, y Ｍ = y ０ +i Ｍ It becomes Δy.

[0058] i' Ｍ = i Ｍ −Lx / 2, j′ Ｍ =j Ｍ -Ly / 2, and R is expressed as in the following equation (4). ＸＹ can be set. ＸＹ The area indicated by is the object area T.

[0059]

[0060] In addition, (i' Ｍ , j' Ｍ Depending on the value of R ＸＹ There is a possibility that a part of the area indicated by R may extend beyond the target space P. ＸＹ If a part of the area indicated by i' goes out of the object space P, the object area detection unit 13 adjusts the area so that it does not go out. Ｍ , j' Ｍ ) may be modified (clipping).

[0061] (Processing Example 2) First, the object region detection unit 13 sets multiple observation regions of a predetermined shape and a predetermined size within the two-dimensional image. Next, the object region detection unit 13 calculates, for each observation region, the sum or average of the I(x, y) coordinates included in each observation region, i.e., the sum or average of the strength of the reflected waves. Then, the object region detection unit 13 detects, as the object region T, an observation region in which the sum or average of the strength of the reflected waves satisfies a predetermined condition (e.g., maximum, greater than or equal to a predetermined value). Note that the object region detection unit 13 may detect one observation region as the object region T, or may detect multiple observation regions as the object region T.

[0062] (Processing Example 3) The object region detection unit 13 may perform contour detection processing or the like on the two-dimensional image and detect, as the object region T, a region surrounded by a contour and satisfying a predetermined condition (for example, a predetermined size or larger).

[0063] Returning to Figure 1, the second image generation unit 14 generates a three-dimensional image based on the radar signal acquired by the radar signal acquisition unit 11, which shows the state of a part of the space within the target space P (imaging space U) through which the target area T detected by the target area detection unit 13 passes when the target area T is moved in the vertical direction of the target space P.

[0064] FIG. 2 shows the relationship between the target space P, the target object Q, the predetermined height region S, the target object region T, and the imaged space U. The imaged space U, which is the portion of the target space P through which the target object region T passes when the target object region T is moved in the height direction, becomes a cylinder as shown in the figure. By appropriately setting the shape and size of the target space T, the imaged space U will encompass the target object Q. Note that the portion of the target space P that the target object region T does not pass through when the target space P is moved in the height direction is not included in the imaged space U. In this embodiment, the height of the imaged space U is the same as the height of the target space P.

[0065] The generation of a three-dimensional image based on a radar signal can be realized by utilizing any of the techniques disclosed in Patent Document 1 and Non-Patent Document 1. Note that a radar image I(x, y, z) may be generated from the radar signal S(n, m, f) based on the above-mentioned formula (3).

[0066] Next, an example of the processing flow of the radar imaging device 10 will be described with reference to the flowchart of FIG.

[0067] First, the radar imaging device 10 controls an antenna that irradiates electromagnetic waves into the target space P and receives reflected waves, thereby acquiring a radar signal (S10).

[0068] Next, based on the radar signal acquired in S10, the radar imaging device 10 generates a two-dimensional image showing the state of a predetermined height area S located at a predetermined height in the target space P and extending in two dimensions (S11).

[0069] Next, the radar imaging device 10 detects an object region T including a predetermined object Q from the two-dimensional image generated in S11 (S12).

[0070] Next, based on the radar signal acquired in S10, the radar imaging device 10 generates a three-dimensional image showing the state of a portion of the target space P (imaging space U) through which the target area T passes when the target area T is moved in the vertical direction of the target space P (S13).

[0071] Based on the three-dimensional image thus generated, various inspections such as baggage inspections are carried out. The details of the various inspections based on the three-dimensional image are not particularly limited, and any technology can be adopted.

[0072] "Effects" The radar imaging device 10 identifies the position of the object Q based on a two-dimensional image showing the state of a predetermined height region S, and then generates a three-dimensional image showing the state of an imaged space U, which is a portion of the object space P and includes the object Q. The images generated by the imaging device 10 are a two-dimensional image showing the state of the predetermined height region S and a three-dimensional image showing the state of the imaged space U, which is a portion of the object space P. Such a radar imaging device 10 can reduce the amount of calculation required by a computer compared to generating a three-dimensional image showing the state of the entire object space P.

[0073] Furthermore, the radar imaging device 10 is positioned at a predetermined height in the target space P, generates a two-dimensional image showing the state of a predetermined height region S extending in two dimensions, and identifies the position of the target Q based on the two-dimensional image. Such a radar imaging device 10 can reduce the amount of computation required by a computer without reducing the number of antennas used, as in the technology disclosed in Non-Patent Document 2. Since there is no need to reduce the number of antennas, it is possible to prevent the target Q from being overlooked in detection.

[0074] Furthermore, the radar imaging device 10 has the above-described characteristic configuration that reduces the amount of calculation required by the computer, so that even if the width of the target space P is made sufficiently wider than the radar aperture, the processing load on the computer and the processing time are not significant. With such a radar imaging device 10, the width of the target space P can be made sufficiently wider than the radar aperture, so that the target Q present in the target space P can be detected regardless of the orientation of the target Q.

[0075] Third Embodiment A radar imaging device 10 according to a third embodiment reduces the amount of calculation by a computer by making the height of the imaging space U lower than the height of the target space P. This will be described in detail below.

[0076] Fig. 8 shows an example of a functional block diagram of the radar imaging device 10 of this embodiment. As shown in the figure, the radar imaging device 10 has a radar signal acquisition unit 11, a first image generation unit 12, an object region detection unit 13, and a second image generation unit 14. The functional block diagram of Fig. 8 differs from the functional block diagram of Fig. 1 in that the first image generation unit 12 and the second image generation unit 14 are connected by a line indicating the transfer of data.

[0077] The first image generating unit 12 generates a plurality of two-dimensional images showing the state of each of a plurality of predetermined height regions S located at each of a plurality of predetermined heights. In the example shown in FIG. 9, three predetermined height regions S located at three predetermined heights of z=0.5, 1.0, and 1.5 [m] are generated. １ ~S ３Three two-dimensional images showing each state are generated. Note that the number of predetermined heights and the values ​​of each predetermined height shown in Figure 9 are merely examples and are not limited to these. The multiple predetermined heights are determined in advance.

[0078] The object region detection unit 13 detects an object region T from each of the plurality of two-dimensional images generated by the first image generation unit 12 .

[0079] The second image generation unit 14 determines the height M of the three-dimensional image to be generated based on the detection result of whether or not the object region T is detected in each of the multiple two-dimensional images. The second image generation unit 14 then generates a three-dimensional image showing the state of the portion (imaging space U) through which the object region T passes when the object region T is moved M in the height direction from the bottom surface of the object space P. Specifically, the second image generation unit 14 acquires multiple predetermined height values ​​from the first image generation unit 12. The second image generation unit 14 also acquires detection results from the object region detection unit 13 indicating whether or not the object region T is detected in each of the multiple two-dimensional images corresponding to each of the multiple predetermined heights. The second image generation unit 14 then determines the above M based on the acquired information. Note that, when the height of the object space P is H, M is any value that satisfies M≦H. That is, the second image generation unit 14 can also set the height M of the three-dimensional image to a value lower than the height H of the object space P.

[0080] For example, the second image generation unit 14 can identify a predetermined height at which the object region T is not detected from among a plurality of predetermined heights, and then set the lowest predetermined height among the identified heights as M. This process will be described with reference to FIG. 9 .

[0081] 9, three predetermined heights are set: z=0.5, 1.0, and 1.5 m. The object region T is detected at z=0.5 and 1.0, but not at z=1.5. In this case, the second image generation unit 14 sets 1.5 to M.

[0082] As another example, assume that five predetermined heights, z=0.5, 1.0, 1.5, 2.0, and 2.5 m, are set, and an object region T is detected at z=0.5 and 1.0, but not at z=1.5, 2.0, or 2.5. In this case, the second image generation unit 14 sets M to 1.5, the lowest of 1.5, 2.0, and 2.5, at which no object region T is detected.

[0083] "Modification" The radar imaging device 10 may determine M by the following process. For example, the height of the object Q present in the target space P may be detected using another sensor such as a visible light camera. Then, the radar imaging device 10 may acquire information indicating the height of the detected object Q.

[0084] The second image generation unit 14 determines M based on the height of the detected object Q. For example, the second image generation unit 14 may set M to a value obtained by adding α (a predetermined value) to the height of the detected object Q. Alternatively, the second image generation unit 14 may set M to a value obtained by multiplying the height of the detected object Q by β (a predetermined value of 1 or more). Note that the calculation examples here are merely examples and are not limited to these. By setting M to a value slightly larger than the height of the detected object Q rather than setting it to M, the problem of the object Q protruding from the imaging space U is suppressed.

[0085] In this modified example, the first image generation unit 12 does not need to generate multiple two-dimensional images corresponding to multiple predetermined heights, but may generate one two-dimensional image corresponding to one predetermined height.

[0086] Other configurations of the radar imaging device 10 of this embodiment are similar to those of the radar imaging devices 10 of the first and second embodiments.

[0087] The radar imaging device 10 of this embodiment achieves the same effects as the radar imaging devices 10 of the first and second embodiments. In addition, the radar imaging device 10 of this embodiment can reduce the amount of computation by lowering the height of the imaging space U.

[0088] Fourth Embodiment A radar imaging device 10 according to a fourth embodiment changes the "predetermined height" for identifying a predetermined height region S for generating a two-dimensional image according to an object Q present in a target space P. This will be described in detail below.

[0089] The first image generation unit 12 acquires information indicating the height of an object Q located in the target space P detected by a predetermined sensor. The sensor may be, but is not limited to, a visible light camera or the like. When the sensor is a visible light camera, the information is an image. The sensor is installed in a position and direction that allows information indicating the height of the object Q to be acquired before the object Q enters the target space P. The sensor and the radar imaging device 10 are configured to be able to communicate with each other. The sensor transmits the generated information to the radar imaging device 10. The first image generation unit 12 calculates the height of the object Q based on the acquired information. The process of analyzing an image and calculating the height of an object (such as a person's height) appearing in the image can be realized using any technology.

[0090] Then, the first image generating unit 12 determines a predetermined height based on the height of the object Q identified by the acquired information. This determines a predetermined height region S in which a two-dimensional image is generated.

[0091] The first image generating unit 12 determines the predetermined height based on a predetermined rule. The rule may be, for example, "the height (h / 2) of the center of the height (h) of the object Q," or may be any other rule.

[0092] Other configurations of the radar imaging device 10 of this embodiment are similar to those of the radar imaging devices 10 of the first to third embodiments.

[0093] The radar imaging device 10 of this embodiment achieves the same effects as the radar imaging devices 10 of the first to third embodiments. Furthermore, the radar imaging device 10 of this embodiment can appropriately set the "predetermined height" for identifying the predetermined height region S for generating a two-dimensional image in accordance with the detection result of the height of the object Q. As a result, the position of the object Q in the target space P can be identified with high accuracy.

[0094] Fifth Embodiment A radar imaging device 10 according to a fifth embodiment has a function of generating a two-dimensional projected image by projecting a three-dimensional image generated by a second image generation unit 14 in a predetermined projection direction. The radar imaging device 10 determines the projection direction based on the position of an object region T in the two-dimensional image generated by a first image generation unit 12. This will be described in detail below.

[0095] 10 shows an example of a functional block diagram of a radar imaging device 10 according to this embodiment. As shown in the figure, the radar imaging device 10 includes a radar signal acquisition unit 11, a first image generation unit 12, an object region detection unit 13, a second image generation unit 14, and a third image generation unit 15. The first image generation unit 12 and the second image generation unit 14 may be connected by a line indicating the transfer of data.

[0096] 11, the third image generation unit 15 generates a two-dimensional projected image by projecting the three-dimensional image of the imaging space U generated by the second image generation unit 14 in a predetermined projection direction V. The third image generation unit 15 determines the projection direction V based on the position of the object region T in the two-dimensional image of the predetermined height region S.

[0097] 12, the object region detection unit 13 can determine the direction connecting an arbitrary position (e.g., the center) on an antenna panel R configured by arranging a plurality of antennas and an arbitrary position (e.g., the center) on the object region T (the y' direction in the figure) as the projection direction V. There are no particular limitations on the process of projecting a three-dimensional image in a predetermined projection direction V to generate a two-dimensional projected image, and any technology can be used.

[0098] The radar imaging device 10 of this embodiment achieves the same effects as the radar imaging devices 10 of the first to fourth embodiments. Furthermore, the radar imaging device 10 of this embodiment can appropriately set the projection direction in the process of generating a two-dimensional projected image by projecting a generated three-dimensional image in a predetermined projection direction. The angle of the surface that is most likely to capture reflections changes depending on the position of the object region T. Therefore, by determining the optimal projection direction V depending on the position of the object region T and generating a two-dimensional projected image, the three-dimensional image can be two-dimensionalized with almost no loss of information from the captured reflections. Two-dimensionalizing a three-dimensional image to generate a two-dimensional projected image facilitates the application of image processing algorithms such as image rendering and object detection.

[0099] <Modifications> Here, a modification that can be applied to all the embodiments will be described. In the above embodiment, it is assumed that the object Q moves within the object space P, but this assumption does not have to be true. For example, a predetermined inspection may be performed on the object Q placed in any location and in any orientation within the object space P.

[0100] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various other configurations may be adopted. The configurations of the above-described embodiments may be combined with each other, or some of the configurations may be replaced with other configurations. Furthermore, various modifications may be made to the configurations of the above-described embodiments without departing from the spirit of the invention. Furthermore, the configurations and processes disclosed in the above-described embodiments and modified examples may be combined with each other.

[0101] In addition, although the flowcharts used in the above explanations show multiple steps (processes) in a sequential order, the order of steps executed in each embodiment is not limited to the order shown. In each embodiment, the order of the steps shown in the drawings can be changed as long as it does not cause any problems in terms of the content. Furthermore, the above-mentioned embodiments can be combined as long as the content is not contradictory.

[0102] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes: 1. A radar imaging device comprising: radar signal acquisition means for acquiring a radar signal by controlling an antenna that receives reflected waves of electromagnetic waves irradiated into a target space; first image generation means for generating, based on the radar signal, a two-dimensional image that shows the state of a predetermined height region that is located at a predetermined height in the target space and extends in two dimensions; object region detection means for detecting an object region that includes a predetermined object from within the two-dimensional image; and second image generation means for generating, based on the radar signal, a three-dimensional image that shows the state of a portion of the target space that is a part of the target space and that the object region passes through when the object region is moved in the height direction of the target space. 1. The radar imaging device according to 1, wherein the first image generation means generates a plurality of two-dimensional images showing the state of each of a plurality of predetermined height regions located at each of the plurality of predetermined heights, the object region detection means detects the object region from each of the plurality of two-dimensional images, and the second image generation means determines the height of the three-dimensional image based on a detection result indicating whether the object region has been detected from each of the plurality of two-dimensional images. 3. The radar imaging device according to 1 or 2, wherein the first image generation means acquires information indicating the height of the object located in the object space detected by a predetermined sensor, and determines the predetermined height in the object space at which the two-dimensional image is to be generated based on the height of the object. 4. The radar imaging device according to any of 1 to 3, further comprising third image generation means that projects the three-dimensional image in a predetermined projection direction to generate a two-dimensional projected image, and the third image generation means determines the projection direction based on the position of the object region in the two-dimensional image. 5. 5. The radar imaging device according to any one of claims 1 to 4, wherein the object region detection means identifies a position in the two-dimensional image where the strength of the reflected wave satisfies a predetermined condition, and detects a predetermined region including the identified position as the object region.6. The radar imaging device according to any one of 1 to 4, wherein the object region detection means sets a plurality of observation regions of a predetermined shape and a predetermined size in the two-dimensional image, calculates the sum or average of the strength of the reflected waves for each observation region, and detects the observation region where the sum or average of the strength of the reflected waves satisfies a predetermined condition as the object region. 7. The radar imaging device according to any one of 1 to 6, wherein the object is a person, and the radar signal acquisition means controls the antenna to irradiate electromagnetic waves at the person moving within the object space and receive reflected waves, thereby acquiring the radar signal. 8. The radar imaging device according to any one of 1 to 7, wherein the object region is a partial region of the predetermined height region. 9. 10. A radar imaging method in which a computer acquires radar signals by controlling an antenna that receives reflected waves of electromagnetic waves irradiated into a target space, generates a two-dimensional image based on the radar signals that shows the state of a predetermined height area located at a predetermined height in the target space and extending in two dimensions, detects an object area including a predetermined object from the two-dimensional image, and generates a three-dimensional image based on the radar signals that shows the state of a portion of the target space that the object area passes through when the object area is moved in the height direction of the target space. A program that causes a computer to function as: radar signal acquisition means that acquires radar signals by controlling an antenna that receives reflected waves of electromagnetic waves irradiated into a target space; first image generation means that generates, based on the radar signal, a two-dimensional image that shows the state of a predetermined height area that is located at a predetermined height in the target space and extends in two dimensions; object area detection means that detects an object area that includes a predetermined object from within the two-dimensional image; and second image generation means that generates, based on the radar signal, a three-dimensional image that shows the state of a portion of the target space that the object area passes through when the object area is moved in the height direction of the target space.

[0103] This application claims priority based on Japanese Patent Application No. 2022-078309, filed May 11, 2022, the disclosure of which is incorporated herein in its entirety.

[0104] REFERENCE SIGNS LIST 10 Radar imaging device 11 Radar signal acquisition unit 12 First image generation unit 13 Object region detection unit 14 Second image generation unit 15 Third image generation unit 1A Processor 2A Memory 3A Input / output I / F 4A Peripheral circuit 5A Bus

Claims

1. a radar signal acquisition means for acquiring a radar signal by controlling an antenna for receiving a reflected wave of an electromagnetic wave irradiated into a target space; a first image generating means for generating a two-dimensional image based on the radar signal, the first image generating means being located at a predetermined height in the target space and showing a state of a predetermined height area extending in a two-dimensional direction; an object region detection means for detecting an object region including a predetermined object from within the two-dimensional image; a second image generating means for generating a three-dimensional image showing a state of a part of the target space through which the target area passes when the target area is moved in a height direction of the target space, based on the radar signal; and A radar imaging device having:

2. the first image generating means generates a plurality of the two-dimensional images showing a state of each of a plurality of the predetermined height regions located at each of the plurality of predetermined heights; The object region detection means detects the object region from each of the plurality of two-dimensional images, 2. The radar imaging device according to claim 1, wherein the second image generating means determines a height of the three-dimensional image based on a detection result of whether or not the object region is detected in each of the plurality of two-dimensional images.

3. The first image generating means includes: Acquire information indicating a height of the object located in the target space detected by a predetermined sensor; 2. The radar imaging system of claim 1, further comprising: determining the predetermined height in the object volume at which the two-dimensional image is generated based on a height of the object.

4. a third image generating means for generating a two-dimensional projected image by projecting the three-dimensional image in a predetermined projection direction; 2. The radar imaging device according to claim 1, wherein the third image generating means determines the projection direction based on a position of the object region in the two-dimensional image.

5. The object region detection means Identifying a position in the two-dimensional image where the intensity of the reflected wave satisfies a predetermined condition; The radar imaging device according to claim 1 , wherein a predetermined area including the identified position is detected as the object area.

6. The object region detection means A plurality of observation regions having a predetermined shape and a predetermined size are set in the two-dimensional image; Calculating the sum or average of the intensity of the reflected waves for each of the observation areas; 2. The radar imaging device according to claim 1, wherein the observation region in which the sum or average of the strength of the reflected waves satisfies a predetermined condition is detected as the object region.

7. the object is a person, 2. The radar imaging device according to claim 1, wherein the radar signal acquisition means controls the antenna to irradiate electromagnetic waves to a person moving within the target space and to receive reflected waves, thereby acquiring the radar signal.

8. 2. The radar imaging device according to claim 1, wherein the object region is a partial region of the predetermined height region.

9. The computer The antenna that receives the reflected waves of the electromagnetic waves irradiated into the target space is controlled to obtain a radar signal. generating a two-dimensional image showing a state of a predetermined height region located at a predetermined height in the target space and extending in a two-dimensional direction based on the radar signal; detecting an object region including a predetermined object from the two-dimensional image; generating a three-dimensional image showing a state of a part of the target space through which the target area passes when the target area is moved in a height direction of the target space, based on the radar signal; Radar imaging methods.

10. Computer, a radar signal acquisition means for acquiring a radar signal by controlling an antenna for receiving a reflected wave of an electromagnetic wave irradiated into a target space; a first image generating means for generating a two-dimensional image based on the radar signal, the first image generating means being located at a predetermined height in the target space and showing a state of a predetermined height area extending in a two-dimensional direction; an object region detection means for detecting an object region including a predetermined object from within the two-dimensional image; a second image generating means for generating a three-dimensional image showing a state of a part of the target space through which the target area passes when the target area is moved in a height direction of the target space, based on the radar signal; A program that functions as a