Patent Application
20220413115
The present invention relates to an object detection apparatus and an object detection method for recognizing or identifying an object to be detected by irradiating the object to be detected with radio waves and detecting radio waves reflected or diffused by the object, and further relates to a computer-readable recording medium in which is recorded a program for realizing the same.
Unlike light, radio waves (microwaves, millimeter waves, terahertz waves, and the like) have superior ability to penetrate objects. Accordingly, in recent years, imaging apparatuses that can image objects under clothes or in bags by utilizing the penetrating ability of radio waves, and furthermore, remote sensing apparatuses that can image the earth's surface from satellites or aircraft by penetrating clouds with radio waves, have been put into practical use.
For example, Patent Document 1 discloses an example of an imaging apparatus (an object detection apparatus) that uses radio waves. The imaging apparatus disclosed in Patent Document 1 uses an active antenna array system. The configuration of the imaging apparatus disclosed in Patent Document 1 will be described here with reference to
As illustrated in
The transmission wave 204 is reflected by the object to be detected 203, producing reflected waves 2051, 2052, . . . , 205N. The reflected waves 2051, 2052, . . . , 205N that have been produced are received by the transmission/reception antennas 2021, 2022, . . . , 202N. The transmission/reception device 201 calculates amplitudes of the radio waves being reflected from the object to be detected 203 on the basis of the received reflected waves 2051, 2052, . . . , 205N. The imaging apparatus then images the object to be detected 203 by imaging the distribution of radio wave amplitudes calculated by the transmission/reception device 201.
Patent Document 1: U.S. Patent Application Publication No. 2014/0167784
However, the imaging apparatus disclosed in Patent Document 1, which employs an active antenna array system, has the following problems.
The first problem with the active array antenna system is that the position where the object to be detected 203 can be detected is limited. This problem will be described in detail. First, the reflected wave 205 produced at the object to be detected 203 has an amplitude dependence on the reflection angle thereof. In particular, when the reflection angle satisfies the specular reflection condition, i.e., when the incident angle of the transmission wave 204 to the object to be detected 203 is equal to the reflection angle of the reflected wave 205 from the object to be detected 203, the amplitude of the reflected wave 205 is maximized. On the other hand, if the reflection angle does not satisfy the specular reflection condition, the amplitude of the reflected wave 205 will be weak.
However, increasing the aperture length of the aperture plane 207 leads to an increase in the size of the transmission/reception device 201, which reduces the ease of installation of the transmission/reception device 201. Additionally, to increase the size of the aperture plane 207, the necessary number of transmission/reception antennas 2021, 2022, . . . , 202N, as well as the number of transceivers connected to each of the transmission/reception antennas 202, increases, which increases the cost of the transmission/reception device 201.
A second problem with the active array antenna system is that the resolution is limited in the imaging of the radio wave amplitude distribution. Specifically, first, the length resolution in the azimuth direction parallel to the aperture plane 207 is proportional to XL/D. Here, X is the wavelength of the transmission wave 204, L is the distance between the transmission/reception device 201 and the object to be detected 203, and D is the aperture length of the aperture plane 207.
The detection accuracy of the object to be detected 203 will decrease if the desired resolution is not achieved. Although it is conceivable to set a large aperture length D for the aperture plane 207 as a means for achieving the desired resolution, setting the aperture length D to a large size leads to an increase in the size and cost of the transmission/reception device 201, as described above. Although it is also conceivable to shorten the distance L between the transmission/reception device 201 and the object to be detected 203 as another means for achieving the desired resolution, in this case, the range of positions which can be detected is limited.
Thus as described thus far, a conventional imaging apparatus using radio waves, including the imaging apparatus disclosed in Patent Document 1, has a problem in that the range of positions in which the object to be detected can be detected is limited, and a problem in that the desired resolution cannot be achieved and the detection accuracy is therefore poor. Attempting to address these problems in the conventional imaging apparatus increases the cost of the apparatus and furthermore greatly increases the size of the apparatus, which limits the applications and opportunities in which the apparatus can actually be used.
An example object of the present invention is to provide an object detection apparatus, an object detection method, and a computer-readable recording medium capable of solving the above-described problems and suppressing an increase in the size and cost of the apparatus while expanding the range of positions for an object to be detected and improving the resolution.
To achieve the above-described example object, an object detection apparatus according to an example aspect of the present invention is an apparatus for detecting an object using radio waves, and includes:
a transmission unit, including a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna;
a reception unit, including a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received; and
a processing device,
wherein the processing device:
calculates an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal, and
furthermore, corrects the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.
Additionally, to achieve the above-described example object, an object detection method according to an example aspect of the present invention is a method for detecting an object using radio waves, and includes,
in an object detection apparatus including a transmission unit, having a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna, and a reception unit, having a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received:
(a) a step of calculating an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal; and
(b) a step of correcting the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.
Furthermore, to achieve the above-described example object, a computer-readable recording medium according to an example aspect of the present invention is a computer-readable recording medium in which is recorded a program for using a computer to detect an object using radio waves, the program including commands for causing the computer to execute,
in an object detection apparatus including a transmission unit, having a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna, and a reception unit, having a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received:
(a) a step of calculating an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal; and
(b) a step of correcting the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.
As described above, according to the present invention, an increase in the size and cost of the apparatus can be suppressed while expanding the range of positions for an object to be detected and improving the resolution.
An object detection apparatus, an object detection method, and a program according to an example embodiment of the present invention will be described hereinafter with reference to
Apparatus Configuration
First, the overall configuration of the object detection apparatus according to the present example embodiment will be described with reference to
An object detection apparatus 1000 according to the present example embodiment illustrated in
The transmission unit 1101 includes a transmission antenna, and uses the transmission antenna to emit a radio wave 1002 serving as a transmission signal toward the target object 1003 present on the target object placement plane 1005. The reception unit 1102 includes a reception antenna, and uses the reception antenna to receive a radio wave 1004 reflected by the target object 1003 as a reception signal. The reception unit 1102 further generates, from the received reception signal, an intermediate frequency signal (called an “IF signal” hereinafter).
Specifically, in the example illustrated in
Additionally, in the example illustrated in
The processing device 1211 first calculates a distribution of the amplitudes of the radio wave reflected by the target object 1003 (called a “reflection amplitude distribution” hereinafter) on the basis of the placement of the transmission antenna, the position of the reception antenna, the frequency of the radio wave 1002 emitted from the transmission antenna, and the IF signal. Then, the processing device 1211 corrects the calculated reflection amplitude distribution using a correction operator calculated from a point spread function (PSF) indicating the characteristics of the transmission unit 1101 and the reception unit 1102.
In this manner, in the present example embodiment, by applying the correction operator to the reflection amplitude distribution of the target object 1003 obtained from measurements by transmitting and receiving radio waves, a true reflection amplitude distribution, unweighted by PSF, is calculated. Therefore, according to the present example embodiment, the range of positions over which the target object 1003 can be detected can be expanded and a higher resolution of detection can be achieved compared to typical imaging apparatuses (object detection apparatuses) using radio waves. In other words, according to the present example embodiment, the range of positions that can be detected can be expanded and the resolution can be increased, which improves the detection accuracy, while avoiding an increase in the size of the aperture, which is a cause of higher costs in the apparatus and a drop in the ease of installation.
The configuration of the transmission/reception device 1001 of the object detection apparatus 1000 according to the present first example embodiment will be described in more detail next with reference to
As illustrated in
In the transmission unit 1101, the oscillator 1201 generates an RF signal (radio wave). The RF signal generated by the oscillator 1201 is transmitted as a transmission signal from the transmission antenna 1202 and emitted to the target object 1003. The radio wave 1004 reflected by the target object 1003 is received by the reception antenna 1203 in the reception unit 1102.
The mixer 1204 generates an IF signal by mixing the RF signal input from the oscillator 1201 via the terminal 1208 with the radio wave received by the reception antenna 1203 (the reception signal). The IF signal generated by the mixer 1204 is transmitted to the processing device 1211 via the interface circuit 1205.
The interface circuit 1205 has a function for converting the IF signal, which is an analog signal, into a digital signal that can be handled by the processing device 1211, and then outputting the obtained digital signal to the processing device 1211.
Additionally, in the example illustrated in
In the example in
In the example illustrated in
The specific configuration of the object detection apparatus according to the present example embodiment will be described in detail next with reference to
As illustrated in
The antenna placement/RF frequency input unit 1302 obtains, from the exterior, information such as the placement of the transmission antenna 1202, the placement of the reception antenna 1203, and the frequency of the radio wave 1002 emitted from the transmission antenna 1202 (the RF frequency). The antenna placement/RF frequency input unit 1302 inputs the obtained information to the PSF calculation unit 1303 and the amplitude calculation unit 1301.
The PSF calculation unit 1303 calculates the PSF (point spread function) on the basis of the information input by the antenna placement/RF frequency input unit 1302. The correction operator calculation unit 1304 calculates the correction operator on the basis of the PSF calculated by the PSF calculation unit 1303. The correction operator is used to calculate the true reflection amplitude distribution, as described above.
The amplitude calculation unit 1301 is activated when the transmission unit 1101 emits the radio wave 1002 and the reception unit 1102 receives the radio wave 1004. The amplitude calculation unit 1301 then calculates the reflection amplitude distribution on the basis of the information input by the antenna placement/RF frequency input unit 1302 and the IF signal generated by the reception unit 1102.
Upon the reflection amplitude distribution being calculated by the amplitude calculation unit 1301, the corrected amplitude calculation unit 1305 corrects the reflection amplitude distribution using the correction operator calculated by the correction operator calculation unit 1304. The corrected amplitude calculation unit 1305 then outputs the corrected reflection amplitude distribution as a corrected amplitude.
On the other hand, as illustrated in
Specifically, as illustrated in
Apparatus Operations
Operations of the object detection apparatus 1000 according to the example embodiment of the present invention will be described next with reference to
As illustrated in
Next, the PSF calculation unit 1303 calculates the PSF (point spread function) of the object detection apparatus 1000 on the basis of the information input in step A1 (the placement of the transmission antenna 1202, the placement of the reception antenna 1203, and the RF frequency) (step A2). Step A2 will be described in greater detail later.
Next, the correction operator calculation unit 1304 calculates the correction operator using the point spread function (step A3). As will be described later, the correction operator is an operator for back-calculating the true reflection amplitude distribution of the target object 1003 from the radio wave amplitude distribution of the reflected wave obtained by the amplitude calculation unit 1301.
Next, in the transmission/reception device 1001, the transmission unit 1101 emits the radio wave 1002 serving as the transmission signal toward the target object 1003 (step A4). At the same time as the emission of the radio wave 1002 serving as the transmission signal, the transmission unit 1101 outputs the transmission signal to the reception unit 1102 via the terminal 1208.
Next, in the transmission/reception device 1001, the reception unit 1102 receives, through the reception antenna 1203, the radio wave reflected by the target object 1003 as the reception signal (step A5).
Next, in the transmission/reception device 1001, the reception unit 1102 generates the IF signal by mixing the transmission signal output from the transmission unit 1101 in step A4 with the reception signal received in step A5 (step A6).
Next, the amplitude calculation unit 1301 calculates the amplitude distribution of the radio wave reflected by the target object 1003 (the reflection amplitude distribution) on the basis of the information input in step A1 (the placement of the transmission antenna 1202, the placement of the reception antenna 1203, and the RF frequency) and the IF signal generated in step A6 (step A7).
Next, the corrected amplitude calculation unit 1305 corrects the reflection amplitude distribution of the reflected wave, calculated in step A7, using the correction operator calculated in step A3 (step A8). Through this, the true reflection amplitude distribution of the target object 1003 can be calculated. Additionally, the corrected amplitude calculation unit 1305 outputs the corrected reflection amplitude distribution as a corrected amplitude.
Note that steps A1 to A3 are processes independent from measurement, while steps A4 to A8 are processes linked to measurement (the emission and reception of radio waves). Accordingly, steps A1 to A3 need only be performed once before measurement as long as the placement of the transmission antenna 1202, the placement of the reception antenna 1203, and the RF frequency of the transmission signal are not changed. On the other hand, steps A4 to A8 are executed with each measurement. Steps A4 to A8 need not be executed sequentially, after the execution of steps A1 to A3.
Here, for comparison, operations by the conventional object detection apparatus 2000 illustrated in
As illustrated in
Of the steps A1 through A7 illustrated in
Step A2
Operations by the PSF calculation unit 1303 in step A2 will be described. The PSF calculation unit 1303 calculates a PSF(r,ro) of the object detection apparatus 1000 on the basis of the information output from the antenna placement/RF frequency input unit 1302, i.e., the placement of the transmission antenna 1202, the placement of the reception antenna 1203, and the information of the RF frequency of the transmission signal transmitted from the transmission antenna 1202.
The PSF(r,ro) is given by a radio wave amplitude distribution P(r) of the reflected wave from the target object 1003 when the target object 1003 is present only at one point at a position ro. ro is the position where the target object 1003 is present. The PSF(r,ro) can be calculated in advance by determining the placement of the transmission antenna 1202, the placement of the reception antenna 1203, an RF frequency f, and a range of positions to be scanned (called a “scanning position” hereinafter) r. Note that “scanning position r” means a position where the radio wave reflected by the target object 1003 is received (the position of the reception antenna).
If the reflection amplitude distribution at the position ro of the target object 1003 is given as σ(ro), the relationship between a reflection amplitude distribution P(r) of the reflected wave from the target object 1003 obtained through measurement and a true reflection amplitude distribution σ(ro) of the target object 1003 is given by the following Expression 1.
P(r)=Bσ(ro) Expression 1
In the above Expression 1, a matrix B is a PSF matrix. The PSF matrix is a matrix obtained by setting the scanning position r to be constant in each row, setting the position ro of the target object 1003 to be constant in each column, and furthermore arranging PSF(r,ro) as elements.
Note that complex values may be set as the reflection amplitude distribution P(r) of the reflected wave from the target object 1003 obtained through measurement, the PSF matrix B, and the true reflection amplitude distribution σ(ro) of the target object 1003.
Step A3
Operations by the correction operator calculation unit 1304 in step A3 will be described next. The correction operator calculation unit 1304 calculates a correction operator B† for back-calculating the true reflection amplitude distribution σ(ro) of the target object 1003 from the reflection amplitude distribution P(r) of the reflected wave obtained by the amplitude calculation unit 1301, on the basis of the relationship in the above Expression 1.
Specifically, the correction operator calculation unit 1304 follows the sequence described hereinafter to generate a regularized pseudoinverse matrix of B, rather than an inverse matrix of the PSF matrix B, as the correction operator B† in order to achieve numerical stability. First, the correction operator calculation unit 1304 performs singular value decomposition of the PSF matrix B using the following Expression 2.
B=UΣV
H Expression 2
In the above Expression 2, U and V are unitary matrices. Σ is a diagonal matrix having singular values as components. The matrix Σ with all elements below a regularization parameter γ set to zero and the nonzero elements set to their reciprocals is taken as Σ†. In this case, the correction operator B† is calculated by the following Expression 3.
B
†
=VΣ
†
U
H Expression 3
Step A7
Operations by the amplitude calculation unit 1301 in step A7 will be described next. The beamformer method can be given as one example of a method for calculating the reflection amplitude distribution of the reflected wave from the target object 1003. A processing sequence using the beamformer method will be described below.
Assume that the IF signal obtained through an nth antenna of the reception antenna 1203, when the radio wave 1002 of the frequency f is transmitted from an mth antenna of the transmission antenna 1202, is denoted as s(m,n,f). In the following, u=(m,n,f) is set, and s(m,n,f) is denoted as s(u). The reflection amplitude distribution of the target object 1003 at position r is set to σ(r). Assuming that the IF signal s(u) and the reflection amplitude distribution σ(ro) at the position ro of the target object 1003 are column vectors, the two can be related by a direction matrix A as follows, as indicated by Expression 4 below.
s(u)=Aσ(r) Expression 4
Additionally, the elements of the direction matrix A are given by a(u,r), indicated by the following Expression 5.
a(u,r)=exp[−j2πf/c·(RTX(m,r)+RRX(n,r))] Expression 5
Here, RTX(m,r) is the distance from the mth antenna of the transmission antenna 1202 to the position r. RRX(nrr) is the distance from the nth antenna of the reception antenna 1203 to the position r. The direction matrix A is configured by placing the elements a(u,r) with u=(m,n,f) constant in each row and the position r constant in each column. The direction matrix A can be calculated in advance by determining the placement of the transmission antenna 1202, the placement of the reception antenna 1203, the transmission frequency f, and the range of positions r to be scanned.
In the beamformer method, the reflection amplitude distribution P(r) of the reflected wave from the target object 1003 is calculated from the IF signal s(u) obtained through measurement and the direction matrix A calculated in advance, through the following Expression 6. In the following Expression 6, the superscript H of the matrix A represents a complex conjugate.
P(r)=AHs(u) Expression 6
In the present example embodiment, the reflection amplitude distribution P(r) of the reflected wave from the target object 1003 may be calculated on the basis of the beamformer method as described above, but the calculation may be performed on the basis of another method.
Step A8
Operations by the corrected amplitude calculation unit 1305 in step A8 will be described next. The corrected amplitude calculation unit 1305 corrects the reflection amplitude distribution P(r) of the reflected wave, calculated by the amplitude calculation unit 1301, on the basis of the correction operator B† calculated by the correction operator calculation unit 1304. Through this, the true reflection amplitude distribution σ(ro) of the target object 1003 can be calculated. Specifically, the corrected amplitude calculation unit 1305 calculates the true reflection amplitude distribution σ(ro) of the target object 1003 on the basis of the following Expression 7.
σ(ro)=B†P(r) Expression 7
Additionally, the corrected amplitude calculation unit 1305 outputs the calculated true reflection amplitude distribution σ(ro) as a corrected amplitude. Furthermore, the corrected amplitude calculation unit 1305 can also output the corrected amplitude calculated in step A8 as an image expressing the reflection amplitude distribution of the reflected wave from the target object 1003.
Here, the aperture plane of the object detection apparatus according to the present example embodiment and the aperture plane of the conventional object detection apparatus will be compared with reference to
As illustrated in
First Variation
A first variation on the object detection apparatus 100 according to the present example embodiment will be described next with reference to
In the present first variation, the corrected amplitude calculation unit 1305 of the processing device 1211 first divides a specific region or a specific space where the target object 1003 is present into a plurality of parts. Then, the corrected amplitude calculation unit 1305 corrects the amplitude distribution for each part obtained by the division (called “partial space” hereinafter), using this partial space as a defining region.
Specifically,
Additionally, like the example in
In this manner, according to the present first variation, the detection space 1400 is divided into K partial spaces, and thus the amount of calculation of the above Expression 7 per partial space is O((N/K)2). Additionally, the detection space 1400 contains K partial spaces, and thus the amount of calculation of the above Expression 7 for the detection space 1400 as a whole is O(N2/K). In other words, if the detection space 1400 is divided into K partial spaces, as in the present first variation, the amount of calculation is reduced by a factor of 1/K compared to a case where the detection space 1400 is not divided. Accordingly, in step A8, it is preferable that the correction process using the above Expression 7 be executed after dividing the detection space 1400 into a plurality of partial spaces.
Second Variation
A second variation on the object detection apparatus 1000 according to the present example embodiment will be described next with reference to
In the present second variation, the object detection apparatus 1000 is connected to an external separate processing device 1212. Additionally, in the present second variation, unlike the processing device 1211 illustrated in
On the other hand, as illustrated in
The obtained information is then input to the amplitude calculation unit 1301 of the processing device 1211 from the separate processing device 1212. The calculation of the PSF and the calculation of the correction operator based on the PSF are performed in the separate processing device 1212, and the correction operator is input to the correction operator input unit 1306 of the processing device 1211 from the separate processing device 1212. In this case, the correction operator input unit 1306 inputs the correction operator, which has been input by the separate processing device 1212, to the corrected amplitude calculation unit 1305.
According to this configuration, in the present second variation, the processing independent from the measurement (steps A1 to A3) among the steps A1 to A8 illustrated in
Additionally, in the present second variation, the processing independent from the measurement (steps A1 to A3) is executed only once by the separate processing device 1212 before the processing related to the measurement (steps A4 to A8) is executed by the processing device 1211. The processing device 1211 then executes the processing related to measurement (steps A4 to A8) with each measurement.
In this manner, according to the present second variation, the processing independent from measurement (steps A1 to A3), which takes a comparatively long processing time, is performed by a processing device separate from the object detection apparatus 1000. As such, according to the present second variation, the processing load on the object detection apparatus 1000 is lightened, and the processing time is shortened.
Effects of the present example embodiment will be described hereinafter with reference to
In the conventional object detection apparatus, as described in the section on the problem to be solved by the invention, the position at which the target object 1003 can be detected is limited to the detection space 1400 surrounded by the aperture plane 1401 and the directly-facing region 1402 as illustrated in
This problem occurs because, in the conventional object detection apparatus, the reflected waves from a target object 1003 outside the detection space 1400 are weaker than reflected waves from a target object 1003 inside the detection space 1400, which makes it difficult to detect a target object 1003 outside the detection space 1400.
In other words, the reflection amplitude distribution P(r) of the reflected wave from the target object 1003 is obtained as a result of interference of the reflection amplitude distribution σ(ro), weighted by the PSF matrix B, as indicated by Expression 1 above. Accordingly, in the conventional object detection apparatus, even if the true reflection amplitude distribution σ(ro) of the target object 1003 has no amplitude difference between the inside and the outside of the detection space 1400, as a result of the interference of the reflection amplitude distribution σ(ro) weighted by the PSF matrix B, the reflection amplitude becomes stronger inside the detection space 1400 and the amplitude becomes weaker outside, causing the image to disappear.
A result of a conventional object detection apparatus imaging the reflection amplitude distribution P(r) of the reflected wave from the target object 1003 using the beamformer method, when the target object 1003 bridges the inside and outside of the detection space 1400 (see
On the other hand, according to the present example embodiment, an effect is achieved in which the target object 1003 can be detected even when the target object 1003 is located outside the detection space 1400. The reason for this is that in the present example embodiment, it is not the radio wave amplitude distribution P(r), which is weighted by the PSF matrix B and has an amplitude difference between the inside and outside of the detection space 1400, but the true reflection amplitude distribution σ(ro) of the target object 1003, which is unweighted by the PSF matrix B, that is ultimately output.
A result of the object detection apparatus 1000 according to the present example embodiment imaging the reflection amplitude distribution P(r) of the reflected wave from the target object 1003 using the beamformer method, when the target object 1003 bridges the inside and outside of the detection space 1400 (see
In the example in
In this manner, in the present example embodiment, the target object 1003 which can be detected need not be located inside the detection space 1400, and the location thereof is not limited to a range restricted by the aperture plane 1401. Therefore, according to the present example embodiment, there is no need to increase the size of the aperture plane 1401 in order to expand the range over which the target object 1003 can be detected, which makes it unnecessary to increase the size of the object detection apparatus 1000, and the ease of installation of the object detection apparatus 1000 is also not impaired.
In addition, in the present example embodiment, because there is no need to increase the size of the object detection apparatus 1000, there is no need to increase the number of transmission antennas 1202, the number of reception antennas 1203, and the number of transceivers accordingly. As a result, according to the present example embodiment, the detection range can be expanded without increasing the cost.
Furthermore, the object detection apparatus 1000 according to the present example embodiment has an effect of achieving a higher resolution than the conventional object detection apparatus. In the conventional object detection apparatus, an image distributed wider than the true reflection amplitude distribution σ(ro) of the target object 1003 due to the influence of the PSF, which represents the spread of points, is obtained as the reflection amplitude distribution P(r), as indicated by the above Expression 1. On the other hand, in the object detection apparatus according to the present example embodiment, the final output is the true reflection amplitude distribution σ(ro) of the target object 1003, from which the effect of PSF representing the spread of points is eliminated, and thus the resolution is improved compared to the conventional object detection apparatus.
Here, the resolution of the object detection apparatus according to the present example embodiment and the resolution of the conventional object detection apparatus will be compared and described, with reference to
As illustrated in
Program
A program according to the present example embodiment may be any program that causes the computer included in the processing device 1211 to execute steps A1 to A3 and A7 to A8 illustrated in
The program according to the present example embodiment may be executed by a computer system constructed from a plurality of computers. In this case, for example, the respective computers may function as one of the amplitude calculation unit 1301, the antenna placement/RF frequency input unit 1302, the PSF calculation unit 1303, the correction operator calculation unit 1304, and the corrected amplitude calculation unit 1305 of the processing device 1211.
Here, the computer that implements the processing device 1211 of the object detection apparatus 1000 by executing the program according to the present example embodiment will be described with reference to
As illustrated in
The CPU 111 loads the program (code) according to the present example embodiment, which is stored in the storage device 113, into the main memory 112, and executes the program according to a prescribed sequence, thereby carrying out various types of operations. The main memory 112 is typically a volatile storage device such as DRAM (Dynamic Random Access Memory) or the like. The program according to the present example embodiment is stored in a computer-readable recording medium 120 and provided in such a state. Note that the program according to the present example embodiment may be distributed over the Internet, which is connected via the communication interface 117.
In addition to a hard disk drive, a semiconductor storage device such as Flash memory or the like can be given as a specific example of the storage device 113. The input interface 114 facilitates data transfer between the CPU 111 and an input device 118 such as a keyboard and a mouse. The display controller 115 can be connected to a display device 119, and controls displays made in the display device 119.
The data reader/writer 116 facilitates data transfer between the CPU 111 and the recording medium 120, reads out programs from the recording medium 120, and writes results of processing performed by the computer 110 into the recording medium 120. The communication interface 117 facilitates data exchange between the CPU 111 and other computers.
A generic semiconductor storage device such as CF (Compact Flash (registered trademark)), SD (Secure Digital), or the like, a magnetic recording medium such as a flexible disk or the like, an optical recording medium such as a CD-ROM (Compact Disk Read Only Memory) or the like, and so on can be given as specific examples of the recording medium 120.
Note that the processing device 1211 of the object detection apparatus 1000 according to the present example embodiment can also be implemented using hardware corresponding to the respective units, instead of a computer in which a program is installed. Furthermore, the processing device 1211 of the object detection apparatus 1000 may be partially implemented by a program, with the remaining parts realized by hardware.
All or parts of the above-described example embodiments can be expressed as Supplementary Note 1 to Supplementary Note 15, described hereinafter, but are not intended to be limited to the following descriptions.
Supplementary Note 1
An object detection apparatus for detecting an object using radio waves, the apparatus including:
a transmission unit, including a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna;
a reception unit, including a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received; and
a processing device,
wherein the processing device:
calculates an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal, and
furthermore, corrects the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.
Supplementary Note 2
The object detection apparatus according to Supplementary Note 1,
wherein the processing device calculates the point spread function on the basis of the placement of the transmission antenna, the placement of the reception antenna, and the frequency of the radio wave emitted from the transmission antenna, calculates the correction operator on the basis of the point spread function calculated, and corrects the amplitude distribution using the correction operator calculated.
Supplementary Note 3
The object detection apparatus according to Supplementary Note 2,
wherein the processing device calculates a pseudoinverse matrix of a matrix that takes the point spread function as an element, and corrects the amplitude distribution using, as the correction operator, the pseudoinverse matrix calculated.
Supplementary Note 4
The object detection apparatus according to Supplementary Note 1,
wherein the processing device accepts an input of the correction operator from outside, and corrects the amplitude distribution using the correction operator for which the input is accepted.
Supplementary Note 5
The object detection apparatus according to any one of Supplementary Notes 1 to 4,
wherein the processing device divides a specific region or a specific space in which the object is present into a plurality of parts, and corrects the amplitude distribution for each of the parts obtained from the dividing using the parts as defining regions.
Supplementary Note 6
An object detection method for detecting an object using radio waves, the method including,
in an object detection apparatus including a transmission unit, having a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna, and a reception unit, having a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received:
(a) a step of calculating an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal; and
(b) a step of correcting the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.
Supplementary Note 7
The object detection method according to Supplementary Note 6, further including:
in the object detection apparatus, (c) a step of calculating the point spread function on the basis of the placement of the transmission antenna, the placement of the reception antenna, and the frequency of the radio wave emitted from the transmission antenna, and calculating the correction operator on the basis of the point spread function calculated,
wherein in the (b) step, the amplitude distribution is corrected using the correction operator calculated.
Supplementary Note 8
The object detection method according to Supplementary Note 7,
wherein in the (c) step, a pseudoinverse matrix of a matrix that takes the point spread function as an element is calculated as the correction operator, and
in the (b) step, the amplitude distribution is corrected using the pseudoinverse matrix.
Supplementary Note 9
The object detection method according to Supplementary Note 6,
wherein in the (b) step, an input of the correction operator from outside is accepted, and the amplitude distribution is corrected using the correction operator for which the input is accepted.
Supplementary Note 10
The object detection method according to any one of Supplementary Notes 6 to 9,
wherein in the (b) step, a specific region or a specific space in which the object is present is divided into a plurality of parts, and the amplitude distribution is corrected for each of the parts obtained from the dividing using the parts as defining regions.
Supplementary Note 11
A computer-readable recording medium in which is recorded a program for using a computer to detect an object using radio waves, the program including commands for causing the computer to execute,
in an object detection apparatus including a transmission unit, having a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna, and a reception unit, having a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received:
(a) a step of calculating an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal; and
(b) a step of correcting the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.
Supplementary Note 12
The computer-readable recording medium according to Supplementary Note 11,
wherein the program further includes commands for causing the computer to execute:
(c) a step of calculating the point spread function on the basis of the placement of the transmission antenna, the placement of the reception antenna, and the frequency of the radio wave emitted from the transmission antenna, and calculating the correction operator on the basis of the point spread function calculated,
wherein in the (b) step, the amplitude distribution is corrected using the correction operator calculated.
Supplementary Note 13
The computer-readable recording medium according to Supplementary Note 12,
wherein in the (c) step, a pseudoinverse matrix of a matrix that takes the point spread function as an element is calculated as the correction operator, and
in the (b) step, the amplitude distribution is corrected using the pseudoinverse matrix.
Supplementary Note 14
The computer-readable recording medium according to Supplementary Note 11,
wherein in the (b) step, an input of the correction operator from outside is accepted, and the amplitude distribution is corrected using the correction operator for which the input is accepted.
Supplementary Note 15
The computer-readable recording medium according to any one of Supplementary Notes 11 to 14,
wherein in the (b) step, a specific region or a specific space in which the object is present is divided into a plurality of parts, and the amplitude distribution is corrected for each of the parts obtained from the dividing using the parts as defining regions.
The configuration of a preferred embodiment of the present invention has been described thus far. However, the content disclosed in the above-described Patent Document and so on can be incorporated into the present invention by reference. Many changes and variations on the example embodiment are possible on the basis of that basic technical spirit, without departing from the scope of the overall disclosure of the present invention (including the scope of the patent claims). Additionally, various elements disclosed can be combined or selected in a variety of ways without departing from the scope of the patent claims of the present invention. In other words, the present invention includes various modifications and variations that can be carried out by one skilled in the art according to the overall disclosure and technical spirit including the scope of the patent claims.
As described above, according to the present invention, an increase in the size and cost of the apparatus can be suppressed while expanding the range of positions for an object to be detected and improving the resolution. The present invention is useful in imaging apparatuses, remote sensing apparatuses, and the like that detect objects using radio waves.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/035587 | 9/10/2019 | WO |
