1. A detection method of an FOD detection device based on a vehicle-mounted distributed aperture radar comprises the steps that the FOD detection device comprises a moving trolley (1) and a radar unit with a plurality of antennas (2), wherein the moving direction of the moving trolley (1) is parallel to an airport runway (3); the antennas (2) are arranged on the moving trolley (1) at intervals and used for transmitting detection signals to the airport runway (3); the multiple antennas (2) form a sparse large-aperture antenna to synthesize a beam with a narrower main lobe beam width to improve the signal-to-noise ratio of a target echo, and the detection method is characterized by comprising the following steps:

1) acquiring target echo signals received by each radar antenna (2); wherein the target echo signals are obtained by returning FMCW pulse signals transmitted by a plurality of radar antennae (2);

2) synthesizing a plurality of target echo signals into a radar beam with a narrower main lobe beam width;

3) processing the radar wave beam to obtain a detection result;

in the step 2), the synthesized radar beam is aligned to the normal direction of the sparse large-aperture antenna.

2. The detection method according to claim 1, wherein in step 3), the processing procedure is: clutter at the grating lobe is suppressed in a pulse dimension or a time domain through an MTD filter, and then the clutter suppression is realized through a space-time filter.

3. The detection method according to claim 2, wherein clutter at the grating lobe is suppressed in a pulse dimension or a time domain by an MTD filter, and the specific process of suppressing the clutter by using a space-time filter is as follows:

suppose that the outputs of the respective antennas (2) are denoted by x₁,x₂,...x_NWherein N is the total number of the antennas (2); the beam forming weight is:

W=[1,1...,1]^H

wherein the superscript H denotes the conjugate transpose, i.e. the beamforming weighting vector is a full 1 vector, the resulting output is:

y_m=x₁+x₂...x_N

wherein y is_mThe M represents the pulse number, the value of the pulse number is more than 1 and less than M, and M is the number of pulses in one CPI;

calculating to obtain the grating lobe position of the sparse large-aperture antenna when the current synthesized beam points to the normal line according to the position of the antenna (2), and assuming that the grating lobe position is theta₁,...θ_LObtaining clutter relative speeds v at the grating lobes according to the measured value of the current vehicle speed₁,...v_LWherein:

V_l=2vsinθ_l/λ

wherein lambda is wavelength, L ranges from 1 to L, and L is clutter number at grating lobe, and based on the above information, designing time domain filter weight w_t;

The range-doppler matrix for detection is then obtained as:

Y=[y₁,y₂...y_M]w_t。

4. the detection method according to claim 3, wherein the detection result is obtained by one-dimensional CFAR processing after outputting the distance dimension data by the distance-Doppler matrix.

5. The detection method according to claim 1, characterized in that a plurality of antennas (2) are arranged uniformly on the side of the moving trolley (1).

6. The detection method according to claim 1, wherein the radar unit is a chirp continuous wave millimeter wave radar.

7. An inspection system for performing the inspection method of any one of claims 1 to 6, comprising:

the first module is used for acquiring target echo signals received by each radar antenna (2); wherein the target echo signals are obtained by returning FMCW pulse signals transmitted by a plurality of radar antennae (2);

a second module for synthesizing the plurality of target echo signals into a radar beam with a narrower main lobe beam width;

and the third module is used for processing the radar beam to obtain a detection result.

Background

Airport runway Foreign Objects (FOD) refer to any foreign object that does not belong to an airport but is present in the operating area of the airport and may cause damage to the airport or to the aircraft, such as stones, metal parts, adhesive tapes, newspapers, leaves, etc. Although the foreign bodies are not large in size, the foreign bodies have great influence on the normal safe operation of an airport and even form air crash events, such as a small plastic cloth is sucked into an engine to cause an air parking, and a small screw or a metal sheet or even a sharp stone can prick a tire to cause a tire burst.

Because the operation environment of the airport is complicated, the position, the time and the like of runway foreign matter invasion are difficult to estimate, and because the visual field of a crew is limited, the damage of the aircraft caused by tiny foreign matters is difficult to find in time, so that the damage of the FOD to the aircraft is huge. Conservative estimates are that direct losses due to FOD are at least $ 30-40 million worldwide each year. FOD not only causes severe direct losses, but also indirect losses such as flight delays, interrupted take-off, closed runways, etc. Statistically, the indirect loss is at least 4 times the direct loss.

In order to avoid serious loss caused by foreign body detection of the airport runway, the main methods adopted at home and abroad at present are as follows:

1. manual detection: namely, related personnel are adopted to carry out timing inspection on the runway, and the domestic airport still follows the regulations formulated by the international civil aviation organization to carry out manual inspection at present. According to the regulations of International Civil Aviation Organization (ICAO), the runway needs to be detected at least 4 times in all directions every day, and the runway needs to be closed during the detection period, so that the runway time is occupied, the traffic flow is obviously reduced, and the economy of an airline operation company is influenced; moreover, human eyes are easily interfered by fatigue, blind areas, lamplight, weather and the like to generate missed picking, and small FOD targets are difficult to find, so that important potential safety hazards exist.

2. Visual image detection: and taking a picture of the field by adopting a camera, and analyzing the picture. However, due to image quality limitations, the main disadvantages are mainly the high exposure to external influences, especially light and weather, the poor detection capability for small objects at a distance, and the inability to work properly in bad weather conditions. Namely, the method based on visual image detection is too sensitive to light and climate conditions, the system robustness is poor, and the environmental adaptability is poor.

3. Radar systems based on parabolic antennas: by adopting a millimeter wave radar system and a parabolic antenna, the radar can realize scanning detection of a monitoring area by relatively narrow radar beams under the condition of cost constraint, and is an advanced technology at present. Specifically, a phased array radar system adopting a parabolic antenna realizes monitoring area scanning through a mechanical rotating antenna, the working flow of the parabolic antenna is shown in fig. 1, a radar generates a millimeter wave waveform to be transmitted, the millimeter wave waveform is transmitted to the parabolic antenna through a power amplifier, a narrow airspace beam is used for detecting a certain direction, and after a radar echo waveform is received, the narrow airspace beam and a current transmission signal are subjected to deskew processing to obtain a baseband signal for transmitting a pulse. And the radar transmits the next pulse signal, transmits a plurality of groups of signals together, performs two-dimensional Fourier transform on the echo signal, and then performs target detection in the range-Doppler unit. The target angle is the pointing angle of the current parabolic antenna, and after the detection of the direction is completed, the rotary table control system drives the rotary table to rotate, so that the target detection of the next direction is realized, and the detection of the whole airspace is realized. However, since an extremely narrow beam cannot be formed, the cost is significantly increased, a large parabolic aperture is required, and the search capability in the airspace is seriously affected.

Namely, a phased array millimeter wave radar detection system adopting a parabolic antenna can find the size of a target but is not satisfactory, especially for some scenes with harsh requirements on FOD (field of view), namely RCS (radar cross section) value, especially military airports, the RCS of the target which can be detected by the current requirement even reaches 0.01m²However, it is difficult for the current system to satisfy such a high level.

4. Vehicle-mounted FOD detection: currently, the operation mode of directly transplanting a tower-type or side-light-type real-aperture scanning FOD equipment is general, but the main problems exist:

4.1, if high-resolution imaging is required, antenna beams as narrow as possible are required, so that a large-aperture millimeter wave antenna needs to be designed and processed, the processing difficulty is high, the system is large in size and weight, and the system needs to be carried by a special vehicle;

4.2, due to the fact that a real aperture scanning mode is adopted, vehicle motion errors have great influence on imaging, the situation cannot be completely covered or the geographic registration difficulty is increased, and if a stable tripod head is equipped, the system size, weight and cost are further increased; and due to the real aperture scanning principle, the suppression capability of the flickering clutter such as raindrops in rainy and snowy days, water splash splashed on the ground and the like is poor, so that the use efficiency is seriously reduced under the severe weather condition.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: aiming at the problems in the prior art, the invention provides a detection method and a detection system of an FOD detection device based on a vehicle-mounted distributed aperture radar, which have strong weak and small target detection capability.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

a detection method of FOD detection device based on vehicle-mounted distributed aperture radar comprises a moving trolley and a radar unit with a plurality of antennas, wherein the moving direction of the moving trolley is parallel to an airport runway; the antennas are arranged on the moving trolley at intervals and used for transmitting detection signals to the airport runway; the multiple antennas form a sparse large-aperture antenna to synthesize a beam with narrower main lobe beam width to improve the signal-to-noise ratio of target echo, and the detection method comprises the following steps:

1) acquiring target echo signals received by each radar antenna; the target echo signals are obtained by returning FMCW pulse signals transmitted by a plurality of radar antennas;

2) synthesizing a plurality of target echo signals into a radar beam with a narrower main lobe beam width;

3) processing the radar wave beam to obtain a detection result;

in the step 2), the synthesized radar beam is aligned to the normal direction of the sparse large-aperture antenna.

As a further improvement of the above technical solution:

in step 3), the treatment process is as follows: clutter at the grating lobe is suppressed in a pulse dimension or a time domain through an MTD filter, and then the clutter suppression is realized through a space-time filter.

The clutter at the grating lobe is suppressed in a pulse dimension or a time domain through an MTD filter, and then the specific process of realizing clutter suppression by adopting a space-time filter is as follows:

suppose that the outputs of the respective antennas are denoted by x₁,x₂,...x_NWherein N is the total number of the antennas; the beam forming weight is:

W=[1,1...,1]^H

wherein the superscript H denotes the conjugate transpose, i.e. the beamforming weighting vector is a full 1 vector, the resulting output is:

y_m=x₁+x₂...x_N

wherein y is_mThe M represents the pulse number, the value of the pulse number is more than 1 and less than M, and M is the number of pulses in one CPI;

calculating to obtain the grating lobe position of the sparse large-aperture antenna when the current synthesized beam points to the normal line according to the position of the antenna, and assuming that the grating lobe position is theta₁,...θ_LObtaining clutter relative speeds v at the grating lobes according to the measured value of the current vehicle speed₁,...v_LWherein:

V_l=2vsinθ_l/λ

wherein lambda is wavelength, L ranges from 1 to L, and L is clutter number at grating lobe, and based on the above information, designing time domain filter weight w_t;

The range-doppler matrix for detection is then obtained as:

Y=[y₁,y₂...y_M]w_t。

after the distance dimensional data is output through the distance-Doppler matrix, the detection result is obtained through one-dimensional CFAR processing.

The antennas are uniformly arranged on the side surface of the moving trolley.

The radar unit is a millimeter wave radar of linear frequency modulation continuous waves.

The invention further discloses a detection system for executing the detection method, which comprises the following steps:

the first module is used for acquiring target echo signals received by each radar antenna; the target echo signals are obtained by returning FMCW pulse signals transmitted by a plurality of radar antennas;

a second module for synthesizing the plurality of target echo signals into a radar beam with a narrower main lobe beam width;

and the third module is used for processing the radar beam to obtain a detection result.

Compared with the prior art, the invention has the advantages that:

according to the invention, a vehicle-mounted distributed aperture millimeter wave radar is adopted, and a plurality of small-aperture radar antennas are arranged on the side of the vehicle body of the moving trolley to form a large sparse aperture antenna (antenna array), so that an extremely narrow beam main lobe can be synthesized, the signal-to-noise ratio of target echoes in a beam is improved, the clutter energy in the main beam is reduced, and the key index, namely the small target detection capability, faced by the current FOD application can be obviously improved; in addition, the device is simple in integral structure and easy to realize.

The invention adopts a millimeter wave radar system of linear frequency modulation continuous waves. When the millimeter waves are transmitted by utilizing an atmospheric window (when the millimeter waves and the submillimeter waves are transmitted in the atmosphere, certain frequency with minimum attenuation caused by resonance absorption of gas molecules is small), the attenuation is small, and the influence of natural light and a heat radiation source is small; the millimeter wave radar is not affected by weather and illumination, and has excellent all-weather and all-day working capacity. In which a frequency modulated continuous wave radar (FMCW) detects a distance and a speed of an object by calculating a frequency difference between a chirp-modulated transmission signal and a reception signal. Because the bandwidth of the received difference frequency signal can be reduced greatly, compared with a typical pulse Doppler radar, the FMCW millimeter wave radar can reduce the complexity of signal processing; compared with other sensors for special application, the FMCW millimeter wave radar has the advantages of low false alarm rate, high distance resolution, low transmitting power, low cost, simple structure and the like.

The MTD filter designed based on the array grating lobe can further reduce the influence of grating lobe clutter and further improve the detection capability of weak and small targets.

The invention utilizes the characteristic of vehicle motion, can only observe the normal direction, realizes the detection of the whole scene along with the vehicle movement, can equivalently scan the scene as a needle-shaped wave beam, and only adopts one-dimensional CFAR processing during the detection, thereby greatly saving the calculated amount.

Drawings

Fig. 1 is a flow chart of the operation of a parabolic antenna in the prior art.

FIG. 2 is a diagram of an embodiment of the detecting device of the present invention in a specific application.

FIG. 3 is a flow chart of an embodiment of a detection method of the present invention.

Fig. 4 is a schematic diagram of increasing the aperture without changing the number of the array elements.

FIG. 5 is a flowchart of an embodiment of a grating lobe clutter suppression method of the present invention.

Illustration of the drawings: 1. moving the trolley; 2. an antenna; 3. a runway.

Detailed Description

The invention is further described below with reference to the figures and the specific embodiments of the description.

As shown in fig. 2, the FOD detection device based on the vehicle-mounted distributed aperture radar of the present embodiment is used for FOD detection of an airport, and specifically includes a moving trolley 1 and a radar unit having a plurality of antennas 2, wherein the moving direction of the moving trolley 1 is parallel to an airport runway 3; the antennas 2 are uniformly arranged on the moving trolley 1 at intervals and used for transmitting detection signals to the airport runway 3; the plurality of antennas 2 form a sparse large aperture antenna to synthesize a beam with a narrower main lobe beamwidth (relative to the single antenna 2) to improve the signal-to-noise ratio of the target echo. Wherein the radar unit adopts a millimeter wave radar of linear frequency modulation continuous waves; the moving trolley 1 is an unmanned trolley and the like.

According to the invention, a vehicle-mounted distributed aperture millimeter wave radar is adopted, and a plurality of small-aperture radar antennas 2 are arranged on the side of the vehicle body of the moving trolley 1 to form a large sparse aperture antenna (antenna array), so that an extremely narrow beam main lobe can be synthesized, the signal-to-noise ratio of target echoes in a beam is improved, the clutter energy in the main beam is reduced, and the key index, namely the small target detection capability, faced by the FOD application at present can be obviously improved.

The invention adopts a millimeter wave radar system of linear frequency modulation continuous waves. When the millimeter waves are transmitted by utilizing an atmospheric window (when the millimeter waves and the submillimeter waves are transmitted in the atmosphere, certain frequency with minimum attenuation caused by resonance absorption of gas molecules is small), the attenuation is small, and the influence of natural light and a heat radiation source is small; the millimeter wave radar is not affected by weather and illumination, and has excellent all-weather and all-day working capacity. In which a frequency modulated continuous wave radar (FMCW) detects a distance and a speed of an object by calculating a frequency difference between a chirp-modulated transmission signal and a reception signal. Because the bandwidth of the received difference frequency signal can be reduced greatly, compared with a typical pulse Doppler radar, the FMCW millimeter wave radar can reduce the complexity of signal processing; compared with other sensors for special application, the FMCW millimeter wave radar has the advantages of low false alarm rate, high distance resolution, low transmitting power, low cost, simple structure and the like.

As shown in fig. 3, the invention also discloses a detection method of the FOD detection device based on the vehicle-mounted distributed aperture radar, which comprises the following steps:

1) acquiring target echo signals received by each radar antenna 2; wherein the target echo signal is obtained by returning FMCW pulse signals transmitted by a plurality of radar antennas 2;

2) synthesizing a plurality of target echo signals into a radar beam with a narrower main lobe beam width;

3) and processing the radar beam to obtain a detection result.

According to the detection method, the radar beam with the narrower main lobe beam width is synthesized by the target echo signals, the signal-to-noise ratio of the target echo in the beam is improved, the clutter energy in the main beam is reduced, and the key index, namely the small target detection capability, in the FOD application at present can be remarkably improved.

Further, in the process of implementing the present invention, it is found that when a sparse aperture radar is used, that is, the number of antenna array elements is kept unchanged, if the aperture of the antenna array is enlarged, grating lobes will appear at this time, that is, side lobes with an amplitude lower than that of the main lobe or even the same height will appear, as shown in fig. 4, when the aperture of the antenna array is continuously enlarged, the number of grating lobes will be further increased, and the grating lobe interval will be reduced, which results in the following: clutter of the original side lobe may appear at the grating lobe position, and the echo of the clutter is enhanced to compete with a target in the main lobe.

It is noted that the positions of the grating lobes formed can be calculated from the antenna array. Simultaneously, there is the difference in grating lobe position and mainlobe position all with the relative speed of radar, so this embodiment suppresses grating lobe department clutter in pulse dimension or time domain through designing MTD (moving target) filter, and then adopts the space-time filter to realize the clutter suppression, and concrete process is:

because the synthesized radar beam points to the normal direction, the beam forming weight is directly added to each array element to obtain the output of the beam after synthesis. Suppose that the outputs of the respective antennas 2 are denoted x respectively₁,x₂,...x_NWherein N is the total number of all the antennas 2 with sparse apertures; the beam forming weight is:

W=[1,1...,1]^H

wherein the superscript H denotes the conjugate transpose, i.e. the beamforming weighting vector is a full 1 vector, the resulting output is:

y_m=x₁+x₂...x_N

wherein y is_mThe M represents the pulse number, the value of which is more than 1 and less than M, and M is the number of pulses in one CPI (coherent processing interval);

according to the position of the array, the grating lobe position of the sparse array when the current beam points to the normal can be calculated, and the assumed grating lobe position theta₁,...θ_LAccording to the measured value of the current vehicle speed, the clutter relative speeds at the grating lobes are respectively v₁,...v_LWherein:

V_l=2vsinθ_l/λ

wherein lambda is wavelength, L ranges from 1 to L, and L is clutter number at grating lobe, and based on the above information, time domain filter weight w can be designed_t;

The range-doppler matrix available for detection is then:

Y=[y₁,y₂...y_M]w_t。

the MTD filter based on the array grating lobe design can further reduce the influence of grating lobe clutter and further improve the weak and small target detection capability.

Further, after outputting distance dimensional data by a distance-doppler matrix, a detection result is obtained by one-dimensional CFAR (constant false alarm probability) processing. The invention utilizes the characteristic of vehicle motion, can only observe the normal direction, realizes the detection of the whole scene along with the vehicle movement, can equivalently scan the scene as a needle-shaped wave beam, and only adopts one-dimensional CFAR processing during the detection, thereby greatly saving the calculated amount.

The invention further discloses a detection system corresponding to the detection method, which specifically comprises the following steps:

the first module is used for acquiring target echo signals received by each radar antenna 2; wherein the target echo signal is obtained by returning FMCW pulse signals transmitted by a plurality of radar antennas 2;

a second module for synthesizing the plurality of target echo signals into a radar beam with a narrower main lobe beam width;

and the third module is used for processing the radar beam to obtain a detection result.

The detection system of the invention also has the advantages of the detection method.

The invention also discloses a computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, performs the steps of the detection method as described above. The invention further discloses a computer device comprising a memory and a processor, the memory having stored thereon a computer program which, when executed by the processor, performs the steps of the detection method as described above. All or part of the flow of the method of the embodiments may be implemented by a computer program, which may be stored in a computer-readable storage medium and executed by a processor, to implement the steps of the embodiments of the methods. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer readable medium may include: any entity or device capable of carrying computer program code, recording medium, U.S. disk, removable hard disk, magnetic disk, optical disk, computer Memory, Read-Only Memory (ROM), Random Access Memory (RAM), electrical carrier wave signals, telecommunications signals, software distribution media, and the like. The memory may be used to store computer programs and/or modules, and the processor may perform various functions by executing or executing the computer programs and/or modules stored in the memory, as well as by invoking data stored in the memory. The memory may include high speed random access memory, and may also include non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), at least one magnetic disk storage device, a Flash memory device, or other volatile solid state storage device.

The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.