MIMO-SAR airport runway imaging system

Abstract

The application relates to a MIMO-SAR airport runway imaging system and relates to the field of imaging, which comprises two rows of transmitting array elements, corner reflectors, two rows of receiving array elements and an image inversion module; the two rows of transmitting array elements are arranged on the two sides of the bottom of an airport runway respectively; the corner reflectors are installed on the two sides of the airport runway; the two rows of receiving array elements are fixed on the wings of an airplane in a uniform arrangement mode; each transmitting array element is used for transmitting a first signal and a second signal, the signal strength of the first signal is larger than that of the second signal, the first signal is emitted towards the airport runway, the first signal forms a reflected wave through the corner reflectors and is received by the receiving array element, the second signal is emitted towards an airplane to be landed, and the second signal is received by the receiving array element as a direct wave; and the image inversion module reconstructs runway light distribution images on the two sides of the airport runway based on a matched filtering algorithm. The application obtains the distribution images of the runway lights on the two sides of the airport runway.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of imaging technology, in particular to a MIMO-SAR airport runway imaging system. BACKGROUND

[0002] Blind landing of an airplane refers to guiding the airplane to land by an instrument landing system (ILS) under low weather standards or weather that the pilot cannot see any visual reference. Unlike visual approach under normal weather, this method realizes the guidance of a heading path and a glide path by radio signals emitted from the ground, provides a fixed glide line and minimum path deviation for the airplane landing, establishes a virtual path from the runway to the sky, and indicates the deviation of the airplane from the virtual path by instruments, so that the pilot adjusts the direction of the airplane according to the deviation, thereby allowing the pilot to land without seeing the actual scene outside the cockpit.

[0003] For blind landing of the I, II, IIIA and IIIB standards, the pilot still needs to visually land after the ILS assisted landing to a certain height, and there are limitations of the decision height and the runway visual range. The III C blind landing has no visual limitation, but there are very few airports with the III C standard qualification, and the accuracy of the equipment and instruments and the technical requirements of the crew are very high. From the perspective of the pilot, it is more desirable to see the runway and other ground features that can be identified to determine whether the airplane is on the correct route, and a method is needed to provide the pilot with intuitive visual perception conditions under adverse weather conditions. SUMMARY

[0004] The purpose of the present application is to provide a MIMO-SAR airport runway imaging system, which obtains the distribution image of the runway lights on both sides of the airport runway, and reduces the risk of blind landing of the airplane under low weather standards.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] The MIMO-SAR airport runway imaging system comprises two rows of transmitting array elements, corner reflectors, two rows of receiving array elements and an image inversion module; the two rows of transmitting array elements are arranged on the two sides of the bottom of the airport runway, the bottom of the airport runway is the end of the airport runway opposite to the direction of the aircraft landing movement, and the two rows of transmitting array elements are located on a straight line perpendicular to the direction of the airport runway; the corner reflectors are installed at the bottom of each runway light on the two sides of the airport runway; the two rows of receiving array elements are fixed on the wings of the aircraft on the two sides in a uniform arrangement; each transmitting array element is used for transmitting a first signal and a second signal, the signal strength of the first signal is greater than that of the second signal, the first signal is transmitted towards the airport runway, the first signal forms a reflected wave through the corner reflectors and is received by the receiving array element, and the second signal is transmitted towards the aircraft to be landed and is received by the receiving array element as a direct wave; the receiving array element on the aircraft to be landed and the two rows of transmitting array elements at the bottom of the airport runway form a MIMO array; and the image inversion module is used for reconstructing the runway light distribution image on the two sides of the airport runway based on a matched filtering algorithm according to the reflected wave and the direct wave.

[0007] Optionally, the transmitting signals of each transmitting array element are distinguished by using a wideband pseudo-code modulation signal.

[0008] Optionally, each receiving array element distinguishes the direct wave and the reflected wave by the time difference of the arrival of the received signals.

[0009] Optionally, each receiving array element is used for generating the same local pseudo-code as the corresponding transmitting array element, and different received signals are distinguished by the local pseudo-codes.

[0010] Optionally, each receiving array element comprises a receiving antenna, a low-noise amplifier, a band-pass filter, a phase compensation circuit, a mixer, an intermediate frequency signal amplifier, an intermediate frequency filter, an A / D converter and a despreading module.

[0011] After the reflected wave is received by the receiving antenna, the reflected wave is sequentially input into the first input end of the mixer through the low-noise amplifier and the band-pass filter; after the direct wave is received by the receiving antenna, the direct wave is sequentially input into the second input end of the mixer as a local oscillation signal through the low-noise amplifier, the band-pass filter and the phase compensation circuit, and the output signal of the mixer is sequentially input into the intermediate frequency signal amplifier, the intermediate frequency filter, the A / D converter and the despreading module to obtain a digital baseband signal matched with the transmitting array element, and the image inversion module is used for reconstructing the runway light distribution image on the two sides of the airport runway according to each digital baseband signal.

[0012] According to the embodiments of the present application, the following technical effects are provided:

[0013] The application discloses a MIMO-SAR (Multi-Input Multi-Output Synthetic Aperture Radar) airport runway imaging system, a receiving array element on a landing aircraft and two rows of transmitting array elements at the bottom of an airport runway form a MIMO array, the transmitting array elements transmit two-way signals of different strengths, the strong transmitting signals are transmitted towards the aircraft runway, are reflected by corner reflectors of two-side runway lights and are received by the receiving array element on the aircraft wing, the weak transmitting signals are directly transmitted to the receiving array element on the aircraft wing, and a distribution image of the two-side runway lights of the airport runway is reconstructed based on a matched filtering algorithm according to reflected waves and direct waves by an image inversion module, so that the distribution image of the two-side runway lights of the airport runway is obtained, and the risk of blind landing of the aircraft is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description only only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on these drawings.

[0015] Figure 1 It is a structural schematic diagram of the MIMO-SAR airport runway imaging system of the present application.

[0016] Figure 2 It is a geometric structure schematic diagram in the airport runway imaging of the present application.

[0017] Figure 3 It is a distribution image schematic diagram of the two-side runway lights of the airport runway of the present application.

[0018] Symbol explanation:

[0019] 1-airport runway, 2-transmitting array element, 3-runway light, 4-corner reflector, 5-receiving array element. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments only are some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0021] The purpose of the present application is to provide a MIMO-SAR airport runway imaging system, which obtains the distribution image of the two-side runway lights of the airport runway and reduces the risk of blind landing of the aircraft.

[0022] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0023] Figure 1 A structural schematic diagram of a MIMO-SAR airport runway imaging system according to the present application is shown in FIG. 1, which comprises two rows of transmitting array elements 2, corner reflectors 4, two rows of receiving array elements 5 and an image inversion module. Figure 1

[0024] The two rows of transmitting array elements 2 are respectively arranged on the two sides of the bottom of the airport runway 1, the bottom of the airport runway 1 is the end of the airport runway 1 opposite to the direction of the landing movement of the aircraft, and the two rows of transmitting array elements 2 are located on a straight line perpendicular to the direction of the airport runway 1; the corner reflectors 4 are installed at the bottom of each runway light 3 on the two sides of the airport runway 1, and the corner reflectors 4 face the direction opposite to the incoming direction of the aircraft to be landed, the corner reflectors 4 are used to enhance the reflection coefficient and highlight the positions of the runway lights 3 in the SAR image; the two rows of receiving array elements 5 are respectively fixed on the wings of the aircraft in a uniform arrangement, and the arrangement direction of the receiving array elements 5 on the wings is the length direction of the wings.

[0025] Each transmitting array element 2 is used to transmit a first signal and a second signal, the signal strength of the first signal is greater than that of the second signal, the first signal is transmitted towards the airport runway 1, the first signal forms a reflected wave through the corner reflector 4 and is received by the receiving array element 5, and the second signal is transmitted towards the aircraft to be landed and is received by the receiving array element 5 as a direct wave; the receiving array element 5 on the aircraft to be landed and the transmitting array element 2 at the bottom of the airport runway form a MIMO array; the image inversion module is used to reconstruct the distribution image of the runway lights 3 on the two sides of the airport runway 1 according to the reflected wave and the direct wave based on a matched filtering algorithm.

[0026] The image inversion module is arranged at the aircraft end, and the aircraft end displays the distribution image of the runway lights 3 on the two sides of the airport runway 1 formed by the image inversion module.

[0027] The transmitting signals of each transmitting array element 2 are distinguished by using wideband pseudo-code modulation signals.

[0028] Each receiving array element 5 is used to generate the same local pseudo-code as the corresponding transmitting array element 2, and different transmitting signals (signal channels) are distinguished by using the local pseudo-codes, that is, the transmitting signals of different transmitting array elements 2 are distinguished.

[0029] Each receiving array element 5 is used to distinguish the direct wave and the reflected wave by the time difference of the arrival of the receiving signals. The relative distance between the receiving array element 5 and the transmitting array element 2 is determined by GNSS positioning, and the direct wave signal is compensated by using the relative distance to compensate the phase of the direct wave signal, and the compensated direct wave signal is used as the local oscillator signal of the receiving array element 5.

[0030] ​Each receiving element 5 comprises a receiving antenna, a low-noise amplifier, a band-pass filter, a phase compensation circuit, a mixer, an intermediate frequency signal amplifier, an intermediate frequency filter, an A / D converter and a despreading module.

[0031] After the reflected wave is received by the receiving antenna, it sequentially passes through the low-noise amplifier and the band-pass filter to input the first input end of the mixer; after the direct wave is received by the receiving antenna, it sequentially passes through the low-noise amplifier, the band-pass filter and the phase compensation circuit to input the second input end of the mixer as the local oscillator signal, and the output signal of the mixer sequentially passes through the intermediate frequency signal amplifier, the intermediate frequency filter, the A / D converter and the despreading module to obtain the digital baseband signal matched with the transmitting element 2. The image inversion module is used to reconstruct the distribution image of the runway lights 3 on both sides of the airport runway 1 according to the digital baseband signals. Specifically, the image inversion module processes the digital baseband signals by a matched filtering algorithm, converts the integral operation in the wave number domain into the integral operation of the frequency, the aircraft elevation angle and the azimuth angle, and completes the reconstruction of the distribution image of the runway lights 3 on both sides of the airport runway 1.

[0032] The position of the aircraft can be obtained by the GNSS positioning system, with an error of about 1 meter in the distance direction and an error of about 10 meters in the height direction, but since the aircraft is far away from the airport, the error can be ignored.

[0033] The geometric configuration of the all-weather MIMO-SAR airport runway imaging system for aircraft blind landing guidance is shown in Figure 2 , wherein and respectively represent the spherical coordinates of the position of the mth transmitting element 2 and the nth receiving element 5, r m , θ m , respectively represent the radial distance, the zenith angle and the azimuth angle of the mth transmitting element 2, r n , θ n , respectively represent the radial distance, the zenith angle and the azimuth angle of the nth receiving element 5. The wideband pseudo-code phase modulation signal used by the MIMO-SAR airport runway imaging system is used to identify different transmitting elements 2 by the receiving elements 5, and the matched intermediate frequency signal enters the image inversion module. The wideband pseudo-code phase modulation process has no effect on the image inversion algorithm, so the calculation process of the wideband pseudo-code phase modulation in the transceiver signal is ignored. Therefore, the transmitting signal of each transmitting element 2 is uniformly represented as:

[0034] s m (t)=u m (t)·e j2πfmt (1)

[0035] In the formula, u m (t) is the complex envelope of the transmitting signal, f mis the carrier frequency, t represents time.

[0036] The signal emitted by the mthtransmitting element 2 is located in the spherical coordinate r, θ, respectively represent the radial distance, the zenith angle and the azimuth angle, and the scattering coefficient is The angular reflector 4 of the runway light 3 on the two sides of the airplane runway 1 reflects the signal emitted by the mthtransmitting element 2, which is received by the nthreceiving element 5, and the time delay is τ mn = (r mp + r pn ) / c, r mp is the distance from the mthtransmitting element 2 to the runway light 3, r pn is the distance from the runway light 3 to the nthreceiving element 5, and c is the speed of light.

[0037] Assuming that the runway light 3 is located in the imaging space V, the signal received by the nthreceiving element 5 through the reflection of the mthtransmitting element 2 on the runway light 3 is:

[0038]

[0039] The received transmitting signal (2) is removed from the carrier frequency and correlated with formula (1), and the following formula is obtained:

[0040]

[0041] Where v mn (t) is the received intermediate frequency signal.

[0042] The Fourier transform is performed on both sides of formula (3), and the following formula is obtained:

[0043]

[0044] Where V mn (f) and U m (f) are the spectra of v mn (t) and u m (t) respectively, considering that the transmitter (transmitting element) is close to the target, and the receiver (receiving element) is far from the target, r m <<r m , r n , r m , r n are the distances from the runway light, the transmitting element, the receiving element to the origin in the spherical coordinate system respectively, then

[0045]

[0046] According to the far field approximation, and Where and Position vector to the position vector and the position vector , then

[0047]

[0048]

[0049] The frequency domain filtering is performed on the formula (7), and the filtering factor is:

[0050]

[0051] The filtering result is:

[0052]

[0053] wherein,

[0054]

[0055] wherein, x, y, z are runway light coordinates in the rectangular coordinate system.

[0056] The formula (10) is substituted into the formula (9) to obtain:

[0057]

[0058] wherein,

[0059]

[0060] The formula (11) can be written as

[0061]

[0062] The formula (13) indicates the Fourier transform relationship between the target image and the wave number domain echo signal G mn (k x ,k y ,k z ). With a transmitting signal having a certain bandwidth and a multiple snapshot of the transmitting array, the distribution range of the echo sample in the wave number domain is large enough, and then the target image can be obtained by performing the Fourier transform on the wave number domain echo G mn (k x ,k y ,k z ).

[0063] The size of the support domain of the echo sample directly affects the imaging resolution; a larger support domain results in better imaging. To achieve sufficient resolution, a sufficient number of uniformly arranged transmitting array elements 2 are installed on airport runway 1, and a sufficient number of uniformly arranged receiving array elements 5 are installed on the aircraft wings. Assume there are M transmitting array elements 2, N receiving array elements 5, and Q frequency sampling points. Each pair of transmitting and receiving array elements forms a channel, resulting in an echo spatial spectrum of M*N*Q points. A sufficient number of transmitting and receiving array elements ensures a sufficiently large wavenumber domain distribution in the echo sample, while a uniform distribution makes the wavenumber domain distribution as uniform and compact as possible.

[0064] The role of the image inversion module is to reconstruct the target image. According to equation (13), theoretically, the target image can be inverted from the echo through Fourier transform. However, since the aircraft undergoes variable speed motion during landing, the position of the receiver on the aircraft wing changes non-uniformly, resulting in a non-uniform wavenumber domain distribution. This makes it difficult to perform target image inversion using traditional FFT processing. Matched filtering, as a universal and robust inversion technique, is applicable to most systems. Therefore, this invention adopts an inversion method based on matched filtering to reconstruct the image.

[0065] Based on airspace target images With wavenumber domain echo G mn (k x ,k y ,k z Theoretically, by performing a Fourier transform on equation (13), the target image can be inverted from the echo.

[0066]

[0067] Matched filtering technology can be used to invert images. This invention uses multiple sets of transmitters and multiple sets of receivers for observation and imaging. The transmitting array elements 2 on both sides of the bottom of the fixed airport runway 1 are fixed, i.e., the transmitting array elements 2... Since it is known, the variable in equation (14) is the position and orientation of the receiving array element 5. Therefore, equation (14) can be expressed in the wavenumber domain (k... x ,k y ,k z The internal integration operation is converted to an operation on frequency f and aircraft pitch angle θ. n Aircraft azimuth This significantly reduces the amount of computation, thereby improving computational efficiency.

[0068] The launch array elements 2 on both sides of the bottom end of the airport runway 1 in the application are fixed, and about ten are installed to ensure imaging resolution. The receiving array elements 5 on the wings of the aircraft need to be installed on each aircraft, and four receiving array elements 5 are installed on each wing of the aircraft to reduce costs as much as possible under the condition of ensuring imaging resolution. The launch array elements 2 on the airport runway 1 and the receiving array elements 5 on the wings of the aircraft are uniformly arranged, and the target of the airport runway light 3 is imaged in continuous time, so that better imaging results can be obtained, and the complete phase information is retained in the image inversion process based on matched filtering. Therefore, the application can provide reliable and accurate airport runway 1 information for aircraft blind landing in low-standard weather, and reduce the risk of aircraft blind landing due to unclear ground runway information.

[0069] Embodiments of the application will be described in detail below.

[0070] Taking a large passenger aircraft as an example, the wing width is 30 meters, and taking a large 4E-class airport as an example, the runway length is generally more than 3000 meters, and the runway width is generally 45-60 meters.

[0071] The imaging system geometry for simulation is shown in Figure 2 The center of the runway is taken as the coordinate origin, the initial position of the aircraft is assumed to be located at a horizontal distance of 5000 m and a height of 2000 m from the center of the airport runway, 1000 m of runway length and 50 m of runway width are set in the simulation, an angle reflector is installed on each runway light at a distance of 100 m on both sides of the runway, and 5 are installed on each side, i.e. 10 target points. Two launch array elements are installed on both sides of the bottom end of the runway. The launch signal adopts a wideband pseudo-code modulation signal, the aircraft descends at a height of 25 meters per second and moves horizontally at a speed of 50 meters per second, and the airport runway light targets are imaged in 20 seconds. Table 1 lists the simulation data.

[0072] Table 1 lists the simulation data

[0073]

[0074] The imaging results after matched filtering Figure 3 As shown in the figure, the target imaging position is accurate and can be matched with the coordinate position of the runway light.

[0075] The MIMO-SAR airport runway imaging system for aircraft blind landing guidance proposed in the application belongs to the technical field of microwave imaging, has the advantages of all-weather and all-day, and can achieve high resolution in the range direction and the azimuth direction by using the distributed transmitters and receivers of the MIMO array, so that the target distribution image information can be accurately obtained in the detection of the runway light targets on both sides of the airport runway. Reliable airport runway information is provided for the crew in the blind landing in bad weather.

[0076] The various embodiments described in this specification are intended to be exemplary only. The various embodiments were chosen and described in order to best explain the principles of the application and its practical application, to thereby enable others skilled in the art to best utilize the application, and to best enable the present application to be performed with determination by those skilled in the art.

[0077] The principles and implementations of the present application are described in the specific examples in this specification, and the above examples are only used to help understand the system of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation and application range will be changed. In view of the above, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A MIMO-SAR airport runway imaging system, characterized in that, The application relates to a signal transmission and image inversion system for airport runway. The system comprises two rows of transmitting array elements, corner reflectors, two rows of receiving array elements and an image inversion module. The two rows of transmitting array elements are arranged on the two sides of the bottom of an airport runway, the bottom of the airport runway is the end of the airport runway opposite to the direction of the landing movement of an airplane, and the two rows of transmitting array elements are located on a straight line perpendicular to the direction of the airport runway; the corner reflectors are installed at the bottom of each runway light on the two sides of the airport runway; the two rows of receiving array elements are fixed on the wings of the airplane in a uniform arrangement; each transmitting array element is used for transmitting a first signal and a second signal, the signal strength of the first signal is greater than that of the second signal, the first signal is transmitted towards the airport runway, the first signal forms a reflected wave through the corner reflectors and is received by the receiving array elements, and the second signal is transmitted towards the airplane to be landed and is received by the receiving array elements as a direct wave; the receiving array elements on the airplane to be landed and the two rows of transmitting array elements at the bottom of the airport runway form a MIMO array; and the image inversion module is used for reconstructing the runway light distribution image on the two sides of the airport runway based on a matched filtering algorithm according to the reflected wave and the direct wave.

2. The MIMO-SAR airport runway imaging system of claim 1, wherein, The transmitting signals of each transmitting array element are distinguished by using wideband pseudo-code modulation signals.

3. The MIMO-SAR airport runway imaging system of claim 1, wherein, Each receiving array element distinguishes the direct wave and the reflected wave by the time difference of the arrival of the received signals.

4. The MIMO-SAR airport runway imaging system of claim 1, wherein, Each receiving array element is used for generating the same local pseudo-code as the corresponding transmitting array element, and different received signals are distinguished by the local pseudo-codes.

5. The MIMO-SAR airport runway imaging system of claim 1, wherein, Each receiving array element comprises a receiving antenna, a low-noise amplifier, a band-pass filter, a phase compensation circuit, a mixer, an intermediate frequency signal amplifier, an intermediate frequency filter, an A / D converter and a despreading module. After the reflected wave is received by the receiving antenna, the reflected wave is sequentially input into the first input end of the mixer through the low-noise amplifier and the band-pass filter; after the direct wave is received by the receiving antenna, the direct wave is sequentially input into the second input end of the mixer as a local oscillation signal through the low-noise amplifier, the band-pass filter and the phase compensation circuit, and the output signal of the mixer is sequentially input into the intermediate frequency signal amplifier, the intermediate frequency filter, the A / D converter and the despreading module to obtain digital baseband signals matched with the transmitting array elements, and the image inversion module is used for reconstructing the runway light distribution image on the two sides of the airport runway according to the digital baseband signals.

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