Imaging radar system for monitoring and early warning of railway tunnel entrance and exit end face collapse

Abstract

The present application relates to the technical field of railway tunnel safety monitoring, and particularly relates to an imaging radar system suitable for railway tunnel entrance and exit end face collapse early warning. The system comprises a servo mechanism, a Ku-band radar subsystem, a Ka-band radar subsystem and a warning module deployed on a host computer. The servo mechanism comprises a rotating arm and a fixed base. The Ku-band radar subsystem is installed on the rotating arm and is used to realize imaging of the railway tunnel entrance and exit area by using two-dimensional arc scanning synthetic aperture imaging technology, obtain deformation information of the target by long-term observation and send the deformation information to the host computer. The Ka-band radar subsystem is installed on the fixed base and is used to realize fixed-point instantaneous observation of multiple points of the railway tunnel entrance and exit by using one-dimensional real aperture micro-deformation measurement technology, obtain deformation information of the target and send the deformation information to the host computer. The warning module is used to fuse and process the two types of deformation information, judge the possibility of collapse and perform early warning.

Description

Technical Field

[0001] This invention relates to the field of railway tunnel safety monitoring technology, and in particular to an imaging radar system for monitoring and early warning of collapses at the entrance and exit faces of railway tunnels. Background Technology

[0002] Deformation at the entrance and exit faces of railway tunnels is a deformation phenomenon caused by natural or human factors. When the deformation reaches a certain level, it can lead to serious consequences such as settlement and collapse, severely affecting the safety of railway construction and operation. Therefore, deformation monitoring has become an important means of preventing collapses at the entrances and exits of railway tunnels.

[0003] Common methods for monitoring deformation at the entrance and exit faces of railway tunnels can be divided into two categories based on their working principles and characteristics: The first category measures the deformation at a single point, estimating the deformation information of the entire target area through this single-point measurement. Common methods include levels, theodolites, and GPS measuring instruments. The second category involves direct planar measurement. This method can not only obtain high-precision deformation data of the target area but also information such as deformation trends. This monitoring technology is represented by laser point cloud mapping and ground-based radar differential interferometry. Compared with traditional single-point measurement methods, it has advantages such as a wider monitoring range, higher sampling rate, and fully automated monitoring process. Among the second type of methods, laser point cloud mapping is easily affected by weather conditions such as rain and fog, while ground-based radar observation can be conducted around the clock and in all weather conditions, making it an important technical means for observing deformation in complex areas under complex weather conditions. Summary of the Invention

[0004] The purpose of this invention is to monitor the deformation of the tunnel entrance and exit faces. This monitoring includes two parts: (1) long-term observation of the deformation trend of the tunnel entrance; and (2) instantaneous deformation of the tunnel entrance face when a vehicle passes through. This invention integrates ground-based arc scanning synthetic aperture imaging technology and static high repetition rate fixed-point observation technology to achieve long-term and instantaneous observation of the tunnel entrance. The health status of the tunnel entrance face is judged from the long-term deformation data and the instantaneous impact response data when a vehicle passes through.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution.

[0006] This invention provides an imaging radar system for monitoring and early warning of collapses at the entrance and exit faces of railway tunnels.

[0007] The system includes: a servo mechanism, a Ku-band radar subsystem, a Ka-band radar subsystem, and an early warning module deployed on a host computer;

[0008] The servo mechanism includes: a rotating arm and a stationary base;

[0009] The Ku-band radar subsystem is mounted on the rotating arm and is used to image the entrance and exit areas of the railway tunnel using two-dimensional arc-scan synthetic aperture imaging technology. It obtains the deformation information of the target through long-term observation and sends it to the host computer.

[0010] The Ka-band radar subsystem is installed on the fixed base and is used to achieve fixed-point instantaneous observation of multiple points at the entrance and exit of the railway tunnel using one-dimensional real aperture micro-deformation measurement technology, obtain the deformation information of the target and send it to the host computer.

[0011] The early warning module is used to fuse the two types of deformation information, determine the possibility of a landslide, and issue an early warning. The system processes the two types of deformation information in real time and issues an early warning when the deformation exceeds the target value.

[0012] As an improvement to the above technical solution, the Ku-band radar subsystem includes: a Ku-band transmitting device, a Ku-band receiving device, and a Ku-band data acquisition and processing device; wherein,

[0013] The Ku-band transmitting device is used to generate and transmit Ku-band stepped-frequency continuous wave signals;

[0014] The Ku-band receiving device is used to receive the echo signal reflected by the target from the Ku-band stepped frequency continuous wave signal and transmit it to the Ku-band data acquisition and processing device.

[0015] The Ku-band data acquisition and processing device is used to process the echo signal of the Ku-band stepped frequency continuous wave signal to obtain the deformation information of the target.

[0016] As an improvement to the above technical solution, the Ku-band transmitting device includes: a first frequency synthesizer, a Ku-band transmitting link, and a Ku-band transmitting antenna; the Ku-band transmitting antenna includes: a Ku-band H-polarized transmitting antenna and a Ku-band V-polarized transmitting antenna; wherein,

[0017] The first frequency synthesizer is used to transmit a Ku-band stepped-frequency continuous wave signal;

[0018] The Ku-band transmission link is used to amplify and filter the Ku-band stepped-frequency continuous wave signal before transmitting it to the Ku-band H-polarized transmitting antenna and the Ku-band V-polarized transmitting antenna.

[0019] The Ku-band H-polarized transmitting antenna and the Ku-band V-polarized transmitting antenna are used to transmit the processed Ku-band stepped-frequency continuous wave signal in H-polarization and V-polarization, respectively.

[0020] As an improvement to the above technical solution, the Ku-band receiving device includes: a Ku-band receiving antenna and a Ku-band receiving link; the Ku-band receiving antenna includes: a Ku-band H-polarized receiving antenna and a Ku-band V-polarized receiving antenna; the Ku-band receiving link includes: a Ku-band H-polarized receiving channel and a Ku-band V-polarized receiving channel; wherein,

[0021] The Ku-band H-polarized receiving antenna and the Ku-band V-polarized receiving antenna are used to receive the echo signals reflected by the target from the Ku-band stepped frequency continuous wave signals transmitted by the Ku-band H-polarized transmitting antenna and the Ku-band V-polarized transmitting antenna, respectively, and transmit them to the Ku-band H-polarized receiving channel and the Ku-band V-polarized receiving channel, respectively.

[0022] The Ku-band H-polarized receiving channel and the Ku-band V-polarized receiving channel are used to process the echo signals they receive and transmit them to the Ku-band data acquisition and processing device.

[0023] As an improvement to the above technical solution, the Ku-band radar subsystem uses arc-scan imaging observation to obtain the deformation information of the target, specifically including:

[0024] The Ku-band radar subsystem is used to perform arc scan observations by rotating the arm to obtain the synthetic aperture.

[0025] The synthetic aperture is processed to obtain a complex image;

[0026] Two images with pixels corresponding to the same observed target are selected for registration.

[0027] Interference fringe patterns are obtained from the two registered complex images, and the changes in micro-deformation are obtained by processing the complex images over time.

[0028] Extract the micro-deformation portion corresponding to the target from the phase image;

[0029] The entangled phase is then untangled in two dimensions to obtain the processed phase map.

[0030] Based on the processed phase diagram, deformation information is calculated through the correspondence between phase and distance.

[0031] As an improvement to the above technical solution, the Ka-band radar subsystem includes: a Ka-band transmitter, a Ka-band receiver, and a Ka-band data acquisition and processing device; wherein,

[0032] The Ka-band transmitting device is used to generate and transmit Ka-band frequency-modulated continuous wave signals.

[0033] The Ka-band receiving device is used to receive the echo signal reflected by the target from the Ka-band frequency-modulated continuous wave signal and transmit it to the data acquisition and processing device.

[0034] The Ka-band data acquisition and processing device is used to process the echo signal of the Ka-band frequency-modulated continuous wave signal to obtain the deformation information of the target.

[0035] As an improvement to the above technical solution, the Ka-band transmitting device includes: a second frequency synthesizer, a Ku-band transmitting link, and a Ka-band transmitting antenna; the Ka-band transmitting antenna includes: a Ka-band H-polarized transmitting antenna and a Ka-band V-polarized transmitting antenna; wherein,

[0036] The second frequency synthesizer is used to transmit Ka-band frequency-modulated continuous wave signals;

[0037] The Ka-band transmission link is used to amplify and filter the Ka-band frequency-modulated continuous wave signal before transmitting it to the Ka-band H-polarized transmitting antenna and the Ka-band V-polarized transmitting antenna.

[0038] The Ka-band H-polarized transmitting antenna and the Ka-band V-polarized transmitting antenna are used to transmit the processed Ka-band frequency-modulated continuous wave signal in H-polarization and V-polarization, respectively.

[0039] As an improvement to the above technical solution, the Ka-band receiving device includes: a Ka-band receiving antenna and a Ka-band receiving link; the Ka-band receiving antenna includes: a Ka-band H-polarized receiving antenna and a Ka-band V-polarized receiving antenna; the Ka-band receiving link includes: a Ka-band H-polarized receiving channel and a Ka-band V-polarized receiving channel; wherein,

[0040] The Ka-band H-polarized receiving antenna and the Ka-band V-polarized receiving antenna are used to receive the echo signals of the Ka-band frequency-modulated continuous wave signals transmitted by the Ka-band H-polarized transmitting antenna and the Ka-band V-polarized transmitting antenna, respectively, after being reflected by the target, and transmit them to the Ka-band H-polarized receiving channel and the Ka-band V-polarized receiving channel, respectively.

[0041] The Ka-band H-polarized receiving channel and the Ka-band V-polarized receiving channel are used to process the echo signals they receive and transmit them to the Ka-band data acquisition and processing device.

[0042] As one improvement to the above technical solution, the Ka-band radar subsystem obtains the deformation information of the target through fixed-point observation, specifically including:

[0043] Observation pulses are transmitted toward the target at a certain pulse repetition frequency;

[0044] Receive the echo signal data of each observation pulse;

[0045] Phase extraction is performed on the echo signal data of each observed pulse in chronological order;

[0046] The extracted phase is subjected to differential interferometry with the phase at the reference position.

[0047] The obtained phase is then unwrapped to obtain accurate phase information corresponding to the deformation information;

[0048] The phase is processed according to the correspondence between phase, wavelength and distance to obtain the deformation information of the target.

[0049] As an improvement to the above technical solution, the system is placed on the side of the entrance and exit of the railway tunnel, and the observation angle and scanning range are set according to the shape and height of the tunnel facade and slope protection.

[0050] The advantages of this invention compared to the prior art are:

[0051] 1. This invention selects a technical solution based on the characteristics of deformation at railway tunnel entrances, enabling simultaneous observation of long-term deformation trends and deformation under instantaneous impact from passing vehicles. By combining long-term and instantaneous observation data, the health status of railway tunnel entrances can be determined.

[0052] 2. This invention addresses the characteristics of deformation at railway tunnel entrances by employing a combined Ku / Ka band observation technique. The Ku band radar uses scanning imaging observation to improve the system's imaging resolution, while the Ka band radar uses fixed-point observation to improve the measurement accuracy of deformation at key points.

[0053] 3. This invention uses separate transmitting and receiving antennas to transmit frequency-modulated continuous waves and uses a descrambling method to reduce signal bandwidth, thereby reducing the sampling frequency;

[0054] 4. This invention employs two different radar signal formats in two frequency bands: the Ku band uses SFCW (Stepped Frequency Continuous Waveform) signals, and the Ka band uses FMCW (Frequency Modulated Continuous Wave) signals. SFCW signals are stable but have a slow sweep speed, making them suitable for long-term deformation trend observation. FMCW signals have a fast sweep speed, enabling high repetition rate observation, and are suitable for observing high-frequency impact vibration signals at tunnel entrances and exits when trains pass.

[0055] 5. The rotating arm length of the scanning imaging radar in this invention is adjustable, and different arm lengths can be used to form an interference baseline, which can be combined with two-dimensional imaging to obtain three-dimensional information of the railway tunnel entrance.

[0056] 6. The method and system proposed in this invention can adjust the radar's viewing angle, scanning angle, signal bandwidth, and repetition rate according to the distance between the observation position and the tunnel entrance, as well as the different viewing angles, which facilitates the installation.

[0057] 7. This invention supports synchronous observation with optical equipment, and the fusion of multi-source data facilitates the identification of deformed regions. Attached Figure Description

[0058] Figure 1 This is a block diagram illustrating the working principle of the system of this invention;

[0059] Figure 2 This is a schematic diagram of imaging radar measurement for monitoring and early warning of collapses at the entrance and exit faces of railway tunnels;

[0060] Figure 3 This is a schematic diagram of Ku-band radar arc scan imaging;

[0061] Figure 4(a) is a block diagram of the overall structure of the radar system of the present invention, Figure 4(b) is a block diagram of the Ku-band radar subsystem, and Figure 4(c) is a block diagram of the Ka-band radar subsystem. Detailed Implementation

[0062] Ground-based radar differential interferometry is a radar active imaging remote sensing technology that is developed based on stepped frequency continuous wave (SFCW) technology or frequency modulated continuous wave (FMCW) technology, synthetic aperture radar imaging technology and differential interferometry technology. It extracts deformation information by repeatedly observing the same target area at different time points to obtain time-series radar images.

[0063] The advantages of ground-based radar interferometry systems in monitoring local deformation are mainly reflected in three aspects:

[0064] First, the repeated observation cycle is short, which enables continuous monitoring of the deformed area at fixed points.

[0065] Secondly, it can achieve high spatial resolution and deformation measurement accuracy. Ground-based radar interferometry systems can achieve high-resolution imaging of target areas, with deformation measurement accuracy reaching the sub-millimeter level.

[0066] Third, it offers high flexibility and operability. Ground-based radar systems use the ground, buildings, or land vehicles as platforms, allowing for the selection of the optimal observation angle based on monitoring needs and the choice of observation time baseline according to the characteristics of the monitored target, demonstrating excellent flexibility and operability.

[0067] In summary, ground-based radar interferometry systems offer advantages such as regional, all-weather, all-time, fixed-point, continuous, and high-precision monitoring. They also possess excellent flexibility and operability. Their non-contact measurement method allows for the acquisition of deformation data of monitored hazardous areas within a safe distance. Furthermore, the acquired information, which is regional deformation information over a large area, is more helpful for understanding and predicting disasters than single-point deformation information, and thus has positive significance for predicting and preventing disasters.

[0068] Therefore, this invention relates to a rotatable dual-frequency ground-based interferometric radar system, wherein a Ku-band radar system is mounted at one end of a rotating wall for rotational measurements, while a Ka-band radar system remains stationary at the rotating base. The Ka and Ku-band radar systems are respectively frequency-modulated continuous wave and stepped-frequency continuous wave radar systems. By combining ground-based arc-scan synthetic aperture imaging technology and static high-repetition-rate fixed-point observation technology, long-term and instantaneous observations of tunnel entrances are achieved.

[0069] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0070] like Figure 1 The diagram shown is a block diagram illustrating the working principle of the system of this invention. This scheme utilizes a dual-frequency radar system mounted on a servo motor with rotation function to construct a ground-based interferometric radar. The Ku-band radar is mounted on a rotating arm with an adjustable length of 1.5-2.5 meters (different arm lengths correspond to different baseline lengths), while the Ka-band radar is mounted on a fixed base at the top of the rotating axis.

[0071] The Ku-band radar consists of a coherent microwave transmitter and receiver operating in the Ku band (center frequency 16.2 GHz, bandwidth 300 MHz), capable of transmitting and receiving stepped-frequency continuous wave (SFCW) signals. Both the transmitter and receiver include two antennas (H-polarized and V-polarized, for a total of four antennas). During operation, a servo mechanism rotates the Ku-band radar to a certain angle. The transmitter generates a stepped-frequency continuous wave signal, which is amplified and transmitted to the H-polarized transmitting antenna. Simultaneously, the transmitted signal is coupled to H-polarized receiving channel 1. The reference signal in receiving channel 1 is amplified, down-converted to an intermediate frequency (IF), and then sent to the digital unit (internal receiver processing, including deskewing). The same receiving process occurs in the V-polarized receiving channel. The V-polarized antenna receives the transmitted signal, amplifies it in receiving channel 2, down-converts it, and then sends it to the digital unit. The digital unit performs sampling, digital down-conversion, amplitude extraction, and phase extraction operations on the echo signals from receiving channels 1 and 2, respectively. After transmitting with H-polarization and receiving with H-polarization / V-polarization, the radar similarly performs V-polarization transmission and H-polarization / V-polarization reception. At each observation angle, the radar system completes two signal scans from low to high frequency, thus acquiring signals across two polarization bandwidths. After observation at one angle, the servo rotates the Ku-band radar to the next angle to repeat the next observation. Observations are performed sequentially at different observation angles within a predetermined scanning angle range, and the next scanning process is repeated after observations at all scanning angles are completed. The Ku-band radar system achieves a circular synthetic aperture by rotating its arm in the azimuth direction, thereby enabling two-dimensional resolution imaging of the tunnel entrance observation area. By repeatedly observing the target with the synthetic aperture and capturing its phase change, its deformation value can be obtained.

[0072] A Ka-band radar consists of a coherent microwave transmitter and receiver operating in the Ka band (center frequency 36 GHz, bandwidth 300 MHz), capable of transmitting and receiving frequency-modulated continuous wave (FMCW) signals. Both the Ka-band radar transmitter and receiver include two antennas (H-polarized and V-polarized, for a total of four antennas). During operation, the transmitter generates an FMCW signal, amplifies it, and transmits it to the H-polarized transmitting antenna. Simultaneously, the transmitted signal is coupled to H-polarized receiving channel 1. The reference signal in receiving channel 1 is amplified, down-converted to an intermediate frequency (IF), and then sent to the digital unit. The same receiving process occurs in the V-polarized receiving channel. The V-polarized antenna receives the transmitted signal, amplifies it, down-converts it, and then sends it to the digital unit after passing through receiving channel 2. The digital unit performs sampling, digital down-conversion, amplitude extraction, and phase extraction operations on the echo signals from receiving channels 1 and 2, respectively. After H-polarized transmission and H / V-polarized reception, the radar similarly performs V-polarized transmission and H / V-polarized reception. At an observation location, a Ka-band radar system performs observations at a specific pulse repetition frequency (PRF). Deformation information can be obtained by performing phase difference processing on the acquired time data sequence.

[0073] After determining the tunnel entrances and exits that need to be observed, the radar is placed to the side of the tunnel entrances and exits based on suitable locations on site. The observation angle and scanning range of the radar are set according to the shape and height of the tunnel facade and slope protection, and then observations are conducted at the tunnel entrances and exits. Figure 2 The image shown is a schematic diagram of imaging radar measurement for monitoring and early warning of collapses at the entrance and exit faces of railway tunnels.

[0074] Ku-band radar is an imaging radar that achieves circular synthetic aperture using an arc scanning method, such as... Figure 3 As shown. The radar azimuth direction is the direction of rotation, and the observation time is represented by η; the radar range direction is the line-of-sight direction, and the observation time is represented by τ. The antenna beamwidth is θ. BW Installed in a length of r a One end of the rotating arm has its antenna beam pointing towards the observation target. The other end of the rotating arm is fixed on the rotation axis O' at a height H. The rotational angular velocity is ω, therefore the azimuth coherent cumulative angle is θ = ωη. Assume there is a point target P, with position P(r) in cylindrical coordinates. p ,θ p When the turntable rotates, the antenna beam just illuminates the target at position A, and the antenna beam leaves the target at position B. The angle between PA and PB is the resultant aperture angle θ. sys The closest slant distance between the antenna and point P is R0, and the distance between the rotation center O' and point P is R. c The antenna forms a synthetic aperture through rotational motion, resulting in a ring-shaped imaging area on the ground. The three-dimensional geometry of the arc-scan imaging is as follows: Figure 3 As shown.

[0075] The minimum slant range between the radar and the point target can be obtained from the imaging geometry shown in the figure:

[0076]

[0077] The instantaneous slant range between the radar and the point target is:

[0078]

[0079] Ku-band radar transmits stepped-frequency continuous wave (SFCW). Let the carrier frequency start frequency be f0, the frequency step increment be Δf, and the number of frequency steps be N. Let t represent the signal time, and n be an integer from 0 to N-1. The transmitted signal can be expressed as:

[0080] S t (n,t)=w a (η)·exp[2π(f0+nΔf)t] (3)

[0081] The received signal scattered back to the radar from target P is:

[0082] S r (n,t,η)=w a (η)·exp[2π(f0+nΔf)(t-2R(η) / c)] (4)

[0083] The intermediate frequency signal obtained after quadrature demodulation is:

[0084]

[0085] The range signal properties of Ku-band radar depend on bandwidth, i.e., range resolution:

[0086]

[0087] Azimuth resolution is determined by the synthetic aperture angle θ sys The azimuth is determined by θ. n If the azimuth wave number is expressed as:

[0088] k u =2k·sin(θ) n (6)

[0089] in,

[0090] k=2π / λ (7)

[0091] The Doppler bandwidth generated by the antenna moving from the starting position A to the ending position B is:

[0092] Ω=k u (θA )-k u (θ B )=4ksin(θ sys / 2) (8)

[0093] Therefore, the azimuth resolution in the dimension of distance is:

[0094]

[0095] In triangle OPA, using the law of sines, we can obtain:

[0096]

[0097] The azimuth resolution can then be expressed as:

[0098]

[0099] Finally, the azimuth angular resolution is obtained as follows:

[0100]

[0101] As can be seen from the above formula, the angular resolution of arc scanning imaging does not change with distance, and the larger the rotation arm length and beamwidth, the higher the resolution.

[0102] The Ku-band radar signal processing process mainly consists of eight steps:

[0103] Step 1: Image Acquisition

[0104] After completing a scan of a circular aperture, the Ku-band radar can obtain a complex image by imaging the data. After scanning the aperture in sequence, the complex images can be combined into a complex image pair, and then the next registration process can be performed.

[0105] The second step is image registration.

[0106] Obtaining target interferometric information requires registering duplicate images, meaning that the pixels in both images must correspond to the same observed target.

[0107] Step 3: Interferogram Generation

[0108] Interference fringe patterns are obtained from the two registered complex images. By processing a series of complex images over time, the changes in micro-deformation can be observed.

[0109] Step 4: ROI Extraction

[0110] Extract the micro-deformation of interest from the phase image.

[0111] Step 5: Phase Untangling

[0112] When the displacement exceeds the wavelength of the signal, the phase will become entangled. In order to accurately recover the phase information, a two-dimensional untangling operation is performed on the entangled phase.

[0113] Step 6 Atmospheric Correction

[0114] Changes in atmospheric parameters such as temperature, humidity, and air pressure can cause deviations in phase measurements. These effects can be eliminated by using stable targets in the scene.

[0115] Step 7: Deformation Calculation

[0116] After obtaining the phase diagram, the deformation is calculated by the correspondence between phase and distance.

[0117] Step 8: Geocoding

[0118] Based on the geographical location and geometric relationship of the observed target, the observation results are mapped to the geographical coordinates of the tunnel entrance.

[0119] The basic principle of Ka-band radar observation is as follows:

[0120] Assume the incident electromagnetic wave signal is:

[0121]

[0122] Considering distance attenuation, the scattered signal can be expressed as:

[0123]

[0124] The scattering matrix can be described as:

[0125]

[0126] Taking VV polarization as an example (other HH, HV, and VH polarizations are similar), then:

[0127]

[0128] Scattering matrix components The echo signal is represented in complex signal form, namely:

[0129]

[0130] The target complex scattering coefficients are expressed as the product of amplitude and phase, i.e. The complex radar data from two consecutive observations in the interferometric process can then be represented as:

[0131]

[0132]

[0133] Multiplying the two signals by their conjugates yields the result.

[0134]

[0135] In the formula, σ1 and σ2 are the complex scattering coefficients of the target in the two observations, respectively, which are determined by the properties of the target itself. Therefore, the interferometric phase can be obtained as shown in the following formula: the phase includes the slant range before and after deformation, the frequency difference, and the scattering phase difference of the monitored target.

[0136]

[0137] When observing targets using Ka-band radar, the signals from two observations have a high correlation, so the difference in the target's scattering phase can be ignored. Therefore, the phase can be expressed as:

[0138]

[0139] The corresponding deformation can be obtained as follows:

[0140]

[0141] The Ka-band radar signal processing process mainly consists of five steps:

[0142] Step 1: Time Series Signal Acquisition

[0143] Phase extraction is performed on the data of each observation pulse in chronological order;

[0144] Second step: differential interferometry processing

[0145] Perform a difference operation between the phase and the phase at the reference position;

[0146] The third step is phase untangling.

[0147] The obtained phase is unwrapped to obtain accurate phase information corresponding to the deformation information;

[0148] Fourth step: Deformation inversion

[0149] The phase is processed according to the correspondence between phase, wavelength, and distance;

[0150] Step 5: Geocoding

[0151] Obtain observation location information and perform geographic coordinate mapping.

[0152] Figure 4(a) shows the overall structural block diagram of the radar system according to an embodiment of the present invention. The structural block diagram of the Ku-band radar subsystem is shown in Figure 4(b), and the structural block diagram of the Ka-band radar subsystem is shown in Figure 4(c).

[0153] During the geographic matching process, corner reflectors can be installed at the tunnel entrance and exit faces as selective control points. These corner reflectors appear as multiple bright spots in the radar processing results, which can be used to determine their position in the radar coordinate system, thereby playing a role in accurately locating the target.

[0154] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An imaging radar system for monitoring and early warning of collapses at the entrance and exit faces of railway tunnels, characterized in that, The system includes: a servo mechanism, a Ku-band radar subsystem, a Ka-band radar subsystem, and an early warning module deployed on a host computer; The servo mechanism includes: a rotating arm and a stationary base; the length of the rotating arm is adjustable; The Ku-band radar subsystem is mounted on the rotating arm and is used to image the entrance and exit areas of the railway tunnel using two-dimensional arc-scan synthetic aperture imaging technology. It obtains the deformation information of the target through long-term observation and sends it to the host computer. The Ka-band radar subsystem is installed on the fixed base and is used to achieve fixed-point instantaneous observation of multiple points at the entrance and exit of the railway tunnel using one-dimensional real aperture micro-deformation measurement technology, obtain the deformation information of the target and send it to the host computer. The Ku band uses SFCW signals, which have a slow frequency sweep speed; the Ka band uses FMCW signals, which have a fast frequency sweep speed. The early warning module is used to fuse the two types of deformation information, determine the possibility of a landslide, and issue an early warning. The Ku-band radar subsystem uses arc-scan imaging to obtain the target's deformation information, specifically including: The Ku-band radar subsystem is used to perform arc scan observations by rotating the arm to obtain the synthetic aperture. The synthetic aperture is processed to obtain a complex image; Two images with pixels corresponding to the same observed target are selected for registration. Interference fringe patterns are obtained from the two registered complex images, and the changes in micro-deformation are obtained by processing the complex images over time. Extract the micro-deformation portion corresponding to the target from the phase image; The entangled phase is then untangled in two dimensions to obtain the processed phase map. Based on the processed phase diagram, deformation information is calculated through the correspondence between phase and distance; The Ka-band radar subsystem obtains target deformation information through fixed-point observation, specifically including: Observation pulses are transmitted toward the target at a certain pulse repetition frequency; Receive the echo signal data of each observation pulse; Phase extraction is performed on the echo signal data of each observed pulse in chronological order; The extracted phase is subjected to differential interferometry with the phase at the reference position. The obtained phase is then unwrapped to obtain accurate phase information corresponding to the deformation information; The phase is processed according to the correspondence between phase, wavelength and distance to obtain the deformation information of the target.

2. The imaging radar system for monitoring and early warning of landslides at the entrance and exit faces of railway tunnels according to claim 1, characterized in that, The Ku-band radar subsystem includes: a Ku-band transmitter, a Ku-band receiver, and a Ku-band data acquisition and processing unit; wherein... The Ku-band transmitting device is used to generate and transmit Ku-band stepped-frequency continuous wave signals; The Ku-band receiving device is used to receive the echo signal reflected by the target from the Ku-band stepped frequency continuous wave signal and transmit it to the Ku-band data acquisition and processing device. The Ku-band data acquisition and processing device is used to process the echo signal of the Ku-band stepped frequency continuous wave signal to obtain the deformation information of the target.

3. The imaging radar system for monitoring and early warning of landslides at the entrance and exit faces of railway tunnels according to claim 2, characterized in that, The Ku-band transmitting device includes: a first frequency synthesizer, a Ku-band transmitting link, and a Ku-band transmitting antenna; the Ku-band transmitting antenna includes: a Ku-band H-polarized transmitting antenna and a Ku-band V-polarized transmitting antenna; wherein... The first frequency synthesizer is used to transmit a Ku-band stepped-frequency continuous wave signal; The Ku-band transmission link is used to amplify and filter the Ku-band stepped-frequency continuous wave signal before transmitting it to the Ku-band H-polarized transmitting antenna and the Ku-band V-polarized transmitting antenna. The Ku-band H-polarized transmitting antenna and the Ku-band V-polarized transmitting antenna are used to transmit the processed Ku-band stepped-frequency continuous wave signal in H-polarization and V-polarization, respectively.

4. The imaging radar system for monitoring and early warning of collapse at the entrance and exit faces of railway tunnels according to claim 3, characterized in that, The Ku-band receiving device includes: a Ku-band receiving antenna and a Ku-band receiving link; the Ku-band receiving antenna includes: a Ku-band H-polarized receiving antenna and a Ku-band V-polarized receiving antenna; the Ku-band receiving link includes: a Ku-band H-polarized receiving channel and a Ku-band V-polarized receiving channel; wherein... The Ku-band H-polarized receiving antenna and the Ku-band V-polarized receiving antenna are used to receive the echo signals reflected by the target from the Ku-band stepped frequency continuous wave signals transmitted by the Ku-band H-polarized transmitting antenna and the Ku-band V-polarized transmitting antenna, respectively, and transmit them to the Ku-band H-polarized receiving channel and the Ku-band V-polarized receiving channel, respectively. The Ku-band H-polarized receiving channel and the Ku-band V-polarized receiving channel are used to process the echo signals they receive and transmit them to the Ku-band data acquisition and processing device.

5. The imaging radar system for monitoring and early warning of collapse at the entrance and exit faces of railway tunnels according to claim 1, characterized in that, The Ka-band radar subsystem includes: a Ka-band transmitter, a Ka-band receiver, and a Ka-band data acquisition and processing unit; wherein... The Ka-band transmitting device is used to generate and transmit Ka-band frequency-modulated continuous wave signals. The Ka-band receiving device is used to receive the echo signal reflected by the target from the Ka-band frequency modulated continuous wave signal and transmit it to the data acquisition and processing device. The Ka-band data acquisition and processing device is used to process the echo signal of the Ka-band frequency-modulated continuous wave signal to obtain the deformation information of the target.

6. The imaging radar system for monitoring and early warning of collapse at the entrance and exit faces of railway tunnels according to claim 5, characterized in that, The Ka-band transmitting device includes: a second frequency synthesizer, a Ku-band transmitting link, and a Ka-band transmitting antenna; the Ka-band transmitting antenna includes: a Ka-band H-polarized transmitting antenna and a Ka-band V-polarized transmitting antenna; wherein... The second frequency synthesizer is used to transmit Ka-band frequency-modulated continuous wave signals; The Ka-band transmission link is used to amplify and filter the Ka-band frequency-modulated continuous wave signal before transmitting it to the Ka-band H-polarized transmitting antenna and the Ka-band V-polarized transmitting antenna. The Ka-band H-polarized transmitting antenna and the Ka-band V-polarized transmitting antenna are used to transmit the processed Ka-band frequency-modulated continuous wave signal in H-polarization and V-polarization, respectively.

7. The imaging radar system for monitoring and early warning of collapse at the entrance and exit faces of railway tunnels according to claim 6, characterized in that, The Ka-band receiving device includes: a Ka-band receiving antenna and a Ka-band receiving link; the Ka-band receiving antenna includes: a Ka-band H-polarized receiving antenna and a Ka-band V-polarized receiving antenna; the Ka-band receiving link includes: a Ka-band H-polarized receiving channel and a Ka-band V-polarized receiving channel; wherein... The Ka-band H-polarized receiving antenna and the Ka-band V-polarized receiving antenna are used to receive the echo signals of the Ka-band frequency-modulated continuous wave signals transmitted by the Ka-band H-polarized transmitting antenna and the Ka-band V-polarized transmitting antenna, respectively, after being reflected by the target, and transmit them to the Ka-band H-polarized receiving channel and the Ka-band V-polarized receiving channel, respectively. The Ka-band H-polarized receiving channel and the Ka-band V-polarized receiving channel are used to process the echo signals they receive and transmit them to the Ka-band data acquisition and processing device.

8. The imaging radar system for monitoring and early warning of landslides at the entrance and exit faces of railway tunnels according to any one of claims 1-7, characterized in that, The system is placed to the side of the entrance and exit of the railway tunnel, and the observation angle and scanning range are set according to the shape and height of the tunnel facade and slope protection.

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