CN116736298A - Imaging radar system for monitoring and early warning collapse of entrance and exit end surfaces of railway tunnel - Google Patents

Abstract

The invention relates to the technical field of railway tunnel safety monitoring, and in particular to an imaging radar system suitable for early warning of collapse of the entrance and exit end faces of railway tunnels. The system includes: a servo mechanism, a Ku-band radar subsystem, a Ka-band radar subsystem and an early warning module deployed on the host computer; the servo mechanism includes: a rotating arm and a fixed base; the Ku-band radar subsystem is installed on the host computer. The above-mentioned rotating arm is used to image the entrance and exit area of the railway tunnel using two-dimensional arc-sweep synthetic aperture imaging technology, and obtain the deformation information of the target through long-term observation and send it to the host computer; the Ka-band radar subsystem is installed on the fixed station. On a moving base, it is used to use one-dimensional real-aperture micro-deformation measurement technology to achieve fixed-point instantaneous observation of multiple points at the entrance and exit of railway tunnels, obtain the deformation information of the target and send it to the host computer; the early warning module is used to detect two types of deformation. Information is fused to determine the possibility of landslides and provide early warning.

Description

Imaging radar system for monitoring and early warning of collapses at the entrance and exit of railway tunnels

Technical field

The invention relates to the technical field of railway tunnel safety monitoring, and in particular to an imaging radar system used for monitoring and early warning of collapse of the entrance and exit end faces of railway tunnels.

Background technique

The deformation of 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 will cause serious consequences such as settlement and collapse, seriously affecting the safety of railway construction and operations. Therefore, deformation monitoring has become an important means of preventing collapse at the entrance and exit of railway tunnels.

Common railway tunnel entrance and exit end face deformation monitoring methods can be divided into two categories according to their working principles and characteristics: The first category is to measure the deformation of a single point, and estimate the deformation information of the entire target area through the measurement of a single point. Common ones include levels, theodolite, GPS measuring instruments, etc. The second type is direct plane measurement. This method can not only obtain high-precision deformation of the target area, but also obtain information such as deformation trends. This monitoring technology is represented by laser point cloud images and ground-based radar differential interferometry. Compared with traditional single-point measurement methods, it has the advantages of wider monitoring range, high sampling rate, and fully automated monitoring process. In the second category of methods, the laser point cloud method is easily affected by weather conditions such as rain, fog, etc., while ground-based radar observation can observe all-day and all-weather, becoming an important technical means for observing complex regional deformation under complex weather conditions.

Contents of the invention

The purpose of the present invention is to monitor the deformation of the entrance and exit end faces of railway tunnels. This monitoring includes two parts: (1) long-term observation of the deformation trend of the tunnel mouth; (2) instantaneous deformation of the end face when a train passes through the tunnel mouth. This invention integrates foundation arc-sweep synthetic aperture imaging technology and static high-repetition frequency fixed-point observation technology to achieve long-term and instantaneous observation of the tunnel entrance, and determine the health status of the tunnel entrance end face from long-term deformation data and instantaneous impact response data during passing.

In order to achieve the above objects, the present invention is achieved through the following technical solutions.

The present invention provides an imaging radar system for monitoring and early warning of collapse at the entrance and exit end of a railway tunnel.

The system includes: servo mechanism, Ku-band radar subsystem, Ka-band radar subsystem and early warning module deployed on the host computer;

The servo mechanism includes: a rotating arm and a fixed base;

The Ku-band radar subsystem is installed on the rotating arm and is used to image the entrance and exit areas of railway tunnels using two-dimensional arc-sweep synthetic aperture imaging technology, obtain target deformation information through long-term observation and send it to the host computer;

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

The early warning module is used to fuse two types of deformation information to determine the possibility of collapse and provide early warning. The system processes two types of deformation information in real time and provides early warning for targets exceeding the deformation limit.

As one of the improvements of 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,

The Ku-band transmitting device is used to generate and transmit a Ku-band step frequency continuous wave signal;

The Ku-band receiving device is used to receive the echo signal of the Ku-band step frequency continuous wave signal reflected by the target, 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 step frequency continuous wave signal to obtain the deformation information of the target.

As one of the improvements of the above technical solution, the Ku-band transmitting device includes: a first frequency synthesizer, a Ku-band transmit link and a Ku-band transmit antenna; the Ku-band transmit antenna includes: a Ku-band H-polarized transmit antenna and Ku band V polarization transmitting antenna; where,

The first frequency synthesizer is used to transmit a step frequency continuous wave signal in the Ku band;

The Ku-band transmitting link is used to amplify and filter the Ku-band step frequency continuous wave signal and then transmit 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 respectively used to perform H-polarized transmission and V-polarized transmission of the processed Ku-band step frequency continuous wave signal.

As one of the improvements of the above technical solution, the Ku-band receiving device includes: Ku-band receiving antenna and Ku-band receiving link; the Ku-band receiving antenna includes: Ku-band H polarization receiving antenna and Ku-band V polarization receiving Antenna; the Ku-band receiving link includes: Ku-band H polarization receiving channel and Ku-band V polarization receiving channel; wherein,

The Ku-band H-polarized receiving antenna and Ku-band V-polarized receiving antenna are respectively used to receive Ku-band step-frequency continuous wave signals emitted by the Ku-band H-polarized transmitting antenna and the Ku-band V-polarized transmitting antenna and reflected by the target. The echo signal is transmitted to the Ku-band H polarization receiving channel and Ku-band V polarization receiving channel respectively;

The Ku-band H polarization receiving channel and the Ku-band V polarization receiving channel are respectively used to process the echo signals received respectively and transmit them to the Ku-band data acquisition and processing device.

As one of the improvements to the above technical solution, the Ku-band radar subsystem uses arc-scan imaging observation to obtain target deformation information, specifically including:

The Ku-band radar subsystem performs arc sweep observation through a rotating arm to obtain a synthetic aperture;

Perform imaging processing on the synthetic aperture to obtain a complex image;

Select two images corresponding to the pixels in the image and the same observation target for registration;

Obtain interference fringe patterns from the two registered complex images, and process the complex images in time series to obtain the change process of micro-deformation;

Extract the micro-deformation part corresponding to the target from the phase image;

And perform a two-dimensional unwrapping operation on the entangled phase to obtain the processed phase map;

According to the processed phase map, the deformation information is calculated through the corresponding relationship between phase and distance.

As one of the improvements of the above technical solution, the Ka-band radar subsystem includes: a Ka-band transmitting device, a Ka-band receiving device and a Ka-band data acquisition and processing device; 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 of the Ka-band FM continuous wave signal reflected by the target, 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.

As one of the improvements of the above technical solution, the Ka-band transmitting device includes: a second frequency synthesizer, a Ku-band transmit link and a Ka-band transmit antenna; the Ka-band transmit antenna includes: a Ka-band H polarized transmit antenna and Ka-band V polarization transmitting antenna; where,

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

The Ka-band transmitting link is used to amplify and filter the Ka-band FM continuous wave signal and then transmit 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 respectively used to perform H-polarized transmission and V-polarized transmission of the processed Ka-band FM continuous wave signal.

As one of the improvements of the above technical solution, the Ka-band receiving device includes: Ka-band receiving antenna and Ka-band receiving link; the Ka-band receiving antenna includes: Ka-band H polarization receiving antenna and Ka-band V polarization receiving Antenna; the Ka-band receiving link includes: Ka-band H polarization receiving channel and Ka-band V polarization receiving channel; wherein,

The Ka-band H-polarized receiving antenna and the Ka-band V-polarized receiving antenna are respectively used to receive the echo of the Ka-band frequency modulated continuous wave signal emitted by the Ka-band H-polarized transmitting antenna and the Ka-band V-polarized transmitting antenna and reflected by the target. The signal is transmitted to the Ka-band H polarization receiving channel and the Ka-band V polarization receiving channel respectively;

The Ka-band H polarization receiving channel and the Ka-band V polarization receiving channel are respectively used to process the echo signals received respectively and transmit them to the Ka-band data acquisition and processing device.

As one of the improvements to the above technical solution, the Ka-band radar subsystem uses fixed-point observation to obtain target deformation information, specifically including:

Emit observation pulses to 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 observation pulse in time sequence;

Perform differential interference processing on the extracted phase and the reference position phase;

And perform phase unwrapping processing on the obtained phase to obtain accurate phase information corresponding to the deformation information;

The phase is processed according to the corresponding relationship between phase, wavelength and distance, and then the deformation information of the target is obtained.

As one of the improvements to the above technical solution, the system is placed at the side of the railway tunnel entrance and exit, and the observation angle and scanning range are set according to the shape and height of the tunnel facade and slope protection.

Compared with the prior art, the advantages of the present invention are:

1. The present invention selects technical solutions based on the deformation characteristics of railway tunnel entrances, and can simultaneously realize long-term deformation trend observation and deformation observation under instantaneous impact of passing vehicles, and combine long-term and instantaneous observation data, thereby improving the health of railway tunnel entrances. Judgment of status;

2. In view of the deformation characteristics of the railway tunnel entrance, the present invention adopts Ku\Ka band joint observation technology. Ku band radar adopts scanning imaging observation method to improve the system imaging resolution; Ka band radar adopts the form of fixed point observation, using To improve the measurement accuracy of special point deformation;

3. The present invention uses separate transmitting and receiving antennas to transmit frequency-modulated continuous waves, and the receiving method adopts a deskewing method to reduce the signal bandwidth, thereby reducing the sampling frequency;

4. The present invention uses two frequency bands with different radar signal forms. The Ku band uses SFCW (Stepped FrequencyContinuous Waveform, stepped frequency continuous wave) signal, and the Ka band uses FMCW (Frequency ModulatedContinuous Wave, frequency modulated continuous wave) signal; the SFCW signal is stable and frequency sweep The speed is slow and suitable for use in long-term deformation trend observation processes; the FMCW signal frequency sweep speed is fast and can achieve high repetition frequency observation, which is suitable for the observation of high-frequency impact vibration signals at the entrance and exit of tunnels when trains pass by;

5. The length of the rotating arm of the scanning imaging radar in the present invention is adjustable, and the interference baseline can be formed through different arm lengths, and the three-dimensional information of the railway tunnel entrance can be obtained in combination with two-dimensional imaging;

6. The method and system proposed by the present invention can adjust the radar's viewing angle, scanning angle, signal bandwidth and repetition frequency according to the distance between the observation position and the tunnel entrance and the different viewing angles, making it easy to set up;

7. The present invention supports synchronous observation with optical equipment, and facilitates the identification of deformation areas after the fusion of multi-source data.

Description of drawings

Figure 1 is a block diagram of the working principle of the system of the present invention;

Figure 2 is a schematic diagram of imaging radar measurement for monitoring and early warning of collapse at the entrance and exit end of a railway tunnel;

Figure 3 is a schematic diagram of Ku-band radar arc scan imaging;

Figure 4(a) is the overall structural block diagram of the radar system of the present invention, Figure 4(b) is the structural block diagram of the Ku-band radar subsystem, and Figure 4(c) is the structural block diagram of the Ka-band radar subsystem.

Detailed ways

Ground-based radar differential interferometry technology is developed based on stepped frequency continuous wave (SFCW) technology or frequency modulated continuous wave technology (FMCW), synthetic aperture radar imaging technology and differential interferometry technology. It is a radar active imaging remote sensing measurement technology. , extract deformation information from time-series radar images obtained through repeated observations of the same target area at different time points.

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

First, the repeated observation period is short, which can realize fixed-point continuous monitoring of the deformation area.

Second, higher spatial resolution and deformation measurement accuracy can be obtained. The ground-based radar interferometry system can achieve high-resolution imaging of the target area, and its deformation measurement accuracy can reach sub-millimeter level.

The third is high flexibility and operability. The ground-based radar system uses the ground, buildings or land vehicles as platforms. It can select the best observation angle according to monitoring needs and select the observation time baseline according to the characteristics of the monitoring target, showing good flexibility and operability.

To sum up, the ground-based radar interferometry system has the advantages of regional, all-weather, all-day, fixed-point, continuous, and high-precision monitoring. It has good flexibility and operability, and its non-contact measurement method can be safely used. Obtain the deformation data of the monitored dangerous area within a distance, and the information collected at the same time is that regional large-area deformation information is more conducive to the understanding and prediction of disasters than single-point deformation information, and has a positive effect on predicting and preventing the occurrence of disasters. significance.

Therefore, the present invention relates to a rotatable dual-frequency ground-based interferometry radar system, in which the Ku-band radar system is installed at one end of the rotating wall for rotation measurement, and the Ka-band radar system remains stationary and fixed at the rotating base. The Ka\Ku band radar systems are frequency modulated continuous wave and stepped frequency continuous wave radar systems respectively. By combining ground-based arc-sweep synthetic aperture imaging technology and static high-repetition frequency fixed-point observation technology, long-term and instantaneous monitoring of tunnel entrances can be achieved. Observation.

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

As shown in Figure 1, it is a block diagram of the working principle of the system of the present invention. This solution uses a dual-frequency radar system installed on a servo with a rotation function to form a ground-based interferometric radar. The Ku-band radar is installed on a rotating arm with an adjustable length of 1.5-2.5 meters (different arm lengths correspond to different baseline lengths ), the Ka-band radar is mounted on a fixed base on top of the rotating axis.

The Ku-band radar consists of a coherent microwave transmitting and receiving device operating in the Ku-band (center frequency 16.2GHz, bandwidth 300MHz), which can transmit and receive stepped frequency continuous wave signals (SFCW). Both the Ku-band radar transmitting and receiving devices include H (horizontal) polarization and V (vertical) polarization antennas (a total of 4 antennas). When working, after the servo mechanism rotates the Ku-band radar to a certain angle, the transmitting device generates a step-frequency continuous wave signal which is amplified and transmitted to the H-polarized transmitting antenna. At the same time, the transmitted signal is coupled to the H-polarized receiving channel 1, and the receiving The reference signal of channel 1 is amplified, down-converted to an intermediate frequency and sent to the digital unit (processed internally in the receiver, these operations include deskewing). The same receiving process is in the V-polarized receiving channel. The V-polarized antenna receiving antenna receives the transmitted signal, which is amplified and down-converted by receiving channel 2 and then sent to the digital unit. The digital unit performs operations such as sampling, digital down-conversion, amplitude extraction, and phase extraction on the echo signals from receiving channel 1 and receiving channel 2 respectively. After H polarization transmission and H polarization\V polarization reception, similarly, the radar performs V polarization transmission and H polarization\V polarization reception. At an observation angle position, the radar system completes two signal scans from low frequency to high frequency, thereby completing the signal collection of two polarization bandwidths. After completing the observation at an observation angle position, the servo rotates the Ku-band radar to the next angle to repeat the next observation. Observations are performed sequentially at different observation angles according to the predetermined scanning angle range, and the next scanning process is repeated after all scanning angle positions are observed. The Ku-band radar system realizes a circular arc synthetic aperture through the rotational movement of the rotating arm in the azimuth direction, thereby achieving two-dimensional resolution imaging of the tunnel entrance observation area. By repeatedly observing the synthetic aperture of the target and taking its phase change, its deformation value can be obtained.

The Ka-band radar consists of a coherent microwave transmitting and receiving device operating in the Ka-band (center frequency 36GHz, bandwidth 300MHz), which can transmit and receive frequency modulated continuous wave signals (FMCW). Both the Ka-band radar transmitting and receiving devices contain H-polarized and V-polarized antennas (a total of 4 antennas). When working, the transmitting device generates a frequency modulated continuous wave signal that is amplified and transmitted to the H-polarized transmitting antenna. At the same time, the transmitted signal is coupled to the H-polarized receiving channel 1. The reference signal of the receiving channel 1 is amplified, down-converted to an intermediate frequency, and then sent to the H-polarized transmitting antenna. Digital unit. The same receiving process is in the V-polarized receiving channel. The V-polarized antenna receiving antenna receives the transmitted signal, which is amplified and down-converted by receiving channel 2 and then sent to the digital unit. The digital unit performs operations such as sampling, digital down-conversion, amplitude extraction, and phase extraction on the echo signals from receiving channel 1 and receiving channel 2 respectively. After H polarization transmission and H polarization\V polarization reception, similarly, the radar performs V polarization transmission and H polarization\V polarization reception. At an observation location, the Ka-band radar system performs observations at a certain pulse repetition frequency (PRF). After performing phase difference processing on the obtained time data sequence, the deformation information can be obtained.

After determining the entrance and exit of the tunnel that needs to be observed, place the radar at the side of the tunnel entrance and exit based on the location of the radar that is suitable for the site. Set the radar's observation angle and scanning according to the shape and height of the tunnel facade and slope protection. After reaching the scope, observe the entrance and exit of the tunnel. As shown in Figure 2, it is a schematic diagram of imaging radar measurement for monitoring and early warning of collapse at the entrance and exit end of a railway tunnel.

Ku-band radar is an imaging radar that realizes arc synthetic aperture in arc sweep mode, as shown in Figure 3. The radar azimuth direction is the rotation direction, and the observation time is represented by eta; the radar range direction is the line of sight direction, and the observation time is represented by τ. The antenna beam width is θ _BW and is installed at one end of a rotating arm with length r _a . The antenna beam is pointed at the observation target. The other end of the rotating arm is fixed on the rotating axis O', with a height of H. The rotation angular velocity is ω, so the azimuth coherent accumulation angle is θ = ωη. Suppose there is a point target P, the position in cylindrical coordinates is P(r _p , θ _p ). When the turntable rotates, the position where the antenna beam just hits the target is A, and the position where the antenna beam leaves the target is B, then PA and PB The angle between them is the synthetic aperture angle θ _sys . The nearest slant distance between the antenna and point P is R ₀ , and the distance between the rotation center O' and point P is R _c . The antenna forms a synthetic aperture through rotational motion, so the imaging area formed on the ground is circular. The three-dimensional geometry of arc-scan imaging is shown in Figure 3.

As shown in the figure, the closest slant distance between the radar and the point target can be obtained as follows:

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

Ku-band radar emits stepped frequency continuous wave (SFCW). Suppose the starting frequency of the carrier frequency is f ₀ , the frequency step increment is Δf, and the number of frequency steps is N. t represents the signal time, n is an integer from 0 to N-1, and the transmitted signal can be expressed as:

S _t (n,t)= _wa (η)·exp[2π(f ₀ +nΔf)t] (3)

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

S _r (n, t, η) = w _a (η)·exp[2π(f ₀ +nΔf)(t-2R(η)/c)] (4)

The intermediate frequency signal obtained after orthogonal demodulation is:

The properties of the Ku-band radar range signal depend on the bandwidth, that is, the range resolution:

The azimuth resolution is determined by the synthetic aperture angle θ _sys , and the azimuth angle is represented by θ _n , then the azimuth wave number is:

k _u =2k·sin(θ _n ) (6)

in,

k=2π/λ (7)

The Doppler bandwidth generated when the antenna moves from the starting position A to the ending position B is:

Ω＝k _u (θ _A )-k _u (θ _B )＝4ksin (θ _sys /2) (8)

Therefore, the azimuth resolution in the distance dimension is:

In the triangle OPA, using the sine theorem we can get:

Then the azimuth resolution can be expressed as:

Finally, the azimuth angle resolution is obtained as follows:

It can be seen from the above formula that the angular resolution of arc scan imaging does not change with distance. The larger the rotating arm length and beam width, the higher the resolution.

There are eight main steps in the Ku-band radar signal processing process, which are:

The first step is to obtain the complex image.

After the Ku-band radar scans an arc aperture, it performs imaging processing on the data to obtain a complex image. After sequentially scanning the apertures, two complex images can form a complex image pair, and the next step of registration processing is performed. ;

Step 2: Complex image registration

Obtaining target interference information requires registering the complex images, which means that the pixels in both images must correspond to the same observation target.

Step 3: Interference pattern generation

The interference fringe pattern is obtained from the two registered complex images. By processing a series of complex images in the time series, the change process of micro-deformation can be seen.

Step 4 ROI extraction

Extract the micro-deformation part of interest from the phase image.

Step 5 Phase Unwrapping

When the displacement exceeds the wavelength of the signal, the phase will be entangled. In order to accurately restore the phase information, a two-dimensional unwrapping operation is performed on the entangled phase.

Step 6 Atmospheric Correction

Changes in parameters such as atmospheric temperature, humidity, and air pressure will lead to deviations in phase measurement. Stable targets in the scene can be used to eliminate these effects.

Step 7 Calculation of deformation amount

After obtaining the phase diagram, the deformation amount is calculated through the corresponding relationship between phase and distance.

Step 8 Geocoding

According to the geographical location and geometric relationship of the observed target, the observation results are mapped to the geographical coordinates of the tunnel entrance.

The basic principles of Ka-band radar observation are as follows:

Assume that the incident electromagnetic wave signal is:

Considering distance attenuation, the scattering signal can be expressed as:

The scattering matrix can be described as:

Taking VV polarization as an example (other HH\HV\VH polarizations are similar), then:

Scattering matrix components And the echo signal is expressed in the form of a complex signal, which is:

The target complex scattering coefficient is expressed as the multiplication of amplitude and phase, that is Then the radar complex data of two consecutive observations in the interference processing can be expressed as:

By conjugate multiplying the two signals we get

In the formula, σ ₁ and σ ₂ are the target complex scattering coefficients of the two previous observations respectively, which are determined by the properties of the target itself. From this, the interferometric phase can be obtained as follows: The phase includes the slant distance before and after deformation, the frequency difference and the scattering phase difference of the monitoring target.

During Ka-band radar observation, the two observed target signals have a high correlation, so the scattering phase difference of the target can be ignored, then the phase can be expressed as:

The corresponding deformation variable can be obtained as

There are five main steps in the Ka-band radar signal processing process, which are:

The first step is to obtain time series signals

Phase extraction is performed on the data of each observed pulse in time sequence;

The second step of differential interference processing

Perform a differential operation on the phase and the reference position phase;

The third step of phase unwrapping processing

Perform phase unwrapping processing on the obtained phase to obtain accurate phase information corresponding to the deformation information;

Step 4: Inversion of deformation variables

Process the phase according to the corresponding relationship between phase, wavelength and distance;

Step 5 Geocoding

Obtain observation location information and perform geographic coordinate mapping.

As shown in Figure 4(a), it is an overall structural block diagram of the radar system according to the 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(b). As shown in 4(c).

In the process of geographical matching, corner reflectors can be installed on the tunnel entrance and exit ends as selective control points. These corner reflectors appear as multiple bright spots on the radar processing results, which can be used to determine their position in the radar coordinate system, thereby calibrating the accurate position of the target.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art will understand that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and they shall all be covered by the scope of the present invention. within the scope of the claims.

Claims (10)

1. An imaging radar system for monitoring and early warning of collapses at the entrance and exit end of railway tunnels, characterized by: The system includes: servo mechanism, Ku-band radar subsystem, Ka-band radar subsystem and early warning module deployed on the host computer; The servo mechanism includes: a rotating arm and a fixed base; The Ku-band radar subsystem is installed on the rotating arm and is used to image the entrance and exit areas of railway tunnels using two-dimensional arc-sweep synthetic aperture imaging technology, obtain target deformation information through long-term observation and send it to the host computer; The Ka-band radar subsystem is installed on the fixed base and is used to use one-dimensional real aperture micro-deformation measurement technology to achieve fixed-point instantaneous observation of multiple points at the entrance and exit of the railway tunnel, obtain the deformation information of the target and send to the upper computer; The early warning module is used to fuse two types of deformation information to determine the possibility of collapse and provide early warning. 2. The imaging radar system for monitoring and early warning of collapse at the entrance and exit of railway tunnels according to claim 1, characterized in that the Ku-band radar subsystem includes: a Ku-band transmitting device, a Ku-band receiving device and Ku-band data Collection and processing device; wherein, The Ku-band transmitting device is used to generate and transmit a Ku-band step frequency continuous wave signal; The Ku-band receiving device is used to receive the echo signal of the Ku-band step frequency continuous wave signal reflected by the target, 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 step frequency continuous wave signal to obtain the deformation information of the target. 3. The imaging radar system for monitoring and early warning of collapse at the entrance and exit end of a railway tunnel according to claim 2, characterized in that, The Ku-band transmitting device includes: a first frequency synthesizer, a Ku-band transmit link and a Ku-band transmit antenna; the Ku-band transmit antenna includes: a Ku-band H-polarized transmit antenna and a Ku-band V-polarized transmit antenna; wherein , The first frequency synthesizer is used to transmit a step frequency continuous wave signal in the Ku band; The Ku-band transmitting link is used to amplify and filter the Ku-band step frequency continuous wave signal and then transmit 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 respectively used to perform H-polarized transmission and V-polarized transmission of the processed Ku-band step frequency continuous wave signal. 4. The imaging radar system for monitoring and early warning of collapse at the entrance and exit 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 Including: Ku-band H polarization receiving channel and Ku-band V polarization receiving channel; among them, The Ku-band H-polarized receiving antenna and Ku-band V-polarized receiving antenna are respectively used to receive Ku-band step-frequency continuous wave signals emitted by the Ku-band H-polarized transmitting antenna and the Ku-band V-polarized transmitting antenna and reflected by the target. The echo signal is transmitted to the Ku-band H polarization receiving channel and Ku-band V polarization receiving channel respectively; The Ku-band H polarization receiving channel and the Ku-band V polarization receiving channel are respectively used to process the echo signals received respectively 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 of railway tunnels according to claim 1, characterized in that the Ku-band radar subsystem uses arc scan imaging observation to obtain the deformation information of the target, specifically including: The Ku-band radar subsystem performs arc sweep observation through a rotating arm to obtain a synthetic aperture; Perform imaging processing on the synthetic aperture to obtain a complex image; Select two images corresponding to the pixels in the image and the same observation target for registration; Obtain interference fringe patterns from the two registered complex images, and process the complex images in time series to obtain the change process of micro-deformation; Extract the micro-deformation part corresponding to the target from the phase image; And perform a two-dimensional unwrapping operation on the entangled phase to obtain the processed phase map; According to the processed phase map, the deformation information is calculated through the corresponding relationship between phase and distance. 6. The imaging radar system for monitoring and early warning of collapse at the entrance and exit of railway tunnels according to claim 1, characterized in that the Ka-band radar subsystem includes: a Ka-band transmitting device, a Ka-band receiving device and a Ka-band data Collection and processing device; 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 of the Ka-band FM continuous wave signal reflected by the target, 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. 7. The imaging radar system for railway tunnel entrance and exit end collapse monitoring and early warning according to claim 6, characterized in that the Ka-band sending device includes: a second frequency synthesizer, a Ku-band transmitting link and a Ka-band Transmitting antenna; the Ka-band transmitting antenna includes: Ka-band H-polarized transmitting antenna and 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 transmitting link is used to amplify and filter the Ka-band FM continuous wave signal and then transmit 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 respectively used to perform H-polarized transmission and V-polarized transmission of the processed Ka-band FM continuous wave signal. 8. The imaging radar system for railway tunnel entrance and exit end collapse monitoring and early warning according to claim 7, characterized in that the Ka-band receiving device includes: a Ka-band receiving antenna and a Ka-band receiving link; the Ka The Ka-band receiving antenna includes: Ka-band H polarization receiving antenna and Ka-band V polarization receiving antenna; the Ka-band receiving link includes: Ka-band H polarization receiving channel and Ka-band V polarization receiving channel; wherein, The Ka-band H-polarized receiving antenna and the Ka-band V-polarized receiving antenna are respectively used to receive the echo of the Ka-band frequency modulated continuous wave signal emitted by the Ka-band H-polarized transmitting antenna and the Ka-band V-polarized transmitting antenna and reflected by the target. The signal is transmitted to the Ka-band H polarization receiving channel and the Ka-band V polarization receiving channel respectively; The Ka-band H polarization receiving channel and the Ka-band V polarization receiving channel are respectively used to process the echo signals received respectively and transmit them to the Ka-band data acquisition and processing device. 9. The imaging radar system for monitoring and early warning of collapse at the entrance and exit of railway tunnels according to claim 1, characterized in that the Ka-band radar subsystem uses fixed-point observation to obtain target deformation information, specifically including: Emit observation pulses to 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 observation pulse in time sequence; Perform differential interference processing on the extracted phase and the reference position phase; And perform phase unwrapping processing on the obtained phase to obtain accurate phase information corresponding to the deformation information; The phase is processed according to the corresponding relationship between phase, wavelength and distance, and then the deformation information of the target is obtained. 10. The imaging radar system for monitoring and early warning of end face collapse of railway tunnel entrances and exits according to any one of claims 1 to 9, characterized in that the system is placed at the side of the railway tunnel entrance and exit, and the system is positioned according to the outside of the tunnel. The shape and height of the facade and slope protection set the observation angle and scanning range.