A terahertz binocular ISAR system and method for three-dimensional imaging

Abstract

The present invention discloses a terahertz binocular ISAR system and method for three-dimensional imaging, including a transmission link and a receiving link; wherein the transmission link is used to generate and transmit a terahertz signal; the receiving link is used to receive two reflected signals of a target object in two positions during two measurements of the terahertz signal, and after recovering two staggered two-dimensional images using an inverse synthetic aperture radar two-dimensional imaging algorithm based on the two reflected signals, the height and spatial position of the target object are reconstructed based on the two two-dimensional images. The system and method utilize the imaging mode of binocular vision, can simplify the radar structure, make the configuration more flexible, and help reduce the cost of the terahertz radar system.

Description

Technical Field

[0001] The present invention belongs to the field of imaging technology, and in particular, relates to a terahertz binocular ISAR (Inverse-Synthetic-Aperture-Radar) system and method for three-dimensional imaging. Background Art

[0002] Terahertz (THz) has a frequency between 0.1 and 10 THz and a wavelength between 0.03 and 3 mm. It is an electromagnetic wave between the microwave band and the infrared band. Due to its special position in the electromagnetic spectrum, terahertz waves have many unique properties and advantages. From an energy perspective, the energy of terahertz waves is at the junction of photons and electrons, and has both photon and electronic properties. For a long time, due to the immaturity of the means of generating and detecting large hertz waves, researchers have had very limited understanding and use of the terahertz band, so the terahertz band is also called the "terahertz gap". In the past few years, some progress has been made in the research of the terahertz frequency band, which has led to the rapid development of terahertz-related technologies and increasingly clear applications. Typical applications include large hertz high-speed wireless communications and terahertz high-resolution imaging.

[0003] According to literature search, Dexin Wu et al. from China published a paper titled "Photonics based microwave dynamic 3D reconstruction of moving targets" in the journal Optic Express in 2018. This paper proposes a method for microwave dynamic 3D reconstruction of moving targets based on photonics. This method uses an optical arbitrary waveform generator (OAWG) based on photon digital-to-analog conversion (PDAC) to generate broadband linear frequency modulation (LFM) microwave signals. The echo reflected by the target is received by two antennas placed at different heights. A polarization-multiplexed dual parallel Mach-Zehnder modulator (PM-DPMZM) is used with a polarization beam splitter (PBS) and two photodetectors (PD) to mix the two received signals and the transmitted signals simultaneously or separately. Combined with two-dimensional inverse synthetic aperture radar (ISAR) imaging processing, the two obtained complex two-dimensional images are interfered to achieve dynamic 3D reconstruction of moving targets. Due to the combination of OAWG and microwave photon parallel mixing, the system can operate at a wide bandwidth and high frequency point. In addition, it has a high frequency tuning range and can flexibly adapt to various environmental conditions. However, the receiving end of the system is relatively complicated because of the need for two-way reception due to image interference.

[0004] A literature search revealed that Jingwen Dong et al. from China published a paper titled "Microwave photonic radar with a fiber-distributed antenna arrayfor three-dimensional imaging" in the journal Optic Express in 2020. The paper proposed and demonstrated a three-dimensional imaging microwave photonic radar based on a fiber-distributed antenna array. Photon frequency doubling, wavelength division multiplexing, and fiber-optic radio technologies are used to generate, replicate, and distribute radar signals. Parallel de-chirping processing is completed in the central processing unit (CO) to achieve multi-channel two-dimensional ISAR imaging and further three-dimensional reconstruction. Experiments were conducted in the Ku band with one transmitter (TX) and 16 equivalent receivers (RXs) to achieve three-dimensional imaging of three trihedral corner reflectors. However, the system has a large number of equivalent antennas and complex testing. In order to improve the coherence of the radar signal, a compensation algorithm is also used, and the system has high device and time costs. Summary of the invention

[0005] In view of the above, an object of the present invention is to provide a terahertz binocular ISAR system and method for three-dimensional imaging, which utilizes binocular vision imaging to simplify the radar structure, make the configuration more flexible, and help reduce the cost of the terahertz radar system.

[0006] To achieve the above-mentioned purpose of the invention, an embodiment provides a terahertz binocular ISAR system for three-dimensional imaging, including a transmitting link and a receiving link;

[0007] The transmission link is used to generate and transmit a terahertz signal;

[0008] The receiving link is used to receive two reflected signals of the terahertz signal relative to the target object in two different postures during the two measurements, and after restoring the two offset two-dimensional images using an inverse synthetic aperture radar two-dimensional imaging algorithm based on the two reflected signals, reconstruct the height and spatial position of the target object based on the two two-dimensional images.

[0009] Preferably, the receiving link includes a terahertz receiver, a pulse compression module and a binocular ISAR information processing module;

[0010] The terahertz receiver is used to receive a reflected signal of the terahertz signal reflected by a target object in space;

[0011] The pulse compression module is used to compress the received reflected signal;

[0012] The binocular ISAR information processing module is used to reconstruct the height and spatial position of the target object based on the two two-dimensional images after obtaining two staggered two-dimensional images based on two reflection signals using an inverse synthetic aperture radar two-dimensional imaging algorithm.

[0013] Preferably, the height of the target object is reconstructed based on the two two-dimensional images, and the process includes:

[0014] Image correction: Eliminate range migration, compensate residual phase and de-skew the two 2D images respectively;

[0015] Azimuth registration: select the marker, and then register the azimuth of the two corrected images so that the azimuth serial numbers of the markers in the two images are the same;

[0016] Target point calibration: set the threshold to filter out the target points in the two images after azimuth registration;

[0017] Information acquisition in the range direction: starting from the range gate with a peak in the first image, search forward and backward at the same position in the second image to find the best matching range gate with the same peak distribution until the last range gate with a peak. If a pair of matching range gates have the same sequence number, the range gate should be skipped, and then the two-dimensional coordinates of the target point corresponding to the peak in the two images are recorded;

[0018] Height calculation: Based on the two-dimensional coordinates of the target point in the two images and the formula for coordinate rotation, the height of the target point can be calculated. The target object contains multiple target points, and the height of the target object is determined based on the height of the target point.

[0019] Preferably, the inverse synthetic aperture radar two-dimensional imaging algorithm includes a range Doppler algorithm, a range migration algorithm, and a linear frequency modulation scaling algorithm.

[0020] Preferably, the terahertz receiver receives the reflected signal of the terahertz signal by down-conversion, and includes a subharmonic mixer, a photoconductive antenna, a Schottky barrier diode or a quantum well photodetector.

[0021] Preferably, the pulse compression module adopts a pulse compression method of hardware mixing and / or a pulse compression method of software matching filtering.

[0022] Preferably, the transmission link uses an electronics-based terahertz radiation source or an optics-based terahertz radiation source to generate a terahertz signal, wherein the electronics-based terahertz radiation source includes a terahertz radiation source based on vacuum electronics technology, a terahertz quantum cascade laser or a terahertz free electron laser; the optics-based terahertz radiation source includes a terahertz radiation source based on ultrafast laser technology or a terahertz radiation source based on optical beat frequency technology.

[0023] Preferably, the system further comprises a terahertz prism, which is arranged at the input end of the receiving link and is used for collimating and focusing the reflected signal and then inputting it into the receiving link.

[0024] To achieve the above-mentioned purpose of the invention, an embodiment further provides a three-dimensional imaging method, wherein the three-dimensional imaging method adopts the above-mentioned terahertz binocular ISAR system, and the method comprises the following steps:

[0025] A terahertz signal is generated and transmitted using a transmitting link;

[0026] The target object is adjusted to a first posture and a first measurement is performed, and a reflection signal of the terahertz signal relative to the target object in the first posture is received by using a receiving link;

[0027] The target object is adjusted to a second posture and a second measurement is performed, and a reflection signal of the terahertz signal relative to the target object in the second posture is received by using a receiving link;

[0028] The receiving link is used to restore the two offset two-dimensional images based on the reflected signals during the two measurements using the inverse synthetic aperture radar two-dimensional imaging algorithm, and then the height and spatial position of the target object are reconstructed based on the two two-dimensional images.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention combines binocular vision with a terahertz radar system. The receiving end link only requires one channel. Through two measurements, the target object can be reconstructed in three dimensions using two staggered images, which greatly reduces the coherence requirements for the terahertz radar signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 is a schematic structural diagram of a terahertz binocular ISAR system for three-dimensional imaging provided in an embodiment;

[0033] Figure 2 is a schematic diagram of two measurements provided in the embodiment;

[0034] Figure 3 is a schematic diagram of the structure of a system using an optical method as a terahertz source provided in an embodiment;

[0035] Figure 4is a flow chart of a three-dimensional imaging method provided in an embodiment. DETAILED DESCRIPTION

[0036] To make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation methods described herein are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0037] The inventive concept of the present invention is: in response to the technical problems of complex structure and high cost of the existing microwave imaging receiving end, the embodiment provides a terahertz binocular ISAR system and method for three-dimensional imaging, which combines binocular vision with a terahertz radar system. The receiving end link only needs one channel. Through two measurements, the target object can be reconstructed in three dimensions using two staggered images, which greatly reduces the coherence requirements for terahertz radar signals.

[0038] Figure 1 Schematic diagram of the structure of a terahertz binocular ISAR system for three-dimensional imaging provided in an embodiment. Figure 1 As shown, the terahertz binocular ISAR system provided in the embodiment includes a transmission link and a receiving link. The transmission link is used to generate a terahertz signal and transmit it to free space, and the terahertz signal is reflected by the target object in free space to form a reflection signal. The receiving link is used to receive the two reflection signals of the target object in two postures relative to the terahertz signal during the two measurements, and after restoring the two staggered two-dimensional images using the inverse synthetic aperture radar two-dimensional imaging algorithm based on the two reflection signals, the height and spatial position of the target object are reconstructed based on the two two-dimensional images.

[0039] like Figure 1 As shown, the transmission link includes a terahertz transmitter, which uses an electronics-based terahertz radiation source or an optics-based terahertz radiation source to generate a terahertz signal, wherein the electronics-based terahertz radiation source includes a terahertz radiation source based on vacuum electronics technology, a terahertz quantum cascade laser or a terahertz free electron laser; the optics-based terahertz radiation source includes a terahertz radiation source based on ultrafast laser technology or a terahertz radiation source based on optical beat frequency technology.

[0040] like Figure 1As shown, the receiving link includes a terahertz receiver, a pulse compression module and a binocular ISAR information processing module; wherein the terahertz receiver is used to receive the reflected signal of the terahertz signal reflected by the target object in space. Specifically, the reflected signal of the terahertz signal is received by down-conversion, including a subharmonic mixer, a photoconductive antenna, a Schottky barrier diode or a quantum well photodetector. In order to better receive the reflected signal, the system also includes a terahertz prism, which is arranged at the input end of the receiving link, that is, at the input end of the terahertz receiver, and is used to collimate and focus the reflected signal and then input it into the terahertz receiver to reduce the free space propagation loss.

[0041] The pulse compression module is used to compress the received reflected signal, specifically, using a pulse compression method of hardware frequency mixing and / or a pulse compression method of software matched filtering.

[0042] The binocular ISAR information processing module is used to reconstruct the height and spatial position of the target object based on the two two-dimensional images after recovering the two reflected signals using the inverse synthetic aperture radar two-dimensional imaging algorithm. Among them, the inverse synthetic aperture radar two-dimensional imaging algorithm includes the range Doppler algorithm, the range migration algorithm, and the linear frequency modulation scaling algorithm.

[0043] Reconstruct the height of the target object based on two 2D images, including:

[0044] Image correction: Eliminate range migration, compensate residual phase and de-skew the two 2D images respectively;

[0045] Azimuth registration: select the marker, and then register the azimuth of the two corrected images so that the azimuth serial numbers of the markers in the two images are the same;

[0046] Target point calibration: set the threshold to filter out the target points in the two images after azimuth registration;

[0047] Information acquisition in the range direction: starting from the range gate with a peak in the first image, search forward and backward at the same position in the second image to find the best matching range gate with the same peak distribution until the last range gate with a peak. If a pair of matching range gates have the same sequence number, the range gate should be skipped, and then the two-dimensional coordinates of the target point corresponding to the peak in the two images are recorded;

[0048] Height calculation: Based on the two-dimensional coordinates of the target point in the two images and the formula for coordinate rotation, the height of the target point can be calculated. The target object contains multiple target points, and the height of the target object is determined based on the height of the target point.

[0049] In the embodiment, when measuring on both sides using the terahertz binocular ISAR system, the angles of the target object are different. For example, Figure 2 As shown, during the first measurement, the target object is presented in the first posture, and during the second measurement, the target object is presented in the second posture. Based on the two two-dimensional images obtained by the two measurements of the two postures, three-dimensional reconstruction is performed to obtain the height and spatial position of the target object.

[0050] When using optical method as terahertz source, such as Figure 3 As shown, in the provided terahertz binocular ISAR system, the transmission link includes a tunable laser 1, an arbitrary waveform generator, an optical modulator, an optical filter, an optical amplifier, a tunable laser 2, a coupler, and a terahertz transmitter; wherein, the optical signal output by the tunable laser 1 is input to the photoelectric modulator, the output signal of the arbitrary waveform generator is connected to the electro-optical modulator to drive the electro-optical modulator to modulate the signal to the optical signal, the modulated optical signal and the optical signal after filtering and amplification by the optical filter and the optical amplifier are input to the coupler, the output signal of the optical amplifier is coupled to the optical signal from the tunable laser 2 through the coupler, the output power of the tunable laser 2 is set according to the output power of the optical amplifier to achieve power matching, and the combined signal is input to the terahertz generator to generate an ultra-wideband terahertz signal through the beat frequency. The frequency of the terahertz signal depends on the frequency difference between the tunable lasers 1 and 2. Among them, the terahertz transmitter uses a single-row carrier photodetector. The terahertz signal generated after the beat frequency is transmitted into the free space through the transmitting antenna, and after being reflected by the target object, it is focused by the terahertz lens to the antenna at the receiving end.

[0051] The terahertz receiver uses a terahertz mixer. The signals received from the two measurements are down-converted at the terahertz receiver, the intermediate frequency signal pulses are compressed, and two staggered two-dimensional images are restored through the algorithm of the inverse synthetic aperture radar. The height of the target point is reconstructed using these two images, and then the spatial position of the target point is reconstructed based on the reference images in the two two-dimensional images.

[0052] Based on the above three-dimensional imaging terahertz binocular ISAR system, the embodiment further provides a three-dimensional imaging method, comprising the following steps:

[0053] Step 1, using a transmission link to generate and transmit a terahertz signal;

[0054] Step 2, adjusting the target object to a first posture and performing a first measurement, using a receiving link to receive a reflection signal of the terahertz signal relative to the target object in the first posture;

[0055] Step 3, adjusting the target object to a second posture and performing a second measurement, using a receiving link to receive a reflection signal of the terahertz signal relative to the target object in the second posture;

[0056] Step 4: After using the receiving link to restore the two offset two-dimensional images based on the reflected signals during the two measurements using an inverse synthetic aperture radar two-dimensional imaging algorithm, the height and spatial position of the target object are reconstructed based on the two two-dimensional images.

[0057] The system and method provided by the above-mentioned embodiments combine binocular vision with a terahertz radar system. The receiving end link only requires one channel. Through two measurements, the target object can be three-dimensionally reconstructed using two offset images, which greatly reduces the coherence requirements for the terahertz radar signal.

[0058] The specific implementation methods described above have described in detail the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A terahertz binocular ISAR system for three-dimensional imaging, characterized in that: Including sending link and receiving link; The transmission link is used to generate and transmit a terahertz signal; The receiving link is used to receive two reflected signals of the terahertz signal relative to the target object in two postures during two measurements, and after recovering two staggered two-dimensional images using an inverse synthetic aperture radar two-dimensional imaging algorithm based on the two reflected signals, reconstruct the height and spatial position of the target object based on the two two-dimensional images, wherein reconstructing the height of the target object based on the two two-dimensional images includes: Image correction: Eliminate range migration, compensate residual phase and de-skew the two 2D images respectively; Azimuth registration: select the marker, and then register the azimuth of the two corrected images so that the azimuth serial numbers of the markers in the two images are the same; Target point calibration: set the threshold to filter out the target points in the two images after azimuth registration; Information acquisition in the range direction: starting from the range gate with a peak in the first image, search forward and backward at the same position in the second image to find the best matching range gate with the same peak distribution until the last range gate with a peak. If a pair of matching range gates have the same sequence number, the range gate should be skipped, and then the two-dimensional coordinates of the target point corresponding to the peak in the two images are recorded; Height calculation: Based on the two-dimensional coordinates of the target point in the two images and the formula for coordinate rotation, the height of the target point can be calculated. The target object contains multiple target points, and the height of the target object is determined based on the height of the target point.

2. The terahertz binocular ISAR system for three-dimensional imaging according to claim 1, characterized in that: The receiving link includes a terahertz receiver, a pulse compression module and a binocular ISAR information processing module; The terahertz receiver is used to receive a reflected signal of the terahertz signal reflected by a target object in space; The pulse compression module is used to compress the received reflected signal; The binocular ISAR information processing module is used to reconstruct the height and spatial position of the target object based on the two two-dimensional images after obtaining two staggered two-dimensional images based on two reflection signals using an inverse synthetic aperture radar two-dimensional imaging algorithm.

3. The terahertz binocular ISAR system for three-dimensional imaging according to claim 1, characterized in that: The inverse synthetic aperture radar two-dimensional imaging algorithm includes a range Doppler algorithm, a range migration algorithm, and a linear frequency modulation scaling algorithm.

4. The terahertz binocular ISAR system for three-dimensional imaging according to claim 2, characterized in that: The terahertz receiver uses down-conversion to receive the reflected signal of the terahertz signal, and includes a subharmonic mixer, a photoconductive antenna, a Schottky barrier diode or a quantum well photodetector.

5. The terahertz binocular ISAR system for three-dimensional imaging according to claim 2, characterized in that: The pulse compression module adopts a pulse compression method of hardware frequency mixing and / or a pulse compression method of software matched filtering.

6. The terahertz binocular ISAR system for three-dimensional imaging according to claim 1, characterized in that: The transmission link uses an electronics-based terahertz radiation source or an optics-based terahertz radiation source to generate a terahertz signal, wherein the electronics-based terahertz radiation source includes a terahertz radiation source based on vacuum electronic technology, a terahertz quantum cascade laser or a terahertz free electron laser; the optics-based terahertz radiation source includes a terahertz radiation source based on ultrafast laser technology or a terahertz radiation source based on optical beat frequency technology.

7. The terahertz binocular ISAR system for three-dimensional imaging according to claim 1, characterized in that: The system also includes a terahertz prism, which is arranged at the input end of the receiving link and is used for collimating and focusing the reflected signal and then inputting it into the receiving link.

8. A three-dimensional imaging method, characterized in that: The three-dimensional imaging method adopts a terahertz binocular ISAR system for three-dimensional imaging according to any one of claims 1 to 7, and the method comprises the following steps: A terahertz signal is generated and transmitted using a transmitting link; The target object is adjusted to a first posture and a first measurement is performed, and a reflection signal of the terahertz signal relative to the target object in the first posture is received by using a receiving link; The target object is adjusted to a second position and a second measurement is performed, and a reflection signal of the terahertz signal relative to the target object in the second position is received by using a receiving link; The receiving link is used to restore the two offset two-dimensional images based on the reflected signals during the two measurements using the inverse synthetic aperture radar two-dimensional imaging algorithm, and then the height and spatial position of the target object are reconstructed based on the two two-dimensional images.

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