A velocity and range resolution coherent correlation imaging lidar system and imaging method

Abstract

The application discloses a speed and spatial resolution coherent correlation imaging laser radar system and an imaging method. The method is as follows: a chirp light source system generates a narrow linewidth chirp modulation signal light and divides the light into a local oscillation signal light and a probe signal light, the probe signal light is irradiated to a target after being amplified and spatially modulated; the target echo light is mixed with the local oscillation signal light to obtain a quadrature low-frequency electric signal. A speed-space two-dimensional joint processing system forms a complex signal from the low-frequency electric signal collected for the first time and performs a short-time Fourier transform to extract a speed spectrum or a speed frequency track of the target, accumulates or integrates a time-frequency distribution image belonging to the target to obtain a probe signal, combines the probe signal with a spatially encoded light field, and reconstructs a spatial image of the first target in the speed dimension through a reconstruction algorithm. The application can separate targets in the same or adjacent spatial resolution units in the speed dimension without increasing an optical aperture and a surface array detector.

Description

Technical Field

[0001] This invention relates to the fields of lidar, coherent detection, correlation imaging, and computational imaging, and particularly to a velocity-dimensional resolved coherent correlation imaging lidar system and imaging method. The system uses a velocity-space two-dimensional joint resolution mechanism, utilizing the velocity frequency or velocity frequency trajectory in the coherent echo to separate spatially aliased targets, and combines the extracted detection signal with a spatially coded light field to reconstruct a spatial image of the target through correlation imaging. Background Technology

[0002] Laser correlation imaging illuminates a target with multiple known or recordable spatially modulated light fields, obtains the target echo intensity corresponding to each spatially modulated light field using a single-pixel detector, and then reconstructs the target's spatial image based on the correlation information between the spatially modulated light fields and the single-pixel echoes. This technique can transfer spatial resolution capabilities from area array detectors to active spatial modulation and computational reconstruction, and is suitable for computational imaging of weak echo targets and distant targets.

[0003] Optical coherent detection mixes the target echo light with the local oscillator light to obtain the beat frequency signal between the two. Compared with direct intensity detection, coherent detection can improve the sensitivity of weak light detection and retain the phase changes caused by target motion. Therefore, the radial velocity, vibration or micro-motion information of the target can be obtained from the Doppler frequency shift.

[0004] The improvement of existing spatial resolution capabilities mainly relies on increasing the optical aperture, improving the resolution of the spatial modulator, reducing the emitted light spot size, or increasing the number of spatial measurements. When two or more targets are located in the same or adjacent spatial resolution cells, the echoes of each target are mixed in the spatial dimension. For targets with complex spatial structures and a large number of scattering units, the mixed echoes will also produce strong coherent superposition and reconstruction crosstalk, resulting in target contour merging, positional deviation, or loss of details.

[0005] The target motion state provides an additional dimension of information for resolving the aforementioned spatial aliasing problem. When targets that cannot be directly distinguished in space have different radial velocities, their coherent echoes can manifest as different Doppler frequency components in the time-frequency domain. If only Doppler information is output as a velocity parameter without forming a single-pixel measurement sequence corresponding to each velocity component with a spatially modulated light field, it is difficult to directly utilize the velocity dimension to improve the spatial target resolution.

[0006] Furthermore, moving targets may maintain an approximately constant velocity, or they may exhibit acceleration, deceleration, periodic oscillations, or other non-stationary motions. Using a single full-time spectrum for non-stationary motion echoes can cause velocity components to broaden or overlap, making it impossible to accurately establish the correspondence between the target's velocity state and spatial measurement data. Therefore, a system and method are needed that uses short-time Fourier transform to extract fixed velocity spectral lines or time-varying velocity frequency trajectories, and combines the extracted velocity dimension information with a correlated imaging measurement model. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a velocity-dimensional resolution coherent correlation imaging lidar system and imaging method. Without increasing the optical aperture and area array detector, the target velocity dimension is used as the spatial target separation dimension. Detection signals are extracted from targets that are in the same or adjacent resolution units in space but whose spectra or spectral trajectories can be distinguished in the time-frequency domain. The spatial images of each target are then reconstructed by combining the spatially encoded light field, thereby achieving joint velocity-space two-dimensional resolution.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a coherent detection-correlated imaging lidar system, comprising a chirped light source system, an amplification system, a spatial modulation system, a spatial transmission system, a spatial receiving system, an IQ coherent processing system, a filtering and acquisition system, a velocity-space two-dimensional joint processing system, and a clock system. The chirped light source system generates a narrow-linewidth chirped modulated signal light and splits it into a local oscillation signal light and a detection signal light. The detection signal light sequentially enters the amplification system and the spatial modulation system to form a spatially encoded light field, which is then projected onto the target by the spatial transmission system, generating a target echo signal. This echo signal is received by the spatial receiving system and input to the IQ coherent processing system. The IQ coherent processing system receives the target echo signal and the local oscillation signal light and performs coherent mixing between them, outputting... , The low-frequency electrical signal is filtered, converted from analog to digital, and synchronously acquired by the filtering and acquisition system; the clock system provides synchronization control signals to the chirped light source system, the spatial modulation system, and the filtering and acquisition system, enabling the... Subspace encoded light field and the first Second-rate Low-frequency electrical signals correspond; the velocity-space two-dimensional joint processing system will... Second-rate , Low-frequency electrical signals are composed of complex signals, which are determined according to the target's speed. The motion within a single chirping cycle is analyzed by performing a short-time Fourier transform over a complex range to obtain the target's time-frequency distribution image; based on the... The velocity spectrum or velocity-frequency trajectory of each target in the time-frequency distribution image is used to extract the corresponding detection signal. The detection signal is then combined with the spatially coded light field, and the target is reconstructed using a reconstruction algorithm. The target in the speed dimension The spatial image below.

[0010] Furthermore, the chirped light source system is a chirped amplitude modulation light source or a chirped phase modulation light source, and its output end is provided with a beam splitting unit, one output being the local oscillation signal light and the other output being the detection signal light; the amplification system includes an optical fiber amplifier, a solid-state optical amplifier, or other optical amplification devices adapted to the wavelength of the chirped light source, used to amplify the detection signal light to the emission power required for target detection, thereby obtaining the amplified detection signal light.

[0011] Furthermore, the spatial modulation system is used to spatially modulate the amplified detection signal light according to a preset spatial coding sequence, in the... Subspace modulation forms a corresponding spatially encoded optical field, in which For integers, The total number of spatial modulations; the two-dimensional distribution of each spatially coded optical field is discretized and straightened to form a corresponding spatial measurement row vector; at the target distance Place, No. The subspace encoded light field is denoted as The spatial modulation system is a digital micromirror device, a spatial light modulator, or a pre-calibrated random speckle modulator.

[0012] Furthermore, the IQ coherent processing system includes An optical bridge and two sets of balanced photodetectors are used to output phase-orthogonal signals. Low-frequency electrical signals and Low-frequency electrical signals are used to preserve the amplitude and phase change information of the target echo.

[0013] Furthermore, the filtering and acquisition system includes a low-pass filter or band-pass filter, an analog-to-digital converter, and a data buffer unit, and, according to the synchronization control signal of the clock system, the data within each spatial modulation cycle... Ordered storage.

[0014] Furthermore, the velocity-space two-dimensional joint processing system along the first... The velocity spectrum or velocity frequency trajectory of a target, for targets belonging to the target By accumulating or integrating the time-frequency spectral intensity, we obtain the first... Subspace modulation, target distance Corresponding detection signal The detection signals obtained from multiple measurements With multiple spatial coding light fields and target By combining the equations, we obtain the interaction equations among the three elements. Using these equations in conjunction with the reconstruction algorithm, we can reconstruct the first... The target in the speed dimension spatial image below .

[0015] Furthermore, the first The target distance mentioned in this measurement The time delay corresponding to the time-frequency signal Confirmed, specifically the target distance. Equal to the speed of light In time delay Half the distance of internal propagation; delay The spectral components introduced by chirping modulation in the time-frequency curve of the target can be used as a reference. Confirmed; the velocity-space two-dimensional joint processing system processes all target aliased signals within the signal pulse acquisition time period. The corresponding complex signal is subjected to short-time Fourier transform; for targets with constant velocity, the velocity spectrum with constant frequency position in the time-frequency domain is extracted; for targets with velocity that changes with time, the velocity frequency trajectory that changes with time in the time-frequency domain is extracted.

[0016] Furthermore, when processing the time-frequency curve, the velocity-space two-dimensional joint processing system decouples the parameters based on the specific relationship between the target's Doppler and micro-Doppler frequencies, and then calculates the target range. Corresponding delay and the speed corresponding to the target ; spectral components introduced by the target due to chirped modulation Modulation rate of chirped light With delay The product of; the Doppler component introduced by the target motion. Spectral components introduced by chirp modulation Synthesized Doppler frequencies For the first The time-frequency composition of each target, and the frequency components on the time-frequency distribution image. One part of the curve is an independent curve, and the other part of the curve comes from... The two components are decoupled to obtain the Doppler component. .

[0017] Secondly, the present invention provides a method for imaging based on the coherent detection correlation imaging lidar system, comprising the following steps:

[0018] Step 1: The clock system controls the chirped light source system, spatial modulation system, and filtering and acquisition system to work synchronously. The spatial modulation system generates [data / signals] sequentially. A spatially encoded light field;

[0019] Step 2, in the When a spatially encoded light field illuminates a target, the space receiving system receives the target's echo light signal, and the IQ coherent processing system 7 outputs... Low-frequency electrical signals and The low-frequency electrical signal is filtered and acquired by the system to obtain the corresponding digital sampled data.

[0020] Step 3, the Second collection Low-frequency electrical signals and The low-frequency electrical signal is used to form a complex signal, and a short-time Fourier transform is performed on the complex signal to obtain a time-frequency distribution image; on the time-frequency distribution image, for a velocity of... The Extract the corresponding chirped modulation spectral components from each target. and Doppler frequency And calculate the delay. Target distance, target speed Based on the target distance, the spatially encoded light field is obtained. ;

[0021] Step 4, for the first The velocity spectrum or time-frequency trajectory of each target is obtained respectively. The detection signal corresponding to the subspace modulation is reconstructed based on the correlation imaging relationship after velocity selection. The target in the speed dimension The spatial image below;

[0022] Step 5: Independently output, overlay, or calibrate the spatial images corresponding to different targets or different velocity layers to achieve spatial target resolution based on the velocity dimension.

[0023] Furthermore, when the first The first goal and the first When two targets are in the same or adjacent spatial resolution units in the spatial dimension, if the difference between their velocity frequencies within at least one short-time Fourier transform time window is not less than the frequency resolution corresponding to that time window, or if their velocity frequency trajectories can be distinguished by a trajectory tracking algorithm, then the detection signals are extracted along the two velocity frequency trajectories respectively and reconstructed accordingly.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The velocity dimension is transformed from a simple target motion parameter output into a target separation dimension for correlated imaging. For targets located in the same or adjacent resolution cells in space but with different velocity states, they can be separated first in the time-frequency domain and then spatially reconstructed separately.

[0026] 2. The velocity frequency within a local time window is obtained by using short-time Fourier transform, so it is applicable to both uniform targets with constant velocity and targets that are accelerating, decelerating, vibrating, or whose velocity changes with time.

[0027] 3. Distance, velocity, and spatial image acquisition can be completed using the same narrow-linewidth chirped light source, the same spatial modulation channel, and the same IQ coherent receiving channel, without the need to add multi-wavelength light sources, area array receivers, or additional spectral channels.

[0028] 4. For targets with complex spatial structures, velocity layering can reduce the effective spatial complexity of each velocity layer and the coherent crosstalk between different moving parts, which helps to reduce reconstruction artifacts and improve target separation stability. Attached Figure Description

[0029] Figure 1 This is a structural block diagram of the coherent detection correlation imaging lidar system based on velocity dimension resolution, i.e., joint velocity-space two-dimensional resolution, according to the present invention.

[0030] Figure 2 The time-frequency distribution image of a single measurement echo signal when the chirped modulation rate is 0 or the translational rate is 0;

[0031] Figure 3 This is a schematic diagram illustrating the principle of joint velocity-space resolution.

[0032] The figures are labeled as follows: 1-Chirped light source system; 2-Amplification system; 3-Spatial modulation system; 4-Spatial transmission system; 5-Target; 6-Spatial receiving system; 7-IQ coherent processing system; 8-Filtering and acquisition system; 9-Velocity-space two-dimensional joint processing system; 10-Clock system. Detailed Implementation

[0033] The following is combined Figure 1 The system composition and imaging process of the present invention will be further described below. It should be understood that the following embodiments are used to illustrate the technical solution of the present invention, and not to limit the scope of protection; without departing from the core concept of the present invention, each module may adopt functionally equivalent devices or processing methods.

[0034] Firstly, such as Figure 1As shown, the present invention provides a velocity-dimensionally resolved coherent correlation imaging lidar system, the system comprising a chirped light source system 1, an amplification system 2, a spatial modulation system 3, a spatial transmission system 4, a spatial receiving system 6, an IQ coherent processing system 7, a filtering and acquisition system 8, a velocity-space two-dimensional joint processing system 9, and a clock system 10, the system being used to detect target 5.

[0035] The probe light output of the chirped light source system 1 is sequentially connected to the amplification system 2, the spatial modulation system 3, and the spatial transmission system 4. The chirped light source system 1 generates a narrow-linewidth chirped modulated signal light. This narrow-linewidth chirped modulated signal light is split into a local oscillation signal light and a probe signal light by an internal or external beam splitter. The local oscillation signal light is input to the IQ coherent processing system 7, and the probe signal light is sequentially input to the amplification system 2, the spatial modulation system 3, and the spatial transmission system 4. The amplification system 2 amplifies the probe signal light to the transmission power required for target detection, and the amplified probe signal light enters the spatial modulation system 3. The spatial modulation system 3 spatially modulates the amplified probe signal light according to a preset spatial coding sequence. Subspace modulation forms a corresponding spatially encoded light field; the space transmission system 4 projects the spatially encoded light field onto the target 5; the target 5 generates a target echo light signal, which is received by the space receiving system 6 and input into the IQ coherent processing system 7; the IQ coherent processing system 7 coherently mixes the target echo light signal with the local oscillation signal light, outputting two orthogonal paths. Low-frequency electrical signals and The low-frequency electrical signal is sent to the filtering and acquisition system 8; the data output terminal of the filtering and acquisition system 8 is connected to the speed-space two-dimensional joint processing system 9, and the filtering and acquisition system 8 processes the signal. Low-frequency electrical signals and The low-frequency electrical signal is filtered, converted from analog to digital, and synchronously acquired, and then input into the velocity-space two-dimensional joint processing system 9. The velocity-space two-dimensional joint processing system 9 will then process the low-frequency electrical signal. Second collection , Two low-frequency electrical signals are combined into a complex signal, which is then analyzed based on the target's speed. The motion within a single chirping cycle is analyzed by performing a short-time Fourier transform on the complex signal over a complex range to obtain the time-frequency distribution image of the target; according to the... The velocity spectrum or velocity-frequency trajectory of each target in the time-frequency distribution image is used to extract the corresponding detection signal. Based on the acquired detection signal, it is combined with the spatially coded light field to reconstruct the first target using a reconstruction algorithm. The target in the speed dimension The spatial image below. Clock system 10 outputs synchronization signals to chirped light source system 1, spatial modulation system 3, and filtering and acquisition system 8 respectively, enabling the... Subspace encoded light field and the first Second-rate Corresponding to low-frequency electrical signals.

[0036] Specifically, the chirped light source system 1 generates narrow-linewidth chirped modulated signal light, specifically a chirped amplitude modulated light source or a chirped phase modulated light source, with a beam splitting unit at its output end. The chirped modulated signal light is specifically a chirped amplitude modulated light signal or a chirped phase modulated light signal. The narrow linewidth ensures that the probe signal light and the local oscillator light can still interfere within the working distance. A wider linewidth results in a shorter working distance. The specific linewidth depends on the working distance. A narrow linewidth is a condition that ensures the two beams can interfere; unless the working distance is specified, the exact linewidth is usually not stated. In this invention, it is only used to indicate that the targets are within the working distance and the returned probe signal light and local oscillator signal light can effectively interfere.

[0037] The amplification system 2 is used to amplify the power of the detection signal light, so that the spatially modulated detection signal light meets the requirements of long-distance illumination and target echo signal-to-noise ratio. The amplification system 2 can be an optical fiber amplifier, a solid-state optical amplifier, or other optical amplification devices adapted to the wavelength of the chirped light source.

[0038] The spatial modulation system 3 spatially modulates the amplified detection signal light according to a preset spatial coding sequence to form a spatially coded light field. The spatial modulation system 3 can employ a digital micromirror device, a liquid crystal spatial light modulator, a phase-type spatial light modulator, or a pre-calibrated random speckle modulator. Subspace modulation forms the first A spatially encoded light field, wherein... From 1 to integers, This represents the total number of spatial modulations. The two-dimensional distribution of each spatially coded optical field is discretized and straightened to form a corresponding spatial measurement row vector; at the target distance... Place, No. The subspace encoded light field is denoted as .

[0039] The space transmission system 4 is used to collimate, expand, and image the space-coded light field and project it onto the area where the target 5 is located, and the target 5 generates a target echo light signal; the space receiving system 6 is used to gather the scattered light returned by the target 5 and couple the target echo light signal into the IQ coherent processing system 7.

[0040] The IQ coherent processing system 7 optically mixes the target echo light signal with the local oscillation signal light, and outputs phase-orthogonal signals. Low-frequency electrical signals and Low-frequency electrical signals. The IQ coherent processing system 7 includes... Optical bridge, the Optical bridges can also be called An optical mixer, including two sets of balanced photodetectors connected to its output, thereby suppressing common-mode noise while retaining echo amplitude and phase change information.

[0041] The filtering and acquisition system 8 is for the... Low-frequency electrical signals and The low-frequency electrical signal is subjected to low-pass or band-pass filtering, analog-to-digital conversion, buffering, and numbering to determine the first... Subspace modulation corresponds to Low-frequency electrical signals and The low-frequency electrical signal and the spatially encoded optical field number are jointly input into the velocity-space two-dimensional joint processing system 9. The filtering and acquisition system 8 may include a low-pass filter or a band-pass filter, an analog-to-digital converter, and a data buffer unit.

[0042] The clock system 10 generates a unified clock and synchronization control signal, synchronously controlling the chirped light source system 1, the spatial modulation system 3, and the filtering and acquisition system 8 to ensure the chirping period, spatial modulation period, and... The sampling periods have a definite temporal relationship, such that the first sampling period... Subspace encoded light field and the first Second-rate Low-frequency electrical signals and Each low-frequency electrical signal corresponds one-to-one. Within each spatial modulation cycle, the filtering and acquisition system 8 acquires signals covering a complete chirp cycle. Low-frequency electrical signals and Low-frequency electrical signals are used for motion analysis within a single chirped cycle or time-frequency trajectory analysis across adjacent chirped cycles.

[0043] The velocity-space two-dimensional joint processing system 9 is used to process the first Second collection , Two low-frequency electrical signals form a complex signal, which is determined according to the target speed. The motion within a single chirping cycle is related to the... , Two low-frequency electrical signals are subjected to short-time Fourier transform in the complex range to obtain the time-frequency distribution image of the target; according to the first... The velocity spectrum or velocity frequency trajectory of a target in the time-frequency distribution image, for targets belonging to the target By accumulating or integrating the time-frequency spectral intensity, we obtain the first... Subspace modulation, target distance Corresponding detection signal and the detection signal is compared with the first Subspace modulation, target distance Corresponding spatial encoded light field Combined, the first is reconstructed through a reconstruction algorithm. The target in the speed dimension spatial image below .

[0044]

[0045]

[0046] in, superscript Indicates the first Subspace modulation, subscript Indicates the first One goal; superscript Indicates the first Subspace modulation, subscript Indicates the distance to the target; Indicates the first The velocity dimension corresponding to each target. For multiple measurements corresponding to the first Time-frequency signal corresponding to each target , For multiple measurements corresponding to the first Spatial encoded light field corresponding to each target .

[0047] The velocity-space two-dimensional joint processing system 9 also processes data according to the target distance. Corresponding round-trip delay Select the distance position and determine the velocity dimension according to the correspondence between the velocity spectrum and the target radial velocity. When at least two targets are located in the same or adjacent spatial resolution cells and their spectra or spectral trajectories can be distinguished in the time-frequency domain, the detection signals corresponding to each target are extracted and the spatial images of each target are reconstructed. The velocity-space two-dimensional joint processing system 9 collects all target aliased signals within the signal pulse acquisition time period. The corresponding complex signal is subjected to short-time Fourier transform; for targets with constant velocity, the velocity spectrum with constant frequency position in the time-frequency domain is extracted; for targets with velocity that changes with time, the velocity frequency trajectory that changes with time in the time-frequency domain is extracted.

[0048] The velocity-space two-dimensional joint processing system 9 determines the correspondence between the spectrum and the target radial velocity according to the following formula:

[0049]

[0050] in, =2 / The Doppler frequency introduced for the target motion, = The distance frequency introduced for chirp modulation, To modulate the center wavelength of the chirped signal light, The modulation rate of the chirped light; for targets whose speed varies with time, This represents the instantaneous velocity at the moment corresponding to the short-time Fourier transform time window.

[0051] In an optional embodiment, the velocity-space two-dimensional joint processing system 9 can also adjust the total number of spatial modulations according to the spatial complexity of the target at each velocity layer. Short-time Fourier transform window length, window function overlap rate, and reconstruction regularization parameters.

[0052] Secondly, the present invention provides an imaging method based on the radar system, comprising the following steps:

[0053] Step 1: The clock system 10 controls the chirped light source system 1, the spatial modulation system 3, and the filtering and acquisition system 8 to work synchronously. The spatial modulation system 3 generates sequentially... The spatially encoded light field. For the first... A spatially encoded optical field, filtered and acquired by an 8-synchronous acquisition system. Low-frequency electrical signals and Low-frequency electrical signals make the first Subspace encoded light field and the first Second-rate It has a definite numbering and timing correspondence.

[0054] Step 2, in the When a spatially encoded light field illuminates target 5, the spatial receiving system 6 receives the target echo light signal. The IQ coherent processing system 7 coherently mixes the target echo light signal with the local oscillator signal light and outputs the signal. Low-frequency electrical signals and Low-frequency electrical signal; will the first Second collection Low-frequency electrical signals and The low-frequency electrical signals of the circuit are used to form a complex signal to obtain the first... The complex signal corresponding to subspace modulation:

[0055]

[0056] in, Sampling time, The unit is the imaginary number. The amplitude of a complex echo signal represents the intensity of the target echo, and the phase change of the complex echo signal represents the relative motion between the target and the system.

[0057] Step 3, for the complex signal containing all target echo optical signals Perform a short-time Fourier transform to obtain the first... Subspace modulation and aliasing of the time-frequency distribution images corresponding to all target echo optical signals. The short-time Fourier transform must be applied to all... All target echo signals are measured. For targets with constant velocity, the velocity spectrum with constant frequency position is extracted; for targets with velocity varying over time, the velocity frequency trajectory varying over time is extracted. The short-time Fourier transform expression is:

[0058]

[0059] in, This is the center moment of the short-time Fourier transform time window. For frequency, The window function can be a Hanning window, Hamming window, Gaussian window, or other time-frequency analysis window; the window length and overlap rate are determined based on the target's velocity change rate and the required velocity resolution.

[0060] Step 4: Perform spectral peak detection, time-frequency ridge detection, or trajectory tracking on the time-frequency distribution image to obtain the first... The velocity spectrum or velocity frequency trajectory corresponding to each target, where Number the target. For targets with changing velocity, This represents the instantaneous velocity corresponding to the velocity frequency trajectory within the current time window, or it represents the velocity dimension parameter used to identify the entire velocity frequency trajectory.

[0061] Step 5: Directly extract the distance frequency introduced by chirp modulation from the time-frequency distribution image obtained in Step 3. And thus determine the time delay. Then determine the target distance according to the following formula. :

[0062]

[0063] in, It is the speed of light. Simultaneously, it utilizes a linear scaling relationship based on the target distance. Standard distance from the designed emission optical system The multiple of the value determines the spatially encoded light field corresponding to each measurement. .

[0064] Step 6: Determine the velocity dimension based on the correspondence between the velocity frequency, range frequency, and target radial velocity in the chirped coherent echo.

[0065]

[0066] in, =2 / The Doppler frequency generated by the target motion, = The distance frequency introduced by the delay of the chirped signal. target distance The spectral characteristic frequencies observed at that location, To modulate the center wavelength of the chirped signal light, To modulate the modulation rate of chirped light, The radial velocity of the target relative to the lidar.

[0067] Since the target distance has been determined in step 5. , and distance frequency term Given a quantity, it can be obtained from... Deduction or compensation Obtain the Doppler frequency And further obtain the target speed. For a target whose speed changes over time, This represents the instantaneous velocity at the moment corresponding to the short-time Fourier transform time window.

[0068] Step 7, for the first The velocity spectrum or velocity frequency trajectory of a target, for targets belonging to the target By accumulating or integrating the time-frequency spectral intensity, we obtain the first... Subspace modulation, target distance Corresponding detection signal The accumulation or integration can be performed within a preset frequency bandwidth covering the target's velocity spectrum or velocity frequency trajectory; due to the target The velocity dimension has been determined by the selected velocity spectrum or velocity frequency trajectory. Do not repeat the marking in the subscript of the detected signal.

[0069] Step 8, the first Subspace encoded light field at target distance The corresponding spatial encoded light field is denoted as , will the The target in the speed dimension The spatial image below is denoted as Suppose the target space is discretized as follows: Each spatial unit encodes the light field. The dimension is Spatial images The dimension is . No. The imaging relationship corresponding to subspace modulation is:

[0070]

[0071] In the formula, superscript Indicates the first Subspace modulation, subscript Indicates the first One goal; superscript Indicates the first Subspace encoded light field, subscript Indicates the distance to the target; subscript Indicates the first One goal, superscript This represents the velocity dimension corresponding to the target.

[0072] Step 9, after Subspace modulation, the first Each detection signal corresponding to the target and each spatial encoding light field Arrange them separately to obtain , The following measurement equation is formed:

[0073]

[0074] Based on the above measurement relationships, the solution for the first pixel can be obtained using traditional association algorithms, compressed sensing algorithms, sparse constraint algorithms, total variation constraint algorithms, or other single-pixel imaging reconstruction algorithms. The target in the speed dimension spatial image below .

[0075] When the The first goal and the first When two targets are located in the same or adjacent spatial resolution cells, if the difference between their velocity frequencies within at least one short-time Fourier transform time window is not less than the frequency resolution corresponding to that time window, or if their velocity frequency trajectories can be distinguished by a trajectory tracking algorithm, then the detection signals are extracted along the two velocity frequency trajectories respectively and reconstructed accordingly. The velocity frequency difference condition can be expressed as:

[0076]

[0077] in, and respectively At that moment, the The first goal and the first The time-frequency corresponding to each target on the time-frequency distribution image. This represents the frequency resolution corresponding to the time-frequency distribution image. For targets whose velocity trajectories intersect, the target number can be maintained by utilizing the continuity of the trajectories before and after the intersection, the target distance, the spatially predicted position, or the continuity of the amplitude. Consistency.

[0078] The velocity-space two-dimensional joint processing system 9 can adjust parameters such as the short-time Fourier transform window length and window function overlap rate based on the distribution of the spectral curves after the short-time Fourier transform. When the velocity spectral spacing is small, the window length can be increased to improve frequency resolution; when the velocity changes rapidly, the window length can be shortened or the overlap rate can be increased to improve time tracking capability.

[0079] The velocity-dimensional-based spatial resolution, also known as velocity-space two-dimensional joint resolution, as described in this invention refers to using the velocity dimension to form independent measurement sequences from the target scattering components that were originally superimposed in a single spatial reconstruction, and then reconstructing their spatial images separately. The velocity dimension performs target sorting, while the spatial dimension performs target image reconstruction; together, they constitute the joint resolution process. This method does not require changes to the optical apertures of the space transmission and reception systems.

[0080] In one embodiment, the chirped light source system 1 uses a center wavelength of A narrow-linewidth continuous-wave laser and a chirped modulator are used. The split probe signal light is amplified by amplification system 2 and then sent to spatial modulation system 3, which employs digital micromirror devices. The digital micromirror devices are sequentially loaded... A binary random pattern, a Hadamard pattern, or other orthogonal / non-orthogonal spatially encoded pattern. Each pattern is imaged onto the target area by the spatial emission system 4 and the corresponding spatial measurement row vector is stored by the velocity-space two-dimensional joint processing system 9; the pattern can also be loaded by a spatial light modulator or generated by a pre-calibrated random speckle modulator.

[0081] Target 5 may include two or more moving targets spaced apart from each other at a distance smaller than the system's conventional spatial resolution scale, or it may include a single complex target with multiple different moving parts. Each target or moving part may be located at the same distance gate, adjacent distance gates, or different distance gates. The space receiving system 6 uses a condenser lens and single-mode or few-mode receiving optical fibers to converge the total echo; therefore, its output is a superimposed echo of the scattered components within the target region.

[0082] The IQ coherent processing system 7 enables the total echo and local oscillation signal light to be processed together. Optical bridge or equivalent The mixing occurs in the optical mixer, and the output is obtained after passing through two sets of balanced photodetectors. Luhe Low-frequency electrical signals. Due to The signal constitutes a complex echo, and the phase change over time can preserve the Doppler or micro-Doppler frequency information of different targets. The filtering and acquisition system 8 acquires the target echo light signal corresponding to each spatial coding pattern during its retention period. The data is stored in an orderly manner according to the synchronization signal of the clock system 10.

[0083] The velocity-space two-dimensional joint processing system 9 first obtains the distance frequency from the time-frequency distribution image obtained by the short-time Fourier transform. Then determine the round-trip time of the target. and distance The chirped coherent echo at the target distance The frequency spectrum at a certain point satisfies the relationship between the target radial velocity and the frequency spectrum at that point. = + =2 / + Once the target distance is determined, the Doppler frequency corresponding to the target's motion can be obtained. For multiple targets within the same range gate, whose range frequency terms are the same or similar, a short-time Fourier transform can be performed on the complex signal corresponding to the range gate, and further separated based on the Doppler frequency difference. If two targets are traveling at constant radial velocities... and When there is motion, two velocity spectral lines with basically unchanged frequency positions are formed in the time-frequency image; if one of the targets is accelerating, the corresponding velocity frequency trajectory will shift continuously with time.

[0084] In the In subspace modulated data, the velocity-space two-dimensional joint processing system 9 along the first... The fixed velocity spectrum or time-varying velocity frequency trajectory of a target, for targets belonging to the target By accumulating or integrating the time-frequency spectral intensity, we obtain the first... Subspace modulation, target distance Corresponding detection signal .right From 1 to Repeat this process to obtain the first... A set of single-pixel velocity measurements selected for each target. This set of measurements contains only echo components that match the selected velocity spectrum or velocity frequency trajectory, thereby suppressing other target components that spatially overlap but have different velocity states.

[0085] Will One detection signal With the corresponding Space measurement row vector The measurement equations are composed, and the correlation imaging reconstruction algorithm is used to solve the first... The target in the speed dimension spatial image below In one embodiment, least-squares reconstruction with total variational constraints is employed; in another embodiment, sparse reconstruction is performed using compressed sensing, orthogonal matching pursuit, iterative threshold shrinkage, or second-order cone programming. Different reconstruction algorithms do not alter the fundamental technical essence of this invention: utilizing the velocity dimension to form independent measurement sequences and combining them with spatially coded light fields to reconstruct spatial images.

[0086] For example, the goal and target The chirping modulation rate is 0 or the translational velocity is 0, and spatial overlap occurs in conventional correlated images, targeting... and target They all vibrate randomly, such as Figure 2 As shown. The velocity-space two-dimensional joint processing system 9 extracts the target respectively. and target The time-velocity spectral trajectory is used to generate two sets of detection signals under each spatial coding pattern, and the target is reconstructed using the same set of spatially coded light fields. and target Images, such as Figure 3 As shown. Thus, even if two targets are indistinguishable in a spatial image without velocity separation, independent spatial images can be obtained after selecting the velocity dimension.

[0087] For complex targets with a stationary main body and vibrating components, zero-velocity or low-velocity components can be used to recover the main body image, while time-varying velocity components corresponding to vibration or periodic motion can be used to recover the moving component image. The velocity-space two-dimensional joint processing system 9 can also superimpose images from each velocity layer to form a complete target image and output the velocity state corresponding to each spatial location.

[0088] When the target velocity difference is small, resulting in partial overlap of velocity spectral lines, the frequency resolution can be improved by extending the short-time Fourier transform window length. When the target velocity changes rapidly, the window length can be shortened or the window function overlap rate can be increased to improve the temporal resolution. The velocity-space two-dimensional joint processing system 9 can adaptively select the window length, overlap rate, and total number of spatial modulations based on the velocity spectral curvature, spectral line spacing, signal-to-noise ratio, and the spatial complexity parameters characterized by the number of non-zero scattering units, connected regions, or total variation of the spatial images of each velocity layer. And refactor the regularization parameters.

[0089] In the above embodiments, the spatial modulation pattern can be a known deterministic pattern or a pre-calibrated random speckle pattern; the distance position can be obtained through short-time Fourier transform; the velocity frequency trajectory can be obtained through different time-frequency ridge extraction methods. Subspace modulation, target distance Corresponding detection signal With spatially encoded light field Combine, reconstruct the first The target in the speed dimension spatial image below The equivalent schemes for separating uniform or variable speed target velocities using short-time Fourier transform are all part of the concept of this invention; the technical essence of the equivalent devices, frequency symbol conventions, or distance-frequency compensation methods used do not change the velocity dimension to form an independent measurement sequence and achieve spatial reconstruction.

Claims

1. A coherent correlation imaging lidar system, characterized in that, It includes a chirped light source system, an amplification system, a spatial modulation system, a spatial transmission system, a spatial receiving system, an IQ coherent processing system, a filtering and acquisition system, a velocity-space two-dimensional joint processing system, and a clock system. The chirped light source system generates narrow-linewidth chirped modulated signal light and splits it into local oscillation signal light and probe signal light. The probe signal light sequentially enters the amplification system and the spatial modulation system to form a spatially encoded light field, which is then projected onto the target by the spatial transmission system, generating a target echo light signal that is received by the spatial receiving system and input to the IQ coherent processing system. The IQ coherent processing system receives the target echo optical signal and the local oscillator signal, coherently mixes them, and outputs... , The low-frequency electrical signal is filtered, converted from analog to digital, and synchronously acquired by the filtering and acquisition system. The clock system provides synchronization control signals to the chirped light source system, spatial modulation system, and filtering and acquisition system, enabling the... Subspace encoded light field and the first Second-rate Low-frequency electrical signals correspond; the velocity-space two-dimensional joint processing system will... Second-rate , Low-frequency electrical signals are composed of complex signals, which are determined according to the target's speed. The motion within a single chirping cycle is analyzed by performing a short-time Fourier transform over a complex range to obtain the time-frequency distribution image of the target; based on the... The velocity spectrum or velocity-frequency trajectory of each target in the time-frequency distribution image is used to extract the corresponding detection signal. The detection signal is then combined with the spatially coded light field, and the target is reconstructed using a reconstruction algorithm. The target in the speed dimension The spatial image below.

2. The coherent correlation imaging lidar system according to claim 1, characterized in that: The narrow linewidth specifically ensures that the detection signal light and the local oscillation light can still interfere within the working distance; the chirped light source system is a chirped amplitude modulation light source or a chirped phase modulation light source, and its output end is equipped with a beam splitting unit, one output being the local oscillation signal light and the other output being the detection signal light; the amplification system includes an optical fiber amplifier, a solid-state optical amplifier, or other optical amplification devices adapted to the wavelength of the chirped light source, used to amplify the detection signal light to the emission power required for target detection, thereby obtaining the amplified detection signal light.

3. The coherent correlation imaging lidar system according to claim 1, characterized in that: The spatial modulation system is used to spatially modulate the amplified detection signal light according to a preset spatial coding sequence, in the... Subspace modulation forms a corresponding spatially encoded optical field, in which For integers, The total number of spatial modulations; the two-dimensional distribution of each spatially coded optical field is discretized and straightened to form a corresponding spatial measurement row vector; at the target distance Place, No. The subspace encoded light field is denoted as The spatial modulation system is a digital micromirror device, a spatial light modulator, or a pre-calibrated random speckle modulator.

4. The coherent correlation imaging lidar system according to claim 1, characterized in that: The IQ coherence processing system includes An optical bridge and two sets of balanced photodetectors are used to output phase-orthogonal signals. Low-frequency electrical signals and Low-frequency electrical signals are used to preserve the amplitude and phase change information of the target echo.

5. The coherent correlation imaging lidar system according to claim 1, characterized in that: The filtering and acquisition system includes a low-pass filter or band-pass filter, an analog-to-digital converter, and a data buffer unit, and, according to the synchronization control signal of the clock system, it loads data within each spatial modulation cycle. Ordered storage.

6. The coherent correlation imaging lidar system according to claim 1, characterized in that: The velocity-space two-dimensional joint processing system along the first The velocity spectrum or velocity frequency trajectory of a target, for targets belonging to the target By accumulating or integrating the time-frequency spectral intensity, we obtain the first... Subspace modulation, target distance Corresponding detection signal The detection signals obtained from multiple measurements With multiple spatial coding light fields and target By combining the equations, we obtain the interaction equations among the three elements. Using these equations in conjunction with the reconstruction algorithm, we can reconstruct the first... The target in the speed dimension spatial image below .

7. The coherent correlation imaging lidar system according to claim 6, characterized in that: No. The target distance mentioned in this measurement Time delay corresponding to the time-frequency distribution image Confirmed, specifically the target distance. Equal to the speed of light In time delay Half the distance of internal propagation; delay The spectral components introduced by chirping modulation in the time-frequency distribution image of the target can be used as a basis. Confirmed; the velocity-space two-dimensional joint processing system processes all target aliased signals within the signal pulse acquisition time period. The corresponding complex signal is subjected to short-time Fourier transform; for targets with constant velocity, the velocity spectrum line with constant frequency position in time-frequency is extracted; for targets with velocity that changes with time, the velocity frequency trajectory that changes with time in time-frequency is extracted.

8. The coherent correlation imaging lidar system according to claim 7, characterized in that: The velocity-space two-dimensional joint processing system, when processing time-frequency distribution images, decouples the target based on the specific relationship between the Doppler and micro-Doppler frequencies of the target, and then solves for the target distance. Corresponding delay and the speed corresponding to the target ; Spectral components introduced by the target due to chirp modulation Modulation rate of chirped light With delay The product of; the Doppler component introduced by the target motion. Spectral components introduced by chirp modulation Synthesized Doppler frequencies For the first The time-frequency composition of each target, and the frequency components on the time-frequency distribution image. One part of the curve is an independent curve, and the other part of the curve comes from... The two components are decoupled to obtain the Doppler component. .

9. A method for imaging using the coherent correlation imaging lidar system according to any one of claims 1-8, characterized in that, Includes the following steps: Step 1: The clock system controls the chirped light source system, spatial modulation system, and filtering and acquisition system to work synchronously. The spatial modulation system generates [data / signals] sequentially. A spatially encoded light field; Step 2, in the When a spatially encoded light field illuminates a target, the space receiving system receives the target's echo light signal, and the IQ coherent processing system (7) outputs... Low-frequency electrical signals and The low-frequency electrical signal is filtered and acquired by the system to obtain the corresponding digital sampled data. Step 3, the Second collection Low-frequency electrical signals and The low-frequency electrical signal is used to form a complex signal, and a short-time Fourier transform is performed on the complex signal to obtain a time-frequency distribution image; on the time-frequency distribution image, for a velocity of... The Extract the corresponding chirped modulation spectral components from each target. and Doppler frequency And calculate the delay. Target distance, target speed ; Based on the target distance, the spatially encoded light field is obtained. ; Step 4, for the first The velocity spectrum or time-frequency trajectory of each target is obtained respectively. The detection signal corresponding to the subspace modulation is reconstructed based on the correlation imaging relationship after velocity selection. The target in the speed dimension The spatial image below; Step 5: Independently output, overlay, or calibrate the spatial images corresponding to different targets or different velocity layers to achieve spatial target resolution based on the velocity dimension.

10. The method according to claim 9, characterized in that: When the When the first target and the qth target are in the same or adjacent spatial resolution units in the spatial dimension, if the difference between their velocity frequencies within at least one short-time Fourier transform time window is not less than the frequency resolution corresponding to that time window, or if their velocity frequency trajectories can be distinguished by a trajectory tracking algorithm, then the detection signals are extracted along the two velocity frequency trajectories respectively and reconstructed accordingly.

Images