Active-passive dual-mode single-photon lidar imaging system and method

Abstract

The application discloses a kind of active-passive dual-mode single-photon laser radar imaging system and method, belong to single-photon laser radar technical field.The system includes transmitting module, receiving module and control module.Transmitting module includes laser and laser amplification unit (1), collimating mirror (2), photoelectric detector (3) and delay controller (4);Receiving module includes support and rotation controller (12), telescope objective (5), rear intercept adjustment lens (6), dichroic beam splitter (7), narrow-band optical filter (8), near-infrared-visible light detector (9) and SPAD detector (10);Control module is control and memory (11).System is through coaxial light path and beam splitting design, and synchronous acquisition wide field of view high-resolution passive two-dimensional image and narrow field of view active single-photon three-dimensional point cloud, and adopts time-intensity-space joint filtering algorithm to carry out fusion processing, generates high-resolution three-dimensional image.

Description

Technical Field

[0001] This invention belongs to the field of single-photon lidar technology, specifically relating to an active-passive dual-mode single-photon lidar imaging system and method. Background Technology

[0002] LiDAR, as an active remote sensing technology, plays a vital role in remote sensing mapping, target detection, and identification. Traditional lidar systems typically employ photodetectors with linear detection modes, such as avalanche photodiodes (APDs). However, even APDs require dozens of photons to generate an effective response, which limits their detection capability and operating range under extremely weak light signal conditions.

[0003] Single-photon lidar is a rapidly developing emerging technology in recent years. It uses a single-photon avalanche photodiode (SPAD) operating in Geiger mode as a detector. SPADs have extremely high sensitivity and can respond to a single photon. Combined with a time-to-digital converter (TDC) for time-of-flight ranging, the system can achieve a longer detection distance with lower laser power, making it particularly suitable for long-distance applications.

[0004] However, single-photon imaging technology based on area-array SPADs faces significant challenges. First, due to the extremely high sensitivity of SPADs, crosstalk noise easily arises between pixels. Second, each pixel requires an independent high-precision TDC, which, limited by current manufacturing processes, restricts the scaling up of SPAD area array detectors. Currently, commercially available SPAD arrays in China are generally small in size (e.g., 64×64 pixels), making it difficult for area-array SPAD-based lidar to simultaneously achieve a large field of view and high spatial resolution. In many practical applications, such as long-range UAV monitoring and remote sensing mapping, a large field of view (for rapid detection and coverage) and high resolution (for accurate identification and mapping) are indispensable core requirements.

[0005] Existing single-photon lidar solutions are mainly divided into two categories: one is to use a single-point SPAD detector for scanning imaging. Although this method can achieve long-distance detection and flexible field of view, the point-by-point scanning method results in slow imaging speed and low efficiency; the other is to use a SPAD array for "flash" imaging. This method has a fast imaging speed, but it is limited by the size of the detector. Under high resolution requirements, its imaging field of view is usually very small, which makes it difficult to meet the needs of wide-area high-resolution imaging.

[0006] Furthermore, in long-range single-photon imaging applications, environmental factors such as atmospheric turbulence can introduce noise and interference, further affecting image quality and the accuracy of depth information. Therefore, overcoming the limitations of SPAD array size and effectively suppressing interference in long-range imaging has become a key issue that urgently needs to be addressed in the development of single-photon lidar technology. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides an active-passive dual-mode single-photon lidar imaging system and method. The active and passive imaging are coaxial, effectively reducing the payload volume and achieving natural image registration. Furthermore, considering the sub-pixel coupling relationship of images under the resolution difference between passive and active coaxial photon imaging, and based on the information complementarity and redundancy characteristics of passive integral imaging and active multi-frame statistical imaging, a single-photon imaging algorithm using time-intensity-space joint filtering is employed to suppress the influence of atmospheric turbulence during long-distance optical imaging and improve the spatial resolution of photon imaging.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A dual-mode active-passive single-photon lidar imaging system, the system comprising:

[0010] The transmitting module is used to generate and emit pulsed laser signals.

[0011] The receiving module is used to collect echo signals through a common aperture and separate the echo signals into an active imaging channel and a passive imaging channel according to a threshold wavelength. The active imaging channel is provided with a single-photon detector array at its end to obtain raw three-dimensional point cloud data, and the passive imaging channel is provided with an area array detector at its end to obtain a two-dimensional intensity image. The field of view of the single-photon detector array is included within the field of view of the area array detector.

[0012] The control module is used to control the coordinated operation of the transmitting module and the receiving module, and to perform fusion processing on the three-dimensional point cloud data and the two-dimensional intensity image to generate the final image.

[0013] On the other hand, the present invention provides an active-passive dual-mode single-photon lidar imaging method, applied to the aforementioned system, comprising:

[0014] Within one detection cycle, a wide-field, high-resolution two-dimensional intensity image and multiple frames of narrow-field single-photon high-noise raw three-dimensional point cloud data are acquired simultaneously.

[0015] Temporal filtering is performed on the multi-frame narrow field-of-view single-photon high-noise original 3D point cloud data to reconstruct a preliminary depth map and generate an effective photon count map;

[0016] The two-dimensional intensity image is registered and fused with the effective photon count image to segment a high-resolution target contour mask;

[0017] The preliminary depth map is spatially filtered using the target contour mask to obtain an optimized target depth map.

[0018] The target depth map and the two-dimensional intensity image are fused together to output the final image.

[0019] Thirdly, the present invention provides an electronic device, comprising: one or more processors; and a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned active-passive dual-mode single-photon lidar imaging method.

[0020] Fourthly, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enable the processor to implement the aforementioned active-passive dual-mode single-photon lidar imaging method.

[0021] The beneficial effects of this invention are as follows:

[0022] The contradiction between field of view and resolution has been resolved: a large-area, high-pixel passive imaging detector is innovatively used to compensate for the inherent limitation of small SPAD array size. Passive imaging provides a large field of view and high-resolution two-dimensional intensity information, while active single-photon imaging provides three-dimensional depth information for key areas. The two work together to effectively overcome the technical bottleneck of traditional single-photon lidar, which cannot simultaneously achieve a large field of view and high spatial resolution.

[0023] Image quality and anti-interference capabilities are improved: By utilizing the rich two-dimensional contour information of passive images, precise spatial filtering and segmentation are performed on the preliminary single-photon depth map, effectively improving the clarity of the target's three-dimensional contour. Simultaneously, leveraging the characteristics of active single-photon multi-frame statistical imaging helps suppress random interference such as atmospheric turbulence during long-distance imaging. Combined with information fusion processing, a high signal-to-noise ratio and high-precision three-dimensional image are ultimately obtained.

[0024] Structural optimization and precise data correlation were achieved: The coaxial optical path design based on a dichroic beam splitter not only effectively reduced the system size, but more importantly, it achieved natural registration of active and passive images, laying a solid foundation for subsequent data fusion processing and ensuring the spatial consistency of information of different modes. Attached Figure Description

[0025] Figure 1 This is a structural diagram of an active-passive dual-mode single-photon lidar imaging system according to the present invention;

[0026] Figure 2 This is a schematic diagram of the time-intensity-space joint filtering algorithm.

[0027] Figure 3 The following are experimental results of the method of the present invention, wherein (a) is an active imaging depth map, (b) is a passive imaging intensity image, and (c) is an active-passive fusion image.

[0028] Figure label:

[0029] 1. Laser and laser amplification unit; 2. Collimating lens; 3. Photodetector; 4. Delay controller; 5. Telescope objective lens; 6. Back cutoff adjustment lens; 7. Dichroic beam splitter; 8. Narrowband filter; 9. Near-infrared-visible light detector; 10. SPAD detector; 11. Control and memory; 12. Support and rotation controller. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] like Figure 1 As shown, the present invention provides an active-passive dual-mode single-photon lidar imaging system, which adopts a common-aperture system design with large field-of-view passive imaging and small field-of-view single-photon active imaging, and coaxial active and passive imaging, effectively reducing the payload volume and achieving natural image registration. The system includes a transmitting module, a receiving module, and a control module, wherein:

[0032] The transmitting module is used to generate and emit pulsed laser signals; specifically, the laser and laser amplification unit 1 generate laser pulses (wavelength λ). L The light beam is then coupled to collimating lens 2 and emitted outwards. Simultaneously, before entering collimating lens 2, a small portion of the light beam is split and enters photodetector 3, generating an electrical signal. After a delay by delay controller 4, this signal serves as the trigger signal for SPAD detector 10 to begin acquisition. The gating imaging distance can be adjusted by controlling the delay of the trigger signal.

[0033] Without loss of generality, the delay controller 4 may not be triggered by an optical signal. Instead, the laser is set to an external trigger state, and the delay controller 4 generates two signals with specific delays to trigger the laser and the SPAD detector 10, respectively.

[0034] The receiving module collects echo signals and separates them into an active imaging channel and a passive imaging channel according to wavelength. A single-photon detector array is installed at the end of the active imaging channel to acquire three-dimensional point cloud data, and an area array detector is installed at the end of the passive imaging channel to acquire two-dimensional intensity images. The field of view of the single-photon detector array is included within the field of view of the area array detector. Specifically, the support and rotation controller 12 controls the rotation of the telescope objective lens 5 to collect echo photon signals. The back cutoff is then adjusted to a suitable back cutoff by the back cutoff adjustment lens 6, followed by a dichroic beam splitter 7, and the signals are separated according to a threshold wavelength λ0 (λ0 < λ). LThe incident light is split into two paths: light with wavelengths less than λ0 is transmitted, while light with wavelengths greater than or equal to λ0 is reflected at 90° (similarly, a dichroic beam splitter with opposite transmission / reflection properties can also be chosen). In the two beam paths after wavelength splitting, the long-wavelength end (wavelength greater than or equal to λ0) uses a SPAD detector 10 array to receive the active laser signal on the image plane, while the short-wavelength path (wavelength less than λ0) uses a near-infrared-visible light detector 9 to receive the passive ambient light signal on the image plane. Additionally, before the SPAD detector 10, a light source with a wavelength λ of the laser pulse used is used... L A matching narrowband filter 8 prevents ambient light from entering the SPAD detector 10, thereby improving the signal-to-noise ratio of laser signal detection.

[0035] The control module controls the coordinated operation of the transmitting and receiving modules, and performs fusion processing on the 3D point cloud data and the 2D intensity image to generate the final image. Specifically, the host computer (e.g., Figure 1 The control and memory unit 11 shown is responsible for controlling the coordinated operation of the laser, laser amplification unit 1, SPAD detector 10, and support and rotation controller 12.

[0036] The system described above will simultaneously acquire single-photon data with a small field of view but containing distance information, as well as passive optical imaging data with a large field of view, a high pixel count, but no distance information.

[0037] like Figure 2 As shown, this invention provides a time-intensity-space joint filtering method to perform dual-mode fusion imaging processing on the active and passive detection data obtained by the aforementioned system, namely, an active-passive dual-mode single-photon lidar imaging method comprising:

[0038] Step 1: Within one detection period τ, the passive imaging near-infrared-visible light detector 9 acquires a frame of intensity image P with a wide field of view and high spatial resolution for the target area; the active imaging SPAD detector 10 acquires m frames of single-photon high-noise raw three-dimensional point cloud data with a narrow field of view and low spatial resolution for the target area.

[0039] Step 2, Temporal Filtering: Using a single-photon imaging algorithm (such as the histogram maximum method), based on m frames of raw single-photon 3D point cloud data, obtain a preliminary depth map with a narrow field of view (key areas), low spatial resolution, and high noise level. ;

[0040] Step 3: Simultaneously with Step 2, use a single-photon imaging algorithm (such as the histogram maximum value method) to count the number of effective photon echoes for each pixel, and obtain an effective photon count map I with a narrow field of view and low spatial resolution;

[0041] Step 4, Intensity Filtering: The high spatial resolution intensity image P and the effective photon count image I are registered, fused, and segmented to obtain a high-resolution target contour mask image I for the key region. s ;

[0042] Step 5, Spatial Filtering: Using the target contour mask image I s Preliminary depth map Spatial filtering (i.e., filtering out background noise and finding the union) is performed to obtain a target depth map with clear outlines. ;

[0043] Step 6, Target Depth Map By registering and fusing with a high spatial resolution intensity image P, a final image P is obtained, consisting of a color point cloud or depth-intensity overlay, with a wide field of view, high spatial resolution, and three-dimensional spatial information in key areas. z The active-passive fusion imaging of single-photon lidar was completed.

[0044] Instance data such as Figure 3 As shown, (a) is the active imaging depth map. (b) is the passive imaging intensity image P, and (c) is the active-passive fusion image P. z As can be seen, the present invention provides better imaging results.

[0045] Thirdly, the present invention provides an electronic device, comprising: one or more processors; and a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned active-passive dual-mode single-photon lidar imaging method.

[0046] Fourthly, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enable the processor to implement the aforementioned active-passive dual-mode single-photon lidar imaging method.

[0047] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual-mode active-passive single-photon lidar imaging system, characterized in that, The system includes: The transmitting module is used to generate and emit pulsed laser signals. The receiving module is used to collect echo signals through a common aperture and separate the echo signals into an active imaging channel and a passive imaging channel according to a threshold wavelength. The active imaging channel is provided with a single-photon detector array at its end to obtain raw three-dimensional point cloud data, and the passive imaging channel is provided with an area array detector at its end to obtain a two-dimensional intensity image. The field of view of the single-photon detector array is included within the field of view of the area array detector. The control module is used to control the coordinated operation of the transmitting module and the receiving module, and to perform fusion processing on the three-dimensional point cloud data and the two-dimensional intensity image to generate the final image; wherein: Within one detection cycle, a wide-field, high-resolution two-dimensional intensity image and multiple frames of narrow-field single-photon high-noise raw three-dimensional point cloud data are acquired simultaneously. Temporal filtering is performed on the multi-frame narrow field-of-view single-photon high-noise original 3D point cloud data to reconstruct a preliminary depth map and generate an effective photon count map; The two-dimensional intensity image is registered and fused with the effective photon count image to segment a high-resolution target contour mask; The preliminary depth map is spatially filtered using the target contour mask to obtain an optimized target depth map. The target depth map and the two-dimensional intensity image are fused together to output the final image.

2. The active-passive dual-mode single-photon lidar imaging system according to claim 1, characterized in that, The emission module includes a laser, an amplifier connected to the laser, and a collimating lens for collimating the amplified laser output.

3. The active-passive dual-mode single-photon lidar imaging system according to claim 1, characterized in that, In the receiving module, the echo photon signal collected by the telescope objective lens is adjusted by the back cutoff adjustment lens, and then passed through a dichroic beam splitter. The incident echo photon signal is split into two paths according to the threshold wavelength. The path with wavelengths greater than the threshold wavelength enters the active imaging channel, and the path with wavelengths less than the threshold wavelength enters the passive imaging channel.

4. The active-passive dual-mode single-photon lidar imaging system according to claim 3, characterized in that, In the active imaging channel, a narrowband filter is also provided in front of the single-photon detector array; in the passive imaging channel, the area array detector is a visible-near-infrared detector.

5. The active-passive dual-mode single-photon lidar imaging system according to claim 1, characterized in that, The time filtering employs histogram statistics or other single-photon imaging methods.

6. The active-passive dual-mode single-photon lidar imaging system according to claim 5, characterized in that, The spatial filtering process involves using the target contour mask to filter out background noise.

7. The active-passive dual-mode single-photon lidar imaging system according to claim 5, characterized in that, The final image is a color point cloud or a depth-intensity overlay image with three-dimensional spatial information.

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