Exposure laser three-dimensional imaging radar installed on a spacecraft for deep space exploration

Abstract

The present application relates to the field of spacecraft space photoelectric measurement and sensing technology, and more particularly to an exposure type laser three-dimensional imaging radar installed on a spacecraft for deep space exploration. The laser of the exposure type laser three-dimensional imaging radar emits pulsed laser to the surface of a measured target through a collimating isolator. After a receiving telescope system receives the echo signal of the measured target, the optical signal is introduced into a Geiger focal plane assembly to realize photoelectric conversion. The data is read out by a readout circuit and transmitted back to a processing unit in real time through a data transmission cable for data processing, so as to complete the three-dimensional topographic mapping of the surface of the measured target and realize long imaging distance, high imaging precision and short imaging time, thereby meeting the light and small application requirements of deep space exploration.

Description

Technical Field

[0001] This invention relates to the field of spacecraft optoelectronic measurement and sensing technology, and in particular to an exposure-type laser three-dimensional imaging radar installed on a spacecraft for deep space exploration. Background Technology

[0002] With the rapid development of laser 3D imaging technology, its application in major aerospace engineering missions is becoming increasingly widespread. Laser 3D imaging technology will play an important role in spacecraft rendezvous and docking, space situational awareness, debris monitoring, on-orbit control, extraterrestrial landing, and deep space exploration.

[0003] NASA's MEMS scanning laser 3D imaging radar uses a MEMS scanning mirror, which is very small and lightweight, giving it a significant technological advantage in scanning speed. However, due to the small mirror size, the aperture of the receiving optical system is limited, thus restricting its effective range. In addition, the small mirror size results in a small laser emission spot, leading to a large laser divergence angle and limiting image resolution accuracy. The imaging time is 0.1 seconds, but the effective range is only 40 meters (see technical documents: Barry L. Stann, Jeff F. Dammann, Mark Del Giorno, et al. Integration and demonstration of MEMS-scanned LADAR for robotic navigation[J]. Proc. of SPIE, 2014, Vol. 9084, 90840J and Barry L. Stann, John F. Dammann, Mark M. Gizaa, et al. MEMS-scanned ladar for small unmanned air vehicles[J]. Proc. of SPIE, 2018, Vol. 10636, 106360E). The unscanning flash lidar (FLASH LIDAR) used by the US OSIRIS-Rex small object exploration mission employs an InGaAs detector, achieving millisecond-level instantaneous imaging. However, its ranging accuracy is only on the order of 15 cm (3-sigma), and its weight is as high as 6.9 kg (see technical document: Beth A. Sornsin, Bradley W. Short, Tyler N. Bourbeau, et al. Global Shutter SolidState Flash Lidar for Spacecraft Navigation and Docking Applications[J]. Proc. of SPIE, 2019, Vol. 11005, 110050W.).

[0004] Deep space exploration missions place extremely high demands on the weight, power consumption, and size of the products used on spacecraft. Based on the need for deep space exploration using spacecraft, there is an urgent need for an exposure-based laser 3D imaging radar with a long imaging range, high imaging accuracy, and short imaging time, meeting the requirements for miniaturized applications in deep space exploration. Summary of the Invention

[0005] The purpose of this invention is to provide an exposure-type laser three-dimensional imaging radar that can be installed on a spacecraft for deep space exploration, which can achieve a large imaging range, high imaging accuracy, and short imaging time, thus meeting the requirements for miniaturized applications in deep space exploration.

[0006] To achieve the above objectives, the present invention provides an exposure-type laser three-dimensional imaging radar installed on a spacecraft for deep space exploration.

[0007] Includes a processing unit and a probe unit;

[0008] The processing unit includes a power board, a processing board, an FPGA board, a bus board, and a laser, and the power board, processing board, FPGA board, bus board, and laser are connected by signals.

[0009] The probe unit includes a beam expander, a collimator isolator, a receiving telescope system, a Geiger focal plane array, a readout circuit, and a drive and temperature control circuit. The beam expander, collimator isolator, receiving telescope system, Geiger focal plane array, readout circuit, and drive and temperature control circuit are mounted on the probe housing.

[0010] The power board provides a primary power input interface. After being converted by the power board, the primary power is used to provide the secondary power input required by the processing board, FPGA board and laser via the bus board, and to provide the secondary power input required by the probe via the cable.

[0011] The FPGA board controls the imaging of the probe and the laser. The laser emits laser pulses according to the instructions of the FPGA board. The FPGA board can issue exposure imaging instructions to the driving and temperature control circuit. The driving and temperature control circuit receives the exposure imaging instructions and synchronizes the signals with the driving and temperature control circuit.

[0012] The processing board is used to receive and store the three-dimensional data transmitted by the probe and preprocessed by the FPGA board, process the acquired three-dimensional data to obtain the three-dimensional shape of the target under test, and communicate with the outside.

[0013] The collimating isolator is connected to the laser via an optical fiber. The laser pulse emitted by the laser is collimated by the collimating isolator and then reaches the beam expander. After being expanded by the beam expander, the beam reaches the target under test and is reflected by the target under test and enters the receiving telescope system. The Geiger focal plane array receives the optical energy collected from the receiving telescope system.

[0014] The readout circuit uses an on-chip phase-locked loop circuit to implement the timing operation of each unit. When the detection signal is generated, the unit circuit of the readout circuit detects the threshold. At the end of each distance switch, the unit cannot be sensitive to the avalanche signal to record the stop count value, thus shielding invalid avalanche events outside the distance gate.

[0015] The drive and temperature control circuit is used to drive the Geiger focal plane assembly and control the temperature of the Geiger focal plane assembly. The required power is provided by the secondary power supply of the power board via a cable.

[0016] Optionally, the field of view of the receiving telescope system is equal to the field of view of the beam expander.

[0017] Optionally, the beam expander has a field of view of 20° × 20°.

[0018] Preferably, the focal length of the receiving telescope system is 35.72 mm, the diffuse spot is no larger than 25 μm, the optical efficiency is no less than 85%, a narrow-band filter is provided at the front end, and the center wavelength is consistent with the wavelength of the laser pulse.

[0019] Preferably, the center wavelength of the laser pulse is 1064±2nm, the peak power is not less than 60kW, the repetition frequency is adjustable between 5kHz and 20kHz, and the pulse width is 2ns.

[0020] Preferably, the diameter of the laser spot after collimation by the collimating isolator is 8 mm, and the divergence angle is 0.2 mrad.

[0021] Preferably, the Geiger focal plane array has a pixel size of 30μm, a pixel array of not less than 128*128, a temporal resolution of 0.5ns, a dark count of not more than 20kHz, a distance gate width adjustable from 50ns to 2μs, and a pixel pitch of 100μm.

[0022] Optionally, the processing board processes the acquired 3D data as follows:

[0023] A. Histogram statistical filtering

[0024] Assuming that the exposure-type laser 3D imaging radar performs N consecutive measurements on the scene in a static or moving state, where 10≤N≤100, for each pixel on the image plane, draw its slant range statistical histogram in the N consecutive measurements, set the width of the bin to 1m, remove large outliers, and retain the bin with the most numbers and its two neighbors.

[0025] B. Polynomial Filtering

[0026] The slope distance after histogram filtering of a pixel is subjected to polynomial filtering, specifically linear least squares fitting:

[0027]

[0028] y=Xβ+ε (2)

[0029] Among them, y n x represents the measured slant distance of a pixel in the nth frame of the image after histogram filtering.n ε represents the measurement time. n To represent the measurement error, the fitting method for the polynomial coefficients is as follows:

[0030]

[0031]

[0032] Calculate the fitting residuals:

[0033] FR i =y i -f(x i (5)

[0034] Remove small outliers until RMS converges:

[0035] abs(FR)>σ FR ×RMS(FR) (6)

[0036] C. RMS Filtering

[0037] By using the RMS of the fitted residuals, some small outliers can be removed:

[0038] abs(y-mean(y))>RMS(FR) (7)

[0039] D. Dynamic compensation

[0040] Assuming the exposure-type laser 3D imaging radar remains relatively stationary with respect to the target, and a priori relative pose is set, 100 frames of images are continuously acquired, and a mean μ = 0 and a variance σ is added to each pixel of each frame. 2 =0.0001 Gaussian measurement noise, with a false alarm rate of 75% for the whole image, is used to simulate measurement noise caused by dark counting. The dark counting noise follows a uniform distribution. Dynamic conditions of the platform are introduced for dynamic compensation.

[0041] Optionally, the bus board is connected to the power board, processing board, FPGA board and laser via cables or internal connectors.

[0042] Preferably, the drive and temperature control circuit can control the temperature of the Geiger focal plane assembly to -40°C with a stability of 0.1°C.

[0043] The above-mentioned technical solution of the present invention has the following advantages: The exposure-type laser three-dimensional imaging radar of the present invention, installed on a spacecraft for deep space exploration, emits pulsed laser through a collimator isolator to reach the surface of the target being measured. After the receiving telescope system receives the echo signal of the target being measured, the optical signal is introduced into the Geiger focal plane array to achieve photoelectric conversion. The data is read out by the readout circuit and transmitted back to the processing unit in real time via a data transmission cable for data processing, thereby completing the three-dimensional topographic mapping of the surface of the target being measured. This achieves a large imaging range, high imaging accuracy, and short imaging time, meeting the requirements for miniaturized applications in deep space exploration. Attached Figure Description

[0044] The accompanying drawings are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not be consistent with the actual product.

[0045] Figure 1 This is a schematic diagram of the connection relationship of various parts of an exposure-type laser three-dimensional imaging radar installed on a spacecraft for deep space exploration, according to an embodiment of the present invention.

[0046] Figure 2 This is a schematic diagram of the working process of the exposure-type laser three-dimensional imaging radar in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the histogram statistical filtering effect in the exposure-type laser three-dimensional imaging radar in this embodiment of the invention;

[0048] Figure 4 This is a schematic diagram of the polynomial filtering effect in the exposure-type laser three-dimensional imaging radar in an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of the RMS filtering effect in the exposure-type laser three-dimensional imaging radar in an embodiment of the present invention;

[0050] Figure 6 This is a schematic diagram illustrating the assumption of static depth acquisition during the processing of three-dimensional data in this embodiment of the invention.

[0051] Figure 7 This is a schematic diagram of the dynamically compensated depth obtained during the processing of three-dimensional data in an embodiment of the present invention.

[0052] In the picture:

[0053] 100: Processing Department;

[0054] 101: Power supply board;

[0055] 1011: Power board electrical connector;

[0056] 102: Processing board;

[0057] 1021: Communication electrical connector;

[0058] 1022: Test electrical connector;

[0059] 103: FPGA board;

[0060] 1031: Data transmission electrical connector;

[0061] 104: Bus board;

[0062] 105: Laser;

[0063] 200: Probe section;

[0064] 201: Beam expander;

[0065] 202: Collimator Isolator;

[0066] 203: Receiving telescope system;

[0067] 204: Geiger focal plane array;

[0068] 205: Readout circuit;

[0069] 206: Drive and temperature control circuit;

[0070] 300: Power supply cable;

[0071] 400: Signal synchronization cable;

[0072] 500: Data transmission cable;

[0073] 600: Fiber optic cable;

[0074] 700: The target being tested. Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0076] FPGA board (FPGA: Field-Programmable Gate Array).

[0077] See Figure 1As shown in the figure, the exposure-type laser three-dimensional imaging radar installed on a spacecraft for deep space exploration provided in this embodiment includes a processing unit 100 and a probe unit 200. The processing unit 100 includes a power board 101, a processing board 102, an FPGA board 103, a bus board 104, and a laser 105. The power board 101, processing board 102, FPGA board 103, bus board 104, and laser 105 are connected by signals, specifically, either via cables or via internal connectors. Internal connectors are preferred.

[0078] The probe unit 200 includes a beam expander 201, a collimator isolator 202, a receiving telescope system 203, a Geiger focal plane assembly 204, a readout circuit 205, and a drive and temperature control circuit 206. The beam expander 201, collimator isolator 202, receiving telescope system 203, Geiger focal plane assembly 204, readout circuit 205, and drive and temperature control circuit 206 are mounted on the probe housing.

[0079] The power board 101 has a power board connector 1011 to realize primary power input, and there is a power supply cable 300 between it and the probe part 200 to realize secondary power supply to the probe part.

[0080] The processing board 102 is equipped with a communication connector 1021 to realize external RS422 communication; it is also equipped with a test connector 1022 for testing the bottom surface of the whole machine.

[0081] The FPGA board 103 has a data transmission connector 1031 to enable external data transmission. There is a signal synchronization cable 400 between the FPGA board 103 and the probe unit 200 to enable signal synchronization between them; there is also a data transmission cable 500 between the FPGA board 103 and the probe unit 200 to enable high-speed data transmission between them.

[0082] The bus board 104 has electrical signal transmission connections with the power board 101, the processing board 102, the FPGA board 103, and the laser 105. These connections can be cables or internal connectors, with internal connectors being the preferred method for electrical signal transmission.

[0083] The power board 101 receives primary power through the power board connector 1011 and converts it into different secondary power supplies, which are then supplied to the bus board 104. The bus board 104 supplies the secondary power to the processing board 102, the FPGA board 103 and the laser 105. At the same time, the secondary power is supplied to the drive and temperature control circuit 206 and the readout circuit 205 of the probe section through the power supply cable 300.

[0084] The FPGA board 103 sends a laser pulse command to the laser 105. The laser 105 emits a laser pulse according to the command. The center wavelength of the laser pulse is 1064±2nm, the peak power is not less than 60kW, the repetition frequency is adjustable between 5kHz and 20kHz, and the pulse width is 2ns.

[0085] The laser pulse reaches the collimator 202 through the optical fiber 600. The diameter of the collimated laser spot after collimation by the collimator 202 is 8mm, and the divergence angle is 0.2mrad.

[0086] The collimated beam spot reaches the beam expander 201, and the expanded field of view is 20°×20°, which is equal to the field of view of the receiving telescope system 203; after being expanded by the beam expander 201, it reaches the target 700.

[0087] The field of view of the receiving telescope system 203 is equal to that of the beam expander 201, which is 20° x 20°. The focal length of the receiving telescope system 203 is 35.72 mm, the blur spot is no larger than 25 μm, the optical efficiency is no less than 85%, a narrowband filter is set at the front end, and the center wavelength is consistent with the laser pulse wavelength.

[0088] The receiving telescope system 203 collects the reflected light signal after being reflected by the target 700 and sends it to the Geiger focal plane array 104. The Geiger focal plane array 104 has a pixel size of 30μm, a pixel array of not less than 128*128, a temporal resolution of 0.5ns, a dark count of not more than 20kHz, a distance gate width adjustable from 50ns to 2μs, and a pixel pitch of 100μm.

[0089] The FPGA board 103 sends an exposure imaging command to the drive and temperature control circuit 206. The drive and temperature control circuit 206 receives the exposure imaging command and completes signal synchronization.

[0090] The drive and temperature control circuit 206 realizes the drive and temperature control of the Geiger focal plane assembly 104. The temperature control level reaches the optimal operating temperature of -40℃ and the stability is 0.1℃. The power required by the drive and temperature control circuit 206 is provided by the power board 101 through the secondary power supply of the power supply cable 300.

[0091] The readout circuit 205 uses an on-chip phase-locked loop circuit to implement the timing operation of each unit. When the detection signal is generated, the readout circuit (ROIC) unit circuit detects the threshold and at the end of each distance switch, the unit cannot be sensitive to the avalanche signal to record the stop count value, so as to shield invalid avalanche events outside the distance gate and complete the signal acquisition of one imaging.

[0092] The driving and temperature control circuit 206 of the probe section 200 achieves high-speed data transmission between the data transmission cable 500 and the FPGA board 103.

[0093] After preprocessing the data, the FPGA board 103 transmits it to the processing board 102. The processing board 102 processes the time data into distance data and obtains the three-dimensional shape data of the target 700, which is then transmitted back to the FPGA board 103.

[0094] The FPGA board 103 transmits the three-dimensional topographic data of the target 700 to the outside via the data transmission connector 1031.

[0095] In this embodiment, the weight of the processing unit is no more than 2.2 kg, the weight of the probe unit is no more than 1.8 kg, that is, the weight of the exposure-type laser three-dimensional imaging radar is no more than 4 kg.

[0096] like Figure 2 As shown, the workflow of an exposure-type laser 3D imaging radar in this embodiment is as follows:

[0097] (1) Exposure-type laser three-dimensional imaging radar is powered on once;

[0098] (2) The power board converts secondary power demand;

[0099] (3) The secondary power supply provides power to each required component;

[0100] (4) The entire machine is in standby mode;

[0101] (5) The processing board receives communication commands;

[0102] (6) The FPGA board issues commands to the laser and probe;

[0103] (7) The laser, drive and temperature control circuits receive commands;

[0104] (8) The laser emits a pulsed laser, and the Geiger focal plane array starts the imaging mode, thus synchronizing the signals between the two.

[0105] (9) The readout circuit reads the data;

[0106] (10) The data of the target under test is transmitted at high speed from the probe to the processing line;

[0107] (11) The FPGA board receives, stores, and preprocesses data;

[0108] (12) The processing board completes the three-dimensional data processing;

[0109] (13) Obtain high-precision three-dimensional shape.

[0110] In some preferred embodiments, during the processing of the acquired 3D data by the processing board of the exposure-type laser 3D imaging radar, a four-step method is used for noise filtering to improve the signal-to-noise ratio and motion accuracy compensation, as follows:

[0111] A. Histogram statistical filtering

[0112] Assume that an exposure-based laser 3D imaging radar performs N consecutive measurements on a scene (10 ≤ N ≤ 100) in either a static or moving state. Due to the influence of dark counts, the actual measured slope range of a pixel may deviate significantly from the true slope range. For each pixel on the phase plane, plot its slope range statistical histogram across the N consecutive measurements. Set the width of each bin to 1m, remove large outliers, and retain the bin with the most occurrences and its two neighbors, such as... Figure 3 As shown.

[0113] B. Polynomial Filtering

[0114] The slope distance after histogram filtering of a pixel is subjected to polynomial filtering, specifically linear least squares fitting:

[0115]

[0116] y=Xβ+ε (2)

[0117] Among them, y n x represents the measured slant distance of a pixel in the nth frame of the image after histogram filtering. n ε represents the measurement time. n This represents the measurement error. The fitting method for the polynomial coefficients is then:

[0118]

[0119]

[0120] Calculate the fitting residuals:

[0121] FR i =y i -f(x i (5)

[0122] Remove small outliers until RMS converges:

[0123] abs(FR)>σ FR ×RMS(FR) (6)

[0124] The result after polynomial filtering is shown below. Figure 4 As shown.

[0125] C. RMS (Root Mean Square) Filtering

[0126] By using the RMS of the fitted residuals, some small outliers can be removed:

[0127] abs(y-mean(y))>RMS(FR) (7)

[0128] The effect of RMS filtering is as follows: Figure 5 As shown.

[0129] D. Dynamic compensation

[0130] Assuming the exposure-type laser 3D imaging radar remains relatively stationary with respect to the target, and a priori relative pose is set, 100 frames of images are continuously acquired, and a mean μ = 0 and a variance σ is added to each pixel of each frame. 2 =0.0001 Gaussian measurement noise. A false alarm rate of 75% is set for the entire map to simulate measurement noise caused by dark counting; the dark count noise follows a uniform distribution. A schematic diagram of the target depth map obtained by the static algorithm is shown below. Figure 6 As shown.

[0131] Introducing platform dynamic conditions, typically six degrees of freedom for velocity and acceleration, and performing dynamic compensation, the resulting target depth map is illustrated below. Figure 7 As shown.

[0132] In summary, the exposure-type laser three-dimensional imaging radar provided by this invention, installed on spacecraft for deep space exploration, uses a laser that emits pulsed laser light through a collimator isolator to reach the surface of the target being measured. After the receiving telescope system receives the echo signal from the target, it introduces the optical signal into the Geiger focal plane array to achieve photoelectric conversion. The readout circuit reads the data and transmits it back to the processing unit in real time via a data transmission cable for data processing, thus completing the three-dimensional topographic mapping of the target surface. This achieves a large imaging range, high imaging accuracy, and short imaging time, meeting the requirements for miniaturized applications in deep space exploration.

[0133] The present invention provides an exposure-type laser 3D imaging radar installed on spacecraft for deep space exploration. By limiting and combining the parameters of various components of the exposure-type laser 3D imaging radar, it can achieve instantaneous imaging and acquire the 3D shape of the target. Compared with traditional laser radar, the imaging time is reduced from 100ms to 20ms, greatly reducing image acquisition time. The data processing time is 1.5s, and the dynamic performance is good, meeting the requirements of platform single-axis angular velocity of 3.5° / s, horizontal velocity ±10m / s, and vertical acceleration ±3 / s. 2 Horizontal acceleration ±0.3m / s² 2 The following method enables rapid acquisition of the 3D topography of the target. A Geiger focal plane array with a time resolution of 0.5 ns is used as the imaging component, increasing the effective range from 40 meters to 1500 meters. Simultaneously, histogram statistical filtering, multinomial filtering, and RMS filtering algorithms are employed to improve the signal-to-noise ratio. The Geiger dynamic compensation algorithm is used to improve the ranging accuracy from 15 cm (3-sigma) to the mm (3-sigma) level.

[0134] The parts of this invention not described in detail are common knowledge to those skilled in the art.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that not every embodiment contains only one independent technical solution, and in the absence of conflict between solutions, the various technical features mentioned in each embodiment can be combined in any way to form other implementation methods that can be understood by those skilled in the art.

[0136] Furthermore, without departing from the scope of the present invention, modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some of the technical features, shall not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An exposure-type laser three-dimensional imaging radar installed on a spacecraft for deep space exploration, characterized in that, Includes a processing unit and a probe unit; The processing unit includes a power board, a processing board, an FPGA board, a bus board, and a laser, and the power board, processing board, FPGA board, bus board, and laser are connected by signals. The probe unit includes a beam expander, a collimator isolator, a receiving telescope system, a Geiger focal plane array, a readout circuit, and a drive and temperature control circuit. The beam expander, collimator isolator, receiving telescope system, Geiger focal plane array, readout circuit, and drive and temperature control circuit are mounted on the probe housing. The power board provides a primary power input interface. After being converted by the power board, the primary power is used to provide the secondary power input required by the processing board, FPGA board and laser via the bus board, and to provide the secondary power input required by the probe via the cable. The FPGA board controls the imaging of the probe and the laser. The laser emits laser pulses according to the instructions of the FPGA board. The FPGA board can issue exposure imaging instructions to the driving and temperature control circuit. The driving and temperature control circuit receives the exposure imaging instructions and synchronizes the signals with the driving and temperature control circuit. The processing board is used to receive and store the three-dimensional data transmitted by the probe and preprocessed by the FPGA board, process the acquired three-dimensional data to obtain the three-dimensional shape of the target under test, and communicate with the outside. The collimating isolator is connected to the laser via an optical fiber. The laser pulse emitted by the laser is collimated by the collimating isolator and then reaches the beam expander. After being expanded by the beam expander, the beam reaches the target under test and is reflected by the target under test and enters the receiving telescope system. The Geiger focal plane array receives the optical energy collected from the receiving telescope system. The readout circuit uses an on-chip phase-locked loop circuit to implement the timing operation of each unit. When the detection signal is generated, the unit circuit of the readout circuit detects the threshold. At the end of each distance switch, the unit cannot be sensitive to the avalanche signal to record the stop count value, thus shielding invalid avalanche events outside the distance gate. The drive and temperature control circuit is used to drive the Geiger focal plane assembly and control the temperature of the Geiger focal plane assembly. The required power is provided by the secondary power supply of the power board via a cable.

2. The exposure-type laser three-dimensional imaging radar according to claim 1, characterized in that: The field of view of the receiving telescope system is equal to the field of view of the beam expander.

3. The exposure-type laser three-dimensional imaging radar according to claim 1 or 2, characterized in that: The beam expander has a field of view of 20°×20°.

4. The exposure-type laser three-dimensional imaging radar according to claim 3, characterized in that: The receiving telescope system has a focal length of 35.72 mm, a diffuse spot size of no more than 25 μm, an optical efficiency of no less than 85%, a narrow-band filter at the front end, and a center wavelength that is consistent with the wavelength of the laser pulse.

5. The exposure-type laser three-dimensional imaging radar according to claim 4, characterized in that: The laser pulse has a center wavelength of 1064±2nm, a peak power of not less than 60kW, a repetition frequency adjustable between 5kHz and 20kHz, and a pulse width of 2ns.

6. The exposure-type laser three-dimensional imaging radar according to claim 5, characterized in that: The collimated laser spot diameter after collimation by the collimator is 8 mm, and the divergence angle is 0.2 mrad.

7. The exposure-type laser three-dimensional imaging radar according to claim 6, characterized in that: The Geiger focal plane array has a pixel size of 30μm, a pixel array of no less than 128*128, a temporal resolution of 0.5ns, a dark count of no more than 20kHz, a distance gate width adjustable from 50ns to 2μs, and a pixel pitch of 100μm.

8. The exposure-type laser three-dimensional imaging radar according to claim 7, characterized in that: The processing board processes the acquired 3D data as follows: A. Histogram statistical filtering Assuming that the exposure-type laser 3D imaging radar performs N consecutive measurements on the scene in a static or moving state (where 10≤N≤100), for each pixel on the phase plane, draw its slant range statistical histogram in the N consecutive measurements, set the width of the bin to 1m, remove large outliers, and retain the bin with the most numbers and its two neighbors. B. Polynomial Filtering The slope distance after histogram filtering of a pixel is subjected to polynomial filtering, specifically linear least squares fitting: y=Xβ+ε (2) Among them, y n x represents the measured slant distance of a pixel in the nth frame of the image after histogram filtering. n ε represents the measurement time. n To represent the measurement error, the fitting method for the polynomial coefficients is as follows: Calculate the fitting residuals: FR i y i -f(x i ) (5) Remove small outliers until RMS converges: abs(FR)>σ FR ×RMS(FR) (6) C. RMS Filtering By using the RMS of the fitted residuals, some small outliers can be removed: abs(y-mean(y))>RMS(FR) (7) D. Dynamic compensation Assuming the exposure-type laser 3D imaging radar remains relatively stationary with respect to the target, and a priori relative pose is set, 100 frames of images are continuously acquired, and a mean μ = 0 and a variance σ is added to each pixel of each frame. 2 =0.0001 Gaussian measurement noise, with a false alarm rate of 75% for the whole image, is used to simulate measurement noise caused by dark counting. The dark counting noise follows a uniform distribution. Dynamic conditions of the platform are introduced for dynamic compensation.

9. The exposure-type laser three-dimensional imaging radar according to claim 1, characterized in that: The drive and temperature control circuit can control the temperature of the Geiger focal plane assembly to -40°C with a stability of 0.1°C.

10. The exposure-type laser three-dimensional imaging radar according to claim 1, characterized in that: The bus board is connected to the power board, processing board, FPGA board and laser via cables or internal connectors.

Images