Laser ranging method and face array laser imaging radar applying same

Abstract

This invention relates to a laser ranging method and a planar laser imaging radar using the same. The laser ranging method includes: S100, emitting a laser signal modulated with a pseudo-random code; S200, modulating the laser signal using a Dammann grating; and S300, capturing the return signal of the laser signal after reflection from the target, and calculating the target distance based on the return signal. The planar laser imaging radar uses this laser ranging method to range and image the target. By modulating the laser signal with a Dammann grating and simultaneously using a pseudo-random code to encode and modulate the array laser, it can effectively filter out background noise, achieving both good noise resistance and imaging quality.

Description

Technical Field

[0001] This invention relates to the field of laser ranging, and more specifically to a laser ranging method and a planar laser imaging radar using the same. Background Technology

[0002] During rendezvous and docking, spacecraft typically use a combination of visible light cameras and lidar to acquire characteristic information about the target satellite's docking position. This allows for the simultaneous acquisition of both depth and texture information, overcoming the challenges of obtaining close-range information in backlit and shadowed areas. However, lidar is still affected by background illumination, resulting in a high false alarm rate at the docking end and impacting the accuracy of depth image measurements. Typical area-array lidar uses flood illumination, uniformly illuminating the field of view after homogenization. However, since homogenization devices often employ microlens arrays or microcylindrical mirrors, the optical path difference of the echo light is significant during detection, leading to cluttered wavefronts and a sharp decline in image quality. Summary of the Invention

[0003] In view of this, the present invention proposes a laser ranging method and a planar laser imaging radar using the same method to solve the problems of low imaging quality caused by background noise in current laser imaging.

[0004] In a first aspect, embodiments of the present invention provide a laser ranging method, the laser ranging method comprising:

[0005] S100 emits laser signals modulated with pseudo-random codes;

[0006] S200, the laser signal is modulated by a Dammann grating;

[0007] S300: Capture the return signal of the laser signal after it is reflected by the target, and calculate the target distance based on the return signal.

[0008] Preferably, after step S100 and before step S200, the method further includes:

[0009] The polarization state of the laser signal is detected. If the laser signal is linearly polarized, the polarization direction of the laser signal is adjusted to ±45°.

[0010] Preferably, after step S100 and before step S200, the method further includes:

[0011] The laser signal is collimated and expanded by a beam expander to increase the diameter of the laser spot.

[0012] Preferably, in step S200, the position of the Damman grating is adjusted so that the laser signal is incident on the center of the Damman grating, and at the same time, the orientation of the Damman grating is adjusted so that the lower edge of the Damman grating is parallel to the horizontal direction.

[0013] Preferably, step S300 includes:

[0014] S310, the returned signal is superimposed using dual-port BRAM;

[0015] S320, perform threshold discrimination on the result of the dual-port BRAM superposition;

[0016] S330, The result of the threshold discrimination is bitwise XORed with the source code of the pseudo-random code;

[0017] S340, determine the maximum correlation value of the current returned signal based on the result of the XOR calculation;

[0018] S350, shift the entire returned signal 1 bit to the right and determine the maximum correlation value of the next pseudo-random code;

[0019] S360 determines the maximum correlation value of the entire code segment and calculates the target distance.

[0020] Preferably, before step S310, the method further includes preprocessing the return signal. For a unit symbol length time, if the single-ended signal is high, the level is pulled high for the corresponding time; if the single-ended signal is not high, the level is pulled low for the corresponding time, so that the single-ended signal sequentially generates a return signal of symbol length.

[0021] Preferably, in step S310, the address bits of the dual-port BRAM are ordered according to the symbol order. Whenever the return signal of the second receiving cycle is stored, the original data of the corresponding BRAM address bit is added to the currently received symbol value to form new BRAM address bit data.

[0022] Preferably, before step S320, the returned signals are sorted according to the pixel position to form an echo sequence for each pixel; in step S320, according to the symbol position, the number of symbols that are 1 received in all cycles is accumulated and the average value is used as a threshold. When the dual-port BRAM is full for a predetermined reception cycle, the data of each address bit is read out bit by bit and compared with the threshold. If it is greater than the threshold, the output is 1; if it is less than the threshold, the output is 0.

[0023] Preferably, in step S330, the result of the threshold discrimination is stored bit by bit in a register of the same length as the code element, and is bit-ORed with the pseudo-random code source code register;

[0024] In step S340, for each symbol, the number of 1s in the XOR calculation result is the correlation value of the current symbol. The correlation values ​​of all symbols of the current returned signal are calculated in turn, and the largest one is taken as the maximum correlation value of the current signal. At the same time, the symbol position corresponding to the maximum correlation value is recorded.

[0025] In step S360, the target distance is calculated by converting the position of the symbol corresponding to the maximum correlation value of the entire symbol segment into a delay time multiplied by half the speed of light.

[0026] In a second aspect, embodiments of the present invention provide a planar laser imaging radar that applies the laser ranging method as described in any one of the first aspects, the planar laser imaging radar comprising:

[0027] A laser, used to emit laser signals;

[0028] A laser modulator for performing pseudo-random code modulation on the laser signal;

[0029] A collimating and beam-expanding lens is used to collimate and expand the laser signal.

[0030] A Dammann grating is used to modulate the optical field of the laser signal;

[0031] A receiving telescope is used to receive the return signal of the laser signal after it has been reflected by the target;

[0032] An array detector is used to detect the returned signal;

[0033] The processing unit is used to process and calculate the returned signal.

[0034] This invention uses a Damman grating for beam splitting, which can convert a single laser beam into several laser beams in an N×N array with minimal energy distribution differences between beams, avoiding the optical path difference problem of homogenizing devices. Simultaneously, a pseudo-random code is used to modulate the continuous laser, intensity-modulating the laser amplitude to create laser pulses with a pseudo-random code intensity field distribution. By receiving the reflected pseudo-random code and performing an XOR operation with the local code, background filtering is achieved. This effectively filters out background noise from area array laser imaging radar, balancing good noise resistance and imaging quality. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic flowchart of the laser ranging method according to an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram comparing a general pulse signal and a pseudo-random code pulse signal.

[0038] Figure 3 This is a schematic diagram of the far-field optical field distribution of the Damman grating according to an embodiment of the present invention;

[0039] Figure 4 This is a flowchart illustrating a sub-process of the laser ranging method according to an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of the composition of a planar laser imaging radar according to an embodiment of the present invention;

[0041] Figure 6 This is a schematic diagram of the laser imaging process of a planar laser imaging radar according to an embodiment of the present invention. Detailed Implementation

[0042] The description of the embodiments in this specification should be taken in conjunction with the accompanying drawings, which should form part of the complete specification. In the drawings, the shape or thickness of the embodiments may be exaggerated and may be indicated in a simplified or convenient manner. Furthermore, parts of the various structures in the drawings will be described separately; it is worth noting that elements not shown in the figures or not described in words are in a form known to those skilled in the art.

[0043] The descriptions of the embodiments herein, including any references to directions and orientations, are for ease of description only and should not be construed as limiting the scope of the invention. The following description of preferred embodiments involves combinations of features, which may exist independently or in combination; the invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims.

[0044] like Figure 1 The diagram shown is a schematic flowchart of a laser ranging method according to an embodiment of the present invention. The method includes:

[0045] S100 emits laser signals modulated with pseudo-random codes; Figure 2 This is a schematic diagram comparing a general pulse signal and a pseudo-random code pulse signal.

[0046] Preferably, the laser signal is pseudo-random code modulated by a laser modulator with a high extinction ratio to minimize the pulse width, thereby improving the resolution of laser ranging.

[0047] Preferably, the polarization state of the emitted laser signal is detected. If the laser signal is linearly polarized, the polarization direction of the laser signal is adjusted to ±45° to ensure that the lower edge of the subsequent array output is horizontal.

[0048] Preferably, the emitted laser signal passes through a collimator and beam expander before reaching the Damman grating. This is mainly used to increase the diameter of the laser signal spot so that the spot covers the Damman grating as large an area as possible. The larger the coverage area, the better the diffraction effect.

[0049] S200, the laser signal is modulated by a Dammann grating; Figure 3 This is a schematic diagram of the far-field optical field distribution of the Damman grating.

[0050] Preferably, the Damman grating is a nematic liquid crystal Damman grating. The nematic liquid crystal Damman grating has a simple structure, fast processing speed, and uniform light effect, and can modulate the light field of the laser signal based on the geometric phase theory.

[0051] Preferably, the position of the Damman grating is adjusted so that the laser signal is incident at the center of the Damman grating. Simultaneously, the orientation of the Damman grating is adjusted so that its lower edge is parallel to the horizontal direction, ensuring that the principal axis of the nematic liquid crystal molecules in the Damman grating is its fast axis direction.

[0052] S300: Capture the return signal of the laser signal after it is reflected by the target, and calculate the target distance based on the return signal.

[0053] The laser signal emitted by the laser is split by a Damman grating and then illuminates the target. After the target reflects the signal, the returned signal is received and the target distance is calculated.

[0054] like Figure 4 As shown, specifically, calculating the target distance in step S300 includes:

[0055] S310, perform dual-port BRAM superposition on the returned signal.

[0056] Before the return signal is superimposed on the dual-port BRAM, it is preprocessed in the following way: for a unit symbol length time, if the single-ended signal is high, the level is pulled high for the corresponding time, that is, the digital signal is 1; if the single-ended signal is not high, the level is pulled low for the corresponding time, that is, the digital signal is 0, so that the single-ended signal generates a return signal of symbol length in sequence.

[0057] A ping-pong storage operation is implemented using a dual-port BRAM. The address bits of the dual-port BRAM are ordered according to the symbol order. Whenever the return signal of the second receive cycle is stored, the original data of the corresponding BRAM address bit is added to the value of the currently received symbol to form a new BRAM address bit data.

[0058] S320, perform threshold discrimination on the result of the dual-port BRAM superposition.

[0059] The returned signals are sorted according to the pixel position to form an echo sequence for each pixel. A pixel refers to the imaging element of each laser beam after the laser signal is split by the Dammann grating.

[0060] According to the symbol position, the number of symbols that are 1 received in all cycles is accumulated and the average value is used as the threshold. When the dual-port BRAM is full for a predetermined reception cycle, the data of each address bit is read out and compared with the threshold. If it is greater than the threshold, the output is 1; if it is less than the threshold, the output is 0.

[0061] S330, the threshold discrimination result is bitwise XORed with the source code of the pseudo-random code.

[0062] The threshold discrimination result is stored bit by bit in a register of the same length as the symbol, and then bit by bit XORed with the pseudo-random code source code register.

[0063] S340, determine the maximum correlation value of the current returned signal based on the result of the XOR calculation.

[0064] For each symbol, the number of 1s in the XOR calculation result is the correlation value of the current symbol. The correlation values ​​of all symbols in the current returned signal are calculated sequentially, and the largest one is taken as the maximum correlation value of the current signal. At the same time, the symbol position corresponding to the maximum correlation value is recorded.

[0065] S350, shift the entire returned signal 1 bit to the right and determine the maximum correlation value of the next pseudo-random code.

[0066] Continue until the correlation calculation for all symbol positions is completed.

[0067] S360 determines the maximum correlation value of the entire code segment and calculates the target distance.

[0068] The target distance is calculated by converting the symbol position corresponding to the maximum correlation value of the entire symbol segment into a delay time, multiplying by the speed of light, and then multiplying by half. It should be noted that the maximum correlation value of the entire symbol segment refers to the largest correlation value among all symbol positions in step S350.

[0069] This invention uses a Damman grating for beam splitting, which can convert a single laser beam into several laser beams in an N×N array with minimal energy distribution differences between beams, avoiding the optical path difference problem of homogenizing devices. Simultaneously, a pseudo-random code is used to modulate the continuous laser, intensity-modulating the laser amplitude to create laser pulses with a pseudo-random code intensity field distribution. By receiving the reflected pseudo-random code and performing an XOR operation with the local code, background filtering is achieved. This effectively filters out background noise from area array laser imaging radar, balancing good noise resistance and imaging quality.

[0070] like Figure 5 The diagram shown is a schematic representation of the components of an area array laser imaging radar according to an embodiment of the present invention. The area array laser imaging radar uses the aforementioned laser ranging method for ranging and imaging. The area array laser imaging radar includes a laser for emitting laser signals; a laser modulator for performing pseudo-random code modulation on the laser signals; a collimating beam expander for collimating and expanding the laser signals; a Dammann grating for modulating the light field of the laser signals; a receiving telescope for receiving the return signal of the laser signals after reflection from the target; an area array detector for detecting the return signal; and a processing unit, including an FPGA, for processing and calculating the return signal.

[0071] Among them, the area array detector can be an InGaAs area array detector.

[0072] like Figure 6 As shown, the following example of a spacecraft rendezvous and docking in orbit illustrates the process of ranging and imaging using a laser ranging method in an embodiment of the present invention.

[0073] Step 1: Turn on the laser and use a high extinction ratio laser modulator to perform pseudo-random code pulse modulation on the laser signal to minimize the pulse width, thereby improving the laser ranging resolution.

[0074] Specifically, the continuous laser emitted by the laser enters the optoelectronic modulator through an optical fiber. The modulation signal is output as an electrical signal through the I / O port of the FPGA board of the processing unit. The electrical signal drives the optoelectronic modulator to modulate the laser signal.

[0075] Step 2: Use a polarization meter to detect the polarization state of the laser output. If the laser is linearly polarized, the laser polarization direction needs to be adjusted to ±45° to ensure that the lower edge of the subsequent array output is horizontal.

[0076] Step 3: Install a laser collimator to ensure a larger laser spot diameter after passing through it. For the same grating constant, a larger laser coverage area results in better diffraction. The magnified laser is then incident into free space through a collimating lens via an optical fiber, further expanding the beam to cover as much of the Dammann grating area as possible.

[0077] Step 4: Adjust the position of the liquid crystal Dammann grating so that the laser is incident at the center of the effective surface of the grating, and adjust the grating orientation so that the bottom edge of the grating is horizontal. The main axis α of the nematic liquid crystal molecules is in the direction of its fast axis.

[0078] Step 5: After the laser is reflected by the target, it enters the InGaAs array detector through the receiving telescope, obtaining continuous frame echo signals carrying distance information, and then transmitting the echo signals to the FPGA.

[0079] Step Six: Under the control of the start ranging signal, the return signal data processing function begins operation. First, the data preprocessing module receives the return signal.

[0080] Step 7: Within the unit symbol length time (symbol interval × number of symbols), if a high level appears in the single-ended signal, the level is pulled high during that time; if no high level appears in the single-ended signal, the level is pulled low during that time, so that the single-ended signal sequentially generates a return signal of symbol length.

[0081] Step 8: After receiving the return signal from the pseudo-random code laser, use a dual-port BRAM to perform ping-pong data storage. The address bits of the dual-port BRAM correspond to the order of the code elements. When storing the return signal of the second receiving cycle, first read the original data at the corresponding address bit of the BRAM, add the currently received code element value, and then store it in the BRAM at that address bit. This process accumulates and stores return signals from multiple receiving cycles.

[0082] Step 9: Sort the echo signals according to the pixel position and form an echo sequence for each pixel.

[0083] Step 10: Based on the symbol position, accumulate the number of "1" symbols received in all cycles, and calculate the average value as the threshold. After the dual-port BRAM is full for the specified reception cycle, read out the data of each address bit and compare it with the threshold. If the data is greater than the threshold, output "1"; if it is less than the threshold, output "0".

[0084] Step 11: After receiving the threshold discrimination output, the return signal output result is stored bit by bit in a register of the same length as the symbol for computation. First, the return signal register and the pseudo-random code source code register are XORed bit by bit. The number of "1"s in the result (i.e., the number of bits that are the same in both codes) is used as the correlation value An. This value is then compared with the currently stored maximum correlation value AxMax (initially 0). If the correlation value is greater than the maximum AxMax, AxMax is set as the current correlation value An, and the symbol position x is changed and recorded as the current symbol position. If the correlation value is less than the maximum AxMax, AxMax remains unchanged, and the recorded symbol position x remains unchanged.

[0085] Step 12: After calculating the correlation value for the current symbol position, shift the entire return signal 1 bit to the right and begin calculating the correlation value for the next pseudo-random code. Once the correlation calculation for all symbol positions is complete, output the maximum correlation value AxMax for the entire symbol segment. At this point, symbol position x represents the phase difference, which, when converted to delay time multiplied by the speed of light and divided by 2, gives the distance information. However, to optimize the ranging results and facilitate data processing, information such as the peak position and maximum correlation value of the correlation values ​​in the ranging results are uploaded to the host computer for processing.

[0086] Through the above steps, the following can be achieved: encoding the array laser using pseudo-random codes and performing correlation detection on individual pixels at the laser receiver effectively filters out the background noise of the area array imaging lidar. The Damman grating is fabricated using nematic liquid crystals and spatial light modulation is performed through geometric phase theory to form a laser array beam. The Damman grating has a simple structure, fast processing speed, and provides uniform light distribution. Pseudo-random code modulation technology is relatively mature, and the extinction ratio of the device can be achieved through secondary cascading. Correlation detection can be simplified through XOR calculations, resulting in low hardware resource requirements on the FPGA.

[0087] The above description is only a preferred embodiment of the present invention and is 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 laser ranging method, characterized by, The laser ranging method includes: S100 emits laser signals modulated with pseudo-random codes; After step S100 and before step S200, the following is also included: The polarization state of the laser signal is detected. If the laser signal is linearly polarized, the polarization direction of the laser signal is adjusted to ±45°. The laser signal is collimated and expanded by a beam expander to increase the laser spot diameter. S200, the laser signal is modulated by a Dammann grating; S300, capturing the return signal of the laser signal after it is reflected by the target, and calculating the target distance based on the return signal, including: S310, the returned signal is superimposed using dual-port BRAM; S320, perform threshold discrimination on the result of the dual-port BRAM superposition; S330, The result of the threshold discrimination is bitwise XORed with the source code of the pseudo-random code; S340, determine the maximum correlation value of the current returned signal based on the result of the XOR calculation; S350, shift the entire returned signal 1 bit to the right and determine the maximum correlation value of the next pseudo-random code; S360 determines the maximum correlation value of the entire code segment and calculates the target distance.

2. The laser ranging method of claim 1, wherein, In step S200, the position of the Damman grating is adjusted so that the laser signal is incident on the center of the Damman grating. At the same time, the orientation of the Damman grating is adjusted so that the lower edge of the Damman grating is parallel to the horizontal direction.

3. The laser ranging method of claim 1, wherein, Before step S310, the return signal is preprocessed. For a unit symbol length time, if the single-ended signal is high, the level is pulled high for the corresponding time; if the single-ended signal is not high, the level is pulled low for the corresponding time, so that the single-ended signal generates a return signal of symbol length in sequence.

4. The laser ranging method of claim 1, wherein, In step S310, the address bits of the dual-port BRAM are ordered according to the symbol order. Whenever the return signal of the second receiving cycle is stored, the original data of the corresponding BRAM address bit is added to the currently received symbol value to form new BRAM address bit data.

5. The laser ranging method according to claim 1, characterized in that, Before step S320, the returned signals are sorted according to the pixel position to form an echo sequence for each pixel; In step S320, according to the symbol position, the number of symbols that are 1 received in all cycles is accumulated and the average value is used as a threshold. When the dual-port BRAM is full for a predetermined reception cycle, the data of each address bit is read out and compared with the threshold. If it is greater than the threshold, the output is 1; if it is less than the threshold, the output is 0.

6. The laser ranging method according to claim 1, characterized in that, In step S330, the result of the threshold discrimination is stored bit by bit in a register of the same length as the code element, and is bit by bit XORed with the pseudo-random code source code register; In step S340, for each symbol, the number of 1s in the XOR calculation result is the correlation value of the current symbol. The correlation values ​​of all symbols of the current returned signal are calculated in turn, and the largest one is taken as the maximum correlation value of the current signal. At the same time, the symbol position corresponding to the maximum correlation value is recorded. In step S360, the target distance is calculated by converting the position of the symbol corresponding to the maximum correlation value of the entire symbol segment into a delay time and then multiplying it by half the speed of light.

7. A staring laser imaging radar applying the laser ranging method according to any one of claims 1 to 6, characterized in that, The area array laser imaging radar includes: A laser, used to emit laser signals; A laser modulator for performing pseudo-random code modulation on the laser signal; A collimating and beam-expanding lens is used to collimate and expand the laser signal. A Dammann grating is used to modulate the optical field of the laser signal; A receiving telescope is used to receive the return signal of the laser signal after it has been reflected by the target; An array detector is used to detect the returned signal; The processing unit is used to process and calculate the returned signal.

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