CN113109834A - High-energy and high-precision underwater three-dimensional imaging laser radar system and method - Google Patents

High-energy and high-precision underwater three-dimensional imaging laser radar system and method Download PDF

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CN113109834A
CN113109834A CN202110411475.XA CN202110411475A CN113109834A CN 113109834 A CN113109834 A CN 113109834A CN 202110411475 A CN202110411475 A CN 202110411475A CN 113109834 A CN113109834 A CN 113109834A
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filtering
energy
laser
signal
target
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许可
万建伟
王玲
马燕新
徐国权
张一帆
顾尚泰
元志安
周笑宇
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National University of Defense Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
    • G01S17/894—3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/4802—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/484—Transmitters

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  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Electromagnetism (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

The application relates to a high-energy and high-precision underwater three-dimensional imaging laser radar system and a method. The system comprises: the system comprises a high-energy laser, an optical receiving system and a signal processing terminal; the high-energy laser comprises a Q-switched laser and an F-P oscillation cavity, wherein the Q-switched laser is used for generating high-peak power and high-energy narrow pulses, the narrow pulses are converted into high-energy and high-frequency laser pulse trains through the F-P oscillation cavity, and the high-energy and high-frequency laser pulse trains irradiate a target in a water body medium to generate echo signals; the optical receiving system receives the echo signal, processes and records the echo signal, and transmits a recording result to the signal processing terminal; and the signal processing terminal performs three-stage filtering processing on the received recording result to obtain the three-dimensional imaging of the target in the water medium. The laser pulse signal output by the laser in the system has higher peak power and energy, the detection capability is improved, the three-section type filtering processing scheme is used for pertinently filtering the noise at different stages, and the imaging precision is improved.

Description

High-energy and high-precision underwater three-dimensional imaging laser radar system and method
Technical Field
The application relates to the technical field of laser radar systems, in particular to a high-energy and high-precision underwater three-dimensional imaging laser radar system and method.
Background
The underwater imaging technology is an important technology for underwater detection, and has important application in various fields such as target detection, marine geographic engineering and the like. The common light source is limited by the characteristics of water body environment, the acting distance is limited, the image noise is large, the blue-green laser has high transmittance in water and can be used for directly detecting underwater targets, wherein the laser with the wavelength of 532nm is the most commonly used underwater detection laser.
At present, most of lasers in a three-dimensional imaging laser radar system for underwater targets adopt a scheme of modulating laser pulses by high-frequency microwaves, and the high-frequency laser pulses obtained by the scheme have low peak power and small energy, so that the underwater target detection capability of the laser radar system is limited. In the aspect of signal processing, because of more stray in a real water area, an image has a large amount of noise, and the imaging quality is influenced.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides an underwater three-dimensional imaging laser radar system with high energy output, and aims to improve the output energy of a laser in the laser radar system, and simultaneously, adopt a three-section filtering technology to filter noise, and improve the overall detection performance and imaging precision of the laser radar.
A high energy, high precision, underwater three dimensional imaging lidar system, comprising:
the high-energy laser comprises a Q-switched laser and an F-P oscillation cavity; the Q-switched laser is used for compressing laser pulses by adopting a Q-switched technology to generate narrow pulses with high peak power and high energy; the F-P oscillation cavity is used for receiving the narrow pulse, converting a narrow pulse signal into a high-energy and high-frequency laser pulse train by utilizing the round-trip part output characteristic of the F-P oscillation cavity, and irradiating the high-energy and high-frequency laser pulse train onto a target in a water body medium to generate an echo signal.
And the optical receiving system is used for receiving the echo signal, processing and recording the echo signal and transmitting a recording result to the signal processing terminal.
The signal processing terminal is used for receiving the recording result sent by the optical receiving system and carrying out three-stage filtering processing to obtain three-dimensional imaging of the target in the water medium
In one embodiment, the Q-switched laser is a semiconductor pumped short cavity sub-nanosecond pulsed laser; the Q-switched laser is used for generating narrow pulses with high peak power and high energy.
In one embodiment, the optical receiving system comprises a stripe camera; the stripe camera is used for converting the received echo signals into electronic images through the photocathode after passing through the slit, then electrons at different positions on a time sequence are scanned to a space position vertical to the stripe direction through a scanning electric field, the conversion from time information to space information is completed, one-dimensional images extracted by the slit are changed into two-dimensional images, the conversion from electric signals to optical signals is completed through multiplication bombardment of a fluorescent screen, and finally, the stripe images are obtained through CCD recording.
In one embodiment, the signal processing terminal comprises a preprocessing module, a band-pass filtering + matched filtering module and a threshold filtering module.
And the preprocessing module is used for filtering background noise of the streak camera in the streak image to obtain a preprocessed signal.
And the band-pass filtering and matched filtering module is used for filtering out direct-current components and low-frequency signals in the preprocessed signals and improving the range resolution of the laser radar.
And the threshold filtering module is used for filtering out low-intensity noise of the signal obtained after the filtering of the band-pass filtering and matched filtering module so as to obtain three-dimensional imaging of the target in the water medium.
A high-energy and high-precision underwater three-dimensional imaging method is applied to any one of the high-energy and high-precision underwater three-dimensional imaging laser radar systems to realize three-dimensional imaging of a target in a water medium; the method comprises the following steps:
generating a high-energy and high-frequency laser pulse train through a high-energy laser, and irradiating the high-energy and high-frequency laser pulse train onto a target in a water body medium to generate an echo signal.
And receiving the echo signal through an optical receiving system, processing and recording the echo signal, and sending the recorded signal to a signal processing terminal.
And receiving the recorded signals through a signal processing terminal, and filtering the recorded signals by adopting a three-section filtering method to obtain the three-dimensional imaging of the target in the water medium.
In one embodiment, the method includes receiving a recorded signal through a signal processing terminal, and performing filtering processing on the recorded signal by using a three-segment filtering method to obtain a three-dimensional image of a target in a water medium, and further includes:
and receiving the recorded signal through a signal processing terminal, preprocessing the recorded signal, and filtering background noise of the streak camera in the streak image to obtain a preprocessed signal.
And performing band-pass filtering and matched filtering on the preprocessed signals, and filtering out direct-current components and low-frequency signals in the preprocessed signals to obtain the laser radar signals with high range resolution.
And carrying out threshold filtering on the laser radar signal with the high distance resolution, and filtering low-intensity noise in the laser radar signal with the high distance resolution to obtain three-dimensional imaging of the target in the water medium.
The high-energy and high-precision underwater three-dimensional imaging laser radar system and the method thereof comprise the following steps: the system comprises a high-energy laser, an optical receiving system and a signal processing terminal; the high-energy laser comprises a Q-switched laser and an F-P oscillation cavity, wherein the Q-switched laser is used for generating high-peak power and high-energy narrow pulses, the narrow pulses are converted into high-energy and high-frequency laser pulse trains through the F-P oscillation cavity, and the high-energy and high-frequency laser pulse trains irradiate a target in a water body medium to generate echo signals; the optical receiving system receives the echo signal, processes and records the echo signal, and transmits a recording result to the signal processing terminal. And the signal processing terminal receives the recording result and performs three-stage filtering processing to obtain three-dimensional imaging of the target in the water medium. The laser pulse signal output by the laser in the system has higher peak power and energy, the detection capability is improved, the three-section type filtering processing scheme is used for pertinently filtering the noise at different stages, and the imaging precision is improved.
Drawings
FIG. 1 is a block diagram of a high energy, high precision, underwater three dimensional imaging lidar system in one embodiment;
FIG. 2 is a schematic flow chart of a high energy, high accuracy underwater three dimensional imaging method in one embodiment;
FIG. 3 is a graph of the results of three filtering methods in one embodiment; wherein FIG. 3(a) is mean filtering, FIG. 3(b) is mean filtering + K-nearest neighbor smoothing filtering, and FIG. 3(c) is mean filtering + neighborhood averaging filtering;
FIG. 4 is a schematic diagram of a resolution target in one embodiment;
FIG. 5 is a graph of the statistical results and the imaging results at 20m in a clean water environment in one embodiment; wherein, FIG. 5(a) is a statistical result chart, and FIG. 5(b) is an imaging result chart at 20m in a clear water environment;
FIG. 6 shows the imaging results at 13m in a clean water environment according to one embodiment; fig. 6(a) is a 3D image, and fig. 6(b) is an intensity image.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The water has stronger absorption and attenuation effects on light irradiated into the water, the absorption of the water on the light is a process of converting partial light energy incident into the water into energy in other forms, and a high-energy laser light source is required to irradiate a target in a water body medium to improve the imaging distance in the water; in addition, because laser is transmitted in water, water molecules and other impurities can generate a strong scattering effect on light, and scattered light signals at a non-target detection distance seriously interfere with the underwater imaging quality of the laser radar. The high-energy and high-precision underwater three-dimensional imaging laser radar system provided by the invention can provide high-energy and high-frequency laser pulse trains, has a signal processing terminal with a high-efficiency filtering processing function, and improves the imaging distance and the imaging precision in a water environment.
In one embodiment, as shown in fig. 1, there is provided a high energy, high precision underwater three dimensional imaging lidar system, comprising: a high-energy laser 10 including a Q-switched laser 101 and an F-P oscillation cavity 102; the Q-switched laser 101 is used for compressing laser pulses by adopting a Q-switched technology to generate narrow pulses with high peak power and high energy; the F-P oscillation cavity 102 is used for receiving the narrow pulse, converting the narrow pulse into a high-energy and high-frequency laser pulse train by utilizing the output characteristic of the round-trip part of the F-P oscillation cavity 102, and irradiating the high-energy and high-frequency laser pulse train onto a target in a water body medium to generate an echo signal.
The high-energy laser adopts a Q-switching technology combined with F-P cavity oscillation output, and a high-energy and high-frequency laser pulse train is directly obtained from a laser signal.
And the optical receiving system 20 is used for receiving the echo signals, processing and recording the echo signals, and transmitting the recording result to the signal processing terminal.
The optical receiving system can adopt the technologies of streak tube underwater three-dimensional imaging, synchronous scanning and the like to realize underwater three-dimensional imaging.
The recorded results are initial three-dimensional imaging data of the target in the aqueous medium obtained by an imaging module in the optical receiving system.
And the signal processing terminal 30 is configured to receive the recording result sent by the optical receiving system 20, and perform three-stage filtering processing to obtain a three-dimensional image of the target in the water medium.
The first stage of the three-stage filtering processing is preprocessing aiming at the self background noise of the streak camera; the second section aims at the low-frequency interference in the echo signal and simultaneously improves the signal-to-noise ratio; and the third stage is to filter the low-intensity residual noise obtained by analyzing the intensity diagram and obtain the high-precision three-dimensional imaging of the target in the water medium.
In the above-mentioned laser radar system of high energy, high accuracy three-dimensional formation of image under water, the said system includes: the system comprises a high-energy laser, an optical receiving system and a signal processing terminal; the high-energy laser comprises a Q-switched laser and an F-P oscillation cavity, wherein the Q-switched laser is used for generating high-peak power and high-energy narrow pulses, the narrow pulses are converted into high-energy and high-frequency laser pulse trains through the F-P oscillation cavity, and the high-energy and high-frequency laser pulse trains irradiate a target in a water body medium to generate echo signals; the optical receiving system receives the echo signal, processes and records the echo signal, and transmits a recording result to the signal processing terminal. And the signal processing terminal receives the recording result and performs three-stage filtering processing to obtain three-dimensional imaging of the target in the water medium. The laser pulse signal output by the laser in the system has higher peak power and energy, the detection capability is improved, the three-section type filtering processing scheme is used for pertinently filtering the noise at different stages, and the imaging precision is improved.
In one embodiment, the Q-switched laser is a semiconductor pumped, short cavity, sub-nanosecond pulsed laser for producing high peak power, high energy, narrow pulses.
Preferably, the high-energy laser adopts an oscillator + amplifier structure, the seed laser is a semiconductor pumped short-cavity subnanosecond pulse laser, the wavelength is 1064nm, the output pulse energy is 300uJ, the pulse width is 770ps, and the repetition frequency is 1Hz-100Hz adjustable. The amplifier adopts a semiconductor side pump module bi-pass two-stage amplification structure, the energy reaches 170mJ after two-stage amplification, and the pulse width is not obviously changed. The 1064nm fundamental frequency light passes through a KTP frequency doubling crystal to obtain 532nm green light output, and the pulse energy can reach 80 mJ. The KTP crystal is arranged in the F-P cavity, and 532nm laser pulses with pulse intervals of about 2ns, namely carrier frequency of about 500MHz are obtained by applying the output characteristic of the round-trip part of the F-P cavity. This process is the process by which a laser generates high energy laser pulses.
In one embodiment, the optical receiving system comprises a stripe camera; the stripe camera is used for converting the received echo signals into electronic images through the photocathode after passing through the slit, then electrons at different positions on a time sequence are scanned to a space position vertical to the stripe direction through a scanning electric field, the conversion from time information to space information is completed, one-dimensional images extracted by the slit are changed into two-dimensional images, the conversion from electric signals to optical signals is completed through multiplication bombardment of a fluorescent screen, and finally, the stripe images are obtained through CCD recording.
The stripe camera is an ultrafast diagnostic instrument with high time, space and light intensity resolution, and mainly comprises a stripe image converter, an image intensifier, a high-low voltage power supply, a scanning electric control system, a front-end input slit optical system, an industrial control module, a rear-end light cone coupling CCD recording system and the like. The echo signal is converted into an electronic image by a photocathode after passing through the slit, then electrons at different positions on a time sequence are scanned to a space position vertical to the direction of the stripe by a scanning electric field, the conversion from time information to space information is completed, a one-dimensional image extracted by the slit is changed into a two-dimensional image, the conversion from an electric signal to an optical signal is completed by multiplying and bombarding a fluorescent screen, and finally the conversion is recorded by a CCD. The core part is a fringe image converter, and the imaging precision is higher when the number of pixels is larger. Meanwhile, the higher the spectral sensitivity of the visible light band is, the higher the signal-to-noise ratio is, and the stronger the detection capability is.
The front-end input slit optical system consists of a slit, an input lens and an output lens, wherein the slit is an adjustable slit with the length of 35mm and the width of 0-3 mm, and the adjustment precision is 0.005 mm.
The fringe image converter is a core module for realizing space-time transformation measurement by a fringe camera, and requires that the spectral sensitivity of a visible light waveband is higher than 50mA/W and the number of pixels is more than 500. In order to meet the requirement that the number of pixels is more than 500, the fringe aberration of the streak tube is reduced by adopting the electronic optical design of spherical input and output windows, the actually measured static spatial resolution is more than 20lp/mm, the dynamic spatial resolution is more than 8lp/mm, and the total number of pixels in a slit with the length of 35mm reaches 560. On the other hand, the preparation process of the photocathode is strictly controlled, and the sensitivity of the streak tube at the wavelength of 550nm reaches 55mA/W through thickness regulation.
The image intensifier is used for amplifying output image signal of the streak tube, and the multiplication efficiency is 102～104And (4) doubling. In order to obtain high gain signal, S25 cathode type image intensifier is selected, its cathode sensitivity is higher than 150 μ A/Lm, and gain is 102～104The range is adjustable to meet the amplification of input signals with different intensities.
The scanning electric control system is mainly used for generating high-voltage linear time-varying signals and realizing space-time transformation of photoelectrons passing through the deflection plate, and has a certain time delay function so as to realize good synchronization of scanning voltage and input measured signals. In order to obtain target imaging with different precision and different distances, three scanning positions are set, namely 5ns, 30ns and 100 ns.
And (3) a stripe camera signal acquisition process: the high-energy and high-frequency laser pulse train is emitted by a high-energy laser, is emitted by an underwater target and is received by a stripe camera, the stripe camera images a received optical signal on a photoelectric cathode of a stripe tube, and an initial image is obtained through signal conversion, deflection and enhancement and is finally acquired to an information processor through the traditional CCD technology.
In one embodiment, the signal processing terminal comprises a preprocessing module, a band-pass filtering + matched filtering module and a threshold filtering module.
And the preprocessing module is used for filtering background noise of the streak camera in the streak image to obtain a preprocessed signal.
And the band-pass filtering and matched filtering module is used for filtering direct-current components and low-frequency signals in the preprocessed signals and improving the range resolution of the laser radar.
And the threshold filtering module is used for filtering the low-intensity noise of the signal obtained after the band-pass filtering and the matched filtering module are used for filtering, so as to obtain the three-dimensional imaging of the target in the water medium.
Preferably, the signal processing terminal receives a signal transmitted from the streak camera, first performs preprocessing on noise generated by the streak camera carried by the signal, and filters background noise of the streak camera by adopting a scheme of 'mean filtering + field average filtering', wherein the mean filtering is signal minus mean, the neighborhood average filtering is a value obtained by filtering a signal by taking a field mean of a certain signal as the signal, and the field view is set to be 5 × 5. And then, a scheme of 'band-pass filtering + matched filtering' is adopted to remove direct-current components and low-frequency signals, the range resolution of the laser radar is improved, the removal effect of the direct-current components influences the size of side lobes of a matched filtering substrate, and the noise of non-carrier frequency band range components can reduce the signal-to-noise ratio. The center frequency of the band-pass filter is the carrier center frequency fmThe width Br of the passband is slightly larger than the bandwidth B of the carrier signalscIs set as Br＞1.25BscAnd the narrower the transition band, the better. The signal after band-pass filtering is xbpf(i) The carrier modulated digital real signal is xm(i) Then the matched filtering process can be expressed as:
xpc＝conv(xbpf,xm) (1)
where conv denotes a convolution operation. Finally, aiming at the residual low-intensity noise, a 'threshold filtering' scheme is adopted, the threshold is set to be one third of the difference between the maximum intensity value and the minimum intensity value, and all signals below the threshold are set to be zero. The process is a three-stage filtering process.
In one embodiment, as shown in fig. 2, a method for high-energy and high-precision underwater three-dimensional imaging is provided, which is applied to any one of the above-mentioned laser radar systems for high-energy and high-precision underwater three-dimensional imaging to realize three-dimensional imaging of a target in a water medium; the method comprises the following steps:
and 200, generating a high-energy and high-frequency laser pulse train by using a high-energy laser, and irradiating the high-energy and high-frequency laser pulse train to a target in a water body medium to generate an echo signal.
And 202, receiving the echo signal through the optical receiving system, processing and recording the echo signal, and sending the recorded signal to the signal processing terminal.
And step 204, receiving the recorded signals through the signal processing terminal, and performing filtering processing on the recorded signals by adopting a three-section filtering method to obtain three-dimensional imaging of the target in the water medium.
In one embodiment, step 204 further comprises: receiving the recorded signal through a signal processing terminal, preprocessing the recorded signal, and filtering background noise of a streak camera in a streak image to obtain a preprocessed signal; performing band-pass filtering and matched filtering on the preprocessed signals, and filtering out direct-current components and low-frequency signals in the preprocessed signals to obtain laser radar signals with high range resolution; and carrying out threshold filtering on the laser radar signal with high distance resolution, and filtering low-intensity noise in the laser radar signal with high distance resolution to obtain three-dimensional imaging of the target in the water medium.
In a verified embodiment of the three-segment filtering method, because background noise of the streak camera is large, each acquired frame of image needs to be subjected to denoising preprocessing firstly, and the method is to perform mean filtering on each frame of image firstly and then adopt a K-nearest neighbor smoothing filter or a neighborhood mean value method for filtering. The filtering effect is shown in fig. 3, in which fig. 3(a) is mean filtering, fig. 3(b) is mean filtering + K neighbor smoothing filtering, and fig. 3(c) is the result of mean filtering + neighborhood averaging filtering. As can be seen from the figure, the filtering effect of the mean filtering and the neighborhood averaging is better because the noise distribution is sparse and the target signal distribution is concentrated, and the neighborhood averaging can effectively inhibit the noise and improve the signal-to-noise ratio.
In a verification embodiment, in order to verify the performance of a high-energy and high-precision underwater three-dimensional imaging laser radar system, a 20m × 1m × 1m glass water tank is built, and an underwater three-dimensional imaging laser radar principle prototype test system is constructed. The experiment is divided into two major parts: clear water environment experiment and muddy water environment experiment, the clear water adopts municipal tap water, and the attenuation coefficient is 0.11m-1In turbid water environment, the grease is injected into the clear waterThe attenuation coefficient of the flour and milk is 0.56m-1。
(1) Underwater imaging distance experiment
As shown in fig. 4, a resolution target with a diameter of 30cm is placed at the end of a water tank in a clear water environment, and is scanned and imaged for multiple times by using a principle prototype to obtain an imaging result, wherein the imaging result shows that a large amount of noise exists in a 3D image, and the target in an intensity image is relatively clear, which shows that the noise intensity is concentrated in a low-intensity section. Performing histogram statistics on each frame of image, and dividing the signal intensity into three segments of low intensity, medium intensity and high intensity, wherein the result is a statistical result graph shown in fig. 5(a), and it can be seen that noise is basically concentrated in the low intensity segment, so that threshold filtering can be adopted, and the threshold α is set as follows:
Figure BDA0003024297910000091
where intensity represents signal strength.
The imaging result of adding the threshold filtering is a 3D image as shown in FIG. 5(b), and it can be seen that the signal-to-noise ratio is obviously improved. Therefore, the principle model can be considered to have the detection capability of being better than 20m under the clean water environment.
(2) Underwater range-extending experiment
In order to verify the effect of the band-pass filtering process range extension, two groups of comparison experiments are set in a turbid water environment, one group of experiments do not use the band-pass filtering process, the other group of experiments use the band-pass filtering process, and the following conclusion is obtained by analyzing the imaging result: target imaging without bandpass filtering is overwhelmed by noise at 5.9m, while target imaging with bandpass filtering still detects the target at 10.7m, extending the range by 81.4%.
(3) Relative distance resolution
The target was placed in a water tank 10m (in a turbid water environment), and a metal plate was placed 10.83m behind the target, i.e., the actual measured distance between the two was 0.83m, and then both were scanned and imaged. The 3D images of the two planes are fitted to obtain corresponding fitted planes, which may be represented as ax + by + cz + E, 0. The target and the metal plate are integrally smooth and are arranged in parallel, so that the obtained fitting coefficients a, b and c of the two planes are consistent, and the actual fitting result also shows that the difference of the fitting coefficients a, b and c of the two planes is very small and can be ignored. Therefore, the coefficients a, b, and c of one of the planes are taken, and the distance between the two is calculated according to the formula (3), and the result is 0.82m with an error of 0.01m, thereby obtaining a relative distance error of 1.20%.
Figure BDA0003024297910000092
Wherein D represents the relative distance between the two, a, b and c represent the fitting coefficients of the two planes, and E1 and E2 represent constants in the fitting formula.
(4) Precision of imaging
The imaging precision experiment is used for verifying the capturing capability of the principle prototype on the details of the target object and is also a core index of the imaging radar. The target of FIG. 4 has a screw 9mm in diameter in the center, and in a clean water environment, the edge of the target at 20m is clearly visible, but the screw is not observed. FIG. 6 is the imaging result of 13m place in clean water environment, wherein FIG. 6(a) is a 3D image, FIG. 6(b) is an intensity image, it can be seen that the screw is clearly visible in both images, which proves that the principle model machine has stronger imaging precision
In addition, the error of the target imaging diameter and the actual diameter is compared, that is, the root mean square error is obtained by randomly taking 5 groups of diameters of the imaging result and calculating the actual diameter, and the formula is as follows:
Figure BDA0003024297910000101
wherein, Δ diIs the deviation of the imaging result diameter from the actual diameter, and S is the root mean square error finally found. The imaging root mean square error of the targets at different positions fluctuates between 0.6cm and 1.2cm, and the imaging root mean square error of the principle prototype is smaller and has higher imaging precision as can be seen from data.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (6)

1. A high energy, high precision, underwater three dimensional imaging lidar system, comprising:
the high-energy laser comprises a Q-switched laser and an F-P oscillation cavity; the Q-switched laser is used for compressing laser pulses by adopting a Q-switched technology to generate narrow pulses with high peak power and high energy; the F-P oscillation cavity is used for receiving the narrow pulse, converting the narrow pulse into a high-energy and high-frequency laser pulse train by utilizing the round-trip part output characteristic of the F-P oscillation cavity, and irradiating the high-energy and high-frequency laser pulse train onto a target in a water body medium to generate an echo signal;
the optical receiving system is used for receiving the echo signal, processing and recording the echo signal and transmitting a recording result to the signal processing terminal;
and the signal processing terminal is used for receiving the recording result sent by the optical receiving system and carrying out three-stage filtering processing to obtain the three-dimensional imaging of the target in the water medium.
2. The system of claim 1, wherein the Q-switched laser is a semiconductor pumped short cavity sub-nanosecond pulsed laser; the Q-switched laser is used for generating narrow pulses with high peak power and high energy.
3. The system of claim 1, wherein the optical receiving system comprises a stripe camera; the stripe camera is used for converting the received echo signals into electronic images through the photocathode after passing through the slit, then electrons at different positions on a time sequence are scanned to a space position vertical to the stripe direction through a scanning electric field, the conversion from time information to space information is completed, one-dimensional images extracted by the slit are changed into two-dimensional images, the conversion from electric signals to optical signals is completed through multiplication bombardment of a fluorescent screen, and finally, the stripe images are obtained through CCD recording.
4. The system of claim 3, wherein the signal processing terminal comprises a pre-processing module, a band-pass filtering + matched filtering module, and a threshold filtering module;
the preprocessing module is used for filtering background noise of the streak camera in the streak image to obtain a preprocessed signal;
the band-pass filtering and matched filtering module is used for filtering direct-current components and low-frequency signals in the preprocessed signals and improving the range resolution of the laser radar;
and the threshold filtering module is used for filtering out low-intensity noise of the signal obtained after the filtering of the band-pass filtering and matched filtering module so as to obtain three-dimensional imaging of the target in the water medium.
5. A method for high-energy and high-precision underwater three-dimensional imaging is characterized in that the method is applied to the high-energy and high-precision underwater three-dimensional imaging laser radar system of any one of claims 1 to 4 to realize three-dimensional imaging of a target in a water body medium; the method comprises the following steps:
generating a high-energy and high-frequency laser pulse train by a high-energy laser, and irradiating the high-energy and high-frequency laser pulse train onto a target in a water body medium to generate an echo signal;
receiving the echo signal through an optical receiving system, processing and recording the echo signal, and sending the recorded signal to a signal processing terminal;
and receiving the recorded signals through a signal processing terminal, and filtering the recorded signals by adopting a three-section filtering method to obtain the three-dimensional imaging of the target in the water medium.
6. The method of claim 5, wherein the receiving of the recorded signals by the signal processing terminal and the filtering of the recorded signals by a three-stage filtering method to obtain the three-dimensional imaging of the target in the water medium comprises:
receiving a recorded signal through a signal processing terminal, preprocessing the recorded signal, and filtering background noise of a streak camera in the streak image to obtain a preprocessed signal;
performing band-pass filtering and matched filtering on the preprocessed signals, and filtering out direct-current components and low-frequency signals in the preprocessed signals to obtain laser radar signals with high range resolution;
and carrying out threshold filtering on the laser radar signal with the high distance resolution, and filtering low-intensity noise in the laser radar signal with the high distance resolution to obtain three-dimensional imaging of the target in the water medium.
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