Ocean laser radar and method for preventing water surface signal saturation

Abstract

The invention discloses an ocean laser radar and method for preventing water surface signal saturation, and belongs to the technical field of laser radars. The ocean laser radar comprises a laser emission system, an optical system, a signal processing system and a data acquisition and processing system. The laser emission system emits laser and generates a trigger pulse; the optical system splits the backward scattered light into first split light and second split light through a beam splitter prism; in the signal processing system, a first processing branch converts first split light into a first electric signal through a first photoelectric detector, a high-speed switch and a first transimpedance amplifier, and a second processing branch converts second split light into a second electric signal through a second photoelectric detector and a second transimpedance amplifier; and the data acquisition and processing system controls laser emission, high-speed switching and electric signal acquisition and processing. According to the ocean laser radar and method for preventing water surface signal saturation, a high-speed switch can be controlled, water surface high-reflection signals are prevented from entering a trans-impedance amplifier, and underwater signals are prevented from being affected.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser radars, and in particular relates to an ocean laser radar and a method for preventing water surface signal saturation. Background Art

[0002] Many parameters and elements in ocean observation and detection are distributed in vertical stratification with depth, such as temperature and salinity. Basic ocean phenomena such as ocean currents, eddies, marine organisms, water particles and sound velocity profiles all require observation of characteristics that change with depth. As an active optical remote sensing technology, ocean lidar can obtain the vertical profile stratification structure of upper seawater particles, and then obtain data products such as underwater particulate organic carbon and primary productivity, realizing effective detection of the three-dimensional ocean profile. Ocean lidar can be carried on satellites, aircraft and scientific research vessels.

[0003] However, marine lidar faces two major challenges. First, strong reflections from the sea surface cause serious saturation of the sea surface signal. The amplifier takes a long time to recover after overload saturation, which saturates the signal at the water surface and a certain depth underwater (up to 30m-40m), and a large number of underwater signals cannot be obtained. Second, the optical parameters of the water body change quickly and the laser signal decays rapidly, requiring high resolution and large bandwidth to collect data, which can easily cause the ringing effect of the water surface overshoot signal, affecting the actual test signal, which is more prominent in high-energy laser and large-aperture receiving lens systems.

[0004] The CALIOP space-borne laser radar is carried on a satellite. Its CALIOP laser radar system uses high and low gain channels. The high gain ADC is used to measure weaker signals, while the low gain ADC is used to capture stronger signals that may be saturated on the high gain ADC. However, this laser radar is not designed for ocean testing. Although the low gain channel used in ocean testing can avoid the problem of surface signal saturation, the saturation and ringing problems of the high gain signal part cannot be solved.

[0005] In addition, a team has developed an underwater photon counting lidar, which is miniaturized and placed underwater to avoid the detection of strong reflected signals from the sea surface. However, compared with airborne, shipborne, and satellite-borne lidars, underwater lidars have slow testing speeds and small coverage, and cannot replace lidar systems that operate above the water surface. Summary of the invention

[0006] In view of the deficiencies existing in the related art, the purpose of the present invention is to provide an ocean laser radar and method for preventing water surface signal saturation, so as to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions: An ocean laser radar for preventing water surface signal saturation, comprising: A laser emitting system, the laser emitting system is used to emit laser toward the water body, and the laser emitting system generates a trigger pulse signal while emitting laser; An optical system, the optical system is used to receive backscattered light from a water body, the optical system includes a beam splitting prism, the beam splitting prism is used to split the backscattered light into a first split light and a second split light according to a set splitting ratio; A signal processing system, the signal processing system is connected to the optical system, the signal processing system is used to convert the backscattered light into an electrical signal, the signal processing system includes a first processing branch and a second processing branch, the first processing branch includes a first photodetector, a high-speed switch and a first transimpedance amplifier connected in sequence, the first processing branch is used to convert the first split light beam into a first electrical signal, the second processing branch includes a second photodetector and a second transimpedance amplifier connected in sequence, the second processing branch is used to convert the second split light beam into a second electrical signal; Data acquisition and processing system: The data acquisition and processing system is connected to the laser emission system and the signal processing system respectively. The data acquisition and processing system is used to control the laser emission system to emit laser and receive trigger pulse signals. The data acquisition and processing system is also used to control the high-speed switch to open or close at a set time and collect and process electrical signals.

[0008] In some of the embodiments, the optical system also includes a receiving lens, an aperture, a collimating lens and a polarization beam splitter connected in sequence, the receiving lens is used to collect and converge the backscattered light, the aperture is used to limit the field of view and the luminous flux, the collimating lens is used to convert the divergent light into parallel light, and the polarization beam splitter is used to split the backscattered light into two polarized lights; the optical system also includes a filter, the filter is connected to the polarization beam splitter and the beam splitter prism; the optical system also includes an attenuation plate, the attenuation plate is connected to the second beam splitting light output end of the beam splitter prism and the second photodetector.

[0009] In some embodiments, the splitting ratio of the beam splitting prism is a:b, wherein a is the splitting ratio of the first split light beam, b is the splitting ratio of the second split light beam, a+b=1 and b≤0.1.

[0010] In some embodiments, the laser emission system includes a first laser driver and a first laser connected and a second laser driver and a second laser connected, the first laser driver and the second laser driver are electrically connected to a data acquisition and processing system, respectively, and the first laser and the second laser are used to emit lasers and generate trigger pulse signals.

[0011] In some embodiments, the data acquisition and processing system includes a main control computer, and a high-speed data acquisition card and a controller electrically connected to the main control computer; the high-speed data acquisition card signal is connected to the first transimpedance amplifier and the second transimpedance amplifier, the high-speed data acquisition card has a trigger input port, and the trigger input port signal of the high-speed data acquisition card is connected to the laser emission system; the controller is electrically connected to the high-speed switch, the controller has a trigger signal receiving end, and the trigger signal receiving end of the controller is connected to the laser emission system.

[0012] A method for preventing water surface signal saturation, using an ocean laser radar for preventing water surface signal saturation, the method comprising the following steps: S1, the controller turns on the high-speed switch, the main control computer controls the first laser to emit light and generate a trigger pulse signal, triggers the high-speed data acquisition card to collect data, collects the first electrical signal, and discards the second electrical signal. The first electrical signal includes the signal in the atmosphere and the signal on the water surface; S2. The main control computer obtains the distance L from the light outlet of the ocean laser radar to the laser incident water surface through the first electrical signal. Assuming that the time from the light outlet of the ocean laser radar to the laser incident water surface is t, and the speed of light in the air is c, then t=L / c. The main control computer calculates the high-speed switch opening delay as T according to the time t; S3, the controller turns off the high-speed switch; S4, the main control computer controls the second laser to emit light and generates a trigger pulse signal, the trigger pulse signal is divided into two paths, one path is used as the controller delay trigger signal, and the other path triggers the high-speed data acquisition card to collect data. The high-speed data acquisition card first only collects the second electrical signal and transmits it to the main control computer for storage. After the controller delays the high-speed switch for a time T, the high-speed data acquisition card simultaneously collects the first electrical signal and the second electrical signal and transmits them to the main control computer for storage; S5, using the electric signal strength coordinate axis as the x-axis, the height coordinate axis as the y-axis, the water surface as the coordinate origin, the coordinate value of the height above the water is positive, and the coordinate value of the height under the water is negative, and according to the collected first electric signal and the second electric signal, draw a relationship graph between the electric signal strength and the height; S6. According to the drawn graph of the relationship between the electrical signal strength and the height, the data of the second electrical signal that does not overlap with the first electrical signal is spliced ​​with the data of the first electrical signal to obtain complete data from the atmosphere to the water surface and then underwater.

[0013] In some embodiments, step S6 includes step S61: taking a partial overlap of the first electrical signal and the second electrical signal, assuming that the height corresponding to the partial overlap is H1-H5, assuming that one point is collected every 1 meter, and the value of the first electrical signal corresponding to the height H1-H5 is S 1-1 , S 1-2 , S 1-3 , S 1-4 and S1-5 , the corresponding value of the second electrical signal is S 2-1 , S 2-2 , S 2-3 , S 2-4 and S 2-5 , assuming that the calibration coefficient is x, multiply the value of the second electrical signal by the calibration coefficient x, and obtain the value of the calibration coefficient x by calculating the minimum root mean square error with the value of the first electrical signal.

[0014] In some embodiments, in step S61, the value of the second electrical signal corresponding to the heights H1 to H5 is multiplied by the calibration coefficient x, and the formula for calculating the root mean square error with the value of the first electrical signal is:

[0015] Make it minimum, that is Minimum, by taking the first derivative, set it to 0, that is Calculate the value of the calibration factor x.

[0016] In some embodiments, step S6 also includes step S62: multiplying the data of the second electrical signal that does not overlap with the first electrical signal by the calibration coefficient x to obtain the data of the calibrated second electrical signal, and splicing the data of the calibrated second electrical signal with the data of the first electrical signal to obtain complete data from the atmosphere to the water surface and then underwater.

[0017] In some embodiments, in step S2, the high-speed switch turn-on delay is T=t+Δt, where Δt is the compensation delay.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The ocean laser radar for preventing surface signal saturation provided by the present invention sets a high-speed switch in front of the first transimpedance amplifier. By controlling its opening time, it accurately avoids the strong reflection signal on the water surface from entering the first processing branch, effectively solving the problem of underwater signal distortion caused by long saturation recovery time and ringing effect.

[0019] 2. In the ocean laser radar for preventing surface signal saturation provided by the present invention, the laser emission system includes a first laser and a second laser. The two lasers emit light alternately to calibrate the distance from the light outlet of the ocean laser radar to the laser incident water surface in a dynamic environment (such as changes in aircraft attitude and shaking of the measurement ship) in real time, and accurately control the high-speed switching delay accordingly to ensure that the strong reflection signal of the first processing branch is isolated. Combined with the signal collected by the second processing branch, interference-free detection of the full-range signal is achieved, significantly improving the measurement accuracy and reliability in complex ocean scenes.

[0020] 3. The method for preventing water surface signal saturation provided by the present invention first measures the distance from the light outlet of the marine laser radar in a dynamic environment to the laser incident water surface through the first laser, accurately calculates the high-speed switch opening delay, effectively solves the distance uncertainty problem caused by platform movement, ensures that the strong reflection signal of the water surface is cut off by the high-speed switch when the second laser emits the laser, and avoids the underwater test signal from being affected by overload saturation and ringing effect. The first electrical signal and the second electrical signal are calibrated in the overlapping area to eliminate the gain difference, realize seamless splicing of full-range data, and provide a solution with strong anti-interference ability and high data integrity for water body detection in dynamic marine environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 A schematic diagram of the principle of an embodiment of an ocean laser radar and method for preventing water surface signal saturation according to the present invention; Figure 2 A method flow chart of an embodiment of an ocean laser radar and method for preventing water surface signal saturation according to the present invention; Figure 3 A graph showing the relationship between the electrical signal strength and the height of the second electrical signal of an embodiment of the ocean laser radar and method for preventing water surface signal saturation of the present invention; Figure 4 A graph showing the relationship between the electrical signal strength and the height of the first electrical signal of an embodiment of the ocean laser radar and method for preventing water surface signal saturation according to the present invention; Figure 5 A graph showing the relationship between the electrical signal strength and height of a spliced ​​first electrical signal and a second electrical signal in accordance with an embodiment of the ocean laser radar and method for preventing water surface signal saturation according to the present invention.

[0022] In the figure: 1. Laser emission system; 11. First laser; 111. First laser driver; 12. Second laser; 121. Second laser driver; 2. Optical system; 21. Beam splitter prism; 22. Receiving lens; 23. Aperture; 24. Collimating lens; 25. Polarization beam splitter; 26. Filter; 27. Attenuation plate; 3. Signal processing system; 31. First processing branch; 311. First photodetector; 312. High-speed switch; 313. First transimpedance amplifier; 32. Second processing branch; 321. Second photodetector; 322. Second transimpedance amplifier; 4. Data acquisition and processing system; 41. Main control computer; 42. High-speed data acquisition card; 43. Controller. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be understood that the terms "center", "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0025] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] Embodiment 1: See attached Figures 1 to 4 , gives a schematic embodiment of the ocean laser radar for preventing water surface signal saturation proposed by the present invention. The ocean laser radar for preventing water surface signal saturation includes a laser emission system 1, an optical system 2, a signal processing system 3 and a data acquisition and processing system 4.

[0027] The laser emitting system 1 is used to emit laser toward the water body, and the laser emitting system 1 generates a trigger pulse signal while emitting laser. The optical system 2 is used to receive the backscattered light of the water body, and the optical system 2 includes a beam splitting prism 21, and the beam splitting prism 21 is used to split the backscattered light into a first split light and a second split light according to a set splitting ratio.

[0028] The signal processing system 3 is connected to the optical system 2, and the signal processing system 3 is used to convert the backscattered light into an electrical signal. The signal processing system 3 includes a first processing branch 31 and a second processing branch 32. The first processing branch 31 includes a first photodetector 311, a high-speed switch 312 and a first transimpedance amplifier 313 connected in sequence. The first processing branch 31 is used to convert the first split light into a first electrical signal and amplify it. The second processing branch 32 includes a second photodetector 321 and a second transimpedance amplifier 322 connected in sequence. The second processing branch 32 is used to convert the second split light into a second electrical signal and amplify it. The high-speed switch 312 is used to dynamically control the on and off of the strong water surface signal to prevent the strong surface reflection signal from entering the first transimpedance amplifier 313 of the first processing branch 31, thereby avoiding the underwater test signal from being affected by the saturation recovery time and the ringing effect. At the same time, the second processing branch 32 continuously and stably collects signals to achieve full-range effective capture of atmospheric, surface and underwater signals.

[0029] The data acquisition and processing system 4 is connected to the laser emission system 1 and the signal processing system 3 respectively. The data acquisition and processing system 4 is used to control the laser emission system 1 to emit laser and receive the trigger pulse signal. According to the received trigger pulse signal, the data acquisition and processing system 4 is also used to control the high-speed switch 312 to open or close at the set time and collect and process the electrical signal. The opening time of the high-speed switch 312 is determined according to the time from the light outlet of the ocean laser radar to the laser incident water surface, so as to ensure that the first processing branch 31 cannot collect the strong reflection signal of the water surface, and the first processing branch 31 can collect the signal below the water surface after the high-speed switch 312 is turned on. By controlling the opening time of the high-speed switch 312 to avoid the strong reflection signal of the water surface from entering the first transimpedance amplifier 313, although the signal of the water surface is lost, the saturation recovery time and ringing effect of the underwater signal are effectively avoided.

[0030] The optical system 2 also includes a receiving lens 22, an aperture 23, a collimating lens 24 and a polarization beam splitter 25 connected in sequence. The receiving lens 22 is used to collect and converge the backscattered light, the aperture 23 is used to limit the field of view and the luminous flux, the collimating lens 24 is used to convert the divergent light into parallel light, and the polarization beam splitter 25 is used to split the backscattered light into two polarized lights. The subsequent processing process of the two polarized lights is completely the same.

[0031] The optical system 2 also includes a filter 26, which is connected to the polarization beam splitter 25 and the beam splitter prism 21; the optical system 2 also includes an attenuation plate 27, which is connected to the second beam splitting light output end of the beam splitter prism 21 and the second photodetector 321. The filter 26 can further filter out ambient stray light. The attenuation plate 27 determines a suitable attenuation multiple to ensure that the surface signal entering the second processing branch 32 is not saturated as much as possible, thereby preventing the second transimpedance amplifier 322 from being overloaded and saturated. The receiving lens 22, the aperture 23, the collimating lens 24, the polarization beam splitter 25, the filter 26, the beam splitter prism 21 and the attenuation plate 27 work together to improve the signal purity and optical path stability, reduce background interference, enhance the detection capability of underwater signals, and provide high-quality input data for subsequent signal processing.

[0032] Among them, the filter 26 can be selected as a narrowband filter. The strong wavelength selectivity of the narrowband filter only allows extremely narrow band light that is highly matched with the wavelength of the emitted laser to pass through, which can effectively filter out stray light in the environment (such as sunlight, water surface reflection light and other non-target wavelength interference), significantly improve the signal-to-noise ratio of the backscattered light signal, and avoid stray light interference with the detector. In addition, the narrowband filter can filter out strong light of non-target wavelengths, reduce the total light flux entering the detector, and reduce the risk of detector saturation due to excessive light intensity, especially in a strong light environment to ensure that the detector works in the linear range.

[0033] The splitting ratio of the beam splitting prism 21 is a:b, where a is the splitting ratio of the first split light, b is the splitting ratio of the second split light, a+b=1 and b≤0.1. In some embodiments, the actual splitting ratio of the beam splitting prism 21 needs to comprehensively consider the laser energy and whether the second photodetector 321 is saturated. In this embodiment, the splitting ratio of the first split light can be 90%, and the splitting ratio of the second split light can be 10%.

[0034] The laser emission system 1 includes a first laser driver 111 and a first laser 11 connected, and a second laser driver 121 and a second laser 12 connected. The first laser driver 111 and the second laser driver 121 are electrically connected to the data acquisition and processing system 4 respectively to control the light emission time of the first laser 11 and the second laser 12. The first laser 11 and the second laser 12 are used to emit lasers and generate trigger pulse signals. Two independent sets of laser drivers and lasers are used, and the first laser 11 and the second laser 12 are controlled by the main control computer 41 to emit lasers in a time-sharing manner. The first laser 11 is used to obtain the water surface distance information to determine the high-speed switch opening delay, and the second laser 12 is used to collect atmospheric signals, surface signals and underwater signals. The two lasers can be configured with different wavelengths, powers and opening times, and can flexibly adapt to the needs of multiple scenarios such as atmospheric detection, surface positioning, underwater detection, etc., to improve the functional scalability of the system.

[0035] The data acquisition and processing system 4 includes a main control computer 41, and a high-speed data acquisition card 42 and a controller 43 electrically connected to the main control computer 41. The high-speed data acquisition card 42 is connected to the first transimpedance amplifier 313 and the second transimpedance amplifier 322 by signal, so as to collect the first electrical signal and the second electrical signal (a total of four signals) of the two polarized lights, and transmit them to the main control computer for signal processing and calculation. The high-speed data acquisition card 42 has a trigger input port, and the trigger input port signal of the high-speed data acquisition card 42 is connected to the laser emission system 1. The controller 43 is electrically connected to the high-speed switch 312, and the controller 43 has a trigger signal receiving end, and the trigger signal receiving end signal of the controller 43 is connected to the laser emission system 1. Through the coordinated control of the main control computer 41, the high-speed data acquisition card 42 and the controller 43, the precise synchronization of the trigger signal and the data acquisition can be achieved. The high-speed data acquisition card 42 receives the trigger pulse signal of the laser to ensure that the acquisition timing is strictly aligned with the laser emission and eliminate the time jitter error. The controller 43 dynamically controls the on and off of the high-speed switch 312 according to the delay time T calculated by the main control computer 41, so that the high-speed switch 312 of the first processing branch 31 is closed during the period of strong surface signals and before, and is opened during the period of underwater signals.

[0036] In the above-mentioned exemplary embodiment, for the first electrical signal that is susceptible to the saturation recovery time and the ringing effect, an ocean laser radar is provided in which a high-speed switch is arranged in front of the first transimpedance amplifier. By controlling the opening time of the high-speed switch, the highly reflected signal on the water surface is prevented from entering the first transimpedance amplifier, thereby preventing the underwater test signal from being affected by the saturation recovery time and the ringing effect.

[0037] Embodiment 2: This embodiment provides a method for preventing water surface signal saturation. The method for preventing water surface signal saturation of the ocean laser radar for preventing water surface signal saturation of embodiment 1 includes the following steps: S1, the controller 43 turns on the high-speed switch 312, the main control computer 41 controls the first laser 11 to emit light and generate a trigger pulse signal, triggering the high-speed data acquisition card 42 to collect data, collect the first electrical signal, and discard the second electrical signal. The first electrical signal includes the signal in the atmosphere and the signal on the water surface; S2. The main control computer 41 obtains the distance L from the light outlet of the ocean laser radar to the laser incident water surface through the first electrical signal. Assuming that the time from the light outlet of the ocean laser radar to the laser incident water surface is t, and the speed of light in the air is c, then t=L / c. The main control computer 41 calculates the opening delay of the high-speed switch 312 as T according to the time t; S3, the controller 43 turns off the high-speed switch 312; S4, the main control computer 41 controls the second laser 12 to emit light and generates a trigger pulse signal, which is divided into two paths, one path is used as a delay trigger signal of the controller 43, and the other path triggers the high-speed data acquisition card 42 to collect data. The high-speed data acquisition card 42 first collects only the second electrical signal and transmits it to the main control computer 41 for storage. After the controller 43 delays the time T to turn on the high-speed switch 312, the high-speed data acquisition card 42 simultaneously collects the first electrical signal and the second electrical signal and transmits them to the main control computer 41 for storage; S5, using the electric signal strength coordinate axis as the x-axis, the height coordinate axis as the y-axis, the water surface as the coordinate origin, the coordinate value of the height above the water is positive, and the coordinate value of the height under the water is negative, and according to the collected first electric signal and the second electric signal, draw a relationship graph between the electric signal strength and the height; S6. According to the drawn graph of the relationship between the electrical signal strength and the height, the data of the second electrical signal that does not overlap with the first electrical signal is spliced ​​with the data of the first electrical signal to obtain complete data from the atmosphere to the water surface and then underwater.

[0038] The propagation time of the laser in the air is used to calculate the opening delay T of the high-speed switch 312, and the strong reflection signal on the water surface is separated from the underwater signal on the time axis to avoid the strong reflection signal causing saturation of the first transimpedance amplifier 313; through time-segment acquisition and timing control, the complete capture of the signal from the atmosphere to the underwater is ensured, providing a basis for subsequent data processing.

[0039] Among them, in step S4, the trigger pulse signal triggers the high-speed data acquisition card 42 to collect data, and the high-speed data acquisition card 42 collects data from the first processing branch 31 and the second processing branch 32 at the same time. The high-speed data acquisition card 42 collects the second electrical signal from the second processing branch 32. Since the high-speed switch 312 is not turned on, the high-speed data acquisition card 42 collects noise from the first processing branch 31. After the two-way data is transmitted to the main control computer 41, the main control computer 41 will discard the noise collected from the first processing branch 31 during the storage process, and only retain the second electrical signal. After the high-speed switch 312 is turned on, the high-speed data acquisition card 42 collects the second electrical signal from the second processing branch 32, and the first electrical signal from the first processing branch 31, which are transmitted to the main control computer 41 for storage.

[0040] See attached Figure 3 and Figure 4, which is a graph showing the relationship between the electric signal strength and height of the second electric signal and the electric signal strength and height of the first electric signal in this embodiment. It can be seen that the second electric signal and the first electric signal begin to overlap at a certain depth underwater. A portion of the overlapped first electric signal and the second electric signal is selected to calculate the calibration coefficient. Then, the data of the second electric signal that does not overlap with the first electric signal is multiplied by the calibration coefficient. Then, the data of the calibrated second electric signal is spliced ​​with the data of the first electric signal to obtain complete data from the atmosphere to the water surface and then underwater. See the attached Figure 5 , is a graph showing the relationship between the electrical signal strength and height of the spliced ​​first electrical signal and the second electrical signal of this embodiment.

[0041] Step S6 includes step S61: taking the partial overlap of the first electrical signal and the second electrical signal, assuming that the height corresponding to the partial overlap is H1-H5, assuming that one point is collected every 1 meter, and the value of the first electrical signal corresponding to the height H1-H5 is S 1-1 , S 1-2 , S 1-3 , S 1-4 and S 1-5 , the corresponding value of the second electrical signal is S 2-1 , S 2-2 , S 2-3 , S 2-4 and S 2-5 , assuming that the calibration coefficient is x, multiply the value of the second electrical signal by the calibration coefficient x, and obtain the value of the calibration coefficient x by calculating the minimum root mean square error with the value of the first electrical signal.

[0042] In this embodiment, see the attached Figure 3 and Figure 4 , the heights H1 to H5 corresponding to the partial overlap of the first electrical signal and the second electrical signal selected in step S61 may be -6m to -10m.

[0043] The calibration coefficient x is calculated using the overlapping area of ​​the first electrical signal and the second electrical signal, and the amplitude calibration of the two signals is achieved by minimizing the root mean square error. The signal amplitude deviation caused by factors such as the difference in the splitting ratio of the beam splitter prism 21 and the inconsistent response of the first photodetector 311 and the second photodetector 321 is eliminated, so that the spliced ​​signal can smoothly transition in the overlapping area to ensure the consistency of the atmosphere-surface-underwater data. The calibration method based on the least squares method can effectively suppress the influence of random noise, improve the accuracy of data splicing, and provide a reliable data basis for subsequent quantitative analysis (such as depolarization ratio calculation and particle classification).

[0044] In step S61, the value of the second electrical signal corresponding to the heights H1 to H5 is multiplied by the calibration coefficient x, and the formula for calculating the root mean square error with the value of the first electrical signal is:

[0045] Make it minimum, that is Minimum, by taking the first derivative, set it to 0, that is Calculate the value of the calibration factor x.

[0046] The optimal solution of the calibration coefficient x is derived by derivation (minimizing the sum of squared errors) to avoid iterative calculations. The calibration coefficient x is quickly solved using a mathematical closed-form solution, and optimal calibration can be achieved without complex algorithms, greatly reducing data processing time and meeting the efficiency requirements in real-time monitoring scenarios. The calibration coefficient x is theoretically ensured to be optimal in a statistical sense, enhancing the stability and anti-interference ability of the calibration process, and achieving high-precision data matching even in signal fluctuation scenarios.

[0047] Step S6 also includes step S62: multiplying the data of the second electrical signal that does not overlap with the first electrical signal by the calibration coefficient x to obtain the data of the calibrated second electrical signal, splicing the data of the calibrated second electrical signal with the data of the first electrical signal to obtain complete data from the atmosphere to the water surface and then underwater. The signals collected in stages are integrated into a continuous height-electrical signal strength relationship diagram, covering the positive value area above water and the negative value area underwater, to achieve seamless connection of full-range data.

[0048] In step S2, the high-speed switch 312 is turned on with a delay of T=t+Δt, where Δt is the compensation delay. The method for determining the value of the compensation delay Δt is to make it as small as possible, by compensating for the inherent delay of the system (such as circuit response time, optical signal transmission delay), ensuring that the high-speed switch 312 is turned on accurately when the laser actually reaches the underwater, and ensuring that no strong signals on the water surface are collected when the aircraft height fluctuates or the measuring ship shakes; dynamic adjustment of Δt can adapt to environmental factors such as changes in the refractive index of the water body and equipment installation errors, improve the timing stability of the system under different working conditions, and ensure the time accuracy of data collection.

[0049] Taking the airborne laser radar as an example, assuming that the laser radar height h is 500m and the inclination angle θ is 10°, then the distance L=h / sinθ from the laser radar's light outlet to the laser incident water surface is 507.7173m. The first laser 11 emits light and generates a trigger pulse signal at the same time, triggering the high-speed data acquisition card 42 to collect data. The measured data shows a water surface reflection peak at time t after the laser emits light. The main control computer 41 calculates t=L / c as 3.3848μs. The main control computer 41 calculates the next opening time of the high-speed switch 312 as time T after the laser emits light, T=t+Δt is 3.3898μs. Here, in order to ensure that the first transimpedance amplifier 313 does not receive a strong reflection signal from the water surface, and considering the opening time of the high-speed switch 312 (such as 10ns), a certain time margin (Δt=0.005μs) is added.

[0050] The high-speed switch 312 is turned off at 5 μs after the first laser 11 emits light, and the second laser 12 is controlled to emit light at 6 μs, and a trigger pulse signal is generated at the same time. The trigger pulse signal triggers the high-speed data acquisition card 42 for data acquisition, and triggers the controller 43 to turn on the high-speed switch 312 after a delay of T. The controller 43 delays 3.3898 μs to turn on the high-speed switch 312. At this time, the signal transmitted from the first photodetector 311 of the first processing branch 31 to the first transimpedance amplifier 313 is already an underwater signal, avoiding the strong reflection signal on the water surface, thereby avoiding the influence of saturation recovery time and ringing. The missing part of the data can be obtained by multiplying the value of the second electrical signal converted by the second processing branch 32 by the calibration coefficient.

[0051] In the above exemplary embodiment, the method for preventing water surface signal saturation is to first measure the distance from the light outlet of the marine laser radar in a dynamic environment to the laser incident water surface by using the first laser, accurately calculate the high-speed switch opening delay, and ensure that the strong reflection signal of the water surface is cut off by the high-speed switch when the second laser emits the laser. The first electrical signal and the second electrical signal are calibrated in the overlapping area to eliminate the gain difference, and achieve seamless splicing of full-range data, providing a solution with strong anti-interference ability and high data integrity for water body detection in a dynamic marine environment.

[0052] Finally, it should be noted that: the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0053] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. An ocean laser radar for preventing water surface signal saturation, characterized in that: include: A laser emitting system, the laser emitting system is used to emit laser toward the water body, and the laser emitting system generates a trigger pulse signal while emitting laser; An optical system, the optical system is used to receive backscattered light from a water body, the optical system comprises a beam splitting prism, the beam splitting prism is used to split the backscattered light into a first split light and a second split light according to a set splitting ratio; A signal processing system, the signal processing system is connected to the optical system, the signal processing system is used to convert the backscattered light into an electrical signal, the signal processing system includes a first processing branch and a second processing branch, the first processing branch includes a first photodetector, a high-speed switch and a first transimpedance amplifier connected in sequence, the first processing branch is used to convert the first split light into a first electrical signal, the second processing branch includes a second photodetector and a second transimpedance amplifier connected in sequence, the second processing branch is used to convert the second split light into a second electrical signal; A data acquisition and processing system, wherein the data acquisition and processing system is connected to the laser emission system and the signal processing system respectively, and is used to control the laser emission system to emit laser and receive trigger pulse signals. The data acquisition and processing system is also used to control the high-speed switch to open or close at a set time and to acquire and process the electrical signal.

2. The ocean laser radar for preventing water surface signal saturation according to claim 1, characterized in that: The optical system further comprises a receiving lens, an aperture, a collimating lens and a polarization beam splitter connected in sequence, wherein the receiving lens is used to collect and converge the backscattered light, the aperture is used to limit the field of view and the light flux, the collimating lens is used to convert the divergent light into parallel light, and the polarization beam splitter is used to split the backscattered light into two polarized lights; The optical system further comprises an optical filter, which is connected to the polarization beam splitter and the beam splitting prism; the optical system further comprises an attenuation plate, which is connected to the second beam splitting light output end of the beam splitting prism and the second photodetector.

3. The ocean laser radar for preventing water surface signal saturation according to claim 1, characterized in that: The beam splitting ratio of the beam splitting prism is a:b, wherein a is the beam splitting ratio of the first split light beam, b is the beam splitting ratio of the second split light beam, a+b=1 and b≤0.

1.

4. The ocean laser radar for preventing water surface signal saturation according to claim 1, characterized in that: The laser emission system includes a first laser driver and a first laser connected and a second laser driver and a second laser connected. The first laser driver and the second laser driver are electrically connected to the data acquisition and processing system respectively. The first laser and the second laser are used to emit lasers and generate trigger pulse signals.

5. The ocean laser radar for preventing water surface signal saturation according to claim 1, characterized in that: The data acquisition and processing system includes a main control computer, and a high-speed data acquisition card and a controller electrically connected to the main control computer; the high-speed data acquisition card signal is connected to the first transimpedance amplifier and the second transimpedance amplifier, the high-speed data acquisition card has a trigger input port, and the trigger input port signal of the high-speed data acquisition card is connected to the laser emission system; the controller is electrically connected to the high-speed switch, the controller has a trigger signal receiving end, and the trigger signal receiving end signal of the controller is connected to the laser emission system.

6. A method for preventing water surface signal saturation, characterized in that: Using the ocean laser radar for preventing water surface signal saturation, the method comprises the following steps: S1, the controller turns on the high-speed switch, the main control computer controls the first laser to emit light and generate a trigger pulse signal, triggers the high-speed data acquisition card to collect data, collects the first electrical signal, and discards the second electrical signal. The first electrical signal includes the signal in the atmosphere and the signal on the water surface; S2. The main control computer obtains the distance L from the light outlet of the ocean laser radar to the laser incident water surface through the first electrical signal. Assuming that the time from the light outlet of the ocean laser radar to the laser incident water surface is t, and the speed of light in the air is c, then t=L / c. The main control computer calculates the high-speed switch opening delay as T according to the time t; S3, the controller turns off the high-speed switch; S4, the main control computer controls the second laser to emit light and generates a trigger pulse signal, the trigger pulse signal is divided into two paths, one path is used as the controller delay trigger signal, and the other path triggers the high-speed data acquisition card to collect data. The high-speed data acquisition card first only collects the second electrical signal and transmits it to the main control computer for storage. After the controller delays the high-speed switch for a time T, the high-speed data acquisition card simultaneously collects the first electrical signal and the second electrical signal and transmits them to the main control computer for storage; S5, using the electric signal strength coordinate axis as the x-axis, the height coordinate axis as the y-axis, the water surface as the coordinate origin, the coordinate value of the height above the water is positive, and the coordinate value of the height under the water is negative, and according to the collected first electric signal and the second electric signal, draw a relationship graph between the electric signal strength and the height; S6. According to the drawn graph of the relationship between the electrical signal strength and the height, the data of the second electrical signal that does not overlap with the first electrical signal is spliced ​​with the data of the first electrical signal to obtain complete data from the atmosphere to the water surface and then underwater.

7. The method for preventing water surface signal saturation according to claim 6, characterized in that: Step S6 includes step S61: taking the partial overlap of the first electrical signal and the second electrical signal, assuming that the height corresponding to the partial overlap is H1-H5, assuming that one point is collected every 1 meter, and the value of the first electrical signal corresponding to the height H1-H5 is S 1-1 , S 1-2 , S 1-3 , S 1-4 and S 1-5 , the corresponding value of the second electrical signal is S 2-1 , S 2-2 , S 2-3 , S 2-4 and S 2-5 , assuming that the calibration coefficient is x, multiply the value of the second electrical signal by the calibration coefficient x, and obtain the value of the calibration coefficient x by calculating the minimum root mean square error with the value of the first electrical signal.

8. The method for preventing water surface signal saturation according to claim 7, characterized in that: In step S61, the value of the second electrical signal corresponding to the heights H1 to H5 is multiplied by the calibration coefficient x, and the formula for calculating the root mean square error with the value of the first electrical signal is: Make it minimum, that is Minimum, by taking the first derivative, set it to 0, that is Calculate the value of the calibration factor x.

9. The method for preventing water surface signal saturation according to claim 7, characterized in that: Step S6 also includes step S62: multiplying the data of the second electrical signal that does not overlap with the first electrical signal by the calibration coefficient x to obtain the data of the calibrated second electrical signal, and splicing the data of the calibrated second electrical signal with the data of the first electrical signal to obtain complete data from the atmosphere to the water surface and then underwater.

10. The method for preventing water surface signal saturation according to claim 6, characterized in that: In step S2, the high-speed switch turn-on delay is T=t+Δt, where Δt is the compensation delay.

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