Marine lidar and method for preventing saturation of water surface signals

Abstract

The present invention discloses an ocean lidar and method for preventing water surface signal saturation, belonging to the technical field of lidar. The ocean lidar includes 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 backscattered light into a first split light and a second split light through a beam splitting prism; in the signal processing system, the first processing branch converts the first split light into a first electrical signal through a first photodetector, a high-speed switch, and a first transimpedance amplifier, and the second processing branch converts the second split light into a second electrical signal through a second photodetector and a second transimpedance amplifier; the data acquisition and processing system controls laser emission, high-speed switch, and electrical signal acquisition and processing. The ocean lidar and method for preventing water surface signal saturation of the present invention can control the high-speed switch, avoid high-reflection signals on the water surface from entering the transimpedance amplifier, and prevent underwater signals from being affected.

Description

Technical Field

[0001] The present invention belongs to the technical field of lidar, and particularly relates to a marine lidar and method for preventing water surface signal saturation. Background Technique

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

[0003] However, marine lidar faces two major problems. One is that strong reflection from the sea surface causes severe saturation of the sea surface signal. After the amplifier is overloaded and saturated, the recovery time is long, resulting in signal saturation at the water surface and a certain depth underwater (up to 30m - 40m at most), and a large amount of underwater signals cannot be obtained. The other is that the optical parameters of the water body change rapidly and the laser signal attenuates quickly. High-resolution and large-bandwidth data acquisition is required, which easily causes the ringing effect of overshoot signals on the water surface, affecting the true test signal, and is more prominent in high-energy laser and large-aperture receiving lens systems.

[0004] The spaceborne lidar CALIOP is carried on a certain satellite. Its CALIOP lidar 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 saturate on the high-gain ADC. However, this lidar is not designed for ocean testing. Although the low-gain channel in its ocean testing can avoid the problem of water 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, miniaturized the lidar and placed it underwater, avoiding the detection of strong reflection signals from the sea surface. However, compared with airborne, shipborne, and spaceborne lidars, the underwater lidar has a slow test speed and a small coverage range, and cannot replace the lidar system working above the water surface. Summary of the Invention

[0006] Aiming at the deficiencies existing in the related technologies, the purpose of the present invention is to provide a marine lidar and method for preventing water surface signal saturation to solve the problems raised in the above background technique.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A marine lidar for preventing water surface signal saturation, comprising:

[0009] A laser emission system, which is used to emit laser light towards a water body, and generates a trigger pulse signal while emitting the laser light;

[0010] An optical system, which is used to receive the backscattered light of the water body. The optical system includes a beam splitting prism, which is used to split the backscattered light into a first split light and a second split light according to a set splitting ratio;

[0011] A signal processing system, which is connected to the optical system and 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, and 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, and is used to convert the second split light into a second electrical signal;

[0012] A data acquisition and processing system, which is respectively connected to the laser emission system and the signal processing system. The data acquisition and processing system is used to control the laser emission system to emit laser light and receive the trigger pulse signal, and is also used to control the high-speed switch to turn on or off at a set time and acquire and process the electrical signal.

[0013] In some embodiments, the optical system further includes a receiving lens, a diaphragm, a collimating lens, and a polarization beam splitter connected in sequence. The receiving lens is used to collect and converge the backscattered light. The diaphragm 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. The polarization beam splitter is used to split the backscattered light into two polarized lights; the optical system further includes a filter, which is connected to the polarization beam splitter and the beam splitting prism; the optical system further includes an attenuation sheet, which is connected to the second split light output end of the beam splitting prism and the second photodetector.

[0014] In some embodiments, the splitting ratio of the beam splitting prism is a:b, where a is the splitting ratio of the first split light and b is the splitting ratio of the second split light, a + b = 1 and b ≤ 0.1.

[0015] 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 respectively electrically connected to the data acquisition and processing system. The first laser and the second laser are used to emit laser light and generate a trigger pulse signal.

[0016] In some of these embodiments, the data acquisition and processing system includes a main control computer, as well as a high-speed data acquisition card and a controller electrically connected to the main control computer; the high-speed data acquisition card is signal-connected to a first transimpedance amplifier and a second transimpedance amplifier, the high-speed data acquisition card has a trigger input port, and the trigger input port of the high-speed data acquisition card is signal-connected to a laser emission system; the controller is electrically connected to a high-speed switch, the controller has a trigger signal receiving end, and the trigger signal receiving end of the controller is signal-connected to the laser emission system.

[0017] A method for preventing water surface signal saturation, using a marine lidar for preventing water surface signal saturation, the method includes the following steps:

[0018] S1. The controller turns on the high-speed switch, the main control computer controls the first laser to emit light and generates a trigger pulse signal to trigger the high-speed data acquisition card to perform data acquisition, collect the first electrical signal, and discard the second electrical signal. The first electrical signal includes signals in the atmosphere and water surface signals;

[0019] S2. The main control computer obtains the distance L from the light exit of the marine lidar to the water surface where the laser is incident through the first electrical signal. Let the time for the emitted laser to travel from the light exit of the marine lidar to the water surface where the laser is incident be t, and the speed of light in air be c. Then t = L / c. The main control computer calculates the opening delay of the high-speed switch as T according to the time t;

[0020] S3. The controller turns off the high-speed switch;

[0021] S4. The main control computer controls the second laser to emit light and generates a trigger pulse signal. This trigger pulse signal is divided into two paths. One path is used as the delay trigger signal of the controller, and the other path triggers the high-speed data acquisition card to perform data acquisition. 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 turns on the high-speed switch with a delay time of 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;

[0022] S5. Taking the electrical signal intensity 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 water height is positive, and the coordinate value of the underwater height is negative. According to the collected first electrical signal and second electrical signal, draw a relationship diagram of electrical signal intensity and height;

[0023] S6. According to the drawn relationship diagram of electrical signal intensity and height, splice the data of the second electrical signal that does not overlap with the first electrical signal with the data of the first electrical signal to obtain the complete data from the atmosphere to the water surface and then to underwater.

[0024] In some of these embodiments, step S6 includes step S61: taking a partial overlap of the first electrical signal and the second electrical signal, setting the height corresponding to this partial overlap as H1 to H5, collecting one point per 1 meter, and the values of the first electrical signal corresponding to the heights H1 to H5 being S 1-1 、S 1-2 、S 1-3 、S 1-4 and S 1-5 , and the values of the corresponding second electrical signal being S 2-1 、S 2-2 、S 2-3 、S 2-4 and S 2-5 . Setting the calibration coefficient as x, multiplying the value of the second electrical signal by the calibration coefficient x, and obtaining the value of the calibration coefficient x by calculating the root mean square error with the value of the first electrical signal being the smallest.

[0025] In some of these embodiments, in step S61, multiplying the values of the second electrical signal corresponding to the heights H1 to H5 by the calibration coefficient x, the formula for calculating the root mean square error with the value of the first electrical signal is:

[0026]

[0027] Making it the smallest, that is being the smallest. By taking the first derivative and setting it to 0, that is Calculating to obtain the value of the calibration coefficient x.

[0028] In some of these embodiments, step S6 further 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 calibrated data of the second electrical signal, and splicing the calibrated data of the second electrical signal with the data of the first electrical signal to obtain the complete data from the atmosphere to the water surface and then to underwater.

[0029] In some of these embodiments, in step S2, the turn-on delay of the high-speed switch is T = t + Δt, where Δt is the compensation delay.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. The marine lidar for preventing water surface signal saturation provided by the present invention sets a high-speed switch in front of the first transimpedance amplifier. By controlling its turn-on time, it accurately avoids the strong reflected signal on the water surface from entering the first processing branch, effectively solving the problems of long saturation recovery time and underwater signal distortion caused by the ringing effect.

[0032] 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.

[0033] 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

[0034] 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:

[0035] 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;

[0036] 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;

[0037] 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;

[0038] 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;

[0039] 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.

[0040] In the figure:

[0041] 1. Laser emission system; 11. First laser; 111. First laser driver; 12. Second laser; 121. Second laser driver; 2. Optical system; 21. Beam splitting prism; 22. Receiving lens; 23. Diaphragm; 24. Collimating lens; 25. Polarizing beam splitter; 26. Filter; 27. Attenuator; 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 implementation manner

[0042] Next, the technical solutions in the embodiments will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0043] In the description of the present invention, it should be understood that the terms "center", "transverse", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the 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 thus should not be construed as a limitation to the present invention.

[0044] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "connection" 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, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0045] Embodiment 1:

[0046] Refer to the attached Figures 1 to 4 , which gives a schematic embodiment of the marine lidar for preventing water surface signal saturation proposed by the present invention. The marine lidar 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.

[0047] The laser emission system 1 is used to emit laser towards the water body, and a trigger pulse signal is generated while the laser emission system 1 emits laser. The optical system 2 is used to receive the backscattered light of the water body. 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.

[0048] The signal processing system 3 is connected to the optical system 2. 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-off of the strong water surface signal, avoiding the strong reflection signal on the water surface from entering the first transimpedance amplifier 313 of the first processing branch 31, thereby avoiding the influence of the underwater test signal on the saturation recovery time and ringing effect. At the same time, the second processing branch 32 continuously and stably collects signals to achieve the full-range effective capture of atmospheric, water surface, and underwater signals.

[0049] The data acquisition and processing system 4 is respectively connected to the laser emission system 1 and the signal processing system 3. 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 a set time and collect and process the electrical signal. The opening time of the high-speed switch 312 is determined according to the time when the emitted laser travels from the light exit of the ocean lidar to the water surface where the laser is incident, so as to ensure that the first processing branch 31 does not collect the strong reflection signal on the water surface, and the first processing branch 31 can collect the signal below the water surface after the high-speed switch 312 is opened. By controlling the opening time of the high-speed switch 312 to avoid the strong reflection signal on the water surface from entering the first transimpedance amplifier 313, although the signal on the water surface part is lost, the saturation recovery time and ringing effect of the underwater signal are effectively avoided.

[0050] The optical system 2 further includes a receiving lens 22, a diaphragm 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 diaphragm 23 is used to limit the field of view and the light flux. The collimating lens 24 is used to convert the divergent light into parallel light. The polarization beam splitter 25 is used to divide the backscattered light into two polarized lights, and the subsequent processing processes of the two polarized lights are exactly the same.

[0051] The optical system 2 further includes a filter 26, and the filter 26 is connected to the polarization beam splitter 25 and the beam splitting prism 21; the optical system 2 further includes an attenuation sheet 27, and the attenuation sheet 27 is connected to the second beam splitting light output end of the beam splitting prism 21 and the second photodetector 321. The filter 26 can further filter out ambient stray light. The attenuation sheet 27 determines an appropriate attenuation multiple to ensure that the water surface signal entering the second processing branch 32 is not saturated as much as possible and prevent 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 splitting prism 21, and the attenuation sheet 27 cooperate to improve the signal purity and the optical path stability, reduce background interference, enhance the detection ability of underwater signals, and provide high-quality input data for subsequent signal processing.

[0052] Among them, the filter 26 can be selected as a narrowband filter. The strong wavelength selectivity of the narrowband filter only allows light in an extremely narrow band highly matching the emission laser wavelength to pass through, which can effectively filter out ambient stray light (such as non-target wavelength interferences such as sunlight and water surface reflected light), significantly improve the signal-to-noise ratio of the backscattered light signal, and avoid interference of stray light on 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 caused by excessive light intensity, especially ensuring that the detector operates in the linear range in a strong light environment.

[0053] The beam splitting ratio of the beam splitting prism 21 is a:b, where a is the beam splitting ratio of the first split light and b is the beam splitting ratio of the second split light, a + b = 1 and b ≤ 0.1. In some embodiments, the actual beam 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 beam splitting ratio of the first split light can be 90%, and the beam splitting ratio of the second split light can be 10%.

[0054] The laser emission system 1 includes a connected first laser driver 111 and a first laser 11 and a connected second laser driver 121 and a second laser 12. The first laser driver 111 and the second laser driver 121 are respectively electrically connected to the data acquisition and processing system 4 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 laser light and generate trigger pulse signals. Two independent sets of laser drivers and lasers are adopted. The main control computer 41 controls the first laser 11 and the second laser 12 to emit laser light at different times. The first laser 11 is used to obtain the water surface distance information to determine the opening delay of the high-speed switch, and the second laser 12 is used to collect atmospheric signals, water surface signals, and underwater signals. The two lasers can be configured with different wavelengths, powers, and opening times, flexibly adapting to the multi-scenario requirements such as atmospheric detection, water surface positioning, and underwater detection, and improving the system function expandability.

[0055] The data acquisition and processing system 4 includes a main control computer 41, 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 signal-connected to a first transimpedance amplifier 313 and a second transimpedance amplifier 322 to acquire a first electrical signal and a second electrical signal of two polarized lights (a total of four signals), 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 of the high-speed data acquisition card 42 is signal-connected to the laser emission system 1. The controller 43 is electrically connected to the high-speed switch 312. The controller 43 has a trigger signal receiving end, and the trigger signal receiving end of the controller 43 is signal-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, precise synchronization of the trigger signal and data acquisition can be achieved. The high-speed data acquisition card 42 receives the trigger pulse signal of the laser, ensuring that the acquisition timing is strictly aligned with the laser emission and eliminating the time jitter error. The controller 43 dynamically controls the on / 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 strong water surface signal and the previous period and opened during the underwater signal period.

[0056] In the above-mentioned exemplary embodiment, for the first electrical signal vulnerable to the saturation recovery time and ringing effect, an ocean lidar with a high-speed switch arranged in front of the first transimpedance amplifier is provided. By controlling the opening time of the high-speed switch, the high-reflection signal on the water surface is prevented from entering the first transimpedance amplifier, thereby avoiding the influence of the saturation recovery time and ringing effect on the underwater test signal.

[0057] Embodiment 2:

[0058] This embodiment provides a method for preventing the saturation of the water surface signal. Using the ocean lidar for preventing the saturation of the water surface signal in Embodiment 1, the method for preventing the saturation of the water surface signal includes the following steps:

[0059] 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 generates a trigger pulse signal to trigger the high-speed data acquisition card 42 to perform data acquisition, acquire the first electrical signal, and discard the second electrical signal. The first electrical signal includes signals in the atmosphere and signals on the water surface;

[0060] S2. The main control computer 41 obtains the distance L from the light outlet of the ocean lidar to the water surface where the laser is incident through the first electrical signal. Assuming that the time for the emitted laser to travel from the light outlet of the ocean lidar to the water surface where the laser is incident 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;

[0061] S3. The controller 43 turns off the high-speed switch 312;

[0062] S4. The main control computer 41 controls the second laser 12 to emit light and generates a trigger pulse signal. The trigger pulse signal is divided into two paths. One path serves as the delay trigger signal for the controller 43, and the other path triggers the high-speed data acquisition card 42 to perform data acquisition. The high-speed data acquisition card 42 first only acquires the second electrical signal and transmits it to the main control computer 41 for storage. After the controller 43 delays for a time T and turns on the high-speed switch 312, the high-speed data acquisition card 42 simultaneously acquires the first electrical signal and the second electrical signal and transmits them to the main control computer 41 for storage;

[0063] S5. Taking the electrical signal intensity coordinate axis as the x-axis, the height coordinate axis as the y-axis, the water surface as the coordinate origin, with the coordinate value of the water surface height being positive and the coordinate value of the underwater height being negative, based on the acquired first electrical signal and second electrical signal, draw a relationship graph of the electrical signal intensity and height;

[0064] S6. According to the drawn relationship graph of the electrical signal intensity and height, splice the data of the second electrical signal that does not overlap with the first electrical signal with the data of the first electrical signal to obtain the complete data from the atmosphere to the water surface and then to underwater.

[0065] Calculate the opening delay T of the high-speed switch 312 using the propagation time of the laser in the air, separate the strong reflection signal on the water surface from the underwater signal on the time axis, and avoid the saturation of the first transimpedance amplifier 313 caused by the strong reflection signal; through segmented acquisition and timing control, ensure the complete capture of the signal from the atmosphere to underwater, providing a basis for subsequent data processing.

[0066] Among them, in step S4, the trigger pulse signal triggers the high-speed data acquisition card 42 to perform data acquisition, and the high-speed data acquisition card 42 simultaneously acquires data from the first processing branch 31 and the second processing branch 32. The second electrical signal is acquired by the high-speed data acquisition card 42 from the second processing branch 32. Since the high-speed switch 312 is not turned on, the noise acquired by the high-speed data acquisition card 42 from the first processing branch 31 is noise. After the two paths of data are transmitted to the main control computer 41, the main control computer 41 will discard the noise acquired 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 second electrical signal is acquired by the high-speed data acquisition card 42 from the second processing branch 32, and the first electrical signal is acquired from the first processing branch 31 and transmitted to the main control computer 41 for storage.

[0067] See Appendix Figure 3 and Figure 4, which is the relationship diagram of the electrical signal strength and height of the second electrical signal and the relationship diagram of the electrical signal strength and height of the first electrical signal in this embodiment. It can be seen that the second electrical signal and the first electrical signal start to overlap at a certain depth underwater. Select a partial overlap from the overlapping first electrical signal and second electrical signal to calculate the calibration coefficient. Then multiply the data of the second electrical signal that does not overlap with the first electrical signal by the calibration coefficient, and then splice the data of the calibrated second electrical signal and the data of the first electrical signal to obtain the complete data from the atmosphere to the water surface and then to underwater. See the appendix Figure 5 , which is the relationship diagram of the electrical signal strength and height of the spliced first electrical signal and second electrical signal in this embodiment.

[0068] Step S6 includes step S61: Take a partial overlap of the first electrical signal and the second electrical signal. Let the height corresponding to this partial overlap be H1~H5. Assume that one point is collected every 1 meter. The values of the first electrical signal corresponding to the heights H1~H5 are S 1-1 、S 1-2 、S 1-3 、S 1-4 and S 1-5 , and the corresponding values of the second electrical signal are S 2-1 、S 2-2 、S 2-3 、S 2-4 and S 2-5 . Let the calibration coefficient be 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 root mean square error with the value of the first electrical signal being the smallest.

[0069] In this embodiment, see the appendix Figure 3 and Figure 4 , the heights H1~H5 corresponding to the partial overlap of the first electrical signal and the second electrical signal selected in step S61 can be -6m~-10m.

[0070] Calculate the calibration coefficient x using the overlapping region of the first electrical signal and the second electrical signal, and realize the amplitude calibration of the two signals by minimizing the root mean square error. Eliminate the signal amplitude deviation caused by factors such as the difference in the splitting ratio of the beam splitting prism 21 and the inconsistent responses of the first photodetector 311 and the second photodetector 321, so that the spliced signals smoothly transition in the overlapping region, ensuring the consistency of the atmosphere-water surface-underwater data. The calibration method based on the least squares method can effectively suppress the influence of random noise, improve the data splicing accuracy, and provide a reliable data basis for subsequent quantitative analysis (such as depolarization ratio calculation, particulate classification).

[0071] In step S61, when multiplying the values of the second electrical signal corresponding to the heights H1~H5 by the calibration coefficient x, the formula for calculating the root mean square error with the value of the first electrical signal is:

[0072]

[0073] Minimize it, that is Minimize it. By taking the first derivative and setting it to 0, that is Calculate the value of the calibration coefficient x.

[0074] Derive the optimal solution of the calibration coefficient x (by minimizing the sum of squared errors) through the derivative method to avoid iterative calculations. Use the mathematical closed-form solution to quickly solve the calibration coefficient x, enabling optimal calibration without complex algorithms, significantly reducing the data processing time, and meeting the high-efficiency requirements in real-time monitoring scenarios. Theoretically ensure that the calibration coefficient x is optimal in the statistical sense, enhancing the stability and anti-interference ability of the calibration process, and enabling high-precision data matching even in signal fluctuation scenarios.

[0075] Step S6 further includes step S62: Multiply the data of the second electrical signal that does not overlap with the first electrical signal by the calibration coefficient x to obtain the calibrated data of the second electrical signal. Then splice the calibrated data of the second electrical signal with the data of the first electrical signal to obtain the complete data from the atmosphere to the water surface and then to underwater. Integrate the signals collected in stages into a continuous height-electric signal intensity relationship graph, covering the positive value area above water and the negative value area underwater, achieving seamless connection of full-range data.

[0076] In step S2, the opening delay of the high-speed switch 312 is 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 delays of the system (such as circuit response time, optical signal transmission delay), ensure that the high-speed switch 312 is accurately opened at the moment when the laser actually reaches underwater, and ensure that strong water surface signals are not collected under the conditions of aircraft altitude fluctuations or measurement ship vibrations; Dynamically adjusting Δt can adapt to environmental factors such as water refractive index changes and equipment installation errors, improving the timing stability of the system under different working conditions and ensuring the time accuracy of data collection.

[0077] Taking an airborne lidar as an example, assume the lidar height h is 500m and the inclination angle θ is 10°. Then, the distance L from the light outlet of the lidar to the water surface where the laser is incident is L = h / sinθ = 507.7173m. The first laser 11 emits light and simultaneously generates a trigger pulse signal to trigger the high-speed data acquisition card 42 for data acquisition. The measured data shows a water surface reflection peak at the time t after the laser emits light. The main control computer 41 calculates t = L / c = 3.3848μs. The main control computer 41 calculates the next opening time T of the high-speed switch 312 as the time after the laser emits light, T = t + Δt = 3.3898μs. Here, it is to ensure that the first transimpedance amplifier 313 does not receive strong water surface reflection signals and considering the opening time of the high-speed switch 312 (such as 10ns), so a certain time margin (Δt = 0.005μs) is added.

[0078] The high-speed switch 312 is turned off at the 5th μs after the first laser 11 emits light, and the second laser 12 is controlled to emit light at the 6th μs. Meanwhile, a trigger pulse signal is generated. One path of the trigger pulse signal triggers the high-speed data acquisition card 42 to perform data acquisition, and the other path triggers the controller 43 to turn on the high-speed switch 312 after a delay time T. The controller 43 turns on the high-speed switch 312 after a delay of 3.3898 μs. At this time, the signal transmitted by the first photodetector 311 of the first processing branch 31 to the first transimpedance amplifier 313 is already an underwater signal, avoiding the strong water surface reflection signal, thus avoiding the influence caused by the 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.

[0079] In the above-mentioned exemplary embodiment, the method for preventing the water surface signal from saturating first measures the distance from the light outlet of the marine lidar in the dynamic environment to the water surface where the laser is incident by the first laser, accurately calculates the delay time for turning on the high-speed switch, and ensures that the strong water surface reflection signal is truncated by the high-speed switch when the second laser emits laser. The first electrical signal and the second electrical signal eliminate the gain difference through overlapping area calibration, realizing seamless splicing of full-range data, and providing a solution with strong anti-interference ability and high data integrity for water body detection in the dynamic ocean environment.

[0080] Finally, it should be noted that: the various embodiments in this specification are described in a progressive manner, and the key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or perform equivalent replacements for some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered within the scope of the technical solutions claimed by the present invention.

Claims

1. An ocean lidar for preventing saturation of water surface signals, characterized in that Including: A laser emission system for emitting laser towards a water body, and generating a trigger pulse signal while emitting the laser; An optical system for receiving the backward scattered light of the water body, the optical system including a beam splitting prism for splitting the backward scattered light into a first split light and a second split light according to a set splitting ratio; A signal processing system connected to the optical system for converting the backward scattered light into an electrical signal, the signal processing system including a first processing branch and a second processing branch, the first processing branch including a first photodetector, a high-speed switch and a first transimpedance amplifier connected in sequence for converting the first split light into a first electrical signal, and the second processing branch including a second photodetector and a second transimpedance amplifier connected in sequence for converting the second split light into a second electrical signal; A data acquisition and processing system respectively connected to the laser emission system and the signal processing system for controlling the laser emission system to emit laser and receiving the trigger pulse signal, and further for controlling the high-speed switch to be turned on or off at a set time and acquiring and processing the electrical signal.

2. The marine lidar for preventing water surface signal saturation according to claim 1, wherein The optical system further includes a receiving lens, a diaphragm, a collimating lens and a polarization beam splitter connected in sequence, the receiving lens for collecting and converging the backward scattered light, the diaphragm for limiting the field of view and the light flux, the collimating lens for converting the divergent light into parallel light, and the polarization beam splitter for splitting the backward scattered light into two polarized lights; The optical system further includes a filter connected to the polarization beam splitter and the beam splitting prism; the optical system further includes an attenuation sheet connected to the second split light output end of the beam splitting prism and the second photodetector.

3. The marine lidar for preventing saturation of water surface signals according to claim 1, wherein The splitting ratio of the beam splitting prism 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.

4. The marine lidar for preventing saturation of water surface signals according to claim 1, wherein, The laser emission system includes a first laser driver and a first laser connected together, and a second laser driver and a second laser connected together, the first laser driver and the second laser driver being respectively electrically connected to the data acquisition and processing system, and the first laser and the second laser for emitting laser and generating a trigger pulse signal.

5. The marine lidar for preventing saturation of water surface signals according to claim 1, wherein The data acquisition and processing system includes a main control computer, a high-speed data acquisition card and a controller electrically connected to the main control computer; the high-speed data acquisition card is signal-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 of the high-speed data acquisition card is signal-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 signal-connected to the laser emission system.

6. A method for preventing water surface signal saturation, characterized in that, Using the marine lidar for preventing water surface signal saturation, the method includes the following steps: S1. The controller turns on the high-speed switch. The main control computer controls the first laser to emit light and generates a trigger pulse signal to trigger the high-speed data acquisition card to perform data acquisition, collect the first electrical signal, and discard the second electrical signal. The first electrical signal includes signals in the atmosphere and water surface signals. S2. The main control computer obtains the distance L from the light-emitting port of the marine lidar to the water surface where the laser is incident through the first electrical signal. Assuming the time for the emitted laser to travel from the light-emitting port of the marine lidar to the water surface where the laser is incident is t and the speed of light in air is c, then t = L / c. The main control computer calculates the delay time T for turning on the high-speed switch 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. This trigger pulse signal is divided into two paths. One path is used as the delay trigger signal for the controller, and the other path triggers the high-speed data acquisition card to perform data acquisition. 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 turns on the high-speed switch with a delay time of 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. Taking the electrical signal intensity 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 below the water is negative. According to the collected first electrical signal and second electrical signal, a relationship diagram of electrical signal intensity and height is drawn. S6. According to the drawn relationship diagram of electrical signal intensity and height, splice the data of the second electrical signal that does not overlap with the first electrical signal with the data of the first electrical signal to obtain complete data from the atmosphere to the water surface and then to underwater.

7. The method for preventing water surface signal saturation according to claim 6, characterized in that, Step S6 includes step S61: Take a partial overlap of the first electrical signal and the second electrical signal. Let the height corresponding to this partial overlap be H1 to H5. Assume that one point is collected every 1 meter. The values of the first electrical signal corresponding to the heights H1 to H5 are S 1-1 , S 1-2 , S 1-3 , S 1-4 and S 1-5 , and the values of the corresponding second electrical signal are S 2-1 , S 2-2 , S 2-3 , S 2-4 and S 2-5 . Let the calibration coefficient be 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 root mean square error with the value of the first electrical signal being the smallest.

8. The method for preventing water surface signal saturation according to claim 7, wherein In step S61, multiply the values of the second electrical signal corresponding to heights H1 to H5 by the calibration coefficient x. The formula for calculating the root mean square error with the values of the first electrical signal is: Minimize it, i.e., Minimize . By taking the first derivative and setting it to 0, i.e., Calculate the value of the calibration coefficient x.

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

10. The method for preventing saturation of water surface signals according to claim 6, wherein In step S2, the delay time T for turning on the high-speed switch is T = t + Δt, where Δt is the compensation delay.

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