A method for obtaining a raman laser radar and a water body profile particle beam attenuation coefficient
Patent Information
- Application Number
- CN202310742410.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-21
- Publication Date
- 2026-10-09
- Estimated Expiration
- 2043-06-21
AI Technical Summary
然而，同时获得高精度激光雷达退偏振信号和漫反射衰减系数仍然是一个挑战
[0015] The reason this application utilizes Raman lidar to obtain Raman backscattered signals is that research has shown that Raman backscattered signals are affected by particle extinction, but generally unaffected by backscattering. Therefore, by acquiring the Raman backscattered light intensity at each water profile, the lidar attenuation coefficient K for each profile can be obtained. lidar .
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Figure CN116794678B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of laser detection technology, specifically to a Raman lidar and a method for obtaining the beam attenuation coefficient of particulate matter in various profiles of water. Background Technology
[0002] Particle beam attenuation coefficient (C) p C0 is an important parameter in oceanography. It quantifies the rate at which a beam of light is absorbed and scattered by suspended particles in seawater. The absorption and scattering of light by suspended particles affect light propagation and the energy available for photosynthesis and other biological processes. Because C0... p Closely related to the concentration, size, shape, and composition of particles in a water column, it provides valuable information about marine ecosystems in terms of physical and biogeochemical aspects. p One of its key applications in oceanography is for estimating the content of particulate organic carbon (POC) in water bodies, a major component of the marine carbon cycle. POCs are produced by primary producers such as phytoplankton and then exported to the deep sea through sinking and vertical mixing processes. The concentration of POCs in seawater is difficult to measure directly, but it is currently estimated using C... p Several indirect algorithms have been developed to investigate the relationship between C and POC. Extensive research indicates that in certain ocean regions, C... p There is a strong relationship between it and POC. It has now been established that C is obtained through remote sensing and in-situ measurements. p The value is an effective method for estimating POC concentration.
[0003] Over the years, various in-situ measurement techniques have been developed to measure the C value of water, which can then be calculated by subtracting the value of pure water (C0.05). w To obtain C through contributions p These techniques include Beer-Lambert's law, stimulated Brillouin scattering, transillumination, and spectrophotometry. While in-situ measurements offer high temporal and spatial resolution, their limited spatial coverage and shallow depth may hinder their ability to capture large-scale changes in ocean systems. Therefore, it is necessary to develop methods for obtaining C values through remote sensing measurements to monitor the temporal and spatial variations of water C values, thus providing a valuable tool for environmental management and research.
[0004] However, accurate inversion of C using passive and active remote sensing technologies is possible. p This remains a challenging task. One approach is to invert chlorophyll concentration (Chl) obtained through passive ocean color remote sensing. However, this method can be affected by physiological processes, such as changes in intracellular pigmentation. Another method for estimating C... pThe method relies on obtaining the depolarization signal and diffuse reflection attenuation coefficient of the lidar, which can be obtained through ocean color remote sensing or Brillouin lidar measurements. However, obtaining high-precision lidar depolarization signal and diffuse reflection attenuation coefficient simultaneously remains a challenge. Summary of the Invention
[0005] The purpose of this application is to overcome the above-mentioned defects or problems in the background technology and provide a method for obtaining the beam attenuation coefficient of particulate matter in various sections of water using Raman lidar, which can obtain the beam attenuation coefficient of particulate matter in various sections of water without simultaneously obtaining the depolarization signal of lidar and the diffuse reflection attenuation coefficient.
[0006] To achieve the above objectives, the following technical solution is adopted: The first technical solution relates to a Raman lidar suitable for detecting water bodies, comprising: a laser generating module for generating pulsed laser; a transmitting and receiving module for transmitting the pulsed laser and receiving backscattered signals, wherein the telescope aperture is greater than or equal to 2 mm and less than 200 mm, and the field of view is greater than or equal to 1 mrad and less than 200 mrad; a filtering module for receiving the backscattered signals, filtering them, and outputting detection signals; wherein the center wavelength is the Raman backscattered signal wavelength of the detected object, and the bandwidth is greater than or equal to 2 nm and less than or equal to 20 nm; and a detection module employing a single-photon detector for measuring the light intensity of the detection signals of each profile of the corresponding detected object.
[0007] The second technical solution is based on the first technical solution, wherein when the emitted laser wavelength is 532nm, the center wavelength of the filtering module is 650nm and the bandwidth is 5-10nm.
[0008] The third technical solution is based on the first technical solution, wherein the field of view of the telescope of the transmitting and receiving module is less than or equal to 20mrad.
[0009] The fourth technical solution is based on the third technical solution, wherein the telescope aperture of the transmitting and receiving module is 21mm and its field of view is 2.1mrad.
[0010] The fifth technical solution is based on the first technical solution, and further includes an acquisition module and a calculation module. The acquisition module converts the electrical signal output by the detection module into digital information, and the calculation module processes the digital information.
[0011] The sixth technical solution relates to a method for obtaining the particle beam attenuation coefficient of each profile of a water body, comprising: obtaining the Raman backscattered light intensity of each profile of the water body; obtaining the lidar attenuation coefficient of each profile based on the Raman backscattered light intensity of each profile of the water body; establishing the relationship between the lidar attenuation coefficient and the total beam attenuation coefficient through semi-analytical Monte Carlo simulation, and obtaining the total beam attenuation coefficient of each profile based on the lidar attenuation coefficient of each profile; and obtaining the particle beam attenuation coefficient of each profile by considering the ratio of the total beam attenuation coefficient of each profile after deducting the total beam attenuation coefficient of water.
[0012] The seventh technical solution is based on the sixth technical solution, wherein the method is suitable for chlorophyll content of 0.01-10 mg / m³. 3 The water body.
[0013] The eighth technical solution is based on the sixth or seventh technical solution, wherein a Raman lidar as described in any one of the first to fifth technical solutions is installed on a ship traveling on the surface of the water to obtain the intensity of Raman backscattered light from various cross sections of the water.
[0014] Compared with existing technologies, the above solution has the following beneficial effects:
[0015] The reason this application utilizes Raman lidar to obtain Raman backscattered signals is that research has shown that Raman backscattered signals are affected by particle extinction, but generally unaffected by backscattering. Therefore, by acquiring the Raman backscattered light intensity at each water profile, the lidar attenuation coefficient K for each profile can be obtained. lidar .
[0016] Raman lidar has been used to detect atmospheric Raman backscattered signals. However, when using Raman lidar to detect Raman backscattered signals in water, the applicant discovered, through numerous experiments, that the acquired signal intensity exhibited a deviation. The applicant's research revealed that this deviation stemmed from chlorophyll fluorescence. Specifically, because the wavelength of the water Raman backscattered signal is close to the wavelength of the chlorophyll fluorescence backscattered signal that may exist in the water, a special filtering module needs to be designed to effectively control the influence of chlorophyll fluorescence. This is achieved by controlling the bandwidth of the filtering module. However, a smaller bandwidth is not always better; a smaller bandwidth results in a weaker signal. To ensure both signal strength and control over the influence of chlorophyll fluorescence on the water Raman backscattered signal, the applicant, through extensive experimental verification, limited the bandwidth to a value greater than or equal to 2 nm and less than or equal to 20 nm, with a preferred bandwidth of 5-10 nm.
[0017] Because in determining K lidarThe process requires the use of β t , and β t The Raman backscattering coefficient β of the object being detected R The backscattering coefficient β of chlorophyll fluorescence F The sum. Therefore, it is necessary to minimize the effect of chlorophyll fluorescence on β. t The impact of chlorophyll concentration is amplified by experimental studies, which have shown that when the bandwidth of the filter module is already selected, an increase in chlorophyll concentration amplifies its impact. Therefore, in the seventh technical solution and related embodiments, the chlorophyll content of the water body detected by Raman lidar is limited to 0.01-10 mg / m³. 3 It can keep the influence of chlorophyll fluorescence within the allowable error range.
[0018] Similarly, the applicant's long-term research and experiments have shown that K only works when the acquired Raman backscattering signal is dominated by quasi-single scattering. lidar The aperture range and field of view of the telescope are determined by the beam attenuation coefficient C. Therefore, this application limits the aperture range and field of view of the telescope to ensure that the acquired signal is mainly a quasi-single-scattering signal, at which point K... lidar Determined by the beam attenuation coefficient C, to facilitate the beam from K lidar The value of C is obtained, and based on the value of C, the C value is subtracted from the C value determined by the model. w Value acquisition C p Therefore, it is not necessary to simultaneously obtain the depolarization signal and diffuse reflection attenuation coefficient of the lidar to obtain the particle beam attenuation coefficient of each water profile.
[0019] One of the key technical contributions of this application is the establishment of K through semi-analytical Monte Carlo simulation. lidar The relationship between K and C, and based on this relationship, from each section K lidar The C value of each profile is obtained.
[0020] This application involves installing a Raman lidar on a ship traveling on the surface of water to obtain the intensity of Raman backscattered light from various sections of the water. Compared to installing it on a satellite, this method can obtain a higher intensity and more accurate signal, while also enabling efficient mobile measurement. Attached Figure Description
[0021] To more clearly illustrate the technical solutions of the embodiments, the accompanying drawings used are briefly described below:
[0022] Figure 1 This is a schematic diagram showing the module connection relationship of the Raman lidar in this embodiment.
[0023] Figure 2 This is a schematic diagram of the field of view of the transmit and receive module in this embodiment.
[0024] Figure 3This is a schematic diagram of the passband of the filtering module in this embodiment.
[0025] Figure 4 This is a flowchart illustrating the method for obtaining the beam attenuation coefficient of particulate matter in various water profiles in this embodiment.
[0026] Figure 5 This is an error analysis diagram of the bandwidth of the filtering module of the Raman lidar in this embodiment.
[0027] Figure 6.a This is one of the results obtained from an off-field experiment of the Raman lidar in this embodiment.
[0028] Figure 6.b This is the second result obtained from an off-field experiment of the Raman lidar in this embodiment.
[0029] Figure 6.c This is the third result obtained from an off-field experiment of the Raman lidar in this embodiment.
[0030] Explanation of key figure labels:
[0031] Laser generating module 1, transmitting and receiving module 2, filtering module 3, detection module 4, acquisition module 5, and calculation module 6. Detailed Implementation
[0032] Unless otherwise specified, the terms “first,” “second,” or “third,” etc., in the claims and description are used to distinguish different objects and not to describe a particular order.
[0033] Unless otherwise specified, in the claims and description, the terms “center,” “lateral,” “longitudinal,” “horizontal,” “vertical,” “top,” “bottom,” “inner,” “outer,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “clockwise,” “counterclockwise,” etc., indicate the orientation or positional relationship based on the orientation and positional relationship shown in the drawings, and are only for the purpose of simplifying the description, and do not imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation.
[0034] Unless otherwise specified in the claims and description, the terms "fixed connection" or "fixed connection" shall be interpreted broadly to mean any connection in which there is no displacement or relative rotation relationship between the two parties, including non-removable fixed connection, detachable fixed connection, integral connection, and fixed connection by other means or components.
[0035] Unless otherwise specified, the terms “comprising,” “having,” and variations thereof in the claims and description shall mean “including but not limited to.”
[0036] Unless otherwise specified, in the claims and description, the term "Chl" means chlorophyll concentration.
[0037] The technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings.
[0038] See Figure 1 This embodiment provides a Raman lidar suitable for detecting water bodies, which includes a laser generating module 1, a transmitting and receiving module 2, a filtering module 3, a detection module 4, an acquisition module 5, and a calculation module 6.
[0039] Laser generation module 1 is used to generate pulsed laser light. A commonly used Raman lidar pulsed laser generator can be used; no special requirements are specified. In this embodiment, the wavelength λ of the pulsed laser is... L It is 532nm.
[0040] Transmitter / receiver module 2, used to transmit pulsed laser light and receive backscattered signals, has a telescope aperture greater than or equal to 2 mm and less than 200 mm, and a field of view greater than or equal to 1 mrad and less than 200 mrad. Preferably, the telescope aperture is less than or equal to 25 mm, and the field of view is less than or equal to 20 mrad. In this embodiment, the telescope aperture is set to 21 mm, and the field of view is 2.1 mrad. Figure 2 As shown, in this embodiment, the transmitting telescope and the receiving telescope are close enough that the degree of overlap of their fields of view can be approximated as 1.
[0041] like Figure 1 and Figure 3 As shown, filter module 3 receives the backscattered signal, filters it, and outputs a detection signal. Its center wavelength is the Raman backscattered signal wavelength of the target object, and its bandwidth is greater than or equal to 2nm and less than or equal to 10nm, or it can be 5-7nm. In this embodiment, the bandwidth is 6nm. The Raman backscattered signal wavelength λ in this embodiment is... R The wavelength was determined to be 650nm, therefore the center wavelength of filter module 3 is 650nm, and experiments have shown that, as Figure 5 As shown, Raman lidar with this bandwidth can detect chlorophyll content in the range of 0.01-10 mg / m³. 3 When in water, the effect of chlorophyll fluorescence can be kept below 5%.
[0042] The detection module 4 employs a single-photon detector to measure the light intensity of the detection signal at each cross-section of the corresponding detection object, and then outputs it as an electrical signal. Since the forward and backward scattering signals and the backscattering signal are separated in the time domain in the signal generated after the detection object is irradiated by the pulsed laser, the lidar can distinguish the photon contributions of the forward and backscattering parts that reach the receiving detection module 4 in the time domain.
[0043] The acquisition module 5 converts the electrical signal output by the detection module 4 into digital information.
[0044] The calculation module 6 receives digital information from the acquisition module 5 and processes the digital information.
[0045] This embodiment also provides a method for obtaining the beam attenuation coefficient of particulate matter in various water profiles, such as... Figure 4 As shown, it includes:
[0046] Step 1: For chlorophyll content between 0.01-10 mg / m³ 3 In water bodies, the aforementioned Raman lidar is installed on a ship traveling on the surface of the water to obtain the intensity of Raman backscattered light from various cross sections of the water.
[0047] Step 2: Obtain the lidar attenuation coefficient for each water profile based on the Raman backscattered light intensity.
[0048] Step 3: Establish the relationship between the lidar attenuation coefficient and the total beam attenuation coefficient through semi-analytical Monte Carlo simulation, and based on this, obtain the total beam attenuation coefficient of each profile based on the lidar attenuation coefficient of each profile.
[0049] Step 4: Based on the total beam attenuation coefficient of each profile, the ratio of the total beam attenuation coefficient of water to the beam attenuation coefficient of particulate matter is used to obtain the particulate matter beam attenuation coefficient of each profile.
[0050] Specifically, the method for obtaining the lidar attenuation coefficient of each water profile based on the Raman backscattered light intensity is as follows:
[0051]
[0052] in, It is λ L and λ R Total Raman lidar attenuation coefficient at a given wavelength;
[0053] λ L Indicates the wavelength of the pulsed laser;
[0054] λ R This represents the wavelength of the Raman backscattered signal;
[0055] z is the distance from the profile to the transmitting and receiving module, i.e., the water depth;
[0056] P m (λ L ,λ R (z) represents the intensity of Raman backscattered light from the water profile;
[0057] Estimated by semi-analytical Monte Carlo simulation and the total light speed attenuation coefficient C total The relationship between them is as follows:
[0058]
[0059] Where m, n, and t are parameters obtained through semi-analytical Monte Carlo simulation. In this embodiment, the value of m is -0.334, the value of n is 1.916, and the value of t is -1.540.
[0060] The method for obtaining the particle beam attenuation coefficient for each profile by considering the ratio of the total beam attenuation coefficient after deducting the total beam attenuation coefficient of water to the particle beam attenuation coefficient is as follows:
[0061]
[0062] in, The total light velocity attenuation coefficient for pure water;
[0063] r R / L The ratio of the particle beam attenuation coefficient to the total particle beam attenuation coefficient is given by r in this embodiment. R / L Represented as r 650 / 532 The resulting error is denoted as Error. r Error caused by chlorophyll fluorescence is denoted as Error. f Taking into account chlorophyll fluorescence and r 650 / 532 Under the influence of various factors, comparative experiments show that the final total error of this method is [Error]. t The maximum value shall not exceed 15%.
[0064] In this embodiment, the lidar was deployed on a ship and began detection in the South China Sea at 20:38:04 on September 5, 2022, ending at 1:10:54. Initially, the Raman lidar collected data with a temporal resolution of 1 second and a depth resolution of 0.5 ns, as shown in the figure. Figure 6.a As shown. To reduce inversion signal errors during the inversion process, the time resolution was adjusted to 15 seconds and the depth resolution to 1 meter. The results are as follows. Figure 6.b and Figure 6.c As shown, Figure 6.b and Figure 6.c C total and C p The inversion results. From Figure 6.a The original signals clearly show the existence of a scattering layer beneath the sea surface, the characteristics of which changed slowly during the Jiageng's cruise. Figure 6.b and Figure 6.c We can observe C total and C p The changes in C. pIt provides a new perspective on the distribution and dynamics of water surface.
[0065] In this embodiment, the detection module 4 uses a single-photon detector, thereby improving the detection sensitivity to the single-photon level.
[0066] In this embodiment, the bandwidth of the filter module 3 is set to 6nm, which can both ensure signal strength and control the influence of chlorophyll fluorescence on the Raman backscattering signal of water.
[0067] In this embodiment, the chlorophyll content of the water body to be tested is limited to 0.01-10 mg / m³. 3 It can keep the influence of chlorophyll fluorescence within the allowable error range.
[0068] In this embodiment, the aperture range of the telescope is limited to 21mm, and the field of view range is 2.1mrad, thereby ensuring that the acquired signal is mainly a quasi-single-scatter signal. At this time, K... lidar Determined by the beam attenuation coefficient C, to facilitate the beam from K lidar The value of C is obtained, and based on the value of C, the C value is subtracted from the C value determined by the model. w Value acquisition C p value.
[0069] In this embodiment, K can be simulated and established through semi-analytical Monte Carlo simulation. lidar The relationship with C.
[0070] In this embodiment, a Raman lidar is installed on a ship traveling on the surface of the water to obtain the Raman backscattered light intensity of various sections of the water. Compared with installation on a satellite, it can obtain a higher intensity and more accurate signal, while also achieving efficient mobile measurement.
[0071] The description of the above specification and embodiments is used to explain the scope of protection of this application, but does not constitute a limitation on the scope of protection of this application.
Claims
1. A method for obtaining the beam attenuation coefficient of particulate matter in various profiles of a water body, characterized in that, include: Obtain the Raman backscattered light intensity of each profile of the water body; The lidar attenuation coefficient of each water profile is obtained based on the Raman backscattered light intensity of each profile. The relationship between the lidar attenuation coefficient and the total beam attenuation coefficient is established by semi-analytical Monte Carlo simulation, and the total beam attenuation coefficient of each profile is obtained based on the lidar attenuation coefficient of each profile. The particle beam attenuation coefficient for each profile is obtained by considering the ratio of the total beam attenuation coefficient of water to the particle beam attenuation coefficient for each profile.
2. The method for obtaining the beam attenuation coefficient of particulate matter in various water profiles as described in claim 1, characterized in that, The method is suitable for chlorophyll contents of 0.01-10 mg / m³. 3 The water body.
3. The method for obtaining the beam attenuation coefficient of particulate matter in various water profiles as described in claim 1 or 2, characterized in that, A Raman lidar is installed on a ship traveling on the surface of water to obtain the intensity of Raman backscattered light from various cross-sections of the water. The Raman lidar is suitable for detecting water bodies and includes: Laser generating module (1), which is used to generate pulsed laser; Transmitter-receiver module (2), which is used to transmit the pulsed laser and receive the backscattered signal, has a telescope aperture greater than or equal to 2 mm and less than 200 mm, and a field of view greater than or equal to 1 mrad and less than 200 mrad; The filtering module (3) receives the backscattered signal, filters it, and outputs a detection signal; its center wavelength is the Raman backscattered signal wavelength of the object being detected, and its bandwidth is greater than or equal to 2 nm and less than or equal to 20 nm; and The detection module (4) uses a single-photon detector and is used to measure the light intensity of the detection signal of each profile of the corresponding detection object.
4. The method for obtaining the beam attenuation coefficient of particulate matter in various water profiles as described in claim 3, characterized in that, The center wavelength of the filter module (3) is 650 nm and the bandwidth is 5-10 nm.
5. The method for obtaining the beam attenuation coefficient of particulate matter in various water profiles as described in claim 3, characterized in that, The field of view of the telescope in the transmitting and receiving module (2) is less than or equal to 20 mrad.
6. The method for obtaining the beam attenuation coefficient of particulate matter in various water profiles as described in claim 5, characterized in that, The telescope aperture of the transmitting and receiving module (2) is 21 mm, and its field of view is 2.1 mrad.
7. The method for obtaining the beam attenuation coefficient of particulate matter in various water profiles as described in claim 3, characterized in that, It also includes a data acquisition module (5) and a calculation module (6). The data acquisition module (5) converts the electrical signal output by the detection module (4) into digital information, and the calculation module (6) is used to process the digital information.