CN114325656A - A laser radar and method for detecting bio-optical characteristic profile of water body - Google Patents

Abstract

The invention discloses a laser radar and a method for detecting a water body biological optical characteristic profile, wherein the laser radar comprises a laser transmitting system, a four-channel signal receiving system and a data acquisition and processing system; the laser emission system is used for emitting laser pulses; the four-channel signal receiving system is used for receiving echo signals containing different wavelengths and polarization information from a water body and converting the echo signals into electric signals, and the data acquisition and processing system is used for acquiring and processing the electric signals received by the four-channel signal receiving system. The invention overcomes the defect that suspended inorganic matters and CDOM are not considered in the classical bio-optical model, and can detect the bio-optical characteristics of the water body in a large range and with high spatial resolution after calibration experiments by establishing a bio-optical characteristic profile inversion algorithm suitable for complex water bodies to obtain the bio-optical characteristic profile of the water body.

Description

A laser radar and method for detecting bio-optical characteristic profile of water body

technical field

The invention belongs to the technical field of laser radar, and in particular relates to a laser radar and a method for detecting biological optical characteristic profiles of water bodies.

Background technique

Marine ecosystems play an important role in global climate change and ecological environment protection. Phytoplankton is the main producer of marine ecosystems, and its net photosynthesis carbon sequestration is approximately equal to the sum of all terrestrial plants; lake ecology The system plays an important role in regulating regional climate and maintaining regional ecological balance, and is also an important freshwater resource reservoir. Eutrophication of water bodies will lead to the outbreak of algal blooms and pollute the water environment.

Chlorophyll is the main pigment of phytoplankton for photosynthesis and is used to characterize the biomass of phytoplankton. At present, the methods of detecting chlorophyll mainly include biochemical methods, in situ instrument measurement, passive remote sensing and active remote sensing. Among them, lidar, as an active optical remote sensing device, can be used to detect the bio-optical characteristic profile of water bodies and perform remote sensing measurement of the vertical distribution structure of the upper ocean. According to the composition of water bodies, water bodies can be divided into first-class water bodies and second-class water bodies. At present, combined with the bio-optical model of a type of water body, lidar has been successfully applied to the research of biomass detection and phytoplankton layer distribution. However, the optical properties of Class II water bodies are not only affected by phytoplankton and related particles, but also by inorganic suspended matter particles and colored dissolved organic matter (CDOM). This makes it difficult for lidar to retrieve bio-optical characteristic profiles of water bodies.

The Chinese patent document with publication number CN110673157A discloses a high spectral resolution lidar system for detecting ocean optical parameters. The system has four channels for detecting polarization information, chlorophyll content, phytoplankton and seawater temperature in the ocean. Detection; Chinese patent document with publication number CN105486664A discloses a device and method for detecting marine phytoplankton biomass and particulate organic carbon, based on high spectral resolution lidar, using marine phytoplankton biomass and POC inversion method, can Achieve simultaneous inversion of phytoplankton biomass and POC. However, the structure of hyperspectral-resolution lidar is complex, and when there are inorganic suspended particles and CDOM in the water body, the single-wavelength lidar cannot accurately obtain the chlorophyll concentration. Existing research proposes to use multi-wavelength lidar to solve the problem that single-wavelength lidar cannot accurately invert chlorophyll concentration. For example, the Chinese patent document with publication number CN112034480A discloses a wavelength-selective method for dual-wavelength ocean lidar detection. Dual-wavelength marine hyperspectral resolution lidar, establishes the inversion model of chlorophyll concentration and CDOM concentration according to the water absorption formula, and establishes an evaluation method for the relative error of parameters, selects the two wavelengths of the lidar, and obtains the best chlorophyll concentration. and CDOM absorption coefficient inversion model. However, the dual-wavelength lidar discussed in this method puts forward higher requirements for the laser, and the system structure is more complicated.

Therefore, there is an urgent need to provide a lidar and method with a simple structure and capable of detecting the bio-optical characteristic profile of a water body with high precision.

SUMMARY OF THE INVENTION

In order to solve the deficiencies in the prior art, the present invention provides a laser radar and a method for detecting the bio-optical characteristic profile of a water body, which can realize fast and accurate detection of the bio-optical characteristic profile.

A laser radar for detecting bio-optical characteristic profiles of water bodies, characterized in that it includes a laser emission system, a four-channel signal receiving system and a data acquisition and processing system;

The laser emission system includes a solid-state pulsed laser, a beam expander and a Glan laser prism; wherein, the solid-state pulsed laser is used to emit pulsed laser to the water body, the beam expander is used to adjust the divergence angle of the pulsed laser, and the Glan laser prism is used to Improve the polarization degree of the outgoing pulsed laser;

The four-channel signal receiving system includes four detachable receiving channels, each receiving channel includes a telescope, a field diaphragm, a converging lens, an interference filter, and a photodetector, wherein the first receiving channel and the The fourth receiving channel also includes a linear polarizer module; the linear polarizer module is used to adjust the polarization direction of the echo signal, the telescope is used to collect the echo light signal from the water body, the field diaphragm is used to adjust the field angle, and the converging lens is used for For the optical signal received quasi-directly, the interference filter is used to suppress the optical signal other than the target wavelength, and the photodetector is used to convert the collected optical signal into an electrical signal;

The data acquisition and processing system includes a data acquisition card and a computer; wherein, the data acquisition card is used to collect the optical trigger signal from the laser emission system and the echo analog electrical signal from the four-channel receiving system, and convert the analog electrical signal into Digital electrical signal, computer is used for real-time regulation of each module of lidar and real-time inversion of chlorophyll concentration in water body.

Further, the optical axis of the transmitting optical path of the laser emission system and the optical axis of the four receiving channels of the four-channel signal receiving system are adjacent and parallel; the light-emitting surface of the Glan laser prism is parallel to the horizontal plane, and the light-emitting surface of the beam expander The surface is parallel to the light-incident surface of the Glan laser prism, and the light-emitting surface of the solid-state pulse laser is parallel to the light-incident surface of the beam expander;

In the four-channel signal receiving system, the light incident surface of the telescope is parallel to the horizontal plane, the linear polarization module is arranged below the light incident surface of the telescope in the first receiving channel and the fourth receiving channel, and the center of the field diaphragm is arranged on the focal plane of the telescope and the condensing lens. The condensing lens is arranged above the field diaphragm, the interference filter is arranged above the condensing lens, and the photodetector is arranged above the interference filter;

In the data acquisition and processing system, the data acquisition card is connected to the four photoelectric detectors of the four-channel signal receiving system through coaxial cables, and the computer is connected to the data acquisition card through wires.

Further, the solid pulse laser adopts a solid pulse laser with a working wavelength of 532 nm, a single pulse energy of not less than 5 mJ, and a pulse width of not more than 10 ns; the beam expander adopts an anti-strong laser beam expander.

The field of view of the four receiving channels is set to be no less than 200mrad; the linear polarization modules in the first receiving channel and the fourth receiving channel can be rotated 360° and have scales;

The center wavelength of the interference filter in the first receiving channel and the fourth receiving channel is 532nm, the bandwidth does not exceed 10nm, and the receiving channels are called parallel polarization channel and vertical polarization channel; the interference filter in the second receiving channel and the third receiving channel The central wavelengths of the light sheet are 650nm and 685nm respectively, the bandwidth does not exceed 20nm, and the receiving channels are called Raman channel and fluorescence channel;

The photodetector adopts a photomultiplier tube with a spectral response range of 185-730 nm, a typical cathode illumination sensitivity of not less than 120 μA/lm and a rise time of not more than 2.2 ns;

The sampling rate of the data acquisition card is not less than 400MSa/s, and the number of quantization bits is not less than 12.

The present invention also provides a method for detecting the bio-optical characteristic profile of a water body, using the above-mentioned laser radar, wherein the laser radar signal generated by the water body at the depth z is expressed as

Among them, B represents the lidar signal corrected by the system environment parameters and the distance squared, the subscripts ⊥, ||, R, f represent the vertical polarization channel, parallel polarization channel, Raman channel and fluorescence channel, respectively, β represents the 180° body Scattering function, k _lidar represents the attenuation coefficient of lidar, superscript 650, 685 represent the corresponding wavelength, if there is no superscript, the wavelength is 532nm;

Specifically include the following steps:

Step S1, calibrate the proportional coefficient A ₁ of the chlorophyll concentration on the surface of the water body detected by the lidar, and compare the chlorophyll concentration Chl(0) of the water surface detected by multiple groups of laboratory fluorescence methods with the signal water meter of the lidar fluorescence channel detected in the same area. The ratio between the value B _f (0) and the Raman channel signal water meter value B _R (0) is linearly fitted to obtain the proportional coefficient A ₁ ;

Step S2, use an inversion algorithm to invert the Raman channel signal of the lidar to obtain the particle diffusion attenuation coefficient K _d,p (0) on the surface of the water body, and compare the Raman channel signal B _f with the parallel polarization channel and the vertical polarization. The sum of the channel signals B _C =B _|| +B _⊥ is calibrated to obtain the particle 180° volume scattering function β _p (0) and the proportionality coefficient A ₂ , and then the particle lidar ratio R(0) on the water surface is obtained, which means for

In step S3, the chlorophyll concentration Chl(0) in the surface layer _of the water body in the detection area is determined from the laser radar fluorescence signal and Raman signal and the proportional coefficient A1 obtained in step S1, and K _d,chl (0) is obtained according to a type of water body bio-optical model, where K _d,chl is the diffusion attenuation coefficient contributed by chlorophyll;

Step S4, using the water surface particle diffusion attenuation coefficient K _d,p (0) and the particle lidar ratio R (0) obtained in step S2 as boundary conditions, use the inversion algorithm to obtain K _d,p (z), β _p (z) and b _bp (z), complete the detection of the optical characteristic profile of the water body;

Step S5, assuming that the contribution of chlorophyll K _{d, chl} (z) in the particle diffusion attenuation coefficient K _d,p (z) detected by the lidar does not change with the depth, the K _d,p (0) obtained in step S2 is used. , K _{d, chl} (0) obtained in step S3 and particle diffusion attenuation coefficient K _{d, p} (z) obtained in step S5 to obtain the diffusion attenuation coefficient K _{d, chl} (z) contributed by chlorophyll, using a class of water bio-optics The model and K _d,chl (z) can obtain the chlorophyll concentration Chl(z) of the water body, and the detection of the biological characteristic profile of the water body is completed.

Further, in step S1, near the water surface, the ratio of the fluorescence signal and the Raman signal is approximately a linear function of the chlorophyll concentration, expressed as:

Among them, A ₁ is a constant related to environmental parameters and system parameters.

In step S2, when the field of view angle is large enough, the lidar attenuation coefficient k _lidar is approximately the diffusion attenuation coefficient K _d ; the particle diffusion attenuation coefficient detected by the Raman channel is expressed as:

为纯水在650nm的漫射衰减系数，

为颗粒物在650nm的漫射衰减系数；Among them, K _d,w is the diffusion attenuation coefficient of pure water at 532nm,

is the diffusion attenuation coefficient of pure water at 650nm,

is the diffusion attenuation coefficient of particles at 650 nm;

The 180° bulk scattering function β _p of particulate matter is approximately proportional to the ratio of the intensities of m scattering and Raman scattering, expressed as

Among them, A ₂ is a constant related to environmental parameters and system parameters.

In step S3, a class of water bio-optical models is expressed as

K _d,chl (z)=χChl(z) ^e ,

Among them, χ and e are parameters related to wavelength.

In step S4, the inversion method used is the Fernald forward algorithm, and the diffusion attenuation coefficient K _d (z) is expressed as

Among them, R _S is the ratio of the particle lidar ratio R to the water molecule lidar ratio R _w , z _c is the boundary depth, and Φ(z) is expressed as

The 180° bulk scattering function β _p (z) of particulate matter is expressed as

The relationship between the particle backscattering coefficient b _bp and the particle 180° volume scattering function β _p (z) is expressed as

b _bp (z)=2πχ _p (π)β _p (z),

where χ _p (π) is the conversion factor when the backscattering angle is 180°.

In step S5, the water chlorophyll concentration Chl(z) is expressed as

Compared with the prior art, the present invention has the following beneficial effects:

The invention adopts the four-channel laser radar working in the blue-green band, establishes a bio-optical characteristic profile inversion method suitable for complex water bodies, expands the application scenarios of the laser radar telemetry bio-optical characteristic profile, and improves the inversion accuracy of chlorophyll in complex water bodies. Overcoming the shortcomings of the classical bio-optical model that does not consider suspended inorganic matter and CDOM, by establishing a bio-optical property profile inversion algorithm suitable for complex water bodies, after performing calibration experiments, the bio-optical properties of water bodies can be measured in a wide range and at high levels. Probing with spatial resolution to obtain bio-optical characteristic profiles of water bodies.

Description of drawings

1 is a schematic structural diagram of a laser radar for detecting the bio-optical characteristic profile of a water body according to the present invention;

Fig. 2 is the flow chart of the method for detecting the bio-optical characteristic profile of the present invention;

Fig. 3 is the fitting result of fluorescence Raman ratio and laboratory result in the embodiment of the present invention;

FIG. 4 is a comparison diagram of a chlorophyll inversion result and an in-situ detection result in an embodiment of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be pointed out that the following embodiments are intended to facilitate the understanding of the present invention, but do not have any limiting effect on it.

As shown in Figure 1, a lidar for detecting the optical characteristic profile of water bodies includes a laser emission system 1, a four-channel signal receiving system 2 and a data acquisition and processing system 3. The laser emission system 1 is used to emit laser pulses; the four-channel signal The receiving system 2 is used to receive echo signals from the water body containing different wavelengths and polarization information and convert them into electrical signals, and the data acquisition and processing system 3 is used to collect and process the electrical signals received by the four-channel receiving system 2 .

The laser emission system 1 includes a solid pulse laser 1-1, a beam expander 1-2 and a Glan laser prism 1-3. The light-emitting surface of the Glan laser prism 1-3 is set parallel to the horizontal plane, the light-emitting surface of the beam expander 1-2 is set parallel to the light-incident surface of the Glan laser prism, and the light-emitting surface of the solid-state pulse laser 1-1 is parallel to the beam expander The light incident surface setting.

The four-channel signal receiving system 2 includes four detachable receiving channels, which are respectively set as a first receiving channel 2-1, a second receiving channel 2-2, a third receiving channel 2-3 and a fourth receiving channel 2-4 ; Wherein, the first receiving channel 2-1 includes a first linear polarizer module 2-1-1, a first telescope 2-1-2, a first field diaphragm 2-1-3, a first condensing lens 2- 1-4. The first interference filter 2-1-5 and the first photodetector 2-1-6. The second receiving channel 2-2 includes a second telescope 2-2-1, a second field diaphragm 2-2-2, a second condensing lens 2-2-3, and a second interference filter 2-2-4 , the second photodetector 2-2-5. The third receiving channel 2-3 includes a third telescope 2-3-1, a third field diaphragm 2-3-2, a third condensing lens 2-3-3, and a third interference filter 2-3-4 , the third photodetector 2-3-5. The fourth receiving channel 2-4 includes a second linear polarizer module 2-4-1, a fourth telescope 2-4-2, a fourth field diaphragm 2-4-3, a fourth condensing lens 2-4-4, The fourth interference filter 2-4-5, the fourth photodetector 2-4-6. The light incident surfaces of the telescopes in each receiving channel are arranged parallel to the horizontal plane, the linear polarization module is arranged below the light incident surfaces of the telescopes of the first receiving channel and the fourth receiving channel, and the center of the field diaphragm is arranged on the focal plane of the telescope and the condensing lens to converge The lens is arranged above the field diaphragm, the interference filter is arranged above the condensing lens, the photodetector is arranged above the interference filter, and the optical axis of the receiving channel is parallel and adjacent to the optical axis of the transmitting channel.

The data acquisition and processing system 3 includes a data acquisition card 3-1 and a computer 3-2. In the data acquisition and processing system 3, the data acquisition card 3-1 is connected to the four photodetectors of the four-channel signal receiving system through coaxial cables, and the computer 3-2 is connected to the data acquisition card 3-1 through wires.

In this embodiment, the solid-state pulse laser adopts a solid-state pulse laser with an operating wavelength of 532 nm, a single pulse energy of not less than 5 mJ, and a pulse width of not more than 10 ns. Energy 10mJ, pulse width 3ns.

The beam expander adopts an anti-strength laser beam expander, such as the BE02-532 high-power beam expander from Thorlabs in the United States, which expands the beam by 3 times.

The field angles of the four receiving channels are set to not less than 200mrad, and appropriate parameters are selected to determine the design of the telescope, field diaphragm and converging lens.

The linear polarization module adopts a 360° rotatable linear polarization module with a scale, such as the FLP20-VIS linear film polarizer of China Lubang Technology Company and the rotating mount of the RM1 model.

The first interference filter and the fourth interference filter are interference filters with a center wavelength of 532nm and a bandwidth of not more than 10nm, such as the MBF03-532 filter of China Lubang Technology Company, with a center wavelength of 532nm and a bandwidth of 6nm; The second interference filter (2-2-4) and the third interference filter (2-3-4) are interference filters with central wavelengths of 650nm and 685nm and bandwidths not exceeding 20nm, such as Thorlabs, USA The FL650-10 and FL680-10 filters have center wavelengths of 650nm and 680nm, respectively, and bandwidths of 20nm.

The photodetector adopts a photomultiplier tube with a spectral response range of 185-730nm, a typical cathode illumination sensitivity of not less than 120μA/lm and a rise time of no more than 2.2ns, such as the R7518 photomultiplier tube from Hamamatsu Photonics, Japan. The spectral response range From 185 to 730 nm, the typical cathodic light sensitivity is 130 μA/lm with a rise time of 2.2 ns.

The data acquisition card adopts a data acquisition card with a sampling rate of not less than 400MSa/s and a quantization number of not less than 12 bits, such as M4i.4481-x8 high-speed data acquisition card from Spectrum, Germany, with a sampling rate of 400MSa/s and a quantization number is 14 bits.

和532nm的颗粒物漫射衰减系数K_d,p(0)的比例系数A₃；采用水体表层的荧光信号、拉曼信号、平行偏振信号与垂直偏振信号之和获得光学参数的边界条件K_d,p(0)、K_d,chl(0)、β_p(0)、R(0)，进而反演得到水体的生物光学特征剖面。Based on the above-mentioned lidar for detecting bio-optical characteristic profiles of water bodies, the method flow for detecting bio-optical characteristic profiles of water bodies is shown in Figure 2. The lidar emits pulsed laser light to the water body. By setting polarizers of different states and interference filters of different central wavelengths , the receiving system receives the parallel polarized signal B _|| , the fluorescent signal B _f , the Raman signal _BR and the vertical _polarized signal B _|| (0)/B _R (0) and chlorophyll Chl(0) proportional coefficient A ₁ , sum of water surface parallel polarization channel and vertical polarization channel signal B _C (0)=B _|| (0)+B _⊥ (0 ) to the Raman signal _BR (0), the ratio B _C (0)/ _BR (0), the proportionality coefficient A ₂ of the 180° volume scattering function β _p (0) of the particulate matter, and the diffusion attenuation coefficient of the 650 nm particulate matter on the surface of the water body

and the proportional coefficient A ₃ of the diffusion attenuation coefficient K _d,p (0) of particles at 532 nm; the boundary condition K _{d of the optical parameters is obtained by the sum of the fluorescence signal, Raman signal, parallel polarization signal and vertical polarization signal of the water surface layer, p} (0), K _{d, chl} (0), β _p (0), R(0), and then invert to obtain the bio-optical profile of the water body.

The lidar signal generated by the water body at depth z can be expressed as

Among them, B represents the lidar signal corrected by the system environmental parameters and the distance squared, the subscripts ⊥, ||, R, and f represent the vertical polarization channel, parallel polarization channel, Raman channel and fluorescence channel, respectively, β represents the 180° body Scattering function, k _lidar represents the lidar attenuation coefficient, superscripts 650 and 685 represent the corresponding wavelengths, and if there is no superscript, the wavelength is 532nm.

The inversion detection of the bio-optical property profile is achieved by the following steps:

The first step, as shown in Figure 3, is to calibrate the proportional coefficient A ₁ of the chlorophyll concentration on the surface of the water body detected by the lidar, which is limited by the signal-to-noise ratio of the signal. Near the water surface, the ratio of the fluorescence signal to the Raman signal can be approximated is a linear function of chlorophyll concentration, expressed as

The ratio of the water surface chlorophyll concentration Chl(0) detected by multiple groups of laboratory fluorescence methods and the signal water meter value B _f (0) of the lidar fluorescence channel detected in the same area to the Raman channel signal water meter value B _R (0) Perform linear fitting to obtain the proportional coefficient A ₁ , and the coefficient of determination reaches 0.9.

In the second step, the ratio of the sum of the signals of the parallel polarization channel and the vertical polarization channel B _C =B _|| +B _⊥ to the Raman channel signal B _f is calibrated, and the 180° bulk scattering functions of multiple groups of particles are obtained with the in-situ instrument. β _p , which is approximately proportional to the ratio of Mie scattering and Raman scattering intensities, is expressed as

和532nm的漫射衰减系数K_d,w之比A₃进行定标，在同一水域A₃近似为常数，用原位仪器获得多组

与K_d,w之比，取均值得到比例系数A₃。Diffuse Attenuation Coefficient for 650nm

It is calibrated with the ratio A ₃ of the diffusion attenuation coefficient K _d,w of 532 nm, and A ₃ is approximately constant in the same water area.

The ratio of K _d,w to K d,w, and the average value is obtained to obtain the proportional coefficient A ₃ .

The third step is to obtain the boundary conditions of the inversion algorithm. The inversion algorithm is used to invert the Raman channel signal of the lidar. When the field of view is large enough, the lidar attenuation coefficient k _lidar is approximately the diffusion attenuation coefficient K _d , and the diffusion attenuation coefficient of the particles detected by the Raman channel is expressed as for

为纯水在650nm的漫射衰减系数，为0.34m^-1。Among them, K _d,w is the diffusion attenuation coefficient of pure water at 532nm, which is 0.045m ^-1 ,

is the diffusion attenuation coefficient of pure water at 650nm, which is 0.34m ^-1 .

According to the formula (3), the 180° volume scattering function β _p (0) of the particles on the surface of the water body is obtained, and the diffusion attenuation coefficient K _d,p (0) of the particles on the surface of the water body is obtained according to the formula (4), and then the particle laser on the surface of the water body is obtained. The radar ratio R(0), expressed as

The chlorophyll concentration Chl(0) on the surface of the water body in the detection area is determined by using the lidar fluorescence signal and Raman signal and the proportionality coefficient A ₁ , and K _d,chl (0) is obtained according to a class of water bio-optical models, where K _d,chl is the diffuse attenuation coefficient contributed by chlorophyll. A class of water bio-optical models is expressed as

K _d,chl (z)=χChl(z) ^e , (6)

Among them, χ and e are wavelength-dependent parameters. At 532 nm, χ is 0.0474 and e is 0.6667.

The fourth step is to use the water surface particle diffusion attenuation coefficient K _d,p (0) and the particle lidar ratio R(0) as the boundary conditions, using the Fernald forward algorithm, K _d,p (z) and β _p ( z) Perform an inversion. The diffuse attenuation coefficient K _d (z) is expressed as

Among them, R _S is the ratio of the particle lidar ratio R to the water molecule lidar ratio R _w , z _c is the boundary depth, and Φ(z) is expressed as

The 180° bulk scattering function β _p (z) of particulate matter is expressed as

The relationship between the particle backscattering coefficient b _bp and the particle 180° volume scattering function β _p (z) is expressed as

b _bp (z)=2πχ _p (π)β _p (z), (10)

Wherein, χ _p (π) is a conversion factor when the backscattering angle is 180°, and in this embodiment, χ _p (π) is 1.

In the fifth step, assuming that the chlorophyll contribution K _d,chl (z) in the particle diffusion attenuation coefficient K _d,p (z) detected by the lidar does not change with depth, the K _d,p ( 0), K _d,chl (0) and the fourth step to obtain K _d,p (z), calculate the diffusion attenuation coefficient K _d,chl (z) contributed by chlorophyll. Using a class of water bio-optical models and K _{d, chl} (z) to obtain the water chlorophyll concentration Chl(z), the water chlorophyll concentration Chl(z) is expressed as

The chlorophyll concentration obtained by the inversion according to the embodiment is shown in Fig. 4, in which the solid line represents the chlorophyll concentration obtained by the laser radar inversion, and the dotted line represents the chlorophyll concentration detected by the in-situ instrument. The acting method is effective.

In this embodiment, the detection and inversion of the water surface optical characteristics K _d,p , β _p and the chlorophyll concentration profile is realized by using the laser radar and the method for detecting the bio-optical characteristic profile of the water body, which is compatible with the in-situ instrument The comparison of detection results is good, which verifies the effectiveness of the present invention.

The above-mentioned embodiments describe the technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned embodiments are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions and equivalent replacements made shall be included within the protection scope of the present invention.

Claims (9)

1. A laser radar for detecting a water body biological optical characteristic section is characterized by comprising a laser emission system (1), a four-channel signal receiving system (2) and a data acquisition and processing system (3);

the laser emission system (1) comprises a solid pulse laser (1-1), a beam expander (1-2) and a Glan laser prism (1-3); the device comprises a solid pulse laser (1-1), a beam expander (1-2), a Glan laser prism (1-3) and a water body, wherein the solid pulse laser (1-1) is used for emitting pulse laser to the water body, the beam expander (1-2) is used for adjusting the divergence angle of the pulse laser, and the Glan laser prism (1-3) is used for improving the polarization degree of the emergent pulse laser;

the four-channel signal receiving system (2) comprises four detachable receiving channels, each receiving channel comprises a telescope, a field diaphragm, a converging lens, an interference optical filter and a photoelectric detector, wherein the first receiving channel (2-1) and the fourth receiving channel (2-4) also comprise linear polaroid modules; the linear polarizer module is used for adjusting the polarization direction of an echo signal, the telescope is used for collecting the echo optical signal from a water body, the field diaphragm is used for adjusting the field angle, the converging lens is used for collimating the received optical signal, the interference optical filter is used for inhibiting the optical signal beyond the target wavelength, and the photoelectric detector is used for converting the collected optical signal into an electric signal;

the data acquisition processing system (3) comprises a data acquisition card (3-1) and a computer (3-2); the data acquisition card (3-1) is used for acquiring optical trigger signals from the laser emission system (1) and echo analog electric signals from the four-channel receiving system (2) and converting the analog electric signals into digital electric signals, and the computer (3-2) is used for regulating and controlling each module of the laser radar in real time and inverting the chlorophyll concentration of the water body in real time.

2. The lidar for detecting the profile of the biological optical property of the water body according to claim 1, wherein the optical axis of the transmitting light path of the laser transmitting system (1) is adjacent to and parallel to the optical axes of the four receiving channels of the four-channel signal receiving system (2); the light-emitting surface of the Glan laser prism (1-3) is parallel to the horizontal plane, the light-emitting surface of the beam expander (1-2) is parallel to the light-in surface of the Glan laser prism (1-3), and the light-emitting surface of the solid pulse laser (1-1) is parallel to the light-in surface of the beam expander (1-2);

the light incident surface of a telescope in the four-channel signal receiving system is parallel to the horizontal plane, the linear polarization module is arranged below the telescope light incident surfaces of the first receiving channel (2-1) and the fourth receiving channel (2-4), the center of a field diaphragm is arranged on the focal plane of the telescope and a convergent lens, the convergent lens is arranged above the field diaphragm, an interference optical filter is arranged above the convergent lens, and a photoelectric detector is arranged above the interference optical filter;

in the data acquisition processing system (3), a data acquisition card (3-1) is connected with four photoelectric detectors of the four-channel signal receiving system (2) through coaxial cables, and a computer (3-2) is connected with the data acquisition card (3-1) through wires.

3. The lidar for detecting the profile of the biological optical property of the water body according to claim 1, wherein the solid pulse laser (1-1) adopts a solid pulse laser with the working wavelength of 532nm, the single pulse energy of not less than 5mJ and the pulse width of not more than 10 ns; the beam expander (1-2) adopts an anti-intense laser beam expander;

the field angles of the four receiving channels are set to be not less than 200 mrad; the linear polarization modules in the first receiving channel (2-1) and the fourth receiving channel (2-4) can rotate for 360 degrees and are provided with scales;

the central wavelength of the interference filters in the first receiving channel (2-1) and the fourth receiving channel (2-4) is 532nm, the bandwidth is not more than 10nm, and the receiving channels are called as a parallel polarization channel and a vertical polarization channel; the central wavelengths of the interference filters in the second receiving channel (2-2) and the third receiving channel (2-3) are 650nm and 685nm respectively, the bandwidth is not more than 20nm, and the receiving channels are called as a Raman channel and a fluorescence channel;

the photoelectric detector adopts a photomultiplier tube with a spectral response range of 185-730 nm, a typical cathode illumination sensitivity of not less than 120 mu A/lm and a rise time of not more than 2.2 ns;

the sampling rate of the data acquisition card (3-1) is not lower than 400MSa/s, and the quantization digit is not lower than 12 digits.

4. A method for detecting a biological optical characteristic profile of a water body, characterized in that the laser radar of any one of claims 1 to 3 is adopted, wherein the laser radar signal generated by the water body with the depth z is expressed as environmental parameters, system parameters and distance square after being corrected

Wherein B represents the laser radar signal after the system environment parameter and the distance square correction, subscripts [ sic ], R, f represent a vertical polarization channel, a parallel polarization channel, a Raman channel and a fluorescence channel respectively, β represents a 180-degree volume scattering function, k represents a volume scattering function_lidarThe attenuation coefficient of the laser radar is represented, the superscripts 650 and 685 represent corresponding wavelengths, and the wavelength is 532nm when the superscripts are not arranged;

the method specifically comprises the following steps:

step S1, detecting the proportional coefficient A of the chlorophyll concentration of the surface layer of the water body by the laser radar₁Calibrating, and measuring chlorophyll concentration Chl (0) of water meter obtained by multiple groups of laboratory fluorescence detection and water meter value B of laser radar fluorescence channel signal detected in the same region_f(0) And Raman channel signal water meter value B_R(0) Linear fitting is carried out on the ratio to obtain a proportionality coefficient A₁；

Step S2, carrying out inversion on the Raman channel signal of the laser radar by adopting an inversion algorithm to obtain the diffusion attenuation coefficient K of the particles on the surface of the water body_d,p(0) For Raman channel signal B_fWith the sum B of the signals of the parallel polarization channel and the perpendicular polarization channel_C＝B_||+B_⊥Calibrating to obtain 180-degree volume scattering function beta of the particles_p(0) And the proportionality coefficient A₂And further obtaining the particle laser radar ratio R (0) of the water body surface, which is expressed as

Step S3, the laser radar fluorescence signal and Raman signal and the proportionality coefficient A obtained in step S1₁Determining chlorophyll concentration Chl (0) of the surface layer of the water body in the detection area, and obtaining K according to a water body biological optical model_d,chl(0) Wherein, K is_d,chlIs the diffuse attenuation coefficient contributed by chlorophyll;

step S4, diffusing and attenuating the particles on the surface of the water body K obtained in the step S2_d,p(0) And the ratio R (0) of the particle laser radar is used as a boundary condition, and K is obtained by using an inversion algorithm_d,p(z)、β_p(z) and b_bp(z) completing the detection of the optical characteristic section of the water body;

step S5, assuming the diffusion attenuation coefficient K of the particulate matter detected by the laser radar_d,pContribution K of chlorophyll in (z)_d,chl(z) K obtained in step S2 is used without change in depth_d,p(0) K obtained in step S3_d,chl(0) And step S5 obtaining the diffusion attenuation coefficient K of the particulate matters_d,p(z) obtaining the diffusion attenuation coefficient K of the chlorophyll contribution_d,chl(z) using a class of water biological optical models and K_d,chlAnd (z) obtaining the chlorophyll concentration Chl (z) of the water body, and completing the detection of the biological characteristic section of the water body.

5. The method for detecting the bio-optical property profile of the water body according to claim 4, wherein in step S1, the ratio of the fluorescence signal to the Raman signal near the water surface is approximately a linear function of the chlorophyll concentration, expressed as a chlorophyll concentration

Wherein A is₁Is a constant related to the environmental parameter and the system parameter.

6. The method for detecting the bio-optical characteristic profile of the water body according to claim 4, wherein in step S2, when the field angle is large enough, the lidar attenuation coefficient k is_lidarApproximated by a diffuse attenuation coefficient K_d(ii) a The diffusion attenuation coefficient of the particles detected by the Raman channel is expressed as

Wherein, K_d,wIs the diffuse attenuation coefficient of pure water at 532nm,

is the diffuse attenuation coefficient of pure water at 650nm,

is the diffusion attenuation coefficient of the particles at 650 nm;

particle 180 ° bulk scattering function β_pApproximately proportional to the ratio of the Mie and Raman scattering intensities, expressed as

Wherein A is₂Is a constant related to the environmental parameter and the system parameter.

7. The method for detecting the profile of the biological optical property of the water body according to claim 4, wherein in step S3, one type of the biological optical model of the water body is represented as K_d,chl(z)＝χChl(z)^e,

Wherein χ and e are wavelength-dependent parameters.

8. The method for detecting the water body biological optical property profile according to the claim 4, wherein the inversion method adopted in the step S4 is Fernald forward algorithm, and the diffusion attenuation coefficient K_d(z) is represented by

Wherein R is_SIs the ratio of particulate matter laser radar to water molecule laser radar_wRatio of z_cFor boundary depth, Φ (z) is expressed as

Particle 180 ° bulk scattering function β_p(z) is represented by

Backscattering coefficient b of particulate matter_bpAnd 180 DEG bulk scattering function beta of particulate matter_pThe relationship of (z) is represented by b_bp(z)＝2πχ_p(π)β_p(z),

Wherein, χ_p(π) is the conversion factor at a backscattering angle of 180 °.

9. The method for detecting the profile of the biological optical property of the water body as claimed in claim 4, wherein the chlorophyll concentration Chl (z) of the water body is expressed as Chl (z) in step S5

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