High-precision visibility measurement method combining mobile transilluminator and laser radar

Abstract

The invention provides a high-precision visibility measurement method combining a mobile transilluminator and a laser radar, and belongs to the field of atmospheric visibility measurement, and the high-precision visibility measurement method comprises the mobile transilluminator and the laser radar, the mobile transilluminator comprises a laser emitting unit, a light receiving unit, a slide rail unit, a trolley unit and a control and data processing unit; the laser radar comprises a laser emitting unit, a light receiving unit and a signal detection and data acquisition unit; according to the invention, the laser radar is used as a main body of visibility measurement, and high-precision measurement of the mobile transilluminator is used for coupling and correction, so that light pollution caused by the atmospheric environment is inhibited, and the non-uniformity of the atmospheric environment within a certain range is measured.

Description

Technical Field

[0001] The invention belongs to the technical field of atmospheric visibility measurement, and in particular relates to a high-precision visibility measurement method and system combining a mobile transmissometer and a laser radar. Background Art

[0002] High-precision visibility measurement has been widely used in the fields of civil aviation and shipping. However, for a long time, atmospheric inhomogeneity and optical pollution under low visibility conditions have been important issues affecting the accuracy of visibility measurement. At present, visibility measurement methods mainly include transmission, forward scattering and backscattering. However, for high-precision visibility measurement, only the transmission method is widely used because it fully complies with the principle of human vision and has good suppression of optical noise. But in practical applications, there are always two important problems in the use of these transmission methods in high-precision visibility measurement. First, it is difficult to accurately measure the inhomogeneous atmospheric environment. Second, the optical lens contamination caused by the aerosol environment will also affect the accuracy of visibility measurement, because the light intensity error between the transmitter and the receiver is inconsistent, which is difficult to avoid through optical design. In theory, among all visibility measurement methods, lidar is the best way to solve the above two problems. However, the background noise and boundary value calculation of lidar itself are not easy to deal with. Therefore, this study expands the high-precision visibility measurement method, which has important guiding significance for land transportation, navigation, navigation, meteorology and other aspects. Summary of the invention

[0003] In view of the defects existing in the prior art, the purpose of the present invention is to propose a high-precision visibility measurement method combining a mobile transmissometer and a laser radar, so as to solve the problem of high-precision measurement of atmospheric visibility and suppress the environmental pollution caused by measuring atmospheric visibility.

[0004] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: to propose a high-precision visibility measurement method combining a mobile transmissometer and a laser radar, comprising the following steps:

[0005] S1. The mobile transmissometer measures the laser signals at different points by moving the receiving end. According to the Beer-Lambert law, a laser atmospheric attenuation model is established, and the influence of lens contamination error is considered. Since only one mobile receiver is used, the lens contamination error at the receiving end can be considered constant, thereby offsetting the contamination error.

[0006] S2. LiDAR inversion calculation under coupled mobile transmissometer. The high-precision measurement results of the mobile transmissometer are used as clean samples and coupled with the LiDAR signal. The LiDAR signal is decomposed and denoised using the empirical mode decomposition method. Based on the measurement results of the mobile transmissometer and the Klett inversion formula, the extinction coefficient and visibility of the LiDAR are calculated.

[0007] Furthermore, in S1, the mobile transmissometer includes a laser emitting unit, a light receiving unit, a slide rail unit, a trolley unit, and a control and data processing unit. The laser emitting unit includes a laser, an emitting optical path system, and an adjustment bracket. The laser expands the beam through the emitting optical path system and emits 532nm green light along the track direction, with a divergence angle of less than 1.5mrad and a spot diameter of 2mm. The light receiving unit is composed of an optical chopper, a photodetector, a phase-locked amplifier, and a receiving optical system. The slide rail unit is composed of two 55-meter-long steel rails with a rail spacing of 0.35m and a height of 0.2m. The trolley unit is composed of a bottom plate, a car cover, a roller, a gear, a servo motor, a reducer, a programmable logic controller, a proximity sensor, and an inverter. A photoelectric receiving unit and a signal acquisition unit are placed on the bottom plate. The control and data processing unit includes an embedded industrial computer, and the entire system adopts a wired transmission method.

[0008] Furthermore, in S2, the laser radar includes a laser emitting unit, a light receiving unit and a signal detection and data acquisition unit. The laser emitting unit uses a diode-pumped Nd...YAG532nm laser as a light source, which is close to the 550nm that the human eye is most sensitive to. The laser beam emitted by the laser is coupled into the transmitting optical fiber through a fiber coupler, collimated and expanded, and then projected horizontally.

[0009] Furthermore, the method for measuring visibility using a mobile transmissometer specifically comprises the following steps:

[0010] (a) According to Beer-Lambert's law, the laser atmospheric attenuation model can be expressed as:

[0011]

[0012] where η i and η0 represent the lens contamination errors of the mobile receiver at the final point i and the initial point 0, respectively. i and L0 represent the moving distance of the mobile receiver at the final point i and the initial point 0 respectively, and σ is the extinction coefficient.

[0013] (b) Since only one mobile receiver is used, the lens contamination error at the receiver can be considered constant, i.e., η i =η0, in this case we can get:

[0014]

[0015] (c) Extinction coefficient σ and final moving distance L i The relationship model between is expressed as:

[0016]

[0017] (d) Visibility can be calculated as:

[0018]

[0019] Furthermore, according to the high-precision measurement of the mobile transmissometer and coupled with the lidar signal, an atmospheric visibility inversion calculation method based on empirical mode decomposition is proposed.

[0020] The beneficial results of the present invention include but are not limited to:

[0021] The laser radar is used as the main body of visibility measurement, and the high-precision measurement of the mobile transmissometer is used for coupling and correction. For the denoising of the laser radar, the high-precision measurement results of the transmissometer are used as clean samples to denoise the laser radar, which effectively solves the problem of insufficient prior information. For the calculation of the laser radar boundary value, the mobile transmissometer can obtain the accurate distribution of the extinction coefficient, which is used to calculate the boundary value to improve the calculation accuracy of visibility. In addition, since the mobile transmissometer adopts a single-end mobile measurement method, only the light intensity at the receiving end is considered in the calculation, which can effectively avoid the measurement error caused by inconsistent light pollution between the transmitting end and the receiving end. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the combination of a laser radar and a mobile transmissometer in an embodiment of the system of the present invention;

[0023] Figure 2 It is a structural schematic diagram of a mobile transmissometer in an embodiment of the system of the present invention;

[0024] Figure 3 Flow chart of laser radar signal decomposition and reconstruction in the system embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0026] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0027] like Figure 1 As shown, in one embodiment of the present invention, a high-precision visibility measurement method combining a mobile transmissometer and a laser radar comprises the following steps:

[0028] S1. The mobile transmissometer measures the laser signals at different points by moving the receiving end. According to the Beer-Lambert law, the laser atmospheric attenuation model is established, and the influence of the lens contamination error is considered. Since only one mobile receiver is used, the lens contamination error at the receiving end can be considered constant, thus offsetting the contamination error.

[0029] S2. LiDAR inversion calculation under coupled mobile transmissometer. The high-precision measurement results of the mobile transmissometer are used as clean samples and coupled with the LiDAR signal. The LiDAR signal is decomposed and denoised using the empirical mode decomposition method. Based on the measurement results of the mobile transmissometer and the Klett inversion formula, the extinction coefficient and visibility of the LiDAR are calculated.

[0030] like Figure 2 As shown, in this embodiment, the present invention first uses a mobile transmissometer for high-precision measurement. The system can measure the laser signal at the i-th point by moving the receiving end. According to the Beer-Lambert law, the laser atmospheric attenuation model can be expressed as:

[0031]

[0032] Where η i and η0 represent the lens contamination errors of the mobile receiver at the final point i and the initial point 0, respectively. i and L0 represent the moving distance of the mobile receiver at the final point i and the initial point 0, respectively. σ is the extinction coefficient.

[0033] For traditional transmissometers, there are different lens contamination errors at the transmitting and receiving ends, namely, η i is not equal to η0, introducing a proportional error η in the calculated extinction coefficient i / η0. However, for our proposed system, since only one mobile receiver is used, the lens contamination error at the receiving end is considered to be constant, i.e., η i =η0. Therefore, compared with the traditional fixed transmission sensor at the receiving end, the contamination error can be offset, which is the biggest advantage of the mobile measurement method. In this case, it can be obtained:

[0034]

[0035] Therefore, the extinction coefficient σ is related to the final moving distance L i The relationship model is expressed as:

[0036]

[0037] Visibility can be calculated as:

[0038]

[0039] In the system proposed in this project, a high-precision extinction coefficient measurement cycle of more than 50m can be achieved through mobile high-precision measurement. The visibility measurement can be coupled with the lidar signal to improve the accuracy of the inversion measurement results.

[0040] like Figure 3 As shown, EMD is well-known for its adaptability and ability to handle nonlinear and non-stationary signals without the need for predefined basis functions. Therefore, an inversion calculation method based on EMD is proposed to calculate atmospheric visibility.

[0041] The signal acquired by the LiDAR is decomposed into multiple intrinsic mode functions using empirical mode decomposition. The LiDAR distance correction signal s0 is fitted using the upper and lower envelopes, and the mean of the upper and lower envelopes is calculated, recorded as m1. Subsequently, we subtract m1 from the signal s0 to obtain a new signal s1. If s1 satisfies the conditions:

[0042]

[0043] It is defined as the intrinsic mode function (IMF) c1; otherwise, it is set to the original signal and the initial step is entered again. (Δ is the value of the standard deviation coefficient) The iterative process s i -m i+1 =s i+1 Repeat K times until s i The condition described above is satisfied, called IMFc1, and we subtract c1 from the signal s0 to generate a new signal, which is reset to As a new iteration of the initial step. Then, c2 can be obtained. This iterative process continues until the signal s0 satisfies. We subtract c1 from the signal s0 to produce a new signal, which is reset to s1 or s0 as a new iteration of the initial step. Then, c2 can be obtained. Finally, the result of the empirical mode decomposition can be expressed as:

[0044]

[0045] By setting a weight coefficient ω for each IMF k , we can get the reconstruction equation of the original signal:

[0046]

[0047] By changing the weight coefficient ω k It can realize the denoising of the laser radar signal. Assuming that the first m weight coefficients are variable weight coefficients, the reconstruction equation can be expressed as follows. Assuming that the first m weight coefficients are variable weight coefficients, the reconstruction equation can be expressed as:

[0048]

[0049] High-precision visibility measurement results can be expressed in discrete form as The measurement points correspond to the measurement points of the laser radar, and their discrete intervals are equal to the distance resolution of the laser radar. Since the boundary values ​​of the laser radar correspond to the high-precision measurement results σ k , based on the Klett inversion formula, the reverse signal of the lidar extinction coefficient can be expressed as:

[0050]

[0051] Where q is a coefficient related to the laser radar wavelength, aerosol refractive index and particle size distribution, ranging from 0.67≤q≤1. l is the detection distance of the laser radar, l k yes The boundary distance corresponding to the measurement point. We can obtain the laser radar extinction coefficient inversion model σ′(ω1,ω2,…,ω m ,l). Based on the discrete values ​​of the high-precision measurement results σ, a least squares model was established. and the laser inversion model σ′(ω1,ω2,…,ω m ,l):

[0052]

[0053] When f(ω1,ω2,…,ω m ) takes the minimum value, the corresponding weight coefficient (ω1,ω2,…,ω m ) is the weight coefficient reconstructed after denoising. After denoising, the inversion model of the lidar signal and the extinction coefficient can be obtained through equations (8) and (9).

[0054] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A high-precision visibility measurement method combining a mobile transmissometer and a laser radar, characterized in that: The following steps are involved: S1. The mobile transmissometer measures the laser signals at different points by moving the receiving end. According to the Beer-Lambert law, the laser atmospheric attenuation model is established, and the influence of the lens contamination error is considered. Since only one mobile receiver is used, the lens contamination error at the receiving end can be considered constant, thus offsetting the contamination error. S2. LiDAR inversion calculation under coupled mobile transmissometer. The high-precision measurement results of the mobile transmissometer are used as clean samples and coupled with the LiDAR signal. The LiDAR signal is decomposed and denoised using the empirical mode decomposition method. Based on the measurement results of the mobile transmissometer and the Klett inversion formula, the extinction coefficient and visibility of the LiDAR are calculated.

2. The high-precision visibility measurement method combining a mobile transmissometer and a laser radar according to claim 1 is characterized in that: In S1, the mobile transmissometer includes a laser emitting unit, a light receiving unit, a slide rail unit, a trolley unit, and a control and data processing unit. The laser emitting unit includes a laser, an emitting optical path system, and an adjustment bracket. The laser expands the beam through the emitting optical path system and emits 532nm green light along the track direction. The divergence angle is less than 1.5mrad and the spot diameter is 2mm. The light receiving unit is composed of an optical chopper, a photodetector, a phase-locked amplifier, and a receiving optical system. The slide rail unit is composed of two 55-meter-long steel rails with a rail spacing of 0.35m and a height of 0.2m. The trolley unit is composed of a base plate, a car cover, a roller, a gear, a servo motor, a reducer, a programmable logic controller, a proximity sensor, and an inverter. A photoelectric receiving unit and a signal acquisition unit are placed on the base plate. The control and data processing unit includes an embedded industrial computer. The entire system adopts a wired transmission method.

3. The high-precision visibility measurement method combining a mobile transmissometer and a laser radar according to claim 1 is characterized in that: In S2, the laser radar includes a laser emitting unit, a light receiving unit and a signal detection and data acquisition unit. The laser emitting unit uses a diode-pumped Nd...YAG532nm laser as a light source, which is close to the 550nm that the human eye is most sensitive to. The laser beam emitted by the laser is coupled into the transmitting optical fiber through a fiber coupler, collimated and expanded, and then projected horizontally.

4. The high-precision visibility measurement method combining a mobile transmissometer and a laser radar according to claim 1 is characterized in that: The method for measuring visibility with a mobile transmissometer specifically comprises the following steps: (a) According to Beer-Lambert's law, the laser atmospheric attenuation model can be expressed as: where η i and η0 represent the lens contamination errors of the mobile receiver at the final point i and the initial point 0, respectively. i and L0 represent the moving distance of the mobile receiver at the final point i and the initial point 0, respectively, and σ is the extinction coefficient; (b) Since only one mobile receiver is used, the lens contamination error at the receiver can be considered constant, i.e., η i =η0, in this case we can get: (c) Extinction coefficient σ and final moving distance L i The relationship model between is expressed as: (d) Visibility can be calculated as:

5. The high-precision visibility measurement method combining a mobile transmissometer and a laser radar according to claim 4 is characterized in that: According to the high-precision measurement of the mobile transmissometer coupled with the lidar signal, an atmospheric visibility inversion calculation method based on empirical mode decomposition is proposed.

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