A method for measuring the fluctuations of atmospheric particle number density

Abstract

The present invention discloses a method for measuring the fluctuation of atmospheric particle number density, belonging to the technical field of optical detection, including: decomposing the refractive index into an average refractive index value and a refractive index fluctuation value; calculating the refractive index fluctuation value of the i-th frame; and calculating the particle number density fluctuation according to the relationship between the refractive index fluctuation value and the particle number density fluctuation. The method for measuring the fluctuation of atmospheric particle number density provided by the present invention solves the technical problems that turbulence in the prior art will cause the image received by the detector to be offset, jittered, and blurred.

Description

Technical Field

[0001] The present invention relates to a method for measuring the fluctuation of atmospheric particle number density, belonging to the technical field of optical detection. Background Art

[0002] Atmospheric turbulence is a random air movement condition. In the field of atmospheric optics, turbulence mainly refers to the random change of refractive index caused by the random change of local temperature and pressure in the atmosphere. When light passes through the atmosphere with uneven and randomly changing refractive index distribution, phenomena such as deflection and phase shift will occur, which have an inestimable impact on aspects such as atmospheric detection and optical imaging detection of aircraft, and will cause the images received by the detector to shift, jitter and blur. However, in fact, it is very difficult to separate the effects of temperature and pressure on the atmospheric refractive index respectively. Therefore, if the effects of temperature and pressure can be considered comprehensively, it can provide certain reference for studying the laws of atmospheric turbulence itself and the effects of the atmosphere in detection, communication and other aspects. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for measuring the fluctuation of atmospheric particle number density, so as to solve the technical problem that turbulence in the prior art will cause the images received by the detector to shift, jitter and blur.

[0004] To achieve the above purpose, the present invention is implemented by adopting the following technical solutions:

[0005] The present invention provides a method for measuring the fluctuation of atmospheric particle number density, including:

[0006] Decompose the refractive index into the average refractive index and the refractive index fluctuation value;

[0007] Calculate the refractive index fluctuation value of the i-th frame;

[0008] Calculate the particle number density fluctuation according to the relationship between the refractive index fluctuation value and the particle number density fluctuation;

[0009] Further, the decomposition of the refractive index into the average refractive index and the refractive index fluctuation value is expressed as:

[0010]

[0011] where n is the refractive index, is the average refractive index, and n' is the refractive index fluctuation value.

[0012] Further, the calculation of the refractive index fluctuation value of the i-th frame includes the following steps:

[0013] Calculate the variance of the deflection angle;

[0014] Obtain the structure constant according to the variance of the deflection angle;

[0015] Substitute the structure constant into the refractive index structure function to obtain the refractive index fluctuation value of the i-th frame.

[0016] Further, the calculation formula for the variance of the deflection angle is:

[0017]

[0018] where is the variance of the deflection angle, M is the total number of frames recorded within the total time, is the deflection angle on the corresponding frame image,

[0019] Further, the calculation formula for the structure constant is:

[0020]

[0021] where D is the diameter of the light beam on the first grating, E is the distance from the laser to the first grating, is the variance of the deflection angle.

[0022] Further, substituting the structure constant into the refractive index structure function to obtain the refractive index fluctuation value of the i-th frame includes the following steps:

[0023]

[0024] where D n (t) is the refractive index structure function, < > represents taking the time average of the parameters inside, n(t) and n(t - △t) represent the refractive indices at different times, △t represents the time interval, and v is the average wind speed during the measurement time.

[0025]

[0026]

[0027] where n′ i is the refractive index fluctuation value of the i-th frame.

[0028] Further, the relationship between the refractive index fluctuation value and the particle number density fluctuation is:

[0029]

[0030] where N' is the particle number density fluctuation, λ is the wavelength of the probing light, L represents the Loschmidt constant, A and B take the relevant parameters of air, and n' is the refractive index fluctuation value.

[0031] Further, the particle number density fluctuation is:

[0032]

[0033] Among them, N' is the particle number density fluctuation.

[0034] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0035] Calculating the particle number density fluctuation by introducing the Moiré tomography technology provides a theoretical reference for studying the laws of atmospheric turbulence itself and the influence of the atmosphere in aspects such as detection and communication, effectively avoiding phenomena such as image offset, jitter, and blurring received by the detector, and at the same time having the characteristics of real-time, stability, non-contact, and 3-D display. Description of the Drawings

[0036] Figure 1 is a flowchart of a method for measuring the fluctuation of atmospheric particle number density provided by an embodiment of the present invention;

[0037] Figure 2 is an experimental device for a method for measuring the fluctuation of atmospheric particle number density provided by an embodiment of the present invention;

[0038] Figure 3 is the Moiré fringe obtained in the experiment;

[0039] Figure 4 is a partial Moiré fringe intercepted;

[0040] Figure 5 is the deflection angle of the 900th frame, 1800th frame, 2700th frame, 3600th frame, 4500th frame, 5400th frame, 6300th frame, and 7200th frame;

[0041] Figure 6 is the situation of the particle number density fluctuation within 2 hours;

[0042] In the figure: 1. Laser; 2. Beam expanding and collimating system; 3. Measured atmosphere; 4. Ronchi grating; 5. Imaging lens; 6. Receiving screen; 7. Filter. Detailed Embodiments

[0043] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and cannot be used to limit the protection scope of the present invention.

[0044] Embodiment 1:

[0045] As Figure 1 shown, this embodiment discloses a method for measuring the fluctuation of atmospheric particle number density, and the present invention will be further described in detail below through specific implementation schemes:

[0046] S1: Decompose the refractive index into the average refractive index and the refractive index fluctuation value;

[0047] The decomposition of the refractive index into the average refractive index and the refractive index fluctuation value can be expressed as:

[0048]

[0049] where n is the refractive index, is the average refractive index, and n' is the refractive index fluctuation value.

[0050] S2: Calculate the refractive index fluctuation value of the i-th frame, including the following steps;

[0051] S21: Calculate the variance of the deflection angle;

[0052] The calculation formula for the variance of the deflection angle is:

[0053]

[0054] where, is the variance of the deflection angle, M is the total number of frames recorded within the total time, is the deflection angle on the corresponding frame image,

[0055] S22: Obtain the structure constant based on the variance of the deflection angle;

[0056] The calculation formula for the structure constant is:

[0057]

[0058] where D is the diameter of the light beam on the first grating, E is the distance from the laser to the first grating, is the variance of the deflection angle.

[0059] S23: Substitute the structure constant into the refractive index structure function to obtain the refractive index fluctuation value of the i-th frame;

[0060] The refractive index structure function is expressed as:

[0061]

[0062] where D n (t) is the refractive index structure function, < > represents taking the time average of the parameters inside, n(t) and n(t - △t) represent the refractive indices at different times, △t represents the time interval, and v is the average wind speed during the measurement time.

[0063] Substituting the structure constant and the variance of the calculated deflection angle into the refractive index structure function gives:

[0064]

[0065] Therefore, according to the deflection angle information of the i-th frame, the refractive index fluctuation value of the i-th frame can be obtained as follows:

[0066]

[0067] where n' i is the refractive index fluctuation value of the i-th frame.

[0068] S3: Calculate the particle number density fluctuation according to the relationship between the refractive index fluctuation value and the particle number density fluctuation;

[0069] The relational expression between the refractive index fluctuation value and the particle number density fluctuation is:

[0070]

[0071] where N' is the particle number density fluctuation, λ is the wavelength of the probing light, L represents the Loschmidt constant, A and B take the relevant parameters of air, and n' is the refractive index fluctuation value.

[0072] Substitute the refractive index fluctuation value of the i-th frame into the relational expression between the refractive index fluctuation value and the particle number density fluctuation to obtain the particle number density fluctuation:

[0073] The particle number density fluctuation is:

[0074]

[0075] where N' is the particle number density fluctuation.

[0076] The particle number density fluctuation calculated by introducing the Moiré tomography technology provides a theoretical reference for studying the laws of atmospheric turbulence itself and the influence of the atmosphere in aspects such as detection and communication. It not only effectively avoids the phenomena of image offset, jitter, and blurring received by the detector, but also has the characteristics of real-time, stability, non-contact, and 3-D display.

[0077] Example 2:

[0078] As Figure 2As shown, it is an experimental device, which includes a laser 1, a beam expanding and collimating system 2, the atmosphere to be measured 3, a Ronchi grating 4, an imaging lens 5, a receiving screen 6, and a filter 7. During the experimental measurement from 20:30 to 22:30 on October 24, 2021, the wavelength λ of the probing light of the laser 1 is 532 nm. The distance from the light output port of the laser 1 to the first grating is E = 2.07 m. In the experiment, the period of the two gratings is d = 1 / 50 mm, the spacing is Z = 0.04 m, and the diameter of the light spot on the first grating is D = 5 cm. In this experiment, it is set that the CCD collects Moiré fringes at a rate of 1 frame per second (i.e., △t = 1 s) and stores them in the computer. Finally, a total of 7200 frames (i.e., M in the first embodiment) are collected.

[0079] As Figure 3 shown, they are the Moiré fringes obtained in the experiment. Among them, (a) is the 1800th frame, (b) is the 3600th frame, (c) is the 5400th frame, and (d) is the 7200th frame. The same position is intercepted for all 7200 frames of pictures for the convenience of subsequent processing. The screenshots of the 1800th frame, 3600th frame, 5400th frame, and 7200th frame are shown in the following figure. It should be noted that we start from the dot position marked in Figure 2 and intercept a region of 360×360 pixels.

[0080] As Figure 4 shown, they are the intercepted partial Moiré fringes (i.e., a region of 360×360 pixels). Among them, (a) is the 1800th frame, (b) is the 3600th frame, (c) is the 5400th frame, and (d) is the 7200th frame. All the fringes in the intercepted parts of the 7200 frames of pictures are thinned, and 7200 groups of position data recorded in the experiment are obtained. On this basis, 7200 deflection angle data will be obtained, and the results are as Figure 4 shown, and the corresponding total time is 2 hours. For authenticity, Figure 5 the dots on it mark the deflection angles of the 900th frame, 1800th frame, 2700th frame, 3600th frame, 4500th frame, 5400th frame, 6300th frame, and 7200th frame.

[0081] During the experiment, the temperature and wind speed were measured synchronously with the Moiré tomography experiment, and 7200 groups of data were also recorded. The average temperature and average wind speed during the measurement time are and v = 0.33 m / s respectively. Based on the particle number density fluctuation we finally derived, the particle number density fluctuation distribution of the temperature during the above time can be calculated, as Figure 6As shown. Similarly, the particle number density fluctuation values at the 900th frame, 1800th frame, 2700th frame, 3600th frame, 4500th frame, 5400th frame, 6300th frame, and 7200th frame are marked in the figure. At the same time, in order to prove the reliability of our method, the measurement results of an anemometer were also used for comparison.

[0082] As Figure 6 shown, it is the particle number density fluctuation situation within 2 hours. Relevant theories and experimental results show that it is feasible to introduce Moiré tomography technology into the measurement of atmospheric particle number density fluctuations.

[0083] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0084] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the flows and / or blocks in the flowchart and / or block diagram can also be implemented. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0085] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means implements the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0086] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide means for implementing the functions specified in Figure 1 one process or multiple processes and / or blocksFigure 1 Steps of functions specified in one or more boxes.

[0087] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for measuring the fluctuations in the number density of atmospheric particles, characterized in that, Including: Decompose the refractive index into the average refractive index and the refractive index fluctuation value; Calculate the refractive index fluctuation value of the frame; Calculate the particle number density fluctuation according to the relationship between the refractive index fluctuation value and the particle number density fluctuation; The calculated refractive index fluctuation value of the nth frame includes the following steps: Calculate the variance of the deflection angle; Obtain the structure constant according to the variance of the deflection angle; Substitute the structure constant into the refractive index structure function to obtain the refractive index fluctuation value of the frame; The calculation formula for the variance of the deflection angle is: ； Among them, is the variance of the deflection angle, is the total number of frames recorded within the total time, , , …, is the deflection angle on the corresponding frame image, ; The calculation formula for the structure constant is: ； where D is the diameter of the light beam on the first grating, is the distance from the laser to the first grating, is the variance of the deflection angle; Substituting the structure constant into the refractive index structure function to obtain the refractive index fluctuation value of the frame, including the following steps: ； Among them, is the refractive index structure function, represents the time average of the parameters inside, and represent the refractive indices at different times, represents the time interval, is the average wind speed within the measurement time; ； , ； Among them, is the refractive index fluctuation value of the th frame; The relationship formula between the refractive index fluctuation value and the particle number density fluctuation is: ； Among them, is the particle number density fluctuation, is the wavelength of the probe light, represents the Loschmidt constant, and takes the relevant parameters of air, is the refractive index fluctuation value.

2. The method for measuring the fluctuation of atmospheric particle number density according to claim 1, wherein The decomposition of the refractive index into the average refractive index and the refractive index fluctuation value is expressed as: ； Among them, is the refractive index, is the average refractive index.

3. The method for measuring the fluctuation of atmospheric particle number density according to claim 1, wherein The particle number density fluctuation is: ； Among them, is the particle number density fluctuation.

Images