A method for measuring atmospheric temperature fluctuations

Abstract

The present invention discloses a method for measuring atmospheric temperature fluctuations, which uses a laser of a moiré tomography device to emit a collimated light beam to obtain moiré fringes; within the measurement time, the moiré fringes are continuously collected frame by frame, and local moiré fringes at the same position of each frame are intercepted; according to the displacement value of the local moiré fringes in time and the spacing of the moiré fringes, the deflection angle of the outgoing light beam after the collimated light beam enters the atmosphere is calculated; finally, the atmospheric refractive index fluctuation is calculated through the deflection angle of the outgoing light beam, and the atmospheric temperature fluctuation is calculated according to the atmospheric refractive index fluctuation. The present invention introduces the moiré tomography technology into the measurement of atmospheric temperature fluctuations, and provides a certain reference for studying the laws of atmospheric turbulence itself and the influence of the atmosphere on detection, communication and other aspects.

Description

Technical Field

[0001] The invention discloses a method for measuring atmospheric temperature fluctuations, and relates 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 changes in refractive index caused by random changes in local temperature and pressure in the atmosphere. When light passes through an atmosphere with uneven refractive index distribution and random changes, deflection, phase shift and other phenomena will occur, which have an important impact on atmospheric detection, aircraft optical imaging detection and other aspects, causing the image received by the detector to be offset, jittered and blurred. In addition, in atmospheric laser communications, the impact of atmospheric turbulence on laser transmission can sometimes seriously affect the performance of the communication system and even cause communication interruptions. These effects brought about by atmospheric turbulence are mainly caused by temperature fluctuations, so it is crucial to accurately measure atmospheric temperature fluctuations. Summary of the invention

[0003] The present invention aims at the defects in the above-mentioned background technology and provides a method for measuring atmospheric temperature fluctuations, which is simple and accurate.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows: a method for measuring atmospheric temperature fluctuations, comprising the following steps:

[0005] Step 1: Use the laser of the moiré tomography device to emit a collimated light beam to obtain moiré fringes on the light screen of the moiré tomography device;

[0006] Step 2: During the measurement time, continuously collect the moiré fringes on the light screen frame by frame, and intercept the local moiré fringes at the same position in each frame to obtain the displacement value of the local moiré fringes in time;

[0007] Step 3: Calculate the deflection angle of the outgoing light beam after the collimated light beam enters the atmosphere according to the temporal displacement value of the local moiré fringes and the spacing of the moiré fringes;

[0008] Step 4: Calculate the atmospheric refractive index fluctuations through the deflection angle of the outgoing light, and calculate the atmospheric temperature fluctuations based on the atmospheric refractive index fluctuations.

[0009] Furthermore, in step one, the moiré tomography device includes: a laser, a beam expansion and collimation system, two gratings, a first imaging lens, a filter, a second imaging lens and a light screen arranged in sequence from left to right along the laser incident direction, and the beam expansion and collimation system includes a first lens and a second lens arranged in sequence along the laser incident direction; a collimated light beam is emitted by a laser to obtain moiré fringes on the light screen.

[0010] Furthermore, in step 3, the calculation of the deflection angle of the outgoing light includes the following steps:

[0011] Perform coordinate system processing on each frame of intercepted local moiré fringes and record the coordinate position of the local moiré fringes;

[0012] Calculate the average position of local moiré fringes across all frames: e[i] is the average position of the stripes in the i-th frame, and N is the total number of frames;

[0013] Calculate the temporal displacement of the local moiré fringe of the i-th frame:

[0014] Calculate the deflection angle of the outgoing light corresponding to the local moiré fringe of the i-th frame:

[0015] Z represents the distance between the two gratings, d represents the grating period, and d m Represents the spacing between moiré fringes. The variation in spacing between adjacent moiré fringes of different frame numbers is negligible.

[0016] Furthermore, in step 4, calculating the atmospheric refractive index fluctuation by the deflection angle of the outgoing light, and calculating the atmospheric temperature fluctuation according to the atmospheric refractive index fluctuation specifically include the following steps:

[0017] Step 1: Calculate the structural constant that characterizes the severity of the random inhomogeneity of the atmospheric refractive index through the deflection angle of the outgoing light:

[0018] Where: D is the diameter of the collimated beam on the first grating, E is the transmission distance of the collimated beam in the atmosphere, is the variance of the deflection angle,

[0019] Refractive index structure function D n (t) describes the fluctuation of the atmospheric refractive index, the refractive index structure function D n (t) and refractive index structure constant The relationship can be expressed as:

[0020]

[0021] Where: n(t) represents the atmospheric refractive index at time t, n(t-Δt) represents the atmospheric refractive index at time (t-Δt),

[0022] Step 2: Calculate the atmospheric refractive index fluctuation:

[0023]

[0024]

[0025] 1≤i≤N

[0026] 1≤i≤N

[0027] Where Δt represents the time interval between two adjacent frames of moiré fringes, v is the average wind speed during the measurement period, and <> represents the time average of the parameters inside.

[0028] Step 3: Calculate the temperature fluctuation term:

[0029]

[0030] 1≤i≤N

[0031] Where: L represents the Rohemitian constant, L = 2.687 × 10 19 cm -3 , κ is the Boltzmann constant, λ is the wavelength of the detection light, A and B are constants related to the types of neutral particles in the atmospheric flow field, A and B are the relevant parameters of air, A = 2.871×10 -4 , B=1.628×10 -6 , is the average pressure in the measured area, is the average temperature of the measured area.

[0032] Furthermore, the local moiré fringes at the same position in each frame are intercepted, and the pixel size of the intercepted area is Q*Q, where Q is a positive integer.

[0033] Furthermore, the coordinate system processing of each frame of moiré fringes includes the following steps: binarization, thinning, bright fringes, coordinate selection of the origin position, the specific steps are processed by matlab, the rgb2gray function is used to first convert the fringe image into a grayscale image, the im2bw function is used for binarization, and the bwmorph function is used for thinning. The upper left corner of the screenshot is the origin, and the horizontal coordinates of the points on the curve are recorded for every pixel of the intercepted moiré fringes and the average is taken.

[0034] Beneficial effects: The present invention proposes a method for measuring atmospheric temperature fluctuations. By establishing the relationship between the atmospheric refractive index fluctuations and the deflection angle and combining the relationship between air temperature and refractive index, a relationship model between temperature fluctuations and the deflection angle is obtained, which provides feasibility for measuring atmospheric temperature fluctuations using moiré tomography technology. Compared with the existing temperature fluctuation measurement methods, the method provided by the present invention is easy to operate and has high precision, and can be used for large-scale, long-term, and systematic measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of the present invention;

[0036] Figure 2 It is a schematic diagram of the process of the present invention;

[0037] Figure 3 (a) is the moiré fringe diagram of the 1800th frame of this embodiment;

[0038] Figure 3 (b) is the moiré fringe diagram of the 3600th frame of this embodiment;

[0039] Figure 3 (c) is the moiré fringe pattern of the 5400th frame of this embodiment;

[0040] Figure 3 (d) is the moiré fringe pattern of the 7200th frame of this embodiment;

[0041] Figure 4 (a) is a local moiré fringe diagram of the 1800th frame of this embodiment;

[0042] Figure 4 (b) is a local moiré fringe diagram of the 3600th frame of this embodiment;

[0043] Figure 4 (c) is a local moiré fringe diagram of the 5400th frame of this embodiment;

[0044] Figure 4 (d) is a local moiré fringe diagram of the 7200th frame of this embodiment;

[0045] Figure 5 (a) is a local moiré fringe refinement diagram of the 1800th frame of this embodiment;

[0046] Figure 5 (b) is a local moiré fringe refinement diagram of the 3600th frame of this embodiment;

[0047] Figure 5 (c) is a local moiré fringe refinement image of the 5400th frame of this embodiment;

[0048] Figure 5 (d) is a local moiré fringe refinement diagram of the 7200th frame of this embodiment;

[0049] Figure 6 is a schematic diagram of deflection angle data of this embodiment;

[0050] Figure 7 Schematic diagram of temperature fluctuation in this embodiment. DETAILED DESCRIPTION

[0051] The implementation of the technical solution is further described in detail below in conjunction with the accompanying 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.

[0052] like Figure 1 The embodiment shown: This embodiment first builds Figure 1 The moiré tomography device shown in the figure comprises: a laser, a beam expansion and collimation system, two Ronchi gratings, a first imaging lens, a filter, a second imaging lens and a light screen arranged in sequence from left to right along the laser incident direction, wherein the beam expansion and collimation system comprises a first lens and a second lens arranged in sequence along the laser incident direction; Moiré fringes are obtained on the light screen by using the interference of the two Ronchi gratings on the light beam, and the Moiré fringes on the light screen are collected by using a CCD and stored in a computer;

[0053] The wavelength of the laser used in the experiment is 532nm (the model of the laser is LSR532NL-400), the distance between the lens 3 and the second Ronchi grating 6 is 85cm (E=85cm), the focal lengths of the first and second imaging lenses are 30cm, the period of the two Ronchi gratings is d=1 / 20mm, and the spacing is Z=0.3m; the CCD is set to collect the moiré fringes on the light screen at a rate of 1 frame / second (i.e., Δt=1s) and store them in the computer. The model of the CCD is MER-125-30UC, and finally N=7200 frames of moiré fringes are collected (a total of 2 hours);

[0054] like Figure 2 An embodiment shown, a method for measuring atmospheric temperature fluctuations, comprises the following steps:

[0055] Step 1: Use Figure 1 The laser of the moiré tomography device shown emits a collimated light beam, and moiré fringes are obtained on the light screen of the moiré tomography device;

[0056] Step 2: During the measurement time, continuously collect the moiré fringes on the light screen frame by frame, and intercept the local moiré fringes at the same position in each frame to obtain the displacement value of the local moiré fringes in time;

[0057] Step 3: Calculate the deflection angle of the outgoing light beam after the collimated light beam enters the atmosphere according to the temporal displacement value of the local moiré fringes and the spacing of the moiré fringes;

[0058] Step 4: Calculate the atmospheric refractive index fluctuations through the deflection angle of the outgoing light, and calculate the atmospheric temperature fluctuations based on the atmospheric refractive index fluctuations.

[0059] In step 3, the calculation of the deflection angle of the outgoing light includes the following steps:

[0060] like Figure 3As shown in (a), (b), (c), and (d), the moiré fringe patterns of the 1800th, 3600th, 5400th, and 7200th frames are selected for processing; and the areas with a pixel size of 320*320 are cut down and to the right from the dot position, respectively, to form the following Figure 4 (a), (b), (c), and (d) show the screenshots of the 1800th, 3600th, 5400th, and 7200th frames of each group; and the captured part of the moiré fringe image is binarized and thinned, and the position of the bright fringe is recorded. The thinned fringe is as follows: Figure 5 As shown in (a), (b), (c) and (d);

[0061] Perform coordinate system processing on each frame of intercepted local moiré fringes and record the coordinate position of the local moiré fringes;

[0062] In this embodiment, the position data of 7200 groups of bright stripes are processed as follows to obtain 7200 deflection angle data.

[0063] Calculate the average position of local moiré fringes across all frames: e[i] is the position of the local moiré fringe in the i-th frame, and N is the total number of frames;

[0064] Calculate the temporal displacement of the local moiré fringe of the i-th frame:

[0065] Calculate the deflection angle of the outgoing light corresponding to the local moiré fringe of the i-th frame:

[0066] Z represents the distance between the two gratings, d represents the grating period, and d m Indicates the moiré fringe spacing.

[0067] In step 4, the calculation of the atmospheric refractive index fluctuation by the deflection angle of the outgoing light and the calculation of the atmospheric temperature fluctuation according to the atmospheric refractive index fluctuation specifically include the following steps:

[0068] Step 1: Calculate the structural constant that characterizes the severity of the random inhomogeneity of the atmospheric refractive index through the deflection angle of the outgoing light:

[0069] Where: D is the diameter of the collimated beam on the first grating, E is the transmission distance of the collimated beam in the atmosphere, is the variance of the deflection angle,

[0070] Refractive index structure function D n (t) describes the fluctuation of the atmospheric refractive index, the refractive index structure function D n (t) and refractive index structure constant The relationship can be expressed as:

[0071]

[0072] Where: n(t) represents the atmospheric refractive index at time t, n(t-Δt) represents the atmospheric refractive index at time (t-Δt),

[0073] Step 2: Calculate the atmospheric refractive index fluctuation:

[0074]

[0075]

[0076] 1≤i≤N

[0077] 1≤i≤N

[0078] Where Δt represents the time interval between two adjacent frames of moiré fringes, v is the average wind speed during the measurement period, and <> represents the time average of the parameters inside.

[0079] Step 3: Calculate the temperature fluctuation term:

[0080]

[0081] 1≤i≤N

[0082] Where: L represents the Rohemitian constant, L = 2.687 × 10 19 cm -3 , κ is the Boltzmann constant, λ is the wavelength of the detection light, A and B are constants related to the types of neutral particles in the atmospheric flow field, A and B are the relevant parameters of air, A = 2.871×10 -4 , B=1.628×10 -6 , is the average pressure in the measured area, is the average temperature of the measured area.

[0083] In this embodiment, the deflection angle results of the 900th frame, 1800th frame, 2700th frame, 3600th frame, 4500th frame, 5400th frame, 6300th frame and 7200th frame are selected as follows: Figure 6 (the corresponding total time is 2 hours); the hollow points in the figure mark the deflection angle data of the 900th frame, 1800 frame, 2700 frame, 3600 frame, 4500 frame, 5400 frame, 6300 frame and 7200 frame.

[0084] The pressure in this embodiment is one atmosphere. The anemometer measures wind speed synchronously, and the Mohr chromatography device measures temperature synchronously, and also records 7200 sets of data; the average temperature and average wind speed during the measurement period are and <v>= 0.29m / s, the diameter of the beam on the first grating is D = 0.05m. Based on the theoretical basis formula we finally derived 1≤i≤N, the temperature fluctuation distribution within the above time can be calculated.

[0085] like Figure 7 As shown, similarly, the temperature fluctuations corresponding to the 900th frame, 1800 frame, 2700 frame, 3600 frame, 4500 frame, 5400 frame, 6300 frame and 7200 frame are marked with hollow points in the figure, and the solid points mark the results of the temperature fluctuations measured by the anemometer at the corresponding time.

[0086] from Figure 7 The temperature fluctuations within 2 hours (h) are given, and it can be seen that the temperature fluctuations measured by Moiré tomography are consistent with the results measured by the anemometer. The relevant theoretical and experimental results show that it is feasible to introduce Moiré tomography technology into the measurement of atmospheric temperature fluctuations.

[0087] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.< / v>

Claims

1. A method for measuring atmospheric temperature fluctuations, characterized in that: The following steps are involved: Moiré fringes are obtained by emitting a collimated beam from the laser of a moiré tomography device; During the measurement time, the moiré fringes are collected continuously frame by frame, and the local moiré fringes at the same position in each frame are intercepted; According to the displacement value of the local moiré fringes in time and the spacing of the moiré fringes, the deflection angle of the outgoing light beam after the collimated light beam enters the atmosphere is calculated; The atmospheric refractive index fluctuations are calculated by the deflection angle of the outgoing light, and the atmospheric temperature fluctuations are calculated based on the atmospheric refractive index fluctuations; The moiré tomography device comprises: a laser, a beam expansion and collimation system, two gratings, a first imaging lens, a filter, a second imaging lens and a light screen arranged in sequence from left to right along the laser incident direction, wherein the beam expansion and collimation system comprises a first lens and a second lens arranged in sequence along the laser incident direction; a collimated beam is emitted by the laser to obtain moiré fringes on the light screen; The calculation of the deflection angle of the outgoing light includes the following steps: Perform coordinate system processing on each frame of intercepted local moiré fringes and record the coordinate position of the local moiré fringes; Calculate the average position of local moiré fringes across all frames: e[i] is the average position of the local moiré fringes in the i-th frame, and N is the total number of frames; Calculate the temporal displacement of the local moiré fringe of the i-th frame: Calculate the deflection angle of the outgoing light corresponding to the local moiré fringe of the i-th frame: Z represents the distance between the two gratings, d represents the grating period, and d m Indicates the moiré fringe spacing.

2. A method for measuring atmospheric temperature fluctuations according to claim 1, characterized in that: The method of calculating the atmospheric refractive index fluctuation by the deflection angle of the outgoing light and calculating the atmospheric temperature fluctuation according to the atmospheric refractive index fluctuation specifically comprises the following steps: Step 1: Calculate the structural constant that characterizes the severity of the random inhomogeneity of the atmospheric refractive index through the deflection angle of the outgoing light: Where: D is the diameter of the collimated beam on the first grating, E is the transmission distance of the collimated beam in the atmosphere, is the variance of the deflection angle, Step 2: Calculate the atmospheric refractive index fluctuation term: Where Δt represents the time interval between two adjacent frames of moiré fringes, and v is the average wind speed during the measurement time; Step 3: Calculate the temperature fluctuation term: Where: L represents the Rohemitian constant, L = 2.687 × 10 19 cm -3 , κ is the Boltzmann constant, λ is the wavelength of the collimated beam, A = 2.871 × 10 -4 , B=1.628×10 -6 , is the average pressure in the measured area, is the average temperature of the measured area.

3. A method for measuring atmospheric temperature fluctuations according to claim 1, characterized in that: The local moiré fringes at the same position in each frame are intercepted, and the pixel size of the intercepted area is Q*Q, where Q is a positive integer.

4. A method for measuring atmospheric temperature fluctuations according to claim 1, characterized in that: The coordinate system processing includes: binarizing and thinning the intercepted moiré fringes, recording the horizontal coordinate position of the point on the bright fringes for every other pixel, and taking the average value of all the recorded horizontal coordinate positions, which is represented by e[i].

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