CN102607798B - Device and method for measuring inner scale of atmospheric turbulence - Google Patents

Abstract

The invention discloses a device and a method for measuring the inner scale of atmospheric turbulence. The device comprises a laser emission unit, a laser receiving and photoelectric conversion unit, a data acquisition unit and a data processing and analysis unit. The method comprises the following steps of: simulating a geometrical approximation condition after plane waves are transmitted through local uniform isotropic atmospheric turbulence, selecting a distorted wave plane after laser is emitted, imaging the distorted wave plane onto a position sensitive detector by using a pinhole diaphragm, converting a position coordinate signal and a relative light intensity signal into digital signals by using an analogue/digital (A/D) converter, and performing acquisition processing and analysis to obtain a value of the inner scale of the atmospheric turbulence. The device is simple; and the method is simple in calculation, high in calculation precision and low in uncertainty.

Description

Device and the measuring method of yardstick in a kind of measurement of Atmospheric Turbulence

Technical field

The invention belongs to yardstick field of measuring technique in atmospheric turbulence, relate to device and the measuring method of yardstick in a kind of measurement of Atmospheric Turbulence.

Background technology

In turbulent atmosphere optical research, yardstick l in atmospheric turbulence ₀be a basic parameter that characterizes atmospheric turbulence characteristic, play very important effect in the effect study of Laser Atmospheric Transmission, in the time of analyse atmos turbulence characteristic and modeling, it is the parameter that must provide simultaneously.

Yardstick l in atmospheric turbulence both at home and abroad ₀research on measuring technique aspect carried out a lot of work, according to adopting the difference of technology, be mainly the measurement based on light intensity flicker.Its ultimate principle is to utilize the propagation in atmosphere theory of laser, laser beam is in propagation in atmosphere process, due to the impact of turbulent flow, the fluctuating of laser beam intensity and phase place will be caused, the characteristic of turbulent flow also will be contained among these statistical informations simultaneously, therefore just can be derived from the interior yardstick l of turbulent flow by measuring these optical correlation amounts ₀value.

The countries such as Germany are the achievement based on Laser Atmospheric Transmission problem is studied from last century the seventies, so far developed the measuring method of a series of atmospheric turbulence parameter, in the reliability of method and degree of ripeness, constantly get a promotion, all direct yardstick l in measurement of Atmospheric Turbulence such as the small-bore scintiloscope of producing as German Scintec company, Dutch Kipp & zonen company ₀.At home, Chinese Academy of Sciences's Anhui ray machine has also been carried out the research work of some atmospheric turbulence parameter measurement aspects, some achievements are obtained, Ma Xiaoshan, red legend are got over, the large-caliber laser isotope of Rao Ruizhong development is mainly used to measure air index textural constant, if be equipped with two cover transmitting or receiving devices, the interior yardstick of all right measurement of Atmospheric Turbulence or the laterally value of wind speed.

Summary of the invention

The problem that the present invention solves is to provide device and the measuring method of yardstick in a kind of measurement of Atmospheric Turbulence, and this device adopts helium-neon laser as transmitting illuminant, measure with Position-Sensitive Detector, and its computational accuracy is high, and uncertainty is little.

The present invention is achieved through the following technical solutions:

A device for yardstick in measurement of Atmospheric Turbulence, comprising:

Laser emission element, launches the collimated laser beam through expanding;

Laser pick-off and photoelectric conversion unit, receive the laser through atmospheric turbulence transmission, and by the corrugated of the distortion in the laser receiving by the imaging of aperture device, then be incident on the photosurface of Position-Sensitive Detector after reflecting by catoptron; Position-Sensitive Detector carries out opto-electronic conversion, obtains the relative light intensity signal of hot spot on photosurface, the simulating signal of position signalling, and by analog signal output to data acquisition unit;

Data acquisition unit comprises converter and data collecting card, and converter is converted to digital signal by simulating signal and is sent to data collecting card, and data collecting card exports data processing and analytic unit to;

Data processing and analytic unit, analyze arrival angle fluctuation and the light intensity flicker of light beam after atmospheric turbulence transmission, obtains scale-value in the atmospheric turbulence on Laser Transmission path by computing.

Described laser emission element comprises He-Ne Lasers transmitter and parallel beam expand device.

Little aperture apparatus in described laser pick-off and photoelectric conversion unit is aperture, before aperture, be provided with the attenuator that same optical axis is placed, after aperture, be provided with one group of catoptron, on the reflected light path of catoptron, be provided with Position-Sensitive Detector, the below of Position-Sensitive Detector is provided with scale.

Described laser pick-off and photoelectric conversion unit are provided with optical filter between aperture and catoptron.

One group of described catoptron comprises two catoptrons staggered relatively, the light path parallel of its incident light being sent by aperture and the light path of emergent light that reflexes to Position-Sensitive Detector.

Described aperture to the optical path distance of Position-Sensitive Detector is d ₁, d ₁round numbers numerical value.

The converter of described data acquisition unit is A/D converter, and A/D converter is converted to digital signal by simulating signal and is sent to data collecting card.

Described laser emission element and laser pick-off and photoelectric conversion unit are placed with optical axis opposite.

A method for yardstick in measurement of Atmospheric Turbulence, comprises the following steps:

1) when laser beam is after the transmission of local uniformity isotropy atmospheric turbulence, L < < l under geometric approximation condition ₀ ²/ λ, has following calculating formula:

$<{\mathrm{\&alpha;}}^2>=3.28C_n^{2}L{l}_0^{-1/3}---\left(1\right)$

${\mathrm{\&sigma;}}_I^2=12.8C_n^2{L}^3{l}_0^{-7/3}---\left(2\right)$

Wherein, L is beam Propagation path distance, and α is the angle of arrival, < α ²> is all sides of arrival angle fluctuation, σ _i ²for light intensity scintillation index;

2) carrying out yardstick l in atmospheric turbulence ₀measurement time, launch laser beam by laser emission element, laser beam is received by laser pick-off and photoelectric conversion unit through atmospheric turbulence to be measured, and reflexes to Position-Sensitive Detector by pinhole imaging system and catoptron, and aperture to the optical path distance of Position-Sensitive Detector is d ₁, read d by scale ₀;

Beam Propagation path distance L is the distance of generating laser to aperture, and aperture is to the distance d=d of Position-Sensitive Detector ₁+ d ₀;

α by Position-Sensitive Detector one-tenth light spot image mass center depart from the distance of mean place and the aperture ratio of distances constant value to Position-Sensitive Detector photosurface;

And α, < α ²> is calculated as follows:

$\mathrm{\&alpha;}=\frac{\sqrt{{(x-x_0)}^2+{(y-y_0)}^2}}{d}---\left(3\right)$

${\mathrm{\&sigma;}}_I^2=\frac{<I^2>-{<I>}^2}{{<I>}^2}---\left(4\right)$

Wherein, x, y are respectively and on Position-Sensitive Detector, become light spot image mass center physical location, x ₀, y ₀be respectively and on Position-Sensitive Detector, become light spot image mass center mean place, d is the distance of aperture to Position-Sensitive Detector, I is the relative light intensity signal numerical value of Position-Sensitive Detector output, and <I> is the assembly average of the relative light intensity signal of Position-Sensitive Detector output;

3) by being set, sampling rate and sample number determine yardstick l in calculating atmospheric turbulence ₀frequency after, triggering collection signal, Position-Sensitive Detector gathers the signal on the relative intensity signal of the hot spot after imaging and x, Gong San road, y both direction position;

Every collection one frame of data acquisition unit is converted into digital signal and is saved in internal memory, after the full sample number of setting of collection, does statistical calculation one time;

4) data processing and analytic unit calculate the arrival angle fluctuation < α of sample value ²> and light intensity scintillation index σ _i ²data, and calculate yardstick l in atmospheric turbulence by following formula ₀:

$l_0=1.975L{\left(\frac{{<\mathrm{\&alpha;}}^2>}{{\mathrm{\&sigma;}}_I^2}\right)}^{12}.$

Described d ₀be set to: in the time that aperture to the distance of Position-Sensitive Detector is 1m, by d ₀value be set to 0m, along the direction d of light transmission ₀for on the occasion of, be negative value in face of the direction of light transmission;

Sampling rate be set to be not less than 300Hz, sample number is for being not less than 3000.

Compared with prior art, the present invention has following useful technique effect:

The device and method of the interior yardstick of measurement of Atmospheric Turbulence provided by the invention, accepts by after the laser through atmospheric turbulence, reflects such light path its arrival angle fluctuation of detection acquisition < α is set through pinhole imaging system, mirror ²> and light intensity scintillation index α data, then by yardstick l in these two calculation of parameter atmospheric turbulences ₀, its device is simple, and calculating is succinct and computational accuracy is high, and uncertainty is little; And the instrument of the interior yardstick of existing measurement of Atmospheric Turbulence generally carrys out the value of yardstick in inversion reckoning atmospheric turbulence by light intensity scintillation effect, its precision can be affected, and uncertainty of measurement is larger.Be applicable to atmospheric science research, and the field such as uranology, atmospheric optics, military affairs.

The device of yardstick in measurement of Atmospheric Turbulence provided by the invention, laser beam, after atmospheric turbulence transfers to receive window, decays once through attenuator, and energy greatly reduces, and this has just been avoided damaging the possibility of Position-Sensitive Detector; The corrugated of distortion is by after aperture, carry out catoptric imaging on the photosurface of Position-Sensitive Detector through catoptron, and optical filter can reduce the impact of parasitic light on measured value, thereby improve to-noise ratio, the effect of two reflecting optics is to increase reduced volume on the basis of light path.

Use the instrument of yardstick in existing measurement of Atmospheric Turbulence mostly only to measure the fluctuating of light intensity with photomultiplier (PMT), do not consider the impact of corrugated phase place; If utilize CCD camera to measure the random variation of facula mass center, need a large amount of reading images gray-scale values, will inevitably affect computing velocity.And the Position-Sensitive Detector only using in the present invention can directly provide position signalling and relative light intensity signal simultaneously, and sampling rate is high, has saved internal memory, has reduced the requirement to computing machine simultaneously.

Brief description of the drawings

Fig. 1 is the structural representation of device of the present invention;

Wherein: 1 is laser emission element, 11 is helium-neon laser, and 12 is parallel beam expand device;

2 is laser pick-off and photoelectric conversion unit, and 21 is attenuator, and 22 is aperture, and 23 is optical filter, and 24,25 is catoptron, and 26 is scale, and 27 is Position-Sensitive Detector;

3 is data acquisition unit, and 31 is A/D converter, and 32 is data collecting card;

4 is data processing and analytic unit, and 41 is computing machine;

Fig. 2 is the schematic flow sheet of detection method of the present invention;

Fig. 3 is dimensional variation result figure in detected atmospheric turbulence under different wind speed condition of different temperatures.

Embodiment

The invention provides device and the measuring method of yardstick in a kind of measurement of Atmospheric Turbulence, simulation plane wave is through the geometric approximation condition of local uniformity isotropy atmospheric turbulence transmission, the corrugated that after Emission Lasers, pinhole diaphragm is chosen distortion is imaged on Position-Sensitive Detector, its position coordinates signal and relative light intensity signal are converted to digital signal by A/D converter, through acquisition process and analysis, obtain the value of yardstick in atmospheric turbulence.Below in conjunction with specific embodiment and accompanying drawing, the present invention is described in further detail, and the explanation of the invention is not limited.

Referring to Fig. 1, the device of yardstick in measurement of Atmospheric Turbulence provided by the invention, comprising: laser emission element 1, laser pick-off and photoelectric conversion unit 2, data acquisition unit 3, data processing and analytic unit 4, wherein:

Laser emission element, launches the laser through atmospheric turbulence;

Laser pick-off and photoelectric conversion unit, place with optical axis with laser emission element, receive the laser through atmospheric turbulence, and by the imaging of aperture device, (laser is after atmospheric turbulence transmission by the corrugated of the distortion in the laser receiving, because the impact of atmospheric turbulence, the corrugated of laser beam produces distortion), then reflex to Position-Sensitive Detector by catoptron;

Position-Sensitive Detector carries out opto-electronic conversion, obtain the relative light intensity signal of hot spot on photosurface, the simulating signal of position signalling (totally 3 road signals: the position signalling of light intensity signal, x, y both direction), and by analog signal output to data acquisition unit;

Data acquisition unit comprises converter and data collecting card, and converter is converted to digital signal by simulating signal (3 tunnel) and is sent to data collecting card, and data collecting card exports data processing and analytic unit to;

Data processing and analytic unit, arrival angle fluctuation and the light intensity flicker of analyzing light beam after atmospheric turbulence transmission obtain scale-value in the atmospheric turbulence on light transmission path by computing.

Concrete: laser emission element 1 comprises He-Ne Lasers transmitter 11 and parallel beam expand device 12, the centre wavelength that He-Ne Lasers transmitter 11 is exported is 632.8nm, output power 30mW, beam diameter 0.65mm, there is volume little, lightweight, be convenient to integrated advantage, it is 10 that the parallel beam expand device 12 configuring expands multiple, and the light beam after this parallel beam expand device expands can be considered plane wave.

Laser pick-off and photoelectric conversion unit 2 comprise attenuator 21, the aperture 22 that same optical axis is placed, after aperture 22, be provided with one group of catoptron 24,25, on the reflected light path of catoptron, be provided with Position-Sensitive Detector 27, the below of Position-Sensitive Detector 27 is provided with scale 26;

Further, between aperture 22 and catoptron 24,25, be provided with optical filter 23; Laser beam, after atmospheric turbulence transfers to receive window, decays once through attenuator 21 (neutral filter) like this, and energy greatly reduces, and this has just been avoided damaging the possibility of Position-Sensitive Detector 27;

The corrugated of distortion, by after aperture 22, is reflected through catoptron 24,25: two catoptrons 24,25 staggered relatively, the light path parallel of its incident light being sent by aperture and the light path of emergent light that reflexes to Position-Sensitive Detector; Then be imaged on the photosurface of Position-Sensitive Detector, and optical filter 23 (narrow-band interference) can reduce the impact of parasitic light on measured value, thereby improve to-noise ratio, the effect of two reflecting optics is to increase reduced volume on the basis of light path.

Aperture is to the distance d=d of Position-Sensitive Detector ₁+ d ₀, aperture to the optical path distance of Position-Sensitive Detector is d ₁, read d by scale ₀; Wherein for the ease of calculating, in the time that aperture to the distance of Position-Sensitive Detector is 1.0m, by d ₀value be set to 0.0m, along the direction d of light transmission ₀for on the occasion of, be negative value in face of the direction of light transmission.

Aperture to the optical path distance of Position-Sensitive Detector is: the distance d of aperture to the optical path distance+catoptron 24 of catoptron 24 to catoptron 25 ₂the distance of+catoptron 25 is to the distance d of Position-Sensitive Detector 27 ₃; For ease of calculating, first three items distance and can be designed to 1.0m,

Aperture is to the distance d=1.0m ± d of Position-Sensitive Detector ₀;

Data acquisition unit 3 comprises A/D converter 31 and data collecting card 32, A/D converter 31 is by simulating signal (2 road position coordinates signal x, y and 1 road relative light intensity signal, amount to 3 tunnel simulating signals) be converted to digital signal and be sent to data collecting card, and export data processing and analytic unit 4 to;

The computing of data processing and analytic unit 4 is specifically undertaken by computing machine 41.

The method of yardstick in measurement of Atmospheric Turbulence, undertaken by following steps:

1) when laser beam is after the transmission of local uniformity isotropy atmospheric turbulence, at geometric approximation condition (L < < l ₀ ²/ λ) under, there is following calculating formula:

$<{\mathrm{\&alpha;}}^2>=3.28C_n^{2}L{l}_0^{-1/3}---\left(1\right)$

${\mathrm{\&sigma;}}_I^2=12.8C_n^2{L}^3{l}_0^{-7/3}---\left(2\right)$

Wherein, L is beam Propagation path distance, and α is the angle of arrival, is defined as the distance that becomes light spot image mass center to depart from mean place on Position-Sensitive Detector and the aperture ratio of distances constant value to Position-Sensitive Detector photosurface, < α ²> is all sides of arrival angle fluctuation, σ _i ²for light intensity scintillation index;

2) carrying out yardstick l in atmospheric turbulence ₀measurement time, launch laser beam by laser emission element, laser beam is received by laser pick-off and photoelectric conversion unit through atmospheric turbulence to be measured, and reflexes to Position-Sensitive Detector by pinhole imaging system and catoptron, and aperture to the optical path distance of Position-Sensitive Detector is d ₁, read d by scale ₀;

Beam Propagation path distance L is the distance of generating laser to aperture, and aperture is to the distance d=d of Position-Sensitive Detector ₁+ d ₀;

And α, < α ²> is calculated as follows:

$\mathrm{\&alpha;}=\frac{\sqrt{{(x-x_0)}^2+{(y-y_0)}^2}}{d}---\left(3\right)$

${\mathrm{\&sigma;}}_I^2=\frac{<I^2>-{<I>}^2}{{<I>}^2}---\left(4\right)$

Wherein, x, y are respectively and on Position-Sensitive Detector, become light spot image mass center physical location, x ₀, y ₀be respectively that on Position-Sensitive Detector, to become light spot image mass center mean place, d be the distance of aperture to Position-Sensitive Detector, <...> represents statistical average; I is the relative light intensity signal numerical value of Position-Sensitive Detector output, and <I> is the assembly average of the relative light intensity signal of Position-Sensitive Detector output;

3) by being set, sampling rate and sample number determine yardstick l in calculating atmospheric turbulence ₀frequency after, triggering collection signal, Position-Sensitive Detector gathers the signal on the relative intensity signal of the hot spot after imaging and x, Gong San road, y both direction position;

Every collection one frame of data acquisition unit is converted into digital signal and is saved in internal memory, after the full sample number of setting of collection, does statistical calculation one time;

Concrete: referring to Fig. 2, first sampling rate to be set, sample number, transmission range L, and the parameter such as image-forming range d; Typical parameters is that sampling rate is not less than 300Hz, and sample number is not less than 3000, and transmission range L is 1.0～10.0m, and image-forming range d is 1.0m.Triggering collection signal immediately after setting completed, after triggering collection signal, with sampling rate 300Hz, sample number 3000 is example, within every 10 seconds, calculates the value of yardstick in an atmospheric turbulence;

When triggering collection signal, Position-Sensitive Detector receives after the hot spot of imaging, A/D converter starts to gather the relative intensity signal of hot spot, position signalling (x, y both direction) totally 3 tunnels, control 3 A/D converters and synchronously change, until A/D stores after converting, every collection one frame is converted into digital signal and is saved in internal memory; If do not arrive the sample number arranging, gather, until do statistical calculation one time after reaching 3000 sample numbers of collection always.

4) data processing and analytic unit calculate the arrival angle fluctuation < α of sample value ²> and light intensity scintillation index σ _i ²data, and calculate yardstick l in atmospheric turbulence by following formula ₀:

$l_0=1.975L{\left(\frac{{<\mathrm{\&alpha;}}^2>}{{\mathrm{\&sigma;}}_I^2}\right)}^{1/2}.$

After calculating the interior yardstick of one group of atmospheric turbulence, releasing memory, conversion and the calculating of preparing next group.Model experiment testing result shown in Figure 3, wherein horizontal ordinate is the horizontal wind speed perpendicular to beam Propagation direction, and unit is m/s, and ordinate is yardstick in atmospheric turbulence, and unit is mm.Curve in this figure be atmospheric temperature in the time of 25 DEG C, yardstick is with the situation of change of wind speed in atmospheric turbulence.Can find out, in atmospheric turbulence, yardstick numerical value, generally between 2～3.5mm, has good consistance with the representative value of real atmosphere; And along with the increase of wind speed, in atmospheric turbulence, yardstick reduces, and meets the Changing Pattern of yardstick in atmospheric turbulence.The presentation of results of Fig. 3 the rationality of yardstick in the atmospheric turbulence of surveying.

Claims (9)

1. a device for yardstick in measurement of Atmospheric Turbulence, is characterized in that, comprising:

Laser emission element (1), launches the collimated laser beam through expanding;

Laser pick-off and photoelectric conversion unit (2), receive the laser through atmospheric turbulence transmission, and by the corrugated of the distortion in the laser receiving by the imaging of aperture device, then be incident on the photosurface of Position-Sensitive Detector after reflecting by catoptron; Position-Sensitive Detector carries out opto-electronic conversion, obtains the relative light intensity signal of hot spot on photosurface, the simulating signal of position signalling, and by analog signal output to data acquisition unit;

Described little aperture apparatus is aperture (22); aperture (22) is provided with the attenuator (21) that same optical axis is placed before; aperture (22) is provided with one group of catoptron afterwards; on the reflected light path of catoptron, be provided with Position-Sensitive Detector (27), the below of Position-Sensitive Detector is provided with scale (26);

Data acquisition unit comprises converter and data collecting card (3), and converter is converted to digital signal by simulating signal and is sent to data collecting card, and data collecting card exports data processing and analytic unit to;

Data processing and analytic unit (4), analyze arrival angle fluctuation and the light intensity flicker of light beam after atmospheric turbulence transmission, obtains scale-value in the atmospheric turbulence on Laser Transmission path by computing.

2. the device of yardstick in a kind of measurement of Atmospheric Turbulence as claimed in claim 1, is characterized in that, described laser emission element (1) comprises He-Ne Lasers transmitter (11) and parallel beam expand device (12).

3. the device of yardstick in a kind of measurement of Atmospheric Turbulence as claimed in claim 1, is characterized in that, described laser pick-off and photoelectric conversion unit (2) are provided with optical filter (23) between aperture (22) and catoptron.

4. the device of yardstick in a kind of measurement of Atmospheric Turbulence as claimed in claim 1, it is characterized in that, one group of described catoptron comprises two catoptrons staggered relatively (24,25), the light path of its incident light being sent by aperture and the light path parallel of emergent light that reflexes to Position-Sensitive Detector.

5. the device of yardstick in a kind of measurement of Atmospheric Turbulence as claimed in claim 1, is characterized in that, described aperture (22) is d1 to the optical path distance of Position-Sensitive Detector (27), d1 round numbers numerical value.

6. the device of yardstick in a kind of measurement of Atmospheric Turbulence as claimed in claim 1, it is characterized in that, the converter of described data acquisition unit (3) is A/D converter (31), and A/D converter (31) is converted to digital signal by simulating signal and is sent to data collecting card (32).

7. the device of yardstick in a kind of measurement of Atmospheric Turbulence as claimed in claim 1, is characterized in that, described laser emission element (1) is placed with optical axis opposite with laser pick-off and photoelectric conversion unit (2).

8. a method for yardstick in measurement of Atmospheric Turbulence, is characterized in that, comprises the following steps:

1) when laser beam is after the transmission of local uniformity isotropy atmospheric turbulence, L < < l under geometric approximation condition ₀ ²/ λ, has following calculating formula:

Wherein, L is beam Propagation path distance, and α is the angle of arrival, < α ²> is all sides of arrival angle fluctuation, σ _i ²for light intensity scintillation index;

2) carrying out yardstick l in atmospheric turbulence ₀measurement time, launch laser beam by laser emission element, laser beam is received by laser pick-off and photoelectric conversion unit through atmospheric turbulence to be measured, and reflexes to Position-Sensitive Detector by pinhole imaging system and catoptron, and aperture to the optical path distance of Position-Sensitive Detector is d ₁, read d by scale ₀;

Beam Propagation path distance L is the distance of generating laser to aperture, and aperture is to the distance d=d of Position-Sensitive Detector ₁+ d ₀;

α by Position-Sensitive Detector one-tenth light spot image mass center depart from the distance of mean place and the aperture ratio of distances constant value to Position-Sensitive Detector photosurface;

And α, < α ²> is calculated as follows:

Wherein, x, y are respectively and on Position-Sensitive Detector, become light spot image mass center physical location, x ₀, y ₀be respectively and on Position-Sensitive Detector, become light spot image mass center mean place, d is the distance of aperture to Position-Sensitive Detector, I is the relative light intensity signal numerical value of Position-Sensitive Detector output, and <I> is the assembly average of the relative light intensity signal of Position-Sensitive Detector output;

3) by being set, sampling rate and sample number determine yardstick l in calculating atmospheric turbulence ₀frequency after, triggering collection signal, Position-Sensitive Detector gathers the signal on the relative intensity signal of the hot spot after imaging and x, Gong San road, y both direction position;

Every collection one frame of data acquisition unit is converted into digital signal and is saved in internal memory, after the full sample number of setting of collection, does statistical calculation one time;

4) data processing and analytic unit calculate the arrival angle fluctuation < α of sample value ²> and light intensity scintillation index data, and calculate yardstick l in atmospheric turbulence by following formula ₀:

。

9. the method for yardstick in measurement of Atmospheric Turbulence as claimed in claim 8, is characterized in that described d ₀be set to: in the time that aperture to the distance of Position-Sensitive Detector is 1m, by d ₀value be set to 0m, along the direction d of light transmission ₀for on the occasion of, be negative value in face of the direction of light transmission;

Sampling rate be set to be not less than 300Hz, sample number is for being not less than 3000.