CN101109702B - Large-caliber laser isotope scanner and method for measuring structure constant atmosphere index of refraction - Google Patents

Abstract

The invention discloses a laser flasher with big diameter for measuring the structure constant of atmospheric refractivity as well as the method for that. The laser flasher comprises two opposite-arranged reflecting telescopes and lasers on the lens cones. The incident lights reach to the secondary plane mirror after being reflected by a main parabolic mirror in the lens cones, pass the openings, attenuating pieces and narrow-band interference filters on the lens cones, and then are converged on a photoelectric detector. At transmission test, two arrangements are placed at the two ends of the transmission path; the emitting system at one end of the path gives out modulated laser signals, after being transmitted by a turbulent atmosphere, the light signals are collected by the telescope at anther end, and go through photoelectric conversion by the photoelectric multiplier near to the focus; then the electric signals enter into a built-in control system for demodulation, sampling, processing, saving and displaying. The invention is of high accuracy and improves the accuracy in the measurements.

Description

Measure the large-caliber laser isotope and the method for air index textural constant

Technical field

The present invention relates to atmospheric optics, remote sensing field, specifically is a kind ofly to measure that the air index textural constant is the method and the instrument of atmospheric turbulence mean intensity on the transmission path.

Background technology

Air index textural constant C _n ²Being the quantitative description of optical turbulence intensity, is one of most important parameter of reflection atmospheric turbulence optical characteristics, understands C _n ²Changing Pattern and it is accurately measured for aspects such as research sound, light and electromagnetic transmission problem, assessment electro-optical system performance, checking turbulence models have very important significance.Utilize the average C in light intensity fluctuation effect measurement path in the turbulent atmosphere _n ²Be a kind of direct effective method, known under weak fluctuation condition, when travel path is even, the normalization variance and the C of light intensity fluctuation _n ²Between proportionate relationship that exist to determine.Yet under the strong turbulence condition, because the appearance of flicker saturated phenomenon, flicker variance and C _n ²Between the proportionate relationship formula be false, scintigraphy is measured C _n ²Lost efficacy.Therefore, solving saturation problem is to measure C with scintigraphy in a wider context _n ²Key.

There is the analysis of researcher by heuristic strong scintillation model nineteen seventies, has proposed a kind of measurement C that can overcome saturation effect _n ²The heavy caliber scintiloscope.Its basic thought is: for the flicker of incoherent light source in the receiving aperture of certain area of certain area, when the emission bore satisfies certain condition with the reception bore, can avoid saturation effect.Observation instrument based on this imagination was succeeded in developing by U.S. NOAA ripple propagation experimentation chamber afterwards.After this in time more than ten years, utilize the various optical flare instrument of visible light, infrared light and microwave radiation to occur one after another, these instruments not only can utilize the turbulence intensity on the light intensity fluctuation measuring route, if be equipped with two cover emission or receiving traps, can also obtain the yardstick or the information of horizontal wind speed in the turbulent flow; Simultaneously because the pixel yardstick of the measurement yardstick of scintiloscope and satellite remote sensing coupling is better, be accompanied by developing rapidly of satellite remote sensing technology since the mid-90 in 20th century, be widely used in the flux experimental study of land, outfield face, become the best checking means of satellite remote sensing inversion result, be with a wide range of applications.

Yet in actual applications, it is also remarkable that generation can be propagated the uniform incoherent area source of great distances, common way is the focus place that is placed on spherical reflector with near-infrared luminous diode, catoptron is approximately the set of pointolite, this way exist human eye invisible, regulate shortcoming such as difficulty, also limited the path that the I of instrument is surveyed simultaneously.If adopt the visible laser wave band, then can effectively overcome above shortcoming, cooperate the large aperture to receive simultaneously, and make the reception bore satisfy certain condition, according to the aperture average effect of laser atmospheric scinillation, still can suppress saturation effect to a certain extent so.Develop large-caliber laser isotope according to this principle, can measure C with scintigraphy in a wider context _n ²If, being equipped with the meteorologic parameter measuring equipment, just can monitor surface flux.

Summary of the invention

The purpose of this invention is to provide a kind of large-caliber laser isotope and method of measuring the air index textural constant, the optical flare effect of light intensity fluctuation when this large-caliber laser isotope transmits in turbulent atmosphere based on laser, the turbulence intensity that the measuring route equivalence is average.

The technical scheme of patent of the present invention is as follows:

Measure the large-caliber laser isotope of air index textural constant, it is characterized in that comprising relatively the laser instrument that on two autocollimators that are provided with and lens barrel, is provided with respectively, laser instrument is connected with modulation signal generator respectively, autocollimator lens barrel rear end is equipped with parabolic primary mirror, there is the plane secondary mirror that tilts to install in lens barrel central authorities, be positioned at parabolic primary mirror front end, incident light arrives the planar contact pair mirror reflection through the opening on the lens barrel through parabolic primary mirror reflection back, attenuator and spike interference filter, converge on the photodetector, the photodetector output signal is linked into data processing equipment.

Described attenuator, spike interference filter, photodetector are fixed on the same cylindrical shell, and this cylindrical shell is installed on the opening of lens barrel one.

Described plane secondary mirror and lens barrel axis are at 45.

The centre wavelength of described laser instrument is 645nm, and the centre wavelength of corresponding spike interference filter is 645nm.

Described photodetector is a photomultiplier.

Measure the method for air index textural constant, it is characterized in that comprising that relatively the centre wavelength that is provided with respectively is the 645nm laser instrument on two autocollimators at the two ends that are arranged on transmission path and lens barrel, laser instrument is driven by the TTL modulation signal, the output square-wave signal, when oscillatory circuit output high level, laser instrument is lighted, and during low level, laser instrument is closed; Autocollimator lens barrel rear end is equipped with parabolic primary mirror, there is the plane secondary mirror that tilts to install in lens barrel central authorities, be positioned at parabolic primary mirror front end, incident light arrives the planar contact pair mirror reflection through the opening on the lens barrel through parabolic primary mirror reflection back, attenuator and centre wavelength are the spike interference filter of 645nm, converge on the photodetector; The light that the laser instrument of transmission path one end sends is after the laser signal of ovennodulation transmits through turbulent atmosphere, autocollimator by the transmission path other end is collected light signal, after the parabolic primary mirror in the autocollimator lens barrel, planar contact pair mirror reflection, receive by photodetector, and carry out opto-electronic conversion, electric signal U after the conversion is directly proportional with incident optical signal I, the normalization variance β of U _U ²Normalization variance β with I _I ²There is following relation in (also being scintillation index):

${\mathrm{\&beta;}}_{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">I</figure-callout>}}^2=\frac{<{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">I</figure-callout>}}^2>-{<I>}^2}{{<I>}^2}=\frac{<{\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">U</figure-callout>}}^2>-{<U>}^2}{{<U>}^2}={\mathrm{\&beta;}}_U^2---\left(1\right)$

In the formula＜expression statistical average, survey U over time, utilize following formula can obtain scintillation index β _I ²According to the light transmission theory, the scintillation index of light intensity fluctuation is air index textural constant C in certain receiving aperture in addition _n ², light wave counts the diameter D of k (k=2 π/λ, λ are optical maser wavelength), transmission range L, receiving aperture, the function of aperture the ratio of obstruction ε:

${\mathrm{\&beta;}}_I^2\left(D\right)=0.132\&times;{\left(2\mathrm{\&pi;k}\right)}^2{\&Integral;}_0^L{C}_n^2\left(z\right)\mathrm{dz}{\&Integral;}_0^{\&infin;}{\sin }^2\left(\frac{{\mathrm{\&kappa;}}^{2}z(L-z)}{2\mathrm{kL}}\right){\mathrm{\&kappa;}}^{-8/3}---\left(6\right)$

$\&times;{\left[\frac{2}{1-{\mathrm{\&epsiv;}}^2}\right]}^2{[\frac{J_1(\mathrm{z\&kappa;D}/2L)}{\mathrm{z\&kappa;D}/2L}-{\mathrm{\&epsiv;}}^2\frac{J_1(\mathrm{\&epsiv;z\&kappa;D}/2L)}{\mathrm{\&epsiv;z\&kappa;D}/2L}]}^2\mathrm{d\&kappa;}$

If known β _I ², k, L, D and ε, just can be according to (6) the anti-C that characterizes turbulence intensity that releases _n ²Method by data fitting is similar to (6) formula, obtains the calibration formula of simplifying:

$A_{\mathrm{annular}\_\mathrm{fit}}={[1+0.214\&times;{\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="kD"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">kD</figure-callout>}}^2}{4L}\right)}^{7/6}]}^{-1}\&times;[0.44\&times;\exp (-\frac{L}{1079.23})+0.5]---\left(11\right)$

${\mathrm{<figure-callout\; id="2"\; label="C\; n"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">C</figure-callout>}}_n^{}=\frac{{\mathrm{\&beta;}}_I^2\left(D\right)}{A_{\mathrm{annular}\_\mathrm{fit}}\&times;{0.496k}^{7/6}{L}^{11/6}}---\left(12\right)$

In sum, utilize the large-caliber laser isotope of the measurement air index textural constant that the present invention proposes to obtain the time dependent electric signal that is proportional to incident intensity, (1) formula of utilization counts the scintillation index of light intensity fluctuation, bring calibration formula (11) and (12) into, parameters such as the diameter of cooperation optical maser wavelength, transmission range, receiving aperture and aperture the ratio of obstruction just can calculate the average air index textural constant in path.

Place attenuator and spike interference filter, it is saturated to avoid incident flux to cross ambassador's photodetector, has improved signal to noise ratio (S/N ratio) simultaneously.

(1), based on the aperture average effect of laser atmospheric scinillation, the structure that adopts laser spots light emitted, heavy caliber telescope to receive when suppressing the flicker saturation effect, enlarging measurement range, has been simplified system and structural design.Laser isotope based on this principle is not seen open report as yet.

(2), adopted modulation-demodulation technique, adopt two timers to form multi-resonant oscillating circuit in the laser instrument emission coefficient, drive laser is sent the laser beam of frequency, EDM Generator of Adjustable Duty Ratio, adopt partiting dc circuit, absolute value detecting circuit to carry out demodulation in the autocollimator receiving system, the influence of ground unrest has been deducted in the utilization of modulation-demodulation technique substantially, the signal to noise ratio (S/N ratio) of instrument is significantly improved, and performance is more stable.

(3), adopt embedded control system, finish collection, calculating, storage and demonstration in real time to data, data are delivered to hard disc of computer by USB port, touching display screen can show live signal or signal statistics value, both provided quantitative criterion intuitively for the light path calibration, also be convenient to experimental data is monitored in real time, judge signal(l)ing condition.

(4), adopt the symmetrical expression design, form by the identical device of two covers, every covering device all comprises laser instrument, receiving telescope and relevant control system, laser instrument is integrated in the top of receiving telescope, during outfield experiments, two complete equipments are placed on the two ends of transmission path respectively, the receiving telescope of one end is surveyed the emission light of the other end, such structural design can utilize the measurement result of two cover systems to judge the homogeneity in path, more experiment information is provided, and this function is not seen open report as yet.

(5), calibrating method is theoretical foundation with the definition of the average factor in aperture, considered the influence of telescope the ratio of obstruction, has very high precision, improved the accuracy of measurement result, this calibrating method is not seen open report as yet.

Description of drawings

Fig. 1 is a system construction drawing of the present invention.

Fig. 2 is the structured flowchart of electric signal processing circuit of the present invention.

Fig. 3 be air index textural constant of the present invention over time.

Embodiment

See also accompanying drawing 1.

Measure the large-caliber laser isotope of air index textural constant, the design of employing symmetrical structure, comprise being that 127mm, focal length are the Newtonian reflector 1 of 430.5mm to two bores that are provided with relatively, and the centre wavelength that is provided with respectively on autocollimator 1 lens barrel is the semiconductor laser 2 of 645nm, output power 15mW, have volume little, in light weight, be convenient to integrated advantage; Laser instrument 2 is connected with modulation signal generator respectively, for improving system signal noise ratio, laser instrument 2 is driven by the TTL modulation signal, the multi-resonant oscillating circuit of two timer component frequencies and EDM Generator of Adjustable Duty Ratio, the regulating circuit parameter, output frequency is that 10kHz, dutycycle are 50% square-wave signal, when oscillatory circuit output high level, laser instrument 2 is lighted, and during low level, laser instrument 2 is closed.Laser instrument 2 is fixed on the two-dimension optical adjustment rack 3, can adjust the position of irradiating light beam in level and vertical direction.The pallet of autocollimator 1 adopts single tine formula altazimuth, can move in level and vertical direction with nine sections speed, is convenient to very much light path and regulates;

Autocollimator 1 lens barrel rear end is equipped with parabolic primary mirror 4, there are 45 ° of plane secondary mirrors 5 that tilt to install in lens barrel central authorities, be positioned at parabolic primary mirror 4 front ends, it is that 645nm, bandwidth are the spike interference filter 8 of 6nm through opening 6, attenuator 7 and centre wavelength on the lens barrel that incident light arrives 5 reflections of plane secondary mirror through parabolic primary mirror 4 reflection backs, converges on the photomultiplier 9.Photomultiplier 9 positions change in the scope of distance focus the place ahead and each 25mm of rear, and photomultiplier 9 is adjusted to the position of focus rear side 15～20mm, make the launching spot diameter be about 5～7mm.Place attenuator 7 and spike interference filter 8, it is saturated to avoid incident flux to cross ambassador's photomultiplier 9, has improved signal to noise ratio (S/N ratio) simultaneously.

Described attenuator 7, spike interference filter 8, photodetector 9 are fixed on the same cylindrical shell, and this cylindrical shell is installed on the opening 6 of lens barrel one.

When experimentizing, two Newtonian reflectors 1 are placed on the two ends of transmission path respectively, and the laser instrument of path one end sends modulated laser, transmit through atmosphere, collect laser signal by the autocollimator of the path other end.

Incident light is collected by the throwing face primary mirror 4 of autocollimator 1 and is converged to focus by plane secondary mirror 5, receive with photomultiplier 9, convert light signal to current signal and preliminary the amplification, enter afterwards that embedded control system amplifies, demodulation, collection, storage and demonstration, as shown in Figure 2.Current signal enters before amplifier carries out current/voltage conversion and amplify once more, at first filters direct current signal by partiting dc circuit, and amplifier only amplifies signal like this, and ground unrest is not responded substantially, has avoided amplifier saturated, has improved signal to noise ratio (S/N ratio).Because what modulation was adopted is square wave, considers the characteristics of square wave itself, only need to use full-wave rectifying circuit can extract envelope, realize detection, therefore adopting only needs the accurate absolute value rectification circuit of a pair of build-out resistor to carry out demodulation.Signal after the demodulation is gathered by the collecting unit of control system, through after the data processing, be kept in the storage unit, can return data to computing machine by USB port, simultaneously by touching display screen with three kinds of mode shows signal: " showing in real time " pattern, be convenient to the aligning of light path and to real time monitoring signals; " data storage " pattern deposits data in file, the current file of full screen display simultaneously data; The mean square value of each data file is added up and shown to " homogeneous state demonstration " pattern successively.Can in three kinds of display modes, switch arbitrarily and can not influence the processing and the calculating of data.Load for the processing and the storage that alleviate control system in addition, reserved signal output port, signal after the demodulation can directly be connected with equipment such as capture cards by this port, and is gathered and handled by computer software control, has increased the dirigibility of data processing.

Measuring principle and method:

The large-caliber laser isotope of the measurement air index textural constant that proposes according to the present invention can obtain the time dependent electric signal U that is proportional to incident intensity I, its normalization variance β _U ²Normalization variance β with I _I ²There is following relation in (also being scintillation index):

${\mathrm{\&beta;}}_{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">I</figure-callout>}}^2=\frac{<{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">I</figure-callout>}}^2>-{<I>}^2}{{<I>}^2}=\frac{<{\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">U</figure-callout>}}^2>-{<U>}^2}{{<U>}^2}={\mathrm{\&beta;}}_U^2---\left(1\right)$

(1) formula of utilization counts β _U ²Just equal to have obtained the scintillation index of light intensity fluctuation.

According to the light transmission theory, wavelength is that the spherical wave of λ is propagated through atmospheric turbulence, and at propagation distance L place, diameter is that the logarithm light intensity fluctuation variance that receives on the aperture of D is

${\mathrm{\&sigma;}}_{\ln I}^2\left(D\right)=4\&times;{\left(2\mathrm{\&pi;k}\right)}^2{\&Integral;}_0^L\mathrm{dz}{\&Integral;}_0^{\&infin;}{\sin }^2\left[\frac{\mathrm{\&gamma;}(L-z)}{2k}{\mathrm{\&kappa;}}^2\right]{\mathrm{\&Phi;}}_n\left(\mathrm{\&kappa;}\right)\mathrm{\&kappa;F}\left(\mathrm{\&gamma;\&kappa;}\right)\mathrm{d\&kappa;}---\left(2\right)$

In the formula: k is light wave number and k=2 π/λ; κ is the space wave number; γ=z/L is the propagation factor of spherical wave;

Φ _n(κ) the spatial spectrum density of expression refractive index fluctuation can be expressed as following form:

${\mathrm{\&Phi;}}_n\left(\mathrm{\&kappa;}\right)={0.033C}_n^2\left(z\right){\mathrm{\&kappa;}}^{-11/3}f\left({\mathrm{\&kappa;l}}_0\right)---\left(3\right)$

C wherein _n ²(z) be the air index textural constant of being asked, f (κ l ₀) be the factor of scale effect in describing, for RANGE IN HOMOGENEOUS ISOTROPIC TURBULENCE, f (κ l ₀)=1; F (κ) is the aperture filter function, because the present invention adopts Newtonian reflector as receiving trap, and the ratio of its plane secondary mirror and the face of throwing primary mirror, promptly therefore aperture the ratio of obstruction ε=0.37 belongs to the annulus receiving aperture, and corresponding aperture filter function is:

$F\left(\mathrm{\&kappa;}\right)={\left[\frac{2}{1-{\mathrm{\&epsiv;}}^2}\right]}^2{[\frac{J_1(\mathrm{\&kappa;D}/2)}{\mathrm{\&kappa;D}/2}-{\mathrm{\&epsiv;}}^2\frac{J_1(\mathrm{\&epsiv;\&kappa;D}/2)}{\mathrm{\&epsiv;\&kappa;D}/2}]}^2---\left(4\right)$

Under weak fluctuation condition, the pass of scintillation index and logarithm light intensity fluctuation variance is:

${\mathrm{\&beta;}}_I^2={\mathrm{\&sigma;}}_{\ln I}^2---\left(5\right)$

For the large-caliber laser isotope that the present invention proposes, if only consider the simplest RANGE IN HOMOGENEOUS ISOTROPIC TURBULENCE, the expression formula of the scintillation index in its receiving aperture is:

${\mathrm{\&beta;}}_I^2\left(D\right)=0.132\&times;{\left(2\mathrm{\&pi;k}\right)}^2{\&Integral;}_0^L{C}_n^2\left(z\right)\mathrm{dz}{\&Integral;}_0^{\&infin;}{\sin }^2\left(\frac{{\mathrm{\&kappa;}}^{2}z(L-z)}{2\mathrm{kL}}\right){\mathrm{\&kappa;}}^{-8/3}---\left(6\right)$

$\&times;{\left[\frac{2}{1-{\mathrm{\&epsiv;}}^2}\right]}^2{[\frac{J_1(\mathrm{z\&kappa;D}/2L)}{\mathrm{z\&kappa;D}/2L}-{\mathrm{\&epsiv;}}^2\frac{J_1(\mathrm{\&epsiv;z\&kappa;D}/2L)}{\mathrm{\&epsiv;z\&kappa;D}/2L}]}^2\mathrm{d\&kappa;}$

If known β _I ²(D),, only need bring optical maser wavelength into, receive bore, aperture the ratio of obstruction and path, just can instead release the average air index textural constant of outbound path according to (6) formula.Yet (6) formula complex forms, can not satisfy the needs that engineering is used, definition according to the average factor in aperture is calibrated the large-caliber laser isotope that the present invention proposes, the approximate expression of (6) formula of acquisition, consider simultaneously for the large-caliber laser isotope that proposes for the present invention, optical maser wavelength, reception bore and aperture the ratio of obstruction are all fixed, have only path different because of experiment condition, so the large-caliber laser isotope that the present invention proposes is calibrated, mainly be to calibrate the funtcional relationship of the interior scintillation index of receiving aperture with path.

Definition according to the average factor in aperture: the scintillation index in the receiving aperture of certain area and the ratio of the scintillation index in the infinitesimal receiving aperture:

$A=\frac{{\mathrm{\&beta;}}_I^2\left(D\right)}{{\mathrm{\&beta;}}_I^2(D=0)}---\left(7\right)$

Denominator is represented the scintillation index of the emission of laser point source, some receiving system, and its expression formula is:

${\mathrm{\&beta;}}_I^2(D=0)=0.496C_n^2{k}^{7/6}{L}^{11/6}---\left(8\right)$

Comprehensively (6), (7) and (8) formula, for the large-caliber laser isotope that the present invention proposes, the average factor in the aperture of its receiving aperture is:

$A_{\mathrm{annular}}=\frac{{\mathrm{\&beta;}}_I^2\left(D\right)}{0.496C_n^2{k}^{7/6}{L}^{11/6}}---\left(9\right)$

The known approximate expression that is applicable to the average factor of circular aperture under spherical wave, heavy caliber, the little interior yardstick condition:

$A_{\mathrm{circlr}\_\mathrm{approx}}={[1+0.214{\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="kD"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">kD</figure-callout>}}^2}{4L}\right)}^{7/6}]}^{-1}---\left(10\right)$

With the ratio value representation accurate formula of the average factor in annulus aperture of (9) formula and (10) formula and the difference of the average factor approximate expression of circular aperture, bring systematic parameter λ=645nm, D=127mm, ε=0.37 into, analyze the variation tendency of ratio with path, and carry out match about path, the analysis showed that, if adopt the match of single order exponential damping, fitting precision is enough to satisfy the needs of engineering survey, and fitting result is:

$A_{\mathrm{annular}\_\mathrm{fit}}={[1+0.214\&times;{\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="kD"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">kD</figure-callout>}}^2}{4L}\right)}^{7/6}]}^{-1}\&times;[0.44\&times;\exp (-\frac{L}{1079.23})+0.5]---\left(11\right)$

Finally, the calibration formula of the average air index textural constant of the large-caliber laser isotope measuring route of utilizing the present invention to propose is:

${\mathrm{<figure-callout\; id="2"\; label="C\; n"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">C</figure-callout>}}_n^{}=\frac{{\mathrm{\&beta;}}_I^2\left(D\right)}{A_{\mathrm{annular}\_\mathrm{fit}}\&times;{0.496k}^{7/6}{L}^{11/6}}---\left(12\right)$

In sum, the electric signal that is proportional to incident intensity that the large-caliber laser isotope that utilizes the present invention to propose is measured, calculate the scintillation index of light intensity fluctuation according to (1) formula, the diameter and the aperture the ratio of obstruction that cooperate optical maser wavelength, path, receiving aperture, (11) formula of utilization and (12) formula just can calculate the average air index textural constant C in path that characterizes turbulence intensity _n ²In addition, according to air index textural constant C _n ²With atmospheric temperature textural constant C _T ²Between relation:

${\mathrm{<figure-callout\; id="2"\; label="C\; n"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">C</figure-callout>}}_n^{}={(\frac{79\mathrm{<figure-callout\; id="2"\; label="P\; T"\; filenames="H200710024298XE00011.png"\; state="\{\{state\}\}">P</figure-callout>}}{T^{}}\&times;{10}^{-6})}^2{C}_T^2---\left(13\right)$

Under the situation of known atmospheric pressure P and temperature T, utilize following formula can obtain C _T ²

The model experiment result:

20:40 to 22 day on the 21st May in 2007,20:40 was fine, the time strong wind is arranged, 26～33 ℃ of temperature are measured the light intensity fluctuating signal, obtain air index textural constant trend such as Fig. 3 over time.

Claims (4)

1. measure the large-caliber laser isotope of air index textural constant, it is characterized in that comprising relatively the laser instrument that is provided with respectively on two autocollimators at the two ends that are arranged on transmission path and lens barrel, laser instrument is connected with modulation signal generator respectively; One opening is arranged on the lens barrel, and attenuator, spike interference filter, photodetector are fixed on the same cylindrical shell, and this cylindrical shell is installed on the opening of described lens barrel; Autocollimator lens barrel rear end is equipped with parabolic primary mirror, and there is the plane secondary mirror that tilts to install in lens barrel central authorities, and are positioned at parabolic primary mirror front end, and the plane secondary mirror becomes 45 degree with the lens barrel axis; The laser instrument of transmission path one end sends after the laser signal of ovennodulation transmits through turbulent atmosphere, autocollimator by the transmission path other end is collected light signal, incident light arrives the planar contact pair mirror reflection through opening, attenuator and spike interference filter on the lens barrel through parabolic primary mirror reflection back, converge on the photodetector, the photodetector output signal is linked into data processing equipment.

2. according to the large-caliber laser isotope of claims 1 described measurement air index textural constant, the centre wavelength that it is characterized in that described laser instrument is 645nm, and the centre wavelength of corresponding spike interference filter is 645nm.

3. the large-caliber laser isotope of measurement air index textural constant according to claim 1 is characterized in that described photodetector is a photomultiplier.

4. measure the method for atmospheric refraction textural constant, it is characterized in that comprising that relatively the centre wavelength that is provided with respectively is the 645nm laser instrument on two autocollimators at the two ends that are arranged on transmission path and lens barrel, laser instrument is driven by the TTL modulation signal, the output square-wave signal, when oscillatory circuit output high level, laser instrument is lighted, and during low level, laser instrument is closed; Autocollimator lens barrel rear end is equipped with parabolic primary mirror, there is the plane secondary mirror that tilts to install in lens barrel central authorities, be positioned at parabolic primary mirror front end, incident light arrives the planar contact pair mirror reflection through the opening on the lens barrel through parabolic primary mirror reflection back, attenuator and centre wavelength are the spike interference filter of 645nm, converge on the photodetector; After the laser signal through ovennodulation that the laser instrument of transmission path one end sends transmits through turbulent atmosphere, autocollimator by the transmission path other end is collected light signal, after the parabolic primary mirror in the autocollimator lens barrel, planar contact pair mirror reflection, receive by photodetector, and carry out opto-electronic conversion, conversion back electric signal U is directly proportional the normalization variance β of U with incident optical signal I ² _uWith scintillation index β ₁ ²In following relation:

${\mathrm{\&beta;}}_l^2=\frac{<I^2>-{<I>}^2}{{<I>}^2}=\frac{<U^2>-{<U>}^2}{{<U>}^2}={\mathrm{\&beta;}}_U^2---\left(1\right)$

In the formula＜expression statistical average, survey U over time, utilize following formula can obtain scintillation index β ₁ ²According to the light transmission theory, the scintillation index of light intensity fluctuation is air index textural constant C in certain receiving aperture in addition _n ², light wave counts k, the function of the diameter D of transmission range L, receiving aperture, aperture the ratio of obstruction ε, k=2 π/λ wherein, λ is an optical maser wavelength:

${\mathrm{\&beta;}}_l^2\left(D\right)=0.132\&times;{\left(2\mathrm{\&pi;k}\right)}^2{\&Integral;}_0^L{C}_n^2\left(z\right)\mathrm{dz}{\&Integral;}_0^{\&infin;}{\sin }^2\left(\frac{{\mathrm{\&kappa;}}^{2}z(L-z)}{2\mathrm{kL}}\right){\mathrm{\&kappa;}}^{-8/3}$

$\&times;{\left[\frac{2}{1-{\mathrm{\&epsiv;}}^2}\right]}^2{[\frac{J_1(\mathrm{z\&kappa;D}/2L)}{\mathrm{z\&kappa;D}/2L}-{\mathrm{\&epsiv;}}^2\frac{J_1(\mathrm{\&epsiv;z\&kappa;D}/2L)}{\mathrm{\&epsiv;z\&kappa;D}/2L}]}^2\mathrm{d\&kappa;}---\left(6\right)$

β ² _uBe meant the normalization variance of the electric signal U after the conversion, β ² _IThe normalization variance of I when (D) the finger batter directly is D; κ is the space wave number; Z be the vertical coordinate integration step from;

Known β ₁ ², k, L, D and ε, just can be according to the anti-C that characterizes turbulence intensity that releases of formula (6) _n ²Method by data fitting is similar to (6) formula, obtains the calibration formula of simplifying:

$A_{\mathrm{annular}\_\mathrm{fit}}={[1+0.214\&times;{\left(\frac{{\mathrm{kD}}^2}{4L}\right)}^{7/6}]}^{-1}\&times;[0.44\&times;\exp (-\frac{L}{1079.23})+0.5]---\left(11\right)$

$C_n^2=\frac{{\mathrm{\&beta;}}_I^2\left(D\right)}{A_{\mathrm{annular}\_\mathrm{fit}}\&times;{0.496k}^{7/6}{L}^{11/6}}---\left(12\right)$

A _{Annular_fit}Expression is through the average factor in the aperture of the receiving aperture of over-fitting;

The large-caliber laser isotope of measurement air index textural constant as claimed in claim 1 can obtain the time dependent electric signal that is proportional to incident intensity, (1) formula of utilization counts the scintillation index of light intensity fluctuation, bring calibration formula (11) and formula (12) into, cooperate the diameter and the aperture the ratio of obstruction parameter of optical maser wavelength, transmission range, receiving aperture, just can calculate the average air index textural constant in path.

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