EA035955B1 - Method for determination of meteorological optical visibility range - Google Patents

Abstract

The invention relates to the field of meteorology, in particular, to meteorological support of aircraft takeoff and landing, road and port services, and to the field of analytical instrument engineering. The objective of the invention is to increase the precision of the optical radiation attenuation and optical visibility range measurement using forward-scatter visibility meters, and to increase service reliability of forward-scatter visibility meters. The purpose of the invention is achieved by the optical visibility range measurement method, wherein light radiation is transmitted to the scattering volume on at least three wavelengths , in two directions at angle between them, signal measurement is carried out at those wavelengths for signals passing through the common scattering volume P() and P() and scattered in it P() and P() by two receivers located opposite to the respective radiation sources; on the basis of the measured signals, spectral scattering factors at angle (,) are determined using the defined regression relationships; spectral attenuation values () are measured; and using attenuation values at wavelengthscorresponding to eye brightness-difference threshold, optical visibility range MOR is determined, which is equal to 3.9/().

Description

The alleged invention relates to the field of meteorology, in particular, it is used for meteorological support for takeoff and landing of aircraft, and can also be used by road and port services.

Meteorological optical range (MOR) is recognized by the International Electrotechnical Commission (IEC, 1987), officially adopted by the World Metrological Organization (WMO, 1993) as a measure of visibility in the atmosphere, and the International Civil Aviation Organization (ICAO) as the main meteorological quantity in determining the range of visibility at runways (runways) [1] (p. 3, 26).

To ensure the determination of the runway visual range required from the point of view of ensuring the safety of takeoff and landing of aircraft, methods and means are used that ensure accurate measurement in the first place (MOR) [1] (pp. 26 - 37). The basis for determining MOR, taking into account the accepted value of the eye contrast sensitivity threshold equal to 0.05, is the measurement of the transmittance m = e ^-d . where σ is the attenuation index of the light beam, l is the path length of the light beam associated with the MOR expression

or the attenuation coefficient σ associated with the MOR expression

MOR = σ

To measure the transmittance (the average value of the transmittance in a horizontal cylinder of air between the transmitter and the receiver of the luminous flux), transmissometers (photometers) [1] (p. 35-36) are used. The most famous transmissometers are Mitras (Yaisala; Finland), Flaminga (Impuls -phusik, Germany), Peleng SF-01 (Peleng Republic of Belarus), photometers FI-1, FI-2, FI-3 (Russia). The range and accuracy of MOR measurement with these devices depends on both the length of the measuring base and the accuracy of measuring the transmittances, which requires the use of conversion tables to optical range for bases of different lengths [1] (p. 26-31).

The attenuation coefficient σ is determined by forward and backward scattering instruments that measure the scattering of light in a certain investigated volume of air illuminated by a collimated light source. Prior to 2000, ICAO recommendations did not consider forward and backscatter instruments as an alternative to transmissometers for determining the runway visual range. At present, they are recommended along with transmissometers for measuring MOR and determining the runway visual range at all aerodromes [1] (p.35). Several types of forward scatter devices have been developed and are used, which include PWD1 / 20/50, FD12 and FD12P (Finland), Fumesens (Germany), Belfort (England), Nandaki (USA), Peleng SL-3 (Republic of Belarus) ). The advantages of forward-scatter meters include the small size and weight of the transmitter and receiver, convenience and ease of maintenance, and most importantly, the MOR measurement in the entire range is carried out with the same error.

Both transmissometers and forward-scatter meters require protection of the optical elements of sources and receivers from contamination of their windows, the appearance of moisture on them; aging control of a photodetector is required - for example, a photomultiplier, a photodiode, which, in turn, requires a self-testing system. Since the parameters of photodetectors can vary depending on temperature, it is necessary to use heating elements [2, 3]. Requires periodic cleaning of objects and receiver caps, calibration. When warning and alarm signals appear, replacement of system elements (sources, receivers), calibration work is mandatory. All this greatly complicates the operational properties of the systems.

Closest to the proposed invention is a method implemented in forward scattering meters [2] (pp. 17-18), including measuring scattered signals at angles of 45 °, determining the scattering coefficients at these angles. The MOR values for the determined scattering coefficients at angles σ (φ) in this range are set using the ratio (σ (φ) / σ «1.45 [1 (p. 33), 4 (p. 458-460)], where σ - attenuation index. The maximum deviation from the value of 1.45 is ± 13%. And since the accuracy of determining the optical range (MOR = 3.9 / ^) has the greatest influence on the accuracy of determining the visibility range on GDP, it is obvious that this requires an increase in accuracy determination of the attenuation coefficient σ, and hence a decrease in the error of the coupling coefficient between σ and σ (φ). In addition, for a more reliable assessment of MOR when using forward scatter meters, it is necessary to identify the atmospheric phenomenon, and also to use the appropriate calibration by the transmissometer. as a light source, white light is used, including the wavelengths of the highest sensitivity of the eye (wavelengths λ = 555-556 nm), then in [2] - infrared, with λ = 875 nm, which, in turn, can also affect the quality of the landing.

The objective of the invention is to develop a method for determining the meteorological optical visibility range, which makes it possible to increase the accuracy of determining the optical attenuation index.

- 1,035,955th radiation and optical visibility in forward scatter meters and their operational reliability.

The task is achieved by the fact that in the method for determining the optical visibility range by sending light radiation into the scattering volume of the medium, measuring the scattering index at a given angle, determining the attenuation index, radiation is sent to the scattering volume of the medium at at least three wavelengths λ in two directions under angle φ between them, at the given wavelengths signals are measured passing through the common scattering volume P1 ^ _£ ) and P ₃ (A) and scattered in it P ₂ (A) and P4 (A) by two receivers located opposite to the corresponding radiation sources , the measured signals determine the spectral values of the scattering coefficients at the angle σ (φ, λ _; ) from the expression

determine the spectral values of the attenuation indices σ (λ _; ) using the relation 1 ₈ σ (λ.) = ς ₀ + Σς ₍ 18σ (φ, λ,), k = \ where the coefficients C _ik are set using the least squares method from the array n = 1, ..., S of the calculated values of σ (λ,) and σ ^ λ ^ φ), set in the range of scatter of the microphysical parameters of the investigated scattering medium, and the angle φ corresponds to the mean over the sample of values σ ^η (λ ^ and σ ^η ( λ ^ φ) errors in determining σ (λ _; ) from the used relationship between σ (λ _; ) and σ (λ ^ φ) when applying a random scatter on σ (λ ^ φ) within the specified limits, and from the values of the attenuation indices at lengths waves λ;, corresponding to the threshold of contrast sensitivity of the eye, determine the optical range of MOR, equal to 3.9σ / (λ _; ).

The essence of the invention is illustrated in FIG. 1 and 2. FIG. 1 shows a block diagram of a device that implements this method (one of the possible). FIG. 2 shows the determination error σ _(λ;) from the error determining σ _(λ;, φ).

Let us consider the implementation of the proposed method on the example of using three wavelengths of the widely used laser (Nd: YAC), including the wavelengths in the region of the highest sensitivity of the eye.

The block diagram includes two sources of optical radiation 1 and 2 (Nd: YAC is considered - a laser emitting at wavelengths of 0.355 μm, 0.532 μm, 1.064 μm), two photodetectors 5 and 6 (for example, photodiodes), located opposite to the corresponding sources , spectrum analyzers 3 and 4, as well as a control unit, registration, processing of recorded signals 7. According to the signals of block 7, the sending of radiation by sources 1 and 2 is alternately triggered, photodetectors 4 and 5 register the light fluxes passed through spectrum analyzers 3 and 4, from the output of the photodetectors devices, the signals are fed to the input of block 7, where they are registered (conversion into digital values, processing with respect to the determined characteristics, display in quantitative MOR values). Block 7 also controls the time of arrival of the transmitted and scattered signals to it. In another variant of the block diagram, spectrum analyzers 3 and 4 can be placed after the sources, and the radiation source can be, for example, an LED, a lamp, etc.

When sending radiation by source 1 for the magnitude of signals recorded at wavelengths λ _; , i = 1, 2, 3, where i = 1 corresponds to λ1 = 0.355 μm, i = 2, λ ₂ = 0.532 μm, i = 3, λ ₃ = 1.064 μm, we can write the following ratios /; (λ =) = ρ „, (Λί) 4, _ι (λί) 7; (λ <) 7 '_< (λί) β _Ο4 (λθ _! (1) /> (λί) = ρ _οι (λί) 4 _{) ι} (λοη (λΟσ ( φ) η (λ _Ι ) Β _Μ (λ _Ι ) _ι (2) where Ρ1 (λί), Ρ ₂ (λί) are recorded signals corresponding to the spectral component of the signal sent by source 1 at λ ^

P ₀₁ - the spectral component of the power of the sent signal at the wavelength Xi;

Aoi - instrumental constant of radiation source 1, corresponding to ki,

T1, T ₃ , T ₄ - transmission coefficients at λ ^ corresponding to the sections between the source 1 and the scattering volume, the scattering volume and receivers 3 and 4;

where li is the length of the sections corresponding to T1, T ₃ ; T4,

В _О3 (Х _; ), В _О4 (Х _; ) are the instrumental constants, respectively, of spectrum analyzers 3, receivers 5 and spectrum analyzers 4, receivers 6 at a wavelength λ ^ σ (φ) is the scattering coefficient of the total scattering volume at an angle φ when radiation is sent to wavelength X _; ...

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Similar expressions can be written for recorded signals at a wavelength λ when radiation is sent by a source 2

Р ₃ (λζ) = Р ₀₂ (λζ) 4 ₂ (λζ) Γ ₂ (λζ) Γ ₃ (λζ) Β ₀₃ (λζ), Ρ ₄ (λζ) = Ρ ₀₂ (λζ) 4 ₂ (λζ) Γ ₂ (λζ) σ (φ) Γ ₄ (λζ) ^ ( ^λ 0>

(3) (4) where A ₀₂ is the instrumental constant of the radiation source 2 corresponding to Ai;

P ₀₂ (Ai) - spectral component of the power of the sent signal at the wavelength Ai;

T ₂ is the transmittance at Ai, corresponding to the section between the source 2 and the scattering volume.

From (1) - (4) we easily obtain the following relation σ- (φ, λ /) = ^ ^{(λί) Λ (λ,)}

Ρ, (λ:) Ρ, (λί) (5)

Similar expressions can be written for the spectral components of signals not only at wavelengths λι = 0.355 μm, λ ₂ = 0.532 μm and λ ₃ = 1.064 μm (harmonics of the Nd: AUG laser), but also for any other spectral range corresponding to other sources radiation (including for white light, including the wavelengths of the highest sensitivity of the eye).

As can be seen from (5), the recorded signals do not include the hardware constants P _0i , A _0i , B _0i , which indicates that a change in these constants does not affect the values of σ (φ), i.e. the instability of the instrumental constants of sources and receivers does not affect the measurement result σ (φ), which means that methodological errors caused by these factors are excluded. Since the instrumental constants also include the degree of contamination of the optical elements of sources and receivers, their dependence on temperature changes, in this scheme these factors will not affect the measurement result σ (φ), which means there is no need to use protection against contamination. Does not affect the result measurements and the environment, since, as can be seen from (5), there are no expressions for T that characterize the transmission of sections.

Thus, since using the proposed measurement scheme excludes methodological errors caused by the instability of the instrumental constants of sources, receivers, contamination of optical elements, changes in the environment, the accuracy of determining σ (φ) will be higher than in the used measurement schemes σ (φ).

As noted above, in order to establish the MOR value, knowledge is required not of σ (φ), but of the attenuation coefficient σ associated with MOR by the ratio MOR = 3.9 ^. A stable relationship between σ (φ) / σ®1.45 with an error of ± 13% was established for angles of ~ 45 °. So, in [2], for example, an angle of 45 ° is used for measurements, in [3] - an angle of 42 °. As noted in [4] (pp. 458 - 460), this coupling coefficient depends on atmospheric situations. It is obvious that the establishment of a more stable (with a smaller error) relationship between σ (φ) and σ will also improve the accuracy of the MOR determination. The possibility of increasing the accuracy of determining the coupling coefficients between σ (φ) and σ by making additional measurements (using spectral measurements σ (λ, φ)) is shown below.

In order to select the optimal angle of reception of scattered radiation (in terms of the accuracy of obtaining the values of σ (λ)), the problem of obtaining regressive relations between σ (λ) and σ (λ, φ) is solved. The values of σ (λ) and σ (λ, φ) were calculated using Mie's formulas [5] (pp. 107-138, 178-183, 602-616). For the purposes just noted, linear regression was used in the form lga (X,) = C, ₀ + £ c ,, lgo (<pA,) (6) in which the logarithms of the quantities σ (λ) and σ (λ, φ), since in this case we are dealing with numbers of the same order, and the absolute error of the logarithm gives an estimate of the relative error of the value itself. The numerical values of the coefficients C _{ik are} determined using the array of calculated values σ (λ) and σ (λ, φ)) by the least squares method

Г (I ² min £ 18σ (λ,) - ς ₀ - £ ς., 18σ (φ, λ,), (7) where n = 1, ..., S is the number of realization of the microphysical parameters of the scattering medium with the corresponding optical characteristics a ^p (A) and σ (λ, φ); S is the sample size (array of calculated values of σ (λ) and σ (λ, φ)); λι = 0.355 μm, λ ₂ = 0.532 μm, λ ₃ = 1.064 μm.

To obtain an ensemble of calculated data consisting of S = 1500 calculated realizations of σ (λ) and σ (λ, φ), we used atmospheric models [6 (pp. 24-76), 7]. Model [7] was adopted for use by the World Meteorological Organization (WMO). The ensemble of calculated data σ (λ) and σ (λ, φ) was obtained by independent uniformly distributed variations in the microphysical characteristics corresponding to the aerosol attenuation and scattering at an angle,

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Σ (φ, λ) = Ν ^ K _a Jm, r, X) f (r) dr о and molecular

8π (/ κ ² -!) ^{2 σ} ” ^(λ) = s

£ (λ, φ) = - (1 + cos ² φ), 4 where N is the concentration of aerosol and molecular particles, m is the refractive index, r is the size of aerosol particles, f (r) is the size distribution function, φ is the angle scattering, KQm, r, / J, K ^ _ip (ιιι, ΐ ', λ) factors of the efficiency of attenuation and scattering at an angle calculated by the Mie theory [5]. The optical characteristics σ (λ) and σ (λ, φ) for aerosol, as well as molecular size, were calculated using randomly set values of microphysical characteristics from the range including both finely dispersed fractions - from 0.03 μm, and large ones up to the size of a raindrop. scattering, over the ensemble of which, by the least squares method, the coefficients C _ik included in the multiple regression equation (6) were established. To take into account the contribution of errors and the scatter of the experimental data on which the model is based, in addition to uniform variation of the microphysical parameters, a 10% random scatter was superimposed on the calculated values of σ (λ, φ) used in (6).

In order to select the optimal angle for measuring the scattered radiation (in terms of the accuracy of obtaining the values of σ (λ ^), the calculation of the average over the sample of values of σ '' (/ i) and σ ^π (% φ) is the error in determining σ (λ ^ (i = 1, 2, 3) from (6) for angles in the range φ = 1-180 °, when superimposed on σ (% φ) of a random spread within 2.5% (which takes into account the sensitivity of the corresponding regression equations to measurement errors σ (λ ^ φ ))

For each φ, the coefficients C _{ik were} determined by the least squares method (7). The calculated dependences δσ (φ) are shown in Fig. 2. As can be seen from the figure, the smallest errors are determined by δσ (φ) correspond to the range of 30-40 °. The multiple regression coefficients (6) for σ (λ) and σ (λ, φ) at an angle of 35 °, corresponding to the above range of scatter of microphysical characteristics, are given in the table.

Determined characteristics Go ’Si c _i2 c _i3 σ (λι), km ^-1 0.8053 0.54 0.178 0.32 σ (λ ₂ ), km ^-1 0.79 0.03 0.53 0.467 σ (λ ₃ ), km ¹ 0.76 0.14 -0.32 1.213

The established C _ik values correspond to the entire range of scatter of the microphysical parameters of the atmosphere, i.e. all atmospheric situations of the World Meteorological Organization (WMO) Atmosphere Model.

The accuracy of determining σ (λ,) from the spectral values of the attenuation coefficient at the indicated angle can be judged from the calculated errors | σ (λ,.) - σ (λ,) | δσ (λ _ζ ) = σ (λ,) where σ (λ ^ and σ * (λ ^ are, respectively, exact and obtained using regressive relation (6) for the attenuation coefficient.

The error in determining σ (λ ^ is for σ (λ ₁ ) = 2.2%, σ (λ ₂ ) = 1.8%, σ (λ ₃ ) = 2.9%. These values of the errors in determining the attenuation coefficient σ (λ ^ obtained within the framework of the used model [6, 7], taking into account 2.5% errors in the measurement of σ ((φ, λ ^. Such errors, and even smaller ones, are achieved when using the scheme described above (Fig. 1) measuring σ (φ, λΐ), excluding methodological errors caused by the spread of the instrumental constants of the measuring equipment, contamination of optical elements, and the influence of the environment.

The estimation of the error in determining σ (λ ^ from the measured values of σ (φΑ) at the above wavelengths was made due to the fact that there is a radiation source at these wavelengths, and / 2 = 0.532 μm corresponds to the range of the highest sensitivity of the human eye.

The proposed method for determining σ (λ) from the value of σ (φ, λ0 can be used at other wavelengths (for example, and for wavelengths corresponding to transmissometers), other angles, including

- 4 035955 tea backscattering, for other atmospheric situations (by setting the corresponding scatter of microphysical characteristics of scattering media, both aerosol and molecular). Establishing the corresponding coefficients C _ik using the proposed algorithms does not present significant difficulties for specialists.

Thus, the proposed method for measuring the optical range of visibility with forward and backward scattering devices makes it possible to increase the accuracy of its measurement both by increasing the accuracy of measuring the scattering index at an angle (by eliminating the methodological errors caused by the above-mentioned components) and by eliminating the error caused by using the coupling coefficient between the scattering factor at an angle σ (φ) and the attenuation factor σ, set with an error of ± 13%. In the proposed method, the relationship between σ (φ) and σ is established with an error of less than 3%, and for λ = 0.532 μm with an error of <2%. In this case, the total error in determining the MOR will be -5% (less than in the currently existing meters). At the same time, the proposed method significantly improves the operational properties of the measuring system by eliminating the need for total control over the contamination of optical elements of sources, receivers, monitoring the temperature of the medium, and conducting frequent calibration measurements. In other words, the system becomes operationally more reliable. This is due to the emerging advantages of measuring σ (φ), which exclude dependence on the measurement of the instrumental constants of the measuring system, on changes in the environment. This, as well as the use of the established coupling coefficient between σ (φ) and σ with an error of <3%, allows at least 2 times to increase the accuracy of determining the MOP by forward scatter meters. It should be noted that these meters measure measurements with the same error over the entire range of MOP changes. In addition, an important advantage is the possibility of eliminating the need to identify atmospheric phenomena, if the scatter of their microphysical characteristics is included in obtaining the coefficients C _ik , i.e. weather sensors may not be used.

Sources of information taken into account

1. Guide to the determination of the visual range at the GDP (RVR). Publishing center ANO Meteoagenstvo Roshydromet, 2006 - S. 3, 26-37.

2. User manual. Yaisala Visibility Sensor PWD10 / 20/50 - file_259.pdf-Adobe Reader.C.17-18.

3. User manual. Visibility sensor FS11- file_14.pdf-Adobe Reader. - S. 17-19.

4. Ivanov A.P. Scattering media optics. Minsk: Science and Technology, 1969. - S. 458-460.

5. Boren K., Hoffman D. Absorption and scattering of light by small particles: trans. from English. M; Mir, 1986 - S.107-138, 178-183, 602-616.

6. Zuev V.E., Krekov G.M. Optical models of the atmosphere, v.2. Leningrad: Gidrometeoizdat. 1986 S. 24 - 76.

7. World Meteorological Organization. World Climate Research Program: A preliminary cloudless standard atmosphere for radiation computation. Geneva: Switzerland, Report WCP-112, WMO / TD-24. 1986.-5-52.

Claims (1)

CLAIM A method for determining meteorological optical visibility range by sending light radiation into the scattering volume of the medium, measuring the scattering index at a given angle, determining the attenuation index, characterized in that the radiation is sent to the scattering volume of the medium at at least three wavelengths λ in two directions at an angle φ between them, at the given wavelengths, signals are measured passing through the common scattering volume P ^ i) and P ₃ ^ i) and scattered in it by P ₂ ^ i) and P ₄ ^ i) by two receivers located opposite to the corresponding radiation sources, the measured signals determine the spectral values of the scattering coefficients at the angle σ (φ, λ) from the expression determine the spectral values of the attenuation indices σ (λ ^ using the relation 1 ₈ σ (λ,) = ς ₀ + Σς ₄ 1 ₈ σ (φ, λ,), к = \ where the coefficients C _ik are set using the method of least squares from the array n = 1, ..., S of calculated values of σ “(Λ) and σ \ λ ^ φ), specified in the range of scatter of the microphysical parameters of the investigated scattering medium, and the angle φ corresponds to the average over the sample of values σ“ (λί) and σ “(λ ^ φ), the error in determining σ (λ ^ from the used relationship between σ (λ ^ and σ (λ ^ φ) when superimposed on σ (λ ^ φ) of a random spread within the specified limits, and the values of the attenuation indices at wavelengths λ-i corresponding to the threshold of the contrast sensitivity of the eye determine the optical MOR visibility range of 3.9 / σ (λ ^.