RU2758843C1 - Method for determining main parameters of structure of air and droplet formations of clouds and fogs - Google Patents

Abstract

FIELD: meteorology.

SUBSTANCE: invention relates to the field of meteorology and can be used for determining the main parameters of the structure of air and droplet formations of clouds and fogs. Substance: the meteorological visibility range is calculated, the water content of the air and droplet formation is measured. Accounting for said parameters, the effective droplet radius is calculated.

EFFECT: simplification of the method.

3 cl

Description

The invention relates to metrology and its use is intended to determine the structure of natural and artificial droplet formations in the form of clouds and fogs. The airborne structure determined using the claimed method is intended to obtain the initial data necessary for calculating the transmission of optical radiation in the thickness of clouds and fogs (radiation with wavelengths from 1 nm to 1 mm and including the ranges of X-ray, ultraviolet, visible and infrared radiation) and can be used by meteorological services in the operation of navigation systems, incl. on land and air transport, control and observation services for objects, used for various optical measurement methods, incl. when conducting thermal imaging surveys of construction and other objects, when conducting scientific research, as well as in other industries where it is necessary to know the optical characteristics of atmospheric air containing droplet formations.

The invention serves to determine the main parameters of the structure of droplet formations in the form of clouds and fogs that affect the transmission of optical radiation: the size of the particles (droplets) contained in it and the number of these particles per unit volume (concentration). The water droplets contained in the air scatter the optical radiation passing through the droplet formation and, depending on the particle size and concentration, reduce its intensity to one degree or another. For example, in the presence of fog, such an important for practice characteristic of fogs as meteorological visibility range in visible light (MPV) can range from several kilometers to several meters. At constant water content (the content of liquid water per unit volume of air), the smaller the droplets are, the less transparent the fog is, and vice versa. With an increase in water content at a constant droplet size, the transparency of the fog decreases. At the same time, fogs are almost always less transparent than the air in which it rains, despite the fact that the water content of the air during rain is many orders of magnitude higher than the water content of fogs.

The concentration of particles of airborne formations such as clouds and fogs practically does not lend themselves to direct measurements and instead of it, its integral value is used in measurements - the water content of droplets, i.e. liquid water content per unit volume of air. At the same time, knowing the water content and the droplet size distribution function, it is possible to recalculate and determine the concentration of droplets for each size and, conversely, the water content can be determined by the number of droplets and the droplet size distribution.

Determination (measurement) of fog water content is an independent important task, for example, for air transport. The conditions for ice formation on the hull and wings of aircraft, both during flights and in the pre-flight state, depend on the water content of the clouds and the temperature regime of the air.

Water content measurement can be done in several different ways. The most common among them are the following:

Determination of water content by inertial droplet sedimentation. The droplets are deposited, for example, on absorbent paper. By the value of the diameter of the resulting wet spot, the mass of settled water is determined and, knowing the air flow rate, i.e. the volume of air from which this mass of water is collected, the water content of the droplet formation is calculated (see, for example, [1]). The use of this method also makes it possible to simultaneously determine the concentration of chemical impurities, for which a chemical reagent is applied to the paper in advance, which changes the color of the paper under the influence of a chemical impurity. By the value of the ratio of the diameters of colored and uncolored spots, the concentration of impurities in fog or cloud water is determined. This method of measuring water content is the easiest to implement and quite accurate in the conditions of surface fogs.

Another well-known method for measuring water content is the electrothermal method [2]. The method is based on measuring the power consumed by a heated probe, which evaporates droplet moisture in a fog or cloud. To implement the method, it is necessary to provide an air flow relative to the probe (or vice versa, the movement of the probe relative to the air, as it happens on vehicles). When determining the water content, the value of the relative velocity of the air flow and the probe is taken into account. This method is often used as a means of detecting and diagnosing possible icing conditions in vehicles, for example, wings and aircraft body.

There is also known a method for remote contactless measurement of water content in fogs and clouds. This is the optical method, which is the basis for the operation of the device under the patent [3]. The method is based on the fact that in a fog or in a cloud there is scattering and a decrease in the transmission of electromagnetic optical radiation, in particular, light that can be measured. The amount of scattering depends on the number of droplets that meet along the path of the radiation. In the method used in [3], the sun is used as a radiation source, and filters are used in front of the photodetectors that polarize sunlight in different directions. Photodetectors receive radiation at several frequencies and, based on the difference in the power of signals of polarized and unpolarized light, by means of calculations, they determine the fraction of radiation scattered by water droplets and, therefore, measure the content of droplet water. In various versions of this method, artificial radiation sources are used instead of sunlight.

Measurement of the droplet size of airborne formations can be carried out by several granulometric methods, common to which is the visualization of droplets. The most simple and common among them are the following:

Capturing droplets in a volume of a viscous liquid that does not mix with the droplets and does not dissolve them (see, for example, [4]). After the interaction of a fog or cloud with such a liquid, the droplet size is observed and measured under a microscope. The disadvantage of this method is the limited area of applicability, low measurement accuracy, as well as low efficiency due to the fact that after capturing the drops, it is necessary to visualize them with the help of additional technical means and measure their sizes. In addition, the collection can only be carried out in the stream, for example, at the outlet of a device that generates artificial fog, or on a vehicle. The method is not applicable for stationary fogs. The low measurement accuracy is due to the coagulation of droplets into droplets of other sizes, both on the surface and inside the absorbing liquid.

Capturing drops on the surface. In this method, droplets are deposited onto a glass surface covered with a hydrophobic film, for example, an oil film. The method is the basis for the operation of a device for measuring droplets [5], which can be installed on an airplane or in a moving car. Sampling is carried out in closed chambers, in which sedimentation occurs during the exposure time, and then photographing is carried out with an increase and measurement of dimensions. This method is simple and easy to use, but it also has disadvantages. For its implementation, it is necessary that the capturing surface is in contact with the fog under conditions of a sufficiently long time, during which the droplets reach the surface not only from the zone of interaction of glass and fog, but also from other zones in which the droplet sizes may differ. In this case, in the process of gravitational sedimentation, droplets in the fog itself can contact each other with a change in their size.

A common disadvantage for these methods for determining the size of drops is that their implementation requires the use of equipment for capturing and settling drops, which can change the measured dimensions and reduce the measurement accuracy. In addition, both of the above methods require thermostating both the measuring system itself and the air in which the measurements are carried out.

The disadvantages of these methods for determining the structure of drip formations are as follows:

The methods for determining the water content are integral, without size detailing and do not allow determining the droplet sizes required for calculating the transmission of optical radiation. Methods for determining the size of droplets do not allow determining their quantitative content, which is also necessary for calculating radiation transmission.

To eliminate these drawbacks, measurement methods are used that allow simultaneously measuring both the sizes of droplets in fogs and clouds and their concentration, which can be used to calculate the water content, while without disturbing their structure. All these methods are based on optical diagnostics of droplet formations and obtaining instant information about their structure based on the established physical laws about the properties of the droplet component of air to interact with radiation passing through it. Most of the known optical diagnostics methods are based on the fact that probing optical radiation with known properties (power, spectral composition, polarization) is sent to the region of droplet formation from the source, and the reflected and (or) scattered radiation is recorded by the receivers. According to the characteristics of the received radiation and the known patterns of radiation scattering, the structure of droplet formations in the air is calculated. The advantage of these methods is that they are non-contact and many of them, under certain conditions, make it possible to obtain the necessary data on the structure of clouds and fogs, including their water content and droplet size distribution. The disadvantage is the complexity of the application of the method in practice, requiring the use of special equipment and special measurement techniques. The disadvantage is also the limited reliability of the data obtained. This is due to the fact that in the mathematical processing of the results obtained, it is necessary to solve the inverse problem - the determination of the microstructure from the obtained integral data in the form of characteristics of the received radiation. The transmission and scattering of light in dispersed systems, which include droplet-air formations, is described by a theory in which all parameters of the microstructure, as well as the spectral composition of the transmitted radiation, are simultaneously used when calculating the scattering coefficient. There are many parameters, their values have different, often opposite effects on the transmission of radiation, and it is not always possible to unambiguously reconstruct the values of all parameters from the value of the scattering coefficient. At the same time, it is technically difficult to ensure the measurement of the required number of radiation characteristics to detail the characteristics of the droplet structure.

Closest to the claimed invention and used as a prototype is the method described in the patent [6]. This method also relates to the optical determination of the microstructure of airborne cloud and fog formations. When using the method, the droplet size distribution and the water content are simultaneously determined. The method is based on the fact that probe radiation pulses with mutually perpendicular polarization planes are successively sent to the airborne formation. The radiation receivers receive the main and orthogonal components of the scattered radiation from these signals. Additionally, radiation is received at angles exceeding the characteristic angles of single (primary) scattering of radiation by drops. In this case, the receiver mainly receives signals formed by multiple scattering by a multitude of particles, incl. on particles of different sizes. Next, the signals are processed and, according to the power and degree of polarization of the received radiation, the droplet size distribution is calculated, according to which the water content of clouds and fogs is calculated.

This method has an advantage over other similar methods, since it allows one to obtain information about the size of droplets in droplet formations, about the size distribution of droplets, on the basis of which it is possible to calculate the water content. But the method also has disadvantages inherent in all optical methods used to diagnose airborne formations containing drops of various sizes. Its implementation requires complex and expensive measuring equipment and mathematical processing of the results. To obtain the necessary information, a complex measurement scheme is required, for example, the sounding of clouds and fogs at different angles, the use of multiple radiation sources and multiple receivers. A big drawback is that the completeness of the obtained information on the structure of clouds and fogs is approximate, and it is not always enough to make accurate calculations of the required properties of clouds and fogs based on the data obtained using this method on the dispersion and concentrations of droplets of various sizes. For example, the droplet structure obtained when using the prototype method may not be complete so that when it is applied in calculating the transmission of clouds and fogs of optical radiation of different spectral composition, accurate results are obtained. A typical example is obtaining initial data for processing the results of infrared temperature diagnostics of various objects in a cloudy atmosphere.

The use of this method, despite its complexity, is quite justified when the detailed structure of the droplet formation is of scientific and practical interest in some way, which is impossible or impractical to obtain by other methods than optical. Such measurements are most in demand, for example, in those cases when the development and optimization of equipment used for the formation of artificial fogs for various purposes is being carried out. When developing such equipment at the stages of research and development of design solutions, it is necessary to diagnose the formed droplets as detailed as possible. Detailed information on the structure of fogs and clouds is also needed in many scientific studies.

However, most of the practical problems associated with the optical properties of clouds and fogs do not require detailed structure of airborne formations. When solving them, the sought-for and difficult-to-determine size distribution function of water droplets can be replaced by a certain effective droplet size. In this case, the effective size of droplets, as well as the effective concentration of droplets when used in calculations, should give results on the scattering and transmission of radiation, similar to a real airborne system. In addition, the effective droplet size is a characteristic by which one can estimate the rate of gravitational sedimentation of fog, predict its dynamics when atmospheric temperature conditions change, and most importantly, using the standard Mie scattering theory [7], it can be used to calculate the transmittances quite simply and accurately fogs, clouds and other airborne formations for optical radiation of various types, including visible light.

An object of the present invention is to provide a simple and reliable method for determining the effective droplet size in airborne formations.

The technical result from the use of the invention is to simplify the description of the structure of airborne formation by using as a geometric parameter only the effective radius of the drops, which is common for the entire drip formation. In addition, the technical result is to simplify measurements to determine the structure of airborne formations of clouds and fogs.

In the delivered technical result, simplification of measurements means not only simplification and reduction of the number of operations required to determine the structure, but also simplification of the used instrumentation and equipment and the most complete elimination of complex procedures for processing results.

The development of the present invention is based on the results of a set of computational experiments on the analysis of optical radiation scattering on airborne formations of various compositions in terms of droplet size, droplet size distribution and the number of droplets per unit volume of air, equivalent to the water content of airborne droplets (liquid water content). As a result of the research, a quantitative relationship was established between the effective droplet size, water content and meteorological visibility in fogs and clouds. The established quantitative relationship formed the basis of the claimed invention.

The claimed method includes the following essential features, each of which is necessary, and in general, sufficient to solve the problem and achieve the claimed technical result:

1. The method for determining the structure of airborne formations of clouds and fogs includes measuring the water content of airborne formations and the size of the droplets.

These signs are restrictive and common with the prototype [6], since it also defines the constituents of the structure of clouds and fogs in the form of droplet size and air water content. The structure determined in the prototype includes the measurement of droplet sizes (distribution of the number of droplets by size). Water content (the content of liquid water per unit volume of air) is also a definable parameter calculated on the basis of measurement of dimensions.

The measurement of water content refers to the limiting feature known from the prototype. Moreover, in the totality of the features of the claimed invention (distinctive and restrictive), it does not indicate how the water content is measured. This means that the water content can be measured or calculated using any method, for example, by droplet deposition [1], or by electrothermal method [2], or by other known methods. At the same time, it is important that the invention does not indicate that the water content should be measured precisely by the optical method [3], which is quite difficult to implement.

At the same time, all other essential features of the prototype in the claimed invention are not used and are not included in the list of restrictive features. In particular, the fact that in order to solve the problem it is necessary to send probing pulses of linearly polarized radiation with mutually perpendicular polarization planes, receive the main and orthogonal components of the reflected radiation by the radiation receiver, separate and determine the profiles of the degree of polarization and the value of the backscattering coefficient , additionally receive reflected radiation at elevated angles of the field of view, process the results and, from the polarization degree profile, obtain data on the size distribution of droplets, according to which the water content is calculated. All these features are necessary to obtain precisely detailed information about the structure of drip formations and are not used in the claimed invention to solve the problem and achieve a technical result. The use of the listed features is permissible, but not mandatory, since it significantly complicates the implementation of the method and serves as a possible source of obtaining incompletely reliable information. In particular, the fact that in the prototype the water content is calculated as a result of measuring the number and size of drops is not used as a feature. In this setting, in relation to the claimed invention, the water content can be determined by any known method.

2. As the size of the droplets, their effective radius is determined.

This feature is essential and distinctive. The significance of the feature is due to the fact that from the whole variety of droplets that make up the fog, droplets are determined not with real multiple, difficult-to-determine sizes, but droplets with a single size that characterizes this formation - the effective radius. The effective radius of the droplets is found by calculation taking into account the equivalence of the optical properties of the effective and real airborne formations. Its use as a characteristic of the structure of an airborne formation makes it possible with sufficient accuracy to calculate most of its physical characteristics necessary for practice, including the degree of transparency and visibility for optical radiation of various spectral composition. With its help, estimates can be performed to predict the dynamics of airborne formations (deposition or growth of fogs) and the probability of precipitation. It is also essential that the effective radius is not measured but determined using calculations and other measured values.

3. Measure the meteorological visibility range (MVR).

This feature is essential and distinctive. The fact that the MPE measurement is carried out before or after the water content measurement is not essential. It is important that both of these parameters must be determined, and only then can the effective radius of the droplets be calculated. The MPE means the distance used in meteorology, at which, according to the generally accepted definition, in a fog or cloud, there is still a contrast of radiation brightness between features on the surface of an object at the level of 2%. If we go to the transmittance of the atmosphere, then the MPE corresponds to the condition for the radiation wavelength range of 0.38-0.78 μm perceived by the human eye, in which the transmittance is τ = 0.02. In the claimed set of essential features of the invention, in the general case, MPD can be measured by any available method, for example, based on the personal experience of the operator or on the basis of measuring the distance to any poorly distinguishable reference objects in fog or cloud. Everything is determined by the required accuracy of calculating the effective radius of the droplets.

4. The effective radius of the droplets is calculated by the formula

where w - water content (g / m ³ ), L - meteorological visibility range (m).

The calculation formula used in this feature for determining the effective radius of droplets is not previously known and is essential in terms of the set of parameters and coefficients used in it. The dependence according to formula (1) was obtained using the Mie theory for the scattering of electromagnetic optical radiation by suspended particles. Dependence (1) establishes a relationship between the calculated value of the effective radius of water droplets, which can be used to describe the optical properties of clouds and fogs, the water content of airborne formation, which lends itself to relatively simple measurements, and the MPE for the light perceived by the human eye, which is also relatively simple. can be measured. When obtaining dependence (1), air droplet formations with different droplet size dispersion and their different concentration in the air volume were used. The MWD distance was calculated taking into account not only the scattering of radiation by droplets, but also taking into account the additional absorption of light radiation by water vapor and carbon dioxide. At the same time, it was taken into account that the content of carbon dioxide in the air corresponds to its average value for the northern hemisphere of 400 ppm, the relative humidity of the air is about 100% (complete equilibrium saturation of air with water vapor due to the presence of liquid moisture dispersed in droplets, or ice floes in winter conditions) ...

The above set of features of the claimed invention refers to independent features necessary and sufficient for its implementation. Each feature from the presented set serves to ensure the problem to be solved and to achieve the technical result, thereby ensuring the unity of the invention. To solve this problem, only water content measurements and MPE measurements are used, which do not require sophisticated equipment and, most importantly, complex processing of measurement results, which is necessary in optical methods and leads to significant errors and partial unreliability of the data obtained.

The claimed invention contains four sets of dependent features, which disclose variants of methods for measuring the MPE, with the help of which its sufficiently accurate value can be obtained.

5. In an airborne droplet formation at wavelengths not exceeding 1.2 μm, the transmittance of air between the source of optical radiation and a receiver remote from it is measured, and the meteorological range of visibility is calculated by the formula

where τ is the transmittance, and l is the distance between the source and the receiver of radiation (m).

This set of indicators shows how the MPE can be measured if there are no other simpler ways to measure it or these methods are complex or do not give the required accuracy.

The measured transmittance is calculated from the results of measuring the radiation intensity of the source (W / m ² ), obtained by the receiver at wavelengths not exceeding 1.2 μm, referred to the intensity of the radiation emitted by the source. The intensity of the radiation emitted by the source must be determined for the same wavelength range and can be either a predetermined value if the source is calibrated and verified, or it can be determined directly by measuring the MPE at a distance close to the source much less than the MPE. The latter method may be more preferable in cases where the structure of airborne formations is determined on vehicles, for example, in an airplane.

Material objects (source and receiver of radiation) present in the formulation of this set of features, which are not defined in the independent claim of the invention, do not violate the unity of features. These objects only indicate that the air transmittance must be measured at a certain distance, and for its measurement, radiation from the source, received by the receiver, can be used. The concepts of source and receiver are used to specify the distance used in formula (2). The type of source and destination is not decisive.

In the given set of features, it is essential that the transmittance is calculated from the results of measurements at wavelengths not exceeding 1.2 μm. It is possible to provide such a limitation on the measurement range if, for example, an appropriate filter is installed in front of the radiation receiver, which cut off long wavelengths, or if a selective receiver or source corresponding to the wavelength range is used. The receiver can be photometric and the signal is integrated over the specified range. The main thing is that the measurements of the intensity of the radiation emitted by the source and received by the receiver are carried out for the same wavelength range.

The requirement to measure the transmittance in the wavelength range not exceeding 1.2 μm is due to the fact that in this case, for droplet sizes of 1 μm and above (these are the droplets that are the components of fogs and clouds), the scattering coefficient, which determines the air transmittance, is weakly depends on the wavelength of radiation and for its measurement can be used a source and a receiver that do not work in strict restrictions on the wavelength range. Visible radiation of 0.38-0.78 μm also falls into the wavelength range less than 1.2 μm, at which the value of the MPE used in formula (1) for calculating the effective radius of droplets is determined.

The use of the features given in clause 5 serves to solve the problem posed in the invention and achieve the set technical result and does not violate the unity of the invention. Measurement of the MPE is carried out, which is necessary to determine the effective radius of the droplets. Measurement of MPE is carried out by a simple optical method using a minimum set of equipment (source and receiver of radiation, as well as a device for measuring the distance, if necessary). To calculate the MDI, no special mathematical processing of the spectral characteristics of the received signal is required.

To calculate the MPE according to this method, only one measurement of the transmittance at any one distance is sufficient. But such a measurement due to various random factors may have an unknown error. The source of the error may be, for example, the fact that in the selected direction of measurement there is a temperature anomaly, a change in pressure or convective flow, which differ from the average values in a cloud or fog. To reduce the error in the invention, the following additional features are used:

6. The measurement of the air transmission coefficient and the calculation of the MPE are carried out for two or more distances between the source and the receiver, and to calculate the effective radius of the droplets, the MPE value obtained by processing the results for all distances is used.

To do this, for each new distance, the transmittance is measured and, according to formula (2), its value of the MPE is calculated. In the ideal case of homogeneous droplet formation and provided that all measurements are carried out simultaneously, the MPE value for each position should remain unchanged. In case of differences in the values of the MPE, the results obtained should be processed and as a result of processing, a reliable value of the MPE and its error should be obtained.

The use of additional distances between the receiver and the source does not require that they all be different. The position of the receiver relative to the source can be at the same distance, but at a different spatial angle relative to the source. In this case, the spatial distribution of the MPE can be measured in the fog or cloud.

Another way to measure MVI is a method described by the following set of features:

7. In the airborne droplet formation at wavelengths not exceeding 1.2 μm, the radiation intensity from the optical radiation source located in it is measured, the measurements are carried out at two different distances from the source, and the MPE is calculated by the formula

where J ₁ and J ₁ are radiation intensities (W / m ² ) measured at distances l ₁ and l ₂ from the optical radiation source (m), respectively.

This method is similar in principle to the previous one, but does not require knowledge or measurement of the intensity of radiation emitted by the source. The measurements simply compare the powers of two signals received by the receiver at different distances from the same source. This method also has a wavelength or wavelength limit of up to 1.2 µm for the measured signal. In order to eliminate errors associated with the fact that the structure of airborne formation can undergo changes in time, measurements at two different distances should be carried out with the shortest possible time interval between them. This may require the use of two receivers.

To reduce errors, the method according to claim 7 can be supplemented with the operations of increasing the number of measuring distances of the MPE. For this, the invention uses the following additional features:

8. Measurement of radiation intensity and calculation of MPE are carried out at more than two distances from the source, and to calculate the effective droplet size, the meteorological visibility range obtained by processing the results for all distances is used.

At the same time, there is no requirement that all distances for measuring the radiation intensity must be different. The main thing is that within one small solid angle relative to the point where the emitter is located, at least only two of them are different.

In formulas (2) and (3) for calculating the MDI, the coefficient 3.91 is | ln (0.02) |, where 0.02 is the transmittance of visible light at the MDI distance.

The method for determining the structure of airborne formations of clouds and fogs is as follows. In an airborne droplet formation, its water content and meteorological visibility range (MVR) are measured.

Water content and MPE measurements can be carried out in parallel or sequentially in any order. For a sufficiently accurate determination of the current value of the effective radius of droplets, the total period of time for both measurements should not be more than 20-30% of the characteristic stability time of airborne formation, during which it approximately retains its physical properties, which include water content and droplet size ... The rate of change in the physical properties of airborne formation can be estimated by the change in air transparency. For example, the characteristic stability time in test chambers where artificial fog is used can be 1-2 hours, morning surface and drive fog under cloudless sky conditions - up to 1 hour, morning surface and drive fog under cloudy sky conditions - 2-5 hours. , clouds, clouds - hours and tens of hours. Changes in weather conditions have a great influence on the state of drip formation.

Measurement of the water content of airborne formation is carried out in any available way. For example, the method of inertial deposition of drops on hygroscopic paper [1] or electrothermal method [2] can be used. The first of these methods is used in surface or near-surface fogs. The second method is used when a vehicle (including an aircraft) is moving in fog or cloud. The second method can be used in continuous measurement mode with automatic output of measurement results, while the first method is based on periodic air pumping and further manual processing of the measurement results. The measurement cycle in the first method can be several minutes.

Determination of MPE can be made on the basis of estimates and measurements of the distance to indistinctly visible objects. In this case, a subjective assessment of the transparency of the air is given in the form of its transmittance value and, according to the Lambert-Bouguer-Baer law, the measured distance is recalculated to the transmittance τ = 0.02, which must correspond to the MWD distance. Such a method for determining the MPE may not be sufficiently accurate and may require a significant amount of time associated with an expert assessment of the transmittance, measuring the distance and carrying out the conversion itself. Errors in determining the MPE and, consequently, in calculating the effective radius of droplets in an airborne formation, can reach 100% or more.

To eliminate this drawback in airborne droplet formation, the MVI is measured.

For this, according to the first option, an optical radiation source is placed in the area of airborne formation. This source may not be limited in terms of the wavelength range, but it must include a range of radiation with wavelengths not exceeding 1.2 µm. An infrared laser with a fixed wavelength and relatively high intensity can be used as a radiation source. In this case, infrared radiation is not visible to the human eye, which in some cases is preferable.

The source, if we are talking about periodically repeating or continuous measurements, can be installed permanently or it is placed in the area of airborne formation for the period of measurements, and then removed. A stationary source can also be installed on a vehicle, for example, on the roof of a rolling stock of a train, a car, on an airplane body, etc. required distance from the source. The radiation receiver can also be installed permanently or periodically removed. After turning on the emitter, the receiver measures the radiation intensity from the source in the form of an electrical signal and, if necessary, converts it into power (W / m) according to the calibration dependencies. Before starting the measurement according to the technical characteristics, if the source is verified, or by means of measurement, the intensity of radiation emitted by the source in the same wavelength range as measured by the receiver is determined. It is recommended to measure the intensity of radiation emitted by a source with the same receiver at a short distance from the source. It is recommended that this distance be no more than 2% of the transmittance measurement distance. In relation to the values of the measured radiation intensities, the air transmittance is calculated and the meteorological visibility range is calculated using the formula (2). To increase the accuracy of calculating the MPE, several measurements of the transmittance are carried out at various points relative to the source. These points can be selected at different distances relative to the source and at the same distance, but in different directions. In the latter case, the spatial structure of the droplet-air formation can be checked and determined. With several measurements, the MPE is determined by processing the measurement results.

According to the second option, the MPE measurement is carried out without measuring the air transmittance, but only by measuring the intensity of the source at various points relative to the source. The distance between the receiver and the source can be two or more, if an increase in the accuracy of the MPE measurement or determination of the spatial structure of a droplet-air formation is required. The choice of distances between the receiver and the source is carried out in such a way that, for each spatial direction, at least two of them are different. For each pair of measurements according to the formula (3), the calculation of the MPE is carried out.

When measuring the MPE in its simple implementation (without carrying out additional measurements to improve the accuracy of determining the MPE), the second option requires the use of a larger number of radiation detectors, but does not require measuring the intensity of the radiation emitted by the source, which introduces additional errors.

The MPE measurements are carried out using a source and receivers using optical radiation in the wavelength range not exceeding 1.2 µm. In this case, the upper limit of the wavelength range is set based on the following provisions. The upper limit of 1.2 μm, located in the infrared region, corresponds to the condition under which the effective droplet radius exceeding r> 3 μm can be determined with sufficient accuracy. Moreover, the larger the effective radius of droplets calculated by formula (1) exceeds 3 μm, the more accurate the results are obtained by its application for calculating the optical properties of clouds and fogs. With a decrease in the value of the determined effective radius, the upper limit of the wavelengths of the radiation used should be reduced when measuring the MPE. For example, with an effective radius of 2 μm, when measuring the MPE, the upper limit of wavelengths should be reduced to a level corresponding to the violet spectrum of visible light, and with an effective radius of 1 μm or less, the MPE measurements should be carried out in the ultraviolet radiation ranges.

After measuring the MPE according to the formula (1), the effective radius of the droplets in the airborne formation is calculated.

An example of using the invention.

It is necessary to conduct an external thermal imaging survey of the construction site in foggy conditions. After thermography, computer processing of the results will be carried out, which serves to correct the temperature field obtained on the thermogram. During computer processing, the possibility of correcting thermograms will be used taking into account the real values of the transmittance of infrared radiation by air, formed by the absorption of radiation by water vapor, carbon dioxide and radiation scattering. Thermography will be carried out in the IR range of 8-14 microns. Measurement conditions - air temperature 0 ° С, relative humidity 100%.

The task of using the invention: to determine two distances for thermography, at which the air transmittance will be two different known values τ = 0.5 and τ = 0.8. During computer processing of thermograms, these two values will be used as correction parameters.

When using the claimed invention, the following results were obtained:

- water content measured by inertial sedimentation - w = 2.5⋅10 ^-2 g / m ³ ;

- meteorological visibility range, measured by radiation intensity at two distances - L = 500 m;

- calculated by the formula (1) the effective radius of droplets in fog - r = 4.9 μm.

According to the results obtained for this airborne formation, the concentration of droplets with an effective radius of 4.9 μm is N = 51 cm ^-3 .

Using these parameters, the thermal imaging distance in the IR range of 8-14 μm, calculated using the Mie theory of radiation scattering and taking into account the absorption of radiation by water vapor and carbon dioxide, will be:

- L '= 115 m for the transmittance τ = 0.5

- L '= 34 m for the transmittance τ = 0.8

Used sources

[1] USSR author's certificate No. 1580302. Method for determining water content in fog. Published: 07.23.1990.

[2] RF Patent No. 2562476. Electrothermal method for determining the water content of an air stream. Published on September 10th, 2015.

[3] RF patent №2167439. Device for remote determination of water content of cloudy and cloudless atmosphere. Published on May 20, 2001.

[4] USSR author's certificate No. 621990. Method for determining fog droplets. Published on 08.30.1978.

[5] RF Patent No. 2630853. Device for measuring droplet sizes in water-air streams. Published on September 13th, 2017.

[6] RF Patent No. 1780599. Method for determining the microstructure of droplet clouds and fogs. Published on 10/15/1994.

[7] Boren K., Huffman D. Absorption and scattering of light by small particles. - M .: Mir, 1986 .-- S. 221-222. - 660 p.

Claims (9)

1. A method for determining the main parameters of the structure of airborne formations of clouds and fogs, including measuring the water content of airborne formations and the size of the droplets, characterized in that their effective radius is determined as the size of the droplets, for which the meteorological visibility is determined, and the effective radius drops in microns are calculated by the formula

, where w is the water content in g / m ³ , L is the meteorological visibility range in m. 2. A method for determining the main parameters of the structure of airborne formations of clouds and fogs according to claim 1, characterized in that the meteorological visibility range is calculated by the formula

where τ is the transmittance of air between the source of optical radiation and a receiver remote from it, measured in an airborne formation at wavelengths not exceeding 1.2 μm, and l is the distance between the source and the receiver of optical radiation (m). 3. A method for determining the main parameters of the structure of airborne formations of clouds and fogs according to claim 1, characterized in that the meteorological visibility range is calculated by the formula

where J ₁ and J ₁ are radiation intensities (W / m ² ) from a source of optical radiation located in an airborne formation, measured at wavelengths not exceeding 1.2 μm, at distances l ₂ and l ₂ from the source (m) ...