TECHNICAL FIELD

The invention relates to a method and apparatus for evaluating the concentration, material and size of microplastics in aqueous medium in real time.

The invention is used in environmental management and protection of the health of the population by a quick and efficient monitoring of presence and concentration of microplastics in aqueous medium.

STATE OF ART

Microplastic pollution is one of the most serious challenges facing humanity in the last 20 years. By microplastics is meant solid particles of various polymeric substances with a size of 1 gm to 5 mm. The growing volume of plastics produced worldwide makes the problem more and more relevant and serious. According to research publications, the concentration of microplastics in open, natural aquatic environments can reach 10,000 particles per m ³ , and the main amount of microplastic particles in water basins (rivers, lakes, seas) is with a size between 70 gm and 500 gm. Microplastic pollution has a number of specifics. On the one hand, it is the low rate of degradation of polymers in the natural environment. On the other hand, plastics age and in the aging process microparticles less than 5 mm in size are realized and spread into the soil and through wind and rain most of them fall into the air and water. Thirdly, the small size of the particles makes it difficult to remove them and facilitates their entry directly or indirectly into the human body. Particularly negative is the impact of the pollution with microplastic of open water basins - rivers, lakes, seas, oceans. Except through drinking and cooking water, microplastics enter the human body through fish, as well as through agricultural products irrigated with water contaminated with microplastics.

This raises the need for a method and device for fast, easy and reliable evaluating of the concentration of microplastics in the water and of their characteristics - size and material.

Currently, the pollution control of water basins with microplastics is generally performed by executing the following sequential actions and processes:

- Sampling on spot;

- Storage of samples;

- Transportation of samples to the laboratory;

- Separation of microplastics in the samples by known methods, density separation is most often applied;

- Filtration;

- Quantitative analysis - the number of particles and their size are determined visually by microscope or by specialized software;

- Qualitative analysis - the material of the microplastic particles is determined by spectroscopic analysis, FTIR (Fourier-Transform InfraRed) is most often used;

- The concentration of microplastic particles is determined on the basis of the total volume of samples collected at the test spot.

The method thus described is slow, laborious, complex and expensive, especially in the case of large-scale surveys in remote and/ or open water sources. Costs are high even in well-designed industrial and civil water infrastructures, as the process requires highly qualified staff and highly specialized expensive equipment. In addition, human intervention is indispensable at every stage which leads to the risk of accumulation of random and systematic errors which statistical analysis is difficult to remove. WO20 17220249A1 discloses a method and device for detecting microparticles in a fluid flow and evaluating the material. The method is based on the comparison of the difference in the attenuation time of the induced fluorescence at different polarization, which is unique for each material, with known and controlled in advance polarization of the radiation in a specific spectrum. The disclosed device operating by the method includes a means for generating fluid flow and a pulsed laser emitting coherent electromagnetic radiation with a specific polarization and wavelength suitable for inducing fluorescence in the microparticles in the flow. The laser beam is directed toward a measurement zone in the fluid flow. The cross section of the measurement zone is determined by the cross section of the beam. An optical system located at the entry of the measurement zone polarizes the laser beam in a specific direction of polarization. A second optical system, located at the exit of the measurement zone redirects the already passed beam to pass through the measurement zone again but in a different direction of polarization. The device also includes first and second spectrometers, which determine the parameters of the induced fluorescence in the molecules of the particles in the flow created by the two polarizations, and the parameters of the pulse, respectively. In particular, the intensity of different wavelengths for different directions of polarization over time is measured. The spectrometers are connected to a data Acquisition and processing device, which according to a preset mathematical model evaluates the difference in the time for attenuation of the induced fluorescence for different polarization. By comparing the survey data with data of previously known or previously generated and controlled polarization of the radiation and the spectrum of this fluorescence, the material of the solid particles in the fluid is evaluated. The disclosed method and device make it possible to detect the presence of solid particles and to evaluate their material but only if fluorescence can be induced in them in the range of wavelengths emitted by the source. For some types of materials, including plastics, it is impossible to induce fluorescence at the wavelengths used for each specific laser used. In addition, the concentration and size of the microparticles cannot be evaluated by this method and device.

The method is not suitable for use in unmodified aquatic medium, as parasitic fluorescence of unavoidable organic impurities in the environment (rivers, lakes, seas) reduces the accuracy and reliability of the results. Beside, the method is complex, time consuming, requires highly qualified personnel and specialized laboratory equipment.

DISCLOSURE OF INVENTION

The task of the invention is to provide a fast, easy and at the same time sufficiently accurate and reliable method for in- situ evaluating the concentration, material and size of microplastic particles in an aqueous medium in real time. Another task of the invention is to provide a device working by the method which is easy to operate and maintain, does not require highly qualified personnel, can work on spot and gives real-time results about the concentration of microplastics in the medium and the size and material of the microparticles.

This problem is solved by the proposed method and device for evaluating the concentration, material and size of microplastics in aqueous medium.

The method includes the following operations in the given sequence:

- a fluid flow W is created at a constant known speed in the studied aqueous medium; - a measurement zone is created in the flow W, representing a virtual cylinder with diameter d _b and length L formed by a laser beam F directed towards the flow W. The measurement zone includes a first part with length Li, where 1500≥L ₁ ≥500 mm, and a second part with length L ₂ ≥400 mm, wherein the volume of said first part of the measurement zone is defined on the basis of maximum expected concentration of microplastics in natural basins of 10000 particles/ m ³ , so that no more than 3 microparticles within one second pass through the measurement zone.

- part of the water in flow W is filtered with a coarse filter retaining particles above 5 mm and directed to the first part of the measurement zone, and the rest of the water in flow W is filtered with a fine filter retaining particles above 10 μm and fed in the second part of the measurement zone.

- the measurement zone is continuously irradiated with a pulsed laser beam F with a diameter d _b ;

- each pulse of the laser beam F contains n number of waves of different length λ _ί , where n≥2, and 1≥i≥n in the range 300-800 nm, the length of each pulse is less than 100 ns, and the frequency of pulse repetition is at least 10 kHz.

- at the entry of the measurement zone the laser beam F is split into two beams with identical characteristics and a predetermined power ratio - a measurement beam F _M , which passes through the measurement zone, and a reflected beam F';

- the reflected beam F' is split within each pulse to its constituent waves λ _ί and at least one measurement of the input power P _oi is done in each pulse for each wavelength λ _ί.

- at the exit of the measurement zone the measuring beam F _M is split within each pulse to its constituent wavelengths λ _ί and within each pulse at least one measurement of the transmitted power P _ti is done for each wavelength λ _ί ;

- the obtained temporary values for input power P _oi and transmitted power P _ti are fed to a data acquisition and processing device;

- on the basis of the obtained temporary values for the P _ti / P _oi ratio in the absence of a microparticle, the absorption coefficient K _awi for the aqueous medium in the measurement zone is determined at least once in each pulse for each every single wavelength.

- the determined value for K _awi is recorded in the data acquisition and processing device and updated over a certain period of time T;

- on the basis of the temporary values from the measurements for P _ti , P _oi and the determined value for K _awi by applying a predefined mathematical model, temporary values of the ratio A _ij between the total coefficients of extinction Q _ext (λ _ί ) and Q _ext (λ _ί ) are determined at least once in each pulse for each wavelength of each individual pair of waves of different length λ _ί , wherein the total number of ratios A _ij is k, where k = n(n-1)/2, 1≥j≥n, i≠j.

- The complex refractive index m = n _r -i.k _r is determined empirically in advance, where n _r and k _r are respectively the real and imaginary component for the most common plastic substances for the wavelengths li used, and under a predefined mathematical model calibration values for A _ij are calculated for the respective pairs of wavelengths of the chosen range for particles of a specific material and size, which are recorded in the data acquisition and processing device;

- by comparing the obtained temporary values for A _ij for the microplastic particles passed through the measurement zone with the recorded calibration values for A _ij , the presence of microplastic particles of a specific material and with a specific size is determined; - the results of the comparisons are recorded in real time in the data acquisition and processing device and after subsequent statistical processing and analysis serve as calibration values for subsequent comparisons.

- After completing the survey of the specific aquatic medium, the concentration of microparticles in the medium is evaluated under a predefined algorithm on the basis of the flow speed W, the geometric parameters of the measurement zone and the stored results of the comparisons between the temporary and the calibration values for A _ij .

The length L ₂ is chosen to be at least an order and a half bigger than the maximum size of the microplastic particles, so that the detectors measuring the transmitted power work in a far-filed regime.

The spectral range is chosen with a view to the optical properties of water and polymers, and in particular, with a view to the complex refractive index m, so to ensure a measurable difference in the absorption of both water and the most frequently used plastic substances for different wavelengths emitted by the laser source.

For particles bigger than 50 μm for the spectral range thus selected, the interaction of the microplastic particles in aqueous medium is described with sufficient accuracy by the Geometric Optics Approximation (GOA).

The method is based on the specific absorption of plastics, and in particular, on the fact that the dispersion of the complex refractive index m is unique for each specific type of material, and that the dispersion of the absorption coefficient K _a is characterized by measurable differences for different polymeric substances.

Preferably, the wavelength λ _ί is in the range 450-750 nm.

When reducing the diameter d _b of the beam F, the accuracy and reliability of the measurement results increase also for microparticles with very small dimensions - less than 100 μm . This is because the ratio of the transmitted power to the input power Pt/P ₀ is a function of the ratio of the cross-sectional area of the microparticle to the cross- sectional area of the beam S _P /S _F. The closer the ratio S _P /S _F to 1, the more accurate is the measurement at the same sensitivity of the detectors used.

Preferably the diameter d _b of the beam F is less than or equal to 6 mm.

The accuracy of the method is rising with increasing the number of waves of different lengths in the determined range as the greater the number of waves of different lengths, the greater the number of temporary values of A _ij , and hence the greater the number of comparisons with the recorded calibration values of A _ij .

Increasing the number of measurements within a single pulse also increases the accuracy and reliability of the method. It is preferable to perform at least ten measurements of the input power P _0i and the transmitted power P _ti , respectively, for each wavelength λ _ί within one pulse.

The time T for updating the value of the absorption coefficient of water K _awi depends on the expected change in the optical properties of the medium and the desired accuracy of the results. It is recommendable the update to be performed as often as possible. It is preferable K _awi to be updated every second or at shorter intervals, even within each pulse.

In a variant of the method according to the invention the measuring beam F _M is split into two parallel beams F _M ' and F _R with identical geometric characteristics and with a predetermined power ratio within each pulse, where the beam F _M · passes through the measurement zone and the beam F _R passes through a reference zone in the flow W which has the same geometric characteristics as the measurement zone. Before entering the reference zone the water flow W is filtered through a second fine filter to remove particles above 10 μm .

At the entry and exit of the reference zone the input power and the transmitted power in the reference zone P _Rol and P _Rti are measured at least once per pulse, the results are submitted to the data acquisition and processing device and serve to calculate the absorption coefficient of the aquatic medium K _awi for each wavelength.

Created is also a device for determining the concentration, material and size of microplastics in aqueous medium working after the proposed method. The device includes a means for generating fluid flow W with a constant speed provided with a speed sensor for measuring the flow speed, and a source of pulsed coherent electromagnetic emission generating a pulsed laser beam F with a diameter d _b consisting of n in number waves of different lengths λ _ί , where 1≥l≥n and n≥2, in the range 300-800 nm. The length of each pulse is < 100 ns and the pulse repetition frequency is ≥10 kHz. The laser beam F is directed towards the water flow W forming in it a measurement zone in a form of a virtual cylinder with a length L and a diameter of the base d _b . The measurement zone consists of a first part with a length Li in the range 500 -1500 mm, and a second part with a length L2 ≥ 400 mm. The device also includes a coarse filter retaining particles above 5 mm, and a fine filter retaining particles above 10 μm , which are located in the flow W immediately in front of the first part and of the second part of the measurement zone, respectively. An input optical system is arranged at the entry of the measurement zone, and an output optical system - at the exit of the measurement zone. The input optical system includes a beam splitter and n-1 in number dichroic mirrors at the entry arranged one after the other in the direction of the beam F' which is reflected in the beam splitter. The input optical system is connected to an input measuring block including input detectors for measuring the input power P _oi . The output optical system includes n-1 in number dichroic mirrors at the exit and is connected to an output measuring block, which includes output detectors for measuring the output power P _ti . The input measuring block, the output measuring block and the speed sensor are connected to a data acquisition and processing device.

For the parameters thus defined the size parameter x=2.π.a/λ> 140, where a is a characteristic size of the microparticle, which excludes scattering in the direction of the output measuring block, respectively excludes this component in the value of the transmitted power P _ti .

In addition, the location of the optical system alongside the axis of the beam F and the long optical path between the microparticle and the output detectors also precludes the possibility to measure scattered emission.

In a variant embodiment of the device according to the invention, the input optical system comprises a second beam splitter and a 100% reflective mirror. The second beam splitter splits the beam FM which has passed through the first beam splitter into two beams FM· and FR with identical geometric characteristics and a predetermined power ratio, wherein the beam F _M · passes through the measurement zone and the beam FR is reflected in the 100% reflecting mirror and irradiates the flow W forming in it a reference zone with diameter d _b and length L, and said reference zone is located between the input optical system and the output optical system after the measurement zone in the direction of water flow W. Between the measurement zone and the reference zone there is a second fine filter retaining particles above 10 μm .

The data acquisition and processing device may have a display for visualizing the information in a proper way. It is possible that workstations are connected interactively to the data acquisition and processing device allowing the results of the monitoring survey data to be displayed in a proper form, and allowing to enter empirical data for the complex refractive index m for new types of polymeric materials, as well as empirically determined calibration values for A _ij for the respective pairs of wavelengths in the selected spectral range for particles of specific material and size. The data acquisition and processing device may contain a transmission block including at least one communication module like LAN, GSM, GPRS, 3G, SMS, VHF, UHF.

Preferably, the length Li is within the range 600 - 1200 mm and the length L2 is greater than 500 mm.

The means for directing the water flow can be in the form of a funnel or a pipe with a rectangular cross section. The means for directing the water flow can be detachable to facilitate the transportation of the device according to the invention to the chosen survey location.

The proposed method allows to determine in a quick and easy way the number, size and material of plastic microparticles, as well as the concentration of microplastics in aqueous medium in real time in situ. The results obtained are of good accuracy and reliability which can be further improved if necessary. The device is easy to service and maintain and does not require special qualification of the service staff. It can be transported by car and carried by hand over short distances. This makes the device universally applicable in survey, monitoring and control of microplastic pollution in natural water basins and water infrastructures. These advantages make it particularly suitable and effective in the surveys of microplastic contamination of large and / or remote water basins. The data can be transmitted in real time and used as a basis for operative decisions related to environmental management and protection of people’s life and health. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic diagram of an exemplary embodiment of a device according to the invention;

Figure 2 is a schematic diagram of an input optical system and an input measuring block of the device of Figure 1 ;

Figure 3 is a schematic diagram of an output optical system and an output measuring block of the device of Figure 1 ;

Figure 4 is a schematic diagram of a variant embodiment of a device according to the invention;

Figure 5 is a schematic diagram of an input optical system and an input measuring block of the device of Figure 4;

Figure 6 is a schematic diagram of an output optical system and an output measuring block of the device of Figure 4;

Figure 7 is a side view of a conditional equivalent particle irradiated along the normal to the base.

Figure 8 is a 3D diagram of the relation between the coefficients of extinction in aqueous medium Q _ext , the absorption coefficient K _a and the reflection coefficient R _n for different materials in the determined wavelength range for three different particle sizes;

Fig. 9 is a diagram of the typical distribution of n _r and k _r for the most widely used materials for λ _ί = 500nm n λ ₂ = 600 nm.

DESCRIPTION OF EMBODIMENTS

Figures 1-3 illustrate an exemplary embodiment of the method and device according to the invention. The device includes a pulsed laser 1 generating a pulse laser beam F and a known means 3 for generating a fluid flow W with a constant speed, for example a funnel with an adaptable variable cross section in which there is a speed sensor 16 for measuring the speed of the flow W. In this embodiment the laser beam F is with a diameter d _b = 6 mm and emits simultaneously in each pulse three waves of different lengths λ _ί , λ ₂ and λ ₃ within the spectral range of 450-800 nm, where the length of each pulse is 100 ns and the pulse repetition frequency is 10 kHz. The laser beam F irradiates the water flow W, forming in it a measurement zone 2, representing a virtual cylinder with a length L and a diameter of the base 6 mm. The measurement zone 2 consists of two parts, in this embodiment the first part 2' is with length L ₁ = 700 mm and the second part 2" is with length L ₂ = 500 mm.

On the way of the flow W, right in front of the first part 2' of the measurement zone 2 stands a coarse filter 14 retaining particles over 5 mm, and right in front of the second part 2" of the measurement zone 2 stands a fine filter 15 retaining particles over 10 μm . There is an input optical system 4 at the entry of the measurement zone 2 and an output optical system 7 at the exit. The input optical system 4 is illustrated in Figure 2. It includes a beam splitter 11 and dichroic mirrors at the entry 12 arranged one after the other in the direction of the reflected beam. The output optical system 7 is illustrated in Figure 3. In this embodiment the output optical system 7 includes two dichroic mirrors at the exit 13. The input optical system 4 is connected to an input measuring block 5 which in this embodiment includes 3 input detectors 6 to measure the input power P _0i and the output optical system 7 is connected to an output measuring block 8 including 3 output detectors 9 for measuring the transmitted power P _ti . The input detectors 6 and the output detectors 9 are connected to a data acquisition and processing device 10. In the funnel 3 directing the flow W to the measurement zone 2 there is a speed sensor 16 for measuring the speed of the water flow which is connected to the data acquisition and processing device 10.

The laser beam F passes through the input optical system 4, where the beam splitter 11 splits it into two beams with equal geometry and power - measuring beam FM and reflected beam F'. The measuring beam FM passes through the measurement zone 2. Dichroic mirrors at the entry and at the exit 12 and 13 split the measuring beam F _M within each pulse to its constituent waves λ _ί , λ ₂ and λ ₃ . The input detectors 6 and the output detectors 9 measure, in this embodiment once per each pulse, respectively the input power Poi, P0 ₂ and P 03 and the transmitted power P _ti , P _t2 and P _t2 for each wavelength. The information from the input and output detectors 6 and 9 is fed to the data acquisition and processing device 10. It contains a database of empirically determined calibration values for A _ij for the respective wavelengths λ _ί , λ ₂ and λ ₃ for particles of a specific polymeric material and size.

The absorption coefficient of the aqueous medium K _awi for each wavelength is determined after a predefined mathematical model, the K _awi value is recorded in the data acquisition and processing device 10 and is updated, in this embodiment, at one-second intervals. Based on the operative temporary data for the input power P _oi and the transmitted power P _ti for each wavelength λ _ί , λ ₂ and λ ₃ and on the actual value for K _awi , the temporary value of the ratio A _ij between the total coefficients of extinction is determined for the three separate pairs of waves of different lengths, which is updated at a given time interval, in this embodiment - once per each pulse.

It is the conditional equivalent particle that is in the basis of the mathematical model for calculating the absorption coefficient of the aquatic medium K _awi and the temporary values of A _ij . The conditional equivalent particle is a homogeneous and isotropic microparticle of polymeric material in the form of a cylinder with a height equal to the diameter d _p of the base, which is irradiated along the normal to its base, i.e. the angle of incidence Θ is 0. For the conditional equivalent particle thus defined the optical length is d _p .

For the reflection coefficient R _n at Θ=0 the following relation is valid:

For the conditional equivalent particle the absorption in the measurement zone 2 is described by the Bear- Lambert relation: where is the total coefficient of extinction, and the power transmitted through the water in the absence of a particle is

For the conditional equivalent particle When φ = 0, i.e. in the absence of a particle in the measurement zone 2, . In this case Ptw depends only on the water absorption coefficient K _a in the measurement zone 2, where K _a =4.π.k/λ. Respectively, Q _ext can be determined for each temporary measurement for the respective wavelength by the formula:

From the relation , where σ _ext is the extinction cross section for a particle of a specific material, which is in fact a measure of the ability of said substance to absorb, reflect and scatter electromagnetic radiation with the respective wavelength, it follows that the total coefficient of extinction for each wavelength Q _ext is directly related to the extinction cross section σ _ext and the cross- sectional area of the particle S _p . Therefore, the beam F includes at least two wavelengths emitted within the same pulse, i.e. at any one time the two wavelengths interact with the same cross section of the particle S _p .

Since for the ratio A _ij between the total coefficients of extinction Q _ext (λ _l and Q _ext (λ _j ) for the different wavelengths the relation valid, it follows that A _ij is unique for each particle of a specific material and of specific optical length, i.e. size.

When the value obtained for A _ij is equal to or tends to 1 within the acceptable error of the input and output detectors 6 and 9, measuring the input and output power P ₀ and Pt, this is an indication that the microparticle is not of plastic. A value for A _ij other than 1 within the acceptable error of the measurement instruments is an indication that the passed microparticle can be defined as made from polymeric material.

At the set in the model maximum particle concentration, pulse repetition rate and number of measurements per pulse, the predominant number of measurements will be in a particle-free medium, which means that the predominant number of values for P _ti /P _oi will be very close and tending to approach the maximum measured value. Based on these values the water absorption coefficient K _awi for each wavelength can be calculated with sufficient accuracy. The defined coefficient is recorded and updated at a given interval, in this case every second.

Figures 4-6 illustrate a variant embodiment of the method and device according to the invention. The device includes a funnel 3 for creating a fluid flow W with a speed sensor 16 for measuring the speed of water and a pulse laser 1 generating a pulse laser beam F. Chosen in this embodiment is a laser beam F with a diameter dp = 5.5 mm and with two waves of different lengths lΐ and l2 in the range 450-700 nm. The length of each pulse is 50 ns, and the pulse repetition frequency is 20 kHz. The input optical system 4 is illustrated in Fig. 5. It includes a beam splitter 11 and a dichroic mirror at the entry 12 located in the direction of the reflected beam F'. The input optical system 4 includes also a second beam splitter 17 and a 100% reflective mirror 18. The second beam splitter 17 splits the beam FM which has passed through the beam splitter 11 into two beams FM' and FR both having equal geometric characteristics and equal input power. The beam FM' reflects in the 100% reflecting mirror 18 and passes through the measurement zone 2, and the beam FR irradiates the flow W, forming in it a reference zone 19 with diameter db and length L, the reference zone being located between the input optical system 4 and the output optical system 7 after the measurement zone 2 in the direction of water flow W.

The measurement zone 2 consists of two parts, in this embodiment the first part 2' is with length L ₁ = 600 mm and the second part 2" is with a length L ₂ = 400 mm.

Along the direction of the flow W, immediately in front of the first part 2' of the measurement zone 2 there is a coarse filter 14 retaining particles over 5 mm, and immediately in front of the second part 2" there is a fine filter 15 retaining particles over 10 μm . Immediately before the reference zone 19 there is a second fine filter 17 retaining particles above 10 μm .

The input and output optical systems 4 and 7 are connected to the input measuring block 5 and the output measuring block 8, respectively. The input measuring block 5 includes input detectors 6 for measuring the input power P _0i in the measurement zone 2 and the reference zone 19. The output measuring block 8 includes output detectors 9 and 9' for measuring the transmitted power P _ti and P _Rti in the measurement zone 2 and the reference zone 19, respectively. The input measuring block 5, the output measuring block 8 and the speed sensor 16 are connected to data acquisition and processing device 10.

The laser beam F passes through the input optical system 4, where a beam splitter 11 divides it into two beams with the same geometric characteristics and, in this embodiment, the same power within each pulse - a measuring beam FM and a reflected beam F'. The measuring beam FM passes through the second beam splitter 17, which splits it into two beams FM' and FR with the same geometric characteristics and the same power emitted simultaneously in each pulse. The beam FM' reflects in 100% mirror 18 and passes through the measurement zone 2, and the beam FR passes through the beam splitter 17 and irradiates the reference zone 19. The coarse filter 14 retains particles above 5 mm, so the water in the first part 2" of the measurement zone 2 does not contain particles above this size. Thanks to the fine filter 15 and the second fine filter 20, the second part 2" of the measurement zone 2 and the reference zone 19 do not contain microparticles larger than 10 μm . The dichroic mirrors at the entry and the exit 12 split the reflected beam P in each pulse to its constituent waves λ _ί and λ ₂ . The input detectors 6 measure the input power P _oi for each wavelength in the measurement zone 2 and the reference zone 19, and the output detectors 9 measure the transmitted power P _ti and P _Rti for each wavelength in the measurement zone 2 and the reference zone 19, respectively. In this embodiment ten measurements are performed per each pulse. The information from the input and output detectors 6 and 9 is fed to the data acquisition and processing device 10, where it is processed and the results are recorded in the database and visualized on the display. The survey results can be transmitted in real time to mobile or stationary workstations - tablets, computers, smartphones wirelessly connected to the data acquisition and processing device.

USE OF INVENTION

The individual modules of the device according to the invention - laser, optical-measuring module, means for directing and measuring the water flow and computer, are transported to the water basin to be monitored. The assembly is done on the spot, the mode of assembling depends on the nature of the water basin. In surveys of open water medium the device is mounted on a specially designed floating platform provided with means for positioning and securing the modules of the device, and the platform is towed at a constant speed. When in the water environment there is no constant current in a given direction, the measurements are done while the platform is moving. In environments with a constant current, the platform is positioned towards the current’s direction and the process of measurement begins. In surveys in closed industrial water infrastructures a water flow in the environment is generated and directed to the device. The device is powered by the civil electrical grid or a generator depending on the available options at the survey location. The device is calibrated before operation. The duration of operation of the device depends on the ability of uninterruptible power supply, the lifetime of the laser active zone and the particular survey design. It is preferable to use laser sources that provide at least 1000 work hours.