EA046482B1 - METHOD FOR DETECTING OIL FILMS ON A WATER SURFACE - Google Patents

Description

The present invention relates to the field of optical location and can be used for monitoring the water surface of water areas in order to detect oil films.

An important task of environmental monitoring of the water surface is the task of detecting oil spills. The solution to this problem is especially relevant for relatively small water areas where there is intensive shipping and unauthorized discharges of oil products into the water are possible. In this case, optical locators (lidars) are used, placed on stationary objects near the sea surface, for example, on bridge supports, to ensure continuous environmental monitoring.

In the process of spreading on the water surface, the thickness of the oil film decreases over time to values on the order of several micrometers, which requires the creation of more advanced detection means.

The physical basis for remote detection of oil films on a water surface using a lidar is the difference in the characteristics of optical radiation signals reflected from a clean water surface and a water surface covered with an oil film. This difference is due to the difference in the refractive indices of oil and water, as well as the effect of smoothing the relief of the water surface by the oil film.

In the case of oil films of large thickness, the penetration of optical radiation into the film is neglected and a threshold method is used to detect an oil film on a water surface. Since the reflectance from the oil film (air-oil interface) will always be greater than the reflectance from the air-water interface, the latter value is used as a detection threshold.

For the case of thin films up to 10 microns thick (Kozintsev V.I. et al. Optical-electronic systems for environmental monitoring of the natural environment. M.: Publishing House of Moscow State Technical University named after N.E. Bauman, 2002. pp. 229-232) reflection optical radiation occurs from the air-oil-water interface, and the reflection coefficient is oscillating due to the phenomenon of interference inside the film, as a result of which detection of the latter becomes difficult.

There is a known method for detecting an oil film on the sea surface (USSR Copyright Certificate No. 1354073, class G01N 21/55, 1987), which consists in irradiating the water surface under study with a pulsed beam of optical radiation, receiving the reflected signal and comparing the signals reflected from the clean surface. and the studied water surface. The number of pulse signals N that exceed the analyzer response threshold is selected as a comparison parameter. When N>Nb, the presence of an oil film is judged, and when N<Nb, its absence is judged, where Nb is a number characterizing the probability of signal reception.

The main disadvantage of this analogue method is the inability to detect thin oil films on the sea surface. Another disadvantage is the low productivity of searching for oil films on the water surface, due to the small size of the viewing area.

There is a known method for detecting oil pollution on the surface of water (patent RU, No. 2387977 C1, G01N 21/55, 2008), including irradiation of the studied water surface with a pulsed optical beam with a radiation wavelength tunable in a narrow spectral range, registration of radiation reflected from the water surface , determining from measurement data the dependence of the power of reflected radiation on the wavelength and finding, based on this dependence, the reflection coefficient and its second derivative with respect to wavelength. A decision on the presence of an oil film on a water surface is made by simultaneously fulfilling two relationships, which include the reflection coefficients from the studied and clean water surfaces and the second derivatives along the wavelength of the reflection coefficient from the studied and clean water surfaces.

The main disadvantage of this analogue method is the small viewing area, and, as a result, the low productivity of searching for oil films on the water surface. Another disadvantage is the need to adjust the radiation wavelength, which requires the use of a technically complex laser, which reduces the reliability of the detection system.

The closest analogue in technical essence to the proposed method is a method for detecting oil films on a water surface, following from the technical implementation of the OS1 High Resolution Imaging Ouster lidar (https://data.ouster.io/downloads/datasheets/datasheet-rev06-v2p4os1.pdf ), in which: the axes of the emitting and receiving optical systems of the lidar are oriented normal to the plane of the water surface in a quiet state, multi-beam laser pulse radiation is generated, the water surface under study is irradiated with pulsed optical signals within a set of M generated laser beams, where M is odd and M>9, for each formed beam, the reflected optical signal is received, optical filtering is performed, the optical signal is converted into an electrical one, analog-to-digital conversion is performed, the power reflectance is calculated, and an image frame is formed from the totality of the reflectance coefficients obtained in one probing cycle.

The main disadvantage of this prototype method is the relatively low probability of detection

- 1 046482 formation of thin films of oil on the water surface, due to the oscillating nature of the dependence of the reflection coefficient on the air-oil-water interface. Detection of oil films is carried out by analyzing the generated image frame containing data on all M laser beams, using the threshold method separately for each beam and making a decision if there is a fact of detection in the majority of M laser beams.

The objective of the invention is to develop a method for detecting oil films on a water surface with a lidar, providing a high probability of detecting thin films of oil on the sea surface in combination with a large viewing area.

The technical result consists of taking into account the dependence of the reflection coefficient of electromagnetic waves on the air-oil-water interface on the irradiation angle and film thickness when performing detection.

To ensure the specified technical result, a known method for detecting oil films on a water surface, in which: the axes of the emitting and receiving optical systems of the lidar are oriented normal to the plane of the water surface in a quiet state, multi-beam laser pulse radiation is generated, the water surface under study is irradiated with pulsed optical signals in within a set of M formed laser beams, where M is odd and M>9, for each formed beam the reflected optical signal is received, optical filtering is performed, the optical signal is converted into an electrical one, analog-to-digital conversion is performed, the power reflectance is calculated based on the totality of the received in one cycle of reflectance sensing, an image frame is formed, new features are introduced:

install an air temperature and humidity sensor at the lidar installation location;

measure air temperature and humidity;

adjusting the power value of the received optical signals;

set the thickness range and step of changing the thickness of the oil film to be detected;

calculate the reference dependence of the reflection coefficient on the air-oil-water interface in terms of power depending on the irradiation angle and the thickness of the oil film;

perform averaging of the power reflectance values obtained during one probing cycle for laser beams with the same inclination angles relative to the normal;

calculate the oil film detection rate

M _{2_}

FW= X[R^ _m ,d _K )-R ₂ ^ _m )], k = 1,K, t=1 where R is the reference dependence of the reflection coefficient on the air-oil-water interface in terms of power depending on the irradiation angle Θ ₁ , m and oil film thickness d _K ; R2 is the average dependence of the reflection coefficient on power for laser beams with the same angles of inclination, obtained during one probing cycle; K is the number of film thicknesses that are used to perform detection; M1 is the number of irradiation angles used;

oil film detection is performed when the condition min F<Δ _O is met, Δ _ο is the detection threshold, min F is the minimum value of the film detection indicator.

Thus, the use of a set of reference dependences of the power reflection coefficient on the irradiation angle and oil film thickness makes it possible to take into account the oscillating nature of the reflection coefficient from the air-oil-water interface during detection, which, in combination with the procedure for correcting the power of received signals and taking into account data on The combination of the obtained values of the power reflectivity within a large lidar viewing area makes it possible to increase the probability of detecting oil films on the water surface.

The implementation of the method is illustrated by the figure.

The figure shows the geometry of the problem of detecting oil films on a water surface, which includes a support 1, a holder 2, a lidar 3 consisting of a laser 4, an optical learning system 5, an optical diffraction element 6, an optical receiving system 7 of a multi-channel optical receiver 8, a block 9 information processing, information display system 10, laser radiation control unit 11, air-water interface 12, temperature and air humidity sensor 13.

The proposed method for detecting oil films on a water surface is implemented in the following way.

The lidar 3 is fixed on the support 1 using a holder 2 and the axes of the emitting optical system 5 and the receiving optical system 7 of the lidar 3 are oriented normal to the plane of the water surface in a quiet state. At the installation location of the lidar 3, a temperature and air humidity sensor 13 is installed on the holder 2.

Multibeam laser pulse radiation is generated as follows. Laser 4 generates a probing pulse at a fixed wavelength, which enters the emitting optical system 5, which directs the pulse to the optical diffraction element 6. Optical diffraction

- 2 046482 element 6 divides the primary laser beam into M laser beams emitted towards the interface 12 of the media.

Also, the probe pulse emitted by laser 4 is supplied to block 11 to control the intensity of laser radiation.

The water surface under study is irradiated with pulsed optical signals within the set of generated laser beams.

The irradiation angles corresponding to the angles of inclination of laser beams θ _m relative to the normal to the interface surface 12 are calculated using the formula in _m = θ ₀ + (m-1) · ΔΘ, /l = 1d7, (1) where

Δθ - step of changing the angle of inclination of the laser beam axis;

θ _ο - initial angle of inclination of the laser beam axis;

M is the number of generated laser beams.

The interface 12 of the media scatters the probing pulses arriving at it towards the lidar 3.

Next, for each generated laser beam, a reflected optical signal is received - a probing pulse using an optical receiving system 7. The optical receiving system 7 directs the received signals to a multi-channel optical receiver 8, with the help of which optical filtering is performed, the optical signal is converted into an electrical one and an analog signal is produced. digital transformation.

Air temperature and humidity are measured using sensor 13.

In information processing block 9, the power value of the received optical signals is adjusted for each generated laser beam

Dr = ^p pr Ί0 , (2) where

P _pr - power of the received optical signal;

p «d - power of the received optical signal after correction;

γ is the attenuation coefficient of the optical signal in the atmosphere;

h is the distance from lidar 3 to the water surface.

The optical signal attenuation coefficient γ as a function of wavelength, temperature and atmospheric humidity is determined according to recommendation MC3-R.P.1817 (08/2007): radio wave propagation data required for the development of terrestrial optical links for free-space communications.

The distance from lidar 3 to the water surface is determined when installed on support 1.

Also in the information processing block 9, the power reflectance is calculated for each generated laser beam. After processing all M laser beams, an array m = CI is obtained

To detect an oil film on a water surface, set the range of oil film thickness by setting the minimum and maximum oil film thickness - dm, _n and d _max , respectively, which will be detected.

The thickness of the oil film within a given thickness range is determined by the formula d(k) = d _mn + _{A =} jj. (3)

L - 1 where K is the number of film thickness gradations within a given thickness range, which determines the step of change in film thickness.

From (3), the step of changing the film thickness is equal to

Dpah - accident

K-1

For calculations, it is advisable to set the value odd and equal to K>101, ad,,,,,, 0.1 µm, d _max = 20 µm.

Calculate the reference dependence of the reflection coefficient on the air-oil-water interface in terms of power depending on the irradiation angle and the thickness of the oil film according to the formula [Born M., Wolf E. Fundamentals of Optics. Ed. 2nd. Translation from English. M.: Nauka, 1973. p. 76-77] _D/Q , _λ Ί2(θ1." _Ι ) + 'έ(θ" _Ι )Τ№) + 2η ₂ (θι, _η ,)^(θ„,)7'№)ε05(2β^ ) ^(θΐ,tL) =----3-------5----------------------------- --------7----------\ ' + ^g 12 (θΐ,/τζ ) ^g 23 (θ/ and УГ(с1к ) + 2/)2 (θΐ,ζτζ ) ^g 23 (θ/ ?? ) ^cos (^m,k) m = \,M, k = 1,K. (4) where n1, n ₂ , n ₃ are the refractive indices of air, oil and sea water, respectively;

λ is the wavelength of the emitted optical signal;

- 3 046482 d _k - oil film thickness;

r ₁₂ - reflection coefficient from the air-oil interface;

r ₂₃ - reflection coefficient from the oil-water interface;

T - oil film transmittance;

θ =0 -----i,m t+yo - _t - + 1^ = 0.5 · -M -1) - irradiation angle of the air-oil or air-water interface;

θ ₂ ^ - irradiation angle of the oil-water interface;

=^»2d _t co _S e _2tm ..... ..

- - auxiliary parameter.

The irradiation angle of the oil-water interface is determined by the formula

0 _{2 t} = arcsin —sin0 _{1 t} _ ⁿ 2 ' (5)

The reflection coefficient from the air-oil interface is calculated using the formula

Z? ₁ COS0 _lw -/l2COS02^ - ^Г 12(θΐ t ) =------7Г-----------> ^t = · ' /7 ₁ COS 0 _1/77 -н L? 2 ^C °S θ2/77 (6)

The reflection coefficient from the oil-water interface is calculated using the formula n ₂ COSe _2>m - «3COS0 _3m - ^r 23^2, t) =----7^-------7^, t = 1 ,M.

"2 ^cose 2, _m +"3 ^cose 3,">

Angle of refraction of laser radiation in an aqueous environment (Ό

The transmission coefficient of the oil film is determined by the formula ( 4l T --7'№) = exp ---k ₂ d _k , k = 1,K, y L J (9) where k ₂ is the oil absorption rate.

Averaging of the power reflectance values obtained during one probing cycle for laser beams with the same angles of inclination relative to the normal is performed according to the formula ^R l( ^Q m+M ₁ \ ⁿ P ^um=1 ^2^1т) ^{= <} Г / \ / \Ί -------- ₅ (1θ) ' 0.5-17?! (Θ _{Λ/1 +2} _ _t ] + (0 _{L//) +/77} ) I,ad = 2.M _g +1 where M ₁ =0.5-(M-1).

Calculate the oil film detection index l/, ₂ ____

F(k)= Σ[“(6,™^·)-“2(6,”)] ,k = l,K. (11) t=\

An oil film is detected when the condition minF<Ao is met, (12) where Δ _ο is the detection threshold, min F is the minimum value of the film detection index.

Based on the totality of the reflection coefficients R1 obtained in one probing cycle, an image frame is formed, which is displayed using the information display system 10.

Let us evaluate the increase in the probability of detecting an oil film on a water surface using the proposed method.

The prototype method implements the detection of an oil film from an image frame using a threshold method separately for each laser beam. A decision on detection is made if there is a fact of detection in the majority of laser beams by a number L of M possible beams, where the number L>0.5M. In this case, the probability of detecting an oil film from a combination of any L of M laser beams is calculated using the formula

Ρι= ΣΟ,/ρο/Ο-ρΧΑ (B) iL where p _O is the probability of detecting an oil film in one laser beam;

„ M-(M-1)...I) ^C LD/ ⁼ ----------j--------- ^z - coefficient.

In the proposed method, detection is carried out by comparing the known dependence of the power reflection coefficient on the irradiation angle and film thickness with the dependence of the power reflection coefficient on the irradiation angle for an unknown oil film thickness. In this case, for comparison, even those laser beams are used in which the power reflectance values are less than the threshold, i.e. in which the film was not detected. Therefore, to perform detection, use

- 4 046482 data on all M laser beams, in this case the probability of detecting an oil film from a set of M laser beams is calculated using the formula

P2 = YC _M ^\\-p^ . (14) /=1

With the probability of detecting a thin film of oil on the water surface in one laser beam equal to 0.6 and typical values M = 9, L = 5, we obtain P ₁ = 0.73, and P ₂ = 0.9997. The increase in the probability of detecting an oil film on the water surface is 36.9%.

Thus, the proposed method for detecting oil films on the water surface provides a high probability of detecting thin oil films on the sea surface in combination with a large viewing area.

The technical result of the invention has been achieved.

Claims (1)

A method for detecting oil films on a water surface, in which the axes of the emitting and receiving optical systems of the lidar are oriented normal to the plane of the water surface in a quiet state, multi-beam laser pulse radiation is generated, the water surface under study is irradiated with pulsed optical signals within a set of M generated laser beams, where M is odd and M>9, for each formed beam the reflected optical signal is received, optical filtering is performed, the optical signal is converted into an electrical signal, an analog-to-digital conversion is performed, the power reflectance is calculated based on the totality of the reflectances obtained in one probing cycle an image frame is formed, characterized in that a temperature and air humidity sensor is installed at the location where the lidar is installed, the temperature and humidity of the air are measured, the power value of the received optical signals is adjusted, the thickness range and step of changing the thickness of the oil film to be detected are set, and the reference dependence of the reflection coefficient is calculated from the air-oil-water interface in terms of power, depending on the irradiation angle and the thickness of the oil film, perform averaging of the power reflectance values obtained in one probing cycle for laser beams with the same inclination angles relative to the normal, calculate the oil film detection index М _ f(*)=Z[WA)-W] ' ^к =^ ^к Т~\ where R is the reference dependence of the reflection coefficient on the air-oil-water interface in terms of power depending on the irradiation angle m and the thickness of the oil film d _K ; R ₂ - averaged dependence of the reflection coefficient on power for laser beams with the same angles of inclination, obtained during one probing cycle; K is the number of film thicknesses that are used to perform detection; M ₁ is the number of irradiation angles used, oil film detection is performed when the condition min F<A _o is met, Δ _ο is the detection threshold, min F is the minimum value of the film detection index.