RU2387977C1 - Non contact method for detection of oil pollutions on water surface - Google Patents

Abstract

FIELD: measurement technique.

SUBSTANCE: invention refers to measurement technique and can be used for operative detection of oil and oil products spills in seas and inland water bodies. The method includes irradiation of water surface in question by pulsed optical beam with tunable in narrow spectral band length of radiation wave, recording radiation reflected from water surface, determination by measurement data of dependence between power of reflected radiation and wave length and obtaining on the base of this dependence the reflection index and its second derivative with respect to wave length. The presence of oil film on water surface is determined by simultaneous execution of two relations which include reflection indices for investigated and pure water surface and the second derivatives with respect to wave length of reflection indices for investigated and pure water surface.

EFFECT: invention makes possible to detect thin films of oil products (with thickness from tenths of microns to microns) with close to one probability of correct detection.

Description

The invention relates to measuring equipment and can be used for the rapid detection of oil spills and oil products in the seas and inland waters.

A known method of detecting an oil film on a water surface [1], which consists in the fact that the investigated water surface is irradiated with a pulsed beam of optical radiation, receive the reflected signal and compare the signals reflected from the clean and the investigated water surface. The number of pulse signals N exceeding the analyzer threshold is selected as a comparison parameter. For N≥N _b, the presence of an oil film is judged, and for N <N _b , its absence (N _b is the number characterizing the probability of receiving signals).

The disadvantage of this method of detecting oil pollution is the low reliability of the detection.

Closest to the invention in technical essence is a method [2] for detecting an oil film on a water surface by irradiating a water surface with a pulsed beam of optical radiation and receiving a reflected signal, followed by comparing signals reflected from a clean and investigated water surface, irradiating the surface and receiving the reflected signal at two wavelengths, as the parameters of the reflected radiation, choose the power ratios of the laser signals received from the studied water surface and the respective power laser signals received from a clean water surface, and the presence of the oil film is judged to fulfill simultaneously two relations:

или

or

;Where

;

λ ₁ , λ ₂ - sounding wavelengths;

P (λ ₁ ), P (λ ₂ ) and P _w (λ ₁ ), P _w (λ ₂ ) are the power of the laser signals at wavelengths λ ₁ , λ ₂ obtained from the investigated and from a clean water surface.

The disadvantage of this method of detecting oil pollution on the water surface is the lack of reliability of detection of thin films of oil products.

This disadvantage can be avoided by the fact that, according to a method for detecting oil pollution on the surface of water bodies, including irradiating the water surface with a pulsed beam of optical radiation, receiving a reflected signal and then comparing the signals reflected from a clean and investigated water surface, the surface length is rearranged in a narrow spectral range upon irradiation radiation waves, determine the dependence of the reflected radiation power on the wavelength, find the reflection coefficient and e on the basis of this dependence the second derivative, and the presence of an oil film is judged by the fulfillment of two ratios simultaneously:

и

and

Where

R _ref ; R _w - reflection coefficients from the investigated and clean water surface;

,

- вторые производные по длине волны коэффициента отражения от исследуемой и чистой водной поверхности

,

- second derivatives with respect to the wavelength of the reflection coefficient from the investigated and clean water surface

The presence of distinctive features indicates compliance with the criterion of "novelty."

These distinguishing features are unknown in the patent literature, and therefore, the proposed technical solution meets the criterion of "inventive step".

Figure 1 schematically shows a device that implements the proposed method.

The device contains tunable wavelength in a narrow spectral range of the optical radiation source 1; a photodetector 2 detecting radiation reflected from the water surface; processing unit 3, which, according to the measurement data, determines the dependence of the reflected radiation power on the wavelength, finds the reflection coefficient and its second derivative based on this dependence, and checks the fulfillment of relations (1), which allows high-accuracy detection of thin films of oil products.

The device operates as follows.

The optical radiation source 1 irradiates the investigated water surface 4 (for example, the radiation source 1 may be on an aircraft carrier). Irradiation of the water surface is carried out vertically down. The radiation wavelength is tuned in a narrow spectral range. The intensity of the reflected radiation is recorded by the photodetector 2. The signal from the photodetector 2 enters the processing unit 3. In the processing unit, the dependence of the reflected radiation power on the wavelength is determined from the measurement data, the reflection coefficient and its second derivative are found on the basis of this dependence, and the fulfillment of the relations (1 ) and concludes that there is or is no oil pollution. The parameters of the reflected radiation for a clean water surface, for example, are recorded at the beginning of measurements when flying over a known clean part of the water surface and are stored in the memory of block 3. When flying around the studied area, the result of block 3 is an array of data on the presence of oil pollution.

Theoretical calculations and experimental studies show that the physical basis for the remote detection of oil pollution on a water surface by optical sensing is the presence of a contrast in the brightness of the reflected radiation from a clean water surface and a water surface covered with an oil film. For a smooth water surface, this contrast is due to the fact that the reflection coefficient R _{ref of the} oil film (three-layer system “air - oil film-water”) differs from the reflection coefficient R _{w of a} clean water surface (two-layer system “air - water”) (see, for example, [3, 4]).

In the case of the presence of oil pollution on the water surface, the reflection coefficient R _ref will depend on the thickness of the oil film d, the optical characteristics of the oil and the radiation wavelength λ. With a vertical incidence of radiation on the surface, for the reflection coefficient of the three-layer system “air - film (oil product) - water” R _ref (λ, d) we have (see, for example, [5]):

,

,

Where

;

;

;

;

;

;

;

;

n _2,3 (λ), k _2,3 (λ) are the refractive indices and absorption of oil and water, respectively;

,

- коэффициенты отражения на границе сред «воздух - нефть» и «нефть - вода» соответственно;

,

- reflection coefficients at the boundary of the air-oil and oil-water media, respectively;

T (λ) is the transmission of the oil film.

Indices 1, 2, 3 refer to air, oil, and water (for air, the refractive index is taken to be 1, and the absorption index to 0).

From the formula for R _ref (λ, d) it can be seen that in the general case, due to the interference of radiation reflected from the interfaces “air - oil film” and “oil film - water”, the reflection coefficient R _ref (λ, d) is a periodic function of the radiation wavelength λ and film thickness d.

; (см. фиг.2, где приведены результаты расчетов для длины волны 0,65 мкм, здесь 1 - R_ref(λ, d),

Это практически не позволяет проводить надежное обнаружение (с высокой вероятностью правильного обнаружения) тонких пленок нефти на водной поверхности при единичных измерениях и существенно ухудшает вероятность правильного обнаружения при усреднении по серии измерений. Фиг.2 приведена для случая относительного среднеквадратического значения шума измерения 4%, однако подобные ситуации возможны и при гораздо меньшем шуме (но они будут более редкие).At a film thickness of tenths and units of micrometers, the periodic dependence of the value of R _ref (λ, d) on the radiation wavelength λ, and the film thickness d is very significant. It leads to the fact that, for thin films, situations are possible when the measured (under the conditions of measurement noise) reflection coefficient of the three-layer system “air - oil film - water” R _ref (λ, d) is (at the minimum points R _ref (λ, d )) approximately equal to or even lower than the reflection coefficient at the boundary of the air-water media

; (see figure 2, which shows the calculation results for a wavelength of 0.65 μm, here 1 is R _ref (λ, d),

This practically does not allow reliable detection (with a high probability of correct detection) of thin oil films on the water surface during single measurements and significantly worsens the probability of correct detection when averaged over a series of measurements. Figure 2 shows for the case of a relative rms value of the measurement noise of 4%, however, similar situations are possible with much less noise (but they will be more rare).

To increase the likelihood of correct detection of thin films of oil on the water surface, it is necessary to attract additional information from the measurement data. One option is to use (to increase the likelihood of correct detection) the measurement results of the second derivative (with respect to the radiation wavelength) of the reflection coefficient of the air-film-oil-water system.

и

, то принимается решение о наличии нефтяной пленки на водной поверхности.The algorithm for detecting oil product films on a water surface may be threshold: if the ratios are simultaneously satisfied

and

, then a decision is made on the presence of an oil film on the water surface.

Thus, in order to detect films of oil products on a water surface, it is necessary to measure the reflection coefficient of the air – oil film – water system, determine its second derivative, and compare them with threshold values (values of the reflection coefficient and its second derivative for a clean water surface). The reflection coefficient at wavelength λ can be determined by measuring the power of reflected radiation at wavelength λ at a known radiation power of the source (for example, using a measurement circuit in which the entire optical beam reflected from the surface enters the receiving lens). The second derivative of the reflection coefficient is calculated from the measurement data of the spectral dependence of the reflection coefficient in a narrow spectral range, which can be realized using a single laser that is tunable along the wavelength of the narrow range of the visible, near or middle IR spectral ranges.

The table shows, as an example, the results of calculations of the probability of correct detection.

Table The probability of the correct detection of oil films on the water surface Film thickness, microns P _by one 2 0.2189 0.41306 0,99519 0.4378 0.64947 1.00000 0.6566 0.83604 1.00000 0.8755 0.93902 1.00000 1,0944 0.98282 1.00000 1.3132 0,99592 1.00000 1,5321 0,99921 1.00000 1,7509 0,99989 1.00000 1.9699 0,99999 1.00000 2,1887 1.00000 1.00000

The calculations in the table were carried out at the minimum points of the reflection coefficient R _ref (λ, d) (see figure 2). At points other than the minimum points R _ref (λ, d), the probability of correct detection is always greater. In the calculations, the value of the relative rms value of the measurement noise was taken to be 1.5%, and the radiation wavelength was 0.65 μm.

The calculations were carried out for two methods of detecting oil films on a water surface:

- a method using only the measurement data of the reflection coefficient R _ref (λ, d) (column 1 of the table);

- the proposed method using the measurement data of the reflection coefficient R _ref (λ, d) and its second derivative (column 2 of the table).

The Table shows that for thin films of oil products (with a film thickness of oil products less than 2 microns), the proposed detection method provides a much greater probability of correct detection.

Thus, the proposed method, based on measuring the reflection coefficient and its second derivative, allows one to detect thin films of oil products (with a thickness from tenths of microns to units of microns) with a probability of correct detection close to unity.

The invention is aimed at solving the problem of increasing the reliability of detection of oil pollution on the water surface. Known methods for detecting oil pollution on the surface of the water can be mistakenly identified as "clean water surface" areas of the water surface with thin films of oil products.

A non-contact method for detecting oil pollution on the surface of the water, based on measuring the reflection coefficient and its second derivative, makes it possible to detect thin films of oil pollution on the water surface with high reliability.

This device can be assembled at the enterprises of the Russian Federation from components and components manufactured in the Russian Federation, and meets the criterion of "industrial applicability".

Information sources

1. USSR author's certificate N1354073, cl. G01N 21/55, 1987.

2. RF patent for the invention No. 2298169, class. G01N 21/55, 2007.

3. Radiophysical monitoring of environmental pollution / Belov M. L., Gorodnichev V. A., Kozintsev V. I. et al. M: Argus, 1994, 107 pp.

4. Optoelectronic systems for ecological monitoring of the environment / Kozintsev V.I., Orlov V.M., Belov M.L. et al. M.: Publishing House of MSTU, 2002, 528 s.

5. Born M., Wolf E. Fundamentals of optics. M .: Nauka, 1973, 719 p.

Claims (1)

A non-contact method for detecting oil pollution on a water surface by irradiating the water surface with a pulsed beam of optical radiation and receiving a reflected signal, followed by comparing the signals reflected from the surface of the clean and test water, to make a decision about the presence of an oil film, characterized in that when the surface is irradiated, it is rebuilt into narrow spectral range of the radiation wavelength, determine the dependence of the reflected radiation power on the wavelength, find on the basis of this dependence reflection coefficient and its second derivative, and the presence of the oil film is judged to fulfill simultaneously two relations

and

where R _ref , R _w - reflection coefficients from the investigated and clean water surfaces;

- the second derivatives of the wavelength of the reflection coefficient from the investigated and clean water surfaces.

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