RU2529886C1 - Detection method of oil films on water surface - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: water surface is irradiated with radio pulses. In an area of the examined water space there installed is an additional passive radar reflector with possibility of rereflection of radio pulses supplied to it from the radar and sea surface to the radar side; accumulation of amplitudes of the received echo signals and their conversion to values of specific effective area of dispersion is performed for an element of spatial resolution, which contains an additional passive radar reflector, filtration of values of specific effective area of dispersion to consider distortions; with that, detection of oil films on water surface is performed as per excess threshold value of specific effective area of dispersion.

EFFECT: increasing detection range of oil film by means of a radar.

2 cl, 1 dwg, 2 ex

Description

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

One of the main tasks of environmental monitoring of the sea surface is the task of detecting oil spills; its solution is especially relevant for port water areas where loading and unloading operations of tankers carrying crude oil and various oil products are carried out.

A known method for detecting oil pollution on the surface of the water (Patent RU, No. 2387977 C1, G01N 21/55, 2008), comprising irradiating the investigated water surface with a pulsed optical beam with a radiation wavelength tunable in a narrow spectral range, detecting radiation reflected from the water surface determination of the dependence of the power of the reflected radiation on the wavelength according to the measurement data and finding, on the basis of this dependence, the reflection coefficient and its second derivative with respect to the wavelength. The decision on the presence of an oil film on the water surface is made by simultaneously fulfilling two relations, which include the reflection coefficients from the studied and the clean water surface and the second wavelength derivatives of the reflection coefficient from the studied and clean water surface.

The main disadvantage of this analogue method is its unsuitability for detecting oil films in difficult weather conditions (in rain, fog, snow, etc.), as well as its short detection range (not exceeding several hundred meters).

A known method for detecting oil films on a water surface using a microwave radiometer (Pelyushenko SA Microwave radiometer system for the detection of oil slicks // Spill Science & Technology Bulletin, 1995. Vol.2 No. 4. P.249-254), including the reception , processing and accumulation of radio thermal signals from the studied area of the water surface, calculation of the brightness temperature of the water surface. The decision on the presence of an oil film on the water surface is made by exceeding the threshold value measured by the brightness temperature of the water surface.

The disadvantages of the above analogue method include the short range of the microwave radiometer (not exceeding several hundred meters) and low spatial resolution. In addition, the detection of oil spills at moving irradiation angles is impossible due to the strong influence of radio thermal radiation from the surface layer of the atmosphere.

A known method (Solberg A. et al. Automatic Detection of Oil Spills in ERS SAR Images // IEEE Trans. Geosci. And Remote Sensing, 1999. Vol.37, P.1916-1924) for detecting oil films on a water surface using a radar installed on an artificial Earth satellite operating in aperture synthesis mode to provide high angular resolution along the motion path. The method includes irradiating the studied area of the water surface with radio pulses, receiving and recording the reflected echo signals, recalculating the amplitudes of the reflected echo signals to the specific effective scattering area for each spatial resolution element. As a result of a radar survey of the studied section of the water surface, a radar image is formed, each pixel of which corresponds to a specific effective scattering area of one spatial resolution element of the radar. After the formation of the radar image, filtering, segmentation, and threshold processing are performed to select sections of the radar image with low brightness values corresponding to oil films on the water surface.

The disadvantages of this analogue method include the dependence on meteorological conditions that distort the generated radar image of the studied section of the water surface, as well as the dependence on the wind speed above the water surface, which should lie in the range from 2 to 10 m / s. Otherwise, the echoes reflected from the water surface have a low amplitude, while the probability of detecting oil films is significantly reduced. In addition, due to the movement of the artificial Earth satellite in orbit, the radar can generate images of the surveyed area with a certain frequency (for example, for RADARSAT-1 from 1 time per day to 1 time in 6 days), which prevents the use of the method for detecting oil films in real time time.

The closest analogue in technical essence to the proposed method is a method for detecting oil films on a water surface using a ship's radar (Patent US, No. 4933678, G01S 13/00, 1990.). The method includes irradiating the studied area of the water surface with horizontal-polarized radio pulses, receiving and recording the reflected echo signals, recalculating the amplitudes of the reflected echo signals to the specific effective scattering area for each spatial resolution element, filtering the values of the specific effective scattering area to take into account distortions, detecting oil films in the water surfaces are produced when the threshold value of the specific effective scattering area is exceeded.

A significant disadvantage of this prototype method is the small detection range (does not exceed 1 km).

The objective of the invention is to develop a method for detecting oil films on a water surface by radar, providing a greater detection range compared with known methods.

The problem is solved due to the fact that in the proposed method, as well as in the well-known one, which includes irradiating the investigated section of the water surface with radio pulses, receiving and registering reflected echo signals, recalculating the amplitudes of the reflected echo signals to the specific effective scattering area for each spatial resolution element, filtering the values of the specific effective scattering area to take into account distortions, the detection of oil films on the water surface is carried out by exceeding sometimes th values of specific effective scattering area. But unlike the known method, the proposed method introduces additional features:

- in the area of the surveyed water area, an additional passive radar reflector is installed with the possibility of re-reflection of the radio pulses arriving at it from the radar and the sea surface towards the radar;

- the amplitudes of the received echo signals are accumulated and converted into values of the specific effective scattering area for the spatial resolution element containing an additional passive radar reflector.

The technical result consists in increasing the detection range of the oil film by radar.

The combination of features formulated in paragraph 2 of the claims characterizes a method in which irradiation of the studied section of the water surface is carried out with circularly polarized radio pulses, reception and registration of echo signals arriving at the radar are performed separately for two orthogonal polarizations - horizontal and vertical, separately for horizontal and vertical polarizations produce the accumulation of amplitudes of the received echo signals and their conversion to the values of the specific effective scattering area for the element spatial resolution, containing an additional passive radar reflector, calculate the average of the accumulated values of the specific effective scattering area, from the wind speed sensor, obtain the value of the surface wind speed in the surveyed water area, calculate the standard deviation of the ordinates of the water surface in the surveyed water area, calculate the value of the coherent component of the complex reflection coefficient, calculate the value of the effective scattering area of the passive radi a waterborne reflector for a water surface without an oil film for horizontal and vertical polarization, calculate the threshold value of the specific effective scattering area for horizontal and vertical polarization, separately for horizontal and vertical polarization, perform a comparison with the threshold value of the average of the accumulated values of the specific effective scattering area, the decision on the availability an oil film on a water surface is taken if the threshold value is exceeded by at least one kind of floor Irization.

The technical result consists in increasing the reliability of detection of oil films on a water surface.

Consider an example implementation of a method for detecting oil films on a water surface, which is illustrated in the drawing, which indicates: 1 - radar and 2 - passive radar reflector

An additional passive radar reflector is installed in the surveyed water area with the possibility of re-reflection of the radio pulses arriving at it from the radar and the sea surface towards the radar. The reflector is mounted on a rod rigidly mounted on a floating buoy, which is held on the water surface using an anchor device at a predetermined distance from the radar. A radar is used to irradiate the studied section of the water surface with radio pulses with horizontal polarization. The reflected echo signals are received and recorded, the amplitudes of the received echo signals are accumulated and converted into values of the specific effective scattering area for the spatial resolution element containing an additional passive radar reflector according to the formula

$${\sigma }^0=\frac{{\left(\mathrm{four}\pi \right)}^3}{{\lambda }^2}\frac{P_r}{P_t}\frac{R^{\mathrm{four}}}{G^{2}A},\left(\mathrm{one}\right)$$

Where

λ is the wavelength of the radiated electromagnetic waves,

R is the distance from the radar to the site of the sea surface,

G is the radar antenna gain,

P _r is the power of the received echo signals,

P _t is the power of the emitted signal,

A is the area of the spatial resolution element.

The area of the spatial resolution element is calculated by the formula

$$A=\frac{c\tau Rtg\left(0.5\Delta {\theta }_2\right)}{\cos {\theta }_{\mathrm{one}}},\left(2\right)$$

Where

c is the speed of light in vacuum,

τ is the duration of the radio pulse in the radiation,

Δθ ₂ - the width of the radiation pattern of the radar antenna in the azimuthal plane,

θ ₁ is the angle of slip.

The slip angle is calculated by the formula

$${\theta }_{\mathrm{one}}=\arcsin \left(\frac{h}{R}\right),\left(3\right)$$

where h is the installation height of the ship’s radar antenna.

Next, filter the values of the specific effective scattering area to take into account distortions, detecting oil films on the water surface by exceeding the threshold value of the specific effective scattering area.

We show the ability to achieve the specified technical result. Let us estimate the detection range of an oil film by a radar using a passive radar reflector.

Represent (1) in the following form:

$${\sigma }^0=\frac{B{R}^{\mathrm{four}}}{A},\text{where b}=\frac{{\left(\text{four}\pi \right)}^3}{{\lambda }^2{G}^2{P}_t}.\left(\mathrm{four}\right)$$

The detection range of the oil film on the sea surface by radar without the use of a passive radar reflector is R ₀ = 1 km. At sliding irradiation angles and at λ = 3 cm, the specific effective scattering area of the sea surface with an oil film (Leontyev V.V., Borodin M.A., Ignatyeva O.A. Bistatic scattering patterns of a sea surface covered with a monomolecular oil film , 2012. No. 7. P.42-43) for horizontal polarization is -78 dB.

At a distance from the radar R ₀ = R = 10 ³ m and with parameters typical for ship’s radars, τ = 500 · 10 ^-9 s, Δθ = 1 ^O , h = 15 m, θ ₁ = 0.86 ^O , the value of parameter B from the formula ( 4) in the case of horizontal polarization is B = 2.08 · 10 ^-17 .

The effective dispersion area of the sea surface area is associated with the specific effective dispersion area by the ratio (Handbook of Radar Edited by M. Skolnik. Volume 1. Basics of Radar. M: Sov. Radio, 1976, P.321):

$$\sigma ={\sigma }^{0}A.\left(5\right)$$

Given (4) and (5), the detection range of the oil film on the water surface

$$R_0=\sqrt[\mathrm{four}]{\frac{\sigma }{B}}.\left(6\right)$$

When using a passive radar reflector with an effective scattering area of σ = 10 m ² , the detection range of the oil film is R ₀ = 2.63 km.

Therefore, the detection range of the oil film on the water surface when using a passive radar reflector increases by 2.63 times.

Thus, the technical result is achieved.

Consider another special case of the implementation of the method for detecting oil films on a water surface.

An additional passive radar reflector is installed in the surveyed water area with the possibility of re-reflection of the radio pulses arriving at it from the radar and the sea surface towards the radar. The reflector is mounted on a rod rigidly mounted on a floating buoy, which is held on the water surface using an anchor device at a predetermined distance from the radar. Radar exposure of the investigated area of the water surface with radio pulses with circular polarization. The echo signals received by the radar are received and recorded separately according to two orthogonal polarizations - horizontal and vertical, separately for horizontal and vertical polarization, the amplitudes of the received echo signals are accumulated and converted into values of the specific effective scattering area for the spatial resolution element containing an additional passive radar reflector according to the formulas (1) - (4). Next, filter the values of the specific effective scattering area to account for distortions, calculate the average of the accumulated values of the specific effective scattering area. From the wind speed sensor, the value of the surface wind speed in the surveyed water area is obtained.

Recalculate the value of the surface wind speed to the wind speed at an altitude of 19.5 m from the water surface:

$$U=\frac{u}{0.4}\cdot Lg\left[\frac{19.5}{0.0000684/u+0.00428u^2-0.000443}\right],\left(7\right)$$

where u is the surface wind speed.

Calculate the standard deviation of the ordinates of the water surface in the surveyed water area:

$$s=\sqrt{\frac{\alpha U^{\mathrm{four}}}{\mathrm{four}\beta g}},\left(8\right)$$

where U is the wind speed at an altitude of 19.5 m, β = 0.74, α = 0.0081, g = 9.81.

The coherent component of the complex reflection coefficient is calculated for horizontal and vertical polarization:

$$G_k=\exp \left(i\psi \right)\cdot \exp \left[-8{\left(\frac{\pi \cdot s\cdot \sin {\theta }_{\mathrm{one}}}{\lambda }\right)}^2\right],\left(9\right)$$

Where

θ ₁ is the slip angle calculated by the formula (3),

λ is the wavelength of the radiated electromagnetic waves,

ψ = π - for horizontal polarization,

ψ = 2π - for vertical polarization,

i is the imaginary unit.

The value of the effective scattering area of the passive radar reflector for the water surface without oil film for horizontal and vertical polarization is calculated:

$${\sigma }_{sc}={\sigma }_r\cdot {|\; |\; |\exp \left(-i\cdot 2\cdot k\cdot H\cdot \sin {\theta }_{\mathrm{one}}\right)+G_k^2\exp \left(i\cdot 2\cdot k\cdot H\cdot \sin {\theta }_{\mathrm{one}}\right)+2\cdot G_k|\; |\; |}^2,\left(10\right)$$

Where

H is the installation height of the radar reflector above the water surface,

k = (2π / λ) is the wave number,

λ is the wavelength of the radiated electromagnetic waves,

σ _r is the value of the effective scattering area of the passive radar reflector in free space,

i is the imaginary unit.

The threshold value of the specific effective scattering area for horizontal and vertical polarization is calculated:

$${\sigma }_{sc}^0=\frac{{\sigma }_{sc.}\cdot \cos {\theta }_{\mathrm{one}}}{c\cdot \tau \cdot R\cdot tg\left(0.5\Delta {\theta }_2\right)},\left(\mathrm{eleven}\right)$$

Where

c is the speed of light in vacuum,

τ is the duration of the radio pulse in the radiation,

Δθ ₂ - the width of the radiation pattern of the radar antenna in the azimuthal plane,

R is the distance from the radar to the passive radar reflector,

θ ₁ is the angle of slip.

Separately, for horizontal and vertical polarization, a comparison is made with the threshold value of the average of the accumulated values of the specific effective scattering area, the decision on the presence of an oil film on the water surface is made when the threshold value is exceeded by at least one type of polarization.

We show the ability to achieve the specified technical result.

The use of radio pulses with horizontal polarization only limits the conditions under which an oil film can be detected on the water surface, since other shipborne radars that also operate on horizontal polarization can interfere with detection, which reduces the reliability of detection. In addition, the level of natural interference caused by various hydrometeorological phenomena (precipitation, fog, etc.) and affecting the operation of the radar also depends on the type of polarization used. Using data on two orthogonal polarizations - vertical and horizontal, allows you to choose from them optimal from the point of view of the noise environment to increase the reliability of detection.

The appearance of an oil film on the water surface leads to a decrease in the high-frequency components of the waves (“smooths” the water surface and reduces the degree of waves), which leads to an increase in the modulus of the reflection coefficient of radio waves from the water surface (formula (9)) from the radar to the passive radar reflector and vice versa (see . figure). An increase in the reflection coefficient modulus, in turn, leads to an increase in the value of the specific effective scattering area (formulas (10) and (11)) of the passive radar reflector, therefore, the value of the specific effective scattering area in the presence of an oil film on the water surface is always greater than in the absence of films.

The threshold value of the specific effective scattering area for detecting an oil film is selected to be larger than the value of the specific effective scattering area of a passive radar reflector for the case of a water surface without a film. When fixing the threshold value, a situation arises when the water surface swell is reduced not due to the presence of an oil film, but for natural reasons (for example, the wind that disperses the waves has stopped blowing), which leads to a false detection of the oil film.

Thus, setting the threshold value of the specific effective scattering area depending on the degree of water surface roughness, determined by the standard deviation of the ordinates of the water surface, allows to increase the reliability of detection, the technical result is achieved.

Claims (2)

1. A method for detecting oil films on a water surface using a radar, including irradiating the studied area of the water surface with radio pulses, receiving and recording the reflected echo signals, recalculating the amplitudes of the reflected echo signals to the specific effective scattering area for each spatial resolution element, filtering the values of the specific effective scattering area for accounting distortions, the detection of oil films on the water surface is performed by exceeding the threshold value of the specific effective scattering area, characterized in that an additional passive radar reflector is installed in the area of the surveyed water area with the ability to re-reflect the incoming radio pulses from the radar and the sea surface towards the radar, the amplitudes of the received echo signals are accumulated and converted into values of the specific effective scattering area for the spatial element permission containing an additional passive radar reflector. 2. The method for detecting oil films on a water surface according to claim 1, characterized in that the irradiated portion of the water surface is irradiated with circularly polarized radio pulses, the reception and registration of incoming radar echoes are performed separately for two orthogonal polarizations - horizontal and vertical, separately for horizontal and of vertical polarization, the amplitudes of the received echo signals are accumulated and converted into values of the specific effective scattering area for the spatial element In order to obtain a resolution containing an additional passive radar reflector, the average of the accumulated values of the specific effective scattering area is calculated, the surface wind speed in the surveyed area is obtained from the wind speed sensor, the standard deviation of the ordinates of the water surface in the surveyed area is calculated, the value of the coherent component of the complex reflection coefficient is calculated, calculate the value of the effective scattering area of the passive radar a tracer for a water surface without an oil film for horizontal and vertical polarization, calculate the threshold value of the specific effective scattering area for horizontal and vertical polarization, separately for horizontal and vertical polarization, perform a comparison with the threshold value of the average of the accumulated values of the specific effective scattering area, the decision on the presence of oil films on the water surface are taken when the threshold value is exceeded by at least one type of polarization.