RU2501037C1 - Radar method of determining parameters of large-scale wave on water surface - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: radar method of determining parameters of a large-scale wave on a water surface using a radio altimeter involves emitting probing pulses vertically downwards towards the water surface (to the nadir), receiving probing pulses reflected from the water surface, recording their shape and determining the height of the large-scale wave on the water surface from the inclination of the leading edge of the reflected pulse. Measurements are taken using an aircraft-mounted compact satellite radio altimeter with a knife-edge beam directed along the direction of flight, and the inclination of the trailing edge of the reflected pulse, taking into account the altitude of the aircraft and the antenna beam width, is used to determine variance of the inclination of the large-scale wave along the direction of flight, and the average length of the surface wave along the flight direction is determined using the measured variance of inclination and height of the large-scale wave on the water surface.

EFFECT: faster determination of parameters of a large-scale wave on a water surface from an aircraft.

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Description

The invention relates to methods for determining the parameters of waves of the water surface and can be used in meteorology and oceanology to monitor the state of the surface layer of the oceans with high spatial resolution by involving civil aviation in the monitoring system, as well as to ensure the safety of a seaplane landing on the water surface.

Specialized aircraft are actively used for remote measurement of water surface parameters, and several methods are known for measuring the dispersion of slopes and the height of large-scale waves (meaning large-scale waves in comparison with the wavelength of the probe radiation of a radio altimeter - within the framework of the well-known two-scale model of a scattering surface). However, to date, there is no way that would simultaneously and quickly determine the parameters of large-scale waves of the water surface, such as the height and dispersion of the slopes of the waves, the average wavelength, and to do this using sufficiently compact equipment that could be placed on board any non-specialized aircraft.

Known methods of measuring the height of waves, which use the HF range (Zubkovich S.G., Method for measuring the height of sea waves from an aircraft, Auth. St. USSR No. 169808. - Bulletin of inventions, 1965, No. 7; Garnakeryan A.A. , Sosunov AS Relationship between phase fluctuations of radio signals reflected from the sea surface and the height of sea waves, Proceedings of the All-Union Seminar on Non-Contact Methods of Measuring Oceanographic Parameters, 1975; Garnakeryan AA, Sosunov AS Backscattering of short-wave radio waves from sea surface, P diotehnika Electronics 1976, №11; Garnakeryan AA, AS Sosunov measurement parameters sea wave radio communications method with an aircraft Meteorol 1973, №12). Data processing confirmed the efficiency of the proposed methods, however, the use of the KB-range leads to a large antenna system, which means that it requires the use of a specialized research aircraft to accommodate the necessary equipment.

Several methods for reconstructing the dispersion of wave tilts are given in well-known works (Garnakeryan A.A., A.S. Sosunov. Sea surface radar, Rostov University Press, 1978, 144 pp .; Hauser D., G. Caudal, S. Guimbard, A .Mouche, A study of the slope propability density function of the ocean waves from radar observations. Journal of Geophysical Research, 2008, v. 113, C02006). The measurements are carried out in the microwave range, which makes the antenna system much more compact. The backscattering cross section is used as a function of the angle of incidence. The algorithms confirmed their efficiency during flight experiments and made it possible to measure the variance of the slopes of large-scale waves. However, the height of the excitement was not restored.

There is also a known measurement method, when due to the use of a scanning radio altimeter (scanning sector ± 22 °) with a narrow antenna pattern (antenna radiation pattern width at a power level of 0.5 ° - 1 °), it was possible to measure the dependence of the backscattering cross section on the flight angle, for small flight altitude (~ 250 m) it was possible to resolve sections of large waves in the resolution element of the radio altimeter and, thus, measure the height spectrum. By integrating the spectrum, one can determine the height of large-scale waves (Walsh E., Banner M., J. Chumside, J. Shaw, D. Vandemark, C. Wright, J. Jensen, S. Lee, 2005, Visual demonstration of three-scale sea surface roughness under light wind conditions, IEEE Transactions Geoscience on Remote Sensing, 43, 1751-1762; Walsh, EJ, DCVandemark, CAFriehe, SPBurns, D. Khelif, RNSwift, and JFScott (1998), Measuring sea surface mean square slope with a 36-GHz scanning radar altimeter, J. Geophys. Res., 103 (C6), 12,587-12,601, doi: 10.1029 / 97JC02443). The height of large-scale waves and the variance of the slopes were measured, however, the described method worked only at low altitudes, with increasing flight altitude, information about the height of the waves was lost, because a narrow antenna pattern was used.

Closest to the technical nature of the proposed method is the method by which satellite radio altimeters operating in a pulsed mode designed to measure sea level and provide concomitant measurement of the height of large-scale waves: emit a short pulse vertically downward towards the water surface, take the pulse reflected from the water surface, its shape is recorded and determined by the slope of the leading edge of the reflected pulse, you OTU agitation of the water surface. A conventional radio altimeter has a narrow antenna pattern.

The problem to which the present invention is directed is the development of a radar method for the rapid determination of parameters of large-scale waves of the water surface, such as wave height, dispersion of wave tilt and average surface wavelength, using fairly informative but compact equipment that can be installed on board an aircraft .

The technical result in the developed method is achieved by the fact that, as in the prototype method, probe pulses are emitted vertically downward towards the water surface (in nadir), probe pulses reflected from the water surface are recorded, their shape is recorded and determined by the slope of the leading edge of the reflected pulse the height of the large-scale disturbance of the water surface.

New in the developed method is that for measurements, a compact satellite radio altimeter placed on an airplane with a knife antenna radiation pattern oriented along the flight direction is used for measurements, and the dispersion of large-scale wave excitations along the tilt of the trailing edge of the reflected pulse taking into account the flight height and antenna radiation pattern flight directions, and also determine the average surface wavelength along the flight direction using the measured inclination variance s height and a large-scale disturbance of the water surface.

The method is illustrated by the following drawings.

Figure 1 presents the classical measurement scheme using a satellite radio altimeter.

Figure 2 shows the process of forming a reflected pulse.

Figure 3 illustrates an example of transformation of the shape of the reflected pulse depending on the height of large-scale waves: the dependence of the shape of the reflected pulse on time for four values of the height of large-scale waves: 1 m, 2 m, 4 m and 8 m, for the flight height H ₀ = 800 km .

, высота крупномасштабного волнения: 1 м, 2 м, 4 м, 8 м; δ=1° (a) и δ=28° (б).Figure 4 shows the result of numerical simulation of the shape of the reflected pulse in cases of using radio altimeters with narrow (a) and wide (b) radiation patterns for measurements from an airplane: τ _u = 6 ns, H ₀ = 10 km, $${\mathrm{<figure-callout\; id="2"\; label="S\; x\; y"\; filenames="00000017.png"\; state="\{\{state\}\}">S\; </figure-callout>}}_{xy}^{}=0.012$$

, the height of large-scale unrest: 1 m, 2 m, 4 m, 8 m; δ = 1 ° (a) and δ = 28 ° (b).

Figure 5 shows the dependence of the reflected pulse shape on the slope dispersion for the case of using a radio altimeter with a wide antenna pattern for the following parameters: τ _u = 6 ns, H ₀ = 10 km, large-scale wave height 2 m, δ = 28 ° and $$S_{x\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="00000017.png"\; state="\{\{state\}\}">y</figure-callout>}}^2=\mathrm{0.008,}\mathrm{0.012,}0.016\mathrm{and}\mathrm{0.02.}$$

At present, the height of large-scale waves is measured by space radio altimeters with a narrow symmetric antenna pattern during nadir sounding of the water surface, for example, JASON, ENVISAT. A well-known theoretical model describes the shape of the reflected pulse for such radars (see, for example, Brown GS The average impulse response of a rough surface and its application // IEEE Transactions on Antennas and Propagation. 1977. V.25. N 1. pp.67 -73; Chelton DB, Walsh EJ, MacArthur JL Pulse compression and sea level tracking in satellite altimetry // Journal of Atmospheric and Oceanic Technology. 1989. V.6. Pp.407-438; S. Zubkovich Statistical characteristics of radio signals reflected from Earth surface, M., Sov. radio, 1968, 224 p.).

Using the developed algorithm, the height of large-scale waves is restored from the leading edge of the reflected pulse. Comparison with the data of contact measurements shows good accuracy of the algorithm - the error in measuring the height of large-scale waves does not exceed 10% or 0.5 m (which is more) (Lee-Lueng Fu, Anny Cazenave, Satellite altimetry and earth sciences. A handbook of techniques and applications, 2001, Academic Press, San Diego, USA, 464 p.).

The measurement scheme is shown in Fig. 1 (Lebedev S.A. Basics of satellite altimetry // Field seminar-school. “State and prospects of monitoring the World Ocean and the Seas of Russia according to remote sensing data and the results of mathematical modeling”, Tarusa, July 9-12, 2010 d): a short pulse is emitted vertically downward towards the water surface. Part of the radiated energy is reflected back and enters the receiving antenna, where the shape of the reflected pulse is recorded.

The process of forming a reflected pulse is shown in Fig.2. With an increase in the delay time, an increase in the area of the illuminated (reflecting) surface occurs and the power of the received signal proportional to this area also grows.

After the falling edge reaches the incident pulse of the reflecting surface, the area of the illuminated area reaches its maximum value and then ceases to change, because the area of the reflecting ring (illuminated surface) is preserved over time. When using a receiving antenna with a narrow radiation pattern, the power of the received signal is weakened with an increase in the delay time, therefore, in existing radio altimeters, after reaching a maximum, a decline is observed at the trailing edge of the reflected pulse due to the influence of the antenna radiation pattern.

As is known, at small angles of incidence, backscattering is quasi-mirror and occurs in regions of a large-scale profile oriented perpendicular to the incident radiation. To describe the reflection of microwave electromagnetic waves by a water surface, the concept of a two-scale surface model is introduced, according to which the wave spectrum is divided into large-scale and small-scale components with respect to the radar wavelength (Base F., Fuchs I. Wave scattering on a statistically rough surface, M., Science, 1972, 424 pp.).

In the General case, the dependence of the power of the reflected signal on time is given by the following expression (Zubkovich SG Method of measuring the height of sea waves from an aircraft. Auth. Certificate. USSR No. 169808. - Bulletin of inventions, 1965, No. 7):

$$P\left(t\right)~{\displaystyle \underset{S_0}{\iint }\exp \left[-\frac{2}{H_0^2}\left(\frac{x^2}{S_x^2}+\frac{y^2}{S_y^2}\right)\right]\times \exp }\left[-\frac{2.76}{H_0^2}\left(\frac{x^2}{{\delta }_x^2}+\frac{y^2}{{\delta }_y^2}\right)\right]dxdy,\left(\mathrm{one}\right)$$

и $$S_y^2$$

- дисперсии наклонов крупномасштабного волнения вдоль осей X and Y; δ_x и δ_y - ширина диаграммы направленности антенны на уровне 0,5 по мощности в угломестной и азимутальной плоскостях; H₀ - высота полета.Where $$S_x^2$$

and $$S_y^2$$

- variances of slopes of large-scale waves along the X and Y axes; δ _x and δ _y are the width of the antenna pattern at the level of 0.5 in power in the elevation and azimuthal planes; H ₀ - flight altitude.

интеграл легко вычисляется аналитически в полярной системе координат: азимутальный угол φ=[0,2π] и переменная ρ зависят от времени.From formula (1) it can be seen that the power of the reflected signal depends on the dispersion of the slopes of the large-scale waves and the antenna pattern. For a symmetric Gaussian antenna pattern (δ _x = δ _y = δ) and isotropic waves of the water surface $$(S_x^2={\mathrm{<figure-callout\; id="2"\; label="S\; y"\; filenames="00000017.png"\; state="\{\{state\}\}">S\; </figure-callout>}}_y^{}=S_{xy}^2)$$

the integral is easily calculated analytically in the polar coordinate system: the azimuthal angle φ = [0.2π] and the variable ρ depend on time.

The leading edge of the reflected pulse is formed from the moment t equal to t ₀ to t ₀ + τ:

$$P\left({\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="00000018.png,00000019.png"\; state="\{\{state\}\}">t</figure-callout>}}_0+\tau \right)~\mathrm{one}-\exp \left[-\frac{c\tau \left(2.76{\mathrm{<figure-callout\; id="2"\; label="S\; x\; y"\; filenames="00000017.png"\; state="\{\{state\}\}">S\; </figure-callout>}}_{xy}^{}+2{\delta }^2\right)}{{\mathrm{<figure-callout\; id="0"\; label="H"\; filenames="00000018.png,00000019.png"\; state="\{\{state\}\}">H</figure-callout>}}_0{\delta }^2{S}_{xy}^2}\right],\left(2\right)$$

where c is the speed of light and t ₀ = 2H ₀ / s.

The trailing edge is formed when t is greater than t ₀ + τ _u :

$$P\left({\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="00000018.png,00000019.png"\; state="\{\{state\}\}">t</figure-callout>}}_0+\tau \right)~A_0\exp \left[-\frac{c\tau \left(2.76{\mathrm{<figure-callout\; id="2"\; label="S\; x\; y"\; filenames="00000017.png"\; state="\{\{state\}\}">S\; </figure-callout>}}_{xy}^{}+2{\delta }^2\right)}{{\mathrm{<figure-callout\; id="0"\; label="H"\; filenames="00000018.png,00000019.png"\; state="\{\{state\}\}">H</figure-callout>}}_0{\delta }^2{S}_{xy}^2}\right],\left(3\right)$$

where the coefficient A ₀ is introduced to reconcile formulas (2) and (3).

These formulas are correct for a flat (even) scattering surface. If we consider an excited water surface, then the surface is not flat, and to find the shape of the reflected pulse, it is necessary to average formulas (2) and (3) using the Gaussian distribution function of wave heights p (ς):

$$p\left(\varsigma \right)=\frac{\exp \left[-\raisebox{1ex}{${\mathrm{<figure-callout\; id="2"\; label="\varsigma "\; filenames="00000017.png"\; state="\{\{state\}\}">\varsigma </figure-callout>}}^2$}\!\left/ \!\raisebox{-1ex}{$2{\sigma }_{\varsigma }^2$}\right.\right]}{\sqrt{2\pi {\sigma }_{\varsigma }^2}},\left(\mathrm{four}\right)$$

- дисперсия высот поверхности.Where $${\sigma }_{\varsigma }^2$$

- dispersion of surface heights.

As a result, the shape of the reflected pulse is calculated as follows:

$$F\left(t\right)=\frac{\mathrm{one}}{\sqrt{2\pi {\sigma }_{\varsigma }^2}}{\displaystyle \underset{-\infty }{\overset{\varsigma m}{\int }}P\left(t-2\varsigma /c\right)\cdot \exp \left[-\frac{{\mathrm{<figure-callout\; id="2"\; label="\varsigma "\; filenames="00000017.png"\; state="\{\{state\}\}">\varsigma </figure-callout>}}^2}{2{\sigma }_{\varsigma }^2}\right]d\varsigma }.\left(5\right)$$

In a reflected pulse for a flat surface measured by a radio altimeter, a leading edge of duration τ _{u is} distinguished when the amplitude of the received signal increases, and a trailing edge is observed at which the decay occurs when the antenna radiation pattern is taken into account in the pulse model. When using a receiving antenna with a narrow radiation pattern, the power of the received signal decreases with an increase in the angle of incidence, therefore, after reaching a maximum, a decline is observed at the trailing edge of the reflected pulse.

Figure 2 shows the shape of the pulse when reflected from a flat surface. In the presence of excitement, the shape of the pulse is distorted, in particular, the leading edge becomes longer, because the first reflected signal arrives when the leading edge reaches the probe pulse of the wave crests, and ends when the falling edge reaches the incident pulse of the troughs.

An example of the transformation of the shape of the reflected pulse depending on the height of large-scale waves is shown in Fig.3.

The observed transformation of the leading edge of the reflected pulse opens up the possibility of measuring the height of large-scale waves. In the standard algorithm for reconstructing the height of large-scale waves, the input parameter is the slope of the leading edge of the reflected pulse at the midpoint (Lee-Lueng Fu, Army Cazenave, Satellite altimetry and earth sciences. A handbook of techniques and applications, 2001, Academic Press, San Diego, USA, 464 p.).

When transferring a satellite radio altimeter with a narrow antenna pattern to an aircraft, the pulse shape is strongly transformed (see Figure 4, a) and it becomes impossible to restore the height of large-scale waves.

The situation is corrected if you use a wide or knife antenna radiation pattern for the radio altimeter, as can be seen from Figure 4, b.

In the case of a wide antenna pattern, the decay of the trailing edge of the reflected pulse is explained primarily by the influence of the slopes of the large-scale waves, and not the antenna pattern. This can be seen from Figure 5, illustrating the dependence of the shape of the reflected pulse on the variance of the slopes.

Thus, it can be seen from the figures that the influence of the height and dispersion of the slopes of large-scale waves of the water surface on the shape of the reflected pulse depends on the flight altitude and the antenna radiation pattern width.

Using an antenna with a symmetrical antenna pattern leads to the loss of azimuthal characteristics of the waves of the water surface. To save this information, it is necessary to use a radio altimeter with a knife antenna radiation pattern, i.e. δ _x >> δ _y .

As a result, the final formulas for the shape of the reflected pulse are as follows:

и $$P\left(t_0+\tau \right)~A_0\exp \left[-\frac{c\tau \left(\mathrm{2,76}{S}_x^2+2{\delta }_x^2\right)}{H_0{\delta }_x^2{S}_x^2}\right].$$

$$P\left({\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="00000018.png,00000019.png"\; state="\{\{state\}\}">t</figure-callout>}}_0+\tau \right)~\mathrm{one}-\exp \left[-\frac{c\tau \left(2.76S_x^2+2{\delta }_x^2\right)}{{\mathrm{<figure-callout\; id="0"\; label="H"\; filenames="00000018.png,00000019.png"\; state="\{\{state\}\}">H</figure-callout>}}_0{\delta }_x^2{S}_x^2}\right]$$

and $$P\left({\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="00000018.png,00000019.png"\; state="\{\{state\}\}">t</figure-callout>}}_0+\tau \right)~A_0\exp \left[-\frac{c\tau \left(2.76S_x^2+2{\delta }_x^2\right)}{{\mathrm{<figure-callout\; id="0"\; label="H"\; filenames="00000018.png,00000019.png"\; state="\{\{state\}\}">H</figure-callout>}}_0{\delta }_x^2{S}_x^2}\right].$$

вдоль ориентации антенны.In this case, the shape of the reflected pulse contains information about the variance of the slopes of the waves $$S_x^2$$

along the orientation of the antenna.

As a result, by independently measuring the dispersion of the slopes and the height H _{S of} large-scale waves, we can determine the average wavelength:

. $$L\approx \sqrt{{\mathrm{<figure-callout\; id="2"\; label="H\; S"\; filenames="00000017.png"\; state="\{\{state\}\}">H\; </figure-callout>}}_S^{}/{\mathrm{<figure-callout\; id="2"\; label="S\; x"\; filenames="00000017.png"\; state="\{\{state\}\}">S\; </figure-callout>}}_x^{}}$$

.

The developed radar method for determining the parameters of large-scale waves of the water surface is as follows.

Using a radio altimeter with a knife antenna pattern oriented along the flight direction, probe pulses are emitted vertically downward towards the water surface (in nadir), probe pulses reflected from the water surface are recorded, their shape is recorded and the large-scale height is determined from the slope of the reflected front of the reflected pulse waves of the water surface, according to the slope of the trailing edge of the reflected pulse, taking into account the flight altitude and the antenna radiation pattern width, the variance of the slopes of the large-scale wave along the flight direction, and also determine the average length of the surface wave along the flight direction, using the measured dispersion of the slopes and the height of the large-scale wave.

Thus, the proposed radar method provides the ability to quickly determine the parameters of large-scale waves of the water surface, such as the height of large-scale waves, the dispersion of the slopes of the waves and the average surface wavelength from an airplane.

Claims (1)

The radar method for determining the parameters of large-scale waves of the water surface using a radio altimeter, which consists in emitting sounding pulses vertically downward towards the water surface (in nadir), receiving sounding pulses reflected from the water surface, registering their shape and determining by the slope of the reflected front pulse height of large-scale waves of the water surface, characterized in that for measurements using compact satellites placed on an airplane the radio altimeter with a knife antenna pattern oriented along the flight direction and the inclination of the trailing edge of the reflected pulse, taking into account the flight height and antenna radiation pattern width, determine the variance of the slopes of the large-scale waves along the flight direction, and also determine the average surface wave length along the flight direction using measured slope dispersion and height of large-scale waves of the water surface.

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