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

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.

5 dwg

The invention relates to methods of determining the parameters of the agitation of the water surface and can be used in meteorology and Oceanography for monitoring the near-surface layer of the World ocean with high spatial resolution at the expense of involvement in the monitoring system of civil aviation, as well as to ensure the safety of landing a seaplane on the water surface.

Specialized aircraft are actively used for remote measurements of parameters of the water surface, and there are several ways of measuring the dispersion slope and height of large-scale disturbances (mean excitement large compared to the wavelength of the probing radiation radioaltimeter within known dvukhmasshtabnoi model of the scattering surface). However, currently there is no way that would allow simultaneously and quickly to determine the parameters of large-scale disturbances of the water surface, such as height and dispersion slope of excitement, the average length of unrest, and to do so with relatively compact equipment, which could be put on Board any General plane.

Known methods of measuring the height of the unrest, in which use the KV-range (Sobkowicz YEAR, the Method of measuring the height of SIDS is their waves with the aircraft, Auth. Mon. The USSR # 169808. - Bulletin of inventions, 1965, No. 7; Carneceria A.A., Piglets, AS the Relationship of the phase fluctuations of radio signals reflected from the sea surface, with the height of the waves, Proceedings of all-Union seminar on non-contact methods of measuring Oceanographic parameters, 1975; Carneceria A.A., Piglets, AS the backscattering of radio waves wavelength range from sea surface technology and electronics, 1976, No. 11; Carneceria A.A., Piglets A.S. Measurement parameters the wave radio method with the aircraft, Meteorology and hydrology, 1973, No. 12). Processing data confirmed the efficiency of the proposed methods, however, the use of KB-band leads to the large size of the antenna system, and thus requires the use of specialized research aircraft to accommodate the necessary equipment.

Several methods of restoring the dispersion slope excitement shows in well-known works (Carneceria A.A., Assonov. Radar sea surface, Rostov University, 1978, 144 S.; 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 were carried out in the microwave range, which makes the antenna system is much more compact. Use the dependence of the cross section of the inverse Russ is a distance from the incidence angle. Algorithms have proved their efficiency during flight experiments and allowed us to measure the variance of the slopes of the large-scale unrest. However, the height of excitement when this was not restored.

There is also known a method of measurement, when through the use of scanning radioaltimeter (sector scan ±22°) with a narrow radiation pattern of the antenna beam width antenna at 0.5 power 1°) were able to measure the dependence of the backscattering cross section on the angle of flight, low altitude flight (~250 m) were able to resolve areas of large waves in the element resolution radioaltimeter and, thus, to measure a range of heights. Prointegrirowany range, you can determine the height of the large-scale disturbances (E. Walsh, M. Banner, 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 on Geoscience Remote Sensing, 43, 1751-1762; Walsh, E.J., D.C.Vandemark, C.A.Friehe, S.P.Burns, D.Khelif, R.N.Swift, and J.F.Scott (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). We measured the height of the large-scale unrest and dispersion slope, however, the described method only worked at low altitudes, with increasing altitude information about the height of excitement was lost, as was used narrow antenna pattern.

The closest in technical essence to appreciate the suggested method is a method, at which carry out their work satellite radioaltimeter operating in pulsed mode, designed to measure Global sea level and provides simultaneous measurement of the height of the large-scale unrest: emit a short pulse of vertically downwards towards the water surface, taking reflected from the water surface momentum, registering its shape and determine the slope of the leading edge of the reflected pulse height of the agitation of the water surface. Normal radioaltimeter has a narrow antenna pattern.

Task to be solved by the present invention is directed, is to develop a radar method of determination of parameters of large-scale disturbances of the water surface, such as the height of the unrest, the dispersion slope of the excitement and the average length of the surface waves, using quite informative, but compact equipment that can be installed on Board the aircraft.

The technical result in the developed method is achieved by the fact that, as in the method prototype emit illuminating pulses vertically down towards the water surface (at Nadir), receive reflected from the water surface of the probe pulses, register their shape and determine the slope of the leading edge of the echo is mpulse the height of the large-scale disturbances of the water surface.

New developed method is that the measurements used are placed on the plane compact satellite radioaltimeter with blade antenna pattern, oriented along the flight direction, and the inclination of the trailing edge of the reflected pulse with the height of the flight and the width of the beam determine the variance of the slopes of large-scale disturbances along the flight direction, and determine the average length of the surface wave along the direction of flight, using the measured variance of the slope and height of the large-scale disturbances of the water surface.

The method is illustrated by the following drawings.

Figure 1 shows the classical scheme of measurement using satellite radioaltimeter.

Figure 2 shows the process of forming the reflected pulse.

Fig 3 illustrates a transformation of the shape of the reflected pulse, depending on the height of the large-scale unrest: shows the dependence of the shape of the reflected pulse from the time for four values of the height of the large-scale unrest: 1 m, 2 m, 4 m and 8 m flight altitude H₀=800 km

Figure 4 shows the result of numerical modeling of the shape of the reflected pulse in the use cases for measurements from the plane of radioaltimeter with narrow and wide (b) diagrams healthy lifestyles is nasty antenna: τ _u=6 NS, H₀=10 km,$$S_{xy}^2=\mathrm{0,012}$$height of large-scale disturbances: 1 m, 2 m, 4 m, 8 m, δ=1° (a) and δ=28° (b).

Figure 5 presents the dependence of the shape of the reflected pulse from the dispersion slope for the case of using radioaltimeter with a wide antenna pattern for the following parameters: τ_u=6 NS, H₀=10 km, the height of the large-scale unrest 2 m, δ=28° and$$S_{xy}^2=\mathrm{0.008,}\mathrm{0.012,}0.016\mathrm{and}\mathrm{0.02.}$$

Currently, the height of the large-scale unrest measure space radioaltimeter with a narrow symmetric antenna pattern at Nadir sounding of the water surface, for example, JASON, ENVISAT. Known theoretical model describes the shape of the reflected pulse for such radars (see, for example. Brown G.S. 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; D.B. Chelton, E.J. Walsh, MacArthur J.L. Pulse compression and sea level tracking in satellite altimetry // Journal of Atmospheric and Oceanic Technology. 1989. V.6. pp.407-438; Sobkowicz C. Statistical characteristics of radio signals reflected from the earth's surface, M, Owls. R is dio, 1968, 224 S.).

Using the developed algorithm restores the height of the large-scale disturbances on the leading edge of the reflected pulse. Comparison with the data contact measurements shows good accuracy of the algorithm, the error of measurement of the height of the large-scale unrest does not exceed 10% or 0.5 m (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 figure 1 (Lebedev S.A. fundamentals of satellite altimetry // seminar-school. "Status and prospects of the monitoring of the oceans and seas of Russia on remote sensing data and numerical modeling results", Tarusa, 9-12 July 2010): emit a short pulse of vertically downwards towards the water surface. Part of the radiated energy is reflected back and falls into the receiving antenna, where record the shape of the reflected pulse.

The process of formation of the reflected pulse is shown in figure 2. With increasing time delay is to increase the area illuminated (reflecting) surface and the power of the received signal, proportional to the square is also growing.

After reaching back-to-back falling pulse of the reflective surface area of the lighted platform reaches a maximum and subsequently ceases to change, because the horse reflecting rings (illuminated surface) in time saved. When using a receiving antenna with a narrow beam pattern is weakening the power of the received signal with increasing time delay, therefore, in the existing radioaltimeter after a maximum decline at the trailing edge of the reflected pulse, due to the influence of antenna directional diagram.

As you know, at small angles of incidence backscatter is kaiserkeller and is in the areas of large-scale profile, oriented perpendicular to the incident light. To describe the reflection of electromagnetic waves in the microwave range water surface the concept dvukhmasshtabnoi surface model, according to which the range of excitement is divided into large-scale and small-scale components relative to the wavelength of the radar (bass, F., Fuchs, I. Scattering of waves by a statistically rough surface, Meters, Science, 1972, 424 S.).

In the General case, the dependence of the power of the reflected signal with time is given by the following expression (Sobkowicz YEAR, the Method of measuring the height of the waves from aircraft. Auth. Mon. The USSR # 169808. - Bulletin of inventions, 1965, No. 7):

$$P\left(t\right)~{\displaystyle \underset{S_0}{\iint }\exp \left[-mfrac>2H_0^2\left(\frac{x^2}{S_x^2}+\frac{y^2}{S_y^2}\right)\right]\times \exp }\left[-\frac{2.76}{H_0^2}\left(\frac{x^2}{{\delta }_x^2}+\frac{y^2}{{\delta }_y^2}\right)\right]dxdy,\left(1\right)$$

where$$S_x^2$$and$$S_y^2$$the dispersion slope of the large-scale unrest along the axes X and Y; δ_xand δ_y- the width of the beam at 0.5 power elevation and azimuthal planes; H₀- the height of the flight.

From the formula (1) shows that the power of the reflected signal depends on the dispersion slope of the large-scale unrest and antenna directional diagram. For simme the ranks Gaussian beam (δ _x=δ_y=δ) and isotropic agitation of the water surface$$(S_x^2=S_y^2=S_{xy}^2)$$the integral is easily calculated analytically in polar coordinates: azimuth angle φ=[0,2π] and the variable ρ depend on time.

The leading edge of the reflected pulse is formed from the moment t is equal to t₀to t₀+τ:

$$P\left(t_0+t\right)~1-\exp \left[-\frac{ct\left(\mathrm{was\; 2.76}{S}_{xy}^2+2{\delta }^2\right)}{H_0{\delta }^2{S}_{xy}^2}\right],\left(2\right)$$

where c is the speed of light and t₀=2H₀/s

Rear front formed when t is greater than t₀+τ_u:

$$P\left(t_0+t\right)~A_0\exp \left[-\frac{ct\left(\mathrm{was\; 2.76}{S}_{xy}^2+2{\delta }^2\right)}{H_0{\delta }^2{S}_{xy}^2}\right],\left(3\right)$$

where the coefficient A₀introduced for approval of the formulas (2) and (3).

These formulas are valid for a flat (smooth) of the scattering surface. If this agitated water surface, then the surface is not flat and for nding the shape of the reflected pulse must be averaging formulas (2) and (3)using the Gaussian distribution function of the heights of excitement p(ς):

$$p\left(\varsigma \right)=\frac{\exp \left[-\raisebox{1ex}{${\varsigma }^2$}\!\left/ \!\raisebox{-1ex}{$2{\sigma }_{\varsigma }^2$}\right.\right]}{\sqrt{2\pi {\sigma }_{\varsigma }^2}},\left(4\right)$$

where$${\sigma }_{\varsigma }^2$$the variance of the surface elevation.

In the shape of the reflected pulse is calculated as follows:

$$F\left(t\right)=\frac{1}{\sqrt{2\pi {\sigma }_{\varsigma }^2}}{\displaystyle \underset{-\infty }{\overset{\varsigma m}{\int }}P\left(t-2\varsigma /c\right)\cdot \exp \left[-\frac{{\varsigma }^2}{2{\sigma }_{\varsigma }^2}\right]d\varsigma }.\left(5\right)$$

In the reflected pulse to a flat surface, measured radioaltimeter, allocate the leading edge duration τ_uwhen there is an increase in the amplitude of the received signal, front and rear, which is the recession and the accounting model of the pulse shape of the antenna directional diagram. When using a receiving antenna with a narrow beam pattern is weakening the power of the received signal when HCS is the chances of improving the angle of incidence, therefore, after reaching a maximum decline at the trailing edge of the reflected pulse.

2 shows the pulse shape in the reflection from a flat surface. When there is unrest, the pulse shape is distorted, in particular, the leading edge becomes longer, because the first reflected signal comes when reaching the leading edge of the probe pulse crests of waves, and ends when reaching the rear front of the falling pulse edge.

An example of transformation of the shape of the reflected pulse, depending on the height of the large-scale disturbances is shown in Figure 3.

The observed transformation of the leading edge of the reflected pulse opens the possibility of measuring the height of the large-scale unrest. In the standard reconstruction algorithm the height of the large-scale unrest input parameter is the tangent of the angle of inclination 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 migrating a satellite radioaltimeter with a narrow radiation pattern of the antenna at the plane shape of the pulse is greatly transformed (see Figure 4,a) and to restore the height of the large-scale unrest becomes impossible.

The situation is improving, if you use a wide knife or the antenna pattern for the of radioaltimeter, as can be seen from Figure 4,B.

In the case of a wide antenna pattern the falling trailing edge of the reflected pulse can be explained primarily by the impact of large-scale slopes of excitement, and not the antenna directional diagram. It can be seen from Figure 5, illustrating the dependence of the shape of the reflected pulse from the dispersion slope.

Thus seen from the figures that the effect of height and dispersion slope of large-scale disturbances of the water surface on the shape of the reflected pulse depends on the flying height and the width of the antenna directional diagram.

The use of antenna with symmetrical radiation pattern of the antenna leads to the loss of azimuthal characteristics of the agitation of the water surface. To save this information, you must use radioaltimeter with blade antenna pattern, i.e. δ_x>>δ_y.

In the end, the final formula for the shape of the reflected pulse are as follows:

$$P\left(t_0+t\right)~1-\exp \left[-\frac{ct\left(\mathrm{was\; 2.76}{S}_x^2+2{\delta }_x^2\right)}{H_0{\delta }_x^2{S}_2^{}}\right]$$and$$P\left(t_0+t\right)~A_0\exp \left[-\frac{ct\left(\mathrm{was\; 2.76}{S}_x^2+2{\delta }_x^2\right)}{H_0{\delta }_x^2{S}_x^2}\right].$$

In this case, the shape of the reflected pulse contains information about the dispersion slope excitement$$S_x^2$$along the orientation of the antenna.

As a result, as measured by independent methods, the variance of the slope and the height H_Slarge-scale unrest, it is possible to determine the average wavelength:

$$L\approx \sqrt{H_S^2/S_x^2}$$.

Developed radar method for determining parameters of large-scale disturbances of the water surface is as follows.

Using radioaltimeter with blade antenna pattern, enteromonas along the direction of flight, emit the excitation pulses vertically down towards the water surface (at Nadir), receive reflected from the water surface of the probe pulses, register their shape and determine the slope of the leading edge of the reflected pulse height large-scale disturbances of the water surface, the inclination of the trailing edge of the reflected pulse with the height of the flight and the width of the beam determine the variance of the slopes of large-scale disturbances along the flight direction, and determine the average length of the surface wave along the direction of flight, using the measured variance of the slope and height of the large-scale unrest.

Thus, the proposed radar method enables rapid determination of parameters of large-scale disturbances of the water surface, such as the height of the large-scale unrest, the dispersion slope of the excitement and the average length of the surface waves from the plane.

Radar method for determining parameters of large-scale disturbances of the water surface using radioaltimeter, namely, that emit illuminating pulses vertically down towards the water surface (at Nadir), receive reflected from the water surface of the probe pulses, register their shape and determine on the bosom of the leading edge of the reflected pulse height large-scale disturbances of the water surface, characterized in that for the measurement of use posted on the airplane compact satellite radioaltimeter with blade antenna pattern, oriented along the flight direction, and the inclination of the trailing edge of the reflected pulse with the height of the flight and the width of the beam determine the variance of the slopes of large-scale disturbances along the flight direction, and determine the average length of the surface wave along the direction of flight, using the measured variance of the slope and height of the large-scale disturbances of the water surface.