RU2152055C1 - Method for radio-acoustic tilt sounding of atmosphere - Google Patents

Abstract

FIELD: meteorology, in particular, methods for measuring parameters of atmospheric boundary layer. SUBSTANCE: method involves round azimuthal static radio- acoustic tilt sounding along axes with constant elevation angle. Width of beam pattern of acoustic emission is equal to angular azimuthal resolution, which is calculated according elevation angle as solution of new equation which takes into account wind profile in atmospheric boundary layer upon different atmosphere stratification. Parameters of acoustic sounding signals conform to given values of maximal sounding height, height resolution and temperature interval. Radio pulses are triangular. Edge duration provides coverage of maximal tile sounding distance. EFFECT: increased safety of aircraft take-off and landing. 3 dwg

Description

 The invention relates to meteorology, and in particular to methods for determining the parameters of the boundary layer of the atmosphere, and can be used in the interests of security services for takeoff and landing of aircraft.

 A known method of radio-acoustic sounding (TIME) of the atmosphere, which includes emitting at a certain angle to the vertical from one point on the earth's surface a packet of acoustic waves, irradiating it from the same point with radio pulses with a wavelength twice that of acoustic, receiving electromagnetic echo at the same point signals and measurement of their parameters, the value of which determines the parameters of the atmosphere (wind speed and air temperature). [1. Kallistratova M.A., Kon A.I. Radio sounding of the atmosphere. M .: Science. 1985, 197 p.], Fig. 1.8, p. 16-18.

 In the known method implemented using the EMAK monostatic radar, the sensing range depends, firstly, on the magnitude of the horizontal wind, and secondly, on the interfering effect of extraneous electromagnetic signals (for example, aerodrome radio equipment), due to the fact that the wind removal of the sound packet from the radiation pattern of the radio antenna and the deterioration of the signal-to-noise ratio under the influence of electromagnetic interference. Moreover, this method itself creates interference, since it uses short rectangular radio pulses having a wide frequency band. Thus, this method does not provide a stable sensing range in real conditions of the airport and does not satisfy the requirements for electromagnetic compatibility.

 Closest to the claimed combination of features is a method of radio-acoustic oblique sounding of the atmosphere [2. Fabricant A.L. A.S. USSR 1290881, IPC G 01 S 13/95 dated 05.24.85. 3. The manufacturer A.L. // Izv. Universities. Radiophysics, 1988, vol. 31, no 10, 1160-1163], including radiation from one point of a packet of acoustic waves, irradiating it from the same point with radio pulses with a wavelength twice as long as acoustic, searching for elevation and azimuth values at which echo signals with maximum intensity are received at the radiation point, the Doppler frequency shift of the echo signal is determined, and the temperature and components of the wind speed vector are found from it.

 The main factor limiting the use of the prototype method at the airport is the inability to measure wind speeds at specific heights. In this method, average wind speeds are determined (averaged over the thickness of the atmosphere from the Earth's surface to a certain height). As shown in [1, p. 164-165], the difference between the local and the average wind increases with increasing sounding height.

Known methods of TIME in which it is possible to measure the values of wind speed and temperature at specific heights. Such methods include both bistatic and monostatic TIME methods, but they do not give a positive result at the airport, since they do not provide a stable range of temperature-wind sounding due to the influence of horizontal wind. According to ICAO requirements, to ensure accident-free take-off and landing of aircraft, horizontal wind values must be recorded at specific altitudes (2, 30, 60, 90, ... m). [4. All-weather specialized meeting. DOC9242, AWO / 78.- Montreal: Ed. ICAO, 1978, 180 pp.]
The basis of the invention is the task of creating a method of radio-acoustic sounding of the atmosphere, which provides a constant range of temperature-wind sounding, independent of the state of the atmosphere, and measuring meteorological values at specific altitude levels when emitting radio pulses, the shape and duration of which overlap the maximum slant range and compensate for attenuation reflected signals with increasing current range, and sounding in and against the wind at an elevation angle calculated from the new about mathematical expression and ensuring the combination of the point of emission of acoustic and electromagnetic waves and the reception of echo signals, the current range is determined from the results of oblique sounding, which eliminates the need for using short edges of the radio pulse, the resolution is determined by the parameters of the sound packet, and its dependence on the shape and duration of the radio pulse is excluded and, therefore, the dependence of the characteristics of the method on the band of necessary radio frequencies is excluded, which allows I can work with increased requirements for electromagnetic compatibility.

,
для профиля ветра в пограничном слое при различной стратификации атмосферы, излучают акустические посылки с периодом следования T_s ≥ R/c_s+τ_s и длительностью τ_s = Δr/c_s, где c_s - приземная скорость звука в воздухе, R = H/sinΘ - наклонная дальность зондирования, H - высота зондирования, Δr - разрешение по наклонной дальности, которое выбирают с учетом оценки Δr ≥ 2λ_s, где λ_s - длина звуковой волны в атмосфере,
акустическую посылку составляют из К временных дискретов, где К выбирают из условия перекрытия интервала температур на дистанции зондирования, в k-ом дискрете (k= l, 2. . .К) частоту устанавливают равной F_sk = F_smin+kΔF_s, где F_smin, ΔF_s задают в зависимости от состояния атмосферы, причем звуковую частоту среднего дискрета устанавливают по приземной температуре,
излучают радиоимпульсы с периодом следования T_e < 1/(2F_s) и длительностью τ_e = 2R/c_e, где С_e - скорость света, причем τ_e = 2τ_ф, τ_ф - время нарастания и спада радиоимпульса,
определяют разность доплеровских сдвигов эхо-сигналов в каждой азимутальной плоскости и выбирают ту азимутальную плоскость, для которой разность доплеровских сдвигов достигает максимального значения (Δ Ω_дmax), вычисляют скорость локального горизонтального ветра по формуле V_г = λ_e Δ Ω_дmax/(8πsinα) , где λ_e - длина радиоволны,
определяют расстояние до зондируемого объема по длительности принимаемого эхо-сигнала и по скорости звука с учетом времени распространения.This technical result is achieved by the fact that in the method of radio-acoustic oblique sounding of the atmosphere, which consists in the fact that from the point on the surface of the earth emit acoustic messages and irradiate them with radio pulses with a wavelength twice as large as acoustic, receive electromagnetic echo signals from different directions and measure their parameters, which determine the characteristics of the atmosphere, according to the invention, inclined sensing is carried out along axes having a constant elevation angle, in the full azimuth angle from is equal to the angular resolution in azimuth, and the width of the acoustic radiation diagram is set equal to the angular resolution in azimuth, and the elevation angle is equal to the interval of elevation angles Θ ₀ = π / 2-α ₀ , where α _{0 is} found from the solution of the equation

,
for the wind profile in the boundary layer at different atmospheric stratifications, acoustic messages emit with a repetition period T _s ≥ R / c _s + τ _s and duration τ _s = Δr / c _s , where c _s is the surface velocity of sound in air, R = H / sinΘ is the inclined sensing range, H is the sensing height, Δr is the inclined range resolution, which is selected taking into account the estimates Δr ≥ 2λ _s , where λ _s is the sound wavelength in the atmosphere,
the acoustic package is made up of K time samples, where K is selected from the condition of the temperature interval overlapping at the sensing distance, in the k-th sample (k = l, 2.. K) the frequency is set equal to F _sk = F _smin + kΔF _s , where F _smin , ΔF _{s are} set depending on the state of the atmosphere, and the sound frequency of the average discrete is set by the surface temperature,
emit radio pulses with a period T _e <1 / (2F _s ) and a duration of τ _e = 2R / c _e , where C _e is the speed of light, and τ _e = 2τ _f , τ _f is the rise and fall times of the radio pulse,
determine the difference of the Doppler shifts of the echo signals in each azimuthal plane and select the azimuthal plane for which the difference of the Doppler shifts reaches its maximum value (Δ Ω _dmax ), calculate the local horizontal wind speed using the formula V _g = λ _e Δ Ω _dmax / (8πsinα) where λ _e is the length of the radio wave,
determine the distance to the probed volume by the duration of the received echo signal and the speed of sound, taking into account the propagation time.

The basis of the proposed method of radio-acoustic oblique sounding is the physical effect associated with the wind deformation of the acoustic wave front during its propagation in the atmosphere. As a result of the wind action, the spherical wave front takes the form of a flattened and elongated ellipsoidal surface in the direction of the wind. On this surface of the acoustic wave front, there are two regions that have the property of reflecting and focusing the reflected radio waves to the point of emission of sound and EM vibrations. Both areas intersect with the azimuthal plane in which the local horizontal wind vector lies. When radiating and receiving radio pulses from the same point in the plane of the local horizontal wind, i.e. downwind and upwind, the Doppler shift of the reflected radio signals is extremely possible (Ω _dmax and Ω _dmin ) compared to sounding in other azimuthal planes. In the proposed method, during circular sounding, the azimuth value is selected for which the Doppler shift difference reaches a maximum ( _{ΔΩ dmax} = Ω _dmax -Ω _dmin ) and the local horizontal wind is calculated by the formula V _g = λ _{e ΔΩ dmax} / (8πsinα).
In the prototype, an echo signal is recorded with a maximum intensity, by which the azimuths and elevation angles of two reflection points are found, in each of which the wind has two horizontal components. According to the results of measuring the Doppler shift of radio waves reflected from the found points, it is possible to determine only the average horizontal components of the wind, i.e. averaged over the thickness of the atmosphere from the surface of the Earth to the points of reflection.

 In other words, in the prototype, the reflection point is found as the root-mean-square center of the reflection region, characterizing the weight distribution of the reflection power, while in the proposed method, the reflection point is the arithmetic average center of the reflection region, which is determined by the principle of the smallest path of the radio beam through the acoustic packet directly connected with Bragg diffraction [1, p. 10-11]. When the phase front is distorted by a horizontal wind, the coordinates of the mean-square and arithmetic mean centers can noticeably differ. Thus, the proposal defines precisely the local horizontal wind.

 To determine the elevation angle, at which it is most likely to see the maximum reflection point on the surface of the reflection region from the sounding point, a numerical simulation was performed taking into account the altitude distribution of the wind in the real atmosphere, the main relationships are given below.

 The determination of the angles of the sensing in the proposed method.

приводит к деформации сферического фронта R₀ ²=c_зв ²t² звуковой волны, распространяющейся в атмосфере. Здесь

- радиус-вектор поверхности, образованной фронтом звуковой волны. Деформация сферического фронта под действием ветра определяется результирующим вектором

его распространения. В результате поверхность деформированного фронта звуковой волны имеет вид
R²(c_зв+u_r)²t², (1)
где u_r - радиальный компонент вектора скорости ветра,

- радиус-вектор.Wind flow action with speed vector

leads to deformation of the spherical front R ₀ ² = c _sv ² t ^{2 of the} sound wave propagating in the atmosphere. Here

is the radius vector of the surface formed by the front of the sound wave. The deformation of a spherical front under the influence of wind is determined by the resulting vector

its distribution. As a result, the surface of the deformed front of the sound wave has the form
R ² (c _sv + u _r ) ² t ² , (1)
where u _r is the radial component of the wind speed vector,

is the radius vector.

где

В уравнении (2) применены следующие обозначения: с_x, c_y, c_z и u_x, u_y, u_z - компоненты векторов скорости звука и ветра в декартовой системе координат, φ и θ - полярные координаты (0≤φ≤2π, 0≤θ≤π/2), угол θ отсчитывается от нормали к поверхности Земли.Expression (1) in the Cartesian coordinate system represents the following parametric equation of the surface:

Where

The following notation is used in equation (2): c _x , c _y , c _z and u _x , u _y , u _z are the components of the sound and wind velocity vectors in the Cartesian coordinate system, φ and θ are polar coordinates (0≤φ≤2π , 0≤θ≤π / 2), the angle θ is measured from the normal to the surface of the Earth.

Уравнение (3) определяет условие получения эхо-сигнала в точке излучения звуковых и электромагнитных колебаний. Решение этого уравнения дает значения следующих основных параметров зондирования:
- азимута главной оси диаграммы направленности антенны РАЗ (φ₀) ;
- угла места той же оси

;
- наклонной дальности R₀f(φ₀,θ₀)) .Taking into account the requirement that the points of reception and emission of electromagnetic waves in the combined antenna ONCE coincide, the normal to the surface of the phase front of the sound wave at point M ₀ (x ₀ , y ₀ , z ₀ ) passes through the origin O (0,0,0). This condition gives the following system of equations for unknown quantities R ₀ , φ ₀ , θ ₀ that determine the orientation of the antenna:

Equation (3) determines the condition for obtaining an echo signal at the point of emission of sound and electromagnetic waves. The solution of this equation gives the values of the following basic sensing parameters:
- azimuth of the main axis of the antenna pattern RAZ (φ ₀ );
- elevation of the same axis

;
- inclined range R ₀ f (φ ₀ , θ ₀ )).

где

В уравнении (4) величина δ₀ представляет угол ориентации вектора скорости ветра относительно оси z.The cross section of the phase front of the sound wave in the xz plane (φ = 0) can be described by the following parametric equation of the curve:

Where

In equation (4), δ ₀ represents the angle of orientation of the wind speed vector relative to the z axis.

Решение дифференциально-трансцендентного уравнения (5) при фиксированном значении R₀ позволяет определить угол места

точки М₀ на фазовом фронте, а также значение наклонной дальности

Идеализированный случай, когда скорость ветра равномерно растет с высотой, т. е.

, достоин внимания по причине того, что на практике реальный профиль ветра всегда можно апроксимировать кусочно-линейными функциями с различными значениями k.The possibility of combining the points of emission and reception of an electromagnetic signal reflected by the vicinity of the phase front of the sound wave with the center at the point M ₀ (z ₀ , x ₀ ) is realized when the condition

The solution of the differential transcendental equation (5) for a fixed value of R ₀ allows you to determine the elevation angle

points M ₀ at the phase front, as well as the value of the slant range

The idealized case when the wind speed increases uniformly with height, i.e.

, is worthy of attention because in practice the real wind profile can always be approximated by piecewise linear functions with different values of k.

уравнение (5) преобразуется к виду
ctg2θ = kt/2. (7)
Из анализа решения данного уравнения следует, что угол места

"рабочей" точки фазового фронта звуковой волны в определенной мере зависит от величины kt. Это свидетельствует о том, что деформация фазового фронта звуковой волны увеличивается с высотой, так как z ≈ ct и u(z) = kt.For the case of horizontal wind

equation (5) is converted to the form
ctg2θ = kt / 2. (7)
From the analysis of the solution of this equation it follows that the elevation angle

the "working" point of the phase front of the sound wave to a certain extent depends on the value of kt. This indicates that the deformation of the phase front of the sound wave increases with height, since z ≈ ct and u (z) = kt.

где v_g - геострофический ветер; χ₀ - параметр шероховатости поверхности; а и b - некоторые постоянные. Атмосферным пограничным слоем (планетарным пограничным слоем) называют прилегающий к поверхности Земли слой воздуха, в котором существенно сказывается динамическое и тепловое влияние подстилающей поверхности. Толщина его зависит от метеорологических условий и колеблется от нескольких сотен метров (в ночные часы при слабом ветре) до 2-3 км (в дневные часы при сильном ветре).In a real atmosphere, typical wind profiles in the boundary layer of the atmosphere [5. Atmosphere. Directory. L .: Gidrometeoizdat, 1991, 509 p. Section 9.1. 6. Panovsky G. N. Planetary boundary layer. / The dynamics of the weather. 1988, p. 351-382] is approximated by an analytic function

where v _g is the geostrophic wind; χ ₀ is the surface roughness parameter; a and b are some constants. The atmospheric boundary layer (planetary boundary layer) is the layer of air adjacent to the Earth's surface, in which the dynamic and thermal influence of the underlying surface significantly affects. Its thickness depends on meteorological conditions and ranges from several hundred meters (at night with a light wind) to 2-3 km (during the daytime with a strong wind).

The solutions of equation (5) are obtained for real profiles of the horizontal wind speed over land in the evening, night, day, which allow you to set the elevation angles of the points of maximum reflection Θ = (40 ^° -45 ^° ) ± 15 ^° . This result agrees well with particular cases experimentally verified in [7. Masuda E. Technique for remote study of the atmosphere using sound waves // Kihon onke gakaysi, 1987. V.43, no 6. S.425-430. Translation R-14158 from 1.8.88, GPNTB, Moscow. 8. Takahashi K., Masuda Y., Matuura N., etc. Analysis of acoustic wave fronts in the atmosphere to profile the temperature and wind with a radio acoustic sounding system.// J. Acoust Soc. Am. Vol. 84 (3), Sept. 1988, 1061-1066] and confirmed in the prototype article [3].

In FIG. 1 shows a structural diagram of a device for implementing the proposed method, indicating the direction of the probe rays. Zenith angles are denoted by α. In FIG. Figure 2 shows the timing diagrams of operation for oblique sounding at elevation angles Θ = 90 ^° -α. Figure 3 presents the echograms of radiation and reception.

A device for implementing the proposed method according to FIG. 1 includes a radar antenna device 1, made in the form of two acousto-electromagnetic antennas EMAK (Fig. 1.8 [1]). In an EMAK antenna, a parabolic mirror is irradiated independently by sound and radio waves, and the optical axes of acoustic and radio emission coincide. In the device for implementing the proposed method, such two parabolic antennas are placed on the same spatial orientation mechanism diametrically opposite in azimuth at the same elevation with the possibility of mechanical scanning around the vertical axis. Each antenna in the antenna device 1 has a beam pattern for acoustic waves in elevation Δθ = ± 15 ^° and in azimuth Δφ ± 8 ^° .

 The indicated values of the angular dimensions of the main lobe of the acoustic radiation pattern are determined from the following considerations. In elevation, the antenna should “see” the angular sector, calculated in this application, in which oblique radio-acoustic sounding is realized, in azimuth, the width of the radiation pattern should provide the angular resolution when measuring the direction of wind speed, which is required in aviation standards [9. Requirements for meteorological equipment designed to obtain meteorological information necessary to ensure takeoff and landing of aircraft at GA aerodromes. // Proceedings of the GGO. L .: Gidrometeoizdat, 1989.V.523. S.2-25].

To ensure sounding inside the elevation angle Δθ = ± 15 ^° and the azimuthal angle Δφ ± 8 ^° , the aperture sizes of the mirrors of the radio-acoustic antenna device are calculated from the condition of obtaining just such a width of the main lobe of the radiation pattern for acoustic waves. The calculation method can be taken, for example, from [10. Markov G.T., Sazonov D.M. Antennas. - M.: Energy, 1975, 528 p. ] Given the ratio of wavelengths according to the Bragg rule, we obtain the antenna radiation pattern for radio waves is wider than for acoustic ones. Therefore, although under the influence of horizontal wind, the volume disturbed by the acoustic package can deviate from the axis of the main lobe of the electromagnetic radiation pattern, but will remain within this lobe and not be "blown out". Thus, the perturbed volume remains in the field of view of the radio antenna, which ensures the achievement of a given sounding height.

 The antenna device 1 through the antenna switch 2 is connected to the radio 3, the shaper of the sound packages 4 and the radio transmitter 5. The spatial orientation mechanism of the antenna device 1 is connected to the orientation unit 6, which is connected to the host computer 7. The computer 7 is connected to the radio 3, synchronizer 8, the recorder 9. The synchronizer 8 is connected to the antenna switch 2, the radio 3, the shaper of the sound packages 4, the radio transmitter 5.

The described radar circuit differs in composition from the well-known circuit of the EMAK monostatic radar [1, Fig. 1.8] in that, in the proposal, the antenna device 1 contains two antennas that together can rotate 180 ^° in azimuth and ± 5 ^° in elevation, in the EMAC scheme, one antenna directed at different angles.

 FIG. 1 will not change if the antenna device 1 is made in the form of an annular array consisting of combined EMAK antennas. In this embodiment, the antenna system remains stationary, the algorithm for controlling the process of radio-acoustic sounding changes, which will be discussed below.

 The method is implemented as follows. If there are two antennas in the antenna device 1, an acoustic pulse is simultaneously supplied to each antenna from the shaper of sound packages 4 through the antenna switch 2, and then in accordance with the time diagram of FIG. 2 - electromagnetic pulses from the radio transmitter 5. The echo signals transmitted to the antenna are transmitted through the antenna switch to the radio receiver 3, where the radio pulse is converted into a video pulse, which is fed to the input of the computer 7 (personal computer). In a computer, the signal is digitized, processed in accordance with the inherent software and is fed to the recorder 9. After supplying N radio pulses, the recorder issues a signal to the computer that it is ready for the next probing cycle. According to the ready signal, the computer gives a signal to the synchronizer 8 and the orientation unit 6, which, in turn, includes an orientation mechanism that changes the position of the antenna device by one angular step in azimuth equal to the azimuthal width of the acoustic radiation pattern. The synchronizer 8 provides signals of readiness for the next cycle of sending an acoustic pulse to blocks 2, 3, 4, 5. The period of acoustic sending is repeated. A half-turn of the antenna system in azimuth allows sounding in the entire space above the ground.

 With an antenna ring array, each subsequent acoustic pulse can be sent to each next pair of diametrically opposed antennas. In contrast to the above description, after the end of the next period of acoustic sending, the orientation unit sends a signal to the device for electric switching of the next pair of antennas.

 Another sensing option in the presence of a ring antenna array is the simultaneous emission of acoustic pulses, and then the simultaneous emission of radio pulses from all partial antennas. In this embodiment, each antenna must be connected to its own radio. The reception of echo signals is carried out simultaneously and independently by each partial antenna and the partial radio receiver connected to it.

The sequence of emission of acoustic and radio pulses and receiving echo signals in one antenna of the device 1 is shown in figure 2. For acoustic parcels, the following period is found: T _s ≥R / c _s + τ _s and duration τ _s = Δr / c _s , where с _s is the surface velocity of sound in air, R = H / sinθ is the inclined sensing range, H is the sounding height , Δr is the slant range resolution selected taking into account the estimate Δr≥2λ _s , where λ _s is the sound wavelength in the surface layer. The acoustic package is made up of K time samples, where K is selected from the condition of the temperature interval overlapping at the sensing distance, in the k-th sample (k = 1.2 ... K) the frequency is set equal to F _sk = F _smin + kΔF _s , where F _smin ΔF _{s is} set depending on the state of the atmosphere, and the sound frequency of the average discrete is determined by the surface temperature, radio pulses are emitted with a repetition period T _e <1 / (2F _s ) and duration τ _e = 2R / c _e , where c _e is the speed of light , and τ _e = 2τ _f , τ _f - the rise and fall times of the radio pulse.

We present a calculation of the time dependence of the amplitude of signals A (Fig. 2) for the following initial data. The sounding height H = 500 m is equal to the height of the circle that the aircraft makes before landing, the carrier frequency of the EM pulses f _e = 1228 MHz (radio wavelength λ _e = 0.244 m) is selected in the middle of the frequency interval 1215 and 1240 MHz, free at a typical aerodrome . The frequency of 1215 MHz is the upper limit of the operation of short-range navigation equipment; 1240 MHz - the lower limit of the operating frequencies of track radars [11. Davydov P.S., Sosnovsky A.A., Khaimovich I.A. Aviation radar. Directory. - M.: Transport, 1984, 223 p. 12. Aeronautical radio navigation. Directory. Ed. A. A. Sosnovsky. - M.: Transport, 1990, 264 p. 13. Aviation radio communications. Directory. Edited by P.V. Olyanjuk. - M.: Transport, 1990, 208 p. ]. According to experimental data [1, Fig. 6.1] for the wave λ _e = 0.244 m, the achieved height of radio-acoustic sounding does not exceed 0.6 km.

The height resolution was chosen ΔH = 30 m, which corresponds to the ICAO requirements for measuring wind shear in layers 30 m thick for heights of 2, 30, 60 m. The acoustic wavelength is selected from the Bragg condition [1] λ _s = λ _e / 2 = 0.122 m. The air temperature range is set equal to ± 40 ^o C (T = 233 - 313 K). From the Laplace equation we find the range of sound velocities. c _s = 20,053 • T ^1/2 = (306.09 - 354.7) m / s, and the corresponding interval of sound frequencies F _s = c _s / λ _s = (2507 - 2907) Hz.

At an azimuth angle θ = 40 ^{° of} radio sounding, the inclined range is R = H / sinΘ = 778 m. The resolution along the oblique range is Δr = ΔH / sinΘ = 47 m. The duration of the acoustic sounding pulse τ _s = Δr / c _s = 140 ms is rounded for mid range of sound speeds (c _s = 335.7 m / s). The acoustic package contains N _s = 385 wavelengths. To ensure the necessary range resolution, according to [1, file (4.26)], the condition N _s <[(π / 2) λ _s γ _T / T] ^-1/2 = 391, where T = 293 K , γ _T = 0.0098 K / m is the dry adiabatic temperature gradient.

In an atmospheric surface layer 500 m thick, the altitude temperature course usually does not exceed ΔT = 7 - 8 K. At T = 273 ± 5 K, the increment of sound frequency per degree of temperature is ΔF _s / ΔT ≈ 5 Hz / K. To cover temperatures in the entire thickness of the layer, the acoustic package is divided into K = 7 time samples in which the carrier frequency of the sound package increases with the sequence number relative to the neighboring one by ΔF _s = (2 - 10 Hz), and the operator sets 2 Hz at a low altitude the course of temperature (in cloudy weather), 10 Hz - in clear weather. In the middle discrete, the operator sets the frequency corresponding to the temperature (and speed of sound) on the surface of the earth. Each time sample of an acoustic pulse contains n _s = N _s / K = 55 wavelengths.

During the time between adjacent acoustic packages, each of them must pass a distance no less than the inclined sensing range. Acoustic packet repetition period (T _s -τ _s ) ≥R / c _s . For the lowest sound frequency, we obtain T _s ≥ 2.68 s or T _s = 2.7 s.

The duration of the radio pulse in the proposed method will be selected from the condition of overlapping slant range by the leading edge. To ensure the minimum band of the radio channel at the minimum possible pulse power, the trailing edge should be equal to the leading edge. Thus, we arrive at a triangular-shaped radio pulse with a duration of τ _e = 2R / c _e = 5.2 μs.

To determine the necessary bandwidth of the radio path, the value of the active width of the frequency spectrum of the pulse signal is usually determined, within which 95% of all its energy is contained. According to the methodology [14. Ovchinnikov N. I. Fundamentals of Radio Engineering. - M .: Military Publishing House, Ministry of Defense of the USSR, 1968, 408 pp.], The active spectral width is expressed by the formula (2Δf) _A ≈ 2ν / τ _n , in which the coefficient ν ≈ 0.56 for τ _f / τ _n = 0.5. To transmit a sequence of triangular radio pulses with a duration of 5.2 μs at the level of the active spectrum width, the necessary frequency band is (2Δf) _A ≈ (2 × 0.56) τ _e ≈ 0.22 MHz. It is also possible to estimate the necessary bandwidth by the width of the main and first two lateral maxima on both sides of the carrier (2Δf) _P. The value (2Δf) _P , corresponding to a power level of -27 dB of the spectral function of the radio signal with a triangular envelope, is (2Δf) _P = (2 × 3) / τ _e ≈ 1.2 MHz.

 In radio-acoustic sounding, both pulsed and continuous electromagnetic radiation can be used. The narrowest band has continuous radiation, it is used in the bistatic method Raz, because in it the radiation and reception are carried out fundamentally from different points (and using different antennas). In the proposed monostatic method, radiation and reception are carried out from one point (and preferably with the same antenna). The use of an extended radio pulse with a rising edge of the aforementioned duration in the proposed method allows us to solve several problems at once: 1) provide a narrow working band of radio frequencies, 2) untie the radiation and reception modes of the same antenna in time, 3) compensate for a decrease in the power level of the reflected radio pulse when increasing the distance from the antenna to the perturbed volume, 4) short-pulse radiation from extraneous stations can be easily filtered and will not introduce distortions into the operation of the proposed method .

 The last two points can be explained by the fact that with a long radio pulse, the greater the range, the longer the interaction time of electromagnetic and acoustic radiation. It follows, firstly, that at short ranges, where the energy of the probe radio pulse is large, the interaction time is short, and at long ranges the interaction time is approximately equal to the duration of the front of the electromagnetic pulse. Secondly, airfield radars operate with pulse durations much shorter than in the proposed method, and therefore the exposure time for these interfering short pulses is significantly less than the signals of the sensing system itself.

The follow-up period of the radio pulses T _{e is} found from the condition of normal phase detection of reflected impulse signals: a discrete function (with a Doppler frequency equal to the sound frequency) should be represented by more than two samples for the follow-up period. Therefore, 1 / T _e > 2F _s , we take 1 / T _e = 10 kHz, i.e. T _e = 100 μs. The time between adjacent radio pulses T _e -τ _{e is} distributed between the time of reception of the reflected radio pulse τ _r = 5.2 μs and the time for data processing τ _p = 89.6 μs. During the time between two adjacent acoustic packages, one can radiate N = (T _s −τ _s ) / T _e = 25600 radio pulses.

Determination of the current values of the slant range and sensing height. In the proposed method, two alternative algorithms are used, which allows to increase the accuracy of the method. For clarification, we will use echograms of radiation and reception (Fig. 3). Echograms of radiation and reception - the dependence of the amplitude of the signals on distance or time show the spatial and temporal location of the acoustic package and one emitted radio pulse. The range R ₀ corresponds to the moment t _{0 of} unlocking the receiver immediately after the emission of the radio pulse, <c _s > is the average value of the speed of sound at a distance from the Earth's surface to the current height, R _max is the maximum inclined sensing range.

To determine the slant range by the duration of the received echo signal, we use the ratio R _s = t _s c _e -Δr / 2, where t _s is the time interval from the trailing edge of the reflected radio pulse to the decay of the received echo signal from the audio signal. The current sounding height at elevation angle Θ is H _s = R _s sinθ.

To find the oblique range in the propagation time of the sound packet, we use the expression R _t = (Δt / -τ _s / 2) <c _s >, where Δt is the measured time interval from the moment of termination of sound transmission to the current time.

 Let us estimate the error of replacing the average speed of sound with a surface one when finding the inclined range by the propagation time of the sound packet.

With the quasi-continuous method of radio-acoustic sounding of the atmosphere, which is the proposed method, the ability to measure range by the radar channel is lost. Nevertheless, it remains possible to measure the range along the acoustic channel based on the known moments of the beginning and end of the acoustic package and the surface velocity of sound. Let us estimate the error in measuring the distance along the acoustic channel for the surface temperature T ₁ .

Погрешность вычисления расстояния x₀ по значениям t₀ и T₁ определим из равенства
Δ = 1-t₀q(T₁)^1/2/x₀. (10)
Пусть приземная температура T₁=293 К, температура на высоте x₀ равна T₂= 301 К. Если температура имеет линейный профиль
T(x)=T₁+ax, T₂=T₁+ax₀, (11)
то из (9), (11) находим

Подставим (12) в (10), получим погрешность при линейном профиле
Δ = 1-2[(T₁T₂)^1/2-T₁]/[(T₂-T₁). (13)
Оценим количественно погрешность измерения дальности по акустическому каналу при наиболее "неблагоприятных" атмосферных условиях. Приземной температуре T₁= 293 К соответствует скорость звука C_s1=qT₁ ^1/2 = 343,2 м/с. Для температуры на высоте 500 м T₂=301K скорость звука C_s2=347,9 м/с. Заметим, что положительное различие температур на минимальном и максимальном высотном уровнях, равное 8К, отображает максимальную мощность приземной температурной инверсии, согласно нашим экспериментальным данным для 500-метрового слоя атмосферы. Отсюда, согласно (13) получаем, что погрешность вычисления дальности Δ не превзойдет 0,7%.During the time dt, the sound travels with the speed c _s (x) = q [T (x)] ^1/2 , where q = 20.053, the distance dx = q [T (x)] ^1/2 dt. Hence, the measured time t ₀ is related to the true distance x _{0 by the} ratio

The error in calculating the distance x ₀ from the values of t ₀ and T _{1 is} determined from the equality
Δ = 1-t ₀ q (T ₁ ) ^1/2 / x ₀ . (10)
Let the surface temperature T ₁ = 293 K, the temperature at a height x ₀ is equal to T ₂ = 301 K. If the temperature has a linear profile
T (x) = T ₁ + ax, T ₂ = T ₁ + ax ₀ , (11)
then from (9), (11) we find

We substitute (12) into (10), we obtain the error with a linear profile
Δ = 1-2 [(T ₁ T ₂ ) ^1/2 -T ₁ ] / [(T ₂ -T ₁ ). (thirteen)
Let us quantify the error in measuring the distance along the acoustic channel under the most “unfavorable” atmospheric conditions. The surface temperature T ₁ = 293 K corresponds to the speed of sound C _s1 = qT ₁ ^1/2 = 343.2 m / s. For a temperature at an altitude of 500 m T ₂ = 301K, the speed of sound C _s2 = 347.9 m / s. Note that the positive temperature difference at the minimum and maximum altitude levels, equal to 8K, reflects the maximum power of surface temperature inversion, according to our experimental data for a 500-meter atmosphere layer. From here, according to (13), we obtain that the error in calculating the range Δ will not exceed 0.7%.

Подставим (15) в (10), получим погрешность при квадратичном температурном профиле, лежащем выше линейного,
Δ₁= 1-XT^1/2/(T₂-T₁)^1/2= 0,449% . (16)
Рассмотрим случай II, когда промежуточные температуры лежат ниже, чем при линейном профиле. В реальной атмосфере подобное высотное изменение температуры характерно, например, для слоя приземной температурной инверсии. В качестве примера рассмотрим погрешность вычисления расстояния при температурном профиле в виде параболы
T-T₁=(ах)^2/3; T₂=T₁+(ax₀)^2/3. (17)
Из (9) и (17) находим с учетом замены переменных (ах)^1/3=y, что t₀= 3Q/(2qa), где

Подставим (18) в (10), получим погрешность при квадратичном температурном профиле, лежащем выше линейного
Δ₂= 1-(3Q/2)T $\genfrac{}{}{0ex}{}{\text{1/2}}{\text{1}}$ (T₂-T₁)^3/2= 0,807% . (19)
Сравнивая погрешности, рассчитанные на основании соотношений (13), (16), (19), видим, что измерение расстояния по акустическому каналу при известных времени t₀ и приземной температуре T₁ можно осуществить в различных атмосферных условиях с достаточно высокой точностью.In a real atmospheric boundary layer, the temperature profile can noticeably differ from the linear one. We consider case I, when the intermediate temperatures lie higher than with a linear profile. In a real atmosphere, a similar altitudinal temperature change is inherent in layers below the elevated temperature inversion. As a specific example, we can consider the error in calculating the distance at a temperature profile in the form of a parabola
T (x) = T ₁ + ax ² , T ₂ = T ₁ + ax ₀ ² . (14)
From (9) and (14) we find that t ₀ = X / (q • a ^1/2 ), where

Substituting (15) into (10), we obtain the error for a quadratic temperature profile lying above the linear one,
Δ ₁ = 1-XT ^1/2 / (T ₂ -T ₁ ) ^1/2 = 0.449%. (16)
Let us consider case II, when the intermediate temperatures lie lower than with a linear profile. In a real atmosphere, a similar altitudinal temperature change is characteristic, for example, of a surface temperature inversion layer. As an example, we consider the error in calculating the distance at a temperature profile in the form of a parabola
TT ₁ = (ah) ^2/3 ; T ₂ = T ₁ + (ax ₀ ) ^2/3 . (17)
From (9) and (17) we find, taking into account the change of variables (ax) ^1/3 = y, that t ₀ = 3Q / (2qa), where

Substituting (18) into (10), we obtain the error for a quadratic temperature profile lying above the linear
Δ ₂ = 1- (3Q / 2) T $\genfrac{}{}{0ex}{}{\text{1/2}}{\text{1}}$ (T ₂ -T ₁ ) ^3/2 = 0.807%. (19)
Comparing the errors calculated on the basis of relations (13), (16), (19), we see that the measurement of the distance along the acoustic channel at known times t ₀ and surface temperature T ₁ can be carried out in various atmospheric conditions with fairly high accuracy.

Air temperature and its fluctuations, as a rule, do not significantly affect the aircraft. From the point of view of the needs of the direct provision of aviation with information about the temperature, it is considered acceptable to measure it with an accuracy of ± 1 ^o C [9]. However, from an economic point of view, the importance of accurate temperature knowledge is of great importance. So, according to the analysis contained in [15. Safety and Economics of Air Transport (French) / Goas Jacques // / Meteorologie, 1991, no 36. P. 35-40], an increase in temperature of 1 ^o C for heavy aircraft entails a decrease in the full commercial load for some types of aircraft by 0.5 tons

 The knowledge of the altitude distribution of temperature over the runway is very important because of the well-known relationship between wind shear and stratification of temperature [16. Shoshin, V.M., On the Relationship between Wind Shear and Stratification of Temperature, Tr. Ukr. region. Research Institute of Goskomhydromet, 1985.T 210.P. 95-99. 17. Jansson P. Low-level vertical windshear and temperature inversions observed at Sundvalls aerodrom / Publ. Zentralast. Meteorol. und Geodyn. Wien. 1981, no 253. P. 197-201]. Information on the nature of temperature stratification often allows one to independently determine the spatio-temporal position of zones of increased wind shear without wind measurements and, based on the dynamics of thermal fields, obtain a short-term forecast of the appearance or decay of zones of strong wind shear.

 Therefore, the proposed method considers the possibility of increasing the accuracy of determining the temperature-wind sounding by clarifying the average speed of sound at a sounding distance.

 Determination of the average speed of sound at a sensing distance.

 The Doppler shift determines the speed of sound in the directions in and against the wind in a certain layer where the reflection region is located.

Среднее арифметическое этих величин равно скорости звука в слое c_s= (c'_s+c''_s)/2. По величине c_s из формулы Лапласа определяют температуру воздуха в слое T=(c_s/q)², где q=(kR/m_в)/^1/2=20,053 - постоянная, слабо зависящая от давления, температуры и влажности воздуха, k - отношение удельных теплоемкостей воздуха при постоянном давлении (С_p) и постоянном объеме (С_v), R - газовая постоянная, m_в - молекулярная масса воздуха.

The arithmetic mean of these quantities is equal to the speed of sound in the layer c _s = (c ' _s + c'' _s ) / 2. The c _s value from the Laplace formula determines the air temperature in the layer T = (c _s / q) ² , where q = (kR / m _c ) / ^1/2 = 20,053 is a constant, slightly dependent on pressure, temperature and humidity, k is the ratio of specific heat capacities of air at constant pressure (C _p ) and constant volume (C _v ), R is the gas constant, m _in is the molecular mass of air.

Таким образом, предложенный способ благодаря новым операциям, указанным в формуле изобретения, позволяет исключить недостатки прототипа, решает поставленную задачу и обеспечивает достижение необходимого технического результата. Предложенный способ дополнительно обладает следующими полезными эффектами.Sound speed average sounding distance

Thus, the proposed method due to the new operations specified in the claims, allows to eliminate the disadvantages of the prototype, solves the problem and ensures the achievement of the necessary technical result. The proposed method additionally has the following beneficial effects.

 1. Inclined two-beam sounding against and against horizontal wind at elevation angles adopted in this method eliminates the limitations of the sensing range due to the wind removal of the sound packet from the radar pattern, and the acoustic and EM radiation and reception patterns are comparable in angular size and do not require the use of large apertures.

 2. Eliminates the need to create a powerful wide-angle acoustic package, a powerful narrow radio beam and scan it.

 3 There is an opportunity to use a radio pulse signal with a small frequency band and low pulse power.

 As we see, the proposed method can be used to monitor the atmospheric boundary layer in the airport area directly above the runway with the required height and height resolution for aviation. In the proposed method, the adaptive oblique TIME can detect dangerous short-term strong wind shifts due to the reduction of the measurement time due to the elimination of time to search for the horizontal wind direction. This turned out to be possible as a result of mathematical modeling and measurement of the parameters of the received signal adequate to the problem.

Claims (1)

The method of radio-acoustic oblique sounding of the atmosphere, which consists in the fact that acoustic messages are emitted from a point on the surface of the earth and irradiated with radio pulses with a wavelength twice as long as acoustic, they receive electromagnetic echo signals from different directions and measure their parameters, which determine the characteristics of the atmosphere characterized in that the inclined sounding is carried out along the axes having a constant elevation angle, in the full azimuthal angle with a step equal to the angular resolution in azimuth, and The acoustic radiation diagram is set equal to the angular resolution in azimuth, and in elevation equal to the interval of elevation angles Θ ₀ = π / 2-α ₀ , where α ₀ is found from the solution of the equation

for the wind profile in the boundary layer at different atmospheric stratifications, acoustic messages emit with a repetition period T _s ≥ R / c _s + τ _s and duration τ _s = Δr / c _s , where c _s is the surface velocity of sound in air, R = H / sinΘ is the inclined sensing range, H is the sensing height, Δr is the inclined range resolution, which is selected taking into account the estimates Δr ≥ 2λ _s , where λ _s is the sound wavelength in the atmosphere, the acoustic package is made up of K time samples, where K is chosen from the condition of overlapping the temperature range at the sensing distance, in k- increments (k = 1, 2 ... K) is set equal to the frequency _{F sk = F smin + kΔF s} , where F _smin, ΔF _s determined depending on the state of the atmosphere, the secondary audio frequency increment is set at surface temperature, emit radio pulses with the period T _e <1 / (2F _s ) and the duration τ _e = 2R / c _e , where c _e is the speed of light, and τ _e = 2τ _f , τ _f is the rise and fall times of the radio pulse, the difference in the Doppler shifts of the echo signals in each azimuthal plane and choose the azimuthal plane for which the difference of Doppler shifts reached a maximum value (Δ Ω _dmax) is calculated rate of local horizontal wind by the formula V _g = λ _e Δ Ω _dmax / (8πsinα), wherein λ _e - length radio waves determine the distance to the probed volume of the duration of the received echo signal and the speed sound taking into account propagation time.

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