RU2465606C1 - Adaptive method for rapid remote measurement of wind speed and direction - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: before taking measurements, the atmosphere is probed in order to determine the size of aerosol irregularities of the atmosphere and then irradiated with a beam which scans in the horizontal plane within a small angle (units of degrees). Signals from scattering volumes in the atmosphere are picked up, wherein the number of scattering volumes is selected based on the required accuracy Δφ of determining 90° of the wind direction:

the dimensions of the measuring bases are identical and equal to the value which is adaptively variable and determined by the size of aerosol irregularities of the atmosphere and wind speed. The minimum value

of mutual structure functions S_1.2i(τ) = 〈[U₁(t) - U_2i(t + τ)]²〉 between the signal U₁(t) from scattering volume 1 and signals U_2i(t), i=1…n from scattering volumes 2HB1…2HBi…2HBn is determined. The wind direction is the direction between the scattering volume 1 and the volume with the least minimum value

of the mutual structure function. The value and sign of wind speed are determined from the position of the minimum of the mutual structure function

of signals for these scattering volumes and the distance between these objects.

EFFECT: high accuracy of rapid remote measurement of wind speed and direction.

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Description

The invention relates to measuring technique and can be used, in particular, in applied meteorology for operational remote measurement of wind speed and direction.

Known methods for measuring the velocity of a gas stream and atmospheric wind, based on the registration (by contact or remote sensing) of random realizations of signals at two points of the flow and further analysis of the measured random realizations or the results of their correlation processing (see, for example, [1-6]). For operational remote measurement of the speed and direction of atmospheric wind, laser remote sensing methods are promising [2-6].

, определяют минимальное значение

взаимно-структурных функций

между сигналом U₁(t) из рассеивающего объема 1 и сигналами U_i(t), i=2…n из рассеивающих объемов 2…i…, n принимают за направление ветра направление между рассеивающим объемом 1 и объемом с наименьшим минимальным значением

взаимно-структурной функции, определяют величину и знак скорости ветра по положению минимума взаимно-структурной функции сигналов для этих рассеивающих объемов и расстоянию между этими объемами.Closest to the proposed method is a method for operative remote determination of wind speed using a lidar [2], which consists in the fact that the atmosphere is irradiated with two probe beams propagating with a small angular distance between them, signals from scattering volumes in the atmosphere are recorded, while the number of scattering volumes n> 2 (a top view for a variant of four scattering volumes is shown in FIG. 1) is selected based on the required accuracy Δφ of determining the direction of the wind

determine the minimum value

cross-structural functions

between the signal U ₁ (t) from the scattering volume 1 and the signals U _i (t), i = 2 ... n from the scattering volumes 2 ... i ..., n, the direction between the scattering volume 1 and the volume with the lowest minimum value is taken as the wind direction

cross-structural function, determine the magnitude and sign of the wind speed from the position of the minimum cross-structural function of the signals for these scattering volumes and the distance between these volumes.

The disadvantage of the method [2] - due to the use of only two laser beams, the distances (measuring bases) between the scattering volume 1 and the scattering volumes 2 ... i ... n are not the same (this is clearly seen from Fig. 1: the distances d2, d3 and d4 differ significantly among themselves) and independent of atmospheric characteristics. The choice of measuring bases unequal and independent of atmospheric characteristics can lead to significant errors in determining wind speed.

(на фиг.2 показано расположение трех из n рассеивающих объемов для возможных направлений ветра: НВ1, НВ2, HB3…HBi…HBn), размеры измерительных баз (расстояний между рассеивающими объемами атмосферы 1 и 2НВ1, 2НВ2, 2HB3…2HBi…2HBn) выбирают одинаковыми и равными величине, адаптивно изменяемой и определяемой размерами аэрозольных неоднородностей атмосферы и скоростью ветра на момент измерений, определяют минимальное значение

взаимно-структурных функций

между сигналом U₁(t) из рассеивающего объема 1 и сигналами U_2i(t), i=1…n из рассеивающих объемов 2HB1…2HBi…2HBn, принимают за направление ветра направление между рассеивающим объемом 1 и объемом с наименьшим минимальным значением

взаимно-структурной функции, определяют величину и знак скорости ветра по положению минимума взаимно-структурной функции

сигналов для этих рассеивающих объемов и расстоянию между этими объемами.It is possible to increase accuracy by the fact that the atmosphere is probed before measurements to determine the size of aerosol inhomogeneities of the atmosphere, then it is irradiated with a beam scanning in a horizontal plane within a small angle (units of degrees), signals from scattering volumes in the atmosphere are recorded, and the number of scattering volumes is selected based on from the required accuracy Δφ of determining the direction of the wind:

(figure 2 shows the location of three of n scattering volumes for possible wind directions: HB1, HB2, HB3 ... HBi ... HBn), the dimensions of the measuring bases (the distances between the scattering volumes of the atmosphere 1 and 2HB1, 2HB2, 2HB3 ... 2HBi ... 2HBn) are selected equal and equal to the value adaptively changed and determined by the size of the aerosol inhomogeneities of the atmosphere and the wind speed at the time of measurement, determine the minimum value

cross-structural functions

between the signal U ₁ (t) from the scattering volume 1 and the signals U _2i (t), i = 1 ... n from the scattering volumes 2HB1 ... 2HBi ... 2HBn, the direction between the scattering volume 1 and the volume with the lowest minimum value is taken as the wind direction

cross-structural function, determine the magnitude and sign of the wind speed from the position of the minimum cross-structural function

signals for these scattering volumes and the distance between these volumes.

To measure the characteristics of atmospheric inhomogeneities, preliminary (prior to measurement) sensing of the atmosphere is carried out along the laser beam (central beam a in FIG. 2). Using a laser source with short pulses and scanning a narrow laser beam in the horizontal plane allows measurements to be made for measuring bases with arbitrary orientation and arbitrary size and adaptively (in accordance with the size of the aerosol inhomogeneities of the atmosphere and wind speed at the time of measurement) to change the size of the measuring bases when changing atmospheric conditions.

Figure 2 shows a top view of the proposed sensing scheme; a, b, c, d - the positions in the space of the scanning laser beam for which the distances between the scattering volume 1 and the scattering volumes 2HB1, 2HB2 and 2HB3 (the figure shows three of n scattering volumes 2HB1 ... 2HBi ... 2HBn) are identical and equal to some optimal the value determined by the conditions on the atmospheric path.

The presence of distinctive features (preliminary sounding to determine the size of aerosol inhomogeneities of the atmosphere and the use of a scanning beam for adaptively changing the measurement bases) indicates compliance with the criterion of "novelty."

These distinctive features are unknown in the scientific, technical and patent literature, and therefore, the proposed technical solution (as a combination of these features) meets the criterion of "inventive step".

A device that implements the proposed method works as follows.

The lidar contains a laser radiation source, a transmitting optical system, a receiving optical system, a photodetector and a processing unit. The radiation from the laser source passes through the transmitting optical system, which forms a probe beam scanning in the horizontal plane within a small (unit of degrees) angle.

The aerosol always contained in the atmosphere scatters the radiation toward the lidar (the sizes of the scattering volumes are determined by the divergence angle of the probe beams, their distance from the lidar and the pulse duration of the radiation source).

The received radiation passes through the receiving optical system, is recorded by the photodetector and enters the processing unit to determine the direction and magnitude of the wind speed.

The following operations are carried out sequentially in the lidar processing unit.

1. Determine (according to the results of preliminary sounding of the atmosphere along the laser beam (central beam a in figure 2)) the size of the aerosol inhomogeneities of the atmosphere [4,5].

2. Determine for the observation time t _{H the} optimal size d of the measuring bases for the existing conditions on the atmospheric path.

между сигналом U₁(t) из рассеивающего объема 1 и сигналами U_2i(t) из рассеивающих объемов 2НВ1, 2НВ2, 2HB3…2HBi…2HBn.3. Determine (according to the results of measurements during the observation time t _H ) the mutual structural functions

between the signal U ₁ (t) from the scattering volume 1 and the signals U _2i (t) from the scattering volumes 2НВ1, 2НВ2, 2HB3 ... 2HBi ... 2HBn.

этих взаимно-структурных функций в их минимумах.4. Determine the position of the minima τ _{i of the} cross-structural functions S _1,2i (τ), i = 1 ... n and the values

these cross-structural functions at their minimums.

) значение

.5. Determine the minimum (among the values found

) value

.

.6. The direction between the scattering volume 1 and the volume of 2HBi min with the lowest minimum value is taken as the direction of the atmospheric wind

.

между сигналами из рассеивающего объема 1 и объема 2HBi min7. The magnitude and sign of the wind speed is determined by the position τ _{i min of the} minimum cross-structural function

between signals from scattering volume 1 and volume 2HBi min

.

.

As a result of the work of the processing unit, an array of data on the magnitude and direction of the wind along the sounding path is formed (with a given discreteness).

To assess the performance of the proposed method for the operational measurement of the speed and direction of the atmospheric wind, mathematical modeling was carried out.

The choice of the optimal size d of the measuring base for the correlation method for measuring wind speed was discussed in [5]. It is shown that the optimal choice is the measuring base d of the order of the size of aerosol inhomogeneities of the atmosphere. However, this conclusion was made for sufficiently large observation times, when aerosol inhomogeneities can collapse and, having passed the first point of the measuring base, may not reach the second point of the measuring base.

The question of choosing the optimal size of the measuring base in the conditions of operational measurements (when the measurement time is short - a few seconds) remains unclear. In this case, the aerosol inhomogeneities of the atmosphere in most cases do not have time to collapse [5], passing from the first to the second point of the measuring base (for a small measuring base), and the optimal size of the measuring base should be determined not only by the size of the aerosol inhomogeneities, but also by the observation time required minimum measured wind speed and signal to noise ratio. Moreover, the sizes of aerosol inhomogeneities of the atmosphere (and their lifetime, depending on the size of the inhomogeneities) vary over a wide range depending on atmospheric conditions [5]. Therefore, preliminary sounding of the atmosphere is necessary for the rapid estimation of the size of aerosol inhomogeneities along the sounding path.

In the simplest case, when the direction of the wind is known, the only parameter to be determined is the wind speed. Figure 3 for this case shows a geometric diagram of the measurements of the correlation wind lidar with a small measuring base, short probing pulses and a scanning laser beam in a horizontal plane. In Fig.3 L - lidar; HB - wind direction; a, b, c, d - position in the space of the scanning laser beam; 1 - position of the first point of the measuring base; 2, 3, 4 - possible positions of the second point of the measuring base.

Lidar L irradiates the atmosphere with a narrow laser beam scanning in the horizontal plane within a certain small scanning angle (of the order of units of degrees). The laser pulse (for each position of the optical axis of the lidar during scanning) is scattered on the atmospheric aerosol (in all directions, including in the direction back to the lidar) and enters the lidar receiving system. The received radiation is gated in range, so that the recorded signal values (for each position of the optical axis of the lidar during scanning) correspond to signals from a sequence of local measurement volumes along the corresponding (a, b, c, d, ...) sensing paths.

With a known wind direction, the measuring base should be located along this direction [5]. Let the first point of the measuring base 1 be located at some distance from the lidar. Then the second point of the measuring base should be on the HB line at some optimal (from the point of view of accuracy of measuring the wind speed) distance from point 1 (at one of points 2, 3, 4 ...).

To determine the optimal size of the measuring base, mathematical modeling was carried out and the dependence of the error of measuring wind speed on the size of the measuring base with a known wind direction was studied.

For mathematical modeling, a set of programs was created that simulated the operation of a laser measuring instrument of atmospheric wind speed. The hypothesis of frozen atmospheric inhomogeneities was used during measurements, i.e. It was believed that inhomogeneities are transported in the atmosphere under the influence of the average wind, without changing their shape. In this case, the correlation method for determining the wind speed V can be simplified [5]:

where d is the measuring base (the distance from point 1 to the second point of the base (one of points 2, 3, 4 ...) along the HB line), τ is the time shift of the maximum of the mutual correlation function of the two signals recorded from the scattering volumes of the atmosphere at point 1 and second base point.

The use of a structural function instead of a correlation function gives smaller errors in measuring wind speed; therefore, in order to determine τ, the signal structural function was used (the time shift τ corresponds to the minimum structural function of two signals recorded from scattering atmospheric volumes).

Mathematical modeling was carried out for different sizes of aerosol inhomogeneities of the atmosphere, with different signal-to-noise ratios in a wide range of wind speeds.

Figure 4 shows an example of the dependence of the average (over 500 realizations of the fields of aerosol inhomogeneities of the atmosphere) error modules for measuring wind speed ΔV on the size of the measuring base d for the size of aerosol inhomogeneities of 5 m (measuring base along the wind direction). The measurement time was 5 s. The parameters of atmospheric inhomogeneities corresponded to the conditions of the horizontal path in the surface layer of the atmosphere. The signal-to-noise ratio is 5. In the figure: 1 - wind speed 4 m / s, 2-8 m / s, 3-12 m / s.

The results of mathematical modeling, shown in figure 4, show that the smallest errors in measuring wind speed are obtained when choosing a measuring base d ~ 14 m

The choice of the required size of the measuring base with an arbitrary (known) wind direction is provided by the possibility of localizing in the space of local measurement volumes due to the angular scanning of a narrow laser beam and the use of a laser with short probe pulses.

Under real measurements, one cannot know in advance whether the hypothesis of frozen atmospheric inhomogeneities during measurements is valid or not. Therefore, it is impossible to determine in advance which measuring base is better (in the sense of ensuring the smallest errors in measuring wind speed) to use: a base selected as described above (for the conditions of frozen inhomogeneities), or a base equal to the size of aerosol inhomogeneities of the atmosphere (for conditions when aerosol inhomogeneities can be destroyed during the observation).

However, this issue can be resolved promptly during the measurement process. The results of mathematical modeling show that the errors in measuring wind speed depend on some parameter Λ = Δ _min / d ^1/2 , where Δ _min is the minimum value of the structural function of the implementation of signals measured at two points of the measuring base (i.e., the value of the structural function with the best combination of the implementation of signals, for which the time shift used to measure wind speed is determined); d is the size of the measuring base. Therefore, the methodology for the operational selection of the measuring base can be as follows.

1. Prior to measurements, atmospheric sounding is carried out along the initial position a of the optical axis of the lidar. The obtained implementation of the signal (it is determined by the spatial realization of the index of backward aerosol scattering of the atmosphere along route a) is used to estimate the characteristic size of the aerosol inhomogeneities of the atmosphere.

2. Measurements are made of the implementation of the signals for the measuring base A, selected as described above (to minimize the errors in measuring wind speed), and for measuring base B, equal to the size of the aerosol inhomogeneities of the atmosphere.

3. The parameter Λ is calculated for measuring base A and base B.

4. A measurement base is selected for which the parameter Λ is less.

Table 1 shows the results of mathematical modeling. Shown here are the average (over 500 realizations of the fields of aerosol inhomogeneities of the atmosphere) error modules for measuring wind speed ΔV for measuring base A (equal to 14 m) and measuring base B (equal to the size of inhomogeneities).

Table 1. Errors in measuring wind speed with a known wind direction s / w Measuring base 5 m Measuring base 14 m Wind speed, m / s Wind speed, m / s four 8 12 four 8 12 2 1.5 3.5 5.1 1.0 1.6 3.0 (1.92) (2.10) (2.19) (1.05) (1.27) (1.31) 5 0.7 1.0 1.3 0.3 0.4 0.6 (0.36) (0.40) (0.41) (0.19) (0.24) (0.25) fifty 0.04 0.08 0.15 0.03 0.04 0.07 (0.005) (0.007) (0.009) (0.003) (0.004) (0.006)

Table 1 was obtained for the size of inhomogeneities of 5 m and for wind speeds V = 4 m / s, V = 8 m / s and V = 12 m / s with a signal to noise ratio (s / w) of 2, 5 and 50, and measurement time 5 s. The values of the parameter Λ are given in parentheses. Table 1 illustrates the advantage of choosing the size of the measuring base A over the choice of measuring base B during operational measurements of wind speed (in the case when the inhomogeneities do not collapse and are transferred to the atmosphere under the influence of wind). It can be seen that by the value of Λ one can judge the errors in measuring wind speed ΔV: a base with a smaller Λ provides smaller errors in measuring wind speed.

. Размеры измерительных баз (расстояния между рассеивающим объемом 1 и рассеивающими объемами атмосферы 2НВ1, 2НВ2, 2HB3…2HBi…2HBn) выбирают одинаковыми и равными величине, адаптивно изменяемой и определяемой размерами аэрозольных неоднородностей.In the general case, when the direction of the wind is unknown, it must be determined together with the wind speed. A diagram that can provide simultaneous operational measurement of wind speed and direction is presented in FIG. 2. In the figure: HB1, HB2, HB3, ... - the directions of the measuring bases, i.e. possible wind directions (their number is determined by the required accuracy of measuring the wind direction). For each direction HB1, HB2, HB3, ... a cycle of processing the measurement results described above is carried out. The direction for which the smallest minimum of structural functions constructed using the signals recorded at the points of the measuring bases is taken is the direction of the wind. The number of measuring bases (the number of scattering volumes 2НВn) is selected based on the required accuracy Δφ of determining the direction of the wind

. The sizes of the measuring bases (the distances between the scattering volume 1 and the scattering volumes of the atmosphere 2НВ1, 2НВ2, 2HB3 ... 2HBi ... 2HBn) are chosen the same and equal to the value adaptively changed and determined by the size of the aerosol inhomogeneities.

An example of the results of mathematical modeling for the unknown direction of the atmospheric wind is presented in table 2. Here are the results of mathematical modeling of the average modules of the errors in measuring the speed (ΔV) and direction (Δα) of the wind. The size of the aerosol inhomogeneities of the atmosphere was set equal to 5 m, the number of directions of the measuring bases (in the sector 180 °) is 19, and the observation time t _H = 5 s. The table shows the results of mathematical modeling for a measuring base of 5 m (in [4,5] it is recommended to choose a measuring base on the order of the size of aerosol inhomogeneities of the atmosphere) and an adaptively selected base (from two options - a base of 5 m and a base of 14 m).

The simulation results show that the described method allows to reduce the error ΔV measurement of wind speed. With a small signal-to-noise ratio (at large distances from the lidar), wind speed measurement errors can decrease by 1.5–2 times.

Thus, the described method allows to increase the accuracy of operational remote measurements of wind speed.

Information sources

1. PCT Application WO 2006/063463. Optical transit time velocimeter. International Publication Date 06/22/2006. International Patent Classification G01P 5/20, G01P 5/26.

2. Patent RU 2404435. A method for operational remote sensing of wind speed and direction. The patent is valid on June 4, 2009. IPC G01P 5/22, G01P 5/26, G01S 17/95.

3. Armstrong R.L., Mason J.B., Barber T. Detection of atmospheric aerosol flow using a transit-time lidar velocimeter // Applied Optics. - 1976. - V.15. - N 11. - P.2891-2895.

4. The use of correlation methods in atmospheric optics / V. M. Orlov, G. G. Matvienko, I. V. Samokhvalov and others. - Novosibirsk: Nauka, 1983. - 160 p.

5. Correlation methods of laser-location measurements of wind speed / G. G. Matvienko, G. O. Zade, E. S. Ferdinandov et al. - Novosibirsk: Nauka, 1985. - 223 p.

6. Matvienko GG, Samokhvalov IV, B.C. Rybalko et al. Operational determination of wind speed components using a lidar // Atmospheric and Ocean Optics. - 1988. - T.1. - N 2. - S. 68-72.

Claims (1)

A method for operative remote measurement of wind speed and direction, which consists in the fact that the atmosphere is probed before measurements to determine the size of the aerosol inhomogeneities of the atmosphere, then it is irradiated with a beam scanning in a horizontal plane within a small angle, signals from scattering volumes in the atmosphere are recorded, and scattering volumes are selected based on the required accuracy Δφ of determining the direction of the wind:

, the dimensions of the measuring bases are chosen the same and equal to the value adaptively changed and determined by the size of the aerosol inhomogeneities of the atmosphere and the wind speed, determine the minimum value

cross-structural functions

between the signal U ₁ (t) from the scattering volume 1 and the signals U _2i (t), i = 1 ... n from the scattering volumes 2HB1, ... 2HBi, ... 2HBn, the direction between the scattering volume 1 and the volume with the lowest minimum value is taken as the wind direction

cross-structural function, determine the magnitude and sign of the wind speed from the position of the minimum cross-structural function

signals for these scattering volumes and the distance between these volumes.

Images