RU2411538C2 - Method of determining error in measuring aircraft velocity with inertial navigation system and onboard navigation system for realising said method - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method is realised by using data received from a coherent onboard radar system (ORS) of the monopulse type with anterolateral view to correct an inertial navigation system (INS) on velocity. Such ORS can receive a radar image of the underlying surface and find the direction of bright points on the radar image on the azimuth and angle of elevation while simultaneously measuring the corresponding Doppler frequency shift. Use of these data together with data of the INS enables to calculate the error of the INS on determination of all three components of the aircraft velocity vector. Errors which are characteristic of Doppler velocity meters, caused by the effect of reflecting properties of the underlying surface, are excluded.

EFFECT: high accuracy of aircraft navigation without using external navigation equipment.

2 cl, 5 dwg

Description

The invention relates to autonomous on-board systems for determining the location of an aircraft (LA) and can be used in the design of aircraft control systems to improve navigation accuracy.

As a rule, the basis of the navigation system of an aircraft is inertial navigation systems (ANS) [1, p. 71-85], a characteristic feature of which is the quadratic law of the increase in the error in determining the location of an aircraft over time. To correct these errors in order to increase the autonomous flight time of an aircraft in navigation systems, radar tools are used to measure the parameters of motion relative to the underlying earth's surface [2, p. 324-326]. These tools are usually a radio altimeter (RV) and a Doppler speed and drift angle meter (DISS). The DISS data can significantly reduce the positioning error. However, the placement of this device, especially on a small aircraft, is difficult. This is due to the fact that antenna systems of a rather large size are required for accurate measurement of the velocity vector using DISS. The same can be said when replacing the DISS with a correlation speed and drift meter (KISS) [2, p. 250-254]. In this case, a significant lateral spacing of the receiving antennas is required to accurately measure the drift angle. For this reason, the on-board control system [3] does not use a radar speed sensor at all, which, of course, can significantly limit its capabilities.

The use of a satellite navigation system (SNA) for the correction of ANNs, as was done in [1, p. 77], deprives the on-board system of autonomy and reduces its effectiveness in case of suppression or shutdown of the SNA.

In [4], data obtained by a coherent airborne monopulse radar system (BMRS) of side view with aperture synthesis are used to correct ANNs. In this case, the BMRS receives a radar image (RLI) of the underlying surface. When comparing the received radar image with the reference one, which is loaded into the memory of the navigation system during flight preparation, the specified location of the aircraft is determined and ANN errors are calculated. The disadvantage of such a system is, firstly, the difficulty of obtaining reliable standards, and secondly, such a system is not operational above the water surface.

It should be noted that all of the above flight control systems [1, 3, 4] include BMRS as the main information sensor that provides the flight mission. The proposed method for correcting ANNs in terms of speed consists in determining with the help of BMRS the geometric position of the bright points of the underlying surface with the simultaneous measurement of the Doppler frequency offset of the signals reflected by these points. The initial data for calculating the ANN error in this case is the difference between the measured Doppler frequencies of the bright points and the calculated Doppler frequencies according to the geometric position of these points using the ANN velocity vector. Since the ANN error changes slowly, this allows it to be estimated in a relatively large time and even with a changing aircraft trajectory. Linking the Doppler frequency shift to specific bright points avoids the main disadvantage of DISS, namely the presence of a systematic measurement error due to the dependence of the average Doppler frequency shift in the spot of light on the type of underlying surface, the so-called “marine effect” [2]. Another problem is partially overcome, associated with a significant decrease in the level of the signal reflected from the water surface with an increase in the angle of incidence. Simultaneous resolution by Doppler frequency and range allows you to highlight the most vivid resolved elements. Moreover, although the average signal level remains low, the signal-to-noise ratio for bright elements may be sufficient to measure their coordinates.

The stated goal is achieved by the fact that in the method for determining the error of measuring the speed of an aircraft by an inertial navigation system, including probing the earth's surface with microwave electromagnetic signals in several directions with a change in azimuth and elevation angle with modulation, which allows measuring the delay time and Doppler frequency shift of signals reflected by resolved elements surface, according to the invention is a coherent reception of reflected signals, selected by global coordinates with the formation of monopulse total and difference azimuthal and elevation channels in the normal coordinate system of the ANN [5]. For each of the channels, a complex radar image (RLI) of the irradiated surface is obtained in coordinates of the Doppler frequency shift — the range during sounding in each i-th direction, i = 1 ... I, I≥3. According to the radar image of the total channel of each sounding direction, the brightest points are found with the determination of their range and Doppler frequency shift. The azimuth and elevation angle of the highlighted bright points are calculated using the radar image of the difference channels. Based on the received radar data and ANN data, errors in measuring the ANN speed are calculated. The highlighting of bright points on the total radar radar is performed as follows: the brightness radar radar equal to the square of the integrated radar radar module of the total channel is calculated, the threshold level is calculated, which is equal to 20 times the average value of the noise radar radar radar, obtained if there are only receiver noise in the received signal, the points are determined the absolute and local maxima of the brightness radar radar and are compared with a threshold level, in case of exceeding which the highlighted maxima are considered bright points. The azimuth β _k and elevation angle ε _{k of the} k-th brightest point are calculated by the formulas

,

,

, - комплексные амплитуды k-той яркой точки в суммарном, разностном азимутальном и разностном угломестном РЛИ, χ_β, χ_ε - комплексные калибровочные коэффициенты азимутальной и угломестной пеленгационной характеристики, β_i, ε_i - положение равносигнального направления диаграммы направленности в нормальной системе координат ИНС при i-том направлении зондирования.Where

,

,

, are the complex amplitudes of the k-th brightest point in the total, difference azimuthal and difference elevation radar radar, χ _β , χ _ε are the complex calibration coefficients of the azimuthal and elevation direction-finding characteristic, β _i , ε _i are the position of the directional directional pattern in the ANN normal coordinate system with the i-th direction of sounding.

When flying over a flat horizontal or water surface, the elevation angle of the k-th brightest point ε _k can be determined by the formula

where H _i is the flight altitude with the i-th direction of sounding, D _k is the distance to the k-th bright point.

The error in measuring the speed of ANN ΔV is determined by the formula

where P is a 3 × K matrix, transforms the residual vector into a velocity measurement error vector, K is the total number of bright points in all sensing directions;

R is the matrix of coordinates of bright points, dimension K × 3, the k-th row of which corresponds to the transposed direction vector to the k-th bright point

, где F_k - доплеровское смещение частоты k-той яркой точки,

- вектор скорости, определяемый ИНС во время зондирования в i-том направлении; I - единичная матрица, λ is the wavelength of the probe signal; ΔF is the residual vector of dimension 1 × K, the k-th element of which is equal to

where F _k is the Doppler frequency offset of the k-th brightest point,

is the velocity vector determined by the ANN during sounding in the i-th direction; I is the identity matrix

, при зондировании в i-том направлении; после зондирования во всех направлениях в БЦВМ вычисляется ошибка измерения вектора скорости в ИНС ΔV, которая с первого выхода БЦВМ подается на вход ИНС для ее коррекции.The stated goal is also achieved by the fact that in the navigation system, which contains a series-connected ANN and an on-board digital computer, to the third input of which a radio altimeter (RV) is connected, the output of the BCMC is connected to the input of the ANN, and a coherent on-board monopulse radar system (BMRS) with anterolateral is additionally introduced review. The BMRS input is connected to the second output of the digital computer, from which the aircraft’s orientation data in the ANN normal coordinate system [5] are received on the BMRS as roll angles γ _i , pitch ϑ _i and yaw ψ _i , taking into account the position of the antenna signal β _i and ε _i during sounding in each i-th direction, the output of the radar detector is connected to the first input of the digital computer, which receives the Doppler offsets and angular coordinates of the bright points F _k , β _k and ε _k received as a result of the sensing, and to the third input of the digital computer from the output of the PB m height value H _i, the corresponding i-to the direction sensed, and a second input from the output of ANN supplied bank angles γ _i, pitch θ _i and yaw rate ψ _i, determining aircraft orientation construction axes normal system INS coordinates and velocity vector is measured ANN,

when probing in the i-th direction; after sounding in all directions, the computer calculates the error of measuring the velocity vector in the ANN ΔV, which from the first output of the computer is fed to the input of the ANN for its correction.

The essence of the proposed solution is illustrated by a further description, drawings and diagrams.

Figure 1 is a structural diagram of a navigation complex.

Figure 2 - geometry of sounding of the underlying surface.

Figure 3 - algorithm for estimating errors ANN.

Figure 4 - RLI sushi.

Figure 5 - RLI water surface.

Figure 1 presents the structural diagram of the navigation system, which adopted the following notation:

1 - airborne monopulse radar system (BMRS);

2 - on-board digital computer (BTsVM);

3 - inertial navigation system (ANN);

4 - radio altimeter (RV).

On the structural diagram of the navigation complex (Fig. 1): BMRS 1, BTsVM 2, ANN 3 connected in series, ANS 3 output is connected to the second input of the BTsVM 2, the second output of which is connected to the input of the BMRS 1, and PB 4 is connected to the third input of the BTsVM 2.

BMRS 1 probes the underlying surface in three directions to obtain the total and differential radar images of its various sections. BMRS 1 should provide coherent reception of reflected signals, measuring range and Doppler frequency shift. This can be done in various ways, given, for example, in [6, p. 368, 369]. The construction of a monopulse antenna system providing reception over the sum and difference channels is described in [7, pp. 16-30]. As a result of sounding, the brightest points of the radar image of the total channel are identified, their range and Doppler frequency shift are determined, and azimuths and elevation angles are calculated in the normal coordinate system of ANN 3. These data are fed to the digital computer 2. Here it should be noted that to obtain radar data in the indicated coordinates 1 should work in the mode of Doppler beam narrowing (DOL) [8, p. 85, 86]. In this mode, the Doppler frequency shift of the highlighted bright point can be considered constant during sounding in this direction. When changing the direction of sounding, not only the azimuth should change, but the elevation angle in at least one of the directions should be no less than the width of the antenna pattern. The orientation parameters of the aircraft in space, i.e. the angles of roll γ _i , pitch ϑ _i and yaw ψ _i are determined in ANN 3 and served in BMRS 1 for accounting when installing the antenna system. When flying over a flat horizontal surface, when the elevation angle is calculated according to (3), the presence of a difference elevation channel is optional. In this case, the height measurement is provided by RV 4. In the digital computer 2, based on the results of sounding in all directions, the errors of ANN 3 for determining the velocity vector are calculated.

Figure 2 presents the geometry of the sounding of the underlying surface. The aircraft is at the point with coordinates: X = 0, Z = 0, Y = H. The underlying surface coincides with the XOZ plane. The coordinates of the bright point 5 in the Doppler frequency offset - range system are determined by the corresponding isodal 6, and the Doppler frequency offset - by the isodope 7. The isodals are formed by the lines of intersection of the underlying surface with spheres of corresponding radii centered at the location of the aircraft. Isodopes are formed by the intersection of the underlying surface with cones whose axis coincides with the direction of the velocity vector V LA. The vector r determines the direction to the bright point 5.

Figure 3 shows the error correction algorithm of the ANN.

8 - installation of the beam antenna BMRLS in the i-th position. Moreover, the angles β _i and ε _i must provide the DOL mode [8, p. 84], due to the fulfillment of the condition

where t _c is the time of surface sensing (synthesis time), which determines the resolving power of the BMS radar by Doppler frequency shift, λ is the wavelength of the probe signal, D is the range.

Installation of the antenna system is carried out in a connected coordinate system [5]. The azimuth β _ic and elevation angle ε _ic in the associated coordinate system, which determine the position of the line of sight in this coordinate system, are calculated by the formulas

и

- векторы-строки выбора составляющих вектора визирования в связанной системе координат;

Where

and

- row vectors of the selection of the components of the vector of sight in the associated coordinate system;

- the vector of sight in the normal coordinate system of the ANN;

- the matrix of the transformation of the vector from normal to the associated coordinate system.

For each direction of sounding, one radar image is obtained for the total and difference channels. From the radar image of the total channel, one can take some of the brightest points and get a system of linear equations for the components of the vector ΔV, however, the system will be poorly conditioned, the variation of angles β and ε will be within the relatively narrow radiation pattern of the BMRS antenna. Therefore, it is necessary to perform sounding in several directions, changing the azimuth and elevation angle as wide as possible, limited by condition (6), and take bright points from radar images of different directions. At the same time, an increase in the total number of bright points used also reduces the measurement error. In the VOL mode, when sensing the surface with a packet of pulsed signals, the radar image can be obtained by coordinated reception of each reflected pulse (range compression) followed by Doppler interperiodic filtering of the signal from each resolved range element (fast Fourier transform of samples of the same range by repetition periods).

9 - highlighting bright points and calculating angular coordinates. The bright maximums are local maxima of the total radar image that exceed the detection threshold, set at a signal-to-noise ratio of 13 dB (20 times). At smaller ratios, the accuracy of direction-finding deteriorates sharply. The highlighting of bright points on the total radar radar is performed as follows: the brightness radar radar equal to the square of the integrated radar radar module of the total channel is calculated, the threshold level is calculated, which is equal to 20 times the average value of the noise radar radar radar, obtained if there are only receiver noise in the received signal, the points are determined the absolute and local maxima of the brightness radar radar and are compared with a threshold level, in case of exceeding which the highlighted maxima are considered bright points. The angular coordinates of the bright points are calculated by formulas (1) and (2). After sounding is completed in 3 or more directions, ΔV is calculated.

10 - calculation of ΔV. The calculation of ΔV according to (4) is based on the linear estimation method with a minimum mean square error [9, p. 49-57]. The calculations are relatively simple, because the dimension of the inverse matrix is 3 × 3.

11 - ANN correction. The correction procedure can be performed by the methods recommended, for example, in [10, p. 217].

The proposed method for correcting the velocity vector was investigated using mathematical modeling of flight over various types of surfaces. The simulation results showed that the velocity vector module can be refined to 0.1-0.3%, and the drift angle to 10-15 ', depending on the accuracy characteristics of the antenna system.

BMRL radar flight tests were also conducted, as a result of which the levels of reflected signals from various surfaces were determined.

Figure 4 shows the XRD plot of land with a surface type meadow with shrubs. The radar image was obtained in tests of a coherent monopulse BMDMS of the centimeter range. The flight was carried out at an altitude of 50 m with a speed of about 50 m / s. It should be noted here that the radar image is a set of bright points.

Figure 5 shows the radar image of the water surface. Flight conditions are the same. The wind speed at the surface did not exceed 1 m / s, and the waves were practically absent. Although the level of the signal reflected to the side of the radar detector for such a surface is very small (40 dB less than over land), there are bright points 12 on the radar, significantly exceeding the noise emissions 13.

Thus, the results of mathematical modeling and flight tests of BMRLS show the high efficiency of the proposed method for compensating ANN errors and the ability to build a navigation system that implements this method.

Literature

1. Aviation control systems. Volume 2. Radio-electronic homing systems. Ed. A.I. Kanaschenkov and V.I. Merkulov. - M.: Radio Engineering, 2003.

2. Vinnitsky A.S. Autonomous radio systems. - M.: Radio and Communications, 1986.

3. RF patent No. 2207613.

4. US Patent No. 5,485,384.

5. GOST 20058-80. The dynamics of the aircraft in the atmosphere.

6. Reference radar. Ed. M. Skolnik. Volume 3. - M .: Sov. Radio, 1978.

7. Handbook of radar. Ed. M. Skolnik. Volume 4. - M .: Sov. Radio, 1978.

8. Radar stations with digital synthesis of the antenna aperture. Ed. V.T. Goryainova. - M.: Radio and Communications, 1988.

9. Bramer K., Ziffling G. Kalman-Bucy Filter. - M.: Science, 1982.

10. Aviation control systems. Volume 3. Command radio control systems. Autonomous and combined guidance systems. Ed. A.I. Kanaschenkov and V.I. Merkulov. - M .: Radio engineering, 2004.

Claims (2)

1. A method for determining the error of measuring the speed of an aircraft (LA) by an inertial navigation system (ANN), including sensing the earth's surface with microwave electromagnetic signals in several directions with a change in azimuth and elevation, with a modulation of the probing signal, which allows measuring delay time and Doppler frequency shift signals reflected by resolved surface elements, characterized in that a coherent one is selected, selected by angular coordinates natam with the formation of monopulse total and differential azimuth and elevation channels in the normal ANN coordinate system, receiving reflected signals, receiving on each channel a complex radar image (RLI) of the irradiated surface in coordinates, the Doppler frequency offset is the distance during sounding in each i-th direction, which differ in the azimuthal and elevation plane by no less than the width of the radiation pattern, i = 1, ... I, I≥3, distinguish a probe on the radar of the total channel of each direction the brightest points by calculating the brightness radar radar, equal to the squared module of the integrated radar radar of the total channel, calculating the threshold level equal to twenty times the average value of the noise radar radar radar, obtained when the received signal contains only the receiver's own noise, determining the points of the absolute and local maxima of the brightness Radar data and comparisons with a threshold level, above which the highlighted maxima are considered bright points, and their ranges and Doppler shift are determined eniya frequency is then calculated using the difference channel radar data, azimuth and elevation angle βk εk k-th luminous point, k = 1 ... K, K - total number of bright points obtained by sensing in all directions, by the formulas

Where

,

,

are the complex amplitudes of the kth bright point in
total, difference azimuthal and difference elevation radar radar, χ _β , χ _ε are the complex calibration coefficients of the azimuthal and elevation direction-finding characteristic, β ₁ , ε ₁ is the position of the signal direction of the radiation pattern in the ANN normal coordinate system for the i-th sensing direction, or, in in case of flight over an even horizontal or water surface, the elevation angle of the kth bright point ε _k is determined by the formula

where H _i - flight altitude in the i-th direction of sounding; D _k - the distance to the k-th brightest point, while the error in measuring the speed of the aircraft inertial navigation system ΔV is determined by the formula

where P is the matrix, dimension ЗхК, the transformation of the residual vector into the error vector of the velocity measurement, P = (R ^T · R + I) ^-1 · R ^T ; R is the coordinate matrix of bright points, dimension K × 3, the kth row of which corresponds to the direction vector to the kth bright point

where λ is the wavelength of the probe signal; ΔF is the residual vector of dimension 1 × K, the kth element of which is equal to

where F _k is the Doppler frequency shift of the k-th bright point,

is the velocity vector determined by the ANN during sounding in the i-th direction; I is the identity matrix

2. Aircraft navigation system (LA) containing an inertial navigation system (ANN) and an on-board digital computer (BCM), to the third input of which a radio altimeter (RV) is connected, the first output of the BCMC is connected to the ANN input, characterized in that it is additionally introduced coherent onboard monopulse radar system (BMRS) with an anterolateral view, the input of which is connected to the second output of the BCMC, through which the BMRS receives information about the orientation of the aircraft construction axes in the normal coordinate system tension ANN in the form angles γ _i roll, pitch, yaw θ _i and ψ _i during sensing in each i-th direction i = 1 ... I, I≥3, BMRLS output is connected to the first input digital computer, which receives the resulting sensing earth surface Doppler displacements, ranges and angular coordinates of the bright points F _k , D _k , β _k and ε _k , while the value of height H _i corresponding to the i-th direction of sounding and the second input from the output go to the third input of the digital computer from the output of the RS ANN feed roll angles γ _i , pitch ϑ _i and yaw ψ _i , which determine the orientation of the building her LA in the normal coordinate system of the ANN, and the velocity vector measured by the ANN,

when probing in the i-th direction; after sounding in all directions, the computer calculates the error of measuring the velocity vector in the ANN ΔV, which from the first output of the computer is fed to the input of the ANN for its correction.

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