RU2304289C1 - Method for restoring radiolocation images of objects with stationary rotation center - Google Patents

Abstract

FIELD: measurements of radio-location chars of equipment object with reproduction of their radiolocation images.

SUBSTANCE: method is based on registration of amplitude diagram of reverse dissipation of object together with mobile supporting reflector S(φ), in form of a function of current observation angle φ within interval of angles Δφ≪1 rad and Fourier transformation S(φ) and computation of square modulus thereof for each fixed angle φ₀, while registered at interval of observation angles Δφ are: reverse dissipation diagram of object without supporting reflector S₀(φ) and reverse dissipation diagram of object together with mobile supporting reflector S₁(φ), mounted on a platform of supporting-rotary device of measuring radiolocation complex at a distance from rotation axis exceeding half the maximal linear dimension of object in direction, perpendicular to pointing direction of object, difference reverse dissipation diagram is built based on them and by means of computation of Fourier transformation ΔS(φ) and square modulus of that transformation, radiolocation image of object is reproduced.

EFFECT: increased dimensions of working zone of measuring radiolocation complexes.

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Description

The invention relates to radio engineering, in particular to the field of measuring radar characteristics (RLH) of objects with the restoration of their radar images (RLI), and can be used to increase the size of the working area of incoherent radar measuring complexes (RIC).

A known method of reconstructing radar images of objects from amplitude DORs, which are measured on incoherent DIRs (Gatilova I.Yu., Ponkin V.A., Uzhakhov TS. Determination of the spatial structure of local reflectors on the surface of an object by amplitude DOR. Radio engineering, 2000, No. 6 , p. 79-84). The method is based on the use of information directly contained in the interference structure of the amplitude DOR S (φ) as a function of the current viewing angle φ over the interval of viewing angles (-Δφ / 2, Δφ / 2).

The radar image was restored by solving the inverse problem of determining the characteristics (location and amplitude) of the radar image. However, in view of the progressive increase in the total number of bases M = N (N-1) / 2, with an increase in the number of LI-N and the resulting difficulties in solving the inverse problem, the applicability of the method is limited by a small number of LI (N <5). Therefore, this method is not applicable to real objects of technology.

The closest set of essential features to the proposed method is a method for reconstructing radar images of objects, based on measuring the amplitude DOR of an object with a stationary center of rotation with the introduction of the spatial carrier frequency of the reference signal by providing simultaneously with the rotation of the object translational with a constant speed of movement of the reference reflector or the object itself and restoration on this basis, radar images of objects (Varganov M.E., Zinoviev Yu.S., Astanin L.Yu. et al. Radar characteristics tatelnyh devices. / Ed. Tuchkov LT, Moscow, Radio and Communications, 1985, s.138-139). To avoid overlapping the reconstructed image of the zero order (containing interference images of the LI due to their interference interaction) and two conjugated images of the first order containing undistorted information about the spatial structure of the LI, it is necessary to fulfill the condition

where v is the rate of change of the phase of the reference signal, ω _in is the angular velocity of rotation of the object, r _max is the largest radius vector LI in the composition of the object, λ is the working wavelength.

Without creating additional equipment that provides linear movement of an object or a movable reference reflector, this method can be implemented on existing RICs by installing a reference movable reflector on a rotating platform on which the measured object is located. When installing the reference reflector on the edge of the platform (in a direction perpendicular to the line of sight of the object), the rate of change of the phase of the signal of the moving reference reflector will be equal to

where r _p is the radius of the RIC platform.

Substituting this value of the rate of change of the phase of the signal of the moving reference reflector in expression (1), we obtain the condition for the implementation of the prototype on existing RIC:

That is, the maximum radius r _{max of the} measured objects using the prototype does not exceed half the radius of the platform r _p / 2.

Considering that the dimensions of the RIC slewing platforms are consistent with the dimensions of the RIC working area and equipment, the fulfillment of condition (1) limits the size of the RIC working area. This is the main disadvantage of the prototype.

The objective of the invention is to increase the size of the working area of the RIC, providing measurement of radar retrieval with the restoration of radar images of complex objects with a stationary center of rotation according to their amplitude DOR.

на интервале углов наблюдения Δφ, регистрируют две ДОР: ДОР объекта совместно с подвижным опорным отражателем S₁(φ), устанавливаемым, как и объект, на поворотной платформе РИК на расстоянии от оси вращения, большем половины максимального линейного размера объекта в направлении, перпендикулярном линии визирования объекта, и ДОР объекта без опорного отражателя S₀(φ), составляют по ним разностную ДОРThe problem is solved due to the fact that in the known method for reconstructing radar images of objects with a stationary center of rotation, based on recording the amplitude backscatter diagram (DOR) of the object together with the movable reference reflector S (φ) as a function of the current viewing angle φ over the angle interval Δφ≪ 1 rad and calculating the squared Fourier transform modulus S (φ) for each fixed angle

on the interval of viewing angles Δφ, two DORs are recorded: the DOR of the object together with the movable support reflector S ₁ (φ), installed, like the object, on the rotary platform of the RIC at a distance from the axis of rotation greater than half the maximum linear size of the object in the direction perpendicular to the line sighting of the object, and the DOR of the object without a reference reflector S ₀ (φ), make up the difference DOR on them

ΔS (φ) = S ₁ (φ) -S ₀ (φ)

and according to it by Fourier transform restore the radar image of the object.

A comparative analysis of the claimed solution with the prototype shows that the proposed method differs from the known combination of new significant features:

- registration on the interval of viewing angles of two DOR, DOR with a movable reference reflector installed at a distance greater than or equal to half the maximum linear size of the object of observation in the direction perpendicular to the average line of sight of the measuring RES and DOR of one object;

- compilation of the differential DOR ΔS (φ), formed by subtracting from the DOR of the object + a movable reflector S ₁ (φ), the DOR of one object S (φ);

- calculation of the Fourier transform of the differential DOR ΔS.

The analysis of the prior art allows us to establish that technical solutions characterized by a combination of features identical to all the features contained in the claims proposed by the applicant are absent, which indicates compliance of the claimed invention with the novelty protection criteria.

Search results for known solutions in this and related fields of technology in order to identify features that match the distinctive features of the claimed device showed that no solutions having features matching its distinctive features were found in publicly available information sources. The prior art also does not confirm the popularity of the influence of the distinctive features of the claimed invention on the technical result indicated by the applicant. Therefore, the claimed invention meets the condition of inventive step.

The proposed technical solution is industrially applicable, since the set of characteristics characterizing it provides the possibility of its existence, performance and reproducibility, since well-known materials and equipment can be used to implement the claimed technical solution.

The proposed sequence of measurements, namely, first register the object DOR - S ₀ (φ) in the radiation field of the RIC, then, along with the object, install a movable reference reflector in the working volume of the RIC, measure the object DOR + reference reflector S ₁ (φ), compose the differential DOR ΔS (φ) = S ₁ (φ) -S ₀ (φ) and restore the location and intensity LI reflection object, the invention provides an embodiment in existing DEC and solution of the problem - the increase in size of the working zone RIC compared with the known method twice. This is confirmed by the results of mathematical analysis, computer simulations and experimental studies conducted at the RIC “Link-33” of the Federal State Research Institute of Electronic Equipment, Electronic Equipment, Economic Defense and Economy of the Russian Ministry of Defense, the essence of which is as follows.

When installing a rotating reference reflector (DO) on a rotating platform, the equation of the amplitude DOR of the "object + DO" system (Fig. 1) obtained by quadratic detection of echo signals at a wavelength λ as a function of the observation angle φ, accurate to a constant factor, will have the form

figure 2 shows a diagram of the formation of the amplitude DOR of the object using a movable reference reflector, where r ₀ , r _i , r _j , r _n , A ₀ , A _i , A _j , A _n , θ ₀ , θ _i , θ _j , θ _n are the radii of rotation, reflection amplitudes and polar angles of observation of the reference, i, j and n are reflectors, respectively, λ is the wavelength, N is the number of PIs (Fig. 2).

For small intervals of observation angles (Δφ≪1) (a fragment of the diagram (3) within φ∈ [-Δφ / 2; Δφ / 2] can be represented as

Where

- the frequency and initial phase of the spatial oscillation due to the interference of waves reflected from the nth LI and an additional reflector

- frequency and initial phase of interference oscillations of the i-th and j-th local scattering centers of the object.

As follows from the analysis of expression (3), for small angular observation intervals (Δφ≪1), it in appearance coincides with the expression for the amplitude radio hologram of the object recorded in the presence of a moving reference reflector, which, in principle, ensures separation of the reconstructed conjugated images. Indeed, restoring a one-dimensional image of an object by calculating the squared modulus of the Fourier transform of expression (3) leads to the following result:

- постоянная составляющая амплитудной ДОР S₁(φ);Where

- the constant component of the amplitude DOR S ₁ (φ);

sinc (X) = sin (X) / X - Fourier transform of a rectangular weight window.

Qualitatively obtained result is illustrated in figure 3. In accordance with Fig. 3, the reconstructed from the actual hologram radar image (7) consists of three components formed by the combination of functions sin (X) / X. The first of them corresponds to the constant component of the amplitude DOR proportional to the sum of the EPR of all reflectors in the working volume of the RIC and is located at zero on the axis of spatial frequencies. The second component of the radar image carries useful information about the spatial structure of the object. It is formed as a result of interference of waves reflected from local reflectors on the object and a moving reference reflector, and consists of two conjugate images 2 and 2` located symmetrically on the frequency axis. Each of the conjugate images is the sum of N weight functions sin (X) / X, reaching maxima at the points ν <sub>0, n</sub> . In this case, the maximum value is proportional to the amplitude of the echo signal from the nth local reflector. The third component 3 and 3` is an interfering image due to the interference of waves scattered by elementary reflectors with each other, and introduces an error in the measurement of the amplitude of signals reflected from local scattering centers.

Figure 3 shows that in (7), depending on the ratio of spatial frequencies ν _0nmax and ν _max , (where ν _0nmax is the maximum frequency of interference oscillations of the reference and nth LI objects, ν _max is the maximum frequency of interference oscillations of the ith and the j-th object LI) there are three possible mutual arrangements of the components of the reconstructed radar image.

If ν _0nmax ≥2ν _max , then the second and third components of the image do not intersect. In this case, the image can be obtained from one record of the amplitude ADOR of the "object - DO" system. The disadvantage of this option is the limitation of the linear dimensions of the measured objects due to the need to double the radius of rotation of the reference reflector of the maximum radius of the object (3).

If 2ν _max > ν _0nmax ≥ν _max , then the interfering image 3 is partially or completely superimposed on the useful image 2. One of the possible ways to compensate for the interfering image, as shown above, is to restore the image of the object from the difference amplitude DOR: the “object - BEFORE »S (φ) and the studied object S (φ). In the approximation of a small sector of viewing angles, the difference amplitude diagram is

A fragment of the difference amplitude diagram (8) in a small sector of the viewing angles can be considered as a real object Fourier hologram free of an interfering interference background.

In this case, the restored image

contains only two components - the image of the constant component 1, equal to the EPR of the reflector, and the conjugate image of the object 2 and 2` (figure 3). In this case, the conjugate images are separated. The advantage of the proposed method is a more complete use of the working volume of the RIC, i.e. the ability to work with large objects.

To separate the conjugate images reconstructed from the actual difference diagram (8), it is necessary that the coordinates of the DO in the sector of the radar image synthesis satisfy the condition

Thus, in the inventive method, as follows from (10), when placing the reference reflector on the edge of the platform in the perpendicular direction to the line of sight of the object, it is sufficient to fulfill the condition

that is, the dimensions of the working area of the RIC of the measured objects in comparison with the prototype can be doubled.

The result obtained has a simple physical interpretation. When implementing the method in the sector of angles Δφ, all local reflectors are located on one side of the line of sight "radar - DO" and, therefore, give (relative to the movable reference reflector) a Doppler frequency shift of the same sign. In this case, conjugate images arising during the restoration process will be located on the frequency axis on opposite sides with respect to zero (ν = 0).

The obtained results of mathematical modeling on a computer also confirm the operability of the proposed method for reconstructing the radar image of an object from their amplitude DOR at the sizes of the measured objects commensurate with the dimensions of the platform. To check, an object consisting of four identical isotropic point reflectors was used. The wavelength of the probe signal was taken equal to λ = 3 cm. The geometric structure of the object, as well as the installation location of the movable reference reflector are shown in Fig. 4. A one-dimensional image of the model of the object, restored in the range of viewing angles of width Δφ = 16 ° for the viewing angle φ ₀ = 15 °, is shown in Fig.5. Computer simulations have shown the possibility of confidently reconstructing the radar image with the following characteristics of the irradiation field: the amplitude decay level at the edges of the working volume is ≤3 dB, the phase incursion is ≤π / 8, which ensures the stability of the fine structure of DOR and the accuracy of measuring the EPR of objects not lower than 0.5 dB at relative highs.

In the course of the studies, the advantage of the proposed method, which is important for practice, as compared with the known one, is found, which consists in its operability, regardless of the total number of local sources observed at the object from a given direction. This is achieved through the use of a differential amplitude DOR, in which there is no component formed by the mutual interference of signals reflected from local sources of secondary radiation.

Figure 1 shows a device that implements the claimed method of restoring radar images of objects with a stationary center of rotation, figure 2 shows a diagram of the formation of the amplitude DOR of an object using a movable reference reflector, figure 3 shows a one-dimensional image of the object restored using a movable reference reflector S ₁ (φ), FIG 4 shows a one-dimensional image of the object restored by part DOR real difference ΔS (φ), Figure 5 shows a one-dimensional image of the object model, Sun tanovlenii in the range of observation angles width Δφ = 16 ° for the angle of sight φ ₀ = 15 °, Figure 6 illustrates a one-dimensional radar image reconstruction real object (KAMAZ) obtained ΔS processing in sector angles Δφ = ± 4 ° with an average angle of sight φ ₀ = 5 °. Figure 7 shows the reconstructed radio image of a real object together with a movable reference reflector 7, identified on the object LI 8, 9, 10, 11, the reconstructed radio image of a movable reference reflector 12, the object of observation - 13 and the movable-reference reflector 14.

The device comprises (Fig. 1) a measuring radar (transceiver) 1, a measuring path 2, a slewing ring (OPU) 3 with a platform 4, an object of measurement 5, a movable reference reflector 6, placed together with the object on the platform 4 of the OPU 3 measuring complexes. In the device that implements the proposed method, typical nodes and elements are used, made at the current level of technological development.

A device that implements the proposed method works as follows.

A preliminary event is carried out aimed at reducing the background level due to reflections from elements of the RIC. The emitted signals from the transmitter of the measuring radar 1 irradiate the object 5 and the movable reference reflector 6, which are installed on the platform 4 of the control panel 3. Using the receiving device of the measuring radar 1, the signals reflected from the object 5 and from the reflector 6 receive and register the joint DOR (S ₁ ( φ) and DOR S ₀ (φ) of the object, make up the difference DOR ΔS (φ) = S ₁ (φ) -S ₀ (φ) according to them and reconstruct the object's radar image by the Fourier transform.

The essence of the proposed method for reconstructing radar images of objects from their DOR obtained at the RIC with an incoherent transceiver system is as follows. For the real radiation field created by the measuring radar 1 and determined by the geometry of the RIC, the DOR of one investigated object 5 of the same object is measured together with the movable reference reflector 6. The difference of the measured DOR is made (9). Using the inverse Fourier transform formula, the function of the secondary sources V (ν) of the object and the square of its module are calculated, restoring the LI distribution on the perpendicular to the direction of sight or in the picture plane, and then by comparing the values obtained for a given viewing angle φ _{0, the} radar images with the characteristic design features of the object are identified the location of the detected LI directly on the surface of the object.

Thus, the claimed solution has new properties consisting in doubling the working area of the RIC, measuring the backscatter pattern of the observation object S ₀ (φ) in the real RIC field and the joint DOR of the object and placed in a certain way on the platform of the RIC perpendicular to the direction of sight "radar - center of rotation") of the movable reference reflector - S ₁ (φ), compiling the differential DOR ΔS (φ) = S ₁ (φ) -S ₀ (φ) and restoring on this basis the radar of the object that are not match properties of known solutions th and determine the achievement of a positive effect, which consists in ensuring the identification of LI of large-sized objects by the results of the reconstruction of radar data obtained by processing (handling) difference amplitude DOR, measured on the RIC with incoherent transceiver devices.

The proposed method aims to increase the maximum size of the working area of the RIC and the implementation of methods for the restoration of radar data on existing RIC. The latter is achieved by the fact that due to the use of differential DOR ΔS (φ), non-overlapping radar images are restored and LIs are identified on the surface of the objects of observation by their amplitude DOR, that is, without using the phase characteristics of the field scattered by the objects. The method for reconstructing radar images of complex shape objects is implemented by expanding well-known measurement procedures that do not require additional material costs and scientific research.

Claims (1)

A method for reconstructing radar images (RLI) of objects with a stationary center of rotation, based on recording the amplitude backscatter diagram (DOR) of the object together with a moving reference reflector S (φ), as a function of the current viewing angle φ over the interval of angles Δφ≪1 rad and the Fourier transform S (φ) and calculating the squared modulus of it for each fixed angle

characterized in that on the interval of observation angles Δφ register the object DOR without a reference reflector S ₀ (φ) and the object DOR together with a movable reference reflector S ₁ (φ), installed, like the object, on the platform of the rotary support device RIC at a distance from axis of rotation greater than half of the maximum linear size of the object in the direction perpendicular to the line of sight of the object, and make up the differential DOR ΔS (φ) = S ₁ (φ) -S ₀ (φ) and by calculating the Fourier transform ΔS (φ) and the squared modulus of this transformation, restore the radar image of the object.

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