RU2211461C2 - Technique of synthesis of radar image and facility for its embodiment - Google Patents

Abstract

FIELD: radiolocation, radar means to scan ground surface, cartography, geodesy, radar photogrammetry, civil aviation, coastal navigation, river navigation. SUBSTANCE: technical result of technique lies in provision for independence of process of synthesis of radar image from trajectory and parameters of movement, phase of input signal, range and parameters of antenna system, in provision for same resolution in all directions on synthesized radar image of sounded region equal to radial resolution of sounding signal independent of azimuthal width of beam of antenna directional pattern. Essence of proposed technique consists in complexion of computation environment invariant to trajectory and parameters of movement and ensuring noncoherent synthesis of radar image of sounded region. Received radar signal is detected by amplitude, spectrum is computed by radial channels, spectral components are weighed and converted to spectrum, raster is formed and elements of raster are accumulated. EFFECT: provision for independence of process of synthesis of radar image from trajectory and parameters of movement. 2 cl, 4 dwg

Description

 The invention relates to the field of radar, in particular to radar means for surveying the earth's surface, and can be used in cartography, geodesy, radar photogrammetry, in civil aviation, in coastal navigation and river navigation, in map-matching navigation.

 A known method of radar survey of the earth's surface and a device for its implementation, implemented in [1]. This method is based on the use of radial resolution, determined by the spectral width of the probe signal, and tangential resolution, determined by the azimuthal beam width of the radiation pattern of the scanning antenna system.

 A device for implementing this method is implemented in the weather storm radar "Thunderstorm-M" ([1], p. 188, Fig. 9.2). It consists of a scanning antenna system narrowly oriented in the azimuthal plane, a transmitting and receiving unit, and an indicator unit.

 The disadvantage of this method and device is the low resolution, the linear angular resolution depending on the range and horizontal aperture of the antenna system, as well as the lack of joint processing of the sensing results in order to increase the resolution on the generated radar image of the probed area.

, 2) входной комплексный сигнал

, отраженный с дальности t при n-ом зондировании умножают на сформированную комплексную опорную функцию, 3) для каждой дальности f по всем зондированиям n над произведениями осуществляют быстрое преобразование Фурье (БПФ), 4) полученные компоненты спектра детектируют по амплитуде и результат выдают на выход:

где J(q, t) - выходной сигнал,
q - тангенциальная координата синтезируемой точки растра (спектральный компонент БПФ или азимут),
t - радиальная координата синтезируемой точки растра или дальность,
n -порядковый номер зондирования,
M - количество зондирований, по которым осуществляется синтез,

- входной комплексный сигнал,

- комплексная опорная функция,
s(t), s'(t), s"(t) - траектория движения и ее временные производные,
|•| - модуль от выражения, обозначенного точкой.Closest to the claimed technical solution for the synthesis of the radar image of the probed region, adopted as a prototype, are the method and device for the synthesis of artificial aperture (aperture) of the antenna, implemented in [2]. This method is based on coherent accumulation during sequential sounding of signals reflected from a fixed range, received during movement in a direction that does not coincide with the direction of sounding. To ensure coherence, the method requires calculation and compensation of the phase incursion of the carrier frequency due to this movement, and consists in the fact that 1) a complex reference function is formed for each range t

, 2) input complex signal

reflected from a range t during the n-th sounding is multiplied by the formed complex reference function, 3) for each range f over all soundings n over the products, a fast Fourier transform (FFT) is performed, 4) the obtained spectrum components are detected by amplitude and the result is output :

where J (q, t) is the output signal,
q is the tangential coordinate of the synthesized raster point (spectral component of the FFT or azimuth),
t is the radial coordinate of the synthesized raster point or range,
n is the ordinal number of sounding,
M is the number of soundings by which the synthesis is carried out,

- input complex signal

- complex support function,
s (t), s' (t), s "(t) - the trajectory of motion and its temporal derivatives,
| • | - the module of the expression indicated by a dot.

 A device for implementing this method is presented in figure 1 in the form of a fragment highlighted by a dashed rectangle. It consists of a support function former 1, a complex multiplier 2, a fast Fourier transform (FFT) block 3, an amplitude detector 4.

 These blocks are connected as follows: the first input of the complex multiplier 2 is the input of the device, its second input is connected to the output of the driver of the support function 1, the output of the complex multiplier 2 is connected to the input of the FFT 3, and the output of the FFT 3 is connected to the input of the amplitude detector 4, the output which is the output of the device.

 The disadvantage of these methods and devices is the narrow scope, due to the mandatory mismatch of the direction of sounding with the direction of motion, the need for movement during sounding during the synthesis, the mandatory requirement of high-precision calculation of the reference function, the need to implement motion compensation by taking into account the increment of the carrier frequency phase with an error of less than one eighth the wavelength of the probe signal (Rayleigh test), the mandatory complexity of the reference function and the input signal ala, addiction support function of the trajectory and dynamic motion parameters. The disadvantage of the indicated method and device is also the dependence of the synthesized angular (transverse to the sounding direction) resolution on the radial range, on the azimuthal beam width of the antenna system, as well as the presence of glare masking the synthesized image, and their filtering requirement.

 The aim of the present invention is to expand the scope by providing the possibility of synthesis when probing both in a stationary state and in motion, eliminating the need for high-precision phase compensation of motion during synthesis, replacing the coherent processing of the complex input signal taking into account the phase of the carrier frequency by incoherent processing of the material signal, eliminating the dependence of the support function on time, trajectory and motion parameters, simplification of the support function to real constants, providing the possibility of storing a pre-calculated sample of the real support function in a digital read-only memory (ROM) and suitable for all really possible cases. In addition, the goal is to ensure the independence of the possibility of synthesis from the angle between the direction of sounding and the direction of motion, to eliminate the dependence on the range of the angular (transverse) resolution on the synthesized radar image of the probed region, to realize in two orthogonal directions on the radar synthesized image of the probed region the same resolution equal to radial resolution of the probe signal, ensuring synthesis independence the resolved resolution from the azimuthal beam width of the antenna pattern and the elimination of glare in the synthesized image.

 This goal is achieved by the fact that in the method the region is probed in a direction that does not coincide with the direction of movement, a highly accurate complex reference function is formed, which depends on the time (range), trajectory and dynamic parameters of the movement, reflected complex input signals of the same radial (range) channels of all probing the parcels are multiplied by the complex support function calculated during the motion, the results are processed together with the use of the discrete finite Fourier transform, then the amplitude is detected and the result is output, according to the invention, the reflected reflected signal, regardless of the direction of sounding and the direction of motion, is detected by the amplitude, then for each sounding package, the spectrum is calculated by all discrete radial channels with a discrete compact Fourier transform, the calculated complex spectral components are multiplied by an invariant in all situations, a real support function independent of time, trajectory, and dynamic parameters of motion is inverted maintaining the inverse discrete finite Fourier transform, the result is detected by amplitude and the resulting output sequence of radial channel signals is transformed into a two-dimensional matrix signal. Then each element of the matrix signal is accumulated by summing the same elements of the matrix signals of all soundings.

где M - число зондирований,
q= q(x, y) - закон подстановки индекса при формировании растровой функции,

- дискретное финитное преобразование Фурье функции дискретного аргумента p, обозначенной (•), λ - номер спектрального дискретного компонента, N - число регистрируемых радиальных каналов,
F $\genfrac{}{}{0ex}{}{\text{-1}}{\text{qλ}}$ {•} - обратное дискретное финитное преобразование Фурье по дискретному спектральному аргументу λ,
H(λ) - вещественная опорная функция.In pulsed radar using time sampling of the input signal, the synthesis equation can be represented in discrete form:

where M is the number of soundings,
q = q (x, y) is the law of index substitution during the formation of the raster function,

is the discrete finite Fourier transform of the function of the discrete argument p denoted by (•), λ is the number of the spectral discrete component, N is the number of recorded radial channels,
F $\genfrac{}{}{0ex}{}{\text{-1}}{\text{qλ}}$ {•} is the inverse discrete compactly supported Fourier transform with respect to the discrete spectral argument λ,
H (λ) is a real support function.

 New in the proposed method in comparison with the prototype is the amplitude detection of the input signal, which opens an incoherent synthesis path using spectral processing of the radial channels of one probe, multiplying the spectral components by a real reference function, previously calculated and independent of the parameters of motion, spectrum inversion, amplitude detection, of forming a partial radar image of the probed region in the form of a matrix signal by substituting q = q (x, y), comparing each radial channel with line number q in the coordinates of the raster (x, y), and, finally, the accumulation of elements of the matrix signal by sounding premises and the output of the accumulation results to the output. All processing of the received signal both through the radial channels and through the probe bursts is incoherent, the reference function does not depend on the synthesis conditions, and the raster resolution elements have a radial resolution in all directions.

 This goal is also achieved by the fact that in the device for the synthesis of the radar image of the probed region (in the dashed rectangle of Fig. 1), containing the driver of the support function 1, the complex multiplier 2, the fast Fourier transform (FFT) 3 and the amplitude detector 4, the first input of the complex the multiplier 2 is the input of the device, its second input is connected to the output of the former of the support function 1, the output of the complex multiplier 2 is connected to the input of the FFT 3, and the output of the FFT 3 is connected to the input of the amplitude d 4, the output of which is the output of the device, according to the invention, the driver of the reference function 1 is made in the form of a ROM, an amplitude detector 5, an FFT unit 6, a raster driver 7 and a drive 8 are additionally introduced, the input of the amplitude detector 5 being the input of the device, the output of the amplitude detector 5 connected to the input of the FFT 6, its output is connected to the first input of the complex multiplier 2, the output of the amplitude detector 4 is connected to the input of the raster forming unit 7, the output of the raster former is connected to the input of the drive 8 whose output is the output of the device.

 New in the proposed device compared to the prototype is the inclusion at the first input of the complex multiplier 2 of an additional amplitude detector 5, the input of which is the input of the device, and the FFT block 6 connected in series with it, the execution of the driver of the support function 1 in the form of a ROM and the inclusion after the amplitude detector 4 serially connected shaper raster 7 and drive 8, the output of which is the output of the device (figure 1).

 The essence of the proposed method consists in the fact that in the known method for synthesizing the radar image of the probed region, an artificial aperture of the antenna is synthesized, co-processing the coherent same-name radial channels of different sounding packages taking into account the trajectory and parameters of movement, and this narrows the beam in the plane of motion, increasing the angular resolution.

 However, in the synthesized beam, the linear angular resolution depends on the range and glare appears on the radar image, which leads to masking and distortion of the radar image relative to the real one. In addition, coherent accumulation requires highly accurate real-time calculation of the complex reference function for each radial channel in each sounding.

 In the present application, direct synthesis of the resolution elements of the entire raster is carried out, processing radially channel signals belonging to one sounding incoherently together, and then averaging the results over all soundings.

 The essence of the proposed device is to integrate a computing environment that is invariant to the trajectory and motion parameters, providing incoherent synthesis of the radar image of the probed area.

 The proposed method for synthesizing a radar image includes the following sequence of operations: a) the input signal is detected by amplitude, b) the spectrum of the detected input signal is calculated, c) the components of the calculated spectrum are multiplied by the universal real reference function, d) the spectrum corrected by multiplication is converted into radial channels, e) detect radial channels in amplitude, e) convert the detection results into a two-dimensional matrix signal (raster), g) accumulate elements of the matrix signal of probing parcels and outputs the accumulation results.

 The radar image synthesis device operates as follows: the input complex signal in the form of a time sequence of radial (range) channels is detected by amplitude in block 5, the material signal obtained at the output of block 5 is transformed in the FFT block 6 into a spectrum along radial channels, the spectral components are multiplied in the block 2 to the universal real support function stored in the ROM unit 1, the sequence of multiplication-corrected spectral components is turned into radial channels in in block 3 of the inverse finite discrete Fourier transform, the signal inverted in block 3 is detected by the amplitude in block 4, the detection result is converted in block 7 into a two-dimensional matrix signal (raster), the raster signal is accumulated by the probe bursts in block 8, and the accumulated results are fed to the output of the device .

 Figure 1 shows the structural diagram of the claimed device for the synthesis of radar images, on which the device selected as a prototype is highlighted by a dashed rectangle.

 The essence of the invention was verified by mathematical modeling of the device and method on a NEC VERSA M / 75 PC, executed on processor 486. The input signal model was a sequence of radial (range) channels, each of which was obtained by summing the pixels in the selected target designation of the circular region in the digitized aerial photograph. Thus, the linear angular resolution of the signal sensor was assumed to be equal to the diameter of the region. Figure 2 shows the printout of the monitor screen, which presents a test aerial view of the area. In the synthesis, the radar signal was reconstructed from this photograph. The number of radial channels involved in the synthesis was 201, the number of soundings was 128. The sensing angles during the sounding were equidistant in the range from 0 to π. The verification result is shown in Fig. 3. One signal sample (out of 128 involved in the synthesis of the radar image) is shown in Fig. 4, where the smoother dashed curve represents the radial channels of the simulated input radar signal, and the rugged one is the result of processing before the formation of the raster.

When implementing the proposed method and device for synthesizing a radar image, a Baguette-25 digital signal processing unit [3] is installed in a multi-machine configuration, consisting of programmable signal processors (PPPs) (up to 19 pieces) and a control computing device (UVU), united by a common VME interchange backbone (Virtual Machine Environment). The faculty consists of a BT55-201A signal processing module with a capacity of at least 50 Mflops or 5 million butterflies, a BT55-401A data buffering module that provides reception, buffering and switching of internal (8 bits) and external (32 bits) information flows and a processor module BT55-202A data, designed to control the process of the teaching staff as a whole. The functional composition of the configuration is as follows:
block 1 - BT63-201 module (LSI Flash-memory, 48 MB, VME system bus),
block 2 - PPP (50 Mflops),
block 3 - faculty (5 million butterflies),
block 4 - PPP (50 Mflops),
block 5 - PPS (5 million butterflies),
block 6 - PPP (50 MFlops),
block 7 - PPP (50 MFlops),
block 8 - PPP (50 Mflops).

 For the joint functioning of the modules as part of a radar image synthesis device, the device is integrated with a UVU.

 The technical result of using the proposed method and device in comparison with the prototype is that the dependence of the possibility of synthesizing a radar image on the angle between the direction of sounding and the direction of movement is eliminated, the requirement of mandatory motion during synthesis is eliminated, the dependence of resolution on the synthesized radar image of the area is eliminated from the coordinates synthesized raster, equality of longitudinal and transverse with of the integrated resolutions of the radial resolution of the radar probe signal, the hardware implementation is simplified due to incoherent signal processing, the materiality of the support function and its independence from the trajectory and motion parameters, which can be used in cartography, geodesy, radar photogrammetry, in civil aviation, in coastal navigation and in river navigation, in map matching navigation.

Literature
1. Aircraft radar systems, edited by KTN P.S. Davydova, Moscow: Transport, 1988.

 2. V.N. Antipov, V.T. Goryainov et al. (9 co-authors), Radar stations with digital synthesis of the antenna aperture, M .: Radio and communication, 1988.

 3. "BAGET" family of computers for special applications, product catalog of the Corund-M design bureau, third edition, tel .: 277 27 10, fax: (095) 274 00 77, Moscow, 2000

Claims (2)

 1. A method for synthesizing a radar image, which consists in receiving an input complex signal (n, t) from a range t in sounding n, characterized in that the input complex signal (n, t) is detected by amplitude, then processed by a discrete Fourier transform range t, the spectral complex components are multiplied by a real reference function independent of time, trajectory and dynamic parameters of motion, the result is subjected to the inverse discrete Fourier transform, detected by amplitude, They are plotted into a two-dimensional matrix signal, each element of the matrix signal is accumulated by soundings n, and the resulting matrix signal is output.  2. A radar image synthesis device comprising a reference function generator 1, a complex multiplier 2, a fast Fourier transform unit (FFT) 3, an amplitude detector 4, and the output of the reference function generator 1 is connected to the second input of the complex multiplier 2, the output of which is connected to series-connected FFT blocks 3 and amplitude detector 4, characterized in that the driver of the support function 1 is made in the form of read-only memory (ROM), an amplitude detector 5 and FFT unit 6, connected in series with the first input of the complex multiplier 2, and the input of the amplitude detector 5 being the input of the device, are additionally introduced and connected in series with the output of the amplitude detector 4, a two-dimensional matrix signal generator 7 and a drive 8, the output of which is the output of the device.

Images