RU2511216C1 - Method of generating image of surface in synthetic aperture radar station - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method involves merging radar images of K partial frames spread on the azimuth, obtained by emitting a coherent pulsed probing signal, irradiating partial areas of the surface with the radar antenna, analogue-to-digital conversion of the received signals, generating two-dimensional arrays of digitised received signals via distribution thereof on range channels and radiation periods and defined digital processing of the generated two-dimensional arrays. Irradiation of the partial areas of the surface with the radar antenna and summation of amplitudes of resolution elements of N radar images is carried out with a sliding method, wherein the value of the azimuthal sliding step of the beam pattern of the radar antenna is equal to or close to its azimuthal half-width, and summation of amplitudes of signals of N radar images, N=3, 4, is carried out element by element in arrays measuring M/2^N-2, where M is the number of generated azimuthal elements while sliding the arrays of the summed elements by the step M/2^N-2.

EFFECT: shorter time for generating a radar image.

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Description

The invention relates to radar technology, in particular to airborne radar stations of aircraft, using the method of synthesizing the antenna aperture, and can be used in civil and military aviation, radar photogrammetry.

A known method of forming a radar image (RLI) of a surface using a synthesized aperture (V.N. Antipov et al. Radar stations with digital synthesis of an aperture of an antenna. M: Sov. Radio. 1988), based on the combination of the RLIs in azimuth-separated K partial frames each of which is obtained by emitting a coherent pulsed sounding signal, irradiating the radar antenna with the corresponding partial portion of the surface being mapped, analog-to-digital conversion of the received reflected signal in, the formation of two-dimensional arrays of digitized signals through their distribution channels by range and emission periods and digitally processing the data contained in the arrays.

In this method, the radar image of partial frames is formed in the form of two-dimensional azimuth-range arrays of digital amplitudes of resolution elements displayed on the display in the form of gradations of pixel brightness of a two-dimensional video image. Irradiation of partial surface areas is carried out during azimuthal scanning of the antenna in the required field of view.

Closest to the proposed method for generating radar images in a radar with synthesizing the antenna aperture is the digital processing method described in (M.Skolnik, Radar Handbook, th.ed., McGrow-Hill, 2008, ch.5.4, fig.5.34).

This method consists of sequentially performing the following digital operations:

a) N-fold execution:

- correction of location in range and phase dependence on range,

- azimuthal presummation, range compression,

- recording the results of range compression in the buffer memory,

- azimuthal phase correction,

- the formation of azimuthal resolution elements through the fast Fourier transform (FFT),

- autofocus,

- amplitude detection and averaging;

b) overlapping separately obtained N radar images by summing the amplitudes of the azimuthal resolution elements in each range channel;

c) compression of the dynamic range of the amplitudes of the radar resolution elements obtained after summing the amplitudes of the azimuthal elements.

Overlay N video images is used to suppress the so-called "Speckle noise", which manifests itself on the formed radar surface in the form of a random change in the brightness of various pixels. In order to smooth out the mosaic radar image thus revealed, an N-fold radar surface survey is performed at different carrier frequencies, followed by summing the amplitudes of the image resolution elements. Moreover, in the prototype for building the partial radar image radar, the central part of the formed FFT of the array of azimuthal resolution elements is used. N exposures of the k-th, k = 1 ... K, partial surface area are performed with the direction of the bisector of the antenna radiation pattern in the center of this partial area.

The main disadvantage of the described method of video overlay is a significant increase in the time of formation of radar images. According to theoretical estimates and experimental results, for an acceptable suppression of speckle noise, the number N of superimposed radar frames should be at least 3-4. Accordingly, in the prototype the formation time of the radar image is increased by the same amount. It is known that the time of formation of the radar image of a partial surface area during the synthesis of aperture by airborne radar with a resolution of several meters is 2-4 seconds. With a three to four-fold overlap, the formation of a partial radar image frame can take about 15 seconds or more. For most applications, this duration of the formation of the radar image of the partial frame is unacceptable.

The technical result of the proposed method of forming an image of the surface in a radar station with the synthesis of the antenna aperture is to reduce the time of formation of the radar image of the surface, consisting of several partial frames.

The essence of the proposed method for surface imaging in a radar station with synthesizing the antenna aperture consists in combining radar images in azimuth of K partial frames obtained by emitting a coherent pulsed sounding signal, irradiating the radar antenna of partial surface areas, analog-to-digital conversion of the received signals, forming two-dimensional arrays digitized received signals by distributing them over range channels and period Am of radiation and digital processing of the formed two-dimensional arrays, consisting of: a) N-fold execution:

- correction of location in range and phase dependence on range,

- azimuthal presummation,

- range compression

- recording the results of range compression in the buffer memory,

- azimuthal phase correction,

- the formation of azimuthal resolution elements through the fast Fourier transform (FFT),

- autofocus,

- amplitude detection and averaging;

b) superimposing separately obtained N radar images by summing the amplitudes of the azimuthal resolution elements in each range channel; and c) compressing the dynamic range of the amplitudes of the resolution elements obtained after superimposing the radar data.

New in the proposed method is that the radar antenna irradiating K partial surface areas and summing the amplitudes of the resolution elements N of the radar detector is carried out in a sliding way, and the magnitude of the azimuthal slip step of the bottom beam is equal to or close to its azimuthal half-width, and the addition of the amplitudes of the radar signals is N radar, N = 3 , 4, is performed element by element in arrays of size M / 2 ^N-2 , where M is the number of azimuthal elements formed by the FFT, with the sliding of arrays of summed elements by the step M / 2 ^N-2 .

Figure 1 shows an example of the formation of a radar image according to the closest technical solution for overlaying 3 images of 3 partial frames.

Figure 2 shows an example of the formation of a radar image of the same viewing area according to the claimed method.

The formation of the radar image in the claimed method is as follows: the antenna starts scanning the viewing area, exposing the bisector of the bottom beam to the left azimuthal boundary of the designated viewing area. In each azimuthal position, the pulse repetition frequency of the probe signal is selected equal to 1.7-1.9 the width of the reflection spectrum along the central lobe of the bottom. The radar irradiates the plotted area with the required number of radio pulses and receives the reflected signals, converting them into digital form. The signal processing system generates azimuthal resolution elements in each range channel and stores the amplitudes of the right half of the generated azimuthal resolution elements in the buffer memory. Next, the DND is transferred in azimuth to the slip angle, which is about half the width of the DND, the formation of an array of azimuthal elements, and the central part of this array is entered into the buffer memory. After the next transfer of the DND to the same azimuthal slip angle, the left half of the array elements is entered into the buffer memory. Upon completion of the processing of 3 arrays of signals received at different positions of the antenna bottom, the radar image of the partial frame is formed by summing the amplitudes of the resolution elements stored in the buffer memory. The formation of radar images of subsequent partial frames is carried out in a similar way. From figure 2 it follows that according to the same scheme, it is possible to summarize 4 radar images received separately, taking into account the sum of разрешения arrays of resolution elements generated by the FFT procedure.

As follows from the description, the application of the proposed method in comparison with the prototype significantly reduces the required number of overlapping partial images N _PC . From the above example, it follows that this number is N _PC = 2K + 1 = 7, where K = 3 is the total number of partial frames in the final radar, while in the prototype N _PC = 3K = 9. Thus, in comparison with the prototype is achieved approximately one and a half reduction in the time of formation of the frame radar.

Claims (1)

A method of forming a surface image in a radar station with synthesizing the antenna aperture, based on the addition of radar images in azimuth of partial frames, each obtained by radiation of a coherent pulse sounding signal, by irradiating the radar antenna with partial sections of the field of view of the surface being mapped, by analog-to-digital conversion of the received reflected signals , the formation of two-dimensional arrays of digitized signals and digital processing contained in the masses Data will be obtained by N-fold correcting the location in range and the phase dependence of the range, azimuthal summation, range compression, recording the results of range compression in the buffer memory, azimuthal phase correction, the formation of azimuthal resolution elements by means of fast Fourier transform (FFT), autofocus , amplitude detection and averaging, then superimposing separately obtained N radar images by summing the amplitudes of the azimuthal resolution elements in each range channel and The dynamic range of the radar resolution element amplitudes obtained after summing the amplitudes of the azimuthal elements, characterized in that the radar antenna irradiates partial sections of the field of view of the mapping surface and the summing of the amplitudes of the azimuth resolution elements in each range channel is performed in a sliding manner, the magnitude of the azimuthal step of the antenna radiation pattern The radar is equal to or close to its azimuthal half-width, and the addition of the amplitudes of the N radar signals, N = 3.4, produces I elementwise arrays size M / 2 ^N-2, where M - the number of generated fast Fourier transform azimuthal elements slidably move on the arrays M / 2 ^N-2.

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