RU2468384C1 - Method of determining speed and direction of ground target using synthetic-aperture radar - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: under the condition of measuring radial speeds of moving targets using synthetic-aperture radar (SAR), and considering that the distance from the aircraft to the ground targets is, as a rule, considerably greater than the flight altitude of the aircraft, the viewing angles of the moving targets are additionally determined on the ground surface at time t₁ and t₂, which correspond to the centres of the first and second aperture synthesis intervals. The full speed and direction of the moving ground target are determined from the corresponding formulae.

EFFECT: determining full speed and direction of a ground target using synthetic-aperture radar mounted on an aircraft in order to provide efficient guidance of other moving objects to a detected moving target.

Description

The invention relates to the field of radar and can be used in airborne SAR for the selection of moving ground targets (SDNTS).

Modern SAR make it possible to obtain a radar image of the earth's surface and objects (targets) located on it with high resolution in azimuth and range, which is close in quality to photographs, at any time of the year or day, regardless of the level of illumination, meteorological conditions, and at long ranges in real time, as well as select moving targets (SDC) against the background of reflections from the earth's surface and measure their radial velocities [see, for example, Sazonov N.A., Scherbinin V.N. Multifrequency method for moving targets selection in SAR. - Radio engineering, 1995, No. 11, p.6-8].

A known method for determining moving ground targets using SAR [RF Patent No. 2084920 from 07.20.97 / Sazonov N.A., Scherbinin V.N.], which consists in the formation of three synthesized apertures at different carrier frequencies of the probe pulses, each of which form its synthesis interval. The value of the synthesis interval is calculated on the basis of a constant resolution in azimuth. The repetition period of the probe pulses is determined based on the condition of a constant number of samples at the synthesis intervals. The centers of these synthesis intervals are aligned in space, while in the channel with a higher carrier frequency of the probe pulses, apertures are formed with a delay depending on the size of the apertures and the speed of the aircraft. Range resolution in each channel is kept constant. Difference signals are generated without a preliminary phase shift of the received signals through the corresponding channels. The radial speed of a moving target is determined.

The disadvantage of this method is that only the radial component of the speed of the ground moving target is measured.

The technical result of the invention is the determination of the full speed and direction of movement of a ground target using an SAR installed on an aircraft to ensure effective guidance of other moving objects to the detected DC.

The specified technical result is achieved by the fact that in the known method for determining the speed and direction of movement of a ground target using radar with synthesizing the antenna aperture, which consists in the formation of three synthesized apertures at different carrier frequencies of the radiation of the probe pulses, each of which is formed with its own synthesis interval, receiving reflected signals separately for three channels, their subsequent processing, in the formation of differential signals without preliminary phase shift of the received signals the corresponding channels and determining the radial velocity of the moving target, additionally determine the viewing angles of the moving target on the earth’s surface θ ₁ and θ ₂ at time t ₁ and t ₂ corresponding to the centers of the first and second intervals of the synthesis of the antenna aperture, and the full speed V _p and the direction of movement ground targets θ _{p are} determined respectively by the formulas

,

,

,

,

where V _R1 and V _R2 are the vectors of radial velocities at time t ₁ and t ₂ corresponding to the centers of the first and second synthesis aperture synthesis intervals of the antenna aperture; θ ₁ and θ ₂ are the angles of observation of a moving target on the earth's surface.

The essence of the method is illustrated by a figure, which shows the geometry of the problem of determining the full speed and direction of movement of a ground target on a plane. In this figure, the following notation: V _LA - aircraft speed vector; θ _p - the angle between the direction of the vector of the full velocity vector DC V _P and the negative direction of the X axis parallel to the vector V _LA (determines the direction of movement of the ground target); θ ₁ and θ ₂ are the viewing angles of the DC on the earth's surface; α ₁ and α ₂ are the angles between the directions of the vectors of full speed and radial velocities V _R1 and V _R2 at time t ₁ and t ₂ corresponding to the centers of the first and second intervals of the synthesis of the antenna aperture.

As seen from the figure

V _R1 = V _P cosα ₁ , V _R2 = V _P cosα ₂ .

Hence,

,

,

Substituting (2) in (1), we obtain an expression for determining the direction of motion of a ground target

Transforming (3) using the formulas for the sum and difference of arccosines [Reference on elementary mathematics / M.Ya. Vygodsky. - M: ACT: Astrel, 2006. p. 433], we obtain an expression that determines the magnitude of the total speed

The angles θ ₁ and θ ₂ in (3) and (4) can be determined in the SAR by the position of the axis of the antenna pattern and the offset of the DC relative to its true position, which is due to the Doppler effect [see, for example, Sazonov NA., Scherbinin V. N., Yarushkin M.M. Selection and determination of the azimuth of moving ground targets. - Radio engineering, 2000, No. 6, pp. 30-33].

The obtained relations (4) and (3) determine the magnitude of the full speed and direction of movement of the ground target in the case of a significant excess of the range to the aircraft center of the aircraft flight altitude.

Using the proposed method for determining the speed and direction of movement of a ground target using radar with synthesizing the aperture of the antenna allows you to accurately determine the full speed and direction of movement of ground targets using a three-frequency SAR to further ensure effective targeting using a SAR to the detected ground DC.

Claims (1)

A method for determining the speed and direction of movement of a ground target using radar with the synthesis of the antenna aperture, which consists in the formation of three synthesized apertures at different carrier frequencies of the radiation of the probe pulses, each of which is formed with its own synthesis interval, receiving the reflected signals separately through three channels, their subsequent processing , in the formation of differential signals without preliminary phase shift of the received signals through the corresponding channels and determining the radial velocity of the driving target, characterized in that it further determines the viewing angles of a moving target on the earth’s surface θ ₁ and θ ₂ at time t ₁ and t ₂ corresponding to the centers of the first and second synthesis aperture synthesis intervals, and the total speed V _P and the direction of movement of the ground target θ _{p are} determined respectively by the formulas

where V _R1 and V _R2 are the vectors of radial velocities at time t ₁ and t ₂ corresponding to the centers of the first and second synthesis aperture synthesis intervals of the antenna aperture; θ ₁ and θ ₂ are the angles of observation of a moving target on the earth's surface.

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