JP2648809B2 - Radar image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverse synthetic aperture processing (I).
The present invention relates to a radar image processing apparatus for estimating a rotational motion of a target from radar image information in order to perform target identification using a radar image created from a radar echo in SAR.

[0002]

2. Description of the Related Art In ISAR, when target identification is performed using a radar image created from a radar echo,
First, the scale estimation of the target is important. For this scale estimation, it is necessary to estimate the rotational motion of the target.

Conventionally, as a method of estimating the rotational motion of a target from a radar image, a method of estimating a change in the radar image due to rotation by comparing two radar images having a time difference, or a method of estimating tracking information of a target. A method of estimating a target rotational angular velocity by reconstructing the trajectory has been adopted.

[0004] However, the former requires at least two radar images to be created, so that not only takes a lot of processing time, but also because the temporal change of the radar image includes components other than the rotational motion, the accuracy of the radar image is high. It was also a problem. In the latter case, it is necessary to process the tracking information accurately over a long period of time, and there is a serious problem in terms of accuracy.

[0005]

As described above, the conventional radar image processing apparatus not only requires a long processing time but also has many problems in terms of accuracy. The present invention has been made to solve the above problems, and has as its object to provide a radar image processing apparatus capable of estimating a target rotational motion in a short time and with high accuracy by a simple method. .

[0006]

In order to achieve the above object, a radar image processing apparatus according to the present invention is provided with a radar image creation apparatus for creating a target radar image by inputting a target signal obtained by a radar receiver. A graphic element extracting device for extracting an arbitrary graphic element from a radar image created by the device, a relative relationship detecting device for estimating a relative relationship of the graphic element in the radar image, A rotational motion estimating device for estimating the rotational motion of the target from the relative relationship.

[0007]

In the radar image processing apparatus having the above configuration,
A simple method of creating only one radar image, reconstructing the target shape model based on the graphic elements, and estimating the distortion amount and rotation angular velocity parameters of the target shape model from the relative relationship of each graphic element. The target rotational angular velocity is estimated with time and high accuracy.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows the configuration of a radar image processing apparatus according to the present invention. A radar image creation apparatus 11 receives a target signal obtained by a radar receiver (not shown) and displays the target radar on a frequency versus range screen. Create an image. This radar image information is sent to the graphic element extraction device 12.

The graphic element extracting device 12 extracts basic graphic elements such as line segments, points, and planes from the radar image as graphic elements. The graphic elements to be extracted may be specified by the operator. The extracted graphic element information is sent to the relative relationship detection device 13.

The relative relation detecting device 13 estimates the relative relation of each graphic element from the radar image information and the graphic element information, for example, the angle formed by a line segment, and the relative position of another point with respect to an arbitrary point. , Surface area ratio and the like are detected. The detected relative relationship information is sent to the rotational motion estimating device 14.

The rotational motion estimating device 14 estimates a rotational motion of a target from relative information of graphic elements. The selection of the graphic element used for the estimation and the relative relationship information may be based on the designation of the operator. Alternatively, a database may be created in advance by obtaining graphic elements and relative relationships (three-dimensional information) for each target, and the rotational motion may be estimated by comparing input information with information stored in the database.

The specific processing operation of the radar image processing apparatus having the above configuration will be described below. First, the case where the ISAR process is performed on the target (aircraft) T shown in FIG. 2 will be considered. Here, for ease of understanding,
Considering only the shape on the two-dimensional plane of the X-Y axis, the rotation axis is perpendicular to the paper surface and the clockwise direction is positive, the nose end of the target T is A, and the main wing ends are B and C, respectively.

The radar image obtained when the target T is observed by the radar RD and the ISAR process is performed by the radar image creating device 11 is conceptually shown in FIG. That is, what is obtained as a radar image is a figure in a radar image space expressed by distance versus Doppler frequency, as shown in FIG.

In FIG. 3, the distance axis coincides with the Y axis in FIG. 2, and the Doppler frequency axis is obtained by converting the X axis direction in FIG. 2 onto the frequency axis. As is clear from this figure, in the radar image as it is, each part of the target T (for example, A, B,
Since the positional relationship C) cannot be specified, target identification is difficult.

In order to specify the positional relationship of each part of the target T from a radar image, this Doppler frequency axis must first be converted into a distance unit. This is made possible by estimating the rotational angular velocity component of the target T.

As a method of estimating the rotational angular velocity component, there is a method of considering a radar image as a moving image and observing a change in a plurality of time-sequential radar images due to a target rotational motion. However, this method is greatly affected by changes with time of the radar image, and thus it is difficult to perform highly accurate estimation.

For this reason, the processing method according to the present invention focuses on the characteristics of a radar image as a still image rather than the characteristics of a moving image, and estimates the rotational motion of a target by converting a real space axis into a frequency axis. Is estimated to be equivalent to estimating the target rotation angular velocity component only from a single radar image.

Here, in order to check the mapping from the real space to the radar image space, consider the point A shown in FIG. In FIG. 2, r represents the distance from the origin O to the point A on the XY coordinate plane, R ¹ represents the distance from the radar RD to the origin O, and R ⁰ represents the distance from the radar RD to the point A. .

In the ISAR process, the Doppler shift caused by the velocity component of each target in the direction of the radar's line of sight is calculated by:
It is developed on the frequency axis of the radar image space for each range cell. The line-of-sight velocity component V _{RLS at the} point A is expressed by the following equation. Here, ω is a parameter representing the motion of the target T.

[0020]

(Equation 1) On the other hand, if the target T exists far enough compared to its size,

[0021]

(Equation 2) Holds, Equation (1) is transformed as follows.

[0022]

(Equation 3) Here,

[0023]

(Equation 4) A unit vector is introduced. That is, the above α is the rotational angular velocity component of the target T estimated from the radar image. At this time, the Doppler shift component δf at the point A is expressed as follows. Here, λ is the transmission frequency of the radar RD.

[0024]

(Equation 5)

The Doppler shift component δf becomes a Doppler frequency axis component in the radar image space. Therefore, the mapping between the real space and the radar image space is defined as follows.

[0026]

(Equation 6)

Next, the target shape is decomposed into graphic elements such as points, line segments, and planes by the graphic element extracting device 12, and the relative relationship is obtained by the relative relationship detecting device 13. Here, the relative relationship does not depend on the detailed structure of the target.
Items such as the existence of a line of symmetry and the existence of a plane of symmetry are factors of occurrence. As a specific relative relationship, for example, 3
Positional relationship between two or more points, distance ratio, angular ratio, positional relationship between three or more line segments, angular ratio, positional relationship between two or more surfaces,
The area ratio can be considered.

For the above-mentioned relative relationship, the following requirements are required for a general aircraft from the symmetry of the body.
FIG. 4 shows an example. First, since the engines are located symmetrically with respect to the fuselage, (a) the distances from the nose to the corresponding engines on both sides are equal, (b) the distances from the nose to the corresponding engines on both sides are equal, (c) the distance from a point on the fuselage to the corresponding engine on each side (eg, r ₁ , r
₂ ) are equal.

Second, since the main wing and the tail wing are located symmetrically with respect to the fuselage, (a) the distances between the wing tip and the tail wing on both sides from the nose are equal, and (b) both wing tips from the nose. (C) The distance from a point on the fuselage to the corresponding engine on each side is equal.

Third, since the main wing and the tail wing are spread at the same angle on both sides with respect to the fuselage (eg, θ ₁ , θ ₂ ), the angle (eg, φ ₁ ) between the main wing and the tail wing on both sides depends on the fuselage.
Divided equally.

Fourth, since the main wing and the tail wing are symmetrical with respect to the fuselage, the areas of the main wing and the tail wing (for example, S ₁ and S ₂ ) are the same on both sides of the fuselage. Hereinafter, as an example of the relative relationship, a positional relationship between three points coming from the existence of a symmetry line will be described.

As three points, in the real space shown in FIG. 5 (a), consider a point A on the symmetry line and points B and C at positions symmetrical with respect to the symmetry line. At this time, the points B and C are located on the circumference around the point A. When these three points are mapped in the radar image space with the coefficient β, the result is as shown in FIG.

That is, the two points B and C which were on the circumference in the real space are on the circumference of an ellipse obtained by deforming the circle in the X-axis direction. Conversely, if it is assumed that points A ', B', and C 'on the radar image are on the circumference of the ellipse, the position of the points B' and C 'on the circumference of the ellipse in FIG. Can be obtained. Therefore, by using the coefficient β, it is possible to easily reconstruct the graphic in the real space in FIG.

In the actual target, the points B and B shown in FIG.
Using the fact that the two points C are on the circumference around the point A and extracting the corresponding points A ', B', and C 'in FIG. Device 13
By applying the above algorithm to the positional relationship, it is possible to easily estimate the coefficient β that determines the mapping. Thus, the rotational motion estimating device 14 can reconstruct the target shape in the real space from the radar image using the mapping F- ¹ , thereby estimating the rotational angular velocity due to the rotational motion of the target.

As described above, according to the processing method of the above apparatus, when a corresponding point in the real space is considered on a single radar image shown in FIG. 3, for example, the point B 'intersects a certain straight line with the point C'. The β in the equations (4) and (5) can be estimated from only the information that the point is located at the symmetric position and the point A ′ is on the line of symmetry, and the rotational angular velocity component α can be estimated.

Therefore, the radar image processing apparatus having the above configuration reconstructs the target shape model based on the graphic element by using only one radar image, and calculates the distortion amount and the rotational angular velocity of the target shape model based on the relative relationship between the graphic elements. With a simple method of estimating the parameters, the target rotational angular velocity can be estimated in a short time and with high accuracy.

In this case, it does not depend on other information (distance, angle) between points. This property is the same for relative relationships other than the above, and does not depend on information other than the information of interest. By the way, when target identification is performed from a radar image, a certain degree of "quality" of the radar image is required. For example, whether target identification is possible when only the engine is observed.

The processing method according to the present invention is based on the premise that the symmetry of the target in the real space can be basically observed from the radar image in the target scale estimation. Therefore, there is a possibility that the method is limited only to the case where scale estimation is performed based on a still image.

However, if the scale estimation is considered as a pre-process of target identification, the definition of “quality” is given as “the symmetry of the target can be observed on the radar image”. Become. Paradoxically,
This method is an effective method when the "quality" of the radar image is satisfied.

The greatest advantage of this method is that it is possible to estimate the conversion format (the relationship between the radar image space and the real space) from the relative relationship between the graphic elements in the target shape in the real space.

[0041] That is, the relative relationship between the graphical elements are not basically depend on the target microstructure, the machine-independent, because a processing for a radar image as a still image, changes in the radar image over time There is an advantage that it is not necessary to take into account the fact that the amount of calculation required for estimating the mapping between the real space and the radar image space is small, and high-speed processing is possible.

Analyzing a radar image is suitable for ISAR processing for estimating a target shape because of its characteristic of being independent of the model. This is because when estimating the target shape using the radar image, known information that the target target is a ship or an aircraft is given in advance.

Further, if the above-mentioned processing method is extended, a plurality of transformation coefficients β of the formula (5) are estimated from a plurality of relative relationships between the respective graphic elements so as to include a model-dependent component. Can also be evaluated.

For example, by introducing a target model, making each part on the radar image correspond to each part of the model, and evaluating a plurality of estimated values of the transform coefficient β based on a plurality of relative relationships,
It is possible to determine the effectiveness of the target model using an index such as a variance of the estimated value.

The present invention is not limited to the above embodiment, and the target is not limited to the aircraft, but may be similarly applied to the motion of a ship according to the distance ratio from the bow to the bridge and the bridge to the stern. It is possible. It goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0046]

As described above, according to the present invention, it is possible to provide a radar image processing apparatus capable of estimating a target rotational angular velocity in a short time and with high accuracy by a simple method.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a radar image processing apparatus according to the present invention.

FIG. 2 is a diagram showing a target shape in a real space according to the embodiment in a two-dimensional coordinate system.

FIG. 3 is a view showing a radar image created for the target shown in FIG. 2 by the radar image creating apparatus of the embodiment.

FIG. 4 is an exemplary view showing an example of a graphic element extracted by the graphic element extraction device of the embodiment and a relative relationship detected by the relative relationship detection device 13;

FIG. 5 is a diagram showing a relative relationship between a graphic element in a real space and a graphic element in a radar image space in the embodiment.

[Explanation of symbols]

11: radar image creating device, 12: graphic element extracting device, 13: relative relationship detecting device, 14: rotational motion estimating device.

Continuation of the front page (72) Inventor Shoji Akai 1 Kosuka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Pref. 4-5157 (JP, B2)

Claims (7)

(57) [Claims] 1. A radar image generating apparatus for generating a target radar image by inputting a target signal obtained by a radar receiver, and a graphic element extracting apparatus for extracting an arbitrary graphic element from the radar image generated by the apparatus. Radar image processing, comprising: a relative relationship detection device for estimating a relative relationship between graphic elements in the radar image; and a rotational motion estimating device for estimating a target rotational motion from the relative relationship between graphic elements obtained by the device. apparatus. 2. The radar image processing apparatus according to claim 1, wherein said graphic element extracting device extracts and uses basic graphics such as points, line segments, and planes as graphic elements from the radar image. 3. The relative relationship detecting device determines a ratio of a distance between two or more graphic elements on the radar image, and the rotational motion estimating device determines a ratio of the distance calculated by the relative relationship detecting device. 2. The radar image processing apparatus according to claim 1, wherein the rotational motion is estimated by comparing a ratio of a corresponding distance of the target shape model obtained in advance. 4. The relative relationship detecting device calculates an angle ratio between two or more graphic elements on the radar image, and the rotational motion estimating device calculates an angular ratio between the angle ratio calculated by the relative relationship detecting device and the rotational motion estimating device. 2. The radar image processing apparatus according to claim 1, wherein the rotational motion is estimated by comparing a ratio of a corresponding angle of the target shape model obtained in advance. 5. The relative relationship detecting device calculates an area ratio between two or more graphic elements on the radar image, and the rotational motion estimating device calculates an area ratio calculated by the relative relationship detecting device. 2. The radar image processing apparatus according to claim 1, wherein the rotational motion is estimated by comparing a corresponding area ratio of the target shape model obtained in advance. 6. The radar image processing apparatus according to claim 3, wherein said rotational motion estimating device utilizes a symmetry of a target shape as said target shape model. apparatus. 7. The radar image processing device according to claim 3, wherein said rotational motion estimating device uses a relative relationship of a target structure as said target shape model.