JP3290845B2 - 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 a radar image processing apparatus for creating a radar image reflecting a target shape from a radar echo from a radar target.

[0002]

2. Description of the Related Art A conventional radar image processing apparatus mainly uses a processing method which is easy to implement in hardware, that is, obtains two-dimensional shape information on a range-Doppler plane from a radar echo from a radar target. Met.

On the other hand, as a processing method for obtaining target three-dimensional shape information, “DA” is completely different from the processing for obtaining a radar image on the range-Doppler plane.
LE A. AUSHERMAN, ADAM KOZMA, et al. Developments in
Radar Imaging, IEEE Transaction on Aerospace and
Electronic Systems, AES-20 (Jul 1984), 363-400 ".

[0004] However, in the method according to the above-mentioned literature,
It is necessary to collect various data on the aspect direction of the radar as viewed from the radar target, which is strongly limited to the movement of the target. For this reason, it is necessary to collect data for a long time, and it is difficult to apply the method to a target other than a target that performs a motion capable of collecting various aspect directions.

For this reason, it is extremely difficult to obtain a three-dimensional radar image in actual operation, and a technique for obtaining information on a three-dimensional shape from a radar image on a range-Doppler plane has been conventionally required. .

[0006]

As described above, there has been a demand for a technique for acquiring information on a three-dimensional shape from a radar image on a range-Doppler plane. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is not necessary to collect data in various aspect directions of a radar when viewed from a radar target. It is an object of the present invention to provide a radar image processing apparatus capable of obtaining target three-dimensional shape information using a radar image obtained.

[0007]

In order to achieve the above object, a radar image processing apparatus according to the present invention provides a two-dimensional radar image consisting of a range-Doppler plane created from radar echoes in an area of a designated size. Image cell selecting means for selecting, for each area, an image cell having the maximum amplitude in each area including the target portion, and for each image cell selected by this means, a radar image one unit time before An image cell tracking unit that outputs a position and a complex value of the point of the image cell having the maximum amplitude as a new selected image cell within an area around the point of the image cell that has been selected, Image cell acceleration calculating means for calculating the phase of the complex value of the image cell point sequence, calculating the second derivative of the phase with respect to time, converting the calculation result into acceleration, and outputting the acceleration; A three-dimensional quantity (range, Doppler frequency, acceleration) obtained by inputting an image and acceleration, and adding an acceleration to a two-dimensional position (range, Doppler frequency) on the range-Doppler plane of the image cell tracking point and the image cell A three-dimensional radar image creating unit that outputs the amount of (range position, Doppler frequency, acceleration, intensity) as the three-dimensional radar image of the image cell tracking point by adjusting the intensity of the tracking point; 3D radar image display means which regards a range position, Doppler frequency, acceleration) as a coordinate point and displays a point indicating its intensity on an orthogonal three-dimensional coordinate system represented by a range axis, a Doppler axis, and an acceleration axis. It is configured so that

[0008]

In the radar image processing apparatus having the above configuration,
The two-dimensional radar image is divided into regions of a designated size, and an image cell having a maximum amplitude in each region including a target portion is selected for each region. For each of the selected image cells, one unit time In the area centered on the image cell point selected for the previous radar image, the position of the image cell having the largest amplitude is determined as a new selected image cell, and its position and complex value are obtained. Calculate the phase of the complex value of the cell point sequence, calculate the second derivative of the phase with respect to time,
The calculation result is converted into acceleration, and a three-dimensional amount (range, Doppler frequency) obtained by applying acceleration to a two-dimensional position (range, Doppler frequency) on the range-Doppler plane of the image cell tracking point from the two-dimensional radar image and acceleration. (Frequency, acceleration) and the intensity of the image cell tracking point
Doppler frequency, acceleration, and intensity) are created as a three-dimensional radar image of the image cell tracking point, and the (range position, Doppler frequency, acceleration) of the three-dimensional radar image is regarded as a coordinate point, and a range axis, a Doppler axis, A point indicating the intensity is displayed on a three-dimensional coordinate system represented by an acceleration axis.

[0009]

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 two-dimensional radar image generating apparatus 11 sequentially receives radar echoes from a radar receiver (not shown) and outputs the echoes on a range-Doppler plane. A dimensional radar image is created continuously at regular intervals. The radar image created here has a complex value consisting of phase and amplitude for each image cell.

As the two-dimensional radar image creating device 11, a conventional device can be used as it is. The radar image created by the device 11 is sent to an image cell selection device 12, an image cell tracking device 13, and an image cell acceleration calculation device 14.

The image cell selecting device 12 sequentially selects image cells to be used for the subsequent processing from the input radar image, and outputs a set of the position on the range-Doppler plane and a complex value to the image cell tracking device 13. I do.

The image cell tracking device 13 selects each of the input radar images selected one unit time ago based on the set of the position on the range-Doppler plane and the complex value from the image cell selection device 12. The image cell of each target part is extracted from the image cell, the movement over the image cell of the target part is tracked, and the image cell including the target part to be targeted is selected. The image cell acceleration calculation device 14 and the three-dimensional radar image creation Output to the device 15.

The image cell acceleration calculating device 14 calculates the phase of the complex value of each selected image cell from the image cell tracking device 13, and calculates the phase of the phase for each selected image cell.
The differential is calculated, the calculation result is converted into acceleration, and the acceleration is output to the three-dimensional radar image creation device 15.

The three-dimensional radar image creating device 15 has two
A three-dimensional radar image is created from one radar image from the three-dimensional radar image creation device 11, the selected image cell from the image tracking device 13, and the acceleration from the image cell acceleration calculation device 14, and the three-dimensional radar image display device 1
Output to 6.

The three-dimensional radar image display device 16 displays the input three-dimensional radar image on a rectangular coordinate system or a skew coordinate system, and changes or rotates the scale factor of the coordinate system according to an instruction from an operator as needed. Do.

The processing procedure of the above configuration will be described below with reference to FIGS. First, the two-dimensional radar image creation device 11 continuously creates a radar image on a range-Doppler plane at regular time intervals from radar echoes from radar targets. The radar image created here has a complex value consisting of phase and amplitude for each image cell.

In the image cell selecting device 12, the input 2
The dimensional radar image is divided into regions of a designated size as shown in FIG. 2, and for example, an image that exceeds a preset threshold for the amplitude of the image cell is detected as an image cell including a target part. The image cell having the largest amplitude in each region including the target portion is selected for each region. For example, a two-dimensional radar image is displayed on a screen of a display device,
An image cell may be selected according to an instruction of the operator.

The image cell selected in this manner is represented by a set of a position on the range-Doppler plane, a complex value, and a position of an area to which the set belongs. Image cell selection device 12
Is used only once at the start for one processing.

Subsequently, a point P with respect to the area A1 shown in FIG.
An example in which 1 is selected will be described with reference to FIG. In the image cell tracking device 13, the point P of the image cell selected for the radar image one unit time ago is selected.
In the area A2 centered at 1, the position and the complex value of the point P2 of the image cell having the maximum amplitude are output as a new selected image cell. Alternatively, a new selected image cell may be output by an operator inputting a target rotational motion or using target rotational motion information from a device not included in the present configuration.

This processing is performed for each of the radar images at fixed time intervals, and the selected image cell rows (P1, P2, P
3, ...). The image cell acceleration calculation device 14 calculates the phase of the complex value of the selected image cell point sequence, calculates the second derivative of the phase with respect to time, converts it into acceleration, and outputs it. For example, the phase is calculated for each of the previously selected image cell rows, and the phase row (PH1, PH2, PH3,
…).

Next, subtraction of adjacent phases, for example, (phase PH2-phase PH1) is performed, and a phase difference sequence (PH2
-PH1, PH3-PH2, PH4-PH3, ...). Assuming that each term of this phase difference sequence is Y and each time is X,
For example, the gradient of the phase difference with respect to time is obtained by the least square method (see FIG. 4). This inclination is converted into acceleration by the following equation.

Acceleration = inclination / (2π) · λ / 2 · 1 / Δt ² [m / s ** 2] Here, Δt represents a time interval at which a radar image is created, and λ represents a radar transmission wavelength.

The three-dimensional radar image creating device 15 receives one radar image, for example, a radar image at the start of processing, and acceleration as inputs, and moves the point P1 to a two-dimensional position (range, Doppler frequency) on the range-Doppler plane. The three-dimensional amount (range, Doppler frequency, acceleration) to which the acceleration is applied and the intensity of the point P1 are combined to obtain (the range position of the point P1, the point P1).
Doppler frequency, acceleration, intensity of point P1)
As a three-dimensional radar image.

The above processing is performed for all the regions in FIG. 2 to obtain a three-dimensional radar image of the selected image cell in each region. This situation will be described with reference to FIGS.

The three-dimensional radar image display device 16 regards the (range position, Doppler frequency, acceleration) of the three-dimensional radar image as a coordinate point, and displays it on an orthogonal three-dimensional coordinate system represented by a range axis, a Doppler axis, and an acceleration axis. Points indicating the intensity, for example, points of different colors depending on the intensity, are displayed. In addition, a display using a three-dimensional skewed coordinate system according to an instruction of an operator,
The rotation of the coordinate system and the change of the scale factor of each axis may be performed.

Further, the Doppler frequency [Hz] → distance [m] or acceleration [m / s ** 2
] → It may be displayed on an orthogonal three-dimensional coordinate system using the distance unit [m] as a unit.

Here, a three-dimensional coordinate system Σ (X, Y, Z) fixed to a target rotating at a constant angular velocity vector ω_ (an underline represents a vector) together with the target is considered. However, for the sake of simplicity, it is assumed that the line of sight of the radar coincides with the Y axis and the angular velocity vector ω_ is included in the YZ plane.
This assumption does not lose generality.

Under these conditions, coordinates (R ', dR / dt, d ² R / dt ² ), which are observable by radar, and the coordinates shown in FIG. In the system, for example, a velocity vector v_ of one wing tip r_ is expressed as follows.

[0029]

(Equation 1) Further, an acceleration vector a_ due to rotation is expressed as follows.

[0030]

(Equation 2) The first derivative dR / dt with respect to the time of the distance R from the radar to the observable target is expressed as a distance R >> | r_ |
Since it matches the projection component of the velocity vector v_ in the line of sight of the radar, it is expressed as follows.

[0031]

(Equation 3) This is modified using the above velocity vector v_ to obtain the following equation.

[0032]

(Equation 4) This is the Doppler axis component of a conventional two-dimensional radar image. Similarly, the second derivative d ² R with respect to the time of the distance R
/ Dt ² is expressed as follows.

[0033]

(Equation 5) Further, the distance R is expressed as follows.

[0034]

(Equation 6) This is the range axis component of a conventional two-dimensional radar image. Since r_ reflects the target shape, the second term of the above equation will be considered below.

[0035]

(Equation 7) Here, the following two vectors are considered as definitions.

[0036]

(Equation 8) From equations (1) to (3), if the three vectors ey_, γ_, and ζ_ are linearly independent, r_ is a point (R ′,
dR / dt, d ² R / dt ² ).

Here, as shown in FIG. 5, γ_ is parallel to the X axis of the three-dimensional coordinate system Σ (X, Y, Z), and as shown in the figure, the rotational angular velocity vector ω_ is not parallel to the Z axis. As far as possible, ζ_ includes a component in the Z-axis direction. This is the traditional range
When the radar image on the Doppler plane is obtained, the same conditions as in the case where information on the Doppler direction is lost when the rotational angular velocity vector ω_ is parallel to the range axis, that is, the Y axis.
That is, if ω is not parallel to the Y axis and the Z axis, the three-dimensional coordinate system Σ (X, Y, Z) becomes the skewed coordinate system Σ ′ (γ, Y, ζ).
Skewed coordinate system Σ '
A point above the point (R ', dR / dt, d 2 R / dt 2) is observed by the radar as.

Therefore, by using the points (R ′, dR / dt, d ² R / dt ² ) consisting of the amounts observable by the radar, each axis of the three-dimensional coordinate system Σ (X, Y, Z) is obtained. Is obtained, for example, by calculating the relative ratio of each point for each axis (FIG. 6).
(B)), or the rotational angular velocity vector ω_
, The inverse transformation of the above coordinate transformation is obtained, and a point on the oblique coordinate system Σ ′ is transformed into a point on the three-dimensional coordinate system Σ. Since the technique for obtaining the inverse transform is a well-known technique, its description is omitted here.

On the other hand, the radar image obtained on a normal range-Doppler plane is the above (R, dR / d
Since the image is composed of the components of t), the target shape X
-A projection component onto the Y plane, and information in the Z-axis direction has been lost (see FIG. 6A).

Since an arbitrary portion of a target on a radar image obtained on a normal range-Doppler plane can be made three-dimensional, there is no need to collect data in various aspects of the radar viewed from the radar target. .

Hereinafter, the processing operation will be described with reference to FIG. Each target portion included in the image cell selected by the image cell selecting device 12 is corrected by the image cell acceleration calculating device 14 for d ² while the image cell tracking device 13 corrects the movement across the image cells between radar images.
R / dt ² is calculated using the phase of the image cell, and this is combined with the position (R ′, dR / dt) of each image cell selected by the image cell selection device 12 to obtain a point ( R ′, dR / dt, d ² R / dt ² ).

The three-dimensional radar image display device 16 uses a set of obtained points (R ', dR / dt, d ² R / dt ² ) in a three-dimensional coordinate system using (ey_, γ_, ζ_) as base vectors. ο (ey _, γ_, ζ_). At the time of display, (ey_, γ_, ζ_) may be replaced with three orthogonal or linearly independent unit vectors. Alternatively, a set of points (R ′, dR / dt, d ² R / dt ² ) is converted into a point on the three-dimensional coordinate system Σ (X, Y, Z) by giving information about the rotational angular velocity vector ω_ from outside. Later, it may be displayed.

As described above, according to the configuration of this embodiment, the data on the range-Doppler plane for which the technology has been established can be obtained without collecting data in various aspects of the radar when viewed from the radar target. The three-dimensional shape information of the target can be obtained from the radar image obtained in step (1).

[0044]

As described above, according to the present invention, a range in which a technique is established without collecting data in various aspects of the radar when viewed from a radar target.
It is possible to provide a radar image processing apparatus capable of obtaining target three-dimensional shape information using a radar image obtained on a Doppler plane.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a two-dimensional radar image for explaining the image cell selection processing of the embodiment.

FIG. 3 is a diagram showing a two-dimensional radar image for explaining the image cell tracking processing of the embodiment.

FIG. 4 is a diagram showing a state in which a gradient of a phase difference with respect to time is obtained in the image cell acceleration calculation processing of the embodiment.

FIG. 5 is a vector diagram for explaining the three-dimensional radar image processing of the embodiment.

FIG. 6 is a diagram for describing three-dimensional radar image image processing of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... 2D radar image creation apparatus 12 ... Image cell selection apparatus 13 ... Image cell tracking apparatus 14 ... Image cell acceleration calculation apparatus 15 ... 3D radar image creation apparatus 16 ... 3D radar image display apparatus

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00-13/95

Claims (8)

(57) [Claims] 1. A two-dimensional radar image composed of a range-Doppler plane created from a radar echo is divided into regions of a designated size, and an image cell having a maximum amplitude in each region including a target portion is defined as a region. An image cell selecting means for selecting each of the image cells, and for each image cell selected by this means, an amplitude maximum and an amplitude within a region centered on a point of the image cell selected for the radar image one unit time ago. Image cell tracking means for outputting a position and a complex value of a point of an image cell as a new selected image cell, calculating a complex value phase of the selected image cell point sequence, and calculating a second derivative of the phase with respect to time. Image cell acceleration calculation means for calculating, converting the calculation result into acceleration, and outputting the acceleration; inputting the two-dimensional radar image and acceleration; Position (range, Doppler frequency) 3-dimensional volume plus acceleration (range, Doppler frequency, acceleration) and the combined strength of the image cell tracking point (range position, the Doppler frequency, acceleration,
3D radar image creating means for outputting the amount of intensity as a 3D radar image of the image cell tracking point; (Range position, Doppler frequency, acceleration) of the 3D radar image are regarded as coordinate points, Doppler axis,
A radar image processing apparatus comprising: three-dimensional radar image display means for displaying a point indicating the intensity on a three-dimensional coordinate system represented by an acceleration axis. 2. The image cell acceleration calculating means receives as input one or more screens of a two-dimensional radar image composed of a range-Doppler plane which is continuously generated at predetermined time intervals from a radar echo, and outputs it for each target region. Detecting acceleration by calculating the phase for each image cell having the range of the range resolution and the Doppler resolution including the above, and obtaining the second-order differential component relating to the time lapse between a plurality of radar images of the phase for each image cell The radar image processing apparatus according to claim 1, wherein: 3. The image cell acceleration calculating means has a function of selecting an image cell for which a phase is to be calculated from a radar image in accordance with an instruction of an operator.
A radar image processing apparatus as described in the above. 4. The image cell selecting means divides a radar image by a region of a predetermined size as an image cell for which a phase is calculated by the image cell acceleration calculating means, and sets an area including a target part. 2. The radar image processing apparatus according to claim 1, further comprising a function of selecting an image cell having a maximum amplitude for each region as said image cell. 5. The image cell tracking means, after selecting an image cell by said image cell selection means, in a next radar image centering on each image cell in a subsequent radar image processing. The selection of a new image cell having the maximum amplitude in the above is repeated for each radar image, and the phase of each of the selected image cells is calculated, thereby rotating the target image between the radar images on the radar image. 2. The radar image processing apparatus according to claim 1, further comprising a function of tracking a target position and correcting movement across image cells for each radar image of each target portion. 6. The image cell tracking means, after externally inputting a rotational movement of the target between the radar images on the radar image, after the selection processing of the image cell selection means, processing of a subsequent radar image. 2. The radar image processing apparatus according to claim 1, further comprising a function of correcting a movement of the target region in each of the target images which crosses an image cell. 7. The three-dimensional radar image display means includes:
2. The radar image processing apparatus according to claim 1, further comprising a function of using a one-dimensional rectangular coordinate system or a three-dimensional skew coordinate system to further change and display a scale factor of each axis. 8. The radar image processing apparatus according to claim 1, wherein said three-dimensional radar image display means has a function of displaying based on a numerical value selected or inputted by an operator.