KR102092278B1 - 2D GO CA-CFAR detection method for detecting targets in heterogeneous clutter environments and system thereof - Google Patents

Abstract

Disclosed is a 2D GO CA-CFAR detection method for detecting a target in a heterogeneous cluster environment. According to an embodiment of the present invention, the 2D GO CA-CFAR detection method for detecting a target in a heterogeneous cluster environment comprises: a guard cell setting step of setting a guard cell based on a preset test cell in a Doppler-distance map composed of a Doppler axis and a range axis; a reference cell setting step of setting 16 areas based on the test cell in the Doppler-distance map and setting a reference cell in the set areas; an evaluation value calculation step of calculating evaluation values for the set 16 areas; a threshold value calculation step of selecting a largest value among the calculated evaluation values for the 16 areas and calculating a threshold value based on the selected value; and a target detection step of detecting the target caught on the Doppler-distance map based on the calculated threshold value.

Description

2D GO CA-CFAR detection method for detecting targets in heterogeneous clutter environments and system thereof}

The present invention relates to a 2D GO CA-CFAR detection method and system for detecting targets in a heterogeneous clutter environment, and more specifically, to minimize false alarms and targets that are likely to occur in a heterogeneous clutter environment. The present invention relates to a 2D GO CA-CFAR detection method and a system capable of accurately detecting it.

The conventionally known 2D GO CA-CFAR (Greatest Of Cell Average-Constant False Alarm Rate) detection method prevents the occurrence of false alarms, which is a disadvantage of the 2D CA-CFAR detection method at the clutter boundary in heterogeneous clutter environments. It is a detection method introduced to improve.

In the 2D GO CA-CFAR detection method, the average power is calculated by dividing the reference cell into left and right sides, and a larger value is selected from the two values to be used in the calculation of the detection threshold. That is, since the detection threshold is calculated based on the reflected power of the clutter, not the noise power, at the clutter boundary, a false alarm phenomenon that may occur at the clutter boundary can be improved.

1 is a diagram showing a reference cell, a guard cell, and a test cell of a conventional 2D GO CA-CFAR detection method.

Referring to FIG. 1, a test cell 110 is located in the center of a Doppler-distance map composed of a doppler axis and a range axis, and the guard cell 130 surrounds the test cell 130. Is arranged in a square shape. When the test cell 110 and the guard cell 130 are determined, the remaining cells become the reference cell 150, and evaluation values of the left and right reference cells of the reference cell can be calculated through Equation (1).

과

은 각각 좌측과 우측의 기준 셀의 개수이고, 보통 시험 셀(110)을 기준으로 좌측, 우측에 위치하는 기준 셀(150)들의 수는 같다. 도 1에서 좌측과 우측의 기준 셀이 같을 때, 간단히 표현하기 위해 기준 셀 개수 N_REF로 표현하기도 한다. In Equation 1, REF _L and REF _R represent left and right reference cells, respectively.

and

Is the number of reference cells on the left and right sides, and the number of reference cells 150 located on the left and right sides based on the test cell 110 is the same. In FIG. 1, when the left and right reference cells are the same, the number of reference cells N _REF may be expressed for simplicity.

In FIG. 1, the length N _D of the reference cell 150 of the Doppler axis and the length N _R of the reference cell 150 of the distance axis are odd, and when dividing the left and right reference cells, floor (N _D / 2) +1 The column containing the test cell 110 is applied to the two reference cells overlapping. The guard cell 130 is set to improve the self masking effect.

는 문턱치 가중치(threshold multiplier)로서, 후술하는 평균 오경보 확률(false alarm probability)인

에 의해 결정된다_. Equation 2 represents an equation for calculating the threshold. In Equation 2

Is a threshold multiplier, which is the average false alarm probability described later.

Is determined by _.

가 각각 10^-4, 10^-5, 10^-6 일 경우, 문턱치 가중치는 각각 8.98, 11.29, 13.62가 된다.Equation 3 represents the average false alarm probability. As an example, in Equation 3

If is 10 ^-4 , 10 ^-5 , and 10 ^-6 respectively, the threshold weights are 8.98, 11.29, and 13.62, respectively.

As described above, when the conventional 2D GO CA-CFAR detection method is used, a high threshold is selected even if both sides of the clutter signal have inhomogeneity at the clutter boundary, so that a false alarm incidence rate is higher than that of using the 2D CA-CFAR detection method. This was lower.

However, if the heterogeneity of the clutter is severe, or in the case of a radar used when mounted on an aircraft, a complex type of clutter environment may occur, and the conventional method accurately calculates a strong clutter reflection signal among surrounding signals. Can't. For example, when the antenna beam is radiated from the aircraft toward the ground, inhomogeneity may occur in the form of a mountainous terrain in a part of the area to which the beam is irradiated, and an urban terrain in the other part. As another example, when the antenna beam is radiated from the aircraft to the sea, inhomogeneity may occur in a part of the area where the beam is irradiated, the sea area having nothing but sea water, and the other part including the sea area including islands and reefs. You can.

As described above, when the environment of the clutter in the received signal exceeds a certain value, noise or low clutter reflected power values are included in both the left and right reference cells, and some high clutter values are not accurately measured. Because it is not possible, an error occurs in the estimation of the evaluation value, and eventually, an error occurs also in the calculation of the threshold value, and there is a problem that a false alarm may occur even if the 2D GO CA-CFAR detection method using the conventional method is improved.

Radar (RADAR), even in a complex clutter environment, requires that the radar (RADAR) accurately detect only the target signal without detecting the clutter signal, so many false alarms caused by the clutter are directly related to the degradation of radar performance.

1. Republic of Korea Patent Publication No. 10-2016-0039383 (2016.04.11. Public) 2. Republic of Korea Patent Publication No. 10-2014-0107799 (2014.09.05. Published)

The technical problem to be solved by the present invention is an improved 2D GO CA-CFAR detection method and system, which further improves the conventional 2D GO CA-CFAR detection method to accurately detect a target even in a heterogeneous clutter environment. To provide.

The method according to an embodiment of the present invention for solving the above technical problem is to set a guard cell based on a preset test cell in a Doppler-distance map composed of a Doppler axis and a range axis. Guard cell setting step; A reference cell setting step of setting 16 zones based on a test cell in the Doppler-distance map and setting a reference cell in the set zone; An evaluation value calculation step of calculating evaluation values for the set 16 areas; A threshold value calculating step of selecting the largest value among the calculated evaluation values for the 16 zones and calculating a threshold value based on the selected value; And a target detection step of detecting a target caught on the Doppler-distance map based on the calculated threshold.

The system according to another embodiment of the present invention for solving the above technical problem sets a guard cell based on a preset test cell in a Doppler-distance map composed of a Doppler axis and a Range axis. And, in the Doppler-distance map, a cell setting unit that sets 16 zones based on a test cell and sets a reference cell in the set zone; Calculate the evaluation values for the set 16 areas, select the largest value among the evaluation values for the calculated 16 areas, calculate a threshold value based on the selected value, and doppler based on the calculated threshold value -Operation unit for detecting the target caught on the distance map; And an iterative control unit that controls the operation to be repeated according to the 16 zones.

One embodiment of the present invention can provide a computer-readable recording medium storing a program for executing the method.

According to the present invention, it is possible to accurately detect a target through a 2D GO CA-CFAR detection method even in an inhomogeneous clutter signal environment.

The present invention is applied to RADAR mounted on an aircraft (fighter), and may be used in an air-to-ground mission for detecting and recognizing ground targets in an aircraft and an air-to-sea mission for detecting and recognizing maritime targets in an aircraft.

In performing the above air-to-ground and air-to-air missions, the ground and offshore clutter environment has a complex and heterogeneous environment, and thus, when using a conventionally known technique, a lot of false alarms occur when detecting a target. According to the present invention, the false alarm is significantly less than that of the conventional technology, so that the target can be accurately detected.

1 is a diagram showing a reference cell, a guard cell, and a test cell of a conventional 2D GO CA-CFAR detection method.
2 is a block diagram of an example of a 2D GO CA-CFAR detection system according to an embodiment of the present invention.
3 is a flowchart illustrating an example of a method performed by a system according to the present invention.
4 shows an example of a Doppler-distance map implemented by the method according to the invention.
5 is a graph showing a relationship between a threshold weight and an average false alarm probability.
6 is a diagram schematically showing an example of simulating a heterogeneous clutter environment and a target signal.
FIG. 7 shows the result of viewing the Doppler-distance map according to FIG. 6 in a top view.
8 is a view showing the results of applying the conventional 2D GO CA-CFAR detection method to the Doppler-distance map according to FIG.
FIG. 9 shows the result of viewing the Doppler-distance map according to FIG. 8 in a top view.
FIG. 10 is a diagram showing a Doppler-distance map when the 2D GO CA-CFAR detection method according to the present invention is applied to the Doppler-distance map according to FIG. 6.
FIG. 11 shows the result of viewing the Doppler-distance map according to FIG. 10 in a top view.

The present invention can be applied to a variety of transformations and may have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. Effects and features of the present invention, and methods for achieving them will be clarified with reference to embodiments described below in detail with reference to the drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, and the same or corresponding components will be denoted by the same reference numerals and redundant description will be omitted when described with reference to the drawings. .

In the following examples, terms such as first and second are not used in a limited sense, but for the purpose of distinguishing one component from other components.

In the following embodiments, singular expressions include plural expressions, unless the context clearly indicates otherwise.

In the following examples, terms such as include or have are meant to mean that features or components described in the specification exist, and do not preclude the possibility of adding one or more other features or components.

When an embodiment can be implemented differently, a specific process order may be performed differently from the described order. For example, two processes described in succession may be performed substantially simultaneously, or may be performed in an order opposite to that described.

2 is a block diagram of an example of a 2D GO CA-CFAR detection system according to an embodiment of the present invention.

2, it can be seen that the 2D GO CA-CFAR detection system 200 according to an embodiment of the present invention includes a cell setting unit 210, a calculation unit 230, and a repetition control unit 250. Each component constituting the system according to FIG. 2 may be a physical unit manufactured to perform a specific function, or a logical module implemented as a program and set to implement each function.

First, the cell setting unit 210 sets a guard cell based on a preset test cell in a Doppler-distance map composed of a Doppler axis and a distance axis, and sets 16 zones based on a test cell in the Doppler-distance map, , Set the reference cell in the set 16 zones.

The calculation unit 230 calculates the evaluation values for the 16 zones set by the cell setting unit 210, selects the largest value among the calculated evaluation values for the 16 zones, and a threshold value based on the selected value ), And detects a target caught on a Doppler-distance map based on the calculated threshold.

The repetition control unit 250 controls the operation to be repeated according to the 16 zones set by the cell setting unit 210.

A detailed description of each function performed by the cell setting unit 210, the operation unit 230, and the repetition control unit 250 will be described later with reference to FIGS. 3 to 11.

3 is a flowchart illustrating an example of a method performed by a system according to the present invention.

Since the method according to FIG. 3 can be implemented by the system described in FIG. 2, the description will be given with reference to FIGS. 1 and 2, and descriptions overlapping with those described in FIGS. 1 and 2 will be omitted.

First, the cell setting unit 210 sets a guard cell based on the test cell in the Doppler-distance map (S310).

In the conventional 2D GO CA-CFAR detection method, the guard cell is set only around the test cell in order to improve only the self-masking effect, but in the present invention, the cell setting unit 210 is present in the test cell. A guard cell is set in the same row and column as the test cell to prevent the sidelobe signal of the target from being included in the reference cell and affecting the estimation of the evaluation value.

4 shows an example of a Doppler-distance map implemented by the method according to the invention.

Referring to FIG. 4, the cell setter 210 is a Doppler of FIG. 1 in that the test cell 410 is located in the center of the Doppler-distance map and the guard cell 430 is centered around the test cell 410. It is the same as the distance map, but it can be seen that the guard cell 430 is additionally set in the same row and column as the test cell by the cell setting unit 210.

As illustrated in FIG. 4, when a guard cell is set in a Doppler-distance map, the influence of a target that may be in the test cell may be reduced when estimating an evaluation value, and thus the evaluation value is estimated by only the surrounding signals excluding the target Since this becomes possible, it is possible to improve the accuracy of estimating the evaluation value.

Subsequently, the cell setting unit 210 sets 16 zones based on the test cell 410 in the Doppler-distance map, and sets the reference cell 450 (S330).

Referring to FIG. 4, it can be seen that 16 zones are set in the Doppler-distance map. Each of the 16 zones is set to a zone having the same width, and according to an embodiment, the 16 zones may be configured to have the same horizontal and vertical lengths, respectively. At this time, the size of the region to be set is set to be the same as the vertical length and the horizontal length, except for the effect of the guard cell for improving the magnetic masking effect. At this time, the reason for setting the size of each zone to be set equally is to make the number of cells used for estimation of the value equal to each other. Each zone may be numbered according to a predetermined method. Referring to FIG. 4, it can be seen that zone numbers 1 to 16 are numbered in order from the upper left to the lower right of the Doppler-distance map.

When the cell setting is completed in the Doppler-distance map, the cell setting unit 210 controls the calculation unit 230 to estimate the evaluation value for each area (S350).

은 각 구역의 기준 셀의 개수를 의미한다.Equation 4 shows an example of the equation used by the operation unit 230 to estimate the evaluation value. In Equation 4, m is the number of each zone, REF _m is the reference cell of each 16 zones,

Indicates the number of reference cells in each zone.

의 값에 따라서 결정된다. 탐지 대상이 되는 셀의 전력을 x라고 할 때, 평균 오경보 확률

은 수학식 7을 통해 얻어질 수 있다.Equations 5 and 6 show an example of an equation used by the operation unit 230 to calculate a threshold value after calculating an evaluation value. In Equation 5, T is a threshold value, and n is a value that satisfies the condition of Equation 6 from 1 to 16. In Equation 5, α is an average false alarm probability as a threshold weight

It depends on the value of. When the power of the cell to be detected is x, the average false alarm probability

Can be obtained through Equation 7.

Equation 7 is an example of the equation used to obtain the average false alarm probability in the present invention. In Equation 7, p _z (z) means a probability density function for _z (hereinafter, PDF).

Equations (8) to (11) show an example of an abbreviation for expanding the equation and an equation used to obtain a PDF of x, y _i . In Equation 10 and Equation 11, p _x (x) and p _y (y) represent probability density functions of x and y _i .

Equation 12 shows an example of the equation for calculating the cumulative distribution function for the variable z. In Equation 12, F _z (z) is a cumulative distribution function for the variable z, and F _y (z) is a cumulative distribution function for the variable y _i . In addition, in Equation 12, y ₁ to y ₁₆ are all independent and identically distributed (hereinafter referred to as IID) and have a probability density function of p _y (y). M is the number of reference cell regions and is 16 in the present invention.

Equation 13 is a probability density function of the variable z and is defined as a derivative of the cumulative distribution function of Equation 12. The calculation unit 230 may substitute Equation 10, Equation 11, and Equation 13 into Equation 7, and finally obtain Equation 14 for the average false alarm probability.

Through the above process, the calculator 230 calculates the threshold weight α on the Doppler-distance map, and detects and discriminates the target.

5 is a graph showing the relationship between the threshold weight and the average false alarm probability according to Equation (15).

Referring to FIG. 5, when the average false alarm probability is 10 ^-4 , 10 ^-5 , and 10 ^-6 , respectively, it can be seen that the threshold weights are 6.554, 8.295, and 10.07, respectively.

When the detection method according to the present invention is used, the intensity of the strongest clutter in the vicinity is estimated as the evaluation value because the largest value among the 16 evaluation values is selected even if there are various types of heterogeneous clutter in the entire reference cell area. Due to this, according to the present invention, it is possible to minimize the occurrence of false alarms in the clutter area when detecting a target, and is not affected by the heterogeneous clutter environment, and the threshold weight is appropriately calculated, even in a heterogeneous clutter situation, The target signal can be accurately detected.

6 is a diagram schematically showing an example of simulating a heterogeneous clutter environment and a target signal.

In FIG. 6, the clutter signal was generated by dividing the Doppler-distance map into arbitrary 16 regions and assuming an exponential distribution with different averages. Referring to FIG. 6, it can be seen that the target signal is located at the distance index 21 and the Doppler index 6.

FIG. 7 shows the result of viewing the Doppler-distance map according to FIG. 6 in a top view.

FIG. 7 is a diagram for emphasizing that the 2D CA-CFAR detection method is an unused heterogeneous clutter environment, and is a diagram for highlighting the effect of the present invention compared to FIGS. 9 and 11 to be described later.

8 is a view showing the results of applying the conventional 2D GO CA-CFAR detection method to the Doppler-distance map according to FIG.

는 10^-5로 설정하였다고 가정한다.In FIG. 8, the white side represents the detection threshold, and the gray side represents the input Doppler-distance map. The average false alarm probability for calculating the threshold weight in FIG. 8

Assume that is set to 10 ^-5 .

In FIG. 8, since a strong clutter signal among the surrounding signals cannot be selected as an evaluation value due to the inhomogeneous clutter, a false alarm is generated at a high probability at the clutter interface portion. In particular, in FIG. 8, since a clutter signal having a weak intensity is included in a reference cell in a clutter area having a stronger intensity than a neighboring cell, the evaluation value is set smaller than the size of the test cell, and as a result, the gray surface over the white surface There are many cases where it breaks through.

FIG. 9 shows the result of viewing the Doppler-distance map according to FIG. 8 in a top view.

In FIG. 9, a circle drawn by a solid line indicates detection of a target, and a circle drawn by a dotted line indicates a false alarm by a clutter. Referring to FIG. 9, when a conventional 2D GO CA-CFAR detection method is used, a target signal is detected, but it can be confirmed that a number of false alarms occur due to inhomogeneous clutter. In FIG. 8, it has been already described that the case where the gray surface protrudes over the white surface indicates that a false alarm is generated.

FIG. 10 is a diagram showing a Doppler-distance map when the 2D GO CA-CFAR detection method according to the present invention is applied to the Doppler-distance map according to FIG. 6.

In FIG. 10, in the same heterogeneous clutter environment, the calculator 230 selects the largest clutter signal in the vicinity as an evaluation value even when the test cell is located at the clutter boundary. Therefore, according to the present invention, even if there is a clutter region having a stronger intensity than a predetermined number of cells compared to the neighboring cells, since the calculator 230 calculates a threshold value using the strongest clutter signal as an evaluation value, the probability of false alarms is greatly reduced.

FIG. 11 shows the result of viewing the Doppler-distance map according to FIG. 10 in a top view.

In FIG. 11, the solid circle represents the target in the same manner as in FIG. 9, and when the detection method according to the present invention is applied, it is clearly shown in FIG. 11 that the target signal is well detected in an inhomogeneous clutter situation but no false alarm is generated at all. You can see that

An object of the present invention is to solve the disadvantage of generating a false alarm in a heterogeneous clutter environment, which is a problem of the prior art, and to eliminate a false alarm in a heterogeneous clutter environment and accurately detect a target.

According to the detection method of the present invention, even if there are various types of heterogeneous clutter in the entire reference cell region, the largest intensity among the 16 evaluation values is selected, and thus the strength of the strongest clutter around is estimated as the evaluation value. Due to this, the false alarm phenomenon occurring in the clutter area when detecting the target is improved, and the target signal can be accurately detected.

The present invention is applied to RADAR mounted on an aircraft (fighter), and may be used in an air-to-ground mission for detecting and recognizing ground targets in an aircraft and an air-to-sea mission for detecting and recognizing maritime targets in an aircraft.

In performing the above air-to-ground and air-to-air missions, the ground and offshore clutter environment has a complex and heterogeneous environment, and thus, when using a conventionally known technique, a lot of false alarms occur when detecting a target. According to the present invention, the false alarm is significantly less than that of the conventional technology, so that the target can be accurately detected.

The embodiment according to the present invention described above may be implemented in the form of a computer program that can be executed through various components on a computer, and such a computer program can be recorded on a computer-readable medium. At this time, the medium includes a hard disk, a magnetic medium such as a floppy disk and a magnetic tape, an optical recording medium such as a CD-ROM and DVD, a magneto-optical medium such as a floptical disk, and a ROM. , Hardware devices specially configured to store and execute program instructions, such as RAM, flash memory, and the like.

Meanwhile, the computer program may be specially designed and configured for the present invention or may be known and available to those skilled in the computer software field. Examples of computer programs may include machine language codes such as those produced by a compiler, as well as high-level language codes that can be executed by a computer using an interpreter or the like.

The specific implementations described in the present invention are examples, and do not limit the scope of the present invention in any way. For brevity of the specification, descriptions of conventional electronic configurations, control systems, software, and other functional aspects of the systems may be omitted. In addition, the connection or connecting members of the lines between the components shown in the drawings are illustrative examples of functional connections and / or physical or circuit connections, and in the actual device, alternative or additional various functional connections, physical It can be represented as a connection, or circuit connections. In addition, unless specifically mentioned, such as "essential", "important", etc., it may not be a necessary component for the application of the present invention.

In the specification (particularly in the claims) of the present invention, the use of the term " above " and similar indication terms may be in both singular and plural. In addition, in the case where a range is described in the present invention, it includes the invention to which the individual values belonging to the range are applied (if there is no contrary description), and describes the individual values constituting the range in the detailed description of the invention. Same as Finally, unless there is a clear or contradictory description of the steps constituting the method according to the invention, the steps can be done in a suitable order. The present invention is not necessarily limited to the order of description of the above steps. The use of all examples or exemplary terms (eg, etc.) in the present invention is merely for describing the present invention in detail, and the scope of the present invention is limited due to the examples or exemplary terms, unless it is defined by the claims. It does not work. In addition, those skilled in the art can recognize that various modifications, combinations, and changes can be configured according to design conditions and factors within the scope of the appended claims or equivalents thereof.

Claims (9)

As a 2D GO CA-CFAR detection method for detecting a target in an inhomogeneous clutter environment, performed by a radar system mounted on an aircraft,
A guard cell setting step of setting a guard cell based on a preset test cell in a Doppler-distance map composed of a Doppler axis and a range axis;
A reference cell setting step of setting 16 zones based on a test cell in the Doppler-distance map and setting a reference cell in the set zone;
An evaluation value calculation step of calculating evaluation values for the set 16 areas;
A threshold value calculating step of selecting the largest value among the calculated evaluation values for the 16 zones and calculating a threshold value based on the selected value; And
2D GO CA-CFAR detection method for detecting a target in a heterogeneous clutter environment, including; a target detection step of detecting a target caught on the Doppler-distance map based on the calculated threshold. According to claim 1,
The guard cell setting step,
2D GO CA-CFAR detection method for detecting a dense target, characterized in that the guard cell is set based on the row and column coordinates of the test cell. According to claim 1,
The reference cell setting step,
2D GO CA-CFAR detection method for detecting a dense target, characterized in that the 16 zones are each set to the same area. According to claim 1,
The reference cell setting step,
2D GO CA-CFAR detection method for detecting a dense target, characterized in that the 16 zones are respectively set to the same length and length. A computer-readable recording medium storing a program for executing the method according to any one of claims 1 to 4. A 2D GO CA-CFAR detection system that is mounted on a radar system mounted on an aircraft and implements a 2D GO CA-CFAR detection method for detecting targets in an inhomogeneous clutter environment,
In a Doppler-distance map composed of a Doppler axis and a range axis, a guard cell is set based on a preset test cell, and in the Doppler-distance map, 16 zones are set based on a test cell, , A cell setting unit for setting a reference cell in the set area;
Calculate the evaluation values for the 16 zones set above,
The largest value among the evaluation values for the calculated 16 areas is selected, and a threshold is calculated based on the selected value,
A calculator configured to detect a target caught on the Doppler-distance map based on the calculated threshold; And
2D GO CA-CFAR detection system for detecting a target in an inhomogeneous clutter environment, including a repetition control unit to control the operation to be repeated according to the 16 zones. The method of claim 6,
The cell setting unit,
2D GO CA-CFAR detection system for detecting a dense target, characterized in that the guard cell is set based on the row and column coordinates of the test cell. The method of claim 6,
The cell setting unit,
2D GO CA-CFAR detection system for detecting a dense target, characterized in that each of the 16 zones are set to the same area. The method of claim 6,
The cell setting unit,
2D GO CA-CFAR detection system for detecting a dense target, characterized in that each of the 16 zones is set to a zone composed of the same horizontal and vertical lengths.

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