JPH062260U - Target detection device - Google Patents

Abstract

(57) [Abstract] [Purpose] Even when the amplitude distribution of clutter follows the K distribution, it is possible to perform target detection while keeping the false alarm probability for clutter constant. [Structure] The product of the root mean square value and the root mean square value of the received signal, and the root mean square value are calculated, and the parameter indicating the characteristics of the K distribution is estimated using these, and the threshold value for the desired false alarm probability is calculated. Is calculated and the target is detected by comparing the target value and the threshold value, the false alarm probability is held constant.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a target detection technique in radar signal processing and the like, and relates to a method and apparatus for suppressing clutter noise according to a K distribution and detecting a target with a constant false alarm probability.

[0002]

[Prior art]

 In recent radars, it is important to keep the false alarm probability constant in order to perform automatic target detection, and this processing is called CFAR (Constant False Alarm Rate). FIG. 3 shows an example of a conventional LOG / CFAR device. In the figure, 26 and 32 are input terminals, 27 is a logarithmic amplifier, 28 is a sigma calculator, 29 is a divider, 30 is a subtractor, 31 is an antilogarithmic amplifier, 33 is a comparator, 34 is an output terminal, 400- 400 + N is a shift register. Hereinafter, LOG / CFAR will be described with reference to FIG.

The probability density function P (x) of the Rayleigh distribution is given by “Equation 1”.

[0004]

[Equation 1]

Here, σ is a shape parameter. The average value E (x) is “Equation 2” and the variance var (x) is “Equation 3”, which depends on the shape parameter σ.

[0006]

[Equation 2]

[0007]

[Equation 3]

A logarithmic amplifier of 26 performs logarithmic conversion such as “Equation 4” on such a signal input from the 26 input terminals.

[0009]

[Equation 4]

Here, a and b are constants determined by the characteristics of the converter. Next, the Σ calculator 28 and the divider 29 calculate the average value of the converted outputs stored in the shift registers 400 to 400 + N. This average value E (y) is expressed by "Equation 5".

[0011]

[Equation 5]

Here, γ is Euler's constant. In the subtractor 30, when the average value E (y) is subtracted from the target value x _T of the shift register 400 + N / 2, the output u becomes “Equation 6”.

[0013]

[Equation 6]

When v is the result of performing antilogarithmic transformation of this u by the antilogarithmic amplifier 31, it is expressed by “Equation 7”.

[0015]

[Equation 7]

Here, m is a constant determined by the characteristics of the antilogarithmic amplifier. The average E (v) of this v is "Equation 8", and the variance var (v) is "Equation 9".

[0017]

[Equation 8]

[0018]

[Equation 9]

Therefore, the CFAR characteristic can be obtained because the signal is converted into a signal having a constant average value and variance without depending on the shape parameter σ. The threshold value V _T is obtained from the relationship with the false alarm probability Pfa of “Equation 10”, is input from the input terminal 30, the target is detected by comparing with v by the comparator 33, and is output from the output terminal 34. It

[0020]

[Equation 10]

[0021]

The conventional LOG / CFAR is effective for clutter whose amplitude distribution follows the Rayleigh distribution, but when the clutter reflection area is small and the grazing angle is small, the amplitude is small. It is known that the distribution does not follow the Rayleigh distribution. It has been reported in recent reports that the amplitude distribution of sea clutter follows the K distribution, and when LOG / CFAR is used for clutter with such a distribution, the false alarm probability deteriorates due to the difference in the probability distribution functions. There was a problem that it would occur.

[0022]

[Means for Solving the Problems]

 A target detection apparatus according to the present invention calculates a root mean square value, a root mean square value, and a root mean square value of a received signal for clutter according to a K distribution, and calculates a product of the mean value and the root mean square value and a cube root. By calculating the ratio with the average value, the parameters that represent the characteristics of the distribution are estimated, and the target detection is performed using the threshold value obtained from the result.

[0023]

[Action]

 The target detection device according to the present invention makes it possible to perform target detection for clutter according to the K distribution while maintaining a constant false alarm rate.

[0024]

【Example】

 Embodiment 1 FIG. 1 is a diagram showing a processing procedure of an embodiment of a target detecting apparatus according to the present invention. In FIG. 1, 1 to 10 are processing steps of one embodiment of the target detecting method. A description will be given below with reference to FIG. The clutter whose amplitude intensity distribution follows the K distribution is represented by "Equation 11" when its probability density function is P (x).

[0025]

[Equation 11]

Here, Γ (ν) is a gamma function, Kν is a modified Bessel function, ν is a shape parameter, and C is a scale parameter. When the n-th moment of P (x) and x ^n, x ⁿ is represented by "the number 12".

[0027]

[Equation 12]

First, the root mean square value of the input signal is calculated. The average value E (x ² ) is expressed by "Equation 13" (step 1).

[0029]

[Equation 13]

A cubic mean value is calculated. The cubic mean value E (x ³ ) is expressed by “Equation 14” (step 2).

[0031]

[Equation 14]

Next, the product of the average value and the cubic mean value is obtained. This result is expressed by "Equation 15" (step 3).

[0033]

[Equation 15]

The mean square value is calculated. The mean-square value E (x ⁵ ) is expressed by “Equation 16” (step 4).

[0035]

[Equation 16]

Next, the ratio of the product of the root mean square value and the root mean square value and the root mean square value is obtained. This result is expressed by "Equation 17".

[0037]

[Equation 17]

From this, the shape parameter ν is obtained (step 5). Further, the scale parameter C is obtained from the root mean square value (step 6). Assuming that the threshold value is V _T , the false alarm probability Pfa is the cumulative probability in “Equation 18” and is represented by “Equation 19”.

[0039]

[Equation 18]

[0040]

[Formula 19]

[0041] Since it is difficult to calculate this than V _T, [nu, obtains the V _T by previously calculated data table V _T for C (Step 7). Finally, the value of _interest is compared with V _T to determine the presence or absence of a target (step 8).

FIG. 2 is a diagram showing an embodiment of the target detecting device according to the present invention. In FIG. 2, 11 is an input terminal, 12 is a square calculator, 13 is a cube calculator, 14 is a cube calculator, 15, 16 and 17 are mean value calculators, 18 is a square root calculator, and 19 is a multiplier. , 20 is a first parameter calculator, 21 is a second parameter calculator, 22 is a memory, 23 is a threshold calculator, 24 is a comparator, 25 is an output terminal, 100-100 + N, 200-200 + N, 300 to 300 + N are shift registers.

The operating principle will be described below with reference to FIG. The amplitude signal input from the input terminal 11 is squared by the squaring unit 12 and stored in the shift registers 100 to 100 + N. The average value calculator 15 calculates the average value of the stages of the shift registers 100 to 100 + N excluding 100 + N / 2 and outputs the average value to the multiplier 19, and the square root calculator 18 calculates the value of the shift stage 100 + N / 2. The square root is calculated and output to the comparator 22 as the value of interest. The other input of the multiplier 19 is generated as follows. The amplitude signal input from the input terminal 11 is cubed by the cube operator 13 and stored in the shift registers 200 to 200 + N. The average value calculator 16 calculates the average value of the stages of the shift registers 200 to 200 + N excluding 200 + N / 2 and outputs it to the multiplier 19 and also to the parameter calculator 2. The multiplier 19 calculates the product of the outputs of the average value calculators 15 and 16 and outputs it to the parameter calculator 20. The other input of the parameter calculator 20 is generated as follows. The amplitude signal input from the input terminal 11 is cubed by the fifth power calculator 14 and stored in the shift registers 300 to 300 + N. The average value calculator 17 calculates the average value of the stages of the shift registers 300 to 300 + N excluding 300 + N / 2, and outputs the average value to the parameter calculator 20. The parameter calculator 20 calculates the shape parameter ν according to “Equation 20” and outputs it to the parameter calculator 21 and the threshold calculator.

[0044]

[Equation 20]

The parameter calculator 21 calculates the scale parameter C from the output results of the average value calculator 15 and the parameter calculator 20 according to “Equation 21”, and outputs the scale parameter C to the threshold calculator 23.

[0046]

[Equation 21]

The memory 22 stores threshold values corresponding to the parameters ν and C at a desired false alarm probability as a data table, and the threshold calculator 21 extracts the threshold value from the memory 20 and outputs it to the comparator. To do. The comparator 24 compares the target value and the threshold value to detect the presence or absence of a target, and outputs it to the output terminal 25.

[0048]

[Effect of device]

 As described above, according to the present invention, it is possible to detect the target while keeping the predetermined false alarm probability constant for clutter whose amplitude intensity distribution of the received signal has a K distribution. obtain.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a processing procedure in an embodiment of a target detecting device according to the present invention.

FIG. 2 is a block diagram of an embodiment of a target detecting device according to the present invention.

FIG. 3 is a block diagram of an example of a conventional target detection apparatus.

[Explanation of symbols]

 11 Input Terminal 12 2nd Calculator 13 3rd Calculator 14 5th Calculator 15 1st Average Value Calculator 16 2nd Average Value Calculator 17 3rd Average Value Calculator 18 Square Root Calculator 19 Multiplier 20 First parameter calculator 21 Second parameter calculator 22 Memory 23 Threshold calculator 24 Comparator 25 Output terminal 26 Input terminal 27 Logarithmic amplifier 28 Σ Calculator 29 Divider 30 Subtractor 31 Inverse logarithmic amplifier 32 Input terminal 33 Comparator 34 output terminal

Claims (1)

[Scope of utility model registration request] 1. A first shift register having a squaring unit for squaring an input signal whose amplitude intensity distribution follows a K distribution and a shift stage for storing a predetermined number of squared input signals. A first average value calculator for calculating an average value of a predetermined stage of the first shift register, a cube operator for cubed input signal, and a predetermined number of cubed input signals. A second shift register having a shift stage for storing,
A second average value calculator for calculating the average value of a predetermined stage of the second shift register, a fifth power calculator for raising the input signal to the fifth power, and a predetermined number of cubed input signals. A third shift register having a shift stage, a third average value calculator for calculating an average value of predetermined stages of the third shift register, an output of the first average value calculator and a second average value calculator A multiplier for multiplying the output of the average value calculator, a first parameter calculator for calculating a shape parameter from the output of the third average value calculator and the output of the multiplier, and a second average value A second parameter calculator that calculates a scale parameter from the output of the calculator and the output of the first parameter calculator;
A threshold calculator for calculating a threshold value from the output of the first parameter calculator, the output of the second parameter calculator, and a preset false alarm probability, and the square root of a predetermined shift stage of the first shift register. 2. A target detecting apparatus comprising: a square root calculator for calculating the above, and a comparator for comparing the output of the square root calculator with the output of the threshold calculator.