JP4387880B2 - Clutter sorting method and clutter sorting system - Google Patents

Description

  The present invention relates to a clutter sorting method and a clutter sorting system for sorting a target and a clutter in the field of radar signal processing.

  2. Description of the Related Art Conventionally, a radar signal processing apparatus that separates clutter, which is an unnecessary reflection signal from a target and other than the target, is known (see, for example, the conventional technology column of Patent Document 1). FIG. 9 is a block diagram showing the configuration of an example of this type of conventional radar signal processing apparatus.

  The radar signal processing apparatus includes an eraser 1, N (N is a positive integer, the same applies hereinafter) filters 2-1 to 2-N, N clutter suppressors 3-1 to 3-N, and a maximum. It has a value selector 4.

  The eraser 1 erases the fixed clutter component that does not include the Doppler component from the input video signal. The input video signal is a digital video signal composed of an I component and a Q component. The video signal from which the fixed clutter component has been erased by the eraser 1 is sent to N filters 2-1 to 2-N.

  The N filters 2-1 to 2-N are composed of N band filters having different pass center frequencies. The N filters 2-1 to 2-N frequency-separate a target included in the video signal from which the fixed clutter component sent from the canceller 1 is deleted and a clutter having a Doppler transition such as a cloud. Used for. The outputs of the N filters 2-1 to 2-N are sent to N clutter suppressors 3-1 to 3-N, respectively.

  The N clutter suppressors 3-1 to 3 -N suppress clutter having Doppler transitions in each frequency band. In each of the N clutter suppressors 3-1 to 3 -N, a CFAR (Constant False Alarm Rate) process capable of keeping the false alarm probability constant and low is generally adopted as a process for suppressing the clutter. The The outputs of the N clutter suppressors 3-1 to 3 -N are sent to the maximum value selector 4.

  The maximum value selector 4 outputs the amplitude value of the signal sent from the N clutter suppressors 3-1 to 3 -N from which the fixed clutter component is eliminated and the clutter having the Doppler shift is suppressed for each range bin. And select the maximum amplitude. Then, the maximum value selector 4 synthesizes the maximum value of the amplitude of each range bin and outputs it as an output video signal.

According to the conventional radar signal processing apparatus, a fixed clutter component having no Doppler transition can be erased by the erasing device 1, and even a clutter having a Doppler transition has a certain extent in the range direction. It can be suppressed by the clutter suppressor 3-1 to 3 -N.
Japanese Patent No. 2865084 Supervised by Takashi Yoshida, “Revised Radar Technology”, IEICE, 1996.

  However, in the radar signal processing apparatus described in the above-described conventional technology column of Patent Document 1, the clutter suppressor is effective only for clutter having a certain extent in the range direction, and the spread in the range direction is not effective. Small clutter is not suppressed, and is included in the output video signal and output.

  The clutter separation method and the clutter separation system using the clutter separation method disclosed in Patent Document 1 are effective for a clutter having a small extent in the range direction and a certain extent in the frequency direction. Clutter having a small spread and a small spread in the frequency direction is not suppressed and is included in the output video signal and output.

  A specific example of such a clutter having a small spread in the range direction and a small spread in the frequency direction is the disappearance of the fixed clutter having a slight Doppler shift output from the eraser. The remaining fixed clutter is not suppressed by the clutter suppressor in the subsequent stage because the spread in the range direction is small. In fact, even fixed clutter is known to have a slight Doppler transition, and the eraser cannot completely erase the fixed clutter, and the remaining fixed clutter is Included in the output. As a result, there is a drawback that the target and the clutter cannot be distinguished.

  The present invention has been made to solve the above-described drawbacks, and it is an object of the present invention to provide a clutter sorting method and a clutter sorting system that can suppress fixed clutter that has remained unerased by an eraser.

  In the present invention, a fixed clutter having a slight Doppler transition is output from the eraser without being completely erased even by the eraser, but its energy is concentrated in the vicinity of the center frequency of zero. This is made by paying attention to the fact that it is possible to determine the presence or absence of a fixed clutter that has disappeared by the output of a bandpass filter having a zero pass center frequency.

That is, in order to solve the above-described problem, the clutter classification method according to the first aspect of the present invention includes a filtering step of passing a signal in which the fixed clutter component is substantially eliminated from the input signal for each of a plurality of bands having different pass center frequencies. A ratio calculating step for calculating a ratio between the amplitude value of the signal that has passed through the band whose pass center frequency is zero in the filtering step and the amplitude value of the signal that has passed the band other than the band whose pass center frequency is zero; and the pass center frequency Clutter processing that judges that a signal whose ratio calculated in the ratio calculation step exceeds a predetermined threshold among the signals that have passed a band other than the zero band is a clutter, and separates the signal by the clutter from the input signal And a step.

  The clutter classification method according to the second aspect of the present invention further includes a clutter suppression step of suppressing a clutter having a Doppler transition from a signal that has passed through a band other than a band having a pass center frequency of zero. A threshold setting step for setting a threshold according to the amplitude value of a signal that has passed through a band of zero frequency, a ratio calculated in the ratio calculation step, and a threshold set in the threshold setting step. A comparison step for generating a selection prohibition signal when the ratio exceeds a threshold as a result of comparison, and a signal corresponding to the selection prohibition signal generated in the comparison step among the signals in which clutter is suppressed in the clutter suppression step And a step of generating an output signal by synthesizing the maximum value of the amplitude of the other signals.

  A clutter classification method according to a third aspect of the present invention is the clutter classification method according to the first aspect of the present invention, wherein a clutter suppression step of suppressing a clutter having a Doppler transition from a signal that has passed through a band other than a band whose pass center frequency is zero. The clutter processing step includes a threshold setting step for setting a threshold according to an amplitude value of a signal that has passed through a band whose pass center frequency is zero, and the ratio and threshold calculated in the ratio calculation step. A comparison step for generating a selection prohibition signal when the ratio exceeds the threshold value as a result of comparison with the threshold value set in the setting step, and a comparison step among the signals whose clutter is suppressed in the clutter suppression step The detection of the target is prohibited based on the signal corresponding to the selection prohibition signal generated in, and the target is detected based on a signal other than the selection prohibition signal. Characterized in that a target detection steps.

  Further, the clutter classification method according to the fourth invention is the clutter classification method according to the first invention, wherein the ratio calculation step includes the amplitude value of the signal that has passed through the band whose pass center frequency is zero among the plurality of band-pass filters. And the amplitude value of the signal that has passed through the band other than the band where the pass center frequency is zero and near the pass center frequency is calculated.

Further, a clutter separation system according to a fifth aspect of the present invention is an eraser that substantially eliminates fixed clutter components from an input signal, and a plurality of bands having different pass center frequencies for passing a signal output from the eraser for each band. Ratio of the filter and the amplitude value of a signal output from a bandpass filter having a pass center frequency of zero among a plurality of bandpass filters to the amplitude value of a signal output from a bandpass filter other than the bandpass filter having a pass center frequency of zero A ratio calculator that calculates the ratio and a signal whose ratio calculated by the ratio calculator out of a band filter other than the bandpass filter whose pass center frequency is zero exceeds a predetermined threshold value as a clutter. And a clutter processing means for discriminating and separating a signal from the clutter from the input signal.

  The clutter classification system according to a sixth aspect of the present invention is the clutter classification system according to the fifth aspect of the present invention, wherein a clutter that suppresses a clutter having a Doppler transition from a signal that has passed through a bandpass filter other than a bandpass filter having a zero pass center frequency. The clutter processing means further includes a suppressor, and the clutter processing means is calculated by a threshold setting unit that sets a threshold according to an amplitude value of a signal output from a bandpass filter having a zero pass center frequency, and a ratio calculator As a result of comparing the ratio with the threshold set by the threshold setting unit, a comparator that generates a selection prohibition signal when the ratio exceeds the threshold and a signal output from the clutter suppressor A maximum value selector with a selection prohibition function for generating an output signal by synthesizing the maximum value of the amplitude of signals other than the signal corresponding to the selection prohibition signal output from the comparator It is characterized in.

  The clutter sorting system according to the seventh invention is the clutter sorting system according to the fifth invention, wherein a Doppler shift is generated from a signal that has passed through a bandpass filter other than the bandpass filter whose pass center frequency is zero among the plurality of bandpass filters. A clutter suppressor that suppresses clutter having a threshold value setter that sets a threshold according to an amplitude value of a signal output from a bandpass filter having a zero pass center frequency; A comparator that generates a selection prohibition signal and a clutter suppressor when the ratio exceeds the threshold value as a result of comparing the ratio calculated by the ratio calculator with the threshold value set by the threshold value setter. The detection of the target based on the signal corresponding to the selection prohibition signal output from the comparator among the signals output from the comparator is prohibited, and the target is detected based on the signal other than the selection prohibition signal. Characterized in that a target detection means for detecting.

  The clutter sorting system according to the eighth invention is the clutter sorting system according to the fifth invention, wherein the ratio calculator is configured to output a signal output from a bandpass filter having a pass center frequency of zero among a plurality of bandpass filters. A ratio between the amplitude value and the amplitude value of a signal output from a bandpass filter having a pass center frequency of zero other than the band pass filter having a pass center frequency of zero is calculated.

According to the clutter classification method according to the first aspect of the present invention, a signal in which the fixed clutter component is substantially eliminated from the input signal is passed through each of a plurality of bands having different pass center frequencies, and passed through a band having a pass center frequency of zero. Calculate the ratio between the amplitude value of the signal and the amplitude value of the signal that has passed through a band other than the band whose pass center frequency is zero, and the ratio of the signals that have passed through the band other than the band whose pass center frequency is zero is a predetermined ratio. Since the signal exceeding the threshold is judged as clutter, it is classified, so when the fixed clutter component is erased from the input signal, it remains unerased and the signal passes through a band other than the band where the pass center frequency is zero. Can be classified as clutter. Therefore, by suppressing the separated clutter, it is possible to suppress the fixed clutter that remains when the fixed clutter component is erased from the input signal.

  In addition, according to the clutter classification method according to the second aspect of the present invention, as a result of comparing the threshold value and the ratio according to the amplitude value of the signal that has passed through the band whose pass center frequency is zero, the ratio exceeds the threshold value. Of the signal other than the signal corresponding to the selection prohibition signal among the signals in which the clutter having the Doppler transition is suppressed from the signal that has passed the band other than the band where the pass center frequency is zero. Since the output signal is generated by synthesizing the maximum value, the signal corresponding to the selection prohibition signal, in other words, the signal remaining when the fixed clutter component is erased from the input signal is excluded from the synthesis of the output signal. . Therefore, it is possible to suppress the fixed clutter that remains when the fixed clutter component is erased from the input signal.

  In addition, according to the clutter classification method according to the third aspect of the present invention, as a result of comparing the threshold value and the ratio according to the amplitude value of the signal that has passed through the band whose pass center frequency is zero, the ratio exceeds the threshold value. Detection of the target based on the signal corresponding to the selection prohibition signal among the signals that suppress the clutter having the Doppler transition from the signal that has passed the band other than the band whose pass center frequency is zero. Since the target is detected based on signals other than the selection prohibition signal, the signal corresponding to the selection prohibition signal, in other words, the signal that remains when the fixed clutter component is erased from the input signal, Excluded from the target. Accordingly, it is possible to prevent erroneous detection of the target due to the fixed clutter that remains when the fixed clutter component is erased from the input signal.

  In addition, according to the clutter classification method according to the fourth aspect of the present invention, the amplitude value of the signal that has passed through the band whose pass center frequency is zero and the band other than the band where the pass center frequency is zero among the plurality of band filters. Since the ratio of the amplitude value of the signal that has passed through the band near the pass center frequency of zero is calculated, the band where there is no fixed clutter remaining when the fixed clutter component is erased from the input signal, that is, the pass center frequency It is not necessary to calculate the ratio for bands other than those near zero. Therefore, the configuration is simplified and the processing for clutter sorting can be performed at high speed.

  Furthermore, according to the clutter sorting system according to the fifth to eighth inventions, the same effects as the clutter sorting methods according to the first to fourth inventions described above can be obtained.

  Hereinafter, embodiments of a clutter sorting method and a clutter sorting system according to the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals as those used in the column of the conventional technology are used for the parts corresponding to the components described in the column of the conventional technology.

  FIG. 1 is a block diagram showing the configuration of the clutter sorting system according to Embodiment 1 of the present invention. This clutter classification system includes an eraser 1, N + 1 filters (F0) 2-0 to filters (FN) 2-N, N clutter suppressors 3-1 to 3-N, and N ratio calculators 5. -1 to 5-N, N comparators 6-1 to 6-N, a threshold setting unit 7 and a maximum value selector 8 with a selection prohibiting function.

  The clutter separation system according to Embodiment 1 of the present invention is different from the conventional clutter separation system shown in FIG. 9 in that a filter (F0) 2-0 that is a bandpass filter having a zero pass center frequency and a ratio calculator 5-1 5-N, comparators 6-1 to 6-N, and a threshold setting device 7 are added, and the maximum value selector 4 is replaced with a maximum value selector 8 with a selection prohibition function. .

  The eraser 1 erases the fixed clutter component not including the Doppler component from the input video signal by performing, for example, a two-pulse canceller process. The input video signal is a digital video signal composed of an I component and a Q component. The video signal in which the fixed clutter having a slight Doppler transition remains despite the deletion of the fixed clutter component by the canceller 1 is sent to N + 1 filters (F0) 2-0 to filters (FN) 2-N. It is done.

  The N filters (F1) 2-1 to the filter (FN) 2-N are composed of N band filters having different center frequencies. The filters 2-1 to 2-N are used to frequency-separate a target included in a video signal from which the fixed clutter component sent from the canceller 1 is deleted and a clutter having a Doppler shift such as a cloud. Is done. The outputs of the filter (F1) 2-1 to filter (FN) 2-N are sent to N clutter suppressors 3-1 to 3-N and N ratio calculators 5-1 to 5-N, respectively. . The filter (F0) 2-0 is a band filter having a center frequency of zero. The output of the filter (F0) 2-0 is sent to N ratio calculators 5-1 to 5-N and a threshold value setter 7.

  The clutter suppressors 3-1 to 3 -N suppress clutter having a Doppler shift in each frequency band. In each of the N clutter suppressors 3-1 to 3 -N, CFAR (Constant False Alarm Rate) processing capable of keeping the false alarm probability constant and low is adopted as processing for suppressing clutter. . The outputs of the clutter suppressors 3-1 to 3-N are sent to the maximum value selector 8 with a selection prohibition function.

  The ratio calculators 5-1 to 5-N delete the fixed clutter components transmitted from the filter (F1) 2-1 to filter (FN) 2-N and perform frequency separation on the amplitude values AF1 to AF1 of the video signal. Ratios AF0 / AF1 to AF0 / AFN between the AFN and the amplitude value AF0 of the video signal including the component having the zero center frequency and the fixed clutter component sent from the filter (F0) 2-0 are calculated. . Here, the ratios AF0 / AF1 to AF0 / AFN can be considered as the ratio of the power of the video signal. The ratios AF0 / AF1 to AF0 / AFN calculated by the ratio calculators 5-1 to 5-N are sent to the comparators 6-1 to 6-N, respectively.

  The threshold setter 7 calculates a threshold based on the amplitude value AF0 of the video signal sent from the filter (F0) 2-0 and sets it in the comparators 6-1 to 6-N. In this case, when the amplitude value AF0 of the video signal is small enough to correspond to the noise level, it is determined that there are few fixed clutters remaining unerased, and the threshold value is set low. When the amplitude value AF0 of the video signal is large, the threshold value is set high in order to prevent the fixed clutter that has remained unerased from being output without being suppressed. Note that the threshold value can be configured to set different values TH1 to THN for each filter in consideration of the difference in the degree of suppression with respect to the fixed clutter of each filter remaining unerased.

  Comparators 6-1 to 6-N are ratios AF0 / AF1 to AF0 / AFN sent from ratio calculators 5-1 to 5-N, and threshold value TH1 sent from threshold setter 7. Input ~ THN and compare. For example, the comparator 6-1 compares the ratio AF0 / AF1 sent from the ratio calculator 5-1 with the threshold value TH1 sent from the threshold setting unit 7, and the ratio AF0 / AF1 is the threshold value. If it is greater than TH1, it is determined that the fixed clutter has disappeared, and a selection prohibition signal is sent to the maximum value selector 8 with a selection prohibition function.

  In the maximum value selector 8 with a selection prohibition function, the selection prohibition signals output from the comparators 6-1 to 6-N and the outputs of the clutter suppressors 3-1 to 3-N are input, and the clutter suppressor 3 is input. The amplitude value of the signal that does not correspond to the selection inhibition signal among the outputs of −1 to 3−N is compared for each same range bin, and the maximum value is selected. Then, the maximum value selector 8 with a selection prohibition function synthesizes the maximum value of the amplitude of each range bin and outputs it as an output video signal.

  Next, the operation of the clutter sorting system according to the first embodiment of the present invention configured as described above will be described with reference to the flowchart shown in FIG.

  First, the fixed clutter component is erased (step S10). That is, the eraser 1 erases the fixed clutter component from the input video signal and sends it to the filter (F0) 2-0 to the filter (FN) 2-N. In this case, in the eraser 1, the fixed clutter component is not completely removed, and a signal in which the fixed clutter having a slight Doppler transition remains is sent to the filter (F0) 2-0 to the filter (FN) 2-N. .

  Next, filtering is performed (step S11). That is, the filter (F0) 2-0 passes a signal in a band whose center frequency is zero, and the filters (F1) to (FN) 2-N pass signals in other frequency bands.

  Next, it is checked whether or not the signal has passed through the filter (F0) (step S12). Here, when it is determined that the signal has passed through the filter (F0), a threshold value is set (step S13). That is, the threshold value setter 7 calculates a threshold value based on the amplitude value AF0 of the video signal sent from the filter (F0) 2-0 and sets it in the comparators 6-1 to 6-N. Thereafter, the sequence proceeds to step S15.

  On the other hand, when it is determined in step S12 that the signal does not pass through the filter (F0), that is, the signal passes through the filter (F1) 2-1 to the filter (FN) 2-N, the ratio is calculated. (Step S14). Specifically, the ratio calculators 5-1 to 5-N include the amplitude values AF1 to AFN of the signals transmitted from the filter (F1) 2-1 to the filter (FN) 2-N and the filter (F0). Ratios AF0 / AF1 to AF0 / AFN with the amplitude value AF0 of the signal sent from 2-0 are calculated. Thereafter, the sequence proceeds to step S15.

  In step S15, a selection prohibition signal is generated. That is, the comparators 6-1 to 6 -N receive the ratios AF 0 / AF 1 to AF 0 / AFN sent from the ratio calculators 5-1 to 5 -N and the threshold sent from the threshold value setter 7. Values TH1 to THN are input and compared individually. As a result of this comparison, a signal whose ratios AF0 / AF1 to AF0 / AFN are larger than the threshold values TH1 to THN is determined to be a fixed clutter that has remained, and a selection prohibition signal is generated. This selection prohibition signal is sent to the maximum value selector 8 with a selection prohibition function.

  Next, clutter suppression is performed (step S16). That is, the clutter suppressors 3-1 to 3-N suppress each of the clutters having Doppler transitions in each frequency band included in the signals sent from the filters (F1) 2-1 to (FN) 2-N. To do. This clutter suppression can be performed at an arbitrary step after the filtering is performed.

  Next, an output video signal is generated (step S17). That is, the maximum value selector 8 with a selection prohibition function outputs the selection prohibition signal output from the comparators 6-1 to 6-N in step S15 and the clutter suppressors 3-1 to 3-N in step S16. And the amplitude value of the signal not corresponding to the selection prohibition signal among the signals output from the clutter suppressors 3-1 to 3-N is compared for each same range bin, and the maximum value is selected. Then, the maximum value selector 8 with a selection prohibition function synthesizes the maximum value of the amplitude of each range bin and outputs it as an output video signal. As a result, even if the disappearance of the fixed clutter having a slight Doppler transition occurs at the output of the eraser 1, an output video signal that does not include that remains is output.

  Next, the operation of the clutter classification was simulated by the clutter classification system configured as described above, and the result will be described.

  Now, an input video signal including a fixed clutter having a certain extent in the frequency direction as shown in FIG. 3A has a filter characteristic in which the gain is minimized when the center frequency is zero as shown in FIG. Consider a case where the data is input to the eraser 1 having the same. In this case, as shown in FIG. 3C, the portion where the passing center frequency is zero is erased, but the fixed clutter having a slight Doppler transition before and after the portion remains unerased. As a result, the remaining fixed clutter (the hatched portion in FIG. 3C) disappears from the filter (F1) and the filter (FN) before and after the filter (F0). Since this fixed clutter has no spread in the range direction, it is output without being suppressed by the clutter suppressors 3-1 to 3 -N.

  In the clutter separation system described in the section of the prior art, the amplitude value of the signal including the remaining fixed clutter output from the clutter suppressor 3-1 to 3-N is compared for each same range bin, and the maximum amplitude value is obtained. Is selected, and the maximum amplitude of each range bin is synthesized and output as an output video signal.

  Therefore, there is a problem that echoes due to non-target clutter are observed. On the other hand, in the clutter classification system according to the first embodiment of the present invention, the amplitude values of the remaining signals excluding the signals including the remaining fixed clutter output from the clutter suppressors 3-1 to 3-N are obtained. For each same range bin, the maximum amplitude value is selected, the maximum amplitude value of each range bin is synthesized, and output as an output video signal. Therefore, no echoes due to non-target clutter are observed.

  FIG. 4 shows the characteristics of the filter (F0) 2-0 to the filter (FN) 2-N. However, in order to simplify the description, the case where N = 1, that is, the case where only the filter (F0) 2-0 and the filter (F1) 2-1 exist is shown. The filter (F0) 2-0 is configured to have the maximum gain when the center frequency is zero, and the filter (F1) 2-1 has the maximum gain when the center frequency is ± 0.5. It is configured as follows.

  Accordingly, when there is a fixed clutter that has disappeared, the filter (F0) 2-0 outputs the fixed clutter almost as it is, and is used to take out the fixed clutter that has disappeared. On the other hand, the filter (F1) 2-1 is used for taking out a target because it outputs almost no fixed clutter and outputs a signal in another band even if there remains a fixed clutter that has disappeared.

  FIG. 5 shows a simulation result when a signal including a target and noise is input to the clutter separation system including the filter (F0) 2-0 and the filter (F1) 2-1 having the characteristics shown in FIG. .

  FIG. 5A shows an input signal including a target and noise, and the horizontal axis shows a signal whose frequency is swept. FIG. 5B shows the amplitude value AF0 of the signal output from the filter (F0) 2-0 and the signal output from the filter (F1) 2-1 when the input signal shown in FIG. 5A is input. The amplitude value AF1 is shown.

  The waveform of the amplitude value AF0 shown in FIG. 5B has the following meaning. That is, as shown in FIG. 4, the gain of the filter (F0) 2-0 is maximized at the position where the frequency is “0”, but the signal appearing at that position is the fixed clutter that has remained unerased by the eraser 1. Therefore, the amplitude value AF0 becomes small. Further, since the gain of the filter (F0) 2-0 is minimized at the position where the frequency is “0.5”, the amplitude value AF0 becomes small at that position. On the other hand, the waveform of the amplitude value AF1 shown in FIG. 5B has the following meaning. That is, as shown in FIG. 4, the gain of the filter (F1) 2-1 is maximized at the position where the frequency is “0.5” and is minimized at the position where the frequency is “0”. Becomes smaller at a position where the frequency is “0 (1.0 is the same)”.

  FIG. 5C shows the ratio AF0 / AF1 output from the ratio calculator 5-1. When this ratio AF0 / AF1 is larger than the threshold value TH1 from the threshold setting device 7, it is determined that the clutter.

  FIG. 6 shows a simulation result when a signal including clutter and noise is input to the clutter sorting system including the filter (F0) 2-0 and the filter (F1) 2-1 having the characteristics shown in FIG. .

  FIG. 6A shows an input signal including clutter and noise, and the horizontal axis indicates the number of samples (time). FIG. 6B shows the amplitude value AF0 of the signal output from the filter (F0) 2-0 and the signal output from the filter (F1) 2-1 when the input signal shown in FIG. 6A is input. The amplitude value AF1 is shown.

  The waveform of the amplitude value AF0 shown in FIG. 6B has the following meaning. That is, the output of the filter (F0) 2-0 shows a high level because the filter (F0) 2-0 passes through the fixed clutter remaining unerased by the eraser 1 as it is. On the other hand, the output of the filter (F1) 2-1 passes only a part of the fixed clutter remaining unerased by the eraser 1, so that the output of the filter (F1) 2-1 is compared with the output of the filter (F0) 2-0. Become a low level.

  FIG. 6C shows the ratio AF0 / AF1 output from the ratio calculator 5-1. When this ratio AF0 / AF1 is larger than the threshold value TH1 from the threshold setting device, it is determined as clutter.

  As described above, according to the clutter sorting system according to the first embodiment of the present invention, the signal from which the fixed clutter component is eliminated from the input signal is passed through each of the plurality of bands having different pass center frequencies, and the pass center frequency is passed. Calculate the ratio between the amplitude value of the signal that has passed through the zero band and the amplitude value of the signal that has passed through the band other than the band whose center frequency is zero, and the signal that has passed through the band whose center frequency is zero. Is compared with the threshold value according to the amplitude value of the signal, and if the ratio exceeds the threshold value, a selection prohibition signal is generated, and the Doppler shift is performed from the signal that has passed through a band other than the band whose pass center frequency is zero. An output signal is generated by synthesizing the maximum value of the amplitude of signals other than the signal corresponding to the selection prohibition signal among the signals with suppressed clutter.

  Therefore, a signal corresponding to the selection prohibition signal, in other words, a signal remaining when the fixed clutter component is erased from the input signal is excluded from the synthesis of the output signal. As a result, it is possible to suppress the fixed clutter that remains when the fixed clutter component is erased from the input signal.

  In addition, the signal whose ratio of the signal that has passed through the band other than the band whose pass center frequency is zero exceeds the predetermined threshold is determined as the clutter and is classified, so that the fixed clutter component is eliminated from the input signal. In this case, the signal that has disappeared and has passed through a band other than the band having a zero pass center frequency is determined as clutter and can be classified. Therefore, by suppressing the sorted clutter, it is possible to suppress the fixed clutter that remains when the fixed clutter component is erased from the input signal.

  The clutter sorting system according to the second embodiment of the present invention is obtained by applying the clutter sorting system according to the first embodiment to a target detection device.

  FIG. 7 is a block diagram showing the configuration of the clutter sorting system according to Embodiment 2 of the present invention. This clutter classification system is configured by replacing the maximum value selector 8 with a selection prohibition function in the clutter classification system according to the first embodiment shown in FIG. 1 with target detectors 9-1 to 9-N with a detection prohibition function. Has been.

  The target detectors 9-1 to 9-N with detection prohibition function receive the outputs of the clutter suppressors 3-1 to 3-N and the selection prohibition signals output from the comparators 6-1 to 6-N, respectively. Only the target detector with detection prohibition function to which the selection prohibition signal is not input outputs the detection information.

  As described above, according to the clutter sorting system according to the second embodiment of the present invention, the target detector with detection prohibition function that has received the selection prohibition signal from the comparators 6-1 to 6-N does not output detection information. Therefore, the signal including the fixed clutter that remains when the fixed clutter component is erased from the input video signal is excluded from the target detection target. Accordingly, it is possible to prevent erroneous detection of the target due to the fixed clutter that remains when the fixed clutter component is erased from the input signal.

  In the clutter classification system according to the third embodiment of the present invention, attention is paid to the fact that the fixed clutter that remains unerased when the fixed clutter component is erased from the input video signal appears before and after the filter having a zero pass center frequency. The selection prohibiting process of the maximum value selector 8 with the selection prohibiting function in the clutter sorting system according to the first embodiment is performed only for the outputs of the filters before and after the filter having a zero pass center frequency.

  FIG. 8 is a block diagram showing the configuration of the clutter sorting system according to Embodiment 3 of the present invention. This clutter sorting system includes ratio calculators 5-2 to 5- (N-1) and comparators 6-2 to 6- (N-1) from the clutter sorting system according to the first embodiment shown in FIG. Removed and configured.

  The operation of the clutter sorting system according to the third embodiment is that only the outputs of the clutter suppressor 3-1 and the clutter suppressor 3-N are subject to selection in the maximum value selector 8 with the selection prohibition function. The operation is the same as that of the clutter sorting system according to the first embodiment.

  As described above, according to the clutter classification system according to the third embodiment of the present invention, the amplitude value of the signal that has passed through the filter (F0) 2-0 and the filters (F1) before and after the filter (F0) 2-0. ) 2-1 and the ratio of the amplitude value of the signal that has passed through the filter (FN) 2-N are calculated, and this ratio is compared with a threshold value to compare the filter (F1) 2-1 and the filter (FN) 2- Since the selection prohibition signal is generated only for the signal that has passed through N, the ratio calculators 5-2 to 5- (N-1) and the comparators 6-2 to 6- (N-1) become unnecessary. .

  As a result, substantially the same effect as the clutter sorting system according to the first embodiment can be obtained, the configuration of the clutter sorting system is simplified, and further, the processing for clutter sorting can be performed at high speed.

  In the clutter separation system according to the third embodiment, only the two filters (F1) 2-1 and the filter (FN) 2-N before and after the filter (F0) 2-0 are used to generate the selection prohibition signal. It is also possible to use three or more filters in the vicinity of the filter (F0) 2-0 to generate the selection prohibition signal.

  The present invention can be applied to a radar device, a sonar device, or the like provided with an eraser for erasing fixed clutter.

It is a block diagram which shows the structure of the clutter classification system which concerns on Example 1 of this invention. It is a flowchart which shows operation | movement of the clutter classification system based on Example 1 of this invention. It is a figure for demonstrating operation | movement of the clutter classification system which concerns on Example 1 of this invention. It is a figure which shows the characteristic of the filter used with the clutter classification system which concerns on Example 1 of this invention. It is a figure which shows the simulation result when the signal containing a target and noise is input into the clutter classification system which concerns on Example 1 of this invention. It is a figure which shows the simulation result when the signal containing a clutter and noise is input into the clutter classification system which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the clutter classification system which concerns on Example 2 of this invention. It is a block diagram which shows the structure of the clutter classification system which concerns on Example 3 of this invention. It is a block diagram which shows the structure of an example of the conventional radar signal processing apparatus.

Explanation of symbols

1 Eraser 2-0 to 2-N Filter 3-1 to 3-N Clutter Suppressor 4 Maximum Value Selector 5-1 to 5-N Ratio Calculator 6-1 to 6-N Comparator 7 Threshold Setting 8 Maximum value selector with selection prohibition function 9-1 to 9-N Target detector with detection prohibition function

Claims (8)

A filtering step of passing a signal, in which the fixed clutter component is substantially eliminated from the input signal, for each of a plurality of bands having different pass center frequencies;
A ratio calculating step for calculating a ratio between an amplitude value of a signal that has passed through a band whose pass center frequency is zero in the filtering step and an amplitude value of a signal that has passed through a band other than the band whose pass center frequency is zero;
A signal whose ratio calculated in the ratio calculation step exceeds a predetermined threshold among signals that have passed through a band other than the band where the pass center frequency is zero is determined as clutter. A clutter processing step for separating signals;
A clutter separation method characterized by comprising: Further comprising a clutter suppression step of suppressing clutter having a Doppler transition from a signal that has passed through a band other than the band where the pass center frequency is zero.
The clutter processing step includes:
A threshold setting step for setting a threshold according to an amplitude value of a signal that has passed through a band in which the pass center frequency is zero;
A comparison step of generating a selection inhibition signal when the ratio exceeds the threshold value as a result of comparing the ratio calculated in the ratio calculation step with the threshold value set in the threshold value setting step; ,
Synthesizing the maximum value of the amplitude of signals other than the signal corresponding to the selection inhibition signal generated in the comparison step among the signals whose clutter is suppressed in the clutter suppression step, and generating an output signal;
The clutter separation method according to claim 1, further comprising: Further comprising a clutter suppression step of suppressing clutter having a Doppler transition from a signal that has passed through a band other than the band where the pass center frequency is zero.
The clutter processing step includes:
A threshold setting step for setting a threshold according to an amplitude value of a signal that has passed through a band in which the pass center frequency is zero;
A comparison step of generating a selection inhibition signal when the ratio exceeds the threshold value as a result of comparing the ratio calculated in the ratio calculation step with the threshold value set in the threshold value setting step; ,
A target that prohibits detection of a target based on a signal corresponding to the selection prohibition signal generated in the comparison step among signals in which clutter is suppressed in the clutter suppression step, and detects a target based on a signal other than the selection prohibition signal A detection step;
The clutter separation method according to claim 1, further comprising: The ratio calculating step includes:
Of the plurality of bandpass filters, the amplitude value of the signal that has passed through the band whose pass center frequency is zero and the band other than the band where the pass center frequency is zero, and pass the band near the pass center frequency is zero. The clutter classification method according to claim 1, wherein a ratio with the amplitude value of the processed signal is calculated. An eraser that generally eliminates the fixed clutter component from the input signal;
A plurality of bandpass filters having different pass center frequencies for passing the signal output from the canceller for each band;
A ratio of an amplitude value of a signal output from a bandpass filter whose pass center frequency is zero among the plurality of bandpass filters to an amplitude value of a signal output from a bandpass filter other than the bandpass filter whose pass center frequency is zero. A ratio calculator to calculate,
Of the signals output from band filters other than the band filter whose pass center frequency is zero, a signal whose ratio calculated by the ratio calculator exceeds a predetermined threshold is determined as clutter, and the input signal A clutter processing means for separating signals from the clutter from
Clutter sorting system characterized by comprising A clutter suppressor for suppressing clutter having a Doppler shift from a signal that has passed through a bandpass filter other than a bandpass filter having a zero pass center frequency;
The clutter processing means includes:
A threshold value setter for setting a threshold value according to the amplitude value of the signal output from the bandpass filter whose pass center frequency is zero;
A comparator that generates a selection prohibition signal when the ratio exceeds a threshold value as a result of comparing the ratio calculated by the ratio calculator with the threshold value set by the threshold value setter; ,
A maximum value selector with a selection prohibition function that generates an output signal by synthesizing the maximum value of the amplitude of signals other than the signal corresponding to the selection prohibition signal output from the comparator among the signals output from the clutter suppressor. When,
The clutter separation system according to claim 5, further comprising: A clutter suppressor for suppressing clutter having a Doppler shift from a signal that has passed through a bandpass filter other than a bandpass filter having a pass center frequency of zero among the plurality of bandpass filters;
The clutter processing means includes:
A threshold value setter for setting a threshold value according to the amplitude value of the signal output from the bandpass filter whose pass center frequency is zero;
A comparator that generates a selection prohibition signal when the ratio exceeds a threshold value as a result of comparing the ratio calculated by the ratio calculator with the threshold value set by the threshold value setter; ,
Target detection means for prohibiting detection of a target based on a signal corresponding to a selection prohibition signal output from the comparator among signals output from the clutter suppressor and detecting a target based on a signal other than the selection prohibition signal When,
The clutter separation system according to claim 5, further comprising: The ratio calculator is
A bandpass filter other than a bandpass filter having a zero pass center frequency and a signal amplitude value output from a bandpass filter having a pass center frequency of zero among the plurality of bandpass filters, wherein the pass center frequency is near zero 6. The clutter sorting system according to claim 5, wherein a ratio with the amplitude value of the signal output from the band filter is calculated.

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