JPH10246776A - Clutter suppressing device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately suppress clutter by obtaining estimated clutter spectrum in accordance with the present state using a frequency spectrum actually obtained. SOLUTION: Out of spectrum waveform of reception signal of a radar separated from a Doppler filter 2, a reference spectrum and a spectrum to be processed are taken and the clutter peak frequency of the spectrum to be processed is detected in a peak frequency detection part 4, clutter peak intensity is detected in a peak intensity detection part 6, and according to these detection results, frequency correction and intensity correction are made in a frequency correction part 5 and an intensity correction part 7 so that an estimation clutter spectrum is produced. Then difference between the obtained estimation clutter spectrum and the spectrum to be processed is calculated so as to suppress the clutter of the spectrum to be processed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clutter suppressing apparatus for a radar, and more particularly to a reflected wave caused by clutter other than a target signal among received signals in a short-wave radar for searching the sea using surface waves in the HF band. The present invention relates to a clutter suppressing device for removing the noise.

[0002]

2. Description of the Related Art A conventional clutter suppressing device for removing unnecessary signals other than reflected echoes from a target signal such as clutter received by an HF band radar is disclosed in, for example, JP-A-7-43452. There is a clutter suppression device. FIG. 13 is a configuration diagram showing a configuration of a conventional clutter suppressing device disclosed in the publication. In the figure, 4a,
4b is a center frequency estimating means, 14a and 14b are median filters, 21a and 21b are bandwidth estimating means, 22a and
22b is a notch filter selecting means, 23a and 23b are filter load adjusting means, 24 is a filter processing section, 25 is a low frequency band pass filter (hereinafter, referred to as LPF), 26 is a high frequency band pass filter (hereinafter, referred to as HPF). ).

Next, the operation of the clutter suppressing apparatus shown in FIG. 13 will be described. First, the received signal is divided into HP signals.
The data is transferred to F26 and LPF25. In these filters, clutter in the positive frequency domain and clutter in the negative frequency domain are respectively extracted. Next, the center frequencies of the extracted positive and negative clutter signals are estimated by the center frequency estimating means 4a and 4b. The method used here is a method of estimating the center frequency of clutter using the lattice reflection coefficient based on the Burg method.

Next, these center frequencies are input to median filters 14a and 14b, and the median is calculated. At the same time, the spectral bandwidth of the clutter in the input signal is estimated by the bandwidth estimating means 21a and 21b, and the result is input to the notch filter selecting means 22a and 22b. The notch filter selecting means 22a, 22b selects a notch filter having an optimum removal bandwidth according to the bandwidth of the clutter from among several kinds of notch filters prepared in advance, and furthermore, the filter load adjusting means 23a, b
, A filter load adjustment for moving the center of the notch to the center frequency of the clutter is performed.
At 4, the unnecessary signal of the received signal is removed.

Next, a description will be given of the Doppler frequency characteristic of a reflected echo from the sea surface in a short-wave radar using a surface wave in the HF band for searching on the sea. Here, FIG.
FIG. 3 is a frequency spectrum diagram showing a reflection echo from the sea surface. The two peaks 31a and 31b correspond to the Bragg line (B
ragg line). This is a schematic representation of the reflection from the sea surface that is significantly different from the others. Considering the slight shift of the Doppler frequency due to ocean currents, the Doppler frequency fB where the Bragg line appears can be expressed by the following equation (1). It has been known.

[0006]

(Equation 1)

In the above equation (1), g is the acceleration of gravity, f0 is the transmission center frequency, and C is the speed of light. The peak intensity and bandwidth of the Bragg line vary significantly with sea level conditions, and the shape of the Bragg line is not always the case, and changes with sea level conditions. In addition, the Bragg line is 20 dB compared to the echo reflected from the target.
Often larger than the extent. 31c is due to multiple reflections from the sea surface called a continuum, and appears between the positive and negative Bragg lines. In the HF band surface wave radar, such a signal from the sea surface becomes clutter,
This is a factor that hinders target detection.

[0008]

SUMMARY OF THE INVENTION The above conventional H
The clutter suppression device in the short wave radar using the F-band surface wave is selected from several types of notch filters prepared in advance.
Since the notch filter having the optimum removal bandwidth according to the bandwidth of the clutter is selected, it is difficult to remove the clutter according to the actual clutter. Further, as shown in FIG. 13, since it is configured by a notch filter in the time domain, only a symmetric notch can be configured. In particular, regarding the Bragg line, it was difficult to select a filter according to the shape of the clutter due to the non-uniform shape. For the above reasons, if the stopband of the filter is too wide, the target other than the clutter will be erased, and if the stopband is too narrow, the clutter will remain and the target will be erroneously set. There were problems such as detection. Also, it is difficult to select a filter that matches the clutter intensity,
If the depth of the notch is too shallow, clutter will disappear,
Conversely, if the notch is too deep, there is a problem that the target may be erroneously detected by the edge.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to obtain an estimated clutter spectrum according to the present situation from an actually obtained frequency spectrum and to accurately suppress clutter. I have.

[0010]

A clutter suppression apparatus according to the present invention is a clutter suppression apparatus for removing unnecessary signal components contained in a received signal received by a radar in order to detect a target. A filter for obtaining a plurality of frequency spectra corresponding to a plurality of ranges from the received signal,
An estimated spectrum generating means for selecting a part of the plurality of frequency spectra obtained by the filter and generating an estimated spectrum based on the selected frequency spectrum; And a difference calculating means for obtaining a difference between the target frequency spectrum and the estimated spectrum.

The above-mentioned part of the frequency spectrum is a frequency spectrum in a range different from the frequency spectrum to be processed.

Further, the above-mentioned estimated spectrum generating means includes:
A frequency spectrum separated from the frequency spectrum to be symmetrical by a predetermined range or more is selected as the partial frequency spectrum.

Further, the estimated spectrum generating means generates an estimated spectrum by detecting the characteristic of the frequency spectrum to be processed and correcting the characteristic of the selected frequency spectrum according to the detection result. It is.

Further, the estimated spectrum generating means detects the characteristics of a plurality of frequency spectra constituting the partial frequency spectrum, and generates an estimated spectrum according to the detection result.

Further, the characteristic is characterized in that it is a peak frequency.

Further, the characteristic is characterized in that it is an intensity of a frequency spectrum.

The estimated spectrum generating means detects a change in the peak frequency in the range direction based on a plurality of frequency spectra constituting the partial frequency spectrum, and generates an estimated spectrum based on the detection result. It is characterized by the following.

The clutter suppression method according to the present invention is a clutter suppression method for removing an unnecessary signal component included in a received signal received by a radar in order to detect a target object. Receiving a wave, a frequency spectrum generating step of obtaining a plurality of frequency spectra corresponding to a plurality of ranges from the received signal obtained in the receiving step, and a plurality of frequency spectra obtained in the frequency spectrum generating step A selection step of selecting a part of the frequency spectrums therein, an estimation spectrum generation step of generating an estimation spectrum based on the frequency spectrum selected in the selection step, and a frequency spectrum to be processed among the plurality of frequency spectrums And the above estimated spectrum generation It is characterized in that it has a, a difference calculation step of calculating a difference between the estimated spectrum generated in step.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. The clutter suppressing apparatus according to this embodiment calculates the spectrum of all the range bins by the Doppler filter of the received signal, and then periodically updates a typical spectrum of the clutter at a short distance as a reference spectrum. After correcting the peak frequency and the peak intensity to match the spectrum of each processing range bin, the reference spectrum after frequency correction and intensity correction is removed from the spectrum of the processing range bin.

Hereinafter, this embodiment will be described with reference to the drawings. FIG. 1 is a block diagram of a clutter suppressing apparatus according to this embodiment. In the figure, reference numeral 1 denotes a receiving unit that receives a reflected wave of a transmitted radio wave and obtains a reception signal of a predetermined number of pulses from the reflected wave. Reference numeral 2 denotes a Doppler filter provided on the output side of the receiving unit 1. Is the Doppler filter 2
Is a reference vector storage unit provided on the output side of
Is a peak frequency detector provided on the output side of the Doppler filter 2, and the peak frequency detector 4 is connected in parallel with the reference spectrum storage 3.

Reference numeral 5 denotes a frequency correction unit provided on the output side of the reference spectrum storage unit 3 and the peak frequency detection unit 4, reference numeral 6 denotes a peak intensity detection unit provided on the output side of the peak frequency detection unit 4, Reference numeral 7 denotes an intensity correction unit provided on the output side of the peak intensity detection unit 6 and the frequency correction unit 5, and reference numeral 8 denotes a clutter removal processing unit provided on the output side of the peak intensity detection unit 6 and the intensity correction unit 7. , 9 are target detection units provided on the output side of the clutter removal processing unit 8.

Next, the operation of the clutter suppressing apparatus according to this embodiment will be described. The receiving unit 1 receives a reflected wave of the transmitted radio wave and outputs a reception signal of a predetermined number of pulses obtained from the reflected wave. A reception signal having a predetermined number of pulses output from the reception unit 1 is input to the Doppler filter 2 and separated into predetermined frequency components for each range bin. The Doppler filter 2 is configured by, for example, an FFT processing circuit. FIG. 2 shows the concept when the Doppler filter 2 is processed by the FFT processing circuit.

In FIG. 2, reference numeral 2 denotes a Doppler filter constituted by an FFT processing circuit. (A) is a reception signal output from the reception unit 1 and input to the FFT processing circuit. The range indicates the distance from the clutter suppressing device, and the hit indicates the received pulse.
(B) shows a frequency spectrum obtained by the Doppler filter 2. The frequency spectrum shown in FIG. 2B shows a spectrum for each range bin. And, in (b), 31a and 31b are frequency spectra appearing by reflection from the sea surface called Bragg lines. The peak frequency of this Bragg line varies with distance and time under the influence of ocean currents. In addition, the intensity and bandwidth of the Bragg line also fluctuate significantly depending on sea surface conditions and time. Such a reflection spectrum from the sea surface called a Bragg line becomes clutter. In (b), reference numeral 32 denotes a spectrum obtained from a reflected echo from the target, that is, a reflected wave from the target.

In order to detect a target accurately with no influence from clutter by extracting only the reflection spectrum from the target from the frequency spectrum shown in FIG. The following processing is performed.

First, of the spectral waveforms obtained for each range bin obtained in this way, there is no reflected echo from the target, and the clutter signal level to noise ratio (C
/ N ratio) is input to the reference spectrum storage unit 3 as a reference spectrum and updated.
Here, the reason why the condition of short distance is set is that generally, the closer the distance is, the larger the C / N is, and therefore, the nature of clutter often appears in the spectrum shape.

The update to the reference spectrum storage unit 3 is performed periodically. The reason why the reference spectrum is periodically updated in this manner is that the clutter spectrum always fluctuates depending on the sea surface condition, and therefore the clutter spectrum always has the current reference spectrum.

Next, the reference spectrum storage unit 3 detects the peak frequency and intensity at the peak frequency of the spectrum waveform input as the reference spectrum, and holds the detection result. Further, the spectrum waveform of each range bin output from the Doppler filter 2 is input to the peak frequency detection unit 4, and the peak frequency of the Bragg line is detected for each range bin.

The method of detecting the peak frequency of the Bragg line will be described in more detail. The peak frequency of the Bragg line when there is no current can be uniquely determined by the frequency of the transmission radio wave as shown in the equation (1). Further, the spectral waveform in the case where there is an ocean current is shifted to the left and right by the Doppler frequency generated by the ocean current. Therefore, by estimating the maximum Doppler shift due to the ocean current from the maximum possible ocean current velocity, and detecting the peak within the range of the maximum Doppler shift due to the ocean current around the Doppler frequency of the Bragg line calculated from the transmission frequency , The peak frequency of the clutter can be determined.

The frequency correction unit 5 shifts the reference spectrum in the frequency direction so that the peak frequency of the reference spectrum matches the peak frequency of the Bragg line of each processing range bin detected by the peak frequency detection unit 4. . Next, the peak intensity detector 6 detects the intensity at the peak frequency of the Bragg line in each processing range bin. The intensity correcting unit 7 corrects the intensity of the reference spectrum so that the intensity of the peak frequency of the reference spectrum matches the intensity at the peak frequency of the Bragg line of each processing range bin detected by the peak intensity detecting unit 6.

The reference spectrum corrected by the frequency correction unit 5 and the intensity correction unit 7 is a result of estimating the clutter spectrum of the processing range bin. Hereinafter, this estimation result is referred to as an estimated clutter spectrum. Then, the clutter removal processing unit 8 removes unnecessary signals such as clutter by removing the estimated clutter spectrum of the processing range bin obtained in this manner from the spectrum of each processing range pin. The spectrum from which the unnecessary signal has been removed is output to the target detection unit 9.
, And subsequent target detection is performed.

FIG. 3 shows a frequency correction unit 5 according to the first embodiment.
FIG. 9 is a frequency spectrum diagram for supplementarily explaining a flow of a series of processes in the intensity correction unit 7 and the clutter removal processing unit 8. In FIG. 3, 31a and 31b are the spectra of the Bragg line, 32 is the target spectrum, 41 is the spectrum of the processing range bin, 42 is the reference spectrum, 45 is the original reference spectrum, 46 is the spectrum after frequency correction,
47 is a reference spectrum after intensity correction, and 48 is a spectrum after clutter removal.

As described above, according to the first embodiment, an estimated clutter spectrum is created by performing frequency and intensity corrections on a reference spectrum of a typical clutter, and is removed in the frequency domain. Unnecessary signals such as clutter can be removed while maintaining the preservation of the target signal, thereby facilitating target detection.

Further, since a spectrum obtained by actual reflection from the sea surface is employed as a reference spectrum for creating an estimated clutter spectrum, an estimated clutter spectrum can be obtained in accordance with the current situation.
Furthermore, by employing, as a reference spectrum, a spectrum obtained from a received signal received at the same time as the processing range bin, accurate target detection can be performed even if there is clutter that changes with time.

Although the case where the FFT circuit is used as the Doppler filter 2 has been described, other circuits may be used. In this specification, the Doppler filter 2 performs a process of converting a time domain into a frequency domain. The Doppler filter 2 is an example of a filter that obtains a plurality of frequency spectra corresponding to a plurality of ranges from the received signal, and the frequency correction unit 5 and the intensity correction unit 7 generate a plurality of frequency spectra obtained by the filters. Select some of the frequency spectra inside,
This is an example of an estimated spectrum generation unit that generates an estimated spectrum based on the selected frequency spectrum, and the clutter removal processing unit 8 calculates a difference between a frequency spectrum to be processed among a plurality of frequency spectra and the estimated spectrum. It is an example of a difference calculating means to take.

Embodiment 2 In the first embodiment, the peak frequency of the spectrum of each processing range bin and the peak frequency of the reference spectrum are individually detected, and the frequency correction is performed using the difference between the peak frequencies. Frequency correction can also be performed using the cross-correlation function of the reference spectrum and the reference spectrum.

FIG. 4 is a functional block diagram of the clutter suppressing apparatus according to this embodiment. In FIG. 4, the corresponding parts are denoted by the same reference numerals as in FIG. 1, and the description thereof will be omitted. In the figure, reference numeral 10 denotes a cross-correlation function provided on the output side of the Doppler filter 2.

Next, the operation will be described. The process of separating the received signal output from the receiving unit 1 into predetermined frequency components by the Doppler filter 2 and updating the reference spectrum in the reference spectrum storage unit 3 is the same as that described in the first embodiment, and thus will be described. Is omitted.

The spectrum of each processing range bin and the reference spectrum are input to the cross-correlation calculation unit 10 to calculate a cross-correlation function. Now, let the spectrum of the processing range bin be x
(F) Assuming that the reference spectrum is y (f), the cross-correlation function is represented by equation (2).

[0039]

(Equation 2) The frequency shift amount τ when the cross-correlation function R (τ) becomes the maximum represents the frequency shift between the processing range bin and the reference spectrum. In the cross-correlation calculation unit 10, the expression (2)
To obtain the frequency shift amount τ.

The frequency correction unit 5 shifts the reference spectrum in the frequency direction by the frequency shift amount τ obtained by the cross-correlation calculation unit 10. That is, the reference spectrum is shifted in the frequency direction such that the spectrum waveform of the processing range bin and the reference spectrum waveform show the most similar tendency.

Next, an estimated clutter spectrum is created by detecting the peak intensity of the processing range bin by the peak intensity detector 6 and correcting the intensity of the reference spectrum by the intensity corrector 7. Then, the clutter removal processing unit 8 removes unnecessary signals such as clutter by removing the estimated clutter spectrum of the processing range bin obtained in this manner from the spectrum of each processing range pin. The spectrum from which the unnecessary signal has been removed is output to the target detection unit 9.
, And subsequent target detection is performed.

In general, it is known that when the sea surface is in a barge state due to wind and rain, the bandwidth of the Bragg line is widened and the symmetry of the right and left is lost. In addition, changes in peak frequency, bandwidth, and shape increase depending on the distance from the radar. In such a case, it becomes difficult to obtain an accurate estimated clutter spectrum by frequency correction using the peak frequency shift of the reference spectrum. However, when the cross-correlation function is used, not only the clutter peak but also the shape of the entire clutter spectrum, including the effects of multi-order echoes around the peak and continuum, is compared, and the processing range bin and the reference spectrum are compared. Since the amount of frequency shift is determined, it is effective in that an accurate estimated clutter spectrum can be obtained.

Embodiment 3 In the first and second embodiments, the reference spectrum which is the basis of the estimated spectrum of the processing range bin is fixed to one type and is appropriately updated. However, based on the spectrum waveform of the clutter reference region near the processing range bin,
It is also possible to estimate the clutter spectrum of the range bin and remove clutter.

FIG. 5 is a functional block diagram of the clutter suppressing apparatus according to this embodiment, and the corresponding parts are denoted by the same reference numerals as in FIG. 1 and description thereof is omitted. Reference numeral 11 denotes a peak frequency averaging processing unit provided on the output side of the peak frequency detection unit 4 and the input side of the frequency correction unit 5, and 12 denotes a peak frequency averaging processing unit provided on the output side of the frequency correction unit 5 and the input side of the clutter removal processing unit 8. The obtained average intensity estimating unit.

Next, the operation will be described. Until the received signal output from the receiving unit 1 is separated into a predetermined frequency component by the Doppler filter 2, the process is the same as that described in the first embodiment. The peak frequency detecting section 4 detects the clutter peak frequency of all the range bins, but the detecting method may be to detect the peak near the frequency of the Bragg line as described in the first embodiment.

The clutter peak frequencies of a plurality of range bins located in the clutter reference area among the clutter peak frequencies of all the range bins detected by the peak frequency detecting section 4 are input to the peak frequency averaging section 11. Here, the range bin located in the clutter reference area is
A range bin exists one or more range bins before and after the processing range bin. The size of the guard is determined in consideration of the pulse width,
In the case of the W-type radar, the determination is made in consideration of the main lobe width generated by the weighting function used in the FFT when generating the range bin.

The peak frequency averaging unit 11 calculates an average value of the clutter peak frequencies of a plurality of range bins located in the clutter reference area. The average value of the clutter peak frequencies calculated in this way is referred to as an average peak frequency. Further, the frequency correction unit 5 shifts in the frequency direction such that the peak of the spectrum waveform of each range bin in the clutter reference region matches the average peak frequency. The spectrum waveform of each range bin in the clutter reference area that has been frequency-corrected in this way is input to the average intensity estimating unit 12. And the average intensity estimator 12
Calculates an average value in the clutter reference region for each Doppler component of the spectrum waveform of each range bin in the frequency-corrected clutter reference region, thereby obtaining an estimated clutter spectrum.

Then, the clutter removal processing unit 8 removes unnecessary signals such as clutter by removing the estimated clutter spectrum of the processing range bin thus obtained from the spectrum of each processing range pin. The spectrum from which the unnecessary signal has been removed is input to the target detection unit 9, and subsequent target detection is performed.

FIG. 6 shows a peak frequency averaging section 11, a frequency correcting section 5, and an average intensity estimating section 1 according to the third embodiment.
FIG. 3 is a frequency spectrum diagram for supplementarily explaining a flow of a series of processing in the second and clutter removal processing units. In the figure, 31a and 31b are the spectra of the Bragg line, 3
2 is the target spectrum, 41 is the processing range bin, 43
a and 43b are guard areas, 44a and 44b are clutter reference areas, 45 is an original spectrum, 46 is a spectrum after frequency correction, 47 is a spectrum after intensity correction, 48 is a spectrum after clutter removal, and 49 is an estimated clutter spectrum. Is shown.

That is, the clutter reference regions 44a, 44a, 43b separated from the processing range bin 41 by the guard regions 43a, 43b.
For a plurality of range bins in 44b, the peak frequency is corrected to the peak frequency of the processing range bin 41. The spectrum after the frequency correction is obtained by this frequency correction. Then, the clutter reference area 4 after the frequency correction
An estimated clutter spectrum 49 is obtained by taking an average value of the intensities of a plurality of range bins in 4a and 44b. The target echo is extracted by removing the estimated clutter spectrum 49 from the processing range bin 41.

As described above, according to the third embodiment, the clutter spectrum of the processing range bin is estimated based on the average value of the peak frequency and the average value of the spectrum intensity of the spectrum of the range bin near the processing range bin. Since the estimated clutter spectrum is removed in the frequency domain from the spectrum of the range bin, even if there is clutter whose peak frequency and bandwidth fluctuate linearly according to the distance from the radar due to the influence of ocean currents, etc. ,
It is possible to easily perform target detection while maintaining the preservation of nearby target signals.

The peak frequency averaging unit 11, the frequency correcting unit 5, and the average intensity estimating unit 12 in this embodiment are an example of an estimated spectrum generating unit.

Embodiment 4 In the third embodiment, the clutter spectrum of the range bin is estimated based on the average value of the peak frequency and the average value of the spectrum intensity of the spectrum in the clutter reference area near the processing range bin, and the estimated clutter spectrum is obtained from the spectrum of the processing range bin. Although the spectrum is removed in the frequency domain, the same processing can be performed based on the average value of the peak frequency and the median of the spectrum intensity in the clutter reference area.

FIG. 7 is a functional block diagram of the clutter suppressing apparatus according to this embodiment. The corresponding parts are denoted by the same reference numerals as in FIG. 5, and description thereof will be omitted. In the figure, 13
Is the output side of the frequency correction unit 5 and the clutter removal processing unit 8
Is a median intensity estimating unit provided on the input side of.

Next, the operation will be described. The flow of a series of processing from the receiving unit 1 to the Doppler filter 2, the peak frequency detecting unit 4, the peak frequency averaging processing unit 11, and the frequency correcting unit 5 is the same as that described in the third embodiment, and thus the description is omitted. I do. The spectrum of each range bin in the clutter reference region whose frequency has been corrected is calculated as a median intensity estimator 1
3 is input. Then, the median intensity estimation unit 13 calculates
A median of the intensity in the clutter reference region is calculated for each Doppler component, and this is used as an estimated clutter spectrum for the processing range bin. The method of calculating the median of the above-described strength is the same as that of the conventional example, and thus the description is omitted.

Thereafter, the estimated clutter spectrum is removed from the spectrum waveform of the processing range bin by the clutter removal processing unit 8 to suppress clutter in the processing range bin, and the spectrum after the removal is used as the target detection unit 9.
Output to

As described above, when the estimated clutter spectrum is obtained, by using the median of the intensity in the clutter reference region, even when the target is present in the clutter reference region, the intensity estimated value increases by the target and the clutter is increased. The intensity estimation error does not increase, and clutter estimation can be performed more accurately.

When the average intensity in the clutter reference region is used, if the target exists in the clutter reference region, the average value is greatly affected by the target signal, and the designated clutter intensity may be largely estimated. Use of the median is effective because the fear can be reduced.

The peak frequency averaging section 11, the frequency correcting section 5, and the median intensity estimating section 13 in this embodiment are an example of an estimated spectrum generating means.

Embodiment 5 FIG. According to the third embodiment, the clutter spectrum of the range bin is estimated based on the average value of the peak frequency and the average value of the spectrum intensity of the spectrum in the clutter reference region near the processing range bin, and the clutter estimation sum is calculated from the spectrum of the processing range bin. Although the vector is removed in the frequency domain, the same processing can be performed based on the median of the peak frequency of the spectrum and the average value of the spectrum intensity in the clutter reference area.

FIG. 8 is a functional block diagram of the clutter suppressing apparatus according to this embodiment. The corresponding parts are denoted by the same reference numerals as in FIG. 5, and description thereof will be omitted. In the figure, 14
Is the output side of the peak frequency detector 4 and the frequency corrector 5
Is a median frequency estimator provided on the input side of.

Next, the operation will be described. The flow of a series of processes from the receiving unit 1 to the Doppler filter 2 and the peak frequency detecting unit 4 is the same as that described in the third embodiment, and a description thereof will be omitted. The clutter peak frequency of the range bin existing in the clutter reference area is detected by the peak frequency detection unit 4, and the detection result is input to the median frequency estimation unit 14. The median frequency estimating unit 14 calculates the median of the clutter peak frequency of the range bin existing in the clutter reference area. Further, the frequency correction unit 5 shifts in the frequency direction such that the peak of the spectrum waveform of each range bin in the clutter reference region matches the median of the clutter peak frequency calculated by the median frequency estimation unit 14. The subsequent processing by the average intensity estimating unit 12 and the clutter removal processing unit 8 is performed and output to the target detecting unit 9.

As described above, when the estimated clutter spectrum is obtained, by using the median of the clutter peak frequency in the clutter reference region, a target having a higher intensity than the clutter exists near the Bragg line in the clutter reference region. However, the frequency estimation value fluctuates due to the target and the clutter frequency estimation error does not increase,
Clutter estimation can be performed more accurately. Therefore,
Even if there is clutter whose peak frequency and bandwidth fluctuate linearly with the distance from the radar due to the influence of ocean currents, etc., it is possible to easily perform target detection while maintaining the preservation of nearby target signals. .

The median frequency estimating unit 14, the frequency correcting unit 5, and the average intensity estimating unit 1 in this embodiment
2 is an example of an estimated spectrum generating unit.

Embodiment 6 FIG. In the fifth embodiment, the clutter spectrum of the range bin is estimated based on the median of the peak frequency of the spectrum and the average value of the spectrum intensity in the clutter reference region near the processing range bin,
Although the estimated clutter spectrum is removed from the spectrum of the processing range bin in the frequency domain, the same processing can be performed based on the median of the peak frequency and the median of the spectrum intensity of the spectrum in the clutter reference area.

FIG. 9 is a functional block diagram showing a clutter suppressing apparatus according to this embodiment.
The same reference numerals are given and the description is omitted. In the figure,
Reference numeral 13 denotes a median intensity estimating unit provided on the output side of the frequency correction unit 5 and the input side of the clutter removal processing unit 8.

Next, the operation will be described. The flow of a series of processes from the receiving unit 1 to the Doppler filter 2, the peak frequency detecting unit 4, the median frequency estimating unit 14, and the frequency correcting unit 5 is the same as that described in the fifth embodiment, and thus the description is omitted. . The spectrum of each range bin in the clutter reference region frequency-corrected by the frequency correction unit 5 is input to the median intensity estimation unit 13. The median intensity estimating unit 13 calculates the median of the intensity for each Doppler component of the input spectrum of each range bin, and uses this as the estimated clutter spectrum in the processing range bin. Thereafter, the clutter removal processing unit 8 removes the estimated clutter spectrum from the spectrum waveform of the processing range bin, thereby suppressing clutter in the processing range bin, and outputs the result to the target detection unit 9.

As described above, when the estimated clutter spectrum is obtained, the median of the intensity in the clutter reference region is used, so that even if the target exists in the clutter reference region, the intensity estimation value is increased by the target and the clutter is increased. Clutter estimation can be performed more accurately without increasing the estimation error of the intensity. Therefore, even if there is clutter whose peak frequency and bandwidth fluctuate linearly with the distance from the radar due to the influence of ocean currents, etc., it is easy to perform target detection while maintaining the preservation of nearby target signals. Can be.

The median frequency estimating section 14, the frequency correcting section 5 and the median intensity estimating section 13 in this embodiment are an example of an estimated spectrum generating means.

Embodiment 7 FIG. In the fifth embodiment, the clutter spectrum of the range bin is estimated based on the median of the peak frequency and the average value of the spectrum intensity of the spectrum in the clutter reference region near the processing range bin,
The estimated clutter spectrum is removed in the frequency domain from the spectrum of the processing range bin, but the estimated frequency is obtained from the approximate curve of the peak frequency versus distance of the spectrum in the clutter reference area, and the estimated intensity is obtained from the average value of the spectrum intensity. The same processing can be performed.

FIG. 10 is a functional block diagram of the clutter suppressing apparatus according to this embodiment. The corresponding parts are denoted by the same reference numerals as in FIG. 8, and the description thereof will be omitted. In the figure, 1
Reference numeral 5 denotes an approximate frequency estimating unit provided on the output side of the peak frequency detecting unit 4 and on the input side of the frequency correcting unit 5.

Next, the operation will be described. The flow of a series of processes from the receiving unit 1 to the Doppler filter 2 and the peak frequency detecting unit 4 is the same as that described in the fifth embodiment. The approximate frequency estimating unit 15 obtains an approximate curve indicating a change in the clutter peak frequency of the range bin in the clutter reference region with respect to the distance. This approximate curve is obtained by using the least squares method or the like so that the deviation from the peak frequency of each range bin is minimized. This approximate curve is obtained for each processing range.

The approximate curve of the spectrum peak frequency versus distance is, for example, the curve shown in FIG. This approximate curve is obtained by connecting the relationship between the distance of each processing range and the peak frequency in that processing range with a line. By obtaining this approximate curve, a change in the peak frequency in the range direction is detected. Then, an estimated value of the peak frequency for each processing range bin can be obtained from the approximate curve. The approximate frequency estimating unit 15 obtains an estimated value of the clutter peak frequency for the processing range bin from the approximate curve.

Further, the frequency correction unit 5 shifts in the frequency direction such that the peak of the spectrum waveform of each range bin in the clutter reference region matches the estimated value obtained by the approximate frequency estimation unit 15. The subsequent processing is performed by the average intensity estimating unit 12 and the clutter removal processing unit 8 and output to the target detecting unit 9.

By using the approximate curve of the clutter peak frequency in the clutter reference region when obtaining the estimated clutter spectrum in this way, even when the Bragg line swells in the distance direction due to a tidal current or the like, the clutter frequency estimation is performed. Clutter estimation can be performed more accurately without increasing errors. Therefore, even if there is clutter whose peak frequency and bandwidth fluctuate in a curve depending on the distance from the radar due to the influence of ocean currents, etc., it is easy to perform target detection while maintaining the preservation of nearby target signals. Can be.

It should be noted that the approximate frequency averaging processing section 15, the frequency correction section 5, and the average intensity estimating section 1 in this embodiment.
2 is an example of an estimated spectrum generating unit.

Embodiment 8 FIG. In the seventh embodiment, the clutter spectrum of the range bin is estimated based on the approximate value of the peak frequency of the spectrum in the clutter reference region near the processing range bin and the average value of the spectrum intensity, and the clutter spectrum of the processing range bin is estimated from the spectrum of the processing range bin. Estimated clutter spectrum is removed in the frequency domain.
Similar processing can be performed based on the approximate value of the peak frequency of the spectrum in the clutter reference area and the median of the spectrum intensity.

FIG. 12 is a functional block diagram of the clutter suppressing apparatus according to this embodiment, and the corresponding parts are denoted by the same reference numerals and description thereof will be omitted. In the figure, reference numeral 13 denotes a median intensity estimating unit provided on the output side of the frequency correction unit 5 and the input side of the clutter removal processing unit 8.

Next, the operation will be described. The flow of a series of processes from the receiving unit 1 to the Doppler filter 2, the peak frequency detecting unit 4, the approximate frequency estimating unit 15, and the frequency correcting unit 5 is the same as that described in the seventh embodiment, and thus the description is omitted. . The spectrum of each range bin in the clutter reference region frequency-corrected by the frequency correction unit 5 is input to the median intensity estimation unit 13. Median intensity estimation unit 1
3 calculates the median of the intensity for each Doppler component of the spectrum of each input range bin, and uses this as the estimated clutter spectrum in the processing range bin. After this,
The clutter removal processing unit 8 removes the estimated clutter spectrum from the spectrum waveform of the processing range bin, thereby suppressing clutter in the processing range bin, and outputs the result to the target detection unit 9.

As described above, when the estimated clutter spectrum is obtained, by using the median of the intensity in the clutter reference region, even when the target is present in the clutter reference region, the intensity estimated value is increased by the target and the clutter is increased. The intensity estimation error does not increase, and clutter estimation can be performed more accurately. Therefore, even if there is clutter whose peak frequency and bandwidth fluctuate in a curve depending on the distance from the radar due to the influence of ocean currents, etc., it is easy to perform target detection while maintaining the preservation of nearby target signals. Can be.

The approximate frequency estimating unit 15, the frequency correcting unit 5, and the median intensity estimating unit 1 in this embodiment
3 is an example of an estimated spectrum generating unit.

[0082]

Since the present invention is configured as described above, it has the following effects.

A clutter suppression apparatus according to the present invention is a clutter suppression apparatus for removing an unnecessary signal component included in a received signal received by a radar in order to detect a target object. And a filter for obtaining a plurality of frequency spectra corresponding to the above, and an estimated spectrum generation for selecting a part of the plurality of frequency spectra obtained by the filter and generating an estimated spectrum based on the selected frequency spectrum Means, and a difference calculating means for calculating a difference between the frequency spectrum to be processed among the plurality of frequency spectra and the estimated spectrum, so that the estimated clutter spectrum according to the current state is obtained from the actually obtained frequency spectrum. And clutter can be suppressed with high accuracy.

Since the partial frequency spectrum has a different range from the frequency spectrum to be processed, it is possible to prevent the target signal in the frequency spectrum to be processed from being suppressed. be able to.

Further, the above-mentioned estimated spectrum generating means includes:
In order to select a frequency spectrum separated from the frequency spectrum to be processed by a predetermined range or more as the partial frequency spectrum, it is possible to prevent even a target signal in the frequency spectrum to be processed from being suppressed. it can.

Further, the estimated spectrum generating means detects the characteristics of the frequency spectrum to be processed and generates the estimated spectrum by correcting the characteristics of the selected frequency spectrum according to the detection result. Thus, it is possible to obtain an estimated spectrum in accordance with the tendency of the frequency spectrum to be processed, and it is possible to accurately suppress clutter.

The estimated spectrum generating means detects the characteristics of a plurality of frequency spectra constituting the partial frequency spectrum and generates an estimated spectrum according to the detection result. Is added, an estimated spectrum closer to the frequency spectrum to be processed can be obtained.

Further, since the characteristic is a peak frequency, an estimated spectrum matching the peak frequency of the frequency spectrum to be processed can be obtained.

Further, since the characteristic is the intensity of the frequency spectrum, an estimated spectrum matching the intensity of the frequency spectrum to be processed can be obtained.

Further, the estimated spectrum generating means detects a change in the peak frequency in the range direction based on the plurality of frequency spectra constituting the partial frequency spectrum, and generates an estimated spectrum based on the detection result. Therefore, a more appropriate estimated spectrum can be obtained even if there is clutter whose peak frequency and bandwidth fluctuate depending on the range due to the influence of the ocean current or the like.

The clutter suppression method according to the present invention is a clutter suppression method for removing an unnecessary signal component included in a received signal received by a radar in order to detect a target object. The clutter suppression method reflects a radio wave transmitted from the radar. Receiving a wave, a frequency spectrum generating step of obtaining a plurality of frequency spectra corresponding to a plurality of ranges from the received signal obtained in the receiving step, and a plurality of frequency spectra obtained in the frequency spectrum generating step A selection step of selecting a part of the frequency spectrums therein, an estimation spectrum generation step of generating an estimation spectrum based on the frequency spectrum selected in the selection step, and a frequency spectrum to be processed among the plurality of frequency spectrums And the above estimated spectrum generation And a difference calculation step of taking a difference from the estimated spectrum generated in the step, so that it is possible to obtain an estimated clutter spectrum in accordance with the current state from the actually obtained frequency spectrum, and to accurately determine the clutter Suppression can be performed.

[Brief description of the drawings]

FIG. 1 is an internal configuration diagram of a clutter suppression device according to a first embodiment.

FIG. 2 is a conceptual diagram showing a process performed by the clutter suppressing apparatus according to the first embodiment.

FIG. 3 is a frequency spectrum diagram showing a processing process of the clutter suppressing device in the first embodiment.

FIG. 4 is an internal configuration diagram of a clutter suppression device according to a second embodiment.

FIG. 5 is an internal configuration diagram of a clutter suppression device according to a third embodiment.

FIG. 6 is a frequency spectrum diagram showing a process performed by a clutter suppression device according to a third embodiment.

FIG. 7 is an internal configuration diagram of a clutter suppression device according to a fourth embodiment.

FIG. 8 is an internal configuration diagram of a clutter suppression device according to a fifth embodiment.

FIG. 9 is an internal configuration diagram of a clutter suppression device according to a sixth embodiment.

FIG. 10 is an internal configuration diagram of a clutter suppression device according to a seventh embodiment.

FIG. 11 is a diagram showing an approximate curve obtained by an approximate frequency estimating unit 15;

FIG. 12 is an internal configuration diagram of a clutter suppression device according to an eighth embodiment.

FIG. 13 is an internal configuration diagram of a conventional clutter suppressing device.

FIG. 14 is a frequency spectrum diagram showing a reflected echo from the sea surface.

[Explanation of symbols]

1 receiver, 2 Doppler filter, 3 reference spectrum storage, 4 peak frequency detector, 5 frequency corrector, 6 peak intensity detector, 7 intensity corrector, 8 clutter removal processor, 9 target detector, 10 cross-correlation Calculation unit, 11 peak frequency average processing unit, 12 average intensity estimation unit, 13 median intensity estimation unit, 14 median frequency estimation unit, 15 approximate frequency estimation unit.

Claims (9)

[Claims] 1. A clutter suppressing apparatus for removing an unnecessary signal component included in a received signal received by a radar for detecting a target, comprising: a plurality of frequency spectrums corresponding to a plurality of ranges from the received signal. And a selected spectrum obtained from the plurality of frequency spectra obtained by the filter, and an estimated spectrum generator configured to generate an estimated spectrum based on the selected frequency spectrum. A clutter suppression device comprising: a difference calculating unit that calculates a difference between a frequency spectrum to be processed in the spectrum and the estimated spectrum. 2. The clutter suppressing apparatus according to claim 1, wherein the part of the frequency spectrum is a frequency spectrum in a range different from the frequency spectrum to be processed. 3. The method according to claim 1, wherein the estimated spectrum generating means selects a frequency spectrum separated from the frequency spectrum to be symmetrical by a predetermined range or more as the partial frequency spectrum. Item 2. The clutter suppressing device according to Item 2. 4. The estimated spectrum generating means detects the characteristic of the frequency spectrum to be processed and generates the estimated spectrum by correcting the characteristic of the selected frequency spectrum according to the detection result. The clutter suppressing device according to any one of claims 1 to 3, wherein: 5. The apparatus according to claim 1, wherein said estimated spectrum generating means detects characteristics of a plurality of frequency spectra constituting said partial frequency spectrum, and generates an estimated spectrum according to a result of the detection. The clutter suppressing device according to claim 3. 6. The clutter suppressing apparatus according to claim 4, wherein the characteristic is a peak frequency. 7. The clutter suppressing apparatus according to claim 4, wherein the characteristic is an intensity of a frequency spectrum. 8. The estimated spectrum generating means detects a change in a range direction of a peak frequency based on a plurality of frequency spectra constituting the partial frequency spectrum, and generates an estimated spectrum based on the detection result. The clutter suppressing device according to claim 1, wherein: 9. A clutter suppressing method for removing an unnecessary signal component included in a received signal received by a radar for detecting a target, comprising: a receiving step of receiving a reflected wave of a radio wave transmitted from the radar. And a frequency spectrum generating step of obtaining a plurality of frequency spectra corresponding to a plurality of ranges from the received signal obtained in the receiving step; and a part of frequencies in the plurality of frequency spectra obtained in the frequency spectrum generating step A selection step of selecting a spectrum; an estimation spectrum generation step of generating an estimation spectrum based on the frequency spectrum selected in the selection step; a frequency spectrum to be processed among the plurality of frequency spectra; and the estimation spectrum generation step Estimated specs generated in Clutter suppression method characterized by having a difference calculating step of calculating a difference between Torr.