JP2596614B2 - Signal processing method and signal processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing method and a signal processing apparatus used together with a radar apparatus to suppress a clutter signal.

2. Description of the Related Art When trying to detect a target ship signal on the sea, it is necessary to suppress a clutter signal generated due to sea surface reflection of a transmission pulse in order to easily determine the target ship signal.

As such a conventional signal processing device, Log-CFAR (c
Some signal processing is performed by an (onstant-false-alarm-rate) processing method. FIG. 9 shows the principle.

The Log-CFAR processing method uses the fact that the clutter signal follows a Rayleigh distribution, so that the deviation around the average value of the log amplifier output signal of the clutter signal is constant. Get the signal.

Referring to FIG. 9, the average value obtained by the moving average means from the log amplifier output signal X of the clutter signal W <
By subtracting X>, it is possible to obtain an output signal V whose false alarm probability is equal to or lower than a certain level.

FIG. 10 shows that the average value of the log amplifier output signal X <X
> Is shown.

In FIG. 10, the moving averaging means includes two sets of N / 2-stage delay elements 2.
1, a delay element 22 therebetween, an addition circuit 23 for calculating the sum of signals from the two sets of delay elements 21, and a sum of outputs of the two addition circuits 23 set to 1 / N, and a moving average value And a division circuit 24 for calculating a signal.

The difference calculator 2 subtracts the moving average signal from the radar video signal to calculate a difference signal (CFAR output signal).

Thus, an output signal having a false alarm probability equal to or lower than a certain level is obtained.

[Problems to be Solved by the Invention] However, when signal processing is performed by the marine radar using the Log-CFAR processing method, not only the sea surface reflection signal is suppressed, but also the average value of the land image signal is subtracted. The signal level of the video signal decreases. For this reason,
There is a problem in that it is difficult to determine a land image, and the situation becomes extremely dangerous in navigating a ship.

The present invention has been made in view of such problems of the conventional technology, and suppresses the sea surface reflection signal, outputs a clear land image signal, and provides effective radar information on the navigation of the ship. It is an object to provide a signal processing method and a signal processing device that can be obtained.

[Means for Solving the Problems] In order to achieve the above object, a signal processing method according to a first aspect of the present invention includes: a moving average step of calculating a moving average value signal from a radar video signal; Calculating a difference from the average value signal and outputting the difference signal; and, after emitting a transmission pulse, selecting and outputting the difference signal if the moving average value signal is larger than a reference signal. And selecting and outputting the radar video signal until the next transmission pulse is emitted when the average signal is smaller than the reference signal.

The signal processing method according to the second aspect of the present invention includes a moving average step and a difference calculation step similar to those of the first aspect of the present invention, a smoothing step of smoothing the moving average value signal and outputting the signal as a smoothed signal, After emitting the pulse, if the smoothed signal is larger than the reference signal, the differential signal is selected and output.If the smoothed signal is smaller than the reference signal, until the next transmission pulse is emitted, A step of selecting and outputting the radar video signal.

The signal processing apparatus according to the third and fourth aspects of the present invention is characterized in that it has means corresponding to each stage of the signal processing method according to the first and second aspects of the present invention.

[Operation] The moving average means calculates a moving average value of the radar video signal output from the radar device, and outputs a moving average value signal.

The difference calculation means obtains a difference between the radar video signal and the moving average signal and outputs the difference as a difference signal.

The selection means selects and outputs the difference signal when the moving average signal is larger than the reference signal after emitting the transmission pulse, and emits the next transmission pulse when the moving average signal is smaller than the reference signal. In the meantime, select and output radar video signal.

In the case where a smoothing means is provided, the smoothing means smoothes the moving average value signal and outputs it as a smoothed signal.

Then, the selection means outputs a difference signal or a radar video signal using the smoothed signal instead of the moving average value signal.

As described above, the sea surface reflection signal has the maximum level immediately after the transmission pulse is emitted, and then attenuates.
Paying attention to the fact that the moving average signal or the smoothed signal is generated after the level becomes lower than the reference signal, the log-CFAR processing by the moving average means suppresses the clutter signal due to sea surface reflection and reduces the radar video signal. By outputting, a land image signal can be clearly obtained.

Embodiments Various embodiments of the present invention will be described below with reference to the drawings.
In the various embodiments, the same parts are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a block diagram showing a schematic configuration of a signal processing apparatus according to one embodiment of the present invention, and FIG. 2 is a flowchart of signal processing according to the present embodiment.

The moving average unit 1 is connected to a reception output unit of a radar device (not shown), receives a radar video signal output from the radar device, delays the signal by N stages, and moves after a predetermined delay time has elapsed. It is output as an average value signal.

As shown in FIG. 3, the moving average means 1 includes an N-stage delay element 6, an addition circuit 7 for calculating the sum of signals in the delay element 6, and 1 / N the output of the addition circuit 7. A dividing circuit 8 for calculating a moving average signal.

The moving averaging means 1 is located between the two sets of N / 2-stage delay elements 21 and the two sets of delay elements 21 as in the conventional example shown in FIG. An addition circuit 23 that calculates the sum of the signals in the element 21 and a division circuit 24 that calculates the moving average signal by dividing the sum of the outputs of the two addition circuits 23 by 1 / N may be used.

The difference means 2 is connected to the reception output section of the radar device and the moving average means 1, inputs the radar video signal and the moving average value signal, subtracts the moving average value signal from the radar video signal, and outputs the difference signal (CFAR Output signal).

The difference means 2 is configured by an arithmetic operation element such as a digital adder (for example, 74LS83A of standard logic IC) and an analog operational amplifier.

The smoothing means 4 is connected to the moving average means 1,
A moving average value signal is input, the sharp change of the moving average value signal is smoothed into a smooth change, and the smoothed signal is output as a smoothed signal.

The smoothing means 4 is constituted by a low-pass filter.

The selection unit 3 is connected to the reception output unit of the radar device, the smoothing unit 4 and the difference unit 2, and receives the radar video signal, the smoothed signal, the difference signal (CFAR output signal) and the reference signal, and outputs the selected signal. It outputs a signal.

As shown in FIG. 4, the selecting means 3 includes a comparing means 12 and
It comprises flip-flop means 13 and switching means 14.

The comparing means 12 compares the magnitude of the predetermined reference signal with the magnitude of the smoothed signal, and when the smoothed signal is smaller than the reference signal (smoothed signal <reference signal), or when the smoothed signal is smaller than the reference signal. In the following case (smoothing signal ≦ reference signal), an active determination signal is output.

The flip-flop means 13 is set by the transmission pulse indicating the timing of the transmission pulse emission,
Is reset by the determination signal from the CPU and outputs a switching signal.

The switching means 14 includes a radar video signal and a differential signal (CF
AR output signal), and according to the control of the switching signal from the flip-flop means 13, after the transmission pulse is emitted, if the smoothed signal from the smoothing means 4 is larger than the reference signal, A differential signal (CFAR output signal) is output, and when the smoothed signal is smaller than the reference signal, a radar video signal is output until the next transmission pulse is emitted.

 Next, the operation will be described.

First, the calculation of the difference signal (CFAR output signal) will be described.

FIG. 5 is a timing chart of the signal processing device of this embodiment.

As shown in FIG. 5, when the n-th time series signal of the radar video signal is Xn, a radar device (not shown)
, X (n-2), X (n-1), X (n), X
(N + 1), X (n + 2)... Are output.

The delay element 6 of the moving averaging means 1 inputs the radar video signal, and outputs a delay signal individually from N continuously connected delay taps.

The delay time in the delay element 6 corresponds to a time interval T required for calculating the average signal, and is generally an interval of about several tens of times the radar transmission pulse width, for example, 8 to 12 μm.
s.

The number N of delay stages of the delay element 6 has a relationship of N = T / S, where T is a time interval required for delay and S is a CFAR calculation cycle.

Generally, N is set to about 16 taps to 32 taps.

The CFAR operation period S is selected to be at least twice the frequency band of the radar video signal according to the sampling theorem.

The adder circuit 7 is connected to the delay element 6, receives the delay signal from the delay element 6, and outputs a sum signal, S (n−
1), Sn, S (n + 1), S (n + 2), S (n + 3) ...
Output as

The division circuit 8 receives the sum signal, calculates an average value, and calculates the average value signals, A (n-1), A (n), A (n + 1), A
Output as (n + 2), A (n + 3).

The average signal is calculated by dividing the sum signal by the number N of stages of the moving average unit 1.

The difference means 2 receives the radar video signal and the average signal, subtracts the average signal from the radar video signal, and outputs a difference signal (CFAR output signal), X (n-3) -A (n
-2), X (n-2) -A (n-1), X (n-1) -A
(N), X (n) -A (n + 1), X (n + 1) -A (n +
2) Output as ...

 Thus, a difference signal (CFAR output signal) is obtained.

Next, signal processing according to the present embodiment will be described with reference to waveforms.

 FIG. 6 is a waveform diagram of the signal processing device of the present embodiment.

As shown in FIG. 6, after transmitting a transmission pulse by a transmission trigger signal (A), a radar video signal (D) is received by radar reflection.

The radar video signal (D) is one of the radar reflected signals.
This is an A scope display of the sweep.

In FIG. 6, P is a transmission pulse leak signal, a is a sea surface reflection signal, b is a land reflection signal, c is a ship reflection signal, and d is a sharply falling portion of the sea surface reflection signal. Show.

The sea surface reflection signal a has a characteristic in which the level is the highest immediately after the transmission pulse oscillation, and thereafter, the intensity attenuates exponentially.

On the other hand, the land signal b is generated as a strong signal after the sea surface reflection signal a is attenuated.

The moving average means 1 outputs the radar video signal (D) as a moving average signal (E).

Further, the moving average signal is output by the smoothing means 4 as a smoothed signal (F).

The radar video signal (D) has a sharply falling portion d, and the moving average signal (E) has the d.
Is not smoothed by the moving average calculation, and is lower than the reference signal level. However, in the smoothed signal (F), d is smoothed, and the influence of the sea surface reflection on the sea surface reflection signal a is reliably terminated. Up to the reference signal level.

For this smoothing process, the falling part d
This prevents erroneous determination of the end of the sea surface reflection signal.

The difference means 2 subtracts the moving average value signal (E) from the radar video signal (D) to obtain a difference signal (CFAR output signal).
(G) is output.

In the difference signal (CFAR output signal) (G), only the changing point of the signal is output, so that the rising portion is output as a pulse signal, and the sea surface reflection signal is suppressed. However, in the difference signal (CFAR output signal) (G), the land signal is similarly suppressed.

For this reason, in the video output by the CFAR process, the land image is an unclear video, and it is extremely difficult to determine.

 First, the following processing is performed there.

The selecting means 3 outputs the smoothed signal (F) by the comparing means 12.
Is compared with the reference signal level, and when the smoothed signal (F) becomes lower than the reference signal level, the comparison signal (B) is output.

The flip-flop means 13 of the selection means 3 outputs a switching signal (C) for switching from the difference signal (CFAR output signal) (G) to the radar video signal (D) according to the comparison signal (B).

The switching means 14 of the selection means 3
Until the smoothed signal gradually attenuates and becomes the same level as the reference signal, the difference signal from the difference means 2 (CFAR output signal)
(G) is output. Therefore, a ship image in which the sea surface reflection signal is suppressed is output.

Further, the switching means 14 outputs a radar video signal (D) by the switching signal (C) when the level of the smoothed signal becomes lower than the reference signal. Therefore, land images that can be easily identified can be obtained.

 Next, a second embodiment of the present invention will be described.

FIG. 7 is a block diagram illustrating a schematic configuration of a signal processing device according to a second embodiment of the present invention, and FIG. 8 is a graph illustrating a waveform of a signal output from the signal processing device according to the second embodiment.
(1) is a radar video signal, (2) is a differential signal (CF
AR output signal), and (3) indicates a selected output signal.

In the present embodiment, the moving average value signal from the moving average means 1 is sent to the selecting means 3 as it is without using the smoothing means 4.

For this reason, the switching means 14 of the selection means 3 controls the difference signal (CFAR) from the difference means 2 until the moving average value signal gradually attenuates from the time of transmission pulse oscillation and reaches the same level as the reference signal.
Output signal) (2). Therefore, a ship image in which the sea surface reflection signal is suppressed is output.

When the moving average signal becomes lower than the reference signal, the switching means 14 outputs a radar video signal (1) according to the switching signal. Therefore, land images that can be easily identified can be obtained.

In the present embodiment, if there is a portion that falls sharper than the reference signal in the sea surface reflection signal, the signal may be affected by sea surface reflection, but with a simpler configuration than the first embodiment, the sea surface reflection signal is suppressed and , Can output clear land video signal.

[Effects of the Invention] According to the signal processing method and the signal processing device according to the present invention, it is possible to suppress a sea surface reflection signal, output a clear land image signal, and obtain effective radar information for navigation of a ship. It is possible.

[Brief description of the drawings]

1 to 6 show a first embodiment of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of a signal processing device, FIG. 2 is a flowchart of signal processing, FIG. 3 is a block diagram showing a schematic configuration of moving average means, and FIG. 4 shows a schematic configuration of a selection means. FIG. 5 is a timing chart of signal processing, FIG. 6 is a graph showing a waveform of a signal output from the signal processing device, and FIG. 7 is a schematic configuration of a signal processing device according to a second embodiment of the present invention. FIG. 8 is a graph showing a waveform of a signal output from the signal processing device of the second embodiment, FIGS. 9 and 10 show a conventional example, and FIG. 9 is a log-CFAR process. FIG. 10 is a block diagram showing the principle of the system, and FIG. 10 is a block diagram showing a schematic configuration of moving average means. 1 moving average means 2 difference means 3 selection means 4 smoothing means 6 delay element 7 addition circuit 8 division circuit 12 comparison means 13 Flip-flop means 14 ... Switching means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Minoru Kondo 2-16-46 Minami Kamata, Ota-ku, Tokyo Tokyo Keiki Co., Ltd. (56) References JP-A-60-244879 (JP, A) 1962-16694 (JP, Y2)

Claims (4)

(57) [Claims] 1. A moving average step of calculating a moving average signal from a radar video signal; a difference calculating step of calculating a difference between the radar video signal and the moving average signal and outputting the difference signal as a difference signal; Comparing the value signal with the reference signal, and after transmitting the transmission pulse, while the moving average value signal continues to be larger than the reference signal, selects and outputs the difference signal. From the time point when becomes smaller than the reference signal, until the next transmission pulse is fired, regardless of the result of comparison between the moving average signal and the reference signal, selecting and outputting the radar video signal. And a signal processing method. 2. A moving average step for calculating a moving average signal from a radar video signal; a difference calculating step for calculating a difference between the radar video signal and the moving average signal and outputting the difference signal as a difference signal; Smoothing the value signal, and outputting the smoothed signal as a smoothing signal; comparing the smoothed signal with a reference signal; and after emitting a transmission pulse, the state where the smoothed signal is larger than the reference signal continues. While the differential signal is selected and output,
After the point at which the smoothed signal becomes smaller than the reference signal,
A signal output step of selecting and outputting the radar video signal regardless of the result of comparison between the smoothed signal and the reference signal until the next transmission pulse is fired. Method. 3. A moving average means for calculating a moving average value of a radar video signal output from the radar device and outputting a moving average value signal, and calculating a difference between the radar video signal and the moving average value signal, A difference calculating means for outputting as a difference signal; and a selecting means for selecting and outputting the difference signal and the radar video signal, wherein the selecting means compares and compares the moving average value signal with a reference signal. Means for outputting a signal, a state in which the comparison signal, after receiving the transmission trigger signal and the comparison signal of the radar device and receiving the transmission trigger signal, indicates that the moving average signal is larger than the reference signal. While continuing, the differential signal is selected and output, and then, after the comparison signal indicates that the moving average signal has become smaller than the reference signal, After that point, until receiving a next transmission trigger signal, regardless of whether the comparison signal, the signal processing apparatus characterized by having a selection output section for selectively outputting the radar video signal. 4. A moving average means for calculating a moving average value of a radar video signal output from the radar apparatus and outputting the moving average value as a moving average value signal, and calculating a difference between the radar video signal and the moving average value signal, Difference calculating means for outputting as a difference signal, smoothing means for smoothing the moving average value signal and outputting as a smoothed signal, and selecting means for selecting and outputting the difference signal and the radar video signal. The selecting means includes: means for comparing the smoothed signal with a reference signal to output a comparison signal; and taking in the transmission trigger signal and the comparison signal of the radar device and receiving the transmission trigger signal. While the comparison signal continues to indicate that the smoothed signal is larger than the reference signal, the differential signal is selected and output, and then the comparison signal is output. But after showing that the smoothed signal is smaller than the reference signal, after that point,
A signal output device that selects and outputs the radar video signal regardless of the comparison signal until a next transmission trigger signal is received.