JPS6219780A - Composite target detection method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a method for detecting a target when the brightness temperature of the target is lower than that of the background and the electromagnetic wave reflectance of the target is higher than that of the background.
Rather than detecting a target based only on the target-background reflected power pattern obtained by irradiating electromagnetic waves, the contrast between the target and background can be detected by combining the target-background pattern obtained without irradiation and taking the difference between them. This invention relates to a composite target detection method that increases the

(Background of the Invention) Conventional radars using microwaves, infrared rays, or the like employ a method of detecting targets based on a reflective covert pattern of irradiated electromagnetic waves. This is useful for target detection when there is almost no reflected power from the background, such as when detecting an aircraft from the ground, or when detecting a target even when there is reflected power from the background, such as when using an aircraft-mounted side-looking radar. This method is effective in detecting changes in the Doppler frequency of a sensor and overlapping multiple pieces of data to obtain high resolution.

On the other hand, passive detection devices that do not emit electromagnetic waves use natural phenomena to detect targets, and in order to be able to detect a target, there must be a brightness temperature difference between the target and the background.

There are two types of phenomena in this case: a case where the target has a higher brightness temperature and a case where the background has a higher brightness temperature. Both have the advantage of being resistant to artificial deception.

Although it is possible to manufacture a device equipped with both the active and passive detection methods described above, the important point is the hardware in the former, and the propagation loss in the latter. However, from the point of view of target identification, it is highly desirable to obtain a greater target-background contrast than when detecting a target using each method alone.

(Prior Art) An example of the prior art will be described using the block diagram of FIG. 3 and the time chart of FIG. 4.

First, the active method will be explained. The output 1 of the transmission source 21 and the output 2 of the pulse generator 23 are connected to the pulse modulator 2.
2 and obtain the pulse modulator output 3. The power is inputted to the power amplifier 24 to obtain a power amplifier output 4, which is irradiated from the transmitting antenna 25 as a transmitting output 5 in the target direction. The reflected waves from the target and the background are received by a receiving antenna 31 as a receiving input 10 and a receiving antenna output 11.
becomes. This signal and the output 12 of the local oscillator 33 are input to the mixer 32, and the output 13 is obtained. This is input to the intermediate frequency amplifier 34 and becomes the intermediate frequency amplifier output 14,
This is input to the wave detector 35 to obtain the wave detector output 15.

Next, the passive method will be explained. This method uses only an active receiving system, that is, a configuration from the receiving antenna 31 to the detector 35. In this case, the receiving input 10 is an electromagnetic wave naturally radiated from the target and the background. The following signal flow overlaps with the above, so it will be omitted.

The time chart in FIG. 4 shows the case where detection is performed alternately by the active method and the passive method, and the brightness temperature of the target is smaller than that of the background. Figure 4 (A
) is the output 2 in Figure 3, (B) is the transmission output 5, (C) is the receiving antenna output 11, and the upper part of (D) is the detector output 15 in the active method. The lower row shows the detector output 15 in the passive method. The search direction is the one in which the measured distance is set to a constant value R and moved in the angular direction, as in the example of the situation shown in FIG. 5, where the target is in the direction of pulse 2.

As shown in these figures, conventionally the detector output 1 in Fig. 4
The target was detected by superimposing one or more of the detection signals of each method shown in 5.

(Problems to be Solved by the Invention) In general, active methods have the advantage of a relatively long detection distance, while passive methods have the advantage of being resistant to interference. However, the range in which the detection signal is effective in the passive method is considerably limited by propagation loss, and it is also affected by weather phenomena and the color and shape of the target.Therefore, great efforts have been made to improve reception performance. There is.

In addition, even in the active method, the target identification ability decreases in situations where the reflected power from the background increases, so hardware improvements such as making various changes to the transmission frequency and processing large amounts of received data at high speed are required. They will be forced to bear a heavy burden.

Furthermore, in the active method, if the brightness temperature difference between the target and the background is small, as in the case of detection using frequencies below the microwave band, the target detection ability is determined by the radar performance and the target's effective reflection area. If the brightness temperature difference between the target and the background is large, the contrast between the target and the background in the active method will deteriorate, and the target detection ability of the radar will deteriorate.

FIG. 2 shows the difference between the received signal by the millimeter wave active method and the received signal by the millimeter wave passive method, using the measured distance R in FIG. 5 as a parameter.

In this Figure 2, (A) shows the received signal in the case of a general microwave radar for reference, (B) shows the received signal by the millimeter wave passive detection method, and (C) shows the reception signal by the millimeter wave active detection method. It's a signal. Among these, it is particularly important to improve the deterioration of the contrast between the target and the background at relatively short distances in the active detection method (C).

(Means for Solving the Problems) In view of the above points, the present invention provides that when a target is detected in an active method, if the brightness temperature of the target is lower than the brightness temperature of the background, if the target is irradiated with electromagnetic waves, the target is detected. - The present invention aims to provide a composite target detection method that improves the deterioration of the contrast between the backgrounds and improves the target detection ability of the radar.

The present invention passively detects a series of signals including both target and background along distance or angular direction at both passively and actively detectable frequencies and ranges to obtain a passive detection signal; An active detection signal is obtained by detecting the same path as the detection path of the passive method, a difference signal is created by taking the difference between this active detection signal and the passive detection signal, and a target difference signal of this difference signal is obtained. The above-mentioned conventional problems are solved by detecting the target based on the difference between the background difference signal part and the background difference signal part.

(Operation) The basic difference between the present invention and the prior art is that detection signals that have been individually obtained and processed using active or passive methods are combined, the difference is taken, and the difference is used as one detection signal. FIG. 4 (
The detector output 15 in D) has opposite polarity in the active method and the passive method. This situation is also shown in FIGS. 2(B) and (C). Therefore, the contrast between the target and the background can be improved by obtaining a difference signal between the detection signals of both types (the difference between the target part and the background part).

(Example) Hereinafter, an example of the composite target detection method according to the present invention will be described with reference to the drawings.

In FIG. 1, the configuration of the active system 21 to 25 and 31 to 35 is the same as the conventional configuration in FIG.
5) and an odd comparator 41 are added. Here, when detection by the active method and detection by the passive method are performed in a time-sharing manner, the comparator 41 also has the function of temporarily storing the detector output 15.

In the above configuration, the detection by the active method and the detection by the passive method are performed alternately, for example, to generate a series of signals including both the target and the background along the distance or angular direction at frequencies and ranges detectable by both methods. is detected by a passive method to obtain a passive method detector output 15, and the same path as the passive method detection path is detected by an active method to obtain an active method detector output 1.
Get 5.

Now, the detector output 15 in FIG. 4 described in the description of the prior art has opposite polarities for the same target in the active method and the passive method. This situation is shown in Figure 2 (B
) and (C).

Therefore, in the comparator 41, the difference between the detector outputs of both methods (the difference between the target signal parts and the difference between the background signal parts)
By calculating the comparator output 42, the contrast between the target and the background will be improved. That is, the difference between the target difference signal portion and the background difference signal portion in the difference signal obtained as the comparator output 42 becomes large.

Since the present invention is effective when the measurement distance R shown in FIG. 2 is relatively short, the reason for contrast improvement will be explained only in this case. Now the signal in Fig. 2 (B) is -27, (k),
Assume that the signal (C) is obtained with 2To(k). The threshold for target detection is 3T in the active method, (k),
Assume that it is -3To(k) in the passive method and is not recognized as a target. However, like the present invention (
If a signal C)-(B) is generated by the comparator 41 and the threshold value is set to 3T, (k), this can be recognized as the target. This is the signal shown in FIG. 2 (D). The signal (D) based on the method of the present invention uses the reflected power itself from the target for target detection, whereas the signal (C) based only on the active detection method detects the target even though the reference is different. - Since it is processed as a contrast between the background, the reflected power from the target is not used effectively for target detection.

In this way, the contrast between the target and the background can be improved by very simple means.

(Supplementary Explanation of Examples) (1) The frequency used may be any frequency that can detect the brightness temperature difference, and may be millimeter waves or infrared rays.

(2) The transmission waveform may be a pulse wave method or a continuous wave method, and the number of devices may be a single device or a plurality of devices depending on the method.

(3) The parameter that makes the present invention more effective than the conventional technology has been explained only in terms of distance, but basically the active method increases the reflected power from the background, and it is sufficient as long as it is within the range that can be detected by the passive method. An angle may also be used as a parameter.

(4) In implementing the method of the present invention, the comparator 41 and the like may be implemented using software of an electronic computer, or may be implemented using hardware.

(Effects of the Invention) As explained above, according to the composite target detection method of the present invention, both the target and the background can be detected along the distance or angular direction at frequencies and ranges that can be detected by both passive and active methods. A series of signals including the above are detected by a passive method to obtain a passive detection signal, and the same path as the detection path of the passive method is detected by an active method to obtain an active detection signal, and this active detection signal and the passive detection signal are detected by an active method. A difference signal is created by calculating the difference between the target and background difference signals, and the target is detected based on the difference between the target difference signal portion and the background difference signal portion of this difference signal, so that the following effects can be obtained.

(1) Even if the reflected power from the background is relatively large, the target can be detected relatively easily.

(2) The present invention requires only some changes, such as the signal processing unit, in the case of a conventional device that uses both active and passive detection methods. Can be used in combination with

(3) Target detection power is improved compared to radars using only the active detection method.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an embodiment of the composite target detection method according to the present invention, Figure 2 is an explanatory diagram showing a comparison of detection signal patterns obtained by each detection method, and Figure 3 is a conventional active method. 4 is a time chart for explaining the operation of FIG. 3, and FIG. 5 is an explanatory diagram of the situation shown in the time chart of FIG. 4. It is. 1... Transmission source output, 2... Pulse generator output, 3...
...Pulse modulator output, 4...Power amplifier output, 5.
...Transmission output, 10...Reception input, 11...Reception antenna output, 12...Local oscillator output, 13...Mixer output, 14...Intermediate frequency amplifier output, 15...
Detector output, 21... Transmission source, 22... Pulse modulator, 23... Pulse generator, 24... Power amplifier,
25... Transmitting antenna, 31... Receiving antenna, 3
2... Mixer, 33... Local oscillator, 34... Intermediate frequency amplifier, 35... Detector, 40... Receiving system,
41... Comparator, 42... Comparator output.

Claims (1)

[Claims] (1) Obtain a passive detection signal by passively detecting a series of signals including both the target and the background along the distance or angular direction at frequencies and ranges detectable by both passive and active methods, and An active detection signal is obtained by detecting the same path as the detection path of the passive method, and a difference signal is created by taking the difference between this active detection signal and the passive detection signal, and a target difference signal portion of this difference signal is obtained. A composite target detection method characterized by detecting a target based on the difference between the signal and the background difference signal.