JPH052111B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a target detection system that is capable of extracting a target by removing unnecessary information such as background noise from a signal obtained by a radial scan device. Regarding the extraction device.

[Conventional technology]

FIG. 2 is a diagram showing an example of the configuration of a conventional target extraction device using a radial scan device, in which 1 is input light, 2 is a radial scan optical system, 3 is a light receiving element, and 4 is a light receiving device. Element output, 5 is sampler, 6 is sampler output, 7 is A/
D converter, 8 is the A/D converter output, 9 is the differential coefficient detector, 10 is the target position signal, 11 is the coordinate converter, 12 is the target position signal (X direction), 13 is the target position signal (Y direction) be.

FIG. 3 is a diagram showing the scanning pattern of the radial scan optical system 2 in FIG. 2, where 14 is the radial scan pattern, 15 is the X coordinate axis, and 16 is the Y coordinate axis.

FIG. 8 is a diagram showing the configuration of the coordinate converter 11 in FIG.
5 is sine memory 2, 46 is cosine memory 1,
47 is cosine memory 2, 48 is adder 1, 49
is adder 2.

The radial scan optical system 2 in FIG. 2 scans within its field of view as shown by the radial scan pattern 14 in FIG. When the radial scan pattern is described by a coordinate system indicated by the X coordinate axis 15 and the Y coordinate axis 16, it becomes as shown in equation (1).

X=φ(−Cos2πf ₁ t+Cos2πf ₂ t)/2 Y=φ(Sin2πf ₁ t+Sin2πf ₂ t)/2 However, ±φ: Scanning field of view f ₁ , f ₂ : f ₂ / f ₁ = k−n/k
A natural number that satisfies (n: the number of petals in the radial scan pattern k: an integer that has no common divisor with n t: time...(1) The light scanned by the radial scan optical system 2 in Fig. 2 is , enters the light-receiving element 3 and is converted into an electrical signal.The light-receiving element output 4 is sampled at regular time intervals by a sampler 5.The sampler output 6 is sampled by an A/D converter 7. It is quantized into N bits (N is a natural number).The differential coefficient detector 9 determines the time when the time rate of change of the A/D converter output 8 is maximum within one scanning time as the target position. That is, if the A/D converter output 8 is AD(T) (T is time, an integer), the target position signal 10 which is the output of the differential coefficient detector 9 is EG(T) in equation (2). This is T when it takes the maximum value among the scanning times of the entire field of view.

EG(T)=|AD(T)−AD(T−K)| …(2) (K is a constant integer) The target position signal 10 is converted to X in FIG. Coordinate axis 15 and Y coordinate axis 1
6 is converted into the coordinate system indicated by 6. Target position signal (X direction) 12 is X _t , target position signal 10 is
If T _nax , then equation (3) holds true from equation (1).

X _t = φ (−cos2πf ₁ Tmax + cos2πf ₂ Tmax)/2 Y _t = φ (sin2πf ₁ Tmax + sin2πf ₂ Tmax)/2 ...(3) In the coordinate converter of Fig. 8, the target position signal 1
0Tmax is input to sine memory 144, sine memory 245, cosine memory 146, and cosine memory 247, and φ/2sin2πf ₁ Tmax, φ/
2sin2πf ₂ Tmax, −φ/2cos2πf ₁ Tmax, φ/2
Output cos2πf ₂ Tmax. These are adder 1
48 and an adder 249, which output a target position signal (X direction) 512 and a target position signal (Y direction) 13, respectively.

[Problem that the invention seeks to solve]

FIG. 4 is an example of an operational conceptual diagram of a target extraction device using a radial scan device, in which 17 is a radial scan device, 18 is a target, 19 is a sea surface, and 20
is a line indicating the center of the visual field, 21 is a line indicating the upper limit of the visual field,
22 is a line indicating the lower limit of the visual field, 23 is the angle of depression at the center of the visual field, 24 is the angle of depression at the upper limit of the visual field, and 25 is the angle of depression at the lower limit of the visual field.

In FIG. 4, the radial scan device 17 is installed so as to look down on the sea surface 19. The radial scan device 17 scans the field of view as shown in the radial scan pattern 14 in FIG. The minimum number of points corresponds to a line 22 indicating the lower limit of the visual field, and the center of the visual field corresponds to a line 20 indicating the center of the visual field. That is, the radial scan device 17 scans the portion sandwiched between a line 21 indicating the upper limit of the visual field and a line 22 indicating the lower limit of the visual field in FIG. During this scanning, the angle of depression at which the light-receiving element 3 looks down on the sea surface 19 changes from the angle of depression 24 at the upper limit of the field of view to the angle of depression 25 at the lower limit of the field of view, centering on the angle of depression 23 at the center of the field of view. Now, if the depression angle at the center of the field of view is θ _c and the scanning field of view of the radial scan is ±φ, then the range of change of the depression angle θ at which the light receiving element 3 looks down on the sea surface 19 due to the radial scan is approximately as shown in equation (4). Become.

θ _c −φθθ _c +φ ...(4) FIG. 5 is a diagram showing an example of the depression angle dependence of background brightness in the infrared region, and 26 indicates the depression angle θ at which the light receiving element 3 looks down on the sea surface 19. , 27 is the background brightness, and 28 is the depression angle dependence curve of the background brightness.

The distance between the light receiving element 3 and the sea surface 19 is
changes depending on the angle of depression θ looking down on the sea surface 19, and therefore, due to the influence of the atmosphere existing between the light receiving element 3 and the sea surface 19, the background brightness has a depression angle dependence as shown in FIG.

FIG. 6 shows an example of the temporal change in the received power of the light receiving element 3 due to a radial scan when the background luminance has the depression angle dependence as shown in FIG. value), 30 is the time axis,
31 is the received power curve of the light receiving element 3, 32 is the scanning time for one petal of the radial scan, 33 is the location of the target, 34 is the location that is likely to be mistaken for the target, 41
is the axis of EG(T) calculated by the differential coefficient detector 9,
42 is EG(T) calculated by the differential coefficient detector 9
This is the characteristic curve of

In Fig. 6, the peak-to-peak value of the background noise caused by the depression angle dependence of the background brightness is considerably larger than the peak-to-peak value of the target signal, and therefore, there are many sources other than the target location 33 that are mistaken for the target. There is a location 34 where it is easy to do so. That is, in the prior art, the differential coefficient detector 9 in FIG.
There is a problem that the location 34 that is easily mistaken for the target may be mistakenly detected as the target, making it impossible to accurately extract the target.

The present invention has been made to solve these problems, and aims to effectively remove background noise caused by temporal changes in background brightness due to radial scanning, and to perform accurate target extraction.

[Means for solving problems]

The target extracting device according to the present invention includes a smoothing device for smoothing a signal obtained by digitally converting a signal from a radial scan device into N bits (N is a natural number), and an output of the smoothing device to be used as a signal from the radial scan device. The subtracter is provided with a subtracter that subtracts the signal from the N-bit digitally converted signal, and a maximum value detector that detects the maximum value of the output of the subtracter.

[Effect]

In this invention, a signal obtained by taking a time average over a certain period of time for each point of a signal from a radial scan device,
By subtracting from the original signal from the radial scan device, a signal is obtained from which the influence of background noise caused by temporal changes in background brightness is removed, and the point where this signal is maximum is detected as the target position.

〔Example〕

FIG. 1 shows the configuration of one embodiment of the present invention, in which 35 is a smoother, 36 is a smoother output, 37 is a subtracter, 38 is a subtracter output, 39 is a maximum value detector, and 43 is a It is a day line.

In FIG. 1, the operations of the radial scan optical system 2, the light receiving element 3, the sampler 5, and the A/D converter 7 are similar to those described in the ``Prior Art'' section.
It is exactly the same as the one in the figure. The smoother 35 averages each point of the A/D converter output 8 over a certain period of time.
In other words, the A/D converter output 8 is AD(T)(T
is time, integer), smoother output 36 is ADS
When (T), equation (5) holds true.

However, c is a constant natural number. The subtracter 37 subtracts the smoothing device output 36 from the value obtained by time-correcting the A/D converter output by the delay line 43. That is, if the subtracter output 38 is Z(T), then equation (6) holds true.

Z(T)=AD(T)−ADS(T)...(6) When the calculation of Z(T) in one scanning period is completed, the maximum value detector 39 calculates Z(T) in the scanning period of the entire field of view. The time _Tt at which T) takes the maximum value is determined, and this is output to the coordinate converter 11 as the target position signal 10.

The operation of the coordinate converter 11 is exactly the same as that in FIG. 2 described in the ``Prior Art'' section.

〔Effect of the invention〕

FIG. 7 is a diagram showing the effect of the present invention, in which 44 is an axis of the subtractor output 38, and 40 is a characteristic curve of the subtractor output 38.

The characteristics in FIG. 7 are the signal shown by the received power curve 31 of the light receiving element 3 in FIG. 6, and the target position 33 in FIG. This signal is obtained by inputting the signal obtained by removing high frequency components present in the subtracter 37 in FIG. 1, and taking the difference between the two. That is, as shown in FIG. 7, the subtracter output 38 characteristic curve 40 has a maximum value at the target location 33, and there are no other locations that could be mistaken for the target. Therefore, the location 33 of the target can be detected accurately.

As described above, according to the present invention, it is possible to efficiently remove the background noise caused by temporal changes in the background brightness of the output of the radial scan device, accurately detect the target signal, and know the location of the target. Therefore, the present invention can greatly contribute to improving the accuracy and reliability of a target extraction device using a radial scan device.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of one embodiment of the present invention;
FIG. 2 is a diagram showing an example of the configuration of a conventional target extraction device using a radial scan device, FIG. 3 is a diagram showing a scanning pattern of the radial scan optical system 2 in FIG. 2, and FIG. 4 is a diagram showing a radial scan optical system 2. A conceptual diagram of the operation of the target extraction device using the device. Figure 5 is a diagram showing an example of the dependence of the background brightness on the depression angle in the infrared region. Figure 6 is a diagram showing the dependence of the background brightness on the depression angle as shown in Figure 5. FIG. 7 is a diagram showing an example of the temporal change in the received power of the light receiving element 3 due to radial scan when there is dependence.
The figure is a diagram showing the effects of the present invention, and FIG. 8 is a configuration diagram showing the coordinate converter 11. In the figure, 2 is a radial scan optical system, 3 is a light receiving element, 5 is a sampler, 7 is an A/D converter, 11 is a coordinate converter, 35 is a smoother, 37 is a subtracter, 39 is a maximum value detector, 43 is a day line. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1. A radial scan optical system that receives light from a target, a light receiving element that converts the light received by this radial scan optical system into an electrical signal, and a sampler that samples the electrical signal output from this light receiving element. , an A/D converter that converts the output of this sampler into a digital signal, a smoothing device that smoothes the output of this A/D converter, a delay line that time-corrects the output of the A/D converter, and this A subtracter that subtracts the output of the smoothing device from the output of the delay line, a maximum value detector that detects the time when the output of this subtracter becomes the maximum within one scanning time, and an output of this maximum value detector. X-Y from the time
A target extraction device comprising: a coordinate converter for calculating coordinates.