JPS636835B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applied to a weather radar device that quantitatively measures meteorological information such as rain and snow using a radar, and eliminates unnecessary information such as mountains, plants, buildings, etc., so-called grand clutter. The present invention relates to a radar signal processing device that can remove unnecessary information and accurately extract only weather information even when the weather is heavy.

As is well known, in conventional air traffic control radar,
There is a moving target indication method, so-called MTI method, which removes unnecessary information such as ground clutter and extracts only target information such as aircraft. It has a function to erase fixed targets such as clutter.

In the case of weather radar, in order to remove ground clutter and extract only weather information, it is necessary to pay attention to the difference in the correlation of each radar transmission pulse of the received signal between fixed targets such as ground clutter and weather information. It is known that quantitative weather information can be measured by using the above MTI method.

Now, a typical weather radar uses a receiver receiving circuit having a logarithmic characteristic in order to display and measure weather information having a very wide range of amplitude levels without saturation. Therefore, in order to measure quantitative weather information by adopting the MTI method in this receiver signal processing stage, logarithmically linear transformation is performed,
It is necessary to use the MTI method with linear characteristics.

In other words, the received power of the ground clutter for each radar transmission pulse from the logarithmic characteristic receiving circuit is 10logPg.
(t), 10logPg (t-T), ..., 10logPg (t-nT),
Also, the received power of weather information is 10logPr(t), 10logPr(t
−T), ..., 10logPr(t-nT), and the received power with ground clutter and weather information superimposed is 10log(Pr
+Pg)(t), 10log(Pr+Pg)(t-T),..., 10log
(Pr+Pg)(t-nT), each is transformed into a logarithm, and Pg(t), Pg(t-T),..., Pg(t-
nT), also Pr(t), Pr(t-T), ..., Pr(t-
nT), (Pr+Pg)(t), (Pr+Pg)(t-T),
..., (Pr+Pg)(t-nT) is obtained. By passing these signals through the MTI circuit, in the case of only ground clutter, the correlation coefficient between Pg(t) and Pg(t-T) approaches 1, and the MTI circuit output becomes almost zero.
Therefore, when ground clutter and weather information are superimposed, the MTI circuit output is (Pr + Pg) (t) - (Pr
+Pg)(t-T)=Pr(t)-Pr(t-T), and only weather information can be extracted.

However, in reality, ground clutter fluctuates to a large extent due to the influence of wind, etc., or due to the superposition of receiver noise. This fluctuation component is
Although it is considerably compressed by using a logarithmic characteristic receiving circuit, by performing logarithmic linear transformation at the MTI circuit input stage, it is detected as a large fluctuation component at the MTI circuit output stage, which has a great influence on the measurement of weather information. was.

The configuration of this conventional radar signal processing device will be explained with reference to FIG. That is, the radar target reflected signal captured by the antenna 1 is supplied to the quantization circuit 3 via a logarithmic characteristic receiving circuit 2, which is comprised of, for example, a logarithmic amplifier, in the receiver. The quantization circuit 3 is composed of, for example, a so-called AD converter, and derives a digital signal quantized in the amplitude direction for each distance sampling signal. Next, this quantization circuit 3 output signal is converted into a linear characteristic signal by a logarithm-linear conversion circuit 4, and this output signal and a delay circuit 5 output signal that gives a one transmission repetition time delay of the radar are introduced into a subtraction circuit 6. The fluctuation components of both output signals are extracted. Next, the output signal of the subtraction circuit 6 is converted into a logarithmic characteristic signal by a linear-to-logarithmic conversion circuit 7 to obtain a logarithmic signal similar to that of a conventional weather radar. FIG. 2 is a signal waveform diagram of the apparatus shown in FIG. 1, in which waveform a is the output signal waveform of the logarithmic characteristic receiving circuit 2, and waveform b is the output signal waveform of the linear-to-logarithmic conversion circuit 7. Further, in waveforms a and b, 21 indicates ground clutter on which fluctuation components are superimposed, 22 indicates rain, and 23 indicates noise. In the conventional device shown in FIG. 1, the ground clutter and the weak fluctuation component 21 superimposed on the output signal of the logarithmic characteristic receiving circuit 2 shown in waveform a in FIG. (24 in waveform b in FIG. 2), and it is difficult to distinguish it from weather information.

The present invention has been made in view of the above drawbacks, and
The object of the present invention is to provide a radar signal processing device that does not deteriorate the quantitative measurement ability of weather information in the MTI method of a conventional radar signal processing device and effectively removes unnecessary information such as ground clutter.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. That is, the target reflected signal captured by the antenna 31 is supplied to a logarithmic characteristic receiving circuit 32 comprising a logarithmic amplifier or the like. The received signal that has been logarithmically amplified by the logarithmic characteristic receiving circuit 32 is subjected to A-to-D conversion of the amplitude level for each distance sampling signal by a quantization circuit 33 such as an A-to-D converter. Now, let the output signal of the quantization circuit 33 be Alog _K P(t), and use this as the first
When passed through the MTI circuit of the conventional device shown in the figure, the output signal Alog _K ΔP(t) is as follows.

Alog _K △P(t)=Alog _K {P(t)−P(t−T)}
......(1) Also, this equation (1) can be transformed as follows.

Alog _K △P(t)=Alog _K P(t) +Alog _K {1-P(t-T)/P(t)} ......(2) Here, P(t)=K ^logKP(t) , P(t-T)=
By setting K ^logKP(tT) , the above equation (2) can be replaced as follows.

Alog _K △P(t)=Alog _K P(t) +Alog _K [1-K-{AlogKP(t) −AlogKP(tT)}/A] ......(3) The device of the present invention uses this formula (3) Take advantage of. That is,
For example, A=10, K=10, and the quantization circuit 33
For example, if the output signal is 10 bits, the output signal for each transmission repetition is 10logP(t), 10logP(t-T),...
is obtained as a 10-bit digital signal. This quantization circuit 33 output signal is supplied to a delay circuit 34 that delays radar transmission repetition time T and a subtraction circuit 35, so that the subtraction circuit 35 output signal becomes {10logP(t)−10logP(t−T)}. Become.

This subtraction circuit 35 output signal is supplied to a conversion circuit 36, which converts the logarithmic conversion output signal 10log[1-10-{10logP] corresponding to {10logP(t)-10log(t-T)}
(t)-10logP(t-T)}/10].

This conversion circuit 36 may be configured such that a central processing unit (CPU) performs a logarithmic operation for each input signal, or the conversion circuit 36 may be configured such that a central processing unit (CPU) performs a logarithmic operation for each input signal, or the output signal value corresponding to the input signal value is calculated and tabulated in advance, and the conversion circuit 36 is read-only. The configuration may be such that a memory (ROM) or the like is configured to read and supply an output signal value corresponding to an input signal value. In this way, the output signal of the conversion circuit 36 and the output signal from the quantization circuit 33 are supplied to the output circuit 37, and the addition circuit 371 performs an addition operation on these two signals.

On the other hand, the output signal of the subtraction circuit 35 is
8, and is compared with the threshold signal generated by the threshold generation circuit 381 in the amplitude comparison circuit 382. Therefore, the output signal of the amplitude comparison circuit 382 is supplied to the gate circuit 372, and only when the output signal of the subtraction circuit 35 is greater than the threshold signal, the addition circuit 3
Gate circuit 372 to output the 71 output signal
control.

FIG. 4 shows signal waveforms of the device according to the present invention, in which waveform a is the output signal waveform of the logarithmic characteristic receiving circuit 32, and waveform b is the output signal waveform of the adder circuit 371. This signal waveform b is the same as that shown in waveform b in FIG. 2, and the ground clutter 41 on which the fluctuation components are superimposed is detected as a large fluctuation component 44 at the output stage of the adder circuit 371. However, the subtraction circuit 35
In the output stage, the ground clutter 45 in which fluctuating components are superimposed as shown in waveform C shown in FIG. 4 is small. The output of this subtraction circuit 35 is applied to a detection circuit 38. This detection circuit 38 is a threshold generation circuit 3 that generates the minimum meteorological information amount detection level (46 in waveform C in FIG. 4).
81 and an amplitude comparison circuit 382 that compares the amplitude of the output signal of the threshold value generation circuit 381 and the output signal of the subtraction circuit 35.
When the output level exceeds the minimum weather information amount detection level, an output signal is derived from the amplitude comparison circuit 382. This output signal is, for example, the waveform d in Figure 4.
It is indicated by. Then, this output signal is added to the adder circuit 37.
This gate circuit 372 is supplied as a gate signal to the gate circuit 372 provided in the first output stage.
, an output signal like the waveform e in FIG. 4, i.e.,
Weather information that does not include noise components 43, for example, a signal 42 representing rain, can be extracted.

In this way, the device of the present invention does not degrade the quantitative measurement ability of weather information in the MTI method of conventional radar signal processing devices, and moreover effectively removes unnecessary information such as ground clutter, thereby making it possible to accurately measure weather information. There are advantages that can be achieved. In addition, in Figure 3,
Although the gate circuit 372 is added to the output stage of the adder circuit 371, the same effect can be obtained by adding it to the input stage of the adder circuit 371.

Furthermore, in the embodiment shown in FIG. 3, a single erasure filter composed of a delay circuit 34, a subtraction circuit 35, a conversion circuit 36, and an output circuit 37 is used. It goes without saying that the present invention can also be applied to a so-called double erasure filter in which one additional circuit is added.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a conventional radar signal processing device, FIG. 2 is a signal waveform diagram for explaining the operation of the device shown in FIG. 1, and FIG. 3 is a diagram of a radar signal processing device according to the present invention. FIG. 4 is a block diagram showing the embodiment, and is a signal waveform diagram for explaining the operation of the apparatus shown in FIG. 3. 31... Antenna, 32... Logarithmic characteristic receiving circuit, 33
...Quantization circuit, 34...Delay circuit, 35...Subtraction circuit, 36...Conversion circuit, 37...Output circuit, 38...Detection circuit.

Claims (1)

[Claims] 1 Target reflected radar signal P captured by antenna
(t) and outputs a signal corresponding to Alog _K P(t) (A is a constant); a quantization circuit that quantizes the output signal of this reception circuit in the amplitude direction; a delay circuit that delays the output signal of the quantization circuit by a radar transmission repetition time; a subtraction circuit that subtracts the output signal of the delay circuit from the output signal of the quantization circuit to derive a signal S(t); a conversion circuit that is supplied with an output signal and derives a signal corresponding to Alog _K {1-K ^-S(t)/A }; and a signal that is supplied with an output signal of the subtraction circuit and that is higher than a predetermined level. A radar signal processing device comprising: a detection means for detecting; and an output means for outputting a sum signal of the output signal of the conversion circuit and the output signal of the quantization circuit only when there is a detection output of the detection means.