JP2720129B2 - Transmitter and receiver for Doppler acoustic radar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitting and receiving apparatus for a Doppler acoustic radar used for observing a wind speed altitude distribution above an airfield.

[0002]

2. Description of the Related Art A Doppler acoustic radar has been used as a device for measuring the wind direction and wind speed at each altitude in the atmospheric boundary layer from the ground for the purpose of observing a wind speed altitude distribution above an airfield and predicting air pollution. I have. This Doppler sound wave radar emits a powerful sound wave pulse from the ground into the air above, and transmits and receives reflected waves of weak energy that are reflected back from the density fluctuation region that is not a little present in the air and return. Sound is collected by a transducer, converted into an electric signal, a signal on a time axis corresponding to a desired measurement altitude is cut out, and a relative Doppler shift amount from a transmission frequency is calculated using a method such as fast Fourier transform (FFT). It is configured to detect and calculate the wind direction and wind speed. When three-dimensionally detecting the wind direction and the wind speed, three transducers are installed while shifting the radiation directions to each other.

[0003] The energy of the reflected wave received by the dual-purpose transmitter / receiver is weak, attenuated to about ^{10-9 10-11 of} the radiation pulse. Meanwhile, the energy of the radiated sound pulse is set to a value as large as several hundred W to 1 KW. As shown in FIG. 5, the waveform of the radiated sound pulse is such that a sine wave (pure sound) of about several thousand Hz is made continuous over a period of about several tens msec to several hundred msec. Also, since the frequency spectrum of the surrounding noise differs depending on the location,
A plurality of frequencies ranging from about 1000 Hz to 5000 Hz can be oscillated, and a frequency having the lowest noise level is selected and transmitted according to the place of use.

[0004]

In the above-mentioned conventional Doppler acoustic wave radar, it is necessary to emit an audible sound of strong energy, and reflection occurs in an unexpected direction depending on atmospheric conditions. You may receive noise complaints. Therefore, in this type of Doppler acoustic wave radar, an important issue is how to reduce the energy of the radiated acoustic waves, but this is considerably difficult because it is necessary to secure an SN ratio with respect to the surrounding noise.

[0005]

According to the present invention, there is provided a transmitting / receiving apparatus for a Doppler acoustic wave radar, which emits a sine wave of a predetermined frequency including a rising portion having a gradually increasing amplitude and a falling portion having a gradually decreasing amplitude as a sound wave. Is configured.

[0006]

According to the present invention, as shown in FIG. 2, the waveform of a radiated sound wave is a sine wave of a predetermined frequency including a rising portion whose amplitude gradually increases and a falling portion whose amplitude gradually decreases as a sound wave. Due to the radiation, the evaluation noise level is reduced by about 5 dB compared to the case of a shock-like waveform that rises sharply as in the conventional example of FIG. That is,
Even if the radiant energy is the same, the degree of harshness can be reduced by about 5 dB by making the rising part and the falling part gradual, as compared with an impact waveform (a so-called kinkin sound). For details of the evaluation noise, refer to “Handbook for Noise and Vibration Countermeasures” edited by the Japan Society of Acoustical Materials, if necessary.

[0007]

FIG. 1 is a block diagram showing a configuration of a Doppler sound wave transmitting / receiving apparatus according to an embodiment of the present invention. Reference numeral 11 denotes a control unit, 12 denotes a variable frequency oscillator that outputs sine wave signals of different frequencies, 13 Is a pulse gate circuit, 14 is a variable low-pass filter (LPF), 15 is a power amplifier, 16
Is a transmission / reception switching circuit, 17 is a preamplifier circuit, 18 is a TVG
Amplifying circuit, 19 is a variable band-pass filtering circuit (BPF), 2
0 is an A / D conversion circuit. Further, 21 is a bus, 22 is a CPU, 23 is a ROM / RAM, 24 is a fast Fourier transform (FFT) circuit, 25 is an input / output (I / O) circuit, 26
Is an input / output interface circuit, 27 is a display / output unit, 2
8 is a keyboard.

[0008] When the CPU 22 receives a measurement start command from the keyboard 28 via the input / output interface unit 26, it activates the control unit 11 via the input / output circuit 25. The started control unit 11 starts the variable frequency oscillation circuit 12, and outputs 1600 Hz, 2400 Hz, 320
CPU 22 out of four frequencies of 0 Hz and 4800 Hz
Output a sine wave of one specified frequency. As the frequency, only one which is expected to have the highest SN ratio based on the noise spectrum measured at the time of installation of the apparatus or prior to the emission of the sound wave pulse is selected by input from the keyboard 28.

A sine wave signal output from the variable frequency oscillation circuit 12 is pulsed by a pulse gate circuit 13 which is opened for several tens to several hundreds of milliseconds in accordance with a command from the control unit 11.
To form a pulse signal having a steep rising portion and a falling portion as shown in FIG.
The signal is supplied to the variable low-pass filtering circuit 14. The pass band of the variable low-pass filter 14 ranges from 0 Hz to 1 / TgH depending on the gate open period Tg set in the pulse gate 13.
It is set in a range of about z. As shown in FIG. 2, the signal passing through the variable low-pass filtering circuit 14 has a waveform whose amplitude gradually increases at the rising portion and gradually decreases at the falling portion. The signal that has passed through the variable low-pass filter circuit 14 is supplied to a power amplifier circuit 15, amplified to a level of several tens of W to 1 KW, passed through a transmission / reception switching circuit 16 and sent to a dual-purpose transmitter / receiver (not shown). It is sent out on a continuous cable C.

[0010] Thereafter, as illustrated in FIG. 3, the reflected wave from the sky is received by the combined transmitter / receiver with a certain time delay from the emission of the sound wave, and appears on the cable C. This reflected wave is supplied to the amplifying circuit 17 via the transmission / reception switching circuit 16, receives low-noise amplification, and is supplied to the TVG amplifying circuit 18. The TVG (time variable gain) amplifier circuit 18 is proportional to, for example, the square of time at an appropriate speed with time in order to compensate for the diffusion loss and absorption loss of energy accompanying the propagation of the radiation acoustic pulse. The speed allows the gain to increase over time. The amplified reflected pulse is 1
600Hz, 2400Hz, 3200Hz, 4800H
After unnecessary frequency components are removed in a variable band-pass filter (BPF) 19 for selectively passing only one actually radiated one of the four frequencies of z in accordance with a command from the control unit 11, A / The signal is supplied to a D conversion circuit 29, converted into a digital signal,
The data is transferred to U22 and taken into ROM / RAM23.

The CPU 22 detects a component on the time axis corresponding to a desired altitude out of the received signal containing the reflected wave taken into the ROM / RAM 23, for example, as shown in FIG. A component having a time width of ΔT at the time is extracted and supplied to the FFT circuit 24. FFT circuit 24
Converts this signal into a frequency spectrum and transfers it to the CPU 22. As illustrated in FIG. 4, the frequency spectrum has a noise component distributed around the frequency of the reflected wave that has undergone the Doppler shift.

The CPU 22 examines the data received from the FFT circuit 24 and calculates the relative Doppler shift amount δf / F by normalizing the Doppler shift amount δf with the corresponding transmission frequency F. The wind direction and wind speed are calculated by multiplying the values. The wind direction is determined from the polarity of the Doppler shift amount δf. The measurement result is displayed on the display / output unit 2 according to a command from the keyboard 28.
7 and displayed on a display, printed out, or stored in a magnetic disk device or the like.

Although the transmitting and receiving apparatus of the present invention has been described with reference to one embodiment, various modified embodiments can be considered within the scope of the present invention. Only the main ones of these modified embodiments will be listed below.

Instead of using a variable low-pass filtering circuit to smooth the rising and falling portions of the steep pulse waveform, a rising portion using a low-pass filtering circuit or a band-pass filtering circuit with a fixed pass band is used. A configuration that smoothes the falling part.

A configuration in which an amplitude modulation circuit is used in place of various filtering circuits to smooth the rising and falling portions of a steep pulse waveform.

A structure in which the pulse gate is gradually opened and gradually closed to smooth the rising and falling portions of the steep pulse waveform.

[0017]

As described above in detail, the transmitting and receiving apparatus of the Doppler acoustic wave radar according to the present invention generates a sine wave of a predetermined frequency including a rising part whose amplitude gradually increases and a falling part whose amplitude gradually decreases. Since the sound wave is radiated as a sound wave, the evaluation noise level is 5d as compared with the conventional case in which the rising part and the falling part emit a sound wave having a steep impact.
B can be reduced.

Further, according to the Doppler sound wave level transmitting / receiving apparatus according to the present invention, the impact of the voltage applied to the electroacoustic transducer can be reduced, so that the life of the element can be extended.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a transmitting and receiving apparatus of a Doppler acoustic radar according to one embodiment of the present invention.

FIG. 2 is a conceptual diagram illustrating a waveform of a radiation pulse transmitted from the transmission / reception device of FIG. 1 to a transducer.

FIG. 3 is a conceptual diagram illustrating a waveform of a reflected wave input to FIG. 1 from a transmitter / receiver.

FIG. 4 is a conceptual diagram illustrating a frequency spectrum of a reflected wave detected by the FFT circuit of FIG. 1;

FIG. 5 is a conceptual diagram illustrating a waveform of a sound pulse emitted from a conventional Doppler sound radar.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Control part 12 Variable frequency oscillation circuit which selectively generates one of sine waves of different frequencies 13 Pulse gate circuit 14 Variable low-pass filter circuit 15 Power amplifier circuit 22 CPU 24 FFT circuit

Claims (1)

(57) [Claims] A sound wave in an audible frequency band is radiated into the atmosphere, a reflected wave reflected from a density fluctuation region existing in the air is received, and a Doppler shift amount of a frequency component included in the reflected wave is obtained. In the transmitting and receiving apparatus of a Doppler acoustic wave radar for detecting a wind speed at a desired altitude, the emitted sound wave is formed of a sine wave of a predetermined frequency including a rising portion whose amplitude gradually increases and a falling portion whose amplitude gradually decreases. A transmission / reception apparatus for a Doppler acoustic radar.