JPH0295294A - Rain and snow discrimination device - Google Patents

Abstract

PURPOSE:To enable one equipment to detect whether or not it rains or snow, discriminate between rain and snow, and detect the percipitation accurately and speedily by sending and receiving electromagnetic wave pulses and measuring the level of its reflected signal. CONSTITUTION:A transmitter 6 oscillates pulses of a sent wave Pt in the microwave band. A circulator 5 switches circuits in synchronism with the pulses and the sent wave Pt is radiated in the air through a radar antenna 1. The sent wave Pt is reflected by rain or fall O and the reflected wave Pr is received by the antenna 1. The reflected signal which is received by a receiver 7 is made into a video signal, which is held by a sample holding circuit 8 for a time corresponding to specific altitude. Then the signal is outputted successively and converted 10 into a digital signal Xi, so that the correlation coefficient is calculated 14. Then a discrimination between rain and snow can be made from a correlation coefficient. Further, the precipitation data can be computed by a rain fall extent converting circuit 16 and an averaging processing circuit 17 from data SIGMAxi outputted from a computing element 11.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a device for identifying rain and snow using radar.

[Conventional technology]

The most accurate and quick way to determine rainfall and snowfall is through sky observation, but since observations cannot be made at unmanned locations and continuous observation is difficult, observations are made using various instruments. . For example, it would be possible to install equipment to observe rain and snow on expressways, etc., and to send the weather information at the site to a management location in real time, and to notify passing vehicles of this information by means of signs, etc. . Equipment for observing rain and snow includes rain gauges and equipment that directly measures the amount of snow on the road using ultrasonic waves or electromagnetic waves to obtain information and determine whether it is rain or snow. These devices cannot determine whether it is raining or snowing until a certain period of time has elapsed since it started raining, which may result in a lack of promptness in providing weather information or taking necessary safety management measures for roads in the area. was there. If we can observe snow when it starts to fall, we can make advance notifications before the snow accumulates, greatly improving safety. There are devices that use temperature sensors and devices that use optical sensors to observe snow when it starts to fall.

[Problem to be solved by the invention]

Devices that use the former type of temperature sensor are not necessarily reliable, as they may malfunction due to rain during cold temperatures, or may malfunction due to freezing of the sensor. Devices using the latter type of optical sensor may malfunction due to fog or other conditions other than rain or snow, and dirt on the surface of the sensor reduces identification ability. The present invention was made to eliminate these drawbacks, and it is possible to measure the presence or absence of rain and snow, distinguish between rain and snow, and measure the amount of precipitation with a single device. To provide a rain/snow identification device whose identification performance is not degraded due to dirt or the like.

[Means to solve the problem]

A rain and snow identification device to which the present invention is applied to solve the above problems will be explained with reference to FIG. 1 corresponding to an embodiment. As shown in the figure, the rain/snow identification device of the present invention has an antenna 1
a radar device 2 that is fixed toward the sky, transmits and receives electromagnetic waves in a pulsed form, and measures the intensity of the reflected signal Pr;
It has an arithmetic circuit 3 that calculates a correlation coefficient that varies between transmission pulses of a reflected signal Pr from rain and snow O received by the radar device 2 during precipitation.

[Effect]

When the intensity of the reflected signal E from a certain altitude is observed using the radar 2, the weather echoes of rain, snow, etc. change over time and statistically follow the Ray distribution. Weather echoes are reflections from a collection of small reflectors such as raindrops and snowflakes, and this is because the amplitude of the electromagnetic field that is vectorially synthesized based on the amplitude and phase relationships of the individual reflected electromagnetic fields is detected. The particle size distribution of raindrops is approximately represented by an exponential distribution. The falling speed of a raindrop is determined by the balance between the raindrop mold and air resistance. The average falling speed is 4.0 to 6.0 m7 seconds, but the falling speed is not constant depending on the size of the raindrops.1.
It has a spread from less than 0 m/sec to a maximum of 9.0 m/sec. On the other hand, the falling speed of snowflakes is about 176 to 8 l/8 of that of average raindrops. Furthermore, the difference in the falling speed of individual snowflakes is smaller than the difference in the falling speed of individual raindrops, and the spread of the speed distribution is small. The factors that change the position of precipitation particles such as raindrops and snowflakes in the pulse packet, which are determined by the beam width of the radar antenna 1 and the transmission pulse width, are the falling speed in the vertical direction and the wind speed in the horizontal direction. The transmission period of the pulses transmitted from the radar 2 is generally about several 100 Hz to several 1000 Hz, and the time interval is on the order of milliseconds. In the case of raindrops, the average vertical position variation between pulses is on the order of 1 cm, and the relative positional relationship also varies on the order of 1 cm due to the different falling speeds of individual raindrops. When the radar transmission frequency is a wavelength of several centimeters, the phase of the reflected electromagnetic field from individual raindrops is reversed by a position change of 1/4 of the radar wavelength, so the reflection from a constant pulse packet between transmitted pulses is The strength of the electromagnetic field varies widely. That is, the fluctuation period of the reflected signal from the rain is fast, and the correlation coefficient between pulses is small. On the other hand, the falling speed of a snowflake is 176 ~
178, the vertical positional variation between pulses is 1fflII+, and the relative positional relationship of the individual snowflakes is of an even smaller order. Therefore, in the radar of several CIl waves, the phase relationship of the electromagnetic fields reflected from individual snowflakes does not change significantly, and the fluctuations in the reflected electromagnetic fields between pulses are small. In other words, the fluctuation period of the reflected signal from snowfall is larger than that of the rain echo. The correlation coefficient between pulses has a large value. The horizontal positional variation of precipitation particles within a pulse packet is influenced by the strength of the wind speed. Assuming a crosswind wind speed of 30 m/s, the horizontal position variation of individual precipitation particles is on the order of at most 10 cm between radar transmission pulses. Furthermore, since the moving speed in the horizontal direction does not depend much on the size of the precipitation particles and is considered to be approximately constant, the relative positional relationship of the precipitation particles in the horizontal direction is expected to be even smaller. The size of the pulse packet is determined by the antenna beam width, pulse width, and observation altitude. For example, assuming that the antenna beam is 1 degree and the pulse width is 1 usec, the altitude is 200m.
The size of the pulse packet is 35 m in diameter in the horizontal direction.
, with a spread of 150m in the altitude direction. Therefore, the rate at which precipitation particles within a pulse packet are replaced due to fluctuations in precipitation particles of only 10 cm in the horizontal direction is small.
If the distance between the observation area and the radar antenna is several hundred meters, the phase fluctuation of the reflected wave caused by horizontal movement is very small and can be ignored. For this reason, the correlation between pulses of snowfall echoes when the crosswind is strong does not become a small value. Because of the above correlation, once the correlation coefficient is calculated by the arithmetic circuit 3, depending on the size of the correlation coefficient, rain,
Able to identify snow.

【Example】

FIG. 1 is a block diagram of an embodiment of a rainfall/snowfall identification device to which the present invention is applied. In the figure, 5 is a circulator, 6 is a transmitter, and 7 is a receiver, and the radar 2 is configured as described above. 8 is a sample hold circuit, 10 is an analog/digital (A/D) converter, 11 is a Σx1 arithmetic unit, and 12 is a Σx
, 2 arithmetic units, 13 is a Σ)'C+++ arithmetic unit, 14 is a correlation coefficient calculator, 15 is a low-pass filter (LPF), 16
1 is a rainfall intensity conversion circuit, 17 is an average processing circuit, and the arithmetic circuit 3 is constituted by the above. In the above circuit, the transmitter 6 oscillates a pulsed transmission wave pt in the microwave band. In the circulator 5, the circuit is switched in synchronization with the pulse, and the transmitted wave pt is radiated toward the sky through the radar antenna l. Rain or snow O is falling from the sky, and the transmitted wave pt hits the rain or snow O and is reflected. The reflected wave Pr is received by the antenna l. Circulator 5 is synchronized with the pulse,
It is switched so that the receiver 7 can receive the reflected signal E at a certain altitude (for example, 200 m altitude). Reception. The signal received at the rocky shore 7 is converted into a video signal and held in the sample-and-hold circuit 8 for a time corresponding to a predetermined altitude. - The once held signal is sequentially output and converted into a digital signal X by an analog/digital conversion circuit, after which a correlation coefficient is calculated. In the computing unit 11, Σ
xi, and the computing unit 12 calculates ΣX1. In the arithmetic unit 13, ΣX1*
1 is calculated respectively. The correlation coefficient calculating circuit 14 calculates the correlation coefficient ρ[jl by calculating the following formula from the above calculation results Σx1, Σxl, and ΣX I+1. Approximately 300 to 500 times is appropriate. Let j=1. Thereby, correlations are calculated for data of adjacent pulses in order. Data of the calculated correlation coefficient passes through a low-pass filter 15 to remove fluctuations due to noise, and is output as a rain/snow identification signal. In the circuit of this embodiment, the rainfall intensity conversion circuit 16 and the averaging circuit 17 calculate precipitation data from the data of Σx1 outputted from the arithmetic unit 11. FIG. 2 is a graph plotting data actually confirmed by the rain/snow identification device of the above-described embodiment. That (A
) is a diagram showing a radar reflection factor representing the strength of reflection of a weather echo with respect to altitude, and (B) is a diagram showing a correlation coefficient between pulses with respect to altitude. The radar transmission frequency uses the X band, and the pulse repetition frequency is 37
It was set to 5Hz. As shown in Figure 2 (A3), the reflection factor near the altitude of 4Klll is extremely large. This is due to the melting of water crystals and snowflakes in the upper atmosphere.Flight band When water or snow melts, it melts from its surroundings, so even if the center is a low-density water crystal or snow, if the surface is covered with a film of water, it will generate electromagnetic waves just like large raindrops. Therefore, the radar reflection factor at the melting layer becomes a large value.At the altitude below the melting layer, all the water and snow melts and becomes water, so its diameter becomes smaller and 1 reflection The factor is small (Naru,
From this, it can be seen that the echoes above the 4 km altitude prite band are reflected echoes from snow and water crystals, and the lower altitudes are the reflected echoes from rain echoes. As shown in FIG. 2(B), the correlation coefficient between the pulses of the radar reflected signal differs greatly at the altitude of the bright band near altitude 4 m. The correlation coefficient is small in the region of rain in the lower layer, and large in the region of snow and water crystals in the upper atmosphere. This shows that the rain/snow identification device of the present invention is operating effectively.

【Effect of the invention】

As explained above, the rain/snow identification device to which the present invention is applied can continuously observe weather conditions even in uninhabited areas. With a single device, it is possible to accurately and quickly detect not only the presence or absence of rain or snow, but also the discrimination between rain and snow, as well as the amount of rainfall and snowfall. This makes it possible to quickly provide weather information and take necessary safety management measures for roads in the area. In particular, the intensity of snowfall can be observed when it starts to fall, and advance notification can be made before snowfall, greatly improving safety. Moreover, since it uses a radio wave radar, there is no fear that the identification performance will deteriorate due to the influence of temperature or dirt on the sensor surface, making it an extremely reliable device. Since the observation altitude of the weather echo is a short distance of several hundred meters, the transmission output of the radar can be small, and the device can be made smaller and cheaper.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a rain/snow identification device to which the present invention is applied, and FIG. 2 is a graph of data confirmed by the rain/snow identification device. l...Antenna 2...Radar device 3...
Arithmetic circuit 5... Circulator 6... Transmitter 7... Receiver 8... Sample hold circuit 10... Analog/digital converter 11... ΣX, Arithmetic unit 12... Σx,' Arithmetic unit 13... Σx9゜1 arithmetic unit 14... Correlation calculator, ]5... Low pass filter 16... Rainfall intensity conversion circuit 17-... Average processing circuit

Claims (1)

[Claims] 1. A radar device having an antenna fixed toward the sky, transmitting and receiving pulsed electromagnetic waves, and measuring the intensity of reflected signals; 1. A rain/snow identification device, comprising: an arithmetic circuit that calculates a correlation coefficient that varies between transmitted pulses of a reflected signal, and distinguishes between rain and snow based on the magnitude of the correlation coefficient.