JPH079469B2 - Snow depth measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a snow depth measuring device for measuring the amount of snow for weather observation and the like.

[Conventional technology]

Conventionally, there is a measurement of the amount of snow in the meteorological observation items.There are a method of measuring by snow with a measuring scale installed on the ground and a method of obtaining from the round-trip propagation time of ultrasonic waves, the latter is suitable for automatic measurement. There is. The ultrasonic method provides a certain level of reception detection, detects the time when the reflected ultrasonic wave from the snow surface exceeds this level, and measures the time difference from the time of transmission to the time of reception. Detection method,
There is a peak time detection method in which the peak point of the received waveform is detected and measured by the time difference from the time of transmission to the time of the received peak.

[Problems to be solved by the invention]

However, the reception time detection method requires a measurement error when the reflection level changes due to snow quality, wind, etc. even if the amount of snowfall is constant, and the measurement error occurs when the snowfall surface is soft. It is also absorbed by snow and the reflected wave from the surface becomes very small, which causes a measurement error. On the other hand, the peak time detection method, when measuring a soft snow surface, the transmitted ultrasonic waves enter the inside of the snow surface, and the reflected wave is generated not only from the surface but also from the hard snow surface below it, Since the combined signal is received, there is a problem that the peak time is delayed from the reflection from only the surface and a measurement error occurs.

[Means for solving problems]

In order to solve such a problem, the present invention predicts the peak time from the reception time of the reflected wave, corrects the value based on this predicted peak value, and the measured value, whichever is shorter, is the detected value. To do.

[Action]

When the reception level is a normal value, a value that is added in advance according to the reception level is used as the predicted peak time, and when the reception level value is extremely smaller than the road surface reflection, the above-mentioned predetermined value is added. For example, the value obtained by subtracting 120 μs corresponding to 2 cm of snow is used as the predicted peak time, and the smaller of the predicted peak time and the actually measured peak time is used as the final peak value, and the snow accumulation is based on that peak time. It is a measure of quantity.

〔Example〕

FIG. 2 is an example of an apparatus configured by applying this method. 1 is a wave transmitter / receiver, 2 is a wave transmission drive circuit, 3 is a wave transmission / reception timing generation circuit, 4 is a CPU, 5 is a wave reception amplification circuit, 6 is a detection circuit, 7a and 7b are A / D conversion circuits, 8 is a temperature detector, 9 is an amplification circuit, 10 is an output circuit, 11 is an LED display circuit, 12 is a crystal oscillator, 13 is RAM, and 14 is ROM. , 15 are transducer height mounting switches. The output circuit outputs an analog output indicated by the symbol A, a digital output indicated by the symbol D, and a telemeter output indicated by the symbol T.

FIG. 3 is a waveform chart of each part of the circuit shown in FIG.
(E) is a waveform of the part of the symbols A to E attached to FIG.

The device thus constructed performs the operation shown in FIG. 1 under the control of the CPU 4. First, as shown in S50, ultrasonic waves are transmitted, which has a frequency of 26 kHz and a pulse width of 1 m, for example.
s, ultrasonic waves with a repetition period of 100 ms are transmitted toward the snow surface. The transmitted ultrasonic wave is reflected on the snow surface, the reflected wave is measured as shown in S51, and the round-trip time required from the transmitted wave to the received wave is measured as shown in S52. S520 processing is S520 ~ S
As shown in detail in 526, it is determined whether or not it is the reception timing in "reception timing start?", As shown in S520. As shown in FIG. 4 (b), the reception timing is, for example, the timing for opening the reception gate for 40 ms 10 ms after the transmission to take in the reception pulse with respect to the transmission timing shown in FIG. 4 (a). is there.

If S520 is "NO", then stop at that step and select "YE
When "S" is reached, the signal passing through the reception gate is sampled as shown in S521. This sampling is performed, for example, every 50 μs, and the sampled signal is A / D converted and supplied to the RAM 13. This process is S522
“Reception timing end?” Is performed for “NO”, and S5
If 22 is determined to be "YES", the peak time tp _{1 in} S523.
Is searched. This search is performed by finding out the time when the peak value is received from the data stored in the RAM 13.

Next, as shown in S524, the predicted peak time tp ₂ is calculated. This calculation adds the next value, which is proportional to the peak value of the received signal, to the start time of the received signal.

This is because the magnitude of the received signal is in the range of 0 to 10V, and the magnitude of the received signal changes as shown in Fig. 5 depending on the state of the propagation path even on a hard snow surface. The rising time t of the received signal until reaching the time is approximately constant 1 ms regardless of the size of the received signal. On the other hand, as shown in FIG. 6, the time at which the threshold level L is exceeded, that is, the start time of the received signal changes depending on the size of the received signal. When the received signal is large, the threshold level is exceeded. It takes a long time to reach the peak from the beginning and a short time when it is small. Therefore, the reception peak time can be predicted by adding the above value to the start time of the reception signal according to the magnitude of the peak value.

The reason for predicting the peak reception time is as follows.
When snow is piled up over many layers, reflected waves are generated from each layer, so the received waveform has several peaks as shown by the dotted line in Fig. 7. When this is detected, the waveform looks like the solid line. Become. In the figure, the time indicated by the symbol "a" is approximately equal to the time received from the surface of the snow, while the time indicated by the symbol "a" is the time received from a few cm below the surface of the snow surface. However,
When the reflection level is very small, the detection waveform becomes like a chain double-dashed line, and the point "A" cannot be detected, and only the point "C" can be observed, resulting in an error. For this reason, when the reflected wave level is very small, the predicted peak time is corrected.

On the other hand, when the snow surface is soft, there is almost no reflected wave from the surface, so the reflected wave comes from the inside, and the snowfall obtained from the predicted peak time predicted by the above method is generally measured several cm lower than the true value. To be done. At this time, focusing on the level of the reflected wave, it is often several tenths or less that of the reflected wave when there is no snow on the road surface. In this way, the level of the reflected wave is, for example, 1/30 of that of the road surface reflected wave when there is no snow.
In the following cases, the measured value is predicted to be about 2 cm lower than the true value, so the value obtained by subtracting 120 μs, which corresponds to 2 cm of snow from the predicted peak time, is the predicted peak time.

When the peak time is obtained by S523 and S524, the peak time tp ₁ and the predicted peak time tp ₂ are compared by S525.
Here, snowfall is usually measured lower than the true value but not higher, so in S525, the shorter value is determined as the peak time used here. .

When the peak time is determined, snow cover calculation processing is performed in S53 based on this data and the temperature obtained in S526. This is, assuming that the data of the transducer mounting height setting switch is H, the time from transmission to reception is tp, the distance from the transducer to the snow surface is 1, the speed of sound is V, and the snowfall is D, the temperature is T. ,
It is calculated by the following process.

l = V * Tp / 2 D = H-1 V = 331.45 + 0.61T When this process is completed, the valid / invalid data determination process is performed as shown in S54. This is to avoid erroneous measurement due to disturbance noise. Specifically, in S540, it is determined by the following equation whether the data is valid data.

x−D <y <x + D This is the past N average data x (cm) that is currently output.
Is to determine whether or not the newly measured snowy y (cm) is within the upper and lower limit range, and D is a value that can be arbitrarily set in the range of 1 to 99 (cm). The outside data is invalid data.

In the case of valid data, the snow value statistical processing is performed in S55, but this prevents the measured values from fluctuating minutely due to wind and other disturbances. Among them, replace the oldest measured value with the latest measured value and calculate the average. This average value is used as the final measurement value, and the average value calculation method is the moving average value method.

In case of invalid data, the invalid data statistical processing is carried out in S56, but this is for checking the invalidity, and when the number of data judged to be invalid reaches N consecutive times, the variance is calculated. I will do it. Then, the variance of invalid data and the variance of valid data are compared. If the variance of invalid data is smaller, the invalid data and valid data are exchanged.

When the above process ends, the output process shown in S57 is performed, and the display output signal, the analog output signal, and the digital output signal are sent out.

Although the present invention has been described for the case of measuring the amount of snow, from the above description, it is clear that the reflecting surface is not snow, but the level of an object that is soft like powder and absorbs a part of ultrasonic waves. It is also effective when measuring.

〔The invention's effect〕

As described above, according to the present invention, the measurement is performed using the measured peak time or the predicted peak time, whichever is shorter. Therefore, there is no measurement error when the snow surface is soft as in the conventional case. Has the effect.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of an apparatus configured by applying the present invention, FIG. 3 is a waveform chart of each part, FIG. 4 is transmission timing and reception. FIG. 5 is a diagram showing the relationship between timings, FIG. 5 is a diagram showing the relationship between signal levels and peak times, FIG. 6 is a diagram showing relationships between signal levels and threshold levels, and FIG. 7 is a diagram showing received waveforms. Is. 1 ... Transceiver, 3 ... Transmit / receive timing generation circuit, 4
…… CPU, 5 …… Received amplifier circuit.

Claims (1)

[Claims] 1. In a snow depth measuring device for measuring the amount of snow from the peak time of an ultrasonic reflected wave, a predetermined time is determined in proportion to the peak level of the received signal with respect to the time when the received signal exceeds a threshold level. A first predicted peak time measuring means for measuring, a second predicted peak time measuring means for calculating a value obtained by adding a correction value to the first predicted peak time, and a first predicted peak time measuring means when the level of the received signal is equal to or higher than a predetermined value. The predicted peak time of 1 is set as the predicted peak time, and when the level of the received signal is less than the predetermined value, the second predicted peak time is set as the predicted peak time, and the shorter of the predicted peak time and the measured peak time is set. A snow depth measuring device, comprising: an expected peak time determining means to be used as a peak time.