JPH1164516A - Ultrasonic snow depth meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precise ultrasonic snow depth meter unaffected by snow depth conditions and by surrounding objects. SOLUTION: A first pulse group and a second pulse group of ultrasonic waves are sent out at an interval between them from a specified height above the ground toward a surface of snow by a transmitter 1. Reflected ultrasonic waves from the surface of the snow are received by a receiver 2 at the specified height above the ground. By using a reference level setting circuit 3, a maximum value L3 of amplitude of waves received within the aforesaid interval after sending-out of the first pulse group is detected, and a first reference level L1 is set up by multiplying the maximum value L3 by a smaller coefficient while a second reference level L2 is set up by multiplying the maximum value L3 by a larger coefficient. By using a clocking means 4, every time an amplitude of waves received after sending-out of the second pulse group exceeds the first reference level L1, a time period from the starting t1 of sending-out of the second pulse group to the exceeding is detected and stored as received- wave rising time, and excess of amplitude of received waves over the second reference level L2 is detected and a received-wave rise time at the time of exceeding the second reference level L2 is measured as a ultrasonic wave going-and-returning time T between the specified height above the ground and the surface of the snow. The depth of the snow is computed from the sound velocity, the going-and-returning time T and the specified height above the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic snow depth meter, and more particularly to an ultrasonic snow depth meter suitable for unmanned observation.

[0002]

2. Description of the Related Art Referring to FIGS. 1, 5, and 6, a transmitter 1 intermittently transmits pulsed ultrasonic waves from a predetermined ground height H to a snow surface (hereinafter, sometimes referred to as a snow surface). The receiver 2 detects that the ultrasonic wave is reflected on the snow-covered surface and returns, and measures the reciprocating time of the sound wave between them, and determines the sound speed and the measured reciprocating time and ground height H. It has been conventionally performed to obtain the snow depth from the snow.
In FIG. 5, a timing chart (b) shows an intermittent pulsed ultrasonic wave to be transmitted, (c) shows a received pulsed ultrasonic wave, and (d) shows a receiver 2 after detection and smoothing. (F) shows the round trip times T1 and T2 of the received reflected ultrasonic waves.

[0003]

Referring to FIG. 5, the normal measurement of the sound wave reciprocation time is performed from the transmission time to the time when the reception level of the receiver first exceeds the predetermined comparison level L0 (FIG. 5 (d)). By measuring the time. However, in practice, the waveform of the received wave changes irregularly due to the distribution of snow quality and the interference of sound waves due to the unevenness of the snow surface, and the amplitude varies widely and greatly. Then, it is often difficult to measure the snow depth accurately. Also,
If an irregularly reflected wave from a surrounding object or the like is received by a receiver before a reflected wave from a snow-covered surface arrives, the irregularly-reflected wave may be erroneously recognized as a reflected wave and the snow depth may be erroneously measured.

A case where a high-level detection signal D shown in FIG. 5E is generated from the output after detection and smoothing shown in FIG. 5D, and the round-trip times T1 and T2 shown in FIG. In
The rise of the reflected wave is slowed down due to the attenuation due to the propagation of the ultrasonic wave during snowfall and the time delay of the receiving circuit, and a time difference of Δt1 and Δt2 is generated between the start point of the reflected wave and the point where the comparison level reaches L0. This time difference also causes a measurement error of the round trip propagation time and the snow depth.

Further, in the conventional ultrasonic snow depth meter, the measured value is recorded in a recording means separately prepared after the measurer confirms the measured value. This is because it was difficult to perform stable and accurate observations in places where no one could approach.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an accurate ultrasonic snow depth gauge which is not affected by snow conditions or surrounding objects. An ultrasonic snow depth meter that is not affected by snow conditions or surrounding objects is suitable for unmanned observations.

[0007]

The present inventor has noticed that one of the causes of the measurement error of the ultrasonic snow depth meter is that the comparison level L0 is fixed. As for the discrimination between the reflected wave from the snow surface and the noise wave, if the reflected wave is detected by comparing the reflected wave level with a high reference level corresponding to the level of the transmitted ultrasonic signal, the accuracy of the discrimination is improved. there is a possibility. In addition, regarding the detection of the start point of the reflected wave from the snow surface, the detection of the rising points of all the received waves is performed with a minimum time delay by comparing with the low reference level,
Combining this with identifying the required reflected wave from all the received waves may increase the detection accuracy of the reflected wave start point. The present invention has been completed based on these possibilities.

Referring to FIGS. 1 and 4, an ultrasonic snow depth meter according to the present invention is configured such that an ultrasonic first pulse group P1 and a second pulse group P2 are spaced from a predetermined ground height H toward the surface of snow. (See FIG. 4 (b)) Transmitter 1; Ultrasonic pulses S2, S3, S from a surface side of snow at a predetermined ground height H
5, a receiver 2 for receiving S6; detecting the maximum value L3 of the amplitude of the ultrasonic pulse reception waves S2 to S3 in the receiver 2 within the interval following the transmission of the first pulse group P1 of ultrasonic waves, and more than 1 A reference level setting circuit 3 for setting a first reference level L1 by multiplying a small coefficient by a maximum value L3 and setting a second reference level L2 by multiplying a maximum coefficient L3 by a large coefficient less than 1 and close to 1; The amplitude of the received waves S5 to S6 at the receiver 2 after the transmission of the pulse group P2 is the first
Every time the reference level L1 is exceeded, the time (t2−t1) and (t3−t1) from the start of transmission of the second pulse group P2 to the exceeding of the second pulse group P2 are detected as the rise time of the reception wave and updated and stored in the register 41. Then, it is detected that the amplitude of the reception waves S5 to S6 at the receiver 2 exceeds the second reference level L2 and the second reference level L2
Rise time of reception wave on register 41 when exceeding (t3-t1)
Means 4 for measuring the ultrasonic wave reciprocating time T (= t3-t1) between the predetermined ground height H and the surface of the snow (see FIG. 4 (d)); It is provided with snow depth calculation means 7b for calculating the snow depth from the ground height H.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The function and operation of the embodiment of FIG. 1 will be described with reference to the flowcharts of FIGS. 2 and 3 and the timing chart of FIG. The microcomputer 7 controls and calculates the components of the ultrasonic snow depth meter. The computer 7 in the illustrated example includes a measurement timing generation unit 7a, a snow depth calculation unit 7b, and a recording unit 7c. However, the present invention is not limited to the use of such a computer 7.

The measurement timing generating means 7a applies the measurement timing signal a of FIG. Transmitter 1
The carrier signal oscillation circuit 1a continuously outputs a square wave of a predetermined ultrasonic frequency, for example, 40 kHz, according to the arrival of the measurement timing signal a. The measurement timing signal a also
The burst signal generation circuit 1b of the transmitter 1 intermittently controls the square wave oscillated by the carrier signal oscillation circuit 1a. For example, the 1 mS output and the 50 mS stop are repeated to repeat the burst signal P1 shown in FIG. , Generating P2. The ultrasonic transmitter 1d driven by the drive circuit 1c of the transmitter 1 transmits the burst signals P1, P2
As a group of ultrasonic pulses from a predetermined ground height H toward the surface of snow cover. In the present invention, the reference signal level is set by transmitting the first ultrasonic pulse group, and the measurement of the ultrasonic round-trip propagation time between the predetermined ground height H and the surface of snow is performed by transmitting the next ultrasonic pulse group. Therefore, the former is called a reference signal level setting cycle, and the latter is called a time measurement cycle.

The receiver 2 receives, at a predetermined ground height H, a reflected wave in which the ultrasonic pulse transmitted from the ultrasonic transmitter 1d is reflected on the snow-covered surface and returns.
a, an amplifier 2b, and a detection / smoothing circuit 2c. The reflection of the ultrasonic wave received by the ultrasonic receiver 2a is converted into an electric signal and then amplified by the amplifier 2b, for example, about 100 times. FIG. 4C shows the output of the amplifier 2b and the pulse group S
1, S4 are the received waveforms of the direct waves of the transmitted pulse groups P1, P2, S3 and S6 show the reflected waves from the snowy surface, S2 and S5
Indicates the noise mixed before the reflected wave from the snow surface arrives.
The detection / smoothing circuit 2c detects and smoothes the amplified received wave and converts it into a DC signal shown in FIG. 4 (d).

The reference level setting unit 3 detects and detects the signal of the receiver 2.
It generates two comparison levels according to the magnitude of the smoothed DC output of the smoothing circuit 2c, and the maximum value detection circuit 3a,
It comprises a first comparison level setting circuit 3b and a second comparison level setting circuit 3c. The maximum value detection circuit 3a responds to an instruction signal g (FIG. 1) from the measurement timing generation means 7a of the computer 7 to generate a maximum value L3 (FIG. 4 (d) of the smoothed DC output in the reference signal level setting cycle. )) Is detected, and this value is held as a reference level until the next reference signal level setting cycle. First comparison level setting circuit
3b is a reference level L3 output from the maximum value detection circuit 3a,
The signal is attenuated by a fixed small ratio, for example, two-tenths, to generate a first comparison level L1 for detecting the rising point of the reception wave. The second comparison level setting circuit 3c is a reference level which is an output of the maximum value detection circuit 3a to detect the presence or absence of reflection from the snow surface.
L3 is a constant large ratio below 1 and close to 1, for example, 10
It is attenuated by 9 / min to generate a second comparison level L2.

The time measuring means 4 responds to an instruction signal h (FIG. 1) of the measuring timing generating means 7a of the computer 7 and smoothes the detection / smoothing circuit 2c from the transmission of the ultrasonic pulse group P2 in the time measuring cycle. The first comparator 4a measures the time T until the output DC output exceeds the first comparison level L1 immediately before exceeding the second comparison level L2.
4b, timing control circuit 4c, clock oscillation circuit 4d, counter 4
e, and a register 4f. The first comparator 4a compares the smoothed DC output of the detection / smoothing circuit 2c with the first comparison level L1, and receives the signal when the DC output of the circuit 2c exceeds the first comparison level L1. A wave rising point detection signal U (see FIG. 4E) is output. The second comparator 4b calculates the smoothed DC output of the detection / smoothing circuit 2c and the second comparison level.
Comparison with L2 is performed, and when the DC output of the circuit 2c exceeds the second comparison level L2, a reflected wave detection signal R (see FIG. 4 (f)) is output. The time measurement control circuit 4c outputs a count operation start signal to the clock oscillation circuit 4d and the counter 4e at the start of transmission of the ultrasonic pulse group P2 in response to the instruction signal h of the measurement timing generation means 7a of the computer 7.

The timekeeping control circuit 4c outputs a count value capture pulse to the register 4f every time it receives the rising edge detection signal U from the first comparator 4a.
When the reflected wave detection signal R from 4b is received, the count value acquisition pulse is not output thereafter.

The clock oscillation circuit 4d continuously oscillates a clock pulse at a predetermined frequency of, for example, 1 MHz, and the counter 4e uses the clock pulse as an input. The counter 4e receives the count operation start signal from the timing control circuit 4c and starts counting clock pulses. When receiving the count value capture pulse from the timekeeping control circuit 4c, the register 4f captures the current count value of the counter 4e, updates the content of the register 4f to the newly captured count value, and stores it. Therefore, the last count value taken by the register 4f in the time measurement cycle is the first comparator 4a immediately before the second comparator 4b outputs the reflected wave detection signal R.
The output time t3 of the detection signal U of the rising edge of the received wave of FIG.
(See (e)). Computer 7 snow depth calculation means 7b
Reads the output time t3 of the received wave rising point detection signal U and calculates the round trip propagation time T from which fluctuations due to noise and other disturbances have been removed. Propagation velocity v of ultrasonic waves in air
Is known from literature or actual measurement, the snow depth W is defined as a difference {W = H− (Tv) / 2} obtained by subtracting half the product of the propagation velocity v and the round trip propagation time T from the predetermined ground height H. You can ask. In the case where the snow depth W is continuously measured, the influence of noise can be reduced by using the value of the individual round-trip propagation time T, which is sequentially obtained, as a round-trip propagation time T after performing statistical processing using the simple moving average method. Can be suppressed.

Moreover, the snow depth determined in this manner is determined by the reflected wave detection signal R based on the comparison between the received wave level and the second comparative level L2, which is affected by the snow condition and the irregular reflection of ultrasonic waves caused by surrounding objects. In addition to being removed by the use, errors due to the slowing of the pulse rise due to the propagation of the ultrasonic wave are practically supported by the use of the reception wave rising point detection signal U based on the comparison between the reception wave level and the small first comparison level L1. It is suppressed to an extent.

Therefore, the object of the present invention is to provide an "accurate ultrasonic snow depth meter which is not affected by snow conditions or surrounding objects".
Is achieved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment of FIG. 1, the temperature of the outside air in contact with snow is measured by a temperature sensor 5 and its output is converted into an electric signal to be applied to a snow depth calculating means 7b of a computer 7. A that responds to the instruction of the snow depth calculation means 7b if necessary
The output of the temperature sensor 5 is converted into a digital quantity by the / D conversion circuit 6 and added to the snow depth calculation means 7b. The digital value of the outside air temperature is read to correct the ultrasonic propagation speed in the air, and the corrected sound velocity And the round trip propagation time to calculate the snow depth. In this case, it is necessary to provide in advance the snow depth calculation means 7b with a correction means comprising a correction program for correcting the sound speed in the air according to the outside air temperature.

When the ultrasonic snow depth meter is of a self-recording type, for example, the storage means, which is a semiconductor storage element 8, is connected to the recording means 7c of the computer 7, and the result of calculation by the snow depth calculation means 7b is obtained. The stored snow depth data can be stored, stored, and stored in the storage element 8. In this case, for example, the time of the snow depth measurement operation indicated by the clock provided in the time measuring means 4 may be stored in the storage element 8 together with the snow depth measurement result.

The output circuit 9 outputs the value of the snow depth by the analog signal A and / or the digital signal B stored in the storage element 8.

Referring now to the flow charts of FIGS. When the measurement is started, a first ultrasonic pulse group P1 (FIG. 4B) is transmitted from the transmitter 1 in step 201. In step 202, the receiver 2 receives the reflected pulse from the snow-covered surface and amplifies it. In step 203, the receiver 2 performs detection and smoothing to output the DC signal shown in FIG. While the true value of the reference signal setting gate signal sg (FIG. 4 (g)) is being applied from the measurement timing generating means 7a, the reference signal setter 3 performs the maximum value L3 of the received wave in steps 204 and 205.
(FIG. 4D) is detected, and in step 206, the first comparison level L1
And a second comparison level L2. These maximum values L3,
The reference signal level including the three values of the first comparison level L1 and the second comparison level L2 is held until the reference signal setting gate signal sg takes the next true value.

Next, after a predetermined interval from the completion of the transmission of the first ultrasonic pulse group P1, a second ultrasonic pulse group P2 (FIG. 4 (b)) is transmitted in step 207, and measurement is started at t1 when the transmission is started. The time means 4 resets the counter 4e in step 208, and then starts time counting. From the measurement timing generating means 7a, the time measurement gate signal mg (FIG. 4 (), the length of which is the longest path time (step 310 in FIG. 3, in this case, counting from the time of transmission of the second ultrasonic pulse group P2). While the true value of h)) is being applied, the receiver 3 receives and amplifies the received wave in step 209, and performs detection and smoothing in step 210. The reference level setting unit 3 compares the value of the received wave with the second comparison level L2 in step 211, and as a result, in step 212
When it is determined that the value of the received wave is equal to or lower than the second comparison level L2, the value of the received wave is compared with the first comparison level L1 in step 213. If it is determined that the value of the received wave is equal to or lower than the first comparison level L1, the control proceeds to step 310 of FIG. 3 as indicated by the symbol α, and determines whether or not the longest path time has elapsed. Find out. If the longest path time has not elapsed, the control proceeds to step 21 as indicated by the symbol β.
Return to 1 and continue to compare the received wave with the comparison level.

If it is determined in step 212 that it is equal to or lower than the second comparison level, but in step 213 it is higher than the first comparison level L1, in step 311 as indicated by the symbol δ, the counter 4
The count value t2-t1 (or t3-t1) of e is taken into the register 4f, and the reception wave rising point detection signal U shown in FIG. 4E is generated. Control then proceeds to step 21 as indicated by the symbol β.
Returning to step 1, the comparison between the received wave and the comparison level is continued, but if it is determined in step 212 that the value exceeds the second comparison level L 2, the reflection in FIG. At the same time as outputting the wave detection signal R, the counting of the counter 4e is stopped, and the taking of the count value into the register 4f is prohibited thereafter. In the illustrated embodiment, in the next step 301, the output of the temperature sensor 5 is digitally converted by the A / D converter 6 and taken into the snow depth calculation means 7b as outside temperature data. Register 302 in step 302
The count value of f is read, and a temperature correction process is performed on the count value (round trip propagation time T = t3-t1) in step 303. The round-trip propagation time corrected in temperature is written in the memory of the semiconductor memory element 8 in step 304, and a simple moving average process of the round-trip propagation time is performed in step 305. The snow depth is calculated in step 306 from the round-trip propagation time after the moving average processing, the separately installed height and the ultrasonic wave propagation velocity in the air. The calculated snow depth data is recorded in the semiconductor memory element 8 together with the time information in step 307, and in step 308, the snow depth and the outside air temperature for each measurement are output from the output circuit 9. Thereafter, the control returns to step 201 immediately after the start of the measurement as indicated by the symbol γ.

If it is determined in step 310 that the longest measurement time has elapsed, the control returns to step 201 immediately after the start of the measurement, as indicated by the symbol γ.

After the reflected wave detection signal R shown in FIG. 4F is generated, the count value is not taken in. Therefore, the count value of the register 4f is determined by the ultrasonic pulse transmitted to the snow-covered surface reflected from the snow-covered surface and returned. Indicates the round-trip propagation time before arrival. Since the second comparison level L2 that triggers the generation of the reflected wave detection signal R is set to a high level, it is possible to avoid an error caused by confusing noise with a reflected wave. Since the count value of the register 4f becomes valid at the time of the rise of the received wave immediately before the generation of the reflected wave detection signal R, the first comparison level L1 is at a low level even if the rise of the reflected wave is slowed down. An error due to the dulling can be prevented.

[0026]

As described above, in the ultrasonic snow depth meter according to the present invention, a low first comparison level and a high second comparison level are determined for each snow depth measurement in accordance with the snow depth to be measured. Since the noise and the reflected wave are discriminated at the high second comparison level and the rise of the reflected wave is measured before the dulling is performed by using the low first comparison level, the following remarkable effects are obtained.

(A) Even if the amplitude of the reflected wave changes due to the existence of objects around the snow and the surrounding surface of the snow itself, the second comparison level is set to follow the change, so that the accurate snow depth Can be measured. (B) Noise and other disturbances can be identified as reflected waves by setting a high second comparison level to prevent measurement errors due to erroneous recognition. (C) The influence of the blunting of the rising portion of the reflected wave due to the propagation of the ultrasonic wave in the snow can be suppressed low by detecting the rising point immediately after the start of the rising by using the first comparative level set low.

(D) Measured values of snow depth can be easily recorded. (E) It is possible to easily correct the snow depth measurement value with respect to the outside air temperature change. (F) Since it is possible to measure and record the exact snow depth while preventing errors due to environmental changes, it is suitable for efficient use in places where people cannot reach and for efficient unmanned observations.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a first part of a flowchart of the operation of the embodiment of FIG. 1;

FIG. 3 is a second part of the flowchart of the operation of the embodiment of FIG. 1;

FIG. 4 is a time chart of signals in the embodiment of FIG.

FIG. 5 is a time chart of a conventional ultrasonic snow depth meter.

FIG. 6 is an explanatory diagram showing an operation principle of the snow depth measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transmitter 2 ... Receiver 3 ... Reference level setting device 4 ... Time measuring means 5 ... Temperature sensor 6 ... A / D conversion circuit 7 ... Computer 8 ... Semiconductor storage element 9 ... Output circuit

Claims (7)

[Claims] A transmitter for transmitting a first pulse group and a second pulse group of ultrasonic waves from a predetermined ground height toward the surface of snow at an interval; A receiver for receiving an ultrasonic pulse; detecting a maximum value of a received wave amplitude of the ultrasonic pulse in the receiver within the interval following the transmission of the first pulse group of the ultrasonic wave; A reference level setting circuit for setting a first reference level by multiplying a maximum value and setting a second reference level by multiplying the maximum value by a large coefficient less than 1 and close to 1;
After transmitting the pulse group, the amplitude of the received wave of the receiver becomes the first
Each time the reference level is exceeded, the time from the start of the transmission of the second pulse group to the exceeding is detected as the rise time of the received wave and updated and stored in a register, and the amplitude of the received wave of the receiver is set to the second reference level. Time-measuring means for detecting exceeding the level and measuring the rise time of the received wave on the register as the ultrasonic reciprocating time between the predetermined ground height and the surface of the snow when the second reference level is exceeded; An ultrasonic snow depth meter comprising snow depth calculating means for calculating a snow depth from the round trip time and the predetermined ground height. 2. An ultrasonic snow depth meter according to claim 1, wherein said calculating means includes a temperature sensor disposed outdoors and a means for correcting the speed of sound relative to temperature. 3. An ultrasonic snow depth meter according to claim 1, wherein a storage element for storing the calculated value of the snow depth is connected to said calculating means. 4. An ultrasonic snow depth measuring apparatus according to claim 3, wherein said time measuring means includes a clock and said memory element stores said calculated value of said snow depth together with said calculated time of said calculated snow depth. Total. 5. An ultrasonic snow depth meter according to claim 1, further comprising an output circuit for transmitting the calculated snow depth as an analog value and / or a digital value. 6. An ultrasonic snow depth meter according to claim 1, further comprising a computer having said reference level setting circuit, time measuring means, and snow depth calculating means. 7. A snow depth gauge according to claim 1, wherein said computer includes a transmitter, a reference level setting circuit, a time measuring means, and a measurement timing generating means connected to the snow depth calculating means. Ultrasonic snow depth gauge.