JPS6046378B2 - Road surface freezing detection method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for detecting a frozen state of a road surface.

Ensuring the safety of drivers by taking appropriate measures to deal with traffic disturbances caused by frozen roads, snow accumulation, etc. is a very important issue in transportation system management. It is also necessary to accurately grasp the road surface condition.

There is a device that uses the optical reflection characteristics of the road surface to identify the condition of the road surface, but wet conditions and frozen conditions show similar reflection characteristics, and this device detects the road surface temperature and Wet and frozen roads are distinguished based on road surface temperature.
However, even if the road is frozen, if a snow melting agent is applied, it will change to a wet state, so it is not possible to accurately detect the road surface state by distinguishing between wet and frozen conditions based only on the road surface temperature.
This invention has been made in view of the above circumstances, and provides a method for accurately detecting whether or not a road surface is frozen, especially when a snow melting agent is sprayed. Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, a pillar 22 is erected on one side of a road 21, and a support arm 23 extends upward from the upper end of the pillar 22.

A light projector 24, a diffuse reflection receiver 25, a specular reflection receiver 26, and a light projection level measuring device 27 are attached to this support arm 23.
are attached to each pillar 22, and a road surface temperature gauge 28 is provided on each pillar 22. The light projector 24 uses a mercury lamp whose emission spectrum includes not only visible light but also near-infrared light. The projector 24 is arranged so as to be directed toward the road surface at an appropriate angle of incidence. The specular reflection receiver 26 receives specularly reflected visible light of the road surface reflected light projected from the light projector 24 and converts it into an electrical signal. The diffused reflection receiver 25 separately detects visible light and near-infrared light reflected from the road surface. The near-infrared light preferably has a wavelength in the range of about 1.5 to 2.5 (μm). The light projection level measuring device 27 directly receives the light from the light projector 24 and measures the light power of the light projector 24, and in this embodiment measures the light power of visible light.
A radiation thermometer is used as the road/surface thermometer 28. In FIG. 2, the projector 24 is driven by a constant power ballast 29 with constant power. The diffuse reflection light receiver 25 includes light receiving elements 31 and 32 for infrared light and visible light, and the outputs of these light receiving elements 31 and 32 are amplified by an amplifier 34, and then noise components are removed by a bandpass filter 35, respectively. be done. The specular reflection light receiver 26 includes a visible light light receiving element 33, and the output signal of this light receiving element 33 is also outputted via an amplifier 34 and a bandpass filter 35. The signals output from the light receivers 25 and 26 are amplified and rectified again by the amplifier 36, respectively, and sent to the comparators 41, 42, and 43. Each of these comparators 41, 42, 43 has one or two reference levels A
, Bl, B2, and C are set, respectively, and the outputs of the respective light receiving elements 31, 32, and 33 are compared with these reference levels. The logic circuit 44 converts these comparison results into status signals, and the output of the logic circuit 44 is sent to the arithmetic processing section 45. As the arithmetic processing section 45, a microprocessor is suitably used. Light emission level measuring device 2
7 includes a visible light light receiving element 30, and this light receiving element 30
After passing through the output or amplifier 37 and bandpass filter 38,
Amplified and rectified by an amplifier 39, each comparator 41,
42 and 43. The above reference levels A, Bl, B2, C of the comparators 41, 42, 43 are adjusted by the output of the measuring device 27. Although the projector 24 is driven with constant power, the amount of light emitted changes due to deterioration of the mercury lamp itself, dirt on the front surface of the projector, and the like. If the amount of projected light changes, the amount of light reflected from the road surface will also change, so if the reference levels of the comparators 41, 42, and 43 are kept constant, false detection may occur. Here, in order to compensate for the change in the amount of light emitted, the comparators 41 and 42 are adjusted according to the change in the amount of light emitted.
, 43 reference levels are adjusted. Since the amount of projected light and the amount of reflected light are considered to be approximately proportional, each comparator 41, 4
The reference levels No. 2 and 43 are changed in proportion to the level of the amount of light emitted. The output of the thermometer 28 is input to the arithmetic processing section 45 . FIG. 3 shows the relative ranges of the output levels of the light receivers 25, 26 and thermometer 28 for dry, wet, snowy, and frozen conditions, as well as the road surface condition determination results obtained from these outputs. .

Regarding visible light, in a dry state, the road surface is a diffusive surface with low reflectance (reflectance of about 30%), so the regular reflection component and the diffuse reflection component have approximately the same value. When the road surface is wet, the road surface becomes a mirror surface and the specular reflection component increases.
The diffused reflection component decreases. In Figure 3, the specular reflection output level of visible light in the wet state extends downward to the level range in the dry state because the water on the road surface has flowed out and the road surface has become damp (therefore, it has not become a specular surface). This is because it is still in a wet state even if it becomes wet. When there is snow that appears white on the road surface, the snow creates a diffusing surface where the light reflectance is close to 100%, so compared to dry conditions, the specular reflection component,
Both diffuse reflection components increase. However, in snow jam conditions or snow soiled with mud, etc., the surface becomes a diffuse surface with low reflectance, and both specular reflection and diffuse reflection components are at approximately the same level as in dry conditions. As vehicles pass on the road,
゛Water almost never freezes in a specular state, and in a frozen state both specular reflection and diffuse reflection components show low values. The two standard temperatures for road surface temperature, 0°C to -2°C, are set because the freezing start temperature and thawing start temperature are different, and -2°C
This is because freezing begins at 0°C and melting begins at 0°C.

The portion where the road surface temperature is lower than -2° C. in a wet state indicates the case where a snow melting agent was sprayed. The characteristics of each road surface condition with respect to infrared light are different from those described above.

FIG. 4 shows the light reflection spectral distribution of snow and dry asphalt. The solid line shows the relative reflectance of snow (density 0.36 g/CTl) with respect to the reflectance of barium sulfate, and the broken line shows the relative reflectance of asphalt. The reason why the reflectance of a snowy surface drastically decreases in the infrared light region is due to absorption by moisture, and the reflectance of a road surface containing moisture similarly shows a smaller value than when it is dry.
In FIG. 3, there is a portion of the infrared light diffused reflection output in the snowy state that extends to the level in the dry state. This part is due to fresh snow. The density of fresh snow is 0.36g/
Since it is smaller than Crl and the absorption of infrared light is reduced accordingly, the relative reflectance becomes higher than that shown by the solid line in FIG. 4, and the output of the light receiving element 31 increases accordingly. In this way, the output levels of the light receivers 25 and 26 change depending on each state of the road surface, and each state has its own range.

Therefore, we set standard level A to a level that can distinguish between dry conditions and other conditions (although dry conditions overlap with some snow conditions (new snow)), and standard level B1 was set to a level that can distinguish between dry conditions and other conditions (although dry conditions overlap with some snow conditions (new snow)), and standard level B1 was set to a level that can distinguish between dry conditions and other conditions (although dry conditions overlap with some snow conditions (new snow)). The reference level B2 is set to a level that can distinguish between the states, and the reference level C is set to a level that allows the snowy and dry states to be distinguished from other states by level B1, and the reference level C is set to a level that can distinguish between the mirror-like wet state and other states. (Although the mirror-like moist state and the white-looking snow state overlap), each is set to a level that allows for differentiation. The outputs of the light receivers 25 and 26 are set to the reference levels A, Bl, and
B2 and C are used for discrimination, and a status signal representing the discrimination result is output.

Based on this state signal, the arithmetic processing unit 45 determines the road surface state according to the following procedure, and outputs a road surface state identification signal of dry, wet, snowy, and frozen. Referring to FIG. 5, each light receiver 25, 26 and thermometer 28 are checked for abnormality (step 1), and if there is no abnormality, the process proceeds to step 2. If there is an abnormality, move on to the process to deal with it (
Step 8) In step 2, based on the infrared light output of the diffuse reflection receiver 25, it is determined whether the road surface condition is dry or other than dry based on the discrimination result based on the reference level A. That is,
If the infrared light output of the light receiver 25 is equal to or higher than level A, it is considered as drying, and if it is equal to or lower than level A, it is considered as other than drying. Here, some of the snow that is determined to be dry is fresh snow (white snow).
It is included. Next, the process proceeds to step 3, in which snowfall is determined using the visible light diffused reflection output.

The snow included in the area determined to be dry in step 2 is white snow, and in the case of this white snow, the visible light diffused reflection output is higher than level B1. Therefore, level B1
In the above case, even what is determined to be dry in step 2 is unconditionally treated as snow. Also, in step 3,
Those between levels B1 and B2 are also detected. If the visible light diffused reflection output is between levels B1 and B2, the road surface condition is either snowy or dry, so the remaining road surface excluding the one determined to be dry in step 2 is assumed to be snowy. In step 4, the wet state is determined by checking whether the visible light specular reflection output is equal to or higher than the reference level C.

At reference level C or higher, the wet state and the snowy state partially overlap. However, since all snow conditions are eliminated in step 3, if the visible light specular reflection output is level C or higher, it is determined to be a wet state. In the determination processing of steps 2 to 4, the frozen state and a part of the wet state are not determined. Therefore,
In step 5, frozen and wet conditions are distinguished based on the output of the thermometer 28. If the road surface temperature is 0°C or higher, it is considered wet, and if it is -2°C or lower, it is frozen. Road surface temperature is 0℃
If the temperature is between -2℃ and 0℃, it is considered wet as it has not yet frozen.
Once the temperature drops below -2°C, it freezes when the temperature exceeds -2°C. Even if it is determined in step 5 that the area is frozen, the area may still be in a wet state. This is the case when snow melting agents are sprayed. Spraying a snow melting agent lowers the freezing point, causing a transition from a snowy or frozen state to a wet state. Therefore, even if it is determined in step 5 that the area is frozen, the area remains wet for a certain period of time after the snow melting agent is sprayed (the effective time of the snow melting agent). This process is performed in step 6. When snow or ice melts and turns into water, the road surface temporarily becomes mirror-like. Therefore, the visible light specular reflection output increases as shown in FIG. 7 and exceeds the reference level C, making it possible to detect that the snow melting agent has been sprayed. Water on the road surface flows to both sides of the road or is scattered by passing cars, so after a while the road surface no longer has a mirror surface and the visible light specular reflection output decreases. Details of the processing in step 6 are shown in FIG.

Referring to this figure, when it is determined that freezing is occurring in step 5, the freezing flag is turned on (step 11), and the fact that freezing has occurred is memorized. Then, check whether the water flag is on (step 12). This water flag is turned on by an interrupt or the like when the visible light specular reflection output exceeds a reference level C. If the water flag is off, it is in a frozen state. If the water flag is on, it means that the snow melting agent has been sprayed, so a timer is started (step 13), and it is determined that the state is wet for a certain period of time, and when the snow melting agent effective time has passed, the snow melting agent is again in a frozen state. (Step 14).
The effective time of the snow melting agent is determined statistically and empirically. When the road surface condition is finally determined in this way, a road surface condition identification signal is output (step 7).

This identification signal is transmitted, for example, to a road surface condition display device installed at a center or on a road, and the road surface condition is monitored and displayed. The above road surface condition determination is performed at appropriate time intervals. In addition, each of the above standard levels A,
Since Bl, B2, C and the reference temperature (0°C, -2°C) vary depending on the installation location, it is preferable to make them variable and change them as appropriate. In the embodiment described above, the road surface condition is determined by the arithmetic processing section (microprocessor), but the road surface condition can also be determined by a logic circuit.

Further, the setting of the reference level that is the basis of the discrimination and the method of combining the compared and discriminated condition signals are not limited to the above example, but can be determined as appropriate depending on the road surface condition to be discriminated. As explained in detail above, according to the present invention, when a snow melting agent is sprayed, this is detected and it is determined that the road surface is wet even if the road surface temperature is freezing. , it is possible to accurately detect whether the road surface is frozen.

In particular, in this invention, since the presence or absence of snow melting agent spraying is detected based on visible light specular reflection output from the road surface, the snow melting agent spraying operator does not need to perform any operations.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing the arrangement of the emitter and receiver;
Figure 2 is a block diagram showing the internal configuration of the road condition identification device, Figure 3 is a diagram showing the relative range of the output level of each light receiver for each road condition, and Figure 4 is the reflection of light from snow and asphalt. A graph showing the spectral distribution, Fig. 5 is a flow chart showing the procedure for determining the road surface condition, Fig. 6 is a flow chart showing the details of the freezing judgment process, and Fig. 7 is the visible light specular reflection output when spraying snow melting agent. It is a graph showing changes. 24... Emitter, 25... Diffuse reflection receiver, 26...
- Specular reflection receiver, 28... Road surface temperature meter, 45... Arithmetic processing unit.

Claims (1)

[Claims] 1. Determine the wet state of the road surface based on the combination of specular reflection output and diffuse reflection output of visible light and infrared light from the road surface,
When the road surface temperature is below a required standard temperature, the road surface becomes frozen.When the road surface is determined to be frozen, the specular reflection output of visible light is inspected, and if the specular reflection output exceeds the required level. A road surface freezing detection method that determines that the road surface is wet regardless of the road surface temperature for the required period of time.