JP4129419B2 - Road surface condition determination method and apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for discriminating a state where water or ice is present on a road surface on a general road or an expressway.

Conventionally, a method and an apparatus for determining a road surface state such as freezing using image processing have been proposed (see, for example, Patent Document 1). This application projects and scans laser light with respect to a predetermined road surface monitoring area, stores the laser light reflected from the road surface as a monitoring image, and compares this monitoring image with a pre-stored determination image to make the most similar The image data for road surface determination to be detected is found, and it is detected whether or not it is in a frozen state.
JP 2002-39861 A

Incidentally, the reflectance Γ when laser light or natural light hits water or ice on the road surface as shown in FIG. 10 can be defined as a function of the relative dielectric constant ε _r as follows.

Here, Ei is the incident energy of electromagnetic waves, Er is the reflected energy, and the relative dielectric constant ε _r = dielectric constant ε of medium / dielectric constant ε ₀ of vacuum.

は、その実数部をε’、虚数部である誘電損失をε''として、デバイの緩和理論から、

となることが知られている。但し、σは導電率、ε₀ ^*は空気の誘電率（８．８５４×１０^-12Ｆ／ｍ）であり、水，氷の場合、導電率σはほぼ０であることから、式（４）の第２項は無視することができ、結局式（４−１）とすることができる。 On the other hand, complex relative permittivity of general materials

From the Debye relaxation theory, the real part is ε 'and the dielectric loss that is the imaginary part is ε''.

It is known that However, σ is the conductivity, ε ₀ ^* is the dielectric constant of air (8.854 × 10 ⁻¹² F / m), and in the case of water and ice, the conductivity σ is almost 0. ) Of the second term can be ignored, and can eventually be expressed as equation (4-1).

は直流電場における比誘電率、

は高周波電場における比誘電率、ωは角周波数、τは誘電緩和時間である。 here,

Is the relative permittivity in a DC electric field,

Is a dielectric constant in a high frequency electric field, ω is an angular frequency, and τ is a dielectric relaxation time.

When the complex relative dielectric constant is calculated by substituting the frequency f of 10 Hz to 1000 GHz and the following values into the equations (3) and (4), the graph shown in FIG. 3 is obtained.

  As is apparent from this graph, the frequency range in which the complex dielectric constant varies greatly between water and ice. In particular, the imaginary part ε ″ of the dielectric constant that changes the reflectance Γ varies greatly in the vicinity of 100 Hz to 100 KHz and in the vicinity of 1 GHz to 100 GHz. However, it is used for laser light and visible light in the above-mentioned conventional publications. For the frequency range of light of several hundred GHz or more, water and ice have the same value (substantially “0”).

Similarly, for the real part ε ′ of the dielectric constant, water and ice have the same value at a frequency of several hundred GHz or more. That is, in the conventional measurement method using the optical reflection intensity including image processing since the relative permittivity ε _r that is the main component of the reflectance Γ does not change in the frequency region of light as in the equation (1), There was a problem that water and ice could not be distinguished. Furthermore, the conventional measuring method has a problem that the thickness of water cannot be determined.

  The present invention is intended to solve the above-described problems, and the object of the present invention is to detect the change in the radio waves generated when the radio waves are irradiated on the water or ice on the road surface. It is an object of the present invention to provide a road surface state determination method and apparatus capable of accurately determining the presence of ice or the thickness of water.

  The road surface state determination method of the present invention achieves the above-described object, and the means of claim 1 irradiates a radio wave toward the road surface, receives a reflected radio wave, and receives the received radio wave with respect to the irradiated radio wave. It is characterized by determining the presence or absence of water or ice on the road surface based on the change.

  According to a second aspect of the present invention, the thickness of water on the road surface is determined based on a change in the received radio wave with respect to the irradiated radio wave.

  According to a third aspect of the present invention, in the road surface state determining method according to the first or second aspect, the change of the received radio wave is a ratio of the received radio wave to the intensity of the irradiated radio wave. The determination is performed by obtaining the amount of attenuation and comparing it with a reference value for the amount of attenuation stored in advance.

  According to a fourth aspect of the present invention, in the road surface state determination method according to any one of the first and second aspects, a change in the received radio wave is obtained as the intensity of the received radio wave, and a reference for the received intensity stored in advance is provided. The discrimination is performed by comparing with a value.

  According to a fifth aspect of the present invention, in the road surface state determination method according to any one of the first and second aspects, the change in the received radio wave is a difference between the received radio wave intensity and the irradiated radio wave intensity. However, the determination is performed by obtaining the amount of radio wave absorption / transmission on the road surface and comparing it with a reference value for the absorption / transmission amount stored in advance.

  According to a sixth aspect of the present invention, in the road surface state determination method according to any one of the first to fifth aspects, the radio wave having a plurality of frequencies is irradiated toward the road surface, and the reflected radio wave is received and irradiated. The discrimination is performed based on changes in received radio waves with respect to radio waves having a plurality of frequencies.

  According to a seventh aspect of the present invention, in the road surface state determination method according to any one of the first to sixth aspects, a radio wave absorber is embedded in a road surface on which a radio wave is irradiated.

  The means of claim 8 is the road surface state determination method according to any one of claims 1 to 7, wherein a radio wave absorber is embedded in the road surface to determine water, ice and dryness. .

  According to a ninth aspect of the present invention, in the road surface state determination method according to any one of the third to eighth aspects, the reference value is obtained in advance for a plurality of thicknesses of water or ice on the road surface or water on the road surface. It is defined as a plurality of value ranges corresponding to the measured radio wave, and it is characterized by determining which value range corresponds to the change of the radio wave irradiated on the road surface and measuring the presence or absence of water or ice or the thickness of water.

  The means of claim 10 is the road surface state determination method according to any one of claims 1 to 9, wherein the frequency range of the radio wave applied to the road surface is a frequency at which a complex relative permittivity of water or ice changes. It is a region.

  The means according to claim 11 is the road surface state determination method according to any one of claims 1 to 10, wherein the road surface state irradiates radio waves having a plurality of frequencies toward the road surface and receives radio waves including reflected waves. Inverse Fourier transform is performed, a radio wave signal reflected from the road surface in the time space after the inverse transformation is extracted, and a change in the radio wave is calculated by a signal obtained by Fourier transforming the extracted signal.

  According to a twelfth aspect of the present invention, in the road surface state determining method according to the eleventh aspect, the radio wave reflected from the road surface is irradiated and then received by multiplying the signal after the inverse Fourier transform by a predetermined filter function. It is characterized in that a peak of a signal appearing in a time-space region corresponding to the time until is extracted.

  According to a thirteenth aspect of the road surface condition determining apparatus of the present invention, a radio wave transmitting means for radiating radio waves toward the road surface, a receiving means for receiving radio waves reflected from the road surface, and a radio wave radiated from the transmitting means. A transmission / reception wave variation calculation unit for calculating the attenuation amount of the radio wave, which is a ratio of the intensity of the radio wave received by the receiving means to the intensity, a reference data storage unit for storing a reference value for the attenuation amount of the radio wave, and a transmission / reception wave A road surface state determination unit that compares the amount of radio wave attenuation calculated by the change amount calculation unit with the reference value stored in the reference data storage unit to determine the presence or absence of water or ice on the road surface.

  The means of claim 14 in the road surface condition judging device of the present invention comprises: a radio wave transmitting means for irradiating a radio wave toward the road surface; a receiving means for receiving a radio wave reflected from the road surface; and a radio wave received by the receiving means. Compare the received intensity measurement unit that measures the intensity, the reference data storage unit that stores the reference value for the received intensity of the radio wave in advance, and the radio wave intensity measured by the received intensity measurement unit and the reference value that is stored in the reference data storage unit And a road surface state determining unit for determining the presence or absence of water or ice on the road surface.

  The means of claim 15 in the road surface condition judging device of the present invention comprises: a radio wave transmitting means for irradiating a radio wave toward the road surface; a receiving means for receiving a radio wave reflected from the road surface; and a radio wave irradiated from the transmitting means. Transmit / receive wave change amount calculation unit that calculates the amount of radio wave absorption / transmission on the road surface, which is the difference in radio wave intensity received by the receiving means with respect to the intensity, and reference data for pre-stored reference values for radio wave absorption / transmission amount A storage unit and a road surface state determination unit that compares the amount of radio wave absorption / transmission calculated by the transmission / reception wave variation calculation unit with the reference value stored in the reference data storage unit to determine the presence or absence of water or ice on the road surface. It is to be prepared.

  The means of claim 16 in the road surface condition discriminating apparatus of the present invention comprises a radio wave transmitting means for radiating radio waves toward the road surface, a receiving means for receiving radio waves reflected from the road surface, and a radio wave radiated from the transmitting means. A transmission / reception wave variation calculation unit for calculating the attenuation amount of the radio wave, which is a ratio of the intensity of the radio wave received by the receiving means to the intensity, a reference data storage unit for storing a reference value for the attenuation amount of the radio wave, and a transmission / reception wave A road surface state determination unit that compares the attenuation amount of the radio wave calculated by the change amount calculation unit with the reference value stored in the reference data storage unit to determine the thickness of water on the road surface.

  The means of claim 17 in the road surface condition discriminating apparatus of the present invention comprises: a radio wave transmitting means for radiating a radio wave toward the road surface; a receiving means for receiving the radio wave reflected from the road surface; and a radio wave received by the receiving means. Compare the received intensity measurement unit that measures the intensity, the reference data storage unit that stores the reference value for the received intensity of the radio wave in advance, and the radio wave intensity measured by the received intensity measurement unit and the reference value that is stored in the reference data storage unit And a road surface state determining unit that determines the thickness of water on the road surface.

  The means of claim 18 in the road surface condition discriminating apparatus of the present invention comprises: a radio wave transmitting means for radiating radio waves toward the road surface; a receiving means for receiving radio waves reflected from the road surface; and a radio wave radiated from the transmitting means. Transmit / receive wave change amount calculation unit that calculates the amount of radio wave absorption / transmission on the road surface, which is the difference in radio wave intensity received by the receiving means with respect to the intensity, and reference data for pre-stored reference values for radio wave absorption / transmission amount A storage unit and a road surface state determination unit that compares the amount of radio wave absorption / transmission calculated by the transmission / reception wave variation calculation unit with the reference value stored in the reference data storage unit to determine the thickness of water on the road surface It is.

  The means of claim 19 is the road surface condition discriminating apparatus according to any one of claims 13 to 18, wherein the transmitting means radiates radio waves of a plurality of frequencies toward the road surface, and the reference data storage unit Stores a value corresponding to each of the radio waves of the plurality of frequencies.

  The means of claim 20 is the road surface state discriminating apparatus according to any one of claims 13 to 19, wherein the transmitting means radiates radio waves having a plurality of frequencies toward the road surface, and the receiving means is reflected. The radio wave change amount calculation unit receives a radio wave including a wave, a Fourier inverse transform unit that performs a Fourier inverse transform process on the radio wave received by the reception unit, and a signal after the Fourier inverse transform of a predetermined filter function The time filter unit for extracting the peak of the signal appearing in the time-space region corresponding to the time until the radio wave reflected from the road surface is received after the radio wave reflected from the road surface, and the Fourier transform for the signal after the extraction A conversion unit, and the change of the radio wave is calculated from the signal after the Fourier transform.

  The present invention has an effect of making it possible to discriminate between water and ice or to discriminate the thickness of water, which could not be discriminated in principle by the conventional measuring method using optical reflection intensity. Furthermore, the present invention discriminates water or ice by focusing on the difference in the remarkable reflection characteristics of water and ice based on the complex relative permittivity for the radio wave irradiated on the road surface. It is also possible to accurately determine the thickness of the water, and in particular, the change in the received radio wave is obtained as the attenuation of the radio wave, which is the ratio of the received radio wave to the intensity of the irradiated radio wave, and the attenuation stored in advance. The road surface condition can be determined with high accuracy by comparing with the reference value for the amount or by comparing with the reference value for the received intensity obtained in advance as the intensity of the received radio wave.

  Also, the change of the received radio wave is obtained as the amount of radio wave absorption / transmission by the road surface, which is the difference between the intensity of the received radio wave and the intensity of the received radio wave, and compared with the reference value for the pre-stored absorption / transmission amount. Since the presence / absence of water or ice on the road surface is discriminated by this, the amount of change can be expanded and expressed, so that the setting of a highly accurate reference value is further facilitated. .

  Furthermore, by utilizing the characteristic that the change in attenuation or absorption / transmission of radio waves for multiple frequencies irradiated on the road surface changes significantly with respect to either water or ice compared to the other, By providing the reference value, water or ice can be distinguished individually and with high accuracy.

  Furthermore, if a radio wave absorber is buried on the road surface, the influence of water or ice can be more pronounced by eliminating the influence of dielectrics such as asphalt and concrete, and the presence or absence of water or ice or the thickness of water can be more accurately determined. Can be determined. Furthermore, on this road surface, it is possible to distinguish between a dry state where no water or ice is present on the road surface and a state where ice is present on the road surface. Furthermore, since the interference due to the irregular reflection component can be removed by using the time domain method, the determination accuracy can be further improved.

  Hereinafter, an embodiment of a road surface state determination device using a road surface state determination method according to the present invention will be described with reference to FIG. FIG. 1 shows a road surface state discriminating device disposed on a road for discriminating road surface state. Reference numeral 1 denotes a transmitting means for irradiating a road surface R with radio waves, and an oscillator for generating radio waves by generating an electric field having an oscillation frequency in the gigahertz range. 11 and a transmission antenna 12 that amplifies the input signal and irradiates the road surface R with radio waves of, for example, 0 GHz to 6 GHz (the lower limit frequency is strictly greater than 0).

  Reference numeral 2 denotes a receiving means, which includes a receiving antenna 22 that receives radio waves reflected from the road surface R and a detector 21 that detects each received radio wave. The transmitting antenna 12 and the receiving antenna 22 are arranged side by side so that radio waves are irradiated onto the road surface R substantially vertically by a support means such as a beam post.

  3 is a ratio of the intensity of the radio wave received by the receiving means with respect to the intensity of the radio wave emitted from the transmitting means, and a transmission / reception wave change amount calculating unit for calculating the attenuation of the radio wave. A reference data storage unit 5 that stores a reference value for the attenuation amount is a road surface state determination unit that compares the attenuation amount from the transmission / reception wave change amount calculation unit 3 with the reference value stored in the reference data storage unit 4.

  Reference numeral 6 denotes a communication means, an output unit that distributes the presence or absence of water or ice on the road surface determined by the road surface state determination unit 5 to a central observation device (not shown), and 7 is a control that stores a program for determining the road surface state A program storage unit 8 is a CPU that controls the above 1 to 6 according to a set value such as a sampling period and an oscillation frequency set by a program of the control program storage unit 7 and a key switch (not shown), and executes road surface state determination. .

  First, the principle of measurement will be described. When a single dielectric layer made of water or ice is present on the road surface made of asphalt as shown in FIG. 8A, a plane wave of a two-layer dielectric made of water or ice and asphalt. The amount of attenuation can be obtained by the following mathematical formula obtained by developing the mathematical formula for obtaining the characteristic impedance for.

は伝送定数を

とすれば、

となる。 Here, when the state of reflection and absorption from water and ice shown in FIG. 8A is shown by an equivalent circuit, FIG. 8B is obtained. In this case, the characteristic impedance of radio wave propagation as seen from the receiving end

Is the transmission constant

given that,

It becomes.

であり、水、氷内を伝搬する平面波の特性インピーダンス

および伝搬定数

は、

Here, the complex relative permittivity and complex relative permeability of water and ice are

The characteristic impedance of plane waves propagating in water and ice

And propagation constants

Is

となり、

を得る。 Here, water and ice are non-magnetic materials

And

Get.

を前記(７)式に代入し、水または氷内を伝搬する平面波の特性インピーダンス

と伝搬定数

を求める。 Then, the complex dielectric constant obtained by substituting the above-mentioned numerical values and frequencies of 0 GHz to 6 GHz for water and ice into the equations (3), (4-1) and (2).

Is substituted into the equation (7), and the characteristic impedance of the plane wave propagating in water or ice

And propagation constants

Ask for.

を求め（５）式に代入すると受端側から見込んだ特性インピーダンス

が求められる。 Further, d, which is the thickness of water or ice, is 2 mm, for example, and the characteristic impedance of radio wave propagation related to asphalt from the complex relative dielectric constant ε _l = 6.0 + 0.4j of typical asphalt

And substituting into equation (5), the characteristic impedance expected from the receiving end

Is required.

として表される。そこで、この求めた反射率Γから図４〜図７に示す０ＧＨｚ〜６ＧＨｚの周波数に対する電波の減衰量（２０log₁₀Γ（ｄＢ））が求められる。なお、図４〜図７の水と氷の電波反射特性には図３に示す周波数において０ＧＨｚ〜６ＧＨｚの複素比誘電率

の変化が反映されており、そのため水に関しては減衰量の変化の大きい曲線として、氷に関しては減衰量の変化の小さい直線として表現されている。 Also, from this characteristic impedance, the reflectivity Γ for this dielectric is as follows:

Represented as: Therefore, the radio wave attenuation (20 log ₁₀ Γ (dB)) with respect to the frequency of 0 GHz to 6 GHz shown in FIGS. 4 to 7 is obtained from the obtained reflectance Γ. Note that the water and ice radio wave reflection characteristics of FIGS. 4 to 7 are complex relative dielectric constants of 0 GHz to 6 GHz at the frequency shown in FIG.

Therefore, water is expressed as a curve with a large change in attenuation, and ice is expressed as a straight line with a small change in attenuation.

  4 shows the attenuation when water or ice and asphalt form two layers, and FIG. 5 shows the attenuation when water or ice and concrete form two layers. 6 shows the attenuation when two layers are formed by water or ice and acrylic, and FIG. 7 shows the attenuation when two layers are formed by water or ice and paint. Yes. As is apparent from these measurement data, the attenuation of radio waves with respect to water and ice or changes in any of the above-mentioned dielectrics that can be constructed on the road are different. The presence or absence of water or ice can be determined.

  Next, the operation will be described according to the flowchart of FIG. First, when a road surface condition determination program is started by detecting an air temperature or a road temperature below a set value by a temperature sensor (not shown), the CPU 8 stores in the reference data storage unit 4 in advance according to the program stored in the control program storage unit 7. A signal having a frequency of the first wave (for example, 3 GHz) is sent to the oscillator 11, and a radio wave of 3 GHz is emitted from the transmitting antenna 12 toward the road surface R (step S1). In addition, it measures as transmission intensity Wo of the electromagnetic wave transmitted at this time, and memorize | stores it in CPU8 temporarily. Next, the radio wave of the same frequency reflected from the road surface R and received by the receiving antenna 22 is detected and output as the received wave intensity Wi of the received radio wave (step S2).

Next, the CPU 8 calculates the ratio (reflectance) of the received radio wave intensity to the transmitted radio wave intensity as an attenuation 20 log ₁₀ (Wi / Wo) in the transmission / reception wave variation calculation unit 3 and temporarily stores it in the CPU 8. (Step S3).

  Next, the CPU 8 uses the road surface state determination unit 5 to calculate the attenuation value calculated by the transmission / reception wave change calculation unit 3 and the reference value x of the attenuation amount for the 3 GHz frequency stored in the reference data storage unit 4 in advance, for example, FIG. And 0 dB> x> −3 dB (step S4) and −10 dB> x> −12 dB (step S5), respectively, and water and ice are discriminated when they are within the reference value.

  The reference value is, for example, the reception status of the radio wave at the measurement place with respect to the attenuation amount (calculated value) of -1.5 dB of water with respect to the radio wave of 3 GHz and -11.0 dB of the attenuation amount (calculated value) of ice. It may be set accordingly. Of course, the reference value may be defined as a value range in which the amount of attenuation differs between water and ice and the two can be distinguished. Further, the frequency of the radio wave to be transmitted is not limited to 3 GHz, and any frequency may be used as long as the attenuation amounts of water and ice are different and can be distinguished from each other.

  If “water” is determined in step S4 and “ice” is determined in step S5, the determination results are distributed from the output unit 6 to the central observation device (steps S6 and S7). Then, if it is determined in step S4 and step S5 that neither the water nor ice standard is satisfied, the process is performed with no notification (step S8). That is, it can be said that the presence or absence of water or ice is determined by this treatment. Further, it is determined whether or not a sampling timer (not shown) that repeats timing simultaneously with the start of the transmission process in step S1 has expired (step S9), and if it is determined that the time has expired, the process returns to step S1 to return to the next frequency ( For example, 4 GHz, 5 GHz, and 6 GHz are executed, and 6 GHz is executed and then the measurement is returned to 1 GHz and the frequency is changed to 2 GHz and 3 GHz. Thus, the accuracy of determination can be improved by measuring a plurality of frequencies.

  However, as is clear from FIG. 4, there is a large difference between the attenuation amounts of water and ice (for example, a difference of 8 dB), so one reference value for determining “water” and “ice”, for example, −6 dB is set. And you may make it compare with the attenuation amount with respect to any frequency in 2 GHz-6 GHz. Further, by utilizing the characteristic that the change in attenuation amount of “water” is larger than that of “ice”, the change amount may be set as a reference value (for example, the attenuation amount for the frequencies of 0.5 GHz and 2 GHz). If the change is 6 dB or more, it is determined to be water. If the change in attenuation is 0.5 dB and 2 GHz, the threshold is 2 dB. If the change in attenuation is 2 dB or less, ice Judgment).

  In addition to the embodiment described above, a reception intensity measurement unit 15 is provided instead of the transmission / reception wave change amount calculation unit 3 of FIG. 1 as shown in FIG. 9, and the reference data storage unit 4 has a reference value as a reference value. The reception intensity (= transmission intensity × reflectance) with respect to the frequency of the radio wave is stored in advance, and the road surface state determination unit 5 compares the reception intensity obtained by the reception intensity measurement unit 15 with the reference value stored in the reference data storage unit. The road surface condition may be determined.

In addition, when the standard for determining the change of radio waves due to water and ice is not the attenuation of radio waves but the amount of absorption / transmission of radio waves by water or ice and the road surface (20 log ₁₀ (1-reflectance)), the above-mentioned radio waves Since the change with respect to the frequency is expressed in an enlarged manner, the setting of the reference value becomes easier. In this case, the embodiment is the same as the embodiment shown in FIGS. 1 and 2 except that the attenuation amount of the above-described embodiment is calculated as the absorption / transmission amount and compared with an appropriate reference value similar to the above.

  In the above embodiment, a method of discriminating water or ice on the road surface using radio waves having a frequency of 0 GHz to 6 GHz has been proposed, but the complex relative permittivity of water changes greatly as is apparent from the graph of FIG. It is possible to determine the road surface state using radio waves in the vicinity of 1 GHz to 100 GHz. Similarly, it is possible to discriminate water or ice on the road surface using radio waves in the region near 100 Hz to about 100 KHz where the complex relative permittivity of ice is greatly changed. However, it is not necessary to discriminate both water and ice simultaneously as in the above-described embodiment, and only one of the necessary states may be discriminated.

  In the present invention, as shown in the above-described logical expression and FIG. 4, when a dielectric having a two-layer structure is irradiated with a radio wave of several hundred GHz or less, the complex relative permittivity changes greatly with respect to the frequency (the above-described implementation). In the form, water + asphalt or other dielectric material) has a characteristic that the attenuation waveform greatly changes due to the attenuation of radio waves, and the side where the change in the complex relative permittivity is small (in the above embodiment, the dielectric material such as ice + asphalt) has a frequency. In contrast to this, a characteristic that does not attenuate radio waves appears. That is, the characteristic that the attenuation of the other of the water and ice changes greatly is used to determine the road surface state of “water” and “ice”.

  Therefore, it is not limited to the embodiment of the present invention, and based on the change of the received radio wave with respect to the irradiated radio wave, a specific reference value is set between the two changes, or water or ice is identified for a specific frequency. Or the presence of water or ice on the road surface to determine the presence or absence of water or ice on the road surface by setting a reference value for changes in received radio waves for a plurality of frequencies. A discriminating method and discriminating device that use changes in the reflection characteristics of radio waves are included in the present invention.

  In the embodiment, the presence or absence of water or ice is determined using the fact that the frequency range in which the complex relative permittivity varies greatly depends on the state of water (liquid or solid). As shown in the figure, it is possible to adopt an embodiment in which the complex relative permittivity depends on the thickness of water, and as a result, the attenuation, reception intensity, and transmission / absorption amount are changed to determine the thickness of water. It is.

  Therefore, in the embodiment for determining the thickness of water described below, it can be realized by a configuration similar to the hardware configuration shown in FIG. 1. However, in the reference data storage unit 4, the amount of change (attenuation) with respect to the transmission frequency is realized. A reference value indicating the amount or the like) is stored for each predetermined thickness of water. FIG. 11 shows the attenuation when a radio wave is transmitted at a frequency of 0 GHz to 2 GHz (strictly speaking, 0 GHz is a frequency greater than 0) and a reflected wave is received by the road surface state determination device according to the present embodiment. Show.

  As shown in the figure, the attenuation varies depending on the thickness of water at each frequency. Therefore, the reference data storage unit 4 stores the value range of the attenuation amount at the frequency to be transmitted as the reference value corresponding to the thickness of the water. For example, in the example shown in FIG. 11, when a 1 GHz radio wave is transmitted, the reference value for 4 mm is 0 dB> x> −3 dB, the reference value for 2 mm is −3 dB ≧ x> −5 dB, and the reference value for 1 mm is −5 dB. If the reference value for ≧ x> −7.5 dB, 0.5 mm is −7.5 dB ≧ x, the water thickness can be determined by comparing the observed attenuation with the reference value.

  As specific processing, steps S1 to S3 and step S9 in FIG. 2 perform the same processing as the processing shown in FIG. 2, and processing different from the embodiment shown in FIG. 2 is performed in steps S4 to S8. That is, in step S4, it is determined whether or not the amount of change acquired in step S3 corresponds to any of the reference values stored in the reference data storage unit 4. The corresponding water thickness is determined, and the determination result is distributed in step S6.

In step S4, when it is not determined that the amount of change acquired in step S3 corresponds to any of the reference values stored in the reference data storage unit 4, processing is performed as no notification as in step S8. Steps S5 and S7 are not performed. Through the above processing, it is possible to determine the thickness of water on the road surface. Of course, in this embodiment, it is only necessary to be able to discriminate the thickness of water, and it is not essential to set the thickness of water to 0.5 mm, 1 mm, 2 mm, or 4 mm. Also good. Further, the water thickness may be used as a reference value for determining the presence or absence of water. For example, it may be determined that “water is present” by detecting water having a thickness of 1 mm or 1 mm or more.

  Furthermore, in the above-described embodiment, the radio wave is irradiated on the road surface such as asphalt, but in order to detect the change of the radio wave more accurately and determine the presence or absence of water or ice on the road surface and the thickness of the water. A radio wave absorber may be embedded in the road surface. For example, it is possible to adopt a configuration in which a sheet obtained by mixing ferrite powder and conductive carbon in a binder such as plastic is embedded in the road surface.

  With respect to such a road surface, when a change in the transmitted radio wave and the received radio wave is detected by the road surface state discriminating apparatus having the configuration as shown in FIG. 1, a change in the radio wave due to water or ice is eliminated by eliminating the influence from the dielectric. Can stand out more. As a result, the presence or absence of water or ice or the thickness of water can be determined more accurately. Furthermore, on this road surface, it is possible to distinguish between a dry state where no water or ice is present on the road surface and a state where ice is present on the road surface.

FIG. 12 shows the reflectivity when the absorber is embedded in the road surface for 0 GHz to 6 GHz as described above, and FIG. 13 shows the attenuation (20 log ₁₀ (reflectance)). As shown in FIG. 12, the reflectivity of 2 mm of water, the reflectivity of 2 mm of ice, and the reflectivity in the dry state are different from each other. As shown in FIG. 13, the reflectivity of 2 mm of water, 2 mm of ice and dry The amount of attenuation varies depending on the state. Since the reflectance in the dry state is “0”, the attenuation amount is −∞, which is not clearly shown in FIG. 13, but in any case, the attenuation amount is different between water, ice, and the dry state. Accordingly, by storing the value ranges for water, ice, and dry conditions in the reference data storage unit 4 as reference values, the attenuation is measured by the road surface condition discriminating apparatus shown in FIG. By comparing, it is possible to distinguish between water, ice, and dry state.

  Furthermore, in order to improve the determination accuracy, a process for removing interference due to the irregular reflection component (a process by the time domain method) may be performed. That is, in the road surface state determination apparatus shown in FIG. 1, the signal received by the receiving antenna 22 is not only the reflected wave reflected from the road surface but also the reflections from various objects (eg, guardrails) near the road surface. State (interference state). Therefore, the configuration shown in FIG. 14 may be employed to eliminate interference.

  In FIG. 14, the phase detection unit 9, the complex signal conversion unit 31, the inverse Fourier transform unit 32, the time filter unit 33, and the Fourier transform unit 34 are configurations added to the road surface state determination device shown in FIG. 1. In such a configuration, the oscillator 11 oscillates a signal having a plurality of frequencies in a predetermined band, and the detector 21 acquires a signal corresponding to the oscillation signal at each frequency as a received wave. The phase detector 9 is connected to the oscillator 11 and the detector 21, detects the phase of the received signal from the output of the oscillator 11 and the output of the detector 21, and sends the phase signal indicating the phase to the transmission / reception wave change calculation unit 3. To supply. The composite signal conversion unit 31 acquires the intensity signal (A (f)) of the received radio wave output from the phase signal and the detector 21, and complex signal data (F (ω) = A (f) (cosωt + jsinωt)). Output as. Note that f is a frequency and ω = 2πf.

に従ってフーリエ逆変換を実施するモジュールであり、フーリエ逆変換後の複素時間信号データｆ（ｔ）を出力する。ここで、ｔは時間である。時間フィルタ部３３は、この複素信号データｆ（ｔ）に対して以下の式

に従って時間フィルタＧ（ｔ）を作用させ、所望の時間帯域における信号データｇ（ｔ）を抽出する。尚、時間フィルタＧ（ｔ）としては、各種関数を採用可能であり、矩形，ガウス，ハミング，ハニング関数等を採用可能である。 The processing by the phase detector 9 and the complex signal converter 31 is performed for each frequency of the signal oscillated by the oscillator 11, and the obtained complex signal data is stored in a memory (not shown). The Fourier inverse transform unit 32 uses the following formula for complex signal data:

The module performs the inverse Fourier transform according to the above, and outputs the complex time signal data f (t) after the inverse Fourier transform. Here, t is time. The time filter unit 33 uses the following equation for this complex signal data f (t).

The time filter G (t) is applied according to the above, and the signal data g (t) in the desired time band is extracted. Note that various functions can be employed as the time filter G (t), such as a rectangle, a Gaussian, a Hamming function, and a Hanning function.

に従ってフーリエ変換し、干渉が除去され、路面からの反射成分を抽出した複素周波数信号データＦ（ω）を取得する。送受波変化量算出部３では、当該干渉を除去した後の複素周波数信号データＦ（ω）から受信電波の強度を算出し、前記発振器１１で出力した送信波の強度を用いて前記減衰量や、受信強度、透過・吸収量を取得する。この結果、干渉の影響を排除し、路面およびその上の水や氷による電波の変化を確実に取得することができ、高精度で水や氷の有無あるいは水の厚みを判別することが可能になる。 Then, the Fourier transform unit 34 converts the extracted signal data g (t) into the following formula:

To obtain the complex frequency signal data F (ω) from which the interference is removed and the reflection component from the road surface is extracted. The transmission / reception wave variation calculation unit 3 calculates the intensity of the received radio wave from the complex frequency signal data F (ω) after removing the interference, and uses the intensity of the transmission wave output from the oscillator 11 to calculate the attenuation amount or , Receive strength, transmission / absorption amount. As a result, the influence of interference can be eliminated, and changes in radio waves due to the road surface and water or ice on it can be acquired reliably, and the presence or absence of water or ice or the thickness of water can be determined with high accuracy. Become.

  15 to 18 are explanatory diagrams for explaining the effect of the processing for removing the interference wave in this way. These drawings are explanatory diagrams for explaining a case where the frequency is changed from 1 GHz to 5 GHz in a state where 2 mm of water is stretched on the road surface located at the lower center of the transmitting antenna and the receiving antenna. FIG. 15 shows the change in the radio wave of the reception wave and the transmission wave in dB without performing the processing in the phase detection unit 9 and the complex signal conversion unit 31 to the Fourier transform unit 34.

  In the spectrum shown in the figure, small peaks are continuous over the entire frequency band, but this is due to the fact that each frequency contains a lot of interference other than radio waves that are reflected on the road surface, and that the effect differs from frequency to frequency. is doing. FIG. 16 shows the absolute value when the inverse Fourier transform is performed on the received wave in this case, the horizontal axis is time (seconds), and the vertical axis is the absolute value. If the transmitted wave is reflected at one point on the road surface and only the reflected wave is received, it should have a large peak at one point on the horizontal axis in FIG. 16, but two large peaks appear in FIG. It contains a lot of small noise components.

  In FIG. 16, the maximum peak on the right side is a reflected wave from the road surface, and the peak on the left side is a radio wave directly incident on the receiving antenna from the transmitting antenna. In addition, other small noises are other parts, irregular reflection components, or noise. In the present invention, the attenuation amount with respect to the received wave should be determined with reference to only the maximum peak of FIG. 16, and the time filter is used for this purpose.

  FIG. 17 shows a state where only the maximum peak is extracted by the time filter. FIG. 18 is a diagram showing the amount of attenuation calculated by the received wave and the transmitted wave with respect to the frequency by Fourier-transforming the extracted signal into a received wave signal. As shown in the figure, the attenuation is very smooth, and it can be seen that the influence of the interference shown in FIG. 15 is eliminated by the above processing. In other words, it is possible to accurately compare the change between the radio wave reflected by the road surface and received by the receiving antenna and the transmitted wave, and accurately determine the presence or absence of water or ice or the thickness of water. Is possible.

In the configuration shown in the above-described embodiment, the transmission antenna and the reception antenna are individually arranged. For example, the directionality for separating transmission and reception between the transmitter 11 and the detector 21 shown in FIG. By using a duplexer and connecting a transmission / reception antenna to the directional duplexer, a single antenna may be used for both transmission and reception. In this case, the incident angle is 0 degree, that is, the radio wave is irradiated perpendicularly to the road surface. As for the incident angle dependence of the attenuation with respect to the incident angle of the radio wave, as shown in FIG. 19 showing a plurality of different incident angles of the attenuation of the radio wave with respect to the water on the asphalt, the radio wave is irradiated perpendicularly to the road surface. Even if it irradiates diagonally with an incident angle of up to 60 degrees, the dependence is small, and it is possible to obtain similar characteristics for water and ice.

ここで、ε_lは、アスファルト等の複素比誘電率であり、前記同様、代表的にはε_l＝６．０＋０．４ｊ程度となる。 In the above-described embodiment, the radio wave is irradiated perpendicularly to the road surface (incidence angle 0 degree). However, the above-described (7) viewed from the receiving end side when irradiating with a specific incident angle θ. The characteristic impedance and transmission constant of radio wave propagation corresponding to the equation () and the characteristic impedance of radio wave propagation relating to asphalt and the reflectance Γ corresponding to the equation (8) are calculated by the following equations, respectively. FIG. 19 shows the results calculated using this theoretical development.

Here, ε _l is a complex relative permittivity of asphalt or the like, and is typically about ε _l = 6.0 + 0.4j as described above.

Furthermore, although there is polarization in the radio wave, as is clear from the experimental results described below, the electric field component is perpendicular to the incident surface of the radio wave (a plane composed of the incident wave and the reflected wave). Since the same attenuation characteristic can be obtained for the wave and the TM wave whose magnetic field component is perpendicular to the incident surface, the measurement result using the TM wave is presented in the above embodiment. FIG. 20 shows the amount of attenuation when an experiment was performed by irradiating a road surface filled with 2 mm of water with a TM wave and a TE wave at an incident angle of 45 °. As shown in the figure, the result is almost the same for both the TE wave and the TM wave. That is, when obtaining the TE wave reflectance Γ, the same determination as in the above embodiment is performed using the following calculation formula instead of the calculation formula for the TM wave.

It is a circuit block diagram which shows an example of the road surface state determination apparatus which concerns on this invention. It is a flowchart which shows operation | movement of a circuit block same as the above. It is a characteristic figure of the complex dielectric constant of water and ice. It is a radio wave reflection characteristic figure of water and ice to asphalt. It is a radio wave reflection characteristic figure of water and ice to concrete. It is a radio wave reflection characteristic figure of water and ice to acrylic. It is a radio wave reflection characteristic figure of water and ice to paint. It is explanatory drawing which shows the principle of measurement. It is a circuit block diagram of another road surface state determination apparatus. It is explanatory drawing which shows the reflectance when a laser beam or natural light hits a road surface. It is an electromagnetic wave reflection characteristic figure by the change of the thickness of water. It is a radio wave reflection characteristic figure of water, ice, and dryness on an absorber. It is a radio wave reflection characteristic figure of water and ice on an absorber. It is a circuit block diagram of the road surface state determination apparatus explaining the process which removes an interference wave. It is explanatory drawing explaining the process which removes an interference wave. It is explanatory drawing explaining the process which removes an interference wave. It is explanatory drawing explaining the process which removes an interference wave. It is explanatory drawing explaining the process which removes an interference wave. It is a figure which shows the incident angle dependence of the attenuation factor of an electromagnetic wave. It is a figure which shows the comparison regarding the attenuation amount of a TE wave and TM wave.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmitting means 11 Oscillator 12 Transmitting antenna 2 Receiving means 21 Detector 22 Receiving antenna 3 Transmitted / received wave change amount calculation unit 4 Reference data storage unit 5 Road surface state determination unit 6 Output unit 7 Control program storage unit 8 CPU
15 Received strength measurement unit

Claims (16)

By radiating radio waves of multiple frequencies toward the road surface, receiving radio waves including reflected waves, inverse Fourier transform, and multiplying the signal after Fourier inverse transform by a predetermined filter function in the time space after inverse transform After the radio wave reflected from the road surface is irradiated, the peak of the signal appearing in the time-space area corresponding to the time until reception is extracted, and the extracted signal is irradiated toward the road surface by the Fourier transform signal A road surface state determination method , comprising: calculating a change of a received radio wave with respect to a received radio wave and determining the presence or absence of water or ice on the road surface based on the change of the radio wave . By radiating radio waves of multiple frequencies toward the road surface, receiving radio waves including reflected waves, inverse Fourier transform, and multiplying the signal after Fourier inverse transform by a predetermined filter function in the time space after inverse transform After the radio wave reflected from the road surface is irradiated, the peak of the signal appearing in the time-space area corresponding to the time until reception is extracted, and the extracted signal is irradiated toward the road surface by the Fourier transform signal A road surface state determination method , comprising: calculating a change of a received radio wave with respect to a received radio wave and determining a thickness of water on the road surface based on the change of the radio wave .   A change in received radio waves is obtained as an attenuation amount of radio waves, which is a ratio of received radio waves to the intensity of irradiated radio waves, and the determination is performed by comparing with a reference value for attenuation stored in advance. The road surface state determination method according to any one of claims 1 and 2.   3. The method according to claim 1, wherein a change in the received radio wave is obtained as an intensity of the received radio wave, and the determination is performed by comparing with a reference value for the received intensity stored in advance. The road surface state determination method described.   By determining the change in the received radio wave as the amount of radio wave absorption / transmission through the road surface, which is the difference between the intensity of the received radio wave and the intensity of the received radio wave, and comparing it with the pre-stored reference value for the absorption / transmission amount The road surface state determination method according to claim 1, wherein the determination is performed.   The radio wave of a plurality of frequencies is irradiated toward a road surface, a reflected radio wave is received, and the determination is performed based on a change of the received radio wave with respect to the irradiated radio waves of a plurality of frequencies. The road surface state determination method according to claim 5.   The road surface state determination method according to any one of claims 1 to 6, wherein a radio wave absorber is embedded in a road surface irradiated with radio waves.   The road surface state determination method according to claim 1, wherein a radio wave absorber is embedded in the road surface, and water, ice, and dryness are determined.   The reference value is defined as a plurality of value ranges corresponding to radio waves measured in advance for a plurality of thicknesses of water or ice on the road surface or water on the road surface, and changes in the radio waves irradiated on the road surface correspond to any value range. The road surface state determination method according to any one of claims 3 to 8, wherein the presence or absence of water or ice or the thickness of water is measured.   10. The road surface state determination method according to claim 1, wherein a frequency range of radio waves applied to the road surface is a frequency range in which a complex relative permittivity of water or ice changes. Radio wave transmission means for radiating radio waves of multiple frequencies toward the road surface;
Receiving means for receiving radio waves including reflected waves reflected from the road surface;
A Fourier inverse transform unit that performs an inverse Fourier transform process on the radio wave received by the receiving means, and after the radio wave reflected from the road surface is irradiated by multiplying the signal after the Fourier inverse transform by a predetermined filter function, A time filter unit that extracts a peak of a signal that appears in a time-space region corresponding to a time until reception, and a Fourier transform unit that Fourier-transforms the extracted signal from the signal after the Fourier transform from the transmission unit. A transmission / reception wave variation calculation unit for calculating the attenuation of the radio wave, which is the ratio of the intensity of the radio wave received by the receiving means to the intensity of the irradiated radio wave;
A reference data storage unit that stores in advance a reference value for each attenuation amount of radio waves of the plurality of frequencies ;
A road surface state determination unit that compares the attenuation amount of the radio wave calculated by the transmission / reception wave variation calculation unit and the reference value stored in the reference data storage unit to determine the presence or absence of water or ice on the road surface;
A road surface state determination device comprising: Radio wave transmission means for radiating radio waves of multiple frequencies toward the road surface;
Receiving means for receiving radio waves including reflected waves reflected from the road surface;
A Fourier inverse transform unit that performs an inverse Fourier transform process on the radio wave received by the receiving unit, and after the radio wave reflected from the road surface is irradiated by multiplying the signal after the Fourier inverse transform by a predetermined filter function, A time filter unit that extracts a peak of a signal appearing in a time-space region corresponding to a time until reception, and a Fourier transform unit that Fourier-transforms the signal after extraction, the signal after the Fourier transform is performed by the receiving unit. A received intensity measuring unit that measures the intensity of the received radio wave;
A reference data storage unit that stores in advance a reference value for each reception intensity of radio waves of the plurality of frequencies ;
A road surface state determination unit that compares the intensity of the radio wave measured by the reception intensity measurement unit with the reference value stored in the reference data storage unit to determine the presence or absence of water or ice on the road surface;
A road surface state determination device comprising: Radio wave transmission means for radiating radio waves of multiple frequencies toward the road surface;
Receiving means for receiving radio waves including reflected waves reflected from the road surface;
A Fourier inverse transform unit that performs an inverse Fourier transform process on the radio wave received by the receiving means, and after the radio wave reflected from the road surface is irradiated by multiplying the signal after the Fourier inverse transform by a predetermined filter function, A time filter unit that extracts a peak of a signal that appears in a time-space region corresponding to a time until reception, and a Fourier transform unit that Fourier-transforms the extracted signal from the signal after the Fourier transform from the transmission unit. A transmission / reception wave variation calculation unit for calculating the amount of radio wave absorption / transmission on the road surface, which is the difference in radio wave intensity received by the receiving means with respect to the intensity of the irradiated radio wave;
A reference data storage unit that stores in advance a reference value for the amount of absorption and transmission of radio waves of the plurality of frequencies ,
A road surface state determination unit that compares the amount of radio wave absorption / transmission calculated by the transmission / reception wave change amount calculation unit with the reference value stored in the reference data storage unit to determine the presence or absence of water or ice on the road surface;
A road surface state determination device comprising: Radio wave transmission means for radiating radio waves of multiple frequencies toward the road surface;
Receiving means for receiving radio waves including reflected waves reflected from the road surface;
A Fourier inverse transform unit that performs an inverse Fourier transform process on the radio wave received by the receiving unit, and after the radio wave reflected from the road surface is irradiated by multiplying the signal after the Fourier inverse transform by a predetermined filter function, A time filter unit that extracts a peak of a signal that appears in a time-space region corresponding to a time until reception, and a Fourier transform unit that Fourier-transforms the extracted signal from the signal after the Fourier transform from the transmission unit. A transmission / reception wave change amount calculation unit for calculating the attenuation amount of the radio wave, which is the ratio of the intensity of the radio wave received by the receiving means to the intensity of the irradiated radio wave;
A reference data storage unit that stores in advance a reference value for each attenuation amount of radio waves of the plurality of frequencies ;
A road surface state determination unit that compares the attenuation amount of the radio wave calculated by the transmission / reception wave variation calculation unit and the reference value stored in the reference data storage unit to determine the thickness of water on the road surface;
A road surface state determination device comprising: Radio wave transmission means for radiating radio waves of multiple frequencies toward the road surface;
Receiving means for receiving radio waves including reflected waves reflected from the road surface;
A Fourier inverse transform unit that performs an inverse Fourier transform process on the radio wave received by the receiving unit, and after the radio wave reflected from the road surface is irradiated by multiplying the signal after the Fourier inverse transform by a predetermined filter function, A time filter unit that extracts a peak of a signal appearing in a time-space region corresponding to a time until reception, and a Fourier transform unit that Fourier-transforms the signal after extraction, the signal after the Fourier transform is performed by the receiving unit. A received intensity measuring unit that measures the intensity of the received radio wave;
A reference data storage unit that stores in advance a reference value for each reception intensity of radio waves of the plurality of frequencies ;
A road surface state determination unit that compares the intensity of the radio wave measured by the reception intensity measurement unit with the reference value stored in the reference data storage unit to determine the thickness of water on the road surface;
A road surface state determination device comprising: Radio wave transmission means for radiating radio waves of multiple frequencies toward the road surface;
Receiving means for receiving radio waves including reflected waves reflected from the road surface;
A Fourier inverse transform unit that performs an inverse Fourier transform process on the radio wave received by the receiving unit, and after the radio wave reflected from the road surface is irradiated by multiplying the signal after the Fourier inverse transform by a predetermined filter function, A time filter unit that extracts a peak of a signal that appears in a time-space region corresponding to a time until reception, and a Fourier transform unit that Fourier-transforms the extracted signal from the signal after the Fourier transform from the transmission unit. A transmission / reception wave variation calculation unit for calculating the amount of radio wave absorption / transmission on the road surface, which is the difference in radio wave intensity received by the receiving means with respect to the intensity of the irradiated radio wave;
A reference data storage unit that stores in advance a reference value for the amount of absorption and transmission of radio waves of the plurality of frequencies ,
A road surface state determination unit that compares the amount of radio wave absorption / transmission calculated by the transmission / reception wave variation calculation unit with the reference value stored in the reference data storage unit to determine the thickness of water on the road surface;
A road surface state determination device comprising:

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