JPH079395B2 - Visibility measurement method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a meteorological observation device, and more particularly to a visibility measurement method which is an important material for safe operation of transportation facilities.

[Prior Art] As a method of measuring the visibility by a conventional instrument, a transmittance measurement method for measuring the transmittance of projected light in the atmosphere and a reflectance (intensity of backscattered light) from a suspended matter in the atmosphere are measured. There is known a reflectance measuring method. The conventional visibility measurement method based on the above two methods will be described. In the transmittance measurement method, the light emitter and the light receiver are arranged in a straight line and face each other like P and D _T , and the light projected from the light emitter P is received by the light receiver D _T. The visibility is obtained from the comparison, that is, the transmittance, which is attenuated until reaching.

On the other hand, the reflectance measurement method uses P and
D _R Gotoku both optical axes are arranged to intersect at an angle of 90 degrees or less, measure the accumulated value by receiving the backward reflected light of the backscattered light generated by the projection light from the projector P by the photodetector D _R Then, it is a method of converting the visibility into the visibility from the known conversion table showing the relationship between the integrated value and the visibility.

[Problems to be Solved by the Invention] In the visibility measurement, the conversion table of the transmittance and the visibility in the transmittance measurement method and the conversion table of the reflected light amount integrated value and the visibility in the reflectance measurement method have a visibility obstacle factor. If it is different (for example, snowstorm, fog, etc.), the conversion scale is generally different.
It is necessary to determine the visibility obstacle factor at that time and input the data, and the conversion process for obtaining visibility becomes complicated,
And the error becomes large.

The present invention relates to a visibility measuring method that solves the problems in the conventional example as described above.

[Means for Solving the Problem] The present invention solves the problem by using a specific angle in an angle range that is not used in the conventional arrangement of the optical axes as the intersection angle of the light emitting / receiving axes. Is. That is, the linear arrangement of the projection / reception axis in the transmittance measurement method (the angle formed by the two optical axes is 180 degrees) and the rear side reflection angle arrangement of the projection / reception axis in the reflectance measurement method (both optical axes Angle from 0 degree to 90 degrees laterally) is not used, and the angle between the light emitting axis and the light receiving axis is 90 degrees or more, and the angle is more than one in the front side angle where no light is directly incident. It utilizes a specific angle of the part.

That is, the inventor of the present application shows that, from a large amount of measurement data, when the crossing angle between the light projecting axis and the light receiving axis is changed, the characteristic indicating the signal output of the light receiver versus the visibility changes, and the crossing angle at a specific angle is changed. , It was found that the signal output of the photodetector in the same visibility is the same for different visibility obstacle factors.
By utilizing this characteristic, a visibility measuring method capable of measuring the visibility by the same process regardless of the type of the visibility obstacle factor is obtained.

[Example] The positional relationship between the projector and the receiver according to the present invention is set to the positional relationship between P and _DF shown in FIG. Although FIG. 6 is actually preferably represented by a solid angle, in order to simplify the drawing, in the present application, it is considered that the drawing is symmetrical in the vertical and forward / backward directions, and the angle display is 0 ° to 90 ° to 180 °. Use to explain.

The arrangement of the optical axes of the present invention will be described with reference to FIG. The projection beam limits the measurement space created by the beam aperture and the beam spread, and the light receiving field is further limited by the light receiving aperture and the viewing angle. That is, the measurement target space is a volume that is integrated 360 degrees with respect to each optical axis of the rectangular ABCD area on the limited plane.

FIG. 2 is a diagram for explaining an implementation sequence of the present invention. Floodlight P
Has a light source such as an incandescent light bulb, a xenon flash, an LED, a laser diode, etc., and has a structure for projecting a beam of light. The photodetector D is a photoelectric conversion element having a sensitivity adapted to the wavelength characteristics and modulation characteristics of each light source. It is composed of an optical system for limiting the light-receiving field, and is equipped with necessary electric circuits.

In the visibility meter according to the embodiment, the projector S and the light receiving axis D fixed to the pillar S and the arm A built on the ground are both directed forward and downward, and the suspended particles existing in the area of the intersecting space SA are separated from each other. It measures forward scattered light.

The larger the diameter and the number of suspended particles in the intersecting space, the larger the amount of light received by the light receiver D. Therefore, the larger the amount of received light, the lower the visibility.

FIG. 4 shows an example of the relationship between the output and the visibility in the bilogarithmic coordinates. This figure is a curve in the case where the particles are the same, and shows the change in the photodetector output when the included angle θ of the optical axis in FIG.

Next, FIG. 5 shows the case where the types of particles are different. Only the vertical axis (receiver output) is logarithmic. The solid line shows the characteristics in case of snowstorm, and the broken line shows the characteristics in case of fog. θ
It can be seen that when is close to 90 degrees and is relatively small, the output is low but the degree of change is large, and therefore the visibility-corresponding value in a narrow range can be obtained by enlarging it within the constant receiver output range. Conversely, θ
When the value is increased to approach 180 degrees in the range where direct light is not received, the output level increases but the degree of change with respect to visibility decreases, and a wide range of visibility can be obtained within a certain output range. I understand.

Further, as is clear from FIG. 5, the characteristics in the case of snowstorm and the characteristics in the case of fog intersect at a specific angle θ _C, which means that the included angle of the light emitting / receiving axis is θ Specific angle θ
By setting to _C , it is possible to obtain a single visibility scale that can be commonly used for both fog and snowstorm phenomena.

FIG. 3 shows an arrangement example of the light shields B _P and B _D. B _P and B _D are arranged in front of the light emitting / receiving axis and further ahead of the intersecting measurement space SA. The surfaces of B _P and B _{D have} a frosted black matte with a low degree of reflection or a louver-like structure set at an angle such that reflection in the optical axis direction of the other party is small. If obstacles due to light reflected from the ground, snow, or water are expected, the light shield B _P , B
By placing _D , these obstacles can be eliminated. Either one of B _P and B _D may be placed depending on the condition of the failure. In the prior art reflectance measuring method using backscattered light, it was impossible in principle to dispose such a light shield integrally with the equipment.

[Effects of the Invention] As described above, the visibility measuring method according to the present invention can use the visibility conversion table having the same scale even if the factors causing the visibility are different. It has become possible to measure the visibility value more easily in an environment where factors are predicted to occur.

According to the present invention, it is expected that useful data can be collected at points (for example, near roads) that are particularly required for meteorological measurement and transportation.

[Brief description of drawings]

1 to 5 are views for explaining an embodiment of the present invention, FIG. 1 is a view showing an optical axis arrangement, FIG. 2 is a structural view,
FIG. 3 is a view for explaining the arrangement of the light shield, FIG. 4 is a graph showing the relationship between the light receiving output and the visibility, FIG. 5 is a graph showing the relationship between the light receiving output and the angle between the light emitting and receiving axis, and the sixth. The figure shows the positional relationship between the light projector and the light receiver by comparing the conventional example with the present invention. (Main symbols) P …… Sender, D …… Receiver B …… Shadow, S …… Stand A …… Arm, SA …… Intersection measurement space θ …… Inclusion angle of the sender and receiver optical axes

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-51647 (JP, A) JP-A-62-9256 (JP, A) Actual Kaihei 1-66058 (JP, U) JP-B-49- 48794 (JP, B1)

Claims (2)

[Claims] 1. A light projector for projecting a light beam having a visible wavelength or a wavelength close to a visible light and a light receiver having a sensitivity sufficient for receiving the light beam and having a limited field of view. It is arranged so that it intersects at θ, and the visibility is obtained by measuring the light quantity of scattered light from floating particles existing in the spatial region where the beam light projection range of the projector and the light receiving visual field of the light receiver overlap. In the visibility measurement method, the intersection angle θ between the projection axis of the projector and the reception axis of the receiver is within the range of 90 degrees or more and the angle at which the beam light does not directly enter the receiver, A visibility measuring method in which the conversion scale for obtaining visibility from the output of the light receiver is set to a specific angle θ _C that provides the same scale for different visibility disturbance phenomena. 2. A light-shielding member is arranged on either one or both of the axis of the light-projecting axis and the axis of the light-receiving axis farther from the overlapping space area between the projection range of the light beam and the light-receiving field of view. Visibility measurement method described.