Process for determining the surface state of highways in particu

Details Process for determining the surface state of highways in particu Process for determining the surface state of highways in particu

1997-10-22

1999-10-05

Hannaher, Constantine

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

2503418, G01N 2155

Patent

active

059628537

DESCRIPTION:

BRIEF SUMMARY
The device relates to a method of ascertaining the surface condition, particularly of traffic routes, according to the preamble to the main claim, and to a device for carrying out the method.
There is known from DE 40 08 280 a method for non-contacting determination of the road surface condition as regards dryness, wetness or icing, in which the surface to be tested is illuminated by a broad-band light source, and the reflected light is simultaneously selectively measured in two wavelength ranges. The measuring wavelengths in this case lie in a wavelength range in which the reflective behaviour reveals a spectral dependence on the surface condition, i.e. in the wavelength range from 2700 nm to 3200 nm, there being formed from the signals at two wavelengths of this wavelength range a quotient which characterises the surface condition. The respectively determined signal quotient is associated with one of the conditions dry, wet or iced.
The known method has the disadvantage that only the direct surface is considered and not the condition directly beneath the surface. Consequently, over- or under-freezing wetness cannot be recognised, as at the wavelengths of 2700 nm to 3200 nm the depth of penetration of the electromagnetic radiation into the surface is extremely low. In particular, the publication also states that an indication of the surface condition is to be obtained independently of the layer thickness.
The object underlying the invention is to provide a method of ascertaining the surface condition particularly of traffic routes as regards dryness, wetness or icing and to provide a corresponding device, which is cost-effective to manufacture and enables rapid and precise determination of the surface condition even in deeper layers of the surface.
This object is achieved according to the invention by the characterising features of the main claim in conjunction with the features of the preamble. Advantageous further developments and designs of this solution arise from the sub-claims for the method and also for the device necessary for carrying out the method.
By means of the present method according to the invention it is for the first time possible to recognise practically instantaneously ice and frost formation on solid surfaces such as road coverings, by means of measurement by spectroscopic analysis, even taking into account the layer thickness of the surface, this being in dependence on the respective degree of crystallisation; the liquid need not exclusively be water, but may also be another protic liquid or solution capable of solidification, i.e. for example a saline solution with lowered freezing point. The degree of crystallisation of the water or of the liquid can be determined from the various absorption bands of at least two spectral sections, spectral ranges being selected in which the difference in the reflection spectrum between liquid and solid aggregate condition becomes particularly clear and in which the depth of penetration is sufficiently great, i.e. of the order of magnitude of the water or ice layers normally present on traffic routes. The influence of the background, caused by the depth of penetration required according to the invention, for example of the roadway covering and a scattering of the material, e.g. of the ice of the surface layer, is determined by measurement of the reflected radiation in two further wavelength ranges, which are influenced to a very small degree by an absorption of the molecules of the protic liquid or solution, independently of the degree of crystallisation. This influence is then compensated for in evaluation of the measurement.
It is advantageous to undertake the spectroscopic measurements both in front of and behind a wheel contact surface of a vehicle, and then to set the evaluations in relation to one another, so that further information, for example between slush and ice layers covered with a film of water, can be undertaken.
By means of the measures indicated in the sub-claims, advantageous further developments and improvements are possible.
A

REFERENCES:
patent: 4274091 (1981-06-01), Decker
patent: 4840706 (1989-06-01), Campbell
patent: 5180122 (1993-01-01), Christian et al.
patent: 5218206 (1993-06-01), Schmitt et al.

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