DE102004001046A1 - Detection and quantification of snow and ice on transports surfaces, whereby different wavelength semiconductor light sources are used sequentially to illuminate the surface and the reflected light is evaluated - Google Patents

Abstract

Method for detecting and quantifying water, snow, slush, ice and frost on road and rail surfaces in which semiconductor radiation sources of different transmission wavelengths are used sequentially with only one being switched on at any time. Their light is directed onto the road or rail surface and the reflected light collected and used to produce a photo-current which is amplified and recorded in an evaluation unit in a manner correlated with the switching on and off of the light sources. An independent claim is made for a device for detecting and quantifying water, snow, slush, ice and frost on road and rail surfaces.

Description

The The invention is directed to a method for fast, non-contact Display of water, mud, snow, frost and ice on roads and Rails or similar Surfaces, the infrared light reflected by characteristic spectrally resolved changes safe and reliable is understood.

Problem Description and state of the art

The simplest but also most unreliable kind the ice warning in traffic consists in the establishment of appropriate traffic warning signs the relevant known warning symbols at particularly vulnerable Stretch. These, however, as the general experience teaches, not always observed, as the danger is not always given. Better Here are already more modern traffic signs, which are controlled by a current temperature measurement of the road surface concerned or precipitation amount measurement, only in case of current ice danger or heavy rain the warning display activate. However, this is also unreliable and seduces the driver to disregard, because it is either on dry roads to none Ice formation can occur or because of salt and other impurities triggered Freezing point of the water even lower temperatures makes it necessary to solidify.

Of the Prior art Ice formation is still describable with the attempt over one briefly over the road surface sliding, the thermometer attached to the car to detect the outside temperature. This outside temperature gauge works however with respect Also similar to an ice alert unreliable. Once it gets through the radiant heat of the engine and / or the exhaust system affected or it feels not the temperature in the vicinity the road surface. most testers Disadvantage of this outdoor thermometer But it's your lazy one Display and non-detection of bridge sections at the Road surface quickly may occupy a different temperature than the air temperature over fixed streets with greater heat capacity. Also leads the Interpretation of the measured outdoor temperature with respect to ice formation, which the driver has to meet alone, to great uncertainties. In the Usually knows the Average motorists nothing of the physicochemical processes leading to a freezing point depression through road salt and other substances. Also depends the latter strongly from the concentrations of these water constituents which are unknown. In apparently dry road, will also be with a built-in outdoor thermometer the ice danger underestimated. Tire formations on certain sections of the route remain so often unrecognized.

Out these reasons is a direct non-contact and rapid measurement of water, mud, ice or frost layers desirable on the surface.

An early technical approach to this ( DE 2912645 , Spinner) proposes the detection of wavelength-specific microwave absorption. As a result, however, only the presence of liquid water can be proved beyond doubt since the dielectric constant of ice is too similar to that of dry asphalt. To remedy this deficiency, various authors ( DE 4040846 Schmitt; DE 19608535 , Kippenberg et al .; DE 19932094 ) proposed to additionally use a wavelength interval of the near infrared light in order to be able to detect the presence of frozen water. This method is sensitive to vehicle movement and can not quantify the detected ice / water. Similar restrictions apply to the idea of connecting a broadband IR channel with a brightness determination in the visible spectral range and an air temperature measurement ( DE 3023444 , Fukamizu et al.)

The spectral scattering power of the surface to be measured at several different wavelengths in the infrared spectral region to detect and evaluate accordingly, is the first time in the patent application of Mr. Decker ( DE 2712199 ) proposed in 1977: The measuring light penetrates the ice / water layer to be measured, is diffused at the road surface, penetrates the layer again and is spectrally selectively detected. From the strength of the absorption is closed to the layer thickness and from their spectral position on the degree of freezing.

• 1. In DE 4205629 (Stork et al.wird eine spektrometrische Anordnung beschrieben, mit deren Hilfe das spektrale Reflektionsvermögen einer Fahrbahnoberfläche im mittleren Infrarot beschrieben wird. Dort wird die Fundamentale der H₂O-Streckschwingung angeregt, die sehr übergangsstark ist, wodurch das Messlicht in der Schicht bereits nach wenigen Mikrometern vollständig absorbiert wird. Hierdurch ist eine Schichtdickenmessung und somit eine Warnung vor Aquaplaninggefahr unmöglich.
• 2. In der Schrift DE 4133359 (Holzwarth et al.) werden die Ergebnisse eines Forschungsverbundes der Automobilindustrie dargelegt: Eine breitbandige Lichtquelle bestrahlt die Fahrbahn und das zurückgestreute Licht wird nach drei Wellenlängenbereichen selektiert nachgewiesen und aus den unterschiedlichen Absorptionen die Dicke einer eventuell auf der Fahrbahn befindlichen Wasserschicht bestimmt. In diesem Ansatz wird schon der Gedanke benutzt, zwei unterschiedlich intensive Resonanzen (1. die zweite Harmonische der Streckschwingung des Wassermoleküls bei ca. 1450 nm und 2. die Kombinationsschwingung bei ca. 1190 nm dieser Oberwelle mit einer Grundbiegeschwingung) zu benutzen. Selbst im unempfindlicheren der hier benutzten Spektralbereiche ist die Eindringtiefe des Lichts noch immer zu gering, um Glatteis unter Wasserpfützen zu detektieren. Weitere Nachteile dieses Ansatzes waren die Bewegungsempfindlichkeit des Aufbaus, sowie die Unmöglichkeit, die thermische Drift der parallel benutzten Verstärkerkanäle langfristig zu beherrschen.
• 3. In der Schrift WO 96/26430 (Huth-Fehre et al.) wird erstmalig die 3. Harmonische der Streckschwingung bei ca. 980 nm Wellenlänge benutzt, mit deren Hilfe man auf Grund der viele Zentimeter betragenden Eindringtiefe auch Unterfrierungen in Pfützen feststellen kann. Als weiterer Vorteil kommt hinzu, dass diese Resonanz komplett im durch preiswerte Siliziumdetektoren messbaren Wellenlängenbereich unter 1050 nm liegt. Der in dieser Schrift vorgestellte Ansatz hat allerdings zwei andere Probleme: 1. Die parallel benutzten Verstärkerkanäle driften zu stark und 2. Der Einfluß des Sonnenlichts, das alle Wasserabsorbtionen der Atmosphäre "mitbringt", wird dort nicht kompensiert.
• 4. Diese beiden Nachteile werden in der Schrift DE 19736138 (Griesinger), die eine Parallelentwicklung zu 3. darstellt, teilweise umgangen, da hier anstatt diskreter Filter und Einzelverstärker ein Gitterspektrometer mit integriertem Zeilendetektor zum Einsatz kommt. Durch die frühe Serialisierung des Signalwegs werden die Driftprobleme beherrschbar, aber der optische Durchsatz eines Gitterspektrometers ist prinzipiell kleiner als der einer Filtereinheit. Dies hat zur Folge, dass mit dieser Technologie dünne Eis- und Wasserschichten bei kurzen Meßzeiten nicht genügend genau erfasst werden können. Zur Kompensation der Sonnenlichteinflüße wird ein Softwarealgorithmus vorgeschlagen, der allerdings nur bei einer genormten Wetterlage funktioniert.
• 5. Zur Verbesserung der Systeme in 3. und 4. wird in der Schrift DE 19747017 (Diebold et al.) die Vennrendung einer Xenonblitzlampe als Lichtquelle vorgeschlagen. Durch die hierdurch mögliche sehr kurzfristige Beleuchtung ist eine gute Diskriminierung gegen Umgebungslicht erreichbar, aber Blitzlampen haben im Wellenlängengebiet zwischen 800 und 1100 nm eine sehr schlechte Effizienz, was die Rauschprobleme an dünnen Schichten verstärkt.

However, this basic idea will not be pursued for more than ten years until it is taken up by five different groups in the 1990s:

• 1. In DE 4205629 (Stork et al., Describe a spectrometric arrangement describing the spectral reflectance of a road surface in the mid-infrared, where the fundamental of the H ₂ O stretching vibration is excited, which is very transient, and the measurement light in the layer is already retarded is completely absorbed by a few micrometers, which makes it impossible to measure the thickness of the layer and thus warn against aquaplaning.
• 2. In Scripture DE 4133359 (Holzwarth et al.) The results of a research network of the automotive industry are presented: A broadband light source irradiates the road and the backscattered light is selected after three wavelength ranges detected and determined from the different absorptions, the thickness of a possibly located on the road surface water layer. In this approach, the idea is already used to use two different intense resonances (1. the second harmonic of the stretching of the water molecule at about 1450 nm and 2. the combination oscillation at about 1190 nm of this harmonic with a fundamental bending vibration). Even in the less sensitive of the spectral ranges used here, the penetration depth of the light is still too low to detect black ice under puddles of water. Other disadvantages of this approach were the motion sensitivity of the structure, as well as the impossibility of long-term control of the thermal drift of the amplifier channels used in parallel.
• 3. In WO 96/26430 (Huth-Fehre et al.), For the first time, the third harmonic of the stretching vibration at a wavelength of approximately 980 nm is used, with the help of which it is possible to determine even underframes in puddles due to the many centimeters of penetration , Another advantage is that this resonance is completely in the measurable by inexpensive silicon detectors wavelength range below 1050 nm. The approach presented in this document, however, has two other problems: 1. The parallel used amplifier channels drift too strong and 2. The influence of sunlight, which "brings" all the water absorbances of the atmosphere, is not compensated there.
• 4. These two disadvantages are in the Scriptures DE 19736138 (Griesinger), which represents a parallel development to 3, partially bypassed, because here, instead of discrete filters and single amplifier, a grating spectrometer with integrated line detector is used. The early serialization of the signal path makes the drift problems manageable, but the optical throughput of a grating spectrometer is in principle smaller than that of a filter unit. As a result, with this technology, thin ice and water layers can not be detected with sufficient accuracy for short measuring times. To compensate for the effects of sunlight, a software algorithm is proposed, which works only in a standardized weather situation.
• 5. To improve the systems in 3rd and 4th will be in Scripture DE 19747017 (Diebold et al.) Proposed the use of a xenon flash lamp as a light source. The resulting very short-term illumination achieves good ambient light discrimination, but flash lamps have very poor efficiencies in the 800- to 1100-nm wavelength range, which enhances the noise problems on thin films.

Task of the here described invention

is to represent a measurement process, with the water, mud, snow and ice layers on road surfaces of thicknesses between 50 microns and 50 millimeters with high accuracy within a few milliseconds measured without contact can be without the measurement result from the spectral nature of the background or extraneous light affected becomes.

The inventive system

• 1. ähnlich wie in der Anmeldung DE 10315676.3 (Huth-Fehre) beschrieben, Halbleiterstrahlungsquellen unterschiedlicher Emissionswellenlängen – vorzugsweise preiswerte Leuchtdioden – so der Reihe nach ein- und wieder ausgeschaltet werden, dass jeweils maximal eine zur Zeit eingeschaltet ist,
• 2. deren Licht auf die zu vermessende Oberfläche gelenkt wird und das zurückgestreute Licht außerhalb des Glanzreflexes eingesammelt und Empfangselement – vorzugsweise eine Photodiode – geleitet wird.
• 3. Der Photostrom verstärkt und von einer Auswerteeinheit – vorzugsweise einem Mikrocontroler – mit dem Ein- und Ausschalten der Quellen korreliert registriert wird.
• 4. Mindestens fünf verschiedene Resonanzen/Wellenlängenbereiche benutzt werden: a) Die zweite Harmonische der Streckschwingung in Eis bei ca. 1520 nm, b) die zweite Harmonische der Streckschwingung in flüssigem Wasser bei ca. 1450 nm, c) ein Referenzpunkt für a) und b) bei ca. 1100 nm, d) die dritte Harmonische der Streckschwingung in flüssigem Wasser bei ca. 980 nm, e) ein Referenzpunkt für d) bei ca. 890 nm.
• 5. Die Quellen so hochfrequent umgeschaltet werden, dass ein "komplettes Spektrum" aller Wellenlängenbereiche in weniger Zeit aufgenommen wird, als die mittlere Schwankungsperiode der Reflektivität der Oberfläche beträgt. Dies ist bei Meßraten von mehreren Kiloherz sichergestellt.
• 6. Ein Teil des Meßlichts direkt aus den Quellen einem separaten Empfänger zugeleitet wird, um als "Referenzspektrum" langfristige Veränderungen der Quellintensitäten kompensieren zu können.
• 7. Entweder nach jedem Durchlauf der verschiedenen Quellen (einem "kompletten Spektrum") oder nach jedem Einschalten einer Quelle eine Pause gemacht wird, in der keine Quelle leuchtet und somit Fehlerströme des Empfängers und eventuell vorhandenes Fremdlicht erfasst und abgezogen werden können.

Essentially different from the above-mentioned prior art ( DE0019927015A1 ) that:

• 1. similar to the application DE 10315676.3 (Huth-Fehre) described, semiconductor radiation sources of different emission wavelengths - preferably inexpensive LEDs - so turn on and off again in such a way that at most one is currently turned on,
• 2. whose light is directed to the surface to be measured and the backscattered light collected outside the gloss reflection and receiving element - preferably a photodiode - is passed.
• 3. The photocurrent is amplified and registered by an evaluation unit - preferably a microcontroller - correlated with the switching on and off of the sources.
• 4. At least five different resonances / wavelength ranges are used: a) the second harmonic of the stretching vibration in ice at about 1520 nm, b) the second harmonic of the stretching vibration in liquid water at about 1450 nm, c) a reference point for a) and b) at approx. 1100 nm, d) the third harmonic of the stretching vibration in liquid water at approx. 980 nm, e) a reference point for d) at approx. 890 nm.
• 5. The sources are switched so high frequency that a "complete spectrum" of all wavelength ranges is recorded in less time than the mean fluctuation period of the reflectivity of the surface is. This is ensured at measurement rates of several kilohertz.
• 6. A part of the measuring light is fed directly from the sources to a separate receiver in order to be able to compensate as a "reference spectrum" long-term changes in the source intensities.
• 7. Either after each run of the various sources (a "complete spectrum") or after each source is turned on Pause is made in which no source lights up and thus fault currents of the receiver and any existing extraneous light can be detected and deducted.

A preferred embodiment of this inventive concept is in 1 is shown schematically and will be explained in the following:
An electronic control and evaluation unit 1 , preferably a microcontroller or Pc, switches by means of an output unit 2 and a driver electronics 3 light emitting semiconductors (light emitting diodes or lasers) 4 so in turn on and off, that only one emitter is currently on. The different LEDs emit at different wavelengths outside and within the water absorption bands. Preferably, the above wavelengths are used in the second and third harmonic ranges of the OH stretch between 800 and 1500 nm. The light of the at least five emitters is produced by means of imaging optics 5 containing at least one lens onto a measuring spot on the surface to be monitored 6 bundled. The backscattered from the surface measuring light is from a receiving coupling optics 7 that contains at least one lens captured and sent directly to a photoreceiver 9 , preferably a photodiode passed. Its photocurrent is through an amplifier 10 converted into a voltage by an analog / digital walker 11 the evaluation unit 1 brought to the knowledge. Thus, the reflectance values of the surface for the different wavelengths can be sequentially determined in rapid succession. If one now inserts between the turn-on periods of the emitter pauses, then in these pauses the intensity of all receiver reactive currents as well as those of the possibly present ambient (mainly solar light) can be measured. If the mean value of the measured values of the two periods comprising the period is subtracted from the measured value of a measurement period with the emitter switched on, the influence of these disturbance variables on the measurement results is eliminated. When all the emitters have been switched on and the respective signals of the receiver 9 are stored in the memory of the evaluation unit 1 a "mini-Rohspektrum" available. Since only a little less than a millisecond is required to record such a mini-spectrum, several such raw spectra can be summed or averaged for noise reduction without the overall measurement rate becoming too low.

One Part of the measuring light is a reference directly from the semiconductor radiation sources a fed to separate identically built receiver and each of the road surface recorded raw spectrum is divided by this reference spectrum, whereby the reflectivity spectra thus obtained only spectral information the surface, but no longer contain the sources and the detector.

The averaged reflectivity spectra can then be determined by the evaluation unit 1 converted into extinction values by logarithmization. If one then subtracts the value determined at 890 nm from that determined at 980 nm and that measured at 1100 nm from the two at 1450 nm and 1520 nm, one obtains three background-compensated substance-dependent extinction values which are directly proportional to the layer thicknesses present 980 can quantify liquid water in layer thicknesses between 0.5 and 50 mm, which is useful for warning against aquaplaning danger, at 1450 nm liquid water in layer thicknesses between 10 and 1000 microns, whose knowledge is important for the assessment of expected coefficients of friction Since these are already measurably reduced by water films from 50 microns thickness, and at 1520 nm even thinnest slices of ice are displayed from 20 microns thickness.

This result can now be determined at regular intervals by the evaluation unit 1 be transmitted by data transfer to the control system of the vehicle, or in stationary use, for example, to a traffic control system.

Advantageous further developments:

• 1. Be the emitter 4 not only switched alternately, but additionally clocked at higher frequency, and in the receiver amplifier 10 preferably amplifies this clock frequency, the signal / noise performance of the entire system improves and the insensitivity to sunlight is further improved.
• 2. Will be the sixth wavelength channel the third harmonic of the stretching vibration in ice at about 1020 nm can be used, both ice layer thicknesses above a Quantify millimeters better than by comparison with the extinction at 980 nm the degree of freezing and the amount of Slush closer determine.
• 3. The molar absorptions of the 3rd harmonic are so small that at thicknesses of less than one millimeter the extinction values are still strongly distorted by the wavelength dependence of the light scattering at the solid measuring surface. Therefore, it is advisable to use not only a reference wavelength (890 nm) for background subtraction, but the values measured at 1100 nm as the second interpolation point of an underground line, such as in the script US 5,962,853 recommended to use.
• 4. If one uses superluminiszente instead of simple light diodes, the whole Vorrich wins a) because the spectral half-widths of the emitted beams become narrower than the resonances to be measured, redundant overlap is reduced; b) the incorporation of stimulated emission can improve the electro-optic efficiency, resulting in higher overall power ratings and c ) the light leaves the diode in a smaller solid angle, so that it can be passed lossless on the measuring surface.
• 5. By the use of semiconductor lasers can be increase the aforementioned benefits; but they have to with higher component prices and a higher one Own noise can be bought.
• 6. Will the illuminating rays be due to vehicle movements not bundled on perfectly the same spot, so they can be right next to each other lying, differently reflecting parts of the surface, what strong signal distortions with you. To minimize this effect, it is advisable to use all semiconductor radiation sources already in their form as bare wafer pieces, the so-called "chips", spatially sealed side by side in the same housing to mount and shine through a common coupling optics on the measuring surface allow.
• 7. Another way the aforementioned disturbing effect the spatial inhomogeneity Reducing the lighting is to connect each source to one to couple separate short optical fiber, these fibers to their free ends to a fiber bundle to summarize and the light emerging there by a common coupling optics on the measuring surface to bundle.
• 8. The effectiveness of the measures in 6. and 7. can be further increased by the coupling optics a mixing element, eg a bundle of thin optical fibers as in US 4150287 described, or is preceded by a common thicker glass fiber or a diffuser.
• 9. The beam homogenization described in 8. can also be used, as in DE 4220705 described by the use of segmented lenses as part of the coupling optics.

Claims (17)

Method for detecting and quantifying water, snow, slush, ice and hoarfrost on traffic route surfaces , characterized in that semiconductor radiation sources of different emission wavelengths are switched on and off in turn so that in each case a maximum of one is switched on at the time whose light is on surveying surface is directed and the backscattered light is collected outside the glossy reflection and directed to a receiving element whose photocurrent is amplified and registered by an evaluation unit with the switching on and off of the sources is registered. Method according to claim 1, characterized in that that at least five different resonances / wavelength ranges to be used: a) The second harmonic of the stretching vibration in ice at about 1520 nm, b) the second harmonic of the stretching vibration in liquid Water at about 1450 nm, c) a reference point for a) and b) at about 1100 nm, d) the third harmonic of the stretching vibration in liquid Water at about 980 nm, e) a reference point for d) at about 890 nm. Method according to claim 1, characterized that the semiconductor radiation sources switched so high frequency be that a "complete Spectrum "of all Wavelength ranges recorded in less time than the mean fluctuation period the reflectivity the surface is. Method according to claim 1, characterized in that that either after each run of different sources (a "complete spectrum") or after each Turning on a source is taking a break, in which no source lights up and thus fault currents Recipient and any existing extraneous light detected and of all the photo-currents in the "bright intervals" in which a semiconductor source is switched on, can be deducted. Method according to claim 1, characterized that part of the measuring light as a reference directly from the semiconductor radiation sources a separate receiver is fed and each recorded by the road surface spectrum this reference spectrum is shared. Method according to claim 1, characterized in that that the semiconductor radiation sources are simple light-emitting diodes. Method according to claim 1, characterized that the semiconductor radiation sources superluminescent LEDs are. Method according to claim 1, characterized in that the semiconductor radiation sources are edge-emitting semiconductor lasers are. Method according to claim 1, characterized in that in that the semiconductor radiation sources are surface-emitting semiconductor lasers are. A method according to claim 1, characterized ge indicates that the semiconductor radiation sources are not only switched alternately, but additionally clocked at high frequency and this clock frequency is preferably amplified in the receiver amplifier. Method according to claim 1, characterized in that that as the sixth wavelength channel the third harmonic of the stretching vibration in ice at about 1020 nm is used. Method according to claim 1, characterized in that that to the underground deduction for the harmonics of the 3rd harmonic not just a reference wavelength (890 nm), but the values measured at approx. 1100 nm as a second base is used to calculate an underground line. Method according to claim 1, characterized in that that all semiconductor sources already in their form as naked Waferstückchen, the so-called "chips", spatially dense side by side in the same housing be mounted and their light through a common coupling optics is bundled on the measuring surface. Method according to claim 1, characterized that each semiconductor radiation source to a separate short optical fiber is coupled, these fibers together at their free ends to form a fiber bundle be caught and the light emerging there by a common Coupling optics on the measuring surface bundled becomes. Method according to claim 1, characterized that the coupling optics a mixing member, e.g. as a separate bundle of thin optical fibers, or in the form of a common thicker glass fiber or a diffuser is connected upstream. Method according to claim 1, characterized in that that the mixing member described in claim 15 through the use is formed by segment lenses as part of the coupling optics. Device for detection and quantification of water, snow, mud, ice and hoarfrost on traffic route surfaces, by characterized in that semiconductor radiation sources are different Emission wavelengths turn on and off again in turn, their light on the surface to be measured is steered and the backscattered Light outside the Glanzreflexes collected and directed to a receiving element whose photocurrent is amplified and from an evaluation unit with the switching on and off of the sources is registered correlated.