WO2014122616A1 - Système de capteurs permettant d'estimer une portée visuelle sur une piste - Google Patents

Système de capteurs permettant d'estimer une portée visuelle sur une piste Download PDF

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Publication number
WO2014122616A1
WO2014122616A1 PCT/IB2014/058859 IB2014058859W WO2014122616A1 WO 2014122616 A1 WO2014122616 A1 WO 2014122616A1 IB 2014058859 W IB2014058859 W IB 2014058859W WO 2014122616 A1 WO2014122616 A1 WO 2014122616A1
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Prior art keywords
light
runway
rvr
scattered
fittings
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PCT/IB2014/058859
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English (en)
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Lawrence A Hisscott
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Lawrence A Hisscott
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Publication of WO2014122616A1 publication Critical patent/WO2014122616A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
    • G01N21/538—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke for determining atmospheric attenuation and visibility
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64F—GROUND OR AIRCRAFT-CARRIER-DECK INSTALLATIONS SPECIALLY ADAPTED FOR USE IN CONNECTION WITH AIRCRAFT; DESIGNING, MANUFACTURING, ASSEMBLING, CLEANING, MAINTAINING OR REPAIRING AIRCRAFT, NOT OTHERWISE PROVIDED FOR; HANDLING, TRANSPORTING, TESTING OR INSPECTING AIRCRAFT COMPONENTS, NOT OTHERWISE PROVIDED FOR
    • B64F1/00—Ground or aircraft-carrier-deck installations
    • B64F1/18—Visual or acoustic landing aids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64F—GROUND OR AIRCRAFT-CARRIER-DECK INSTALLATIONS SPECIALLY ADAPTED FOR USE IN CONNECTION WITH AIRCRAFT; DESIGNING, MANUFACTURING, ASSEMBLING, CLEANING, MAINTAINING OR REPAIRING AIRCRAFT, NOT OTHERWISE PROVIDED FOR; HANDLING, TRANSPORTING, TESTING OR INSPECTING AIRCRAFT COMPONENTS, NOT OTHERWISE PROVIDED FOR
    • B64F1/00—Ground or aircraft-carrier-deck installations
    • B64F1/18—Visual or acoustic landing aids
    • B64F1/20—Arrangement of optical beacons
    • B64F1/205—Arrangement of optical beacons arranged underground, e.g. underground runway lighting units

Definitions

  • This invention relates to a method for assessing visibility along a runway by measuring light scattered from the beams emitted by runway light fittings.
  • Runway Visual Range is an assessment of the visual guidance available to pilots of aircraft using a runway for take-off or on the approach to landing and during deceleration after landing.
  • RVR is a very important weather parameter for airport operations since it can preclude aircraft from operating in adverse conditions.
  • critical values of RVR are used to define operational limits e.g. for CAT I, CAT II and CAT III (a,b,c) categories of
  • RVR The range over which the pilot of an aircraft on the centre line of a runway can see the runway surface markings or the lights delineating the runway or identifying its centre line.
  • the Eighth Air Navigation Conference (Montreal 1974) modified this definition to: 'Since, in practice, RVR cannot be measured directly on the runway a RVR observation should be the best possible assessment s the range over which the pilot of an aircraft on the on the centre line of a runway can see the runway surface markings or the lights delineating the runway or identifying its centre line '
  • RVR observations may be made by human observers but the International Civil Aviation Organisation (ICAO) Document 9328 'Manual of Runway Visual Range Observing and Reporting Practices' recommends the use of instruments to assess RVR (Instrumented RVR, or IRVR) for CAT I operations and IRVR assessments are compulsory for CAT II and CAT III operations.
  • IAO International Civil Aviation Organization
  • the instruments currently used to assess IRVR may be 'transmissometers' or 'forward scatter meters'.
  • Transmissometers measure the optical transmittance of the atmosphere over a defined baseline distance (normally around 15 to 20 metres).
  • Forward scatter meters generate a beam of light and measure the amount of light scattered from that beam by aerosol particles, water droplets, snowflakes or hailstones.
  • Forward scatter meters measure light scattered through an angle of less than 90 degrees (usually in a defined sample volume of a few litres).
  • sensors which measure light scattered by an angle greater than 90 degrees (and often close to 180 degrees) and known as 'backward scatter meters' may be used to assess visibility.
  • this invention is a method to employ the principle of scatter meters for sensors to measure light scattered from the beams produced by the runway light fittings. This would enable assessment of IRVR on the runway and along its length.
  • the sensors monitor scattering of the actual light output from runway fittings (forward and/or backward scattered light), automatically compensating for variation in output due to ageing, contamination, electrical supply variation, etc.
  • the use of a larger number of sensors statistically reduces the error associated with the assessment and provides more information about spatial variation of visibility over a much smaller scale than is possible using current methods. It is also possible to obtain information about background light levels in the actual vicinity of the runway lights and/or markings which provide guidance to pilots, which enhances the calculation of RVR.
  • the main advantage of this method is that it allows assessment of IRVR actually on the runway and along its length.
  • Document 9328 (ICAO, 2005) describes many factors which can adversely affect the assessment of IRVR, such as contamination and ageing of lights which reduce their actual output, differences between actual and assumed light intensity, errors in measuring background luminance, differences in background luminance on the runway from where it is measured, etc.
  • the assessment also depends on the intensity selected for variable intensity runway lighting systems (often 1% to 100% in defined increments, selectable by Air Traffic Control personnel) and many conventional IRVR systems require the actual current supplied to the lighting electrical circuit(s) to be monitored directly (rather than assuming the selected setting is actually being applied to the lights), adding complexity to the lighting system.
  • sensors measure light scattered from the beams emitted by the actual runway lights and the background luminance level in their vicinity, so factors such as those mentioned above are automatically included in the assessment of RVR.
  • accuracy of instrument types currently employed is generally considered to decrease from transmissometers to forward-scatter-meters to backward-scatter-meters
  • the use of an array of multiple sensors in this (scattering) method can be used to statistically reduce errors in the overall assessment of IRVR.
  • the calculation algorithm can use forward and/or backward scattering measurements and can also incorporate information from a conventional sensor 'present weather' to optimise the assessment. Also, knowledge of the variation in visibility with distance along the runway is much improved, which is important in the case of spatially inhomogeneous fog and fog patches.
  • Figure 1 When a beam of light passes through the atmosphere some of the light is scattered out of the beam by atmospheric aerosol particles such as dust or water droplets.
  • the graph shows the angular distribution of scattered light corresponding to a visibility of one kilometre, taken from Dietze, 1957. (The synoptic definition of 'fog' is visibility less than one kilometre.)
  • FIG. 2 A schematic diagram showing the principle of operation of a 'transmissometer', an instrument which measures the transmittance of a light beam over a path through the atmosphere.
  • 'T' is the light source, or transmitter
  • 'R' is the light receiver.
  • the distance between T and R, the baseline 'b', is usually around 15 to 20 metres (although sometimes a mirror is used in a 'folded-baseline' configuration, with T and R located in the same unit).
  • Figure 3 A schematic diagram showing the principle of operation of a 'forward scatter meter'.
  • 'T' is the light source and 'R' is the light receiver.
  • 'R' is the light receiver.
  • the distance between 'T' and 'R' is usually around one to two metres, with a scattering angle of around 30 to 50 degrees (the 'sample volume' of atmosphere is shown in black).
  • Figure 4 A schematic diagram showing the principle of operation of a 'backward-scatter meter'. Again 'T' is the light source and 'R' is the light receiver, with no direct optical path between them. Light scattered 'backwards' from the sample volume (shown in black) is collected by the receiver 'R'. The distance between 'T' and 'R' is usually small so that the scattering angle is close to 180 degrees (the distance T-R and scattering angle are exaggerated in the diagram for clarity).
  • transmissometers and scatter meters can be found in ICAO, 2005.
  • Figure 5 Isocandela contours for a runway centre line light (new light at maximum intensity setting) with 30 metre longitudinal spacing showing the position of pilot's eyes in the beam at various eye heights and distances, taken from ICAO, 2005.
  • Figure 6 Plan view of a typical runway light fitting, inset into the runway surface.
  • the diameter is usually around 200 to 400mm.
  • the apertures TV shown cross-hatched
  • the apertures TV contain an optical system (prism(s) and/or lens(es)) which emit a light beam along the runway direction with an angular distribution similar to that shown in figure 5.
  • the example shown provides single bi-directional beams although other configurations can produce one or more beams in one or both directions along the runway or taxiway.
  • Figure 7 A cross-section through the typical light fitting shown above in figure 6, along the line X-X in that figure.
  • the line X-X in this figure also shows the level of the runway with most of the light fitting body sub-surface.
  • TV again shows the optical system, in this case producing a beam of light directed towards the right of the page.
  • Figure 8 Shows a typical four-aperture inset runway light fitting modified so that the TVs are the usual light-emitting sources but the 'B's are light receiving sensors.
  • Figure 9 A schematic diagram illustrating how the 'forward scatter' principle can be applied to runway lights.
  • the light-beam source 'T' and the scattered-light receiver 'R' are both incorporated into adjacent lights (normally spaced 15 or 30 metres apart).
  • Figure 10 An illustration employing the 'forward scatter' principle of figure 9 extended to an array of runway lights. LI, L2, L3, etc are adjacent lights located along a runway.
  • Figure 11 A schematic diagram showing how the 'backward scatter' principle can be applied to runway lights. This uni-directional light is modified so that the aperture 'A' emits a light-beam along the runway (towards the right of the page) while the aperture 'B' contains a sensor to detect light scattered in a backward direction (the 'sample volume' is shaded black).
  • Figure 12 An illustration employing the 'backward scatter' principle of figure 11 extended to an array of runway lights (for this example the centre line lights are spaced at 15 metre intervals and the edge lights at 30 metres, with the size of the light fittings enlarged for clarity).
  • the brightness of runway lights can be controlled by 'pulse width modulation' of the electrical supply to the light emitter (for example, modulation of the voltage or current supplied to a light-emitting diode (LED), gas-discharge or incandescent lamp).
  • Figure 13 shows the light output as a function of time (both arbitrary units) for a high-intensity light setting (where the light is 'on' for most of the time), whereas figure 14 shows a low- intensity setting where the light is 'on' for a much shorter time than it is "off.
  • Figure 15 An illustration of the variation of scattered-light detector output with time (again arbitrary units) for runway light at high-intensity in poor visibility (e.g. fog).
  • the level 'G' corresponds to the scattered light intensity when the light is 'on' (for backward scatter light) or when the adjacent light is 'on' (for forward scattered light) and the level ⁇ ' corresponds to the 'background' light level when the appropriate light is 'off'.
  • Figure 16 Illustrates the detector output for high-intensity light setting when the visibility is much higher than in the case of figure 15. In this case, both the scattered-light peak intensity 'J' and the 'background' light level 'K' are much lower (since the amount of light scattered, both 'forwards' and 'backwards', is much lower in good visibility).
  • Figures 17 and 18 correspond to figures 15 and 16, respectively, for the case of low- intensity light setting in poor and good visibility (respectively).
  • Runway Visual Range is defined as the range over which a pilot can see runway lights or runway surface markings (ICAO, 2005). RVR is assessed by calculation based on
  • the intensity of a beam of light passing through the atmosphere reduces as the distance from the source increases, mainly due to scattering and absorption by aerosols. Scattering is the dominant process for fog, rain and snow (which are the most prevalent weather conditions causing reduced visibility), although absorption contributes in dust, haze and smoke.
  • Figure 1 shows the variation of scattered light intensity with angle from the original beam (in this example for a visibility of one kilometre; the synoptic definition of 'fog' is visibility less than one kilometre). It can be seen from the graph that a large proportion of the light is scattered forwards i.e. close to the original beam direction, the intensity of scattered light decreases to a minimum around 110-120 degrees from the beam then increases again towards 180 degrees. Light scattered through an angle less than 90 degrees is said to be 'forward scattered' whereas light scattered through more than 90 degrees is said to be 'backward scattered'.
  • Figure 2 illustrates the principle of operation of a 'transmissometer', an instrument which measures the transmittance of a light beam over a path through the atmosphere.
  • 'T' is the light source, or transmitter
  • 'R' is the light receiver.
  • the distance between T and R, the baseline is usually around 15 to 20 metres (although sometimes a mirror is used in a 'folded-baseline' configuration).
  • Measurement of the amount of light received at R compared with the intensity of the beam emitted from T enables calculation of 'meteorological optical range' (MOR) which is used in the calculation of RVR.
  • Transmissometers are relatively expensive to install and operate and require very stable bases for the light transmitter and light receiver units (or reflector unit) to preserve the optical alignment.
  • FIG 3 illustrates the principle of operation of a 'forward scatter meter'.
  • 'T' is the light source and 'R' is the light receiver.
  • 'R' is the light receiver.
  • the distance between 'T' and 'R' is usually around one to two metres, with a scattering angle of around 30 to 50 degrees (the 'sample volume' of atmosphere is shown in black).
  • the amount of scattered light received at R varies inversely with visibility and its measurement enables calculation of MOR.
  • Forward scatter meters are much less costly to install and maintain than transmissometers. They require a rigid, precision construction to preserve the optical alignment, although the whole instrument can be mounted on a single frangible pole.
  • FIG 4 illustrates the principle of operation of a 'backward -scatter meter'.
  • 'T' is the light source and 'R' is the light receiver, with no direct optical path between them.
  • Light scattered 'backwards' from the sample volume is collected by the receiver 'R'.
  • the distance between 'T' and 'R' is usually small so that the scattering angle is close to 180 degrees (the distance T-R and scattering angle are exaggerated in the diagram for clarity). Measurement of the amount of scattered light received at R enables calculation of MOR.
  • Backward scatter meters (BSMs) also require rigid construction and can be mounted on a single frangible pole. The cost associated with the installation and operation of BSMs is of the same order as for FSMs.
  • Transmissometers FSMs and BSMs all require a stable, well-defined source beam of light and a stable light receiver with well-defined optical acceptance geometry.
  • a background luminance sensor BLS is also required to quantify the background illumination level to enable calculation of RVR.
  • runway light fittings also provide a stable source of light with a precisely-defined beam pattern.
  • Such fittings are mounted in physically stable bases with precision alignment to preserve the optical geometry of the light beams (and hence the guidance path provided to pilots approaching or departing from the runway).
  • the light scattered from the beams provided by runway lights can, using the operating principles of FSMs and BSMs, be used to measure MOR and background luminance level.
  • the runway light fittings can provide physically stable bases for both the emitted light beams and the photo-sensitive receivers.
  • Figure 5 shows a diagram of isocandela contours for a runway centre line light (new light at maximum intensity setting) with 30 metre longitudinal spacing, also showing the position of a pilot's eyes in the beam at various eye heights and distances, taken from ICAO, 2005.
  • the light beam is concentrated in a 'narrow cone' subtending a fairly small solid-angle and the intensity decreases rapidly with increasing angle from the beam-centre (which slopes upwards away from the source at an angle around 3.5 degrees above the runway surface).
  • Similar diagrams are used to define the beam pattern of runway edge lights which have a precise 'toe-in' angle relative to the runway direction (the angle varies with width of the runway in order to provide the correct guidance).
  • FIG. 6 A plan view of a typical flush-fitting (or inset) runway light fitting is shown in figure 6 (diameter is usually around 200 to 400mm).
  • the apertures TV shown cross-hatched
  • the apertures TV contain an optical system (prism(s) and/or lens(es)) which emit a light beam along the runway direction with an angular distribution similar to that shown in figure 5.
  • the example shown provides single beams along the runway in both directions. Other configurations are available which produce one or more beams in one or both directions along the runway or taxiway.
  • Figure 7 shows a cross-section through the typical light fitting shown in figure 6, along the line X-X in that figure.
  • the line X-X in this figure also shows the level of the runway, the light fitting is inset into the runway surface with most of the body sub-surface and the top protruding around 12-25mm above the surface.
  • TV again shows the optical system, in this case producing a beam of light directed towards the right of the page.
  • fittings can be modified to include one or more photo-sensor receivers.
  • figure 8 shows a typical four- aperture inset runway light fitting modified so that the apertures marked TV are the usual light-emitting sources but the apertures marked 'B' contain light receiving sensors.
  • Figure 9 is a schematic diagram illustrating how the 'forward scatter' principle can be applied to runway lights.
  • the light-beam source 'T' and the scattered-light receiver 'R' are both incorporated into adjacent light fittings (normally spaced 15 or 30 metres apart).
  • This idea is developed in figure 10 which shows how the 'forward scatter' principle of figure 9 can be extended to an array of runway lights.
  • LI, L2, L3, etc are adjacent lights located along a runway (the lights can be either on the centreline or along the edge, or both can be used). Each light produces a well-defined beam (directed upwards at a small angle, towards the right).
  • Light scattered from the beams by aerosols is measured by photo-sensors located in adjacent fittings and the information can be used to assess RVR along the length of the runway.
  • Figure 11 shows a schematic diagram illustrating how the 'backward scatter' principle can be applied to runway lights.
  • This uni-directional light is modified so that the aperture 'A' emits a light-beam along the runway (towards the right of the page) while the aperture 'B' contains a sensor to detect light scattered in a backward direction (the 'sample volume' is shaded black).
  • This idea is extended in figure 12 which indicates how the 'backward scatter' principle of figure 11 can be extended to an array of runway lights (for this example the centre line lights are spaced at 15 metre intervals and the edge lights at 30 metres, with the size of the light fittings enlarged for clarity).
  • the photo-sensor apertures denoted 'B' in figures 8 and 11 can employ an optical system to define the required scattered-light acceptance geometry for either forward -scattered or backward-scattered light or both.
  • An electronic or mechanical 'solar shutter' can also be incorporated to protect sensors from direct sun.
  • the brightness of a runway light system can be varied in order to provide optimum visual guidance to pilots in various conditions of ambient light and visibility (see ICAO 2005 for further details).
  • the light setting in use is normally expressed as a percentage of the maximum output of the light units employed.
  • the brightness of runway lights is controlled by modulation of the electrical supply (voltage and/or current) supplied to the light source.
  • the example shown below and in the following figures is for LED light sources which are usually controlled by 'pulse width modulation' (PWM), although sinusoidal or thyristor waveforms could equally well be used e.g. for gas- discharge lamps, etc.
  • PWM pulse width modulation'
  • FIGS 13 and 14 show PWM-controlled LED light output for high and low intensity settings, respectively.
  • Figure 13 shows the light output as a function of time (both arbitrary units) for a high- intensity light setting (where the light is for most of the time), whereas figure 14 shows a low-intensity setting where the light is for a much shorter time than it is 'off'.
  • the frequency of on/off switching is high enough that the human eye is unaware of the 'flashing' (due to persistence of vision) but the total light energy received by the eye is integrated over time and perceived as relative brightness.
  • Figures 15 to 18 illustrate the scattered-light detector response for high and low intensity settings in both good and poor visibility.
  • the time axis in each diagram corresponds to the time axis of the light source in figures 13 and 14 (the detector response is virtually in phase with the PWM of the source) but the relative intensity axes are quite arbitrary (for illustration).
  • Figure 15 shows the variation of detector output with time for runway lights at high-intensity in poor visibility (e.g. fog).
  • the level 'G' corresponds to the scattered light intensity when the light is 'on' (for backward scatter light) or when the adjacent light is 'on' (for forward scattered light) and the level ⁇ ' corresponds to the 'background' light level when the appropriate light is 'off.
  • Figure 16 illustrates the detector output for high-intensity light setting when the visibility is much higher than in the case of figure 15.
  • both the scattered-light peak intensity 'J' and the 'background' light level 'K' are much lower (since the amount of light scattered, both 'forwards' and 'backwards', is much lower in good visibility).
  • Figures 17 and 18 correspond to figures 15 and 16, respectively, for the case of low- intensity light setting in poor and good visibility (respectively).
  • the detected levels of scattered light (L and N) and of background light (M and P) are higher in conditions of poor visibility and lower in good visibility.
  • the levels of peak scattered light detected can be used to estimate MOR whereas the levels of light detected during the 'light-off period (H, K, M and P) can be used to estimate the background luminance level. Both measurements can then be incorporated into the calculation of RVR.
  • the forward scatter and backward scatter geometries can be used independently or in combination.
  • the calculation algorithm can be further refined by incorporating information from one or more conventional 'present weather sensors' to allow for variation in the scattering profile of different aerosols e.g. mist, fog, rain, snow, dust, smoke, etc.
  • Such an array of lights with sensors would also enable continuous monitoring of individual light performance and/or failure.
  • the photo-sensors can be protected from direct sun by employing electronic or mechanical solar shutters.

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Abstract

Les pilotes manœuvrant vers ou à partir d'un aérodrome doivent avoir des informations de visibilité dans les environs. Par mauvais temps, ceci est complété par l'estimation de la portée visuelle de piste (PVP). La PVP est souvent estimée au moyen de capteurs de visibilité situés à proximité de la piste mais, pour des raisons de sécurités, à une certaine distance du bord. Le procédé de l'invention fait appel aux principes de la géométrie de diffusion de la lumière vers l'avant et/ou vers l'arrière en utilisant les feux de balisage de la piste comme sources de lumière, pour permettre une estimation réelle de la PVP sur la piste. Le grand nombre de capteurs permet également d'améliorer la connaissance de la variation spatiale et temporelle de la visibilité le long de la longueur de la piste. Le diagramme montre une partie d'un réseau de feux de balisage de piste L1, L2, L3, etc., chacun produisant des faisceaux bien définis (vers la droite). La lumière diffusée à partir des faisceaux par des aérosols est mesurée par des capteurs photosensibles situés sur des installations adjacentes. Les mesures peuvent être utilisées pour estimer la PVP le long de la longueur de la piste.
PCT/IB2014/058859 2013-02-10 2014-02-07 Système de capteurs permettant d'estimer une portée visuelle sur une piste WO2014122616A1 (fr)

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GBGB1302316.3 2013-02-10
GB201302316A GB2510617B (en) 2013-02-10 2013-02-10 Sensor System for Assessing Visual Range on a Runway

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DE102021201417A1 (de) 2020-12-02 2022-06-02 Volkswagen Aktiengesellschaft Fußauflage für ein Kraftfahrzeug

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB794472A (en) * 1955-10-17 1958-05-07 Cfcmug Improvements in or relating to the determination of oblique visibility
US3299769A (en) * 1963-03-08 1967-01-24 Donald J Byers Method and means for ascertaining visibility conditions
US3393321A (en) * 1964-07-18 1968-07-16 Frungel Frank Visual range measuring system including a plurality of spaced lamps
US3650627A (en) * 1968-09-13 1972-03-21 Thorn Bendix Ltd Measurement of visual range in fog
DE2359240B1 (de) * 1973-11-28 1975-03-20 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Einrichtung für die Messung der Sichtweite auf dem Gleitpfad von Flughafen
DE3316600A1 (de) * 1983-05-06 1984-11-15 Impulsphysik Gmbh, 2000 Hamburg Augensicheres schraegsichtmessgeraet
US6119055A (en) * 1998-01-23 2000-09-12 Mcdonnell Douglas Corporation Real time imaging system and method for use in aiding a landing operation of an aircraft in obscured weather conditions

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1559821A (en) * 1976-07-16 1980-01-30 Civil Aviat Authority Apparatus for monitoring runway visual range
ZA801538B (en) * 1979-03-19 1981-04-29 United Kingdom Government Method and apparatus for estimating slant visibility in fog

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB794472A (en) * 1955-10-17 1958-05-07 Cfcmug Improvements in or relating to the determination of oblique visibility
US3299769A (en) * 1963-03-08 1967-01-24 Donald J Byers Method and means for ascertaining visibility conditions
US3393321A (en) * 1964-07-18 1968-07-16 Frungel Frank Visual range measuring system including a plurality of spaced lamps
US3650627A (en) * 1968-09-13 1972-03-21 Thorn Bendix Ltd Measurement of visual range in fog
DE2359240B1 (de) * 1973-11-28 1975-03-20 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Einrichtung für die Messung der Sichtweite auf dem Gleitpfad von Flughafen
DE3316600A1 (de) * 1983-05-06 1984-11-15 Impulsphysik Gmbh, 2000 Hamburg Augensicheres schraegsichtmessgeraet
US6119055A (en) * 1998-01-23 2000-09-12 Mcdonnell Douglas Corporation Real time imaging system and method for use in aiding a landing operation of an aircraft in obscured weather conditions

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