US20020159060A1 - Device for determining the values of at least one parameter of particles, in particular water droplets - Google Patents
Device for determining the values of at least one parameter of particles, in particular water droplets Download PDFInfo
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- US20020159060A1 US20020159060A1 US09/979,886 US97988601A US2002159060A1 US 20020159060 A1 US20020159060 A1 US 20020159060A1 US 97988601 A US97988601 A US 97988601A US 2002159060 A1 US2002159060 A1 US 2002159060A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/02—Investigating particle size or size distribution
- G01N15/0205—Investigating particle size or size distribution by optical means, e.g. by light scattering, diffraction, holography or imaging
- G01N15/0227—Investigating particle size or size distribution by optical means, e.g. by light scattering, diffraction, holography or imaging using imaging, e.g. a projected image of suspension; using holography
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- the present invention relates to a device for determining the values of at least one parameter, especially the size, of particles such as water droplets.
- said device is applicable more particularly to the detection and to the characterization of icing conditions on aircraft, especially civil transport airplanes, by making it possible to measure the size and the number of water droplets present in particular in the clouds and the fogs through which an aircraft passes.
- the known devices used to this end, are generally intended to determine the particle size distribution of clouds, that is to say the size, the number and the shape of the water droplets present in these clouds, and they can be classified in two categories:
- integrators which sum the contributions from all the particles present in a measuring volume.
- Optical Array Probe implements, in a standard manner, the principle called linear array shadowgraphy.
- a particle passing through a collimated light beam produces a shadow directly related to its diameter on a linear array of detectors spaced apart at equal intervals.
- the light beam illuminates all the detectors.
- a loss of light due to scattering, refraction and absorption of the particle generates a signal at the output of the detectors.
- the number of detectors showing a variation in amplitude of more than a specific threshold (for example 50%) is summed in order that the size of the particle is given directly.
- this known device has a limited measurement range and is not able to measure particles accurately, if their diameter is less than 100 ⁇ m.
- a device which is known by the term “Cloud Particle Imager” generates two laser beams. The intersection of these two lasers beams defines a rectangular sampling area. Any particle which passes through this rectangular sampling area is properly focused and actuates illumination by an imaging laser, for the purpose of acquiring an image. Detectors are placed facing the laser beams: they make it possible to detect the passage of particles by measuring the decrease in intensity produced as these particles pass through. The diameter of the particles is measured from the image of the properly focused particle.
- this known device is bulky and has too large a volume to improve the operational difficulties stated above and linked to the devices currently used in in-flight testing.
- a measuring device is known by document FR-2 689 247, in particular comprising:
- a rod comprising a measuring region which is intended to accommodate the particles to be analyzed
- illumination means capable of illuminating said measuring region, using at least one laser beam
- image acquisition means capable of acquiring images of said measuring region illuminated by said illumination means
- processing means capable of determining the values of said parameter, from said images.
- the latter known device emits a pulsed light beam that is transported by optical fiber and which is focused onto the measuring region.
- the image is also transported by optical fiber up to a beam splitter which divides and orients the beam toward the image acquisition means comprising two “CCD”-type sensors.
- a first image is recorded along a particular sighting axis on one of the sensors.
- a second image is recorded along the same sighting axis on the other sensor.
- a dark/light doublet is obtained which stands out well against the uniform background, from which it is possible to deduce the size and the velocity of the imaged particles.
- This known device makes it possible to remove the majority of background defects. This is because the image acquisition means with a double sensor behave like a double shutter and only see the field for two very short periods of time.
- this known device has a small measuring volume. It is known that the measuring volume analyzed per second is equal to the measuring volume associated with each image, multiplied by the image rate of the image acquisition means.
- the various known devices comprise various drawbacks which are problematic for the aforementioned preferred application.
- the known devices are, in general, poorly adapted to the envisaged meteorological and operational constraints, in particular because of the following difficulties, namely a long and difficult installation in an aircraft, a very large bulk, difficult exploitation of the results, etc.
- the majority of these known devices have a range for measuring of the size of the droplets which is small, and especially are not able to detect and analyze, at the same time, the small droplets and the large supercooled droplets (water at a temperature less than 0° C.) which, as is known, promote the appearance of ice.
- the present invention relates to a device for determining the values of at least one parameter, especially the size, of particles, in particular of water droplets, which makes it possible to overcome the aforementioned drawbacks and which especially comprises an increased measuring volume.
- said device of the type comprising:
- a measuring element comprising a measuring region which is intended to accommodate the particles
- illumination means capable of illuminating said measuring region
- image acquisition means comprising at least one camera capable of acquiring at least one image of said measuring region illuminated by said illumination means
- processing means capable of determining the values of said parameter, from said image acquired by the camera, is noteworthy in that said illumination means are constituted so as to produce a point illumination source using a light beam, the light rays of which are focused on an objective optic of the image acquisition means.
- the contrast (on the image or images acquired) of the shadow of the particles located in the measuring region is increased.
- This increase in contrast leads to an improved observability of the particles at the expense of focus and therefore an increase in the depth of field, since the image remains observable for higher defocused values.
- This increase in depth of field itself leads to an increase in the measuring volume which, as indicated above, depends on the size of the sensor and on the depth of field.
- said illumination means comprise at least one optical assembly comprising:
- a light source preferably a laser source, capable of generating a light beam
- an optical fiber connected by a first end to said light source and capable of transmitting a light beam generated by the latter;
- a field optic fitted to a second end opposite said first end of said optical fiber and focusing the light beam emerging from said optical fiber onto the center of the objective optic of the camera of said image acquisition means.
- said optical fiber is a monomode fiber, that is to say a fiber which, by construction, makes it possible to transmit only a single mode of a laser beam. This makes it possible to prevent the appearance of unwanted noise.
- said illumination means comprise a light source generating a coherent light beam, which makes it possible to increase the aforementioned contrast;
- a camera which has a high image acquisition rate
- said camera comprises means which open the latter in order to acquire an image
- said illumination means produce illumination in the form of light flashes, and are controlled so as to emit at least two light flashes during one and the same opening of the camera on acquiring an image.
- the measuring volume which is observed during the camera opening period is increased.
- said illumination means comprise a pulsed laser with a saturable absorber in order to emit said light flashes, that is to say a laser making it possible to emit light flashes of very short durations. This makes it possible to compensate for the flow velocity of the particles. In effect, the light flash freezes the particles.
- said illumination means are constituted so as to emit in a sequential manner at least two light beams dedicated to measuring different diameters.
- said illumination means comprise two laser sources associated with optics of different magnifications respectively
- said image acquisition means comprise a single camera and optical means making it possible to direct the two laser beams emitted by said two laser sources, onto said camera.
- said processing means are constituted so as to determine said parameter by shadowgraphy.
- said illumination means are constituted so as to emit two light flashes spaced apart by a predetermined duration
- said camera is constituted so as to acquire an image on emission of each of said light flashes
- said processing means are constituted so as to determine, as a parameter, the velocity vector of said particles, from the superposition of two images relating to said two light flashes and from said predetermined duration.
- said illumination means preferably comprise a light source and an optical fiber which is connected to said light source.
- the device according to the invention further comprises:
- an interference filter which is fitted to the entrance of said camera, in order to filter out the unwanted light which might reach the camera;
- a measuring region which is delimited by at least one window
- [0053] means to blow air, preferably filtered air, over the external face of said window, which prevents the appearance of dirt on said window.
- said measuring element is a rod provided with a through opening, preferably oblong, at a first of its ends, said through opening containing said measuring region.
- the device according to the invention also comprises a protection specified below, which protects the entire said device, except. for at least said first end of the rod which is itself placed directly into the environment containing said particles, against said particles which are generally moving.
- At least said first end of the rod is electrically insulated so as to make the device according to the invention unattractive to lightning, for example, if said device is fitted onto an aircraft, as specified below.
- the device according to the invention is particularly well suited to provide certification authorities with reliable quality information on the conditions encountered by an aircraft during in-flight tests.
- certification authorities with reliable quality information on the conditions encountered by an aircraft during in-flight tests.
- Another beneficial application relates to the prevention and anticipation of icing conditions on an aircraft.
- the majority of existing devices only warn the pilot once the ice is established on the sensitive regions of the aircraft.
- the understanding of the conditions which lead to the formation of ice by studying droplets which form the cloud, combined with temperature information makes it possible to anticipate this ice formation.
- a device according to the invention which makes it possible to study water droplets over the whole measurement range involved, it is possible to warn the pilot of the probable formation of ice before the latter is formed on the sensitive regions of the aircraft.
- the present invention also relates to an aircraft, in particular a civil transport airplane, which is noteworthy in that it comprises a device as mentioned above, for determining the values of said parameter of water droplets present outside said aircraft.
- said aircraft further comprises a sleeve:
- the device according to the invention can be mounted and dismantled easily and quickly.
- the aerodynamics of the aircraft are only slightly altered.
- FIG. 1 illustrates schematically a device according to the invention.
- FIG. 2 is an optical diagram making it possible to illustrate the principle of operation of the device according to the invention.
- FIGS. 3 and 5 are schematic lateral and bottom views, respectively, of a preferred embodiment of the device according to the invention.
- FIG. 4 is a schematic section along line IV-IV of FIG. 3.
- FIG. 6 illustrates schematically a particular embodiment of the invention.
- FIGS. 7 and 8 partially show a fuselage of an aircraft intended to accommodate a device according to the invention, in the presence and in the absence, respectively, of such a device.
- the device 1 according to the invention is intended to determine at least one parameter, such as the size, the velocity or the direction of movement of particles such as water droplets, for example.
- said device 1 comprises, in a known and general manner, as shown in a preferred embodiment in FIGS. 3 to 5 :
- a measuring element 2 comprising a measuring region ZM which is intended to accommodate said particles
- illumination means Ml specified above capable of illuminating said measuring region ZM, using at least one light beam 7 A, 7 B;
- image acquisition means M 2 comprising at least one camera 3 capable of acquiring at least one image of said measuring region ZM illuminated by said illumination means M 1 ;
- a processing unit 4 connected to said image acquisition means M 2 via a connection 5 and capable of determining, preferably by shadowgraphy, the values of said parameter, from said image acquired by the camera 3 .
- said illumination means M 1 are constituted so as to produce point illumination, using a light beam 7 A, 7 B comprising light rays RA, RB which are focused in the manner indicated above.
- said illumination means M 1 comprise, as shown schematically in FIG. 1, at least one optical assembly 5 A, 5 B comprising;
- a light source 6 A, 6 B preferably a laser source, capable of generating a light beam 7 A, 7 B;
- an optical fiber 8 A, 8 B connected by a first end 9 A, 9 B to said light source 6 A, 6 B and capable of transmitting a light beam 7 A, 7 B generated by the latter;
- a field optic 10 A, 10 B fitted to a second end 11 A, 11 B opposite said first end 9 A, 9 B of said optical fiber 8 A, 8 B and focusing the light beam 7 A, 7 B emerging from said optical fiber 8 A, 8 B onto an objective optic 12 A, 12 B of the camera 3 of said image acquisition means M 2 .
- the field optic 10 A, 10 B focuses the light beam 7 A, 7 B emerging from the optical fiber 8 A, 8 B, preferably a laser beam, at the center of the objective optic 12 A, 12 B, that is to say channels the rays RA, RB of said emerging light beam 7 A, 7 B.
- the objective optic 12 A, 12 B forms the image of the object in the conjugate plane.
- the object plane P 1 and the plane P 2 of the camera 3 are shown in FIG. 2.
- the contrast (on the image or images acquired) of the shadow of the particles located in the measuring region ZM (plane P 1 ) is increased.
- This increase in contrast leads to improved observability of the particles at the expense of focus and therefore an increase in the depth of field, since the image remains observable for higher defocused values.
- This increase in the depth of field itself leads to an increase in the measuring volume which depends in a known manner both on the size of the sensor, preferably a CCD sensor, on the camera 3 and on the depth of field.
- the optical fiber 8 A, 8 B is a monomode fiber.
- this type of fiber makes it possible to transmit only one mode of the laser beam 7 A, 7 B and therefore prevents any unwanted noise.
- the surface of the “source” is therefore reduced to a diameter of a few microns.
- the use of an optical fiber makes it possible for the light source 6 A, 6 B to be easily fitted in a protected region, for example in the cabin of an airplane.
- the field optic 10 A, 10 B and the objective optic 12 A, 12 B may be single lenses or sets of lenses.
- the diameter of the objective optic 12 A, 12 B is dimensioned so that the accuracy of measurements is not degraded by diffraction phenomena. These phenomena are related to the size of the entrance pupil (diameter of the objective optic) and to the wavelength used.
- a laser source of the doubled “YAG” type at a preferred wavelength of 532 nm is used.
- said illumination means M 1 comprise at least one light source 6 A, 6 B, preferably a laser source, generating a coherent light beam 7 A, 7 B, which makes it possible to increase the aforementioned contrast;
- said camera 3 comprises known means (not shown), which open the latter in order to acquire an image, said illumination means M 1 produce illumination in the form of light flashes and are controlled so as to emit at least two light flashes during an opening of the camera 3 on acquiring an image.
- said measuring volume observed during the opening period of the camera 3 is increased.
- the use of short-duration light flashes makes it possible to compensate for the flow velocity of the particles. In effect, such a light flash freezes the particle.
- the device 1 according to the invention therefore makes it possible to measure the characteristics of particles such as water droplets, for almost zero velocities up to high velocities (V >150 m/s). Nevertheless, for high velocities, it is necessary to illuminate the droplets with light flashes with a short enough duration to freeze them in their movement. For air velocities of around 100 to 150 m/s, the duration of the flash must not exceed 5 to 10 ns.
- the preferred laser source is a pulsed laser with a saturable absorber (of the “Q-switch”type) which generates pulses of duration less than 1 ns.
- this laser source has the advantage of being lightweight and of low bulk.
- the illumination means M 1 comprise, according to the invention, as shown in FIGS. 1 and 5, the two aforementioned optical assemblies 5 A and 5 B, each emitting in a sequential manner a laser beam 7 A and 7 B of different diameter adapted to the field observed.
- This difference in diameter which is due in particular to different magnifications of the optics 12 A, 12 B, is illustrated in FIG. 1 by rectangular parallelepipeds 13 A and 13 B of different sizes.
- the optics 12 B and 12 A can be adjusted in order to procure, respectively, a magnification of 3 , adapted to observing small droplets (from about 10 ⁇ m to 50 ⁇ m) present in a first measuring space ZM 1 shown in FIG. 4, and a magnification of 0.66 capable of observing large droplets (from 50 ⁇ m to 600 ⁇ m) present in a second measuring space ZM 2 , which makes it possible to obtain overall a measurement range from 10 ⁇ m to 600 ⁇ m.
- these magnifications make it possible to cover the entire diameter range without distortion in the overlap region.
- the device 1 comprises a single camera 3 and the image acquisition means M 2 in addition comprise, as shown in FIGS. 1 and 5:
- a return prism 14 placed in the optical path of a first beam 7 A of said beams 7 A, 7 B;
- a semireflecting plate 16 placed in the optical path of the second beam 7 B, and in the return optical path of the first beam 7 A, downstream of the return prism 14 .
- the wavelength, the size of the optics and the magnification make it possible to define the minimum size of the particles that can be measured.
- the diameter of the diffraction spot or Airy disk is related to the wavelength and to the diameter of the pupil.
- the magnification makes it possible to choose the number of pixels which are covered by the smallest particle that it is desired to observe. In order to observe particles of size greater than or less than the aforementioned measurement range, the optical characteristics, that is the wavelength, the diameter of the optics and/or the magnification, should therefore be altered.
- the depth of field is yet further increased by using the known principle of shadowgraphy in order to determine the size from images acquired by the image acquisition means M 2 .
- suitable and standard algorithms are integrated into the processing unit 4 .
- the device 1 additionally comprises:
- a measuring element 2 in the form of a rod, which is provided close to its free end 2 A with a through opening 19 containing the measuring region ZM which comprises the two aforementioned measuring spaces ZM 1 and ZM 2 .
- the particles to be measured pass through the opening 19 in a flow direction E;
- a system 24 for blowing filtered air for example controlled manually by means of a button 25 and preferably comprising a plurality of injectors (not shown) for blowing air over the external faces of the windows 20 A, 20 B, 21 A and 21 B, as illustrated by arrows f, so as to prevent any deposition of dirt (capable of causing optical perturbance) on these windows.
- the blowing system 24 makes it possible to deice the windows 20 A, 20 B, 21 A and 21 B if necessary. The blown air therefore has a temperature high enough to remove any ice from said windows;
- an interference filter (not shown) which is fitted to the entrance of the camera 3 and which makes it possible to remove unwanted light capable of reaching said camera 3 ;
- a control button 26 controlling the illumination means M 1 and the image acquisition means M 2 , as illustrated by means of links 27 and 28 , respectively.
- all the optics of the device 1 are, preferably, subjected to an antireflection treatment in order to prevent interference.
- said illumination means M 1 are constituted so as to emit two light flashes 7 B spaced apart by a predetermined duration; said camera 3 is constituted so as to acquire an image on emission of each of said two light flashes 7 B; and
- said processing unit 4 is constituted so as to determine the velocity vector of the particles, from the two images relating to said two light flashes 7 B and from said predetermined duration.
- the illumination means M 1 comprise a single light source 6 B and an optical fiber 8 B which is connected to said light source 6 B, in order to emit two light flashes 7 B spaced apart by a predetermined duration.
- a delay line 15 comprising an optical fiber, preferably coiled, may be assembled in parallel to said optical fiber 8 B, via optical couplers 17 , 18 .
- the first half of the latter corresponding to a first light flash
- the other half which corresponds to the second light flash
- the velocity vector of the particles measured in this way can be used to calibrate the device 1 so as to obtain a representation of the flow in the measuring region ZM with respect to the flow in the environment in which the rod 2 is placed.
- the delay line 15 makes it possible to calibrate the device thereby giving an indication of the velocity vector of the particles. This indication makes it possible to determine whether the rod 2 is properly positioned with respect to the flow of the environment in which it is immersed. Once the correct position is identified and any risk of turbulent flow, which may be detrimental to the quality of the measurement, is prevented, the delay line is removed.
- the device 1 according to the invention is assembled on an aircraft, for example a civil transport airplane, only part of the fuselage F of which is shown in FIGS. 7 and 8, in order to detect the size of water droplets present outside the aircraft so as to be able to characterize icing conditions and, if necessary, warn the pilot or pilots of the aircraft of the need to activate a deicing system.
- an aircraft for example a civil transport airplane, only part of the fuselage F of which is shown in FIGS. 7 and 8, in order to detect the size of water droplets present outside the aircraft so as to be able to characterize icing conditions and, if necessary, warn the pilot or pilots of the aircraft of the need to activate a deicing system.
- the fuselage F of the aircraft is provided with a sleeve 29 :
- the device 1 according to the invention may be assembled and dismantled, easily and quickly.
- the aerodynamics of the aircraft are altered as little as possible.
- said part 2 B of the rod 2 is electrically insulated so as to make the device 1 unattractive to lightning. Consequently, the device 1 according to the invention makes it possible, in the aforementioned application, especially to:
- the processing unit 4 comprises or is combined with at least one storage unit (not shown); differentiate between water droplets and crystals; and
- a preferred application of the device 1 according to the invention therefore relates to the prevention and anticipation of icing conditions on an aircraft.
Abstract
Description
- The present invention relates to a device for determining the values of at least one parameter, especially the size, of particles such as water droplets.
- Although not exclusively, said device is applicable more particularly to the detection and to the characterization of icing conditions on aircraft, especially civil transport airplanes, by making it possible to measure the size and the number of water droplets present in particular in the clouds and the fogs through which an aircraft passes.
- It is known that the problem of rapid formation of ice on an aircraft is a serious problem which may lead to accidents when it occurs suddenly and when it could not be detected in time.
- By means of documents U.S. Pat. No. 5,484,121, EP-0 405 625 and GB-2 158 939, devices are known for detecting the presence of ice on the external parts of an aircraft, especially the wings, once this ice is formed. These devices use, to this end, light beams and involve the reflection of these light beams in order to detect the presence of ice. If necessary, a signal is emitted in order to inform the pilot that it is necessary to activate a deicing device.
- These known devices especially have the drawback of warning the pilot only when the ice is already formed. Therefore they do not allow the phenomenon of ice formation to be anticipated so that decisions suited to the climatic conditions can be taken before a problem appears.
- Other devices are known for characterizing icing conditions, especially during development or test flights. It is known that, during development flights, it must be demonstrated that the conditions encountered comply properly with the regulatory requirements decreed by the certification authorities, which then validates the behavior of the airplane under such conditions.
- The known devices, used to this end, are generally intended to determine the particle size distribution of clouds, that is to say the size, the number and the shape of the water droplets present in these clouds, and they can be classified in two categories:
- particle counters which determine the characteristics of each particle, taken individually; and
- integrators which sum the contributions from all the particles present in a measuring volume.
- These known devices may also be classified according to their measurement principle, namely in particular:
- imaging or shadowgraphy,
- the Doppler effect, or
- light scattering (measurement along given angles).
- By way of illustration, it is possible to mention some examples of known devices implementing imaging and shadowgraphy principles and acting, for example, as particle counters.
- Firstly, a device which is known by the term “Optical Array Probe” implements, in a standard manner, the principle called linear array shadowgraphy. In this case, a particle passing through a collimated light beam produces a shadow directly related to its diameter on a linear array of detectors spaced apart at equal intervals. When there is no particle in the measuring volume in question, the light beam illuminates all the detectors. On the other hand, when a particle passes through said measuring volume, a loss of light due to scattering, refraction and absorption of the particle generates a signal at the output of the detectors. The number of detectors showing a variation in amplitude of more than a specific threshold (for example 50%) is summed in order that the size of the particle is given directly. However, this known device has a limited measurement range and is not able to measure particles accurately, if their diameter is less than 100 μm.
- Secondly, a device which is known by the term “Cloud Particle Imager” generates two laser beams. The intersection of these two lasers beams defines a rectangular sampling area. Any particle which passes through this rectangular sampling area is properly focused and actuates illumination by an imaging laser, for the purpose of acquiring an image. Detectors are placed facing the laser beams: they make it possible to detect the passage of particles by measuring the decrease in intensity produced as these particles pass through. The diameter of the particles is measured from the image of the properly focused particle. However, this known device is bulky and has too large a volume to improve the operational difficulties stated above and linked to the devices currently used in in-flight testing.
- Thirdly, a measuring device is known by document FR-2 689 247, in particular comprising:
- a rod comprising a measuring region which is intended to accommodate the particles to be analyzed;
- illumination means capable of illuminating said measuring region, using at least one laser beam;
- image acquisition means capable of acquiring images of said measuring region illuminated by said illumination means; and
- processing means capable of determining the values of said parameter, from said images.
- More specifically, the latter known device emits a pulsed light beam that is transported by optical fiber and which is focused onto the measuring region. The image is also transported by optical fiber up to a beam splitter which divides and orients the beam toward the image acquisition means comprising two “CCD”-type sensors. A first image is recorded along a particular sighting axis on one of the sensors. After a very short time, a second image is recorded along the same sighting axis on the other sensor. On subtracting these two images, a dark/light doublet is obtained which stands out well against the uniform background, from which it is possible to deduce the size and the velocity of the imaged particles. This known device makes it possible to remove the majority of background defects. This is because the image acquisition means with a double sensor behave like a double shutter and only see the field for two very short periods of time.
- However, this known device has a small measuring volume. It is known that the measuring volume analyzed per second is equal to the measuring volume associated with each image, multiplied by the image rate of the image acquisition means.
- As to the measuring volume associated with each image, this is related to the size of the sensor (divided by the magnification) and to the depth of field.
- Consequently, in particular because of its small measuring volume, the known device disclosed by document FR-2 689 247 is not suitable for the applications envisaged in the present invention, relating to the measurement of water droplet parameters since, especially because of the often relatively low concentrations of water droplets present in the clouds analyzed during tests, a large measuring volume is needed for such an application.
- It will be noted, moreover, that the various known devices comprise various drawbacks which are problematic for the aforementioned preferred application. This is because the known devices are, in general, poorly adapted to the envisaged meteorological and operational constraints, in particular because of the following difficulties, namely a long and difficult installation in an aircraft, a very large bulk, difficult exploitation of the results, etc. Furthermore, the majority of these known devices have a range for measuring of the size of the droplets which is small, and especially are not able to detect and analyze, at the same time, the small droplets and the large supercooled droplets (water at a temperature less than 0° C.) which, as is known, promote the appearance of ice.
- The present invention relates to a device for determining the values of at least one parameter, especially the size, of particles, in particular of water droplets, which makes it possible to overcome the aforementioned drawbacks and which especially comprises an increased measuring volume.
- To this end, according to the invention, said device of the type comprising:
- a measuring element comprising a measuring region which is intended to accommodate the particles;
- illumination means capable of illuminating said measuring region;
- image acquisition means comprising at least one camera capable of acquiring at least one image of said measuring region illuminated by said illumination means; and
- processing means capable of determining the values of said parameter, from said image acquired by the camera, is noteworthy in that said illumination means are constituted so as to produce a point illumination source using a light beam, the light rays of which are focused on an objective optic of the image acquisition means.
- Thus, by means of this point illumination, the contrast (on the image or images acquired) of the shadow of the particles located in the measuring region is increased. This increase in contrast leads to an improved observability of the particles at the expense of focus and therefore an increase in the depth of field, since the image remains observable for higher defocused values. This increase in depth of field itself leads to an increase in the measuring volume which, as indicated above, depends on the size of the sensor and on the depth of field.
- In a preferred embodiment, in order to produce said point illumination, said illumination means comprise at least one optical assembly comprising:
- a light source, preferably a laser source, capable of generating a light beam;
- an optical fiber connected by a first end to said light source and capable of transmitting a light beam generated by the latter; and
- a field optic fitted to a second end opposite said first end of said optical fiber and focusing the light beam emerging from said optical fiber onto the center of the objective optic of the camera of said image acquisition means.
- Preferably, said optical fiber is a monomode fiber, that is to say a fiber which, by construction, makes it possible to transmit only a single mode of a laser beam. This makes it possible to prevent the appearance of unwanted noise.
- Furthermore, in order to yet further increase the measuring volume, in an advantageous manner:
- said illumination means comprise a light source generating a coherent light beam, which makes it possible to increase the aforementioned contrast; and/or
- a camera is used which has a high image acquisition rate; and/or
- said camera comprises means which open the latter in order to acquire an image, said illumination means produce illumination in the form of light flashes, and are controlled so as to emit at least two light flashes during one and the same opening of the camera on acquiring an image. Thus, the measuring volume which is observed during the camera opening period is increased.
- In order to implement the last characteristic, preferably, said illumination means comprise a pulsed laser with a saturable absorber in order to emit said light flashes, that is to say a laser making it possible to emit light flashes of very short durations. This makes it possible to compensate for the flow velocity of the particles. In effect, the light flash freezes the particles.
- Moreover, in order to increase the size range of measured particles, especially of water droplets, in an advantageous manner, said illumination means are constituted so as to emit in a sequential manner at least two light beams dedicated to measuring different diameters.
- In order to do this, in a preferred embodiment, said illumination means comprise two laser sources associated with optics of different magnifications respectively, and said image acquisition means comprise a single camera and optical means making it possible to direct the two laser beams emitted by said two laser sources, onto said camera.
- In order to yet further increase the measurement range, said processing means are constituted so as to determine said parameter by shadowgraphy.
- Moreover, advantageously, said illumination means are constituted so as to emit two light flashes spaced apart by a predetermined duration, said camera is constituted so as to acquire an image on emission of each of said light flashes, and said processing means are constituted so as to determine, as a parameter, the velocity vector of said particles, from the superposition of two images relating to said two light flashes and from said predetermined duration.
- To this end, said illumination means preferably comprise a light source and an optical fiber which is connected to said light source.
- In addition, advantageously, the device according to the invention further comprises:
- an interference filter which is fitted to the entrance of said camera, in order to filter out the unwanted light which might reach the camera; and/or
- an antireflection treatment in order to prevent interference; and/or
- a measuring region which is delimited by at least one window; and/or
- means to blow air, preferably filtered air, over the external face of said window, which prevents the appearance of dirt on said window.
- In a preferred embodiment, said measuring element is a rod provided with a through opening, preferably oblong, at a first of its ends, said through opening containing said measuring region.
- In addition, advantageously, the device according to the invention also comprises a protection specified below, which protects the entire said device, except. for at least said first end of the rod which is itself placed directly into the environment containing said particles, against said particles which are generally moving.
- In addition, advantageously, at least said first end of the rod is electrically insulated so as to make the device according to the invention unattractive to lightning, for example, if said device is fitted onto an aircraft, as specified below.
- Moreover, it will be noted that the device according to the invention is particularly well suited to provide certification authorities with reliable quality information on the conditions encountered by an aircraft during in-flight tests. Of course, there may be other possibilities of use thereof, such as the certification of helicopters during stationary flights, the verification of conditions produced in icing wind tunnels, measurements on the ground during poor conditions of visibility (fog, etc.), etc.
- Another beneficial application relates to the prevention and anticipation of icing conditions on an aircraft. Specifically, as indicated above, the majority of existing devices only warn the pilot once the ice is established on the sensitive regions of the aircraft. In contrast, the understanding of the conditions which lead to the formation of ice by studying droplets which form the cloud, combined with temperature information, makes it possible to anticipate this ice formation. Thus, by means of a device according to the invention which makes it possible to study water droplets over the whole measurement range involved, it is possible to warn the pilot of the probable formation of ice before the latter is formed on the sensitive regions of the aircraft.
- The present invention also relates to an aircraft, in particular a civil transport airplane, which is noteworthy in that it comprises a device as mentioned above, for determining the values of said parameter of water droplets present outside said aircraft.
- Advantageously, said aircraft further comprises a sleeve:
- which is fitted into the fuselage of the aircraft so as to create a through opening;
- which has a diameter adapted to the diameter of the aforementioned rod of the device according to the invention such that the latter can be fitted in a sealed manner in said sleeve; and
- which is capable of being closed in a sealed manner, in the absence of said rod.
- Thus the device according to the invention can be mounted and dismantled easily and quickly. In addition, the aerodynamics of the aircraft are only slightly altered.
- The figures of the appended drawing will make it easy to understand how the invention may be produced. In these figures, identical references denote similar elements.
- FIG. 1 illustrates schematically a device according to the invention.
- FIG. 2 is an optical diagram making it possible to illustrate the principle of operation of the device according to the invention.
- FIGS. 3 and 5 are schematic lateral and bottom views, respectively, of a preferred embodiment of the device according to the invention.
- FIG. 4 is a schematic section along line IV-IV of FIG. 3.
- FIG. 6 illustrates schematically a particular embodiment of the invention.
- FIGS. 7 and 8 partially show a fuselage of an aircraft intended to accommodate a device according to the invention, in the presence and in the absence, respectively, of such a device.
- The
device 1 according to the invention is intended to determine at least one parameter, such as the size, the velocity or the direction of movement of particles such as water droplets, for example. - To this end, said
device 1 comprises, in a known and general manner, as shown in a preferred embodiment in FIGS. 3 to 5: - a
measuring element 2 comprising a measuring region ZM which is intended to accommodate said particles; - illumination means Ml specified above capable of illuminating said measuring region ZM, using at least one
light beam - image acquisition means M2 comprising at least one
camera 3 capable of acquiring at least one image of said measuring region ZM illuminated by said illumination means M1; and - a
processing unit 4 connected to said image acquisition means M2 via aconnection 5 and capable of determining, preferably by shadowgraphy, the values of said parameter, from said image acquired by thecamera 3. - According to the invention, said illumination means M1 are constituted so as to produce point illumination, using a
light beam - To this end, in a preferred embodiment, said illumination means M1 comprise, as shown schematically in FIG. 1, at least one
optical assembly - a
light source light beam - an
optical fiber first end light source light beam - a
field optic second end first end optical fiber light beam optical fiber objective optic camera 3 of said image acquisition means M2. - The
field optic light beam optical fiber objective optic light beam - The
objective optic camera 3 are shown in FIG. 2. - By means of this “point” illumination, the contrast (on the image or images acquired) of the shadow of the particles located in the measuring region ZM (plane P1) is increased. This increase in contrast leads to improved observability of the particles at the expense of focus and therefore an increase in the depth of field, since the image remains observable for higher defocused values. This increase in the depth of field itself leads to an increase in the measuring volume which depends in a known manner both on the size of the sensor, preferably a CCD sensor, on the
camera 3 and on the depth of field. - It will be noted that with standard shadowgraphy by illumination which is hot point illumination (i.e. diffuse illumination) as disclosed, for example, by the aforementioned document FR-2 689 247, the shadows produced by each point of the light source do not exactly overlap. The shadow of the object is therefore illuminated by the unwanted light coming from said source, which, of course, is detrimental to the contrast. This problem is efficiently remedied by virtue of the present invention.
- According to the invention, the
optical fiber laser beam light source - Furthermore, according to the invention, the
field optic objective optic - In addition, the diameter of the
objective optic - Furthermore,in order to yet further increase the measuring volume, especially thereby contributing to an increase in contrast, in an advantageous manner:
- said illumination means M1 comprise at least one
light source coherent light beam - a
camera 3 is used which has a high image acquisition rate, for example a camera of the “CAD6” type, enabling a rate of 262 frames/second with a resolution of 512=512 pixels to be achieved; and - in a particular embodiment, said
camera 3 comprises known means (not shown), which open the latter in order to acquire an image, said illumination means M1 produce illumination in the form of light flashes and are controlled so as to emit at least two light flashes during an opening of thecamera 3 on acquiring an image. Thus the measuring volume observed during the opening period of thecamera 3 is increased. - This is only possible by decreasing the intensity of the laser beam so as not to saturate the
camera 3. In practice, it is preferred to limit the number of light flashes to two or three, since this technique has the drawback of decreasing the signal/noise ratio. Thus the volume observed during the opening period of the camera is multiplied by the number of light flashes provided per image. - It will be noted that the periodicity of these light flashes takes account of the dump time of the pixels from the camera3 (dead time during which the acquisition of a new image is not possible).
- In addition, the use of short-duration light flashes makes it possible to compensate for the flow velocity of the particles. In effect, such a light flash freezes the particle. The
device 1 according to the invention therefore makes it possible to measure the characteristics of particles such as water droplets, for almost zero velocities up to high velocities (V >150 m/s). Nevertheless, for high velocities, it is necessary to illuminate the droplets with light flashes with a short enough duration to freeze them in their movement. For air velocities of around 100 to 150 m/s, the duration of the flash must not exceed 5 to 10 ns. It is for this reason that the preferred laser source is a pulsed laser with a saturable absorber (of the “Q-switch”type) which generates pulses of duration less than 1 ns. In addition, this laser source has the advantage of being lightweight and of low bulk. - Moreover, in order to increase the range of measurement of the size of particles or water droplets, the illumination means M1 comprise, according to the invention, as shown in FIGS. 1 and 5, the two aforementioned
optical assemblies laser beam optics rectangular parallelepipeds - By way of illustration, the
optics - In said preferred embodiment, the
device 1 comprises asingle camera 3 and the image acquisition means M2 in addition comprise, as shown in FIGS. 1 and 5: - a
return prism 14, of the standard type, placed in the optical path of afirst beam 7A of saidbeams - a
semireflecting plate 16, of the standard type, placed in the optical path of thesecond beam 7B, and in the return optical path of thefirst beam 7A, downstream of thereturn prism 14. - It will be noted that the wavelength, the size of the optics and the magnification make it possible to define the minimum size of the particles that can be measured. The diameter of the diffraction spot or Airy disk is related to the wavelength and to the diameter of the pupil. The magnification makes it possible to choose the number of pixels which are covered by the smallest particle that it is desired to observe. In order to observe particles of size greater than or less than the aforementioned measurement range, the optical characteristics, that is the wavelength, the diameter of the optics and/or the magnification, should therefore be altered.
- The depth of field is yet further increased by using the known principle of shadowgraphy in order to determine the size from images acquired by the image acquisition means M2. To this end, suitable and standard algorithms are integrated into the
processing unit 4. - In the preferred embodiment shown in FIGS.3 to 5, the
device 1 additionally comprises: - a
measuring element 2 in the form of a rod, which is provided close to itsfree end 2A with a throughopening 19 containing the measuring region ZM which comprises the two aforementioned measuring spaces ZM1 and ZM2. The particles to be measured pass through theopening 19 in a flow direction E; - two pairs of
windows device 1 with respect to said flow of particles; - two
return prisms - a
system 24 for blowing filtered air, partially shown in FIG. 3, for example controlled manually by means of abutton 25 and preferably comprising a plurality of injectors (not shown) for blowing air over the external faces of thewindows system 24 makes it possible to deice thewindows - an interference filter (not shown) which is fitted to the entrance of the
camera 3 and which makes it possible to remove unwanted light capable of reaching saidcamera 3; and - a
control button 26 controlling the illumination means M1 and the image acquisition means M2, as illustrated by means oflinks - In addition, all the optics of the
device 1 are, preferably, subjected to an antireflection treatment in order to prevent interference. - Moreover, in a particular embodiment, shown partially and schematically in FIG. 6:
- said illumination means M1 are constituted so as to emit two
light flashes 7B spaced apart by a predetermined duration; saidcamera 3 is constituted so as to acquire an image on emission of each of said twolight flashes 7B; and - said
processing unit 4 is constituted so as to determine the velocity vector of the particles, from the two images relating to said twolight flashes 7B and from said predetermined duration. - The illumination means M1 comprise a single
light source 6B and anoptical fiber 8B which is connected to saidlight source 6B, in order to emit twolight flashes 7B spaced apart by a predetermined duration. Adelay line 15, comprising an optical fiber, preferably coiled, may be assembled in parallel to saidoptical fiber 8B, viaoptical couplers - When the
laser source 6B emits a light pulse, the first half of the latter, corresponding to a first light flash, is sent directly to thecamera 3 by means of theoptical fiber 8B and the other half, which corresponds to the second light flash, enters, at thecoupler 17, thedelay line 15 which has, for example, a length of 200 meters, and is then sent to thecamera 3 via thecoupler 18 and theoptical fiber 8B, with a delay corresponding to the time taken to pass through thedelay line 15. - The velocity vector of the particles measured in this way can be used to calibrate the
device 1 so as to obtain a representation of the flow in the measuring region ZM with respect to the flow in the environment in which therod 2 is placed. Thedelay line 15 makes it possible to calibrate the device thereby giving an indication of the velocity vector of the particles. This indication makes it possible to determine whether therod 2 is properly positioned with respect to the flow of the environment in which it is immersed. Once the correct position is identified and any risk of turbulent flow, which may be detrimental to the quality of the measurement, is prevented, the delay line is removed. - Moreover, in a preferred application, the
device 1 according to the invention is assembled on an aircraft, for example a civil transport airplane, only part of the fuselage F of which is shown in FIGS. 7 and 8, in order to detect the size of water droplets present outside the aircraft so as to be able to characterize icing conditions and, if necessary, warn the pilot or pilots of the aircraft of the need to activate a deicing system. - In this case, the fuselage F of the aircraft is provided with a sleeve29:
- which is fitted in said fuselage F of the aircraft so as to create a through opening;
- which has a diameter adapted to the diameter of the
rod 2 of thedevice 1 such that the latter can be fitted in a sealed manner in said sleeve 29 (FIG. 7); and - which is capable of being closed in a sealed manner, by means of a suitable and
standard plug 30, in the absence of said rod 2 (FIG. 8). - Consequently, the
device 1 according to the invention may be assembled and dismantled, easily and quickly. In addition, the aerodynamics of the aircraft are altered as little as possible. - Furthermore, with the exception of the
part 2B (comprising at least theend 2A) of therod 2 which is outside the fuselage F, all the rest of thedevice 1 is protected from the external environment and, in particular, from said particles, by said fuselage F. - In addition, said
part 2B of therod 2 is electrically insulated so as to make thedevice 1 unattractive to lightning. Consequently, thedevice 1 according to the invention makes it possible, in the aforementioned application, especially to: - measure the size of water droplets present in clouds;
- measure the concentration of droplets, that is to say count their number per unit volume. This requires an accurate knowledge of the volume of the measuring spaces ZM1, ZM2;
- provide the pilot with real time data required to carry out in-flight tests;
- record all the information on board the aircraft. To this end, the
processing unit 4 comprises or is combined with at least one storage unit (not shown); differentiate between water droplets and crystals; and - measure the velocity (in a plane) of said water droplets.
- A preferred application of the
device 1 according to the invention therefore relates to the prevention and anticipation of icing conditions on an aircraft. - However, numerous other applications can also be envisaged, such as providing certification authorities with reliable quality information on the conditions encountered by an aircraft during in-flight tests, the certification of helicopters during stationary flights, the verification of conditions produced in icing wind tunnels, measurements on the ground during poor conditions of visibility (fog, etc.), etc.
Claims (20)
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR0004432 | 2000-04-07 | ||
FR0004432A FR2807522B1 (en) | 2000-04-07 | 2000-04-07 | DEVICE FOR DETERMINING THE VALUES OF AT LEAST ONE PARAMETER OF PARTICLES, ESPECIALLY WATER DROPLETS |
FR00/04432 | 2000-04-07 | ||
PCT/FR2001/000842 WO2001077644A1 (en) | 2000-04-07 | 2001-03-21 | Device for determining the values of at least one parameter of particles, in particular water droplets |
Publications (2)
Publication Number | Publication Date |
---|---|
US20020159060A1 true US20020159060A1 (en) | 2002-10-31 |
US6813020B2 US6813020B2 (en) | 2004-11-02 |
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ID=8848964
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/979,886 Expired - Lifetime US6813020B2 (en) | 2000-04-07 | 2001-03-21 | Device for determining the values of at least one parameter of particles, especially of water droplets |
Country Status (10)
Country | Link |
---|---|
US (1) | US6813020B2 (en) |
EP (1) | EP1183518B1 (en) |
AU (1) | AU4428501A (en) |
BR (1) | BR0106106A (en) |
CA (1) | CA2372297C (en) |
DE (1) | DE60111143T2 (en) |
ES (1) | ES2240433T3 (en) |
FR (1) | FR2807522B1 (en) |
RU (1) | RU2226671C2 (en) |
WO (1) | WO2001077644A1 (en) |
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EP1489402A1 (en) | 2003-06-20 | 2004-12-22 | Airbus France | Method for illuminating particles for generating their images |
US7175136B2 (en) * | 2003-04-16 | 2007-02-13 | The Boeing Company | Method and apparatus for detecting conditions conducive to ice formation |
US20080231854A1 (en) * | 2007-03-20 | 2008-09-25 | Jenoptik Laser, Optik, Systeme Gmbh | Apparatus and method for determining the particle size and/or particle shape of a particle mixture |
EP2615301A1 (en) * | 2012-01-10 | 2013-07-17 | Nordex Energy GmbH | Method for operating a wind energy assembly, for which the risk of icing is determined on the basis of meteorological data and wind energy assembly for implementing the method |
US20130240672A1 (en) * | 2012-01-05 | 2013-09-19 | The Boeing Company | Laser-Based Supercooled Large Drop Icing Condition Detection System |
US20150035944A1 (en) * | 2013-07-31 | 2015-02-05 | Pla University Of Science And Technology | Method for Measuring Microphysical Characteristics of Natural Precipitation using Particle Image Velocimetry |
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US20190020825A1 (en) * | 2017-07-11 | 2019-01-17 | Arkray, Inc. | Analysis apparatus and focusing method |
EP3477277A3 (en) * | 2017-10-05 | 2019-07-31 | Honeywell International Inc. | Apparatus and method for increasing dynamic range of a particle sensor |
CN110686608A (en) * | 2019-11-11 | 2020-01-14 | 国网湖南省电力有限公司 | Portable icing thickness measuring device for power transmission line and measuring method thereof |
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KR101021759B1 (en) | 2003-08-20 | 2011-03-15 | 더 보잉 컴파니 | Methods and systems for detecting icing conditions |
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CN114048552B (en) * | 2022-01-12 | 2022-03-29 | 中国空气动力研究与发展中心计算空气动力研究所 | Rotor wing surface large water drop mass flow calculation method considering secondary impact and terminal |
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US7175136B2 (en) * | 2003-04-16 | 2007-02-13 | The Boeing Company | Method and apparatus for detecting conditions conducive to ice formation |
US20040257450A1 (en) * | 2003-06-20 | 2004-12-23 | Airbus France | Method for illuminating particles for the purpose of forming their images |
FR2856536A1 (en) * | 2003-06-20 | 2004-12-24 | Airbus France | METHOD FOR LIGHTING PARTICLES FOR THE FORMATION OF THEIR IMAGES |
US7120173B2 (en) | 2003-06-20 | 2006-10-10 | Airbus France | Method for illuminating particles for the purpose of forming their images |
EP1489402A1 (en) | 2003-06-20 | 2004-12-22 | Airbus France | Method for illuminating particles for generating their images |
US20080231854A1 (en) * | 2007-03-20 | 2008-09-25 | Jenoptik Laser, Optik, Systeme Gmbh | Apparatus and method for determining the particle size and/or particle shape of a particle mixture |
US7907279B2 (en) | 2007-03-20 | 2011-03-15 | Jenoptik Laser, Optik, Systeme Gmbh | Apparatus and method for determining the particle size and/or particle shape of a particle mixture |
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US20130240672A1 (en) * | 2012-01-05 | 2013-09-19 | The Boeing Company | Laser-Based Supercooled Large Drop Icing Condition Detection System |
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CN104569478A (en) * | 2014-12-31 | 2015-04-29 | 吉林大学 | Device for testing flow velocity of liquid drop under gravity on material surfaces at different temperatures |
DE102015110826B4 (en) | 2015-07-06 | 2023-03-30 | Dimeto Gmbh | Device and method for measuring precipitation |
US20190020825A1 (en) * | 2017-07-11 | 2019-01-17 | Arkray, Inc. | Analysis apparatus and focusing method |
CN109246350A (en) * | 2017-07-11 | 2019-01-18 | 爱科来株式会社 | Analytical equipment and focus alignment methods |
US10798287B2 (en) * | 2017-07-11 | 2020-10-06 | Arkray, Inc. | Analysis apparatus and focusing method |
EP3477277A3 (en) * | 2017-10-05 | 2019-07-31 | Honeywell International Inc. | Apparatus and method for increasing dynamic range of a particle sensor |
US10591422B2 (en) | 2017-10-05 | 2020-03-17 | Honeywell International Inc. | Apparatus and method for increasing dynamic range of a particle sensor |
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CN113435401A (en) * | 2021-07-14 | 2021-09-24 | 中国气象科学研究院 | Aircraft cloud physical detection and identification method and device for cold water passing area and storage medium |
Also Published As
Publication number | Publication date |
---|---|
FR2807522A1 (en) | 2001-10-12 |
WO2001077644A1 (en) | 2001-10-18 |
DE60111143D1 (en) | 2005-07-07 |
BR0106106A (en) | 2002-03-12 |
RU2226671C2 (en) | 2004-04-10 |
EP1183518A1 (en) | 2002-03-06 |
AU4428501A (en) | 2001-10-23 |
CA2372297C (en) | 2008-05-20 |
FR2807522B1 (en) | 2002-06-14 |
ES2240433T3 (en) | 2005-10-16 |
US6813020B2 (en) | 2004-11-02 |
EP1183518B1 (en) | 2005-06-01 |
DE60111143T2 (en) | 2006-05-18 |
CA2372297A1 (en) | 2001-10-18 |
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