Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/88—Lidar systems specially adapted for specific applications
  • G01S17/95—Lidar systems specially adapted for specific applications for meteorological use
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
  • G01S17/06—Systems determining position data of a target
  • G01S17/46—Indirect determination of position data
  • G01S17/48—Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4818—Constructional features, e.g. arrangements of optical elements using optical fibres
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/497—Means for monitoring or calibrating
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
  • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Definitions

• the present invention relates to the field of lidar systems, commonly called lidars, and in particular lidars, so-called atmospheric, used to probe the atmosphere.
• lidars commonly called lidars, and in particular lidars, so-called atmospheric, used to probe the atmosphere.
• Atmospheric lidars are used to remotely determine atmospheric parameters such as the concentration of gases or aerosols, wind speed, temperature.
• the present invention relates to an atmospheric lidar calibration device for calibrating distance, velocity, and lidar efficiency measurements.
• LIDAR is an acronym derived from the English term "LIght Detection And Ranging”, describing an optical technique for measuring physical parameters of a distant target. This technique is based on the analysis of the variations of the optical properties of a beam emitted from a transmission channel of a device and then returned by the target to be analyzed to an analysis channel of said device.
• the lidar In the case of atmospheric lidars, the lidar emits an optical beam towards a part of the atmosphere and analyzes the beams returned by the gases and / or aerosols of the atmosphere.
• the metrological accuracy of atmospheric lidar measurements is closely related to the calibration of devices arranged to implement said measurements. The devices in question, commonly referred to as lidar, therefore need to be calibrated rigorously and regularly.
• lidar calibration is generally performed outdoors, on a natural or artificial remote target whose specific characteristics, such as, in addition, the distance, the speed and the reflectivity are known precisely. Outdoor calibration requires an external site with a distance equivalent to the measurement conditions when operating the lidar and a target. In addition, outdoor calibration involves taking into account the characteristics of the propagation medium and that these characteristics are constant during calibration. This type of calibration requires usually the presence of a reference lidar to know the characteristics of the atmosphere in real time. The reference lidar must also be calibrated, which is a source of uncertainty.
• An object of the invention is in particular to overcome all or part of the disadvantages associated with external calibration processes.
• an object of the invention is to provide a device and a reduced size calibration process that can operate without a real atmosphere.
• Another aim is to propose a calibration device and method that can be integrated directly into a lidar.
• Another aim is to propose a device and a calibration method for performing regular calibration of the lidar without changing its configuration.
• Another object of the invention is to provide a device and a calibration method for giving greater accuracy to distance calibration, speed and the measurement of lidar efficiency.
• Another object of the invention is to provide a self-diagnostic tool integrable lidar.
• an atmospheric lidar calibration device comprising:
• an optical fiber arranged to propagate at least a portion of a beam emitted by the lidar
• the optical fiber comprises diffusers distributed along the optical fiber and backscattering fractions of the at least part of the beam propagating in the optical fiber, and in that it comprises:
• a coupling device arranged to couple:
• the lidar At least a part of said fractions backscattered by the diffusers, and at least a part of a beam reflected by the reflector element.
• the optical fiber can be single mode.
• the optical fiber is a multimode optical fiber.
• the optical fiber has a core whose diameter may be less than 200 ⁇ m, preferably less than 100 ⁇ m.
• the reflective element may be any semi-reflective technical means known to those skilled in the art, such as, in particular, a diopter located at the fiber end or an external optical surface of controlled reflectivity.
• the at least a portion of the beam emitted by the lidar and coupled to the optical fiber can be defined as the incident beam.
• the set of backscattered fractions, by the diffusers, of the at least part of the beam propagating in the optical fiber can be defined as a backscattered part of the at least part of the beam propagating in the optical fiber.
• the reflector element may be located at an output of the optical fiber.
• the coupling device may be located between the lidar and an input of the optical fiber.
• At least a portion of the diffusers may be defects in the homogeneity of the optical fiber.
• the diffusers are atoms constituting the optical fiber.
• a portion of the signal backscattered by the optical fiber comes from the backscattering of the constituent atoms of the optical fiber.
• the backscattering of the constituent atoms of the optical fiber may be a Rayleigh backscatter.
• the defects of homogeneity of the optical fiber may be intrinsic defects of the optical fiber.
• Intrinsic defects may be inherent in the method of manufacturing the optical fiber.
• the defects of homogeneity of the optical fiber may be defects voluntarily provided to the optical fiber.
• the defects of homogeneity can be generated by all the treatments known to those skilled in the art, such as, in particular:
• Faults can be generated over the entire length of the optical fiber.
• Faults can be generated in localized areas of the optical fiber.
• the optical fiber may comprise diffusers distributed over the entire length of the optical fiber and arranged to reproduce backscattering and / or extinguishing effects generated by an inhomogeneous atmosphere on a beam emitted by a lidar.
• the defects can be distributed uniformly over the entire length of the optical fiber.
• the defects can be randomly distributed over the entire length of the optical fiber.
• the backscattering of the fractions of the at least part of the beam propagating in the optical fiber by the diffusers distributed along the optical fiber can also be defined as a volume backscattering generated by the diffusers.
• the volume backscattering generated by the diffusers can also be likened to a linear diffusion distributed over the length of the optical fiber.
• homogeneous atmosphere a slice of atmosphere in which the interactions of a given optical beam with said homogeneous atmosphere are substantially equivalent over the entire thickness of said atmosphere slice.
• the optical fiber may comprise diffusers located in one or more defined zones of the optical fiber, called diffusing zones, said diffusers being arranged in such a way that said diffusing zone or zones have adjustable backscattering and extinction coefficients so as to to reproduce backscattering and / or extinguishing effects caused by one or more types of atmospheric aerosols on a beam emitted by a lidar.
• the extinction coefficient can be defined as the sum of the absorption coefficient and the diffusion coefficient.
• a diffusing zone may comprise several diffusers located within said zone.
• Backscattering and extinguishing effects of diffusers located within scattering zones may be different from backscattering and extinguishing effects of diffusers distributed over the length of the optical fiber.
• At least a portion of the localized diffusers and / or at least a portion of the diffusers distributed over the entire length of the optical fiber may be intrinsic defects of the optical fiber.
• At least a portion of the localized diffusers and / or at least a portion of the diffusers distributed over the entire length of the optical fiber may be defects voluntarily provided to the optical fiber.
• At least one of the diffusers may have an optical backscattering coefficient and / or an optical extinction coefficient different from an optical backscattering coefficient and / or an optical extinction coefficient of at least one other of the diffusers.
• the diffusers may have an optical extinction coefficient and / or an identical optical backscattering coefficient.
• a diffuser may have an optical extinction coefficient and / or an optical backscattering coefficient different from an optical extinction coefficient and / or an optical backscattering coefficient of one or more other diffusers.
• Each diffuser may have an optical extinction coefficient and / or a different optical backscattering coefficient.
• At least one of the diffusers distributed along the optical fiber may have an optical extinction coefficient and / or an optical backscattering coefficient different from the optical backscattering coefficient and / or the optical extinction coefficient of at least one of the diffusers. located.
• the diffusers distributed along the optical fiber may have an optical extinction coefficient and / or an optical backscattering coefficient different from the optical backscattering coefficient and / or the optical extinction coefficient of all the localized diffusers.
• Diffusers distributed along the optical fiber may have an optical extinction coefficient and / or an identical optical backscattering coefficient.
• Diffusers located within the same scattering zone may have an optical extinction coefficient and / or an identical optical backscattering coefficient.
• Diffusers located within a scattering zone may have an optical extinction coefficient and / or an optical backscattering coefficient different from diffusers located within another diffusing zone.
• a scattering zone may have an optical extinction coefficient and / or an optical backscattering coefficient different from an optical extinction coefficient and / or an optical backscattering coefficient from another scattering zone.
• the processing unit can modulate the extinction coefficient (s) of one or more diffusing zones.
• the optical fiber may consist of a set of optical fibers having different characteristics.
• the characteristics of an optical fiber can be, among other things: the diameter of the heart,
• the coupling device may comprise an optical attenuator arranged to attenuate a power of an incident beam, said incident beam being defined as said at least part of the beam emitted by the lidar and coupled with the optical fiber.
• the optical attenuator may be any type of attenuator known to those skilled in the art, such as, in particular, a fixed attenuator.
• the optical attenuator may be any type of attenuator known to those skilled in the art, such as, in particular, a variable attenuator.
• the optical attenuator may be a device that defocuses or offsets the beam portions coupled in the fiber.
• the attenuator can also be defined as a neutral density optical filter, namely a filter which equally absorbs radiation in a given spectral range.
• the coupling system can be composed of an optical attenuator and an optical objective.
• the optical objective may be any type of objective known to those skilled in the art such as, in particular, a convergent mirror or a convergent lens.
• the device can comprise:
• a detector located downstream of the reflector element with respect to the direction of propagation of the incident beam, arranged to measure a power of a part of the incident beam not reflected by the reflector element, said device being characterized in that 'He understands : a processing unit configured to calculate the power of the incident beam.
• the power of the incident beam can be calculated from the power of the part of the beam not reflected by the reflector element.
• the power of the incident beam can be calculated from a transmission coefficient and / or a reflection coefficient of the reflective element.
• the power of the incident beam can be calculated from the power of the part of the beam not reflected by the reflector element and from a transmission coefficient and / or a reflection coefficient of the reflector element.
• the processing unit can be any type of technical calculation means known to those skilled in the art.
• the processing unit can be connected to the attenuator and / or the lidar, and configured to modulate a beam power emitted by the lidar and / or the power of the incident beam, by means of the attenuator, so that that beam characteristics backscattered by defects in homogeneity of the optical fiber, and characteristics of the at least one reflected beam are in the range of parameters of a lidar detection chain used in the case of outdoor atmospheric measurements .
• a backscattered beam can be defined as an optical signal returning to the lidar after reflection by inhomogeneities.
• the attenuator may preferably be a variable attenuator whose optical density is adjustable.
• the optical attenuator may comprise several attenuators, such as, in particular, a fixed attenuator and a variable attenuator.
• the processing unit can modulate the power of the beam emitted by the lidar, in particular, by means of a modulation of the power emitted by a LASER included in a transmission chain of the lidar.
• the device according to the invention may comprise a phase scrambling device arranged to generate variations of paths. in the optical fiber greater than a wavelength of the beam emitted by the lidar.
• the phase scrambling device may be arranged to modulate, in particular, the signal phase of at least one backscattered beam so as to average the coherence effects between the signals of the fractions of the at least part of the propagating signal. in the optical fiber and obtain a measurement equivalent to a signal backscattered by a dynamic atmosphere.
• the phase scrambling device can include:
• a mechanical system arranged to generate vibrations on all or part of the optical fiber, and / or
• thermal device for heating and / or cooling, non-homogeneous, of at least a part of the optical fiber, and / or
• a modulation of a frequency of the laser source of the lidar preferably between 1 kHz and 10 GHz.
• the modulation of the laser source frequency of the lidar can be between 1 kHz and 10 GHz, preferably between 10 kHz and 1 GHz, it can be defined by those skilled in the art as a fine modulation.
• the mechanical system may be, in particular, a vibrating device connected to the optical fiber and arranged to generate phase interference on all or part of the optical fiber.
• the scrambling device may comprise several mechanical systems and / or several thermal heating and / or cooling devices.
• the translational movement can be generated by the mechanical system in a random direction.
• the reflective element may consist of an output plane of the optical fiber, said output plane forming an angle with a plane perpendicular to an axis of revolution of the core of the optical fiber.
• the output plane of the optical fiber can be defined as the diopter located on the output side of the optical fiber.
• the angle can be generated by any suitable technique, such as, in particular, cleavage, polishing, etching, abrasion, filing.
• the optical fiber may have a length L such that the maximum distance measurable by the lidar is greater than L / n, where n is an effective index of the transverse mode of propagation of the optical fiber.
• the angle formed between the plane of exit of the optical fiber and a plane perpendicular to the axis of revolution of the core of the optical fiber may be between 0 and 80 °, preferably between 0 and 40 °, more preferably between 0 and 20 °.
• an atmospheric lidar in which is integrated a calibration device according to the first aspect of the invention, said calibration device being arranged to control, when the lidar is in operation, lidar calibration:
• the device can preferably be integrated into the lidar structure.
• the processing unit can be configured to alert a user if the parameters of the signal received by the lidar are drifting.
• a third aspect of the invention it is proposed a use of the calibration device according to the first aspect of the invention, for the implementation of a calibration method of an atmospheric lidar.
• the calibration method may be any method of calibration of a lidar known to those skilled in the art.
• a method of calibrating an atmospheric lidar characterized in that it comprises a calculation of calibration parameters of the lidar from, in addition, data from:
• the scattered fractions, by diffusers distributed over the entire length of the optical fiber, of the at least one beam propagating in the optical fiber may be backscattered fractions.
• the end of the optical fiber downstream from which the reflector element is located, with respect to the direction of the incident beam, can be defined as an output of the optical fiber.
• the other end of the optical fiber to which the beam, or part of the beam, emitted by the lidar is coupled with the optical fiber can be defined as an input of the optical fiber.
• the coupling step of the beam, or part of the beam, emitted by the lidar can be performed by a coupling device.
• the coupling step of a portion of the backscattered and attenuated fractions of the at least one beam propagating in the optical fiber with the lidar can be performed by the coupling device.
• the backscattering of the fractions of the at least part of the beam propagating in the optical fiber by the diffusers distributed along the Optical fiber can also be defined as a volume backscattering generated by the broadcasters.
• Diffusers distributed over the entire length of the optical fiber may comprise defects distributed randomly along the entire length of the optical fiber.
• the method of calibrating a lidar according to the invention can comprise:
• a parameter input of the lidar detection chain in technical means, equivalent to the parameters used for an external atmospheric measurement, and / or
• a parameter input of the lidar transmission chain in technical means, equivalent to the parameters used for an atmospheric measurement.
• the calibration parameters may be calculated from data from one or more signals of one or more fractions of the at least one beam propagating in the optical fiber diffused by one or more localized scattering zones comprising broadcasters; said at least one localized scattering zone has adjustable backscatter and extinction coefficients so as to reproduce backscattering and / or quenching effects caused by inhomogeneous atmospheric aerosols on a beam emitted by a lidar.
• the backscattering and / or quenching effects produced by the localized diffusers may be different from the backscattering and / or quenching effects produced by diffusers distributed over the entire length of the optical fiber.
• the data from the at least one signal of the at least one beam propagating in the optical fiber diffused can be associated, during the step of calculating the calibration parameters, with the data coming from the signal of the reflected by a reflective element in an optical fiber, the at least one beam propagating in said optical fiber and the data from the signals of the backscattered fractions, by diffusers distributed over the entire length of the optical fiber, the at least one beam propagating in the optical fiber.
• the calibration method according to the invention may comprise:
• the beams scattered by the defects of homogeneity of the optical fiber may be backscattered beams.
• the incident beam may be the only beam propagating along a direction connecting the input and the output of the optical fiber.
• Multiple beams may propagate in the direction connecting the input and output of the optical fiber when:
• the portion or portions of the beam emitted by the lidar and propagating in the at least one delay line are injected into the optical fiber, and / or
• the portion or portions of the beam emitted by the lidar and propagating in the at least one delay line are coupled with the optical fiber.
• the calibration method according to the invention may comprise a step of generating, by at least one scrambling device, at least one optical path variation in the optical fiber, said at least one optical path variation being greater than one wavelength of the beam emitted by the lidar.
• the at least one optical path variation can be generated by the scrambling system by:
• the calibration parameters calculated during the implementation of the calibration method according to the invention may comprise:
• the evaluation of the efficiency can be obtained by calculating a ratio between the power of the beams backscattered by the optical fiber and measured by the lidar and the power of the beam emitted by the lidar and coupled with the optical fiber.
• the echo lidar spread can be defined as the time duration during which a signal, or signals, corresponding to the beam, or beams, reflected is detected by the lidar detection chain.
• the calibration method according to the invention can be implemented concomitantly with an atmospheric measurement by deporting part of the beam emitted by the lidar to a calibration device, preferably a calibration device according to the first aspect of the invention. invention.
• the calibration method according to the invention can be implemented at a regular time interval, moreover during a time interval separating two consecutive atmospheric measurements, by deporting the beam emitted by the lidar to a calibration device, preferably a calibration device according to the first aspect of the invention.
• the calibration method when the calibration device is integrated in the lidar, may include a step of alerting the user in case of drift of the received signal.
• FIG. 1 is a schematic representation of a device for calibrating a lidar according to a first aspect of the invention
• FIGURE 2 is a schematic representation of a lidar calibration device according to a second aspect of the invention.
• FIGURES 3 and 4 are curves illustrating the characteristics of reflected and backscattered parts, coupled in a lidar detection channel, of a beam emitted by an emission channel of said lidar.
• variants of the invention comprising only a selection of characteristics described, isolated from the other characteristics described (even if this selection is isolated within a sentence including these other characteristics), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art.
• This selection comprises at least one feature, preferably functional without structural details, or with only a portion of the features. structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art.
• a calibration device 1 for an atmospheric lidar 2 comprising an optical fiber 3 arranged to propagate at least one part (not shown) of a beam
• the lidar 2 to be calibrated is a lidar whose emission and reception objectives are confounded, the skilled person qualifies such a monostatic configuration arrangement.
• the lidar 2 transmits in pulsed mode in the infrared at 1550 nm.
• the calibration device 1 also comprises a reflector element 6 located at one end of the optical fiber 3 and arranged to reflect in the optical fiber 3 a portion 7 of the at least part of the beam is propagating in the optical fiber 3.
• the at least part of the beam propagating in the optical fiber 3 corresponds, according to the particular embodiment, to the portion 4 of the beam 5 emitted by the lidar 2 coupled with the optical fiber.
• the at least one part 4 of the beam 5 emitted by the lidar 2 coupled with the optical fiber 3 is designated by the term incident beam 4.
• the reflective element 6 consists of a cleavage of the optical fiber 3, the output plane 11 of the optical fiber 3 after cleavage having an angle of 5 ° with a plane perpendicular to the axis of revolution of the core of the optical fiber 3
• the reflected portion 7 of the incident beam 4 propagating in the optical fiber 3 depends on the selected propagation mode. According to the embodiment, the signal of the reflected portion 7 is equivalent to 2% of the indicative beam 4 propagating in the optical fiber 3.
• the optical fiber 3 comprises diffusers (not shown) distributed along the optical fiber 3 and backscattering fractions of the incident beam 4 propagating in the optical fiber 3.
• the optical fiber 3 used is a commercial multimode optical fiber of core diameter. 100 pm.
• the optical fiber 3 has intrinsic defects distributed over the entire length of the optical fiber 3, said defects generating a uniform backscattering representative of that caused by a inhomogeneous atmosphere.
• the incident beam 4 propagating in the optical fiber 3 is backscattered 8, said backscattered beam 8 being constituted by all the backscattered fractions of the incident beam 4.
• the length of the optical fiber 3 is calculated so that the maximum distance measurable by the lidar 1 is greater than L / n, where L is the length of the optical fiber and n is the effective index of the transverse fundamental optical mode of the optical fiber 3. Its effective index is equal to 1.46.
• the length of the optical fiber 3 is 10 kilometers.
• the calibration device 1 also comprises a coupling device 9 arranged to couple:
• the at least one reflected beam 7 corresponds to the portion 7 of the incident beam 4 reflected by the reflector element 6.
• the coupling device 9 comprises an optical attenuator 10 and a convergent optical lens 12 focusing a portion 4 of the beam 5 emitted by the lidar 2 and couples with the lidar 2 a portion 81 of the signal of the backscattered beam 8 and a portion 71 of the reflected beam
• the optical attenuator 10 used is an optical filter 10 having an adjustable optical density.
• the calibration device 1 comprises, at the head of the optical fiber 3, a phase jamming device 13 for averaging, during the measurement, the interference related to the static position of the diffusers.
• the phase jamming device 13 is constituted by a vibratory pot (not shown) on which is mounted a portion of the optical fiber 3.
• the phase jamming device 13 modulates the coupling of the at least one part 4 of the beam 5 issued by lidar 2 with optical fiber 3 in different modes propagation and therefore the signal phase of the portions 81 of the backscattered beam 8 coupled with the lidar 2.
• the calibration device 1 also comprises a detector 14 located downstream of the output plane 11 of the optical fiber 3.
• the detector 14 is arranged to measure the signal power of the portion 15 of the incident beam 4 not reflected by the element reflector 6.
• the calibration device 1 comprises a processing unit 16 to which is connected the adjustable optical density optical filter 10 and the detector 14.
• the processing unit 16 is configured to calculate the power of the incident beam 4 from the power the signal of the portion 15 of the incident beam 4 not reflected by the reflector element 6.
• the processing unit 16 is also configured to measure the power of the incident beam 4 and to allow the optical density of the adjustable filter 10 to be modulated, in such a way that the portions 81 of the backscattered beam 8 and the portion 71 of the reflected beam 7 coupled with the lidar are in the range of the measurement parameters, or nominal measurement dynamic, of the detection chain.
• a variant of the first embodiment describes a calibration device 1 in which the optical fiber 3 further comprises diffusers located in two diffusing zones 17 of the optical fiber 3. All the elements of FIGURE 1 are present in FIGURE 2 and the references of said elements are identical in both FIGURES.
• Each of the two diffusing zones 17 comprises a plurality of diffusers.
• the scattering zones 17 have adjustable backscattering coefficients, the value of the backscattering coefficient of the scattering zones 17 has been adjusted so as to reproduce the extinction and backscattering effects commonly generated by atmospheric aerosols on a beam emitted by an atmospheric lidar .
• Each scattering zone 17 is arranged to generate a backscattering of an additional fraction 18 of the incident beam 4.
• FIGS. 3 and 4 show curves illustrating the characteristics of the reflected and backscattered portions 21,28, coupled in a detection channel of a lidar 2, of a beam emitted by an emission channel of said lidar 2.
• the data, from which the curves are plotted, are acquired through the detection chain of lidar 2.
• the power of the received signal 19 by the lidar is represented in logarithmic scale on the ordinate of the curve, said curve being plotted as a function of time 20.
• n effective index of the transverse fiber mode in which the beam propagates
• D the distance traveled by the beam in the optical fiber
• c is the speed of light in the vacuum.
• the abscissae 20 of the curve represent, by a factor, the propagation distance of the beam in the optical fiber and the propagation time of the beam in the optical fiber.
• a method of calibrating an atmospheric lidar 2 comprising a calculation of calibration parameters of the lidar from, in addition, data from a reflected portion 21 of the incident beam 4 propagating in the optical fiber 3.
• the portion 21 is a beam having reflected on a reflector element 6 in the optical fiber 3.
• This reflector element 6 is located at one end of the optical fiber 3 by in relation to a direction of the incident beam 4.
• Said incident beam 4 is defined as a beam, or part of a beam, emitted by the lidar 2 and coupled with the optical fiber 3 at another end of said optical fiber 3.
• the step of calculating the calibration parameters of a lidar of the atmospheric lidar calibration method according to the invention also comprises data coming from a signal 22 of a portion 81 of the backscattered beam 8, by diffusers distributed over the entire length of the optical fiber 3, coupled to lidar 2, said diffusers being arranged to reproduce backscattering and quenching effects generated by an inhomogeneous atmosphere on a beam emitted by a lidar 2.
• the method is implemented by means of a lidar 2 operating in pulse mode and the at least one beam is propagating in the optical fiber 3 corresponds to the signal 5 emitted by the lidar and coupled, by a bidirectional coupling device 9, to the optical fiber 3.
• the maximum power 23 of the signal 21 of the portion 71, of the reflected part 7 of the beam incident 4 propagating in the optical fiber 3, coupled with the lidar 2 is measured by the lidar 2.
• the energy 24 of the signal 21 is calculated from the data acquired by the lidar 2.
• the round trip delay 25 of the incident beam 4 propagating in the optical fiber 3 corresponds to the time elapsed between the emission by the lidar 2 of the beam 5, at a time t 0 26, and the detection by the lidar 2, at a time ti 27, of the part 7 reflected by the reflector element 6, the beam propagating in the optical fiber 3.
• the signal 21 of the portion 71, of the reflected portion 7 of the incident beam 4 propagating in the optical fiber 3, coupled with the lidar 2 is designated by echo lidar.
• FIGURE 4 there is described in a variant of the second embodiment, a calibration method in which the calibration parameters are calculated from the data of the second embodiment and additional data from the signals. 28 corresponding to the portions 181 of the backscattered fractions 18 coupled with the lidar 2.
• the calibration parameters comprise a calibration of the distance measurement from the characteristics of the signal 21 of the reflected beam 7 by the reflector element 6.
• This round-trip propagation time is identical to that obtained on an atmosphere wafer of thickness nD.
• the calibration parameters also include a calibration of the spatial resolution from characteristics of a time lag of the echo lidar 7.
• the distance resolution is computed by the spreading of the lidar response on the reflector element 6 located at the end of optical fiber 3, constituting a hard obstacle whose distance is identical for all the points of the beam 5 emitted by the lidar 2.
• the spatial resolution of the lidar is a depending on the pulse duration and the signal processing parameters.
• the calibration parameters also include a calibration of the speed measurement based on the spectral characteristics of the signals 28 of the backscattered fractions 18, 8 by the diffusers, of the incident beam 4 propagating in the optical fiber 3.
• the diffusers are at a high speed. zero in the optical fiber 3 unlike atmospheric aerosols. The measurement of zero velocity by the Doppler lidar is therefore direct and precise.
• the calibration parameters also include a calibration of the speed resolution, from a standard deviation of the speed measurement, said standard deviation being modulated:
• the calibration parameters also include an evaluation of the efficiency of the lidar by calculating a ratio between the power of the signals 22,28 of the backscattered beams 18,8 by the optical fiber 3 and measured by the lidar 2 and the power, calculated from the measurement made by the detector 14, the beam 5 emitted by the lidar 2 and coupled in the optical fiber 3.
• the processing unit 16 is also configured to modulate the extinction coefficients of the scattering zones 17.
• the various features, shapes, variants and embodiments of the invention may be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other.

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• 2017
  • 2017-11-17 FR FR1760842A patent/FR3073950B1/fr active Active
• 2018
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  • 2018-11-15 EP EP18812070.3A patent/EP3710861A1/de active Pending

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