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
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
  • G01P5/26—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave
• • 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
  • G01S17/50—Systems of measurement based on relative movement of target
  • G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
• • 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 a method and a device for detecting and measuring wind at the front of an aircraft.
• an aircraft reference system a spatial reference system linked to the aircraft, referred to as an aircraft reference system.
• this aircraft reference system is defined in the usual way by a longitudinal direction of the aircraft, a transverse direction of the aircraft and a third direction, orthogonal to the other two, which by convention is called the vertical direction although does not coincide - at least in flight - with the "vertical" of a terrestrial reference as provided by gravity.
• the "vertical" of the terrestrial reference is called the direction of gravity.
• wind refers to the total movement of air at a given point, which results from the superposition of the average air movement (laminar flow) and turbulence at that point.
• Turbulence is an agitation that is constituted by complex and disordered movements, in continual transformation.
• Turbulence has adverse effects on the aircraft. It can in particular induce: vertical accelerations of the aircraft likely to move objects or passengers in the cabin; a change in altitude levels, which may in particular lead to a risk of collision with another aircraft; an excess of loads on the wing; important moments of rolling; a feeling of discomfort in the cabin ...
• turbulence Because they increase the loads on the wing, the turbulence forces to reinforce the structure of the aircraft; they therefore have an impact on the mass of the latter. In addition, the turbulence tires the structure of the aircraft and can thus limit its life, or at least penalize its operational profitability by imposing frequent controls of the structure and equipment of the aircraft. Also and most importantly, turbulence is the number one cause of injury to passengers, excluding fatal accidents. The detection and measurement of turbulence, as well as the implementation of corresponding palliative actions, therefore represent important issues.
• lidars ascronym for "Light Detection And Ranging", which means light wave detection and telemetry
• a lidar is an active sensor comprising a laser emitting a directed incident light beam, a telescope which collects the wave backscattered by the particles encountered by the incident beam, and processing means.
• FR 2 870 942 teaches to use a only lidar with a scan in four directions (two vertical and two transverse). In the aircraft reference system, the measurement points targeted during this scanning are located on the same sphere centered on the lidar.
• this sweep forms a square in a plane located at the distance "d" at the front of the aircraft. If, moreover, the displacement of the aircraft during the scanning is neglected, the vector difference between the velocity vectors (which are parallel to the direction of the lidar sight) obtained at two measurement points -forming a pair of measuring points-of the scanning can be assimilated to the component, according to the direction connecting said measurement points, of the wind speed at a point of the atmosphere located (at the time of measurement) between these two measuring points. For example, a pair of measuring points located on the same vertical axis provides an assessment of the vertical component of the wind speed at the point between these two measurement points.
• a pair of measuring points located on the same transverse axis provides an evaluation of the transverse component of the wind speed at the point between these two measurement points.
• the device of FR 2 870 942 makes it possible to obtain an evaluation of the vertical component of the wind speed at one or more points situated at the distance "d" at the front of the aircraft, as well as an evaluation the transverse component of the wind speed at one or more points located at the distance "d” at the front of the aircraft.
• US Pat. No. 5,724,125 describes a method for determining the wind speed at a target location located at altitude Z. The wind speed at the target location is calculated from measurements made on a cone of scan and at target altitude Z; in other words, the measurement points are all located on the ellipse defined by the intersection between the scan cone and the target altitude Z.
• FR 2 883 983 describes a device comprising three or four lidars and for measuring wind speeds - according to the respective sighting direction of each lidar - at four measurement points located at the front of the aircraft, at a distance of same distance from the latter greater than 30 meters. Given the weight and size of a lidar, the use of such a device (which comprises three or four) is difficult to envisage especially in a passenger aircraft.
• calculated wind speeds are generally used to establish avoidance or control strategies.
• they are used for the determination of control commands transmitted to the actuators of various movable control surfaces (control surfaces, ailerons, nozzles, spoilers, flaps ...) of the aircraft.
• control surfaces are thus controlled so as to reduce the loads incurred by the aircraft and the resulting disturbances.
• the turbulence that the aircraft will actually encounter must be evaluated as accurately as possible.
• the known devices described above provide interesting information but whose accuracy and relevance may be considered insufficient.
• the invention aims to overcome these disadvantages by proposing a device and a wind detection and measurement method that make it possible to determine with greater precision the turbulence occurring in the front of an aircraft.
• the invention also aims to enable the risks of excitation of the aircraft or of a part thereof to be evaluated at a frequency corresponding to a rigid eigen mode or a flexible mode of its structure. .
• the invention relates to a wind detection and measurement device embedded in an aircraft, comprising a lidar for the cyclic measurement of wind speeds in at least a pair of measuring points located at the same distance, said distance measurement, the nose of the aircraft.
• the device according to the invention is characterized in that it is adapted to measure at each cycle, using said lidar, wind speeds in a plurality of pairs of measuring points located at different measurement distances, the difference between the largest measurement distance and the smallest measurement distance being greater than 100 meters.
• the invention extends to the detection and measurement method performed by the device according to the invention.
• the invention also relates to a wind detection and measurement method implemented in an aircraft, in which cyclic measurements, using a lidar, wind speeds in at least a couple of points of measured at the same distance, the so-called measuring distance, from the nose of the aircraft.
• the method according to the invention is characterized in that wind speeds are measured at each cycle by means of said lidar at a plurality of pairs of measuring points situated at different measurement distances, the difference between the distance the largest measurement and the smallest measurement distance being greater than 100 meters.
• the difference between the largest measurement distance and the smallest measurement distance is greater than 200 meters, preferably greater than 500 meters, or even greater than 800 meters.
• wind speeds of at least three, preferably at least six, measurement distances are measured at each cycle, and the device according to the invention is adapted for this purpose.
• the measurement of the wind at different distances from the nose of the aircraft and over a measurement interval greater than at least 100 meters makes it possible to gain considerably in precision. Indeed, we know that the precision of a lidar decreases with distance. Thanks to the invention, the measurement of the wind at a location initially located at a great distance from the aircraft can be refined as the aircraft approaches this location. In addition, the prior devices all assume that the wind is stationary over the duration d / V (where "d" is the sighting distance of the lidar and V the speed of movement of the aircraft). This hypothesis is further removed from reality because the distance "d" is large and / or the turbulence is important. The device according to the invention makes it possible to obtain a plurality of measurements at the same given location of the atmosphere as the aircraft moves.
• location here means a point of the atmosphere (defined in a reference not linked to the aircraft, for example a terrestrial reference, unlike the measurement points that are defined in the aircraft reference) or a zone of limited size around a point of the atmosphere, the various successive measurements taking place precisely at this point or in the immediate vicinity thereof.
• the device according to the invention thus makes it possible to take into account the variations of the wind, at a given location, which occur between the first measurement made at this location and the moment when the aircraft arrives at said location.
• the device according to the invention is adapted to construct at each cycle at least one signal, said wind profile signal in a direction said direction of excitation, from a plurality of measurements including the last or optionally the penultimate measurement made at each of the measurement distances for at least a pair of measurement points aligned in the direction of excitation, said wind profile signal representing at a given moment in an aircraft reference system the component, according to said direction of excitation, the wind speed at the front of the aircraft as a function of the distance "x" in the longitudinal direction (this distance being expressed relative to the nose of the aircraft).
• at least one wind profile signal as previously defined is advantageously constructed at each cycle.
• the device according to the invention is adapted to construct:
• a wind profile signal in the vertical direction in a median vertical longitudinal plane (plane of symmetry) of the aircraft said signal representing at a given moment the vertical component of the wind speed in this median plane; it is established from measurements of wind speed in a pair of measurement points belonging to said median plane, at each measurement distance for which such a pair is acquired,
• At least one wind profile signal in the vertical direction in a port plane of the aircraft said signal representing at a given moment the vertical component of the wind speed in a vertical plane facing the port wing of the aircraft; aircraft; it is established from measurements of wind speed in a pair of measuring points belonging to said port plane, at each measurement distance for which such a pair is acquired,
• At least one wind profile signal in the vertical direction in a starboard plane of the aircraft said signal representing at a given moment the vertical component of the wind speed in a vertical plane facing the starboard wing of the aircraft. aircraft; it is established from measurements of wind speed in a pair of measuring points belonging to said starboard plane, at each measurement distance for which such a pair is acquired, - at least one wind profile signal in the transverse direction, representing at a given moment the transverse component of the wind speed in a plane, called a horizontal plane, orthogonal to the vertical direction; this signal is established from measurements of wind speed in a pair of measurement points belonging to said horizontal plane, at each measurement distance for which such a pair is acquired.
• the device according to the invention is also preferably adapted to process this wind profile signal so as to determine a frequency content.
• the frequency, at a given distance x, of such a wind profile signal is representative of the frequency at which the aircraft will be excited according to the direction of excitation (of said profile) when it reaches the position of the wind. atmosphere corresponding to this given distance x.
• the determination of the frequency content of this signal therefore makes it possible to estimate the frequencies at which the aircraft is likely to be excited as it moves.
• this information which no prior known device is able to provide, is extremely useful in the choice of control surfaces to actuate and corresponding actuation parameters.
• the wind detection and measurement device is adapted to process a wind profile signal so as to determine whether it or a part thereof comprises at least one frequency included in at least one predefined frequency range.
• the device is adapted to: - treat the wind profile signal so as to determine whether it or a part thereof comprises at least a frequency close to a rigid eigenmode of the aircraft.
• the device in the case of a wind profile signal in the vertical direction, is advantageously adapted to process said signal so as to determine whether it or a part thereof comprises at least a frequency close to a rigid eigenmode of the aircraft known as incidence oscillation frequency; the treatment is thus advantageously adapted to make it possible to determine whether the wind profile signal comprises at least one frequency less than 0.5 Hz (the incidence oscillation frequency of an aircraft being generally of the order of 0.2 Hz at 0.4Hz);
• processing the wind profile signal so as to determine whether it or a part thereof comprises at least a frequency close to a flexible eigen mode of the aircraft and in particular of its wing, its fuselage or its empennages (vertical and horizontal).
• a frequency close to a flexible eigen mode of the aircraft and in particular of its wing, its fuselage or its empennages vertical and horizontal.
• the treatment is advantageously adapted to make it possible to determine whether a part of the wind profile signal corresponding to the range of distances [0; 400m] or [0; 2s] has at least one frequency greater than 0.5 Hz.
• the treatment is advantageously adapted to make it possible to determine whether a part of the profile signal wind in the vertical direction corresponding to the range of distances [0; 200m] or [0; 1s] -or optionally [200m; 400m] or [1s; 2s] - comprises at least one frequency greater than or equal to 1 Hz.
• the treatment is advantageously adapted to make it possible to determine whether a part of the signal of wind profile in the vertical direction corresponding to the range of distances [0; 200m] or [0; 1s] - even [0; 100m] or [0; 0.5s] or [100m; 200m] or [0.5s; 1s] - comprises at least one frequency greater than or equal to 2.5 Hz (or even greater than or equal to 3 Hz depending on the aircraft).
• the power of a lidar usually determines its range of sight.
• the lidar of the device according to the invention is therefore preferably chosen as a function of the desired maximum measurement distance. However, if this maximum distance is very large, it is also possible to use a lidar power less than that required and able to compensate for its lack of power by delivering incident light pulses grouped by packet. This limits the on-board power required for the operation of the device according to the invention.
• the device according to the invention is suitable for measuring wind speeds at a plurality of measurement points located on the same direction of view, at different measurement distances, from the same incident light pulse or of the same packet of incident light pulses grouped.
• its lidar comprises for example a telescope equipped with a shutter controlled so as to be able to open successively at different times corresponding to the different measurement distances after each incident light pulse or each delivered packet.
• the device according to the invention can be adapted to acquire, from one and the same incident light pulse or from the same group of grouped pulses, all measurement points located on the same sighting distance or only a part of these measuring points.
• the device is also adapted to deliver several incident light pulses or several packets of pulses grouped for each direction of sight.
• This preferred version does not exclude the possibility of providing a wind detection and measurement device adapted to deliver an incident light pulse (or possibly a group of pulsed pulses) for each measurement point.
• the device preferably has a variable power and means for adjusting the power, at each incident light pulse delivered, depending on the measurement distance of the corresponding measurement point.
• a fixed power lidar preferably chosen as a function of the maximum measurement distance, which has the advantage of reducing the measurement error for small measurement distances - that is, say when getting closer to the aircraft-.
• the device according to the invention is adapted to make it possible to define each measurement distance not only in unit of length, for example in meters or feet, but also in units of time, preferably in seconds.
• it advantageously comprises calculation means able to calculate the distance (expressed in unit length) between the lidar and each measurement point, from the measurement distance expressed in time and data representative of the speed of measurement.
• flight of the aircraft provided in real time by a processing unit of the aircraft.
• These calculation means may be integrated in said processing unit of the aircraft or in a processing unit specific to lidar.
• the device according to the invention is suitable for measuring wind speeds up to measurement distances of up to 4 seconds or 800 meters, or even 5 seconds or 1000 meters, or possibly even 7 seconds or 1400 meters.
• the maximum measurement distance of the device according to the invention is chosen as a function of the smallest frequency that one wishes to detect.
• the device according to the invention is adapted for measuring wind speeds in at least six measuring points at each measurement distance, which points form, at each measurement distance, three pairs, called vertical pairs, of measuring points aligned in the vertical direction and at least one pair, said transverse torque, measuring points aligned in the transverse direction.
• the device according to the invention is suitable for measuring wind speeds in at least ten measurement points forming five vertical pairs of measuring points.
• the device according to the invention is adapted to measure wind speeds at least a measurement distance close to the aircraft, for example less than 250ms or 50m and preferably less than 150ms or 30m, in order to offer an alternative device to the anemometer of the aircraft.
• the device according to the invention is suitable for measuring wind speeds at measurement distances that are closer and closer to each other in the direction of the aircraft, or that are more and more distant from each other at the same time. as one moves away from the aircraft.
• ⁇ x advantageously increases with x. For example, ⁇ x grows exponentially.
• the wind detection and measurement device is connected to a processing unit of the aircraft itself connected to sensors of the aircraft chosen from: an inertial unit able to measure the vertical speed Vz of the aircraft with respect to the ground, the angle ⁇ of inclination of the wings of the aircraft relative to the horizontal, the attitude ⁇ of the aircraft and its pitching speed q; an airspeed sensor, usually used to measure the speed Vtas of the aircraft relative to the air mass in which the aircraft operates; an incidence probe, usually used to measure the angle of incidence ⁇ of the aircraft; a skid probe, usually used to measure the skid angle ⁇ of the aircraft.
• the device according to the invention and one or more of the aforementioned sensors can then advantageously be used to hybridize the signal in order to improve the accuracy of the measurement.
• FIG. 1 is a diagrammatic perspective view of an aircraft and of the environment at the front thereof, on which measurement points targeted by a device according to the invention are shown,
• FIG. 2 is a diagram showing a wind profile signal constructed using a device according to the invention.
• the aircraft illustrated in FIG. 1 is equipped with a wind detection and measurement device which, according to the invention, comprises a lidar and is adapted to measure wind speeds at a plurality of pairs of measuring points located at different distances, called measurement distances, from the nose of the aircraft.
• this device comprises a single lidar and therefore has a limited weight and bulk.
• this lidar comprises a laser capable of emitting incident light pulses directed, separated or grouped in packets, a telescope which collects the wave backscattered by the particles encountered by the incident beam.
• the device according to the invention further comprises computer processing means (software and hardware) microprocessor (s).
• the telescope and the processing means are advantageously adapted to collect, at each incident light pulse or at each packet of group pulses emitted by the laser, the backscattered wave at different times t n from the moment the pulse is transmitted.
• the distance ⁇ x between two consecutive measurement distances increases with x, for example exponentially.
• the laser advantageously has a wavelength located in the ultraviolet, which offers a good resolution. It also has a power adapted to measure wind speeds at a maximum measurement distance between 500m and 1500m, for example of the order of 1000m or 5s. However, it may have a lower power and in this case deliver incident light pulses grouped in packets, in order to compensate for a power that is a priori insufficient (for long distances measurement).
• the device according to the invention furthermore comprises means for adjusting the aiming direction of its lidar, making it possible to modify the aiming direction between two transmitted incident light pulses (or between two packets).
• the device is programmed to emit incident light pulses along twelve viewing directions. In other words, at least for certain measuring distances X n , the device is able to measure wind speeds in twelve measuring points 1 to 12.
• the measuring points located at the same measurement distance belong to the same sphere centered on the lidar in the aircraft reference system.
• FIG. 1 By approximation, they are represented in FIG. 1 as belonging to the same plane, called the measuring plane, orthogonal to the longitudinal direction L of the aircraft and located at a distance from the nose of the aircraft equal to the measurement distance.
• the measuring plane orthogonal to the longitudinal direction L of the aircraft and located at a distance from the nose of the aircraft equal to the measurement distance.
• the measurement points 1 and 11 form a vertical pair of measuring points providing, by vectorial difference of the speeds measured at these points, an evaluation of the vertical component W Z A of the wind speed at a point in the atmosphere located facing the longitudinal direction of a central or distal portion (that is to say close to the end) of the starboard wing of the aircraft,
• the measurement points 2 and 10 form a vertical pair of measuring points providing, by vectorial difference, an evaluation of the vertical component W Z B of the wind speed at a location in the opposite atmosphere - according to the direction longitudinal-a proximal portion (that is to say close to the root) or central portion of the starboard wing of the aircraft,
• the measurement points 3 and 9 form a vertical pair of measuring points providing, by vectorial difference, an evaluation of the vertical component W z c of the wind speed at a point in the atmosphere situated on a central longitudinal axis of the aircraft, that is to say facing the longitudinal direction of the nose and the fuselage of the aircraft,
• the measuring points 4 and 8 form a vertical pair of measuring points providing, by vectorial difference, an evaluation of the vertical component W Z D of the wind speed at a location of the atmosphere located opposite the longitudinal direction of a proximal portion (ie - say close to the root) or central port wing of the aircraft
• the measuring points 5 and 7 form a vertical pair of measuring points providing, by vector difference, an evaluation of the vertical component W Z E of the wind speed at a location in the atmosphere opposite - in the longitudinal direction - a central or distal portion (that is, near the tip) of the port wing of the aircraft
• measuring points 1 and 5 form a transverse pair of measuring points providing, by vectorial difference, an evaluation of the transverse component W t A of the wind speed in one place of the atmosphere located in a vertical longitudinal plane year (plane of symmetry) of the aircraft, above the central longitudinal axis of the aircraft,
• the measurement points 6 and 12 form a transverse pair of measuring points providing, by vectorial difference, an evaluation of the transverse component W t B of the wind speed at a location of the atmosphere situated on the central longitudinal axis of the aircraft, that is to say, facing the nose and the fuselage of the aircraft,
• the measurement points 11 and 7, or the measuring points 10 and 8 form a transverse pair of measuring points providing, by vectorial difference, an evaluation of the transverse component W t c of the wind speed at a location of the atmosphere located in the median vertical longitudinal plane of the aircraft, below the central longitudinal axis of the aircraft.
• each series of measurement points comprises at least four measurement points distributed over the range of distances [0; 200m] or [0; 1s] and at least three other measuring points distributed over the range of distances [200m; 1000m] or [1s; 5s].
• the number of measurement points per series and their distribution may vary from one series to one other.
• the series of measurement points 3 and 9, which provide evaluations of the vertical component W 2 C of the wind speed opposite the fuselage of the aircraft, advantageously comprise a relatively large number of measurement points, of which at least eight (and preferably at least 16) measuring points distributed over the range of distances [0; 200m] or [0; 1s] and at least six (and preferably at least twelve) other measuring points distributed over the range of distances [200m; 1000m] or [1s; 5s].
• the series of measuring points 2, 10, 4 and 8 for example may comprise a smaller number of measuring points, in particular in the range of distances [200m; 1000m] or [1s; 5s].
• the device preferably operates as follows.
• a first light pulse is emitted in the first direction of view passing through the measuring points 1; this pulse makes it possible to acquire the frequency of the backscattered wave at the measurement point 1 for each measurement distance (of the series), and thus to measure the wind speed according to the first direction of sight at each measuring point 1.
• the adjustment means are then actuated to change the aiming direction of the lidar, so that it points to the measuring points 2.
• a second light pulse is then emitted in the second direction of view (passing through the measuring points 2); this pulse makes it possible to acquire the frequency of the backscattered wave for the series of measurement points 2, and thus to measure the wind speed according to the second direction of sight for each of said measurement points 2.
• the adjustment means are then actuated to change the sighting direction of the lidar, so that it points to the measuring points 3, then a third light pulse is emitted according to this new -third-direction of sight, and so on for all the sighting directions.
• the acquisition of measurements for the twelve series of measurement points constitutes a measurement cycle, which is repeated indefinitely iteratively.
• the device according to the invention is advantageously adapted to perform a complete measurement cycle in less than 60ms.
• the wind sensor and wind measurement processing means calculate, by vector difference, the vertical component W Z A of the wind speed in each measurement plane from the measured speeds for measuring points 1 and 11 of said plane of measured.
• the vertical component W 2 B of the wind speed in each measurement plane is calculated analogously from the speeds measured for the measuring points 2 and 10 of said measurement plane, and so on for all the vertical components.
• the processing means also calculate, by vector difference, the transverse component W t A of the wind speed in each measurement plane from the speeds measured for the measuring points 1 and 5 (or 2 and 4) of said measurement plane , as well as the transverse component W t B - respectively W t c - of the wind speed in each measurement plane from the speeds measured for the measurement points 12 and 6 - respectively 11 and 7 (or 10 and 8) - of said measurement plan.
• the means for processing the wind detection and measurement device may optionally calculate wind speed components from measured speeds for different measurement cycles (successive or otherwise) and / or for points measured at different measurement distances (consecutive or not), in order to take into account the distance traveled by the aircraft in the terrestrial reference system during a measurement cycle.
• the processing means can be programmed to calculate the vertical component W Z A of the wind speed at a distance Xj for the cycle j from, on the one hand, of the speed measured for the measuring point 11 on the distance Xj for the cycle j-1, and secondly from the speed measured for the measuring point 1 to the distance Xj for the cycle j (provided that the direction of "rotation" of the measuring cycle is the one described more high).
• the processing means can be programmed to calculate the vertical component W z c of the wind speed at a distance Xj for the cycle j from, on the one hand, the speed measured for the measuring point 3 to the distance Xj + i for the cycle j-1, and on the other hand the speed measured for the point of measure 9 at the distance Xj for the cycle j.
• Each wind profile signal represents at a given instant the component in a direction of excitation (vertical or transverse) of the wind speed at the front of the aircraft as a function of the distance x.
• the set of components W z c calculated for the different measurement distances and for the same measurement cycle is used to construct a wind profile signal in the vertical direction in the median plane of the aircraft.
• FIG. 2 illustrates this signal which, in the example, is a continuous signal (which may however be in steps) obtained by interpolation from the calculated components W z c . This signal makes it possible to predict the pitching excitations of the aircraft.
• the set of components W Z B calculated for the different measurement distances and for the same measurement cycle can be used to construct a wind profile signal in the vertical direction in a starboard plane of the aircraft.
• the set of components W Z D calculated for the different measurement distances and for the same measurement cycle can be used to construct a wind profile signal in the vertical direction in a port plane of the aircraft.
• the other calculated velocity components can be used in a similar way to construct other wind profile signals if necessary, or to refine the previous signals in certain situations.
• Each wind profile signal thus constructed characterizes the atmospheric environment of the aircraft at a given moment and is updated continuously at least every 60 ms (duration of a measurement cycle).
• the processing means of the device according to the invention are also advantageously adapted to process at least one wind profile signal, and for example the wind profile signal W z c , so as to determine a frequency content.
• the treatments applied to determine this frequency content depend on the frequencies sought and therefore on the excitation direction concerned, that is to say on the profile of the wind profile analyzed.
• the following description relates to the signal W z c (direction of vertical excitation, wind in the median plane of the aircraft).
• This wind profile signal W z c makes it possible, in particular, to detect whether pitching phenomena of the aircraft (which generate great discomfort for persons) are likely to occur.
• the processing means are adapted to look for whether the wind profile signal W z c comprises at least one frequency close to the incidence oscillation frequency of the aircraft.
• Such an incidence oscillation frequency is generally of the order of 0.3 Hz.
• the lidar preferably has a maximum sighting distance of some 5s or 1000m, and on the other hand at least four and preferably at least eight measuring points are provided over the range of distances. [0; 5s] or [0; 1000m] or, for the reasons given below, over the range of distances [1s; 5s] or [200m; 100Om].
• the pitching phenomena are advantageously countered using one or more mobile control surfaces of the tail of the aircraft.
• Such moving surfaces have an indirect effect on the loads experienced by the fuselage and wing of the aircraft. It is therefore preferable to detect the corresponding turbulence as soon as possible, that is to say at a great distance from the nose of the aircraft. Therefore, the part of the wind profile signal corresponding to the range of distances [1s; 5s] or [200m; 100Om].
• the processing means advantageously process the whole of the signal W z c or the above-mentioned signal part so as to determine whether the latter or this comprises frequencies lower than 0.5 Hz.
• the wind profile signal W z c also makes it possible to detect the presence of turbulence likely to endanger the structure of the aircraft, and in particular its wing.
• the processing means of the device according to the invention are advantageously adapted to investigate whether the wind profile signal W z c comprises at least a frequency close to a natural mode of oscillation in bending of the wing.
• the first natural bending mode of the wing of an aircraft is generally between 1.1 Hz and 1.5 Hz. To observe such a frequency, it suffices to analyze the wind profile signal over a period of 0.67s to 1s.
• the effects of such turbulence are advantageously countered using one or more movable wing control surfaces.
• the processing means therefore preferably treat the part of the wind profile signal W z c corresponding to the range of distances [0; 1s] or [0; 200m] so as to determine if it has frequencies greater than 1 Hz.
• the processing means are advantageously adapted to process the part of the wind profile signal corresponding to the range of distances [0; 2s] or [0; 400m] so as to determine if it has frequencies greater than 0.5Hz.
• the processing means comprise at least one low-pass filter and at least one high-pass filter.
• the low-pass filter makes it possible to attenuate or even eliminate the high frequencies and thus to detect the low frequencies; the high-pass filter allows reverse to detect high frequencies.
• Said filters are chosen according to the desired frequency ranges. In the example, it is advantageous to use firstly a low-pass filter whose cutoff frequency (frequency above which the frequencies are attenuated or eliminated) is equal to 0.5Hz, and secondly a high-pass filter whose cutoff frequency (frequency below which the frequencies are attenuated or eliminated) is substantially equal to 0.5 Hz or 1 Hz.
• the processing means are adapted to evaluate an average period of the wind profile signal on the part of signal to be processed (that is to say on the interval [0; 400m] or [ 0; 2s], or the interval [0; 200m] or [0; 1s], or the whole of the signal, depending on the desired frequency range), as a function of the number of passages of said signal by the value zero on this part .
• the inverse of this average period thus evaluated provides an average frequency of the signal on the treated part.
• the processing means are adapted to estimate an average standard deviation of the wind profile signal on the part of the signal to be processed, based on the maximum amplitude of the signal on this part and a coefficient constant predetermined empirically and statistically, which coefficient represents the average ratio between the standard deviation and the maximum amplitude of a wind profile signal. They are also adapted to compare the estimated standard deviation with a range of standard deviations corresponding to the desired frequency range, which range of standard deviations is previously determined by integrating a part of a Von Karman spectrum. or Kolmogorov, which represents a density of energy as a function of spatial frequency and is empirically and statistically predefined.
• the processing means may be adapted to similarly process other wind profile signals.
• the invention may be subject to numerous variations with respect to the illustrated embodiment, provided that these variants fall within the scope delimited by the claims.

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