Measuring wind speed using one or more lidar systems

Abstract

Disclosed is a method for measuring wind speed using one or more LIDAR systems (1) located on board a carrier (10), which combines two Doppler-effect measurements taken successively while aiming at the same target location (Z), which is transversely offset with respect to a path (T) of the carrier. The method enables two-dimensional evaluation of wind speed at the target location, with an improved evaluation reliability. It is thus possible to obtain evaluations of vertical and horizontal components of the wind speed ahead of an aeroplane.

Description

Description Title: MEASUREMENT OF WIND SPEED USING ONE OR MORE LIDAR SYSTEMS Technical field

[0001] This description relates to a method for measuring wind speed using one or more LIDAR systems. It also relates to equipment which comprises the LIDAR system(s) used as well as an aircraft on board which this equipment is carried. Prior art

[0002] FR 2 942 043 describes a system and method for detecting and determining atmospheric anomalies remotely.

[0003] FR 2 938 075 describes a device and method for detecting and measuring wind for aircraft.

[0004] Remotely measuring wind speed, and consequently characterizing atmospheric turbulence that is likely to be present in specific areas, is useful for many applications. Such measurements are particularly sought after in the field of air transport, in particular to detect the presence of air flows that have speed components perpendicular to a nominal direction of movement of an aircraft. Indeed, the presence of a wind speed component that is vertical and / or a horizontal wind speed component that is transverse to a front-rear direction of an aircraft can cause risks during the cruising flight phase or during landing of the aircraft. Remote measurement of such wind speed components is also sought to reduce the load that exists on the wings of an aircraft.Other applications that are of interest in such remote wind speed measurements include meteorological applications, the control of stratospheric platform stations (HAPS), the control of drones flying in areas of atmospheric turbulence, the monitoring of airflow around a moving vehicle such as a truck, etc.

[0005] It is known to use LIDAR systems, for "Light-Detection And Ranging" in English or systems for detecting and measuring distances by light, to carry out air velocity measurements. Such measurements are based on Mie backscattering which is produced by particles present in suspension in the air, such as aerosols, dust or ice grains, and / or on Rayleigh backscattering which is produced by molecules in the composition of the air. However, velocity measurements which are carried out using a LIDAR system are limited to measurements of the velocity component which is parallel to the line of sight of the LIDAR system.

[0006] However, for many applications, the velocity components whose measurements are most useful are those that are perpendicular to a direction of separation between the instantaneous position of the LIDAR system and the location in the atmosphere concerned by the measurement. Thus, the lateral and vertical components of wind speed that exist at a distance in front of the nose of an aircraft in flight are particularly sought. A first method for this could consist of placing several LIDAR systems on board the aircraft, which are offset from the front-rear centerline of the aircraft and whose lines of sight are directed obliquely towards an area in front of the nose of the aircraft. But such an installation of several LIDAR systems on board an aircraft outside its front-rear centerline is very difficult, if not impossible, due to the lack of locations available for such a multiple installation.A second method, as described for example in the article entitled "Gust load alleviation for a long-range aircraft with and without anticipation", by N. Fezans et al., CEAS Aeronautical Journal (2019), 10: 1033-1057, Springer, consists of installing a single LIDAR system in the nose of the aircraft, directing its line of sight obliquely to the front-rear centerline of the aircraft according to several azimuth and elevation values, and performing several measurements which are thus angularly distributed around this axis. A velocity component value perpendicular to the front-rear centerline of the aircraft is then deduced from these multiple measurements. But a significant error can affect the result thus obtained when the air velocity field is not uniform, because the multiple measurements used are relative to different locations, and therefore to wind speeds which are a priori different.Finally, a third method consists of carrying out successive measurements along a constant line of sight direction, oblique to the axis. median front-rear axis of the aircraft, during the movement of the aircraft in flight, to group together several such measurements which are therefore carried out according to different lines of sight but which concern places located in a plane which is fixed in the terrestrial reference frame and perpendicular to the median front-rear axis of the aircraft, then to extrapolate to the point of intersection between this axis and the plane of the reconstructed values ​​of perpendicular component of airspeed. But this third method does not seem to provide reliable results either, in particular because it also uses measurements which are relative to different places in space. Technical problem

[0007] From this situation, an aim of the present invention is to provide an evaluation of an air velocity component which is oriented perpendicular to the movement of a LIDAR system carrier, with improved reliability compared to the methods of the prior art.

[0008] An additional aim of the invention is to be able to be easily implemented on board an aircraft to deliver evaluations of airspeed components which are perpendicular to the movement of the aircraft. Summary of the invention

[0009] To achieve at least one of these aims or another, a first aspect of the invention proposes a new method for measuring a wind speed using at least one LIDAR system which is on board a carrier, the measurement relating to at least two components of this wind speed as it exists at a location external to the carrier, called the target location. This method of the invention firstly comprises the following two steps: / 1 / at a first instant during a movement of the carrier, carry out a first measurement by directing a line of sight of the LIDAR system towards the target location, the line of sight then being parallel to a first axis, and by deducing from this first measurement, by means of a Doppler effect characterization, an estimate of a projection on the first axis, of the wind speed which exists at the target location; then 121 at a second instant during the movement of the carrier, perform a second wind speed measurement using the same LIDAR system as in step / 1 / or another LIDAR system that is also on board the carrier.

[0010] According to the invention, for the second measurement of the wind speed which is carried out in step 121, the line of sight of the LIDAR system which is used in step 121 is again directed towards the target location, but being parallel to a second axis which is angularly offset from the first axis, this second measurement being used to deduce therefrom, by means of the Doppler effect characterization, an estimate of a projection on the second axis, of the wind speed which exists at the target location.

[0011] The method of the invention then further comprises the following additional step: 131 deducing, from the estimates of the projections of the wind speed on the first and second axes, as obtained in steps / 1 / and 121, a two-dimensional estimate of this wind speed which exists at the target location, this two-dimensional estimate being parallel to a plane which contains the first and second axes.

[0012] The method of the invention has improved reliability, since the first and second measurements both relate to the same location external to the wearer, at which the wind speed is to be determined. In other words, the two-dimensional wind speed estimate obtained by steps / 1 / to 131 is not disturbed by spatial inhomogeneities that the wind speed field may have.

[0013] Since both measurements are performed while the line of sight of the LIDAR system used for each measurement is successively parallel to two axes that are angularly offset from each other, two components of the wind speed can be determined, which are parallel to the plane of the two axes. For this reason, the estimate of the wind speed that exists at the target location, as provided by the method of the invention, is said to be two-dimensional.

[0014] Generally, the measurements that are carried out in steps / 1 / and 121 may be carried out using two separate LIDAR systems that are on board the carrier, or by using the same LIDAR system. When two LIDAR systems are used, they are preferably located at the same location on board the carrier, or at respective locations on the carrier that are close or very close, relative to the distance that exists between the carrier and the target location. Thanks to such proximity on board the carrier, the installation of the two LIDAR systems, or more than two LIDAR systems where appropriate, to implement the method of the invention, is facilitated, in particular when the carrier is an aircraft. For example, all the LIDAR systems used can be installed in the nose or cockpit of an aircraft. However, since the first and second measurements are carried out at two different times during the movement of the carrier, the same LIDAR system can be used for both measurements of steps Z1Z and 121. By the same LIDAR system, it is meant that the radiation which is emitted to carry out each of the two measurements comes from the same laser source and is transmitted by the same optical path inside the LIDAR system. Thanks to this use of a single LIDAR system, the means which are necessary to implement the method of the invention can be reduced in size and weight.

[0015] Generally for the invention, a separation time between the two measurements can be adjusted or determined as a function of a speed of movement of the wearer, of the angular differences which exist between a direction of movement of the wearer and each of the first and second axes, and possibly also as a function of a distance of the target location from the wearer at one and / or the other of the first and second instants.

[0016] In preferred embodiments of the invention, at least one of the following additional features may be optionally reproduced, alone or in combination of several of them: - a separate LIDAR system may be used for each orientation of the line of sight, i.e., a first LIDAR system may be used for each measurement that is made with the line of sight parallel to the first axis, and a second LIDAR system may be used for each other measurement that is made with the line of sight parallel to the second axis. When additional measurements are made, while the line of sight is parallel to additional axes, an additional LIDAR system may be used for each additional axis; - the first and second axes can form between them an angle which is greater than 10° (degree), preferably less than 45°, in particular to provide sufficient precision to the two-dimensional estimation which is obtained for the wind speed; - the carrier may be an aircraft, in which case the movement of the carrier is a movement of the aircraft in flight; - when the movement of the carrier is rectilinear or locally rectilinear, the target location may be offset relative to a trajectory of the carrier in accordance with a transverse offset value, and the duration between the first and second instants may be selected as a function of this transverse offset value and the speed of movement of the carrier. In this case in particular, the transverse offset value may be between 10 m (meter) and 200 m; and - the first axis and the trajectory of the carrier can form an angle which is between 10° and 30°, and the second axis and the trajectory of the carrier can form another angle between them which is between 20° and 60°.

[0017] According to a first improvement of the invention usable when the movement of the carrier is rectilinear or locally rectilinear, steps / 1 / to 131 are executed for the target location and repeated for another target location which is symmetrical to the first with respect to the trajectory of the carrier, so as to separately obtain two two-dimensional estimates of wind speed, one for the target location and one for the so-called other target location. Then, a two-dimensional estimate to be attributed to a point of the trajectory of the carrier can be calculated as an average of the two-dimensional estimates relating respectively to the target location and to the other target location, the point being at an intersection of the trajectory of the carrier with a rectilinear segment which connects the target location and the other target location.Thus, the method of the invention can provide an evaluation of the air velocity component which is perpendicular to the trajectory of the carrier, while being compatible with an installation of the LIDAR system(s) on board the carrier at a front-rear median axis of this carrier.

[0018] When at least two LIDAR systems are used with this first improvement, the executions of step / 1 / for the target location and the other target location can be simultaneous, each being carried out with a dedicated LIDAR system. Similarly, the executions of step 121 for the target location and the other target location can also be simultaneous, when they are carried out in the same way using two LIDAR systems.

[0019] According to a second improvement of the invention which can also be used when the movement of the carrier is rectilinear or locally rectilinear, steps / 1 / to 131 can be executed separately for two target locations located in two respective measurement planes which each contain the trajectory of the carrier but which are angularly offset from each other around this trajectory, so as to provide two-dimensional estimates relating one to one to each target location. Advantageously, the two measurement planes can be perpendicular to each other around the trajectory of the carrier. For example, this can be a vertical plane and a horizontal plane.

[0020] When at least two LIDAR systems are used with this second improvement, the executions of step / 1 / for each measurement plane can be simultaneous, each being carried out with a LIDAR system dedicated to the measurement plane. Similarly, the executions of step 121 for each measurement plane can also be simultaneous, when they are carried out in the same way using two LIDAR systems.

[0021] Furthermore, the first and second improvements just mentioned can be combined, so that steps / 1 / to 131 of the invention are carried out separately for the target location and for the other target location which is symmetrical to it with respect to the trajectory of the carrier, separately also for each of the two measurement planes. Then, a three-dimensional estimate of the wind speed which exists at the point of the trajectory of the carrier can be deduced from the two-dimensional estimates obtained respectively for one and the other of the two measurement planes.

[0022] Generally, steps / 1 / to 131 may be repeated for a series of target locations that are offset parallel to the carrier's trajectory. It is thus possible to carry out atmospheric turbulence monitoring that is continuous or quasi-continuous during the movement of the carrier. In particular, successive executions of the first and / or second improvement of the invention, or their combination, may be carried out during the movement of the carrier, in order to obtain a series of two-dimensional or three-dimensional evaluations of the wind speed relating to successive points of the carrier's trajectory, ahead of the carrier.

[0023] A second aspect of the invention proposes LIDAR equipment which comprises at least one LIDAR system adapted to measure a wind speed, and which further comprises a calculation unit configured to provide for each measurement, from a Doppler effect characterization, an estimate of a projection onto a line of sight of the LIDAR system, of the wind speed which exists at a target location situated on this line of sight. According to the invention, this calculation unit is further configured to deduce a two-dimensional estimate of the wind speed which exists at the target location, from the projection estimates of the wind speed provided by two measurements for which the respective lines of sight intersect at the target location, the projection estimates being relative to this target location. In other words, the calculation unit is configured to execute steps Z1Z to 131 of a method according to the first aspect of the invention.It can further be configured to implement the first and / or second improvement(s) of this method which has (have) been cited above, as well as the additional characteristics which have also been cited.

[0024] Finally, a third aspect of the invention provides an aircraft which comprises LIDAR equipment in accordance with the second aspect of the invention, and on board the aircraft. Such an aircraft may in particular be an airplane, a helicopter, a drone or a stratospheric platform station. Advantageously, the LIDAR equipment is installed on board the aircraft on a front-rear median axis thereof. Brief description of the figures

[0025] The characteristics and advantages of the present invention will appear more clearly in the detailed description below of non-limiting examples of implementation, with reference to the appended figures among which:

[0026] [Fig. 1] illustrates an implementation of the invention for an aircraft in flight;

[0027] [Fig. 2] illustrates a first possible improvement of the invention, based on the implementation of [Fig. 1];

[0028] [Fig. 3] illustrates a second possible improvement of the invention, based on the implementation of [Fig. 2]; and

[0029] [Fig. 4] corresponds to [Fig. 2] for an implementation variant. Detailed description of the invention

[0030] For the sake of clarity, the dimensions shown in these figures do not correspond to actual dimensions or to actual dimensional ratios. Furthermore, identical references shown in different figures designate identical elements or those having identical functions.

[0031] The invention is now described in the context of an application on board an aircraft, but it is understood that it can be applied in a similar manner to any type of carrier, air, land or sea. The parts of the description which are provided in connection with [Fig. 1] to [Fig. 3] correspond to implementations which may use only one LIDAR system, and the parts of the description provided in connection with [Fig. 4] correspond to other implementations which use several LIDAR systems. In each case, the LIDAR equipment which is carried on board the aircraft includes the LIDAR system(s) used.

[0032] The aircraft in flight is designated by the reference 10, and its flight path by the reference T. It is assumed that this path T can be considered rectilinear on the scale of the execution time of the method of the invention. The path T is oriented in the direction of movement of the aircraft. For the invention, at least one LIDAR system 1 is installed on board the aircraft 10, for example at the nose of this aircraft so that the LIDAR system 1 can carry out wind speed measurements relating to locations which are contained in the half-space located in front of the aircraft. The purpose of such measurements relating to locations located in front of the aircraft is to obtain wind speed estimates useful for adapting flight and / or trajectory parameters. However, in certain circumstances, it may be useful to implement the invention alternatively or additionally in the direction of a half-space which is located behind an aircraft.

[0033] The LIDAR 1 system is a model suitable for measuring wind speed in the Earth's atmosphere. In general, such a LIDAR system is monostatic, i.e., the same optic is used to emit electromagnetic radiation towards a target location, and to collect a portion of this radiation that has been backscattered by a content of the atmosphere present at this target location. Models of such LIDAR systems for wind measurements are known to man of the trade. They can be alternatively heterodyne detection or direct detection. In principle, a LIDAR system can only directly measure the wind speed component that is parallel to its line of sight, this being defined as its direction of radiation emission, merged with its direction of collection of the backscattered part of this radiation.

[0034] In [Fig. 1], ti and t2 are two instants during the movement of the aircraft 10 on its trajectory T, at which two wind speed measurements are made. Each measurement can be considered as being instantaneous or quasi-instantaneous. The position of the aircraft 10 is represented for each of the instants ti and t2, the instant ti being prior to the instant t2. To implement the invention, the target location at which the wind measurement is to be made is first identified, in front of the aircraft 10 while being offset transversely with respect to the trajectory T. This target location is designated by the reference Z, and is targeted by the LIDAR system 1 at each of the two instants ti and t2. The line of sight of the LIDAR system 1 is thus the axis Ai at time ti, making an angle en with the trajectory T, then is the axis A2 at time t2, then making another angle 02 with the trajectory T, the two angles en and 02 being different.For example, when the target location Z is located 200 m ahead of the position of aircraft 10 at time ti, according to a measurement in projection on the trajectory T, with a transverse offset d of 80 m measured perpendicular to the trajectory T, the angles α and β may be equal to 15° and 30°, respectively. The angle between the two axes Ai and A2 is then c(2-ai = 15°. As is known, the measurement carried out at time ti provides a value of the projection of the wind speed that exists at the target location Z, on the line of sight Ai. This projection on the line of sight Ai is noted Vci in the figure. In the same way, the measurement carried out at time t2 provides a value of the projection Vc2 of the wind speed that exists at the target location Z, on the line of sight A2. Then, a method for determining the perpendicular projection of the wind speed in the plane of the two lines of sight Ai and A2 can be the following:. - the two projections Vci and Vc2 are plotted in the form of respective vectors from the same common point, for example from a point of the target location Z as shown in [Fig. 1], The vector of the projection Vci (respectively Vc2) is thus superimposed on the line of sight Ai (resp. A2); - in the plane of the two lines of sight Ai and A2, a straight line Pi which is perpendicular to the line of sight Ai is drawn from the end of the projection vector Vci; - similarly, and also in the plane of the two lines of sight Ai and A2, another straight line P2 which is perpendicular to the line of sight A2 is drawn from the end of the vector of the projection Vc2; - the perpendicular projection of the wind speed in the plane of the two lines of sight Ai and A2, noted V12, can then be determined as the vector which connects the point of the target location Z to the intersection of the two lines Pi and P2. Such a method of obtaining the V12 projection of the wind speed is a possible execution mode for step 131 which has been stipulated in the general part of the present description. This method can be easily executed by a programmable computing unit (not shown). The measurements made at times ti and t2 correspond to steps / 1 / and 121, respectively. The V12 projection has been called a two-dimensional estimation of the wind speed, because it has two speed coordinates within the plane of the lines of sight Ai and A2.

[0035] The lines of sight Ai and A2 can be produced successively by a variable deflection system which is arranged at the output of the emission optics of the LIDAR system 1. For example, such a variable deflection system can be constituted by deflectors with fixed deflection angles which are mounted on a rotating support, and a rotation speed of this support is adjusted according to the speed of movement of the aircraft 10.

[0036] In the first improvement of the invention which is illustrated by [Fig. 2], the measurements carried out at times ti and t2, both aiming at the same target location Z using the LIDAR system 1 on board the aircraft 10, are identical to those which have just been described with reference to [Fig. 1], resulting in the two-dimensional evaluation V12 of wind speed, parallel to the plane of the lines of sight Ai and A2, and relative to the target location Z. The target location noted Z' is symmetrical to the target location Z with respect to the trajectory T. Additional measurements are carried out at times ti' and t2' during the movement of the aircraft 10 on its trajectory T, both relative to the target location Z'. Thus, the additional measurement which is carried out at time ti' implements the line of sight Ai', and the additional measurement which is carried out at time t2' implements the line of sight A2'.These additional measurements of times ti' and t2' result in the evaluation. two-dimensional V12' of the wind speed that exists at the target location Z'. This V12' evaluation is parallel to the plane of the lines of sight Ai' and A2', and therefore parallel to the plane of the two-dimensional V12 evaluation relating to the target location noted Z. Then, an average result that is calculated on the two two-dimensional evaluations V12 and V12' constitutes a new two-dimensional wind speed evaluation, which is noted VM and can be attributed to the midpoint M of the segment that connects the two target locations Z and Z'. By construction, the point M is located on the trajectory T, and the two-dimensional VM evaluation is parallel to the plane that contains this trajectory T and the two target locations Z and Z'. For example, this plane can be a vertical plane in the terrestrial reference frame, noted PV in the following.

[0037] Alternatively, the target location Z' which is targeted for the measurements carried out at times ti' and t2, may be in a horizontal plane PH which contains the trajectory T, instead of being in the vertical plane PV. Thus, the target location Z is still transversely offset in the vertical plane PV relative to the trajectory T, while the target location Z' is transversely offset in the horizontal plane PH also relative to the trajectory T. The planes PV and PH constitute two measurement planes, each of which contains the front-rear centerline of the aircraft 10 and which are distinct around the trajectory T. For such a measurement configuration, the two-dimensional wind speed evaluation V12, which is relative to the target location Z, is parallel to the vertical plane PV, while the two-dimensional wind speed evaluation V12', which is relative to the target location Z', is then parallel to the horizontal plane PH.Such an implementation corresponds to the second improvement of the invention which was cited in the general part of this description.

[0038] [Fig. 3] illustrates a combination of this second improvement of the invention with the first improvement as illustrated by [Fig. 2]. The target locations denoted Zv and Zv' are symmetrical to each other with respect to the trajectory T and contained in the vertical plane PV. Simultaneously, the target locations denoted ZH and ZH' are also symmetrical to each other with respect to the trajectory T but contained in the horizontal plane PH. All four of them can be transversely offset by the same distance d with respect to the trajectory T. Furthermore, the target locations Zv, Zv', ZH and ZH' are located in the same transverse plane which is perpendicular to the trajectory T. M denotes the point of intersection of this transverse plane with the trajectory T. During the movement of the aircraft 10 on its trajectory T, the four target locations are successively targeted by the LIDAR system 1, each twice, according to the following sequence: the target location Zv is targeted at times ti v and t2v, the target location ZH is targeted at times ti H and t2H, the target location Zv' is targeted at times Wet t2v', and the target location ZH' is targeted at times ti n' and t2H. The measurements of the instants tiv, tiv', t2v and t2v' provide a first two-dimensional evaluation of the wind speed that exists at point M, which is parallel to the vertical plane PV, in accordance with what has been described with reference to [Fig. 2]. In the same way, the measurements of the instants ti H, ti H', t2H and t2H provide a second two-dimensional evaluation of the wind speed that exists at point M, which is this time parallel to the horizontal plane PH. The combination of these two two-dimensional evaluations then constitutes a three-dimensional evaluation of the wind speed that exists at point M.

[0039] By appropriately selecting the deflection angles of the lines of sight that are directed toward the four target locations Zv, Zv', ZH and ZH', relative to the trajectory T, as a function of the speed of movement of the aircraft 10, the successive measurement instants tiv, tin, tiv', tin', t2v, t2H, t2v' and t2H can be separated by intermediate durations that are identical. Furthermore, this sequence of measurements can be repeated periodically during the movement of the aircraft 10 to obtain repeated three-dimensional evaluations of the wind speeds that exist on the trajectory T ahead of the aircraft 10. These three-dimensional evaluations are relative to successive points of the trajectory T, which are progressively shifted, correlatively with the movement of the aircraft 10.

[0040] [Fig. 4] illustrates another implementation of the invention, in which a separate LIDAR system is separately assigned to each line-of-sight orientation. In other words, several LIDAR systems are installed on board the aircraft 10, for example all at the nose of this aircraft. Thus, these LIDAR systems are close to each other on board the aircraft. LIDAR system 1 then has a fixed line-of-sight orientation, defined by the axis Ai; LIDAR system 2 has another fixed line-of-sight orientation, defined by the axis A2; LIDAR system 1' has yet another fixed line-of-sight orientation, defined by the axis Ai'; and LIDAR system 2' has a fourth fixed line-of-sight orientation, defined by the axis A2'. Two Doppler effect measurements are then performed at time ti, using simultaneously but independently LIDAR systems 1 and T, then two other Doppler effect measurements are performed at time t2 using simultaneously LIDAR systems 2 and 2'. The axes Ai and Ai' are symmetrical to each other with respect to the trajectory T, as are the axes A2 and A2'. The target location Z is then at the intersection of the lines of sight of LIDAR systems 1 and 2, as existing at times ti and t2, respectively, and the location Z' is at the intersection of the lines of sight of LIDAR systems T and 2', also as existing at times ti and t2, respectively. These target locations Z and Z' are therefore also symmetrical with respect to the trajectory T, and the transverse plane of these target locations Z and Z', perpendicular to the trajectory T and in front of the aircraft 10, is determined by the duration between the measurement times ti and t2, as well as by the speed of movement of the aircraft 10.Obtaining the two-dimensional estimates V12 and V12', then that of VM, can then be identical to those described with reference to [Fig. 2],.

[0041] Furthermore, the following variations can be applied to the implementation methods already described: - in the implementation of [Fig. 4] and while maintaining the arrangement of the target locations Z and Z' symmetrically with respect to the trajectory T, it is not essential that the LIDAR systems 1 and T carry out simultaneous measurements, nor the LIDAR systems 2 and 2'. The respective orientations of the lines of sight of the four LIDAR systems 1, T, 2 and 2' are then adapted according to the separation times between all the measurements; - two separate LIDAR systems 1 and 2, whose respective line-of-sight orientations are fixed, parallel to the axes Ai and A2, can be used in the implementation of [Fig. 1]; and - eight separate LIDAR systems, the orientations of whose respective lines of sight are fixed, may be used in the implementation of [Fig. 3], all installed on board the aircraft 10. In this case, it is possible for four first measurements to be carried out simultaneously by four first of the LIDAR systems, the respective lines of sight of which are angularly distributed on a first cone whose axis is formed by the trajectory T, then four other measurements are carried out simultaneously by four other of the LIDAR systems, the respective lines of sight of which are angularly distributed on a second cone whose axis is also formed by the trajectory T, the half-angle at the apex of the second cone being greater than that of the first cone.

[0042] It is understood that the invention may be reproduced by modifying secondary aspects of the embodiments which have been described in detail above, while retaining at least some of the advantages cited. In particular, all the numerical values ​​which have been cited have been cited only for illustration purposes, and may be changed depending on the application considered.

Claims

Claims

1. Method for measuring a wind speed using at least one LIDAR system (1) which is on board a carrier (10), the measurement relating to at least two components of the wind speed such that said wind speed exists at a location external to the carrier, called the target location (Z), the method comprising the following two steps: / 1 / at a first instant (ti) during a movement of the carrier (10), carry out a first measurement by directing a line of sight of the LIDAR system (1) towards the target location (Z), said line of sight then being parallel to a first axis (Ai), and by deducing from said first measurement, by means of a Doppler effect characterization, an estimate of a projection (Vci) on the first axis, of the wind speed which exists at the target location; then 121 at a second time (t2) during the movement of the carrier (10), performing a second measurement of the wind speed using the same LIDAR system (1) as in step / 1 / or another LIDAR system which is also on board the carrier, wherein, for the second measurement of the wind speed which is performed in step 121, the line of sight of the LIDAR system (1) used in said step 12 / is again directed towards the target location (Z), but being parallel to a second axis (A2) which is angularly offset from the first axis (Ai), said second measurement being used to deduce therefrom, by means of the Doppler effect characterization, an estimate of a projection (Vc2) on the second axis, of the wind speed which exists at the target location, and the method further comprising the following additional step: / 3 / deducing, from the estimates of the projections (Vci, Vc2) of the wind speed on the first and second axes, as obtained in steps / 1 / and 121, a two-dimensional estimate (V12) of said wind speed which exists at the target location (Z), said two-dimensional estimate being parallel to a plane which contains the first and second axes (Ai, A2), in which method, when the movement of the carrier (10) is rectilinear or locally rectilinear, the target location (Z) is offset relative to a trajectory (T) of the carrier in accordance with a transverse offset value (d), and a duration between the first and second instants (ti, t2) is selected as a function of the transverse offset value and of a speed of movement of the carrier, the method being characterized in that steps / 1 / to 131 are executed for the target location (Z) and repeated for another target location (Z') which is symmetrical to said target location with respect to the trajectory (T) of the carrier (10), so as to separately obtain two two-dimensional estimates (V12, V12') of wind speed, one for said target location and one for said other target location, then a two-dimensional estimate (VM) attributed to a point (M) of the trajectory (T) of the carrier (10) is calculated as an average of the two-dimensional estimates (V12, V12') relating respectively to the target location (Z) and to the other target location (Z'), the point being at an intersection of the trajectory of the carrier with a rectilinear segment which connects said target location and said other target location.

2. Method according to claim 1, according to which the first and second axes (Ai, A2) form between them an angle which is greater than 10°, preferably less than 45°.

3. A method according to claim 1 or 2, wherein the carrier (10) is an aircraft, and the movement of the carrier is a movement of the aircraft in flight.

4. Method according to one of the preceding claims, according to which steps / 1 / to 131 are executed separately for two target locations (Zv, ZH) situated in two respective measurement planes (PV, PH) which each contain the trajectory (T) of the carrier (10) but are angularly offset from each other around said trajectory, so as to provide two-dimensional estimates relating one to one to each target location.

5. Method according to claim 4, according to which steps / 1 / to 131 are executed separately for the target location (Z) and for the other target location (Z') which is symmetrical to said target location with respect to the trajectory (T) of the carrier (10), and separately also for each of the two measurement planes (PV, PH), and according to which a three-dimensional estimate of the wind speed which exists at the point (M) of the trajectory (T) of the carrier (10) is deduced from the two-dimensional estimates obtained respectively for one and the other of the two measurement planes.

6. Method according to one of the preceding claims, according to which steps / 1 / to 131 are repeated for a series of target locations which are offset parallel to the trajectory (T) of the carrier (10).

7. LIDAR equipment, comprising at least one LIDAR system (1) adapted to measure a wind speed, and further comprising a calculation unit configured to provide for each measurement, from a Doppler effect characterization, an estimate of a projection (Vci, Vc2) on a line of sight of the LIDAR system, of the wind speed which exists at a target location (Z) located on the line of sight, the calculation unit being further configured to deduce from the projection estimates (Vci, Vc2) of the wind speed provided by two measurements for which the respective lines of sight intersect at the target location (Z), the projection estimates being relative to said target location, a two-dimensional estimate (V12) of the wind speed which exists at said target location, the calculation unit being further configured to execute a method according to one of the preceding claims.

8. Aircraft (10) comprising LIDAR equipment, said LIDAR equipment being according to claim 7 and carried on board the aircraft, preferably installed on a front-rear median axis of said aircraft.

Images