Method for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway

Abstract

Method for three-dimensional localization of an aircraft within a landing scene comprising at least one runway. The invention relates to a method (40) for localizing an aircraft within a scene comprising at least the following steps: - in a radar reference frame, obtaining (42) at least: - the radar distance and the circular distance of a point in the scene, - the ground distance along the radar line of sight; - determining (44) a matrix for changing the reference frame from said radar reference frame to a local geographic reference frame using the aircraft's attitude; - determining (46), in the radar reference frame, the elevation of said point corresponding to the arcsine of the solution to an equation obtained by determining the component of said predetermined point along the altitude axis of said local geographic reference frame, both from said ground distance, the attitude, and the application of said matrix to the coordinates of said point. Figure for the abstract: Figure 2

Description

Title of the invention: Method for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway

[0001] The present invention relates to a method for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway, said aircraft being equipped with at least one radar, the landing scene being considered substantially flat in the field of view of said radar.

[0002] The invention also relates to a computer program comprising software instructions which, when implemented by a programmable electronic device, implement such a process.

[0003] The invention also relates to an electronic device for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway, said aircraft being equipped with at least one radar, the landing scene being considered substantially flat in the field of view of said radar.

[0004] The invention also relates to a landing aid system comprising at least one radar and such a device.

[0005] The invention also relates to an aircraft comprising such a landing aid system.

[0006] The invention relates to the field of aircraft navigation. In this field in particular, it is known to equip aircraft with landing aid devices capable, in particular, of determining the position of the aircraft relative to the landing runway.

[0007] In particular, to land in conditions of reduced visibility, especially in the presence of fog, snow, heavy rain, etc., the crew or pilot of an aircraft generally relies on onboard equipment corresponding to such landing aid devices, including, in particular, known instrument landing systems (ILS), microwave landing systems (MLS), a GPS receiver enabling, in particular, the acquisition of a geolocated position of the aircraft, etc., and also relies on ground-based landing aid infrastructure such as approach lights, a Precision Approach Path Indicator (PAPI), and the markers used by the instrument landing system (ILS) such as the runway centerline and the runway plan. oblique descent leading to the runway, the runway threshold, the runway itself, the wheel touchdown zone, etc.

[0008] However, when visibility and / or radio navigation conditions are insufficient, such conventional solutions are limited because they do not offer sufficient accuracy to comply with air navigation safety objectives applied to different types of approach and landing, or require one or more specific infrastructures that are costly or impossible to implement regardless of the landing area.

[0009] To remedy this, it is generally proposed to determine the angular deviations of the aircraft from its ideal final approach segment (FAS), particularly from radar measurements.

[0010] However, due to the geometry of its radar antenna(s), each radar antenna having a width substantially six times greater than its height, the determination of the elevation of a predetermined point of the landing scene in the predetermined radar frame associated with the radar, in particular a point of interest, is doomed to failure in accuracy, said elevation corresponding to the opposite of the angle formed from the vector from the origin of the radar frame to said predetermined point of said landing scene, to the projection of this vector in the projection plane of the circulars, the circular of said predetermined point corresponding to the angle formed from the line of sight of the radar to the projection of said predetermined point of said landing scene in the projection plane of the circulars, this plane being defined by the line of sight of the radar, and the axis of angular measurements of said radar frame.

[0011] The aim of the invention is then to propose a solution providing, to conventional solutions for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway, a supplement of precision which is in accordance with the air navigation safety objectives applied to the different types of approach and landing.

[0012] To this end, the invention relates to a method for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway, said aircraft being equipped with at least one radar, the landing scene being considered substantially flat within the angular aperture range of said radar, said method comprising at least the following successive steps:

[0013] - in a predetermined radar reference frame associated with said radar, the origin of which corresponds to the phase center of the antenna of said at least one radar, obtaining at least:

[0014] - the radar distance and the circular distance of at least one predetermined point in the scene landing, obtained from measurements of said radar, the circular of said at least one predetermined point corresponding to the angle formed from the radar's line of sight to the projection of said at least one predetermined point of said scene landing in the projection plane of the circulars, this plane being defined by the radar's line of sight, and the axis of angular measurements of said radar reference frame, and

[0015] - the ground distance along the radar's line of sight, from the phase center of the antenna of said at least one radar;

[0016] - determination of a change-of-reference matrix allowing passage of said predetermined radar reference to a predetermined local geographic reference whose origin corresponds to the phase center of the antenna of said radar and whose two axes correspond respectively to the longitudinal axis and the transverse axis of said runway, using the roll, pitch and yaw angles defining the attitude of the aircraft, these angles being provided beforehand by an inertial navigation system of the aircraft;

[0017] - determination, in the radar frame, of the elevation of said at least one pre-point determined of said landing scene, said elevation corresponding to the opposite of the angle formed from the vector from the origin of the radar reference frame to said at least one predetermined point of said landing scene, to the projection of this vector into the projection plane of the circulars, said elevation corresponding to the arcsine of the solution of a second-degree equation obtained by determining the component of said at least one predetermined point of said landing scene along the altitude axis of said local geographic reference frame, both from said ground distance in the radar line of sight and from said pitch angle, and from the application of said coordinate system transformation matrix to the coordinates of said at least one predetermined point of the landing scene measured and expressed in said radar reference frame;

[0018] - determination, in said radar frame, of the three-dimensional location of said at less a predetermined point of said landing scene, from said radar distance, of said circular and of said elevation of said at least a predetermined point of said landing scene.

[0019] Thus, the present invention proposes to determine with precision, in the radar reference frame, the elevation of at least one predetermined point of the landing scene in order to improve the accuracy of the subsequent localization of the aircraft as such.

[0020] More specifically, the present invention proposes to take advantage of the fact that the radar's height relative to the circular projection plane is unique for any predetermined point along the radar's line of sight, assuming a flat landing scene within the radar's angular aperture range. Thus, knowing, on the one hand, the aircraft's pitch and the ground distance along the line of sight, which is insensitive to roll, and on the other hand, applying the said coordinate transformation matrix to the coordinates of said predetermined point of the landing scene measured and expressed in said radar frame, it is possible to precisely determine said previously unknown elevation.

[0021] According to other advantageous aspects of the invention, the tridi localization method The mention of an aircraft within a landing scene comprising at least one landing runway includes one or more of the following characteristics, taken individually or in all technically possible combinations:

[0022] - the process further comprises the following steps:

[0023] - determination of the three-dimensional location of said at least one point pre determined of said landing scene expressed in said local geographic coordinate system by applying said coordinate system change matrix to said three-dimensional location of said at least one predetermined point of said landing scene in said radar coordinate system;

[0024] - from the three-dimensional location expressed in the geographical coordinate system local, obtaining the three-dimensional location of said radar expressed in a predetermined reference frame of the landing runway whose origin is a predetermined point of said landing runway and whose two axes correspond respectively to the longitudinal axis and the transverse axis of the runway, said obtaining including the inversion of the sign of the component along the altitude axis of said at least one predetermined point of the landing scene expressed in said local geographic reference frame;

[0025] - the determination of the vertical angular deviation of said aircraft with respect to a reference approach trajectory, using the three-dimensional location of said radar translated along the x-axis from the runway reference frame to the GPIP point of intersection of the reference approach trajectory with the landing runway;

[0026] - the determination of the lateral angular deviation of said aircraft with respect to the tra reference approach jectory, using the three-dimensional location of said radar, translated along the x-axis from the runway reference point to the GARP reference point for determining lateral deviations;

[0027] - said at least one predetermined point of said landing scene corresponds to the midpoint S of the threshold of said landing strip;

[0028] - said at least one predetermined point of said landing scene corresponds to a intersection point A of two perpendicular approach light lines, and in which the magnitude of the vector going from said intersection point A to the midpoint S of the threshold of said runway is also taken into account (58), when determining (56) the vertical angular deviation and the lateral angular deviation, by translating, by said magnitude, the position of said radar, expressed in the predetermined frame of said runway along the x-axis;

[0029] - said determination of a change-of-reference matrix comprises three successive changes of reference points, namely:

[0030] - a first change of reference frame from the radar reference frame to the reference frame of the aircraft used by said inertial navigation system to provide the roll, pitch and yaw angles defining the aircraft's attitude, using the inclination of said radar; then

[0031] - a second change of reference frame from the aircraft's reference frame to a georeferenced reference frame intermediate graph showing: an origin corresponding to the phase center of the antenna of said radar, an x-axis along the geographic North direction, an y-axis along the geographic East direction and an altitude axis along the local geographic vertical;

[0032] - a third change of reference from the intermediate geographical reference frame to said predetermined local geographic reference point defined relative to the landing scene plan.

[0033] - the method further comprises, prior to obtaining the tridi localization dimensional of said radar expressed in a predetermined frame of the landing runway, the application of a rotation around the altitude axis of the local geographical frame by a predetermined angle representative of the error in determining the yaw angle W by said inertial navigation system of the aircraft, said predetermined angle representing the error in determining the yaw angle being obtained, prior to the application of said rotation, from a point Q defined by its spherical coordinates in the radar frame, such as:

[0034] - its distance to the phase center of the antenna of said radar is unit,

[0035] - its circularity is equal to the orientation of the longitudinal axis of said track landing speed expressed in the radar reference frame and previously obtained from said measurements of said radar;

[0036] - its angle of elevation is zero,

[0037] the point Q being then expressed in Cartesian coordinates in said local geographical frame by means of said change-of-frame matrix, said predetermined angle ew representing the error in determining the yaw angle being such that sv- atan2^yQ, xG]-

[0038] The invention also relates to a computer program comprising software instructions which, when executed by a computer, implement a method for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway, as defined above.

[0039] The invention also relates to an electronic device for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway, said aircraft being equipped with at least one radar, the landing scene being considered substantially planar within the angular aperture range of said radar, said device comprising:

[0040] - a first module configured to implement, in a pre-radar reference frame determined associated with said radar, whose origin corresponds to the phase center of the antenna of said at least one radar, obtaining at least:

[0041] - the radar distance and the circularity of at least one predetermined point in the scene landing, obtained from measurements of said radar, the circular of said predetermined point of said landing scene corresponding to the angle formed from the radar line of sight to the projection of said at least one predetermined point in the projection plane of the circulars, this plane being defined by the radar line of sight and the axis of angular measurements of said radar reference frame, and

[0042] - the ground distance, along the radar's line of sight, from the phase center of the antenna of said at least one radar;

[0043] - a second module configured to determine a change matrix of reference point enabling the conversion of said predetermined radar reference point to a predetermined local geographic reference point whose origin corresponds to the phase center of the antenna of said radar and whose two axes correspond respectively to the longitudinal axis and the transverse axis of said runway, using the roll, pitch and yaw angles defining the attitude of the aircraft, these angles being provided beforehand by an inertial measurement unit of the aircraft;

[0044] - a third module configured to determine, in the radar frame, the elevation said at least one predetermined point of said landing scene said elevation corresponding to the opposite of the angle formed from the vector from the origin of the radar reference frame to said at least one predetermined point of said landing scene, up to the projection of this vector in the projection plane of the circulars, said elevation corresponding to the arcsine of the solution of a second-degree equation obtained by determining the component of said at least one predetermined point of said landing scene along the altitude axis of said local geographic reference frame, both from said ground distance in the radar line of sight and from said pitch angle, and from the application of said coordinate system transformation matrix to the coordinates of said at least one predetermined point of the landing scene measured and expressed in said radar reference frame;

[0045] - a fourth module configured to determine, in said radar reference frame, the location three-dimensional representation of said at least one predetermined point of said landing scene, based on said radar distance, said circular distance, and said elevation of said at least one predetermined point of said landing scene

[0046] The invention also relates to a landing aid system comprising at least one radar and such an electronic device for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway.

[0047] The invention also relates to an aircraft comprising such a landing aid system.

[0048] The invention will become clearer upon reading the following description, given solely as a non-limiting example, and made with reference to the drawings in which:

[0049] [Fig.1] [Fig.1] is a block diagram of the main functional blocks of an electronic three-dimensional localization device of an aircraft within a landing scene comprising at least one landing runway;

[0050] [Fig.2] [Fig.2] is a flowchart of the main steps of a loca process three-dimensional rendering of an aircraft within a landing scene including at least one landing runway;

[0051] [Fig.3] [Fig.3] illustrates the successive changes of reference frame implemented according to the present invention.

[0052] In the following description, the expression "approximately equal to" is understood as a relationship of equality plus or minus 10%, that is to say with a variation of at most 10%, preferably also as a relationship of equality plus or minus 5%, that is to say with a variation of at most 5%.

[0053] Fig. 1 illustrates an embodiment of an electronic device 10 for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway according to an embodiment of the invention.

[0054] Such a device is suitable for integration within a landing aid system, not shown, comprising at least one radar, in particular millimeter radar, not shown, said landing system itself being suitable for being carried on board an aircraft not shown.

[0055] More specifically, the electronic three-dimensional localization device 10, according to the present invention, is suitable for implementing the three-dimensional localization method of an aircraft within a landing scene comprising at least one landing runway which will be described later in relation to [Fig.2].

[0056] To achieve this, such a device 10 first comprises a first acquisition module 12 configured to obtain, in a predetermined radar reference frame associated with said radar as illustrated hereafter in relation to [Fig. 3], the origin of which corresponds to the phase center of the antenna of said at least one radar, at least:

[0057] - the distance p to the radar and the circular a of at least one predetermined point of the landing scene, obtained from measurements of said radar, the circular of said predetermined point corresponding to the angle formed from the radar's line of sight to the projection of said predetermined point of said landing scene into the projection plane of the circulars, this plane being defined by the radar's line of sight and the axis of angular measurements of said radar reference frame, and

[0058] - the ground distance D along the radar's line of sight, from the phase center of the antenna of said at least one radar.

[0059] Furthermore, the device 10 includes a first configured determination module 14 to determine a change-of-reference matrix enabling the transition, as illustrated later in relation to [Fig.3], from said predetermined radar reference frame to a predetermined local geographic reference frame whose origin corresponds to the phase center of the antenna of said radar and whose two axes correspond respectively to the longitudinal axis and the transverse axis of said runway, using the roll, pitch and yaw angles defining the attitude of the aircraft, these angles being provided beforehand by an inertial measurement unit of the aircraft.

[0060] Next, the device 10 includes a second determination module 16, configured to determine in the radar frame, the elevation [3 of said predetermined point of said landing scene, said elevation corresponding to the opposite of the angle formed from the vector from the origin of the radar frame to said predetermined point of said landing scene, to the projection of this vector in the projection plane of the circulars, said elevation [3 corresponding to the arcsine of the solution of a second degree equation obtained by determining the component of said predetermined point of said landing scene along the altitude axis of said local geographical frame, both from said ground distance in the radar line of sight and from said pitch angle, and from the application of said coordinate system change matrix to the coordinates of said predetermined point of the landing scene measured and expressed in said radar frame.

[0061] The device 10 also includes a third module 18 for determining, in said radar reference frame, the three-dimensional location of said at least one predetermined point of said landing scene, from said radar distance, said circular and said elevation of said predetermined point of said landing scene.

[0062] As an optional complement, as shown in dotted lines, said electronic three-dimensional localization device 10, according to the present invention, further includes a fourth determination module 20 configured to determine the three-dimensional location of said at least one predetermined point of said landing scene expressed in said local geographic reference frame by applying said reference frame change matrix to said three-dimensional location of said at least one predetermined point of said landing scene in said radar reference frame.

[0063] According to this optional addition, said device 10 also includes a second acquisition module 22 configured to obtain, from the three-dimensional location expressed in the local geographic coordinate system, the three-dimensional location of said radar expressed in a predetermined coordinate system of the runway whose origin is a predetermined point of said runway and whose two axes correspond respectively to the longitudinal axis and the transverse axis of the runway, said acquisition including the inversion of the sign of the component along the altitude axis of said predetermined point of the landing scene expressed in said geographic coordinate system. local graph.

[0064] Furthermore, according to this optional supplement, said device 10 also includes a fifth determination module 24, configured to determine the vertical angular deviation of said aircraft from a reference approach path, using the three-dimensional location of said radar translated along the x-axis from the runway reference to the GPIP point of intersection of the reference approach path with the landing runway (Glide Path Intercept Point).

[0065] Finally, according to this optional supplement, said device 10 also includes a sixth determination module 26, configured to determine the lateral angular deviation of said aircraft from the reference approach path, using the three-dimensional location of said radar, translated along the x-axis from the runway reference point to the GARP reference point for determining lateral deviations (from the English GNSS Azimuth Reference point).

[0066] The GARP and GPIP points are the references for the lateral and vertical deviations respectively as defined in DO-229E document in paragraphs 2.2.4.3.1 and 2.2.4.4.2.3 of the Radio Technical Commission for Aeronautics (RTCA).

[0067] According to another optional addition, said device 10 further comprises an application module 28 configured to apply, prior to obtaining the three-dimensional location of said radar expressed in a predetermined frame of the landing runway, a rotation around the altitude axis of the local geographic frame by a predetermined angle ew representative of the error in determining the yaw angle V by said inertial navigation system of the aircraft, said predetermined angle representing the error in determining the yaw angle being obtained, prior to the application of said rotation, from a point Q defined by its spherical coordinates in the radar frame, such that:

[0068] - its distance to the phase center of the antenna of said radar is unit,

[0069] - its circularity is equal to the orientation of the longitudinal axis of said track landing speed expressed in the radar reference frame and previously obtained from said measurements of said radar;

[0070] - its angle of elevation is zero,

[0071] the point Q being then expressed in Cartesian coordinates in said local geographical frame by means of said change-of-frame matrix, said predetermined angle sw representing the error in determining the yaw angle being such that Exp — atan2 ( y Xo j ■

[0072] Following the example of [Fig. 1], an electronic three-dimensional localization device 10 for an aircraft within a landing scene comprises a unit of The processing unit 30, for example, consists of a memory 32 and a processor 34 associated with the memory, and the device 10 is at least partly implemented as software, or a software component, executable by the processor, including the first acquisition module 12, the first determination module 14, the second determination module 16, the third determination module 18, and optionally the fourth determination module 20, the second acquisition module 22, the fifth determination module 24, the sixth determination module 26, and the application module 28. The memory 32 of the electronic three-dimensional localization device 10 for an aircraft within a landing scene is then capable of storing such software or software components, and the processor 34 is then capable of executing them.

[0073] In an alternative not shown, the first acquisition module 12, the first determination module 14, the second determination module 16, the third determination module 18, and optionally the fourth determination module 20, the second acquisition module 22, the fifth determination module 24, the sixth determination module 26 and the application module 28 are each implemented as a programmable logic component, such as an FPGA (Field Programmable Gate Array) or as a dedicated integrated circuit, such as an ASIC (Application Specified Integrated Circuit).

[0074] When a portion of the electronic three-dimensional localization device 10 for an aircraft within a landing scene according to the present invention is implemented in the form of one or more software programs, i.e., in the form of a computer program, this portion is also capable of being stored on a computer-readable medium (not shown). The computer-readable medium is, for example, a medium capable of storing electronic instructions and being connected to a bus of a computer system. By way of example, the readable medium is an optical disc, a magneto-optical disc, a ROM, a RAM, any type of non-volatile memory (e.g., EPROM, EEPROM, FLASH, NVRAM), a magnetic card, or an optical card. A computer program containing software instructions is then stored on the readable medium.

[0075] An example of the operation of the electronic three-dimensional localization device 10 of an aircraft within a landing scene according to the present invention, as illustrated previously in relation to [Fig.1], is described below in relation to [Fig.2].

[0076] More specifically, the method 40 for three-dimensional localization of an aircraft within a landing scene generally comprises a first step 42 of obtaining OBT(p, a, D) at least, on the one hand, the radar distance, denoted p, and the circular distance, denoted a, of at least one predetermined point in the landing scene, obtained from measurements of said radar, the circular distance a of said corresponding predetermined point to the angle formed from the radar line of sight to the projection of said predetermined point of said landing scene in the projection plane of the circulars, this plane being defined by the radar line of sight, and the axis of angular measurements of said radar reference, and on the other hand of the ground distance D in the radar line of sight, from the phase center of the antenna of said at least one radar.

[0077] The elements p, a, D are obtained in the predetermined radar frame associated with said radar, the origin of which corresponds to the phase center of the antenna of said at least one radar as illustrated subsequently in relation to [Fig.3].

[0078] Moreover, such elements are capable of being obtained according to different variants.

[0079] For example, according to a first variant, the elements are capable of being obtained at least in part using a solution based on artificial intelligence learning by means of a deep learning tool based in particular on attention mechanisms applied in a non-trivial way specifically to radar measurements as described in the patent application whose filing number is FR2309055 in the name of the Applicant.

[0080] According to another variant, these elements are capable of being obtained at least in part using the solution described in patent FR 3 103 178 in the name of the Applicant.

[0081] The method 40 for three-dimensional localization of an aircraft within a landing scene then generally includes a step 44 for determining DET_M of a matrix M for changing reference frames allowing, as illustrated later in relation to [Fig.3], to go from said predetermined radar reference frame to a predetermined local geographic reference frame whose origin corresponds to the phase center of the antenna of said radar and whose two axes correspond respectively to the longitudinal axis and the transverse axis of said landing strip, using the roll, pitch and yaw angles defining the attitude of the aircraft, these angles being provided beforehand by an inertial measurement unit of the aircraft.

[0082] The method 40 for three-dimensional localization of an aircraft within a landing scene then generally comprises a step 46 of determining DET_ [3, in the radar frame, the elevation [3] of said predetermined point of said landing scene, said elevation corresponding, as explained hereafter in relation to [Fig. 3], to the opposite of the angle formed from the vector from the origin of the radar frame to said predetermined point of said landing scene, up to the projection of this vector onto the projection plane of the circulars, said elevation corresponding to the arcsine of the solution of a quadratic equation obtained by determining the component of said predetermined point of said landing scene along the altitude axis of said local geographic frame, both from said ground distance along the radar line of sight and from said pitch angle, and from the application of said coordinate system change matrix to the coordinates of said predetermined point of the landing scene measured and expressed in said radar coordinate system.

[0083] The method 40 for three-dimensional localization of an aircraft within a landing scene then includes, in general, a step 48 of determining DET_LOCr in said radar frame, the three-dimensional localization of said at least one predetermined point of said landing scene, from said radar distance p, said circular a and said elevation [3 of said predetermined point of said landing scene.

[0084] As an optional complement, the method 40 for three-dimensional localization of an aircraft within a landing scene also includes a step 50 for determining DET_LOCg the three-dimensional location of said at least one predetermined point of said landing scene expressed in said local geographic frame by applying said frame change matrix M to said three-dimensional location of said at least one predetermined point of said landing scene in said radar frame.

[0085] Optionally, as shown in dashed lines, the method 40 for three-dimensional localization of an aircraft within a landing scene also includes a step 52 of applying a rotation ROT around the altitude axis of the local geographic reference frame at a predetermined angle representative of the error in determining the yaw angle by said inertial navigation system of the aircraft, said predetermined angle representing the error in determining the yaw angle being obtained, prior to the application of said rotation, from a point Q defined by its spherical coordinates in the radar reference frame, such as:

[0086] - its distance to the phase center of the antenna of said radar is unit,

[0087] - its circularity is equal to the orientation of the longitudinal axis of said track landing speed expressed in the radar reference frame and previously obtained from said measurements of said radar;

[0088] - its angle of elevation is zero,

[0089] the point Q being then expressed in Cartesian coordinates in said local geographical frame by means of said change-of-frame matrix, said angle s'i; predetermined representative of the error in determining the yaw angle being such that en, = atan2 yo, Xq j •

[0090] As an optional addition, the method 40 for three-dimensional localization of an aircraft within a landing scene also includes, starting from said three-dimensional localization expressed in the local geographic coordinate system, a step 54 for obtaining OBT_LOC(R)P the three-dimensional localization of said radar R expressed in a predetermined coordinate system of the runway whose origin is a predetermined point of said landing runway and whose two axes correspond respectively to the longitudinal axis and the transverse axis of the runway, said obtaining including the inversion of the sign of the component along the altitude axis of said predetermined point of the landing scene expressed in said local geographical frame, the index P being here representative of the fact that the location is in the frame of the runway.

[0091] As an optional complement, the method 40 for three-dimensional localization of an aircraft within a landing scene also includes a step 56 for determining DET_DEVv of the vertical angular deviation of said aircraft with respect to a reference approach path, using the three-dimensional localization of said radar translated along the x-axis from the runway reference frame to the GPIP point of intersection of the reference approach path with the landing runway.

[0092] Optionally, as illustrated in dashed Figure 2, said at least one predetermined point of said landing scene corresponds to an intersection point A of two perpendicular approach light lines, the magnitude of the vector AS going from said intersection point A to the midpoint S of the threshold of said landing runway is then also taken into account according to optional substep 58, when determining 56 the vertical angular deviation, by translating, by said magnitude, the position of said radar, expressed in the predetermined frame of said runway along the x-axis.

[0093] Finally, as an optional complement as illustrated by [Fig.2], the method 40 for three-dimensional localization of an aircraft within a landing scene also includes a step 60 for determining DET_DEVL the lateral angular deviation of said aircraft with respect to the reference approach path, using the three-dimensional localization of said radar, translated along the x-axis from the runway reference point to the GARP reference point for determining lateral deviations.

[0094] It should be noted that, in a manner not shown, when said at least one predetermined point of said landing scene corresponds to an intersection point A of two perpendicular approach light lines, the magnitude of the vector as going from said intersection point A to the midpoint S of the threshold of said landing runway is then also taken into account according to the optional substep 58 when determining 60 the lateral angular deviation, by translating, by said magnitude, the position of said radar, expressed in the predetermined frame of said runway along the x-axis.

[0095] An example of implementation of the steps of the process 40 previously mentioned is described below in detail in relation to [Fig.3] illustrating the successive changes of reference frame implemented according to the present invention.

[0096] More specifically, according to the example illustrated in [Fig. 3], a predetermined radar frame 62 is used, the origin O of which corresponds to the phase center of the radar antenna. Furthermore, the x-axis of the abscissa of the predetermined radar frame 62 is along the axis of radar sighting, while the y-axis of the ordinates in the 64 projection plane of the circulars is perpendicular to this x-axis of sighting, and parallel to the line of transmitters (i.e., to the width of the radar), and in particular oriented to the right when looking along the radar sighting. The z-axis of altitudes, according to this example, is such that the radar frame 62 is right-handed orthonormal (i.e.

[0097] downwards if the aircraft's attitude is zero).

[0098] As indicated previously, the first step 42 of the method 40 according to the present invention consists of obtaining, on the one hand, the radar distance, in particular in meters, denoted p on the [Fig.3], and the circular denoted a, in particular in radians, of at least one predetermined point P of the landing scene, obtained from measurements of said radar, the circular a of said predetermined point corresponding to the angle formed from the x-axis of the radar to the projection of said predetermined point of said landing scene in the plane 64 of projection of the circulars, this plane 64 being defined by the x-axis of the radar, and the axis of the angular measurements of said radar reference frame, and on the other hand, the ground distance D in the radar's line of sight, in particular in meters, from the phase center of the antenna of said at least one radar, and corresponding to the distance of said center to the point Po of intersection (not shown) with the ground.

[0099] In particular, on the example of [Fig.3], the circular denoted a is thus defined in the radar frame 62 and corresponds to the angle formed from the origin O and the line of sight x of the radar, in the plane 64 (O, x, y) and oriented positively along the rotation around (O, z).

[0100] As previously indicated, different variants are suitable for use in the implementation of said obtaining step such as a solution based on artificial intelligence learning by means of a deep learning tool based in particular on attention mechanisms applied in a non-trivial way specifically to radar measurements as described in the patent application whose filing number is FR2309055 in the name of the Applicant or the solution described in patent FR 3 103 178 in the name of the Applicant.

[0101] In particular, said at least one predetermined point corresponds to a plurality of points P; identifying in particular the threshold and the runway edges, or the axes of the approach lights.

[0102] Another variant of obtaining 42 consists of identifying the runway contour by detection or segmentation applied to the "radar grid". The straight segments of this contour are then located by Hough transform or linear regression, and a check is carried out to ensure that the segments of the runway edges and threshold thus identified are such that: the runway edges are substantially parallel (in particular with an orientation error of less than 1°), the runway threshold is perpendicular to the edges (in particular with an orientation error of less than 2°), and that the The runway is a rectangle with plausible dimensions (for example, the runway edges are spaced less than 18m apart and longer than 300m). According to this variant, the intersection of the median of the runway edges with the runway threshold is the point S corresponding to the midpoint S of the threshold of said landing runway, and the runway orientation V, expressed in the radar coordinate system, is derived from the slope a, expressed in the radar coordinate system, of the median line of the runway edges such that y = ataiïl(a, 1).

[0103] Thus, as illustrated by [Fig.3], in such a radar frame 62, we consider P to be one of these points Pi, defined by its distance to the radar p and its angles a and [3 such that: a being the circular of P as defined previously and [3 the elevation of said predetermined point corresponding to the opposite of the angle formed from the vector from the origin of the radar frame to said predetermined point P of said landing scene in the plane 66 (O, P, z), up to the projection of this vector in the plane 64 of projection of the circulars.

[0104] The Cartesian coordinates of P in such a radar frame 62, also called frame R, are then such that: = p ■ cos ( a ) • cos ( fi ), y[Æ] = p ■ sin( a ) ■ cos( / ?) and = p ■ sin(^)

[0105] However, as previously stated, the determination of the elevation [3 of a predetermined point of the landing scene, in particular a point of interest, is bound to fail in accuracy, it is therefore considered unknown at this stage of the process and as represented by means of a question mark on [Fig.3].

[0106] As indicated previously, the second step 44 of the method consists, in parallel or not with the previously described obtaining step 42, of determining a reference frame change matrix enabling the conversion of said predetermined radar reference frame 62, also called reference frame R, to a predetermined local geographic reference frame G' whose origin corresponds to the phase center of the antenna of said radar and whose two axes correspond respectively to the longitudinal axis and the transverse axis of said landing strip, using the roll, pitch and yaw angles defining the attitude of the aircraft, these angles being provided beforehand by an inertial measurement unit of the aircraft.

[0107] More specifically, said determination 44 of a change-of-reference matrix comprises three successive changes of reference, namely a first change of reference 68 from the radar reference frame 62 to the aircraft reference frame 70, also hereafter referred to as reference frame B, used by said inertial navigation system to provide the angles of:

[0108] - roll q> around the roll axis 72 corresponding to the longitudinal axis of the aircraft, and therefore, in the presence of pitch, which is most often non-zero and positive if tilted to the right,

[0109] - pitch 0 around the pitch axis 74, in particular defined with respect to the ho- plane terrestrial and positive reclining rice, and

[0110] - yaw rp around the yaw axis 76, notably defined with respect to geo north terrestrial graph, and positive towards the East.

[0111] defining the attitude of the aircraft to within plus or minus 0.05°, using the inclination i of said radar defined with respect to the aircraft's center of gravity plane and in particular positive if the radar is pointing downwards.

[0112] The change-of-reference matrix used during this first change of reference is subsequently called R2B.

[0113] Furthermore, said determination 44 of a change-of-reference matrix includes a second change of reference from the aircraft reference frame 70 to an intermediate geographic reference frame G not shown having: an origin corresponding to the phase center of the antenna of said radar, an abscissa axis x along the geographic North direction, an ordinate axis y along the geographic East direction and an altitude axis z along the local geographic vertical.

[0114] The change-of-reference matrix, called B2G, used during this second change of reference from the aircraft's reference frame 70 to an intermediate geographical reference frame G is such that it is the transpose of the matrix G2B allowing the transition from the intermediate geographical reference frame to the aircraft's reference frame 70, such that:

[0115] / cos(v')-cos(0) sin(y>)-cos(0) -sin(^) \ G2B = cos(v)-sin(S)-sin]^)-sin(y>)-cos(p) sin(y>) -sinf 6*)-sin(p) +cos(y')-cos(^) cos(0)-sin(^) \cos(y>) ■ sin( 0) ■ cos(p) +sin( y.') • sin(<p) sin( y;) ■ sin(^) ■ cos(y> ) -cos( >p) ■ sin(^) cos(0) ■ cos( <p) /

[0116] où G2B(n, p) désigne le terme en ligne n et colonne P, l’ordre des rotations dans ce deuxième changement de repère G2B ; cap (^), puis tangage (0), puis roulis (9).

[0117] The order of rotations is advantageous. As previously stated, the ground distance along the line of sight is insensitive to roll, and because in the order of rotations defining the aircraft's attitude, roll is applied after pitch, it is possible to determine the radar height relative to the ground independently of roll.

[0118] In other words, p2G — (G?#)^' ct 'a matrix R2B associated with the first change of reference frame is defined as G2B but considering that 0 = i and ip — (p — 0, i being the inclination of said radar defined with respect to the plane of the aircraft and in particular positive if the radar points downwards.

[0119] It should be noted that, given the definition of vertical and lateral angular deviations commonly adopted by Instrument Landing Systems (ILS) and radar measurements, said determination 44 of a change-of-reference matrix includes a third change of reference frame from the unrepresented intermediate geographic reference frame to said predetermined local geographic reference frame, denoted G', defined relative to the landing scene plane, using a change-of-reference matrix G2G' associated with this third change of reference point.

[0120] In other words, arrow 78 of [Fig.3] represents a direct application of the second and then the third change of reference frame mentioned above to go directly from the aircraft reference frame 70 to the said predetermined local geographical reference frame.

[0121] This predetermined local geographic reference is defined in relation to the inclination i of the radar and to the plane of the approach scene (i.e. landing scene) considered, according to the present invention, substantially planar in the domain of the angular opening of said radar.

[0122] In particular, the axes of this predetermined local geographic coordinate system coincide with those of the aforementioned unrepresented intermediate geographic coordinate system when the longitudinal slopes Si and transverse slope st of the approach scene, which are known (such as entries), as well as the geographic orientation of the runway, also known along the direction of landing, notably defined with respect to true terrestrial north and positive towards the east, are all zero. The longitudinal slope Si of the approach scene is notably defined with respect to the horizontal terrestrial plane and positive if the scene is rising, while the transverse slope st, zero in principle, is defined with respect to the horizontal terrestrial plane and positive if the scene slopes to the right when viewed along the runway axis in the direction of landing.

[0123] Note that for reasons of cost constraints, the aircraft and runway headings are generally only approximately known, that is to say to within a few degrees.

[0124] The x-axis of the predetermined local geographic reference is oriented along the runway axis, in the direction of landing and at the level of the TDZ (Touch Down Zone), with correction using the known input parameters corresponding to the geographic orientation of the rppiste runway and the longitudinal slope Si of the approach scene.

[0125] The y-axis of the predetermined local geographic coordinate system is oriented along the transverse axis of the runway at the level of the TDZ contact zone, with correction using the same rppiste and st parameters.

[0126] The altitude axis z of the predetermined local geographic reference frame is in particular oriented such that (O, x, y, z) is orthonormal direct.

[0127] The origin of this reference frame remains the phase center of the radar antenna O as illustrated in radar reference frame 62.

[0128] The change-of-reference matrix G2G' associated with this third change of reference is such that G2G' is then defined as G2B but with = and and tp — st.

[0129] According to [Fig.3], the predetermined local geographical reference point as described above is represented by the reference frame 80 after translation of said predetermined local geographic reference frame, the origin of which remains the phase center of the radar antenna O, at the middle S of the threshold of runway 82. Note that the angular error of the axes of this local geographic reference frame 80 due to the distance SO (< 1 NM) remains negligible (2 / 100° at 2 km) with regard to the required performance (from 2 to 4 / 10°) taking into account the Earth's radius (approximately 6400 km).

[0130] By assumption of the approach scene, the plurality of points P, identifying in particular the threshold and runway edges, or the axes of the approach lights, are all located in the same plane, and by definition a predetermined local geographic reference frame as described above, the "height" h of the radar relative to the plane of the approach scene (i.e., its coordinate along the z-axis of the predetermined local geographic reference frame G') is then such that q^ / ^l^pD-sin^

[0131] The matrix M enabling the conversion of said predetermined radar reference frame to a predetermined local geographic reference frame is such that M = G2G ■ B2G ■ R2B = R^G'

[0132] In the equation defining the Cartesian coordinates 'M ^gq of said at least one predetermined point of said landing scene expressed in said predetermined local geographic frame G' as a function of said matrix M and the coordinates 3'[Aj of said at least one predetermined point of said landing scene expressed in the radar frame R, the only unknowns are / i and consequently 3¼ V'I car = p ■ cos ( a ) • COS (fi ), y , = p ■ sin ( a ) • cos ( fi ) et^p-sin^)-

[0133] Applying the change-of-reference equation to the z component then allows us to determine [3 from ,, 7 \ because the height z of the radar relative to the plane vVI -VT m] / (O, x, y) of the predetermined local geographic coordinate system G' is unique, and this holds true for every point P under the assumption of a flat scene. Therefore, an equation of the following form is obtained:

[0134] ^ = 0-811)(0+1 + .¾) =R2G (3,1) -p-cos(a) -cos(^) + R2G (3,2) ' / rsin / fz) -cos(^) + Æ2G (3,3) ■

[0135] This equation is of the form: A ■ cos( / 7) + B ■ sin( / 3) = C, where:

[0136] A — p-R2G(3,l) -cos(a) + p-R2G(3,2) -sin(a)

[0137] B = p-R2G (3,3)

[0138] C = D-sin(0)

[0139] Considering: cos2 ( fi ) = 1 - sure (fi) and setting: X = sin ( fi ) the equation becomes, the term in square root being isolated and the equation squared:

[0140] (A2 + b2).X2 2. (BC) -X+(C2-A2) =0

[0141] The roots of this quadratic equation are as follows, according to a for- mulation with reduced discriminant:

[0142] (bc) (bc)2- (a2+b2 i) X: — ------------5 ----------- ' A2+B2

[0143] noting that there is no solution to be retained for this equation if the reduced discriminant is strictly negative, or if two solutions are negative, said at least one predetermined point being assumed below the aircraft's flight plane.

[0144] The determination of the solution Xj then allows, as indicated previously, the determination of the elevation [3 of said predetermined point, of which it is the arcsine, and consequently the determination of the Cartesian coordinates ^[«1 of said point at minus a predetermined point expressed in the radar coordinate system with:

[0145] x[Æ] = p-cos(a) ■cos(^),y[ / î] = p-sin(a) -cosO) and ^M = p- sin(^)-

[0146] Once this determination 48 of the Cartesian coordinates ■'W ZLR] of said at least one predetermined point expressed in the radar frame has been carried out, it is then possible to determine 50 the Cartesian coordinates 9g'| of said at minus a predetermined point expressed in the predetermined local geographic coordinate system G' by application of the coordinate system change matrix R2G'.

[0147] As an optional complement, said at least one predetermined point of said landing scene corresponds to the midpoint S of the threshold of said landing runway.

[0148] As previously stated, as an alternative to the above optional complement, said at least one predetermined point of said landing scene corresponds to an intersection point A of two perpendicular approach light lines, and in which the magnitude of the vector going from said intersection point A to the midpoint S of the threshold of said landing runway is also taken into account 58, when determining 56 the vertical angular deviation and the lateral angular deviation, by translating, by said magnitude, the position of said radar, expressed in the predetermined frame of said runway along the x-axis.

[0149] As shown in Figure 2, prior to obtaining 54 the three-dimensional location of said radar expressed in a predetermined frame of the runway as illustrated in Figure 3 by the predetermined frame 86, the method includes an optional step 52 of applying a rotation ROT around the altitude axis of the local geographic frame by a predetermined angle Σw representative of the error in determining the yaw angle W by said inertial navigation system of the aircraft, said predetermined angle representing the error in determining the yaw angle being obtained, prior to the application of said rotation, from a point Q defined by its spherical coordinates in the radar frame, such that:

[0150] - its distance to the phase center of the antenna of said radar is unit,

[0151] - its circularity is equal to the orientation of the longitudinal axis of said track landing speed expressed in the radar reference frame and previously obtained from said measurements of said radar;

[0152] - its angle of elevation is zero,

[0153] the point Q being then expressed in Cartesian coordinates in said local geographical frame by means of said change-of-frame matrix, said predetermined angle representing the error in determining the yaw angle being such that:

[0154] £ _ atan2 yXq ) •

[0155] Indeed, by definition of the predetermined local geographical frame G', its x-axis should theoretically coincide with the runway axis, which then theoretically implies that the orientation of the runway axis expressed in the predetermined local geographical frame G' is zero.

[0156] However, given the specific nature of the uncertainty in the inertial measurement of the heading and the risk of inaccuracy in the orientation of the runway (particularly in databases), the predetermined local geographic reference frame G' must be corrected by a rotation of angle around the altitude axis z of this reference frame so that the X axis of the local geographic reference frame is parallel to the axis of the runway in order to meet the objective for which such a reference frame is defined.

[0157] Such a rotation 52 when applied then defines a corrected frame G” not shown, whose origin remains O, the phase center of the radar.

[0158] It should be noted that if the geographical orientation of the runway is not known (i.e. Upist= 0 by default), then this correction by rotation will determine it.

[0159] As previously stated, such a rotation is for example applied to the predetermined point corresponding to the middle of the runway or, according to another example, to the point of intersection between two perpendiculars of approach lights, in particular cross-shaped approach lights as referenced in the International Civil Aviation Organization ICAO document, Annex 14, Volume I, paragraph 5.3.4.

[0160] Considering the midpoint of the track S, its expression in this corrected frame G” is then in the following form: 5^”] = G'2G'' 1 Sjy]

[0161] with: COS (fi, / ;) sm(fiv;) °\ G2G” = -sin(ev,) cos(tv) 0 ' 0 0 J

[0162] and to determine £' / ', as previously stated, a point Q is considered defined, by its spherical coordinates in the frame R, such that pQ = 1, aQ = y / s / , [3Q = 0 with y / s / the orientation of the track axis expressed in the radar frame R.

[0163] This point Q is then expressed in the frame G', in the same way as for a predetermined point P as described previously and $_Xgr]j'

[0164] It should be noted that yIR / the orientation of the runway axis expressed in the radar frame R is likely to be obtained according to different variants.

[0165] According to a first embodiment, the yIRI orientation is obtained using the aforementioned solution based on artificial intelligence learning by means of a deep learning tool relying in particular on attention mechanisms applied in a non-trivial manner specifically to radar measurements, as described in patent application number FR2309055 filed by the Applicant. Such artificial intelligence learning of the angle y / s / (i.e. in the radar frame R) is implemented from the "ground" reality. In particular, in the radar frame R, y!Rl represents the angle formed by the line of the runway axis with the plane of the radar circular "0".In other words, it is the projection of the runway axis into the (O, x, y) plane of radar reference frame 62, and the plane of the radar circular '0' is defined as containing the phase center O of the radar antenna and its aiming axis Ox, and is vertical when the radar installation reference is horizontal.

[0166] According to a second variant, the determination of ylRh to be applied at each measurement instant comprises determining the three-dimensional geographic position of two substantially distant points located on the runway axis, typically the midpoint S of the runway threshold and the predetermined point P GPIP, by accessing a data platform such as GéoPortail© or GoogleEarth®. From the three-dimensional geographic positions of these two points, the average longitudinal slope Si of the runway between these points and the runway heading (i.e., the geographic orientation of the runway) are deduced. Then, it is confirmed that the runway does not have a transverse slope st = 0 and, failing that, the transverse slope st is then determined. Then, the position of S, the midpoint of the runway threshold, and similarly that of point P, the predetermined point GPIP, are determined in an intermediate geographic coordinate system G:

[0167] / ^-Rn\ > = ^Lon ' ^Alt

[0168] with "Lat" representing latitude, "Lon" representing longitude, and "Alt" representing altitude, and based on the known definition of radii terrestrial:

[0169]

[0170] ôLat = Lat (S)- Lat(O), ôLm = Lon (S) - Lon(O), ôAlt = Alt (O)- Alt (S) ^}-e^sin2(Lat) j et nt. RF = .............■■■■■.....— ■ y le^sirt ( Lat ) \ ?

[0171] Lat = = 6378137 m, p2 = 2 - f_f2, j - 298.257223563.

[0172] These positions in the intermediate geographic frame G are then brought back into the radar frame R such that 5^] — B2R ■ G2B ■ and = B2R ■ G2B ■ P^ with B2R and G2B as previously defined and considering that — ( RP B )1 with the exponent T representing the transpose. The orientation ylRl is then obtained such that

[0173] y = atan2 _ y approximation of arcs by straight lines on the Earth's surface over the radar range which is less than 2108 m. and this taking into account the error y - atan2 xSP

[0174] Furthermore, the translation between the origins of the frames G and G' is taken into account at the level of the calculation of deviations as finalized below, and by definition a vector, SP does not depend on the origin of the frame.

[0175] According to a third alternative variant of the previous variant, the determination of yIRh includes the conversion of the coordinates of S and P into geocentric coordinates in the ECEF frame (from the English earth-centered, early fixed and then into local north, east, down NED coordinates in the local geographic NED frame at the radar (in O), and then into the radar frame R, via the matrix GPR — G'2R with st = Si = rppiste = 0), and includes the calculation of the vector in this Cartesian frame of the radar by differentiation of the coordinates,

[0176] Finally, [Fig.3] illustrates via arrow 84 the last change of reference implemented during the aforementioned step 54 of obtaining the three-dimensional location of said radar expressed in a predetermined reference frame 86 of the landing runway whose origin is a predetermined point, in particular, according to an example, the midpoint S of the threshold of said landing runway and whose two axes correspond respectively to the longitudinal axis and the transverse axis of the runway, said obtaining including the inversion of the sign of the component along the altitude axis of said predetermined point of the landing scene expressed in said local geographical reference frame.

[0177] In other words, this inversion makes it possible, in particular, to represent the three-dimensional location of the radar with index R expressed in the runway frame 86: [xR[runway] \ / \. The runway frame 86 is defined such that its origin corresponds, -^Z?[piŸte] I — -Xs'[G ] \^7?[ / ùîff] / \ “As[G ] / According to a first example illustrated by [Fig. 3], at the midpoint S of the runway threshold, its x-axis is aligned with the runway axis, oriented positively towards aircraft on approach for landing, its y-axis is in the plane of the runway, perpendicular dicular to the x-axis, oriented to the right when looking along the x-axis, and its altitude axis z such that the frame 86 (S, x, y, z) is orthonormal right (i.e. downwards if the aircraft is in zero pitch).

[0178] As previously stated, to reference the position of the radar with respect to the points GARP and GPIP, it is sufficient to add DGARP and DGP1P respectively to its abscissa.

[0179] Furthermore, as previously stated, in the case of an offset runway threshold or radar measurements referenced to an intersection between two perpendiculars of the approach lights, the distance separating the true threshold S from the midpoint of the offset threshold or the considered intersection of the approach lights || || is added to the abscissa of the position of the radar along the x-axis expressed in the runway coordinate system.

[0180] Finally, to reference the aircraft's position instead of the radar's position, the radar lever arms relative to the aircraft are represented by the vector KO^, with K the aircraft's reference point for angular deviations, such that the aircraft's center of gravity K is: KS[cn = with = G2G"B2GXO[b] and such as defined above. The vertical deviation, determined 56 according to the present invention, with respect to the track reference frame in GPIP (i.e., the track reference frame having its origin GPIP, hereafter denoted [GPIP] in the equations), is then expressed in the following form:

[0181] / ~Zr\C'PJP] \ Vertical deviation - dv - atan .............-(.---2..........- -GPAG"i

[0182] The lateral deviation, determined 60 according to the present invention, is defined with respect to the track reference frame in GARP (i.e. the track reference frame having its origin GARP, hereafter denoted [GARP] in the equations):

[0183] Lateral deviation -ôl = atan ( j

[0184] And to bring these deviations back into the horizontal terrestrial plane at the landing threshold point LTP (from the English landing thresholdpoint) and GARP, the slopes of the runway Si and st are to be taken into account, using the change of reference frame G 2G with V' — 0, and the vertical offset represented by the difference (GPIP - LTP), is taken into account by reducing the height ZR[runway] as a consequence of this deviation as also introduced in patent FR 3 103 178 in the name of the Applicant.

[0185] A person skilled in the art will understand that the invention is not limited to the embodiments described, nor to the particular examples of the description, the embodiments and variants mentioned above being capable of being combined with each other to generate new embodiments of the invention.

[0186] The present invention thus makes it possible to determine with precision the elevation of at least one predetermined point of the landing scene in order to improve the accuracy of the subsequent localization of the aircraft as such.

[0187] Thanks to this improved accuracy, it is then possible to determine the lateral and vertical angular deviations of the aircraft from the ideal final approach segment (FAS), regardless of the aircraft's attitude, by determining, for example, the midpoint of the runway threshold S and the orientation F of the runway centerline from radar measurements and according to one of the aforementioned variants, in particular the variant using the aforementioned solution based on artificial intelligence learning by means of a deep learning tool relying in particular on attention mechanisms applied in a non-trivial manner specifically to radar measurements as described in patent application FR2309055 filed by the Applicant. Then, it is thus possible to bring this information into the local geographic coordinate system of the runway, and then to invert the location coordinate system (i.e.runway as seen from the aircraft relative to the aircraft as seen from the runway), and finally to translate this reference point according to the lever arms and the definition of deviations to the final approach segment FAS.

Claims

1. Claims Method (40) for three-dimensional localization of an aircraft within a landing scene comprising at least one landing runway, said aircraft carrying at least one radar, the landing scene being considered substantially planar in the domain of the angular aperture of said radar, said method comprising at least the following successive steps: - in a predetermined radar reference associated with said radar, the origin of which corresponds to the phase center of the antenna of said at least one radar, obtaining (42) at least: - the distance to the radar and the circular of at least one predetermined point of the landing scene, obtained from measurements of said radar, the circular of said at least one predetermined point corresponding to the angle formed from the line of sight of the radar to the projection of said at least one predetermined point of said landing scene in the plane of projection of the circulars, this plane being defined by the line of sight of the radar, and the axis of the angular measurements of said radar reference mark, and - the distance to the ground in the line of sight of the radar, from the phase center of the antenna of said at least one radar; - determination (44) of a reference change matrix making it possible to pass from said predetermined radar reference to a predetermined local geographical reference whose origin corresponds to the phase center of the antenna of said radar and whose two axes correspond respectively to the longitudinal axis and the transverse axis of said landing runway, using the roll, pitch and yaw angles defining the attitude of the aircraft, these angles being supplied beforehand by an inertial unit of the aircraft; - determination (46), in the radar reference frame, of the elevation of said at least one predetermined point of said landing scene, said elevation corresponding to the opposite of the angle formed from the vector starting from the origin of the radar reference frame to said at least one predetermined point of said landing scene, up to the projection of this vector in the projection plane of the circulars, said elevation corresponding to the arc sine of the solution of a second degree equation obtained by determining the component of said at least one predetermined point of said landing scene along the axis of altitudes of said local geographical reference frame, both from said distance to the ground in the radar line of sight and of said pitch angle, and from the application of said reference frame change matrix to the coordinates of said at least one predetermined point of the landing scene measured and expressed in said radar reference frame; - determination (48), in said radar reference frame, of the three-dimensional location of said at least one predetermined point of said landing scene, from said radar distance, said circular and said elevation of said at least one predetermined point of said landing scene.

2. The method (40) of claim 1, further comprising the steps of: - determining (50) the three-dimensional location of said at least one predetermined point of said landing scene expressed in said local geographic reference frame by applying said reference frame change matrix to said three-dimensional location of said at least one predetermined point of said landing scene in said radar reference frame; - from the three-dimensional location expressed in the local geographical reference frame, obtaining (54) the three-dimensional location of said radar expressed in a predetermined reference frame of the landing runway whose origin is a predetermined point of said landing runway and whose two axes correspond respectively to the longitudinal axis and to the transverse axis of the runway, said obtaining comprising the inversion of the sign of the component along the axis of the altitudes of said at least one predetermined point of the landing scene expressed in said local geographical reference frame; - determining (56) the vertical angular deviation of said aircraft relative to a reference approach trajectory, using the three-dimensional location of said radar translated along the x-axis from the runway reference to the GPIP point of intersection of the reference approach trajectory with the landing runway; - determining (60) the lateral angular deviation of said aircraft relative to the reference approach trajectory, using the three-dimensional location of said radar, translated along the x-axis from the runway reference to the GARP reference point for determining the lateral deviations.

3. Method (40) according to claim 1 or 2, wherein said at least one predetermined point of said landing scene corresponds to the threshold midpoint S of said landing runway.

4. Method (40) according to claim 2, in which said at least one predetermined point of said landing scene corresponds to a point of intersection A of two lines of approach lights perpendicular to each other, and in which the norm of the vector going from said point of intersection A to the middle S of the threshold of said landing runway is also taken into account (58), when determining (56) the vertical angular deviation and the lateral angular deviation, by translating, from said norm, the position of said radar, expressed in the predetermined reference frame of said runway along the x axis.

5. Method (40) according to any one of claims 1 to 4, wherein said determination (44) of a reference frame change matrix comprises three successive reference frame changes, namely: - a first reference frame change (68) from the radar reference frame (62) to the aircraft reference frame (70) used by said inertial unit to provide the roll, pitch and yaw angles defining the attitude of the aircraft, using the inclination of said radar; then - a second reference frame change from the aircraft reference frame (70) to an intermediate geographical reference frame having: an origin corresponding to the phase center of the antenna of said radar, an abscissa axis along the terrestrial geographic North direction, an ordinate axis along the terrestrial geographic East direction and an altitude axis along the terrestrial geographic local vertical;- a third change of reference from the intermediate geographical reference to said predetermined local geographical reference (80) defined relative to the plane of the landing scene.;

6. Method (40) according to any one of the preceding claims, further comprising, prior to obtaining (54) the three-dimensional location of said radar expressed in a predetermined reference frame of the landing runway, applying a rotation (52) around the altitude axis of the local geographical reference frame according to a predetermined angle representative of the error in determining the yaw angle V' by said inertial unit of the aircraft, said predetermined angle representative of the error in determining the yaw angle being obtained, prior to applying said rotation, from a point Q defined by its spherical coordinates in the radar reference frame, such that: - its distance from the phase center of the antenna of said radar is unitary, - its circularity is equal to the orientation of the longitudinal axis of said landing runway expressed in the radar reference frame and previously obtained from said measurements of said radar; - its elevation angle is zero, point Q then being expressed in Cartesian coordinates in said local geographic reference frame by means of said reference frame change matrix, said predetermined angle representative of the error in determining the yaw angle being such that _ atan2^ v

7. A computer program comprising software instructions which, when implemented by a programmable electronic device, implement a method for determining the vertical and horizontal angular deviations of an aircraft according to claims 1 to 6.

8. Electronic device (10) for three-dimensional location of an aircraft within a landing scene comprising at least one landing runway, said aircraft carrying at least one radar, the landing scene being considered substantially planar in the domain of the angular aperture of said radar, characterized in that said device comprises: - a first module (12) configured to implement, in a predetermined radar reference associated with said radar, the origin of which corresponds to the phase center of the antenna of said at least one radar, the obtaining of at least: - the distance to the radar and the circular of at least one predetermined point of the landing scene, obtained from measurements of said radar, the circular of said predetermined point of said landing scene corresponding to the angle formed from the line of sight of the radar to the projection of said at least one predetermined point in the plane of projection of the circulars,this plane being defined by the radar sighting axis and the axis of the angular measurements of said radar reference frame, and - the distance to the ground, in the radar sighting axis, from the phase center of the antenna of said at least one radar; - a second module (14) configured to determine a reference frame change matrix making it possible to pass from said predetermined radar reference frame to a predetermined local geographical reference frame whose origin corresponds to the phase center of the antenna of said radar and whose two axes correspond respectively to the longitudinal axis and the transverse axis of said landing runway, using the roll and pitch angles, and yaw defining the attitude of the aircraft, these angles being provided beforehand by an inertial unit of the aircraft; - a third module (16) configured to determine, in the radar reference frame, the elevation of said at least one predetermined point of said landing scene, said elevation corresponding to the opposite of the angle formed from the vector starting from the origin of the radar reference frame to said at least one predetermined point of said landing scene, up to the projection of this vector in the projection plane of the circulars, said elevation corresponding to the arc sine of the solution of a second degree equation obtained by determining the component of said at least one predetermined point of said landing scene along the axis of altitudes of said local geographical reference frame, both from said distance to the ground in the radar line of sight and from said pitch angle, and from the application of said reference frame change matrix to the coordinates of said at least one predetermined point of the landing scene measured and expressed in said radar reference frame; - a fourth module (18) configured to determine, in said radar reference frame, the three-dimensional location of said at least one predetermined point of said landing scene, from said radar distance, said circular and said elevation of said at least one predetermined point of said landing scene.

9. Aircraft landing assistance system comprising at least one radar and one electronic three-dimensional location device according to claim 8.

10. Aircraft comprising an inertial unit and a landing aid system according to claim 9.

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