Method for positioning an aircraft in flight

Abstract

The invention relates to a method for positioning an aircraft (12) in flight by means of a positioning device (24) comprising at least one sensor and a radar (32), the method comprising: a first phase of determining the position of the aircraft (12) (referred to as the first position) by means of the at least one sensor on the basis of signals provided by the sensor or the at least one sensor, b. a second phase of determining the position of the aircraft (12) (referred to as the second position) by means of the radar, simultaneously with the first determination phase, and c. a phase of comparing the data associated with the first position and the data associated with the second position, after which the first position is confirmed as valid or invalid.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for positioning an aircraft in flight. The invention further relates to a related positioning device. The invention further relates to an aircraft comprising such a positioning device. BACKGROUND

[0002] Aircraft are generally equipped with on-board devices for assisting in piloting the aircraft. In particular, when the visibility conditions are reduced (fog, snow or heavy rain), the crew or the pilot of the aircraft refers to such devices, for example during the approach and landing phases.

[0003] To enable correct operation of such devices, the aircraft comprises a device for positioning the aircraft, generally based on inertial sensors and / or radio navigation sensors.

[0004] However, such positioning devices have operational limitations. In particular, the position obtained by the inertial sensors is not sufficiently accurate. Radio navigation sensors are very dependent on the environment and are therefore likely to be disturbed or affected by malfunctions.

[0005] There is therefore a need for a method for complementing conventional aircraft positioning solutions. SUMMARY

[0006] To this end, the subject of the present description is a method for positioning an aircraft in flight, the aircraft flying over a spatial zone comprising on the ground at least characteristic elements arranged in a row, the positioning method being implemented by a positioning device carried by the aircraft, the positioning device comprising a first positioning unit and a second positioning unit, the first positioning unit comprising at least one sensor chosen from among inertial sensors and radio navigation sensors, the second positioning unit comprising a radar, the method comprising:

[0007] - a first stage of determination of the position of the aircraft (called first position) by the first positioning unit from the signal(s) provided by the sensor or sensors,

[0008] - a second stage of determination of the position of the aircraft (called second position) by the second positioning unit, simultaneous with the first stage of determination, the second stage of determination comprising:

[0009] o detection by the radar of the characteristic elements of the overflown zone, each detection being associated with coordinates,

[0010] o determination, from the coordinates of the detected elements, of:

[0011] ■ the distance of the orthogonal projection of the horizontal projection of the radar on a straight line passing through the row of elements or at least one row of elements (called first distance), the horizontal projection of the radar being the orthogonal projection on the ground of the position of the radar,

[0012] ■ the distance of the orthogonal projection of the horizontal projection of the radar on a straight line perpendicular to the row of elements or at least one row of elements (called second distance),

[0013] o determining a second position as a function of the determined first and second distances.

[0014] - a phase of comparing the data associated with the first position and the data associated with the second position, after which the first position is validated or invalidated.

[0015] According to other advantageous aspects of the application, the method comprises one or more of the following features taken separately or according to all technically possible combinations:

[0016] - the overflight zone is a landing site for the aircraft and the characteristic elements are characteristic elements of the landing site, such as beacons;

[0017] - the landing site comprises a runway having a longitudinal axis equidistant from the longitudinal edges of the runway (called runway centerline), the characteristic elements being distributed in at least two longitudinal rows and at least one transverse row on the runway, the longitudinal rows being substantially parallel to the runway centerline, in which the two longitudinal rows are each arranged along a different longitudinal edge of the runway, the transverse row or each transverse row being substantially perpendicular to the runway centerline, the last transverse row in the direction of landing of the aircraft on the runway being called the runway threshold, the first distance being the distance of the orthogonal projection of the horizontal projection of the radar on the runway centerline (called axial offset), the second distance being the distance of the orthogonal projection of the horizontal projection of the radar on a straight line passing through the runway threshold (called distance to the runway threshold);

[0018] - the phase of comparison comprises triggering an alert when the first position is determined to be invalid, the method comprising a phase of modifying the trajectory of the aircraft;

[0019] - the first position is associated with a first standard deviation and the second position is associated with a second standard deviation, the uncertainty of the first position being displayed as a first ellipsoid, the center of which is the first position, the radius of which depends on the first standard deviation, the uncertainty of the second position being displayed as a second ellipsoid, the center of which is the second position, the radius of which depends on the second standard deviation, the first position being determined to be invalid at the phase of comparison when the second ellipsoid and the first ellipsoid do not intersect;

[0020] - when the first position has been determined to be valid, the method comprises a phase of merging the first and second positions to obtain an optimized position of the aircraft;

[0021] - the comparison phase comprises displaying on the display of the positioning device an image of the overflight zone determined from the first position from among a set of images in a database, the displayed image comprising characteristic elements of the zone overflown by the aircraft, the comparison phase further comprising superimposing on the displayed image a pattern of characteristic elements of the overflight zone detected by the radar during the determination of the second position, the first position being determined as valid when the characteristic elements superimposed on the image have substantially the same position on the displayed image as the corresponding characteristic elements already present on the displayed image, and as invalid otherwise;

[0022] - the phase of determining the second position comprises determining an angular offset between the radar axis and a straight line parallel or perpendicular to the row of elements or at least one row of elements, referred to as a reference line, the first distance and the second distance being determined as a function of the angular offset determined;

[0023] - during the phase of determining the second position, the determination of the angular offset comprises:

[0024] - converting the coordinates of each detection into Cartesian coordinates,

[0025] - for each angular offset value in a predetermined range of values, determining for each detection the Cartesian coordinate along the abscissa axis corrected according to said angular offset value,

[0026] - for each angular offset value in a predetermined range of values, determining the number of detections corresponding to each Cartesian coordinate corrected along the x axis, and the angular offset value associated with the maximum number of detections being the angular offset between the radar axis and the reference line.

[0027] - during the phase of determining the second position, the reference line is the center line of the runway, the determination of the distances comprising:

[0028] - calculating the Cartesian coordinates of each detection corrected for the angular offset determined in the determination step, referred to as optimal Cartesian coordinates,

[0029] - determining a position histogram along the x axis of each detection as a function of the optimal Cartesian coordinates of each detection, the histogram having at least two peaks, and

[0030] - determining the axial offset as a function of the Cartesian coordinates along the abscissa axis of the at least two peaks of the histogram.

[0031] - during the phase of determining the second position, the reference line is the center line of the runway, the determination of the distances comprising:

[0032] - calculating the Cartesian coordinates of each detection corrected for the angular offset determined in the determination step, referred to as optimal Cartesian coordinates,

[0033] - A histogram determining the y-axis position of each probe based on the optimal Cartesian coordinates for each probe, the histogram having at least one peak, and

[0034] The distance to the runway entrance is determined by the Cartesian coordinates of the y-axis along the peak of the histogram.

[0035] This specification further relates to an apparatus for locating an aircraft in flight over a space region comprising at least one row of characteristic elements on the ground, the electronic positioning device being carried by the aircraft, the positioning device comprising a first positioning unit and a second positioning unit, the first positioning unit comprising at least one sensor selected from an inertial sensor and a radio navigation sensor, the second positioning unit comprising a radar, the positioning device being configured to implement the method described above.

[0036] This specification further relates to an aircraft that includes the positioning device described above. [Attached Image Description]

[0037] Other features and advantages of the invention will become apparent upon reading the following description of embodiments following the invention, which is given by way of limiting example only and with reference to the following figures:

[0038] -[ Figure 1 ] Figure 1 This is a schematic diagram of an aircraft in flight. The area the aircraft flies over includes the runway and the aircraft's landing point.

[0039] -[ Figure 2 ] Figure 2 This is a schematic plan view of an example of the horizontal projection of the runway and aircraft radar onto the runway plane.

[0040] -[ Figure 3 ] Figure 3 This is a schematic diagram of an example of an electronic calculator.

[0041] -[ Figure 4 ] Figure 4 This is a flowchart of an example of a positioning device, and

[0042] -[ Figure 5 ] Figure 5 yes Figure 4 The flowchart shows an example of the second stage of the positioning method for determining location.

Detailed Implementation Methods

[0043] Figure 1 The image shows a zone of space 9 and an aircraft 12 flying over the zone of space 9.

[0044] In this particular example, the spatial area 9 is a landing site, more precisely a runway 10, and the aircraft 12 is an airplane. In this example, the aircraft 12 is approaching the runway 10 in order to land on the runway 10.

[0045] As Figure 2 illustrated, the runway 10 is a rectangular surface for the landing and takeoff of an aircraft. The runway 10 comprises longitudinal edges (two) and transverse ends (two) which delimit the runway 10.

[0046] The length of the runway 10 is for example between 3 kilometers (km) and 4 kilometers. The width of the runway 10 is for example between 25 meters and 45 meters.

[0047] In the example illustrated in Figure 2 , the runway 10 has a longitudinal axis along the longitudinal direction of the runway 10 and at an equal distance from the longitudinal edges of the runway 10. The longitudinal axis is called the runway centerline Y. An axis perpendicular to the runway centerline Y is also denoted by the reference "X" in Figure 2 .

[0048] The runway 10 comprises a set of characteristic elements 16. For the sake of clarity, only certain characteristic elements 16 are labeled in Figure 2 . The characteristic elements 16 are for example lights, also called light beacons. In one variant, the characteristic elements 16 are radar reflectors such as trihedrons or Luneberg lenses. In another variant, the characteristic elements 16 are other elements found on a runway.

[0049] In the present example, the characteristic elements 16 are distributed in at least two longitudinal rows 18A, 18B and at least one transverse row 20 on the runway 10.

[0050] The longitudinal rows 18A, 18B are substantially parallel to the runway centerline Y. Two of them are each arranged along a different longitudinal edge of the runway 10. The term "arranged along" means that these rows are arranged at a distance of less than three meters from the respective longitudinal edge.

[0051] This or each transverse row 20 is substantially perpendicular to the runway centerline Y. In the example illustrated in Figure 2 , the runway 10 comprises three transverse rows 20A, 20B, 20C of characteristic elements 16. The last transverse row 20A along the direction of landing of the aircraft on the runway 10 is called the runway threshold (the example of the transverse row 20A in Figure 2 .

[0052] In one variant, the runway 10 comprises at least three longitudinal rows: two longitudinal rows 18A, 18B and a third longitudinal row 18C (not shown) which are arranged along the runway centerline Y and located downstream of the runway entrance.

[0053] The skilled person will understand that this example is given by way of illustration. The spatial zone 9 is more generally a transit zone, comprising predetermined characteristic elements 16 (reflectors) arranged in at least one row on the ground, the relief or a known surface. Thus, the spatial zone 9 is for example a landing site which does not comprise a runway or a controlled zone which does not allow the aircraft 12 to land. Furthermore, in one variant, the aircraft 12 is a helicopter or a drone.

[0054] The aircraft 12 further comprises an electronic positioning device 24. The positioning device 24 is carried by the aircraft 12.

[0055] Figure 1 One example of the positioning device 24 is shown. In this example, the positioning device 24 comprises a first positioning unit 26, a second positioning unit 28 and a calculator 29.

[0056] The first positioning unit 26 implements a so-called conventional positioning scheme chosen from among an inertial positioning scheme, a radio navigation positioning scheme and a scheme resulting from a combination of inertial and radio navigation schemes.

[0057] The first positioning unit 26 comprises at least one sensor chosen from among an inertial sensor and a radio navigation sensor. The inertial sensor is for example an accelerometer, a gyroscopic tester or a gyroscope. The radio navigation sensor is for example a GPS (acronym for "Global Positioning System").

[0058] More precisely, in the case of a radio navigation scheme, the first positioning unit 26 comprises for example a VOR system (abbreviation for "Very High Frequency Omnidirectional Range"), a DME system (abbreviation for "Distance Measuring Equipment"), a GPS, an SBAS, a GBAS or an ILS. These systems for example meet the requirements of various types of landing approaches (NPA, LNAV, VNAV, LPV, ILS, etc.).

[0059] The second positioning unit 28 implements a positioning scheme by radar.

[0060] The second positioning unit 28 comprises at least one radar 32 in communication with a calculator, such as the calculator 29 of the positioning device 24. In one variant, the second positioning unit 28 comprises a calculator dedicated thereto for directly processing the measurements made by the radar 32.

[0061] The radar 32 defines a reference frame in the Cartesian reference frame Figure 1 with the abscissa XR , ordinate Y R and altitude Z R . The center is at O R . Ordinate Y R is the longitudinal axis of the probe, called the radar axis. When the radar 32 is correctly positioned on the aircraft 12, the radar axis Y R substantially coincides with the trajectory of the aircraft 12.

[0062] The radar 32 is advantageously a millimeter wave radar. Preferably, the distance resolution of the radar is of the order of a few meters and the angular resolution of the radar is very good, i.e. of the order of a few tenths of a degree.

[0063] The radar 32 preferably comprises at least three reception channels for measuring, for each probe, the radial distance of the probe, the circumferential angle of the probe in the radar 32 coordinate system and the negative elevation angle of the probe in the radar 32 coordinate system. The radial distance from an arbitrary point M is its distance from the origin O R of the coordinate system. The circumferential angle or circumferential is the projected angle on the angular plane (O R X R Y R ) carried by the axis (O R Y R ) and the straight line (O R C) passing through the target point C. The negative elevation angle is the angle formed between the plane (O R X R Y R ) of the radar 32 and the straight line from the radar 32 to the target point C.

[0064] The calculator 29 is for example a computer.

[0065] In the example illustrated in Figure 3 , the calculator 29 comprises a processor 40 comprising a data processing unit 42, a memory 44, a data storage reader 46 and optionally a man-machine interface 48 comprising a keyboard 50 and a display 52.

[0066] The calculator 42 interacts with a computer program product. This computer program product comprises a data storage medium. This data storage medium is a medium readable by the processing unit 42. The readable data storage medium is a medium suitable for storing electronic instructions and easily connectable to the bus of a computer system.

[0067] For example, the data storage medium is a USB key, a magnetic or optical disk, a CD-ROM, a magneto-optical disk, a ROM, a RAM, an EPROM, an EEPROM, a magnetic or optical card.

[0068] The computer program containing the program instructions is stored on a storage medium.

[0069] The computer program can be loaded into the data processing unit 42 and is adapted to implement the positioning method, which will be described below in this specification.

[0070] In another embodiment (not shown), the calculator 29 is produced in the form of one or more programmable logic components (such as an FPGA (Field Programmable Gate Array)), or further in the form of one or more application-specific integrated circuits (such as an ASIC). In this case, the calculator 29 is configured to implement a positioning method, which will be described below in this specification.

[0071] Now we will combine Figure 4 Describe the operation of the positioning device 24. Figure 4 An implementation example of the positioning method is illustrated schematically.

[0072] This positioning method is designed to be implemented during flight over an area that includes the characteristic element 16 on the ground. In particular, this positioning method is especially suitable for the phase when the aircraft 12 approaches the landing site for the aircraft 12.

[0073] The advantage is that this positioning method is implemented in real time, that is, at every instant.

[0074] The positioning method includes a first phase 100 in which a first positioning unit 26 determines the position (referred to as the first position) of the aircraft 12 based on signals provided by the sensor or at least one sensor provided by the first positioning unit 26.

[0075] The first position is thus obtained using conventional inertial and / or radio navigation methods. The first position provides the first coordinates.

[0076] Advantageously, the speed of the aircraft 12 was also obtained at the end of the first determination phase 100.

[0077] The positioning method includes a second phase 110 in which the second positioning unit 28 determines the position of the aircraft 12 (referred to as the second position).

[0078] The second determination phase 110 is carried out simultaneously with the first determination phase 100, and its purpose is to assess the position of the aircraft 12 at the same time. Figure 5 An implementation example of the second determination phase 110 is shown.

[0079] The second determination phase 110 includes: in step 200, radar 32 detects the flyby area (especially...). Figure 1 and Figure 2 Feature element 16 of the runway 10 in the example shown.

[0080] Each detection is associated with a coordinate. In particular, each detection is defined by a radial distance, a circular angle in the coordinate system of the radar 32 and a negative pitch angle in the coordinate system of the radar 32. Thereby, at the end of the detection step, a radar image is obtained on which the detections are represented.

[0081] Equivalently, after changing the coordinate system, each detection can be defined by a radial distance D, a pitch angle S defined with respect to the local horizontal line of the aircraft 12 and a bearing angle G defined with respect to the longitudinal axis of the aircraft 12.

[0082] To convert for example from the coordinates (altitude, circumference) = (E, C) to (elevation, bearing) = (S, G), the Cartesian direction vectors ux= cos E. cos C, uy= cos E. sin C and uz= sin E are first computed. Then a rotation matrix corresponding to the opposite direction of the radar elevation setting angle, a rotation matrix corresponding to the opposite direction of the aircraft roll and a rotation matrix corresponding to the opposite direction of the aircraft pitch are applied successively to said vectors. The obtained vectors are expressed in Cartesian coordinates in the local horizontal coordinate system of the aircraft and the elevation and bearing values are obtained by performing a conversion from Cartesian coordinates to polar coordinates. This operation includes knowing the radar elevation setting angle (related to the mechanical installation of the radar on the aircraft) and the roll and pitch angles of the aircraft (usually provided by the aircraft inertial unit).

[0083] Advantageously, the radar 32 applies a processing such as a constant false alarm rate (CFAR) to the obtained radar image, which allows better detection of the feature elements 16. Thus, in time, the "radar image" is formed by the signals backscattered by the ground and received by the radar. The CFAR processing is applied to said image, which can provide a list of detections with coordinates.

[0084] The second determination phase 110 comprises, in a step 210, determining, from the coordinates of the detected feature elements 16, an angle T between the radar axis Y R and a straight line parallel or perpendicular to the row of elements or at least one row of elements, called reference line. The reference line is a predetermined line according to the geometry of the crossing zone and of the feature elements 16 on the crossing zone. In the example shown, the reference line is the runway centerline Y. The determination step 210 is implemented by the calculator 29. Figure 1 and Figure 2 In the example shown, the reference line is the runway centerline Y. The determination step 210 is implemented by the calculator 29.

[0085] The step of determining the angular offset T comprises for example:

[0086] - converting the coordinates of each detection into Cartesian coordinates,

[0087] - for each angular offset value T test , a Cartesian coordinate along the transverse coordinate axis is determined for each detection corrected for said angular offset value T test ,

[0088] - for each angular offset value T test , the number of detections corresponding to each Cartesian coordinate along the transverse coordinate axis corrected is determined, and the angular offset value T test associated with the maximum number of detections is the angular offset T between the radar axis Y R and the reference line.

[0089] A more specific example of determining the angular offset T is given when the reference line is the Y axis of the runway 10 (and Figure 1 and Figure 2 ). This example takes advantage of the fact that the characteristic elements 16 are arranged in a row parallel to the centerline Y of the runway.

[0090] In said example, the step of determining the angular offset T comprises converting the coordinates of the detected elements into Cartesian coordinates. The Cartesian coordinates are obtained by the following equations:

[0091] x = D.cosS.sinG (1)

[0092] y = D.cosS.cosG (2)

[0093] where:

[0094] • x is the Cartesian coordinate along the transverse coordinate axis,

[0095] • y is the Cartesian coordinate along the longitudinal coordinate axis,

[0096] • D is the radial distance,

[0097] • S is the elevation angle, and

[0098] • G is the bearing angle.

[0099] Then, the determining step 210 comprises: for each angular offset test value T test , a Cartesian coordinate along the transverse coordinate axis is determined for each detection corrected for said angular offset value T test . The angular offset test values T test are values within a predetermined interval of values with a predetermined step. The interval of values is comprised between, for example, -10 degrees (°) and 10°, and the predetermined step is equal to one tenth of a degree. Thus, for each angular offset test value T test, the Cartesian coordinates along the x axis of the detections are obtained by the following formula:

[0100] x = D. cos S. sin (G + T) (2) test

[0101] Then, for each angular offset test value T test , the determining step 210 comprises determining the number of detections corresponding to each Cartesian coordinate corrected along the transverse axis. The angular offset value T test associated with the maximum number of detections is the angular offset between the radar axis Y R and the runway centerline Y. The above is equivalent to producing, for each angular offset test value T test , a histogram of positions along the x axis and calculating for each interval along the x axis the number of detections giving the highest peak (whatever the x value) of its x position, which reflects the case where the detections have been best possible aligned with respect to the runway centerline Y.

[0102] Optionally, the angular offset T is refined by finding the position of the maximum of the second order regression around the peak.

[0103] In a second example, the angular offset T is obtained by performing a principal component analysis (PCA) on the list of detections. In this case, a covariance matrix of the (x, y) pairs is first computed, from which the eigenvectors can be derived and finally the angular offset T.

[0104] In a third example, the angular offset T is obtained by applying a Hough transform on the list of detections, and the accumulation of points gives the angular offset T.

[0105] However, the results obtained by the second and third examples are not as robust as the first example, since each feature element does not always correspond to a detection (probability of detection < 1), or some detections can not be feature elements 16 (other objects in the vicinity of the runway that can cause detections or false alarms).

[0106] At the end of the determining step 210, the Cartesian coordinates of the detections corrected for the angular offset T (called optimal Cartesian coordinates) are obtained by the following formula:

[0107] x = D. cos S. sin (G + T) (4)

[0108] y = D. cos S. cos (G + T) (5)

[0109] ​The second determination phase 110 comprises, in a step 220, determining the relative position of the aircraft 12 with respect to the overflight zone from the determined angular offset T and the coordinates of the detected characteristic elements 16. The determination step 220 is implemented by the calculator 29.

[0110] To this end, the horizontal projection P H of the radar is determined. H is the orthogonal projection of the position of the radar on the ground plane.

[0111] At the same time, the horizontal projection P H of the radar is determined.

[0112] Then, from the determined first distance D1 and second distance D2, a second position of the aircraft 12 is obtained.

[0113] If the overflight zone is an example of a runway 10, Figure 1 and Figure 2 , the first distance D1 is the distance of the orthogonal projection of the horizontal projection P H of the radar 32 on the runway centerline Y (called axial offset D A ). The horizontal projection P H of the radar 32 is the orthogonal projection of the position of the radar 32 on the horizontal plane of the runway 10. The second distance D2 is the distance of the orthogonal projection of the horizontal projection P H of the radar 32 on a straight line passing through the runway threshold (called distance to the runway threshold D SHT ).

[0114] A more specific example of determining the axial offset D A and the distance to the runway threshold D SHT is given below.

[0115] The axial offset D A is obtained, for example, by determining a position histogram along the x-axis of Cartesian coordinates of each detection from the best Cartesian coordinates of each detection. The obtained histogram has as many peaks as there are longitudinal rows of characteristic elements 16 on the runway 10. Thus, the histogram comprises at least two side peaks, corresponding to the two longitudinal rows 18A, 18B extending along the longitudinal edges of the runway 10. The axial offset D A corresponds to the average of the coordinates along the x-axis of the two side peaks, for example.

[0116] In one variation, when runway 10 also has longitudinally arranged feature elements 16 extending along the runway centerline Y, the resulting histogram also has a central peak between the two side peaks. In this case, the axial offset D A For example, the x-position of the central peak.

[0117] For example, the distance D to the runway threshold can be obtained by determining a histogram of the position along the y-axis of each probe based on the optimal Cartesian coordinates for each probe. SHT The resulting histogram has as many peaks as the transverse feature elements 16 on runway 10. In this case, the distance D to the runway threshold... SHT It is the coordinate along the y-axis (on the y-axis) of the farthest peak (i.e., the peak with the largest y-coordinate).

[0118] Optionally, the second determining stage 110 further includes: in step 230, determining the aircraft 12 relative to a reference line (in Figure 1 and Figure 2 In the case of the runway centerline Y), the horizontal velocity is expressed by two components, Vx and Vy, which depend on the changes of the first distance D1 and the second distance D2 over time. The Vx component is the component of the projected velocity on the x-axis. The Vy component is the component of the projected velocity on the y-axis. Step 140 is determined by calculator 29.

[0119] exist Figure 1 and Figure 2 An example of implementing the steps is given in the case of (runway 10).

[0120] In particular, the distance D to the runway entrance SHT The time-varying velocity component Vy is given, and the axial offset D is also given. A The time-varying aspect gives the velocity component Vx. For example, a Kalman filter can be used to calculate these time-varying aspects.

[0121] The positioning method includes a stage 120 that compares data associated with a first position determined in stage 100 and data associated with a second position determined in stage 110. At the end of comparison stage 120, the first position is determined to be valid or invalid. When the first position is determined to be invalid, for example, an alarm is triggered. Comparison stage 120 is implemented by calculator 29.

[0122] In a first embodiment of the comparison phase 120, the first position is compared with the second position to determine whether the first position is valid or not. In particular, the first position is associated with a first standard deviation and the second position is associated with a second standard deviation. The uncertainty of the first position is displayed as a first ellipsoid, the center of which is the first position and the radius of which depends on the first standard deviation. The uncertainty of the second position is displayed as a second ellipsoid, the center of which is the second position and the radius of which depends on the second standard deviation. The comparison phase comprises determining that the first position is not valid when the first ellipsoid and the second ellipsoid do not intersect, in particular when the second ellipsoid is not included in the first ellipsoid. In this case, an alert is triggered for example.

[0123] An example of implementing the comparison is given below. For each position data (d = position denoted by p or speed denoted by v) of the aircraft (denoted by A) from the two sources (s = primary source (inertial and / or radio navigation sensors, phase 100) denoted by capital letters P or V or secondary source (radar, phase 110) denoted by small letters p or v), let us name σ d_s_e :

[0124] σ d_s_e is the square root of the diagonal of the straight line e of the covariance matrix and denotes the covariance matrix of the position (P) of the aircraft (A) (derived from the primary source (capital letter P) and expressed in the coordinate system ReperePiste).

[0125] Thus, σ d_s_X , σ d_s_Y and σ d_s_Z denote respectively the lateral, longitudinal and vertical standard deviations of the position data of the aircraft to be guided.

[0126] The distance between the position data from the two sources is calculated in ReperePiste by the Euclidean norm:

[0127] and

[0128] Let us name Δ d_e the projection of the distance between the position data (d = position, speed) from the two sources on the axes (e = X, Y and Z) of ReperePiste.

[0129] Let us name Max d_eThe maximum uncertainty is for example known.

[0130] Let us rename the acceptable error probability of the position data d from source s to P SensorError (i) = ProbaErr d_s .

[0131] Let us rename the coefficient applied to the standard deviation of the position data d with the source s to k d_s to provide a consistent radius of protection of the integrity target of said source: where k d_s • σ d_s_e represents the uncertainty of the data d from source s and along the e axis.

[0132] If the following relationship is satisfied on any one of the three e axes (at least one), the integrity warning is cancelled for the position data d (si = primary source of the position data d and s2= secondary source of the position data d):

[0133] Δ d_e +k d_s1 • σ d_s1_e > Max d_e

[0134] or Δ d_e +k d_s2 • σ d_s2_e > k d_s1 • σ d_s1_e

[0135] By applying said algorithm and assuming that the sources si, s2are independent, the error probability of the position data d resulting:

[0136] P SystemError_d = ProbaErr d_s1 • ProbaErr d_s2 .

[0137] This comparison phase can control the resulting position error within a certain range at an integrity level according to the safety target set for the flight phase. This is possible, among other things, because the above positioning scheme with radar is independent of the conventional schemes (inertial and radio navigation).

[0138] The skilled person will understand that the comparison stage 120 comprises, in a previous step, changing the coordinate system of the coordinates of the obtained first position and second position so as to place them in the same geometric coordinate system. Indeed, the second position is expressed for example in a coordinate system associated with the ground (for example, the runway), whereas the first position is expressed for example in the terrestrial geographic coordinate system WGS-84. Since the approach and landing constraints are expressed for example with respect to the runway, it is preferable to impute the first position and the second position in the runway coordinate system.

[0139] In a second embodiment, the comparison stage 120 comprises displaying on the display of the positioning device 24 an image of the overflight zone determined from the first position from the set of images from the database. This image is indeed selected as a function of the first position so as to display the current zone flown over by the aircraft 12. Thus, the displayed image comprises the characteristic elements of the zone flown over by the aircraft 12. The database is stored for example in the memory of the calculator 29.

[0140] Such a display is for example an SVGS (Synthetic Visual Guidance System). The SVGS is an instrument approach procedure with vertical guidance that reduces the decision height from the 200 feet standard height of a Category I approach to 150 feet. Such an approach is defined in particular in the standard RTCA DO-359, AC 20-167A and AC 20-185. In the SVGS, the positioning of the aircraft 12 is the basis of the guidance system and of the synthetic visualization system.

[0141] The display stage further comprises superimposing on the displayed image a pattern of characteristic elements 16 of the overflight zone that the radar 32 has detected during the determination of the second position. The pattern of characteristic elements 16 is for example a marking such as a cross or a circle. Said pattern aims to present the characteristic elements 16 by their position.

[0142] Then, when the pattern of characteristic elements 16 superimposed on the image has substantially the same position on the image as the corresponding characteristic elements 16 already present on the image, the first position is validated. Otherwise, the first position is invalidated. In this way, more information can be provided to the pilot and the pilot is convinced of the feasibility of the position.

[0143] Thus, in the present embodiment, the data associated with the first position comprise the image determined in the database as a function of the first position. The data associated with the second position comprise the pattern of characteristic elements 16 detected by the radar and from which the second position is obtained.

[0144] It should be noted that the first embodiment and the second embodiment of the comparison stage 120 are suitable for being combined together.

[0145] Optionally, the positioning method comprises a phase 130 of modifying the trajectory of the aircraft 12 when the first position is determined to be invalid (for example, when the alert is triggered). The modification phase 130 is implemented by the calculator 29. Optionally, said phase is implemented automatically (autopilot). In one variant, said phase is implemented by the pilot or crew.

[0146] Typically, the modification of the trajectory comprises a re-climb of the altitude by the aircraft 12 when the landing conditions are not met (i.e. when the alert is triggered).

[0147] Optionally, when the first position has been determined to be valid, the positioning method comprises a phase 140 of merging the first and second positions to obtain an optimized position. The accuracy of the obtained position is thereby improved.

[0148] In one embodiment, the fusion phase 140 comprises a fusion of the positions obtained in the first determination phase 100 and in the second determination phase 110 by means of a Kalman filter.

[0149] The method thereby makes it possible to combine the positions resulting from the conventional positioning methods (inertial and radio navigation) by means of radar positioning. In particular, radar positioning is used to verify the conventional positioning when the safety objectives of the in-flight navigation cannot be achieved with the conventional positioning methods (for example, approach and landing phases in conditions of no visibility).

[0150] The method thereby improves the level of integrity and / or continuity and / or accuracy of one or more conventional positioning schemes. The positioning is thereby more reliable and safer.

[0151] The automatic piloting of the aircraft (autopilot) is based on the deviation of the position from the final approach segment. The lateral and vertical deviations are expressed for example in meters or in degrees (standard DO-253). In category I approach and landing, the standard AC 120-118 requires an integrity of the positioning scheme greater than 1-107and an angular accuracy better than 0.2° vertically and better than 0.4° laterally. The method makes it possible to achieve these levels of integrity by combining the conventional positioning methods with said radar method.

[0152] The method is for example applicable to the descent phase of the aircraft below 200 feet and landing on a runway in conditions of no visibility with a conventional ILS ("Instrument Landing System") category I positioning scheme and / or LPV (Satellite Vertical Navigation Precision Approach) enhanced by the radar positioning scheme described above.

[0153] During the approach and landing phase, for example below the decision altitude or height, the crew or pilot should have acquired the visual references required for landing (approach lights, threshold and runway edge and wheel contact area). The positioning system 24 can lower the decision threshold below the normal values, since these values are determined by the normal positioning scheme. Thereby, when the above is not possible and the alarm is triggered, the landing approach is interrupted, while the aircraft resumes altitude.

[0154] The implemented radar positioning does not require a database of images, and therefore can be used for all types of overflown areas, even if the area is not referenced. Unlike the schemes based on databases that occupy a large amount of storage space, the implemented radar scheme is more easily portable on board the aircraft. Moreover, the method does not require any modification or addition to the infrastructure of the landing site (airport).

[0155] The person skilled in the art will understand that the above embodiments can be combined with each other when such a combination is compatible.

[0156] One application example relates for example to the landing of an aircraft on a runway. However, the present method is also applicable to other landing sites, such as helipads for helicopters, or landing sites outside the conventional landing sites. Similarly, the present method is applicable to other phases of flight, such as taxiing, take-off, cruising or further descent.

Claims

1. A method for locating an aircraft (12) in flight, the aircraft (12) flying over a space region (9) comprising, on the ground, at least one row of characteristic elements (16) arranged (18A, 18B, 20A, 20B, 20C), the locating method being implemented by a locating device (24) carried by the aircraft (12), the locating device (24) comprising a first locating unit (26) and a second locating unit (28), the first locating unit (26) comprising at least one sensor selected from an inertial sensor and a radio navigation sensor, the second locating unit (28) comprising a radar (32), the method comprising: a. The first positioning unit (26) determines the position of the aircraft (12) based on the signal provided by the sensor or at least one sensor, referred to as the first position, in the first stage. b. The second positioning unit (28) determines the position of the aircraft (12), referred to as the second position, in a second stage that occurs simultaneously with the first stage. The second stage includes: i. The radar (32) detects the characteristic elements (16) of the area it flies over, and each detection is associated with coordinates. ii. Based on the coordinates of the detected element, determine: (1) The horizontal projection (P) of the radar (32) H The distance of the orthogonal projection onto a straight line passing through the row of elements or at least one row (18A, 18B, 20A, 20B, 20C) is called the first distance (D1), and the horizontal projection (P) of the radar (32) is the distance of the horizontal projection onto the straight line passing through the row of elements or at least one row of elements (18A, 18B, 20A, 20B, 20C). H ) is the orthogonal projection of the position of the radar (32) on the ground. (2) The horizontal projection (P) of the radar (32) H The distance of the orthogonal projection onto a straight line perpendicular to the row of elements or at least one row (18A, 18B, 20A, 20B, 20C) is called the second distance (D2). iii. Determine the second position based on the determined first and second distances (D1, D2). c. A stage of comparing the data associated with the first position and the data associated with the second position, after which the validity or invalidity of the first position is confirmed. The flyover area is the landing point of the aircraft (12), and the feature element (16) is a feature element of the landing point. The landing site includes a runway (10) having a longitudinal axis equidistant from the longitudinal edges of the runway, referred to as the runway centerline (Y). The feature element (16) is distributed on the runway (10) in at least two longitudinal rows (18A, 18B) and at least one transverse row (20A, 20B, 20C). The longitudinal rows (18A, 18B) are substantially parallel to the runway centerline (Y), with each of the two longitudinal rows (18A, 18B) arranged along a different longitudinal edge of the runway (10). The transverse row, or each transverse row (20A, 20B, 20C), is substantially perpendicular to the runway centerline (Y). The last transverse row (20A) of the aircraft in the landing direction on the runway (10) is referred to as the runway threshold. The first distance (D1) is the horizontal projection (P) of the radar (32). H The distance of the orthogonal projection onto the runway centerline (Y) is called the axial offset (D). A The second distance (D2) is the horizontal projection (P) of the radar (32). H The distance of the orthogonal projection of the line passing through the runway threshold is called the distance to the runway threshold (D). SHT ).

2. The method according to claim 1, wherein the characteristic element of the landing site is a beacon.

3. The method according to claim 1 or 2, wherein the comparison stage includes: An alarm is triggered when the first position is determined to be invalid; the method includes a phase of modifying the trajectory of the aircraft (12) when the alarm is triggered.

4. The method of claim 1 or 2, wherein the first position is associated with a first standard deviation, the second position is associated with a second standard deviation, the uncertainty of the first position is displayed as a first ellipse, the center of the first ellipse being the first position, the radius of the first ellipse depending on the first standard deviation, the uncertainty of the second position is displayed as a second ellipse, the center of the second ellipse being the second position, the radius of the second ellipse depending on the second standard deviation, and the first position is determined to be invalid in the comparison phase when the second ellipse and the first ellipse do not intersect.

5. The method of claim 4, wherein when the first position has been determined to be valid, the method includes the step of merging the first and second positions to obtain an optimized position of the aircraft (12).

6. The method according to claim 1 or 2, wherein the comparison phase includes displaying on the display of the positioning device (24) an image of the fly-over area determined from a set of images in a database according to the first position, the displayed image including feature elements of the area fly-over by the aircraft (12), the comparison phase further including superimposing a pattern of feature elements (16) of the fly-over area detected by the radar (32) during the determination of the second position onto the displayed image, wherein the first position is determined to be valid when the feature elements superimposed on the image have substantially the same position on the displayed image as corresponding feature elements already present on the displayed image, otherwise the first position is determined to be invalid.

7. The method according to claim 1 or 2, wherein the step of determining the second position includes determining the radar axis (Y). R The angular offset (T) between the line parallel or perpendicular to the row of elements or at least one row (18A, 18B, 20A, 20B, 20C) of elements, referred to as the baseline, is used to determine the first distance (D1) and the second distance (D2).

8. The method of claim 7, wherein in the step of determining the second position, determining the angular offset (T) includes: a. Convert the coordinates of each probe into Cartesian coordinates. b. For each angular offset value (T) included within the predetermined value range test For each detection, the determined angular offset value (T) is... test Corrected Cartesian coordinates along the horizontal axis. c. For each angular offset value (T) within the predetermined value range test ), determine the number of probes corresponding to each Cartesian coordinate corrected along the said horizontal axis, and the angular offset value (T) associated with the maximum number of probes. test ) is the radar axis (Y) R The angular offset (T) between the baseline and the reference line.

9. The method of claim 7, wherein the baseline is the runway centerline (Y), and in the stage of determining the second position, the distance determination includes: a. Calculate the Cartesian coordinates of each probe for correction to the angular offset (T) determined in the determination step, referred to as the optimal Cartesian coordinates. b. Determine a position histogram along the x-axis for each probe based on the optimal Cartesian coordinates for each probe, wherein the histogram has at least two peaks, and c. Determine the axial offset (D) based on the Cartesian coordinates of the x-axis along at least two peaks of the histogram. A ).

10. The method of claim 7, wherein the baseline is the runway centerline (Y), and in the stage of determining the second position, the distance determination includes: a. Calculate the Cartesian coordinates of each probe for correction to the angular offset (T) determined in the determination step, referred to as the optimal Cartesian coordinates. b. Determine a histogram of the y-axis position for each probe based on the optimal Cartesian coordinates for each probe. This histogram has at least one peak. c. Determine the distance to the runway threshold based on the Cartesian coordinates of the y-axis along one or more peaks of the histogram (D). SHT ).

11. A device (24) for locating an aircraft (12) in flight, the aircraft (12) flying over a space region (9) which includes, on the ground, at least one row of characteristic elements (16) arranged (18A, 18B, 20A, 20B, 20C), the positioning device (24) being carried by the aircraft (12), the positioning device (24) comprising a first positioning unit (26) and a second positioning unit (28), the first positioning unit (26) comprising at least one sensor selected from an inertial sensor and a radio navigation sensor, the second positioning unit (28) comprising a radar (32), the positioning device being configured to implement the method according to any one of claims 1 to 10.

12. An aircraft comprising the positioning device (24) according to claim 11.

Images