Method and device for aircraft navigation assistance
The method and device enhance navigation by predicting vertical protection levels using a mesh-based calibration of GNSS and barometric data, enabling continued flight and compliance with regulatory standards during satellite signal loss.
Patent Information
- Application Number
- FR2023014189
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-12-14
- Publication Date
- 2025-11-07
- Estimated Expiration
- 2043-12-14
Smart Images
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Abstract
Description
Title of the invention: Method and device for aircraft navigation assistance
[0001] The present invention relates to a method for aiding the navigation of an aircraft comprising a GNSS signal receiver and an altimeter.
[0002] The present invention also relates to a corresponding aircraft navigation aid device, as well as a computer program comprising instructions which lead such a navigation aid device to perform the aircraft navigation aid method.
[0003] The present invention belongs to the field of aircraft navigation aids involving a receiver of navigation signals from a constellation of GNSS (Global Navigation Satellite Systems) type satellites.
[0004] The performance of such navigation aids is evaluated in particular by means of two indicators: accuracy and integrity.
[0005] Accuracy qualifies the position (or speed) error observed in nominal operation, i.e. in the absence of failure or signal loss.
[0006] Positioning integrity refers to the degree of confidence that the user can place in the position (or speed) information provided by the navigation aid system. Integrity includes the system's ability to provide an alarm in case of loss of integrity.
[0007] Integrity can be expressed by specifying, for each calculated position or speed, a confidence interval within which the actual position (or speed) may fall outside this interval due to an undetected failure of the navigation system. The confidence interval can be defined according to a risk level predetermined by the user. Integrity can also be expressed by issuing an alarm signal if the confidence interval is excessive relative to a given limit for performing the operation.
[0008] The navigation aid system makes it possible in particular to establish an altitude in a given geometric frame of reference and to associate it with a geometric vertical protection level.
[0009] The geometric vertical protection level corresponds to half the length of a segment on the vertical axis (i.e. the axis perpendicular to the horizontal plane of a reference ellipsoid, for example the WGS-84 ellipsoid) of an ellipsoid whose center is the current measured position of the aircraft and which describes the region assured of containing the position of the aircraft with a given confidence level.
[0010] Depending on the type of aircraft, a more or less low level of vertical protection is imposed by the regulations applicable to the flight area. For example, for unmanned aircraft such as drones, the required level of vertical protection is typically on the order of a few tens of meters.
[0011] Satellite systems are supplemented by so-called augmentation systems to guarantee vertical integrity to within a few tens of meters, since the redundancy of GPS signals alone does not necessarily guarantee this level of integrity for the vertical position. Augmentation systems calculate and transmit correction messages for the satellite data. These correction messages increase the accuracy of the measurements and / or guarantee the integrity of the navigation system at a particularly low level of autonomous failure risk (Pr), typically on the order of 10⁷ per flight hour.
[0012] However, in the event of a loss of integrity of the navigation solution, the required level of vertical protection may no longer be guaranteed for all or part of the future trajectory.
[0013] Document EP 1 462 761 describes a method for augmented vertical integrity navigation assistance in which altitude measurements are obtained, in the event of the loss of one satellite signal among the n normally accessible satellite signals, by hybridizing GPS and barometric measurements. The barometric measurements are regularly recalibrated using GPS measurements and optionally temperature compensation.
[0014] However, since this method relies solely on the redundancy of GPS signals and not on augmentation systems or complementary measurements provided by other GNSS constellations, it cannot guarantee vertical integrity with a high risk of failure, for example, 10⁷ per hour, and with vertical protection of only a few tens of meters. Furthermore, this method cannot limit the drift in accuracy of the altitude estimated from barometric measurements alone in the absence of a temperature sensor, so that navigation based solely on barometric measurements is only possible to a very limited extent.
[0015] One object of the invention is then to propose a navigation aid method enabling the prediction of the evolution of the level of vertical protection associated with barometric measurements when an integrated altitude measurement from the signals of the satellite constellation is no longer available, in particular in order to allow optimal decision-making on the continuation of a mission to be carried out by an aircraft using barometric altitude measurements.
[0016] To this end, the invention relates to a method for aiding the navigation of an aircraft comprising at least one GNSS signal receiver and a barometric altimeter, the method comprising the following steps: - provision of a mesh of an aircraft evolution area including a current position of the aircraft at a current date for calibration, the mesh comprising a plurality of cells; - Mesh calibration, including assigning each cell a calibration model based on: i) of GNSS signals received on the current date allowing a vertical protection level to be established with respect to a given risk and, where applicable, at least one date prior to the current date, (ii) at least one barometric measurement carried out on the current date and, where applicable, on that date prior to the current date, and iii) a model for propagating uncertainties between the current position and the grid cell over a geometric altitude that would be determined at any position of this grid cell from a barometric measurement; and - for at least one future planned aircraft position within the aircraft's operating area, an estimate of an uncertainty on a geometric altitude that would be determined from a barometric measurement at the future position and the calibration of the mesh retained at the current date.
[0017] At any point of interest in the evolution zone, the calibration model of the mesh in which this point of interest is located makes it possible to know, from the uncertainty propagation model, the accuracy of the determination of the geometric altitude from the barometric altitude which would be determined from barometric measurements at the point of interest and the current calibration of the altimeter.
[0018] Thanks to the calibration model assignment step, this accuracy is also the best possible accuracy in the presence of the set of measurement data collected on the current date, but also prior to the current date if necessary.
[0019] In the end, it is therefore possible to predict, for a plurality of points of a portion of the trajectory of the future aircraft, the minimum vertical protection limit that can be associated with each of these points in the event of loss of integrity of the GNSS signals leading to a purely barometric altitude measurement, the vertical protection limit being estimated on the basis of the GNSS and barometric measurements available on the current date.
[0020] Thanks to this prediction, the aircraft can be kept in flight as long as the vertical protection limit thus provided allows it, navigation being ensured from barometric measurements as long as the integrity of the satellite signals is not restored.
[0021] It is therefore understood that the method according to the invention makes it possible to extend the flight time of the aircraft in many cases of loss of integrity of satellite signals, while respecting local regulations, the flight being carried out on the basis of barometric measurements alone and an optimized calibration of these measurements until the integrity of the signals is restored.
[0022] According to other advantageous aspects of the invention, the method comprises one or more of the following features, taken individually or in all technically possible combinations:
[0023] - the process includes a decision step on whether to continue a mission to to be performed by the aircraft from the current position, the decision step including the evaluation of integrity performance with GNSS signals at the current date, and: I) if the assessment is positive, continuation of the mission, and otherwise, II) estimation of a remaining flight time under the assumption that the uncertainty in the aircraft's barometric altitude for all future positions planned from the current position during this remaining flight time remains below a predetermined threshold from the latest available calibration model for each grid cell, and III) depending on the remaining flight time, the provision of a landing instruction or a mission continuation instruction for a maximum duration calculated from the remaining flight time;
[0024] - The mesh calibration step includes: a) the determination of a first geometric altitude of the current position from the GNSS signals received on the current date and a first barometric altitude of the current position from the barometric altitude measurement carried out on the current date, b) for each grid cell, the construction of a candidate calibration model at the current date configured to estimate, at an estimation date the same as or later than the current date, a geometric altitude of the aircraft at any position in the grid cell from a barometric measurement taken at that position on the estimation date, and c) for each stitch: (a) if a previous calibration model, corresponding to a candidate calibration model at a date prior to the current date, was assigned to the grid cell at the previous date, and if an uncertainty in a geometric elevation estimated at a reference point of the grid cell with the previous calibration model is less than that of the candidate calibration model, the assignment of the previous calibration model to the respective mesh, and otherwise, |3) the assignment of the candidate calibration model to this mesh;
[0025] - the evolution zone is subdivided into meshes along a vertical direction along in which the altitude is measured;
[0026] - the subdivision of the evolution zone into meshes is further carried out according to two horizontal directions perpendicular to the vertical direction;
[0027] - the calibration and estimation steps are repeated periodically;
[0028] - the mesh provisioning step is performed before the first iteration of the calibration stage, the area of evolution being chosen so that a predetermined trajectory to be followed by the aircraft is entirely contained within the area of evolution;
[0029] - the mesh provisioning step is performed before each iteration of the step calibration, the evolution zone comprising for each supply step at least a portion of a predetermined trajectory to be followed by the aircraft from the current position;
[0030] - the calibration step includes, after step c), a grouping step d), during which, for each of the outermost cells of the mesh along at least one predetermined direction, if the same calibration model has been assigned at the current date to said cell and to a neighboring cell along the predetermined direction, only the calibration model of the neighboring cell is retained;
[0031] - a number of mesh cells is fixed for all iterations of the step of mesh supply, and for an iteration of the supply step subsequent to a grouping step d), the volume of the evolution zone for said iteration of the supply step is equal to the volume of all the meshes retained at the end of said step d).
[0032] - at the calibration stage, the GNSS signals received on the current date allowing to establish a vertical protection level against a given risk and, where appropriate, at least one date prior to the current date, are signals transmitted to the receiver by at least one aircraft-independent auxiliary GNSS signal receiving device, these signals transmitted to the receiver having been received by at least one auxiliary receiving device prior to the current date, the process then being implemented in a predictive mode.
[0033] The invention also relates to an aircraft navigation aid device comprising: - at least one GNSS signal receiver, - at least one barometric altimeter, - a meshing module, configured to implement the step of providing a mesh of an aircraft's movement area in the aircraft navigation aid process as described above, - a calibration module, configured to implement the mesh calibration step of the aircraft navigation aid process as described above - a determination module, configured to estimate, for at least one planned future aircraft position within the aircraft's operating area, an uncertainty on a geometric altitude that would be determined from a barometric measurement at the future position and a mesh calibration retained at a current date by the calibration module.
[0034] According to other advantageous aspects of the invention, the device comprises the following feature
[0035] a decision module, configured to implement the decision step of the aircraft navigation aid process as described above.
[0036] The invention also relates to a computer program comprising instructions which lead the device as defined above to execute the navigation aid method as defined above.
[0037] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:
[0038] [Fig-1] [Fig.1] is a schematic representation of an aircraft comprising an navigation aid device according to the invention;
[0039] [Fig.2] [Fig.2] is a flowchart representation of a mode of implementation of a process implemented by the device of [Fig.1];
[0040] [Fig. 3] [Fig. 3] is a representation of the process of [Fig. 1], on which are shown the input and output data of the different stages;
[0041] [Fig.4] [Fig.4] is a two-dimensional schematic representation of the evolution of a fixed mesh provided at the end of a mesh provision step of the process of [Fig.2] or [Fig.3], for an example of aircraft trajectory between two instants t1 and t2;
[0042] [Fig.5] [Fig.5] is a two-dimensional schematic representation of the evolution of an adaptive mesh provided at the end of a mesh provision step of the process of [Fig.2] or [Fig.3], for an example of aircraft trajectory between two instants t1 and t2;
[0043] [Fig.6] [Fig.6] is a two-dimensional representation of the optional steps grouping and refining a vertical mesh at a current date t of a calibration step of the process of [Fig.2] or [Fig.3].
[0044] The invention relates to a method for aiding the navigation of an aircraft 100.
[0045] Aircraft 100 is shown schematically in [Fig.1].
[0046] The aircraft 100 includes a GNSS (Geolocation and Navigation by Satellite System - in English, "Global Navigation Satellite Systems") signal receiver 110, a barometric altimeter 120 and a navigation aid device 130 according to the invention.
[0047] Alternatively, the aircraft 100 comprises several GNSS signal receivers 110 forming a navigation solution which combines the measurements of these receivers 110.
[0048] The receiver or, where applicable, the receivers 110 are configured to receive satellite signals, or equivalently GNSS signals, designated by S(GNSS) in the figures, from a plurality of navigation satellites of one or more GNSS systems.
[0049] The signals processed can be emitted by one or more constellations including GPS, Galileo, GLONASS or Beidou.
[0050] The satellite signals include navigation messages, the receiver 110 being configured to determine at least three geographic coordinates of the aircraft 100 from the navigation messages.
[0051] The receiver 110 can also be configured to receive augmented navigation messages from one or more satellite-based geolocation accuracy augmentation systems.
[0052] The accuracy enhancement system can be ground-based. This is then a LAAS type system or equivalent GBAS (in English, "Local Area Augmentation System" or "Ground Based Augmentation System").
[0053] Alternatively or in addition, the accuracy enhancement system may include geostationary satellites. This is then a type of SBAS (Spatial Based Augmentation System), such as EGNOS, WAAS, MSAS, etc.
[0054] In the following, the expression "GNSS signals" refers to augmented or unaugmented signals.
[0055] Augmented navigation messages include, for example, information correction of geolocation measurements made by the 110 receiver and information characterizing the integrity of the GNSS system(s), where applicable.
[0056] Information characterizing the integrity of the GNSS system may include instructions to reject the use of one or more satellites identified as faulty, and / or vertical and / or horizontal protection level information.
[0057] Alternatively or in addition, the 110 receiver, or where applicable the navigation solution, may rely on the redundancy of satellite signals and / or measurements provided by the different 110 receivers, and / or integrity messages transmitted by satellite signals, and / or the combination of satellite signals on several frequencies to eliminate the ionospheric component of propagation errors. signals, so as to ensure vertical autonomous integrity (in English, "Vertical Advanced Receiver Autonomous Integrity Monitoring").
[0058] The barometric altimeter 120 is configured to measure a pressure difference between the current position and a reference position.
[0059] The navigation aid device 130 is configured to receive data from the receiver 110 and the barometric altimeter 120.
[0060] Device 130 includes means for implementing the navigation aid method 200 described below.
[0061] The device 130 includes in particular a meshing module 130A, a calibration module 130B, a determination module 130C and a decision module 130D.
[0062] Each of the modules 130A, 130B, 130C, 130D is implemented at least partially by a programmable logic circuit of the FPGA type and / or by software.
[0063] In the latter case, the device 130 further includes at least one memory storing such software and at least one processor enabling it to be executed.
[0064] The navigation aid method 200 is described with reference to Figures 2 to 6.
[0065] This method is implemented when, for example, aircraft 100 begins a mission of scheduled flight, or during the scheduled mission of aircraft 100. The mission of aircraft 100 can only begin or continue if a degree of vertical protection lower than the regulation imposed in the geographical area in which the mission of the aircraft takes place is respected.
[0066] At a current date t of implementation of the method 200, the aircraft is considered to be at a current position A(t). This position A(t) may be on the ground if the mission has not yet started or if the aircraft 100 has landed during the mission. During the mission, the aircraft is generally in flight at position A(t).
[0067] The navigation aid method 200 includes a step of providing 210 a mesh of an aircraft evolution area including the current position A(t) of the aircraft 100.
[0068] The mesh supply step 210 is implemented by the mesh module 130A.
[0069] The mesh supply step 210 includes the supply of a set of N meshes M_i, N being an integer greater than 1, preferably strictly greater than 1.
[0070] The set of N meshes tiles a predetermined geographical volume V, in which is included the current position A(t) of the aircraft 100.
[0071] The predetermined geographical volume V is chosen so that a geographical area of planned evolution of the aircraft 100 from the current position A(t) is included in the geographical volume V.
[0072] In particular, at least a portion, advantageously the whole, of a planned TR trajectory of the aircraft from the current position A(t) can be included in the geographical volume V.
[0073] Advantageously, each mesh M_i is parallelepiped.
[0074] Advantageously, all the meshes M_i have the same volume V_i = V / N.
[0075] If the mesh consists of equidistributed parallelepiped cells M_i, each cell M_i can be characterized by the geographical coordinates of a reference point of the cell, for example the altitude Z_i, the latitude Lat_i, and the longitude Lon_i of this reference point.
[0076] The reference point is, for example, the center of the rectangular parallelepiped forming the mesh M_i.
[0077] The mesh is at least vertical, as shown in Figures 4 and 5. In other words, the geographical volume V is subdivided into at least two cells M_i of different altitudes Z_i along a vertical direction Z with respect to which the altitudes are defined.
[0078] Advantageously, the mesh is also made along at least one direction among two horizontal directions X, Y orthogonal to the vertical direction, as shown in two dimensions in [Fig.4].
[0079] Advantageously, the meshes M_i are equidistributed along at least one of the horizontal directions X, Y, preferably along both horizontal directions X and Y, as shown in [Fig.4].
[0080] The mesh supply step 210 may include: a) the provision by an operator to the mesh module 130A of device 130 of the predetermined geographic volume V and / or the planned trajectory TR and the number N of cells M_i, and b) the subdivision of the geographic volume V into N cells by the mesh module 130A, the geographic volume V being either provided to the mesh module 130A, or determined by the mesh module 130A from the planned trajectory TR. The latter case is represented in [Fig.4].
[0081] The mesh calibration step 220 follows the mesh supply step 210.
[0082] The calibration step 220 includes assigning to each mesh M_i a calibration model C_i(t) at the current date t at which the process 100 is implemented.
[0083] The calibration step 220 is carried out using a calibration module 130B of the device 130.
[0084] The calibration module 130B receives from the receiver 110 at least three geometric coordinates characterizing the position of the aircraft 100 at the current time t, determined from the satellite signals received by receiver 110 at the current date t.
[0085] The three geometric coordinates are for example a geometric altitude Z_geo(t) along the vertical direction Z, a latitude Lat_geo(t) and a longitude Lon_geo(t).
[0086] The calibration module 130B also receives at least one barometric altitude Z_baro(t) characterizing the position of the aircraft 100 at the current date, determined from at least one barometric measurement made by the barometric altimeter 120 at the current date t.
[0087] Calibration step 220 includes the construction of a candidate calibration model C_can (t) at the current date t.
[0088] The candidate calibration model C_can (t) is configured to estimate, at the estimation date t_est, a so-called "reconstituted" geometric altitude Z_geo, rec (A', t_est) of the aircraft 100 at any position A' which would be determined from a barometric altitude measurement Z_baro (A', t_est) carried out at this position A' at the estimation date t_est, as well as its uncertainty.
[0089] By way of example, at the current position A(t), if the GNSS signals are intact at the current time t, the following candidate calibration parameters are calculated from the GNSS signals: - the candidate calibration itself, which is the difference ô_alt between the geometric altitude Z_geo(t) determined by the GNSS receivers and the barometric altitude Z_baro(t) measured at the current position A(t): ô_alt = Z_geo(t) - Z_baro(t); - a reference standard deviation o_cantA.t) of the candidate calibration error at the current date t, which is equal to the vertical positioning standard deviation ov,GNss(A(t)) of the geolocation using intact GNSS signals, possibly including augmented navigation messages, received by receiver 110 at the current position A(t): o_can = ov,GNss(A(t)); and
[0090] - a reference bias B_can of the candidate calibration at the current date t, which is equal to the estimation bias of the standard deviation of the vertical positioning error ov,gnss (A(t)): B_can= Bv,GNss(A(t)); and
[0091] - memorization of position A and calibration time t.
[0092] The calibration module 130B implements an uncertainty propagation model between the current position A(t) and any mesh M_i, i ranging from 1 to N, the uncertainty propagation model being chosen to evaluate the uncertainty on the reconstructed geometric altitude Z_geo,rec (A', t_est).
[0093] For each mesh M_i, in order to select the best calibration between the previous calibration and the candidate calibration, the uncertainty can then be calculated, for example expressed in terms of vertical protection limit, on the accuracy of the reconstructed geometric altitude Z_geo,rec (A', t_est)i, from the uncertainty propagation model.
[0094] To select the best calibration, the estimation date t_est can be chosen to be equal to the current date t.
[0095] For example, the model for propagating calibration uncertainties at any position A' and at the estimation date t_est can take into account one or more of the following terms, advantageously all of the following terms:
[0096] a) a horizontal accuracy degradation oH, characterizing the degradation of the standard deviation due to the horizontal separation between the position A' and the current position chosen for calibration A(t), which can be evaluated according to the following equation:
[0097] (7H = kHdH ([Lat^j Lon^], [LatA^Lon^]) (1)
[0098] where dH is the horizontal distance between position A' and the current position for calibration A(t) and kH is a predetermined horizontal degradation rate. For example, kH can be equal to 2.7 x 10⁴ m / m;
[0099] b) a temporal accuracy degradation ot, characterizing the degradation of the standard deviation due to the temporal separation between the estimation date t_est and the current date for calibration t, which can be evaluated according to the following equation: [oioo] a = (2) 'rest il coit t \ /
[0101] where kt is a predetermined temporal degradation rate. For example, kt may be equal to 4.2 x 10³ m / s;
[0102] c) a vertical accuracy degradation ov, characterizing the degradation of the standard deviation due to the vertical separation between the position A' and the current position A chosen for calibration, which can be evaluated according to the following equation:
[0103] (rv = kv\ZgeoA'-ZgeoA\ (3)
[0104] where kv is a predetermined vertical degradation rate. For example, kv may be equal to 1.066 x 10⁻¹ m / m.
[0105] In the case where the three terms oH, ot, t_est and ov are calculated, the standard deviation ocan associated with the candidate calibration model C_can(t) on the reconstructed geometric altitude Z_geo,rec (A', t_est) from a barometric measurement which would be carried out at point A' at time t_est is obtained with the following equation: ^can ( A'-' ^A^ ^est ) “ ^canAit)
[0107] Advantageously, in the case where the signals received by receiver 110 include augmented navigation messages: - the total uncertainty associated with each candidate calibration model C_ can(t) includes uncertainty terms calculated from the augmented navigation messages, and / or -1'reference standard deviation o_can,A(t) of the candidate calibration error at current date t and / or the reference bias B_can of the candidate calibration are calculated from the augmented navigation messages.
[0108] The vertical protection limit DPVican at the risk Pr of the barometric altitude at the reference point of the grid M_i and at time t_est associated with the candidate calibration model C_can(t) of the grid M_i will be given by the following equation: P «Z> ^z> ^est ) ~ K-md&can(Lat^ Lont, (5)
[0110] where Kmd is the normalized threshold for missed detection at risk level Pr, namely: [01111 (fi)
[0112] In the case where the mesh is only vertical, the calibration module 130B advantageously assigns to all the cells M_i the latitudes and longitudes of the current position, so that Lat_i=Lat_geo(t) and Lon_i =Lon_geo(t) for all the cells M_i.
[0113] For each grid cell M_i, if a calibration model C_i(t') has been assigned at a date t' prior to the current date t, the calibration module 130B compares the uncertainty on the reconstructed geometric altitude Z_geo,rec(i, t_est) which would be determined from a barometric measurement at the reference point of grid cell M_i at the date t_est associated with the candidate calibration model C_can(t) and that which is associated with the previous calibration model C_i(t').
[0114] For example, the calibration module 130B compares, for each mesh M_i, the vertical protection limit DPVi>can at the risk Pr associated with the candidate calibration model C_can(t) and that which is associated with the previous calibration model C_i(t').
[0115] If the uncertainty on the altitude Z_geo,rec(i, t_est) associated with the previous calibration model C_i(t') is strictly less than that of the candidate calibration model C_ can(t), the previous calibration model C_i(t') is assigned to the grid M_i at the current date t and becomes the current calibration model C_i(t).
[0116] If no prior calibration model has been assigned or if the uncertainty on the reconstructed geometric altitude Z_geo,rec(i, t_est) associated with the prior calibration model C_i(t') is greater than or equal to that of the candidate calibration model C_ can(t), the candidate calibration model C_ can(t) is assigned to the grid M_i at the current date t and becomes the current calibration model C_i(t).
[0117] This step is schematically represented in [Fig.4] in which the geographical volume V containing the entire planned trajectory TR has been subdivided into eight parallelepiped cells of the same volume.
[0118] At a first current position A(ti) corresponding to a first date tb, a first calibration step 220 was carried out. First calibration models C_i(ti) were assigned to each of the cells Mi to M8.
[0119] At a second date t2 subsequent to date tb the aircraft 100 is at a second current position A(t2) at which a second calibration step 220 is implemented while keeping the same mesh.
[0120] In this example, a previous calibration model is therefore available for each of the cells, namely the calibration model assigned at date tb
[0121] Following the comparison of the candidate calibration model C_can(t2) with the previous calibration model C_i(ti) for each mesh M_i: - a new, more precise calibration model C_i(t2) is assigned to each of the M4, M5, M7 and M8 meshes thanks to the new satellite signals received at the second date t2; - on the other hand, based on the satellite signals received at the first date ti and the second date t2, it appears that the earlier calibration model C_i(ti) is more accurate for the Mb M2, M3 and M6 meshes and should be kept as the calibration model at the second date t2.
[0122] Optionally, the calibration step 220 includes a grouping step 220A, which is shown in [Fig.6].
[0123] For the grouping step 220A, the calibration module 130B identifies the M_b cells said to be external to the volume V. The M_b cells are the cells of which one face forms at least a part of a face of the volume V in at least one determined direction - for example, the vertical direction Z if the mesh is vertical.
[0124] The grouping step 220A includes, for each mesh M_b external to the volume V, the comparison of the current calibration model C_b(t) and C_vois,b(t) retained for the mesh M_b and for a neighboring mesh M_vois,b in the determined direction.
[0125] If these calibration models are identical: - the calibration module 130B links the mesh M_b to the neighboring mesh, which will be called the innermost mesh of the volume V. This operation is symbolized by the angular arrow between the meshes M4 and M5 on the [Fig.6]. - and only the calibration model C_vois,b(t) of the innermost mesh M_vois,b is stored in memory by the calibration module 130B.
[0126] If the mesh is both vertical and horizontal, the grouping step 220A can be carried out in at least two predetermined directions.
[0127] The grouping step 220A reduces the memory cost of the process.
[0128] Alternatively, if the number of calibration models stored in memory at the end of the grouping step 220A is less than a predetermined number of meshes N provided in the supply step 210, the grouping step 220A can be followed by a mesh refinement step 220B, as shown in [Fig.6].
[0129] The mesh refinement step 220B is implemented by the calibration module 130B. It includes the subdivision into N sub-meshes of the volume covered by all the meshes for which a calibration model has been stored in memory at the end of the grouping step, followed by a calibration of the N sub-meshes, on the principle of the calibration described above.
[0130] In the example of [Fig.6], the geographical volume V containing the planned trajectory TR was subdivided vertically into five parallelepiped cells Mi to M5 of the same volume following a mesh supply step 210.
[0131] At the current position A(t) corresponding to time t, a first calibration 220 was performed according to the principle described above. Calibration models C_i(t) were assigned to the cells Mi to M5.
[0132] During the grouping step 220A, it is observed that the mesh M5, which is at the boundary of the volume V along the vertical direction Z, has a calibration model C5(t) identical to that of the neighboring mesh M4. The mesh M5 is therefore grouped with the mesh M4.
[0133] In the refinement step 220B, the volume corresponding to the four units Mi to M4 for which a calibration model C_i(t) has been retained is subdivided into five new units M1 to M'5, with volumes smaller than that of the units Mi to M5. A new candidate calibration model is then calculated for each of these units M'i to M'5. Finally, a final calibration model C'i(t) to C'5(t) is assigned to the units M'i to M'5 according to the procedure described above, with unit M5 remaining linked to unit M'5.
[0134] This arrangement makes it possible to obtain a more accurate calibration model in the entire geographical volume V at a constant memory cost.
[0135] Once the mesh has been calibrated, the determination step 230 is implemented by the determination module 130C for at least one future position of the aircraft 100 planned Apian at a date tpian later than the current date t included in the evolution zone of the aircraft 100.
[0136] The determination step 230 includes the estimation of an uncertainty on a reconstructed geometric altitude Z_geo,rec (Apian, tp kn) which would be determined from a barometric measurement Z_baro (Apian, tpian) at the future position Apian at the date tpian and the calibration of the mesh retained at the current date t.
[0137] In particular, the vertical protection limit DPVk at the risk Pr associated with the calibration model C_k(t) retained at the current date t for a grid M_k in which the future position Apian is located, or whose reference point is closest to the future position, may be associated with the reconstructed geometric altitude Z_geo,rec (Apian, tpian).
[0138] The difference between a reconstructed geometric altitude Z_geo,rec (Apian) of the position Apian (tpian>t) and its barometric altitude Z_baro (Apian, tpian) can be estimated according to the following equation:
[0139] Zgeoree(Ap]an J -Zbaro(Apjan) = 5(lltck(f) (?)
[0140] Alternatively, a vertical protection limit DPV(Apian, tpian) can be calculated by interpolating the vertical protection limits DPV; the risk Pr associated with the calibration model C_i(t) retained at the current date t for a plurality of neighboring cells M_p, including the cell M_k in which the future position Apian (tpian) is located or the closest to this future position, can be associated with the reconstructed geometric altitude Z_geo,rec(Apian, tpian), according to the following equation, the set of neighboring cells M_p being designated by MV:
[0141] DP^A,*» t,, / „„)= interp^, ((LMp lmp Zr). BVp Ait?,J) + ((Latp Loup a2fta„(Lat„ Lon^ Zp, Xi / * J) (8)
[0142] The difference between the geometric altitude Z_geo(Apian) of the Apian position and its barometric altitude can be estimated according to the following equation: Apkln) = interPMV ((LatP2 L°ni> Zp)2
[0143] For a vertical mesh, the neighboring cells M_p can include the two consecutive cells whose reference point altitudes bracket the current estimated altitude.
[0144] For a vertical and horizontal mesh, the neighboring meshes M_p can include the eight meshes whose reference point positions are closest and frame the Apian position (tpian>t).
[0145] If these eight meshes are not available in the supplied mesh, the number of meshes can be reduced to four, two or one depending on the location of the Apian position (tpian> t) in relation to the geographical volume V covered by the mesh.
[0146] Advantageously, the determination step 230 is carried out for a plurality of future positions distributed over a fraction or over the whole of the planned trajectory TR.
[0147] Advantageously, the uncertainty on a reconstructed geometric altitude Z_geo, rec(Apian, tpian) is the largest uncertainty among all those calculated for passage dates within an interval [tpian-Atpian, tp^-At^], Atpian being an uncertainty on the passage date q at the future position Apian.
[0148] Advantageously, the process 200 includes a decision step 240 following the determination step 230, carried out using the decision module 130D.
[0149] Decision step 240 includes the evaluation of an IN integrity performance of vertical positioning from the GNSS S(GNSS) signals received at the current date, i.e. vertical positioning based on the GNSS navigation solution alone, without taking into account barometric measurements.
[0150] If the evaluation is positive, i.e. that the vertical protection level of the solution does not exceed a first predetermined threshold for the mission, the mission of aircraft 100 is continued, this case being symbolized by the notation PM on the [Fig.3], and the calibration 220, determination 230 and decision 240 steps will be advantageously repeated later.
[0151] Otherwise, the decision module 130D estimates a remaining flight time t_vol under the assumption that the uncertainty on the reconstructed geometric altitude Z_geo, rec(Apian, tpian) of the aircraft 100 for all future planned positions Apian from the current position A(t) during this remaining flight time t_vol remains below a second predetermined threshold.
[0152] Preferably, the first threshold and the second threshold are equal.
[0153] For this purpose, the decision module 130D estimates the uncertainty on the reconstructed geometric altitude Z_geo, rec(Apian, tpian) of a plurality of future planned Apian positions included in the planned trajectory TR from the calibration models last assigned to the grids M_i.
[0154] Preferably, if no candidate calibration model has been previously calculated for one or more given grid cells M_i, an initial uncertainty model, such as a model supplied by the manufacturer and based on an uncertainty on the barometric altitude determined during the manufacture of the altimeter 120, is assigned to each of these grid cells.
[0155] The remaining flight time t_vol is then the time remaining before the planned passage date to the last of the plurality of planned future positions for which the uncertainty on the reconstructed geometric altitude is less than a predetermined threshold.
[0156] For example, the remaining flight time t_vol is the time remaining before the planned passage date to the last of the plurality of planned future positions for which the vertical protection limit DPV associated with the reconstituted geometric altitude is less than a predetermined threshold.
[0157] If the remaining flight time is less than or equal to a duration T_att required for the landing of aircraft 200, the decision module 130D advantageously provides a landing instruction, in response to which aircraft 100 is configured to begin landing maneuvers.
[0158] If the flight time is strictly greater than the duration T_att, the decision module 130D provides an instruction to continue the mission of aircraft 100 for a maximum duration equal to the difference between the remaining flight time t_vol and the duration T_att if the integrity of the GNSS signals is not restored.
[0159] The calibration steps 220, determination 230 and decision 240 are advantageously repeated later.
[0160] Advantageously, all the calibration 220, determination 230 and decision 240 steps are repeated periodically.
[0161] In a particular embodiment, the mesh supply step 210 is also repeated.
[0162] For example, the mesh provision step 210 is repeated before each calibration step 220. This arrangement allows the mesh to be dynamically adapted as the aircraft 100 evolves along its planned trajectory TR.
[0163] In particular, if the calibration module 130B is configured to require that the geographic volume V covers the entire forward trajectory from the current position A(t), this volume V decreases over time. Consequently, with a constant number of cells N, the provided mesh can be refined over time. Alternatively, with a constant volume V_i of cells M_i, the number of cells can be reduced as the aircraft 100 advances.
[0164] Alternatively, if only a portion of the TR trajectory is covered by the geographic volume V, the mesh can be adapted according to the evolution of the aircraft 100.
[0165] This step is schematically represented in [Fig.4], for which the geographical volume V contains at the first and second dates ti and t2 only a portion of the planned trajectory TR from the respective current position.
[0166] The volume V(ti) was subdivided in a first supply step 210 of the mesh into three parallelepiped cells of the same predetermined volume Vmaine, so as to cover all the planned altitudes of the aircraft on the portion of the trajectory concerned.
[0167] At the first current calibration position A(ti), corresponding to the first date tb, a first calibration was performed. Calibration models C_i(ti) were therefore assigned to the cells Mi to M3 during a first calibration step 220.
[0168] At the second date t2 subsequent to the first date tb the aircraft 100 is at a second current calibration position A(t2).
[0169] The volume V(t2) is subdivided into four parallelepiped meshes in a second supply step 210 of the prior mesh of the same predetermined volume Vmaiiie, so as to cover all the planned altitudes of the aircraft on the new portion of trajectory concerned.
[0170] A second calibration step 220 is then implemented
[0171] In this example, a previous calibration model is available for the cells Mi, M2 and M3, namely the calibration model C_i(ti) assigned at time tb
[0172] No prior calibration model is available for mesh M4, which is therefore assigned the candidate calibration model C_can(t2) calculated for this mesh.
[0173] Following the comparison of the candidate model C_can(t2) with the previous available calibration models C_i(ti), a new calibration model C_3(t2) = C_can(t2) is assigned to the mesh M3 thanks to the new satellite signals received at time t2.
[0174] On the other hand, based on the satellite signals received at time ti and at time t2, it appears that the previous calibration model is more accurate for the Mb M2 meshes, and should be retained.
[0175] Advantageously, if the mesh supply step 210 is repeated before each calibration step 220, the calibration step 220 also includes a grouping step 220A and a refinement step 220B.
[0176] In a particular embodiment, the GNSS signals received are only signals received at one or more dates t' prior to the current calibration date t 220, calibration carried out before the start of the aircraft 100 mission and at the current date t.
[0177] These GNSS signals may then have been received directly and / or indirectly by the receiver 110. In particular, the GNSS signals may have been transmitted to the receiver 110 after reception by one or more other GNSS signal receiving devices independent of the aircraft 100. In particular, this may only be almanac data associated with the satellite solution(s) implemented.
[0178] The uncertainty propagation model is then constructed solely from these signals prior to the current date t and it allows to predict the performance of the GNSS signals which will potentially be received at the planned position, or even on a portion or the entirety of the planned trajectory TR.
[0179] This embodiment is therefore purely predictive.
[0180] Alternatively, the GNSS signals received at the current calibration date t 220 include or consist of the GNSS signals actually and directly received by the receiver 110 at the current date t if such signals are available. In this case, the method allows for a real-time update of the calibration model.
[0181] In the case of the purely predictive embodiment, the decision step 240 on whether to continue the task to be performed may include, if the evaluation is negative, i.e., if the vertical protection level of the solution exceeds the first threshold predetermined during the planned trajectory portion TR under consideration, a sub-step of generating one or more alternative planned trajectories.
[0182] Each alternative planned trajectory has the same starting point and the same ending point as the planned trajectory and is generated under the constraint that the vertical protection level of the solution does not exceed the first predetermined threshold.
[0183] If no alternative planned trajectory can be generated, decision step 240 may include a decision not to engage the mission or to provide one or more contingency landing areas, i.e. areas configured for an emergency landing, along the planned trajectory TR for each of the points in the planned trajectory TR for which the vertical protection level of the solution might not be sufficient in the event of loss of satellite signals.
[0184] If at least one alternative planned trajectory can be generated, decision step 240 may include the selection of an alternative planned trajectory and the start of the mission.
[0185] It should be noted that the substep of generating one or more alternative planned trajectories can also be combined with the real-time implementation mode.
Claims
Demands
1. Method (200) for assisting the navigation of an aircraft (100) comprising at least one GNSS signal receiver (110) and a barometric altimeter (120), the method comprising the following steps of: - providing (210) a mesh of an area of evolution of the aircraft comprising a current position (A(t)) of the aircraft (100) at a current date (t) for calibration, the mesh comprising a plurality of cells (M_i);- calibration (220) of the mesh, including the assignment to each mesh (M_i) of a calibration model (C_i(t)) on the basis of: i) GNSS signals received at the current date (t) allowing to establish a level of vertical protection with respect to a given risk and, where applicable, at least one date (t') prior to the current date (t), ii) at least one barometric measurement carried out at the current date (t) and, where applicable, at said date prior to the current date, and iii) a model of propagation of uncertainties between the current position (A(t)) and the mesh (M_i) on a geometric altitude (Z_geo, rec (A',t_est)) which would be determined at any position (A') of this mesh (M_i) from a barometric measurement;and - for at least one future planned aircraft position (Apian(tpian)) within the aircraft's evolution zone (100), an estimate (230) of an uncertainty (DPV(Apian,tpian)) on a geometric altitude (Z_geo,rec(Apian,tpian)) which would be determined from a barometric measurement (Z_baro(Apian,tpian)) at the future position (Apian(tpian)) and the calibration of the mesh retained at the current date (t).;
2. A method (200) according to the preceding claim, further comprising a decision step (240) regarding the continuation of a mission to be performed by the aircraft (100) from the current position (A(t)), the decision step (240) comprising: - evaluating an integrity performance (IN) with the GNSS signals at the current date, and: I) if the evaluation is positive, continuing the mission, and otherwise, II) estimating a remaining flight time (t_vol) under the assumption that the uncertainty in the barometric altitude of the aircraft (100) for all future positions planned from the current position during this remaining flight time (t_vol) remains below a threshold predetermined from the latest calibration model available for each mesh, and III) depending on the remaining flight time (t_vol), the provision of a landing instruction or a mission continuation instruction for a maximum duration calculated from the remaining flight time.
3. A method (200) according to any one of the preceding claims, wherein the mesh calibration step (220) comprises: a) determining a first geometric altitude (Z_geo(t)) of the current position (A(t)) from the GNSS signals received at the current date (t) and a first barometric altitude (Z_baro(t)) of the current position (A(t)) from the barometric altitude measurement taken at the current date (t); b) for each cell (M_i), constructing a candidate calibration model (C_i_can(t)) at the current date (t) configured to estimate, at an estimation date (t_est) the same as or later than the current date (t), a geometric altitude (Z_geo, rec(A', t_est)) of the aircraft at any position (A') in the cell M_i from a barometric measurement taken at that position (A') at the date estimation (t_est), and c) for each mesh (M_i): a) if a previous calibration model,corresponding to a candidate calibration model at a date prior to the current date, was assigned to the grid cell at the prior date, and if an uncertainty (DPV (A', t_est)) on a geometric altitude (Z_geo, rec) estimated at a reference point of the grid cell with the prior calibration model is less than that of the candidate calibration model (C_i_can(t)), the prior calibration model is assigned to the respective grid cell, and otherwise, |3) the candidate calibration model is assigned to that grid cell.
4. Method (200) according to any one of the preceding claims, wherein the evolution zone is subdivided into meshes (M_i) along a vertical direction (Z) along which the altitude is measured.
5. Method (200) according to claim 4, wherein the subdivision of the evolution zone into meshes is further carried out along two horizontal directions (X, Y) perpendicular to the vertical direction (Z).
6. A method (200) according to any one of the preceding claims, wherein the calibration (220) and estimation (230) steps are repeated periodically.
7. A method (200) according to claim 6, wherein the mesh supply step (210) is carried out before the first iteration of the calibration step (220), the evolution zone being chosen so that a predetermined trajectory (TR) to be followed by the aircraft (100) is entirely contained within the evolution zone.
8. Method (200) according to claim 6, wherein the mesh supply step (210) is performed before each iteration of the calibration step (220), the evolution zone comprising for each supply step at least a portion of a predetermined trajectory (TR) to be followed by the aircraft (100) from the current position (A(t)).
9. A method (200) according to claim 8 and claim 3, wherein the calibration step (220) comprises after step c), a grouping step d) (220A), during which, for each of the outermost cells (M_b) of the mesh along at least one predetermined direction, if the same calibration model has been assigned at the current date to said cell and to a neighboring cell (M_vois,b) along the predetermined direction, only the calibration model (C_vois,b(t)) of the neighboring cell is retained.
10. A method (200) according to claim 9, wherein a number of meshes (N) is fixed for all iterations of the mesh supply step (210), and wherein for an iteration of the supply step (210) subsequent to a grouping step (d) (220A), the volume of the evolution zone for said iteration (220B) of the supply step is equal to the volume of all the meshes retained at the end of said step (d).
11. A method (200) according to any one of claims 1 to 10, wherein, at the calibration step (220), the GNSS signals received at the current date (t) enabling the establishment of a vertical protection level with respect to a given risk and, where applicable, at at least one date (t') prior to the current date (t), are signals transmitted to the receiver (110) by at least one auxiliary GNSS signal receiving device independent of the aircraft (100), these signals transmitted to the receiver (110) having been received by at least one auxiliary receiving device prior to the current date (t), the process (200) is then implemented in a predictive mode.
12. A device (130) for the navigation of an aircraft (100) comprising: - at least one GNSS signal receiver (110), - at least one barometric altimeter (120), - a meshing module (130A), configured to implement the step (210) of providing a mesh of an area of flight of the aircraft (100) of the method (200) for the navigation of the aircraft (100) according to any one of claims 1 to 10, - a calibration module (130B), configured to implement the step (220) of calibrating the mesh of the method (200) for the navigation of the aircraft (100) according to any one of claims 1 to 10, and - a determination module (130C), configured to estimate, for at least one future planned position of the aircraft (Apian(tpian)) included in the aircraft's operating area (100), an uncertainty (DPV(Apian,tpian)) on a geometric altitude (Z_geo,rec(Apian,tpian )) which would be determined from a barometric measurement (Z_baro (Apian,tpian)) at the future position (Apian(tpian)) and a calibration of the mesh selected at a current date (t) by the calibration module (130B).,
13. Navigation aid device (130) according to claim 12, further comprising a decision module (130D), configured to implement the decision step (240) of the method (200) for navigation aid of an aircraft (100) according to claim 2.
14. Computer program comprising instructions that cause the device according to claim 12 or claim 13 to perform the navigation aid method (200) according to any one of claims 1 to 11.