Aircraft navigation and positioning method and system

Abstract

The present invention discloses a method and system for aircraft navigation and positioning, which belongs to the field of terrain-assisted navigation technology. First, the actual nearest echo distance at multiple acquisition points and the geographic information within the coverage range of the radar beam are used to determine a set of candidate position coordinates that may be the actual position coordinates of the aircraft, and combine them into a candidate flight trajectory that may be the actual flight trajectory of the aircraft. Finally, the actual shape information carried by the theoretical flight trajectory is fully utilized to match each candidate flight trajectory with the theoretical flight trajectory, find the actual flight trajectory from the candidate flight trajectory, and then determine the actual position coordinates of the aircraft, so as to achieve precise navigation and positioning during terrain-assisted navigation. The horizontal positioning accuracy of the present invention is within 6 meters, and the elevation positioning accuracy is within 2.5 meters. Compared with the horizontal positioning accuracy of 10-100 meters and the elevation positioning accuracy of 5-15 meters of the existing terrain matching assisted navigation and positioning method, the navigation and positioning accuracy is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of terrain-assisted navigation, and more specifically, relates to an aircraft navigation and positioning method and system. Background Art

[0002] For aircraft with cruise missions, long or long-distance flights cause the INS (Inertial Navigation System) to continuously accumulate positioning errors, resulting in a continuous decline in navigation accuracy. Due to the fragility of GNSS (Global Navigation Satellite System) signals, GNSS signals are subject to denial, intentional or unintentional interference, or spoofing, making it impossible to rely on external means for navigation and positioning. For such applications, existing technologies often use terrain matching assisted navigation technology, which uses geographical information from the terrain below the aircraft to correct for the horizontal perturbation drift errors of the INS. Among them, traditional terrain matching assisted navigation and positioning methods include: TERCOM (Terrain Contour Matching), SITAN (Sandia Terrain Aided Navigation), TERPROM (Terrain Profile Matching), and PTAN (Precision Terrain Aided Navigation System). Their positioning accuracy is: horizontal positioning accuracy of 30-100 meters, and elevation positioning accuracy of 5-15 meters. Currently, more accurate terrain matching assisted navigation and positioning methods, such as the inertial navigation-terrain matching-satellite composite guidance method, have a horizontal positioning accuracy of only 10 meters and an elevation positioning accuracy of only 5 meters. Through analysis, it was found that the above-mentioned terrain-assisted navigation technologies require the use of the measured terrain elevation curve of the terrain matching area to match the geographic elevation information stored by the aircraft to correct the accumulated error of the aircraft's horizontal position disturbance drift. However, in the terrain matching process, the closest echo distance measured by the radio altimeter is accurate, but the calculation of the closest echo distance as the height above the ground is inaccurate, resulting in an inaccurate terrain elevation curve and the final positioning accuracy is also inaccurate. Summary of the Invention

[0003] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides an aircraft navigation and positioning method and system to solve the technical problem that the prior art cannot achieve accurate navigation and positioning during terrain-assisted navigation.

[0004] To achieve the above objectives, in a first aspect, the present invention provides an aircraft navigation and positioning method, comprising:

[0005] S1. When the aircraft flies at a fixed altitude over a certain terrain area, a theoretical flight trajectory of the aircraft is intercepted from the flight record. The flight trajectory includes: M collection points collected in chronological order; the information at the i-th collection point includes: the actual closest echo distance L of the aircraft at the i-th collection point i and theoretical position coordinates (X i * ,Y i * ,H); where i = 1, 2, …, M, M ≥ 2; H is a height value selected from [H0-σH0, H0+σH0]; H0 is the measured height of the pressure altimeter on the aircraft; 0<σ<1;

[0006] S2, sampling the position coordinates in the local area of ​​the i-th collection point, and obtaining N candidate position coordinates of the aircraft (X ij ,Y ij ,H), j=1,2,…,N,N≥2, thereby forming a candidate position coordinate set at the position of the i-th collection point; any position coordinate point in the local area has the same theoretical height H as the i-th collection point, and the distance between the two is less than or equal to the preset distance;

[0007] S3, in (X ij ,Y ij ,H) coordinate sampling is performed within the ground coverage area corresponding to K i Terrain position coordinates (X ijk ,Y ijk ,Z ijk ), k=1,2,…,K i , K i ≥2; where the ground coverage range is from (X ij ,Y ij ,H) the coverage of the downwardly transmitted radar beam on the terrain area; Z ijk =S(X ijk ,Y ijk ); S(·) is the terrain surface fitting function of the terrain area;

[0008] S4, calculate (X ij ,Y ij ,H) and the distance between each terrain position coordinate, and the minimum distance is taken as the nearest echo distance L ij ;

[0009] S5. Determine L ij With L i Is the absolute value of the difference less than or equal to the preset value L? sIf so, then retain the (X ij ,Y ij ,H), otherwise, delete the (X ij ,Y ij ,H), thereby realizing the screening of candidate location coordinate sets;

[0010] S6. After the screening is completed, all candidate flight trajectories of the aircraft are obtained; the candidate flight trajectories are obtained by selecting a candidate position from the candidate position coordinate set at each collection point and sorting them in the order of the collection points;

[0011] S7. Match each candidate flight trajectory with the theoretical flight trajectory, retain the successfully matched candidate flight trajectory, and use the candidate flight trajectory with the smallest absolute value of the difference in shape features with the theoretical flight trajectory as the actual flight trajectory of the aircraft, and the candidate position coordinates on it as the actual position coordinates of the aircraft, thereby achieving aircraft navigation and positioning, and ending the operation.

[0012] Further preferably, the above-mentioned shape features include direction features, trajectory step length features and linear features;

[0013] Directional features include: the direction of each trajectory line vector on the flight trajectory;

[0014] Trajectory step length feature: the length of each trajectory line vector on the flight trajectory;

[0015] Linear features include: the angle of each vector group on the flight trajectory;

[0016] The trajectory vector is the vector from the first to the second of two adjacent collection points on the flight trajectory.

[0017] Every two adjacent trajectory line vectors on the flight trajectory form a vector group; the angle of the vector group is the angle between the two trajectory line vectors in the vector group.

[0018] Further preferably, the successfully matched candidate flight trajectory satisfies:

[0019] The absolute value of the difference between the direction of each trajectory line vector on the candidate flight trajectory and the direction of the corresponding trajectory line vector on the theoretical flight trajectory is less than or equal to the preset direction difference;

[0020] The absolute value of the difference between the length of each trajectory line vector on the candidate flight trajectory and the length of the corresponding trajectory line vector on the theoretical flight trajectory is less than or equal to the preset step size difference;

[0021] The absolute value of the difference between the angle of each vector group on the candidate flight trajectory and the angle of the corresponding vector group on the theoretical flight trajectory is less than or equal to the linear preset difference.

[0022] Further preferably, the absolute value of the difference between the shape feature of the candidate flight trajectory and the theoretical flight trajectory is: a weighted sum of the absolute value of the difference between the direction feature, the absolute value of the difference between the trajectory step feature and the linear feature of the candidate flight trajectory and the theoretical flight trajectory;

[0023] The absolute value of the difference in directional features is the sum of the absolute values ​​of the differences between the directions of the trajectory line vectors on the candidate flight trajectory and the directions of the corresponding trajectory line vectors on the theoretical flight trajectory.

[0024] The absolute value of the difference of the trajectory step length feature is the sum of the absolute values ​​of the difference between the length of each trajectory line vector on the candidate flight trajectory and the length of the corresponding trajectory line vector on the theoretical flight trajectory;

[0025] The absolute value of the difference of the linear feature is the sum of the absolute values ​​of the difference between the angles of each vector group on the candidate flight trajectory and the angles of the corresponding vector group on the theoretical flight trajectory.

[0026] Further preferably, the absolute value of the difference between the direction of the trajectory line vector on the candidate flight trajectory and the direction of the corresponding trajectory line vector on the theoretical flight trajectory is the absolute value of the angle between the trajectory line vector on the candidate flight trajectory and the corresponding trajectory line vector on the theoretical flight trajectory.

[0027] Further preferably, the above-mentioned aircraft navigation and positioning method further includes the following steps performed between S5 and S6: determining whether the candidate position coordinate set is an empty set, and if so, adjusting L s , and go to S5; otherwise, go to S6.

[0028] Further preferably, the above step S7 further includes:

[0029] When all candidate flight trajectories are not successfully matched, H is adjusted and the process goes to step S3 for iteration. When the number of iterations exceeds the preset number of iterations, the positioning is determined to have failed and the operation ends.

[0030] The above adjustment of H includes: selecting a height value that has not been selected from [H0-σH0, H0+σH0] and updating H.

[0031] Further preferably, the terrain surface fitting function of the terrain area is obtained by performing surface fitting on discrete terrain points in a digital elevation map of the terrain area.

[0032] In a second aspect, the present invention provides an aircraft navigation and positioning system, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor executes the aircraft navigation and positioning method provided in the first aspect of the present invention when executing the computer program.

[0033] In a third aspect, the present invention further provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is executed by a processor, the device where the storage medium is located is controlled to execute the aircraft navigation and positioning method provided in the first aspect of the present invention.

[0034] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0035] 1. The present invention provides a method for navigation and positioning of an aircraft. First, the actual nearest echo distances at multiple acquisition points and geographic information within the coverage area of ​​a radar beam are used to determine a set of candidate position coordinates that may be the actual position coordinates of the aircraft, and then combine them into a candidate flight trajectory that may be the actual flight trajectory of the aircraft. Finally, the actual shape information carried by the theoretical flight trajectory is fully utilized to match the candidate flight trajectories with the theoretical flight trajectory, and the actual flight trajectory is found from the candidate flight trajectories. Then, the actual position coordinates of the aircraft are determined, which can achieve precise navigation and positioning in terrain-assisted navigation.

[0036] 2. Furthermore, in the aircraft navigation and positioning method provided by the present invention, shape features include directional features, trajectory step length features, and linear features. The directional features ensure the directional consistency of the trajectory vector, the trajectory length features ensure the consistency of the trajectory length, and the linear features ensure the consistency of the trajectory shape. Through comprehensive weighting, accurate matching can be achieved, thereby obtaining the precise true position coordinates of the aircraft, with a high success rate, enabling more accurate navigation and positioning.

[0037] 3. Furthermore, the aircraft navigation and positioning method provided by the present invention uses a surface fitting function to perform surface fitting on discrete terrain points in a digital elevation map of a terrain area, obtaining a continuous terrain representation. This method enables more precise positioning accuracy compared to discrete terrain data. Furthermore, digital elevation map data represents the surface terrain through a series of regularly or irregularly distributed discrete points, encompassing a variety of discrete point distributions. This makes it adaptable to a wider range of positioning methods compared to other terrain data. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of an aircraft navigation and positioning method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0040] For aircraft with cruise missions, long-duration or long-distance flights cause the INS to accumulate positioning errors, leading to a continuous decline in navigation accuracy. Due to the fragility of GNSS signals, they can be blocked, intentionally or unintentionally jammed, or spoofed, rendering external navigation and positioning impossible.

[0041] Existing technologies often use terrain matching assisted navigation technology for this application context. This is an assisted navigation technology that uses geographic information about the terrain below the aircraft to correct the horizontal perturbation drift error of the INS. Typical terrain matching systems include TERCOM, SITAN, TERPROM, and PTAN. When using terrain matching guidance, this method requires matching the measured terrain elevation curve of the terrain matching area with the geographic elevation information stored by the aircraft to correct the aircraft's horizontal cumulative error and elevation perturbation error. However, during the terrain matching process, the nearest echo distance measured by the radio altimeter is accurate, but calculating the nearest echo distance as the height above the ground is inaccurate, resulting in an inaccurate terrain elevation curve and ultimately inaccurate positioning accuracy.

[0042] To this end, the first aspect of the present invention provides an aircraft navigation and positioning method. This autonomous positioning method improves the accuracy of the existing terrain matching navigation and positioning methods, increasing horizontal positioning accuracy from 10-100 meters to within 6 meters, and elevation positioning accuracy from 5-15 meters to within 2.5 meters. The overall framework is as follows: During dynamic flight, the shortest radar echo information is generated in real time. This shortest radar echo information and terrain data are used to generate possible flight trajectories. These possible flight trajectories are matched with recorded flight trajectories. A dynamic trajectory matching algorithm is used to determine the optimal path, which is the actual flight trajectory. This allows for simultaneous and precise correction of positioning errors in the three dimensions of the aircraft's INS.

[0043] Specifically, the aircraft navigation and positioning method provided by the present invention includes:

[0044] S1. When the aircraft flies at a fixed altitude above a certain terrain area (i.e., the terrain matching area), a theoretical flight trajectory of the aircraft is intercepted from the flight record; the flight trajectory includes: M collection points collected in chronological order; the information at the i-th collection point includes: the actual closest echo distance L of the aircraft at the i-th collection point iand theoretical position coordinates Where i = 1, 2, …, M, M ≥ 2; H is a height value selected from [H0-σH0, H0+σH0]; H0 is the measured height of the pressure altimeter on the aircraft; σ is a preset ratio, 0<σ<1;

[0045] In an optional implementation, based on considerations of matching success rate and real-time performance, the matching probability of a trajectory with fewer than three acquisition points is only 75% at most, while the matching probability of a trajectory with more than four acquisition points is over 99%, but the matching time gradually increases. Therefore, a trajectory with four acquisition points is set, and the value of M is 4.

[0046] In one embodiment, σ is 1%. In another embodiment, σ is 2%. Preferably, [H0-σH0, H0+σH0] is [H0-10, H0+10], in meters.

[0047] It should be noted that, while the aircraft's altitude remains constant, it flies along a predetermined route and captures a theoretical flight trajectory from the flight log. This trajectory has multiple airborne radar echo information collection points, and the nearest echo information corresponding to each collection point is obtained. The distance between adjacent collection points can be equal or variable, depending on the situation. The distance should be appropriate to match the aircraft's flight speed and collection efficiency. In one optional embodiment, the captured theoretical flight trajectory has four airborne radar echo information collection points, with the distance between adjacent collection points in the trajectory being 25 meters.

[0048] S2, sampling the position coordinates in the local area of ​​the i-th collection point, and obtaining N candidate position coordinates of the aircraft (X ij ,Y ij ,H), j=1,2,…,N,N≥2; and then form the candidate position coordinate set {Ψ i}; Among them, any coordinate point in the local area has the same theoretical height H as the i-th collection point, and the distance between the two is less than or equal to the preset distance R, which satisfies

[0049] In an optional implementation manner, the local area of ​​the i-th collection point can be a circular area, a square area, an elliptical area, etc. centered at the i-th collection point, which is not limited here. In an optional implementation manner, based on the magnitude of the horizontal drift error, the preset distance R is set to 200 m.

[0050] In an optional implementation, based on a horizontal drift error of 200 meters, the number of grid points with a spacing of 1 meter within a 200-meter square is 40,000, and the value of N is 40,000.

[0051] S3, in (Xij ,Y ij ,H) coordinate sampling is performed within the ground coverage area corresponding to K i Terrain position coordinates (X ijk ,Y ijk ,Z ijk ), k=1,2,…,K i , K i ≥2; among them, The corresponding ground coverage range is from (X ij ,Y ij ,H) The coverage of the downward-emitting radar beam on the terrain area; Z ijk =S(X ijk ,Y ijk ); S(·) is the terrain surface fitting function of the terrain area;

[0052] Specifically, the above (X ijk ,Y ijk ,Z ijk )satisfy:

[0053]

[0054] Where θ is the radar beam angle.

[0055] In one optional embodiment, θ=3°; based on the radar beam angle θ=3° and the effective altitude of 3000 meters above the ground, the number of coordinates sampled within the radar beam ground coverage is calculated to be no more than (tan1.5°×3000) 2 =6400, that is, K i The value is 6400.

[0056] It should be noted that the terrain surface fitting function of the terrain area is obtained by performing surface fitting on discrete terrain points in the terrain area of ​​sampled geographic information. Preferably, under an optional embodiment, the terrain surface fitting function of the terrain area is obtained by performing surface fitting on discrete terrain points in a digital elevation map of the terrain area. Specifically, the three-dimensional coordinates of each discrete terrain point in the digital elevation map of the terrain area are known. Taking into account the discontinuity of terrain data at discrete terrain points in the digital elevation map of the terrain area, the present invention implements surface fitting of the terrain area by interpolating existing discrete points to generate a continuous elevation surface, so that the surface height can be effectively estimated on a finer grid, thereby obtaining a more accurate terrain representation and more comprehensive terrain data. The coordinate information of missing terrain points is supplemented by the interpolation method to obtain the coordinate information of all terrain points within the ground coverage range of the ranging radar beam, so that the discrete grid points within the coverage range of the radar beam are fitted to form a continuous surface, which is convenient for the subsequent dynamic trajectory matching and the improvement of navigation and positioning accuracy. Among them, there are many interpolation methods that can be used, such as cubic interpolation method, polynomial interpolation method, triangular interpolation method, spline interpolation method, etc.

[0057] The following is an example of how to use bicubic interpolation in the cubic interpolation method to fit discrete terrain points in a digital elevation map into a continuous terrain surface. For each point to be interpolated, the 16 nearest neighboring points around the point to be interpolated are considered. A cubic polynomial is first used to obtain the interpolation weight, and then the weight is used to perform a weighted average of the elevation values ​​of the 16 known data points to obtain the elevation z of the point to be interpolated. The bicubic interpolation method is then used to traverse all the points to be interpolated, fitting the discrete grid points in the digital elevation map into a smooth and continuous surface. The specific process is as follows:

[0058] 1. Coordinates of the point to be interpolated: The coordinates of the point to be interpolated are denoted as (x, y).

[0059] 2. Known data point: Let the coordinates of the known data point be (x i ,y i , z i ), where i = 0, 1, 2, ..., 15, these points constitute the 16 nearest neighbor points around the point to be interpolated (x, y).

[0060] 3. Weight calculation: For each known data point, calculate the distance weight from it to the point to be interpolated. The weight function w(u, υ) can be in many forms, one of the most common is the bicubic weight function:

[0061] w(u,υ)=(1-|u| 3 ) 2 (3|u| 2 -2|u|3 )+sgn(u)(u 3 -5|u| 2 +8|u|-4)+(1—|υ|3) 2 (3|υ| 2 -2|υ| 3 )+sgn(υ)(|υ| 3 -5|υ| 2 +8|υ|-4)

[0062] Where u = xx i ,υ=yy i , sgn is the sign function; when v is a positive number, sgn(υ) = 1; when v is a negative number, sgn(υ) = -1.

[0063] 4. Interpolation formula: Use weights to perform weighted averaging on the elevation values ​​of known data points to obtain the elevation z of the point to be interpolated:

[0064] 5. Implementation: In Matlab, you can use the griddata function to implement cubic interpolation, specifying the method as 'cubic'.

[0065] S4, in (X ij , Y ij , find the nearest echo distance L within the ground coverage area corresponding to H) ij .

[0066] Specifically, L ij =min{L ijk},

[0067]

[0068] Among them, X ij 、Y ij and H represent the candidate position coordinates of the aircraft in the x, y and z directions respectively; ijk , Y ijk and Z ijk Respectively represent the coordinates of the terrain points in the x-direction, y-direction, and z-direction on the terrain area; i = 1, 2, ..., M; j = 1, 2, ..., N; k = 1, 2, ..., K i In an optional embodiment, the coordinate system is a left-handed coordinate system, with the x-axis facing north, the y-axis facing east, and the z-axis facing the sky, and the coordinate in the z direction represents the altitude.

[0069] S5. Calculate the nearest echo distance L ij Distance L from the true echo i Is the absolute value of the difference less than or equal to the preset value L? s , that is, whether |Lij -Li|≤L s ; If so, then the candidate position coordinate set {Ψ i}Retain the (X ij , Y ij ,H), otherwise, delete the (X ij , Y ij , H), thereby realizing the candidate position coordinate set {Ψ i}Filter;

[0070] In an optional implementation manner, the above-mentioned preset value L s The value is 1m.

[0071] S6. After the screening is completed, the filtered coordinate set {Ψ i} Based on the basic data, all candidate flight trajectories of the aircraft are obtained; the candidate flight trajectories are obtained by selecting a candidate position from the candidate position coordinate set at each collection point and sorting them in the order of the collection points;

[0072] S7. Match each candidate flight trajectory with the theoretical flight trajectory, retain the successfully matched candidate flight trajectory, and use the candidate flight trajectory with the smallest absolute value of the difference in shape features with the theoretical flight trajectory as the actual flight trajectory of the aircraft, and the candidate position coordinates on it as the actual position coordinates of the aircraft, thereby achieving aircraft navigation and positioning, and ending the operation.

[0073] In an optional embodiment, the shape feature includes a direction feature, a trajectory step feature, and a linear feature;

[0074] Directional features include: the direction of each trajectory line vector on the flight trajectory;

[0075] Trajectory step length feature: the length of each trajectory line vector on the flight trajectory;

[0076] Linear features include: the angle of each vector group on the flight trajectory;

[0077] The trajectory vector is the vector from the first to the second of two adjacent collection points on the flight trajectory.

[0078] Every two adjacent trajectory line vectors on the flight trajectory form a vector group; the angle of the vector group is the angle between the two trajectory line vectors in the vector group.

[0079] In an optional implementation manner, the successfully matched candidate flight trajectory satisfies:

[0080] The absolute value of the difference between the direction of each trajectory line vector on the candidate flight trajectory and the direction of the corresponding trajectory line vector on the theoretical flight trajectory |α i|Less than or equal to the preset direction difference α ※ , that is |α i |≤α ※ Preferably, the angle based on the deviation of one grid size is arc tan (1 / 25) = 2.3°, and the direction preset difference value is α ※ The value is 2.3°.

[0081] The absolute value of the difference between the length of each trajectory line vector on the candidate flight trajectory and the length of the corresponding trajectory line vector on the theoretical flight trajectory |β i |Less than or equal to the preset step size difference β ※ , that is |β i |≤β ※ In an optional embodiment, the second preset difference corresponding to a certain trajectory line vector on the candidate flight trajectory is a preset ratio of the length of the corresponding trajectory line vector on the theoretical flight trajectory, and the preset ratio is usually a positive number less than or equal to 0.02. Preferably, based on a ratio of a grid spacing to a step size of 1 / 25=0.04, the step size preset difference β ※ The value is 0.04.

[0082] The absolute value of the difference between the angle of each vector group on the candidate flight trajectory and the angle of the corresponding vector group on the theoretical flight trajectory |γ i |Less than the third preset difference γ ※ , that is |γ i |≤γ ※ Preferably, based on the vertex deviation of a certain side by one grid size, the angle deviation angle is arctan (1 / 25) = 2.3°, and the linear preset difference γ ※ The value is 2.3°.

[0083] Through the above method, candidate flight trajectories with direction consistency, trajectory step length consistency and linear consistency with the theoretical flight trajectory were screened out.

[0084] In an optional embodiment, the absolute value of the difference between the shape features of the candidate flight trajectory and the theoretical flight trajectory (difference cost value) Γ is: the weighted sum of the absolute value of the difference between the directional features α, the absolute value of the difference between the trajectory step features β, and the absolute value of the difference between the linear features γ, that is, Γ = θ1·α+θ2·β+θ3·γ;

[0085] The absolute value of the difference in directional features α is the sum of the absolute values ​​of the difference between the direction of each trajectory line vector on the candidate flight trajectory and the direction of the corresponding trajectory line vector on the theoretical flight trajectory, that is, M is the number of flight trajectory collection points;

[0086] The absolute value of the difference of the trajectory step length feature β is the sum of the absolute values ​​of the difference between the length of each trajectory line vector on the candidate flight trajectory and the length of the corresponding trajectory line vector on the theoretical flight trajectory, that is, M is the number of flight trajectory collection points;

[0087] The absolute value of the difference of the linear feature γ is the sum of the absolute values ​​of the difference between the angles of each vector group on the candidate flight trajectory and the angles of the corresponding vector group on the theoretical flight trajectory, that is, M is the number of flight trajectory collection points.

[0088] In one optional implementation, since the three types of difference band values ​​have different dimensions, α and β need to be dimensionless. Based on the maximum directional and linear deviation of 180°, α and β are both divided by 180°, i.e., α / 180° and β / 180°, respectively, to obtain a dimensionless numerical solution Γ. Here, θ1, θ2, and θ3 are the weights of α, β, and γ, respectively. Based on the influence of α, β, and γ on the success of the match and the dimensionless factor, the weights are set to θ1 = 2, θ2 = 10, and θ3 = 5, respectively. Finally, the candidate flight trajectory corresponding to the minimum difference cost value min(Γ) is taken as the true flight trajectory, and the positioning error is corrected.

[0089] In an optional embodiment, the absolute value of the difference between the direction of the trajectory line vector on the candidate flight trajectory and the direction of the corresponding trajectory line vector on the theoretical flight trajectory is the absolute value of the angle between the trajectory line vector on the candidate flight trajectory and the corresponding trajectory line vector on the theoretical flight trajectory.

[0090] It should be noted that when expressing the angle, in addition to using the angle itself, it can also be expressed by the sine value of the angle, etc., and there is no limitation here.

[0091] In an optional embodiment, the above-mentioned aircraft navigation and positioning method further includes the following steps performed between S5 and S6: determining whether the candidate position coordinate set is an empty set, and if so, adjusting L s , and go to S5; otherwise, go to S6.

[0092] Preferably, the preset value L s The value is 1m; if {Ψ i} is an empty set, then εL s The step size gradually increases the preset value L s The size of {Ψ i In an alternative embodiment, ε is 0.1.

[0093] In an optional implementation manner, the above step S7 further includes:

[0094] When all candidate flight trajectories are not successfully matched, H is adjusted and the process goes to step S3 for iteration. When the number of iterations exceeds the preset number of iterations, the positioning is determined to have failed and the operation ends.

[0095] The above adjustment of H includes: selecting a height value that has not been selected from [H0-σH0, H0+σH0] and updating H.

[0096] Preferably, in an optional embodiment, the height value H selected from [H0-σH0, H0+σH0] in step S1 is the smallest H0-σH0. The above adjustment of H includes: selecting a height value from [H0-σH0, H0+σH0] in ascending order in units of 1 meter and iteratively updating H.

[0097] In an optional implementation manner, the preset number of iterations is 100 times.

[0098] It should be noted that if a matching candidate flight trajectory is successfully obtained, the altitude and horizontal position are both accurate, indicating that it is the true flight trajectory. The three-dimensional disturbance drift error of the aircraft INS is corrected based on the true flight trajectory points. If a matching candidate flight trajectory is not obtained, the altitude is inaccurate and needs to be adjusted for matching.

[0099] It's important to note that in three-dimensional positioning and navigation, altitude and horizontal position are interdependent and complementary. When both have perturbation drift errors, it's difficult to accurately correct both errors simultaneously. An INS with significant perturbation drift errors in altitude cannot obtain the closest echo information of the aircraft's true position, and thus cannot correct for horizontal positioning errors. Simultaneously, an INS with significant perturbation drift errors in horizontal position cannot accurately determine altitude, despite having the closest echo information of the true position. Horizontal position, being a two-dimensional system, has a larger range of values ​​and a larger cumulative error than altitude, a single-dimensional measurement. This makes it more challenging to use as a starting point. Starting with altitude in a single dimension can reduce the difficulty by an order of magnitude. Among existing altitude data, the available reference is the altitude measured by a barometric altimeter with perturbation errors. In one alternative embodiment, the widely used FRTTS-02 high-precision barometric altimeter provided by Fuaotong Technology is used. It is primarily used for military and civilian aircraft and aviation ground equipment. It measures altitudes from 200 to 10,000 meters with an accuracy of 10 meters and a resolution of 1 meter. Therefore, the aircraft's altitude is iteratively updated and re-matched within a range of 10 meters within the barometric altimeter's measured altitude H0 until both the altitude and horizontal position are successfully matched.

[0100] like Figure 1The figure shows a schematic diagram of the aircraft navigation and positioning method provided by an embodiment of the present invention; it can be seen from the figure that the actual closest echo distance L at multiple acquisition points is used. i (dashed line with arrow) and the terrain position coordinates (X i ※ , Y i ※ , H), it is possible to determine the candidate position coordinate set {Ψ i}({Ψ i}N candidate position coordinates (X ij , Y ij , H) are composed of a five-pointed star, circle, and triangle (as shown in the figure above), thereby obtaining a set of candidate flight trajectories that may be the aircraft's true flight trajectory (as shown in the figure above, by the solid, dotted, and dashed lines connecting the candidate position coordinates). Then, using the true shape information carried by the flight record trajectories (the solid line connecting the V-shaped shape), each candidate flight trajectory is matched with the flight record trajectories based on shape features. The true flight trajectory is found from the candidate flight trajectories, and the aircraft's coordinate position is corrected.

[0101] In order to further illustrate the aircraft navigation and positioning method provided by the present invention, the effectiveness of the aircraft navigation and positioning method of the present invention is further analyzed and explained through Matlab simulation comparison experiments.

[0102] Six different true values ​​of aircraft altitude (i.e., altitude) were set: 1000.5 meters, 1500.5 meters, 2000.5 meters, 3000.5 meters, 5000.5 meters, and 7500.5 meters. For each aircraft altitude, a 21-order square matrix was randomly generated, with all matrix elements ranging from [300, 700]. This matrix was used to simulate the terrain elevation data of a 500-meter square terrain matching area (the resolution of the digital elevation map (DEM) was 25 meters).

[0103] It's important to note that the configuration of terrain matching zones is very complex. Both their size and number must meet certain requirements. If the terrain matching zone is too small, more zones must be added throughout the flight corridor. However, these requirements are very high, and suitable areas for terrain matching are limited. Due to trajectory planning and support costs, only a few terrain matching zones are typically set throughout the flight corridor. If the distance between adjacent matching zones is too long, it will result in greater drift error, requiring the matching zones to be sufficiently long. The flight distance between adjacent matching zones will result in a drift error of approximately half the length of the matching zone, so the size of the matching zone is determined based on this drift error. Furthermore, the matching algorithm consumes approximately the same amount of time as it takes the aircraft to travel half the length of the matching zone. The matching algorithm time of the present invention is 1 second (experimental machine: DESKTOP-DMGL7L9; CPU: Intel(R) Core(TM) i7-7700K CPU@4.20GHz; GPU: NVIDIAGeForce GTX 1650; memory: 16GB; operating system: Windows 10; simulation software: MATLAB). The flight speed of the aircraft is set to 0.7 times the speed of sound, and the drift error of adjacent matching areas is set to 200 meters. Taking all factors into consideration, a terrain matching area with a length of 250*2=500 meters is set.

[0104] The aircraft flies level over the north-south centerline of the region (250.3 meters from the westernmost edge of the region). Starting from 50.4 meters from the southernmost edge of the region, 7 groups of sequences are set every 50 meters along the north-south centerline of the region. Each group of sequences has 4 radar echo collection points, and adjacent collection points are separated by 25 meters until it is 74.6 meters from the northernmost edge of the region. It should be noted that if the sequence length is too short during sequence matching, the same sequence to be matched may find multiple matching sequences that meet the requirements in the matching area, resulting in mismatching. Therefore, the sequence length cannot be too short. However, if the sequence length is too long, the calculation time will be too long, which does not meet the requirements of the matching area size setting. According to the situation in this embodiment, a sequence length of 3*25=75 meters is set, the calculation time is 1 second, and the probability of mismatch is less than 1%.

[0105] The drift error of the INS in this embodiment is within 200 meters. Within a 200-meter radius centered on each radar echo acquisition point, a coordinate point cloud with the shortest echo length from that acquisition point is found as the possible aircraft coordinates. The four possible aircraft coordinate sets are combined into multiple possible flight trajectory sets, which are then matched against the recorded theoretical flight trajectory. If the step length similarity, direction similarity, and linear similarity all meet threshold requirements, the trajectory with the lowest comprehensive weight index is selected as the optimal trajectory and the actual flight trajectory. The actual trajectory point coordinates are then used to simultaneously correct for altitude disturbance measurement errors and accumulated horizontal position drift errors. The navigation positioning results at different altitudes are shown in Tables 1 to 6.

[0106] Table 1 Positioning results when the aircraft is actually at an altitude of 1000.5 meters (meters)

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[0109] Table 2 Positioning results when the aircraft is actually at an altitude of 1500.5 meters (meters)

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[0111] Table 3 Positioning results when the aircraft is actually at an altitude of 2000.5 meters (meters)

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[0113]

[0114] Table 4 Positioning results when the aircraft is actually at an altitude of 3000.5 meters (meters)

[0115]

[0116] Table 5 Positioning results when the aircraft is at an actual altitude of 5000.5 meters (meters)

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[0119] Table 6 Positioning results when the aircraft is actually at an altitude of 7500.5 meters (meters)

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[0121] Tables 1 through 6 show that in simulations of aircraft navigation and positioning over terrain-matching areas with significant undulations, navigation and positioning at lower altitudes performed better than at higher altitudes. For aircraft altitudes below 3,000 meters, the positioning method provided by the present invention consistently yielded accurate three-dimensional coordinates, with horizontal positioning accuracy within 5.92 meters and vertical positioning accuracy within 2.5 meters.

[0122] Traditional terrain matching assisted navigation and positioning methods include: TERCOM (Terrain Contour Matching), SITAN (Sandia Terrain Aided Navigation), TERPROM (Terrain Profile Matching), and PTAN (Precision Terrain Aided Navigation System). The terrain matching assisted navigation and positioning method with higher accuracy at present is the inertial navigation-terrain matching-satellite composite guidance method. A comparison of the positioning results of the present invention and the existing terrain matching assisted navigation and positioning methods is shown in Table 7. As can be seen from Table 7, in comparison, the autonomous positioning effect of the present invention is better than that of the existing terrain matching system in terms of both horizontal positioning accuracy and elevation positioning accuracy. The simulation experiment results verify the effectiveness and accuracy of the autonomous positioning of the present invention over the terrain matching area with large terrain undulations.

[0123] Table 7 Comparison of positioning results between the present invention and the existing terrain matching system (meters)

[0124]

[0125] In general, due to the fragility of GNSS signals, especially in mountainous airborne navigation applications where GNSS signals are susceptible to denial, intentional or unintentional interference, or spoofing, terrain matching remains a reliable source of autonomous positioning and navigation information. This invention enables accurate autonomous positioning in terrain-matching areas with large terrain fluctuations, while simultaneously correcting the aircraft's horizontal position drift error and altitude disturbance error output by the inertial navigation system. This significantly improves the accuracy of single autonomous positioning for terrain-assisted navigation, effectively enhancing the aircraft's navigation and positioning capabilities in complex terrain conditions and its low-altitude penetration capability.

[0126] In summary, when there is denial, intentional or unintentional interference or deception of GNSS signals, the typical terrain matching navigation has the problem of inaccurate positioning. The present invention provides an aircraft navigation and positioning method based on dynamic trajectory matching. The overall idea is to match the flight trajectory recorded during dynamic flight with the generated possible flight trajectory, and use dynamic trajectory matching to obtain the optimal trajectory, that is, the real flight trajectory, and then correct the three-dimensional coordinate error of the aircraft. It avoids the problem of large errors in the traditional terrain height matching method that uses the shortest echo distance of the airborne ranging radar as the height of the aircraft from the ground, improves the accuracy of height measurement and positioning, and solves the problem of inaccurate autonomous positioning of terrain matching assisted navigation. The horizontal positioning accuracy is within 5.92 meters, and the elevation positioning accuracy is within 2.5 meters. In particular, the horizontal positioning accuracy has been improved by an order of magnitude, realizing autonomous and precise navigation and positioning, saving the cost and difficulty of track planning and data assurance.

[0127] In a second aspect, the present invention provides an aircraft navigation and positioning system, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor executes the aircraft navigation and positioning method provided in the first aspect of the present invention when executing the computer program.

[0128] The related technical solutions are the same as the aircraft navigation and positioning method provided in the first aspect of the present invention, and will not be described in detail here.

[0129] In a third aspect, the present invention further provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is executed by a processor, the device where the storage medium is located is controlled to execute the aircraft navigation and positioning method provided in the first aspect of the present invention.

[0130] The related technical solutions are the same as the aircraft navigation and positioning method provided in the first aspect of the present invention, and will not be described in detail here.

[0131] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for navigation and positioning of an aircraft, characterized in that: include: S1. When the aircraft is flying at a fixed altitude over a certain terrain area, a theoretical flight trajectory of the aircraft is intercepted from the flight record; The flight trajectory includes: M collection points collected in chronological order; the information on the i-th collection point includes: the actual closest echo distance L of the aircraft at the i-th collection point i and theoretical position coordinates Where i = 1, 2, …, M, M ≥ 2; H is a height value selected from [H0-σH0, H0+σH0]; H0 is the measured height of the pressure altimeter on the aircraft; 0 < σ < 1; S2, sampling the position coordinates in the local area of ​​the i-th acquisition point, and obtaining N candidate position coordinates of the aircraft (X ij ,Y ij ,H), j=1,2,…,N,N≥2, thereby forming a candidate position coordinate set at the position of the i-th collection point; any position coordinate point in the local area has the same theoretical height H as the i-th collection point, and the distance between the two is less than or equal to the preset distance; S3, in (X ij ,Y ij ,H) coordinate sampling is performed within the ground coverage area corresponding to K i Terrain position coordinates (X ijk ,Y ijk ,Z ijk ), K i ≥2; the ground coverage range is from (X ij ,Y ij ,H) the coverage of the downwardly transmitted radar beam on the terrain area; Z ijk =S(X ijk ,Y ijk ); S(·) is the terrain surface fitting function of the terrain area; S4, calculate (X ij ,Y ij ,H) and the distance between each terrain position coordinate, and the minimum distance is taken as the nearest echo distance L ij ; S5. Determine L ij With L i Is the absolute value of the difference less than or equal to the preset value L? s If so, then retain the (X ij ,Y ij ,H), otherwise, delete the (X ij ,Y ij ,H), thereby realizing the screening of candidate location coordinate sets; S6. After the screening is completed, all candidate flight trajectories of the aircraft are obtained; the candidate flight trajectories are obtained by selecting a candidate position from the candidate position coordinate set at each collection point and sorting them in the order of the collection points; S7. Match each candidate flight trajectory with the theoretical flight trajectory, retain the successfully matched candidate flight trajectory, and use the candidate flight trajectory with the smallest absolute value of the difference in shape features with the theoretical flight trajectory as the actual flight trajectory of the aircraft, and the candidate position coordinates on it as the actual position coordinates of the aircraft, thereby achieving aircraft navigation and positioning, and ending the operation.

2. The aircraft navigation and positioning method according to claim 1, characterized in that: The shape features include direction features, trajectory step features and linear features; The directional features include: the direction of each trajectory line vector on the flight trajectory; The trajectory step length feature: the length of each trajectory line vector on the flight trajectory; The linear features include: the angle of each vector group on the flight trajectory; The trajectory vector is the vector from the first to the second of two adjacent collection points on the flight trajectory; Every two adjacent trajectory line vectors on the flight trajectory form a vector group; the angle of the vector group is the angle between the two trajectory line vectors in the vector group.

3. The aircraft navigation and positioning method according to claim 2, characterized in that: The candidate flight trajectories that are successfully matched meet the following requirements: The absolute value of the difference between the direction of each trajectory line vector on the candidate flight trajectory and the direction of the corresponding trajectory line vector on the theoretical flight trajectory is less than or equal to the preset direction difference; The absolute value of the difference between the length of each trajectory line vector on the candidate flight trajectory and the length of the corresponding trajectory line vector on the theoretical flight trajectory is less than or equal to the preset step size difference; The absolute value of the difference between the angle of each vector group on the candidate flight trajectory and the angle of the corresponding vector group on the theoretical flight trajectory is less than or equal to the linear preset difference.

4. The aircraft navigation and positioning method according to claim 2, characterized in that: The absolute value of the difference between the shape features of the candidate flight trajectory and the theoretical flight trajectory is: a weighted sum of the absolute value of the difference between the direction features of the candidate flight trajectory and the theoretical flight trajectory, the absolute value of the difference between the trajectory step features, and the absolute value of the difference between the linear features; The absolute value of the difference of the directional feature is the sum of the absolute values ​​of the difference between the direction of each trajectory line vector on the candidate flight trajectory and the direction of the corresponding trajectory line vector on the theoretical flight trajectory; The absolute value of the difference of the trajectory step length feature is the sum of the absolute values ​​of the difference between the length of each trajectory line vector on the candidate flight trajectory and the length of the corresponding trajectory line vector on the theoretical flight trajectory; The absolute value of the difference of the linear features is the sum of the absolute values ​​of the differences between the angles of the vector groups on the candidate flight trajectory and the angles of the corresponding vector groups on the theoretical flight trajectory.

5. The aircraft navigation and positioning method according to claim 1, wherein: Also includes: The following steps are performed between S5 and S6: Determine whether the candidate position coordinate set is an empty set. If so, adjust L s , and go to S5; otherwise, go to S6.

6. The aircraft navigation and positioning method according to claim 1, characterized in that: The terrain surface fitting function of the terrain area is obtained by performing surface fitting on discrete terrain points in a digital elevation map of the terrain area.

7. The aircraft navigation and positioning method according to any one of claims 1 to 6, characterized in that: The step S7 further comprises: When all candidate flight trajectories are not successfully matched, H is adjusted and the process goes to step S3 for iteration. When the number of iterations exceeds the preset number of iterations, it is determined that the positioning has failed and the operation ends. The adjusting H includes: selecting a height value that has not been selected from [H0-σH0, H0+σH0] and updating H.

8. An aircraft navigation and positioning system, characterized in that: include: A memory and a processor, wherein the memory stores a computer program, and the processor executes the aircraft navigation and positioning method according to any one of claims 1 to 7 when executing the computer program.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium includes a stored computer program, wherein when the computer program is executed by a processor, the device where the storage medium is located is controlled to execute the aircraft navigation and positioning method according to any one of claims 1 to 7.

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