Method for detecting autonomous landing parameters by using airborne radar equipment

Abstract

In order to help pilots relying on manual visual inspection to realize autonomous landing more safely, the invention provides a method for assisting autonomous landing by using an airborne Doppler navigation radar and an airborne radar altimeter. Firstly, the glide speed can be obtained by directly utilizing the existing speed detection data of the airborne Doppler navigation radar. And secondly, calculating an inclination angle in a vertical plane by using detection data of Doppler frequency shift by a Doppler navigation radar, thereby obtaining a glide angle. Or the glide angle is calculated according to the trigonometric function relation by using the three-dimensional velocity component measured by the airborne Doppler navigation radar. And then on the basis of acquiring height measurement data by using an airborne radar altimeter, calculating a glide distance by using the acquired glide angle and a trigonometric function relationship. Furthermore, if the aircraft is further provided with a flight management system, an automatic driving system and the like, technical support can be provided for semi-automatic landing by using landing data provided by an airborne Doppler navigation radar and a radar altimeter.

Description

Technical Field

[0001] This invention relates to radio navigation technology, and more specifically to a method for detecting landing parameters using existing airborne radar equipment during autonomous landing based on manual visual inspection. Background Technology

[0002] The process of landing using the aircraft's own onboard equipment rather than airport ground guidance equipment is generally referred to as autonomous landing. In this case, the aircraft relies on its own navigation, control, and sensor systems to land, without depending on ground guidance equipment.

[0003] To describe autonomous landing within a very standardized technical framework, the aircraft needs to have highly advanced autonomous navigation and control capabilities, as well as employ precise sensor systems to achieve safe and reliable autonomous landing.

[0004] For example:

[0005] 1. High-precision Global Positioning System (GPS): Aircraft need to have a high-precision GPS system to ensure that the aircraft can accurately determine its position and altitude.

[0006] 2. Inertial Navigation System (INS): INS can provide precise position and attitude information of the aircraft, which is very important for autonomous landing.

[0007] 3. Flight Management System (FMS): The FMS calculates the aircraft's descent path and landing procedures to ensure that the aircraft can land safely.

[0008] 4. High-precision radar altimeter (RADALT): RADALT can provide altitude information for the aircraft, which is essential for autonomous landing.

[0009] 5. Autopilot system: Used to assist the pilot in landing, including autopilot and automatic thrust control system.

[0010] In reality, however, in many situations, pilots must rely solely on visual observation to achieve autonomous landing. In such cases, the most basic onboard equipment may consist of only general aviation instruments, such as altimeters, airspeed indicators, and compasses, providing essential information about the aircraft's altitude, speed, and direction. In these situations, pilots must depend on their flying skills, experience, judgment, and accurate observation of the terrain and environment to achieve a successful landing. Autonomous landing in these scenarios places extremely high demands on the pilot's skills and decision-making abilities. Summary of the Invention

[0011] To help pilots relying on manual visual estimation achieve safer autonomous landings, this invention proposes a method for assisting autonomous landing using an airborne Doppler navigation radar and an airborne radar altimeter. First, the glide slope velocity can be obtained directly from the existing velocity detection data of the airborne Doppler navigation radar. Second, the tilt angle in the vertical plane can be calculated using the Doppler frequency shift detection data of the Doppler navigation radar, thus obtaining the glide slope angle. Alternatively, the glide slope angle can be calculated using trigonometric functions based on the three-dimensional velocity components measured by the airborne Doppler navigation radar. Then, based on the altitude measurement data obtained from the airborne radar altimeter, the glide slope distance can be calculated using trigonometric functions using the already obtained glide slope angle. Furthermore, if the aircraft is also equipped with a flight management system and an autopilot system, the landing data provided by the airborne Doppler navigation radar and radar altimeter can provide technical support for semi-automatic landing.

[0012] This invention is achieved through the following technical solution:

[0013] The aircraft is equipped with a Doppler navigation radar and a radar altimeter.

[0014] The axial velocity of the aircraft, also known as the glide velocity, is calculated using the Doppler frequency shift detection data from the airborne Doppler navigation radar.

[0015] The glide slope angle can be obtained by calculating the tilt angle in the vertical plane using the Doppler frequency shift detection data from the Doppler navigation radar; alternatively, the glide slope angle can be calculated using the three-dimensional velocity components measured by the airborne Doppler navigation radar.

[0016] The flight altitude is obtained using an airborne radar altimeter. Based on the glide angle and flight altitude, the glide distance is calculated using trigonometric relationships.

[0017] From an engineering design perspective, if the aircraft is also equipped with a flight management system and an autopilot system, it can provide technical support for semi-automatic landing by utilizing landing data provided by airborne Doppler radar and altimeter.

[0018] Specifically, the following steps are included:

[0019] Step 1: The aircraft has been equipped with a Doppler navigation radar and a radar altimeter. At this time, the beam deflection angle β in the horizontal plane of the aircraft's coordinate system is... h and the beam deflection angle β in the vertical plane of the body coordinate system v These are all known, fixed, and unchanging data that were acquired after the antenna feed equipment for the airborne Doppler radar was installed.

[0020] Step 2: Calculate the heading yaw angle using the Doppler frequency shift detection results from the Doppler navigation radar:

[0021]

[0022] In the formula: δ is the heading deflection angle; f d1 and f d2 It is the Doppler frequency shift; β h It is the beam deflection angle in the horizontal plane of the body coordinate system.

[0023] Step 3: Calculate the longitudinal velocity of the aircraft, i.e., its descent speed, using the Doppler frequency shift detection results from the Doppler navigation radar.

[0024]

[0025] In the formula: v w λ is the longitudinal velocity of the aircraft; λ is the wavelength; β v It is the beam deflection angle in the vertical plane of the body coordinate system.

[0026] Step 4: Use the Doppler navigation radar to detect the Doppler frequency shift and calculate the tilt angle in the vertical plane, which is the glide slope angle of the aircraft.

[0027]

[0028] Where the ratio is:

[0029]

[0030] In the formula: α v θ is the tilt angle in the vertical plane; θ is the glide angle of the aircraft.

[0031] Step 5: Alternatively, the vertical speed of the aircraft can be utilized.

[0032]

[0033] The ratio of the glide velocity to the glide angle is obtained using the trigonometric sine function:

[0034]

[0035] When the deflection angle is small, sinδ≈tgδ. Therefore, by comparing equation (6) and equation (3), we can see that the tilt angle in the vertical plane can also be obtained from the ratio of the velocity components.

[0036] Step 6: Obtain the flight altitude using the airborne radar altimeter. Based on the glide slope angle and flight altitude, calculate the horizontal distance between the aircraft and the expected landing area using trigonometric relationships.

[0037]

[0038] The glide slope distance can also be calculated at the same time:

[0039]

[0040] In the formula: h is the aircraft altitude; r is the glide slope distance; d is the horizontal distance.

[0041] Step 7: Furthermore, if the aircraft is also equipped with a flight management system and an autopilot system, it can provide technical support for semi-automatic landing by utilizing landing data provided by airborne Doppler radar and altimeter.

[0042] Features of the present invention:

[0043] 1. It reduces the stress on pilots when relying on human visual inspection to carry out autonomous landing.

[0044] 2. It enhances the maneuverability of aircraft with poor landing performance.

[0045] 3. If the airborne flight management system and autopilot system are further configured to meet the required autonomous guidance performance, the existing airport's ground guidance equipment can be appropriately reduced, thereby lowering airport management costs.

[0046] 4. Corrected an error in the existing Doppler frequency shift equation expression for four-beam Doppler navigation radar. From the perspective of physical measurement standards, there is a mismatch between the planar synthesis velocity and the beam deflection angle in the existing frequency shift equation for four-beam Doppler navigation radar. Attached Figure Description

[0047] Figure 1 Geometric model of the body coordinate system

[0048] Figure 2 Geometric model of the horizontal coordinate system

[0049] Figure 3 Schematic diagram of the glide path of the aircraft

[0050] Figure 4 Relative calculation error of glide slope angle

[0051] Figure 5 Measurement error of glide slope angle Detailed Implementation

[0052] The following is in conjunction with the appendix Figure 1 —Appendix Figure 5 The invention will be further explained in terms of how it is implemented.

[0053] Example

[0054] A method for assisting pilots in achieving autonomous landing guidance using onboard radar equipment during visual landing. (Appendix) Figure 1It is a geometric model of the body coordinate system; attached Figure 2 It is a geometric model of a horizontal coordinate system; attached. Figure 3 A geometric schematic diagram of the aircraft's glide trajectory is provided; (attached) Figure 4 This is the relative calculation error of the glide slope angle; Appendix Figure 5 It is the measurement error of the glide slope angle.

[0055] This invention patent expands the application scenarios of airborne Doppler navigation radar and provides a method to assist pilots in autonomous landing using airborne radar equipment when landing by manual visual inspection.

[0056] Theoretically, existing four-beam Doppler navigation radars can also be used to calculate autonomous landing parameters. However, in practice, there are some errors in the technical analysis of existing four-beam Doppler navigation radars. The main problem is that in constructing the expression for the Doppler frequency shift equation, the composite velocity on the horizontal plane of the horizontal coordinate system is used on the one hand, while the beam deflection angle measured based on the aircraft's longitudinal axis is used on the other. This is a mismatch in terms of physical measurement references. If the composite velocity on the horizontal plane of the horizontal coordinate system is used, then the beam deflection angle measured based on the direction of the composite velocity on the horizontal plane of the horizontal coordinate system must also be used. If the beam deflection angle measured based on the aircraft's longitudinal axis is used, then the composite velocity in the direction of the aircraft's longitudinal axis in the aircraft coordinate system must be used.

[0057] In other words, the existing error is that it fails to distinguish between the composite velocity on the horizontal plane in the horizontal coordinate system and the composite velocity along the longitudinal axis of the aircraft in the aircraft coordinate system. Furthermore, existing technical tutorials for four-beam Doppler navigation radar do not include calculations of the tilt angle (glide slope) in the vertical plane, nor do they utilize Doppler frequency shift detection data to solve for the composite velocity along the longitudinal axis of the aircraft.

[0058] In this regard, this invention patent will mainly analyze the technical solution given in the already filed invention patent (a definite solution calculation method for Doppler navigation parameters using only a single-direction dual-beam, application number: 202310314850.8), and the analysis shows that the tilt angle and synthesis velocity based on frequency shift detection can be obtained in a simple way by using a dual coordinate system for derivation.

[0059] This embodiment describes a method for modifying the existing four-beam Doppler frequency shift equation during the proof process.

[0060] I. Principle of Unidirectional Dual-Beam Doppler Navigation

[0061] 1. Deflection angle

[0062] Assume the aircraft has a forward and backward tilt angle during flight, but no left or right tilt. (See attached image) Figure 1 As shown, in the body coordinate system, the Doppler frequency shift obtained by each beam is:

[0063]

[0064]

[0065] In the formula: f d1 and f d2 It is the Doppler frequency shift; λ is the wavelength; v w It is the axial velocity of the aircraft; β h It is the deflection angle of the beam in the horizontal plane; β v It is the deflection angle in the vertical plane; δ is the heading deflection angle.

[0066] Among them, beam deflection angle β h and β v These are all fixed values ​​known after the antenna feeder equipment was installed.

[0067] First, eliminate the axial velocity v using the ratio of the two Doppler frequency shifts. w :

[0068]

[0069] Therefore, the heading yaw angle in the body coordinate system can be calculated:

[0070]

[0071] 2. Vertical axis velocity

[0072] After obtaining the deflection angle, subtracting the two Doppler frequency shift formulas yields:

[0073]

[0074] The vertical velocity can be obtained from this:

[0075]

[0076] 3. Velocity relationship between the two planes

[0077] In the horizontal coordinate system, we have:

[0078] v y =v p cosδ p (7)

[0079] In the formula: v y The velocity component along the y-axis in the horizontal coordinate system; v p It is the resultant velocity on the horizontal plane in the horizontal coordinate system; δ pIt is the heading deviation angle in the horizontal coordinate system.

[0080] As attached Figure 2 As shown, in the body coordinate system, we have:

[0081] v yw =v w cosδcosα v (8)

[0082] In the formula: v yw The velocity component along the y-axis in the body coordinate system; α v It is the angle of inclination within the vertical plane.

[0083] There is a relationship between the two coordinate systems:

[0084] v w cosδcosα v =v p cosδ p (9)

[0085] From this, we can conclude that:

[0086]

[0087] We can also obtain the following using the velocity component along the y-axis:

[0088] v z =v y tgα v =v p cosδ p tgα v =v w cosδsinα v (11)

[0089] In the formula: v z It is the velocity component in the vertical plane.

[0090] 4. Frequency shift formula in the horizontal plane

[0091] In a horizontal coordinate system, if the resultant velocity v on the horizontal plane is used... p Given an angle of inclination, strictly in mathematical terms, we should have:

[0092]

[0093]

[0094] Where: β hp It is the deflection angle of the beam in the horizontal plane; β vp It is the deflection angle of the beam in the vertical plane.

[0095] However, the calculation formulas given in existing literature do not distinguish between the different beam deflection angles in the two coordinate systems. Instead, they directly calculate based on the beam deflection angle in the body coordinate system, i.e.:

[0096]

[0097]

[0098] This is because, in reality, only the deflection angle β, measured based on the longitudinal axis of the body, is known. h and β v Based on fundamental physical concepts, the selection of geometric parameters must follow the physical measurement reference. Therefore, the frequency shift equation can only use the resultant velocity v on the plane of the body coordinate system. w As a correction to the existing Doppler frequency shift equation for airborne navigation radar, the frequency shift equation in the horizontal coordinate system should be:

[0099]

[0100]

[0101] Simulation results also show that only by using the vertical axis velocity v w Only then can the correct result be obtained. Furthermore, the vertical velocity must also be calculated according to the planar composite velocity v in the body coordinate system. w Perform the transformation:

[0102] v z =v w cosδsinα v (11a)

[0103] 5. Inclination angle in the vertical plane

[0104] Substituting the formula (11a) for calculating the vertical velocity into the equation, we get:

[0105]

[0106]

[0107] Item relocation processing:

[0108]

[0109]

[0110] The ratio of the two equations above:

[0111]

[0112] set up:

[0113]

[0114] From this, the angle of inclination in the vertical plane can be obtained:

[0115]

[0116] For example, the composite velocity on the flight plane:

[0117]

[0118] Substituting, we get:

[0119]

[0120] 6. Vertical velocity component

[0121] Using the obtained tilt angle, the expression for the vertical velocity based on the Doppler frequency shift detection data can be obtained:

[0122]

[0123] The basic form is very similar to the results in existing literature.

[0124] 7. x-axis velocity component

[0125] In the body coordinate system, the velocity component along the x-axis can be directly obtained based on geometric relationships:

[0126] v xw =v w sinδ (27)

[0127] In the formula: v xw It is the velocity component along the x-axis in the body coordinate system.

[0128] Furthermore, based on geometric relationships, we can also directly obtain:

[0129] v x =v xw (28)

[0130] In the formula: v x It is the velocity component along the x-axis in the horizontal coordinate system.

[0131] Therefore, once the synthesis speed v is... w By substituting, you can obtain:

[0132]

[0133] This calculation formula is exactly the same as the results in existing literature.

[0134] 8. y-axis velocity component

[0135] There are two methods:

[0136] (1) Using the tangent theorem

[0137] Depend on Solve directly:

[0138]

[0139] (2) Using projection method

[0140] Projecting the resultant velocity from the body coordinate system onto the y-axis of the horizontal coordinate system, we have:

[0141]

[0142] The results obtained by the two methods are exactly the same.

[0143] 9. Heading angle on the horizontal plane

[0144] According to equation (28), using the velocity solution along the x-axis in both coordinate systems, we have:

[0145]

[0146] By further utilizing equation (10), the heading angle on the horizontal plane can be obtained:

[0147] ctgδ p =cosα v ctgδ (33)

[0148] II. Calculation of Autonomous Landing Guidance Parameters

[0149] The aircraft's descent trajectory is shown in the attached figure. Figure 3 As shown. In fact, parameters such as heading and drift angle are all important to consider during autonomous landing. This embodiment only analyzes and calculates the main parameters.

[0150] 1. The longitudinal velocity of the aircraft, i.e., the glide velocity, is obtained by using the detection results of the Doppler frequency shift by a dual-beam Doppler navigation radar:

[0151]

[0152] 2. Calculate the glide angle directly using the tilt angle in the vertical plane of the aircraft.

[0153] When the aircraft is gliding and landing, the angle of inclination of the aircraft in the vertical plane is the glide angle, which can be obtained directly using equation (25):

[0154]

[0155] 3. Solve for the glide angle using velocity components.

[0156] Based on vertical velocity components:

[0157]

[0158] The glide angle is solved using the axial velocity component in the body coordinate system and the y-axis velocity component in the horizontal plane coordinate system, respectively.

[0159] (1) Utilizing the axial velocity component in the body coordinate system

[0160] Using the axial velocity calculation formula (6) for the aircraft, we can obtain the following from the trigonometric sine function:

[0161]

[0162] In the formula: θ is the glide slope angle.

[0163] Comparing equations (32) and (35), when the deflection angle is small, we have: sinδ≈tgδ, so the two equations are actually basically the same.

[0164] (2) Utilizing the y-axis velocity component in the horizontal coordinate system

[0165] Using the formula (30) for calculating the y-axis velocity component, the following can be obtained from the tangent function:

[0166]

[0167] In fact, the cosα in the denominator on the right side of the above equation v Move to the left side of the equation, and because: α v =θ, therefore we have:

[0168]

[0169] That is, the result is exactly the same as that of equation (34).

[0170] 4. Glide height and glide distance

[0171] After measuring the aircraft's altitude using a radar altimeter, the horizontal distance between the aircraft and the expected landing area is calculated using trigonometric functions based on the calculated glide angle.

[0172]

[0173] The glide slope distance can also be calculated at the same time:

[0174]

[0175] In the formula: h is the aircraft altitude; r is the glide slope distance; d is the horizontal distance.

[0176] III. Simulation Calculation

[0177] 1. Simulation method:

[0178] This section only presents the analysis results of the accuracy of the glide slope calculation. The accuracy of Doppler radar velocity measurement is not discussed further; simulations were also performed, and the velocity measurement results were correct. In fact, Doppler velocity measurement is a mature technology. After verifying the glide slope angle, the glide distance and glide slope range were further calculated, and the accuracy of these calculations was excellent; therefore, there is no need for graphical representation.

[0179] First, manually set the speed in the longitudinal direction, then specify the heading yaw angle so that the glide slope angle in the vertical plane changes linearly within the range of [0°, 15°]; or specify the glide slope angle so that the heading yaw angle changes within the range of [-5°, +5°].

[0180] Based on this, the theoretical value of the Doppler frequency shift is calculated according to the revised formulas (18) and (19). Then, the three-dimensional velocity components of the co-directional dual-beam Doppler navigation radar are calculated using the theoretical value of the Doppler frequency shift, which includes the calculation of the glide velocity. The glide angle and glide distance are further calculated. Finally, the calculated values ​​of the glide angle and glide distance are compared with the pre-given values ​​to obtain the relative calculation error.

[0181] 2. Parameter Determination

[0182] The selected parameters are only for simulation calculations and are irrelevant to actual engineering design.

[0183] (1) Based on existing engineering design data, select the beam deflection angle in the body coordinate system:

[0184] β = 65°

[0185] β v =70°

[0186] In the formula: β is the deflection angle between the beam and the longitudinal axis of the aircraft: β v It is the deflection angle in the vertical plane.

[0187] Using the angle calculation formula for a regular triangular pyramid, the deflection angle in the horizontal plane of the body coordinate system can be obtained:

[0188]

[0189] (2) The heading deviation angle δ = 3° was artificially selected.

[0190] (3) The resultant velocity on the horizontal plane in the body coordinate system is artificially selected: v w =100m / s.

[0191] (4) The operating frequency can be arbitrarily selected, and the wavelength is determined by the relationship between speed, wavelength and frequency.

[0192] 3. Relative calculation error of the glide slope angle

[0193] A specified heading yaw angle was used to linearly vary the glide slope angle in the vertical plane within the range of [0°, 15°]. Simulation results show that the tilt angle α obtained based on frequency shift measurements... v The calculation accuracy is very good. To avoid the overlap of curves with the same accuracy, which would make the graph difficult to read, only the glide angle given by the velocity component was simulated. The relative calculation formula is:

[0194]

[0195] In the formula: θ is a linearly varying glide angle specified by the user within a given interval; θ j It is the glide angle given using the velocity component.

[0196] Appendix Figure 4 The relative calculation error curve for the glide slope angle is presented. Although mathematical analysis proves that based on v... w and v y The obtained glide angles are equivalent, but simulations show that the accuracy of the glide angle calculation using only the y-axis velocity component in the horizontal coordinate system is very good. However, in engineering calculations, it is preferable to use the tilt angle in the vertical plane calculated based on the Doppler frequency shift, because the glide angle obtained using the y-axis velocity component includes the tilt angle.

[0197] In addition, a method was used to simulate the relative calculation error of the glide slope angle by specifying the glide slope angle and allowing the heading yaw angle to vary within the range of [-5°, +5°]. The characteristics of the obtained relative calculation error are the same.

[0198] IV. Error Analysis

[0199] Preset transition function:

[0200] P s =f d1 -p·f d2

[0201] Q s =f d1 -f d2

[0202] The partial derivatives of the transition function with respect to the Doppler frequency shift are as follows:

[0203]

[0204] 1. Error components of the tilt angle in the vertical plane

[0205] For clarity, let:

[0206]

[0207] in:

[0208]

[0209] The partial derivatives of the glide slope angle with respect to the Doppler frequency shift are as follows:

[0210]

[0211]

[0212] In the formula, the glide slope angle plus the subscript 'w' on the right indicates that it is calculated based on the tilt angle in the vertical plane. 2. Error components of the glide slope angle calculated based on the body coordinate system.

[0213] For clarity, let:

[0214]

[0215] in:

[0216]

[0217] The partial derivatives of the glide slope angle with respect to the Doppler frequency shift are as follows:

[0218]

[0219]

[0220] In the formula, the subscript 's' on the right-hand side indicates that the glide angle is calculated in the body coordinate system.

[0221] 3. Glide slope error components calculated based on the horizontal coordinate system

[0222] For clarity, let:

[0223]

[0224] in:

[0225]

[0226] The partial derivatives of the glide slope angle with respect to the Doppler frequency shift are as follows:

[0227]

[0228]

[0229] In the formula, the subscript t on the right-hand side of the glide angle indicates that the glide angle is calculated in the horizontal coordinate system.

[0230] 3. Simulation calculation

[0231] According to error analysis theory, the measurement error of the glide slope angle is:

[0232]

[0233] In the formula: σ f σ is the root mean square value of the Doppler measurement error, which is taken in the analysis and calculation. f =10Hz.

[0234] Pre-selection:

[0235] (1) The resultant velocity on the horizontal plane of the body coordinate system: v w =100m / s.

[0236] (2) The heading yaw angle in the body coordinate system: δ = 3°.

[0237] Simulation calculations show that the angle measurement error is highly dependent on the value of the angle β between the beam and the aircraft's longitudinal axis. Simulation results indicate that the three calculation methods yield angle measurement errors of essentially the same order of magnitude; therefore, only one method is shown in the graphical representation. (Appendix) Figure 5 Error curves are presented using a horizontal coordinate system calculation method, allowing the glide angle in the vertical plane to vary linearly within the range of [0°, 15°], and for different values ​​of the deflection angle β. Simulation calculations show that to ensure good angular measurement accuracy, the value of β must be less than 70 degrees. Specifically, when β = 70°, due to the... v Since the angles are the same at 70°, a singularity will occur.

[0238] 4. Mathematical explanation

[0239] Mathematically, as the value of β decreases, the cosine of the angle, cosβ, will increase. This is because calculating β... h formula:

[0240]

[0241] This will lead to an increase in the remaining chord values, which means that β... h It will become smaller. And the angle measurement error and β h The angle is proportional to the sine function. Therefore, this will lead to a smaller angle measurement error.

[0242] Simulation calculations show that as long as the value of β is less than 70 degrees, the flight speed, heading yaw angle, and deflection angle β in the vertical plane will all be affected. v The changes in β have little impact on the accuracy of angle measurement. Analysis and calculations also show that as long as the value of β is less than 70 degrees, the requirement for Doppler measurement error is also very low, and can be relaxed to σ. f=100Hz is fine.

Claims

1. A method for detecting landing parameters using existing airborne radar equipment during autonomous landing based on manual visual inspection, characterized by directly using an airborne Doppler navigation radar to detect descent speed and descent angle, while simultaneously using an airborne radar altimeter to obtain altitude values, and calculating the descent distance using trigonometric relationships, specifically including the following steps: Step 1: The aircraft has been equipped with a Doppler navigation radar and a radar altimeter. At this time, the beam deflection angle β in the horizontal plane of the aircraft's coordinate system is... h and the beam deflection angle β in the vertical plane of the body coordinate system v These are all known, fixed, and unchanging data that were acquired after the antenna feed equipment for the airborne Doppler radar was installed. Step 2: Calculate the heading yaw angle using the Doppler frequency shift detection results from the Doppler navigation radar: In the formula: δ is the heading deflection angle; f d1 and f d2 It is the Doppler frequency shift; β h It is the beam deflection angle in the horizontal plane of the body coordinate system. Step 3: Calculate the longitudinal velocity of the aircraft, i.e., its descent speed, using the Doppler frequency shift detection results from the Doppler navigation radar. In the formula: v w λ is the longitudinal velocity of the aircraft; λ is the wavelength; β v It is the beam deflection angle in the vertical plane of the body coordinate system. Step 4: Use the Doppler navigation radar to detect the Doppler frequency shift and calculate the tilt angle in the vertical plane, which is the glide slope angle of the aircraft. Where the ratio is: In the formula: α v θ is the tilt angle in the vertical plane; θ is the glide angle of the aircraft. Step 5: Alternatively, the vertical speed of the aircraft can be utilized. The ratio of the glide velocity to the glide angle is obtained using the trigonometric sine function: When the deflection angle is small, sinδ≈tgδ. Therefore, by comparing equation (6) and equation (3), we can see that the tilt angle in the vertical plane can also be obtained from the ratio of the velocity components. Step 6: Obtain the flight altitude using the airborne radar altimeter. Based on the glide slope angle and flight altitude, calculate the horizontal distance between the aircraft and the expected landing area using trigonometric relationships. The glide slope distance can also be calculated at the same time: In the formula: h is the aircraft altitude; r is the glide slope distance; d is the horizontal distance. Step 7: Furthermore, if the aircraft is also equipped with a flight management system and an autopilot system, it can provide technical support for semi-automatic landing by utilizing landing data provided by airborne Doppler radar and altimeter.

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