Aircraft terrain clearance measuring method and system and computer program product

Abstract

The invention relates to an aircraft terrain clearance measuring method and system and a computer program product, and belongs to the field of signal processing. The method comprises the following steps: preprocessing received GNSS direct signals and reflected signals to obtain corresponding synchronous digital signals; according to the synchronous digital signals corresponding to the GNSS direct signal and the reflection signal, determining a waveform peak value position difference between the GNSS direct signal and the reflection signal; according to the waveform peak value position difference, determining a path delay difference between a GNSS direct signal and a reflection signal; establishing a signal reflection model of path delay difference and aircraft terrain clearance by combining terrain reflection characteristics, vegetation coverage and a mirror reflection geometric structure; and determining the terrain clearance of the aircraft according to the signal reflection model and the path delay difference. The method can be suitable for measuring the terrain clearance of the aircraft under different earth surface conditions, and has high concealment, accuracy and applicability.

Description

Technical Field

[0001] The present invention relates to the field of signal processing technology, and in particular to a method, system and computer program product for measuring the height of an aircraft from the ground. Background Art

[0002] At present, various types of aircraft have been widely used in many aspects. For their operation to complete the target task, the height above the ground is one of the important parameters. At present, commonly used airborne altimeters include: LiDAR, GNSS (Global Navigation Satellite System), barometer, etc. Among them, LiDAR is an active sensor with poor concealment and cannot be used on water bodies. Its effective range is limited, generally only 300-500m. The elevation information obtained by GNSS is relative to the earth's reference ellipsoid rather than the actual earth's surface, and it cannot directly obtain the height of the aircraft above the ground. Using a barometer to obtain height above the ground information requires the assistance of ground pressure data, and the accuracy is low. GNSS-R technology can provide drones with a concealed, unlimited range, and direct height measurement observation value. Summary of the invention

[0003] In order to solve the above problems, the inventors have made the present invention, which provides a method, system and computer program product for measuring the height of an aircraft above the ground.

[0004] In a first aspect, the present invention provides a method for measuring the height of an aircraft from the ground, comprising the following steps:

[0005] Preprocessing the received GNSS direct signal and reflected signal to obtain corresponding synchronized digital signals;

[0006] Determine the waveform peak position difference between the GNSS direct signal and the reflected signal according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal;

[0007] Determining the path delay difference between the GNSS direct signal and the reflected signal according to the waveform peak position difference;

[0008] Combined with the terrain reflection characteristics and vegetation coverage, a signal reflection model of path delay difference and aircraft altitude is established;

[0009] The height of the aircraft above the ground is determined according to the signal reflection model and the path delay difference.

[0010] Optionally, the received GNSS direct signal and reflected signal are preprocessed to obtain corresponding synchronous digital signals, including the following steps: receiving the GNSS direct signal and reflected signal respectively through the upward right-hand circularly polarized antenna and the downward left-hand circularly polarized antenna of the aircraft; performing RF front-end processing on the GNSS direct signal and reflected signal, and using a common local oscillator and a common clock for the two channels to obtain channel-time synchronized GNSS direct signal and reflected signal; performing analog-to-digital conversion on the channel-time synchronized GNSS direct signal and reflected signal at a high sampling rate to obtain synchronized digital signals of the GNSS direct signal and reflected signal.

[0011] Optionally, the GNSS direct signal and the reflected signal are subjected to RF front-end processing, and the two channels share a local oscillator and a clock to obtain a GNSS direct signal and a reflected signal with channel time synchronization, including the following steps: mixing the GNSS direct and reflected RF signals to obtain intermediate frequency signals of the GNSS direct and reflected signals; using a common clock local oscillator signal to time synchronize the direct channel and the reflected channel of the intermediate frequency signal to obtain a GNSS direct signal and a reflected signal with channel time synchronization.

[0012] Optionally, determining the waveform peak position difference between the GNSS direct signal and the reflected signal according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal includes the following steps: determining multiple peak points of the GNSS direct signal and the reflected signal according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal; performing interpolation according to the multiple peak points to obtain the GNSS direct signal waveform and the reflected signal waveform respectively; determining the waveform peak position difference between the GNSS direct signal and the reflected signal according to the GNSS direct signal waveform and the reflected signal waveform.

[0013] Alternatively, the waveform peak position difference between the GNSS direct signal and the reflected signal is determined based on the synchronous digital signals corresponding to the GNSS direct signal and the reflected signal, including the following steps: correlating the synchronous digital signals corresponding to the GNSS direct signal and the reflected signal with the local code respectively to obtain the GNSS direct signal waveform and the reflected signal waveform; and determining the waveform peak position difference between the GNSS direct signal and the reflected signal based on the GNSS direct signal waveform and the reflected signal waveform.

[0014] Optionally, the path delay difference between the GNSS direct signal and the reflected signal is determined based on the waveform peak position difference, including the following steps: determining the code phase delay between the GNSS direct signal and the reflected signal based on the code phase of the waveform peak position of the GNSS direct signal and the reflected signal; determining the path delay difference between the GNSS direct signal and the reflected signal based on the code phase delay and the GNSS signal propagation speed.

[0015] Optionally, the signal reflection model is: ΔH represents the height of the aircraft from the ground, Δd represents the path delay difference between the direct GNSS signal and the reflected signal, and δ atm represents the tropospheric delay error, δ hw represents the deviation between the direct channel and the reflected channel caused by hardware error, δ r Indicates the deviation of the reflecting surface caused by terrain reflectivity and vegetation coverage, δ att represents the attitude error of the hovering drone, δ m represents the measurement error, ε represents the unmodeled error, θ represents the satellite elevation angle, and d represents the vertical distance between the upward-looking antenna and the downward-looking antenna of the aircraft.

[0016] Optionally, determining the height of the aircraft above the ground based on the signal reflection model and the path delay difference includes the following steps: collecting signal data of multiple locations on the aircraft's flight path, the signal data including satellite elevation angles, GNSS direct signals, and path delay differences of reflected signals; screening out at least one location from the multiple locations in descending order of satellite elevation angles; and inputting the signal data of the screened location into the signal reflection model to obtain the height of the aircraft above the ground at the corresponding location.

[0017] Optionally, when the screened locations include multiple locations, the above-mentioned method for measuring the height of the aircraft above the ground also includes the following steps: using a sliding average method to smooth the signal data of the multiple screened locations; generating a distribution map of the aircraft's height above the ground on the aircraft's flight path based on the signal data of the multiple locations after the smoothing process; and measuring the aircraft's height above the ground based on the aircraft's height above the ground distribution map and the position of the aircraft on the flight path.

[0018] In a second aspect, the present invention provides a system for measuring the height of an aircraft from the ground, comprising:

[0019] A GNSS radio frequency signal receiving module, used to receive GNSS direct signals and reflected signals respectively;

[0020] The signal processing module is used to pre-process the received GNSS direct signal and reflected signal to obtain corresponding synchronous digital signals; determine the waveform peak position difference between the GNSS direct signal and the reflected signal according to the synchronous digital signals corresponding to the GNSS direct signal and the reflected signal; determine the path delay difference between the GNSS direct signal and the reflected signal according to the waveform peak position difference; establish a signal reflection model of the path delay difference and the height of the aircraft above the ground in combination with the terrain reflection characteristics and the vegetation coverage; determine the height of the aircraft above the ground according to the signal reflection model and the path delay difference.

[0021] In a third aspect, the present invention provides a computer program product, comprising a computer program / instruction, which implements the aforementioned method for measuring the height of an aircraft above the ground when executed by a processor.

[0022] The beneficial effects of the above technical solution provided by the present invention include at least:

[0023] By using GNSS reflected signals (GNSS-R), the present invention can more effectively avoid interference under complex terrain, weather and atmospheric conditions. By analyzing the reflected waveform of the satellite signal, the height of the aircraft from the ground can be more accurately determined, especially in environments with dense vegetation and complex terrain, with high concealment, adaptability and accuracy. The present invention uses reflected signals combined with terrain reflection characteristics and vegetation coverage to calculate altitude, and can adapt to complex terrain environments. Based on GNSS signal reception and processing, the GNSS receiving equipment has a relatively low cost and simple maintenance requirements, making the present invention more advantageous in application scenarios with limited resources.

[0024] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 This is a flow chart of a method for measuring the height of an aircraft above the ground using GNSS-R technology in an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the geometric structure of the GNSS-R UAV height above the ground in an embodiment of the present invention;

[0029] Figure 3 Schematic diagram of terrain reflectance characteristics and vegetation coverage in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0031] In order to solve the problems existing in the prior art, the embodiments of the present invention provide a method, system and aircraft for measuring the height of an aircraft from the ground. GNSS-R (Global Navigation Satellite System-Remote) technology uses the L-band ranging signal broadcast by Beidou / GNSS satellites to the ground, so the technology has strong concealment and the effective range can cover the entire near-earth space. GNSS-R signals can be reflected on both the land surface and the water surface.

[0032] The embodiment of the present invention provides a method for measuring the height of an aircraft from the ground, the process of which is as follows: Figure 1 As shown, the following steps are included:

[0033] Step S1: pre-process the received GNSS direct signal and reflected signal to obtain corresponding synchronous digital signals; determine the waveform peak position difference between the GNSS direct signal and the reflected signal according to the synchronous digital signals corresponding to the GNSS direct signal and the reflected signal; determine the path delay difference between the GNSS direct signal and the reflected signal according to the waveform peak position difference.

[0034] In some optional embodiments, the received GNSS direct signal and reflected signal are preprocessed to obtain corresponding synchronous digital signals, including the following steps: receiving the GNSS direct signal and reflected signal respectively through the upward right-hand circularly polarized antenna (upward-looking antenna) and the downward left-hand circularly polarized antenna (downward-looking antenna) of the aircraft; performing RF front-end processing on the GNSS direct signal and reflected signal, and using a common local oscillator and a common clock for the two channels to obtain channel-time synchronized GNSS direct signal and reflected signal; performing analog-to-digital conversion on the channel-time synchronized GNSS direct signal and reflected signal at a sampling rate higher than a sampling rate threshold to obtain synchronized digital signals of the GNSS direct signal and reflected signal.

[0035] Specifically, Figure 1 As shown, the GNSS direct signal and reflected signal from the satellite are received by the right-handed and left-handed circularly polarized antennas. The GNSS receiving module records the original signal, including the direct signal and the reflected wave. The signal is converted to digital using a high sampling rate to capture the high-bandwidth signal characteristics and saved as a digital signal for subsequent processing.

[0036] The received direct and reflected signals are processed by the RF front end to extract the intermediate frequency component of the signal. The direct and reflected channels are synchronized using a common clock local oscillator signal to ensure the time consistency of the data. In some optional embodiments, the GNSS direct and reflected signals are processed by the RF front end, and the two channels share a local oscillator and a clock to obtain the GNSS direct and reflected signals with channel time synchronization, including the following steps: mixing the GNSS direct and reflected RF signals to obtain the intermediate frequency signals of the GNSS direct and reflected signals, which enable the amplifier to work stably and reduce interference; using a common clock local oscillator signal to synchronize the direct and reflected channels of the intermediate frequency signal to obtain the GNSS direct and reflected signals with channel time synchronization.

[0037] Preprocessing also includes filtering the signal to reduce the noise in the signal. The filtering method can be differential filtering, etc.

[0038] In some optional embodiments, the above-mentioned method for determining the height of the aircraft from the ground further includes: obtaining the propagation delay information of the reflected signal according to the synchronous digital signal of the reflected signal. Specifically, the following steps are included: determining the synchronous digital signal of the corresponding GNSS direct signal according to the synchronous digital signal of the reflected signal; and obtaining the propagation delay information of the reflected signal according to the time interval between the synchronous digital signal of the reflected signal and the synchronous digital signal of the corresponding GNSS direct signal.

[0039] Based on the propagation delay information, the non-correlated integration time in the subsequent steps can be set or adjusted to obtain a better signal-to-noise ratio.

[0040] In addition, the signal strength of the reflected signal can also be extracted, and the reflected signal and its delay with the direct signal can be more accurately identified based on the extracted signal strength of the reflected signal.

[0041] In some optional embodiments, the waveform peak position difference between the GNSS direct signal and the reflected signal is determined according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal, including the following steps: determining multiple peak points of the GNSS direct signal and the reflected signal according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal; interpolating according to the multiple peak points to obtain the GNSS direct signal waveform and the reflected signal waveform respectively; determining the waveform peak position difference between the GNSS direct signal and the reflected signal according to the GNSS direct signal waveform and the reflected signal waveform. Specifically, the cubic spline interpolation method can be used for interpolation.

[0042] The waveform peak position difference between the GNSS direct signal and the reflected signal can also be determined by the incoherent integration method. In other optional embodiments, the waveform peak position of the GNSS direct signal and the reflected signal is determined according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal, including the following steps: the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal is respectively correlated with the aircraft local code to obtain the GNSS direct signal waveform and the reflected signal waveform, wherein the correlation processing can be based on the correlation integration of the signal and then non-correlated integration; according to the GNSS direct signal waveform and the reflected signal waveform, the waveform peak position difference between the GNSS direct signal and the reflected signal is determined. Wherein, when performing incoherent integration, the incoherent integration time is adjusted to obtain the GNSS direct signal waveform and the reflected signal waveform with a higher signal-to-noise ratio. Through incoherent integration, the signal-to-noise ratio of the GNSS direct signal waveform and the reflected signal waveform can be improved.

[0043] In some optional embodiments, the path delay difference between the GNSS direct signal and the reflected signal is determined based on the difference in waveform peak positions of the GNSS direct signal and the reflected signal, including the following steps: determining the code phase delay between the GNSS direct signal and the reflected signal based on the difference in code phase of the waveform peak positions of the GNSS direct signal and the reflected signal; determining the path delay difference between the GNSS direct signal and the reflected signal based on the code phase delay and the GNSS signal propagation speed.

[0044] Step S2: Combining terrain reflectance characteristics, vegetation coverage and Figure 2 The mirror reflection geometry shown is used to establish a signal reflection model of the path delay difference and the height of the aircraft above the ground; the height of the aircraft above the ground is determined based on the signal reflection model and the path delay difference.

[0045] The reflection and scattering effects of the signal are analyzed, and the mathematical model of the reflected signal and the height of the aircraft above the ground is established by combining the terrain reflection characteristics and vegetation coverage. The geometric structure of the GNSS-R UAV height measurement is as follows: Figure 2 As shown, the upward-looking antenna of the aircraft receives the direct signal, and the downward-looking antenna of the aircraft receives the reflected signal. When the GNSS direct signal reaches the reflection point of the reflecting surface, the GNSS direct signal has not yet reached the upward-looking antenna of the aircraft. When the GNSS direct signal reaches the upward-looking antenna of the aircraft, the GNSS direct signal has been reflected from the reflection point and a corresponding reflected signal has been emitted. At this time, the reflected signal needs to pass through a path length of Δρ to reach the downward-looking antenna of the aircraft. According to Figure 2 From the geometric relationship shown, it can be inferred that Δρ=(2ΔH+d)sinθ, where θ represents the satellite elevation angle, d represents the vertical distance between the upward-looking antenna and the downward-looking antenna of the aircraft, and ΔH represents the height of the aircraft above the ground. Figure 2 middle, represents the unit vector between the satellite and the phase center of the upward-looking antenna, represents the vector between the phase centers of the upward-looking antenna and the downward-looking antenna, The modulus of is equal to d.

[0046] There are many error factors related to the actual chip path delay, such as atmospheric refraction, hardware bias, reflecting surface bias, platform attitude error, measurement error, and other unmodeled errors. The attitude of the drone will produce a certain tilt, resulting in a decrease in the vertical distance between the two antennas, that is, it is no longer constant. Since the reflected signal needs to go through an additional path compared to the direct signal, it will cause tropospheric refraction. One of the main errors included in the path delay measurement is the ranging error of the code. Therefore, the path delay difference Δd between the GNSS direct signal and the reflected signal can be more fully expressed as follows:

[0047] Δd=Δρ+δ atm +δ hw +δ r +δ att +δ m +ε

[0048] In some optional embodiments, the signal reflection model is:

[0049] ΔH represents the height of the aircraft from the ground, Δd represents the path delay difference between the direct GNSS signal and the reflected signal, and δ atm represents the tropospheric delay error, δ hw represents the deviation between the direct channel and the reflected channel caused by hardware error, δ r Indicates the deviation of the reflecting surface caused by terrain reflectivity and vegetation coverage, δ att represents the attitude error of the hovering drone, δ m represents the measurement error, ε represents the unmodeled error, θ represents the satellite elevation angle, and d represents the vertical distance between the upward-looking antenna and the downward-looking antenna of the aircraft.

[0050] like Figure 3 As shown in the figure, due to reasons such as ground vegetation, when the reflection point is obviously higher than the ground, the reflection surface deviation δ r Adjustments are made to improve the accuracy of the adaptability of the signal reflection model.

[0051] The above signal reflection model includes a sine function of the satellite elevation angle θ, the satellite elevation angle has a value range of 0 to 90 degrees, the derivative of the sine function is a cosine function, and the value of the cosine function gradually decreases within the range of 0 to 90 degrees, indicating that the value change rate of the sine function gradually decreases. Therefore, when the satellite elevation angle θ is large, the error of the satellite elevation angle θ has a small effect on its sine function, so selecting a higher satellite elevation angle can reduce the effect of the error of the satellite elevation angle θ on its sine function, which helps to reduce the total error. In some optional embodiments, the height of the aircraft above the ground is determined based on the signal reflection model and the path delay difference, including the following steps: collecting signal data of multiple locations on the flight path of the aircraft, the signal data including the satellite elevation angle, the path delay difference of the GNSS direct signal and the reflected signal; selecting at least one location from multiple locations in the order of the satellite elevation angle from high to low; inputting the signal data of the selected location into the signal reflection model to obtain the height of the aircraft above the ground at the corresponding location.

[0052] In some optional embodiments, when the screened locations include multiple locations, the above-mentioned method for measuring the height of the aircraft above the ground also includes the following steps: using a sliding average method to smooth the signal data of the multiple screened locations; generating a distribution map of the aircraft's height above the ground on the aircraft's flight path based on the signal data of the multiple locations after smoothing; and measuring the aircraft's height above the ground based on the aircraft's height above the ground distribution map and the position of the aircraft on the flight path.

[0053] Under the same terrain reflection characteristics and vegetation coverage, the aircraft altitude determined by the method is compared with the measured data of the aircraft altitude, and the reflection surface deviation δ in the signal reflection model is calculated. r Make corrections.

[0054] exist Figure 1In the illustrated embodiment, the real-time kinematic (RTK) terminal measures the measured data H of the height of the aircraft above the ground. The height ΔH and H of the aircraft measured by the present invention are compared to perform height measurement accuracy analysis and correct the parameters in the signal reflection model. For different terrain reflection characteristics and vegetation coverage, the corresponding parameter vectors in the signal reflection model are obtained. Multiple signal reflection model parameter vectors form a signal reflection model parameter matrix. By correcting the parameters of the signal reflection model parameter matrix, under different measurement conditions, such as different terrain reflection characteristics, vegetation coverage or satellite signal coverage, the corresponding parameters are selected from the signal reflection model parameter matrix to obtain the corresponding signal reflection model, and the height measurement is performed to further improve the accuracy and adaptability of the aircraft height measurement. Furthermore, combined with the measured data, comparative analysis is performed to correct the system error, and the flight route of the aircraft is dynamically adjusted according to the terrain, vegetation density and satellite signal coverage, and the route with smaller signal reflection model error parameters is selected to further improve the measurement accuracy. The present invention ensures flight stability and continuity of data collection through the dynamic path planning function of the aircraft flight control system; and realizes real-time data processing and large-scale distributed information output in conjunction with the data storage and transmission system.

[0055] In the above method of this embodiment, by using GNSS reflected signals (GNSS-R), the present invention can more effectively avoid interference under complex terrain, weather and atmospheric conditions. By analyzing the reflected waveform of the satellite signal, the height of the aircraft from the ground can be more accurately determined, especially in an environment with dense vegetation and complex terrain, with high adaptability and accuracy. The present invention uses reflected signals in combination with terrain features and vegetation coverage to calculate the height, which can adapt to complex terrain environments. Based on GNSS signal reception and processing, high-cost laser radar, radar equipment and their complex maintenance requirements are avoided. The GNSS receiving equipment is relatively low in cost and has simple maintenance requirements, making the present invention more advantageous in application scenarios with limited resources. Through real-time data analysis, the present invention can calculate the height of the aircraft from the ground in real time during flight, which is helpful for flight safety and emergency response. The height information obtained by GNSS-R technology is calculated by the propagation path difference between the direct signal and the signal reflected by the surface. Whether it is the land surface or the water surface, its signal can be reflected, and the concealment is good. Therefore, the measured height is the height from the ground, no conversion is required, and it is applicable to various surface environments such as land and water.

[0056] The above technical solution is based on the GNSS-R technology. The method for measuring the height of an aircraft above the ground is implemented through the following steps: First, the GNSS receiving module receives the direct and reflected signals from the navigation satellite and records the original reflected signal data; second, the received reflected signal is pre-processed, including noise filtering, signal strength analysis, and propagation delay measurement to ensure the reliability and accuracy of the data; then, by deeply analyzing the characteristics of the reflected signal, combined with the characteristics of the reflecting surface, vegetation coverage density, and terrain influence, a mathematical model between the reflected signal and the height of the aircraft above the ground is constructed; based on this model, the height of the aircraft above the ground is accurately calculated using parameters such as the intensity and propagation time of the reflected signal. The aircraft collects vegetation height data at multiple points in real time on the flight path, and the signal processing module is combined to process and store the data in real time, and finally generates the distribution information of the height of the aircraft above the ground and outputs the results.

[0057] In the above method, the GNSS receiving device realizes efficient signal capture and recording; the signal processing module optimizes data quality through filtering, delay estimation and reflection intensity analysis; based on the established signal reflection model of the reflected signal and the height of the aircraft above the ground, the height of the aircraft above the ground is accurately calculated. In addition, the aircraft flight control system ensures the stability of the flight path and the continuity of data collection, and transmits the measurement results to the ground control platform in real time through the wireless transmission system; the data storage and transmission system further processes and analyzes the data collected by the aircraft to ensure efficient storage and distribution. In order to optimize the measurement efficiency, the aircraft flight path planning comprehensively considers factors such as terrain, vegetation density and satellite signal coverage, and dynamically adjusts the flight route to ensure that each measurement point obtains the best reflection signal. Through the predetermined trajectory and automatic navigation function, the aircraft realizes efficient measurement and data collection in a large area, thus providing effective technical support for the accurate measurement of the height of the aircraft above the ground.

[0058] Those skilled in the art can change the above sequence without departing from the protection scope of the present invention.

[0059] Another embodiment of the present invention provides a system for measuring the height of an aircraft from the ground, comprising:

[0060] GNSS radio frequency receiving module, used for receiving GNSS direct signal and reflected signal respectively;

[0061] The signal processing module is used to pre-process the received GNSS direct signal and reflected signal to obtain corresponding synchronous digital signals; determine the waveform peak position difference between the GNSS direct signal and the reflected signal according to the synchronous digital signals corresponding to the GNSS direct signal and the reflected signal; determine the path delay difference between the GNSS direct signal and the reflected signal according to the waveform peak position difference; establish a signal reflection model of the path delay difference and the height of the aircraft above the ground in combination with the terrain reflection characteristics and vegetation coverage; determine the height of the aircraft above the ground according to the signal reflection model and the path delay difference.

[0062] The GNSS receiving module is installed on the aircraft. The signal processing module can be set on the aircraft or the edge server. When the signal processing module is deployed on the edge server, the edge server sends a signal including the measured value of the height of the aircraft from the ground to the aircraft or the aircraft control terminal. The present invention has significant uniqueness and adaptability in system design, which is reflected in the optimization of lightweight and portability, making it easy to integrate into the UAV platform, and is particularly suitable for a wide range of measurement tasks in complex terrains such as forests, mountainous areas and farmlands. With the passive characteristics of GNSS-R technology, the system does not require active signal transmission equipment, which not only reduces energy consumption and hardware complexity, but also enables it to maintain stable measurement performance in severe weather and strong occlusion environments, showing a high degree of environmental adaptability. In addition, through high-precision analysis of the path delay of the GNSS reflection signal, combined with optimized incoherent integration technology and cubic spline interpolation method, the system achieves centimeter-level measurement accuracy, and adopts dynamic high-elevation angle observation value screening strategy and sliding average algorithm to effectively reduce random errors and significantly enhance the smoothness and reliability of the measurement results.

[0063] Regarding the system in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0064] In this embodiment, by using GNSS reflected signals (GNSS-R), the present invention can more effectively avoid interference under complex terrain, weather and atmospheric conditions. By analyzing the reflected waveform of the satellite signal, the height of the aircraft from the ground can be measured more accurately, especially in an environment with dense vegetation and complex terrain, with high adaptability and accuracy. The present invention uses reflected signals in combination with terrain features and vegetation coverage to calculate the height, which can adapt to complex terrain environments. Based on GNSS signal reception and processing, high-cost laser radar, radar equipment and their complex maintenance requirements are avoided. The GNSS receiving equipment is relatively low in cost and has simple maintenance requirements, making the present invention more advantageous in application scenarios with limited resources. Through real-time data analysis, the present invention can calculate the height of the aircraft from the ground in real time during flight, which is helpful for flight safety and emergency response. The height information obtained by GNSS-R technology is calculated by the propagation path difference between the direct signal and the signal reflected by the surface. Whether it is the land surface or the water surface, its signal can be reflected. Therefore, the measured height is the height from the ground, without conversion, and is applicable to a variety of surface environments such as land and water.

[0065] The present invention is based on GNSS-R technology, making full use of the reflected signals of global navigation satellites to measure the height of the aircraft from the ground, without the need for active signal transmission equipment, effectively reducing the hardware cost and complexity. By introducing a dual-polarized antenna design (a right-hand circularly polarized antenna receives direct signals, and a left-hand circularly polarized antenna receives reflected signals), the present invention achieves efficient signal capture and separation processing, ensuring the accuracy and real-time performance of signal analysis.

[0066] At the same time, in some optional embodiments, the signal processing module of the above-mentioned aircraft height measurement system also integrates an efficient filtering algorithm, a path delay calculation and a reflection intensity analysis algorithm, thereby further reducing noise interference and improving measurement accuracy. The height calculation is based on the constructed signal reflection model, combined with parameters such as path delay and reflection intensity, to accurately calculate the true height of the aircraft from the ground. In addition, the present invention ensures flight stability and continuity of data collection through the dynamic path planning function of the aircraft flight control system; in conjunction with the data storage and transmission system, it realizes real-time data processing and large-scale distributed information output.

[0067] Based on the same inventive concept, an embodiment of the present invention further provides a computer program product, including a computer program / instruction, which implements the aforementioned method for measuring the height of an aircraft above the ground when executed by a processor.

[0068] Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention shall still fall within the patent scope of the present invention.

Claims

1. A method for measuring the height of an aircraft from the ground, characterized in that: The following steps are involved: Preprocessing the received GNSS direct signal and reflected signal to obtain corresponding synchronized digital signals; Determine the waveform peak position difference between the GNSS direct signal and the reflected signal according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal; Determining the path delay difference between the GNSS direct signal and the reflected signal according to the waveform peak position difference; Combined with the terrain reflection characteristics and vegetation coverage, a signal reflection model of path delay difference and aircraft altitude is established; The height of the aircraft above the ground is determined according to the signal reflection model and the path delay difference.

2. The method according to claim 1, characterized in that The received GNSS direct signal and reflected signal are preprocessed to obtain corresponding synchronous digital signals, including the following steps: The GNSS direct signal and reflected signal are received by the aircraft's upward right-hand circularly polarized antenna and downward left-hand circularly polarized antenna respectively; Perform RF front-end processing on the GNSS direct signal and reflected signal. The two channels share the local oscillator and clock to obtain the GNSS direct signal and reflected signal with channel time synchronization. The analog-to-digital conversion is performed on the channel time-synchronized GNSS direct signal and reflected signal at a high sampling rate to obtain synchronized digital signals of the GNSS direct signal and reflected signal.

3. The method according to claim 2, characterized in that The GNSS direct signal and the reflected signal are processed by the RF front end, and the two channels share the local oscillator and the clock to obtain the GNSS direct signal and the reflected signal with channel time synchronization, including the following steps: Perform mixing processing on the GNSS direct and reflected radio frequency signals to obtain intermediate frequency signals of the GNSS direct and reflected signals; A common clock local oscillator signal is used to time synchronize the direct channel and the reflected channel of the intermediate frequency signal to obtain a GNSS direct signal and a reflected signal with channel time synchronization.

4. The method according to claim 1, characterized in that Determining the waveform peak position difference between the GNSS direct signal and the reflected signal according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal includes the following steps: Determine multiple peak points of the GNSS direct signal and the reflected signal according to the synchronous digital signals corresponding to the GNSS direct signal and the reflected signal; perform interpolation according to the multiple peak points to obtain the GNSS direct signal waveform and the reflected signal waveform respectively; determine the waveform peak position difference between the GNSS direct signal and the reflected signal according to the GNSS direct signal waveform and the reflected signal waveform; Alternatively, the synchronous digital signals corresponding to the GNSS direct signal and the reflected signal are correlated with the local code respectively to obtain the GNSS direct signal waveform and the reflected signal waveform; based on the GNSS direct signal waveform and the reflected signal waveform, the waveform peak position difference between the GNSS direct signal and the reflected signal is determined.

5. The method according to claim 1, characterized in that Determining the path delay difference between the GNSS direct signal and the reflected signal according to the waveform peak position difference includes the following steps: The code phase delay of the GNSS direct signal and the reflected signal is determined according to the code phase of the waveform peak position of the GNSS direct signal and the reflected signal; the path delay difference between the GNSS direct signal and the reflected signal is determined according to the code phase delay and the GNSS signal propagation speed.

6. The method according to any one of claims 1 to 5, characterized in that: The signal reflection model is: ΔH represents the height of the aircraft from the ground, Δd represents the path delay difference between the direct GNSS signal and the reflected signal, and δ atm represents the tropospheric delay error, δ hw represents the deviation between the direct channel and the reflected channel caused by hardware error, δ r Indicates the deviation of the reflecting surface caused by terrain reflectivity and vegetation coverage, δ att represents the attitude error of the hovering drone, δ m represents the measurement error, ε represents the unmodeled error, θ represents the satellite elevation angle, and d represents the vertical distance between the upward-looking antenna and the downward-looking antenna of the aircraft.

7. The method according to claim 6, characterized in that Determining the height of the aircraft from the ground according to the signal reflection model and the path delay difference comprises the following steps: Collecting signal data at multiple locations on the flight path of the aircraft, the signal data including satellite elevation angle, path delay difference between GNSS direct signal and reflected signal; Selecting at least one location from the plurality of locations in descending order of satellite elevation angles; The signal data of the selected locations are input into the signal reflection model to obtain the height of the aircraft above the ground at the corresponding locations.

8. The method according to claim 7, characterized in that When the selected locations include multiple locations, the method for measuring the height of the aircraft above the ground further includes the following steps: Use the sliding average method to smooth the signal data of multiple selected locations; Generate a distribution map of the height of the aircraft above the ground on the flight path of the aircraft based on the signal data of the multiple locations after smoothing; The height of the aircraft above the ground is determined according to the aircraft height distribution map and the position of the aircraft on the flight path.

9. A system for measuring the height of an aircraft from the ground, characterized in that: include: A GNSS radio frequency signal receiving module, used to receive GNSS direct signals and reflected signals respectively; A signal processing module, used for pre-processing the received GNSS direct signal and reflected signal to obtain corresponding synchronous digital signals; Determine the waveform peak position difference between the GNSS direct signal and the reflected signal according to the synchronous digital signal corresponding to the GNSS direct signal and the reflected signal; The path delay difference between the GNSS direct signal and the reflected signal is determined based on the waveform peak position difference. A signal reflection model of the path delay difference and the aircraft's height above the ground is established in combination with the terrain reflection characteristics and vegetation coverage. The aircraft's height above the ground is determined based on the signal reflection model and the path delay difference.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the method for measuring the height of an aircraft above the ground as claimed in any one of claims 1 to 8 is implemented.

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