186 results about "Altimeter" patented technology

The invention relates to the technical field of underwater intelligent navigation and integrated navigation, in particular to a submersible integrated navigation multi-source data fusion method based on an elastic random model, which comprises the following steps: preprocessing multi-source navigation data output by an inertial navigation system (INS), a Doppler velocimeter, an ultra-short baseline / long baseline, an altimeter and a depthometer; constructing a state space model containing navigation parameter errors and sensor errors, and screening an optimal sensor combination mode; the method comprises the following steps: constructing an elastic correction parameter model and a dynamic adjustment state and observation noise covariance matrix by combining an elastic PNT framework, performing local filtering on multi-source data by adopting a plurality of parallel elastic self-adaptive robust volume Kalman filters (CKF), outputting a fusion resolving result, and realizing optimal estimation of a global navigation state through a dynamic information distribution strategy. The method has relatively high anti-interference performance, self-adaptive capability and combination switching robustness, and is suitable for navigation and positioning tasks of a high-precision submersible in a complex underwater environment.

The embodiment of the invention provides an airborne multi-sensor integrated navigation and positioning method, device, equipment and medium, and relates to the technical field of aviation navigation, and the method comprises the following steps: a Beidou navigation system, an altimeter and a radio navigation system are respectively combined with an inertial navigation system, each combination outputs an observation value through a sub-filter, and the observation value is calculated through a sub-filter; the observation value output by each sub-filter and the predicted value of the inertial navigation system are fused and then a positioning result is output, and fault detection and repair are respectively carried out on data output by the inertial navigation system, the Beidou navigation system and the altimeter; carrying out anomaly detection on the observation value output by each sub-filter by utilizing the state parameter estimation and the residual vector, and repairing the detected abnormal value by adopting a robust filtering mode; and performing anomaly detection and restoration on the observation value output by each sub-filter, calculating new state parameter estimation, and performing anomaly detection on the dynamic model of the sub-filter based on the new state parameter estimation. The scheme is beneficial to improving the fault tolerance rate of integrated navigation positioning.

A millimeter wave radar altimeter structure disclosed by the present invention comprises a shell, the shell is provided with a plurality of functional areas and integrates a plurality of functional units, the functional units comprise a radio frequency unit, an intermediate frequency processing unit and a signal control unit, and the plurality of functional units are compactly arranged in the shell. The radio frequency unit comprises at least one high-power emission chip, the chip is installed on a heat conduction substrate, and the substrate is in contact with the shell to form a heat conduction path. The shell is made of a high-heat-conductivity material, and a plurality of heat dissipation structures are arranged outside the shell, so that the heat dissipation efficiency under natural convection is improved. The heat conduction substrate, the shell material and the heat dissipation structure form a continuous heat dissipation path from the chip to the environment, heat accumulation is effectively restrained, and stable work of the chip is guaranteed. The shell further comprises a sealing structure, a sealed space is formed by a sealing groove, a sealing element, the antenna cover and the packaging cover plate, and environment sealing protection is achieved. The signal control unit is connected with peripheral equipment through an external interface, and the interface supports power supply and data communication of the altimeter.

The invention relates to the field of radio measurement, in particular to a radio height simulation device and method. The radio height simulation device comprises a fixed attenuator, a photoelectric conversion module Tx, a first optical path control member, a second optical path control member, a photoelectric conversion module Rx, a numerical control attenuator and a host. One end of the fixed attenuator is connected with the radio altimeter, one end of the photoelectric conversion module Tx is connected with the fixed attenuator, the other end of the photoelectric conversion module Tx is connected with the first optical path control element, the first optical path control element is externally connected with at least one optical fiber, and the optical fiber is connected with the second optical path control element; according to the invention, the dependence on a digital signal processor and a long-distance radio frequency cable is reduced, the hardware cost is reduced, the radio altimeter can be tested according to the radio height simulation device, the device can be calibrated by using a vector network analyzer, and the accuracy of height simulation is further ensured.

The embodiment of the invention provides a method and a system for processing ocean multi-parameter wide-width imaging data of a Beidou interference altimeter, and relates to the technical field of GNSS-R. The method comprises the following steps: constructing a set of complete and strict data processing chain; through precise calculation of a GNSS-R direct signal and reflection signal delay inequality interference geometric model and correction of actual measurement delay inequality errors, systematic errors in the process of converting original signals into geophysical parameters are remarkably reduced, and the precision and reliability of parameters obtained through final inversion are improved. And on the basis of a self-adaptive data collection strategy of parameter space-time transformation characteristics and a spatial interpolation reconstruction process, discrete strip data is intelligently'woven 'into a continuously-covered wide-swath imaging type data product, so that the data format better meets the analysis requirements in the fields of oceanography, climatics and the like, and the intuition and usability of the product are improved.

The invention relates to the technical field of elevation measurement, in particular to an unmanned aerial vehicle height measurement method and system based on data fusion. The method comprises the following steps: acquiring various influence data of the unmanned aerial vehicle at each moment; according to the distribution condition of the influence data, the abnormal degree of each influence data is obtained, and then effective influence data is screened out; based on the effective influence data and the distribution condition of the abnormal degree of the effective influence data, obtaining a reliability degree; and correcting the fixed weight of each altimeter according to the reliability degree of each type of influence data and the abnormal degree of each type of influence data at the termination moment of the preset time period, obtaining the corrected fixed weight, and then obtaining the real height of the unmanned aerial vehicle. According to the invention, each type of influence data is analyzed, the modified fixed weight of each height measuring instrument is accurately determined, the real height of the unmanned aerial vehicle is accurately obtained according to the modified fixed weight of each height measuring instrument, and the flight state of the unmanned aerial vehicle is accurately analyzed.

The invention discloses a low-altitude aircraft accurate positioning method based on Beidou satellite data, and the method comprises the following steps: collecting the multi-source data of Beidou positioning, IMU, barometer and altimeter in the flight process, and generating an original positioning data set; after multi-source data are aligned, a fusion data sequence is constructed; carrying out error modeling by adopting zero offset correction, drift compensation and scale normalization, and outputting a calibrated data sequence; an improved FGO algorithm is input, factors such as Beidou satellite pseudo-range, IMU integration and process prior are processed in a combined mode, track combined optimization is executed, and a preliminary positioning result is output; performing error correction by combining a ground differential base station and satellite-based enhanced data, and outputting a high-precision positioning result sequence; and abnormal point elimination and trajectory smoothing are realized through consistency discrimination and confidence evaluation, and a final positioning result is obtained. The method improves the positioning precision and robustness of the low-altitude aircraft, and is suitable for high-precision positioning application in a complex environment.

A method includes generating an output radio frequency (RF) signal. The method includes communicating the output RF signal to an antenna module. The method includes receiving a bit stream from the antenna module. The bit stream includes data representing the output RF signal prior to transmission of an output RF waveform associated with the output RF signal at the antenna module and data representing a return RF signal associated with a return RF waveform received at the antenna module following transmission of the output RF waveform as part of a sensing operation. The method includes analyzing one or more values of the data representing the return RF signal to generate an altitude indication for a vehicle, a ground speed indication for the vehicle, or a combination thereof.

The invention provides a point and surface target altimeter echo simulator. Comprising a real-time simulation unit and a target echo radio frequency generation unit. The real-time simulation unit is composed of a main control computer and a real-time simulation machine and is responsible for man-machine interaction, system setting, flight path real-time display, terrain matching, map data real-time calculation and echo data real-time calculation. The target echo radio frequency generation unit comprises a down-conversion assembly, an up-conversion assembly, an intermediate frequency processing assembly and a short delay assembly. Convolution operation, echo signal attenuation control and delay control, target echo radio frequency signal generation and short-distance echo signal simulation of target echoes are realized. According to the invention, frequency modulation continuous wave and pulse system altimeter echo continuous simulation is completed, altimeter echo signals of a point target and a terrain surface target are simulated, after data such as flight position information of an aircraft are received, the echo signals are transmitted to an altimeter in real time, and the requirements of a semi-physical simulation test of the altimeter are met.

The invention discloses a radio altimeter test data anomaly detection method and system, and relates to the technical field of altimeter testing, and the method comprises the steps: obtaining historical test data, outputting a first analysis result, collecting real-time flight parameters, calculating dynamic statistic data according to the first analysis result, building a self-adaptive baseline, and constructing a first anomaly detection model; according to the method, the dynamic baseline is constructed, self-adaptive anomaly detection of radio altimeter test data is achieved, accuracy is improved, fusion analysis is carried out in combination with multi-mode flight parameters, and the reliability of the radio altimeter test data is improved, so that the reliability of the radio altimeter test data is improved, and the reliability of the radio altimeter test data is improved. According to the altimeter anomaly detection method, the detection comprehensiveness is enhanced, a physical verification mechanism is introduced, the anomaly detection reliability is ensured, meanwhile, alarm levels are divided according to anomaly results, real-time response is achieved, a powerful guarantee is provided for flight safety, and the intelligence and safety of altimeter anomaly detection are remarkably improved.

The present disclosure relates to the technical field of model construction, and provides a river water dynamics model construction method based on multi-source remote sensing, which comprises the following steps: acquiring a river remote sensing image to obtain a water edge line, acquiring water level data by means of an altimeter satellite, and giving an elevation value to a water edge line corresponding point according to the water edge line and the water level data; for a straight river section, a value is taken according to a specific rule, and for a curved river section, the value is determined according to linear fitting of multiple elevation measuring point values on a river section; based on the elevation values of the water edge lines of the straight and curved river sections, a river terrain digital raster model is further constructed by interpolation along the water edge line, the river water dynamics model is constructed by using the river terrain digital raster model, the simulation effect of the water dynamics model is determined by comparing the water level consistency or the water surface vector form consistency, and the calibration and verification of the river water dynamics model are realized. The present disclosure realizes accurate simulation of the river water dynamics process. The present disclosure can reduce the cost of model parameter acquisition.

The invention discloses an optical flow assisted unmanned aerial vehicle nonlinear robust federated filtering navigation method and system, and the method specifically comprises the steps: constructing a robust weight matrix based on observation residual errors, and constructing a robust robust filter based on the robust weight matrix; an SINS / GNSS sub-filter and an SINS / VIO sub-filter are constructed, the SINS / GNSS sub-filter is subjected to combined filtering through an IMU, a GNSS, a magnetometer and an altimeter, and the SINS / VIO sub-filter is subjected to combined filtering through an IMU, a GNSS, a VIO and an altimeter; solving the robust adversarial filter by using an iteration method; constructing a self-adaptive federated filter, and adopting a mahalanobis distance as an information distribution factor of the self-adaptive federated filter; and based on an adaptive federated filter, fusing an SINS / GNSS sub-filter and an SINS / VIO sub-filter to carry out unmanned aerial vehicle position estimation. According to the invention, robust autonomous operation of the unmanned aerial vehicle in a forest environment can be realized.

The invention innovatively provides an engineering height measurement method and system for an inertial navigation system based on a barometer as error compensation, engineering equipment is modeled, the modeling comprises the shape and characteristics of the equipment and the installation position of the inertial navigation system, different sensor parameters are adjusted through a simulation model, and the engineering height measurement accuracy is improved. Observing a starting jumping rule and a stopping jumping rule of the sensor, analyzing error performance of the sensor under different moving distances, and obtaining an inertial navigation simulation model through a simulation training strategy; collecting data of an inertial navigation system and a barometer in real time; inputting the inertial navigation data into the simulation model, and performing simulation correction on the inertial navigation data according to the inertial navigation data and a simulation algorithm; and the error compensation module is used for acquiring the corrected inertial navigation data and barometer data, acquiring an inertial navigation height through an inertial navigation model, calculating and acquiring an engineering height through a data fusion algorithm, and performing error compensation on the inertial navigation model by utilizing the engineering height through an error compensation strategy.

The present invention provides a method and system for simultaneous positioning and mapping of a laser radar, the method comprising: obtaining ranging data of a carrier through an altimeter, and obtaining point cloud data of the carrier through a laser radar; solving the ranging data through an IMU to obtain external posture data of the carrier on a height channel; the external posture data includes the height of the carrier from the ground, the roll angle, and the pitch angle; solving the point cloud data through an IMU to obtain internal posture data of the carrier on a horizontal channel; the internal posture data includes the x position, y position, and heading angle of the carrier; performing posture estimation based on the external posture data and the internal posture data to obtain the posture data of the carrier. The present invention can solve the problem of reduced positioning accuracy of laser radar in a degraded environment.

The invention discloses a 5G and Beidou fused vehicle positioning navigation system. The system comprises a multi-source heterogeneous positioning module; a high-precision map and a dynamic traffic information base; a self-adaptive multi-layer map matching module; the dynamic path planning module considers steering limitation and real-time position feedback; and a central information fusion and decision unit. According to the invention, multi-source heterogeneous positioning data such as Beidou / GPS, 5G positioning, high-precision IMU, a vehicle-mounted atomic clock and a barometric altimeter are fused, and a tight combination algorithm based on ESKF or a factor graph is adopted, so that the system can realize accurate positioning in an environment with good satellite signals, partial shielding and even serious loss. Continuous, smooth and high-precision vehicle state estimation can be output, particularly when the number of visible satellites is insufficient, double-satellite positioning can be achieved by using the vehicle-mounted atomic clock to predict the clock error and combining the elevation constraint of the barometric altimeter, and the usability and robustness of positioning are improved.

The invention discloses a method and a device for detecting marginal sea significant wave height by a spaceborne altimeter, relates to the technical field of ocean remote sensing, and aims to solve the problem of poor marginal sea significant wave height detection precision of the spaceborne altimeter in the prior art. The method comprises the following steps: acquiring sub-satellite point echo waveform data acquired by a spaceborne altimeter; the method comprises the following steps: determining the waveform category of each echo waveform in sub-satellite point echo waveform data collected by a spaceborne altimeter by using an echo waveform classification model constructed based on the sub-satellite point echo waveform data collected by a SWIM spectrometer, and obtaining a first echo waveform classification library; obtaining a first edge sea echo waveform from a first echo waveform classification library, determining a target characteristic parameter of the first edge sea echo waveform, and determining an effective wave height of the first edge sea echo waveform by using an effective wave height inversion model constructed based on sub-satellite point echo waveform data collected by an SWIM spectrometer and wave height data in ERA5; therefore, the edge sea significant wave detection precision is improved.

The invention discloses a river water level inversion method taking altimeter footprint heterogeneity into consideration. The method comprises the following steps: acquiring an observation waveform of an SAR altimeter; space geometric parameters are calculated through footprint gridding and observation geometric modeling; constructing a water distribution scene based on the water mask and the river network, and classifying the water into a main river channel, a flood area and an adjacent isolated water body; electromagnetic scattering numerical integration is carried out based on the differentiated surface roughness parameters, and a simulated echo waveform is generated; waveform retracking and parameter inversion are realized through coarse grid search and local optimization solution; calculating an absolute water level and carrying out geophysical correction; performing multi-index quality control based on the interpretation rate of the analog waveform and the residual whitening degree; and finally outputting a water level product. According to the method, the defects of insufficient inversion precision and robustness of an existing method in a complex earth surface mixed scene are overcome, and the accuracy, reliability and physical interpretability of inland river water level monitoring are remarkably improved.

The invention discloses an unmanned aerial vehicle height estimation method, and belongs to the technical field, and the method comprises the steps: S1, data collection: controlling an unmanned aerial vehicle to vertically climb or descend by H meters in situ, and continuously collecting images and air pressure height data during the period; s1-1, collecting a first group of data; s1-2, collecting a second group of data; s1-3, carrying out data pairing; s2, calculating the height of each image to the ground at the acquisition moment; s3, calculating the relation between the air pressure height and the height to the ground; and S4, calculating the relation. The unmanned aerial vehicle height estimation method is low in cost, does not need to additionally add a sensor, can realize ground height estimation by using an existing visual system and a barometer of the unmanned aerial vehicle, greatly reduces hardware cost, is suitable for vertical motion scenes of the unmanned aerial vehicle, especially has good performance in low-speed scenes such as landing, makes up for the dependence on horizontal displacement speed in the prior art, and has good application prospects. Through multi-group data acquisition, feature matching and linear fitting, the accuracy and reliability of ground height estimation are improved.

The invention discloses a twenty-two-axis vertical take-off and landing aircraft and a control method thereof. The twenty-two-axis vertical take-off and landing aircraft mainly comprises a parachute bag, a cabin and a power device. The twenty-two shafts comprise ten propellers, eight rotating shafts and four movable wings which are powered by independent power devices. The attitude, the position, the speed, the height and the course parameters of the aircraft are set on a computer according to the use requirements, and the attitude, the position, the speed, the height and the course parameters of the aircraft are calculated through sensors installed on twenty-two axes and an inertial reference system / attitude course reference system, an atmospheric data system, a global navigation satellite system, a course assisting and correcting system, a radio altimeter and an atmospheric temperature sensor in a cabin. A computer carries out data fusion and sends instruction signals to a power device for controlling ten propellers, eight rotating shafts and four movable wings, so that state control of the aircraft is realized, flight environment safety is intelligently diagnosed, and risk early warning and active avoidance are provided.

The application discloses a calibrator star-based altimeter calibration system and method, which utilizes a calibrator star carrying a calibrator to correct the system error of a spaceborne radar altimeter, thereby completing the calibration of the altimeter to the earth. The calibrator can modulate and retransmit the pulse emitted by the altimeter, and the calibration factor can be calculated according to the echo of the calibrator without relying on the ground calibration field, and then the calibration task can be completed by substituting into the ground target echo equation. The method utilizes the calibrator star to convert the calibration task from the original single "air-ground" data acquisition to an integrated calibration system of "altimeter-load platform-ground target", and the calibrator is moved from the ground to the space, so that the ground clutter can be reduced or even eliminated, the system error and the atmospheric error can be separated, and the coupling problem of the system error and the atmospheric error can be indirectly completed.

A method includes receiving an output radio frequency (RF) signal. The method includes generating a digitized output RF signal representing the output RF signal. The method includes transmitting an output RF waveform associated with the output RF signal. The method includes receiving a return RF waveform based on transmission of the output RF waveform. The method includes generating a digitized return RF signal representing a return RF signal associated with the return RF waveform. The method includes serializing the digitized output RF signal and the digitized return RF signal to generate a serialized baseband signal. The method includes communicating a bit stream based on the serialized baseband signal to an RF unit. The RF unit is configured to generate an altitude measurement, a ground speed measurement, or both for a vehicle based on the serialized baseband signal.

The embodiment of the invention provides an interactive multi-model factor graph integrated navigation method based on tight coupling attitude constraint. In a specific embodiment, the method comprises the following steps: constructing an integrated navigation system; constructing an inertial measurement unit factor pre-integrated by the inertial navigation system; constructing a direct celestial navigation factor and a refraction celestial navigation factor which are respectively and tightly coupled with an inertial measurement unit factor based on the star sensor observation condition of the celestial navigation system; constructing a horizontal radio navigation factor and a vertical radio navigation factor based on the position information of the land-based radio navigation system; acquiring height measurement data of the barometric altimeter to construct barometric altimeter factors; dynamically adjusting the weight ratio of the height measurement data of the vertical radio navigation factor to the height measurement data of the barometric altimeter factor through an interactive multi-model algorithm; and carrying out global state estimation of the integrated navigation system on a factor graph framework formed by the factors.

1. The name of this design product: altimeter body. 2. Purpose of the product of this design: The whole product is an altimeter used to measure height; the part of the product is the main body of the altimeter. 3. The key design point of this design product lies in the shape of the solid line part in the figure. 4. The picture or photo that best illustrates the design points: Stereoscopic drawing 1. 5. Other situations that need to be explained Other explanations: The dotted part in the figure is the content that is not requested to be protected.

The application discloses a kind of offshore recovery height filtering calculation methods of liquid carrier rocket, it is related to reusable rocket technical field, this method is updated by inertial measurement data real-time launch carrier rocket in the inertial system position, geocentric vector radius and rocket body ellipsoid height, extracts geocentric vector radius unit vector;Establish measurement vector by receiving radio altimeter detection measurement height, constructs measurement innovation in combination with state step prediction and measurement matrix, executes abnormal determination according to chi-square distribution detection quantity covariance matrix calculation, extracts no abnormal data as filtering measurement value;Establish fifteen-dimensional Kalman filter to construct measurement matrix, input filtering measurement value executes state transition and fusion, solves launch inertial system position error;Dynamic correction compensation is carried out using the error, and the modified rocket body ellipsoid height is set as relative sea level height.This will absolute position calculation be converted into relative position maintenance, ensure high-precision relative sea level height.

The invention relates to the technical field of navigation satellite reflection remote sensing, in particular to a water level measurement method and device based on LEO-IR, and the method comprises the steps: obtaining LEO observation data and LEO broadcast ephemeris of a shore-based LEO station adjacent to a target water area; calculating angle information of the LEO satellite relative to the shore-based LEO station based on the LEO broadcast ephemeris and the actual position of the shore-based LEO station; calculating a reflection height and a precision attenuation factor of the reflection height according to LEO observation data, angle information and LEO-IR; and calculating the water level height of the target water area based on the reflection height, the precision attenuation factor and the height of the antenna phase center. According to the embodiment of the invention, the method employs a larger number of LEO satellites with a higher moving speed to construct a time-consistent satellite arc-to-height rate error correction model and a precision attenuation factor model, solves a problem that the time resolution or spatial resolution or precision is lower in the related technology, and improves the accuracy of the satellite arc-to-height rate error correction model. The method has obvious application prospects and advantages in water level fluctuation monitoring in extreme weather such as earthquakes, tsunami and storm surge.

The present disclosure provides for a device and system for aqueous wave measurement. The system may comprise at least one altimeter that may collect one or more measurements from a vertical orientation. The system may comprise at least one stabilization sensor that may interface with at least one positioning device. The stabilization sensor may, with fixed coordinates received from the positioning device, allow the drone to maintain a constant altitude above the variable, changing surface of water. The system may comprise one or more analytics that produce meaningful metrics from information received from the aqueous wave measurement device. The system may comprise at least one GUI that presents the analytics in an understandable way based on the expertise of a user viewing the analytics. The device may store collected measurements locally, or may transmit the measurements via at least one transmitting device, or both.

The utility model discloses an autonomous water taking device based on an altimeter, and relates to the technical field of water taking devices, the autonomous water taking device comprises a temperature-salinity-depth profiler body, the top of the temperature-salinity-depth profiler body is fixedly provided with a cable, and the inner side of the top of the temperature-salinity-depth profiler body is provided with a water taking assembly and a connecting assembly; the water taking assembly comprises a first connector, a second connector, a plurality of water taking tanks, a first electromagnetic valve, a second electromagnetic valve, a manual drain valve and a connecting cable; according to the technical scheme, the water taking assembly is arranged, specifically, according to the fact that the temperature-salinity-depth section plotter body is released to a certain depth of the bottom of the sea level, then the controller of the ship body controls the first electromagnetic valve and the second electromagnetic valve to be opened through the connecting cable, liquid is automatically poured into the water taking tank at the moment, and rapid and automatic water taking is carried out; and a plurality of water taking tanks are adopted, so that different types of seawater can be sampled, and the device is convenient to use.

This invention discloses a method for improving the orbital accuracy of a lunar probe based on reflective prism constraints. The method first utilizes laser ranging data obtained from a known reflective prism on the lunar surface using an onboard laser altimeter, and constructs an error equation set by combining this data with a dynamic orbital model. Next, a high-resolution camera is used to perform multiple imaging operations on the lunar reflective prism from different orbits and perspectives. Using the bundle adjustment principle, the observed image point coordinates are combined with the dynamic model to construct the error equation set. Finally, laser ranging observations from the reflective prism and multi-temporal photogrammetry observations are used as two different types of geometric constraints to construct a joint adjustment model of multi-source observation data. The high-precision orbital parameters are then calculated using a least-squares algorithm. This invention uses laser ranging data and an optical image database to add new constraints to the estimated orbit, ultimately correcting and further improving the orbital accuracy of the lunar probe.

An extended reality (XR) system, comprises a head-mounted display (HMD) configured for displaying virtual content to a user, a first altimeter carried by the HMD, a hand-held control, and a second altimeter carried by the hand-held control. The first altimeter configured for outputting first atmospheric pressure data indicative of an elevation of the HMD, while the second altimeter is configured for outputting second atmospheric pressure data indicative of an elevation of the hand-held control. The XR system further comprises at least one processor configured for determining a relative elevation between the first altimeter and the second altimeter based on the first atmospheric pressure data and the second atmospheric pressure data.

The invention relates to a radio altimetry system capable of being loaded on board an aircraft. The invention relates to a radio altimetry system (101) capable of being loaded on an aircraft and capable of providing a height of the aircraft from the ground level, the radio altimetry system comprising: a first subsystem (201) based on FMCW technology and providing a first height value (V1); a second subsystem (202) based on UWB technology and providing a second altitude value (V2); and merging electronic circuitry (203) (configured to: compare the second value with a predetermined threshold; if the second value is less than or equal to the threshold, determining a merge value (VC) based on the first value and the second value; and if the second value is greater than the threshold, determining a merge value (VC) based on the first value irrespective of the second value. In this way, the proposed radio altimetry system is resistant to various interferences.