A method for low-altitude target detection by combining beidou positioning and radar

Abstract

The application relates to the field of radar technology and particularly discloses a Beidou positioning and radar cooperative low-altitude target detection method, which comprises the following steps: obtaining Beidou ephemeris data to solve a Beidou receiver position sequence, and establishing a time corresponding relationship by using radar pulse emission and the arrival time recorded by the Beidou receiver to obtain a continuous deviation trajectory of a radar local clock relative to Beidou time. Under a unified time reference, echo candidate points are extracted from radar echo signals to form echo trajectories, a propagation time sequence is obtained from the trajectories that pass the stability verification, target direction information is inversed by combining the beam pointing angles and echo intensity distribution recorded in the radar scanning process, the target distance is obtained according to the propagation time, the position of the target in a radar coordinate system is determined together with the direction information, the target space position is obtained by combining the Beidou receiver position sequence, and stable detection of the low-altitude target is realized.

Description

Technical Field

[0001] This invention relates to the field of radar technology, specifically to a method for low-altitude target detection that combines BeiDou positioning with radar coordination. Background Technology

[0002] In low-altitude airspace, the number of aircraft, drones, and small, slow-moving targets is constantly increasing. Their low flight altitude, small size, and complex movement patterns pose significant challenges to existing detection systems. Traditional radars typically rely on their local clock and echo signals for distance and direction estimation when scanning low-altitude targets. However, due to drift and errors in the radar's local clock, time reference instability can easily occur during long-term scanning or multi-pulse observations, affecting the accuracy of echo time measurements and leading to accumulated errors in target distance calculations. Furthermore, during continuous scanning, echo signals between different pulses may be affected by noise, clutter, and multipath propagation, making it difficult to establish stable correlations between echo points and reducing the reliability of target trajectory extraction and identification. In addition, during radar beam scanning, echo intensity fluctuates with beam direction; without stable spatiotemporal reference information for auxiliary analysis, it is often difficult to accurately reflect the true directional characteristics of the target. Summary of the Invention

[0003] The purpose of this invention is to provide a low-altitude target detection method that combines BeiDou positioning with radar, thereby solving the aforementioned technical problems.

[0004] The objective of this invention can be achieved through the following technical solutions: A method for low-altitude target detection using BeiDou positioning and radar coordination includes the following steps: Obtain ephemeris data output by the BeiDou system, and calculate the BeiDou receiver position sequence based on the ephemeris data; The radar is activated to perform low-altitude scanning, and the local transmission time corresponding to each radar transmission pulse is recorded. Each transmission pulse is fed into the Beidou receiver, and the arrival time of each transmission pulse to the Beidou receiver is measured. Based on the local transmission time and arrival time, the continuous deviation trajectory of the radar local clock relative to Beidou time is obtained. Multiple echo candidate points are extracted from the radar echo signal, the echo trajectory is obtained based on the echo candidate points of multiple echo signals, and the echo trajectory that has passed the stability verification and the corresponding propagation time series are recorded. Record the radar beam pointing angle corresponding to each transmitted pulse, establish a correlation between each echo point in the echo trajectory and the beam pointing angle of the corresponding transmitted pulse, and invert the target's true direction vector relative to the radar based on the echo intensity distribution; The target distance is obtained from the propagation time series. The target's position coordinates in the radar coordinate system are generated by combining the true direction vector and the target distance. The target's position coordinates in the radar coordinate system are then correlated with the position sequence of the Beidou receiver to output the target detection result.

[0005] As a further aspect of the present invention: obtaining the continuous deviation trajectory includes: The original time difference is obtained by subtracting the local transmission time of each transmission pulse from its corresponding arrival time. The original time difference values ​​of multiple consecutive transmission pulses are subjected to quality checks, and abnormal samples whose differences from the preceding and following samples exceed the preset mutation threshold are removed. The remaining samples are arranged in chronological order of transmission time to form a time difference sample sequence. The time difference sample sequence is input into a recursive estimation algorithm. The recursive estimation algorithm estimates the clock deviation, clock drift rate, and clock drift acceleration at the current moment based on the distribution pattern of the time difference samples. The estimated clock deviation, clock drift rate, and clock drift acceleration are used to generate a continuous deviation trajectory covering the entire scan cycle.

[0006] As a further aspect of the present invention: selecting candidate echo points includes: Envelope detection is performed on the echo signal of each transmitted pulse to obtain the waveform of the echo amplitude changing with the sampling time. All local maxima points whose amplitude exceeds the preset detection threshold are searched on the waveform. The sampling time corresponding to each local maximum point is recorded as the echo arrival time, and the amplitude value of each local maximum point is recorded as the echo intensity. All local maximum points extracted from the same transmitted pulse are arranged in chronological order to form a set of candidate echo points for the transmitted pulse.

[0007] As a further aspect of the present invention: obtaining the echo trajectory includes: The echo arrival time of each candidate echo point is converted into an absolute arrival time using a continuous deviation trajectory. The candidate echo points of each transmitted pulse are marked on a unified time axis according to their absolute arrival times. Starting from the first transmitted pulse, the candidate echo points of each subsequent transmitted pulse are traversed sequentially. For each candidate echo point of the current transmitted pulse, the candidate echo point in the previous transmitted pulse with the closest absolute arrival time and a time difference less than a preset pulse interval threshold is searched. If a candidate echo point that meets the condition exists, the two are marked as a potential correlation pair and the process continues. When three or more consecutive transmitted pulses have correlation pairs that meet the time proximity condition, the candidate echo points corresponding to the correlation pairs are connected to form an echo trajectory. If no correlation pair exists, an error is reported.

[0008] As a further aspect of the present invention: obtaining the propagation time series includes: For each echo trajectory, the absolute arrival time interval between adjacent echo points in the echo trajectory is calculated, and it is determined whether the difference between the absolute arrival time interval and the radar pulse repetition period is less than a preset period matching threshold. The propagation time variation between adjacent echo points is calculated, and it is determined whether the propagation time variation is less than a preset motion continuity threshold. The average echo intensity of all echo points in the echo trajectory is calculated, and it is determined whether the absolute value of the difference between the echo intensity of each echo point and the average echo intensity is less than a preset intensity fluctuation threshold. Echo trajectories that meet the above conditions are determined to be verified echo trajectories. The propagation time of each echo point is extracted from the verified echo trajectory, and the propagation times are arranged in chronological order to form a propagation time sequence.

[0009] As a further aspect of the present invention: the retrieved target's true direction vector relative to the radar includes: The beam azimuth and beam elevation angles corresponding to each transmitted pulse are read from the radar servo control system memory. The beam azimuth and beam elevation angles are combined to form the beam pointing angle vector of the transmitted pulse. According to the sequence number of the transmitted pulse, each echo point in the echo trajectory is matched one-to-one with the beam pointing angle vector with the same sequence number to form a pairing list of echo points and beam pointing angles.

[0010] As a further aspect of the present invention: the retrieved target's true direction vector relative to the radar also includes: In the pairing list, a distribution curve of echo intensity as a function of beam pointing angle is plotted with beam pointing angle as the independent variable and echo intensity as the dependent variable. The beam pointing angle corresponding to the maximum echo intensity is searched on the distribution curve. This angle is used as the initial direction estimate. Multiple neighboring beam pointing angles and their corresponding echo intensities are selected with the initial direction estimate as the center. The selected angles and intensities are weighted and averaged, with the weighting coefficient being the echo intensity values. The weighted average beam azimuth and beam elevation angles are calculated. The weighted average beam azimuth and beam elevation angles are combined to form the true direction vector of the target relative to the radar.

[0011] The beneficial effects of this invention compared to the prior art are as follows: This invention systematically processes multiple key aspects of low-altitude target detection, enabling a stable correlation between temporal, echo, and spatial information, thereby improving the reliability of detection results. By continuously estimating and processing the time difference data generated during detection, a stable time deviation variation pattern can be established, ensuring a consistent time reference throughout continuous scanning and guaranteeing the continuity and consistency of echo time information. Simultaneously, by extracting candidate points, correlating trajectories, and verifying the stability of echo signals from multiple transmitted pulses, echo trajectories with continuous characteristics can be effectively identified, reducing the impact of noise and clutter on target identification and improving the stability of target trajectory extraction. Furthermore, by analyzing the relationship between echo intensity and beam pointing, the directional characteristics of the target in space can be more accurately reflected, making the target orientation estimation results more stable. Through comprehensive calculation of distance and orientation information, a complete target spatial location result can be generated, thus enhancing the continuity, stability, and accuracy of the low-altitude target detection process. Attached Figure Description

[0012] The invention will now be further described with reference to the accompanying drawings.

[0013] Fig. 1 This is a flowchart illustrating a low-altitude target detection method based on BeiDou positioning and radar coordination according to the present invention. Fig. 2 This is a schematic diagram illustrating the process of retrieving the true direction vector of a target relative to the radar according to the present invention. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Please see Figs. 1-2 As shown, this invention is a method for low-altitude target detection using BeiDou positioning and radar coordination, comprising the following steps: Obtain ephemeris data output by the BeiDou system, and calculate the BeiDou receiver position sequence based on the ephemeris data; The radar is activated to perform low-altitude scanning, and the local transmission time corresponding to each radar transmission pulse is recorded. Each transmission pulse is fed into the Beidou receiver, and the arrival time of each transmission pulse to the Beidou receiver is measured. Based on the local transmission time and arrival time, the continuous deviation trajectory of the radar local clock relative to Beidou time is obtained. In a preferred embodiment of the present invention, obtaining a continuous deviation trajectory includes: The original time difference is obtained by subtracting the local transmission time of each transmission pulse from its corresponding arrival time. The original time difference values ​​of multiple consecutive transmission pulses are subjected to quality checks, and abnormal samples whose differences from the preceding and following samples exceed the preset mutation threshold are removed. The remaining samples are arranged in chronological order of transmission time to form a time difference sample sequence. The time difference sample sequence is input into a recursive estimation algorithm. The recursive estimation algorithm estimates the clock deviation, clock drift rate, and clock drift acceleration at the current moment based on the distribution pattern of the time difference samples. The estimated clock deviation, clock drift rate, and clock drift acceleration are used to generate a continuous deviation trajectory covering the entire scan cycle.

[0016] Specifically, when acquiring ephemeris data output by the BeiDou system, the BeiDou receiver parses orbital parameter information from the navigation message in the on-orbit satellite broadcast signal. Ephemeris data is a set of parameters describing the satellite's orbital position and operational status, including information such as the satellite's semi-major axis, orbital eccentricity, orbital inclination, ascending node longitude, reference time, and satellite clock bias parameters. These parameters can be used to calculate the satellite's spatial position at any given time. After receiving navigation signals from multiple satellites, the BeiDou receiver decodes the navigation message and extracts the ephemeris data for each satellite, using time stamps to correlate the satellite signal reception time with the reference time in the navigation message. Subsequently, the ephemeris data is used to calculate the spatial position of each satellite at the current observation time, and combined with pseudorange measurements received by the BeiDou receiver for positioning, obtaining the spatial coordinates of the BeiDou receiver at continuous observation times. This forms a chronologically ordered sequence of BeiDou receiver positions, reflecting the changes in the receiver's spatial position throughout the entire observation period.

[0017] After acquiring the position sequence, the radar initiates low-altitude scanning. During operation, the radar periodically transmits electromagnetic pulses into space according to a pre-defined pulse repetition pattern. Each pulse transmission records a transmission time stamp in the radar's local control circuit. This time stamp, derived from the radar's internal clock counter, indicates the transmission time of the pulse under the radar's local time reference. To establish the correspondence between radar time and BeiDou time, the radar's transmitted pulses are introduced into the BeiDou receiver via an RF coupling channel, enabling the BeiDou receiver to directly receive the pulse signals emitted by the radar. Upon detecting the pulse signal, the BeiDou receiver uses its own time counting module to record the pulse's arrival time stamp, which is referenced to BeiDou time.

[0018] For each radar transmission pulse, a set of time records is obtained, including the radar's local transmission time and the arrival time recorded by the BeiDou receiver. The original time difference for each transmission pulse is calculated by correlating these two values. This time difference reflects the instantaneous deviation of the radar's local clock relative to BeiDou time. Since individual pulse measurements may be affected by interference or signal distortion, the continuously obtained original time difference values ​​need to undergo quality checks. The changes in the difference between adjacent samples are compared. When the change in the difference between a time difference sample and the samples before and after it exceeds a pre-set abrupt change threshold, the sample is considered abnormal data and removed from the sequence. The remaining valid samples are arranged in chronological order of radar transmission times, forming a continuous time difference sample sequence. This time difference sample sequence is then input into a recursive estimation algorithm for processing. The recursive estimation algorithm is a time series estimation method that continuously updates the current state estimation result using historical observation data. In this embodiment, the radar clock state is represented by three continuously changing parameters: the clock deviation at the current moment, the clock drift rate, and the clock drift acceleration. The algorithm updates the estimated values ​​of the three parameters based on the changing trends between samples each time a new set of time difference samples is received, so that the estimation results can reflect the continuous characteristics of the radar local clock changing over time. As sample sequences are continuously input, the recursive estimation algorithm gradually generates a clock deviation change curve covering the entire radar scanning cycle. This curve is the continuous deviation trajectory of the radar local clock relative to BeiDou time, which can describe the change of the radar local time relative to BeiDou standard time throughout the entire observation process.

[0019] Multiple echo candidate points are extracted from the radar echo signal, the echo trajectory is obtained based on the echo candidate points of multiple echo signals, and the echo trajectory that has passed the stability verification and the corresponding propagation time series are recorded. In a preferred embodiment of the present invention, selecting candidate echo points includes: Envelope detection is performed on the echo signal of each transmitted pulse to obtain the waveform of the echo amplitude changing with the sampling time. All local maxima points whose amplitude exceeds the preset detection threshold are searched on the waveform. The sampling time corresponding to each local maximum point is recorded as the echo arrival time, and the amplitude value of each local maximum point is recorded as the echo intensity. All local maximum points extracted from the same transmitted pulse are arranged in chronological order to form a set of candidate echo points for the transmitted pulse.

[0020] In a preferred embodiment of this invention, obtaining the echo trajectory includes: The echo arrival time of each candidate echo point is converted into an absolute arrival time using a continuous deviation trajectory. The candidate echo points of each transmitted pulse are marked on a unified time axis according to their absolute arrival times. Starting from the first transmitted pulse, the candidate echo points of each subsequent transmitted pulse are traversed sequentially. For each candidate echo point of the current transmitted pulse, the candidate echo point in the previous transmitted pulse with the closest absolute arrival time and a time difference less than a preset pulse interval threshold is searched. If a candidate echo point that meets the condition exists, the two are marked as a potential correlation pair and the process continues. When three or more consecutive transmitted pulses have correlation pairs that meet the time proximity condition, the candidate echo points corresponding to the correlation pairs are connected to form an echo trajectory. If no correlation pair exists, an error is reported.

[0021] In another preferred embodiment, obtaining the propagation time series includes: For each echo trajectory, the absolute arrival time interval between adjacent echo points in the echo trajectory is calculated, and it is determined whether the difference between the absolute arrival time interval and the radar pulse repetition period is less than a preset period matching threshold. The propagation time variation between adjacent echo points is calculated, and it is determined whether the propagation time variation is less than a preset motion continuity threshold. The average echo intensity of all echo points in the echo trajectory is calculated, and it is determined whether the absolute value of the difference between the echo intensity of each echo point and the average echo intensity is less than a preset intensity fluctuation threshold. Echo trajectories that meet the above conditions are determined to be verified echo trajectories. The propagation time of each echo point is extracted from the verified echo trajectory, and the propagation times are arranged in chronological order to form a propagation time sequence.

[0022] Specifically, after obtaining the continuous deviation trajectory covering the entire scanning cycle, the echo signals corresponding to each transmitted pulse output by the radar receiving channel enter the candidate point extraction process. The echo signal refers to the electrical signal reflected by a spatial target and returned to the receiver after the radar transmits an electromagnetic pulse. This electrical signal usually exhibits an amplitude sequence that changes continuously with the sampling time. It includes both effective echoes formed by real targets and non-target responses caused by ground clutter, thermal noise, occasional interference, and receiver link fluctuations. Therefore, arbitrary fluctuations in the original echo waveform cannot be directly identified as target information. Instead, envelope detection processing is required for the echo signal of each transmitted pulse. Envelope detection is the process of extracting the amplitude profile of high-frequency oscillating echoes. Its function is to remove the fast oscillation components of the carrier frequency and retain only the slowly varying shape that reflects the energy distribution of the echo, so that subsequent detection can be carried out around the energy peak.

[0023] Within a specific processing cycle, the receiver discretely samples the receiving window corresponding to a single transmitted pulse at a fixed sampling frequency. For example, within a pulse receiving window, 256 or 512 sampling points are obtained, arranged in ascending order of time. This discrete sequence is then rectified and smoothed to form a waveform curve showing the echo amplitude changing with sampling time. A preset detection threshold is used to distinguish between effective peak values ​​and background noise. This threshold can be set as a fixed amplitude standard based on the current background noise level of the receiving channel, historical spatial observation results, or a pre-calibrated noise floor statistical interval. Alternatively, it can be adaptively adjusted based on the local noise mean within the same batch of data. In this embodiment, it is only required to have the ability to suppress low-amplitude noise and retain obvious peak values.

[0024] Local maxima are searched point by point along the sampling time direction on the waveform curve. A local maximum is a point whose amplitude is not lower than the previous point and higher than the next point when comparing adjacent sampling points, or, in the case of a flat peak, a representative point corresponding to the center of the platform. When the amplitude of a local maximum exceeds a preset detection threshold, the point is identified as an echo candidate point. Each candidate point needs to record two basic attributes: the sampling time corresponding to the candidate point and the peak amplitude corresponding to the candidate point. The sampling time is the time stamp in the sampling sequence. Combined with the transmission start time of the current pulse, it can represent the local arrival time of the echo of the candidate point under the radar local time reference. The peak amplitude is used as the echo intensity of the candidate point for intensity analysis in subsequent trajectory verification and direction inversion. Since a transmit pulse may have multiple peak values ​​exceeding the threshold within the receive window, such as three local peak values ​​appearing at 2.1 microseconds, 2.4 microseconds, and 3.0 microseconds in the same reception, there are usually more than one candidate point corresponding to the same transmit pulse. All local maxima points extracted within the pulse need to be arranged in ascending order of sampling time to form the echo candidate point set of the transmit pulse.

[0025] After extracting candidate points from multiple transmitted pulses, each pulse corresponds to a set of candidate points organized chronologically. However, the time stamps of these candidate points are still within the radar's local clock framework and cannot be directly used for cross-pulse correlation. Therefore, it is necessary to call the aforementioned continuous deviation trajectory to convert the echo arrival time of each candidate point into an absolute arrival time. The absolute arrival time refers to the echo arrival time after using BeiDou time as a unified reference. It is generated by uniformly correcting the echo arrival time based on the local transmission time of the transmitted pulse to which the candidate point belongs, the corresponding continuous deviation trajectory value, and the sampling delay of the candidate point relative to the transmission start point. This ensures that echo candidate points obtained from different transmitted pulses and different scanning periods are mapped to the same continuous time coordinate axis. The continuous deviation trajectory consists of a series of continuously changing deviation estimates over time. Each deviation estimate corresponds to the instantaneous difference between the radar's local clock and BeiDou time. During candidate point conversion, the corresponding position in the deviation trajectory needs to be read based on the transmission times adjacent to the candidate point. For candidate points located between two estimation nodes, smooth interpolation can be performed chronologically to obtain a deviation correction amount matching the arrival time of that candidate point. After this processing, each candidate point is converted from its original local time stamp to an absolute arrival time under a unified standard.

[0026] For example, during a radar scan, a transmitted pulse is recorded as being transmitted at 100.000000 seconds by the radar's local clock. After sampling the echo signal of this pulse in the receiving channel, a local maximum is detected in the sampling sequence. The echo arrival time corresponding to this maximum is 100.000012 seconds. Based on the continuous deviation trajectory obtained from previous transmission pulses fed into the BeiDou receiver, the clock deviation between the radar's local time and BeiDou time near this transmission time can be found to be 0.000003 seconds. Using this deviation value to correct the echo arrival time, subtracting the corresponding deviation from 100.000012 seconds yields 100.000009 seconds, which is the absolute arrival time of the echo signal under the unified BeiDou time reference. When subsequent candidate echo points in other transmitted pulses are also time-corrected in the same way, all candidate points are mapped onto a unified time axis, enabling direct comparison of echo arrival times and trajectory correlation between different pulses.

[0027] After the absolute arrival time is calibrated, the candidate points of each transmitted pulse are sequentially projected onto the same time axis according to the pulse number, forming a set of cross-pulse time points. This set of time points retains three types of information for each candidate point: the pulse number, the absolute arrival time, and the echo intensity. The pulse number indicates which transmitted pulse the candidate point comes from, the absolute arrival time indicates the position of the candidate point under the unified time reference, and the echo intensity indicates the echo energy characteristics of the candidate point.

[0028] The acquisition of echo trajectories is based on the temporal continuity between adjacent pulses. This is because echoes from the same target typically exhibit slow changes in arrival time during continuous pulse observation, without irregular jumps between adjacent pulses. Therefore, the principle of absolute arrival time proximity can be used to establish cross-pulse correlations. Starting with the first transmitted pulse, each candidate point in its candidate point set is read. Then, the candidate points in the second transmitted pulse are traversed, searching for the point closest to the current candidate point in the previous pulse along the absolute arrival time dimension, and calculating the time difference between them. When this time difference is less than a preset pulse interval threshold, the two candidate points are considered to satisfy the temporal continuity characteristic of the same target in adjacent pulses, and are marked as a potential correlation pair. A potential correlation pair refers to a set of candidate point correspondences that have not yet been definitively confirmed as trajectory members but already satisfy the temporal proximity condition between adjacent pulses. This marking is used for subsequent propagation and verification. If, in the third transmitted pulse, a candidate point can be found whose absolute arrival time is closest to that of the candidate point associated with the previous pulse and whose difference is still less than the preset pulse interval threshold, then this association is extended to the next pulse. When there are association pairs that meet the time proximity condition in three or more consecutive transmitted pulses, these candidate points connected in pulse order are identified as the same echo trajectory. Here, an echo trajectory refers to a time-series chain formed by connecting candidate points belonging to the same target in multiple consecutive transmitted pulses in chronological order. Each chain node corresponds to one echo point, and there is a clear pulse inheritance relationship and an absolute arrival time continuity relationship between adjacent nodes.

[0029] To avoid the same candidate point being repeatedly occupied by multiple trajectories, when forming potential association pairs and confirming trajectories, candidate points already belonging to a certain trajectory need to be marked as occupied. This ensures that subsequent searches are prioritized on unoccupied candidate points. Only when there are multiple competing points with approximately equal time differences are their consistency with the propagation time change of the previous node and the smoothness of the echo intensity change compared, in order to select a candidate point that better matches the continuous target response characteristics as the continuation node. When no candidate point satisfying the time proximity condition is found for the current trajectory in a certain pulse, the extension of the trajectory terminates at that point. If no valid association pair is found after traversing backwards for a starting candidate point, an error is reported. In this embodiment, the error refers to generating an unassociated marker and outputting the corresponding trajectory construction failure information to indicate that the candidate point failed to form a trajectory that meets the continuity requirement and will not be included in the subsequent stability verification process.

[0030] Through the aforementioned cross-pulse correlation processing, several echo trajectories can be extracted from a large number of discrete candidate points. However, these trajectories may still contain accidental continuous noise, clutter concatenation, or pseudo-trajectories formed by unstable reflections. Therefore, it is necessary to verify the stability of each echo trajectory and extract the corresponding propagation time sequence after successful verification. Propagation time refers to the time interval between the emission of an electromagnetic pulse from the radar transmitter and the detection of the corresponding echo point by the receiver. In specific processing, it can be obtained by correlating the absolute arrival time of the echo point with the absolute transmission time of its corresponding transmitted pulse. Since the aforementioned continuous deviation trajectory has established a conversion relationship between the local transmission time and BeiDou time for each transmitted pulse, each echo point can obtain a propagation time marker consistent with the unified time reference. For each formed echo trajectory, the absolute arrival times of two adjacent echo points are read sequentially, their time interval is calculated, and this time interval is compared with the radar pulse repetition period. The radar pulse repetition period refers to the time interval between two consecutive pulse transmissions, which is determined by the radar operating parameters and reflects the theoretical time distance between adjacent transmitted pulses. If adjacent echo points in a trajectory do indeed originate from the same target corresponding to consecutive transmitted pulses, their absolute arrival time interval should be consistent with or approximately consistent with the pulse repetition period. Therefore, when the difference between the two is less than a preset period matching threshold, the adjacent point pair is considered to meet the period consistency requirement. The period matching threshold is used to accommodate receiver link jitter, sampling quantization errors, and small-amplitude clock residual errors. Its value should allow for limited fluctuations in normal target echoes between consecutive pulses, while preventing obviously mismatched cross-pulse candidate points from entering the valid trajectory. Continue reading the propagation time of adjacent echo points in the trajectory and calculate the change between adjacent propagation times. The change in propagation time reflects the continuity of the target's distance change rate relative to the radar on the pulse interval scale. Since the spatial displacement of low-altitude targets is usually limited within several consecutive pulse periods, the propagation time will not change abruptly. When the change in propagation time between adjacent echo points is less than a preset motion continuity threshold, the trajectory is considered to meet the motion continuity requirement. The motion continuity threshold is used to constrain the range of distance changes of the target between adjacent observation times. Essentially, it is a criterion for judging the smoothness of the temporal changes of echo points in the trajectory, filtering out abnormal time jumps caused by random noise and sudden reflections from multiple paths. Subsequently, the echo intensity of all echo points along the entire echo trajectory is statistically analyzed to obtain the mean echo intensity of the trajectory. The mean echo intensity characterizes the overall energy level of the trajectory throughout the continuous observation process. After obtaining the mean, the absolute value of the difference between the echo intensity of each echo point and the mean is compared. When the intensity deviation of each echo point does not exceed a preset intensity fluctuation threshold, the trajectory is considered to meet the intensity stability requirement. The intensity fluctuation threshold is used to suppress abnormal peaks caused by instantaneous noise spikes, occasional interference, or unstable gain at the scan edge, ensuring that the retained trajectory has a relatively consistent intensity distribution.Only echo trajectories that simultaneously meet the three conditions of periodic consistency, motion continuity, and intensity stability are considered valid echo trajectories.

[0031] For verified trajectories, the propagation time is extracted point-by-point according to the chronological order of echo points in the trajectory, and these propagation times are used to construct a propagation time series. The propagation time series is an ordered sequence of time data describing the distance change process of the same target during continuous pulse observation. Each element corresponds one-to-one with a specific pulse number and a specific echo point, preserving the distance evolution information of the target during the scanning process and maintaining strict synchronization with the subsequent beam pointing angle pairing. To ensure the consistency between the propagation time series and the trajectory itself, the node order must be maintained the same as the echo trajectory when extracting the propagation time. Intermediate nodes are not rearranged or interpolated across nodes; nodes are only removed when there are confirmed invalid markers at individual sampling points, avoiding the introduction of artificial sequences inconsistent with the original trajectory. Thus, starting from the original echo signal, after envelope detection, local maximum detection, candidate point extraction, continuous deviation trajectory time correction, unified calibration of absolute arrival time, close correlation of adjacent pulse times, construction of trajectories of three or more consecutive pulses, and stability verification based on period, propagation time, and intensity, the verified echo trajectory and its corresponding propagation time series can be obtained.

[0032] It should be noted that each pulse emitted by the radar during low-altitude scanning is reflected by the target and returned to the receiver after propagating in space. The echo signal recorded by the receiving channel is essentially a time-varying electrical signal sequence, which includes the echo response generated by the real target, as well as environmental clutter, receiver noise, and occasional interference signals. If the original echo waveform is used directly for target identification, random fluctuations can easily be mistaken for the real target response. Therefore, it is necessary to extract the shape of the echo energy changing over time through envelope detection, so that the high-frequency oscillation signal can be converted into an amplitude curve that can reflect the echo intensity distribution. Searching for local maxima exceeding the detection threshold on this curve can separate the echo response with obvious energy characteristics from the continuous waveform, thereby forming echo candidate points.

[0033] Because radar repeatedly observes the same spatial region during continuous pulse transmission, echoes from the same target in adjacent pulses typically appear at similar propagation time positions. Their arrival times exhibit a slow, continuous variation with the distance between the target and the radar. Therefore, associating candidate points from multiple pulses in chronological order allows for the gradual connection of echo responses belonging to the same target, forming a trajectory, utilizing temporal continuity. To ensure that the time information from different pulses is within the same reference frame, continuous deviation trajectories are used to uniformly correct the echo arrival times, converting the time stamps of each candidate point into absolute arrival times under a unified time reference. This avoids the impact of radar local clock drift on time association, ensuring consistency in time comparisons between different pulses. When performing cross-pulse association on the absolute time axis, only candidate points maintaining close time positions between adjacent pulses can form stable connections. Random noise or clutter typically does not repeat at similar time positions in multiple consecutive pulses; therefore, utilizing time proximity effectively distinguishes between real target echoes and random noise. The time correlation of three or more consecutive pulses can further improve the reliability of target identification, because the real target exists continuously for a short period of time, and its echo response will maintain a certain stability in continuous pulse observation, while random noise is difficult to maintain a consistent time structure in multiple pulses.

[0034] After the trajectory is established, its stability still needs to be verified. This is because multipath reflection or clutter accumulation may occur in complex low-altitude environments, and these interferences may also form brief continuous responses in some cases. Therefore, by comparing the relationship between the absolute arrival time interval between adjacent echo points and the pulse repetition period, it can be confirmed that the trajectory nodes do indeed originate from the observation results of continuously transmitted pulses. By judging whether the propagation time change is smooth, it can be confirmed that the distance change between the target and the radar conforms to the characteristics of continuous motion. By analyzing the fluctuation of echo intensity on the trajectory, abnormal peaks caused by accidental strong interference can be eliminated. Only when the time period characteristics, distance change characteristics, and echo energy distribution characteristics remain stable can the trajectory reflect the continuous response process of the real target in space. The propagation time series obtained after these processes has a clear temporal order and stable physical meaning, and can accurately describe the propagation process changes of the electromagnetic pulse from transmission to echo reception. This time information has continuous consistency under a unified time reference, providing a reliable basis for subsequent inversion of target direction and further calculation of target spatial position by combining radar beam pointing information, enabling the temporal and spatial characteristics of low-altitude targets in continuous scanning to be stably extracted and utilized.

[0035] Record the radar beam pointing angle corresponding to each transmitted pulse, establish a correlation between each echo point in the echo trajectory and the beam pointing angle of the corresponding transmitted pulse, and invert the target's true direction vector relative to the radar based on the echo intensity distribution; In another preferred embodiment of the present invention, the retrieved true direction vector of the target relative to the radar includes: The beam azimuth and beam elevation angles corresponding to each transmitted pulse are read from the radar servo control system memory. The beam azimuth and beam elevation angles are combined to form the beam pointing angle vector of the transmitted pulse. According to the sequence number of the transmitted pulse, each echo point in the echo trajectory is matched one-to-one with the beam pointing angle vector with the same sequence number to form a pairing list of echo points and beam pointing angles.

[0036] In a preferred embodiment, the retrieved target's true direction vector relative to the radar further includes: In the pairing list, a distribution curve of echo intensity as a function of beam pointing angle is plotted with beam pointing angle as the independent variable and echo intensity as the dependent variable. The beam pointing angle corresponding to the maximum echo intensity is searched on the distribution curve. This angle is used as the initial direction estimate. Multiple neighboring beam pointing angles and their corresponding echo intensities are selected with the initial direction estimate as the center. The selected angles and intensities are weighted and averaged, with the weighting coefficient being the echo intensity values. The weighted average beam azimuth and beam elevation angles are calculated. The weighted average beam azimuth and beam elevation angles are combined to form the true direction vector of the target relative to the radar.

[0037] Specifically, after obtaining the echo trajectory and corresponding propagation time series that have passed stability verification, it is necessary to further utilize the beam pointing information recorded during radar scanning to determine the spatial orientation of the target relative to the radar.

[0038] During low-altitude scanning, the radar uses a servo mechanism to drive the antenna to rotate continuously or in stages, allowing the transmitted beam to scan the space within a set angular range. Each time a pulse is transmitted, the antenna is in a specific spatial pointing state, described by the beam azimuth and beam elevation angles. The beam azimuth angle represents the rotation angle of the radar antenna relative to a reference direction in the horizontal plane, typically using the radar's true north direction as the reference zero degree and increasing clockwise to represent the horizontal rotation position. The beam elevation angle represents the vertical tilt of the radar beam relative to the horizontal plane; the elevation angle is positive when the beam is pointing upwards and negative when the beam is pointing downwards.

[0039] During antenna scanning, the radar servo control unit continuously records the antenna attitude information corresponding to each transmitted pulse and stores this information in the servo control memory. The stored content is arranged in order of the transmitted pulse number, so that each pulse corresponds to a specific set of beam azimuth and beam elevation angle data. When reading these records, the angle data in the memory is extracted sequentially according to the transmitted pulse number. The beam azimuth and beam elevation angles corresponding to the same pulse are combined to represent the beam pointing angle vector of that pulse. The beam pointing angle vector describes the pointing direction of the radar transmitted beam in three-dimensional space. Its direction is determined by the horizontal rotation angle and the vertical tilt angle. Therefore, when a transmitted pulse forms an echo, it can be considered that the echo originates from a spatial location within the coverage area of ​​that pulse beam. In the echo trajectory formed in the previous stage, each echo point corresponds to a specific transmitted pulse number. Therefore, the echo point can be mapped to the beam pointing angle vector with the same number according to the pulse number, so that each echo point in the echo trajectory is accompanied by a set of beam azimuth and beam elevation angle information. After organizing these correspondences, a pairing list between echo points and beam pointing angles is obtained. Each record in the pairing list contains the echo point number, echo intensity, propagation time, and the corresponding beam azimuth and beam elevation angles.

[0040] As radar beams gradually sweep across the target's direction during scanning, the received echo intensity gradually increases as the beam approaches the target and gradually decreases as the beam moves away from the target. Therefore, the echo intensity and beam pointing angle typically exhibit a relationship of initial increase followed by decrease. This characteristic can be used to deduce the target's true orientation in space based on the changes in echo intensity at different beam angles.

[0041] In specific processing, the beam pointing angle and echo intensity data corresponding to each echo point are extracted from the pairing list. The beam pointing angle is used as the lateral variation variable, and the echo intensity is used as the corresponding amplitude. A distribution curve of echo intensity as a function of beam pointing angle is formed in a unified coordinate frame. This distribution curve reflects the change in echo energy received by the radar beam when it passes through different angular positions during the scanning process. Searching this distribution curve can find the position where the echo intensity reaches its maximum value. The beam pointing angle corresponding to this position represents the moment when the radar beam is closest to the target direction during the scanning process. Therefore, this beam pointing angle is used as the initial direction estimate of the target direction.

[0042] Because radar antenna beams have a certain width, multiple observation points with high intensity often appear near the peak of the echo intensity. Using only a single peak may be affected by local noise or sampling fluctuations. Therefore, it is necessary to select several neighboring beam pointing angles and their corresponding echo intensity data near the initial direction for further calculation. The selection of neighboring angles is based on the difference between them and the initial direction angles being within a preset angle range. For example, angle data corresponding to several adjacent scan pulses before and after the initial direction can be selected so that these angle samples can cover the echo intensity peak region. For these selected angle samples, the beam azimuth and beam elevation angles corresponding to each sample are established with their respective echo intensities, and a weighted average is performed using the echo intensity as a weighting coefficient. The weighted average process means that observation points with higher echo intensity have a greater weight in the direction estimation, while observation points with lower echo intensity have a smaller impact on the results. This method can comprehensively utilize the information from multiple neighboring observation points and reduce the impact of single-point fluctuations on the direction estimation results. After weighted processing, new average beam azimuth and beam elevation angles are obtained. These two angle values ​​together describe the spatial orientation of the target in the radar coordinate system. The weighted beam azimuth and beam elevation angles are combined to form the target’s true direction vector relative to the radar. This direction vector represents the direction information from the radar antenna position to the target’s spatial position, and together with the propagation time series obtained in the previous stage, it constitutes the basic data for target spatial positioning calculation.

[0043] It should be noted that during the scanning process, the radar antenna gradually changes its beam direction according to a set angular sequence. After the transmitted pulse propagates into space, only targets within the coverage area of ​​the main lobe of the beam can generate a strong echo signal. Therefore, there is a clear correspondence between the echo intensity and the beam direction and the target's true direction. As the beam gradually approaches the target's direction, the target is in the energy concentration area of ​​the main lobe, and the echo energy received by the receiving channel gradually increases. As the beam deviates from the target's direction, the target gradually enters the edge region of the beam, and the received echo energy weakens accordingly. This change in echo intensity with the scanning angle reflects the target's true position relative to the radar. By recording the beam azimuth and elevation angles corresponding to each transmitted pulse, the pointing state of the radar beam in space during each transmission can be accurately described. By establishing a correlation between the echo points in the echo trajectory and the beam pointing angle of the corresponding transmitted pulse, the correspondence between echo intensity and beam angle can be obtained.

[0044] In this correspondence, the location of the intensity peak is usually closest to the target direction because the radar beam center points to the target area at this moment, resulting in the highest concentration of electromagnetic energy and thus the strongest received signal. Using the location of the intensity peak as the initial direction estimate can quickly determine the approximate range of the target direction. However, since the radar beam has a certain width, multiple observation points with high intensity are often distributed near the echo peak. These observation points collectively reflect the target's response changes during beam scanning. By weighting the echo intensity of these neighboring angles, the influence of noise or sampling fluctuations on a single observation point can be reduced by integrating multiple observation information, making the obtained direction result more stable.

[0045] When echo intensity is used as a weight in angle averaging, observation points with higher intensity contribute more to the result, while those with weaker intensity have less impact. This approach allows the final calculated angle to more closely approximate the true target direction. The azimuth and elevation angles obtained in this way can jointly describe the spatial direction from the radar to the target. When this direction information is combined with the distance information corresponding to the propagation time obtained earlier, the spatial position of the target in the radar coordinate system can be determined. Therefore, using the echo intensity distribution formed during the scanning process to invert the target direction can effectively recover the target's spatial orientation characteristics using the radar's own observation data.

[0046] The target distance is obtained from the propagation time series. The target's position coordinates in the radar coordinate system are generated by combining the true direction vector and the target distance. The target's position coordinates in the radar coordinate system are then correlated with the position sequence of the Beidou receiver to output the target detection result.

[0047] Specifically, after obtaining the echo trajectory and corresponding propagation time sequence that have passed stability verification, and completing the inversion of the target's true direction vector, the distance relationship between the target and the radar can be determined using the propagation time information. Propagation time refers to the time interval during which the electromagnetic wave propagates through space to the target, is reflected by the target, and returns to the receiver after the radar emits an electromagnetic pulse. This time information has been corrected using a unified time reference in the aforementioned processing and formed into a propagation time sequence according to the echo trajectory order. Since the propagation speed of electromagnetic waves in space is a stable physical constant, the propagation time directly reflects the round-trip propagation path length between the radar and the target. To obtain the actual distance between the target and the radar, distance conversion needs to be performed on each propagation time value in the propagation time sequence. The conversion process uses the electromagnetic wave propagation speed as a reference, converting the round-trip propagation path length corresponding to the propagation time into a one-way spatial distance between the target and the radar. After the conversion, each echo point corresponds to a target distance value, which represents the radial distance of the target relative to the radar antenna position at the time of the emitted pulse observation.

[0048] Meanwhile, in the previous stage, the target's true direction vector relative to the radar was obtained based on the echo intensity distribution during beam scanning. This direction vector is described by the beam azimuth and beam elevation angles, where the beam azimuth represents the target's directional position in the horizontal plane, and the beam elevation angle represents the target's vertical tilt angle relative to the radar's horizontal plane. The direction vector describes the directional information pointing from the radar antenna to the target's spatial position. When this directional information is combined with the target range, the target's position in the radar's local spatial coordinate frame can be determined. The radar coordinate system is a spatial coordinate representation established with the radar antenna phase center as the origin. In this coordinate system, the direction directly in front of the radar is usually used as the reference direction, and the horizontal plane is used as the reference plane. The target's position in three-dimensional space is determined by the direction angle and range information. After obtaining the target range and target direction vector corresponding to a certain echo point, the range can be extended along this direction based on the pointing relationship of the direction vector in three-dimensional space, thereby determining the target's spatial position coordinates in the radar coordinate system. Because the echo trajectory contains multiple consecutive echo points, a set of target spatial coordinates arranged in chronological order can be obtained at multiple consecutive observation times. These coordinates reflect the target's trajectory in the radar coordinate system. To further convert these relative positions into spatially meaningful locations, it is necessary to correlate the target's position coordinates in the radar coordinate system with the BeiDou receiver position sequence. The BeiDou receiver position sequence is a sequence of receiver spatial coordinates calculated from BeiDou satellite navigation signals within the observation period. This sequence reflects the positional changes of the radar platform within the geographic coordinate frame. By matching each target spatial coordinate with the corresponding BeiDou receiver position, the position of the radar origin in the geographic coordinate frame can be determined. Based on this, the target's relative position in the radar coordinate system is converted into its absolute spatial position in the geographic coordinate frame. After this correlation is completed, each target observation point simultaneously possesses time information, spatial position, and corresponding observation trajectory information, ultimately forming a complete target detection result used to represent the spatial position of low-altitude targets in the observation area and their movement over time.

[0049] It is worth noting that low-altitude targets generate a series of echo responses during continuous radar scanning across multiple transmitted pulses. These echo responses contain distance information between the target and the radar, as well as the target's direction relative to the radar beam. However, in actual detection environments, the radar's local clock drifts, and noise and clutter are mixed into the echo signals. Without a stable time reference and continuous observation correlation, the echo time and direction information are difficult to maintain consistency across different pulses, thus affecting the accuracy of target trajectory identification and spatial positioning. Utilizing the unified time reference provided by the BeiDou satellite navigation signal allows for continuous correction of the radar's local time, ensuring that the time information obtained from different transmitted pulses is within the same reference frame, thereby guaranteeing the consistency of echo arrival times across continuous observations. Extracting candidate echo points under a unified time reference and correlating their temporal continuity across multiple transmitted pulses allows echo responses belonging to the same target to be connected to form a stable echo trajectory. Noise or clutter typically cannot maintain the same temporal characteristics across continuous pulses; therefore, trajectory verification can effectively distinguish real target echoes. As the radar antenna gradually changes its beam direction during scanning, the echo intensity generated by the target at different beam angles varies as the beam approaches or moves away from the target. Therefore, the distribution of echo intensity across the scanning angle reflects the target's true spatial orientation. By associating echo points in the echo trajectory with the beam direction information of the corresponding transmitted pulse and analyzing the changes in echo intensity at different angles, the target's orientation relative to the radar can be recovered from the scanning observation data. When the distance information corresponding to the propagation time is combined with the orientation information, the target's spatial position in the radar coordinate system can be determined. By associating this position with the BeiDou receiver's position sequence, the relative position can be converted into an absolute position within a unified geographic coordinate framework, allowing the continuously observed target position to form a stable spatial trajectory. Through continuous processing of a unified time reference, echo trajectory extraction, orientation inversion, and spatial position association, the temporal and spatial information of low-altitude targets in complex environments can be stably utilized, thereby improving the reliability of target detection results in terms of temporal consistency and spatial positioning.

[0050] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A method for low-altitude target detection using BeiDou positioning and radar coordination, characterized in that, Includes the following steps: Obtain ephemeris data output by the BeiDou system, and calculate the BeiDou receiver position sequence based on the ephemeris data; The radar is activated to perform low-altitude scanning, and the local transmission time corresponding to each radar transmission pulse is recorded. Each transmission pulse is fed into the Beidou receiver, and the arrival time of each transmission pulse to the Beidou receiver is measured. Based on the local transmission time and arrival time, the continuous deviation trajectory of the radar local clock relative to Beidou time is obtained. Multiple echo candidate points are extracted from the radar echo signal, the echo trajectory is obtained based on the echo candidate points of multiple echo signals, and the echo trajectory that has passed the stability verification and the corresponding propagation time series are recorded. Record the radar beam pointing angle corresponding to each transmitted pulse, establish a correlation between each echo point in the echo trajectory and the beam pointing angle of the corresponding transmitted pulse, and invert the target's true direction vector relative to the radar based on the echo intensity distribution; The target distance is obtained from the propagation time series. The target's position coordinates in the radar coordinate system are generated by combining the true direction vector and the target distance. The target's position coordinates in the radar coordinate system are then correlated with the position sequence of the Beidou receiver to output the target detection result.

2. The low-altitude target detection method based on BeiDou positioning and radar coordination according to claim 1, characterized in that, Obtaining the continuous deviation trajectory includes: The original time difference is obtained by subtracting the local transmission time of each transmission pulse from its corresponding arrival time. The original time difference values ​​of multiple consecutive transmission pulses are subjected to quality checks, and abnormal samples whose differences from the preceding and following samples exceed the preset mutation threshold are removed. The remaining samples are arranged in chronological order of transmission time to form a time difference sample sequence. The time difference sample sequence is input into a recursive estimation algorithm. The recursive estimation algorithm estimates the clock deviation, clock drift rate, and clock drift acceleration at the current moment based on the distribution pattern of the time difference samples. The estimated clock deviation, clock drift rate, and clock drift acceleration are used to generate a continuous deviation trajectory covering the entire scan cycle.

3. The low-altitude target detection method based on BeiDou positioning and radar coordination according to claim 2, characterized in that, The selection of echo candidate points includes: Envelope detection is performed on the echo signal of each transmitted pulse to obtain the waveform of the echo amplitude changing with the sampling time. All local maxima points whose amplitude exceeds the preset detection threshold are searched on the waveform. The sampling time corresponding to each local maximum point is recorded as the echo arrival time, and the amplitude value of each local maximum point is recorded as the echo intensity. All local maximum points extracted from the same transmitted pulse are arranged in chronological order to form a set of candidate echo points for the transmitted pulse.

4. The low-altitude target detection method based on BeiDou positioning and radar coordination according to claim 3, characterized in that, Obtaining the echo trajectory includes: The echo arrival time of each candidate echo point is converted into an absolute arrival time using a continuous deviation trajectory. The candidate echo points of each transmitted pulse are marked on a unified time axis according to their absolute arrival times. Starting from the first transmitted pulse, the candidate echo points of each subsequent transmitted pulse are traversed sequentially. For each candidate echo point of the current transmitted pulse, the candidate echo point in the previous transmitted pulse with the closest absolute arrival time and a time difference less than a preset pulse interval threshold is searched. If a candidate echo point that meets the condition exists, the two are marked as a potential correlation pair and the process continues. When three or more consecutive transmitted pulses have correlation pairs that meet the time proximity condition, the candidate echo points corresponding to the correlation pairs are connected to form an echo trajectory. If no correlation pair exists, an error is reported.

5. The low-altitude target detection method based on BeiDou positioning and radar coordination according to claim 4, characterized in that, Obtaining the propagation time series includes: For each echo trajectory, the absolute arrival time interval between adjacent echo points in the echo trajectory is calculated, and it is determined whether the difference between the absolute arrival time interval and the radar pulse repetition period is less than a preset period matching threshold. The propagation time variation between adjacent echo points is calculated, and it is determined whether the propagation time variation is less than a preset motion continuity threshold. The average echo intensity of all echo points in the echo trajectory is calculated, and it is determined whether the absolute value of the difference between the echo intensity of each echo point and the average echo intensity is less than a preset intensity fluctuation threshold. Echo trajectories that meet the above conditions are determined to be verified echo trajectories. The propagation time of each echo point is extracted from the verified echo trajectory, and the propagation times are arranged in chronological order to form a propagation time sequence.

6. The low-altitude target detection method based on BeiDou positioning and radar coordination according to claim 5, characterized in that, The retrieved true direction vector of the target relative to the radar includes: The beam azimuth and beam elevation angles corresponding to each transmitted pulse are read from the radar servo control system memory. The beam azimuth and beam elevation angles are combined to form the beam pointing angle vector of the transmitted pulse. According to the sequence number of the transmitted pulse, each echo point in the echo trajectory is matched one-to-one with the beam pointing angle vector with the same sequence number to form a pairing list of echo points and beam pointing angles.

7. A low-altitude target detection method combining BeiDou positioning and radar according to claim 6, characterized in that, The retrieved target's true direction vector relative to the radar also includes: In the pairing list, a distribution curve of echo intensity as a function of beam pointing angle is plotted with beam pointing angle as the independent variable and echo intensity as the dependent variable. The beam pointing angle corresponding to the maximum echo intensity is searched on the distribution curve. This angle is used as the initial direction estimate. Multiple neighboring beam pointing angles and their corresponding echo intensities are selected with the initial direction estimate as the center. The selected angles and intensities are weighted and averaged, with the weighting coefficient being the echo intensity values. The weighted average beam azimuth and beam elevation angles are calculated. The weighted average beam azimuth and beam elevation angles are combined to form the true direction vector of the target relative to the radar.

Images