A method for evaluating skywave radar tracking effect

Abstract

The present invention discloses a method for evaluating the tracking effect of a skywave radar. The method evaluates the tracking effect of a skywave radar based on a three-stage cascade evaluation process of "detection path modeling - echo data preprocessing - target tracking processing." By separately evaluating various influencing factors at each stage and thereby obtaining the effect of each stage, and ultimately obtaining an overall evaluation based on the evaluation effect of each stage, the effect of skywave radar target tracking can be evaluated more comprehensively and effectively. The present invention evaluates the effect of each process of skywave radar target tracking separately, and comprehensively evaluates the evaluation results of the three stages. This not only ensures the comprehensiveness and accuracy of the evaluation results, but also further determines the specific stage where the error in the target tracking result originates, thereby further facilitating the improvement of skywave radar target tracking.

Description

Technical Field

[0001] The invention belongs to radar technology, and in particular relates to a skywave radar tracking effect evaluation method. Background Art

[0002] Skywave over-the-horizon radar (OTHR) has attracted significant attention in many countries for its outstanding advantages, including wide-area surveillance, anti-target stealth, and early warning capabilities. OTHR operates in the shortwave band (3-30 MHz). It utilizes electromagnetic wave reflection between the ionosphere and the ground, or diffraction along the Earth's surface, to transmit high-frequency energy. This allows it to detect moving targets in the air or at sea at extremely long distances, below the horizon, beyond the reach of conventional radar. Its range is not limited by the Earth's curvature.

[0003] Since skywave radar detects and tracks targets through ionospheric reflection, the factors that affect the target tracking capability of skywave radar are mainly in the following three stages:

[0004] 1) Skywave radar detection path modeling

[0005] 2) Skywave radar echo data preprocessing

[0006] 3) Skywave radar target tracking processing

[0007] Therefore, in order to evaluate the target tracking capability of skywave radar, it is necessary to start from the above three aspects. In the skywave radar detection path modeling link, ionosphere modeling should be considered to obtain the electron concentration, and then the radar detection path should be obtained according to the PD (Path-Distance) transformation; on the basis of path modeling, the possible multi-mode, multipath and phase-path interference of radar echoes should be analyzed, and preprocessing measures should be taken; on the basis of preprocessing, different tracking algorithms should be introduced to evaluate the radar tracking performance.

[0008] However, traditional skywave radar target tracking capability assessment methods only focus on one or several of the above aspects, resulting in one-sided assessment results. It is also difficult to determine the specific links and causes that affect tracking accuracy, making it inconvenient for subsequent radar improvements. Summary of the Invention

[0009] The present invention proposes a method for evaluating the tracking effect of skywave radar, and proposes a method for evaluating the tracking effect of skywave radar based on a three-stage cascade of "detection path modeling - echo data preprocessing - target tracking processing". By evaluating each stage separately and then conducting an overall evaluation, the effect of skywave radar target tracking can be evaluated more comprehensively and effectively.

[0010] The technical solution to realize the present invention is: a method for evaluating the tracking effect of skywave radar, comprising the following steps:

[0011] Step 1: Model the skywave radar detection path.

[0012] Step 2: Evaluate the pre-processing capability based on the skywave radar detection path.

[0013] Step 3: Evaluate based on the preprocessed tracking results.

[0014] Compared with the existing technology, the present invention has the following significant advantages: each process of skywave radar target tracking is evaluated separately, and the evaluation results of the three stages are comprehensively evaluated as a whole. This not only ensures the comprehensiveness and accuracy of the evaluation results, but also further determines at which stage the error in the target tracking result specifically comes, thereby being more conducive to the improvement of skywave radar target tracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of PD conversion of the present invention.

[0016] Figure 2 This is a flow chart of the skywave radar tracking effect evaluation method of the present invention. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0019] The following will further introduce the specific implementation methods, as well as the technical difficulties and inventive points of this invention in combination with this design example.

[0020] The present invention integrates the target tracking process of skywave over-the-horizon radar and proposes a three-stage cascade skywave radar tracking effect evaluation method, which examines the following three aspects respectively:

[0021] (1) Detection path modeling, mainly examining the influence of ionospheric electron concentration modeling and measurement errors during PD conversion.

[0022] (2) Echo data preprocessing, mainly to examine the ability to remove multimode, multipath, and phase-path interference.

[0023] (3) Target tracking processing, examining the matching degree of the algorithm to the tracking situation.

[0024] Afterwards, the relevant capabilities of these three stages are cascaded and estimated, and finally a more comprehensive estimation result is formed, making the tracking effectiveness evaluation of the skywave radar more comprehensive.

[0025] Combine Figure 1 and Figure 2 ,A method for evaluating the tracking effect of skywave radar, the steps are as follows:

[0026] Step 1: Modeling the skywave radar detection path

[0027] Skywave radar tracks and detects targets based on the refraction of high-frequency electromagnetic waves by the ionosphere. Therefore, the detection path of skywave radar is closely related to the characteristics of the ionosphere. Therefore, first examining the establishment of an ionospheric structure model is crucial for evaluating tracking capabilities.

[0028] At present, in order to better adapt to the dynamic changes of the ionosphere, a multi-layer quasi-parabolic model of the ionosphere can be established. The number of ionosphere layers is K, and K can take values of 1, 2, or 3. A value of 1 usually corresponds to the period from one hour after sunset to one hour before sunrise; a value of 2 usually corresponds to one hour before sunrise to one hour after sunrise, and one hour before sunset to one hour after sunset; a value of 3 corresponds to the rest of the day. The specific time nodes are related to the latitude and month of the location, and the electron concentration expression is:

[0029]

[0030] N e (t): time-varying electron concentration, unit 10 6 / cm 3 .

[0031] r: ray distance relative to the center of the earth, in km.

[0032] r mk (t): The height of the maximum electron concentration in the kth layer (relative to the center of the earth), unit: km.

[0033] y mk (t): half-layer thickness of the kth layer, in km.

[0034] r bk (t): height of the bottom of the kth layer (relative to the center of the earth), unit: km.

[0035] N mk (t): Maximum electron concentration in the kth layer, unit 10 6 / cm 3 .

[0036] t: current time, in seconds.

[0037] The negative sign indicates a regular parabolic layer, and the positive sign indicates an inverted parabolic layer. The inverted parabolic layer achieves a smooth transition from the top of the lower regular parabolic layer to the bottom of the higher regular parabolic layer. The above parameters are all functions of time and are often relatively stable within the hourly range. These parameters are measured using ionospheric vertical survey maps.

[0038] The vertical map of the ionosphere is evaluated and the evaluation results are expressed as a 11 =min{k 11 ,e1} means, where k 11 is the standard for whether the vertical survey map data exists. If the vertical survey map data exists, k 11 =1, the ionospheric modeling is more reliable. If the vertical survey data does not exist, k 11 =0.5, at this time the ionospheric modeling is unreliable; e1 is the accuracy evaluation result of the vertical survey map, and its value is usually above 0.9.

[0039] With the real-time electron concentration of the ionosphere, the propagation path of the skywave radar can be calculated. That is, the propagation path and ground distance are calculated and transformed through PD transformation (Path-Distance, abbreviated as PD), as shown in the figure. Figure 1 shown.

[0040] Depend on Figure 1 It can be seen that the length of the skywave radar propagation path P includes the straight line AB, arc BC, and straight line CD connected in sequence. The length of the ground path D is arc AD. By integrating the skywave radar propagation path P and the ground distance D, we can get:

[0041]

[0042]

[0043] Where n is the refractive index of the electromagnetic wave at r; β is the incident angle of the electromagnetic wave at r (complementary to the incident angle); r0 is the radius of the earth (approximately 6370 km); β0 is the launch elevation angle, r t is the distance from the ray reflection vertex to the center of the earth; s t is the path length from the emission point to the reflection vertex, θ t is the incident angle corresponding to the reflection vertex.

[0044] When the influence of the Earth's magnetic field is not considered and the collision effects between electrons and molecules and ions are neglected, n is:

[0045]

[0046] Where plasma angular frequency f p is the plasma frequency, e, N e 、m e are electron charge, electron number density and electron mass respectively, f is the transmission frequency, θ0 is the incident angle of the radar electromagnetic wave, ε0 is the vacuum dielectric constant, and ω is the operating frequency of the radar.

[0047] Then, by taking the derivative of equation (3), we can get the relationship between the propagation path P of the skywave radar and the ionospheric electron density N: e Partial derivatives of :

[0048]

[0049] From the analysis of formula (5), we can see that the rate of change of the path The distance r from the ray reflection vertex to the center of the earth t and the corresponding electron number density N e The error is related to the detection capability of the radar itself. Therefore, the error comes from the abnormal data generated by the ionosphere changes and the measurement error of the radar itself. Therefore, the evaluation of radar tracking effect also starts from the following aspects.

[0050] A) Evaluation of Abnormal Data

[0051] Due to the dynamic changes of the ionosphere, the signal delay data received by the skywave radar may have obvious anomalies. How to eliminate these anomalies has a great impact on the radar's target tracking ability. The score of abnormal data in the evaluation is b. 21 , with a value between 0 and 1. The fewer abnormal data, the higher the score.

[0052] B) Measurement error assessment

[0053] In general, measurement errors are more common, and b 22 It indicates that the value is between 0 and 1. The smaller the error, the higher the score.

[0054] Since abnormal data has little impact on tracking results, a is often given when calculating the overall evaluation value of the PD algorithm. 22 Assign a larger weight so that the overall evaluation value can be expressed as a 12 =0.95b 22 +0.05b 21 .

[0055] C) Evaluation of backscattering patterns obtained by PD transformation

[0056] By establishing a signal transceiver system near the radar measurement range, sending a signal to the transceiver system through the skywave radar, and receiving its echo, the signal delay with continuously changing frequency can be measured to obtain the ionospheric backscattering map, that is, the backscattering map is calculated using formula (5), and its evaluation result is expressed as a 13 =min{k 13 ,e3} means, where k 13 is the criterion for whether the backscattering data exists. If the vertical survey data exists, k 13 =1, the ionospheric modeling is more reliable. If the vertical survey data does not exist, k 13 =0.8, at this time the ionospheric modeling is unreliable; e3 is the accuracy evaluation result of the backscatter image, and its value is usually above 0.9.

[0057] Since the ionospheric vertical survey map and the backscatter map are two connected processes, the total evaluation value a1 of the ionospheric modeling is: a1 = a 11 *a 12 *a 13 If the value of a1 is above 0.8, it proves that the skywave radar has excellent detection capability. If it is below 0.8, it means that the model data of the ionosphere needs further precise measurement.

[0058] Go to step 2.

[0059] Step 2: Evaluate the pre-processing capability based on the skywave radar detection path

[0060] 2.1 Evaluating Multipath Removal Capabilities

[0061] Multipath propagation means that due to the layered characteristics of the ionosphere, different echoes of the same target may have different reflection heights, and the radar receiver obtains data from multiple paths, which affects the target tracking effect and increases the difficulty of positioning. In order to eliminate multipath interference, Hough transform and path fusion technology can be used. In the evaluation process, a 21 The evaluation results are shown in Table 2. Since multipath propagation is closely related to the structure of the ionosphere, in theory a 21 is a function of a1.

[0062] 2.2 Evaluating Multimodality Capabilities

[0063] Since skywave radar transmits signals based on reflection from the ionosphere, changes in the ionosphere can result in different propagation paths corresponding to the same time delay, which can also affect the radar's target tracking and detection. In order to avoid the influence of multimode propagation, the frequency is usually selected based on the vertical survey map of the ionosphere. 22 Indicates that the stronger the multi-mode capability, the 22 The bigger.

[0064] 2.3 Evaluation of the ability to resist phase disturbance

[0065] Phase disturbance refers to the phase modulation effect on electromagnetic waves caused by the dynamic changes of the ionosphere, which causes the spectrum of electromagnetic waves to broaden or drift, thereby destroying the coherent information of the echo and affecting the target tracking of the radar. 23 Indicates that the stronger the anti-phase interference ability is, the 23 The bigger.

[0066] Since multimode interference and multipath interference are independent of each other, and multipath interference will further affect the processing of the former two, the evaluation result of the entire preprocessing is a2=a 23 *(a 22 +a 21 ) / 2. If the value of a2 is above 0.75, the skywave radar has excellent detection capabilities, and the process goes to step 3. If it is below 0.75, the radar preprocessing algorithm needs further improvement.

[0067] Step 3: Tracking result evaluation based on preprocessing

[0068] Since the choice of tracking algorithm has a certain impact on the overall tracking results, choosing the appropriate tracking algorithm according to the situation is also one of the evaluation criteria. The following two algorithms are used as examples to illustrate.

[0069] 3.1 Kalman Tracking Algorithm

[0070] The Kalman filter algorithm, also known as a linear dynamic system based on Gaussian processes, maps the state space to the observation space through the state transfer matrix to track and detect targets.

[0071] 3.2 Probabilistic Multi-Hypothesis Tracking Algorithm

[0072] The probabilistic multi-hypothesis tracking algorithm does not rely on the mutual conversion between radar coordinates and geographic coordinates, which makes the algorithm process simpler and easier to implement.

[0073] The difficulty and adaptability of the comprehensive tracking algorithm are evaluated as a3.

[0074] Because the evaluation process is a cascaded process, the overall system evaluation value A = a1 * a2 * a3. If the value of A is above 0.7, it proves that the skywave radar has excellent target tracking capabilities. If it is below 0.7, it indicates that the radar's target tracking capabilities are poor and need further improvement.

[0075] Example 1

[0076] Taking a radar in a certain actual situation as an example, the evaluation values at each stage are:

[0077] a11 =0.97, a 13 =0.95, b 21 =0.98, b 22 =0.95, a 21 =0.97, a 22 =0.75, a 23 =0.96, a3=0.85

[0078] After calculation, the final evaluation value is A=0.632

[0079] After evaluation, it was found that a 22 The evaluation value of a3 is too low, indicating that the factors affecting the radar tracking capability appear in the two stages of demultimodal capability and tracking algorithm. By improving the corresponding preprocessing method, a can be effectively improved. 22 and the value of a3, if after improvement, a 22 The value of a3 is increased to 0.95, and the recalculated evaluation result A is * =0.789.

[0080] From the results, we can analyze that the effectiveness of radar tracking has been significantly improved, with an improvement percentage of 24.9%.

Claims

1. A method for evaluating the tracking effect of a skywave radar, characterized in that: Here are the steps: Step 1: Model the skywave radar detection path; Step 2: Evaluate the pre-processing capability based on the skywave radar detection path; Step 3: Evaluate based on the preprocessed tracking results; The length of the skywave radar propagation path P includes the straight line AB, arc BC, and straight line CD connected in sequence. The length of the ground path D is arc AD. The skywave radar propagation path P and the ground distance D are integrated to obtain: Where n is the refractive index of the electromagnetic wave at r; β is the incident angle of the electromagnetic wave at r; r0 is the radius of the earth; β0 is the launch elevation angle, r t is the distance from the ray reflection vertex to the center of the earth; s t is the path length from the emission point to the reflection vertex, θ t is the incident angle corresponding to the reflection vertex; When the influence of the Earth's magnetic field is not considered and the collision effects between electrons and molecules and ions are neglected, n is: Where, the plasma angular frequency f p is the plasma frequency, e, N e 、m e are electron charge, electron number density and electron mass respectively, f is the transmission frequency, θ0 is the incident angle of the radar electromagnetic wave, ε0 is the vacuum dielectric constant, and ω is the operating frequency of the radar; Then, we can differentiate equation (3) and get the relationship between the propagation path P of the skywave radar and the ionospheric electron density N. e Partial derivatives of : Analyzing formula (5), the rate of change of the path The distance r from the ray reflection vertex to the center of the earth t and the corresponding electron number density N e The evaluation of radar tracking effect is based on the following aspects: A) Evaluation of Abnormal Data Due to the dynamic changes in the ionosphere, the score of abnormal data is b during evaluation. 21 , the value is between 0 and 1, the fewer abnormal data, the higher the score; B) Measurement error assessment Usually, the measurement error is expressed as b 22 It indicates that the value is between 0 and 1, and the smaller the error, the higher the score; The overall evaluation value is expressed as a 12 =0.95b 22 +0.05b 21 ; C) Evaluation of backscattering patterns obtained by PD transformation By establishing a signal transceiver system near the radar measurement range, sending a signal to the transceiver system through the skywave radar, and receiving its echo, the signal delay with continuously changing frequency can be measured to obtain the ionospheric backscattering map, that is, the backscattering map is calculated using formula (5), and its evaluation result is expressed as a 13 =min{k 13 ,e3} means, where k 13 is the criterion for whether the backscattering data exists. If the vertical survey data exists, k 13 =1, the ionospheric model is reliable. If the vertical survey data does not exist, k 13 =0.8, at this time the ionospheric model is unreliable; e3 is the accuracy evaluation result of the backscatter image, and the value is usually above 0.9; Since the ionospheric vertical survey map and the backscatter map are two connected processes, the total evaluation value a1 of the ionospheric modeling is: a1 = a 11 *a 12 *a 13 If the value of a1 is above 0.8, it proves that the skywave radar has excellent detection capability. If it is below 0.8, it means that the model data of the ionosphere needs further precise measurement.

2. The skywave radar tracking effect evaluation method according to claim 1, characterized in that: In step 1, the skywave radar detection path is modeled as follows: The ionospheric structure model is established using a multi-layer quasi-parabolic model of the ionosphere. The number of ionosphere layers is K, and K takes values of 1, 2, and 3. K = 1, corresponding to the period from 1 hour after sunset to 1 hour before sunrise; K = 2, corresponding to 1 hour before sunrise to 1 hour after sunrise, and 1 hour before sunset to 1 hour after sunset; K = 3 for the rest of the day; The specific time node is related to the latitude and month of the location, and its electron concentration expression is: N e (t): time-varying electron concentration, unit 10 6 / cm 3 ; r: ray distance relative to the center of the earth, in km; r mk (t): the height of the maximum electron concentration in the kth layer, in km; y mk (t): half-layer thickness of the kth layer, in km; r bk (t): bottom height of the kth layer, in km; N mk (t): Maximum electron concentration in the kth layer, unit 10 6 / cm 3 ; t: current time, in seconds; Among them, the negative sign represents a conventional parabolic layer, and the positive sign represents an inverted parabolic layer. The inverted parabolic layer realizes a smooth transition from the top of the low conventional parabolic layer to the bottom of the high conventional parabolic layer. The above parameters are all functions of time, and the measurements of the above parameters are obtained through ionospheric vertical survey maps. The vertical map of the ionosphere is evaluated and the evaluation results are expressed as a 11 =min{k 11 ,e1} means, where k 11 is the standard for whether the vertical survey map data exists. If the vertical survey map data exists, k 11 =1, the ionospheric modeling is more reliable. If the vertical survey data does not exist, k 11 =0.5, at this time the ionospheric modeling is unreliable; e1 is the accuracy evaluation result of the vertical survey map, and its value is usually above 0.

9.

3. The skywave radar tracking effect evaluation method according to claim 1, characterized in that: In step 2, the pre-processing capability based on the skywave radar detection path is evaluated as follows: 2.1 Evaluating Multipath Removal Capabilities In order to eliminate multipath interference, Hough transform and path fusion technology are used. 21 The evaluation results are shown in Table 2. Since multipath propagation is closely related to the structure of the ionosphere, in theory a 21 A function of a1: 2.2 Evaluating Multimodality Capabilities To multi-mode capability, use a 22 Indicates that the stronger the multi-mode capability, the 22 The bigger; 2.3 Evaluation of the ability to resist phase disturbance When evaluating the ability to resist phase disturbance, the rating is a 23 Indicates that the stronger the anti-phase interference ability is, the 23 The bigger; Since multimode interference and multipath interference are independent of each other, and multipath interference will further affect the processing of the former two, the evaluation result of the entire preprocessing is a2=a 23 *(a 22 +a 21 ) / 2; if the value of a2 is above 0.75, it proves that the skywave radar has excellent detection capability; if it is below 0.75, it means that the radar preprocessing algorithm needs further improvement.

4. The skywave radar tracking effect evaluation method according to claim 3, characterized in that: The tracking result evaluation based on preprocessing in step 3 specifically includes the Kalman tracking algorithm and the probabilistic multi-hypothesis tracking algorithm.

5. The skywave radar tracking effect evaluation method according to claim 4, characterized in that: The difficulty and adaptability of the comprehensive tracking algorithm are evaluated and expressed as a3. Since the evaluation process is a cascade relationship, the overall evaluation value of the system is A = a1*a2*a3. If the value of A is above 0.7, it proves that the skywave radar has excellent target tracking capability. If it is below 0.7, it means that the radar's target tracking capability is poor and needs further improvement.

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