An ionosphere virtual height estimation method applied to short-wave active-passive integrated radar

Abstract

The application relates to an ionosphere virtual height estimation method applied to a short-wave active-passive integrated radar, which comprises the following steps: 1: an integrated detection system receives active radar detection echoes and passive radar detection echoes, and a main-passive detection channel is respectively subjected to distance, speed and azimuth sorting to obtain an active radar point track measurement set and a passive radar point track measurement set; 2: a group of points is respectively taken out from the two measurement sets, and the ionosphere virtual height is calculated by assuming the points as matched points; 3: the active radar measurement and the passive radar measurement are converted to the northeast sky coordinate system according to the calculated ionosphere virtual height; 4: a threshold method is used for global matching on the converted measurement sets to obtain a matching result, and a cost function value is calculated according to the matching result; 5: the two measurement sets are respectively traversed, and the steps 2, 3 and 4 are repeated, and the ionosphere virtual height corresponding to the minimum cost function is taken as the ionosphere virtual height in a detection environment. The application is used in the field of high-frequency over-the-horizon radar signal processing.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high frequency over-the-horizon radar signal processing, in particular to an ionospheric virtual height estimation method applied to a short wave active-passive integrated radar, which can be applied to the estimation of ionospheric virtual height under a short wave active-passive integrated radar system. BACKGROUND

[0002] In recent years, high frequency over-the-horizon radar has become increasingly important in the strategic position of national security in China. As a basic type of high frequency ground wave radar, its typical working frequency band is located in 3-30MHz, and generally uses vertically polarized electromagnetic waves as the transmitting signal, which can break through the curvature limit of the earth and realize over-the-horizon detection, with a detection distance of several hundred kilometers. Compared with microwave radar, it has the advantages of anti-stealth, anti-low-altitude penetration, all-weather and all-day operation, etc.

[0003] Short wave passive radar uses the short wave signal transmitted by a third party (such as a radio station) for target detection, and its working frequency is also between 3-30MHz. Using the sky-to-ground mode for detection is a new emerging system of short wave passive radar. The transmitting station of the sky-to-ground mode is located inland, and the electromagnetic wave is transmitted to the specific observation sea area in the sky wave propagation mode; the receiving station is established along the coast, and the ground wave path return wave of the target along the sea plane is received, and then over-the-horizon detection of the target is realized. Short wave passive radar has the advantage of radio silence, and can simultaneously use multiple detection sources for detection, and has the advantages of anti-radiation missile and multi-transmit-single-receive distributed system. However, its positioning accuracy is affected by ionospheric parameters, and the positioning accuracy is low, which is the main factor affecting the performance of short wave passive radar. SUMMARY

[0004] The purpose of the present application is to solve the problem of estimating the sky wave channel parameters in the short wave active-passive integrated detection system, and to propose an ionospheric virtual height estimation method applied to a short wave active-passive integrated radar.

[0005] The application is directed to a short wave active and passive integrated detection system composed of a high frequency ground wave radar and a short wave passive radar. The integrated detection system adopts a centralized structure, that is, the high frequency ground wave radar and the short wave passive radar share a receiving antenna and a receiving site, and the receiving station has the echo information of the two system radars. The purpose of the application is to solve the ionospheric parameter estimation problem in a detection environment and improve the passive radar target detection and positioning accuracy. The ray tracing positioning method, as a widely used ionospheric inversion method in sky wave radars, requires the cooperation of the transmitting station and the receiving station. Since the detection source used by the passive radar is occasional, and there is a lack of synchronization information between the transmitting station and the receiving station, the ionospheric detection means of the passive radar is difficult to support accurate ionospheric inversion, and the ray tracing positioning method is difficult to play a role. The application uses the equivalent principle of ionospheric propagation for target positioning, uses the advantage of stable ground wave channel detection, uses the method of nonlinear integer programming, and accurately estimates the ionospheric parameters through the mutual matching of the detection results of the ground wave radar and the passive radar, so as to improve the positioning accuracy of the short wave passive radar in the short wave active and passive integrated detection system.

[0006] An ionospheric virtual height estimation method applied to a short wave active and passive integrated radar, the specific process comprising the following steps:

[0007] Step 1: The integrated detection system receives active radar detection echoes and passive radar detection echoes, and the active and passive detection channels are respectively sorted by distance, speed and azimuth to obtain an active radar plot measurement set and a passive radar plot measurement set;

[0008] Step 2: A group of points is respectively taken out from the two measurement sets, and the ionospheric virtual height is calculated assuming that the points are matched;

[0009] Step 3: The active radar measurement and the passive radar measurement are converted to the northeast sky coordinate system according to the calculated ionospheric virtual height;

[0010] Step 4: The converted measurement set obtained in step 3 is globally matched according to the threshold method to obtain a matching result, and the matching result is substituted into a pre-set cost function to calculate a cost function value;

[0011] Step 5: The two measurement sets are traversed respectively, and steps 2, 3 and 5 are repeated, and the ionospheric virtual height corresponding to the minimum cost function value is taken as the ionospheric virtual height in the detection environment.

[0012] Further,

[0013] In step 3, the active and passive radar measurements are converted from the radar coordinate system to the geographic coordinate system; the specific process is as follows:

[0014] Step 3.1: Transform the active radar measurement from radar coordinate system to geographic coordinate system, wherein the geographic coordinate system is the north-east sky coordinate system with the active-passive radar cooperative system receiving station as the original place;

[0015] Let X represent the detection result of the active radar in the radar coordinate system, and g(X) is the transformation function of transforming the ground wave radar from the radar coordinate system to the geographic coordinate system, so the position of the ground wave radar measurement in the geographic coordinate system is g(X).

[0016] Step 3.2: Transform the passive radar measurement from the radar coordinate system to the geographic coordinate system according to the ionospheric virtual height calculated in step 2, and the specific process of the mixed system radar working is as follows:

[0017] Let Y represent the detection result of the passive radar in the radar coordinate system, and let s(Y; h) be the transformation function of transforming the passive radar from the radar coordinate system to the geographic coordinate system, wherein h is a function of the ionosphere. When the measurement coordinates Y are known, that is, the group distance R g and the azimuth θ of the trace relative to the receiving station, and the ionospheric height h, s(Y; h) can be obtained by the following method:

[0018] Suppose the receiving station is at the geographic coordinate origin, and the geographic coordinates of the transmitting station are (x s ,y s ), and the baseline distance of the transmitting and receiving stations is:

[0019]

[0020] The radar measurement is then positioned by the transformation function

[0021]

[0022] , wherein Az is the angle between the receiving station and the target on the baseline, and r1 is the distance between the measurement corresponding trace and the receiving station after conversion to the geographic coordinate system.

[0023] The step 4 is to globally match the conversion results in step 3, and the matching results are brought into the calculation of the cost function, and the specific process is as follows:

[0024] Step 4.1: According to the threshold method, the matched results are obtained by globally matching the converted measurements obtained in step 3.

[0025] The threshold method is to calculate the Euclidean distance of all points in the other group in the coordinate system for the to-be-matched point, and to consider that there is a pairing possibility for the point whose Euclidean distance value is within the threshold and is the minimum value among all points.

[0026] Step 4.2: Substitute the matching results into the pre-set cost function to calculate the cost function value.

[0027] The definition of the cost function is as follows: let G={X i ; i=1, …, m} and T={Y j ; j=1, …, n} represent the point track results detected by the active radar and the passive radar respectively.

[0028] There are three cases for the elements in the two sets of point tracks: ① the targets found in both the passive radar and the active radar can be matched with each other; ② the targets found in only one of the passive radar and the active radar are real but cannot be matched; ③ false alarms that do not correspond to any real target and thus cannot be matched; the number and specific matching conditions of the matched points in S and G are unknown; define the matched target set as:

[0029] P={(X i , Y j ) | X i ∈ G, Y j ∈ T}

[0030] and the projection sets of P on G and T are and where g(X i ) in step 3.1 is a conversion function for converting the ground wave radar from the radar coordinate system to the geographic coordinate system; s(Y j ; h) in step 3.2 is a conversion function for converting the passive radar from the radar coordinate system to the geographic coordinate system, which is a function of the measured coordinates Y j and the virtual height h; find the set P and the parameter h to minimize the following cost function:

[0031]

[0032] where and represent the number of unmatched point tracks in the sets G and T respectively, and the constants λ and κ represent the cost of the unmatched point tracks, which can be used to control the association range of the point track matching; when they are small, missing matching occurs, i.e., there are more remaining point tracks; when they are large, overmatching occurs, i.e., point tracks that do not belong to the same target are paired; D(·,·) in the formula represents the distance of the matched points in the geographic coordinate system.

[0033] The beneficial effects of the present application are:

[0034] The purpose of the present application is to obtain a more accurate estimation of the ionospheric virtual height in the detected environment by using the short wave active and passive integrated radar.

[0035] The application provides a method for ionosphere virtual height estimation suitable for passive radar, in an integrated detection system, ionosphere parameters are accurately estimated through the matching of active radar and passive radar detection results by using the high positioning accuracy of ground wave radar. The parameter estimation method solves the problem that the existing ionosphere inversion method is not suitable for passive radar, and the equivalent principle of ionosphere propagation is adopted, which creates favorable conditions for improving the positioning accuracy of short wave passive radar. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a working schematic diagram of a short wave active and passive integrated radar in the embodiment;

[0037] Figure 2 is a general flowchart of the application;

[0038] Figure 3 is an ionosphere virtual height schematic diagram in the embodiment;

[0039] Figure 4 is a working schematic diagram of a mixed system radar of sky-to-ground and ground-to-sky in the embodiment. DETAILED DESCRIPTION

[0040] Specific implementation one: the specific process of the ionosphere virtual height estimation method applied to the short wave active and passive integrated radar in the embodiment is as follows:

[0041] Step 1: the integrated detection system receives active radar detection echoes and passive radar detection echoes, the active and passive detection channels are respectively sorted by distance, speed and azimuth, and active radar track measurement sets and passive radar track measurement sets are respectively obtained, and a short wave active and passive integrated radar working schematic diagram is as shown in Figure 1 .

[0042] Step 2: a group of points are respectively taken out from the two measurement sets, and the ionosphere virtual height is calculated by assuming that the points are matching points, and an ionosphere virtual height schematic diagram is as shown in Figure 3 .

[0043] Step 3.1: the active radar measurement is converted from the radar coordinate system to the geographic coordinate system, wherein the geographic coordinate system is the northeast celestial coordinate system with the active and passive radar cooperative system receiving station as the original place, and the specific process is as follows:

[0044] Let X represent the detection result of the active radar in the radar coordinate system, and g(X) is the conversion function of converting the ground wave radar from the radar coordinate system to the geographic coordinate system, so the position of the ground wave radar measurement in the geographic coordinate system is g(X).

[0045] Step 3.2: the passive radar measurement is converted from the radar coordinate system to the geographic coordinate system according to the ionosphere virtual height calculated in step 2, and a mixed system radar working schematic diagram of sky-to-ground and ground-to-sky is as shown inFigure 4 The specific process is shown as follows:

[0046] Let Y represent the passive radar detection result in the radar coordinate system, and let s(Y; h) be the conversion function from the radar coordinate system to the geographic coordinate system, where h is a function of the ionosphere. When the measured coordinates Y are known, i.e., the group distance R g and the bearing θ of the plot relative to the receiving station, and the ionosphere height h, s(Y; h) can be obtained by the following method:

[0047] Assume that the receiving station is at the origin of the geographic coordinate system, and the geographic coordinates of the transmitting station are (x s ,y s ), and the baseline distance between the transmitting and receiving stations is:

[0048]

[0049] The radar measurement result is then converted by the conversion function:

[0050]

[0051] to perform positioning, where Az is the angle between the receiving station and the target at the baseline, and r1 is the distance between the corresponding plot of the measurement and the receiving station after conversion to the geographic coordinate system.

[0052] The passive radar measurement is brought into the above conversion function.

[0053] Step 4.1: For the converted measurement set obtained in step 3, global matching is performed according to the threshold method to obtain a matching result.

[0054] The threshold method is that for a to-be-matched point, the Euclidean distance of all points in another set in the coordinate system is calculated, and the point with a Euclidean distance value within the threshold and the smallest value among all points is considered to have a possible pairing.

[0055] Step 4.2: Substitute the matching result into the pre-set cost function to calculate the cost function value.

[0056] The cost function is defined as follows: Let G = {X i ; i = 1, …, m} and T = {Y j ; j = 1, …, n} represent the plot results detected by the active radar and the passive radar, respectively. There are three cases for the elements in the two plot sets: ① The target is found in both the passive radar and the active radar, and the two can be matched with each other; ② The target is found in only one of the passive radar and the ground wave radar, the target is real, but cannot be matched; ③ False alarm point, which does not correspond to any real target, and therefore cannot be matched; According to the actual situation, the number of matched points in S and G and the specific matching situation are unknown. Define the matched target set as

[0057] P={(X i ,Y j )|X i ∈G,Y j ∈T}

[0058] And let the projection sets of P on G and T be and Where g(X i ) is the same as step 3.1, which is the conversion function for converting the ground wave radar from the radar coordinate system to the geographic coordinate system. j h) Same as step 3.2, is the conversion function of the passive radar from the radar coordinate system to the geographic coordinate system, which is the measurement coordinate Y j and a function of the imaginary height h. We strive to find a set P and parameter h that minimizes the following cost function:

[0059]

[0060] in, and where λ and κ represent the number of unmatched points in sets G and T, respectively. Constants λ and κ represent the cost of unmatched points. These two constants can be used to control the correlation range of point matching. When both are small, missed matches occur, meaning that many points remain; when both are large, overmatching occurs, meaning that points that do not belong to the same target tend to be paired. In the formula, D(·,·) represents the distance between the matching points in the geographic coordinate system. There are many common distance functions, such as Euclidean distance or the vector modulus function.

[0061] Step 5: Traverse the two measurement sets separately, repeat steps 2, 3, and 4, and use the ionospheric virtual height corresponding to the minimum cost function as the ionospheric virtual height in the detection environment.

[0062] The following examples are used to verify the beneficial effects of the present invention:

[0063] Example 1:

[0064] Combine Figure 2 This embodiment describes a method for estimating the ionospheric virtual height applied to a shortwave active-passive integrated radar, which is implemented in the following steps:

[0065] The radar measurement set is generated based on the radar measurement error, the coordinates of the transmitting and receiving stations, the simulated target data, and the ionospheric parameters. The radar measurement error is shown in Table 1, the coordinates of the transmitting and receiving stations are shown in Table 2, and the coordinate system is the northeast sky coordinate system with the receiving station as the origin. The main parameters of the simulated target are shown in Table 3, and the ionospheric parameters are shown in Table 4.

[0066] Table 1 Radar measurement error

[0067]

[0068] Table 2 Coordinates of transmitting and receiving stations

[0069]

[0070] Table 3 Simulation target parameter settings

[0071]

[0072] Note: The measurement form is (group distance, target bearing), where the group distance is in km and the bearing is in degrees, with the north direction of the active / passive radar receiving station as the starting point of clockwise rotation

[0073] Table 4 Ionospheric parameters

[0074]

[0075] Step 1: According to the four sets of simulation target parameters and ground wave radar measurement errors described above, part of the active radar measurements are simulated, and at the same time, according to the ionospheric parameters, the simulation target parameters are combined with the short-wave passive radar measurement errors to obtain the corresponding passive radar measurements. Then, combined with the actual situation, six sets of active radar measurements are randomly generated within a certain range to represent false alarm points and targets detected only by active radar, and eleven sets of passive radar measurements are randomly generated within a certain range to represent false alarm points and targets detected only by passive radar. Finally, the active radar measurement set containing ten sets of measurements and the passive radar set containing fifteen sets of measurements are obtained, which are represented as G = {X i ; i = 1, …, 10} and T = {Y j ; j = 1, …, 15}, respectively, where X i represents the i-th set of measurements in the active radar measurement set, Y j represents the j-th set of measurements in the passive radar measurement set, and when i = 1, …, 4, j = 1, …, 4, X i , Y j represent the real measurements of the simulation targets set.

[0076] Step 2: Take one set of measurements from the active radar measurement set and the passive measurement set, respectively: X i , Y j . Assume that (X i , Y j ) is the correct matching pair, and solve the ionospheric virtual height h under this condition.

[0077] Step 3: According to the obtained ionospheric virtual height h, the transformation function s(Y j; h) converting all points in the passive radar measurement set T from the radar coordinate system to the geographic coordinate system, the active radar measurements can be considered to have been converted to the geographic coordinate system and do not need to be further processed.

[0078] Step 4: converting all points s(Y j ; h), j = 1,..., 15 to the geographic coordinate system in the passive radar measurement set T, and matching with the geographic coordinates X i , i = 1,..., 10 of all targets in G using a threshold method. The cost function value after matching is calculated according to the cost function E(P, h).

[0079] Step 5: let i be equal to 1,..., 10 in turn, then for each value of i, j is equal to 1,..., 15. For each group i, j, repeat steps 2, 3, 4, and the ionospheric virtual height corresponding to the minimum cost function is taken as the ionospheric virtual height in the detection environment.

[0080] Table 5 matching results

[0081]

[0082] Table 6 ionospheric parameter estimation results

[0083]

[0084] The simulation results prove that:

[0085] It can be seen from the matching results in Table 5 that compared with the traditional nearest neighbor method, the global matching method based on nonlinear programming used in the present application has fewer matching errors and better matching effect, which lays a good foundation for further estimation of ionospheric parameters.

[0086] As can be seen from Table 6, the ionospheric virtual height estimated by the present application has a certain error compared with the actual value, but is relatively close, which is conducive to improving the positioning accuracy of the short wave passive radar, and can prove the effectiveness of the present method.

[0087] The present application also has other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. A method for estimating ionospheric false height applied to a shortwave active-passive integrated radar, characterized by: The method comprises the following steps: Step 1: The integrated detection system receives active radar detection echoes and passive radar detection echoes. The active and passive detection channels perform range, speed, and azimuth sorting respectively to obtain active radar point trace measurement sets and passive radar point trace measurement sets respectively. Step 2: Take a set of points from the two measurement sets respectively and calculate the ionospheric height by assuming them as matching points; Step 3: Convert the active radar measurements and passive radar measurements to the northeast celestial coordinate system based on the calculated ionospheric height; Step 4: Perform global matching on the converted measurement set obtained in step 3 according to the threshold method to obtain a matching result, and substitute the matching result into a pre-set cost function to calculate the cost function value; Step 5: Traverse the two measurement sets separately, repeat steps 2, 3, and 4, and use the ionospheric virtual height corresponding to the minimum cost function as the ionospheric virtual height in the detection environment.

2. The method for estimating ionospheric false height applied to a shortwave active-passive integrated radar according to claim 1, characterized in that: In step 3, the active and passive radar measurements are converted from the radar coordinate system to the geographic coordinate system; the specific process is: Step 3.1: Convert the active radar measurements from the radar coordinate system to the geographic coordinate system, where the geographic coordinate system is the northeast celestial coordinate system with the active and passive radar cooperative system receiving station as the origin; Let X represent the detection result of the active radar in the radar coordinate system, g(X) is the conversion function that converts the active radar from the radar coordinate system to the geographic coordinate system, so the position of the active radar measurement result in the geographic coordinate system is g(X); Step 3.2: Convert the passive radar measurements from the radar coordinate system to the geographic coordinate system based on the ionospheric height calculated in Step 2. The specific operation process of the hybrid radar system is as follows: Let Y represent the detection result of the passive radar in the radar coordinate system, let s(Y;h) be the conversion function that converts the passive radar from the radar coordinate system to the geographic coordinate system, where h is a function of the ionosphere. When the measurement coordinate Y is known, that is, the group distance R is known g When the sum trace is relative to the receiving station azimuth θ and the ionospheric height h, s(Y; h) is obtained as follows: Assume that the receiving station is at the origin of geographical coordinates and the geographical coordinates of the transmitting station are (x s ,y s ), the baseline distance between the transceiver station is: The radar measurement results are converted into Positioning, where A z is the angle between the receiving station and the target and the baseline, r1 is the distance between the corresponding point and the receiving station after conversion to the geographic coordinate system; Simply substitute the passive radar measurements into the above conversion function.

3. The method for estimating ionospheric false height applied to a shortwave active-passive integrated radar according to claim 2, characterized in that: In step 4, a global match is performed on the conversion result in step 3, and the matching result is brought into the calculation cost function for calculation. The specific process is: Step 4.1: Perform global matching on the converted measurement set obtained in step 3 according to the threshold method to obtain the matching result; The threshold method is to calculate the Euclidean distance of all points in the other group in the coordinate system for the point to be matched, and consider the point whose Euclidean distance value is within the threshold and is the minimum value among all points to be possible to be matched; Step 4.2: Substitute the matching result into the pre-set cost function to calculate the cost function value; The cost function is defined as follows: Let G = {X i ; i=1,…,m} and T={Y j ; j = 1,…, n} represents the point trace results detected by active radar and passive radar respectively; There are three situations for elements in the two sets of point traces: ① Targets detected by both the passive radar and the active radar can be matched; ② Targets detected by only one of the passive and active radars are real, but cannot be matched; ③ False alarms do not correspond to any real targets and therefore cannot be matched; The number of matching points in S and G and the specific matching conditions are unknown. The matching target set is defined as: P={(X i ,AND j )|X i ∈G,Y j ∈T} And let the projection sets of P on G and T be and where g(X i ) is the same as step 3.1, which is the conversion function for converting the active radar from the radar coordinate system to the geographic coordinate system; s(Y j h) Same as step 3.2, is the conversion function of the passive radar from the radar coordinate system to the geographic coordinate system, which is the measurement coordinate Y j and a function of the imaginary height h; find the set P and the parameter h so that the following cost function is minimized: in, and where λ and κ represent the number of unmatched points in the sets G and T, respectively. The constants λ and κ represent the cost of unmatched points. These two constants are used to control the association range of point matching. When both are small, missed matches occur, that is, more points remain. When both are large, overmatching occurs, that is, points that do not belong to the same target tend to be paired. Where D(·,·) represents the distance between matching points in the geographic coordinate system.

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