A method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interferometry principle

Abstract

The present invention provides a method for obtaining the spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle, which relates to the field of space environment detection technology, and includes the following steps: S1: performing phase correction on actual echo signals to obtain system phase deviation; S2: obtaining the cross-correlation amplitude spectrum of the scattered echoes of the target inhomogeneities, and screening effective information; S3: obtaining the relationship between the phase difference between different radar arrays and the azimuth and elevation of the echo signals to perform system phase correction and three-dimensional spatial structure positioning of the inhomogeneities. The present invention is simple to execute, reasonable, and makes full use of signal processing inferences and mathematical models, converting the difficulty of detecting ionospheric inhomogeneities into the computational difficulty of data processing, greatly reducing the stringent requirements on detection equipment; in addition, the echo information can be screened and the phase deviation correction can be performed, effectively improving the accuracy and reliability of the detection results.

Description

Technical Field

[0001] The present invention relates to the technical field of space environment detection.

[0002] In particular, the present invention relates to a method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle. Background Art

[0003] The Earth's space environment includes the Earth's upper atmosphere in neutral and ionized states, the Earth's external magnetic field, and the solar radiation that affects them, which is closely related to human survival and activities. Ionospheric inhomogeneities appear in cloud-like structures with different ionization densities in the regular ionosphere. Their electron density is higher or lower than the average ionization density of the surrounding medium. The maximum relative change in electron density is usually only a few percent, and can reach 10 to 20 percent in individual cases or small areas. The impacts of ionospheric inhomogeneities mainly include ionospheric interference, turbulent interference, etc. For most electronic systems, these effects are usually harmful. Therefore, when designing radio systems, it is necessary to try to reduce the impact of inhomogeneities.

[0004] Due to the anisotropy of the spatial arrangement of ionospheric inhomogeneities, their long axes are arranged along the direction of the Earth's magnetic field. Therefore, their scattering cross-section changes with the angle between the radar beam direction and the Earth's magnetic field lines. When the beam direction is perpendicular to the magnetic field lines, the scattering cross-section is the largest. Therefore, the antenna array of the coherent scattering radar is erected in an east-west direction so that the direction of its synthesized beam is perpendicular to the Earth's magnetic field lines, thereby increasing the energy of the echo signal.

[0005] Due to the characteristics of inhomogeneous bodies, it is usually difficult to observe, so the real-time acquisition technology for the distribution characteristics of inhomogeneous bodies is constantly being developed. For example, the Chinese patent invention patent CN112526618A discloses an ionospheric tomography measuring instrument based on multi-band multi-constellation satellite signals and its observation method. The measuring instrument includes a data integration processing unit, a low-orbit satellite beacon ionospheric measurement component electrically connected to the data integration processing unit, a GNSS satellite signal ionospheric measurement component, a data storage unit, a power supply unit and a data display and control unit. The ionospheric tomography measuring instrument based on multi-band multi-constellation satellite signals disclosed in the above invention combines the measurement of medium-high orbit and low-orbit satellite signals to improve the measurement accuracy of ionospheric electron density; combines multiple GNSS satellite navigation systems to expand the satellite observation path and provide a more accurate TEC distribution; combines multi-band satellite signals to achieve comprehensive measurement of multi-band wide-scale ionospheric scintillation and inhomogeneous body parameters.

[0006] However, the above observation method still has the following disadvantages: complex structure, too high requirements on inhomogeneous body detection equipment, no screening of echo information, inability to perform phase deviation correction, and insufficient accuracy and reliability of detection results.

[0007] Therefore, in order to solve the above problems, it is necessary for us to design a reasonable method based on the interference principle to obtain the spatial distribution characteristics of ionospheric inhomogeneities. Summary of the invention

[0008] The purpose of the present invention is to provide a method for obtaining the spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle, which is simple to execute, reasonable and fully utilizes signal processing inferences and mathematical models, converts the difficulty of detecting ionospheric inhomogeneities into the computational difficulty of data processing, and greatly reduces the stringent requirements on detection equipment; in addition, the echo information can be screened and the phase deviation can be corrected, effectively improving the accuracy and reliability of the detection results.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle comprises the following steps:

[0011] S1: Perform phase correction on the actual echo signal to obtain the system phase deviation;

[0012] S2: Obtain the cross-correlation amplitude spectrum of the target inhomogeneous body scattered echo and filter out effective information;

[0013] S3: Obtain the relationship between the phase difference between different radar arrays and the target inhomogeneity and the azimuth and elevation of the echo signal, and perform system phase correction and three-dimensional spatial structure positioning of the inhomogeneity.

[0014] As a preferred embodiment of the present invention, when executing step S1, the following steps are specifically included:

[0015] S11: select the direction angle, elevation angle and altitude of the target area, and calculate the latitude, longitude and altitude of each position;

[0016] S12: Input the obtained spatial information of the target point, calculate the geomagnetic field vector of each position, and obtain the vertical component, the latitudinal component and the longitudinal component;

[0017] S13: inputting the echo data received by the actual radar to obtain the phase dispersion information under the actual situation;

[0018] S14: Compare the predicted echo region with the corresponding phase difference range, perform phase correction on the actual echo signal, and obtain the system phase deviation.

[0019] As a preferred embodiment of the present invention, when executing step S12, the geomagnetic field vector of each position is calculated using the IGRF model.

[0020] As a preferred embodiment of the present invention, before executing step S1, the position data of each radar in the radar array is obtained and stored in a one-to-one correspondence according to the labels.

[0021] As a preferred embodiment of the present invention, when executing step S2, the following steps are specifically included:

[0022] S21: Obtain the cross-correlation amplitude spectrum of the target scattered echo;

[0023] S22: Calculate the phase difference by cross-correlation interferometry;

[0024] S23: Use the interferometry equation to calculate the three-dimensional spatial characteristics and establish a spherical coordinate mathematical model based on the arrangement characteristics of the scattering radar array;

[0025] S24: Filter available phase information according to phase deviation and signal correlation quality.

[0026] As a preferred embodiment of the present invention, when executing step S21, the following steps are specifically included:

[0027] S211: Obtaining the time difference when different radar arrays receive echo signals;

[0028] S212: Calculate and obtain the phase difference between two echo signals at the same time;

[0029] S213: The echo signal is mixed, filtered, and Fourier transformed;

[0030] S214: further performing cross-correlation operation to obtain a normalized cross-correlation spectrum.

[0031] As a preferred embodiment of the present invention, before executing step S24, the signal correlation quality value is preset in advance.

[0032] As a preferred embodiment of the present invention, when executing step S3, the following steps are specifically included:

[0033] S31: After filtering out valid information, the phase deviation correction result in step S1 is used to calculate the azimuth and elevation of the target inhomogeneous body according to the position relationship of the inhomogeneous body in the spherical coordinate system;

[0034] S32: Calculate the three-dimensional spatial distribution characteristics of the inhomogeneous body according to the echo distance.

[0035] As a preferred embodiment of the present invention, when executing step S32, the error caused by the radius of curvature of the earth is eliminated.

[0036] As a preferred embodiment of the present invention, the method further comprises step S4: projecting the echo signal into a three-dimensional coordinate system to visualize the spatial position of the inhomogeneous body.

[0037] The beneficial effects of the method for obtaining the spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle of the present invention are: simple execution, reasonable and full use of signal processing inferences and mathematical models, converting the difficulty of detecting ionospheric inhomogeneities into the calculation difficulty of data processing, greatly reducing the stringent requirements on detection equipment; in addition, the echo information can be screened and the phase deviation can be corrected, effectively improving the accuracy and reliability of the detection results. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic flow chart of a method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle of the present invention;

[0039] Figure 2 This is a process schematic diagram of step S1 in a method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle of the present invention;

[0040] Figure 3 A basic principle diagram of a spatial interferometry method in a method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interferometry principle of the present invention;

[0041] Figure 4 The present invention discloses a distribution diagram of a detection radar antenna array in a method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle. DETAILED DESCRIPTION

[0042] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0043] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangements of modules and structures set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.

[0044] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0045] Technologies and methods known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate circumstances, technologies and methods should be considered as part of the authorization specification.

[0046] Embodiment 1: Figures 1 to 4 As shown, it is only one of the embodiments of the present invention, a method for obtaining the spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle, comprising the following steps:

[0047] S1: Perform phase correction on the actual echo signal to obtain the system phase deviation;

[0048] When executing step S1, the following steps are specifically included:

[0049] S11: Select the distribution range of the inhomogeneous body that may be observed by pointing the radar beam, including the direction angle, elevation angle and altitude range, and calculate the latitude, longitude and altitude of each position;

[0050] S12: Input the obtained spatial information of the target point, calculate the geomagnetic field vector of each position, and obtain the vertical component, the latitudinal component and the longitudinal component; here, the geomagnetic field vector of each position is calculated using the IGRF model;

[0051] S13: Input the echo data received by the actual radar to obtain the phase dispersion information under the actual situation; in fact, it is to use the sensitive characteristics of the ionospheric field in the direction of the inhomogeneous body to calculate the angle between the beam direction vector and the geomagnetic field vector, and select the azimuth and elevation angle that meet the conditions; with different altitude ranges, the three-dimensional spatial distribution map of the predicted echo area can be drawn to obtain the phase dispersion information of the echo under ideal conditions. The selection conditions are:

[0052]

[0053] Where α is the directional sensitivity of the inhomogeneous body.

[0054] S14: Compare the predicted echo region with the corresponding phase difference range, perform phase correction on the actual echo signal, and obtain the system phase deviation.

[0055] Generally speaking, the system phase calibration is performed once a month to collect the echo information received by the radar within 30 days. Read the azimuth and zenith angle observation values ​​Recorded_elevation and Recorded_azimuth from the original data file, and calculate the phase between the echoes received by the antenna:

[0056]

[0057] Among them: 17° is the tilt zenith angle of the antenna beam, d12 is the distance between array 1 and array 2; d23 is the distance between array 2 and array 3, and the bate value is the angle between d12 and the y-axis. Plot the phase dispersion information under actual conditions and compare it with the prediction results of the IGRF model in the previous step. It can be seen that the phase dispersion information obtained in actual observations has a certain deviation from the theoretical prediction results, which is caused by the system phase deviation. Correct the calculated theoretical prediction echo area center and the actual observation data center position, add the observed data phase difference to the offset so that it falls within the predicted echo area, and obtain the system phase deviation Bias value.

[0058] The actual step S1 is to obtain the phase dispersion information under ideal conditions by setting the parameters of the IGRF model (International Geomagnetic Reference Field Model, a digital model used to calculate the Earth's main magnetic field, i.e., the Earth's core magnetic field, from 1900 to the present).

[0059] Of course, before executing step S1, the position data of each radar in the radar array is obtained and stored one by one according to the mark. The radar array is arranged as follows: Figure 4 As shown, it includes at least array 1, array 2 and array 3.

[0060] S2: Obtain the cross-correlation amplitude spectrum of the target inhomogeneous body scattered echo and filter out effective information;

[0061] Here, when executing step S2, the following steps are specifically included:

[0062] S21: Obtain the cross-correlation amplitude spectrum of the target scattered echo;

[0063] S22: Calculate the phase difference by cross-correlation interferometry;

[0064] S23: Use the interferometry equation to calculate the three-dimensional spatial characteristics and establish a spherical coordinate mathematical model based on the arrangement characteristics of the scattering radar array;

[0065] S24: Filter available phase information according to phase deviation and signal correlation quality.

[0066] And, when executing step S21, the following steps are specifically included:

[0067] S211: Obtain the time difference when different radar arrays receive echo signals; when different radar arrays receive echo signals generated by scattering of distant targets, it can be regarded that the two beams of echoes come from the same direction, but because of the distance difference between different arrays, the echo signals will have a distance difference r, so different radar arrays will have a time difference when receiving echo signals. This is reflected in the definition of the echo fluctuation form:

[0068]

[0069] S212: Calculate the phase difference between the two echo signals at the same time; that is, the phase difference between the two echo signals at the same time is expressed as:

[0070]

[0071] S213: The echo signal is mixed, filtered, and Fourier transformed to obtain its mathematical expression:

[0072]

[0073] S214: Further perform cross-correlation operation to obtain a normalized cross-correlation spectrum:

[0074]

[0075] Among them, |SEW(ω)| represents the amplitude of the cross-correlation spectrum of the antenna arrays on both sides, also known as the cross-correlation coefficient. The larger the amplitude, the higher the probability that the receivers on the east and west sides receive the same target object. Represents the phase difference obtained by the cross-correlation interferometry method.

[0076] In the actual detection process, the target that generates the echo is not a single point. Inhomogeneous bodies may be distributed in a larger area, a smaller area, or even multiple areas. If the echo signal generated by the scattering of the inhomogeneous body comes from a single small area, then its correlation is large. On the contrary, if the echo comes from a larger area, or from different small areas in the detection area, its correlation is small. Therefore, to determine whether the received echo signals come from the same target, the phase information must be screened. The judgment criteria include signal coherency and phase deviation.

[0077] Of course, before executing step S24, the signal correlation quality value is preset in advance. Generally, the preset coherency value is 0.8, that is:

[0078] coherency value ≥ 0.8

[0079] |Δφ21+Δφ32-Δφ31|≤3°

[0080] For example: Perform Fourier transform on the first antenna array 1 to obtain the complex form FFT_CHA_Plural, and then obtain the spectrum Sum_CHA. Because 16 non-co-directional integrations are performed, the final average value Average_CHA = Sum_CHA / 16 is taken. The data of antenna arrays 2 and 3 are processed in the same way. Take the conjugate of FFT_CHA_Plural and multiply it with FFT_CHB_Plural to perform cross-correlation operation, and multiply it by their respective moduli to obtain the normalized cross-correlation spectrum SBA of the echo signals of arrays 1 and 2. Similarly, obtain the normalized cross-correlation spectrum SCA and SCB of arrays 1, 3 and 2, 3. Draw the cross-correlation amplitude spectrum and phase spectrum according to the calculation results in the previous step. Obtain the intersection of abs(SBA)>0.8, abs(SCA)>0.8, abs(SCB)>0.8, and convert the phase difference into angle values ​​Δφ21, Δφ32, and Δφ31. Filter out all points that meet the conditions according to the above judgment conditions.

[0081] S3: Obtain the relationship between the phase difference between different radar arrays and the target inhomogeneity and the azimuth and elevation of the echo signal, and perform system phase correction and three-dimensional spatial structure positioning of the inhomogeneity.

[0082] Here, when executing step S3, the following steps are specifically included:

[0083] S31: After filtering out valid information, the phase deviation correction result in step S1 is used to calculate the azimuth and elevation of the target inhomogeneous body according to the position relationship of the inhomogeneous body in the spherical coordinate system;

[0084] By obtaining the relationship between the phase difference between different arrays and the target and the azimuth and elevation of the echo signal, the system phase correction and the three-dimensional spatial structure positioning of the inhomogeneous body can be performed. After obtaining effective information, the azimuth and elevation of the target can be calculated based on the position relationship of the inhomogeneous body in the spherical coordinate system using the first-step phase deviation correction result:

[0085]

[0086] Where l and m are integer constants, which are determined before drawing the ideal phase dispersion diagram in the first step;

[0087] S32: Calculate the three-dimensional spatial distribution characteristics of the inhomogeneous body based on the echo distance:

[0088]

[0089] Moreover, when executing step S32, the error caused by the earth's curvature radius Re is eliminated, that is:

[0090]

[0091] In short, the phase difference information is added to the system deviation Bias value to complete the phase correction. The spherical coordinate coefficient mathematical model of the antenna array is established to deduce the relationship between the azimuth angle and the elevation angle and the phase difference. The azimuth angle φ and the elevation angle θ can be calculated based on the phase difference information of the points that meet the screening conditions. The horizontal position and height are calculated based on the distance r of the echo. The estimation of the height needs to consider the radius of curvature Re of the earth. At this point, the three-dimensional spatial distribution characteristics of the target inhomogeneous body have been obtained.

[0092] Finally, the present invention further includes step S4: projecting the echo signal into a three-dimensional coordinate system to visualize the spatial position of the inhomogeneous body, that is, projecting the echo position information into three mutually perpendicular planes, drawing a three-dimensional projection diagram of the target inhomogeneous body, and intuitively expressing its spatial distribution characteristics.

[0093] The method for obtaining the spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle of the present invention is simple to execute, reasonable and fully utilizes signal processing inferences and mathematical models, converts the difficulty of detecting ionospheric inhomogeneities into the calculation difficulty of data processing, and greatly reduces the stringent requirements on detection equipment; in addition, the echo information can be screened and the phase deviation can be corrected, effectively improving the accuracy and reliability of the detection results.

[0094] The present invention is not limited to the above specific implementations, and the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the above implementations based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for obtaining the spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle, characterized in that: The following steps are involved: S1: Perform phase correction on the actual echo signal to obtain the system phase deviation; S2: Obtain the cross-correlation amplitude spectrum of the target inhomogeneous body scattered echo and filter out effective information; S3: Obtain the relationship between the phase difference between different radar arrays and the target inhomogeneity and the azimuth and elevation of the echo signal, perform system phase correction and locate the three-dimensional spatial structure of the inhomogeneity; When executing step S1, the following steps are specifically included: S11: Select the distribution range of the inhomogeneous body that may be observed by pointing the radar beam, including the direction angle, elevation angle and altitude range, and calculate the latitude, longitude and altitude of each position; S12: Input the obtained spatial information of the target point, calculate the geomagnetic field vector of each position, and obtain the vertical component, the latitudinal component and the longitudinal component; S13: inputting the echo data received by the actual radar to obtain the phase dispersion information under the actual situation; S14: Compare the phase difference range corresponding to the predicted echo area, perform phase correction on the actual echo signal, and obtain the system phase deviation; When executing step S2, the following steps are specifically included: S21: Obtain the cross-correlation amplitude spectrum of the target scattered echo; S22: Calculate the phase difference by cross-correlation interferometry; S23: Use the interferometry equation to calculate the three-dimensional spatial characteristics and establish a spherical coordinate mathematical model based on the arrangement characteristics of the scattering radar array; S24: Filter available phase information according to phase deviation and signal correlation quality; When executing step S21, the following steps are specifically included: S211: Obtaining the time difference when different radar arrays receive echo signals; S212: Calculate and obtain the phase difference between two echo signals at the same time; S213: The echo signal is mixed, filtered, and Fourier transformed; S214: further performing a cross-correlation operation to obtain a normalized cross-correlation spectrum; When executing step S3, the following steps are specifically included: S31: After filtering out valid information, the phase deviation correction result in step S1 is used to calculate the azimuth and elevation of the target inhomogeneous body according to the position relationship of the inhomogeneous body in the spherical coordinate system; S32: Calculating the three-dimensional spatial distribution characteristics of the inhomogeneous body according to the echo distance; When executing step S32, the error caused by the radius of curvature of the earth is eliminated.

2. The method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle according to claim 1, characterized in that: When executing step S12, the geomagnetic field vector of each position is calculated using the IGRF model.

3. The method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle according to claim 1, characterized in that: Before executing step S1, the position data of each radar in the radar array is obtained and stored in a one-to-one correspondence according to the labels.

4. The method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle according to claim 1, characterized in that: Before executing step S24, the signal correlation quality value is preset in advance.

5. The method for obtaining spatial distribution characteristics of ionospheric inhomogeneities based on the interference principle according to claim 1, characterized in that: The method further comprises step S4: projecting the echo signal into a three-dimensional coordinate system to visualize the spatial position of the inhomogeneous body.

Images