Scattering of Short Waves in Anisotropic Ionosphere and Its Method for Predicting and Verifying Field Strength

Abstract

The present invention belongs to the field of shortwave technology, and discloses a method for shortwave scattering in an anisotropic ionosphere and verification of its field strength prediction. The present invention mainly conducts computational analysis on the influence of the anisotropy of the ionosphere on radio wave propagation, and conducts research on three aspects: model establishment, algorithm derivation, scattering characteristic calculation, and field strength prediction. First, through the structural analysis of the ionosphere, the advantages and disadvantages of various models are summarized, an anisotropic ionosphere model is established, and the calculation method is derived; then, typical frequency bands of military communication, namely very long wave and short wave, are selected to study their scattering characteristics and propagation laws in the anisotropic ionosphere; finally, based on the anisotropic ionosphere scattering model, the median value of the skywave field strength is predicted and verified. The results show that the algorithm of the present invention is significantly closer to the measured data than the field strength prediction results of the statistical model, thereby verifying the accuracy of the anisotropic ionosphere model of the present invention.

Description

Technical Field

[0001] The present invention belongs to the technical field of shortwave, and particularly relates to a method for scattering of shortwave in an anisotropic ionosphere and prediction and verification of its field strength. Background Technique

[0002] Due to the short wavelength of high-frequency electromagnetic waves and the small variation of the ionosphere within one wavelength, the ray theory is commonly used in the propagation problem of HF in the ionosphere. Currently, the commonly used ray tracing is roughly divided into two types, namely analytical ray tracing and digital ray tracing.

[0003] An ionosphere model capable of obtaining an analytical solution of ray path parameters is a necessary condition for analytical ray tracing. This method usually uses theoretical ionosphere models, such as the QP ionosphere model and the QPS ionosphere model. This method has certain limiting conditions. First, the analytical method cannot analyze the influence of the geomagnetic field on propagation and is only applicable under the limiting conditions of spherical symmetry or simple inclination of the ionosphere. In summary, although this method is convenient for calculation, it is not applicable to non-uniform ionosphere models and the calculation accuracy is lacking. The other is digital ray tracing, whose advantage is that the calculation result is relatively accurate because it uses a numerical calculation method, but the defect is that the calculation amount of this method is so large that it is difficult to be used in practical engineering. Therefore, scholars have begun to study fast ray tracing methods to achieve a balance between calculation accuracy and calculation time. Generally, some parameters or calculation methods are simplified in the two-dimensional digital ray tracing method, and the geomagnetic field and collision effects are often ignored. If the inhomogeneity of the ionosphere is to be fully considered, it is necessary to solve the Haselgrove equation to achieve three-dimensional digital ray tracing.

[0004] In 2008, Liu Wen, Jiao Peinan et al. proposed the three-dimensional ray tracing technology of shortwave in the ionosphere. The calculation results show that whether the ray tracing method that ignores the influence of the geomagnetic field or does not consider the inhomogeneity of the ionosphere will affect the accuracy of shortwave propagation prediction. Especially for applications such as high-frequency radar positioning that are sensitive to accuracy, the calculation results will cause obvious deviations. In 2009, they proposed a fast algorithm to improve the calculation speed of numerical calculation. In 2012, Cheng Jianquan, Yang Yuhong et al. carried out a simulation study on the three-dimensional ray tracing technology of shortwave under geomagnetic field conditions and found that the geomagnetic field will affect the shortwave ray path, including the deviation direction and deviation amplitude.

[0005] High-frequency skywave propagation prediction is a field being studied in various countries, and there are many prediction methods, such as the Kazantsev method, the Beckmann semi-empirical method, the Australian method, etc. Currently, the most widely used high-frequency skywave prediction method is the prediction method in the ITU-Rp.533 recommendation. Systems such as the ITS HF Propagation in the United States and the Wrap spectrum management software system in Sweden are all based on the method of ITU-Rp.533 for improvement research. Domestic scientific research institutions represented by the China Institute of Radiowave Propagation also have certain research on shortwave propagation prediction models. For example, Zhang Xiuqiang et al. proposed an improved method for high-frequency frequency prediction based on the ITU-Rp.533 method, combined with the Chinese reference ionosphere. Comparing with the measured data proves that the prediction accuracy of this method is good.

[0006] The above various theoretical models analyze the changes in the morphological structure of the ionosphere. They are fast in calculation and small in occupancy, but the parameter accuracy is not high enough, and the inhomogeneity and time-variability of the ionosphere are not well reflected. To establish a higher-precision ionosphere model, this paper selects to obtain relatively accurate actual parameters based on the IRI empirical model, horizontally stratify the ionosphere to overcome the inhomogeneity in height, and explains the dielectric constant tensor of each layer of the anisotropic ionosphere, fully considering the influence of the geomagnetic field on radio wave propagation. Finally, a more realistic anisotropic horizontally stratified ionosphere model is established to obtain more accurate ionospheric scattering characteristics.

[0007] The analytical ray tracing method is based on an ionosphere model that obtains the analytical solution of the ray path parameters. This method usually uses theoretical ionosphere models, such as the QP ionosphere model and the QPS ionosphere model. This method has certain limitations. First, the analytical method cannot analyze the influence of the geomagnetic field on propagation and is only applicable under the limited conditions of spherical symmetry or simple tilt of the ionosphere. In summary, although this method is convenient for calculation, it is not applicable to non-uniform ionosphere models and the calculation accuracy is lacking. The other is digital ray tracing, which uses numerical calculation methods to make the calculation results relatively accurate, but the defect is that the calculation amount is so large that it is difficult to be used in actual engineering. Therefore, currently, scholars have begun to study fast ray tracing methods to achieve a balance between calculation accuracy and calculation time. This method generally simplifies some parameters or calculation methods on the basis of the two-dimensional digital ray tracing method. The most often ignored ones are the geomagnetic field and collision effects. To fully consider the inhomogeneity of the ionosphere, it is necessary to solve the Haselgrove equation to achieve three-dimensional digital ray tracing.

[0008] In 2008, Liu Wen, Jiao Peinan and others proposed the three-dimensional ray tracing technology for short-wave in the ionosphere. The calculation results show that the ray tracing method that ignores the influence of the geomagnetic field or the inhomogeneity of the ionosphere will have a great impact on the accuracy of short-wave propagation prediction. In 2012, Cheng Jianquan, Yang Yuhong and others carried out a simulation study on the three-dimensional ray tracing technology for short-wave under geomagnetic field conditions. The research found that the geomagnetic field will affect the short-wave ray path, including the deviation direction and deviation amplitude. It can be seen that if accurate results of electromagnetic scattering in the ionosphere are to be obtained, the inhomogeneity of the ionosphere and the influence of the geomagnetic field must be fully considered. However, the three-dimensional ray tracing technology has a huge amount of calculation and a complex calculation process, which greatly limits its application scope.

[0009] Through the above analysis, the problems and defects existing in the prior art are as follows:

[0010] The three-dimensional ray tracing technology has a huge amount of calculation and a complex calculation process, which greatly limits its application scope. Summary of the Invention

[0011] In view of the problems existing in the prior art, the present invention provides a method for scattering of short-wave in an anisotropic ionosphere and prediction and verification of its field strength.

[0012] The present invention is implemented as follows. A method for scattering of short-wave in an anisotropic ionosphere and prediction and verification of its field strength includes:

[0013] Step 1, through the structural analysis of the ionosphere, summarize the advantages and disadvantages of various models, establish an anisotropic ionosphere model and deduce the calculation method;

[0014] Step 2, select the typical bands of military communication, namely very low frequency and short-wave, and study their scattering characteristics and propagation laws in the anisotropic ionosphere;

[0015] Step 3, based on the anisotropic ionosphere scattering model, predict and verify the median value of the sky-wave field strength.

[0016] Further, the method for establishing the anisotropic ionosphere model:

[0017] z represents the ground height, and the xoy plane represents the horizontal starting plane; the angles with the x, y, and z axes are α, β, and γ respectively;

[0018] The ionosphere connection constant is

[0019]

[0020] The elements in the matrix are respectively:

[0021]

[0022] In the formula, ω is the frequency of the incident wave, ω0 is the plasma frequency, ωT is the magnetic rotation frequency, and υ is the collision frequency. Additionally, H0 is the intensity of the geomagnetic field, N0 is the electron density, me is the electron mass, and e is the charge. The values of N0 and υ can be queried through IRI, and there are

[0023] ω02 = (N0e2) / (meε0), ωT = (μ0eH0) / me(3);

[0024] Based on this model, the transfer matrix applicable to any anisotropic medium is derived according to the principle of the transfer matrix method.

[0025] Furthermore, the transfer matrix method:

[0026] There are n layers of dielectric materials; each layer is a homogeneous anisotropic medium, and its electromagnetic parameters can be expressed in tensor form: [εij], [μij] (i, j = 1, 2, 3); the electromagnetic parameters of each layer can be in any form different from each other; it is assumed that the thickness of each layer is equal; all are d; the electromagnetic wave is obliquely incident, the incident angle is θ, and the incident plane is the xoz plane; the eigen-equation of the electromagnetic field in the nth layer of material can be obtained:

[0027]

[0028] Here the matrix A is:

[0029]

[0030] where εij, μij (i, j = 1, 2, 3) are the electromagnetic parameters of this layer, and δ = sinθ;

[0031] Let the eigenvalues and eigenvectors of formula (4) be γ(M) and W(M) (4×4 matrix) respectively, where γ(M) = [γ(M)1, γ(M)2, γ(M)3, γ(M)4], γ(M)1 = -γ(M)3, γ(M)2 = -γ(M)4; the field distribution in the M-layer region can be written as:

[0032]

[0033] Here η = 120π, the elements of the diagonal array X(M) are X(M)(j, j) = exp(k0γ(M)j(z+(M - 1)d)), (j = 1, 2, 3, 4); the diagonal array G(j, j) = exp(k0(xδ)); u(M)1, v(M)1, u(M)2, v(M)2 are the amplitudes of the upper and lower waves of the TE wave and TM wave in material M respectively;

[0034] Similarly, the field distributions in the (M - 1)-layer and (M + 1)-layer regions can be obtained, and the field relationship between the two sub-interfaces of the M-layer can be established;

[0035] Q = W(M)·X(M)·W(M)-1·P(6)

[0036] The transfer matrix from layer 1 to layer N is given by

[0037] T = T(1)×T(2)×…T(N-1)×T(N)(7)

[0038] The eigenvectors in free space are as follows:

[0039]

[0040] where β = cosθ;

[0041] At z = 0, there is only a transmitted wave and no reflected wave; then, the relationship between the free space field at z = -Nd and the field at z = 0 is as follows:

[0042]

[0043] Here

[0044]

[0045] where F = W (0) -1 ·T·W (0) .

[0046] Define the following relationship

[0047]

[0048] The reflection matrix R can be obtained from equation (8):

[0049]

[0050] Furthermore, the R matrix represents the generalized reflection coefficient that includes multiple optical reflection processes.

[0051] Furthermore, the R11 is the reflection coefficient of the type I wave reflected into another type I wave.

[0052] Furthermore, the R22 is the reflectivity of the type I wave reflected into another type I wave; R12 and R21 are the reflection coefficients of the type I wave reflected into the type II wave and the type II wave reflected into the type I wave, respectively; these coefficients capture the coupling characteristics between the type I wave and the type II wave.

[0053] Another object of the present invention is to provide a system for predicting and verifying the scattering and field strength of short waves in the anisotropic ionosphere, including:

[0054] A model establishment module, which is used to summarize the advantages and disadvantages of various models through the structural analysis of the ionosphere, establish an anisotropic ionosphere model and deduce the calculation method;

[0055] A selection module, which is used to select typical bands of military communication, namely very low frequency and short wave, and study their scattering characteristics and propagation laws in the anisotropic ionosphere;

[0056] A prediction and verification module, which is used to predict and verify the median value of the sky wave field strength based on the anisotropic ionosphere scattering model.

[0057] Another object of the present invention is to provide a computer device, which includes a memory and a processor. When the computer program stored in the memory is executed by the processor, the processor executes the steps of the method for scattering of short waves in the anisotropic ionosphere and prediction and verification of its field strength.

[0058] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which when executed by a processor, causes the processor to execute the steps of the method for scattering of short waves in the anisotropic ionosphere and prediction and verification of its field strength.

[0059] Another object of the present invention is to provide an information data processing terminal, which is used to implement the system for scattering of short waves in the anisotropic ionosphere and prediction and verification of its field strength.

[0060] Combined with the above technical solutions and solved technical problems, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0061] First, the present invention constructs a more scientific anisotropic ionosphere structure model based on a hierarchical idea, conducts scattering characteristic calculation and analysis for different short wave propagation application scenarios such as diurnal variation, seasonal variation, different incident angles, different latitudes and different propagation directions, and obtains a series of electromagnetic wave propagation laws that are closer to the actual effect, providing a good reference value for guiding actual short wave communication.

[0062] The present invention mainly conducts computational analysis on the influence of the anisotropy of the ionosphere on radio wave propagation, and conducts research on three aspects: model establishment, algorithm derivation, scattering characteristic calculation, and field strength prediction. First, through the structural analysis of the ionosphere, the advantages and disadvantages of various models are summarized, and an anisotropic ionosphere model is established and the calculation method is derived; then, the typical frequency bands of military communication, namely very low frequency and short wave, are selected to study their scattering characteristics and propagation laws in the anisotropic ionosphere; finally, based on the anisotropic ionosphere scattering model, the median value of the sky wave field strength is predicted and verified. The results show that the algorithm of the present invention is significantly closer to the measured data than the field strength prediction results of the statistical model, thus verifying the accuracy of the anisotropic ionosphere model of the present invention.

[0063] Second, the technical problems of the existing technologies solved by the present invention are mainly reflected in the scattering of short waves in the anisotropic ionosphere and the accuracy and reliability of their field strength prediction. The existing ionosphere models and field strength prediction methods often rely on simplified assumptions or specific application scenarios, and fail to fully consider the anisotropic characteristics of the ionosphere and the influence of complex environmental factors on short wave propagation. Therefore, there are often large errors and uncertainties in practical applications.

[0064] By deeply analyzing the structural characteristics and scattering mechanisms of the ionosphere, the present invention establishes a more accurate anisotropic ionosphere model and derives a calculation method applicable to this model. This model can more accurately describe the anisotropic characteristics of the ionosphere, as well as the scattering and propagation laws of short waves therein. Based on this model, the present invention can more reliably predict the median value of the sky wave field strength, providing more powerful support for military communication and other related applications.

[0065] The significant technological advancements obtained by the present invention are mainly reflected in the following aspects:

[0066] 1. Improved accuracy of field strength prediction: By considering the anisotropic characteristics of the ionosphere and complex environmental factors, the present invention can more accurately predict the field strength distribution of short waves in the ionosphere, reducing prediction errors.

[0067] 2. Broadened application scenarios: The present invention is not only applicable to the field of military communication, but can also be widely applied to other fields such as satellite communication and remote sensing detection, providing more reliable ionosphere scattering and field strength prediction methods for these fields.

[0068] 3. Promoted the development of ionosphere research: The embodiments of the present invention not only provide a practical prediction and verification method, but also provide new ideas and methods for ionosphere research, helping to promote the further development of the ionosphere research field.

[0069] The present invention has achieved remarkable technological progress by solving the problems of short-wave scattering and field strength prediction in the anisotropic ionosphere, providing strong support for the development and application of related fields.

[0070] Third, the present invention provides a method for verifying the scattering of short waves in the anisotropic ionosphere and its field strength prediction, especially the details of establishing the anisotropic ionosphere model and the transfer matrix method. Here, the main descriptions are about mathematical modeling and simulation methods, which involve the prediction and analysis of the propagation of electromagnetic waves in complex media.

[0071] 1) Establishment of the anisotropic ionosphere model:

[0072] The model takes the ground height \(z\) and the horizontal starting plane \(xoy\) as references.

[0073] The parameters and states of the ionosphere are defined by the angles \(\alpha\), \(\beta\), \(\gamma\) with the coordinate axes. The physical constants (contact constants) of the ionosphere, the electron density \(N_0\), the collision frequency \(\nu\), the geomagnetic field strength \(H_0\), etc., can all be obtained through specific physical formulas and existing databases (such as IRI). Parameters such as the incident wave frequency, plasma frequency, and magnetic rotation frequency are calculated by formulas, laying a foundation for the application of the transfer matrix method.

[0074] 2) Transfer matrix method:

[0075] Consider \(n\) layers of dielectric material layers with different electromagnetic properties. Each layer is a homogeneous anisotropic medium, and its parameters are represented by the electromagnetic parameter tensors \([ε_{ij}]\), \([μ_{ij}]\). Assuming that the thickness of each layer of material is the same and the electromagnetic wave is obliquely incident at a specific angle. By establishing the eigen-equations and eigenvalues / vectors of the electromagnetic field of each layer of material, the field distribution within the layer can be obtained, and then the field relationship between layers can be established to form a complete transfer matrix.

[0076] 3) Technological progress and problem-solving:

[0077] The present invention accurately describes the propagation and scattering phenomena of electromagnetic waves in the anisotropic ionosphere through a mathematical model. The present invention provides a systematic prediction method, which can be used to analyze and verify the electromagnetic wave propagation characteristics in applications such as short-wave communication and radar detection. The technical method of the present invention not only enhances the prediction ability of the theoretical model but also provides a scientific basis for practical engineering applications. The present invention has important application values in the fields of communication, remote sensing, radar, etc., and can help engineers and researchers better understand and predict the behavior of electromagnetic waves in the anisotropic ionosphere. Description of the Drawings

[0078] Figure 1It is a flow chart of the method for scattering of short waves in an anisotropic ionosphere and verification of its field strength prediction provided by an embodiment of the present invention.

[0079] Figure 2 It is a structural block diagram of the system for scattering of short waves in an anisotropic ionosphere and verification of its field strength prediction provided by an embodiment of the present invention.

[0080] Figure 3 It is a horizontal multi-layer anisotropic structure diagram of the ionosphere model provided by an embodiment of the present invention.

[0081] Figure 4 It is a structural diagram of an anisotropic horizontal layered multi-layer medium provided by an embodiment of the present invention.

[0082] Figure 5 It is a frequency curve diagram of R11 before and after introducing the geomagnetic field provided by an embodiment of the present invention.

[0083] Figure 6 It is a frequency curve diagram of R11 before and after introducing the geomagnetic field provided by an embodiment of the present invention.

[0084] Figure 7 It is a curve diagram of the electron concentration distribution in a certain place provided by an embodiment of the present invention.

[0085] Figure 8 It is an analysis diagram of the influence of the diurnal and seasonal variations of the ionosphere on the reflection coefficient provided by an embodiment of the present invention.

[0086] Figure 9 It is an analysis diagram of the influence of the incident angle on the reflection coefficient provided by an embodiment of the present invention.

[0087] Figure 10 It is an analysis diagram of the influence of DIP on the reflection coefficient provided by an embodiment of the present invention.

[0088] Figure 11 It is an analysis diagram of the influence of the radio wave propagation direction on the reflection coefficient provided by an embodiment of the present invention.

[0089] Figure 12 It is a flow chart of experimental verification provided by an embodiment of the present invention.

[0090] Figure 13 It is a comparison diagram of the measured and predicted MUF in May and June provided by an embodiment of the present invention.

[0091] Figure 14 It is a schematic diagram of the radio wave propagation path of the scattering model provided by an embodiment of the present invention.

[0092] Figure 15 It is a schematic diagram of the distribution of detection stations provided by an embodiment of the present invention.

[0093] Figure 16It is the original data graph of two detection links provided by the embodiments of the present invention.

[0094] Figure 17 It is a schematic diagram of the field strength calculation result of the first link in May provided by the embodiments of the present invention.

[0095] Figure 18 It is a schematic diagram of the field strength calculation result of the first link in June provided by the embodiments of the present invention.

[0096] Figure 19 It is a schematic diagram of the field strength calculation result of the second link in May provided by the embodiments of the present invention.

[0097] Figure 20 It is a schematic diagram of the field strength calculation result of the second link in June provided by the embodiments of the present invention.

[0098] Figure 21 It is a comparison graph of the field strength prediction errors between the scattering model and the reference model provided by the embodiments of the present invention. Detailed implementation manners

[0099] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0100] As Figure 1 shown, a method for scattering of short waves in an anisotropic ionosphere and verification of its field strength prediction provided by the embodiments of the present invention includes the following steps:

[0101] S101, through the structural analysis of the ionosphere, the advantages and disadvantages of various models are summarized, and an anisotropic ionosphere model is established and the calculation method is derived;

[0102] S102, select typical bands of military communication, namely very long waves and short waves, and study their scattering characteristics and propagation laws in the anisotropic ionosphere;

[0103] S103, based on the anisotropic ionosphere scattering model, predict and verify the median value of the sky wave field strength.

[0104] The method for scattering of short waves in an anisotropic ionosphere and verification of its field strength prediction provided by the present invention mainly focuses on aspects such as the characteristics of the ionosphere, the selection of bands, and the prediction and verification of field strength.

[0105] First, the ionosphere is a complex medium, and its properties exhibit anisotropy at different frequency bands and conditions. This anisotropy directly affects the behavior of electromagnetic waves propagating in it. Therefore, in step S101, by deeply analyzing the structure of the ionosphere, the advantages and disadvantages of different models can be summarized, and a more accurate anisotropic ionosphere model can be established based on these analyses. This model not only considers the physical properties of the ionosphere but also combines the mathematical description of the propagation of electromagnetic waves in it, thereby deriving a calculation method applicable to the anisotropic ionosphere.

[0106] Next, in step S102, the very low frequency (VLF) and short wave bands commonly used in military communications are selected for research. This is because these bands have important application values in military communications, and at the same time, their propagation characteristics in the anisotropic ionosphere are also relatively complex. By studying the scattering characteristics and propagation laws of these bands, a deeper understanding of the behavior of electromagnetic waves in the ionosphere can be obtained, providing a basis for subsequent field strength prediction verification.

[0107] Finally, in step S103, based on the previously established anisotropic ionosphere scattering model, the median value of the skywave field strength is predicted and verified. The core of this step is to use the model to simulate the propagation process of electromagnetic waves in the ionosphere and predict the median value of the field strength. To verify the accuracy of this prediction, it is also necessary to compare it with actual observation data. If the prediction result is consistent with the actual data, it indicates that the established model and calculation method have high reliability; if not, the model and calculation method need to be further corrected and optimized.

[0108] The method for scattering of short waves in an anisotropic ionosphere and prediction and verification of its field strength provided by the present invention is a systematic and scientific process. It combines knowledge in multiple aspects such as the physical properties of the ionosphere, the propagation laws of electromagnetic waves, and mathematical models, aiming to more accurately predict and verify the behavior of electromagnetic waves in the ionosphere. This has important application values in fields such as military communications and satellite communications.

[0109] The method for establishing an anisotropic ionosphere model provided by the embodiments of the present invention:

[0110] z represents the ground height, and the xoy plane represents the horizontal starting plane; the angles with the x, y, and z axes are α, β, and γ respectively;

[0111] The ionosphere contact constant is

[0112]

[0113] The elements in the matrix are respectively:

[0114]

[0115] In the formula, ω is the frequency of the incident wave, ω0 is the plasma frequency, ωT is the magnetic rotation frequency, and υ is the collision frequency; in addition, H0 is the intensity of the geomagnetic field, N0 is the electron density, me is the electron mass, and e is the charge; the values of N0 and υ can be queried through IRI, and there is

[0116] ω02 = (N0e2) / (meε0), ωT = (μ0eH0) / me(3);

[0117] Based on this model, the transfer matrix applicable to any anisotropic medium is derived according to the principle of the transfer matrix method.

[0118] The transfer matrix method provided by the embodiments of the present invention:

[0119] There are n layers of dielectric materials; each layer is a homogeneous anisotropic medium, and its electromagnetic parameters can be expressed in tensor form: [εij], [μij] (i, j = 1, 2, 3); the electromagnetic parameters of each layer can be in any form different from each other; it is assumed that the thickness of each layer is equal; all are d; the electromagnetic wave is obliquely incident, the incident angle is θ, and the incident plane is the xoz plane; the eigen-equation of the electromagnetic field in the nth layer of material can be obtained:

[0120]

[0121] Here the matrix A is:

[0122]

[0123] Where εij, μij (i, j = 1, 2, 3) are the electromagnetic parameters of this layer, and δ = sinθ;

[0124] Let the eigenvalues and eigenvectors of formula (4) be γ(M) and W(M) (4×4 matrix) respectively, where γ(M) = [γ(M)1, γ(M)2, γ(M)3, γ(M)4], γ(M)1 = -γ(M)3, γ(M)2 = -γ(M)4; the field distribution in the M-layer region can be written as:

[0125]

[0126] Here η = 120π, the elements of the diagonal array X(M) are X(M)(j, j) = exp(k0γ(M)j(z+(M - 1)d)), (j = 1, 2, 3, 4); the diagonal array G(j, j) = exp(k0(xδ)); u(M)1, v(M)1, u(M)2, v(M)2 are the amplitudes of the upper and lower waves of the TE wave and TM wave in material M respectively;

[0127] Similarly, the field distributions in the (M-1)th and (M+1)th layer regions can be obtained, and the field relationship between the two sub-interfaces of the Mth layer can be established;

[0128] Q = W(M)·X(M)·W(M)-1·P(6)

[0129] The transfer matrix from layer 1 to layer N is given by the following formula

[0130] T = T(1)×T(2)×…T(N-1)×T(N)(7)

[0131] The eigenvectors in free space are as follows:

[0132]

[0133] where β = cosθ;

[0134] At z = 0, there is only a transmitted wave and no reflected wave; then, the relationship between the free space field at z = -Nd and the field at z = 0 is as follows:

[0135]

[0136] Here

[0137]

[0138] where F = W (0) -1 ·T·W (0) .

[0139] Define the following relationship

[0140]

[0141] The reflection matrix R can be obtained from equation (8):

[0142]

[0143] The R matrix provided by the embodiments of the present invention represents the generalized reflection coefficient including multiple optical reflection processes.

[0144] The R11 provided by the embodiments of the present invention is the reflection coefficient of the I-type wave reflected into another I-type wave.

[0145] The R22 provided by the embodiments of the present invention is the reflectivity of the I-type wave reflected into another I-type wave; R12 and R21 are respectively the reflection coefficients of the I-type wave reflected into the II-type wave and the II-type wave reflected into the I-type wave; these coefficients capture the coupling characteristics between the I-type wave and the II-type wave.

[0146] As Figure 2As shown in the figure, a system for short-wave scattering in an anisotropic ionosphere and its field strength prediction and verification provided by an embodiment of the present invention includes:

[0147] A model establishment module, which is used to summarize the advantages and disadvantages of various models through the structural analysis of the ionosphere, establish an anisotropic ionosphere model, and deduce the calculation method;

[0148] A selection module, which is used to select typical bands of military communication, namely very low frequency and short wave, and study their scattering characteristics and propagation laws in the anisotropic ionosphere;

[0149] A prediction and verification module, which is used to predict and verify the median value of the sky-wave field strength based on the anisotropic ionosphere scattering model.

[0150] Another object of the present invention is to provide a computer device, which includes a memory and a processor. When a computer program stored in the memory is executed by the processor, the processor executes the steps of the method for short-wave scattering in an anisotropic ionosphere and its field strength prediction and verification.

[0151] Another object of the present invention is to provide a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of the method for short-wave scattering in an anisotropic ionosphere and its field strength prediction and verification.

[0152] Another object of the present invention is to provide an information data processing terminal, which is used to implement the system for short-wave scattering in an anisotropic ionosphere and its field strength prediction and verification.

[0153] Specific implementation of the present invention:

[0154] 1. The present invention proposes a calculation method for short-wave ionospheric scattering based on the transmission matrix of a complex anisotropic multi-layer medium. First, according to the characteristic that the electron density of the ionosphere changes with height, the ionosphere is divided into several horizontal thin layers (the electron density within each thin layer is approximately uniform), the ionosphere is constructed as a multi-layer horizontal anisotropic stratified structure, and the electromagnetic scattering characteristics of short waves in the ionosphere are calculated using the transmission matrix of the anisotropic multi-layer medium. Through comparison, it is found that the calculation results of this method are closer to the actual measured values than the traditional scattering calculation method based on an isotropic ionosphere.

[0155] 2. Multi-layer anisotropic ionosphere model

[0156] 2.1 Theoretical analysis

[0157] The electromagnetic parameters of the ionosphere are determined by the number of electrons in the ionosphere, and the number of electrons varies greatly with altitude. The electron spin caused by the presence of the geomagnetic field leads to the anisotropy of the ionospheric electromagnetic parameters. The entire ionosphere is considered a non-magnetic anisotropic medium with inhomogeneous electromagnetic parameters that vary with altitude.

[0158] Based on the above characteristics of the ionosphere, in order to accurately analyze the electromagnetic properties of the ionosphere, a horizontally stratified ionosphere model is first established, as Figure 3 shown. The geomagnetic field can be considered uniform in the altitude space of the entire ionosphere. In Figure 3 , z represents the ground altitude, and the xoy plane represents the horizontal starting plane. The bottom of the ionosphere lies in this plane, and the entire inhomogeneous anisotropic ionosphere is horizontally divided into several layers according to altitude. The altitude of each layer is much smaller than the wavelength. By using a reasonable number of layers, it is ensured that the electrons in each layer are uniform. According to the above model, the ionosphere can be regarded as composed of a set of multi-layer anisotropic media. Assume Figure 3 the direction of the geomagnetic field in

[0159] is arbitrary, and the angles with the x, y, and z axes are α, β, and γ respectively.

[0160]

[0161] The elements in the

[0162]

[0163] matrix are respectively

[0164] where ω is the frequency of the incident wave, ω0 is the plasma frequency, ωT is the magnetic rotation frequency, and υ is the collision frequency. In addition, H0 is the intensity of the geomagnetic field, N0 is the electron density, me is the electron mass, and e is the charge. The values of N0 and υ can be queried through IRI, and there are

[0165] ω02 = (N0e2) / (meε0), ωT = (μ0eH0) / me (3)

[0165] In the following sections, this model will be systematically discussed, and the transfer matrix applicable to any anisotropic medium will be derived based on the principle of the transfer matrix method.

[0166] 3. Transfer Matrix Method

[0167] 3.1. Theoretical Derivation

[0168] In the study of the anisotropic ionosphere, the electromagnetic propagation in anisotropic multi-layer structures has been deeply investigated. Since the electromagnetic parameters of anisotropic multi-layer media are represented as tensors, they bring complexity to the electromagnetic fields within the structure, making the calculation of their electromagnetic properties a challenging task. To address this complexity, the concept of the transfer matrix is introduced. This enables the careful derivation of the electromagnetic wave transmission characteristics of multi-layer structures including arbitrary anisotropic materials. This is achieved through the comprehensive analysis and calculation of various anisotropic media.

[0169] The general structure of an anisotropic horizontally layered multi-layer medium is as Figure 4 shown. There are n layers of dielectric materials. Each layer is a homogeneous anisotropic medium, and its electromagnetic parameters can be expressed in tensor form: [εij], [μij] (i, j = 1, 2, 3). The electromagnetic parameters of each layer can be in any form that is different from each other. For simplicity, it is assumed that the thickness of each layer is equal; all are d. The electromagnetic wave is obliquely incident, with the incident angle being θ, and the incident plane being the xoz plane. The eigen-equation of the electromagnetic field in the nth layer of material can be obtained

[0170]

[0171] where the matrix A is

[0172] where εij, μij (i, j = 1, 2, 3) are the electromagnetic parameters of this layer, and δ = sinθ.

[0173] Let the eigenvalues and eigenvectors of formula (4) be γ(M) and W(M) (4×4 matrices) respectively, where γ(M) = [γ(M)1, γ(M)2, γ(M)3, γ(M)4], γ(M)1 = -γ(M)3, γ(M)2 = -γ(M)4. The field distribution in the Mth layer region can be written

[0174]

[0175] where η = 120π, the elements of the diagonal array X(M) are X(M)(j, j) = exp(k0γ(M)j(z+(M - 1)d)), (j = 1, 2, 3, 4); the diagonal array G(j, j) = exp(k0(xδ)); u(M)1, v(M)1, u(M)2, v(M)2 are the amplitudes of the up and down waves of the TE wave and TM wave in material M respectively.

[0176] Similarly, the field distributions in the (M - 1)th layer and (M + 1)th layer regions can be obtained, and the field relationship between the two sub-interfaces of the Mth layer can be established;

[0177] Q = W(M)·X(M)·W(M)-1·P (6)

[0178] The field relationship between two interfaces is determined by the matrix T(M) = W(M)·X(M)·W(M)-1, and T(M) is called the transfer matrix of the M-layer medium. The transfer matrix establishes the connection between the fields on any two interfaces of a multi-layer structure. By simply multiplying the transfer matrices of each layer, the total transfer matrix of the multi-layer structure can be obtained. The transfer matrix from layer 1 to layer N is given by

[0179] T = T(1)×T(2)×…T(N - 1)×T(N) (7)

[0180] The eigenvectors in free space are as follows:

[0181]

[0182] where β = cosθ.

[0183] At z = 0, there is only a transmitted wave and no reflected wave. Then, the relationship between the free-space field at z = -Nd and the field at z = 0 is as follows:

[0184]

[0185] Here

[0186]

[0187] where F = W (0) -1 ·T·W (0) .

[0188] Define the following relationship

[0189]

[0190] The reflection matrix R can be obtained from equation (8):

[0191]

[0192] The matrix R represents the generalized reflection coefficient that includes multiple optical reflection processes. This matrix contains four complex elements. R11 is the reflection coefficient of the type-I wave reflected into another type-I wave, and R22 is the reflectivity of the type-I wave reflected into another type-I wave. R12 and R21 are the reflection coefficients of the type-I wave reflected into the type-II wave and the type-II wave reflected into the type-I wave, respectively. These coefficients capture the coupling characteristics between the type-I wave and the type-II wave.

[0193] 4. Analysis and Verification of Shortwave Electromagnetic Scattering in the Inhomogeneous Anisotropic Ionosphere

[0194] 4.1 Influence of Ionospheric Anisotropy on the Highest Frequency

[0195] Short waves are significantly affected by the high ionosphere, mainly reflected in the critical frequency, also known as the maximum reflection frequency. In this section, a uniform sharp-boundary F-layer ionosphere model is first established, and the traditional method and the method of the present invention are used to calculate the changes in the short-wave critical frequency before and after considering the influence of the geomagnetic field. In the traditional method, the critical frequency fc can be expressed as [XX]

[0196]

[0197] Here, Nmax is the maximum electron concentration at the ionosphere reflection point, generally located in the F2 layer. For the highest reflection frequency of obliquely incident radio waves is

[0198]

[0199] Here, θ0 is the angle of incidence.

[0200] Taking the statistical average of the ionospheric electrical parameters in the F2 layer during summer days, that is, Nmax = N e = 1×10^12 m -3 , the collision frequency v = 10 3 times / s, the angle of incidence is 30°, and the calculated maximum reflection frequency is 10.3 MHz. Subsequently, the average geomagnetic field of 5×10 -5 (unit) is introduced. At this time, the F2 layer shows uniform electromagnetic anisotropy, and its equivalent dielectric constant is calculated according to Section 2.1, and the algorithm of the present invention is used to calculate that the maximum reflection frequency is about 9.6 MHz. Figure 5 Is the comparison curve for the above calculations.

[0201] From Figure 5 It can be seen that, first, when only considering the isotropic uniform high ionosphere, the critical frequency calculated by using the transfer matrix method is basically consistent with the traditional method, which can verify the availability of this method in the short-wave frequency band to a certain extent; second, under the uniform sharp-boundary F-layer ionosphere model, the anisotropy of the ionosphere mainly affects the critical frequency. When considering the geomagnetic field, the maximum reflection frequency drops by about 0.8 MHz, indicating that the anisotropy of the ionosphere has a certain impact on short waves. In addition, it can be seen from the figure that before the frequency reaches the maximum reflection frequency, the modulus of the reflection coefficient approaches 1 because the collision frequency in the F layer is low and the absorption loss is small. It is concluded that only considering the simple high ionosphere cannot fully describe the propagation characteristics of short waves in the ionosphere.

[0202] 4.2 Calculation and comparison of simple ionospheric stratification

[0203] In this section, the entire ionosphere is simply divided into three layers: D, E, and F. The electrical parameters of each layer are uniform, and the empirical values during summer days are taken. Specifically, the thickness of the D layer is 30 km, and the collision frequencies at 60 km and 150 km are 10^7 s -1 、10^5 s-1 、103 s -1 , with electron densities of 2.5×10 9 m -3 、2×10 11 m -3 、1×10 12 m -3 respectively. The incident angle of the radio wave remains 30°, and the average value of the geomagnetic field is 5×10 -5 (unit). The reflection coefficients before and after introducing the geomagnetic field are calculated respectively using the method of the present invention.

[0204] Combined with Figure 5 and Figure 6 it can be seen that when considering the complete ionosphere, the modulus value of the reflection coefficient no longer approaches 1 infinitely, but the maximum reflection frequency changes little, indicating that different regions of the ionosphere have different effects on short-wave propagation. The D and E layers mainly affect the absorption loss, and the F layer mainly affects the maximum reflection frequency. At the same time, after establishing the complete ionosphere, the geomagnetic field not only affects the maximum reflection frequency, but also affects the amplitude of the reflection coefficient, that is, the absorption loss. When considering anisotropy, the absorption loss during the propagation of short waves in the ionosphere increases, and the maximum reflectable frequency decreases. The tremors at the end of the figure are due to numerical tremors that sometimes occur when the calculation results tend to 0 during matrix calculation, presenting a phenomenon of burrs in the curve graph.

[0205] 4.3 Precise Calculation of Electromagnetic Scattering in a Complex Anisotropic Ionosphere

[0206] To study the precise scattering characteristics of short waves in an anisotropic ionosphere model, in this section, a complete anisotropic ionosphere model is first established according to Section 2.1. The dielectric constants of each layer are obtained from Equation Error! Reference source not found., and the electrical parameters of each layer are from IRI-2016. Ionospheric data at heights of 60 - 400 km are taken, and the variation laws of the anti-transmission coefficient are calculated when parameters such as electron density, incident angle, geomagnetic dip angle, and radio wave propagation direction change, and the scattering laws of short waves in the anisotropic ionosphere are summarized and concluded, and the influence of the complex anisotropic ionosphere on short-wave propagation is summarized.

[0207] Taking a specific location as an example, the ionospheric electron densities at four typical time periods from 60 to 400 km in height at this location are obtained, namely summer day, summer night, winter day, and winter night, to analyze and compare the seasonality and diurnal variability of the ionosphere. As Figure 7 (a) shows, the electron concentration during the day is significantly higher than that at night, and the peak difference is close to an order of magnitude; as can be seen from 7(b), the peak electron concentration in summer is slightly higher than that in winter, and the peak height at night is higher than that during the day.

[0208] Taking the above electron concentration distribution as the electrical parameters of the anisotropic ionosphere model, calculate the reflection coefficient at this time. The collision frequency takes the statistical values of each layer, and the geomagnetic field strength takes 5×10-5. Compare the changes in the reflection coefficient between night and day. From Figure 8 (a), it can be seen that the critical frequency during the day is about 5.5Mhz higher than that at night. The reason is that the electron density during the day is significantly higher than that at night; the modulus value of the reflection coefficient at the critical frequency at night is about 0.1 higher than that during the day. The reason is that the ionosphere is more active during the day and the absorption loss is higher than at night. Compare the changes in the reflection coefficient between summer and winter. From Figure 8 (b), it can be seen that the critical frequency of the ionosphere in summer is about 3.5Mhz higher than that in winter, and the amplitudes of the reflection coefficients at the critical frequencies of the two are almost the same. The reason is that the electron density in summer is slightly higher than that in winter, but the difference in the ion activity of the ionosphere is not as large as that between day and night. In summary, the seasonal and diurnal variations of the ionosphere have an important impact on the propagation of short waves in it. The propagation effect in summer is higher than that in winter, and the propagation effect during the day is higher than that at night. The diurnal variation has a greater impact on short wave propagation than the seasonal variation. The reason is that the change in the direct solar radiation during the diurnal variation is higher than that during the seasonal variation.

[0209] Analyze the influence of the incident angle on the reflection and transmission coefficients. Take the incident angles as 0°, 30°, and 60° respectively. From Figure 9 it can be obtained that as the incident angle increases, the critical frequency increases, and the amplitude of the reflection coefficient at the critical frequency also decreases slightly. It can be obtained that in the anisotropic ionosphere model, as the incident angle changes significantly, the maximum reflection frequency increases, and the ionospheric absorption loss increases to a certain extent.

[0210] DIP is defined as the angle between the geomagnetic field and the vertical direction, that is, complementary to the geomagnetic inclination. Analyze the influence of DIP on the reflection coefficient. As Figure 10 shown, as the complementary angle of the geomagnetic inclination increases, the maximum reflection frequency of the horizontally polarized wave increases, and the law of the vertically polarized wave is opposite to it, that is, the anisotropy of the ionosphere caused by the geomagnetic field in the equatorial region has the least impact on short wave propagation, and the impact is the greatest in the polar regions.

[0211] The angle between the horizontal component of the geomagnetic field and the propagation direction is φ. When propagating eastward, φ = 90°, and when propagating northward, it is 0°. Combining Figure 11It can be seen that for horizontally polarized waves, the anisotropy has less impact on north-south propagation than on east-west propagation. For vertically polarized waves, the situation is opposite and the difference is more obvious. This is because when propagating in the north-south direction, the electric field direction is approximately parallel to the magnetic field direction, and the Lorentz force generated by the magnetic field on free electrons is close to 0. However, in practical applications, it is found that the east-west propagation effect is sometimes better than the north-south propagation. The reason is that the degree of ionospheric variation in the north-south direction of some propagation links is greater than that in the east-west direction. The ionospheric model of the present invention is horizontally stratified and insufficiently considers the horizontal inhomogeneity of the ionosphere, so there are limitations. Therefore, when selecting the propagation direction in actual communication, not only the influence of the geomagnetic field should be considered, but also the inhomogeneity of the ionosphere in the horizontal span of the link should be considered.

[0212] The burr phenomenon that appears in the curve of the reflection coefficient varying with frequency in this section is due to the numerical overflow and tremor phenomena generated by the computer when performing matrix cascade calculations, if the calculation amount is too large or the calculation results tend to infinity and zero.

[0213] In summary, considering the non-uniform anisotropy, the accurate scattering characteristics of short waves propagating in the ionosphere are analyzed. Factors such as diurnal variation, seasonal variation, different incident angles, different latitudes, and different propagation directions are carefully studied, and a series of propagation laws are obtained. These findings have important reference value for improving the practicability of short-wave communication.

[0214] 5. Comparative verification

[0215] To verify the accuracy of the anisotropic ionospheric scattering model and its algorithm established above, this chapter selects two links during a certain long voyage as the background, takes the measured data as the benchmark, predicts the median value of the sky-wave field strength, and compares the field strength prediction results of this algorithm with those of the field strength prediction based on the ITU-R P.533 statistical model. The verification process is as Figure 12 shown.

[0216] 5.1 Prediction of the median value of the sky-wave field strength

[0217] To complete the prediction of the sky-wave field strength of a certain point-to-point communication link, the working MUF of this link is required. Therefore, the higher the accuracy of frequency prediction, the more accurate the result of field strength calculation. It is necessary to select a suitable frequency prediction method. Currently, the most commonly used method is provided by Recommendation ITU-R P.533-12. On this basis, Zhang Xiuqiang, Wang Jian, etc. proposed an improved method for high-frequency frequency prediction. The author of this article went to the China Institute of Radiowave Propagation for research, obtained the authorization of some measured frequency data and predicted frequency data of the improved method, as well as some Chinese reference ionospheric data, which are used as the pre-input data for the field strength prediction method.

[0218] 5.1.1 Frequency prediction method

[0219] This improved high-frequency frequency prediction method is based on the methods in ITU-R P.533-12 and ITU-R P.1240 Recommendations, and introduces the Chinese reference ionospheric model and the Asia-Pacific ionosphere to form an improved high-frequency frequency prediction method. The method is introduced as follows:

[0220] The basic MUF of the E layer is calculated by the formula Error! Reference source not found.

[0221] E(D)MUF = M E ·foE(0.0.1)

[0222] Where:

[0223] M E = 3.94 + 2.80x - 1.70x 2 - 0.60x 3 + 0.96x 4 (0.0.2)

[0224] x = min(D / 1150 - 10.74) (0.0.3)

[0225] D = a 0 ×arccos[sinλ t sinλ r + cosλ t cosλ r cos(θ t - θ r ). (0.0.4)

[0226] In the formula: D is the great circle path distance, a 0 is the radius of the earth, in km; λ t is the latitude of the emission point, θ t is the longitude of the emission point, λ r is the latitude of the receiving point, θ r is the longitude of the receiving point, in rad.

[0227] The basic MUF of the F1 layer is calculated by the formula Error! Reference source not found.:

[0228] F1(D)MUF = M Fl ·foF1(0.0.5)

[0229] Where:

[0230] M F1 = J 0 - 0.01(J 0 - J 100 )R12 (0.0.6)

[0231] J 0 = 0.16 + 2.64×10 -3 D - 0.40×10 -6 D 2 (0.0.7)

[0232] J 100 = -0.52 + 2.69×10 -3 D - 0.39×10 -6 D 2 (0.0.8)

[0233] The basic MUF of the F2 layer in single-hop mode, when D ≤ d max , the radio wave propagation is in single-hop mode, the control point is the midpoint of the path, and the basic MUF of the F2 layer is calculated by formula (9):

[0234]

[0235] In the formula, f H is the electron gyrofrequency at a height of 300 km at the corresponding control point, with the unit of Mhz; C 3000 is the value of C when d is 3000 km d , and C d is calculated by formula Error! Reference source not found.; d max is the maximum skip distance of the F2 layer mode, with the unit of km, and is calculated by formula Error! Reference source not found.:

[0236] C d = 0.74 - 0.591Z - 0.424Z 2 - 0.090Z 3 + 0.088Z 4 + 0.181Z 5 + 0.096Z 6 (0.0.10)

[0237] Where:

[0238] Z = 1 - 2D / d max (0.0.11)

[0239]

[0240]

[0241] x = max(foF2 / foE2) (0.0.14)

[0242] The basic MUF calculation of the F2 layer in the multi-hop mode is as follows: When D > d max , the radio wave propagation is in the multi-hop mode, and the control point is at d 0 / 2 from the transmitting and receiving points. The basic MUF of the F2 layer is calculated by the formula Error! Reference source not found.:

[0243] F2(D)MUF = min[F2(d max )MUF 1 , F2(d max )MUF 2 (0.0.15)

[0244] Where: F2(d max )MUF 1 is the F2(dmax)MUF of the lowest-hop mode at the control point near the transmitting end; F2(d max )MUF 2 is the F2(dmax)MUF of the lowest-hop mode at the control point near the receiving end.

[0245] The working MUF is calculated by the formula Error! Reference source not found.:

[0246] MUF = max[E(D)MUF, F1(D)MUF, F2(D)MUF·R op (0.0.16)

[0247] Where R op is the ratio of the working MUF to the basic MUF of the F2 layer, as listed in Table 1.

[0248] Table 1 Ratio R of the working MUF to the basic MUF of the F2 layer op

[0249]

[0250] Table 2 Modes in the basic MUF and corresponding electron gyrofrequency calculations

[0251]

[0252]

[0253] Based on this algorithm, combined with the ionospheric basic parameter data of two air routes in the Chinese reference ionosphere from May 1 to June 30, 2015, the monthly median values of the predicted frequencies at each moment of the two air routes in these two months are obtained. The predicted MUF and the prediction results are compared with the observed results, and the results are asFigure 13 It can be seen that the prediction effect of the improved method is close to the measured data, and the predicted data is valid and can be used as the input data for subsequent field strength calculation.

[0254] 5.1.2 Median Field Strength Prediction Method

[0255] The skywave field strength prediction method of the reference statistical model used in this paper mainly combines the method provided by Recommendation ITU-R P.533-12 which is widely used currently. In the field strength prediction model after considering anisotropy, hereinafter referred to as the scattering model, the field strength prediction method mainly corrects the ionospheric absorption loss part in the recommendation and replaces the empirical formula with the reflection coefficient of the control point.

[0256] (1) Statistical Model Field Strength Prediction Method

[0257] For a path distance less than 7000 km, the median field strength is calculated as follows:

[0258] E w = 136.6 + P t + G t + 20 log f - L b (0.0.17)

[0259] where: f is the transmitting frequency (Mhz), P t is the transmitter power (dB), G t is the transmitting antenna power (dB), L b is the basic transmission loss of the path, which is calculated by the following formula:

[0260] L b = 32.45 + 20 log f + 20 log p′ + L i + L m + L g + L h + L z (0.0.18)

[0261] where p′ is the virtual slant range (km), L i is the absorption loss (), L m is the loss "above MUF", L g is the sum of the ground reflection losses, L h is the factor considering aurora and other signal losses, L z is other influences of skywave propagation not included in this method.

[0262] For a path exceeding 7000 km, the median field strength formula is

[0263]

[0264] where

[0265] E 0 = 139.6 - 20 log p′ (0.0.20)

[0266]

[0267] f H is the average value of the electron gyro frequencies determined at two control points, f M is determined by the MUF, f L is determined by the LUF.

[0268] (2) Scattering model field strength prediction method

[0269] Taking one-hop as an example, the radio wave propagation mode of the scattering model is as Figure 14 , the radio wave frequency takes the MUF at this time obtained by the improved high-frequency prediction algorithm in Section 5.1.2, and the radiation power density in the maximum radiation direction of the antenna is

[0270]

[0271] Combined with the direction function at this time r is the free space propagation distance from the emission point to the ionospheric incidence point, obtained according to the propagation mode, the ionospheric reflection point height, and the communication distance. Subsequently, the radiation field strength E at the ionospheric incidence point is obtained 1 ,

[0272]

[0273] As can be seen from subsection 4, the ionosphere in the scattering model is a horizontally stratified model. Therefore, it can be assumed that the propagation trajectory of the radio wave in the ionosphere is a symmetric parabola. At this time, the highest point of the parabola is denoted as the control point, and the ionosphere at this point is modeled as a horizontally stratified anisotropic ionosphere. The source of the electrical parameters is the Chinese reference ionosphere. Taking the horizontally polarized wave as the research object, the reflection coefficient R at this control point is calculated 11 , and the radiation field strength E of the radio wave at the ionospheric exit point at this time can be obtained 2 is

[0274] E 2 = E 1 |R 11 | (0.0.24)

[0275] After the radio wave has been reflected by the ionosphere, it passes through a section of free space loss and additional system loss to reach the receiving point. Finally, the field strength E at the receiving point is obtained 3 . The free space propagation loss is denoted as L 0 , and the additional system loss is denoted as L p , where

[0276] L 0= 32.45 + 20lgf + 20lgr (0.0.25)

[0277] Assume that the overall radio wave propagation path is symmetric. In the above formula, r is the free space propagation distance from the emergence point of the radio wave in the ionosphere to the receiving point, which can be of the same magnitude as the distance variable in Equation Error! Reference source not found., and both are denoted as r. L p The calculation method is shown in Recommendation ITU-R P.533-12. When there are multiple hops, it is necessary to recalculate the radio wave propagation path related parameters such as the incident angle and free space transmission distance, and the remaining methods are the same as for a single hop.

[0278] To sum up, the scattering model calculation method is obtained by combining the reflection coefficients calculated based on semi-empirical formulas and anisotropic ionosphere models. Compared with the statistical model, it takes into account the anisotropy and height inhomogeneity of the ionosphere, and the ionosphere model is more accurate. The following is a comparative analysis of its calculation results.

[0279] 5.2 Data Analysis and Verification

[0280] 5.2.1 Analysis of Measured Data

[0281] The transmitting stations and receiving stations of the measured data are as Figure 15 shown.

[0282] The detection data time is from May 1, 2015 to June 30, 2015. For the cir1 link, more than 1190 effective data were collected in May and June, and for the cir2 link, more than 1140 effective data were collected in May and June. The link schematic diagram is as Figure 15 shown. The specific content of the detection equipment and data is as follows:

[0283] (1) Detection frequency: 2 - 30 MHz

[0284] (2) Detection power: 5000 W

[0285] (3) Working mode: logarithmic sweep mode

[0286] (4) Detection signal type: pulse or coded form

[0287] (5) Detection data type: frequency-height diagram and spectrogram. After processing, the maximum observed frequency (MOF), maximum usable frequency (MUF), optimum working frequency (OWF), and highest probable frequency (HPF) can be obtained

[0288] The original figure obtained by the experimental equipment is as Figure 16 shown. UT is Coordinated Universal Time. The gray dots are noise points. After the equipment's judgment, processing will be carried out, and finally the formatted data will be obtained. It can be seen from the above figure that:

[0289] (1) The measured values have obvious diurnal variation patterns, which stem from the diurnal variation patterns of the ionospheric electron concentration. Moreover, the measured values at night are relatively stable because the solar radiation changes little at night and the ionosphere is relatively stable.

[0290] (2) The minimum value observed in Link 1 is higher than that in Link 2 because the propagation distance of Link 1 is 7100 km and that of Link 2 is 6400 km. The longer the propagation distance, the higher the required frequency.

[0291] (3) The patterns presented by the observed values in May and June show little difference, and this is the case for both links. The reason for the analysis is that the two months are relatively close to each other, and the seasonal variation degree of the ionosphere is small.

[0292] 5.2.2 Data Comparison and Verification

[0293] To fully verify the accuracy of the field strength prediction model considering anisotropy, taking the measured field strength as the benchmark, the prediction results of the scattering model are compared with the calculation results of the statistical model.

[0294] Starting from the propagation mechanism in the short-wave frequency band, since the propagation distances of the two links exceed 4000 km and the farthest reaches 7000 km, the multi-hop mode of the E layer is no longer considered, and only the multi-hop mode of the F2 layer is considered. The following specifically analyzes the field strength in the 1-hop - 6-hop modes of the F2 layer. They are the field strengths of multiple hop numbers obtained based on the statistical reference model, the field strengths of multiple hop numbers of the F2 layer calculated based on the ionospheric scattering model, and the field strengths of multiple hop numbers obtained by inverting the measured MUF.

[0295] Explanation of the situation: Since the HF communication radio on large ships currently uses automatic gain control technology, that is, it can automatically adjust the gain according to the signal strength, the received field strength information cannot truly represent the objective environmental field strength. Therefore, in this verification session, the field strength obtained by inverting and calculating based on MOF is used as the benchmark, that is, the "true field strength" close to the objective environment. The calculation process of obtaining the field strength by inverting the measured MOF is as follows: According to the actually detected MOF, the method provided in Recommendation ITU-R P.533 is used to invert and derive the calculation of the field strength of multiple hop numbers of the F2 layer. The field strength calculation results for the first link in May are as Figure 17 shown, the field strength calculation results for the first link in June are as Figure 18 shown, the field strength calculation results for the second link in May are as Figure 19 shown, and the field strength calculation results for the second link in June are as Figure 20As shown

[0296] Among them, the solid black line represents the multi-hop secondary field strength curve of the F2 layer obtained by inverting the measured MOF of the observed data (referred to as the measured curve), the red dashed line represents the multi-hop secondary field strength curve of the F2 layer obtained by calculating the ionospheric scattering model (referred to as the theoretical curve); the blue dotted line represents the field strength curve of the multi-hop secondary of the F2 layer obtained based on the statistical reference model (referred to as the statistical curve). From left to right, and from top to bottom, they are the comparisons of 1-hop, 2-hop, 3-hop, 4-hop, 5-hop, and 6-hop of the F2 layer respectively.

[0297] The trends of these three curves are basically the same. The theoretical curve is closer to the measured curve, and the error of the statistical curve is slightly larger. The statistical analysis of the errors in different hop modes is shown in Table 3. Comparison of the field strength prediction errors between the scattering model and the reference model is as Figure 21 。

[0298] Table 3 Analysis of field strength prediction errors

[0299] Tab.5.3 Error analysis of field strength prediction

[0300]

[0301] In the above table, the minimum error of the scattering model is 3.0167 dB. The minimum field strength error calculated by the statistical model is 5.5691 dB. Both are the results of the 6-hop mode, and the minimum is 7.1342 dB in the 1-hop and 2-hop modes. Thus, it can prove that the field strength calculation method of the scattering model mentioned in this paper is better than the statistical method.

[0302] For the scattering model, it can be seen from the mean error of the field strength of different hop numbers that the error is the largest at 1-hop. This is because the radio wave has the farthest lateral depth in the ionosphere at 1-hop. Due to the limitation of the horizontal stratification model, the horizontal inhomogeneity of the ionosphere is difficult to reflect, but it is still lower than the average error of the statistical model. As the number of hops increases, the error decreases significantly. In the commonly used 2-3 hops for long-distance short-wave propagation, the prediction accuracy is good.

[0303] To sum up, considering the anisotropy of the ionosphere, the scattering model has good accuracy in long-distance short-wave field strength prediction. This model is closer to the actual ionosphere and has certain reference significance for guiding short-wave communication.

[0304] Based on the anisotropic ionospheric scattering model, this chapter predicts the median value of the skywave field strength and conducts a comparative analysis by combining the data collected during the long-distance voyage. The propagation distances of the measured communication links 1 and 2 are 7100 km and 6400 km respectively, both belonging to the long-distance multi-hop propagation mode, which is of typical significance. In the field strength prediction, the average error of the scattering model is generally smaller than that of the statistical model. When the number of hops is 2 or more, the accuracy is better improved, proving that the field strength calculation method of the scattering model mentioned in this paper is superior to the statistical method. Therefore, the construction of the field strength prediction method based on the ionospheric scattering model can provide support for the evaluation of the shortwave communication effectiveness or field strength prediction during the long-distance voyage.

[0305] It should be noted that the embodiments of the present invention can be implemented through hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. Those of ordinary skill in the art can understand that the above devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code is provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuits of programmable hardware devices such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips and transistors, or field programmable gate arrays and programmable logic devices, can also be implemented by software executed by various types of processors, or can be implemented by a combination of the above hardware circuits and software such as firmware.

[0306] The above is only the specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention by those skilled in the art within the technical scope disclosed by the present invention shall be covered by the protection scope of the present invention.

Claims

1. A method for shortwave scattering in anisotropic ionosphere and its field intensity prediction and verification, characterized in that: The following steps are involved: Step 1: By analyzing the structure of the ionosphere, the advantages and disadvantages of various models are summarized, an anisotropic ionosphere model is established and the calculation method is derived; Step 2: Select typical bands for military communications, namely very long waves and short waves, and study their scattering characteristics and propagation laws in the anisotropic ionosphere; Step 3: Based on the anisotropic ionosphere model, the median sky wave field strength is predicted and verified; The method for establishing anisotropic ionosphere model: z represents the height from the ground, and xoy plane represents the horizontal starting plane; the angles with the x, y, and z axes are α, β, and γ, respectively; The ionospheric contact constant is The elements in the matrix are: Where ω is the frequency of the incident wave, ω0 is the plasma frequency, and ω T is the magnetic rotation frequency, υ is the collision frequency; in addition, H0 is the strength of the Earth's magnetic field, N0 is the electron density, me is the electron mass, and e is the charge; N The values ​​of 0 and υ are queried through IRI. oh0 2 =(N0e 2 ) / (meε0),ω T =(μ0eH0) / me(3); According to the principle of transfer matrix method, a transfer matrix applicable to any anisotropic medium is derived.

2. A system for shortwave scattering in anisotropic ionosphere and its field intensity prediction verification, which implements the method for shortwave scattering in anisotropic ionosphere and its field intensity prediction verification as claimed in claim 1, characterized in that: The shortwave scattering in the anisotropic ionosphere and its field intensity prediction verification system include: The model building module is used to analyze the structure of the ionosphere, summarize the advantages and disadvantages of various models, establish anisotropic ionosphere model and derive calculation methods; The selection module is used to select typical bands for military communications, namely very long waves and short waves, to study their scattering characteristics and propagation laws in the anisotropic ionosphere; The prediction and verification module is used to predict and verify the median sky wave field strength based on the anisotropic ionosphere model.

3. A computer device, characterized in that: The computer device includes a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method for verifying the scattering of short waves in the anisotropic ionosphere and its field intensity prediction as claimed in claim 1.

4. A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the steps of the method for verifying the scattering of shortwave in anisotropic ionosphere and its field intensity prediction as claimed in claim 1.

5. An information data processing terminal, characterized in that: The information data processing terminal is used to implement the shortwave scattering in the anisotropic ionosphere and its field intensity prediction and verification system as described in claim 2.

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