High-sea-condition evaporation waveguide radio wave propagation loss prediction method

Abstract

The invention relates to a high-sea-condition evaporation waveguide radio wave propagation loss prediction method, and belongs to the technical field of communication. The method comprises the following steps: firstly, establishing an evaporation waveguide refractive index profile by adopting a P-J model, and describing an atmospheric structure of an evaporation waveguide; establishing a three-dimensional wide-angle parabolic equation model and solving by using a distributed Fourier transform algorithm; setting an initial field and boundary conditions; fine modeling is carried out on the two-dimensional rough sea surface, and distribution of sea surface height fluctuation on a two-dimensional plane is simulated by adopting a linear filtering method; processing the irregular sea surface contour by using a topographic transformation method, and introducing a correction processing sea surface of a Miller-Brown model roughness factor; and finally, calculating radio wave propagation loss under the evaporation waveguide condition by calculating a radio wave propagation factor and an attenuation factor. According to the method, the radio wave propagation loss under the high sea condition can be predicted more accurately, and radio wave propagation research under the complex sea environment is supported.

Description

Technical Field

[0001] The invention belongs to the field of communication technology and relates to a method for predicting propagation loss of evaporative wave and conductive wave in high sea conditions. Background Art

[0002] The marine evaporation duct is an important electromagnetic wave propagation mechanism, which traps electromagnetic waves in the atmosphere at a certain height above the surface. Its structure is stable and has a wide coverage. The evaporation duct is one of the main mechanisms for over-the-horizon propagation in the marine troposphere environment and is of great significance to marine communications and navigation.

[0003] The existing parabolic equation full-wave analysis method has advantages in modeling and calculation, but it is difficult to accurately predict the radio wave propagation loss under high sea conditions. The existing method is mainly based on a flat sea surface model, but under high sea conditions, the waves are violent, which will cause stronger scattering and refraction effects on radio wave propagation. The existing method does not accurately describe the roughness of the sea surface and cannot truly simulate the radio wave propagation characteristics in a complex ocean environment.

[0004] The purpose of the present invention is to provide a method for predicting the propagation loss of evaporative wave conduction in high sea conditions, which can more accurately predict the propagation loss of radio waves under high sea conditions and support the research on radio wave propagation in complex marine environments. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for predicting radio wave propagation loss in an evaporative waveguide under high sea conditions. The present invention aims at predicting the radio wave propagation loss in an offshore evaporative waveguide environment, especially considering the influence of high sea conditions, and accurately describes the details of the sea surface roughness to achieve a true simulation of offshore radio wave propagation, and predicts the propagation loss under the condition of a complex and rough sea surface, so as to support the research on radio wave propagation in a complex marine environment.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The method comprises the following steps:

[0008] Step 1: Establish the refractive index profile of the evaporation duct: Use the Paulus-Jeske refractive index model (PJ model for short) in the model diagnosis method to describe the atmospheric structure of the evaporation duct;

[0009] Step 2: Establish and solve a three-dimensional wide-angle parabolic equation model: Consider the three-dimensional radio wave propagation problem on a flat ground. The ground satisfies the impedance boundary condition. Only the radio wave propagation along the positive direction of the x-axis is considered. The vector wave equation in the uniform passive region is obtained according to Maxwell's equations, and the differential operator Q is expressed by Feit-Fleck approximation. The wide-angle parabolic equation model (WideAngleParabolicEquationModel) expressed by the potential function can be obtained; the first-order partial differential equation is solved according to the PEM, and the distributed Fourier transform algorithm (split-stepfastfouriertransformed) is used to solve it;

[0010] Step 3: Initial field setting: Setting the two-dimensional initial field of the 3DPE model based on the current distribution function;

[0011] Step 4: Set boundary conditions: The upper boundary condition is obtained by multiplying two Cosine-taper window functions; the lower boundary condition is the impedance boundary condition;

[0012] Step 5: Detailed modeling of two-dimensional rough sea surface: Use linear filtering method to simulate the distribution of sea surface height fluctuations on a two-dimensional plane to establish a rough sea surface;

[0013] Step 6: Sea surface contour correction: Use terrain transformation method to process irregular sea surface contour, and introduce the correction of Miller-Brown model roughness factor to process the sea surface;

[0014] Step 7: Electric wave propagation loss under evaporation waveguide: Calculate the electric wave propagation loss under evaporation waveguide conditions.

[0015] Optionally, the step 1 is specifically as follows:

[0016] Steps: The PJ model is used to describe the atmospheric structure of the evaporation waveguide, and the corrected refractive index is expressed as:

[0017]

[0018] Where M 0 The refractive index of the bottom atmosphere of the waveguide is corrected, which is 330. 0 and z 0 is a constant, which can be c 0 =0.125, z 0 =0.00015. d is the waveguide height, when h d = 0m, M(z) represents standard atmosphere;

[0019] Optionally, the step 2 is specifically as follows:

[0020] Step 2-1: In the Cartesian coordinate system, the electric field vector and magnetic field vector for:

[0021]

[0022] Electric field vector and magnetic field vector Satisfies the vector wave equation:

[0023]

[0024] In the formula, k 0 represents the wave number in free space, the atmospheric refractive index is represented by n, and the electric field vector and magnetic field vector It has the characteristic of no divergence and can be used as electric vector potential and magnetic vector potential Representation; any field component can be obtained according to the relationship between the potential function and the field component. and The relationship between them is:

[0025]

[0026] In the formula, μ≈μ 0 Represents the magnetic permeability of the medium, ε=ε r ε 0 represents the dielectric constant of the medium, ω represents the angular frequency of the electromagnetic wave; the vector wave equation represented by the potential function in the uniform passive region is:

[0027]

[0028] If the scalar ψ e and ψ m Respectively represent vector and Any right-angle component of also satisfies the homogeneous scalar wave equation;

[0029] when and When e represents an arbitrary TM field. Assume Representing the TM field of z, we can get ψ e The relationship between the various components of the electromagnetic field:

[0030]

[0031] Among them, η 0 =120π is the free space wave impedance;

[0032] when and When mrepresents an arbitrary TE field. Assume Representing the TE field at z, we can get ψ m The relationship between the various components of the electromagnetic field:

[0033]

[0034] In a homogeneous passive region, any field can be expressed as a superposition of a TM field and a TE field, and we can set ψ = ψ e +ψ m is an arbitrary scalar field component, then ψ satisfies:

[0035]

[0036] use Substituting ψ, we get:

[0037]

[0038] In the formula, represents the transverse Laplace operator;

[0039] When the atmosphere is uniformly distributed This formula can be decomposed into:

[0040]

[0041] Where Q represents the pseudo differential operator. The pseudo differential operator Q is calculated using the Feit-Feck approximation method as follows:

[0042]

[0043] Substituting into the forward parabola equation we get:

[0044]

[0045] Step 2-2: Let the initial field ψ be ψ(x 0 ,y,z), and solve equation (12) to get:

[0046]

[0047] In the formula, Δx=xx 0 It indicates that the step is long;

[0048] Step 2-2: Separate the refractive index term and the diffraction index term to obtain:

[0049]

[0050] Step 2-3: Treat the refractive index term as a constant factor and perform a 2D Fourier transform on the remaining part in the (y,z) plane:

[0051]

[0052] The next step entry value can be obtained as follows:

[0053]

[0054] In the formula represents the component in the x direction, represents the two-dimensional inverse Fourier transform;

[0055] Step 2-4: For the propagation of radio waves in the space above the surface, ignore the creeping waves on the ground and objects, and only consider the influence of reflected waves, then Represents the superposition of the direct wave and the reflected wave at the step:

[0056]

[0057] Among them, Γ(k z ) represents the ground reflection coefficient, for TM z Wave and TE z wave, Γ(k z ) are:

[0058]

[0059] In the formula, Δ g Represents the normalized impedance of the earth's surface:

[0060]

[0061] Steps 2-5: Using the odd-even decomposition method, first decompose the field ψ into an odd and even part, substitute it into equation (17) for calculation, and then use the two-dimensional FFT technology to achieve fast calculation;

[0062] The field ψ can be decomposed into:

[0063]

[0064] Substituting into equation (17) and simplifying it, we can obtain:

[0065]

[0066] In the formula, and is e,o The two-dimensional Fourier transform in the (y,z) plane is:

[0067]

[0068] Step 2-6: Use the odd-even decomposition method to expand the calculation area above the original ground surface to the -z direction, which meets the upper and lower limit requirements of Fourier transform. FFT technology can be used in the (y, z) plane to speed up the calculation, thereby improving the operation efficiency. y and k z It can be expressed as:

[0069]

[0070] Optionally, the step three is specifically:

[0071] Step 3-1: The initial field of 3DPE is composed of a height of H t of Direction of current source The current distribution function is f e (y,z), then:

[0072]

[0073] In the formula, I 0 l is the current moment, usually 1, and δ(·) is the Dirac function. is the TM wave with respect to z, the electric vector potential

[0074] Step 3-2: According to the Maxwell equations in the active area, at the initial position:

[0075]

[0076] It can be seen that the distribution of the initial field in the upper half space (z ≥ 0) is:

[0077]

[0078] Step 3-3: Perform a two-dimensional Fourier transform on the initial field distribution to obtain:

[0079]

[0080] Step 3-4: Set up Direction, height is H t , the elevation angle of the main beam is α 0 Gaussian current source, the initial field component H y Distribution:

[0081]

[0082] In the formula, σ z is the standard deviation.

[0083] Steps 3-5: We can get:

[0084]

[0085]

[0086] Step 3-6: Set the elevation angle to 0, and you get:

[0087]

[0088] therefore:

[0089]

[0090] We can get:

[0091]

[0092] Steps 3-7: In k y Copy N in the direction y The matrix composed of columns is Again Performing a two-dimensional inverse Fourier transform can obtain the initial field of the 3DPE;

[0093] Optionally, the step 4 is specifically as follows:

[0094] Step 4-1: The absorption boundary condition makes the electromagnetic wave completely absorbed at the boundaries in the ±y and ±z directions. The Tukey window function needs to be set in the ±y and ±z directions:

[0095]

[0096] By multiplying the two window functions, we can get the absorbing boundary function of the three-dimensional parabolic equation (3DPE) on the (y,z) plane:

[0097] W(j,k)=w(j)·w(k),j=1:N y ,k=1:N z (36)

[0098] Step 4-2: In the impedance boundary condition, set is the unit vector of the outer normal of the boundary surface, Δg is the normalized impedance, then:

[0099]

[0100] For horizontal boundary surfaces, That is n x =n y =0,n z =1. We can get:

[0101]

[0102] For vertical surface boundaries, That is n z =0 and We can get:

[0103]

[0104] Optionally, the step five is specifically as follows:

[0105] Step 5-1: The wave spectrum is the power density function of the sea surface. The Fourier transform of the sea spectrum can obtain the sea surface fluctuation correlation function. In the polar coordinate system, the two-dimensional wave spectrum is in the form of:

[0106]

[0107] Where ψ(k) is the omnidirectional sea spectrum, is the direction function, and the size of k is Among them, k x and k y are the components of k along the x and y directions of the rectangular coordinate system, is the wave number direction angle, is the wind direction angle.

[0108] Step 5-2: Establish the Elfouhaily spectrum model. The specific form of the power spectrum function is:

[0109]

[0110] Among them, B L (k), B S (k) represent the long-wave spectrum and the short-wave spectrum, respectively.

[0111] Step 5-3: The long wave spectrum is:

[0112]

[0113] Where, the large-scale generalized equilibrium parameter is Ω=U 10 / c(k p ) is the dimensionless inverse wave age, and the wave number corresponding to the peak of the wave number spectrum is g is the acceleration due to gravity, which is 9.81 m / s 2 , c(k p ) is the phase velocity of the wave, U 10 is the wind speed at a height of 10m above the sea surface. If the ocean current speed and water depth are ignored, the wave phase velocity can be obtained. Long wave action function F p for:

[0114]

[0115] Where, L PM and J P The expression is:

[0116] L PM =exp[-1.25(k / k p ) -2 ] (44)

[0117] J p =γ B (45)

[0118] The other parameters in the formula are:

[0119]

[0120]

[0121]

[0122]

[0123] In the formula, Ω c is the peak inverse wave age, dimensionless wind zone X is the wind domain, X 0 =2.2×10 4 ;

[0124] Step 5-4: The shortwave spectrum is:

[0125]

[0126] Where, the small-scale generalized equilibrium parameter is:

[0127]

[0128] Wave number k corresponding to the peak value of the gravity-capillary wave in the curvature spectrum m ≈370rad / m, u f is the sea surface friction wind speed, and its relationship with the sea surface wind speed is:

[0129]

[0130] Among them, C 10 =(0.8+0.064u 10 )×10 -3 ;

[0131] Shortwave action function F m for:

[0132]

[0133] Step 5-5: In order to accurately describe the anisotropic characteristics of the wave spectrum, the directional function is introduced to reflect the changing directional characteristics of the waves and the energy change relationship of the waves of various frequency components caused by the wind direction above the sea surface. The Elfouhaily directional function is used, and the expression is:

[0134]

[0135] Where Δ(k) is called the adverse side wind proportional factor, which is related to wave speed, wind speed, etc.:

[0136]

[0137] Steps 5-6: Based on the Elfouhaily wave power spectrum function, a linear filtering method is used to generate the distribution of linear sea surface height fluctuations on the two-dimensional sea surface;

[0138] The mean sea surface is placed on the xOy plane formed by the x-axis and the y-axis. For the time-varying sea surface, the sea surface height fluctuation h at a certain time t generated by the linear filtering method is:

[0139]

[0140] To make the result of fast Fourier transform a real number, when m = -M / 2 or n = -N / 2, let F(k m ,k n )=0, other cases are:

[0141]

[0142] In the formula, * indicates taking the complex conjugate, L x and L y is the length of the sea surface sample in the x-axis and y-axis directions, M and N are the number of sampling points, i = -M / 2 ~ M / 2-1, j = -N / 2 ~ N / 2-1, and the sampling interval in the spatial domain is Δx = L x / M and Δy=L y / N, the sampling interval in the wavenumber domain is Δk x =2π / L x and Δk y =2π / L y , k m =mΔk x , k n =nΔk y , x=iΔx, y=jΔy, m'=-m, n'=-n, χ m,n =N m (0,1)+iN n (0,1) is a complex Gaussian random number.

[0143] Optionally, the step six is ​​specifically as follows:

[0144] Step 6-1: Use the dual-scale roughness model to divide the sea surface roughness into two parts and represent them separately, which can describe more details of the sea surface roughness and represent a more complex rough sea surface;

[0145] Step 6-2: In the large-scale roughness, the sea wave simulation method is used to represent it, and the sea wave height field is treated as terrain. For terrain transformation, the continuous shift terrain transformation method is used. Through coordinate transformation, a new coordinate system is established on the rough sea surface terrain, and then the parabolic equation coordinates are transformed to the plane terrain for solution;

[0146] The three-dimensional scalar wave equation is:

[0147]

[0148] Among them, (u, v, w) is the new coordinate system on the irregular terrain. The terrain height is w = T (u, w);

[0149] Take a point on the irregular terrain as the origin of the coordinate system and establish a new coordinate system (x, y, z) that satisfies:

[0150] x=u,y=w,z=vT(u) (60)

[0151] Let Φ(u,w,v)=φ(x,y,z), transform the wave equation in the (u,w,v) coordinate system into the form in the (x,y,z) coordinate system, and get the parabolic equation:

[0152]

[0153] The three-dimensional parabolic equation for radio wave propagation on three-dimensional terrain is to equate the effect of terrain on radio waves to a series of single-edge diffractions without considering the lateral slope, that is, Let φ=ψe iθ Substituting into formula (58) we can obtain:

[0154]

[0155] in, The phase factor θ(x,y,z) is to be determined.

[0156] Factoring the above equation, we can get the forward parabola equation as follows:

[0157]

[0158] Let phase factor θ(x,y,z) = K 0zT'+f(y)+f(x), mainly considering the effect of radio wave diffraction on irregular terrain, let f'(y)=0, we can get:

[0159]

[0160] Will

[0161]

[0162] in, Using the approximate formula Substituting into formula (61), we can obtain:

[0163]

[0164] To eliminate The first-order term, So: K = K 0 , let f'(x)=K 0 (-1+T' 2 ), the three-dimensional irregular terrain parabolic equation can be obtained as:

[0165]

[0166] The SSFT solution is:

[0167]

[0168] Step 6-3: Miller-Brown type roughness attenuation factor is:

[0169]

[0170] In the formula, I 0 represents the first kind of zero-order modified Bessel function, γ represents the Rayleigh roughness parameter, and the expression is:

[0171] γ=2k 0 h m sinθ (70)

[0172] In the formula, θ represents the angle between the incident angle and the horizontal plane, h m is the root mean square error of height fluctuation, and its expression is:

[0173]

[0174] U 10 Indicates the wind speed 10m above the sea surface;

[0175] Step Six-Four: For small-scale roughness, the roughness factor will be corrected on the basis of the Miller-Brown type roughness correction factor, using h Elfouhaliy to replace the root mean square error h m , and its expression is:

[0176]

[0177] In the formula, S(k) represents the Elfouhaliy sea wave spectrum;

[0178] Optionally, the specific content of Step Seven is as follows:

[0179] Step Seven-One: The radio wave propagation factor in three-dimensional space can be represented by the relative value of the actual field and the field in free space. Using the initial field H y calculate the attenuation factor of radio wave propagation. When excited by a Gaussian current source, the distribution of H y in free space is:

[0180]

[0181] Among them, represents the distance between the transmitter and the receiver, x and y represent the coordinates of the projection point of the receiving point on the (x,y) plane;

[0182] Step Seven-Two: The radio wave propagation attenuation factor relative to free space can be defined as:

[0183]

[0184] Among them, H y (x,y,z) represents the field strength at a certain position;

[0185] In the radio wave propagation over the sea, the loss mainly consists of two parts: free space propagation loss and the propagation loss of the medium itself. Therefore, the propagation loss calculation formula is:

[0186] L = 32.45 + 20lgf + 20lgr - L bf (75)

[0187] The beneficial effects of the present invention are as follows: Under high sea state conditions, by comprehensively considering factors such as the atmospheric structure of evaporation ducts, three-dimensional radio wave propagation characteristics, and sea surface roughness, the radio wave propagation loss in complex marine environments can be predicted more accurately; through the fine modeling of two-dimensional rough sea surfaces and the correction of sea surface profiles, the present invention can more realistically simulate sea surface conditions, improving the applicability and accuracy of the prediction model.

[0188] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0189] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0190] Figure 1 This is a schematic diagram of radio wave propagation;

[0191] Figure 2 is the cross-section of the evaporation waveguide;

[0192] Figure 3 Schematic diagram of the calculation space for three-dimensional parabolic equations;

[0193] Figure 4 is a three-dimensional window function graph;

[0194] Figure 5 The predicted loss diagram of the 3DPE model in the evaporation waveguide environment;

[0195] Figure 6 Figure 2 is the predicted loss diagram of the 3DPE model in the evaporative waveguide environment. DETAILED DESCRIPTION

[0196] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0197] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0198] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0199] like Figure 1 As shown, the method for predicting the propagation loss of evaporative wave and conductive wave in high sea conditions described in the present invention comprises the following steps:

[0200] Step 1: Establish the refractive index profile of the evaporation duct: Use the PJ refractive index model in the model diagnosis method to describe the atmospheric structure of the evaporation duct;

[0201] Figure 2 This is a cross-sectional view of the evaporation waveguide.

[0202] Steps: The PJ model is used to describe the atmospheric structure of the evaporation waveguide, and the corrected refractive index is expressed as:

[0203]

[0204] Where M 0 The refractive index of the waveguide bottom atmosphere is corrected, usually 330. 0 and z 0 is a constant, which can be c 0 =0.125, z 0 =0.00015. d is the waveguide height, when h d = 0m, M(z) represents standard atmosphere;

[0205] Step 2: Establish a three-dimensional wide-angle parabolic equation model and solve it: Consider the three-dimensional radio wave propagation problem on flat ground. The ground satisfies the impedance boundary condition. Only the radio wave propagation along the positive direction of the x-axis is considered. The vector wave equation in the uniform passive region is obtained according to Maxwell's equations, and the differential operator Q is expressed by Feit-Fleck approximation, and the WAPE expressed as a potential function can be obtained; the first-order partial differential equation is solved according to PEM, and the SSFT algorithm is used to solve it;

[0206] Figure 3 Schematic diagram of the calculation space for three-dimensional parabolic equations;

[0207] Step 2-1: In the Cartesian coordinate system, the electric field vector and magnetic field vector for:

[0208]

[0209] Electric field vector and magnetic field vector Satisfies the vector wave equation:

[0210]

[0211] In the formula, k 0 represents the wave number in free space, the atmospheric refractive index is represented by n, and the electric field vector and magnetic field vector It has the characteristic of no divergence and can be used as electric vector potential and magnetic vector potential Representation; any field component can be obtained according to the relationship between the potential function and the field component. and The relationship between them is:

[0212]

[0213] In the formula, μ≈μ 0 Represents the magnetic permeability of the medium, ε=ε r ε 0 represents the dielectric constant of the medium, ω represents the angular frequency of the electromagnetic wave; the vector wave equation represented by the potential function in the uniform passive region is:

[0214]

[0215] If the scalar ψ e and ψ m Respectively represent vector and Any right-angle component of also satisfies the homogeneous scalar wave equation;

[0216] when and When e represents an arbitrary TM field. Assume Representing the TM field of z, we can get ψ e The relationship between the various components of the electromagnetic field:

[0217]

[0218] Among them, η 0 =120π is the free space wave impedance;

[0219] when and When m represents an arbitrary TE field. Assume Representing the TE field at z, we can get ψ m The relationship between the various components of the electromagnetic field:

[0220]

[0221] In a homogeneous passive region, any field can be expressed as a superposition of a TM field and a TE field, and we can set ψ = ψ e +ψ m is an arbitrary scalar field component, then ψ satisfies:

[0222]

[0223] use Substituting ψ, we get:

[0224]

[0225] In the formula, represents the transverse Laplace operator;

[0226] When the atmosphere is uniformly distributed This formula can be decomposed into:

[0227]

[0228] Where Q represents the pseudo differential operator. The pseudo differential operator Q is calculated using the Feit-Feck approximation method as follows:

[0229]

[0230] Substituting into the forward parabola equation we get:

[0231]

[0232] Step 2-2: Let the initial field ψ be ψ(x 0 ,y,z), and solve equation (12) to get:

[0233]

[0234] In the formula, Δx=xx 0 It indicates that the step is long;

[0235] Step 2-2: Separate the refractive index term and the diffraction index term to obtain:

[0236]

[0237] Step 2-3: Treat the refractive index term as a constant factor and perform a 2D Fourier transform on the remaining part in the (y,z) plane:

[0238]

[0239] The next step entry value can be obtained as follows:

[0240]

[0241] In the formula represents the component in the x direction, represents the two-dimensional inverse Fourier transform;

[0242] Step 2-4: For the propagation of radio waves in the space above the surface, ignore the creeping waves on the ground and objects, and only consider the influence of reflected waves, then Represents the superposition of the direct wave and the reflected wave at the step:

[0243]

[0244] Among them, Γ(k z ) represents the ground reflection coefficient, for TM z Wave and TE z wave, Γ(k z ) are:

[0245]

[0246] In the formula, Δ g Represents the normalized impedance of the earth's surface:

[0247]

[0248] Steps 2-5: Using the odd-even decomposition method, first decompose the field ψ into an odd and even part, substitute it into equation (17) for calculation, and then use the two-dimensional FFT technology to achieve fast calculation;

[0249] The field ψ can be decomposed into:

[0250]

[0251] Substituting into equation (17) and simplifying it, we can obtain:

[0252]

[0253] In the formula, and is e,o The two-dimensional Fourier transform in the (y,z) plane is:

[0254]

[0255] Step 2-6: Use the odd-even decomposition method to expand the calculation area above the original ground surface to the -z direction, which meets the upper and lower limit requirements of Fourier transform. FFT technology can be used in the (y, z) plane to speed up the calculation, thereby improving the operation efficiency. y and k z It can be expressed as:

[0256]

[0257] Step 3: Initial field setting: Setting the two-dimensional initial field of the 3DPE model based on the current distribution function;

[0258] Step 3-1: The initial field of 3DPE is composed of a height of H t of Direction of current source The current distribution function is f e (y,z), then:

[0259]

[0260] In the formula, I 0 l is the current moment, usually 1, and δ(·) is the Dirac function. is the TM wave with respect to z, the electric vector potential

[0261] Step 3-2: According to the Maxwell equations in the active area, at the initial position:

[0262]

[0263] It can be seen that the distribution of the initial field in the upper half space (z ≥ 0) is:

[0264]

[0265] Step 3-3: Perform a two-dimensional Fourier transform on the initial field distribution to obtain:

[0266]

[0267] Step 3-4: Set up Direction, height is H t , the elevation angle of the main beam is α 0 Gaussian current source, the initial field component H y Distribution:

[0268]

[0269] In the formula, σ z is the standard deviation.

[0270] Steps 3-5: We can get:

[0271]

[0272]

[0273] Step 3-6: Set the elevation angle to 0, and you get:

[0274]

[0275] therefore:

[0276]

[0277] We can get:

[0278]

[0279] Steps 3-7: In k y Copy N in the direction y The matrix composed of columns is Again Performing a two-dimensional inverse Fourier transform can obtain the initial field of the 3DPE;

[0280] Step 4: Set boundary conditions: The upper boundary condition is obtained by multiplying two Cosine-taper window functions; the lower boundary condition is the impedance boundary condition;

[0281] Figure 4 is a three-dimensional window function graph;

[0282] Step 4-1: The absorption boundary condition makes the electromagnetic wave completely absorbed at the boundaries in the ±y and ±z directions. The Tukey window function needs to be set in the ±y and ±z directions:

[0283]

[0284] By multiplying the two window functions, we can get the absorbing boundary function of the three-dimensional parabolic equation (3DPE) on the (y,z) plane:

[0285] W(j,k)=w(j)·w(k),j=1:N y ,k=1:N z (36)

[0286] Figure 5 The predicted loss diagram of the 3DPE model in the evaporation waveguide environment; Figure 6 Figure 2 is the predicted loss diagram of the 3DPE model in the evaporative waveguide environment.

[0287] Step 4-2: In the impedance boundary condition, set is the unit vector of the outer normal of the boundary surface, Δg is the normalized impedance, then:

[0288]

[0289] For horizontal boundary surfaces, That is n x =n y =0,n z =1. We can get:

[0290]

[0291] For vertical surface boundaries, That is n z =0 and We can get:

[0292]

[0293] Step 5: Detailed modeling of two-dimensional rough sea surface: Use linear filtering method to simulate the distribution of sea surface height fluctuations on a two-dimensional plane to establish a rough sea surface;

[0294] Step 5-1: The wave spectrum is the power density function of the sea surface. The Fourier transform of the sea spectrum can obtain the sea surface fluctuation correlation function. In the polar coordinate system, the two-dimensional wave spectrum is in the form of:

[0295]

[0296] Where ψ(k) is the omnidirectional sea spectrum, is the direction function, and the size of k is Among them, k x and k y are the components of k along the x and y directions of the rectangular coordinate system, is the wave number direction angle, is the wind direction angle.

[0297] Step 5-2: Establish the Elfouhaily spectrum model. The specific form of the power spectrum function is:

[0298]

[0299] Among them, B L (k), B S (k) represent the long-wave spectrum and the short-wave spectrum, respectively.

[0300] Step 5-3: The long wave spectrum is:

[0301]

[0302] Where, the large-scale generalized equilibrium parameter is Ω=U10 / c(k p ) is the dimensionless inverse wave age, and the wave number corresponding to the peak of the wave number spectrum is g is the acceleration due to gravity, which is 9.81 m / s 2 , c(k p ) is the phase velocity of the wave, U 10 is the wind speed at a height of 10m above the sea surface. If the ocean current speed and water depth are ignored, the wave phase velocity can be obtained. Long wave action function F p for:

[0303]

[0304] Where, L PM and J P The expression is:

[0305] L PM =exp[-1.25(k / k p ) -2 ] (44)

[0306] J p =γ B (45)

[0307] The other parameters in the formula are:

[0308]

[0309]

[0310]

[0311]

[0312] In the formula, Ω c is the peak inverse wave age, dimensionless wind zone X is the wind domain, X 0 =2.2×10 4 ;

[0313] Step 5-4: The shortwave spectrum is:

[0314]

[0315] Where, the small-scale generalized equilibrium parameter is:

[0316]

[0317] Wave number k corresponding to the peak value of the gravity-capillary wave in the curvature spectrum m ≈370rad / m, u fis the sea surface friction wind speed, and its relationship with the sea surface wind speed is:

[0318]

[0319] Among them, C 10 =(0.8+0.064u 10 )×10 -3 ;

[0320] Shortwave action function F m for:

[0321]

[0322] Step 5-5: In order to accurately describe the anisotropic characteristics of the wave spectrum, the directional function is introduced to reflect the changing directional characteristics of the waves and the energy change relationship of the waves of various frequency components caused by the wind direction above the sea surface. The Elfouhaily directional function is used, and the expression is:

[0323]

[0324] Where Δ(k) is called the adverse side wind proportional factor, which is related to wave speed, wind speed, etc.:

[0325]

[0326] Steps 5-6: Based on the Elfouhaily wave power spectrum function, a linear filtering method is used to generate the distribution of linear sea surface height fluctuations on the two-dimensional sea surface;

[0327] The mean sea surface is placed on the xOy plane formed by the x-axis and the y-axis. For the time-varying sea surface, the sea surface height fluctuation h at a certain time t generated by the linear filtering method is:

[0328]

[0329] To make the result of the fast Fourier transform a real number, when m = -M / 2 or n = -N / 2, let F(k m ,k n )=0, other cases are:

[0330]

[0331] In the formula, * indicates taking the complex conjugate, L x and L y is the length of the sea surface sample in the x-axis and y-axis directions, M and N are the number of sampling points, i = -M / 2 ~ M / 2-1, j = -N / 2 ~ N / 2-1, and the sampling interval in the spatial domain is Δx = L x / M and Δy=L y / N, the sampling interval in the wavenumber domain is Δkx =2π / L x and Δk y =2π / L y , k m =mΔk x , k n =nΔk y , x=iΔx, y=jΔy, m'=-m, n'=-n, χ m,n =N m (0,1)+iN n (0,1) is a complex Gaussian random number.

[0332] Step 6: Sea surface contour correction: Use terrain transformation method to process irregular sea surface contour, and introduce the correction of Miller-Brown model roughness factor to process the sea surface;

[0333] Step 6-1: Use the dual-scale roughness model to divide the sea surface roughness into two parts and represent them separately, which can describe more details of the sea surface roughness and represent a more complex rough sea surface;

[0334] Step 6-2: In the large-scale roughness, the sea wave simulation method is used to represent it, and the sea wave height field is treated as terrain. For terrain transformation, the continuous shift terrain transformation method is used. Through coordinate transformation, a new coordinate system is established on the rough sea surface terrain, and then the parabolic equation coordinates are transformed to the plane terrain for solution;

[0335] The three-dimensional scalar wave equation is:

[0336]

[0337] Among them, (u, v, w) is the new coordinate system on the irregular terrain. The terrain height is w = T (u, w);

[0338] Take a point on the irregular terrain as the origin of the coordinate system and establish a new coordinate system (x, y, z) that satisfies:

[0339] x=u,y=w,z=vT(u) (60)

[0340] Let Φ(u,w,v)=φ(x,y,z), transform the wave equation in the (u,w,v) coordinate system into the form in the (x,y,z) coordinate system, and get the parabolic equation:

[0341]

[0342] The three-dimensional parabolic equation for radio wave propagation on three-dimensional terrain is to equate the effect of terrain on radio waves to a series of single-edge diffractions without considering the lateral slope, that is, Let φ=ψe iθ Substituting into formula (58) we can obtain:

[0343]

[0344] in, The phase factor θ(x,y,z) is to be determined.

[0345] Factoring the above equation, we can get the forward parabola equation as follows:

[0346]

[0347] Let phase factor θ(x,y,z) = K 0 zT'+f(y)+f(x), mainly considering the effect of radio wave diffraction on irregular terrain, let f'(y)=0, we can get:

[0348]

[0349] Will

[0350]

[0351] in, Using the approximate formula Substituting into formula (61), we can obtain:

[0352]

[0353] To eliminate The first-order term, So: K = K 0 , let f'(x)=K 0 (-1+T' 2 ), the three-dimensional irregular terrain parabolic equation can be obtained as:

[0354]

[0355] The SSFT solution is:

[0356]

[0357] Step 6-3: Miller-Brown type roughness attenuation factor is:

[0358]

[0359] In the formula, I 0 represents the first kind of zero-order modified Bessel function, γ represents the Rayleigh roughness parameter, and the expression is:

[0360] γ=2k 0h m sinθ (70)

[0361] In the formula, θ represents the angle between the incident angle and the horizontal plane, h m is the root mean square error of height fluctuation, and its expression is:

[0362]

[0363] U 10 Indicates the wind speed 10m above the sea surface;

[0364] Step 6-4: For small-scale roughness, the roughness factor will be corrected based on the Miller-Brown type roughness correction factor, using h Elfouhaliy Instead of the root mean square error h m , whose expression is:

[0365]

[0366] Where S(k) represents the Elfouhaliy wave spectrum;

[0367] Step 7: Electric wave propagation loss under evaporation waveguide: Calculate the electric wave propagation loss under evaporation waveguide conditions.

[0368] Step 7-1: The radio wave propagation factor in three-dimensional space can be expressed by the relative value of the actual field and the field in free space, with the initial field H y Calculate the attenuation factor of radio wave propagation. When excited by Gaussian current source, H y The distribution in free space is:

[0369]

[0370] in, Indicates the distance between the transmitter and the receiver x, y represent the coordinates of the projection point of the receiving point on the (x, y) plane;

[0371] Step 7-2: The attenuation factor of radio wave propagation relative to free space can be defined as:

[0372]

[0373] Among them, H y (x, y, z) represents the field strength at a certain location;

[0374] Step 7-3: The propagation loss of radio waves at sea is mainly composed of free space propagation loss and medium propagation loss. Therefore, the propagation loss calculation formula is:

[0375] L=32.45+20lgf+20lgr-L bf (75).

[0376] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for predicting the propagation loss of evaporative wave and conductive wave in high sea conditions, characterized by: The method comprises the following steps: Step 1: Establish the refractive index profile of the evaporation duct: Use the Paulus-Jeske refractive index model, namely the PJ model, in the model diagnosis method to describe the atmospheric structure of the evaporation duct; Step 2: Establish a three-dimensional wide-angle parabolic equation model and solve it: Consider the three-dimensional radio wave propagation problem on a flat ground. The ground satisfies the impedance boundary condition. Only the radio wave propagation along the positive direction of the x-axis is considered. The vector wave equation in the uniform passive region is obtained according to Maxwell's equations, and the differential operator Q is expressed by Feit-Fleck approximation to obtain a wide-angle parabolic equation model expressed by a potential function; solve the first-order partial differential equation according to PEM, and solve it using the distributed Fourier transform algorithm; Step 3: Initial field setting: Setting the two-dimensional initial field of the 3DPE model based on the current distribution function; Step 4: Set boundary conditions: The upper boundary condition is obtained by multiplying two Cosine-taper window functions; the lower boundary condition is the impedance boundary condition; Step 5: Detailed modeling of two-dimensional rough sea surface: Use linear filtering method to simulate the distribution of sea surface height fluctuations on a two-dimensional plane to establish a rough sea surface; Step 6: Sea surface contour correction: Use terrain transformation method to process irregular sea surface contour, and introduce the correction of Miller-Brown model roughness factor to process the sea surface; Step 7: Electric wave propagation loss under evaporation waveguide: Calculate the electric wave propagation loss under evaporation waveguide conditions.

2. The method for predicting propagation loss of evaporative waveguide in high sea conditions according to claim 1, characterized in that: The step 1 is specifically as follows: Steps: The PJ model is used to describe the atmospheric structure of the evaporation duct, and the corrected refractive index is expressed as: Where, M0 is the corrected refractive index of the bottom atmosphere of the waveguide, which is 330; c0 and z0 are constants, c0 = 0.125, z0 = 0.00015; h d is the waveguide height, when h d When =0m, M(z) represents standard atmosphere.

3. The method for predicting propagation loss of evaporative waveguide in high sea conditions according to claim 2, characterized in that: The step 2 is specifically as follows: Step 2-1: In the Cartesian coordinate system, the electric field vector and magnetic field vector for: Electric field vector and magnetic field vector Satisfies the vector wave equation: Where k0 represents the wave number in free space, the atmospheric refractive index is n, and the electric field vector and magnetic field vector It has the characteristic of no divergence, using electric vector potential and magnetic vector potential Representation; obtain any field component according to the relationship between the potential function and the field component; and The relationship between them is: In the formula, μ≈μ0 represents the magnetic permeability of the medium, ε=ε r ε0 represents the dielectric constant of the medium, ω represents the angular frequency of the electromagnetic wave; The vector wave equation represented by the potential function in a homogeneous passive region: If the scalar ψ e and ψ m Respectively represent vector and Any right-angle component of also satisfies the homogeneous scalar wave equation; when and When e represents an arbitrary TM field; let Denote the TM field for z, and we get ψ e The relationship between the various components of the electromagnetic field: Among them, η0 = 120π is the free space wave impedance; when and When m represents any TE field; let Denotes the TE field with respect to z, and we get ψ m The relationship between the various components of the electromagnetic field: In the homogeneous passive region, any field is represented as the superposition of TM field and TE field, assuming ψ = ψ e +ψ m is an arbitrary scalar field component, then ψ satisfies: use Substituting ψ, we get: In the formula, represents the transverse Laplace operator; When the atmosphere is uniformly distributed This formula decomposes into: Where Q represents the pseudo differential operator. The pseudo differential operator Q is calculated using the Feit-Feck approximation method as follows: Substituting into the forward parabola equation we get: Step 2-2: Assume the initial field ψ is ψ(x0,y,z), and solve equation (12) to obtain: In the formula, Δx=x-x0 represents the step length; Step 2-2: Separate the refractive index term and the diffraction index term to obtain: Step 2-3: Treat the refractive index term as a constant factor and perform a 2D Fourier transform on the remaining part in the (y,z) plane: The next step is to get the value of the field: In the formula represents the component in the x direction, represents the two-dimensional inverse Fourier transform; Step 2-4: For the propagation of radio waves in the space above the surface, ignore the creeping waves on the ground and objects, and only consider the influence of reflected waves, then Represents the superposition of the direct wave and the reflected wave at the step: Among them, Γ(k z ) represents the ground reflection coefficient, for TM z Wave and TE z wave, Γ(k z ) are: In the formula, Δ g Represents the normalized impedance of the earth's surface: Steps 2-5: Using the odd-even decomposition method, first decompose the field ψ into an odd and even part, substitute it into equation (17) for calculation, and then use the two-dimensional FFT technology to achieve fast calculation; The field ψ is decomposed into: Substituting into equation (17) and simplifying it, we get: In the formula, and is e,o The two-dimensional Fourier transform in the (y,z) plane is: Step 2-6: Use the odd-even decomposition method to expand the calculation area above the original surface to the -z direction to meet the upper and lower limit requirements of Fourier transform, and use FFT technology in the (y, z) plane to speed up the calculation and improve the operation efficiency; k after odd-even decomposition y and k z It is expressed as:

4. The method for predicting propagation loss of evaporative conductive wave in high sea conditions according to claim 3 is characterized by: The step three is specifically as follows: Step 3-1: The initial field of 3DPE is composed of a height of H t of Direction of current source The current distribution function is f e (y,z), then: Where I0l is the current moment of 1, δ(·) is the Dirac function; is the TM wave with respect to z, the electric vector potential Step 3-2: According to the active area Maxwell equation, at the initial position: The distribution of the initial field in the upper half space (z ≥ 0) is: Step 3-3: Perform a two-dimensional Fourier transform on the initial field distribution to obtain: Step 3-4: Set up Direction, height is H t , radiating a Gaussian current source with a main beam elevation angle of α0, and obtaining the initial field component H y Distribution: In the formula, σ z is the standard deviation; Steps 3-5: have to: Step 3-6: Set the elevation angle to 0, and you get: have to: Steps 3-7: In k y Copy N in the direction y The matrix composed of columns is Again Perform two-dimensional inverse Fourier transform to obtain the initial field of 3DPE.

5. The method for predicting propagation loss of evaporative conductive wave in high sea conditions according to claim 4, characterized in that: The step 4 is specifically as follows: Step 4-1: The absorption boundary condition makes the electromagnetic wave completely absorbed at the boundaries in the ±y and ±z directions. The Tukey window function needs to be set in the ±y and ±z directions: Multiplying the two window functions together gives the absorbing boundary function of the three-dimensional parabolic equation (3DPE) on the (y,z) plane: W(j,k)=w(j)·w(k),j=1:N y ,k=1:N z (36) Step 4-2: In the impedance boundary condition, set is the unit vector of the outer normal of the boundary surface, Δg is the normalized impedance, then: For horizontal boundary surfaces, That is n x =n y =0,n z =1; have to: For vertical surface boundaries, That is n z =0 and have to:

6. The method for predicting propagation loss of evaporative waveguide in high sea conditions according to claim 5, characterized in that: The step five is specifically as follows: Step 5-1: The wave spectrum is the power density function of the sea surface. The Fourier transform of the sea spectrum is used to obtain the sea surface fluctuation correlation function. In the polar coordinate system, the two-dimensional wave spectrum is in the form of: Where ψ(k) is the omnidirectional sea spectrum, is the direction function, and the size of k is Among them, k x and k y are the components of k along the x and y directions of the rectangular coordinate system, is the wave number direction angle, is the wind direction angle; Step 5-2: Establish the Elfouhaily spectrum model. The specific form of the power spectrum function is: Among them, B L (k), B S (k) represent long-wave spectrum and short-wave spectrum respectively; Step 5-3: The long wave spectrum is: Where, the large-scale generalized equilibrium parameter is Ω=U 10 / c(k p ) is the dimensionless inverse wave age, and the wave number corresponding to the peak of the wave number spectrum is g is the acceleration due to gravity, which is 9.81 m / s 2 , c(k p ) is the phase velocity of the wave, U 10 is the wind speed at a height of 10m above the sea surface. If the ocean current speed and water depth are ignored, the wave phase velocity is obtained. Long wave action function F p for: Where, L PM and J P The expression is: J p =c B (45) The other parameters in the formula are: In the formula, Ω c is the peak inverse wave age, dimensionless wind zone X is the wind domain, X0=2.2×10 4 ; Step 5-4: The shortwave spectrum is: Where, the small-scale generalized equilibrium parameter is: Wave number k corresponding to the peak value of the gravity-capillary wave in the curvature spectrum m ≈370rad / m, u f is the sea surface friction wind speed, and its relationship with the sea surface wind speed is: Among them, C 10 =(0.8+0.064u 10 )×10 -3 ; Shortwave action function F m for: Step 5-5: In order to accurately describe the anisotropic characteristics of the wave spectrum, a directional function is introduced to reflect the changing directional characteristics of the waves and the energy change relationship of waves of various frequency components caused by the wind direction above the sea surface. The Elfouhaily directional function is used, and the expression is: Where Δ(k) is called the adverse side wind proportional factor, which is related to the wave speed and wind speed: Steps 5-6: Based on the Elfouhaily wave power spectrum function, a linear filtering method is used to generate the distribution of linear sea surface height fluctuations on the two-dimensional sea surface; The mean sea surface is placed on the xOy plane formed by the x-axis and the y-axis. For the time-varying sea surface, the sea surface height fluctuation h at a certain time t generated by the linear filtering method is: To make the result of fast Fourier transform a real number, when m = -M / 2 or n = -N / 2, let F(k m ,k n )=0, other cases are: In the formula, * indicates taking the complex conjugate, L x and L y is the length of the sea surface sample in the x-axis and y-axis directions, M and N are the number of sampling points, i = -M / 2 ~ M / 2-1, j = -N / 2 ~ N / 2-1, and the sampling interval in the spatial domain is Δx = L x / M and Δy=L y / N, the sampling interval in the wavenumber domain is Δk x =2π / L x and Δk y =2π / L y , k m =mΔk x , k n =nΔk y , x=iΔx, y=jΔy, m'=-m, n'=-n, χ m,n =N m (0,1)+iN n (0,1) is a complex Gaussian random number.

7. The method for predicting propagation loss of evaporative waveguide in high sea conditions according to claim 6, characterized in that: The step six is ​​specifically as follows: Step 6-1: Use the dual-scale roughness model to divide the sea surface roughness into two parts and represent them separately, describing more sea surface roughness details and representing a more complex rough sea surface; Step 6-2: In the large-scale roughness, the sea wave simulation method is used to represent it, and the sea wave height field is treated as terrain. For terrain transformation, the continuous shift terrain transformation method is used. Through coordinate transformation, a new coordinate system is established on the rough sea surface terrain, and then the parabolic equation coordinates are transformed to the plane terrain for solution; The three-dimensional scalar wave equation is: Among them, (u, v, w) is the new coordinate system on the irregular terrain; the terrain height is w = T(u, w); Take a point on the irregular terrain as the origin of the coordinate system and establish a new coordinate system (x, y, z) that satisfies: x=u,y=w,z=vT(u)(60) Let Φ(u,w,v)=φ(x,y,z), transform the wave equation in the (u,w,v) coordinate system into the form in the (x,y,z) coordinate system, and get the parabolic equation: The three-dimensional parabolic equation for radio wave propagation on three-dimensional terrain is to equate the effect of terrain on radio waves to a series of single-edge diffractions without considering the lateral slope, that is, Let φ=ψe iθ Substituting into formula (58) we get: in, The phase factor θ(x,y,z) is to be determined; Factoring the above equation, we get the forward parabola equation: Assume the phase factor θ(x,y,z) = K0zT' + f(y) + f(x), and mainly consider the effect of radio wave diffraction on irregular terrain. Let f'(y) = 0, and we get: Will in, Using the approximate formula Substituting into formula (61) we get: To eliminate The first-order term, So: K = K0, let f'(x) = K0(-1+T' 2 ), the three-dimensional irregular terrain parabola equation is: The SSFT solution is: Step 6-3: Miller-Brown type roughness attenuation factor is: Where I0 represents the first-kind zero-order modified Bessel function, γ represents the Rayleigh roughness parameter, and the expression is: γ=2k0h m sinθ(70) In the formula, θ represents the angle between the incident angle and the horizontal plane, h m is the root mean square error of height fluctuation, and its expression is: U 10 Indicates the wind speed 10m above the sea surface; Step 6-4: For small-scale roughness, the roughness factor will be corrected based on the Miller-Brown type roughness correction factor, using h Elfouhaliy Instead of the root mean square error h m , whose expression is: Where S(k) represents the Elfouhaliy wave spectrum.

8. The method for predicting propagation loss of evaporative conductive wave in high sea conditions according to claim 7, characterized in that: The step seven is specifically as follows: Step 7-1: The radio wave propagation factor in three-dimensional space is expressed by the relative value of the actual field and the field in free space, with the initial field H y Calculate the attenuation factor of radio wave propagation. When excited by Gaussian current source, H y The distribution in free space is: in, Indicates the distance between the transmitter and the receiver. x, y represent the coordinates of the projection point of the receiving point on the (x, y) plane; Step 7-2: The attenuation factor of radio wave propagation relative to free space is defined as: Among them, H y (x, y, z) represents the field strength at a certain location; Step 7-3: The propagation loss of radio waves at sea is mainly composed of free space propagation loss and medium propagation loss. The propagation loss calculation formula is: L=32.45+20lgf+20lgr-L bf (75).

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