Three-dimensional rough sea surface electromagnetic reflection coefficient calculation method based on wind direction factor

Abstract

The invention relates to a wind direction factor-based three-dimensional rough sea surface electromagnetic reflection coefficient calculation method. The method comprises the following steps of collecting radar frequency, a polarization mode, an incident angle, a wind speed and wind direction data; constructing an ocean wave spectrum model based on the PM-ITTC direction; inputting wind speed and wind direction vector data into the PM-ITTC direction sea wave spectrum model to obtain a three-dimensional sea surface roughness correction factor; inputting the radar frequency, the polarization mode and the incident angle into a Fresnel formula to obtain a Fresnel reflection coefficient of electromagnetic waves on the sea surface; and calculating a three-dimensional rough sea surface electromagnetic reflection coefficient based on the wind direction factor according to the three-dimensional sea surface roughness correction factor and the Fresnel reflection coefficient. According to the method, the influence of the wind direction on the roughness correction factor is considered, the wind speed and wind direction information is vectorized, the sea wave parameter information is combined, the roughness correction factor is corrected, and the calculation precision of the sea surface electromagnetic reflection coefficient is improved.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic wave scattering, and particularly relates to a method for calculating the electromagnetic reflection coefficient of a three-dimensional rough sea surface based on wind direction factors. Background Art

[0002] The electromagnetic reflection coefficient of the sea surface is a key parameter in the fields of ocean remote sensing, ocean environmental monitoring, ocean resource exploration, and climate change research. The reflection characteristics of the sea surface are affected by the frequency, polarization mode, incident angle of the incident wave, the dielectric constant of seawater, and the sea surface roughness.

[0003] Traditional calculation methods for the rough sea surface reflection coefficient are mainly divided into measured methods, analytical approximation methods, and numerical calculation methods. In existing research, the asymmetric influence of the wind direction on the energy distribution of ocean waves is ignored. The wind direction is a key factor affecting the sea surface roughness distribution, which determines the propagation direction and energy concentration area of ocean waves, and thus affects the scattering characteristics of electromagnetic waves. Summary of the Invention

[0004] The technical problem of the present invention is to consider the influence of wind direction factors on the sea surface reflection coefficient and improve the accuracy and efficiency of calculating the rough sea surface reflection coefficient by processing the full grazing angle range.

[0005] The technical solution of the present invention is a method for calculating the electromagnetic reflection coefficient of a three-dimensional rough sea surface based on wind direction factors, including the following steps: S1: Collect radar frequency, polarization mode, incident angle, wind speed, and wind direction data; S2: Construct a PM-ITTC directional ocean wave spectrum model; S3: Input the wind speed and wind direction vector data into the PM-ITTC directional ocean wave spectrum model to obtain a three-dimensional sea surface roughness correction factor; S4: Input the radar frequency, polarization mode, and incident angle into the Fresnel formula to obtain the Fresnel reflection coefficient of electromagnetic waves on the sea surface; S5: Calculate the electromagnetic reflection coefficient of the three-dimensional rough sea surface based on wind direction factors according to the three-dimensional sea surface roughness correction factor and the Fresnel reflection coefficient.

[0006] Optimally, the PM-ITTC directional ocean wave spectrum model in step S2 includes a PM spectrum and an ITTC direction extension function. By introducing the wind speed and wind direction, it is used to characterize the sea surface roughness, and then simulate the spectrum and direction distribution of ocean waves.

[0007] Furthermore, the PM spectrum characterizes the spectrum characteristics of wind waves in the form of a natural exponential function, quantifies the energy distribution at different wave numbers, and is then used to analyze the scattering and reflection characteristics of ocean waves on electromagnetic waves. The PM spectrum expression is: ; where exp( ) represents the natural exponential function, represents the wave number vector, represents the magnitude of the wave number vector, and represent empirical constants, represents the wind speed vector, U 10 represents the wind speed magnitude.

[0008] Optimized, ITTC is the directional spreading function, which describes the energy distribution of ocean waves in different directions through the angle between the ocean wave direction and the wind direction, and reflects the roughness characteristics in three-dimensional space. The expression is: ; where is the angle between the ocean wave direction and the wind direction.

[0009] Furthermore, step S3 includes inputting the wind speed and wind direction vector data into the PM-ITTC directional ocean wave spectrum model to obtain the spectral density function of the sea surface, and using the spectral density function to calculate the root mean square height and correlation length, and then calculating the sea surface structure parameters; 1) The calculation formula for the spectral density function of the sea surface is: ; where A and B represent constants, f p represents the peak frequency, f represents the radar frequency, and exp( ) represents taking the exponential calculation; 2) The calculation formula for the root mean square height is: ; where f represents the radar frequency; θ represents the ocean wave direction angle, and S( ) is the spectral density function. 3) Calculate the adjusted wave energy at all frequencies and directions to obtain the correlation length. The calculation formula for the correlation length is: ; where f represents the radar frequency, in Hz; θ represents the ocean wave direction angle, in radians. S(f, θ) represents the spectral density function, corresponding to the wave energy distribution at different frequencies and directions under the direction angle θ. The integration range is from 0 to infinity in the frequency domain and from 0 to 2π in the direction range, represents adjusting the spectral density function. 4) The calculation formula for the sea surface structure parameters is: ; where W( ) represents the three-dimensional sea surface roughness correction factor containing wind direction information, represents the wind direction angle of the wind speed, represents the incident angle, represents the root mean square height of the ocean wave, Represents the correlation length of ocean waves, Represents the wavelength of radar electromagnetic waves, Represents the exponential operation.

[0010] Furthermore, in step S4, it includes the following sub-steps: 1) Calculate the electromagnetic wave wavelength, and the calculation formula is: ; In the formula, c represents the speed of light, and f represents the radar frequency.

[0011] 2) Seawater dielectric constant. Use the empirical formula to calculate the relative dielectric constant of seawater. The dielectric constant is divided into the real part dielectric constant and the imaginary part dielectric constant, and the calculation formulas are respectively: ; ; In the formula, Represents the real part dielectric constant, Represents the imaginary part dielectric constant, where and Represent constants related to temperature and salinity, and i represents the counting unit.

[0012] Optimized, in step S4, the Fresnel formula is used to calculate the reflection characteristics of electromagnetic waves in different polarization states respectively, and the calculation formula is: ; ; In the formula, Represents the vertical polarization result, Represents the horizontal polarization result.

[0013] Optimized, in step S5, the calculation of the three-dimensional rough sea surface electromagnetic reflection coefficient based on the wind direction factor, and the calculation formula is: ; In the formula, Represents the Fresnel reflection coefficient of electromagnetic waves on the sea surface.

[0014] Compared with the prior art, the beneficial effects of the present invention include: 1) The present invention considers the influence of wind direction on the roughness correction factor, vectorizes the wind speed and wind direction information, and combines the ocean wave parameter information to correct the roughness correction factor, improving the accuracy of the calculation of the sea surface electromagnetic reflection coefficient.

[0015] 2) The present invention adopts the method of analytical approximation, avoiding complex numerical calculations and improving the calculation efficiency of the sea surface electromagnetic reflection coefficient.

[0016] 3) The method for calculating the electromagnetic reflection coefficient of the sea surface in the present invention is applicable to electromagnetic waves with different frequencies, polarization modes, and incident angles, improving the practicability of calculating the electromagnetic reflection coefficient of the sea surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below in conjunction with the drawings and embodiments.

[0018] Figure 1 It is a flowchart of the method for calculating the electromagnetic reflection coefficient of the sea surface in the embodiment of the present invention.

[0019] Figure 2 It is a schematic diagram of the rough sea surface model and the calculation of the reflection coefficient in the embodiment of the present invention.

[0020] Figure 3 It is the three-dimensional PM-ITTC directional wave number spectrum combined with the ITTC direction expansion function in the embodiment of the present invention.

[0021] Figure 4 It is a comparison diagram of the sea surface models under different wind speeds and wind directions in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] As Figure 1 shown, the three-dimensional rough sea surface electromagnetic reflection coefficient calculation method based on the wind direction factor includes the following steps: S1: Collect radar frequency, polarization mode, incident angle, wind speed, and wind direction data; The preset sea surface environmental parameters of wind speed, wind direction, longitude, and latitude are as Figure 2 shown.

[0023] S2: Construct a PM-ITTC directional sea wave spectrum model; In step S2, the PM-ITTC directional sea wave spectrum model includes a PM spectrum and an ITTC direction expansion function. By introducing wind speed and wind direction, it is used to characterize the sea surface roughness, and then simulate the spectrum and direction distribution of sea waves.

[0024] The PM spectrum characterizes the spectrum characteristics of wind waves in the form of a natural exponential function, quantifies the energy distribution at different wave numbers, and is then used to analyze the scattering and reflection characteristics of sea waves on electromagnetic waves. The PM spectrum expression is: ; In the formula, exp( ) represents the natural exponential function, represents the wave number vector, represents the modulus of the wave number vector, and represent empirical constants, represents the wind speed vector, and U 10 represents the wind speed magnitude.

[0025] The ITTC is a direction expansion function that describes the energy distribution of ocean waves in different directions through the angle between the wave direction and the wind direction, reflecting the roughness characteristics in three-dimensional space. The expression is as follows: ; In the formula, is the angle between the wave direction and the wind direction.

[0026] S3: Input the wind speed and wind direction vector data into the PM-ITTC directional ocean wave spectrum model to obtain the three-dimensional sea surface roughness correction factor; As Figure 3 shown, step S3 includes inputting the wind speed and wind direction vector data into the PM-ITTC directional ocean wave spectrum model to obtain the spectral density function of the sea surface, and using the spectral density function to calculate the root mean square height and correlation length, and then calculating the sea surface structure parameters; 1) The calculation formula for the spectral density function of the sea surface is: ; In the formula, A and B represent constants, f p represents the peak frequency, f represents the radar frequency, and exp( ) represents taking the exponential calculation; 2) The calculation formula for the root mean square height is: ; In the formula, f represents the radar frequency, θ represents the wave direction angle, and S( ) is the spectral density function. 3) The calculation formula for the correlation length is: ; In the formula, f represents the radar frequency, θ represents the wave direction angle, and S( ) represents the spectral density function.

[0027] 4) The calculation formula for the sea surface structure parameter is: ; In the formula, W( ) represents the three-dimensional sea surface roughness correction factor containing wind direction information, represents the wind direction angle of the wind speed, represents the incident angle, represents the root mean square height of the ocean wave, represents the correlation length of the ocean wave, represents the wavelength of the radar electromagnetic wave, represents the exponential operation.

[0028] S4: Input the radar frequency, polarization mode, and incident angle into the Fresnel formula to obtain the Fresnel reflection coefficient of the electromagnetic wave on the sea surface; In step S4, the following sub-steps are included: 1) Calculate the wavelength of the electromagnetic wave. The calculation formula is: ; In the formula, c represents the speed of light, and f represents the radar frequency.

[0029] 2) Dielectric constant of seawater. Use the empirical formula to calculate the relative dielectric constant of seawater. The dielectric constant is divided into the real part dielectric constant and the imaginary part dielectric constant. The calculation formulas are respectively: ; ; In the formula, represents the real part dielectric constant, represents the imaginary part dielectric constant, where and represent the constants related to temperature and salinity, and i represents the counting unit.

[0030] In step S4, the Fresnel formula is used to calculate the reflection characteristics of the electromagnetic wave in different polarization states. The calculation formula is: ; ; In the formula, represents the vertical polarization result, represents the horizontal polarization result.

[0031] S5: Calculate the electromagnetic reflection coefficient of the three-dimensional rough sea surface based on the wind direction factor according to the three-dimensional sea surface roughness correction factor and the Fresnel reflection coefficient.

[0032] In step S5, the calculation formula for the electromagnetic reflection coefficient of the three-dimensional rough sea surface based on the wind direction factor is: ; In the formula, represents the Fresnel reflection coefficient of the electromagnetic wave on the sea surface.

[0033] To verify the effectiveness of the method proposed by the invention, data of different wind speeds, wind directions, and radar frequencies are selected as input parameters. As shown in Table 1, wind speeds of 3 m / s, 6 m / s, 10 m / s, and 15 m / s, wind directions of 0° to 360° with a step of 40°, radar frequencies of 1 GHz, 5 GHz, 10 GHz, and 20 GHz, and polarization modes of HH and VV combinations are selected as input parameters.

[0034] Table 1

[0035] A correction factor is introduced to consider the influence of sea surface roughness. Combining with the Fresnel reflection coefficient, the final corrected electromagnetic reflection coefficient of the sea surface is calculated, as shown in Table 2.

[0036] Table 2

[0037] The traditional model cannot reflect the directional change of the reflection coefficient on the sea surface under different wind speeds and wind directions. The present invention can accurately reflect the changes in different wind directions and wind speeds, approaching the real sea surface undulation.

[0038] As Figure 4 shown, the proposed method for calculating the electromagnetic reflection coefficient of a three-dimensional rough sea surface based on wind direction effectively solves the error problem existing in the traditional method by introducing a more accurate sea surface model and a dynamic wind direction correction factor, providing a more reliable theoretical basis and calculation tool for fields such as ocean remote sensing and environmental monitoring.

[0039] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The protection scope of the present invention should be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, the equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for calculating electromagnetic reflection coefficient of three-dimensional rough sea surface based on wind direction factors, characterized in that: The following steps are involved: S1: Collect radar frequency, polarization mode, incident angle, wind speed and wind direction data; S2: Construct a directional wave spectrum model based on PM-ITTC; S3: Input the wind speed and wind direction vector data into the PM-ITTC directional wave spectrum model to obtain the three-dimensional sea surface roughness correction factor; S4: Input the radar frequency, polarization mode and incident angle into the Fresnel formula to obtain the Fresnel reflection coefficient of the electromagnetic wave on the sea surface; S5: Based on the three-dimensional sea surface roughness correction factor and the Fresnel reflection coefficient, the three-dimensional rough sea surface electromagnetic reflection coefficient based on the wind direction factor is calculated.

2. The method for calculating electromagnetic reflection coefficient of three-dimensional rough sea surface based on wind direction factor according to claim 1 is characterized in that: In step S2, the PM-ITTC directional wave spectrum model includes a PM spectrum and an ITTC directional expansion function, which is used to characterize the roughness of the sea surface by introducing wind speed and wind direction, thereby simulating the spectrum and directional distribution of waves.

3. The method for calculating electromagnetic reflection coefficient of three-dimensional rough sea surface based on wind direction factor according to claim 2 is characterized in that: The PM spectrum characterizes the spectral characteristics of wind waves in the form of a natural exponential function, and quantifies the energy distribution under different wave numbers, and is then used to analyze the scattering and reflection characteristics of electromagnetic waves by sea waves. The PM spectrum expression is: ； Where exp( ) represents the natural exponential function, represents the wave number vector, represents the magnitude of the wave number vector, and represents the empirical constant, represents the wind speed vector, U 10 Indicates wind speed.

4. The method for calculating electromagnetic reflection coefficient of three-dimensional rough sea surface based on wind direction factor according to claim 2 is characterized in that: The ITTC is a directional spread function that describes the energy distribution of waves in different directions through the angle between the wave direction and the wind direction, and reflects the roughness characteristics in three-dimensional space. The expression is: ； In the formula, It is the angle between the wave direction and the wind direction.

5. According to the method for calculating electromagnetic reflection coefficient of three-dimensional rough sea surface based on wind direction factor in claim 1, step S3 includes inputting wind speed and wind direction vector data into PM-ITTC directional wave spectrum model to obtain the spectral density function of the sea surface, and then using the spectral density function to calculate the root mean square height and correlation length, and then calculating the parameters characterizing the sea surface structure; the calculation formula of the three-dimensional sea surface roughness correction factor is: ； Where W( ) represents the three-dimensional sea surface roughness correction factor including wind direction information, The wind direction angle indicating the wind speed, represents the angle of incidence, is the root mean square height of the waves, represents the correlation length of the wave, represents the wavelength of the radar electromagnetic wave, Represents an exponential operation.

6. According to the method for calculating the electromagnetic reflection coefficient of a three-dimensional rough sea surface based on wind direction factors according to claim 1, in step S4, the Fresnel formula is used to respectively calculate the reflection characteristics of electromagnetic waves under different polarization states, and the calculation formula is: ； ； In the formula, represents the vertical polarization result, Indicates horizontal polarization results.

7. According to the method for calculating the electromagnetic reflection coefficient of the three-dimensional rough sea surface based on the wind direction factor of claim 1, in step S5, the electromagnetic reflection coefficient of the three-dimensional rough sea surface based on the wind direction factor is calculated using the following formula: ； In the formula, Represents the Fresnel reflection coefficient of electromagnetic waves on the sea surface.

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