Method for extracting significant wave height from first order bragg peak of shipborne high frequency ground wave radar using a single antenna

Abstract

The method for extracting effective wave height from the first-order Bragg peak of a ship-borne high-frequency ground wave radar by using a single antenna belongs to the field of sea state inversion, and aims to solve the problem of sea wave parameter inversion by using the second-order Doppler spectrum of the ship-borne high-frequency ground wave radar.The method comprises the following steps: step one, obtaining sea clutter echo channel data by using the ship-borne high-frequency ground wave radar, dividing the radar observation area into grid-shaped sea wave units, and then obtaining the ratio R of the positive and negative first-order Bragg peaks of each sea wave unit; step two, obtaining a wind direction-sea wave spreading factor relationship curve of the wind direction alpha and the sea wave spreading factor s of each sea wave unit from the ratio R of the positive and negative first-order Bragg peaks of each sea wave unit; step three, determining the corresponding wind direction and sea wave spreading factor of the unit according to the wind direction-sea wave spreading factor relationship curve; step four, obtaining the sea surface wind speed U according to the sea wave spreading factor s; and step five, obtaining the effective wave height according to the wind speed inversion.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of sea state inversion. BACKGROUND

[0002] Significance of the Invention Sea surface significant wave height is one of the main parameters describing the characteristics of sea waves, and its real-time and accurate measurement is of great significance for maritime transportation, safety production, fishery, disaster prevention and reduction, and marine weather forecast. After years of development, the shore-based significant wave height inversion technology has been relatively mature, but its detection range is limited due to the influence of the carrying platform. Therefore, it is considered to place the high-frequency ground wave radar on a ship-borne platform to utilize its mobility and flexibility to monitor the specified sea area at a closer distance.

[0003] The parameter information of sea waves is contained in the second-order sea surface echo spectrum of HFSWR (high-frequency surface wave radar). The forward movement of the ship-borne platform will cause the broadening of the second-order Doppler spectrum peak, resulting in the mutual aliasing between the second-order Doppler spectrum peaks. The broadened first-order Bragg peak will also cover the second-order Doppler spectrum region. The additional broadening peak caused by the six-degree oscillation movement of the ship-borne platform will also seriously pollute the second-order Doppler spectrum. In addition, the signal-to-noise ratio of the second-order Doppler spectrum is low and is easily polluted by noise. Therefore, at the present stage, complete second-order Doppler spectrum information cannot be obtained, and it will be particularly difficult to use the second-order Doppler spectrum of the ship-borne HFSWR to perform sea wave parameter inversion. SUMMARY

[0004] In view of the problems existing in the sea wave parameter inversion using the second-order Doppler spectrum of the ship-borne high-frequency ground wave radar, the present application provides a method for extracting the significant wave height from the first-order Bragg peak of the ship-borne high-frequency ground wave radar using a single antenna.

[0005] The method for extracting the significant wave height from the first-order Bragg peak of the ship-borne high-frequency ground wave radar using a single antenna provided by the present application comprises the following steps:

[0006] Step one, acquiring the sea clutter echo channel data of the ship-borne high-frequency ground wave radar, dividing the radar observation area into a grid shape according to the distance resolution and the angle resolution, each grid representing a sea wave unit, and then obtaining the ratio R of the positive and negative first-order Bragg peaks of each sea wave unit;

[0007] Step two, obtaining a wind direction-sea wave spread factor relationship curve of the wind direction and the sea wave spread factor of each sea wave unit from the ratio R of the positive and negative first-order Bragg peaks of each sea wave unit;

[0008] Step three, any sea cell gets the unique intersection point of the wind direction-sea spreading factor relationship curve of the one or two adjacent cells, and then determines the corresponding wind direction and sea spreading factor s of the cell according to the intersection point;

[0009] Step four, the sea surface wind speed U is obtained according to the following formula and the sea spreading factor s determined in step three,

[0010]

[0011] In the formula, f0 is the radar operating frequency, unit: MHz;

[0012] Step five, the effective wave height H is obtained according to the following formula s :

[0013]

[0014] In the formula, a and b are constant coefficients, a=0.0081 and b=0.74, and g is the acceleration of gravity.

[0015] Preferably, the process of obtaining the wind direction-sea spreading factor relationship curve in step two is as follows:

[0016] Step two one: when the amplitude and frequency of each degree of freedom oscillation motion are zero, the first-order sea surface electromagnetic scattering cross section equation of the ship-borne high-frequency ground wave radar in the case of uniform linear motion of the ship-borne platform can be expressed as:

[0017]

[0018] In the formula, represents the angle between the motion direction of the ship-borne platform and the incident direction of the sea surface echo, wherein, is the incident direction of the sea surface echo, θ v is the forward direction of the ship-borne platform; ω is the Doppler angular frequency; g is the acceleration of gravity; m=±1 represents the Doppler frequency shift sign; represents the radar wave vector; k0 is the radar electromagnetic wave number; v represents the motion speed of the ship-borne platform; δ(·) represents the Dirichlet function; S(·) represents the directional wave spectrum, and the directional wave spectrum S(ω, θ) is expressed as a general parameter model of the undirectional wave spectrum S(ω) and the cardioid direction factor G(θ) product, that is, S(ω, θ)=S(ω)·G(θ), θ is the sea wave propagation direction;

[0019] Step two two: the ratio R of the positive and negative first-order Bragg peak intensities is:

[0020]

[0021] In the formula, B + and B -respectively represent the intensity of positive and negative first order Bragg peak;

[0022] ratio By step two one formula simplifies to:

[0023]

[0024] In the formula, θ + and θ - respectively represent the sea wave towards and away from the radar, ω' d =2k0vcosφ, represents the Doppler shift caused by the forward movement of the ship-borne platform, represents the positive first order Bragg peak angular frequency, and α is the sea surface wind direction, and the sea wave spreading factor s in the expression of the cardioid directional factor G(θ) is a variable:

[0025]

[0026] In the formula, ξ represents the upwind and downwind intensity ratio, which is determined by the actual marine environment, and here ξ=0.004, and θ is the sea wave propagation direction;

[0027] Step two three: let the intermediate parameter The wind direction can be obtained:

[0028]

[0029] The ratio of the positive and negative first order Bragg peak intensity can be expressed as:

[0030]

[0031] Step two four: according to the ratio R expression constructed in step two three, the wind direction- sea wave spreading factor relationship curve of the wind direction α and the sea wave spreading factor s of each sea wave unit is obtained from the ratio R of the positive and negative first order Bragg peak of each sea wave unit.

[0032] Preferably, the specific process of step three is:

[0033] The sea wave units A, B and C are three continuous adjacent units, and the unique sea wave spreading factor of the sea wave unit B is obtained under the following two conditions:

[0034] Case one, the wind direction-sea wave spreading factor relationship curve of the sea wave unit A and the sea wave unit B has a curve intersection point, then the wind direction and the sea wave spreading factor s corresponding to the sea wave unit B are determined according to the intersection point;

[0035] Case two, the wind direction-sea wave spreading factor relationship curve of sea wave unit A and sea wave unit B has two curve intersection points, then the wind direction-sea wave spreading factor relationship curve of sea wave unit C is added, the common intersection point of the wind direction-sea wave spreading factor relationship curve of sea wave unit B and the wind direction-sea wave spreading factor relationship curve of sea wave unit A and C is taken as the only intersection point, and the wind direction and the sea wave spreading factor s corresponding to sea wave unit B are determined according to the intersection point.

[0036] Preferably, the specific process of step four for obtaining the sea surface wind speed U is as follows:

[0037] Step four one: the corresponding relationship between the momentum transfer factor μ and the sea wave spreading factor s is as follows:

[0038]

[0039] The relationship between the momentum transfer factor μ and the sea surface wind speed U is as follows:

[0040]

[0041] In the formula, f0 is the radar operating frequency, and the unit is MHz;

[0042] Step four two: when μ>0.1, the relationship between the sea wave spreading factor and the wind speed is as follows:

[0043]

[0044] In the formula, U * The minimum wind speed applicable to the present application is related to the radar operating frequency, and is

[0045] Step four three: the relationship for solving the sea surface wind speed from the sea wave spreading factor of step four two is as follows:

[0046]

[0047] Preferably, the process of obtaining the sea clutter echo channel data by using the shipborne high-frequency ground wave radar in step one is as follows:

[0048] The sea clutter echo data is obtained by monitoring using the shipborne high-frequency ground wave radar, and after the sea clutter echo data is processed by desloping, waveform alignment and Doppler, the sea clutter echo channel data is obtained.

[0049] Preferably, after the sea clutter echo data is obtained by monitoring using the shipborne high-frequency ground wave radar, more echo data is obtained by using the moving sliding window method; the influence of the ocean current on the Doppler spectrum is reduced by the overall translation method, and the first-order Bragg broadening spectrum of the measured data is fitted by using the least square method.

[0050] Preferably, after step four, the following steps are further included: after obtaining the sea surface wind speed, the wind speed is optimized: the wind speed is optimized with the forecast range, if the sea wave unit wind speed falls within the forecast range, the average value of the wind direction of the sea wave unit is calculated, and the average value of the wind speed is denoted as a av , av ; for the sea wave unit of the edge area, if the wind speed is not within the forecast range, the wind direction and the wind speed are replaced by a av , av ; for the sea wave unit of the internal area, if the wind speed is not within the forecast range, the wind direction and the wind speed of the sea wave unit are replaced by the average value of the adjacent area sea wave unit, at this time, if the wind speed of the adjacent area sea wave unit is not within the forecast range, the wind direction and the wind speed of the sea wave unit are replaced by a av , av ; all the sea wave units are traversed to obtain the optimized wind field data.

[0051] The beneficial effects of the present application: the method for extracting the effective wave height from the first-order Bragg peak of the ship-borne HFSWR using a single receiving antenna provides a new idea for the application of ship-borne high-frequency ground wave radar in sea state remote sensing. Due to the flexibility of the ship-borne platform, the ship-borne platform used in the present application effectively solves the problem of limited detection range of the shore-based high-frequency ground wave radar, and expands the measurement distance of the effective wave height on the sea surface. At the same time, compared with the second-order Doppler spectrum which has low signal-to-noise ratio and is easily disturbed, the method of the present application simply and effectively uses the first-order Bragg broadening spectrum, and due to the broadening characteristics of the first-order Bragg peak of the ship-borne high-frequency ground wave radar, a single antenna can be used without the need for digital beam forming, therefore, the present application greatly saves the cost of the radar system, and is more suitable for the ship-borne platform with limited deck space.

[0052] By comparing Figure 5 and Figure 7 , it can be seen that the effective wave height obtained by the ship-borne HFSWR and the forecast chart has good consistency. From Figure 7 , it can be considered that the actual effective wave height range of the detected sea area during the observation period is 2-3m. From Figure 5 , it can be directly seen that the effective wave height of most sea wave units falls within the actual effective wave height range. Figure 8 In , there are 23310 effective wave height samples, the average value of the radar-derived effective wave height is 2.58m, and the standard deviation is 0.57m. 63.84% of the radar-derived effective wave height is within the actual effective wave height range. Considering the influence of factors such as vibration motion of the ship-borne platform, complex marine environment, ocean current and forecast error, the expanded range of the effective wave height is studied, and 92.78% of the radar-derived effective wave height is distributed in the expanded range of 1.5-3.5m. The experimental results are acceptable within the maximum detection range of 120km. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 is a flow chart of the method for extracting significant wave height from the first order Bragg peak of ship-borne high frequency surface wave radar using a single antenna according to the present application;

[0054] Figure 2 is a grid map of the detection area of ship-borne high frequency surface wave radar;

[0055] Figure 3 is a method chart for determining wind direction and sea swell spreading factor;

[0056] Figure 4 is an optimized wind field chart inversed from ship-borne HFSWR;

[0057] Figure 5 is a significant wave height chart inversed from ship-borne HFSWR;

[0058] Figure 6 is a wind field forecast chart provided by Fujian Ocean Forecast, released at 20:00 on December 2, 2016, and the forecast time is 20:00 on December 2, 2016;

[0059] Figure 7 is a significant wave height forecast chart provided by Fujian Ocean Forecast, released at 20:00 on December 2, 2016, and the forecast time is 20:00 on December 2, 2016;

[0060] Figure 8 is a histogram of the statistical results of significant wave height inversed from ship-borne HFSWR in the observation period.

[0061] In the drawings: 1, ship-borne high frequency surface wave radar, 2, buoy. DETAILED DESCRIPTION

[0062] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0063] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0064] The present application will be further described below with reference to the drawings and specific embodiments, but is not limited by the present application.

[0065] Specific embodiment one: the present application will be described below with reference to the drawings and specific embodiments. Figures 1 to 3This embodiment describes a method for extracting the effective wave height from the first-order Bragg peak of a shipborne high-frequency ground wave radar using a single antenna. The method includes the following steps:

[0066] Step 1: Acquire sea clutter echo channel data using shipborne high-frequency ground wave radar. Based on range resolution and angular resolution, divide the radar observation area into a grid pattern, such as... Figure 2 As shown, each grid represents a wave cell, and the ratio R of the positive and negative first-order Bragg peaks of the sea clutter in each wave cell is obtained.

[0067] The process of acquiring sea clutter echo channel data using shipborne high-frequency ground wave radar is as follows:

[0068] Sea clutter echo data was obtained by monitoring with shipborne high-frequency ground wave radar. After deslope processing, waveform alignment and Doppler processing were performed on the sea clutter echo data, sea clutter echo channel data was obtained.

[0069] Furthermore, after obtaining sea clutter echo data using shipborne high-frequency ground wave radar, more radar data were obtained using the moving sliding window method; the influence of ocean currents on the Doppler spectrum was reduced by the overall translation method, and the first-order Bragg broadened spectrum of the measured data was fitted using the least squares method.

[0070] Step 2: Obtain a wind direction-wave spread factor relationship curve for each wave unit by using the ratio R of the positive and negative first-order Bragg peaks.

[0071] The process of obtaining the wind direction-wave spread factor relationship curve by setting the wave spread factor s as a variable is as follows:

[0072] Step 21: When the amplitude and frequency of the oscillating motion of each degree of freedom are zero, under the condition of uniform linear motion of the shipborne platform, the first-order sea surface electromagnetic scattering cross-section equation of the monostatic shipborne high-frequency ground wave radar can be expressed as:

[0073]

[0074] In the formula, This represents the angle between the direction of motion of the shipborne platform and the incident direction of the sea surface echo, where, Let θ be the incident direction of the sea surface echo. v ω represents the forward direction of the shipborne platform; g represents the Doppler angular frequency; m = ±1 represents the Doppler frequency shift sign. represents the radar wave vector; k0 is the radar electromagnetic wave number; v represents the motion speed of the ship-borne platform; δ(·) represents the Dirichlet function; S(·) represents the directional wave spectrum, the directional wave spectrum S(ω, θ) is represented as a general parameter model in which the undirectional wave spectrum S(ω) and the cardioid direction factor G(θ) are multiplied, that is, S(ω, θ) = S(ω)·G(θ), and θ is the wave propagation direction;

[0075] Step two: the ratio R of the positive and negative first-order Bragg peak intensities is:

[0076]

[0077] In the formula, B + and B - respectively represent the positive and negative first-order Bragg peak intensities;

[0078] The ratio R is: The ratio R is simplified by the formula in step two one:

[0079]

[0080] In the formula, θ + and θ - respectively represent the waves towards and away from the radar, ω' d = 2k0vcosφ, represents the Doppler frequency shift caused by the forward motion of the ship-borne platform, represents the positive first-order Bragg peak angular frequency, α is the sea surface wind direction, and the wave spreading factor s in the expression of the cardioid direction factor G(θ) is a variable:

[0081]

[0082] In the formula, ξ represents the upwind and downwind intensity ratio, which is determined by the actual marine environment, and here, ξ = 0.004, and θ is the wave propagation direction;

[0083] Step two three: let the intermediate parameter The wind direction α is obtained:

[0084]

[0085] The ratio of the positive and negative first-order Bragg peak intensities can be represented as:

[0086]

[0087] Step two four: according to the ratio R expression constructed in step two three, a wind direction- wave spreading factor relationship curve of the wind direction α and the wave spreading factor of each wave unit is obtained from the ratio R of the positive and negative first-order Bragg peaks of each wave unit.

[0088] Take three adjacent ABC sea wave units as an example, see Figure 3 The wind direction-sea wave spreading factor relationship curves of the three sea wave units obtained according to the method of the step are sea unit A, sea unit B and sea unit C respectively, and the purpose of constructing the curves is to obtain the unique intersection point of sea unit B to determine the current wind direction and sea wave spreading factor.

[0089] Step three, any sea wave unit obtains the unique intersection point of the unit and the adjacent unit according to the wind direction-sea wave spreading factor relationship curve of the adjacent unit or two units, and further determines the corresponding wind direction and sea wave spreading factor s according to the intersection point;

[0090] For a fully developed sea area, the wind direction can be considered as slowly changing or constant, so the unique sea wave spreading factor and wind direction of sea wave unit B can be determined according to the intersection point of the wind direction and sea wave spreading factor curves of adjacent sea surface scattering units A and B.

[0091] The specific process is as follows:

[0092] Sea wave units A, B and C are three continuous adjacent units, and the unique wind direction and sea wave spreading factor of sea wave unit B are obtained as follows:

[0093] Case one, see Figure 3 (a), the wind direction-sea wave spreading factor relationship curves of sea wave unit A and sea wave unit B have one curve intersection point, so the wind direction and sea wave spreading factor s corresponding to sea wave unit B are determined according to the intersection point;

[0094] Case two, see Figure 3 (b), the wind direction-sea wave spreading factor relationship curves of sea wave unit A and sea wave unit B have two curve intersection points, then the wind direction-sea wave spreading factor relationship curve of sea wave unit C is added as an auxiliary, and the common intersection point of the wind direction-sea wave spreading factor relationship curve of sea wave unit B and the wind direction-sea wave spreading factor relationship curves of sea wave units A and C is taken as the unique intersection point to be solved, and the wind direction and sea wave spreading factor s corresponding to sea wave unit B are determined according to the intersection point.

[0095] Step four, the sea surface wind speed U is obtained according to the following formula and the sea wave spreading factor s determined in step three,

[0096]

[0097] In the formula, f0 is the radar operating frequency, unit: MHz;

[0098] The specific process of obtaining the sea surface wind speed U is as follows:

[0099] Step four one: the corresponding relationship between the momentum transfer factor μ and the sea wave spreading factor s is:

[0100]

[0101] The relationship between momentum transfer factor μ and sea surface wind speed U is as follows:

[0102]

[0103] In the formula, f0 is the radar operating frequency, in MHz;

[0104] Step 42: When μ > 0.1, the relationship between the wave spread factor and wind speed is:

[0105]

[0106] In the formula, U * The minimum wind speed to which this invention applies is related to the radar operating frequency.

[0107] Step 43: The relationship between the wave spread factor in Step 42 and the sea surface wind speed is:

[0108]

[0109] Step 5: Obtain the effective wave height H using the following formula. s :

[0110]

[0111] In the formula, a and b are constant coefficients, a = 0.0081, b = 0.74, and g is the acceleration due to gravity.

[0112] The sea surface is set as a fully developed sea state, and the significant wave height is inverted based on the relationship between wind speed and significant wave height.

[0113] Specific Implementation Method Two: The following is combined with... Figures 4 to 8 This embodiment further explains embodiment one, and after step four, it also includes the following steps: After obtaining the sea surface wind speed, the wind speed is optimized: using the forecast range (e.g., Figure 6 (As shown) Optimized wind speeds range from 8 m / s to 13.8 m / s. If the wind speed of a wave unit falls within the forecast range, the average wind direction and wind speed of that wave unit are calculated and denoted as α. av U av For wave units in the marginal region, if the wind speed is outside the forecast range, then the wind direction and speed are represented by α. av U av For wave cells in the inner region, if the wind speed is outside the forecast range, the wind direction and speed of that wave cell are replaced by the average value of wave cells in the adjacent region. If the wind speed of wave cells in the adjacent region is also outside the forecast range, the wind direction and speed of that wave cell are determined by α. av Uav Instead; for one of the sea clutter echo data, traverse all the sea wave cells, get the optimized wind field data, as shown in Figure 4 .

[0114] Set the sea surface to be fully developed sea state, according to the relationship between the wind speed and the significant wave height, the significant wave height is inverted, and the significant wave height corresponding to the wind field is as shown in Figure 4 . Figure 5

[0115] By comparing Figure 5 and Figure 7 , it can be seen that the significant wave height obtained by the ship-borne HFSWR and the forecast chart has good consistency. From Figure 7 , it can be considered that the actual significant wave height of the detection sea area during the observation period is in the range of 2-3m. From Figure 5 , it can be intuitively seen that the significant wave height of most sea wave cells falls within the range of the actual significant wave height. The significant wave height data during the ship-borne HFSWR detection is as shown in Figure 8 . Figure 8 The significant wave height sample in Figure 8 is 23310, the average value of the significant wave height inverted by the radar is 2.58m, and the standard deviation is 0.57m. The significant wave height inverted by the radar has 63.84% within the range of the actual significant wave height. Considering the influence of factors such as vibration motion of the ship-borne platform, complex marine environment, ocean current and prediction error, the expanded range of the significant wave height is studied, and 92.78% of the significant wave height inverted by the radar is distributed in the expanded range of 1.5-3.5m. The experimental results are acceptable within the maximum detection range of 120km.

[0116] Although the present application is described herein with reference to particular embodiments, it is to be understood that these embodiments are merely exemplary of the principles and applications of the present application. It is therefore to be understood that numerous modifications can be made to the illustrative embodiments and that other arrangements can be devised without departing from the spirit and scope of the present application as defined by the appended claims. It is to be understood that different dependent claims and features described herein can be combined with each other in different ways. It is also to be understood that features described in relation to one embodiment can be used in other described embodiments.

Claims

1. A method for extracting significant wave height from the first order Bragg peak of a ship-borne high frequency ground wave radar using a single antenna, characterized in that, The method comprises the following steps: Step one, obtaining sea clutter echo channel data by using shipborne high-frequency ground wave radar, dividing the radar observation area into a grid according to the distance resolution and angle resolution, each grid representing a sea wave unit, and then obtaining the ratio R of the first-order positive and negative Bragg peaks of each sea wave unit; Step two, obtaining a wind direction-sea wave spread factor relationship curve of the unit from the ratio R of the first-order positive and negative Bragg peaks of each sea wave unit; Step three, obtaining the unique intersection point of the unit and the adjacent unit according to the wind direction-sea wave spread factor relationship curve of one or two adjacent units of any sea wave unit, and then determining the corresponding wind direction and sea wave spread factor s of the unit according to the intersection point; Step four, obtaining the sea surface wind speed U according to the following formula and the sea wave spread factor s determined in step three, In the formula, f0 is the radar operating frequency, unit: MHz; Step five, the significant wave height H is obtained as follows s : In the formula, a and b are constant coefficients, a=0.0081, b=0.74, and g is the acceleration of gravity.

2. The method for extracting significant wave height from the first order Bragg peak of a ship-borne high frequency ground wave radar using a single antenna as claimed in claim 1, wherein, The obtaining process of the wind direction-sea wave spread factor relationship curve in step two is as follows: Step two one: when the amplitude and frequency of each degree of freedom oscillation motion are zero, the first-order sea surface electromagnetic scattering cross section equation of the monostatic shipborne high-frequency ground wave radar under the condition of uniform linear motion of the shipborne platform can be expressed as: wherein, denotes the angle between the direction of motion of the shipborne platform and the direction of incidence of the sea surface echo, wherein, is the direction of incidence of the sea surface echo, θ v is the direction of advance of the shipborne platform; ω is the Doppler angular frequency; g is the gravitational acceleration; m = ±1 represents the Doppler frequency shift sign; denotes the radar wave vector; k0is the radar electromagnetic wave number; v denotes the motion speed of the shipborne platform; δ(·) represents the Dirac function; S(·) denotes the directional sea wave spectrum, the directional sea wave spectrum S(ω, θ) is represented as a general parametric model of the product of the undirectional sea wave spectrum S(ω) and the cardioid directional factor G(θ), i.e. S(ω, θ) = S(ω) · G(θ), θ being the sea wave propagation direction; Step two two: the ratio R of the first-order positive and negative Bragg peak intensities is: In the formula, B + and B - respectively represent the intensity of positive and negative first-order Bragg peaks. Ratio By step two the equation simplifies to: where θ + and θ - represent the sea wave approaching and receding from the radar, respectively, and ω' d = 2k0vcosφ, represents the Doppler shift due to the forward motion of the ship-borne platform, represents the positive first-order Bragg peak angular frequency, and α is the sea surface wind direction. The sea wave spreading factor s is a variable in the expression for the cardioid directivity factor G(θ): In the formula, ξ represents the ratio of the upwind and downwind intensities, and ξ takes the value 0.004; θ is the sea wave propagation direction; Step two three: let the intermediate parameter Available wind direction: The ratio of the first-order positive and negative Bragg peak intensities can be expressed as: Step two four: a wind direction-sea wave spread factor relationship curve of the unit is obtained from the ratio R of the first-order positive and negative Bragg peaks of each sea wave unit according to the ratio R expression constructed in step two three.

3. The method for extracting significant wave height from the first order Bragg peak of a ship-borne high frequency ground wave radar using a single antenna as recited in claim 1, wherein, The specific process of step three is as follows: Sea wave units A, B and C are three continuous adjacent units, and the unique wind direction and sea wave spread factor of sea wave unit B are determined in the following two cases: Case one: the wind direction-sea wave spread factor relationship curves of sea wave unit A and sea wave unit B have one curve intersection point, and then the corresponding wind direction and sea wave spread factor s of sea wave unit B are determined according to the intersection point; Case two: the wind direction-sea wave spread factor relationship curves of sea wave unit A and sea wave unit B have two curve intersection points, then the wind direction-sea wave spread factor relationship curve of sea wave unit C is added, the common intersection point of the wind direction-sea wave spread factor relationship curve of sea wave unit B and the wind direction-sea wave spread factor relationship curves of sea wave units A and C is taken as the unique intersection point, and then the corresponding wind direction and sea wave spread factor s of sea wave unit B are determined according to the intersection point.

4. The method for extracting significant wave height from the first order Bragg peak of a ship-borne high frequency ground wave radar using a single antenna as recited in claim 1, wherein, The specific process of step four for obtaining the sea surface wind speed U is as follows: Step four one: the corresponding relationship between the momentum transfer factor μ and the sea wave spread factor s is: The relationship between the momentum transfer factor μ and the sea surface wind speed U is: In the formula, f0 is the radar operating frequency, unit: MHz; Step four two: when μ>0.1, the relationship between the sea wave spread factor and the wind speed is: wherein U * is the minimum wind speed applicable to the present application, related to the radar operating frequency, is U * = 14.13 f0 -2 / 5 ; Step four three: the relationship for solving the sea surface wind speed from the sea wave spread factor in step four two is:

5. The method for extracting significant wave height from the first order Bragg peak of a ship-borne high frequency ground wave radar using a single antenna as recited in claim 1, wherein, The process of obtaining the sea clutter echo channel data in step one by using the shipborne high-frequency ground wave radar is as follows: The sea clutter echo channel data is obtained after the sea clutter echo data monitored by the shipborne high-frequency ground wave radar is processed by deslope, waveform alignment and Doppler.

6. The method for extracting significant wave height from the first order Bragg peak of a ship-borne high frequency ground wave radar using a single antenna as claimed in claim 5, wherein, After the sea clutter echo data monitored by the shipborne high-frequency ground wave radar, more echo data is obtained by using the moving sliding window method; the influence of the ocean current on the Doppler spectrum is reduced by the overall translation method, and the measured data first-order Bragg broadening spectrum is fitted by using the least square method.

7. The method for extracting significant wave height from the first order Bragg peak of a ship-borne high frequency ground wave radar using a single antenna as claimed in claim 4, wherein, After step four, the following steps are included: after obtaining the sea surface wind speed, the wind speed is optimized: the wind speed is optimized with the forecast range, if the sea wave unit wind speed falls within the forecast range, the wind direction of the sea wave unit is calculated and averaged, the average value of the wind speed is denoted as α av , U av ; for the sea wave unit of the edge area, if the wind speed is not within the forecast range, the wind direction and the wind speed are replaced by α av , U av ; for the sea wave unit of the internal area, if the wind speed is not within the forecast range, the wind direction and the wind speed of the sea wave unit are replaced by the average values of the adjacent area sea wave units, at this time, if the wind speed of the adjacent area sea wave unit is not within the forecast range, the wind direction and the wind speed of the sea wave unit are replaced by α av , U av ; all the sea wave units are traversed to obtain the optimized wind field data.

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