Effective wave height extraction method based on synthetic aperture radar image

Abstract

The invention provides an effective wave height extraction method based on a synthetic aperture radar image, and the method comprises the steps: 1, obtaining data, carrying out the matching of an altimeter effective wave height and synthetic aperture radar interference imaging mode data, and obtaining a sample data set; 2, counting the data volume of the effective wave height of the altimeter in different incidence angle ranges, and obtaining the value distribution of the effective wave height of the altimeter in the global offshore range; and step 3, performing quality control on the normalized variance of the backscattering coefficient of the synthetic aperture radar and the effective wave height of the altimeter to obtain effective wave height and normalized variance data. And 4, establishing a linear relationship between the significant wave height and the normalized variance. And step 5, evaluating and verifying the estimated value of the effective wave height of the synthetic aperture radar, and obtaining the effective wave height only by inputting the normalized variance of the single image parameter. The method not only considers the open ocean wave mode of the synthetic aperture radar, but also relates to offshore research, and provides technical support for the development of related projects in coastal areas.

Description

Technical Field

[0001] The invention relates to a method for processing ocean data, and in particular to a method for extracting effective wave height based on synthetic aperture radar images. Background Art

[0002] Significant wave height (SWH) is defined as the average height of 1 / 3 of the highest wave height in a given wave train. my country is a maritime power. About 23%-37% of the world's population lives within 100 kilometers of the coastline. Measuring wave height in coastal areas plays an important role in coastal protection, coastal safety and coastal risk assessment research. With the rapid development of the marine economy, human activities on the ocean are increasing. Ships and various marine industries need information about wave height for route planning. In addition, natural disasters are very harmful to marine operations. The occurrence of natural disasters such as typhoons and storm surges will inevitably cause changes in marine wave parameters. Carrying out research and application of wave height measurement and forecasting sea conditions can effectively improve human ability to prevent natural disasters and reduce national economic losses under extreme disaster conditions. Ocean surface wave measurement is valuable to all fields. Significant wave height is one of the most important parameters for wave observation, so it is necessary to measure the significant wave height.

[0003] Early measurements of significant wave height were made at in-situ measurement stations including buoys, but their distribution locations were limited, and many local fluctuations had not been measured. Satellite altimetry effectively made up for this shortcoming. Its measurement principle is to estimate the propagation time of radar pulses from satellites to the ground and back, so that the significant wave height can be estimated based on the generated waveform. However, satellite altimetry still has limitations and is only applicable to spatially uniform areas, such as open sea surfaces. For uneven sea surfaces, it is difficult to accurately analyze the significant wave height on the water surface.

[0004] With the development of satellite radar altimeters, the emergence of time-delay Doppler altimeters and the launch of the first synthetic aperture radar altimeter CryoSat-2 ushered in a new era of ocean remote sensing. Raney (1998) proposed the concept of time-delay Doppler altimeter and introduced the idea of ​​aperture synthesis into the altimeter. The resolution along the track has been increased from several kilometers to about 300 meters, greatly improving the accuracy of height measurement. Since the height measurement accuracy of synthetic aperture radar altimeter is 1 times higher than that of traditional altimeter, it will play an important role in mesoscale measurement of the ocean, ocean depth detection, and high-precision ocean gravity field measurement. Major space powers have successively launched multiple radar altimeter satellites.

[0005] At present, the technology of using satellite radar altimeters is quite mature. Janssen used the triple matching method to prove the high accuracy of Envisat altimeter data. Li and Holt used buoys and Envisat to verify the accuracy of North Atlantic and European wave models. The effective wave heights of the North Atlantic and European empirical models were basically consistent with the altimeter and buoy observations. Park used buoys in the waters around South Korea to prove that the accuracy error of the effective wave height data of Topex / Poseidon, Envisat, Jason-1 and Jason-2 is very small. Therefore, high-precision satellite radar altimeters and the National Data Buoy Center (NDBC) of the National Oceanic and Atmospheric Administration (NOAA) of the United States are often used as independent data sources to evaluate and verify the accuracy of other methods for obtaining effective wave heights.

[0006] Spaceborne synthetic aperture radar (SAR) is a powerful tool for detecting sea conditions based on effective wave height. Compared with the traditional time-consuming and labor-intensive method of observing waves on the spot, it can provide high spatial resolution wave spectra all day and all weather, showing unique ability and potential for wave observation. The ocean surface is determined by the sea conditions, and the basic parameter of the sea conditions is the effective wave height. Therefore, it is of great significance to use the SAR measured data to invert the wave inversion model of effective wave height. There are two types of synthetic aperture radar effective wave height inversion schemes. The first method is to invert the wave spectrum through the SAR image spectrum to obtain the effective wave height, such as the Max Planck Institute model and the semi-parametric inversion model. However, due to the influence of the velocity bunching of the special imaging mechanism of SAR, SAR images often appear very blurred in azimuth, and the derived spectrum is prone to distortion. Since the random motion of the waves will cause the Doppler frequency shift of the synthetic aperture radar backscattered echo signal, the wave imaging process will show strong nonlinearity, resulting in the inability of SAR to observe waves smaller than the azimuth cutoff wavelength, which in turn affects SAR imaging. Therefore, only by introducing other numerical model results as prior information or through the cross-spectrum of SAR images can it be possible to obtain a complete wave spectrum. Among them, the calculation process of the cross-spectrum of synthetic aperture radar images does not require initial guess information, which solves the problem of 180° ambiguity in the propagation direction of waves. However, the obtained wave spectrum cannot resolve the information of high-frequency short waves. It can be seen that the method of obtaining effective wave height by inverting the wave spectrum through the SAR image spectrum still has limitations. The second type of method is the empirical model, which can directly extract the effective wave height from the SAR image, no longer rely on the wave spectrum to calculate the wave parameters, and avoid the complicated inversion process. The CWAVE model was first proposed by Schulz-Stellenfleth. The radar cross section, variance and other parameters are extracted from the SAR image. The relationship between these parameters and the effective wave height can be directly established to obtain the effective wave height. Based on the CWAVE model, Schulz-Stellenfleth et al. established CWAVE_ERS based on ERS2 data. Based on the CWAVE-ERS model, Li and Stopa et al. proposed the CWAVE_ENV model for ENVISAT ASAR data and the CWAVE-S1A model for Sentinel-1A data. In addition, with the continuous progress of the inversion research of wave parameters, people gradually realized that there is a strong correlation between the azimuth cutoff wavelength and the effective wave height, which can be used for the inversion research of effective wave height. The azimuth cutoff wavelength is the minimum wavelength observable in the along-track direction and can be used as a measure of the azimuth resolution of synthetic aperture radar. Therefore, Stopa et al. established the CWAVE_Fnn model based on Sentinel-1 data by using the neural network algorithm and the strong dependence between the azimuth cutoff wavelength and the effective wave height.The above empirical models do not involve complex transfer modulation functions, and can directly establish the relationship between SAR image spectrum and effective wave height, with relatively high inversion accuracy. However, these empirical models are developed and verified for open ocean wave modes, and have not yet been studied for near-coast interferometric imaging modes, which have sea area limitations. Summary of the invention

[0007] 1. Technical problems to be solved:

[0008] How to establish an empirical model to obtain effective wave height in a complex ocean environment. Empirical models usually require multiple input parameters to obtain effective wave height. The algorithm's calculation amount and processing process are relatively complex, making it difficult to invert effective wave height on a global scale.

[0009] 2. Technical solution:

[0010] In order to solve the above problems, the present invention provides a method for extracting effective wave height based on synthetic aperture radar images, comprising the following steps:

[0011] Step 1: Obtain the data of synthetic aperture radar interferometry imaging mode and altimeter effective wave height in the sea area studied for many years, match the altimeter effective wave height with the synthetic aperture radar interferometry imaging mode data, set the appropriate time matching window and space matching distance, and obtain the matched sample data set.

[0012] Step 2: Select the altimeter effective wave height data of the sample data set, analyze the global distribution of the altimeter effective wave height, divide it into different incidence angle ranges, count the data volume of the altimeter effective wave height in different incidence angle ranges, and obtain the numerical distribution of the altimeter effective wave height in the global near-coast range.

[0013] Step 3: Perform quality control on the normalized variance of the backscatter coefficient of the synthetic aperture radar and the effective wave height of the altimeter in the sample data set. Use the confidence ellipse fitting method, set the quality control conditions for confidence ellipse fitting, and obtain the fitted effective wave height and normalized variance data.

[0014] Step 4: Perform linear fitting on the fitted effective wave height and normalized variance data under different incident angle ranges to obtain the fitting coefficients at each incident angle, establish a linear relationship between the effective wave height and the normalized variance, input the normalized variance, and obtain the synthetic aperture radar effective wave height estimate through the model.

[0015] Step 5: Use the altimeter and buoy significant wave height data to evaluate and verify the estimated SAR significant wave height. Compare the average deviation of the SAR significant wave height estimate at each incidence angle compared to the altimeter significant wave height. Calculate the deviation and standard deviation of the SAR significant wave height estimate compared to the buoy significant wave height.

[0016] In step 1, the altimeters used include Cryosat-2 and Sentinel-3_a launched by the European Space Agency, Jason-2 launched by the Delta-2 launch vehicle, Jason-3 launched by the Falcon 9 launch vehicle, SARAL launched by the French National Center for Space Studies and the Indian Space Research Institute, with a resolution of 6 km, and the global near-coast significant wave height data from 2019 to 2022 are selected.

[0017] In step 1, the synthetic aperture radar used is the interferometric imaging mode of the Sentinel-1 in the European Space Agency's Copernicus program, with a resolution of 10m and a synthetic aperture radar image size of 250kmx250km.

[0018] The time matching window and space matching distance are as follows: in terms of time, ±1.5 hours are used as the time matching window; in terms of space, the center position of the effective wave height obtained by the altimeter is taken as the center of the circle, and the data points on the synthetic aperture radar image are matched within a circular range with a radius of 3 km. The altimeter circular range with a synthetic aperture radar image pixel less than 500 is eliminated, and the matching is completed.

[0019] In step 2, the sample effective wave height data are distributed in the near coast of the world, and the incident angle ranges are divided into 32°±1°, 34°±1°, 36°±1°, 38°±1° and 40°±1°. The sample data sets exceed 67,000, of which more than 12,000 are within the incident angle range of 38°±1°, and 6,000±100 are within the incident angle range of 32°±1°. In the near coast of the world, the effective wave height is mainly concentrated around 2m±0.5, with more than 5,000, showing a Weibull distribution.

[0020] The global near coasts include the coast of Hawaii, the east and west coasts of the United States, the west coast of Europe, the southeast coast of Africa, the southeast coast of China and the coast of Japan.

[0021] In step 3, the quality control is performed for all data points using a confidence ellipse fitting method, where the normalized variance consists of a mean and a standard deviation, and the formula is as follows:

[0022]

[0023] Among them, σ is the standard deviation, μ is the mean, and Nvar is the normalized variance.

[0024] In step 4, the linear fitting is a one-dimensional polynomial fitting, and the calculation formula is:

[0025] y=ax+b

[0026] Where y is the estimated value of the effective wave height of the synthetic aperture radar, x is the normalized variance, and a and b are the fitting coefficients of the polynomial.

[0027] In step 5, the buoy effective wave height uses the effective wave height data of global coastal waters from 2019 to 2022 from the National Data Buoy Center of the National Oceanic and Atmospheric Administration of the United States.

[0028] In step 5, the specific method includes the following steps:

[0029] Step 101: Use the altimeter effective wave height to evaluate the estimated value of the synthetic aperture radar effective wave height, and compare the average deviation of the estimated value of the synthetic aperture radar effective wave height at each incident angle compared with the altimeter effective wave height, also known as the weighted deviation, which is calculated as follows:

[0030]

[0031] Among them, w1, w2, ... ..., w n is the weight of the synthetic aperture radar effective wave height estimate, x1, x2, ... ... , x n is the median value of the synthetic aperture radar effective wave height estimate for each 0.2m interval, is the weight bias of the synthetic aperture radar effective wave height estimate;

[0032] Step 102: Use the effective wave height data observed on site to verify the estimated effective wave height of the synthetic aperture radar, and calculate the deviation and standard deviation of the estimated effective wave height of the synthetic aperture radar compared with the effective wave height observed on site.

[0033] The deviation is calculated as follows:

[0034] bias(x)=yf(x)#(4)

[0035] Where y is the estimated value of the effective wave height of the synthetic aperture radar, f(x) is the effective wave height observed on site, and bias(x) is the deviation of the estimated value of the effective wave height of the synthetic aperture radar compared with the effective wave height observed on site.

[0036] The standard deviation is calculated as follows:

[0037]

[0038] Where X is a single SAR effective wave height estimate, μ is the average of SAR effective wave height estimates, N is the total number of samples of SAR effective wave height estimates, and STD is the standard deviation of SAR effective wave height estimates.

[0039] 3. Beneficial effects:

[0040] The present invention only needs to input the normalized variance of a single image parameter to obtain the effective wave height through the empirical model. Compared with the traditional method, the present invention does not need to rely on multiple input parameters, which improves the simplicity of model calculation. The present invention not only takes into account the open ocean wave mode of synthetic aperture radar, but also involves near-coast research. The present invention provides technical support for the development of related topics in coastal areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a technical flow chart of extracting effective wave height based on synthetic aperture radar images in the present invention;

[0042] Figure 2 Figure 3. Quality control of effective wave height and normalized variance and establishment of empirical model. (a) shows the confidence ellipse fitting and linear fitting at an incident angle of 36°±1°, and (b) shows the comparison of linear fitting results at all incident angles. DETAILED DESCRIPTION

[0043] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0044] The present invention provides a method for extracting effective wave height from synthetic aperture radar images in near-coast interferometric imaging mode, which establishes an empirical model based on a single parameter and only inputs the normalized variance to obtain the SAR effective wave height estimation value. Figure 1 As shown, the method specifically comprises the following steps:

[0045] Step 1: Obtain the data of synthetic aperture radar interferometry imaging mode and altimeter effective wave height in the sea area studied for many years, match the altimeter effective wave height with the synthetic aperture radar interferometry imaging mode data, set the appropriate time matching window and space matching distance, and obtain the matched sample data set.

[0046] In one embodiment, there are five altimeters, namely Cryosat-2 and Sentinel-3_a launched by the European Space Agency, Jason-2 launched by the Delta-2 carrier rocket, Jason-3 launched by the Falcon 9 carrier rocket, and SARAL launched by the French National Center for Space Studies and the Indian Space Research Institute, with a spatial resolution of 6 km, and effective wave height data for global nearshore waters from 2019 to 2022 were selected.

[0047] In one embodiment, the synthetic aperture radar used is the Sentinel-1 in the Copernicus program of the European Space Agency, and its working mode is an interferometric imaging mode, with a spatial resolution of 10 m and a SAR image size of 250 km x 250 km.

[0048] Due to the different spatial resolutions of the altimeter and synthetic aperture radar, temporal and spatial data matching is required. In terms of time, ±1.5 hours is used as the time matching window; in terms of space, the center position of the effective wave height obtained by the altimeter is used as the center of the circle, and the circular range with a radius of 3km is used to match the data points on the synthetic aperture radar image. The altimeter circular range with synthetic aperture radar image pixels less than 500 is eliminated, and all matched data points are used as sample data sets for model construction.

[0049] Step 2: Select the altimeter effective wave height data of the sample data set, analyze the global distribution of the altimeter effective wave height, divide it into different incidence angle ranges, count the data volume of the altimeter effective wave height in different incidence angle ranges, and study the numerical distribution of the altimeter effective wave height on a global scale.

[0050] The sample significant wave height data are distributed in the global coastal areas. In one embodiment, the global coastal areas include the coast of Hawaii, the east and west coasts of the United States, the west coast of Europe, the southeast coast of Africa, the southeast coast of China and the coast of Japan.

[0051] In one embodiment, there are more than 67,000 data points in the sample data set, and the incident angle ranges of 32°±1°, 34°±1°, 36°±1°, 38°±1° and 40°±1° are selected. The data volume is the largest in the 38°±1° incident angle range, exceeding 12,000, and the data volume is the least in the 32°±1° incident angle range, about 6,000. The data volume in each incident angle range is sufficient to support research. In the global near-coast range, the effective wave height is mainly concentrated at around 2m, exceeding 5,000, showing a Weibull distribution.

[0052] Step 3: Perform quality control on the normalized variance of the backscatter coefficient of the synthetic aperture radar and the effective wave height of the altimeter in the sample data set. Use the confidence ellipse fitting method, set the quality control conditions for confidence ellipse fitting, and obtain the fitted effective wave height and normalized variance data.

[0053] The mean and standard deviation of the synthetic aperture radar backscatter coefficient are the two most commonly used parameters to describe the statistical characteristics of the image. From a statistical point of view, they represent the first-order moment and second-order moment of the radar echo respectively. The combination of these two variables is called the normalized variance, and its formula is as follows:

[0054]

[0055] Among them, σ is the standard deviation, μ is the mean, and Nvar is the normalized variance.

[0056] For the quality control of Nvar and SWH of sample data points, in one embodiment, confidence ellipse fitting is adopted, the confidence ellipse standard deviation is set to 1.5, the screening conditions are that the effective wave height range is [0,6], the normalized variance range is less than 0.15, and the incident angle range is 36°±1°. Figure 2 As shown in (a), the obtained red ellipse is the fitted confidence ellipse, with a minor axis length of 0.07, a major axis length of 2.95, a center of (0.07, 1.99), and a central rotation angle of 179.4°.

[0057] Step 4: Perform linear fitting on the fitted effective wave height and normalized variance data under different incident angle ranges to obtain the fitting coefficients at each incident angle, establish a linear relationship between the effective wave height and the normalized variance, and only input the normalized variance to obtain the estimated value of the synthetic aperture radar effective wave height through the model.

[0058] The linear fitting formula is as follows:

[0059] y=ax+b

[0060] Where y is the estimated value of the SAR effective wave height, x is the normalized variance, and a and b are the fitting coefficients of the polynomial. In one embodiment, the fitting coefficients a corresponding to the above-mentioned incident angle range are 41.87, 40.49, 40.71, 41.57, and 42.39, respectively, and the fitting coefficients b are -1.11, -0.87, -0.79, -0.92, and -0.88, respectively. The linear fitting results under all incident angles are compared, as shown in FIG. Figure 2 As shown in (b), it can be found that the linear fitting results at different incident angles are generally not much different and have no dependence on the incident angle.

[0061] Step 5: Use the altimeter and buoy significant wave height data to evaluate and verify the estimated SAR significant wave height. Compare the average deviation of the SAR significant wave height estimate at each incidence angle compared to the altimeter significant wave height. Calculate the deviation and standard deviation of the SAR significant wave height estimate compared to the buoy significant wave height.

[0062] The operational process for result evaluation and verification is as follows:

[0063] Step 101: Use the altimeter effective wave height to evaluate the estimated value of the synthetic aperture radar effective wave height, and compare the average deviation of the estimated value of the synthetic aperture radar effective wave height at each incident angle compared with the altimeter effective wave height, also known as the weighted deviation, which is calculated as follows:

[0064]

[0065] Among them, w1, w2, ... ..., w nare the weights of the synthetic aperture radar effective wave height estimation, x1, x2, ... ..., x n is the median value of the synthetic aperture radar effective wave height estimate for each 0.2m interval, is the weight bias of the synthetic aperture radar effective wave height estimate.

[0066] Step 102: Use the effective wave height data observed in situ to verify the estimated value of the effective wave height of the synthetic aperture radar, and calculate the deviation and standard deviation of the estimated value of the effective wave height of the synthetic aperture radar compared with the effective wave height observed in situ.

[0067] The deviation is calculated as follows:

[0068] bias(x)=yf(x)

[0069] Where y is the estimated value of the synthetic aperture radar effective wave height, f(x) is the effective wave height observed in situ, and bias(x) is the deviation of the SAR effective wave height estimate compared to the effective wave height observed in situ.

[0070] The formula for calculating the standard deviation is as follows:

[0071]

[0072] Where X is a single SAR significant wave height estimate, μ is the average of the SAR significant wave height estimates, N is the total number of samples of the SAR significant wave height estimates, and STD is the standard deviation of the SAR significant wave height estimates.

[0073] In one embodiment, the buoy effective wave height uses the effective wave height data of the global coastal waters from 2019 to 2022 from the National Data Buoy Center of the National Oceanic and Atmospheric Administration of the United States.

[0074] Compared with the altimeter effective wave height, the deviation of the SAR effective wave height estimation value at each incident angle is between [-2,2], and the deviation of most data is concentrated between [-0.5,0.5]. The calculated SAR effective wave height weight deviation corresponding to the incident angle range is 0.07982, -0.05852, -0.13482, -0.0728, and -0.14888. Compared with the buoy effective wave height, the effective wave height data obtained by the National Data Buoy Center of the National Oceanic and Atmospheric Administration of the United States is used, with about 4,000 data. The deviation of the SAR effective wave height estimation value is -0.29m, the standard deviation is 1.28m, and most of the data deviation is concentrated between [-0.6,0]. After evaluation and verification, it can be seen that the error of the SAR effective wave height estimation value is very small compared with the altimeter and buoy effective wave height, and it is accurate and reliable.

Claims

1. A method for extracting effective wave height based on synthetic aperture radar images, characterized in that; The following steps are involved: Step 1: Obtain the data of synthetic aperture radar interferometric imaging mode and altimeter effective wave height in the sea area studied for many years, match the altimeter effective wave height with the synthetic aperture radar interferometric imaging mode data, set the appropriate time matching window and space matching distance, and obtain the matched sample data set; Step 2: Select the altimeter effective wave height data of the sample data set, analyze the global distribution of the altimeter effective wave height, divide it into different incidence angle ranges, count the data volume of the altimeter effective wave height in different incidence angle ranges, and obtain the numerical distribution of the altimeter effective wave height in the global near-coast range; Step 3: Perform quality control on the normalized variance of the backscatter coefficient of the synthetic aperture radar and the effective wave height of the altimeter in the sample data set. Use the confidence ellipse fitting method, set the quality control conditions to perform confidence ellipse fitting, and obtain the effective wave height and normalized variance data after fitting. Step 4: Perform linear fitting on the fitted effective wave height and normalized variance data under different incident angle ranges to obtain the fitting coefficients under each incident angle, establish a linear relationship between the effective wave height and the normalized variance, input the normalized variance, and obtain the estimated value of the synthetic aperture radar effective wave height through the model; Step 5: Use the altimeter and buoy significant wave height data to evaluate and verify the estimated SAR significant wave height. Compare the average deviation of the SAR significant wave height estimate at each incidence angle compared to the altimeter significant wave height. Calculate the deviation and standard deviation of the SAR significant wave height estimate compared to the buoy significant wave height.

2. The method for extracting effective wave height based on synthetic aperture radar images according to claim 1, characterized in that: In step 1, the altimeters used include Cryosat-2 and Sentinel-3_a launched by the European Space Agency, Jason-2 launched by the Delta-2 launch vehicle, Jason-3 launched by the Falcon 9 launch vehicle, SARAL launched by the French National Center for Space Studies and the Indian Space Research Institute, with a resolution of 6 km, and the global near-coast significant wave height data from 2019 to 2022 are selected.

3. The method for extracting effective wave height based on synthetic aperture radar image according to claim 2, characterized in that: In step 1, the synthetic aperture radar used is the interferometric imaging mode of the Sentinel-1 in the European Space Agency's Copernicus program, with a resolution of 10m and a synthetic aperture radar image size of 250kmx250km.

4. The method for extracting effective wave height based on synthetic aperture radar images according to claim 3, characterized in that: The time matching window and space matching distance are as follows: in terms of time, ±1.5 hours are used as the time matching window; in terms of space, the center position of the effective wave height obtained by the altimeter is taken as the center of the circle, and the data points on the synthetic aperture radar image are matched within a circular range with a radius of 3 km. The altimeter circular range with a synthetic aperture radar image pixel less than 500 is eliminated, and the matching is completed.

5. The method for extracting effective wave height based on synthetic aperture radar image according to claim 1, characterized in that ; In step 2, the sample effective wave height data are distributed in the near coast of the world, and the incident angle ranges are divided into 32°±1°, 34°±1°, 36°±1°, 38°±1° and 40°±1°. The sample data set exceeds 67,000, of which more than 12,000 data are within the 38°±1° incident angle range, and 6,000 ±100 data are within the 32°±1° incident angle range. In the near-coast range of the world, the effective wave height is mainly concentrated around 2m±0.5, with more than 5,000 data, showing a Weibull distribution.

6. The method for extracting effective wave height based on synthetic aperture radar images according to claim 5, characterized in that: The global near coasts include the coast of Hawaii, the east and west coasts of the United States, the west coast of Europe, the southeast coast of Africa, the southeast coast of China and the coast of Japan.

7. The method for extracting effective wave height based on synthetic aperture radar images according to claim 1, characterized in that: In step 3, the quality control is performed for all data points using a confidence ellipse fitting method, where the normalized variance consists of a mean and a standard deviation, and the formula is as follows: Among them, σ is the standard deviation, μ is the mean, and Nvar is the normalized variance.

8. The method for extracting effective wave height based on synthetic aperture radar images according to claim 1, characterized in that: In step 4, the linear fitting is a one-dimensional polynomial fitting, and the calculation formula is: Where y is the estimated value of the effective wave height of the synthetic aperture radar, x is the normalized variance, and are the fitted coefficients of the polynomial.

9. The method for extracting effective wave height based on synthetic aperture radar images according to claim 1, characterized in that: In step 5, the buoy effective wave height uses the effective wave height data of global nearshore waters from 2019 to 2022 from the National Data Buoy Center of the National Oceanic and Atmospheric Administration of the United States.

10. The method for extracting effective wave height based on synthetic aperture radar images according to claim 9, characterized in that: In step 5, the specific method includes the following steps: Step 101: Use the altimeter effective wave height to evaluate the estimated value of the synthetic aperture radar effective wave height, and compare the average deviation of the estimated value of the synthetic aperture radar effective wave height at each incident angle compared with the altimeter effective wave height, also known as the weighted deviation, which is calculated as follows: in, is the weight of the synthetic aperture radar effective wave height estimate, is the median value of the synthetic aperture radar effective wave height estimate for each 0.2m interval, is the weight bias of the synthetic aperture radar effective wave height estimate; Step 102: Use the effective wave height data observed on site to verify the estimated effective wave height of the synthetic aperture radar, and calculate the deviation and standard deviation of the estimated effective wave height of the synthetic aperture radar compared with the effective wave height observed on site. The deviation is calculated as follows: in, is the estimated value of synthetic aperture radar effective wave height, To observe the effective wave height on site, is the deviation of the estimated effective wave height of synthetic aperture radar compared with the effective wave height observed in situ, The standard deviation is calculated as follows: in, is the estimated value of effective wave height of a single synthetic aperture radar, is the average of the synthetic aperture radar effective wave height estimates, is the total number of samples of SAR effective wave height estimation, and STD is the standard deviation of SAR effective wave height estimation.

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