A method for determining the NRCS of a Ku-band scatterometer under rain conditions

Abstract

The application discloses a method for determining the NRCS of a Ku-band scatterometer under rainfall conditions, and relates to the field of satellite ocean remote sensing and meteorological detection, which comprises the following steps: considering the action mechanism of rainfall in the atmosphere on a radar signal, and constructing a sea surface radar backscattering theory model based on a wind-generated sea surface spectrum and a double-scale Bragg scattering theory; obtaining a rainfall attenuation coefficient, a normalized radar backscattering cross section of raindrop body scattering contribution, and dual-polarization normalized radar backscattering cross sections of C-band and Ku-band based on the sea surface radar backscattering theory model; and obtaining the normalized radar backscattering cross section of the Ku-band scatterometer under rainfall conditions according to the rainfall attenuation coefficient, the normalized radar backscattering cross section of raindrop body scattering contribution, and the dual-polarization normalized radar backscattering cross sections of C-band and Ku-band, so that the application can obtain an accurate normalized radar backscattering cross section of the Ku-band scatterometer under rainfall conditions.

Description

Technical Field

[0001] This application relates to the fields of satellite ocean remote sensing and meteorological observation, and in particular to a method for determining the NRCS of a Ku-band scatterometer under rainfall conditions. Background Technology

[0002] Spaceborne scatterometers, with their continuous and wide-ranging global sea surface observations, have become an important means of acquiring global sea surface wind field information and have been widely applied. However, under rainy sea conditions, Ku-band scatterometers are greatly affected by precipitation due to their short wavelengths. In tropical regions and tropical cyclone sea conditions, rainfall is often present, and up to 10% of Ku-band scatterometer data is affected by rainfall. However, the signal is affected by rainfall and is not entirely caused by wind, so it cannot be directly used for wind field inversion. Existing technologies mostly rely on empirical statistics or multi-source data fusion for rainfall correction, that is, based on the assumption that C-band scatterometer signals are not affected by rainfall, and correction is performed by matching scatterometer products of different bands with precipitation data. However, these methods introduce errors when matching different data and have problems such as incomplete consideration of physical mechanisms, resulting in the inability to obtain accurate Normalized Radar Cross Section (NRCS) of Ku-band scatterometers under rainy conditions. This affects the accuracy of scatterometer wind field inversion to some extent. Summary of the Invention

[0003] The purpose of this application is to provide a method for determining the NRCS of a Ku-band scatterometer under rainfall conditions, which can obtain an accurate normalized radar backscattering cross section of the Ku-band scatterometer under rainfall conditions.

[0004] To achieve the above objectives, this application provides the following solution: This application provides a method for determining the NRCS of a Ku-band scatterometer under rainfall conditions, including: considering the mechanism of precipitation in the atmosphere on radar signals, and constructing a theoretical model of sea surface radar backscattering based on wind-generated sea surface spectrum and dual-scale Bragg scattering theory.

[0005] Based on the theoretical model of sea surface radar backscattering, the rainfall attenuation coefficient, the dual-polarization normalized radar backscattering cross section of the C-band, the dual-polarization normalized radar backscattering cross section of the Ku-band, and the normalized radar backscattering cross section contributed by raindrop scattering are obtained.

[0006] The normalized radar backscattering cross section (RSC) of the Ku-band scatterometer under rainfall conditions is obtained based on the rainfall attenuation coefficient, the dual-polarization normalized radar backscattering cross section of the C-band, the dual-polarization normalized radar backscattering cross section of the Ku-band, and the normalized radar backscattering cross section contributed by raindrop scattering.

[0007] According to the specific embodiments provided in this application, this application has the following technical effects: This application provides a method for determining the NRCS of a Ku-band scatterometer under rainfall conditions. This application constructs a theoretical model of sea surface radar backscattering based on wind-generated sea surface spectrum and dual-scale Bragg scattering theory. It simulates the dual-polarization normalized radar backscattering cross section of C-band (not affected by precipitation) and Ku-band (severely affected by precipitation). In the process of constructing the theoretical model of sea surface radar backscattering, the different mechanisms of precipitation on radar signals in the atmosphere are fully considered. It can obtain an accurate normalized radar backscattering cross section of the Ku-band scatterometer under rainfall conditions. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 This is a flowchart illustrating a method for determining the NRCS of a Ku-band scatterometer under rainfall conditions, provided as an embodiment of this application.

[0010] Figure 2 This is a schematic diagram of the wind field of Hurricane Lee as observed by the FY3E satellite on September 12, 2023.

[0011] Figure 3 This is a comparison chart of the measured data and model simulation results from the FY3E satellite. Detailed Implementation

[0012] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0013] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] In one exemplary embodiment, such as Figure 1 As shown, a method for determining the NRCS of a Ku-band scatterometer under rainfall conditions is provided, including the following steps 201 to 203.

[0015] Step 201: Considering the mechanism of precipitation's effect on radar signals in the atmosphere, construct a theoretical model of sea surface radar backscattering based on wind-generated sea surface spectrum and two-scale Bragg scattering theory.

[0016] Step 202: Based on the theoretical model of sea surface radar backscattering, obtain the rainfall attenuation coefficient, the dual-polarization normalized radar backscattering cross section of the C-band, the dual-polarization normalized radar backscattering cross section of the Ku-band, and the normalized radar backscattering cross section contributed by raindrop scattering.

[0017] Step 203: Based on the rainfall attenuation coefficient, the dual-polarization normalized radar backscattering cross section of the C-band, the dual-polarization normalized radar backscattering cross section of the Ku-band, and the normalized radar backscattering cross section contributed by raindrop scattering, the normalized radar backscattering cross section of the Ku-band scatterer under rainfall conditions is obtained.

[0018] In another exemplary embodiment of this application, the sea surface radar backscattering theoretical model includes a sea surface NRCS theoretical simulation module based on wind-generated sea surface spectrum and two-scale Bragg scattering theory, as well as a precipitation attenuation module and a volume scattering module that consider the effect of precipitation on radar signals in the atmosphere.

[0019] The sea surface NRCS theoretical simulation module is used to obtain the dual-polarization normalized radar backscattering cross section (RSC) of the C-band and the dual-polarization normalized radar backscattering cross section of the Ku-band.

[0020] The rainfall attenuation module is used to obtain the rainfall attenuation coefficient.

[0021] The volume scattering module is used to obtain the normalized radar backscattering cross section of the raindrop volume scattering contribution.

[0022] In another exemplary embodiment of this application, the dual-polarization normalized radar backscattering cross section includes the VV-polarization normalized radar backscattering cross section and the HH-polarization normalized radar backscattering cross section; the sea surface NRCS theoretical simulation module includes a dual-scale theoretical model, which is as follows: .

[0023] .

[0024] .

[0025] .

[0026] 。

[0027] A dual-scale theoretical model was constructed to simulate the sea surface normalized radar backscattering cross section under rainless conditions in the C-band and Ku-band, with VV polarization and HH polarization. This represents the C-band VV-polarized normalized radar backscattering cross section. This represents the C-band HH polarization normalized radar backscattering cross section. This represents the VV-polarized normalized radar backscattering cross section in the Ku-band. This represents the normalized radar backscattering cross section in the Ku-band HH polarization. Represents pi (π). Indicates the C-band radar wave number. Indicates the Ku-band radar wave number. express The sine value, Indicates the local incident angle of radar waves The weighting factor representing HH polarization, The weighting factor representing VV polarization, express The sine value, The local incident angle of the radar wave after the influence of long-wave tilt. This represents the angle between the radar signal and the incident plane of the radar signal after considering the long-wave tilt. This indicates the angle between the radar signal and the vertical plane after considering the long-wave tilt; the vertical plane is the plane perpendicular to the incident plane of the radar signal. Represents a two-dimensional sea surface wavenumber spectrum. This represents the wave number that oscillates in the x-direction. This represents the wave number that oscillates in the y-direction.

[0028] In another exemplary embodiment of this application, the rainfall attenuation module includes a precipitation attenuation coefficient formula, which is: A rainfall attenuation module was constructed, and the precipitation attenuation coefficient was calculated using an integral formula to obtain the component of radar signal attenuated by raindrops in the atmosphere. This represents the precipitation attenuation coefficient, which is a function of the rainfall rate. This represents the integral of radar signal attenuation along its path. It is also related to the attenuation coefficient due to rainfall. The solution first requires calculating the integral of the radar signal attenuation along the path, and the calculation formula is: ,in The upper limit of integration represents the path length of the radar signal attenuated by precipitation, measured in decibels (dB). The precipitation coefficient is a function related to the precipitation rate. , where RR is the rainfall rate in mm / h, a and b are coefficients determined by the radar frequency (a=0.018945, b=1.15), and r represents the path length of the radar signal attenuated by precipitation.

[0029] Raindrops falling from the air, in addition to attenuating the signal from the sea surface scatterometer, also produce volume scattering. In another exemplary embodiment of this application, the volume scattering module includes a volume scattering component calculation formula, which is as follows: A volume scattering module is constructed to calculate the normalized radar backscattering cross section of the raindrop volume scattering contribution, wherein... Normalized radar backscattering cross section contributing to raindrop scattering Indicates the local incident angle of the radar wave. This indicates the path of the radar signal from the clouds to the sea surface. Represents the volume scattering coefficient. This represents the precipitation attenuation coefficient. Indicates the integral over s, This indicates the path of the radar signal from the clouds to the sea surface.

[0030] In another exemplary embodiment of this application, ,in, Represents pi (π). Indicates the wavelength of the electromagnetic wave emitted by the scatterometer. The refractive index function of water, which is related to wavelength and temperature of the substance, can be approximated as 0.93 for rainfall. Let | represent the reflectivity factor of raindrops in the air, and | denote the absolute value. For rainfall, the calculation... The formula applies to frequencies below 10 GHz. The relationship between rainfall rate (RR) and precipitation size distribution depends on the rainfall particle size and can be approximated as: .

[0031] In another exemplary embodiment of this application, the rainfall attenuation coefficient, the dual-polarization normalized radar backscattering cross section of the C-band, the dual-polarization normalized radar backscattering cross section of the Ku-band, and the normalized radar backscattering cross section contributed by raindrop volume scattering are obtained based on the theoretical model of sea surface radar backscattering. Specifically, the following steps are taken: obtaining the C-band radar wavenumber, the Ku-band radar wavenumber, the local incident angle of the radar wave, the two-dimensional sea surface wavenumber spectrum, the angle between the radar signal and the incident surface after considering the long-wave tilt, the integral of the radar signal attenuation along the path, the volume scattering coefficient, the path of the radar signal from the cloud layer to the sea surface, and the path of the radar signal in the atmosphere.

[0032] By inputting the C-band radar wavenumber, Ku-band radar wavenumber, local incident angle of radar waves, two-dimensional sea surface wavenumber spectrum, angle between radar signal and incident surface after considering long-wave tilt, integral of radar signal attenuation along the path, volume scattering coefficient, path of radar signal from cloud layer to sea surface and path of radar signal in atmosphere into the theoretical model of sea surface radar backscattering, the precipitation attenuation coefficient, C-band dual-polarization normalized radar backscattering cross section, Ku-band dual-polarization normalized radar backscattering cross section and normalized radar backscattering cross section contributed by raindrop volume scattering are obtained.

[0033] In another exemplary embodiment of this application, the C-band radar wavenumber, Ku-band radar wavenumber, local incident angle of radar wave, two-dimensional sea surface wavenumber spectrum, angle between radar signal and incident surface after considering long-wave tilt, integral of radar signal attenuation along path, volume scattering coefficient, path of radar signal from cloud layer to sea surface, and path of radar signal in atmosphere are input into the sea surface radar backscattering theoretical model to obtain the rainfall attenuation coefficient, C-band dual-polarization normalized radar backscattering cross section, Ku-band dual-polarization normalized radar backscattering cross section, and normalized radar backscattering cross section contributed by raindrop volume scattering. Specifically, the C-band radar wavenumber, Ku-band radar wavenumber, local incident angle of radar wave, two-dimensional sea surface wavenumber spectrum, and angle between radar signal and incident surface after considering long-wave tilt are input into the sea surface NRCS theoretical simulation module to obtain the C-band dual-polarization normalized radar backscattering cross section and the Ku-band dual-polarization normalized radar backscattering cross section.

[0034] The integral of the radar signal attenuation along the path is input into the rainfall attenuation module to obtain the rainfall attenuation coefficient.

[0035] Rainfall attenuation coefficient, volume scattering coefficient, and local incident angle of radar waves were used. The normalized radar backscattering cross section, which is calculated by inputting the radar signal path from the cloud layer to the sea surface and the radar signal path through the atmosphere into the volume scattering module, is obtained from the raindrop scattering contribution.

[0036] In another exemplary embodiment of this application, the normalized radar backscattering cross section of the Ku-band scatterometer under rainfall conditions is obtained based on the rainfall attenuation coefficient, the dual-polarization normalized radar backscattering cross section of the C-band, the dual-polarization normalized radar backscattering cross section of the Ku-band, and the normalized radar backscattering cross section contributed by raindrop scattering. Specifically, the normalized radar backscattering cross section of the sea surface under wind field is obtained based on the dual-polarization normalized radar backscattering cross section of the C-band and the dual-polarization normalized radar backscattering cross section of the Ku-band.

[0037] The normalized radar backscattering cross section (RSC) of the Ku-band scatterometer under rainfall conditions is obtained based on the rainfall attenuation coefficient, the normalized radar backscattering cross section of the sea surface under wind field, and the normalized radar backscattering cross section contributed by raindrop scattering.

[0038] Raindrops have two main effects on the NRCS received by the scatterometer during their descent: firstly, electromagnetic waves reflected from the sea surface are attenuated, leading to a decrease in NRCS; secondly, raindrops scatter additional NRCS through volume scattering. The attenuated NRCS is superimposed on the additional NRCS generated by volume scattering. The NRCS received by the scatterometer can be described by a superposition formula. In another exemplary embodiment of this application, the normalized radar backscattering cross section (NRCS) of the Ku-band scatterometer under rainfall conditions is obtained based on the rainfall attenuation coefficient, the normalized radar backscattering cross section of the sea surface under wind conditions, and the normalized radar backscattering cross section contributed by raindrop volume scattering. Specifically, according to the formula... Calculate the normalized radar backscattering cross section of a Ku-band scatterometer under rainfall conditions. , As the NRCS ultimately observed by the scatterometer, among which, This represents the normalized radar backscattering cross section of the sea surface under the influence of wind fields. According to , , and The simulation results show that the NRCS is solely caused by wind, and the specific simulation process is well-known.

[0039] Based on a comprehensive consideration of the scattering characteristics of electromagnetic waves by rainfall in the atmosphere, this application establishes a theoretical model of wind and rain coupled backscattering of sea surface radar. Through simulation using this theoretical model, the dependence of wind speed and radar backscattering cross-section on rainfall rate under different incident angles and azimuth angles is revealed, establishing a theoretical model of sea surface radar backscattering suitable for Ku-band scatterometers and incorporating rainfall factors.

[0040] This application constructs a theoretical model of backscattering of sea surface radar and comprehensively considers the attenuation of electromagnetic waves by rainfall in the atmosphere and the volume scattering effect. It is applicable to radar signal simulation and rainfall error correction in sea surface wind field inversion of Ku-band spaceborne scatterometers.

[0041] This application can simulate the sea surface NRCS caused by wind in rainless sea states, which is beneficial for considering the multiple mechanisms by which precipitation in the atmosphere affects radar signals, analyzing the impact of precipitation on radar signals, and thus improving the backscattering signal of the Ku-band scatterometer under the influence of rainfall, reducing the impact of precipitation on the scatterometer wind field inversion, and improving the accuracy of wind field inversion.

[0042] This application also provides an embodiment for verifying a theoretical model of backscattering from a sea surface radar. Since the NRCS of a Ku-band scatterometer is affected by rainfall by an order of magnitude more than that of the C-band, and wind field inversion using the C-band scatterometer NRCS is almost unaffected under low to moderate rainfall, this embodiment simulates the C-band NRCS, approximating it as the true value unaffected by rainfall. The band ratio results of the simulated Ku-band and C-band NRCS, including the rainfall effect, are compared with the band ratios obtained from measured data to verify the model's accuracy. The simulated NRCS is compared with measured data from WindRAD carried by the FY3E satellite, such as... Figure 2 and Figure 3 As shown, Figure 2 The black box in the middle represents the area to be verified. Figure 3 Parts (a) and (b) show the band ratios of the Ku and C bands under VV and HH polarization, respectively. The red, yellow, blue, and magenta solid lines represent the NRCS of the Ku and C bands simulated by the model when the precipitation rate is 10 mm / h, the azimuth angles are 0° and 90°, and the incident angles are 39° and 46°, respectively. The wind speed range is from 2 m / s to 40 m / s. The solid scatter points are the measured data from FY3E, and the color intensity represents the density of the data points. Based on the comparison between the NRCS of the sea surface wind field of Hurricane Lee in 2023 monitored by FY3E and the model simulation results, it can be seen that the model basically matches the measured data in terms of the magnitude and trend of the simulated NRCS, which proves the feasibility of the model.

[0043] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0044] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for NRCS determination for Ku-band scatterometer under rain conditions, characterized in that, The method for determining the NRCS of the Ku-band scatterometer under rainfall conditions comprises the following steps: Considering the mechanism of the effect of precipitation on radar signals in the atmosphere, a sea surface radar backscattering theory model is constructed based on wind-generated sea surface spectrum and double-scale Bragg scattering theory; Based on the sea surface radar backscattering theory model, the rainfall attenuation coefficient, the C-band dual-polarization normalized radar cross section, the Ku-band dual-polarization normalized radar cross section and the normalized radar cross section of raindrop body scattering contribution are obtained; According to the rainfall attenuation coefficient, the C-band dual-polarization normalized radar cross section, the Ku-band dual-polarization normalized radar cross section and the normalized radar cross section of raindrop body scattering contribution, the normalized radar cross section of the Ku-band scatterometer under rainfall conditions is obtained.

2. The method for NRCS determination for Ku-band scatterometer under rain conditions according to claim 1, characterized in that, The sea surface radar backscattering theory model comprises a sea surface NRCS theoretical simulation module constructed based on wind-generated sea surface spectrum and double-scale Bragg scattering theory, and a rainfall attenuation module and a body scattering module constructed by considering the mechanism of the effect of precipitation on radar signals in the atmosphere; The sea surface NRCS theoretical simulation module is used to obtain the C-band dual-polarization normalized radar cross section and the Ku-band dual-polarization normalized radar cross section; The rainfall attenuation module is used to obtain the rainfall attenuation coefficient; The body scattering module is used to obtain the normalized radar cross section of raindrop body scattering contribution.

3. The method for NRCS determination for Ku-band scatterometers in rain conditions according to claim 2, characterized in that, The dual-polarization normalized radar cross section comprises a VV polarization normalized radar cross section and a HH polarization normalized radar cross section; the sea surface NRCS theoretical simulation module comprises a double-scale theory model, and the double-scale theory model is as follows: ； ； ； ； wherein represents the c-band normalized radar backscatter cross section for VV polarization, represents the c-band normalized radar backscatter cross section for HH polarization, represents the ku-band normalized radar backscatter cross section for VV polarization, represents the ku-band normalized radar backscatter cross section for HH polarization, represents the circular constant, represents the c-band radar wave number, represents the ku-band radar wave number, is the sine value of is the sine value of represents the local incidence angle of the radar wave, represents the weighting factor for HH polarization, represents the weighting factor for VV polarization, is the sine value of is the sine value of is the local incidence angle of the radar wave after the influence of the long wave tilt, represents the angle between the radar signal and the radar signal incidence plane after the consideration of the long wave tilt, represents the angle between the radar signal and the vertical plane after the consideration of the long wave tilt; the vertical plane is a plane perpendicular to the radar signal incidence plane, represents the two-dimensional sea surface wave number spectrum, represents the wave number fluctuating in the x direction, represents the wave number fluctuating in the y direction, | | represents the absolute value.

4. The method for NRCS determination for Ku-band scatterometer under rain conditions according to claim 2, characterized in that, The rain attenuation module includes a rain attenuation coefficient formula, the rain attenuation coefficient formula being: wherein, represents the rain attenuation coefficient, represents the integral of the attenuation of the radar signal along the path.

5. The method for NRCS determination for Ku-band scatterometer under rain conditions according to claim 2, wherein, The volume scattering module includes a volume scattering component calculation formula, the volume scattering component calculation formula is: wherein, denotes a normalized radar backscatter cross section of raindrop volume scattering contribution, denotes a local incidence angle of the radar wave, denotes a path of the radar signal from the cloud layer to the sea surface, denotes a volume scattering coefficient, denotes a precipitation attenuation coefficient, denotes an integral of s, denotes a path of the radar signal in the atmosphere.

6. The method for NRCS determination for Ku-band scatterometer under rain conditions according to claim 2, wherein, Based on the sea surface radar backscattering theory model, the rainfall attenuation coefficient, the C-band dual-polarization normalized radar cross section, the Ku-band dual-polarization normalized radar cross section and the normalized radar cross section of raindrop body scattering contribution are obtained, specifically as follows: The C-band radar wave number, the Ku-band radar wave number, the local incidence angle of radar waves, the two-dimensional sea surface wave number spectrum, the included angle between the radar signal and the incident surface after considering the long-wave tilt, the integral of the path attenuation of the radar signal, the body scattering coefficient, the path of the radar signal from the cloud layer to the sea surface and the path of the radar signal in the atmosphere are obtained; The C-band radar wave number, the Ku-band radar wave number, the local incidence angle of radar waves, the two-dimensional sea surface wave number spectrum, the included angle between the radar signal and the incident surface after considering the long-wave tilt, the integral of the path attenuation of the radar signal, the body scattering coefficient, the path of the radar signal from the cloud layer to the sea surface and the path of the radar signal in the atmosphere are input into the sea surface radar backscattering theory model, so as to obtain the rainfall attenuation coefficient, the C-band dual-polarization normalized radar cross section, the Ku-band dual-polarization normalized radar cross section and the normalized radar cross section of raindrop body scattering contribution.

7. The method for NRCS determination for Ku-band scatterometers in rain conditions according to claim 6, characterized in that, The C-band radar wave number, Ku-band radar wave number, radar wave local incidence angle, two-dimensional sea surface wave number spectrum, radar signal and incidence surface angle after considering long wave tilt, integral of radar signal along path attenuation, volume scattering coefficient, radar signal path from cloud layer to sea surface and radar signal path in atmosphere are input into the sea surface radar backscattering theory model to obtain rain attenuation coefficient, C-band dual polarization normalized radar backscattering cross section, Ku-band dual polarization normalized radar backscattering cross section and raindrop volume scattering contribution normalized radar backscattering cross section, and the specific steps are as follows: The C-band radar wave number, Ku-band radar wave number, radar wave local incidence angle, two-dimensional sea surface wave number spectrum and radar signal and incidence surface angle after considering long wave tilt are input into the sea surface NRCS theoretical simulation module to obtain C-band dual polarization normalized radar backscattering cross section and Ku-band dual polarization normalized radar backscattering cross section. The integral of radar signal along path attenuation is input into the rain attenuation module to obtain rain attenuation coefficient. The rain attenuation coefficient, the volume scattering coefficient, the local incidence angle of the radar wave The path of the radar signal from the cloud layer to the sea surface and the path of the radar signal through the atmosphere input the volume scattering module to obtain the normalized radar backscatter cross section of the raindrop volume scattering contribution.

8. The method for NRCS determination for Ku-band scatterometer under rain conditions according to claim 1, wherein, According to the rain attenuation coefficient, C-band dual polarization normalized radar backscattering cross section, Ku-band dual polarization normalized radar backscattering cross section and raindrop volume scattering contribution normalized radar backscattering cross section, the Ku-band scatterometer normalized radar backscattering cross section under the condition of rain is obtained, and the specific steps are as follows: According to the C-band dual polarization normalized radar backscattering cross section and Ku-band dual polarization normalized radar backscattering cross section, the sea surface normalized radar backscattering cross section under the action of wind field is obtained. According to the rain attenuation coefficient, sea surface normalized radar backscattering cross section under the action of wind field and raindrop volume scattering contribution normalized radar backscattering cross section, the Ku-band scatterometer normalized radar backscattering cross section under the condition of rain is obtained.

9. The method for NRCS determination for Ku-band scatterometers in rain conditions according to claim 8, characterized in that, The normalized radar backscattering cross section of the Ku-band scatterometer under rainfall condition is specifically obtained according to the rainfall attenuation coefficient, the normalized radar backscattering cross section of the sea surface under the action of the wind field and the normalized radar backscattering cross section of the raindrop body scattering contribution, and is specifically as follows according to the formula The normalized radar backscattering cross section of the Ku-band scatterometer under rainfall condition is calculated , wherein represents the normalized radar backscattering cross section of the sea surface under the action of the wind field, represents the rainfall attenuation coefficient, represents the normalized radar backscattering cross section of the raindrop body scattering contribution.

10. The method for NRCS determination for Ku-band scatterometer under rain conditions according to claim 5, wherein, wherein, denotes the mathematical constant pi, denotes the wavelength of the scatterometer electromagnetic wave, denotes the refractive index function of water, denotes the reflectivity factor of an airborne raindrop, | | denotes taking the absolute value.

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