Sea clutter simulation method based on space-based bistatic radar system

Abstract

The application provides a sea clutter simulation method based on an air-based bistatic radar system, which comprises the following steps: a radar carried on a satellite launch platform irradiates a sea surface to be monitored, and a sea area irradiated by each radar in a coherent processing interval (CPI) is divided into multiple sub-regions; a sea clutter frequency domain algorithm is used to determine a single-beam monopulse sea clutter signal corresponding to each sub-region based on the frequency domain characteristics of each sea surface scattering point in the sub-region; and an echo signal corresponding to a beam in the coherent processing interval (CPI) of each radar is determined according to the single-beam monopulse sea clutter signal corresponding to each sub-region. The sea clutter frequency domain algorithm can convert a relatively complex Fourier transform into frequency shift and linear calculation, thereby reducing the calculation amount of simulation and improving the simulation efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radar, in particular to a sea clutter simulation method based on an air-based bistatic radar system. BACKGROUND

[0002] The air-based bistatic radar system refers to a radar transmitter and a receiver located on different platforms. For a radar system with satellite transmission and unmanned aerial vehicle reception to detect the ocean surface, the ocean surface condition needs to be modeled and the sea clutter echo needs to be simulated. In some cases, the distribution of sea clutter signals may appear long tailing. Traditional statistical distribution models are difficult to fit the long tailing part, and the model accuracy is limited. Moreover, since the sea clutter is the echo of a complex object composed of multiple scatterers, the number of scatterers contributing to the echo will obey different statistical characteristics under different sea conditions. A fixed statistical distribution model is difficult to adapt to all complex sea conditions. In order to improve the accuracy of simulation, the sea clutter simulation method driven by a physical model models the sea surface as a physical field of waves with different frequencies and different directions of propagation, and uses a classical composite double-scale model to complete the mapping of sea state information to sea surface clutter scattering unit parameters, so as to realize high simulation accuracy and strong applicability of the sea clutter.

[0003] The patent document with publication number CN117828255A discloses a "spaceborne bistatic radar multi-channel sea clutter modeling method and system". The method is aimed at a spaceborne bistatic radar system, establishes a sea surface model driven by a physical model, and realizes the simulation generation of sea clutter signals. However, the method only analyzes the sea clutter signal generation from the time domain, without considering the frequency domain, and cannot intuitively reflect the Doppler effect caused by the relative motion of the sea surface scattering point and the receiver. SUMMARY

[0004] In order to solve the above problems in the prior art, the present application provides a sea clutter simulation method based on an air-based bistatic radar system, which specifically comprises:

[0005] In a first aspect, the present application provides a sea clutter simulation method based on an air-based bistatic radar system, which comprises:

[0006] The radar carried on the satellite transmission platform irradiates the sea surface to be monitored, and the radar irradiated sea area in each radar coherent processing interval (CPI) is divided into multiple sub-regions. The radar coherent processing interval (CPI) is the single irradiation time of the radar, and each beam in the radar coherent processing interval (CPI) contains multiple pulse signals.

[0007] Through a sea clutter frequency domain algorithm, the frequency domain characteristics of each sea surface scattering point in each sub-region are determined to determine the single-beam monopulse sea clutter signal corresponding to each sub-region;

[0008] According to the corresponding single-beam monopulse sea clutter signal in each sub-region, the echo signal corresponding to the beam in each radar coherent processing interval (CPI) is determined.

[0009] The present application has the following beneficial effects:

[0010] The sea clutter simulation method based on the space-based bistatic radar system provided by the present application can utilize the sea clutter frequency domain algorithm to convert the relatively complex Fourier transform into frequency shift and linear calculation, reduce the calculation amount of simulation, and improve the simulation efficiency.

[0011] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The present application provides a space-based bistatic radar system schematic diagram;

[0013] Figure 2 The present application provides a flowchart of a sea clutter simulation method based on the space-based bistatic radar system;

[0014] Figure 3 The present application provides a set of simulation result schematic diagrams. DETAILED DESCRIPTION

[0015] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0016] To solve the problems in the prior art, the present application provides a sea clutter simulation method based on a space-based bistatic radar system, which quantizes the Doppler frequency after preliminary modeling of the ocean surface, selects the Doppler frequency point closest to the Doppler frequency of the scattering point in the quantization interval, performs frequency shift on the frequency domain to obtain the signal waveform component, constructs different scattering point clutter data by combining the signal delay component and the amplitude component, and performs inverse fast Fourier transform after superposition to obtain the final echo signal. This method starts from the signal Doppler frequency domain, explores the frequency domain expression of sea clutter simulation, explains the influence of Doppler frequency shift in the generation of sea clutter signal simulation, perfects the sea clutter frequency domain algorithm, and converts the Fourier transform into frequency shift and linear calculation of the radar transmitted signal through the quantization processing of the Doppler frequency domain, which can reduce the simulation calculation amount of the frequency domain method and improve the calculation efficiency.

[0017] The space-based bistatic radar system according to the present application comprises a satellite transmitting platform and an unmanned aerial vehicle receiving platform, as shown in the following figure. Figure 1 The satellite transmitting platform sends radar signals, which are scattered by the sea surface and then received by the aerial receiving platform. Due to the limited coverage of the radar signals, the sea detection range needs to be divided into different areas of scattering points, and the echoes of all scattering points are superimposed to generate sea clutter.

[0018] Figure 2 The flowchart of the sea clutter simulation method based on the space-based bistatic radar system according to the present application is shown in the following figure. Figure 2 The method comprises the following steps.

[0019] S201, irradiate the sea surface to be monitored by the radar carried on the satellite transmitting platform, and divide the sea area irradiated by each radar in a radar coherent processing interval (CPI) into multiple sub-regions.

[0020] The radar coherent processing interval (CPI) is the single irradiation time of the radar, and each beam in the radar coherent processing interval (CPI) contains multiple pulse signals.

[0021] For example, in a single CPI (i.e. a frame of signals), the 50km×100km sea surface is divided into multiple elliptical clutter patches based on the single irradiation area of the transmitting platform, and each clutter patch is uniformly divided into multiple sub-regions according to a size of 2km×2km.

[0022] The calculation formula of the uniformly divided sub-regions of the sea surface is as follows:

[0023]

[0024] where ΔR is the division interval, ρ is the compression coefficient, adjusting the coefficient can adjust the calculation amount and simulation accuracy, c represents the speed of light, and B represents the maximum bandwidth of the radar signal.

[0025] Before step S201, the method further comprises building a simulation scene, i.e. setting a satellite transmitting platform and an unmanned aerial vehicle receiving platform, and selecting a sea area as a region to be monitored.

[0026] It should be noted that the sea surface region can be divided by using the uniform division method as shown above, or other division methods such as the equidistance ring division method.

[0027] S202, determine the single-beam monopulse sea clutter signal corresponding to each sub-region based on the frequency domain characteristics of each sea surface scattering point in each sub-region by using a sea clutter frequency domain algorithm.

[0028] S203, determining the echo signal corresponding to the beam in each radar coherent processing interval (CPI) according to the single-beam monopulse sea clutter signal corresponding to each sub-region.

[0029] Specifically, the above process is repeated in one CPI to obtain a multi-pulse echo signal; all receiving beam directions are traversed to obtain a single CPI echo signal under all beam directions (beam number x pulse number x distance sampling), which is stored in the system.

[0030] The sea clutter simulation method based on the space-based bistatic radar system provided by the application can utilize the sea clutter frequency domain algorithm to convert the relatively complex Fourier transform into frequency shift and linear calculation, reduce the calculation amount of simulation, and improve the simulation efficiency.

[0031] The step S201 of determining the single-beam monopulse sea clutter signal corresponding to each sub-region based on the frequency domain characteristics of each sea surface scattering point in each sub-region by the sea clutter frequency domain algorithm will be described in further detail as follows:

[0032] In one possible implementation, the step of determining the single-beam monopulse sea clutter signal corresponding to each sub-region based on the frequency domain characteristics of each sea surface scattering point in each sub-region by the sea clutter frequency domain algorithm includes the following steps A1 and A2:

[0033] A1, for any first sea surface scattering point in each sea surface scattering point in each sub-region, determining the Doppler frequency value of the first sea surface scattering point and finding the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point in the preset quantization interval; after performing Fourier transform on the radar transmission signal currently irradiated on the first sea surface scattering point, performing frequency shift processing on the Fourier transform result corresponding to the radar transmission signal according to the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point to obtain a first signal; determining the single-beam monopulse sea clutter signal corresponding to the first sea surface scattering point according to the first signal.

[0034] A2, determining the single-beam monopulse sea clutter signal corresponding to each sub-region according to the single-beam monopulse sea clutter signal corresponding to all sea surface scattering points in each sub-region under each pulse signal in one radar coherent processing interval (CPI).

[0035] The step A1 will be described in further detail as follows:

[0036] Optionally, in step A1, determining the Doppler frequency value of the first sea surface scattering point and finding the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point within a preset quantization interval includes: d Quantization obtains the quantization interval, and the number of quantization bits is N q ; Calculate the Doppler frequency value f of the first sea surface scattering point di ; Find the Doppler frequency value f of the first sea surface scattering point within the quantization interval di The nearest Doppler frequency f di0 .

[0037] Among them, the quantization interval is expressed as:

[0038] F d =-f dmax :df d :f dmax , f dmax Indicates the maximum Doppler frequency value in the quantization interval, df d Represents the quantization interval, : represents the step. The quantization bit and the quantization interval satisfy the relationship Need to be adjusted according to the amount of calculation and accuracy.

[0039] Optionally, in step A1, after performing Fourier transform on the radar transmission signal currently irradiated at the first sea surface scattering point, frequency shift processing is performed on the Fourier transform result corresponding to the radar transmission signal according to the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point to obtain the first signal, including: performing Fourier transform on the radar transmission signal s(t) currently irradiated at the first sea surface scattering point, and performing frequency shift processing on the Fourier transform result corresponding to the radar transmission signal according to the Doppler frequency point f closest to the Doppler frequency value of the first sea surface scattering point di0 , perform frequency shift on the Fourier transform result to obtain the first signal s(f+f di0 ).

[0040] Optionally, in step A1, determining a single-beam monopulse sea clutter signal corresponding to the first sea surface scattering point based on the first signal includes the following steps a1-a6:

[0041] a1. Under a single pulse signal, establish the sea surface parameter field of the sub-region where the first sea surface scattering point is located.

[0042] Optionally, under a single pulse signal, establishing a sea surface parameter field of the sub-region where the first sea surface scattering point is located includes the following steps a1.1-a1.3:

[0043] a1.1. Under a single pulse signal: Based on the sea surface parameters of the sub-region where the first sea surface scattering point is located, establish the wave height field. The corresponding expression is:

[0044] z(x, y, t) = z l (x, y, t) + z s (x, y, t),

[0045] where z l (x, y, t) represents the long wave component, z s (x, y, t) represents the short wave component, x represents the azimuthal coordinate, y represents the range coordinate, and t represents time,

[0046]

[0047] k x and k y represent the azimuthal and range wave numbers of the sea wave, respectively, represents the phase of the sea wave with the wave number vector (k x , k y ), represents the angular frequency of the sea wave with the wave number vector (k x , k y ), g represents the gravitational acceleration, represents the long wave amplitude, represents the short wave amplitude.

[0048] Specifically, the amplitude can be obtained according to the amplitude of the wave spectrum density, and the specific expression is:

[0049]

[0050] where E h (k x , k y ) represents the wave spectrum density, E l (k x , k y ) represents the long wave spectrum density, E s (k x , k y ) represents the short wave spectrum density, and ξ0 represents a normalization factor. A suitable ξ0 is selected to satisfy:

[0051]

[0052] where is the root mean square of the long wave component of the sea wave height, H s is the significant wave height.

[0053] Specifically, the long wave spectrum density E l (k x , k y ) can be represented as:

[0054]

[0055] wherein a represents the Phillips parameter describing the spectral intensity, k p represents the peak wavenumber of the strong exchange spectrum, φ p represents the angle between the wave propagation direction of the main wave and the direction along the orbit, μ represents the peak enhancement factor, Γ() represents the gamma function, arctan() represents the inverse tangent function, exp represents the exponential function, ln() represents the logarithm with base e, cos represents the cosine function, σ J is assumed to be the following expression:

[0056]

[0057] The expansion factor p in the expansion function is:

[0058]

[0059] wherein U represents the wind speed at a preset height, such as 19.5 m.

[0060] Specifically, the short wave spectral density E s (k x ,k y ) can be represented as:

[0061]

[0062] wherein β represents the Phillips parameter describing the short wave spectral intensity.

[0063] a1.2, determining the incidence angle and the receiving angle of the first sea surface scattering point.

[0064] Optionally, determining the incidence angle and the receiving angle of the first sea surface scattering point comprises the following steps a1.2.1 and a1.2.2:

[0065] a1.2.1, establishing a sea surface local coordinate system for the sub-region where the first sea surface scattering point is located, the x-axis of the sea surface local coordinate system is the azimuth direction, and the y-axis is the distance direction, and the corresponding expression is:

[0066]

[0067] wherein M represents the total number of scattering points of the sub-region where the first sea surface scattering point is located in the x direction, N represents the total number of scattering points of the sub-region where the first sea surface scattering point is located in the y direction, m represents the x direction scattering point serial number, n represents the y direction scattering point serial number, ΔR represents the division interval, ρ represents the compressibility, c represents the speed of light, and B represents the maximum bandwidth of the radar signal.

[0068] a1.2.2. convert the coordinates of the first sea surface scattering points in the sea surface local coordinate system into the incident angle and the receiving angle in the geodetic coordinate system, and the corresponding expression is:

[0069]

[0070] wherein θ T represents the incident angle, and θ R represents the receiving angle, represents the direction vector of the first sea surface scattering point pointing to the satellite transmitting platform, represents the direction vector of the first sea surface scattering point pointing to the receiving platform, represents the normal vector of the first sea surface scattering point in the sub-region section, |·| represents the modulus operation, and (·) represents the vector inner product.

[0071] Specifically, the geodetic coordinate system is the 2000 national geodetic coordinate system, i.e., the CGCS2000 coordinate system.

[0072] a1.3. establish the radial velocity field of the satellite transmitting platform and the receiving platform relative to the first sea surface scattering point according to the incident angle and the receiving angle of the first sea surface scattering point, and the corresponding expression is:

[0073]

[0074] wherein θ T and θ R respectively represent the incident angle and the receiving angle of the sea surface scattering point, represents the radial velocity field of the first sea surface scattering point relative to the satellite transmitting platform, represents the radial velocity field of the first sea surface scattering point relative to the receiving platform.

[0075] The determination process of the radial velocity field of the sea surface scattering point relative to the satellite transmitting platform and the radial velocity field of the sea surface scattering point relative to the receiving platform is the same, and the determination process of the radial velocity field is described in further detail below through a group of general expressions:

[0076] Specifically, the sea surface to be monitored is modeled as a water particle with simultaneous translation motion and vibration, the radial velocity field includes an average velocity component and a random velocity component, and is expressed as:

[0077]

[0078] wherein v r (x,y,t) is the average velocity component, and u r (x,y,t) is the random velocity component,

[0079] For the average velocity component:

[0080] The average velocity component can be expressed as:

[0081]

[0082] where the first term is the radial component of the ocean current velocity, and the second term is the radial long-wave orbital velocity field,

[0083]

[0084] For the random velocity component:

[0085] For the random velocity component, the short-wave related motion of a scattering point is modeled as a random Gaussian distribution with mean 0 and standard deviation , specifically:

[0086]

[0087] Further, the radial velocity field is simplified, and the average velocity component v r (x,y,t) is expanded into a Taylor series up to the second order at , to obtain:

[0088]

[0089] where a r (x,y,t) represents the long-wave related radial orbital acceleration,

[0090]

[0091] The change in velocity caused by the radial orbital acceleration is modeled as a Gaussian random velocity:

[0092]

[0093] where T a is the radar illumination time.

[0094] Further, the two are combined into a random variable, and there is

[0095]

[0096] Assuming that the motion processes of long waves and short waves are independent, the standard deviation of u r (x,y,t) can be expressed as:

[0097]

[0098] a2、According to the sea surface parameter field of the sub-region where the first sea surface scattering point is located, the time delay of the first sea surface scattering point and the normalized radar scattering cross section corresponding to the first sea surface scattering point are determined.

[0099] Optionally, the time delay of the first sea surface scattering point is determined according to the sea surface parameter field of the sub-region where the first sea surface scattering point is located, comprising: determining actual distances from the satellite transmitting platform and the receiving platform to the first sea surface scattering point respectively according to the radial velocity field of the satellite transmitting platform and the receiving platform relative to the first sea surface scattering point; and determining the time delay of the first sea surface scattering point according to the actual distances from the satellite transmitting platform and the receiving platform to the first sea surface scattering point.

[0100] The corresponding expression is:

[0101]

[0102] wherein, R T0 represents the distance from the satellite transmitting platform to the first sea surface scattering point at t0, R R0 represents the distance from the receiving platform to the first sea surface scattering point at t0, Δt T represents the time delay of the satellite transmitting platform to the first sea surface scattering point at t0, Δt R represents t the time delay of the receiving platform to the first sea surface scattering point at t0, c represents the speed of light, v a represents the moving speed of the receiving platform, and τ represents the time delay of the first sea surface scattering point.

[0103] Optionally, the normalized radar cross section corresponding to the first sea surface scattering point is determined according to the sea surface parameter field of the sub-region where the first sea surface scattering point is located, comprising: determining the normalized radar cross section corresponding to the first sea surface scattering point according to the sea wave height field corresponding to the sub-region where the first sea surface scattering point is located.

[0104] The corresponding expression is:

[0105]

[0106] wherein, σ 0 (x, y, t) represents the normalized radar cross section corresponding to the first sea surface scattering point, represents the normalized radar cross section corresponding to the first sea surface scattering point under the inclination modulation, κ hydr (x, y, t) represents the hydrodynamic modulation factor, κ hydr (x, y, t) = 1 + z l (x, y, t) · k p , k p represents the dominant wave number.

[0107] Specifically, for a radar system with a transceiver channel split, its normalized radar cross section (NRCS) is composed of two parts, which is represented as:

[0108]

[0109] Among them, κ hydr (x,y,t) is the hydrodynamic modulation factor, which represents the scattering component of fluid mechanics,

[0110] κ hydr (x m ,y n ,t)=1+z l (x,y,t)·k p ,

[0111] Among them, k p is the dominant wave number.

[0112] is the normalized radar cross section under tilt modulation. Taking horizontal-horizontal (HH) polarization as an example, its calculation formula is:

[0113]

[0114] Where k is the wave number of the electromagnetic wave; θ is the angle of incidence or reflection. When calculating the radar cross section of the scattering point relative to the launch platform, the incident angle θ is used. T , when calculating the radar cross section of the scattering point relative to the receiving platform, input the reflection angle θ R ;

[0115] δ x and δ y Respectively expressed as:

[0116]

[0117] and and They are:

[0118]

[0119] Where ε is the relative dielectric constant of seawater,

[0120] a3. Determine the amplitude component corresponding to the first sea surface scattering point based on the normalized radar cross section corresponding to the first sea surface scattering point.

[0121] Optionally, an amplitude component corresponding to the first sea surface scattering point is determined according to a normalized radar cross section corresponding to the first sea surface scattering point, and is expressed as:

[0122]

[0123] Among them, Ai represents the amplitude component corresponding to the i-th sea surface scattering point, P av is the average transmit power, G T and G R are the transmit antenna gain and receive gain, respectively, and γ(x, y) represents the normalized radar cross section σ 0 (x, y, t) of the first sea surface scattering point, λ is the radar operating wavelength, B is the radar bandwidth, PRT is the pulse repetition period, R0 is the slant range distance, L s is the system loss, and i represents the sea surface scattering point index.

[0124] a4, determining a delay component corresponding to the first sea surface scattering point according to the time delay of the first sea surface scattering point.

[0125] Optionally, the time delay of the first sea surface scattering point is determined according to the delay component corresponding to the first sea surface scattering point, and is expressed as:

[0126]

[0127] wherein e represents a constant, f represents a frequency, and f di0 represents the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point, τ i represents the time delay of the i-th scattering point, and i represents the sea surface scattering point index.

[0128] a5, determining a signal waveform component corresponding to the first sea surface scattering point according to the first signal;

[0129] a6, determining a single-beam mono-pulse sea clutter signal corresponding to the first sea surface scattering point according to the amplitude component, the delay component, and the signal waveform component corresponding to the first sea surface scattering point.

[0130] Optionally, the single-beam mono-pulse sea clutter signal corresponding to the first sea surface scattering point is determined according to the amplitude component, the delay component, and the signal waveform component corresponding to the first sea surface scattering point, and includes: superimposing the amplitude component, the delay component, and the signal waveform component corresponding to the first sea surface scattering point to obtain a second signal.

[0131] The corresponding expression is:

[0132]

[0133] wherein r(f) represents the second signal, MN represents the number of individual sub-region scattering points, M represents the total number of scattering points of the sub-region in which the first sea surface scattering point is located in the x direction, N represents the total number of scattering points of the sub-region in which the first sea surface scattering point is located in the y direction, s(f+f di0 ) represents the frequency shift of the radar signal, and s'(f+fdi0 ) is a derivative of f di s(f+f di0 ) and s'(f+f di0 ) represent the Doppler frequency values of the first sea surface scattering points, and s(f+f di ) and s'(f+f di0 ) represent the signal waveform components corresponding to the first sea surface scattering points.

[0134] The present application can intuitively reflect the influence of the Doppler effect on the simulation generation of the sea clutter signal by analyzing the frequency domain of the sea clutter signal and deriving the frequency domain expression; the simulation calculation amount can be effectively reduced by quantizing the Doppler frequency and then approximately processing the Doppler frequency of the scattering points through the frequency domain fast generation algorithm, which converts the relatively complex Fourier transform into frequency shift and linear calculation.

[0135] The technical effects of the present application will be further described in detail below in combination with a simulation experiment.

[0136] 1. Simulation conditions:

[0137] In the air-based bistatic radar system, one space-based transmitting platform and one air-based receiving platform are set, the orbit height of the transmitting platform is 36000 km, the height of the air-based receiving platform is 20 km, the flight speed v a = 50 m / s, and the wind speed is 6.2 m / s, and the significant wave height H s = 1.2 m.

[0138] The hardware environment of the simulation is that the CPU is Intel(R) Core(TM) i7-12700H with Radeon Graphics, the main frequency is 2.30Ghz, and the main memory is 16GB. The software environment is Windows 11 Home Chinese Edition, and the simulation software is MATLAB R2024a.

[0139] 2. Simulation content

[0140] The sea surface parameters are set, the ocean surface wave height field, the radial velocity field, and the normalized radar scattering cross section field are modeled. According to these parameters, the sea clutter echo under the bistatic radar is calculated and generated, and the probability model (K distribution) of the echo generated by the high-precision grid general sea surface model is compared, and the results are shown in Figure 3 .

[0141] As can be seen from Figure 3 , compared with the K distribution model, the similarity of the amplitude probability distribution of the sea clutter echo generated by the present application can reach 97.39%, which verifies the effectiveness of the physical driving model sea clutter echo simulation method based on the air-based bistatic radar system proposed by the present application.

[0142] Therefore, the sea clutter simulation method suitable for the air-based bistatic radar system is provided, the sea surface is modeled as the physical field of different frequency and different direction propagation waves by the physical model driving, and the simulation calculation amount is reduced by using the sea clutter frequency domain algorithm.

[0143] The terms "first", "second", "third", etc. are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0144] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the art to which the present application belongs, a number of simple deductions or replacements can be made without departing from the concept of the present application, and all should be considered within the protection scope of the present application.

Claims

1. A sea clutter simulation method based on an airborne bistatic radar system, characterized in that: include: The radar onboard the satellite launch platform illuminates the sea surface to be monitored, and the radar-illuminated sea area within each radar coherent processing interval (CPI) is divided into multiple sub-areas. The radar coherent processing interval (CPI) is the time for a single radar illumination, and the beam within each radar coherent processing interval (CPI) contains multiple pulse signals. For any first sea surface scattering point among the sea surface scattering points within each of the sub-areas, a Doppler frequency value of the first sea surface scattering point is determined, and a Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point is found within a preset quantization interval; after performing Fourier transform on a radar transmit signal currently irradiated on the first sea surface scattering point, a frequency shift processing is performed on a Fourier transform result corresponding to the radar transmit signal according to the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point to obtain a first signal; and, using a single pulse signal, a sea surface parameter field of the sub-area where the first sea surface scattering point is located is established; determining, based on a sea surface parameter field of a subregion where the first sea surface scattering point is located, a time delay of the first sea surface scattering point and a normalized radar cross section corresponding to the first sea surface scattering point; Determine the amplitude component corresponding to the first sea surface scattering point according to the normalized radar cross section corresponding to the first sea surface scattering point, expressed as: Among them, A i represents the amplitude component corresponding to the i-th sea surface scattering point, P av is the average transmit power, G T and G R are the transmitting antenna gain and receiving gain respectively, γ(x,y) means that the mean is 0, and the variance is the normalized radar cross section σ corresponding to the first sea surface scattering point 0 The random complex reflectivity of (x, y, t), x represents the azimuth coordinate, y represents the range coordinate, t represents time, λ is the radar operating wavelength, B is the radar bandwidth, PRT is the pulse repetition period, R0 is the slant range, L s is the system loss, i represents the sea surface scattering point index, and ΔR is the division interval; Determine a delay component corresponding to the first sea surface scattering point based on the time delay of the first sea surface scattering point, expressed as: Among them, e represents a constant, f represents frequency, and f di0 Indicates the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point, τ i represents the time delay of the i-th scattering point, i represents the sea surface scattering point index; determining, based on the first signal, a signal waveform component corresponding to the first sea surface scattering point; Determine a single-beam monopulse sea clutter signal corresponding to the first sea surface scattering point based on the amplitude component, delay component, and signal waveform component corresponding to the first sea surface scattering point. A second signal is obtained by superimposing the amplitude component, delay component, and signal waveform component corresponding to the first sea surface scattering point. The corresponding expression is: Where r(f) represents the second signal, MN represents the number of scattering points in a single sub-region, M represents the total number of scattering points in the x-direction of the sub-region where the first sea surface scattering point is located, N represents the total number of scattering points in the y-direction of the sub-region where the first sea surface scattering point is located, and s(f+f di0 ) represents the first signal, s′(f+f di0 ) is s(f+f di0 ), f di Indicates the Doppler frequency value of the first sea surface scattering point, s(f+f di0 )+s′(f+f di0 )(f di -f di0 ) represents the signal waveform component corresponding to the first sea surface scattering point; determining, according to the single-beam monopulse sea clutter signals corresponding to all sea surface scattering points in each sub-area under each pulse signal within a radar coherent processing interval CPI, the single-beam monopulse sea clutter signals corresponding to each sub-area; According to the single-beam monopulse sea clutter signals corresponding to the sub-areas, the echo signals corresponding to the beams within the coherent processing intervals CPI of each radar are determined.

2. The method according to claim 1, characterized in that The step of establishing the sea surface parameter field of the sub-region where the first sea surface scattering point is located under a single pulse signal includes: Under a single pulse signal: According to the sea surface parameters of the sub-region where the first sea surface scattering point is located, the wave height field is established, and the corresponding expression is: z(x,y,t)=z l (x,y,t)+z s (x,y,t), Among them, z l (x, y, t) represents the long-wave component, z s (x, y, t) represents the shortwave component, x represents the azimuth coordinate, y represents the distance coordinate, and t represents the time. k x and k y represent the azimuth wave number and distance wave number of the ocean waves, respectively. The wave number vector is (k x ,k y )’s wave phase, The wave number vector is (kx,k y ) is the angular frequency of the waves, g represents the acceleration due to gravity, represents the long-wave amplitude, represents the shortwave amplitude; determining an incident angle and a receiving angle of the first sea surface scattering point; Based on the incident angle and receiving angle of the first sea surface scattering point, the radial velocity fields of the satellite launch platform and the receiving platform relative to the first sea surface scattering point are established. The corresponding expressions are: Among them, θ T and θ R denote the incident angle and receiving angle of the sea surface scattering point, respectively. represents the radial velocity field of the first sea surface scattering point relative to the satellite launch platform, represents the radial velocity field of the first sea surface scattering point relative to the receiving platform.

3. The method according to claim 2, characterized in that Determining the time delay of the first sea surface scattering point according to the sea surface parameter field of the sub-region where the first sea surface scattering point is located includes: The actual distances of the satellite launching platform and the receiving platform from the first sea surface scattering point are determined based on the radial velocity fields of the satellite launching platform and the receiving platform relative to the first sea surface scattering point. The corresponding expressions are: Among them, R T0 R represents the distance from the satellite launch platform to the first sea surface scattering point at time t0, R0 represents the distance from the receiving platform to the first sea surface scattering point at time t0, Δt T represents the time delay from the satellite launch platform to the first sea surface scattering point at time t0, Δt R represents the time delay from the receiving platform to the first sea surface scattering point at time t0, c represents the speed of light, v a Indicates the moving speed of the receiving platform; The time delay of the first sea surface scattering point is determined according to the actual distances between the satellite transmitting platform and the receiving platform and the first sea surface scattering point. The corresponding expression is: where τ represents the time delay of the first sea surface scattering point.

4. The method according to claim 3, characterized in that Determining a normalized radar cross section corresponding to the first sea surface scattering point according to a sea surface parameter field of a sub-region where the first sea surface scattering point is located includes: The normalized radar cross section (NRCS) corresponding to the first sea surface scattering point is determined based on the wave height field corresponding to the sub-region where the first sea surface scattering point is located. The corresponding expression is: Among them, σ 0 (x, y, t) represents the normalized radar cross section corresponding to the first sea surface scattering point, represents the normalized radar cross section corresponding to the first sea surface scattering point under tilt modulation, κ hydr (x,y,t) represents the hydrodynamic modulation factor, κ hydr (x,y,t)=1+z l (x,y,t)·k p , k p Indicates the dominant wave number.

5. The method according to any one of claims 2 to 4, characterized in that: The determining the incident angle and the receiving angle of the first sea surface scattering point includes: A local sea surface coordinate system is established for the sub-region where the first sea surface scattering point is located. The x-axis of the local sea surface coordinate system is the azimuth direction, and the y-axis is the distance direction. The corresponding expression is: Where M represents the total number of scattering points in the x-direction of the sub-region where the first sea surface scattering point is located, N represents the total number of scattering points in the y-direction of the sub-region where the first sea surface scattering point is located, m represents the scattering point number in the x-direction, n represents the scattering point number in the y-direction, and ΔR is the division interval; The coordinates of each scattering point on the first sea surface in the local sea surface coordinate system are converted into the incident angle and the receiving angle in the geodetic coordinate system. The corresponding expressions are: Among them, θ T represents the angle of incidence, θ R represents the acceptance angle, Indicates the direction vector of the first sea surface scattering point pointing to the satellite launch platform, Indicates the direction vector of the first sea surface scattering point pointing to the receiving platform, represents the normal vector of the sub-region section where the first sea surface scattering point is located, |·| represents the modulo operation, and (·) represents the vector inner product.

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