Bistatic radar clutter spectrum generation method based on double base inner and outer scattering coefficients

Abstract

The application discloses a bistatic radar clutter spectrum generation method based on double base inner and outer scattering coefficients, and the application divides a clutter unit in a bistatic radar space; respectively calculates the ground wiping angles of each clutter unit relative to a transmitting platform and a receiving platform; calculates equivalent ground wiping angles by using a bistatic equivalent monostatic principle; confirms clutter parameters, calculates the inner clutter scattering coefficients before correction; corrects the inner scattering model by calculating the outer plane angles corresponding to each clutter unit, and obtains the corrected clutter scattering coefficients; respectively calculates space-time two-dimensional direction vectors and clutter unit echo amplitudes, and generates a clutter echo spectrum by using all the obtained echo amplitudes. The application corrects the inner scattering model by using the outer plane angles corresponding to each clutter unit, and obtains the clutter scattering coefficients under the outer plane scattering condition. The application can be used for generating corresponding clutter spectra of various clutter types, and simultaneously reduces the scattering coefficient errors in the engineering implementation process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radar, and further relates to a bistatic radar clutter spectrum generation method based on bistatic in-plane and out-of-plane scattering coefficients in the technical field of radar signal processing. BACKGROUND

[0002] The bistatic radar system is transceiver-separated and the receiver is passive, and has the advantages of wide coverage, anti-stealth and anti-interference, and has great application potential in the future. At present, a large number of projects have completed the implementation of the monostatic clutter spectrum, but for the bistatic radar, due to the complexity of the scattering characteristics, the bistatic clutter spectrum is difficult to obtain a complete bistatic clutter scattering model in engineering application, and the reason is that the bistatic radar has a more complex geometric structure than the monostatic radar, and the scattering coefficient is related to the geometric structure.

[0003] A method for inverting the undirected sea wave spectrum from the ocean echo of a bistatic high-frequency ground wave radar is disclosed in the patent document "A method for inverting the undirected sea wave spectrum from the ocean echo of a bistatic high-frequency ground wave radar" (application number: 202111053482.3, application date: 2021.09.09, application publication number: CN 113900096 A) applied by Wuhan University. The implementation steps of the method are: first step: processing the original echo data of the narrow-beam bistatic high-frequency ground wave radar to obtain discretized echo Doppler spectrum data; second step: constructing a ratio column vector and an ocean scattering coefficient matrix from the discretized echo Doppler spectrum data; third step: calculating the pseudo-inverse matrix of the ocean scattering coefficient by singular value decomposition, and performing matrix multiplication operation on the obtained pseudo-inverse matrix of the ocean scattering coefficient and the ratio column vector to obtain the discretized undirected sea wave spectrum. The deficiency of the method is that the particularity of the bistatic out-of-plane scattering is ignored at the scattering angle corresponding to the radar range element, and it is assumed that all distance elements corresponding to the bistatic are located in the same plane. Since the method only considers the special case of in-plane scattering corresponding to the in-plane angle, the generated clutter spectrum has deviation compared with the true situation.

[0004] A full polarization bistatic radar target dynamic echo simulation method is disclosed in the patent document "A full polarization bistatic radar target dynamic echo simulation method" (application number: 201611129997.6, application publication number: CN 106772290 A) applied by the University of Defense Science and Technology of the Chinese People's Liberation Army. The implementation steps of the method are: first, establish a target coordinate system, a transmitting station rectangular coordinate system, a receiving station rectangular coordinate system, and a polarization coordinate system, then solve the observation angle pitch angle and azimuth angle of the transmitting station and the receiving station in the target coordinate system through the transmitting station position, the receiving station position, and the target position and attitude, then solve the rotation angle of the transmitting station and the receiving station polarization relative to the target coordinate system polarization by using the target attitude, the transmitting station and the receiving station position, and the line of sight angle, and finally, first, obtain the scattering matrix in the target coordinate system by looking up the table and interpolating the observation angle, and then obtain the dynamic echo of the bistatic receiving station by coordinate rotation through the polarization rotation angle. The deficiency of the method is that for a non-satellite-borne bistatic radar system, the change of the coordinate system position caused by the small range of the range unit is very small, and the change of the position relationship between the clutter unit and the transmitting and receiving platform in a small range will cause a large error in the generation of the clutter spectrum. Moreover, the method obtains the relative scattering coefficient of the bistatic receiving station through the conversion between the target coordinate system, the transmitting station rectangular coordinate system, the receiving station rectangular coordinate system, and the polarization coordinate system, greatly increasing the calculation complexity and being not conducive to meeting the real-time requirements in engineering implementation. SUMMARY

[0005] The purpose of the present application is to overcome the deficiencies of the prior art and provide a bistatic radar clutter spectrum generation method based on bistatic in-plane and out-of-plane scattering coefficients, which solves the problems of ignoring the particularity of bistatic out-of-plane scattering in bistatic radar echo engineering, high calculation complexity, and inability to meet the real-time requirements of signal processing.

[0006] The idea for achieving the purpose of the present application is that the present application can calculate the in-plane clutter scattering coefficient of the selected clutter unit before correction and the corresponding out-of-plane angle without complex coordinate conversion. By using a quadratic function to simulate the out-of-plane scattering coefficient model through the interpolation method, the in-plane scattering model is corrected. The echo scattering coefficient model obtained by only considering in-plane scattering in this special case deviates from the real application scenario, and the total clutter scattering coefficient in the real application scenario of the bistatic radar is obtained, reducing the scattering coefficient error caused by the out-of-plane angle of the bistatic radar. The in-plane scattering coefficient in the present application faces multiple types of clutter and fully considers the two types of clutter, i.e., ground clutter and sea clutter. In the process of generating the clutter spectrum, multiple selectable clutter simulation models are provided for different clutter types and conditions, reducing the scattering coefficient error caused by not setting different clutter models for different clutter types in the engineering implementation process.

[0007] The technical scheme for achieving the object of the application comprises the following steps:

[0008] Step 1, dividing a clutter cell in a bistatic radar space;

[0009] Step 2, selecting an unselected clutter cell, and calculating the transmission station and receiving station ground angles of the selected clutter cell relative to the transmission platform and the receiving platform respectively;

[0010] Step 3, calculating an equivalent ground angle;

[0011] Step 4, calculating an in-plane clutter scattering coefficient before correction;

[0012] Step 5, correcting an in-plane scattering model by using the calculated out-of-plane angle of the selected clutter cell, to obtain a clutter scattering coefficient in an out-of-plane scattering condition;

[0013] Step 6, calculating a space-time two-dimensional steering vector and a clutter cell echo amplitude respectively, and generating a clutter echo spectrum by using all the echo amplitudes obtained by repeating steps 2-5.

[0014] Compared with the prior art, the application has the following advantages:

[0015] First, the application corrects the echo scattering coefficient model obtained by only considering the in-plane scattering in a special condition, which deviates from the actual application scenario, reduces the scattering coefficient error caused by the out-of-plane angle of the bistatic radar, and the corrected in-plane scattering model expression obtained by the application is simple and clear, without the need for complex coordinate conversion to calculate the in-plane clutter scattering coefficient before correction, and the calculation complexity is low.

[0016] Second, the in-plane scattering coefficient in the application faces multiple types of clutter, fully considers the two types of clutter, i.e., ground clutter and sea clutter, and provides multiple selectable clutter simulation models for different clutter types and conditions in the process of generating the clutter spectrum, thereby reducing the scattering coefficient error caused by not setting different clutter models for different clutter types in the engineering implementation process. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a flowchart of the application;

[0018] Figure 2 is a bistatic clutter scattering region division schematic diagram of the application;

[0019] Figure 3 is a bistatic clutter scattering coefficient modeling curve established by the application;

[0020] Figure 4 is a sea clutter spectrum result diagram of the simulation experiment of the application. DETAILED DESCRIPTION

[0021] The application will be further described in detail below with reference to the accompanying drawings and examples.

[0022] Reference Figure 1 The specific implementation steps of the embodiments of the application are further described.

[0023] Step 1, divide the clutter unit in the bistatic radar space.

[0024] Step 1.1, establish a coordinate system O-XYZ, with the center of the earth as the origin, the Y axis as the position where the 0° meridian points from the origin, the X axis perpendicular to the Y axis, the XOY plane as the equatorial plane, and the Z axis as the vector pointing to the sky through the origin and perpendicular to the XOY plane.

[0025] Place the transmitting platform and the receiving platform in the same coordinate system to facilitate subsequent vector calculation and angle solving.

[0026] Step 1.2, divide the clutter equidistance unit ring.

[0027] For a bistatic radar, the echoes of all clutter scattering units on the equidistance ring are superimposed to form the distance gate echo signal. All clutter units of the distance gate are located on the long-axis rotating ellipsoid with the transmitting platform and the receiving platform as the foci, and at the same time, the clutter units are also located on the earth's spherical surface, so the intersection line of the ellipsoid and the spherical surface is the clutter equidistance ring. The ellipsoid equation and the earth's spherical surface equation are combined:

[0028]

[0029] where x o , y o , z o represent the coordinate values of the equidistance unit ring corresponding to the X axis, Y axis, and Z axis in the O-XYZ coordinate system respectively, a and b represent the ellipsoid half-long axis and the ellipsoid half-short axis of the ellipsoid formed with the receiving platform and the transmitting platform as the foci respectively, R s represents the range sum of the bistatic radar, L represents the baseline distance of the bistatic radar, and R e represents the earth's radius.

[0030] Step 1.3, divide each clutter equidistance ring into individual clutter units with an interval of 1 m to obtain the position coordinates of each clutter unit.

[0031] Divide the clutter equidistance ring into individual clutter units with the same interval to ensure that the areas of the individual clutter units are consistent, obtain the position coordinates of each clutter unit, and facilitate vector calculation in the subsequent steps.

[0032] Step 2, randomly select one unselected scatterer, calculate the incidence and exit grazing angles of the selected scatterer relative to the transmitting and receiving platforms.

[0033] Step 2.1, calculate the direction vector of each scatterer to the receiving or transmitting platform.

[0034] Determine the vector expression of the selected scatterer relative to the transmitting and receiving platforms through the position coordinates of the selected scatterer:

[0035]

[0036] wherein, represents the direction vector of the cthscatterer to the receiving or transmitting platform, x NaH , y NaH , z NaH represents the coordinate values of the X-axis, Y-axis, and Z-axis of the receiving or transmitting platform position in the O-XYZ coordinate system, respectively.

[0037] Step 2.2, calculate the incidence and exit grazing angles of each scatterer relative to the transmitting and receiving platforms.

[0038] Calculate the grazing angle formed by the direction vector of the selected scatterer and the receiving or transmitting platform on the ground according to the vector angle formula:

[0039]

[0040] wherein, ψ c,NaH represents the grazing angle formed by the direction vector of the cthscatterer and the receiving or transmitting platform on the ground, represents the unit vector of the X-axis.

[0041] Step 3, calculate the equivalent grazing angle.

[0042] In the area where the grazing angle is small, the arithmetic mean of the incidence and exit grazing angles is generally used to replace the grazing angle in the single-base scattering coefficient model, and in other areas, the geometric mean of the sine values of the incidence and exit grazing angles is generally used to replace the sine value of the grazing angle in the single-base scattering coefficient model according to the modified single-dual base equivalent principle, and the equivalent grazing angle is calculated according to the following formula:

[0043]

[0044] wherein, ψ c,g represents the equivalent grazing angle of the cthscatterer, ψ c,T represents the grazing angle formed by the direction vector of the cthscatterer and the transmitting platform on the ground, ψ c,Rrepresents the ground-rubbing angle formed by the cth clutter cell and the steering vector of the receiving platform on the ground.

[0045] Step 4, calculate the in-plane clutter scattering coefficient before correction.

[0046] The in-plane clutter scattering coefficient is calculated according to different models of different types of clutter.

[0047] When the clutter type is ground clutter, the in-plane angular scattering coefficient of each clutter cell is calculated according to the Morchin model as follows.

[0048]

[0049] wherein, σc,0 represents the in-plane scattering coefficient corresponding to the cth clutter cell, A represents the Morchin model parameter of ground clutter, represents the Morchin model parameter of ground clutter, and λ represents the wavelength of the bistatic radar. c,g When ψ c , β0 represents the Morchin model parameter of ground clutter, and λ represents the wavelength of the bistatic radar. c,g When ψ c , μ represents the Morchin model parameter of ground clutter, f0 represents the carrier frequency of the bistatic radar, and B represents the Morchin model parameter of ground clutter.

[0050] The Morchin model parameters corresponding to different types of ground are shown in the following table:

[0051] Table of Morchin model parameters corresponding to different types of ground

[0052] Terrain A B [CDATA[β0]] Desert 0.00126 π / 2 0.14 Farmland 0.004 π / 2 0.2 Forest 0.0126 π / 2 0.4 Mountainous region 0.04 1.24 0.5

[0053] When the clutter type is sea clutter, the in-plane angular scattering coefficient of each clutter cell is calculated according to the Morchin model as follows.

[0054]

[0055] wherein, s represents the sea state number, and β represents the Morchin model parameter, β = [2.44(s+1) 1.08 ] / 57.29;

[0056] When the clutter type is sea clutter, the in-plane angular scattering coefficient of each clutter cell is calculated according to the GIT model as follows.

[0057]

[0058] where G i represents the interference factor, G i = κ 4 / (1+κ 4 ), represents the wind direction factor, represents the angle between the wind direction and the radar observation direction, G w represents the wind speed factor, G w =[1.9425v w / (1+v w / 15)] q , v w represents the wind speed.

[0059] Step 5, correct the in-plane scattering model with the calculated out-of-plane angle of the selected clutter element to obtain the clutter scattering coefficient in the out-of-plane scattering case.

[0060] Step 5.1, obtain the projection of the direction vector of each clutter element to the receiving platform in the XOY plane.

[0061] Referring to Figure 2 , the out-of-plane angle is the angle between the projection of the direction vector of the clutter element to the receiving platform in the XOY plane and the X axis. In the figure, the clutter element is taken as the origin, the z axis is the vector from the center of the earth to the clutter element, the xoy plane coincides with the XOY plane, the incident vector represents the incident wave emitted by the transmitting platform to the clutter element, and the outgoing vector represents the outgoing wave reflected by the clutter element to the receiving platform. Φ is the out-of-plane angle corresponding to the clutter element.

[0062] The projection vector of the direction vector of the selected clutter element to the receiving platform in the XOY plane is as follows:

[0063]

[0064] wherein, represents the projection of the direction vector of the cth clutter element to the receiving platform in the XOY plane, x c,R , y c,R represent the coordinate values of the direction vector of the cth clutter element to the receiving platform in the O-XYZ coordinate system corresponding to the X axis and the Y axis, respectively.

[0065] Step 5.2, calculate the out-of-plane angle corresponding to each clutter element.

[0066] According to the vector angle formula, the out-of-plane angle corresponding to the selected clutter element is calculated as follows:

[0067]

[0068] wherein, Φ cdenotes the out-of-plane angle corresponding to the cth clutter cell.

[0069] Step 5.3, modifying the in-plane scattering model.

[0070] The out-of-plane scattering coefficient rule summarized from the existing measured data is as follows:

[0071] (1) when the out-of-plane angle Φ≥140°, approximate to the in-plane value, the difference is within 5dB;

[0072] (2) Φ=0°, take the maximum value, which is the maximum value of the in-plane mirror ridge region;

[0073] (3) Φ≤40°, approximate to the in-plane value, the difference is within 5dB;

[0074] (4) take the minimum value near Φ=90°, which is 10-20dB lower than the monostatic case (Φ=180°, θ i =θ s ).

[0075] According to the above conclusion, a modified bistatic out-of-plane scattering model is proposed, which is referred to Figure 3 , a quadratic function fitting is used for each section, and the vertex of the quadratic curve is selected at the left endpoint or the right endpoint of each section, and the fitting function of each section is as follows:

[0076]

[0077] where σ c denotes the modified scattering coefficient corresponding to the cth clutter cell.

[0078] Step 6, respectively calculate the space-time two-dimensional steering vector and clutter echo amplitude, and generate the clutter echo spectrum by repeating steps 2-5 to obtain all echo amplitudes.

[0079] The clutter echo of the lth range ring is:

[0080]

[0081] where N c denotes the total number of clutter cells, A denotes the echo amplitude of each clutter cell, and s s,t (f c,s , f c,d ) denotes the space-time two-dimensional steering vector corresponding to each clutter cell.

[0082] Step 6.1, calculate the spatial frequency and Doppler frequency corresponding to each clutter cell.

[0083]

[0084]

[0085] where f c,s represents the spatial frequency corresponding to the cth clutter cell, represents the steering vector of the cth clutter cell to the receiving platform, f c,d represents the Doppler frequency corresponding to the cth clutter cell, represents the velocity vector of the transmitting platform, represents the steering vector of the cth clutter cell to the transmitting platform, represents the velocity vector of the receiving platform.

[0086] Step 6.2, calculate the space-time two-dimensional steering vector corresponding to each clutter cell.

[0087] The space-time two-dimensional steering vector of each clutter cell is obtained by the Kronecker product of the spatial steering vector and the time steering vector composed of the spatial frequency and the Doppler frequency corresponding to the clutter cell:

[0088]

[0089] where s s,t (f c,s ,f c,d ) represents the space-time two-dimensional steering vector corresponding to the cth clutter cell.

[0090] Step 6.3, calculate the echo amplitude of each clutter cell.

[0091] According to the radar equation, the echo amplitude of each clutter cell is calculated:

[0092]

[0093] where A c represents the echo amplitude of the clutter cell, P T represents the transmitting power of the bistatic radar, G T represents the transmitting antenna gain of the bistatic radar, G R represents the receiving antenna gain of the bistatic radar, A represents the area of the clutter cell, π represents the circular constant, R T represents the pattern propagation factor of the transmitting platform of the bistatic radar, R R represents the pattern propagation factor of the receiving platform of the bistatic radar.

[0094] The effect of the present application is further illustrated below in combination with a simulation experiment:

[0095] 1. Simulation experiment conditions:

[0096] The hardware platform of the simulation experiment of the application is: the processor is Intel(R) Core(TM) i7-10700 CPU, the main frequency is 2.90 GHz, and the memory is 16 GB.

[0097] The software platform of the simulation experiment of the application is: Windows 10 operating system and MATLAB R2022b.

[0098] The parameter setting of the simulation experiment of the application is: the launch platform adopts a geosynchronous satellite, the orbital height is about 36000 km, the longitude thereof is 128.15 °E, the dimension thereof is 0.31 °N, the receiving platform height is about 10 km, the longitude thereof is 128.15 °E, the dimension thereof is 22.44 °N, the sea clutter scattering model is selected as "Morchin model", and the sea condition number is selected as 3.

[0099] 2. Simulation content and result analysis:

[0100] The simulation experiment of the application is to simulate the cross-domain bistatic radar with the launch platform being a geosynchronous satellite by using the method proposed in the application. In a real application scenario, there are generally two different types of clutter, i.e. ground clutter and sea clutter. The simulation of the application selects sea clutter to simulate the scattering coefficient model, and obtains the result graph of the scattering coefficient intensity about the longitude and latitude of the sea clutter scattering unit under the sea clutter Morchin model generated by the simulation software MATLAB R2022b, and the result is as shown in Figure 4 .

[0101] The effect of the simulation experiment of the application will be further described below. Figure 4

[0102] Figure 4 (a) is a three-dimensional graph of the sea clutter scattering coefficient intensity about the longitude and latitude of the sea clutter scattering unit obtained in the simulation experiment of the application, Figure 4 the X axis in (a) is the latitude of the sea clutter scattering unit, the unit is angle, the Y axis is the longitude of the sea clutter scattering unit, the unit is angle, and the Z axis is the scattering coefficient intensity, the unit is dB. Figure 4 The color bar in (a) represents the scattering coefficient intensity.

[0103] Figure 4 (b) is a two-dimensional projection graph of the sea clutter scattering coefficient intensity about the longitude and latitude of the sea clutter scattering unit obtained in the simulation experiment of the application, Figure 4 the horizontal axis in (b) is the longitude of the sea clutter scattering unit, the unit is angle, and the vertical axis is the latitude of the sea clutter scattering unit, the unit is angle. Figure 4 The color bar in (b) represents the scattering coefficient intensity. ​

[0104] Figure 4 (c) is the sea clutter power spectrum diagram obtained in the simulation experiment of the application, Figure 4 (c) the horizontal axis is the spatial frequency, and the vertical axis is the normalized Doppler frequency.

[0105] Figure 4 (a) and Figure 4 (b) reflects the corresponding relationship between the scattering coefficient and the grazing angle, and proves that the influence of the out-of-plane angle on the scattering coefficient cannot be ignored in the bistatic radar; the closer to the receiving platform, the larger the grazing angle, and the larger the scattering coefficient; the scattering unit in the fourth quadrant where the transmitting platform is located corresponds to the highest scattering coefficient. Figure 4 Figure 4 (c) the obtained sea clutter power spectrum diagram has obvious peak value, the angle-Doppler trace is approximately linear, and the clutter power spectrum is only slightly broadened; in engineering application, the clutter echo spectrum of the application will be closer to the clutter spectrum obtained in the actual environment.

Claims

1. A method for generating a bistatic radar clutter spectrum based on the in- and out-scattering coefficients of the bi-static basis, characterized in that, The method comprises the following steps: Step 1, dividing the bistatic radar space into clutter units; Step 2, selecting an unselected clutter unit, and calculating the transmission ground angle and the receiving ground angle of the selected clutter unit relative to the transmission platform and the receiving platform respectively; Step 3, calculating the equivalent ground angle; Step 4, calculating the in-plane clutter scattering coefficient before correction; Step 5, correcting the in-plane scattering model by using the out-of-plane angle corresponding to the selected clutter unit to obtain the clutter scattering coefficient in the out-of-plane scattering condition; Step 6, calculating the space-time two-dimensional steering vector and the clutter unit echo amplitude respectively, and generating the clutter echo spectrum by using all the echo amplitudes obtained by repeating steps 2-5.

2. The method of claim 1, wherein the method is based on the bi-static in- plane and out-of-plane scattering coefficients. The bistatic radar space in step 1 refers to establishing a coordinate system O-XYZ, taking the earth center as the origin, taking the position of the 0° meridian as the Y axis, taking the X axis perpendicular to the Y axis, and taking the XOY plane as the equatorial plane.

3. The method of claim 1, wherein the method is based on the bi-static in- plane and out-of-plane scattering coefficients. The dividing of the clutter units in step 1 refers to Firstly, dividing the clutter equidistant unit ring according to the following formula: ， wherein, respectively represent the coordinate values of the equidistance unit ring corresponding to the X-axis, the Y-axis and the Z-axis in the O-XYZ coordinate system, and a and b respectively represent the ellipsoid semi-major axis and the ellipsoid semi-minor axis corresponding to the ellipsoid formed by taking the receiving platform and the transmitting platform as the foci, , represents the range and the velocity of the bistatic radar, , L represents the baseline distance of the bistatic radar, represents the radius of the earth; Secondly, dividing each clutter equidistant ring into each clutter unit by taking 1 m as the unit to obtain the position coordinates of each clutter unit.

4. The method of claim 3, wherein the bi-static radar clutter spectrum is generated based on the bi-static in-plane and out-of-plane scattering coefficients. The transmission ground angle and the receiving ground angle of the selected clutter unit relative to the transmission platform and the receiving platform in step 2 are calculated according to the following formula: Firstly, calculating the steering vector of each clutter unit to the receiving or transmission platform according to the following formula: ， wherein, represents a steering vector of the cthhetero element to the receiving or transmitting platform, respectively represent the coordinate values of the X-axis, Y-axis, and Z-axis corresponding to the position of the receiving or transmitting platform in the O-XYZ coordinate system; Secondly, calculating the transmission ground angle and the receiving ground angle of each clutter unit relative to the transmission platform and the receiving platform according to the following formula: ， wherein, represents the ground angle formed by the cthhetero element and the steering vector of the receiving or transmitting platform at the ground, represents the unit vector of the X axis.

5. The method of claim 4, wherein the bi-static radar clutter spectrum is generated based on the bi-static in-plane and out-of-plane scattering coefficients. The equivalent ground angle in step 3 is obtained according to the following formula: ， wherein, represents the equivalent ground angle of the cthhetero-element, represents the ground angle formed by the cthhetero-element and the guidance vector of the launch platform on the ground, represents the ground angle formed by the cthhetero-element and the guidance vector of the receiving platform on the ground.

6. The method of claim 5, wherein the method is based on the bi-static in- plane and out-of-plane scattering coefficients. The in-plane clutter scattering coefficient in step 4 is calculated according to different models of different types of clutter: When the clutter type is ground clutter, the in-plane angular scattering coefficient of each clutter unit is calculated according to the Morchin model of the following formula: ， wherein, denotes the in-plane scattering coefficient corresponding to the cth clutter cell, A denotes the ground clutter M0rchin model parameter, denotes the ground clutter M0rchin model parameter, when denotes the ground clutter M0rchin model parameter, denotes the bistatic radar wavelength, when denotes the ground clutter M0rchin model parameter, denotes the bistatic radar carrier frequency, B denotes the ground clutter M0rchin model parameter;​​​​​ When the clutter type is sea clutter, the in-plane angular scattering coefficient of each clutter unit is calculated according to the Morchin model of the following formula: ， wherein s represents a sea state number, denotes a sea clutter Morchin model parameter, ; When the clutter type is sea clutter, the in-plane angular scattering coefficient of each clutter unit is calculated according to the GIT model of the following formula: ， wherein, represents an interference factor, , represents a wind direction factor, , represents an angle between the wind direction and the radar observation direction, represents a wind speed factor, , , represents a wind speed.

7. The method of claim 6, wherein the method is based on the bi-static in- plane and out-of-plane scattering coefficients. The out-of-plane angle corresponding to the selected clutter unit in step 5 is calculated according to the following formula: Firstly, obtaining the projection of the steering vector of each clutter unit to the receiving platform in the XOY plane according to the following formula: ， wherein, represents the projection of the guiding vector of the cth hetero-unit to the receiving platform in the XOY plane, respectively represent the coordinate values of the guiding vector of the cth hetero-unit to the receiving platform corresponding to the X-axis and Y-axis in the O-XYZ coordinate system. Secondly, calculating the out-of-plane angle corresponding to each clutter unit according to the following formula: ， wherein denotes the external face angle corresponding to the cth hetero unit.

8. The method of claim 7, wherein the method is based on the bi-static in- plane and out-of-plane scattering coefficients. The in-plane scattering model in step 5 is corrected according to the following formula: ， wherein represents the modified scattering coefficient corresponding to the cth hetero unit.

9. The method of claim 8, wherein the method is based on the bi-static in- plane and out-of-plane scattering coefficients. The space-time two-dimensional steering vector in step 6 refers to: Firstly, calculating the spatial frequency and the Doppler frequency corresponding to each clutter unit according to the following formula: ， in, This represents the spatial frequency corresponding to the c-th clutter unit. This represents the steering vector from the c-th clutter element to the receiving platform. This represents the Doppler frequency corresponding to the c-th clutter unit. This represents the velocity vector of the launch platform. This represents the steering vector from the c-th clutter element to the transmission platform. Represents the velocity vector of the receiving platform; Secondly, calculating the space-time two-dimensional steering vector corresponding to each clutter unit according to the following formula: ， wherein denotes the space-time two-dimensional steering vector corresponding to the cthhetero element.

10. The method of claim 9, wherein the method is based on the bi-static in- plane and out-of-plane scattering coefficients. The clutter unit echo amplitude in step 6 is obtained according to the following formula: ， wherein, represents the monostatic cell echo amplitude, represents the bistatic radar transmit power, represents the bistatic radar transmit antenna gain, represents the bistatic radar receive antenna gain, A represents the monostatic cell area, represents the circle constant, represents the bistatic radar transmit platform’s pattern propagation factor, represents the bistatic radar receive platform’s pattern propagation factor.

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