A clutter analysis method under spaceborne bistatic conditions

Abstract

The present invention discloses a clutter analysis method for spaceborne bistatic conditions, comprising the following steps: establishing a spaceborne bistatic radar geometric configuration; calculating the range and azimuth resolutions of the spaceborne bistatic radar, and dividing the scene into intervals based on the resolutions; dividing the clutter scattering points according to the actual resolutions, and then establishing a clutter signal model; and analyzing the clutter characteristics of the clutter signal using its space-time distribution curve and power spectrum. The present invention is suitable for analyzing clutter characteristics under any spaceborne bistatic configuration, providing a reference for subsequent spaceborne bistatic radar detection technologies.

Description

Technical Field

[0001] The present invention relates to a clutter analysis method for a spaceborne radar, in particular to a clutter analysis method under spaceborne bistatic conditions. Background Art

[0002] As an active Earth observation system, spaceborne radar offers all-weather, all-day, high-resolution, and wide-range capabilities, making it widely used in a wide range of fields, including defense, economy, agriculture, and environmental monitoring. In recent years, with increasing application demands, the need for spaceborne radar to achieve efficient Earth observation while also achieving greater flexibility and anti-interference capabilities has become a key development direction.

[0003] Spaceborne bistatic radars offer the advantages of high flexibility, wide detection range, and strong anti-interference capabilities, enabling them to acquire observational data on ground areas of interest under varying viewing angles. However, due to their bistatic configuration, clutter exhibits space-time coupling and range dependence, and clutter characteristics vary rapidly with the bistatic configuration. These factors complicate clutter suppression, hindering target detection. In practical applications, it is essential to explore bistatic configurations that facilitate detection and to study the clutter characteristics under different spaceborne bistatic configurations. This can provide theoretical support for spaceborne bistatic radar detection in practical engineering applications.

[0004] Under the conditions of spaceborne bistatic radar, the clutter characteristics are more complex due to its separate transmitter and receiver configuration: on the one hand, the Doppler frequency of the clutter is affected by the joint modulation of the transmitting and receiving platforms, while the spatial frequency is determined only by the receiving platform, which makes the clutter exhibit space-time coupling and distance dependence. On the other hand, the clutter characteristics under different bistatic configurations vary greatly. Due to the complex positional and velocity relationships between the transmitter and receiver in three-dimensional space, it is difficult to give a general change law of the clutter spectrum. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a clutter analysis method under spaceborne bistatic conditions, which is suitable for analyzing the clutter characteristics under any spaceborne bistatic configuration and provides a reference for subsequent spaceborne bistatic radar detection technology.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] A clutter analysis method under a spaceborne bistatic condition comprises the following steps:

[0008] 10) Establish the geometric configuration of a spaceborne bistatic radar;

[0009] 20) Calculate the range and azimuth resolutions of the spaceborne bistatic radar and divide the scene into intervals based on the resolutions;

[0010] 30) After dividing the clutter scattering points according to the actual resolution, establish the clutter signal model;

[0011] 40) Analyze the clutter characteristics through the space-time distribution curve and power spectrum of the clutter signal.

[0012] Furthermore, in step 10), the orbital altitude, velocity direction, and baseline length of the transmitter and receiver are first determined; the three parameters are divided into two categories: same orbital altitude and different orbital altitudes, coplanar and non-coplanar velocities, and short baseline and long baseline. By classifying the three parameters, clutter characteristics under various bistatic radar geometric configurations are simulated and analyzed. Under the bistatic radar geometric configuration with the same orbital altitude, coplanar velocity, and short baseline, the broadening of the clutter spectrum is minimized.

[0013] Furthermore, a relative coordinate system O-XYZ was established: T is the transmitter, R is the receiver, the center of the earth O is the origin, the straight line from the center of the earth to the receiver is the Z axis, the plane where the baseline S1S2 is located is the XOZ plane, and the Y axis is determined according to the right-hand rule. denote the elevation angle and azimuth angle respectively;

[0014] In the coordinate system O-XYZ, the position vectors of the transmitter and receiver are expressed as:

[0015] ,

[0016] In the coordinate system O-XYZ, the equation of the rotating ellipsoid is expressed as:

[0017] ,

[0018] in, , represents the double baseline distance, Indicates the baseline and The angle between the axes; the parametric equation of the earth's spherical surface is:

[0019] ,

[0020] in, denote the elevation angle and azimuth angle respectively. By combining the above parametric equations, we can obtain the clutter equidistance ring equation as follows:

[0021] ,

[0022] The solution is:

[0023] ,

[0024] in,

[0025] ;

[0026] right Perform traversal scanning and calculate the corresponding , only when and The value of the formula satisfies the condition hour, and The value of is meaningful. Substituting it into the formula, we can get the position vector [x, y, z] of the clutter unit on the equidistant ring;

[0027] Based on the dual-base range loop obtained from the above simulation model, the limitation of the earth's curvature on the radar detection range under spaceborne conditions should also be considered. When the radar line of sight is tangent to the earth's surface, the maximum detection range is reached. Therefore, the maximum detection range between the transmitter and the receiver is expressed as:

[0028] ,

[0029] The transmitter and receiver cover different areas on the earth's surface. Only when the ground clutter block is illuminated by the transmitting beam and the receiving beam at the same time will an effective clutter echo signal be generated.

[0030] Furthermore, step 20) is specifically as follows: based on the clutter geometric model, a clutter signal model for each range is established, the range ring is divided into grids, each grid can be regarded as a scattering unit, and all clutter echoes in a single range ring are the superposition of the echoes of all scattering units within it. By strictly calculating the range resolution and azimuth resolution of the space-based bistatic radar, the scene is divided into intervals according to the resolution:

[0031] ;

[0032] ;

[0033] Where: represents the speed of light; Indicates wavelength; Indicates the signal bandwidth; The angle between the two vectors representing the clutter scattering unit pointing to the transmitting station and the receiving station; Indicates accumulation time; and denote the angular velocity vectors of the transmitting station and the receiving station respectively; is the direction of the constant Doppler gradient.

[0034] Furthermore, the step 30) is specifically as follows: after dividing the clutter scattering points according to the actual resolution, the clutter signal of the lth range unit is represented as the superposition of a large number of clutter scattering unit echo signals in multiple equidistant rings with range ambiguity, that is:

[0035] ,

[0036] Among them, Na is the range ambiguity number, Nc is the number of clutter scattering units on an equidistant ring, is the Kronecker product, , ,as well as They represent the spatial steering vector, time steering vector and space-time two-dimensional steering vector of the i-th clutter unit of the m-th fuzzy range ring respectively. The specific expression is:

[0037] ,

[0038] .

[0039] Furthermore, the step 40) is specifically as follows: using a 1300 km low-orbit satellite in a dual-base configuration with the same orbital altitude, coplanar velocity, and short baseline, to perform a simulation analysis of clutter characteristics:

[0040] 41) Space-time distribution curve

[0041] The space-time distribution curve shows the relationship between the spatial azimuth angle of the clutter scattering point relative to the receiver and the Doppler frequency at different range rings. The Doppler frequency of the clutter point of the bistatic radar is and spatial frequency Respectively expressed as:

[0042] ,

[0043] ,

[0044] Where, is the spacing of the receiving channels, is the signal wavelength, is the transmitter speed, is the receiver speed; and are the flight direction of the transmitter and the flight direction of the receiver, and are the azimuth and elevation angles of the transmitter relative to the target point P, and are the azimuth and elevation angles of the receiver relative to the target point P, respectively;

[0045] 42) Bistatic radar clutter power spectrum

[0046] For the lth range ring, according to the expression of the clutter echo signal, the space-time clutter data of the kth pulse received by the nth channel is recorded as , therefore, the expression of the space-time two-dimensional data of the lth range ring is:

[0047] ,

[0048] Where: Indicates the number of selected distance rings;

[0049] The clutter spectrum is represented by the high-resolution minimum variance spectrum, which is defined as follows:

[0050] ;

[0051] Where P is the clutter power spectrum, is the space-time two-dimensional steering vector, It represents the estimated clutter plus noise covariance matrix of the lth range ring, and its expression is:

[0052] .

[0053] Compared to existing technologies, the present invention has the following advantages: by establishing a reasonable spaceborne bistatic radar geometry and clutter signal model, it is applicable to the analysis of clutter characteristics in multiple bistatic configurations, compared to traditional bistatic clutter analysis methods that only apply to a single configuration. Furthermore, the present invention considers the two-dimensional space-varying nature of resolution, calculates the actual two-dimensional resolution, and divides the scene into intervals based on the resolution. This facilitates the search for bistatic configurations that are conducive to detection and provides theoretical support for spaceborne bistatic radar detection in practical engineering projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The present invention is a flowchart of a clutter analysis method under spaceborne dual-base conditions.

[0055] Figure 2 It is a schematic diagram of the geometric configuration of a spaceborne bistatic radar.

[0056] Figure 3 Schematic diagram of a single equidistant ring in the same orbital altitude-velocity coplanar-short baseline configuration.

[0057] Figure 4 This is the resulting graph of the space-time distribution curve.

[0058] Figure 5 This is the result of the power spectrum of the clutter signal. DETAILED DESCRIPTION

[0059] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0060] A bistatic configuration design method under space-based dynamic geometric conditions is adopted to carry out simulation analysis of clutter signals under space-borne bistatic radar conditions.

[0061] like Figure 1 As shown, the present invention provides a dual-base configuration design method under space-based dynamic geometric conditions, comprising the following steps:

[0062] 10) Establish the geometric configuration of spaceborne bistatic radar.

[0063] A specific bistatic configuration requires determining the orbital altitude, velocity direction, and baseline length of the transmitter and receiver. These three parameters are divided into two categories: same orbital altitude vs. different orbital altitudes, coplanar vs. non-coplanar velocities, and short vs. long baselines. By classifying these three parameters, simulations and analysis of the clutter characteristics under various bistatic configurations were conducted. It was found that the bistatic configuration with the same orbital altitude, coplanar velocity, and short baseline minimizes the broadening of the clutter spectrum, which is beneficial for improving detection capabilities. Subsequent simulation and analysis examples also use this configuration. By establishing a geometric configuration model for a spaceborne bistatic radar applicable to any of the above parameters, clutter characteristics analysis under any spaceborne bistatic configuration can be achieved.

[0064] The geometric model of the spaceborne bistatic radar is as follows: Figure 2 As shown in Figure 1, where T is the transmitter and R is the receiver. To describe the relative positional relationship between the two satellites, a relative coordinate system, O-XYZ, was established. Since dual-base systems typically use space-time adaptive processing of echo signals received by the receiving station to suppress clutter, the construction of the space-time steering vector is based on the receiving station. Therefore, when establishing the coordinate system, the origin is the Earth's center, O, the straight line from the Earth's center to the receiver is the Z axis, the plane containing the baseline S1S2 is the XOZ plane, and the Y axis is determined according to the right-hand rule. represent the elevation angle and azimuth angle respectively.

[0065] In the coordinate system O-XYZ, the position vectors of the transmitter and receiver can be expressed as:

[0066] ,

[0067] In the coordinate system O-XYZ, the equation of the rotating ellipsoid can be expressed as:

[0068] ,

[0069] in, , represents the double baseline distance, Indicates the baseline and The angle between the axes. The parametric equation of the earth's spherical surface is:

[0070] ,

[0071] in, Denote the elevation angle and azimuth angle respectively. Combining the above parametric equations, we get the clutter equidistance ring equation as follows:

[0072] ,

[0073] Solving this equation, we get:

[0074] ,

[0075] in,

[0076] ,

[0077] right Perform traversal scanning and calculate the corresponding , only when and The value of the formula satisfies the condition hour, and The value of is meaningful. By substituting it into the formula, we can get the position vector [x, y, z] of the clutter unit on the equidistant ring.

[0078] Based on the dual-base range loop solved by the above simulation model, the limitation of the Earth's curvature on the radar detection range under spaceborne conditions should also be considered. The maximum detection range is achieved when the radar's line of sight is tangent to the Earth's surface. Therefore, the maximum detection range between the transmitter and the receiver can be expressed as:

[0079] ,

[0080] The transmitter and receiver cover different areas on the Earth's surface. Only when the ground clutter block is illuminated by both the transmit and receive beams will an effective clutter echo signal be generated. For spaceborne bistatic radars, the beam coverage ranges under different orbital configurations vary greatly, and there is a mismatch between the ground coverage of the transmit and receive beams. A single equidistant ring under a bistatic configuration with the same orbital altitude, coplanar velocity, and short baseline is shown in Figure 2. Figure 3 shown.

[0081] 20) Strictly calculate the range and azimuth resolutions of the spaceborne bistatic radar and divide the scene into intervals based on the resolutions.

[0082] Based on the established clutter geometry model, a clutter signal model for each range is established. The range ring is divided into a grid, with each grid cell considered a scattering unit. All clutter echoes within a single range ring are the sum of the echoes from all scattering units within it. The uniform division of ground scattering units used in spaceborne bistatic radars ignores spatial distortion of resolution. This invention rigorously calculates the range and azimuth resolutions of the spaceborne bistatic radar and divides the scene into intervals of resolution.

[0083] ,

[0084] ,

[0085] Where: represents the speed of light; Indicates wavelength; Indicates the signal bandwidth; The angle between the two vectors representing the clutter scattering unit pointing to the transmitting station and the receiving station; Indicates accumulation time; and denote the angular velocity vectors of the transmitting station and the receiving station respectively; is the direction of the constant Doppler gradient.

[0086] 30) After dividing clutter scattering points according to actual resolution, a clutter signal model is established. This clutter model, which divides scattering points according to resolution, has two impacts compared to a uniformly divided model. First, when resolution deteriorates significantly, the scattering area of ​​each scattering element increases, increasing the clutter amplitude. Second, Doppler ambiguity occurs. Deteriorating azimuth resolution increases the azimuth width of each scattering element, corresponding to a larger spatial cone angle range at the receiving station. Consequently, multiple spatial cone angles correspond to the same Doppler frequency, causing clutter spectrum broadening. Considering the non-uniform division of scattering elements in practical situations, this study explores the characteristics of bistatic clutter that are beneficial for studying actual engineering applications, providing theoretical support for spaceborne bistatic radar detection in practical applications.

[0087] After dividing the clutter scattering points according to the actual resolution, the clutter signal of the lth range unit can be expressed as the superposition of a large number of clutter scattering unit echo signals in multiple equidistant rings with range ambiguity, that is,

[0088] ,

[0089] Among them, Na is the range ambiguity number, Nc is the number of clutter scattering units on an equidistant ring, is the Kronecker product. , ,as well as They represent the spatial steering vector, time steering vector and space-time two-dimensional steering vector of the i-th clutter unit of the m-th fuzzy range ring respectively. The specific expression is

[0090] ,

[0091] ,

[0092] 40) Analyze the clutter characteristics through the space-time distribution curve and power spectrum of the clutter signal

[0093] A simulation analysis of clutter characteristics is conducted using a 1300km low-orbit satellite in a dual-base configuration with the same orbital altitude, coplanar velocity and short baseline.

[0094] 41) Space-time distribution curve

[0095] The space-time distribution curve shows the relationship between the spatial azimuth angle of the clutter scattering point relative to the receiver and the Doppler frequency at different range rings. The Doppler frequency of the clutter point of the bistatic radar and spatial frequency Respectively expressed as:

[0096] ,

[0097] ,

[0098] Where, is the spacing of the receiving channels, is the signal wavelength, is the transmitter speed, is the receiver speed; and are the flight direction of the transmitter and the flight direction of the receiver, and are the azimuth and elevation angles of the transmitter relative to the target point P, and are the azimuth and elevation angles of the receiver relative to the target point P, respectively.

[0099] According to the above formula, the space-time distribution curve is as follows: Figure 4 In the figure, the solid line represents the space-time distribution curve corresponding to the clutter unit in the effective area covered by the receiver and the transmitter; the dotted line represents the space-time distribution curve corresponding to the clutter unit in the invalid area.

[0100] 42) Bistatic radar clutter power spectrum

[0101] For the lth range ring, according to the expression of the clutter echo signal, the space-time clutter data of the kth pulse received by the nth channel is recorded as Therefore, the expression of the space-time two-dimensional data of the first range ring is:

[0102] ,

[0103] Where: Indicates the number of selected distance rings.

[0104] The clutter spectrum is represented by the high-resolution minimum variance distortionless response (MVDR), which is defined as follows:

[0105] ,

[0106] Where P is the clutter power spectrum, is the space-time two-dimensional steering vector, It represents the estimated clutter plus noise covariance matrix of the lth range ring, and its expression is:

[0107] ,

[0108] Its minimum variance spectrum is as follows Figure 5 shown.

Claims

1. A clutter analysis method under spaceborne bistatic conditions, characterized in that The steps include: 10) Establish the geometric configuration of a spaceborne bistatic radar; 20) Calculate the range and azimuth resolutions of the spaceborne bistatic radar and divide the scene into intervals based on the resolutions; 30) After dividing the clutter scattering points according to the actual resolution, establish the clutter signal model; 40) Analyze the clutter characteristics through the space-time distribution curve and power spectrum of the clutter signal; In step 10), the orbital altitude, velocity direction, and baseline length of the transmitter and receiver are first determined; the three parameters are classified into two categories: same orbital altitude and different orbital altitude, coplanar and non-coplanar velocity, and short baseline and long baseline; by classifying the three parameters, clutter characteristics under various bistatic radar geometric configurations are simulated and analyzed. The clutter spectrum broadening degree is minimized under the bistatic radar geometric configuration with the same orbital altitude, coplanar velocity, and short baseline. The step 20) is specifically as follows: based on the establishment of the clutter geometric model, a clutter signal model for each range exchange is established, the range ring is divided into grids, each grid can be regarded as a scattering unit, and all clutter echoes in a single range ring are the superposition of the echoes of all scattering units within it. By strictly calculating the range resolution and azimuth resolution of the space-based bistatic radar, the scene is divided into intervals according to the resolution: ； ； Where: represents the speed of light; Indicates wavelength; Indicates the signal bandwidth; The angle between the two vectors representing the clutter scattering unit pointing to the transmitting station and the receiving station; Indicates accumulation time; and denote the angular velocity vectors of the transmitting station and the receiving station respectively; is the gradient direction of the equal Doppler line; The step 30) is specifically as follows: after dividing the clutter scattering points according to the actual resolution, the clutter signal of the lth range unit is represented as the superposition of a large number of clutter scattering unit echo signals in multiple equidistant rings with range ambiguity, that is: ， Among them, Na is the range ambiguity number, Nc is the number of clutter scattering units on an equidistant ring, is the Kronecker product, , ,as well as They represent the spatial steering vector, time steering vector and space-time two-dimensional steering vector of the i-th clutter unit of the m-th fuzzy range ring respectively. The specific expression is: ， ； The step 40) is specifically as follows: using a 1300km low-orbit satellite in a dual-base configuration with the same orbital altitude, coplanar velocity, and short baseline, to perform a simulation analysis of the clutter characteristics: 41) Space-time distribution curve The space-time distribution curve shows the relationship between the spatial azimuth angle of the clutter scattering point relative to the receiver and the Doppler frequency at different range rings. The Doppler frequency of the clutter point of the bistatic radar is and spatial frequency Respectively expressed as: ， ， Where, is the spacing of the receiving channels, is the signal wavelength, is the transmitter speed, is the receiver speed; and are the flight direction of the transmitter and the flight direction of the receiver, and are the azimuth and elevation angles of the transmitter relative to the target point P, and are the azimuth and elevation angles of the receiver relative to the target point P, respectively; 42) Bistatic radar clutter power spectrum For the lth range ring, according to the expression of the clutter echo signal, the space-time clutter data of the kth pulse received by the nth channel is recorded as , therefore, the expression of the space-time two-dimensional data of the lth range ring is: ， Where: Indicates the number of selected distance rings; The clutter spectrum is represented by the high-resolution minimum variance spectrum, which is defined as follows: ； Where P is the clutter power spectrum, is the space-time two-dimensional steering vector, It represents the estimated clutter plus noise covariance matrix of the lth range ring, and its expression is: 。 2. The clutter analysis method under spaceborne bistatic conditions according to claim 1, characterized in that A relative coordinate system O-XYZ is established: T is the transmitter, R is the receiver, the center of the earth O is the origin, the straight line from the center of the earth to the receiver is the Z axis, the plane where the baseline S1S2 is located is the XOZ plane, and the Y axis is determined according to the right-hand rule. denote the elevation angle and azimuth angle respectively; In the coordinate system O-XYZ, the position vectors of the transmitter and receiver are expressed as: ， In the coordinate system O-XYZ, the equation of the rotating ellipsoid is expressed as: ， in, , represents the double baseline distance, Indicates the baseline and The angle between the axes; the parametric equation of the earth's spherical surface is: ， in, denote the elevation angle and azimuth angle respectively. By combining the above parametric equations, we can obtain the clutter equidistance ring equation as follows: ， The solution is: ， in, ； right Perform traversal scanning and calculate the corresponding , only when and The value of the formula satisfies the condition hour, and The value of is meaningful. Substituting it into the formula, we can get the position vector [x, y, z] of the clutter unit on the equidistant ring; Based on the dual-base range loop obtained from the above simulation model, the limitation of the earth's curvature on the radar detection range under spaceborne conditions should also be considered. When the radar line of sight is tangent to the earth's surface, the maximum detection range is reached. Therefore, the maximum detection range between the transmitter and the receiver is expressed as: ， The transmitter and receiver cover different areas on the earth's surface. Only when the ground clutter block is illuminated by the transmitting beam and the receiving beam at the same time will an effective clutter echo signal be generated.

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