A method for modeling k-distributed sea clutter for airborne radars

Abstract

The present application relates to a kind of airborne radar K distribution sea clutter modeling method, first according to the observation sea clutter unit of airborne radar detection geometric relationship is divided, then the electromagnetic scattering model of different sea state is generated using TSC model sea clutter sequence, finally it is combined with K distribution model and simulates the complex K distribution sea clutter model under different sea state conditions.The present application method can simulate the echo time sequence of sea clutter complex model under different sea state conditions, can provide sufficient simulation data input for the design of airborne radar system and check performance evaluation.The whole link simulation process proposed in the present application can simulate the beam main lobe accurate pointing target and sea clutter scattering unit, and can simulate the echo time sequence of airborne radar sea clutter K distribution, improve the accuracy of airborne radar sea clutter modeling.

Description

Technical Field

[0001] This invention belongs to the field of radar signal processing, specifically relating to a K-distribution sea clutter simulation method for airborne radar, applicable to sea clutter modeling and simulation of airborne maritime detection radar systems. Background Technology

[0002] Airborne radar maritime surveillance faces extensive and complex sea clutter echo interference. Acquiring measured sea clutter data is extremely resource-intensive, and ideal data acquisition methods are limited; it is difficult to obtain sea clutter echo data under different observation parameters through a single experiment. Therefore, accurate modeling and simulation of airborne radar sea clutter echo data are crucial for a thorough study of sea clutter characteristics, providing ample sample input for the design of airborne maritime surveillance radar systems and the research on target detection performance.

[0003] Existing sea clutter echo simulation methods mainly focus on amplitude statistics and Doppler characteristics, failing to fully consider actual airborne radar detection parameters and sea state variations. This leads to inaccurate matching of simulated sea clutter data models and low fit to measured data. Therefore, comprehensively considering the entire link process of airborne radar sea detection, analyzing the formation mechanism and amplitude distribution of sea clutter in detail, and simulating airborne radar sea clutter echo data based on sea clutter backscattering characteristics is of great significance for improving the target detection performance of airborne sea detection radar. Summary of the Invention

[0004] The technical problem to be solved by this invention is:

[0005] To address the shortcomings of existing airborne radar sea clutter simulation performance, this invention comprehensively considers the detection scenarios of airborne radar systems and the relationship between sea clutter characteristics and sea state. It uses the TSC model to establish backscattering coefficient models for different sea state levels, establishes a correlation model between backscattering coefficient and echo power based on airborne radar system parameters, and uses the Spherically Invariant Random Process (SIRP) method to simulate the K-distribution time series of sea clutter with Gaussian power spectrum, thereby improving the accuracy of airborne radar sea detection echo data.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for modeling K-distribution sea clutter using airborne radar, characterized by the following steps:

[0008] Step 1: Airborne platform observation of sea clutter scattering unit division

[0009] Based on the relevant parameters of the airborne platform, define the airborne platform velocity azimuth vector:

[0010] V=[coswcosδ,coswsinδ,sinw]

[0011] Where: w represents the velocity pitch angle; δ represents the velocity azimuth angle;

[0012] Unit vector of scattering unit:

[0013] S=[cosφcosθ,cosφsinθ,sinφ]

[0014] Where φ represents the pitch angle of the scattering unit, and θ represents the azimuth angle of the scattering unit; therefore, the angle ψ between the aircraft velocity direction vector and the scattering unit vector is:

[0015] ψ=cos -1 (coswcosδcosφcosθ+coswsinδcosφsinθ+sinwsinφ)

[0016] The area of ​​the unit resolution cell for modeling sea clutter is:

[0017]

[0018] Where c represents the speed of light, B is the radar operating bandwidth, and L is the distance between the radar's projection point on the ground and the scattering element; the Doppler frequency shift of the scattering element can be obtained as:

[0019]

[0020] By differentiating the azimuth angle of the scattering unit, the angular resolution of the scattering unit is obtained:

[0021]

[0022]

[0023] To ensure frequency resolution and computational complexity, the following conditions must be met:

[0024]

[0025] Under the constraint of δ-θ=90°, the azimuth resolution of the scattering point is obtained as follows:

[0026]

[0027] The total number of scattering units N is obtained. e =[2π / Δθ min The azimuth angle of the nth scattering unit:

[0028]

[0029] Further derivation yields the pitch angle of the range loop resolution cell:

[0030]

[0031] Among them, R i The expression for i is:

[0032]

[0033]

[0034] Step 2: Construct the echo power model of a unit scattering cell

[0035] According to the formula for calculating the area of ​​the resolution unit The radar target cross-section σ(φ) is calculated by combining it with the unit backscattering coefficient σ0(φ) obtained from the TSC model; the radiation pattern function of the airborne radar antenna is established.

[0036]

[0037] The relationship between b1, b2 and the half-power beamwidth is as follows:

[0038]

[0039] Then the antenna gain is G(θ,φ)=G0×F(θ,φ), and the echo power per unit scattering element can be obtained as:

[0040]

[0041] Step 3: Construct a clutter sequence with Doppler frequency shift characteristics

[0042] Based on the Doppler frequency shift expression of airborne radar obtained in step 1, the clutter phase sequence with Doppler frequency shift characteristics can be defined as:

[0043]

[0044] Step 4: Construct time series of single echo signals from sea clutter scattering units

[0045] The echo signal of a single clutter scattering unit in the electromagnetic scattering model under different sea states can be defined as follows:

[0046]

[0047] Wherein, P(θ) n ,φ i The echo power is θ; sea clutter sequences z(θ) with different amplitude K distributions are generated using the SIRP method. n ,φ iBy combining the echo signal (t) with the echo signal under the electromagnetic scattering model, we obtain the echo signal sequence of a single clutter scattering unit with statistical characteristics:

[0048]

[0049] Step 5: Construct the time series of coherent sea clutter echo signals

[0050] Summing the echo signals along the azimuth dimension yields the clutter echo signals for the entire range loop:

[0051]

[0052] To obtain a coherent clutter model, range ambiguity needs to be considered, satisfying the relationship between the maximum unambiguous distance and the speed of light and the pulse repetition frequency:

[0053]

[0054] The coherent clutter model can be expressed as:

[0055] R l =R m +n l ·R u (N0≤n l ≤N l ,0≤R m ≤R u )

[0056] Where N satisfies l =R max / R u N0 = H / R u Given the conditions, the coherent clutter echo signals of multiple range loops can be obtained as follows:

[0057]

[0058] A computer system is characterized by comprising: one or more processors, and a computer-readable storage medium for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method described above.

[0059] A computer-readable storage medium is characterized by storing computer-executable instructions, which, when executed, are used to implement the above-described method.

[0060] The beneficial effects of this invention are as follows:

[0061] This invention provides a method for modeling K-distribution sea clutter using airborne radar. First, the observed sea clutter units are divided according to the detection geometry of the airborne radar. Then, a Two-Scale Composite model (TSC) is used to generate sea clutter sequences of electromagnetic scattering models under different sea conditions. Finally, these sequences are combined with the K-distribution model to simulate composite K-distribution sea clutter models under different sea conditions, thereby improving the accuracy of airborne radar sea clutter modeling.

[0062] The method of this invention can simulate the echo time series of sea clutter composite models under different sea states, providing sufficient simulation data input for the design and performance evaluation of airborne radar systems. Simulation results show that the proposed end-to-end simulation process can accurately simulate the beam main lobe pointing towards the target and sea clutter scattering units, and can simulate the K-distribution echo time series of sea clutter for airborne radar. It has the following advantages:

[0063] 1. Based on the airborne radar system parameters and detection scenario, the antenna main lobe is directed to the clutter unit position and the sea clutter echo signal is simulated by integrating the entire radar link process.

[0064] 2. Capable of generating airborne radar sea clutter time series that follow a K-distribution under different sea state conditions;

[0065] 3. The spatiotemporal two-dimensional sea clutter sequences obtained from simulation under different sea conditions can accurately correspond to the theoretical sea conditions and amplitude models. Attached Figure Description

[0066] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0067] Figure 1 Flowchart for simulation of K-distributed composite sea clutter model;

[0068] Figure 2 The following are the sea clutter time-domain sequences of the composite model under different sea state levels: (a) sea clutter time-domain sequence at sea state level 2; (b) sea clutter time-domain sequence at sea state level 3; (c) sea clutter time-domain sequence at sea state level 4; (d) sea clutter time-domain sequence at sea state level 5.

[0069] Figure 3 The sea clutter spectra of the composite model under different sea state levels are: (a) Sea clutter spectrum at sea state level 2; (b) Sea clutter spectrum at sea state level 3; (c) Sea clutter spectrum at sea state level 4; (d) Sea clutter spectrum at sea state level 5. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0071] like Figure 1 As shown, this embodiment provides an airborne K-distribution sea clutter modeling method, including the following steps:

[0072] Step 1: Divide the airborne platform into observation units for sea clutter scattering. Based on the relevant parameters of the airborne platform, define the airborne platform velocity azimuth vector:

[0073] V=[coswcosδ,coswsinδ,sinw]

[0074] Where: w represents the velocity pitch angle; δ represents the velocity azimuth angle.

[0075] Unit vector of scattering unit:

[0076] S=[cosφcosθ,cosφsinθ,sinφ]

[0077] Where φ represents the pitch angle of the scattering unit, and θ represents the azimuth angle of the scattering unit. Therefore, the angle ψ between the aircraft velocity direction vector and the scattering unit vector is:

[0078] ψ=cos -1 (coswcosδcosφcosθ+coswsinδcosφsinθ+sinwsinφ)

[0079] The area of ​​the unit resolution cell for modeling sea clutter is:

[0080]

[0081] Where c represents the speed of light, B is the radar operating bandwidth, and L is the distance between the radar's projection point on the ground and the scattering element. The Doppler frequency shift of the scattering element can be obtained as:

[0082]

[0083] By differentiating the azimuth angle of the scattering unit, the angular resolution of the scattering unit is obtained:

[0084]

[0085]

[0086] To ensure frequency resolution and computational complexity, the following conditions must be met:

[0087]

[0088] Under the constraint of δ-θ=90°, the azimuth resolution of the scattering point is obtained as follows:

[0089]

[0090] The total number of scattering units N is obtained. e =[2π / Δθ min The azimuth angle of the nth scattering unit:

[0091]

[0092] Further derivation yields the pitch angle of the range loop resolution cell:

[0093]

[0094] Among them, R i The expression for i is:

[0095]

[0096]

[0097] Step 2: Construct the echo power model of a unit scattering cell

[0098] According to the formula for calculating the area of ​​the resolution unit This is combined with the unit backscattering coefficient σ0(φ) obtained from the TSC model to calculate the radar target cross-section σ(φ) = S × σ0(φ). The airborne radar antenna pattern function is then established.

[0099]

[0100] The relationship between b1, b2 and the half-power beamwidth is as follows:

[0101]

[0102] Then the antenna gain is G(θ,φ)=G0×F(θ,φ), and the echo power per unit scattering element can be obtained as:

[0103]

[0104] Step 3: Construct a clutter sequence with Doppler frequency shift characteristics. Based on the Doppler frequency shift expression for airborne radar obtained in Step 1, a clutter phase sequence with Doppler frequency shift characteristics can be defined as:

[0105]

[0106] Step 4: Construct the time series of individual echo signals from a sea clutter scattering unit. According to the literature, the echo signal of a single clutter scattering unit in the electromagnetic scattering model under different sea states can be defined as:

[0107]

[0108] Wherein, P(θ) n ,φ i The echo power is θ. Based on this, sea clutter sequences z(θ) with different amplitude K distributions are generated using the SIRP method. n ,φ i By combining the echo signal (t) with the echo signal under the electromagnetic scattering model, we obtain the echo signal sequence of a single clutter scattering unit with statistical characteristics:

[0109]

[0110] Step 5: Construct a time series of coherent sea clutter echo signals. Summing the echo signals along the azimuth dimension yields the clutter echo signals for the entire range loop:

[0111]

[0112] To obtain a coherent clutter model, range ambiguity needs to be considered, satisfying the relationship between the maximum unambiguous distance and the speed of light and the pulse repetition frequency:

[0113]

[0114] The coherent clutter model can be expressed as:

[0115] R l =R m +n l ·R u (N0≤n l ≤N l ,0≤R m ≤R u )

[0116] Where N satisfies l =R max / R u N0 = H / R u The condition for the coherent clutter echo signal is:

[0117]

[0118] Simulations were performed using sea clutter data for each range cell, with parameter settings shown in Table 1.

[0119] Table 1 Parameter Settings

[0120] PRF 20kHz Maximum Unambiguous Distance 7.5km Distance resolution 150m Frequency resolution 312.5Hz Beam azimuth 30° Beam pitch angle 10° Aircraft speed pitch angle 0° Aircraft speed azimuth angle 0° pulse count 64 Sea state rating 2、3、4、5

[0121] Table 2 shows the simulated beam main lobe pointing positions under different sea states compared to the theoretical main lobe positions:

[0122] Table 2 shows the theoretical and simulation results for high repetition rates.

[0123] Main lobe Doppler frequency Main lobe clutter unit distance Theoretical main lobe 5685Hz 17276m Sea state level 2 5703.125Hz 17250m Sea state level 3 5625Hz 17100m Sea state level 4 5546.875Hz 17100m Sea state level 5 5468.75Hz 17400m

[0124] By comparing the theoretical main lobe position with the main lobe position under different sea conditions, it can be found that at medium and high repetition rates, the distance error exceeds the distance resolution, while the Doppler error does not exceed the frequency resolution. Therefore, there is distance ambiguity, but no Doppler ambiguity.

[0125] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. An airborne radar K-distributed sea clutter modeling method, characterized in that The steps are as follows: Step 1: Division of sea clutter scattering unit observed by airborne platform According to the relevant parameters of the airborne platform, the airborne platform velocity azimuth vector is defined: wherein: w denotes the speed pitch angle; denotes the speed yaw angle; The unit vector of the scattering unit is: where: represents the scattering unit elevation angle, represents the scattering unit azimuth angle; thus, the angle between the carrier velocity direction vector and the scattering unit vector is: The sea clutter is modeled, and the unit resolution unit area is: wherein, denotes the speed of light, is the radar operating bandwidth, is the distance between the ground projection point of the radar and the scattering unit; the Doppler shift of the scattering unit can be obtained as: The azimuth angle of the scattering unit is calculated by differential calculation, and the scattering unit angle resolution is obtained: To ensure the frequency resolution and the amount of calculation, the condition needs to be met: Under the constraint condition of the azimuthal resolution of the scattering point is obtained as Total number of scattering elements is obtained Azimuth of the nth scattering element: The elevation angle of the distance ring resolution unit is further derived: wherein and the expression is: ， Step 2: Constructing echo power model of unit scattering unit According to the resolution unit area calculation formula And the unit backscattering coefficient obtained according to the TSC model Combined to calculate the radar target cross section area ; Establish the airborne radar antenna pattern function: wherein The relationship with the half-power beamwidth is: ， The antenna gain is then The unit scattering cell echo power is obtained as Step 3: Constructing sea clutter sequence with Doppler shift characteristics According to the Doppler shift expression of the airborne radar obtained in step 1, the sea clutter phase sequence with Doppler shift characteristics can be defined as: Step 4: Constructing sea clutter scattering unit single echo signal time sequence The echo signal of a single sea clutter scattering unit of the electromagnetic scattering model under different sea conditions can be defined as: wherein, The echo power is generated by using the SIRP method to generate a sea clutter sequence with different amplitudes of K distribution In combination with the echo signal under the electromagnetic scattering model, the echo signal sequence of a single clutter scattering unit with statistical characteristics is obtained: Step 5: Constructing coherent sea clutter echo signal time sequence Summing the echo signals along the azimuth dimension, the sea clutter echo signal of the entire distance ring is obtained: In order to obtain the coherent clutter model, the distance ambiguity needs to be considered, and the relationship between the maximum unambiguous distance and the speed of light, the pulse repetition frequency needs to be met: The coherent clutter model can be expressed as: wherein the condition , is satisfied, the coherent clutter echo signals of the multiple range rings are obtained as 。 2. A computer system, characterized by Including: One or more processors, a computer readable storage medium for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the method of claim 1.

3. A computer-readable storage medium, characterized in that There are computer executable instructions stored, which when executed are used to implement the method of claim 1.

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