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

Abstract

The invention provides a sea clutter simulation method based on an air-based bistatic radar system, and the method comprises the steps: irradiating a to-be-monitored sea surface through a radar carried on a satellite launching platform, and dividing a radar irradiation sea area in each radar coherent processing interval CPI into a plurality of sub-regions; determining 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 each sub-region through a sea clutter frequency domain algorithm; and according to the corresponding single-beam monopulse sea clutter signal in each sub-region, determining an echo signal corresponding to a beam in each radar coherent processing interval CPI, so that a sea clutter frequency domain algorithm can be utilized to convert relatively complex Fourier transform into frequency shift and linear calculation, the calculation amount of simulation is reduced, and the simulation efficiency is improved.

Description

Technical Field

[0001] The invention relates to the field of radar technology, and in particular to a sea clutter simulation method based on an air-based bistatic radar system. Background Art

[0002] An airborne bistatic radar system refers to a radar transmitter and receiver located on different platforms. For a radar system that transmits satellites and receives drones to detect the ocean surface, it is necessary to model the ocean surface conditions and simulate sea clutter echoes. In some cases, the distribution of sea clutter signals will have long tails, and traditional statistical distribution models are difficult to fit the long tail parts, and the model accuracy is limited. In addition, since sea clutter is the echo of a complex object constructed by multiple scatterers, the number of scatterers that contribute to the echo will obey different statistical characteristics under different sea conditions, and a fixed statistical distribution model is difficult to adapt to all complex sea conditions. In order to improve the precision of the simulation, the sea clutter simulation method driven by the physical model models the sea surface as a physical field of waves propagating at different frequencies and directions, and uses a classic composite dual-scale model to complete the mapping of sea condition information to sea surface clutter scattering unit parameters, so that the sea clutter simulation achieved is high in accuracy and applicability.

[0003] The patent document with publication number CN117828255A discloses "a method and system for modeling multi-channel sea clutter for a spaceborne bistatic radar". This method is aimed at a spaceborne bistatic radar system, and uses a physical model to drive the establishment of an ocean surface model, thereby achieving the simulation generation of sea clutter signals. However, this method only analyzes the generation of sea clutter signals from a time domain perspective, without considering the frequency domain, and cannot intuitively reflect the Doppler effect caused by the relative motion of the sea surface scattering points and the receiver. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a sea clutter simulation method based on an airborne bistatic radar system, which specifically includes:

[0005] In a first aspect, the present invention provides a sea clutter simulation method based on an airborne bistatic radar system, comprising:

[0006] The sea surface to be monitored is illuminated by a radar carried on a satellite launch platform, 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 single radar illumination time, and the beam within each radar coherent processing interval CPI contains multiple pulse signals;

[0007] Through the sea clutter frequency domain algorithm, based on the frequency domain characteristics of each sea surface scattering point in each sub-area, the single beam monopulse sea clutter signal corresponding to each sub-area is determined;

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

[0009] Beneficial effects of the present invention:

[0010] The sea clutter simulation method based on an airborne bistatic radar system provided by the present invention uses a radar carried on a satellite launch platform to illuminate a sea surface to be monitored, and divides the radar-illuminated sea area within each radar coherent processing interval CPI into a plurality of sub-areas; uses a sea clutter frequency domain algorithm to determine a single-beam monopulse sea clutter signal corresponding to each sub-area based on the frequency domain characteristics of each sea surface scattering point within each sub-area; and determines an echo signal corresponding to a beam within each radar coherent processing interval CPI according to the single-beam monopulse sea clutter signal corresponding to each sub-area. The sea clutter frequency domain algorithm can be used to convert a relatively complex Fourier transform into a frequency shift and a linear calculation, thereby reducing the amount of simulation calculation and improving the simulation efficiency.

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

[0012] Figure 1 A schematic diagram of an airborne bistatic radar system provided by the present invention;

[0013] Figure 2 A schematic diagram of a flow chart of a sea clutter simulation method based on an airborne bistatic radar system provided by the present invention;

[0014] Figure 3 A set of schematic diagrams of simulation results provided by the present invention. DETAILED DESCRIPTION

[0015] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0016] In order to solve the problems existing in the prior art, the present invention provides a sea clutter simulation method based on an airborne 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 in the frequency domain to obtain the signal waveform component, and constructs the clutter data of different scattering points by combining the signal delay component and the amplitude component, and performs inverse fast Fourier transform after superposition to obtain the final echo signal. Starting from the signal Doppler frequency domain, the method explores the frequency domain expression of sea clutter simulation, explains the influence of Doppler frequency shift in the simulation generation of sea clutter signals, improves the sea clutter frequency domain algorithm, and converts the Fourier transform into the frequency shift and linear calculation of the radar transmission signal by quantizing the Doppler frequency domain, which can reduce the simulation calculation amount of the frequency domain method and improve the calculation efficiency.

[0017] The present invention relates to an air-based bistatic radar system, comprising a satellite launch platform and an unmanned aerial vehicle receiving platform, such as Figure 1 As shown, the satellite launch platform sends radar signals, which are scattered by the sea surface and then received by the aerial moving receiving platform. Due to the limited coverage of radar signals, it is necessary to divide the ocean detection range into scattering points in different areas, and the echoes of all scattering points are superimposed to generate sea clutter.

[0018] Figure 2 A schematic diagram of a flow chart of a sea clutter simulation method based on an airborne bistatic radar system provided by the present invention, such as Figure 2 As shown, the method includes:

[0019] S201, irradiating the sea surface to be monitored by a radar carried on a satellite launch platform, and dividing the radar-irradiated sea area within each radar coherent processing interval CPI into a plurality of sub-areas.

[0020] The radar coherent processing interval CPI is the single illumination time of the radar, and each beam within the radar coherent processing interval CPI contains multiple pulse signals.

[0021] Exemplarily, within a single CPI (i.e., one frame of signal), the sea surface of 50km×100km is divided into multiple elliptical clutter plates based on the single irradiation area of ​​the transmitting platform, and each clutter plate is evenly divided into multiple sub-areas of 2km×2km.

[0022] The calculation formula for the sub-areas evenly divided by the sea surface is:

[0023]

[0024] Among them, ΔR is the division interval, ρ is the compression coefficient. Adjusting this 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 includes building a simulation scene, that is, setting up a satellite launch platform and a UAV receiving platform, and selecting a sea area as the area to be monitored.

[0026] It should be noted that the sea area can be divided by the uniform division method shown above, or other division methods, such as the equidistant ring division method, can be used.

[0027] S202. 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 each sub-region by using a sea clutter frequency domain algorithm.

[0028] S203: Determine the echo signal corresponding to the beam within each radar coherent processing interval CPI according to the single beam monopulse sea clutter signal corresponding to each sub-area.

[0029] Specifically, the above process is repeated within 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 (number of beams × number of pulses × distance sampling), and stored in the system.

[0030] The sea clutter simulation method based on an airborne bistatic radar system provided by the present invention uses a radar carried on a satellite launch platform to illuminate a sea surface to be monitored, and divides the radar-illuminated sea area within each radar coherent processing interval CPI into a plurality of sub-areas; uses a sea clutter frequency domain algorithm to determine a single-beam monopulse sea clutter signal corresponding to each sub-area based on the frequency domain characteristics of each sea surface scattering point within each sub-area; and determines an echo signal corresponding to a beam within each radar coherent processing interval CPI according to the single-beam monopulse sea clutter signal corresponding to each sub-area. The sea clutter frequency domain algorithm can be used to convert a relatively complex Fourier transform into a frequency shift and a linear calculation, thereby reducing the amount of simulation calculation and improving the simulation efficiency.

[0031] The following further describes in detail 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 using the sea clutter frequency domain algorithm:

[0032] In a possible implementation, a single-beam monopulse sea clutter signal corresponding to each sub-region is determined based on the frequency domain characteristics of each sea surface scattering point in each sub-region through a sea clutter frequency domain algorithm, including the following steps A1 and A2:

[0033] A1. For any first sea surface scattering point among the sea surface scattering points in each sub-area, determine the Doppler frequency value of the first sea surface scattering point, and find the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point within a preset quantization interval; after Fourier transforming the radar transmission signal currently irradiated on 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 a first signal; and determine the single-beam single-pulse sea clutter signal corresponding to the first sea surface scattering point according to the first signal.

[0034] A2. Determine 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 within a radar coherent processing interval CPI.

[0035] The following is a further detailed description of step A1:

[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, and : represents the step. The quantization bit number 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 Fourier transforming the radar transmission signal currently irradiated at the first sea surface scattering point, frequency shifting the Fourier transform result corresponding to the radar transmission signal is performed 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 frequency shifting 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 , frequency shift 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 according to 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-area 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: According to the sea surface parameters of the sub-area where the first sea surface scattering point is located, establish the wave height field, and the corresponding expression is:

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

[0045] 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.

[0046]

[0047] k x and k y They represent the azimuth wave number and distance wave number of the ocean wave respectively. The wave number vector is (k x ,k y )’s wave phase, The wave number vector is (k x ,k y ) is the angular frequency of the waves, g is the acceleration due to gravity, represents the long wave amplitude, Indicates shortwave amplitude.

[0048] Specifically, the amplitude According to the amplitude of the spectral density, the specific expression can be obtained:

[0049]

[0050] Among them, E h (k x ,k y ) represents the spectral density, E l (k x ,k y ) represents the long-wave spectral density, E s (k x ,k y ) represents the shortwave spectral density, ξ0 represents the normalization factor, and a suitable ξ0 is selected to satisfy:

[0051]

[0052] in, is the root mean square of the long wave component of the wave height, H s Significant wave height.

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

[0054]

[0055] Among them, α is the Phillips parameter describing the spectral intensity, k p represents the peak wave number of the strong exchange spectrum, φ p represents the angle between the propagation direction of the main wave and the direction along the track, 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 the constant e as the base, cos represents the cosine function, and the width parameter σ of the JONSWAP spectrum J Assume 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 19.5m.

[0060] Specifically, the shortwave spectral density E s (k x ,k y ) can be expressed as:

[0061]

[0062] Among them, β represents the Phillips parameter describing the shortwave spectrum intensity.

[0063] a1.2. Determine the incident angle and receiving angle of the first sea surface scattering point.

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

[0065] a1.2.1. Establish a local sea surface coordinate system 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:

[0066]

[0067] Wherein, 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 sequence number of the scattering point in the x-direction, n represents the sequence number of the scattering point in the y-direction, ΔR represents the division interval, ρ represents the compression coefficient, c represents the speed of light, and B represents the maximum bandwidth of the radar signal.

[0068] a1.2.2. Convert the coordinates of each scattering point on the first sea surface in the local sea surface coordinate system into the incident angle and receiving angle in the geodetic coordinate system. The corresponding expressions are:

[0069]

[0070] Among them, θ T is the incident angle, θ R represents the receiving angle, Represents 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.

[0071] Specifically, the geodetic coordinate system is the 2000 National Geodetic Coordinate System, that is, the CGCS2000 coordinate system.

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

[0073]

[0074] 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.

[0075] The determination process of the radial velocity field of the sea surface scattering point relative to the satellite launch platform is the same as that of the radial velocity field of the sea surface scattering point relative to the receiving platform. The determination process of the radial velocity field is further described in detail below through a set of general formulas:

[0076] Specifically, the sea surface to be monitored is modeled as a water particle that is simultaneously moving and vibrating in translation. The radial velocity field includes an average velocity component and a random velocity component, which can be expressed as:

[0077]

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

[0079] For the mean velocity component:

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

[0081]

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

[0083]

[0084] For random velocity components:

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

[0086]

[0087] Then, simplify the radial velocity field and transform the average velocity component v r (x,y,t) Expanding it into a Taylor series, and retaining it to second order, we get:

[0088]

[0089] Among them, a r (x,y,t) represents the radial orbital acceleration associated with the long wave,

[0090]

[0091] The velocity variation due to the radial orbital acceleration is modeled as a Gaussian random velocity:

[0092]

[0093] Among them, T a Lighting time for the radar.

[0094] Then, we combine the two into one random variable,

[0095]

[0096] Assuming that the motions of long and short waves are independent, we can evaluate u r The standard deviation of (x,y,t) is expressed as:

[0097]

[0098] a2. Determine the time delay of the first sea surface scattering point and the normalized radar cross section corresponding to 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.

[0099] Optionally, determining the time delay of the first sea surface scattering point according to the sea surface parameter field of the sub-area where the first sea surface scattering point is located includes: determining the actual distances of the satellite launching platform and the receiving platform to the first sea surface scattering point respectively according to the radial velocity fields of the satellite launching 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 of the satellite launching platform and the receiving platform to the first sea surface scattering point.

[0100] The corresponding expression is:

[0101]

[0102] Among them, R T0 represents the distance from the satellite launch platform to the first sea surface scattering point at time t0, R 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 express t The time delay from the receiving platform to the first sea surface scattering point at time 0, 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, determining a normalized radar cross section corresponding to the first sea surface scattering point based on a sea surface parameter field of a sub-area where the first sea surface scattering point is located includes: determining a normalized radar cross section corresponding to the first sea surface scattering point based on a wave height field corresponding to the sub-area where the first sea surface scattering point is located.

[0104] The corresponding expression is:

[0105]

[0106] 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 Represents the dominant wave number.

[0107] Specifically, for a radar system with separate transmit and receive channels, its normalized radar cross section (NRCS) consists of two parts, expressed 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 according to the normalized radar cross section corresponding to the first sea surface scattering point.

[0121] Optionally, the amplitude component corresponding to the first sea surface scattering point is determined according to the normalized radar cross section corresponding to the first sea surface scattering point, which 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 transmission 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), λ is the radar operating wavelength, B is the radar bandwidth, PRT is the pulse repetition period, R0 is the slant distance, L s is the system loss, and i represents the sea surface scattering point index.

[0124] a4. Determine 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 determines the delay component corresponding to the first sea surface scattering point, expressed as:

[0126]

[0127] Among them, e represents a constant, f represents a 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, and i represents the sea surface scattering point index.

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

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

[0130] Optionally, determining a single-beam monopulse sea clutter signal corresponding to the first sea surface scattering point according to the amplitude component, delay component and signal waveform component corresponding to the first sea surface scattering point includes: obtaining a second signal by superimposing the amplitude component, delay component and signal waveform component corresponding to the first sea surface scattering point.

[0131] The corresponding expression is:

[0132]

[0133] 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 sub-region where the first sea surface scattering point is located in the x direction, N represents the total number of scattering points in the sub-region where the first sea surface scattering point is located in the y direction, s(f+f di0 ) represents the frequency shift of the radar signal, s′(f+fdi0 ) is its derivative, 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.

[0134] The present invention derives a frequency domain expression by analyzing the frequency domain of sea clutter signals, thereby being able to intuitively reflect the influence of the Doppler effect on the simulation generation of sea clutter signals; through a frequency domain rapid generation algorithm, the Doppler frequency is quantified and then the Doppler frequency of the scattering point is approximated, and the relatively complex Fourier transform is converted into frequency shift and linear calculation, which can effectively reduce the amount of simulation calculation.

[0135] The technical effects of the present invention are further described in detail below in conjunction with simulation experiments.

[0136] 1. Simulation conditions:

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

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

[0139] 2. Simulation content

[0140] Set the sea surface parameters, and model the wave height field, radial velocity field, and normalized radar cross section field of the ocean surface. Based on these parameters, calculate and generate sea clutter echoes under dual bases, and compare their amplitude probability distribution with the probability model (K distribution) of echoes generated by the high-precision grid universal sea surface model. The results are as follows: Figure 3 shown.

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

[0142] It can be seen that the present invention provides a sea clutter simulation method suitable for an airborne bistatic radar system. Driven by a physical model, the sea surface is modeled as a physical field of waves propagating at different frequencies and in different directions. The sea clutter frequency domain algorithm is used to reduce the amount of simulation calculations.

[0143] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0144] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A sea clutter simulation method based on an airborne bistatic radar system, characterized in that: include: The sea surface to be monitored is illuminated by a radar carried on a satellite launch platform, and the radar illuminated sea area within each radar coherent processing interval CPI is divided into multiple sub-areas, wherein the radar coherent processing interval CPI is a single radar illumination time, and the beam within each radar coherent processing interval CPI contains multiple pulse signals; Determining a single beam monopulse sea clutter signal corresponding to each of the sub-areas based on the frequency domain characteristics of each sea surface scattering point in each of the sub-areas by a sea clutter frequency domain algorithm; 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 determining of the single beam monopulse sea clutter signal corresponding to each of the sub-areas based on the frequency domain characteristics of each sea surface scattering point in each of the sub-areas by using a sea clutter frequency domain algorithm includes: For any first sea surface scattering point among the sea surface scattering points in each of the sub-areas, determine the Doppler frequency value of the first sea surface scattering point, and find the Doppler frequency point closest to the Doppler frequency value of the first sea surface scattering point within a preset quantization interval; after Fourier transforming the radar transmission signal currently irradiated on 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 a first signal; and determine the single-beam single-pulse sea clutter signal corresponding to the first sea surface scattering point according to the first signal; According to the single-beam single-pulse 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 single-pulse sea clutter signals corresponding to each sub-area are determined.

3. The method according to claim 2, characterized in that The determining, according to the first signal, a single-beam monopulse sea clutter signal corresponding to the first sea surface scattering point comprises: Under a single pulse signal, establishing a sea surface parameter field of the sub-region where the first sea surface scattering point is located; determining, according to a sea surface parameter field of a sub-region 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; determining an amplitude component corresponding to the first sea surface scattering point according to a normalized radar cross section corresponding to the first sea surface scattering point; determining a delay component corresponding to the first sea surface scattering point according to the time delay of the first sea surface scattering point; determining, according to the first signal, a signal waveform component corresponding to the first sea surface scattering point; A single-beam monopulse 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.

4. The method according to claim 3, 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 comprises: 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 They represent the azimuth wave number and distance wave number of the ocean wave respectively. The wave number vector is (k x ,k y )’s wave phase, The wave number vector is (k x ,k y ) is the angular frequency of the waves, g is the acceleration due to gravity, represents the long wave amplitude, represents the short wave amplitude; Determining an incident angle and a receiving angle of the first sea surface scattering point; According to the incident angle and receiving angle of the first sea surface scattering point, the radial velocity field of the satellite launch platform and the receiving platform relative to the first sea surface scattering point is established, and the corresponding expression is: 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.

5. The method according to claim 4, 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: According to the radial velocity fields of the satellite launch platform and the receiving platform relative to the first sea surface scattering point, the actual distances of the satellite launch platform and the receiving platform to the first sea surface scattering point are determined respectively, and the corresponding expressions are: Among them, R T0 represents the distance from the satellite launch platform to the first sea surface scattering point at time t0, R 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; According to the actual distances from the satellite transmitting platform and the receiving platform to the first sea surface scattering point, the time delay of the first sea surface scattering point is determined, and the corresponding expression is: Where τ represents the time delay of the first sea surface scattering point.

6. The method according to claim 5, 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: According to the wave height field corresponding to the sub-region where the first sea surface scattering point is located, the normalized radar cross section corresponding to the first sea surface scattering point is determined, and 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 Represents the dominant wave number.

7. The method according to claim 6, characterized in that The determining of the amplitude component corresponding to the first sea surface scattering point according to the normalized radar scattering cross section corresponding to the first sea surface scattering point is expressed as: Among them, A i represents the amplitude component corresponding to the i-th sea surface scattering point, P av is the average transmission 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), λ is the radar operating wavelength, B is the radar bandwidth, PRT is the pulse repetition period, R0 is the slant distance, L s is the system loss, and i represents the sea surface scattering point index.

8. The method according to claim 7, characterized in that The time delay of the first sea surface scattering point is used to determine the delay component corresponding to the first sea surface scattering point, which is expressed as: Among them, e represents a constant, f represents a 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, and i represents the sea surface scattering point index.

9. The method according to claim 8, characterized in that The determining, according to the amplitude component, the delay component and the signal waveform component corresponding to the first sea surface scattering point, the single beam monopulse sea clutter signal corresponding to the first sea surface scattering point comprises: According to the amplitude component, delay component and signal waveform component corresponding to the first sea surface scattering point, the second signal is obtained by superposition, and 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 sub-region where the first sea surface scattering point is located in the x direction, N represents the total number of scattering points in the sub-region where the first sea surface scattering point is located in the y direction, 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.

10. The method according to any one of claims 4 to 9, characterized in that: The determining the incident angle and the receiving angle of the first sea surface scattering point comprises: A sea surface local coordinate system is established 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. The corresponding expression is: Wherein, M represents the total number of scattering points in the sub-region where the first sea surface scattering point is located in the x direction, N represents the total number of scattering points in the sub-region where the first sea surface scattering point is located in the y direction, 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 is the incident angle, θ R represents the receiving angle, Represents 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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