CN113253230B - Sub-aperture processing-based space-based early warning radar aerial moving target detection method and system - Google Patents

Sub-aperture processing-based space-based early warning radar aerial moving target detection method and system Download PDF

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CN113253230B
CN113253230B CN202110523895.7A CN202110523895A CN113253230B CN 113253230 B CN113253230 B CN 113253230B CN 202110523895 A CN202110523895 A CN 202110523895A CN 113253230 B CN113253230 B CN 113253230B
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占木杨
黄鹏辉
陈江源
刘兴钊
陆晴
林欣
孙永岩
万向成
刘艳阳
陈国忠
陈筠力
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Shanghai Jiaotong University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G01S7/411—Identification of targets based on measurements of radar reflectivity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
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Abstract

The invention provides a sub-aperture processing-based space-based early warning radar air moving target detection method and system, which comprises the following steps: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data; performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction; dividing the echo data after the distance walk correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture; clutter suppression is completed in each sub-aperture by using a post-Doppler space-time adaptive processing technology, preliminary accumulation is completed in each sub-aperture, and then a target to be detected is extracted through constant false alarm detection of a low threshold; and performing phase compensation on the extracted targets to be detected one by one, performing Fourier transform along the direction of the sub-apertures to realize coherent accumulation among the sub-apertures and further improve the output signal-to-noise-ratio of target signals, and finally rejecting false alarms and reserving real target points through high-threshold detection.

Description

Sub-aperture processing-based space-based early warning radar aerial moving target detection method and system
Technical Field
The invention relates to the field of radar signal processing, in particular to a subaperture processing-based space-based early warning radar airborne moving target detection method and system, and more particularly to a subaperture coherent accumulation transform (SCA) -based space-based early warning radar AMTI method.
Background
The space-based early warning radar has the advantages of global continuous coverage, strong anti-stealth capability, high safety and the like, and plays a very important role in national defense construction. With the high-speed development of aerospace technology, advanced air flight targets often show the characteristics of small radar scattering cross section (RCS), high speed and high maneuverability, so that the energy of echo signals is weak; furthermore, due to the high speed motion of the space-borne platform, the observed moving targets are often submerged in an extended ground/sea clutter background, making target detection extremely challenging. The space-time adaptive processing (STAP) technology can be applied to a multi-channel space-based early warning radar system, so that effective clutter suppression is realized, and the output signal-to-noise-ratio (SCNR) of a target is improved.
Energy is taken out by prolonging the accumulation time, which is an effective way for improving the detection performance of the weak and small targets, but under long-time observation, span walk and cross Doppler frequency walk can occur due to the maneuvering characteristics of non-cooperative targets, and the output SCNR can be reduced. The method for solving the problem comprises three schemes of coherent accumulation, non-coherent accumulation and mixed accumulation. The coherent accumulation method improves the output SCNR by performing coherent accumulation on a plurality of azimuth pulses, but generally needs to set a multidimensional parameter matching filter, and is not suitable for engineering real-time processing; non-coherent accumulation transforms suffer from insufficient output SNR. The hybrid accumulation method can deal with the contradiction between low gain of traditional non-coherent accumulation and large calculation of coherent accumulation, and the hybrid accumulation method completes coherent accumulation in sections by segmenting accumulation time, and further completes non-coherent accumulation, namely intra-section coherent accumulation and inter-section non-coherent accumulation, on the basis of coherent accumulation results in each section. Typical methods include combination of Hough transform, dynamic programming, and pre-detection Tracking (TBD). However, under the background of the space-based radar AMTI, the target echo distance is large, direct coherent accumulation pulses in the section are few, the accumulation gain is small, and the detection of weak airborne moving targets of the space-based early warning radar is not facilitated. The coherent accumulation time is increased as much as possible, the target energy accumulation in the track is fully utilized, the maximum accumulation gain is obtained, and the method is the effort direction of the weak air moving target detection of the space-based early warning radar.
Patent document CN102288948B (application number: 201110123779.2) discloses a method for detecting moving targets in high-speed air of a high-speed platform based on STAP. The invention belongs to the technical field of aerial moving target detection. A detection step: (1) performing Keystone transformation on space-time two-dimensional data received by the high-speed platform phased array radar to correct clutter distance walking; (2) estimating a clutter covariance matrix for the data after clutter walk correction according to the data of the reference unit; (3) the clutter suppression is realized by multiplying the inverse matrix of the clutter covariance matrix by data transformed by Keystone; (4) converting the suppressed data to a distance frequency domain to prepare for target distance walking compensation; (5) constructing a fuzzy number set according to the speed range of the aerial moving target and the radar system parameters; (6) constructing a filter bank according to the fuzzy number set; (7) and 4, realizing target distance walking correction by the data of the filter bank and realizing target accumulation by performing space-time two-dimensional beam forming on a correction result. The invention simultaneously detects different multiple targets of the fuzzy number through parallel processing, and has the advantages of high operation speed, convenient engineering realization and the like.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method and a system for detecting an airborne moving target of a space-based early warning radar based on sub-aperture processing.
The invention provides a sub-aperture processing-based space-based early warning radar air moving target detection method, which comprises the following steps:
step S1: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;
step S2: performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction;
step S3: dividing the echo data after the distance walk correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;
step S4: clutter suppression is completed in each sub-aperture by using a post-Doppler space-time adaptive processing technology, preliminary accumulation of coherent signals is completed in each sub-aperture, and then a target to be detected is extracted through constant false alarm detection of a low threshold;
step S5: and performing phase compensation on the extracted targets to be detected one by one, and performing Fourier transform along the direction of the sub-apertures to complete coherent accumulation among the sub-apertures, further improving the output signal-to-noise ratio of target signals, eliminating false alarms through high threshold detection and reserving real target points.
Preferably, the preprocessing of the radar echo data in step S1 includes: echoes, clutter and noise of moving targets in the air;
the preprocessed moving target echo in the air of the mth channel is represented as:
Figure BDA0003065024810000031
wherein,
Figure BDA0003065024810000032
representing the target amplitude, Pt，τ，B，GT(θAzi,t,θEl,t)，GR_Sub(θAzi,t,θEl,t)，λ，LsAnd sigma respectively represents peak power, pulse width, bandwidth, transmitting antenna full aperture gain, receiving antenna subchannel gain, signal wavelength, radar system loss and target RCS; r0Is the nearest slope distance; thetaEl,tAnd thetaAzi,tRespectively a lower viewing angle and an azimuth angle of the target; and cos (theta)Cone,t)＝cos(θEl,t)cos(θAzi,t)；θCone,tRepresenting a spatial cone angle; t is trAnd taRespectively representing the fast distance time and slow direction time variables; t isaRepresenting the accumulation time, rect (-) and sinc (-) respectively representing a rectangular window function and a sinc function; c represents the speed of light; j represents an imaginary unit; r0t,m(ta) In order to utilize the slope distance of the platform parameter after deramp compensation:
Figure BDA0003065024810000033
wherein R is0Is the nearest slope distance; d represents the size of the antenna square dimension DmRepresenting the channel spacing;
ve＝vysinθAzi,tsinθEl,t-vrxcosθAzi,tsinθEl,trepresents the equivalent radial velocity; v. ofrx＝v-vxRelative platform velocity; v denotes the platform velocity, vxRepresenting the target azimuth velocity; v. ofyRepresenting a target radial velocity;
Figure BDA0003065024810000034
representing the equivalent acceleration.
Preferably, the step S1 includes: and preprocessing multi-channel echoes of the space-based early warning radar, including distance compression, platform motion parameter compensation, frequency down-modulation and clutter Doppler center compensation.
Preferably, the step S2 includes: distance walk rectification is completed before sub-aperture division by using Keystone transformation, and distance migration in sub-apertures and between sub-apertures is removed.
Preferably, the step S5 includes: phase compensation is carried out on the extracted targets to be detected one by one, the phase relation among the sub-aperture echoes is deduced and compensated, Fourier transform is carried out along the sub-aperture direction, coherent accumulation among the sub-apertures is completed, and the output signal-to-noise ratio of target signals is further improved;
the step of performing phase compensation on the extracted targets to be detected one by one comprises the following steps:
Figure BDA0003065024810000035
wherein,
Figure BDA0003065024810000036
representing the equivalent acceleration of the search; λ represents a signal wavelength; j represents an imaginary unit; l represents the number of subapertures; t iscRepresenting the accumulation time within the sub-aperture; tau isa,1A time variable representing a reference sub-aperture;
the echo signals are subjected to coherent accumulation in each sub-aperture by azimuth Fourier transform, and are subjected to coherent accumulation among the sub-apertures by sub-aperture Fourier transform; after sub-aperture coherent accumulation, the echo signal is finally expressed as:
Figure BDA0003065024810000041
wherein,
Figure BDA0003065024810000042
representing the accumulated amplitude; m represents the number of channels; pavRepresents the radar average power; gTRepresenting the transmit antenna full aperture gain; gR-SubRepresenting receive antenna subchannel gains; f. ofaAnd flRespectively representing the Doppler frequency and the sub-aperture frequency variables; l represents the sub-aperture number; b representsA signal bandwidth; t is trRepresenting a distance fast time variable; r0Representing nearest slope, c light speed, TcDenotes the sub-aperture integration time, λ denotes the signal wavelength, veRepresenting the equivalent radial velocity, NcIndicating the number of azimuth pulses within the sub-aperture, D indicating the azimuth dimension of the antenna, thetaEl,tRepresenting the target down-viewing angle, thetaAzi,tRepresenting the target azimuth.
The invention provides a sub-aperture processing-based space-based early warning radar air moving target detection system, which comprises:
module M1: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;
module M2: performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction;
module M3: dividing the echo data after the distance walk correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;
module M4: clutter suppression is completed in each sub-aperture by using a post-Doppler space-time adaptive processing technology, initial coherent accumulation is completed in each sub-aperture, and then a target to be detected is extracted through constant false alarm detection of a low threshold;
module M5: and performing phase compensation on the extracted targets to be detected one by one, and performing Fourier transform along the direction of the sub-apertures to complete coherent accumulation among the sub-apertures, further improving the output signal-to-noise ratio of target signals, eliminating false alarms through high threshold detection and reserving real target points.
Preferably, the pre-processed radar echo data in the module M1 includes: echoes, clutter and noise of moving targets in the air;
the preprocessed moving target echo in the air of the mth channel is represented as:
Figure BDA0003065024810000043
wherein,
Figure BDA0003065024810000044
representing the target amplitude, Pt，τ，B，GT(θAzi,t,θEl,t)，GR_Sub(θAzi,t,θEl,t)，λ，LsAnd sigma respectively represents peak power, pulse width, bandwidth, transmitting antenna full aperture gain, receiving antenna subchannel gain, signal wavelength, radar system loss and target RCS; r0Is the nearest slope distance; thetaEl,tAnd thetaAzi,tRespectively a lower viewing angle and an azimuth angle of the target; and cos (theta)Cone,t)＝cos(θEl,t)cos(θAzi,t)；θCone,tRepresenting a spatial cone angle; t is trAnd taRespectively representing the fast distance time and slow direction time variables; t isaRepresenting the accumulation time, rect (-) and sinc (-) respectively representing a rectangular window function and a sinc function; c represents the speed of light; j represents an imaginary unit; r0t,m(ta) In order to utilize the slope distance of the platform parameter after deramp compensation:
Figure BDA0003065024810000051
wherein R is0Is the nearest slope distance; d represents the size of the antenna square dimension DmRepresenting the channel spacing;
ve＝vysinθAzi,tsinθEl,t-vrxcosθAzi,tsinθEl,trepresents the equivalent radial velocity; v. ofrx＝v-vxRelative platform velocity; v denotes the platform velocity, vxRepresenting the target azimuth velocity; v. ofyRepresenting a target radial velocity;
Figure BDA0003065024810000052
representing the equivalent acceleration.
Preferably, said module M1 comprises: and preprocessing multi-channel echoes of the space-based early warning radar, including distance compression, platform motion parameter compensation, frequency down-modulation and clutter Doppler center compensation.
Preferably, said module M2 comprises: distance walk rectification is completed before sub-aperture division by using Keystone transformation, and distance migration in sub-apertures and between sub-apertures is removed.
Preferably, said module M5 comprises: phase compensation is carried out on the extracted targets to be detected one by one, the phase relation among the sub-aperture echoes is deduced and compensated, Fourier transform is carried out along the sub-aperture direction, coherent accumulation among the sub-apertures is completed, and the output signal-to-noise ratio of target signals is further improved;
the step of performing phase compensation on the extracted targets to be detected one by one comprises the following steps:
Figure BDA0003065024810000053
wherein,
Figure BDA0003065024810000054
representing the equivalent acceleration of the search; λ represents a signal wavelength; j represents an imaginary unit; l represents the number of subapertures; t iscRepresenting the accumulation time within the sub-aperture; tau isa,1A time variable representing a reference sub-aperture;
the echo signals are subjected to coherent accumulation in each sub-aperture by azimuth Fourier transform, and are subjected to coherent accumulation among the sub-apertures by sub-aperture Fourier transform; after sub-aperture coherent accumulation, the echo signal is finally expressed as:
Figure BDA0003065024810000061
wherein,
Figure BDA0003065024810000062
representing the accumulated amplitude; m represents the number of channels; pavRepresents the radar average power; gTRepresenting the transmit antenna full aperture gain; gR-SubRepresenting receive antenna subchannel gains; f. ofaAnd flRespectively representing dopplerThe lux and subaperture frequency variables; l represents the sub-aperture number; b represents the signal bandwidth; t is trRepresenting a distance fast time variable; r0Representing nearest slope, c light speed, TcDenotes the sub-aperture integration time, λ denotes the signal wavelength, veRepresenting the equivalent radial velocity, NcIndicating the number of azimuth pulses within the sub-aperture, D indicating the azimuth dimension of the antenna, thetaEl,tRepresenting the target down-viewing angle, thetaAzi,tRepresenting the target azimuth.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a space-based early warning air moving target detection method based on sub-aperture coherent accumulation, which can simultaneously realize coherent accumulation in sub-apertures and among sub-apertures and overcome the defect that the output SCNR of the existing mixed accumulation algorithm is insufficient; compared with a maximum likelihood-based coherent accumulation algorithm, the method has more advantages in computational complexity; therefore, the method ensures that the SCNR is output with relatively high calculation efficiency, and is very suitable for improving the detection capability of the air weak target through long-time observation under the space-based early warning background.
The invention can realize coherent accumulation detection between sub-apertures and in sub-apertures simultaneously, effectively improves output SCNR and is very suitable for completing air moving target detection under the space-based early warning background.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a diagram of the main implementation steps of a space-based early warning AMTI method based on sub-aperture coherent accumulation according to the present invention;
FIG. 2 is a multi-channel observation model for observing an aerial moving target by a space-based radar;
FIG. 3 is a flow chart of a method for detecting an airborne moving target of a space-based early warning radar based on sub-aperture processing;
FIG. 4 is a schematic diagram of a clutter spectrum of a space-based early warning radar;
FIG. 5 is a schematic diagram of results of clutter suppression and moving target detection directly using STAP;
fig. 6 is a schematic diagram of a clutter suppression result using a sub-aperture STAP (totally divided into 8 sub-apertures);
FIG. 7 is a graph illustrating the results of a low threshold CFAR detection (8.5 dB);
FIG. 8 is a schematic diagram of search curves for targets 1-3 and false alarm points; f. of
FIG. 9 is a graph showing the comparison of the mixed accumulation and sub-aperture coherent accumulation of target 1;
FIG. 10 is a graph showing the comparison of the mixed accumulation and sub-aperture coherent accumulation of target 2;
FIG. 11 is a graph showing the comparison of the mixed accumulation and sub-aperture coherent accumulation of target 3;
FIG. 12 is a schematic diagram of the detection results after sub-aperture coherent accumulation;
FIG. 13 is a diagram illustrating the result of the CFAR detection.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
The invention aims to provide an AMTI (antenna-based early warning radar) method based on sub-aperture coherent integration (SCA) to overcome the defects that the traditional hybrid accumulation method has limited output SCNR and does not fully utilize the phase relation between sub-apertures, so that the moving target detection performance is not ideal.
Example 1
The invention provides a sub-aperture processing-based space-based early warning radar air moving target detection method, which comprises the following steps:
step S1: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;
step S2: performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction;
step S3: dividing the echo data after the distance walk correction along the azimuth sub-apertures according to the basis that the Doppler frequency walk does not occur in each sub-aperture, and ensuring that the Doppler diffusion does not occur in the sub-apertures;
step S4: clutter suppression is completed by utilizing a post-Doppler space-time adaptive processing technology (STAP) in each sub-aperture, coherent primary accumulation is completed in each sub-aperture, and then a target to be detected is extracted through Constant False Alarm Rate (CFAR) detection of a low threshold;
step S5: and performing phase compensation on the extracted targets to be detected one by one, and performing Fourier transform along the direction of the sub-apertures to complete coherent accumulation among the sub-apertures, further improving the output signal-to-noise-ratio (SCNR) of target signals, eliminating false alarms through high-threshold CFAR detection, and reserving real target points.
Specifically, the preprocessing of the radar echo data in step S1 includes: echoes, clutter and noise of moving targets in the air;
the preprocessed moving target echo in the air of the mth channel is represented as:
Figure BDA0003065024810000081
wherein,
Figure BDA0003065024810000082
representing the target amplitude, Pt，τ，B，GT(θAzi,t,θEl,t)，GR_Sub(θAzi,t,θEl,t)，λ，LsAnd sigma respectively represents peak power, pulse width, bandwidth, transmitting antenna full aperture gain, receiving antenna subchannel gain, signal wavelength, radar system loss and target RCS; r0Is the nearest slope distance; thetaEl,tAnd thetaAzi,tRespectively a lower viewing angle and an azimuth angle of the target; and cos (theta)Cone,t)＝cos(θEl,t)cos(θAzi,t)；θCone,tRepresenting a spatial cone angle; t is trAnd taRespectively representing the fast distance time and slow direction time variables; t isaRepresenting the accumulation time, rect (-) and sinc (-) respectively representing a rectangular window function and a sinc function; c represents the speed of light; j represents an imaginary unit; r0t,m(ta) In order to utilize the slope distance of the platform parameter after deramp compensation:
Figure BDA0003065024810000083
wherein R is0Is the nearest slope distance; d represents the size of the antenna square dimension DmRepresenting the channel spacing;
ve＝vysinθAzi,tsinθEl,t-vrxcosθAzi,tsinθEl,trepresents the equivalent radial velocity; v. ofrx＝v-vxRelative platform velocity; v denotes the platform velocity, vxRepresenting the target azimuth velocity; v. ofyRepresenting a target radial velocity;
Figure BDA0003065024810000084
representing the equivalent acceleration.
Specifically, the step S1 includes: and preprocessing multi-channel echoes of the space-based early warning radar, including distance compression, platform motion parameter compensation, frequency down-modulation and clutter Doppler center compensation.
Specifically, the step S2 includes: distance walk rectification is completed before sub-aperture division by using Keystone transformation, and distance migration in sub-apertures and between sub-apertures is removed.
Specifically, the step S5 includes: phase compensation is carried out on the extracted targets to be detected one by one, the phase relation among the sub-aperture echoes is deduced and compensated, Fourier transform is carried out along the sub-aperture direction, coherent accumulation among the sub-apertures is completed, and the output signal-to-noise ratio of target signals is further improved;
the step of performing phase compensation on the extracted targets to be detected one by one comprises the following steps:
Figure BDA0003065024810000091
wherein,
Figure BDA0003065024810000092
representing the equivalent acceleration of the search; λ represents a signal wavelength; j represents an imaginary unit; l represents the number of subapertures; t iscRepresenting the accumulation time within the sub-aperture; tau isa,1A time variable representing a reference sub-aperture;
the echo signals are subjected to coherent accumulation in each sub-aperture by azimuth Fourier transform, and are subjected to coherent accumulation among the sub-apertures by sub-aperture Fourier transform; after sub-aperture coherent accumulation, the echo signal is finally expressed as:
Figure BDA0003065024810000093
wherein,
Figure BDA0003065024810000094
representing the accumulated amplitude; m represents the number of channels; pavRepresents the radar average power; gTRepresenting the transmit antenna full aperture gain; gR-SubRepresenting receive antenna subchannel gains; f. ofaAnd flRespectively representing the Doppler frequency and the sub-aperture frequency variables; l represents the sub-aperture number; b represents the signal bandwidth; t is trRepresenting a distance fast time variable; r0Representing nearest slope, c light speed, TcDenotes the sub-aperture integration time, λ denotes the signal wavelength, veRepresenting the equivalent radial velocity, NcIndicating the number of azimuth pulses within the sub-aperture, D indicating the azimuth dimension of the antenna, thetaEl,tRepresenting the target down-viewing angle, thetaAzi,tRepresenting the target azimuth.
The sub-aperture coherent accumulation-based space-based early warning air moving target detection method provided by the invention firstly utilizes Keystone transformation to carry out distance walking correction, then completes clutter suppression and preliminary detection through sub-aperture division and sub-aperture STAP, further improves output SCNR through compensating the phase relation among the sub-apertures of echoes of the moving target and carrying out sub-aperture coherent accumulation, and finally identifies a real target through high threshold CFAR detection.
The invention provides a sub-aperture processing-based space-based early warning radar air moving target detection system, which comprises:
module M1: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;
module M2: performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction;
module M3: dividing the echo data after the distance walk correction along the azimuth sub-apertures according to the basis that the Doppler frequency walk does not occur in each sub-aperture, and ensuring that the Doppler diffusion does not occur in the sub-apertures;
module M4: clutter suppression is completed by utilizing a post-Doppler space-time adaptive processing technology (STAP) in each sub-aperture, coherent primary accumulation is completed in each sub-aperture, and then a target to be detected is extracted through Constant False Alarm Rate (CFAR) detection of a low threshold;
module M5: and performing phase compensation on the extracted targets to be detected one by one, and performing Fourier transform along the direction of the sub-apertures to complete coherent accumulation among the sub-apertures, further improving the output signal-to-noise-ratio (SCNR) of target signals, eliminating false alarms through high-threshold CFAR detection, and reserving real target points.
Specifically, the pre-processed radar echo data in the module M1 includes: echoes, clutter and noise of moving targets in the air;
the preprocessed moving target echo in the air of the mth channel is represented as:
Figure BDA0003065024810000101
wherein,
Figure BDA0003065024810000102
representing the target amplitude, Pt，τ，B，GT(θAzi,t,θEl,t)，GR_Sub(θAzi,t,θEl,t)，λ，LsAnd sigma respectively represents peak power, pulse width, bandwidth, transmitting antenna full aperture gain, receiving antenna subchannel gain, signal wavelength, radar system loss and target RCS; r0Is the nearest slope distance; thetaEl,tAnd thetaAzi,tRespectively a lower viewing angle and an azimuth angle of the target; and cos (theta)Cone,t)＝cos(θEl,t)cos(θAzi,t)；θCone,tRepresenting a spatial cone angle; t is trAnd taRespectively representing the fast distance time and slow direction time variables; t isaRepresenting the accumulation time, rect (-) and sinc (-) respectively representing a rectangular window function and a sinc function; c represents the speed of light; j represents an imaginary unit; r0t,m(ta) In order to utilize the slope distance of the platform parameter after deramp compensation:
Figure BDA0003065024810000103
wherein R is0Is the nearest slope distance; d represents the size of the antenna square dimension DmRepresenting the channel spacing;
ve＝vysinθAzi,tsinθEl,t-vrxcosθAzi,tsinθEl,trepresents the equivalent radial velocity; v. ofrx＝v-vxRelative platform velocity; v denotes the platform velocity, vxRepresenting the target azimuth velocity; v. ofyRepresenting a target radial velocity;
Figure BDA0003065024810000104
representing the equivalent acceleration.
Specifically, the module M1 includes: and preprocessing multi-channel echoes of the space-based early warning radar, including distance compression, platform motion parameter compensation, frequency down-modulation and clutter Doppler center compensation.
Specifically, the module M2 includes: distance walk rectification is completed before sub-aperture division by using Keystone transformation, and distance migration in sub-apertures and between sub-apertures is removed.
Specifically, the module M5 includes: phase compensation is carried out on the extracted targets to be detected one by one, the phase relation among the sub-aperture echoes is deduced and compensated, Fourier transform is carried out along the sub-aperture direction, coherent accumulation among the sub-apertures is completed, and the output signal-to-noise ratio of target signals is further improved;
the step of performing phase compensation on the extracted targets to be detected one by one comprises the following steps:
Figure BDA0003065024810000111
wherein,
Figure BDA0003065024810000112
representing the equivalent acceleration of the search; λ represents a signal wavelength; j represents an imaginary unit; l represents the number of subapertures; t iscRepresenting the accumulation time within the sub-aperture; tau isa,1A time variable representing a reference sub-aperture;
the echo signals are subjected to coherent accumulation in each sub-aperture by azimuth Fourier transform, and are subjected to coherent accumulation among the sub-apertures by sub-aperture Fourier transform; after sub-aperture coherent accumulation, the echo signal is finally expressed as:
Figure BDA0003065024810000113
wherein,
Figure BDA0003065024810000114
representing the accumulated amplitude; m represents the number of channels; pavRepresents the radar average power; gTRepresenting the transmit antenna full aperture gain; gR-SubRepresenting receive antenna subchannel gains; f. ofaAnd flRespectively representing the Doppler frequency and the sub-aperture frequency variables; l represents the sub-aperture number; b represents a signalA bandwidth; t is trRepresenting a distance fast time variable; r0Representing nearest slope, c light speed, TcDenotes the sub-aperture integration time, λ denotes the signal wavelength, veRepresenting the equivalent radial velocity, NcIndicating the number of azimuth pulses within the sub-aperture, D indicating the azimuth dimension of the antenna, thetaEl,tRepresenting the target down-viewing angle, thetaAzi,tRepresenting the target azimuth.
The sub-aperture coherent accumulation-based space-based early warning air moving target detection method provided by the invention firstly utilizes Keystone transformation to carry out distance walking correction, then completes clutter suppression and preliminary detection through sub-aperture division and sub-aperture STAP, further improves output SCNR through compensating the phase relation among the sub-apertures of echoes of the moving target and carrying out sub-aperture coherent accumulation, and finally identifies a real target through high threshold CFAR detection.
Example 2
Example 2 is a preferred example of example 1
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
The invention provides a sub-aperture coherent accumulation-based space-based AMTI (advanced mechanical transmission) early warning method, which specifically comprises the following steps of: as shown in fig. 1 and 3:
the method comprises the following steps: and establishing a satellite-borne multi-channel observation model, and completing preprocessing such as distance compression, platform parameter phase compensation and frequency reduction.
Specifically referring to fig. 2, in a three-dimensional coordinate O-XYZ, the satellite platform height is H, the platform velocity is v, and the direction is along the X-axis direction; the three-dimensional coordinate of the air moving target is (x)0,y0,z0) The along-track speed and the vertical-track speed are vxAnd vy(ii) a The transmitting antenna adopts full aperture transmission, the receiving antenna is divided into M sub-arrays, the channel spacing is dmM-d, M-0, 1, M-1, where d represents the adjacent channel spacing; thetaEl,t,θAzi,tAnd thetaCone,tRespectively, down-angle, azimuth, and space cone angle.
According to FIG. 2, the equivalent self-raising and self-retracting slope distance of the mth channel can be expressed as
Figure BDA0003065024810000121
In the formula, taThe azimuth slow time is represented, and D ═ Md represents the antenna azimuth dimension. From the second order Taylor expansion and the deramp processing with platform parameters, the slope distance can be further expressed in the form:
Figure BDA0003065024810000122
in the formula,
Figure BDA0003065024810000123
at the nearest slope distance, vrx＝v-vxIs the relative platform velocity, ve＝vysinθAzi,tsinθEl,t-vrxcosθAzi,tsinθEl,tWhich represents the equivalent radial velocity of the radial direction,
Figure BDA0003065024810000124
representing the equivalent acceleration.
Thus, the echo signal of the mth channel can be expressed as
Figure BDA0003065024810000125
In the formula,
Figure BDA0003065024810000126
representing the target amplitude, Pt，τ，B，GT(θAzi,t,θEl,t)，GR_Sub(θAzi,t,θEl,t)，λ，LsAnd sigma represents the peak power, pulse width, bandwidth, and total number of transmitting antennas, respectivelyAperture gain, receive antenna subchannel gain, signal wavelength, system loss, and target RCS. t is trRepresenting the range fast time, rect (-) and sinc (-) represent the rectangular window function and the 'sinc' function, respectively.
Step two: and (5) completing distance system rectification by using Keystone transformation.
Keystone Transform (KT) is widely applied to the field of radars because the KT does not need any prior information of moving targets and is suitable for multi-target scenes, and echo signals corrected by adopting the KT can be represented as
Figure BDA0003065024810000131
In the formula, τaRepresenting the new orientation time variable after KT. It is emphasized that the purpose of distance correction with KT prior to sub-aperture division is to simultaneously remove distance walk of objects within and between sub-apertures. dmDenotes the channel spacing, veDenotes the equivalent radial velocity, aeRepresenting the equivalent radial acceleration.
Step three: and performing sub-aperture division on the echo data along the azimuth direction.
Specifically, the azimuth direction is divided into sub-apertures, and the coherent integration time T is obtainedaEqually dividing the aperture into L sub-apertures, wherein the accumulation time and the number of sampling points of each sub-aperture are respectively Tc＝TaL and Mc＝TcThe ratio of the specific molecular weight to the specific molecular weight is/PRT. At this time, the echo signal may be written as
Figure BDA0003065024810000132
Where the echo of the first sub-aperture can be written as
Figure BDA0003065024810000133
In the formula, τa,lIndicating the azimuth time variation of the ith sub-aperture. Since KT is already rightThe distance walk is corrected, so that the Doppler walk is not generated in each sub-aperture; the orientation FT is carried out on the segmented echo to obtain the orientation
Figure BDA0003065024810000134
In the formula,
Figure BDA0003065024810000135
representing the magnitude of the accumulation in the subaperture, PavRepresenting the average power of the radar, faRepresenting the doppler frequency variation.
Step four: and (3) completing clutter suppression in each sub-aperture by utilizing a space-time adaptive processing technology, and extracting a target to be detected through low-threshold CFAR detection.
Specifically, the multi-channel space-based early warning radar echo in the range-doppler domain can be represented as the following form after being divided by the sub-apertures
Figure BDA0003065024810000141
In the formula, suppose H1And H0Respectively representing the existence of a target and the nonexistence of the target; st,l(tr0,fa0)，Sc,l(tr0,fa0) And nl(tr0,fa0) Respectively representing multi-channel moving target echoes, clutter and noise; multichannel target echo St,l(tr0,fa0)＝[St,1,l(tr0,fa0),...,St,M,l(tr0,fa0)]TMultiple channel clutter Sc,l(tr0,fa0) This can be achieved by setting the along-track speed and the vertical-track speed to zero.
Clutter suppression is performed within each sub-aperture, and the process can be expressed as
Figure BDA0003065024810000142
Wherein S is a target steering vector, WlIn order to be a weight vector, the weight vector,
Figure BDA0003065024810000143
is the clutter covariance matrix estimated from the ith sub-aperture. The optimal weight vector is
Figure BDA0003065024810000144
The output signal after clutter suppression can be expressed as
Figure BDA0003065024810000145
In the formula, Xl(tr0,fa0) Representing the echo signal in the range-doppler domain for the ith sub-aperture containing the clutter signal, target signal and noise signal. Then, carrying out low-threshold CFAR detection on the reference sub-aperture to extract a potential target point, wherein partial false alarm points exist at the same time; the process is represented as
Figure BDA0003065024810000146
In the formula, VLTIndicating a low detection threshold.
Step five: and performing phase compensation on the extracted targets to be detected one by one, performing Fourier transform in the sub-aperture direction, completing sub-aperture coherent accumulation, further improving output SCNR, and finally, providing a false alarm through high threshold CFAR detection and reserving a real target point.
Specifically, s 'is assumed't,l(tr,τa,l) Representing two-dimensional time domain signals subjected to sub-aperture clutter suppression, and the sub-aperture azimuth time variable satisfying taua,l＝τa,1+l·TcTherefore, the first sub-aperture echo and the reference sub-aperture echo have the following relationship
Figure BDA0003065024810000151
Where the phase difference is related to the target motion parameter and the number of sub-apertures, it can be expressed as
Figure BDA0003065024810000152
In the formula, there is a fixed initial phase difference between the ith sub-aperture and the reference sub-aperture and a doppler shift term related to the equivalent acceleration. The following compensation function is constructed to eliminate the Doppler shift term associated with the phase term associated with the target acceleration, i.e.
Figure BDA0003065024810000153
Then, the echo signals can complete the preliminary coherent accumulation in each sub-aperture by the azimuth FT, and further complete the secondary coherent accumulation between sub-apertures by the sub-aperture FT. After sub-aperture coherent accumulation, the echo signal can be finally written as
Figure BDA0003065024810000154
In the formula,
Figure BDA0003065024810000155
representing the amplitude of the final spatial domain synthesis and sub-aperture coherent accumulation. It can be seen that the target peaks at its corresponding slant range, doppler and subaperture. And finally, carrying out false alarm rejection and real target point extraction through a high threshold CFAR. The process can be expressed as
Figure BDA0003065024810000156
In the formula, VHTIndicating a high detection threshold. The methodThe processing flow chart of the method is shown in fig. 3.
The effects of the present invention can be further illustrated by the following simulations:
(1) simulation conditions
The simulation experiment platform parameters and the moving target parameters are respectively given in table 1 and table 2, and the implementation steps of this embodiment are all performed on the MATLAB2016 simulation platform.
TABLE 1 simulation parameters Table
Figure BDA0003065024810000157
Figure BDA0003065024810000161
TABLE 2 airborne moving object parameters
Figure BDA0003065024810000162
(2) Emulated content
This section presents the results of the simulation process to verify the proposed algorithm. And 3 fast moving targets are added in the space-based early warning radar echo to carry out analog simulation.
FIG. 4 is a space-based early warning radar clutter spectrum; FIG. 5 shows the results of clutter suppression and moving target detection using STAP directly; FIGS. 6 and 7 are the results of using sub-aperture STAP and performing low-threshold CFAR detection (8.5dB), respectively; FIG. 8 is a search curve for targets 1-3 and a false alarm point; FIGS. 9 to 11 show the results of the comparison of the mixed accumulation and the sub-aperture coherent accumulation of the targets 1 to 3, respectively; fig. 12 to 13 show the high threshold CFAR (13.2dB) detection results of the proposed method.
As can be seen from FIG. 4, the moving target is submerged in the severely extended space-based clutter spectrum and cannot be effectively detected; fig. 5 is a range-doppler spectrum after clutter suppression, which shows that although clutter is effectively suppressed, a target cannot be effectively detected because both range and doppler dimensions are defocused due to range walk and doppler frequency walk; fig. 6 and 7 respectively show results of clutter suppression of the sub-aperture STAP (totally divided into 8 sub-apertures) and low-threshold (8.5dB) CFAR detection, where there are many false alarm points while visible clutter is effectively suppressed; FIG. 8 is search curves of targets 1-3 and false alarm points, and it can be seen that the search curve of a real target will have a peak value along with an acceleration search curve, and the false alarm point will not; fig. 9 to 11 show the comparison results of the mixed accumulation and the sub-aperture coherent accumulation of the targets 1 to 3, respectively, and it can be seen that compared with the conventional mixed accumulation detection method, the proposed method has lower side lobe, i.e. better output SCNR. Fig. 12 and 13 are final processing results after sub-aperture coherent accumulation and high threshold CFAR detection, respectively, and it can be seen that three weak targets can be effectively detected.
In conclusion, the simulation experiment verifies the correctness, the effectiveness and the reliability of the method.
It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Those skilled in the art will appreciate that, in addition to implementing the systems, apparatus, and various modules thereof provided by the present invention in purely computer readable program code, the same procedures can be implemented entirely by logically programming method steps such that the systems, apparatus, and various modules thereof are provided in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system, the device and the modules thereof provided by the present invention can be considered as a hardware component, and the modules included in the system, the device and the modules thereof for implementing various programs can also be considered as structures in the hardware component; modules for performing various functions may also be considered to be both software programs for performing the methods and structures within hardware components.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims (8)

1. A space-based early warning radar air moving target detection method based on sub-aperture processing is characterized by comprising the following steps:
step S1: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;
step S2: performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction;
step S3: dividing the echo data after the distance walk correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;
step S4: clutter suppression is completed in each sub-aperture by using a post-Doppler space-time adaptive processing technology, preliminary accumulation of coherent signals is completed in each sub-aperture, and then a target to be detected is extracted through constant false alarm detection of a low threshold;
step S5: performing phase compensation on the extracted targets to be detected one by one, and then performing Fourier transform along the direction of the sub-apertures to complete coherent accumulation among the sub-apertures, further improving the output signal-to-noise ratio of target signals, eliminating false alarms through high threshold detection and reserving real target points;
the step S5 includes: phase compensation is carried out on the extracted targets to be detected one by one, the phase relation among the sub-aperture echoes is deduced and compensated, Fourier transform is carried out along the sub-aperture direction, coherent accumulation among the sub-apertures is completed, and the output signal-to-noise ratio of target signals is further improved;
the step of performing phase compensation on the extracted targets to be detected one by one comprises the following steps:
Figure FDA0003545843980000011
wherein,
Figure FDA0003545843980000012
representing the equivalent acceleration of the search; λ represents a signal wavelength; j represents an imaginary unit; l represents the number of subapertures; t iscRepresenting the accumulation time within the sub-aperture; tau isa,1A time variable representing a reference sub-aperture;
the echo signals are subjected to coherent accumulation in each sub-aperture by azimuth Fourier transform, and are subjected to coherent accumulation among the sub-apertures by sub-aperture Fourier transform; after sub-aperture coherent accumulation, the echo signal is finally expressed as:
Figure FDA0003545843980000013
wherein,
Figure FDA0003545843980000014
representing the accumulated amplitude; m represents the number of channels; pavRepresents the radar average power; gTRepresenting the transmit antenna full aperture gain; gR-SubRepresenting receive antenna subchannel gains; f. ofaAnd flRespectively representing the Doppler frequency and the sub-aperture frequency variables; l represents the sub-aperture number; b represents the signal bandwidth; t is trRepresenting a distance fast time variable; r0Representing nearest slope, c light speed, TcDenotes the sub-aperture integration time, λ denotes the signal wavelength, veRepresenting the equivalent radial velocity, NcIndicating the number of azimuth pulses within the sub-aperture, D indicating the azimuth dimension of the antenna, thetaEl,tRepresenting the target down-viewing angle, thetaAzi,tRepresenting the target azimuth.
2. The subaperture-processing-based space-based pre-warning radar airborne target detection method of claim 1, wherein the preprocessing of the radar echo data in step S1 comprises: echoes, clutter and noise of moving targets in the air;
the preprocessed moving target echo in the air of the mth channel is represented as:
Figure FDA0003545843980000021
wherein,
Figure FDA0003545843980000022
representing the target amplitude, Pt，τ，B，GT(θAzi,t,θEl,t)，GR_Sub(θAzi,t,θEl,t)，λ，LsAnd sigma respectively represents peak power, pulse width, bandwidth, transmitting antenna full aperture gain, receiving antenna subchannel gain, signal wavelength, radar system loss and target RCS; r0Is the nearest slope distance; thetaEl,tAnd thetaAzi,tRespectively a lower viewing angle and an azimuth angle of the target; and cos (theta)Cone,t)＝cos(θEl,t)cos(θAzi,t)；θCone,tRepresenting a spatial cone angle; t is trAnd taRespectively representing the fast distance time and slow direction time variables; t isaRepresenting the accumulation time, rect (-) and sinc (-) respectively representing a rectangular window function and a sinc function; c represents the speed of light; j represents an imaginary unit; r0t,m(ta) In order to utilize the slope distance of the platform parameter after deramp compensation:
Figure FDA0003545843980000023
wherein R is0Is the nearest slope distance; d represents the size of the antenna square dimension DmRepresenting the channel spacing;
ve＝vysinθAzi,tsinθEl,t-vrxcosθAzi,tsinθEl,trepresents the equivalent radial velocity; v. ofrx＝v-vxRelative platform velocity; v denotes the platform velocity, vxRepresenting the target azimuth velocity; v. ofyRepresenting a target radial velocity;
Figure FDA0003545843980000024
representing the equivalent acceleration.
3. The subaperture-processing-based space-based pre-warning radar airborne target detection method of claim 1, wherein the step S1 comprises: and preprocessing multi-channel echoes of the space-based early warning radar, including distance compression, platform motion parameter compensation, frequency down-modulation and clutter Doppler center compensation.
4. The subaperture-processing-based space-based pre-warning radar airborne target detection method of claim 1, wherein the step S2 comprises: distance walk rectification is completed before sub-aperture division by using Keystone transformation, and distance migration in sub-apertures and between sub-apertures is removed.
5. A space-based early warning radar air moving target detection system based on sub-aperture processing is characterized by comprising:
module M1: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;
module M2: performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction;
module M3: dividing the echo data after the distance walk correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;
module M4: clutter suppression is completed in each sub-aperture by using a post-Doppler space-time adaptive processing technology, initial coherent accumulation is completed in each sub-aperture, and then a target to be detected is extracted through constant false alarm detection of a low threshold;
module M5: performing phase compensation on the extracted targets to be detected one by one, and then performing Fourier transform along the direction of the sub-apertures to complete coherent accumulation among the sub-apertures, further improving the output signal-to-noise ratio of target signals, eliminating false alarms through high threshold detection and reserving real target points;
the module M5 includes: phase compensation is carried out on the extracted targets to be detected one by one, the phase relation among the sub-aperture echoes is deduced and compensated, Fourier transform is carried out along the sub-aperture direction, coherent accumulation among the sub-apertures is completed, and the output signal-to-noise ratio of target signals is further improved;
the step of performing phase compensation on the extracted targets to be detected one by one comprises the following steps:
Figure FDA0003545843980000031
wherein,
Figure FDA0003545843980000032
representing the equivalent acceleration of the search; λ represents a signal wavelength; j represents an imaginary unit; l represents the number of subapertures; t iscRepresenting the accumulation time within the sub-aperture; tau isa,1A time variable representing a reference sub-aperture;
the echo signals are subjected to coherent accumulation in each sub-aperture by azimuth Fourier transform, and are subjected to coherent accumulation among the sub-apertures by sub-aperture Fourier transform; after sub-aperture coherent accumulation, the echo signal is finally expressed as:
Figure FDA0003545843980000033
wherein,
Figure FDA0003545843980000034
representing the accumulated amplitude; m represents the number of channels; pavRepresents the radar average power; gTRepresenting the transmit antenna full aperture gain; gR-SubRepresenting receive antenna subchannel gains; f. ofaAnd flRespectively representing the Doppler frequency and the sub-aperture frequency variables; l represents the sub-aperture number; b tableIndicating the signal bandwidth; t is trRepresenting a distance fast time variable; r0Representing nearest slope, c light speed, TcDenotes the sub-aperture integration time, λ denotes the signal wavelength, veRepresenting the equivalent radial velocity, NcIndicating the number of azimuth pulses within the sub-aperture, D indicating the azimuth dimension of the antenna, thetaEl,tRepresenting the target down-viewing angle, thetaAzi,tRepresenting the target azimuth.
6. The subaperture-processing-based space-based pre-warning radar airborne target detection system of claim 5, wherein the pre-processing of the radar echo data in the module M1 comprises: echoes, clutter and noise of moving targets in the air;
the preprocessed moving target echo in the air of the mth channel is represented as:
Figure FDA0003545843980000041
wherein,
Figure FDA0003545843980000042
representing the target amplitude, Pt，τ，B，GT(θAzi,t,θEl,t)，GR_Sub(θAzi,t,θEl,t)，λ，LsAnd sigma respectively represents peak power, pulse width, bandwidth, transmitting antenna full aperture gain, receiving antenna subchannel gain, signal wavelength, radar system loss and target RCS; r0Is the nearest slope distance; thetaEl,tAnd thetaAzi,tRespectively a lower viewing angle and an azimuth angle of the target; and cos (theta)Cone,t)＝cos(θEl,t)cos(θAzi,t)；θCone,tRepresenting a spatial cone angle; t is trAnd taRespectively representing the fast distance time and slow direction time variables; t isaRepresenting the accumulation time, rect (-) and sinc (-) respectively representing a rectangular window function and a sinc function; c represents the speed of light; j represents an imaginary unit; r0t,m(ta) For using the slope distance after deramp compensation of platform parameters：
Figure FDA0003545843980000043
Wherein R is0Is the nearest slope distance; d represents the size of the antenna square dimension DmRepresenting the channel spacing;
ve＝vysinθAzi,tsinθEl,t-vrxcosθAzi,tsinθEl,trepresents the equivalent radial velocity; v. ofrx＝v-vxRelative platform velocity; v denotes the platform velocity, vxRepresenting the target azimuth velocity; v. ofyRepresenting a target radial velocity;
Figure FDA0003545843980000044
representing the equivalent acceleration.
7. The subaperture-processing-based space-based pre-warning radar airborne target detection system of claim 5, wherein the module M1 comprises: and preprocessing multi-channel echoes of the space-based early warning radar, including distance compression, platform motion parameter compensation, frequency down-modulation and clutter Doppler center compensation.
8. The subaperture-processing-based space-based pre-warning radar airborne target detection system of claim 5, wherein the module M2 comprises: distance walk rectification is completed before sub-aperture division by using Keystone transformation, and distance migration in sub-apertures and between sub-apertures is removed.
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