CN-122017826-A - Space-time rapid forward looking imaging method for forward looking array radar of moving platform

CN122017826ACN 122017826 ACN122017826 ACN 122017826ACN-122017826-A

Abstract

The invention discloses a space-time rapid forward-looking imaging method for a forward-looking array radar of a moving platform, which comprises the steps of firstly, recording a forward-looking area echo by a multichannel radar system based on a notch direction, and obtaining distance-pulse-channel three-dimensional echo data by sampling; the method comprises the steps of carrying out distance to high resolution processing, pulse compression and distance migration correction on data, traversing each distance gate, carrying out azimuth Fourier transform on space-time two-dimensional data of each frame-multichannel, intercepting a dominant Doppler unit larger than an energy threshold in Doppler spectrum, carrying out inverse Fourier transform to a time domain, namely carrying out dimension reduction processing in the Doppler domain, carrying out rank reduction processing based on low rank characteristics of a covariance matrix, analyzing energy of a reserved signal through a main component, and finally estimating position and amplitude information of a target through an adaptive iterative algorithm, and carrying out projection to obtain a final two-dimensional imaging result. The invention effectively improves the forward-looking resolution, simultaneously remarkably reduces the calculation complexity and greatly improves the operation efficiency.

Inventors

WU DI
REN LINGYUN
LI ZHENYUAN
TIAN BIN
ZHU DAIYIN
YAN HE
JIN GUODONG

Assignees

南京航空航天大学
南京航空航天大学深圳研究院

Dates

Publication Date: 20260512
Application Date: 20251225

Claims (9)

1. A space-time rapid forward looking imaging method for a forward looking array radar of a moving platform is characterized by comprising the following steps: (1) The data preprocessing comprises the steps of acquiring echoes of a front view area by utilizing a multichannel radar system in a track cutting direction to obtain distance-pulse-channel three-dimensional data, and then realizing high-resolution processing in the distance direction by pulse compression and distance migration correction; (2) The Doppler domain dimension reduction comprises traversing each range gate, carrying out azimuth Fourier transform on a corresponding space-time two-dimensional data matrix, and carrying out inverse Fourier transform by only intercepting a dominant Doppler unit larger than an energy threshold value in the Doppler spectrum by utilizing the characteristics of a foreground Doppler spectrum set; (3) Performing space-time rank reduction processing, namely performing characteristic decomposition on a sampling covariance matrix, arranging the sampling covariance matrix in descending order according to characteristic values, reserving energy of signals, further compressing the data scale and suppressing noise; (4) And super-resolution imaging, namely estimating the azimuth position and the scattering intensity of the target by adopting a self-adaptive iterative algorithm for the data subjected to dimension and rank reduction, and projecting an estimation result to a two-dimensional plane to form a high-resolution forward-looking imaging diagram.
2. The space-time fast forward-looking imaging method for a moving platform forward-looking array radar of claim 1, wherein said step (1) is implemented as follows: One revolution of beam scanning, the entire imaging scan process is with respect to a single point target The specific form of the obtained echo is as follows: Wherein, the Is the scattering coefficient, the coordinates are , Reference array element and target for radar array antenna The oblique distance between the two adjacent grooves is equal to the oblique distance between the two adjacent grooves, As the azimuth angle of the object, For the pitch angle of the target, Representing a rectangular window function that is used to represent the window, For the distance to the fast time domain variable, For the carrier frequency of the radar transmit signal, For a linear frequency adjustment in the distance direction, Representing a two-way antenna pattern in azimuth, which varies over time The change, representing the modulation of the azimuth direction, Representing the beam center sweep of an antenna to a point target Time of (2); to transmit signals to a target Target for back menstruation Reflect to the first The propagation delay of the individual channels is determined, Representing the channel spacing, then the time delay The method comprises the following steps: Wherein, the In order to achieve the light velocity, the light beam is, Performing down-conversion treatment on the echo, and then performing range pulse compression and migration correction, namely multiplying a pulse compression reference function and a migration correction phase factor in a range frequency domain to realize range high-resolution imaging, wherein the echo is expressed as follows after range inverse Fourier transform: 。
3. The space-time fast forward imaging method for a moving platform forward array radar according to claim 2, wherein the multiplying the pulse compression reference function and the migration correction phase factor in the distance frequency domain is implemented as follows: the distance direction FFT is carried out on the echo of each channel after the down-conversion, and the distance direction FFT is obtained: Wherein, the For the bandwidth of the signal, For the distance to the frequency domain, multiplying the frequency domain by the following pulse compression reference function: The method comprises the following steps: multiplying the following migration correction phase factors in the distance frequency domain to eliminate the influence caused by the platform motion: i.e. in the distance frequency domain multiplied by the following function: thereby achieving high resolution imaging in the distance direction.
4. The space-time fast forward-looking imaging method for a moving platform forward-looking array radar of claim 1, wherein said step (2) is implemented as follows: for a distance of Is the first of (2) Directional echo of individual channels, point target Is expressed as: grid division is carried out on the forward-looking imaging area, and division is carried out A plurality of distance gates are arranged on the surface of the frame, The azimuth angle of the potential target is expressed as For the first A coherent pulse interval CPI, in which the beam center is pointed at Space-time two-dimensional signal Expressed as: Wherein, the Is the azimuth angle The scattering coefficient of the object at which it is located, Is a space-time pilot vector which is used for the channel estimation, The steering vector is represented by the kronecker product of the spatial steering vector and the temporal steering vector: ; Space-time two-dimensional signal The azimuth fourier transform is performed to the doppler domain, Wherein, the ; The core dimension reduction process is realized by screening and identifying dominant Doppler units through an energy threshold, sorting unit energy based on an energy method, and selecting an index set meeting the condition : Wherein, the The threshold value is reserved for the energy and, Is the number of Doppler units selected and satisfies ; The dimension-reducing operation is performed by selecting a basis vector corresponding to the selected cell Structured projection matrix The method is realized by projecting the data into a dimension-reducing subspace, and the dimension-reducing data of the Doppler domain is that Thereby, by performing inverse fourier transform on the doppler domain compressed data, a space-time data matrix after the dimension reduction is obtained: Raw data cube by orthogonal projection Is converted into a dimension-reducing space 。
5. The method for space-time fast forward imaging for a moving platform forward array radar of claim 4, wherein said spatial steering vector And a time domain pilot vector Calculated from the following formulas: 。
6. a space-time fast forward imaging method for a moving platform forward array radar as defined in claim 4 wherein said energy retention threshold The value is between 0.95 and 1.
7. The space-time fast forward-looking imaging method for a moving platform forward-looking array radar of claim 1, wherein said step (3) is implemented as follows: in a space-time covariance matrix formed by space-time snapshots The characteristic value characterizes the distribution characteristic of signal energy along the direction of the corresponding characteristic vector, the large characteristic value corresponds to the dominant signal component, the characteristic vector captures the space-time coupling structure of the target or the strong clutter, and the small characteristic value is tensed into a noise subspace which is orthogonal with the signal subspace; Setting an energy retention threshold by Performing principal component analysis and before preserving Space-time covariance matrix Is expressed as: Wherein, the Comprising signal subspace correspondence The number of dominant feature vectors is the number of dominant feature vectors, Comprising corresponding characteristic values arranged in descending order, To tense into a feature vector of the noise subspace, Representing the noise component; Before reservation Obtaining a compression covariance matrix from the eigenvectors Further by Constructing a dimension-reducing space-time guide matrix, And constructing a space-time snapshot after dimension and rank reduction.
8. A space-time fast forward imaging method for a moving platform forward array radar according to claim 7, wherein said energy retention threshold is 95% of the total energy.
9. The space-time fast forward-looking imaging method for a moving platform forward-looking array radar of claim 1, wherein said step (4) is implemented as follows: covariance matrix with dimension and rank reduction And (3) carrying out azimuth spectrum reconstruction of single snapshot by using an iterative algorithm, wherein the azimuth spectrum reconstruction is obtained according to a least square criterion: introducing an iterative algorithm, and initially: calculating an autocorrelation matrix of the signal based on the signal , , Represented as a diagonal matrix in which each diagonal element The autocorrelation matrix of the echo is calculated as: Wherein, the In order for the parameters to be regularized, Performing rank reduction processing on the autocorrelation matrix, substituting the rank reduction processing into an iterative process, and repeatedly estimating the azimuth spectrum The azimuth spectrum estimated in each iteration is used for updating the signal autocorrelation matrix, so that the autocorrelation matrix of the echo is updated, and the iteration is continued until convergence is achieved; And finally, estimating the azimuth spectrum corresponding to each distance-CPI unit, and performing projection, space coordinate conversion and display to obtain a final forward-looking imaging result.

Description

Space-time rapid forward looking imaging method for forward looking array radar of moving platform Technical Field The invention belongs to the technical field of radar imaging, relates to an airborne radar forward-looking imaging signal processing technology, and particularly relates to a space-time rapid forward-looking imaging method for a forward-looking array radar of a motion platform. Background Current radar forward-looking imaging techniques face significant bottlenecks in acquiring cross-heading high resolution. This technical challenge stems from the minimal change in doppler shift observed in the forward looking geometry, which makes the target difficult to distinguish effectively in the frequency domain. In addition, the symmetrical topography features produce nearly identical Doppler features, further exacerbating the difficulty of target separation. Conventional real aperture radars generate low resolution images by mechanical scanning, the azimuthal resolution of which is inherently limited by the physical antenna characteristics. In order to improve the observation capability of a front visual area of a motion platform, researchers in the past decade propose two main technical paths, namely a time domain enhancement method based on a deconvolution theory and a space domain optimization method adopting super-resolution spectrum estimation. Deconvolution performs image reconstruction by building a convolution model of the antenna pattern and the target scattering characteristics, but as a typical inverse problem solution, it is extremely sensitive to measurement noise and systematic errors. Another class of solutions employs a multi-antenna configuration with tangential heading, integrating the super-resolution processing directly into the imaging link. The method can break through the traditional beam width limit and realize the resolution improvement of a plurality of times. A variety of sophisticated algorithms have been developed in the field of array signal processing, including adaptive beamforming and subspace decomposition methods, among others. Notably, although the Doppler change in the forward looking scene is weak, it is potentially valuable for resolution improvement. At present, the space-time combined super-resolution forward-looking imaging technology is taken as a new technical means of radar forward-looking imaging, has been gradually accepted and paid attention to by related research institutions, and is one of effective means for solving the problem of radar forward-looking imaging of a motion platform in the future. However, in forward-looking imaging applications, computational efficiency is equally important as resolution improvement. Although the existing super-resolution method can effectively improve the azimuth resolution, challenges of too high computational complexity are often faced, how to optimize an algorithm, the operation efficiency is greatly improved while the imaging precision is maintained, and finally the problem to be solved in the field of forward-looking imaging is to be solved. Disclosure of Invention Aiming at a forward-looking radar system working in a dynamic environment, the invention provides a space-time sparsity self-adaptive forward-looking imaging method for an airborne array radar, which can obviously improve the operation efficiency without losing the imaging resolution. The invention relates to a space-time sparsity self-adaptive forward-looking imaging method for an airborne array radar, which comprises the following steps of: (1) The data preprocessing comprises the steps of acquiring echoes of a front view area by utilizing a multichannel radar system in a track cutting direction to obtain distance-pulse-channel three-dimensional data, and then realizing high-resolution processing in the distance direction by pulse compression and distance migration correction; (2) The Doppler domain dimension reduction comprises traversing each range gate, carrying out azimuth Fourier transform on a corresponding space-time two-dimensional data matrix, and carrying out inverse Fourier transform by only intercepting a dominant Doppler unit larger than an energy threshold value in the Doppler spectrum by utilizing the characteristics of a foreground Doppler spectrum set; (3) Performing space-time rank reduction processing, namely performing characteristic decomposition on a sampling covariance matrix, arranging the sampling covariance matrix in descending order according to characteristic values, reserving energy of signals, further compressing the data scale and suppressing noise; (4) And super-resolution imaging, namely estimating the azimuth position and the scattering intensity of the target by adopting a self-adaptive iterative algorithm for the data subjected to dimension and rank reduction, and projecting an estimation result to a two-dimensional plane to form a high-resolution forward-looking imaging diagram. Further, the implementation process