WO2024045362A1

WO2024045362A1 - Time-domain imaging method for vehicle-borne doppler-division-multiple-access mimo synthetic aperture radar

Info

Publication number: WO2024045362A1
Application number: PCT/CN2022/133528
Authority: WO
Inventors: 徐刚; 张邦杰; 姬昂; 张慧; 洪伟; 郭坤鹏; 冯友怀
Original assignee: 南京隼眼电子科技有限公司; 东南大学
Priority date: 2022-08-31
Filing date: 2022-11-22
Publication date: 2024-03-07
Also published as: CN115128608A; CN115128608B

Abstract

A time-domain imaging method for a vehicle-borne Doppler-division-multiple-access MIMO synthetic aperture radar. The method comprises: collecting echo data of a linear frequency-modulated signal, which is transmitted to a target by a MIMO synthetic aperture radar that moves along a linear trajectory at a preset speed (S101); performing Doppler filtering on the echo data to obtain echo data corresponding to each channel, and according to the echo data corresponding to each channel, obtaining a transformed echo matrix corresponding to the channel, and projecting the echo matrix into a two-dimensional imaging coordinate system, so as to obtain a two-dimensional imaging result of the channel (S102); sequentially dividing a synthetic aperture of the synthetic aperture radar into a plurality of sub-apertures, and synthesizing two-dimensional imaging results of all channels corresponding to each sub-aperture, so as to obtain an imaging result corresponding to the sub-aperture (S103); and performing image fusion on imaging results corresponding to all the sub-apertures, so as to obtain a total imaging result corresponding to the synthetic aperture (S104). Thus, wide-angle-of-view high-resolution imaging is realized.

Description

车载多普勒分集MIMO合成孔径雷达时域成像方法Time domain imaging method of vehicle-mounted Doppler diversity MIMO synthetic aperture radar

技术领域Technical field

本发明涉及雷达信号处理技术领域，尤其涉及一种车载多普勒分集MIMO合成孔径雷达时域成像方法。The invention relates to the technical field of radar signal processing, and in particular to a vehicle-mounted Doppler diversity MIMO synthetic aperture radar time domain imaging method.

背景技术Background technique

作为一种全天时、全天候微波传感工具，雷达在许多工程领域发挥了重要作用。其中，由于具有低成本、低功耗和尺寸小等优点，工作在毫米波段的调频连续波(FMCW，Frequency-Modulated Continuous Wave)***已被广泛应用于车辆自动驾驶。目前，L2级自动驾驶已基本实现，L3及更高级别的自动驾驶技术则对毫米波雷达的性能提出了更为严格的要求。As an all-weather, all-weather microwave sensing tool, radar plays an important role in many engineering fields. Among them, Frequency-Modulated Continuous Wave (FMCW) systems operating in the millimeter wave band have been widely used in vehicle autonomous driving due to their advantages such as low cost, low power consumption and small size. At present, L2 level autonomous driving has been basically realized, while L3 and higher level autonomous driving technology puts forward more stringent requirements for the performance of millimeter wave radar.

车载雷达的成像主要有点云和合成孔径两种技术形式。点云在成像过程包含恒虚警检测等步骤，仅保留了感兴趣目标的图像，丢弃了场景的环境信息。而且点云通常比较稀疏，一般需要对图像进行多帧融合才能用于目标检测与识别。The imaging of vehicle radar mainly has two technical forms: point cloud and synthetic aperture. The point cloud imaging process includes steps such as constant false alarm detection, which only retains the image of the target of interest and discards the environmental information of the scene. Moreover, point clouds are usually sparse, and it is generally necessary to fuse multiple frames of images to be used for target detection and recognition.

与点云不同，车载合成孔径雷达(SAR，Synthetic Aperture Radar)使用宽带发射波形和雷达平台的运动实现二维高分辨率成像，同时保留了场景内所有位置的散射信息。相较于传统的机载或星载SAR，车载SAR目前存在一些独特的挑战：车载雷达距待观测区域较近，不满足远场条件；车载SAR需要提供很宽的视野(FOV，Field of View)，这对运动补偿和弯曲校正等提出了很高的要求；车载SAR要求算法有较好的实时成像性能，这要求算法具有高度的并行性。Unlike point clouds, vehicle-mounted synthetic aperture radar (SAR) uses broadband emission waveforms and the motion of the radar platform to achieve two-dimensional high-resolution imaging while retaining scattering information at all locations within the scene. Compared with traditional airborne or spaceborne SAR, vehicle-mounted SAR currently has some unique challenges: vehicle-mounted radar is relatively close to the area to be observed and does not meet far-field conditions; vehicle-mounted SAR needs to provide a wide field of view (FOV, Field of View). ), which puts forward high requirements for motion compensation and bending correction; vehicle-mounted SAR requires the algorithm to have better real-time imaging performance, which requires the algorithm to have a high degree of parallelism.

针对车载毫米波SAR成像存在的问题，国内外学者做了很多相关的工作，如能够提供高实时成像性能和宽视野的FMCW-SAR是亟需解决的问题。In response to the problems existing in vehicle-mounted millimeter wave SAR imaging, domestic and foreign scholars have done a lot of related work. For example, FMCW-SAR that can provide high real-time imaging performance and wide field of view is an urgent problem that needs to be solved.

技术问题technical problem

本发明提供了一种车载多普勒分集MIMO合成孔径雷达时域成像方法，通过对于发射机进行DDM编码并且滤波得到每一单通道对应的回波数据并基于该回波数据二维成像，实现宽视角高分辨成像。The present invention provides a vehicle-mounted Doppler diversity MIMO synthetic aperture radar time domain imaging method. By performing DDM encoding and filtering on the transmitter, the echo data corresponding to each single channel is obtained and two-dimensional imaging is achieved based on the echo data. Wide viewing angle and high resolution imaging.

技术解决方案Technical solutions

第一方面，提供了一种车载多普勒分集MIMO合成孔径雷达时域成像方法，所述方法包括：In a first aspect, a vehicle-mounted Doppler diversity MIMO synthetic aperture radar time domain imaging method is provided. The method includes:

采集以预设的速度沿直线轨迹运动的MIMO合成孔径雷达向目标发射的线性调频信号的回波数据，其中，所述MIMO合成孔径雷达的不同发射机具有不同的DDM编码；Collecting echo data of chirp signals emitted by a MIMO synthetic aperture radar moving along a straight line trajectory at a preset speed to the target, wherein different transmitters of the MIMO synthetic aperture radar have different DDM codes;

针对所述回波数据进行多普勒滤波得到每一通道对应的回波数据，并针对每一通道对应的回波数据进行距离向傅里叶变换以得到该通道对应的变换后的回波矩阵，以及按照预设算法将所述变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果；Doppler filtering is performed on the echo data to obtain the echo data corresponding to each channel, and distance Fourier transform is performed on the echo data corresponding to each channel to obtain the transformed echo matrix corresponding to the channel. , and project the transformed echo matrix into the two-dimensional imaging coordinate system according to the preset algorithm to obtain the two-dimensional imaging result of the channel;

将所述MIMO合成孔径雷达的合成孔径依序划分为多个子孔径，将每一子孔径对应的所有所述通道的二维成像结果进行合成得到该子孔径对应的成像结果；Divide the synthetic aperture of the MIMO synthetic aperture radar into multiple sub-apertures in sequence, and synthesize the two-dimensional imaging results of all the channels corresponding to each sub-aperture to obtain the imaging results corresponding to the sub-aperture;

将所有所述子孔径对应的所述成像结果进行融合得到所述合成孔径对应的总的成像结果。The imaging results corresponding to all the sub-apertures are fused to obtain a total imaging result corresponding to the synthetic aperture.

进一步地，所述针对所述回波数据进行多普勒滤波得到每一通道对应的回波数据包括：Further, performing Doppler filtering on the echo data to obtain echo data corresponding to each channel includes:

针对所述MIMO合成孔径雷达的每个通道，设该通道由第p个发射机以及第q个接收机组成，则通过如下方式得到该通道对应的回波数据：For each channel of the MIMO synthetic aperture radar, assuming that the channel is composed of the p-th transmitter and the q-th receiver, the echo data corresponding to the channel is obtained in the following way:

针对所述第q个接收机接收到的回波数据

沿第m行做离散傅里叶变换得到： For the echo data received by the q-th receiver

Doing the discrete Fourier transform along the m-th row gives:

根据上式对回波数据

进行多普勒域滤波以分离出该通道对应的回波数据

According to the above formula, the echo data

Perform Doppler domain filtering to separate the echo data corresponding to the channel

其中，m为单个脉冲内采样点索引，n为脉冲索引，且n＝1,2……N，j为虚数单位，h为多普勒单元索引，

为多普勒调制相位，PRF为脉冲重复频率。 Among them, m is the sampling point index within a single pulse, n is the pulse index, and n=1,2...N, j is the imaginary unit, h is the Doppler unit index,

is the Doppler modulation phase, and PRF is the pulse repetition frequency.

进一步地，针对每一所述子孔径，将该子孔径对应的所有所述通道的二维成像结果进行合成得到该子孔径对应的成像结果包括：Further, for each sub-aperture, the two-dimensional imaging results of all the channels corresponding to the sub-aperture are synthesized to obtain the imaging results corresponding to the sub-aperture, including:

根据所述MIMO合成孔径雷达成像范围内的感兴趣区域的主波束指向以及波束宽度确定每一通道对应的权重系数；Determine the weight coefficient corresponding to each channel according to the main beam direction and beam width of the area of interest within the MIMO synthetic aperture radar imaging range;

将所述每一通道的像素点乘以该通道对应的权重系数后得到每一通道对应的权重图像；Multiply the pixels of each channel by the weight coefficient corresponding to the channel to obtain the weight image corresponding to each channel;

将所有通道对应的权重图像进行合成得到该子孔径对应的成像结果。The weighted images corresponding to all channels are synthesized to obtain the imaging result corresponding to the sub-aperture.

进一步地，所述针对每一通道对应的回波数据进行距离向傅里叶变换以得到该通道对应的变换后的回波矩阵，并按照预设算法将所述变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果包括：Further, the range Fourier transform is performed on the echo data corresponding to each channel to obtain the transformed echo matrix corresponding to the channel, and the transformed echo matrix is projected to the The two-dimensional imaging results of this channel in the two-dimensional imaging coordinate system include:

(1)基于该通道对应的所述回波矩阵估计该通道对应的多普勒中心频率以及多普勒调频率；(1) Estimate the Doppler center frequency and Doppler modulation frequency corresponding to the channel based on the echo matrix corresponding to the channel;

(2)基于所述多普勒中心频率以及所述多普勒调频率确定该通道对应的雷达当前航行速度估计值；(2) Determine the current radar navigation speed estimate corresponding to the channel based on the Doppler center frequency and the Doppler modulation frequency;

(3)针对每个所述二维成像坐标系下的像素点，根据该像素点在所述二维成像坐标系下的坐标值确定该像素点对应的距离单元索引，并基于所述当前航行速度估计值确定该像素点的相干累加所需的补偿相位因子；(3) For each pixel point in the two-dimensional imaging coordinate system, determine the distance unit index corresponding to the pixel point according to the coordinate value of the pixel point in the two-dimensional imaging coordinate system, and determine the distance unit index corresponding to the pixel point based on the current navigation The velocity estimate determines the compensation phase factor required for coherent accumulation of the pixel;

(4)针对每个所述像素点，根据其对应的补偿相位因子以及距离单元索引和所述变换后的回波矩阵进行相干累加以得到该像素点的成像值。(4) For each pixel, perform coherent accumulation according to its corresponding compensation phase factor and distance unit index and the transformed echo matrix to obtain the imaging value of the pixel.

进一步地，所述基于该通道对应的回波矩阵估计该通道对应的多普勒中心频率包括：Further, estimating the Doppler center frequency corresponding to the channel based on the echo matrix corresponding to the channel includes:

针对该通道对应的所述回波矩阵的每个行向量，设该行向量为S _a，则通过执行如下操作估计该通道对应的多普勒中心频率： For each row vector of the echo matrix corresponding to the channel, assuming that the row vector is S _a , then estimate the Doppler center frequency corresponding to the channel by performing the following operations:

按照下式对该行向量S _a进行自相关以得到该行向量对应的自相关矩阵R _a； Carry out autocorrelation on the row vector S _a according to the following formula to obtain the autocorrelation matrix R _a corresponding to the row vector;

R _a＝S _a*S ^* _a/N ₀； R _a =S _a *S ^* _a /N ₀ ;

其中，N ₀表示所述回波矩阵的列数，S ^* _a是S _a的共轭转置； Among them, N ₀ represents the number of columns of the echo matrix, and S ^* _a is the conjugate transpose of S _a ;

根据下式确定该通道对应的所述多普勒中心频率f _dc： Determine the Doppler center frequency f _dc corresponding to the channel according to the following formula:

其中，A为回波矩阵的行数，R _a′是R _a的逆傅里叶变换，angle()表示取相位操作，f _s是该通道对应的接收机的采样频率。 Among them, A is the number of rows of the echo matrix, R _a ′ is the inverse Fourier transform of R _a , angle() represents the phase operation, and f _s is the sampling frequency of the receiver corresponding to the channel.

进一步地，根据下式确定该通道对应的所述多普勒调频率估计值γ _d： Further, the Doppler modulation frequency estimate γ _d corresponding to the channel is determined according to the following formula:

其中，γ为调频率，PRF为脉冲重复频率，N为脉冲索引，ΔR为通过所述回波矩阵计算得到的前后视图的移动量。Among them, γ is the modulation frequency, PRF is the pulse repetition frequency, N is the pulse index, and ΔR is the movement amount of the front and rear views calculated through the echo matrix.

进一步地，所述根据所述多普勒调频率以及所述多普勒中心频率确定该通道对应的所述雷达当前航行速度估计值包括：Further, determining the estimated current navigation speed of the radar corresponding to the channel based on the Doppler modulation frequency and the Doppler center frequency includes:

根据下式确定所述雷达当前航行速度估计值：The estimated current navigation speed of the radar is determined according to the following formula:

其中，v为所述雷达当前航行速度估计值，R ₀为场景中心距离，λ为MIMO所述MIMO合成孔径雷达的载频对应的波长，f _dc为所述通道对应的多普勒中心频率，γ _d为所述通道对应的多普勒调频率估计值。 Among them, v is the current navigation speed estimate of the radar, R ₀ is the scene center distance, λ is the wavelength corresponding to the carrier frequency of the MIMO synthetic aperture radar, f _dc is the Doppler center frequency corresponding to the channel, γ _d is the Doppler modulation frequency estimate corresponding to the channel.

进一步地，所述按照预设算法将所述变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果包括：Further, projecting the transformed echo matrix into a two-dimensional imaging coordinate system according to a preset algorithm to obtain the two-dimensional imaging result of the channel includes:

按照预设的网格划分模式将所述MIMO合成孔径雷达的成像区域划分成网格以构成所述二维成像坐标系，并且所述网格中的每个网格元素分区构成一个所述像素点。The imaging area of the MIMO synthetic aperture radar is divided into grids according to a preset grid division mode to constitute the two-dimensional imaging coordinate system, and each grid element partition in the grid constitutes one of the pixels point.

进一步地，所述针对每个所述二维成像坐标系下的像素点，根据该像素点在所述二维成像坐标系下的坐标值确定该像素点对应的距离单元索引，包括：Further, for each pixel point in the two-dimensional imaging coordinate system, determining the distance unit index corresponding to the pixel point according to the coordinate value of the pixel point in the two-dimensional imaging coordinate system includes:

按照下式计算第n个脉冲内雷达天线相位中心到像素点x,y的斜距R _n(x,y)： Calculate the slant distance R _n (x, y) from the radar antenna phase center to the pixel point x, y in the nth pulse according to the following formula:

其中，y为该像素点的纵坐标，x是该像素点的横坐标，v为所述雷达当前航行速度估计值，PRF为脉冲重复频率；Among them, y is the ordinate of the pixel, x is the abscissa of the pixel, v is the estimated current navigation speed of the radar, and PRF is the pulse repetition frequency;

根据下式确定第n个脉冲下该像素点对应的所述距离单元索引Id _n： The distance unit index Id _n corresponding to the pixel point under the n-th pulse is determined according to the following formula:

其中，Δr为采样前的信号采样间隔，β为插值倍数，

表示向上取整操作。 Among them, Δr is the signal sampling interval before sampling, β is the interpolation multiple,

Indicates rounding up operation.

进一步地，针对每个所述二维成像坐标系下的像素点，基于所述当前航行速度估计值确定该像素点的相干累加所需的补偿相位因子包括：Further, for each pixel point in the two-dimensional imaging coordinate system, determining the compensation phase factor required for coherent accumulation of the pixel point based on the current navigation speed estimate includes:

根据该像素点对应的所述斜距确定该像素点的相干累加所需的所述补偿相位因子。The compensation phase factor required for coherent accumulation of the pixel is determined based on the slope distance corresponding to the pixel.

进一步地，所述根据该像素点对应的所述斜距确定该像素点的相干累加所需的所述补偿相位因子包括：Further, the compensation phase factor required for determining the coherent accumulation of the pixel point based on the slant distance corresponding to the pixel point includes:

根据下式确定第n个脉冲下该像素点对应的所述补偿相位因子

Determine the compensation phase factor corresponding to the pixel under the nth pulse according to the following formula:

其中，R _n(x,y)为第n个脉冲内雷达天线相位中心到像素点x,y的斜距，λ为所述MIMO合成孔径雷达的载频对应的波长。 Among them, R _n (x, y) is the slant distance from the radar antenna phase center to the pixel point x, y in the n-th pulse, and λ is the wavelength corresponding to the carrier frequency of the MIMO synthetic aperture radar.

进一步地，所述针对每个所述像素点，根据其对应的补偿相位因子以及距离单元索引以及所述变换后的回波矩阵进行相干累加以得到该像素点的成像值包括：Further, for each pixel, performing coherent accumulation according to its corresponding compensation phase factor and distance unit index and the transformed echo matrix to obtain the imaging value of the pixel includes:

根据下式计算每一所述像素点对应的所述成像值：The imaging value corresponding to each pixel is calculated according to the following formula:

其中，I表示第n个脉冲下该像素点对应的成像值，s _r(Id,n)表示所述变换后的回波矩阵s _r中该第n个脉冲下该像素点对应的距离单元索引Id _n所指示的矩阵元素，j为虚数单位，

为第n个脉冲下该像素点对应的所述补偿相位因子。 Among them, I represents the imaging value corresponding to the pixel point under the n-th pulse, and s _r (Id, n) represents the distance unit index corresponding to the pixel point under the n-th pulse in the transformed echo matrix s _r . The matrix element indicated by Id _n , j is the imaginary unit,

is the compensation phase factor corresponding to the pixel point under the nth pulse.

进一步地，所述网格中的每个网格元素分区的面积不大于所述MIMO合成孔径雷达的最小分辨面积。Further, the area of each grid element partition in the grid is not larger than the minimum resolution area of the MIMO synthetic aperture radar.

有益效果beneficial effects

在本发明中，对每一个通道而言，由于对发射机的发射脉冲进行了DDM编码，因此，可以将回波数据进行多普勒滤波得到每一个通道对应的回波数据，针对每一个通道的回波数据进行成像，再根据对于子孔径的划分，将所有通道对应的成像结果合成为每一个子孔径的成像结果，最终根据所有子孔径对应的成像结果融合得到总的成像结果，从而有效解决了近场和广角聚焦问题，从而使得合成孔径雷达具有较高的成像性能以及较宽的成像视野。进一步地，在得到所有通道对应的权重系数后，在对每一子孔径的成像结果进行合成时之前，将该子孔径的每一通道中图像的像素点均乘以该通道对应的权重系数之后，将子孔径的所有通道对应的乘以权重系数后的权重图像进行合成，从而得到该子孔径的图像，将所有子孔径的图像进行融合从而得到合成孔径的成像结果，一方面，本发明可以根据感兴趣区域的主波束指向以及宽度从而得到每一个通道对应的权重系数，使得感兴趣区域的成像效果更好，另一方面，如果感兴趣区域只占据成像区域某一小部分，那么使用本发明提出的方法可以明显降低计算复杂度，提高实时成像性能。In the present invention, for each channel, since the transmit pulse of the transmitter is DDM encoded, the echo data can be Doppler filtered to obtain the echo data corresponding to each channel. For each channel The echo data is imaged, and then according to the division of sub-apertures, the imaging results corresponding to all channels are synthesized into the imaging results of each sub-aperture. Finally, the total imaging result is obtained based on the fusion of the imaging results corresponding to all sub-apertures, thus effectively The problem of near-field and wide-angle focusing is solved, so that the synthetic aperture radar has high imaging performance and a wide imaging field of view. Further, after obtaining the weight coefficients corresponding to all channels, before synthesizing the imaging results of each sub-aperture, multiply the pixels of the image in each channel of the sub-aperture by the weight coefficient corresponding to the channel. , synthesize the weight images multiplied by the weight coefficients corresponding to all channels of the sub-aperture to obtain the image of the sub-aperture, and fuse the images of all sub-apertures to obtain the imaging result of the synthetic aperture. On the one hand, the present invention can According to the main beam direction and width of the area of interest, the weight coefficient corresponding to each channel is obtained, so that the imaging effect of the area of interest is better. On the other hand, if the area of interest only occupies a small part of the imaging area, then use this The method proposed by the invention can significantly reduce computational complexity and improve real-time imaging performance.

附图说明Description of drawings

为了更清楚地说明本发明或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作一简单地介绍，显而易见地，下面描述中的附图是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的实施例。In order to explain the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are of the present invention. For some embodiments of the invention, those of ordinary skill in the art can also obtain other embodiments based on these drawings without exerting creative efforts.

图1是本发明实施例中车载多普勒分集MIMO合成孔径雷达时域成像方法的流程图；Figure 1 is a flow chart of a vehicle-mounted Doppler diversity MIMO synthetic aperture radar time domain imaging method in an embodiment of the present invention;

图2是本发明实施例中MIMO合成孔径雷达成像几何；Figure 2 is the imaging geometry of MIMO synthetic aperture radar in the embodiment of the present invention;

图3是本发明实施例中MIMO合成孔径雷达在成像过程中照射范围的示意图；Figure 3 is a schematic diagram of the illumination range of the MIMO synthetic aperture radar during the imaging process in the embodiment of the present invention;

图4是本发明实施例中实验一的单通道SAR成像实验波形参数图；Figure 4 is a waveform parameter diagram of a single-channel SAR imaging experiment in Experiment 1 in the embodiment of the present invention;

图5a是本发明实施例中实验一的单通道SAR成像对应的光学图像；Figure 5a is an optical image corresponding to single-channel SAR imaging in Experiment 1 in the embodiment of the present invention;

图5b是本发明实施例中实验一的单通道SAR成像实验结果图；Figure 5b is a single-channel SAR imaging experiment result diagram of Experiment 1 in the embodiment of the present invention;

图6是本发明实施例中实验二的MIMO SAR成像实验波形参数图；Figure 6 is a waveform parameter diagram of the MIMO SAR imaging experiment of Experiment 2 in the embodiment of the present invention;

图7是本发明实施例中实验二的MIMO SAR成像实验天线排布模式图；Figure 7 is a diagram of the antenna arrangement pattern of the MIMO SAR imaging experiment in Experiment 2 in the embodiment of the present invention;

图8是本发明实施例中实验二的MIMO SAR成像实验某一通道距离-多普勒图；Figure 8 is a certain channel distance-Doppler diagram of the MIMO SAR imaging experiment in Experiment 2 in the embodiment of the present invention;

图9a是本发明实施例中实验二的MIMO SAR成像结果；Figure 9a is the MIMO SAR imaging result of Experiment 2 in the embodiment of the present invention;

图9b是本发明实施例中实验二的单通道SAR成像结果；Figure 9b is the single-channel SAR imaging result of Experiment 2 in the embodiment of the present invention;

图10是本发明实施例中实验二的MIMO SAR成像实验成像场景光学图；Figure 10 is an optical diagram of the MIMO SAR imaging experimental imaging scene in Experiment 2 in the embodiment of the present invention;

图11是本发明实施例中实验二的MIMO SAR成像实验功率模式对比图；Figure 11 is a comparison diagram of MIMO SAR imaging experiment power modes in Experiment 2 in the embodiment of the present invention;

图12是本发明实施例中实验二的MIMO SAR单车辆位置成像图；Figure 12 is a MIMO SAR single vehicle position imaging diagram in Experiment 2 in the embodiment of the present invention;

图13a-13d是本发明实施例中实验二的MIMO SAR成像实验单孔径成像对比图。Figures 13a-13d are single-aperture imaging comparison diagrams of the MIMO SAR imaging experiment of Experiment 2 in the embodiment of the present invention.

本发明的实施方式Embodiments of the invention

为使本发明的目的、技术方案和优点更加清楚，下面将结合本发明中的附图，对本发明中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention. , not all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

由于雷达工作时周期性发送脉冲信号，在脉冲间隔时间内对回波信号进行采样。回波采样间隔与脉冲重复间隔(脉冲周期)虽然在一个时间轴上，但是在量级上差别非常大，所以将回波采样间隔与脉冲重复周期分成了两个维度，分别称为快时间和慢时间。将每个脉冲间隔内的回波分割出来作为一行，以二维数组的形式存储采样到的回波信号，那么时间轴上的横轴表示快时间，纵轴表示慢时间。Since the radar periodically sends pulse signals during operation, the echo signals are sampled within the pulse interval. Although the echo sampling interval and the pulse repetition interval (pulse period) are on the same time axis, they are very different in magnitude. Therefore, the echo sampling interval and the pulse repetition period are divided into two dimensions, called fast time and pulse period respectively. Slow time. Divide the echo within each pulse interval as a row and store the sampled echo signal in the form of a two-dimensional array. Then the horizontal axis on the time axis represents fast time and the vertical axis represents slow time.

MIMO(Multiple-Input Multiple-Output，多输入多输出)技术是指在发射端和接收端分别使用多个发射天线和接收天线，使信号通过发射端与接收端的多个天线传送和接收，从而改善通信质量。它能充分利用空间资源，通过多个天线实现多发多收，在不增加频谱资源和天线发射功率的情况下，可以成倍的提高***信道容量，显示出明显的优势、被视为下一代移动通信的核心技术。MIMO (Multiple-Input Multiple-Output, Multiple Input Multiple Output) technology refers to the use of multiple transmitting antennas and receiving antennas at the transmitting end and receiving end respectively, so that signals are transmitted and received through multiple antennas at the transmitting end and receiving end, thereby improving Communication quality. It can make full use of space resources and achieve multiple transmissions and multiple receptions through multiple antennas. It can double the system channel capacity without increasing spectrum resources and antenna transmission power. It shows obvious advantages and is regarded as the next generation of mobile phones. The core technology of communication.

DDM(Doppler Division Multiple access，多普勒分集)波形又称为紧密交错型频分复用正交波形，它的频谱几乎重叠，拥有较好的多输入单输出对消比，可避免不同频率信号引起的目标或杂波RCS(Radar Cross Section，雷达截面积)去相关。DDM波形之间的频率偏移量△f很小，使用多普勒滤波器组可将不同发射单元的信号相互分离。DDM (Doppler Division Multiple access, Doppler diversity) waveform is also called tightly interleaved frequency division multiplexing orthogonal waveform. Its spectrum almost overlaps and has a good multiple input single output cancellation ratio, which can avoid signals of different frequencies. The target or clutter RCS (Radar Cross Section, radar cross section) caused by the decorrelation. The frequency offset Δf between DDM waveforms is very small, and the signals of different transmitting units can be separated from each other using a Doppler filter bank.

下面结合图1-12详细描述本发明的车载多普勒分集MIMO合成孔径雷达时域成像方法。The vehicle Doppler diversity MIMO synthetic aperture radar time domain imaging method of the present invention will be described in detail below with reference to Figures 1-12.

如图1所示，本发明提供了一车载多普勒分集MIMO合成孔径雷达时域成像方法，该方法包括：As shown in Figure 1, the present invention provides a vehicle-mounted Doppler diversity MIMO synthetic aperture radar time domain imaging method, which method includes:

S101、采集以预设的速度沿直线轨迹运动的MIMO合成孔径雷达向目标发射的线性调频信号的回波数据，其中，MIMO合成孔径雷达的不同发射机具有不同的DDM编码。S101. Collect echo data of linear frequency modulation signals emitted by a MIMO synthetic aperture radar moving along a straight line trajectory at a preset speed to the target. Different transmitters of the MIMO synthetic aperture radar have different DDM codes.

在发明中，合成孔径雷达可以为车载合成孔径雷达，该雷达的工作场景需要满足是以下两个条件：(1)合成孔径雷达以预设的速度沿直线轨迹运动，发射线性调频信号；(2)发射信号期间，合成孔径雷达正侧视工作，并且雷达波束中心指向不变，由于本发明中是针对于合成孔径雷达的，合成孔径雷达的工作场景必须要满足发射信号期间，合成孔径雷达正侧视工作，并且雷达波束中心指向不变，因此上述步骤中隐含了条件(2)。In the invention, the synthetic aperture radar can be a vehicle-mounted synthetic aperture radar. The working scenario of the radar needs to meet the following two conditions: (1) the synthetic aperture radar moves along a straight trajectory at a preset speed and emits linear frequency modulation signals; (2) ) During the signal transmission period, the synthetic aperture radar works looking sideways, and the center direction of the radar beam does not change. Since the present invention is directed to synthetic aperture radar, the working scenario of the synthetic aperture radar must meet the requirement that during the signal transmission period, the synthetic aperture radar is facing forward. The side view works, and the radar beam center direction does not change, so the condition (2) is implicit in the above steps.

对发射脉冲进行DDM编码的具体方法为：调频连续波雷达的第p个发射机的发射脉冲

可表示为： The specific method of DDM encoding the transmitted pulse is: the transmitted pulse of the p-th transmitter of the frequency modulated continuous wave radar

It can be expressed as:

其中，t _r为脉冲间的快时间，t _m为脉冲间的慢时间，G _p为发射增益，T为脉冲宽度，f _c是雷达载频，γ为调频率，rect()为矩形窗函数，

为多普勒调制相位，以四个发射机的情况为例，DDM编码分别为

其中，PRF(pulse repetition frequency)为脉冲重复频率。 Among them, t _r is the fast time between pulses, t _m is the slow time between pulses, G _p is the transmission gain, T is the pulse width, f _c is the radar carrier frequency, γ is the modulation frequency, and rect() is the rectangular window function ,

is the Doppler modulation phase. Taking the case of four transmitters as an example, the DDM codes are

Among them, PRF (pulse repetition frequency) is the pulse repetition frequency.

S102、针对回波数据进行多普勒滤波得到每一通道对应的回波数据，并针对每一通道对应的回波数据进行距离向傅里叶变换以得到该通道对应的变换后的回波矩阵，以及按照预设算法将变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果。S102. Perform Doppler filtering on the echo data to obtain the echo data corresponding to each channel, and perform distance Fourier transform on the echo data corresponding to each channel to obtain the transformed echo matrix corresponding to the channel. , and project the transformed echo matrix into the two-dimensional imaging coordinate system according to the preset algorithm to obtain the two-dimensional imaging result of the channel.

S103、将MIMO合成孔径雷达的合成孔径依序划分为多个子孔径，针对每一子孔径，将该子孔径对应的所有通道的二维成像结果进行合成得到该子孔径对应的成像结果。S103. Divide the synthetic aperture of the MIMO synthetic aperture radar into multiple sub-apertures in sequence, and for each sub-aperture, synthesize the two-dimensional imaging results of all channels corresponding to the sub-aperture to obtain the imaging result corresponding to the sub-aperture.

S104、将所有子孔径对应的成像结果进行融合得到合成孔径对应的总的成像结果。S104. Fusion of the imaging results corresponding to all sub-apertures to obtain a total imaging result corresponding to the synthetic aperture.

在本发明中，对每一个通道而言，由于对发射机的发射脉冲进行了DDM编码，因此，可以将回波数据进行多普勒滤波得到每一个通道对应的回波数据，针对每一个通道的回波数据进行成像，再将每一子孔径对应的所有通道的二维成像结果进行合成得到该子孔径对应的成像结果，最终根据所有子孔径对应的成像结果融合得到总的成像结果，从而有效解决了近场和广角聚焦问题，从而使得合成孔径雷达具有较高的成像性能以及较宽的成像视野，实现了实现宽视角高分辨成像。In the present invention, for each channel, since the transmit pulse of the transmitter is DDM encoded, the echo data can be Doppler filtered to obtain the echo data corresponding to each channel. For each channel The echo data is imaged, and then the two-dimensional imaging results of all channels corresponding to each sub-aperture are synthesized to obtain the imaging results corresponding to the sub-aperture. Finally, the total imaging result is obtained based on the fusion of the imaging results corresponding to all sub-apertures, thus It effectively solves the problems of near-field and wide-angle focusing, so that the synthetic aperture radar has high imaging performance and a wide imaging field of view, realizing wide viewing angle and high-resolution imaging.

进一步地，针对回波数据进行多普勒滤波得到每一通道对应的回波数据包括：Further, Doppler filtering is performed on the echo data to obtain echo data corresponding to each channel, including:

针对MIMO合成孔径雷达的每个通道，设该通道由第p个发射机以及第q个接收机组成，则通过如下方式得到该通道对应的回波数据：For each channel of the MIMO synthetic aperture radar, assuming that the channel is composed of the p-th transmitter and the q-th receiver, the echo data corresponding to the channel is obtained in the following way:

针对第q个接收机接收到的回波数据

Doing the discrete Fourier transform along the m-th row gives:

根据上式对回波数据

进行多普勒域滤波以分离出该通道对应的回波数据

According to the above formula, the echo data

is the Doppler modulation phase, and PRF is the pulse repetition frequency.

在本实施例中，对针对回波数据进行多普勒滤波得到每一通道对应的回波数据之前，对回波数据进行解线性调频操作并做模数转换，而后对回波数据进行多普勒滤波，具体地：In this embodiment, before performing Doppler filtering on the echo data to obtain the echo data corresponding to each channel, the echo data is de-chirped and analog-to-digital converted, and then Doppler is performed on the echo data. Le filtering, specifically:

单个通道的离散中频信号表达式为：The expression of the discrete IF signal of a single channel is:

其中，f _c是雷达载频，G _q为接收增益，m＝1，2，...，M为单个脉冲内采样点索引，n＝1，2，...，N为脉冲索引，k＝1，2，...，K为散射点索引，σ _k为第k个散射点的反射系数，散射点是分布在场景中的目标上的，与目标相对应。

为对于由第p个发射机以及第q个接收机组成的通道中对于第k个散射点，天线阵元位置产生的相位差，在远场和平面波条件下可以表示为： Among them, f _c is the radar carrier frequency, G _q is the receiving gain, m=1, 2,..., M is the sampling point index within a single pulse, n=1, 2,..., N is the pulse index, k =1, 2,..., K is the scattering point index, σ _k is the reflection coefficient of the kth scattering point, and the scattering points are distributed on the target in the scene and correspond to the target.

is the phase difference produced by the position of the antenna array element for the k-th scattering point in the channel composed of the p-th transmitter and the q-th receiver. Under far-field and plane wave conditions, it can be expressed as:

其中，λ为雷达载频对应的波长，θ _k为第k个散射点相对于垂直阵列方向的夹角，d _p和d _q分别为发射机和接收机在阵列中的基线长度。进一步的，第q个接收机对应的离散中频信号

表达式为： Among them, λ is the wavelength corresponding to the radar carrier frequency, θ _k is the angle of the k-th scattering point relative to the vertical array direction, d _p and d _q are the baseline lengths of the transmitter and receiver in the array respectively. Further, the discrete intermediate frequency signal corresponding to the q-th receiver

The expression is:

对上述信号，沿第m行做离散傅里叶变换，可得：For the above signal, perform discrete Fourier transform along the m-th row to get:

其中，

h为多普勒单元索引，可以看出经过DDM编码，不同发射通道的回波信号在多普勒域中占据不同带宽，因此可通过多普勒滤波分离出单通道信号。 in,

h is the Doppler unit index. It can be seen that after DDM encoding, the echo signals of different transmission channels occupy different bandwidths in the Doppler domain, so the single-channel signal can be separated by Doppler filtering.

进一步地，针对于每一子孔径，将该子孔径对应的所有通道的二维成像结果进行合成得到该子孔径对应的成像结果包括：Further, for each sub-aperture, the two-dimensional imaging results of all channels corresponding to the sub-aperture are synthesized to obtain the imaging results corresponding to the sub-aperture, including:

根据MIMO合成孔径雷达成像范围内的感兴趣区域的主波束指向以及波束宽度确定每一通道对应的权重系数；Determine the weight coefficient corresponding to each channel according to the main beam direction and beam width of the area of interest within the MIMO synthetic aperture radar imaging range;

将每一通道的像素点乘以该通道对应的权重系数后得到每一通道对应的权重图像；Multiply the pixels of each channel by the weight coefficient corresponding to the channel to obtain the weight image corresponding to each channel;

在本步骤中，可以采用基于交替方向乘子法的数字波束形成算法得到权重系数，也可以基于二维图像坐标的传统数字波束形成方法得到权重系数，其中，基于二维图像坐标的传统数字波束形成方法得到权重系数的具体步骤为：In this step, a digital beamforming algorithm based on the alternating direction multiplier method can be used to obtain the weight coefficient, or a traditional digital beamforming method based on two-dimensional image coordinates can be used to obtain the weight coefficient. Among them, the traditional digital beamforming method based on two-dimensional image coordinates The specific steps of forming the method to obtain the weight coefficient are:

在距离-方位图像上，根据坐标换算得到坐标点(x,y)对应的角度

并设置权重向量： On the distance-azimuth image, the angle corresponding to the coordinate point (x, y) is obtained according to the coordinate conversion.

And set the weight vector:

其中，P和Q分别为雷达的发射机以及接收机的总数，因此，权重向量中的一个元素对应于一个通道，也即是该通道的权重系数。Among them, P and Q are the total number of transmitters and receivers of the radar respectively. Therefore, one element in the weight vector corresponds to a channel, which is the weight coefficient of the channel.

在此基础上，将±45°的宽视野均匀划分为L个网格，θ _l处的功率模式可以表示为： On this basis, the ±45° wide field of view is evenly divided into L grids, and the power pattern at θ _l can be expressed as:

其中，||·|| ₂表示取向量的二范数。用最小均方误差来衡量实际功率模式P(θ _l)与期望功率模式D(θ _l)的近似程度，得到一个优化问题，目标函数为： Among them, ||·|| ₂ represents the second norm of the orientation vector. The minimum mean square error is used to measure the approximation between the actual power mode P(θ _l ) and the desired power mode D(θ _l ), and an optimization problem is obtained. The objective function is:

引入两个新变量：Introduce two new variables:

那么优化问题可以更简洁地描述为：Then the optimization problem can be described more concisely as:

其中，E为第一个元素为1，其他元素为0的对角矩阵。直接求解上式十分困难，可引入辅助变量v，原问题形式变为：Among them, E is a diagonal matrix whose first element is 1 and other elements are 0. It is very difficult to directly solve the above equation. An auxiliary variable v can be introduced, and the original problem form becomes:

改写后的问题形式只包含相互独立的u和v的二次项，可以在ADMM框架下求解。增广拉格朗日函数可表示为The rewritten problem form only contains mutually independent quadratic terms of u and v, and can be solved under the ADMM framework. The augmented Lagrangian function can be expressed as

其中，r ₁和r ₂为对偶变量，ρ ₁和ρ ₂为惩罚系数。接下推导

关于变量u和v的共轭梯度： Among them, r ₁ and r ₂ are dual variables, and ρ ₁ and ρ ₂ are penalty coefficients. Next derivation

Regarding the conjugate gradient of variables u and v:

在每次迭代，直至收敛的过程中In each iteration until convergence

(1)更新u：以u为变量，

可表示为 (1) Update u: use u as a variable,

can be expressed as

上式关于u的共轭梯度为The conjugate gradient of the above formula with respect to u is

令上式为0，那么第i次迭代中有Let the above formula be 0, then in the i-th iteration we have

其中in

(2)更新v：类似于更新u的过程，第i次迭代中有(2) Update v: similar to the process of updating u, in the i-th iteration

其中in

(3)更新对偶变量：根据前面的结果，对偶变量

和

可以更新为 (3) Update dual variables: According to the previous results, the dual variables

and

can be updated to

迭代结束，输出u ⁽ⁱ⁺¹⁾和v ⁽ⁱ⁺¹⁾。 At the end of the iteration, u ⁽ⁱ⁺¹⁾ and v ⁽ⁱ⁺¹⁾ are output.

在迭代结束后，根据u得到权重向量中每一个元素，从而确定所有通道对应的权重系数。After the iteration is completed, each element in the weight vector is obtained according to u, thereby determining the weight coefficients corresponding to all channels.

由此，可以根据感兴趣区域的主波束指向，波束宽度计算出所有通道对应的权重系数。From this, the weight coefficients corresponding to all channels can be calculated based on the main beam direction and beam width of the area of interest.

在得到所有通道对应的权重系数后，在对每一子孔径的成像结果进行合成时之前，将该子孔径的每一通道中图像的像素点均乘以该通道对应的权重系数之后，将子孔径的所有通道对应的乘以权重系数后的权重图像进行合成，从而得到该子孔径的图像，将所有子孔径的图像进行融合从而得到合成孔径的成像结果。一方面，本发明可以根据感兴趣区域的主波束指向以及宽度从而得到每一个通道对应的权重系数，使得感兴趣区域的成像效果更好，另一方面，如果感兴趣区域只占据成像区域某一小部分，那么使用本发明提出的方法可以明显降低计算复杂度，提高实时成像性能。After obtaining the weight coefficients corresponding to all channels, before synthesizing the imaging results of each sub-aperture, multiply the pixels of the image in each channel of the sub-aperture by the weight coefficient corresponding to the channel, and then The weight images multiplied by the weight coefficients corresponding to all channels of the aperture are synthesized to obtain the image of the sub-aperture, and the images of all sub-apertures are fused to obtain the imaging result of the synthetic aperture. On the one hand, the present invention can obtain the weight coefficient corresponding to each channel according to the main beam direction and width of the area of interest, so that the imaging effect of the area of interest is better. On the other hand, if the area of interest only occupies a certain area of the imaging area, A small part, then using the method proposed by the present invention can significantly reduce the computational complexity and improve the real-time imaging performance.

进一步地，针对每一通道对应的回波数据进行距离向傅里叶变换以得到该通道对应的变换后的回波矩阵，并按照预设算法将变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果包括：Further, the range Fourier transform is performed on the echo data corresponding to each channel to obtain the transformed echo matrix corresponding to the channel, and the transformed echo matrix is projected to the two-dimensional imaging coordinates according to the preset algorithm System to obtain the two-dimensional imaging results of this channel include:

(1)基于该通道对应的回波矩阵估计该通道对应的多普勒中心频率以及多普勒调频率；(1) Estimate the Doppler center frequency and Doppler modulation frequency corresponding to the channel based on the echo matrix corresponding to the channel;

(2)基于多普勒中心频率以及多普勒调频率确定该通道对应的雷达当前航行速度估计值；(2) Determine the current radar navigation speed estimate corresponding to the channel based on the Doppler center frequency and Doppler modulation frequency;

(3)针对每个二维成像坐标系下的像素点，根据该像素点在二维成像坐标系下的坐标值确定该像素点对应的距离单元索引，并基于当前航行速度估计值确定该像素点的相干累加所需的补偿相位因子；(3) For each pixel in the two-dimensional imaging coordinate system, determine the distance unit index corresponding to the pixel based on the coordinate value of the pixel in the two-dimensional imaging coordinate system, and determine the pixel based on the current navigation speed estimate. Compensation phase factor required for coherent accumulation of points;

(4)针对每个像素点，根据其对应的补偿相位因子以及距离单元索引和变换后的回波矩阵进行相干累加以得到该像素点的成像值。(4) For each pixel, perform coherent accumulation based on its corresponding compensation phase factor and distance unit index and the transformed echo matrix to obtain the imaging value of the pixel.

进一步地，基于该通道对应的回波矩阵估计该通道对应的多普勒中心频率包括：Further, estimating the Doppler center frequency corresponding to the channel based on the echo matrix corresponding to the channel includes:

针对该通道对应的回波矩阵的每个行向量，设该行向量为S _a，则通过执行如下操作估计该通道对应的多普勒中心频率： For each row vector of the echo matrix corresponding to the channel, assuming that the row vector is _Sa , estimate the Doppler center frequency corresponding to the channel by performing the following operations:

R _a＝S _a*S ^* _a/N ₀； R _a =S _a *S ^* _a /N ₀ ;

其中，N ₀表示回波矩阵的列数，S ^* _a是S _a的共轭转置； Among them, N ₀ represents the number of columns of the echo matrix, and S ^* _a is the conjugate transpose of S _a ;

根据下式确定该通道对应的多普勒中心频率f _dc： Determine the Doppler center frequency f _dc corresponding to the channel according to the following formula:

其中，A为回波矩阵的行数，R _a ^′是R _a的逆傅里叶变换后的矩阵，angle()表示取相位操作，f _s是该通道对应的接收机的采样频率。 Among them, A is the number of rows of the echo matrix, R _a ^′ is the matrix after the inverse Fourier transform of R _a , angle() represents the phase operation, and f _s is the sampling frequency of the receiver corresponding to the channel.

进一步地，根据下式确定该通道对应的多普勒调频率估计值γ _d： Further, determine the Doppler modulation frequency estimate γ _d corresponding to the channel according to the following formula:

其中，γ为调频率，PRF为脉冲重复频率，N为脉冲索引，ΔR为通过回波矩阵计算得到的前后视图的移动量。Among them, γ is the modulation frequency, PRF is the pulse repetition frequency, N is the pulse index, and ΔR is the movement amount of the front and rear views calculated through the echo matrix.

进一步地，根据多普勒调频率以及多普勒中心频率确定该通道对应的雷达当前航行速度估计值包括：Further, determining the current radar navigation speed estimate corresponding to the channel based on the Doppler modulation frequency and the Doppler center frequency includes:

根据下式确定雷达当前航行速度估计值：Determine the estimated current navigation speed of the radar according to the following formula:

其中，v为雷达当前航行速度估计值，R ₀为场景中心距离，λ为合成孔径雷达的载频对应的波长，f _dc为通道对应的多普勒中心频率，γ _d为通道对应的多普勒调频率估计值。具体地，场景为成像区域，场景中心距离为场景的中心到合成孔径雷达之间的垂直距离，示例性地，场景的距离向为[a,b]，方位向为[-c,c]，那么场景的中心为[(a+b)/2,0]，λ是雷达载频对应的波长。 Among them, v is the estimated current navigation speed of the radar, R ₀ is the scene center distance, λ is the wavelength corresponding to the carrier frequency of the synthetic aperture radar, f _dc is the Doppler center frequency corresponding to the channel, and γ _d is the Doppler corresponding to the channel. An estimate of the torp frequency. Specifically, the scene is the imaging area, and the scene center distance is the vertical distance between the center of the scene and the synthetic aperture radar. For example, the range direction of the scene is [a, b], and the azimuth direction is [-c, c]. Then the center of the scene is [(a+b)/2,0], and λ is the wavelength corresponding to the radar carrier frequency.

更进一步地，还可以通过多普勒中心频率确定雷达视线角θ ₀，计算公式如下： Furthermore, the radar line of sight angle θ ₀ can also be determined through the Doppler center frequency. The calculation formula is as follows:

可以通过雷达视线角θ ₀判断合成孔径雷达是否正侧视工作。 Whether the synthetic aperture radar is working as a side view can be judged by the radar line of sight angle θ ₀ .

进一步地，按照预设算法将变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果包括：Further, projecting the transformed echo matrix into the two-dimensional imaging coordinate system according to the preset algorithm to obtain the two-dimensional imaging result of the channel includes:

按照预设的网格划分模式将合成孔径雷达的成像区域划分成网格以构成二维成像坐标系，并且网格中的每个网格元素分区构成一个像素点。The imaging area of the synthetic aperture radar is divided into grids according to the preset grid division mode to form a two-dimensional imaging coordinate system, and each grid element partition in the grid constitutes a pixel point.

进一步地，针对每个二维成像坐标系下的像素点，根据该像素点在二维成像坐标系下的坐标值确定该像素点对应的距离单元索引，包括：Further, for each pixel point in the two-dimensional imaging coordinate system, the distance unit index corresponding to the pixel point is determined according to the coordinate value of the pixel point in the two-dimensional imaging coordinate system, including:

其中，y为该像素点的纵坐标，x是该像素点的横坐标，v为雷达当前航行速度估计值，PRF为脉冲重复频率；Among them, y is the ordinate of the pixel, x is the abscissa of the pixel, v is the estimated current navigation speed of the radar, and PRF is the pulse repetition frequency;

根据下式确定第n个脉冲下该像素点对应的距离单元索引Id _n： Determine the distance unit index Id _n corresponding to the pixel point under the nth pulse according to the following formula:

其中，Δr为采样前的信号采样间隔，β为插值倍数，

Indicates rounding up operation.

在本实施例中，在进行投影之前，先要构建合成孔径雷达到目标之前的距离模型，由于本发明中合成孔径雷达的工作场景为(1)合成孔径雷达以预设的速度沿直线轨迹运动，发射线性调频信号；(2)发射信号期间，合成孔径雷达正侧视工作，并且雷达波束中心指向不变，如图2所示，由于发射脉冲宽度和电磁波传播时延都远小于脉冲重复间隔时间，对于同一脉冲可以认为雷达在同一位置发射和接收散射回波。定义雷达运动方向为x轴正方向，雷达波束中心指向为y轴正方向，在此不考虑脉冲间的快时间

的影响，距离模型可以近似为： In this embodiment, before projection, a distance model of the synthetic aperture radar before it reaches the target must be constructed first. Since the working scenario of the synthetic aperture radar in the present invention is (1) the synthetic aperture radar moves along a straight trajectory at a preset speed. , transmit linear frequency modulation signals; (2) During the signal transmission, the synthetic aperture radar works looking sideways, and the radar beam center direction remains unchanged, as shown in Figure 2, because the transmit pulse width and electromagnetic wave propagation delay are much smaller than the pulse repetition interval Time, for the same pulse, it can be considered that the radar emits and receives scattered echoes at the same location. Define the radar movement direction as the positive x-axis direction, and the radar beam center pointing as the positive y-axis direction. The fast time between pulses is not considered here.

Influence of , the distance model can be approximated as:

其中，t _m为脉冲间的慢时间，v ₀为雷达速度。进一步地，t _m＝(n-1)/PRF，因此，可得第n个脉冲内雷达天线相位中心到像素点x,y的斜距R _n(x,y)： Among them, t _m is the slow time between pulses, and v ₀ is the radar speed. Further, t _m =(n-1)/PRF, therefore, the slant distance _{R n} (x, y) from the radar antenna phase center to the pixel point x, y in the n-th pulse can be obtained:

进一步地，针对每个二维成像坐标系下的像素点，基于当前航行速度估计值确定该像素点的相干累加所需的补偿相位因子包括：Further, for each pixel in the two-dimensional imaging coordinate system, the compensation phase factor required to determine the coherent accumulation of the pixel based on the current navigation speed estimate includes:

根据该像素点对应的斜距确定该像素点的相干累加所需的补偿相位因子。The compensation phase factor required for coherent accumulation of the pixel is determined based on the slant distance corresponding to the pixel.

具体地，根据该像素点对应的斜距确定该像素点的相干累加所需的补偿相位因子包括：Specifically, determining the compensation phase factor required for coherent accumulation of the pixel based on the slant distance corresponding to the pixel includes:

根据下式确定第n个脉冲下该像素点对应的补偿相位因子

其中，R _n(x,y)为第n个脉冲内雷达天线相位中心到像素点x,y的斜距，λ为合成孔径雷达的载频对应的波长。 Among them, R _n (x, y) is the slant distance from the radar antenna phase center to the pixel point x, y in the n-th pulse, and λ is the wavelength corresponding to the carrier frequency of the synthetic aperture radar.

进一步地，针对每个像素点，根据其对应的补偿相位因子以及距离单元索引以及变换后的回波矩阵进行相干累加以得到该像素点的成像值包括：Further, for each pixel, coherent accumulation is performed based on its corresponding compensation phase factor and distance unit index and the transformed echo matrix to obtain the imaging value of the pixel, including:

根据下式计算每一像素点对应的成像值：Calculate the imaging value corresponding to each pixel according to the following formula:

其中，I表示第n个脉冲下该像素点对应的成像值，s _r(Id,n)表示变换后的回波矩阵s _r中该第n个脉冲下该像素点对应的距离单元索引Id _n所指示的矩阵元素，j为虚数单位，

为第n个脉冲下该像素点对应的补偿相位因子。 Among them, I represents the imaging value corresponding to the pixel point under the n-th pulse, and s _r (Id, n) represents the distance unit index Id _n corresponding to the pixel point under the n-th pulse in the transformed echo matrix s _r . The indicated matrix element, j is the imaginary unit,

is the compensation phase factor corresponding to the pixel under the nth pulse.

进一步地，网格中的每个网格元素分区的面积不大于合成孔径雷达的最小分辨面积。Further, the area of each grid element partition in the grid is not greater than the minimum resolution area of the synthetic aperture radar.

更进一步地，为精确补偿相位进行相干积累成像，在划分成像网格时，划分的网格大小尽量小于SAR成像分辨率，即：Furthermore, in order to accurately compensate the phase for coherent accumulation imaging, when dividing the imaging grid, the size of the divided grid should be as small as possible as small as the SAR imaging resolution, that is:

其中，Δx为成像平面方位向网格大小，Δy为距离向网格大小。Among them, Δx is the azimuth grid size of the imaging plane, and Δy is the range grid size.

为说明本发明SAR成像方法的有效性，使用TI(Texas Instruments)毫米波级联雷达的RF(Wireless Module)模块和DSP(Digital Signal Processing)模块，通过在典型场景停车场实地实验并处理实测数据来进行进一步的论证：In order to illustrate the effectiveness of the SAR imaging method of the present invention, the RF (Wireless Module) module and DSP (Digital Signal Processing) module of the TI (Texas Instruments) millimeter wave cascade radar were used to conduct field experiments in a typical scene parking lot and process the measured data. To make further arguments:

实验一experiment one

1、实验参数1. Experimental parameters

参照图3，实验过程中车载毫米波雷达理想运动轨迹为沿x轴正方向以速度v ₁运动，雷达波束中心始终沿y轴正方向。实验过程中雷达采取单发单收工作模式，图4给出了波形参数，表1给出了单通道SAR成像实验***参数。 Referring to Figure 3, during the experiment, the ideal motion trajectory of the vehicle-mounted millimeter wave radar is to move along the positive direction of the x-axis at a speed v ₁ , and the radar beam center is always along the positive direction of the y-axis. During the experiment, the radar adopted a single-transmitter and single-receiver working mode. Figure 4 shows the waveform parameters, and Table 1 shows the parameters of the single-channel SAR imaging experiment system.

对单通道回波信号，无需进行DDM编码和多普勒滤波，使用回波数据估计运动参数后，进行二维成像即可。For single-channel echo signals, there is no need to perform DDM encoding and Doppler filtering. It is enough to use the echo data to estimate motion parameters and then perform two-dimensional imaging.

表1Table 1

***参数System parameters	变量variable
距离向分辨率range resolution	0.15m0.15m
最大无模糊距离Maximum blur-free distance	76.8m76.8m
方位向分辩率Azimuth resolution	≈0.2m≈0.2m
最大无模糊速度Maximum blur-free speed	≈±4.7m/s≈±4.7m/s

2、实验过程与结果2. Experimental process and results

图5a为实际场景光学图像，图5b为单通道二维成像结果。对比图5a以及图5b可以看出，其中1为井盖，2为空车位，SAR成像结果清晰显示了汽车的轮廓，反映了车辆的停车位置以及空车位的位置，同时也能从SAR图像中观察到井盖和混凝土块之间的交界处。成像区域距雷达平台10～30米，视野范围为±45°，成像结果的边缘未出现几何畸变，这也说明了本发明提出的成像方法在近场和宽视野条件下的高分辨率性能。Figure 5a is the optical image of the actual scene, and Figure 5b is the single-channel two-dimensional imaging result. Comparing Figure 5a and Figure 5b, we can see that 1 is a manhole cover and 2 is an empty parking space. The SAR imaging results clearly show the outline of the car, reflecting the parking position of the vehicle and the location of the empty parking space. It can also be observed from the SAR image Go to the junction between the manhole cover and the concrete block. The imaging area is 10 to 30 meters away from the radar platform, and the field of view range is ±45°. There is no geometric distortion at the edge of the imaging result, which also illustrates the high-resolution performance of the imaging method proposed in the present invention under near-field and wide field of view conditions.

实验二 Experiment 2

为进一步说明本发明提出的基于DDM的多通道二维成像方法的有效性，通过以下MIMO SAR实验进行验证：In order to further illustrate the effectiveness of the DDM-based multi-channel two-dimensional imaging method proposed in this invention, it is verified through the following MIMO SAR experiments:

1、实验参数1. Experimental parameters

同样参照图3，实验过程中车载毫米波雷达理想运动轨迹为沿x轴正方向以速度v ₁运动，雷达波束中心始终沿y轴正方向,雷达以正侧视对某处停车场进行观测。实验过程中雷达采取2发8收工作模式，2个发射机DDM编码为0或者π，因此最大无模糊速度变为理论值的一半。图6给出了波形参数，图7展示了天线阵列的排布模式，表2给出了MIMO SAR成像实验***参数。 Referring also to Figure 3, during the experiment, the ideal movement trajectory of the vehicle-mounted millimeter wave radar is to move along the positive direction of the x-axis at a speed v _1. The center of the radar beam is always along the positive direction of the y-axis. The radar observes a certain parking lot with a front-side view. During the experiment, the radar adopted a 2-transmit and 8-receive working mode, and the DDM codes of the two transmitters were 0 or π, so the maximum unambiguous speed became half of the theoretical value. Figure 6 shows the waveform parameters, Figure 7 shows the antenna array arrangement pattern, and Table 2 shows the MIMO SAR imaging experimental system parameters.

表2Table 2

***参数System parameters	变量variable
距离向分辩率distance resolution	0.0586m0.0586m
最大无模糊距离Maximum blur-free distance	30m30m
方位向分辩率Azimuth resolution	≈0.05m≈0.05m
最大无模糊速度Maximum blur-free speed	≈±9.5541m/s≈±9.5541m/s

某个接收机回波信号信道分离前其距离-多普勒图像，如图8所示，可以看出两个发射通道对应的回波在图像中占据不同的位置，这也印证了本发明提出的成像方法中关于多普勒滤波的分析。对回波信号进行多普勒滤波，分离出共16个单通道信号。The range-Doppler image of a certain receiver's echo signal before channel separation is shown in Figure 8. It can be seen that the echoes corresponding to the two transmission channels occupy different positions in the image, which also confirms the proposal of the present invention. Analysis of Doppler filtering in imaging methods. Doppler filtering is performed on the echo signal to separate a total of 16 single-channel signals.

为展示本发明使用的基于交替方向乘子法的数字波束形成算法的优点，首先基于经典的数字波束形成方法对单通道SAR图像进行融合，如图9a和图9b分别给出了MIMO SAR和单通道SAR成像结果，图10是对应的场景光学图像。可以看出，相较于单通道图像，MIMO阵列提供了额外的高增益，因此成像结果中汽车车身轮廓更加清晰一些。In order to demonstrate the advantages of the digital beamforming algorithm based on the alternating direction multiplier method used in this invention, single-channel SAR images are first fused based on the classic digital beamforming method. Figure 9a and Figure 9b show MIMO SAR and single-channel SAR images respectively. Channel SAR imaging results, Figure 10 is the corresponding optical image of the scene. It can be seen that compared with single-channel images, the MIMO array provides additional high gain, so the car body outline in the imaging results is clearer.

为演示基于交替方向乘子法的数字波束方法，基于16个元素的均匀线性阵列进行仿真实验。感兴趣区域设置为主波束指向10°，波束宽度为20°。在使用本发明提出的成像方法后，经过约40次迭代后算法收敛，图11给出了期望与算法结果的功率方向图对比结果，将这组权向量应用到16个通道的二维成像结果中。为便于观察，感兴趣区域为一个车辆位置，图12为成像场景中一个车辆位置的结果，图13a～13c分别展示了对同一车辆位置三个孔径的成像结果，图13d则是前三幅图像在图像域的合成结果。可以看出，与单孔径图像相比，多孔径合成图像中感兴趣区域对应的车身轮廓更加完整，后视镜等结构更加清晰，这表明即使仅在图像域中进行非相干，合成多孔径图像质量仍有明显提升。In order to demonstrate the digital beam method based on the alternating direction multiplier method, a simulation experiment was conducted based on a uniform linear array of 16 elements. The area of interest is set with the main beam pointing at 10° and the beam width at 20°. After using the imaging method proposed by the present invention, the algorithm converged after about 40 iterations. Figure 11 shows the power pattern comparison results of the expected and algorithm results. This set of weight vectors is applied to the two-dimensional imaging results of 16 channels. middle. To facilitate observation, the area of interest is a vehicle position. Figure 12 shows the results of a vehicle position in the imaging scene. Figures 13a to 13c respectively show the imaging results of three apertures for the same vehicle position. Figure 13d is the first three images. Synthesis results in the image domain. It can be seen that compared with the single-aperture image, the body contour corresponding to the area of interest in the multi-aperture synthetic image is more complete, and structures such as rearview mirrors are clearer, which shows that even if only incoherent in the image domain, the synthetic multi-aperture image Quality is still significantly improved.

单通道SAR成像和MIMO SAR成像实验结果表明，本发明所提出的基于DDM的MIMO车载毫米波雷达多通道二维成像方法无需波形设计即可完成MIMO信道分离，有效解决了进场成像和广角聚焦问题，数字波束灵活可控，并最终实现了高分辨率SAR成像。Single-channel SAR imaging and MIMO SAR imaging experimental results show that the DDM-based MIMO vehicle-mounted millimeter wave radar multi-channel two-dimensional imaging method proposed by the present invention can complete MIMO channel separation without waveform design, effectively solving the problem of approach imaging and wide-angle focusing. problem, the digital beam is flexible and controllable, and finally achieves high-resolution SAR imaging.

最后应说明的是：以上实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的精神和范围。Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be used Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent substitutions are made to some of the technical features; however, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

一种车载多普勒分集MIMO合成孔径雷达时域成像方法，其特征在于，所述方法包括：A vehicle-mounted Doppler diversity MIMO synthetic aperture radar time domain imaging method, characterized in that the method includes:

采集以预设的速度沿直线轨迹运动的MIMO合成孔径雷达向目标发射的线性调频信号的回波数据，其中，所述MIMO合成孔径雷达的不同发射机具有不同的DDM编码；Collecting echo data of chirp signals emitted by a MIMO synthetic aperture radar moving along a straight line trajectory at a preset speed to the target, wherein different transmitters of the MIMO synthetic aperture radar have different DDM codes;

针对所述回波数据进行多普勒滤波得到每一通道对应的回波数据，并针对每一通道对应的回波数据进行距离向傅里叶变换以得到该通道对应的变换后的回波矩阵，以及按照预设算法将所述变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果；Doppler filtering is performed on the echo data to obtain the echo data corresponding to each channel, and distance Fourier transform is performed on the echo data corresponding to each channel to obtain the transformed echo matrix corresponding to the channel. , and project the transformed echo matrix into the two-dimensional imaging coordinate system according to the preset algorithm to obtain the two-dimensional imaging result of the channel;

将所述MIMO合成孔径雷达的合成孔径依序划分为多个子孔径，针对每一所述子孔径，将该子孔径对应的所有所述通道的二维成像结果进行合成得到该子孔径对应的成像结果；The synthetic aperture of the MIMO synthetic aperture radar is divided into multiple sub-apertures in sequence. For each sub-aperture, the two-dimensional imaging results of all the channels corresponding to the sub-aperture are synthesized to obtain the imaging corresponding to the sub-aperture. result;

将所有所述子孔径对应的所述成像结果进行融合得到所述合成孔径对应的总的成像结果。The imaging results corresponding to all the sub-apertures are fused to obtain a total imaging result corresponding to the synthetic aperture.
如权利要求1所述的方法，其特征在于，所述针对所述回波数据进行多普勒滤波得到每一通道对应的回波数据包括：The method of claim 1, wherein performing Doppler filtering on the echo data to obtain echo data corresponding to each channel includes:

针对所述MIMO合成孔径雷达的每个通道，设该通道由第p个发射机以及第q个接收机组成，则通过如下方式得到该通道对应的回波数据：For each channel of the MIMO synthetic aperture radar, assuming that the channel is composed of the p-th transmitter and the q-th receiver, the echo data corresponding to the channel is obtained in the following way:

针对所述第q个接收机接收到的回波数据
沿第m行做离散傅里叶变换得到： For the echo data received by the q-th receiver
Doing the discrete Fourier transform along the m-th row gives:

根据上式对回波数据
进行多普勒域滤波以分离出该通道对应的回波数据
According to the above formula, the echo data
Perform Doppler domain filtering to separate the echo data corresponding to the channel

其中，m为单个脉冲内采样点索引，n为脉冲索引，且n＝1,2……N，j为虚数单位，h为多普勒单元索引，
为多普勒调制相位，PRF为脉冲重复频率。 Among them, m is the sampling point index within a single pulse, n is the pulse index, and n=1,2...N, j is the imaginary unit, h is the Doppler unit index,
is the Doppler modulation phase, and PRF is the pulse repetition frequency.
如权利要求1所述的方法，其特征在于，针对每一所述子孔径，将该子孔径对应的所有所述通道的二维成像结果进行合成得到该子孔径对应的成像结果包括：The method according to claim 1, characterized in that, for each sub-aperture, synthesizing the two-dimensional imaging results of all the channels corresponding to the sub-aperture to obtain the imaging results corresponding to the sub-aperture includes:

根据所述MIMO合成孔径雷达的成像范围内的感兴趣区域的主波束指向以及波束宽度确定每一通道对应的权重系数；Determine the weight coefficient corresponding to each channel according to the main beam direction and beam width of the area of interest within the imaging range of the MIMO synthetic aperture radar;

将所述每一通道的像素点乘以该通道对应的权重系数后得到每一通道对应的权重图像；Multiply the pixels of each channel by the weight coefficient corresponding to the channel to obtain the weight image corresponding to each channel;

将所有通道对应的权重图像进行合成得到该子孔径对应的成像结果。The weighted images corresponding to all channels are synthesized to obtain the imaging result corresponding to the sub-aperture.
如权利要求1所述的方法，其特征在于，所述针对每一通道对应的回波数据进行距离向傅里叶变换以得到该通道对应的变换后的回波矩阵，并按照预设算法将所述变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果包括：The method of claim 1, wherein the range Fourier transform is performed on the echo data corresponding to each channel to obtain the transformed echo matrix corresponding to the channel, and the transformed echo matrix is transformed according to a preset algorithm. Projecting the transformed echo matrix into the two-dimensional imaging coordinate system to obtain the two-dimensional imaging results of the channel includes:

(1)基于该通道对应的所述回波矩阵估计该通道对应的多普勒中心频率以及多普勒调频率；(1) Estimate the Doppler center frequency and Doppler modulation frequency corresponding to the channel based on the echo matrix corresponding to the channel;

(2)基于所述多普勒中心频率以及所述多普勒调频率确定该通道对应的雷达当前航行速度估计值；(2) Determine the current radar navigation speed estimate corresponding to the channel based on the Doppler center frequency and the Doppler modulation frequency;

(3)针对每个所述二维成像坐标系下的像素点，根据该像素点在所述二维成像坐标系下的坐标值确定该像素点对应的距离单元索引，并基于所述当前航行速度估计值确定该像素点的相干累加所需的补偿相位因子；(3) For each pixel point in the two-dimensional imaging coordinate system, determine the distance unit index corresponding to the pixel point according to the coordinate value of the pixel point in the two-dimensional imaging coordinate system, and determine the distance unit index corresponding to the pixel point based on the current navigation The velocity estimate determines the compensation phase factor required for coherent accumulation of the pixel;

(4)针对每个所述像素点，根据其对应的补偿相位因子以及距离单元索引和所述变换后的回波矩阵进行相干累加以得到该像素点的成像值。(4) For each pixel, perform coherent accumulation according to its corresponding compensation phase factor and distance unit index and the transformed echo matrix to obtain the imaging value of the pixel.
如权利要求4所述的方法，其特征在于，所述基于该通道对应的回波矩阵估计该通道对应的多普勒中心频率包括：The method of claim 4, wherein estimating the Doppler center frequency corresponding to the channel based on the echo matrix corresponding to the channel includes:

针对该通道对应的所述回波矩阵的每个行向量，设该行向量为S _a，则通过执行如下操作估计该通道对应的多普勒中心频率： For each row vector of the echo matrix corresponding to the channel, assuming that the row vector is S _a , then estimate the Doppler center frequency corresponding to the channel by performing the following operations:

按照下式对该行向量S _a进行自相关以得到该行向量对应的自相关矩阵R _a； Carry out autocorrelation on the row vector S _a according to the following formula to obtain the autocorrelation matrix R _a corresponding to the row vector;

R _a＝S _a*S ^* _a/N ₀； R _a =S _a *S ^* _a /N ₀ ;

其中，N ₀表示所述回波矩阵的列数，S ^* _a是S _a的共轭转置； Among them, N ₀ represents the number of columns of the echo matrix, and S ^* _a is the conjugate transpose of S _a ;

根据下式确定该通道对应的所述多普勒中心频率f _dc： Determine the Doppler center frequency f _dc corresponding to the channel according to the following formula:

其中，A为回波矩阵的行数，R _a′是R _a的逆傅里叶变换后的矩阵，angle()表示取相位操作，f _s是该通道对应的接收机的采样频率。 Among them, A is the number of rows of the echo matrix, R _a ′ is the matrix after the inverse Fourier transform of R _a , angle() represents the phase operation, and f _s is the sampling frequency of the receiver corresponding to the channel.
如权利要求4所述的方法，其特征在于，根据下式确定该通道对应的所述多普勒调频率估计值γ _d： The method according to claim 4, characterized in that the Doppler modulation frequency estimate γ _d corresponding to the channel is determined according to the following formula:

其中，γ为调频率，PRF为脉冲重复频率，N为脉冲索引，ΔR为通过所述回波矩阵计算得到的前后视图的移动量。Among them, γ is the modulation frequency, PRF is the pulse repetition frequency, N is the pulse index, and ΔR is the movement amount of the front and rear views calculated through the echo matrix.
如权利要求6所述的方法，其特征在于，所述根据所述多普勒调频率以及所述多普勒中心频率确定该通道对应的所述雷达当前航行速度估计值包括：The method of claim 6, wherein determining the estimated current navigation speed of the radar corresponding to the channel based on the Doppler modulation frequency and the Doppler center frequency includes:

根据下式确定所述雷达当前航行速度估计值：The estimated current navigation speed of the radar is determined according to the following formula:

其中，v为所述雷达当前航行速度估计值，R ₀为场景中心距离，λ为所述MIMO合成孔径雷达的载频对应的波长，f _dc为所述通道对应的多普勒中心频率，γ _d为所述通道对应的多普勒调频率估计值。 Among them, v is the current navigation speed estimate of the radar, R ₀ is the scene center distance, λ is the wavelength corresponding to the carrier frequency of the MIMO synthetic aperture radar, f _dc is the Doppler center frequency corresponding to the channel, γ _d is the Doppler modulation frequency estimate corresponding to the channel.
如权利要求4-7中任一项所述的方法，其特征在于，所述按照预设算法将所述变换后的回波矩阵投影到二维成像坐标系内以得到该通道的二维成像结果包括：The method according to any one of claims 4 to 7, characterized in that the transformed echo matrix is projected into a two-dimensional imaging coordinate system according to a preset algorithm to obtain the two-dimensional imaging of the channel. Results include:

按照预设的网格划分模式将所述MIMO合成孔径雷达的成像区域划分成网格以构成所述二维成像坐标系，并且所述网格中的每个网格元素分区构成一个所述像素点。The imaging area of the MIMO synthetic aperture radar is divided into grids according to a preset grid division mode to constitute the two-dimensional imaging coordinate system, and each grid element partition in the grid constitutes one of the pixels point.
如权利要求8所述的方法，其特征在于，所述针对每个所述二维成像坐标系下的像素点，根据该像素点在所述二维成像坐标系下的坐标值确定该像素点对应的距离单元索引，包括：The method of claim 8, wherein for each pixel point in the two-dimensional imaging coordinate system, the pixel point is determined according to the coordinate value of the pixel point in the two-dimensional imaging coordinate system. The corresponding distance unit index includes:

按照下式计算第n个脉冲内雷达天线相位中心到像素点x,y的斜距R _n(x,y)： Calculate the slant distance R _n (x, y) from the radar antenna phase center to the pixel point x, y in the nth pulse according to the following formula:

其中，y为该像素点的纵坐标，x是该像素点的横坐标，v为所述雷达当前航行速度估计值，PRF为脉冲重复频率；Among them, y is the ordinate of the pixel, x is the abscissa of the pixel, v is the estimated current navigation speed of the radar, and PRF is the pulse repetition frequency;

根据下式确定第n个脉冲下该像素点对应的所述距离单元索引Id _n： The distance unit index Id _n corresponding to the pixel point under the n-th pulse is determined according to the following formula:

其中，Δr为采样前的信号采样间隔，β为插值倍数，
表示向上取整操作。 Among them, Δr is the signal sampling interval before sampling, β is the interpolation multiple,
Indicates rounding up operation.
如权利要求9所述的方法，其特征在于，针对每个所述二维成像坐标系下的像素点，基于所述当前航行速度估计值确定该像素点的相干累加所需的补偿相位因子包括：The method of claim 9, wherein, for each pixel point in the two-dimensional imaging coordinate system, determining the compensation phase factor required for coherent accumulation of the pixel point based on the current navigation speed estimate includes: :

根据该像素点对应的所述斜距确定该像素点的相干累加所需的所述补偿相位因子。The compensation phase factor required for coherent accumulation of the pixel is determined based on the slope distance corresponding to the pixel.
如权利要求10所述的方法，其特征在于，所述根据该像素点对应的所述斜距确定该像素点的相干累加所需的所述补偿相位因子包括：The method of claim 10, wherein determining the compensation phase factor required for coherent accumulation of the pixel point based on the slant distance corresponding to the pixel point includes:

根据下式确定第n个脉冲下该像素点对应的所述补偿相位因子
Determine the compensation phase factor corresponding to the pixel under the nth pulse according to the following formula:

其中，R _n(x,y)为第n个脉冲内雷达天线相位中心到像素点x,y的斜距，λ为所述MIMO合成孔径雷达的载频对应的波长。 Among them, R _n (x, y) is the slant distance from the radar antenna phase center to the pixel point x, y in the n-th pulse, and λ is the wavelength corresponding to the carrier frequency of the MIMO synthetic aperture radar.
如权利要求10所述的方法，其特征在于，所述针对每个所述像素点，根据其对应的补偿相位因子以及距离单元索引以及所述变换后的回波矩阵进行相干累加以得到该像素点的成像值包括：The method of claim 10, wherein for each pixel, coherent accumulation is performed based on its corresponding compensation phase factor and distance unit index and the transformed echo matrix to obtain the pixel. The imaging values of points include:

根据下式计算每一所述像素点对应的所述成像值：The imaging value corresponding to each pixel is calculated according to the following formula:

其中，I表示第n个脉冲下该像素点对应的成像值，s _r(Id,n)表示所述变换后的回波矩阵s _r中该第n个脉冲下该像素点对应的距离单元索引Id _n所指示的矩阵元素，j为虚数单位，
为第n个脉冲下该像素点对应的所述补偿相位因子。 Among them, I represents the imaging value corresponding to the pixel point under the n-th pulse, and s _r (Id, n) represents the distance unit index corresponding to the pixel point under the n-th pulse in the transformed echo matrix s _r . The matrix element indicated by Id _n , j is the imaginary unit,
is the compensation phase factor corresponding to the pixel point under the nth pulse.
如权利要求8所述的方法，其特征在于，所述网格中的每个网格元素分区的面积不大于所述MIMO合成孔径雷达的最小分辨面积。The method of claim 8, wherein the area of each grid element partition in the grid is not greater than the minimum resolution area of the MIMO synthetic aperture radar.