CN117491998A - Stepping frequency synthetic aperture imaging method and system - Google Patents
Stepping frequency synthetic aperture imaging method and system Download PDFInfo
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- CN117491998A CN117491998A CN202311454816.7A CN202311454816A CN117491998A CN 117491998 A CN117491998 A CN 117491998A CN 202311454816 A CN202311454816 A CN 202311454816A CN 117491998 A CN117491998 A CN 117491998A
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- 238000003384 imaging method Methods 0.000 title claims abstract description 49
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Abstract
The invention relates to a stepping frequency synthetic aperture imaging method and a stepping frequency synthetic aperture imaging system, which belong to the technical field of target detection and comprise the following steps: sequentially processing the echo data, and suppressing background noise in the processed data in the current azimuth; presetting the number of azimuth grids and distance-direction grid data, establishing coordinate positions for each grid point, and calculating the distance between each grid and the radar when the radar position is the set position; calculating delay time corresponding to each grid distance and signal frequency step between adjacent grids to obtain phases corresponding to the grid points; and mapping the processed data into grids according to the delay time and the radar set position and azimuth, performing phase compensation calculation on the grid data, and performing cumulative calculation on grid values according to the radar azimuth. The invention improves the accuracy of the synthetic aperture imaging by carrying out the processing of the preset amplitude range, the frequency domain interpolation and the like on the stepping frequency echo signal, and improves the signal to noise ratio of imaging data by calculating phase compensation, echo accumulation and the like.
Description
Technical Field
The invention relates to the technical field of target detection, in particular to a stepping frequency synthetic aperture imaging method and system.
Background
The synthetic aperture imaging plays an important role in target detection application, and in large target scattering characteristic detection application of ships, vehicles, airplanes and the like, the incoming radar scattering cross section can directly reflect the target electromagnetic scattering characteristic, so that the rapid detection of the target surface coating performance is realized; the radar cross section data of the surface of the detection target can be rapidly acquired in a synthetic aperture imaging mode, and the parameters of the surface coating are calculated in an inversion mode, so that support is provided for equipment design, production and maintenance.
The conventional synthetic aperture imaging adopts a large aperture or darkroom detection environment, has high data precision and signal to noise ratio, but has huge equipment volume, complex operation and high cost, and is difficult to popularize and use.
Disclosure of Invention
The invention aims to overcome the defects of high requirements on detection environment and complex algorithm flow in the prior art, provides a stepping frequency synthetic aperture imaging method and a stepping frequency synthetic aperture imaging system, and solves the defects of the conventional synthetic aperture imaging method.
The aim of the invention is achieved by the following technical scheme: a stepped frequency synthetic aperture imaging method, the imaging method comprising:
echo data preprocessing: sequentially carrying out interpolation and inverse Fourier transform on the echo data, and inhibiting background noise in the data processed in the current azimuth;
an imaging area grid setting step: presetting the number of azimuth grids and the distance-direction grid data, establishing a coordinate position for each grid point, and calculating the distance between each grid and the radar when the radar position is the set position;
an echo data phase estimation step: calculating delay time corresponding to each grid distance and signal frequency step between adjacent grids to obtain phases corresponding to the grid points;
a composite image pixel accumulation step: and mapping the processed data into grids according to the delay time and the radar set position and azimuth, performing phase compensation calculation on the grid data, and performing cumulative calculation on grid values according to the radar azimuth.
The echo data preprocessing step specifically comprises the following steps:
according to radar azimuth, echo data is obtained when the radar is positioned at the mth azimuth positionInterpolation processing is carried out, and the interpolated data is +.>The interpolated data length is N r ；
For dataPerforming inverse Fourier transform to obtain data->
According to the reflected echo theoretical parameter e of the specific target of the region of interest 0 Estimating an environmental dynamic threshold e L Data under current orientationSuppressing mid-background noise, i.e.)>
The imaging area grid setting step specifically includes the following steps:
according to the desired detection region [ R ] min ,R max ]And imaging precision sigma, presetting azimuth grid quantity D a ＝L a Number of distance-oriented gridsL a Is the length of the synthetic aperture;
establishing coordinate positions for each grid point by taking the radar initial position as an origin and the azimuth direction and the distance direction as direction axesPlacing to obtainWherein d i,j ＝(i·σ,j·σ+R min )，i＝1,2,…D a ，j＝1,2,…D r ；
From the grid point positions, the radar position is calculated as (x m 0) each grid is distant from radarWherein m=1, 2, …, L a /ΔL，i＝1,2,…D a ，j＝1,2,…D r Δl is the azimuthal spacing.
The echo data phase estimation step specifically comprises the following steps:
calculating delay time corresponding to each grid distancec is the speed of light;
on the premise of near field small-range imaging, calculating signal frequency steps between adjacent gridsf dmax And f dmin The adjusted maximum frequency and the adjusted minimum frequency are respectively;
obtaining the grid distance r i,j The corresponding phase is
The synthetic image pixel accumulating step specifically includes the following:
based on the delay time and the radar position (x) m Azimuth data at 0)Mapping to grid D, grid valuationWherein v is i,j (m)＝e rN ，e rN For data->Nth sample, and->floor () represents a rounding down calculation;
by compensating calculation methodsPerforming phase compensation calculation on the grid data to obtain a compensated network value of +.>Wherein exp { } represents natural exponent calculation;
according toAnd carrying out accumulated calculation on the grid values according to the radar azimuth.
The imaging method further comprises the step of presetting key system parameters, and specifically comprises the following steps:
setting the lowest frequency f of electromagnetic wave emitted by the system min Highest frequency spectrum f max Frequency step Δf, transmit time T, sub-pulse duration T p Range of detection distance [ R ] min ,R max ]Azimuth distance Δl and synthetic aperture length L a ；
Setting the sampling interval delta T of the system and meeting
The imaging system comprises a parameter setting module, an echo data preprocessing module, an imaging area grid setting module, an echo data phase estimation module and a synthetic image phase accumulation module;
the parameter setting module is used for: the working parameters of the system are set according to the requirements;
the echo data preprocessing module is used for: the method comprises the steps of sequentially carrying out interpolation and inverse Fourier transform on echo data, and inhibiting background noise in the data processed in the current azimuth;
the imaging region grid setting module: the method comprises the steps of presetting the number of azimuth grids and the distance grid data, establishing coordinate positions for each grid point, and calculating the distance between each grid and the radar when the radar position is the set position;
the echo data phase estimation module: the method comprises the steps of calculating delay time corresponding to each grid distance and signal frequency steps between adjacent grids to obtain phases corresponding to the grid points;
the composite image pixel accumulation module: the method is used for mapping the processed data into the grid according to the azimuth according to the delay time and the radar setting position, carrying out phase compensation calculation on the grid data, and carrying out cumulative calculation on the grid value according to the radar azimuth.
The invention has the following advantages: the step frequency synthetic aperture imaging method and system has raised synthetic aperture imaging accuracy through the preset amplitude range, frequency domain interpolation, etc. of step frequency echo signal, phase compensation, echo accumulation, etc. calculation and raised signal-to-noise ratio of the imaging data.
Drawings
FIG. 1 is a schematic flow chart of the method of the present invention.
Detailed Description
For the purposes of making the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, which are generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Accordingly, the following detailed description of the embodiments of the present application, provided in connection with the accompanying drawings, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, are intended to be within the scope of the present application. The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, one embodiment of the present invention relates to a step frequency synthetic aperture imaging method, which specifically includes the following steps:
s1, presetting key system parameters;
s101, setting minimum frequency f of electromagnetic wave emitted by system min Highest frequency spectrum f max Frequency step Δf, transmit time T, sub-pulse duration T p Range of detection distance [ R ] min ,R max ]Azimuth distance Δl and synthetic aperture length L a Etc.;
s102, setting a system receiving sampling interval delta T and meeting the requirement of
S2, preprocessing echo data;
s201, according to radar azimuth, when the radar is positioned at the mth azimuth position, echo data are obtainedInterpolation processing is carried out, and the interpolated data is +.>The interpolated data length is N r ，N r The value of (2) is related to the number of the imaged pixels;
s202, dataPerforming inverse Fourier transform to obtain data ∈>
S203, according to the reflected echo theoretical parameter e of the specific target of the region of interest 0 Estimating an environmental dynamic threshold e L Data under current orientationSuppressing mid-background noise, i.e.)>
Wherein the dynamic threshold e L The value of the standard substance is uncertain in a non-darkroom environment, and the standard substance is used for measuring and counting for multiple times in actual engineering.
S3, setting an imaging area grid;
s301, detecting the region [ R ] according to expectations min ,R max ]And imaging precision sigma, presetting azimuth grid quantity D a And distance to grid quantity D r Wherein D is a ＝L a /σ，Normally N r ＞2·D r Wherein N is r As in S201, in the case where the mesh parameters are determined, the interpolation data length in step S201 should be set accordingly.
S302, establishing coordinate positions for each grid point by taking the radar initial position as an origin and the azimuth direction and the distance direction as direction axesWherein d is i,j ＝(i·σ,j·σ+R min )，i＝1,2,…D a ，j＝1,2,…D r ；
S303, calculating the radar position as (x) according to the grid point position in S302 m 0) each grid is distant from radarm＝1,2,…,L a and/ΔL, wherein,i＝1,2,…D a ，j＝1,2,…D r 。
s4, estimating the phase of echo data;
s401, calculating corresponding delay time for each grid distance in S303Where c is the light velocity constant.
S402, calculating signal frequency steps between adjacent grids on the premise of near field small-range imagingWherein,floor () is a rounding down calculation, f dmax And f dmin The adjusted maximum frequency and the adjusted minimum frequency, respectively.
S403, grid distance r in step S303 i,j The corresponding phase is
S5, accumulating synthesized image pixels;
s501, according to the delay time, the radar position is (x) m Azimuth data at 0)Mapping to grid D, grid value +.>m＝1,2,…,L a ΔL, where v i,j (m)＝e rN ，e rN For data->Nth sample, and->floor () is a round-down calculation;
s502, performing phase compensation calculation on the grid data, wherein the compensation calculation method comprises the following steps:exp is natural index calculation, the compensated network takes the value of,
s503, carrying out accumulated calculation on the grid values according to the radar azimuth, wherein the calculation method is that,
another embodiment of the invention is directed to a step frequency synthetic aperture imaging system comprising: the system comprises a parameter setting module, an echo data preprocessing module, an imaging area grid setting module, an echo data phase estimation module and a synthetic image phase accumulation module;
the parameter setting module is used for: the working parameters of the system are set according to the requirements;
the echo data preprocessing module is used for: the method comprises the steps of sequentially carrying out interpolation and inverse Fourier transform on echo data, and inhibiting background noise in the data processed in the current azimuth;
the imaging region grid setting module: the method comprises the steps of presetting the number of azimuth grids and the distance grid data, establishing coordinate positions for each grid point, and calculating the distance between each grid and the radar when the radar position is the set position;
the echo data phase estimation module: the method comprises the steps of calculating delay time corresponding to each grid distance and signal frequency steps between adjacent grids to obtain phases corresponding to the grid points;
the composite image pixel accumulation module: the method is used for mapping the processed data into the grid according to the azimuth according to the delay time and the radar setting position, carrying out phase compensation calculation on the grid data, and carrying out cumulative calculation on the grid value according to the radar azimuth.
The foregoing is merely a preferred embodiment of the invention, and it is to be understood that the invention is not limited to the form disclosed herein but is not to be construed as excluding other embodiments, but is capable of numerous other combinations, modifications and adaptations, and of being modified within the scope of the inventive concept described herein, by the foregoing teachings or by the skilled person or knowledge of the relevant art. And that modifications and variations which do not depart from the spirit and scope of the invention are intended to be within the scope of the appended claims.
Claims (7)
1. A step frequency synthetic aperture imaging method, characterized by: the imaging method comprises the following steps:
echo data preprocessing: sequentially carrying out interpolation and inverse Fourier transform on the echo data, and inhibiting background noise in the data processed in the current azimuth;
an imaging area grid setting step: presetting the number of azimuth grids and the distance-direction grid data, establishing a coordinate position for each grid point, and calculating the distance between each grid and the radar when the radar position is the set position;
an echo data phase estimation step: calculating delay time corresponding to each grid distance and signal frequency step between adjacent grids to obtain phases corresponding to the grid points;
a composite image pixel accumulation step: and mapping the processed data into grids according to the delay time and the radar set position and azimuth, performing phase compensation calculation on the grid data, and performing cumulative calculation on grid values according to the radar azimuth.
2. A step frequency synthetic aperture imaging method according to claim 1 wherein: the echo data preprocessing step specifically comprises the following steps:
according to radar azimuth, echo data is obtained when the radar is positioned at the mth azimuth positionInterpolation processing is carried out, and the interpolated data is +.>The interpolated data length is N r ；
For dataPerforming inverse Fourier transform to obtain data->
According to the reflected echo theoretical parameter e of the specific target of the region of interest 0 Estimating an environmental dynamic threshold e L Data under current orientationSuppressing mid-background noise, i.e.)>
3. A step frequency synthetic aperture imaging method according to claim 1 wherein: the imaging area grid setting step specifically includes the following steps:
according to the desired detection region [ R ] min ,R max ]And imaging precision sigma, presetting azimuth grid quantity D a ＝L a Number of distance-oriented gridsL a Is the length of the synthetic aperture;
the radar initial position is taken as an original point, the azimuth direction and the distance direction are taken as direction axes, and coordinate positions are established for each grid point to obtainWherein d i,j ＝(i·σ,j·σ+R min )，i＝1,2,…D a ，j＝1,2,…D r ；
From the grid point positions, the radar position is calculated as (x m 0) each grid is distant from radarWherein,i＝1,2,…D a ，j＝1,2,…D r Δl is the azimuthal spacing.
4. A step frequency synthetic aperture imaging method according to claim 3 wherein: the echo data phase estimation step specifically comprises the following steps:
calculating delay time corresponding to each grid distancec is the speed of light;
on the premise of near field small-range imaging, calculating signal frequency steps between adjacent gridsf dmax And f dmin The adjusted maximum frequency and the adjusted minimum frequency are respectively;
obtaining the grid distance r i,j The corresponding phase is
5. A step frequency synthetic aperture imaging method according to claim 4 wherein: the synthetic image pixel accumulating step specifically includes the following:
based on the delay time and the radar position (x) m Azimuth data at 0)Mapping to grid D, grid valuationWherein v is i,j (m)＝e rN ，e rN For data->Nth sample, and->floor () represents a rounding down calculation;
by compensating the calculation squareMethod ofPerforming phase compensation calculation on the grid data to obtain a compensated network value of +.>Wherein exp { } represents natural exponent calculation;
according toAnd carrying out accumulated calculation on the grid values according to the radar azimuth.
6. A step frequency synthetic aperture imaging method according to any of claims 1-5 wherein: the imaging method further comprises the step of presetting key system parameters, and specifically comprises the following steps:
setting the lowest frequency f of electromagnetic wave emitted by the system min Highest frequency spectrum f max Frequency step Δf, transmit time T, sub-pulse duration T p Range of detection distance [ R ] min ,R max ]Azimuth distance Δl and synthetic aperture length L a ；
Setting the sampling interval delta T of the system and meeting
7. A step frequency synthetic aperture imaging system, characterized by: the imaging system comprises a parameter setting module, an echo data preprocessing module, an imaging area grid setting module, an echo data phase estimation module and a synthetic image phase accumulation module;
the parameter setting module is used for: the working parameters of the system are set according to the requirements;
the echo data preprocessing module is used for: the method comprises the steps of sequentially carrying out interpolation and inverse Fourier transform on echo data, and inhibiting background noise in the data processed in the current azimuth;
the imaging region grid setting module: the method comprises the steps of presetting the number of azimuth grids and the distance grid data, establishing coordinate positions for each grid point, and calculating the distance between each grid and the radar when the radar position is the set position;
the echo data phase estimation module: the method comprises the steps of calculating delay time corresponding to each grid distance and signal frequency steps between adjacent grids to obtain phases corresponding to the grid points;
the composite image pixel accumulation module: the method is used for mapping the processed data into the grid according to the azimuth according to the delay time and the radar setting position, carrying out phase compensation calculation on the grid data, and carrying out cumulative calculation on the grid value according to the radar azimuth.
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