WO2017198162A1

WO2017198162A1 - Three-dimensional image rebuilding method and device based on synthetic aperture radar imaging

Info

Publication number: WO2017198162A1
Application number: PCT/CN2017/084636
Authority: WO
Inventors: 郭令霞; 祁春超; 陈寒江; 吴光胜; 赵术开; 丁庆
Original assignee: 深圳市太赫兹科技创新研究院有限公司; 深圳市无牙太赫兹科技有限公司
Priority date: 2016-04-29
Filing date: 2017-05-17
Publication date: 2017-11-23
Also published as: CN106054183A

Abstract

A three-dimensional image rebuilding method and device based on Synthetic Aperture Radar imaging. The method comprises: using a transmission signal of an antenna as a local oscillator signal, de-modulating an original collected echo signal reflected from a scanned object, to obtain a first intermediate signal (S11); removing residual video phase in the first intermediate signal to obtain a second intermediate signal (S12); sequentially performing Fourier transformation on the second intermediate signal in the height direction and in the azimuth direction to obtain a third intermediate signal (S13); and performing an inverse non-uniform fast Fourier transformation on the third intermediate signal to obtain a three-dimensional image of the scanned object (S14). The invention can shorten the time required for rebuilding a three-dimensional image while improving the accuracy of image rebuilding.

Description

Three-dimensional image reconstruction method and device based on synthetic aperture radar imaging

Technical field

The invention relates to the field of Synthetic Aperture Radar (SAR) technology, in particular to a three-dimensional image reconstruction method and device based on synthetic aperture radar imaging.

Background technique

In order to ensure public safety, security inspection systems are usually installed in places like stations and customs. Current security systems include metal detectors for human detection. Metal detectors are very effective in detecting metal products carried by human bodies, but they are not effective for non-metallic products such as ceramic knives and liquid explosives. In response to this problem, although X-ray detectors can detect various contraband products such as ceramic knives and liquid explosives, they are harmful to the human body and therefore cannot be applied to human body security systems.

In view of this situation, a three-dimensional imaging security instrument for human body security is currently proposed, and a synthetic aperture radar imaging technique is used in the three-dimensional imaging security instrument. Commonly used synthetic aperture radar imaging techniques are planar synthetic aperture imaging and cylindrical synthetic aperture imaging. However, in the image reconstruction process of these two synthetic aperture imaging methods, linear interpolation of non-uniform wavenumber domain sampling data is required.

In other words, in the existing planar synthetic aperture three-dimensional imaging algorithm, it is necessary to homogenize the non-uniform wavenumber domain sampling data by linear interpolation operation, and then complete the three-dimensional image reconstruction by uniform inverse Fourier transform. However, in practical applications, obtaining high-quality reconstructed images requires high precision for linear interpolation operations, and the operation of the existing linear interpolation operations itself is cumbersome, resulting in a long time-consuming 3D image reconstruction; Existing linear interpolation operations also introduce large interpolation errors and reduce the accuracy of reconstructed images.

Summary of the invention

Based on this, the three-dimensional image reconstruction method and device based on synthetic aperture radar imaging provided by the invention can shorten the time required for reconstructing the three-dimensional image and improve the accuracy of reconstructing the image.

One aspect of the present invention provides a three-dimensional image reconstruction method based on synthetic aperture radar imaging, including:

Using the transmitted signal of the antenna as a local oscillator signal, performing demodulation processing on the original echo signal reflected back by the acquired scanned target to obtain a first intermediate signal;

Eliminating the residual video phase in the first intermediate signal to obtain a second intermediate signal;

Performing a Fourier transform of the height direction and the azimuth direction on the second intermediate signal to obtain a third intermediate signal;

Performing an inverse non-uniform fast Fourier transform on the third intermediate signal to obtain a three-dimensional image of the scanned object.

Another aspect of the present invention provides a three-dimensional image reconstruction apparatus based on synthetic aperture radar imaging, comprising:

The demodulation module is configured to use the transmit signal of the antenna as a local oscillator signal, and perform demodulation processing on the original echo signal reflected back by the acquired scanned target to obtain a first intermediate signal;

a compensation module, configured to cancel a residual video phase in the first intermediate signal to obtain a second intermediate signal;

a compression module, configured to perform a Fourier transform on the second intermediate signal in a height direction and an azimuth direction to obtain a third intermediate signal;

The image reconstruction module is configured to perform inverse non-uniform fast Fourier transform on the third intermediate signal to obtain a three-dimensional image of the scanned target.

In the above technical solution, by using the transmitted signal of the antenna as a local oscillator signal, the collected original echo signal is subjected to demodulation processing to obtain a first intermediate signal; the residual video phase in the first intermediate signal is eliminated, and a second intermediate signal is obtained. Performing a Fourier transform of the height direction and the azimuth direction on the second intermediate signal to obtain a third intermediate signal; performing inverse non-uniform fast Fourier transform on the third intermediate signal, A three-dimensional image to the scanned target. The solution of the above embodiment of the invention shortens the time required for reconstructing the three-dimensional image, reduces the interpolation error, and is beneficial to improving the accuracy of reconstructing the image.

DRAWINGS

1 is a schematic flow chart of a method for reconstructing a three-dimensional image based on synthetic aperture radar imaging according to an embodiment;

2 is a schematic diagram of a three-dimensional imaging of a planar synthetic aperture according to an embodiment;

FIG. 3 is a schematic structural diagram of a three-dimensional image reconstruction apparatus based on synthetic aperture radar imaging according to an embodiment.

detailed description

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

FIG. 1 is a schematic flowchart of a method for reconstructing a three-dimensional image based on synthetic aperture radar imaging according to an embodiment; as shown in FIG. 1 , the method for reconstructing a three-dimensional image based on synthetic aperture radar imaging in the embodiment includes the following steps:

S11, using the transmit signal of the antenna as a local oscillator signal, performing demodulation processing on the original echo signal reflected back by the collected scanned target to obtain a demodulated signal (ie, a first intermediate signal);

In the embodiment of the present invention, the basic idea of the demodulation processing is: adopting a chirp signal with the same frequency as the transmitting signal of the antenna, or using the transmitting signal of the antenna as the local oscillator signal, and delaying the local oscillator signal to obtain a reference. The signal is conjugate-mixed with the collected original echo signal, and the time difference between the original echo signal and the reference signal can be converted into different difference frequency.

In the embodiment of the present invention, the transmitting signal is represented as a chirp signal:

The corresponding original echo signal can be expressed as:

s _R (x', y'; t) = σ(x, y, z) s _T (t-τ _d ),

Where f ₀ is the center frequency of the transmitted signal, K is the modulation frequency of the FM signal; (x', y', z') is the position coordinate of the center of the antenna aperture, and (x, y, z) is the position of the scanned target The coordinates, σ(x, y, z) are the reflection coefficients of the scanned target, and τ _d represents the time difference between the time when the transmitted signal is emitted and the receiving time of the corresponding echo signal, and s _T (t-τ _d ) is t- The transmitted signal at time τ _d , τ represents the time of emission of the transmitted signal, R(τ) is the instantaneous distance between the center of the antenna aperture and the scanned target at time τ, and R(τ+τ _d ) represents the antenna at time τ+τ _d The instantaneous distance between the center of the aperture and the object being scanned, and c is the speed of light.

S12, eliminating residual video phase in the first intermediate signal to obtain a second intermediate signal;

After frequency demodulation, different frequency components produce a delay in time, resulting in different frequency components not aligned in time, resulting in a redundant phase called residual video phase (RVP) in the frequency domain. If the RVP is large, the image geometric distortion and resolution loss will occur, so the residual video phase in the first intermediate signal needs to be eliminated first. In this embodiment, the second intermediate signal is obtained by multiplying the demodulated signal by a complex conjugate of the corresponding reference signal (second reference signal) to eliminate the residual video phase in the demodulated signal. Residual video phase compensated signal).

S13, performing a Fourier transform of the height direction and the azimuth direction on the second intermediate signal to obtain a third intermediate signal;

In this embodiment, the second intermediate signal is subjected to a Fourier transform of height and azimuth in sequence, and a corresponding non-uniform three-dimensional spectrum signal can be obtained.

Preferably, after the height intermediate Fourier transform is performed on the second intermediate signal, there are coupling terms in the high frequency domain and the azimuth time domain simultaneously (the coupling term is k _{y '} vτ _n term based on the above signal), so Before the azimuthal Fourier transform, the height-transformed signal is also multiplied by a preset first filter function to remove the coupling term in the height-Fourier-transformed signal. interference. Where k _{y '} represents the wave number in the y' direction, v is the scanning speed of the antenna, τ _n = nT _x , and T _x is the transmitting pulse period (the time interval of the transmitting signals of the antennas of the adjacent two columns in the same row in the x direction), n = 0, 1, ..., N-1, N is the total number of sampling points in the x direction.

S14: performing inverse non-uniform fast Fourier transform on the third intermediate signal to obtain a three-dimensional image of the scanned target.

Preferably, before the inverse non-uniform fast Fourier transform is performed on the third intermediate signal, the third intermediate signal is further simplified by using a stationary phase principle to obtain a reduced signal. Since the complex exponential imaginary part of the integrand is a sinusoidal function, its corresponding integral value in the integral interval is zero. The real and cosine functions of the real part of the cosine function cancel each other out, and the integral value is close to zero. Therefore, the phase change is small only in the vicinity of the corresponding angle derivative zero, and the phase value stays for a long time to make the integral significantly non-zero. This point is the stationary phase point. Based on this principle, the integral form after the Fourier transform can be used. Simplification.

Further, in the embodiment of the present invention, the simplified signal is filtered to improve the signal to noise ratio. For example, the simplification signal may be filtered by a filter function determined by the distance from the center of the antenna aperture to the center of the scene of the scanned object to correct the distance curvature of the scatter point in the simplified signal, thereby improving the signal of the signal. Noise ratio.

Preferably, the simplified signal can be filtered by the following second filter function:

Where k _{x '} , k _{y '} denote the wave number in the x', y' direction, respectively, k _r is the total wave number; R _ref is the distance from the center of the antenna aperture to the center of the scene of the scanned object.

In this embodiment, the center of the scene of the scanned object is set as the origin of the coordinate system, and the position coordinates of the center of the antenna aperture are represented by (x', y', z'), and (x, y, z) represents the target of the scanned object. Position coordinates. Since (x', y', z') is the same as the coordinate system of (x, y, z), the two can be interchanged, that is, the x' direction, that is, the x direction, in the practice of the present invention. The y' direction is the y direction. By observation, we can find that (x, y, z) and

Is a Fourier transform pair, where k _x , k _y , k _z represent the wavenumbers in the x, y, and z directions, respectively, and k _r is the total wave number. Therefore, in the actual imaging process, uniform sampling data is obtained by discrete equal interval sampling in the spatial domain and the frequency domain, and after corresponding two-dimensional Fourier transform and filtering processing, the obtained signals are at k _x , k _y , k _{r .} The wavenumber domain is equally spaced, but corresponds to the z direction

The domains are not equally spaced. At this time, to reconstruct the image by Fourier transform, the signal must be homogenized first. In order to achieve this goal, the traditional three-dimensional imaging algorithm re-samples in the corresponding frequency domain, and then combines the interpolation operation to convert the signal into an equally spaced k _x , k _y , k _z wave number domain grid, and then through the integral operation The single target signal is extended to a surface or spatial target, and finally the signal containing k _x , k _y , k _z is passed through a three-dimensional inverse Fourier transform to reconstruct a three-dimensional image of the scanned object. It is seen, conventional three-dimensional imaging algorithm, the need to non-uniform three-dimensional linear interpolation operation spectrum signals, the signal obtained after the k _x, k _y, k _z wavenumber domain uniformly distributed to the three-dimensional inverse Fourier transform Reconstruct the corresponding 3D image. However, since the reconstruction of the three-dimensional image requires high precision for the linear interpolation operation, and the conventional linear interpolation operation requires repeated repetitions in the height direction and the azimuth direction, the imaging takes a long time.

In response to this shortcoming, the embodiment of the present invention directly homogenizes the signal by inverse non-uniform fast Fourier transform, which replaces the two operations of linear interpolation operation and three-dimensional inverse Fourier transform, and can realize three-dimensional more quickly. Reconstruction of the image.

Further, a three-dimensional image reconstruction method according to the above embodiment of the present invention will be described below by taking a security imaging system based on planar aperture three-dimensional imaging as an example. Since the synthesis of the synthetic aperture in the general planar aperture three-dimensional imaging includes two steps, that is, the lateral electronic scanning of the one-dimensional linear array and the longitudinal mechanical scanning of the linear array, in the embodiment of the present invention, the selected antenna is a one-dimensional linear array. The antenna The working mode is a combination of horizontal electronic scanning and vertical mechanical scanning.

In the above-mentioned security imaging system based on planar aperture three-dimensional imaging, the center of the scene of the scanned object is set as the origin of the coordinate system, and the position coordinates of the center of the antenna aperture are represented by (x', y', z'), , y, z) represents the position coordinates of the scanned object, and the reflection coefficient of the scanned object is represented by σ(x, y, z). Set the transmit signal of the antenna to the chirp signal s _t (t), which is expressed as:

Where f ₀ is the center frequency of the transmitted signal and K is the modulation frequency of the frequency modulated signal.

The s _T (t-τ _d ) is used to represent the transmitted signal at time t-τ _d . Correspondingly, the acquired original echo signal s _R (x', y'; t) can be expressed as:

s _R (x', y'; t) = σ(x, y, z) s _T (t-τ _d );

Where τ represents the transmission time of the transmitted signal, τ _d represents the time difference between the emission time of the transmitted signal and the reception time of the corresponding echo signal, and R(τ) is the instantaneous distance between the center of the antenna aperture and the scanned target at time τ R(τ+τ _d ) represents the instantaneous distance between the center of the antenna aperture and the object being scanned at τ+τ _d , and c is the speed of light.

It can be understood that since the distance between the center of the antenna aperture and the scanned target is usually very close in the security imaging system, there is still

Based on the above application scenario, the three-dimensional image reconstruction method of the present invention includes the following processes:

In the first step, the collected original echo signal s _R (x', y'; t) is subjected to demodulation processing. The process is as follows:

The transmitting signal is used as a local oscillator signal, and after a delay processing with a time length of τ _c , as a demodulation reference signal, specifically:

s _L (t)=exp(j2πf ₀ (t-τ _c )+jπK(t-τ _c ) ² );

The conjugate mixing of the demodulated reference signal s _L (t) with the original echo signal s _R (x', y'; t) can obtain the first intermediate signal as:

Process 2, eliminating residual video phase (RVP) present in the first intermediate signal.

After demodulation, a time delay occurs between different frequency components, which is not aligned in time, and thus generates a redundant phase, that is, a residual video phase RVP, in the frequency domain. If the item is too large, it will cause geometric distortion of the reconstructed image and loss of image resolution, and the RVP item will bring a lot of inconvenience to subsequent processing, so the RVP item is removed before performing subsequent processing. In this embodiment, the first intermediate signal is multiplied by a complex conjugate of the preset second reference signal to cancel the residual video phase in the first intermediate signal, and the second reference signal is:

s _c (t)=exp(-jπK(t-τ _c ) ² );

Multiplying the complex conjugate of the reference signal with the first intermediate signal to obtain the compensated signal (ie, the second intermediate signal) is:

In the third process, the second intermediate signal is subjected to a Fourier transform of the height direction and the azimuth direction; wherein the height direction and the azimuth direction can be referred to the coordinate system shown in FIG. 2 .

First, the emission time of the original transmitted signal needs to be expressed as τ = τ _n + τ _m + t = nT _x + mT _y + t. Wherein, T _x and T _y are respectively a transmission pulse period (a time interval of a transmission signal of an antenna of two adjacent columns in the same row) and a sampling period in a y direction (a time interval of a transmission signal of an antenna of two adjacent rows of the same column), n =0,1,...,N-1;m=0,1,...,M-1,N is the number of antenna array units (ie the total number of sampling points in the x direction), M is the total number of sampling points in the y direction, τ _m The total sampling time for the y direction.

Substituting the above transmission time representation into the second intermediate signal

In the expression, a two-dimensional Fourier transform is performed on the signal along the x' direction and the y' _m (y' _m = vτ _m = vmT _y ) direction to obtain a third intermediate signal:

Where R _c represents the reference distance corresponding to the demodulation reference signal, that is, the distance of the current transmitting antenna to the center of the scene of the scanned object, R _c =cτ _c /2.

Substituting f = K(t - τ _c ) into the expression of the third intermediate signal and solving it by the stationary phase principle, ie at the phase Φ(k _x' , k _{y '} , f; x', y' _m , τ _n ) The first-order partial differential-zero stationary phase point solves the phase, including:

Obtaining a phase point

The value corresponding to x' ₀ is substituted into Φ(k _x' , k _y' , f; x', y' _m , τ _n ) to obtain the reduced signal:

In the fourth process, the simplified signal is filtered by the second filter function related to R _ref to correct the distance curvature of the scatter point of the simplified signal, thereby improving the signal to noise ratio of the signal; the second filter function Can be:

k _{x '} , k _{y '} denotes the wave number in the x', y' direction, respectively, k _r is the total wave number; R _ref is the distance from the center of the antenna aperture to the center of the scene of the scanned object, that is, the reference distance during the focusing process;

After filtering, the signal can be obtained:

Where R ₀ = -z', R ₀ represents the distance from the antenna to the origin of the coordinate, and v is the scanning speed of the antenna.

In the above-described Fourier transform of the height direction and the azimuth direction, since the intermediate signal has both the high frequency domain and the azimuth time domain k _{y '} vτ _n term interference, after the height Fourier transform, Before the azimuthal Fourier transform, the height-transformed signal is multiplied by the first filter function to remove the k _y' vτ _n term interference in the height-to-Fourier transformed signal; The first filter function is:

Where y' _m = vτ _m , k _{y '} represents the wave number in the y' direction, k _r is the total wave number; R _c represents the reference distance corresponding to the demodulation reference signal; τ _n = nT _x , T _x is the transmitting pulse The period, n=0, 1, ..., N-1, N is the total number of sampling points in the x direction.

After performing the azimuthal Fourier transform, the azimuth Fourier transformed signal is multiplied by the second filter function to correct the distance of the scattering point toward the bend.

In the fifth process, the signal obtained in the fourth process is subjected to inverse non-uniform fast Fourier transform, thereby obtaining a three-dimensional image of the scanned object.

In the embodiment of the present invention, since the coordinate systems of (x', y', z') and (x, y, z) are the same, the two can be interchanged, and it can be found by observing the signal processed by the process four filtering, (x, y, z) and

Is the Fourier transform pair. In the actual imaging process, uniform sampling data can be obtained by discrete equally spaced sampling in the spatial domain and the frequency domain, and after the above two-dimensional Fourier transform and filtering process, the signal is in the k _x , k _y , k _r domain. Is equally spaced, but in the z direction

The domains are not equally spaced. The embodiment of the present invention processes the signal obtained by the fourth process by using the non-uniform fast Fourier transform instead of the interpolation operation and the inverse Fourier transform, and the reconstruction of the three-dimensional image can be realized more quickly than the conventional imaging method.

In the embodiment of the present invention, the method obtained for the fourth process is

The non-equally spaced signals in the domain are processed by the inverse non-uniform fast Fourier transform algorithm to obtain a three-dimensional reconstructed image of the scanned object. The specific process includes:

The domain non-uniform signal is subjected to one-dimensional non-uniform inverse Fourier transform, and then the obtained signal is subjected to two-dimensional inverse Fourier transform, and finally a three-dimensional reconstructed image is obtained.

Among them, the one-dimensional non-uniform inverse Fourier transform process is:

For non-uniform signals x _n , n = 0, 1, ... N-1, the corresponding Fourier transform is:

In order to obtain a uniformly distributed X(ω), the interpolation coefficient {u _jk } needs to be calculated before the Fourier coefficient is obtained, and the Fourier coefficient calculation formula can be obtained:

_l l [tau] represents a Fourier coefficients, interpolation coefficients {u _jk} related to the total number of multiples of the difference, e.g. 2-fold difference, the interpolation coefficients {u _jk} is always 2N.

Uniform Fourier transform using the above Fourier coefficients:

By performing the scaling process on the above formula, a uniformly distributed signal X _j can be obtained, that is,

Where s _j represents a scaling factor.

Therefore, applying the above process to the embodiment of the present invention can be abbreviated as:

S _F (k _x' , k _y' , z; R _c )=INUFFT _z (S _F (k _x' , k _y' , k _r ; R _c ))

Then, the signal S _F (k _x' , k _{y '} , z; R _c ) is inverse Fourier transformed along the x, y direction to obtain a three-dimensional reconstructed image of the scanned object:

f(x, y, z) = IFFT _{x, y} (S _F (k _x' , k _y' , z; R _c )).

The embodiment of the invention can complete the process from the non-uniformly distributed frequency domain signal to the three-dimensional image reconstruction by the inverse non-uniform fast Fourier transform algorithm, which is an important improvement to the traditional algorithm. Shorten the time required to reconstruct a 3D image while improving the accuracy of the reconstructed image.

It should be noted that this algorithm can be applied not only to the planar synthetic aperture 3D imaging algorithm, but also to scenes such as cylindrical synthetic aperture 3D imaging.

It should be noted that, for the foregoing method embodiments, for the sake of brevity, they are all described as a series of action combinations, but those skilled in the art should understand that the present invention is not limited by the described action sequence, because In the present invention, certain steps may be performed in other orders or simultaneously.

Based on the same idea as the three-dimensional image reconstruction method based on synthetic aperture radar imaging in the above embodiment, the present invention also provides a three-dimensional image reconstruction apparatus based on synthetic aperture radar imaging, which can be used to perform the above-described three-dimensional image based on synthetic aperture radar imaging. Reconstruction method. For the convenience of description, in the structural schematic diagram of the embodiment of the three-dimensional image reconstruction apparatus based on synthetic aperture radar imaging, only the parts related to the embodiment of the present invention are shown, and those skilled in the art can understand that the illustrated structure does not constitute the apparatus. The definition may include more or fewer components than those illustrated, or some components may be combined, or different component arrangements.

FIG. 3 is a schematic structural diagram of a three-dimensional image reconstruction apparatus based on synthetic aperture radar imaging according to an embodiment of the present invention; as shown in FIG. 3, the three-dimensional image reconstruction apparatus based on synthetic aperture radar imaging of the present embodiment includes: a demodulation module 310, the compensation module 320, the compression module 330 and the image reconstruction module 340, each module is as follows:

The demodulation module 310 is configured to use a transmit signal of the antenna as a local oscillator signal, and perform demodulation processing on the original echo signal reflected back by the collected scanned target to obtain a first intermediate signal;

Preferably, the demodulation module 310 specifically includes: a delay submodule for transmitting the antenna The signal is used as a local oscillator signal, and the local oscillator signal is subjected to delay processing to obtain a corresponding demodulation reference signal; and a demodulation submodule is configured to reflect the demodulated reference signal and the collected scanned target back The original echo signal is conjugate-mixed to obtain a first intermediate signal.

The compensation module 320 is configured to cancel the residual video phase in the first intermediate signal to obtain a second intermediate signal;

The compression module 330 is configured to sequentially perform a height direction and an azimuth Fourier transform on the second intermediate signal to obtain a third intermediate signal;

The image reconstruction module 340 is configured to perform inverse non-uniform fast Fourier transform on the third intermediate signal to obtain a three-dimensional image of the scanned target.

Preferably, the image reconstruction module 340 specifically includes: a simplification solution sub-module, configured to simplify the third intermediate signal by using a stationary phase principle to obtain a reduced signal; and perform the simplification signal Filtering processing to improve the signal-to-noise ratio; and an image reconstruction sub-module for performing inverse non-uniform fast Fourier transform on the filtered processing signal output by the simplification solving sub-module to obtain a three-dimensional image of the scanned target .

It should be noted that, in the embodiment of the above-described three-dimensional image reconstruction apparatus based on synthetic aperture radar imaging, the information interaction, the execution process, and the like between the modules are based on the same concept as the foregoing method embodiments of the present invention. The technical effects of the present invention are the same as those of the foregoing method embodiments of the present invention. For details, refer to the description in the method embodiment of the present invention, and details are not described herein again.

In addition, in the embodiment of the above-described three-dimensional image reconstruction apparatus based on synthetic aperture radar imaging, the logical division of each functional module is merely an example, and the actual application may be implemented according to requirements, for example, according to configuration requirements of corresponding hardware or software implementation. For the convenience of consideration, the above-mentioned function allocation is completed by different functional modules, that is, the internal structure of the three-dimensional image reconstruction device based on synthetic aperture radar imaging is divided into different functional modules to complete all or part of the functions described above. Each of these functions The module can be implemented in the form of hardware or in the form of a software function module.

It will be understood by those skilled in the art that all or part of the processes in the above embodiments may be implemented by a computer program to instruct related hardware, and the program may be stored in a computer readable storage medium as Independent product sales or use. The program, when executed, may perform all or part of the steps of an embodiment of the methods described above. The storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

In the above embodiments, the descriptions of the various embodiments are all focused, and the parts that are not detailed in a certain embodiment can be referred to the related descriptions of other embodiments. It will be understood that the terms "first", "second", and the like, as used herein, are used herein to distinguish an object, but these are not limited by these terms.

The above-described embodiments are merely illustrative of several embodiments of the invention and are not to be construed as limiting the scope of the invention. It should be noted that a number of variations and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be determined by the appended claims.

Claims

A three-dimensional image reconstruction method based on synthetic aperture radar imaging, which comprises:

Using the transmitted signal of the antenna as a local oscillator signal, performing demodulation processing on the original echo signal reflected back by the acquired scanned target to obtain a first intermediate signal;

Eliminating the residual video phase in the first intermediate signal to obtain a second intermediate signal;

Performing a Fourier transform of the height direction and the azimuth direction on the second intermediate signal to obtain a third intermediate signal;

Performing an inverse non-uniform fast Fourier transform on the third intermediate signal to obtain a three-dimensional image of the scanned object.
The method for reconstructing a three-dimensional image based on synthetic aperture radar imaging according to claim 1, wherein the transmitting signal of the antenna is used as a local oscillator signal, and the original echo signal reflected back by the collected scanned object is subjected to demodulation processing. , get the first intermediate signal, including:

Taking the transmitting signal of the antenna as a local oscillator signal, delaying the local oscillator signal to obtain a corresponding demodulation reference signal;

The demodulated reference signal is conjugate-mixed with the original echo signal reflected back from the acquired scanned target to obtain a first intermediate signal.
The three-dimensional image reconstruction method based on synthetic aperture radar imaging according to claim 2, wherein the transmission signal is a chirp signal:

The corresponding original echo signals are:

s R (x', y'; t) = σ(x, y, z) s T (t-τ d ),

Where f 0 is the center frequency of the transmitted signal, K is the modulation frequency of the FM signal; (x', y', z') is the position coordinate of the center of the antenna aperture, and (x, y, z) is the position of the scanned target The coordinates, σ(x, y, z) are the reflection coefficients of the scanned target, and τ d represents the time difference between the time when the transmitted signal is emitted and the receiving time of the corresponding echo signal, and s T (t-τ d ) is t- The transmitted signal at time τ d , τ represents the time of emission of the transmitted signal, R(τ) is the instantaneous distance between the center of the antenna aperture and the scanned target at time τ, and R(τ+τ d ) represents the antenna at time τ+τ d The instantaneous distance between the center of the aperture and the object being scanned, c is the speed of light;

Performing delay processing on the transmitted signal, using a parameter τ c to represent a delay time, and obtaining a corresponding demodulation reference signal; conjugate mixing the demodulated reference signal with the original echo signal to obtain a first intermediate signal:
The three-dimensional image reconstruction method based on synthetic aperture radar imaging according to claim 3, wherein the residual video phase in the first intermediate signal is eliminated, and the second intermediate signal is obtained, including:

Multiplying the first intermediate signal by a complex conjugate of the preset second reference signal to cancel the residual video phase in the first intermediate signal to obtain a second intermediate signal;

Wherein the second reference signal is:

s c (t)=exp(-jπK(t-τ c ) 2 );

The second intermediate signal obtained is:
The method for reconstructing a three-dimensional image based on synthetic aperture radar imaging according to claim 3, wherein the step of performing a Fourier transform of the height direction and the azimuth direction on the second intermediate signal comprises:

The height-transformed signal is multiplied by a predetermined first filter function to remove interference from the height- and azimuth coupling terms in the signal.
The method according to claim 5, wherein the first filter function is:

Where y' m = vτ m , k y ' represents the wave number in the y' direction, k r is the total wave number; R c represents the reference distance corresponding to the demodulation reference signal; τ n = nT x , T x is the transmitting pulse The period, n=0, 1, ..., N-1, N is the total number of sampling points in the x direction.
The three-dimensional image reconstruction method based on synthetic aperture radar imaging according to claim 5, wherein the performing the inverse non-uniform fast Fourier transform on the third intermediate signal further comprises:

The third intermediate signal is simplified by the stationary phase principle to obtain a reduced signal; and the reduced signal is filtered to correct the distance curvature of the scattered point in the reduced signal.
The three-dimensional image reconstruction method based on synthetic aperture radar imaging according to claim 7, wherein the filtering the signal after the simplification comprises:

Filtering the reduced signal by a preset second filter function, the second filter function is:

k x ' , k y ' denote the wave number in the x', y' direction, respectively, k r is the total wave number; R ref is the distance from the center of the antenna aperture to the center of the scene of the scanned object.
A three-dimensional image reconstruction device based on synthetic aperture radar imaging, comprising:

The demodulation module is configured to use the transmit signal of the antenna as a local oscillator signal, and perform demodulation processing on the original echo signal reflected back by the acquired scanned target to obtain a first intermediate signal;

a compensation module, configured to cancel a residual video phase in the first intermediate signal to obtain a second intermediate signal;

a compression module, configured to perform a Fourier transform on the second intermediate signal in a height direction and an azimuth direction to obtain a third intermediate signal;

The image reconstruction module is configured to perform inverse non-uniform fast Fourier transform on the third intermediate signal to obtain a three-dimensional image of the scanned target.
The three-dimensional image reconstruction device based on synthetic aperture radar imaging according to claim 9, wherein the demodulation module comprises:

a delay sub-module, configured to use the transmit signal of the antenna as a local oscillator signal, and delay processing the local oscillator signal to obtain a corresponding demodulation reference signal;

a demodulation submodule, configured to perform conjugate mixing on the demodulated reference signal and the original echo signal reflected back by the collected scanned target to obtain a first intermediate signal;

The image reconstruction module includes:

The simplification solving sub-module is configured to simplify the third intermediate signal by using a stationary phase principle to obtain a simplified signal; and filter the simplified signal to improve a signal to noise ratio thereof;

The image reconstruction sub-module is configured to perform inverse non-uniform fast Fourier transform on the signal output by the simplification solving sub-module to obtain a three-dimensional image of the scanned target.