CN111580107B - Radio frequency interference suppression method and device for SAR echo signal and imaging method - Google Patents
Radio frequency interference suppression method and device for SAR echo signal and imaging method Download PDFInfo
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- CN111580107B CN111580107B CN202010640070.9A CN202010640070A CN111580107B CN 111580107 B CN111580107 B CN 111580107B CN 202010640070 A CN202010640070 A CN 202010640070A CN 111580107 B CN111580107 B CN 111580107B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/36—Means for anti-jamming, e.g. ECCM, i.e. electronic counter-counter measures
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
Abstract
The invention discloses a method, a device and an imaging method for inhibiting radio frequency interference of SAR echo signals, wherein the method for inhibiting the radio frequency interference of the SAR echo signals comprises the following steps: carrying out distance Fourier transform on the received initial echo signal to obtain an initial frequency spectrum; performing notch processing on the initial frequency spectrum based on a preset notch interference detection threshold value to obtain a notch processed frequency spectrum; filtering the frequency spectrum subjected to notch processing to obtain a filtered frequency spectrum; performing spectrum extrapolation processing on the filtered spectrum based on a preset prediction model to obtain forward extrapolation spectrum data and backward extrapolation spectrum data; carrying out reconstruction processing based on the forward extrapolation frequency spectrum data, the backward extrapolation frequency spectrum data and the filtered frequency spectrum to obtain a target frequency spectrum without loss; and recovering the frequency modulation information of the distance direction signal based on the target frequency spectrum without deletion to obtain a target echo signal which inhibits interference and has a complete frequency spectrum. The invention can accurately inhibit the radio frequency interference.
Description
Technical Field
The invention relates to the technical field of crossing of aerospace and microwave remote sensing, in particular to a method and a device for inhibiting radio frequency interference of SAR echo signals and an imaging method.
Background
The SAR (Synthetic Aperture Radar) technology is an active space and aviation remote sensing means, the microwave imaging technology has the characteristics of all-weather and all-weather work, has wide application in the aspects of environmental protection, disaster monitoring, ocean observation, resource exploration, fine agriculture, geological mapping and the like, and is one of the most important means for high-grade earth observation and global resource management at present. However, SAR is susceptible to RFI (Radio Frequency Interference) in a complex electromagnetic environment, especially in low bands (L-band, P-band), thereby degrading image quality and affecting target detection and image recognition.
The operating Frequency of the low-Frequency SAR is a VHF (Very High Frequency) or UHF (Ultra High Frequency) Frequency band, which is first allocated to a ground broadcast television System, a communication System, a GPS (Global Positioning System) and a ground alert radar by ITU (International Telecommunications Union), even if the anti-interference technology is considered in the design of the SAR System, a large number of interference signals still enter a receiver of the SAR System, and finally the imaging quality of the SAR System is reduced.
The existing RFI suppression methods mainly comprise: frequency domain notch method, subspace decomposition method, interference extraction method, etc. Since the conventional frequency domain notch method is easy to cause the loss of useful signals, and the subspace projection method is excessively dependent on the orthogonality of subspaces, when the power of interference signals is large, the subspace misjudgment can be caused. And the calculation complexity of the interference extraction method is too high, the mathematical model of the radio frequency interference is quite complex, model mismatching can occur, model parameter estimation errors are generated, and further the RFI estimation is inaccurate.
Disclosure of Invention
The embodiment of the invention aims to provide a method and a device for inhibiting radio frequency interference of SAR echo signals and an imaging method, which are used for solving the problem that the radio frequency interference inhibition in the prior art is not accurate enough.
In order to solve the technical problem, the embodiment of the application adopts the following technical scheme: a radio frequency interference suppression method of SAR echo signals comprises the following steps:
carrying out distance Fourier transform on the received initial echo signal to obtain an initial frequency spectrum corresponding to the initial echo signal;
performing notch processing on the initial frequency spectrum based on a preset notch interference detection threshold value to obtain a notch processed frequency spectrum;
filtering the frequency spectrum subjected to notch processing to obtain a filtered frequency spectrum;
performing spectrum extrapolation processing on the filtered spectrum based on a preset prediction model to obtain forward extrapolation spectrum data and backward extrapolation spectrum data;
reconstructing the forward extrapolated spectrum data, the backward extrapolated spectrum data and the filtered spectrum to obtain a target spectrum without loss;
and recovering the frequency modulation information of the distance direction signal based on the target frequency spectrum without deletion to obtain a target echo signal which inhibits interference and has a complete frequency spectrum.
Optionally, the notching the initial spectrum based on a preset notch interference detection threshold value to obtain a notched spectrum, specifically including:
performing notch processing on the initial frequency spectrum based on a preset first notch interference detection threshold value to obtain a first frequency spectrum;
and performing notch processing on the first frequency spectrum based on a preset second notch interference detection threshold value to obtain the frequency spectrum after notch processing.
Optionally, the reconstructing based on the forward-extrapolated spectrum data, the backward-extrapolated spectrum data, and the filtered spectrum to obtain a target spectrum without loss specifically includes:
carrying out missing spectrum reconstruction based on the forward extrapolation frequency spectrum and the backward extrapolation frequency spectrum to obtain a missing spectrum;
and splicing the filtered frequency spectrum and the missing frequency spectrum to obtain the target frequency spectrum without missing.
Optionally, the prediction model comprises an AR linear prediction model; the method further comprises the step of constructing the AR linear prediction model, and the method specifically comprises the following steps:
determining the order of the AR linear prediction model based on the number of the distance direction sampling points;
calculating coefficients of the AR linear prediction model based on a preset calculation method;
and constructing the AR linear prediction model based on the order and the coefficient.
Optionally, the preset method includes one or more of the following: berger's algorithm and improved covariance algorithm.
An embodiment of the present application provides a radio frequency interference suppression device for an SAR echo signal, including:
the transformation module is used for carrying out distance Fourier transformation on the received initial echo signal to obtain an initial frequency spectrum corresponding to the initial echo signal;
the notch processing module is used for carrying out notch processing on the initial frequency spectrum based on a preset notch interference detection threshold value to obtain a frequency spectrum after notch processing;
the filtering processing module is used for filtering the frequency spectrum subjected to the notch processing to obtain a filtered frequency spectrum;
the spectrum extrapolation processing module is used for carrying out spectrum extrapolation processing on the filtered spectrum based on a preset prediction model to obtain forward extrapolation spectrum data and backward extrapolation spectrum data;
the reconstruction module is used for carrying out reconstruction processing on the basis of the forward extrapolation frequency spectrum data, the backward extrapolation frequency spectrum data and the filtered frequency spectrum to obtain a target frequency spectrum without loss;
and the recovery module is used for recovering the frequency modulation information of the distance direction signal based on the target frequency spectrum without deletion to obtain a target echo signal which inhibits interference and has a complete frequency spectrum.
Optionally, the notching module is specifically configured to:
performing notch processing on the initial frequency spectrum based on a preset first notch interference detection threshold value to obtain a first frequency spectrum;
and performing notch processing on the first frequency spectrum based on a preset second notch interference detection threshold value to obtain the frequency spectrum after notch processing.
Optionally, the reconstruction module is specifically configured to:
carrying out missing spectrum reconstruction based on the forward extrapolated spectrum and the backward extrapolated spectrum to obtain a missing spectrum;
and splicing the filtered frequency spectrum and the missing frequency spectrum to obtain the target frequency spectrum without missing.
Optionally, the prediction model comprises an AR linear prediction model; the apparatus further comprises a building module for building the AR linear prediction model, the building module being specifically configured to:
determining the order of the AR linear prediction model based on the number of the distance direction sampling points;
calculating coefficients of the AR linear prediction model based on a preset calculation method;
and constructing the AR linear prediction model based on the order and the coefficient.
An embodiment of the present application provides an imaging method, including the steps of:
obtaining corresponding two-dimensional SAR data based on a target echo signal obtained by the SAR echo signal radio frequency interference suppression method;
and imaging the target object by using the two-dimensional SAR data.
According to the method, the echo signals are subjected to notch processing and the spectrum extrapolation processing is performed on the notched spectrum, so that the radio frequency interference can be accurately inhibited, the problem that the radio frequency interference inhibition in the prior art is not accurate enough is solved, meanwhile, the technical defect that details of the traditional notch method are lost is overcome, and the method is beneficial to subsequent imaging based on SAR data.
Drawings
Fig. 1 is a flowchart of a method for suppressing radio frequency interference of a SAR echo signal according to an embodiment of the present invention;
fig. 2 is a block diagram of an apparatus for suppressing radio frequency interference of SAR echo signals according to another embodiment of the present invention;
FIG. 3 is a flow chart of another method of implementing an imaging method of the present invention.
Detailed Description
Various aspects and features of the present application are described herein with reference to the accompanying drawings.
It should be understood that various modifications may be made to the embodiments of the present application. Accordingly, the foregoing description should not be construed as limiting, but merely as exemplifications of embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the application.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with a general description of the application given above and the detailed description of the embodiments given below, serve to explain the principles of the application.
These and other characteristics of the present application will become apparent from the following description of preferred forms of embodiment, given as non-limiting examples, with reference to the attached drawings.
It should also be understood that, although the present application has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of application, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.
The above and other aspects, features and advantages of the present application will become more apparent in view of the following detailed description when taken in conjunction with the accompanying drawings.
Specific embodiments of the present application are described hereinafter with reference to the accompanying drawings; however, it is to be understood that the disclosed embodiments are merely exemplary of the application, which can be embodied in various forms. Well-known and/or repeated functions and mechanisms have not been described in detail so as not to obscure the present application with unnecessary or unnecessary detail. Therefore, specific mechanical and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present application in virtually any appropriately detailed structure.
The specification may use the phrases "in one embodiment," "in another embodiment," "in yet another embodiment," or "in other embodiments," which may each refer to one or more of the same or different embodiments in accordance with the application.
The embodiment of the invention provides a radio frequency interference suppression method of an SAR echo signal, which comprises the following steps:
step S101, carrying out distance Fourier transform on the received initial echo signal to obtain an initial frequency spectrum corresponding to the initial echo signal;
in the specific implementation process, the step is to perform distance-to-fourier transform on a received initial echo signal, that is, an SAR echo signal X (N), to obtain an echo signal X (N) of an azimuth time domain and distance frequency domain, that is, an initial spectrum, which may also be called an echo distance line spectrum, where-N r /2≤n≤N r /2-1，N r Representing the number of distance-to-sample points.
Step S102, carrying out notch processing on the initial frequency spectrum based on a preset notch interference detection threshold value to obtain a notch processed frequency spectrum;
in the specific implementation process of the step, the initial frequency spectrum needs to be subjected to notch processing based on a preset first notch interference detection threshold value to obtain a first frequency spectrum; and then carrying out notch processing on the first frequency spectrum based on a preset second notch interference detection threshold value to obtain the frequency spectrum after notch processing. I.e. the initial spectrum is notched twice.
More specifically, first, a first threshold notch is performed on an initial frequency spectrum, and the specific steps are as follows: calculating a first notch interference detection threshold lambda 1 The calculation formula is as follows:
λ 1 ＝μ 1 +σ 1 (1)
wherein, mu 1 Means representing the spectrum of the echo range line; x (n) represents a frequency spectrum of the echo distance line signal, i.e., an initial frequency spectrum; sigma 1 A standard deviation representing the spectrum of the echo range line; n is a radical of hydrogen r The number of sampling points representing the distance direction; n is a radical of 0 Representing the number of transition zone points.
After calculating to obtain lambda by using the above calculation formula 1 Then, it can be based on λ 1 Carrying out first trapping on the initial frequency spectrum X (n), namely meeting the condition that | X (n) | > lambda 1 The signal sampling point is set to zero to obtain a first frequency spectrum X of the echo signal after the primary trap 1 (n)：
Wherein X (n) represents the frequency spectrum of the echo distance line, λ 1 Representing the threshold value of the first notch, | · | representing the absolute value of the signal.
A first frequency spectrum X is obtained 1 (n), then performing a second threshold notching on the echo signal, specifically comprising the following steps: first, a second notch interference detection threshold value lambda is calculated 2 The calculation formula is as follows:
λ 2 ＝μ 2 +σ 2 (5)
wherein, mu 2 Representing the mean of the non-zero frequency spectrum after the first notch; x 1 (n) a first spectrum which is a spectrum of the echo signal after the first notch; sigma 2 Representing the standard deviation of the non-zero frequency spectrum after the first notch; n is a radical of 1 The number of interference frequency points is set to zero after the first time of trap; n is a radical of hydrogen r The number of sampling points representing the distance direction; n is a radical of 0 Representing the number of transition band points.
Second notching the echo signal spectrum, i.e. meeting | X 1 (n)|＞λ 2 The signal sampling point is set to zero to obtain the frequency spectrum X of the echo signal after the secondary trap 2 (n)：
Wherein, X 1 (n) represents a spectrum of distance lines after a first notch of the echo signal, X (n) represents a spectrum of echo distance lines, and λ 2 A threshold value representing the second notch, |, represents the absolute value of the signal.
Obtaining a second notch interference detection threshold value lambda in the calculation 2 Then, it can be based on λ 2 For the first frequency spectrum X 1 (n) performing a second notching, i.e. meeting | X | 1 (n)|＞λ 2 The signal sampling point is set to zero to obtain the frequency spectrum X of the echo signal after the secondary trap processing 2 (n)。
Step S103, filtering the frequency spectrum after the notch processing to obtain a filtered frequency spectrum;
in the specific implementation process of the step, the notched frequency spectrum X is obtained 2 After (n), X can be treated 2 (n) distance matching filtering is carried out to obtain the frequency spectrum X after matching filtering 3 (n) the formula is:
X 3 (n)＝X 2 (n)·H(f) (9)
wherein, the matched filter H (f) is:
wherein rect (-) represents a rectangular window function, X 2 (n) is the frequency spectrum of the echo signal after the second-order notch, f is the range frequency, K r For distance-to-frequency modulation, B r Is the signal bandwidth.
Step S104, performing spectrum extrapolation processing on the filtered spectrum based on a preset prediction model to obtain forward extrapolation spectrum data and backward extrapolation spectrum data;
the prediction module in this step includes an AR linear prediction model. The AR linear prediction model is obtained by pre-construction, and the construction steps comprise: determining the order of the AR linear prediction model based on the number of the distance direction sampling points; calculating coefficients of the AR linear prediction model based on a preset calculation method; and constructing the AR linear prediction model based on the order and the coefficient.
More specifically, in this embodiment, before performing the spectrum extrapolation process, the order M and the coefficient a (M) of the AR linear prediction model need to be determined, so as to construct the AR linear prediction model. Namely, determining the order of the AR linear prediction model based on the number of sampling points in the distance direction, wherein the number of the sampling points in the distance direction is N r Then the order M of the AR linear prediction model is generally N r /3～N r A value between/2. The coefficients a (m) of the AR linear prediction model can be calculated using the Burg algorithm, modified covariance, and the like.
After determining the order M and the coefficients a (M) of the AR linear prediction model, it can be based on the filtered spectrum X 3 (n) extrapolating the missing frequency spectrum by using the prediction module to respectively obtain forward extrapolated frequency spectrums X 4 (n) and backward extrapolated spectrum X 5 (n) of (a). Forward extrapolated spectrum X 4 (n) and backward extrapolated spectrum X 5 (n) is calculated by using two formulas of AR linear prediction modes, wherein the formulas are as follows:
wherein, X 3 (n) represents a distance-matched filtered spectrum; m represents the order of the prediction model; a (m) represents the prediction model coefficients; a is a * (m) represents the complex conjugate of the prediction model coefficients; f. of Low,l And f Hig,l Respectively representing the lowest frequency and the highest frequency of the l-th missing spectral slot; Δ f denotes a frequency sampling interval.
Step S105, carrying out reconstruction processing based on the forward extrapolation frequency spectrum data, the backward extrapolation frequency spectrum data and the filtered frequency spectrum to obtain a target frequency spectrum without loss;
in the specific implementation process of the step, missing spectrum reconstruction needs to be performed on the basis of the forward extrapolated spectrum and the backward extrapolated spectrum to obtain a missing spectrum; and then splicing the filtered frequency spectrum and the missing frequency spectrum to obtain the target frequency spectrum without missing.
More specifically, the forward extrapolated spectrum X is obtained 4 (n) and backward extrapolated spectrum X 5 After (n), the forward extrapolated spectrum data X can be obtained 4 (n) and backward extrapolated spectrum data X 5 (n) weighting according to the following calculation formula to obtain the final result of missing data reconstruction
The calculation formula is as follows:
wherein, the first and the second end of the pipe are connected with each other,
indicating a missing spectrum; n is a radical of Low,l And N Hig,l Respectively representing the frequency points corresponding to the lowest frequency and the highest frequency of the ith missing spectrum gap; x 3 (n) represents a distance-matched filtered spectrum; m represents the order of the prediction model; a (m) represents the prediction model coefficients; a is * (m) representing the complex conjugate of the prediction model coefficients; f. of Low,l And f Hig,l Respectively representing the lowest and highest frequencies of the l-th missing spectral slot; Δ f denotes a frequency sampling interval.
In obtaining missing spectrum
Then, the missing spectrum may be based on the acquisition>
And a filtered spectrum X 3 (n) performing splicing processing by using the following formula to obtain a target frequency spectrum X without loss 6 (n) the formula is:
wherein H * (f) Is a complex conjugate of H (f), X 6 And (n) is the matched filtered signal spectrum without loss.
And S106, recovering the frequency modulation information of the distance direction signal based on the target frequency spectrum without deletion to obtain a target echo signal which inhibits interference and has a complete frequency spectrum.
The step is to obtain the target frequency spectrum X 6 After (n), the frequency modulation information of the SAR data range direction signal can be recovered through the following formula, and the target echo signal X with interference suppression and complete frequency spectrum is obtained 7 (n) the formula is:
X 7 (n)＝X 6 (n)·H * (f) (15)
wherein H * (f) Is a complex conjugate of H (f), X 6 And (n) is a target spectrum which is a signal spectrum after matching filtering without loss.
According to the method, the spectrum extrapolation is added after the secondary trap, so that the trapped spectrum is restored again, the radio frequency interference can be accurately inhibited, and the problem that the radio frequency interference inhibition is not accurate in the prior art is solved. The method not only has the advantages of the traditional method, but also makes up the defects of the traditional method, is beneficial to improving the quality of the SAR image, and improves the recognition degree of the detail part in the image. Meanwhile, the method reduces the calculation complexity and improves the operation efficiency.
Another embodiment of the present invention provides a radio frequency interference suppression device for an SAR echo signal, including:
the device comprises a transformation module 1, a processing module and a processing module, wherein the transformation module is used for carrying out distance Fourier transformation on a received initial echo signal to obtain an initial frequency spectrum corresponding to the initial echo signal;
the notching processing module 2 is used for notching the initial frequency spectrum based on a preset notching interference detection threshold value to obtain a frequency spectrum after notching processing;
a filtering processing module 3, configured to perform filtering processing on the frequency spectrum after the notch processing, so as to obtain a filtered frequency spectrum;
the spectrum extrapolation processing module 4 is used for carrying out spectrum extrapolation processing on the filtered spectrum based on a preset prediction model to obtain forward extrapolation spectrum data and backward extrapolation spectrum data;
a reconstruction module 5, configured to perform reconstruction processing based on the forward extrapolated spectrum data, the backward extrapolated spectrum data, and the filtered spectrum, to obtain a target spectrum without loss;
and the recovery module 6 is configured to recover the frequency modulation information of the range-wise signal based on the target frequency spectrum without loss, and obtain a target echo signal with interference suppression and a complete frequency spectrum.
In a specific implementation process of this embodiment, the notching processing module is specifically configured to: performing notch processing on the initial frequency spectrum based on a preset first notch interference detection threshold value to obtain a first frequency spectrum; and performing notch processing on the first frequency spectrum based on a preset second notch interference detection threshold value to obtain the frequency spectrum after notch processing.
In a specific implementation process of this embodiment, the reconstruction module is specifically configured to: carrying out missing spectrum reconstruction based on the forward extrapolation frequency spectrum and the backward extrapolation frequency spectrum to obtain a missing spectrum;
and splicing the filtered frequency spectrum and the missing frequency spectrum to obtain the target frequency spectrum without missing.
In a specific implementation process of this embodiment, the prediction model includes an AR linear prediction model; the apparatus further comprises a building module for building the AR linear prediction model, the building module being specifically configured to: determining the order of the AR linear prediction model based on the number of the distance direction sampling points; calculating coefficients of the AR linear prediction model based on a preset calculation method; and constructing the AR linear prediction model based on the order and the coefficient. The preset calculation method in the embodiment includes: berger's algorithm and improved covariance algorithm.
According to the invention, the notch processing module is used for carrying out secondary notch post-processing on the initial frequency spectrum, and the frequency spectrum extrapolation module is used for recovering the notched frequency spectrum, so that the radio frequency interference can be accurately suppressed. The method not only has the advantages of the traditional method, but also makes up the defects of the traditional method, is beneficial to improving the quality of the SAR image, and improves the recognition degree of the detail part in the image. Meanwhile, the method reduces the calculation complexity and improves the operation efficiency.
Another embodiment of the present invention provides an imaging method, including: obtaining corresponding two-dimensional SAR data based on the target echo signal obtained by the SAR echo signal radio frequency interference suppression method; and imaging the target object by using the two-dimensional SAR data. The method specifically comprises the following steps:
step S301, echo data sampling is carried out on each azimuth direction of a target object based on sampling time, and initial echo signals corresponding to each azimuth direction are obtained;
step S302, performing distance Fourier transform on each initial echo signal to obtain an initial frequency spectrum corresponding to each initial echo signal;
step S303, performing notch processing on each initial frequency spectrum based on a preset notch interference detection threshold value to obtain a notch processed frequency spectrum corresponding to each initial frequency spectrum;
step S304, filtering each of the notch-processed frequency spectrums to obtain filtered frequency spectrums corresponding to each of the notch-processed frequency spectrums;
step S305, performing spectrum extrapolation processing on each filtered spectrum based on a preset prediction model to obtain forward extrapolation spectrum data and backward extrapolation spectrum data corresponding to each filtered spectrum;
step S306, carrying out reconstruction processing based on each filtered frequency spectrum, forward extrapolation frequency spectrum data corresponding to the filtered frequency spectrum and backward extrapolation frequency spectrum data to obtain a target frequency spectrum without loss corresponding to each initial echo signal;
in step S307, frequency modulation information of the range-oriented signal is restored based on each of the target frequency spectrums without loss, and target echo signals corresponding to each of the initial echo signals are obtained.
Step S308, acquiring two-dimensional SAR data corresponding to a target object based on each target echo signal;
step S309, imaging processing is carried out based on the two-dimensional SAR data, and an SAR image of the target object is obtained.
In the implementation process of the embodiment of the present invention, the specific implementation process of steps S302 to S307 may include the steps in the method for suppressing radio frequency interference of an SAR echo signal provided in the above embodiment, and will not be described again.
The spectrum extrapolation processing is carried out on the spectrum after the secondary notch, so that the spectrum after the notch can be restored again, the radio frequency interference is accurately inhibited, the quality of the SAR image is improved, and the recognition degree of the detail part in the image is improved. Meanwhile, the method reduces the calculation complexity and improves the operation efficiency. Better imaging effect can be obtained in shorter time, namely, the imaging effect and the operation efficiency are improved simultaneously.
The above embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and the scope of the present invention is defined by the claims. Various modifications and equivalents of the invention may be made by those skilled in the art within the spirit and scope of the invention, and such modifications and equivalents should also be considered as falling within the scope of the invention.
Claims (8)
1. A radio frequency interference suppression method of SAR echo signals is characterized by comprising the following steps:
carrying out distance Fourier transform on the received initial echo signal to obtain an initial frequency spectrum corresponding to the initial echo signal;
performing notch processing on the initial frequency spectrum based on a preset notch interference detection threshold value to obtain a notch processed frequency spectrum; the method specifically comprises the following steps: performing notch processing on the initial frequency spectrum based on a preset first notch interference detection threshold value, calculating a first notch interference detection threshold value, performing first notch processing on the initial frequency spectrum based on the first notch interference detection threshold value, and obtaining a first frequency spectrum of an echo signal after the first notch processing; performing notch processing on the first frequency spectrum based on a preset second notch interference detection threshold value, calculating a second notch interference detection threshold value, and performing secondary notch processing on the first frequency spectrum based on the second notch interference detection threshold value to obtain a frequency spectrum subjected to secondary notch processing;
filtering the frequency spectrum subjected to notch processing to obtain a filtered frequency spectrum;
performing spectrum extrapolation processing on the filtered spectrum based on a preset prediction model to obtain forward extrapolation spectrum data and backward extrapolation spectrum data;
reconstructing the forward extrapolated spectrum data, the backward extrapolated spectrum data and the filtered spectrum to obtain a target spectrum without loss;
and recovering the frequency modulation information of the distance direction signal based on the target frequency spectrum without deletion to obtain a target echo signal which inhibits interference and has a complete frequency spectrum.
2. The method according to claim 1, wherein the performing reconstruction processing based on the forward-extrapolated spectrum data, the backward-extrapolated spectrum data, and the filtered spectrum to obtain a target spectrum without loss specifically includes:
carrying out missing spectrum reconstruction based on the forward extrapolated spectrum and the backward extrapolated spectrum to obtain a missing spectrum;
and splicing the filtered frequency spectrum and the missing frequency spectrum to obtain the target frequency spectrum without missing.
3. The method of claim 1, wherein the predictive model comprises an AR linear predictive model; the method further comprises the step of constructing the AR linear prediction model, and the method specifically comprises the following steps:
determining the order of the AR linear prediction model based on the number of the distance direction sampling points;
calculating coefficients of the AR linear prediction model based on a preset calculation method;
and constructing the AR linear prediction model based on the order and the coefficient.
4. The method of claim 3, wherein the predetermined calculation method comprises one or more of: berger's algorithm and improved covariance algorithm.
5. A radio frequency interference suppression device for SAR echo signals, comprising:
the transformation module is used for carrying out distance Fourier transformation on the received initial echo signal to obtain an initial frequency spectrum corresponding to the initial echo signal;
the notch processing module is used for carrying out notch processing on the initial frequency spectrum based on a preset notch interference detection threshold value to obtain a frequency spectrum after notch processing; the notching processing module is specifically configured to: performing notch processing on the initial frequency spectrum based on a preset first notch interference detection threshold value, calculating a first notch interference detection threshold value, performing first notch processing on the initial frequency spectrum based on the first notch interference detection threshold value, and obtaining a first frequency spectrum of an echo signal after the first notch processing; performing notch processing on the first frequency spectrum based on a preset second notch interference detection threshold value, calculating a second notch interference detection threshold value, and performing second notch processing on the first frequency spectrum based on the second notch interference detection threshold value to obtain a frequency spectrum subjected to secondary notch processing;
the filtering processing module is used for filtering the frequency spectrum subjected to the notch processing to obtain a filtered frequency spectrum;
the spectrum extrapolation processing module is used for carrying out spectrum extrapolation processing on the filtered spectrum based on a preset prediction model to obtain forward extrapolation spectrum data and backward extrapolation spectrum data;
a reconstruction module, configured to perform reconstruction processing based on the forward extrapolated spectrum data, the backward extrapolated spectrum data, and the filtered spectrum, to obtain a target spectrum without loss;
and the recovery module is used for recovering the frequency modulation information of the distance direction signal based on the target frequency spectrum without loss to obtain a target echo signal which inhibits interference and has a complete frequency spectrum.
6. The apparatus of claim 5, wherein the reconstruction module is specifically configured to:
carrying out missing spectrum reconstruction based on the forward extrapolation frequency spectrum and the backward extrapolation frequency spectrum to obtain a missing spectrum;
and splicing the filtered frequency spectrum and the missing frequency spectrum to obtain the target frequency spectrum without missing.
7. The apparatus of claim 5, wherein the predictive model comprises an AR linear predictive model; the apparatus further comprises a building module for building the AR linear prediction model, the building module being specifically configured to:
determining the order of the AR linear prediction model based on the number of the distance direction sampling points;
calculating coefficients of the AR linear prediction model based on a preset calculation method;
and constructing the AR linear prediction model based on the order and the coefficient.
8. An imaging method, comprising the steps of:
obtaining corresponding two-dimensional SAR data based on a target echo signal obtained by the method of any of claims 1-4;
and imaging the target object by using the two-dimensional SAR data.
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