CN112180370B - SAR range reference signal processing method and device - Google Patents
SAR range reference signal processing method and device Download PDFInfo
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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
- G01S13/9004—SAR image acquisition techniques
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- G—PHYSICS
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- 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
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- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
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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
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- G01S7/40—Means for monitoring or calibrating
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
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Abstract
The invention provides a SAR distance direction reference signal processing method and device, which mainly comprises the steps of normalizing the transmitting pulse time width of SAR linear frequency modulation signals, advancing an internal calibration response signal with time delay to an origin, and carrying out least square and orthogonal polynomial double fitting on the amplitude and phase value curves of the internal calibration reference signal to reconstruct the distance direction reference signal. The SAR range-oriented reference signal constructed by the method fits the inherent nonlinear component of the SAR positioning response signal, simultaneously suppresses random spurious and crosstalk on signal interference, can meet the requirements of numerical stability and precision as an SAR range-oriented matching function, and performs range-oriented pulse compression test on the SAR range-oriented reference signal and actual SAR echo data containing a ground corner reflector target, so that the result is close to the response effect of the ideal point target.
Description
Technical Field
The invention relates to the technical field of synthetic aperture radar (Synthetic Aperture Radar, SAR) signal processing, in particular to a SAR range-wise reference signal processing method and device.
Background
SAR is an important earth observation means and has all-day and all-weather imaging capability. Generally, the SAR radar uses a linear frequency modulation pulse as a radar transmitting signal, and a system response function of the SAR radar is used as a reference function to carry out matched filtering with SAR range echo data so as to obtain range resolution. Along with the improvement of the distance resolution, nonlinear distortion is continuously generated in a response function of the SAR system while the bandwidth of a transmitted signal is increased, so that the phenomena of peak value offset, main lobe broadening, side lobe rising, asymmetry and the like occur after pulse compression.
The SAR internal calibration is used for measuring the amplitude-phase characteristics of the radar, can work in the front, middle and later stages of an SAR data acquisition task in a time-sharing mode, and the acquired internal calibration data can reflect the actual amplitude-phase characteristics of an SAR radar receiving and transmitting channel. Therefore, the SAR positioning response signal contains the signal distortion of the SAR system, and an error compensation method is used for eliminating the influence of the signal distortion.
The error compensation method utilizes the numerical deviation between the SAR internal calibration response signal and the ideal linear frequency modulation signal to realize amplitude correction and phase compensation during distance pulse compression. In signal processing, the amplitude and phase error data replicas of the SAR-defined response signal may be used directly or the error data may be fitted to a quadrature (legendre) polynomial model.
However, this method requires either the acquisition of amplitude and phase error data or the creation of an error model, and is complex in algorithm and limited in compensation effect. Preliminary application and evaluation in series of satellite-borne SAR systems such as Terra SAR-X and Sentinel-1A show that: due to the nonlinearity of radar receiving and transmitting channels and the existence of image interference, the fitting data of the amplitude and the phase of 5-order polynomials is imperfect, the sidelobe level of a target is improved, and the requirements of SAR distance matching function on logarithmic stability and accuracy cannot be met.
Disclosure of Invention
First, the technical problem to be solved
In view of this, in order to overcome at least one aspect of the above problems, the present invention provides a SAR ranging reference signal processing method and apparatus thereof.
(II) technical scheme
In one aspect, the present invention provides a method for processing a SAR range reference signal, including: performing time normalization on SAR emission pulse width to obtain SAR linear frequency modulation signals, and performing centering zero padding on the SAR linear frequency modulation signals to the number of distance pulse compression processing points to obtain linear frequency modulation reference signals; extracting SAR internal calibration loop sample data from SAR original data, obtaining an initial internal calibration loop response signal, pre-zeroing the initial internal calibration loop response signal to the number of distance pulse compression processing points, and finishing mean value processing to obtain an internal calibration response signal; performing pulse compression on the linear frequency modulation reference signal and the internal calibration response signal to obtain an internal calibration pulse pressure signal, subtracting the peak position of the internal calibration pulse pressure signal from the ideal pulse pressure position of the linear frequency modulation signal to obtain a time delay amount, performing prepositioning zero padding on the internal calibration response signal to complete time delay compensation, and constructing the internal calibration reference signal; performing double polynomial fitting of least square and orthogonal polynomials on the internal calibration reference signals to obtain a second double fitting polynomial of amplitude and phase; constructing a polynomial constant value model based on the amplitude and phase second fitting polynomial, and centering zero padding the polynomial constant value model to obtain a distance reference signal; dividing the SAR original data into scenes to obtain scene SAR original echo data, and sequentially centering and zero-filling distance data in the scene SAR original data to form standard scene SAR echo data; and sequentially performing range-wise pulse compression on the standard scene SAR echo data and the range-wise reference signal to obtain a range-Doppler image.
Optionally, the performing time normalization on the SAR transmission pulse width to obtain a SAR chirp signal includes: constructing the SAR chirp signal as follows:
wherein B is SAR system bandwidth; t is the emission pulse width; t is the time, the time step delta t=2/(t.samp), samp is the sampling frequency, the chirp signal h ref Sample points N of (t) rr ＝T·Samp。
Optionally, the SAR localization loop sample data comprises: transmitting intra-scaled sample data, receiving intra-scaled sample data, and common intra-scaled sample data.
Optionally, the performing pre-zero padding includes: leading the internal calibration response signal, and adding zero to the rear side of the internal calibration response signal to the number of points of distance pulse compression processing; the completion delay compensation includes: subtracting the ideal pulse pressure position of the linear frequency modulation signal from the subscript variable value corresponding to the peak value of the internal calibration pulse pressure signal to obtain a delay amount, taking the delay amount as the subscript initial position of the internal calibration response signal subjected to the pre-zero padding, advancing the internal calibration response signal subjected to the pre-zero padding, wherein the rear side of the internal calibration response signal is subjected to zero padding, the zero padding number is the delay amount, and the ideal pulse pressure position is 1/2 of the sampling point number.
Optionally, the performing a double polynomial fit of the least squares and orthogonal polynomials on the internal calibration reference signal comprises: acquiring an amplitude and phase numerical curve to be fitted from the internal calibration reference signal; according to the initial fitting order, respectively carrying out least square polynomial fitting on the amplitude and phase numerical curves to be fitted to obtain an amplitude and phase initial fitting polynomial; solving square errors of the amplitude and phase preliminary fitting polynomials, and judging whether a fitting result is not more than a preset square error or not: if the fitting result is not greater than the preset square error, the fitting precision requirement is met, otherwise, the fitting order is increased until the increased square error still can meet the fitting precision requirement, and the highest fitting order, the amplitude and phase first re-fitting polynomial are obtained; respectively carrying out orthogonal polynomial fitting on the amplitude and phase first re-fitting polynomials according to the highest fitting order to obtain amplitude and phase orthogonal fitting polynomials; and respectively carrying out coefficient optimization on the amplitude and phase orthogonal fitting polynomials to form an amplitude and phase second fitting polynomial.
Optionally, the performing least square polynomial fitting on the magnitude and phase numerical curves to be fitted includes: fitting the amplitude and phase numerical curves to be fitted as follows:
Wherein,,least square fitting coefficients for amplitude and phase, respectively; t is the moment; n is n 0 For the initial fitting order, +.>And respectively performing primary fitting polynomial for amplitude and primary fitting polynomial for phase.
Optionally, the performing the orthogonal polynomial fitting on the amplitude and phase first re-fitting polynomials respectively includes: fitting the amplitude and phase first re-fit polynomial to:
wherein,,orthogonal fitting coefficients of amplitude and phase respectively; t is the moment; n is the highest fittable order;respectively performing orthogonal fitting polynomials for amplitude and phase; p (P) i (t) is an orthogonal basis function, P i (t) is:
optionally, the coefficient optimization includes: cutting off the high-order coefficient with the coefficient value approaching zero in the amplitude orthogonal fitting polynomial, and taking the low-order coefficient with a larger value and effectiveness to form an amplitude second fitting polynomial; and cutting off the high-order coefficient with the coefficient value approaching zero in the phase orthogonal fitting polynomial, taking the effective low-order coefficient with a larger value, and setting the 1-order coefficient and the 2-order coefficient to zero to form a phase second fitting polynomial.
Optionally, the performing the foreground division on the SAR original data to obtain a foreground SAR original echo data, and centering the distance in the foreground SAR original echo data to zero, to form standard foreground SAR echo data includes: reading SAR original data, and sequentially arranging distance data along the azimuth direction to form a scene SAR original echo data; and centering the distance direction data in the original echo data of the scene SAR, and carrying out zero padding before and after the distance direction data until the distance direction echo data processing points are counted to form standard scene SAR echo data.
Another aspect of the present invention provides a SAR ranging reference signal processing apparatus, comprising: the first generation module is used for carrying out time normalization on SAR emission pulse width to obtain SAR linear frequency modulation signals, and carrying out centering zero padding on the SAR linear frequency modulation signals to the number of distance pulse compression processing points to generate linear frequency modulation reference signals; the second generation module is used for extracting SAR internal calibration loop sample data to obtain an initial internal calibration loop response signal, pre-zeroing the initial internal calibration loop response signal to the number of distance pulse compression processing points, finishing average value processing, and generating an internal calibration response signal; the first construction module is used for carrying out pulse compression on the linear frequency modulation reference signal and the internal calibration response signal to obtain an internal calibration pulse pressure signal, carrying out prepositioning zero padding on the internal calibration response signal, completing time delay compensation and constructing an internal calibration reference signal; the double fitting module is used for carrying out double polynomial fitting of least square and orthogonal polynomials on the internal calibration reference signals to obtain a second double fitting polynomial of amplitude and phase; the second construction module is used for constructing a polynomial constant value model according to the amplitude and phase second fitting polynomial, centering zero padding the polynomial constant value model and obtaining a distance reference signal; the third generation module is used for dividing the SAR original data into scenes to obtain scene SAR original echo data, and sequentially centering and zero-filling distance data in the scene SAR original data to form standard scene SAR echo data; and the third construction module is used for sequentially carrying out distance pulse compression on the standard scene SAR echo data and the distance reference signal to construct a distance Doppler image.
(III) beneficial effects
Compared with the prior art, the invention has the beneficial effects that:
(1) In the prior art, the distance reference function is a linear frequency modulation pulse signal, the variable range of the time domain signal is SAR emission pulse width, and the value is usually in the order of microseconds. When polynomial fitting is performed, fitting coefficients above second order are too small, and model accuracy is not easy to guarantee. The invention adopts a SAR radar pulse width time normalized linear frequency modulation signal model, the pulse width time variation range is unified to be between-1 and-1, the problem that the polynomial coefficient is too small after numerical fitting is solved, and the method is suitable for the numerical fitting of polynomials.
(2) According to the method, the SAR internal calibration response signal is moved forward to the original point through the delay compensation of the SAR internal calibration response signal, so that the problem that the more the interval of the distribution of the fitting nodes deviates from the original point, the more serious the pathological condition of the normal equation set is in polynomial fitting is solvedThe problem is that the 10-order polynomial fitting of the amplitude and phase numerical curve of the internal calibration reference signal is realized, and the square error of the fitted amplitude fitting is less than or equal to 3.3 multiplied by 10 -10 The method comprises the steps of carrying out a first treatment on the surface of the The square error of the phase fitting is less than or equal to 1.5X10 -9 Fitting accuracy is satisfied.
(3) In the prior art, a single polynomial fitting or a quadrature (legendre) polynomial fitting is generally adopted for the amplitude and phase value curve fitting of the internal calibration reference signal, and the two fitting modes cannot be used for carrying out high-precision fitting on the random interference signals on the amplitude and phase value curve. The invention adopts a least square and orthogonal polynomial double fitting method: firstly, utilizing a high-order (more than 10-order) least square fitting polynomial to fit inherent characteristics on amplitude and phase numerical value curves, and constructing a smooth fitting curve; and then carrying out orthogonal polynomial quadratic fitting, wherein the fitting result has orthogonality, so that the coefficient of the high-valence item which tends to zero can be conveniently set to zero, and the random error can be effectively removed. The distance constructed by double polynomial fitting is used as a matching function to the reference signal, and the response effect of an ideal point target can be approximated after pulse compression.
Drawings
Fig. 1 schematically shows a block flow diagram of a SAR range reference signal processing method according to an embodiment of the invention.
FIG. 2 is a flow chart of a two-fold polynomial fit of least squares and orthogonal polynomials for an internal calibration reference signal according to an embodiment of the present invention.
FIG. 3 is a graph of magnitude values of an initial inner-scaling loop response signal according to an embodiment of the present invention.
Fig. 4 is a graph of the phase values of an initial inner-scaling loop response signal according to an embodiment of the present invention.
Fig. 5 is a graph of magnitude values to be fitted according to an embodiment of the present invention.
Fig. 6 is a graph of phase values to be fitted according to an embodiment of the present invention.
Fig. 7 is a range-doppler image of a ground corner reflector (# 3-15503) according to an embodiment of the present invention.
Figure 8 is a range-doppler image of a ground corner reflector (# 4-16160) in accordance with an embodiment of the present invention.
FIG. 9 is a schematic diagram of a ground corner reflector (# 3-15503) respectively pointing at a distance from a reference signal H according to an embodiment of the present invention fit (t) and chirped reference signal H ref And (t) is the comparison result of the pulse compression effect of the matching function and the ideal point target response.
FIG. 10 is a schematic diagram of a ground corner reflector (# 4-16160) respectively pointing at a distance from a reference signal H according to an embodiment of the present invention fit (t), chirp reference signal H ref And (t) is the comparison result of the pulse compression effect of the matching function and the ideal point target response.
Fig. 11 schematically shows a block diagram of a SAR range-oriented reference signal processing apparatus according to an embodiment of the present invention.
Detailed Description
The present invention will be further described in detail below with reference to specific embodiments and with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the description is only illustrative and is not intended to limit the scope of the invention. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It may be evident, however, that one or more embodiments may be practiced without these specific details. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the present invention.
It should be noted that, in the embodiments of the present invention, the "first" and the "second" are merely for distinguishing technical terms and convenience in description, and should not be construed as limiting the embodiments of the present invention. The terms "comprises," "comprising," and the like, indicate the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.
It should be understood that the point number i of the abscissa in the drawing of the present invention is the sampling point number N of dividing a time between-1 and 1 into a chirp signal rr At is such that
Wherein: delta t is the time step length, t is the time of signal processing, and t is more than or equal to-1 and less than or equal to 1. I.e. a sampling point is formed every other time step within a preset time of signal processing.
Fig. 1 schematically shows a flowchart of a SAR range-oriented reference signal processing method according to an embodiment of the present invention.
As shown in fig. 1, the SAR range reference signal processing method according to the embodiment of the present invention may include, for example, operations S1 to S7.
Referring to fig. 1, the invention provides a SAR distance reference signal processing method, comprising the following steps:
s1, performing time normalization on SAR emission pulse width to obtain SAR linear frequency modulation signals, and performing centering zero padding on the SAR linear frequency modulation signals to the number of distance pulse compression processing points to obtain linear frequency modulation reference signals.
Specifically, a time-normalized chirp signal h is performed using SAR transmit pulse width ref (t) is:
wherein B is SAR system bandwidth; t is the emission pulse width; t is the time.
The linear frequency modulation signal h ref (t) centering, and respectively filling zero on the left side and the right side of the signal. To achieve the number of zero padding to the distance to pulse compression processing points, one side (left side and right side) is padded with zero padding number N r The method comprises the following steps: n (N) r ＝(NN r -N rr ) 2, wherein NN r Counting the number of processing points for distance pulse compression; n (N) rr The number of sampling points for the linear frequency modulation signal is N rr T×samp, where Samp is the sampling frequency.
From the above, the chirped reference signal H ref (t) is:
in an embodiment of the present invention, the method of step S1 is described with the original parameters of a certain SAR radar system.
Parameters of a certain SAR radar system include: SAR system bandwidth B is 360MHz; the emission pulse width T is 25 μm; the sampling frequency Samp is 480MHz; number of processing points NN of distance pulse compression r 28384.
Time-normalized chirp signal h ref (t) is:
available, number of samples N of the chirp signal rr 12000 number N of zero padding on one side (left side and right side) r The method comprises the following steps: n (N) r ＝(NN r -N rr )/2＝8192。
Chirped reference signal H ref (t) is
S2, extracting SAR internal calibration loop sample data from SAR original data, obtaining an initial internal calibration loop response signal, pre-zeroing the initial internal calibration loop response signal to the number of distance-oriented pulse compression processing points, and finishing mean value processing to obtain an internal calibration response signal.
The SAR original data may be, for example, a task data segment-sar.raw data file actually acquired, and SAR positioning loop sample data in a file header is read. The SAR inner calibration loop sample data includes transmit inner calibration sample data, receive inner calibration sample data, and common inner calibration sample data.
Specifically, from an actually obtained task data segment-SAR. Raw data file, reading sample data of an SAR inner calibration loop in a file header to obtain an initial inner calibration loop response signal h cal (t) is:
wherein T is cal Scaling the sample data for the transmit inner; r is R cal To receive the inner scaled sample data; CE (CE) cal Sample data is scaled for common internal.
Will initially calibrate the loop response signal h cal (t) front-end, signal h cal (t) rear zero padding, number NN of zero padding p For NN p ＝NN r -N p Wherein NN r As previously described; n (N) p The number of samples of the loop response signal is initially calibrated.
Obtaining the internal calibration loop response signal H cal (t) is:
after mean value processing, obtaining an internal calibration response signalThe method comprises the following steps:
wherein N is the total number of internal scaling and a positive integer; j is the internal standard times, and the value is 1,2,3 and … … N; h cal，j The loop response signal is internally scaled for the jth internal scaling.
In an embodiment of the present invention, sample data of an SAR internal calibration loop in a file header is read from an actually acquired task data segment-SAR. Raw data file to obtain an initial internal calibration loop response signal h cal (t)。
FIG. 3 is a graph of magnitude values of an initial inner-scaling loop response signal according to an embodiment of the present invention. Fig. 4 is a graph of the phase values of an initial inner-scaling loop response signal according to an embodiment of the present invention.
Referring to fig. 3 and 4, the number of sampling points N of the inner calibration loop p 16128, the number of internal calibration times N is 4, NN r As previously described. The number NN of zero padding p The method comprises the following steps: NN (N) p ＝28384-16128＝12256。
Inner scaling loop response signal H cal (t) is:
thus, the internal calibration response signal after mean processing is obtainedThe method comprises the following steps:
and S3, performing pulse compression on the linear frequency modulation reference signal and the internal calibration response signal to obtain an internal calibration pulse pressure signal, subtracting the peak position of the internal calibration pulse pressure signal from the ideal pulse pressure position of the linear frequency modulation signal to obtain a time delay amount, performing prepositioning zero padding on the internal calibration response signal to complete time delay compensation, and constructing the internal calibration reference signal.
Wherein, carry out leading zero padding includes: leading the internal calibration response signal, and adding zero to the rear side of the internal calibration response signal until the number of points is counted in the distance pulse compression process;
wherein completing the delay compensation comprises: and subtracting the ideal pulse pressure position (1/2 value of the sampling point number) of the linear frequency modulation signal from the subscript variable value corresponding to the peak value of the internal calibration pulse pressure signal to obtain a delay quantity, taking the delay quantity as the subscript initial position of the internal calibration response signal subjected to the pre-zero padding, advancing the internal calibration response signal subjected to the pre-zero padding, and performing rear zero padding on the internal calibration response signal, wherein the rear zero padding number is the delay quantity.
Specifically, the reference signal H is chirped ref (t) and internal definitionTarget response signalPulse compression is carried out to obtain an internal standard pulse pressure signal y cal (t) is
Wherein fft is a fourier transform symbol; ifft is the inverse fourier transform symbol; conj is a complex conjugate symbol.
Take the signal y cal Variable index i corresponding to amplitude peak of (t) cal Is i cal ＝|max(y cal (t))| i Wherein i is the subscript corresponding to the variable. The delay amount of the delay compensation is delta cal ＝i cal -N rr 2, wherein N rr As previously described.
Calibrating the response signalLeading zero padding to distance pulse compression processing point NN p . Further, the delay amount compensated by the time delay is taken as the initial position of the subscript of the pre-zero-added internal calibration response signal to obtain the delay amount delta cal The compensated internal calibration reference signal is:
wherein,,is->The variable subscript start position of the signal;Is->The variable of the signal subscribes to the final position.
In one embodiment of the present invention, the reference signal H is chirped ref (t) and internal calibration response signalsPulse compression is carried out to obtain an internal standard pulse pressure signal y cal (t)。
Obtaining an internal calibration pulse pressure signal y cal The variable index corresponding to the amplitude peak of (t) is i cal ＝|max(y cal (t))| i =6468, the delay amount of the delay compensation is Δ cal ＝i cal -N rr 2=468, where N rr As previously described.
Calibrating the response signalLeading zero padding to distance pulse compression processing point NN p ，NN p As previously described. Further, the delay amount is used as the subscript initial position of the pre-zero-added internal calibration response signal to obtain the delay amount delta cal The compensated internal calibration reference signal is:
and S4, performing double polynomial fitting of least square and orthogonal polynomials on the internal calibration reference signals to obtain a second double fitting polynomial of amplitude and phase.
And (3) acquiring amplitude and phase value curves of the internal calibration reference signals obtained in the step (S3), and respectively performing polynomial fitting. The polynomial fit may be, for example, a double fit of a least squares and an orthogonal polynomial. And obtaining a magnitude second fitting polynomial and a phase second fitting polynomial through the polynomial fitting.
FIG. 2 is a flowchart of polynomial fitting of the internal calibration reference signal according to an embodiment of the present invention.
Referring to fig. 2, polynomial fitting of the internal calibration reference signal is performed, comprising the sub-steps of:
s41, acquiring an amplitude and phase numerical curve to be fitted from the internal calibration reference signal.
The internal calibration reference signal obtained in the step S3 has completed the time delay compensation of the internal calibration response signal, so that the amplitude value curve can be directly read, the average value of the amplitude value curve is taken, and inversion processing is carried out, so that the amplitude value curve to be fitted is obtained. And (3) directly reading the phase value curve of the internal calibration reference signal obtained in the step (S3) to be used as a phase value curve to be fitted.
Specifically, for the internal calibration reference signal in step S3, taking the mean value of the amplitude value curve thereof and performing inversion processing to obtain the amplitude value curve to be fittedThe method comprises the following steps:
wherein N is rr As previously described; t is t i Is thatVariable subscript of signal, wherein i is point number and the value is 1,2, … …, N rr 。
Correspondingly, the phase value curve to be fittedThe method comprises the following steps:
in an embodiment of the present invention, the amplitude value curve of the internal calibration reference signal in step S3 is directly read, the average value thereof is obtained, and inversion processing is performed to obtain an amplitude value curve to be fitted:
fig. 5 is a graph of magnitude values to be fitted according to an embodiment of the present invention.
Meanwhile, the phase value curve of the internal calibration reference signal is directly read, and the phase value curve to be fitted is obtained.
Fig. 6 is a graph of phase values to be fitted according to an embodiment of the present invention.
S42, fitting the amplitude and phase numerical curves to be fitted with least square polynomials respectively according to the initial fitting order, and obtaining an amplitude and phase initial fitting polynomial.
Specifically, the magnitude and phase numerical curves to be fitted are fitted as follows:
wherein,,least square fitting coefficients for amplitude and phase, respectively; n is n 0 The initial fitting order is given;and respectively performing primary fitting polynomial for amplitude and primary fitting polynomial for phase.
In addition, the amplitude least square fitting coefficient matrix and the phase least square fitting coefficient matrix are expressed asThe definition is as follows:
in an embodiment of the present invention, the magnitude numerical curve to be fitted shown in fig. 5 is fitted by a least square polynomial to obtain a magnitude preliminary fitting polynomial, where the magnitude preliminary fitting polynomial is:
wherein the initial fitting order n 0 The value is 10, and the least square fitting coefficient matrix thereofIs that
Similarly, the least square polynomial fitting is performed on the phase numerical curves to be fitted shown in fig. 6 to obtain a phase preliminary fitting polynomial, where the phase preliminary fitting polynomial is:
wherein the initial fitting order n 0 The value is 10, and the least square fitting coefficient matrix thereofIs that
S43, solving the square error of the amplitude and phase preliminary fitting polynomial, and judging whether the fitting result is not more than a preset square error: if the fitting result is not greater than the preset square error, the fitting precision requirement is met, otherwise, the fitting order is increased until the increased square error still can meet the fitting precision requirement, and the highest fitting order, the amplitude and phase first re-fitting polynomial are obtained;
specifically, the square errors of the amplitude and phase preliminary fitting polynomials obtained in step S42 are obtained as
Wherein NN r As previously described;respectively, magnitude and phase value curves to be fitted, < ->Preliminary fitting polynomials for amplitude and phase respectively,/->Is the amplitude and phase squared error.
The predetermined square error may include, for example, an amplitude predetermined square error and a phase predetermined square error, and the amplitude predetermined square error may be, for example, 3.3X10 -10 The phase preset square error may be, for example, 1.5X10 -9 . The preset square error can be set as required, and the present invention is not particularly limited.
Increasing the fitting order will increase the square error. Specifically, the determining whether the fitting result is not greater than the preset square error may be, for example: if the fitted amplitude square error D is less than or equal to 3.3X10 -10 And the fitted phase square error D is less than or equal to 1.5X10 -9 The fitting error requirement is met, and at the moment, the amplitude and phase first re-fitting polynomial is the amplitude and phase preliminary fitting polynomial obtained in the step S42; otherwise, returning to step S42, increasing the fitting order, continuing to perform least square polynomial fitting until the increased square error meets the fitting precision requirement, obtaining a first amplitude and phase re-fitting polynomial, expressed asAnd->The amplitude and phase first re-fit polynomial is now different from the amplitude and phase preliminary fit polynomial obtained in step S42.
In an embodiment of the present invention, the least square error of the amplitude preliminary fitting polynomial and the phase preliminary fitting polynomial are calculated as follows:
from the above, the fitting results all meet the preset square error requirement of the amplitude and the phase, the highest fittable order is 10 at this moment, and the amplitude and the phase first fitting polynomial is obtained, and this moment, the amplitude and the phase first fitting polynomial is identical to the amplitude and the phase preliminary fitting polynomial obtained in the step S42.
And S44, respectively carrying out orthogonal polynomial fitting on the amplitude and phase first re-fitting polynomials according to the highest fitting order to obtain amplitude and phase orthogonal fitting polynomials.
Specifically, the amplitude and phase first re-fit polynomial is fit to:
wherein,,orthogonal fitting coefficients of amplitude and phase respectively; t is the moment; n is the highest fittable order;Respectively performing orthogonal fitting polynomials for amplitude and phase; p (P) i (t) is an orthogonal basis function, P i (t) is:
in addition, let the amplitude orthogonal fitting coefficient matrix and the phase orthogonal fitting coefficient matrix be expressed as The definition is as follows:
in one embodiment of the present invention, the first re-fitting polynomial is obtained in step S43Performing orthogonal polynomial fitting on the numerical curve of (2) to obtain an amplitude orthogonal fitting polynomial, wherein the amplitude orthogonal fitting polynomial is as follows:
Wherein the highest fittable order n is 10, P i (t) is an orthogonal basis function, orthogonal fitting coefficient matrixThe method comprises the following steps:
a first re-fitting polynomial to the phase obtained in step S43Performing a quadrature polynomial fit to the numerical curves of (2) to obtain a phase quadrature fit polynomial as:
wherein the highest fittable order n is 10, P i (t) is an orthogonal basis function, orthogonal fitting coefficient matrixThe method comprises the following steps:
and S45, respectively carrying out coefficient optimization on the amplitude and phase orthogonal fitting polynomials to form an amplitude and phase second fitting polynomial.
The coefficient optimization may include, for example:
cutting off the high-order coefficient with the coefficient value approaching zero in the amplitude orthogonal fitting polynomial, and taking the low-order coefficient with a larger value and effectiveness to form an amplitude second fitting polynomial;
and cutting off the high-order coefficient with the coefficient value approaching zero in the phase orthogonal fitting polynomial, taking the effective low-order coefficient with a larger value, and setting the 1-order coefficient and the 2-order coefficient to zero to form a phase second fitting polynomial.
In particular, in the amplitude orthogonal polynomial coefficient matrixWherein, the coefficient with the logarithmic value smaller than the first preset value is truncated to obtain an amplitude orthogonal polynomial coefficient matrix ++>The method comprises the following steps:
The first preset value may be, for example, 0.1, and the first preset value may be set according to needs, which is not particularly limited in the present invention.
Corresponding magnitude second fitting polynomialThe method comprises the following steps:
in particular, in the phase quadrature polynomial coefficient matrixSetting the 1-order coefficient and the 2-order coefficient to zero, and performing truncation processing on the coefficients with the values smaller than the second preset value in other coefficients to obtain a phase orthogonal polynomial coefficient matrix +.>The method comprises the following steps:
the second preset value may be, for example, 0.02. The second preset value may be set as needed, and the present invention is not particularly limited.
Corresponding phase second fitting polynomialThe method comprises the following steps:
in one embodiment of the invention, the coefficient matrix of the 10-order amplitude orthogonal polynomialIn the method, coefficients with the logarithmic value smaller than 0.1 are subjected to truncation treatment to obtain a 2-order amplitude orthogonal fitting polynomial ++>The method comprises the following steps:
wherein, refer to step S44, P k (t) is defined as:
and, amplitude orthogonal polynomial coefficient matrixIs that
In one embodiment of the present invention, in the phase quadrature polynomial coefficient matrixWherein, the 1-order coefficient and the 2-order coefficient are set to zero, and the coefficient with the logarithmic value smaller than 0.02 is cut off to obtain 6-order phase fitting orthogonal polynomial ∈>
Wherein, refer to step S44, P i (t) is defined as:
and, a matrix of coefficients of the phase quadrature polynomialIs that
And S5, constructing a polynomial constant model based on the amplitude and phase second fitting polynomial, and centering the polynomial constant model for zero padding to obtain a distance reference signal.
Specifically, a second fitting polynomial based on the amplitude and phase obtained in step S5Respectively calculating amplitude and phase polynomials to obtain an amplitude constant polynomial A fit (t) and phase constant polynomial +.>Constructing a polynomial constant model h fit (t) is:
modeling the polynomial constant value h fit (t) centering, h fit (t) number N of zero padding on left and right sides and one side (left and right sides) r As described in step S1.
Available, distance-to-reference signal H fit (t) is:
in one embodiment of the invention, for a 2-order magnitude orthogonal polynomialAnd 6 th order phase quadrature polynomial +.>Respectively performing polynomial calculation to obtain amplitude constant valuePolynomial A fit (t) and phase constant polynomial +.>Correspondingly obtaining a polynomial constant model h fit (t) is:
wherein:
number N of zero padding r If S1 is 8192, the distance direction reference signal H is obtained fit (t) is:
s6, dividing the SAR original data into scenes to obtain scene SAR original echo data, and centering the distance in the scene SAR original echo data to zero to form standard scene SAR echo data.
Step S6 comprises the following sub-steps:
s61, reading SAR original data, and sequentially arranging distance data along the azimuth direction to form a scene SAR original echo data;
and S62, centering distance direction data in the original echo data of the one-scene SAR, and performing zero padding before and after the distance direction data to the number of distance direction data processing points to form standard scene SAR echo data.
Specifically, a scene SAR original echo data is separated from sar.raw original data as s (l α ，j β )
Wherein: l (L) α Is azimuth data; alpha is the number of azimuth sampling points; j (j) β Is distance data; beta is the distance sampling point number.
Distance data j in the one-scene SAR echo data β Centering zero-padding to distance-oriented data processing point NN r The standard scene SAR echo data are formed as follows:
in an embodiment of the present invention, a scene SAR original echo data is read as s (l α ，j β ) Wherein l α For azimuth data, the sampling point number α=18000; j (j) β For distance data, the sampling point number β=16384. NN (N) r 28384 as described in S1.
Distance data j β Centering zero-padding to distance-oriented data processing point NN r The standard scene SAR echo data can be obtained as follows:
and S7, sequentially performing distance direction pulse compression on the standard scene SAR echo data and the distance direction reference signal to obtain a distance Doppler image.
Specifically, the distance obtained in step S6 is directed to the reference signal H fit (t) and the standard scene SAR echo data S (l) obtained in the step S5 α ，j k ) Sequentially performing range-direction pulse compression to obtain a range-Doppler image I fit (τ α ，r k ) I is
|I(τ α ，r k )|＝|ifft(fft(S(l α ，j k ))×conj(fft(H fit (t))))|
Wherein fft is a fourier transform symbol; ifft is the inverse fourier transform symbol; conj is a complex conjugate symbol.
In one embodiment of the present invention, the distance is set to the reference signal H fit (t) and standard scene SAR echo data s (l α ，j k ) Sequentially performing range-direction pulse compression to obtain a range-Doppler image I fit (τ α ，r k )|。
|I fit (τ α ，r k )|＝|ifft(fft(S(l α ，j k ))×conj(fft(H fit (t))))|
In the embodiment of the present invention, the steps have no strict sequence, for example, operations S1, S2, S6 may be executed in parallel, and operations S5, S6 may also be executed in parallel, and the specific sequence of the steps is not limited by the present invention.
The SAR raw data of the embodiment of the invention contains a plurality of ground corner reflector signals, so that the SAR raw data is in a range Doppler image I fit (τ α ，r k ) The distance pulse compression is performed on multiple ground corner reflector signals in the I, so that the actual SAR echo original data result containing the ground corner reflector target is used for illustrating the technical effect of the method.
Fig. 7 is a range-doppler image of a ground corner reflector (# 3-15503) according to an embodiment of the present invention. Figure 8 is a range-doppler image of a ground corner reflector (# 4-16160) in accordance with an embodiment of the present invention.
Referring to fig. 7, the range-doppler image of the ground corner reflector #3-15503 obtained by the method of the present invention isIts peak value is +.>
Referring to fig. 8, the range-doppler image of the ground corner reflector #4-16160 obtained by the method of the present invention isIts peak value is +.>
In order to compare the pulse compression effect, the chirp reference signal H obtained in step S1 is directly subjected to the following ref (t) and the standard scene SAR echo data S (l) obtained in the step S6 α ，j k ) Sequentially performing range-wise pulse compression to obtain a reference range-Doppler image I ref (τ α ，r k ) The I is:
|I ref (τ α ，r k )|＝|ifft(fft(S(l α ，j k ))×conj(fft(H ref (t))))|
as can be derived from the above equation, the reference range-doppler image for the ground corner reflector #3-15503 is:and, the reference range-doppler image for the ground corner reflectors #4-16160 is:
thus, for the ground corner reflectors #3-15503, H is taken as fit (t) the obtained range-Doppler peak value is a reference functionSpread in the distance direction to +>And by H ref (t) as a reference function, the range-Doppler peak value +.>Spread along the distance direction as
In addition, the ideal point target responds with a chirped reference signal H ref (t) pulse compression for point targets:
|I ideal (t)|＝|ifft(fft(H ref (t))×conj(fft(H ref (t))))|
from the above formula, the ideal point target response peak value is spread along the distance to be I ideal (14192-20：14192+20)|。
Table 1 shows a comparison of the pulse compression effect under the conditions of the examples, wherein for each of the ground corner reflectors, the three range-doppler images of the range-doppler image, the reference range-doppler image and the ideal point target response of the present invention were used as a comparison to test the pulse compression results of the ground corner reflectors of the method of the present invention.
TABLE 1
FIG. 9 is a schematic diagram of a ground corner reflector (# 3-15503) respectively pointing at a distance from a reference signal H according to an embodiment of the present invention fit (t) and chirped reference signal H ref And (t) is the comparison result of the pulse compression effect of the matching function and the ideal point target response.
The range-doppler images obtained in fig. 7 and 8 are three-dimensional images, and the range-wise expansion functions are each represented by taking 20 sampling points around the peak position. In order to facilitate observation of the contrast effect, fig. 9 and fig. 10 in the present application are images of a function of spreading a peak value formed by taking 3 sampling points from left and right of a peak value position along a distance, and the images are one-dimensional images.
The short-dashed image in FIG. 9 is directed to the reference signal H at a distance of the present invention fit (t) pulse compression effect as a matching function with peak along distance expansion function as
The long-dashed image in fig. 9 is obtained by chirping the reference signal H ref (t) pulse compression effect as a matching function with peak along distance expansion function as
The solid line image in FIG. 9 is the pulse compression effect of the ideal point target response with peak along distance expansion function of I ideal (14192-3：14192+3)|。
FIG. 10 is a schematic view of a ground corner reflector (# 4-16160) oriented at a distance of an embodiment of the present invention, respectively Reference signal H fit (t), chirp reference signal H ref (t) is a comparison of the pulse compression effect of the matching function with the ideal point target response, wherein:
the short-dashed image in FIG. 10 is directed to the reference signal H at a distance of the present invention fit (t) pulse compression effect as a matching function with peak along distance expansion function as
The long-dashed image in FIG. 10 is obtained by chirping the reference signal H ref (t) pulse compression effect as a matching function with peak along distance expansion function as
The solid line image in FIG. 10 is the pulse compression effect of the ideal point target response with peak along distance expansion function of I ideal (14192-3：14192+3)|。
Referring to fig. 9 and 10, the distance reference signal H fit (t), chirp reference signal H ref (t) as a matching function, the range-wise reference signal H can be seen by comparing the range-Doppler obtained by the range-wise pulse compression with the actual SAR echo data containing the ground corner reflector target, respectively fit (t) the pulse compression result of the ground corner reflector is closer to the ideal point target response effect.
In the embodiment of the invention, the transmitting pulse time width of the SAR linear frequency modulation signal is normalized so as to be beneficial to the value of the polynomial fitting coefficient; advancing the internal calibration response signal with time delay to an origin, and starting the node distribution for realizing polynomial fitting with the origin; and performing double fitting of least square and orthogonal polynomials on the amplitude and phase value curves of the internal calibration reference signals to construct the distance reference signals. The SAR distance constructed by the invention fits the inherent nonlinear component of the SAR positioning response signal to the reference signal, and simultaneously suppresses random spurious and crosstalk. The method overcomes the phenomena of peak value offset, main lobe broadening, side lobe rising and the like of a simple low-order polynomial numerical fitting model after pulse compression, and can meet the requirements of SAR distance matching function on logarithmic stability and precision. After pulse compression test is carried out on the actual SAR echo data containing the ground corner reflector target, the result approaches to the response effect of the ideal point target.
Fig. 11 schematically shows a block diagram of a SAR range-oriented reference signal processing apparatus according to an embodiment of the present invention. The apparatus may perform the above-described SAR range reference signal processing method.
As shown in fig. 11, the SAR range reference signal processing apparatus 300 of the embodiment of the present invention may include, for example, a first generation module 310, a second generation module 320, a first construction module 330, a double fitting module 340, a second construction module 350, a third generation module 360, and a third construction module 370.
A first generating module 310, configured to perform time normalization on a SAR transmission pulse width to obtain a SAR chirp signal, and perform centering zero padding on the SAR chirp signal to a number of distance pulse compression processing points, so as to generate a chirp reference signal;
the second generating module 320 is configured to extract SAR internal calibration loop sample data, obtain an initial internal calibration loop response signal, pre-zero-padding the initial internal calibration loop response signal to a number of distance-oriented pulse compression processing points, and complete mean value processing, so as to generate an internal calibration response signal;
a first construction module 330, configured to perform pulse compression on the chirped reference signal and the internal calibration response signal to obtain an internal calibration pulse pressure signal, perform pre-zero padding on the internal calibration response signal, and perform delay compensation to construct an internal calibration reference signal;
The double fitting module 340 is configured to perform polynomial fitting on the internal calibration reference signal to obtain an amplitude second double fitting polynomial and a phase second double fitting polynomial;
a second construction module 350, configured to construct a polynomial constant model according to the amplitude and phase second fitting polynomial, and center the polynomial constant model for zero padding, so as to obtain a distance reference signal;
a third generating module 360, configured to divide the SAR original data into views to obtain a view SAR original echo data, and sequentially center zero padding the distance data in the view SAR original data to form standard view SAR echo data;
and a third construction module 370, configured to sequentially perform range-wise pulse compression on the standard scene SAR echo data and the range-wise reference signal, and construct a range-doppler image.
It should be noted that, the embodiment mode of the SAR range-to-reference signal processing apparatus portion is similar to the embodiment mode of the SAR range-to-reference signal processing method portion, and the achieved technical effects are also similar, and specific details refer to the embodiment mode portion of the SAR range-to-reference signal processing method portion and are not described herein.
While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.
Claims (9)
1. A SAR range-wise reference signal processing method, comprising:
performing time normalization on SAR emission pulse width to obtain SAR linear frequency modulation signals, and performing centering zero padding on the SAR linear frequency modulation signals to the number of distance pulse compression processing points to obtain linear frequency modulation reference signals;
extracting SAR internal calibration loop sample data from SAR original data, obtaining an initial internal calibration loop response signal, pre-zeroing the initial internal calibration loop response signal to the number of distance pulse compression processing points, and finishing mean value processing to obtain an internal calibration response signal;
performing pulse compression on the linear frequency modulation reference signal and the internal calibration response signal to obtain an internal calibration pulse pressure signal, subtracting the peak position of the internal calibration pulse pressure signal from the ideal pulse pressure position of the linear frequency modulation signal to obtain a time delay amount, performing prepositioning zero padding on the internal calibration response signal to complete time delay compensation, and constructing the internal calibration reference signal;
Performing double polynomial fitting of least square and orthogonal polynomials on the internal calibration reference signals to obtain a second double fitting polynomial of amplitude and phase;
constructing a polynomial constant value model based on the amplitude and phase second fitting polynomial, and centering zero padding the polynomial constant value model to obtain a distance reference signal;
dividing the SAR original data into scenes to obtain scene SAR original echo data, and sequentially centering and zero-filling distance data in the scene SAR original data to form standard scene SAR echo data;
sequentially performing range-wise pulse compression on the standard scene SAR echo data and the range-wise reference signal to obtain a range-Doppler image;
wherein said performing a double polynomial fit of a least squares and an orthogonal polynomial on said internal calibration reference signal comprises:
acquiring an amplitude and phase numerical curve to be fitted from the internal calibration reference signal;
according to the initial fitting order, respectively carrying out least square polynomial fitting on the amplitude and phase numerical curves to be fitted to obtain an amplitude and phase initial fitting polynomial;
solving square errors of the amplitude and phase preliminary fitting polynomials, and judging whether a fitting result is not more than a preset square error or not: if the fitting result is not greater than the preset square error, the fitting precision requirement is met, otherwise, the fitting order is increased until the increased square error still can meet the fitting precision requirement, and the highest fitting order, the amplitude and phase first re-fitting polynomial are obtained;
Respectively carrying out orthogonal polynomial fitting on the amplitude and phase first re-fitting polynomials according to the highest fitting order to obtain amplitude and phase orthogonal fitting polynomials;
and respectively carrying out coefficient optimization on the amplitude and phase orthogonal fitting polynomials to form an amplitude and phase second fitting polynomial.
2. The SAR range-to-reference signal processing method of claim 1, wherein the time normalizing the SAR transmit pulse width to obtain the SAR chirp signal comprises:
constructing the SAR chirp signal as follows:
wherein B is SAR system bandwidth; t is the emission pulse width; t is the time, the time step delta t=2/(t.samp), samp is the sampling frequency, the chirp signal h ref Sample points N of (t) rr ＝T·Samp。
3. The SAR range-oriented reference signal processing method of claim 1, wherein the SAR-internal calibration loop sample data comprises: transmitting intra-scaled sample data, receiving intra-scaled sample data, and common intra-scaled sample data.
4. The SAR range-to-reference signal processing method of claim 1, wherein pre-zeroing the inner calibration response signal, completing delay compensation comprises:
Wherein the performing pre-zero padding comprises: leading the internal calibration response signal, and adding zero to the rear side of the internal calibration response signal to the number of points of distance pulse compression processing;
wherein the completion delay compensation comprises: subtracting the ideal pulse pressure position of the linear frequency modulation signal from the subscript variable value corresponding to the peak value of the internal calibration pulse pressure signal to obtain a delay amount, taking the delay amount as the subscript initial position of the internal calibration response signal subjected to the pre-zero padding, advancing the internal calibration response signal subjected to the pre-zero padding, wherein the rear side of the internal calibration response signal is subjected to zero padding, the zero padding number is the delay amount, and the ideal pulse pressure position is 1/2 of the sampling point number.
5. The SAR range-to-reference signal processing method of claim 1, wherein the least squares polynomial fitting of the magnitude and phase numerical curves to be fitted, respectively, comprises:
fitting the amplitude and phase numerical curves to be fitted as follows:
wherein,,least square fitting coefficients for amplitude and phase, respectively; t is the moment; n is n 0 For the initial fitting order to be chosen,and respectively performing primary fitting polynomial for amplitude and primary fitting polynomial for phase.
6. The SAR range-to-reference signal processing method of claim 1, wherein said respectively orthometric polynomial fitting the amplitude and phase first re-fitting polynomials comprises:
fitting the amplitude and phase first re-fit polynomial to:
wherein,,orthogonal fitting coefficients of amplitude and phase respectively; t is the moment; n is the highest fittable order;respectively performing orthogonal fitting polynomials for amplitude and phase; p (P) i (t) is an orthogonal basis function, P i (t) is:
7. the SAR range-wise reference signal processing method of claim 1, wherein the coefficient optimization comprises:
cutting off the high-order coefficient with the coefficient value approaching zero in the amplitude orthogonal fitting polynomial, and taking the low-order coefficient with a larger value and effectiveness to form an amplitude second fitting polynomial;
and cutting off the high-order coefficient with the coefficient value approaching zero in the phase orthogonal fitting polynomial, taking the effective low-order coefficient with a larger value, and setting the 1-order coefficient and the 2-order coefficient to zero to form a phase second fitting polynomial.
8. The SAR range-wise reference signal processing method of claim 1, wherein the performing the foreground segmentation on the SAR original data to obtain a foreground SAR original echo data, and the centering zero padding of the range-wise data in the foreground SAR original echo data to form the standard foreground SAR echo data comprises:
Reading SAR original data, and sequentially arranging distance data along the azimuth direction to form a scene SAR original echo data;
and centering the distance direction data in the original echo data of the scene SAR, and carrying out zero padding before and after the distance direction data until the distance direction echo data processing points are counted to form standard scene SAR echo data.
9. A SAR range-wise reference signal processing apparatus, comprising:
the first generation module is used for carrying out time normalization on SAR emission pulse width to obtain SAR linear frequency modulation signals, and carrying out centering zero padding on the SAR linear frequency modulation signals to the number of distance pulse compression processing points to generate linear frequency modulation reference signals;
the second generation module is used for extracting SAR internal calibration loop sample data to obtain an initial internal calibration loop response signal, pre-zeroing the initial internal calibration loop response signal to the number of distance pulse compression processing points, finishing average value processing, and generating an internal calibration response signal;
the first construction module is used for carrying out pulse compression on the linear frequency modulation reference signal and the internal calibration response signal to obtain an internal calibration pulse pressure signal, carrying out prepositioning zero padding on the internal calibration response signal, completing time delay compensation and constructing an internal calibration reference signal;
The double fitting module is used for carrying out double polynomial fitting of least square and orthogonal polynomials on the internal calibration reference signals to obtain a second double fitting polynomial of amplitude and phase;
the second construction module is used for constructing a polynomial constant value model according to the amplitude and phase second fitting polynomial, centering zero padding the polynomial constant value model and obtaining a distance reference signal;
the third generation module is used for dividing the SAR original data into scenes to obtain scene SAR original echo data, and sequentially centering distance direction data in the scene SAR original data to zero to form standard scene SAR echo data;
the third construction module is used for sequentially carrying out distance pulse compression on the standard scene SAR echo data and the distance reference signal to construct a distance Doppler image;
wherein, the double fitting module is specifically used for:
acquiring an amplitude and phase numerical curve to be fitted from the internal calibration reference signal;
according to the initial fitting order, respectively carrying out least square polynomial fitting on the amplitude and phase numerical curves to be fitted to obtain an amplitude and phase initial fitting polynomial;
solving square errors of the amplitude and phase preliminary fitting polynomials, and judging whether a fitting result is not more than a preset square error or not: if the fitting result is not greater than the preset square error, the fitting precision requirement is met, otherwise, the fitting order is increased until the increased square error still can meet the fitting precision requirement, and the highest fitting order, the amplitude and phase first re-fitting polynomial are obtained;
Respectively carrying out orthogonal polynomial fitting on the amplitude and phase first re-fitting polynomials according to the highest fitting order to obtain amplitude and phase orthogonal fitting polynomials;
and respectively carrying out coefficient optimization on the amplitude and phase orthogonal fitting polynomials to form an amplitude and phase second fitting polynomial.
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| CN104635221A (en) * | 2015-03-05 | 2015-05-20 | 北京航空航天大学 | Sub-band splicing method based on internal calibration data |
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