CN105572648B - A kind of synthetic aperture radar echo data range migration correction method and apparatus - Google Patents
A kind of synthetic aperture radar echo data range migration correction method and apparatus Download PDFInfo
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- CN105572648B CN105572648B CN201610069577.7A CN201610069577A CN105572648B CN 105572648 B CN105572648 B CN 105572648B CN 201610069577 A CN201610069577 A CN 201610069577A CN 105572648 B CN105572648 B CN 105572648B
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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
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Abstract
The invention discloses a kind of synthetic aperture radar (SAR) echo data range migration (RCM) bearing calibration, Range compress is carried out to echo data and geometry RCM is corrected, the time domain data after Range compress is obtained；Sub-aperture segmentation is carried out to the time domain data after the Range compress, sub-aperture data are obtained, and choose the sub-block data in each sub-aperture data with highest signal to noise ratio (SCR) respectively；According to each sub-block data of selection, the remaining RCM of each sub-aperture data is determined；Full aperture combination is carried out to the remaining RCM of each sub-aperture data, remaining RCM full aperture combination is obtained；Combined according to remaining RCM full aperture, correct the remaining RCM of the echo data；It is imaged using correction remnants RCM echo data.The invention also discloses a kind of SAR echo datas RCM means for correctings.
Description
Technical field
Skill is corrected the present invention relates to the echo-signal of synthetic aperture radar (SAR, Synthetic Aperture Radar)
Art, more particularly to a kind of (RCM, the Range Cell Migration) bearing calibration of SAR echo datas range migration and device.
Background technology
SAR has round-the-clock, the ability of round-the-clock carry out high-resolution imaging, and key player is played in remote sensing fields.
However, in carried SAR system, mainly the kinematic error as caused by carrier aircraft trajector deviation can cause the distance for receiving initial data
Delay and orientation phase error (APE, Azimuth Phase Errors), this can seriously reduce the quality of image.Small-sized
In airborne ultrahigh resolution (VHR, Very High Resolution) SAR system, the problem of being brought by kinematic error is tighter
Weight：On the one hand, because light weight, size are small, small-sized carried SAR system is more likely disturbed by atmospheric turbulance；It is another
Aspect, the raising of two-dimensional space resolution ratio can increase kinematic error, and it is single that target echo there may be several or even tens distances
The remaining migration and significant high-order APE of member.Therefore, the correction of kinematic error needs the accurate movable information of aircraft platform.
Generally, movable information can be by high-precision inertial navigation system (INS, Inertial Navigation System) and the whole world
Alignment system (GPS, Global Positioning Systems) is obtained；However, be limited to cost and Payload, INS and
GPS can not always accurate compensation campaign error, particularly in the case of small-sized carried SAR system, or even can be entirely ineffective.
Therefore, it should estimated using self-focusing technology and correct remaining RCM and the APE in initial data.
Current self-focusing method, can be largely classified into two classes：It is parameter and non-parametric.In nonparametric technique, phase
Potential gradient self-focusing (PGA, Phase Gradient Autofocus) technology is the most famous, and be proved to various scenes and
The phase error function of different imaging patterns has very strong robustness (Robustness).In parametric technique, through frequently with
APE multinomial model, such as figure move (MD, Map Drift) technology, reflectivity deflection method etc..In addition, in SAR self-focusings neck
Domain also includes：Method based on cost function, this method can be parameter or non-parametric, depending on setting before
The parameter model of fixed APE functions.But, above-mentioned self-focusing method only considered APE, and ignore remaining RCM；However, right
For small-sized airborne VHR SAR sensors, remaining RCM is inevitable, it is necessary to goes to estimate and compensates, and otherwise can not be obtained
Focus on good high-quality SAR image.
Therefore, how accurately to estimate SAR echo data RCM, realize ultrahigh resolution synthetic aperture radar echo data
RCM accurate correction, is urgent problem to be solved.
The content of the invention
In view of this, the embodiment of the present invention is expected to provide a kind of SAR echo datas RCM bearing calibrations and device, can be accurate
The RCM of SAR echo datas is estimated on ground, realizes ultrahigh resolution synthetic aperture radar echo data RCM accurate correction, and then obtain
To the good high-quality SAR image of focusing.
To reach above-mentioned purpose, the technical proposal of the invention is realized in this way：
The embodiments of the invention provide a kind of SAR echo datas RCM bearing calibrations, methods described includes：
Range compress and geometry RCM corrections are carried out to echo data, the time domain data after Range compress is obtained；
Sub-aperture segmentation is carried out to the time domain data after the Range compress, sub-aperture data is obtained, each son is chosen respectively
There is the sub-block data of highest signal to noise ratio (SCR, signal-to-clutter ratio) in pore size data；
According to each sub-block data of selection, the remaining RCM of each sub-aperture data is determined；
Full aperture combination is carried out to the remaining RCM of each sub-aperture data, remaining RCM full aperture combination is obtained；
Combined according to remaining RCM full aperture, correct the remaining RCM of the echo data.
In such scheme, the time domain data to after the Range compress carries out sub-aperture segmentation, obtains sub-aperture number
According to, and the sub-block data in each sub-aperture data with highest SCR is chosen respectively；Including：
By the time domain data after the Range compress along azimuth segmentation be sub-aperture data；
Selection processing is carried out to each sub-aperture data using sliding window, determines that there is highest in each sub-aperture data
SCR sub-block data；
The length of the sub-aperture is 1st/1 to three/2nds of length of synthetic aperture.
In such scheme, each sub-block data according to selection determines the remaining RCM of each sub-aperture；Including：
Enter row distance to each sub-block data respectively down-sampled to liter sampling and orientation, obtain corresponding distance to liter
Sampling and the down-sampled data of orientation；
Respectively to each distance to liter sampling and the down-sampled data of orientation, using exponential type average distance picture
(ARP, Averaged Range Profile) is calculated, and obtains corresponding reference distance picture (RRP, Referred Range
Profile) data；
Adopted respectively according to each distance to liter sampling RRP data corresponding with itself with the data that orientation is down-sampled
Corresponding RCM is estimated with the cost function based on Entropy principle；
According to the value of three points near the minimum entropy position of the RCM respectively estimated, the RCM respectively estimated is calibrated, is obtained
Take the accurate RCM of each sub-aperture data；
Each accurate RCM is carried out rising sampling using simple interpolations, the remaining RCM of each sub-aperture is obtained.
In such scheme, the remaining RCM to each sub-aperture carries out full aperture combination, obtains remaining RCM full aperture
Combination；Including：
Using the mixed filtering method for including higher order polynomial-fitting and discrete cosine transform, by the remnants of each sub-aperture
RCM carries out full aperture combination, obtains remaining RCM full aperture combination.
It is described to be combined according to remaining RCM full aperture in such scheme, correct the remaining RCM of the echo data；Bag
Include：
Fixed phase multiplication is being carried out apart from frequency domain to the echo data, the echo data to correcting remnants RCM is obtained；
Thick phase compensation is carried out to echo data according to the combination of remaining RCM full aperture.
In such scheme, methods described also includes：
Self-focusing is carried out to the echo data of the correction remnants RCM, and carries out Azimuth Compression, SAR image is obtained；
The method of the self-focusing, including：PGA.
The embodiment of the present invention additionally provides a kind of SAR echo datas RCM means for correctings, and described device includes：Pre-treatment mould
Block, remaining RCM determining modules, correction module, wherein,
The pre-processing module, for carrying out Range compress and geometry RCM corrections to echo data, is obtained after Range compress
Time domain data；
The remaining RCM determining modules, are used for：
Sub-aperture segmentation is carried out to the time domain data after the Range compress, sub-aperture data is obtained, each son is chosen respectively
There is highest SCR sub-block data in pore size data；
According to each sub-block data of selection, the remaining RCM of each sub-aperture data is determined；
Full aperture combination is carried out to the remaining RCM of each sub-aperture data, remaining RCM full aperture combination is obtained；
The correction module, for being combined according to remaining RCM full aperture, corrects the remaining RCM of the echo data.
In such scheme, the remaining RCM determining modules, specifically for：
By the time domain data after the Range compress along azimuth segmentation be sub-aperture data；
Selection processing is carried out to each sub-aperture data using sliding window, determines that there is highest in each sub-aperture data
SCR sub-block data；
The length of the sub-aperture is 1st/1 to three/2nds of length of synthetic aperture.
In such scheme, the remaining RCM determining modules, specifically for：
Enter row distance to each sub-block data respectively down-sampled to liter sampling and orientation, obtain corresponding distance to liter
Sampling and the down-sampled data of orientation；
Each distance is calculated to liter sampling and the down-sampled data of orientation using exponential type ARP respectively, acquisition pair
The RRP data answered；
Adopted respectively according to each distance to liter sampling RRP data corresponding with itself with the data that orientation is down-sampled
Corresponding RCM is estimated with the cost function based on Entropy principle；
According to the value of three points near the minimum entropy position of the RCM respectively estimated, the RCM respectively estimated is calibrated, is obtained
Take the accurate RCM of each sub-aperture data；
Each accurate RCM is carried out rising sampling using simple interpolations, the remaining RCM of each sub-aperture is obtained.
In such scheme, the remaining RCM determining modules, specifically for：
Using the mixed filtering method for including higher order polynomial-fitting and discrete cosine transform, by the remnants of each sub-aperture
RCM carries out full aperture combination, obtains remaining RCM full aperture combination.
In such scheme, the correction module, specifically for：
Fixed phase multiplication is being carried out apart from frequency domain to the echo data, the echo data to correcting remnants RCM is obtained；
Thick phase compensation is carried out to echo data according to the combination of remaining RCM full aperture；
Described device, in addition to image-forming module, self-focusing is carried out for the echo data to the correction remnants RCM, and
Azimuth Compression is carried out, SAR image is obtained.
SAR echo data RCM bearing calibrations and device that the embodiment of the present invention is provided, row distance pressure is entered to echo data
Contracting and geometry RCM corrections, obtain the time domain data after Range compress；Sub-aperture is carried out to the time domain data after the Range compress
Segmentation, obtains sub-aperture data, and choose the sub-block data in each sub-aperture data with highest SCR respectively；According to selection
Each sub-block data, determines the remaining RCM of each sub-aperture data；Full aperture combination is carried out to the remaining RCM of each sub-aperture data, obtained
Full aperture to remaining RCM is combined；Combined according to remaining RCM full aperture, correct the remaining RCM of the echo data；Using
Correction remnants RCM echo data is imaged；In this way, can accurately estimate the RCM of SAR echo datas, super-resolution is realized
Rate synthetic aperture radar echo data RCM accurate correction, and then obtain focusing on good high-quality SAR image.
Brief description of the drawings
Fig. 1 is the schematic flow sheet of SAR echo data RCM bearing calibrations of the embodiment of the present invention；
Fig. 2 is the schematic flow sheet that sub-aperture of the embodiment of the present invention is split and sub-block is chosen；
Fig. 3 is the schematic flow sheet of the remaining RCM estimation steps of each sub-aperture of the embodiment of the present invention；
The calculation step schematic flow sheet that Fig. 4 estimates for the remaining RCM of sub-aperture of the embodiment of the present invention；
Fig. 5 carries out full aperture combination diagram for the remaining RCM of each sub-aperture data of the embodiment of the present invention；
Fig. 6 is Sliding spotlight SAR measured data result schematic diagram of the embodiment of the present invention；
Fig. 7 is that Sliding spotlight SAR of embodiment of the present invention measured data has carried out remaining RCM estimations contrast schematic diagram；
Fig. 8 is the amplification comparative analysis schematic diagram before and after measured data representative region self-focusing of the embodiment of the present invention；
Fig. 9 is the composition structural representation of SAR echo data RCM means for correctings of the embodiment of the present invention.
Embodiment
In the embodiment of the present invention, Range compress and geometry RCM are carried out to echo data and corrected, obtain after Range compress when
Numeric field data；Sub-aperture segmentation is carried out to the time domain data after the Range compress, sub-aperture data are obtained, and choose each son respectively
There is highest signal to noise ratio SCR sub-block data in pore size data；According to each sub-block data of selection, each sub-aperture data are determined
Remaining RCM；Full aperture combination is carried out to the remaining RCM of each sub-aperture data, remaining RCM full aperture combination is obtained；According to residual
Remaining RCM full aperture combination, corrects the remaining RCM of the echo data；Carried out into using correction remnants RCM echo data
Picture.
With reference to embodiment, the present invention is further described in more detail.
SAR echo datas RCM bearing calibrations provided in an embodiment of the present invention, as shown in figure 1, methods described includes：
Step 101：Range compress and geometry RCM corrections are carried out to echo data, the time domain data after Range compress is obtained；
Specifically, it is necessary to complete some pre-treatment steps before remaining RCM estimates and corrects, including Range compress and
Geometry RCM is corrected.Here it is possible to which using improved Chirp Scaling algorithms (CSA), CSA can be well adapted for kinematic error
Correction.After orientation Chirp Scaling, Range compress and consistent RCM corrections has been carried out, SAR signals are in the discrete of time domain
Time domain data after form, i.e. Range compress can be represented with expression formula (1)：
Wherein, A0Represent any complex constant, ωa() represents orientation envelope (sinc squares of type function), and m represents orientation
Pulse sequence number, n represents range cell sequence number, Δ TaPulse recurrence interval is represented, x represents the orientation position of arbitrary target in scene
Coordinate is put, V represents carrier aircraft flying speed, BdRepresent the bandwidth of transmission signal, Δ TrDistance samples interval is represented, r represents flight boat
Mark is to the nearest oblique distance of target, and c represents propagation velocity of electromagnetic wave, and Δ R (m) represents aircraft motion error, fcRepresent radar carrier frequency,
R0(m) represent target to the instantaneous oblique distance in course line.
Step 102：Sub-aperture segmentation is carried out to the time domain data after the Range compress, sub-aperture data are obtained, respectively
Choose the sub-block data in each sub-aperture data with highest SCR；
Specifically, as shown in Fig. 2 step 102 includes：
Step 1021：By the time domain data after the Range compress along azimuth segmentation be sub-aperture data；
Specifically, range-aligned method needs to meet such hypothesis：In whole coherent accumulation time (CPI, Coherent
Processing Interval) in, there is high similarity between Range Profile；Inverse SAR (ISAR, Inverse SAR) system is led to
Such condition is often met, because short CPI ISAR data are commonly used to the imaging of noncooperative target, such target includes
Aircraft, ship etc..However, compared with carried SAR data, the CPI of ISAR data would generally increase by tens times；In addition, except staring
Beam bunching mode, the region that radar beam is irradiated to can also change with the change of observation time.Above-mentioned factor can all reduce away from
From the similitude as between.In order to solve this problem, by the time domain data after Range compress along azimuth segmentation be sub-aperture；
Here it is possible to the length of sub-aperture is divided into 1st/1 to three/2nds of length of synthetic aperture, so, it is ensured that every
High similitude in individual sub-aperture.Assuming that full aperture data are divided into P sub-aperture, according to expression formula (1), it can represent
Pth sub- pore size data, can be represented with expression formula (2)：
Wherein, window function rectp (m), can be represented with expression formula (2)：
The window function rectp(m) it is a rectangular window function, m0And NaInterval and the length of sub-aperture are represented respectively.Need
The remaining RCM of different sub-apertures estimate to be combined using the overlapping pulses of adjacent subpulse, so Na>m0, weight
The number of folded pulse is Na-m0。
Step 1022：Selection processing is carried out to each sub-aperture data using sliding window, determined in each sub-aperture data
Sub-block data with highest SCR；
Range-aligned is to be imaged and design for ISAR originally, and the irradiation area of wherein ISAR wave beams is mainly artificial mesh
Mark, and their size is very limited.However, the mapping band of SAR image is generally wider, tens kms can be reached.Meanwhile, away from
May be smaller than 10cm from pixel size.In this case, it is possible to need distance to thousands of sampled point to cover photograph
Region is penetrated, therefore data volume is very huge.In addition, in the data of Range compress, the regions of some antiradar reflectivities may be by
To noise and the severe jamming of clutter, this can be negatively affected to remnants RCM estimations.It is that distance is constant to sky in remaining RCM
This chooses the son with highest SCR using sliding window method under the hypothesis that wide swath is also set up to each sub-aperture
Block number evidence.By means of which, the computational efficiency and estimated accuracy of self-focusing method can all be improved.According to expression formula (2), from
The sub-block data chosen in p sub-aperture can be represented with expression formula (4)：
Wherein, rect (n) is a rectangular window function, can be represented with expression formula (5)：
Wherein, q0For sliding window sequence number corresponding with the data block selected, n0And NrSliding window interval and length are represented respectively
Degree.
Step 103：According to each sub-block data of selection, the remaining RCM of each sub-aperture data is determined；
, it is necessary to estimate the remaining RCM of each sub-aperture using the sub-block data chosen after being handled by step 102.
Entropy minimization method based on range-aligned has robustness to noise and clutter, and technical solution of the present invention is improved, and is used for
Remaining RCM estimations；Specific processing is as shown in Figure 3.
Step 1031：Enter row distance to each sub-block data respectively down-sampled to liter sampling and orientation, obtain correspondence
Distance to liter sampling and the down-sampled data of orientation；
, can be to data with the proposition of cross-correlation methodEnter row distance down-sampled to liter sampling and orientation
To reduce computational load and improve the mobile sensitivity of distance.Assuming that G (k, l), 0≤k≤K, 0≤l≤L-1 be by distance to
Rise after sampling and the down-sampled processing of orientation, the corresponding distance of the sub-block chosen in p-th of sub-aperture is to liter sampling and side
Position to down-sampled data, wherein, K=α Nr, L=Na/β。
Step 1032：It is average using exponential type respectively to each distance to liter sampling and the down-sampled data of orientation
Range Profile (ARP, Averaged Range Profile) is calculated, and obtains corresponding reference distance picture (RRP, Referred
Range Profile) data；
Here, on the one hand, if be only directed at current distance picture with neighbor distance picture, drift error and transition just occurs
Error.On the other hand, due to the change in azimuth and beam region, the similitude between Range Profile can be spaced over time
Increase and be gradually reduced.Therefore, RRP is regarded as ARP after range-aligned and unreasonable.In order to solve the above problems, use
A kind of exponential type ARP calculates RRP.Here, the normalization RRP expression formulas of (l+1) the individual echo used can use expression formula
(6) represent：
Wherein, Gl(k) it is l-th of pulse in data；For Gl(k) echo after calibrated；ω is one positive real
Number scalar, and meet 0<ω<1；It is the primary condition of algorithm.
Step 1033：Respectively according to each distance to liter sampling it is corresponding with itself with the data that orientation is down-sampled described in
RRP data, corresponding RCM is estimated using the cost function based on Entropy principle；
Being risen and fallen by strong background noise and back scattering is influenceed, and conventional cross-correlation method can be reduced to the performance that RCM estimates,
It can not even realize at all.The Minimum entropy method based on range-aligned applied to ISAR data processings is unwise to noise and fluctuating
Sense, therefore have the potentiality applied to SAR data.So, technical solution of the present invention is estimated using the cost function based on Entropy principle
Count RCM；It is estimated that Rl+1And G (k)l+1(k) RCM, can be represented with expression formula (7)：
Wherein,For Gl(k) normalized form.
Step 1034：According to the value of three points near the minimum entropy position of the RCM respectively estimated, each estimation is calibrated
RCM, obtain the accurate RCM of each sub-aperture data；
In order to realize the measurement of subpixel accuracy, the liter sampling of Range Profile has been carried out in the incipient stage of estimation.However,
Calculated load can rapidly increase with interpolation factor α increase；Accordingly, it would be desirable to select appropriate α come coordination accuracy degree and
The relation of efficiency.In order to preferably improve the accuracy of estimated result, the method that conic fitting can be used.This method is led to
Cross using the value of three points near minimum entropy position to improve the RCM of estimation.The accurate RCM of p-th of sub-aperture can use expression
Formula (8) is represented：
Wherein,
Step 1035：Each accurate RCM is carried out rising sampling using simple interpolations, the remnants of each sub-aperture are obtained
RCM。
Specifically, obtaining remaining RCM by interpolation to each accurate RCM.In order to obtain remaining RCM valueUtilize
Simple interpolations are by RCM amountsSampling is risen, makes length and sub-aperture equal length after liter sampling.
In practical application, step 103 can use the calculation process such as Fig. 4, estimate the remaining RCM of each sub-aperture.
Step 104：Full aperture combination is carried out to the remaining RCM of each sub-aperture data, remaining RCM full aperture group is obtained
Close；
Specifically, it is necessary to which they are combined after the remaining RCM of whole sub-apertures is obtained.In fact, due to
RRP difference, the lap of adjacent sub-aperture may have small difference.In technical solution of the present invention, using overlapping
Partial average remaining RCM is discontinuous to avoid, and the remaining RCM laps of sub-aperture are as shown in Figure 5；
Although minimum entropy theory is robust to noise, error can be substantially reduced, some hairs are still there may be
Thorn, particularly when the contrast of irradiation area is very low.In order to improve combination remnants RCM accuracy, while removing various each
The interference of sample, technical solution of the present invention can use the mixed filtering method comprising higher order polynomial-fitting and discrete cosine transform
Full aperture combination is carried out to the remaining RCM.
Step 105：Combined according to remaining RCM full aperture, correct the remaining RCM of the echo data；
Combined according to the remaining RCM of determination full aperture, by carrying out fixed phase phase to echo data apart from frequency domain
Multiply to realize remaining RCM correction, this can overcome can only move the limitation of integer range cell in the time domain.Meanwhile,
It can combine RCM to realize thick phase compensation by the remaining RCM of determination full aperture.
SAR echo datas RCM bearing calibrations provided in an embodiment of the present invention, methods described also includes：To correction remnants RCM
Echo data carry out self-focusing, and carry out Azimuth Compression, obtain SAR image；
Specifically, in order to which APE compensation carries out conventional self-focusing；In remaining RCM calibration phases, sub-pixel is estimated remaining
RCM, and it is enough to be directed under a range resolution ratio cell width Range Profile of bending.However, coming to APE compensation
Say, RCM precision must reach sub-wavelength magnitude, this can substantially exceed the limit of power of existing range-aligned method.Therefore, need
Accurate APE is estimated using self-focusing technology, and is compensated.Wherein, the self-focusing technology, including：PGA；
, it is necessary to carry out Azimuth Compression after completion self-focusing, the SAR image of well focussed is ultimately generated.
The present invention is played a part of being described in further detail with reference to specific example.
Example of the present invention is using the airborne Sliding spotlight SAR pattern outfield measured data checking of C-band technical side of the invention
Case.
Fig. 6 is the result schematic diagram obtained using technical solution of the present invention to the processing of Sliding spotlight SAR measured data, can be with
It was found that the image realizes good focusing effect.
In order to prove the validity of technical solution of the present invention, remaining RCM is carried out to Sliding spotlight SAR measured data and estimated
Meter.As shown in fig. 7, Fig. 7 (a) be remnants RCM correct before distance to compress image；Fig. 7 (b) is after remnants RCM are corrected
Distance to compression image；Fig. 7 (c) is the remaining RCM curves estimated using technical solution of the present invention；Fig. 7 (d) is to be used to correct for
Final RCM curves；Fig. 7 (e) is the remaining RCM figures estimated using cross-correlation method；Fig. 7 (f) is mutual for neighbor distance picture
Relation number figure.Fig. 7 (b) and Fig. 7 (a) are contrasted, straightened after the track bent originally is calibrated, it was demonstrated that context of methods result
Well；Fig. 7 (c) and Fig. 7 (d) are contrasted, it can be seen that estimate in Fig. 7 (c) after liter sampling could with Fig. 7 (d)
Orientation pulse is of equal value；Fig. 7 (e) and Fig. 7 (c) is contrasted, it can be seen that the remaining RCM obtained using conventional cross-correlation method is estimated
It is worth poor performance；The cross-correlation coefficient of neighbor distance picture as little as 0.4 in Fig. 7 (f), illustrates the failure of conventional cross-correlation method.
Thereby confirm the validity of the invention.
For the performance of further displaying context of methods, choose respectively at two in Fig. 6 before and after representative region progress self-focusing
Amplification comparative analysis.As shown in figure 8, Fig. 8 (a) and Fig. 8 (b) is the thick focusedimage before self-focusing；Fig. 8 (c) and Fig. 8 (d)
To carry out the image after self-focusing using PGA；Fig. 8 (e) and Fig. 8 (f) is using this patent institute inventive technique scheme progress autohemagglutination
Defocused image；Image after the obvious technical finesse is had compared to before processing and using the image after the processing of PGA methods
Very big improvement, picture quality obtains very big lifting.Thereby confirm the success of the invention.
SAR echo datas RCM means for correctings provided in an embodiment of the present invention, as shown in figure 9, described device includes：Preceding place
Module 91, remnants RCM determining modules 92, correction module 93 are managed, wherein,
The pre-processing module 91, for carrying out Range compress and geometry RCM corrections to echo data, obtains Range compress
Time domain data afterwards；
Specifically, it is necessary to complete some pre-treatment steps before remaining RCM estimates and corrects, including Range compress and
Geometry RCM is corrected.Here it is possible to which the correction of kinematic error can be well adapted for using improved CSA, CSA.Carrying out orientation
After Chirp Scaling, Range compress and consistent RCM are corrected, SAR signals time domain discrete form, i.e., after Range compress
Time domain data can be represented with expression formula (1)；
Wherein, A0Represent any complex constant, ωa() represents orientation envelope (sinc squares of type function), and m represents orientation
Pulse sequence number, n represents range cell sequence number, Δ TaPulse recurrence interval is represented, x represents the orientation position of arbitrary target in scene
Coordinate is put, V represents carrier aircraft flying speed, BdRepresent the bandwidth of transmission signal, Δ TrDistance samples interval is represented, r represents flight boat
Mark is to the nearest oblique distance of target, and c represents propagation velocity of electromagnetic wave, and Δ R (m) represents aircraft motion error, fcRepresent radar carrier frequency,
R0(m) represent target to the instantaneous oblique distance in course line.
The remaining RCM determining modules 92, for carrying out sub-aperture segmentation to the time domain data after the Range compress, are obtained
Sub-aperture data are taken, the sub-block data in each sub-aperture data with highest SCR is chosen respectively；
The remaining RCM determining modules 92, specifically for：By the time domain data after the Range compress along azimuth segmentation
For sub-aperture data；Selection processing is carried out to each sub-aperture data using sliding window, determines have in each sub-aperture data
Highest SCR sub-block data；
Specifically, range-aligned method needs to meet such hypothesis：In whole CPI, there is height between Range Profile
Similitude；ISAR systems generally meet such condition because short CPI ISAR data be commonly used to noncooperative target into
Picture, such target includes aircraft, ship etc..However, compared with carried SAR data, the CPI of ISAR data would generally increase by tens
Times；In addition, except staring beam bunching mode, the region that radar beam is irradiated to can also change with the change of observation time.On
The similitude between Range Profile can all be reduced by stating factor.In order to solve this problem, by the time domain data edge side after Range compress
Position is to being divided into sub-aperture；Here it is possible to by the length of sub-aperture be divided into length of synthetic aperture 1 to three/2nds/
One, so, it is ensured that the high similitude in each sub-aperture.Assuming that full aperture data are divided into P sub-aperture, according to table
Up to formula (1), pth sub- pore size data can be represented, can be represented with expression formula (2)；Wherein, window function rectp(m), may be used
To be represented with expression formula (2)；
The window function rectp(m) it is a rectangular window function, m0And NaInterval and the length of sub-aperture are represented respectively.Need
The remaining RCM of different sub-apertures estimate to be combined using the overlapping pulses of adjacent subpulse, so Na>m0, weight
The number of folded pulse is Na-m0；
Range-aligned is to be imaged and design for ISAR originally, and the irradiation area of wherein ISAR wave beams is mainly artificial mesh
Mark, and their size is very limited.However, the mapping band of SAR image is generally wider, tens kms can be reached.Meanwhile, away from
May be smaller than 10cm from pixel size.In this case, it is possible to need distance to thousands of sampled point to cover photograph
Region is penetrated, therefore data volume is very huge.In addition, in the data of Range compress, the regions of some antiradar reflectivities may be by
To noise and the severe jamming of clutter, this can be negatively affected to remnants RCM estimations.It is that distance is constant to sky in remaining RCM
This chooses the son with highest SCR using sliding window method under the hypothesis that wide swath is also set up to each sub-aperture
Block number evidence.By means of which, the computational efficiency and estimated accuracy of self-focusing method can all be improved.According to expression formula (2), from
The sub-block data chosen in p sub-aperture can be represented with expression formula (4)；Wherein, rect (n) is a rectangular window function, can
To be represented with expression formula (5)；Wherein, q0For sliding window sequence number corresponding with the data block selected, n0And NrSliding window is represented respectively
Interval and length.
The remaining RCM determining modules 92, are additionally operable to, and according to each sub-block data of selection, determine each sub-aperture data
Remaining RCM；
Obtain after sub-block data, it is necessary to estimate the remaining RCM of each sub-aperture using the sub-block data chosen.Based on distance
The entropy minimization method of alignment has robustness to noise and clutter, and technical solution of the present invention is improved, and estimates for remaining RCM
Meter.Specific processing includes：
Enter row distance to each sub-block data respectively down-sampled to liter sampling and orientation, obtain corresponding distance to liter
Sampling and the down-sampled data of orientation；
Specifically, with the proposition of cross-correlation method, can be to dataEnter row distance to liter sampling and an orientation
The down-sampled sensitivity to reduce computational load and improve distance movement.Assuming that G (k, l), 0≤k≤K, 0≤l≤L-1 be by
Distance is adopted to liter sampling distance corresponding with the sub-block after the down-sampled processing of orientation, chosen in p-th of sub-aperture to liter
Sample and the down-sampled data of orientation, wherein, K=α Nr, L=Na/β。
Respectively to each distance to liter sampling and the down-sampled data of orientation, using exponential type average distance as ARP
Calculate, obtain corresponding reference distance as RRP data；
Specifically, on the one hand, if be only directed at current distance picture with neighbor distance picture, drift error and jump just occurs
Become error.On the other hand, due to the change in azimuth and beam region, the similitude between Range Profile can be spaced over time
Increase and be gradually reduced.Therefore, RRP is regarded as ARP after range-aligned and unreasonable.In order to solve the above problems, adopt
RRP is calculated with a kind of exponential type ARP.Here, the normalization RRP expression formulas of (l+1) the individual echo used can use expression
Formula (6) is represented；Wherein, Gl(k) it is l-th of pulse in data；For Gl(k) echo after calibrated；ω be one just
Real number scalar, and meet 0<ω<1；It is the primary condition of algorithm.
Adopted respectively according to each distance to liter sampling RRP data corresponding with itself with the data that orientation is down-sampled
Corresponding RCM is estimated with the cost function based on Entropy principle；
Specifically, being risen and fallen by strong background noise and back scattering is influenceed, the performance that conventional cross-correlation method is estimated RCM
It can reduce, or even can not realize at all.The Minimum entropy method based on range-aligned applied to ISAR data processings to noise and
Rise and fall insensitive, therefore there are the potentiality applied to SAR data.So, technical solution of the present invention utilizes the cost based on Entropy principle
Function estimates RCM；It is estimated that Rl+1And G (k)l+1(k) RCM, can be represented with expression formula (7)；Wherein,For Gl
(k) normalized form.
According to the value of three points near the minimum entropy position of the RCM respectively estimated, the RCM respectively estimated is calibrated, is obtained
Take the accurate RCM of each sub-aperture data；
Specifically, the measurement in order to realize subpixel accuracy, the liter for having carried out Range Profile in the incipient stage of estimation is adopted
Sample.However, calculated load can rapidly increase with interpolation factor α increase；Accordingly, it would be desirable to select appropriate α to coordinate essence
The relation of exactness degree and efficiency.In order to preferably improve the accuracy of estimated result, the method that conic fitting can be used.
This method improves the RCM of estimation by using the value of three points near minimum entropy position.The accurate RCM of p-th of sub-aperture can
To be represented with expression formula (8)；Wherein,
Each accurate RCM is carried out rising sampling using simple interpolations, the remaining RCM of each sub-aperture is obtained；
Specifically, obtaining remaining RCM by interpolation to each accurate RCM.In order to obtain remaining RCM valueUtilize
Simple interpolations are by RCM amountsSampling is risen, makes length and sub-aperture equal length after liter sampling.
In practical application, the calculation process such as Fig. 4 can be used by estimating the remaining RCM of each sub-aperture.
The remaining RCM determining modules 92, are additionally operable to：Full aperture combination is carried out to the remaining RCM of each sub-aperture data, obtained
Full aperture to remaining RCM is combined；
Specifically, it is necessary to which they are combined after the remaining RCM of whole sub-apertures is obtained.In fact, due to
RRP difference, the lap of adjacent sub-aperture may have small difference.In technical solution of the present invention, using overlapping
Partial average remaining RCM is discontinuous to avoid, and the remaining RCM laps of sub-aperture are as shown in Figure 5；
Although minimum entropy theory is robust to noise, error can be substantially reduced, some hairs are still there may be
Thorn, particularly when the contrast of irradiation area is very low.In order to improve combination remnants RCM accuracy, while removing various each
The interference of sample, technical solution of the present invention can use the mixed filtering method comprising higher order polynomial-fitting and discrete cosine transform
Full aperture combination is carried out to the remaining RCM.
The correction module 93, for being combined according to remaining RCM full aperture, corrects the remaining RCM of the echo data.
Specifically, being combined according to the remaining RCM of determination full aperture, by being referred to apart from frequency domain to echo data
Phase multiplication realizes remaining RCM correction, and this can overcome can only move the limitation of integer range cell in the time domain.Together
When, it can also combine RCM to realize thick phase compensation by the remaining RCM of determination full aperture.
SAR echo datas RCM means for correctings provided in an embodiment of the present invention, described device also includes：Image-forming module 94, is used
Self-focusing is carried out in the echo data to correcting remnants RCM, and carries out Azimuth Compression, SAR image is obtained；
Specifically, in order to which APE compensation carries out conventional self-focusing；In remaining RCM calibration phases, sub-pixel is estimated remaining
RCM, and it is enough to be directed under a range resolution ratio cell width Range Profile of bending.However, coming to APE compensation
Say, RCM precision must reach sub-wavelength magnitude, this can substantially exceed the limit of power of existing range-aligned method.Therefore, need
Accurate APE is estimated using self-focusing technology, and is compensated.Wherein, the self-focusing technology, including：PGA；
, it is necessary to carry out Azimuth Compression after completion self-focusing, the SAR image of well focussed is ultimately generated.
In actual applications, pre-processing module 91, remnants RCM determining modules 92, correction module 93, image-forming module 94 can be by
Central processing unit (CPU), microprocessor (MPU), digital signal processor (DSP) or field-programmable gate array in SAR system
(FPGA) etc. is arranged to realize.
It is described above, it is only the good embodiment of the present invention, is not intended to limit the scope of the present invention, it is all at this
Any modifications, equivalent substitutions and improvements made within the spirit and principle of invention etc., should be included in the protection model of the present invention
Within enclosing.
Claims (10)
1. a kind of synthetic aperture radar SAR echo datas range migration RCM bearing calibrations, it is characterised in that methods described includes：
Range compress and geometry RCM corrections are carried out to echo data, the time domain data after Range compress is obtained；
Sub-aperture segmentation is carried out to the time domain data after the Range compress, sub-aperture data is obtained, each sub-aperture is chosen respectively
There is highest signal to noise ratio SCR sub-block data in data；
According to each sub-block data of selection, the remaining RCM of each sub-aperture data is determined；
Full aperture combination is carried out to the remaining RCM of each sub-aperture data, remaining RCM full aperture combination is obtained；
Combined according to remaining RCM full aperture, correct the remaining RCM of the echo data；
Each sub-block data according to selection, determines the remaining RCM of each sub-aperture data；Including：
Enter row distance to each sub-block data respectively down-sampled to liter sampling and orientation, obtain corresponding distance to a liter sampling
The down-sampled data with orientation；
Respectively to each distance to liter sampling and the down-sampled data of orientation, using exponential type average distance as ARP calculating,
Corresponding reference distance is obtained as RRP data；
Respectively according to each distance to liter sampling RRP data corresponding with itself with the data that orientation is down-sampled, using base
Corresponding RCM is estimated in the cost function of Entropy principle；
According to the value of three points near the minimum entropy position of the RCM respectively estimated, the RCM respectively estimated is calibrated, obtains each
The accurate RCM of sub-aperture data；
Each accurate RCM is carried out rising sampling using simple interpolations, the remaining RCM of each sub-aperture is obtained.
2. according to the method described in claim 1, it is characterised in that the time domain data to after the Range compress carries out son
Aperture segmentation, obtains sub-aperture data, and choose the sub-block data in each sub-aperture data with highest SCR respectively；Including：
By the time domain data after the Range compress along azimuth segmentation be sub-aperture data；
Selection processing is carried out to each sub-aperture data using sliding window, determines there is highest SCR's in each sub-aperture data
Sub-block data；
The length of the sub-aperture is 1st/1 to three/2nds of length of synthetic aperture.
3. according to the method described in claim 1, it is characterised in that the remaining RCM to each sub-aperture carries out full aperture group
Close, obtain remaining RCM full aperture combination；Including：
Using the mixed filtering method for including higher order polynomial-fitting and discrete cosine transform, the remaining RCM of each sub-aperture is entered
Row full aperture is combined, and obtains remaining RCM full aperture combination.
4. according to the method described in claim 1, it is characterised in that described to be combined according to remaining RCM full aperture, correction is described
The remaining RCM of echo data；Including：
Fixed phase multiplication is being carried out apart from frequency domain to the echo data, the echo data to correcting remnants RCM is obtained；
Thick phase compensation is carried out to echo data according to the combination of remaining RCM full aperture.
5. the method according to any one of Claims 1-4, it is characterised in that methods described also includes：
Self-focusing is carried out to the echo data of the correction remnants RCM, and carries out Azimuth Compression, SAR image is obtained；
The method of the self-focusing, including：Phase gradient autofocus PGA.
6. a kind of SAR echo datas RCM means for correctings, it is characterised in that described device includes：Pre-processing module, remnants RCM are true
Cover half block, correction module, wherein,
The pre-processing module, is corrected for carrying out Range compress and geometry RCM to echo data, obtain after Range compress when
Numeric field data；
The remaining RCM determining modules, are used for：
Sub-aperture segmentation is carried out to the time domain data after the Range compress, sub-aperture data is obtained, each sub-aperture is chosen respectively
There is highest SCR sub-block data in data；
According to each sub-block data of selection, the remaining RCM of each sub-aperture data is determined；
Full aperture combination is carried out to the remaining RCM of each sub-aperture data, remaining RCM full aperture combination is obtained；
The correction module, for being combined according to remaining RCM full aperture, corrects the remaining RCM of the echo data；
Each sub-block data according to selection, determines the remaining RCM of each sub-aperture data；Including：
Enter row distance to each sub-block data respectively down-sampled to liter sampling and orientation, obtain corresponding distance to a liter sampling
The down-sampled data with orientation；
Respectively to each distance to liter sampling and the down-sampled data of orientation, using exponential type average distance as ARP calculating,
Corresponding reference distance is obtained as RRP data；
Respectively according to each distance to liter sampling RRP data corresponding with itself with the data that orientation is down-sampled, using base
Corresponding RCM is estimated in the cost function of Entropy principle；
According to the value of three points near the minimum entropy position of the RCM respectively estimated, the RCM respectively estimated is calibrated, obtains each
The accurate RCM of sub-aperture data；
Each accurate RCM is carried out rising sampling using simple interpolations, the remaining RCM of each sub-aperture is obtained.
7. device according to claim 6, it is characterised in that the remaining RCM determining modules, specifically for：
By the time domain data after the Range compress along azimuth segmentation be sub-aperture data；
Selection processing is carried out to each sub-aperture data using sliding window, determines there is highest SCR's in each sub-aperture data
Sub-block data；
The length of the sub-aperture is 1st/1 to three/2nds of length of synthetic aperture.
8. device according to claim 6, it is characterised in that the remaining RCM determining modules, specifically for：
Enter row distance to each sub-block data respectively down-sampled to liter sampling and orientation, obtain corresponding distance to a liter sampling
The down-sampled data with orientation；
Each distance is calculated to liter sampling and the down-sampled data of orientation using exponential type ARP respectively, obtained corresponding
RRP data；
Respectively according to each distance to liter sampling RRP data corresponding with itself with the data that orientation is down-sampled, using base
Corresponding RCM is estimated in the cost function of Entropy principle；
According to the value of three points near the minimum entropy position of the RCM respectively estimated, the RCM respectively estimated is calibrated, obtains each
The accurate RCM of sub-aperture data；
Each accurate RCM is carried out rising sampling using simple interpolations, the remaining RCM of each sub-aperture is obtained.
9. device according to claim 6, it is characterised in that the remaining RCM determining modules, specifically for：
Using the mixed filtering method for including higher order polynomial-fitting and discrete cosine transform, the remaining RCM of each sub-aperture is entered
Row full aperture is combined, and obtains remaining RCM full aperture combination.
10. device according to claim 6, it is characterised in that the correction module, specifically for：
Fixed phase multiplication is being carried out apart from frequency domain to the echo data, the echo data to correcting remnants RCM is obtained；
Thick phase compensation is carried out to echo data according to the combination of remaining RCM full aperture；
Described device, in addition to image-forming module, carry out self-focusing, and carry out for the echo data to the correction remnants RCM
Azimuth Compression, obtains SAR image.
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