CN103995260A - Synthetic aperture radar SAR imaging method and device - Google Patents

Abstract

The invention discloses a synthetic aperture radar SAR imaging method which comprises the following steps: distance-direction non-space-variant motion compensation processing is performed on original SAR data, and distance-direction compression processing is performed on the motion-compensated SAR data; distance-direction space-variant phase gradient auto-focusing PGA processing is performed on the distance-direction compressed SAR data, and the residual error phase of the SAR data is acquired and corrected; and azimuth-direction compression processing is performed on the corrected SAR data. The invention further discloses an SAR imaging device.

Description

A kind of synthetic aperture radar image-forming method and device

Technical field

The present invention relates to airborne radar imaging technical field, relate in particular to a kind of synthetic-aperture radar (SAR, Synthetic Aperture Radar) formation method and device.

Background technology

SAR is a kind of microwave remote sensing device with round-the-clock, round-the-clock feature, is widely used in the fields such as topographic mapping, marine monitoring, forecast of natural calamity and target identification.SAR can be arranged on satellite or aircraft to obtain the high-resolution microwave image of observation scene.Due to the disturbance of atmosphere, there is certain deviation with respect to desirable course line in the actual course line of carried SAR platform, thereby cause SAR image to have fuzzy and distortion, causes defocusing of SAR image.Therefore the SAR image that kinematic error, how to remove exactly carried SAR platform obtains vernier focusing is to be badly in need of at present the major issue that solves.

Summary of the invention

The technical matters existing for prior art, the embodiment of the present invention provides a kind of SAR formation method and device.

The embodiment of the present invention provides a kind of SAR formation method, and described method comprises:

Original SAR data are carried out to distance to non-space-variant motion compensation process;

SAR data after motion compensation are carried out to distance to be processed to compression;

Carry out distance by adjusting the distance to compression SAR data after treatment and process to space-variant phase gradient self-focusing (PGA, Phase Gradient Autofocus), obtain and proofread and correct the residual error phase place of SAR data;

SAR data after proofreading and correct are carried out to orientation to be processed to compression.

In such scheme, described original SAR data are carried out to distance to non-space-variant motion compensation process: to observe scene center as reference point, according to the error phase of the original SAR data of obtaining, original SAR data are carried out to distance to non-space-variant motion compensation process.

In such scheme, described taking observation scene center as reference point, according to the error phase of the original SAR data of obtaining, original SAR data are carried out to distance to before non-space-variant motion compensation process, described method also comprises:

According to the original SAR data in the geometric relationship of airborne actual flight path and Desired Track and navigational system, obtain the kinematic error side-play amount of actual flight path with respect to Desired Track, according to the kinematic error side-play amount of original SAR data, obtain the error phase of original SAR data.

In such scheme, describedly SAR data after motion compensation are carried out to distance be treated to compression: utilize linear frequency to become mark algorithm (CSA, Chirp Scaling Algorithm) the SAR data after motion compensation are carried out to distance to compression processing.

In such scheme, the SAR data of the described CSA of utilization after to motion compensation carry out processing and comprising to compression without orientation:

SAR data after adopting CSA to motion compensation are carried out frequency modulation (PFM), and the range migration residual quantity of the SAR data after frequency modulation (PFM) is proofreaied and correct to processing;

The migration residual quantity of adjusting the distance in 2-d spectrum territory is proofreaied and correct SAR data after treatment and is carried out successively distance to compression, second-compressed and consistent range migration correction processing;

At Doppler domain, consistent range migration correction SAR data after treatment being carried out to orientation proofreaies and correct to compression and additive phase.

In such scheme, described in adjust the distance and carry out distance to compression SAR data after treatment and comprise to space-variant PGA processing:

Will apart to compression data after treatment along distance to being divided into each SAR data block, by each SAR data block along orientation to divide sub-aperture, standard P GA processing is carried out in every sub-aperture in each SAR data block, obtain the residual error phase place in every sub-aperture in each SAR data block.

In such scheme, described in obtain SAR data residual error phase place comprise:

Respectively the lap existing between the sub-aperture in each SAR data block is carried out to the splicing of residual error phase place, obtain the residual error phase curve of each SAR data block;

The residual error phase place of residual error phase place using between each SAR data block as each SAR data block middle distance to temporary location respectively, utilize interpolating function to carry out interpolation fitting processing to the residual error phase place of each range unit in each SAR data block, obtain the residual error phase place of whole distance to the SAR data of unit.

The embodiment of the present invention also provides a kind of SAR imaging device, and described device comprises: compensating module, compression module, focusing processing module; Wherein,

Described compensating module, for carrying out distance to non-space-variant motion compensation process to original SAR data; And the residual error phase place of the SAR data that send according to described focusing processing module, the residual error phase place of correction SAR data;

Described compression module, processes to compression for the SAR data after described compensating module motion compensation being carried out to distance; And the SAR data after proofreading and correct are carried out to orientation and process to compression;

Described focusing processing module, for processing to space-variant PGA by described compression module distance is carried out to distance to compression SAR data after treatment, obtain the residual error phase place of SAR data, and the residual error phase place of the SAR data of obtaining is sent to described compensating module.

In such scheme, described compensating module, specifically for taking observation scene center as reference point, carries out distance to non-space-variant motion compensation process according to the error phase of the original SAR data of obtaining to original SAR data.

In such scheme, described compression module, carries out distance specifically for the SAR data after utilizing CSA to motion compensation and processes to compression.

In such scheme, described focusing processing module, specifically for will apart to compression data after treatment along distance to being divided into each SAR data block, by each SAR data block along orientation to divide sub-aperture, standard P GA processing is carried out in every sub-aperture in each SAR data block, obtain the residual error phase place in every sub-aperture in each SAR data block.

In such scheme, described focusing processing module, specifically also for: respectively the lap existing between the sub-aperture of each SAR data block is carried out to the splicing of residual error phase place, obtains the residual error phase curve of each SAR data block;

The residual error phase place of residual error phase place using between each SAR data block as each SAR data block middle distance to temporary location respectively, utilize interpolating function to carry out interpolation fitting processing to the residual error phase place of each range unit in each SAR data block, obtain the residual error phase place of whole distance to the SAR data of unit.

The SAR formation method that the embodiment of the present invention provides, described method comprises: original SAR data are carried out to distance to non-space-variant motion compensation process, the SAR data after motion compensation are carried out to distance and process to compression; Carry out distance by adjusting the distance to compression SAR data after treatment and process to space-variant phase gradient self-focusing PGA, obtain and proofread and correct the residual error phase place of SAR data; SAR data after proofreading and correct are carried out to orientation and process to compression, so, can obtain the SAR image of the complexity observation scene of vernier focusing.

Brief description of the drawings

The SAR formation method schematic flow sheet that Fig. 1 provides for the embodiment of the present invention one;

The airborne actual flight path that Fig. 2 provides for the embodiment of the present invention one, two and the geometric relationship schematic diagram of Desired Track;

The distance that Fig. 3 provides for the embodiment of the present invention one, two is processed the method schematic diagram of distance to packed data to space-variant PGA;

The standard P GA self-focusing processing method schematic flow sheet that Fig. 4 provides for the embodiment of the present invention one, two;

The SAR imaging device structural representation that Fig. 5 provides for the embodiment of the present invention two;

In prior art, after motion compensation, there is the SAR image defocusing in Fig. 6;

Fig. 7 is through standard P GA SAR image after treatment in prior art;

The SAR image that Fig. 8 provides for the embodiment of the present invention three;

Fig. 9 is the SAR image of observing scenario A in prior art after standard P GA processes;

The SAR image of the observation scenario A that Figure 10 provides for the embodiment of the present invention three;

Figure 11 is the SAR image of observing scenario B in prior art after standard P GA processes;

The SAR image of the observation scenario B that Figure 12 provides for the embodiment of the present invention three.

Embodiment

In order to understand content of the present invention, the present invention first introduces the method for obtaining High Resolution SAR image in prior art.Motion compensation (MOCO, Motion Compensation) technology is the important technical that solves High Resolution SAR image defocus problem.In traditional MOCO scheme, first inertial measuring unit (the IMU that utilizes airborne platform to carry, Inertial Measurement Units) realize SAR data distance to non-space-variant motion compensation, the range migration problem causing to eliminate high-resolution situation lower platform kinematic error; Secondly on this basis, then adopt various auto-focus methods further to eliminate the phase error of scattering point, thereby obtain High Resolution SAR image.Here in the situation that there is no IMU, can adopt the method for data estimation to realize distance to non-space-variant motion compensation.

But traditional MOCO scheme designs based on subdued topography itself, for complex-terrain, traditional MOCO scheme is under high-resolution condition, and the problem that defocuses that topographic relief is caused is helpless.And in actual applications, this scene is a large amount of existence, thereby be necessary to seek the High Resolution SAR image imaging method under a kind of MODEL OVER COMPLEX TOPOGRAPHY.

Based on this, in various embodiment of the present invention: original SAR data are carried out to distance to non-space-variant motion compensation process; SAR data after motion compensation are carried out to distance to be processed to compression; Carry out distance by adjusting the distance to compression SAR data after treatment and process to space-variant phase gradient self-focusing PGA, obtain and proofread and correct the residual error phase place of SAR data; SAR data after proofreading and correct are carried out to orientation and process to compression, can obtain the SAR image of the observation scene of vernier focusing.

Below by drawings and the specific embodiments, technical scheme of the present invention is described in further detail.

Embodiment mono-

The embodiment of the present invention provides a kind of SAR formation method, and as shown in Figure 1, the method mainly comprises the following steps:

Step 101, carries out distance to non-space-variant motion compensation process to original SAR data;

In this step, first according to the original SAR data in the geometric relationship of airborne actual flight path and Desired Track and navigational system, obtain the kinematic error side-play amount of actual flight path with respect to Desired Track, according to the kinematic error side-play amount of original SAR data, obtain the error phase of original SAR data; And taking observation scene center as reference point, according to the error phase of original SAR data, original SAR data are carried out to distance to non-space-variant motion compensation process.

Particularly, Fig. 2 shows airborne actual flight path under positive side-looking pattern and the geometric relationship of Desired Track; Wherein, X-axis refers to Desired Track, and curve refers to actual flight path; At t _min the moment, the antenna phase center (APC, Antenna Phase Center) of Desired Track is [Vt _m, 0, H], the APC of actual flight path is [Vt _m+ Δ x (t _m), Δ y (t _m), H+ Δ z (t _m)].

Wherein, described V refers to the speed of airborne platform; Described H refers to the speed of airborne platform; Described Vt _mrefer at t _mmoment, the speed of airborne platform; Described Δ x (t _m) referring to that airborne platform is in X-direction, actual flight path is with respect to the kinematic error side-play amount of Desired Track; Described Δ y (t _m) referring to that airborne platform is in Y direction, actual flight path is with respect to the kinematic error side-play amount of Desired Track; Described Δ z (t _m) referring to that airborne platform is in Z-direction, actual flight path is with respect to the kinematic error side-play amount of Desired Track.[Δ x (t _m), Δ y (t _m), Δ z (t _m)] composition actual flight path is with respect to the kinematic error side-play amount of Desired Track.

Here the P in Fig. 2, _nfor the strong scattering point in observation scene, coordinate is (x _n, y _n, z _n), described P _nminimum distance to the APC of actual flight path is R ₀, at t _mmoment, P _ninstantaneous distance to the APC of actual flight path is:

$\begin{array}{c}{R}_a\left(t_m\right)=\sqrt{{({\mathrm{Vt}}_m+\mathrm{\Δx}\left(t_m\right)-x_n)}^2+{(\mathrm{\Δy}\left(t_m\right)-y_n)}^2+{(H+\mathrm{\Δz}\left(t_m\right)-z_n)}^2}\\ =R_i\left(t_m\right)+\mathrm{\ΔR}\left(t_m\right)\end{array}---\left(1\right)$

Wherein, $R_i\left(t_m\right)=\sqrt{{R_0^2+({\mathrm{Vt}}_m-x_n)}^2}---\left(2\right)$

$\mathrm{\ΔR}\left(t_m\right)\≈\frac{2V{t}_m+\mathrm{\Δx}\left(t_m\right)-2x_n}{2}\·\mathrm{\Δx}\left(t_m\right)+\sin \mathrm{\θ}\·\mathrm{\Δy}\left(t_m\right)+\cos \mathrm{\θ}\·\mathrm{\Δz}\left(t_m\right)---\left(3\right)$

Here described R, _i(t _m) refer at t _mmoment, P _narrive the instantaneous distance of the APC of Desired Track; Described Δ R (t _m) refer at t _min the moment, actual flight path is with respect to the kinematic error side-play amount of Desired Track; Described θ is the incident angle of observation scene center; Described cos θ=(H-Z _n)/R ₀, described Z _nrefer to the observation elevation of observation scene center any point.

If when observation scene is subdued topography, Z _n=Z, θ can be according to the oblique distance r Precise Representation of observation scene center so:

$\cos \mathrm{\θ}=\frac{H-Z}{r}---\left(4\right)$

So, can find out in conjunction with formula (3) and formula (4), kinematic error side-play amount is that part is relevant to distance, that is: Δ R (t _m)=f (t _m, r).

Concrete, if scene is observed in all angles, have,

$\cos {\mathrm{\θ}}_c=\frac{H-Z_c}{r_c}---\left(5\right)$

Wherein, described θ _crefer to the incident angle of observation scene center; Described Z _crefer to observation elevation; Described r _crefer to the oblique distance of observation scene center.

Now, distance to non-space-variant kinematic error is:

$\mathrm{\ΔR}\left(t_m\right)\≈\frac{2V{t}_m+\mathrm{\Δx}\left(t_m\right)-2x_n}{2}\·\mathrm{\Δx}\left(t_m\right)+\sqrt{1-{\left(\frac{H-z_c}{r_c}\right)}^2}\·\mathrm{\Δy}\left(t_m\right)+\frac{H-z_c}{r_c}\·\mathrm{\Δz}\left(t_m\right)---\left(6\right)$

Error phase is: ${\mathrm{\φ}}_{\mathrm{\ϵc}}\left(t_m\right)=\frac{4\mathrm{\π\ΔR}\left(t_m\right)}{\mathrm{\λ}}---\left(7\right)$

By the exponential function exp (j of error phase ^*φ _{ε c}(t _m)) multiply each other with original SAR data, complete the distance of original SAR data to non-space-variant motion compensation process; Wherein, described λ is carrier wavelength.

Step 102, carries out distance to the SAR data after motion compensation and processes to compression;

Here, the SAR data after utilizing CSA to motion compensation are carried out distance and are processed to compression.

Particularly, the SAR data after first adopting CSA to motion compensation are carried out frequency modulation (PFM), so that SAR data complete change of scale; And the range migration residual quantity of the SAR data after the modulation of different distance door upper frequency is proofreaied and correct, so that all SAR data have consistent range migration; The SAR data of secondly adjusting the distance after the correction of migration residual quantity in 2-d spectrum territory are carried out distance successively to compression, second-compressed and consistent range migration correction processing, finally at Doppler domain, consistent range migration correction SAR data after treatment being carried out to orientation proofreaies and correct to compression and additive phase, obtain distance to packed data, so far, distance is finished dealing with to compression.

Step 103, carries out distance by adjusting the distance to compression SAR data after treatment and processes to space-variant PGA, obtains and proofread and correct the residual error phase place of SAR data;

In this step, as shown in Figure 3, first will be apart from being divided into each SAR data block along distance to zero lap to compression SAR data after treatment by the data width apart from upwards fixing, the data width of upwards fixing with orientation again and certain Duplication by each SAR data block along orientation to divide sub-aperture, standard P GA processing is carried out in every sub-aperture in each SAR data block, obtain the residual error phase place in every sub-aperture in each SAR data block.Here, described SAR data at least comprise k SAR data block, and k is natural number; Each SAR data block at least comprises m sub-aperture, and m is natural number.

Wherein, the set of all SAR data blocks is overall data, all sub-apertures data acquisition be whole orientation to data, comprised whole orientation to information along distance to the each SAR data block after dividing; The data width that described distance is upwards fixed can suitably be adjusted according to the difference of the frequency of SAR data, resolution, the data width that described orientation is upwards fixed and certain Duplication can be set to definite value, such as, can data width be set to 1/4 of length of synthetic aperture, Duplication is arranged to 1/2 of overlapping region.

Here, described standard P GA is the Autofocus processing that carries out SAR image based on distance to non-space-variant hypothesis, as shown in Figure 4, mainly comprises the following steps:

Step 401, selects strong scattering point;

In this step, in each range unit, be selected in the scattering point with high s/n ratio, use this scattering point can improve the precision of error phase; Wherein, described range unit refers to the SAR data acquisition upwards of all orientation with same distance, is equivalent to the every a line in two-dimensional matrix.

Step 402, carries out ring shift processing to scattering point;

In this step, the strong scattering point of each range unit of selecting, along orientation to ring shift to picture centre, and is alignd all strong scattering points, with evaluated error phase place more effectively.

Step 403, carries out windowing process to ring shift scattering point after treatment;

In this step, strong scattering point, along orientation to carrying out windowing process, is suppressed to the interference of noise and adjacent scattering point, increase the signal to noise ratio (S/N ratio) of this scattering point, make the error phase of estimation more accurate

Step 404, carries out phase gradient to the scattering point after windowing process and estimates to process;

In this step, suppose that the view data after windowing is g _n(x), to g _n(x) carry out inverse Fourier transform and draw G _n(u),

G _n(u)＝|G _n(u)|exp(j[φ _ε(u)+θ _n(u)]) (8)

Wherein, described φ _ε(u) refer to orientation to kinematic error phase place, described θ _n(u) refer to strong scattering and put relevant phase function.

So, estimate that based on linear unbias minimum variance (LUMV, Linear Unbiased Minimum Variance) residual error phase gradient is:

${\widehat{\mathrm{\Φ}}}_{\mathrm{LUMV}}\left(u\right)=\frac{{\mathrm{\Σ}}_n\mathrm{Im}\left\{G_n^{*}\left(u\right)G_n\left(u\right)\right\}}{{\mathrm{\Σ}}_n{\left|G_n\left(u\right)\right|}^2}={\stackrel{\·}{\mathrm{\φ}}}_{\mathrm{\ϵ}}\left(u\right)+\frac{{\mathrm{\Σ}}_n{\left|G_n\left(u\right)\right|}^2{\stackrel{\·}{\mathrm{\θ}}}_n\left(u\right)}{{\mathrm{\Σ}}_n{\left|G_n\left(u\right)\right|}^2}---\left(9\right)$

Or, estimate that based on maximum likelihood (ML, Maximum-Like) residual error phase gradient is:

${\widehat{\mathrm{\Φ}}}_{\mathrm{ML}}\left(u\right)=\arg \left\{\underset{n}{\mathrm{\Σ}}{G}_n(u+\mathrm{\Δu})G_n^{*}\left(u\right)\right\}---\left(10\right)$

Step 405, estimates that to phase gradient scattering point after treatment carries out iterative phase and proofreaies and correct processing.

In this step, residual error phase gradient integration is obtained after residual error phase place, and residual error phase place is compensated to processing; Repeat above operation until error is less than the thresholding of default error.

Particularly, after processing by above-mentioned standard P GA, can estimate the residual error phase place in every sub-aperture in each SAR data block, respectively the lap existing between the sub-aperture of each SAR data block be carried out to the splicing of residual error phase place, complete the splicing in all sub-apertures according to this principle; After having spliced, obtain the residual error phase curve of corresponding SAR data block; The residual error phase place of residual error phase place using between each SAR data block as each SAR data block middle distance to temporary location respectively, utilize the interpolating function in MATLAB to carry out interpolation fitting processing to the residual error phase place of the each range unit of each SAR data block, to obtain the residual error phase curve of whole distance to the SAR data of unit, realize in whole distance the residual error phase estimation to unit; Wherein, described each SAR data block at least comprises n range unit, and n is natural number.

Wherein, in described lap, the sub-aperture of SAR data block has identical residual error phase place; The error phase of described each SAR data block of obtaining is all the error phase value of corresponding SAR data block for range units all in each SAR data block, and the object of interpolation is in order to obtain more accurate error phase, the i.e. error phase of each range unit.

Particularly, the error phase of supposing each SAR data block is respectively φ _{ε, 1}(u) ..., φ _{ε, i}(u) ..., φ _{ε, I}(u), carry out interpolation processing by the error phase in each SAR data block, obtain the residual error phase place of the SAR data of range unit n:

φ _ε(n,u)＝interp{[r _c,1,...,r _c,i,...,r _c,I],[φ _ε,1(u),...,φ _ε,i(u),...,φ _ε,I(u)],r _n} (11)

Particularly, according to the residual error phase of obtaining _ε(n, u), by the exponential function exp (j of residual error phase place ^*φ _ε(n, u)) and multiply each other apart from the SAR data after compression, the residual error phase place of SAR data is carried out to Transformatin, complete compensation, realize the residual error phase correction of distance to space-variant.Wherein, described i be distance to i SAR data block; Described r _c,irefer to that the distance of i SAR data block is to center; Described r _nrefer to range unit n.

Step 104, carries out orientation to the SAR data after proofreading and correct and processes to compression.

In this step, SAR data are carried out to orientation after compression processing, can obtain the SAR image of final vernier focusing.

The SAR formation method that the embodiment of the present invention provides, is a kind of high-resolution SAR imaging technique that is applicable to complex-terrain, can obtain the SAR image of the observation scene of vernier focusing.

Embodiment bis-

With respect to embodiment mono-, the embodiment of the present invention also provides a kind of SAR imaging device, and as shown in Figure 5, this device comprises: compensating module 51, compression module 52, focusing processing module 53; Wherein,

Described compensating module 51, for carrying out distance to non-space-variant motion compensation process to original SAR data; And the residual error phase place of the SAR data that send according to described focusing processing module 53, the residual error phase place of correction SAR data;

Described compression module 52, processes to compression for the SAR data after described compensating module 51 motion compensation being carried out to distance; And the SAR data after described compensating module 51 corrections are carried out to orientation and process to compression.

Described focusing processing module 53, for processing to space-variant PGA by described compression module 52 distances are carried out to distance to compression SAR data after treatment, get the residual error phase place of SAR data, and the residual error phase place of the SAR data of obtaining is sent to described compensating module 51.

Wherein, described compensating module 51, specifically for: first according to the original SAR data in the geometric relationship of airborne actual flight path and Desired Track and navigational system, obtain the kinematic error side-play amount of actual flight path with respect to Desired Track, according to the kinematic error side-play amount of original SAR data, obtain the error phase of original SAR data again; And taking observation scene center as reference point, according to the error phase of original SAR data, original SAR data are carried out to distance to non-space-variant motion compensation process.

Here, Fig. 2 shows airborne actual flight path under positive side-looking pattern and the geometric relationship of Desired Track; Wherein, X-axis refers to Desired Track, and curve refers to actual flight path; At t _min the moment, the antenna phase center (APC, Antenna Phase Center) of Desired Track is [Vt _m, 0, H], the APC of actual flight path is [Vt _m+ Δ x (t _m), Δ y (t _m), H+ Δ z (t _m)].

Wherein, described V refers to the speed of airborne platform; Described H refers to the speed of airborne platform; Described Vt _mrefer at t _mmoment, the speed of airborne platform; Described Δ x (t _m) referring to that airborne platform is in X-direction, actual flight path is with respect to the kinematic error side-play amount of Desired Track; Described Δ y (t _m) referring to that airborne platform is in Y direction, actual flight path is with respect to the kinematic error side-play amount of Desired Track; Described Δ z (t _m) referring to that airborne platform is in Z-direction, actual flight path is with respect to the kinematic error side-play amount of Desired Track.[Δ x (t _m), Δ y (t _m), Δ z (t _m)] composition actual flight path is with respect to the kinematic error side-play amount of Desired Track.

Here the P in Fig. 2, _nfor the strong scattering point in observation scene, coordinate is (x _n, y _n, z _n), described P _nminimum distance to the APC of actual flight path is R ₀, at t _mmoment, P _ninstantaneous distance to the APC of actual flight path is:

$\begin{array}{c}{R}_a\left(t_m\right)=\sqrt{{({\mathrm{Vt}}_m+\mathrm{\Δx}\left(t_m\right)-x_n)}^2+{(\mathrm{\Δy}\left(t_m\right)-y_n)}^2+{(H+\mathrm{\Δz}\left(t_m\right)-z_n)}^2}\\ =R_i\left(t_m\right)+\mathrm{\ΔR}\left(t_m\right)\end{array}---\left(1\right)$

Wherein, $R_i\left(t_m\right)=\sqrt{{R_0^2+({\mathrm{Vt}}_m-x_n)}^2}---\left(2\right)$

$\mathrm{\ΔR}\left(t_m\right)\≈\frac{2V{t}_m+\mathrm{\Δx}\left(t_m\right)-2x_n}{2}\·\mathrm{\Δx}\left(t_m\right)+\sin \mathrm{\θ}\·\mathrm{\Δy}\left(t_m\right)+\cos \mathrm{\θ}\·\mathrm{\Δz}\left(t_m\right)---\left(3\right)$

Here described R, _i(t _m) refer at t _mmoment, P _narrive the instantaneous distance of the APC of Desired Track; Described Δ R (t _m) refer at t _min the moment, actual flight path is with respect to the kinematic error side-play amount of Desired Track; Described θ is the incident angle of observation scene center; Described cos θ=(H-Z _n)/R ₀, described Z _nrefer to the observation elevation of observation scene center any point.

If when observation scene is subdued topography, Z _n=Z, θ can be according to the oblique distance r Precise Representation of observation scene center so:

$\cos \mathrm{\θ}=\frac{H-Z}{r}---\left(4\right)$

So, can find out in conjunction with formula (3) and formula (4), kinematic error side-play amount is that part is relevant to distance, that is: Δ R (t _m)=f (t _m, r).

Concrete, if scene is observed in all angles, have,

$\cos {\mathrm{\θ}}_c=\frac{H-Z_c}{r_c}---\left(5\right)$

Wherein, described θ _crefer to the incident angle of observation scene center; Described Z _crefer to observation elevation; Described r _crefer to the oblique distance of observation scene center.

Now, distance to non-space-variant kinematic error is:

$\mathrm{\ΔR}\left(t_m\right)\≈\frac{2V{t}_m+\mathrm{\Δx}\left(t_m\right)-2x_n}{2}\·\mathrm{\Δx}\left(t_m\right)+\sqrt{1-{\left(\frac{H-z_c}{r_c}\right)}^2}\·\mathrm{\Δy}\left(t_m\right)+\frac{H-z_c}{r_c}\·\mathrm{\Δz}\left(t_m\right)---\left(6\right)$

Error phase is: ${\mathrm{\φ}}_{\mathrm{\ϵc}}\left(t_m\right)=\frac{4\mathrm{\π\ΔR}\left(t_m\right)}{\mathrm{\λ}}---\left(7\right)$

By the exponential function exp (j of error phase ^*φ _{ε c}(t _m)) multiply each other with original SAR data, complete the distance of original SAR data to non-space-variant motion compensation process; Wherein, described λ is carrier wavelength.

When described compensating module 51 completes, original SAR data are carried out to distance after non-space-variant motion compensation, described compression module 52, specifically for: the SAR data after first adopting CSA to motion compensation are carried out frequency modulation (PFM), so that SAR data complete change of scale; And the range migration residual quantity of SAR data to different distance door upper frequency modulation proofreaies and correct, so that all SAR data have consistent range migration; The SAR data of secondly adjusting the distance after the correction of migration residual quantity in 2-d spectrum territory are carried out distance successively to compression, second-compressed and consistent range migration correction processing; Finally at Doppler domain, consistent range migration correction SAR data after treatment are carried out to orientation and proofread and correct to compression and additive phase, obtain distance to packed data, so far, distance is finished dealing with to compression.

When described compression module 52 completes SAR data distance after compression processing, described focusing processing module 53, specifically for: as shown in Figure 3, first will be apart from being divided into each SAR data block along distance to zero lap to compression SAR data after treatment by the data width apart from upwards fixing, the data width of upwards fixing with orientation again and certain Duplication by each SAR data block along orientation to divide sub-aperture, standard P GA processing is carried out in every sub-aperture in each SAR data block, obtain the residual error phase place in every sub-aperture in each SAR data block.

Wherein, the set of all SAR data blocks is overall data, all sub-apertures data acquisition be whole orientation to data, comprised whole orientation to information along distance to the each SAR data block after dividing; The data width that described distance is upwards fixed can suitably be adjusted according to the difference of the frequency of SAR data, resolution, the data width that described orientation is upwards fixed and certain Duplication can be set to definite value, such as, can data width be set to 1/4 of length of synthetic aperture, Duplication is arranged to 1/2 of overlapping region; Described SAR data at least comprise k SAR data block, and k is natural number; Described each SAR data block at least comprises m sub-aperture, and m is natural number.

Here, described standard P GA is the Autofocus processing that carries out SAR image based on distance to non-space-variant hypothesis, as shown in Figure 4, mainly comprises the following steps:

Step 401, selects strong scattering point;

In this step, in each range unit, be selected in the scattering point with high s/n ratio, use this scattering point can improve the precision of error phase; Wherein, described range unit refers to the SAR data acquisition upwards of all orientation with same distance, is equivalent to the every a line in two-dimensional matrix.

Step 402, carries out ring shift processing to scattering point;

In this step, the strong scattering point of each range unit of selecting, along orientation to ring shift to picture centre, and is alignd all strong scattering points, with evaluated error phase place more effectively.

Step 403, carries out windowing process to ring shift scattering point after treatment;

In this step, strong scattering point, along orientation to carrying out windowing process, is suppressed to the interference of noise and adjacent scattering point, increase the signal to noise ratio (S/N ratio) of this scattering point, make the error phase of estimation more accurate

Step 404, carries out phase gradient to the scattering point after windowing process and estimates to process;

In this step, suppose that the view data after windowing is g _n(x), to g _n(x) carry out inverse Fourier transform and draw G _n(u),

G _n(u)＝|G _n(u)|exp(j[φ _ε(u)+θ _n(u)]) (8)

Wherein, described φ _ε(u) refer to orientation to kinematic error phase place, described θ _n(u) refer to strong scattering and put relevant phase function.

So, estimate that based on linear unbias minimum variance (LUMV, Linear Unbiased Minimum Variance) residual error phase gradient is:

${\widehat{\mathrm{\Φ}}}_{\mathrm{LUMV}}\left(u\right)=\frac{{\mathrm{\Σ}}_n\mathrm{Im}\left\{G_n^{*}\left(u\right)G_n\left(u\right)\right\}}{{\mathrm{\Σ}}_n{\left|G_n\left(u\right)\right|}^2}={\stackrel{\·}{\mathrm{\φ}}}_{\mathrm{\ϵ}}\left(u\right)+\frac{{\mathrm{\Σ}}_n{\left|G_n\left(u\right)\right|}^2{\stackrel{\·}{\mathrm{\θ}}}_n\left(u\right)}{{\mathrm{\Σ}}_n{\left|G_n\left(u\right)\right|}^2}---\left(9\right)$

Or, estimate that based on maximum likelihood (ML, Maximum-Like) residual error phase gradient is:

${\widehat{\mathrm{\Φ}}}_{\mathrm{ML}}\left(u\right)=\arg \left\{\underset{n}{\mathrm{\Σ}}{G}_n(u+\mathrm{\Δu})G_n^{*}\left(u\right)\right\}---\left(10\right)$

When described focusing processing module 53 completes after above-mentioned standard P GA processing, can estimate the residual error phase place in every sub-aperture in each SAR data block; Described focusing processing module 53 specifically also for: respectively the lap existing between the sub-aperture of each SAR data block is carried out to the splicing of residual error phase place, completes the splicing in all sub-apertures according to this principle; After having spliced, obtain the residual error phase curve of corresponding SAR data block; The residual error phase place of residual error phase place using between each SAR data block as this SAR data block middle distance to temporary location respectively, utilize the interpolating function in MATLAB to carry out interpolation fitting processing to the residual error phase place of each range unit in each SAR data block, to obtain the residual error phase curve of whole distance to the SAR data of unit, realize in whole distance the residual error phase estimation to unit.

Wherein, in described lap, the sub-aperture of SAR data block has identical residual error phase place; The error phase of described each SAR data block of obtaining is all the error phase value of corresponding SAR data block for range units all in each SAR data block, and the object of interpolation is in order to obtain more accurate error phase, the i.e. error phase of each range unit; Described each SAR data block at least comprises n range unit, and n is natural number.

Particularly, the error phase of supposing each SAR data block is respectively φ _{ε, 1}(u) ..., φ _{ε, i}(u) ..., φ _{ε, I}(u), carry out interpolation processing by the error phase in each SAR data block, obtain the residual error phase place of the SAR data of range unit n:

φ _ε(n,u)＝interp{[r _c,1,...,r _c,i,...,r _c,I],[φ _ε,1(u),...,φ _ε,i(u),...,φ _ε,I(u)],r _n} (11)

Described focusing processing module 53 is adjusted the distance and is carried out after distance is disposed to space-variant PGA to compression SAR data after treatment, described compensating module 51, specifically for: according to the residual error phase of obtaining _ε(n, u), by the exponential function exp (j of residual error phase place ^*φ _ε(n, u)) and multiply each other apart from the SAR data after compression, the residual error phase place of SAR data is carried out to Transformatin, complete compensation, realize the residual error phase correction of distance to space-variant.Wherein, described i be distance to i SAR data block; Described r _c,irefer to that the distance of i SAR data block is to center; Described r _nrefer to range unit n.

SAR data after described compensating module 51 is to the residual error phase correction of SAR data are carried out orientation to compression processing, can obtain the SAR image of final vernier focusing.

When practical application, described compensating module 51, compression module 52 and focusing processing module 53 can be by the central processing unit (CPU in SAR imaging device, Central Processing Unit), digital signal processor (DSP, Digital Signal Processor) or programmable logic array (FPGA, Field-Programmable Gate Array) realization.

Embodiment tri-

In order to verify accuracy and the reliability of above-described embodiment, the present embodiment is taking resolution as certain mountain area of 0.15 meter as example, and the radar imaging method providing with the radar imaging method in prior art scheme and each embodiment of the present invention is respectively made comparison to SAR image.Fig. 6 shows the SAR image that in prior art, existence defocuses after motion compensation; Fig. 7 shows in prior art through standard P GA SAR image after treatment; Fig. 8 shows the SAR image that the embodiment of the present invention provides; From these images, can find out, compared with prior art, the SAR formation method that adopts the embodiment of the present invention to provide can be realized the vernier focusing of SAR image, thereby gets good SAR image.

Meanwhile, two observation scenario As, B are got in certain mountain area that the present embodiment is 0.15 meter in resolution, and wherein, Fig. 9 shows the SAR image of observing scenario A in prior art after standard P GA processes; The SAR image of the observation scenario A that Figure 10 embodiment of the present invention provides; Figure 11 shows the SAR image of observing scenario B in prior art after standard P GA processes; The SAR image of the observation scenario B that Figure 12 embodiment of the present invention provides.Can obviously be found out by above-mentioned image, compared with prior art SAR image after treatment, the SAR formation method that the embodiment of the present invention provides has been realized the vernier focusing of SAR image, can get good SAR image, further verify accuracy and the reliability of the SAR formation method that various embodiments of the present invention provide.

Those skilled in the art should understand, embodiments of the invention can be provided as method, system or computer program.Therefore, the present invention can adopt hardware implementation example, implement software example or the form in conjunction with the embodiment of software and hardware aspect.And the present invention can adopt the form at one or more upper computer programs of implementing of computer-usable storage medium (including but not limited to magnetic disk memory and optical memory etc.) that wherein include computer usable program code.

The present invention is with reference to describing according to process flow diagram and/or the block scheme of the method for the embodiment of the present invention, equipment (system) and computer program.Should understand can be by the flow process in each flow process in computer program instructions realization flow figure and/or block scheme and/or square frame and process flow diagram and/or block scheme and/or the combination of square frame.Can provide these computer program instructions to the processor of multi-purpose computer, special purpose computer, Embedded Processor or other programmable data processing device to produce a machine, the instruction that makes to carry out by the processor of computing machine or other programmable data processing device produces the device for realizing the function of specifying at flow process of process flow diagram or multiple flow process and/or square frame of block scheme or multiple square frame.

These computer program instructions also can be stored in energy vectoring computer or the computer-readable memory of other programmable data processing device with ad hoc fashion work, the instruction that makes to be stored in this computer-readable memory produces the manufacture that comprises command device, and this command device is realized the function of specifying in flow process of process flow diagram or multiple flow process and/or square frame of block scheme or multiple square frame.

These computer program instructions also can be loaded in computing machine or other programmable data processing device, make to carry out sequence of operations step to produce computer implemented processing on computing machine or other programmable devices, thereby the instruction of carrying out is provided for realizing the step of the function of specifying in flow process of process flow diagram or multiple flow process and/or square frame of block scheme or multiple square frame on computing machine or other programmable devices.

The above, be only preferred embodiment of the present invention, is not intended to limit protection scope of the present invention, all any amendments of doing within the spirit and principles in the present invention, is equal to and replaces and improvement etc., within all should being included in protection scope of the present invention.

Claims (12)

1. a synthetic-aperture radar SAR formation method, is characterized in that, described method comprises:

Original SAR data are carried out to distance to non-space-variant motion compensation process;

SAR data after motion compensation are carried out to distance to be processed to compression;

Carry out distance by adjusting the distance to compression SAR data after treatment and process to space-variant phase gradient self-focusing PGA, obtain and proofread and correct the residual error phase place of SAR data;

SAR data after proofreading and correct are carried out to orientation to be processed to compression.

2. formation method according to claim 1, it is characterized in that, described original SAR data are carried out to distance to non-space-variant motion compensation process: to observe scene center as reference point, according to the error phase of the original SAR data of obtaining, original SAR data are carried out to distance to non-space-variant motion compensation process.

3. formation method according to claim 2, it is characterized in that, described taking observation scene center as reference point, according to the error phase of the original SAR data of obtaining, original SAR data are carried out to distance to before non-space-variant motion compensation process, described method also comprises:

According to the original SAR data in the geometric relationship of airborne actual flight path and Desired Track and navigational system, obtain the kinematic error side-play amount of actual flight path with respect to Desired Track, according to the kinematic error side-play amount of original SAR data, obtain the error phase of original SAR data.

4. formation method according to claim 1, is characterized in that, describedly SAR data after motion compensation are carried out to distance is treated to compression: utilize linear frequency to become the SAR data of mark algorithm CSA after to motion compensation and carry out distance to compression processing.

5. formation method according to claim 4, is characterized in that, the SAR data of the described CSA of utilization after to motion compensation carry out processing and comprising to compression without orientation:

SAR data after adopting CSA to motion compensation are carried out frequency modulation (PFM), and the range migration residual quantity of the SAR data after frequency modulation (PFM) is proofreaied and correct to processing;

The migration residual quantity of adjusting the distance in 2-d spectrum territory is proofreaied and correct SAR data after treatment and is carried out successively distance to compression, second-compressed and consistent range migration correction processing;

At Doppler domain, consistent range migration correction SAR data after treatment being carried out to orientation proofreaies and correct to compression and additive phase.

6. formation method according to claim 1, is characterized in that, described in adjust the distance and carry out distance to compression SAR data after treatment and comprise to space-variant PGA processing:

Will apart to compression data after treatment along distance to being divided into each SAR data block, by each SAR data block along orientation to divide sub-aperture, standard P GA processing is carried out in every sub-aperture in each SAR data block, obtain the residual error phase place in every sub-aperture in each SAR data block.

7. formation method according to claim 6, is characterized in that, described in obtain SAR data residual error phase place comprise:

Respectively the lap existing between the sub-aperture in each SAR data block is carried out to the splicing of residual error phase place, obtain the residual error phase curve of each SAR data block;

The residual error phase place of residual error phase place using between each SAR data block as each SAR data block middle distance to temporary location respectively, utilize interpolating function to carry out interpolation fitting processing to the residual error phase place of each range unit in each SAR data block, obtain the residual error phase place of whole distance to the SAR data of unit.

8. a SAR imaging device, is characterized in that, described device comprises: compensating module, compression module, focusing processing module; Wherein,

Described compensating module, for carrying out distance to non-space-variant motion compensation process to original SAR data; And the residual error phase place of the SAR data that send according to described focusing processing module, the residual error phase place of correction SAR data;

Described compression module, processes to compression for the SAR data after described compensating module motion compensation being carried out to distance; And the SAR data after proofreading and correct are carried out to orientation and process to compression;

Described focusing processing module, for processing to space-variant PGA by described compression module distance is carried out to distance to compression SAR data after treatment, obtain the residual error phase place of SAR data, and the residual error phase place of the SAR data of obtaining is sent to described compensating module.

9. imaging device according to claim 8, is characterized in that, described compensating module, specifically for taking observation scene center as reference point, carries out distance to non-space-variant motion compensation process according to the error phase of the original SAR data of obtaining to original SAR data.

10. imaging device according to claim 8, is characterized in that, described compression module carries out distance specifically for the SAR data after utilizing CSA to motion compensation and processes to compression.

11. imaging devices according to claim 8, it is characterized in that, described focusing processing module, specifically for will apart to compression data after treatment along distance to being divided into each SAR data block, by each SAR data block along orientation to divide sub-aperture, standard P GA processing is carried out in every sub-aperture in each SAR data block, obtain the residual error phase place in every sub-aperture in each SAR data block.

12. imaging devices according to claim 11, it is characterized in that, described focusing processing module, specifically also for: respectively the lap existing between the sub-aperture of each SAR data block is carried out to the splicing of residual error phase place, obtains the residual error phase curve of each SAR data block;

The residual error phase place of residual error phase place using between each SAR data block as each SAR data block middle distance to temporary location respectively, utilize interpolating function to carry out interpolation fitting processing to the residual error phase place of each range unit in each SAR data block, obtain the residual error phase place of whole distance to the SAR data of unit.