CN104678393B - Subaperture wave number domain imaging method for squint sliding spotlight SAR (Synthetic Aperture Radar) - Google Patents

Abstract

The invention discloses a subaperture wave number domain imaging method for a squint sliding spotlight SAR (Synthetic Aperture Radar). A traditional sliding spotlight SAR subaperture method is improved aiming at squint conditions. The subaperture wave number domain imaging method comprises the following steps: firstly, overlapping a whole aperture and dividing subapertures; taking an extended wave number domain method used for the squint conditions as a subaperture basic imaging method; and finishing azimuth processing in a distance Doppler domain by adopting an improved BAS method to splice the subapertures, so as to obtain a whole aperture image under the squint conditions. With the adoption of the subaperture wave number domain imaging method, the problems of the squint sliding spotlight SAR of large data size, non-zero azimuth Doppler center and oversized Doppler bandwidth are solved, and the practical value is larger.

Description

The sub-aperture wave-number domain imaging method of stravismus slip pack sar

Technical field

The present invention relates to radar imaging technology field, more particularly, to a kind of sub-aperture wave-number domain of stravismus slip pack sar Imaging method.

Background technology

Synthetic aperture radar is one kind high-resolution imaging radar all-time anf all-weather, all sends out in dual-use field Wave significant role.Slip beam bunching mode is a kind of new synthetic aperture radar (synthetic aperture radar, sar) Imaging pattern, it, by controlling the translational speed on ground for the antenna irradiated site come control azimuth resolution, obtains and compares beam bunching mode Bigger imaging area, higher than same antenna size band pattern azimuth resolution.Therefore, slip beam bunching mode is in machine Carry and spaceborne sar suffers from being widely applied.

Under slip beam bunching mode, the synthetic aperture time of target is long, and the Doppler frequency center of echo is with target Position of orientation changes, and leads to the strain of its doppler bandwidth phase big.In order to avoid aliasing in azimuth spectrum it is necessary to meet pulse weight Complex frequency (pulse repetition frequency, prf) is more than doppler bandwidth.

Azimuth spectrum aliasing be can solve the problem that by the method dividing sub-aperture.Sub-aperture shot is to be divided into full aperture overlap The individual sub-aperture of n (n >=2), is processed to each sub-aperture Dynamic data exchange, finally data splicing is helped resolution image.At sub-aperture Reason not only can solve orientation spectral aliasing, and relatively low to request memory, when echo data amount is larger, has good spirit Activity.But it is adaptable to positive side sub-aperture shot optionally can not be completely applicable for stravismus situation.

Content of the invention

The technical problem to be solved is the defect for background technology, provides a kind of stravismus slip pack sar Sub-aperture wave-number domain imaging method.

The present invention is to solve above-mentioned technical problem to employ the following technical solutions:

The sub-aperture wave-number domain imaging method of stravismus slip pack sar, comprises the steps:

Step 1), by n_a×n_rFull aperture radar return data overlap be divided into several sub-aperture, each sub-aperture is returned Wave number evidence is n_ai×n_r, and sub-aperture is determined according to the size of lap between the size dividing sub-aperture and sub-aperture Number:Round downwards and Jia 1；

Wherein, n_aFor full aperture radar echo pulse number, n_rIt is distance to sampling number, n_aiFor each sub-aperture echo Pulse number, i is the index of sub-aperture, and δ n is the size of lap between sub-aperture；

Step 2), to the sub-aperture dividing respectively using extension space virtual detection techniques: first to the sub-aperture after pulse pressure Echo data carries out orientation fft, is then unanimously compressed and stolt interpolation in two-dimensional frequency, and last length obtains to ifft To basic imaging results；

Step 3), the base band orientation in the case of stravismus becomes mark process and realizes sub-aperture stitching: enters in range-Dopler domain Row orientation calibrate, then sub-aperture stitching, the full aperture data obtaining is carried out derotation and orientation compression obtain final Sar image.

Look side ways the further prioritization scheme of sub-aperture wave-number domain imaging method of slip pack sar as the present invention, described Step 2) specifically comprise the following steps that

Step 2.1), pulse compression is carried out to echo data, obtains apart from frequency domain, orientation time domain data；

Step 2.2), orientation Fourier transformation is carried out to data after pulse pressure, obtains two-dimensional frequency data；

Step 2.3), complete unanimously to compress in two-dimensional frequency, realize first main focus steps, the expression of reference function Formula is:

$h_1=\exp \{j\frac{4\mathrm{\π}}{c}{r}_{ref}\[\sqrt{{(f_{\mathrm{\τ}}+f_c)}^2-{\left(\frac{f_{a}c}{2v_a}\right)}^2}{\mathrm{cos\θ}}_s+\frac{f_{a}c}{2v_a}{\mathrm{sin\θ}}_s\]\}$

Wherein, h₁For the expression formula of reference function, j is the ultimate unit of imaginary number, r_ref=r₀/cosθ_sFor reference distance, r₀ For the shortest oblique distance, f_τAnd f_aBe respectively distance to orientation frequency, f_cFor radar center frequency, c is the light velocity, v_aFor radar side Position is to speed, θ_sFor angle of strabismus；

Step 2.4), complete stolt interpolation in two-dimensional frequency, realize the focusing of point target at non-reference distance, stolt inserts Value makes original frequency of distance f by substitution of variable_τIt is mapped as new frequency of distance f '_τ, its formula is as follows:

$\sqrt{{(f_{\mathrm{\τ}}+f_c)}^2-{\left(\frac{f_{a}c}{2v_a}\right)}^2}{\mathrm{cos\θ}}_s+\frac{f_{a}c}{2v_a}{\mathrm{sin\θ}}_s=f_c+f_{\mathrm{\τ}}^{\′};$

Step 2.5), eliminate orientation skew, and distance is moved at reference distance to time centre, specially will Data after stolt interpolation is multiplied by following phase function:

$h_2=\exp \{-j\frac{2{\mathrm{\πf}}_a{r}_{ref}}{v_a}{\mathrm{sin\θ}}_s-j\frac{4\mathrm{\π}(f_c+f_{\mathrm{\τ}}^{\′})r_{ref}}{c}\}$

Wherein, h₂Expression formula for phase function；

Step 2.6), distance, to ifft, is transformed into range-Dopler domain.

Look side ways the further prioritization scheme of sub-aperture wave-number domain imaging method of slip pack sar as the present invention, described Step 3) specifically comprise the following steps that

Step 3.1), it is multiplied by orientation scaling factor in range-Dopler domain:

$h_3=\exp \{j2{\mathrm{\πt}}_v{f}_a+j\frac{{\mathrm{\πf}}_a^2}{k_{scl}\left(r\right)}\}$

Wherein, h₃For orientation scaling factor, r is distance axis,λ For wavelength, f_dc=2v_asinθ_s/ λ is full aperture doppler centroid；

Step 3.2), orientation inverse Fourier transform is transformed into orientation time domain, carries out sub-aperture stitching in orientation time domain and obtains To full aperture data, comprise the following specific steps that:

Step 3.2.1), define n_a×n_rThe complete opening drive matrix of size, by the n of first sub-aperture_aiIndividual pulse is assigned to entirely The front n of aperture matrix_aiIndividual pulse；

Step 3.2.2), calculate the overlaid pixel unit δ n=kn of orientation_ai, successively by i-th (i ＞ 1) individual sub-aperture δ n/2+1 row to n-th_aiThe n of row_aiN/2-1 pulse of-δ is assigned to (i-1) (n of full aperture_ai- δ n)+δ n/2+1 row To (i-1) (n_ai-δn)+n_aiOK, complete the splicing of sub-aperture, wherein, k is overlap ratio；

Step 3.3), each benefit n about complete opening drive matrix orientation_a/ 2 zero, comprise the following specific steps that:

Step 3.3.1), define n'_aThe new matrix of × nr size, wherein, n'_a=2n_a；

Step 3.3.2), original matrix is assigned to the n-th of new matrix_a/ 2+1 row is to n-th '_a-n_a/ 2 row, complete orientation and mend Zero；

Step 3.4), full aperture orientation derotation:

$h_4=\exp \{{\mathrm{j\πk}}_{rot}{t}_{a\_all}^2-j2h_{dc\_all}{t}_{a\_all}\}$

Wherein, h₄It is the fixed phase of derotation,v_fFor beam Area's sliding speed, t_{a_all}And f_{dc_all}It is respectively full aperture orientation time and orientation mid frequency；

Step 3.5), orientation Fourier transformation, carry out orientation pulse pressure in orientation frequency domain, the pulse pressure factor is:

$h_5=\exp \left\{j\frac{{\mathrm{\πf}}_a^2}{k_{eff}\left(r\right)}\right\}$

Wherein, h₅For the pulse pressure factor, k_eff(r)=k_rot-k_scl(r)；

Step 3.6), orientation inverse Fourier transform obtains full aperture sar image.

Look side ways the further prioritization scheme of sub-aperture wave-number domain imaging method of slip pack sar, step as the present invention 1) the sub-aperture size described in is:

$t_{sub}\≤\frac{prf-\max b_{a,proc}}{\left|k_{rot}\right|}$

Wherein, t_subThe size of the sub-aperture for dividing, prf is azimuth sample rate, b_a,procOrientation for single sub-aperture Bandwidth.

The present invention adopts above technical scheme compared with prior art, has following technical effect that

1. overcome the big problem of the data volume of stravismus slip pack sar presence；

2. overcome the problem of orientation Doppler center non-zero；

3. overcome the excessive problem of doppler bandwidth.

Brief description

Fig. 1 is stravismus slip pack sar geometric model；

Fig. 2 is method flow diagram；

Fig. 3 is point target simulation result that angle of strabismus is when 0 °；

Fig. 4 is point target simulation result that angle of strabismus is when 20 °；

Fig. 5 is point target simulation result that angle of strabismus is when 30 °；

Fig. 6 is point target simulation result that angle of strabismus is when 40 °.

Specific embodiment

Below in conjunction with the accompanying drawings technical scheme is described in further detail:

The present embodiment is made checking using sar emulation data and is analyzed to this method, and emulation data is provided that radar Carry a width of 300mhz, carrier frequency is 10ghz, a width of 20 μ s during signal, impulse sampling frequency is 360mhz, pulse recurrence frequency prf For 1000hz, the carrier aircraft speed of a ship or plane is 120m/s, and the translational speed on ground for the antenna irradiated site is 60m/s, and carrier aircraft height is 10km. Sar emulates data orientation sampling number n_rFor 16384, distance is to sampling number n_aFor 16384, the orientation of single sub-aperture Sampling number n_aiFor 8192, angle of strabismus takes 0 °, 20 °, 30 °, 40 ° to be emulated respectively.

With reference to Fig. 1, Fig. 2, flying platform speed is v_a, radar beam center is on ground with the uniform velocity v_gScanning, o and o ' are respectively For aperture center and scene center point, o_rotFor rotary middle point, θ_sFor angle of strabismus, r₀And r_rotIt is respectively aperture the shortest to scene Distance and aperture are to center of rotation beeline.P is scene any point, and the sub-aperture wave-number domain of stravismus slip pack sar becomes Image space method comprises the steps:

Step 1: by n_a×n_rFull aperture radar return data overlap be divided into several sub-aperture, each sub-aperture is returned Wave number evidence is n_ai×n_r, wherein n_a=16384 is full aperture radar echo pulse number, n_rIt is distance to sampling number, n_ai= 8192 is each sub-aperture radar echo pulse number, if the overlap ratio of sub-aperture is 1/4, then the sub-aperture number dividing is 2.

Step 2: the imaging of wave-number domain method is extended to i-th sub-aperture echo data, comprises the following specific steps that:

Step 2-1: pulse compression is carried out to echo data, obtains orientation time domain, apart from frequency domain data；

Step 2-2: orientation Fourier transformation is carried out to data after pulse pressure, obtains two-dimensional frequency data；

Step 2-3: complete unanimously to compress in two-dimensional frequency, realize first main focus steps.The expression of reference function Formula is as shown in (1)

$h_1=\exp \{j\frac{4\mathrm{\π}}{c}{r}_{ref}\[\sqrt{{(f_{\mathrm{\τ}}+f_c)}^2-{\left(\frac{f_{a}c}{2v_a}\right)}^2}{\mathrm{cos\θ}}_s+\frac{f_{a}c}{2v_a}{\mathrm{sin\θ}}_s\]\}---\left(1\right)$

Wherein, r_ref=r0/cos (θ_s) it is reference distance, r₀For the shortest oblique distance, f_τAnd f_aBe respectively distance to and orientation Frequency, f_c=10ghz is radar center frequency, c=3 × 10⁸For the light velocity, v_a=120m/s is radar bearing to speed, θ_sFor oblique Visual angle.

Step 2-4: complete stolt interpolation in two-dimensional frequency, realize the focusing of the point target at non-reference distance.

Stolt interpolation makes original frequency of distance f by substitution of variable_τIt is changed into new frequency of distance f '_τ

$\sqrt{{(f_{\mathrm{\τ}}+f_c)}^2-{\left(\frac{f_{a}c}{2v_a}\right)}^2}{\mathrm{cos\θ}}_s+\frac{f_{a}c}{2v_a}{\mathrm{sin\θ}}_s=f_c+f_{\mathrm{\τ}}^{\′}---\left(2\right)$

Step 2-5: for sub-aperture stitching below, need to be multiplied by formula (3)

$h_2=\exp \{-j\frac{2{\mathrm{\πf}}_a{r}_{ref}}{v_a}{\mathrm{sin\θ}}_s-j\frac{4\mathrm{\π}(f_c+f_{\mathrm{\τ}}^{\′})r_{ref}}{c}\}---\left(3\right)$

Wherein Section 1 eliminates orientation skew, and distance is moved at reference distance by Section 2 to time centre.

Step 2-6: distance, to ifft, is transformed into range-Dopler domain.

Step 3: the base band orientation of stravismus situation becomes mark and processes, and comprises the following specific steps that:

Step 3-1: be multiplied by orientation scaling factor in range-Dopler domain.

$h_3=\exp \{j2{\mathrm{\πt}}_v{f}_a+j\frac{{\mathrm{\πf}}_a^2}{k_{scl}\left(r\right)}\}---\left(4\right)$

Wherein, r is distance axis,

Step 3-2: orientation inverse Fourier transform is transformed into orientation time domain, carries out sub-aperture stitching in orientation time domain and obtains Full aperture data.Comprise the following specific steps that:

Step 3-2-1: define the complete opening drive matrix of 16384 × 16384 sizes, by 8192 pulses of first sub-aperture It is assigned to front 8192 pulses of complete opening drive matrix.

Step 3-2-2: the overlaid pixel unit δ n=2048 of note orientation.By the 1025th row of the 2nd sub-aperture to 7168 pulses of 8192 row are assigned to the 8193rd row of full aperture battle array to the 15360th, complete the splicing of sub-aperture.

Step 3-3: respectively mend 8192 zero about complete opening drive matrix orientation.Comprise the following specific steps that:

Step 3-3-1: set n'_a=32768, define the new matrix of 32768 × 16384 sizes.

Step 3-3-2: original matrix is assigned to the 8193rd row of new matrix to the 24576th row, completes orientation zero padding.

Step 3-4: full aperture orientation derotation:

$h_4=\exp \{{\mathrm{j\πk}}_{rot}{t}_{a\_all}^2-j2{\mathrm{\πf}}_{dc\_all}{t}_{a\_all}\}---\left(5\right)$

Wherein,v_f=60m/s is the movement on ground for the antenna irradiated site Speed, t_{a_all}And f_{dc_all}It is respectively full aperture orientation time and orientation mid frequency.

Step 3-5: orientation Fourier transformation, carry out orientation pulse pressure in orientation frequency domain, the pulse pressure factor is:

$h_5=\exp \left\{j\frac{{\mathrm{\πf}}_a^2}{k_{eff}\left(r\right)}\right\}---\left(6\right)$

Wherein, k_eff(r)=k_rot-k_scl(r).

Step 3-6: orientation inverse Fourier transform obtains full aperture sar image.Fig. 3,4,5,6 sets forth angle of strabismus For point target simulation result when 0 °, 20 °, 30 °, 40 °.

Further, the sub-aperture size described in step 1 is:

$t_{sub}=\frac{prf-b_{a,proc}}{\left|k_{rot}\right|}---\left(7\right)$

Wherein, prf is azimuth sample rate, b_a,procThe orientation bandwidth of single sub-aperture.

The above is only the preferred embodiment of the present invention, and not the present invention is made with any pro forma restriction.Should Point out, any those skilled in the art, without departing from technical solution of the present invention scope, the technology according to the present invention is real Matter, within the spirit and its principle of the present invention, any simple modification, equivalent and improvement that above example is made Deng belonging within the protection domain of technical solution of the present invention.

Claims (3)

1. the sub-aperture wave-number domain imaging method of stravismus slip pack sar is it is characterised in that comprise the steps:

Step 1), by n_a×n_rFull aperture radar return data overlap be divided into several sub-aperture, each sub-aperture number of echoes According to for n_ai×n_r, and sub-aperture number is determined according to the size of the size and lap between sub-aperture that divide sub-aperture:Round downwards and Jia 1；

Wherein, n_aFor full aperture radar echo pulse number, n_rIt is distance to sampling number, n_aiFor each sub-aperture echo impulse Number, i is the index of sub-aperture, and δ n is the size of lap between sub-aperture；

Step 2), to the sub-aperture dividing respectively using extension space virtual detection techniques: first to the sub-aperture echo after pulse pressure Data carries out orientation fft, is then unanimously compressed and stolt interpolation in two-dimensional frequency, and last length obtains base to ifft This imaging results；

Step 2.1), pulse compression is carried out to echo data, obtains apart from frequency domain, orientation time domain data；

Step 2.2), orientation Fourier transformation is carried out to data after pulse pressure, obtains two-dimensional frequency data；

Step 2.3), complete unanimously to compress in two-dimensional frequency, realize first main focus steps, the expression formula of reference function For:

$h_1=\exp \left\{j\frac{4\mathrm{\π}}{c}{r}_{ref}\[\sqrt{{(f_{\mathrm{\τ}}+f_c)}^2-{\left(\frac{f_{a}c}{2v_a}\right)}^2}{\mathrm{cos\θ}}_s+\frac{f_{a}c}{2v_a}{\mathrm{sin\θ}}_s\]\right\}$

Wherein, h₁For the expression formula of reference function, j is the ultimate unit of imaginary number, r_ref=r₀/cosθ_sFor reference distance, r₀For Short oblique distance, f_τAnd f_aBe respectively distance to orientation frequency, f_cFor radar center frequency, c is the light velocity, v_aFor radar bearing to Speed, θ_sFor angle of strabismus；

Step 2.4), complete stolt interpolation in two-dimensional frequency, realize the focusing of point target at non-reference distance, stolt interpolation is led to Crossing substitution of variable makes original frequency of distance f_τIt is mapped as new frequency of distance f '_τ, its formula is as follows:

$\sqrt{{(f_{\mathrm{\τ}}+f_c)}^2-{\left(\frac{f_{a}c}{2v_a}\right)}^2}{\mathrm{cos\θ}}_s+\frac{f_{a}c}{2v_a}{\mathrm{sin\θ}}_s=f_c+f_{\mathrm{\τ}}^{\′};$

Step 2.5), eliminate orientation skew, and distance is moved at reference distance to time centre, specially stolt is inserted Data after value is multiplied by following phase function:

$h_2=\exp \{-j\frac{2{\mathrm{\πf}}_a{r}_{ref}}{v_a}{\mathrm{sin\θ}}_s-j\frac{4\mathrm{\π}(f_c+f_{\mathrm{\τ}}^{\′})r_{ref}}{c}\}$

Wherein, h₂Expression formula for phase function；

Step 2.6), distance, to ifft, is transformed into range-Dopler domain；

Step 3), the base band orientation in the case of stravismus becomes mark process and realizes sub-aperture stitching: in the range-Dopler domain side of carrying out Position calibration, then sub-aperture stitching, carries out derotation to the full aperture data obtaining and orientation compression obtains final sar figure Picture.

2. the sub-aperture wave-number domain imaging method of stravismus slip pack sar according to claim 1 is it is characterised in that institute State step 3) specifically comprise the following steps that

Step 3.1), it is multiplied by orientation scaling factor in range-Dopler domain:

$h_3=\exp \{j2{\mathrm{\πt}}_v{f}_a+j\frac{{\mathrm{\πf}}_a^2}{k_{scl}\left(r\right)}\}$

Wherein, h₃For orientation scaling factor, r is distance axis,λ is ripple Long, f_dc=2v_asinθ_s/ λ is full aperture doppler centroid；

Step 3.2), orientation inverse Fourier transform is transformed into orientation time domain, carries out sub-aperture stitching in orientation time domain and obtains entirely Pore size data, comprises the following specific steps that:

Step 3.2.1), define n_a×n_rThe complete opening drive matrix of size, by the n of first sub-aperture_aiIndividual pulse is assigned to full aperture square The front n of battle array_aiIndividual pulse；

Step 3.2.2), calculate the overlaid pixel unit δ n=kn of orientation_ai, successively by the of i-th (i ＞ 1) individual sub-aperture δ n/2+1 row is to n-th_aiThe n of row_aiN/2-1 pulse of-δ is assigned to (i-1) (n of full aperture_ai- δ n)+δ n/2+1 row to (i-1)(n_ai-δn)+n_aiOK, complete the splicing of sub-aperture, wherein, k is overlap ratio；

Step 3.3), each benefit n about complete opening drive matrix orientation_a/ 2 zero, comprise the following specific steps that:

Step 3.3.1), define n'_aThe new matrix of × nr size, wherein, n'_a=2n_a；

Step 3.3.2), original matrix is assigned to the n-th of new matrix_a/ 2+1 row is to n-th '_a-n_a/ 2 row, complete orientation zero padding；

Step 3.4), full aperture orientation derotation:

$h_4=\exp \{{\mathrm{j\πk}}_{rot}{t}_{a\_all}^2-j2{\mathrm{\πf}}_{dc\_all}{t}_{a\_all}\}$

Wherein, h₄It is the fixed phase of derotation,v_fSlide for beam area Dynamic speed, t_{a_all}And f_{dc_all}It is respectively full aperture orientation time and orientation mid frequency；

Step 3.5), orientation Fourier transformation, carry out orientation pulse pressure in orientation frequency domain, the pulse pressure factor is:

$h_5=\exp \left\{j\frac{{\mathrm{\πf}}_a^2}{k_{eff}\left(r\right)}\right\}$

Wherein, h₅For the pulse pressure factor, k_eff(r)=k_rot-k_scl(r)；

Step 3.6), orientation inverse Fourier transform obtains full aperture sar image.

3. the sub-aperture wave-number domain imaging method of stravismus slip pack sar according to claim 2 is it is characterised in that walk Sub-aperture size described in rapid 1) is:

$t_{sub}\≤\frac{prf-\max b_{a,proc}}{\left|k_{rot}\right|}$

Wherein, t_subThe size of the sub-aperture for dividing, prf is azimuth sample rate, b_a,procOrientation bandwidth for single sub-aperture.