CN105549008A - Parameter optimization method of variable parameter high squint satellite-borne beam bunching SAR system - Google Patents

Abstract

The present invention discloses a parameter optimization design method of a variable parameter high squint satellite-borne beam bunching SAR (Synthetic Aperture Radar) system. The method comprises: obtaining basic parameters of an earth observation task; calculating system parameters derived from the basic parameters; fitting a satellite orbit coordinate polynomial, and estimating the initiation and termination sampling time scales; setting an orientation sampling number, and calculating a sampling time interval and an earth surface drift angle sequence corresponding to a scene center; determining a satellite sampling position sequence, the slope distance sequence of the scene center and a time sampling interval sequence; verifying constraint condition of a point echo interference without transmission pulse shielding and satellite; and calculating the time variant regulation rule of radar platform parameters. According to the invention, a theoretical basis and a realization method are provided for the design requirement of a variable parameter high squint satellite-borne beam bunching SAR system.

Description

The parameter optimization method of the spaceborne Spotlight SAR Imaging system of the large stravismus of a kind of variable element

Technical field

The present invention relates to synthetic-aperture radar (SyntheticApertureRadar, SAR) technical field, specifically refer to the parameter optimization method of the spaceborne Spotlight SAR Imaging system of the large stravismus of a kind of variable element.

Background technology

Spaceborne Spotlight SAR Imaging is a kind of high resolving power earth observation microwave imaging instrument, and the parameter designing of traditional Spaceborne SAR System needs carry out according to radar imagery pattern, then selects suitable image processing method by the systematic parameter of Texas tower, space geometry configuration.But for the spaceborne Spotlight SAR Imaging system under large stravismus data acquisition configuration, the strong two dimension that the equal reason of most of image processing method large stravismus configuration is introduced in echoed signal is coupled and lost efficacy.Polar format algorithm (PolarFormatAlgorithm, PFA) potentiality of process large stravismus Spotlight SAR Imaging data are possessed, its according to separate signal after line frequency modulation time, frequency domain equivalent characteristic, the two dimension coupling of echo is corrected at wavenumber domain, Fast Fourier Transform (FFT) (FastFourierTransform, FFT) is finally utilized to realize figure image focu.But the distance wave number bandwidth that the data acquisition configuration of large stravismus will cause effective distance wave number bandwidth much smaller than the independent azimuth sample moment, this will cause the deterioration of range resolution, under serious conditions, effective distance wave number bandwidth may be zero, now then can not complete imaging processing.For above-mentioned defect, patent applicant proposes a kind of spaceborne large stravismus Spotlight SAR Imaging system based on time-varying parameter, adjusts the distribution of echo at wavenumber domain, and then PFA algorithm can be adopted to complete high-resolution imaging processing from system aspect.

Summary of the invention

The object of the invention is the design problem for solving the spaceborne Spotlight SAR Imaging system of the large stravismus of variable element, proposing the parameter optimization method of the spaceborne Spotlight SAR Imaging system of the large stravismus of variable element of complete set.This method considers two-dimensional resolution demand, two dimension simultaneously and samples without aliasing and to block without transponder pulse and without the constraint of substar echo interference to System Parameter Design in the process of carrying out System Parameter Design, give the minimum two-dimentional sampling number meeting earth observation task, operand can be controlled in minimum degree like this, system imaging treatment effeciency is maximized.

The parameter optimization method of the spaceborne Spotlight SAR Imaging system of the large stravismus of a kind of variable element of the present invention, comprises following step:

The basic parameter of step one, acquisition earth observation task, comprises target scenario parameters, the basic reference parameter of radar emission signal, the basic parameter of radar spatial sampling and the equalisation of over-sampled signals factor.

Step 2, calculate the SAR system parameter derived by every basic parameter in step one, comprise radar emission signal derived parameter, 2D signal sampling derived parameter and spatial sampling derived parameter.

The track sampled point sequence of step 3, foundation input utilizes the polynomial expression of least square fitting satellite orbit coordinate, estimates the time scale t meeting the starting sample point of the satellite orbit of azimuthal resolution demand _startwith the time scale t stopping sampled point _end.

Step 4, setting azimuth sample are counted, and calculate the sampling time interval under even azimuth sample condition, between t _startwith t _endbetween co-ordinates of satellite sequence rise sampling M doubly after calculate the earth's surface drift angle sequence α of each point relative to scene center _dense.

Step 5, calculate to count with azimuth sample corresponding, meet echo data at wavenumber domain along orientation to equally distributed earth's surface drift angle sequence α _tgt, according to α _tgtdetermine the sampled satellite position sequence P of space-variant _satF, calculate P _satFthe oblique distance sequence R of each sampling location and scene center _cF, calculate P _satFtime sampling interval sequence I _satF.

Step 6, checking P _satFwhether meet and to block without transponder pulse and without the constraint condition of substar echo interference.If do not meet constraint, with Δ N _acount for step-length increases azimuth sample, carry out interative computation with step 4 to step 6, work as P _satFmeet simultaneously and to block without transponder pulse and without the constraint condition of substar echo interference, or azimuth sample is counted and to be reached in iteration in limited time, stopping interative computation.

Step 7, according to P _satFwith the relative position relation of scene center point, calculate Texas tower parameter time become adjustment law.

The invention has the advantages that:

(1) method for optimally designing parameters of the spaceborne Spotlight SAR Imaging system of the large stravismus of a kind of variable element is proposed, for the system of the spaceborne Spotlight SAR Imaging of the large stravismus of variable element provides theoretical foundation and implementation method;

(2) this method considers two-dimentional resolution characteristic, without aliasing sampling with block without transponder pulse, without the constraint of substar echo interference to system platform parameter, spatial sampling parameter, can carry out complete reception to the echo of target scene;

(3) this method is based on the time-frequency equivalent characteristic of signal after two dimension solution line frequency modulation, and the Texas tower parameter become when devising has the distance wave number of strong space-variant in azimuth for correcting large stravismus condition, after making focusing, image has good distance to resolution characteristic.

Accompanying drawing explanation

Fig. 1 is method flow diagram of the present invention;

Fig. 2 asked for scene central vertical in the schematic diagram of the vector of unit length of earth surface in the present invention;

Fig. 3 is initial, the method flow diagram of time scale that stops sampled point of asking for satellite orbit in the present invention;

Fig. 4 completes the schematic diagram that Texas tower parameter adjustment back echo distributes at wavenumber domain in the present invention.

Fig. 5 is the schematic diagram of the spatial sampling sequence coordinate of embodiment of the present invention Satellite;

Fig. 6 is the error schematic diagram of actual earth's surface drift angle sequence and drift angle, target earth's surface sequence in the embodiment of the present invention;

Fig. 7 is the schematic diagram of the spatial sampling time interval sequence of embodiment of the present invention Satellite;

The schematic diagram of adjustment law is become when Fig. 8 is Texas tower parameter in the embodiment of the present invention.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in further detail.

The parameter optimization method of the spaceborne Spotlight SAR Imaging system of the large stravismus of a kind of variable element of the present invention, process flow diagram as shown in Figure 1, comprises following step:

The basic parameter of step one, acquisition earth observation task, comprises target scenario parameters, the basic reference parameter of radar emission signal, the basic parameter of radar spatial sampling and the equalisation of over-sampled signals factor.Be specially:

(1) obtain the target scenario parameters of earth observation task, comprise the distance of scene to width S _wr, orientation is to width S _wa, distance to observation resolution ρ _rwith orientation to observation resolution ρ _a;

(2) obtain the basic reference parameter that SAR linear frequency modulation (LinearFrequencyModulated, LFM) transmits, comprise with reference to carrier frequency f _c0with reference pulse width T _p0;

(3) obtain the spatial sampling basic parameter of SAR, comprise satellite orbital altitude H, satellite speed V in orbit _s, scene center P _sceat earth rotation coordinate system E _gin coordinate (x _sce, y _sce, z _sce), SAR is at synthetic aperture central instant t _csampling point position P _sat0at E _gin coordinate (x _sat0, y _sat0, z _sat0) and satellite orbit with P _sat0centered by the coordinate sequence A of track sampled point _sat0, wherein earth rotation coordinate system E _gbe defined as follows:

True origin: the earth's core, is designated as O _g;

X-axis is designated as X _g: under the line in plane, point to zero degree warp direction;

Y-axis is designated as Y _g: under the line in plane, point to east longitude 90 degree of warp directions;

Z axis is designated as Z _g: along earth's axis, point to the positive arctic (north latitude 90 degree of directions).

(4) equalisation of over-sampled signals factor gamma is obtained.

Step 2, calculate the SAR system parameter derived by every basic parameter in step one, comprise radar emission signal derived parameter, 2D signal sampling derived parameter and spatial sampling derived parameter.Be specially:

(1) calculate the derivation reference parameter of radar emission signal, comprise the reference bandwith B of LFM signal ₀, with reference to frequency modulation rate K _r0:

$B_0=\frac{c}{2{\mathrm{\ρ}}_r}---\left(1\right)$

Wherein: c represents the light velocity.

$K_{r0}=\frac{B_0}{T_p}---\left(2\right)$

(2) t under calculating ellipsoid earth model _cthe relative P of moment SAR _sceincident angle β ₀:

In the earth model of ellipsoid, if cross P _sceperpendicular to earth's surface, the vector of unit length deviating from the earth's core with Z _gthe intersection point of axle is O _d, as shown in Figure 2.If O _dat Z _gthe coordinate of axle is z _od, then z _odcan be calculated by space geometry relation

$z_{od}=\frac{(x_{sce}^2+y_{sce}^2)z_{sce}+z_{sce}^3-z_{sce}{b}^2}{z_{sce}^2-b^2}---\left(3\right)$

Wherein: b is the length of the semi-minor axis in ellipsoid model of globe.Can be in the hope of by formula (3)

Wherein

$R_n=\sqrt{x_{sce}^2+y_{sce}^2+{(z_{sce}-z_{od})}^2}---\left(5\right)$

If by P _scepoint to P _sat0vector can be expressed as then β ₀can be calculated by following formula

Wherein || represent modulo operation.

(3) calculate the distance of signal to sampling request, comprise reference sample rate F _s0, without aliasing minor increment sampling number N _r, distance wave number supporting domain width K _yB:

$F_{s0}=\frac{2{\mathrm{\γK}}_{r0}{S}_{wr}}{c}---\left(7\right)$

$N_r=\frac{2S_{wr}{F}_{s0}}{c}+T_{p0}{F}_{s0}----\left(8\right)$

$K_{yB}=\frac{4{\mathrm{\πK}}_{r0}{N}_r{\mathrm{sin\β}}_0}{{\mathrm{cF}}_{s0}}---\left(9\right)$

(4) calculate the orientation of signal to sampling request, comprise the scope α of the earth's surface accumulation subtended angle in the synthetic aperture time _b, orientation wave number supporting domain minimum widith K _xB, without the minimum orientation of aliasing to sampling number N _amin:

${\mathrm{\α}}_B=2a\tan \left(\frac{c}{4{\mathrm{\ρ}}_a\left(f_{c0}-\frac{K_{r0}{N}_r}{2F_{s0}}\right){\mathrm{sin\β}}_0}\right)---\left(10\right)$

Wherein atan () represents arctan function.

$K_{xB}=\frac{8\mathrm{\π}}{c}\left(f_{c0}-\frac{K_{r0}{N}_r}{2F_{s0}}\right)tan\left(\frac{{\mathrm{\α}}_B}{2}\right){\mathrm{sin\β}}_0---\left(11\right)$

$N_{a\min }=\frac{{\mathrm{\λS}}_{wa}{K}_{xB}}{2\mathrm{\π}}---\left(12\right)$

The track sampled point sequence of step 3, foundation input utilizes the polynomial expression of least square fitting satellite orbit coordinate, estimates the time scale t meeting the starting sample point of the satellite orbit of azimuthal resolution demand _startwith the time scale t stopping sampled point _end.Be specially:

(1) respectively according to A _sat0x, Y and the coordinate fitting coordinate of Z-direction about the polynomial expression of azimuth sample time t:

Be described for X-coordinate fitting of a polynomial.If X _sat0for by A _sat0the matrix of the X-coordinate composition of middle extraction, dimension is Q × 1, and wherein Q is A _sat0in the quantity of sampled point that comprises.If W is the top step number of fitting of a polynomial, t _ifor A _sat0in each sampled point with t _cfor the time coordinate at zero point, wherein i=1,2 ..., Q, by t _iwith W can the observing matrix G of generator polynomial matching be

If the coefficient of polynomial fitting Matrix C oE of X-coordinate to be solved _xfor

CoE _x＝[e ₀,e ₁,e ₂,…,e _W] ^T(14)

Wherein superscript T representing matrix transposition, i.e. CoE _xfor the matrix that dimension is (W+1) × 1.So far least square problem transforms to ask following formula CoE under least square constraint _xsolution.

GCoE _x＝X _sat0(15)

From optimization method, the least square solution of formula (15) can be expressed as

CoE _x＝(G ^TG) ^-1G ^TX _sat0(16)

Wherein representing matrix inverse of subscript-1.

By the calculation process shown in Y-coordinate to be solved, Z coordinate repetitive (14) to formula (16), the coefficient of polynomial fitting Matrix C oE of Y, Z coordinate can be tried to achieve _ywith CoE _z.

(2) the starting point time scale t meeting the satellite orbit of azimuthal resolution demand is estimated _startwith terminating point time scale t _end:

Calculate A _sat0the general bearing time interval Δ t of middle sampled point ₀as follows

${\mathrm{\Δt}}_0=\frac{1}{Q-1}\underset{m=1}{\overset{Q-1}{\Σ}}\frac{P_{sat}(m+1)-P_{sat}\left(m\right)}{V_s}---\left(17\right)$

Wherein P _satrepresent A _sat0the coordinate of sampled point in sequence.

Compute vector at the projection vector of imaging plane then can be expressed as

With t _cfor initial time, with Δ t ₀for step-length increases the orientation time gradually, utilize CoE _x, CoE _ywith CoE _zestimate the co-ordinates of satellite P of current time _satE0.Note vector at the projection vector of imaging plane be then can be expressed as

If with folded angle is α _t, then α _tcan be expressed as

If α _t< α _b/ 2, then with Δ t ₀for step-length continues to increase orientation time t, the calculating of repetitive (19), formula (20), until α _t> α _b/ 2, the orientation moment is now t _end.

Similarly, with t _cmoment is initial time, with Δ t ₀for step-length reduces the orientation time gradually, the calculating of repetitive (19), formula (20), until α _t> α _b/ 2, the orientation moment is now t _start.Fig. 3 illustrates and solves t _start, t _endtime iterative calculation method.

Step 4, setting azimuth sample are counted, and calculate the sampling time interval under even azimuth sample condition, between t _startwith t _endbetween co-ordinates of satellite sequence rise sampling M doubly calculate the earth's surface drift angle sequence α of each point relative to scene center _dense.Be specially:

Setting azimuth sample is counted as N _a.When performing step 4 first, make N _a=N _amin.N _athe time interval Δ t of the uniform azimuth sample that individual azimuth sample point is corresponding _dcan approximate representation

${\mathrm{\&Delta;t}}_d\&ap;\frac{t_{end}-t_{start}}{N_a-1}---\left(21\right)$

After M doubly rises sampling, the time interval Δ t of uniform azimuth sample sequence _dUcan be expressed as

${\mathrm{\&Delta;t}}_{dU}=\frac{{\mathrm{\&Delta;t}}_d}{M}---\left(22\right)$

With t _startfor initial time, t _endfor the termination time, Δ t _dUthe sampling instant sequence after sampling is doubly risen for step-length generates M, and according to CoE _x, CoE _ywith CoE _zestimate the co-ordinates of satellite value of each sample point, generate the co-ordinates of satellite sequence P after rising sampling _satd.Now drift angle, earth's surface sequence α _densecan be expressed as

Wherein

Step 5, calculate to count with azimuth sample corresponding, meet echo data at wavenumber domain along orientation to equally distributed earth's surface drift angle sequence α _tgt, according to α _tgtdetermine the sampled satellite position sequence P of space-variant _satF, calculate P _satFthe oblique distance sequence R of each sampling location and scene center _cF, calculate P _satFtime sampling interval sequence I _satF.Be specially:

For orientation to sampling number N _a, meet echo data at wavenumber domain along orientation to equally distributed earth's surface drift angle sequence α _tgtcan be expressed as

${\mathrm{\&alpha;}}_{tgt}\left(k\right)={\tan }^{-1}\left(\frac{2}{N_a-1}tan\left(\frac{{\mathrm{\&alpha;}}_B}{2}\right)k\right),\left(k=-\frac{N_a}{2}+1,...,\frac{N_a}{2}\right)---\left(25\right)$

Get α successively _tgtin value at α _densethe immediate value of middle searching, makes P _satdin make α _denseobtain closest to α _tgtthe co-ordinates of satellite when coordinate of the sampled satellite point of each point value is final data acquisition, so can obtain final sampled satellite sequence P heterogeneous _satF.P _satFin each sampling location to P _sceoblique distance sequence R _cFcan be expressed as

P _satFin the time series I of sampling interval between each sampled point _satFcan be expressed as

$I_{satF}\left(k_1\right)=\frac{P_{satF}(k_1+1)-P_{satF}\left(k_1\right)}{V_s},\left(k_1=-\frac{N_a}{2}+1,...,\frac{N_a}{2}-1\right)---\left(27\right)$

Step 6, checking P _satFwhether meet and to block without transponder pulse and without the constraint condition of substar echo interference.If do not meet constraint, with Δ N _acount for step-length increases azimuth sample, carry out interative computation with step 4 to step 6, work as P _satFmeet simultaneously and to block without transponder pulse and without the constraint condition of substar echo interference, or azimuth sample is counted and to be reached in iteration in limited time, stopping interative computation.Be specially:

If P _satFmeet and block constraint condition without transponder pulse, then need the echo frontier of the point ensureing nearest scene objects place larger than the delay on edge after current transponder pulse, and after the echo of the point at scene place farthest, edge is less than the delay in next transponder pulse forward position.Now can be calculated by space geometry relation

$\frac{2R_{cF}\left(k\right)-S_{wr}}{c}>\underset{m=k}{\overset{k+M_0}{\&Sigma;}}{I}_{sat}\left(m\right)+T_p+\mathrm{\&delta;}p,\left(k=-\frac{N_a}{2}+1,...,\frac{N_a}{2}\right)---\left(28\right)$

$\frac{2R_{cF}\left(k\right)+S_{wr}}{c}<\underset{m=k}{\overset{k+M_0+1}{\&Sigma;}}{I}_{sat}\left(m\right)-\mathrm{\&delta;}p,\left(k=-\frac{N_a}{2}+1,...,\frac{N_a}{2}\right)---\left(29\right)$

Wherein M ₀represent in data acquisition the transponder pulse interval quantity transmitted and between corresponding Received signal strength, guard time when δ p is sending and receiving beam switchover.

If P _satFmeet without substar echo interference, then it meets following one of two things: the first, along time delay after the leading edge time when the substar echo occurred in pre-echo window postpones to be greater than scene echoes; Second, when after the substar echo occurred in pre-echo window along time delay be less than scene echoes leading edge time postpone, if substar Echo width is two pulse widths, and a kth exomonental scene echoes and p exomonental substar echo were received in the same recurrent interval, the corresponding following relation of the first situation

$\left\{\begin{array}{c}\frac{2H}{c}-T_p+\underset{m=k}{\overset{p}{\&Sigma;}}{I}_{sat}\left(m\right)-\mathrm{\&delta;}p>\frac{2\left(R_{cF}\right(k)+S_{wr}/2)}{c}\\ \frac{2H}{c}+T_p+\underset{m=k}{\overset{p-1}{\&Sigma;}}{I}_{sat}\left(m\right)+\mathrm{\&delta;}p<\frac{2\left(R_{cF}\right(k)-S_{wr}/2)}{c}\end{array}\right.---\left(30\right)$

The corresponding following relation of the second situation

$\left\{\begin{array}{c}\frac{2H}{c}+T_p+\underset{m=k}{\overset{p}{\&Sigma;}}{\mathrm{PI}}_{sat}\left(m\right)+\mathrm{\&delta;}p<\frac{2R_{cF}\left(k\right)-S_{wr}}{c}\\ \frac{2H}{c}-T_p+\underset{m=k}{\overset{p+1}{\&Sigma;}}{\mathrm{PI}}_{sat}\left(m\right)-\mathrm{\&delta;}p>\frac{2R_{cF}\left(k\right)+S_{wr}}{c}\end{array}\right.---\left(31\right)$

Formula (30) is identical with the value of the middle k of formula (28) with the value of k in formula (31).If P _satFmeet the constraint condition that formula (28), formula (29) and formula (30) are formed, or meet the constraint condition that formula (28), formula (29) and formula (31) are formed, then think that spatial sampling parameter designing meets the System Parameter Design demand making the echo of target field scene area be able to complete reception.Now P _satFbe the final sampled point sequence of satellite.If P _satFnamely the constraint condition that formula (28), formula (29) and formula (30) are formed is not met, do not meet the constraint condition that formula (28), formula (29) and formula (31) are formed, then think that orientation is N to sampling number yet _aspatial sampling patten's design failure.At this moment need with Δ N _afor step-length increases N _avalue, repeat step 4 carry out interative computation to step 6, until P _satFcan meet and to block without transponder pulse and without the constraint condition of substar echo interference.

In addition, under meeting the condition without aliasing sampling, increase N _acan not improve the resolution of earth observation, but it is to the processing load increasing imaging system, reduces the imaging processing efficiency of system.Therefore utilize process of iteration to ask for meet to block without transponder pulse and constraint condition without substar echo interference time, a permission N should be set _athe maximal value numerical value of N obtained _aIMif work as N _abe less than N _aIMtime without any a P _satFsequence can meet simultaneously to block without transponder pulse and without the constraint condition of substar echo interference, then think that the large stravismus of the variable element spaceborne Spotlight SAR Imaging system met under given earth observation demand condition is non-existent, interative computation stops.

Step 7, according to P _satFwith the relative position relation of scene center point, calculate Texas tower parameter time become adjustment law.Be specially:

(1) method described in step 2 Chinese style (3) ~ formula (6) is adopted to calculate P _satFin each sampling location relative to scene center P _sceincident angle sequence β _f.

(2) method described in step 5 Chinese style (23) is adopted to calculate P _satFin each sampling location relative to scene center P _scedrift angle, earth's surface sequence α _f.

(3) according to β _f, α _fwith Texas tower reference parameter f _c0, K _r0, F _s0, T _p0the adjustment law of the Texas tower parameter become during calculating, comprises carrier frequency f _c, frequency modulation rate K _r, pulse width T _pwith signal sampling rate F _stime become adjustment law.

After making solution line frequency modulation for avoiding the steric configuration of large stravismus, signal has the distance wave number of serious space-variant, and the Texas tower parameter of the spaceborne Spotlight SAR Imaging system of the large stravismus of variable element carries out adjusting to improve the distribution mode of signal at wavenumber domain with the relative position relation of radar and target scene in good time.Specifically, the adjustment law of radar parameter can be divided into the following two kinds mode:

Mode one: the sampling rate F of radar transmitted pulse _s, pulse width T _pconstant, adjustment carrier frequency f _cwith frequency modulation rate K _ras follows

$\left\{\begin{array}{c}{f}_c=\frac{{\mathrm{sin\&beta;}}_0}{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{f}_{c0}\\ K_r=\frac{{\mathrm{sin\&beta;}}_0}{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{K}_{r0}\\ T_p=T_{p0}\\ F_s=F_{s0}\end{array}\right.---\left(32\right)$

Mode two: the frequency modulation rate K of radar transmitted pulse _rconstant, adjust the carrier frequency f transmitted _c, sampling rate F _sand pulse width T _pas follows

$\left\{\begin{array}{c}{f}_c=\frac{{\mathrm{sin\&beta;}}_0}{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{f}_{c0}\\ F_s=\frac{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{{\mathrm{sin\&beta;}}_0}{F}_{s0}\\ T_p=\frac{{\mathrm{sin\&beta;}}_0}{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{T}_{p0}\\ K_r=K_{r0}\end{array}\right.---\left(33\right)$

Fig. 4 illustrates and adopts any one parameter adjustment mode to complete the distribution mode of the echo after parameter adjustment at wavenumber domain.Although the object that the adjustment mode of above-mentioned two kinds of radar parameters adjusts is different, its effect is identical.In actual applications, the parameter which kind of mode specifically should be adopted to adjust Texas tower need be formed according to the hardware platform of reality to be selected.

So far, the System Parameter Design of the spaceborne Spotlight SAR Imaging of the large stravismus of variable element completes.

embodiment

Apply the present invention to instantiation, concrete steps are as follows:

Step one, the target scenario parameters obtaining earth observation task, the basic reference parameter of radar emission signal and the basic parameter of radar spatial sampling, obtain the equalisation of over-sampled signals factor.The basic parameter obtained is as shown in table 1.

The large stravismus of table 1 variable element spaceborne Spotlight SAR Imaging earth observation task basic parameter

Step 2, calculate the SAR system parameter derived by every basic parameter in step one, comprise radar emission signal derived parameter, 2D signal sampling derived parameter and spatial sampling derived parameter.The radar system derived parameter calculated is as shown in table 2

The large stravismus of table 2 variable element spaceborne Spotlight SAR Imaging earth observation task derived parameter

The track sampled point sequence of step 3, foundation input utilizes the polynomial expression of least square fitting satellite orbit coordinate, estimates the time scale t meeting the starting sample point of the satellite orbit of azimuthal resolution demand _startwith the time scale t stopping sampled point _end.

If the fitting of a polynomial exponent number W=5 of the three-dimensional coordinate of satellite orbit, now for the radar parameter provided in step one, step 2, the matrix of coefficients CoE of the polynomial fitting of the satellite orbit three-dimensional coordinate adopting least square method to calculate _x, CoE _yand CoE _zparameters as shown in table 3.

The coefficient of polynomial fitting of satellite orbit three-dimensional coordinate in table 3 synthetic aperture

By A _sat0calculate the general bearing time interval Δ t of sampled point ₀=0.0013s.

With Δ t ₀for step iteration calculates t _start=-3.4742s, t _end=3.3297s.

Step 4, setting azimuth sample are counted, and calculate the sampling time interval under even azimuth sample condition, between t _startwith t _endbetween co-ordinates of satellite sequence rise sampling M doubly after calculate the earth's surface drift angle sequence α of each point relative to scene center _dense.

When performing step 4 first, make azimuth sample points N _a=12005.Setting rises sampling multiple M=8.

Calculate N _athe time interval Δ t of the even azimuth sample that individual azimuth sample point is corresponding _d=5.38 × 10 ^-4s, 8 times of time interval Δ t rising evenly azimuth sample after sampling _dU=6.72 × 10 ^-5s

Work as N _awhen=12005, co-ordinates of satellite is relative to P _scedrift angle, earth's surface sequence α _densestatistical information as shown in table 4.

Table 4 α _densestatistical information (N _a=12005)

Parameter name	Numerical value
		Sampled point quantity	101169
α denseAngle of minimum deviation (rad)	-0.0369
		α denseSail angle (rad)	0.0369

Step 5, calculate to count with azimuth sample corresponding, meet echo data at wavenumber domain along orientation to equally distributed earth's surface drift angle sequence α _tgt, according to α _tgtdetermine the sampled satellite position sequence P of space-variant _satF, calculate P _satFthe oblique distance sequence R of each sampling location and scene center _cF, calculate P _satFtime sampling interval sequence I _satF.

The α calculated _tgt, P _satF, R _cFand I _satFstatistical information as shown in table 5.

The large stravismus of table 5 variable element spaceborne Spotlight SAR Imaging spatial sampling parameter (N _a=12005)

Step 6, checking P _satFwhether meet and to block without transponder pulse and without the constraint condition of substar echo interference.If do not meet constraint, with Δ N _acount for step-length increases azimuth sample, carry out interative computation with step 4 to step 6, work as P _satFmeet simultaneously and to block without transponder pulse and without the constraint condition of substar echo interference, or azimuth sample is counted and to be reached in iteration in limited time, stopping interative computation.

If the iteration upper limit that azimuth sample is counted is N _aIM, in this example, make N _aIM=14407.

Empirical tests works as N _awhen=12005, P _satFcan not meet simultaneously to block without transponder pulse and without the constraint of substar echo interference.With Δ N _a=10 is step-length increase sampled point N _anumerical value, checking obtain working as N _awhen=12646, P _satFcan meet simultaneously to block without transponder pulse and without the constraint condition of substar echo interference.N now _afor with Δ N _athe minimum azimuth sample of the met earth observation mission requirements obtained for step size computation is counted.

Step 7, according to P _satFwith the relative position relation of scene center point, calculate Texas tower parameter time become adjustment law.

To utilizing the spaceborne Spotlight SAR Imaging system of the large stravismus of variable element to carry out in the task of earth observation in the present embodiment, time become Texas tower parameter adjustment statistical information as shown in table 6.

The large stravismus of table 6 variable element spaceborne Spotlight SAR Imaging Texas tower parameter adjustment statistical information

So far the systematic parameter optimal design of the spaceborne Spotlight SAR Imaging of the large stravismus of variable element completes, and designs the sampled satellite point coordinate (X, Y and Z coordinate) that obtains as shown in Figure 5, actual earth's surface drift angle sequence α _fwith target earth's surface drift angle sequence α _tgterror amount as shown in Figure 6, orientation to sampling time interval as shown in Figure 7, the Texas tower parameter become when Fig. 8 illustrates, wherein Fig. 8 (a) illustrates the Changing Pattern of carrier frequency, frequency modulation rate in the first parameter adjustment mode, and Fig. 8 (b) illustrates the Changing Pattern of carrier frequency, sampling rate and pulse width in the second parameter adjustment mode.

The present invention proposes the Optimization Design of the spaceborne Spotlight SAR Imaging systematic parameter of the large stravismus of variable element of complete set, the method is that the design of the large stravismus of variable element spaceborne Spotlight SAR Imaging radar platform and mode of operation provides theoretical foundation and implementation method.

Claims (1)

1. a parameter optimization method for the spaceborne Spotlight SAR Imaging system of the large stravismus of variable element, comprises following step:

The basic parameter of step one, acquisition earth observation task, comprises target scenario parameters, the basic reference parameter of radar emission signal, the basic parameter of radar spatial sampling and the equalisation of over-sampled signals factor, is specially:

(1) obtain the target scenario parameters of earth observation task, comprise the distance of scene to width S _wr, orientation is to width S _wa, distance to observation resolution ρ _rwith orientation to observation resolution ρ _a;

(2) obtain the basic reference parameter of radar emission signal, comprise with reference to carrier frequency f _c0with reference pulse width T _p0;

(3) obtain radar spatial sampling basic parameter, comprise satellite orbital altitude H, satellite speed V in orbit _s, scene center P _sceat earth rotation coordinate system E _gin coordinate (x _sce, y _sce, z _sce), SAR is at synthetic aperture central instant t _csampling point position P _sat0at E _gin coordinate (x _sat0, y _sat0, z _sat0) and satellite orbit with P _sat0centered by the coordinate sequence A of track sampled point _sat0, wherein earth rotation coordinate system E _gbe defined as follows:

True origin: the earth's core, is designated as O _g;

X-axis is designated as X _g: under the line in plane, point to zero degree warp direction;

Y-axis is designated as Y _g: under the line in plane, point to east longitude 90 degree of warp directions;

Z axis is designated as Z _g: along earth's axis, point to the positive arctic and north latitude 90 degree of directions;

(4) equalisation of over-sampled signals factor gamma is obtained;

Step 2, calculate the SAR system parameter derived by every basic parameter in step one, comprise radar emission signal derived parameter, 2D signal sampling derived parameter and spatial sampling derived parameter; Be specially:

(1) calculate the derivation reference parameter of radar emission signal, comprise the reference bandwith B of LFM signal ₀, with reference to frequency modulation rate K _r0:

$B_0=\frac{c}{2{\mathrm{\&rho;}}_r}---\left(1\right)$

Wherein: c represents the light velocity;

$K_{r0}=\frac{B_0}{T_p}---\left(2\right)$

(2) t under calculating ellipsoid earth model _cthe relative P of moment SAR _sceincident angle β ₀:

In the earth model of ellipsoid, if cross P _sceperpendicular to earth's surface, the vector of unit length deviating from the earth's core with Z _gthe intersection point of axle is O _dif, O _dat Z _gthe coordinate of axle is z _od, then z _odcalculated by space geometry relation

$z_{od}=\frac{(x_{sce}^2+y_{sce}^2)z_{sce}+z_{sce}^3-z_{sce}{b}^2}{z_{sce}^2-b^2}---\left(3\right)$

Wherein: b is the length of the semi-minor axis in ellipsoid model of globe; Tried to achieve by formula (3)

Wherein

$R_n=\sqrt{x_{sce}^2+y_{sce}^2+{(z_{sce}-z_{od})}^2}---\left(5\right)$

If by P _scepoint to P _sat0vector representation be then β ₀calculated by following formula

Wherein || represent modulo operation;

(3) calculate the distance of signal to sampling request, comprise reference sample rate F _s0, without aliasing minor increment sampling number N _r, distance wave number supporting domain width K _yB:

$F_{s0}=\frac{2{\mathrm{\&gamma;K}}_{r0}{S}_{wr}}{c}---\left(7\right)$

$N_r=\frac{2S_{wr}{F}_{s0}}{c}+T_{p0}{F}_{s0}---\left(8\right)$

$K_{yB}=\frac{4{\mathrm{\&pi;K}}_{r0}{N}_r{\mathrm{sin\&beta;}}_0}{{\mathrm{cF}}_{s0}}---\left(9\right)$

(4) calculate the orientation of signal to sampling request, comprise the scope α of the earth's surface accumulation subtended angle in the synthetic aperture time _b, orientation wave number supporting domain minimum widith K _xB, without the minimum orientation of aliasing to sampling number N _amin:

${\mathrm{\&alpha;}}_B=2a\tan \left(\frac{c}{4{\mathrm{\&rho;}}_a(f_{c0}-\frac{K_{r0}{N}_r}{2F_{s0}}){\mathrm{sin\&beta;}}_0}\right)---\left(10\right)$

Wherein atan () represents arctan function;

$K_{xB}=\frac{8\mathrm{\&pi;}}{c}(f_{c0}-\frac{K_{r0}{N}_r}{2F_{s0}})tan\left(\frac{{\mathrm{\&alpha;}}_B}{2}\right){\mathrm{sin\&beta;}}_0---\left(11\right)$

$N_{a\min }=\frac{{\mathrm{\&lambda;S}}_{wa}{K}_{xB}}{2\mathrm{\&pi;}}---\left(12\right)$

The track sampled point sequence of step 3, foundation input utilizes the polynomial expression of least square fitting satellite orbit coordinate, estimates the time scale t meeting the starting sample point of the satellite orbit of azimuthal resolution demand _startwith the time scale t stopping sampled point _end; Be specially:

(1) respectively according to A _sat0x, Y and the coordinate fitting coordinate of Z-direction about the polynomial expression of azimuth sample time t:

X-coordinate fitting of a polynomial is specially: establish X _sat0for by A _sat0the matrix of the X-coordinate composition of middle extraction, dimension is Q × 1, and wherein Q is A _sat0in the quantity of sampled point that comprises; If W is the top step number of fitting of a polynomial, t _ifor A _sat0in each sampled point with t _cfor the time coordinate at zero point, wherein i=1,2 ..., Q, by t _iwith the observing matrix G of W generator polynomial matching be

If the coefficient of polynomial fitting Matrix C oE of X-coordinate to be solved _xfor

CoE _x＝[e ₀,e ₁,e ₂,…,e _W] ^T(14)

Wherein superscript T representing matrix transposition, i.e. CoE _xfor the matrix that dimension is (W+1) × 1; So far least square problem transforms to ask following formula CoE under least square constraint _xsolution;

GCoE _x＝X _sat0(15)

The least square solution of formula (15) is expressed as

CoE _x＝(G ^TG) ^-1G ^TX _sat0(16)

Wherein representing matrix inverse of subscript-1;

In like manner, the coefficient of polynomial fitting Matrix C oE of Y, Z coordinate is tried to achieve _ywith CoE _z;

(2) the starting point time scale t meeting the satellite orbit of azimuthal resolution demand is estimated _startwith terminating point time scale t _end:

Calculate A _sat0the general bearing time interval Δ t of middle sampled point ₀as follows

${\mathrm{\&Delta;t}}_0=\frac{1}{Q-1}\underset{m=1}{\overset{Q-1}{\&Sigma;}}\frac{P_{sat}(m+1)-P_{sat}\left(m\right)}{V_s}---\left(17\right)$

Wherein P _satrepresent A _sat0the coordinate of sampled point in sequence;

Compute vector at the projection vector of imaging plane then be expressed as

With t _cfor initial time, with Δ t ₀for step-length increases the orientation time gradually, utilize CoE _x, CoE _ywith CoE _zestimate the co-ordinates of satellite P of current time _satE0; Note vector at the projection vector of imaging plane be then be expressed as

If with folded angle is α _t, then α _tbe expressed as

If α _t< α _b/ 2, then with Δ t ₀for step-length continues to increase orientation time t, the calculating of repetitive (19), formula (20), until α _t> α _b/ 2, the orientation moment is now t _end;

Similarly, with t _cmoment is initial time, with Δ t ₀for step-length reduces the orientation time gradually, the calculating of repetitive (19), formula (20), until α _t> α _b/ 2, the orientation moment is now t _start;

Step 4, setting azimuth sample are counted, and calculate the sampling time interval under even azimuth sample condition, between t _startwith t _endbetween co-ordinates of satellite sequence rise sampling M doubly calculate the earth's surface drift angle sequence α of each point relative to scene center _dense;

Be specially:

Setting azimuth sample is counted as N _a, when performing step 4 first, make N _a=N _amin, N _athe time interval Δ t of the uniform azimuth sample that individual azimuth sample point is corresponding _dbe expressed as

${\mathrm{\&Delta;t}}_d\&ap;\frac{t_{end}-t_{start}}{N_a-1}---\left(21\right)$

After M doubly rises sampling, the time interval Δ t of uniform azimuth sample sequence _dUbe expressed as

${\mathrm{\&Delta;t}}_{dU}=\frac{{\mathrm{\&Delta;t}}_d}{M}---\left(22\right)$

With t _startfor initial time, t _endfor the termination time, Δ t _dUthe sampling instant sequence after sampling is doubly risen for step-length generates M, and according to CoE _x, CoE _ywith CoE _zestimate the co-ordinates of satellite value of each sample point, generate the co-ordinates of satellite sequence P after rising sampling _satd, now drift angle, earth's surface sequence α _densebe expressed as

Wherein

Step 5, calculate to count with azimuth sample corresponding, meet echo data at wavenumber domain along orientation to equally distributed earth's surface drift angle sequence α _tgt, according to α _tgtdetermine the sampled satellite position sequence P of space-variant _satF, calculate P _satFthe oblique distance sequence R of each sampling location and scene center _cF, calculate P _satFtime sampling interval sequence I _satF;

Be specially:

For orientation to sampling number N _a, meet echo data at wavenumber domain along orientation to equally distributed earth's surface drift angle sequence α _tgtbe expressed as

${\mathrm{\&alpha;}}_{tgt}\left(k\right)={\tan }^{-1}\left(\frac{2}{N_a-1}tan\right(\frac{{\mathrm{\&alpha;}}_B}{2}\left)k\right),(k=-\frac{N_a}{2}+1,...,\frac{N_a}{2})---\left(25\right)$

Get α successively _tgtin value at α _densethe immediate value of middle searching, makes P _satdin make α _denseobtain closest to α _tgtthe co-ordinates of satellite when coordinate of the sampled satellite point of each point value is final data acquisition, obtains final sampled satellite sequence P heterogeneous _satF, P _satFin each sampling location to P _sceoblique distance sequence R _cFbe expressed as

P _satFin the time series I of sampling interval between each sampled point _satFbe expressed as

$I_{satF}\left(k_1\right)=\frac{P_{satF}(k_1+1)-P_{satF}\left(k_1\right)}{V_s},(k_1=-\frac{N_a}{2}+1,...,\frac{N_a}{2}-1)---\left(27\right)$

Step 6, checking P _satFwhether meet and to block without transponder pulse and without the constraint condition of substar echo interference; If do not meet constraint, with Δ N _acount for step-length increases azimuth sample, carry out interative computation with step 4 to step 6, work as P _satFmeet simultaneously and to block without transponder pulse and without the constraint condition of substar echo interference, or azimuth sample is counted and to be reached in iteration in limited time, stopping interative computation;

Be specially:

If P _satFmeet and block constraint condition without transponder pulse, now calculated by space geometry relation

$\frac{2R_{cF}\left(k\right)-S_{wr}}{c}>\underset{m=k}{\overset{k+M_0}{\&Sigma;}}{I}_{sat}\left(m\right)+T_p+\mathrm{\&delta;}p,(k=-\frac{N_a}{2}+1,...,\frac{N_a}{2})---\left(28\right)$

$\frac{2R_{cF}\left(k\right)+S_{wr}}{c}<\underset{m=k}{\overset{k+M_0+1}{\&Sigma;}}{I}_{sat}\left(m\right)-\mathrm{\&delta;}p,(k=-\frac{N_a}{2}+1,...,\frac{N_a}{2})---\left(29\right)$

Wherein M ₀represent in data acquisition the transponder pulse interval quantity transmitted and between corresponding Received signal strength, guard time when δ p is sending and receiving beam switchover;

If P _satFmeet without substar echo interference, then it meets following one of two things: the first, along time delay after the leading edge time when the substar echo occurred in pre-echo window postpones to be greater than scene echoes; Second, when after the substar echo occurred in pre-echo window along time delay be less than scene echoes leading edge time postpone, if substar Echo width is two pulse widths, and a kth exomonental scene echoes and p exomonental substar echo were received in the same recurrent interval, the corresponding following relation of the first situation

$\left\{\begin{array}{c}\frac{2H}{c}-T_p+\underset{m=k}{\overset{p}{\&Sigma;}}{I}_{sat}\left(m\right)-\mathrm{\&delta;}p>\frac{2\left(R_{cF}\right(k)+S_{wr}/2)}{c}\\ \frac{2H}{c}+T_p+\underset{m=k}{\overset{p-1}{\&Sigma;}}{I}_{sat}\left(m\right)+\mathrm{\&delta;}p<\frac{2\left(R_{cF}\right(k)-S_{wr}/2)}{c}\end{array}\right.---\left(30\right)$

The corresponding following relation of the second situation

$\left\{\begin{array}{c}\frac{2H}{c}+T_p+\underset{m=k}{\overset{p}{\&Sigma;}}{\mathrm{PI}}_{sat}\left(m\right)+\mathrm{\&delta;}p<\frac{2R_{cF}\left(k\right)-S_{wr}}{c}\\ \frac{2H}{c}-T_p+\underset{m=k}{\overset{p+1}{\&Sigma;}}{\mathrm{PI}}_{sat}\left(m\right)-\mathrm{\&delta;}p>\frac{2R_{cF}\left(k\right)+S_{wr}}{c}\end{array}\right.---\left(31\right)$

Formula (30) is identical with the value of the middle k of formula (28) with the value of k in formula (31); If P _satFmeet the constraint condition that formula (28), formula (29) and formula (30) are formed, or meet the constraint condition that formula (28), formula (29) and formula (31) are formed, then think that spatial sampling parameter designing meets the System Parameter Design demand making the echo of target field scene area be able to complete reception; Now P _satFbe the final sampled point sequence of satellite; If P _satFnamely the constraint condition that formula (28), formula (29) and formula (30) are formed is not met, do not meet the constraint condition that formula (28), formula (29) and formula (31) are formed, then think that orientation is N to sampling number yet _aspatial sampling patten's design failure, with Δ N _afor step-length increases N _avalue, repeat step 4 carry out interative computation to step 6, until P _satFmeet and to block without transponder pulse and without the constraint condition of substar echo interference;

Setting N _athe maximal value numerical value of N obtained _aIMif work as N _abe less than N _aIMtime without any a P _satFsequence meets simultaneously to block without transponder pulse and without the constraint condition of substar echo interference, then think that the large stravismus of the variable element spaceborne Spotlight SAR Imaging system met under given earth observation demand condition is non-existent, interative computation termination;

Step 7, according to P _satFwith the relative position relation of scene center point, calculate Texas tower parameter time become adjustment law; Be specially:

(1) method described in step 2 Chinese style (3) ~ formula (6) is adopted to calculate P _satFin each sampling location relative to scene center P _sceincident angle sequence β _f;

(2) method described in step 5 Chinese style (23) is adopted to calculate P _satFin each sampling location relative to scene center P _scedrift angle, earth's surface sequence α _f;

(3) according to β _f, α _fwith Texas tower reference parameter f _c0, K _r0, F _s0, T _p0the adjustment law of the Texas tower parameter become during calculating, comprises carrier frequency f _c, frequency modulation rate K _r, pulse width T _pwith signal sampling rate F _stime become adjustment law;

Select a kind of adjustment law of radar parameter according to actual conditions, the adjustment law of radar parameter is divided into the following two kinds mode:

Mode one: the sampling rate F of radar transmitted pulse _s, pulse width T _pconstant, adjustment carrier frequency f _cwith frequency modulation rate K _ras follows

$\left\{\begin{array}{c}{f}_c=\frac{{\mathrm{sin\&beta;}}_0}{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{f}_{c0}\\ K_r=\frac{{\mathrm{sin\&beta;}}_0}{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{K}_{r0}\\ T_p=T_{p0}\\ F_s=F_{s0}\end{array}\right.---\left(32\right)$

Mode two: the frequency modulation rate K of radar transmitted pulse _rconstant, adjust the carrier frequency f transmitted _c, sampling rate F _sand pulse width T _pas follows

$\left\{\begin{array}{c}{f}_c=\frac{{\mathrm{sin\&beta;}}_0}{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{f}_{c0}\\ F_s=\frac{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{{\mathrm{sin\&beta;}}_0}{F}_{s0}\\ T_p=\frac{{\mathrm{sin\&beta;}}_0}{{\mathrm{sin\&beta;}}_F{\mathrm{cos\&alpha;}}_F}{T}_{p0}\\ K_r=K_{r0}\end{array}\right.---\left(33\right).$