CN103616683A - A method for generating a two-dimensional distribution multiphase screen of ionosphere scintillation phases of a GEO SAR - Google Patents

Abstract

The invention provides a method for generating a two-dimensional distribution multiphase screen of a geostationary orbit synthetic aperture radar. With power spectrum inversion and split-step Fourier transform, the method may achieve distribution generation of ionosphere scintillation two-dimensional random fluctuation phases, resolves a core problem of an ionosphere scintillation effect simulation in large-scale scene imaging simulation of the geostationary orbit synthetic aperture radar, namely a problem of a generating method of scintillation phase two-dimensional distribution, and achieves analogue simulation of the influence of ionosphere scintillation on GEO SAR large-scale scene imaging in order to facilitate compensation method research in ionosphere scintillation effect in the future.

Description

The Two dimensional Distribution leggy screen generating method of the ionospheric scintillation phase place of GEO SAR

Technical field

The invention belongs to synthetic-aperture radar research field and ionospheric scintillation research field, relate in particular to a kind of Two dimensional Distribution leggy screen generating method of synchronous orbit synthetic-aperture radar.

Background technology

Synthetic-aperture radar (SAR) is a kind of high-resolution microwave remotely sensed image radar of round-the-clock, round-the-clock, can be arranged on the flying platforms such as aircraft, satellite, guided missile.Since the invention fifties in last century, obtained in a lot of fields application more and more widely, fields such as disaster control, vegetational analysis, microwave remote sensing.

Geostationary orbit synthetic-aperture radar (GEO SAR) is the SAR satellite operating on the synchronous elliptical orbit of the 36000km height earth.Than low rail SAR (LEO SAR, orbit altitude is lower than 1000Km), GEO SAR has many obvious superiority, be mainly reflected in and survey and draw width length, monitor area coverage large, the cycle of heavily visiting is shorter, the aspects such as anti-strike and anti-lethality are strong, have become study hotspot both domestic and external at present.

The research of ionospheric effect is an importance of GEO SAR research.Due to factors such as GEO SAR track are higher, the synthetic aperture time is long, GEO SAR imaging is subject to the even more serious of ionospheric impact for LEO SAR.But, what for the research of GEO SAR, mainly consider at present is the aspects such as the System Parameter Design of GEO SAR own and analysis, imaging mechanism Mechanism Study, imaging processing algorithm and star driftage control, ionosphere has received less concern for the impact of GEO SAR system, so ionosphere is a problem demanding prompt solution to the modeling of GEO SAR systematic influence.In fact, ionosphere is divided into again background ionosphere and two kinds of impacts of ionospheric scintillation to the impact of GEO SAR, and ionospheric scintillation becomes a difficult point in GEO SAR research because its random fluctuation and mechanism of production uncertainty make it.To the more use of research of ionospheric scintillation, be at present Multiple-Phase-Screen method, but in GEO SAR field there are 2 deficiencies in this method: the one, and current Multiple-Phase-Screen method is used in LEO SAR system more, for GEO SAR system aspects, lacks corresponding application; The 2nd, it is that one dimension phase place generates and many documents and materials all have detailed generation method narration that current Multiple-Phase-Screen method majority relates to, be that in synthetic aperture radar image-forming process, phase fluctuation distribution is that the one-dimensional space distributes, lack relatively ripe two-dimensional phase space distribution generation method.And in fact, spatial scene in synthetic aperture radar image-forming process distributes and often relates to multipoint targets, an applicability is not had in the distributional assumption of original one dimension flicker phase place, and the generation method of therefore two-dimentional ionospheric scintillation phase place screen becomes a problem demanding prompt solution.

Summary of the invention

For addressing the above problem, the Two dimensional Distribution leggy screen generating method of a kind of synchronous orbit synthetic-aperture radar of the present invention, can be by power spectrum inverting and substep Fourier transform, and the distribution that realizes ionospheric scintillation two-dimensional random fluctuating phase place generates.

The Two dimensional Distribution leggy screen generating method of the ionospheric scintillation phase place of GEO SAR of the present invention comprises the following steps:

Step 1, according to ionosphere distribution situation structure electron density fluctuating power spectrum, utilizes described electron density fluctuating power spectrum to obtain the power spectrum of ionospheric scintillation phase place;

Step 2, the power spectrum of the ionospheric scintillation phase place obtaining according to described step 1, utilizes formula (3) to obtain the ionospheric single phase place screen random phase of differing heights and distributes:

u(x，y，z _n)=u(x，y，z _n-1)exp[jφ _n-1，n(x，y)] (3)

Wherein, j φ _{n-1, n}(x, y)=exp[χ (x, y)-jS (x, y)], z _nand z _n-1represent respectively the height that the propagation of GEO SAR signal reaches, phase place screen is considered to the random medium of layer, in z=(z _n-1+ z _nthe position of)/2; J φ _{n-1, n}(x) be a plural phase place, the phase fluctuation S (x, y) that comprises plural phase place and amplitude scintillation χ (x, y), x and y represent that in imaging scene, ionospheric two-dimensional space distributes;

Step 3, the single phase place screen random phase obtaining according to step 2 distributes rise and fall formula for relation (5) and formula (6) expression of power spectrum of power spectrum and ionosphere Multiple-Phase-Screen random fluctuation phase place of ionospheric electron density;

${\mathrm{\&Phi;}}_{\mathrm{\&chi;}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)=\frac{\mathrm{\&pi;}}{2}{k}^2\frac{{C^2<N_e>}^2}{1-C<N_e>}\mathrm{\&Delta;Z}{\sin }^2\left(\frac{{\mathrm{\&kappa;}}^{2}z}{2k}\right){\mathrm{\&Phi;}}_{\mathrm{\&xi;}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)---\left(5\right)$

${\mathrm{\&Phi;}}_S({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)=\frac{\mathrm{\&pi;}}{2}{k}^2\frac{{C^2<N_e>}^2}{1-C<N_e>}\mathrm{\&Delta;Z}{\cos }^2\left(\frac{{\mathrm{\&kappa;}}^{2}z}{2k}\right){\mathrm{\&Phi;}}_{\mathrm{\&xi;}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)---\left(6\right)$

Wherein, κ is that two-dimensional space wave number distributes, and it meets relation.Height is in z=(z _n-1+ z _nthe amplitude of the simulation screen of)/2 and phase deviation can utilize Fourier transformation method to come numerical value to produce, and establishing each lateral dimension of shielding is mutually L _m* L _n, and be divided into M * N equal portions, point (x=i Δ x, the random magnitude at y=j Δ place and for phase fluctuation formula (7) represent:

Wherein, i=0,1,2 ..., M-1, j=0,1,2 ..., N-1 Δ x=L _m/ M, Δ y=L _n/ N, Δ κ _x=2 π/L _m, Δ κ _y=2 π/L _n, and random phase angle

with

the Two Dimensional Uniform of obeying on 0～2 π distributes;

Step 4, modifies to described formula (7) according to Fourier transform and inverse Fourier transform, obtains result of calculation, and this result of calculation is suc as formula shown in (8), (9), (10):

$\begin{array}{c}{s}_{n-1,n}={\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(s1\right)\right]+j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s1\right)]+j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(s1\right)\right]-N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s1\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(s2\right)\right]+j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s2\right)]-j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(s2\right)\right]+N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s2\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(s3\right)\right]-j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s3\right)]+j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(s3\right)\right]+N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s3\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(s4\right)\right]-j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s4\right)]-j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(s4\right)\right]-N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s4\right)]\end{array}---\left(9\right)$

$\begin{array}{c}{x}_{n-1,n}={\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(x1\right)\right]+j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x1\right)]+j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(x1\right)\right]-N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x1\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(x2\right)\right]+j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x2\right)]-j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(x2\right)\right]+N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x2\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(x3\right)\right]-j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x3\right)]+j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(x3\right)\right]+N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x3\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(x4\right)\right]-j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x4\right)]-j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(x4\right)\right]-N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x4\right)]\end{array}---\left(11\right)$

Wherein, FFT _x, FFT _y, IFFT _x, IFFT _ywhat represent respectively is Fourier transform and the inverse Fourier transform of x direction and y direction;

Step 5, the result of calculation obtaining according to step 4 utilizes split-step fourier transform to realize the propagation of GEO SAR radar signal between phase place screen, obtains random fluctuation phase place, and it meets formula (12) and (13):

$\begin{array}{c}u(x,y,z_2)=\exp [-\mathrm{jk}\left(\mathrm{\&Delta;z}\right)]\&CenterDot;{(1/2\mathrm{\&pi;})}^2\&CenterDot;\\ {\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}U({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y,z_1)\exp [{-\mathrm{j\&kappa;}}^2\left(\mathrm{\&Delta;z}\right)/2k]\exp [-j({\mathrm{\&kappa;}}_{x}x+{\mathrm{\&kappa;}}_{y}y)]{\mathrm{d\&kappa;}}_x{\mathrm{d\&kappa;}}_y\end{array}---\left(12\right)$

$U({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y,z)={\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}u(x,y,z)\exp [-i({\mathrm{\&kappa;}}_{x}x+{\mathrm{\&kappa;}}_{y}y)]\mathrm{dxdy}---\left(13\right)$

Wherein, Δ z is the interval between phase place screen;

Step 6, introduces GEO SAR echoed signal by the random fluctuation phase place of trying to achieve in step 5;

Ionospheric scintillation represents the formula for impact (14) of GEO SAR echoed signal:

Wherein

the phase fluctuation that ionospheric scintillation produces, A _iono(t) be the amplitude scintillation that ionospheric scintillation produces, in each PRT time, distance is T to the variation range of time _p, T _psignal pulse time width, will with

regard the spatial variations with scene areas as, be denoted as

with

Beneficial effect of the present invention is:

The distribution that the present invention has realized ionospheric scintillation two-dimensional random fluctuating phase place generates, having solved the key problem of ionospheric scintillation effect emulation in geostationary orbit synthetic-aperture radar large scene imaging simulation---flicker phase place Two dimensional Distribution generates method problem, and realized the analogue simulation of ionospheric scintillation to GEO SAR large scene Imaging, be convenient to the problems such as compensation method research of ionospheric scintillation effect in the future.

Accompanying drawing explanation

Random medium and the distribution plan that shields mutually position when Fig. 1 is GEO SAR signal of the present invention through ionosphere;

Fig. 2 is the three-dimensional structure schematic diagram of ionospheric scintillation phase place of the present invention to GEO SAR effect of signals;

Fig. 3 is electron density fluctuating σ of the present invention _ξunder=0.05 condition, one dimension ionospheric scintillation Multiple-Phase-Screen random fluctuation PHASE DISTRIBUTION figure;

Fig. 4 is electron density fluctuating σ of the present invention _ξunder=0.05 condition, two-dimentional ionospheric scintillation Multiple-Phase-Screen random fluctuation PHASE DISTRIBUTION figure.

Embodiment

The Two dimensional Distribution leggy screen generating method that the invention provides a kind of synchronous orbit synthetic-aperture radar, concrete steps are as follows:

Step 1, ionospheric scintillation phase power spectrum structure.

The reason that causes ionospheric scintillation is mainly that instability due to ionospheric plasma, ionosphere are with the dynamic processes such as coupling between thermosphere and magnetosphere, therefore, ionospheric electron density fluctuations is very complicated and irregular, thus the propagation problem of Technologies Against Synthetic Aperture Radar signal in ionosphere to carry out descriptive statistics be very convenient and necessary.Multiple-Phase-Screen theoretical foundation is autocorrelation function based on ionospheric scintillation and the structure of power spectrum, so first need according to ionosphere distribution situation structure electron density fluctuating power spectrum and ionospheric scintillation phase power spectrum.

With spectrum index p, characterize ionosphere irregular body, Shkarofsky has introduced related function and power spectrum in general sense:

${\mathrm{\&Phi;}}_{\mathrm{\&xi;}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)=\frac{{{\mathrm{\&sigma;}}_{\mathrm{\&xi;}}^2\left(k_0{r}_0\right)}^{(p-3)/2}{r}_0^3{K}_{p/2}\left(r_0\sqrt{({\mathrm{\&kappa;}}_x^2+{\mathrm{\&kappa;}}_y^2)+k_0^2}\right)}{{\left(2\mathrm{\&pi;}\right)}^{3/2}{K}_{(p-3)/2}\left(k_0{r}_0\right)}\&CenterDot;{\left(r_0\sqrt{({\mathrm{\&kappa;}}_x^2+{\mathrm{\&kappa;}}_y^2)+k_0^2}\right)}^{-p/2}---\left(1\right)$

In formula (1), r ₀the inside dimension of irregular body, l ₀=2 π/k ₀the external dimensions of irregular body, K _vthat exponent number is the Bessel function of the Equations of The Second Kind revision of v, κ _x=2 π/L _x, κ _y=2 π/L _yfor two-dimensional space wave number, L _xand L _yfor the ionosphere two-dimensional space distribution x of calculating and the total length of y direction.σ _ξionosphere irregular body electron density fluctuating standard deviation, because Multiple-Phase-Screen method is only applicable to fluctuating situation a little less than ionosphere, so its span is generally between 0～0.3.

The power spectrum that can obtain ionosphere Multiple-Phase-Screen random fluctuation phase place by the structure of ionospheric electron density fluctuating power spectrum, the relation between the two is as follows:

${\mathrm{\&Phi;}}_{{\mathrm{\&phi;}}_{n-1,n}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)=\frac{\mathrm{\&pi;}}{2}{k}^2{\&Integral;}_{z_{n-1}}^{z_n}\frac{C^2{<N_e>}^2}{1-C<N_e>}\mathrm{dz}{\mathrm{\&Phi;}}_{\mathrm{\&xi;}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)---\left(2\right)$

Wherein, C=e ²/ m ω ²ε ₀=80.6/f ², f is the carrier frequency of signal; <N _e> is background ionosphere electron density;

for the wave number in medium,

the wave number in free space, < ε _r> is the average of ionosphere relative dielectric constant, and it meets < ε _r>=1-e ²<N _e>/m ω ²ε ₀=1-C<N _ethe relation of >; z _n-1and z _nrepresent that respectively differing heights ionospheric scintillation phase place shields height of living in, that ξ represents is height (z _n-1+ Z _nionosphere, place)/2 horizontal direction electron density rises and falls; Φ _ξ(κ _x, κ _y) power spectrum that rises and falls for ionospheric electron density.

Step 2, produces the ionospheric single phase place screen random phase of differing heights and distributes:

Multiple-Phase-Screen method is that whole ionosphere is equivalent to shielding mutually at random of producing by series of values, is vacuum mutually between screen, and signal often shields mutually by one, just increases a random phase, and as shown in Figure 1, it can be represented by following formula:

u(x，y，z _n)=u(x，y， _zn-1)exp[jφ _n-1，n(x，y)] (3)

jφ _n-1,n(x，y)=exp[χ(x,y)-jS(x,y)] (4)

Z _nand z _n-1represent respectively the height that the propagation of GEO SAR signal reaches, phase place screen is considered to the random medium of layer, in z=(z _n-1+ z _nthe position of)/2.J φ _{n-1, n}(x) be a plural phase place, the phase fluctuation S (x, y) that comprises plural phase place and amplitude scintillation χ (x, y), x and y represent that in imaging scene, ionospheric two-dimensional space distributes.

Z in Fig. 1 ₀, z ₁..., z _n-1, z _nposition be respectively signal while passing ionosphere the position of differing heights of process, and at z=(z _n-1+ z _nposition)/2, in figure, the represented position of each dotted line is that phase place is shielded residing position, signal increases a corresponding random phase when shielding through phase place, but the signal propagation between phase place screen belongs to vacuum, propagates.

Therefore, formula (2) can be further refined as:

${\mathrm{\&Phi;}}_{\mathrm{\&chi;}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)=\frac{\mathrm{\&pi;}}{2}{k}^2\frac{{C^2<N_e>}^2}{1-C<N_e>}\mathrm{\&Delta;Z}{\sin }^2\left(\frac{{\mathrm{\&kappa;}}^{2}z}{2k}\right){\mathrm{\&Phi;}}_{\mathrm{\&xi;}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)---\left(5\right)$

${\mathrm{\&Phi;}}_S({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)=\frac{\mathrm{\&pi;}}{2}{k}^2\frac{{C^2<N_e>}^2}{1-C<N_e>}\mathrm{\&Delta;Z}{\cos }^2\left(\frac{{\mathrm{\&kappa;}}^{2}z}{2k}\right){\mathrm{\&Phi;}}_{\mathrm{\&xi;}}({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y)---\left(6\right)$

Wherein, κ is that two-dimensional space wave number distributes, and it meets

relation.Height is in z=(z _n-1+ z _nthe amplitude of the simulation screen of)/2 and phase deviation can utilize Fourier transformation method to come numerical value to produce.Suppose that each lateral dimension of shielding is mutually L _m* L _n, and be divided into M * N equal portions, random magnitude and the phase fluctuation at point (x=i Δ x, y=j Δ y), located can be described as:

Wherein, i=0,1,2 ..., M-1, j=0,1,2 ..., N-1 Δ x=L _m/ M, Δ y=L _n/ N, Δ κ _x=2 π/L _m, Δ κ _y=2 π/L _n, and random phase angle

with

the Two Dimensional Uniform of obeying on 0～2 π distributes.But formula (7) calculation of complex, calculated amount is larger, in emulation, will certainly expend the more time, therefore formula (7) is modified result of calculation is obtained by Fourier transform and inverse Fourier transform operation as far as possible, so it is as follows to obtain producing the formula of random fluctuation phase place and amplitude:

$\begin{array}{c}{s}_{n-1,n}={\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(s1\right)\right]+j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s1\right)]+j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(s1\right)\right]-N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s1\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(s2\right)\right]+j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s2\right)]-j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(s2\right)\right]+N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s2\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(s3\right)\right]-j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s3\right)]+j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(s3\right)\right]+N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s3\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(s4\right)\right]-j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s4\right)]-j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(s4\right)\right]-N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(s4\right)]\end{array}---\left(9\right)$

$\begin{array}{c}{x}_{n-1,n}={\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(x1\right)\right]+j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x1\right)]+j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(x1\right)\right]-N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x1\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(x2\right)\right]+j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x2\right)]-j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(x2\right)\right]+N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x2\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(x3\right)\right]-j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x3\right)]+j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(x3\right)\right]+N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x3\right)]\\ +{\mathrm{FFT}}_x\left[{\mathrm{FFT}}_y\left(x4\right)\right]-j\&CenterDot;{\mathrm{FFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x4\right)]-j\&CenterDot;N\&CenterDot;{\mathrm{IFFT}}_x\left[{\mathrm{FFT}}_y\left(x4\right)\right]-N\&CenterDot;{\mathrm{IFFT}}_x[M\&CenterDot;{\mathrm{IFFT}}_y\left(x4\right)]\end{array}---\left(11\right)$

Wherein, FFT _x, FFT _y, IFFT _x, IFFT _ywhat represent respectively is Fourier transform and the inverse Fourier transform of x direction and y direction.

Step 3, calculates the propagation of signal between phase place screen.

Signal is propagated and can be utilized split-step fourier transform to realize between screen, and it meets formula (12) and (13):

$\begin{array}{c}u(x,y,z_2)=\exp [-\mathrm{jk}\left(\mathrm{\&Delta;z}\right)]\&CenterDot;{(1/2\mathrm{\&pi;})}^2\&CenterDot;\\ {\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}U({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y,z_1)\exp [{-\mathrm{j\&kappa;}}^2\left(\mathrm{\&Delta;z}\right)/2k]\exp [-j({\mathrm{\&kappa;}}_{x}x+{\mathrm{\&kappa;}}_{y}y)]{\mathrm{d\&kappa;}}_x{\mathrm{d\&kappa;}}_y\end{array}---\left(12\right)$

$U({\mathrm{\&kappa;}}_x,{\mathrm{\&kappa;}}_y,z)={\&Integral;}_{-\&infin;}^{\&infin;}{\&Integral;}_{-\&infin;}^{\&infin;}u(x,y,z)\exp [-i({\mathrm{\&kappa;}}_{x}x+{\mathrm{\&kappa;}}_{y}y)]\mathrm{dxdy}---\left(13\right)$

Wherein, Δ z is the interval between phase place screen.

Step 4, introduces GEO SAR echoed signal by random fluctuation phase place.

Ionospheric scintillation can be expressed as for the impact of GEO SAR echoed signal

Wherein

the phase fluctuation that ionospheric scintillation produces, A _iono(t) be the amplitude scintillation that ionospheric scintillation produces.As shown in Figure 2, A _iono(t) and room and time in imaging scene distribute and can obtain by methods such as Multiple-Phase-Screens, its corresponding each grid is to having for the random fluctuation phase place of each PRT of GEO SAR in the time and the distribution of random fluctuation amplitude, ripple for each target in imaging scene is introduced a fluctuating phase place and relief intensity according to formula (14), in addition, each PRT is in the time, and distance is T to the variation range of time _p, i.e. signal pulse time width, and T _ptime is very short, can think that ionospheric scintillation temporal evolution is negligible in a PRT, thereby can be by

with regard the spatial variations with scene areas as, be denoted as

with

It should be noted that ionospheric scintillation rises and falls in weak situation, signal fluctuation amplitude is less, impact on GEO SAR imaging is less, for GEO SAR system imaging, mainly focuses on the variation of signal phase to be embodied as picture simultaneously, therefore, actual emulation is only considered phase place

and ignore amplitude

Embodiment:

At this example, correlation parameter is as follows:

The inside dimension r of irregular body ₀=15m, external dimensions L ₀=2.5km, the spectrum index p=4 of ionosphere irregular body; The lateral dimension range L that shield mutually in ionosphere _m=500km, L _n=500km; Horizontal range number of samples is respectively M=1024 and N=1024; Electron density rises and falls as σ _ξ=0.05; Wherein the sampling interval of vertical height is Δ _z=5km, utilizes IRI2001 software, has generated the background ionosphere electron density (ionospheric scintillation activity is region comparatively obviously) of height 50km～500km.We obtain two-dimentional Multiple-Phase-Screen phase fluctuation simulation result as shown in Figure 4 by correlation parameter substitution (1) (2) (3) (4) (5) formula.

Fig. 3 has shown that traditional one dimension Multiple-Phase-Screen phase place bears results, what Fig. 4 showed is that two-dimentional Multiple-Phase-Screen phase place bears results, the two operation parameter is identical, from numerical range, the result difference of the two is little, but for GEO SAR emulation, there is significant advantage in the latter, for one-dimensional random fluctuating phase place, its echoed signal that certainly will require scene in GEO SAR imaging simulation is a plane completely, it can introduce echoed signal by random fluctuation phase place by (14) like this, but actual simulation process, scene echoes is from each scattering point in two-dimensional space, therefore there is serious deficiency in the introducing mode of one-dimensional random fluctuating phase place, ionospheric scintillation phase place by two-dimentional Multiple-Phase-Screen generates, can reflect preferably that ionospheric scintillation is for the impact of GEO SAR signal, and then can observe better ionospheric scintillation for the impact of GEO SAR imaging.

Certainly; the present invention also can have other various embodiments; in the situation that not deviating from spirit of the present invention and essence thereof; those of ordinary skill in the art are when making according to the present invention various corresponding changes and distortion, but these corresponding changes and distortion all should belong to the protection domain of the appended claim of the present invention.

Claims (1)

1. a dimension distribution leggy screen generating method for the ionospheric scintillation phase place of GEO SAR, is characterized in that, comprising:

Step 1, according to ionosphere distribution situation structure electron density fluctuating power spectrum, utilizes the described electron density power spectrum that cooks meals to obtain the power spectrum of ionospheric scintillation phase place;

Step 2, whole ionosphere is equivalent to shielding mutually immediately of producing by series of values, synchronous orbit synthetic-aperture radar signal often shields mutually by one, increase a random phase, according to the power spectrum of described ionospheric scintillation phase place, utilize formula (3) to obtain the ionospheric single phase place screen random phase of differing heights thus and distribute:

u(x，y，z _n)=u(x，y，z _n-1)exp[jφ _n-1，n(x，y)] (3)

Wherein, j φ _{n-1, n}(x, y)=exp[χ (x, y)-jS (x, y)], z _nand z _n-1represent respectively the height that the propagation of GEO SAR signal reaches, phase place screen is considered to the random medium of layer, in z=(z _n-1+ z _nthe position of)/2; J φ _{n-1, n}(x) be a plural phase place, the phase fluctuation S (x, y) that comprises plural phase place and amplitude scintillation χ (x, y), x and y represent that in imaging scene, ionospheric two-dimensional space distributes;

Step 3, between the single phase place screen that described synchronous orbit synthetic-aperture radar signal obtains in step 2, carry out vacuum propagation, according to the amplitude of single phase place screen and phase deviation by rise and fall formula for relation (5) and formula (6) expression of power spectrum of power spectrum and ionosphere Multiple-Phase-Screen random fluctuation phase place of ionospheric electron density;

Wherein, κ is that two-dimensional space wave number distributes, and it meets relation.Height is in z=(z _n-1+ z _nthe amplitude of the simulation screen of)/2 and phase deviation can utilize Fourier transformation method to come numerical value to produce, and establishing each lateral dimension of shielding is mutually L _m* L _n, and be divided into M * N equal portions, point (x=i Δ x, the random magnitude at y=j Δ place and for phase fluctuation formula (7) represent:

Wherein, i=0,1,2 ..., M-1, j=0,1,2 ..., N-1 Δ x=L _m/ M, Δ y=L _n/ N, Δ κ _x=2 π/LM, Δ κ _y=2 π/L _n, and random phase angle

with

the Two Dimensional Uniform of obeying on 0～2 π distributes;

Step 4, modifies to described formula (7) according to Fourier transform and inverse Fourier transform, obtains result of calculation, and this result of calculation is suc as formula shown in (8), (9), (10):

Wherein, FFT _x, FFT _y, IFFT _x, IFFT _ywhat represent respectively is Fourier transform and the inverse Fourier transform of x direction and y direction;

Step 5, the result of calculation obtaining according to step 4 utilizes split-step fourier transform to realize the propagation of GEO SAR radar signal between phase place screen, obtains random fluctuation phase place, and it meets formula (12) and (13):

Wherein, Δ z is the interval between phase place screen;

Step mule 6, introduces GEO SAR echoed signal by the random fluctuation phase place of trying to achieve in step 5;

Ionospheric scintillation represents for the formula for impact (14) of GEO SAR echoed signal:

Wherein

the phase fluctuation that ionospheric scintillation produces, A _iono(t) be the amplitude scintillation that ionospheric scintillation produces, in each PRT time, distance is T to the variation range of time _p, T _psignal pulse time width, will

with

regard the spatial variations with scene areas as, be denoted as

with

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