CN101587500A - Computer emulation method for sea-surface imaging of bistatic synthetic aperture radar - Google Patents

Abstract

The invention provides a computer emulation method for sea-surface imaging of a bistatic synthetic aperture radar, and relates to the technical field of synthetic aperture radar imaging and the field of oceanography. The method simplifies and decomposes emulated true scenes into seven suitable computer emulations in an approximation degree, namely, emulation of sea-surface waves, emulation of tilt modulation generated by wave surfaces of first-scale waves, emulation of fluid power modulation generated by interaction between sea-surface waves, sea-surface bistatic correlation time simulation, divided wave spectrum emulation, sea-surface bistatic electromagnetic scattering emulation, and sea-surface synthetic aperture radar image emulation, and develops software to solve the problems one by one to generate a final emulated bistatic synthetic aperture radar sea-surface image. The method takes files as ports, integrates emulation problems of several subjects, and not only meets the requirement of final emulation, but also facilitates the development of software modules.

Description

The computer emulation method of sea-surface imaging of bistatic synthetic aperture radar

Technical field

The invention belongs to thalassography and sea technical field of imaging, relate to synthetic-aperture radar sea imaging technique, relate to a kind of computer emulation method of sea-surface imaging of bistatic synthetic aperture radar specifically.

Background technology

Synthetic aperture radar (SAR) is a kind of active microwave remote sensing means that grow up late 1950s, compare with other remote sensing means, the resolution height is arranged, round-the-clock, round-the-clock, resolution is not with advantages such as oblique distance variations, a large amount of successful application have all been obtained in a lot of fields, ocean remote sensing is exactly the important applied field of SAR, first Synthetic Aperture Radar satellite SeaSAT of U.S.'s emission in 1978 uses at ocean remote sensing, afterwards some Synthetic Aperture Radar satellite such as ERS-1, ERS-2, EnviSAT, RADARSAT etc. have obtained a large amount of application aspect ocean remote sensing, as utilize SAR image inverting Ocean Wind-field, the wave of the sea spectrum, ocean current, submarine topography etc.

Because the restriction of technical merit, ripe at present spaceborne, carried SAR mainly are list station SAR systems.Yet, the advantage that two station SAR have many single station SAR not possess, each national technician has begun to be devoted to the development of two station SAR theories and system.In 2007, there has been French technician to publish the document of sea, two station ship Wake radar imagery emulator, in addition do not see that other open source literatures relate to this aspect, prior art focuses on the emulation of sea ship Wake, it comprises the emulation of sea, naval vessel Kelvin's tail elevation, and the emulation of the wave spectrum after the tail disturbance, utilization improve emulation and the synthetic aperture imaging emulation that two yardstick scattering models generate the average scattering cross section.The prior art has only been considered the sea bistatic radar imaging of naval vessel Kelvin's tail, can not directly extend to other oceans and use (as oil film, submarine topography and tide current etc.); Secondly, being created in the whole simulation method of average scattering cross section, sea is a very important ingredient, its levels of precision directly determines the accuracy of imaging results, in the prior art, what utilize is that two yardstick surface scattering models obtain ship Wake average scattering cross section, sea, and in generally being familiar with now, three yardstick surface scattering models are than two yardstick surface scattering models accurate and effective more, and studies show that, second order Prague wave scatter also can produce significantly influence to the average scattering cross-sectional sizes, and prior art is not considered the wave scatter influence of second order Prague.

Summary of the invention

In order to solve prior art problems, the computer emulation method that the purpose of this invention is to provide a kind of sea-surface imaging of bistatic synthetic aperture radar, utilizing two station synthetic-aperture radar (biSAR) when the sea is observed, the real scene of emulation is simplified the particular problem that is decomposed into seven suitable Computer Simulations under certain degree of approximation, so that directly emulation on computers.

For achieving the above object, the technical scheme that the present invention deals with problems provides the computer emulation method of sea-surface imaging of bistatic synthetic aperture radar, and its step is as described below:

Step 1: be used for hydrodynamic force and the two-dimentional wave spectrum emulation module of first yardstick, second yardstick wave two dimension wave spectrum and Prague wave that the modulation of tilting is calculated, receive emulation sea scene domain, scattering resolution element size, sea situation parameter and two stations synthetic-aperture radar observed parameter, generate the two-dimentional wave spectrum file of first yardstick, second yardstick and Prague wave that are used for Fluid Computation power and tilt to modulate under the Cartesian coordinates;

Step 2: wind set-up modulating action emulation module, receive first yardstick two dimension wave spectrum file, be used to generate the wave-number vector file and the first yardstick flow field file of local observation angle file, polarization factor file, local Prague wave;

Step 3: the hydrodynamic force modulation simulation module of surface wave-Bo effect, receive the two-dimentional wave spectrum file of the first yardstick wave, the two-dimentional wave spectrum file of the second yardstick wave and the two-dimentional wave spectrum file of Prague wave, be used to generate the wave spectrum file of Prague wave of the second yardstick wave spectrum file of modulation and modulation;

Step 4: two station, sea emulation module correlation time, the wave spectrum file and the local observation angle file of the second yardstick wave of reception modulation are used to generate two station, sea file correlation time;

Step 5: cut apart the wave spectrum emulation module, receive the two-dimentional wave spectrum file of the second yardstick wave of two-dimentional wave spectrum file, the modulation of the first yardstick wave, be used to generate the wave spectrum file of the first yardstick wave of cutting apart again and the wave spectrum file of the second yardstick wave cut apart again;

Step 6: the two station electromagnetic scattering in sea emulation module, receive the wave-number vector file of wave spectrum file, the wave spectrum file of the second yardstick wave, local observation angle file, polarization factor file and local Prague wave of the first yardstick wave of cutting apart again, generate the average scattering cross section NRCS file of each scattering resolution element;

Step 7: two station, sea synthetic aperture radar image-forming emulation module, receive average scattering cross section NRCS file, two station, sea file correlation time and the first yardstick flow field file, be used to generate two station, sea diameter radar image of emulation.

The invention has the beneficial effects as follows: the present invention by file as interface, will be referred to fluid mechanics is integrated together with how much mathematics, Electromagnetic theory and the several interdisciplinary simulation problems of signal Processing, both can satisfy the requirement of last emulation, simulation problems can be dissolved again and be the less several theoretical simulation problems of correlativity, greatly facilitate the exploitation of software module.Emulation mode of the present invention is utilized the scattering properties of target different incidence angles, scattering angle, improves the ability of SAR target detection, classification, identification greatly, can improve application power and the level of SAR greatly; Emulation mode of the present invention has promoted security and the disguised two station SAR that all are better than single station SAR greatly that the remotely sensed image on sea is used, the emulation of the two station of the present invention SAR militarily also has good application prospects, can provide foundation for imaging, detection, classification and the identification of military ocean target.The present invention has promoted to carry out in two stations SAR mode the application of sea feature (wave spectrum, wind field etc.) inverting.

Description of drawings

Fig. 1 is a process flow diagram of the present invention;

Embodiment

Below in conjunction with accompanying drawing the present invention is described in detail, be to be noted that described embodiment only is intended to be convenient to the understanding of the present invention, and it is not played any qualification effect.

Raising and breakthrough along with restrictions such as signal phase simultaneous techniques, time synchronized, the location technology pair gordian technique level that station SAR develop, the increasing concern that two station SAR research has been subjected to, there is the researchist of a lot of countries to propose the plan and the scheme of some two/multistation SAR satellites formations and networking, as TechSAT 21, BISAT, Cartwheel etc., there are some schemes to begin development.Some domestic in recent years units and researchist also begin to be devoted to the exploitation of two stations SAR theory, Study on Technology and equipment.In the near future, two station SAR remote sensing epoch are coming.

Ocean remote sensing is one of important application of two stations SAR remote sensing of the earth, and the SAR ocean remote sensing of two stations is compared with single station SAR can obtain the more scattered information at multiple scattering angle of sea, can be finally inversed by information such as ocean current, ocean wave spectrum more accurately.The sea is different from the land target, it be a random motion the time become the random rough face, in the SAR synthetic aperture time, can produce significantly motion, therefore not only relevant in the SAR ocean imaging of two stations with two stations scattering properties on sea, also relevant with the random motion characteristic on sea, its mechanism is the field, forward position of current sea SAR remote sensing more than land fixed target complexity; And the sea-surface imaging of bistatic synthetic aperture radar technical research relates to the very complicated problems of subjects such as fluid mechanics, marine physics, calculating electromagnetic field, signal Processing, has a lot of phenomenons and problem all need find in experiment, analyze and verify.But truly test costly, and the ocean is very complicated, various hydrometeorological conditions are difficult to control and measure, and computer simulation experiment is because condition is controlled, it is convenient to implement, thereby become a kind of important analysis means of synthetic aperture radar (SAR) sea, the two station of understanding imaging mechanism, rules, and provide a general numerical simulation platform for further two station SAR ocean remote sensing applied researcies.Domestic without any relevant therewith systematic simulation work and patent, so the present invention will lay the first stone for China carries out two/multistation SAR ocean remote sensing applied research, for the development of China's two station SAR ocean remote sensing equipment provides reference and theoretical foundation.

The primary difference of the present invention and the prior art is, the prior art focuses on the emulation of sea ship Wake, and the present invention focuses on the computer emulation method of wave of the sea radar imagery, because the sea all types of target is (as the naval vessel, oil film, submarine topography and tide current etc.) all under the wave background, exist, various sea-surface targets can join on certain theoretical model basis in the wave radar imagery emulation, therefore the present invention not only can extend to the radar imagery computer emulation method of naval vessel, sea imaging tail simply, can also extend to the radar imagery of other all types of targets of sea very simply, thus versatility, extensibility is better; Secondly, in French technician's existing open emulator, what adopt is that two yardstick scattering models are described two station, sea scattering properties, the present invention then adopts three yardstick scattering models based on the second order Bragg diffraction, because the present invention has considered influence and the second order Prague wave scatter of mesoscale ripple in the scattering of two stations more, compared with two yardstick scattering models, it will be more accurate that the scattering properties that obtains distributes, thereby make the bistatic radar imaging results more accurately reach rationally; At last, the present invention is selecting wave spectrum discretize stepping wave number different in addition with the principle of cutting apart the wave number value at interval with existing open emulator, existing emulator has only been considered to divide according to simulating scenes scope and plane number, and the present invention is from physical significance and model essence angle, the wave spectrum division principle that will carry out the hydrodynamic force modulation separates with the wave spectrum division principle that calculates the scattering cross-section distribution, thereby make whole simulation method refinement more among the present invention, physical significance is clearer and more definite.

The computer emulation method of sea-surface imaging of bistatic synthetic aperture radar of the present invention, it simplifies the particular problem that is decomposed into seven suitable Computer Simulations with the real scene of emulation under degree of approximation:

A), according to the emulation sea scene domain, scattering resolution element size, sea situation parameter of input for example: wind speed size and direction, two stations SAR observed parameter for example: overall incident angle, overall scattering angle, overall incident orientation angle, overall scattering position angle, the radar carrier frequency generates the two-dimentional wave spectrum that is used for Fluid Computation power and first yardstick, the second yardstick wave and Prague wave of the modulation of tilting under the Cartesian coordinates;

B), the corrugated of the first yardstick wave that generates according to emulation, the emulation of the modulation of tilting;

C), according to the fluid mechanics modulation theory between the first yardstick wave and the second yardstick wave, Prague wave, utilize sea first yardstick, the second yardstick wave and Prague wave to interact, the emulation module of the hydrodynamic force modulation of generation;

D), according to the wave spectrum of this locality second yardstick wave after the hydrodynamic force modulation, calculate sea, the two station correlation time in each scattering resolution element;

E), according to the partition principle that first yardstick, the second yardstick wave Scattering cross section calculate, will be used for Fluid Computation power and the wave spectrum of first yardstick of the modulation of tilting, the second yardstick wave is repartitioned and become to be used to calculate two first yardstick of scattering cross-section, two-dimentional wave spectrums of the second yardstick wave of standing;

F), two stations electromagnetic scattering emulation on sea;

G), two station, sea diameter radar image emulation.

The present invention is at rationally simplification, theoretical analysis and extensively investigate on the basis, above seven particular problems of the computer emulation method of two stations synthetic-aperture radar (biSAR) sea imaging is simplified being decomposed into seven parts, and the relation between seven parts is as follows:

A), the emulation of wave of the sea spectrum: under wind action, atmosphere and water surface mutual friction mutually, after wind acting force and wave breaking reach equilibrium state and can produce wave stable on the statistical significance and compose.Here relate generally to thalassography and fluid mechanics problem.

B), inclination modulation simulation: the second yardstick wave is distributed on the corrugated of the first yardstick wave, position, corrugated at the first different yardstick waves, can make, Scattering of Vector produces different skews under local coordinate system, thereby change that this locality is gone into, Scattering of Vector, Prague wave vector and polarization factor size.Relate to fluid mechanics and how much mathematics.

C), Bo-Bo modulation simulation: can produce change after interacting between the wave, the wave of the sea spectrum after the generation disturbance to the wave of the sea statistical framework.Here relate generally to thalassography and fluid mechanics problem.

D), two station sea emulation correlation time:, need represent that scatterer over time correlation time with the sea because the sea is in the middle of the random motion constantly.Here relate to electromagnetics and synthetic aperture radar (SAR) signal Processing.

E), cut apart wave spectrum emulation: modulation is relevant with the resolution element size because hydrodynamic force is modulated, tilted, and that first yardstick, the second yardstick wave Scattering cross section and Kirchhoff's integral formula are simplified principle is relevant, therefore to simplify principle according to the Kirchhoff's integral formula when obtaining the scattering cross-section in each resolution element, cut apart the wave spectrum of first yardstick, the second yardstick wave again.Here relate to electromagnetic scattering and mathematics interpolation theory.

F), two stations electromagnetic scattering emulation on sea: wave is the key issue of emulation to the modulation of radar signal, wave and electromagnetic wave interact, under the Bragg resonance theory, two stations synthetic-aperture radar (biSAR) are relatively more responsive to the micro-scaled structures on sea, detected by two station synthetic-aperture radar (biSAR) thereby wave-wave effect and tilting action have changed the micro-scaled structures on sea.Here relate generally to Electromagnetic theory.

G), two stations synthetic-aperture radar (biSAR) image simulation: on the Microwave Backscattering Model basis of wave in conjunction with wave the time become, kinetic characteristic, just can obtain two synthetic-aperture radar (biSAR) emulating images of standing by the synthetic aperture radar (SAR) signal processing analysis.Here relate generally to synthetic-aperture radar signal Processing and thalassography problem.

Above-mentioned seven parts can conduct a research and simulation work on present computer technology level and scientific theory level.

The whole simulation system of computer emulation method of the present invention, be to adopt establishment simulation software under the MATLAB environment on computers, be divided into following seven emulation modules: be used for hydrodynamic force and the two-dimentional wave spectrum emulation module 1 of first yardstick, second yardstick wave two dimension wave spectrum and Prague wave that the modulation of tilting is calculated; Wind set-up modulating action emulation module 2; The hydrodynamic force modulation simulation module 3 of surface wave-Bo effect; Two station, sea emulation module correlation time 4; Cut apart wave spectrum emulation module 5; The two station electromagnetic scattering in sea emulation module 6; Two station, sea synthetic aperture radar image-forming emulation module 7, respectively corresponding above-mentioned seven parts are to solve the problem of each part.The composition and the relation of the system architecture that the present invention is formed are described below below:

Be used for hydrodynamic force and the two-dimentional wave spectrum emulation module 1 of first yardstick, second yardstick wave two dimension wave spectrum and Prague wave that the modulation of tilting is calculated, receive emulation sea scene domain, scattering resolution element size, sea situation parameter, two stations synthetic-aperture radar observed parameter, generate the two-dimentional wave spectrum file of first yardstick, second yardstick and Prague wave that are used for Fluid Computation power and tilt to modulate under the Cartesian coordinates;

Wind set-up modulating action emulation module 2 is connected with two-dimentional wave spectrum emulation module 1, receive first yardstick two dimension wave spectrum file, be used to generate the wave-number vector file and the first yardstick flow field file of local observation angle file, polarization factor file, local Prague wave;

The hydrodynamic force modulation simulation module 3 of surface wave-Bo effect is connected with two-dimentional wave spectrum emulation module 1, receive the two-dimentional wave spectrum file of first yardstick two dimension wave spectrum file, second yardstick two dimension wave spectrum file and Prague wave, be used to generate the wave spectrum file of Prague wave of the second yardstick ripple wave spectrum file of modulation and modulation;

Two station, sea emulation module correlation time 4 is connected with wind set-up modulating action emulation module 2 with the hydrodynamic force modulation simulation module 3 of surface wave-Bo effect respectively, receive the second yardstick ripple wave spectrum file and the local observation angle file of modulation, be used to generate two station, sea file correlation time;

Cutting apart wave spectrum emulation module 5 is connected with hydrodynamic force modulation simulation module 3 with two-dimentional wave spectrum emulation module 1, receive the two-dimentional wave spectrum file of the second yardstick wave of two-dimentional wave spectrum file, modulation of the first yardstick wave and the two-dimentional wave spectrum file of Prague wave, be used to generate the wave spectrum file of the first yardstick wave of cutting apart again and the wave spectrum file of the second yardstick wave cut apart again;

The two station electromagnetic scattering in sea emulation module 6 respectively with cut apart wave spectrum emulation module 5 and be connected with wind set-up modulating action emulation module 2, receive first yardstick cut apart again and the wave-number vector file of the wave spectrum file of the second yardstick wave, local observation angle file, polarization factor file and local Prague wave, generate the average scattering cross section NRCS file of each scattering resolution element;

Two station, sea synthetic aperture radar image-forming emulation module 7 is connected with wind set-up modulating action emulation module 2, two station, sea emulation module 4 correlation time and the two station electromagnetic scattering in sea emulation module 6, receive the first yardstick flow field file, two station, sea file correlation time and average scattering cross-section NRCS file, be used to generate two station, sea diameter radar image of emulation.

As shown in Figure 1, the integrated step of computer emulation method emulation of the present invention comprises:

Step 1: input emulation sea scene domain, scattering resolution element size, sea situation parameter (wind speed size and direction), two stations SAR observed parameter: overall incident angle, overall scattering angle, overall incident orientation angle, overall scattering position angle, radar carrier frequency, adopting at present, general in the world wave spectrum model comes the wave spectrum of emulation first yardstick, the second yardstick wave and the wave spectrum of Prague wave.

In emulation of the present invention, fully utilize DHH, Banner, the wave spectrum that Plant proposes is called the D spectrum for short, and form is as follows:

F(k，φ)＝F(k，0)D(k，φ) (1)

Wherein, (k φ) represents angle exhibition function to D, and wind direction is represented in φ=0.We adopt DHH experiment measuring gained the angle exhibition functional form here:

D(k，φ)＝sech ²(Bφ) (1a)

For the gravity wave number field, B changes as follows:

$B_g=\left\{\begin{array}{cc}1.22& k/k_p\&le;0.31\\ 2.61{(k/k_p)}^{0.65}& 0.31<k/k_p\&le;0.97\\ 2.28{(k/k_p)}^{-0.65}& 0.97<k/k_p\&le;2.56\\ {10}^{[-0.4+0.8393\exp (-0.56\ln (k/k_p))]}& 2.56<k/k_p\&le;30/k_p\end{array}\right.---\left(1b\right)$

Wherein, k _pExpression ocean wave spectrum density peaks place wave number.

Utilize the wave spectrum form near the gravity wave-number range the wave spectrum peak wave-number range that Banner provides as follows in the emulation of the present invention:

$F_g(k,0)=\left(\frac{\mathrm{\&alpha;}}{k^4}\right)\exp \{-{\left(\frac{k_p}{k}\right)}^2\}{G}^H---\left(1c\right)$

Wherein, α=0.001776 (U/c _p) ^0.5, k _p=g/c _p, $H=\exp [-\frac{{({(k/k_p)}^{0.5}-1)}^2}{2s^2}]---\left(1d\right)$

$G=\left\{\begin{array}{cc}1.7& U/c_p<1\\ 1.7+6.0\log (U/c_p)& 1\&le;U/c_p<5\\ 2.7{(U/c_p)}^{0.57}& U/c_p\&GreaterEqual;5\end{array}\right.---\left(1e\right)$

$s=\left\{\begin{array}{cc}0.08[1+4{(U/c_p)}^{-3}]& U/c_p<5\\ 0.16& U/c_p\&GreaterEqual;5\end{array}\right.---\left(1f\right)$

Wherein, g represents acceleration of gravity; U represents 10 meters highly wind speed at place; c _pExpression has maximum spectral density phase velocity of wave.

The unidirectional wave spectrum form that Plant obtains in the capillary wave wavelength coverage is as follows:

$F_c(k,0)=\frac{A{u}_{*}^2}{c^2{k}^4}---\left(1g\right)$

Wherein, u _*Expression friction wind speed; C is the phase velocity of the wave of wave number k; A gets 0.002.

The unidirectional wave spectrum that last all-wave is counted scope is defined as:

F(k，0)＝F _g(k，0)(1-α)+F _c(k，0)α (1h)

Angle exhibition function is as follows:

B＝B _g(k，0)(1-α)+0.84α (1i)

Wherein, $\mathrm{\&alpha;}=0.165+0.835\tanh [(k-5\sqrt{U})/25\sqrt{U}]---\left(1j\right)$

Because the present invention is an emulation two dimension real scene, therefore need obtain the two-dimentional wave spectrum under the Cartesian coordinates.For the hydrodynamic force and the inclination modulation simulation of carrying out the back, need obtain the two-dimentional wave spectrum of first yardstick and the second yardstick wave respectively according to emulation sea scene domain and scattering resolution element size.Here be used for hydrodynamic force and tilt to modulate first yardstick, the second yardstick wave division principle that calculate as follows:

Suppose that two-dimentional real scene direction is respectively x, y, their pairing scene width are respectively L _x, L _y, subscript l represents the first yardstick wave, and the scene resolution element size of x, y direction is respectively Δ x, Δ y, radar incident wave wave number is k _e, subscript i represents the second yardstick wave, so:

The two-dimentional wave spectrum x of the first yardstick wave, the sampling interval Δ K of y direction _x ^l, Δ K _y ^lBe respectively:

$\mathrm{\&Delta;}{K}_x^l=\frac{2\mathrm{\&pi;}}{L_x}---\left(2a\right)$

$\mathrm{\&Delta;}{K}_y^l=\frac{2\mathrm{\&pi;}}{L_y}---\left(2b\right)$

The two-dimentional wave spectrum x of the first yardstick wave, the maximum wave number k of y direction _Xmax ^l, k _Ymax ^lBe respectively:

$k_{x\max }^l=\frac{\mathrm{\&pi;}}{\mathrm{\&Delta;x}}---\left(3a\right)$

$k_{y\max }^l=\frac{\mathrm{\&pi;}}{\mathrm{\&Delta;y}}---\left(3b\right)$

The two-dimentional wave spectrum x of the second yardstick wave, the sampling interval Δ K of y direction _x ⁱ, Δ K _y ⁱBe respectively:

$\mathrm{\&Delta;}{K}_x^i=\frac{2\mathrm{\&pi;}}{\mathrm{\&Delta;x}}---\left(4a\right)$

$\mathrm{\&Delta;}{K}_y^i=\frac{2\mathrm{\&pi;}}{\mathrm{\&Delta;y}}---\left(4b\right)$

The two-dimentional wave spectrum x of the second yardstick wave, the maximum wave number k of y direction _Xmax ⁱ, k _Ymax ⁱBe respectively:

$k_{x\max }^i=2k_e---\left(5a\right)$

$k_{y\max }^i=2k_e---\left(5b\right)$

In addition, in order to calculate wave Scattering cross section, second order Prague, the present invention also needs to calculate the wave spectrum of Prague wave, the wave-number vector k of Prague, two station wave _BBe expressed as follows:

Wherein, θ _i, θ _sRepresent overall incident angle and overall scattering angle respectively;

Overall incident orientation angle and the overall scattering position angle of representing relative simulating scenes x direction respectively.

The wave spectrum of first yardstick of the two dimension on the sea, the second yardstick wave under the Cartesian coordinates and the wave spectrum of Prague wave be can calculate according to above-mentioned formula and division principle, thereby the two-dimentional wave spectrum of first yardstick, the second yardstick wave and the two-dimentional wave spectrum file of Prague wave generated.

Step 2: because the variation of the first yardstick wave gradient can make the wave-number vector of local incident angle, scattering angle, incident orientation angle, scattering position angle, polarization factor and Prague wave change.

In inclination modulating action emulation module, utilize the wave spectrum of the first yardstick wave of step 1 generation, just can calculate the first yardstick wave at the plane of incidence and the gradient distribution Z that is orthogonal to plane of incidence direction _x, Z _y:

$Z_x=\underset{0}{\overset{k_{x\max }^l}{\&Integral;}}i\&CenterDot;\cos (\mathrm{\&phi;}+{\mathrm{\&phi;}}_w)\&CenterDot;k\&CenterDot;a_l\left(\stackrel{\&RightArrow;}{k}\right)\mathrm{dk}---\left(7a\right)$

$Z_y=\underset{0}{\overset{k_{y\max }^l}{\&Integral;}}i\&CenterDot;\sin (\mathrm{\&phi;}+{\mathrm{\&phi;}}_w)\&CenterDot;k\&CenterDot;a_l\left(\stackrel{\&RightArrow;}{k}\right)\mathrm{dk}---\left(7b\right)$

$a_l\left(\stackrel{\&RightArrow;}{k}\right)=\sqrt{F_l\left(\stackrel{\&RightArrow;}{k}\right)}\&CenterDot;e^{\mathrm{i\&gamma;}\left(\stackrel{\&RightArrow;}{k}\right)}/\mathrm{dk}---\left(7c\right)$

Wherein, φ _wAngle between expression wind direction and the synthetic-aperture radar incident direction.

Can obtain the first yardstick wave flow field distribution from formula (7c), be expressed as follows:

$U_l\left(\stackrel{\&RightArrow;}{k}\right)=-\mathrm{\&omega;}{a}_l\left(\stackrel{\&RightArrow;}{k}\right)/\tanh \left(\mathrm{kd}\right)---\left(8\right)$

$\mathrm{\&omega;}=\sqrt{g\left|\stackrel{\&RightArrow;}{k}\right|+\frac{\mathrm{\&tau;}}{\mathrm{\&rho;}}{\left|\stackrel{\&RightArrow;}{k}\right|}^3}---\left(8a\right)$

Therefore, the corrugated that utilizes the first yardstick wave to generate can obtain because the tilting action of the first yardstick wave, in the plane of incidence, be orthogonal to bias angle theta, δ in the plane of incidence;

θ＝atg(-Z _x) (9a)

δ＝atg[Z _ycosθ] (9b)

Utilize mathematics how much, the local incident angle θ ' of each resolution element that obtains _i, local scatteringangle ' _s, local incident orientation angle With local scattering position angle

θ′ _i＝arccos[cos(θ+θ _i)cosδ] (10a)

(10b)

(10d)

So the local observation angle of each resolution element is brought into the wave-number vector k ' that formula (6) just can obtain the local Prague wave in each resolution element _B

In addition, in inclination modulating action emulation module, local polarization factor and overall polarization factor are also different because of tilting action.A horizontal polarization incident wave E ₀In local coordinate system, can regard a level and a vertical incidence ripple as, be expressed as:

E _H′＝(H′·H)E ₀ (11a)

E _V′＝(V′·H)E ₀ (11b)

Wherein, H, V are level, the vertical polarization directions of incident wave in the global coordinate system, and H ', V ' are level, the vertical polarization directions of incident wave in the local coordinate system.

According to scattering theory, represent with scattering matrix by the local scattered field that above-mentioned incident wave produces:

$\left[\begin{array}{c}{E}_{V^{\&prime;}}^s\\ E_{H^{\&prime;}}^s\end{array}\right]=\left[\begin{array}{cc}{S}_{V_S^{\&prime;}{V}^{\&prime;}}& S_{V_S^{\&prime;}{H}^{\&prime;}}\\ S_{H_S^{\&prime;}{V}^{\&prime;}}& S_{H_s^{\&prime;}{H}^{\&prime;}}\end{array}\right]\left[\begin{array}{c}{E}_{V^{\&prime;}}\\ E_{H^{\&prime;}}\end{array}\right]---\left(12\right)$

S wherein _{P ' q '}The scattered field of representation unit incident field also is a polarization factor; H _s, V _sLevel, vertical polarization directions for scattering wave in the global coordinate system; H ' _s, V ' _sLevel, vertical polarization directions for scattering wave in the local coordinate system.Be the scattered field in innings coordinate system of demanding perfection, need E _{V '} ^sAnd E _{H '} ^sTransform in the global coordinate system:

$\left[\begin{array}{c}{E}_{\mathrm{VH}}^s\\ E_{\mathrm{HH}}^s\end{array}\right]=\left[\begin{array}{cc}{V}_s\&CenterDot;V_s^{\&prime;}& V_s\&CenterDot;H_s^{\&prime;}\\ H_s\&CenterDot;V_s^{\&prime;}& H_s\&CenterDot;H_s^{\&prime;}\end{array}\right]\left[\begin{array}{c}{E}_{V^{\&prime;}}^s\\ E_{H^{\&prime;}}^s\end{array}\right]---\left(13\right)$

$E_{\mathrm{VH}}^s=[(V_s\&CenterDot;{V_s}^{\&prime;})S_{V^{\&prime;}{V}^{\&prime;}}(V^{\&prime;}\&CenterDot;H)+(V_s\&CenterDot;{H_s}^{\&prime;})S_{H^{\&prime;}{V}^{\&prime;}}(V^{\&prime;}\&CenterDot;H)$

(14a)

$+(V_s\&CenterDot;{V_s}^{\&prime;})S_{V^{\&prime;}{H}^{\&prime;}}(H^{\&prime;}\&CenterDot;H)+(V_s\&CenterDot;{H_s}^{\&prime;})S_{H^{\&prime;}{H}^{\&prime;}}(H^{\&prime;}\&CenterDot;H)]E_0$

$E_{\mathrm{HH}}^s=[(H_s\&CenterDot;{V_s}^{\&prime;})S_{V^{\&prime;}{V}^{\&prime;}}(V^{\&prime;}\&CenterDot;H)+(H_s\&CenterDot;{H_s}^{\&prime;})S_{H^{\&prime;}{V}^{\&prime;}}(V^{\&prime;}\&CenterDot;H)$

(14b)

$+(H_s\&CenterDot;{V_s}^{\&prime;})S_{V^{\&prime;}{H}^{\&prime;}}(H^{\&prime;}\&CenterDot;H)+(H_s\&CenterDot;{H_s}^{\&prime;})S_{H^{\&prime;}{H}^{\&prime;}}(H^{\&prime;}\&CenterDot;H)]E_0$

In like manner can get the scattered field that the vertical polarization incident wave produces:

$E_{\mathrm{VV}}^s=[(V_s\&CenterDot;{V_s}^{\&prime;})S_{V^{\&prime;}{V}^{\&prime;}}(V^{\&prime;}\&CenterDot;V)+(V_s\&CenterDot;{H_s}^{\&prime;})S_{H^{\&prime;}{V}^{\&prime;}}(V^{\&prime;}\&CenterDot;V)$

(14c)

$+(V_s\&CenterDot;{V_s}^{\&prime;})S_{V^{\&prime;}{H}^{\&prime;}}(H^{\&prime;}\&CenterDot;V)+(V_s\&CenterDot;{H_s}^{\&prime;})S_{H^{\&prime;}{H}^{\&prime;}}(H^{\&prime;}\&CenterDot;V)]E_0$

$E_{\mathrm{HV}}^s=[(H_s\&CenterDot;{V_s}^{\&prime;})S_{V^{\&prime;}{V}^{\&prime;}}(V^{\&prime;}\&CenterDot;V)+(H_s\&CenterDot;{H_s}^{\&prime;})S_{H^{\&prime;}{V}^{\&prime;}}(V^{\&prime;}\&CenterDot;V)$

(14d)

$+(H_s\&CenterDot;{V_s}^{\&prime;})S_{V^{\&prime;}{H}^{\&prime;}}(H^{\&prime;}\&CenterDot;V)+(H_s\&CenterDot;{H_s}^{\&prime;})S_{H^{\&prime;}{H}^{\&prime;}}(H^{\&prime;}\&CenterDot;V)]E_{\text{0}}$

By the ensemble average of above-mentioned various mould square, according to scattering theory and inclination modulating action emulation module, the polarization factor that can try to achieve under the global coordinate system is:

<|Γ _HH| ²>＝<(H _s·V _s′) ²|S _V′V′| ²(V′·H) ²>+<(H _s·H _s′) ²|S _H′V′| ²(V′·H) ²>

+<(H _s·V _s′) ²|S _V′H′| ²(H′·H) ²>+<(H _s·H _s′) ²|S _H′H′| ²(H?′·H) ²>+

2<(H _s·V _s′)(V′·H)(H _s·H _s′)(V′·H)Re{S _V′V′S ^* _H′V′}>+

2<(H _s·V _s′)(V′·H)(H _s·V _s′)(H′·H)Re{S _V′V′S ^* _V′H′}>+ (15a)

2<(H _s·V _s′)(V′·H)(H _s·H _s′)(H′·H)Re{S _V′V′S ^* _H′H′}>+

2<(H _s·H _s′)(V′·H)(H _s·V _s′)(H′·H)Re{S _H′V′S ^* _V′H′}>+

2<(H _s·H _s′)(V′·H)(H _s·H _s′)(H′·H)Re{S _H′V′S ^* _H′H′}>+

2<(H _s·V _s′)(H′·H)(H _s·H _s′)(H′·H)Re{S _V′H′S ^* _H′H′}>

<|Γ _VV| ²>＝<(V _s·V _s′) ²|S _V′V′| ²(V′·V) ²>+<(V _s·H _s′) ²|S _H′V′| ²(V′·V) ²>

+<(V _s·V _s′) ²|S _V′H′| ²(H′·V) ²>+<(V _s·H _s′) ²|S _H′H′| ²(H′·V) ²>+

2<(V _s·V _s′)(V′·V)(V _s·H _s′)(V′·V)Re{S _V′V′S ^* _H′V′}>+

2<(V _s·V _s′)(V′·V)(V _s·V _s′)(H′·V)Re{S _V′V′S ^* _V′H′}>+ (15b)

2<(V _s·V _s′)(V′·V)(V _s·H _s′)(H′·V)Re{S _V′V′S ^* _H′H′}>+

2<(V _s·H _s′)(V′·V)(V _s·V _s′)(H′·V)Re{S _H′V′S ^* _V′H′}>+

2<(V _s·H _s′)(V′·V)(V _s·H _s′)(H′·V)Re{S _H′V′S ^* _H′H′}>+

2<(V _s·V _s′)(H′·V)(V _s·H _s′)(H′·V)Re{S _V′H′S ^* _H′H′}>

Wherein, Γ _HH, Γ _VVRepresent HH, VV polarization factor under the global coordinate system respectively; S _{P ' q '}Represent the polarization factor under the local coordinate system, p '=H ', V ' is for receiving polarization mode; Q '=H ', V ' is the emission polarization mode; H, V are level, the vertical polarization directions of incident wave in the global coordinate system, and H ', V ' are level, the vertical polarization directions of incident wave in the local coordinate system; H _s, V _sLevel, vertical polarization directions for scattering wave in the global coordinate system; H ' _s, V ' _sLevel, vertical polarization directions for scattering wave in the local coordinate system; Wherein:

$H^{\&prime;}\&CenterDot;H=V^{\&prime;}\&CenterDot;V=\frac{\cos \mathrm{\&delta;}\sin (\mathrm{\&theta;}+{\mathrm{\&theta;}}_i)}{\sin {\mathrm{\&theta;}}_i^{\&prime;}}$

$V^{\&prime;}\&CenterDot;H=-V\&CenterDot;H^{\&prime;}=\frac{\sin \mathrm{\&delta;}}{\sin {\mathrm{\&theta;}}_i^{\&prime;}}$

$H_s\&CenterDot;H_s^{\&prime;}=V_s\&CenterDot;V_s^{\&prime;}$

Polarization factor under the local coordinate system is tried to achieve by following formula:

$R_v=\frac{(\cos {\mathrm{\&theta;}}_i^{\&prime;}-\sqrt{\mathrm{\&epsiv;}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_i^{\&prime;}})}{(\cos {\mathrm{\&theta;}}_i^{\&prime;}+\sqrt{\mathrm{\&epsiv;}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_i^{\&prime;}})}$ $R_h=\frac{(\mathrm{\&epsiv;}\cos {\mathrm{\&theta;}}_i^{\&prime;}-\sqrt{\mathrm{\&epsiv;}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_i^{\&prime;}})}{(\mathrm{\&epsiv;}\cos {\mathrm{\&theta;}}_i^{\&prime;}+\sqrt{\mathrm{\&epsiv;}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_i^{\&prime;}})}---\left(16f\right)$

According to the above-mentioned theory model, utilize the wave spectrum of the first yardstick wave of step 1 generation, can write the wave-number vector emulation module of the local observation angle in modulation back, polarization factor and local Prague wave, generate the wave-number vector file of the wave current field of the first yardstick wave of each scattering resolution element, local observation angle, polarization factor and local Prague wave.

Step 3: since the first yardstick wave and the second yardstick wave (perhaps Prague wave) between the fluid mechanics modulating action, the second yardstick wave of each scattering resolution element (perhaps Prague wave) wave spectrum is not consistent on the sea, the wave spectrum of the first yardstick wave is to the second yardstick wave (perhaps Prague wave) wave spectrum effect, described hydrodynamic force modulation simulation module is according to the weak interaction theory, obtain Bo-Bo modulation theory model, thereby try to achieve through the second yardstick wave after the wave spectrum modulation of the first yardstick wave or the wave spectrum F ' (k of Prague wave _s, x):

$F^{\&prime;}(k_s,x)=F(k_s,x)/(1+\frac{\mathrm{\&delta;Q}(K,k_s,t)}{Q_0})---\left(17\right)$

$\frac{\mathrm{\&delta;Q}(K,k_s,t)}{Q_0}=\&Integral;\&Integral;\left\{\frac{j[k_s\&CenterDot;u(K,{\mathrm{\&omega;}}_c)](K\&CenterDot;{\&dtri;}_{k_s}{Q}_0)}{-\mathrm{j\&omega;}-\mathrm{\&mu;}+j(c_g+U_0)\&CenterDot;K}\exp \right[j(K\&CenterDot;x-{\mathrm{\&omega;}}_{c}t)]+c.c.\}\mathrm{dKd}{\mathrm{\&omega;}}_c---\left(17a\right)$

Wherein, F ' (k _s, x) be the wave spectrum of the second yardstick wave (perhaps Prague wave) after the wave spectrum modulation of the first yardstick wave, F (k _s, x) be the wave spectrum of the second yardstick wave (perhaps Prague wave) before the modulation, $N_0(k,x,t)=F(k,x,t)\frac{\mathrm{\&rho;\&omega;}\left(k\right)}{k}=\frac{1}{Q_0}$ Be the action spectrum before modulating.Q ₀Be defined as N ₀Inverse, δ Q is modulation back Q ₀Variable quantity; C.c. represent conjugation, k _s, K represents the wave-number vector of the second yardstick wave (Prague wave) and the first yardstick wave respectively, and x, t be representation space coordinate and time variable respectively, and μ is the relaxation rate of seawater, and ρ is a density of sea water; ω represents that the wave wave number is the angular frequency of k, gets the angular frequency of the first yardstick wave here, $c_g\left(k_s\right)=\frac{\mathrm{d\&omega;}\left(k_s\right)}{\mathrm{dk}}{\hat{k}}_s$ The group velocity of expression small scale ripple; U (K, ω _c) expression the first yardstick wave the wavenumber domain Flow Field Distribution; ω _cExpression is for the Fourier domain frequency of t, U ₀The DC component of representing the Flow Field Distribution of the first yardstick wave;

Expression is asked gradient to wavenumber domain.

According to the above-mentioned theory model, utilize the wave spectrum of the first yardstick wave, the second yardstick wave and Prague wave that step 1 generates can write wave-wave modulation simulation module, generate the second yardstick wave after Bo-Bo modulation of each scattering resolution element and the wave spectrum file of Prague wave.

Step 4: because the sea is in the motion all the time, two station, sea emulation module correlation time is to need in radar imagery with characterizing same scatterer correlation time in difference correlativity constantly, according to sea electromagnetic theory and Radar Signal Processing, sea, two station τ correlation time _sBe expressed as follows:

${\mathrm{\&tau;}}_s=\frac{\sqrt{2}}{\sqrt{\&Integral;\{{(k_{\mathrm{iz}}+k_{\mathrm{sz}})}^2+{[(k_{\mathrm{sh}}^i-k_{\mathrm{ih}}^i)\&CenterDot;\hat{k}]}^2\}{F}^{\&prime;}(k,x)\mathrm{\&omega;dk}}}---\left(18\right)$

k _iz＝k _ecosθ′ _i (18c)

k _sz＝k _ecosθ′ _s (18d)

Wherein, k _Ih, k _ShBe respectively incident and scattering wave vector component at surface level; k _Iz, k _SzBe respectively incident wave number and scattering wave-number vector component in vertical direction;

The angle of representing the second yardstick wave and incident direction, scattering direction respectively; (k x) represents the wave spectrum of the second yardstick wave after the modulation of each scattering unit to F '.

Because in each scattering resolution element, the first yardstick wave can be thought of as definite, therefore calculating sea, two station during correlation time, the influence that only needs to consider the second yardstick wave gets final product.

According to the above-mentioned theory model, utilize the wave spectrum file of the second yardstick wave after step 2, the 3 local observation angle files that generate and Bo-Bo modulate can write two stations emulation modules correlation time, generate two stations file correlation time of each resolution element.

Step 5: first yardstick that in step 1, generates, the wave spectrum file of the second yardstick wave, be to divide according to scattering resolution element size and simulating scenes scope, purpose is that yardstick is regarded as the second yardstick wave less than the wave of resolution element size, because radar is what can't differentiate less than the scatterer of resolution element, therefore we can be regarding definite as greater than the wave of resolution element, think that they are to the second yardstick wave less than resolution element tilt modulation and Bo-Bo modulating action, in order to meet the requirement of radar resolution and physical significance.

And cut apart the wave spectrum scope that the wave spectrum emulation module need be repartitioned first yardstick and the second yardstick wave according to the electromagnetic scattering theory, meet the requirement of calculating two stations scattering cross-section with this.First yardstick and the boundary line wave number of cutting apart of two yardstick waves be k _l, it need satisfy following principle:

$k_e^2{(\cos {\mathrm{\&theta;}}_i+\cos {\mathrm{\&theta;}}_s)}^2\underset{k_1}{\overset{\&infin;}{\&Integral;}}F\left(k\right)\mathrm{kdk}\&le;10---\left(19\right)$

In the formula: k _eBe radar incident wave wave number, k is a wave wave number scalar.In order to cut apart wave spectrum again, need use interpolation algorithm, be similar to the method for quadratic spline interpolation because not meeting the wave spectrum Changing Pattern is not suitable for use in the wave spectrum interpolation method, the present invention utilizes the two-dimensional linear interpolation method just can reach certain precision in order to improve counting yield.

According to mentioned above principle, utilize the wave spectrum of the wave spectrum of the first yardstick waves that step 1,3 generates and the second yardstick wave after each resolution element internal modulation can write wave spectrum and repartition emulation module, regenerate first yardstick of each scattering resolution element, the wave spectrum file of the second yardstick wave.

Step 6: according to multiple dimensioned surface scattering model at random, the wave spectrum autocorrelation function can resolve into the autocorrelation function of the first yardstick wave and the second yardstick wave, therefore two station scattering cross-section σ _QpCan be divided into following two parts:

${\mathrm{\&sigma;}}_{\mathrm{qp}}={\mathrm{\&sigma;}}_{\mathrm{qp}}^l+{\mathrm{\&sigma;}}_{\mathrm{qp}}^{\mathrm{is}}---\left(20\right)$

Wherein, σ _Qp ^lRepresent the first yardstick wave Scattering cross section:

(21)

$\frac{-(S_{\mathrm{xy}}(k_{\mathrm{sx}}-k_x)(k_{\mathrm{sy}}-k_y)-S_{\mathrm{xx}}{(k_{\mathrm{sx}}-k_x)}^2-2S_{\mathrm{yy}}{(k_{\mathrm{sy}}-k_y)}^2)}{2\&CenterDot;{(k_{\mathrm{sx}}-k_x)}^2(S_{\mathrm{xx}}+S_{\mathrm{yy}}-S_{\mathrm{xy}})}$

Wherein, S _Xx, S _Yy, S _XyThe mean square gradient of representing x, y, xy direction respectively:

σ _Qp ^IsRepresent the second yardstick wave Scattering cross section:

${\mathrm{\&sigma;}}_{\mathrm{qp}}^{\mathrm{is}}=\frac{{\mathrm{<figure-callout\; id="2"\; label="k\; e"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">k</figure-callout>}}_e^{}}{4\mathrm{\&pi;}}{\left|{\mathrm{\&Gamma;}}_{\mathrm{qp}}\right|}^2---\left(22\right)$

| Γ _Qp| ²Polarization factor under the expression global coordinate system;

The autocorrelation function of representing the second yardstick wave surface; k _BRepresent local Prague wave-number vector.It should be noted that

Scope comprised the Bradley lattice wave, therefore the second yardstick wave Scattering cross section formula has comprised traditional single order Prague wave Scattering contribution.

In order to consider the influence of second order Prague scattering of wave to a resolution element scattering properties, according to improved aggregate surface model, wave Scattering cross section, a faceted Prague is:

${\mathrm{\&sigma;}}_{\mathrm{qp}}^s=T(Z_x,Z_y)F\left(k_B\right)---\left(23\right)$

Z wherein _xAnd Z _yBe respectively the slope of x, y, $T(Z_x,Z_y)=\sqrt{1+Z_x^2+{\mathrm{<figure-callout\; id="2"\; label="Z\; y"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_y^{}}{\left|{\mathrm{\&Gamma;}}_{\mathrm{qp}}\right|}^2{(k_{\mathrm{sz}}+k_z)}^2$

σ _Qp ^sTaylor expansion as follows:

${\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)\&ap;{\mathrm{\&sigma;}}_{\mathrm{qp}0}^s+\frac{\&PartialD;{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_x}{|}_{Z_x=0}{Z}_x+\frac{\&PartialD;{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_y}{|}_{Z_y=0}{Z}_y$

$+\frac{1}{2}\frac{{\&PartialD;}^2{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_x^2}{|}_{Z_x=0}{Z}_x^2+\frac{1}{2}\frac{{\&PartialD;}^2{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;{\mathrm{<figure-callout\; id="2"\; label="Z\; y"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_y^{}}{|}_{Z_x=0}{\mathrm{<figure-callout\; id="2"\; label="Z\; y"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_y^{}+\frac{\&PartialD;{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_x}{|}_{Z_x=0}\frac{\&PartialD;{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_y}{|}_{Z_y=0}{Z}_x{Z}_y---\left(24\right)$

$\&CenterDot;(1+\&Integral;H\left(k\right)F\left(k\right)\exp (\mathrm{ik}\&CenterDot;x)+c.c.\mathrm{dk})$

Wherein, H (k) expression hydrodynamic force modulating function.

The scattering of wave cross section, average Prague of a scattering resolution element is as follows so:

${\mathrm{\&sigma;}}_{\mathrm{qp}}^r=<{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)>={\mathrm{\&sigma;}}_{\mathrm{qp}0}^s+\underset{k_{\mathrm{res}}<\left|k\right|<k_s}{\&Integral;}\left\{\mathrm{Re}\right[i(\frac{\&PartialD;{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_x}{k}_x+\frac{\&PartialD;{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_y}{k}_y)H\left(k\right)]$

$+\frac{1}{2}\frac{{\&PartialD;}^2{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_x^2}{|}_{Z_x=0}{k}_x^2+\frac{1}{2}\frac{{\&PartialD;}^2{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;{\mathrm{<figure-callout\; id="2"\; label="Z\; y"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">Z</figure-callout>}}_y^{}}{|}_{Z_x=0}{\mathrm{<figure-callout\; id="2"\; label="k\; y"\; filenames="A2008101124250027H1.png"\; state="\{\{state\}\}">k</figure-callout>}}_y^{}+\frac{\&PartialD;{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_x}{|}_{Z_x=0}\frac{\&PartialD;{\mathrm{\&sigma;}}_{\mathrm{qp}}^s\left(x\right)}{\&PartialD;Z_y}{|}_{Z_y=0}{k}_x{k}_y\}F\left(k\right)\mathrm{dk}---\left(25\right)$

$={\mathrm{\&sigma;}}_{\mathrm{qp}0}^s+{\mathrm{\&sigma;}}_{\mathrm{qp}2}^s$

Because the scattering of Bradley lattice wave single order has been included in the second yardstick wave Scattering cross section, do not repeated to consider, if therefore take into account the first yardstick wave and the second yardstick wave Scattering again, the average scattering cross section of a scattering resolution element is the first interior yardstick of each scattering resolution element and the summation in the second yardstick wave Scattering cross section and wave scatter cross section, second order Prague so, and is as follows:

${\mathrm{\&sigma;}}_{\mathrm{qp}}={\mathrm{\&sigma;}}_{\mathrm{qp}}^l+{\mathrm{\&sigma;}}_{\mathrm{qp}}^{\mathrm{is}}+{\mathrm{\&sigma;}}_{\mathrm{qp}2}^s---\left(26\right)$

According to the above-mentioned theory model, utilize the two station electromagnetic scattering in the wave spectrum file edit sea emulation modules of polarization factors that step 2,3,5 generates, Prague wave spectrum after the modulation, the first yardstick wave of repartitioning, the second yardstick wave, generate average scattering cross section (NRCS) file of each scattering resolution element.

Step 7: because the sea the time become and the random motion characteristic, the emulation difficulty of two stations synthetic-aperture radar (biSAR) sea-surface target will be far longer than two synthetic-aperture radar (biSAR) emulation of standing of fixed target.According to speed pack theory, suppose that there is the point target P of a motion on the sea, the echo signal amplitude on sea is:

$A(t,x_0)=\sqrt{\mathrm{\&sigma;}}\exp \{-j[{\mathrm{\&phi;}}_0(t,x_0)+\mathrm{\&phi;}(t,x_0)+{(\mathrm{\&tau;}/{\mathrm{\&tau;}}_s)}^2\left]\right\}---\left(27\right)$

Wherein, σ is the average scattering cross section on sea; J is an imaginary unit; φ ₀(t, x ₀) be equally distributed random phase, represent that the scattering amplitude space of different resolution elements is uncorrelated; (τ/τ _s) ²The time correlation of expression scattering amplitude, τ _sBe sea, two station correlation time, τ is a time variable.

Under parallel flight of radar transmitter and the stravismus situation, according to the geometric relationship of two station SAR, phase of echo φ (t, x with receiver ₀) can be written as:

$\mathrm{\&phi;}(t,x_0)=\underset{i=t,r}{\mathrm{\&Sigma;}}\left\{k\right[{(R_{\mathrm{ic}}-\mathrm{\&Delta;}{R}_i(t,x_0))}^2+{(\mathrm{Vt}+R_{\mathrm{ic}}\sin {\mathrm{\&alpha;}}_i-x_0-\mathrm{\&Delta;}{x}_i(t,x_0))}^2$

$-2(R_{\mathrm{ic}}-\mathrm{\&Delta;}{R}_i(t,x_0))(\mathrm{Vt}+R_{\mathrm{ic}}\sin {\mathrm{\&alpha;}}_i-x_0-\mathrm{\&Delta;}{x}_i(t,x_0))\sin {\mathrm{\&alpha;}}_i{]}^{1/2}\}---\left(28\right)$

Wherein, R _IcDuring for carrier of radar platform beam central line definite object and the distance of this point target P; α _iAngle of squint for emission or receiving platform; Δ R _i(t, x ₀) and Δ x _i(t, x ₀) be respectively the displacement of targets that distance produces to the motion of sea long wave to, orientation; I=t, r represents transmitter and receiver respectively; V is the carrier of radar flying speed, supposes transmitter and receiver platform flying speed unanimity here; x ₀Position of orientation for target P.

Come the echo of the two station of emulation synthetic-aperture radar according to the average scattering cross section of following formula and each resolution element, write two stations synthetic-aperture radar echo simulation software in view of the above.

Then with synthetic-aperture radar echo file as input, utilize existing two stations synthetic aperture radar image-forming algorithm can generate the two station of final emulation synthetic-aperture radar sea level chart pictures.

The above; only be the embodiment among the present invention; but protection scope of the present invention is not limited thereto; anyly be familiar with the people of this technology in the disclosed technical scope of the present invention; can understand conversion or the replacement expected; all should be encompassed in of the present invention comprising within the scope, therefore, protection scope of the present invention should be as the criterion with the protection domain of claims.

Claims (9)

1, the computer emulation method of sea-surface imaging of bistatic synthetic aperture radar is characterized in that, comprises the steps:

Step 1: be used for hydrodynamic force and the two-dimentional wave spectrum emulation module of first yardstick, second yardstick wave two dimension wave spectrum and Prague wave that the modulation of tilting is calculated, receive emulation sea scene domain, scattering resolution element size, sea situation parameter and two stations synthetic-aperture radar observed parameter, generate the two-dimentional wave spectrum file of first yardstick, second yardstick and Prague wave that are used for Fluid Computation power and tilt to modulate under the Cartesian coordinates;

Step 2: wind set-up modulating action emulation module, receive the two-dimentional wave spectrum file of the first yardstick wave, be used to generate the wave-number vector file and the first yardstick flow field file of local observation angle file, polarization factor file, local Prague wave;

Step 3: the hydrodynamic force modulation simulation module of surface wave-Bo effect, receive the two-dimentional wave spectrum file of the first yardstick wave, the two-dimentional wave spectrum file of the second yardstick wave and the two-dimentional wave spectrum file of Prague wave, be used to generate the wave spectrum file of Prague wave of the wave spectrum file of the second yardstick wave of modulation and modulation;

Step 4: two station, sea emulation module correlation time, the wave spectrum file and the local observation angle file of the second yardstick wave of reception modulation are used to generate two station, sea file correlation time;

Step 5: cut apart the wave spectrum emulation module, receive the two-dimentional wave spectrum file of the second yardstick wave of two-dimentional wave spectrum file, the modulation of the first yardstick wave, be used to generate the wave spectrum file of the first yardstick wave of cutting apart again and the wave spectrum file of the second yardstick wave cut apart again;

Step 6: the two station electromagnetic scattering in sea emulation module, receive the wave-number vector file of wave spectrum file, the wave spectrum file of the second yardstick wave, local observation angle file, polarization factor file and local Prague wave of the first yardstick wave of cutting apart again, generate the average scattering cross section NRCS file of each scattering resolution element;

Step 7: two station, sea synthetic aperture radar image-forming emulation module, receive average scattering cross section NRCS file, two station, sea file correlation time and the first yardstick flow field file, be used to generate two station, sea diameter radar image of emulation.

2, computer emulation method as claimed in claim 1 is characterized in that, is used for hydrodynamic force in the described two-dimentional wave spectrum emulation module and tilts to modulate first yardstick, the second yardstick wave division principle that calculate as follows:

The division of the first yardstick wave comprises as follows:

The two-dimentional wave spectrum x of the first yardstick wave, the sampling interval Δ K of y direction _x ^l, Δ K _y ^lBe respectively:

${\mathrm{\&Delta;K}}_x^l=\frac{2\mathrm{\&pi;}}{L_x},$ ${\mathrm{\&Delta;K}}_y^l=\frac{2\mathrm{\&pi;}}{L_y},$

The two-dimentional wave spectrum x of the first yardstick wave, the maximum wave number k of y direction _Xmax ^l, k _Ymax ^lBe respectively:

$k_{x\max }^l=\frac{\mathrm{\&pi;}}{\mathrm{\&Delta;x}},$ $k_{y\max }^l=\frac{\mathrm{\&pi;}}{\mathrm{\&Delta;y}},$

The division of the second yardstick wave comprises as follows:

The two-dimentional wave spectrum x of the second yardstick wave, the sampling interval Δ K of y direction _x ⁱ, Δ K _y ⁱBe respectively:

${\mathrm{\&Delta;K}}_x^i=\frac{2\mathrm{\&pi;}}{\mathrm{\&Delta;x}},$ ${\mathrm{\&Delta;K}}_y^i=\frac{2\mathrm{\&pi;}}{\mathrm{\&Delta;y}},$

The two-dimentional wave spectrum x of the second yardstick wave, the maximum wave number k of y direction _Xmax ⁱ, k _Ymax ⁱBe respectively:

$k_{x\max }^i=2k_e,$ $k_{y\max }^i=2k_e,$

Wherein, two-dimentional real scene direction is respectively x, y, and their pairing scene width are respectively L _x, L _y, subscript l represents the first yardstick wave; The scene resolution element size of x, y direction is respectively Δ x, Δ y, and radar incident wave wave number is k _e, subscript i represents the second yardstick wave.

3, computer emulation method as claimed in claim 1, it is characterized in that, described inclination modulating action emulation module, it is the corrugated that utilizes the first yardstick wave to generate, by in the plane of incidence, be orthogonal to the bias angle theta, the δ that produce in the plane of incidence, utilize mathematics how much, obtain the local incident angle θ ' of each resolution element _i, local scatteringangle ' _s, local incident orientation angle

, local scattering position angle

According to angle θ ' _i, θ ' _s,

Conversion set up the inclination modulation simulation, utilize angle θ ' _i, θ ' _s,

Obtain the wave-number vector k ' of local Prague wave of each resolution element _BDescribed angle θ ' _i, θ ' _s,

Be expressed as:

θ′ _i＝arc?cos[cos(θ+θ _i)cosδ]

In the formula: θ _i, θ _sRepresent overall incident angle and overall scattering angle respectively;

Overall incident orientation angle and the overall scattering position angle of representing relative simulating scenes x direction respectively.

4, computer emulation method as claimed in claim 1 is characterized in that, described inclination modulating action emulation module is expressed as follows according to the polarization factor under scattering theory and the inclination modulating action acquisition global coordinate system:

<|Γ _HH| ²>＝<(H _s·V _s′) ²|S _V′V′| ²(V′·H) ²>+<(H _s·H _s′) ²|S _H′V′| ²(V′·H) ²>

+<(H _s·V _s′) ²|S _V′H′| ²(H′·H) ²>+<(H _s·H _s′) ²|S _H′H′| ²(H′·H) ²>+

2<(H _s·V _s′)(V′·H)(H _s·H _s′)(V′·H)Re{S _V′V′S ^* _H′V′}>+

2<(H _s·V _s′)(V′·H)(H _s·V _s′)(H′·H)Re{S _V′V′S ^* _V′H′}>+

2<(H _s·V _s′)(V′·H)(H _s·H _s′)(H′·H)Re{S _V′V′S ^* _H′H′}>+

2<(H _s·H _s′)(V′·H)(H _s·V _s′)(H′·H)Re{S _H′V′S ^* _V′H′}>+

2<(H _s·H _s′)(V′·H)(H _s·H _s′)(H′·H)Re{S _H′V′S ^* _H′H′}>+

2<(H _s·V _s′)(H′·H)(H _s·H _s′)(H′·H)Re{S _V′H′S ^* _H′H′}>

<|Γ _VV| ²>＝<(V _s·V _s′) ²|S _V′V′| ²(V′·V) ²>+<(V _s·H _s′) ²|S _H′V′| ²(V′·V) ²>

+<(V _s·V _s′) ²|S _V′H′| ²(H′·V) ²>+<(V _s·H _s′) ²|S _H′H′| ²(H′·V) ²>+

2<(V _s·V _s′)(V′·V)(V _s·H _s′)(V′·V)Re{S _V′V′S ^* _H′V′}>+

2<(V _s·V _s′)(V′·V)(V _s·V _s′)(H′·V)Re{S _V′V′S ^* _V′H′}>+

2<(V _s·V _s′)(V′·V)(V _s·H _s′)(H′·V)Re{S _V′V′S ^* _H′H′}>+

2<(V _s·H _s′)(V′·V)(V _s·V _s′)(H′·V)Re{S _H′V′S ^* _.V′H′}>+

2<(V _s·H _s′)(V′·V)(V _s·H _s′)(H′·V)Re{S _H′V′S ^* _H′H′}>+

2<(V _s·V _s′)(H′·V)(V _s·H _s′)(H′·V)Re{S _V′H′S ^* _H′H′}>

Wherein, Γ _HH, Γ _VVRepresent HH, VV polarization factor under the global coordinate system respectively; S _{P ' q '}Represent the polarization factor under the local coordinate system, p '=H ', V ' is for receiving polarization mode; Q '=H ', V ' is the emission polarization mode; H, V are level, the vertical polarization directions of incident wave in the global coordinate system, and H ', V ' are level, the vertical polarization directions of incident wave in the local coordinate system; H _s, V _sLevel, vertical polarization directions for scattering wave in the global coordinate system; H ' _s, V ' _sLevel, vertical polarization directions for scattering wave in the local coordinate system;

$H^{\&prime;}\&CenterDot;H=V^{\&prime;}\&CenterDot;V=\frac{\cos \mathrm{\&delta;}\sin (\mathrm{\&theta;}+{\mathrm{\&theta;}}_i)}{\sin {\mathrm{\&theta;}}_i^{\&prime;}}$ $V^{\&prime;}\&CenterDot;H=-V\&CenterDot;H^{\&prime;}=\frac{\sin \mathrm{\&delta;}}{\sin {\mathrm{\&theta;}}_i^{\&prime;}}$

$H_s\&CenterDot;H_s^{\&prime;}=V_s\&CenterDot;V_s^{\&prime;}$

5, computer emulation method as claimed in claim 1, it is characterized in that, described hydrodynamic force modulation simulation module is according to the weak interaction theory, obtain Bo-Bo modulation theory model, thereby try to achieve through the second yardstick wave after the wave spectrum modulation of the first yardstick wave or the wave spectrum F ' (k of Prague wave _s, x):

$F^{\&prime;}(k_s,x)=F(k_s,x)/(1+\frac{\mathrm{\&delta;Q}(K,k_s,t)}{Q_0})$

$\frac{\mathrm{\&delta;Q}(K,k_s,t)}{Q_0}=\&Integral;\&Integral;\left\{\frac{j[k_s\&CenterDot;u(K,{\mathrm{\&omega;}}_c)](K\&CenterDot;{\&dtri;}_{k_s}{Q}_0)}{-\mathrm{j\&omega;}-\mathrm{\&mu;}+j(c_g+U_0)\&CenterDot;K}\exp \right[j(K\&CenterDot;x-{\mathrm{\&omega;}}_{c}t)]+c.c.\}d{\mathrm{Kd\&omega;}}_c$

Wherein, F (k _s, x) be the second yardstick wave before the modulation or the wave spectrum of Prague wave, $N_0(k,x,t)=F(k,x,t)\frac{\mathrm{\&rho;\&omega;}\left(k\right)}{k}=\frac{1}{Q_0}$ Be the action spectrum before modulating; Q ₀Be defined as N ₀Inverse, δ Q is modulation back Q ₀Variable quantity; C.c. represent conjugation, k _sRepresent the wave-number vector of the second yardstick wave or Prague wave, K represents the wave-number vector of the first yardstick wave, and x, t be representation space coordinate and time variable respectively, and μ is the relaxation rate of seawater, and ρ is a density of sea water; ω represents that the wave wave number is the angular frequency of k, gets the angular frequency of the first yardstick wave here, $c_g\left(k_s\right)=\frac{\mathrm{d\&omega;}\left(k_s\right)}{\mathrm{dk}}{\hat{k}}_s$ The group velocity of representing the second yardstick wave; U (K, ω _c) expression the first yardstick wave the wavenumber domain Flow Field Distribution; ω _cExpression is for the Fourier domain frequency of t, U ₀The DC component of representing the Flow Field Distribution of the first yardstick wave;

Expression is asked gradient to wavenumber domain.

6, computer emulation method as claimed in claim 1, it is characterized in that, two station, described sea emulation module correlation time is with characterizing on the sea same scatterer correlation time in difference correlativity constantly in radar imagery, according to sea electromagnetic theory and Radar Signal Processing, sea, two station τ correlation time _sBe expressed as follows:

${\mathrm{\&tau;}}_s=\frac{\sqrt{2}}{\sqrt{\&Integral;\{{(k_{\mathrm{iz}}+k_{\mathrm{sz}})}^2+{[(k_{\mathrm{sh}}^i+k_{\mathrm{ih}}^i)\&CenterDot;\hat{k}]}^2\}{F}^{\&prime;}(k,x)\mathrm{\&omega;dk}}}$

Wherein:

k _iz＝k _e?cosθ′ _i，k _sz＝k _e?cosθ′ _s，

k _Ih, k _ShBe respectively incident and scattering wave-number vector component at surface level; k _Iz, k _SzBe respectively incident wave number and scattering wave-number vector component in vertical direction;

The angle of representing the second yardstick wave and incident direction, scattering direction respectively; (k x) represents the wave spectrum of the second yardstick wave after the modulation of each scattering unit to F '.

7, computer emulation method as claimed in claim 1, it is characterized in that, the described wave spectrum emulation module of cutting apart, repartition the wave spectrum scope of first yardstick and the second yardstick wave according to the electromagnetic scattering theory, meet the requirement of calculating two stations scattering cross-sections with this, described first yardstick and the second yardstick wave cut apart boundary line wave number k _lNeed satisfy following principle:

$k_e^2{(\cos {\mathrm{\&theta;}}_i+\cos {\mathrm{\&theta;}}_s)}^2\underset{k_1}{\overset{\&infin;}{\&Integral;}}F\left(k\right)\mathrm{kdk}\&le;10$

Utilize interpolating function by mentioned above principle, the wave spectrum file of first yardstick of just being cut apart again, the second yardstick wave is in the formula: k _eBe radar incident wave wave number, k is a wave wave number scalar.

8, computer emulation method as claimed in claim 1, it is characterized in that, the generation of described average scattering cross section NRCS file, according to multiple dimensioned at random surface scattering model based on second order Prague wave scatter, try to achieve first yardstick and the second yardstick wave Scattering cross section and wave scatter cross section, second order Prague in each scattering resolution element, last addition just generates the average scattering cross-section file of each resolution element.

9, computer emulation method as claimed in claim 1, it is characterized in that, two stations synthetic-aperture radar echo simulation in the synthetic aperture radar image-forming emulation module of two station, described sea is: different with permanent echo according to the sea radar return, suppose that there is a point target P who moves on the sea that is in motion, echo signal amplitude A (t, the x on sea ₀) be:

$A(t,x_0)=\sqrt{\mathrm{\&sigma;}}\exp \{-j[{\mathrm{\&phi;}}_0(t,x_0)+\mathrm{\&phi;}(t,x_0)+{(\mathrm{\&tau;}/{\mathrm{\&tau;}}_s)}^2\left]\right\}$

In the formula: σ is the average scattering cross section on sea; φ ₀(t, x ₀) be equally distributed random phase, represent that the scattering amplitude space of different resolution elements is uncorrelated; J is an imaginary unit; φ (t, x ₀) be phase of echo; (τ/τ _s) ²The time correlation of expression scattering amplitude, τ _sBe sea echo correlation time, τ is a time variable;

Under parallel flight of radar transmitter and stravismus situation with receiver, phase of echo φ (t, x ₀) be written as:

$\mathrm{\&phi;}(t,x_0)=\underset{i=i,r}{\mathrm{\&Sigma;}}\left\{k_e\right[{(R_{\mathrm{ic}}-{\mathrm{\&Delta;R}}_i(t,x_0))}^2+{(\mathrm{Vt}+R_{\mathrm{ic}}\sin {\mathrm{\&alpha;}}_i-x_0-{\mathrm{\&Delta;x}}_i(t,x_0))}^2$

$-2(R_{\mathrm{ic}}-{\mathrm{\&Delta;R}}_i(t,x_0))(\mathrm{Vt}+R_{\mathrm{ic}}{\sin \mathrm{\&alpha;}}_i-x_0-{\mathrm{\&Delta;x}}_i(t,x_0))\sin {\mathrm{\&alpha;}}_i{]}^{1/2}\}$

Wherein, R _IcDuring for carrier of radar platform beam central line definite object and the distance of this point target P; α _iAngle of squint for emission or receiving platform; Δ R _i(t, x ₀) and Δ x _i(t, x ₀) be respectively the displacement of targets that distance produces to the motion of sea long wave to, orientation; I=t, r represents transmitter and receiver respectively; V is the carrier of radar flying speed, supposes transmitter and receiver platform flying speed unanimity here; x ₀Position of orientation for target P;

According to phase of echo φ (t, x ₀) the average scattering cross section of formula and each space cell comes the echo of the two station of emulation synthetic-aperture radar, makes up the diameter radar image emulation of two station, sea in view of the above.

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