CN102879768A - Satellite-borne synthetic aperture radar (SAR) high-fidelity echo simulation method based on steady-state radar cross section (RCS) - Google Patents

Abstract

The invention discloses a satellite-borne synthetic aperture radar (SAR) high-fidelity echo simulation method based on steady-state radar cross section (RCS). The method comprises the following steps of: 1, acquiring satellite-borne SAR echo simulation parameters according to simulation parameters; 2, determining the coordinates of each scatterer T(i,j); 3, determining the coordinates of a satellite at an azimuth moment m; 4, acquiring an azimuth angle; 5, reading different back scattering characteristics of a scene; 6, acquiring antenna pattern weighting characteristic Wm(i,j) of each scatterer T(i,j) in the scene at the azimuth moment m and slope distance Sm_T(i,j) between each scatterer T(i,j) and an effective load; 7, constructing a linear frequency modulation signal, modulating the back scattering characteristics and the antenna pattern weighting characteristic, and overlapping a Doppler effect according to the change of the slope distance; 8, writing a frame of processed echo signal at the azimuth moment m into a data file; and 9, judging whether all pulses are simulated. The method is high in practicability and can meet requirements of a satellite-borne SAR high-resolution imaging mode on a high-accuracy simulation signal.

Description

A kind of satellite-borne SAR high-fidelity echo simulation method based on stable state RCS

Technical field

The invention belongs to the signal process field, particularly a kind of satellite-borne SAR based on stable state RCS (Radar Cross-Section) (Synthetic Aperture Radar) high-fidelity echo simulation method.

Background technology

Satellite-borne synthetic aperture radar (SAR) is a kind of high-definition remote sensing explorer satellite radar of the earth being observed based on spatial altitude.Since the SAR satellite can overcome cloud and mist sleet and dark night condition restriction carry out on a surface target imaging, can realize round-the-clock, round-the-clock, high resolving power, wide cut earth observation, therefore have broad application prospects at numerous areas such as military affairs, ocean, agricultural and forestry.But the Spaceborne SAR System image-forming principle is very complicated, and data processing and imaging processing equipment are huge, expensive, therefore all be unable to do without echo simulation in SAR scheme Design and imaging processing algorithm research process.

The satellite-borne SAR useful load is observed on a surface target by initiatively launching linear FM signal, for improving azimuth resolution, need to observe target in different positions.Because when target is shone by the different angles incoming wave, the backscattering characteristic that presents exists difference, especially for sharp-featured buildings and military target, there is obvious difference in its backward scattering properties, and the backscattering characteristic of target is the function of space angle in brief.Therefore along with the SAR antenna with the relative position relation between the target variation has occured, also be different at the backscattering characteristic of different position detection targets.Tradition SAR echo simulation method thinks that the target backscattering characteristic has unchangeability, has ignored the space angular spectrum variation characteristic of target, can't reflect really that target is at the back scattering variation characteristic of whole synthetic aperture in the time.Traditional SAR echo simulation method can't reflect echoed signal from the whole flow process of emission, propagation, reception and processing in addition, and the fidelity of SAR emulating image is relatively relatively poor.Along with the development of satellite-borne SAR technology and the raising of resolution, traditional SAR echo simulation method has been difficult to satisfy the SAR scheme Design, and particularly (such as beam bunching mode and slip beam bunching mode) this demand seems particularly urgent under the high-resolution imaging pattern.

Summary of the invention

The objective of the invention is in order to address the above problem, can't truly reflect SAR principle of work and process for existing satellite-borne SAR echo simulation, a kind of satellite-borne SAR high-fidelity echo simulation method based on stable state RCS has been proposed, utilize the present invention can accurately describe and reconstruct SAR echo simulation signal, the space angular spectrum variation characteristic that has reflected target in the echo simulation process reflects that truly target is at the back scattering variation characteristic of whole synthetic aperture in the time.

A kind of satellite-borne SAR high-fidelity echo simulation method based on stable state RCS comprises following several step:

Step 1: obtain satellite-borne SAR echo simulation parameter by the simulation parameter table, comprising: satellite orbit semi-major axis a, orbit inclination i, orbital eccentricity e, simulation centre is τ constantly, and simulation centre is antenna boresight focal position longitude Λ at the earth's surface;on the face of the globe constantly ₀, latitude Φ ₀, antenna beam downwards angle of visibility β, antenna bearingt is to length L _a, antenna distance is to length L _r, wavelength X, frequency modulation rate b, earth semi-minor axis E _a, earth semi-major axis E _b, earth mean angular motion speed n, earth gravitational field gravitational constant μ;

Step 2: scene set, under the rotation geocentric coordinate system, scene is mapped to ground, determine each scatterer T _{I, j}Coordinate;

Specifically comprise following step:

(a) scene set dot matrix T _a* T _r, take simulation centre moment antenna boresight focus at the earth's surface;on the face of the globe as the scene center point, wherein, T _aFor the scene orientation to dot matrix number, T _rFor scene distance to the dot matrix number, and the set scene orientation is to lattice spacing D _a, distance is to lattice spacing D _r, the scene coordinate system is take scene center as initial point, and X-axis is along North and South direction, refers to north for just, and Y-axis is along east-west direction, refers to eastern for just;

(b) obtain each scatterer T _{I, j}Coordinate (x_t under the scene coordinate system _{I, j}, y_t _{I, j});

(c) obtain each scatterer T _{I, j}Longitude, latitude (Λ _{I, j}, Φ _{I, j});

(d) obtain each scatterer T _{I, j}At the coordinate (X_t that rotates under the geocentric coordinate system _{I, j}, Y_t _{I, j}, Z_t _{I, j});

Step 3: the coordinate (X_s that determines satellite a certain moment m in the orientation according to star ground space geometry relation and Keplerian orbit equation _m, Y_s _m, Z_s _m);

Specifically comprise following step:

(a) determine the average nearly heart angle M of a certain moment m in orientation according to the Keplerian orbit equation, eccentric angle E, very near heart angle θ, satellite radius vector r;

(b) determine the coordinate (x_s of satellite under orbital coordinate system according to satellite radius vector r and very near heart angle θ _m, y_s _m, z_s _m);

(c) obtain satellite at the coordinate (X_s that rotates under the geocentric coordinate system _m, Y_s _m, Z_s _m);

Step 4: determine that orientation moment m satellite with the relative position relation of scene center, obtains orientation angles Specifically comprise following step:

(a) obtain scene center at the coordinate (X_t that rotates under the geocentric coordinate system ₀, Y_t ₀, Z_t ₀);

(b) obtain moment m satellite with the relative position vector (X_s_t of scene center _m, Y_s_t _m, Z_s_t _m);

(c) obtain moment m satellite with the orientation angles of scene center

Step 5: according to orientation angles Difference read the different backscattering coefficient matrix of scene

Specifically comprise following step:

(a) according to the orientation angles of moment m satellite with scene center

Table look-up and obtain the back scattering matrix of scene

(b) at the back scattering matrix

In obtain each scatterer T in the scene _{I, j}Backscattering coefficient

Step 6: obtain each scatterer T in this moment scene _{I, j}The antenna radiation pattern weighting characteristic and with the oblique distance of useful load;

Specifically comprise following step:

(a) obtain each scatterer T in the scene _{I, j}Oblique distance S with useful load _m_ T _{I, j}

(b) obtain each scatterer T in the scene _{I, j}With the orientation of useful load to off-axis angle

And distance is to off-axis angle

(c) obtain each scatterer T in the scene _{I, j}The orientation to antenna radiation pattern weighting Wa _m(i, j) and distance are to antenna radiation pattern weighting Wr _m(i, j);

(d) obtain each scatterer T in the scene _{I, j}Antenna radiation pattern weighting W _m(i, j);

Step 7: construct linear FM signal, and modulate with backscattering characteristic and antenna radiation pattern weighting characteristic, and change the stack Doppler effect according to oblique distance;

Specifically comprise following step:

(a) structure linear FM signal

(b) change the stack Doppler effect according to oblique distance

(c) obtain each scatterer echoed signal Signal of scene _m(i, j);

Step 8: will be through the orientation of above processing constantly in the frame echoed signal data writing file of m;

Step 9: judge whether to finish the emulation of all pulses, begin the repetition subsequent step as then not returning for the 3rd step, otherwise finish emulation.

The invention has the advantages that:

(1) authenticity.Than traditional SAR echo simulation method, method proposed by the invention has considered that the backscattering characteristic of target is the function of space angle, along with the change of target with the dimensional orientation angle between the SAR useful load, use different backscattering characteristics, consider the Space Angle spectral property of target, therefore true reflection target more can truly reflect SAR real work principle and process at the back scattering variation characteristic of whole synthetic aperture in the time.

(2) hi-fi.The obtained simulation result of method that the present invention proposes has very high precision, the sharp-featured buildings of emulation and military target that can high-fidelity, the reproduction SAR image of high fidelity.

(3) practicality.The present invention has very strong practicality, especially is embodied in to utilize this method can satisfy satellite-borne SAR high-resolution imaging pattern to the simulate signal high-precision requirement.

Description of drawings

Fig. 1 is a kind of satellite-borne SAR high-fidelity echo simulation method process flow diagram based on stable state RCS.

Fig. 2 is the method flow diagram of step 2 of the present invention.

Fig. 3 is the method flow diagram of step 3 of the present invention.

Fig. 4 is the method flow diagram of step 4 of the present invention.

Fig. 5 is the method flow diagram of step 5 of the present invention.

Fig. 6 is the method flow diagram of step 6 of the present invention.

Fig. 7 is the method flow diagram of step 7 of the present invention.

Fig. 8 is different visual angles traditional simulation method imaging results figure of the present invention

Fig. 9 utilizes as a result figure of simulation imaging that the present invention obtains.

Embodiment

The present invention is described in further detail below in conjunction with drawings and Examples.

This method is a kind of satellite-borne SAR high precision echo simulation method based on stable state RCS, and method flow specifically may further comprise the steps as shown in Figure 1:

Step 1: obtain satellite-borne SAR echo simulation parameter by the simulation parameter table, comprising: satellite orbit semi-major axis a, orbit inclination i, orbital eccentricity e, simulation centre is τ constantly, and simulation centre is antenna boresight focal position longitude Λ at the earth's surface;on the face of the globe constantly ₀, latitude Φ ₀, antenna beam downwards angle of visibility β, antenna bearingt is to length L _a, the astronomical phenomena distance is to length L _r, wavelength X, frequency modulation rate b, earth semi-minor axis E _a, earth semi-major axis E _b, earth mean angular motion speed n, earth gravitational field gravitational constant μ;

Step 2: scene set, under the rotation geocentric coordinate system, scene is mapped on the ground, determine each scatterer T _IjCoordinate;

Flow process arranges the scene of corresponding size as shown in Figure 2 according to user's request, the union space coordinate conversion is obtained each scatterer T in the scene _IjCoordinate rotating under the geocentric coordinate system specifically comprises following step:

(a) scene set dot matrix T _a* T _r, take simulation centre moment antenna boresight focus at the earth's surface;on the face of the globe as the scene center point, wherein, T _aFor the scene orientation to dot matrix number, T _rFor scene distance to the dot matrix number, and the set scene orientation is to lattice spacing D _a, distance is to lattice spacing D _r, the scene coordinate system is take scene center as initial point, and X-axis is along North and South direction, refers to north for just, and Y-axis is along east-west direction, refers to eastern for just.

(b) obtain each scatterer T _{I, j}Coordinate (x_t under the scene coordinate system _{I, j}, y_t _{I, j}); Method is as shown in Equation (1):

x_t _i,j＝D _a·(i-T _a/2)

（1）

y_t _i，j＝D _r·(j-T _r/2)

Wherein: i represents that the scene dot matrix is capable, and j represents the scene point array;

i＝0,1,2…,T _a-1，j＝0,1,2…,T _r-1。

(c) obtain each scatterer T _{I, j}Longitude, latitude (Λ _{I, j}, Φ _{I, j}); Method is as shown in Equation (2):

${\mathrm{\Λ}}_{i,j}={\mathrm{\Λ}}_0+y\_t_{i,j}\·\frac{\sqrt{E_b^2{\cos }^2{\mathrm{\Φ}}_0+E_a^2{\sin }^2{\mathrm{\Φ}}_0}}{E_a{E}_b\cos {\mathrm{\Φ}}_0}$ （2）

${\mathrm{\Φ}}_{i,j}={\mathrm{\Φ}}_0+x\_t_{i,j}\·\frac{\sqrt{E_b^2{\cos }^2{\mathrm{\Φ}}_0+E_a^2{\sin }^2{\mathrm{\Φ}}_0}}{E_a{E}_b}$

(d) obtain each scatterer T _{I, j}At the coordinate (X_t that rotates under the geocentric coordinate system _{I, j}, Y_t _{I, j}, Z_t _{I, j}); Method is as shown in Equation (3):

$X\_t_{i,j}=\frac{E_a{E}_b\cos {\mathrm{\Φ}}_{i,j}\cos {\mathrm{\Λ}}_{i,j}}{\sqrt{E_b^2{\cos }^2{\mathrm{\Φ}}_{i,j}+E_a^2{\sin }^2{\mathrm{\Φ}}_{i,j}}}$

$Y\_t_{i,j}=\frac{E_a{E}_b\cos {\mathrm{\Φ}}_{i,j}\sin {\mathrm{\Λ}}_{i,j}}{\sqrt{E_b^2{\cos }^2{\mathrm{\Φ}}_{i,j}+E_a^2{\sin }^2{\mathrm{\Φ}}_{i,j}}}---\left(3\right)$

$Z\_t_{i,j}=\frac{E_a{E}_b\cos {\mathrm{\Φ}}_{i,j}}{\sqrt{E_b^2{\cos }^2{\mathrm{\Φ}}_{i,j}+E_a^2{\sin }^2{\mathrm{\Φ}}_{i,j}}}$

Step 3: determine that according to star ground space geometry relation and Keplerian orbit equation satellite is at the coordinate (X_s of orientation moment m _m, Y_s _m, Z_s _m);

Flow process is utilized satellite-borne SAR space geometry relation and Keplerian orbit equation as shown in Figure 3, obtains the coordinate that rotates satellite definite moment in the orientation under the geocentric coordinate system, specifically comprises following step:

(a) obtain the constantly average near heart angle M of m of orientation, eccentric angle E, very near heart angle θ, satellite radius vector r; Method is as shown in Equation (4):

M＝n·(m-τ)

$E=M+e\·(1-\frac{1}{8}{e}^2+\frac{1}{192}{e}^4)\·\sin M+e^2\·(\frac{1}{2}-\frac{1}{6}{e}^2)\·\sin 2M$

$+e^3\·(\frac{3}{8}-\frac{27}{128}{e}^2)\·\sin 3M+\frac{1}{3}{e}^4\·\sin 4M+\frac{125}{384}{e}^5\·\sin 5M---\left(4\right)$

$\mathrm{\θ}=2\·a\tan (\sqrt{\frac{1+e}{1-e}}\·\tan \frac{E}{2})$

$r=\frac{a\·(1-e^2)}{1+e\·\cos \mathrm{\θ}}$

(b) obtain the constantly coordinate (x_s of m satellite under orbital coordinate system of orientation _m, y_s _m, z_s _m); Method is as shown in Equation (5):

x_s _m＝r·cosθ

y_s _m＝r·sinθ （5）

z_s _m＝0

(c) obtain the constantly coordinate (X_s of m satellite under the rotation geocentric coordinate system of orientation _m, Y_s _m, Z_s _m); Method is as shown in Equation (6):

$\left[\begin{array}{c}X\_s_m\\ Y\_s_m\\ Z\_s_m\end{array}\right]=A_{\mathrm{gv}}\left[\begin{array}{c}x\_s_m\\ y\_s_m\\ z\_s_m\end{array}\right]---\left(6\right)$

Wherein: A _GvFor orbit coordinate is tied to the rotationally coordinate transition matrix of heart coordinate system;

Step 4: determine that orientation moment m satellite with the relative position relation of scene center, obtains orientation angles

Process flow diagram utilizes the coordinate under the rotation geocentric coordinate system of this moment satellite and scene center as shown in Figure 4, obtains their relative position relation, and obtains corresponding orientation angles with this, specifically comprises following step:

(a) obtain scene center at the coordinate (X_t that rotates under the geocentric coordinate system ₀, Y_t ₀, Z_t ₀); Method is as shown in Equation (7):

$X\_t_0=\frac{E_a{E}_b\cos {\mathrm{\Φ}}_0\cos {\mathrm{\Λ}}_0}{\sqrt{E_b^2{\cos }^2{\mathrm{\Φ}}_0+E_a^2{\sin }^2{\mathrm{\Φ}}_0}}$

$Y\_t_0=\frac{E_a{E}_b\cos {\mathrm{\Φ}}_0\sin {\mathrm{\Λ}}_0}{\sqrt{E_b^2{\cos }^2{\mathrm{\Φ}}_0+E_a^2{\sin }^2{\mathrm{\Φ}}_0}}---\left(7\right)$

$Z\_t_0=\frac{E_a{E}_b\cos {\mathrm{\Φ}}_0}{\sqrt{E_b^2{\cos }^2{\mathrm{\Φ}}_0+E_a^2{\sin }^2{\mathrm{\Φ}}_0}}$

(b) obtain moment m satellite with the relative position vector (X_s_t of scene center _m, Y_s_t _m, Z_s_t _m); Method is as shown in Equation (8):

$\left[\begin{array}{c}X\_s\_t_m\\ Y\_s\_t_m\\ Z\_s\_t_m\end{array}\right]=\left[\begin{array}{c}X\_s_m-X\_t_0\\ Y\_s_m-Y\_t_0\\ Z\_s_m-Z\_t_0\end{array}\right]---\left(8\right)$

(d) obtain the orientation constantly the m satellite with the orientation of scene center to angle

Method is as shown in Equation (9):

Step 5: according to orientation angles

Difference read the different backscattering characteristic of scene

Process flow diagram as shown in Figure 5, the orientation angles of utilizing step 4 to obtain

And the scene back scattering matrix under the different angles that provide in advance, obtain the back scattering matrix of scene under this orientation angles

Further obtain each scatterer T in the scene _{I, j}Corresponding backscattering coefficient

Specifically comprise following step:

(a) according to moment m satellite with the orientation of scene center to angle

Table look-up and obtain the back scattering matrix of scene

(b) at backscattering characteristic

Obtain each scatterer T in the moment m scene dot matrix in the table _{I, j}Corresponding backscattering coefficient

The expression orientation is to moment m, satellite with the orientation of the capable j row of i point target in the dot matrix to angle;

Step 6: obtain each scatterer T in the orientation moment m scene _{I, j}Antenna radiation pattern weighting characteristic W _m(i, j) and with the oblique distance S of useful load _m_ T _{I, j}

Process flow diagram as shown in Figure 6, each scatterer T in the scene _{I, j}Orientation with useful load is different to off-axis angle to off-axis angle and distance, and corresponding antenna radiation pattern weighting is not identical yet, and each scatterer is not identical with the oblique distance of useful load yet in the scene in addition, specifically comprises following step:

(a) obtain each scatterer T in the moment m scene dot matrix _{I, j}Oblique distance S with useful load _m_ T _{I, j}Method is as shown in Equation (10):

$\left[\begin{array}{c}x\_s_m\_t_{i,j}\\ y\_s_m\_t_{i,j}\\ z\_s_m\_t_{i,j}\end{array}\right]=A_{\mathrm{ag}}\left[\begin{array}{c}X\_s_m-X\_t_{i,j}\\ Y\_s_m-Y\_t_{i,j}\\ Z\_s_m-Z\_t_{i,j}\end{array}\right]---\left(10\right)$

$S_m\_T_{i,j}=\sqrt{x\_s_m\_t_{i,j}^2+y\_s_m\_t_{i,j}^2+z\_s_m\_t_{i,j}^2}$

(b) obtain each scatterer T in the scene _{I, j}With the orientation of useful load to off-axis angle

And distance is to off-axis angle

Method is as shown in Equation (11):

（11）

(c) obtain each scatterer T in the orientation moment m scene dot matrix _{I, j}The orientation to antenna radiation pattern weighting Wa _m(i, j) and distance are to antenna radiation pattern weighting Wr _m(i, j);

Method is as shown in Equation (12):

（12）

(d) obtain each scatterer T in the scene _{I, j}Antenna radiation pattern weighting W _m(i, j); Method is as shown in Equation (13):

W _m(i,j)＝Wa _m(i,j)·Wr _m(i,j) （13）

Step 7: construct linear FM signal, and modulate with backscattering characteristic and antenna radiation pattern weighting characteristic, and change the stack Doppler effect according to oblique distance;

Process flow diagram as shown in Figure 7, construct linear FM signal, and according to the variation of oblique distance stack Doppler effect, at last according to linear FM signal and the Doppler effect of structure, obtain the echoed signal of each scatterer in the scene, specifically comprise following step:

(a) structure linear FM signal

(b) change the stack Doppler effect according to oblique distance

(c) by formula (14) obtain each scatterer echoed signal Signal of scene _m(i, j); Method is as shown in Equation (14):

Step 8: will be through the orientation of above processing constantly in the frame echoed signal data writing file of m;

Step 9: judge whether to finish the emulation of all pulses, begin the repetition subsequent step as then not returning for the 3rd step, otherwise finish emulation.

Embodiment:

For validity of the present invention is described, carry out the Area Objects emulation experiment, simulation parameter is got T as shown in Table 1 in the present embodiment _a=136, T _r=136, D _a=0.2m, D _r=0.2m chooses the consequent scattering coefficient of three tanks under the different visual angles in the experiment, at first utilize classic method to they respectively imagings, obtains imaging results as shown in Figure 8; Then utilize emulation mode of the present invention, read corresponding consequent scattering coefficient according to the orientation to the angle difference, the imaging results that finally obtains as shown in Figure 9.

Form 1 simulation parameter

Can be found out by Fig. 8 and Fig. 9, traditional emulation mode is utilized the consequent scattering coefficient under the angle in the whole course of work, and emulation mode of the present invention, difference according to the dimensional orientation angle in whole process reads different consequent scattering coefficients, resulting simulation imaging as a result figure can effectively be finished the emulation of satellite-borne SAR high-fidelity, reflect more really the target backscattering characteristic, obtain the more details characteristic of target, therefore the emulating image that obtains is truer, and meanwhile the present invention is well positioned to meet satellite-borne SAR high-resolution imaging pattern to the simulate signal high-precision requirement.By above-mentioned experiment, authenticity of the present invention, hi-fi and practicality have been verified.

Consider the space angular spectrum variation characteristic of target, reflect that truly target is at the back scattering variation characteristic of whole synthetic aperture in the time, thereby accurately describe and reconstruct SAR echo simulation signal, improved the verisimilitude of SAR emulating image, development has important using value to Spaceborne SAR System for this.

Claims (7)

1. the satellite-borne SAR high precision echo simulation method based on stable state RCS is characterized in that, specifically may further comprise the steps:

Step 1: obtain satellite-borne SAR echo simulation parameter by the simulation parameter table, comprising: satellite orbit semi-major axis a, orbit inclination i, orbital eccentricity e, simulation centre is τ constantly, and simulation centre is antenna boresight focal position longitude Λ at the earth's surface;on the face of the globe constantly ₀, latitude Φ ₀, antenna beam downwards angle of visibility β, antenna bearingt is to length L _a, antenna distance is to length L _r, wavelength X, frequency modulation rate b, earth semi-minor axis E _a, earth semi-major axis E _b, earth mean angular motion speed n, earth gravitational field gravitational constant μ;

Step 2: scene set, under the rotation geocentric coordinate system, scene is mapped on the ground, determine each scatterer T _{I, j}Coordinate (X_t _{I, j}, Y_t _{I, j}, Z_t _{I, j});

The scene of corresponding size is set according to user's request, and the union space coordinate conversion is obtained each scatterer T in the scene _{I, j}At the coordinate (X_t that rotates under the geocentric coordinate system _{I, j}, Y_t _{I, j}, Z_t _{I, j});

Step 3: determine that according to star ground space geometry relation and Keplerian orbit equation satellite is at the coordinate (X_s of orientation moment m _m, Y_s _m, Z_s _m);

Utilize satellite-borne SAR space geometry relation and Keplerian orbit equation, obtain the coordinate (X_s that rotates satellite definite moment in the orientation under the geocentric coordinate system _m, Y_s _m, Z_s _m);

Step 4: determine that orientation moment m satellite with the relative position relation of scene center, obtains orientation angles

Utilize the coordinate under the rotation geocentric coordinate system of this moment satellite and scene center, obtain their relative position relation, and obtain corresponding orientation angles with this;

Step 5: according to orientation angles

Difference read the different backscattering characteristic of scene

The orientation angles of utilizing step 4 to obtain

And the scene back scattering matrix under the different angles that provide in advance, obtain the back scattering matrix of scene under this orientation angles

Further obtain each scatterer T in the scene _{I, j}Corresponding backscattering coefficient

Step 6: obtain each scatterer T in the orientation moment m scene _{I, j}Antenna radiation pattern weighting characteristic W _m(i, j) and with the oblique distance S of useful load _m_ T _{I, j}

Step 7: construct linear FM signal, and modulate with backscattering characteristic and antenna radiation pattern weighting characteristic, and change the stack Doppler effect according to oblique distance;

Construct linear FM signal, and according to the variation of oblique distance stack Doppler effect, according to linear FM signal and the Doppler effect of structure, obtain each scatterer T in the scene at last _{I, j}Echoed signal;

Step 8: will be through the orientation of above processing constantly in the frame echoed signal data writing file of m;

Step 9: judge whether to finish the emulation of all pulses, begin the repetition subsequent step as then not returning for the 3rd step, otherwise finish emulation.

2. a kind of satellite-borne SAR high precision echo simulation method based on stable state RCS according to claim 1 is characterized in that, described step 2 specifically comprises following step:

(a) scene set dot matrix T _a* T _r, take simulation centre moment antenna boresight focus at the earth's surface;on the face of the globe as the scene center point, wherein, T _aFor the scene orientation to dot matrix number, T _rFor scene distance to the dot matrix number, and the set scene orientation is to lattice spacing D _a, distance is to lattice spacing D _r, the scene coordinate system is take scene center as initial point, and X-axis is along North and South direction, refers to north for just, and Y-axis is along east-west direction, refers to eastern for just;

(b) obtain each scatterer T _{I, j}Coordinate (x_t under the scene coordinate system _{I, j}, y_t _{I, j}); Method is as shown in Equation (1):

x_t _i，j＝D _a·(i-T _a/2)

（1）

y_t _i,j＝D _r·(j-T _r/2)

Wherein: i represents that the scene dot matrix is capable, and j represents the scene point array;

i＝0,1,2…,T _a-1，j＝0,1,2…,T _r-1；

(c) obtain each scatterer T _{I, j}Longitude, latitude (Λ _{I, j}, Φ _{I, j}); Method is as shown in Equation (2):

（2）

(d) obtain each scatterer T _{I, j}At the coordinate (X_t that rotates under the geocentric coordinate system _{I, j}, Y_t _{I, j}, Z_t _{I, j}); Method is as shown in Equation (3):

。

3. a kind of satellite-borne SAR high precision echo simulation method based on stable state RCS according to claim 1 is characterized in that, described step 3 specifically comprises following step:

(a) obtain the constantly average near heart angle M of m of orientation, eccentric angle E, very near heart angle θ, satellite radius vector r; Method is as shown in Equation (4):

M＝n·(m-τ)

(b) obtain the constantly coordinate (x_s of m satellite under orbital coordinate system of orientation _m, y_s _m, z_s _m); Method is as shown in Equation (5):

x_s _m＝r·cosθ

y_s _m＝r·sinθ （5）

z_s _m＝0

(c) obtain the constantly coordinate (X_s of m satellite under the rotation geocentric coordinate system of orientation _m, Y_s _m, Z_s _m); Method is as shown in Equation (6):

Wherein: A _GvFor orbit coordinate is tied to the rotationally coordinate transition matrix of heart coordinate system.

4. a kind of satellite-borne SAR high precision echo simulation method based on stable state RCS according to claim 1 is characterized in that, described step 4 specifically comprises following step:

(a) obtain scene center at the coordinate (X_t that rotates under the geocentric coordinate system ₀, Y_t ₀, Z_t ₀); Method is as shown in Equation (7):

(b) obtain moment m satellite with the relative position vector (X_s_t of scene center _m, Y_s_t _m, Z_s_t _m); Method is as shown in Equation (8):

(d) obtain the orientation constantly the m satellite with the orientation of scene center to angle

Method is as shown in Equation (9):

。

5. a kind of satellite-borne SAR high precision echo simulation method based on stable state RCS according to claim 1 is characterized in that, described step 5 specifically comprises following step:

(a) according to moment m satellite with the orientation of scene center to angle

Table look-up and obtain the back scattering matrix of scene

(b) at backscattering characteristic Obtain each scatterer T in the moment m scene dot matrix in the table _{I, j}Corresponding backscattering coefficient The expression orientation is to moment m, satellite with the orientation of the capable j row of i point target in the dot matrix to angle.

6. a kind of satellite-borne SAR high precision echo simulation method based on stable state RCS according to claim 1 is characterized in that, described step 6 specifically comprises following step:

(a) obtain each scatterer T in the moment m scene dot matrix _{I, j}Oblique distance S with useful load _m_ T _{I, j}Method is as shown in Equation (10):

(b) obtain each scatterer T in the scene _{I, j}With the orientation of useful load to off-axis angle

And distance is to off-axis angle

Method is as shown in Equation (11):

（11）

(c) obtain each scatterer T in the orientation moment m scene dot matrix _{I, j}The orientation to antenna radiation pattern weighting Wa _m(i, j) and distance are to antenna radiation pattern weighting Wr _m(i, j);

Method is as shown in Equation (12):

（12）

(d) obtain each scatterer T in the scene _{I, j}Antenna radiation pattern weighting W _m(i, j);

Method is as shown in Equation (13):

W _m(i,j)＝Wa _m(i,j)·Wr _m(i,j) （13）

。

7. a kind of satellite-borne SAR high precision echo simulation method based on stable state RCS according to claim 1 is characterized in that, described step 7 specifically comprises following step:

(a) structure linear FM signal

(b) change the stack Doppler effect according to oblique distance

(c) by formula (14) obtain each scatterer echoed signal Signal of scene _m(i, j); Method is as shown in Equation (14):

Images