CN104597446B - Space-borne synthetic aperture radar ground range resolution representation and parameter design method - Google Patents

Abstract

The invention provides a space-borne synthetic aperture radar ground range resolution representation and parameter design method. According to the method, synthetic aperture time and an emission signal bandwidth can be designed by representation of a long axis ground range resolution rho l and a short axis ground range resolution rho s of an acquired space-borne synthetic aperture radar according to resolution l needed by the radar, and radar related parameters are adjusted, so that the adjusted radar resolution is smaller than or equal to the l. The method overcomes the shortcoming that the ground range resolution is represented by azimuth and range direction ground range resolution, the ground range resolution capacity of the SAR (synthetic aperture radar) can be more comprehensively reflected, and the resolution in all directions of a ground range plane meets system index requirements.

Description

A kind of satellite-borne synthetic aperture radar ground range resolution characterizes and Parameters design

Technical field

The invention belongs to Synthetic Aperture Radar Technique field is and in particular to a kind of satellite-borne synthetic aperture radar ground range resolution Characterize and Parameters design.

Background technology

Synthetic aperture radar (SAR) is a kind of round-the-clock, round-the-clock high-resolution microwave remote sensing imaging radar, can pacify It is contained on the flying platforms such as aircraft, satellite, spaceship.In environmental monitoring, oceanographic observation, resource exploration, Crop Estimation, survey Paint with the application of the aspects such as military affairs on have uniqueness advantage, the effect that other remote sensings are difficult to play can be played.

Satellite-borne synthetic aperture radar refers to the synthetic aperture radar with satellite as carrier.Satellite-borne synthetic aperture radar can be transported Row is in circular orbit or elliptic orbit.In circular orbit, satellite the earth's core earth fixes (ECEF) coordinate system velocity attitude perpendicular to defending Star the earth's core line direction, that is, satellite-borne SAR be in and flat fly state.In elliptic orbit, satellite ECEF coordinate system velocity attitude does not hang down Directly in satellite the earth's core line direction, that is, satellite-borne SAR is in dive status.

The mode of operation of satellite-borne SAR can be divided into positive side pattern and strabismus mode.In positive side pattern, beam direction Perpendicular to satellite ECEF coordinate system velocity attitude.In strabismus mode, beam direction is not orthogonal to satellite ECEF coordinate system Velocity attitude.Compared to positive side pattern, strabismus mode can obtain more preferable covering and revisit performance, and can provide different angles The target scattering characteristics of degree.Thus strabismus mode has a wide range of applications in satellite-borne SAR.

SAR application quality quality is generally dependent on the ground range resolution of SAR image.Generally adopt the ground in secondary lobe direction at present Away from resolution ratio, that is, orientation and distance, to ground range resolution, to characterize the distance resolution capability of SAR.However, above-mentioned distance is differentiated Rate characterizing method is suitable only for circular orbit positive side pattern.When satellite-borne SAR runs on elliptic orbit or is operated in strabismus mode bar When under part, distance two dimension secondary lobe out of plumb, ground resolution skewness, orientation ground range resolution and range resolution Can not comprehensively represent the ground range resolution ability of satellite-borne SAR.In addition, existing resolution parameter (includes closing Become aperture time and transmitted signal bandwidth) it is all based on orthogonal secondary lobe, that is, in elliptic orbit or strabismus mode and inapplicable.

Content of the invention

In view of this, the purpose of the present invention is to propose to a kind of satellite-borne synthetic aperture radar ground range resolution sign is set with parameter Meter method.The method is directed to and runs on elliptic orbit or be operated in satellite-borne synthetic aperture radar under the conditions of strabismus mode, is given The complete statement of ground range resolution is so that the resolution ratio of distance plane all directions is satisfied by system index demand.

The inventive method is achieved through the following technical solutions：

A kind of satellite-borne synthetic aperture radar ground range resolution characterizes and Parameters design, and detailed process is：

Step one, the major axis ground range resolution ρ of acquisition satellite-borne synthetic aperture radar_lWith short axle ground range resolution ρ_sSign；

Wherein, parameter m, n and p can be expressed as：

In formula, ρ_rFor oblique distance plan range to resolution ratio, ρ_aFor oblique distance flat orientation to resolution ratio, β is downwards angle of visibility, and α is Dive angle, φ is azimuth, and δ is geocentric angle, and θ is angle of squint；

Step 2, utilize described major axis ground range resolution ρ_lWith short axle ground range resolution ρ_sSign, to be reached according to radar Resolution ratio l arriving, adjustment radar associated arguments are so that the radar resolution after adjustment is less than or equal to l.

Further, the detailed process of step 2 of the present invention is：

Step 21, set the radar now needing resolution sizes as l, then make major axis ground range resolution ρ_lNumerically with l phase Deng ρ_l/ρ_sThere is minimum of a value γ,It is calculated short axle ground range resolution ρ_sFor：

Step 22, the ρ being determined according to step 21_lAnd ρ_s, calculate the synthetic aperture time T of radar_aWith transmitted signal bandwidth B：

In formula, K_grWith K_gaBe respectively distance to orientation distance spreading coefficient, c is the light velocity, and λ is signal wavelength, and V is Satellite the earth's core earth fixes ECFE coordinate system speed, and oblique distance R is between synthetic aperture time centre moment satellite-borne SAR and target Distance；

Step 23, by according to synthetic aperture time of calculating and transmitted signal bandwidth, adjust satellite-borne synthetic aperture radar Emission system so that satellite-borne synthetic aperture radar resolution ratio be less than or equal to l.

Brief description

Fig. 1 satellite-borne SAR geometrical relationship；

Fig. 2 resolution ellipse；

Fig. 3 ellipse resolution major axis and short axle；

Fig. 4 ellipse resolution major axis and Y_gThe angle of axle；

Fig. 5 synthetic aperture time；

Fig. 6 transmitted signal bandwidth；

Specific embodiment

With reference to the accompanying drawings and examples the inventive method is further described.

The present invention provides a kind of satellite-borne synthetic aperture radar ground range resolution to characterize and Parameters design, detailed process For：

Step one, the major axis ground range resolution ρ of acquisition satellite-borne synthetic aperture radar_lWith short axle ground range resolution ρ_sSign；

Wherein, parameter m, n and p can be expressed as：

In formula, ρ_rFor oblique distance plan range to resolution ratio, ρ_aFor oblique distance flat orientation to resolution ratio, β is downwards angle of visibility, and α is to bow The angle of attack, φ is azimuth, and δ is geocentric angle, and θ is angle of squint；

In this step major axis ground range resolution ρ is given below_lWith short axle ground range resolution ρ_sSpecifically the deriving of sign Journey：

Step 11, satellite dive angle α is determined according to orbit parameter and satellite-borne SAR geometrical relationship.

The geometrical relationship of satellite-borne SAR is as shown in Figure 1.O is earth center, and S is satellite position, and T is target location, and ST is ripple Bundle direction of illumination, the length of ST is oblique distance R, and wherein oblique distance is between synthetic aperture time centre moment satellite-borne SAR and target Distance.XYZ coordinate system is a kind of satellite platform coordinate system, and Z axis point to satellite by the earth's core, and satellite ECEF speed V is in YOZ plane Interior, X-axis determines according to the right-hand rule.The plane that oblique distance is located with satellite ECEF speed V is oblique distance plane.X_gY_gCoordinate system is ground Areal coordinate system, Y_gAxle vertical beam direction of illumination on the ground, X_gAxle vertical Y on the ground_gAxle.Downwards angle of visibility β is beam side To the angle with Z axis, geocentric angle δ is the angle of target the earth's core line and Z axis, and azimuth φ is beam direction in X/Y plane Angle between the projection of X/Y plane of projection and satellite ECEF speed V.Angle of squint θ is that satellite ECEF velocity attitude is shone with wave beam Penetrate the angle in direction.Dive angle α is the angle of satellite ECEF velocity attitude and vertical satellite distance line direction.

According to elliptic orbit semi-major axis a, orbit inclination angle i, orbital eccentricity e, argument of perigee ω and latitude argument u Lai really Determine satellite dive angle α, formula is as follows

Wherein, ω_eFor rotational-angular velocity of the earth, ω_sFor orbit angular velocity, R_sFor the height in satellite distance the earth's core,For R_s Derivative to the time, can be expressed as

Wherein, μ is Gravitational coefficient of the Earth, and numerical value is 398600.5km³/s².

Sign () is sign function, can be expressed as

Step 12, angle of squint is determined according to the geometrical relationship of satellite-borne SAR.

Beam direction determines according to application demand, it is possible to use downwards angle of visibility β is characterized with azimuth φ.Angle of squint θ can To be expressed as

θ=arccos (cos α sin β cos φ+sin α cos β) (4)

Step 13, determine satellite-borne SAR ground range resolution.

The resolution ratio of SAR is generally analyzed by ambiguity function, and the ambiguity function of satellite-borne SAR can be expressed as

Wherein, A and B is the position vector of two adjacent point targets；Φ be tapered plane distance to unit vector, its direction with Oblique distance direction is identical；Γ is tapered plane orientation unit vector, and direction is vertical with Φ, ρ_rWith ρ_aFor oblique distance flat orientation to away from Descriscent resolution ratio, can be expressed as

Wherein, c is the light velocity, and B is transmitted signal bandwidth, and λ is signal wavelength, T_aFor the synthetic aperture time.If A and B is on ground Along X in anomaly face_gAxle, Y_gThe interval of axle is represented by

B-A=x_gu_x+y_gu_y(7)

Wherein, u_xWith u_yIt is respectively along X_gAxle, Y_gAxial unit vector, x_g、y_gIt is respectively between target B and target A Every along X_gAxle, Y_gAxial component.According to oblique distance plane and the interplanar projection relation of distance, can get following relation：

Wherein, coefficient k₁, k₂, k₃Can be expressed as

According to (7), ambiguity function (5) can be expressed as

According to (9), the ground range resolution region of satellite-borne SAR is approximately an ellipse, as shown in Figure 2.Elliptic equation is

Oval long axis length and minor axis length can be defined as major axis ground range resolution ρ_lWith short axle ground range resolution ρ_s, Can be expressed as

Wherein, parameter m, n and p can be expressed as

Major axis ground range resolution direction and Y_gThe angle in direction is

In addition, traditional SAR's differentiates the resolution ratio representing SAR in rate theory using orientation and distance to ground range resolution Ability.Orientation ground range resolution ρ can be derived by according to (7) and (9)_gaWith distance to ground range resolution ρ_grAs follows

Wherein, K_grWith K_gaBe respectively distance to orientation distance spreading coefficient, can be expressed as

Distance to orientation ground range resolution direction and Y_gThe angle in direction is respectively ψ_rWith ψ_a

Major and minor axis ground range resolution is ground range resolution maxima and minima in distance all directions for the SAR.Orientation To with distance to ground range resolution be only along orientation and distance to ground range resolution, neither distance plane all directions Middle highest ground range resolution, is not minimum ground range resolution.Thus, major and minor axis ground range resolution can more comprehensively react SAR Ground range resolution ability.

Step 2, utilize described major axis ground range resolution ρ_lWith short axle ground range resolution ρ_sSign, to be reached according to radar Resolution ratio l arriving, adjustment radar associated arguments are so that the radar resolution after adjustment is less than or equal to l.

The detailed process of this step is：

Step 21, set the radar needing resolution sizes as l, then make major axis ground range resolution ρ_lIt is numerically equal with l, It is calculated short axle ground range resolution ρ_sFor：

Step 22, the ρ being determined according to step 21_lAnd ρ_s, according to formula (6), (11) and (12), it is possible to obtain realize specific Resolution ellipse major axis can be expressed as with the synthetic aperture time needed for short axle and transmitted signal bandwidth

According to (18), ρ_l/ρ_sThere is minimum of a value γ

Work as ρ_l/ρ_sWhen taking minimum of a value γ, formula (18) with abbreviation can be

Synthetic aperture time and transmitted signal bandwidth that step 23, basis calculate, adjustment satellite-borne synthetic aperture radar Emission system is so that the resolution ratio of satellite-borne synthetic aperture radar is less than or equal to l.

Beneficial effect

The present invention proposes to represent ground range resolution using the long and short axle ground range resolution of the ellipse of ground range resolution, is given The complete statement of long and short axle ground range resolution, and provide the size of long and short axle ground range resolution and the accurate calculating in direction Method.Using above-mentioned long and short axle ground range resolution, synthetic aperture time and transmitted signal bandwidth can be designed so that ground anomaly The resolution ratio of face all directions is satisfied by system index demand.

Embodiment

Embodiment one:On elliptic orbit, each parameter of track is specific as follows shown for satellite transit：

Earth radius：6371.004km

Semi-major axis of orbit：42164km

Orbit inclination angle：50°

Orbital eccentricity：0.1

Perigee of orbit argument：90°

Beam position parameter is as follows

Downwards angle of visibility：4.5°

Azimuth：15 degree, 30 degree, 45 degree, 60 degree, 75 degree, 90 degree

Resolution ratio relevant parameter is as follows

Transmitted signal bandwidth：15MHz

The synthetic aperture time：75s

The echo of emulation point target is simultaneously imaged using back-projection algorithm.The major axis of assessment imaging results is divided with short axle distance Resolution, and carry out contrast as shown in table 1 with result of calculation.Result of calculation is consistent with assessment result, and error is less.

Table 1 major axis and short axle ground range resolution assessment result are contrasted with result of calculation

, on elliptic orbit, each parameter of track is specific as follows shown for embodiment two, satellite transit：

Earth radius：6371.004km

Semi-major axis of orbit：10000km

Orbit inclination angle：50°

Orbital eccentricity：0.1

Perigee of orbit argument：90°

Beam position parameter is as follows

Downwards angle of visibility：20°

Azimuth：45°

Aerial radiation parameter is as follows：

Antenna size：10m x 10m

Signal wavelength：0.1m

Receiver noise factor：3dB

System loss：5dB

Antenna efficiency：60%

Equivalent backscattering coefficient：-20dB

1. ground range resolution

If transmitted signal bandwidth is 30MHz, the synthetic aperture time is 30s, then attainable ellipse resolution major axis As shown in Figure 3 with short axle.Major axis and Y_gThe angle in direction is as shown in Figure 4.

2. synthetic aperture time and transmitted signal bandwidth

If major axis resolution ratio is 30m, major axis is minimum with the ratio of short axle, then the synthetic aperture time needing is as shown in figure 5, need The transmitted signal bandwidth wanted is as shown in Figure 6.

Since then, it is achieved that a kind of satellite-borne synthetic aperture radar ground range resolution characterizes and Parameters design.According to Upper embodiment, diagram and specific embodiment understand, a kind of satellite-borne synthetic aperture radar ground range resolution is characterized and set with parameter Meter method can be fully described the resolution character of satellite-borne SAR, and can design synthetic aperture time and transmitted signal bandwidth with Realize the ground range resolution specified.

Above-described specific descriptions, have been carried out further specifically to the purpose of invention, technical scheme and beneficial effect Bright, be should be understood that the specific embodiment that the foregoing is only the present invention, the protection model being not intended to limit the present invention Enclose, all any modification, equivalent substitution and improvement within the spirit and principles in the present invention, done etc., should be included in the present invention Protection domain within.

Claims (2)

1. a kind of satellite-borne synthetic aperture radar ground range resolution characterizes with Parameters design it is characterised in that including following walking Suddenly：

Step one, the major axis ground range resolution ρ of acquisition satellite-borne synthetic aperture radar_lWith short axle ground range resolution ρ_sSign；

$\left\{\begin{array}{c}{\mathrm{\ρ}}_l=\frac{2\sqrt{2}}{{\[(m+n)-\sqrt{{(m-n)}^2+4p^2}\]}^{1/2}}\\ {\mathrm{\ρ}}_s=\frac{2\sqrt{2}}{{\[(m+n)+\sqrt{{(m-n)}^2+4p^2}\]}^{1/2}}\end{array}\right.$

Wherein, parameter m, n and p can be expressed as：

$\left\{\begin{array}{c}m=\frac{{k_1}^2}{{({\mathrm{\ρ}}_r/2)}^2}+\frac{{k_2}^2}{{({\mathrm{\ρ}}_a/2)}^2}\\ n=\frac{{k_3}^2}{{({\mathrm{\ρ}}_a/2)}^2}\\ p=\frac{k_2{k}_3}{{({\mathrm{\ρ}}_a/2)}^2}\end{array}\right.$

$\left\{\begin{array}{c}{k}_1=\sin (\mathrm{\β}+\mathrm{\δ})\\ k_2=\frac{\cos (\mathrm{\β}+\mathrm{\δ})\·(\cos \mathrm{\α}\cos \mathrm{\β}\cos \mathrm{\φ}-\sin \mathrm{\α}\sin \mathrm{\β})}{\sin \mathrm{\θ}}\\ k_3=\frac{\cos \mathrm{\α}\sin \mathrm{\φ}}{\sin \mathrm{\θ}}\end{array}\right.$

In formula, ρ_rFor oblique distance plan range to resolution ratio, ρ_aFor oblique distance flat orientation to resolution ratio, β is downwards angle of visibility, and α is to dive Angle, φ is azimuth, and δ is geocentric angle, and θ is angle of squint；

Step 2, utilize described major axis ground range resolution ρ_lWith short axle ground range resolution ρ_sSign, to be reached according to radar Resolution ratio l, adjustment radar associated arguments are so that the radar resolution after adjustment is less than or equal to l.

2. a kind of satellite-borne synthetic aperture radar ground range resolution characterizes and Parameters design as claimed in claim 1, step Two detailed process is：

Step 21, set the radar now needing resolution sizes as l, then make major axis ground range resolution ρ_lNumerically equal with l, ρ_l/ ρ_sThere is minimum of a value γ,It is calculated short axle ground range resolution ρ_sFor：

${\mathrm{\ρ}}_s=\frac{l}{\mathrm{\γ}}$

Step 22, the ρ being determined according to step 21_lAnd ρ_s, calculate the synthetic aperture time T of radar_aWith transmitted signal bandwidth B：

$\left\{\begin{array}{c}B=K_{gr}\·\frac{c}{2{\mathrm{\ρ}}_l}\·\sqrt{\frac{2{\mathrm{\γ}}^2}{1+{\mathrm{\γ}}^2}}\\ T_a=K_{ga}\·\frac{\mathrm{\λ}R}{2{\mathrm{\ρ}}_{l}V\sin \mathrm{\θ}}\·\sqrt{\frac{2{\mathrm{\γ}}^2}{1+{\mathrm{\γ}}^2}}\end{array}\right.$

In formula, K_grWith K_gaBe respectively distance to orientation distance spreading coefficient, c be the light velocity, λ be signal wavelength, V be satellite ground ECFE coordinate system speed fixed by heart ball, and oblique distance R is the distance between synthetic aperture time centre moment satellite-borne SAR and target；

Step 23, by according to synthetic aperture time of calculating and transmitted signal bandwidth, the sending out of adjustment satellite-borne synthetic aperture radar Penetrate system so that the resolution ratio of satellite-borne synthetic aperture radar is less than or equal to l.