CN103675760A - Satellite-borne geosynchronous orbit synthetic aperture radar posture guiding method - Google Patents

Abstract

The invention discloses a satellite-borne geosynchronous orbit synthetic aperture radar posture guiding method. Optimal ground range resolution can be achieved by using a small posture guiding angle through the utilization of the satellite-borne geosynchronous orbit synthetic aperture radar posture guiding method. According to the satellite-borne geosynchronous orbit synthetic aperture radar posture guiding method, firstly, the expression of a satellite speed direction and a ground range resolution ellipse area is obtained according to the conditions of given orbital parameters, downwards angles of visibility and the like; then the optimal azimuth angle of the optimal ground range resolution is worked out by utilizing the optimal solution when the ground range resolution ellipse area is minimum; finally, a wave beam is made to point to the direction where the optimal azimuth angle locates through pitching roll guiding or roll pitching guiding, the posture guiding of the optimal resolution is completed, and the posture guiding angle is small.

Description

A kind of spaceborne geostationary orbit synthetic-aperture radar attitude guidance method

Technical field

The present invention relates to Synthetic Aperture Radar Technique field, be specifically related to a kind of spaceborne geostationary orbit synthetic-aperture radar attitude guidance method.

Background technology

Synthetic aperture radar (SAR) is a kind of round-the-clock, round-the-clock high-resolution microwave remote sensing imaging radar, can be arranged on the flying platforms such as aircraft, satellite, spaceship.In the application of the aspects such as environmental monitoring, oceanographic observation, resource exploration, Crop Estimation, mapping and military affairs, there is unique advantage, can bring into play the effect that other remote sensings are difficult to performance.For SAR, apply so widely, its application quality quality generally depends on the image resolution ratio of SAR.

Spaceborne geostationary orbit (GEO) synthetic-aperture radar refer to be positioned at geostationary orbit, synthetic-aperture radar that the satellite of take is carrier.Spaceborne geostationary orbit synthetic-aperture radar (GEO SAR) has the advantages such as overlay area is wide, revisit time is short.In the orbital period of a GEO SAR, the direction variation range of earth center rotating (ECR) coordinate system speed is large.When GEO SAR is positioned at equator, ECR velocity reversal approaches range direction.Now, to be projected in the two-dimentional secondary lobe on ground will be no longer quadrature to ambiguity function.This cause orientation to ground range resolution much larger than orientation to slant range resolution, ground range resolution severe exacerbation.

Synthetic-aperture radar can improve range resolution by improving transmitted bandwidth, can improve azimuth resolution by extending the synthetic aperture time.But because distance is to, orientation to bidimensional quadrature no longer, even may overlap, thereby only by improving transmitted bandwidth and extending the synthetic aperture time and be difficult to effectively improve resolution.

Synthetic-aperture radar can also be guided and be changed beam position by attitude, and then improves ground range resolution.Attitude guiding refers to as reaching the adjustment of the attitude of satellite that certain ideal behavior carries out.In earth low orbit (LEO) synthetic-aperture radar, the object of attitude guiding normally reduces Doppler frequency.The conventional attitude guidance method of LEOSAR has one dimension Yaw steering and complete zero Doppler's guiding at present, and the former can reduce Doppler frequency, and it is zero that the latter can make Doppler frequency.In GEO SAR, Yaw steering can effectively reduce the deterioration of ground range resolution, but required guiding angle is large, to platform stance control system require high.Complete zero Doppler's guiding not only needs larger guiding angle, and can not reduce the deterioration of ground range resolution.

Summary of the invention

In view of this, the invention provides a kind of spaceborne geostationary orbit synthetic-aperture radar attitude guidance method, can utilize less attitude guiding angle to realize optimum ground range resolution.

Spaceborne geostationary orbit synthetic-aperture radar attitude guidance method of the present invention, comprises the following steps:

Step 1, definitely apart from differentiating ellipse area:

Wherein, S is-area of 3dB ground range resolution ellipse, ρ _afor oblique distance azimuth resolution; ρ _rfor oblique distance range resolution; α is the angle of pitch of radar; β is the downwards angle of visibility of radar; position angle for radar;

$\mathrm{\α}=\arctan \left(\frac{\mathrm{sign}({\mathrm{\ω}}_s-{\mathrm{\ω}}_e\cos i)\·{\stackrel{\·}{R}}_s/R_s}{\sqrt{{\left({\mathrm{\ω}}_e\sin i\cos u\right)}^2+{({\mathrm{\ω}}_s-{\mathrm{\ω}}_e\cos i)}^2}}\right)$

Wherein,

$\left\{\begin{array}{c}{\mathrm{\ω}}_s=\sqrt{\mathrm{\μa}(1-e^2)}/R_s^2\\ R_s=\frac{a(1-e^2)}{1+e\cos (u-\mathrm{\ω})}\\ {\stackrel{\·}{R}}_s=e\sin (u-\mathrm{\ω})\sqrt{\frac{\mathrm{\μ}}{a(1-e^2)}}\end{array}\right.$

Wherein, ω _sfor orbit angular velocity, ω _efor rotational-angular velocity of the earth, R _sfor the height in satellite distance the earth's core, for R _sderivative to the time, i is orbit inclination, and u is latitude argument, and μ is Gravitational coefficient of the Earth, and a is semi-major axis of orbit, and e is orbital eccentricity, and ω is argument of perigee;

Step 2, base area is apart from resolution ellipse area definition top optimization direction angle:

Solve

draw top optimization direction angle

for

Wherein, positive sign represents that right side looks, and negative sign represents that left side looks;

Step 3, determines attitude guiding angle according to top optimization direction angle, carries out attitude guiding:

If adopt the guidance mode of pitching after first roll, roll guiding angle θ _r, pitching guiding angle θ _pbe respectively

If adopt the guidance mode of roll after first pitching, roll guiding angle θ _r, pitching guiding angle θ _pbe respectively

Wherein, $\mathrm{\φ}=\arctan \left(\frac{\sin i\cos u}{{\mathrm{\ω}}_s/{\mathrm{\ω}}_e-\cos i}\right).$

Beneficial effect:

The present invention utilizes distance to differentiate hour ground range resolution optimum of ellipse area, calculate the top optimization direction angle of optimum ground range resolution, then by pitching roll, guide or roll pitching guiding makes place, beam position top optimization direction angle direction, complete the guiding of optimal resolution attitude, attitude guiding angle is little.

Accompanying drawing explanation

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

Fig. 2 is coordinate angle schematic diagram of the present invention.

Fig. 3 is that the attitude guiding roll angle of pitching guidance mode after the first roll of employing changes.

Fig. 4 is that the attitude guiding angle of pitch of pitching guidance mode after the first roll of employing changes.

Fig. 5 is distance ambiguity function after attitude guiding.

Embodiment

Below in conjunction with the accompanying drawing embodiment that develops simultaneously, describe the present invention.

The invention provides a kind of spaceborne geostationary orbit synthetic-aperture radar attitude guidance method, first according to conditions such as known orbit parameter, downwards angle of visibilities, obtain the expression formula of satellite velocities direction and distance resolution ellipse area.Then base area, apart from the expression formula of differentiating ellipse area, solves and realizes the minimum required top optimization direction angle of ellipse area of differentiating.Finally, by pitching roll, guide or roll pitching guiding makes place, beam position above-mentioned top optimization direction angle direction, as shown in Figure 1.Concrete steps are as follows.

Step 1, determines satellite velocities direction and distance resolution ellipse area according to orbit parameter and downwards angle of visibility.

Step 1.1, determines satellite velocities direction.

According to semi-major axis of orbit a, orbit inclination i, orbital eccentricity e, argument of perigee ω, latitude argument u, determine the velocity reversal of satellite in earth fixed coordinate system.Wherein, earth fixed coordinate system initial point is positioned at earth centroid, and x axle points to Greenwich meridian in earth equatorial plane, and z axle is along earth rotation direction directed north, and y axle and x axle, z axle form right hand rectangular coordinate system.

Under earth fixed coordinate system, the direction of satellite velocities can be used crab angle φ and angle of pitch α to represent, crab angle φ and angle of pitch α computing formula are as follows:

$\left\{\begin{array}{c}\mathrm{\φ}=\arctan \left(\frac{\sin i\cos u}{{\mathrm{\ω}}_s/{\mathrm{\ω}}_e-\cos i}\right)\\ \mathrm{\α}=\arctan \left(\frac{\mathrm{sign}({\mathrm{\ω}}_s-{\mathrm{\ω}}_e\cos i)\·{\stackrel{\·}{R}}_s/R_s}{\sqrt{{\left({\mathrm{\ω}}_e\sin i\cos u\right)}^2+{({\mathrm{\ω}}_s-{\mathrm{\ω}}_e\cos i)}^2}}\right)\end{array}\right.---\left(1\right)$

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 _sderivative to the time, can be expressed as

$\left\{\begin{array}{c}{\mathrm{\ω}}_s=\sqrt{\mathrm{\μa}(1-e^2)}/R_s^2\\ R_s=\frac{a(1-e^2)}{1+e\cos (u-\mathrm{\ω})}\\ {\stackrel{\·}{R}}_s=e\sin (u-\mathrm{\ω})\sqrt{\frac{\mathrm{\μ}}{a(1-e^2)}}\end{array}\right.---\left(2\right)$

Wherein, μ is Gravitational coefficient of the Earth, and numerical value is 398600.5km ³/ s ²; Sign () is sign function, can be expressed as

$\mathrm{sign}\left(x\right)=\left\{\begin{array}{cc}1& x>0\\ -1& x<0\end{array}\right.---\left(3\right)$

Step 1.2, definitely apart from differentiating ellipse area

The cartographic represenation of area of can use-3dB of ground range resolution resolution ellipse, its formula is

Wherein, S is-area of 3dB resolution ellipse, ρ _afor oblique distance azimuth resolution, ρ _rfor oblique distance range resolution.Angle of squint γ is the angle of beam position and ECR velocity reversal, position angle

for beam position is at the projection of surface level and the angle between the projection of ECR speed at surface level, β is downwards angle of visibility, position angle

determine according to actual beam position with downwards angle of visibility β.

As shown in Figure 2, wherein V is ECR speed to above-mentioned angle, and R is beam position, and O point is the earth's core.

γYu position angle, angle of squint

between there is following relation:

Thereby ground range resolution area can be expressed as

Step 2, base area is apart from resolution ellipse area definition top optimization direction angle.

If ground range resolution area is minimum, need to meet equation

Solving equation (7), can obtain the top optimization direction angle corresponding to optimum ground range resolution:

Wherein,

be top optimization direction angle, positive sign represents that right side looks, and negative sign represents that left side looks.

Step 3, determines attitude guiding angle according to top optimization direction angle.

In initial time beam position substar, position, beam position top optimization direction angle after attitude guiding.Attitude guiding strategy is the guiding of roll pitching two dimension.Beam position before attitude guiding can represent

u'＝[0,0,-1] ^T (9)

Beam position after attitude guiding can be expressed as

Attitude guided procedure can be expressed as

u'＝Au(11)

Wherein, A is that attitude is guided corresponding rotation matrix.

If adopt the strategy of pitching after first roll, rotation matrix can be expressed as

Wherein, θ _rfor roll guiding angle, θ _pfor pitching guiding angle.By rotation matrix substitution equation (11), solving equation (11) can obtain attitude guiding angle and be

If adopt the strategy of roll after first pitching, rotation matrix can be expressed as

$A=\left[\begin{array}{ccc}\cos {\mathrm{\&theta;}}_R& \sin {\mathrm{\&theta;}}_P\sin {\mathrm{\&theta;}}_R& -\cos {\mathrm{\&theta;}}_P\sin {\mathrm{\&theta;}}_{\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HDA0000432293680000013.png,HDA0000432293680000021.png"\; state="\{\{state\}\}">R</figure-callout>}}\\ 0& \cos {\mathrm{\&theta;}}_P& \sin {\mathrm{\&theta;}}_P\\ \sin {\mathrm{\&theta;}}_R& -\sin {\mathrm{\&theta;}}_P\cos {\mathrm{\&theta;}}_R& \cos {\mathrm{\&theta;}}_P\cos {\mathrm{\&theta;}}_R\end{array}\right]---\left(14\right)$

Rotation matrix substitution equation (11), solving equation (11) can obtain attitude guiding angle and be

Since then, just realized a kind of satellite-borne synthetic aperture radar attitude guidance method.

Satellite transit is on elliptical orbit, shown in each parameter of track is specific as follows: earth radius is 6371.004km; Semi-major axis of orbit is 42100km; Orbit inclination is 50 °; Orbital eccentricity is 0.1; Perigee of orbit argument is 90 °; Downwards angle of visibility is 7 °; Slant range resolution is 1m; Rotational-angular velocity of the earth is 7.292115 * 10 ^-5rads.The mode of pitching after the first roll of attitude guiding employing.Attitude is guided required roll angle as shown in Figure 3, and the angle of pitch as shown in Figure 4.Ground range resolution ambiguity function after attitude guiding as shown in Figure 5.From Fig. 3, Fig. 4, it is less that the required attitude of geostationary orbit synthetic-aperture radar optimal resolution attitude guidance method is guided angle.As shown in Figure 5, after carrying out the guiding of geostationary orbit synthetic-aperture radar optimal resolution attitude, it is vertical that distance is differentiated two secondary lobes, and ground range resolution is optimum.

In sum, these are only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any modification of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (1)

1. a spaceborne geostationary orbit synthetic-aperture radar attitude guidance method, is characterized in that, comprises the following steps:

Step 1, definitely apart from differentiating ellipse area:

Wherein, S is-area of 3dB ground range resolution ellipse, ρ _afor oblique distance azimuth resolution; ρ _rfor oblique distance range resolution; α is the angle of pitch of radar; β is the downwards angle of visibility of radar;

position angle for radar;

$\mathrm{\&alpha;}=\arctan \left(\frac{\mathrm{sign}({\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_e\cos i)\&CenterDot;{\stackrel{\&CenterDot;}{R}}_s/R_s}{\sqrt{{\left({\mathrm{\&omega;}}_e\sin i\cos u\right)}^2+{({\mathrm{\&omega;}}_s-{\mathrm{\&omega;}}_e\cos i)}^2}}\right)$

Wherein,

$\left\{\begin{array}{c}{\mathrm{\&omega;}}_s=\sqrt{\mathrm{\&mu;a}(1-e^2)}/R_s^2\\ R_s=\frac{a(1-e^2)}{1+e\cos (u-\mathrm{\&omega;})}\\ {\stackrel{\&CenterDot;}{R}}_s=e\sin (u-\mathrm{\&omega;})\sqrt{\frac{\mathrm{\&mu;}}{a(1-e^2)}}\end{array}\right.$

Wherein, ω _sfor orbit angular velocity, ω _efor rotational-angular velocity of the earth, R _sfor the height in satellite distance the earth's core,

for R _sderivative to the time, i is orbit inclination, and u is latitude argument, and μ is Gravitational coefficient of the Earth, and a is semi-major axis of orbit, and e is orbital eccentricity, and ω is argument of perigee;

Step 2, base area is apart from resolution ellipse area definition top optimization direction angle:

Solve

draw top optimization direction angle

for

Wherein, positive sign represents that right side looks, and negative sign represents that left side looks;

Step 3, determines attitude guiding angle according to top optimization direction angle, carries out attitude guiding:

If adopt the guidance mode of pitching after first roll, roll guiding angle θ _r, pitching guiding angle θ _pbe respectively

If adopt the guidance mode of roll after first pitching, roll guiding angle θ _r, pitching guiding angle θ _pbe respectively

Wherein, $\mathrm{\&phi;}=\arctan \left(\frac{\sin i\cos u}{{\mathrm{\&omega;}}_s/{\mathrm{\&omega;}}_e-\cos i}\right).$

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