CN103675760B - A kind of spaceborne geostationary orbit synthetic-aperture radar attitude guidance method - Google Patents

Abstract

The invention discloses a kind of spaceborne geostationary orbit synthetic-aperture radar attitude guidance method.Use the present invention that less attitude guiding angle can be utilized to realize optimum ground range resolution.First the present invention differentiates the expression formula of ellipse area according to the condition acquisition satellite velocities directions such as known orbit parameter, downwards angle of visibility and distance, when then utilizing distance resolution ellipse area minimum, ground range resolution is optimum, calculate the top optimization direction angle of optimum ground range resolution, direction, place, beam position top optimization direction angle is made finally by pitching roll guiding or roll pitching guiding, complete the guiding of optimal resolution attitude, attitude steering angle is little.

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.Application in environmental monitoring, oceanographic observation, resource exploration, Crop Estimation, mapping and military affairs etc. has unique advantage, the effect that other remote sensings are difficult to play can be played.Apply so widely for SAR, 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, take satellite as the synthetic-aperture radar of carrier.Spaceborne geostationary orbit synthetic-aperture radar (GEOSAR) has the advantages such as overlay area is wide, revisit time is short.In the orbital period of a GEOSAR, the direction variation range that earth center rotates (ECR) coordinate system speed is large.When GEOSAR is positioned at equator, ECR velocity reversal is close to range direction.Now, ambiguity function is projected in the two-dimentional secondary lobe on ground will be no longer orthogonal.This causes 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 no longer orthogonal to bidimensional to, orientation, even may overlap, thus only by raising transmitted bandwidth with extend the synthetic aperture time and be difficult to effectively improve resolution.

Synthetic-aperture radar can also change beam position by attitude guiding, and then improves ground range resolution.Attitude guiding refers to the adjustment for reaching the attitude of satellite that certain ideal behavior is carried out.In earth low orbit (LEO) synthetic-aperture radar, the object of attitude guiding normally reduces Doppler frequency.The attitude guidance method that current LEOSAR is conventional has one dimension Yaw steering and complete zero Doppler to guide, and the former can reduce Doppler frequency, and the latter can make Doppler frequency be zero.In GEOSAR, Yaw steering effectively can reduce the deterioration of ground range resolution, but required guiding angle is large, high to the requirement of platform stance control system.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, less attitude guiding angle can be utilized 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 the 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; for the position angle of 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 _sto the derivative of 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 determination top optimization direction angle:

Solve draw top optimization direction angle for

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

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

According to the guidance mode of pitching after first roll, then roll guiding angle θ _r, pitching guiding angle θ _pbe respectively

According to the guidance mode of roll after first pitching, then 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:

When the present invention utilizes distance resolution ellipse area minimum, ground range resolution is optimum, calculate the top optimization direction angle of optimum ground range resolution, then guided by pitching roll or roll pitching guiding make direction, place, beam position top optimization direction angle, complete the guiding of optimal resolution attitude, attitude steering 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 adopting first roll changes.

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

Fig. 5 is distance ambiguity function after attitude guiding.

Embodiment

To develop simultaneously embodiment below in conjunction with accompanying drawing, describe the present invention.

The invention provides a kind of spaceborne geostationary orbit synthetic-aperture radar attitude guidance method, first differentiate the expression formula of ellipse area according to the condition acquisition satellite velocities directions such as known orbit parameter, downwards angle of visibility and distance.Then base area is apart from the expression formula differentiating ellipse area, solves the top optimization direction angle realized needed for minimum resolution ellipse area.Finally, guided by pitching roll or roll pitching guiding make direction, place, beam position above-mentioned top optimization direction angle, as shown in Figure 1.Concrete steps are as follows.

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

Step 1.1, determines satellite velocities direction.

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

Under earth fixed coordinate system, the direction of satellite velocities can use crab angle φ and angle of pitch α to represent, crab angle φ and angle of pitch α computing formula 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 _sto the derivative of 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

Ground range resolution can use the cartographic represenation of area of-3dB resolution ellipse, and its formula is

Wherein, S is the 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 of ECR speed between the projection of surface level, β is downwards angle of visibility, position angle determine according to the beam position of reality 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.

Angle of squint γ and position angle between there is following relation:

Thus, ground range resolution area can be expressed as

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

If ground range resolution area is minimum, demand fulfillment 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 is looked, and negative sign represents that left side is looked.

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 the rotation matrix of attitude guiding correspondence.

According to the strategy of pitching after first roll, rotation matrix can be expressed as

Wherein, θ _rfor roll guiding angle, θ _pfor pitching guiding angle.Rotation matrix is substituted into equation (11), solving equation (11) can obtain attitude steering angle and be

According to the strategy of roll after first pitching, rotation matrix can be expressed as

$A=\left[\begin{array}{ccc}\cos {\mathrm{\&theta;}}_R& \sin {\mathrm{\&theta;}}_P\sin {\mathrm{\&theta;}}_R& -\cos {\mathrm{\&theta;}}_P\sin {\mathrm{\&theta;}}_R\\ 0& \cos {\mathrm{\&theta;}}_P& \sin {\mathrm{\&theta;}}_P\\ \sin {\mathrm{\&theta;}}_R& -\sin {\mathrm{\&theta;}}_P\cos {\mathrm{\&theta;}}_R& \cos {\mathrm{\&theta;}}_P\cos {\mathrm{\&theta;}}_R\end{array}\right]---\left(14\right)$

Rotation matrix substitutes into equation (11), and solving equation (11) can obtain attitude steering angle and be

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

Satellite transit 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.As shown in Figure 3, the angle of pitch as shown in Figure 4 for roll angle needed for attitude guiding.Ground range resolution ambiguity function after attitude guides as shown in Figure 5.From Fig. 3, Fig. 4, the attitude steering angle needed for geostationary orbit synthetic-aperture radar optimal resolution attitude guidance method is less.As shown in Figure 5, after carrying out the guiding of geostationary orbit synthetic-aperture radar optimal resolution attitude, it is vertical that distance differentiates 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 amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (1)

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

Step 1, definitely apart from differentiating ellipse area:

Wherein, S is the 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; for the position angle of radar;

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

Wherein, sign () is sign function, can be expressed as $sign\left(x\right)=\left\{\begin{array}{cc}1& x>0\\ -1& x<0\end{array}\right.;$

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

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 _sto the derivative of 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 determination top optimization direction angle:

Solve draw top optimization direction angle for

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

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

According to the guidance mode of pitching after first roll, then roll guiding angle θ _r, pitching guiding angle θ _pbe respectively

According to the guidance mode of roll after first pitching, then roll guiding angle θ _r, pitching guiding angle θ _pbe respectively

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