CN101430379A - Synthetic aperture radar three-dimensional microwave imaging method for circular track of earth synchronization orbit - Google Patents

Abstract

The invention discloses a circular synthetic aperture radar (CSAR) 3D microwave imaging method for an earth synchronous orbit. In the method, parameters of the earth synchronous orbit are designed to cause a synthetic aperture radar (SAR) satellite platform to make a flight with an annular track around a target zone and above the target zone, and an antenna beam is caused to irradiate the target zone all the time by a circular synthetic aperture radar mode, and a ground object target is subject to continuous large-area fixed point observation to acquire high-resolution 3D imaging information of the ground object target. A CSAR system of the earth synchronous orbit provided by the system can acquire high-resolution 3D images of the ground object, solves the problem that the existing space-borne SARs are hard to acquire the high-resolution 3D information of the ground object; and is applicable to areas with complex and steep terrains as elevation information does not interfere with phase ambiguity in the SAR. The CSAR system of the earth synchronous orbit can realize the fixed point continuous observation of large-area zones, and solve the problems that the existing space-borne SARs have small observation zones and long revisit period.

Description

The circular track of earth synchronization orbit synthetic aperture radar three-dimensional microwave imaging method

Technical field

The invention belongs to the synthetic-aperture radar microwave Imaging Technique, relate to satellite-borne synthetic aperture radar three-dimensional microwave imaging method at rail.

Background technology

Compare with other remote sensing means, the synthetic aperture radar (SAR) microwave Imaging Technique has resolution height, round-the-clock, round-the-clock advantage, therefore becomes the important tool of earth observation.Realize that coverage count just must be used satellite-borne SAR over the ground.But present satellite-borne SAR technology in mapping band scope, to the long-time high repeated measures of target, obtain and all have suitable deficiency aspect the three-dimensional information, seriously limited the application of SAR aspect military and civilian.

All be low orbit satellite at the SAR of rail satellite at present.For a fixed area, it is very short that it's the top time is past low orbit satellite, and the time of being observed by SAR often is no more than 1 minute, and the cycle of heavily visiting is very long, reaches tens days even tens days, and this is totally unfavorable for long-time high repeated measures target.

The movement velocity of the relative earth of low orbit satellite is very fast, generally more than 7000 meter per seconds, and the ultimate principle of SAR has determined whenever the pass by distance of a resolution element of SAR will launch pulsatile once at least, and the pulse repetition rate of SAR is just very high like this, usually more than 1500Hz.And for conventional strips S AR, for fear of distance to fuzzy, whole distance will receive between two pulses to the echo of mapping band, so the distance of SAR is just very limited to the mapping width, and distance approximately is the 100km magnitude to the mapping bandwidth under the intermediate resolution situation.

At present the satellite-borne SAR at rail does not have the ability of obtaining the high resolving power elevation information in real time, and the quantity of information that this can reduce target is difficult to estimate the volume and the tonnage of target.Some researchist adopts heavy rail interference SAR satellite to obtain the atural object elevation information, but the cycle of satellite heavy rail reaches tens days even tens days, can only obtain the elevation information of throughout the year constant or gradual target, often can only be applied in the limited application such as the monitoring landform is gradual, and precision be very low.The ripe at present technology of obtaining elevation information is to hand over rail interference SAR (CrossTrack Interference SAR) technology, airborne friendship rail interference SAR technology is comparative maturity, but to realize on satellite that interference SAR need reach tens meters baseline, this is undoubtedly a great challenge to satellite technology, has only the U.S. once to realize the interference SAR (SRTM in 2000) of long baseline at present on space shuttle.In addition, there is the elevation phase fuzzy problem in the interference SAR technology, only is applicable to the gradual zones of landform such as mountain area, is not suitable for the zone of the complicated abrupt change of ground object targets such as city, military base.

How carrying out the continuous monitoring of large tracts of land fixed point over the ground, obtaining the atural object elevation information is the hot issue of SAR research field in recent years, domestic and international many scholars have proposed such as multi-beam wide swath SAR, method and schemes such as low rail satellite-borne SAR formation, however these methods are still not fully up to expectations on to the time coverage of target area and real-time response ability.

Summary of the invention

Existing satellite-borne SAR microwave remote sensing technique exist the observation area area little, heavily the visit cycle long, be difficult to obtain the high-resolution three-dimensional information, and there is phase ambiguity in elevation information, can not be applicable to the problems such as zone of the complicated abrupt change of ground object targets such as city, military base, the objective of the invention is to carry out over the ground the continuous monitoring of large tracts of land fixed point, obtain atural object high-resolution three-dimension information, for this reason, the present invention proposes a kind of large-area three-dimensional microwave imaging method based on circular track of earth synchronization orbit synthetic-aperture radar (Circular SAR is hereinafter to be referred as CSAR).

In order to realize purpose of the present invention, circular track of earth synchronization orbit synthetic-aperture radar large-area three-dimensional microwave imaging method provided by the invention, step comprises:

Step 1: design geostationary orbit parameter makes the Synthetic Aperture Radar satellite platform do annular track flight in overhead surrounding target zone in the target area;

Step 2: adopt circle track synthetic-aperture radar CSAR pattern, make antenna beam shine the target area all the time,, obtain the high resolution three-dimensional imaging information of ground object target to atural object realization of goal large tracts of land fixed point Continuous Observation.

According to embodiments of the invention, the flight path of described satellite is projected as circle in XOY plane, and the semi-major axis a of track, eccentric ratio e, argument of perigee ω, inclination angle i must satisfy:

A ≈ 42164.2km, i=2e, ω=0.5 π or 1.5 π

According to embodiments of the invention, described geostationary orbit CSAR system is at the resolution δ of XOY plane _rFor:

${\mathrm{\δ}}_r\≈\frac{4.8\mathrm{\λ}(a-X_{A0z})}{8\mathrm{\πae}}$

Wherein: the center, target area is at the coordinate X of Z axle _A0z, electromagnetic wavelength λ, the semi-major axis a of track, eccentric ratio e.

According to embodiments of the invention, described geostationary orbit CSAR system is at the resolution δ of Z-direction _zFor:

${\mathrm{\δ}}_z=\frac{c}{2B}$

Wherein: light velocity c, system bandwidth B.

According to embodiments of the invention, pulse repetition rate and the long-pending design criteria of mapping zone face are in the described geostationary orbit CSAR system:

When mapping zone is projected as border circular areas and the satellite flight path is a bowlder at the XOY face in the XOY face, the instantaneous doppler bandwidth of CSAR system satellite around target area one approximate constant in week, this moment is the most favourable to the CSAR system, it is long-pending to obtain maximum mapping zone face with the pulse repetition rate of minimum, at this moment doppler bandwidth B _aJust minimum pulse repetition rate is approximately:

$B_a\≈\frac{8\mathrm{ae}{\mathrm{\ω}}_{e}r}{\mathrm{\λ}(a-X_{A0Z})}$

Wherein: the target area is at XOY face projection radius r, center, the target area coordinate X at the Z axle _A0Z, the semi-major axis a of track, eccentric ratio e, rotational-angular velocity of the earth ω _e, electromagnetic wavelength λ.

According to embodiments of the invention, the maximum of described target area mapping region area S _MaxFor:

$S_{\max }\≈\mathrm{\π}\frac{c}{16\mathrm{ae}{\mathrm{\ω}}_e}\frac{\mathrm{\λ}(a-X_{A0Z})\sin ({\mathrm{\α}}_{\min }+\mathrm{\β})}{\cos {\mathrm{\α}}_{\min }}\frac{R_e}{X_{A0Z}}$

Wherein: the semi-major axis a of light velocity c, track, eccentric ratio e, rotational-angular velocity of the earth ω _e, electromagnetic wavelength λ, center, target area be at the coordinate X of Z axle _A0Z, the minimum grazing angle α on antenna beam and ground in satellite annular one all processes _Min, radar visual angle β, earth radius R _e

According to embodiments of the invention, average power P in the described geostationary orbit CSAR system _aFor:

$P_a=\frac{{\left(4\mathrm{\&pi;}\right)}^3{R}^4\left(k_0{T}_0{F}_{n}L\right)}{{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="A200710176924E00181.png"\; state="\{\{state\}\}">G</figure-callout>}}^2{\mathrm{\&lambda;}}^2{s}_r\stackrel{\&OverBar;}{\mathrm{NE}{\mathrm{\&sigma;}}_0}{T}_s}$

Wherein: system sensitivity

Target oblique distance R, Boltzmann constant K ₀, the receiver absolute temperature T ₀, receiver noise factor F _n, system loss L, antenna gain G, electromagnetic wavelength λ, resolution element area s _r, target area backscattering coefficient σ ₀, synthetic aperture time span T _s, the synthetic aperture time of geostationary orbit CSAR is 1 day=86400 seconds.

The synchronous CSAR of the earth proposed by the invention system can obtain atural object high-resolution three-dimension image, solved the problem that present satellite-borne SAR is difficult to obtain atural object high-resolution three-dimension information, and there is not the phase fuzzy problem in the interference SAR in elevation information, is applicable to the zone of abrupt change with a varied topography; The synchronous CSAR of earth system can realize large area region fixed point Continuous Observation, and it is little to solve present satellite-borne SAR observation area, heavily long problem of visit cycle.

Description of drawings

Fig. 1 is the present invention's circle track synthetic-aperture radar (CSAR) synoptic diagram;

Fig. 2 is the annular flight path of geo-synchronous orbit satellite of the present invention in the ground projection;

Fig. 3 is the locus track of the relative earth of geo-synchronous orbit satellite of the present invention;

Fig. 4 is a target area of the present invention synoptic diagram;

Description of symbols in the accompanying drawing:

The SAR platform---1; The observation area---2;

The satellite motion track is in earth plane projection---and 3;

The antenna beam irradiation area---4; The satellite motion track---5;

The earth---6; The equator---7.

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.

We propose to adopt on geostationary orbit circle track synthetic-aperture radar (Circular SAR is hereinafter to be referred as CSAR) pattern to realize ocean weather station observation over the ground, large area region three-dimensional microwave imaging in the present invention.

As Fig. 1 is that the annular broken of top is SAR platform 1 running orbit, the zone that observation area, below 2 is shone all the time for antenna beam shown in the present invention's circle track synthetic-aperture radar (CSAR) synoptic diagram.The conventional relatively strips S AR pattern of this CSAR mode of operation, length of synthetic aperture is very long, can obtain the full azimuth information of target, therefore, can obtain the horizontal two-dimension image of very high-resolution on surface level, and resolution can reach wavelength magnitude; Because the target focus function of this pattern is relevant with elevation, therefore can obtain elevation information in addition.

CSAR in the resolution of elevation direction (Z-direction) is:

${\mathrm{\&delta;}}_z=\frac{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A200710176924E00181.png"\; state="\{\{state\}\}">c</figure-callout>}}{2\cos \mathrm{\&theta;B}}---\left(1\right)$

Wherein c is the light velocity, and θ is the downwards angle of visibility of radar to target, and B is the radar system bandwidth.

If downwards angle of visibility is 10 °, the elevation resolution that reach 5 meters only needs the bandwidth about 30MHz just passable.

If ignore the decoherence of target in all directions scattering, CSAR theoretical resolution in the horizontal direction is:

${\mathrm{\&delta;}}_h=\frac{4.8\mathrm{\&lambda;}}{4\mathrm{\&pi;}\sin \mathrm{\&theta;}}---\left(2\right)$

Wherein λ is an electromagnetic wavelength, and θ is the downwards angle of visibility of radar to target.

Horizontal resolution is suitable with wavelength magnitude as can be seen from formula (2), even can be less than wavelength, and irrelevant with system bandwidth, need not very high bandwidth and just can obtain high horizontal resolution, we know under same case bandwidth, and the mini system complicacy is low more more, and signal to noise ratio (S/N ratio) is high more.

Because airborne CSAR area coverage is little, low orbit satellite is difficult to obtain the circle flight path again, and therefore, this technology can not get due attention for a long time in the remote sensing field.

The analysis showed that can be so that satellite be done annular flight in the sky, target area by design geostationary orbit parameter, thereby provides possibility for spaceborne CSAR.

The principal element that influences the geosynchronous satellite track has following four:

1) simple harmonic oscillation on the latitude that causes by the satellite orbit orbit inclination;

2) simple harmonic oscillation on the longitude that causes by eccentricity of satellite orbit;

3) linear drift on the longitude that causes by the error of satellite orbit radius;

4) since the satellite that causes of eccentricity of satellite orbit to the simple harmonic oscillation of geocentric distance.

For simplicity, we consider not have perturbation but geo-synchronous orbit satellite when having orbit error, and for desirable geostationary orbit, orbit inclination i is 0, eccentricity e is 0, semi-major axis of orbit a=42164.2km.If there is a less error, orbit inclination is i, and eccentricity is e, and semi-major axis is r=a+d, and then the change in location approximation to function of geosynchronous satellite is:

Y≈ai?sin(s-Ω)

X≈-1.5d(s-s ₀)+2ae?sin(s-Ω-ω) (3)

r＝a+d-ae?cos(s-Ω-ω)

Wherein Y is the displacement of satellite toward the latitude deviation in driction equatorial plane, and X is the displacement that satellite departs from the mean longitude face, and r is that satellite is to geocentric distance, s is the satellite sidereal hour angle, s0 is a satellite initial star hour angle, and Ω is a satellite ascending node equator longitude, and ω is an argument of perigee.From formula (3), control the satellite flight path for the sense of rotation of circle, ellipse and flight path or allow satellite slowly drift about simultaneously by control i, e, orbit parameters such as ω, d as can be seen along the equator.Can draw more complicated flight path if consider some other perturbation factors.

Formula (3) is analyzed and can be known, the projection of satellite transit track 5 on ground is that sub-circular is when satisfying following condition:

D=0, i=2e, e＜＜1, ω=0.5 π or 1.5 π

The ground track that for example will make satellite is that radius moves in a circle with 6160Km, and then inclination angle i ≈ is 8.4 °, and eccentric ratio e ≈ 0.074, ω=90 °, semi-major axis error d=0.With this satellite flight path projection on earth of STK software emulation, as Fig. 2 geo-synchronous orbit satellite shown in the annular flight path of ground projection, the big annular trace suitable with earth size is the projection 3 of satellite motion track 5 on earth plane among the figure, and little annular region is satellite antenna wave beam illumination footprint territory 4.

Because satellite is also done simple harmonic oscillation to the distance in the earth's core, the phase place of its vibration is identical with latitudinal vibration or opposite, therefore, movement locus at the relative earth 6 of space centre halfback's star is an inclination disk, shown in the locus track of the relative earth 6 of Fig. 3 geo-synchronous orbit satellite, shown in the figure be: SAR platform 1, satellite motion track 5, the earth 6 and equator 7, the dotted circle that the left side tilts is the flight path of the relative earth of geo-synchronous orbit satellite.

All target echoes all must receive between two pulse emissions in the mapping band of SAR, so the pulse repetition rate of SAR is high more, and its mapping zone is narrow more.And the pulse repetition rate of SAR simultaneously also be SAR in the orientation to sampling rate, low orbit satellite is because relatively velocity of shuttle flight is very fast, so sampling rate requires very highly, so the mapping region of low orbit satellite is limited, is generally the 100km magnitude.And the relative earth movement velocity of geo-synchronous orbit satellite is low, therefore the orientation can be lower to sampling rate, so geostationary orbit SAR satellite can obtain much larger than the mapping bandwidth of low rail SAR satellite, with L-band SAR is example, can reach thousands of kilometers even higher mapping bandwidth according to a preliminary estimate.

Analysis by front geostationary orbit CSAR satellite as can be seen can realize the large-area three-dimensional imaging, has provided the design criteria of the some key parameters in this system below.

Geostationary orbit Circular SAR key parameter design criteria:

1. resolution is calculated

The position vector of supposing the target A that will focus on is X _A, near another target B A is in X _B=X _A+ d carries out distance after compression to echo, and when target A was focused on, the signal intensity of target B was:

$\mathrm{\&chi;}(X_A,X_B)=\&Integral;\sin c\left[\frac{2B(|X_s\left(t\right)-X_A|-|X_s\left(t\right)-X_B)|}{c}\right]$ (4)

$\exp \{-\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}(|X_s\left(t\right)-X_A|-|X_s\left(t\right)-X_B|)\}\mathrm{dt}$

Wherein B is the radar system bandwidth, and c is the light velocity, X _s(t) put vector for the time displacement of satellite.

Make in formula (3) that semi-major axis error d is 0, because departing from the distance of desirable rest point compares very little at e＜＜1 o'clock satellite position with semi-major axis of orbit, therefore satellite just can be approximated to be satellite at the Z axial coordinate to the distance in the earth's core, and the satellite position vector is approximately like this:

X _s(t)≈[2aesin(ω _et-Ω-ω)，aisin(ω _et-Ω)，a-aecos(ω _et-Ω-ω)]

＝[0，0，a]+a[2esin(ω _et-Ω-ω)，isin(ω _et-Ω)，-ecos(ω _et-Ω-ω)] (5)

＝X _s0+x _s(t)

X wherein _S0=[0,0, a], ω _eBe rotational-angular velocity of the earth, x _s(t) be the relative X of satellite _S0Skew.

$|X_s\left(t\right)-X_A|-|X_s\left(t\right)-X_B|\&ap;\frac{[X_s\left(t\right)-X_A]\&CenterDot;d}{|X_s\left(t\right)-X_A|}---\left(6\right)$

With (6) substitution (4)

$\mathrm{\&chi;}(X_A,X_B)=\&Integral;\sin c\left[\frac{2B}{c}\frac{[X_s\left(t\right)-X_A]\&CenterDot;d}{|X_s\left(t\right)-X_A|}\right]\exp \{-\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\frac{[X_s\left(t\right)-X_A]\&CenterDot;d}{|X_s\left(t\right)-X_A|}\}\mathrm{dt}---\left(7\right)$

Because geostationary orbit is much larger than earth radius, under e＜＜1 situation,

$\frac{X_s\left(t\right)-X_A}{|X_s\left(t\right)-X_A|}$

$=\frac{[x_{\mathrm{sx}}\left(t\right)-X_{\mathrm{Ax}}]\hat{x}+[x_{\mathrm{sy}}\left(t\right)-X_{\mathrm{Ay}}]\hat{y}+[a-X_{\mathrm{Az}}+x_{\mathrm{sz}}\left(t\right)]\hat{z}}{\sqrt{{(a-X_{\mathrm{Az}})}^2+{x_{\mathrm{sz}}}^2\left(t\right)+2(a-X_{\mathrm{Az}})x_{\mathrm{sz}}\left(t\right)+{[x_{\mathrm{sx}}\left(t\right)-X_{\mathrm{Ax}}]}^2+{[x_{\mathrm{sy}}\left(t\right)-X_{\mathrm{Ay}}]}^2}}---\left(8\right)$

$\&ap;\frac{[x_{\mathrm{sx}}\left(t\right)-X_{\mathrm{Ax}}]\hat{x}+[x_{\mathrm{sy}}\left(t\right)-X_{\mathrm{Ay}}]\hat{y}+[a-X_{\mathrm{Az}}+x_{\mathrm{sz}}\left(t\right)]\hat{z}}{(a-X_{\mathrm{Az}})[1+\frac{{[x_{\mathrm{sx}}\left(t\right)-X_{\mathrm{Ax}}]}^2+{[x_{\mathrm{sy}}\left(t\right)-X_{\mathrm{Ay}}]}^2}{2{(a-X_{\mathrm{Az}})}^2}+\frac{x_{\mathrm{sz}}\left(t\right)}{(a-X_{\mathrm{Az}})}]}$

Wherein: Be X, Y, Z-direction unit vector, x _Sx(t), x _Sy(t), x _Sz(t) be x _s(t) x _s(t) X, Y, Z axle component, X _Ax, X _Ay, X _AzBe X _AX, Y, Z axle component.

Ignore $\frac{{[x_{\mathrm{sx}}\left(t\right)-X_{\mathrm{Ax}}]}^2+{[x_{\mathrm{sy}}\left(t\right)-X_{\mathrm{Ay}}]}^2}{2{(a-X_{\mathrm{Az}})}^2},\frac{{x_{\mathrm{sz}}}^2\left(t\right)}{(a-X_{\mathrm{Az}})},$

$\frac{x_{\mathrm{sz}}\left(t\right)[x_{\mathrm{sx}}\left(t\right)-X_{\mathrm{Ax}}]}{(a-X_{\mathrm{Az}})},$

Formula (8) can be approximated to be:

When target B in the XOY face, depart from one of A little apart from dr, at this moment

Wherein

Be AB line and X-axis angle, like this:

Wherein:

When $\mathrm{dr}<<\frac{c}{2B},$ Formula can be approximated to be:

$\mathrm{\&chi;}(X_A,X_B)\&ap;\&Integral;\exp \left\{\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="A200710176924E00191.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\frac{X_A\&CenterDot;d}{a-X_{\mathrm{Az}}}[1-\frac{x_{\mathrm{sz}}\left(t\right)}{a-X_{\mathrm{Az}}}]\right\}$

(12)

J wherein ₀[] is 0 rank Bessel's function, and the resolution in XOY plane is like this:

X wherein _A0zFor the center, target area will make the resolution unanimity of XOY plane all directions at the coordinate of z axle, then

Must satisfy between orbital eccentricity e, argument of perigee ω, the inclination angle i like this:

I=2e, e＜＜1, ω=0.5 π or 1.5 (15)

With formula (15) substitution, this moment, the resolution of XOY plane was:

${\mathrm{\&delta;}}_r\&ap;\frac{4.8\mathrm{\&lambda;}(a-X_{A0z})}{8\mathrm{\&pi;ae}}---\left(16\right)$

When target B Z-direction depart from one of A little apart from dr, i.e. d=[0,0, dr], at this moment,

[X _s(t)-X _A]d≈dr (17)

Substitution formula (7) can get:

$\mathrm{\&chi;}(X_A,X_B)=\&Integral;\sin c\left(\frac{2B}{c}\mathrm{dr}\right)\exp (-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="A200710176924E00191.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\mathrm{dr})\mathrm{dt}\&ap;T_s\exp (-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="A200710176924E00191.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\mathrm{dr})\sin c\left(\frac{2B}{c}\mathrm{dr}\right)---\left(18\right)$

Therefore at the resolution δ of Z-direction _zFor:

${\mathrm{\&delta;}}_z\&ap;\frac{c}{2B}---\left(19\right)$

2. PRF (pulse repetition rate) and mapping area design criterion

The pulse repetition rate of SAR be exactly the orientation of SAR to sample frequency, it must satisfy sampling thheorem, just sample frequency must be greater than the orientation to bandwidth.The residing position of hypothetical target is X _A, satellite position is X _s(t), phase of echo then

For:

Then the instantaneous frequency f of phase place (t) is:

Formula (9) substitution can be got:

$f\left(t\right)=\frac{2}{\mathrm{\&lambda;}}\{\frac{[x_{\mathrm{sx}}\left(t\right)-X_{\mathrm{Ax}}]\hat{x}+[x_{\mathrm{sy}}\left(t\right)-X_{\mathrm{Ay}}]\hat{y}}{(a-X_{\mathrm{Az}})}+\hat{z}\}\&CenterDot;X_s^{\&prime;}\left(t\right)$ (22)

$=\frac{2}{\mathrm{\&lambda;}}\{[\frac{x_{\mathrm{sx}}\left(t\right)\hat{x}+x_{\mathrm{sy}}\left(t\right)\hat{y}}{a-X_{\mathrm{Az}}}+\hat{z}]\&CenterDot;X_s^{\&prime;}\left(t\right)-\left[\frac{X_{\mathrm{Ax}}+X_{\mathrm{Ay}}}{a-X_{\mathrm{Az}}}\right]\&CenterDot;X_s^{\&prime;}\left(t\right)\}$

Work as X _AWhen the position traveled through whole target area, the difference of the minimum and maximum value of f (t) was Doppler's instant bandwidth.Obviously working as the target area is a border circular areas on the XOY projecting plane, and satellite flight path X _s(t) also be that a bowlder Doppler instant bandwidth will be similar to and remain unchanged in the projection of XOY face, this moment is the most favourable to the CSAR system, and it is long-pending to obtain maximum mapping zone face with the pulse repetition rate of minimum.

The hypothetical target zone is at the XOY circle that to be projected as a radius be r promptly:

X wherein _A0x, X _A0yBe the coordinate of center, target area in X, Y-axis, doppler bandwidth B like this _aFor:

$B_a\&ap;\frac{8\mathrm{ae}{\mathrm{\&omega;}}_{e}r}{\mathrm{\&lambda;}(a-X_{A0Z})}---\left(24\right)$

Wherein r is the target area at XOY face projection radius, center, the target area coordinate X at the Z axle _A0z, the semi-major axis a of track, eccentric ratio e, rotational-angular velocity of the earth ω _e, electromagnetic wavelength λ.

Synthetic-aperture radar is with pulse mode work, and the echo of whole mapping region must be returned between two subpulses, and just mapping band oblique distance scope must satisfy:

$R_{\max }-R_{\min }<\frac{c}{2B_a}---\left(25\right)$

Suppose in satellite annular one all processes that the minimum grazing angle with ground is α _Min, β is that antenna beam and ground grazing angle are α _MinThe time correspondence the radar visual angle, shown in the synoptic diagram of Fig. 4 target area of the present invention, SAR platform 1, observation area 2, satellite motion track 5, the earth 6 and equator 7 have been shown.

Then the target area radius that projects to the XOY face is to the maximum:

$r<\frac{c}{2B_a}\frac{\sin ({\mathrm{\&alpha;}}_{\min }+\mathrm{\&beta;})}{\cos {\mathrm{\&alpha;}}_{\min }}---\left(26\right)$

With formula (24) substitution formula (26), can get:

$r<\sqrt{\frac{c}{16\mathrm{ae}{\mathrm{\&omega;}}_e}\frac{\mathrm{\&lambda;}(a-X_{A0z})\sin ({\mathrm{\&alpha;}}_{\min }+\mathrm{\&beta;})}{\cos {\mathrm{\&alpha;}}_{\min }}}---\left(27\right)$

Maximum mapping region area is approximately:

$S_{\max }\&ap;\mathrm{\&pi;}\frac{c}{16\mathrm{ae}{\mathrm{\&omega;}}_e}\frac{\mathrm{\&lambda;}(a-X_{A0Z})\sin ({\mathrm{\&alpha;}}_{\min }+\mathrm{\&beta;})}{\cos {\mathrm{\&alpha;}}_{\min }}\frac{R_e}{X_{A0Z}}---\left(28\right)$

Wherein

With the circular projection of the XOY face enlarged areas factor to earth surface, c is that the light velocity, a are that semi-major axis, the e of track is excentricity, ω _eFor earth order tarnsition velocity, λ are electromagnetic wavelength, X _A0zBe coordinate, the α of center, target area at the Z axle _MinBe the minimum grazing angle on antenna beam and ground in satellite annular one all processes, β is that antenna beam and ground grazing angle are α _MinThe time correspondence the radar visual angle, R _eBe earth radius.

With L-band SAR is example, and wavelength is 0.25 meter, and longitude centroid is identical with the satellite mean longitude in the target area, and latitude is 0 o'clock, is 0.5 meter if require XOY face resolution, and then eccentricity of satellite orbit e is:

$e=\frac{4.8\mathrm{\&lambda;}(a-R_e)}{8\mathrm{\&pi;}{\mathrm{a\&delta;}}_h}=0.0811---\left(29\right)$

So minimum grazing angle and visual angle thereof are:

Therefore maximum mapping zone radius is:

$r<\sqrt{\frac{c}{16\mathrm{ae}{\mathrm{\&omega;}}_e}\frac{\mathrm{\&lambda;}(a-X_{A0z})\sin ({\mathrm{\&alpha;}}_{\min }+\mathrm{\&beta;})}{\cos {\mathrm{\&alpha;}}_{\min }}}=1801\mathrm{km}---\left(31\right)$

Maximum mapping area is:

$r_{\max }={\mathrm{\&pi;<figure-callout\; id="2"\; label="r\; max"\; filenames="A200710176924E00181.png"\; state="\{\{state\}\}">r</figure-callout>}}_{\max }^{}=1.02*{10}^7{\mathrm{km}}^2---\left(32\right)$

3. transmission power estimation criteria

Radar equation is:

$\mathrm{SNR}=\frac{{\mathrm{<figure-callout\; id="2"\; label="P\; t\; G"\; filenames="A200710176924E00181.png"\; state="\{\{state\}\}">P</figure-callout>}}_t{G}^{}{}^2{\mathrm{\&lambda;}}^2\mathrm{\&sigma;}}{{\left(4\mathrm{\&pi;}\right)}^3{R}^4\left(k_0{T}_0{\mathrm{BF}}_{n}L\right)}---\left(33\right)$

P wherein _tFor antenna peak power, G are that antenna gain, λ are that wavelength, σ are for the target area backscattering cross is long-pending, R is target oblique distance, k ₀Be Boltzmann constant, T ₀For receiver absolute temperature, B are that receiver bandwidth, L are system loss, F _nBe receiver noise factor.

To compression, the multiple that signal to noise ratio (S/N ratio) improves is through distance:

N _r＝BT _p (34)

T wherein _pBe the duration of pulse;

To synthetic aperture, the multiple that signal to noise ratio (S/N ratio) improves is through the orientation:

SNR _a＝F _rT _s (35)

F wherein _rBe pulse repetition rate, T _sBe the synthetic aperture time span, for geostationary orbit CSAR its synthetic aperture time be 1 day be T _s=24 * 3600 seconds.

The signal to noise ratio (S/N ratio) of final goal is:

$\frac{S}{N}=\frac{P_a{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="A200710176924E00181.png"\; state="\{\{state\}\}">G</figure-callout>}}^2{\mathrm{\&lambda;}}^2{s}_r{\mathrm{\&sigma;}}_0{T}_s}{{\left(4\mathrm{\&pi;}\right)}^3{R}^4\left(k_0{T}_0{F}_{n}L\right)}---\left(36\right)$

P wherein _a=P _tT _pF _rBe average power, s _rBe the resolution element area.

Therefore, the computing formula of power is:

$P_a=\frac{{\left(4\mathrm{\&pi;}\right)}^3{R}^4\left(k_0{T}_0{F}_{n}L\right)}{{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="A200710176924E00181.png"\; state="\{\{state\}\}">G</figure-callout>}}^2{\mathrm{\&lambda;}}^2{s}_r\stackrel{\&OverBar;}{\mathrm{NE}{\mathrm{\&sigma;}}_0}{T}_s}---\left(37\right)$

Wherein

Be system sensitivity, the scattering coefficient of correspondence when system signal noise ratio is 0dB just, R is the target oblique distance, K ₀Be Boltzmann constant, T ₀Be receiver absolute temperature, F _nBe receiver noise factor, L is system loss, and G is an antenna gain, and λ is an electromagnetic wavelength, s _rBe resolution element area, σ ₀Be target area backscattering coefficient, T _sBe the synthetic aperture time span, the synthetic aperture time of geostationary orbit CSAR is 1 day=86400 seconds.

Implementation step:

Can draw design geostationary orbit Circular SAR system according to top analysis

The step of parameter:

1. determine XOY face resolution, Z axle resolution, mapping coverage and the system sensitivity of requirement according to application requirements;

2. determine orbital eccentricity according to XOY face resolution and formula (16);

3. determine orbit inclination and argument of perigee according to orbital eccentricity and formula (15);

4. determine system bandwidth according to Z axle resolution and formula (19);

5. determine the minimum pulse repetition frequency that Circular SAR needs according to formula (24);

6. determine the maximum radius of mapping zone according to formula (27) in the projection of XOY face;

7. determine the average power of system according to system sensitivity formula (37).

Actual SAR systematic parameter design is very complicated process, and its intermediate-resolution, mapping area, system sensitivity etc. all are the indexs of mutual restriction, and the compromise that needs to carry out repeatedly in conjunction with application demand in the design is considered.

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 (7)

1, the circular track of earth synchronization orbit synthetic aperture radar three-dimensional microwave imaging method is characterized in that, step is as follows:

Step 1: design geostationary orbit parameter makes satellites with synthetic aperture radar satellite platform do annular track flight in overhead surrounding target zone in the target area;

Step 2: adopt circle track synthetic-aperture radar (CSAR) pattern, make antenna beam shine the target area all the time,, obtain the high resolution three-dimensional imaging information of ground object target to atural object realization of goal large tracts of land fixed point Continuous Observation.

2, according to the described circular track of earth synchronization orbit synthetic aperture radar three-dimensional microwave imaging method of claim 1, it is characterized in that, the flight path of described satellite is at the circle that is projected as of XOY plane, and the semi-major axis a of track, eccentric ratio e, argument of perigee ω, inclination angle i must satisfy:

A ≈ 42164.2km, i=2e, ω=0.5 π or 1.5 π.

According to the described circular track of earth synchronization orbit synthetic aperture radar three-dimensional microwave imaging method of claim 1, it is characterized in that 3, described geostationary orbit CSAR system is at the resolution δ of XOY plane _rFor:

${\mathrm{\&delta;}}_r\&ap;\frac{4.8\mathrm{\&lambda;}(a-X_{A0Z})}{8\mathrm{\&pi;ae}}$

Wherein: the center, target area is at the coordinate X of Z axle _A0z, electromagnetic wavelength λ, the semi-major axis a of track, eccentric ratio e.

According to the described circular track of earth synchronization orbit synthetic aperture radar three-dimensional microwave imaging method of claim 1, it is characterized in that 4, described geostationary orbit CSAR system is at the resolution δ of Z-direction _zFor:

${\mathrm{\&delta;}}_z=\frac{c}{2B}$

Wherein: light velocity c, system bandwidth B.

According to the described circular track of earth synchronization orbit synthetic aperture radar three-dimensional microwave imaging method of claim 1, it is characterized in that 5, pulse repetition rate and the long-pending design criteria of mapping zone face are in the described geostationary orbit CSAR system:

When mapping zone is projected as border circular areas and the satellite flight path is a bowlder at the XOY face in the XOY face, the instantaneous doppler bandwidth of CSAR system satellite around target area one approximate constant in week, it is long-pending to obtain maximum mapping zone face with the pulse repetition rate of minimum, at this moment doppler bandwidth B _aJust minimum pulse repetition rate is approximately:

$B_a\&ap;\frac{8\mathrm{ae}{\mathrm{\&omega;}}_{e}r}{\mathrm{\&lambda;}(a-X_{A0Z})}$

Wherein: the target area is at XOY face projection radius r, center, the target area coordinate X at the Z axle _A0Z, the semi-major axis a of track, eccentric ratio e, rotational-angular velocity of the earth ω _e, electromagnetic wavelength λ.

6, according to the described circular track of earth synchronization orbit synthetic aperture radar three-dimensional microwave imaging method of claim 1, it is characterized in that the maximum mapping region area S of described target area _MaxFor:

$S_{\max }\&ap;\mathrm{\&pi;}\frac{c}{16\mathrm{ae}{\mathrm{\&omega;}}_e}\frac{\mathrm{\&lambda;}(a-X_{A0Z})\sin ({\mathrm{\&alpha;}}_{\min }+\mathrm{\&beta;})}{\cos {\mathrm{\&alpha;}}_{\min }}\frac{R_e}{X_{A0Z}}$

Wherein: the semi-major axis a of light velocity c, track, eccentric ratio e, rotational-angular velocity of the earth ω _e, electromagnetic wavelength λ, center, target area be at the coordinate X of Z axle _A0Z, the minimum grazing angle α on antenna beam and ground in satellite annular one all processes _Min, radar visual angle β, earth radius R _e

7, according to the described circular track of earth synchronization orbit synthetic aperture radar three-dimensional microwave imaging method of claim 1, it is characterized in that average power P in the described geostationary orbit CSAR system _aFor:

$P_a=\frac{{\left(4\mathrm{\&pi;}\right)}^3{R}^4\left(k_0{T}_0{F}_{n}L\right)}{G^2{\mathrm{\&lambda;}}^2{s}_r\stackrel{\&OverBar;}{\mathrm{NE}{\mathrm{\&sigma;}}_0}{T}_s}$

Wherein: system sensitivity

Target oblique distance R, Boltzmann constant K ₀, the receiver absolute temperature T ₀, receiver noise factor F _n, system loss L, antenna gain G, electromagnetic wavelength λ, resolution element area s _r, target area backscattering coefficient σ ₀, synthetic aperture time span T _s, the synthetic aperture time of geostationary orbit CSAR is 1 day=86400 seconds.

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