CN102346249B - Implementation method for wide swath earth observation step scanning mode of synthetic aperture radar - Google Patents

Abstract

The invention discloses an implementation method for a wide swath earth observation step scanning mode of a synthetic aperture radar, and relates to a synthetic aperture radar technique. In each sub-band, an antenna is along a track direction in azimuth direction, performs step scanning from back to front and receives returning waves, and the resolution ratio is changed by controlling the azimuth scanning speed of the antenna; and after the sub-band is scanned, in range direction, the beam position is switched to ensure that the antenna illuminates different sub-bands so as to realize wide swath. By the implementation method, the scallop effect of a normal scanning (ScanSAR) mode is obviously improved, and the azimuth resolution, the fuzzy ratio and the noise equivalent coefficients in a whole scene are uniform. When the scanning capacity of the antenna is strong, by the wide swath earth observation step scanning mode, a resolution ratio which is superior to that of the ScanSAR mode can be acquired.

Description

The implementation method of synthetic-aperture radar wide swath earth observation step-scan pattern

Technical field

The present invention relates to the Synthetic Aperture Radar Technique field, be a kind of synthetic-aperture radar (Synthetic Aperture Radar, the implementation method of SAR) high resolving power wide swath earth observation step-scan (Terrain Observation by Progressive Scans:TOPS) pattern abbreviates the TOPSAR pattern as.Fundamental purpose is when keeping scanning (ScanSAR) pattern advantage, overcomes the shortcoming of ScanSAR pattern.

Background technology

Synthetic aperture radar (SAR) has round-the-clock, round-the-clock imaging characteristics has a wide range of applications in national economy and national defence field.As a kind of imaging radar, improving the mapping bandwidth is pursuing one's goal of SAR.The ScanSAR pattern can improve mapping band fabric width under the prerequisite of sacrificing resolution, realize observation on a large scale.ScanSAR utilizes periodically conversion distance to antenna beam, makes it point to several subbands, obtains wide mapping band and covers; Simultaneously wide distance will make low orbit satellite shorten and heavily visit the time to covering.These advantages of ScanSAR have had widely it and use, but under many circumstances, the shortcoming of ScanSAR has hindered its application.ScanSAR mainly contains two aspect shortcomings, and the firstth, there is the scallop effect in magnitude image, makes that the ScanSAR calibration is very difficult; The secondth, resolution, fuzzy ratio and equivalent noise scattering coefficient are inhomogeneous, change with the orientation.Though look number by increasing, the problems referred to above are easier to solve more, and geometric resolution will reduce same multiple.

The TOPSAR pattern is a kind of new high resolving power wide swath imaging pattern, and is identical with ScanSAR, has mapping bandwidth, characteristics that heavily visit rate is low, but remedied the inherent defect of ScanSAR pattern simultaneously.It has eliminated the scallop effect, obtains uniform noise equivalent coefficient and resolution at whole sub-swaths; It has stronger fuzzy inhibition ability, obtains uniform blur level at whole sub-swaths; Because subband is longer, its rim effect loss is littler.These characteristics make TOPSAR not reducing resolution even improving under the situation of resolution, obtain better picture quality.These characteristics make TOPSAR have widely and use, become preferred version in the high resolving power wide swath is used.

Realize spaceborne TOPSAR pattern at present in the world, obtained TOPSAR image and the ScanSAR image of areal as the TerraSAR-X of Germany, demonstrated fully the advantage of TOPSAR; Following Sentinel-1 also with the TOPSAR pattern as the groundwork pattern.In China, do not possess the SAR satellite of TOPSAR function at present.In 2009, the electron institute carried out first to this pattern that airborne school flies, and has obtained lot of data, has realized the TOPSAR function, has obtained preferable image.

Summary of the invention

The implementation method that the purpose of this invention is to provide a kind of synthetic-aperture radar wide swath earth observation TOPS pattern, to overcome the deficiency that the ScanSAR pattern is used, this method for designing is applied in carried SAR.

For achieving the above object, technical solution of the present invention is:

A kind of implementation method of synthetic-aperture radar wide swath earth observation TOPS pattern, its in each subband, antenna in the orientation to along trajectory direction, from after scan and receive echo forward, change resolution by the control antenna orientation to sweep velocity; Behind the subband end of scan, distance to, point to by switching-beam and to make the subband that antenna irradiation is different, to realize wide swath.

The implementation method of described synthetic-aperture radar wide swath earth observation TOPS pattern, its concrete steps are as follows:

A) input pointer: total fabric width and systemic resolution are with in mapping;

B) require and the actual antennas size according to input pointer, determine the azimuthal resolution that can reach and the fabric width of each subband when wave beam does not scan;

C) be with total fabric width according to subband azimuthal resolution, fabric width and mapping, determine number of sub-bands, then according to the antenna scanning ability, optimization system resolution;

D) determine sweep time, the scanning angle of wave beam by primary Calculation;

E) according to scan capability and the stepping characteristic of antenna, further accurate Calculation above-mentioned parameter is to satisfy the ability need of antenna actual scanning;

F) carry out parameter and adjust, if the requirement of discontented toe mark, according to step a)～e) recomputate each parameter, up to satisfying index request; Then according to the orientation that calculates to the scan angle scope, on the SAR platform, progressively regulate the orientation with certain step interval and point to beam center, make its from negative orientation to scan angle, scan positive orientation and finish to scan angle;

G) behind subband end of scan, regulate antenna distance to beam position to next subband, according to design parameter, still progressively regulate the orientation with certain step interval and point to beam center, make its from negative orientation to scan angle, scan positive orientation and finish to scan angle;

H) subband behind the end of scan, comes back to first subband one by one, and circulation is carried out.

The implementation method of described synthetic-aperture radar wide swath earth observation TOPS pattern, its described e) in the step, the scan characteristic of antenna need be according to stepping characteristic and the scan capability of antenna, and further each parameter of accurate Calculation comprises that step is as follows:

1. according to antenna stepping angle, the initial count value of antenna scan angle upwards is grouped into the scanning angle that antenna can reach, as antenna actual scanning angle;

2. calculate antenna scan angle poor of antenna actual scanning angle and primary Calculation;

3. according to antenna actual scanning angle, the resident umber of pulse of each stepping when calculating actual scanning;

4. calculate the actual residence time of each subband;

5. calculate the actual scanning cycle;

6. calculate each subband antenna effective scanning track;

7. computing platform movement locus in a scan period;

8. calculate residence time poor of the actual residence time of each subband and each subband primary Calculation, and will add up the mistiming.

The implementation method of described synthetic-aperture radar wide swath earth observation TOPS pattern, its described f) in the step, carrying out parameter adjusts, if can both satisfying antenna effective scanning track, each subband is greater than or equal to platform at a scan period movement locus, the parameter that obtains in the parameter accurate Calculation is exactly final practical flight parameter, resolution requirement can be satisfied, the TOPSAR pattern can be used for realizing; If can not satisfy, can cause occurring the zone that resolution reduces along the orientation to track, concrete solution is as follows:

1. recomputate time margin;

2. time margin is brought in the computing formula, is obtained new parameter through primary Calculation, then repeating step e) and f).

The invention has the beneficial effects as follows, obviously improved the scallop effect of ScanSAR pattern, the azimuthal resolution in the whole scene, fuzzy ratio and noise equivalent coefficient all compare evenly.When the scan capability of antenna is strong, can obtain to be better than the resolution of ScanSAR pattern.

Description of drawings

Fig. 1 is the implementation method process flow diagram of synthetic-aperture radar wide swath earth observation TOPS pattern of the present invention.

Fig. 2 is TOPSAR model resolution calculation flow chart of the present invention;

Fig. 3 is TOPSAR mode parameter primary Calculation process flow diagram of the present invention;

Fig. 4 is TOPSAR mode parameter accurate Calculation process flow diagram of the present invention;

Fig. 5 is that TOPSAR mode parameter of the present invention is adjusted process flow diagram.

Embodiment

The implementation method of a kind of synthetic-aperture radar wide swath earth observation TOPS pattern of the present invention, in each subband, antenna in the orientation to along trajectory direction, from after scan and receive echo forward, change resolution by the control antenna orientation to sweep velocity; Behind the subband end of scan, distance to, point to by switching-beam and to make the subband that antenna irradiation is different, to realize wide swath.

Accompanying drawing 1 is seen in concrete operations, comprise: total fabric width, systemic resolution and actual antennas size are with in the mapping according to basic input parameters (comprising: earth radius, podium level, platform speed, time margin, subband beam center geocentric angle) and requirement, determine azimuthal resolution and the fabric width of each subband when antenna does not scan, and then definite number of sub-bands.After satisfying the azimuthal resolution restrictive condition, according to the actual antennas scan capability, can optimization system resolution, i.e. antenna scanning ability is strong, and resolution can improve, on the contrary then resolution must reduce.

After having determined resolution, by the parameter primary Calculation, determine residence time, the scanning angle of each subband.Primary Calculation result does not consider actual antennas scanning quantification problem, but directly calculates according to formula, is a kind of idealized design to the antenna scanning ability.Need be according to the scan capability of antenna and the stepping characteristic of antenna, further each parameter of accurate Calculation.After the accurate Calculation, carry out parameter and adjust, if the requirement of discontented toe mark need be recomputated.If satisfy index request, according to the orientation that calculates to the scan angle scope, on the SAR platform, progressively regulate the orientation with certain step interval and point to beam center, make its from negative orientation to scan angle, progressively scan positive orientation and finish to scan angle.Behind the subband end of scan, regulate antenna distance to beam position, make wave beam shine next subband, according to design parameter, still progressively regulate the orientation with certain step interval and point to beam center, make its from negative orientation to scan angle, finish to scan angle to positive orientation.Subband behind the end of scan, comes back to subband 1 one by one.

The implementation method of a kind of TOPSAR pattern of the present invention, it is synthetic aperture radar (SAR) imaging implementation method, be applied to the SAR imaging field, its fundamental purpose is: overcome the intrinsic defective of traditional wide swath ScanSAR pattern, improve SAR picture quality and using value.

No longer use ScanSAR mode computation formula and come computer azimuth resolution, but according to the geometric relationship of TOPSAR pattern, compromise consideration azimuthal resolution, antenna bearingt scanning angle, the restriction relation of antenna subband between sweep time obtain the resolution that is better than the ScanSAR pattern.It is identical with the ScanSAR pattern that the TOPSAR pattern distance points to the control implementation to beam center, and it is opposite with the SAR beam bunching mode that the control implementation is pointed to beam center in the orientation.Specifically may further comprise the steps:

(1) resolution is determined

Total mapping band fabric width, systemic resolution index, actual antennas size and basic parameter as requested (comprising: earth radius, podium level, platform speed, time margin, subband beam center geocentric angle) determined azimuthal resolution and fabric width when each subband does not scan.The subband azimuthal resolution is:

ρ _a＝k ₁·k ₀·Da/2

In the formula, ρ _aBe the subband azimuthal resolution, Da be antenna bearingt to size, k ₀Be the orientation to the ceofficient of spread of antenna beamwidth, not during broadening, k ₀=0.886, k ₁It is the ceofficient of spread that various errors cause, comprise: the orientation is to imaging processing weighting ceofficient of spread, the broadening factor that the doppler frequency rate error causes, the amplitude weighting ceofficient of spread that the orientation is brought to the field strength distribution characteristic, and the ceofficient of spread that causes of various errors such as propagated error, quantization error, difference error.

According to subband fabric width and total fabric width, determine number of sub-bands.Then according to subband azimuthal resolution, number of sub-bands, in conjunction with antenna scanning ability optimization system azimuthal resolution.Process flow diagram as shown in Figure 2.The azimuthal resolution of TOPSAR pattern azimuthal resolution and subband satisfies following relation:

ρ _Tops＞N·ρ _strip

Wherein, ρ _TopsBe azimuthal resolution, N is number of sub-bands, ρ _StripBe the azimuthal resolution of each subband when not scanning.By following formula as seen, as long as the azimuthal resolution of TOPSAR pattern is the azimuthal resolution when not scanning greater than N subband doubly; And ScanSAR pattern azimuthal resolution must be greater than or equal to N+1 subband azimuthal resolution doubly, so the relative ScanSAR pattern of TOPSAR pattern azimuthal resolution azimuthal resolution increases.TOPSAR pattern distance resolution determines that method is identical with the ScanSAR pattern.

(2) parameter primary Calculation

Determined after the azimuthal resolution that calculate other parameter below, process flow diagram is seen Fig. 3.Not considering actual antennas scanning quantification problem during primary Calculation, directly calculate according to formula, is Utopian result of calculation.At first with formula

$R_c^{\left(n\right)}=\sqrt{{(R_e+H)}^2+{R_e}^2-2\·R_e\·(R_e+H)\·\cos \left({\mathrm{\β}}^{\left(n\right)}\right)}$

Calculate the center oblique distance of each subband.In the formula,

Be n subband center oblique distance, n=1,2 ..., N, N are total sub band number, R _eBe earth radius, H is podium level, β ⁽ⁿ⁾Be n subband beam center geocentric angle.

Then with formula

$k_{\mathrm{\ω}}^{\left(n\right)}=({\mathrm{\ρ}}_{\mathrm{Tops}}/{\mathrm{\ρ}}_{\mathrm{strip}}-1)\·\frac{V_s}{R_c^{\left(n\right)}}$

Calculate antenna scanning angular velocity.In the formula, Be subband antenna scanning angular velocity, V _sIt is the relative velocity on platform and ground.

With formula

${\mathrm{\θ}}_0^{\left(n\right)}=k_0\·\mathrm{\λ}/\mathrm{Da}$

Calculate the subband orientation to beam angle.In the formula,

Be the orientation to beam angle, λ is wavelength.

With the formula group

$\left(\right|k_{\mathrm{\ω}}^{\left(n\right)}|T_B^{\left(n\right)}-{\mathrm{\θ}}_0^{\left(n\right)})R_c^{\left(n\right)}+V_s{T}_B^{\left(n\right)}=V_s{T}_R$

$T_R=T_B^{\left(1\right)}+T_B^{\left(2\right)}\·\·\·+T_B^{\left(n\right)}+T_G$

Calculate the residence time of subband Wherein

Be the subband beam angle, Be the subband residence time, T _RBe the scan period, T _GIt is time margin.During primary Calculation, T _G=T _G0, T _G0It is the time margin of changing between the subband.Total N+1 equation in this group formula.

With formula

${\mathrm{\θ}}^{\left(n\right)}=\frac{k_{\mathrm{\ω}}^{\left(n\right)}\·T_B^{\left(n\right)}}{2}$

Calculate the azimuth scan angle of each subband.In the formula, θ ⁽ⁿ⁾It is the azimuth scan angle of subband.

With formula

L _airborne＝V _s·T _R

Calculate one-period inner platform movement locus length.In the formula, L _AirborneBe one-period inner platform movement locus length.

Having provided the primary Calculation result above, is the Utopian design result of antenna, does not consider actual antennas control situation.

(3) parameter accurate Calculation

For phased array antenna, adopt the step-scan mode, can not accomplish wave beam continuous sweep, can not scan arbitrarily angledly, therefore need be optimized processing to above-mentioned result of calculation, processing flow chart is seen Fig. 4.

Suppose that antenna stepping angle is d θ, formula calculates the actual antennas scanning angle below adopting:

${\mathrm{\θ}}_{\mathrm{real}}^{\left(n\right)}=\mathrm{ceil}({\mathrm{\θ}}^{\left(n\right)}/\mathrm{d\θ})\·\mathrm{d\θ}$

In the formula, ceil () represents to round up number,

It is the actual antennas scanning angle.

With formula

$\mathrm{\Δ}{\mathrm{\θ}}^{\left(n\right)}={\mathrm{\θ}}_{\mathrm{real}}^{\left(n\right)}-{\mathrm{\θ}}^{\left(n\right)}$

Calculate the poor of antenna actual scanning angle and desirable antenna scan angle, in the formula, Δ θ ⁽ⁿ⁾Be the poor of antenna actual scanning angle and desirable antenna scan angle.

With formula

$N_{\mathrm{pulse}}^{\left(n\right)}=\mathrm{ceil}(\frac{T_B^{\left(n\right)}\·{\mathrm{PRF}}^{\left(n\right)}}{2\·{\mathrm{\θ}}_{\mathrm{real}}^{\left(n\right)}}\·\mathrm{d\θ})$

The resident umber of pulse of each stepping when calculating actual scanning, in the formula,

The resident umber of pulse of each stepping when being actual scanning, PRF ⁽ⁿ⁾It is pulse repetition rate.

With formula

$T_{B\_\mathrm{real}}^{\left(n\right)}=\frac{N_{\mathrm{pulse}}^{\left(n\right)}\·2\·{\mathrm{\θ}}_{\mathrm{real}}^{\left(n\right)}}{{\mathrm{PRF}}^{\left(n\right)}\·\mathrm{d\θ}}$

Calculate the actual residence time of each subband, in the formula,

The actual residence time of subband.

With formula

$T_{R\_\mathrm{real}}=T_{B\_\mathrm{real}}^{\left(1\right)}+T_{B\_\mathrm{real}}^{\left(2\right)}\·\·\·+T_{B\_\mathrm{real}}^{\left(n\right)}+T_{G0}$

Calculate the actual scanning cycle, in the formula, T _{R_real}It is the actual scanning cycle.

With formula

$L_{\mathrm{scan}}^{\left(n\right)}=(2\·{\mathrm{\θ}}_{\mathrm{real}}^{\left(n\right)}-{\mathrm{\θ}}_0^{\left(n\right)})\·R_c^{\left(n\right)}+V_s\·T_{B\_\mathrm{real}}^{\left(n\right)}$

Calculate subband effective scanning track, in the formula,

It is subband effective scanning track.

With formula

L _{R_airborne}＝V _s·T _{R_real}

Computing platform is movement locus in a scan period, in the formula, and L _{R_airborne}It is a scan period inner platform movement locus.

Obtain being applicable to the parameter of practical flight by above-mentioned steps, but whether can satisfy the systemic resolution requirement, still need to carry out parameter and adjust.

(4) parameter is adjusted

Be greater than or equal to platform at a scan period movement locus if each subband can both satisfy antenna effective scanning track, namely satisfy:

$L_{\mathrm{scan}}^{\left(n\right)}\≥L_{R\_\mathrm{airborne}}$

The parameter that obtains in (3) is exactly final practical flight parameter, can be used for realizing the TopSAR pattern.Be greater than or equal to platform movement locus in a scan period if can not satisfy antenna effective scanning track, can cause occurring the zone that resolution reduces along the orientation to track.The way that addresses this problem is exactly suitably to increase time margin, recomputates parameter according to the method for describing in (2) and (3) then, and process flow diagram is seen Fig. 5.The time margin that increases is as follows:

With formula

$\mathrm{\Δ}{T}^{\left(n\right)}=T_{B\_\mathrm{real}}^{\left(n\right)}-T_B^{\left(n\right)}$

Calculate the time that each scanning subband need replenish, in the formula, Δ T ⁽ⁿ⁾It is the time that the scanning subband need replenish.

With formula

$T_G=T_{G0}+\underset{n}{\mathrm{\Σ}}\mathrm{\Δ}{T}^{\left(n\right)}$

Calculate new time margin.

According to new time margin, repeat the calculation procedure of (2) and (3), obtain new parameter.If having satisfied subband antenna effective scanning track, new argument is greater than or equal to platform at a scan period movement locus, then result of calculation is exactly end value, otherwise recomputate time margin according to describing in (4), and then repeat the calculation procedure of (2) and (3), be greater than or equal to platform at a scan period movement locus until satisfying each subband antenna effective scanning track.Said process generally need repeat 2～3 times can be satisfied.

Claims (1)

1. the implementation method of a synthetic-aperture radar wide swath earth observation step-scan pattern, it is characterized in that, in each subband, antenna in the orientation to along trajectory direction, from after scan and receive echo forward, change resolution by the control antenna orientation to sweep velocity; Behind the subband end of scan, distance to, point to by switching-beam and to make the subband that antenna irradiation is different, to realize wide swath; Its concrete steps are as follows:

A) input pointer: total fabric width and systemic resolution are with in mapping;

B) require and the actual antennas size according to input pointer, determine the azimuthal resolution that can reach and the fabric width of each subband when wave beam does not scan;

C) be with total fabric width according to subband azimuthal resolution, fabric width and mapping, determine number of sub-bands, then according to the antenna scanning ability, optimization system resolution;

D) determine sweep time, the scanning angle of wave beam by primary Calculation;

E) according to scan capability and the stepping characteristic of antenna, further accurate Calculation sweep time and scanning angle are to satisfy the ability need of antenna actual scanning;

F) carry out parameter and adjust, if the requirement of discontented toe mark, according to step a)～e) recomputate each parameter, up to satisfying index request; Then according to the orientation that calculates to the scan angle scope, on the SAR platform, progressively regulate the orientation with certain step interval and point to beam center, make its from negative orientation to scan angle, finish to scan angle to positive orientation;

G) behind subband end of scan, regulate antenna distance to beam position to next subband, according to design parameter, progressively regulate the orientation with certain step interval and point to beam center, make its from negative orientation to scan angle, finish to scan angle to positive orientation;

H) behind the end of scan, a scan period finishes subband one by one, and antenna beam is got back to first subband, restarts scanning;

Wherein, calculate sweep time and scanning angle described in the step e), need be according to stepping characteristic and the scan capability of antenna, further each parameter of accurate Calculation comprises that step is as follows:

1. according to antenna stepping angle d θ, formula calculates antenna actual scanning angle below adopting:

${\mathrm{\θ}}_{\mathrm{real}}^{\left(n\right)}=\mathrm{ceil}({\mathrm{\θ}}^{\left(n\right)}/\mathrm{d\θ})\·\mathrm{d\θ}$

In the formula, ceil () represents to round up number, θ ⁽ⁿ⁾The antenna scan angle of expression primary Calculation, It is antenna actual scanning angle;

2. calculate antenna scan angle poor of antenna actual scanning angle and primary Calculation;

3. according to antenna actual scanning angle, the resident umber of pulse of each stepping when calculating actual scanning;

4. calculate the actual residence time of each subband;

5. calculate the actual scanning cycle;

6. calculate each subband antenna effective scanning track;

7. computing platform movement locus in a scan period;

8. calculate residence time poor of the actual residence time of each subband and each subband primary Calculation, and will add up the mistiming;

In the step f), carrying out parameter adjusts, be greater than or equal to platform at a scan period movement locus if each subband can both satisfy antenna effective scanning track, the parameter that obtains in the parameter accurate Calculation is exactly final practical flight parameter, can satisfy resolution requirement; Be greater than or equal to platform at a scan period movement locus if can not satisfy antenna effective scanning track, can cause occurring the zone that resolution reduces along the orientation to track, concrete solution is as follows:

1. recomputate time margin;

2. time margin is brought in the computing formula, is obtained new parameter group through primary Calculation, then repeating step e) and f).

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