CN101957449A - Optimization method for azimuth ambiguity in space-borne TOPSAR mode - Google Patents

Abstract

The invention discloses an optimization method for azimuth ambiguity in a space-borne TOPSAR mode, which comprises the following steps: reading in relevant parameters; acquiring azimuth beam 3dB width, the shortest slant distance from a satellite to a target, a mixed factor, the shortest slant distance from the satellite to an equivalent rotation point, the maximum angle of center beam scanning, separation of azimuth antenna array elements, coordinates of a selected position of the azimuth, and the azimuth ambiguity of a selected position of the azimuth; drawing a changing curve of the azimuth ambiguity; and acquiring the worst value of the azimuth ambiguity under different pulse recurrence frequencies and drawing the worst value curve of the azimuth ambiguity. In the invention, when the azimuth ambiguity is acquired, the space-variant characteristic with the azimuth is considered fully, and the result has higher reliability; the azimuth ambiguities in different positions are acquired independently and can be parallel processed to improve the processing efficiency; and the changing curve of the azimuth ambiguities with the azimuth positions visually reflects the changing condition of the azimuth ambiguities in the whole azimuth scene.

Description

The orientation is to the optimization method of blur level under a kind of spaceborne TOPSAR pattern

Technical field

The invention belongs to the signal Processing field, relate to a kind of optimization method, the orientation is to the optimization method of blur level under particularly a kind of spaceborne TOPSAR pattern.

Background technology

Synthetic-aperture radar (Synthetic Aperture Radar, SAR) be a kind of active imaging microwave radar over the ground, than the ordinary optical imaging radar, it is not subjected to weather and climatic influences, can be round-the-clock, the earth observation task of finishing of round-the-clock, therefore obtained using widely at aspects such as military surveillance, resource detection, oceanographic observation, ecological monitoring.

The orientation is a important indicator in the satellite-borne SAR to blur level, and it has directly reflected the orientation to the size of secondary lobe signal to main lobe signal annoyance level, and in system design, when the ripple position is chosen, the azimuth ambiguity degree is one of main performance assessment criteria.In imaging processing, we at be that the echoed signal of (beam angle of normalization round trip antenna radiation pattern-6dB correspondence) in the main lobe is carried out matched filter processing at frequency domain, but (be called pulse repetition rate because the impulse sampling frequency is limited, PRF) and the orientation to the existence of antenna sidelobe, therefore in frequency domain, when the frequency of side-lobe signal correspondence surpasses the impulse sampling frequency, will arrive the orientation in main lobe by reflexed, cause interference, as shown in Figure 1, for example indicated A among the figure main lobe _{+ 1}And A _-1The reflexed synoptic diagram, other regional A _{+ 2}, A _{+ 3}, A _-2, A _-3Also equally reflexed within the main lobe.Therefore when carrying out system design, need be optimized design to blur level to the orientation.Because pulse repetition rate has determined the position of confusion region, therefore especially need the paired pulses repetition frequency to be optimized design, make the interior energy of confusion region as far as possible little.

Wide observation band is an important development direction of satellite-borne SAR always.Traditional implementation method is to adopt scan pattern (ScanSAR pattern), but its defective is under the ScanSAR mode of operation, be in the target of orientation to diverse location, its orientation is different to blur level, this orientation will cause SAR image vision sense variation to the space-variant phenomenon, be unfavorable for the subsequent applications processing.And in the last few years, produced a kind of new mode of operation---TOPSAR (Terrain Observation by ProgressiveScans), under this pattern, antenna beam scans along heading, the orientation all will be subjected to complete orientation to each target and modulate to antenna radiation pattern, therefore its orientation is identical to the blurred signal size, its mode of operation as shown in Figure 2, R wherein ₁Be the nearest oblique distance of satellite to the equivalent point of rotation, R ₀Be the nearest oblique distance of satellite to target, θ _3dBBe the beam angle of normalization round trip antenna radiation pattern-6dB correspondence, SW _{_ a}For the orientation to the mapping bandwidth, SW _{_ j}The coordinate of selected location, γ _jBe the angle of certain moment satellite and target, β _jFor certain moment antenna beam is swept angle, S partially _jPosition coordinates for certain moment satellite.But in fact, what present SAR antenna adopted is phased array antenna, and sweeping partially of phase place will make graing lobe occur, as shown in Figure 3, only sweeping angle partially with antenna among this figure is 2 degree, and the angle variation range illustrates that for-20 situations of spending when 20 spend are example sweeping partially of antenna beam will cause the generation of graing lobe.In fact, the graing lobe size changes with the scan angle conversion, therefore in different orientation on the position, the scan angle difference that it is corresponding, the graing lobe of generation varies in size, so the orientation is to blur level also difference slightly.And at present under spaceborne TOPSAR mode of operation, have the orientation of consideration to blur level and scan angle with the phenomenon of orientation to change in location, the also not optimization that realizes the azimuth ambiguity degree that is provided with by the paired pulses repetition frequency simultaneously.Therefore, at this mode of operation of spaceborne TOPSAR, the present invention proposes the optimization method of orientation blur level under a kind of spaceborne TOPSAR pattern, utilize the present invention can reflect more accurately the orientation to blur level with the phenomenon of orientation to change in location, make graing lobe not enter the confusion region by pulse repetition rate rationally is set simultaneously, realize that the orientation is to the blur level optimization in Properties.

Summary of the invention

The objective of the invention is under the present spaceborne TOPSAR mode of operation, do not consider the orientation to blur level and scan angle with the phenomenon of orientation to change in location, also not by this problem of optimization that realizes the azimuth ambiguity degree that is provided with of paired pulses repetition frequency, the optimization method of orientation blur level under a kind of spaceborne TOPSAR pattern is proposed simultaneously.

The optimization method of orientation blur level under a kind of spaceborne TOPSAR pattern of the present invention comprises following step:

Step 1: get parms by the Spaceborne SAR System parameter list, comprising: pulse repetition rate PRF variation range, pulse repetition rate change step Δ PRF, antenna length Aa, the orientation is to antenna TR number of components TR _{_ a}, the feed of each TR assembly is counted n _{_ a}, the wavelength X of signal, radar earth observation centre visual angle α, earth mean radius Re, the satellite flight height H, satellite equivalence flying speed V, the orientation is to design resolution ρ _a, the orientation is to resolution ceofficient of spread K, and the orientation is to mapping bandwidth SW _{_ a}, the orientation is to chosen position number N a, and frequency is divided number Fa, and number Ma is selected in the confusion region;

Step 2: obtain the orientation to wave beam 3dB width θ _3db

Method is as shown in Equation (1):

${\mathrm{\θ}}_{3\mathrm{db}}=\frac{\mathrm{\λ}}{\mathrm{Aa}}\·0.886---\left(1\right)$

Step 3: obtain the nearest oblique distance R of satellite to target ₀

Method is as shown in Equation (2):

${\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HSA00000073571600071.png"\; state="\{\{state\}\}">R</figure-callout>}}_0=\mathrm{Re}\&CenterDot;\frac{\sin (a\sin (\frac{\mathrm{Re}+H}{\mathrm{Re}}\&CenterDot;\sin \left(\mathrm{\&alpha;}\right))-\sin \left(\mathrm{\&alpha;}\right))}{\sin \left(\mathrm{\&alpha;}\right)}---\left(2\right)$

Step 4: obtain hybrid cytokine B;

Method is as shown in Equation (3):

$B=\frac{{2\mathrm{\&rho;}}_a}{K\&CenterDot;A_a}---\left(3\right)$

Step 5: obtain the nearest oblique distance R of satellite to the equivalent point of rotation ₁

Method is as shown in Equation (4):

$R_1=\frac{R_0}{B-1}---\left(4\right)$

Step 6: obtain central beam scanning maximum angle β _Max

Method as formula (shown in the 5a～5d):

${\mathrm{\&beta;}}_{\max }=\frac{{-b}_1-\sqrt{{b_1}^2-{4a}_1\&CenterDot;c_1}}{{2a}_1}---\left(5a\right)$

Wherein:

$a_1=R_1\&CenterDot;\tan (-\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2})---\left(5b\right)$

$b_1=\frac{{\mathrm{SW}}_{\_a}}{2}\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)-R_1-R_0---\left(5c\right)$

$c_1={\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HSA00000073571600071.png"\; state="\{\{state\}\}">R</figure-callout>}}_0\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)+\frac{{\mathrm{SW}}_{\_a}}{2}---\left(5d\right)$

Step 7: obtain the orientation to bay interval d;

Method is as shown in Equation (6):

$d=\frac{\mathrm{Aa}}{{\mathrm{TR}}_{\_a}\&CenterDot;n_{\_a}}---\left(6\right)$

Step 8: obtain the coordinate SW of orientation to some selected locations _{_ i}

Method is as shown in Equation (7):

${\mathrm{SW}}_{\_i}=-\frac{{\mathrm{SW}}_{\_a}}{2}+i\&CenterDot;\frac{{\mathrm{SW}}_{\_a}}{\mathrm{Na}-1}$ (0, Na-1), i is integer (7) to i ∈

Step 9: to the result that step 8 obtains, obtain the orientation to some selected location SW according to step 1 _{_ i}The azimuth ambiguity degree at place;

According to preceding sight line irradiation position SW _{_ i}The time central beam sweep angle beta partially ₁, retracement line irradiation position SW _{_ i}The time central beam sweep angle beta partially ₂, obtaining the central beam angle of sweeping partially constantly is β _jThe time, main lobe signal energy P _{J_0}With side-lobe signal energy P _{J_n}, respectively main lobe energy and secondary lobe energy are sued for peace, obtain the azimuth ambiguity degree AASR at this some place _i

Step 10: draw the azimuth ambiguity degree with the curve of orientation to change in location, find the maximal value of curve, promptly the orientation is to the worst-case value AASR of blur level _p, carry out record;

Wherein the ordinate of curve is the size of azimuth ambiguity degree, and horizontal ordinate is the coordinate of orientation to the selected location;

Step 11: according to pulse repetition rate change step Δ PRF, change pulse repetition rate, repeating step one is to step 10, obtains under the different pulse repetition orientation to the worst-case value AASR of blur level _p, until the maximal value that arrives the pulse repetition rate variation range;

Step 12: draw the orientation to the worst-case value of blur level change curve, finish to the optimization of orientation to blur level with pulse repetition rate;

Wherein the ordinate of curve is the size of orientation to the worst-case value of blur level, and horizontal ordinate is a pulse repetition rate, rationally chooses pulse repetition rate, makes graing lobe not enter the confusion region, finishes the optimization of orientation to the blur level performance index.

The invention has the advantages that:

(1) accurately high.When the present invention obtains antenna radiation pattern, employing be that aerial array synthetic technology and actual conditions are more approached, so the result is more accurately and reliable.

(2) reliability height.In the process of carrying out system design, the azimuth ambiguity degree accurately for the expansion of follow-up work with make a strategic decision significantly, the present invention taken into full account the characteristic of its space-variant, so the result has higher reliability when obtaining azimuth ambiguity and spend.

(3) practical.In the system optimization design, pulse repetition rate is an important parameters optimization, the present invention under different pulse repetition raties, obtain different orientation to blur level with the curve of orientation to change in location, by analyzing these different change curves, rational pulse repetition rate is set, realizes the optimization of orientation to blur level.

(4) efficient height.The orientation at diverse location place can independently obtain to blur level among the present invention, but therefore parallel processing has significantly improved treatment effeciency.

(5) intuitive is good.By the present invention can obtain the orientation to blur level with the curve of orientation to evolution, therefore can reflect very intuitively the orientation to blur level in whole orientation the situation of change in scene, therefore form of expression intuitive is strong as a result, is convenient to system designer and decision maker and makes correct selection by curve.

Description of drawings

Fig. 1 is that the orientation is to the signal ambiguity synoptic diagram;

Fig. 2 is a TOPSAR mode of operation synoptic diagram;

Fig. 3 is that the orientation of antenna when sweeping partially is to round trip normalization antenna radiation pattern;

Fig. 4 is a method flow diagram of the present invention;

Fig. 5 is that space geometry of the present invention concerns synoptic diagram;

Fig. 6 is the schematic flow sheet of step 9 of the present invention;

Fig. 7 is the schematic flow sheet of step C in the step 9 of the present invention;

Fig. 8 be among the embodiment orientation to blur level with the curve map of orientation to variable in distance.

Fig. 9 is the curve map that the poorest orientation changes with pulse repetition rate to blur level among the embodiment.

Embodiment

The present invention is described in further detail below in conjunction with drawings and Examples.

This method is that the orientation is to the optimization method of blur level under a kind of spaceborne TOPSAR pattern, and idiographic flow may further comprise the steps as shown in Figure 4:

Step 1: get parms by the Spaceborne SAR System parameter list, comprising: pulse repetition rate PRF variation range, pulse repetition rate change step Δ PRF, antenna length Aa, the orientation is to antenna TR number of components TR _{_ a}, the feed of each TR assembly is counted n _{_ a}, the wavelength X of signal, radar earth observation centre visual angle α, earth mean radius Re, the satellite flight height H, satellite equivalence flying speed V, the orientation is to design resolution ρ _a, the orientation is to resolution ceofficient of spread K, and the orientation is to mapping bandwidth SW _{_ a}, the orientation is to chosen position number N a, and frequency is divided number Fa, and number Ma is selected in the confusion region.

Wherein, concrete parameter is in the present embodiment: PRF=2500～6000Hz, Δ PRF=50Hz, Aa=10m, TR _{_ a}=30, n _{_ a}=10, λ=0.056m, α=30deg, Re=6371140m, H=632639m, V=7530m/s, ρ _a=25m, K=1.2, SW _{_ a}=100km, Na=51, Fa=51, Ma=10.

Step 2: obtain the orientation to wave beam 3dB width θ _3db

Method is as shown in Equation (1):

${\mathrm{\&theta;}}_{3\mathrm{db}}=\frac{\mathrm{\&lambda;}}{\mathrm{Aa}}\&CenterDot;0.886---\left(1\right)$

Wherein, concrete parameter is in the present embodiment: Aa=10m, λ=0.056m obtains θ _3db=0.0049616rad.

Step 3: obtain the nearest oblique distance R of satellite to target ₀, as shown in Figure 5, wherein V is a flying speed.

Method is as shown in Equation (2):

${\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HSA00000073571600071.png"\; state="\{\{state\}\}">R</figure-callout>}}_0=\mathrm{Re}\&CenterDot;\frac{\sin (a\sin (\frac{\mathrm{Re}+H}{\mathrm{Re}}\&CenterDot;\sin \left(\mathrm{\&alpha;}\right))-\sin \left(\mathrm{\&alpha;}\right))}{\sin \left(\mathrm{\&alpha;}\right)}---\left(2\right)$

Wherein, concrete parameter is in the present embodiment: Re=6371140m, and H=632639m, α=30deg obtains R ₀=743027.04m.

Step 4: obtain hybrid cytokine B.

Method is as shown in Equation (3):

$B=\frac{{2\mathrm{\&rho;}}_a}{K\&CenterDot;A_a}---\left(3\right)$

Wherein, concrete parameter is in the present embodiment: ρ _a=25m, K=1.2, Aa=10m obtains B=4.1667.

Step 5: obtain the nearest oblique distance R of satellite to the equivalent point of rotation ₁, as shown in Figure 2.

Method is as shown in Equation (4):

$R_1=\frac{R_0}{B-1}---\left(4\right)$

Wherein, concrete parameter is in the present embodiment: R ₀=743027.04m, B=4.1667 obtains R ₁=234640.12m.

Step 6: obtain central beam scanning maximum angle β _Max

Usually under the situation, system attitude has higher limit to scanning angle, necessarily requires β _MaxLess than this higher limit.

Method as formula (shown in the 5a～5d):

${\mathrm{\&beta;}}_{\max }=\frac{{-b}_1-\sqrt{{b_1}^2-{4a}_1\&CenterDot;c_1}}{{2a}_1}---\left(5a\right)$

Wherein:

$a_1=R_1\&CenterDot;\tan (-\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2})---\left(5b\right)$

$b_1=\frac{{\mathrm{SW}}_{\_a}}{2}\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)-R_1-R_0---\left(5c\right)$

$c_1={\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HSA00000073571600071.png"\; state="\{\{state\}\}">R</figure-callout>}}_0\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)+\frac{{\mathrm{SW}}_{\_a}}{2}---\left(5d\right)$

Wherein, concrete parameter is in the present embodiment: SW _{_ a}=100km, R ₀=743027.04m, R ₁=234640.12m, θ _3db=0.0049616rad obtains β _Max=0.05298rad.

Step 7: obtain the orientation to bay interval d.

Method is as shown in Equation (6):

$d=\frac{\mathrm{Aa}}{{\mathrm{TR}}_{\_a}\&CenterDot;n_{\_a}}---\left(6\right)$

Wherein, concrete parameter is in the present embodiment: Aa=10m, TR _{_ a}=30, n _{_ a}=10, obtain d=0.03333m.

Step 8: obtain the coordinate SW of orientation to some selected locations _{_ i}

Method is as shown in Equation (7):

${\mathrm{SW}}_{\_i}=-\frac{{\mathrm{SW}}_{\_a}}{2}+i\&CenterDot;\frac{{\mathrm{SW}}_{\_a}}{\mathrm{Na}-1}$ (0, Na-1), i is integer (7) to i ∈

Wherein, concrete parameter is in the present embodiment: SW _{_ a}=100km, Na=51, the different values according to i obtain SW _{_ i}

Step 9: to the result that step 8 obtains, obtain the orientation to some selected location SW according to step 1 _{_ i}The azimuth ambiguity degree at place as shown in Figure 6, specifically comprises following step:

A, obtain before sight line irradiation position SW _{_ i}The time, central beam is swept angle beta partially ₁

Method as formula (shown in the 8a～8d):

${\mathrm{\&beta;}}_1=\frac{-b_2-\sqrt{{b_2}^2-{4a}_2\&CenterDot;c_2}}{{2a}_2}---\left(8a\right)$

Wherein:

$a_2=R_1\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)---\left(8b\right)$

$b_2=-{\mathrm{SW}}_{\_i}\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)-R_1-R_0---\left(8c\right)$

$c_2={-\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HSA00000073571600071.png"\; state="\{\{state\}\}">R</figure-callout>}}_0\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)+{\mathrm{SW}}_{\_i}---\left(8d\right)$

Wherein, concrete parameter is in the present embodiment: R ₀=743027.04m, R ₁=234640.12m, θ _3db=0.0049616rad, SW _{_ i}By formula (7) obtain.

B, obtain retracement line and shine this position SW _{_ i}The time, central beam is swept angle beta partially ₂

Method as formula (shown in the 9a～9d):

${\mathrm{\&beta;}}_2=\frac{-b_3-\sqrt{{b_3}^2-{4a}_3\&CenterDot;c_3}}{{2a}_3}---\left(9a\right)$

Wherein:

$a_3=R_1\&CenterDot;\tan (-\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2})---\left(9b\right)$

$b_3={\mathrm{SW}}_{\_i}\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)-R_1-R_0---\left(9c\right)$

$c_3={\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="HSA00000073571600071.png"\; state="\{\{state\}\}">R</figure-callout>}}_0\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)+{\mathrm{SW}}_{\_i}---\left(9d\right)$

Wherein, concrete parameter is in the present embodiment: R ₀=743027.04m, R ₁=234640.12m, θ _3db=0.0049616rad, SW _{_ i}By formula (7) obtain.

C, to obtain the central beam angle of sweeping partially constantly be β _jThe time, main lobe signal energy P _{J_0}With side-lobe signal energy P _{J_n}, flow process as shown in Figure 7, its concrete steps are further divided into:

A, obtain position SW _{_ i}In the illuminated process, central beam constantly sweep angle beta partially _j

Method is as shown in Equation (10):

${\mathrm{\&beta;}}_j={\mathrm{\&beta;}}_1+j\&CenterDot;\frac{{\mathrm{\&beta;}}_2-{\mathrm{\&beta;}}_1}{\mathrm{Fa}-1}$ (0, Fa-1), j is integer (10) to j ∈

Wherein, concrete parameter is in the present embodiment: β ₁By formula (8a～8d) obtains, β ₂By formula (the different values according to j obtain β for 9a～9d) obtain, Fa=51 _j

B, obtain certain position coordinates S of satellite constantly _j

Method is as shown in Equation (11):

S _j＝R ₁·tan(β _j)(11)

Wherein, concrete parameter is in the present embodiment: β _jBy formula (10) obtain, R ₁=234640.12m.

C, obtain certain angle γ of satellite and target constantly _j

Method is as shown in Equation (12):

${\mathrm{\&gamma;}}_j=a\tan \left(\frac{{\mathrm{SW}}_{\_i}-S_j}{R_0}\right)---\left(12\right)$

Wherein, concrete parameter is in the present embodiment: SW _{_ i}By formula (7) obtain, S _jBy formula (11) obtain, R ₀=743027.04m.

D, obtain certain main lobe signal energy P constantly _{J_0}

Method as formula (shown in the 13a～13b):

$P_{j\_0}=\frac{{\left|{\mathrm{<figure-callout\; id="0"\; label="Q"\; filenames="HSA00000073571600071.png"\; state="\{\{state\}\}">Q</figure-callout>}}_0\right|}^4}{{({\mathrm{TR}}_{\_a}\&CenterDot;n_{\_a})}^4}---\left(13a\right)$

${\mathrm{<figure-callout\; id="0"\; label="Q"\; filenames="HSA00000073571600071.png"\; state="\{\{state\}\}">Q</figure-callout>}}_0=\underset{p=0}{\overset{({\mathrm{TR}}_{\_a}-1)}{\mathrm{\&Sigma;}}}\underset{q=0}{\overset{(n_{\_a}-1)}{\mathrm{\&Sigma;}}}\exp \{\frac{2\&CenterDot;\mathrm{\&pi;}\&CenterDot;d}{\mathrm{\&lambda;}}\&CenterDot;((p\&CenterDot;{\mathrm{TR}}_{\_a}+q)\&CenterDot;\sin \left({\mathrm{\&beta;}}_j\right)-p\&CenterDot;{\mathrm{TR}}_{\_a}\&CenterDot;\sin \left({\mathrm{\&gamma;}}_j\right))\}---\left(13b\right)$

Wherein, concrete parameter is in the present embodiment: TR _{_ a}=30, n _{_ a}=10, λ=0.056m, γ _jBy formula (12) obtain, β _jBy formula (10) obtain.

E, obtain certain pairing angle γ of secondary lobe signal constantly _{J_n}

Method is as shown in Equation (14):

${\mathrm{\&gamma;}}_{j\_n}=\frac{\mathrm{\&lambda;}}{2\&CenterDot;V}\&CenterDot;a\sin (\frac{2\&CenterDot;V}{\mathrm{\&lambda;}}\&CenterDot;\sin ({\mathrm{\&gamma;}}_j+n\&CenterDot;\mathrm{PRF}))$ (n is integer (14) to n ∈ for Ma ,+Ma) n ≠ 0

Wherein, concrete parameter is in the present embodiment: V=7530m/s, PRF=3000Hz, λ=0.056m, Ma=10, γ _jBy formula (12) obtain.

F, obtain certain secondary lobe signal energy P constantly _{J_n}

Method as formula (shown in the 15a～15b):

$P_{j\_n}=\frac{{\left|Q_n\right|}^4}{{({\mathrm{TR}}_{\_a}\&CenterDot;n_{\_a})}^4}---\left(15a\right)$

$Q_n=\underset{p=0}{\overset{({\mathrm{TR}}_{\_a}-1)}{\mathrm{\&Sigma;}}}\underset{q=0}{\overset{(n_{\_a}-1)}{\mathrm{\&Sigma;}}}\exp \{\frac{2\&CenterDot;\mathrm{\&pi;}\&CenterDot;d}{\mathrm{\&lambda;}}\&CenterDot;((p\&CenterDot;{\mathrm{TR}}_{\_a}+q)\&CenterDot;\sin \left({\mathrm{\&beta;}}_j\right)-p\&CenterDot;{\mathrm{TR}}_{\_a}\&CenterDot;\sin \left({\mathrm{\&gamma;}}_{j\_n}\right))\}---\left(15b\right)$

Wherein, concrete parameter is in this example: TR _{_ a}=30, n _{_ a}=10, λ=0.056m, γ _{J_n}By formula (14) obtain, β _jBy formula (10) obtain.

G, repeating step a～f shine position SW until obtaining retracement line _{_ i}, it is β that central beam is swept angle partially ₂The time.

D, according to The above results, respectively main lobe energy and secondary lobe energy are sued for peace, obtain the azimuth ambiguity degree AASR at this some place _i

Method is as shown in Equation (16):

${\mathrm{AASR}}_i=10\&CenterDot;\log 10\left(\frac{\underset{n=-\mathrm{Ma}}{\overset{n=-1}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{\mathrm{Fa}-1}{\mathrm{\&Sigma;}}}{P}_{j\_n}+\underset{n=1}{\overset{n=\mathrm{Ma}}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{\mathrm{Fa}-1}{\mathrm{\&Sigma;}}}{P}_{j\_n}}{\underset{j=0}{\overset{\mathrm{Fa}-1}{\mathrm{\&Sigma;}}}{P}_{j\_0}}\right)---\left(16\right)$

Wherein, concrete parameter is in the present embodiment: Ma=10, P _{J_0}By formula (13a～13b) obtain, P _{J_n}(15a～15b) obtain by formula.

E, repeating step A～D are until obtaining each selected location SW _{_ i}The azimuth ambiguity degree.

Step 10: draw the azimuth ambiguity degree with the curve of orientation to change in location, find the maximal value of curve, promptly the orientation is to the worst-case value AASR of blur level _p, carry out record;

Because when system design, need the orientation of everywhere all to meet the demands to the blur level index, wherein the ordinate of curve is the size of azimuth ambiguity degree, horizontal ordinate is the coordinate of orientation to the selected location.

Step 11: according to pulse repetition rate change step Δ PRF, change pulse repetition rate, repeating step 1～step 10 is obtained under the different pulse repetition orientation to the worst-case value AASR of blur level _p, until the maximal value that arrives the pulse repetition rate variation range.

Wherein, the maximal value that the present embodiment pulse repetition rate changes is PRF=6000Hz, and p ∈ (1,71) p is a positive integer.

Step 12: draw the change curve of the poorest blur level with pulse repetition rate.Wherein the ordinate of curve is the size of the poorest azimuth ambiguity degree, and horizontal ordinate is a pulse repetition rate.

The orientation to blur level with the orientation to the curve of change in location reflect intuitively the orientation to blur level in the size of different azimuth to the position, obtain on different positions blurred signal to the influence of final SAR image.The orientation reflects that with the change curve of pulse repetition rate the orientation can reflect especially that to the performance of blur level graing lobe exists the influence of orientation to blur level under the different pulse repetition to the poorest blur level very intuitively.Because the existence of graing lobe, orientation under some pulse repetition rate can extremely worsen to blur level, therefore can be by the orientation to the change curve of the poorest blur level with pulse repetition rate, rational strobe pulse repetition frequency, make the orientation be optimized, therefore have important engineering application value to the blur level performance index.

Embodiment:

For feasibility of the present invention, accuracy and practicality can better be described, verify by emulated data.Utilize the present invention in the emulation respectively under different pulse repetition raties, orientation in the whole audience scape is calculated to blur level, by the result who calculates, it is best to compare under that pulse repetition rate orientation blur level result, realizes the optimization to system performance.

Table 1 has provided simulation parameter.As example, when Fig. 8 has provided pulse repetition rate and has been 2000Hz, 3000Hz, 3000Hz, 4000Hz, 5000Hz, 6000Hz, the orientation to blur level with the change curve of orientation to the position.Fig. 9 has provided the orientation to the change curve of blur level worst-case value with pulse repetition rate.

Table 1 simulation parameter

As seen from Figure 8, when pulse repetition rate was 2000Hz, 3000Hz, 4000Hz, this moment, graing lobe did not enter fuzzy region, and its orientation improves to the increase of blur level with pulse repetition rate, and the orientation is less to the change in location amplitude with the orientation to blur level.And when pulse repetition rate is 5000Hz, its graing lobe has entered fuzzy region, big owing to the mutually biased angle of sweeping in the orientation to edge, the graing lobe influence is obvious further, therefore in the orientation to the edge orientation to the rapid variation of blur level, and along with pulse repetition rate further is increased to 6000Hz, graing lobe is gradually away from fuzzy region, and this moment, the orientation improved again gradually to blur level.

As seen from Figure 9, the orientation to the poorest blur level along with the pulse repetition rate fluctuations, in fact this fluctuations is exactly because under some pulse repetition rate, it is caused that graing lobe enters the confusion region, and can it is evident that from figure those pulse repetition raties are near (the curve crests among the figure) that can not select, and be optional (near curve trough place among the figure) under those pulse repetition raties, and then can carry out the setting of pulse repetition rate, finish the optimal design of orientation to blur level.

According to the present invention, can reflect very directly perceived, accurately the orientation to blur level with the variation of orientation to the position, and can be optimized design to the blur level index to the orientation, therefore its reliable results, effectively has important engineering application value.

Claims (3)

1. the orientation is characterized in that to the optimization method of blur level under the spaceborne TOPSAR pattern, may further comprise the steps:

Step 1: get parms by the Spaceborne SAR System parameter list, comprising: pulse repetition rate PRF variation range, pulse repetition rate change step Δ PRF, antenna length Aa, the orientation is to antenna TR number of components TR _{_ a}, the feed of each TR assembly is counted n _{_ a}, the wavelength X of signal, radar earth observation centre visual angle α, earth mean radius Re, the satellite flight height H, satellite equivalence flying speed V, the orientation is to design resolution ρ _a, the orientation is to resolution ceofficient of spread K, and the orientation is to mapping bandwidth SW _{_ a}, the orientation is to chosen position number N a, and frequency is divided number Fa, and number Ma is selected in the confusion region;

Step 2: obtain the orientation to wave beam 3dB width θ _3db

Method is as shown in Equation (1):

${\mathrm{\&theta;}}_{3\mathrm{db}}=\frac{\mathrm{\&lambda;}}{\mathrm{Aa}}\&CenterDot;0.886---\left(1\right)$

Step 3: obtain the nearest oblique distance R of satellite to target ₀

Method is as shown in Equation (2):

$R_0=\mathrm{Re}\&CenterDot;\frac{\sin (a\sin (\frac{\mathrm{Re}+H}{\mathrm{Re}}\&CenterDot;\sin \left(\mathrm{\&alpha;}\right))-\sin \left(\mathrm{\&alpha;}\right))}{\sin \left(\mathrm{\&alpha;}\right)}---\left(2\right)$

Step 4: obtain hybrid cytokine B;

Method is as shown in Equation (3):

$B=\frac{2{\mathrm{\&rho;}}_a}{K\&CenterDot;A_a}---\left(3\right)$

Step 5: obtain the nearest oblique distance R of satellite to the equivalent point of rotation ₁

Method is as shown in Equation (4):

$R_1=\frac{R_0}{B-1}---\left(4\right)$

Step 6: obtain central beam scanning maximum angle β _Max

Method as formula (shown in the 5a～5d):

${\mathrm{\&beta;}}_{\max }=\frac{-b_1-\sqrt{{b_1}^2-4a_1\&CenterDot;c_1}}{2a_1}---\left(5a\right)$

Wherein:

$a_1=R_1\&CenterDot;\tan (-\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2})---\left(5b\right)$

$b_1=\frac{{\mathrm{SW}}_{\_a}}{2}\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)-R_1-R_0---\left(5c\right)$

$c_1=R_0\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)+\frac{{\mathrm{SW}}_{\_a}}{2}---\left(5d\right)$

Step 7: obtain the orientation to bay interval d;

Method is as shown in Equation (6):

$d=\frac{\mathrm{Aa}}{{\mathrm{TR}}_{\_a}\&CenterDot;n_{\_a}}---\left(6\right)$

Step 8: obtain the coordinate SW of orientation to some selected locations _{_ i}

Method is as shown in Equation (7):

${\mathrm{SW}}_{\_i}=-\frac{{\mathrm{SW}}_{\_a}}{2}+i\&CenterDot;\frac{{\mathrm{SW}}_{\_a}}{\mathrm{Na}-1}$ (0, Na-1), i is integer (7) to i ∈

Step 9: to the result that step 8 obtains, obtain the orientation to some selected location SW according to step 1 _{_ i}The azimuth ambiguity degree at place;

According to preceding sight line irradiation position SW _{_ i}The time central beam sweep angle beta partially ₁, retracement line irradiation position SW _{_ i}The time central beam sweep angle beta partially ₂, obtaining the central beam angle of sweeping partially constantly is β _jThe time, main lobe signal energy P _{J_0}With side-lobe signal energy P _{J_n}, respectively main lobe energy and secondary lobe energy are sued for peace, obtain the azimuth ambiguity degree AASR at this some place _i

Step 10: draw the azimuth ambiguity degree with the curve of orientation to change in location, find the maximal value of curve, promptly the orientation is to the worst-case value AASR of blur level _p, carry out record;

Wherein the ordinate of curve is the size of azimuth ambiguity degree, and horizontal ordinate is the coordinate of orientation to the selected location;

Step 11: according to pulse repetition rate change step Δ PRF, change pulse repetition rate, repeating step one is to step 10, obtains under the different pulse repetition orientation to the worst-case value AASR of blur level _p, until the maximal value that arrives the pulse repetition rate variation range;

Step 12: draw the orientation to the worst-case value of blur level change curve, finish to the optimization of orientation to blur level with pulse repetition rate;

Wherein the ordinate of curve is the size of orientation to the worst-case value of blur level, and horizontal ordinate is a pulse repetition rate, rationally chooses pulse repetition rate, makes graing lobe not enter the confusion region, finishes the optimization of orientation to the blur level performance index.

2. the orientation is characterized in that to the optimization method of blur level described step 9 specifically comprises following step under a kind of spaceborne TOPSAR pattern according to claim 1:

A, obtain before sight line irradiation position SW _{_ i}The time, central beam is swept angle beta partially ₁

Method as formula (shown in the 8a～8d):

${\mathrm{\&beta;}}_1=\frac{-b_2-\sqrt{{b_2}^2-4a_2\&CenterDot;c_2}}{2a_2}---\left(8a\right)$

Wherein:

$a_2=R_1\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)---\left(8b\right)$

$b_2=-{\mathrm{SW}}_{\_i}\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)-R_1-R_0---\left(8c\right)$

$c_2=-R_0\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)+{\mathrm{SW}}_{\_i}---\left(8d\right)$

B, obtain retracement line irradiation position SW _{_ i}The time, central beam is swept angle beta partially ₂

Method as formula (shown in the 9a～9d):

${\mathrm{\&beta;}}_2=\frac{-b_3-\sqrt{{b_3}^2-4a_3\&CenterDot;c_3}}{2a_3}---\left(9a\right)$

Wherein:

$a_3=R_1\&CenterDot;\tan (-\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2})---\left(9b\right)$

$b_3={\mathrm{SW}}_{\_i}\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)-R_1-R_0---\left(9c\right)$

$c_3=R_0\&CenterDot;\tan \left(\frac{{\mathrm{\&theta;}}_{3\mathrm{dB}}}{2}\right)+{\mathrm{SW}}_{\_i}---\left(9d\right)$

C, to obtain the central beam angle of sweeping partially constantly be β _jThe time, main lobe signal energy P _{J_0}With side-lobe signal energy P _{J_n}

According to position SW _{_ i}In the illuminated process central beam constantly sweep angle beta partially _j, certain position coordinates S of satellite constantly _j, certain angle γ of satellite and target constantly _j, certain pairing angle γ of secondary lobe signal constantly _{J_n}, obtain certain main lobe signal energy P constantly _{J_0}With certain moment secondary lobe signal energy P _{J_n}Sweep angle beta partially according to central beam _jVariation, obtain different central beam respectively and sweep angle beta partially _jThe time main lobe signal energy P _{J_0}With secondary lobe signal energy P _{J_n}, shine position SW until retracement line _{_ i}, it is β that central beam is swept angle partially ₂The time;

D, according to The above results, respectively main lobe energy and secondary lobe energy are sued for peace, obtain the azimuth ambiguity degree AASR at this some place _i

Method as shown in the formula:

${\mathrm{AASR}}_i=10\&CenterDot;\log 10\left(\frac{\underset{n=-\mathrm{Ma}}{\overset{n=-1}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{\mathrm{Fa}-1}{\mathrm{\&Sigma;}}}{P}_{j\_n}+\underset{n=1}{\overset{n=\mathrm{Ma}}{\mathrm{\&Sigma;}}}\underset{j=0}{\overset{\mathrm{Fa}-1}{\mathrm{\&Sigma;}}}{P}_{j\_n}}{\underset{j=0}{\overset{\mathrm{Fa}-1}{\mathrm{\&Sigma;}}}{P}_{j\_0}}\right)$

E, repeating step A～D are until obtaining each selected location SW _{_ i}The azimuth ambiguity degree.

3. the orientation is characterized in that to the optimization method of blur level under a kind of spaceborne TOPSAR pattern according to claim 2, among the described step C, specifically comprises following step:

A, obtain position SW _{_ i}In the illuminated process, central beam constantly sweep angle beta partially _j

Method is as shown in Equation (10):

${\mathrm{\&beta;}}_j={\mathrm{\&beta;}}_1+j\&CenterDot;\frac{{\mathrm{\&beta;}}_2-{\mathrm{\&beta;}}_1}{\mathrm{Fa}-1}$ (0, Fa-1), j is integer (10) to j ∈

B, obtain certain position coordinates S of satellite constantly _j

Method is as shown in Equation (11):

S _j＝R ₁·tan(β _j) (11)

C, obtain certain angle γ of satellite and target constantly _j

Method is as shown in Equation (12):

${\mathrm{\&gamma;}}_j=a\tan \left(\frac{{\mathrm{SW}}_{\_i}-S_j}{R_0}\right)---\left(12\right)$

D, obtain certain main lobe signal energy P constantly _{J_0}

Method as formula (shown in the 13a～13b):

$P_{j\_0}=\frac{{\left|Q_0\right|}^4}{{({\mathrm{TR}}_{\_a}\&CenterDot;n_{\_a})}^4}---\left(13a\right)$

$Q_0=\underset{p=0}{\overset{({\mathrm{TR}}_{\_a}-1)}{\mathrm{\&Sigma;}}}\underset{q=0}{\overset{(n_{\_a}-1)}{\mathrm{\&Sigma;}}}\exp \{\frac{2\&CenterDot;\mathrm{\&pi;}\&CenterDot;d}{\mathrm{\&lambda;}}\&CenterDot;((p\&CenterDot;{\mathrm{TR}}_{\_a}+q)\&CenterDot;\sin \left({\mathrm{\&beta;}}_j\right)-p\&CenterDot;{\mathrm{TR}}_{\_a}\&CenterDot;\sin \left({\mathrm{\&gamma;}}_j\right))\}---\left(13b\right)$

E, obtain certain pairing angle γ of secondary lobe signal constantly _{J_n}

Method is as shown in Equation (14):

${\mathrm{\&gamma;}}_{j\_n}=\frac{\mathrm{\&lambda;}}{2\&CenterDot;V}\&CenterDot;a\sin (\frac{2\&CenterDot;V}{\mathrm{\&lambda;}}\&CenterDot;\sin ({\mathrm{\&gamma;}}_j+n\&CenterDot;\mathrm{PRF})),n\&Element;(-\mathrm{Ma},+\mathrm{Ma}),n\&NotEqual;0,$ N is integer (14)

F, obtain certain secondary lobe signal energy P constantly _{J_n}

Method as formula (shown in the 15a～15b):

$P_{j\_n}=\frac{{\left|Q_n\right|}^4}{{({\mathrm{TR}}_{\_a}\&CenterDot;n_{\_a})}^4}---\left(15a\right)$

$Q_n=\underset{p=0}{\overset{({\mathrm{TR}}_{\_a}-1)}{\mathrm{\&Sigma;}}}\underset{q=0}{\overset{(n_{\_a}-1)}{\mathrm{\&Sigma;}}}\exp \{\frac{2\&CenterDot;\mathrm{\&pi;}\&CenterDot;d}{\mathrm{\&lambda;}}\&CenterDot;((p\&CenterDot;{\mathrm{TR}}_{\_a}+q)\&CenterDot;\sin \left({\mathrm{\&beta;}}_j\right)-p\&CenterDot;{\mathrm{TR}}_{\_a}\&CenterDot;\sin \left({\mathrm{\&gamma;}}_{j\_n}\right))\}---\left(15b\right)$

G, repeating step a～f shine position SW until obtaining retracement line _{_ i}, it is β that central beam is swept angle partially ₂The time.

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