CN110208801B - Universal SAR imaging PRF optimization design method - Google Patents
Universal SAR imaging PRF optimization design method Download PDFInfo
- Publication number
- CN110208801B CN110208801B CN201910576771.8A CN201910576771A CN110208801B CN 110208801 B CN110208801 B CN 110208801B CN 201910576771 A CN201910576771 A CN 201910576771A CN 110208801 B CN110208801 B CN 110208801B
- Authority
- CN
- China
- Prior art keywords
- prf
- value
- distance
- radar
- height
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 238000000034 method Methods 0.000 title claims abstract description 59
- 238000003384 imaging method Methods 0.000 title claims abstract description 57
- 238000013461 design Methods 0.000 title claims abstract description 33
- 238000005457 optimization Methods 0.000 title claims abstract description 29
- 238000013507 mapping Methods 0.000 claims abstract description 49
- 208000004350 Strabismus Diseases 0.000 claims abstract description 26
- 230000009189 diving Effects 0.000 claims abstract description 14
- 230000001133 acceleration Effects 0.000 claims description 56
- 239000013598 vector Substances 0.000 claims description 19
- 230000009471 action Effects 0.000 claims description 17
- 241000283070 Equus zebra Species 0.000 claims description 15
- 239000006185 dispersion Substances 0.000 claims description 9
- 230000015572 biosynthetic process Effects 0.000 claims description 7
- 238000003786 synthesis reaction Methods 0.000 claims description 7
- 230000005540 biological transmission Effects 0.000 claims description 4
- 230000001678 irradiating effect Effects 0.000 claims description 4
- 230000002194 synthesizing effect Effects 0.000 claims description 4
- 230000000295 complement effect Effects 0.000 claims description 3
- 230000010354 integration Effects 0.000 claims description 3
- 230000001186 cumulative effect Effects 0.000 claims description 2
- 230000007480 spreading Effects 0.000 claims description 2
- 238000002592 echocardiography Methods 0.000 claims 2
- 238000012545 processing Methods 0.000 abstract description 6
- 230000000007 visual effect Effects 0.000 description 12
- 230000008569 process Effects 0.000 description 11
- 238000010586 diagram Methods 0.000 description 8
- 238000004088 simulation Methods 0.000 description 8
- 230000008859 change Effects 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 3
- 238000012772 sequence design Methods 0.000 description 3
- 238000009825 accumulation Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000010365 information processing Effects 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 238000010187 selection method Methods 0.000 description 1
- 230000008054 signal transmission Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
Landscapes
- Engineering & Computer Science (AREA)
- Remote Sensing (AREA)
- Radar, Positioning & Navigation (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Radar Systems Or Details Thereof (AREA)
Abstract
The invention discloses a universal SAR imaging PRF optimization design method, which comprises the following specific steps: the SAR platform is set to be a curve track with deep diving large squint, the factors of no fuzzy limitation of direction, no fuzzy limitation of distance, no fuzzy limitation of surveying and mapping zone, no interference of altitude echo, no movement, system error and the like of the SAR platform pulse repetition frequency design are comprehensively considered, the PRF of the height-divided sections divided based on the skew interval is adopted for optimized selection, and the PRF values corresponding to different skew intervals in each height section are selected in a traversing mode. The invention realizes the radar echo data recording without blurring and pulse shielding by using less PRF adjusting times, thereby reducing the system complexity. The method can meet the PRF design and SAR imaging processing of different working modes such as beam bunching/banding and the like under different motion states such as dive/horizontal flight and the like, and has universality.
Description
Technical Field
The invention belongs to the technical field of radar signal processing, and particularly relates to a universal SAR imaging PRF optimization design method which can be used for PRF design of different working modes such as bunching/banding and the like under different motion states such as dive/level flight and the like.
Background
Synthetic Aperture Radar (SAR) draws attention of experts in radar fields at home and abroad due to the unique advantages of all weather, all-day time, long action distance, high resolution and the like, is rapidly developed, and shows excellent value in military fields and civil fields as a microwave active imaging system.
With the continuous development of information processing technology and the continuous upgrade of signal processing equipment, the carrying platforms of the SAR are not limited to platforms with simple motion trajectories, such as airplanes and satellites, but also include high-speed mobile platforms, such as high-speed unmanned planes and missiles. Because complex conditions such as terrain avoidance, tactical avoidance, downward diving and the like are faced in the flying process, the high-speed unmanned airborne SAR, missile-borne SAR and the like have flexible and diverse flying tracks, the echo characteristics of the high-speed unmanned airborne SAR and missile-borne SAR are relatively complex, and the corresponding Pulse Repetition Frequency (PRF) time sequence design is also greatly different from the traditional SAR imaging. The existing PRF time sequence design method cannot provide an accurate calculation method for the PRF lower limit, and does not consider the characteristic that the height of a radar platform changes in real time due to a complex motion state.
Disclosure of Invention
In order to solve the above problems, the present invention aims to provide a universal method for optimally designing a PRF for SAR imaging. Deducing a beam coverage area equation through a geometric model, and on the basis, providing an equidistant loop-based method to calculate the bandwidth caused by Doppler center shift to obtain a PRF lower limit under the condition of considering a system and motion errors; a method for dynamically selecting the PRF in the height-divided sections based on the slope distance interval division is provided, a proper PRF value is selected in a specific height section according to the real-time acting distance range of the radar, the radar echo data are recorded without blurring and pulse shielding with fewer PRF adjustment times, the complexity of the system is reduced, and meanwhile, the method is suitable for different motion states and bunching or stripe working modes of the SAR radar and has universality.
The technical idea of the invention is as follows: taking an SAR platform as an example of curve track dive large squint, comprehensively considering factors such as azimuth non-fuzzy limitation, distance non-fuzzy limitation, mapping zone non-fuzzy limitation, altitude echo non-interference, motion, system error and the like of SAR platform pulse repetition frequency design, adopting height-divided segment PRF optimization selection based on slope interval division, and selecting PRF values corresponding to different slope intervals in each height segment in a traversal mode to realize dynamic optimization selection of PRF.
In order to achieve the above object, the present invention adopts the following technical solutions.
A universal SAR imaging PRF optimization design method comprises the following steps:
step 1, establishing an SAR imaging geometric model and an oblique distance model to obtain Doppler bandwidth B after acceleration compensation a (ii) a Establishing a radar beam coverage area equation according to the SAR imaging geometric model, traversing all distance units by an equidistant loop method, determining the maximum value of Doppler center frequency offset, and obtaining the bandwidth brought by the Doppler center offset, namely the Doppler center offset bandwidth B d (ii) a Doppler bandwidth B after compensating acceleration a And Doppler center shift bandwidth B d Add to obtainAzimuth bandwidth B to the echo signal; obtaining a PRF lower limit according to the orientation without fuzzy limit;
step 2, for a given SAR platform height, obtaining the minimum action distance R from the SAR platform to the beam coverage area through a slant range model min And a maximum distance of action R max Obtaining the radar echo dispersion time in the observation area; then, according to the distance without fuzzy limitation, obtaining the PRF upper limit;
wherein, the minimum acting distance R from the SAR platform to the beam coverage area min Namely the minimum value of the slant range and the maximum action distance R from the SAR platform to the beam coverage area max Namely the maximum value of the slope distance;
step 3, for a given SAR platform height, obtaining the minimum acting distance R from the SAR platform to the beam coverage area through a slant range model min And a maximum distance of action R max (ii) a Giving a fuzzy number range of the mapping band, traversing the fuzzy number range of the mapping band according to the non-fuzzy limit of the mapping band, and obtaining a PRF limit interval caused by the fuzzy mapping band;
step 4, for a given SAR platform height, obtaining the minimum acting distance R from the SAR platform to the beam coverage area through a slant range model min And a maximum distance of action R max (ii) a Giving a distance fuzzy number range, traversing the distance fuzzy number range according to the interference-free limit of the altitude echo, and obtaining a PRF limit interval brought to clutter by the altitude;
step 5, for a given SAR platform height, obtaining a Doppler bandwidth error brought by acceleration according to the acceleration of the radar; correspondingly obtaining azimuth bandwidth errors brought by the speed errors and the squint angle errors according to the speed errors and the squint angle errors of the radar; further obtaining the azimuth bandwidth under the condition of considering the acceleration, the speed error and the oblique angle error, namely obtaining the PRF lower limit considering the error;
taking intersection according to the corresponding PRF limit intervals obtained in the steps 1-5 to obtain the PRF optimized value range under any SAR platform height; the step 1-5 is the PRF optimization design principle;
if the motion mode of the SAR platform is linear horizontal flight, traversing a lower view angle value range of the radar for the flight height of the SAR platform, implementing according to the steps 1-5, obtaining a PRF value range corresponding to each skew distance, and drawing a corresponding zebra pattern so as to obtain a corresponding relation between a skew distance interval and the PRF value range; according to a PRF value principle, the corresponding relation between the slant range interval and the PRF value can be obtained, and further the optimized PRF value of the linear level flight SAR imaging is obtained; if the motion mode of the SAR platform is curve track diving, turning to step 6;
wherein, the PRF value principle is as follows: (a) Judging whether a value which can be evenly divided by 1000 exists in a PRF interval to be subjected to value selection, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection; if more than two PRF intervals exist, selecting the value closest to the midpoint of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken; if not, turning to (b);
(b) Judging whether a value which can be evenly divided by 500 exists in a PRF interval to be subjected to value selection, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection; if more than two PRF intervals exist, selecting the value closest to the midpoint of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken; if not, go to (c);
(c) Judging whether a value which can be evenly divided by 100 exists in a PRF interval to be subjected to value taking, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value taking, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value taking; if more than two PRF intervals exist, selecting the value closest to the midpoint of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken;
step 7, drawing a zebra chart of the height section according to all the slope intervals in the height section and all the corresponding PRF value ranges thereof obtained in the step 6, and determining the PRF value ranges corresponding to different slope intervals in the height section; traversing all the height sections to obtain PRF value ranges corresponding to different slope distance intervals in each height section; determining corresponding PRF values of different slope distance intervals in each height section according to a PRF value-taking principle; and selecting an optimized PRF value according to the actual slope distance value in each height section, and finishing the PRF height-divided section optimization selection based on slope distance interval division.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, the PRF lower limit without considering errors is calculated by the Doppler bandwidth based on the slant range model and the equidistant loop method based on the beam coverage area equation, the influence of various motion errors on the PRF lower limit is quantitatively calculated by formula derivation, the PRF lower limit with considering errors is obtained, and the problem that the PRF lower limit cannot be accurately calculated by the traditional PRF time sequence design method is solved.
(2) The method has universality, and can meet the PRF design and SAR imaging processing procedures of different working modes such as bunching/banding and the like under different motion states such as dive/level flight and the like only by adjusting partial parameter values.
(3) Under the dive mode of the SAR platform, the PRF height division section optimization selection method based on the slope distance interval division can reduce PRF adjustment times to the maximum extent and reduce system complexity.
Drawings
The invention is described in further detail below with reference to the figures and the specific embodiments.
FIG. 1 is a flow chart of the method for selecting and optimizing PRF based on height segment division according to the present invention;
FIG. 2 is a curved trajectory dive large squint SAR imaging geometry model in the present invention;
FIG. 3 is a schematic diagram of a radar beam illuminating the ground in a forward looking and forward looking-down mode; wherein, fig. 3 (a) is a schematic diagram of the radar beam irradiating the ground in a forward looking mode, and fig. 3 (b) is a schematic diagram of the radar beam irradiating the ground in a forward looking mode;
FIG. 4 is a schematic diagram of solving parameters of an elliptical equation for frustum beveling;
FIG. 5 is a zebra plot of pulse repetition frequency for known track information in an embodiment of the present invention;
FIG. 6 is a zebra plot of a 24km-27km height section in an embodiment of the present invention;
fig. 7 is a zebra diagram of the 27km-30km height section in the embodiment of the invention.
Detailed Description
The embodiments and effects of the present invention will be described in further detail below with reference to the accompanying drawings.
Referring to fig. 1, a flow diagram of a generalized SAR imaging PRF optimization design method based on the present invention is shown. Taking curve track dive large squint as an example, the method comprises the following specific implementation steps:
step 1, establishing an SAR imaging geometric model and an oblique distance model to obtain Doppler bandwidth B after acceleration compensation a (ii) a Establishing a radar beam coverage area equation according to the SAR imaging geometric model, traversing all distance units by an equidistant loop method, determining the maximum value of Doppler center frequency offset, and obtaining the bandwidth brought by the Doppler center offset, namely the Doppler center offset bandwidth B d (ii) a Doppler bandwidth B after compensating acceleration a And Doppler center offset bandwidth B d Adding to obtain the azimuth bandwidth B of the echo signal; obtaining a PRF lower limit according to the orientation without fuzzy limit;
(1.1) establishing a curve track dive large squint SAR imaging geometric model and a slope distance model to obtain Doppler bandwidth B after acceleration compensation a (ii) a The method is implemented according to the following steps:
(1.1 a) acquiring coordinate system OX of SAR platform in northeast through inertial navigation system on SAR platform 1 Y 1 Z 1 The motion parameter of (1); wherein the motion parameter is the three-dimensional velocity v' = (v) of the platform e ，v n ，v s ) And three-dimensional acceleration a' = (a) e ，a n ，a s ) (ii) a Wherein v is e Is the east velocity component, v, of the SAR platform n Is the north velocity component, v, of the SAR platform s Is SAR flatA table velocity component; a is e Is the east acceleration component of the SAR platform, a n Is the north acceleration component of the SAR platform, a s Is the sky-direction acceleration component of the SAR platform;
will north velocity v n And east velocity v e Performing vector synthesis to obtain a synthesis speed, wherein the direction of the synthesis speed is Y 2 An axial direction; velocity v in the direction of the sky s In the direction of Z 2 Axial direction, establishing a right-hand spatial coordinate system OX 2 Y 2 Z 2 (ii) a Then the east direction acceleration a is measured e And a north acceleration a n Respectively along X 2 Projecting the direction, synthesizing the projected two vectors to obtain a right-hand space coordinate system OX 2 Y 2 Z 2 Inner platform at X 2 Acceleration component a of direction x (ii) a Will accelerate the east direction a e And a north acceleration a n Respectively along Y 2 Projecting in a direction, synthesizing the two projected vectors to obtain a right-hand space coordinate system OX 2 Y 2 Z 2 Inner platform at Y 2 Acceleration component a of direction y The speed and acceleration in the direction of the day being constant, i.e. v s ＝v z ，a s ＝a z (ii) a Obtaining a right-hand spatial coordinate system OX 2 Y 2 Z 2 Velocity vector v = (0,v) of inner platform y ，v z ) And acceleration vector a = (a) x ，a y ，a z )。
(1.1 b) referring to the geometric relationship in FIG. 2, setting that the radar moves from M point to N point within the sub-aperture time, and at the azimuth zero moment, the position of the platform is C point, the intersection point of the beam center line and the ground is P point, the O point is the projection point of the C point on the ground, the OP is the ground projection line of the beam center line, the height of the platform is H, the ground wiping angle is beta, the beam down viewing angle is theta (complementary to the ground wiping angle), the yaw angle is gamma, and the included angle between the velocity vector and the beam center sight vector is gamma
Center slant distance of R s The corresponding spatial squint angle is theta s . For beam coverage when the radar moves to point TA point Q (point Q and point P along OY) 2 Axial distance of y n ) The model of the slant distance between the radar and any point of the beam coverage area is as follows:
wherein the radar has a right-hand spatial coordinate system OX 2 Y 2 Z 2 Inner coordinate is (x) T ，y T ，z T ) Any point in the beam footprint is in the right-hand spatial coordinate system OX 2 Y 2 Z 2 The inner coordinate is (x) Q ，y Q ，z Q )，t m Is the azimuth slow time;
(1.1 c) at azimuth zero time, i.e. t m =0, calculating a second derivative of a slant range model of any point of the radar and the beam coverage area to obtain the Doppler bandwidth B of the radar aa The expression is as follows:
wherein λ is the wavelength, T a The cumulative time of the sub-aperture;
the above equation is simplified as:
wherein, a r Is the equivalent acceleration of the radar, i.e. the projection of the acceleration in the direction of the beam line of sight, v is the modulus of the radar's velocity,
is the equivalent velocity of the radar, i.e. the projection of the velocity in the direction of the beam line of sight.
(1.1 d) solution in reference Beam bunching modeThe method for treating the Deramp by frequency spectrum aliasing introduces an acceleration Deramp factor K aa Compensating the equivalent acceleration of the radar, and combining the relation between the height of the radar and the slope distance: r is s = H/cos θ, obtaining the compensated Doppler bandwidth B a The expression of (c) is:
(1.1 e) setting the range-to-range lateral resolution of the radar image at the inclined plane to ρ a Then the relationship between range-lateral resolution and doppler bandwidth is:
the sub-aperture accumulation time T can be obtained from the above formula a Substituting the compensation data into the expression of the compensated Doppler bandwidth to obtain the compensated Doppler bandwidth B a 。
(1.2) establishing a radar beam coverage area equation according to the imaging geometric model, traversing all distance units by an equidistant loop method, and determining the maximum value of Doppler center frequency offset to obtain a bandwidth B brought by the Doppler center offset d ；
(1.2 a) in a diving section of the radar, in an echographic time period for realizing quick-look imaging by adopting the sub-aperture, the fact that the wave beam does not move is approximately considered, namely, the irradiation scene is the same in the accumulation time of the sub-aperture, and the method is similar to the beaming SAR. When the SAR is imaged in a high squint manner, the wave beam pointing deviation causes the bandwidth brought by Doppler center frequency deviation; the maximum value of the Doppler center frequency shift Δ f within the coverage of one beam dc Comprises the following steps:
wherein,
to know that
Respectively representing the included angles between the pointing direction and the speed of any two different wave beams in the wave beam range;
to represent
And
the maximum value of the difference between the cosines of the two included angles. For accurate calculation of Δ f dc The invention provides a method for determining the maximum value of Doppler center deviation based on an equidistant loop method. Firstly, determining an equation of beam projection on the ground in a dive mode, namely a beam coverage area equation, through beam rotation; a series of equidistant rings are then set according to the range sampling interval, and the maximum value of the doppler center frequency offset is determined by its intersection with the beam footprint equation.
As shown in fig. 3 (a), at the azimuth zero time, the radar is located at point C, and it is assumed that the radar transmits horizontal and elevation beam widths θ in the positive Y-axis direction a And theta r The platform height is H and the beam down-view angle is θ. The radar transmitting beam is represented as an oblate cone in space, a beam coverage area is obtained by irradiating the radar transmitting beam to the ground in an oblique downward view, the oblate cone is obliquely cut by a plane, a section is represented as an ellipse, as shown in fig. 4, an oblique ellipse is equivalent to the beam coverage area, the semi-major axis of the ellipse is set to be a, and the semi-minor axis of the ellipse is set to be b. It is easy to know that the semi-major axis of the ellipse of the beam coverage area is half of the projection length of the beam width in the elevation direction on the ground, that is, the semi-major axis of the ellipse is:
(1.2 b) enabling the distance from the center of the ellipse of the beam coverage area to the ground intersection point of the central line of the beam to be delta, and enabling the distance from the oblate cone cross section ellipse where the center of the circle is located to be h:
because the center of the ellipse of the beam coverage area is positioned on the intersection line of the ellipse and the oblate cross section ellipse, the semiminor axis b of the ellipse of the beam coverage area is half of the length of the intersection line of the ellipse and the oblate cross section ellipse. As shown in fig. 4, the semi-major axis and semi-minor axis of the oblate conic cross section ellipse are:
constructing a coordinate system X ' O ' Y ' by taking the circle center of the oblate cone cross section ellipse as an origin, and establishing an ellipse equation of the oblate cone cross section:
it is easy to know that the two ellipses are intersected at the position where x '= delta. Cos theta, and substituting x' = delta. Cos theta into the elliptic equation of the oblate cone transverse section to obtain half of the length of the intersection line of the two ellipses, namely the semiminor axis of the beam coverage area ellipse: b = y'. The ellipse equation of the beam footprint in the forward looking mode in fig. 3 (a) can thus be obtained as:
(1.2 c) in practice, the operation mode of the imaging radar is not forward looking but forward looking, so the real beam coverage area is rotated on the basis of forward looking, and assuming that the complementary angle (yaw angle) of the radar oblique ground projection is γ, namely, it is equivalent to rotate the beam coverage area clockwise by γ degrees along the Z axis, as shown in fig. 3 (b), then the equation of the beam coverage area in the forward looking mode is obtained as follows:
(1.2 d) setting equidistant rings as shown in fig. 3 (B) at intervals of projection of distance to the resolution on the ground, wherein each equidistant ring has two intersection points (except the range of the beam coverage areas of two end points) with the beam coverage area, traversing all distance units in the beam coverage area, and obtaining the bandwidth B brought by the maximum Doppler frequency deviation d 。
(1.3) obtaining a PRF lower limit according to the orientation without fuzzy limit;
namely, according to the condition that the PRF is larger than the azimuth bandwidth to ensure that the signal does not generate azimuth aliasing, the lower limit of the pulse repetition frequency is obtained as follows:
PRF≥1.2*B，
B＝B a +B d ；
step 2, for a given SAR platform height, obtaining the minimum action distance R from the SAR platform to the beam coverage area through a slant range model min And a maximum distance of action R max Obtaining the radar echo dispersion time in the observation area; then, according to the distance without fuzzy limitation, obtaining the PRF upper limit;
wherein, the minimum acting distance R from the SAR platform to the beam coverage area min Namely the minimum value of the slant range and the maximum action distance R from the SAR platform to the beam coverage area max I.e. the maximum value of the pitch.
Under the conditions of high flying height and long acting distance of the radar, the round trip of the echo usually needs a plurality of pulse repetition periods, so that the PRF is designed to ensure that the echo at the far end of the coverage area of the antenna beam is received by a radar receiver before the next near-end echo arrives, namely the radar echo dispersion time in the observation areaNo more than one pulse interval; thus, the distance-free ambiguity limits the minimum value of the pulse repetition time. The upper limit of the pulse repetition frequency PRF is limited by the reciprocal relationship between the pulse repetition time PRT and the pulse repetition frequency PRF. As shown in FIG. 1, the radar echo dispersion time T in the observation area w Comprises the following steps:
wherein c is the speed of light, T p To emit pulse width, theta r And theta is the beam width in the elevation direction of the radar, and theta is the beam down-view angle. In practice, the beam width theta of the radar in the pitching direction r Generally small, according to the substitution criterion of infinitesimal equivalence: sinx-x (x → 0), the radar echo dispersion time in the observation area can be simplified as:
according to the requirement that the pulse repetition time is greater than the radar echo spreading time, the lower limit of the PRT, namely the upper limit of the PRF, can be obtained:
wherein (T) w ) max The maximum value of the radar echo dispersion time in the observation area is selected for a fixed PRF over a period of time.
Step 3, for a given SAR platform height, obtaining the minimum acting distance R from the SAR platform to the beam coverage area through a slant range model min And a maximum distance of action R max (ii) a Setting a fuzzy number range of the surveying and mapping zone, traversing the fuzzy number range of the surveying and mapping zone according to the condition that the surveying and mapping zone has no fuzzy limit, and obtaining a PRF limit interval caused by the fuzzy surveying and mapping zone;
due to the complexity of the system, the radar generally uses a transmitting and receiving common antenna, so that the radar cannot receive echo signals within the signal transmission time, i.e. when echo pulses enter a transmission pulse packetThe distance shielding phenomenon can occur when the door is closed, so that the echo information is lost. To avoid this, the swath unambiguous limit is translated into the following two constraints: firstly, the echo time delay of the radar reaching the nearest distance of the surveying and mapping belt can not be less than m.PRT + T p Wherein m represents a fuzzy number of a surveying and mapping zone, the value of the fuzzy number is a natural number, PRT is pulse repetition time, and otherwise aliasing is generated between the fuzzy number and the (m + 1) th emission pulse; secondly, the echo time delay of the farthest distance of the radar reaching the surveying and mapping zone cannot be larger than (m + 1) PRT-T p Otherwise, aliasing will occur with the m +2 th transmit pulse. These two conditions ensure that the radar echo in the swath is received within the same pulse repetition period, taking into account that the switching of the radar antenna transmission and reception requires a guard time τ r The constraint to obtain a swath without ambiguity limit can be expressed as:
wherein, T p To transmit the pulse width.
According to the fuzzy limitation of the mapping zone, traversing the fuzzy number range of the mapping zone, which is specifically as follows:
starting from the smaller end value of the fuzzy number range of the mapping zone, adding 1 to the fuzzy number of the mapping zone each time until the larger end value of the fuzzy number range of the mapping zone is obtained, and traversing the fuzzy number range of the mapping zone; calculating a PRT range meeting the constraint condition according to the constraint condition that the mapping band has no fuzzy limit when taking a fuzzy number of the mapping band, and further obtaining a corresponding PRF range;
and (4) taking intersection of all the PRF ranges corresponding to the fuzzy numbers of the mapping bands meeting the fuzzy limit of the mapping bands, so as to obtain the PRF limit interval caused by the fuzzy limit of the mapping bands.
I.e. the effect of the unambiguous band limit on the pulse repetition frequency PRF.
Step 4, for a given SAR platform height, obtaining the minimum action distance R from the SAR platform to the beam coverage area through a slant range model min And a maximum distance of action R max (ii) a Giving a range of distance ambiguity numbers; according to the heightWave interference-free limitation, traversing a range of distance fuzzy numbers to obtain a PRF limitation interval brought by the height to the clutter;
in the radar motion process, the ground projection point is nearest to the radar and generates specular reflection, and the influence is generated on the in-band echo of the mapping band, so that the height direction echo needs to be avoided when the echo is received, otherwise, the interference of the height direction echo with high energy can form bright stripes on a radar image, and the imaging result is influenced. To avoid this, two constraints are set: firstly, the difference between the time of the radar reaching the nearest distance of the surveying and mapping zone and the time of the height direction echo to the radar can not be less than n-PRT +2T p Wherein n represents a distance fuzzy number, and the value of the distance fuzzy number is a natural number; 2T of p If the pulse width of the signal is the height clutter, otherwise, the (n + 1) th height echo enters a radar echo signal; secondly, the difference between the time of the radar reaching the farthest distance of the surveying and mapping strip and the time of the altitude echo to the radar cannot be larger than (n + 1) PRT-T p Otherwise, the (n + 2) th altitude would be echoed back into the radar echo signal. The two conditions ensure that the radar echo receiving avoids the high echo interference, and the expression of the constraint condition of the high echo interference-free band is as follows:
the method for traversing the range of the distance fuzzy number according to the interference-free limitation of the height echo specifically comprises the following steps:
starting from the smaller end value of the range of the distance fuzzy number, adding 1 to the distance fuzzy number each time until the larger end value of the range of the distance fuzzy number is obtained, and completing traversing the range of the distance fuzzy number; calculating a PRT range meeting the constraint condition according to the constraint condition of the interference-free limit of the altitude echo after each distance fuzzy number is taken, and further obtaining a PRF range meeting the condition;
and (4) taking intersection of all PRF ranges corresponding to the distance fuzzy numbers meeting the interference-free limit of the altitude echo, so as to obtain a PRF limit interval brought by the interference-free limit of the altitude echo.
I.e. a high degree of echo without interference on the pulse repetition frequency PRF.
Step 5, for a given SAR platform height, obtaining a Doppler bandwidth error brought by acceleration according to the acceleration of the radar; correspondingly obtaining azimuth bandwidth errors brought by the speed errors and the squint angle errors according to the speed errors and the squint angle errors of the radar; further obtaining the azimuth bandwidth under the condition of considering the acceleration, the speed error and the oblique angle error, namely obtaining the PRF lower limit considering the error;
(5.1) Doppler bandwidth error caused by acceleration, which is specifically as follows: in the radar flight process, the existence of three-dimensional acceleration can directly influence the Doppler bandwidth, so that the lower limit of PRF is influenced, and the Doppler bandwidth error caused by the acceleration is obtained as follows:
wherein, T a Is the sub-aperture integration time.
(5.2) Doppler center shift bandwidth error brought by velocity error and azimuth bandwidth error brought by squint angle error are specifically as follows: the PRF value is influenced by factors such as unstable airflow and self-shaking, and motion errors such as speed errors and beam pointing errors exist in the flying process of the radar, so that the PRF value is influenced.
First, the velocity error directly affects the azimuth bandwidth, assuming a horizontal velocity error of Δ v y And a vertical velocity error of Δ v z The obtained doppler center offset bandwidth error caused by the velocity error is:
wherein,
and
respectively representing any two differences within the beam rangeThe beam pointing direction of (a) and the speed;
to represent
And
the maximum value of the difference between the cosines of the two included angles; v denotes a velocity vector of the radar.
Secondly, the beam pointing error directly affects the azimuth bandwidth, and the error of the radar velocity vector and the beam pointing angle is assumed as
The azimuth bandwidth error caused by the squint angle error is obtained as follows:
in addition, the system design has a beam broadening problem, and the azimuth or elevation beam broadening can cause the ground projection area to be widened, so that the bandwidth caused by Doppler center shift is influenced, and the PRF lower limit is further influenced.
And (4) taking intersection according to the corresponding PRF limit intervals obtained in the steps 1-5 to obtain the PRF optimized value range under any SAR platform height.
For the SAR working in a dive large squint mode, the platform height H and the downward view angle θ constantly change, and the fixed PRF value cannot ensure that the radar meets the requirements of no blurring and no pulse shielding in the imaging time, so the PRF needs to be constantly adjusted according to the height and the downward view angle, but frequent adjustment of the PRF brings great difficulty to the system design, and is not beneficial to implementation.
(6.1) height segment division:
setting the PRF adjustment times of the system as M, wherein one height section corresponds to one PRF value, and uniformly dividing the dive part of the SAR platform into M height sections.
Wherein the length of the dive part of the SAR platform is L.
(6.2) height interval division:
for any height section, the distance step amount is set to be delta l, the distance step amount is generally taken to be 10-100 m, and the height section is divided into
And taking the height value corresponding to the midpoint position of each height section as the height of the section.
(6.3) determining PRF by height interval:
for any altitude interval, traversing all lower visual angle value ranges (which are related to the system design of the SAR platform, generally taking the upper limit and the lower limit of the radar working lower visual angle to meet various conditions in the flying process of the platform), and obtaining a series of slope distance values of the altitude interval and a PRF value range corresponding to each slope distance value according to a PRF optimization design principle; and traversing all height intervals in the height section to obtain all slope values in the height section and a PRF value range corresponding to each slope value.
The traversing all the lower view angle value ranges specifically include: and setting a lower visual angle value range and a lower visual angle step amount, and moving one step amount at a time from the lower limit of the lower visual angle value range to correspondingly obtain a lower visual angle until the lower visual angle value range is moved to the upper limit of the lower visual angle value range.
Wherein, a radar range (namely an inclined distance value) is determined by one height interval and one lower visual angle, and one inclined distance value corresponds to one PRF value range.
For the SAR platform working in a diving state, the change range of the lower view angle in a certain height section is generally smaller, so that interval division can be performed according to the slope distance uniquely determined by the height and the lower view angle, and PRF values corresponding to different slope distance intervals in the height section are predetermined. In the whole dive imaging process, the PRF value of a few times is adjusted according to the radar platform position information provided by the inertial navigation system, so that the unambiguous and pulse-free shielding and recording of the echo data of the surveying and mapping belt in the imaging time can be realized, and the problem that the PRF value cannot be adjusted in real time along with the height change of the SAR platform is solved. In the large squint SAR imaging of the mobile platform, because the SAR images are output at a certain frame rate, the echo data of the same PRF are selected as a group for imaging processing, so that the change of the PRF can not influence the SAR imaging.
Step 7, drawing a zebra diagram of the height section according to all the slant range sections in the height section and all the PRF value ranges corresponding to the slant range sections obtained in the step 6, and determining the PRF value ranges corresponding to different slant range sections in the height section; traversing all the height sections to obtain PRF value ranges corresponding to different slope distance intervals in each height section; determining corresponding PRF values of different slope distance intervals in each height section according to a PRF value-taking principle; and selecting an optimized PRF value according to the actual slope distance value in each height section, and finishing the PRF height-divided section optimization selection based on slope distance interval division.
The PRF value-taking principle is specifically as follows: (a) Judging whether a value which can be evenly divided by 1000 exists in a PRF interval to be subjected to value selection, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection; if more than two PRF intervals exist, selecting the value closest to the midpoint of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken; if not, go to (b);
(b) Judging whether a value which can be evenly divided by 500 exists in a PRF interval to be subjected to value selection, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection; if more than two PRF intervals exist, selecting the value closest to the midpoint of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken; if not, go to (c);
(c) Judging whether a value which can be evenly divided by 100 exists in a PRF interval to be subjected to value taking, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value taking, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value taking; and if more than two PRF intervals exist, selecting the value closest to the middle point of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken.
In the present invention, if the acceleration is set to zero, i.e., a = (a) x ，a y ，a z ) =0, the optimized PRF value of the linear dive SAR imaging can be obtained by implementing the steps 1-7, and the optimized selection of the PRF height-divided section based on the slope distance interval division of the linear dive SAR imaging is completed;
if the set acceleration and the day-direction speed are both zero, the three-dimensional acceleration a' = (a) e ，a n ，a s ) =0 and v s =0, traversing the lower view angle range of the radar for the fixed platform height, performing according to the steps 1-5, obtaining a PRF value range corresponding to each slope distance, and drawing a corresponding zebra diagram, thereby obtaining the corresponding relation between the slope distance interval and the PRF value range; according to a PRF value principle, the corresponding relation between the slant range interval and the PRF value can be obtained, and further the optimized PRF value of the linear level flight SAR imaging is obtained;
in the above process, when the zebra crossing map obtains the corresponding relationship between the skew distance interval and the PRF value range, the zebra crossing map needs to be divided according to actual design requirements.
If the Doppler center frequency deviation is set to be zero, when the maximum value of the Doppler center frequency deviation in the step (1.2 a) is 0, the steps 1-7 are carried out, and the optimized PRF value of SAR imaging under the strip mode of curve track diving and large squint can be obtained.
Therefore, the SAR imaging method based on the beam forming and the beam focusing can be suitable for PRF design and SAR imaging processing of different working modes such as beam forming and banding under different motion states such as dive and level flight of the SAR platform, and has universality.
Simulation experiment
The effectiveness of the invention is verified by simulation experiments below, and the simulation parameters are shown in the table.
TABLE 1 System simulation parameters
The whole simulation process is divided into two parts, wherein the first part verifies the effectiveness of the method under the condition of known track information (including information such as platform height, platform speed, acceleration and the like); and in the second part, under the condition of unknown track information, pre-estimating corresponding non-fuzzy and non-pulse-shielding PRF values of different slope distance intervals in different height sections so as to select a proper PRF value according to the height and slope distance information in real-time imaging.
The method comprises the following steps of (A) selecting PRF experiment simulation parameters according to known track information (fixed height section): the platform height is 28km, the central downward viewing angle is 64 degrees, the downward viewing angle fluctuation range is +/-2 degrees, the three-dimensional speed and the three-dimensional acceleration of the platform in a northeast coordinate system are respectively (128, 910, -320) m/s and (8.2, -7.1, -12.4) m/s 2 The synthetic aperture time is 0.5s, and the lower limit of PRF corresponding to the central lower visual angle is 3541Hz under the condition of not considering errors; assuming that the speed error of the platform along the northeast direction is +/-5 m/s, the beam pointing error is +/-0.2 degrees, and under the condition of considering the errors, the PRF value corresponding to the central lower view angle is 3812Hz. Since the PRF upper limit is greater than 10000Hz, it is not considered here.
Fig. 5 is a PRF zebra plot with known track information, where the black areas are swath blur areas, the gray areas are high clutter interference areas, the white areas are PRF selectable areas, and the central downward viewing angle is 64 °. When selecting the PRF, the fuzzy area and the high clutter interference area of the swath are avoided, and the range is within the range of the upper and lower limits selectable by the PRF, as shown in fig. 5, under the condition that a certain margin is left (in the practical engineering application, that is, the skew distance interval of the PRF is relatively large, a certain space is left between the PRF value and the fuzzy area and the interference area in the zebra chart, and meanwhile, the PRF is rounded as much as possible), the PRF is set to 5800Hz, so that the requirement in the practical engineering can be met.
Under the general condition, the actual working track information of the maneuvering platform cannot be known in advance, and in order to prevent real-time calculation in the working process of the radar and ensure that the SAR imaging is influenced by selecting proper PRF, the conditions of different heights and lower visual angles need to be considered in advance, and corresponding PRF values are designed. Before imaging, the system judges the height section and the lower visual angle according to inertial navigation parameters and the like to determine the range of the slope distance, so that a corresponding PRF value is selected, and finally, a non-fuzzy and non-shielding SAR image is obtained.
Selecting PRF experiment simulation parameters from unknown track information (selecting PRF according to height sections): two height segment ranges were selected: 24km to 27km and 27km to 30km, a height step of 10m, a lower viewing angle range of 30 DEG to 70 DEG, and a lower viewing angle step of 0.01 deg.
Fig. 6 shows a PRF zebra plot of a 24km-27km altitude section, fig. 7 shows a PRF zebra plot of a 27km-30km altitude section, and PRF values corresponding to different slope ranges in different altitude sections are obtained according to preset PRF values, as shown in tables 2 and 3.
TABLE 2 24km-27km altitude segment slope interval division and PRF selection Table
TABLE 3 27km-30km altitude segment slope distance interval division and PRF selection table
In the radar working process, the change of the lower view angle in a certain height section is very small, so that the range of the slope distance of the radar working is easily obtained, and a proper PRF value can be selected according to the PRF values corresponding to different range of the slope distance of the height section, namely, the PRF values shown in the tables 2 and 3, so that in the whole diving process, the non-shielding irradiation of the transmission signal to the whole imaging area can be realized only by changing the PRF value of the set adjustment times. As can be seen from FIG. 7, in the height section, when the working distance is 64km, selecting the PRF of 5800Hz can ensure no pulse shielding, which is identical with the simulation result of the known track information, and further proves the effectiveness of the method for selecting the PRF in the height section. The method can greatly reduce the PRF conversion times and is suitable for engineering application.
Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present invention, and shall cover the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A universal SAR imaging PRF optimization design method is characterized by comprising the following steps:
step 1, establishing an SAR imaging geometric model and an oblique distance model to obtain Doppler bandwidth B after acceleration compensation a (ii) a Establishing a radar beam coverage area equation according to the SAR imaging geometric model, traversing all distance units by an equidistant loop method, determining the maximum value of Doppler center frequency offset, and obtaining the bandwidth brought by the Doppler center offset, namely the Doppler center offset bandwidth B d (ii) a Doppler bandwidth B after compensating acceleration a And Doppler center offset bandwidth B d Adding to obtain the azimuth bandwidth B of the echo signal; obtaining a PRF lower limit according to the orientation without fuzzy limit;
wherein PRF is the pulse repetition frequency;
step 2, for a given SAR platform height, obtaining the minimum action distance R from the SAR platform to the beam coverage area through a slant range model min And maxDistance of action R max Obtaining the radar echo dispersion time in the observation area; then, according to the distance without fuzzy limitation, obtaining the PRF upper limit;
wherein, the minimum acting distance R from the SAR platform to the beam coverage area min Namely the minimum value of the slant distance and the maximum action distance R from the SAR platform to the beam coverage area max Namely the maximum value of the slope distance;
step 3, for a given SAR platform height, obtaining the minimum acting distance R from the SAR platform to the beam coverage area through a slant range model min And a maximum distance of action R max (ii) a Setting a fuzzy number range of the surveying and mapping zone, traversing the fuzzy number range of the surveying and mapping zone according to the condition that the surveying and mapping zone has no fuzzy limit, and obtaining a PRF limit interval caused by the fuzzy surveying and mapping zone;
step 4, for a given SAR platform height, obtaining the minimum acting distance R from the SAR platform to the beam coverage area through a slant range model min And a maximum distance of action R max (ii) a Giving a distance fuzzy number range, traversing the distance fuzzy number range according to the interference-free limit of the altitude echo, and obtaining a PRF limit interval brought to clutter by the altitude;
step 5, for a given SAR platform height, obtaining a Doppler bandwidth error brought by acceleration according to the acceleration of the radar; correspondingly obtaining an azimuth bandwidth error brought by the speed error and an azimuth bandwidth error brought by the squint angle error according to the speed error and the squint angle error of the radar; further obtaining the azimuth bandwidth under the condition of considering the acceleration, the speed error and the oblique angle error, namely obtaining the PRF lower limit considering the error;
taking intersection according to the corresponding PRF limit intervals obtained in the steps 1-5 to obtain a PRF optimized value range under the given SAR platform height; the step 1-5 is the PRF optimization design principle;
if the motion mode of the SAR platform is linear horizontal flight, traversing a lower view angle value range of the radar for the flight height of the SAR platform, implementing according to the steps 1-5, obtaining a PRF value range corresponding to each skew distance, and drawing a corresponding zebra pattern so as to obtain a corresponding relation between a skew distance interval and the PRF value range; according to a PRF value principle, the corresponding relation between the slant range interval and the PRF value can be obtained, and further the optimized PRF value of the linear level flight SAR imaging is obtained; if the motion mode of the SAR platform is curve track diving, turning to step 6;
wherein, the PRF value principle is as follows: (a) Judging whether a value which can be evenly divided by 1000 exists in a PRF interval to be subjected to value selection, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection; if more than two PRF intervals exist, selecting the value closest to the midpoint of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken; if not, turning to (b);
(b) Judging whether a value which can be evenly divided by 500 exists in a PRF interval to be subjected to value selection, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value selection; if more than two PRF intervals exist, selecting the value closest to the midpoint of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken; if not, go to (c);
(c) Judging whether a value which can be evenly divided by 100 exists in a PRF interval to be subjected to value taking, if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value taking, and if so, selecting the value as the PRF value corresponding to the PRF interval to be subjected to value taking; if more than two PRF intervals exist, selecting the value closest to the midpoint of the PRF interval to be taken as the PRF value corresponding to the PRF interval to be taken;
step 6, dividing a diving part of the SAR platform into a plurality of height sections according to the motion track of the SAR platform; dividing each height section into a plurality of height intervals; for any height section, traversing a lower view angle value range of the radar according to the platform height in any height section in the height section, and obtaining an inclined distance interval corresponding to the height section and a PRF value range corresponding to each inclined distance according to a PRF optimization design principle; traversing all height intervals in the height section to obtain all slope distance intervals corresponding to the height section and all PRF value ranges corresponding to the slope distance intervals;
step 7, drawing a zebra chart of the height section according to all the slope intervals in the height section and all the corresponding PRF value ranges thereof obtained in the step 6, and determining the PRF value ranges corresponding to different slope intervals in the height section; traversing all the height sections to obtain PRF value ranges corresponding to different slope distance intervals in each height section; determining corresponding PRF values of different slope distance intervals in each height section according to a PRF value-taking principle; and selecting an optimized PRF value according to the actual slope distance value in each height section, and finishing the PRF height-divided section optimization selection based on slope distance interval division.
2. The generalized SAR imaging PRF optimization design method according to claim 1, characterized in that in step 1, for curve trajectory dive large squint SAR, the SAR imaging geometric model and the slant range model are established to obtain Doppler bandwidth B after acceleration compensation a (ii) a The method is implemented according to the following steps:
(1.1 a) acquiring coordinate system OX of SAR platform in northeast through inertial navigation system on SAR platform 1 Y 1 Z 1 The motion parameter of (1); wherein the motion parameter is the three-dimensional velocity v' = (v) of the platform e ，v n ，v s ) And three-dimensional acceleration a' = (a) e ，a n ，a s )；
Wherein v is e Is the east velocity component, v, of the SAR platform n Is the north velocity component, v, of the SAR platform s Is the space velocity component of the SAR platform; a is e Is the east acceleration component of the SAR platform, a n Is the north acceleration component of the SAR platform, a s Is the sky-direction acceleration component of the SAR platform;
will north velocity v n And east velocity v e Vector synthesis is carried out to obtain a synthesis velocity v y Synthetic velocity v y In the direction of Y 2 An axial direction; velocity v in the direction of the sky s In the direction of Z 2 Axial direction, establishing a right-hand spatial coordinate system OX 2 Y 2 Z 2 (ii) a Obtaining a right-hand spatial coordinate system OX 2 Y 2 Z 2 Velocity vector v = (0,v) of inner platform y ，v z ) And acceleration vector a = (a) x ，a y ，a z )；
Wherein v is y Is the north velocity v n And east velocity v e Carrying out vector synthesis to obtain a synthesis speed; v. of z Is a right-hand spatial coordinate system OX 2 Y 2 Z 2 Inner platform in Z 2 A velocity component of direction, and v z ＝v s ；a x For a right-hand spatial coordinate system OX 2 Y 2 Z 2 Inner platform at X 2 The acceleration component of the direction, which is specifically: will accelerate east to a e And a north acceleration a n Respectively along X 2 Projecting in a direction, and synthesizing the two projected vectors to obtain the vector; a is a y For a right-hand spatial coordinate system OX 2 Y 2 Z 2 Inner platform at Y 2 The acceleration component of the direction, which is specifically: will accelerate east to a e And a north acceleration a n Respectively along Y 2 Performing directional projection, and synthesizing the projected two vectors to obtain the directional projection; a is z For a right-hand spatial coordinate system OX 2 Y 2 Z 2 Inner platform in Z 2 Acceleration component of direction, and a z ＝a s ；
(1.1 b) setting a slant distance model of any Q point of the radar and the beam coverage area when the radar moves to the T point as follows:
wherein, when the radar moves to the T point, the space coordinate system OX of the right hand 2 Y 2 Z 2 The inner coordinate is (x) T ，y T ，z T ) Any Q point in the beam coverage area is in the right-hand space coordinate system OX 2 Y 2 Z 2 The inner coordinate is (x) Q ，y Q ，z Q )，t m Is the azimuth slow time; h is the platform height, theta is the angle of view under the beam, R s Is a center slope distance, theta s Is a spatial oblique view angle, y n Point Q and point P are in OY 2 The distance in the direction, P point is the intersection point of the beam central line and the ground;
(1.1 c) at the azimuth zero moment, solving a second derivative of the slant distance model of any Q point of the radar and the beam coverage area to obtain the Doppler bandwidth B of the radar aa The expression is as follows:
wherein λ is the carrier wavelength, T a Is the sub-aperture integration time;
the above equation is simplified as:
wherein, a r Is the equivalent acceleration of the radar, i.e. the projection of the acceleration in the direction of the beam line of sight, v is the modulus of the radar's velocity,
is the equivalent velocity of the radar, i.e. the projection of the velocity in the beam line-of-sight direction;
the included angle between the velocity vector and the sight line vector of the beam center is obtained;
(1.1 d) introducing an acceleration Deramp factor K aa Equivalent acceleration a to radar r Compensation is carried out, and the relation between the height and the slope distance of the radar is combined: r s = H/cos θ, obtaining the compensated Doppler bandwidth B a The expression of (a) is:
(1.1 e) setting the radar imaging to be inclined and flatTransverse resolution of the distance of the faces is rho a Then the relationship between range-lateral resolution and doppler bandwidth is:
from the above equation, the sub-aperture cumulative time T is obtained a Substituting the compensated Doppler bandwidth B a Is expressed as (A), the Doppler bandwidth B is obtained a 。
3. The generalized SAR imaging PRF optimization design method according to claim 1, characterized in that in step 1, for curve trajectory dive large squint SAR, a radar beam coverage equation is established according to SAR imaging geometric model, all distance units are traversed by equidistant loop method, the maximum value of Doppler center frequency offset is determined, and the bandwidth brought by Doppler center offset, namely Doppler center offset bandwidth B, is obtained d (ii) a The method is implemented according to the following steps:
(1.2 a) setting a dive part of a radar, wherein the irradiation scenes in the accumulated time of the sub-apertures are the same, and when a dive large squint SAR is imaged, the beam pointing offset causes the bandwidth brought by Doppler center frequency offset; the maximum value of the Doppler center frequency shift Δ f within the coverage of one beam dc Comprises the following steps:
where λ is the carrier wavelength, v is the mode of the radar's velocity,
and
respectively representing the included angles between the pointing direction and the speed of any two different wave beams in the wave beam range;
represent
And
the maximum value of the difference between the cosines of the two included angles;
(1.2 b) the radar transmitting beam is a flat cone in space, the beam coverage area is obtained by irradiating the beam to the ground in an oblique downward view, namely the flat cone is obliquely cut by a plane, the section is a flat cone cross section ellipse, the beam coverage area is an oblique ellipse, the semimajor axis of the oblique ellipse is set to be a, the semiminor axis of the oblique ellipse is set to be b, the semimajor axis of the oblique ellipse is half of the projection length of the beam width in the pitching direction on the ground, namely the semimajor axis of the oblique ellipse is:
wherein H is the radar platform height, theta is the angle of view under the beam, theta a For radar transmission in the positive Y-axis direction with horizontal beam width, theta r Transmitting the width of a pitching wave beam to the positive direction of the Y axis for the radar;
and (3) setting the distance from the circle center of the oblique ellipse to the ground intersection point of the central line of the wave beam as delta and the distance from the oblate cross section ellipse to the position of the radar at the azimuth zero moment as h, then:
the semimajor axis a 'and semiminor axis b' of the oblate conic cross section ellipse are respectively:
constructing a coordinate system X ' O ' Y ' by taking the circle center of the oblate cone cross section ellipse as an origin, and establishing an ellipse equation of the oblate cone cross section as follows:
obtaining the intersection of the oblique ellipse and the ellipse of the transverse section of the oblate cone at the position of x ' = delta · cos theta, and substituting the x ' = delta · cos theta into an oblique ellipse equation to obtain a semi-minor axis b = y ' of the oblique ellipse; thus, the ellipse equation of the beam coverage area under the forward-looking mode is obtained as follows:
(1.2 c) setting a yaw angle gamma of the radar, namely setting the complementary angle of the radar oblique-view ground projection as gamma, namely clockwise rotating the beam coverage area by gamma degrees along the Z axis, and obtaining a beam coverage area equation under a front oblique-view mode as follows:
(1.2 d) setting equidistant rings by taking projection of distance to resolution ratio on the ground as an interval, wherein each equidistant ring and a beam coverage area have an intersection point, traversing all distance units in the beam coverage area, solving the maximum value of Doppler center frequency deviation, and further obtaining Doppler center deviation bandwidth B d 。
4. The generalized SAR imaging PRF optimization design method according to claim 1, characterized in that in step 1, the PRF lower limit is obtained without fuzzy limit according to the orientation; the method comprises the following steps:
according to the condition that the PRF is not less than the azimuth bandwidth to ensure that the signal does not generate azimuth aliasing, the lower limit of the obtained pulse repetition frequency is as follows:
PRF≥1.2*B，
B＝B a +B d 。
5. the PRF optimization design method for general SAR imaging according to claim 1, characterized in that in step 2, for curve-track dive large squint SAR, the distance is not fuzzy limited to that the radar echo dispersion time in the observation area does not exceed one pulse interval; radar echo dispersion time T within the observation area w Comprises the following steps:
where c is the speed of light, H is the radar platform height, T p To emit pulse width, theta r The width of a wave beam in the pitching direction of the radar is regarded as theta, and the lower view angle of the wave beam is regarded as theta;
according to the equivalent infinitesimal replacement criterion, the above equation is simplified as:
according to the relationship that the pulse repetition time and the pulse repetition frequency are reciprocal to each other, the lower limit of the pulse repetition time, namely the upper limit of the pulse repetition frequency is obtained:
PRT≥(T w ) max i.e. by
Wherein PRT is pulse repetition time, and PRF is pulse repetition frequency; (T) w ) max And selecting the maximum value of the radar echo spreading time in the observation area within the period for presetting the PRF.
6. The generalized SAR imaging PRF optimization design method according to claim 1, wherein in step 3, traversing the range of the fuzzy number of the mapping band according to the non-fuzzy constraint of the mapping band specifically comprises:
first, the swath unambiguous limit is translated into the following two constraints: firstly, the echo time delay of the nearest distance of the radar reaching mapping zone cannot be less than m.PRT + T p (ii) a Secondly, the echo time delay of the farthest distance of the radar reaching the surveying and mapping zone cannot be larger than (m + 1) PRT-T p (ii) a The expression of the constraint condition that the corresponding mapping band has no ambiguity limit is:
wherein m represents the fuzzy number of the mapping zone, and PRT is the pulse repetition time and is reciprocal to PRF; tau. r Protection time required for switching between transmitting and receiving of radar antenna, c is speed of light, H is radar platform height, T p To emit pulse width, theta r The width of a wave beam in the pitching direction of the radar is regarded as theta, and the lower view angle of the wave beam is regarded as theta;
secondly, starting from the smaller end value of the fuzzy number range of the mapping zone, adding 1 to the fuzzy number of the mapping zone each time until the larger end value of the fuzzy number range of the mapping zone is obtained, and traversing the fuzzy number range of the mapping zone; calculating a PRT range meeting a constraint condition according to the constraint condition that the mapping zone has no fuzzy limit when taking a mapping zone fuzzy number, and further obtaining a corresponding PRF range;
and finally, taking intersection of all PRF ranges corresponding to the fuzzy numbers of the mapping bands meeting the fuzzy limit of the mapping bands, and obtaining the PRF limit interval caused by the fuzzy limit of the mapping bands.
7. The generalized SAR imaging PRF optimization design method according to claim 1, characterized in that, in step 4, according to the high echo interference-free limit, the range of distance ambiguity is traversed, which specifically is:
firstly, the height echo interference-free limit is converted into the following two constraints: first, the time and height of the nearest distance from the radar to the surveying and mapping belt are reflected toThe time difference of the radar can not be less than n-PRT +2T p (ii) a Secondly, the difference between the time of the radar reaching the farthest distance of the surveying and mapping strip and the time of the height direction echo to the radar cannot be larger than (n + 1) · PRT-T p (ii) a The expression of the constraint condition of the corresponding high echo interference-free limit is:
where c is the speed of light, H is the radar platform height, T p To emit pulse width, theta r For the radar elevation beam width, theta is the beam down-view angle, n represents the range ambiguity number, 2T p Is the signal pulse width of the elevation clutter;
secondly, starting from the smaller end value of the range of the distance fuzzy number, adding 1 to the distance fuzzy number each time until the larger end value of the range of the distance fuzzy number is obtained, and then traversing the range of the distance fuzzy number; calculating a PRT range meeting the constraint condition according to the constraint condition of the interference-free limit of the altitude echo after each distance fuzzy number is taken, and further obtaining a PRF range meeting the condition;
and finally, taking intersection sets of all PRF ranges corresponding to the distance fuzzy numbers meeting the interference-free limit of the altitude echoes, so as to obtain a PRF limit interval brought by the interference-free limit of the altitude echoes.
8. The generalized SAR imaging PRF optimization design method according to claim 2, characterized in that for curve trajectory dive large squint SAR, the Doppler bandwidth error caused by the acceleration is expressed as:
wherein, T a Is the sub-aperture integration time;
for curve track dive large squint SAR, the Doppler center offset bandwidth error caused by the speed error is expressed as:
wherein,
and
respectively representing the included angles between the pointing direction and the speed of any two different wave beams in the wave beam range;
to represent
And
the maximum value of the difference between the cosines of the two included angles; v represents a mode of the velocity of the radar; Δ v y Velocity error in Y-axis direction, Δ v z Is the speed error in the Z-axis direction;
for a curve track dive large squint SAR, the azimuth bandwidth error caused by the squint angle error is expressed as follows:
wherein,
the error of the angle between the radar velocity vector and the beam pointing direction is shown.
9. The generalized SAR imaging PRF optimization design method according to claim 1, characterized in that step 6 is implemented according to the following steps:
(6.1) height section division:
setting the PRF adjustment times of the system as M, wherein one height section corresponds to one PRF value, and uniformly dividing the diving part of the SAR platform into M height sections;
wherein the length of the diving part of the SAR platform is L;
(6.2) height interval division:
for any height segment, a distance step amount is set to be delta l, and the height segment is divided into
Taking a height value corresponding to the midpoint position of each height interval as the height of the interval;
(6.3) determining PRF by height interval:
for any height interval, traversing all the lower view angle value ranges, and obtaining a series of slope distance values of the height interval and a PRF value range corresponding to each slope distance value according to a PRF optimization design principle; traversing all height intervals in the height section to obtain all slope values in the height section and a PRF value range corresponding to each slope value;
wherein, an altitude interval and a downward viewing angle jointly determine an inclination distance value, and one inclination distance value corresponds to a PRF value range.
10. The generalized SAR imaging PRF optimization design method according to any of claims 2-9, characterized by that if the set acceleration is zero, a = (a =) x ，a y ，a z ) =0, the optimized PRF value of the linear dive SAR imaging can be obtained by implementing the steps 1-7, and the optimized selection of the PRF height-divided section based on the slope distance interval division of the linear dive SAR imaging is completed;
if the Doppler center frequency offset is set to be zero, the maximum value of the Doppler center frequency offset is 0, and the steps 1-7 are carried out, so that the optimized PRF value of SAR imaging under the strip mode of curve track diving and large squinting can be obtained.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910576771.8A CN110208801B (en) | 2019-06-28 | 2019-06-28 | Universal SAR imaging PRF optimization design method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910576771.8A CN110208801B (en) | 2019-06-28 | 2019-06-28 | Universal SAR imaging PRF optimization design method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN110208801A CN110208801A (en) | 2019-09-06 |
| CN110208801B true CN110208801B (en) | 2022-12-27 |
Family
ID=67795382
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201910576771.8A Active CN110208801B (en) | 2019-06-28 | 2019-06-28 | Universal SAR imaging PRF optimization design method |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN110208801B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112068134B (en) * | 2020-09-09 | 2022-07-08 | 中国航空工业集团公司雷华电子技术研究所 | Angular error slope value detection method, device and equipment |
| CN112198512A (en) * | 2020-09-21 | 2021-01-08 | 北京理工大学 | Satellite-borne SAR (synthetic Aperture Radar) azimuth sampling time sequence design method based on continuous adjustment of pulse intervals |
| CN113359876B (en) * | 2021-06-23 | 2022-02-11 | 中国电子科技集团公司第三十八研究所 | Control method and device for large-bearing eccentric shaft platform of airborne SAR (synthetic aperture radar) |
| CN113406638A (en) * | 2021-06-28 | 2021-09-17 | 南京工程学院 | Parameter integrated setting method based on multi-rotor unmanned aerial vehicle SAR imaging system |
| CN115166735A (en) * | 2022-05-25 | 2022-10-11 | 北京理工雷科电子信息技术有限公司 | Synthetic aperture radar imaging online adaptive waveform parameter adjusting method |
| CN115129291B (en) * | 2022-08-31 | 2022-11-22 | 中国人民解放军国防科技大学 | Three-dimensional oblique photography measurement model visualization optimization method, device and equipment |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61193088A (en) * | 1985-02-22 | 1986-08-27 | Nec Corp | Synthetic aperture radar equipment |
| CN101526614A (en) * | 2009-04-03 | 2009-09-09 | 北京理工大学 | SAR echo rapid simulation method based on sub-aperture and equivalent scatterer |
| EP2574957A1 (en) * | 2011-09-30 | 2013-04-03 | Thales | Method for estimating the unambiguous Doppler frequency of a moving target, in particular marine, and radar implementing said method |
| CN105785327A (en) * | 2016-01-19 | 2016-07-20 | 西安电子科技大学 | Frequency diversity array synthetic aperture radar high resolution and wide swath imaging method |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9864054B2 (en) * | 2014-03-10 | 2018-01-09 | Mitsubishi Electric Research Laboratories, Inc. | System and method for 3D SAR imaging using compressive sensing with multi-platform, multi-baseline and multi-PRF data |
-
2019
- 2019-06-28 CN CN201910576771.8A patent/CN110208801B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61193088A (en) * | 1985-02-22 | 1986-08-27 | Nec Corp | Synthetic aperture radar equipment |
| CN101526614A (en) * | 2009-04-03 | 2009-09-09 | 北京理工大学 | SAR echo rapid simulation method based on sub-aperture and equivalent scatterer |
| EP2574957A1 (en) * | 2011-09-30 | 2013-04-03 | Thales | Method for estimating the unambiguous Doppler frequency of a moving target, in particular marine, and radar implementing said method |
| CN105785327A (en) * | 2016-01-19 | 2016-07-20 | 西安电子科技大学 | Frequency diversity array synthetic aperture radar high resolution and wide swath imaging method |
Non-Patent Citations (2)
| Title |
|---|
| A sub-aperture imaging algorithm for highly squinted SAR based on frequency phase correction;Zhenyu Li et al.;《APSAR》;20150904;第254-257页 * |
| 弹载下降段大前斜聚束SAR成像时序设计;邓欢 等;《系统工程与电子技术》;20160531;第38卷(第5期);第1032-1038页 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN110208801A (en) | 2019-09-06 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN110208801B (en) | Universal SAR imaging PRF optimization design method | |
| CN106226768B (en) | Ultrahigh resolution agility SAR satellites slide beam bunching mode System Parameter Design method | |
| US4546354A (en) | Range/azimuth ship imaging for ordnance control | |
| CN102508243B (en) | Beam position design method of inclined geosynchronous orbit synthetic aperture radar | |
| CN107132537B (en) | A kind of SAR satellite on-orbit performance method for improving based on electromechanical combination scanning | |
| CN107092014B (en) | Optimization method for missile-borne double-base forward-looking SAR ship target positioning | |
| JPS62231188A (en) | Synthetic opening radar imaging method and device for ship | |
| CN107390181B (en) | Radar high-resolution imaging method based on multi-beam scanning | |
| CN111965640B (en) | Large squint high-orbit SAR two-dimensional beam scanning method | |
| CN110161503B (en) | Short-range and wide-range SAR high-resolution imaging method based on three-dimensional equidistant circle model | |
| CN112084676B (en) | Path planning method for distributed radar short-time aperture synthesis | |
| CN104090277B (en) | A kind of slidingtype circumferential synthetic aperture radar formation method | |
| CN108267736A (en) | A kind of GEO SAR staring imagings mode orientation fuzziness determines method | |
| KR20190084730A (en) | Sar and sar signal processor for squinted spotlight mode under nonlinear flight path and method thereof | |
| CN115792907A (en) | Method for designing azimuth imaging parameters of spaceborne SAR squint sliding bunching mode | |
| RU2735744C1 (en) | Method for survey of single-position trilateration incoherent radar ranging of aerial targets | |
| CN107589421B (en) | Array foresight SAR imaging method | |
| CN110261852B (en) | Frequency diversity inverse synthetic aperture radar imaging system and method | |
| CN110389339A (en) | A kind of radar DBS imaging geometry distortion correction and subgraph joining method | |
| CN102176013B (en) | Mixing degree extracting method for Missile-borne non-ideal staring spotlight SAR (synthetic aperture radar) | |
| CN107271996B (en) | Airborne CSSAR (compact spherical synthetic aperture radar) ground moving target imaging method | |
| CN105974382A (en) | Accurate repeat-pass interference SAR system antenna side-looking mounting angle calibration method | |
| CN110579762A (en) | Terahertz circular track SAR rapid back projection imaging method | |
| RU2660159C1 (en) | Method of side-looking airborne radar determination of aircraft demolition angle | |
| CN116148891A (en) | Satellite-ground double-base sea surface two-dimensional flow field measurement method based on along-track interference |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |