CN112014840B - On-orbit implementation design method of satellite-borne SAR mosaic mode - Google Patents

On-orbit implementation design method of satellite-borne SAR mosaic mode Download PDF

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CN112014840B
CN112014840B CN202010752732.1A CN202010752732A CN112014840B CN 112014840 B CN112014840 B CN 112014840B CN 202010752732 A CN202010752732 A CN 202010752732A CN 112014840 B CN112014840 B CN 112014840B
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CN112014840A (en
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冯帆
贺荣荣
高阳
杨娟娟
孙嘉
郭磊
党红杏
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Xian Institute of Space Radio Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
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    • 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
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Abstract

The invention relates to an on-orbit implementation design method of a spaceborne SAR mosaic mode, which comprises the steps of firstly establishing a design constraint condition of the mosaic mode according to the geometric resolution, the scene width and the required number of pitching beams to be achieved by a spaceborne SAR image; secondly, designing an attitude maneuver mode of the satellite platform in the mosaic mode imaging process according to the constraint conditions; and thirdly, solving each time of the antenna beam switching in the pitching direction according to the resolution requirement, the antenna beam squint angle at the initial moment and the maneuvering curve of the satellite attitude along with the time. And finally, analyzing and confirming according to the designed attitude maneuver curve and the beam switching time: 1) the azimuth resolution reaches the technical index; 2) and adjacent sub-block images in the mosaic can be effectively spliced in the azimuth direction, so that the integrity of the whole scene image is ensured.

Description

On-orbit implementation design method of satellite-borne SAR mosaic mode
Technical Field
The invention relates to an on-orbit implementation design method of a satellite-borne SAR mosaic mode, and belongs to the technical field of space microwave remote sensing.
Background
In order to improve the azimuth resolution and the range mapping width of the satellite-borne SAR image, the mosaic mode of the reflecting surface satellite-borne SAR utilizes the satellite platform to flexibly increase the azimuth synthetic aperture time and increase the range coverage area through pitching beam scanning so as to achieve the purpose. The key to realizing the mode is the method design of satellite platform attitude maneuver and SAR antenna beam scanning, so as to ensure the following two targets to be achieved: 1) the resolution of each sub-block image of the mosaic meets the technical requirements; 2) all the sub-block images can be seamlessly spliced in the azimuth direction, and the integrity of the whole scene image is ensured.
At present, the research on the mosaic mode still stays in the aspects of theoretical analysis and simulation calculation of technical indexes such as resolution, imaging width and the like, no document is provided how to design a specific working implementation mode of the satellite-borne SAR mosaic mode according to the technical indexes or system parameters such as imaging resolution, scene width, satellite orbit, antenna beam width and the like, and the most central content in the specific working implementation mode of the mosaic mode is to determine a satellite platform attitude maneuver method and distance-to-beam switching time in the imaging process.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the defects of the prior art are overcome, and an on-orbit implementation design method of a satellite-borne SAR mosaic mode is provided.
The technical solution of the invention is as follows:
an on-orbit implementation design method of a satellite-borne SAR mosaic mode comprises the following steps:
step 1: determining design constraint conditions of a satellite-borne SAR mosaic mode to obtain a complete SAR image meeting the technical index of resolution;
step 2: designing an attitude maneuver mode of a satellite platform in the imaging process of the satellite-borne SAR mosaic mode according to design constraint conditions;
and step 3: determining each moment of switching the distance to the wave beam in the imaging process of the mosaic mode;
And 4, step 4: and evaluating the effectiveness of the design result of the mosaic mode to ensure the integrity of the whole scene image.
In the step 1, the design constraint conditions of the satellite-borne SAR mosaic mode are as follows:
1) in each sub mapping zone in the distance direction, a certain overlap must be formed between two adjacent sub block images in the azimuth direction to ensure effective splicing;
2) the resolution of each sub-block image in the azimuth direction needs to meet the technical index requirement.
When a certain sub-block scene is imaged in order to satisfy the design constraint conditions of step 1)Beam travel distance LslipThe following formula is required:
Figure BDA0002610555950000021
wherein N iseFor the number of distance vector swaths, LaIs the coverage length of the beam in the azimuth direction.
Azimuthal resolution ρ of sliding bunching modeslipThe following formula needs to be satisfied:
Figure BDA0002610555950000022
ρmosaicthe azimuthal resolution ultimately achieved for the mosaic mode.
In the step 2, the maneuvering triaxial pointing unit vector of the satellite platform in the mosaic mode meets the following requirements:
z-axis pointing of satellite at a certain time
Figure BDA0002610555950000023
Is composed of
Figure BDA0002610555950000024
Y-axis pointing of satellite
Figure BDA0002610555950000025
To be perpendicular to
Figure BDA0002610555950000026
And
Figure BDA0002610555950000027
plane formed thereby
Figure BDA0002610555950000028
Is composed of
Figure BDA0002610555950000029
Figure BDA00026105559500000210
To be connected with
Figure BDA00026105559500000211
To a right-hand coordinate system, i.e.
Figure BDA00026105559500000212
Figure BDA00026105559500000213
Is the satellite position vector at that time,
Figure BDA00026105559500000214
is the position vector of the center of rotation at that moment,
Figure BDA00026105559500000215
Is the satellite velocity vector at that time.
The implementation manner of the step 3 is as follows:
in the imaging process of the satellite-borne SAR mosaic mode, the switching sequence of the distances of the SAR loads to the antenna beams is 1 → 2 → · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · N · · · · · · · · · · · · · · · · · · N · · N · · · N ·, N ·, which ise→1→2→···→Ne，NeThe number of distance vector swaths; at a starting time T0The system geometric model of the SAR antenna is used as a reference, and the azimuth oblique angle of the virtual synthetic large-beam front edge of the SAR antenna at the moment is theta0＝θstart+θaz/2，θstartFor beam centre squint angle at the start time, thetaazIs the azimuth antenna beam width;
the Doppler frequency f of the echo signal at the starting time P0 by taking the intersection point P0 of the front edge of the antenna beam and the ground as an analysis pointdop0Is shown as
Figure BDA0002610555950000031
Wherein, VsThe flight speed of the satellite platform is shown, and lambda is the wavelength;
finally realizing azimuth resolution rho by the mosaic modemosaicTo obtain rhomosaicDesired azimuthal Doppler bandwidth Bmosaic：
Figure BDA0002610555950000032
VgGround speed of travel, V, for beam footprint in stripe modeg＝Re·ωs·cos(βe) R in the formulaeIs the radius of the earth, omegasIs the angular velocity, beta, of the flight of the satellite platformeThe geocentric angle corresponding to the scene center;
according to BmosaicI.e. the T of the first beam switch can be determined1At this time, the solution method is as follows:
T1at the moment, the squint angle θ between the antenna and P01Need to satisfy
Figure BDA0002610555950000033
From which theta is solved1Is resolved into
Figure BDA0002610555950000034
Based on the solved position coordinate of P0 and the orbit of the satellite, the squint angle of the antenna can be determined to be theta1The position of the satellite
Figure BDA0002610555950000035
Recombined to the position of the satellite at the imaging start time
Figure BDA0002610555950000036
The beam switching time T is solved using the following equation1：
Figure BDA0002610555950000041
Vs(T) satellite platform flight speed at time T, T0The moment when the satellite initiates imaging.
By analogy, based on the derived θ1Sequentially solve the 2 nd to the N theCorresponding antenna beam squint angle at the time of secondary beam switching
Figure BDA0002610555950000042
Then is provided with
Figure BDA0002610555950000043
The position coordinates of the point P0 and the satellite orbit can be found to be the 2 nd to N th pointseSecond beam switching time T2～TNe；
Completing the 1 st to N th in antenna beameAfter the switching of the secondary beam, by TNeIntersection point P of forward edge of beam direction of time antenna and groundNeFor analyzing the reference point, the Nth point is determined in the same manner as abovee+1～2NeAnd at the time of sub-beam switching, designing the subsequent beam switching time according to the process until the imaging process of the whole scene is completed.
In step 4, the method for evaluating the design result of the mosaic pattern is as follows:
(7.1) calculating the azimuth resolution of each sub-block image, evaluating whether the sub-block images meet the resolution requirement, and entering the step (7.2) if all the sub-block images meet the resolution requirement; if a certain sub-block image does not meet the resolution requirement, the azimuth resolution rho of the sliding bunching mode is improved slipStarting the subsequent design of attitude maneuver and beam switching time to ensure that the resolution of all the sub-block images finally meets the requirement, and entering the step (7.2);
(7.2) determining each sub-block image inThe starting position and the ending position of the azimuth direction are used for evaluating whether the sub-block images can be effectively spliced or not, and if the sub-block images can be effectively spliced, the process is ended; if the sub-block images cannot be spliced effectively, the beam travel distance L in the imaging period of the sub-block images is further reducedslipAnd then, the overlapping interval between the adjacent sub-block images is increased, and the subsequent design of attitude maneuver and beam switching time is started to ensure that the overlapping rate between the sub-block images meets the splicing requirement, and the process is finished.
In the step (7.1), when determining the azimuth resolution of each sub-block image, the azimuth start position target, the center target, and the end position target in each sub-block image need to be respectively confirmed, and the sub-block image is considered to meet the resolution requirement only when the azimuth resolutions of the three targets meet the requirement.
Determining the azimuth resolution of a certain target in the sub-block images according to the following method:
let the coordinate of a certain target in the block image be
Figure BDA0002610555950000058
Its doppler start frequency f when the beam covers the sub-block image dop_startIs composed of
Figure BDA0002610555950000051
Its Doppler end frequency f when the beam leaves the sub-block imagedop_endIs composed of
Figure BDA0002610555950000052
Wherein
Figure BDA0002610555950000053
And
Figure BDA0002610555950000054
satellite position vectors as beams enter and leave the sub-block image, respectivelyAmount, VsIs the satellite platform flight speed;
doppler bandwidth B of the targetdopSatisfy the requirement of
Bdop＝fdop_start-fdop_end
Azimuthal resolution ρ of the targetaIs composed of
Figure BDA0002610555950000055
VgIs the ground travel speed of the beam footprint in strip mode.
In the step (7.2), the starting position and the ending position of each sub-block image in the azimuth direction are determined according to the following method:
starting position L of each sub-block image in azimuth directionstartSatellite position S when leaving it by a beamendBeam squint angle thetaendAzimuth antenna beam width thetaazAnd the front side view observation slope distance R of the sub-block imagecA joint decision, expressed as
Figure BDA0002610555950000056
The end position L of the sub-block image in the azimuth directionendSatellite position S when entering it by a beamstartBeam squint angle thetastartAzimuth antenna beam width thetaazAnd the front side view observation slope distance R of the sub-block imagecA joint decision, expressed as
Figure BDA0002610555950000057
Compared with the prior art, the invention has the advantages that:
the invention overcomes the defects of the prior art, provides an on-orbit implementation method of a satellite-borne SAR mosaic mode for the first time, in particular to a complete design process of satellite platform attitude maneuver and a corresponding beam scanning strategy, provides a method for converting the mosaic mode into an equivalent sliding bunching mode to simplify the design of the platform attitude maneuver, and provides a method for determining the switching time of the distance direction beam of the mosaic mode based on the azimuth direction resolution and the attitude maneuver curve, so that on one hand, the requirement of the mosaic mode image resolution and the imaging scene size can be met, on the other hand, the space-variant effect of the echo signal Doppler frequency in the distance direction does not exist, thereby carrying out batch imaging processing on echoes and improving the processing efficiency.
Drawings
FIG. 1 is a schematic diagram of a satellite platform attitude maneuver and beam switching time design flow in a spaceborne SAR mosaic mode according to the present invention;
FIG. 2 is a schematic diagram of distance-oriented three-subband mosaic mode imaging;
FIG. 3 is a schematic diagram of sliding beamforming mode virtual synthesis of large beams;
fig. 4 shows beam directions after switching between the initial time and the third beam in the mosaic imaging process;
fig. 5 is a schematic diagram of a calculation flow of mosaic mode beam switching time;
fig. 6 is a schematic diagram of a method for determining the azimuth start-stop position of a scene image in the mosaic mode.
Detailed Description
The invention provides a complete design method and a complete design process for attitude maneuver of a platform and antenna beam scanning in a satellite-borne SAR mosaic mode, and ensures that the resolution of each sub-block image, the overlapping rate of the images and the size of the whole scene meet the technical requirements.
As shown in fig. 1, the method comprises the following specific steps:
step 1: determining design constraint conditions of a satellite-borne SAR mosaic mode to obtain a complete SAR image meeting the technical index of resolution;
the mosaic mode is an imaging mode combining pitching scanning and azimuth sliding bunching, and in order to ensure that the mosaic mode can obtain a complete SAR image meeting the technical index of resolution, the mosaic mode has the following two constraint conditions:
1) In each sub mapping zone from the distance direction, a certain overlap must be formed between two adjacent sub images in the azimuth direction to ensure effective splicing;
2) the resolution of each sub-image in the azimuth direction needs to meet specification requirements.
Next, how to guarantee the above two conditions in the design will be analyzed.
For sliding bunching mode, its azimuthal resolution ρslipCan be expressed as
ρslip＝A·ρstrip (1)
Wherein A is a sliding bunching mode improvement factor, rhostripIs the azimuthal resolution of the banding pattern. The above formula can be further expressed as
Figure BDA0002610555950000071
Wherein VslipBeam ground footprint travel speed for sliding bunching mode, BdIs the azimuth Doppler bandwidth in the strip mode, which can be expressed as
Figure BDA0002610555950000072
Wherein VsIs the satellite platform flight speed, thetaazλ is the wavelength for the antenna beam azimuth width.
Compared with the sliding bunching mode, the mosaic mode needs to divide the whole synthetic aperture formed by the sliding bunching into a plurality of sub mapping zones in the distance direction, so that the finally realized azimuth resolution rho of the mosaic modemosaicWill be compared with rhoslipThe difference, the corresponding degradation factor D, can be expressed as
Figure BDA0002610555950000073
Wherein L isaIs the coverage length of the beam in azimuth direction (As noted in fig. 2), LslipThe distance traveled by the beam when imaging a small scene (as noted in fig. 2). Thus the azimuthal resolution ρ ultimately achieved by the mosaic mode mosaicCan be expressed as
ρmosaic＝D·ρslip (5)
Taking the distance-oriented three-segment swath mosaic pattern as an example, fig. 2 shows the corresponding working schematic diagram, and the imaging sequence is 1 → 2 → 3 → 4 → 5 → 6 in sequence.
In order to ensure that two adjacent azimuth sub-images can be spliced effectively, a certain area of overlap is required between the two adjacent azimuth sub-images. The constraint conditions for this requirement are as shown in equation (6): wherein L1a、L2aAnd L3aAzimuth coverage length of the antenna beam in sub swaths 1, 2 and 3, L1, respectivelyslip、L2slipAnd L3slipThe beam advance distances when imaging the small scenes of the sub swaths 1, 2 and 3, respectively.
Figure BDA0002610555950000081
Because the view span of the subsatellite point corresponding to the whole scene width of the satellite-borne SAR is small, the method has the advantages that
L1a≈L2a≈L3a (7)
And
L1slip≈L2slip≈L3slip (8)
substituting the formula (7) and the formula (8) into the formula (6) can obtain the constraint condition for ensuring the splicing of the azimuth subblock images as
Figure BDA0002610555950000082
Wherein N iseNumber of bands for range vector (here N)e3). From this, a degradation factor of the mosaic pattern can be derived
Figure BDA0002610555950000083
If the final realized azimuth resolution of the mosaic mode is rhomosaicThen the azimuth resolution corresponding to the sliding bunching mode needs to satisfy the constraint condition
Figure BDA0002610555950000084
Equations (9) and (10) are two constraints in the mosaic pattern design process.
In the mosaic mode, the used multiple elevation antenna beam footprints are co-linear, so that a virtual synthetic large beam can be used to approximate the antenna beam used for the sliding beamforming mode, as shown in fig. 3. The azimuth width of the virtual large beam is the same as that of the three sub-beams, and the elevation width of the virtual large beam is the total span from the near end of the beam 1 to the far end of the beam 3.
Step 2: determining a satellite platform attitude maneuver mode in the whole mosaic mode imaging process according to the satellite orbit, the antenna beam width, the azimuth resolution and the scene azimuth length;
in a patent "satellite platform attitude maneuver method for realizing satellite-borne SAR ultrahigh resolution sliding bunching mode" (CN106291557B), we have given how to design the maneuver process of satellite attitude according to the resolution and scene width in the sliding bunching mode. Based on this method, the azimuthal resolution ρ of the sliding bunching mode derived in step 1slipThe position of a virtual rotation point in the mosaic mode imaging process can be determined
Figure BDA0002610555950000091
According to the position of the satellite at each moment
Figure BDA0002610555950000092
And the position of the virtual rotation point
Figure BDA0002610555950000093
Determining Z-axis orientation of satellite at various times
Figure BDA0002610555950000094
Is composed of
Figure BDA0002610555950000095
Y-axis pointing of satellite
Figure BDA0002610555950000096
To be perpendicular to
Figure BDA0002610555950000097
With satellite velocity vector
Figure BDA0002610555950000098
Plane formed thereby
Figure BDA0002610555950000099
Is composed of
Figure BDA00026105559500000910
Finally, the process is carried out in a batch,
Figure BDA00026105559500000911
to be connected with
Figure BDA00026105559500000912
To a right-hand coordinate system, i.e.
Figure BDA00026105559500000913
Equations (11) to (13) are three-axis pointing unit vectors of the satellite platform maneuvering in the mosaic imaging mode.
And step 3: solving each time of the antenna beam switching in the pitching direction according to the resolution requirement, the antenna beam squint angle at the initial moment and the maneuvering curve of the satellite attitude along with the time;
After the satellite platform attitude maneuver design in the mosaic mode is completed, the beam switching time in the imaging process needs to be further determined. Still taking the distance three beams as an example, the beam switching order of the whole imaging phase is 1 → 2 → 3 → 1 → 2 → 3. The geometric model of the system at the starting time T0 is used as a reference to describe how to determine the antenna beam switching time and the satellite position for the first three times, and the following switching times are analogized in turn until the squint angle of the antenna beam center exceeds the terminal squint angle of the whole attitude maneuver process.
Fig. 4 shows the beam direction after the mosaic mode starts to operate and the third beam is switched. Wherein T0 is the imaging start time of the whole mosaic pattern, and is also the imaging start time of this sub-image, and the azimuth oblique angle of the leading edge of the virtual synthesized large beam (as shown in fig. 3) of the SAR antenna is θ0＝θstart+θaz/2(θstartFor beam centre squint angle at the start time, thetaazAzimuth antenna beamwidth) and the intersection with the ground is P0.
Starting from its Doppler frequency f at P0 as analysis pointdop0Can be expressed as
Figure BDA0002610555950000101
Then rhomosaicThe required azimuth Doppler bandwidth B can be obtainedmosaicIs composed of
Figure BDA0002610555950000102
VgThe ground travel speed, which is the beam footprint in stripe mode, can be expressed as V g＝Re·ωs·cos(βe). In the formula ReIs the radius of the earth, omegasIs the angular velocity, beta, of the satellite flighteThe corresponding geocentric angle of the scene center. From equations (14) and (15), T for the first beam switch can be determined1Between the time-of-day antenna and P0Oblique angle of view theta1Need to satisfy
Figure BDA0002610555950000103
By the formula (16), θ can be obtained1Is resolved into
Figure BDA0002610555950000104
Theta obtained based on the formula (17)1The position coordinates of P0 and the orbit of the satellite, the oblique angle theta can be determined1The position of the satellite
Figure BDA0002610555950000105
Then combining the position of the satellite starting time
Figure BDA0002610555950000106
The beam switching time T is solved using the following equation1。
Figure BDA0002610555950000107
Similarly, based on the obtained θ1Further T for the second beam switch can be obtained by using equations (19) and (20)2T for time and third beam switching3Squint angle theta between time satellite and point P02And theta3。
Figure BDA0002610555950000108
Figure BDA0002610555950000109
By theta2And theta3And the satellite orbit and the position of the point P0 can respectively obtain a beam for the second time and a beam for the third timeSwitching time T2And T3。
After three beam switchings of the antenna beam, the pointing direction of the antenna beam and the intersection point P3 of the front edge with the ground are as shown in fig. 4. In this case, the beam switching timings of the fourth, fifth and sixth times are determined in the same manner as described above with P3 as an analysis point. FIG. 5 shows a schematic of this progressive process: wherein is formed by T 0Antenna beam pointing at time, beam front ground intersection point P0, and Doppler bandwidth BmosaicThe first three times of beam switching time T can be obtained1、T2And T3(ii) a Then by T3The antenna beam pointing direction, the beam front ground intersection point and the Doppler bandwidth of the time can further obtain T4、T5And T6And repeating the steps until the imaging process of the whole scene is completed.
For a certain sub-image, the starting end in the azimuth direction is the intersection point of the rear edge of the beam at the imaging end time of the beam pair and the ground, and the ending end in the azimuth direction is the intersection point of the front edge of the beam at the imaging start time of the beam pair and the ground. Taking the first sub-image in the mosaic mode as an example, the azimuth start-stop position is shown in fig. 6.
And 4, step 4: design result evaluation of mosaic pattern
After the design of the attitude maneuver mode of the satellite platform in the mosaic mode and the beam switching time is completed, the range of each sub-block image in the azimuth direction (as listed in table 1) and the achieved azimuth direction resolution (as listed in table 2) are given so as to evaluate whether the sub-block images can be spliced effectively and meet the resolution requirement.
TABLE 1 Azimuth Range of sub-block images in mosaic mode
Figure BDA0002610555950000111
TABLE 2 results of azimuthal resolution of each sub-block image in mosaic mode
Figure BDA0002610555950000121
The method for determining the starting and ending positions of each sub-block image in the azimuth direction is as follows:
starting position L in azimuthstartSatellite position S when leaving it by a beamendBeam squint angle thetaendAzimuth antenna beam width thetaazAnd the front side view observation slope distance R of the sub-block imagecA joint decision, expressed as
Figure BDA0002610555950000122
The azimuth end position L of the sub-block imageendSatellite position S when entering it by a beamstartBeam squint angle thetastartAzimuth antenna beam width thetaazAnd the front side view observation slope distance R of the sub-block imagecA joint decision, expressed as
Figure BDA0002610555950000123
Based on equations (21) and (22), and the beam switching time determined in step 3, the satellite position and the beam squint angle corresponding to each switching time, the azimuth start and end positions of each sub-block image in table 1 can be obtained.
The method for determining the azimuth resolution of each position in each sub-block image is as follows:
let the coordinate of a certain target in the block image be
Figure BDA0002610555950000124
Its doppler start frequency f when the beam covers the sub-block imagedop_startIs composed of
Figure BDA0002610555950000131
Its Doppler end frequency f when the beam leaves the sub-block imagedop_endIs composed of
Figure BDA0002610555950000132
Wherein
Figure BDA0002610555950000133
And
Figure BDA0002610555950000134
the satellite position vectors as the beam enters and leaves the sub-block image, respectively. From (23) and (24), the Doppler bandwidth B of the target can be obtained dopAnd final azimuthal resolution ρaIs composed of
Bdop＝fdop_start-fdop_end (25)
Figure BDA0002610555950000135
Based on the results given by equations (25) and (26), the azimuthal resolution results of the point target at the start position, the center position, and the end position of each sub-block image in table 2 can be obtained.
For confirming the azimuth resolution of each sub-block image, it is necessary to confirm the azimuth start position target, the center target, and the end position target in each sub-block image respectively (the antenna azimuth directions experienced by the three position point targets are different), so as to ensure that the azimuth resolution of the whole sub-block image meets the requirement.
During evaluation, whether the azimuth resolution of each sub-block image meets the technical index requirement is firstly analyzed, and if the azimuth resolution of the sub-block image is out of tolerance, the azimuth resolution rho of the equivalent sliding bunching mode is further improved under the constraint condition of the formula (10)slipAnd then starting the subsequent design of attitude maneuver and beam switching time to ensure the image resolution rho of all the final sub-blocksmosaicAll meet the requirements.
Secondly, whether the overlapping rate of the adjacent sub-block images in each sub-swath of the distance direction meets the requirement of effective image splicing is analyzed. If the overlap ratio is insufficient, the beam footprint travel length L during sub-block image imaging is further reduced on the basis of equation (9) slipThereby increasing an overlapping section between adjacent subblock images. And then starting the subsequent design of attitude maneuver and beam switching time to ensure that the overlapping rate between the sub-block images meets the splicing requirement.
The invention provides a complete design flow of satellite platform attitude maneuver and a corresponding beam scanning strategy in a satellite-borne SAR mosaic mode for the first time. A method for converting a mosaic mode into an equivalent sliding bunching mode to simplify the design of the attitude maneuver of the platform is provided for the first time. A method for determining the switching time of the distance direction wave beams of the mosaic mode based on the azimuth direction resolution and the attitude maneuver curve is provided for the first time.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.

Claims (9)

1. An on-orbit implementation design method of a satellite-borne SAR mosaic mode is characterized by comprising the following steps:
step 1: determining design constraint conditions of a satellite-borne SAR mosaic mode to obtain a complete SAR image meeting the technical index of resolution;
step 2: designing an attitude maneuver mode of a satellite platform in the imaging process of the satellite-borne SAR mosaic mode according to design constraint conditions;
and step 3: determining each moment of switching the distance to the wave beam in the imaging process of the mosaic mode;
The implementation manner of the step 3 is as follows:
in the imaging process of the satellite-borne SAR mosaic mode, the switching sequence of the distances of the SAR loads to the antenna beams is 1 → 2 → · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · N · · · · · · · · · · · · · · · · · · N · · N · · · N ·, N ·, which ise→1→2→···→Ne，NeMeasuring the number of the drawing bands for the distance vector; at a starting time T0With reference to the geometric model of the system, at which point the virtual synthetic large beam front of the SAR antenna is squareThe oblique angle of view is theta0＝θstart+θaz/2，θstartFor beam centre squint angle at the start time, thetaazIs the azimuth antenna beam width;
the Doppler frequency f of the echo signal at the starting time P0 by taking the intersection point P0 of the front edge of the antenna beam and the ground as an analysis pointdop0Is shown as
Figure FDA0003543570900000011
Wherein, VsThe flight speed of the satellite platform is shown, and lambda is the wavelength;
finally realizing azimuth resolution rho by the mosaic modemosaicTo obtain rhomosaicDesired azimuthal Doppler bandwidth Bmosaic：
Figure FDA0003543570900000012
VgGround speed of travel, V, for beam footprint in stripe modeg＝Re·ωs·cos(βe) R in the formulaeIs the radius of the earth, omegasIs the angular velocity, beta, of the flight of the satellite platformeThe geocentric angle corresponding to the scene center;
according to BmosaicI.e. the T of the first beam switch can be determined1At this time, the solution method is as follows:
T1at the moment, the squint angle θ between the antenna and P01Need to satisfy
Figure FDA0003543570900000021
From which theta is solved1Is resolved into
Figure FDA0003543570900000022
Based on the solved position coordinate of P0 and the orbit of the satellite, the squint angle of the antenna can be determined to be theta 1The position of the satellite
Figure FDA0003543570900000023
Recombined to the position of the satellite at the imaging start time
Figure FDA0003543570900000024
The beam switching time T is solved using the following equation1：
Figure FDA0003543570900000025
Vs(T) satellite platform flight speed at time T, T0The moment when the satellite starts imaging;
by analogy, based on the derived θ1Sequentially solve the 2 nd to the N theCorresponding antenna beam squint angle at the time of secondary beam switching
Figure FDA0003543570900000026
Then by
Figure FDA0003543570900000027
The position coordinates of the point P0 and the satellite orbit can be obtainedeSecondary beam switching time T2～TNe；NeThe number of distance vector swaths;
completing the 1 st to N th in antenna beameAfter the switching of the secondary beam, by TNeIntersection point P of forward edge of beam direction of time antenna and groundNeFor analyzing the reference point, the Nth point is determined in the same manner as abovee+1～2NeAt the time of secondary beam switching, designing the subsequent beam switching time according to the process until the imaging process of the whole scene is completed;
and 4, step 4: and evaluating the effectiveness of the design result of the mosaic mode to ensure the integrity of the whole scene image.
2. The on-orbit implementation design method for the spaceborne SAR mosaic mode according to claim 1, characterized in that: in the step 1, the design constraint conditions of the satellite-borne SAR mosaic mode are as follows:
1) In each sub mapping zone in the distance direction, two adjacent sub block images must be overlapped in the azimuth direction to ensure effective splicing;
2) the resolution of each sub-block image in the azimuth direction needs to meet the technical index requirement.
3. The on-orbit implementation design method for the spaceborne SAR mosaic mode according to claim 2, characterized in that: in order to satisfy the design constraint condition of step 1), the beam travel distance L when a certain sub-block scene is imagedslipThe following formula is required:
Figure FDA0003543570900000031
wherein N iseFor the number of distance vector swaths, LaIs the coverage length of the beam in the azimuth direction.
4. The on-orbit implementation design method for the spaceborne SAR mosaic mode according to claim 3, characterized in that: azimuthal resolution ρ of sliding bunching modeslipThe following formula needs to be satisfied:
Figure FDA0003543570900000032
ρmosaicthe azimuthal resolution ultimately achieved for the mosaic mode.
5. The on-orbit implementation design method for the spaceborne SAR mosaic mode according to claim 1, characterized in that: in the step 2, the maneuvering triaxial pointing unit vector of the satellite platform in the mosaic mode satisfies the following conditions:
z-axis pointing of satellite at a certain time
Figure FDA0003543570900000033
Is composed of
Figure FDA0003543570900000034
Y-axis pointing of satellite
Figure FDA0003543570900000035
To be perpendicular to
Figure FDA0003543570900000036
And
Figure FDA0003543570900000037
Plane formed thereby
Figure FDA0003543570900000038
Is composed of
Figure FDA0003543570900000039
Figure FDA00035435709000000310
To be connected with
Figure FDA00035435709000000311
To a right-hand coordinate system, i.e.
Figure FDA00035435709000000312
Figure FDA00035435709000000313
Is the satellite position vector at that time,
Figure FDA00035435709000000314
is the position vector of the center of rotation at that moment,
Figure FDA00035435709000000315
is the satellite velocity vector at that time.
6. The on-orbit implementation design method for the spaceborne SAR mosaic mode according to claim 1, characterized in that: in step 4, the method for evaluating the design result of the mosaic pattern is as follows:
(7.1) calculating the azimuth resolution of each sub-block image, evaluating whether the sub-block images meet the resolution requirement, and entering the step (7.2) if all the sub-block images meet the resolution requirement; if a certain sub-block image does not meet the resolution requirement, the azimuth resolution rho of the sliding bunching mode is improvedslipStarting the subsequent design of attitude maneuver and beam switching time to ensure that the resolution of all the sub-block images finally meets the requirement, and entering the step (7.2);
(7.2) determining the starting position and the ending position of each sub-block image in the azimuth direction, evaluating whether the sub-block images can be effectively spliced or not, and finishing if the sub-block images can be effectively spliced; if the sub-block images cannot be spliced effectively, the beam travel distance L in the imaging period of the sub-block images is further reduced slipAnd then, the overlapping interval between the adjacent sub-block images is increased, and the subsequent design of attitude maneuver and beam switching time is started to ensure that the overlapping rate between the sub-block images meets the splicing requirement, and the process is finished.
7. The on-orbit implementation design method for the spaceborne SAR mosaic mode according to claim 6, characterized in that: in the step (7.1), when determining the azimuth resolution of each sub-block image, the azimuth start position target, the center target, and the end position target in each sub-block image need to be respectively confirmed, and the sub-block image is considered to meet the resolution requirement only when the azimuth resolutions of the three targets meet the requirement.
8. The on-orbit implementation design method for the spaceborne SAR mosaic mode according to claim 7, characterized in that: determining the azimuth resolution of a certain target in the sub-block images according to the following method:
let the coordinate of a certain target in the sub-block image be
Figure FDA0003543570900000045
Its doppler start frequency f when the beam covers the sub-block imagedop_startIs composed of
Figure FDA0003543570900000041
Its Doppler end frequency f when the beam leaves the sub-block imagedop_endIs composed of
Figure FDA0003543570900000042
Wherein
Figure FDA0003543570900000043
And
Figure FDA0003543570900000044
the satellite position vector, V, of the beam entering and leaving the sub-block image, respectively sIs the satellite platform flight speed;
doppler bandwidth B of the targetdopSatisfy the requirement of
Bdop＝fdop_start-fdop_end
Azimuthal resolution ρ of the targetaIs composed of
Figure FDA0003543570900000051
VgIs the ground travel speed of the beam footprint in stripe mode.
9. The on-orbit implementation design method for the spaceborne SAR mosaic mode according to claim 6, characterized in that: in the step (7.2), the starting position and the ending position of each sub-block image in the azimuth direction are determined according to the following method:
starting position L of each sub-block image in azimuth directionstartSatellite position S when leaving it by a beamendBeam squint angle thetaendAzimuth antenna beam width thetaazAnd the front side view observation slope distance R of the sub-block imagecA joint decision, expressed as
Figure FDA0003543570900000052
The end position L of the sub-block image in the azimuth directionendSatellite position S when entering it by a beamstartBeam squint angle thetastartAzimuth antenna beam width thetaazAnd the front side view observation slope distance R of the sub-block imagecA joint decision, expressed as
Figure FDA0003543570900000053
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