CN110596704B - Satellite platform attitude maneuver method for satellite-borne SAR multi-azimuth repeated observation - Google Patents

Satellite platform attitude maneuver method for satellite-borne SAR multi-azimuth repeated observation Download PDF

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CN110596704B
CN110596704B CN201910765450.2A CN201910765450A CN110596704B CN 110596704 B CN110596704 B CN 110596704B CN 201910765450 A CN201910765450 A CN 201910765450A CN 110596704 B CN110596704 B CN 110596704B
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CN110596704A (en
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冯帆
贺荣荣
雷少敏
孙嘉
金阿鑫
侯若涵
杨娟娟
党红杏
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Xian Institute of Space Radio Technology
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    • 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
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/27—Adaptation for use in or on movable bodies
    • H01Q1/28—Adaptation for use in or on aircraft, missiles, satellites, or balloons
    • H01Q1/288—Satellite antennas
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/02—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system using mechanical movement of antenna or antenna system as a whole

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Abstract

The invention relates to a satellite platform attitude maneuver method for satellite-borne SAR multi-azimuth repeated observation, comprising the steps of s1, determining a satellite platform attitude maneuver mode of primary imaging, namely determining the position of a satellite platform at the initial imaging moment, the satellite attitude and a virtual rotation center in the primary imaging process; s2, performing sliding bunching imaging, and determining the satellite position at the next imaging starting moment; s3, determining satellite attitudes in the maneuvering process between two adjacent imaging and a virtual rotation center in the next imaging process according to the satellite position of the next imaging starting moment and the distance between the center of the beam after maneuvering and the scene, and adjusting the beam direction to the azimuth direction starting position of the scene in the attitude maneuvering adjustment process; s4, repeating the steps s2 and s3 until the imaging work is finished; in the sliding beamforming imaging process, the beam center of the satellite platform always points to the virtual rotation center determined in the imaging process.

Description

Satellite platform attitude maneuver method for satellite-borne SAR multi-azimuth repeated observation
Technical Field
The invention belongs to the technical field of space microwave remote sensing, and particularly relates to a satellite platform attitude maneuver method.
Background
In order to improve the reconnaissance efficiency of the satellite-borne SAR, the multi-azimuth repeated observation capability of the satellite-borne SAR on the military sensitive area in a single transit process is required. If the phased array antenna system is used for realizing the purpose, the phased array antenna system realizes beam scanning and repeated observation by controlling the phase shifting codes of the receiving and transmitting channels, and the method has the advantages that the satellite platform does not need to be maneuvered, but has the defect that the gain of antenna beams is reduced along with the increase of the rotation angle. This will result in a loss of the echo signal-to-noise ratio and a drastic degradation of the SAR image quality. If the method is realized by using the reflector antenna, the method needs to be realized by maneuvering of the satellite platform, and the method has the advantages that the peak antenna gain can be always pointed to an observation area and cannot be changed along with the change of the rotation angle, but the attitude maneuvering mode of the satellite platform needs to be designed to ensure that the SAR load stably works in orbit. There is no suitable solution to the above problems.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method overcomes the defects of the prior art and provides a satellite platform attitude maneuver method for satellite-borne SAR multi-azimuth repeated observation.
The technical scheme of the invention is as follows: a satellite platform attitude maneuver method for satellite-borne SAR multi-azimuth repeated observation comprises the following steps:
s1, determining the attitude maneuver mode of the satellite platform for the first imaging, namely determining the position of the satellite platform at the initial imaging moment, the satellite attitude and the virtual rotation center in the first imaging process;
s2, performing sliding bunching imaging, and determining the satellite position at the next imaging starting moment;
s3, determining satellite attitudes in the maneuvering process between two adjacent imaging and a virtual rotation center in the next imaging process according to the satellite position of the next imaging starting moment and the distance between the center of the beam after maneuvering and the scene, and adjusting the beam direction to the azimuth direction starting position of the scene in the attitude maneuvering adjustment process;
s4, repeating the steps s2 and s3 until the imaging work is finished;
in the sliding beamforming imaging process, the beam center of the satellite platform always points to the virtual rotation center determined in the imaging process.
Preferably, the virtual center of rotation during the first imaging in step s1 is determined by:
initial squint angle theta by sliding bunch imaging1sSatellite platform flight speed VsAnd beam footprint speed in stripe modeDegree VgAnd the intersection point of the antenna beam center and the ground at the initial imaging moment of the satellite
Figure GDA0003171895360000021
Determining satellite imaging start time position
Figure GDA0003171895360000022
Starting time position by satellite imaging
Figure GDA0003171895360000023
Intersection of antenna beam center and ground
Figure GDA0003171895360000024
Satellite Z-axis pointing to determine starting imaging time
Figure GDA0003171895360000025
Starting time position by satellite imaging
Figure GDA0003171895360000026
Satellite Z-axis pointing at start time
Figure GDA0003171895360000027
And determining a virtual rotation center position by using the sliding bunching resolution improvement factor A
Figure GDA0003171895360000028
Preferably, the satellite imaging start time position
Figure GDA0003171895360000029
The determination is made by:
determining the satellite imaging initial time, the intersection point of the antenna beam center and the ground
Figure GDA00031718953600000210
And scene center
Figure GDA00031718953600000211
The distance in the azimuth direction is further determined, and the intersection point of the antenna beam center and the ground is further determined
Figure GDA00031718953600000212
A location;
Figure GDA00031718953600000213
according to the intersection point of the antenna beam center and the ground
Figure GDA00031718953600000214
Position, determining the intersection point
Figure GDA00031718953600000215
Satellite position at zero doppler time
Figure GDA00031718953600000216
Determining connections
Figure GDA00031718953600000217
And
Figure GDA00031718953600000218
vector and join of two points
Figure GDA00031718953600000219
And
Figure GDA00031718953600000220
angle theta between vectors of two pointsmax；
According to the angle thetamaxDetermining the imaging start time position
Figure GDA00031718953600000221
Above, LaIs the azimuth length of the scene, RcAs the scene center zero Doppler timePositive side view skew angle, thetaazThe azimuth beamwidth of the antenna.
Preferably, the included angle θmaxAccording to the relation
Figure GDA00031718953600000222
And (4) determining.
Preferably, the virtual center of rotation position
Figure GDA00031718953600000223
The following relationship is satisfied:
Figure GDA00031718953600000224
Figure GDA00031718953600000225
to be started from a satellite
Figure GDA00031718953600000226
Pointing to first sliding spotlight imaging virtual center of rotation
Figure GDA00031718953600000227
The vector of (2).
Preferably, step s2 is implemented by:
determining the satellite position of the imaging ending time according to the position of the imaging starting time of the satellite, the imaging time length and the flight orbit;
determining the satellite attitude at the imaging termination time and the intersection point of the satellite attitude and the ground according to the determined satellite position at the imaging termination time and the virtual rotation center of the imaging process;
and determining the satellite position at the moment of starting the next imaging after maneuvering according to the determined satellite position at the moment of ending the imaging and given attitude maneuvering time between two times of imaging.
Preferably, step s3 is implemented by:
from the satellite position at the end of this imaging
Figure GDA0003171895360000031
Satellite position at the start of next imaging
Figure GDA0003171895360000032
And the intersection point of the beam center and the ground at the imaging termination moment
Figure GDA0003171895360000033
Determining the plane determined by the three points and the distance D between the center of the beam and the scene after maneuvering to determine the intersection point between the center of the beam and the ground after the attitude maneuvering is adjusted
Figure GDA0003171895360000034
Satellite position adjusted by attitude maneuver
Figure GDA0003171895360000035
And intersection of beam center and ground
Figure GDA0003171895360000036
Obtaining the Z-axis direction of the satellite at the maneuvering ending moment;
by vector
Figure GDA0003171895360000037
And
Figure GDA0003171895360000038
to determine the virtual center of rotation of the satellite platform during the maneuvering between two adjacent images
Figure GDA0003171895360000039
By virtual centre of rotation of a motorised process
Figure GDA00031718953600000310
Determining the three-axis attitude of the satellite in the whole maneuvering process;
by
Figure GDA00031718953600000311
And determining the virtual rotation center of the next sliding bunching imaging by using the sliding bunching resolution improvement factor A
Figure GDA00031718953600000312
Preferably, the distance D is calculated as follows:
Figure GDA00031718953600000313
wherein theta isendThe oblique angle of the beam center at the end of the sliding beam bunching imaging is RcPositive side-view skew distance, theta, at zero Doppler time from the center of the sceneazThe azimuth beamwidth of the antenna.
Preferably, the intersection of the beam center and the ground
Figure GDA00031718953600000314
Is determined by the following steps:
firstly, a vector parallel to the azimuth edge of the scene is made at a position which is at a distance D from the azimuth front edge of the scene
Figure GDA0003171895360000041
Then, the vector is determined
Figure GDA0003171895360000042
And plane surface
Figure GDA0003171895360000043
The intersection point of the antenna beam center pointing to the ground at the moment of termination of the maneuver
Figure GDA0003171895360000044
As described above
Figure GDA0003171895360000045
The plane is the satellite position of the current imaging end time
Figure GDA0003171895360000046
Satellite position at the starting time of next imaging
Figure GDA0003171895360000047
And the intersection point of the beam center and the ground at the current imaging end moment
Figure GDA0003171895360000048
The plane determined by the three points.
Preferably, the beam rotation angular velocity during the attitude maneuver adjustment is greater than the beam rotation angular velocity during the sliding beamforming imaging.
Compared with the prior art, the invention has the beneficial effects that:
in order to improve the reconnaissance efficiency of the satellite-borne SAR, the multi-azimuth repeated observation capability of the satellite-borne SAR on the military sensitive area in a single transit process is required. Aiming at the aim, the invention provides a method realized by attitude maneuver of a satellite platform. Through attitude maneuver of the satellite platform, the peak value of an antenna directional diagram can always point to an observation scene, so that the highest echo signal-to-noise ratio and the optimal image quality are obtained. The method is designed based on the system parameters of the load, the longitude and latitude position information of an observation target, and finally realized relevant indexes such as resolution, breadth, the number of times of repeated observation and the like: 1) a satellite attitude stable maneuvering mode in each observation process; 2) and the satellite attitude is quickly adjusted in a maneuvering way between two observation processes so as to ensure that the satellite can stably work in an imaging way.
The method has the following two advantages:
1) in the attitude maneuver process of satellite imaging, the designed three-axis pointing of the satellite ensures that all range gates have the same Doppler frequency in the echo received each time, thereby simplifying the difficulty in later ground imaging processing.
2) In the satellite platform attitude rapid maneuvering process between two adjacent imaging, the Z axis with the fastest maneuvering is always positioned in a two-dimensional plane determined by the satellite position at the current imaging termination time, the satellite position at the next imaging starting time and the current Z axis direction. Therefore, compared with maneuvering in three-dimensional space, the method can minimize the maneuvering amplitude and speed of the satellite, so that two adjacent imaging can be transited more smoothly.
Drawings
FIG. 1 is a schematic diagram of the multi-azimuth observation mode of the present invention;
FIG. 2 is a schematic view of the whole process of two sliding bunching observations and the rapid attitude maneuver adjustment beam pointing between them of the present invention;
FIG. 3 is a schematic diagram of the start time and position of a satellite according to the present invention;
FIG. 4 is a flow chart of the present invention for determining a satellite platform position and attitude at an initial imaging time;
FIG. 5 is a flowchart illustrating the method for determining the virtual point position of the beam pointing direction during the first imaging process and the position of the beam pointing direction at the imaging end time according to the present invention;
FIG. 6 is a schematic diagram of a process of the satellite platform rapidly maneuvering to achieve antenna beam pointing from a scene terminal to a starting end;
FIG. 7 is a diagram of the intersection point of the center of the antenna beam and the ground at two moments
Figure GDA0003171895360000051
And
Figure GDA0003171895360000052
is a schematic diagram of the position relation;
FIG. 8 is a flow chart of the design of the fast maneuvering mode of the satellite platform between two adjacent sliding beamforming imaging according to the present invention.
Detailed Description
The invention is further illustrated by the following examples.
The new multi-azimuth observation mode requires the satellite platform to maneuver within a large rotation angle range of the azimuth direction so as to realize the imaging of the multiple sliding bunching mode in the military area. Between two adjacent imaging, the satellite platform needs to be quickly maneuvered, the antenna beam direction is adjusted to the initial position of the scene again, and the next sliding beam-bunching imaging process is started again.
Figure 1 shows the working principle of the multi-azimuth observation mode. In the stage 1 noted in the figure, the satellite-borne SAR starts to perform azimuth super-large squint angle sliding bunching imaging on the scene; after the work of the stage is completed, the satellite platform starts to rapidly maneuver, the beam direction is adjusted to the initial position of the scene again, and the sliding beamforming imaging of the 2 nd stage is started. And analogizing in sequence until the whole satellite finishes all n times of sliding bunching imaging, thereby realizing multi-azimuth repeated observation of the SAR load on the area.
The following will give an example of the first and second imaging observation processes of the mode and the maneuvering process between them, how to design the attitude maneuvering mode of the satellite in the whole working process according to multiple conditions such as imaging resolution, imaging width, antenna beam width, and maneuvering time constraint.
In fig. 2, the whole process of two sliding beamforming observations and the fast attitude maneuver between them to adjust the beam pointing is shown. It can be seen from the figure that the two adjacent sliding bunching imaging processes are attitude rotation around different virtual rotation centers (the first time is O)1The second time is O2) (ii) a In addition, the rotating angular speed of the wave beam in the process of quick maneuvering is obviously greater than that of the wave beam in the process of sliding beam bunching imaging. In attached table 1, the working parameters and constraint conditions that need to be given in advance in the design process of the attitude maneuver are given:
TABLE 1 relevant parameters for Multi-azimuthal repeat Observation
Serial number System/imaging parameters (symbol) Remarks for note
1. Scene center side view slope distance Rc System parameter
2. Satellite flight velocity Vs System parameter
3. Beam ground speed (stripe pattern) Vg System parameter
4. System carrier frequency wavelength λ System parameter
5. Antenna azimuth beam width θa System parameter
6. Azimuthal resolution requirement ρa Constraint conditions
7. Azimuth length of scene La Constraint conditions
8. Azimuth beam center squint angle at initial sliding convergence moment θ1s Initial conditions
9. Angular range of azimuthal strabismus observation ±θsq_max Constraint conditions
10. Platform maneuver time between two sliding gather imaging Tm Constraint conditions
Under the condition that the system parameters and the constraint conditions are given, the attitude change mode of the satellite platform in the sliding bunching imaging process and the maneuvering process between the sliding bunching imaging process and the maneuvering process is designed to ensure that continuous multiple times of observation can be realized.
(1) Step 1: satellite platform attitude maneuver mode for determining primary imaging
During the first step of analysis, the following three parameters need to be determined according to the system parameters and constraints listed in attached table 1:
Figure GDA0003171895360000061
platform of first slip spotlight imaging process fliesThe line distance is as follows: l iss1；
Figure GDA0003171895360000062
Beam center squint angle at the first sliding beamforming imaging termination time: theta1e；
Figure GDA0003171895360000063
Beam rotation angular velocity at the first sliding beamforming termination time: omega1e；
When the load is in the strip mode, its azimuthal resolution may be ρa_stripCan be expressed as
Figure GDA0003171895360000071
Wherein VsIs the satellite platform flight speed, VgThe beam footprint travel speed when the satellite-borne SAR load is operating in strip mode.
Based on the formula (1) to give the azimuth resolution of the strip mode and the azimuth resolution required by the sliding bunching mode, the improvement factor A of the sliding bunching mode can be obtained as
Figure GDA0003171895360000072
Then combines with the center slant distance R of the front side view fieldcThe slant distance R of the sliding bunching rotation center can be obtainedtotIs composed of
Figure GDA0003171895360000073
When the azimuth oblique angle of the antenna beam center is theta1sThe length L of the area covered by the beam in azimuth directionbIs composed of
Figure GDA0003171895360000074
Therefore, the travel distance L of the beam on the ground in the first sliding beam bunching imaging stage1Is the azimuth length L of the sceneaAnd beam azimuth coverage length LbSum of
L1＝La+Lb (5)
Combining with the sliding bunching resolution improvement factor A, the flight distance L of the satellite platform can be obtaineds1Is composed of
Figure GDA0003171895360000075
Distance of flight L through satellite platforms1Beam center starting squint angle theta of antenna1sAnd center of rotation slope distance R of sliding bunchingtotThe beam center squint angle theta at the sliding bunching termination moment can be obtained1eIs composed of
Figure GDA0003171895360000076
At the end time of the first sliding beam bunching imaging, the corresponding beam center rotation angular velocity omega1eIs composed of
Figure GDA0003171895360000077
After the first imaging is finished, the satellite platform starts to rapidly maneuver, and the beam direction is adjusted to the azimuth initial position of the scene.
In the specific implementation process of step 1, the scene center position based on the scene is firstly determined
Figure GDA0003171895360000081
Scene size La×LrAnd maximum squint angle operation capability of antenna beam [ -theta [ ]1s,θ1s]To determine: 1) satellite platformPosition at the time of initial imaging
Figure GDA0003171895360000082
2) Attitude of satellite at that time
Figure GDA0003171895360000083
3) Beam center pointing virtual point in primary imaging process
Figure GDA0003171895360000084
When the satellite is at the starting position
Figure GDA0003171895360000085
When the antenna beam has a maximum squint angle theta1sAnd the beam front edge just meets the scene edge.
Based on the above analysis, the intersection point of the antenna beam center and the ground at the satellite initial position can be obtained
Figure GDA0003171895360000086
The distance from the center of the scene in the azimuth direction is:
Figure GDA0003171895360000087
wherein L isaIs the azimuth length of the scene, RcPositive side-view skew distance, theta, at zero Doppler time from the center of the sceneazThe azimuth beamwidth of the antenna. In addition, the first and second substrates are,
Figure GDA0003171895360000088
and
Figure GDA0003171895360000089
are positioned in the same distance door.
At the determined intersection point
Figure GDA00031718953600000810
After the position of (2), its corresponding zero doppler time can be determinedAnd the position of the satellite at that moment
Figure GDA00031718953600000811
The starting position of the satellite can then be determined on the orbit
Figure GDA00031718953600000812
Satisfies the relationship: connection of
Figure GDA00031718953600000813
And
Figure GDA00031718953600000814
vector and join of two points
Figure GDA00031718953600000815
And
Figure GDA00031718953600000816
the angle between the vectors of the two points is thetamax(as noted in FIG. 3), θmaxIs thetasq_max(i.e. theta)1s) The relationship between is
Figure GDA00031718953600000817
Wherein VsIs the satellite platform flight speed, and VgThe beam ground travel speed when the load is operating in strip mode. Theta can be obtained by the formula (10)maxAnd the starting position of the satellite
Figure GDA00031718953600000818
Finally, from the starting position of the satellite
Figure GDA00031718953600000819
And intersection of beam center and ground
Figure GDA00031718953600000820
The starting moment can be determined in the antenna beamDirection of heart
Figure GDA00031718953600000821
Because the antenna and the satellite are fixedly connected, the beam center pointing of the antenna is the Z-axis pointing of the satellite
Figure GDA00031718953600000822
Y-axis pointing of satellite
Figure GDA00031718953600000823
Perpendicular to
Figure GDA00031718953600000824
With satellite velocity
Figure GDA00031718953600000825
Form a slant plane, the X-axis of the satellite pointing
Figure GDA00031718953600000826
And
Figure GDA00031718953600000827
become the right hand rule.
At this time, the initial position of the satellite, the direction of the antenna beam at the initial time and the attitude information of the whole satellite in the multi-azimuth observation mode are obtained. In fig. 4, a flow chart for determining the satellite platform position and attitude at the time of the initial imaging is given.
Next, the coordinates of the beam pointing to the virtual center during the first imaging process need to be determined. During first sliding spotlight imaging, the flying distance L of the platform iss1As shown in equation (6), in combination with the satellite flight velocity VsThe working time T of the first sliding spotlight imaging can be obtainedacq。
Figure GDA0003171895360000091
Wherein
Figure GDA0003171895360000092
Combining the satellite initial position obtained in the early stage
Figure GDA0003171895360000093
The position of the stage at the time of termination of the first imaging can be obtained
Figure GDA0003171895360000094
As shown in formula (12)
Figure GDA0003171895360000095
During sliding beamforming imaging, the antenna beam center will always point at a certain rotational center. Therefore, the rotation point is necessarily at the vector
Figure GDA0003171895360000096
And the center of rotation
Figure GDA0003171895360000097
The following relationship must be satisfied:
Figure GDA0003171895360000098
based on formula (13) and the result obtained in step 1
Figure GDA0003171895360000099
Vector, the center of rotation can be determined
Figure GDA00031718953600000910
The position of (a). Fig. 5 shows the determination of the position of the beam pointing virtual point during the first imaging and the position of the beam pointing at the end of the imaging.
(2) Step 2: determining a fast maneuvering adjustment mode of a platform between two adjacent images
As can be seen from FIG. 2, the maneuvering angular velocity of the satellite platform during the maneuvering process between adjacent images is significantly greater than during the imagingThe angular velocity. The course of the angular speed during the maneuver is thus an angular speed ω from the moment of termination of the imaging phase 11eAccelerating and then decelerating to the angular velocity omega at the starting moment of the imaging stage 22sTo ensure the continuity and the smoothness of the working process. The relevant parameters that the process needs to determine are listed below:
Figure GDA00031718953600000911
beam rotation angular velocity acceleration time: t is1；
Figure GDA00031718953600000912
Acceleration during beam rotational acceleration: a is1；
Figure GDA0003171895360000101
Beam rotation acceleration deceleration time: t is2；
Figure GDA0003171895360000102
Acceleration during beam rotation deceleration: a is2
The allowable time of attitude maneuver of the satellite platform is T based on the given satellite platform in the attached table 1mAfter the attitude quick maneuver adjustment, the beam center squint angle theta at the initial moment of the second sliding beam bunching imaging2sIs composed of
Figure GDA0003171895360000103
The beam rotation angular velocity ω at that time2sIs composed of
Figure GDA0003171895360000104
Based on the beam center squint angle at the second starting time obtained by the equations (14) and (15) and the required beam rotation angular velocity, a system of equations for parameters such as acceleration time, acceleration, deceleration time, acceleration during deceleration, etc. of the maneuvering process can be established, as listed in equation (16)
Figure GDA0003171895360000105
The first equation represents that the sum of the acceleration time and the deceleration of the rotation of the satellite platform is the total maneuvering time T allowed by the platformm(ii) a The second equation shows that the beam rotation angular velocity at the initial time of the imaging phase 2 is exactly ω after acceleration and deceleration processes from the beam rotation velocity at the end time of the imaging phase 12s(ii) a The third equation shows that the angle through which the antenna beam turns throughout the maneuver is exactly the difference between the azimuthal squint angle from the end of phase 1 and the start of phase 2. The above three equations contain 4 unknowns, so it is necessary to design an acceleration time T first1And the other three parameters are determined. The corresponding analytical solution is:
T2＝Tm-T1 (17)
Figure GDA0003171895360000106
Figure GDA0003171895360000107
wherein T is used for ensuring the stable maneuvering process of the whole satellite1Is to ensure a1And a2The difference between them is sufficiently small.
Maneuvering time T based on platform between two adjacent imagingmIt needs to be determined at TmThe beam of the satellite platform is pointed during the maneuvering time. Fig. 6 shows the process of the satellite platform rapidly maneuvering to realize the antenna beam pointing from the scene terminal to the beginning.
In the context of figure 6 of the drawings,
Figure GDA0003171895360000111
for the platform position at the end of the first sliding spotlight imaging,
Figure GDA0003171895360000112
is the intersection of the antenna beam center and the ground at that moment.
Figure GDA0003171895360000113
The platform position after the maneuvering process is completed (namely the platform position at the starting moment of the second sliding bunching imaging),
Figure GDA0003171895360000114
the antenna beam center is pointed at the intersection point with the ground at that moment.
Figure GDA0003171895360000115
And
Figure GDA0003171895360000116
the relationship between can be expressed as
Figure GDA0003171895360000117
By passing
Figure GDA0003171895360000118
And
Figure GDA0003171895360000119
the position of the satellite at the end of the maneuvering process can be obtained
Figure GDA00031718953600001110
In obtaining
Figure GDA00031718953600001111
And
Figure GDA00031718953600001112
after three position vectors, the position vector needs to be determined on the ground
Figure GDA00031718953600001113
To ensure that the beam center vectors of the ending moment of the first sliding bunching and the starting moment of the second sliding bunching can have an intersection point (the antenna beam center always points to the point in the whole maneuvering process). If there is an intersection point between the two beam center vectors, then
Figure GDA00031718953600001114
And
Figure GDA00031718953600001115
four points must be on one plane. Will be determined by these three points
Figure GDA00031718953600001116
First of all, the first step is to,
Figure GDA00031718953600001117
must be at a distance from the azimuthally forward edge of the scene
Figure GDA00031718953600001118
Wherein theta is1eThe beam center squint angle at the end moment of the previous sliding beam bunching imaging is shown.
FIG. 7 shows the intersection point of the antenna beam center and the ground at two moments in time
Figure GDA00031718953600001119
And
Figure GDA00031718953600001120
is a positional relationship. From this figure, it can be seen that the determination
Figure GDA00031718953600001130
Two steps are required: headFirstly, a vector parallel to the azimuth edge of the scene is made at a position which is at a distance D from the azimuth front edge of the scene
Figure GDA00031718953600001121
The second step is to determine the vector
Figure GDA00031718953600001122
And plane surface
Figure GDA00031718953600001123
The intersection point of the antenna beam center pointing to the ground at the moment of termination of the maneuver
Figure GDA00031718953600001124
In that
Figure GDA00031718953600001125
After the determination, the intersection point of the beam center vector at the first sliding bunching termination time and the beam center vector at the second sliding bunching starting time can be determined
Figure GDA00031718953600001126
When in use
Figure GDA00031718953600001127
After the determination, the beam center is always pointed in the whole platform maneuvering process
Figure GDA00031718953600001128
Therefore, the direction of the Z axis of the platform can be obtained
Figure GDA00031718953600001129
Next, the orientations of the Y-axis and the X-axis of the stage can be obtained according to the same method as step 1. FIG. 8 shows the design flow of the fast maneuvering mode of the satellite platform between two adjacent sliding bunching imaging.
And (3) after the platform maneuvering process in the step (2) is finished, obtaining the beam center squint angle at the initial moment of the second sliding beam bunching imaging.
(3) And step 3: platform attitude maneuver adjustment mode for determining next sliding bunching imaging
After the squint angle and the rotation angular velocity at the initial stage of the 2 nd sliding bunching imaging are obtained in step 2, the following key parameters need to be determined in step 3:
Figure GDA0003171895360000121
the flying distance of the platform for the 2 nd sliding convergence imaging is L2s；
Figure GDA0003171895360000122
Beam center squint angle theta at 2 nd sliding convergence imaging termination moment2e；
Figure GDA0003171895360000123
Beam rotation angular velocity ω at the end time of the 2 nd sliding-focusing imaging2e。
Azimuth oblique viewing angle theta based on 2 nd sliding convergence imaging starting moment2sThe distance L traveled by the antenna beam on the ground at this stage can be derived2The sum of the azimuth length of the scene and the azimuth coverage length of the beam is:
Figure GDA0003171895360000124
then, by using the sliding bunching factor A, the flying distance L of the satellite platform in the sliding bunching stage 2 can be obtaineds2Is composed of
Figure GDA0003171895360000125
Oblique view angle theta at starting moment of 2 nd sliding bunching imaging phase2sA platform flight distance Ls2And the slant distance R of the sliding bunching rotation centertotThe step can be obtainedAzimuthal strabismus angle theta of segment at termination time2eIs composed of
Figure GDA0003171895360000126
Finally, the beam squint angle theta at the termination time of the sliding bunching stage 2 is obtained according to the formula (25)2eThen, the beam rotation angular velocity ω corresponding to the time can be obtained2eIs composed of
Figure GDA0003171895360000127
And after the second sliding bunching imaging process is finished, the step 2 is performed again to determine the platform attitude maneuver process between the second sliding bunching imaging and the third sliding bunching imaging. The two steps are alternately carried out (until the azimuth oblique angle of the antenna beam exceeds the effective working range), and the satellite platform attitude requirements of each sliding beam-bunching imaging and maneuvering processes between two adjacent imaging can be obtained.
In the implementation process of the algorithm, the following process may be specifically performed:
1) according to the carrier frequency wavelength lambda of the SAR system and the satellite flight speed VsBeam footprint velocity V in stripe modegAnd SAR loaded antenna azimuth beam width thetaazAnd calculating the azimuth resolution rho in the strip modea_strip；
2) According to the azimuth resolution rho achieved under the multi-azimuth sliding bunching observation modeaAnd ρ obtained in the step 1)a_stripObtaining a resolution improvement factor A of the sliding bunching mode;
3) side-looking forward slope distance R according to scene centercAnd 2) obtaining a sliding bunching resolution improvement factor A obtained in the step 2), and obtaining a sliding bunching rotation center slope distance Rtot；
4) Starting squint angle theta according to current sliding bunching imaging1sAzimuth beam width theta of antennaaFront side view slope distance R of scene centercTo obtain the timeLength L of area covered upward in azimuthb；
5) From LbAnd the azimuth length L of the sceneaDetermining the travel distance L of the antenna beam footprint in the first sliding beam bunching imaging process1；
6) L obtained from step 5)1And determining the flight distance L of the platform in the first imaging process by using the sliding bunching improvement factor As1And a working time Tacq；
7) From LbAnd the azimuth length L of the sceneaDetermining the intersection point of the antenna beam center and the ground at the initial imaging moment of the satellite
Figure GDA0003171895360000131
8) Initial squint angle theta by sliding bunch imaging1sSatellite flight velocity VsAnd beam footprint velocity V in stripe modegAnd obtained in step 7)
Figure GDA0003171895360000132
The position of the satellite imaging initial moment can be obtained
Figure GDA0003171895360000133
9) Starting time position by satellite imaging
Figure GDA0003171895360000134
Intersection of antenna beam center and ground
Figure GDA0003171895360000135
Satellite Z-axis pointing for determining starting time
Figure GDA0003171895360000136
10) Starting time position by satellite imaging
Figure GDA0003171895360000137
Satellite Z-axis of starting timeTo the direction of
Figure GDA0003171895360000138
And determining a virtual rotation center position by using the sliding bunching resolution improvement factor A
Figure GDA0003171895360000139
11) In the first sliding spotlight imaging process, the Z axis of the satellite platform always points
Figure GDA0003171895360000141
The Y-axis direction of the satellite is directed from the Z-axis direction and the satellite flying speed VsThe direction is determined by a right-hand rule, and the X-axis direction is determined by a Y-axis and a Z-axis through the right-hand rule;
12) according to the position of the starting moment of the first imaging of the satellite
Figure GDA0003171895360000142
Length of imaging time TacqAnd the flight orbit, the satellite position at the first imaging end time can be obtained
Figure GDA0003171895360000143
(i.e. the
Figure GDA0003171895360000144
)；
13) Obtained in step 12)
Figure GDA0003171895360000145
And virtual center of rotation for a first imaging procedure
Figure GDA0003171895360000146
The attitude of the satellite at the termination time of the first imaging and the intersection point of the satellite and the ground are obtained
Figure GDA0003171895360000147
14) Obtained in step 12)
Figure GDA0003171895360000148
And given the attitude maneuver time T between two imagingmDetermining the position of the satellite after maneuvering (the start time of the next imaging)
Figure GDA0003171895360000149
15) By
Figure GDA00031718953600001410
And
Figure GDA00031718953600001411
determining the plane determined by the three points and the distance D between the center of the beam and the scene after the maneuvering so as to determine the intersection point of the center of the beam and the ground after the maneuvering is finished
Figure GDA00031718953600001412
16) Satellite position after completion of maneuver
Figure GDA00031718953600001413
And intersection of beam center and ground
Figure GDA00031718953600001414
Obtaining the Z-axis direction of the satellite at the maneuvering ending moment;
17) by vector
Figure GDA00031718953600001415
And
Figure GDA00031718953600001416
to determine the virtual center of rotation of the satellite platform during the maneuvering between two adjacent images
Figure GDA00031718953600001417
18) By virtual centre of rotation of a motorised process
Figure GDA00031718953600001418
Determining the three-axis attitude of the satellite in the whole maneuvering process;
19) by
Figure GDA00031718953600001419
And determining the virtual rotation center of the second sliding bunching imaging by using the sliding bunching resolution improvement factor A
Figure GDA00031718953600001420
20) Entering the 11) step to the 14) step to carry out next sliding bunching imaging;
21) entering the steps 15) to 18) to carry out the next attitude maneuver adjustment process;
22) and (5) alternating the step (20) to the step (21) until the imaging work is finished.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.

Claims (10)

1. A satellite platform attitude maneuver method for satellite-borne SAR multi-azimuth repeated observation is characterized by being realized in the following mode:
s1, determining the attitude maneuver mode of the satellite platform for the first imaging, namely determining the position of the satellite platform at the initial imaging moment, the satellite attitude and the virtual rotation center in the first imaging process;
s2, performing sliding bunching imaging, and determining the satellite position at the next imaging starting moment according to the satellite platform attitude maneuver mode determined in S1 for the first imaging;
s3, determining satellite attitudes in the maneuvering process between two adjacent imaging and a virtual rotation center in the next imaging process according to the satellite position of the next imaging starting moment and the distance between the center of the beam after maneuvering and the scene, and adjusting the beam direction to the azimuth direction starting position of the scene in the attitude maneuvering adjustment process;
s4, repeating the steps s2 and s3 until the imaging work is finished;
in the sliding beamforming imaging process, the beam center of the satellite platform always points to the virtual rotation center determined in the imaging process.
2. The method according to claim 1, characterized in that the virtual center of rotation during the first imaging in step s1 is determined by:
initial squint angle theta by sliding bunch imaging1sSatellite platform flight speed VsAnd beam footprint velocity V in stripe modegAnd the intersection point of the antenna beam center and the ground at the initial imaging moment of the satellite
Figure FDA0003171895350000011
Determining satellite imaging start time position
Figure FDA0003171895350000012
Starting time position by satellite imaging
Figure FDA0003171895350000013
Intersection of antenna beam center and ground
Figure FDA0003171895350000014
Satellite Z-axis pointing to determine starting imaging time
Figure FDA0003171895350000015
Starting time position by satellite imaging
Figure FDA0003171895350000016
Satellite Z-axis pointing at start time
Figure FDA0003171895350000018
And determining a virtual rotation center position by using the sliding bunching resolution improvement factor A
Figure FDA0003171895350000017
3. The method of claim 2, wherein: the satellite imaging start time position
Figure FDA00031718953500000112
The determination is made by:
determining the satellite imaging initial time, the intersection point of the antenna beam center and the ground
Figure FDA0003171895350000019
And scene center
Figure FDA00031718953500000111
The distance in the azimuth direction is further determined, and the intersection point of the antenna beam center and the ground is further determined
Figure FDA00031718953500000110
A location;
Figure FDA0003171895350000021
according to the intersection point of the antenna beam center and the ground
Figure FDA0003171895350000022
Position, determining the intersection point
Figure FDA0003171895350000023
Satellite position at zero doppler time
Figure FDA0003171895350000024
Determining connections
Figure FDA0003171895350000025
And
Figure FDA0003171895350000026
vector and join of two points
Figure FDA0003171895350000027
And
Figure FDA0003171895350000028
angle theta between vectors of two pointsmax；
According to the angle thetamaxDetermining the imaging start time position
Figure FDA0003171895350000029
Above, LaIs the azimuth length of the scene, RcPositive side-view skew distance, theta, at zero Doppler time from the center of the sceneazThe azimuth beamwidth of the antenna.
4. The method of claim 3, wherein: the included angle thetamaxAccording to the relation
Figure FDA00031718953500000210
And (4) determining.
5. The method of claim 2, wherein: the virtual rotation center position
Figure FDA00031718953500000211
The following relationship is satisfied:
Figure FDA00031718953500000212
Figure FDA00031718953500000213
to be started from a satellite
Figure FDA00031718953500000214
Pointing to first sliding spotlight imaging virtual center of rotation
Figure FDA00031718953500000215
The vector of (2).
6. The method of claim 1, wherein: step s2 is implemented by:
determining the satellite position of the imaging ending time according to the position of the imaging starting time of the satellite, the imaging time length and the flight orbit;
determining the satellite attitude at the imaging termination time and the intersection point of the satellite attitude and the ground according to the determined satellite position at the imaging termination time and the virtual rotation center of the imaging process;
and determining the satellite position at the moment of starting the next imaging after maneuvering according to the determined satellite position at the moment of ending the imaging and given attitude maneuvering time between two times of imaging.
7. The method of claim 1, wherein: step s3 is implemented by:
from the satellite position at the end of this imaging
Figure FDA00031718953500000216
Satellite position at the start of next imaging
Figure FDA00031718953500000217
And the beam center and the ground at the end of the imagingIntersection point
Figure FDA00031718953500000218
Determining the plane determined by the three points and the distance D between the center of the beam and the scene after maneuvering to determine the intersection point between the center of the beam and the ground after the attitude maneuvering is adjusted
Figure FDA0003171895350000031
Satellite position adjusted by attitude maneuver
Figure FDA0003171895350000032
And intersection of beam center and ground
Figure FDA0003171895350000033
Obtaining the Z-axis direction of the satellite at the maneuvering ending moment;
by vector
Figure FDA0003171895350000034
To determine the virtual center of rotation of the satellite platform during the maneuvering between two adjacent images
Figure FDA0003171895350000035
By virtual centre of rotation of a motorised process
Figure FDA0003171895350000036
Determining the three-axis attitude of the satellite in the whole maneuvering process;
by
Figure FDA0003171895350000037
And determining the virtual rotation center of the next sliding bunching imaging by using the sliding bunching resolution improvement factor A
Figure FDA0003171895350000038
8. The method of claim 7, wherein: the distance D is calculated according to the following formula:
Figure FDA0003171895350000039
wherein theta isendThe oblique angle of the beam center at the end of the sliding beam bunching imaging is RcPositive side-view skew distance, theta, at zero Doppler time from the center of the sceneazThe azimuth beamwidth of the antenna.
9. The method of claim 7, wherein: intersection of the beam center and the ground
Figure FDA00031718953500000310
Is determined by the following steps:
firstly, a vector parallel to the azimuth edge of the scene is made at a position which is at a distance D from the azimuth front edge of the scene
Figure FDA00031718953500000311
Then, the vector is determined
Figure FDA00031718953500000312
And plane surface
Figure FDA00031718953500000313
The intersection point of the antenna beam center pointing to the ground at the moment of termination of the maneuver
Figure FDA00031718953500000314
As described above
Figure FDA00031718953500000315
The plane is the satellite position of the current imaging end time
Figure FDA00031718953500000316
Satellite position at the starting time of next imaging
Figure FDA00031718953500000317
And the intersection point of the beam center and the ground at the current imaging end moment
Figure FDA00031718953500000318
The plane determined by the three points.
10. The method of claim 1, wherein: the beam rotation angular velocity in the attitude maneuver adjustment process is greater than that in the sliding beamforming imaging process.
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