CN115792907A - Method for designing azimuth imaging parameters of spaceborne SAR squint sliding bunching mode - Google Patents
Method for designing azimuth imaging parameters of spaceborne SAR squint sliding bunching mode Download PDFInfo
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Abstract
The invention discloses a method for designing azimuth imaging parameters of a spaceborne SAR squint sliding bunching mode, which aims to obtain an azimuth beam scanning rule during imaging and realize accurate pointing control of a high-resolution wide-coverage spaceborne SAR large squint imaging beam. The azimuth imaging parameters comprise azimuth resolution, imaging length, starting oblique view angle, ending oblique view angle and beam scanning angular speed; the method comprises the steps of firstly calculating the imaging time length according to a sliding bunching imaging principle by utilizing high-precision satellite ephemeris forecast data and imaging area position information, and then determining a starting oblique view angle and a finishing oblique view angle according to the relation between satellite-ground oblique distance and a velocity space vector; the method has two key points, namely, the satellite ephemeris forecast data is required to be data after two-dimensional attitude guidance of the yaw angle and the pitch angle, and the influence factor of the azimuth resolution is fully considered. The method has been successfully applied to the on-orbit SAR satellite to obtain the high-quality satellite-borne SAR image, and has important engineering practical value.
Description
Technical Field
The invention belongs to the field of satellite-borne synthetic aperture radar imaging, and particularly relates to a method for designing azimuth imaging parameters of a satellite-borne SAR squint sliding bunching mode.
Background
Since the successful application of sliding spotlight mode imaging on German TerrraSAR-X satellites in 2007, the sliding spotlight mode imaging has become a main imaging mode for acquiring high-resolution wide-coverage images by satellite-borne SAR at home and abroad in recent years, and a large number of high-quality high-resolution remote sensing images are acquired by a plurality of satellite-borne SAR satellites in China by adopting the mode and are used for earth observation in the military and civil fields.
Limited by the scanning capability of antenna beams, the satellite-borne SAR sliding beam-bunching mode imaging at home and abroad at present basically adopts small scanning angle front side view imaging, namely the satellite-ground relative speed at the imaging center is vertical to the sight direction of the antenna beams, and the scanning angle is not more than 10 degrees. With the development of satellite-borne SAR technology in China and the requirement on high resolution, multi-angle and multi-target imaging application, the strabismus sliding bunching mode is becoming an indispensable imaging mode. In addition, with the proposal and implementation of multi-satellite networking and collaborative observation application modes, on-orbit rapid autonomous imaging parameter calculation becomes an on-satellite essential function. Therefore, a parameter design method and an engineering implementation strategy for quickly and accurately designing the squint sliding bunching mode of the satellite-borne SAR are problems which need to be researched and solved.
Josef Mittermaker et al published a text of Sliding spot SAR processing for terrorist SAR-X using a new formulation of the extended chip scaling algorithm in the International society for Earth science and remote sensing (IGARSS 2003) in 2003, and provided a method for calculating parameters such as a start scanning angle, an end scanning angle, imaging time and the like of a satellite-borne Sliding spotlight mode according to a virtual rotation center principle and a geometric relation of a flat satellite and successfully applied to a terroris-X satellite. The Chinese patent application CN103792536A discloses a method for acquiring the sliding bunching azimuth parameters of a satellite-borne synthetic aperture radar, and the proposed design method is successfully applied to on-orbit SAR satellites such as remote sensing satellite No. 29, high-score No. 3, high-score No. 10, test satellite No. 11 and Zellu-one. However, the two methods are calculated according to the fixed virtual rotation center principle, the approximate linear satellite flight path and the local plane satellite-ground geometric relation of the imaging area, and are suitable for the conditions of small oblique angle (not more than 3 degrees) and short imaging time (not more than 15 s). Under the condition of a large squint angle, the satellite-ground slant distance is far, the satellite-ground slant distance is influenced by a satellite curved orbit and a curved surface of the earth, the calculation of the squint angle is inaccurate, the beam is deflected, the signal-to-noise ratio of an image is reduced, and a false target caused by distance blurring and azimuth blurring appears in the image in serious cases. Han Xiaolei, etc. provide chinese patent application CN106226768a, which is a parameter design method for an ultra-high resolution agile SAR satellite sliding beamforming mode system, and this method considers performing parameter design using high-precision orbit data and target position data, but the method is only suitable for realizing a beam control strategy required by front-side view sliding beamforming mode imaging by using satellite attitude maneuver, and is not suitable for realizing a beam control strategy by phased array antenna electrical scanning.
In summary, the high-resolution spaceborne SAR sliding bunching mode parameter design methods mentioned in the literature and engineering application at present are not suitable for the large squint sliding bunching mode.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for designing azimuth imaging parameters of a spaceborne SAR squint sliding beam-bunching mode, which is characterized in that appropriate key parameters required by engineering realization of a start squint angle, an end squint angle, an antenna azimuth length, azimuth resolution and imaging length are designed according to a constraint relation among the start squint angle, the end squint angle, the antenna azimuth length, the azimuth resolution and the imaging length, and during imaging, the method is used for accurately controlling the antenna beam direction, so that the beam center moves on the ground at a fixed speed to acquire an SAR image meeting the requirements of azimuth resolution and imaging length.
In order to realize the purpose of the invention, the invention adopts the following technical scheme:
setting input conditions, wherein the input conditions comprise high-precision ephemeris forecast data during imaging, target initial position vectors and target end position vectors of the scene center of an imaging area along the azimuth direction, and imaging starting time;
defining azimuth parameters, wherein the azimuth parameters comprise azimuth resolution, azimuth imaging length, imaging starting squint angle, imaging ending squint angle and antenna beam scanning angular velocity;
determining the ground speed of the wave beam in the squint sliding bunching mode according to the linear relation between the antenna azimuth length of the SAR, the ground speed of the wave beam and the azimuth resolution of the SAR;
determining the imaging time length according to the time relationship among the satellite-ground geometric model of the spaceborne SAR squint sliding bunching mode, the direction position imaging length and the beam ground speed in the sliding bunching mode;
determining an imaging starting squint angle according to the geometric definition of the satellite-borne SAR squint angle by using a distance vector and a satellite velocity vector from a satellite to a target;
determining the imaging ending time according to the imaging time length by taking the imaging starting time as a reference, and calculating an imaging ending squint angle;
determining the scanning angular velocity of the antenna beam according to the oblique angle variation and the imaging time length in the imaging period;
the azimuth imaging length is the length of a section of continuous imaging area on the ground along the beam advancing direction; the imaging starting squint angle is an azimuth beam center pointing angle at the imaging starting moment; the end squint angle is an azimuth beam center pointing angle at the imaging end moment; the antenna beam scanning angular velocity is the angular range over which the beam center points during imaging changes every second.
Further, the input conditions are given by a user according to earth observation task requirements, satellite flight orbits and SAR imaging capacity in advance; the high-precision ephemeris forecast data comprises satellite position vectors and velocity vectors, and target initial position vectors and target end position vectors are defined in a WGS84 coordinate system;
the high-precision ephemeris forecast data are data after yaw and pitch two-dimensional attitude guidance, and the satellite speed direction is ensured to be vertical to the sight direction of the antenna beam when the azimuth beam is not scanned;
the formula of the control law of yaw guidance is as follows:
wherein,
in order to control the angle of yaw,
in order to be the angular velocity of the satellite,
is the angular velocity of the earth's rotation,
in order to obtain the inclination angle of the track,
is satellite latitude argument;
related to radar when looking from left to right and from right to left
Left side view time
；
The control rule formula of the pitching guidance is as follows:
wherein,
in order to control the angle of the pitching wave,
in order to determine the eccentricity of the track,
is the true proximal angle.
It should be noted that, in the following description,
and
two calculation formulas are needed to complete the calculation function in the mission planning system and are included in the input conditions of the invention.
Further, the antenna azimuth length of the SAR is a SAR system parameterBy using
Representing; the azimuth resolution of strabismus sliding bunching mode is used as a design index
Represents;
for ground speed of beam in strabismus sliding bunching mode
Expressed, the calculation formula is:
wherein,
for a fixed beam pointing to the corresponding antenna beam ground speed,
the azimuth resolution broadening coefficient of the SAR is obtained.
The azimuth resolution broadening coefficient of the SAR is the main content of the target simulation of the squint sliding bunching mode point of the satellite-borne SAR and is also a key input parameter of SAR azimuth parameter design, whether the azimuth resolution of an SAR image product can meet the design requirement or not is determined, the imaging time length is directly influenced, and the calculation result of starting and ending squint angles is finally influenced. The azimuth resolution broadening coefficient of the SAR is related to various influence factors, and azimuth directional diagram weighting, imaging processing weighting, doppler parameter estimation errors, target single-point synthetic aperture time approximation errors at different positions and imaging algorithm approximation errors are mainly considered.
The calculation formula is as follows:
wherein,
，
，
，
，
the 5 azimuth resolution influencing factors respectively cause the resolution broadening coefficients.
Wherein,
the 3dB beam width corresponds to the azimuth resolution broadening coefficient caused by the azimuth directional diagram weighting
The value is 1.11.
Wherein,
the azimuth resolution broadening coefficient caused by the imaging processing weighting is used, the imaging processing weighting aims to obtain point target low side lobe,
the value size of the weighted point target is related to the adopted weighting function, and the value size can be determined by comparing the ratio of the azimuth resolution after weighting and the azimuth resolution before weighting through point target simulation.
Wherein,
and estimating an azimuth resolution broadening coefficient caused by errors for the Doppler parameters. Doppler parameter estimation errors refer to Doppler center frequency estimation errors and Doppler chirp rate estimation errors introduced by ephemeris data errors and satellite-to-ground slope errors, when using for example RD, CS and
when the imaging algorithm is in an equal frequency domain, the azimuth resolution is widened.
The value of (2) can be determined by comparing the ratio of the ephemeris data error and the satellite-ground slope distance error to the front and back azimuth resolution through point target simulation.
Wherein,
and (3) synthesizing the azimuth resolution broadening coefficients caused by the time approximation errors of the aperture for the target single points at different positions. According to the sliding bunching mode imaging principle, the effective slant distance and the effective slant angle corresponding to different point targets are different in size and variable quantity, and theoretically, the single-point synthetic aperture time corresponding to different point targets is slightly different. The ground processing system considers the timeliness of the imaging algorithm realization, and generally adopts approximately the same single-point synthetic aperture time to process echo data of a whole scene or a part of scenes, so that the azimuth resolution difference of targets at different points is brought.
The value size of (a) can be determined by point target simulation according to the adopted imaging algorithm.
Wherein,
and (4) approximating the azimuth resolution broadening coefficients caused by errors for an imaging algorithm. The imaging algorithm approximation error refers to some assumed preconditions in the imaging algorithm derivation process, such as that the satellite trajectory approximates to a straight line in a short time, the satellite speed is constant, and the like. Considering the difficulty of realizing the large squint angle of the on-board SAR system,
the value of (A) is generally not more than 1.02.
Further, the azimuth imaging length is a design index
Representing;
a ground length corresponding to the beam width
The SAR azimuth beam width and the distance between a target and a satellite are calculated;
length of imaging time
Expressed, the calculation formula is:
further, according to the imaging principle of a spaceborne SAR squint sliding bunching mode, an imaging start squint angle is defined as an included angle formed by a distance vector between a satellite and a target at the imaging start moment and a satellite velocity vector under a WGS84 coordinate system minus half azimuth beam width; knowing a distance vector and a satellite velocity vector, and determining an imaging starting squint angle according to a space vector scalar product formula;
determining a distance vector between the satellite at the imaging starting time and the target according to a known input condition, wherein the distance vector is determined by a position vector of the satellite at the imaging starting time and a position vector of a starting point of an imaging area under a WGS84 coordinate system;
the imaging start time and the position vector of the target are known input parameters, determined by the user and the ground task management and control system.
For starting oblique view angle of imaging
Expressed, the calculation formula is:
wherein,
the distance vector from the satellite to the target at the imaging start time,
for the satellite velocity vector at the imaging start time,
the azimuth beam width of the SAR;
further, the imaging ending squint angle is an included angle between a distance vector between a satellite and a target at the imaging ending time and a satellite velocity vector under a WGS84 coordinate system and a half azimuth beam width; knowing a distance vector and a satellite velocity vector, and determining an imaging end squint angle according to a space vector scalar product formula;
for end of imaging squint angle
Expressed, the calculation formula is:
wherein,
the distance vector from the satellite to the target at the imaging end time,
the satellite velocity vector is the imaging end time;
the imaging end time is equal to the imaging start time plus the imaging time length.
Determining a distance vector between the satellite at the imaging ending time and the target according to a known input condition by using a position vector of the satellite at the imaging ending time and a position vector of an imaging area ending point under a WGS84 coordinate system;
the imaging end time and the position vector of the target are known input parameters and are provided by the user and the ground task management and control system.
Further, the antenna beam scanning angular velocity is equal to a ratio of an absolute variation amount of the imaging start squint angle and the imaging end squint angle to the imaging time length.
For angular velocity of antenna beam scanning
Expressed, the calculation formula is:
advantageous effects
The invention aims to obtain the azimuth beam scanning rule during imaging and realize the accurate pointing control of the high-resolution wide-coverage spaceborne SAR large squint imaging beam. The method is characterized in that high-precision ephemeris forecast data and target precise position information after two-dimensional attitude guidance of satellite yaw and pitching are firstly utilized, a space vector scalar product formula is combined according to an oblique sliding bunching mode imaging principle, and the design is compromised among an oblique angle, resolution and imaging band length, so that the resolution and imaging band length performance can reach the optimal design under the condition that the oblique angle can be realized.
The squint angle calculation method provided by the invention is irrelevant to a wave beam control mode, and is suitable for a phased array antenna wave beam electric scanning system and a satellite attitude maneuver realization wave beam scanning system.
The squint angle calculation method is not limited to a large squint sliding bunching mode, is also suitable for spaceborne SAR imaging such as a squint strip mode, a squint ScanSAR mode and the like, has very high universality, can achieve the maximum squint angle of more than 45 degrees, and lays a solid design foundation for high-resolution spaceborne SAR multi-angle and multi-target imaging design and application.
The design method provided by the invention is successfully applied to a high-resolution multi-angle and multi-target imaging mode of a high-resolution 12 # SAR satellite in China, a large number of high-quality squint sliding bunching mode images are obtained, and the effectiveness and the practicability of the design method are verified.
Drawings
FIG. 1 is a schematic diagram of a squint sliding bunching mode of a satellite-borne SAR;
FIG. 2 is a schematic diagram of a satellite-borne SAR satellite-ground slope distance vector relationship under a WGS84 coordinate system;
FIG. 3 is a flow chart of a method for designing the azimuth imaging parameters of the spaceborne SAR squint sliding bunching mode of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, the technical features involved in the respective embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The first aspect of the invention is that three input parameters are appointed as known conditions, including high-precision ephemeris forecast data during imaging, a satellite position vector matrix and a speed vector matrix with time intervals of 0.001s, a starting position vector and an ending position vector of a scene mapping zone center of an imaging area along an azimuth direction target, and an imaging starting time.
To achieve the object of the present invention, a second aspect of the present invention is to define 5 items of azimuth parameters including azimuth resolution, imaging length, start squint angle, end squint angle, beam scanning angular velocity.
In order to achieve the purpose of the invention, the third aspect of the invention is to derive an azimuth parameter calculation formula in the squint sliding bunching mode according to the on-board SAR squint sliding bunching imaging principle and the satellite-ground geometric relation.
As shown in fig. 1, the variables required by the geometric relationship between the spaceborne SAR squint sliding bunching mode and the satellite are as follows:
As shown in fig. 2, variables required by the position and slant range vector relationship between the satellite and the target at any time of the satellite-borne SAR are defined as:
is a satellite position vector at any time;
a target position vector of any point on the ground is obtained;
the distance vector from the satellite to the target at any time,
。
as shown in fig. 1 and fig. 2, the calculation formula of the azimuth parameters in the strabismus sliding bunching mode is derived as follows:
(1) Beam ground speed in squint sliding bunching mode:
for ground speed of beam in strabismus sliding bunching mode
Expressed, the calculation formula is:
wherein,
the antenna azimuth length of the SAR is a satellite-borne SAR system parameter.
The azimuth resolution broadening coefficient of the SAR is a SAR system parameter.
The azimuth resolution of the squint sliding bunching mode is a design index, and the physical meaning is the capability of distinguishing azimuth adjacent point targets on the image.
The ground speed of the antenna beam corresponding to the fixed beam pointing is provided by a ground mission planning system.
(2) Imaging time length:
length of imaging time
Expressed, the calculation formula is:
wherein,
the length is a design index for the azimuth imaging length.
The azimuth beam width of the SAR is a SAR system parameter.
The closest slant distance from the satellite to the target is provided by the ground mission planning system.
(3) The slant distance vector between the satellite and the target at the imaging starting moment:
for the vector of the slant distance between the satellite and the target at the start of imaging
Expressed, the calculation formula is:
(4) Imaging start oblique angle: according to the imaging principle of a spaceborne SAR squint sliding bunching mode, an imaging start squint angle is defined as the difference between the distance vector from a satellite at the imaging start time to a target (the imaging area start point at this time) and the satellite velocity vector at the imaging start time minus half azimuth beam width under a WGS84 coordinate system; knowing a distance vector and a satellite velocity vector, and determining a starting squint angle according to a space vector scalar product formula;
for starting oblique angle of view of image formation
Expressed, the calculation formula is:
(5) Imaging end time:
for end of imaging
Expressed, the calculation formula is:
wherein,
and the imaging starting time is provided by a ground task planning system.
And determining the position vector and the velocity vector of the satellite at the imaging ending time according to the imaging ending time and the satellite orbit forecast data, wherein the satellite orbit forecast data is provided by a ground task planning system.
(6) The slant distance vector from the satellite to the target at the imaging end time:
distance vector from satellite to target at imaging end time
Expressed, the calculation formula is:
(7) Imaging end squint angle: the imaging finishing squint angle is the half azimuth beam width added by the included angle between the satellite velocity vector and the distance vector from the satellite to the target (the imaging area termination point at the moment) at the imaging finishing moment in the WGS84 coordinate system; knowing the distance vector and the satellite velocity vector, and determining an imaging finishing squint angle according to a space vector scalar product formula;
for end of imaging squint angle
Expressed, the calculation formula is:
(8) Antenna beam scanning angular velocity: and the scanning angular speed of the antenna beam is equal to the ratio of the absolute variation of the imaging starting oblique angle and the imaging ending oblique angle to the imaging time length.
For angular velocity of antenna beam scanning
Expressed, the calculation formula is:
the derivation of the above expression is based on the following principle:
(1) The satellite-borne SAR point target azimuth resolution is in direct proportion to the antenna beam ground speed, and the squint sliding beam-forming mode reduces the beam ground speed and improves the azimuth resolution by controlling the antenna beam pointing change during imaging.
(2) And the azimuth resolution of the corresponding point target when the antenna beam is fixed during the satellite-borne SAR imaging is half of the azimuth length of the antenna.
(3) The imaging time length of the spaceborne SAR squint sliding bunching mode is the time of the antenna beam sliding through the imaging length plus the length corresponding to the beam width.
(4) The space-to-earth slant range vector is the difference between the position vector of the satellite and the target position vector in the WGS84 coordinate system.
(5) The spaceborne SAR squint angle is determined according to the scalar product of two space vectors of a slant range vector and a satellite velocity vector.
In order to achieve the purpose of the invention, the fourth aspect of the invention is to determine the implementation flow of the design method of the imaging parameters of the satellite-borne SAR squint sliding bunching mode azimuth direction according to the imaging principle of the satellite-borne SAR squint sliding bunching and the satellite-ground geometric relation, by combining with known input conditions such as satellite orbit position and speed forecast data, imaging start and stop point position vectors, resolution indexes, imaging length indexes and the like and a related calculation formula.
As shown in fig. 3, the input parameters include two types, namely, a mission planning input parameter and an SAR parameter, and according to the related formula, the intermediate variables such as the beam ground speed, the slant range vector and the like are sequentially calculated, and three key parameters, namely, an imaging start slant angle, an imaging end slant angle and a beam scanning angular speed, are obtained and output.
The method for designing the azimuth imaging parameters of the spaceborne SAR squint sliding bunching mode mainly comprises the steps of deducing related calculation formulas according to an imaging principle, gradually calculating all the formulas according to input conditions and output parameters according to the sequence, and describing the method in detail by combining with the figure 3.
The satellite-borne SAR imaging is completed by the mutual cooperation of a satellite platform, an SAR system and a ground task planning system, basic relevant parameters are required to be predicted in the imaging azimuth parameter design of the squint sliding bunching mode, and the basic relevant parameters comprise:
a. satellite position vector in WGS84 coordinate system according to 0.001s time interval in imaging time
Matrix and velocity vector
A matrix;
b. in the imaging area sceneTarget starting position vector of center along azimuth starting point and ending point in WGS84 coordinate system
And a termination position vector
；
c. Closest slope distance from satellite to target
；
d. Antenna beam ground speed corresponding to fixed beam pointing
；
e. Imaging start time
。
The above data is provided by a ground mission planning system. The following parameters and indicators are also included:
antenna azimuth length of SAR
；
Azimuth beamwidth of SAR
；
Azimuthal resolution broadening factor of SAR
;
i. Length of azimuthal imaging
；
g. Squint sliding spotlight mode azimuth resolution
。
Wherein f, h and g are SAR system parameters, and i and g are SAR design indexes.
1) And (3) calculating the ground speed of the beam in the squint sliding bunching mode according to the formula (1).
2) The imaging time length is calculated according to formula (2).
3) And (4) calculating the slant distance vector between the satellite and the target at the imaging starting moment according to the formula (3).
And searching the satellite position vector corresponding to the imaging starting moment from the task planning input parameter satellite position vector matrix.
4) The imaging start squint angle is calculated according to the formula (4).
And searching the satellite velocity vector corresponding to the imaging starting moment from the mission planning input parameter velocity vector matrix.
5) The imaging end time is calculated according to formula (5).
6) And (4) calculating the slant distance vector between the satellite and the target at the imaging ending moment according to the formula (6).
And searching the satellite position vector corresponding to the imaging ending moment from the task planning input parameter satellite position vector matrix.
7) The imaging end oblique angle is calculated according to formula (7).
And searching the satellite velocity vector corresponding to the imaging ending moment from the mission planning input parameter velocity vector matrix.
8) The antenna beam scanning angular velocity during imaging is calculated according to equation (8).
Implementation requires mission planning input parameters the satellite position vector matrix and velocity vector matrix must contain orbit parameters corresponding to the start and end times of imaging.
And outputting the imaging start oblique angle, the imaging end oblique angle and the beam scanning angular velocity.
Parts of the invention not described in detail are well known in the art. It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A method for designing azimuth imaging parameters of a spaceborne SAR squint sliding bunching mode is characterized by comprising the following steps:
setting input conditions, wherein the input conditions comprise high-precision ephemeris forecast data during imaging, a target starting position vector and a target ending position vector of the center of a scene in an imaging area along the azimuth direction, and imaging starting time;
defining azimuth parameters, wherein the azimuth parameters comprise azimuth resolution, azimuth imaging length, imaging starting squint angle, imaging ending squint angle and antenna beam scanning angular velocity;
determining the ground speed of the wave beam in the squint sliding bunching mode according to the linear relation between the antenna azimuth length of the SAR, the ground speed of the wave beam and the azimuth resolution of the SAR;
determining the imaging time length according to the time relationship among the satellite-ground geometric model of the spaceborne SAR squint sliding bunching mode, the direction position imaging length and the beam ground speed in the sliding bunching mode;
determining an imaging starting squint angle according to the geometric definition of the satellite-borne SAR squint angle by using a distance vector and a satellite velocity vector from a satellite to a target;
determining the imaging ending time according to the imaging time length by taking the imaging starting time as a reference, and calculating an imaging ending squint angle;
determining the scanning angular velocity of the antenna beam according to the squint angle variation and the imaging time length during imaging;
the azimuth imaging length is the length of a section of continuous imaging area on the ground along the advancing direction of the wave beam; the imaging starting squint angle is an azimuth beam center pointing angle at the imaging starting moment; the end squint angle is an azimuth beam center pointing angle at the imaging end moment; the antenna beam scanning angular velocity is the angular range over which the beam center points during imaging changes every second.
2. The method for designing the azimuth imaging parameters of the spaceborne SAR squint sliding bunching mode as recited in claim 1,
the input conditions are given by a user according to earth observation task requirements, satellite flight orbits and SAR imaging capacity in advance; the high-precision ephemeris forecast data comprise satellite position vectors and velocity vectors; the target start position vector and the target end position vector are defined in a WGS84 coordinate system;
the high-precision ephemeris forecast data are data after yaw and pitch two-dimensional attitude guidance, and the satellite speed direction is ensured to be vertical to the sight direction of the antenna wave beam when the azimuth wave beam is not scanned;
the formula of the control law of yaw guidance is as follows:
wherein,
in order to control the angle of yaw,
in order to be the angular velocity of the satellite,
is the angular velocity of the earth's rotation,
in order to obtain the inclination angle of the track,
is satellite latitude argument;
related to radar when looking from left to right and from right to left
Left side view time
；
The control rule formula of the pitching guidance is as follows:
wherein,
in order to control the angle of the pitching motion,
in order to determine the eccentricity of the track,
is the true proximal angle.
3. The method for designing the azimuth imaging parameters of the spaceborne SAR squint sliding bunching mode as recited in claim 1,
the antenna azimuth length of the SAR is an SAR system parameter
Represents; the azimuth resolution of strabismus sliding bunching mode is used as a design index
Represents;
for ground speed of beam in strabismus sliding bunching mode
Expressed, the calculation formula is:
wherein,
for a fixed beam pointing to the corresponding antenna beam ground speed,
for the azimuth resolution broadening coefficient of the SAR, the calculation formula is as follows:
wherein,
，
，
，
，
the 5 azimuth resolution influencing factors respectively cause the resolution broadening coefficients.
4. The method for designing the azimuth imaging parameters of the spaceborne SAR squint sliding bunching mode as claimed in claim 3, wherein the azimuth imaging length is a design index and is used
Represents;
a ground length corresponding to the beam width
The SAR azimuth beam width and the distance between a target and a satellite are calculated;
length of imaging time
Expressed, the calculation formula is:
5. the method for designing the azimuth imaging parameters of the spaceborne SAR squint sliding bunching mode as claimed in claim 1, wherein the imaging start squint angle is used
Expressed, the calculation formula is:
wherein,
the distance vector from the satellite to the target at the imaging start time,
for the satellite velocity vector at the imaging start time,
is the azimuth beam width of the SAR;
determining a distance vector between the satellite at the imaging starting time and the target according to a known input condition, wherein the distance vector is determined by a position vector of the satellite at the imaging starting time and a position vector of a starting point of an imaging area under a WGS84 coordinate system;
the imaging start time and the position vector of the imaging area starting point are known input parameters and are determined by a user and a ground task management and control system.
6. The method for designing the azimuth imaging parameters in the strabismus sliding bunching mode of the spaceborne SAR as claimed in claim 1, wherein the oblique view angle at the end of imaging is used
Express, calculate the publicThe formula is as follows:
wherein,
the distance vector from the satellite to the target at the imaging end time,
the satellite velocity vector is the imaging end time;
the azimuth beam width of the SAR;
the imaging ending time is equal to the imaging starting time plus the imaging time length;
determining a distance vector between the satellite at the imaging ending time and the target according to a known input condition by using a position vector of the satellite at the imaging ending time and a position vector of an imaging area ending point under a WGS84 coordinate system;
the imaging end time and the position vector of the imaging area end point are known input parameters and are provided by a user and a ground task management and control system.
7. The method for designing spaceborne SAR squint sliding bunching mode azimuth imaging parameters as claimed in claim 1, wherein the antenna beam scanning angular velocity is used
Expressed, the calculation formula is:
wherein,
starting an oblique view angle for imaging;
in order to end the imaging at the oblique viewing angle,
is the imaging time length.
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