CN118052081B - A method for designing parameters of high-orbit SAR system - Google Patents
A method for designing parameters of high-orbit SAR system Download PDFInfo
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Abstract
The invention discloses a parameter design method of a high-orbit SAR system, which comprises the following steps: step 1: uploading the requirements of the satellite on the resolution of the strip; step 2: calculating the distance resolution of the high-orbit SAR according to the satellite observation incident angle, the radar emission signal bandwidth and the squint angle; step 3: calculating the azimuth resolution of the high-orbit SAR according to the azimuth antenna caliber of the high-orbit SAR, the footprint ground speed of the satellite beam and the speed of the satellite relative to the earth; step 4: and (3) calculating the residence time of the ground target according to the azimuth resolution ratio obtained in the step (3) and the slant distance of the ground target. The method is suitable for the high-orbit SAR system, and realizes the accurate calculation of the distance resolution and the azimuth resolution of the high-orbit SAR.
Description
Technical Field
The invention belongs to the technical field of radars, and particularly relates to a parameter design method of a high-orbit SAR system.
Background
Starting from the first SAR (SYNTHETIC APERTURE RADAR ) satellite SEASAT transmitted in the united states in 1978, many countries have been actively conducting research on-board SAR.
The striping mode is the most commonly used imaging mode for space-borne SAR, and when the striping mode is in operation, the radar irradiates the ground with a fixed viewing angle, and does not scan in both the range and azimuth directions. Early on-board SAR systems, such as sea at, SIR-a, ERS-1/2, had only one fixed view angle and also had only one mode of operation in stripe mode due to technical limitations of phased array antennas and satellite platforms. The general spaceborne SAR has a strip mode, the later spaceborne SAR can generally have a plurality of wave positions, and can be seen from side to side, particularly on advanced spaceborne SAR systems such as Radarsat-1/2, ALOS, COSMO-SkyMed and the like, and the later spaceborne SAR also has a plurality of strip modes by adjusting the antenna beam. Taking Radarsat-2 as an example, it inherits the standard, wide, low view, high view, fine and other stripe modes of the Radarsat-1, and adds the standard four-polarization, fine multi-view, ultra-fine and other additional modes.
In the low-orbit SAR strip working mode, the working mode parameter design is simplified, the relation between the distance resolution and the signal bandwidth is generally simplified into the constraint relation between the incident angle and the signal bandwidth, and in the analysis of the azimuth resolution, the low-orbit SAR satellite generally considers that the azimuth resolution is one half of the antenna caliber. However, in the high-orbit SAR, although operating in the stripe mode, the range resolution, the azimuth resolution, and other parameter indexes are greatly affected by the earth rotation, and the azimuth resolution improvement factor and the like are essentially different from those of the low-orbit SAR due to the strabismus imaging caused by the earth rotation. Therefore, the design of the high-rail SAR operating mode parameters requires a new selection and design.
Disclosure of Invention
The invention aims to provide a high-track SAR system parameter design method, which aims to solve the problem that the parameter design of the existing low-track SAR strip working mode cannot be suitable for a high-track SAR system.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
a parameter design method for a high-orbit SAR system specifically comprises the following steps:
step 1: the requirement of the uploading satellite on the strip resolution is specifically divided into a distance resolution requirement and an azimuth resolution requirement;
step 2: calculating the distance resolution of the high-orbit SAR according to the satellite observation incident angle, the radar emission signal bandwidth and the squint angle;
step 3: calculating the azimuth resolution of the high-orbit SAR according to the azimuth antenna caliber of the high-orbit SAR, the footprint ground speed of the satellite beam and the speed of the satellite relative to the earth;
step 4: and (3) calculating the residence time of the ground target according to the azimuth resolution ratio obtained in the step (3) and the slant distance of the ground target.
Further, in step 2, the range resolution expression of the high-rail SAR is as follows:
Wherein:
ρ range —distance resolution of high-rail SAR;
C-the speed of light, the value is 3X 10 8 m/s;
b-radar transmit signal bandwidth;
-pitch angle;
-satellite observing the complementary angle of incidence, i.e. the ground-wiping angle;
θ—the complementary angle of the perspective projection of the squint angle on the ground, i.e., the ground perspective.
Further, in step 3, the azimuth resolution of the high-rail SAR is expressed as:
Wherein:
ρ a —azimuthal resolution of high-rail SAR;
-azimuth antenna aperture of high-rail SAR;
-satellite beam footprint ground speed;
-the velocity of the satellite relative to the earth;
-orientation imaging processing weighting induced broadening coefficients;
-a stretching coefficient introduced by an azimuthal doppler frequency modulation estimation error;
-azimuth-to-two-pass antenna pattern weighting-induced broadening coefficients.
Further, the azimuthal resolution of the high-rail SAR is expressed as:
Wherein:
-projection distance of the centroid to the beam footprint at the centroid and the undersea point line;
-distance of satellite from earth center;
-track inclination;
-latitude argument;
-geocentric angle;
-the radar beam is directed, 1 when left view and-1 when right view.
Further, the residence time of the ground target is:
Wherein:
-residence time;
-radar operating frequency wavelength;
r is the slant distance of the ground target;
ρ a —azimuthal resolution of high-rail SAR.
Compared with the prior art, the invention has the beneficial effects that:
Compared with the research results which are reported and published at present, the invention provides the creative expression of the design method:
(1) Accurate calculation of the high-track SAR range-to-resolution can be achieved. The conventional low-orbit SAR distance resolution only considers the relation with the observation incident angle and the signal bandwidth, and the high-orbit SAR system parameter design method is different from the conventional low-orbit SAR, and the distance resolution is related with the observation incident angle, the signal bandwidth, the pitch angle and the squint angle.
(2) Accurate calculation of the high-track SAR azimuth resolution can be achieved. The effect of earth rotation is ignored in the analysis of low-track SAR azimuth resolution. Because the low-orbit SAR ground beam speed is very high, the influence of the earth rotation on the low-orbit SAR ground beam speed is very small, and the influence of the earth rotation on the low-orbit SAR azimuth resolution can be ignored. However, since the satellite angular velocity of the high orbit SAR is the same as the earth rotation angular velocity, the earth rotation has a serious influence on the ground beam velocity, and thus the influence of the earth rotation is considered in the azimuth resolution analysis of the present invention.
(3) In the implementation process, the residence time of the ground target can be determined according to the azimuth resolution obtained by the method, and the satellite starting-up time can be determined, if the SAR satellite observation time exceeds the residence time of the ground target, intermittent shutdown can be selected, so that the purposes of saving satellite energy and prolonging the starting-up time can be achieved.
Drawings
FIG. 1 is a flow chart of a method of designing parameters of a high-rail SAR system of the present invention.
FIG. 2 is a range resolution at selected simulation parameters;
FIG. 3 is azimuthal resolution at selected simulation parameters;
fig. 4 is a resident view time of an azimuth beam.
Detailed Description
The practice of the invention is described in further detail below.
The application scene of the invention is as follows:
the invention provides a high-orbit SAR strip working mode parameter design method, which considers the motion characteristics, resolution characteristics and the like of the high-orbit SAR, can be used for accurately calculating the high-orbit SAR strip working mode parameters, can be popularized to large-elliptical orbit SAR, medium-orbit SAR systems and low-orbit ultrahigh-resolution SAR imaging systems, realizes the accurate calculation of the SAR strip working mode parameters, further improves SAR image quality, and better applies SAR images to the fields of emergency observation, disaster relief, military reconnaissance, target hitting and the like, and has important application value. As shown in fig. 1, the method of the present invention is implemented as follows:
step 1: the requirement of the uploading satellite on the resolution of the strip is specifically divided into the requirement of the resolution of the distance direction and the resolution of the azimuth direction.
Unlike low-track SAR, the resolution of the different track segments of the high-track SAR track may exhibit variability due to the effects of earth's rotation, thus requiring the need to place a wager on resolution according to the different track locations.
Step 2: and calculating the range resolution of the high-orbit SAR according to the satellite observation incident angle, the radar emission signal bandwidth and the squint angle.
In particular, the distance-wise resolution loss due to high-rail strabismus observation needs to be considered. Unlike conventional low-orbit SAR, the range resolution of high-orbit SAR is related to satellite observation incident angle, radar transmission signal bandwidth, pitch angle, squint angle, expressed as follows:
（1）
Wherein:
ρ range —distance resolution of high-rail SAR;
C-the speed of light, the value is 3X 10 8 m/s;
B-radar transmit signal bandwidth (-3 dB signal bandwidth);
-pitch angle;
-satellite observing the complementary angle of incidence, i.e. the ground-wiping angle;
the residual angle of the theta-squint angle projected on the ground, namely the ground squint angle;
step 3: the azimuth resolution of the high-orbit SAR is calculated according to the azimuth antenna caliber of the high-orbit SAR, the ground speed of the satellite beam footprint and the speed of the satellite relative to the earth.
The influence of the earth rotation is ignored in the analysis of the azimuth resolution of the low-orbit SAR, and the earth is approximately considered to be stationary. Because the ground beam speed of the low-orbit SAR is large, the influence of the earth rotation on the ground beam speed is small, the earth is approximately considered to be stationary, and the influence of the earth rotation on the azimuth resolution of the low-orbit SAR can be ignored. However, since the high-orbit SAR earth rotation has a serious influence on the ground beam velocity, the influence of the earth rotation must be considered in the azimuth resolution analysis.
The azimuth resolution of high orbit SAR is independent of wavelength and target skew, and is related to azimuth antenna pattern weighting, ground speed, satellite attitude, and imaging process weighting spread, and can be expressed as:
(2)
Wherein:
ρ a —azimuthal resolution of high-rail SAR;
-azimuth antenna aperture of high-rail SAR;
-satellite beam footprint ground speed;
-the velocity of the satellite relative to the earth;
-orientation imaging processing weighting induced broadening coefficients;
-a stretching coefficient introduced by an azimuthal doppler frequency modulation estimation error;
-azimuth-to-two-pass antenna pattern weighting-induced broadening coefficients.
Further expressed as:
（3）
Wherein:
-projection distance of the centroid to the beam footprint at the centroid and the undersea point line;
-distance of satellite from earth center;
-track inclination;
-latitude argument;
-geocentric angle;
-the radar beam is directed, 1 when left view and-1 when right view.
Step 4: according to the azimuth resolution ratio obtained in the step 3 and the slant distance of the ground target, calculating the residence time of the ground target as follows:
（4）
Wherein:
-residence time of the ground target;
-radar operating frequency wavelength;
r is the slant distance of the ground target;
ρ a —azimuthal resolution of high-rail SAR.
From there, the method of the present invention ends.
In the implementation process, the resident observation time of the azimuth beam can be determined according to the azimuth resolution ratio, so that the satellite starting-up time is determined, if the SAR satellite observation time exceeds the beam resident time, intermittent shutdown can be selected, and therefore satellite energy can be saved, and the purpose of starting-up time is prolonged.
In order to verify the effect of the method of the invention, a group of parameters are selected for simulation, and the simulation parameters are as follows: the track dip angle is 20 degrees, the right ascent intersection point is 106 degrees, the near-site amplitude angle is 90 degrees, the eccentricity is 0, the radar working center frequency is 1.25GHz, the antenna caliber is 20m, the signal bandwidth is 60MHz, the pitch angle is 2.2-4.13 degrees, and the squint angle is 0.1 degrees. Under the set of parameters, the range-wise resolution is as shown in fig. 2, and in the case of the existence of the oblique viewing angle, the range-wise resolution has a widening effect, and the influence needs to be considered in calculation. The azimuth resolution is shown in fig. 3, and it can be seen that the azimuth resolution is consistent with the full-orbit value of the azimuth resolution of the low-orbit SAR and is equal to 1/2 of the caliber of the antenna, and in the high-orbit SAR, the azimuth resolution is improved due to the fact that the ground speed of the beam footprint is greatly different from the speed of the satellite relative to the earth, so that the effect similar to beam focusing observation is formed. And because the beam footprint ground speed and the satellite speed relative to the earth are time-varying in the full orbit, its azimuth resolution is also time-varying. The dwell time of the azimuth beam at an azimuth resolution of 20m is shown in fig. 4. It can be seen that unlike low-rail SAR, the high-rail SAR beam dwell time also varies over time. In summary, the method of the invention realizes the accurate calculation of the distance resolution and the azimuth resolution of the high-orbit SAR, and can be well adapted to the high-orbit SAR.
Claims (3)
1. The parameter design method for the high-orbit SAR system is characterized by comprising the following steps of:
step 1: the requirement of the uploading satellite on the strip resolution is specifically divided into a distance resolution requirement and an azimuth resolution requirement;
step 2: calculating the distance resolution of the high-orbit SAR according to the satellite observation incident angle, the radar emission signal bandwidth and the squint angle; the range resolution expression of the high-rail SAR is as follows:
Wherein:
ρ range —distance resolution of high-rail SAR;
C-the speed of light, the value is 3X 10 8 m/s;
b-radar transmit signal bandwidth;
-pitch angle;
-satellite observing the complementary angle of incidence, i.e. the ground-wiping angle;
the residual angle of the theta-squint angle projected on the ground, namely the ground squint angle;
Step 3: calculating the azimuth resolution of the high-orbit SAR according to the azimuth antenna caliber of the high-orbit SAR, the footprint ground speed of the satellite beam and the speed of the satellite relative to the earth; the azimuth resolution of the high-rail SAR is expressed as:
Wherein:
ρ a —azimuthal resolution of high-rail SAR;
-azimuth antenna aperture of high-rail SAR;
-satellite beam footprint ground speed;
-the velocity of the satellite relative to the earth;
-orientation imaging processing weighting induced broadening coefficients;
-a stretching coefficient introduced by an azimuthal doppler frequency modulation estimation error;
-a widening factor introduced by the azimuth double-pass antenna pattern weighting;
step 4: and (3) calculating the residence time of the ground target according to the azimuth resolution ratio obtained in the step (3) and the slant distance of the ground target.
2. The high-track SAR system parameter design method of claim 1, wherein the azimuthal resolution of the high-track SAR is expressed as:
Wherein:
-projection distance of the centroid to the beam footprint at the centroid and the undersea point line;
-distance of satellite from earth center;
-track inclination;
-latitude argument;
-geocentric angle;
-the radar beam is directed, 1 when left view and-1 when right view.
3. The method for designing parameters of a high-rail SAR system according to claim 2, wherein in step 4, the residence time of the ground target is:
Wherein:
-residence time;
-radar operating frequency wavelength;
r is the slant distance of the ground target;
ρ a —azimuthal resolution of high-rail SAR.
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| CN102288964A (en) * | 2011-08-19 | 2011-12-21 | 中国资源卫星应用中心 | Imaging processing method for spaceborne high-resolution synthetic aperture radar |
| CN111965640A (en) * | 2020-07-01 | 2020-11-20 | 西安电子科技大学 | Large squint high-orbit SAR two-dimensional beam scanning method |
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| CN101493520B (en) * | 2009-01-16 | 2012-07-11 | 北京航空航天大学 | A SAR image change detection method based on two-dimensional Gamma distribution |
| KR102654879B1 (en) * | 2021-12-14 | 2024-04-05 | 국방과학연구소 | Spaceborne multistatic synthetic aperture radar(SAR) system and method of generating high-resolution SAR image using the same |
| CN115184929A (en) * | 2022-05-17 | 2022-10-14 | 北京理工大学 | A method for imaging off-track curve of SAR satellite |
| CN115792907B (en) * | 2023-02-07 | 2023-04-14 | 中国科学院空天信息创新研究院 | Method for designing azimuth imaging parameters of spaceborne SAR squint sliding bunching mode |
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| CN102288964A (en) * | 2011-08-19 | 2011-12-21 | 中国资源卫星应用中心 | Imaging processing method for spaceborne high-resolution synthetic aperture radar |
| CN111965640A (en) * | 2020-07-01 | 2020-11-20 | 西安电子科技大学 | Large squint high-orbit SAR two-dimensional beam scanning method |
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