CN115184929A - SAR satellite non-tracking curve imaging method - Google Patents
SAR satellite non-tracking curve imaging method Download PDFInfo
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- CN115184929A CN115184929A CN202210539371.1A CN202210539371A CN115184929A CN 115184929 A CN115184929 A CN 115184929A CN 202210539371 A CN202210539371 A CN 202210539371A CN 115184929 A CN115184929 A CN 115184929A
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- 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
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- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
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- 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
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
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Abstract
The invention provides an imaging method suitable for observing a non-tracking curve scene by an SAR satellite, which can overcome the problem that the traditional imaging method cannot efficiently observe a diagonal curve scene due to tracking constraint, solve the problem of system design in a non-tracking curve imaging mode of the SAR satellite, and realize high-efficiency and high-resolution observation on the non-tracking diagonal curve scene; the method has the advantages that the curve beam footprint is generated by fitting according to the maximum irradiation quantity, two input modes of non-tracking scene trends are comprehensively considered at the same time, and the problem that the beam footprint trend of the SAR satellite is single under the observation of the traditional tracking mode is solved; the orbit selection method is used for screening the orbit by combining the lower view angle space-variant characteristic of the non-tracking curve beam footprint, so that the problem of orbit selection under the non-tracking observation of the SAR satellite is solved; the satellite configuration design method can solve the problem of non-uniform azimuth resolution in SAR satellite non-tracking imaging by controlling the moving speed of the ground beam footprint center.
Description
Technical Field
The invention belongs to the technical field of Synthetic Aperture radars (SAR for short), and particularly relates to a SAR satellite non-tracking curve imaging method.
Background
A satellite-borne Synthetic Aperture Radar (SAR) is an active microwave remote sensing Radar imaging system which works on a satellite platform and can carry out high-resolution observation on the earth surface all day long. The synthetic aperture radar performs signal processing on the echo accumulated by the continuously irradiated target, effectively utilizes Doppler frequency bandwidth in the target echo, equivalently improves the length of the azimuth antenna, and thus realizes azimuth high resolution. The satellite-borne synthetic aperture radar is not limited by environmental factors such as sunlight intensity, weather and the like, can complete important tasks such as topographic mapping, resource exploration, battlefield situation investigation and the like, and plays an important role in economic development and national defense construction.
The main imaging modes of the conventional satellite-borne synthetic aperture satellite include a strip mode, a beamforming mode, a sliding beamforming mode, a scanning mode and a TOPS mode. The strip mode is the most basic imaging mode of the conventional satellite-borne SAR, the antenna of the strip mode has no scanning, the azimuth resolution is only determined by the azimuth size of the antenna, and the azimuth imaging strip width is large; in the beam focusing mode, the beam stares at a fixed area, the azimuth resolution can be very high, but the width of an imaging belt is smaller and is only the size of a ground wave foot; in the sliding beam bunching mode, the beam scanning enables the ground surface beam footprint moving speed to be slower than that in the strip mode, the azimuth resolution is higher than that in the strip mode, and the azimuth imaging band width is between the strip mode and the bunching mode. In the scanning mode, the azimuth resolution is lower than that in the strip mode, and the wave beams can be switched among different sub-imaging bands, so that the larger distance imaging bandwidth is realized. The beam in the TOPS mode can also be switched between different sub-imaging bands, but the ground beam footprint moves faster than in the scan mode, so it can achieve a larger azimuthal imaging bandwidth relative to the scan mode. The imaging bands of the above conventional mode are all distributed along the satellite track direction, i.e. are all along-track straight imaging bands. The extension direction is single, and the observation mode is not flexible. An actual target scene often has a certain observation included angle with the satellite track direction, and the geography trend is changeable and irregular, such as a coastline, a road and an earthquake zone and other oblique curve scenes. The single imaging band of conventional imaging modalities often has difficulty completely covering these target scenes.
If a single imaging band cannot completely cover a target area, a conventional solution is to perform splicing observation on a plurality of tracking imaging bands, and the following two implementation modes are provided:
observation in a single track time sharing mode: expanding the range imaging band width at the expense of azimuth resolution, and performing beam switching between different imaging bands within a single-track observation time, such as a scanning mode or a TOPS mode;
observation of "multiple-track revisit": and at the cost of greatly sacrificing observation efficiency and image consistency, each satellite revisit respectively images different imaging bands, and the distance to the imaging band width is enlarged.
When the scene is fat and has large extension in distance and azimuth, splicing observation by adopting a plurality of imaging bands along the satellite track is feasible. However, when the scene is "thin", has a large geographical extension, and does not follow the satellite track, it is inefficient to use multiple imaging bands along the satellite track for stitching observation. In addition to the problems of low azimuth resolution and long data acquisition period caused by single track time sharing and multi-track revisiting, the common problem of large data redundancy also exists: the target area only occupies a small proportion of the imaging band after the band splicing, and a large amount of echoes of the region without interest can be simultaneously stored and processed, so that large satellite resources are wasted. The two methods cannot simultaneously meet two observation requirements of high observation efficiency and high resolution, and become a problem to be solved in the traditional mode.
Disclosure of Invention
In view of this, the present invention provides a method for imaging a non-tracking curve of an SAR satellite, which can solve the problem of observing an oblique curve scene by a conventional satellite-borne synthetic aperture radar satellite.
A SAR satellite non-tracking curve imaging method comprises the following steps:
step one, generating a beam footprint according to an input observation target point or an observation scene trend;
selecting a proper satellite orbit observation arc section according to the beam footprint;
thirdly, acquiring a satellite observation configuration, the start-up and shutdown time of the satellite and an attitude control instruction based on the observation resolution requirement, the satellite orbit observation arc section orbit parameters and the satellite platform capacity;
fourthly, based on a time-varying relation of the beam center slope distance under the satellite observation configuration, wave position design of the SAR is carried out;
controlling the satellite to execute an attitude control instruction based on the satellite orbit observation arc section, and controlling the SAR to transmit signals according to wave position design; and imaging the received echo signals within the time range of the satellite on/off to obtain an imaging result.
Preferably, the second step includes:
step 21, deducing a satellite orbit;
step 22, calculating all orbit observation arc sections capable of observing the non-tracking curve beam footprint and a lower view angle change range corresponding to each orbit observation arc section based on the satellite orbit;
step 23, based on the satellite orbit height, the satellite beam width and the observation width, calculating to obtain a lower view angle range corresponding to the most proximal end and the most distal end of the beam, and setting the lower view angle range as a first observable range threshold value TH1; the range of the lower visual angle observable by the satellite is used as a second observable range threshold TH2, and the orbit observation arc sections with the lower visual angle variation range within the range of the first observable range threshold TH1 and the second observable range threshold TH2 are screened in step 22.
Preferably, in the third step, the method for establishing a satellite observation configuration includes:
assuming that the target P is present at a position on the center of the beam footprint, the projection of the beam onto the ground moves at the target P along the beam footprint center at a velocity V g Intercept in direction of l res ；
Defining the slope distance course of the SAR satellite relative to the target P as R p Then the object isDoppler modulation frequency of beam irradiation center time is K a Comprises the following steps:
wherein λ is the wavelength corresponding to the working frequency of the SAR satellite, t is the azimuth time, and tc is the beam irradiation center time;
obtaining an azimuthal resolution ρ a With Doppler modulation frequency of K a The relationship between them is:
wherein l res Is the satellite velocity, H is the orbital altitude, R E Is the radius of the earth;
a plurality of position points are taken from the center of the beam footprint at the same interval, and the projection edge V of the beam of different position points of the center of the beam footprint on the ground surface is obtained based on the geometric relationship between the satellite orbit and the beam footprint g Intercept in the direction l res (ii) a Based on formula (1), calculating Doppler frequency K of different positions of beam footprint center at beam irradiation center time a (ii) a Inputting a desired azimuth resolution ρ of an observation task a Calculating the moving speed V of the center of the ground surface beam footprint at different positions of the center of the beam footprint based on the formula (2) g The size of (d); ground surface beam footprint center moving speed V based on interval of adjacent position points g And central observation time T 0 And calculating to obtain the corresponding relation between the movement of the central position of the beam footprint and time, namely the relation of the beam pointing direction of the SAR radar changing along with time, thereby determining the satellite observation configuration of the non-tracking curve.
Preferably, the wave position design method in the fourth step includes:
determining a subsatellite point echo sheltering area and a transmitting pulse sheltering area on a two-dimensional plane taking pulse repetition frequency as a horizontal axis and beam center slant distance as a vertical axis, finding an area avoiding the subsatellite point echo sheltering area and the transmitting pulse sheltering area, determining a pulse repetition frequency range of the area, and performing wave position design in the range.
Preferably, in the first step, if the input is the observation target point, the target point is selected based on the principle that the maximum target point can be irradiated by the SAR in one observation task;
preferably, in the first step, if the input is an observation scene, the target points are set at set intervals along the scene moving direction on the scene moving central line.
Preferably, the corresponding satellite startup time T is obtained according to the corresponding time of the starting point and the ending point of the center of the beam footprint in the non-tracing curve observation configuration 1 And shutdown time T 2 。
The invention has the following beneficial effects:
the invention provides an imaging method suitable for observing a non-tracking curve scene by an SAR satellite, which can overcome the problem that the traditional imaging method cannot efficiently observe an oblique curve scene due to tracking constraint, solve the system design problem under the non-tracking curve imaging mode of the SAR satellite, and realize high-efficiency and high-resolution observation of the non-tracking oblique curve scene;
in the first step, a curve beam footprint is generated by fitting with the maximum irradiation quantity as a criterion, and two input modes of non-tracking scene trends are comprehensively considered at the same time, so that the problem that the beam footprint trend of the SAR satellite is single under the observation of the traditional tracking mode is solved; the orbit selection method of the second step, combine the empty variable characteristic of lower viewing angle of the curve beam footprint of non-tracing to screen the orbit, has solved the orbit selection problem under SAR satellite non-tracing observation;
the configuration design method of the third step can solve the problem of uneven azimuth resolution in SAR satellite non-tracking imaging by controlling the moving speed of the ground surface beam footprint center.
The system design method of the step four can solve the serious problem of echo receiving loss caused by large change of the satellite beam center slope distance under non-tracking observation of the SAR satellite by adopting a continuous variable pulse interval technology.
Drawings
FIG. 1 is a system design flow chart of a SAR satellite non-tracking curve imaging method;
FIG. 2 is a schematic view of observation configuration of SAR satellite non-tracking curve imaging method
FIG. 3 is a target distribution and beam footprint for SAR satellite non-tracking curve imaging method simulation;
fig. 4 (a) and fig. 4 (b) are respectively the results of selecting the simulated orbit and the orbit arc segment of the SAR satellite non-tracking curve imaging method;
FIG. 5 is a design result of an observation configuration simulated by the SAR satellite non-tracking curve imaging method;
FIG. 6 is a design result of attitude control simulated by SAR satellite non-tracking curve imaging method;
FIGS. 7 (a) and 7 (b) are Zebra map and wave position design results of SAR satellite non-tracking curve imaging method simulation, respectively;
FIG. 8 is a point target imaging result of SAR satellite non-tracking curve imaging method simulation;
fig. 9 (a), 9 (b) and 9 (c) are respectively a scene center point target imaging result evaluation, a distance profile and an orientation profile of the SAR satellite non-along-track curve imaging method simulation.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
The invention provides an SAR satellite non-tracking curve imaging method, as shown in figure 1, the specific steps include:
step one, generating a non-tracing curve beam footprint according to an input observation target point or an input observation scene trend.
(1) If the input is an observation target point, selecting the target point on the basis that the SAR can irradiate the maximum target point in one observation task; if the input is an observation scene, setting target points at certain intervals along the scene trend on the scene trend central line.
(2) And fitting to generate a non-tracing curve beam footprint based on the selected longitude and latitude coordinates of the target point.
And secondly, performing orbit prediction based on the input satellite orbit parameters, and calculating the orbit observation arc section and the lower view angle change range of the non-tracking curve beam footprint. And selecting a proper orbit observation arc section according to the observation width requirement and the observation angle range under the observation of the satellite.
Step 21, inputting satellite orbit parameters including but not limited to six orbit numbers and Greenwich mean time shown in the table 1, and deducing the orbit.
TABLE 1 satellite orbital parameters
And step 22, calculating all track observation arc sections capable of observing the non-tracking curve beam footprint and the lower view angle change range corresponding to each track observation arc section based on the derived track.
Step 23, based on the satellite orbit height, the satellite beam width and the observation width, calculating to obtain a lower view angle range corresponding to the most proximal end and the most distal end of the beam, and setting the lower view angle range as a first observable range threshold value TH1; the range of the lower visual angle observable by the satellite is used as a first threshold TH2 of the observable range, and the orbit observation arc segment with the lower visual angle variation range within the threshold TH1 and the threshold TH range is screened in step 22.
And thirdly, designing a non-tracking observation configuration based on the observation resolution requirement, the orbit parameters and the satellite platform capacity to obtain the startup and shutdown time and the attitude control design result of the satellite.
Step 31, establishing a non-tracking curve observation configuration based on the observation resolution requirement, the orbit parameters of the orbit observation arc section screened out in the step 23 and the satellite platform capability, specifically:
the scene center is defined as the length center position of the beam footprint, the position of the SAR satellite relative to the minimum downward view angle of the scene center on the orbit observation arc section is defined as the satellite observation center position, and the moment is marked as T 0 . The observation configuration is shown in FIG. 2, the satellite speed is Vr, the orbit height is H, and the center slant distance is R. The moving speed of the center of the ground surface beam footprint is Vg, and the direction of the tangent line of the direction beam footprint is tangent. Extending along the scene in the positive X-axis directionAnd the direction from the starting point to the end point of the beam footprint is defined as the azimuth direction of non-tracking imaging. The positive direction of the Y axis is perpendicular to the extending direction of the scene and is defined as a distance direction, and the Z axis points to the center of the earth. Alpha is the included angle of the positive direction of the Y axis and the ground projection vector Rg of the center slant distance, and is defined as 'observation oblique angle' to represent the beam squint degree. If the positive direction of the Y axis is cross-multiplied with the Rg to be the positive direction of the Z axis, alpha is positive, otherwise, the positive direction is negative; and theta is an included angle between the trend of the scene and the track of the satellite point under the satellite, is defined as a 'scene inclination angle' and represents the inclination degree of the target scene relative to the satellite track. Wa and Wr respectively represent the azimuth and the range imaging band width.
Assuming that the target P is present at a location centered on the beam footprint, the surface beam ellipse has an intercept l in the Vg direction at the target P res As shown in fig. 2. At different positions in the center of the beam footprint, the surface beam elliptical intercept, l res Different.
Defining the slope distance course of the SAR satellite relative to the target P as R p The Doppler frequency of the target at the central moment of beam irradiation is K a Comprises the following steps:
wherein, λ is the wavelength corresponding to the working frequency of the SAR satellite, t is the azimuth time, t c Is the beam irradiation center time.
Defining p a For azimuthal resolution, the azimuthal resolution ρ can be obtained a With Doppler modulation frequency of K a The relationship between them is:
wherein R is E The radius of the earth.
Setting points P at different positions on the center of a beam footprint at the same interval 1 ，P 2 ，P 3 ,...,P n Obtaining different positions P of the center of the beam footprint based on the geometric relationship between the satellite orbit and the beam footprint i Intercept l of the surface beam ellipse of (i =1,. N) in the Vg direction res . Calculating different positions P of beam footprint center based on formula (1) i (i = 1.. N) Doppler modulation frequency K at the beam irradiation center time a . Desired azimuth resolution ρ of the input observation task a Based on the formula (2), different positions P of the center of the beam footprint can be calculated i (i =1,. N) ground beam footprint center movement speed V g The size of (2). Based on adjacent P i (i =1,. N) position interval, ground beam footprint center movement speed V g To observe the time T with the center 0 And calculating to obtain the corresponding relation between the movement of the central position of the beam footprint and time, namely the relation of the beam pointing direction of the SAR radar changing along with time, thereby determining the satellite observation configuration of the non-tracking curve.
Step 32, according to the corresponding time of the starting point and the terminating point of the beam footprint center in the non-tracking curve observation configuration, obtaining the corresponding satellite startup time T 1 And shutdown time T 2 。
And step 33, calculating the yaw angle, the pitch angle and the roll angle of the satellite at each moment according to the time-varying relation of the beam direction in the non-tracking curve observation configuration. And generating an attitude control instruction based on the yaw angle, the pitch angle and the roll angle sequence to obtain a satellite attitude control design result.
And fourthly, performing wave position design based on the time-varying relation of the beam center slope distance under the non-tracking observation configuration to obtain a system design result of the SAR satellite non-tracking curve imaging method.
And 41, determining an azimuth sampling frequency range according to the center slope distance change history and the observation instantaneous bandwidth of the non-tracking observation configuration.
And 42, based on the azimuth sampling frequency range and the center slope distance process, carrying out wave position design on the premise of realizing echo receiving to the maximum extent to obtain a system design result of the SAR satellite non-tracking curve imaging method.
And fifthly, controlling the satellite to execute an attitude control instruction and a system design instruction based on the observable track arc section, transmitting a linear frequency modulation signal and receiving an echo signal. And imaging the received echo signal to obtain an imaging result.
(1) Controlling the satellite to start at the starting time T based on the available orbit observation arc section obtained in the step two 1 And starting the computer. And C, controlling the yaw angle, the pitch angle and the roll angle of the satellite in real time based on the satellite attitude control instruction obtained in the step three, so that the center of the satellite beam points to the foot print of the expected beam. Meanwhile, based on the system design result obtained in the fourth step, transmitting a linear frequency modulation signal and receiving an echo signal until the satellite is turned off at the time T 2 And (5) shutting down.
(2) And imaging the received echo signal to obtain an imaging result.
The embodiment is as follows:
table 2 shows coordinate information parameters of the input target, table 3 shows orbit parameters, and table 4 shows satellite simulation parameters.
TABLE 2 object parameter List
TABLE 3 satellite orbit parameters List
TABLE 4 Radar satellite Key parameter List
| Parameter name | Numerical value | Unit of |
| Height of track | 600 | km |
| |
15 | deg |
| Scene dip | 14.3543 | deg |
| Width in the |
10 | km |
| Width in |
120 | |
| Carrier frequency | ||
| 10 | | |
| Pulse width | ||
| 15 | us |
In order to verify the SAR satellite non-tracking curve imaging method, the following simulation is performed. The input target coordinates are shown in table 2, the parameters in table 3 are used for simulation, and a back projection imaging algorithm is adopted to obtain an imaging result and observe the imaging capability of the imaging result.
Step one, generating a non-tracing curve beam footprint according to an input observation target point or an input observation scene trend.
<1> target points the distribution of the target points is shown as a triangle (". DELTA") in FIG. 3, for a total of fifteen targets, with the selected target locations located along the east coast of peninsula malaysia.
<2> five objects in the center of the scene are selected for beam footprint fitting, and the beam footprints are obtained and shown by curves in fig. 3, and the starting points and the ending points of the beam footprints are shown by circles (") in fig. 3.
And secondly, performing orbit prediction based on the input satellite orbit parameters, and calculating the orbit observation arc sections and the lower viewing angle change ranges corresponding to different positions of the non-tracking curve beam footprint. And selecting a proper orbit observation arc section according to the observation width requirement and the observation angle range under the observation of the satellite.
<1> the inputted satellite orbit parameters are shown in table 3, and orbit deduction is performed based on the orbit parameters to obtain an orbit Q1, where the orbit deduction time is 2 hours. In fig. 4, the background sphere is the earth model, fig. 4 (a) is an orbit diagram, and fig. 4 (b) is a partially enlarged view. The deduction orbit Q1 is a dark curve which circles the earth in fig. 4 (a), and the beam footprint designed in the first step is a light curve of the earth model surface.
<2> according to the derived orbit Q1, screening the orbit observation arc sections of which the lower view angle variation range is within the range of the first observable range threshold TH1 and the second observable range threshold TH2, namely using the arc section orbit Q2, wherein the satellite position at the time of the minimum lower view angle is the circular ring position in the graph 4.
And thirdly, designing a non-tracking observation configuration based on the observation resolution requirement, the orbit parameters and the satellite platform capacity to obtain the startup and shutdown time and the attitude control design result of the satellite.
<1> designing the non-tracing observation configuration to obtain the observation configuration design result, as shown in FIG. 5. Fig. 5 (a) is a plot of center slope distance versus time for a non-trayed curvilinear viewing configuration, fig. 5 (b) is a plot of down-viewing angle versus time for a non-trayed curvilinear viewing configuration, and fig. 5 (c) is a plot of slope angle versus time for a non-trayed curvilinear viewing configuration.
<2>Obtaining the satellite startup time T according to the non-tracking observation configuration 1 Is 202224/21/33/15/s/year and shutdown time T 2 33 minutes and 27 seconds at 21 days 4, 24 and 2022, and 12 seconds of observation time. The results of the attitude control design for the satellite are shown in fig. 6. Fig. 6 (a) is a time-dependent yaw angle of the satellite, fig. 6 (b) is a time-dependent pitch angle of the satellite, and fig. 6 (c) is a time-dependent roll angle of the satellite.
And fourthly, performing wave position design based on the time-varying relation of the beam center slope distance under the non-tracking observation configuration to obtain a system design result of the SAR satellite non-tracking curve imaging method.
And <1> according to the observation requirement and the slope distance process of the satellite, the upper limit of the designed azimuth sampling frequency is 7200Hz, and the lower limit of the azimuth sampling frequency is 5600Hz.
And (2) with the pulse repetition frequency (unit is Hz) as a horizontal axis and the beam center slant range (unit is km) as a vertical axis, determining a substellar point echo shielding area (black part) and a transmission pulse shielding area (dark gray part in the figure) on the two-dimensional plane, drawing to obtain a zebra diagram shown in a figure 7 (a), finding an area avoiding the substellar point echo shielding area and the transmission pulse shielding area in the zebra diagram, determining a pulse repetition frequency range of the area, designing a wave position area corresponding to a light gray part 7 (a) in the figure, designing the wave position in the area, and obtaining the pulse repetition frequency capable of adapting to the time-varying center slant range to realize complete echo transceiving. The time-dependent change curve of the pulse repetition frequency is shown in fig. 7 (b), and the non-tracking curve imaging method is completed by system design.
And fifthly, controlling the satellite to execute an attitude control instruction and a system design instruction based on the observable track arc section, transmitting a linear frequency modulation signal and receiving an echo signal. And imaging the received echo signal to obtain an imaging result.
And <1> controlling the starting time and the ending time of the simulation based on the available orbit observation arc section obtained in the step two. And controlling the yaw angle, the pitch angle and the roll angle of the satellite based on the satellite attitude control instruction obtained in the step three, so that the center of the satellite beam points to the foot print of the expected beam. And performing echo simulation based on the system design result obtained in the step four to obtain an echo signal.
And <2> the imaging algorithm adopted by the simulation is a back projection time domain imaging algorithm, and the definitions of the azimuth direction and the distance direction of the imaging grid are consistent with those in the third step. Fig. 8 shows the results of the 15-point target simulation, which are good in terms of homo-focusing. Fig. 9 and table 5 show the evaluation results of the 8 th target in the center of the scene.
TABLE 5 evaluation of scene center point imaging
| Theoretical resolution | Actual resolution | Peak to side lobe ratio | Integral sidelobe ratio | |
| Orientation | 2.4576m | 2.4533m | -13.6645 | -11.93 |
| Ground distance | 2.2500m | 2.2431m | -13.3969 | -10.90 |
And evaluating that the theoretical resolution of the scene center point target is consistent with the actual resolution. The two-dimensional peak sidelobe ratio is less than-13 dB, and the two-dimensional integral sidelobe ratio is less than-10 dB, thereby meeting the index requirements.
In the embodiment, multi-point target simulation is used, the imaging result meets the index requirement, and the feasibility of the SAR satellite non-tracking curve imaging method is verified.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A SAR satellite non-tracking curve imaging method is characterized by comprising the following steps:
step one, generating a beam footprint according to an input observation target point or an observation scene trend;
selecting a proper satellite orbit observation arc section according to the beam footprint;
thirdly, obtaining a satellite observation configuration, the on-off time of the satellite and an attitude control instruction based on the observation resolution requirement, the satellite orbit observation arc section orbit parameters and the satellite platform capability;
fourthly, based on a time-varying relation of the beam center slope distance under the satellite observation configuration, wave position design of the SAR is carried out;
controlling the satellite to execute an attitude control instruction based on the satellite orbit observation arc section, and controlling the SAR to transmit signals according to wave position design; and imaging the received echo signals within the time range of the satellite on/off to obtain an imaging result.
2. The SAR satellite non-tracking curve imaging method according to claim 1, wherein the second step comprises:
step 21, deducing a satellite orbit;
step 22, calculating all orbit observation arc sections capable of observing the non-tracking curve beam footprint and a lower view angle change range corresponding to each orbit observation arc section based on the satellite orbit;
step 23, based on the satellite orbit height, the satellite beam width and the observation breadth, calculating to obtain a lower view angle range corresponding to the most proximal end and the most distal end of the beam, and setting the lower view angle range as a first observable range threshold value TH1; the range of the lower visual angle observable by the satellite is used as a second observable range threshold TH2, and the orbit observation arc sections with the lower visual angle variation range within the range of the first observable range threshold TH1 and the second observable range threshold TH2 are screened in step 22.
3. The SAR satellite non-tracking curve imaging method as claimed in claim 1 or 2, characterized in that in the third step, the method for establishing the satellite observation configuration comprises:
assuming that the target P is present at a position on the center of the beam footprint, the projection of the beam onto the ground moves at the target P along the beam footprint center at a velocity V g Intercept in the direction of l res ；
Defining the slant range course of the SAR satellite relative to the target P as R p Then the Doppler frequency of the target at the beam irradiation center time is K a Comprises the following steps:
wherein, λ is the wavelength corresponding to the working frequency of the SAR satellite, t is the azimuth time, t c Is the beam irradiation center time;
obtaining an azimuthal resolution ρ a With Doppler modulation frequency of K a The relationship between them is:
wherein l res Is the satellite velocity, H is the orbital altitude, R E Is the radius of the earth;
taking multiple location points at the center of the beam footprint at equal intervals based on satellite orbit and beamThe geometric relationship of the footprints obtains the projection edge V of the beam of different position points of the center of the beam footprint on the ground surface g Intercept in the direction l res (ii) a Based on formula (1), calculating Doppler frequency K of different positions of beam footprint center at beam irradiation center time a (ii) a Inputting a desired azimuth resolution ρ of an observation task a Calculating the moving speed V of the center of the ground surface beam footprint at different positions of the center of the beam footprint based on the formula (2) g The size of (d); ground surface beam footprint center moving speed V based on interval of adjacent position points g And central observation time T 0 And calculating to obtain the corresponding relation between the movement of the central position of the beam footprint and time, namely the relation of the beam pointing direction of the SAR radar changing along with time, thereby determining the satellite observation configuration of the non-tracking curve.
4. The SAR satellite non-tracking curve imaging method as claimed in claim 1 or 2, characterized in that the wave position design method in the fourth step comprises:
determining a subsatellite point echo sheltering area and a transmitting pulse sheltering area on a two-dimensional plane taking pulse repetition frequency as a horizontal axis and beam center slant distance as a vertical axis, finding an area avoiding the subsatellite point echo sheltering area and the transmitting pulse sheltering area, determining a pulse repetition frequency range of the area, and performing wave position design in the range.
5. The SAR satellite non-tracking curve imaging method as claimed in claim 1 or 2, characterized in that in the step one, if the input is an observation target point, the target point is selected on the basis that SAR can irradiate the maximum target point in an observation task.
6. The SAR satellite non-tracking curve imaging method as claimed in claim 1 or 2, characterized in that in the first step, if the input is an observation scene, target points are set at set intervals along the scene strike on the scene strike center line.
7. As claimed in claim 1 or 2The SAR satellite non-tracking curve imaging method is characterized in that the corresponding satellite startup time T is obtained according to the corresponding time of the starting point and the ending point of the center of the beam footprint in the non-tracking curve observation configuration 1 And shutdown time T 2 。
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| CN117932195A (en) * | 2024-03-22 | 2024-04-26 | 中国科学院空天信息创新研究院 | On-orbit positioning iteration initial value calculation method for satellite-borne SAR image |
| CN118052081A (en) * | 2024-04-16 | 2024-05-17 | 西安空间无线电技术研究所 | Parameter design method for high-orbit SAR system |
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| CN117932195A (en) * | 2024-03-22 | 2024-04-26 | 中国科学院空天信息创新研究院 | On-orbit positioning iteration initial value calculation method for satellite-borne SAR image |
| CN117932195B (en) * | 2024-03-22 | 2024-05-28 | 中国科学院空天信息创新研究院 | On-orbit positioning iteration initial value calculation method for satellite-borne SAR image |
| CN118052081A (en) * | 2024-04-16 | 2024-05-17 | 西安空间无线电技术研究所 | Parameter design method for high-orbit SAR system |
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