Satellite-borne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics

Abstract

The invention relates to a satellite-borne SAR (synthetic aperture radar) beam pointing calibration method based on antenna installation deviation and difference beam image characteristics. The method comprises the following steps: calculating beam pointing deviation caused by satellite installation of an antenna before a satellite is launched; loading the beam pointing deviation caused by satellite loading of the antenna to a satellite attitude control subsystem, and roughly compensating the beam pointing deviation of the SAR antenna; after a satellite is launched, distance direction beam pointing deviation introduced by in-orbit space environment changes is obtained according to the distance direction difference beam antenna directional diagram null depth of an imaging result, and the distance direction beam pointing deviation of the SAR antenna is precisely compensated; after the satellite is launched, according to an imaging result and difference beam image accumulation characteristics of azimuth beam pointing deviation, azimuth beam pointing deviation introduced by in-orbit space environment change is obtained, and the azimuth beam pointing deviation of the SAR antenna is precisely compensated; and the satellite performs fine compensation according to the calibration period. The method can effectively solve the problems that the ground target aiming precision is poor and the SAR image quality is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of spaceborne synthetic aperture radar, and in particular to a spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics. Background Art

[0002] SAR beam pointing refers to the spatial pointing of the SAR antenna toward the ground as the satellite image the earth in orbit. For spaceborne SAR, the antenna is fixedly connected to the satellite body, and the installation angle between the two directly determines the beam pointing during imaging. The installation deviation directly introduces the beam pointing deviation. At the same time, stress during satellite launch, antenna deployment in orbit, and changes in space temperature during in-orbit flight will cause mechanical and thermal deformation of instruments such as the antenna deployment mechanism, antenna array, and star sensor, resulting in a certain deviation between the actual beam pointing of the SAR antenna in orbit and the theoretical value, making it impossible to accurately aim at ground targets and obtain accurate SAR image imaging parameters. To this end, beam pointing calibration must be carried out before and after the satellite launch to obtain and compensate for the beam pointing deviation, so that the satellite can accurately aim at the target and obtain high-quality SAR images, allowing users to aim at the target accurately and see the target clearly.

[0003] SAR antenna beam pointing is usually expressed in two angles: range and azimuth. The azimuth is along the satellite flight direction, and the range is perpendicular to the satellite flight direction. Beam pointing calibration is to calibrate the beam pointing deviation and compensate it by different means during satellite development, the initial launch, and a certain stage of operation. At present, the research on satellite-borne SAR beam pointing calibration mainly focuses on estimating the beam pointing deviation using post-orbit image parameters, and eliminating the Doppler center offset caused by the earth's rotation through satellite two-dimensional attitude guidance technology. It does not fully consider the impact of the antenna installation angle deviation during the satellite assembly and integration stage and the beam pointing deviation caused by the change of the space environment after the satellite is launched on the SAR image quality. Summary of the invention

[0004] In order to solve the technical problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a satellite-borne SAR beam pointing calibration method, electronic device and storage medium based on antenna installation deviation and difference beam image characteristics, which can solve the problems of poor ground target aiming accuracy and SAR image quality degradation caused by SAR antenna beam pointing deviation.

[0005] To achieve the above-mentioned object of the invention, the present invention provides a method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics, comprising the following steps:

[0006] Step S1, before the satellite is launched, based on the angle relationship between the star sensor reference mirror and the SAR antenna reference mirror, the beam pointing deviation caused by the antenna installation is calculated;

[0007] Step S2, loading the beam pointing deviation caused by the antenna installation into the satellite attitude control subsystem to roughly compensate the SAR antenna beam pointing deviation;

[0008] Step S3, after the satellite is launched, based on the imaging result of the tropical rain forest area of ​​the range differential beam and the null depth of the range differential beam antenna pattern, the range beam pointing deviation introduced by the change of the on-orbit space environment is obtained, and loaded into the satellite attitude control subsystem to accurately compensate for the SAR antenna range beam pointing deviation;

[0009] Step S4, after the satellite is launched, based on the azimuth difference beam tropical rain forest area imaging results, according to the azimuth difference beam image accumulation characteristics containing beam pointing deviation, the azimuth beam pointing deviation introduced by the on-orbit space environment change is obtained, and loaded into the satellite attitude control subsystem to accurately compensate for the SAR antenna azimuth beam pointing deviation;

[0010] Step S5: The satellite executes the steps S3 to S4 according to the calibration cycle to perform precise compensation for the beam pointing deviation of the SAR antenna in the range direction and the beam pointing deviation of the SAR antenna in the azimuth direction.

[0011] According to a technical solution of the present invention, in step S5, the calibration period is 1 to 2 years.

[0012] According to a technical solution of the present invention, in step S1, it specifically includes:

[0013] Step S11: In the satellite assembly and integration stage, the SAR antenna reference mirror is used as the main reference for satellite installation accuracy measurement, and the angle between the star sensor reference mirror and the SAR antenna reference mirror is measured to be σ xz , σ yz , σ zz ;

[0014] Step S12, establishing the geometric projection relationship of the antenna beam normal direction in the satellite body coordinate system after the SAR antenna is installed on the satellite;

[0015] Step S13: Calculate the azimuth beam pointing deviation α caused by the SAR antenna installation g and range beam pointing deviation β g :

[0016] According to the projection relationship of the SAR antenna beam normal in the satellite body coordinate system, the azimuth beam pointing deviation α caused by the SAR antenna installation is determined. g and range beam pointing deviation βg The relationship between the three-axis angles of the star sensor and the SAR antenna reference mirror is:

[0017]

[0018] According to the ground installation experience and the above formula, the initial values ​​of the range beam pointing deviation and the azimuth beam pointing deviation are selected, and the azimuth beam pointing deviation α is obtained by the least squares method. g and range beam pointing deviation β g ;

[0019] Step S14: Adjust the angle between the satellite and the SAR antenna installation interface until the angle α is satisfied. g ≤1° and β g ≤1°.

[0020] According to a technical solution of the present invention, in step S2, coarse compensation is performed by correcting the conversion matrix from the SAR antenna coordinate system to the orbital coordinate system, which specifically includes:

[0021] Step S21, calculate the correction transformation matrix from the SAR antenna coordinate system to the orbital coordinate system, expressed as

[0022]

[0023] Among them, S TO is the ideal attitude matrix from the SAR antenna coordinate system to the orbital coordinate system calculated according to the two-dimensional yaw guidance theory, is the azimuth beam pointing deviation α caused by the SAR antenna installation g and range beam pointing deviation β g The correction matrix corresponding to the ideal posture matrix obtained is expressed as

[0024]

[0025] Among them, α and β are the azimuth beam pointing deviation and range beam pointing deviation obtained by ground-based precise measurement or on-orbit estimation, respectively. The azimuth beam pointing deviation and range beam pointing deviation obtained by ground-based precise measurement are α g and β g The azimuth beam pointing deviation and range beam pointing deviation obtained by on-orbit estimation are α f and β f , and α and β are both less than 1°; roll, pitch and yaw are the roll angle, pitch angle and yaw angle of the satellite respectively, R x (θ), R y (θ) and R z(θ) are the rotation matrices for rotating θ around the x, y, and z axes, respectively, and R -1 (·) is the inverse matrix of R(·), R x (θ), R y (θ) and R z (θ) is expressed as

[0026]

[0027] Step S22: When the satellite is imaging the earth, the correction conversion matrix S is used. so Perform two-dimensional yaw guidance and satellite attitude control to complete coarse compensation of SAR beam pointing.

[0028] According to a technical solution of the present invention, in step S3, it specifically includes:

[0029] Step S31: Select a range difference beam position i, where the theoretical viewing angle corresponding to the difference beam notch position of the range difference beam position is γ i0 , the satellite images the tropical rain forest area, obtains the range differential beam tropical rain forest area imaging data and transmits it to the ground data transmission station;

[0030] Step S32: the ground application system performs segmentation of the auxiliary data and the range original echo data according to the range difference beam tropical rain forest area imaging data, analyzes the orbit, attitude and SAR payload corresponding to the range original echo data, calculates Doppler parameter imaging processing, and obtains a focused first SAR image;

[0031] Step S33: Count the power variation curve of the first SAR image along the range direction, and obtain the actual downward viewing angle γ during imaging according to the null depth of the range difference beam antenna pattern. i1 ;

[0032] Step S34: Calculate the range beam pointing deviation β caused by the change of the satellite's on-orbit space environment fi , expressed as:

[0033] β fi =γ i1 -γ i0

[0034] Step S35: Select the range difference beam positions with different left and right side views, repeat steps S31 to S35, and obtain several groups of range beam pointing deviation sample values ​​β f1 , ..., β fN , calculate the average value to get the accurate range beam pointing deviation β after being on orbit f , expressed as:

[0035]

[0036] Wherein, N represents the number of groups of range beam pointing deviation sample values ​​obtained;

[0037] Step S36: Repeat step S2 to correct the conversion matrix Complete precise compensation of range beam pointing deviation.

[0038] According to a technical solution of the present invention, in the step S34, it specifically includes:

[0039] According to the range difference beam antenna pattern null depth G R dB, look for a power curve with a depth greater than G R dB range gate interval, and obtain the range gate N corresponding to the notch position of the range gate interval R ;

[0040] Calculate the slant distance R corresponding to the notch point distance gate and the actual downward viewing angle γ when acquiring the image i1 , expressed as:

[0041]

[0042] Where C is the speed of light, τ0 is the radar start sampling time, and f s is the distance sampling frequency, R e is the radius of the earth and H is the orbital altitude.

[0043] According to a technical solution of the present invention, in step S4, it specifically includes:

[0044] Step S41, select the azimuth difference beam position j, the theoretical slant angle corresponding to the difference beam notch position of the azimuth difference beam position is ψ j0 , the satellite images the tropical rain forest area, obtains the azimuth difference beam position tropical rain forest area imaging data and transmits it to the ground data transmission station;

[0045] Step S42: Based on the azimuth difference beam position tropical rain forest area imaging data, the ground application system intercepts two synthetic aperture azimuth original echo data, analyzes the orbit, attitude and SAR payload corresponding to the synthetic aperture azimuth original echo data, calculates Doppler parameter imaging processing, and obtains a focused second SAR image;

[0046] Step S43, cutting off half of the synthetic aperture length image in both ends of the focused second SAR image in azimuth;

[0047] Step S44: Calculate the power variation curve of the intercepted second SAR image along the azimuth direction, find the inflection point of the curve, and calculate the azimuth incomplete aperture accumulation length L according to the accumulation characteristics of the difference beam image containing the beam pointing deviation in the azimuth direction. A ;

[0048] Step S45: Calculate the actual oblique angle ψ during imaging j1 , expressed as:

[0049]

[0050] The azimuth pointing deviation is positive when the incomplete aperture is in the first half of the curve and negative in the second half. a is the azimuth beamwidth, T a is the synthetic aperture time, PRF is the pulse repetition frequency;

[0051] Step S46: Calculate the azimuth beam pointing deviation α caused by the change of the satellite's on-orbit space environment fj , expressed as

[0052] α fj =ψ j1 -ψ j0

[0053] Step S47, select different azimuth difference beam positions, repeat steps S41 to S46, and obtain several groups of azimuth beam pointing deviation sample values ​​α f1 , ..., α fM , calculate the average value to get the accurate azimuth beam pointing deviation α after being on orbit f , expressed as

[0054]

[0055] Wherein, M represents the number of groups of azimuth beam pointing deviation sample values ​​obtained;

[0056] Step S48: Repeat step S2 to correct the conversion matrix Complete precise compensation of azimuth beam pointing deviation.

[0057] According to one aspect of the present invention, an electronic device includes: one or more processors, one or more memories, and one or more computer programs; wherein the processor is connected to the memory, and the one or more computer programs are stored in the memory. When the electronic device is running, the processor executes the one or more computer programs stored in the memory, so that the electronic device executes the above-mentioned spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics.

[0058] According to one aspect of the present invention, a computer-readable storage medium is characterized in that it is used to store computer instructions, and when the computer instructions are executed by a processor, the above-mentioned space-borne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics is implemented.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The satellite-borne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics provided by the present invention can effectively solve the problems of poor ground target aiming accuracy and reduced SAR image quality caused by SAR antenna beam pointing deviation. The present invention uses the SAR antenna installation angle deviation measured in the ground assembly integration stage to roughly compensate for the beam pointing deviation, and uses the difference beam image characteristics after satellite launch to precisely compensate for the beam pointing deviation, fully considering the influence of the pointing deviation caused by the antenna installation and the beam pointing deviation caused by the change of the space environment after the satellite launch on the SAR image quality, has a better compensation effect, and can effectively improve the SAR imaging quality.

[0061] The present invention also provides a specific method for compensating beam pointing deviation through an attitude subsystem, which is easy to operate, suitable for practical engineering applications, and has wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0063] Figure 1 A flowchart of a method for calibrating the beam pointing of a space-borne SAR based on antenna installation deviation and difference beam image characteristics is schematically shown according to one embodiment of the present invention;

[0064] Figure 2 Schematically represents the geometric projection relationship of the SAR antenna beam normal in the satellite body coordinate system;

[0065] Figure 3 A schematic diagram schematically showing the characteristics of a range-difference beam image;

[0066] Figure 4 A schematic diagram schematically showing the azimuth disparity beam image characteristics. DETAILED DESCRIPTION

[0067] The description of the embodiments of this specification should be combined with the corresponding drawings, which should be considered as part of the complete specification. In the drawings, the shape or thickness of the embodiments may be enlarged and indicated for simplification or convenience. Furthermore, the parts of each structure in the drawings will be described separately. It is worth noting that the elements not shown in the drawings or not described in words are in a form known to ordinary technicians in the relevant technical field.

[0068] The description of the embodiments herein and any reference to directions and orientations are only for the convenience of description and are not to be construed as any limitation on the scope of protection of the present invention. The following description of the preferred embodiments may involve combinations of features, which may exist independently or in combination, and the present invention is not particularly limited to the preferred embodiments. The scope of the present invention is defined by the claims.

[0069] like Figure 1 As shown, the present invention provides a method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics, comprising the following steps:

[0070] Step S1, before the satellite is launched, based on the angle relationship between the star sensor reference mirror and the SAR antenna reference mirror, the beam pointing deviation caused by the antenna installation is calculated;

[0071] In the step S1, it specifically includes:

[0072] Step S11: In the satellite assembly and integration stage, the SAR antenna reference mirror is used as the main reference for satellite installation accuracy measurement, and a special accuracy detection device such as a theodolite or a laser tracker is used to measure and obtain the angle between the star sensor reference mirror and the SAR antenna reference mirror.

[0073]

[0074] where σ xx represents the angle between the x-axis of the satellite coordinate system and the x-axis of the SAR antenna, σ yx represents the angle between the satellite coordinate system y-axis and the SAR antenna x-axis, σ zx represents the angle between the z-axis of the satellite coordinate system and the x-axis of the SAR antenna, σ xy represents the angle between the x-axis of the satellite coordinate system and the y-axis of the SAR antenna, σ yy represents the angle between the satellite body coordinate system y-axis and the SAR antenna y-axis, σ zy represents the angle between the z-axis of the satellite coordinate system and the y-axis of the SAR antenna, σ xz represents the angle between the x-axis of the satellite coordinate system and the z-axis of the SAR antenna, σ yz represents the angle between the satellite coordinate system y-axis and the SAR antenna z-axis, σ zz It represents the angle between the z-axis of the satellite coordinate system and the z-axis of the SAR antenna;

[0075] Step S12, establishing the geometric projection relationship of the antenna beam normal direction in the satellite body coordinate system after the SAR antenna is installed on the satellite;

[0076] like Figure 2 As shown, α gIt is the azimuth beam pointing deviation caused by the SAR antenna installation, which is defined as the angle between the projection of the antenna beam normal on the XOZ plane of the satellite coordinate system and the Z axis. When the angle between the projection of the antenna beam normal on the XOZ plane of the satellite coordinate system and the X axis is less than 90°, the azimuth beam is tilted forward, and when it is greater than 90°, the azimuth beam is tilted backward; β g It is the range beam pointing deviation caused by the SAR antenna installation, which is defined as the angle between the projection of the antenna beam normal on the YOZ plane of the satellite body coordinate system and the Z axis. When the angle between the projection of the antenna beam normal on the YOZ plane of the satellite body coordinate system and the Y axis is less than 90°, it is viewed on the left side, and greater than 90°, it is viewed on the right side.

[0077] If the conversion sequence from the antenna coordinate system to the satellite coordinate system is 3-2-1, that is, the satellite attitude is converted from the antenna coordinate system to the satellite coordinate system in the order of yaw angle-pitch angle-roll angle, then the azimuth beam pointing deviation of the SAR antenna after installation is α g , the range beam pointing deviation is β g ;

[0078] Step S13: Calculate the azimuth beam pointing deviation α caused by the SAR antenna installation g and range beam pointing deviation β g :

[0079] According to the projection relationship of the SAR antenna beam normal in the satellite body coordinate system, the azimuth and range beam pointing deviations α are determined. g , β g The relationship between the three-axis angles of the star sensor and the SAR antenna reference mirror is:

[0080]

[0081] According to the ground installation experience and the above formula, the initial values ​​of the range beam pointing deviation and the azimuth beam pointing deviation are selected, and the azimuth beam pointing deviation α is obtained by the least squares method. g and range beam pointing deviation β g ;

[0082] Step S14: Adjust the angle between the satellite and the SAR antenna installation interface until the angle α is satisfied. g ≤1° and β g ≤1°.

[0083] The azimuth beam pointing deviation α calculated in step S13 is determined g and range beam pointing deviation β g Whether α is satisfied g ≤1° and β g≤1°. If not, adjust the angle relationship between the satellite structure and the SAR antenna installation interface (unlocking hinge, support rod and mounting boss, etc.), and repeat steps S11 to S13 until the requirement is met.

[0084] Step S2, loading the beam pointing deviation caused by the antenna installation into the satellite attitude control subsystem to roughly compensate the SAR antenna beam pointing deviation;

[0085] In step S2, rough compensation is performed by correcting the conversion matrix from the SAR antenna coordinate system to the orbital coordinate system, which specifically includes:

[0086] Step S21, calculate the correction transformation matrix from the SAR antenna coordinate system to the orbital coordinate system, expressed as

[0087]

[0088] Among them, S TO is the ideal attitude matrix from the SAR antenna coordinate system to the orbital coordinate system calculated according to the two-dimensional yaw guidance theory, is the azimuth beam pointing deviation α caused by the SAR antenna installation g and range beam pointing deviation β g The correction matrix corresponding to the ideal posture matrix obtained is expressed as

[0089]

[0090] Among them, α and β are the azimuth beam pointing deviation and range beam pointing deviation obtained by ground-based precise measurement or on-orbit estimation, respectively. The azimuth beam pointing deviation and range beam pointing deviation obtained by ground-based precise measurement are α g and β g The azimuth beam pointing deviation and range beam pointing deviation obtained by on-orbit estimation are α f and β f , and α and β are both less than 1°; roll, pitch and yaw are the roll angle, pitch angle and yaw angle of the satellite respectively, R x (θ), R y (θ) and R z (θ) are the rotation matrices for rotating θ around the x, y, and z axes, respectively, and R -1 (·) is the inverse matrix of R(·), R x (θ), R y (θ) and R z (θ) is expressed as

[0091]

[0092] Step S22: When the satellite is imaging the earth, the correction conversion matrix S is used. SO Perform two-dimensional yaw guidance and satellite attitude control to complete coarse compensation of SAR beam pointing.

[0093] Step S3, after the satellite is launched, based on the imaging result of the tropical rain forest area of ​​the range differential beam and the null depth of the range differential beam antenna pattern, the range beam pointing deviation introduced by the change of the on-orbit space environment is obtained, and loaded into the satellite attitude control subsystem to accurately compensate for the SAR antenna range beam pointing deviation;

[0094] In the step S3, it specifically includes:

[0095] Step S31: Select the range difference beam position i, and the theoretical viewing angle corresponding to the difference beam notch position is γ i0 , the satellite images the tropical rain forest area, obtains the range differential beam tropical rain forest area imaging data and transmits it to the ground data transmission station;

[0096] Step S32: the ground application system performs segmentation of the auxiliary data and the range original echo data according to the range difference beam tropical rain forest area imaging data, analyzes the orbit, attitude and SAR payload corresponding to the range original echo data, calculates Doppler parameter imaging processing, and obtains a focused first SAR image;

[0097] Step S33: Count the power variation curve of the first SAR image along the range direction, and obtain the actual downward viewing angle γ during imaging according to the null depth of the range difference beam antenna pattern. i1 ;

[0098] according to Figure 3 The range differential beam antenna pattern null depth G is shown R dB, look for a power curve with a depth greater than G R dB range gate interval, and obtain the range gate N corresponding to the notch position of the range gate interval R ;

[0099] Calculate the slant distance R corresponding to the notch point distance gate and the actual downward viewing angle γ when acquiring the image i1 , expressed as:

[0100]

[0101]

[0102] Where C is the speed of light, τ0 is the radar start sampling time, and f s is the distance sampling frequency, R e is the radius of the earth, H is the orbital altitude;

[0103] Step S34: Calculate the range beam pointing deviation β caused by the change of the satellite's on-orbit space environment fi , expressed as:

[0104] β fi =γ i1 -γ i0

[0105] Step S35: Select the range difference beam positions with different left and right side views, repeat steps S31 to S35, and obtain several groups of range beam pointing deviation sample values ​​β f1 , ..., β fN , calculate the average value to get the accurate range beam pointing deviation β after being on orbit f , expressed as:

[0106]

[0107] Wherein, N represents the number of groups of range beam pointing deviation sample values ​​obtained;

[0108] Step S36: Repeat step S2 to correct the conversion matrix Complete precise compensation of range beam pointing deviation.

[0109] After the satellite is launched, the range difference beam position is selected to image the tropical rain forest area, the SAR image power variation curve along the range direction is statistically analyzed, the actual viewing angle of imaging is calculated according to the null depth of the range difference beam antenna pattern, and compared with the viewing angle under the difference beam position theory to obtain the range beam pointing deviation, and step S2 is repeated to complete the precise compensation of the range beam pointing deviation.

[0110] Step S4, after the satellite is launched, based on the azimuth difference beam tropical rain forest area imaging results, according to the azimuth difference beam image accumulation characteristics containing beam pointing deviation, the azimuth beam pointing deviation introduced by the on-orbit space environment change is obtained, and loaded into the satellite attitude control subsystem to accurately compensate for the SAR antenna azimuth beam pointing deviation;

[0111] In the step S4, it specifically includes:

[0112] Step S41, select the azimuth difference beam position j, the theoretical slant angle corresponding to the difference beam notch position is ψ j0 , the satellite images the tropical rain forest area, obtains the azimuth difference beam position tropical rain forest area imaging data and transmits it to the ground data transmission station;

[0113] Step S42: Based on the azimuth difference beam position tropical rain forest area imaging data, the ground application system intercepts two synthetic aperture azimuth original echo data, and the synthetic aperture length of the two synthetic aperture azimuth original echo data is N. A, expressed as:

[0114] N A =Int(2T a ×PRF)

[0115] Among them, T a is the synthetic aperture time, PRF is the radar pulse repetition frequency, and Int(·) indicates rounding;

[0116] Analyzing the orbit, attitude and SAR payload corresponding to the two synthetic aperture azimuth original echo data, calculating Doppler parameter imaging processing, and obtaining a focused second SAR image;

[0117] Step S43, cutting off half of the synthetic aperture length image in both ends of the focused second SAR image in azimuth;

[0118] Step S44, counting the power variation curve of the intercepted second SAR image along the azimuth direction, and finding the inflection point of the curve; according to Figure 4 The difference beam image accumulation characteristics with beam pointing deviation in azimuth are shown, and the incomplete aperture accumulation length L in azimuth is calculated. A ;

[0119] Step S45: Calculate the actual oblique angle ψ during imaging j1 , expressed as:

[0120]

[0121] The azimuth pointing deviation is positive when the incomplete aperture is in the first half of the curve and negative in the second half. a is the azimuth beamwidth, T a is the synthetic aperture time, PRF is the pulse repetition frequency;

[0122] Step S46: Calculate the azimuth beam pointing deviation α caused by the change of the satellite's on-orbit space environment fj , expressed as

[0123] αx j =ψ j1 -ψ j0

[0124] Step S47, select different azimuth difference beam positions, repeat steps S41 to S47, and obtain several groups of azimuth beam pointing deviation sample values ​​α f1 , ..., α fM , calculate the average value to get the accurate azimuth beam pointing deviation α after being on orbit f , expressed as

[0125]

[0126] Wherein, M represents the number of groups of azimuth beam pointing deviation sample values ​​obtained;

[0127] Step S49: Repeat step S2 to correct the conversion matrix Complete accurate compensation of azimuth beam pointing deviation

[0128] After the satellite is launched, the azimuth difference beam position is selected to image the tropical rain forest area, and the original echo data of two synthetic aperture lengths in azimuth are intercepted for imaging processing. The images of half the synthetic aperture length are removed from both ends of the focused SAR image in azimuth, and the image power variation curve along the azimuth is statistically analyzed. The actual squint angle is calculated according to the accumulation characteristics of the difference beam image containing beam pointing deviation in azimuth, and compared with the theoretical squint angle of the difference beam position, the azimuth beam pointing deviation is obtained, and step S2 is repeated to complete the precise compensation of the azimuth beam pointing deviation.

[0129] Step S5: The satellite executes the steps S3 to S4 according to the calibration cycle to perform precise compensation for the beam pointing deviation of the SAR antenna in the range direction and the beam pointing deviation of the SAR antenna in the azimuth direction.

[0130] The calibration period may be 1 to 2 years, that is, the satellite performs steps S3 to S4 once every 1 to 2 years.

[0131] According to one aspect of the present invention, an electronic device is provided, comprising: one or more processors, one or more memories, and one or more computer programs; wherein the processor is connected to the memory, and the one or more computer programs are stored in the memory, and when the electronic device is running, the processor executes the one or more computer programs stored in the memory, so that the electronic device performs the spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics as described in any one of the above technical solutions.

[0132] According to one aspect of the present invention, a computer-readable storage medium is provided for storing computer instructions. When the computer instructions are executed by a processor, a space-borne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics as described in any one of the above technical solutions is implemented.

[0133] It should be noted that the above is a preferred embodiment of the present invention. It should be pointed out that although the preferred embodiment of the present invention has been described, once the basic creative concept of the present invention is known, a number of improvements and modifications can be made by a person skilled in the art without departing from the principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention. Therefore, the attached claims are intended to be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the embodiments of the present invention.

Claims

1. A method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics, characterized in that: The following steps are involved: Step S1, before the satellite is launched, based on the angle relationship between the star sensor reference mirror and the SAR antenna reference mirror, the beam pointing deviation caused by the antenna installation is calculated; Step S2, loading the beam pointing deviation caused by the antenna installation into the satellite attitude control subsystem to roughly compensate the SAR antenna beam pointing deviation; Step S3, after the satellite is launched, based on the imaging result of the tropical rain forest area of ​​the range differential beam and the null depth of the range differential beam antenna pattern, the range beam pointing deviation introduced by the change of the on-orbit space environment is obtained, and loaded into the satellite attitude control subsystem to accurately compensate for the SAR antenna range beam pointing deviation; Step S4, after the satellite is launched, based on the azimuth difference beam tropical rain forest area imaging results, according to the azimuth difference beam image accumulation characteristics containing beam pointing deviation, the azimuth beam pointing deviation introduced by the on-orbit space environment change is obtained, and loaded into the satellite attitude control subsystem to accurately compensate for the SAR antenna azimuth beam pointing deviation; Step S5: The satellite executes the steps S3 to S4 according to the calibration cycle to perform precise compensation for the beam pointing deviation of the SAR antenna in the range direction and the beam pointing deviation of the SAR antenna in the azimuth direction.

2. The method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics according to claim 1, characterized in that: In step S5, the calibration period is 1 to 2 years.

3. The method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics according to claim 1, characterized in that: In the step S1, it specifically includes: Step S11: In the satellite assembly and integration stage, the SAR antenna reference mirror is used as the main reference for satellite installation accuracy measurement, and the angle between the star sensor reference mirror and the SAR antenna reference mirror is measured to be σ xz , σ yz , σ zz ; Step S12, establishing the geometric projection relationship of the antenna beam normal direction in the satellite body coordinate system after the SAR antenna is installed on the satellite; Step S13: Calculate the azimuth beam pointing deviation α caused by the SAR antenna installation g and range beam pointing deviation β g : According to the projection relationship of the SAR antenna beam normal in the satellite body coordinate system, the azimuth beam pointing deviation α caused by the SAR antenna installation is determined. g and range beam pointing deviation β g The relationship between the three-axis angles of the star sensor and the SAR antenna reference mirror is: According to the ground installation experience and the above formula, the initial values ​​of the range beam pointing deviation and the azimuth beam pointing deviation are selected, and the azimuth beam pointing deviation α is obtained by the least squares method. g and range beam pointing deviation β g ; Step S14: Adjust the angle between the satellite and the SAR antenna installation interface until the angle α is satisfied. g ≤1° and β g ≤1°.

4. The method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics according to claim 1, characterized in that: In step S2, rough compensation is performed by correcting the conversion matrix from the SAR antenna coordinate system to the orbital coordinate system, which specifically includes: Step S21, calculate the correction transformation matrix from the SAR antenna coordinate system to the orbital coordinate system, expressed as Among them, S TO is the ideal attitude matrix from the SAR antenna coordinate system to the orbital coordinate system calculated according to the two-dimensional yaw guidance theory, is the azimuth beam pointing deviation α caused by the SAR antenna installation g and range beam pointing deviation β g The correction matrix corresponding to the ideal posture matrix obtained is expressed as Among them, α and β are the azimuth beam pointing deviation and range beam pointing deviation obtained by ground-based precise measurement or on-orbit estimation, respectively. The azimuth beam pointing deviation and range beam pointing deviation obtained by ground-based precise measurement are α g and β g The azimuth beam pointing deviation and range beam pointing deviation obtained by on-orbit estimation are α f and β f , and α and β are both less than 1°; roll, pitch and yaw are the roll angle, pitch angle and yaw angle of the satellite respectively, R x (θ), R y (θ) and R z (θ) are the rotation matrices for rotating θ around the x, y, and z axes, respectively, and R -1 (·) is the inverse matrix of R(·), R x (θ), R y (θ) and R z (θ) is expressed as Step S22: When the satellite is imaging the earth, the correction conversion matrix S is used. so Perform two-dimensional yaw guidance and satellite attitude control to complete coarse compensation of SAR beam pointing.

5. The method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics according to claim 4, characterized in that: In the step S3, it specifically includes: Step S31: Select a range difference beam position i, where the theoretical viewing angle corresponding to the difference beam notch position of the range difference beam position is γ i0 , the satellite images the tropical rain forest area, obtains the range differential beam tropical rain forest area imaging data and transmits it to the ground data transmission station; Step S32: the ground application system performs segmentation of the auxiliary data and the range original echo data according to the range difference beam tropical rain forest area imaging data, analyzes the orbit, attitude and SAR payload corresponding to the range original echo data, calculates Doppler parameter imaging processing, and obtains a focused first SAR image; Step S33: Count the power variation curve of the first SAR image along the range direction, and obtain the actual downward viewing angle γ during imaging according to the null depth of the range difference beam antenna pattern. i1 ; Step S34: Calculate the range beam pointing deviation β caused by the change of the satellite's on-orbit space environment fi , expressed as: b fi =c i1 -c i0 Step S35: Select the range difference beam positions with different left and right side views, repeat steps S31 to S35, and obtain several groups of range beam pointing deviation sample values ​​β f1 , ..., β fN , calculate the average value to get the accurate range beam pointing deviation β after being on orbit f , expressed as: Wherein, N represents the number of groups of range beam pointing deviation sample values ​​obtained; Step S36: Repeat step S2 to correct the conversion matrix Complete precise compensation of range beam pointing deviation.

6. The method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics according to claim 5, characterized in that: In the step S34, it specifically includes: According to the range difference beam antenna pattern null depth G R dB, look for a power curve with a depth greater than G R dB range gate interval, and obtain the range gate N corresponding to the notch position of the range gate interval R ; Calculate the slant distance R corresponding to the notch point distance gate and the actual downward viewing angle γ when acquiring the image i1 , expressed as: Where C is the speed of light, τ0 is the radar start sampling time, and f s is the distance sampling frequency, R e is the radius of the earth and H is the orbital altitude.

7. The method for calibrating the beam pointing of a spaceborne SAR based on antenna installation deviation and difference beam image characteristics according to claim 6, characterized in that: In the step S4, it specifically includes: Step S41, select the azimuth difference beam position j, the theoretical slant angle corresponding to the difference beam notch position of the azimuth difference beam position is ψ j0 , the satellite images the tropical rain forest area, obtains the azimuth difference beam position tropical rain forest area imaging data and transmits it to the ground data transmission station; Step S42: Based on the azimuth difference beam position tropical rain forest area imaging data, the ground application system intercepts two synthetic aperture azimuth original echo data, analyzes the orbit, attitude and SAR payload corresponding to the synthetic aperture azimuth original echo data, calculates Doppler parameter imaging processing, and obtains a focused second SAR image; Step S43, cutting off half of the synthetic aperture length image in both ends of the focused second SAR image in azimuth; Step S44: Calculate the power variation curve of the intercepted second SAR image along the azimuth direction, find the inflection point of the curve, and calculate the azimuth incomplete aperture accumulation length L according to the accumulation characteristics of the difference beam image containing the beam pointing deviation in the azimuth direction. A ; Step S45: Calculate the actual oblique angle ψ during imaging j1 , expressed as: The azimuth pointing deviation is positive when the incomplete aperture is in the first half of the curve and negative in the second half. a is the azimuth beamwidth, T a is the synthetic aperture time, PRF is the pulse repetition frequency; Step S46: Calculate the azimuth beam pointing deviation α caused by the change of the satellite's on-orbit space environment fj , denoted as α fj =ψ j1 -ψ j0 Step S47, select different azimuth difference beam positions, repeat steps S41 to S46, and obtain several groups of azimuth beam pointing deviation sample values ​​α f1 , ..., α fM , calculate the average value to get the accurate azimuth beam pointing deviation α after being on orbit f , expressed as Wherein, M represents the number of groups of azimuth beam pointing deviation sample values ​​obtained; Step S48: Repeat step S2 to correct the conversion matrix Complete precise compensation of azimuth beam pointing deviation.

8. An electronic device, characterized in that: include: One or more processors, one or more memories, and one or more computer programs; wherein the processor is connected to the memory, and the one or more computer programs are stored in the memory; when the electronic device is running, the processor executes the one or more computer programs stored in the memory, so that the electronic device executes the spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics as described in any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that: Used to store computer instructions, which, when executed by a processor, implement the space-borne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics as described in any one of claims 1 to 7.

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