Beam pointing calibration method for spaceborne SAR based on antenna installation deviation and difference beam image characteristics

Abstract

The present invention relates to a satellite-borne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics, comprising the following steps: calculating the beam pointing deviation caused by antenna installation before satellite launch; loading the beam pointing deviation caused by antenna installation into the satellite attitude control subsystem to coarsely compensate for the SAR antenna beam pointing deviation; after satellite launch, obtaining the range beam pointing deviation introduced by on-orbit space environment changes based on the null depth of the range difference beam antenna pattern obtained from imaging results, and finely compensating for the SAR antenna range beam pointing deviation; after satellite launch, obtaining the azimuth beam pointing deviation introduced by on-orbit space environment changes based on imaging results and the accumulation characteristics of the difference beam image containing the azimuth beam pointing deviation, and finely compensating for the SAR antenna azimuth beam pointing deviation; the satellite performs fine compensation according to a calibration cycle. The present invention can effectively solve the problems of poor ground target aiming accuracy and degraded SAR image quality.

Description

Technical Field

[0001] The present 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 orientation of the SAR antenna toward the ground as the satellite image the Earth in orbit. For spaceborne SAR, the antenna is rigidly connected to the satellite body, and the mounting angle between the two directly determines the beam pointing during imaging. Installation deviations directly introduce beam pointing deviations. Furthermore, stress during satellite launch and antenna deployment, as well as changes in spatial temperature during in-orbit flight, can cause mechanical and thermal deformations in instruments such as the antenna deployment mechanism, antenna array, and star sensors. This can cause the actual beam pointing of the SAR antenna in orbit to deviate from the theoretical value, making it impossible to precisely aim at ground targets and obtain accurate SAR image parameters. Therefore, beam pointing calibration must be performed before and after satellite launch to obtain and compensate for beam pointing deviations, enabling the satellite to accurately aim at the target and obtain high-quality SAR images, allowing users to accurately aim and clearly see the target.

[0003] SAR antenna beam pointing is typically expressed in terms of range and azimuth angles, with the azimuth angle being along the direction of satellite flight and the range angle perpendicular to the direction of satellite flight. Beam pointing calibration involves calibrating and compensating for beam pointing deviations through various means during satellite development, the initial launch phase, and certain stages of operation. Current research on spaceborne SAR beam pointing calibration focuses primarily on estimating beam pointing deviations using post-orbit image parameters and eliminating Doppler center offsets caused by Earth rotation through two-dimensional satellite attitude guidance technology. However, the impact of antenna installation angle deviations during satellite assembly and integration, and beam pointing deviations caused by changes in the space environment after satellite launch, on SAR image quality have not been fully considered. 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 space-borne SAR beam pointing calibration method, electronic equipment 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, 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, the beam pointing deviation caused by the antenna installation is calculated based on the angular relationship between the star sensor reference mirror and the SAR antenna reference mirror;

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

[0008] Step S3: After the satellite is launched, based on the imaging results of the tropical rainforest area using the range differential beam and the null depth of the range differential beam antenna pattern, the range 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 range beam pointing deviation;

[0009] Step S4: After the satellite is launched, based on the azimuth difference beam imaging results of the tropical rainforest area and the accumulation characteristics of the difference beam image containing the azimuth 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 steps S3 to S4 according to the calibration cycle to perform precise compensation for the SAR antenna range beam pointing deviation and the SAR antenna azimuth beam pointing deviation.

[0011] According to a technical solution of the present invention, in step S5, the calibration cycle 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 as σ xz , σ yz , σ zz ;

[0014] Step S12: establishing a geometric projection relationship of the antenna beam normal direction in the satellite body coordinate system after the SAR antenna is mounted 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 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 orbit coordinate system, specifically including:

[0021] Step S21: Calculate the correction conversion matrix from the SAR antenna coordinate system to the orbit coordinate system, expressed as

[0022]

[0023] Among them, S TO is the ideal attitude matrix from the SAR antenna coordinate system to the orbit 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 and β, respectively. g and β g The azimuth beam pointing deviation and range beam pointing deviation obtained by on-board 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, the following steps are specifically included:

[0029] Step S31: Select the range difference beam position i, 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 rainforest area, obtains range differential beam tropical rainforest 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 based on the range difference beam tropical rainforest 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 sets 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 step S34, the following steps are specifically included:

[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, 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 starting sampling time, 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 rainforest 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: Cut off half of the synthetic aperture length image at 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 azimuth. A ;

[0048] Step S45: Calculate the actual squint 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 and repeat steps S41 to S46 to 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 to enable the electronic device to perform 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, which, when executed by a processor, implement the above-mentioned spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics.

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

[0060] The present invention provides a spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics, effectively resolving the issues of poor ground target aiming accuracy and degraded SAR image quality caused by SAR antenna beam pointing deviation. The method uses the SAR antenna installation angle deviation measured during the ground assembly and integration phase to coarsely compensate for beam pointing deviation, and uses the difference beam image characteristics measured after satellite launch to finely compensate for beam pointing deviation. This method fully considers the impact of pointing deviation caused by antenna installation and beam pointing deviation caused by changes in the space environment after satellite launch on SAR image quality, resulting in improved compensation and effectively improving 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] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0063] Figure 1 Schematically showing a flow chart of a spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics 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 difference beam image characteristics. DETAILED DESCRIPTION

[0067] The description of the embodiments in this specification should be combined with the corresponding drawings, which should be considered a complete part of this specification. In the drawings, the shapes and thicknesses of the embodiments may be exaggerated and indicated for simplicity or convenience. Furthermore, the various structural components in the drawings will be described separately. It is worth noting that components not shown in the drawings or not described in words are known to those of ordinary skill in the art.

[0068] The description of the embodiments herein and any references to directions and orientations are for ease of description only and are not to be construed as limiting the scope of the present invention. The following description of the preferred embodiments may involve combinations of features, which may exist independently or in combination. The present invention is not specifically 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 spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics, comprising the following steps:

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

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

[0072] Step S11: During the satellite assembly and integration phase, the SAR antenna reference mirror is used as the main reference for satellite installation accuracy measurement. A dedicated precision 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 y-axis of the satellite coordinate system and the y-axis of the SAR antenna, 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 y-axis of the satellite coordinate system and the z-axis of the SAR antenna, σ zz Indicates the angle between the z-axis of the satellite coordinate system and the z-axis of the SAR antenna;

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

[0076] like Figure 2 As shown, α gβ 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. g The range beam pointing deviation caused by the SAR antenna installation is defined as the angle between the projection of the antenna beam normal on the YOZ plane of the satellite coordinate system and the Z axis. When the angle between the projection of the antenna beam normal on the YOZ plane of the satellite coordinate system and the Y axis is less than 90°, it is considered left viewing, and greater than 90°, it is considered right viewing.

[0077] If the conversion order 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 for the SAR antenna beam pointing deviation;

[0085] In step S2, coarse compensation is performed by correcting the conversion matrix from the SAR antenna coordinate system to the orbit coordinate system, specifically including:

[0086] Step S21: Calculate the correction conversion matrix from the SAR antenna coordinate system to the orbit coordinate system, expressed as

[0087]

[0088] Among them, S TO is the ideal attitude matrix from the SAR antenna coordinate system to the orbit 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 and β, respectively. g and β g The azimuth beam pointing deviation and range beam pointing deviation obtained by on-board 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 results of the tropical rainforest area using the range differential beam and the null depth of the range differential beam antenna pattern, the range 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 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 rainforest area, obtains range differential beam tropical rainforest 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 based on the range difference beam tropical rainforest 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 null depth G of the range-differential beam antenna pattern is shown R dB, look for a power curve with a depth greater than G R dB range gate interval, 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 starting sampling time, 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 sets 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-direction differential beam position is selected to image the tropical rainforest area. The SAR image power variation curve along the range direction is statistically calculated. The actual imaging viewing angle is calculated based on the null depth of the range-direction differential beam antenna pattern. This is compared with the viewing angle under the theoretical differential beam position to obtain the range-direction beam pointing deviation. Step S2 is repeated to complete the precise compensation of the range-direction beam pointing deviation.

[0110] Step S4: After the satellite is launched, based on the azimuth difference beam imaging results of the tropical rainforest area and the accumulation characteristics of the difference beam image containing the azimuth 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, and 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: Cut off half of the synthetic aperture length image at both ends of the focused second SAR image in azimuth;

[0118] Step S44: Calculate the power variation curve of the intercepted second SAR image along the azimuth direction and find the inflection point of the curve; 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 squint 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] α fj =ψ j1 -ψ j0

[0124] Step S47: Select different azimuth difference beam positions and repeat steps S41 to S47 to 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 azimuth beam pointing deviation compensation

[0128] After the satellite is launched, the azimuth difference beam position is selected to image the tropical rainforest area. 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. The image power variation curve along the azimuth is statistically analyzed. The actual squinting angle is calculated based on the accumulation characteristics of the difference beam image containing beam pointing deviation in azimuth. The actual squinting angle is compared with the theoretical squinting angle of the difference beam position to obtain the azimuth beam pointing deviation. Step S2 is repeated to complete the precise compensation of the azimuth beam pointing deviation.

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

[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. 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, the spaceborne SAR beam pointing calibration method based on antenna installation deviation and difference beam image characteristics as described in any 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 noted that although the preferred embodiment of the present invention has been described, it is clear that those skilled in the art, once they understand the basic inventive concept of the present invention, can make various improvements and modifications without departing from the principles of the present invention. Such improvements and modifications should also be considered as within the scope of protection of the present invention. Therefore, the appended 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, the beam pointing deviation caused by the antenna installation is calculated based on the angular relationship between the star sensor reference mirror and the SAR antenna reference mirror; Step S2: loading the beam pointing deviation caused by the antenna installation into the satellite attitude control subsystem to roughly compensate for the SAR antenna beam pointing deviation; Step S3: After the satellite is launched, based on the imaging results of the tropical rainforest area using the range differential beam and the null depth of the range differential beam antenna pattern, the range 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 range beam pointing deviation; Step S4: After the satellite is launched, based on the azimuth difference beam imaging results of the tropical rainforest area and the accumulation characteristics of the difference beam image containing the azimuth 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 steps S3 to S4 according to the calibration cycle to perform precise compensation for the SAR antenna range beam pointing deviation and the SAR antenna azimuth beam pointing deviation.

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 cycle 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: During the satellite assembly and integration phase, 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 as σ. xz , σ yz , σ zz ; Step S12: establishing a geometric projection relationship of the antenna beam normal direction in the satellite body coordinate system after the SAR antenna is mounted 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 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, coarse compensation is performed by correcting the conversion matrix from the SAR antenna coordinate system to the orbit coordinate system, specifically including: Step S21: Calculate the correction conversion matrix from the SAR antenna coordinate system to the orbit coordinate system, expressed as Among them, S TO is the ideal attitude matrix from the SAR antenna coordinate system to the orbit 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 and β, respectively. g and β g The azimuth beam pointing deviation and range beam pointing deviation obtained by on-board 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 the range difference beam position i, 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 rainforest area, obtains range differential beam tropical rainforest 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 based on the range difference beam tropical rainforest 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 sets 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, 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 starting sampling time, 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 rainforest 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: Cut off half of the synthetic aperture length image at 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 azimuth. A ; Step S45: Calculate the actual squint 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 , expressed as a fj =ψ j1 -ψ j0 Step S47: Select different azimuth difference beam positions and repeat steps S41 to S46 to 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 to enable the electronic device to perform 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 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.

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