An agile single-line array satellite attitude precision improvement method

Abstract

The application discloses a method for improving the attitude precision of a single-line array satellite, and comprises the following steps: calculating the geometric positioning error of a control area according to a geometric positioning model; solving the low-frequency error model parameters through an image geometric positioning model; obtaining the variation law of the low-frequency error with time and latitude according to the low-frequency error model parameters, and calculating the low-frequency error value of the attitude at any time; and correcting the attitude value of the single-line array photographing time according to the obtained low-frequency error value, eliminating the low-frequency error caused by the star sensor, and further improving the geometric precision of the single-line array satellite.

Description

Technical Field

[0001] This invention relates to a method for improving the attitude accuracy of agile single-line array satellites, which is applicable to high-precision positioning of stereo mapping cameras on aerospace remote sensing satellites. Background Technology

[0002] Improving the geometric positioning accuracy of mapping satellites without ground control points is a current research hotspot in the field of aerospace remote sensing both domestically and internationally. With the rapid development of mapping satellites both at home and abroad, the geometric positioning accuracy has improved from tens of meters to the ten-meter level. However, further improvements in geometric positioning accuracy face significant challenges. The satellite's orbit and attitude accuracy directly affect image positioning accuracy. Since orbit determination accuracy can reach sub-meter levels both domestically and internationally, the satellite's attitude processing accuracy has become a limiting factor for improving geometric positioning accuracy. Mapping satellites use star sensors and gyroscopes for measurement, employing a combination of star sensors and gyroscopes for attitude determination. Affected by factors such as the alternating hot and cold environmental changes on the satellite due to sunlight exposure, and changes in the star sensor's viewing angle, the angle between the star sensor's optical axis and the camera's optical axis undergoes periodic changes; this change can be referred to as low-frequency attitude error.

[0003] Domestic and international experts and scholars have proposed compensation measures for low-frequency errors based on existing conditions. Internationally, in addition to employing higher-precision star sensors, the overall satellite structure has been optimized to reduce the impact of solar illumination on the optical lenses. Domestically, Academician Wang Renxiang, based on the influence of pitch and yaw angle changes on vertical parallax, introduced a small-area array EFP beam adjustment technique on the Tianhui-1 satellite to correct the exterior orientation elements of low-frequency errors, achieving an uncontrolled accuracy of 1:50,000. Jin Tao, Li Zhen, and others proposed using a different-side stereo observation mode to reduce elevation errors and employing high-frequency attitude measurement equipment and angle detection devices to meet high-precision stereo mapping requirements. The main goal of domestic mapping satellites is to continuously improve absolute positioning accuracy and achieve a mapping scale of 1:10,000 when ground control points are unavailable. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a method for improving the attitude accuracy of agile single-line array satellites, thereby solving the problem of low-frequency attitude error compensation for single-line array mapping satellites and improving the accuracy of uncontrolled positioning.

[0005] The technical solution of this invention is: a method for improving the attitude accuracy of an agile single-line array satellite, comprising:

[0006] Calculate the geometric positioning error of the control area based on the geometric positioning model;

[0007] Low-frequency error model parameters are solved using an image geometric positioning model;

[0008] Based on the low-frequency error model parameters, the variation law of low frequency with time and latitude is obtained, and the attitude low-frequency error value at any time is calculated.

[0009] Based on the obtained low-frequency error values, the attitude values ​​at the single-line array photography time are corrected to eliminate the low-frequency errors caused by the star sensor, thereby improving the geometric accuracy of the single-line array satellite.

[0010] The calculation of the geometric positioning error of the control area based on the geometric positioning model is specifically as follows:

[0011] ΔX=X-X0

[0012] ΔY=Y-Y0

[0013] In the formula, ΔX and ΔY are the geometric positioning errors, (X,Y) are the ground coordinates of the control point calculated based on the geometric positioning model, and (X0,Y0) are its actual geographic coordinates.

[0014] The process of solving the low-frequency error model parameters using the image geometric positioning model includes: directly solving for the multi-level Fourier series model parameters A0, B0, and A using the geometric errors of all control points in the control area. n B n , ω0, specifically:

[0015]

[0016]

[0017] In the formula, (ΔX, ΔY) represents the geometric positioning error, A0 and B0 represent the initial amplitude at the calibration time, and A n B n The amplitude of low-frequency fluctuations. ω0 represents the initial phase; H represents the orbital altitude. Roll angle, ω pitch angle, n is the Fourier series, Lat is the latitude of the ground area corresponding to the time of the photograph, T is the time interval between the two calibrations, and t is the current time.

[0018] The Fourier fitting level n is selected as 3-5 levels.

[0019] The step of obtaining the variation law of low frequency with time and latitude based on the low frequency error model parameters and calculating the attitude low frequency error value at any time includes:

[0020]

[0021]

[0022] In the formula δω represents the low-frequency error of the roll angle, δω represents the low-frequency error of the pitch angle, and A0 and B0 are the values ​​obtained at the calibration time. n B n The amplitude of the low-frequency fluctuation is given by , n is the Fourier series, and Lat is the latitude of the ground region corresponding to the time of the photograph. T is the time interval between the two calibrations, and t is the current time. ω0 is the initial phase.

[0023] The step of correcting the attitude value at the moment of single-line array photography based on the obtained low-frequency error value is as follows:

[0024]

[0025]

[0026] in δω represents the low-frequency error of the roll angle, and δω represents the low-frequency error of the pitch angle. The correction matrix is ​​obtained from the calculation of low-frequency errors. The rotation matrix from the satellite body to its orbit. This is the rotation matrix from the satellite body to its orbit obtained through measurement.

[0027] The advantages of this invention compared to existing technologies are as follows: Current technologies compensate for low-frequency satellite attitude errors through adjustment methods, while this invention directly models the low-frequency satellite attitude errors, calculates the values ​​of these errors directly using a ground-based error calculation model, and then corrects them. Compared to traditional methods, this invention offers a novel approach to low-frequency satellite attitude compensation, is simpler and easier to operate, and is not constrained by control points, thus having a wider range of applications. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of ground deviation caused by attitude measurement error.

[0029] Figure 2 This is a flowchart of the method of the present invention. Detailed Implementation

[0030] Star-sensor measurement errors are divided into those in the roll angle. Errors in the three angles—pitch (ω), yaw (κ)—cause offset errors in the linear array on the ground, such as... Figure 1 As shown;

[0031] In satellite agile imaging, when the roll angle, pitch angle, and yaw angle are not 0, according to Figure 1 The error in the X direction caused by the pitch angle δω can be obtained as follows:

[0032]

[0033] Roll angle The error in the Y direction is caused by:

[0034]

[0035] The image point offsets Δx and Δy caused by the yaw angle δκ are:

[0036]

[0037] In the above formula, x represents the number of image columns. As the formula shows, the image square error caused by yaw angle error is related to the distance from the center of the linear array. Typically, δκ is measured in arcseconds. Therefore, in small field-of-view situations, the impact of yaw angle error on ground accuracy can be ignored. Therefore, the following mainly studies roll angle error. Model construction for pitch angle error δω.

[0038] After a single calibration of an agile single-line array mapping satellite, the attitude data exhibits periodic changes along different latitudes within a short time T (between two calibration times). This can be represented as the superposition of multiple periodic sine functions, as shown in the following equation:

[0039]

[0040]

[0041] In the formula, A0 and B0 are the values ​​obtained at the calibration time, A n B n The amplitude of low-frequency fluctuations. ω0 represents the initial phase, n represents the Fourier series, and Lat represents the latitude of the ground region corresponding to the time of photography.

[0042] Therefore, the roll angle error can be obtained. The relationship between the pitch angle error δω and the positioning errors on the ground along the X and Y directions of the rail and vertical rail:

[0043]

[0044]

[0045] Within the control point region, the ground coordinates (X, Y, Z) of known image points are calculated using a geometric positioning model. These coordinates are then compared with the corresponding true geographic coordinates (X0, Y0, Z0) to calculate the geometric positioning error (ΔX, ΔY). Through analysis of numerous control point regions, the unknown parameters in the model are calculated, completing the construction of a single-line array satellite attitude error model. This model can be used for attitude correction of roll and pitch angles during two calibration cycles.

[0046] The following points should be noted when calculating model parameters:

[0047] 1) The control point area should cover a latitude range of [-70° to 70°] on the ground and be distributed as evenly as possible;

[0048] 2) The number of checkpoints in each control point area shall not be less than 50;

[0049] 3) When performing multi-level Fourier fitting, the fitting level needs to be adjusted to select the optimal fitting level (between 3 and 5 levels is acceptable).

[0050] Finally, the satellite's attitude data is corrected using a low-frequency error model. Let the rotation matrix from the satellite body to its orbit be... The rotation matrix from the satellite body to the orbit, calculated from the attitude measurement data, is: Then the true pose matrix and the measured attitude matrix The following relationship exists:

[0051]

[0052] in The attitude correction matrix is ​​derived from the roll angle error. The pitch angle error δω is calculated as follows:

[0053]

[0054] like Figure 2 As shown, this scheme establishes a low-frequency error model based on the principles of more than 10 strips, each 500 kilometers long, with a large latitudinal span, and aiming to cover as much high-precision control area as possible. The specific model solution steps are as follows:

[0055] Step 1: Calculate the ground coordinates (X, Y, Z) of the control points based on the geometric positioning model. The calculation formula used is as follows:

[0056]

[0057] In the formula, [X,Y,Z]WGS84 represents the ground coordinates corresponding to the image point, and [X,Y,Z]Sat represents the satellite position measured by GPS. The transformation matrix from the J2000 coordinate system to the WGS84 coordinate system is obtained after a series of corrections for precession, nutation, polar motion, and Earth's rotation. It is the transformation matrix from the satellite body coordinate system to the J2000 coordinate system, which is obtained by joint attitude determination using attitude data measured by star sensors and gyroscopes; This is the mounting matrix from the satellite linear array camera to the satellite body, provided when the satellite leaves the factory.

[0058] Based on the (X,Y,Z) obtained from the above formula, the geometric positioning error (ΔX,ΔY) is calculated by comparing it with the corresponding real geographic coordinates (X0,Y0,Z0).

[0059] ΔX=X-X0

[0060] ΔY=Y-Y0

[0061] Control points in China can be obtained using high-precision control imagery from across the country, while control points in overseas regions can be obtained using Google imagery.

[0062] Step 2: Perform attitude low-frequency Fourier multi-level model calculation for each control point region. The calculation formula used is as follows:

[0063]

[0064]

[0065] Step 3: Calculate the roll angle error at the required shooting time based on the low-frequency attitude error model. The pitch angle error δω is calculated using the following formula:

[0066]

[0067]

[0068] Where Lat is the ground latitude corresponding to the satellite at the time of the photograph, and t is the time series starting from the calibration time.

[0069] Step 4: Based on the roll angle error The attitude correction is calculated using the following formula, which is based on the pitch angle error δω:

[0070]

[0071] The correction amount is used to correct the transformation matrix from the satellite body to the orbit:

[0072]

[0073] in The rotation matrix from the satellite body to its orbit. This is the rotation matrix from the satellite body to its orbit obtained through measurement.

[0074] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for improving the attitude accuracy of an agile single-line array satellite, characterized in that, include: Calculate the geometric positioning error of the control area based on the geometric positioning model; Low-frequency error model parameters are solved using a geometric positioning model; Based on the low-frequency error model parameters, the variation law of low frequency with time and latitude is obtained, and the attitude low-frequency error value at any time is calculated. Based on the obtained low-frequency error values, the attitude values ​​at the single-line array photography time are corrected to eliminate the low-frequency errors caused by the star sensor, thereby improving the geometric accuracy of the single-line array satellite. The calculation of the geometric positioning error of the control area based on the geometric positioning model is specifically as follows: In the formula , The geometric positioning error is (X,Y), where (X,Y) are the ground coordinates of the control point calculated based on the geometric positioning model, and (X0,Y0) are its actual geographic coordinates. The process of solving low-frequency error model parameters using a geometric positioning model includes: directly solving for the parameters of a multi-level Fourier series model using the geometric errors of all control points in the control area. , , , , , Specifically: In the formula ( , () represents the geometric positioning error. , The initial amplitude at the calibration time, , The amplitude of low-frequency fluctuations. and H is the initial phase; H is the orbital altitude. Roll angle, Pitch angle, n is the Fourier series, Lat is the latitude of the ground area corresponding to the time of the photo, T is the time interval between the two calibrations, and t is the current time.

2. The method for improving the attitude accuracy of an agile single-line array satellite according to claim 1, characterized in that, The Fourier fitting level n is selected as 3-5 levels.

3. The method for improving the attitude accuracy of an agile single-line array satellite according to claim 1, characterized in that, The step of obtaining the variation law of low frequency with time and latitude based on the low frequency error model parameters and calculating the attitude low frequency error value at any time includes: In the formula For low-frequency error of roll angle, For low-frequency error of pitch angle, , The value obtained at the calibration time. , The amplitude of the low-frequency fluctuation is given by , n is the Fourier series, Lat is the latitude of the ground region corresponding to the time of the photograph; T is the time interval between the two calibrations, and t is the current time. and This is the initial phase.

4. The method for improving the attitude accuracy of an agile single-line array satellite according to claim 3, characterized in that, The step of correcting the attitude value at the moment of single-line array photography based on the obtained low-frequency error value is as follows: in For low-frequency error of roll angle, For low-frequency error of pitch angle, The correction matrix is ​​obtained from the calculation of low-frequency errors. The rotation matrix from the satellite body to its orbit. This is the rotation matrix from the satellite body to its orbit obtained through measurement.

Images