Motion-compensated imaging method and system for improving signal-to-noise ratio of space-borne imaging spectrometers

Abstract

This invention provides a motion-compensated imaging method and system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer, comprising: Step 1: defining the latitude and longitude of the starting and ending points of the imaging target area, the imaging compensation factor, and the initial orbital elements of the satellite; Step 2: recursively calculating the satellite orbital elements within a subsequent orbital period; Step 3: determining the push-broom imaging times for the starting and ending points of the target area; Step 4: designing the starting and ending time points of the compensation imaging period based on the principle of optimizing imaging spatial resolution; Step 5: designing the guidance rules for the satellite's pitch and roll angles within the compensation imaging period; Step 6: calculating the yaw angle based on the principle that the optical axis movement direction is consistent with the target phase shift velocity direction. The solution provided by this invention can achieve precise motion-compensated imaging of any specific area on the Earth's surface by a satellite, improving the signal-to-noise ratio of the imaging spectrometer, and can be used for high spatial resolution spectroscopic remote sensing missions.

Description

Technical Field

[0001] This invention relates to the field of satellite remote sensing imaging technology, and more specifically, to a motion-compensated imaging method and system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer. Background Technology

[0002] Imaging spectrometers, capable of simultaneously acquiring spatial and spectral information of targets, and thus able to analyze their external features and identify their internal components, are widely used in various types of remote sensing imaging satellite missions. However, because imaging spectrometers divide surface target information into multiple spectral channels, the amount of light received by each pixel in the spectrometer's detector is significantly reduced, consequently affecting the signal-to-noise ratio (SNR) of the spectrometer's imaging. Particularly for spectrometers requiring high spatial resolution imaging, the pixel size is further reduced, making the SNR insufficient for the imaging mission requirements. Currently, onboard imaging spectrometers primarily improve the imaging SNR through the following three methods:

[0003] 1) An imaging spectrometer based on electron multiplication is used. This method determines whether electron multiplication should be performed on each pixel within a single frame image and switches the spectral signal multiplication gain accordingly to improve the signal-to-noise ratio for weak signals. The working principle and system composition of this method are detailed in the invention patent (Spectral Image Synthesis System Based on Electron Multiplication, 2019) with publication number CN107635107B.

[0004] 2) An array-slit imaging spectrometer is employed. This method utilizes an array of slits instead of a traditional single slit, improving light throughput and signal-to-noise ratio through mixed exposure of the slit array. The principle of this method and the composition of the array-slit imaging spectrometer system are detailed in the invention patent with publication number CN111623876A (A Pushbroom Hyperspectral Imaging System and Method Based on an S-Matrix Slit Array, 2020).

[0005] 3) A motion compensation method based on a compensating scanning mirror is adopted. This method increases the pixel imaging integration time and improves the signal-to-noise ratio by adding a compensating scanning mirror to the front end of the imaging spectrometer's main mirror for motion compensation. The principle of motion compensation based on the compensating scanning mirror is explained in the article "Design and Development of the Gaofen-5 Visible-Shortwave Infrared Hyperspectral Camera" (Journal of Remote Sensing, Vol. 24, No. 4, 2020), and the on-orbit use method of the compensating scanning mirror and the motion compensation imaging effect on the Gaofen-5 satellite are given. The invention patent (CN102607531B, Space Low-Speed ​​High-Precision Two-Dimensional Image Shift Compensation Pointing Control System, 2012) provides the implementation scheme and hardware composition of the compensating scanning mirror and its control drive system. The article "Image Registration of a Dual-Channel Spaceborne Hyperspectral Imager under Motion Compensation" (Infrared and Laser Engineering, Vol. 50, No. 3, 2021) provides geometric modeling of motion compensation imaging based on the compensating scanning mirror and the design method of the scanning mirror compensation angle during motion compensation imaging.

[0006] While the methods described above can improve the signal-to-noise ratio (SNR) of imaging spectrometers, they all significantly increase the difficulty of instrument design and manufacturing. Method 1, to achieve weak signal detection and electron multiplication, requires additional components and circuits such as a preamplifier group, video processor group, and imaging controller, increasing circuit design difficulty and instrument complexity. Method 2 uses an array slit, which, compared to the original single slit, adds a high-precision electrically controlled displacement stage, further increasing the difficulty of instrument design, manufacturing, and assembly. Method 3, while not increasing the design difficulty of the imaging spectrometer itself, uses a compensating scanning mirror and its control system, further increasing the design difficulty and weight / volume of the entire optical payload. According to the compensation principle, adjusting the optical axis through the compensating scanning mirror requires the scanning mirror size to be close to the primary mirror size. As the demand for imaging spatial resolution gradually increases, the primary mirror aperture requirement also increases. Continuing to use a scanning mirror will inevitably lead to a significant increase in the overall satellite weight, design difficulty, and launch cost, a cost that will be unacceptable for the overall satellite development and launch. In conclusion, there is an urgent need to design a method to improve the imaging SNR without changing the existing imaging spectrometer design. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a motion-compensated imaging method and system for improving the signal-to-noise ratio of spaceborne imaging spectrometers.

[0008] The motion-compensated imaging method for improving the signal-to-noise ratio of a spaceborne imaging spectrometer according to the present invention includes:

[0009] Step 1: Define the latitude and longitude information of the starting and ending points of the ground target area, the imaging compensation factor, and the initial orbital elements of the satellite;

[0010] Step 2: Based on the initial orbital elements of the satellite, recursively calculate the number of satellite orbital elements for the next orbital period;

[0011] Step 3: Based on the latitude and longitude information of the starting and ending points of the ground target area and the recursive results of the satellite orbital elements, determine the push-broom imaging time for the initial point of the target area and the push-broom imaging time for the ending point of the target area;

[0012] Step 4: Based on the principles of optimizing the imaging compensation factor and imaging spatial resolution, design the start and end time points of the compensation imaging period;

[0013] Step 5: Design the guidance rules for the satellite pitch and roll angles at each moment during the compensation imaging period based on the real-time satellite orbit elements and ground target area information during the compensation imaging period.

[0014] Step 6: Calculate the yaw angle based on the principle that the direction of optical axis movement is consistent with the direction of target phase shift velocity. The result of the yaw angle calculation is the guidance law of satellite yaw angle.

[0015] Preferably, in step 1, the latitude and longitude information of the starting point and the ending point of the ground target area, the imaging compensation factor k, and the six initial orbital elements of the satellite are set, including the semi-major axis a0, inclination i0, eccentricity e0, right ascension of the ascending node Ω0, argument of perigee ω0, and true perigee f0.

[0016] In step 2, based on the initial six orbital elements of the satellite, in addition to the two-body motion, the non-spherical perturbation of the Earth, the gravitational perturbation of the Sun and Moon, atmospheric drag, and light pressure are added. The six orbital elements of the satellite in the subsequent orbital period are recursively derived based on the orbital mechanics equations, including the orbital semi-major axis a(t), inclination i(t), eccentricity e(t), right ascension of the ascending node Ω(t), argument of perigee ω(t), and true perigee f(t).

[0017] In step 3, the push-broom imaging time t for the initial point of the target area is determined based on the latitude and longitude information of the starting and ending points of the target area and the recursive result of the satellite orbital elements. A and push-broom imaging time t for the end point of the target region B , where t A t is the time when the elevation angle required for the initial point of the satellite's optical axis pointing towards the target area is 0°. B The calculation process for the moment when the required elevation angle of the satellite's optical axis pointing to the end point of the target area is 0° includes the following steps:

[0018] Step 3.1: Calculate the position vector R of the initial point in the Earth-fixed coordinate system based on the latitude and longitude information of the initial point in the target area. fs ;

[0019] Step 3.2: Based on the satellite orbital elements at each moment within one orbital period, calculate the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment. fo (t), to obtain the position vector R of the initial point in the satellite orbit coordinate system. os (t), the expression is:

[0020] R os (t)=C fo (t)R fs

[0021] Step 3.3: According to R os The x-component R of the unit vector of (t) osu (1) Calculate the elevation angle θ of the satellite pointing to the initial point of the target area at each time. s (t), the expression is:

[0022]

[0023] Step 3.4: Solve for the pitch angle θ s The (t) sequence contains two time points θ. s The value equals zero, where the distance |R| between the initial point of the target area and the satellite is zero. os (t)| A smaller time is the push-broom imaging time t for the initial point of the target area. A ;

[0024] Step 3.5: Calculate the position vector R of the endpoint in the Earth-fixed coordinate system based on the latitude and longitude information of the endpoint in the target area. fe ;

[0025] Step 3.6: Based on the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment... fo (t), to obtain the position vector R of the endpoint in the satellite orbit coordinate system. oe (t), the expression is:

[0026] R oe (t)=C fo (t)R fe

[0027] Step 3.7: According to R oe The x-component R of the unit vector of (t) along the x-axis oeu (1) Calculate the elevation angle θ of the satellite pointing to the end point of the target area at each time. e (t), the expression is:

[0028]

[0029] Step 3.8: Solve for the pitch angle θ eThe (t) sequence contains two time points θ. e The distance |R| between the endpoint of the target area and the satellite is equal to zero. oe (t)| A smaller time is the push-broom imaging time t for the end point of the target area. B .

[0030] Preferably, in step 4, based on the principle of optimizing imaging spatial resolution, the starting time point T of the compensation imaging period is... A and the final time point T B They are respectively:

[0031]

[0032]

[0033] Preferably, in step 5, the latitude and longitude of the target point that the satellite optical axis should point to at each moment during the compensation imaging period are linearly planned based on the latitude and longitude information of the starting and ending points of the target area. Then, combined with the number of satellite orbital elements at each moment during the compensation imaging period, the required pitch angle θ(t) and roll angle of the satellite optical axis pointing to the corresponding ground target point at each moment are calculated. The calculation process for the two angles includes the following steps:

[0034] Step 5.1: For a given time t, calculate the position vector R of the target point in the Earth-fixed coordinate system based on the latitude and longitude information of the target point at that time. f (t);

[0035] Step 5.2: Combine the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at this moment. fo (t), obtain the position vector R of the target point in the satellite orbit coordinate system. o (t), the expression is:

[0036] R o (t)=C fo (t)R f (t)

[0037] Step 5.3: According to R o The x-component R of the unit vector of (t) along the x-axis ou (1) and y-axis component R ou (2) Calculate the elevation angle θ(t) and roll angle of the satellite pointing towards the target point at that moment. The expression is:

[0038] θ(t)=arcsin(R ou (1)),

[0039]

[0040] Preferably, in step 6, calculating the satellite yaw angle includes the following steps:

[0041] Step 6.1: Based on the target point's latitude and longitude and satellite orbit information at each moment during the compensation imaging period, as well as the elevation angle θ(t) and roll angle obtained in the previous step... Based on the angular velocity information, determine the transformation matrix C from the Earth-fixed coordinate system to the payload image plane coordinate system. fp (t), obtain the projection position vector R of the ground target point in the load image plane coordinate system. p (t), the expression is:

[0042] R p (t)=C fp (t)R f (t)

[0043] Step 6.2: For R p (t) Differentiate to obtain the image velocity vector V p (t), the expression is:

[0044]

[0045] Step 6.3: The yaw angle ψ(t) is:

[0046]

[0047] Among them, V p1 (t), V p2 (t) and V p3 (t) represents the forward, lateral, and longitudinal image displacement velocities of the image plane, respectively.

[0048] The motion-compensated imaging system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer, according to the present invention, comprises:

[0049] Module M1: Defines the latitude and longitude information of the starting and ending points of the ground target area, the imaging compensation factor, and the initial orbital elements of the satellite;

[0050] Module M2: Recursively calculates the number of satellite orbit elements in the next orbital period based on the initial satellite orbit elements;

[0051] Module M3: Based on the latitude and longitude information of the starting and ending points of the ground target area and the recursive results of the satellite orbital elements, determine the push-broom imaging time for the initial point of the target area and the push-broom imaging time for the ending point of the target area;

[0052] Module M4: Based on the optimization principles of imaging compensation factor and imaging spatial resolution, the start and end time points of the compensation imaging period are designed;

[0053] Module M5: Based on the real-time satellite orbit elements and ground target area information during the compensation imaging period, design the guidance rules for the satellite pitch and roll angles at various moments during the compensation imaging period.

[0054] Module M6: Calculates the yaw angle based on the principle that the direction of optical axis movement is consistent with the direction of target phase shift velocity. The result of the yaw angle calculation is the guidance law for the satellite yaw angle.

[0055] Preferably, in module M1, the latitude and longitude information of the starting point and ending point of the ground target area, the imaging compensation factor k, and the six initial orbital elements of the satellite are set, including the orbital semi-major axis a0, inclination i0, eccentricity e0, right ascension of the ascending node Ω0, argument of perigee ω0, and true perigee f0;

[0056] In module M2, based on the initial six orbital elements of the satellite, in addition to the two-body motion, the non-spherical perturbation of the Earth, the gravitational perturbation of the Sun and Moon, atmospheric drag, and light pressure are added. Based on the orbital mechanics equations, the six orbital elements of the satellite in the subsequent orbital period are recursively calculated, including the orbital semi-major axis a(t), inclination i(t), eccentricity e(t), right ascension of the ascending node Ω(t), argument of perigee ω(t), and true perigee f(t).

[0057] In module M3, the push-broom imaging time t for the initial point of the target area is determined based on the latitude and longitude information of the starting and ending points of the target area and the recursive result of the satellite orbital elements. A and push-broom imaging time t for the end point of the target region B , where t A t is the time when the elevation angle required for the initial point of the satellite's optical axis pointing towards the target area is 0°. B The calculation process for the moment when the required elevation angle of the satellite's optical axis pointing to the end point of the target area is 0° includes the following modules:

[0058] Module M3.1: Calculates the position vector R of the initial point in the Earth-fixed coordinate system based on the latitude and longitude information of the initial point in the target area. fs ;

[0059] Module M3.2: Calculate the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment within one orbital period, based on the satellite orbital elements at each moment. fo (t), to obtain the position vector R of the initial point in the satellite orbit coordinate system. os (t), the expression is:

[0060] R os (t)=C fo (t)R fs

[0061] Module M3.3: Based on R os The x-component R of the unit vector of (t) along the x-axis osu (1) Calculate the elevation angle θ of the satellite pointing to the initial point of the target area at each time. s (t), the expression is:

[0062] θ s (t)=arcsin(R osu (1)),

[0063] Module M3.4: Solved pitch angle θ s The (t) sequence contains two time points θ. s The value equals zero, where the distance |R| between the initial point of the target area and the satellite is zero. os (t)| A smaller time is the push-broom imaging time t for the initial point of the target area. A ;

[0064] Module M3.5: Calculates the position vector R of the endpoint in the Earth-fixed coordinate system based on the latitude and longitude information of the endpoint in the target area. fe ;

[0065] Module M3.6: Based on the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment. fo (t), to obtain the position vector R of the endpoint in the satellite orbit coordinate system. oe (t), the expression is:

[0066] R oe (t)=C fo (t)R fe

[0067] Module M3.7: Based on R oe The x-component R of the unit vector of (t) along the x-axis oeu (1) Calculate the elevation angle θ of the satellite pointing to the end point of the target area at each time. e (t), the expression is:

[0068] θ e (t)=arcsin(R oeu (1)),

[0069] Module M3.8: Solved pitch angle θ e The (t) sequence contains two time points θ. e The distance |R| between the endpoint of the target area and the satellite is equal to zero. oe (t)| A smaller time is the push-broom imaging time t for the end point of the target area. B .

[0070] Preferably, in module M4, based on the principle of optimizing imaging spatial resolution, the starting time point T of the compensation imaging period is... A and the final time point T B They are respectively:

[0071]

[0072]

[0073] Preferably, in module M5, the latitude and longitude of the target point that the satellite optical axis should point to at each moment during the compensation imaging period are linearly planned based on the latitude and longitude information of the starting and ending points of the target area. Then, combined with the orbital elements of the satellite at each moment during the compensation imaging period, the required pitch angle θ(t) and roll angle of the satellite optical axis pointing to the corresponding ground target point at each moment are calculated. The calculation process for the two angles includes the following modules:

[0074] Module M5.1: For a given time t, calculate the position vector R of the target point in the Earth-fixed coordinate system based on the latitude and longitude information of the target point at that time. f (t);

[0075] Module M5.2: Combines the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at this moment. fo (t), obtain the position vector R of the target point in the satellite orbit coordinate system. o (t), the expression is:

[0076] R o (t)=C fo (t)R f (t)

[0077] Module M5.3: Based on R o The x-component R of the unit vector of (t) along the x-axis ou (1) and y-axis component R ou (2) Calculate the elevation angle θ(t) and roll angle of the satellite pointing towards the target point at that moment. The expression is:

[0078] θ(t)=arcsin(R ou (1)),

[0079]

[0080] Preferably, module M6, which calculates the satellite yaw angle, includes the following modules:

[0081] Module M6.1: Based on the target point's latitude and longitude and satellite orbit information at each moment during the compensation imaging period, as well as the pitch angle θ(t) and roll angle obtained in the previous module. Based on the angular velocity information, determine the transformation matrix C from the Earth-fixed coordinate system to the payload image plane coordinate system. fp (t), obtain the projection position vector R of the ground target point in the load image plane coordinate system. p (t), the expression is:

[0082] R p (t)=C fp (t)R f (t)

[0083] Module M6.2: For R p (t) Differentiate to obtain the image velocity vector V p (t), the expression is:

[0084]

[0085] Module M6.3: Yaw angle ψ(t) is:

[0086]

[0087] Among them, V p1 (t), V p2 (t) and V p3 (t) represents the forward, lateral, and longitudinal image displacement velocities of the image plane, respectively.

[0088] Compared with the prior art, the present invention has the following beneficial effects:

[0089] (1) The method provided by the present invention can realize precise motion compensation imaging of satellites for any location and direction of the Earth's surface. The latitude and longitude information of the target area and the compensation factor can be set freely by humans. The method has good applicability and can be used for various motion compensation imaging tasks.

[0090] (2) The method provided by the present invention adopts a nonlinear guidance strategy for the satellite's three-axis attitude, which can realize linear push-broom observation and ensure uniform motion compensation imaging of each point on the ground strip during the imaging process.

[0091] (3) Compared with previous methods to improve the signal-to-noise ratio, the present invention does not require modification of the imaging spectrometer. The existing traditional imaging spectrometer can be directly fixed and installed on the satellite, which reduces the design and manufacturing difficulty of the imaging spectrometer. Compared with the motion compensation method based on the compensation scanning mirror, the present invention improves the pixel integration time by adjusting the optical axis push-broom speed to the ground through the whole satellite maneuver. There is no need to add a compensation scanning mirror on the satellite, which can avoid the problems of increased satellite weight, increased satellite design difficulty and increased launch cost caused by the use of scanning mirror. Attached Figure Description

[0092] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0093] Figure 1 A calculation flowchart for a motion-compensated imaging method to improve the signal-to-noise ratio of a spaceborne imaging spectrometer, provided by the present invention;

[0094] Figure 2 A schematic diagram illustrating a motion-compensated imaging method for improving the signal-to-noise ratio of a spaceborne imaging spectrometer, provided by the present invention;

[0095] Figures 3a to 3f The figures shown are the planning results of three-axis attitude angles and angular velocities for a set of simulation examples provided by this invention. Detailed Implementation

[0096] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0097] Example 1

[0098] This invention provides a motion-compensated imaging method to improve the signal-to-noise ratio of a spaceborne imaging spectrometer, such as... Figure 1 As shown, the specific steps include the following:

[0099] Step 1: Set the starting point latitude and longitude of the target area on the ground, such as... Figure 2 As shown at midpoint A, set the latitude and longitude of the endpoint, as follows: Figure 2 As shown at midpoint B, set the required imaging compensation factor k, and the six initial orbital elements of the satellite, including the semi-major axis a0, inclination i0, eccentricity e0, right ascension of the ascending node Ω0, argument of perigee ω0, and true perigee f0;

[0100] Step 2: Based on the initial orbital elements of the satellite, recursively deduce the satellite orbital elements for the next orbital period, including the semi-major axis a(t), inclination i(t), eccentricity e(t), right ascension of the ascending node Ω(t), argument of perigee ω(t), and true anomaly f(t);

[0101] Step 3: Based on the latitude and longitude information of the starting point A and ending point B of the target area and the recursive result of the satellite orbital elements, determine the push-broom imaging time t for the initial point of the target area. A and push-broom imaging time t for the end point of the target region B . t A and tB The specific calculation process includes the following steps:

[0102] Step 3.1: Calculate the position vector R of the initial point A in the Earth-fixed coordinate system based on the latitude and longitude information of the initial point A in the target area. fs ;

[0103] Step 3.2: Considering factors such as Earth's rotation, calculate the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment within one orbital period, based on the satellite orbital elements at each moment. fo (t), to obtain the position vector R of the initial point A in the satellite orbit coordinate system. os (t), the expression is:

[0104] R os (t)=C fo (t)R fs (1)

[0105] Step 3.3: According to R os The x-component R of the unit vector of (t) along the x-axis osu (1) Calculate the elevation angle θ of the satellite pointing to the initial point A of the target area at each time. s (t), the expression is:

[0106]

[0107] Step 3.4: The pitch angle θ obtained from the above steps s The (t) sequence will contain two time points θ. s The value equals zero, where the distance |R| between the initial point A of the target region and the satellite is zero. os (t)| The smaller time is the push-broom imaging time t for point A. A At this time, the elevation angle of the satellite pointing to point A is 0°, such as Figure 2 As shown.

[0108] Step 3.5: Calculate the position vector R of endpoint B in the Earth-fixed coordinate system based on the latitude and longitude information of endpoint B in the target area. fe ;

[0109] Step 3.6: Based on the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment... fo (t), to obtain the position vector R of the endpoint B in the satellite orbit coordinate system. oe (t), the expression is:

[0110] R oe (t)=C fo (t)R fe (3)

[0111] Step 3.7: According to R oe The x-component R of the unit vector of (t) along the x-axis oeu (1) Calculate the elevation angle θ of the satellite pointing to the end point B of the target area at each time. e (t), the expression is:

[0112]

[0113] Step 3.8: The pitch angle θ obtained from the above steps e The (t) sequence will contain two time points θ. e The distance |R| between the target region endpoint B and the satellite is equal to zero. oe (t)| The smaller time is the push-broom imaging time t for point B. B At this moment, the elevation angle of the satellite pointing to point B is 0°, as shown below. Figure 2 As shown.

[0114] Step 4: Based on the principle of optimizing imaging spatial resolution, compensate for the starting time point T of the imaging period. A and the final time point T B They are respectively:

[0115]

[0116]

[0117] See the diagram of the compensation imaging period. Figure 2 .

[0118] Step 5: Based on the latitude and longitude information of the starting point A and ending point B of the target area, use linear interpolation to plan the latitude and longitude of the target point that the satellite optical axis should point to at each moment during the compensation imaging period. Then, combine the orbital elements of the satellite at each moment during the compensation imaging period to calculate the required pitch angle θ(t) and roll angle of the satellite optical axis pointing to the corresponding ground target point at each moment. The specific calculation process for the two angles includes the following steps:

[0119] Step 5.1: For a given time t, calculate the position vector R of the target point in the Earth-fixed coordinate system based on the latitude and longitude information of the target point at that time. f (t);

[0120] Step 5.2: Combine the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at this moment. fo (t), obtain the position vector R of the target point in the satellite orbit coordinate system. o (t), the expression is:

[0121] R o (t)=C fo (t)Rf (t) (7)

[0122] Step 5.3: According to R o The x-component R of the unit vector of (t) along the x-axis ou (1) and y-axis component R ou (2) Calculate the elevation angle θ(t) and roll angle of the satellite pointing towards the target point at that moment. The expression is:

[0123]

[0124]

[0125] Step 6: Calculating the satellite yaw angle includes the following steps:

[0126] Step 6.1: Based on the compensation imaging time period T A ~T B The target point's latitude and longitude and satellite orbit information at each moment, as well as the pitch angle θ(t) and roll angle obtained in the previous step. Based on the angular velocity information, determine the transformation matrix C from the Earth-fixed coordinate system to the payload image plane coordinate system. fp (t), obtain the projection position vector R of the ground target point in the load image plane coordinate system. p (t), the expression is:

[0127] R p (t)=C fp (t)R f (t) (10)

[0128] Step 6.2: For R p (t) Differentiate to obtain the image velocity vector V p (t), the expression is:

[0129]

[0130] Step 6.3: The yaw angle ψ(t) is given by the expression:

[0131]

[0132] Without loss of generality, a set of simulation examples are given below to illustrate the effectiveness of the method of the present invention.

[0133] Perform step 1, setting the starting point A of the ground target area to longitude 51.6° and latitude -3.03°, and the ending point B to longitude 52.2° and latitude -3.70°. The arc distance between the two points along the Earth's surface is approximately 100km. Set the required imaging compensation factor k to 8, and the initial six elements of the satellite orbit: semi-major axis a0 = 6771km, inclination i0 = 45°, eccentricity e0 = 0.001, right ascension of ascending node Ω0 = 50°, argument of perigee ω0 = 0°, and true anomaly f0 = 0°.

[0134] Perform step 2 to obtain the satellite orbital elements for the next orbital period, semi-major axis a(t), inclination i(t), eccentricity e(t), right ascension of ascending node Ω(t), argument of perigee ω(t), and true anomaly f(t);

[0135] Perform step 3 to obtain the push-broom imaging time t for the initial point of the target area. A The push-broom imaging time t for the endpoint of the target region is 2830.9 s from the initial time. B The time was 2845.4s, meaning that under normal push-broom imaging conditions, the push-broom imaging time for the AB segment of the ground surface was 14.5s.

[0136] Step 4: Based on the principle of optimizing imaging spatial resolution and according to the 8x compensation, the starting time point T of the compensated imaging period can be obtained. A The time is 2780.2s, and the final time point T is... B The time was 2896.2s, and the time for compensation imaging was 116s;

[0137] By performing steps 5 and 6, 8x motion compensation can be achieved, and the satellite pitch angle θ(t) and roll angle during the entire compensation imaging period can be obtained. The calculation results for the yaw angle ψ(t) and the angular velocities of the three are shown in Figure 3.

[0138] The simulation results show that this method indeed achieves an 8-fold increase in motion-compensated imaging time, increasing the time from 14.5 seconds for pushbroom imaging with a zero elevation angle to 116 seconds for compensated imaging. Throughout the compensated imaging process, the elevation angle nonlinearly changes from 41.5° to -41.5° to adjust the optical axis and achieve motion compensation; the roll angle nonlinearly changes from -2.40° to 2.40° to ensure the satellite's optical axis accurately points to the ground target, compensating for the Earth's rotation; and the yaw angle nonlinearly changes to ensure image shift matching. The three-axis attitude angles work together to complete the motion-compensated imaging task.

[0139] Example 2

[0140] The present invention also provides a motion compensation imaging system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer. The motion compensation imaging system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer can be implemented by executing the process steps of the motion compensation imaging method for improving the signal-to-noise ratio of a spaceborne imaging spectrometer. That is, those skilled in the art can understand the motion compensation imaging method for improving the signal-to-noise ratio of a spaceborne imaging spectrometer as a preferred embodiment of the motion compensation imaging system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer.

[0141] The motion-compensated imaging system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer, provided by the present invention, comprises: Module M1: defining the latitude and longitude information of the starting and ending points of the ground target area, the imaging compensation factor, and the initial orbital elements of the satellite; Module M2: recursively calculating the number of satellite orbital elements in the subsequent orbital period based on the initial orbital elements of the satellite; Module M3: determining the push-broom imaging time for the initial point of the target area and the push-broom imaging time for the ending point of the target area based on the latitude and longitude information of the starting and ending points of the ground target area and the recursive result of the number of satellite orbital elements; Module M4: designing the starting and ending time points of the compensation imaging period based on the imaging compensation factor and the principle of optimizing imaging spatial resolution; Module M5: designing the guidance rules for the satellite pitch angle and roll angle at each moment during the compensation imaging period based on the real-time satellite orbital elements and ground target area information during the compensation imaging period; Module M6: calculating the yaw angle based on the principle that the direction of optical axis movement is consistent with the direction of target phase shift velocity, and the calculation result of the yaw angle is the guidance rule for the satellite yaw angle.

[0142] In module M1, the latitude and longitude information of the starting point and ending point of the ground target area, the imaging compensation factor k, and the six initial orbital elements of the satellite are set, including the orbital semi-major axis a0, inclination i0, eccentricity e0, right ascension of the ascending node Ω0, argument of perigee ω0, and true perigee f0.

[0143] In module M2, based on the initial six orbital elements of the satellite, in addition to the two-body motion, the non-spherical perturbation of the Earth, the gravitational perturbation of the Sun and Moon, atmospheric drag, and light pressure are added. Based on the orbital mechanics equations, the six orbital elements of the satellite in the subsequent orbital period are recursively calculated, including the orbital semi-major axis a(t), inclination i(t), eccentricity e(t), right ascension of the ascending node Ω(t), argument of perigee ω(t), and true perigee f(t).

[0144] In module M3, the push-broom imaging time t for the initial point of the target area is determined based on the latitude and longitude information of the starting and ending points of the target area and the recursive result of the satellite orbital elements. A and push-broom imaging time t for the end point of the target region B , where t A t is the time when the elevation angle required for the initial point of the satellite's optical axis pointing towards the target area is 0°.B The calculation process for the moment when the required elevation angle of the satellite's optical axis pointing to the end point of the target area is 0° includes the following modules:

[0145] Module M3.1: Calculates the position vector R of the initial point in the Earth-fixed coordinate system based on the latitude and longitude information of the initial point in the target area. fs ;

[0146] Module M3.2: Calculate the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment within one orbital period, based on the satellite orbital elements at each moment. fo (t), to obtain the position vector R of the initial point in the satellite orbit coordinate system. os (t), the expression is:

[0147] R os (t)=C fo (t)R fs

[0148] Module M3.3: Based on R os The x-component R of the unit vector of (t) along the x-axis osu (1) Calculate the elevation angle θ of the satellite pointing to the initial point of the target area at each time. s (t), the expression is:

[0149] θ s (t)=arcsin(R osu (1)),

[0150] Module M3.4: Solved pitch angle θ s The (t) sequence contains two time points θ. s The value equals zero, where the distance |R| between the initial point of the target area and the satellite is zero. os (t)| A smaller time is the push-broom imaging time t for the initial point of the target area. A ;

[0151] Module M3.5: Calculates the position vector R of the endpoint in the Earth-fixed coordinate system based on the latitude and longitude information of the endpoint in the target area. fe ;

[0152] Module M3.6: Based on the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment. fo (t), to obtain the position vector R of the endpoint in the satellite orbit coordinate system. oe (t), the expression is:

[0153] R oe (t)=C fo (t)R fe

[0154] Module M3.7: Based on R oe The x-component R of the unit vector of (t) along the x-axis oeu (1) Calculate the elevation angle θ of the satellite pointing to the end point of the target area at each time. e (t), the expression is:

[0155] θ e (t)=arcsin(R oeu (1)),

[0156] Module M3.8: Solved pitch angle θ e The (t) sequence contains two time points θ. e The distance |R| between the endpoint of the target area and the satellite is equal to zero. oe (t)| A smaller time is the push-broom imaging time t for the end point of the target area. B .

[0157] In module M4, based on the principle of optimizing imaging spatial resolution, the starting time point T of the compensation imaging period is calculated. A and the final time point T B They are respectively:

[0158]

[0159]

[0160] In module M5, the latitude and longitude of the target point that the satellite optical axis should point to at each moment during the compensation imaging period are linearly planned based on the latitude and longitude information of the starting and ending points of the target area. Then, combined with the orbital elements of the satellite at each moment during the compensation imaging period, the required pitch angle θ(t) and roll angle of the satellite optical axis pointing to the corresponding ground target point at each moment are calculated. The calculation process for the two angles includes the following modules:

[0161] Module M5.1: For a given time t, calculate the position vector R of the target point in the Earth-fixed coordinate system based on the latitude and longitude information of the target point at that time. f (t);

[0162] Module M5.2: Combines the transformation matrix C from the Earth-fixed coordinate system to the satellite orbital coordinate system at this moment. fo (t), obtain the position vector R of the target point in the satellite orbit coordinate system. o (t), the expression is:

[0163] R o (t)=C fo (t)R f (t)

[0164] Module M5.3: Based on R o The x-component R of the unit vector of (t) along the x-axis ou (1) and y-axis component R ou (2) Calculate the elevation angle θ(t) and roll angle of the satellite pointing towards the target point at that moment. The expression is:

[0165] θ(t)=arcsin(R ou (1)),

[0166]

[0167] Module M6, which calculates the satellite yaw angle, includes the following modules:

[0168] Module M6.1: Based on the target point's latitude and longitude and satellite orbit information at each moment during the compensation imaging period, as well as the pitch angle θ(t) and roll angle obtained in the previous module. Based on the angular velocity information, determine the transformation matrix C from the Earth-fixed coordinate system to the payload image plane coordinate system. fp (t), obtain the projection position vector R of the ground target point in the load image plane coordinate system. p (t), the expression is:

[0169] R p (t)=C fp (t)R f (t)

[0170] Module M6.2: For R p (t) Differentiate to obtain the image velocity vector V p (t), the expression is:

[0171]

[0172] Module M6.3: Yaw angle ψ(t) is:

[0173]

[0174] Among them, V p1 (t), V p2 (t) and V p3 (t) represents the forward, lateral, and longitudinal image displacement velocities of the image plane, respectively.

[0175] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0176] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A motion-compensated imaging method for improving the signal-to-noise ratio of a spaceborne imaging spectrometer, characterized in that, include: Step 1: Define the latitude and longitude information of the starting and ending points of the ground target area, the imaging compensation factor, and the initial orbital elements of the satellite; Step 2: Based on the initial orbital elements of the satellite, recursively calculate the number of satellite orbital elements for the next orbital period; Step 3: Based on the latitude and longitude information of the starting and ending points of the ground target area and the recursive results of the satellite orbital elements, determine the push-broom imaging time for the initial point of the target area and the push-broom imaging time for the ending point of the target area; Step 4: Based on the principles of optimizing the imaging compensation factor and imaging spatial resolution, design the start and end time points of the compensation imaging period; Step 5: Design the guidance rules for the satellite pitch and roll angles at each moment during the compensation imaging period based on the real-time satellite orbit elements and ground target area information during the compensation imaging period. Step 6: Calculate the yaw angle based on the principle that the direction of optical axis movement is consistent with the direction of target phase shift velocity. The result of the yaw angle calculation is the guidance law of satellite yaw angle. In step 1, the latitude and longitude information of the starting point and the ending point of the ground target area are set, along with the imaging compensation factor. k And the six initial orbital elements of the satellite, including the semi-major axis of the orbit. a 0. Inclination angle i 0. Eccentricity e 0. Right ascension of the ascending node Ω 0. Perigee angle ω 0 and true nearest angle f 0; In step 2, based on the initial six orbital elements of the satellite, in addition to the two-body motion, the Earth's non-spherical perturbation, the gravitational perturbation of the Sun and Moon, atmospheric drag, and light pressure are added. The six orbital elements for the subsequent orbital period are then recursively calculated using the orbital mechanics equations, including the semi-major axis of the orbit. a ( t ),inclination i ( t ), eccentricity e ( t ), ascending node right ascension Ω ( t Perimeter argument ω ( t True nearest angle f ( t ); In step 3, the push-broom imaging time for the initial point of the target area is determined based on the latitude and longitude information of the starting and ending points of the target area and the recursive result of the satellite orbital elements. t A Push-broom imaging time for the end point of the target region t B ,in, t A This refers to the moment when the satellite's optical axis points to the initial point of the target region with a required elevation angle of 0°. t B The calculation process for the moment when the required elevation angle of the satellite's optical axis pointing to the end point of the target area is 0° includes the following steps: Step 3.1: Calculate the position vector of the initial point in the Earth-fixed coordinate system based on the latitude and longitude information of the initial point in the target area. R fs ; Step 3.2: Based on the satellite orbital elements at each moment within one orbital period, calculate the transformation matrix from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment. C fo ( t This allows us to obtain the position vector of the initial point in the satellite orbit coordinate system. R os ( t The expression is: Step 3.3: According to R os ( t The unit vector in x Components of the axis R osu (1) Calculate the elevation angle of the satellite pointing to the initial point of the target area at each time. θ s ( t The expression is: Step 3.4: Solving for the pitch angle θ s ( t The sequence contains two time points. θ s The value is equal to zero, where the distance between the initial point of the target area and the satellite is zero. |R os ( t ) | A smaller timeframe is the push-broom imaging timeframe for the initial point of the target area. t A ; Step 3.5: Calculate the position vector of the endpoint in the Earth-fixed coordinate system based on the latitude and longitude information of the endpoint in the target area. R fe ; Step 3.6: Based on the transformation matrix from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment. C fo ( t This allows us to obtain the position vector of the endpoint in the satellite orbit coordinate system. R oe ( t The expression is: Step 3.7: According to R oe ( t The unit vector in x Components of the axis R oeu (1) Calculate the elevation angle of the satellite pointing to the end point of the target area at each time. θ e ( t The expression is: Step 3.8: Solving for the pitch angle θ e ( t The sequence contains two time points. θ e The value is zero, where the distance between the endpoint of the target area and the satellite is zero. |R oe ( t ) | A smaller timeframe is the push-broom imaging timeframe for the endpoint of the target region. t B ; In step 5, the latitude and longitude of the target point that the satellite optical axis should point to at each moment during the compensation imaging period are linearly planned based on the latitude and longitude information of the starting and ending points of the target area. Then, combined with the orbital elements of the satellite at each moment during the compensation imaging period, the required elevation angle of the satellite optical axis pointing to the corresponding ground target point at each moment is calculated. θ ( t and roll angle φ ( t The calculation process for the two angles includes the following steps: Step 5.1: For a specific moment t Based on the latitude and longitude information of the target point at that moment, the position vector of the target point in the Earth-fixed coordinate system is calculated. R f ( t ); Step 5.2: Combine the transformation matrix from the Earth-fixed coordinate system to the satellite orbital coordinate system at this moment. C fo ( t This allows us to obtain the position vector of the target point in the satellite orbit coordinate system. R o ( t The expression is: Step 5.3: According to R o ( t The unit vector in x Components of the axis R ou (1) and y Axial components R ou (2) Calculate the elevation angle of the satellite pointing to the target point at that moment. θ ( t and roll angle φ ( t The expression is: 。 2. The motion-compensated imaging method for improving the signal-to-noise ratio of a spaceborne imaging spectrometer according to claim 1, characterized in that, In step 4, based on the principle of optimizing imaging spatial resolution, the starting time point of the imaging period is compensated. T A and end time point T B They are respectively: 。 3. The motion-compensated imaging method for improving the signal-to-noise ratio of a spaceborne imaging spectrometer according to claim 1, characterized in that, Step 6, calculating the satellite yaw angle, includes the following steps: Step 6.1: Based on the target point's latitude and longitude and satellite orbit information at each moment during the compensation imaging period, and the elevation angle obtained in the previous step... θ ( t and roll angle φ ( t Based on the information of the image and its angular velocity, determine the transformation matrix from the Earth-fixed coordinate system to the payload image plane coordinate system. C fp ( t This obtains the projected position vector of the ground target point in the load image plane coordinate system. R p ( t The expression is: Step 6.2: For R p ( t Differentiating the vector yields the image velocity vector. V p ( t The expression is: Step 6.3: Yaw Angle ψ ( t )for: in, , and These represent the forward, lateral, and longitudinal image movement velocities of the image plane, respectively.

4. A motion-compensated imaging system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer, characterized in that, include: Module M1: Defines the latitude and longitude information of the starting and ending points of the ground target area, the imaging compensation factor, and the initial orbital elements of the satellite; Module M2: Recursively calculates the number of satellite orbit elements in the next orbital period based on the initial satellite orbit elements; Module M3: Based on the latitude and longitude information of the starting and ending points of the ground target area and the recursive results of the satellite orbital elements, determine the push-broom imaging time for the initial point of the target area and the push-broom imaging time for the ending point of the target area; Module M4: Based on the optimization principles of imaging compensation factor and imaging spatial resolution, the start and end time points of the compensation imaging period are designed; Module M5: Based on the real-time satellite orbit elements and ground target area information during the compensation imaging period, design the guidance rules for the satellite pitch and roll angles at various moments during the compensation imaging period. Module M6: Calculates the yaw angle based on the principle that the direction of optical axis movement is consistent with the direction of target phase shift velocity. The result of the yaw angle calculation is the guidance law for the satellite yaw angle. In module M1, the latitude and longitude information of the starting point and ending point of the ground target area, as well as the imaging compensation factor, are set. k And the six initial orbital elements of the satellite, including the semi-major axis of the orbit. a 0. Inclination angle i 0. Eccentricity e 0. Right ascension of the ascending node Ω 0. Perigee angle ω 0 and true nearest angle f 0; In module M2, based on the initial six orbital elements of the satellite, in addition to two-body motion, the perturbations of Earth's non-spherical shape, the gravitational perturbations of the Sun and Moon, atmospheric drag, and light pressure are added. The six orbital elements for the subsequent orbital period are recursively calculated based on the orbital mechanics equations, including the orbital semi-major axis. a ( t ),inclination i ( t ), eccentricity e ( t ), ascending node right ascension Ω ( t Perimeter argument ω ( t True nearest angle f ( t ); In module M3, the push-broom imaging time for the initial point of the target area is determined based on the latitude and longitude information of the starting and ending points of the target area and the recursive result of the satellite orbital elements. t A Push-broom imaging time for the end point of the target region t B ,in, t A This refers to the moment when the satellite's optical axis points to the initial point of the target region with a required elevation angle of 0°. t B The calculation process for the moment when the required elevation angle of the satellite's optical axis pointing to the end point of the target area is 0° includes the following modules: Module M3.1: Calculates the position vector of the initial point in the Earth-fixed coordinate system based on the latitude and longitude information of the initial point in the target area. R fs ; Module M3.2: Calculates the transformation matrix from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment within one orbital period, based on the satellite orbital elements at each moment. C fo ( t This allows us to obtain the position vector of the initial point in the satellite orbit coordinate system. R os ( t The expression is: Module M3.3: According to R os ( t The unit vector in x Components of the axis R osu (1) Calculate the elevation angle of the satellite pointing to the initial point of the target area at each time. θ s ( t The expression is: Module M3.4: Solved pitch angle θ s ( t The sequence contains two time points. θ s The value is equal to zero, where the distance between the initial point of the target area and the satellite is zero. |R os ( t ) | A smaller timeframe is the push-broom imaging timeframe for the initial point of the target area. t A ; Module M3.5: Calculates the position vector of the endpoint in the Earth-fixed coordinate system based on the latitude and longitude information of the endpoint in the target area. R fe ; Module M3.6: Based on the transformation matrix from the Earth-fixed coordinate system to the satellite orbital coordinate system at each moment. C fo ( t This allows us to obtain the position vector of the endpoint in the satellite orbit coordinate system. R oe ( t The expression is: Module M3.7: According to R oe ( t The unit vector in x Components of the axis R oeu (1) Calculate the elevation angle of the satellite pointing to the end point of the target area at each time. θ e ( t The expression is: Module M3.8: Solved pitch angle θ e ( t The sequence contains two time points. θ e The value is zero, where the distance between the endpoint of the target area and the satellite is zero. |R oe ( t ) | A smaller timeframe is the push-broom imaging timeframe for the endpoint of the target region. t B ; In module M5, the latitude and longitude of the target point that the satellite optical axis should point to at each moment during the compensation imaging period are linearly planned based on the latitude and longitude information of the starting and ending points of the target area. Then, combined with the number of satellite orbital elements at each moment during the compensation imaging period, the required elevation angle of the satellite optical axis pointing to the corresponding ground target point at each moment is calculated. θ ( t and roll angle φ ( t The calculation process for the two angles includes the following modules: Module M5.1: For a specific moment t Based on the latitude and longitude information of the target point at that moment, the position vector of the target point in the Earth-fixed coordinate system is calculated. R f ( t ); Module M5.2: Combines the transformation matrix from the Earth-fixed coordinate system to the satellite orbital coordinate system at this moment. C fo ( t This allows us to obtain the position vector of the target point in the satellite orbit coordinate system. R o ( t The expression is: Module M5.3: According to R o ( t The unit vector in x Components of the axis R ou (1) and y Axial components R ou (2) Calculate the elevation angle of the satellite pointing to the target point at that moment. θ ( t and roll angle φ ( t The expression is: 。 5. The motion-compensated imaging system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer according to claim 4, characterized in that, In module M4, based on the principle of optimizing imaging spatial resolution, the starting time point of the compensation imaging period is determined. T A and end time point T B They are respectively: 。 6. The motion-compensated imaging system for improving the signal-to-noise ratio of a spaceborne imaging spectrometer according to claim 4, characterized in that, Module M6, which calculates the satellite yaw angle, includes the following modules: Module M6.1: Based on the target point's latitude and longitude and satellite orbit information at each moment during the compensation imaging period, and the elevation angle obtained in the previous module. θ ( t and roll angle φ ( t Based on the information of the image and its angular velocity, determine the transformation matrix from the Earth-fixed coordinate system to the payload image plane coordinate system. C fp ( t This obtains the projected position vector of the ground target point in the load image plane coordinate system. R p ( t The expression is: Module M6.2: For R p ( t Differentiating the vector yields the image velocity vector. V p ( t The expression is: Module M6.3: Yaw Angle ψ ( t )for: in, , and These represent the forward, lateral, and longitudinal image movement velocities of the image plane, respectively.

Images