Space target spectral imaging simulation method based on space observation scene

Abstract

The application provides a space target spectral imaging simulation method based on a space observation scene, comprising the following steps: (1) inputting space target and spectral imager attitude and orbit parameters, simulation time parameters; (2) establishing a space observation scene by using the parameters in step (1), and obtaining position, attitude and speed information; (3) performing target visibility analysis, first performing a shadow area judgment; (4) performing a line-of-sight occlusion judgment; (5) performing an imager field of view constraint judgment; (6) performing radiation transmission modeling, analyzing facet visibility and calculating a spectral radiance image at the entrance pupil of the spectral imager; (7) performing spectral imager modeling, and generating a simulation image by using the spectral radiance image at the entrance pupil obtained in step (6). The method combines orbit and relative motion for dynamic simulation, considers factors affecting target visibility in detail, considers material directional reflection characteristics and different facet visibility, and constructs a full-link simulation method under a space observation scene.

Description

Technical Field

[0001] This invention relates to a method for spectral imaging simulation of space targets in space-based observation scenarios, belonging to the field of optical imaging data acquisition, simulation and recording, and is applicable to the research on spectral simulation image generation in space-based observation scenarios. Background Technology

[0002] Space target surveillance is crucial for the development and sustainable development of outer space resources. Establishing space-based observation platforms is currently a vital means of detecting, identifying, and monitoring space targets, and the application of spectral analysis technology can provide richer information for space target detection. However, due to insufficient measured data, the high cost of launching and operating space-based remote sensing payloads, and the difficulty in obtaining high-quality optical observation data in deep space environments, current research often uses simulation analysis to compensate for the lack of measured data. Nevertheless, in my country, space-based imaging systems for space targets are still in the preliminary research stage, and imaging results are difficult to predict.

[0003] Existing simulation analysis work on space target observation can be divided into two main categories: space target detection simulation and space target observation data simulation.

[0004] Space target detection simulation refers to the simulation analysis of scenarios involving the detection of space targets using detectors, and it is a prerequisite for space target observation simulation. First, the detector searches for targets within its field of view. Then, the target is distinguished from the background or other non-target objects, tracked, and preliminarily classified and its characteristic information recorded. Researchers have used simulation methods to detect and track 100 pre-assigned geosynchronous orbit objects and 200 unassigned geosynchronous orbit objects using a space-based detector placed in a sun-synchronous orbit. Simulation analysis of the detectability of space targets in the infrared spectrum was also conducted, and the reflection and emission characteristics of the targets were modeled separately. Reflection sources include direct solar radiation, albedo radiation from the Earth and Moon, infrared thermal radiation from the Earth, and cosmic background radiation. Emission sources include the object's own heat generation and the energy radiation from its aerodynamic heating system. Noise sources involved in the simulation system mainly include absorption and scattering effects from the Earth's atmosphere and cosmic background radiation. Researchers have also used data-driven methods to model and simulate the future evolution of the number of targets based on spacecraft launch data and trends, and historical data on spacecraft explosions and clearance.

[0005] After a space target is detected, the observation data of the space target can be simulated under the corresponding observation conditions. For example, the photometric curve simulation analysis of geostationary orbit satellites of different shapes and sizes was carried out based on the Phong model. The results show that the simulation error of the satellite photometric curve considering the directional reflection characteristics is about 3%, which is much more accurate than the simulation results using the diffuse reflection model.

[0006] In summary, the existing space target observation simulation methods have three unresolved challenges: (1) a lack of modeling and simulation for near-range full-link spectral imaging of space targets; (2) the models employ numerous simplifications, treating the target as a Lambertian object without considering its directional reflection characteristics, resulting in significant discrepancies between simulation results and measured data; and (3) the lack of dynamic simulation incorporating orbital and relative motion, and the failure to consider in detail the three factors affecting target visibility in the space environment: ground shadow constraints, line-of-sight occlusion constraints, and imager field-of-view constraints. To provide a theoretical and data foundation for the feasibility analysis of using space-based observation platforms to detect and identify space targets, it is urgent to conduct full-link research on space target spectral imaging simulation based on space-based observation. Summary of the Invention

[0007] The purpose of this invention is to realize the entire chain of space target spectral imaging simulation based on space-based observation scenarios, and to provide a space target spectral imaging simulation method based on space-based observation scenarios.

[0008] The technical solution of this invention is as follows: A space-based observation scenario is established based on the actual orbital data of the space target and the spectral imager; various data of the space target and the spectral imager under dynamic scenarios are acquired; and a visualization analysis of the space target is performed based on the actual motion data. After the visualization analysis is completed, the surface visibility of the three-dimensional model of the space target is analyzed pixel by pixel. Considering the directional reflection characteristics of different materials, the observation angle is calculated sequentially for each visible surface element. The entrance pupil spectral radiance image of the spectral imager is calculated by combining the radiation transmission modeling results and the surface optical property modeling results of the space target. The imaging principle of the spectral imager is analyzed, and five aspects in the imaging process—radiative response, spectral response, motion blur, random noise, and image quantization—are modeled to finally obtain a simulated image of the space target based on the space-based observation scenario.

[0009] This invention is a space target spectral imaging simulation method based on space-based observation scenarios, the steps of which are as follows:

[0010] (1) Input the attitude and orbit parameters of the space target and the spectral imager, the simulation start and end times, and the simulation step size;

[0011] (2) Input the three types of parameters input in step (1) into STK: the attitude and orbit parameters of the space target and the spectral imager, the simulation start and end time, and the simulation step size. Establish a specific scenario for the space-based spectral imager to observe and image the space target. Obtain six types of parameters at each simulation moment: the position of the Earth in the geocentric coordinate system, the position and velocity of the space target, the position and velocity of the spectral imager, the position of the Sun, and the attitude of the space target in the space target trajectory coordinate system.

[0012] (3) Determine whether the space target is in the Earth's shadow zone at the current simulation time. Treat the space target as a point in the space-based observation scenario. First, use the position coordinates of the space target, the sun and the earth obtained in step (2), and use the cylindrical Earth shadow model to describe the Earth's shadow zone. Calculate whether the position coordinates of the space target are in the Earth's shadow zone. If the space target is in the Earth's shadow zone, the simulation at the current simulation time ends, enter the next simulation time and re-execute step (3), otherwise execute step (4).

[0013] (4) Determine whether the line of sight of the spectral imager is blocked by the Earth at the current simulation time. Using the position coordinates of the spectral imager, the space target and the Earth obtained in step (2), the Earth is regarded as a standard ellipsoid. Solve whether the line vector connecting the spectral imager and the space target intersects with the Earth. If there is no intersection or the two intersections are not located between the spectral imager and the space target, the line of sight of the spectral imager is not blocked by the Earth at the current simulation time. Execute step (5). Otherwise, the simulation at the current simulation time ends, enter the next simulation time and re-execute step (3).

[0014] (5) Make a field-of-view constraint judgment for the spectral imager at the current simulation time. Use the position coordinates of the spectral imager and the space target obtained in step (2) to construct the relative position relationship between the two. Calculate the boundary point set of the intersection coordinates of all probe rays and the object plane where the space target is located. Determine the single-scene coverage range that the spectral imager can achieve without attitude adjustment and the panoramic coverage range that can be achieved through attitude adjustment. If the space target is in both single-scene and panoramic coverage range at the current time, or the space target is in panoramic but not in single-scene range at the current time, and the space target is not in the ground shadow area or the line-of-view occlusion area and is in panoramic range at the next time, it indicates that the spectral imager can perform observation imaging. Execute step (6). Otherwise, the simulation at the current simulation time ends, enter the next simulation time and re-execute step (3).

[0015] (6) Model the transmission process of the radiation characteristics of the space target. Consider the three-dimensional detailed structure and material distribution of the space target. Segment the space target based on the triangular element representation method. Model the space target in three dimensions by determining the vertex, normal vector and corresponding material type of each triangular element. Use the three-dimensional model of the space target and the seven types of parameters obtained in step (2) to obtain the two radiation transmission paths and relative position relationship between the sun-space target-spectral imager and the earth-space target-spectral imager. Based on the space radiation transmission calculation method, obtain the solar radiation intensity and the earth albedo radiation intensity received at the space target. Use ray tracing to calculate the observation angle between the probe ray emitted by the spectral imager and the normal vector of the intersecting element in the two radiation transmission paths. Use the bidirectional reflection distribution function and the calculated observation angle to calculate the spectral reflectance of the two radiation transmission paths respectively. Combine the spectral radiation intensity and the spectral reflectance under the corresponding path to obtain the spectral radiance at the entrance pupil of the spectral imager. Complete the calculation of the entrance pupil spectral radiance image.

[0016] (7) Model the imaging process of the spectral imager, and establish the spectral imager imaging model by comprehensively analyzing five aspects: radiation response, spectral response, motion blur, random noise, and image quantization. The final simulation image is generated using the spectral radiance image at the entrance pupil obtained by step (6).

[0017] In step (1), the attitude and orbit parameters of the space target and the spectral imager, the simulation start and end times, and the simulation step size are input. The orbit parameters are defined in the six-root format, including the semi-major axis, eccentricity, orbital inclination, argument of the pericenter, longitude of the ascending node, and true anomaly. The attitude parameters of the space target include four types: solar three-axis stability, geostationary three-axis stability, solar spin, and geostationary spin. The simulation start and end times are defined in Coordinated Universal Time (UTC) format, and the simulation step size is in seconds.

[0018] In step (2), the three types of parameters input in step (1) are the attitude and orbit parameters of the space target and the spectral imager, the simulation start and end time, and the simulation step size. The specific scene of the space-based spectral imager observing and imaging the space target is established. The position of the Earth, the position and velocity of the space target, the position and velocity of the spectral imager, and the position of the Sun are obtained at each simulation moment in the geocentric-geocentric coordinate system. The attitude of the space target in the space target track coordinate system is also obtained. The parameters required for establishing the space-based observation scene are input into the STK to establish a specific observation scene of the space-based spectral imager observing and imaging the space target. Two types of information are obtained using the report format preset by the STK system. One type is the position and velocity of the space target, the position and velocity of the spectral imager, and the position of the Sun, based on the geocentric-geocentric coordinate system. The other type is the attitude angle of the space target based on the space target track coordinate system, including the roll angle, pitch angle, and yaw angle. When the position coordinates of the spectral imager, the space target, the Sun, and the Earth are all known at each simulation moment and are in the same coordinate system, the relative positional relationship is determined accordingly.

[0019] In step (3), it is determined whether the space target is in the Earth's shadow at the current simulation time. The space target is regarded as a point in the space-based observation scenario. First, the position coordinates of the space target, the sun and the earth obtained in step (2) are used to describe the Earth's shadow area using a cylindrical ground shadow model. The position coordinates of the space target are calculated to determine whether they are in the Earth's shadow area. If the space target is in the shadow area, the simulation at the current simulation time ends, and the next simulation time is entered and step (3) is executed again. Otherwise, step (4) is executed: Based on the relative positional relationship of the space target, the imager, the sun and the earth obtained in step (2), it is determined whether the space target is in the Earth's shadow at the current simulation time. The sunlight received at the space position near the earth is approximated as parallel light. A cylindrical ground shadow model is used to describe the Earth's shadow area. The angle between the geocentric vector of the target and the geocentric vector of the sun is calculated. The calculation formula is as follows:

[0020]

[0021] In the formula The vector obtained by representing the position coordinates of the target in the Earth-centered Earth-fixed coordinate system. Let α be the vector obtained by finding the position coordinates of the Sun in the Earth-centered Earth-fixed coordinate system, and α be the angle between the two vectors. 0 ≤ α ≤ π. When 0 ≤ α ≤ π / 2, the target is not in the Earth's shadow and can be observed. When π / 2 ≤ α ≤ π, if the target is not in the Earth's shadow, the following relationship must be satisfied:

[0022]

[0023] In the formula R eSince is a constant and defined as the average radius of the Earth, the constraint condition for a space target to be located in the non-shadow region under the cylindrical ground shadow model is:

[0024]

[0025] If the space target is in the Earth's shadow area, the simulation at the current simulation moment ends, and the next simulation moment begins and step (3) is executed again; otherwise, step (4) is executed.

[0026] In step (4), it is determined whether the line of sight of the spectral imager is blocked by the Earth at the current simulation moment. Using the position coordinates of the spectral imager, the space target and the Earth obtained in step (2), the Earth is regarded as a standard ellipsoid. It is calculated whether the line vector connecting the spectral imager and the space target intersects with the Earth. If there is no intersection or the two intersections are not located between the spectral imager and the space target, the line of sight of the spectral imager is not blocked by the Earth at the current simulation moment, and step (5) is executed. Otherwise, the simulation at the current simulation moment ends, and the next simulation moment is entered and step (3) is executed again: the space target and the spectral imager are regarded as a point in the space-based observation scenario, the Earth is regarded as a standard ellipsoid, and the detection ray vector is obtained by subtracting the coordinate vectors of the spectral imager and the space target obtained in step (2). The calculation method is as follows:

[0027] (kx,ky,kz)=(obj_x-sat_x,obj_y-sat_y,obj_z-sat_z)

[0028] In the formula, kx, ky, and kz are the three-dimensional coordinates of the probe ray vector, obj_x, obj_y, and obj_z are the three-dimensional coordinates of the space target in the geocentric-geostatic coordinate system, and sat_x, sat_y, and sat_z are the three-dimensional coordinates of the spectral imager in the geocentric-geostatic coordinate system. The coefficients of the simultaneous equations are obtained from the method for calculating whether a vector intersects with an ellipsoid in three-dimensional space:

[0029]

[0030] In the formula, A, B, and C are the polynomial coefficients in the simultaneous equations, and a, b, and c are the radii of the Earth on the x, y, and z axes, respectively. If the probe ray intersects the Earth, the calculation method is as follows:

[0031]

[0032]

[0033] In the formula, t1 and t2 are variables in the calculation process. Since the coordinates of the two intersection points are vectors, the constraint that the line of sight of the spectral imager is not blocked by the Earth is as follows:

[0034]

[0035] In the formula and The values ​​are (obj_x,obj_y,obj_z) and (sat_x,sat_y,sat_z). If the line of sight of the spectral imager is not blocked by the Earth at the current simulation time, step (5) is executed; otherwise, the simulation at the current simulation time ends, and the next simulation time is entered and step (3) is executed again.

[0036] In step (5), the field-of-view constraint of the spectral imager at the current simulation moment is determined. The relative positional relationship between the spectral imager and the spatial target is constructed using the position coordinates obtained in step (2). The boundary point set of the intersection coordinates of all probe rays and the object plane where the spatial target is located is calculated. The single-view coverage range that the spectral imager can achieve without attitude adjustment and the panoramic coverage range that can be achieved through attitude adjustment are determined. If the spatial target is simultaneously within both single-view and panoramic coverage at the current moment, or if the spatial target is in panoramic coverage but not within single-view coverage at the current moment, and the spatial target is not in the ground shadow area or the line-of-view obstruction area and is in panoramic coverage at the next moment, it indicates that the spectral imager can... Perform observation imaging and execute step (6); otherwise, the simulation ends at the current simulation moment, proceed to the next simulation moment, and re-execute step (3): Based on the determined relative position information, use imaging geometry to determine the single-scene coverage range and maximum coverage range of the spectral imager. The single-scene coverage range is defined as the imaging area that the spectral imager can actually observe at a specific moment and a specific attitude angle of the spectral imager. The maximum coverage range is the union of all imaging areas that the spectral imager can observe through attitude adjustment, assuming that the attitude adjustment time of the spectral imager is 0. The single-scene coverage range at a specific moment is a subset of the maximum coverage range at the same moment, that is:

[0037] C cat (t,i)=f(pos(t),yaw(t,i),pitch(t,i),roll(t,i),sensortype)

[0038] C poss (t)=∑ i C cat (t,i)

[0039]

[0040] In the formula, pos(t) is the relative positional relationship matrix of the spectral imager, the target, and the Earth at time t; yaw(t,i), pitch(t,i), and roll(t,i) are the i-th combination of the attitude angles of the spectral imager at time t, including yaw, pitch, and roll angles; sensortype represents the field of view angle of the spectral imager; and C... cat (t,i) represents the single-scene coverage of the spectral imager at time t and the i-th attitude angle combination, C poss (t,i) represents the maximum coverage area of ​​the spectral imager at time t, which is equal to the union of the coverage areas of all individual scenes at that time. f represents the coordinates of the intersection points of all probe rays and the object plane where the spatial target is located under the i-th attitude angle combination at time t. To save computational resources, the coverage area is defined as a rectangle, and the coverage area of ​​the spectral imager is represented by the boundary point set corresponding to the four vertices of the coverage area, thus obtaining the individual scene coverage area and the maximum coverage area. The probe ray vector at each vertex of the coverage area is calculated as follows:

[0041]

[0042] In the formula R x ,R y ,R z Let be a three-axis rotation matrix, e0 be the center detection ray vector of the spectral imager at time t, and set the center detection vector of the spectral imager at the initial simulation time to point from the spectral imager to the Earth's center. At non-initial simulation times, the center detection vector has the same direction as the previous simulation time. e is the detection ray vector at a vertex of the spectral imager's coverage area at time t. θ, φ, and ψ are the rotation angles of the detection ray vector at a vertex of the spectral imager's coverage area around the x, y, and z axes with the center detection ray as the reference. In the calculation of the single-scene coverage area, θ, φ, and ψ are substituted in as follows:

[0043]

[0044] In the formula, HFOV is the horizontal field of view of the spectral imager, and VFOV is the vertical field of view of the spectral imager. θ, φ, and ψ are substituted into the formula as follows during the calculation of the panoramic coverage:

[0045]

[0046] In the formula Roll max Pitch is the maximum roll angle of the spectral imager. maxLet be the maximum pitch angle of the spectral imager. Set the plane containing the spatial target to include the coordinates of the spatial target and perpendicular to the detection vector of the spectral imager center. Using the above formula, obtain the detection ray vectors at the four vertices of the single-scene coverage and panoramic coverage at the current simulation time, and calculate the intersection point set with the plane containing the spatial target. Then, determine whether the spatial target position coordinates at the current simulation time are within the maximum coverage or single-scene coverage. There are four situations. The first situation is that the spatial target is simultaneously within the single-scene and panoramic coverage at the current time, indicating that the spectral imager can observe and image the spatial target at the current simulation time. Execute step (6). The second situation is that the spatial target is in the panoramic but not in the single-scene range at the current time. At the next moment, the spatial target is not in the ground shadow area or the line-of-sight obstruction area and is in the panoramic range. This indicates that the spectral imager cannot observe and image at the current moment, but can observe and image at the next simulation moment through attitude adjustment. The simulation of the current moment ends, and the next simulation moment is entered and the adjusted attitude angle is calculated. After the attitude angle is calculated, step (6) is executed. The third case is that the spatial target is not in the panoramic coverage range of the imaging spectrometer at the current simulation moment, indicating that the spatial target cannot be observed and imaged at the current simulation moment. The next simulation moment is entered and step (3) is executed. The fourth case is that the spatial target is in the panoramic but not in the single scene range at the current moment, and the spatial target is in at least one of the three areas of outside the panoramic range, ground shadow area, and line-of-sight occlusion area at the next simulation moment, indicating that the spectral imager cannot observe and image the spatial target at both the current simulation moment and the next simulation moment. The next simulation moment is entered and step (3) is executed.

[0047] When the spectral imager needs to adjust its attitude angles, the yaw angle cannot be adjusted to ensure the imager's trajectory is correct; only the pitch and roll angles can be adjusted. To achieve the best observation results, the space target should be placed at the center of the single-view coverage area, that is, the center probe ray of the spectral imager should be pointed towards the target. The specific calculation formula is as follows:

[0048]

[0049] In the formula Operators represent the calculation of two vectors The included angle, and They represent Projection vectors on the xOz and yOz planes of the spectral imager coordinate system. Pitch represents the vector pointing from the spectral imager to the space target. cal and Roll cal These represent the calculated pitch and roll angle adjustments, respectively. Let x and y be the direction vectors of the spectral imager's trajectory coordinate system, respectively. The z-axis of the spectral imager's trajectory coordinate system points from the spectral imager to the Earth's center, and the x-axis points from the spectral imager to the velocity direction. The y-axis direction of the spectral imager is determined by the right-hand rule. Since the coverage area of ​​a single scene cannot exceed the maximum coverage area, it is necessary to further limit the attitude adjustment of the spectral imager. Therefore, the actual attitude angle adjustment should be:

[0050]

[0051] In the formula, Pitch is the pitch angle of the spectral imager after attitude adjustment, and Roll is the roll angle of the spectral imager after attitude adjustment. Thus, the spatial target visibility analysis and the calculation of the attitude adjustment amount of the spectral imager at the current simulation moment are completed.

[0052] In step (6), the radiation characteristic transmission process of the space target is modeled. Considering the three-dimensional detailed structure and material distribution of the space target, the space target is segmented based on the triangular element representation method. The three-dimensional model of the space target is performed by determining the vertex, normal vector and corresponding material type of each triangular element. Using the three-dimensional model of the space target and the seven types of parameters obtained in step (2), the two radiation transmission paths and their relative positions, namely the sun-space target-spectral imager and the earth-space target-spectral imager, are obtained. Based on the space radiation transmission calculation method, the solar radiation intensity and the earth's albedo radiation intensity received at the space target are obtained. The observation angles of the probe rays emitted by the spectral imager and the normal vectors of the intersecting surface elements in the two radiation transmission paths are calculated using ray tracing. The spectral reflectance of the two radiation transmission paths is calculated using the bidirectional reflectance distribution function and the observation angles. The spectral radiance at the entrance pupil of the spectral imager is obtained by combining the spectral radiance and the spectral reflectance under the corresponding path. The calculation of the entrance pupil spectral radiance image is completed. The first step is to consider the three-dimensional detailed structure and material distribution of the spatial target. The spatial target is segmented based on the triangular surface element representation method. The three-dimensional model of the spatial target is performed by determining the vertices, normal vectors and corresponding material types of each triangular surface element.

[0053] The second step is to perform surface visibility analysis on the three-dimensional model of the spatial target, which is the process of determining the visibility of each surface element on the surface of the spatial target. This is the process of determining whether the light rays corresponding to the pixels of the imaging plane intersect with each surface element. The method of finding the intersection of spatial rays and triangular surface element sets is used to calculate the intersection points of rays emanating from the imaging center and passing through each pixel with each surface element on the surface of the spatial target. That is, the observation points recorded for each pixel. An imager with an M×N pixel size is used to emit M×N light rays from the observation points. The light rays pass through the center of the pixel grid of the imaging plane. The intersection of this light ray set with the triangular surface element set of the target surface is calculated to determine the observed surface element corresponding to each pixel.

[0054] The third step is to construct the space radiation transmission path. In the visible light band, the radiation sources received by space targets are mainly direct solar radiation and solar radiation reflected from the Earth. Direct solar radiation can be obtained using measured data. Earth-reflected radiation refers to the radiation component of sunlight that is reflected into outer space after reaching the Earth's surface. It is related to the Earth's surface reflection characteristics and the solar irradiance value received on the ground. To simplify the problem, the average albedo model is used to describe the Earth's reflection characteristics. The direct solar radiation received at any point in outer space at any given time is determined by the distance between the target's location and the Sun at that time, as well as the solar constant. The calculation formula is as follows:

[0055]

[0056] In the formula, r so Let r0 be the straight-line distance between the spatial target location and the Sun at that moment, r0 be the average Earth-Sun distance, λ be the wavelength, and E0(λ) be the solar constant. Its physical meaning is the light energy received per unit area of ​​the Earth's upper atmosphere per unit time and per unit wavelength range at the average Earth-Sun distance, with units of W / m2 / nm, and it is a function of wavelength λ. sun (λ) represents the direct solar radiation component received by a space target within a specific wavelength range;

[0057] Given that the average albedo of the Earth's surface is ρ = 0.35, the Earth's albedo radiation can be expressed as:

[0058] E earth (λ)=ρE sun (λ)

[0059] In the formula E earth (λ) represents the Earth's albedo radiation component received by a space target within a specific wavelength range;

[0060] The fourth step is to calculate the observation angles of the corresponding surface elements for each pixel along different radiation transmission paths, including the incident angle and the exit angle. The incident angle and the exit angle are further divided into azimuth angle and zenith angle, respectively. The calculation formula is as follows:

[0061]

[0062] In the formula, and These are the vectors pointing from the intersection of the probe ray and the surface element to the radiation source and from the intersection of the probe ray and the surface element to the spectral imager, respectively. This is the normal vector of the surface element, and also the z-axis direction vector of the surface element's coordinate system. Let x be the x-axis coordinate vector of the surface element coordinate system. and They are respectively and In the surface element coordinate system X f O f Y f The projection vector on the plane is calculated using the following formula:

[0063]

[0064]

[0065] The fifth step is to calculate the entrance pupil radiance curve pixel by pixel. The Davies model is used to calculate the amount of light energy entering the entrance pupil of the imager after reflection from the surface material of the spatial target. The specific calculation formula is as follows:

[0066]

[0067] In the formula Let σ be the reflectance of a certain material at a specific observation angle and wavelength, λ be the root mean square of the surface roughness, and σ be the reflectance of the material at a specific observation angle and wavelength. α ρ is the surface autocorrelation length. dh,s The directional hemispherical reflectance of a smooth surface can be determined by the Fresnel formula. Finally, the entrance pupil radiance curve is calculated pixel by pixel, and the calculation formula is as follows:

[0068] E final (λ)=E sun (λ)·f r,λ,sun +E earth (λ)·f r,λ,earth

[0069] In the formula E final (λ) represents the spectral entrance pupil radiance for a specific wavelength range ultimately obtained at the entrance pupil of the spectral imager, f r,λ,sun The reflectance, f, is calculated in the radiative transfer path of the solar-space target-spectral imager. r,λ,earth The reflectance is calculated in the Earth-space target-spectral imager radiative transfer path.

[0070] In step (7), the imaging process of the spectral imager is modeled. The imaging model of the spectral imager is established by comprehensively analyzing five aspects: radiation response, spectral response, motion blur, random noise, and image quantization. The final simulation image is generated using the spectral radiance image at the entrance pupil calculated in step (6). The first step is to calculate the radiation response and convert the light radiation signal into an electrical signal. The specific calculation formula is as follows:

[0071] S(λ)=E final (λ)·a _rc +b _rc

[0072] In the formula, S(λ) is the signal value of the spectral entrance pupil radiance in a certain wavelength range after radiometric calibration, and a _rc ,b _rc These are the radiation calibration coefficients;

[0073] The second step involves calculating the spectral response. Based on the set center wavelength, full width at half maximum (FWHM), and response function type, a spectral response function R(λ) is generated. Then, the signal obtained from the radiative response in the first step is integrated pixel by pixel. The specific calculation is as follows:

[0074]

[0075] In the formula DN s (λ) is the signal value in a certain wavelength range obtained after spectral response calculation;

[0076] The third step involves considering the motion blur problem caused by the spatial target's velocity. The lengths of the spread functions at the orbital and perpendicular points are determined using the norms of the spatial target's orbital and perpendicular velocities. The DN obtained pixel-by-pixel in the second step is then used to... s (λ) The image is then processed into a two-dimensional image and convolved with the spread functions of the vertical and along-track points respectively. The squares of the convolution results in both directions are then summed and the L2 norm is calculated to obtain the final two-dimensional image DN considering motion blur. t,h,w (λ), where h,w are the height and width of the two-dimensional image;

[0077] The fourth step involves considering the noise present in the system imaging, generating random Gaussian noise based on the set signal-to-noise ratio, and adding it to the image generated in the third step to obtain the DN. n,h,w (λ);

[0078] The fifth step is to perform n-bit quantization on the final spectral image, mapping the image pixel values ​​to 0-2. n The image is stored within the range of -1 and is used as the final simulation image. h,w (λ).

[0079] The advantages of this invention compared with the prior art are as follows: (1) This method is a full-link modeling and simulation of close-range spectral imaging of space targets. It considers the three-dimensional structure of space targets, performs visibility analysis on different surface elements, and establishes a full-link simulation model of attitude and orbit modeling, radiation transmission modeling, and imager modeling; (2) It combines orbit and relative motion for dynamic simulation, uses the real position, attitude, and velocity information in the dynamic scene, and performs quantitative analysis on the three types of factors affecting the visibility of targets in the space environment, namely, ground shadow constraints, line-of-sight occlusion constraints, and imager field-of-view constraints, before the generation of the simulation image; (3) This method does not simplify much when modeling the optical properties of the surface of space targets. It considers the directional reflection characteristics of different materials instead of treating the target as a Lambertian body. It can simulate the directional characteristics of different visible surface elements under the same observation scene due to different observation angles, making the simulation effect more in line with the actual situation. Detailed Implementation

[0080] To better illustrate the space target spectral imaging simulation method of this invention, the observation process is simulated using actual equatorial orbit data, and spectral images are generated following the AOTF imaging mode. Only a spectral image in a specific wavelength band is generated at each simulation moment, with the calculated wavelength range being 400nm to 1000nm. The space target is set as a three-dimensional model of Gaofen-6. The specific implementation steps are as follows:

[0081] (1) Input the attitude and orbital parameters of the space target and the spectral imager, the start and end times of the simulation, and the simulation step size: Input the semi-major axis of the space target's orbit as 7078137m, eccentricity 0, orbital inclination 0°, right ascension of the ascending node 0°, perigee angular distance 0°, true perigee 150°, the space target's rotation around the sun is 0.1r / min, the semi-major axis of the spectral imager's orbit as 7082137m, eccentricity 0, orbital inclination 0°, right ascension of the ascending node 0°, perigee angular distance 0°, true perigee 150°, the simulation time range is from 08:21:00 on 2021-10-23 to 08:21:30 on 2021-10-23, and the simulation step size is 5s.

[0082] (2) Input the three types of parameters input in step (1) into STK: the attitude and orbit parameters of the space target and the spectral imager, the simulation start and end time, and the simulation step size. Establish a specific scenario for the space-based spectral imager to observe and image the space target. Obtain six types of parameters at each simulation moment: the position of the Earth in the geocentric-geo-fixed coordinate system, the position and velocity of the space target, the position and velocity of the spectral imager, and the position of the Sun. Also obtain the attitude of the space target in the space target track coordinate system. Input the parameters required for establishing the space-based observation scenario into STK. Establish a specific observation scenario for the space-based spectral imager to observe and image the space target. Use the report format preset by the STK system to obtain two types of information: one is the position and velocity of the space target, the position and velocity of the spectral imager, and the position of the Sun, based on the geocentric-geo-fixed coordinate system; the other is the attitude angle of the space target based on the space target track coordinate system, including roll angle, pitch angle, and yaw angle. When the position coordinates of the spectral imager, the space target, the Sun, and the Earth are all known and are in the same coordinate system at each simulation moment, the relative positional relationship is determined accordingly.

[0083] (3) Determine whether the space target is in the Earth's shadow at the current simulation moment. Treat the space target as a point in the space-based observation scenario. First, use the position coordinates of the space target, the sun and the earth obtained in step (2), and use a cylindrical ground shadow model to describe the Earth's shadow interval. Calculate whether the position coordinates of the space target are in the Earth's shadow interval. If the space target is in the shadow interval, the simulation at the current simulation moment ends, and the next simulation moment begins and step (3) is executed again. Otherwise, execute step (4): Based on the relative positional relationship between the space target, the imager, the sun and the earth obtained in step (2), determine whether the space target is in the Earth's shadow at the current simulation moment. Approximate the sunlight received at the space location near the earth as parallel light, use a cylindrical ground shadow model to describe the Earth's shadow interval, and calculate the angle between the geocentric vector of the target and the geocentric vector of the sun. The calculation formula is as follows:

[0084]

[0085] In the formula The vector obtained by representing the position coordinates of the target in the Earth-centered Earth-fixed coordinate system. Let α be the vector obtained by finding the position coordinates of the Sun in the Earth-centered Earth-fixed coordinate system, and α be the angle between the two vectors. 0 ≤ α ≤ π. When 0 ≤ α ≤ π / 2, the target is not in the Earth's shadow and can be observed. When π / 2 ≤ α ≤ π, if the target is not in the Earth's shadow, the following relationship must be satisfied:

[0086]

[0087] In the formula R eSince is a constant and defined as the average radius of the Earth, the constraint condition for a space target to be located in the non-shadow region under the cylindrical ground shadow model is:

[0088]

[0089] If the space target is in the shadow region, the simulation ends at the current simulation moment, and the next simulation moment is entered and step (3) is executed again; otherwise, step (4) is executed. The simulation results show that the space target is not in the shadow region during the 6 simulation moments included in this simulation.

[0090] (4) Determine whether the line of sight of the spectral imager is blocked by the Earth at the current simulation moment. Using the position coordinates of the spectral imager, the space target and the Earth obtained in step (2), and considering the Earth as a standard ellipsoid, solve for whether the line vector connecting the spectral imager and the space target intersects with the Earth. If there is no intersection or the two intersection points are not located between the spectral imager and the space target, the line of sight of the spectral imager is not blocked by the Earth at the current simulation moment, and execute step (5). Otherwise, the simulation at the current simulation moment ends, enters the next simulation moment and executes step (3) again: Consider the space target and the spectral imager as a point in the space-based observation scenario, and consider the Earth as a standard ellipsoid. Use the subtraction of the coordinate vectors of the spectral imager and the space target obtained in step (2) to obtain the detection ray vector. The calculation method is as follows:

[0091] (kx,ky,kz)=(obj_x-sat_x,obj_y-sat_y,obj_z-sat_z)

[0092] In the formula, kx, ky, and kz are the three-dimensional coordinates of the probe ray vector, obj_x, obj_y, and obj_z are the three-dimensional coordinates of the space target in the geocentric-geostatic coordinate system, and sat_x, sat_y, and sat_z are the three-dimensional coordinates of the spectral imager in the geocentric-geostatic coordinate system. The coefficients of the simultaneous equations are obtained from the method for calculating whether a vector intersects with an ellipsoid in three-dimensional space:

[0093]

[0094]

[0095] In the formula, A, B, and C are the polynomial coefficients in the simultaneous equations, and a, b, and c are the radii of the Earth on the x, y, and z axes, respectively. If the probe ray intersects the Earth, the calculation method is as follows:

[0096]

[0097] In the formula, t1 and t2 are variables in the calculation process. Since the coordinates of the two intersection points are vectors, the constraint that the line of sight of the spectral imager is not blocked by the Earth is as follows:

[0098]

[0099] In the formula and The values ​​are (obj_x,obj_y,obj_z) and (sat_x,sat_y,sat_z). If the line of sight of the spectral imager is not blocked by the Earth at the current simulation time, step (5) is executed. Otherwise, the simulation at the current simulation time ends, and the next simulation time is entered and step (3) is executed again. The simulation results show that the line of sight of the spectral imager is not blocked in any of the 6 simulation times included in this simulation.

[0100] (5) Determine the field-of-view constraint of the spectral imager at the current simulation moment. Construct the relative positional relationship between the spectral imager and the space target using the position coordinates obtained in step (2). Calculate the boundary point set of the intersection coordinates of all probe rays and the object plane where the space target is located. Determine the single-view coverage range that the spectral imager can achieve without attitude adjustment and the panoramic coverage range that can be achieved through attitude adjustment. If the space target is simultaneously within the single-view and panoramic coverage range at the current moment, or if the space target is in the panoramic range but not within the single-view range at the current moment, and the space target is not in the ground shadow area or the line-of-view occlusion area and is in the panoramic range at the next moment, it indicates that the spectral imager can perform observation. Imaging, proceed to step (6), otherwise the simulation ends at the current simulation moment, proceed to the next simulation moment and re-execute step (3): Based on the determined relative position information, use imaging geometry to determine the single-scene coverage range and maximum coverage range of the spectral imager. The single-scene coverage range is defined as the imaging area that the spectral imager can actually observe at a specific moment and a specific attitude angle of the spectral imager. The maximum coverage range is the union of all imaging areas that the spectral imager can observe through attitude adjustment, assuming that the attitude adjustment time of the spectral imager is 0. The single-scene coverage range at a specific moment is a subset of the maximum coverage range at the same moment, that is:

[0101] C cat (t,i)=f(pos(t),yaw(t,i),pitch(t,i),roll(t,i),sensortype)

[0102] C poss (t)=∑ i C cat (t,i)

[0103]

[0104] In the formula, pos(t) is the relative positional relationship matrix of the spectral imager, the target, and the Earth at time t; yaw(t,i), pitch(t,i), and roll(t,i) are the i-th combination of the attitude angles of the spectral imager at time t, including yaw, pitch, and roll angles; sensortype represents the field of view angle of the spectral imager; and C... cat (t,i) represents the single-scene coverage of the spectral imager at time t and the i-th attitude angle combination, C poss (t,i) represents the maximum coverage area of ​​the spectral imager at time t, which is equal to the union of the coverage areas of all individual scenes at that time. f represents the coordinates of the intersection points of all probe rays and the object plane where the spatial target is located under the i-th attitude angle combination at time t. To save computational resources, the coverage area is defined as a rectangle, and the coverage area of ​​the spectral imager is represented by the boundary point set corresponding to the four vertices of the coverage area, thus obtaining the individual scene coverage area and the maximum coverage area. The probe ray vector at each vertex of the coverage area is calculated as follows:

[0105]

[0106] In the formula R x ,R y ,R z Let be a three-axis rotation matrix, e0 be the center detection ray vector of the spectral imager at time t, and set the center detection vector of the spectral imager at the initial simulation time to point from the spectral imager to the Earth's center. At non-initial simulation times, the center detection vector has the same direction as the previous simulation time. e is the detection ray vector at a vertex of the spectral imager's coverage area at time t. θ, φ, and ψ are the rotation angles of the detection ray vector at a vertex of the spectral imager's coverage area around the x, y, and z axes with the center detection ray as the reference. In the calculation of the single-scene coverage area, θ, φ, and ψ are substituted in as follows:

[0107]

[0108] In the formula, HFOV is the horizontal field of view of the spectral imager, and VFOV is the vertical field of view of the spectral imager. θ, φ, and ψ are substituted into the formula as follows during the calculation of the panoramic coverage:

[0109]

[0110] In the formula Roll max Pitch is the maximum roll angle of the spectral imager. maxLet be the maximum pitch angle of the spectral imager. Set the plane containing the spatial target to include the coordinates of the spatial target and perpendicular to the detection vector of the spectral imager center. Using the above formula, obtain the detection ray vectors at the four vertices of the single-scene coverage and panoramic coverage at the current simulation time, and calculate the intersection point set with the plane containing the spatial target. Then, determine whether the spatial target position coordinates at the current simulation time are within the maximum coverage or single-scene coverage. There are four situations. The first situation is that the spatial target is simultaneously within the single-scene and panoramic coverage at the current time, indicating that the spectral imager can observe and image the spatial target at the current simulation time. Execute step (6). The second situation is that the spatial target is in the panoramic but not in the single-scene range at the current time. At the next moment, the spatial target is not in the ground shadow area or the line-of-sight obstruction area and is in the panoramic range. This indicates that the spectral imager cannot observe and image at the current moment, but can observe and image at the next simulation moment through attitude adjustment. The simulation of the current moment ends, and the next simulation moment is entered and the adjusted attitude angle is calculated. After the attitude angle is calculated, step (6) is executed. The third case is that the spatial target is not in the panoramic coverage range of the imaging spectrometer at the current simulation moment, indicating that the spatial target cannot be observed and imaged at the current simulation moment. The next simulation moment is entered and step (3) is executed. The fourth case is that the spatial target is in the panoramic but not in the single scene range at the current moment, and the spatial target is in at least one of the three areas of outside the panoramic range, ground shadow area, and line-of-sight occlusion area at the next simulation moment, indicating that the spectral imager cannot observe and image the spatial target at both the current simulation moment and the next simulation moment. The next simulation moment is entered and step (3) is executed.

[0111] When the spectral imager needs to adjust its attitude angles, the yaw angle cannot be adjusted to ensure the imager's trajectory is correct; only the pitch and roll angles can be adjusted. To achieve the best observation results, the space target should be placed at the center of the single-view coverage area, that is, the center probe ray of the spectral imager should be pointed towards the target. The specific calculation formula is as follows:

[0112]

[0113] In the formula Operators represent the calculation of two vectors The included angle, and They represent Projection vectors on the xOz and yOz planes of the spectral imager coordinate system. Pitch represents the vector pointing from the spectral imager to the space target. cal and Roll cal These represent the calculated pitch and roll angle adjustments, respectively. Let x and y be the direction vectors of the spectral imager's trajectory coordinate system, respectively. The z-axis of the spectral imager's trajectory coordinate system points from the spectral imager to the Earth's center, and the x-axis points from the spectral imager to the velocity direction. The y-axis direction of the spectral imager is determined by the right-hand rule. Since the coverage area of ​​a single scene cannot exceed the maximum coverage area, it is necessary to further limit the attitude adjustment of the spectral imager. Therefore, the actual attitude angle adjustment should be:

[0114]

[0115] In the formula, Pitch is the pitch angle of the spectral imager after attitude adjustment, and Roll is the roll angle of the spectral imager after attitude adjustment. Thus, the visibility analysis of the space target and the calculation of the attitude adjustment amount of the spectral imager at the current simulation time are completed. The simulation results show that the spectral imager can observe and image the space target at simulation times 1, 3, and 5. It cannot image at simulation times 2 and 4, and the attitude angle of the spectral imager is adjusted so that the spectral imager can observe and image at simulation times 3 and 5. Simulation time 6 is the last simulation time, and it is impossible to observe and image the space target. At the same time, the simulation ends after the spectral imager adjusts its attitude angle. Therefore, it will not observe and image the space target at the next simulation time.

[0116] (6) Model the radiation characteristic transmission process of the space target. Considering the detailed three-dimensional structure and material distribution of the space target, the space target is segmented based on the triangular element representation method. The space target is three-dimensionally modeled by determining the vertices, normal vectors and corresponding material types of each triangular element. Using the three-dimensional model of the space target and the seven types of parameters obtained in step (2), the two radiation transmission paths and their relative positions, namely, the sun-space target-spectral imager and the earth-space target-spectral imager, are obtained. Based on the space radiation transmission calculation method, the solar radiation intensity and the earth's albedo radiation intensity received at the space target are obtained. Ray tracing calculates the observation angles of the probe rays emitted by the spectral imager and the normal vectors of intersecting surface elements in two radiative transmission paths. Using the bidirectional reflectance distribution function and the calculated observation angles, the spectral reflectance of the two radiative transmission paths is calculated respectively. Combining the spectral radiation intensity and the spectral reflectance under the corresponding path, the spectral radiance at the entrance pupil of the spectral imager is obtained, and the calculation of the entrance pupil spectral radiance image is completed. The first step is to consider the three-dimensional detailed structure and material distribution of the spatial target, and to segment the spatial target based on the triangular surface element representation method. The three-dimensional model of the spatial target is performed by determining the vertices, normal vectors and corresponding material types of each triangular surface element.

[0117] The second step is to perform surface visibility analysis on the three-dimensional model of the spatial target, which is the process of determining the visibility of each surface element on the surface of the spatial target. This is the process of determining whether the light rays corresponding to the pixels of the imaging plane intersect with each surface element. The method of finding the intersection of spatial rays and triangular surface element sets is used to calculate the intersection points of rays emanating from the imaging center and passing through each pixel with each surface element on the surface of the spatial target. That is, the observation points recorded for each pixel. An imager with an M×N pixel size is used to emit M×N light rays from the observation points. The light rays pass through the center of the pixel grid of the imaging plane. The intersection of this light ray set with the triangular surface element set of the target surface is calculated to determine the observed surface element corresponding to each pixel.

[0118] The third step is to construct the space radiation transmission path. In the visible light band, the radiation sources received by space targets are mainly direct solar radiation and solar radiation reflected from the Earth. Direct solar radiation can be obtained using measured data. Earth-reflected radiation refers to the radiation component of sunlight that is reflected into outer space after reaching the Earth's surface. It is related to the Earth's surface reflection characteristics and the solar irradiance value received on the ground. To simplify the problem, the average albedo model is used to describe the Earth's reflection characteristics. The direct solar radiation received at any point in outer space at any given time is determined by the distance between the target's location and the Sun at that time, as well as the solar constant. The calculation formula is as follows:

[0119]

[0120] In the formula, r so Let r0 be the straight-line distance between the spatial target location and the Sun at that moment, r0 be the average Earth-Sun distance, λ be the wavelength, and E0(λ) be the solar constant. Its physical meaning is the light energy received per unit area of ​​the Earth's upper atmosphere per unit time and per unit wavelength range at the average Earth-Sun distance, with units of W / m2 / nm, and it is a function of wavelength λ. sun (λ) represents the direct solar radiation component received by a space target within a specific wavelength range;

[0121] Given that the average albedo of the Earth's surface is ρ = 0.35, the Earth's albedo radiation can be expressed as:

[0122] E earth (λ)=ρE sun (λ)

[0123] In the formula E earth (λ) represents the Earth's albedo radiation component received by a space target within a specific wavelength range;

[0124] The fourth step is to calculate the observation angles of the corresponding surface elements for each pixel along different radiation transmission paths, including the incident angle and the exit angle. The incident angle and the exit angle are further divided into azimuth angle and zenith angle, respectively. The calculation formula is as follows:

[0125]

[0126]

[0127] In the formula, and These are the vectors pointing from the intersection of the probe ray and the surface element to the radiation source and from the intersection of the probe ray and the surface element to the spectral imager, respectively. This is the normal vector of the surface element, and also the z-axis direction vector of the surface element's coordinate system. Let x be the x-axis coordinate vector of the surface element coordinate system. and They are respectively and In the surface element coordinate system X f O f Y f The projection vector on the plane is calculated using the following formula:

[0128]

[0129] The fifth step is to calculate the entrance pupil radiance curve pixel by pixel. The Davies model is used to calculate the amount of light energy entering the entrance pupil of the imager after reflection from the surface material of the spatial target. The specific calculation formula is as follows:

[0130]

[0131] In the formula Let σ be the reflectance of a certain material at a specific observation angle and wavelength, λ be the root mean square of the surface roughness, and σ be the reflectance of the material at a specific observation angle and wavelength. α ρ is the surface autocorrelation length. dh,s The directional hemispherical reflectance of a smooth surface can be determined by the Fresnel formula. Finally, the entrance pupil radiance curve is calculated pixel by pixel, and the calculation formula is as follows:

[0132] E final (λ)=E sun (λ)·f r,λ,sun +E earth (λ)·f r,λ,earth

[0133] In the formula E final (λ) represents the spectral entrance pupil radiance for a specific wavelength range ultimately obtained at the entrance pupil of the spectral imager, f r,λ,sun The reflectance, f, is calculated in the radiative transfer path of the solar-space target-spectral imager. r,λ,earth The reflectance is calculated in the Earth-space target-spectral imager radiative transfer path.

[0134] (7) Model the imaging process of the spectral imager. Analyze the five aspects of radiation response, spectral response, motion blur, random noise, and image quantization to establish the spectral imager imaging model. Use the spectral radiance image at the entrance pupil obtained from step (6) to generate the final simulation image: First, perform radiation response calculation, converting the light radiation signal into an electrical signal. The specific calculation formula is as follows:

[0135] S(λ)=E final (λ)·a _rc +b _rc

[0136] In the formula, S(λ) is the signal value of the spectral entrance pupil radiance in a certain wavelength range after radiometric calibration, and a _rc ,b _rc These are the radiation calibration coefficients, set to 1.1 and 0.2, respectively.

[0137] The second step involves calculating the spectral response. The center wavelength range is 400nm-1000nm, with an initial value of 400nm. The center wavelength is increased by 50nm each time the simulation progresses, resulting in values ​​of 400nm, 450nm, 500nm, 550nm, 600nm, and 650nm. The full width at half maximum (FWHM) is set to 10nm, and the response function type is set to Gaussian. Based on the set center wavelength, FWHM, and response function type, a spectral response function R(λ) is generated. Then, the signal is integrated pixel-by-pixel with the signal obtained from the radiative response in the first step. The specific steps are as follows:

[0138]

[0139] In the formula DN s (λ) is the signal value in a certain wavelength range obtained after spectral response calculation;

[0140] The third step involves considering the motion blur problem caused by the spatial target's velocity. The lengths of the spread functions at the orbital and perpendicular points are determined using the norms of the spatial target's orbital and perpendicular velocities. The DN obtained pixel-by-pixel in the second step is then used to... s (λ) The image is then processed into a two-dimensional image and convolved with the spread functions of the vertical and along-track points respectively. The squares of the convolution results in both directions are then summed and the L2 norm is calculated to obtain the final two-dimensional image DN considering motion blur. t,h,w (λ), where h,w are the height and width of the two-dimensional image;

[0141] Fourth, considering the noise present in the system imaging, the signal-to-noise ratio is set to 30. Random Gaussian noise is generated based on the set signal-to-noise ratio and added to the image generated in the third step to obtain DN. n,h,w (λ);

[0142] The fifth step is to perform 10-bit quantization on the final spectral image, mapping the image pixel values ​​to the range of 0-1023 and storing them as the final simulation image. h,w (λ), and finally three Gaofen-6 simulation images based on the space-based observation scenario are generated at the 1st, 3rd and 5th simulation times.

[0143] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. The implementation of each step can vary, and all equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A simulation method for spectral imaging of space targets based on space-based observation scenarios, characterized in that: It includes the following steps: (1) Input the attitude and orbit parameters of the space target and the spectral imager, the start and end times of the simulation, and the simulation step size; (2) Input the three types of parameters input in step (1) into STK: the attitude and orbit parameters of the space target and the spectral imager, the simulation start and end time, and the simulation step size. Establish a specific scenario for the space-based spectral imager to observe and image the space target. Obtain seven types of parameters at each simulation moment: the position of the Earth in the geocentric coordinate system, the position of the space target, the velocity of the space target, the position of the spectral imager, the velocity of the spectral imager, the position of the Sun, and the attitude of the space target in the space target trajectory coordinate system. (3) Determine whether the space target is in the Earth's shadow zone at the current simulation time. Treat the space target as a point in the space-based observation scenario. First, use the position coordinates of the space target, the sun and the earth obtained in step (2), and use the cylindrical Earth shadow model to describe the Earth's shadow zone. Calculate whether the position coordinates of the space target are in the Earth's shadow zone. If the space target is in the Earth's shadow zone, the simulation at the current simulation time ends, enter the next simulation time and repeat step (3). Otherwise, execute step (4). (4) Determine whether the line of sight of the spectral imager is blocked by the Earth at the current simulation moment. Using the position coordinates of the spectral imager, the space target and the Earth obtained in step (2), the Earth is regarded as a standard ellipsoid. Solve whether the line vector connecting the spectral imager and the space target intersects the Earth. If there is no intersection or the two intersections are not located between the spectral imager and the space target, the line of sight of the spectral imager is not blocked by the Earth at the current simulation moment. Execute step (5). Otherwise, the simulation at the current simulation moment ends, enter the next simulation moment and re-execute step (3). (5) Perform field-of-view constraint judgment of the spectral imager at the current simulation moment. Construct the relative positional relationship between the spectral imager and the space target using the position coordinates of the spectral imager and the space target obtained in step (2). Calculate the boundary point set of the intersection coordinates of all probe rays and the object plane where the space target is located. Determine the single-scene coverage range that the spectral imager can achieve without attitude adjustment and the panoramic coverage range that can be achieved through attitude adjustment. And process according to the following situations: If the space target is within the single-scene coverage range at the current simulation moment, then execute step (6); If the space target is within the panoramic coverage range but not within the single-scene coverage range at the current simulation moment, and the space target is not in the ground shadow area at the next simulation moment, the spectral imager's line of sight is not blocked by the earth, and the space target is not in the ground shadow area at the next simulation moment, and the space target is not blocked by the earth, then the space target is not in the ground shadow area at the next simulation moment. If the target is within the panoramic coverage area, the current simulation time ends and the next simulation time begins. The attitude of the spectral imager is calculated and adjusted, and step (6) is executed. If the spatial target is outside the panoramic coverage area at the current simulation time, the next simulation time begins and step (3) is executed. If the spatial target is within the panoramic coverage area but not within the single scene coverage area at the current simulation time, and at least one of the following situations occurs in the next simulation time: the spatial target is in the Earth's shadow area, the spectral imager's line of sight is blocked by the Earth, or the spatial target is outside the panoramic coverage area, the next simulation time begins and step (3) is executed. The panoramic coverage area is the union of all single scene coverage areas at this time. The method for calculating the probe ray vector at the vertex of each coverage area is as follows: ； In the formula Let be the probe ray vector at a vertex within the coverage area of ​​the spectral imager at time t. It is a three-axis rotation matrix. Let be the center detection ray vector of the spectral imager at time t; (6) Model the transmission process of the radiation characteristics of the space target. Consider the three-dimensional detailed structure and material distribution of the space target. Based on the triangular element representation method, the space target is segmented. The space target is modeled in three dimensions by determining the vertex, normal vector and corresponding material type of each triangular element. Using the three-dimensional model of the space target and the seven types of parameters obtained in step (2), the two radiation transmission paths and their relative positions of the sun-space target-spectral imager and the earth-space target-spectral imager are obtained. Based on the space radiation transmission calculation method, the solar radiation intensity and the earth albedo radiation intensity received at the space target are obtained. Using the ray tracing method, the observation angle of the incident radiation direction relative to the normal vector of the intersecting element and the observation angle of the outgoing radiation direction relative to the normal vector of the intersecting element are calculated respectively. Based on the calculated observation angle, the spectral reflectance of the two radiation transmission paths is calculated respectively using the bidirectional reflectance distribution function. The spectral radiance at the entrance pupil of the spectral imager is obtained by combining the spectral radiation intensity and the spectral reflectance under the corresponding path. The calculation of the entrance pupil spectral radiance image is completed. (7) Model the imaging process of the spectral imager, and establish the spectral imager imaging model by comprehensively analyzing five aspects: radiation response, spectral response, motion blur, random noise, and image quantization. The final simulation image is generated using the spectral radiance image at the entrance pupil obtained by step (6).

2. The space target spectral imaging simulation method based on a space-based observation scenario according to claim 1, characterized in that, The steps (1) include inputting the attitude and orbit parameters of the space target and the spectral imager, the simulation start and end times, and the simulation step size: the orbit parameters are defined in the six-root format, including the semi-major axis, eccentricity, orbital inclination, argument of the pericenter, right ascension of the ascending node, and true anomaly. The attitude parameters of the space target include four types: solar three-axis stability, geostationary three-axis stability, solar spin, and geostationary spin. The simulation start and end times are defined in the Coordinated Universal Time format, and the simulation step size is in seconds.

3. The space target spectral imaging simulation method based on a space-based observation scenario according to claim 1, characterized in that, Step (2) further includes: inputting the parameters required for establishing the space-based observation scenario into STK, establishing a specific space-based spectral imager observation and imaging scenario for space targets, and using the report format preset by the STK system to obtain two types of information: one is the position and velocity of the space target, the position and velocity of the spectral imager, and the position of the sun, based on the geocentric coordinate system; the other is the attitude angle of the space target based on the space target track coordinate system, including roll angle, pitch angle, and yaw angle. When the position coordinates of the spectral imager, the space target, the sun, and the earth are all known at each simulation moment and are in the same coordinate system, the relative positional relationship is determined accordingly.

4. The space target spectral imaging simulation method based on a space-based observation scenario according to claim 1, characterized in that, Step (3) further includes: determining whether the space target is in the Earth's shadow at the current simulation moment based on the relative positional relationship of the space target, imager, sun and earth obtained in step (2), approximating the sunlight received at the space location near the earth as parallel light, using a cylindrical Earth shadow model to describe the Earth's shadow region, and calculating the angle between the geocentric vector of the target and the geocentric vector of the sun, with the following calculation formula: ； In the formula The vector obtained by representing the position coordinates of the target in the Earth-centered Earth-fixed coordinate system. This is a vector obtained by representing the position coordinates of the Sun in the Earth-centered Earth-fixed coordinate system. The angle between the two vectors. ,when The target is not in Earth's shadow and can be observed. If the target is not in Earth's shadow, the following relationship must be satisfied: ； In the formula Since is a constant and defined as the average radius of the Earth, the constraint condition for a space target to be located in the non-shadow region under the cylindrical ground shadow model is: ； If the space target is in the Earth's shadow area, the simulation at the current simulation time ends, and the next simulation time begins and step (3) is executed again; otherwise, step (4) is executed.

5. The space target spectral imaging simulation method based on a space-based observation scenario according to claim 1, characterized in that, Step (4) further includes: treating the space target and the spectral imager as a point in the space-based observation scenario, treating the Earth as a standard ellipsoid, and subtracting the coordinate vectors of the spectral imager and the space target obtained in step (2) to obtain the detection ray vector, calculated as follows: ； In the formula These are the three-dimensional coordinates of the probe ray vector. These represent the three-dimensional coordinates of the space target in the Earth-centered, Earth-fixed coordinate system. Let be the three-dimensional coordinates of the spectral imager in the geocentric-geofixed coordinate system. The coefficients of the simultaneous equations can be obtained from the method for calculating whether a vector intersects with an ellipsoid in three-dimensional space: ； ； ； In the formula The coefficients of the polynomials in the simultaneous equations are denoted as . These represent the radii of the Earth along the x, y, and z axes, respectively. If the probe ray intersects the Earth, the calculation method is as follows: ； ； ； ； In the formula To calculate process variables, Since the coordinates of the two intersection points are vectors, the constraint that the line of sight of the spectral imager is not blocked by the Earth is as follows: ； In the formula and They are respectively and If the spectral imager’s line of sight is not blocked by the Earth at the current simulation time, proceed to step (5); otherwise, the simulation at the current simulation time ends, proceed to the next simulation time and re-execute step (3).

6. The space target spectral imaging simulation method based on a space-based observation scenario according to claim 1, characterized in that, Step (5) further includes: based on the determined relative position information, using imaging geometry, determining the single-view coverage range and panoramic coverage range of the spectral imager. The single-view coverage range is defined as the imaging area that the spectral imager can actually observe at a specific time and a specific attitude angle of the spectral imager. The single-view coverage range at a specific time is a subset of the panoramic coverage range at the same time. The relationship between the single-view coverage range and the panoramic coverage range is as follows: ； ； ； In the formula It is the matrix showing the relative positions of the spectral imager, the target, and the Earth at time t. These three represent the i-th combination of the attitude angles of the spectral imager at time t. Indicates the field of view of the spectral imager. Let represent the single-scene coverage of the spectral imager at time t and the i-th attitude angle combination. This represents the panoramic coverage area of ​​the spectral imager at time t, which is equal to the union of the coverage areas of all individual scenes at that time. Let t represent the coordinates of the intersection points of all probe rays and the object plane where the spatial target is located under the i-th attitude angle combination. Define the coverage area as a rectangle, and use the boundary point set corresponding to the four vertices of the coverage area to represent the coverage area of ​​the spectral imager, thus obtaining the single-scene coverage area and the panoramic coverage area. The probe ray vector at each vertex of the coverage area is calculated as follows: ； ； ； ； The initial simulation time of the spectral imager is set so that the center detection vector points from the spectral imager to the Earth's center. At subsequent simulation times, the center detection vector maintains the same direction as the previous simulation time. Let be the probe ray vector at a vertex within the coverage area of ​​the spectral imager at time t. These are the rotation angles of the probe ray vector at a certain vertex within the coverage area of ​​the spectral imager, relative to the central probe ray, around the x, y, and z axes, respectively, during the calculation of single-scene coverage. Substitute the following methods: ； In the formula The horizontal field of view of the spectral imager. The vertical field of view of the spectral imager is used in the calculation of panoramic coverage. Substitute the following methods: ； In the formula This is the maximum roll angle of the spectral imager. Let be the maximum pitch angle of the spectral imager. Set the object plane containing the coordinates of the spatial target and the plane perpendicular to the detection vector of the spectral imager center. Use the above formula to obtain the detection ray vectors at the four vertices of the single-scene coverage and panoramic coverage at the current simulation time, and calculate the intersection point set with the object plane containing the spatial target. Then, it can be determined whether the position coordinates of the spatial target at the current simulation time are located in the panoramic coverage or the single-scene coverage. There are four situations. The first situation is that the spatial target is simultaneously within the single-scene and panoramic coverage at the current time, indicating that the spectral imager can observe and image the spatial target at the current simulation time. Execute step (6). The second situation is that the spatial target is in the panoramic but not in the single-scene range at the current time. At the next moment, the spatial target is not in the ground shadow area or the line-of-sight occlusion area and is in the panoramic range. The first case is that the spectral imager cannot observe and image at the current time, but it can be observed and imaged through attitude adjustment at the next simulation time. The simulation at the current time ends, and the next simulation time is entered to calculate the adjusted attitude angle. After the attitude angle is calculated, step (6) is executed. The second case is that the spatial target is not within the panoramic coverage of the imaging spectrometer at the current simulation time, which means that the spatial target cannot be observed and imaged at the current simulation time. The next simulation time is entered and step (3) is executed. The third case is that the spatial target is within the panoramic coverage of the imaging spectrometer at the current time, which means that the spatial target cannot be observed and imaged at the current simulation time. The fourth case is that the spatial target is within the panoramic coverage but not within the single scene coverage at the current time, and the spatial target is within at least one of the three areas of outside the panoramic coverage, ground shadow area, and line-of-sight occlusion area at the next simulation time. This means that the spectral imager cannot observe and image the spatial target at both the current simulation time and the next simulation time. The next simulation time is entered and step (3) is executed. When the spectral imager needs to adjust its attitude angles, the yaw angle cannot be adjusted to ensure the imager's trajectory is correct. Only the pitch and roll angles need to be adjusted. To achieve the best observation results, the space target should be placed in the center of the single-view coverage area, that is, the center probe ray of the spectral imager should be pointed towards the target. The specific calculation formula is as follows: ； ； In the formula Operators represent the calculation of two vectors The included angle, and They represent Projection vectors on the xOz and yOz planes of the spectral imager coordinate system. This represents the vector pointing from the spectral imager to the space target. and These represent the calculated pitch and roll angle adjustments, respectively. Let x and y be the direction vectors of the spectral imager's trajectory coordinate system, respectively. The z-axis of the spectral imager's trajectory coordinate system points from the spectral imager to the Earth's center, and the x-axis points from the spectral imager to the velocity direction. The y-axis direction of the spectral imager is determined by the right-hand rule. Since the coverage area of ​​a single scene cannot exceed the coverage area of ​​the entire scene, it is necessary to further limit the attitude adjustment of the spectral imager. Therefore, the actual attitude angle adjustment should be: ； ； In the formula It is the pitch angle of the spectral imager after its attitude has been adjusted. It is the roll angle of the spectral imager after adjusting its attitude; This completes the spatial target visibility analysis and the calculation of the spectral imager attitude adjustment at the current simulation time.

7. The space target spectral imaging simulation method based on a space-based observation scenario according to claim 1, characterized in that, The step (6) further includes: First, considering the three-dimensional detailed structure and material distribution of the spatial target, the spatial target is segmented based on the triangular facet representation method, and the spatial target is three-dimensionally modeled by determining the vertices, normal vectors and corresponding material types of each triangular facet. The second step is to perform surface visibility analysis on the three-dimensional model of the spatial target, which is the process of determining the visibility of each surface element on the surface of the spatial target. This is the process of determining whether the light rays corresponding to the pixels of the imaging plane intersect with each surface element. The method of finding the intersection of spatial rays and triangular surface element sets is used to calculate the intersection points of rays emanating from the imaging center and passing through each pixel with each surface element on the surface of the spatial target. That is, the observation points recorded for each pixel. An imager with an M×N pixel size is used to emit M×N light rays from the observation points. The light rays pass through the center of the pixel grid of the imaging plane. The intersection of this light ray set with the triangular surface element set of the target surface is calculated to determine the observed surface element corresponding to each pixel. The third step is to construct the space radiation transmission path. In the visible light band, the radiation sources received by the space target include direct solar radiation and solar radiation reflected from the Earth. Direct solar radiation is obtained using measured data. Earth-reflected radiation refers to the radiation component of sunlight that is reflected into outer space after reaching the Earth's surface, and it is related to the Earth's surface reflection characteristics and the solar irradiance value received at the ground. The average albedo model is used to describe the Earth's reflection characteristics. The direct solar radiation received at any point in outer space at any given time is determined by the distance between the target's location and the Sun at that time, as well as the solar constant. The calculation formula is as follows: ； In the formula, This represents the straight-line distance between the spatial target's location and the sun at that moment. The average distance between the Earth and the Sun. Indicates wavelength. The solar constant, in its physical sense, represents the amount of light energy received per unit area of ​​the Earth's upper atmosphere per unit time and per unit wavelength range at the average Earth-Sun distance. The function, This refers to the direct solar radiation received by a space target within a specific wavelength range. Given that the average albedo of the Earth's surface is ρ = 0.35, the Earth's albedo radiation can be expressed as: ； In the formula The Earth's albedo radiation component received for a specific wavelength range of a space target; The fourth step is to calculate the observation angles of the corresponding surface elements for each pixel along different radiation transmission paths, including the incident angle and the exit angle. The incident angle and the exit angle are further divided into the azimuth angle and the zenith angle, respectively. The calculation formula is as follows: ； ； ； ； In the formula, and These are the vectors pointing from the intersection of the probe ray and the surface element to the radiation source and from the intersection of the probe ray and the surface element to the spectral imager, respectively. This is the normal vector of the surface element, and also the z-axis direction vector of the surface element's coordinate system. Let x be the x-axis coordinate vector of the surface element coordinate system. and They are respectively and In the surface element coordinate system The projection vector on the plane is calculated using the following formula: ； ； The fifth step is to calculate the entrance pupil radiance curve pixel by pixel. The Davies model is used to calculate the amount of light energy entering the entrance pupil of the imager after reflection from the surface material of the spatial target. The specific calculation formula is as follows: ； In the formula The reflectivity of a certain material at a specific viewing angle and wavelength. The root mean square of the surface roughness. The surface autocorrelation length, The directional hemispherical reflectance of a smooth surface can be determined by the Fresnel formula. Finally, the entrance pupil radiance curve is calculated pixel by pixel, and the calculation formula is as follows: ； In the formula This refers to the spectral entrance pupil radiance within a specific wavelength range ultimately obtained at the entrance pupil of the spectral imager. The reflectance calculated in the radiative transfer path of the Sun-Space Target-Spectral Imager. The reflectance is calculated in the Earth-space target-spectral imager radiative transfer path.

8. The space target spectral imaging simulation method based on a space-based observation scenario according to claim 1, characterized in that, Step (7) further includes: First, performing radiation response calculation, converting the optical radiation signal into an electrical signal, with the specific calculation formula as follows: ； In the formula The signal value obtained after radiometric calibration of the entrance pupil radiance within a certain wavelength range. These are the radiation calibration coefficients, For wavelength, This refers to the spectral entrance pupil radiance of a specific wavelength range ultimately obtained at the entrance pupil of the spectral imager. The second step is to calculate the spectral response, generating a spectral response function based on the set center wavelength, full width at half maximum (FWHM), and response function type. Then, the signal obtained from the first step of radiometric response is integrated pixel by pixel to calculate the result, as follows: ； In the formula This refers to the signal value within a certain wavelength range obtained after spectral response calculation. The third step involves considering the motion blur caused by the spatial target's velocity. The lengths of the spread functions at the orbital and perpendicular points are determined using the norms of the target's orbital and perpendicular velocities. This is then applied pixel-by-pixel to the data obtained in the second step. The image is then formatted into a two-dimensional image and convolved with the spread functions of the points perpendicular to the orbit and along the orbit, respectively. The squares of the convolution results in both directions are then summed, and the L2 norm is calculated to obtain the final two-dimensional image considering motion blur. ,in The height and width of the two-dimensional image; The fourth step involves considering the noise present in the system imaging, generating random Gaussian noise based on the set signal-to-noise ratio, and adding it to the image generated in the third step. ; The fifth step is to perform n-bit quantization on the final spectral image, mapping the image pixel values ​​to 0~2. n Within the range of -1, and stored as the final simulation image. .

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