Stereophotogrammetry method for dusting characteristics of lunar dust under plume effect

Abstract

The invention discloses a stereoscopic photogrammetry method for the dusting characteristic of lunar dust under the plume effect, and relates to the technical field of spaceflight exploration, a measuring system composed of a high-speed camera, a pitching adjusting mechanism, a rotating mechanism and the like is built in a vacuum cabin, and reliable work of a camera under the vacuum environment is achieved through a camera protection cover; the view field of the binocular camera is overlapped by adjusting the pitch angle and the rotation angle, and an internal reference matrix and a conversion matrix are solved based on standard checkerboard calibration; binocular images under the plume effect are synchronously collected, the three-dimensional coordinates of feature points are inversely calculated based on the triangulation principle, and three-dimensional reconstruction of the contour and depth of the corrosion pit and dust particle motion trail and speed calculation are completed. The method realizes quantitative measurement of corrosion pit morphology and particle motion in a vacuum environment, provides high-precision data support for a lunar dust dusting model, is suitable for plume effect evaluation and protection technology research and development in lunar exploration, and has the advantages of accurate measurement, non-contact type, complete spatio-temporal data and the like.

Description

Technical Field

[0001] The present invention relates to the field of aerospace exploration technology, and in particular to a stereoscopic photogrammetry method for measuring the dust emission characteristics of lunar dust under the action of plumes. Background Art

[0002] During lunar exploration missions, the interaction between the engine plume and the loose lunar regolith during landing and takeoff is a critical issue affecting mission safety. The plume's impact on the lunar surface can cause lunar dust particles to be swept into the plume field, forming erosion craters on the surface. This can cause contamination of the lander's optical systems, thermal control failure, and even structural damage, leading to mission failure in severe cases. Therefore, accurately assessing the interaction between plume effects and lunar dust is a core requirement for ensuring the safety of lunar spacecraft.

[0003] In existing technologies, lunar surface erosion models under plume action mainly rely on on-orbit image fitting or simulation experiments in atmospheric environments, and the data accuracy is insufficiently consistent with the vacuum environment. Traditional image capture can only perform qualitative observations of erosion pit morphology, and cannot obtain the spatiotemporal evolution of erosion pit morphology in a vacuum environment and quantitative parameters of particle motion (such as particle spatial position, excitation velocity, etc.), making it difficult to meet the needs of plume-lunar dust interaction mechanism research and dust generation model development. In addition, some experiments use contact measurement methods such as profile observation, which may interfere with the natural process of plume action and cause data distortion.

[0004] In view of this, this application is hereby filed. Summary of the Invention

[0005] The purpose of the present invention is to provide a stereoscopic photogrammetric method for the dust emission characteristics of lunar dust under the action of plumes, so as to solve the problems mentioned in the above background technology.

[0006] To solve the above technical problems, the present invention provides a stereoscopic photogrammetric method for measuring the dust emission characteristics of lunar dust under the action of a plume, comprising the following steps:

[0007] Step 1: Build the measurement system in the vacuum chamber: Set up the profile frame, test bench base plate, three-axis three-dimensional translation stage, lunar dust container and lunar dust, and install the nozzle through the nozzle fixing frame; Place two high-speed cameras in the camera protective cover composed of the camera protective cover shell, bellows connector, camera protective cover front cover and quartz glass, connect the pitch adjustment mechanism and rotation mechanism through the adapter plate, and lead the camera connection line out of the vacuum chamber; Use the vacuum chamber environment to simulate the vacuum conditions on the lunar surface to ensure the authenticity of the experiment of the interaction between the plume and lunar dust; The design of the camera protective cover and bellows connector ensures the reliable operation and signal transmission of the high-speed camera in the vacuum environment, providing the hardware foundation for subsequent measurements;

[0008] Step 2: Adjust the binocular camera parameters: Use the pitch adjustment mechanism to set the pitch angle δ between the shooting axis and the horizontal plane, and use the rotation mechanism to set the rotation angle β between the two shooting axes, so that the field of view covers the specified area and overlaps. The adjustable pitch angle δ and rotation angle β achieve flexible coverage and overlap of the binocular camera field of view, ensuring that there are no blind spots in the shooting area, and providing multi-angle image data for subsequent three-dimensional reconstruction of stereo photogrammetry.

[0009] Step 3: Camera calibration: Use a standard checkerboard to capture images, identify matching feature points, and solve the camera's intrinsic parameter matrix and transformation matrix. Through standard checkerboard calibration, an accurate mapping relationship between the camera imaging model and the world coordinate system is established, improving the accuracy of subsequent 3D coordinate inverse calculations and ensuring the reliability of measurement data.

[0010] Step 4: Image acquisition and reconstruction: Turn on the nozzle to generate a plume, and simultaneously collect binocular images. Based on the internal parameter matrix and the transformation matrix, the three-dimensional coordinates of the target point are inverted to complete the quantitative description of the crater morphology, measure the spatial position of the particles and calculate the excitation velocity. Through the synchronous acquisition and three-dimensional reconstruction of binocular images, the temporal and spatial evolution process of the crater morphology under the action of the vacuum plume is quantitatively captured. Not only can the geometric parameters of the crater be obtained, but also the trajectory and velocity of the particles can be tracked, providing key data support for both qualitative and quantitative analysis for the development of the lunar dust emission model.

[0011] Furthermore, in step one, the camera protective cover is connected to the equipment outside the vacuum chamber through a bellows connector to realize signal transmission of the high-speed camera in a vacuum environment; the design of the bellows connector allows the camera cable to pass through and connect to external equipment while maintaining the sealing of the vacuum chamber, and the camera protective cover is used to realize reliable operation of the camera in a vacuum environment, thereby ensuring the continuity of the experiment.

[0012] Furthermore, in step one, the two high-speed cameras are arranged obliquely above the lunar dust container to form a binocular vision system to synchronously capture images of the erosion process under the action of the plume; the binocular vision system arranged obliquely above can effectively capture the entire picture of lunar dust emission under the action of the plume, and the synchronously captured images ensure temporal consistency, providing a reliable time-series image sequence for subsequent spatiotemporal evolution analysis.

[0013] Furthermore, in step 2, the angles between the shooting axes of the two high-speed cameras and the horizontal plane are both δ, and the projection angles of the two shooting axes on the horizontal plane are β; by setting the standardized pitch angle δ and projection angle β, it is ensured that the optical path of the binocular camera forms a stable triangulation structure, thereby improving the accuracy and consistency of the three-dimensional coordinate calculation of the feature points.

[0014] Furthermore, in step three, the transformation matrix is ​​obtained by performing feature point identification, matching, and fitting calculations on the captured image of a standard checkerboard, and is used to realize the conversion of two-dimensional image coordinates to three-dimensional space coordinates; the standardized transformation matrix solution process ensures the accurate calibration of camera parameters, so that the two-dimensional image coordinates can be accurately mapped to the three-dimensional space, thereby improving the accuracy and repeatability of the measurement results.

[0015] Furthermore, in step four, the stereo photogrammetry is based on the principle of triangulation, and common feature points are identified from images taken from different angles by two high-speed cameras, and the three-dimensional spatial coordinates of the feature points are determined by ray tracing; the principle of triangulation is used to realize reverse reproduction from two-dimensional images to three-dimensional space, and the spatial coordinates of the feature points can be obtained without contact measurement, avoiding interference with the lunar dust erosion process under the action of the plume, and ensuring the objectivity and real-time nature of the measurement.

[0016] Furthermore, in step four, the quantitative description of the pit morphology includes three-dimensional reconstruction of the pit's outline and depth, and the particle spatial position measurement is used to draw the motion trajectory of the dust particles and calculate the excitation velocity; through three-dimensional reconstruction and particle tracking, the limitation of traditional image capture that can only perform qualitative analysis is broken through, and the quantitative measurement of the pit's geometric characteristics and particle motion parameters is achieved, providing key data for in-depth research on the interaction mechanism between plumes and lunar dust.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. 3D Reconstruction and Quantitative Analysis: This method uses binocular high-speed cameras to synchronously capture images and, based on triangulation principles, reconstructs the contours and depths of erosion craters under the influence of vacuum plumes. This overcomes the limitations of conventional image capture, which is limited to qualitative analysis. Furthermore, by tracking the spatial positions of particles near the lunar surface, particle motion trajectories can be mapped and their lift-off velocities calculated, providing key quantitative data for dynamic analysis of the interaction between plumes and lunar dust.

[0019] 2. Adaptability to vacuum environments and equipment reliability: The measurement system uses a camera cover (composed of a camera cover housing, a bellows connector, a front cover, and quartz glass) to achieve sealing and signal transmission for the equipment inside the vacuum chamber. The bellows connector allows the camera connection to be led out of the chamber while maintaining the vacuum environment, allowing the camera to be placed inside the vacuum chamber and operate reliably, ensuring continuous and reliable experimentation.

[0020] 3. Integrity of spatiotemporal evolution data: The overlapping area of ​​the binocular camera field of view is optimized by adjusting the pitch angle δ and rotation angle β to ensure coverage of key areas throughout the erosion process. Combined with the high frame rate shooting capability of the high-speed camera, the dynamic changes of the erosion pit morphology over time can be captured, providing a complete spatiotemporal data chain for establishing a lunar dust emission model under the action of plumes.

[0021] 4. Objectivity of non-contact measurement: The non-contact method based on stereo photogrammetry avoids the interference of traditional contact measurement (such as profile observation) on the plume-lunar dust interaction process, ensuring that the measurement results truly reflect the natural erosion process in a vacuum environment, and improving the objectivity and credibility of the data.

[0022] 5. Model optimization and engineering application value: The acquired 3D reconstruction data has both qualitative (crater morphology) and quantitative (particle velocity, crater volume, etc.) characteristics. It can be directly used to verify and optimize the lunar dust emission model, provide a scientific basis for the design of plume protection measures for lunar spacecraft, reduce the technical risks of lunar exploration missions, and has significant engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the overall measurement system for a stereoscopic photogrammetry method of lunar dust emission characteristics under the action of plumes.

[0024] Figure 2 A partial view of the camera layout used in a stereo photogrammetry method for measuring the characteristics of lunar dust emission under plume effects.

[0025] Figure 3 A schematic diagram of the relative positions of binocular cameras in a stereoscopic photogrammetry method for measuring the characteristics of lunar dust emission under plume effects.

[0026] Figure 4 1 is a standard chessboard real-shot image and plane feature points in an embodiment of the present invention.

[0027] In the picture:

[0028] 1. Profile frame; 2. Camera protective cover shell; 3. Bellows connector; 4. Adapter plate; 5. Pitch adjustment mechanism; 6. Rotation mechanism; 7. Three-axis three-dimensional translation stage; 8. Test bench base plate; 9. Lunar dust container; 10. Lunar dust; 11. Nozzle; 12. Nozzle fixing bracket; 13. High-speed camera; 14. Front cover of camera protective cover; 15. Quartz glass. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] See also Figure 1-Figure 4The present invention provides a technical solution: a stereoscopic photogrammetric method for measuring the dust emission characteristics of lunar dust under the action of a plume, comprising:

[0031] 1. Measurement system construction and equipment installation

[0032] 1. Vacuum Chamber Environment Preparation

[0033] The test bench bottom plate 8 is fixed horizontally in the vacuum chamber to ensure its stability.

[0034] A lunar dust container 9 is placed on the test bench base plate 8, and lunar dust 10 of thickness H is evenly laid in the container to simulate the loose lunar soil layer on the lunar surface. A three-axis three-dimensional translation stage 7 is installed on the test bench base plate 8.

[0035] 2. Nozzle system installation

[0036] The nozzle 11 is installed directly above or obliquely above the lunar dust container 9 through the nozzle fixing frame 12, and the vertical distance between the nozzle outlet and the lunar dust surface is adjusted to L to ensure that the plume can evenly flush the lunar dust surface.

[0037] 3. Binocular Camera System Construction

[0038] Camera hood assembly: Install two high-speed cameras 13 within the camera hood housing 2, with the camera lenses facing the lunar dust container 9. The camera hood consists of the housing 2, bellows connector 3, front cover 14, and quartz glass 15. The quartz glass 15 serves as a light-transmitting window to ensure a clear field of view.

[0039] Adjustment mechanism connection: The pitch adjustment mechanism 5 and the rotation mechanism 6 are fixedly connected to the camera protection cover housing 2 through the adapter plate 4 to form an adjustable camera bracket. The rotation mechanism 6 is installed on the profile frame 1.

[0040] Signal transmission processing: The power line and data line of the high-speed camera 13 are led out of the vacuum chamber through the bellows connector 3 and connected to the external data acquisition system, power supply and control equipment to ensure the normal operation of the equipment in the vacuum environment.

[0041] 4. Installation of auxiliary components

[0042] If three-dimensional displacement adjustment is required, a three-axis three-dimensional displacement stage 7 can be installed between the test bench base plate 8 and the camera protective cover to fine-tune the relative position of the camera and the lunar dust container.

[0043] 2. Binocular Camera Parameter Adjustment and Field of View Matching

[0044] 1. Pitch angle (δ) adjustment

[0045] The shooting axes of the two high-speed cameras 13 are adjusted through the pitch adjustment mechanism 5 so that the angles between them and the horizontal plane ABCD are both δ (usually 30°-60°, determined according to the depth of the shooting area), ensuring that the lens can cover the full height range of the lunar dust container 9.

[0046] 2. Rotation angle (β) adjustment

[0047] The shooting axes of the two high-speed cameras 13 are adjusted by the rotating mechanism 6 so that the projection angle of the two axes on the horizontal plane ABCD is β (usually 45°-90°, determined according to the binocular parallax requirements), and the two axes intersect at point M above the center of the lunar dust container 9, forming a triangulation optical path.

[0048] 3. Visual field overlap verification

[0049] Turn on the high-speed camera 13 and observe the real-time picture to ensure that the fields of view of the two cameras cover the central area of ​​the lunar dust container (9) and the overlapping area is not less than 50% of the field of view area to meet the stereo matching requirements.

[0050] 3. Camera Calibration and Transformation Matrix Solution

[0051] 1. Standard checkerboard calibration

[0052] The standard chessboard ( Figure 4 ) is placed in the measurement area above the lunar dust container 9, ensuring that the checkerboard plane is parallel to the horizontal plane ABCD.

[0053] Two high-speed cameras 13 are controlled to capture at least 10 groups of chessboard images from different angles, and each group of images must include different positions and postures of the chessboard.

[0054] 2. Feature point recognition and matching

[0055] Image processing software is used to detect corner points of the captured chessboard image and identify the corner points of the chessboard as feature points.

[0056] The feature points in the two camera images are matched by epipolar constraints and normalized cross-correlation algorithms, and the two-dimensional coordinate pairs (x1, y1) and (x2, y2) of the feature points with the same name are obtained.

[0057] 3. Transformation matrix calculation

[0058] Based on Zhang Zhengyou calibration method, the intrinsic parameter matrix (K1, K2), rotation matrix (R1, R2) and displacement vector (t1, t2) of the two cameras are calculated by least squares fitting, and the transformation matrix is ​​constructed to establish the mapping relationship between the image coordinate system and the world coordinate system.

[0059] Verify calibration accuracy: Calculate the reprojection error of the feature point's 3D coordinates to ensure that the error is less than 1 pixel, otherwise recalibrate.

[0060] 4. Image Acquisition and Data Processing under Plume

[0061] 1. Vacuum environment simulation and plume generation

[0062] Close the vacuum chamber and pump until the ambient pressure is less than 10 -2 Pa, simulating the vacuum conditions on the lunar surface.

[0063] The nozzle 11 is opened and a simulated propellant (such as nitrogen or argon) is introduced to generate a high-speed plume that washes the surface of the lunar dust 10 for a duration of T seconds. The two high-speed cameras 13 are synchronously triggered to shoot synchronously at a frame rate f (usually f ≥ 1000 fps to ensure that the details of the particle movement are captured).

[0064] 2. Binocular Image Acquisition

[0065] Collect binocular image sequences of lunar dust erosion during the plume process. Each set of images contains grayscale or color images of the left and right cameras at the same moment.

[0066] 3. 3D Coordinate Inversion and Pit Reconstruction

[0067] Each set of binocular images is preprocessed (such as denoising and contrast enhancement), and feature points such as pit edges and particles are extracted using the SIFT or SURF algorithm.

[0068] Based on the solved transformation matrix, triangulation is performed on the feature points with the same name, and their three-dimensional spatial coordinates (x0, y0, z0) are calculated. A three-dimensional model of the erosion pit is constructed using the point cloud data, and the geometric parameters of the erosion pit, such as its contour, depth, and volume, are obtained.

[0069] 4. Particle motion trajectory and velocity calculation

[0070] Track the same particle in multiple consecutive frames of images, record its three-dimensional coordinates at different times, and draw its motion trajectory.

[0071] The three-dimensional velocity vector (u, v, w) of the particle is calculated by time difference of the trajectory, and the movement direction and velocity distribution of the dust particles are analyzed.

[0072] It should be noted here that:

[0073] To facilitate illustration of the relative layout of the binocular cameras, a partial view of the relative positions of the binocular cameras is provided. The dotted box ABCD represents a horizontal plane, which is parallel to the mounting plane of the rotating mechanism 6. O1M and O2M are the shooting axes of the two high-speed cameras 13, intersecting the horizontal plane ABCD at point M. The dotted lines N1M and N2M are the projections of the shooting axes O1M and O2M onto the horizontal plane ABCD. The angles between the shooting axes O1M and O2M and the horizontal plane ABCD are both δ (pitch angle), and the angle between the shooting axes O1M and O2M is β (rotation angle). The pitch adjustment mechanism 5 is used to adjust the pitch angle δ between the shooting axes O1M and O2M of the two high-speed cameras 13 and the horizontal plane ABCD. The rotating mechanism 6 is used to adjust the rotation angle β between the shooting axes O1M and O2M of the two high-speed cameras 13. By properly adjusting the pitch angle δ and the rotation angle β, the binocular camera field of view can cover the designated shooting area, and the binocular camera fields of view can overlap.

[0074] Stereophotogrammetry method:

[0075] Stereo photogrammetry technology is based on the principle of triangulation to reverse the projection process. Based on the common feature points of the target identified on the plane images taken from different angles, ray tracing is drawn from the camera shooting origin through the common points on the plane. The three-dimensional spatial coordinates of the feature points can be obtained by determining the intersection of the rays.

[0076] The key to stereo photogrammetry technology lies in the reverse simulation projection process. In the forward projection process, the projection coordinates (x1, y1) and (x2, y2) of the spatial feature point coordinates (x0, y0, z0) projected onto the image plane satisfy the following relationship:

[0077]

[0078] Among them, K1 and K2 are the internal parameter matrices of the two cameras, R1 and R2 are the rotation matrices of the two cameras, and t1 and t2 are the displacement vectors of the two cameras. The above matrices and vectors together constitute the transformation matrix during the camera shooting process. The corresponding solution can be obtained by shooting calibration with a standard chessboard, identifying and matching feature points, and extracting plane coordinates and then fitting them. The calibration and transformation matrix solution process is shown in the figure. Figure 4 .

[0079] The dust emission characterization experiment used two high-speed cameras positioned diagonally above the lunar dust container, forming a binocular camera. After calibration and solving the transformation matrix, images of the erosion process under the influence of the plume were collected. Two real-time images taken at the same moment were selected, and the target key points were identified and their 2D coordinates in both images were obtained. The actual 3D coordinates of the target points were then calculated based on the transformation matrix. Combined with a sufficient number of feature point clouds, a quantitative description of the crater morphology was achieved. Stereoscopic photography technology not only reconstructs the geometric information of the contours and depth of the craters formed by the plume's impact on the lunar surface in 3D, but also measures the spatial position of particles near the lunar surface to map the particle motion trajectories during the dust emission process. This, combined with time, further calculates the particle's agitation velocity.

[0080] In summary, the present invention achieves high-precision quantitative analysis of the dust emission characteristics of lunar dust under the action of plumes by constructing a stereo photogrammetry system based on binocular high-speed cameras in a vacuum chamber, combining the principle of triangulation with equipment modification. This method breaks through the limitations of qualitative analysis in the existing technology, can accurately capture the spatiotemporal evolution process of erosion pit morphology and particle motion trajectory, and provides reliable experimental data support for the lunar dust emission model. At the same time, the vacuum environment adaptability design of the measurement system ensures the stable operation of the equipment, and the non-contact measurement method ensures the objectivity of the data. The present invention provides a new technical means for the development of plume effect evaluation and protection technology in lunar exploration. It has the advantages of accurate measurement, comprehensive data, and strong engineering applicability. It is of great significance to improving the safety and scientific nature of my country's deep space exploration missions.

Claims

1. A stereophotogrammetric method for measuring the characteristics of lunar dust emission under plume conditions, characterized by: The following steps are involved: Step 1: Build a measurement system in a vacuum chamber: set up a profile frame (1), a test bench base plate (8), a three-axis three-dimensional displacement stage (7), a lunar dust container (9) and lunar dust (10), and install the nozzle (11) through the nozzle fixing frame (12); place two high-speed cameras (13) in a camera protective cover composed of a camera protective cover shell (2), a bellows connector (3), a camera protective cover front cover (14) and quartz glass (15), connect the pitch adjustment mechanism (5) and the rotation mechanism (6) through an adapter plate (4), and lead the camera connection line out of the vacuum chamber; Step 2: Adjust the binocular camera parameters: set the pitch angle δ between the shooting axis and the horizontal plane through the pitch adjustment mechanism (5), and set the rotation angle β between the two shooting axes through the rotation mechanism (6) so that the field of view covers the specified area and overlaps; Step 3: Camera calibration: Use a standard checkerboard to capture images, identify matching feature points, and solve the camera intrinsic parameter matrix and transformation matrix; Step 4: Image acquisition and reconstruction: Open the nozzle (11) to generate plume, synchronously acquire binocular images, inversely calculate the three-dimensional coordinates of the target point based on the internal parameter matrix and the transformation matrix, complete the quantitative description of the erosion pit morphology, measure the particle spatial position and calculate the excitation velocity.

2. The stereophotogrammetric method for measuring the characteristics of lunar dust emission under the action of a plume according to claim 1, characterized in that: In the step 1, the camera protection cover is connected to the equipment outside the vacuum chamber via a bellows connector (3) to achieve signal transmission of the high-speed camera (13) in a vacuum environment.

3. The stereophotogrammetric method for measuring the characteristics of lunar dust emission under the action of a plume according to claim 1, characterized in that: In the step 1, the two high-speed cameras (13) are arranged obliquely above the lunar dust container (9) to form a binocular vision system to synchronously capture images of the erosion process under the action of the plume.

4. The stereophotogrammetric method for measuring the characteristics of lunar dust emission under the action of a plume according to claim 1, characterized in that: In the step 2, the angles between the shooting axes of the two high-speed cameras (13) and the horizontal plane are both δ, and the projected angles of the two shooting axes on the horizontal plane are β.

5. The stereophotogrammetric method for measuring the characteristics of lunar dust emission under the action of a plume according to claim 1, characterized in that: In the step three, the conversion matrix is ​​obtained by performing feature point recognition, matching and fitting calculations on the captured image of the standard checkerboard, and is used to realize the conversion of two-dimensional image coordinates to three-dimensional space coordinates.

6. The stereophotogrammetric method for measuring the characteristics of lunar dust emission under the action of a plume according to claim 1, characterized in that: In the step 4, the stereo photogrammetry is based on the principle of triangulation, and common feature points are identified from images taken from different angles by two high-speed cameras (13), and the three-dimensional spatial coordinates of the feature points are determined by ray tracing.

7. The stereophotogrammetric method for measuring the characteristics of lunar dust emission under the action of a plume according to claim 1, characterized in that: In the step 4, the quantitative description of the pit morphology includes three-dimensional reconstruction of the pit contour and depth, and the particle spatial position measurement is used to draw the movement trajectory of the dust particles and calculate the excitation speed.

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