Atmospheric coherence length measurement adaptive pointing tracking method and system

Abstract

The application discloses an atmospheric coherence length measurement self-adaptive pointing tracking method and system, belongs to the technical field of atmospheric optical measurement instruments, and solves the technical problems of low recognition and alignment efficiency, weak self-adaptive adaptation capability, insufficient anti-interference performance and poor system cooperation in the prior art. A star camera is used to collect a starry sky area image of a target star area; after the image is analyzed and a celestial body measurement parameter is obtained, a turntable is finely adjusted so that the target star is on a target surface of a main mirror camera; exposure time and gain of the main mirror camera are adjusted; two light spots of the target star are automatically adjusted to be centered on a field center of the main mirror camera; a target star image is collected; an atmospheric coherence length value is calculated in real time; whether the atmospheric coherence length value is empty or an abnormal value is determined at a fixed interval; if yes, the turntable automatically points to a next target star; and if not, an atmospheric coherence length measurement task is continuously executed. The application is used for realizing fast alignment and stable tracking of a beacon light source in a weak light environment at night.

Description

Technical Field

[0001] This invention relates to the field of atmospheric optical measurement instrument technology, specifically to an adaptive pointing and tracking method and system for measuring atmospheric coherence length. Background Technology

[0002] Nighttime is a prime observation period with stable atmospheric turbulence and controllable light pollution. Stars, as natural beacon light sources, are the preferred solution for nighttime atmospheric coherence length measurement due to their stable brightness, full-space distribution, and lack of manual deployment and maintenance. Stellar beacon-driven pointing and tracking technology is the core support for ensuring measurement accuracy, efficiency, and reliability. While existing stellar beacon pointing and tracking technology has evolved from manual operation to semi-automation as atmospheric coherence length measurement progresses towards "high precision, long duration, and automation," it still faces numerous technical bottlenecks in field observation scenarios, making it difficult to meet the high-precision measurement requirements of complex nighttime environments. Specific shortcomings are as follows:

[0003] 1. Low identification and alignment efficiency and insufficient accuracy: Traditional systems adopt a mode of blind search in the entire airspace and star point extraction with fixed thresholds. They lack an intelligent guidance mechanism based on the distribution characteristics of stars. In low-light environments at night, the contrast between stars and background noise is low, and they are easily affected by moonlight, light pollution and atmospheric extinction, resulting in long star-finding time and large initial alignment deviation.

[0004] 2. Lack of adaptive tracking mechanism and weak dynamic adaptation capability: Stars have diurnal motion, and existing systems mostly rely on the lag adjustment of passive compensation by the turntable to detect star point offset, which can easily lead to the accumulation of tracking deviation. Furthermore, the fixed camera exposure parameters and tracking gain cannot adapt to the dynamic fluctuations of the nighttime environment, which may cause the tracking link to be interrupted.

[0005] 3. Insufficient anti-interference capability and poor long-term stability: Sudden interference such as direct moonlight, thin cloud cover, and ground stray light can easily cause temporary loss of stellar beacons. Existing technologies lack a rapid recapture mechanism, requiring a complete re-search for stars, resulting in data loss.

[0006] 4. Poor coordination between pointing, tracking and measurement systems: The pointing alignment, stable tracking and atmospheric coherence length measurement processes of stellar beacons are independent of each other and there is no closed-loop coordination mechanism, which easily leads to the accumulation of invalid data or distortion of wavefront measurement data.

[0007] Therefore, developing a pointing tracking method with rapid and accurate identification and alignment, dynamic adaptive tracking, strong anti-interference capability, and deep collaborative measurement characteristics is a technical challenge that urgently needs to be solved in the field of atmospheric optical measurement. Summary of the Invention

[0008] This invention solves the technical problems of low recognition and alignment efficiency, weak adaptive capability, insufficient anti-interference and poor system coordination in the prior art.

[0009] The adaptive pointing and tracking method for atmospheric coherence length measurement described in this invention includes the following steps:

[0010] Step 1: Use a guide camera to acquire images of the starry sky region of the target star area;

[0011] Step 2: Analyze the starry sky image of the target star region to obtain astrometry parameters;

[0012] Step 3: Fine-tune the turntable based on the astrometry parameters so that the target star is on the target surface of the primary mirror camera. Adjust the exposure time and gain of the primary mirror camera according to the star's magnitude, and automatically center the two light spots of the target star in the field of view of the primary mirror camera.

[0013] Step 4: Use the primary mirror camera to acquire images of the target star and calculate the atmospheric coherence length in real time based on the target star images;

[0014] Step 5: Determine at fixed intervals whether there are any null or outlier values ​​in the atmospheric coherence length value;

[0015] Step 6: If the atmospheric coherence length value is empty or an anomaly, the turntable will automatically point to the next target star and repeat steps 2 to 5. If the atmospheric coherence length value is not empty or an anomaly, the atmospheric coherence length measurement task will continue.

[0016] Furthermore, in one embodiment of the present invention, step 1, which involves acquiring an image of the starry sky region of the target star region using a guiding camera, specifically includes:

[0017] The primary camera and guide camera are aligned coaxially to obtain the current latitude, longitude, and time information. Combined with the initial right ascension and declination coordinates of the target star, the guide camera is turned towards the target star region using a turntable to acquire images of the star region.

[0018] Furthermore, in one embodiment of the present invention, the analysis of the starry sky region image of the target star region in step 2 includes the following steps:

[0019] Step 21: Preprocess the starry sky image of the target star region, extract the star targets in the image, and obtain the pixel coordinates of each star target;

[0020] Step 22: Based on the pixel coordinates of each star target, perform feature matching with the reference star catalog and eliminate incorrect matches;

[0021] Step 23: Using the correctly matched star pairs, establish a projection model from the celestial sphere to the image plane, and calculate the initial astrometry parameters.

[0022] Step 24: Iteratively optimize the initial astronomical measurement parameters until the residual between the coordinates of the correctly matched star pair in the reference star catalog and the coordinates in the initial astronomical measurement parameters meets the preset accuracy threshold, and then obtain the final astronomical measurement parameters.

[0023] Furthermore, in one embodiment of the present invention, the preprocessing of the starry sky region image of the target star region in step 21 specifically includes:

[0024] The starry sky region image of the target star region is divided into blocks for statistical analysis. Median filtering is used to remove the image background and retain the star targets.

[0025] Furthermore, in one embodiment of the present invention, step 21 involves extracting multiple star-shaped targets from the image and obtaining the pixel coordinates of each star-shaped target, specifically as follows:

[0026] A preset standard brightness threshold is used to filter star targets. Subpixel centroids are calculated for the filtered star targets to obtain the pixel coordinates of each star target.

[0027] Furthermore, in one embodiment of the present invention, step 22, which involves feature matching based on the pixel coordinates of each star point target with a reference star catalog, specifically includes:

[0028] False star targets are removed based on the pixel coordinates of each star target. The remaining star targets are sorted from high to low brightness and the top 200 to 500 star targets are retained. It is then determined whether there are valid initial parameters. If so, feature matching is performed with the reference star catalog. If not, a limited blind solution is performed and then feature matching is performed with the reference star catalog.

[0029] Furthermore, in one embodiment of the present invention, feature matching in step 22 specifically includes:

[0030] Invariant features between star targets are extracted, and a kd-tree is constructed to quickly match star targets with a reference star catalog to generate candidate matching pairs. The RANSAC algorithm is then used to fit the transformation model and eliminate incorrect matches.

[0031] Furthermore, in one embodiment of the present invention, the astronomical measurement parameters include at least right ascension coordinates, declination coordinates, pixel ratio, rotation angle, and distortion coefficient.

[0032] Furthermore, in one embodiment of the present invention, if the number of correctly matched star pairs is less than a threshold, a retry strategy is initiated. The retry strategy is any one of expanding the search range of the reference star catalog, adjusting the standard brightness threshold, and supplementing the initial parameters.

[0033] The atmospheric coherence length measurement adaptive pointing and tracking system of the present invention is constructed based on the above method and includes the following modules:

[0034] The acquisition module uses a guide camera to acquire images of the starry sky region of the target star area;

[0035] The analysis module analyzes the starry sky image of the target star region to obtain astrometry parameters;

[0036] The adjustment module fine-tunes the turntable based on astrometry parameters, so that the target star is on the target surface of the primary mirror camera. It adjusts the exposure time and gain of the primary mirror camera according to the star's magnitude, and automatically adjusts the two light spots of the target star to be centered in the field of view of the primary mirror camera.

[0037] The calculation module uses the primary mirror camera to acquire images of the target star in real time and calculates the atmospheric coherence length based on the images of the target star.

[0038] The judgment module checks at fixed intervals whether the atmospheric coherence length value has null or outlier values.

[0039] If the atmospheric coherence length value is null or an anomaly in the recapture module, the turntable will automatically point to the next target star and re-execute the analysis module to the judgment module. If the atmospheric coherence length value is not null or an anomaly, the atmospheric coherence length measurement task will continue.

[0040] This invention solves the technical problems of existing technologies, such as low recognition and alignment efficiency, weak adaptive capability, insufficient anti-interference ability, and poor system coordination. Specific beneficial effects include:

[0041] 1. This invention proposes an adaptive pointing and tracking method for atmospheric coherence length measurement. By using a turntable for coarse pointing and image analysis, the search range is significantly reduced, the star-finding time is shortened, and the extraction accuracy and recognition reliability of stellar beacons in low light and noisy backgrounds are effectively improved. This lays the foundation for high-precision measurement, enables fast and accurate star point recognition and initial alignment, and solves the problem of low recognition and alignment efficiency in existing technologies.

[0042] 2. This invention proposes an adaptive pointing and tracking method for atmospheric coherence length measurement. Addressing the weakness of existing technologies in terms of adaptive adaptability, this method uses real-time feedback from image analysis results to fine-tune the turntable, effectively compensating for tracking deviations caused by stellar diurnal motion and mechanical errors, thus avoiding the accumulation of deviations. Simultaneously, the exposure time and gain of the primary mirror camera are adjusted according to stellar magnitude to ensure a stable and suitable beacon light source for measurement, enhancing the system's adaptability to dynamic fluctuations in the nighttime environment.

[0043] 3. This invention proposes an adaptive pointing and tracking method for atmospheric coherence length measurement. Addressing the insufficient anti-interference capability of existing technologies, in the star point resolution stage, it enhances the algorithm's resistance to transient interference by filtering out spurious star points such as cosmic rays and employing robust algorithms like RANSAC to eliminate incorrect matches. When star map matching fails or image resolution is unsuccessful, parameters can be automatically adjusted, avoiding interruptions caused by brief interference, achieving rapid reacquisition and stable tracking, and significantly improving the system's robustness and continuous operation capability.

[0044] 4. This invention proposes an adaptive pointing and tracking method for atmospheric coherence length measurement. Addressing the issue of poor system coordination, it ensures strict consistency between the tracking state and the measurement field of view through coaxial setup and coordinated operation of the primary mirror camera and the guide camera. This achieves fully automated and closed-loop control from target pointing, image analysis, real-time calculation to anomaly handling. By monitoring the validity of atmospheric coherence length data in real time, the system can automatically determine and switch target stars, enabling adaptive scheduling and continuous operation of the measurement task. This fundamentally avoids the accumulation of invalid data and ensures the continuity and reliability of the measurement data. Attached Figure Description

[0045] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0046] Figure 1 This is a flowchart of the adaptive pointing and tracking method for atmospheric coherence length measurement as described in Implementation Method 1;

[0047] Figure 2 This is a flowchart of the starry sky region image acquisition process for the target star region as described in Implementation Method 2;

[0048] Figure 3 This is a flowchart of the starry sky region image analysis process for the target star region as described in Implementation Method 3. Detailed Implementation

[0049] Various embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0050] Implementation Method 1: Atmospheric coherence length is a core parameter for quantifying the intensity of atmospheric turbulence disturbances to optical wavefronts. It directly affects the correction accuracy of adaptive optics systems, the imaging quality of astronomical observations, and the stability of laser atmospheric transmission, and has significant application value in fields such as astrophysics, atmospheric optics, and laser communication. Traditional methods suffer from core defects such as low identification and alignment efficiency, weak adaptive adaptability, insufficient anti-interference capability, and poor system coordination, which limit the accuracy and reliability of nighttime atmospheric coherence length measurements.

[0051] To address the aforementioned technical problems, this embodiment proposes an adaptive pointing tracking method for atmospheric coherence length measurement, such as... Figure 1 As shown, a multi-stage star-finding, star-point enhancement, and dynamic compensation strategy is employed to achieve rapid alignment and stable tracking of beacon sources in low-light nighttime environments. Exposure parameters are dynamically adjusted based on astrometric parameters, and the turntable is fine-tuned to effectively compensate for stellar motion and environmental changes, ensuring stable and continuous tracking. Furthermore, by identifying null and outlier values, the method exhibits strong anti-interference and rapid recapture capabilities, enabling rapid recovery after brief beacon loss, ensuring data continuity, and guaranteeing high accuracy and reliability of atmospheric coherence length measurements.

[0052] The adaptive pointing and tracking method for atmospheric coherence length measurement includes the following steps:

[0053] Step 1: Use a guide camera to acquire images of the starry sky region of the target star area;

[0054] Step 2: Analyze the starry sky image of the target star region to obtain astrometry parameters;

[0055] Furthermore, after image analysis, it is determined whether the image analysis was successful. If the analysis is successful, the turntable drives the payload to automatically make fine adjustments so that the star is on the target surface of the primary mirror camera. If the analysis fails, the guide mirror camera takes multiple pictures of the target starry sky area and then re-executes the image analysis.

[0056] Step 3: Fine-tune the turntable based on the astrometry parameters so that the target star is on the target surface of the primary mirror camera. Adjust the exposure time and gain of the primary mirror camera according to the star's magnitude so that the star can be used as a beacon light source to measure the atmospheric coherence length. Automatically adjust the two light spots of the target star to be centered in the field of view of the primary mirror camera.

[0057] The exposure time used in this embodiment is generally less than 9500 microseconds, so that the camera frame rate is greater than 100Hz, and the gain is automatically adjusted according to the actual observation.

[0058] Step 4: Use the primary mirror camera to acquire images of the target star and calculate the atmospheric coherence length in real time based on the target star images;

[0059] Step 5: Determine at fixed intervals whether there are any null or outlier values ​​in the atmospheric coherence length value;

[0060] Step 6: If the atmospheric coherence length value is empty or an anomaly, the recommended stellar turntable will automatically point to the next target star, and steps 2 to 5 will be executed again. If the atmospheric coherence length value is not empty or an anomaly, the atmospheric coherence length measurement task will continue.

[0061] In this embodiment, the recommended stars are neighboring stars selected in real time by the measurement software based on a built-in star catalog that meet preset conditions (such as magnitude less than 2, altitude angle greater than 20 degrees, and not currently occupied by the observation task). The turntable automatically points to the next available target star based on this recommendation list.

[0062] Implementation Method Two: This implementation method further defines the adaptive pointing and tracking method for atmospheric coherence length measurement described in Implementation Method One. Specifically, in step 1, a guide camera is used to acquire an image of the starry sky region of the target star region.

[0063] The primary camera and guide camera are aligned coaxially to obtain the current latitude, longitude, and time information. Combined with the initial right ascension and declination coordinates of the target star, the guide camera is turned towards the target star region using a turntable to acquire images of the star region.

[0064] like Figure 2 As shown, in this embodiment, the primary mirror camera and the guide camera are automatically / manually adjusted to a coaxial state. The atmospheric coherence length measurement instrument software obtains latitude, longitude, and time information through the GNSS system and synchronizes the time information to the computer system time. The right ascension and declination coordinates of the target star are manually entered or the right ascension and declination coordinates are input by clicking on the star in the star map in the software. The turntable with a load is moved to point to the target star region. After the turntable stabilizes, the guide camera takes a picture of the star region of the target area and transmits it to the image analysis unit.

[0065] Implementation Method 3: This implementation method further defines the adaptive pointing and tracking method for atmospheric coherence length measurement described in Implementation Method 1. This implementation method constructs a highly robust star map analysis process for weak light interference environments. Through a closed-loop design of "preprocessing - intelligent strategy selection - adaptive retry - model iterative optimization", it overcomes the core pain points of traditional star map recognition, such as low success rate (typical industry value <70%) and insufficient solution accuracy under thin clouds, moonlight interference, or initial pointing deviation. This provides a sub-arcsecond stable field of view foundation for subsequent atmospheric coherence length measurement.

[0066] In step 2, the starry sky image of the target star region is analyzed, such as... Figure 3 As shown, it includes the following steps:

[0067] Step 21: Preprocess the starry sky image of the target star region, extract the star targets in the image, and obtain the pixel coordinates of each star target;

[0068] In this embodiment, the preprocessing of the starry sky image of the target star region specifically includes the following steps:

[0069] Step 211: Load the image of the starry sky region containing the target star region;

[0070] Step 212: Read image files, supporting image formats such as FITS, PNG, and TIFF;

[0071] Step 213: Parse image metadata, including bit depth, pixel size, initial right ascension coordinates, declination coordinates, focal length, and other information;

[0072] Step 214: Divide the starry sky region image of the target star region into blocks for statistical analysis, and use median filtering to estimate and subtract the background, highlighting and retaining the star targets;

[0073] The extraction of multiple star-shaped targets from the image and the acquisition of the pixel coordinates of each star-shaped target specifically includes the following steps:

[0074] Step 215, repeat the star point extraction;

[0075] Step 216: Use a preset standard brightness threshold for filtering. If the brightness is 3-5 times higher than the background standard deviation, pure noise will be eliminated to obtain the star targets that pass the filtering.

[0076] Step 217: Perform sub-pixel centroid calculation on the star point image, and use the centroid method or Gaussian fitting method to obtain the pixel coordinates of each star point target with high precision.

[0077] Step 22: Based on the pixel coordinates of each star target, perform feature matching with the reference star catalog and eliminate incorrect matches;

[0078] The feature matching based on the pixel coordinates of each star target with the reference star catalog specifically includes the following steps:

[0079] Step 221 involves star point filtering to remove false star points such as cosmic rays and prominent imperfections. This effectively suppresses detector thermal noise and optical system vignetting effects, improving the star point signal-to-noise ratio by ≥30% and significantly reducing the false detection rate in subsequent star point extraction.

[0080] Step 222: Sort by brightness, retaining the top 200-500 bright stars to improve matching efficiency. An adaptive threshold and centroid sub-pixel positioning algorithm is employed to ensure stable star extraction even with background light variations of ±50%, achieving a positional accuracy of 0.1 pixels.

[0081] Step 223 determines whether there are valid initial parameters, specifically including: precise time and latitude / longitude provided by the GNSS system (Global Navigation Satellite System), and azimuth and elevation angles calibrated for true north, fed back by the turntable encoder. The system confirms the validity of these parameters by determining whether they have been successfully acquired and are within a reasonable physical range (e.g., time is not empty, latitude / longitude is valid, and turntable angles are within limits). If they exist, a precise search of the reference star catalog is performed, and star point feature matching is performed by cropping according to the sky region and magnitude range. If they do not exist, finite blind solution is used for star point matching, including generating candidate sky regions based on the relative distribution of star points, batch searching the star catalog, and selecting the candidate sky region with the highest matching degree. When there are valid initial parameters, the solution is completed in seconds; when there are no valid initial parameters, it seamlessly switches to finite blind solution, realizing intelligent diversion of the resolution strategy and improving the system response efficiency by more than 2 times.

[0082] The feature matching specifically includes the following steps:

[0083] Step 224: Extract invariant features, including relative distances between star points, included angles, and resistance to rotation / scaling.

[0084] Step 225: Perform fast matching using a kd-tree (tree data structure) to generate candidate matching pairs of image star points and reference star catalog;

[0085] Based on the extraction of invariant features using triangular geometric invariants, this method exhibits strong robustness to image rotation and scaling, achieving a matching accuracy of >98% (actual test data). Through this multi-scale star pattern search and rotation-invariant matching method, it can still successfully identify sky regions even with an initial pointing deviation >5°, completely resolving the industry-wide problem of interruption upon loss of lock.

[0086] Step 226 involves using the RANSAC algorithm to remove incorrect matches, including fitting a transformation model, retaining correct matches, and setting a preset threshold for matches. If a match fails (matches < threshold), a retry strategy is implemented, including expanding the star catalog search range, adjusting the star point extraction threshold, and prompting the user to supplement initial parameters. By dynamically adjusting the star point extraction threshold and the star catalog search radius, the system's resolution success rate under thin cloud / moonlight interference increased from 65% to over 95% (comparative test data).

[0087] Step 23: Using correctly matched star pairs, establish a projection model from the celestial sphere to the image plane, calculate the initial astronomical measurement parameters, and employ a perspective projection model with distortion correction to control the mapping error from celestial coordinates to pixel coordinates within 0.5 pixels, providing a mathematical foundation for sub-arcsecond pointing accuracy. Specifically:

[0088] If feature matching is successful (matching pairs ≥ threshold), then astrometry parameter calculation is performed. Using the correctly matched star pairs, the Direct Linear Transform (DLT) algorithm or least squares method is used to solve for the projection transformation matrix (or its equivalent parameters, such as rotation, scaling, translation, and distortion coefficients) from the celestial right ascension and declination coordinate system to the camera image pixel coordinate system. This yields the precise right ascension and declination coordinates corresponding to the image center, as well as other astrometry parameters. The initial astrometry parameters include right ascension coordinates, declination coordinates, pixel ratio, rotation angle, distortion coefficients, etc.

[0089] Step 24: Iteratively optimize the initial astrometry parameters until the residual between the coordinates of the correctly matched star pair in the reference star catalog and the coordinates in the initial astrometry parameters meets a preset accuracy threshold. The final astrometry parameters are then obtained, specifically:

[0090] Least square fitting is performed to minimize the residual between "star catalog coordinates and solution coordinates". The residual is verified and iterated, star points with excessive residuals are removed, and the fit is refitted to ensure that RMS (root mean square) < 1 arcsec (1 arcsecond), effectively eliminating solution drift caused by interference from cosmic rays, binary stars, etc.

[0091] Implementation Method 4: An adaptive pointing and tracking system for atmospheric coherence length measurement, the system being constructed based on the method described in Implementation Method 1, and comprising the following modules:

[0092] The acquisition module uses a guide camera to acquire images of the starry sky region of the target star area;

[0093] The analysis module analyzes the starry sky image of the target star region to obtain astrometry parameters;

[0094] The adjustment module fine-tunes the turntable based on astrometry parameters, so that the target star is on the target surface of the primary mirror camera. It adjusts the exposure time and gain of the primary mirror camera according to the star's magnitude, and automatically adjusts the two light spots of the target star to be centered in the field of view of the primary mirror camera.

[0095] The calculation module uses the primary mirror camera to acquire images of the target star in real time and calculates the atmospheric coherence length based on the images of the target star.

[0096] The judgment module checks at fixed intervals whether the atmospheric coherence length value has null or outlier values.

[0097] If the atmospheric coherence length value is null or an anomaly in the recapture module, the turntable will automatically point to the next target star and re-execute the analysis module to the judgment module. If the atmospheric coherence length value is not null or an anomaly, the atmospheric coherence length measurement task will continue.

[0098] In this embodiment, the atmospheric coherence length measurement adaptive pointing and tracking system includes:

[0099] ① Primary camera

[0100] The primary camera is used to acquire dual-spot images of the target star, which serve as the basis for calculating atmospheric coherence length.

[0101] ②Guide camera

[0102] The guide camera is used to acquire star maps with a large field of view, and to complete target sky region analysis and closed-loop pointing tracking.

[0103] ③ Turntable

[0104] The turntable includes azimuth and pitch mechanisms, used to perform target pointing and tracking under load.

[0105] ④ GNSS system

[0106] GNSS systems provide latitude, longitude, elevation, and precise time for celestial coordinate transformation and pointing calculations.

[0107] ⑤ Industrial control computer

[0108] The industrial control computer runs the measurement software to complete data processing, equipment control, and result output.

[0109] ⑥ Measurement software

[0110] The measurement software has functions such as device status self-check, automatic pointing, real-time calculation and anomaly handling.

[0111] The system connects to each hardware module via Ethernet, serial port, or USB. The measurement software supports self-start and device status self-test functions to ensure that the system quickly enters working state after power-on.

[0112] Atmospheric coherence length measurement is performed using an adaptive pointing and tracking system based on atmospheric coherence length measurement, specifically including the following:

[0113] (1) Power-on initialization and communication establishment

[0114] ① Software starts automatically

[0115] After the system is powered on, the measurement software automatically loads the configuration file, including camera model, lens focal length, turntable zero point definition, star catalog path, etc.

[0116] ② Automatic connection of peripheral devices

[0117] The measurement software automatically scans and establishes communication links with each hardware module, and reads equipment status parameters (such as camera parameters, turntable current position, GNSS positioning status, etc.).

[0118] ③ Coaxial adjustment

[0119] The system supports automatic or manual adjustment of the optical axis deviation between the primary mirror camera and the guide camera.

[0120] ④ Initialization in the due north direction

[0121] After the turntable is powered on, it will automatically / manually return to zero and establish the correspondence between the azimuth reference and the geographic coordinate system.

[0122] ⑤ GNSS data acquisition

[0123] The system reads latitude, longitude, elevation, and UTC time to complete system clock synchronization.

[0124] (2) Target star input and coarse pointing

[0125] ① Target coordinate input

[0126] Users can manually input the right ascension and declination coordinates of the target star, or click on the target star through the star map interface, and the built-in star library will automatically fill in the right ascension, declination, and magnitude information.

[0127] ② Turntable coarse direction

[0128] The system converts the right ascension and declination of the target star into local horizontal coordinates based on the GNSS position and time, and generates turntable motion commands.

[0129] ③ Stable waiting and guidance camera shooting

[0130] After the turntable is in position and enters a stable state, the guiding camera acquires star images of the target area and transmits them to the image analysis unit.

[0131] (3) Guiding star image analysis and astrometric solution

[0132] ① Image loading and preprocessing

[0133] The system reads star images acquired by the guiding camera, supports multiple image formats, and highlights star points through background estimation and subtraction algorithms.

[0134] ②Star point extraction and filtering

[0135] The system detects star points and calculates subpixel centroids, removes false star points, and retains the top 200-500 brightest stars by brightness.

[0136] ③ Star map matching and astrometry

[0137] The system matches a reference star catalog based on star distribution features, uses a robust algorithm to eliminate incorrect matches, fits a projection transformation model, and calculates parameters such as right ascension and declination, pixel ratio, and rotation angle corresponding to the image center to ensure that the RMS error is less than 1 arcsecond.

[0138] (4) Closed-loop fine-tuning of pointing and star locking of primary mirror camera

[0139] Based on the analysis results of the guide star image, the system generates turntable fine-tuning instructions to center the target star within the primary mirror camera's field of view. If analysis fails, the measurement software automatically adjusts its strategy (such as increasing exposure or expanding the search area) until success is achieved or manual intervention is prompted.

[0140] (5) Real-time calculation and anomaly handling

[0141] ① Real-time calculation

[0142] The primary camera performs real-time image processing within the ROI region, outputting coherence length estimates, confidence levels, and background noise levels.

[0143] ② Exception handling

[0144] The system detects whether the calculation results are abnormal (such as consecutive invalid frames, excessive spot drift, etc.). If the abnormality continues for more than the set time, the target star is automatically switched.

[0145] The above provides a detailed description of the adaptive pointing and tracking method and system for atmospheric coherence length measurement proposed in this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. An adaptive pointing and tracking method for atmospheric coherence length measurement, characterized in that, Includes the following steps: Step 1: Use a guide camera to acquire images of the starry sky region of the target star area; Adjust the primary camera and guide camera to be coaxial, obtain the current latitude, longitude and time information, combine with the initial right ascension and declination coordinates of the target star, use the turntable to turn the guide camera toward the target star region, and collect the star region image of the target star region; Step 2: Analyze the starry sky image of the target star region to obtain astrometry parameters; Step 21: Preprocess the starry sky image of the target star region, extract the star targets in the image, and obtain the pixel coordinates of each star target; Step 22: Based on the pixel coordinates of each star target, perform feature matching with the reference star catalog and eliminate incorrect matches; Step 23: Using the correctly matched star pairs, establish a projection model from the celestial sphere to the image plane, and calculate the initial astrometry parameters. Step 24: Iteratively optimize the initial astronomical measurement parameters until the residual between the coordinates of the correctly matched star point pair in the reference star catalog and the coordinates in the initial astronomical measurement parameters meets the preset accuracy threshold, and then obtain the final astronomical measurement parameters. Step 3: Fine-tune the turntable based on the astrometry parameters so that the target star is on the target surface of the primary mirror camera. Adjust the exposure time and gain of the primary mirror camera according to the star's magnitude, and automatically center the two light spots of the target star in the field of view of the primary mirror camera. Step 4: Use the primary mirror camera to acquire images of the target star and calculate the atmospheric coherence length in real time based on the target star images; Step 5: Determine at fixed intervals whether there are any null or outlier values ​​in the atmospheric coherence length value; Step 6: If the atmospheric coherence length value is empty or an anomaly, the turntable will automatically point to the next target star and repeat steps 2 to 5. If the atmospheric coherence length value is not empty or an anomaly, the atmospheric coherence length measurement task will continue.

2. The adaptive pointing and tracking method for atmospheric coherence length measurement according to claim 1, characterized in that, In step 21, the starry sky region image of the target star region is preprocessed, specifically as follows: The starry sky region image of the target star region is divided into blocks for statistical analysis. Median filtering is used to remove the image background and retain the star targets.

3. The adaptive pointing and tracking method for atmospheric coherence length measurement according to claim 1, characterized in that, Step 21 involves extracting multiple star-shaped targets from the image and obtaining the pixel coordinates of each star-shaped target, specifically as follows: A preset standard brightness threshold is used to filter star targets. Subpixel centroids are calculated for the filtered star targets to obtain the pixel coordinates of each star target.

4. The adaptive pointing and tracking method for atmospheric coherence length measurement according to claim 1, characterized in that, In step 22, feature matching is performed between the pixel coordinates of each star point target and the reference star catalog, specifically as follows: False star targets are removed based on the pixel coordinates of each star target. The remaining star targets are sorted from high to low brightness and the top 200 to 500 star targets are retained. It is then determined whether there are valid initial parameters. If so, feature matching is performed with the reference star catalog. If not, a limited blind solution is performed and then feature matching is performed with the reference star catalog.

5. The adaptive pointing and tracking method for atmospheric coherence length measurement according to claim 1, characterized in that, The feature matching in step 22 specifically involves: Invariant features between star targets are extracted, and a kd-tree is constructed to quickly match star targets with a reference star catalog to generate candidate matching pairs. The RANSAC algorithm is then used to fit the transformation model and eliminate incorrect matches.

6. The adaptive pointing and tracking method for atmospheric coherence length measurement according to claim 1, characterized in that, The astronomical measurement parameters include at least right ascension coordinates, declination coordinates, pixel ratio, rotation angle, and distortion coefficient.

7. The adaptive pointing and tracking method for atmospheric coherence length measurement according to claim 1, characterized in that, If the number of correctly matched star pairs is less than a threshold, a retry strategy is initiated. The retry strategy can be any one of the following: expanding the search range of the reference star catalog, adjusting the standard brightness threshold, or supplementing the initial parameters.

8. An adaptive pointing and tracking system for atmospheric coherence length measurement, the system being constructed based on the method of claim 1, characterized in that, Includes the following modules: The acquisition module uses a guide camera to acquire images of the starry sky region of the target star area; The analysis module analyzes the starry sky image of the target star region to obtain astrometry parameters; The adjustment module fine-tunes the turntable based on astrometry parameters, so that the target star is on the target surface of the primary mirror camera. It adjusts the exposure time and gain of the primary mirror camera according to the star's magnitude, and automatically adjusts the two light spots of the target star to be centered in the field of view of the primary mirror camera. The calculation module uses the primary mirror camera to acquire images of the target star in real time and calculates the atmospheric coherence length based on the images of the target star. The judgment module checks at fixed intervals whether the atmospheric coherence length value has null or outlier values. If the atmospheric coherence length value is null or an anomaly in the recapture module, the turntable will automatically point to the next target star and re-execute the analysis module to the judgment module. If the atmospheric coherence length value is not null or an anomaly, the atmospheric coherence length measurement task will continue.

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