Method, device, data center and storage medium for ship trajectory monitoring

Abstract

This invention discloses a method, apparatus, data center, and storage medium for ship trajectory monitoring. The method includes: determining a multi-satellite message copy corresponding to each Automatic Identification System (AIS) message sent by the current ship from a message data stream acquired from multiple time-synchronized satellites. The message data stream includes the AIS message received by each satellite, the reception time, and the satellite status. Based on the time difference between the reception times of two satellites in each set of multi-satellite message copies, the solved position information of the current ship corresponding to each AIS message is determined, and this information is cleaned and optimized to obtain optimized position information. Based on the optimized position information and the corresponding satellite status, the transmission time of each AIS message sent by the current ship is determined. Based on the transmission time and the corresponding optimized position information, the movement trajectory of the current ship is determined. This achieves high-precision independent positioning and improves the accuracy of ship monitoring.

Description

Technical Field

[0001] This invention relates to the field of satellite technology, and in particular to methods, devices, data centers, and storage media for monitoring ship trajectories. Background Technology

[0002] With the continuous development of my country's maritime transport industry, traditional surveillance facilities and technologies, due to their low accuracy, narrow coverage, high operating costs, and insufficient security, can no longer adequately meet the rapidly evolving needs of maritime traffic control. Currently, global ship monitoring can be achieved by receiving Automatic Identification System (AIS) messages broadcast by ships via low-Earth orbit satellite constellations. However, the inherent characteristics of satellite AIS data pose significant challenges to its data quality, including: the lack of transmission timestamps in AIS messages, with the satellite recording the reception time, leading to time sequence discrepancies; intermittent coverage of a specific sea area by a single satellite, resulting in sparse and discontinuous ship trajectory points; and signal attenuation, collisions, and human tampering (such as AIS spoofing) during long-distance transmission, which can produce erroneous data in fields such as position and speed. Therefore, traditional single-satellite data processing results in low accuracy and poor reliability of ship trajectory reconstruction, thus the accuracy of ship trajectory monitoring needs further improvement. Summary of the Invention

[0003] To address the aforementioned problems in the prior art, this invention provides a method, apparatus, data center, and storage medium for ship trajectory monitoring. The technical problem to be solved by this invention is achieved through the following technical solution: The first aspect of this invention provides a method for monitoring ship trajectories, comprising: In the message data stream obtained from multiple time-synchronized satellites, determine the multi-satellite message copy corresponding to each Automatic Identification System (AIS) message sent by the ship. The message data stream includes the AIS message received by each satellite, the reception time, and the satellite status. Based on the time difference between the reception times of two satellites in each group of multi-satellite message copies, the current ship's position information corresponding to each AIS message is determined. Based on the position information, the decoded position information of each AIS message is cleaned and optimized to obtain the corresponding optimized position information. Based on the optimized location information and the corresponding satellite status, determine the transmission time of each AIS message sent by the ship. The current vessel's trajectory is determined based on the transmission time of each AIS message sent by the vessel and the corresponding optimized location information.

[0004] A second aspect of the present invention provides an apparatus for monitoring ship trajectories, comprising: The acquisition group module is configured to determine, from the message data stream acquired from multiple time-synchronized satellites, the multi-satellite message copy corresponding to each Automatic Identification System (AIS) message sent by the current ship, wherein the message data stream includes the AIS message received by each satellite, the reception time, and the satellite status; The optimization module is configured to determine the current ship's position information corresponding to each AIS message based on the time difference between the reception times of two satellites in each group of multi-satellite message copies, and to clean and optimize the decoded position information of each AIS message based on the decoded position information to obtain the corresponding optimized position information. The backtracking determination module is configured to determine the transmission time of each AIS message sent by the ship based on the optimized location information and the corresponding satellite status. The orbit determination module is configured to determine the current vessel's trajectory based on the transmission time of each AIS message sent by the vessel and the corresponding optimized position information.

[0005] A third aspect of the present invention provides an apparatus for monitoring ship trajectories, the apparatus including a processor and a memory storing program instructions, the processor being configured to execute the above-described method for monitoring ship trajectories when executing the program instructions.

[0006] A fourth aspect of the present invention provides a data center, comprising: a device body; The aforementioned device for monitoring ship trajectories is installed on the main body of the equipment.

[0007] A fifth aspect of the present invention provides a storage medium storing program instructions, which, when executed, perform the above-described method for monitoring ship trajectories.

[0008] The beneficial effects of this invention are: Based on the difference in reception time between multiple time-synchronized satellites receiving AIS messages, the system can clean and optimize the message data stream acquired by multiple satellites, and trace back the transmission time of the ship's AIS messages. This provides a unified and accurate time reference for all data, achieving independent positioning with higher accuracy than single-satellite or self-reported positions. Furthermore, based on the transmission time and optimized position information, it can generate high-precision and highly reliable ship trajectory data, effectively compensating for satellite coverage gaps, generating smooth trajectories that conform to the ship's motion patterns, improving trajectory jump problems, and meeting the needs of ship monitoring and management.

[0009] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings.

[0010] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of a ship trajectory monitoring system provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating a method for monitoring ship trajectory provided in an embodiment of the present invention. Figure 3 This is a flowchart illustrating a method for monitoring ship trajectory provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of a ship trajectory monitoring device provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of a ship trajectory monitoring device provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of a data center device provided in an embodiment of the present invention. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0013] Low Earth Orbit (LEO) satellites are satellites that operate at relatively low altitudes above the Earth's surface, typically between 400 and 2000 km. Due to their advantages such as close proximity to the ground, high speed, and strong signal strength, LEO satellites have experienced rapid development in recent years across various application fields, including communication, remote sensing, meteorology, and navigation. High-precision real-time orbit data is fundamental for these applications. In this embodiment, multiple LEO satellites can communicate with ships, receive AIS messages sent by the ships, and transmit the received message data streams to a ground data center periodically or in real-time. The ground data can then clean and optimize these message data streams to determine the transmission time of the AIS messages sent by the ships, providing a unified and accurate time reference for all data. This achieves higher accuracy independent positioning than single-satellite or self-reported positions. Furthermore, through cross-validation of independently calculated and self-reported positions using TDOA (Time-of-Operation Optimization) and combined with a multi-dimensional adaptive dynamic threshold strategy, it is possible to identify and correct tampered AIS signals with high confidence, significantly reducing false alarm rates and greatly improving data reliability. Furthermore, based on the transmission time and optimized data, high-precision and high-reliability ship trajectory data is generated, effectively compensating for satellite coverage gaps, generating smooth trajectories that conform to the laws of ship motion, improving the trajectory jump problem, and meeting the needs of ship monitoring and management.

[0014] Figure 1 This is a schematic diagram of a ship trajectory monitoring system provided by an embodiment of the present invention. Figure 1 As shown, the ship trajectory monitoring system includes: two or more satellites 100, a ship 200 that is underway, and a data center 300 located on the ground.

[0015] Among them, Satellite 100 is a low-orbit satellite that can operate near the ground. Each satellite carries an AIS receiving payload. The onboard atomic clocks of each Satellite 100 are synchronized with time through a satellite navigation system, such as GPS, to ensure that the receiving time of each Satellite 100 receiving AIS messages is consistent with a high-precision Coordinated Universal Time (UTC) time reference.

[0016] The vessel 200 can be a boat, speedboat, etc. In this embodiment of the invention, the vessel 200 must have the function of sending AIS messages. There can be one, two, or more vessels 200 currently underway. Each vessel can send AIS messages at regular intervals or when certain conditions are met. Taking one vessel as an example, this vessel is the current vessel, and the AIS message it is sending is the current AIS message. In this way, when two or more satellites 100 receive the current AIS message, each satellite 100 records a high-precision reception time based on Coordinated Universal Time (UTC) on its payload when it receives a current AIS message. At the same time, each satellite 100 can also record the precise orbital position (ECEF coordinates) and velocity vector of the satellite corresponding to the reception time. The position and velocity information corresponding to the satellite's reception time can then be obtained through the satellite's GPS receiver and ephemeris.

[0017] Each satellite can communicate with a ground-based data center periodically or in real-time, transmitting acquired data to the data center. This data includes message data streams, which contain AIS messages received by each satellite, the reception time, and satellite status. The satellite status includes position and velocity information.

[0018] Therefore, ground-based data centers can clean and optimize the message data streams obtained from multiple time-synchronized satellites, determine the sending time of each AIS message sent by the ship, as well as the corresponding location information, and thus generate high-precision, high-reliability ship trajectory data, improving the accuracy of ship monitoring.

[0019] like Figure 2 As shown, the first aspect of this invention provides a method for monitoring ship trajectories, wherein the process of monitoring ship trajectories by a data center may include: Step 201: In the message data stream obtained from multiple time-synchronized satellites, determine the multi-satellite message copy corresponding to each broadcast Automatic Dependent Surveillance (AIS) message currently sent by the ship, wherein the message data stream includes the AIS message received by each satellite, the reception time, and the satellite status.

[0020] The onboard atomic clocks of low-Earth orbit (LEO) satellites are synchronized with time via satellite navigation systems such as GPS, meaning that LEO satellites are already time-synchronized and are also equipped with AIS receiving payloads.

[0021] In this way, when the ship 100 is currently sailing and sends a current AIS message, depending on the distribution of low-orbit satellites and the coverage of each satellite, one, two, or more satellites may receive the current AIS message through the configured AIS receiving payload and record the corresponding current reception time. In addition, the satellite also obtains and records the current position and current speed information of the satellite corresponding to the current reception time through the satellite's GPS receiver and ephemeris.

[0022] Since each satellite can transmit acquired data to a ground-based data center at regular intervals or in real time, the data center can obtain message data streams from multiple time-synchronized satellites. These message data streams include the AIS messages received by each satellite, the reception time, and the satellite status. The satellite status includes satellite position information and satellite speed information.

[0023] The message data stream includes AIS messages sent by multiple ships and received by multiple satellites. Therefore, it is necessary to determine the AIS message currently being sent by the ship from the message data stream and to combine the original AIS message sent by the ship and the corresponding messages received by two or more satellites into a multi-satellite message copy. That is, for one transmission event of the ship, the corresponding AIS messages received by two or more satellites form a multi-satellite message copy. In some embodiments, determining the multi-satellite message copy corresponding to each AIS message sent by the ship includes: determining the current multi-satellite candidate message based on the ship's unique identification information from the message data stream obtained from multiple satellites within the current first sliding window time; and determining the current multi-satellite candidate message obtained from two or more satellites with identical content bytes as the current multi-satellite message copy.

[0024] Based on the unique identification information, messages received by multiple satellites corresponding to AIS messages from the same ship can be grouped into multi-satellite candidate messages. Then, the messages in the multi-satellite candidate messages are grouped according to the content bytes, ensuring that each group of messages comes from two or more satellites.

[0025] In some embodiments of the present invention, when determining multi-satellite message replicas, matching can be performed based on message type and hash value, and verification can be performed based on time. This further ensures the correctness of the data. Therefore, determining the multi-satellite message replica corresponding to each AIS message currently sent by the ship includes: determining a first current multi-satellite candidate message based on the maritime mobile service identification code and message type from the message data streams acquired from multiple satellites within the current first sliding window time; performing CRC verification on each first current multi-satellite candidate message, and determining the first current multi-satellite candidate message that passes the CRC verification and has a matching hash value as a second current multi-satellite candidate message; determining the time difference between the reception times corresponding to the second current multi-satellite candidate messages, and determining the second current multi-satellite candidate message with a time difference less than a set time threshold as a current multi-satellite message replica.

[0026] Since the data center can receive the message data stream transmitted by each satellite in real time, a sliding window can be used to intercept the data stream and process the intercepted data accordingly. The first sliding window time can be relatively short, such as 2 seconds or 3 seconds. For example, if the current vessel is a civilian vessel, the data center can group the message data streams acquired from multiple satellites within the current 2-second sliding window according to the Maritime Mobile Service Identity (MMSI) and message type (Message ID), thus obtaining the first current multi-satellite candidate message corresponding to the current vessel. The MMSI is a globally unique nine-digit code that is transmitted via radio channels to identify vessels, coastal radio stations, and search and rescue units. Messages with completely identical MMSIs and Message IDs form the first current multi-satellite candidate message corresponding to the current vessel. Messages with identical hash values ​​are considered to originate from the same transmission event. Therefore, for the first current multi-satellite candidate message, a CRC check is performed. For the first current multi-satellite candidate message that passes the CRC check, the corresponding hash value (such as SHA-256) can be calculated. Messages with the same hash value are grouped into the corresponding second current multi-satellite candidate messages. That is, the second current multi-satellite candidate message corresponding to each transmission event is obtained. The second current multi-satellite candidate messages may be received by different satellites. Although their corresponding reception times may be different, they are AIS messages corresponding to the same transmission event. Therefore, the time difference between reception times cannot be too large and must be less than the theoretical maximum value determined based on satellite distribution. That is, the set time can be preset or determined based on the theoretical maximum value determined by satellite distribution. For example, the set time threshold is 100ms. In this way, the reception time corresponding to the second current multi-satellite candidate message is determined. Second current multi-satellite candidate messages whose time difference between reception times is greater than or equal to the set time threshold are eliminated. That is, second current multi-satellite candidate messages whose time difference is less than the set time threshold are determined as current multi-satellite message copies.

[0027] Step 102: Based on the time difference between the reception times of the two satellites in each group of multi-satellite message copies, determine the current ship's location information corresponding to each AIS message, and clean and optimize the decoded location information of each AIS message based on the location information, and obtain the corresponding optimized location information.

[0028] During the current voyage, the ship sends multiple AIS messages. For some of these AIS messages, the data center obtains corresponding multi-satellite message copies. For each set of multi-satellite message copies, two satellites can be arbitrarily selected to receive the messages and related data, and a hyperbolic positioning equation (TDOA) can be constructed and solved to obtain the current ship's position information corresponding to each AIS message. Furthermore, the signals sent by the ship will be received by the satellites after passing through the atmosphere. Therefore, atmospheric propagation needs to be considered when constructing the TDOA. Thus, in some embodiments, determining the current ship's position information corresponding to each AIS message includes: constructing a hyperbolic positioning equation as shown in formula (1) based on the time difference Δt between the reception times of the two satellites receiving the current AIS message; solving the hyperbolic positioning equation to obtain the position information P corresponding to the current ship when sending the current AIS message. v ; c Δt{I,j}=│P v P sati │ │P v P satj │+δ atmos_i,j (1) Where: c is the speed of light, P sati P sati These are the location information of the two satellites when they receive the current AIS message, δ atmos_i,j It is the atmospheric propagation delay difference obtained by estimating and correcting the integrated ionospheric and tropospheric delay models.

[0029] In some embodiments, δatmos_{i,j} can be estimated and corrected by integrating ionospheric and tropospheric delay models. Both ionospheric and tropospheric delays are caused by refraction effects on the signal as it passes through the ionosphere. The magnitude of the ionospheric delay is inversely proportional to the square of the signal frequency, while the magnitude of the tropospheric delay depends on the signal path length and atmospheric conditions. Therefore, in some embodiments, using the Klobuchar model or the NeQuick model, the ionospheric delay of satellite i can be determined as I based on the positions of the satellite and the AIS receiving payload. iAnd, the ionospheric delay of satellite j is I j Therefore, the corresponding ionospheric delay difference can be obtained as δ. ionoi,j =I i I j The tropospheric delay T for satellites i and j can be estimated using the Saastamoinen or Hopfield models, based on atmospheric conditions and the satellite's geometry. i T j And the corresponding tropospheric delay difference is obtained as δ. tropi,j =T i T j This leads to the atmospheric propagation delay difference δ. atmosi,j =δ ionoi,j +δ tropi,j .

[0030] The data stream obtained by the data center from multiple satellites includes the AIS message received by each satellite, the satellite reception time, and the satellite status. The satellite status includes the location information corresponding to the satellite receiving the AIS message. Therefore, in one embodiment, if the current multi-satellite message copy corresponding to the current AIS message sent by the ship includes: message 1 received by satellite 1, message 4 received by satellite 2, and message 8 received by satellite 3, then the corresponding time difference Δt = t_rx_sat1 - t_rx_sat2 can be obtained based on t_rx_sat1 corresponding to message 1 received by satellite 1 and t_rx_sat2 corresponding to message 4 received by satellite 2. That is, i=1, j=2. This observation Δt contains rich geometric information. It can be equal to the time difference between the current AIS message propagating from the ship to the two satellites. Then, after estimation and correction by integrating ionospheric and tropospheric delay models, the atmospheric propagation delay difference δ is obtained. atmosi,j Then, the hyperbolic positioning equation (TDOA) as shown in formula (1) can be constructed. From the message data streams obtained from multiple satellites, the position information P of satellite 1 when it receives message 1 corresponding to the current AIS message can be determined. sat1 And, the location information of satellite 2 when it receives message 4 corresponding to the current AIS message. Psat2 Then, the hyperbolic positioning equation is solved to obtain the position information P corresponding to the current ship sending the current AIS message. v .

[0031] Of course, in some embodiments, when determining the current ship's location information corresponding to each AIS message, δ may not be considered. atmos_i,j That is, the equation for the hyperbola can be c. Δt {i,j} =│Pv P sati │ │P v P satj Thus, the hyperbolic positioning equation can be solved to obtain the position information P corresponding to the time the ship sends the current AIS message. v .

[0032] Therefore, regardless of whether δ is considered atmos_i,j For each set of multi-satellite message copies, the corresponding current vessel's solution location information can be obtained. That is, for each AIS message sent by the current vessel corresponding to each set of multi-satellite message copies, the corresponding current vessel's solution location information is determined. The data center can also decode each AIS message to obtain the corresponding decoded location information.

[0033] Generally, ships also have positioning modules. Therefore, through these modules, ships can obtain corresponding position information, and thus, the AIS messages currently sent by the ship can carry position information. In some embodiments, the AIS messages sent by the ship can also carry ground speed and heading. Therefore, the position information carried can be cleaned and optimized based on the decoded position information corresponding to each AIS message. Therefore, in some embodiments, cleaning and optimizing the decoded position information decoded from each AIS message includes: decoding the current AIS message to obtain the current decoded position information; and if the position difference between the current solved position information and the current decoded position information corresponding to the current AIS message is greater than a set value, determining the current solved position information as the current optimized position information.

[0034] Any AIS message sent by the ship at the moment is considered the current AIS message. Decoding the current AIS message yields the current decoded position information P_initial. Using formula (1), the current solved position information P is obtained. v We can obtain D=|P v P_initial|, where d can be a set value, determined based on the performance of the ship, satellite, etc., or preset. If D > d, the currently solved location information Pac can be determined as the current optimized location information. Conversely, if D ≤ d, the currently decoded location information value P_initial can be determined as the current optimized location information. Thus, the location information carried in the AIS message can be cleaned and optimized based on the solved location information.

[0035] In some embodiments, the set value can be dynamic and determined based on propagated static attributes, dynamic navigation information, and navigation area geographical location information, etc. Specifically, cleaning and optimizing the decoded location information obtained from each AIS message includes: decoding the current AIS message to obtain the current decoded location information; if the location difference between the current solved location information and the current decoded location information corresponding to the current AIS message is greater than a set dynamic threshold, then the current solved location information is determined as the current optimized location information. The set dynamic threshold is determined based on one or more of the following: the current static attribute information of the current vessel, the current dynamic navigation information, the current navigation area geographical location information, and the reception time corresponding to the previous optimized location information. Of course, in some embodiments, cleaning and optimizing the decoded location information obtained from each AIS message also includes: if the location difference is less than or equal to the set dynamic threshold, then the current decoded location information is determined as the current optimized location information; or, a weighted average is performed based on the current solved location information and the current decoded location information to determine the obtained location information as the current optimized location information.

[0036] Ship static attributes include information from the ship static archive, such as ship type, length, and beam. These static attributes determine the ship's maximum physical speed and maneuverability. The dynamic threshold for Very Large Crude Carriers (VLCCs) should be lower than that for high-speed patrol boats. Ship dynamic status includes the most recently reported speed, heading, and AIS navigation status. Based on this dynamic status, the ship's current movement pattern can be determined. For ships in 'anchored' or 'berthed' status, an extremely strict dynamic threshold is used, such as 100-500 meters. In this case, any significant position jump is highly likely to be an error or deception. Navigation area geographic information includes the overlay relationship between the ship's position and geographic elements such as electronic charts, port polygons, channel boundaries, and exclusive economic zone boundaries. Different threshold precisions are applied to different areas. High-precision dynamic thresholds (100-1000 meters) are used in ports, narrow channels, and sensitive boundaries, while a more lenient threshold (3-10 kilometers) is used in open ocean areas. Of course, the dynamic threshold can be determined based on the time interval between the current receiving location and the receiving time of the previous optimized location information. The dynamic threshold can be appropriately relaxed as the time interval increases.

[0037] Therefore, a dynamic threshold T can be determined and set based on one or more of the following: the current static attribute information of the vessel, the current dynamic navigation information, the current geographical location information of the navigation area, and the reception time corresponding to the previously optimized location information. As above, if D=│P v After P_initial│, if D>T, then the current solution location information P can be...v The current optimized position information P_optimized is determined. Of course, if D≤T, the current decoded position information value P_initial can be determined as the current optimized position information P_optimized, or P... v After weighted averaging with P_initial, the resulting position information is determined as the current optimized position information P_optimized. Therefore, the position information carried in the AIS message can be cleaned and optimized based on the solved position information. The weight coefficients corresponding to the currently solved and decoded position information can be preset, or determined based on the current ship performance and historical data.

[0038] Step 203: Based on the optimized location information and the corresponding satellite status, determine the transmission time for each AIS message sent by the current ship.

[0039] The satellite status includes satellite position information. Therefore, by using the optimized position information P_optimized and the satellite position, the actual transmission time t_tx of the message can be calculated more accurately using formula (2).

[0040] t_tx = t_rx_sat - |P_optimized - P_sat| / c(1) Where: c is the speed of light, t_rx_sat is the reception time of one satellite in the multi-satellite message copy corresponding to the current AIS message, P_sat is the location information corresponding to the satellite when receiving the current AIS message, and P_optimized is the optimized location information corresponding to the current AIS message.

[0041] Therefore, the calculable t_tx becomes the valid timestamp of the current AIS message, solving the problem of the lack of a source timestamp.

[0042] Step 204: Determine the current vessel's trajectory based on the transmission time of each AIS message sent by the vessel and the corresponding optimized location information.

[0043] Through the above steps 202 and 203, the optimized location information P_optimized and the transmission time t_tx corresponding to each AIS message are obtained, which can then form a series of optimized data points (P_optimized, t_tx). Based on these data, the current ship's motion trajectory can be generated.

[0044] The cleaned and optimized data points are input into a ship-based kinematic model, such as a Kalman filter or a fixed-interval smoother. The kinematic model predicts the ship's next state based on physical laws and fuses this prediction with the observations. The final output is a smooth, continuous, consistent, and high-precision four-dimensional trajectory (longitude, latitude, altitude, and time), including estimated velocity and acceleration information. Therefore, in some embodiments, determining the current ship's trajectory involves: inputting data points consisting of transmission time and optimized position information into a Kalman filter; obtaining the current four-dimensional trajectory of the ship after prediction and updating using a Kalman filter constant-velocity (CV) model or constant-rotational-rate (CTRV) model, where the four-dimensional trajectory includes longitude, latitude, altitude, and time.

[0045] For example, after the above processing, a series of optimized data points (P_optimized, t_tx) are obtained. These data points are input into a Kalman filter, which predicts and updates the trajectory based on a constant velocity CV model, ultimately outputting a smooth trajectory. For example, with an initial position of (x0, y0, z0) and an initial velocity of (vx0, vy0, vz0), the filter will gradually correct the trajectory based on these initial values ​​and subsequent observations, eventually generating and outputting a high-precision four-dimensional trajectory. This greatly improves the trajectory skipping problem caused by satellite coverage gaps and data sparsity.

[0046] As can be seen, in this embodiment of the invention, by cross-validating the independently calculated position using TDOA with the self-reported position, and combining it with a multi-dimensional adaptive dynamic threshold strategy, tampered AIS signals can be identified and corrected with high confidence, while significantly reducing the false alarm rate and greatly improving the reliability of the data. Furthermore, relying on the clock-bias-free observations provided by the high-precision spaceborne atomic clock, combined with TDOA geometric calculation, the limitations of GPS accuracy inherent in AIS messages are overcome, achieving independent positioning with higher accuracy than single-satellite or self-reported positions. Moreover, by accurately tracing back the transmission time, a unified and accurate time reference is provided for all data, laying the foundation for multi-source data fusion and accurate trajectory calculation. Based on the transmission time and the optimized data, high-precision, high-reliability ship trajectory data is generated, effectively compensating for satellite coverage gaps, generating smooth trajectories that conform to the ship's motion patterns, improving the trajectory jump problem, and meeting the needs of ship monitoring and management. The process of dynamically determining the set threshold can intelligently adjust the detection sensitivity according to the ship type, behavior status, and geographical location, ensuring optimal cleaning efficiency in different scenarios such as ports, waterways, and the open ocean, enhancing the practicality and robustness of ship monitoring.

[0047] The following describes the operational process in a specific embodiment, illustrating the ship trajectory monitoring process provided by the embodiments of the present invention.

[0048] In one embodiment of the present invention, the ship trajectory monitoring system can be as follows: Figure 1 As shown, the ships can be civilian vessels, and each low-Earth orbit satellite is equipped with an AIS receiving payload for time synchronization. Figure 3 As shown, the method for monitoring ship trajectories includes the following steps: Step 301: The data center receives message data streams from multiple time-synchronized satellites.

[0049] The message data stream includes the AIS message received by each satellite, the reception time, and the satellite status, while the satellite status includes: satellite position information and velocity information.

[0050] Step 302: The data center uses a 2-second sliding window to extract data from the message data stream. The AIS messages in each segment of the extracted data are grouped according to MMSI and Message ID to obtain the first multi-satellite candidate message corresponding to each AIS message sent by the current ship.

[0051] Step 303: The data center determines the packets with completely identical hash values ​​in each group of first multi-star candidate packets as second multi-star candidate packets, and determines the packets in each group of second multi-star candidate packets whose corresponding reception time difference is less than a set time as the current multi-star packet replica.

[0052] Each first multi-satellite candidate message is subjected to CRC verification. Messages with the same hash value are identified as second multi-satellite candidate messages. The second multi-satellite candidate messages are then subjected to reception time verification to determine the multi-satellite message copy corresponding to each transmission event, i.e., each AIS message sent by the current ship.

[0053] Step 304: The data center identifies a set of multi-satellite message copies as the current multi-satellite message copy.

[0054] Step 305: The data center determines the atmospheric propagation delay difference δatmos_{i,j} based on the time difference Δt between the reception times of the current AIS message received by the two satellites in the current multi-satellite message copy, by integrating the ionospheric and tropospheric delay models, and obtains the solution location information P corresponding to the current ship sending the current AIS message using formula (1). v .

[0055] Step 306: The data center decodes the current AIS message to obtain the current decoded location information P_initial and the corresponding error distance value D. Based on the current static attribute information of the current ship, the current dynamic navigation information, the current navigation area geographical location information, and one or more of the reception time corresponding to the previous optimized location information, the dynamic threshold T is determined.

[0056] D=│P v P_initial│.

[0057] Step 307: Is D>T true? Proceed to step 308; otherwise, proceed to step 309.

[0058] Step 308, the data center will send the current solution location information P v Once the current optimized location information is confirmed, proceed to step 310.

[0059] Step 309, the data center will send the current solution location information P v The weighted fusion value of the current decoded position information P_initial is determined as the current optimized position information, and the process proceeds to step 310.

[0060] Step 310: Based on the current optimized location information P_optimized and the satellite location, the data center can backtrack and calculate the actual sending time t_tx of the current AIS message using formula (2).

[0061] Step 311: Determine if each group of multi-satellite message replicas is a replica of the current multi-satellite message. If yes, proceed to step 312; otherwise, return to step 304.

[0062] Step 312: The data center constructs a data point (P_optimized, t_tx) based on the optimized location information P_optimized and the sending time t_tx corresponding to each AIS message.

[0063] Step 313: The data center inputs the data points (P_optimized, t_tx) into the Kalman filter to obtain the current four-dimensional motion trajectory of the ship after the Kalman filter predicts and updates according to the constant velocity CV model, which includes estimated speed and acceleration information.

[0064] As can be seen, in this embodiment, the data center can clean and optimize the message data stream acquired by multiple satellites based on the difference between the reception times of AIS messages received by multiple time-synchronized satellites, and trace back the transmission time of the AIS messages sent by the ship. This achieves independent positioning with higher accuracy than single-satellite or self-reported positions. Furthermore, it can independently calculate the position and cross-validate the self-reported position through TDOA, and combine this with a multi-dimensional adaptive dynamic threshold strategy to identify and correct tampered AIS signals with high confidence, while significantly reducing the false alarm rate and greatly improving data reliability. Then, based on the cleaned and optimized data, high-precision and high-reliability ship trajectory data is generated, effectively compensating for satellite coverage gaps and generating smooth trajectories that conform to ship motion patterns, meeting the needs of ship monitoring and management. Of course, it can also intelligently determine and set dynamic thresholds based on ship type, behavior status, and geographical location, i.e., adjust the detection sensitivity, so that the solution can maintain optimal cleaning efficiency in different scenarios such as ports, waterways, and the open ocean, enhancing the practicality and robustness of the method.

[0065] Based on the above process of ship trajectory monitoring, a device for ship trajectory monitoring can be constructed. Figure 4 The device for monitoring ship trajectories provided in this embodiment of the invention can be applied in data centers, such as... Figure 4 As shown, the device 400 includes: a group acquisition module 410, a determination and optimization module 420, a backtracking determination module 430, and a trajectory generation module 440.

[0066] The acquisition group module 410 is configured to determine, from the message data stream acquired from multiple time-synchronized satellites, the multi-satellite message copy corresponding to each broadcast Automatic Dependent Surveillance (AIS) message currently sent by the ship, wherein the message data stream includes the AIS message received by each satellite, the reception time, and the satellite status.

[0067] The optimization module 420 is configured to determine the current ship's position information corresponding to each AIS message based on the time difference between the reception times of two satellites in each group of multi-satellite message copies, and to clean and optimize the decoded position information of each AIS message based on the decoded position information to obtain the corresponding optimized position information.

[0068] The backtracking determination module 430 is configured to determine the transmission time of each AIS message sent by the ship based on the optimized location information and the corresponding satellite status.

[0069] The orbit determination module 440 is configured to determine the current vessel's trajectory based on the transmission time of each AIS message sent by the vessel and the corresponding optimized position information.

[0070] In some embodiments, the group acquisition module 410 includes: The first determining unit is configured to determine the first current multi-satellite candidate message from the message data streams acquired from multiple satellites within the current first sliding window time, based on the maritime mobile service identification code and message type.

[0071] The second determining unit is configured to perform CRC verification on each first current multi-satellite candidate message, and determine the first current multi-satellite candidate message that passes the CRC verification and whose hash value matches as the second current multi-satellite candidate message.

[0072] The third determining unit is configured to determine the time difference between the receiving times of the second current multi-satellite candidate messages, and to determine the second current multi-satellite candidate messages whose time difference is less than a set time threshold as current multi-satellite message copies.

[0073] In some embodiments, the optimization module 420 includes: The building unit is configured to base its data on the time difference Δt between the reception times of the current AIS messages received by the two satellites. {i,j} Construct the hyperbolic positioning equation as shown in formula (1).

[0074] The solving unit is configured to solve the hyperbolic positioning equation to obtain the solved position information P corresponding to the time the ship sends the current AIS message. v ; c Δt{I,j}=│P v P sati │ │P v P satj │+δ atmos_i,j (1) Where: c is the speed of light, P sati P sati These are the location information of the two satellites when they receive the current AIS message, δ atmos_i,j It is the atmospheric propagation delay difference obtained by estimating and correcting the integrated ionospheric and tropospheric delay models.

[0075] In some embodiments, the optimization module 420 includes: The decoding unit is configured to decode the current AIS message to obtain the current decoding location information.

[0076] The first optimization unit is configured to determine the current solved location information as the current optimized location information when the location difference between the current solved location information and the current decoded location information corresponding to the current AIS message is greater than a set dynamic threshold. The set dynamic threshold is determined based on one or more of the following: the current static attribute information of the current ship, the current dynamic navigation information, the current navigation area geographical location information, and the reception time corresponding to the previous optimized location information.

[0077] In some embodiments, the optimization module 420 further includes: The second optimization unit is configured to determine the current decoded position information as the current optimized position information when the position difference is less than or equal to a set dynamic threshold; or, to determine the position information obtained by weighted averaging based on the current solved position information and the current decoded position information as the current optimized position information.

[0078] In some embodiments, the orbit determination module 440 is specifically configured to input data points consisting of transmission time and optimized position information into a Kalman filter; and obtain the current four-dimensional motion trajectory of the ship after the Kalman filter predicts and updates according to the constant speed CV model or the constant speed CTRV model. The four-dimensional motion trajectory includes: longitude, latitude, altitude, and time.

[0079] As can be seen, in this embodiment of the invention, the device for ship trajectory monitoring can clean and optimize the message data stream acquired by multiple satellites based on the difference between the reception times of AIS messages received by multiple time-synchronized satellites, and trace back the transmission time of the ship's AIS messages. This achieves independent positioning with higher accuracy than single-satellite or self-reported position. Furthermore, based on the transmission time and the optimized position information, it can generate high-precision and high-reliability ship trajectory data, effectively compensating for satellite coverage gaps, generating smooth trajectories that conform to the ship's motion patterns, improving the trajectory jump problem, and meeting the needs of ship monitoring and management.

[0080] Combination Figure 5 This invention provides a device 500 for monitoring ship trajectories, comprising: The processor 1000 and memory 1001 may further include a communication interface 1002 and a bus 1003. The processor 1000, communication interface 1002, and memory 1001 can communicate with each other via the bus 1003. The communication interface 1002 can be used for information transmission. The processor 1000 can call logical instructions stored in the memory 1001 to execute the method for ship trajectory monitoring described in the above embodiment.

[0081] Furthermore, the logic instructions in the aforementioned memory 1001 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium.

[0082] The memory 1001, as a computer-readable storage medium, can be used to store software programs and computer-executable programs, such as program instructions / modules corresponding to the methods in the embodiments of the present invention. The processor 1000 executes functional applications and data processing by running the program instructions / modules stored in the memory 1001, that is, it implements the method for ship trajectory monitoring in the above method embodiments.

[0083] The memory 1001 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the terminal device. Furthermore, the memory 1001 may include high-speed random access memory and may also include non-volatile memory.

[0084] This invention provides a device for monitoring ship trajectory, comprising: a processor and a memory storing program instructions, wherein the processor is configured to execute a method for monitoring ship trajectory when executing the program instructions.

[0085] like Figure 6 This invention provides a data center, comprising: a device body 600, and the aforementioned device 400 (500) for ship trajectory monitoring. The device for ship trajectory monitoring is installed on the device body 600. The installation relationship described herein is not limited to placement within the product, but also includes installation connections with other components of the product, including but not limited to physical connections, electrical connections, or signal transmission connections. Those skilled in the art will understand that the device 400 (500) for ship trajectory monitoring can be adapted to a feasible device body 600 to achieve other feasible embodiments.

[0086] This invention provides a storage medium storing program instructions, which, when executed, perform the method for monitoring ship trajectories as described above.

[0087] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0088] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0089] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0090] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for monitoring ship trajectory, characterized in that, include: In the message data stream obtained from multiple time-synchronized satellites, determine the multi-satellite message copy corresponding to each Automatic Identification System (AIS) message sent by the ship. The message data stream includes the AIS message received by each satellite, the reception time, and the satellite status. Based on the time difference between the reception times of two satellites in each group of multi-satellite message copies, the current ship's position information corresponding to each AIS message is determined. Based on the position information, the decoded position information of each AIS message is cleaned and optimized to obtain the corresponding optimized position information. Based on the optimized location information and the corresponding satellite status, determine the transmission time of each AIS message sent by the ship. The current vessel's trajectory is determined based on the transmission time of each AIS message sent by the vessel and the corresponding optimized location information.

2. The method as described in claim 1, characterized in that, The process of determining the multi-satellite message copy corresponding to each AIS message currently sent by the ship includes: Within the current first sliding window time, the first current multi-satellite candidate message is determined based on the maritime mobile service identification code and message type from the message data stream acquired from multiple satellites. Perform CRC check on each first current multi-satellite candidate message, and determine the first current multi-satellite candidate message that passes the CRC check and has a matching hash value as the second current multi-satellite candidate message; Determine the time difference between the receiving times of the second current multi-satellite candidate messages, and identify the second current multi-satellite candidate messages whose time difference is less than a set time threshold as current multi-satellite message replicas.

3. The method as described in claim 1, characterized in that, The determination of the current ship's location information corresponding to each AIS message includes: Based on the time difference Δt between the reception times of the current AIS messages received by the two satellites. {i,j} Construct the hyperbolic positioning equation as shown in formula (1); Solving the hyperbolic positioning equation yields the solved position information P corresponding to the time the ship sends the current AIS message. v ; c Δt {i,j} =│P v P sati │ │P v P satj │+δ atmos_i,j (1) Where: c is the speed of light, P sati P sati These are the location information of the two satellites when they receive the current AIS message, δ atmos_i,j It is the atmospheric propagation delay difference obtained by estimating and correcting the integrated ionospheric and tropospheric delay models.

4. The method as described in claim 1, characterized in that, The cleaning and optimization of the decoded location information obtained from each AIS message includes: Decode the current AIS message to obtain the current decoding position information; If the position difference between the current solved position information and the current decoded position information corresponding to the current AIS message is greater than a set dynamic threshold, the current solved position information is determined as the current optimized position information. The set dynamic threshold is determined based on one or more of the following: the current static attribute information of the current vessel, the current dynamic navigation information, the current navigation area geographical location information, and the reception time corresponding to the previous optimized position information.

5. The method as described in claim 1, characterized in that, The cleaning and optimization of the decoded location information obtained from each AIS message also includes: If the position difference is less than or equal to the set dynamic threshold, the current decoded position information is determined as the current optimized position information; or, a weighted average is performed based on the current solved position information and the current decoded position information to determine the obtained position information as the current optimized position information.

6. The method according to any one of claims 1-5, characterized in that, Determining the current trajectory of the ship includes: The data points, consisting of transmission time and optimized location information, are input into the Kalman filter; The four-dimensional motion trajectory of the current ship is obtained after the Kalman filter predicts and updates the trajectory based on the constant speed CV model or the constant rotational speed CTRV model. The four-dimensional motion trajectory includes longitude, latitude, altitude, and time.

7. A device for monitoring ship trajectory, characterized in that, include: The acquisition group module is configured to determine, from the message data stream acquired from multiple time-synchronized satellites, the multi-satellite message copy corresponding to each Automatic Identification System (AIS) message sent by the current ship, wherein the message data stream includes the AIS message received by each satellite, the reception time, and the satellite status; The optimization module is configured to determine the current ship's position information corresponding to each AIS message based on the time difference between the reception times of two satellites in each group of multi-satellite message copies, and to clean and optimize the decoded position information of each AIS message based on the decoded position information to obtain the corresponding optimized position information. The backtracking determination module is configured to determine the transmission time of each AIS message sent by the ship based on the optimized location information and the corresponding satellite status. The orbit determination module is configured to determine the current vessel's trajectory based on the transmission time of each AIS message sent by the vessel and the corresponding optimized position information.

8. A device for monitoring ship trajectory, the device comprising a processor and a memory storing program instructions, characterized in that, The processor is configured to perform the method for monitoring ship trajectory as described in any one of claims 1 to 6 when executing the program instructions.

9. A data center, characterized in that, include: Equipment body; The device for monitoring ship trajectory as described in claim 7 or 8 is installed on the device body.

10. A storage medium storing program instructions, characterized in that, When the program instructions are executed, they perform the method for monitoring ship trajectory as described in any one of claims 1 to 6.

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